GASP XXIV. The History of Abruptly Quenched Galaxies in Clusters

Abstract

The study of cluster post starburst galaxies gives useful insights on the physical processes quenching the star formation in the most massive environments. Exploiting the MUSE data of the GAs Stripping Phenomena in galaxies (GASP) project, we characterise the quenching history of 8 local cluster galaxies that were selected for not showing emission lines in their fiber spectra. We inspect the integrated colors, and the Hβ rest frame equivalent widths (EW), star formation histories (SFHs) and luminosityweighted age (LWA) maps finding no signs of current star formation throughout the disks of these early-spiral/S0 galaxies. All of them have been passive for at least 20 Myr, but their SF declined on different timescales. In most of them the outskirts reached undetectable SFRs before the inner regions ("outside-in quenching"). Our sample includes three post-starforming galaxies, two passive galaxies and three galaxies with intermediate properties. The first population shows blue colors, deep Hβ in absorption (EW>>2.8Å), young ages (8.8< log(LWA[yr]) <9.2). Two of these galaxies show signs of a central SF enhancement before quenching. Passive galaxies have instead red colors, EW(Hβ)<2.8 A, ages in the range 9.2< log(LWA[yr]) <10. Finally, the other galaxies are most likely in transition between a post starforming and passive phase, as they quenched in an intermediate epoch and have not lost all the star forming features yet. The outside-in quenching, the morphology and kinematics of the stellar component, along with the position of these galaxies within massive clusters (σ cl = 550-950 km s −1 ) point to a scenario in which ram pressure stripping has removed the gas, leading to quenching. Only the three most massive galaxies might alternatively have entered the clusters already quenched. These galaxies are therefore at the final stage of the rapid evolution galaxies undergo when they enter the cluster environment.

The environmental dependence of rapidly quenching and rejuvenating galaxies

“…This strongly suggests that, while the effectiveness of environment-induced quenching is lower in low-mass halos, it is still a factor. This is an intriguing result, which is also consistent with other previous studies (Zabludoff et al 1996;Paccagnella et al 2019;Vulcani et al 2020). The environmental effect clearly can not be dependent only on halo mass, but perhaps instead some other physical feature which correlates with halo mass, such as relative velocity and intragroup gas density.…”

“…It has been clear since the early days, when the proportion of cluster galaxies classified as E+A's varied from ∼ 30 per cent to 2 per cent (Couch & Sharples 1987;Poggianti et al 1999;Balogh et al 1999), that the relatively small sample sizes of E+A's combined with their sensitive dependence on the details of the target selection, spectroscopic reduction and parameter estimation, could have a big impact on the interpretation. These uncertainties have continued, and the literature is unsettled on many of the major questions about E+A environmental dependencies (Zabludoff et al 1996;Paccagnella et al 2019;Owers et al 2019), morphological composition (Pracy et al 2009;Swinbank et al 2012;French et al 2016) and triggering mechanisms (Zabludoff et al 1996;Bekki 2014;Yesuf et al 2014;Pawlik et al 2019;Vulcani et al 2020).…”

Star formation quenching stages of active and non-active galaxies

“…Outside-in star-formation quenching may also be induced by ram-pressure stripping in galaxy cluster environments (e.g. Bekki 2009;Vulcani et al 2020).…”

The role of environment on quenching, star formation and AGN activity

“…5). These are totally devoid of emission lines, are typically located between 0.5 and 1 cluster virial radii (Owers et al 2019;Vulcani et al 2020) and have been quenched outside-in (the disk outskirts first) as expected in the ram pressure stripping scenario (Gavazzi et al 2013).…”

“…The vertical bars at the bottom of the right panel indicate the size of 1 kpc in units of re for each galaxy. FromVulcani et al (2020).…”