Near-infrared imaging of 222 nearby H -strong galaxies from the Sloan Digital Sky Survey

Abstract

We present UFTI K‐band imaging observations of 222 galaxies that are selected from the Sloan Digital Sky Survey to have unusually strong Hδ absorption equivalent widths, W○(Hδ) > 4 Å. Using gim2d, the images are fitted with two‐dimensional surface‐brightness models consisting of a simple disc and bulge component to derive the fraction of luminosity in the bulge B/T. We find that the galaxies with weak or absent Hα or [O ii]λ3727 emission (known as k+a galaxies) are predominantly bulge‐dominated (with a mode of B/T∼ 0.6), while galaxies with nebular emission [known as e(a) galaxies] are mostly disc‐dominated (B/T∼ 0.1). The morphologies and (r−k) colours of most k+a galaxies are inconsistent with the hypothesis that they result from the truncation of star formation in normal, spiral galaxies. However, their (u−g) and (r−k) colours, as well as their Hδ line strengths, form a sequence that is well matched by a model in which >5 per cent of the stellar mass has been produced in a recent starburst. The lack of scatter in the dust‐sensitive (r−k) colours suggests that the unusual spectra of k+a galaxies are not due to the effects of dust. The e(a) galaxies, on the other hand, have a colour distribution that is distinct from the k+a population, and typical of normal or dusty (τV∼ 2) spiral galaxies. We conclude that many e(a) galaxies are not progenitors of k+a galaxies, but are a separate phenomenon. Both k+a and e(a) galaxies reside in environments (characterized by the local density of galaxies brighter than Mr=−20) that are typical of normal galaxies and that are inconsistent with overdense regions like rich galaxy clusters.

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

“…Therefore, the precursors of post-starbursts are unlikely to grow in mass via multiple mergers in the time it takes them to quench. The burst fraction (amount of new stars formed) in a merger is typically <20% of the total mass (Norton et al 2001;Balogh et al 2005;Kaviraj et al 2007;Wild et al 2009;Swinbank et al 2012). Hence, it also does not significantly contribute to the mass increase on the starburst sequence.…”

“…As such, they display both early-type morphologies and signs of interactions (Schweizer 1982;Zabludoff et al 1996;Quintero et al 2004;Balogh et al 2005;Yang et al 2008;Pracy et al 2009). Similarly, many post-starburst galaxies are observed to be blue-centered with positive color gradients and have central (within ∼4 kpc) A-star populations (e.g., Yamauchi & Goto 2005;Goto et al 2008;Yang et al 2008;Swinbank et al 2012).…”

K+a galaxies in the zCOSMOS survey

“…In some studies, post-starburst galaxies are found to be mostly bulge-dominated and/or have a morphology that is consistent with being early-type (Goto & SDSS collaboration 2003;Quintero et al 2004;Tran et al 2004;Blake et al 2004;Goto 2005;Balogh et al 2005;Poggianti et al 2009), and in some others have a high incidence of disks and spiral arms (e.g., Franx 1993;Couch et al 1994;Dressler et al 1994;Caldwell & Rose 1997;Dressler et al 1999). For example, Quintero et al (2004) visually inspected a sample of 160 galaxies from the SDSS at 0.05 < z < 0.20, and classified 90% of them as bulge-dominated systems.…”

Physical Properties and Environments of Nearby Galaxies

“…Any method using Hα is preferable in this respect. Second, they use full spectral fits rather than Balmer line equivalent widths (e.g., Balogh et al 2005). This selection alters slightly the "purity" of the sample, as any sufficiently blue continuum will lead to a K+A classification, regardless of A star content.…”