The Detection of Ultra-faint Low Surface Brightness Dwarf Galaxies in the Virgo Cluster: A Probe of Dark Matter and Baryonic Physics

Journal
Date Issued
2015
Author(s)
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Fassbender, R.
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DOI
Description
We thank the referee for useful comments which have significantly improved our paper. We also thank M. Dickinson for critical reading. Observations have been carried out using the Large Binocular Telescope at Mt. Graham, AZ. The LBT is an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University; and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota, and University of Virginia.
Abstract
We have discovered 11 ultra-faint (r ≲ 22.1) low surface brightness (LSB, central surface brightness 23 ≲ μr ≲ 26) dwarf galaxy candidates in one deep Virgo field of just 576 arcmin2 obtained by the Large Binocular Camera at the Large Binocular Telescope. Their association with the Virgo cluster is supported by their distinct position in the central surface brightness—total magnitude plane with respect to the background galaxies of similar total magnitude. They have typical absolute magnitudes and scale sizes, if at the distance of Virgo, in the range -13 ≲ Mr ≲ -9 and 250 ≲ rs ≲ 850 pc, respectively. Their colors are consistent with a gradually declining star formation history with a specific star formation rate of the order of 10-11 yr-1, i.e., 10 times lower than that of main sequence star-forming galaxies. They are older than the cluster formation age and appear to be regular in morphology. They represent the faintest extremes of the population of low luminosity LSB dwarfs that has recently been detected in wider surveys of the Virgo cluster. Thanks to the depth of our observations, we are able to extend the Virgo luminosity function down to Mr ̃ -9.3 (corresponding to total masses M ̃ 107 M☉), finding an average faint-end slope α ≃ -1.4. This relatively steep slope puts interesting constraints on the nature of the dark matter and, in particular, on warm dark matter (WDM) often invoked to solve the overprediction of the dwarf number density by the standard cold dark matter scenario. We derive a lower limit on the WDM particle mass >1.5 keV.
Volume
813
Issue
1
Start page
68
Uri
Url
Issn Identifier
0004-637X
Ads BibCode
2015ApJ...813...68G
Rights
open.access
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