Origin of E+A galaxies - I. Physical properties of E+A galaxies formed from galaxy merging and interaction

Abstract

We investigate the structural, kinematical and spectrophotometric properties of ‘E+A’ galaxies – those with strong Balmer absorption lines but no significant [O ii] emission – using numerical simulations combined with stellar population synthesis codes. We particularly focus on the two‐dimensional (2D) distributions of line‐of‐sight velocity, velocity dispersion, colour and line index in E+A galaxies formed via the interaction and merging of two gas‐rich spirals. Our numerical simulations demonstrate that E+A elliptical galaxies formed by major galaxy merging have positive radial colour gradients and negative radial Hδ gradients by virtue of their central post‐starburst populations. Furthermore, we show that the projected kinematical and spectroscopic properties of the simulated E+A galaxies can be remarkably different for different major merger models. For example, the simulated E+A ellipticals with kinematically decoupled cores clearly show regions of strong Hδ absorption which are very flattened, with differences in rotation and velocity dispersion between the old and young stars. E+A ellipticals are highly likely to show more rapid rotation and a smaller central velocity dispersion in young stars than in old ones. E+A galaxies formed from the strong tidal interaction between gas‐rich spirals have discy morphologies with thick discs and are highly likely to be morphologically classified as barred S0 galaxies. We also provide specific predictions on the structural, kinematical and spectrophotometric properties of young globular cluster systems in E+A galaxies. Based on these results, we discuss the importance of spatially resolved, integral field unit spectroscopy on large (8–10 m) ground‐based telescopes in confirming the formation of kinematically distinct cores in elliptical galaxies produced via dissipative merging and determining the most probable physical mechanism(s) for E+A formation with discy and spheroidal morphologies.

From Starburst to Quiescence: Testing Active Galactic Nucleus Feedback in Rapidly Quenching Post-Starburst Galaxies

“…Theoretical models argue that post-starbursts are the end products of galaxy mergers (Hopkins et al 2006Bekki et al 2001Bekki et al , 2005Snyder et al 2011). Assuming a uniform merger (production) rate since z ∼ 2 (last 10 Gyr), then the total production of post-starbursts in our adopted mass range would be about 5700 galaxies.…”

“…Hayward et al 2012). Since post-starbursts are believed to be the results of such mergers (Hopkins et al 2006Bekki et al 2001Bekki et al , 2005Snyder et al 2011), it is plausible that they exist in dust-obscured phase as they quench (Poggianti & Wu 2000;Bekki et al 2001;Shioya et al 2001). Thus, we search for dust-obscured objects in our sample that likely bridge the gap between starbursts and FPSBs.…”

Post‐starburst galaxies and the transformation of blue into red galaxies

“…Therefore, a simple cessation of star formation in a fraction of the blue galaxies followed by fading and reddening cannot explain this buildup of the red sequence. Starbursts are often suggested as a way of increasing a blue galaxy's stellar mass before letting it fade onto the red sequence (Bell et al 2004;Labbé et al 2007), with mergers and interactions as possible starburst triggers (Bekki et al 2005;Di Matteo et al 2008). Mergers and starbursts have the additional appeal that they offer an explanation for the cessation of star formation: gas is being consumed by the starburst (Di Matteo et al 2007) and is being expelled by active galactic nucleus (AGN) or supernova feedback (Buyle et al 2008;Kaviraj et al 2007).…”

“…However, not all PSGs can be associated with mergers and, obviously, more than one evolutionary pathway can lead to a post-starburst galaxy (Tran et al 2003;Dressler et al 1999). Numerical simulations show that PSGs can indeed be formed via a major merger of two gas-rich spiral galaxies (Bekki et al 2005). A disk-disk merger event then triggers a starburst, which consumes, or, by feedback, expels most of the available gas and then subsides.…”

Astrophysics in 2005

“…• EϩA galaxies (meaning ellipticals but with spectra displaying the absorption lines of A stars), which are not the same as IRAS galaxies, another sort of poststarburst (Goto 2005); not all the same sort of beasts (Pracy et al 2005); not another sort of proto-elliptical, but arguably a form of proto-S0 (Bekki et al 2005); not inhabitants of rich clusters, being found mostly in small groups and the field now (Blake et al 2004); not to be confused with e(a) galaxies, which display nebular emission lines (Balogh et al 2005, who prefer to call EϩA's kϩa, meaning a mix of stellar K and A spectral types, which, if you were a star might get you declared symbiotic. 12 It probably is easier not to be a number of different things simultaneously than to be a number of different things simultaneously.…”