My Research

1. Research Projects


Research Projects

1. The SAMI-Fornax Survey

Together with Nic Scott (Sydney) I set up a program to obtain IFU data of dwarf galaxies in the Fornax Cluster with SAMI, but at resolution R=5000. Since we could observe  up to 12 galaxies at the same time, we could afford to spend long integration times on each object. In 3 observing runs we obtained useful spectra for 40 dwarfs galaxies, together with some giants, UCDs and other objects. Our spectral resolution of σ=10km/s made it possible to study the dynamics of objects down to a stellar mass of 107 MSun. This is lower than anyone else has been doing outside the Local Group. This sample has allowed us to study a number of unique aspects of dwarf galaxies in Fornax:
- In Paper I (Scott et al. 2020) we find that dwarf galaxies are not rotationally supported, both stat forming and non star-forming ones. This agrees with galaxies in the Local Group, but is very different from more massive galaxies.
- In Paper II (Eftekhari et al. 2022) we study the Stellar Mass Fundamental Plane, showing that the dark matter fraction in dwarfs goes up when going down in mass.
- In Paper III (Romero-Gomez et al. 2023) we study the α/Fe abundance ratio, an indication of star formation speed. When adding samples of massive galaxies and of faint Local Group galaxies, we find a U-shape in the α/Fe vs. stellar mass diagram.  α/Fe is large in massive ellipticals and in Ultra Faint dwarfs, showing that the star formation histories in galaxies of 107 - 108 MSun. are the most extended.
- In Paper IV (Romero-Gomez et al. 2023, submitted) we present the star formation histories of the sample, showing the same results as in Paper III with more detail.
- In Paper V (Romero-Gomez et al. 2023, submitted) we study how dwarf galaxies in Fornax are quenched by their environment, and compare with simulations.

2. Euclid

I am part of the Euclid team, and co-lead of the work package on dwarfs of the Local Universe Science Working Group. With my team in Groningen we prepare for analyzing the properties of dwarf galaxies with Euclid Data, and use this to understand some basic cosmological problems, such as the Missing Dwarf Problem. At present I am working on some Early Research Observations (ERO's), to prepare for the first release. Euclid, with its high spatial resolution, is similar to HST, but observing about 10000 square degrees rather deeply.

3. New techniques in astronomy

With my colleagues from computer science from the SUNDIAL team (see previous research) we are continuing to work on improving algorithms that can be usefully applied in astronomy.

- 1-DREAM. Filament detection in astronomy. In SUNDIAL,  a team, including Peter Tino (Birmingham), Kerstin Bunte (Bernoulli Institute, Groningen), myself and Rory Smith (KASI, Korea, now Chile), with several PhD students, developed a probabilitic modelling pipeline to define filaments in n-dimensional point-clouds (Taghribi et al. 2020, Canducci et al., 2022). This allows a detailed study of the manifolds, along or perpendicular to it. This method allows a large variety of applications. Petra Awad, a common student between Kerstin Bunte and myself, has applied the method to the Cosmic Web, and shown in Awad et al. (2023) that the method performs better than the often used code DisPerSE (Sousbie et al. 2011). The second application has been to streams in Gaia. In Awad et al. (2023, submitted) we can separate the stream Jhelum in a broad and a narrow one. Another PhD student, Felipe Contreras is currently applying 1-DREAM to N-body models of the Cosmic Web.

- MTO. Faint galaxy detection. To detect faint galaxies, powerful methods are needed. People mostly have been using SExtractor in various configurations. We have been working on the code MTO (Teeninga et al. 2016), which gives better results (see Haigh et al. 2021, Venhola et al. 2022).  Currently,as followup to SUNDIAL, Michael Wilkinson (Bernoulli Institute, Groningen) and I have a new PhD Student, Mohammad Faezi, who is working on improving MTO, especially for multi-band photometry.


4. Educado

From Jan. 1, 2024, I will be deputy-PI of a new EU Doctoral Network, named Educado. t will run for 4 years, and, like SUNDIAL, it will be about techniques in astronomy to be developed in cooperation with computer scientists. 60% of the partners is the same as in SUNDIAL.


