THE NEXT GENERATION VIRGO CLUSTER SURVEY. X. PROPERTIES OF ULTRA-COMPACT DWARFS IN THE M87, M49, AND M60 REGIONS

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Published 2015 October 6 • © 2015. The American Astronomical Society. All rights reserved.
, , Citation Chengze Liu et al 2015 ApJ 812 34 DOI 10.1088/0004-637X/812/1/34

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1 Center for Astronomy and Astrophysics, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China; czliu@sjtu.edu.cn

2 Shanghai Key Lab for Particle Physics and Cosmology, Shanghai Jiao Tong University, Shanghai 200240, China

3 Department of Astronomy, Peking University, Beijing 100871, China; peng@pku.edu.cn

4 Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, China

5 Herzberg Institute of Astrophysics, National Research Council of Canada, Victoria, BC V9E 2E7, Canada

6 Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile

7 Millennium Institute of Astrophysics, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile

8 Department of Astronomy, Case Western Reserve University, Cleveland, OH, USA

9 National Astronomical Observatories, Chinese Academy of Sciences, A20 Datun Rd, Chaoyang District, Beijing 100012, China

10 Chinese Academy of Sciences South America Center for Astronomy, Camino EI Observatorio #1515, Las Condes, Santiago, Chile

11 Observatoire Astronomique de Strasbourg, Université de Strasbourg & CNRS, UMR 7550, 11 rue de l'Université, F-67000 Strasbourg, France

12 CEA/IRFU/SAp, Laboratoire AIM Paris-Saclay, CNRS/INSU, Université Paris Diderot, Observatoire de Paris, PSL Research University, F-91191 Gif-sur-Yvette Cedex, France

13 Aix-Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, F-13388, Marseille, France

14 Department of Physics and Astronomy, Youngstown State University, One University Plaza, Youngstown, OH 44555, USA

15 AIM Paris Saclay, CNRS/INSU, CEA/Irfu, Université Paris Diderot, Orme des Merisiers, F-91191 Gif sur Yvette cedex, France

16 UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA

17 Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA

18 GEPI, Observatoire de Paris, CNRS, University of Paris Diderot, Paris Sciences et Lettres (PSL), 61, Avenue de l'Observatoire F-75014, Paris France

19 University of Paris Denis Diderot, University of Paris Sorbonne Cité (PSC), F-75205 Paris Cedex 13, France

20 California Institute of Technology, Pasadena, CA 91125, USA

Author notes

21 CAS-CONICYT Fellow.

22 Authors to whom all correspondence should be addressed.

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Dates

  1. Received 2015 April 17
  2. Accepted 2015 August 26
  3. Published
Keywords

galaxies: dwarf; galaxies: individual (M87, M49, M60); galaxies: nuclei; galaxies: star clusters: general

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0004-637X/812/1/34

ABSTRACT

We use imaging from the Next Generation Virgo cluster Survey (NGVS) to present a comparative study of ultra-compact dwarf (UCD) galaxies associated with three prominent Virgo sub-clusters: those centered on the massive red-sequence galaxies M87, M49, and M60. We show how UCDs can be selected with high completeness using a combination of half-light radius and location in color–color diagrams (u*iKs or u*gz). Although the central galaxies in each of these sub-clusters have nearly identical luminosities and stellar masses, we find large differences in the sizes of their UCD populations, with M87 containing ∼3.5 and 7.8 times more UCDs than M49 and M60, respectively. The relative abundance of UCDs in the three regions scales in proportion to sub-cluster mass, as traced by X-ray gas mass, total gravitating mass, number of globular clusters (GCs), and number of nearby galaxies. We find that the UCDs are predominantly blue in color, with ∼85% of the UCDs having colors similar to blue GCs and stellar nuclei of dwarf galaxies. We present evidence that UCDs surrounding M87 and M49 may follow a morphological sequence ordered by the prominence of their outer, low surface brightness envelope, ultimately merging with the sequence of nucleated low-mass galaxies, and that envelope prominence correlates with distance from either galaxy. Our analysis provides evidence that tidal stripping of nucleated galaxies is an important process in the formation of UCDs.

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Footnotes

  • 23 

    A working definition of UCDs has recently been proposed by Willman & Strader (2012), who take UCDs to be systems with sizes 10 ≤ rh ≤ 100 pc and absolute magnitudes −13 ≤ MV ≤ −9. However, a variety of such definitions exist, and it is worth remembering that all such definitions remain subjective in nature.

  • 24 

    Outside of the M87 region, r-band imaging is available at only a fraction of the full survey depth, ranging from 1374 to 4461 s.

  • 25 

    See http://www.cfht.hawaii.edu/Instruments/Imaging/WIRCam/IiwiVersion2Doc.html

  • 26 

    These are equivalent to aperture radii of 0farcs28, 0farcs37, 0farcs47, 0farcs56, 0farcs65, 0farcs75, 1farcs5, and 3farcs0. In physical units, these radii are 22, 30, 37, 45, 52, 60, 120, and 240 pc at the distance of Virgo.

  • 27 

    Here rt and rc are tidal and core radius, respectively.

  • 28 

    The blue luminosities of the three galaxies are quite similar, differing from their mean luminosity by only ≲25%.

  • 29 

    A fourth subcluster is probably associated with M86 (VCC763), located ≃1fdg5 WNW of M87 (e.g., Binggeli 1999; Schindler et al. 1999; Mei et al. 2007).

  • 30 

    Three of these 11 objects were not detected in the NGVS due to their proximity to bright stars.

  • 31 

    We note that none of these fields contains a known galaxy cluster with z ≲ 0.1, although a galaxy group, located at z ∼ 0.02 (Crook et al. 2007), does fall within the BG4 field.

  • 32 

    These 64 objects refer to the sample of 80 nuclei that appear in the SExtractor catalog after discarding the 16 bright (g < 18.5 mag) nuclei that are saturated in the deep NGVS images.

  • 33 

    We choose 25Re to make sure that the NUCD count areas are in our survey regions.

  • 34 

    For more information, see http://www2.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/megapipe/docs/filters.html

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10.1088/0004-637X/812/1/34