Abstracts
Abstracts are most easily found through links in the .html version of the program, available here .
Fernando Camilo - SARAO
MeerKAT status and updates
Abstract: not available
Natasha Maddox - University of Bristol
Progress update from MIGHTEE-HI
Abstract: MIGHTEE is one of the MeerKAT Large Survey Programs currently underway. I will review results from the MIGHTEE-HI Early Science data, along with the valuable lessons learned, and how these lessons inform the next phase of data already in hand. I will also describe ongoing work studying an HI-rich dwarf galaxy association, which nicely illustrates the strength of HI observations in detecting galaxy group structures.
Erwin de Blok - ASTRON/UCT/Kapteyn
First science from MHONGOOSE - a new view on the low-column density HI universe
Abstract: In my presentation I will give an overview of the MHONGOOSE survey. I will present new results obtained using our first set of ~15 full-depth galaxy HI observations. These show that the low-column density environment of nearby galaxies is complex and dynamic. I will discuss a few case studies of individual galaxies where a powerful combination of deep optical and HI imaging allows us to identify separate interaction and accretion processes. Finally I discuss the prospects for future SKA surveys based on the first results from MHONGOOSE.
Sarah Blyth - University of Cape Town
LADUMA: Looking At the Distant Universe with the MeerKAT Array
Abstract: The LADUMA survey is one of the Large Survey Projects on the MeerKAT radio telescope and aims to observe the HI content of galaxies over two-thirds the age of the Universe within a single pointing encompassing the Extended Chandra Deep Field South. I will present an update on the survey progress and some recent results.
Julia Blue Bird - NRAO, Socorro NM
CHILES: Overview of the CHILES Survey and Science
Abstract: The COSMOS HI Large Extragalactic Survey (CHILES) is a 1000-hour observing program using the Karl G. Jansky Very Large Array. With CHILES, we study the content, morphology, and kinematics of HI gas in galaxies over a continuous redshift range of 0 < z < 0.5. In this talk, we will give a status of the CHILES survey and share some of the ongoing science.
Nissim Kanekar - National Centre for Radio Astrophysics, India
The GMRT-CATz1 Survey: The HI properties of star-forming galaxies at z~0.7-1.5
Abstract: The weakness of the hyperfine HI 21cm line, the main tracer of the HI content of galaxies, has meant that we know little about the atomic gas mass of high-redshift galaxies and its evolution. Indeed, the evolution of the HI content of galaxies is one of the main open questions in galaxy evolution today. Stacking of the HI 21cm emission signals from a large sample of galaxies, observed simultaneously with a radio interferometer, can allow one to determine the HI properties of the galaxy population. In this talk, I will present results from the Giant Metrewave Radio Telescope Cold HI AT z~1 (GMRT-CATz1) survey, which has obtained measurements of the average HI mass and the HI scaling relations of star-forming galaxies out to z~1.5. I will also describe the implications of our results for gas accretion onto galaxies and the HI mass function towards the end of the epoch of peak star formation activity in the Universe.
Betsey Adams - ASTRON / Kapteyn
The Apertif HI Surveys
Abstract: Apertif wasa phased-array feed for the Westerbork Synthesis Radio Telescope (WSRT), providing forty instantaneous beams and 300 MHz of bandwidth. The significant increase in field of view turned WSRT-Apertif into a natural survey instrument, and WSRT-Apertif was dedicated to a large scale survey program from 1 July 2019 - 28 Feb 2022, consisting of an imaging survey with a wide and medium-deep tier plus a time-domain survey. The imaging surveys provide simultaneous sensitive radio continuum, polarization and spectral line data with a resolution of ~15''x15''/sin(declination). The wide tier covers ~2250 square degrees of northern extragalactic sky, and the medium-deep tier provides up to ~3x the depth in ~135 square degrees of focused regions selected for multi-wavelength data coverage and interesting large-scale structure.
I will present the first data release, which consists of the first year of survey observations, with a footprint of ~1000 square degrees. Processed data products, including continuum multi-frequency synthesis (mfs) images and uncleaned line cubes, along with the primary beam images for each Apertif primary beam, were released via a Virtual Observatory interface. For a typical noise value of 1.6 mJy/beam in a 36.6 kHz channel, the 3-sigma HI column density sensitivity is 1.8 x 10^20 atoms cm-2 over 20 km/s (for a median angular resolution of 24''x15'').
I will also highlight plans and ongoing efforts to future data releases. This includes automated HI source finding to provide advanced HI data products and improving the initial data calibration to account for direction-dependent effects (arising from malfunctioning elements on individual phased-array feeds).
James Dawson - Rhodes University & SARAO
Release of the HI legacy data for MGCLS An overview of constituent data statistics and early science
Abstract: The MeerKAT Galaxy Cluster Legacy Survey (MGCLS) is a MeerKAT programme of deep targeted radio observations of clusters in the Southern Hemisphere. The first data release contains 115 target fields observed at 1.28 GHz and provides a treasure trove of legacy data products to the astronomical community. MGCLS now showcases 27 clusters as having been reduced to HI data cubes, with completed source detection and data products ready for release to the astronomical community. I will detail the global statistics of this dataset, including an analysis of HI properties across the clusters, as well as early science results and proposed future avenues of research which would benefit from the exquisite sensitivities that MeerKAT has delivered in this dataset. Focus will be placed on demonstrating the vast increase in homogeneous data for HI galaxy cluster science with this data release, and how it will stand as a baseline for future surveys with MeerKAT+ and SKA.
Moses Mogotsi - SALT, SAAO
MeerChoirs: Unveiling the resolved HI in Nearby Choirs Groups with MeerKAT
Abstract: Environment is a key factor to consider when studying galaxy evolution. MeerChoirs is a MeerKAT HI survey of 15 nearby (23-151 Mpc) Choir groups. These groups were selected from a HI-selected survey of nearby galaxies that were observed in H-alpha, R-band and UV (SINGG, SUNGG). These groups cover a wide range of compactness, number of members and HI-richness, and therefore they cover a wide range of group environments and properties. This makes them a great laboratory for studying different environments and their effects on galaxy evolution. The groups range from those in cluster environments, Arp objects, compact groups to much less compact groups. MeerKAT is the ideal telescope to study nearby groups due to its unparalleled combination of large field of view, high sensitivity and good spatial resolution. This has allowed us to study the MeerChoirs groups and their constituent galaxies, trace gas flows and intra-group gas in better detail than before. This will shed light into how the galaxies are interacting, and how these interactions affect the constituent galaxies and the HI in the groups. It has also enabled us to detect new group members and better characterize the groups. We have other multi-wavelength data that can be used in conjunction with the HI to better understand these groups. This survey provides a good template for how MeerKAT will be used to study galaxy environments in the future. In this talk I will present the MeerChoirs survey, preliminary data and results from the MeerKAT observations of the groups.
Filippo Maccagni - ASTRON
MAGNHIFFIC - MeerKAT AGN HI feeding and feedback investigation close-by
Abstract: The vast amount of energy released by the supermassive black holes (SMBHs) drives the evolution of galaxies, ultimately transforming them from young, gas-rich and star-forming into old, red and quiescent. The accretion of cold gas from the interstellar medium (ISM) onto the SMBH is thought to trigger these so-called Active Galactic Nuclei (AGN). Yet, which processes regulate the gas accretion onto the SMBH is unknown (i.e. feeding mechanisms). We also do not know how AGN change the physical conditions of the ISM, over which timescales, and how they shape the evolution of galaxies (i.e. feedback mechanisms). The main observational limitations to detect the cold gas in AGN have so far been the small field of view and the lack of sensitivity of the radio telescopes used. The new MeerKAT radio interferometer in South Africa is now fundamentally changing this with its large field of view and extreme sensitivity. MAGNHIFFIC (MeerKAT AGN HI feeding and feedback investigation close-by) is a ground-breaking project that will study the process of feeding and feedback in 22 nearby AGN (<100 Mpc) with different energetic outputs, ages, hosts and environments. It leverages the sensitive MeerKAT HI observations (down to a few times 10^17 cm-2) to simultaneously probe, for the first time, the small scales near the black hole, the larger scales of the galactic disks and the environments of these AGN.
In this talk, I will show the first results of the MAGNHIFFIC survey on a sub-sample of Seyfert and radio-loud galaxies which allowed us to shed new light on the role of cold gas in the nuclear activity of galaxies. By integrating with information on the molecular and ionised gas (from ALMA and MUSE observations), I will highlight the crucial synergy between multi-wavelength spatially resolved spectral line observations to better understand the mechanisms of gas accretion in AGNs and the impact of AGNs on the surrounding interstellar medium, distinguishing, for example, between 'external' phenomena (i.e. mergers and interactions) and 'internal' phenomena (i.e. cold chaotic accretion, secular events). Lastly I will focus on the recent HI observations of Centaurus A which allowed for the very first time to trace a coherent cold gas outflow from the innermost regions out to 20 kpc from the SMBH, along filaments of ionised gas where positive feedback is taking place. This suggests that part of the outflowing HI is the primary fuel reservoir for the newly born star forming regions.