5. The CAVITY project

In this project we are studying the properties of galaxies in voids with the use of Integral Field Spectroscopy and ultradeep imaging from the INT. Although this project is its early phase, some papers have already been publish, like this Nature publication of Dominguez et al. (2023).


6. WEAVE

Soon, WEAVE will be available, an instrument that can observe 1000 objects at the same. WEAVE will be very useful, for example to follow up Euclid sources. I am involved in the WEAVE-CLUSTERS survey of WEAVE, to obtain mini-IFU observations, to do similar science as in SAMI-Fornax, but now for about 20 clusters.




Previous Research

1. SUNDIAL

I was leading the SUNDIAL EU International Training Network (2017-2021), consisting of 9 nodes across Europe. For more details see here. See also SUNDIAL Science, SUNDIAL Outreach, and the SUNDIAL BLOG.

SUNDIAL is an interdisciplinary network. It contains researchers in astronomy and computer science. In one sentence: I am studying dwarf galaxies using tools developed in SUNDIAL. Here I list my most important contributions in the network.
a) Detection of faint galaxies. We are still continuing the development of MTO.
b) Filament detection in astronomy. In SUNDIAL. This led to the 1-DREAM code.
c) Studying dwarf galaxy properties in the Fornax Cluster. See for this the FDS project, just below this section.
d) Studying point-like sources, such as globular clusters and UCDs in the Fornax Cluster. Since the FDS is very deep, it offers possibilities studying sources that point-like or almost point-like from the ground, like globular clusters and UCDs. It is thought that the globular cluster (GC) system reflects the initial situation of the galaxy, at the first formation of its stars (see Harris et al. 2013), and that the number of GCs correlates with the dark halo mass. We have studied the GC system in all dwarf galaxies of the FDS Dwarf Catalogue (Venhola et al. 2018), and are trying to undestand the dark halo masses. This is the work of the master thesis of Lorraine Putman. We have also investigated a population of compact galaxies that has not been studied much, the Ultra Compact Dwarfs. Teymoor Saifollahi has made the first unbiased study of UCDs in the whole Fornax Cluster, finding several UCDs that are not associated with other galaxies.
e) Zooniverse citizen science

2. FDS, the Fornax Deep Survey

In recent years it has been shown that galaxies are surrounded by stellar streams that are remnants from past interactions. These streams are invaluable fossils of the interaction history of galaxies with their environment, providing a new and very powerful way of studying galaxy evolution. At the same, wide field imaging camera's have become available, which make it possible to study large parts of the sky, to look for such streams. In this project we perform an ultradeep multiband (u,g,r and i) survey of the Fornax cluster, a nearby galaxy cluster, to study the interaction of galaxies with their environment. The survey is performed using the OmegaCAM camera at the VLT Survey Telescope (VST) , situated at the Paranal observatory of the European Southern Observatory . In depth and design, the FDS survey is similar to the NGVS survey at the CFHT, imaging the much larger and environmentally different Virgo cluster.

The FDS survey, started in 2013, and finished in 2022, uses the telescopes at the European Southern Observatory and is performed by an international team consisting from researchers in various ESO member states and Chile. The survey is supported by observations using various other instruments and telescopes, amongst which VIRCAM on the VISTA telescope, and VIMOS and MUSE at the VLT.

