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The frequency of dwarf galaxy multiples at low redshift in SDSS versus cosmological expectations

Besla, Gurtina and Patton, David R. and Stierwalt, Sabrina and Rodriguez-Gomez, Vicente and Patel, Ekta and Kallivayalil, Nitya J. and Johnson, Kelsey E. and Pearson, Sarah and Privon, George C. and Putman, Mary E. (2018) The frequency of dwarf galaxy multiples at low redshift in SDSS versus cosmological expectations. Monthly Notices of the Royal Astronomical Society, 480 (3). pp. 3376-3396. ISSN 0035-8711.

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We quantify the frequency of companions of low-redshift (0.013 < z < 0.0252) dwarf galaxies (2 × 10^8 M⊙ < M_(star) < 5 × 10^9 M⊙) that are isolated from more massive galaxies in SDSS and compare against cosmological expectations using mock observations of the Illustris simulation. Dwarf multiples are defined as two or more dwarfs that have angular separations >55 arcsec, projected separations r_p < 150 kpc, and relative line-of-sight velocities ΔV_(LOS) < 150 km s^(−1). While the mock catalogues predict a factor of two more isolated dwarfs than observed in SDSS, the mean number of observed companions per dwarf is N_c ∼ 0.04, in good agreement with Illustris when accounting for SDSS sensitivity limits. Removing these limits in the mock catalogues predicts N_c ∼ 0.06 for future surveys (LSST, DESI), which will be complete to M_(star) = 2 × 10^8 M⊙. The 3D separations of mock dwarf multiples reveal a contamination fraction of ∼40 per cent in observations from projection effects. Most isolated multiples are pairs; triples are rare and it is cosmologically improbable that bound groups of dwarfs with more than three members exist within the parameter range probed in this study. We find that <1 per cent of LMC-analogues in the field have an SMC-analogue companion. The fraction of dwarf “Major Pairs” (stellar mass ratio >1:4) steadily increases with decreasing Primary stellar mass, whereas the cosmological “Major Merger rate” (per Gyr) has the opposite behaviour. We conclude that cosmological simulations can be reliably used to constrain the fraction of dwarf mergers across cosmic time.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Stierwalt, Sabrina0000-0002-2596-8531
Rodriguez-Gomez, Vicente0000-0002-9495-0079
Johnson, Kelsey E.0000-0001-8348-2671
Privon, George C.0000-0003-3474-1125
Alternate Title:The Frequency of Dwarf Galaxy Multiples at Low Redshift in SDSS vs. Cosmological Expectations
Additional Information:© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2018 July 20. Received 2018 July 14; in original form 2018 April 23. Published: 01 August 2018. We thank Marla Geha, Greg Snyder, and Nicolas Garavito-Camargo for useful conversations that have facilitated this work. We also thank the Illustris collaboration for making their subhalo catalogues and merger trees publicly available. GB acknowledges that this material is based on work supported by the National Science Foundation under grant AST 1714979. NK is supported by NSF CAREER award 1455260. DRP acknowledges the support of the Natural Sciences and Engineering Research Council of Canada (NSERC). The analysis in this study was carried out using the El Gato cluster at the University of Arizona, which is funded by the National Science Foundation through Grant No. 1228509. This work has also used catalogues from the NASA Sloan Atlas and the SDSS. Funding for the NASA Sloan Atlas has been provided by the NASA Astrophysics Data Analysis Program (08-ADP08-0072) and the NSF (AST- 1211644). Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science. The SDSS-III web site is SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, Harvard University, the Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York University, Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington, and Yale University. This research also utilized: IPython (Perez & Granger 2007), numpy (van der Walt, Colbert & Varoquaux 2011), and matplotlib (Hunter 2007).
Funding AgencyGrant Number
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Alfred P. Sloan FoundationUNSPECIFIED
Participating InstitutionsUNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
Subject Keywords:galaxies: dwarf – galaxies: groups: general –Magellanic Clouds
Issue or Number:3
Record Number:CaltechAUTHORS:20181130-090308539
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Official Citation:Gurtina Besla, David R Patton, Sabrina Stierwalt, Vicente Rodriguez-Gomez, Ekta Patel, Nitya J Kallivayalil, Kelsey E Johnson, Sarah Pearson, George C Privon, Mary E Putman; The frequency of dwarf galaxy multiples at low redshift in SDSS versus cosmological expectations, Monthly Notices of the Royal Astronomical Society, Volume 480, Issue 3, 1 November 2018, Pages 3376–3396,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:91351
Deposited By: Tony Diaz
Deposited On:30 Nov 2018 17:41
Last Modified:09 Mar 2020 13:19

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