Ivy Wong - CSIRO Space & Astronomy
Updates of HI science with ASKAP
Abstract: The Australian SKA Pathfinder (ASKAP) completed both their pilot survey phases and began trialling its full survey mode towards the end of 2022. In this talk I'd like to provide an update on the status of ASKAP together with some highlights from the ASKAP HI surveys (WALLABY, DINGO and FLASH).
Nathan Deg - Queen's University
HI Kinematics of the Southern Sky: The WALLABY Kinematic Models of PDR1 and Beyond
Abstract: The recent WALLABY Pilot Data Release 1 (PDR1) contained ~600 unique sources. The majority of these (like any untargetted survey) are marginally resolved and have a low S/N. In order to kinematically model these galaxies we developed the WALLABY Kinematic Analysis Proto-Pipeline (WKAPP). WKAPP using multiple modelling software packages and was able to successfully model ~110 galaxies. This talk will describe WKAPP as well as the population of PDR1 galaxies. In addition, we will discuss the development of a new modelling pipeline using completely custom software that builds on the strengths of WKAPP and is optimized for the low S/N and marginally resolved regime of most emission-line surveys.
Hayley Roberts - University of Colorado Boulder
The OH Megamaser Revival in Next-Generation HI Surveys
Abstract: OH megamasers (OHMs) are rare, luminous masers found in (ultra-)luminous infrared galaxies ([U]LIRGs) with dominant masing lines at 1667 MHz. In the 40 years since their discovery, only ~120 OHMs have been discovered despite numerous searches for these unique sources. However, next-generation HI surveys reaching groundbreaking sensitivities and redshifts, such as those on the Square Kilometre Array (SKA) and its precursors, will be able to detect OHMs at an unprecedented rate. However, the masing lines produced by OHMs can spoof the HI emission line in these surveys when spectroscopic redshifts are not available to determine the rest frequency of the emission line, creating a potential source of contamination in HI surveys and allowing OHMs to elude detection. We present new predictions for the number of OHMs that will be detected by these surveys, including fiducial surveys on the first phase of the SKA, and discuss how the contamination rate depends on survey sensitivity and redshift. We also present methods for distinguishing OHMs from HI sources without spectroscopic redshifts by using a k-Nearest Neighbors machine learning algorithm applied to near- to mid-IR photometry. These methods have been tested using existing HI survey data and preliminary data from SKA precursors. We present an exciting first look at some new detections and discuss the complementary science these contaminants offer for HI surveys.
This work has been supported by the National Science Foundation through grant AST-1814648.
Thomas Jarrett - University of Cape Town
Scientific Analysis in Data Space: Using VR to get the most out of your 3D Data
Abstract: In this presentation, I discuss scientific visualization of spectral imaging and large-scale structure using VR technology, showing that it can be very effective in providing new insights into complex and subtle features deep within multi-dimensional data. At UCT, and in collaboration with international partners (Aus, Neth, Ita), we have developed a software system that enables user-interaction and immersive exploration of 3D data, notably designed to work with HI spectral cubes from radio interferometers. Referred to as iDaVIE-v (immersive Data Visualization Interactive Explorer for volumetric rendering), it combines virtual reality (VR) technology and custom-built software to work with particle and volume data sets. Originally developed to serve the HI Radio Astronomy community for HI source identification, the software is now in the public sphere, with greater capabilities that will benefit the broader astronomy community (e.g., redshift catalogues, cosmological simulations). I show examples in which the VR software has been used to analyze real data from the SKA Pathfinders, and notably report on the MeerKAT discovery of an extraordinary HI cloud complex found using this technology.
Thijs van der Hulst - Kapteyn Astronomical Institute, University of Groningen
SoFIA: current status and future perspective
Abstract: Abstract: SoFiA, the HI Source Finding Application, has matured to the point that it now has many users across the globe. The purpose of this talk is to describe the current status and possible future developments. In addition the success of SoFiA in the SKA Science Data Challenge 2 will be discussed as well as the routine use of SoFiA for ASKAP and Apertif source finding. In addition to SoFiA related tools have been developed, the most important one being the SoFiA Imaging Pipeline which produces useful plots and tables from the source catalogues and images provided by SoFiA. The connection of SoFiA results with the virtual reality visualisation software iDaVIE will also be touched upon.
Jacinta Delhaize - University of Cape Town
An update on LADUMA HI and OH source finding
Abstract: I will report on the progress of the LADUMA Source Finding Working Group. The group has been testing several different manual, automated and hybrid source finding methods to search for HI and OH detections in the MeerKAT L-band and UHF-band data. I will present a comparison of these methods, some of the outcomes, and the construction of our master catalogue.
Leyya Stockenstroom - LADUMA Team based at UCT
Spectral-line source finding for the LADUMA survey
Abstract: The initial phase of the Looking At the Distant Universe with the MeerKAT Array (LADUMA) survey is sensitive to HI emissions from galaxies at redshift z<0.58 and OH emission from megamasers at z<0.85, thanks to the use of MeerKATs L-band receivers. To analyse these observations, an important step is to find these spectral line sources in the extremely large data cubes produced by LADUMA. I will describe our use of the fully automated Source Finding Application (SoFiA) which allows us to efficiently detect source in early LADUMA data. By comparing visual source-finding and source-finding performed by matched filtering to SoFiAs source-finding, we can optimise the inputted parameters to ensure that the catalogue produced by SoFiA is as complete and reliable as possible. I will also discuss the use of two extensions of the basic SoFiA package, SoFiA-X, which is used to run SoFiA more effectively, and the SoFiA Imaging Pipeline (SIP) which creates images and spectra of sources detected by SoFiA to our LADUMA data.
Hengxing Pan - University of the Western Cape
Mapping IGM and CGM with FAST
Abstract: The intergalactic (IGM) and circumgalactic (CGM) mediums trace the matter flow from large-scale structures to galaxies, and play important roles in the process of galaxy formation and evolution. In this talk, I will present our efforts to detect the IGM and CGM using HI emission line with the world's largest single-dish radio telescope-FAST combined with MeerKAT. To achieve this, we took 13-hours FAST observation in L-band on the COSMOS field, overlapping with one of the MIGHTEE fields. The initial analysis demonstrates that we have reached the N_HI < 10^18 cm^-2 regime, where the diffuse HI gas becomes ubiquitous in the cosmic web.
Nickolas Pingel - University of Wisconsin-Madison
Modern Approaches to the Short-Spacing Correction
Abstract: Aperture synthesis imparts radio interferometers with the capability of resolving structure down to sub-arcsecond scales. However, the discrete spacing between individual antenna elements produces irregular or incomplete sampling of the Fourier plane, especially at the shortest baselines, resulting in the inability to detect flux at the largest angular scales. The remedy for this well-known 'short-spacing' problem is to combine the high-angular resolution interferometric data with complementary single dish data that captures the large-scale flux. I will present an overview of several prominent methods used in the combination of interferometric and single dish observations to recover flux over a continuous range of angular scales and introduce several new assessment tools that enable evaluation and statistical comparisons between combination methods. These python-based tools are publicly available and modular, making it possible to easily incorporate them into current and future data processing pipelines.
Alessandro Bianchetti - University of Padova, INAF
HI scaling relations at z<0.5 combining the MIGHTEE and CHILES surveys
Abstract: Thanks to MeerKat and the SKA-MID generation, HI is getting accessible at higher z, making it possible to explore galaxy scaling relations involving gas mass at z>0. Probing the evolutionary path of such relations would allow to understand how cold hydrogen reservoirs impact star formation and galaxy evolution. Recent works exploiting stacking of the 21 cm line with the MIGHTEE survey datacubes, on the COSMOS field, have been unveiling the trends of the HI mass vs stellar mass and SFR at about z~0.4. However, scaling relations built via stacking are typicaly computed with few data points and would ideally need to be expanded at lower stellar mass to better constrain slope. Employing MIGHTEE HI observations on the COSMOS field in combination with 1000 hrs of VLA observations provided by the CHILES survey, on a subregion of COSMOS, would enable the detection of HI in galaxies with lower stellar masses. In this talk, I\'d like to present my work on the derivation of scaling relations creating a combined stacking of MIGHTEE and CHILES images. First, we check that stacking CHILES and MIGHTEE separately on the radio-undetected galaxies leads to the same HI mean mass estimate, validating the consistency of the two surveys. Moreover, our analysis shows whether combining MIGHTEE and CHILES significantly increases the statistics on the field, thus leading to a more robust estimate of the HI scaling relations. This would assess our current knowledge about scaling relations, and on the other hand pave the way to the future steps of this work: extending HI scaling relation to higher redshift (up to z=1), thanks to the SUPERMIGHTEE survey.