The research in my group concentrates on the dwarf galaxies in the Fornax cluster. Aku Venhola, who finished his thesis in 2019 in Groningen with a double degree with Oulu, did the full data reduction, and defined the dwarf catalog (FDSDC, Venhola et al. 2018). A second catalog was added later, including many very low surface brightness galaxies (Venhola et al. 2022). Seyda Sen (graduated in 2020) worked on  detailed stellar population modelling of the stellar populations in dwarf galaxies in Fornax (see Sen et al. 2022). Elaheh Hamraz (graduated in 2020) worked on young populations in dwarfs in the Fornax and Virgo cluster Hamraz et al. 2019). Sara Eftekhari was analyzing Integral Field Spectroscopy, to study the internal kinematics of dwarfs, and their resolved stellar populations. In the SUNDIAL project there are also other people outside Groningen, who work on the FDSDC: Alan Su (Oulu) was analyzing detailed morphology and nuclear clusters (Su et al. 2021, 2022).. Shivangee Rathi (Gent) is working on the stellar populations in the very outer parts, from deep colour profiles. Michele Mastropietro has been doing simulations on dwarf galaxies falling into the Fornax Cluster, with a particular emphasis on NGC 1427A (Mastropietro et al. 2021)

We are also using FDS in a Citizen's Science project. Since it is difficult to find out whether a galaxy in the FDS field is a dwarf galaxy in the cluster, or a large, massive galaxy behind it, we have tried developing algorithms to do this, but have also built a programme on Zooniverse, where members of the public can answer this question. This programme is called Space Fluff. Space Fluff has been set up by Anna Lanteri, as a SUNDIAL internship student in Groningen, and analyzed by bachelor student Christiaan Seerden.


You can find all FDS-related papers here.

The most important FDS papers are these:

Iodice et al. 2016, Iodice et al. 2017, Venhola et al. 2017, Venhola et al. 2018, Iodice et al. 2019, Venhola et al. 2019, Raj et al. 2019, Spavone et al. 2020, Peletier et al. 2020 (data release), Cantiello et al. 2020, Raj et al. 2020, Su et al. 2021, Su et al. 2022, Venhola et al. 2022.

A counterpart for the FDS in the field and in groups is the VEGAS survey, led by my Italian collaborators, in particular, Enrica Iodice.


3. The X-Shooter Spectral Library (XSL) project

The X-Shooter Spectral Library is a collection of 300025000 Å all stellar spectra observed at a resolving power of R = λ/Δλ ~ 10 000 with the medium-resolution spectrograph X-shooter at the Very Large Telescope (VLT). The library enables a new generation of stellar population models to study the stellar populations in galaxies. The library is used to make stellar population models for integrated stellar populations. When making the library, we paid particular attention to cool stars, to optimize the models in the near-infrared.

I am a co-PI of this project. The project is led by Scott Trager, and the other co-PI is Ariane Lancon (Strasbourg). Involved, amongst others, are the ex-Kapteyn postdoc Mariya Lyubenova, Anais Gonneau, ex-Kapteyn postdoc and Matthijs Dries, Kapteyn PhD student, as well as my ex-PhD student Yanping Chen. Also collaborators Alexandre Vazdekis, Jesus Falcon-Barroso, Paola Coelho, Philippe Prugniel and Patricia Sanchez-Blazquez are involved. Most of the work in the last 2 years was done by my PhD student Kristiina Verro.

The project was finished in 2022. We published the following papers. Three data release papers:

2014: Chen et al. 'The X-shooter Spectral Library (XSL). I. DR1: Near-ultraviolet through optical spectra from the first year of the survey'

2020: Gonneau et al.: The X-shooter Spectral Library (XSL): Data Release 2

2022: Verro et al.: The X-shooter Spectral Library (XSL): Data Release 3.

And one paper with the stellar population models:

2022: Verro et al.: Modelling Simple Stellar Populations from UV to NIR with the X-shooter Stellar Library (XSL)

and 4 papers dealing with aspects of the library:

2016: Gonneau et al.: Carbon stars in the X-shooter Stellar Library

2017: Gonneau et al.: Carbon stars in the X-shooter Stellar Library. II: Comparison with Models

2019: Arentsen et al.: Stellar atmospheric parameters for 764 spectra from the X-shooter Spectral Library

2021: Lancon et al.: A comparison between X-shooter spectra and PHOENIX models across the HR-diagram

We also published several conference proceedings.


