The origins of post-starburst galaxies at z < 0.05

Abstract

Post-starburst galaxies can be identified via the presence of prominent Hydrogen Balmer absorption lines in their spectra. We present a comprehensive study of the origin of strong Balmer lines in a volume-limited sample of 189 galaxies with 0.01 < z < 0.05, log(M /M ) > 9.5 and projected axis ratio b/a > 0.32. We explore their structural properties, environments, emission lines and star formation histories, and compare them to control samples of star-forming and quiescent galaxies, and simulated galaxy mergers. Excluding contaminants, in which the strong Balmer lines are most likely caused by dust-star geometry, we find evidence for three different pathways through the post-starburst phase, with most events occurring in intermediate-density environments: (1) a significant disruptive event, such as a gas-rich major merger, causing a starburst and growth of a spheroidal component, followed by quenching of the star formation (70% of post-starburst galaxies at 9.5 < log(M /M ) < 10.5 and 60% at log(M /M ) > 10.5); (2) at 9.5 < log(M /M ) < 10.5, stochastic star formation in blue-sequence galaxies, causing a weak burst and subsequent return to the blue sequence (30%); (3) at log(M /M ) > 10.5, cyclic evolution of quiescent galaxies which gradually move towards the high-mass end of the red sequence through weak starbursts, possibly as a result of a merger with a smaller gas-rich companion (40%). Our analysis suggests that AGN are 'on' for 50% of the duration of the post-starburst phase, meaning that traditional samples of post-starburst galaxies with strict emission line cuts will be at least 50% incomplete due to the exclusion of narrow-line AGN.

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

“…Spectral fitting of low-redshift poststarburst galaxies has led to useful constraints on the burst strengths and timescales involved in the burst, which help to pin down the cause of the starburst as well as the quenching processes. At low-redshift, burst mass fractions of as much as 70% strongly implicate major mergers as the cause of the burst in low-redshift post-starburst galaxies, consistent with their morphological features, while the rapid decline rate in star formation, alongside the decline in molecular gas, implicates AGN feedback as a quenching process, at least at high mass (Kaviraj et al 2007;Pawlik et al 2018;French et al 2018).…”

“…The consensus for low-redshift post-starburst galaxies is that a large fraction are transition galaxies, forming the evolutionary link between gas-rich major mergers, ultraluminous infrared galaxies (ULIRGs), and future quiescent elliptical galaxies. However, with high quality data it is possible to identify post-starburst features arising from three separate processes (Pawlik et al 2018): traditional blue→red quenching, cyclical evolution within the blue sequence, as well as rejuvenation of red-sequence galaxies. These results are in qualitative agreement with cosmological hydrodynamical simulations (Pawlik et al 2019), however more work is required to determine whether the relative fraction of the different processes is correctly reproduced in the simulations, especially because different selection methods lead to observed samples with different physical properties (Pawlik et al 2018;French et al 2018).…”

The whole picture of the large-scale structure of the CL1604 supercluster at z ∼ 0.9

“…In the model of stellar population synthesis, we assume the SSP or smooth history of star formation declining exponentially with time, which means that the model can not take account of the small starburst occurred re-cently and/or on-going weak dusty star formation. Recent studies of post-starburst galaxies with strong Balmer absorption which are selected by principal component analysis (PCA) show that there are post-starburst galaxies in red sequence rejuvenated by a minor merger with a gasrich galaxy and dusty starburst galaxies are a population of major contaminants of post-starburst galaxies (Pawlik et al 2018;Pawlik et al 2019). Given the facts, the second small starburst in the later phase can change the strength of spectral indices (Kauffmann et al 2003;Marcillac et al 2006;Lemaux et al 2012).…”

Heterogeneity of inverted calcium ii H:K ratio cluster galaxies

“…Blake et al 2004;Wilkinson et al 2017) and may offer an additional method or cut to apply to a sample to identify a transitioning post-starburst galaxy (cf. Pawlik et al 2018;Wild et al 2009).…”

“…Indeed, given that any trigger capable of causing a starburst can also be likely to cause an AGN phase as well, it is plausible that an inverted H:K ratio may -but certainly not always -herald a later AGN phase (cf. Cid Fernandes et al 2004;Yan et al 2006;Sell et al 2014;Pawlik et al 2018; see also Pimbblet et al 2013 who point out the issue that the site of any interaction that triggers AGN in clusters is likely long since obfuscated given the lag between the trigger event and subsequent observable AGN indicators).…”