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Title: HIDING IN PLAIN SIGHT: RECORD-BREAKING COMPACT STELLAR SYSTEMS IN THE SLOAN DIGITAL SKY SURVEY

Motivated by the recent, serendipitous discovery of the densest known galaxy, M60-UCD1, we present two initial findings from a follow-up search, using the Sloan Digital Sky Survey, Subaru/Suprime-Cam, and Hubble Space Telescope imaging, and SOuthern Astrophysical Research (SOAR)/Goodman spectroscopy. The first object discovered, M59-UCD3, has a similar size to M60-UCD1 (half-light radius of r{sub h} ∼ 20 pc) but is 40% more luminous (M{sub V} ∼ −14.6), making it the new densest-known galaxy. The second, M85-HCC1, has a size like a typical globular cluster (GC; r{sub h} ∼ 1.8 pc) but is much more luminous (M{sub V} ∼ −12.5). This hypercompact cluster is by far the densest confirmed free-floating stellar system, and is equivalent to the densest known nuclear star clusters. From spectroscopy, we find that both objects are relatively young (∼9 and ∼3 Gyr, respectively), with metal-abundances that resemble those of galaxy centers. Their host galaxies show clear signs of large-scale disturbances, and we conclude that these dense objects are the remnant nuclei of recently accreted galaxies. M59-UCD3 is an ideal target for follow-up with high-resolution imaging and spectroscopy to search for an overweight central supermassive black hole as was discovered in M60-UCD1. These findings also emphasize the potentialmore » value of ultra-compact dwarfs and massive GCs as tracers of the assembly histories of galaxies.« less
Authors:
; ;  [1] ;  [2] ; ;  [3] ; ;  [4] ;  [5] ;  [6] ;  [7] ; ;  [8]
  1. Department of Physics and Astronomy, San José State University, One Washington Square, San Jose, CA 95192 (United States)
  2. Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States)
  3. Harvard–Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  4. Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)
  5. University of California Observatories, 1156 High Street, Santa Cruz, CA 95064 (United States)
  6. Australian Astronomical Observatory, P.O. Box 915, North Ryde, NSW 1670 (Australia)
  7. Max Planck Institut für Astronomie, Königstuhl 17, D-69117, Heidelberg (Germany)
  8. Centre for Astrophysics and Supercomputing, Swinburne University, Hawthorn, VIC 3122 (Australia)
Publication Date:
OSTI Identifier:
22518914
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 808; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTROPHYSICS; BLACK HOLES; DISTURBANCES; DWARF STARS; GALAXIES; GALAXY NUCLEI; METALS; RESOLUTION; SPACE; SPECTROSCOPY; STAR CLUSTERS; TELESCOPES; VISIBLE RADIATION