TY - JOUR
T1 - An ultra-compact dwarf around the sombrero galaxy (M104)
T2 - The nearest massive UCD
AU - Hau, George K T
AU - Spitler, Lee R.
AU - Forbes, Duncan A.
AU - Proctor, Robert N.
AU - Strader, Jay
AU - Trevor Mendel, J.
AU - Brodie, Jean P.
AU - Harris, William E.
PY - 2009/3
Y1 - 2009/3
N2 - We report the discovery of an ultra-compact dwarf (UCD) associated with the Sombrero galaxy (M104). This is the closest massive UCD known and the first spectroscopically verified massive UCD which is located in a low-density environment. The object, we name SUCD1, was identified in Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) imaging and confirmed to be associated with the Sombrero galaxy by its recession velocity obtained from Keck spectra. The light profile is well fitted by a Wilson model. We measure a half-light size of 14.7 ±1.4 pc, an absolute magnitude of Mv = - 12.3 mag (MK = -15.1 mag) and an internal velocity dispersion of 25.0 ± 5.6 km s-1. Such values are typical of UCDs. From Lick spectral indices we measure a luminosity-weighted central age of 12.6 ± 0.9 Gyr, [Fe/H] of -0.08 ± 0.08 dex and [α/Fe] of 0.06 ± 0.07 dex. The lack of colour gradients suggests these values are representative of the entire UCD. The derived stellar and virial masses are the same, within errors, at ~3.3 × 107 M. Thus, we find no strong evidence for dark matter or the need to invoke a non-standard initial mass function. We also report arguably the first X-ray detection of a bona fide UCD, which we attribute to the presence of low-mass X-ray binaries. The X-ray luminosity of LX = 0.56 × 1038 ergs-1 is consistent with the values observed for globular clusters (GCs) of the same metallicity. Overall, we find SUCD1 has properties similar to other known UCDs and massive GCs.
AB - We report the discovery of an ultra-compact dwarf (UCD) associated with the Sombrero galaxy (M104). This is the closest massive UCD known and the first spectroscopically verified massive UCD which is located in a low-density environment. The object, we name SUCD1, was identified in Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) imaging and confirmed to be associated with the Sombrero galaxy by its recession velocity obtained from Keck spectra. The light profile is well fitted by a Wilson model. We measure a half-light size of 14.7 ±1.4 pc, an absolute magnitude of Mv = - 12.3 mag (MK = -15.1 mag) and an internal velocity dispersion of 25.0 ± 5.6 km s-1. Such values are typical of UCDs. From Lick spectral indices we measure a luminosity-weighted central age of 12.6 ± 0.9 Gyr, [Fe/H] of -0.08 ± 0.08 dex and [α/Fe] of 0.06 ± 0.07 dex. The lack of colour gradients suggests these values are representative of the entire UCD. The derived stellar and virial masses are the same, within errors, at ~3.3 × 107 M. Thus, we find no strong evidence for dark matter or the need to invoke a non-standard initial mass function. We also report arguably the first X-ray detection of a bona fide UCD, which we attribute to the presence of low-mass X-ray binaries. The X-ray luminosity of LX = 0.56 × 1038 ergs-1 is consistent with the values observed for globular clusters (GCs) of the same metallicity. Overall, we find SUCD1 has properties similar to other known UCDs and massive GCs.
UR - http://www.scopus.com/inward/record.url?scp=73949150968&partnerID=8YFLogxK
U2 - 10.1111/j.1745-3933.2009.00618.x
DO - 10.1111/j.1745-3933.2009.00618.x
M3 - Letter
AN - SCOPUS:73949150968
VL - 394
SP - L97–L101
JO - Monthly Notices of the Royal Astronomical Society: Letters
JF - Monthly Notices of the Royal Astronomical Society: Letters
SN - 1745-3925
IS - 1
ER -