Marc Verheijen - Kapteyn Astronomical Institute, University of Groningen
The baryonic Tully-Fisher relation at z = 0.2 based on direct H I detections
Abstract: I will present H I-based B- and R-band Tully-Fisher relations (TFRs) and the Baryonic TFR (BTFR) at z=0.2 using direct H I detections from the Blind Ultra-Deep H I Environmental Survey (BUDHIES). Deep photometry from the Isaac Newton Telescope was used for 36 out of 166 H I sources, matching the quality criteria required for a robust TFR analysis. Two velocity definitions at 20 and 50 per cent of the peak flux were measured from the global H I profiles and adopted as proxies for the circular velocities. I compare our results with an identically constructed z=0 TFR from the Ursa Major association (UMa) of galaxies. To ensure an unbiased comparison of the TFR, all the samples were treated identically regarding sample selection and applied corrections. There are catalogues and an atlas showcasing the properties of the galaxies. The analysis is focused on the zero points of the TFR and BTFR with their slopes fixed to the z=0 relation. The main results are: (1) The BUDHIES galaxies show more asymmetric H I profiles with shallower wings compared to the UMa galaxies, which is likely due to the environment in which they reside, (2) The luminosity-based z=0.2 TFRs are brighter and bluer than the z=0 TFRs, even when cluster galaxies are excluded from the BUDHIES sample, (3) The BTFR shows no evolution in its zero point over the past 2.5 billion yr and does not significantly change on the inclusion of cluster galaxies, and (4) proper sample selection and consistent corrections are crucial for an unbiased analysis of the evolution of the TFR.
Anastasia Ponomareva - University of Oxford
The first MeerKAT HI mass function over the last billion years
Abstract: One of the most critical measurements that can be made directly from a blind HI survey, is the measurement of the HI mass function (HIMF), and consequently the study of its evolution with redshift. The HIMF defines the number of galaxies per cubic Mpc as a function of HI mass, and its shape determines how the neutral gas in the Universe is distributed over galaxies of different masses. A well-constrained HI mass function puts major constraints on theoretical models of galaxy formation and evolution. Therefore, any successful theory of galaxy formation and evolution should be able to reproduce HIMF simultaneously at any redshift. In my talk I will present a measurement of the first HI mass function determined from MeerKAT data and the first using interferometry data over a non-targeted overdensity. The HIMF is based on 276 direct detections from the MIGHTEE Survey Early Science data covering a period of approximately a billion years (0 < z < 0.084). I will discuss the variations of the HIMF as a function of redshift, as well as the effects of the survey volume on the properties of the HI mass function. I will conclude with the lessons learned in preparation for the full survey data.
Amir Kazemi-Moridani - Rutgers, The State University of New Jersey
Measuring the HI Mass Function in Early LADUMA Data
Abstract: The LADUMA (Looking At the Distant Universe with the MeerKAT Array) deep HI survey aims to observe neutral hydrogen in emission out to redshifts > 1 using the L-band and the UHF-band receivers on the MeerKAT array. An important recent focus for the survey has been the preparation of an initial release of more than 125 hours of L-band data, which will ultimately be made public and enable a variety of scientific analyses. I will discuss the challenges of preparing this data release and report on the measurement of the HI mass function (HIMF) from a sample of more than 150 spectral line detections.
Barbara Siljeg - ASTRON, Kapteyn Institute
Low mass galaxies in the Apertif HI surveys
Abstract: Low mass galaxies present great challenges for the current leading cosmological model LCDM. Hydrodynamical simulations based on LCDM have been unsuccessful in reproducing a number of galaxy properties at these scales, such as the diversity in the shapes of rotation curves as well as the scatter seen in scaling relations such as the baryonic Tully-Fisher (BTFR). Additionally, predicted masses of dark matter halos from abundance matching show discrepancies with masses inferred from rotation curve measurements (the too-big-to-fail). In general, there is currently a poor understanding of how the baryonic content of galaxies connects to the dark matter content at low mass scales. In this work, we aim to contribute to this understanding by studying resolved neutral hydrogen (HI) content which allows us to conduct kinematic modeling of galaxy rotation using 3D-Barolo. We select our sample using the first few months of observations from the Apertif HI surveys with spatial resolution of 15x15/sin(Dec) arcsec and sensitivity of around 1.6 mJy/beam over 36.6 kHz (around 8 km/s). By basing our selection on a blind HI survey, we are able to find galaxies independent of their stellar content, meaning we are able to easily find optically faint galaxies. To study the complete baryonic content, we complement our HI data with Pan-STARRS 1 photometric survey to obtain stellar masses and surface brightness profiles of the sample. Interestingly, out of 20 galaxies in the final sample, 6 (30%) are found as part of a pair, some of which were previously treated as a single source in lower resolution, single-dish HI surveys such as ALFALFA. We explore the placement of our HI-selected low mass galaxies with regards to samples from the literature in various scaling relations (BTFR, mass-size relations, surface brightness-size relations, etc.) as well as studying their dark matter contents by determining enclosed dynamical masses. Furthermore, we explore how the observed diversity depends on individual galaxy properties o!f both the HI gas and the stars.
Cecilia Bacchini - INAF - Astronomical Observatory of Padova
The volumetric star formation law Linking HI and star formation from dwarf to spiral galaxies
Abstract: Investigating the laws regulating star formation is key to understand galaxy formation and evolution. Generally, the Kennicutt law is adopted to link the surface densities of the star formation rate (SFR) and total cold gas (HI+H_2) in galaxies. However, this empirical relation breaks down in low-density and HI-dominated environments, such as the outskirts of spirals and dwarf galaxies. The Kennicutt law shows indeed a break in the slope at low densities, which is ascribed to a density threshold for star formation. Crucially, the observed surface densities are subject to projection effects due to the gas disc thickness and flaring, while the intrinsic and desirable quantities to build empirical star formation laws are the volume densities. Converting surface densities to volume densities is problematic as this requires the gas disc thickness, which varies both with galactocentric radius and between different galaxies. Measuring the gas disc thickness directly from observations is also extremely challenging and feasible for very few galaxies.
We adopted a robust approach based on the hydrostatic equilibrium to calculate the disc thickness for 22 nearby star-forming galaxies, including both dwarfs and spirals, and our Milky Way. We derived the total cold gas and SFR volume densities and found a volumetric star formation (VSF) law with no break in slope over five orders of magnitude and a smaller scatter than the Kennicutt law. The absence of the break in the VSF law disfavours the existence of a density threshold for star formation. Remarkably, a tight correlation between HI alone and SFR emerges when the volume densities are used, contrary to previous works neglecting the HI disc flaring. This correlation suggests that atomic gas play a key role in star formation. These volumetric correlations are the only empirical laws that hold for both spiral and dwarf galaxies, even where the HI dominates the local gas density. These results highlight the importance of probing the vertical structure of gas discs in galaxies, a perfect task for deep HI surveys in the future.
Pavel Mancera Pina - Leiden Observatory
The tight relation between gas content and angular momentum in disc galaxies
Abstract: Since early models of galaxy formation, it became clear that mass and angular momentum are two fundamental parameters controlling the formation and evolution of galaxies. While the relation between stellar mass and stellar specific angular momentum has been broadly studied in the literature, its baryonic counterpart remains relatively unexplored. The main reason for this is that the relation between gas mass and gas specific angular momentum has not been well characterized for large galaxy samples. Yet, with the large-volume HI surveys coming soon, it is important to start taking this into account to fully exploit the information given by such surveys. In this talk, I will present results regarding the baryonic specific angular momentum of disc galaxies, which we have recently derived using a large sample of galaxies with the highest available quality in their stellar surface brightness profiles and gas kinematics. We find that the relation between the baryonic mass (M_bar) and the baryonic specific angular momentum (j_bar) of disc galaxies is a well defined, unbroken power law across four orders of magnitude in M_bar and j_bar, with spiral and dwarf galaxies lying along the same sequence, opposite to previous claims. Moreover, we find a clear correlation between the gas content of galaxies and their mass and baryonic angular momentum. The plane defined by these quantities has an extremely low intrinsic scatter, making our new relation one of the tightest empirical scaling relations of galaxies. Even extreme galaxies like ''super-spiral'', ''super-thin'', or ''ultra-diffuse'' galaxies follow this relation rather closely, despite being outliers of other important scaling relations. This highlights the fundamental nature of the new law. I will briefly discuss the possible physical mechanisms that give rise (or not) to such relation, in particular those related to gas disc instabilities.
