A census of nuclear stellar discs in early-type galaxies

Abstract

Nuclear stellar discs (NSDs), of a few tens to hundreds of parsec across, are a common and yet poorly studied feature of early-type galaxies. Still, such small discs represent a powerful tool to constrain the assembling history of galaxies, since they can be used to trace to the epoch when galaxies experienced their last major merger event. By studying the fraction and stellar age of NSDs, it is thus possible to test the predictions for the assembly history of early-type galaxies according to the current hierarchical paradigm for galaxy formation. In this paper we have produced the most comprehensive census of NSDs in nearby early-type galaxies by searching for such discs in objects within 100 Mpc and by using archival images from the Hubble Space Telescope. We found that NSDs are present in approximately 20 per cent of early-type galaxies, and that the fraction of galaxies with NSDs depends neither on their Hubble type nor on their galactic environment, whereas the incidence of NSDs appears to decline in the most massive systems. Furthermore, we have separated the light contribution of 12 such discs from that of their surrounding stellar bulge in order to extract their physical properties. This doubles the number of decomposed NSDs and although the derived values for their central surface brightness and scalelength are consistent with previous studies, they also give a hint of possible different characteristics due to different formation scenario between nuclear discs and other kinds of large galactic discs

Multiband photometric decomposition of nuclear stellar disks

“…Afterward, nuclear stellar disks (NSDs) and larger scale embedded disks were reported in a large number of early-type galaxies as a results of photometric (Lauer et al 1995;Carollo et al 1997;Ravindranath et al 2001;Rest et al 2001;Tran et al 2001;Ferrarese et al 2006;Seth et al 2006;Simões Lopes et al 2007;Kormendy et al 2009) and spectroscopic surveys (Halliday et al 2001;Kuntschner et al 2006;McDermid et al 2006) respectively. Given that nuclear disks are easiest to detect when nearly edgeon (Rix & White 1990), the observed fraction is consistent with NSDs being a common structure in early-type galaxies (Ledo et al 2010). At the center of spiral galaxies NSDs are also present but these are relatively rare in late types (Pizzella et al 2002;Falcón-Barroso et al 2006;Peletier et al 2007;Balcells et al 2007;Morelli et al 2008).…”

The Abell 85 Bcg: A Nucleated, Coreless Galaxy

“…For instance, Ledo et al (2010) compile a census of nuclear stellar disks in early-type galaxies. Several of these NSDs have sizes of a few hundred parsecs with two of them having sizes larger than 1 kpc.…”

“…To give more context, we remark that the catalog of Ledo et al (2010) is limited to galaxies within 108 Mpc while Abell 85 is at more than twice this distance. Also, the Abell 85 BCG is brigther than the sample studied by Ledo et al (2010). With the current data, we favor a Nuclear Stellar Disk as the physical explanation for the nuclear structure present in the core of the Abell 85 BCG.…”

The Carnegie-Irvine Galaxy Survey. I. Overview and Atlas of Optical Images

“…While most of the recent attention has focused on the phenomenon of "pseudobulges" (Kormendy & Kennicutt 2004, and references therein), there has also been a growing appreciation that even the classical bulges may have experienced a rather dynamic evolutionary history. Apart from the prevalence of features such as kinematically distinct or counterrotating cores, which are indicative of discrete accretion events (e.g., Forbes et al 1995), many early-type galaxies contain nuclear gaseous disks and dust lanes (e.g., van Dokkum & Franx 1995;Tran et al 2001) and central stellar disks (e.g., Rix & White 1992;Ledo et al 2010), concrete reminders that these are continually evolving systems. In addition, a large fraction of disk galaxies (∼30%; Lütticke et al 2000), including S0s (Aguerri et al 2005), possess boxy or peanut-shaped bulges, which are believed to be not actual bulges at all but edge-on bars (e.g., Bureau & Freeman 1999;Athanassoula 2005;Kormendy & Barentine 2010).…”