4. The KIWICS project and the WEAVE surveys

Deep INT imaging data of nearby galaxy clusters, to obtain photometric properties of their dwarf galaxies, to use dwarf galaxies as probes to study the evolution of galaxies in cluster. The PI's of KIWICS are Alfonso Aguerri (IAC) and myself. We published 2 papers on Ultra Diffuse Galaxies in KIWICS (Mancera Pina et al. (2018, 2019). Choque-Challapa et al. 2021, Sen et al. 2023).  This work is done in preparation of the WEAVE Cluster survey. In the WEAVE project I am co-leader (with Alfonso Aguerri) of the nearby tear of the WEAVE Cluster survey.


My Research Group

  • Javier Roman, Margarita Salas postdoc, 2022-
  • Maria Angela Raj, EU Marie Curie Fellow, 2022-
  • Lei Titutlaer, Master student 2023-
  • Farhan Shah, Master student 2023-
  • Sara Eftekhari, PhD Student, Working on a project to measure stellar populations, dynamics and black hole masses in dwarf galaxies and UCDs, in collaboration with Steffen Mieske (ESO, Santiago). .2017-2023 (Dec 19)
  • Petra Awad, PhD Student, Working on filament extraction in astronomy, with applications towards GAIA and the Cosmic Web. Co-supervising with Kerstin Bunte (Bernoulli Institute for Computer Science, RUG), 2020-
  • Mohammad Faezi, PhD Student, Working on faint object detection in astronomy. Co-supervising with Michael Wilkinson (Bernoulli Institute for Computer Science, RUG), 2020-
  • Xu Xin, PhD Student, working on Understanding the Nature of Faint Dwarf Galaxies, 2021-
  • Felipe Contreras, PhD Student, working on Cosmological Simulations, double degree with University of Valparaiso, Chile. Double Degree, supervised together with Kerstin Bunte, and Graeme Candlish from the Univ. de Valparaiso. 2022-
  • 2nd supervisor of Jann Aschersleben, PhD Student, working on Combining Artificial Intelligence and Morphology for Dark Matter Searches. 1st supervisor Manuela Vecchi, other 2nd supervisor: Michael Wilkinson, 2020-
  • 2nd supervisor of Marta Borchiellini, PhD Student, working on particle astrophysics. 1st supervisor Manuela Vecchi