Neal Katz - University of Massachusetts, Amherst
Galaxy Formation Simulations of the HI Content of Galaxies: Problems and Answers
Abstract: Detailed numerical simulations are critical to interpret and understand HI observations. Unfortunately, simulations are sensitive to wind implementations. Interactions at wind/halo gas interfaces in the CGM occur on scales that are much below the resolution of any current or near future galaxy formation simulation, making a ''brute force'' approach not viable. To mitigate this impassewe propose to implement a new wind algorithm that explicitly models the ''subgrid physics'' in the wind-halo gas interaction within a simulation, using the simulation to provide the physical characteristics that will inform the interaction. Previous simulations using more standard wind model approaches reproduce many observed properties of galaxies but our new wind implementation will allow us to tie empirical successes, and failures, more securely to the underlying wind physics and to make more robust predictions.
Kyle Oman - Durham University
Learning to distinguish DM cusps and baryon-induced cores with simulated HI observations
Abstract: Simulated ''observations'' of cosmological hydrodynamical simulations are a powerful tool to interpret 21-cm observations. We created high-resolution 21-cm 'observations' of simulated dwarfs produced in two variations of the EAGLE galaxy formation model: one where supernova-driven gas flows redistribute dark matter and form constant-density central 'cores', and another where the central 'cusps' survive intact. We observed each galaxy along multiple sight lines and derived a rotation curve for each observation using conventional tilted-ring models. We found that the modelling process introduces systematic discrepancies between the recovered rotation curve and the actual circular velocity curve such that dwarfs with dark matter cusps often appear to have a core, whilst the inverse error is less common. If similar effects affect the rotation curves of observed dwarfs, a late-type dwarf population in which all galaxies have sizeable dark matter cores is most likely incompatible with current measurements.
Nadine Hank - Kapteyn Astronomical Institute
Exploring HI asymmetries in spatially resolved SIMBA galaxies
Abstract: Observations have revealed that many galaxies exhibit distorted and asymmetric morphologies in their stellar and/or gaseous components. Various astrophysical processes, such as galaxy-galaxy interactions and mergers, ram-pressure stripping, and gas accretion, have been proposed as possible origins. As such, studying galaxy asymmetries in large samples and relating these asymmetries to the processes that caused them has become a key research topic to aid in our understanding of the relative importance of these processes and how they govern galaxy evolution. Until recently, research on asymmetries in the neutral atomic hydrogen (HI) content of galaxies has been largely limited to targeted galaxy samples in the local Universe. However, the latest generation of untargeted HI surveys on the Square Kilometre Array (SKA) pathfinder telescopes will enable detailed studies exploring the HI in galaxies using much larger samples than previously available. In the lead-up to these new datasets, we utilise the SIMBA hydrodynamical simulations to investigate HI asymmetries in spatially resolved, low redshift galaxies in order to understand and contextualise the state of disturbances in the HI reservoirs of galaxies.
Eric Maina - Rhodes University
MALS HI observations of Klemola 31: emission and absorption
Abstract: We present MeerKAT Absorption Line Survey (MALS) observations of the HI gas in the Klemola 31 galaxy group (z = 0.029), located along the line of sight to the radio-loud quasar PKS 2020-370 (z = 1.048). The system is known to show the HI line in absorption as well as emission and therefore enables us to combine the respective information. Other than HI absorption studies alone, our data allow us to access the origin of the absorbing component by comparing kinematic and morphological information. In the case of the Klemola 31-PKS 2020-370 system, it is not straightforward to identify the absorption line with gas in the main HI disk. Instead, it might be extraplanar gas, perhaps originating from tidal interaction, fitting to the HI deficiency of the whole group. MALS promises the detection of several absorption-emission line systems in the near future. We will discuss our findings of the Klemola 31 data and give an outlook on the prospect of MALS to study samples of emission-absorption line systems in greater detail.
Julia Healy - ASTRON
Anomalous HI gas around MHONGOOSE galaxy NGC 5068
Abstract: How galaxies replenish their gas supply in order to sustain star formation, is a research topic of many of the new and upcoming neutral atomic hydrogen (HI) surveys on the SKA precursor instruments. I present recent deep HI observations of NGC 5068, an isolated nearby star-forming galaxy observed by MeerKAT as part of the MHONGOOSE survey. This survey is the deepest HI survey of nearby galaxies until the advent of the SKA and is reaching column densities of NHI (3sigma) ~3x10^19 cm^-2 at 11'' to ~7x10^17 cm^-2 at 90'' resolution. These deep observations show that the galaxy comprises of three components: a settled, regularly rotating inner disk that is coincident with the star-forming disk, a more chaotic warped outer disk, and a third component that comprises of a number of clouds to the north west of the galaxy that appear to be linked to ''fingers'' of HI seen stretching out from the inner HI disk. While the origin of these features remains a mystery for now, the dynamics of the main galaxy disk and the warped outer disk, as well as the morphology of the fingers and clouds, do not seem to suggest a previous merger event. It is possible that we are observing accretion of HI onto the disk of NGC 5068.
Nikki Zabel - University of Cape Town
HI at unprecedented sensitivities: early results from MHONGOOSE galaxy UGCA320 and neighbours
Abstract: One of the key questions in the field of galaxy evolution is ''How do galaxies assemble and evolve?''. Neutral atomic hydrogen (HI), being distributed widely across galaxies, and accreted onto, as well as removed from them relatively easily, plays a key role in studies working towards answering this question. With the commissioning of MeerKAT, and soon MeerKAT+ and SKA, HI can now be studied in more detail than ever before. The ''MeerKAT HI Observations of Nearby Galactic Objects - Observing Southern Emitters (MHONGOOSE)'' uses MeerKAT to observe the HI in a variety of 30 nearby galaxies, down to column densities as low as ~5x10^17 cm^-2. In this talk I will show early results from one of the MHONGOOSE targets, UGCA320 and neighbours - it is part of a small group. I will present an analysis of their HI distributions and velocity fields, and discuss their possible interpretations in the context of the group environment.
Simone Veronese - ASTRON, Kapteyn Astronomical Institute
Extended neutral hydrogen filamentary network in NGC 2403
Abstract: I present new neutral hydrogen (HI) VLA observations of the nearby galaxy NGC 2403 to determine the nature of a low-column density cloud that was detected earlier by the Green Bank Telescope. I find that this cloud is the tip of a complex of filaments of extraplanar gas that is coincident with the main disk. The total HI mass of the complex is 2 10^7 Msun or 0.6% of the total HI mass of the galaxy. The main structure, previously referred to as the 8-kpc filament, is now seen to be even more extended, along a 20 kpc stream. The kinematics and morphological properties of the filaments are unlikely to be the result of outflows related to galactic fountains. It is more likely that the 20 kpc filament is related to a recent galaxy interaction. In this context, a ~50 kpc long stellar stream has been recently detected connecting NGC 2403 with the nearby dwarf satellite DDO 44. Intriguingly, the southern tip of this stream overlaps with that of 20 kpc HI filament. I conclude that the HI anomalies in NGC 2403 are the result of a recent (~2 Gyr) interaction with DDO 44 leading to the observed filamentary complex.
Sriram Sankar - SAAO/UCT
Looking for Anomalous gas in interacting galaxies
Abstract: The HI distributions in galaxies have been found to deviate from a simple axisymmetric, thin, differentially rotating disc in several ways. Both disturbed and undisturbed discs have been shown to feature warps and flaring in the outer regions. Kinematic features such as Extra-Planar Gas (EPG), tails, spurs, High-velocity clouds, anomalous gas, etc have also been associated with HI discs. In this era of resolved, sensitive HI observations, one of the key possibilities is the identification of anomalous gas associated with a wide range of discs residing in various environments. Such studies of gas kinematics and galaxy dynamics across several environments will deepen our understanding of the baryon cycle, galaxy interactions, and the environmental dependence of galaxy evolution. However, this task is non-trivial due to the fundamental limitation induced by instrumental effects (ex: spatial and spectral resolution), projection effects, and systematic effects (ex: assumptions, methods). The MeerChoirs survey channels the exquisite sensitivity of MeerKAT to characterise the neutral hydrogen in 15 groups in order to study the impact of the environment on galaxy evolution. In this talk, I will present the neutral hydrogen distribution in J1403-06, which hosts an interacting galaxy pair, three dwarfs, and impressive HI features that have never been seen before. I will also compare three different approaches for separating anomalous gas from the HI discs and posit certain important considerations through the context of the limitations.
Ed Elson - University of the Western Cape
MeerKAT HI-line observations of the nearby interacting galaxy pair NGC 1512/1510
Abstract: I will present the results of a study based on MeerKAT HI line imaging of the nearby interacting galaxy pair NGC 1512/1510. The data yield high-fidelity image sets characterised by an excellent combination of high angular resolution, dynamic range and sensitivity, thereby offering the most detailed view of this well-studied systems neutral atomic hydrogen content. We find the stellar bulge and bar of NGC 1512 to be located within a central HI depression where surface densities fall below 10^20 atoms/cm^2, while the galaxy's starburst ring coincides with a well-defined HI annulus delimited by higher surface densities. Our high-resolution imaging is used to quantitatively explore the spatial correlation between HI and far-ultraviolet flux over a large range of HI mass surface densities spanning the outer disk. The results indicate the systems HI content to play an important role in setting the pre-conditions required for wide-spread, high-mass star formation. This work serves as a demonstration of the remarkable efficiency and accuracy with which MeerKAT can image nearby systems in HI line emission.
