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Gaia Streams Challenge

Update 19 May 2014: there is a new version of the mock halo consistent with the published version. The main difference is in the addition of several large streams that complete the high end of the luminosity function (the old halo was limited to streams with velocity dispersion less than 20 km/s).

Please see also the Gaia Challenge Wiki and especially its page about streams to understand what this is all about.

I have created a mock Galactic stellar halo for use in testing various algorithms for recovering the Milky Way's gravitational potential from measurements of the phase space positions of tidal streams. Currently the test data for a spherical halo is available but I hope to add axisymmetric and triaxial potentials shortly. The process generating the satellites that dissolve into streams is decoupled from the potential in which the streams are integrated, so that the same set of progenitor satellites can be compared across different potentials.

Spherical Halo

This challenge comes in two parts: (I) determine the form of the spherical potential in which the streams are orbiting and (II) determine the best-fit parameters for that form. You may choose to do part II only, or both parts I and II. The answers can be found in Section 3.1 of Sanderson, Helmi, & Hogg (2014), which should be cited in any work involving this data.

The mock halo has been provided by Robyn Sanderson (questions/comments to sanderson at astro dot rug dot nl) and can be downloaded as a tarball here.

The tarball includes 5 ASCII data files, listed below, which contain the information about the stars in the mock halo. Details of how the halo was generated can be found in Section 3.2 of Sanderson, Helmi, & Hogg (2014). In all files, the first line is the number of lines after that line in the file. So to read things in, read the first integer to get n_lines, then read n_lines of data.

MilkyWay1.dat includes the positions (in kpc) and velocities (in km/s) of the stars in the halo after convolution with the Gaia error model. Information on the error convolution is in Section 3.3 of Sanderson, Helmi, & Hogg (2014). are the same positions/velocities before error convolution.

MilkyWay1.obs.dat are the coordinates and errors in the observed space. The 11 columns are visual magnitude, right ascension (rad), declination (rad), parallax (mas), par error, mu_alpha (proper motion in RA, mas/yr), pm error, mu_delta (proper motion in dec, mas/yr), pm error, radial velocity (km/s), RV error.

MilkyWay1.sats.dat is a list of the locations of the first star in each progenitor satellite in the above three files. The stars are in the same order in all three files, sorted by progenitor, so the stars belonging to progenitor i are at positions sats(i):(sats(i+1) -1) in the arrays holding the positions/velocities (assuming zero-indexed arrays). contains the properties of the progenitor satellites that produced the streams in the data set. The 9 columns are satellite ID# (from the larger sample that these are drawn from), total number of [RGB] stars in the satellite, time since infall in Myr, log luminosity in solar units, log *total* mass (stars+dark matter) in solar masses, scale radius in kpc, velocity dispersion in km/s, orbital apocenter radius in kpc, and orbital circularity [from 0 (=radial) to 1 (=circular)].

A copy of this page is also included as README.html.

Publication policy

Please do not use the mock halo data for purposes other than testing potential-fitting codes without asking Robyn first. Thanks for your understanding!

When making use of this data, please cite the Gaia Challenge Wiki and Sanderson, Helmi, & Hogg 2014, ApJ subm., arXiv:1404.6534.

Good luck!