Ages and abundances in large-scale stellar discs of nearby S0 galaxies

Abstract

By undertaking deep long‐slit spectroscopy with the focal reducer Spectral Camera with Optical Reducer for Photometrical and Interferometrical Observations (SCORPIO) of the Russian 6 m telescope, we studied stellar population properties and their variation with radius in 15 nearby S0 galaxies sampling a wide range of luminosities and environments. For the large‐scale stellar discs of S0s, we have measured simple stellar population (SSP)‐equivalent metallicities ranging from the solar one down to [ Z/H ]=−0.4 to −0.7, rather high magnesium‐to‐iron ratios, [Mg/Fe] ≥ +0.2, and mostly old SSP‐equivalent ages. Nine of 15 (60 ± 13 per cent) galaxies have large‐scale stellar discs older than 10 Gyr, and among those we find all the galaxies which reside in denser environments. The isolated galaxies may have intermediate‐age stellar discs which are 7–9 Gyr old. Only two galaxies of our sample, NGC 4111 and NGC 7332, reveal SSP‐equivalent ages of their discs of 2–3 Gyr. Just these two young discs appear to be thin, while the other, older discs have scale heights typical for thick stellar discs. The stellar populations in the bulges at radii of 0.5re are on the contrary more metal rich than the solar Z⊙, with the ages homogeneously distributed between 2 and 15 Gyr, being almost always younger than the discs. We conclude that S0 galaxies could not form in groups at z ≈ 0.4 as is thought now; a new scenario of the general evolution of disc galaxies is proposed instead.

Evolution induced by dry minor mergers onto fast-rotator S0 galaxies

“…There is a general agreement about the merger-related origin of ellipticals Naab et al 2006Naab et al , 2007Duc et al 2011), as well as that the wide spread of structural and dynamical properties of S0s are evidence of different evolutionary paths for them (see Laurikainen et al 2010;Cappellari et al 2011;Erwin et al 2012;Kormendy & Bender 2012). Recent studies tend to support secular evolutionary scenarios for S0s in which mergers play a secondary role (van den Bosch & Emsellem 1998;Bekki et al 2002;Aragón-Salamanca et al 2006;Buta et al 2010;Sil'chenko et al 2012;Laurikainen et al 2010Laurikainen et al , 2013. But many S0s exhibit clear signs of having experienced recent mergers (Falcón-Barroso et al 2004;Chilingarian et al 2009;Kim et al 2012).…”

“…Naab et al 2009;Lotz et al 2011;Oser et al 2012;McLure et al 2013). Therefore, an evolutionary scenario in which major mergers at earlier epochs give rise to a population of initial S0s, that later minor mergers can evolve into different dynamical systems is quite plausible (e.g., the scenario proposed by Sil'chenko et al 2012, to explain the age and metallicity properties of S0 galaxies). A mixture of both types of mergers and of environmental and secular processes must have shaped galaxies in general (especially S0s) in a complex scenario (Kannappan et al 2009;Huertas-Company et al 2010;Aguerri 2012).…”

Formation of S0 galaxies through mergers

“…The relevant temporal stages of the scenario we are testing are shown in different colours. Based on the average age estimated for the old stellar populations in the discs of present-day S0s (see Sil'chenko et al 2012;Sil'chenko 2013), we consider that all the old stellar particles have an age of 11 Gyr at z = 0 regardless of the progenitor they come from. This assumption thus sets the age of the old stellar particles at any time, and in particular at z ∼ 0.8, when we consider the remnant to be already in place.…”

Mathematical Problems in Creating Large Astronomical Catalogs

“…High-precision multicolor photometric star catalogs are in great demand in a substantial part of astronomy and its applications, and the studies cited here (Gorynya et al 1996;Shakura et al 1998;Popov & Prokhorov 2006;Samus et al 2009;Sil'chenko et al 2012), which we selected based on our subjective opinion, cover only a small part of the applications of these catalogs.…”