Alessandro Loni - (1) Armagh Observatory and Planetarium (2) Istituto Nazionale di Astrofisica
NGC 1436: the making of a lenticular galaxy in the Fornax cluster
Abstract: There is evidence that quiescent galaxies in dense environments are the end-products of the evolution of star-forming spirals. However, it is very rare to observe this morphological transformation in action. Recently, the MeerKAT Fornax Survey observed a case of a truncated HI disc, which is currently moving from a spiral to a lenticular structure: NGC 1436.
The disc of this galaxy is made of two main components: an inner, gas-rich, star-forming disc, which still shows a spiral structure, and an outer quiescent disc with no spiral arms and no cold gas. Using MeerKAT (MeerKAT Fornax survey), ALMA (ALMA Fornax Cluster Survey) and MUSE (Fornax 3D survey) data, we performed a joint analysis of the ISM properties as well as of the star formation histories of the two parts of the disc trying to address the question of whether the cluster environment played a role in this morphological transformation. Multi-wavelength analysis which are able to provide a snapshot of the current evolutionary state of a galaxy as well as to provide information about its past interactions, are powerful tools to shed light on the physical processes which have driven galaxy evolution so far.
Karina Santana - WITS
MeerKAT's new perspective of a local universe post-merger dual AGN system
Abstract: NGC 6240 is a nearby post-merger galaxy that hosts a sub-kpc dual AGN. It has been studied for decades across the electromagnetic spectrum by most major ground and space-based observatories showing significant AGN and starburst-driven gas outflows/inflows. In this talk I present MeerKAT HI observations that provide a new perspective on the gas dynamics near the dual AGN and as well the larger-scale interaction history. Comparisons such this with the high-velocity ionized and molecular gas outflows in archetype local-universe systems like NGC 6240, preview SKA1-mid observations at higher redshifts where the galaxy merger rate, AGN prevalence, and cosmic star formation rate density are significantly higher. Systems such as NGC 6240 may also be more common in the increasingly high-reshift galaxies that SKA HI pathfinder/precursor surveys are beginning to uncover.
Junhyun Baek - Yonsei University
Circumnuclear medium around the central AGN in a cool-core cluster, A1644-South
Abstract: We present the active galactic nucleus (AGN) jet and the circumnuclear multi-phase gas properties of the brightest cluster galaxy in the center of Abell 1644-South (A1644-S). The primary goal is to investigate how the large-scale cluster cooling environment ultimately affects small-scale AGN activity at the cluster center. The sharply peaked X-ray surface brightness profile of A1644-S implies the presence of a cooling gas flow. Also, its prototypical X-ray hot gas sloshing indicates that A1644-S is in a merging system where intracluster medium (ICM) cooling has recently started. In order to probe how the flow of cooling gas fuels the central supermassive black hole and leads the AGN activities in the early stage of a cool-core cluster, we analyze the ALMA CO and CN (1-0) data, JVLA HI data, and KaVA 22 GHz data for the central region of A1644-S. Based on the spatially resolved morphology and kinematics of CO gas, we suggest a connection between the cold molecules and the hot ICM cooling. HI and CN gas is detected in absorption with an extended redshift tail, suggesting the cool gas is falling to the nucleus and then fed to the central AGN. Indeed, we find a parsec-scale bipolar jet at 22 GHz in the center of A1644-S, which implies that this AGN has been (re)triggered quite recently. Combining this, we discuss the role of circumnuclear cool gas in fueling the centrally located cluster AGN in the cool-core environment.
Se-Heon Oh - Sejong University, South Korea
HI gas properties of galaxy pairs in cluster environment from WALLABY pilot survey
Abstract: We examine the HI gas kinematics of galaxy pairs in two clusters and a group using Australian Square Kilometre Array Pathfinder (ASKAP) WALLABY pilot survey observations. We compare the HI properties of galaxy pair candidates in the Hydra I and Norma clusters, and the NGC 4636 group, with those of non-paired control galaxies selected in the same fields. We construct HI super-profiles of the sample galaxies by stacking their line profiles. We then decompose each super-profile into kinematically narrow and broad components with respect to their velocity dispersions using a double Gaussian model. We investigate the effect of the cluster environment on the HI properties of galaxy pairs by dividing the cluster environment into three sub-cluster regions (i.e. outskirts, infalling, and central regions) on the phase-space diagram. We find that the denser cluster environment (i.e. infalling and central regions) is likely to impact the HI gas properties of galaxies in a way of decreasing the fraction of the kinematically narrow HI gas (MHI_narrow/MHI_total), and increasing the Toomre Q values of the infalling and central galaxies. This tendency is likely to be more enhanced for galaxy pairs in the cluster environment.
Dane Kleiner - ASTRON
First results from the MFS - HI tails and gas loss in the Fornax Cluster.
Abstract: The MeerKAT Fornax Survey (MFS) is now ~75% complete and I will present the important factors that were required for the MFS to successfully get to this point. More importantly, I will present the first results of the MFS. Thanks to the exquisite combined sensitivity and resolution of the MeerKAT telescope, we are exploring the resolved, low column density (~ 10^18 - 10^19 atoms cm^-2) HI emission in the Fornax cluster. For the first time, we have detected a number of long, one-sided, star-less HI tails that are radially oriented within the cluster. While this is the first unambiguous evidence of ram pressure acting on the galaxies, we argue that both tidal interactions and ram pressure are required to produce the HI tails. We also detect (and resolve in most cases) HI in 16 dwarf galaxies in the Fornax cluster, that range between ~ 10^6 - 10^9 Msol. I will present the collection of evidence indicating that dwarf galaxies lose their HI in a few hundred Myr once the tidal and / or hydrodynamical forces start to remove their HI. The rapid HI removal from dwarf galaxies is responsible for flattening the slope of the HI mass function in the Fornax cluster. I will connect these results to those obtained in lower density environments as part of MHONGOOSE that has detected an interacting triplet, containing massive amounts of extra-planar gas as well extended HI tails connecting satellite galaxies.
Tirna Deb - University of Western Cape
Atomic Hydrogen disks as tracers of galaxy transformation in Abell 2626 and beyond
Abstract: The extended, fragile, collisional atomic hydrogen (HI) gas discs in galaxies are excellent diagnostic tracers of gravitational and hydrodynamic processes in the cosmic environment they are residing in and also reservoirs for star formation. Within a galaxy cluster, both gravitational perturbations (tidal interactions, harassment, etc.) and hydrodynamic processes (thermal evaporation, ram pressure stripping (RPS), etc.) are at play. However, it is not clear yet which of these processes dominate the transformation of galaxies from star forming and gas rich, to quiescent and gas poor. I am investigating the influences of the global and local cosmic environment on the evolution of galaxies, both from the HI morphologies of galaxies in different locations of cluster substructures and the multi-wavelength case studies of the striking galaxies. From the new MeerKAT telescope observations of the A2626 volume, I am studying the spatially resolved morphologies of the HI detected galaxies, covering a range of cosmic environments. By identifying the cluster substructures and characterising their environments, I investigated the relative importance and effects of the various physical mechanisms that are responsible for reshaping galaxies. In addition, I also studied the detailed cases of HI gas stripping in jellyfish galaxies, the extreme examples of RPS with in-situ star formation in the tails. I have analysed the multi-phase (neutral, molecular, ionised gas) ISM of jellyfish galaxies JW100 and JO204 from multi-wavelength MeerKAT or JVLA, MUSE and ALMA observations. I will talk about how HI observations contribute to understanding the multiphase gas stripping in these jellyfish galaxies.
Xola Ndaliso - University of Witwatersrand
HI gas kinematics of marginally resolved galaxies in Abell 3408
Abstract: The dense environment of galaxy clusters has a significant role on the nature of member galaxies. We use HI line observations from the MeerKAT to try and understand the effects cluster environment poses on individual galaxies. This is done by modelling the gas kinematics of individual galaxies in the galaxy cluster Abell 3408, at redshift z~0.04202, D = 187.54 Mpc. A total of 64 galaxies are detected in HI in this X-ray-detected galaxy cluster. These MeerKAT HI observations have a spatial resolution of ~13 arcseconds (robust = 0.5) and a velocity resolution of 45 km/s. To model the dynamics of several galaxies, we started development of a monitored pipeline based on 3DBBarolo, that requires little to no prior information about the galaxy kinematic parameters. Despite the coarse resolution of our MeerKAT HI Abell 3408 observations, our pipeline successfully models 20 individual galaxies. The remainder of the galaxies are only marginally resolved, resulting to unsuccessful modelling of the dynamics. We use the HI maps and velocity fields to probe for 2D asymmetries in each detected galaxy, and potential links to the cluster environment. As SKA precursors and pathfinders continue to dramatically increase the sample size of spatially resolved HI galaxies, semi-automated analysis pipelines such as this will become increasingly important.
