Globular cluster clustering and tidal features around ultra-compact dwarf galaxies in the halo of NGC 1399

Abstract

We present a novel approach to constrain the formation channels of ultra-compact dwarf galaxies (UCDs). They most probably are an inhomogeneous class of objects, composed of remnants of tidally stripped dwarf elliptical galaxies and star clusters that occupy the high mass end of the globular cluster luminosity function. We use three methods to unravel their nature: 1) we analyzed their surface brightness profiles; 2) we carried out a direct search for tidal features around UCDs; and 3) we compared the spatial distribution of GCs and UCDs in the halo of their host galaxy. Based on FORS2 observations under excellent seeing conditions, we studied the detailed structural composition of a large sample of 97 UCDs in the halo of NGC 1399, the central galaxy of the Fornax cluster, by analyzing their surface brightness profiles. We found that 13 of the UCDs were resolved above the resolution limit of 23 pc and we derived their structural parameters fitting a single Sérsic function. When decomposing their profiles into composite King and Sérsic profiles, we find evidence for faint stellar envelopes at µ =∼ 26 mag arcsec −2 , surrounding the UCDs up to an extension of 90 pc in radius. We also show new evidence for faint asymmetric structures and tidal tail-like features surrounding several of these UCDs, a possible tracer of their origin and assembly history within their host galaxy halos. In particular, we present evidence for the first discovery of a significant tidal tail with an extension of ∼350 pc around UCD-FORS 2. Finally, we studied the local overdensities in the spatial distribution of globular clusters within the halo of NGC 1399 out to 110 kpc to see if they are related to the positions of the UCDs. We found a local overabundance of globular clusters on a scale of ≤1 kpc around UCDs, when we compared it to the distribution of globulars from the host galaxy. This effect is strongest for the metal-poor blue GCs. We discuss how likely it is that these clustered globulars were originally associated with the UCD, either as globular cluster systems of a nucleated dwarf galaxy that was stripped down to its nucleus, or as a surviving member of a merged super star cluster complex.

Upper Limits on the Presence of Central Massive Black Holes in Two Ultra-compact Dwarf Galaxies in Centaurus A

“…Such features were detected around UCDs in the Fornax and Perseus clusters (Voggel et al 2016;Wittmann et al 2016). A tidal stream of 1.5 kpc was recently found around a newly discovered very massive (M=4.2×10…”

“…Finally, many UCDs, including UCD 330, have two-component profiles, extra-tidal light, or tidal tails (Martini & Ho 2004;Evstigneeva et al 2007;Voggel et al 2016;Wittmann et al 2016). These are expected for stripped galaxy nuclei, as the inner component tracks the original NSC, while the outer section is the remnants of the remaining galaxy (Pfeffer & Baumgardt 2013).…”

Metal-poor nuclear star clusters in two dwarf galaxies near Centaurus A suggesting formation from the in-spiraling of globular clusters

“…Therefore, extended sizes of GCs at these low masses and metallicities could give further evidence of NSC-origin. Examples of faint envelopes around compact GC-like objects have been found in the Virgo (Liu et al 2015) as well as in the Fornax cluster (Voggel et al 2016).…”

THE FORNAX DEEP SURVEY WITH VST. I. THE EXTENDED AND DIFFUSE STELLAR HALO OF NGC 1399 OUT TO 192 kpc

“…This galaxy has been studied in detail over a wide wavelength range, from radio to X-ray. NGC1399 is characterized by a large number of compact stellar systems (GCs and UCDs), for which several studies have provided the number-density distribution and stellar population estimates (Dirsch et al 2003;Mieske et al 2004;Bassino et al 2006;Schuberth et al 2010;Puzia et al 2014;Voggel et al 2016).…”