Former Members of my Research Group

  • Ignacio del Moral Castro, Margarita Salas Postdoc, 2023
  • Frouke Vonk, Bachelor student 2022-23
  • Suzanne Schakel, Master student, 2022-23
  • Kristiina Verro, PhD Student, Working on the XSL Stellar Library and Models. Co-supervising with Scott Trager, 2017-2022
  • Giuseppe Ussia, master student working on measuring the night sky brightness, 2022
  • Lorena Nicotera, master student working on measuring the night sky brightness, 2022
  • 2nd supervisor of Abolfazl Taghribi, PhD Student, SUNDIAL, working on developing probabilistic modelling algorithms to detect faint features in astronomy. 1st supervisor Kerstin Bunte (Bernoulli Institute for Computer Science, RUG), 2018-2022
  • 2nd supervisor of Marco Vasquez Beltran, PhD Student, working on developing piezoelectric deformable mirrors, with Bayu Jayawardhana (ENTEG), 2018-2022
  • 2nd supervisor of Jonas Bremer, PhD Student, working on the Epoch of Galaxy Formation, with Pratika Dayal, 2017-2022
  • 2nd supervisor of Michele Mastropietro, PhD Student, working on Simulations of Dwarf Galaxies in the Fornax Cluster, double degree with Gent University, SUNDIAL, co-supervising with Sven de Rijcke (Gent) and Michael Biehl (Bernoulli Institute for Computer Science, RUG), 2017-2021
  • Bahar Bidaran, PhD Student, SUNDIAL, Honorary Group Member, working on kinematics and stellar populations of an infalling group in the Virgo Cluster. Supervisors: Anna Pasquali, Eva Grebel, Heidelberg, 2017-2022
  • Alan (Hung-Shuo) Su, PhD Student, SUNDIAL, Honorary Group Member, working on detailed morphology of dwarf galaxies in the Fornax Cluster. Supervisor: Heikki Salo, Oulu, 2017-2022
  • Nelvy Choque, worked on a project to study the population of dwarf galaxies and UDGs in nearby galaxy clusters, in preparation for the WEAVE-Cluster survey. Finished her PhD in June 2022.
  • Teymoor Saifollahi, SUNDIAL PhD Student, working on the FDS Project, 2017-2022
  • Lorraine Putman, MSc student, worked on the Globular Cluster Distribution in Fornax dwarf galaxies. Finished July 2021.
  • Antonio la Marca, MSc Student, worked on the dwarf and UDG population in the Hydra Cluster, Exchange Student, University of Naples, Italy. Finished February 2021.
  • Christiaan Seerden, Bachelor Student, worked on analyzing the Space Fluff Zooniverse results, Finished July 2021
  • Jesper Karsten, Bachelor Student, worked on faint object detection, Finished July 2021
  • Douwe Nobels, Bachelor Students, worked on Asymmetries in Dwarf Galaxies, Finished July 2021
  • Jill Straat and Alessandro Angrilli Muglia, Honours College students, worked on GAIA trails of globular clusters, 2021
  • Fabian Gunnink, Honours College student, worked on MUSE data of the active galaxy Fornax A, 2021
  • Lasse Vulto, Bachelor Student, worked on Darkness Measurements in the North of the Netherlands, Finished July 2021
  • Aku Venhola, PhD student, did a double degree in both Groningen and Oulu in Finland. Co-supervisor Heikki Salo. Worked on the FDS project. 2019
  • Elaheh Hamraz, PhD student, worked on young populations in Fornax Dwarfs. 2020
  • Seyda Sen, PhD student, worked on detailed stellar populations in dwarf elliptical galaxies. 2020
  • Nynke Visser, Bachelor Student,worked on Citizen Science to create awareness for Light Pollution, 2019
  • Kyung Lin Dong, Bachelor Student, worked on AGN activity in Jellyfish galaxies, 2019
  • Jaco Mentz, did a double degree with NWU in Potchefstroom, South Africa. Co-supervisor Ilani Loubser, working on dwarf galaxies in the Fornax Cluster. 2018
  • Pavel Mancera Pina, Master Student, worked on the population of dwarf galaxies and UDGs in nearby galaxy clusters, in collaboration with Alfonso Lopez Aguerri. 2018
  • Miguel Rodin Rodriguez, Master Student, studied the UDG population in the Coma cluster. 2018
  • Reinier Koet, Bachelor Student, worked on stellar population modelling, 2017
  • Akke Corporaal, Bachelor Student,worked on dust in Fornax dwarf galaxies, 2017
  • Mustafa Yildiz, PhD Student, worked on star formation and HI in elliptical galaxies, 2017
  • Anastasia Ponomareva, PhD Student, worked on Infrared Scaling Relations in Spiral Galaxies. 2017
  • 2nd supervisor of Benny Roeck, PhD Student, worked on Infrared Stellar Populations, IAC Tenerife, 1st supervisor Alexandre Vazdekis
  • Pece Podigacoski, PhD Student, worked on star formation in AGNs using Herschel data, so-supervised by Peter Barthel, 2016
  • Sofia Meneses-Goytia, PhD Student, worked in Infrared Stellar Population Models, co-supervised with Scott Trager, 2015
  • Anais Gonneau, PhD Student, worked on Carbin Stars in the X-shooter stellar library, double degree with the University of Strasbourg, supervised by Ariane Lancon (Strasbourg) and Scott Trager, 2015
  • Yanping Chen, PhD Student, worked on the X-shooter Stellar Library, co-supervised with Scott Trager, 2014
  • Mark den Brok, PhD Student, worked on Dynamics and Stellar Populations of Small Stellar Systems, 2012
  • Guido van der Wolk, PhD Student, worked on Mid-Infrared Imaging of Dust in Galaxies, 2011


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