Sushma Kurapati - University of Cape Town
The Local Void as traced by the MeerKAT Galactic Plane Legacy Survey
Abstract: The Local Void is one of the nearest and large voids which lies largely in the Zone of Avoidance (ZOA) behind the Galactic bulge and is extremely difficult to observe. We use HI 21 cm emission observations from the MeerKAT Galactic Plane Survey (b < ~1.5 deg) to study the Local Void and its surroundings in the ZOA over the Galactic longitude range 330 deg < l < 55 deg and we have detected a total of 291 galaxies. We categorize the galaxies based on their environment, and we find that 29 galaxies are deep inside the Local Void, 76 galaxies are at the edge of the Void, while the remaining 186 galaxies are in average density environments. We find that the extent of the Void is ~58 Mpc and it is severely underdense in the region 350 deg < l < 35 deg up to redshift z < 4500 km/s. The galaxies in the Void tend to have HI masses lower by 0.25 dex than their average density counterparts. We find several candidates for small groups of galaxies of which two groups (with 3 members and 5 members) are consistent with galaxies lying along intra-void filaments which may suggest the ongoing growth of these galaxies along a filament inside the Void.
Sambatriniaina Rajohnson - University of Cape Town
Unveiling the hidden core of the Vela Supercluster (VSCL) with MeerKAT HI-surveys
Abstract: The extended massive Vela supercluster (VSCL) has been mapped through a spectroscopic campaign along the outer bands of the Zone of Avoidance (ZOA) in Vela (l ~ 275 , |b| ~ 6-10). Little is known about its structure and mass in between these bands because of the obscuration by the Milky Way. To get a first insight into the inner core and foremost the continuity of the two main VSCL walls across the Galactic Plane, we have conducted two densely packed contiguous systematic HI surveys of a few hundred pointings with MeerKAT. We have analysed HI data over dl=30 along the MeerKAT Galactic Plane Legacy survey (MKT-GPS) in Vela (-2< b<1) and the MeerKAT VSCL survey (MKT-VSCL), an extension to higher latitudes (|b|<7). With a mean rms of 0.39 mJy/beam, we have detected in MKT-GPS 869 highly obscured galaxies out to cz < 25500 km/s where only 39 galaxies have been detected before with the Parkes HIZOA survey (with cz < 10000 km/s). The analysis of the redshift and spatial distribution of the newly identified galaxies reveal two wall-like overdensities which possibly cross at l ~ 270 - 277 at the VSCL distance (cz > 16000 km/s) and suggests the presence of filaments. We will also present the preliminary results from MKT-VSCL extension which together will link to known structures beyond the ZOA.
Graham Lawrie - University of the Witwatersrand
A serendipitous MeerKAT discovery of a HI-rich galaxy group with megaparsec-scale filamentary structure.
Abstract: Neutral hydrogen (HI) is an important component within and tracer of galaxy evolution. Environmental effects within cosmological overdensities like galaxy groups and clusters have been shown to impact galaxies and their HI reservoirs, making the study of a wide range of environments important. This presentation will report the discovery and properties of an HI galaxy group at z~0.04. The group presents itself in a peculiar, Mpc-scale filamentary-like structure. Dark Energy Survey (DES) DR2, and Wide-field Infrared Survey Explorer (WISE) data is used to provide the star formation rates, stellar masses, and stellar morphologies enabling several additional group properties to be derived. The HI data used in this serendipitous discovery is from MeerKAT Galaxy Cluster Legacy Survey (MGCLS), suggesting many more such groups might be discovered to build up a large sample of HI groups with spatially resolved HI morphologies and dynamics.
Ma Yin-Zhe - University of KwaZulu-Natal
21-cm stacking to probe HI in halos and filaments
Abstract: 21-cm intensity mapping is a novel probe of large-scale structure in the Universe. In this talk, I will discuss the stacking of 2dF central and satellite galaxies on the Parkes 21-cm intensity map, and obtain, for the first time, the stacked 21-cm emission signal of neutral hydrogen from the stacked dark matter halos. I will show how this result can put constraints on the HI concentration parameter and the HI-halo mass correlation function. In addition, I will show how the stacking of pairs of the central galaxies on HI intensity map can reveal the neutral hydrogen gas in the filaments. I will further present the astrophysical implication of such stacking, and how it can reveal the status for the circumgalactic medium.
Kelley Hess - IAA/ASTRON
CHILES: A first look at resolved atomic and molecular hydrogen beyond z=0.1
Abstract: Understanding the relationship between the gas reservoir of galaxies and the change in their star formation rate with cosmic time is a major goal of galaxy evolution studies which (will) combine observations from the SKA, and its precursors, with complementary mm/submm telescopes. We present first results from the highest redshift sample of galaxies with both resolved atomic and molecular gas measurements to date, derived from the full CHILES 1000-hour image cubes, and targeted follow-up of HI detected galaxies with ALMA in CO (1-0). In the CHILES data, we re-detect 12 of 14 galaxies presented as detections in Epoch 1 data by Hess et al (2019). In the ALMA data we detect 5 of the 14 galaxies in CO. In all 5 cases, the CO spectrum exhibits a double-horned profile, is centrally concentrated, and is spatially coincident with the highest stellar mass surface density region of the galaxy. In only one galaxy is the CO peak outside the galaxy center, with the suggestion of an offset CO hole. The HI detections show a range of morphology, but the HI reservoir is generally more extended than the CO when both are detected. We compare the total gas fraction and H_2-to-HI ratios as a function of redshift for CHILES and other samples to search for evidence of evolution in the gas reservoirs, and compare the gas content with measured star formation rates to estimate the star formation efficiency with respect to each gas component.
Mario Santos - UWC
A first detection of neutral hydrogen intensity mapping on Mpc scales at z~0.32 and z~0.44
Abstract: We report the first direct detection of the cosmological power spectrum using the intensity signal from 21-cm emission of neutral hydrogen (HI), derived from interferometric observations with the L-band receivers of the new MeerKAT radio telescope. Intensity mapping is a promising technique to map the three-dimensional matter distribution of the Universe at radio frequencies and probe the underlying Cosmology as well the HI mass distribution. We present independent measurements of the HI power spectrum at redshifts 0.32 and 0.44 with high statistical significance using a foreground avoidance method (at 8.0\\sigma and 11.5\\sigma respectively). We constrain the rms of the fluctuations of the HI distribution to be sigma_HI = 0.44 +-0.04 mK and sigma_HI = 0.63 +-0.03 mK respectively at scales of 1.0 Mpc. Furthermore, the information contained in the power spectrum measurements allows us to probe the parameters of the HI mass function and HI halo model.
Francesco Sinigaglia - Universit degli Studi di Padova
Constraints on HI at z~0.37 from stacking on MIGHTEE-HI data
Abstract: The Neutral Hydrogen (HI) plays a key role in galaxy formation and evolution, as it constitutes the primary ingredient to form molecular Hydrogen (H2), and therefore the raw fuel of star formation. While the HI can be probed through the 21-cm emission line, it has been so far revealed via direct detections almost only in the nearby Universe (z<0.1), remaining mostly unprobed at higher redshift, except for results based on few works adopting spectral line stacking.
In this talk we present our recent findings obtained applying spectral line stacking to MIGHTEE-HI data, acquired with the MeerKAT telescope. Using a sample of >9000 galaxies with known spectroscopic redshift, we have presented the first detection of scaling relations of star-forming galaxies at a median redshift z~0.37 and beyond the nearby universe, thereby adding new fundamental constraints on our understanding of the role of HI in galaxy evolution.
In addition, I will present new recent results of ongoing studies where we have applied the same spectral stacking methodology to unravel the HI content of galaxy as a function of the large-scale structure environment (field, filaments, knots), as well as semi-analytical constraints on the HI mass function and on OmegaHI that I have derived from the aforementioned scaling relations.
Balpreet Kaur - National Centre for Radio Astrophysics - Tata Institute of Fundamental Research
The HI properties of star-forming galaxies at z~1 in the COSMOS field.
