The star formation histories of z ∼ 1 post-starburst galaxies

Abstract

We present the star formation histories of 39 galaxies with high quality rest-frame optical spectra at 0.5 < z < 1.3 selected to have strong Balmer absorption lines and/or Balmer break, and compare to a sample of spectroscopically selected quiescent galaxies at the same redshift. Photometric selection identifies a majority of objects that have clear evidence for a recent short-lived burst of star formation within the last 1.5 Gyr, i.e. "post-starburst" galaxies, however we show that good quality continuum spectra are required to obtain physical parameters such as burst mass fraction and burst age. Dust attenuation appears to be the primary cause for misidentification of post-starburst galaxies, leading to contamination in spectroscopic samples where only the [OII] emission line is available, as well as a small fraction of objects lost from photometric samples. The 31 confirmed post-starburst galaxies have formed 40-90% of their stellar mass in the last 1-1.5 Gyr. We use the derived star formation histories to find that the post-starburst galaxies are visible photometrically for 0.5-1 Gyr. This allows us to update a previous analysis to suggest that 25-50% of the growth of the red sequence at z∼1 could be caused by a starburst followed by rapid quenching. We use the inferred maximum historical star formation rates of several 100-1000 M /yr and updated visibility times to confirm that sub-mm galaxies are likely progenitors of post-starburst galaxies. The short quenching timescales of 100-200 Myr are consistent with cosmological hydrodynamic models in which rapid quenching is caused by the mechanical expulsion of gas due to an AGN.

From starburst to quiescence: post-starburst galaxies and their large-scale clustering over cosmic time

“…The SFHs of PSB galaxies, as measured by Wild et al (2020), suggest that they have peak SFRs consistent with those derived for SMGs (20-1030 M ⊙ yr −1 , Swinbank et al 2014), which affirms their association. The two populations are also similar in their sizes.…”

“…Smail et al 1997;Barger et al 1998;Hughes et al 1998), the latter being the most luminous star-forming galaxies in the Universe. A number of properties of these two populations are highly comparable: similar characteristic stellar masses of log(M * /M ⊙ ) ∼ 10.4 − 10.5 (Simpson et al 2014;Wild et al 2016) and PSB galaxies having space densities several times higher at ∼ 6 − 7 × 10 −5 Mpc −3 , but an observable time-scale up to an order of magnitude longer (100 Myr for SMGs, a maximum visibility timescale of 1 Gyr for PSB galaxies Chapman et al 2005;Swinbank et al 2006;Hainline et al 2011;Wild et al 2016Wild et al , 2020.…”

“…We assess the robustness of the COSMOS classification 1 We note that the procedure and criteria for classifying PSB galaxies in the UDS field differ from those used in Wild et al (2020), where they employ the spectral fitting package bagpipes (Carnall et al 2018) to derive SFHs. Moreover, they showed that many PSB galaxies that are identifed spectroscopically but not photometrically (i.e., by their SCs) tend not to have PSB-like SFHs, with slowly declining SFRs.…”

“…Some of these transition galaxies, post-starburst (PSB) galaxies (also often known as "k+a" or "E+A" galaxies), are identified by characteristic strong Balmer absorption lines (Dressler & Gunn 1983;Wild et al 2009) and a lack of nebular emission or ultraviolet flux, which indicates the excess of A-type stars and a deficiency of O-and Btype stars, respectively. The spectral features observed in PSB galaxies, in addition to their star formation histories (SFHs Wild et al 2020), demonstrate that these galaxies have undergone a rapid termination of star formation, (Dressler et al 1999;Poggianti et al 1999;Goto et al 2004;Dressler et al 2004), having formed a significant fraction of their stellar mass in the last Gyr (Norton et al 2001;Yang et al 2004;Kaviraj et al 2007;Wild et al 2020). PSB galaxies are relatively short-lived (< 1 Gyr), while their rarity is emphasised by their observed fractions of up to ∼ 3% of the entire galaxy population (Goto et al 2003;Wild et al 2009Wild et al , 2016Alatalo et al 2016a;Rowlands et al 2018).…”

Recent insights into massive galaxy formation from observing structural evolution (Review)

“…Belli et al (2019) found that most galaxies at z ∼ 1.5 are not "quenching" particularly quickly: perhaps 20% pass through a post-starburst phase. Wild et al (2020) inferred a fraction 25-50% that is smaller but still implies that rapidly quenched galaxies are a minority. By necessity, the post-starburst fraction increases with redshift (galaxies cannot end star formation early and slowly), but even at z ∼ 2.2 Belli et al (2019) find that post-starbursts account for half of the growth of the red sequence.…”