A metal-poor ultra compact dwarf galaxy at a kiloparsec distance from the low-mass elliptical galaxy FCC47. (arXiv:1904.01041v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Fahrion_K/0/1/0/all/0/1">Katja Fahrion</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Georgiev_I/0/1/0/all/0/1">Iskren Georgiev</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hilker_M/0/1/0/all/0/1">Michael Hilker</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lyubenova_M/0/1/0/all/0/1">Mariya Lyubenova</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ven_G/0/1/0/all/0/1">Glenn van de Ven</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Alfaro_Cuello_M/0/1/0/all/0/1">Mayte Alfaro-Cuello</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Corsini_E/0/1/0/all/0/1">Enrico M. Corsini</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sarzi_M/0/1/0/all/0/1">Marc Sarzi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+McDermid_R/0/1/0/all/0/1">Richard M. McDermid</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zeeuw_T/0/1/0/all/0/1">Tim de Zeeuw</a>

Photometric surveys of galaxy clusters have revealed a large number of ultra
compact dwarfs (UCDs) around predominantly massive elliptical galaxies. Their
origin is still debated as some UCDs are considered to be the remnant nuclei of
stripped dwarf galaxies while others seem to mark the high-mass end of the star
cluster population. We aim to characterise the properties of a UCD found at
very close projected distance (1.1 kpc) from the centre of the low-mass
(M~10^10 M_sun) early-type galaxy FCC47. This is a serendipitous discovery from
MUSE adaptive optics science verification data. We explore the potential origin
of this UCD as either a massive cluster or the remnant nucleus of a dissolved
galaxy. We use archival Hubble Space Telescope data to study the photometric
and structural properties of FCC47-UCD1. In the MUSE data, the UCD is
unresolved, but we use its spectrum to determine the radial velocity and
metallicity. FCC47-UCD1’s surface brightness is best described by a single King
profile with low concentration C = R_t/R_c ~ 10 and large effective radius (r_e
= 24pc). Its integrated magnitude and a blue colour (G = -10.6 mag, g-z = 1.46
mag) combined with with a metallicity of [M/H] = -1.12+-0.10 dex and an age > 8
Gyr obtained from the full fitting of the MUSE spectrum suggests a stellar
population mass of M_star = 4.87×10^6 M_sun. The low S/N of the MUSE spectrum
prevents detailed stellar population analysis. Due to the limited spectral
resolution of MUSE, we can only give an upper limit on the velocity dispersion
(sig < 17km/s), and consequently on its dynamical mass (M_dyn < 1.3x10^7 M_sun). The origin of the UCD cannot be constrained with certainty. The low metallicity, old age and magnitude are consistent with a star cluster origin, whereas the extended size is consistent with an origin as the stripped nucleus of a dwarf galaxy with a initial stellar mass of a few 10^8 M_sun.

Photometric surveys of galaxy clusters have revealed a large number of ultra
compact dwarfs (UCDs) around predominantly massive elliptical galaxies. Their
origin is still debated as some UCDs are considered to be the remnant nuclei of
stripped dwarf galaxies while others seem to mark the high-mass end of the star
cluster population. We aim to characterise the properties of a UCD found at
very close projected distance (1.1 kpc) from the centre of the low-mass
(M~10^10 M_sun) early-type galaxy FCC47. This is a serendipitous discovery from
MUSE adaptive optics science verification data. We explore the potential origin
of this UCD as either a massive cluster or the remnant nucleus of a dissolved
galaxy. We use archival Hubble Space Telescope data to study the photometric
and structural properties of FCC47-UCD1. In the MUSE data, the UCD is
unresolved, but we use its spectrum to determine the radial velocity and
metallicity. FCC47-UCD1’s surface brightness is best described by a single King
profile with low concentration C = R_t/R_c ~ 10 and large effective radius (r_e
= 24pc). Its integrated magnitude and a blue colour (G = -10.6 mag, g-z = 1.46
mag) combined with with a metallicity of [M/H] = -1.12+-0.10 dex and an age > 8
Gyr obtained from the full fitting of the MUSE spectrum suggests a stellar
population mass of M_star = 4.87×10^6 M_sun. The low S/N of the MUSE spectrum
prevents detailed stellar population analysis. Due to the limited spectral
resolution of MUSE, we can only give an upper limit on the velocity dispersion
(sig < 17km/s), and consequently on its dynamical mass (M_dyn < 1.3×10^7
M_sun). The origin of the UCD cannot be constrained with certainty. The low
metallicity, old age and magnitude are consistent with a star cluster origin,
whereas the extended size is consistent with an origin as the stripped nucleus
of a dwarf galaxy with a initial stellar mass of a few 10^8 M_sun.

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