Abstract: Understanding galaxy evolution critically requires information on the evolution of the neutral gas content of galaxies across cosmic time. Unfortunately, the weakness of the HI 21cm transition makes it difficult to detect HI 21cm emission from individual high-redshift galaxies with current telescopes. However, it is possible to measure the average HI mass of a population of high-z galaxies, which have accurate redshifts and position, by stacking their redshifted HI 21cm emission signals. In this talk, I will present results from a deep Giant Metrewave Radio Telescope HI 21cm emission survey of star-forming galaxies at z~1 in the COSMOS field, which aims to measure the average HI mass of these galaxies via the above HI 21cm stacking approach. The outstanding multi-wavelength data available for the COSMOS galaxies will allow us to determine the dependence of their average HI properties upon their stellar properties, including the stellar mass, SFR, morphology, etc.
Lerothodi Leeuw - University of the Western Cape
Atomic Gas as a Tracer and Critical Test of Galaxy Evolution in Observations and Cosmological Simulations
Abstract: We will report on our on-going exploitation of atomic gas as a tracer and critical test of galaxy evolution in observations and cosmological simulations, that include MeerKAT observations and TNG 50 simulations.
Jeein Kim - Yonsei University
HI imaging study on the nearby X-ray selected AGN hosts
Abstract: We present the neutral hydrogen (HI) gas properties of nearby (z<0.0275) AGN host galaxies. Our local X-ray AGNs are selected based on the BAT AGN Spectroscopic Survey (BASS), i.e., hard X-ray all-sky observation followed by optical spectroscopy. Our sample consists of ~10 HI-rich (log M(HI) > 10 solar) galaxies. The goal is to establish the dynamic state of the cool gas reservoir of AGN host galaxies and to probe the recent gas accretion history associated with the sample. In this work, we describe the details of the HI morphology and kinematics of our local X-ray AGN host galaxies. We discuss the role of the HI gas in the AGN feeding and the impact of AGN activity on the cool gas reservoir.
Nomthendeleko Motha - University of the Western Cape
Investigating the synergy between radio and optical data
Abstract: Next-generation radio surveys from the Square Kilometre Array (SKA) mid-frequency telescope and its precursors will observe the universe with high spectral precision. The 21-cm neutral hydrogen (HI) emission line detected from these surveys is ideal for obtaining more accurate constraints on cosmological parameters. However, the HI line is intrinsically faint and difficult to detect at high redshift. In 2017, Harrison, Lochner, and Brown developed a Bayesian technique to estimate the redshift from a radio spectrum by fitting a standard model to the HI emission. We propose an extension of this work by incorporating photometric redshift and spatial information from optical surveys such as the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST). In this talk, we go into depth on the methods used to combine data from instruments such as the SKA and LSST to maximise potential scientific gain.
Gauri Sharma - University of the Western Cape
Optical plus HI galaxy surveys: A key to trace the evolution of dark matter halos over cosmic time.
Abstract: In the concordance cosmological scenario, the cold collisionless dark matter component dominates the mass budget of galaxies and interacts with baryons only via gravity. There is growing evidence from simulations that the former, instead, responds to the baryonic (feedback) processes which modify its density distribution over cosmic time. However, due to a lack of high-resolution data from high-redshift, until recently, it was not possible to test simulations across cosmic time. Thanks to the development of new-generation integral field spectrographs, it is now possible to observe and resolve distant galaxies. Thus, allowing us to solve the biggest mysteries of the Universe, such as the nature of dark matter. Concerning the same, I have analysed resolved observations of star-forming galaxies (SFGs) at 0.3 < z < 2.0, studied the shape of their velocity profiles (kinematics) and the distribution of dark matter and compared the results with their counterparts in the local Universe as well as in state-of-the-art galaxy simulations. I found a significant expansion in dark matter halos of SFGs over 6.5 Gyrs (Sharma at al. 2022, 2021A,B). At this conference, (i) I will present an analysis of resolved observations of SFGs at 0.3 < z < 2.0, and (ii) interpret these results in light of possible physical mechanisms that can drive an expansion in dark matter halos. Furthermore, I will show how new generation radio telescopes, such as MeerKAT-based HI surveys (LADUMA and MIGHTEE), can be used in tracing the dynamical evolution of dark matter halos and unveiling the true nature of dark matter.
Betsey Adams, John Cannon, SHIELD Team - ASTRON / Kapteyn
SHIELD: Survey of HI in Extremely Low-mass Dwarfs
Abstract: The Survey of HI in Extremely Low-mass Dwarfs (SHIELD) targets the 82 lowest HI-mass galaxies from the ALFALFA blind HI survey, selected to have HI masses below 10^7.2 based on flow model distances. SHIELD is a comprehensive effort to obtain multi-wavelength data for these galaxies, including (warm) Spitzer, ground-based H-alpha imaging, and higher resolution HI data. In particular, all 82 SHIELD galaxies now have VLA-C data, plus VLA-D or WSRT, providing 20-arcsec HI images for the full sample. In addition, 32 of the galaxies have VLA-B data, providing higher angular resolution images. I will highlight the SHIELD HI data and discuss plans for its release.
Henco Arlow - University of Cape Town
The gas content of Luminous Compact Blue Galaxies in the COSMOS field.
Abstract: Luminous compact blue galaxies (LCBGs) are a heterogeneous subset of starburst galaxies that are abundant at intermediate redshifts, but rare locally. This makes them a very rapidly evolving class of galaxies and hence good candidates for studying galactic evolution. We aimed to use the CHILES survey, covering a redshift range of z=0 to z=0.45 centring the COSMOS field, along with auxiliary data from the CHILES Continuum Polarisation survey to search for LCBG detections and study their HI properties to better understand the nature of these objects as they evolve to the present day.
Aeree Chung - Yonsei University
Local Cool-Gas Monsters: Resolving HI Gas and Star Formation Properties
Abstract: We present the resolved HI properties of 10 gas-rich galaxies in 0.04 < z < 0.06. The targets have high HI mass with M(HI) > 3e10 solar and (HI+H2)/M(sun) of 0.2 to 1.1, making good candidates for the examples at their early stage of baryonic mass accretion. Using HI morphology and kinematics, we discuss the signs of recent gas accretion and probe the origin of gas in the sample. We discuss why these galaxies are not actively forming stars in spite of a large cold gas reservoir.
Mikhail de Villiers - SAAO/UCT
Probing optical and radio diffuse gas in MHONGOOSE galaxies
Abstract: HIPASSJ1153-28 is an edge-on, spiral galaxy (Sd) part of the MHONGOOSE survey. We are looking for signatures of extraplanar gas associated with this galaxy and aim to characterise the kinematics of the disc as well as the extensive gaseous layers. Deep HI data from MHONGOOSE makes this possible as it allows us to probe the inner regions as well as the regions further out of this galaxy. The high sensitivity achieved by MeerKAT makes it possible to detect the faint extraplanar gas. The kinematics of the galaxy is studied primarily by using early release MHONGOOSE data through the means of tilted-ring modelling using 3D Barolo. We are also studying the diffuse and extraplanar diffuse ionized gas for this galaxy using high-resolution spectroscopic SALT data whereby the analysis of the Hα and [NII] emission lines allows for studying the dynamics of the galaxy. This also enables us to probe for diffuse ionized gas as well as extraplanar diffuse ionized gas. This will allow us to determine the galaxy kinematics, the properties of the extraplanar gas in both its atomic and ionized phases and the correlation between these phases of gas in addition to how they are related to the galactic disc. This work illustrates how sensitive HI observations can be examined in conjunction with optical SALT data to further our understanding of the origins of extraplanar gas, its kinematic behaviour and the baryon cycle.
Richard Dodson - ICRAR / UWA
Progress on CHILES imaging at ICRAR.
Abstract: not available
Narusha Isaacs-Klein - University of the Western Cape
New methods of extracting resolved galaxy properties from HI spectra.
Abstract: I aim to extract spatially-resolved information from unresolved data such as LADUMA detections. I have written Python code to do this using 3D-Barolo. I will test the method using real galaxies from WHISP and THINGS. Then I will apply this routine to the thousands of HI spectra from ALFALFA. I could potentially significantly increase the number of galaxies for which we have rotation curves and MHI profiles and this would be a great contribution to galaxy evolution studies.
Minsu Kim - Sejong University, Seoul, South Korea
Global HI properties of galaxies via super-profile analysis.
Abstract: We present a new method of constructing HI super-profiles of galaxies. A super-profile is a high-S/N stacked profile that is made by co-adding individual line-of-sight profiles in a cube. The method works by decomposing an HI data cube with a statistically determined optimal number of Gaussian components. These components are then aligned in velocity with respect to their centroid velocities and then stacked. We tested our new method on 64 high-resolution HI data cubes of nearby galaxies in the local Universe from THINGS and LITTLE THINGS observed with Very Large Array. In addition, we constructed HI super-profile following two conventional methods; i) using symmetrical profiles and ii) using velocity profiles where the centroid velocities are determined from Hermite h3 polynomial fitting. We find that the HI super-profiles constructed with the new method have comparatively narrower central parts and broader wings. This is mainly due to the removal of asymmetric velocity profiles that bias the conventional methods. We discuss how the new HI super-profiles' shape profiles correlate with the sample galaxies' global star formation rates.
