TY - JOUR
T1 - Hiding in plain sight
T2 - Record-breaking compact stellar systems in the sloan digital sky survey
AU - Sandoval, Michael A.
AU - Vo, Richard P.
AU - Romanowsky, Aaron J.
AU - Strader, Jay
AU - Choi, Jieun
AU - Jennings, Zachary G.
AU - Conroy, Charlie
AU - Brodie, Jean P.
AU - Foster, Caroline
AU - Villaume, Alexa
AU - Norris, Mark A.
AU - Janz, Joachim
AU - Forbes, Duncan A.
N1 - Publisher Copyright:
© 2015. The American Astronomical Society. All rights reserved..
PY - 2015/7/20
Y1 - 2015/7/20
N2 - 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 rh ∼ 20 pc) but is 40% more luminous (MV ∼ -14.6), making it the new densest-known galaxy. The second, M85-HCC1, has a size like a typical globular cluster (GC; rh ∼ 1.8 pc) but is much more luminous (MV ∼ -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 potential value of ultra-compact dwarfs and massive GCs as tracers of the assembly histories of galaxies.
AB - 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 rh ∼ 20 pc) but is 40% more luminous (MV ∼ -14.6), making it the new densest-known galaxy. The second, M85-HCC1, has a size like a typical globular cluster (GC; rh ∼ 1.8 pc) but is much more luminous (MV ∼ -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 potential value of ultra-compact dwarfs and massive GCs as tracers of the assembly histories of galaxies.
KW - galaxies: fundamental parameters
KW - galaxies: nuclei
KW - galaxies: star clusters: general
UR - http://www.scopus.com/inward/record.url?scp=84937800630&partnerID=8YFLogxK
U2 - 10.1088/2041-8205/808/1/L32
DO - 10.1088/2041-8205/808/1/L32
M3 - Article
AN - SCOPUS:84937800630
SN - 2041-8205
VL - 808
JO - Astrophysical Journal Letters
JF - Astrophysical Journal Letters
IS - 1
M1 - L32
ER -