Ilani Loubser - North-West University
Spectroscopic follow-up of HI-detected galaxies from the MeerKAT Fornax Survey
Abstract: We present results from our campaign to follow-up interesting, individual galaxies in the Fornax cluster, chosen from MeerKAT Fornax Survey (MFS) HI results, with spatially-resolved optical spectroscopy from the Southern African Large Telescope (SALT). Our overall aim with the spectroscopy is to study the stellar populations of the galaxies, and connect it to their gas content. The physical process(es) that describe the transition in colour of blue galaxies to red galaxies is of particular importance. We present measurements of optical parameters to separate galaxies governed by secular evolution (ageing) from systems whose star formation was interrupted during the last ~Gyr (quenching). We also combine our SALT spectra with spectra from other surveys (Fornax3D, SAMI Fornax Dwarf survey).
Filippo Maccagni - ASTRON
The low-column density gas in and around the spiral star-forming galaxy NGC1566
Abstract: The star formation (SF) history of a galaxy is regulated by the availability of its cold gas, which in turn is driven by the balance between material accreting from intergalactic space and gas expelled from the galactic disk. Atomic neutral hydrogen (HI) is an excellent tracer of this process. Nevertheless, past HI observations have always been limited by a trade off between field of view, spatial resolution and sensitivity, preventing studies of the very faint HI gas from the inter-galactic environment as well as the very compact sub-kpc HI distributions within the main disk and its link with SF regions. The MHONGOOSE large survey of MeerKAT is bringing the study of the HI in nearby galaxies (< 30 Mpc) to the next level: thanks to deep (55 hours) high spatial (>7'') and spectral (1.4 km/s) resolution observations over a wide field of view (1.5 degrees), we are able to identify and study the kinematics of the HI gas in star forming galaxies down to M(HI)=10^6 Msun for individual clouds and column densities ~5x10^18 cm-2 (3sigma detection limit at 20'' at 5 km/s). In this talk, I will focus on the interaction history of the massive (M(HI) 10^10 Msun) star-forming face-on galaxy NGC1566 (DL=18 Mpc) and the impact on its SF. For the very first time, the MHONGOOSE observations identify that a past tidal interaction with a massive companion (NGC1581) has left several gaseous debris clouds in the environment. The low-column density (a few times 10^17 cm-2) HI filaments connecting the disk of N1566 with nearby dwarf galaxies (M(HI) 2x10^6 Msun), suggest that more minor interactions are still on-going, actively contributing to the accretion of HI onto the galactic disk. Lastly, I will demonstrate the great potential of deep MeerKAT HI observations in not only detecting satellite low-mass satellite dwarfs, but also in studying their HI kinematics and relating it to the stellar population, thus providing novel information on the evolution of of low mass (10^8-9 Msun) haloes.
Nazir Makda - SAAO
Searching for HI-rich UDGs and LSBs in Hydra I
Abstract: Ultra-diffuse Galaxies (UDGs) are low surface brightness galaxies with a very low stellar mass component, however, their sizes are comparable to Milky Way-sized galaxies. These galaxies are predominantly found in clusters although they are expected to be cannibalized by the cluster’s strong tidal fields. The Hydra I galaxy cluster is a nearby (z ~ 0.0126, D ~ 55 Mpc) intermediate mass southern galaxy cluster. Hydra has been identified as a site of ongoing galaxy interactions and evolution through various studies at optical wavelengths. Recently Iodice et al. (2020) and La Marca et al. (2022) discovered 21 UDG candidates and 28 other Low Surface Brightness (LSB) galaxies in the central region of Hydra using deep optical imaging from the VLT Survey Telescope. Here I will present a MeerKAT HI study of Hydra where we follow-up on the UDGs and LSB galaxies.
Pavel Mancera Pina - Leiden Observatory
The extreme dark matter haloes of gas-rich ultra-diffuse galaxies
Abstract: Ultra-diffuse galaxies (UDGs) are a subset of low surface brightness galaxies characterised by their large optical disc scale lengths. Their formation mechanism is one of the most actively discussed subjects in extra-galactic astronomy during the last few years. Yet, no clear consensus has been reached regarding their evolutionary pathways, with a number of simulations producing UDG-like galaxies using very different feedback prescriptions and even with different dark matter haloes properties. To test such simulations it is necessary to improve the current observational constraints on UDGs; obtaining resolved kinematic measurements can be a powerful tool to such end.
I will present results regarding recent HI interferometric observations on a sample of isolated gas-rich UDGs. Robust kinematic modelling shows that the galaxies have very low circular speeds for their baryonic mass, making them outliers of the baryonic Tully-Fisher relation. Through rotation curve decomposition, we find that the dark matter fractions of our UDGs are very low in scales as large as 10 kpc. Within the context of CDM, the only way to explain our observations is if UDGs have extremely low concentration parameters, off from the expected dark matter concentration-mass relation. I will highlighting the potential of studying the dynamics of UDGs to obtain insights into the nature of dark matter itself.
Tumelo Mangena - University of Cape Town
HI stacking of AGN vs non-AGN with MIGHTEE.
Abstract: We aim to study the atomic neutral hydrogen (HI) content of the active galactic nuclei (AGN) and non-AGN galaxies in the COSMOS field with MIGHTEE-HI radio data. We present preliminary results based on two sub-samples at lower-z (z < 0.084) and higher-z (0.22 < z < 0.5). In order to perform HI stacking, we establish a source catalogue using data from MIGHTEE radio continuum Early Science catalogue which contains both spectroscopic and photometric redshifts. To increase our spectroscopic sample, we crossmatch this catalogue with the Deep Extragalactic VIsible Legacy Survey (DEVILS) master redshift catalogue (Davies, Cook, private communication) and gain 10 percent more of spectroscopic redshifts. From these catalogues, we will create redshift- and stellar mass-matched samples of HERGS/star forming galaxies and LERGS/giant ellipticals. Our ultimateaim is to investigate and compare the HI content of HERGs, LERGs and star forming galaxies using the stacking technique.
Tilman Oelgeschlager - University of Cape Town
The Cosmic Web in the LADUMA Field
Abstract: Cosmic web filaments are an intermediate density environment which have been shown to play a role in a galaxy’s evolution. In order to accurately identify cosmic web filaments in a volume, a complete sample of galaxies with accurate distance measurements is required. For this reason, studies which identify filaments and investigate the properties of galaxies within them have been mostly restricted to the local Universe, where complete samples of galaxies with spectroscopic redshift measurements are available. This includes recent studies investigating the HI content of galaxies in cosmic web filaments. Our study focuses on the cosmic volume being investigated by the LADUMA survey on MeerKAT. LADUMA's deep HI measurements will allow for the study of the HI content of galaxies in filaments beyond the local Universe - however, LADUMA's ancillary data catalogue provides a limited sample of spectroscopic redshift measurements for different redshift ranges. We investigate the effects of using an incomplete spectroscopic sample on the output of the filament finder DisPerSE using Simba cosmological simulation data. Potential methods of using photometric redshift measurements to improve the accuracy of the output of DisPerSE and the effects of redshift uncertainties on filament-finding are also investigated.
Kyle Oman - University of Cape Town
Low-mass galaxy rotation curves that fail as dynamical mass tracers
Abstract: It is routinely assumed that galaxy rotation curves are equal to their circular velocity curves (modulo some corrections) such that they are good dynamical mass tracers. We took a somewhat unconventional, visualisation-driven approach to analysing 33 low-mass galaxies from the APOSTLE simulation suite exploring the limits of the validity of this assumption. Only 3 galaxies have rotation curves nearly equal to their circular velocity curves; the rest are undergoing a wide variety of dynamical perturbations. We used our visualisations to guide an assessment of how many galaxies are likely to be strongly perturbed by processes in several categories: mergers/interactions, bulk gas flows, non-spherical DM halo, warps, and IGM ram pressure. Most galaxies fall into more than one of these categories; only 5/33 are not in any of them. The sum of these effects leads to an underestimation of the low-velocity slope of the baryonic Tully-Fisher relation that is difficult to avoid, and could plausibly be the source of a significant portion of the observed diversity in low-mass galaxy rotation curve shapes.
Martin Shanobe - University of Cape Town
Radio properties of post-starburst galaxies in the Cosmos field
Abstract: Understanding galaxy formation and evolution requires a thorough understanding of gas cycles in and around galaxies and how they relate to galaxy characteristics like stellar mass and star formation rate. Post-starburst (or "E+A") galaxies trace the most rapid and dramatic processes in galaxy evolution, making them excellent systems to study the mechanisms underlying galaxy evolution. MIGHTEE and CHILES, sensitive surveys, will be used to better understand the radio properties of post-starburst galaxies in the H-I and radio continuum.