The EDGE-CALIFA survey: exploring the role of molecular gas on galaxy star formation quenching

Abstract

Understanding how galaxies cease to form stars represents an outstanding challenge for galaxy evolution theories. This process of "star formation quenching" has been related to various causes, including active galactic nuclei activity, the influence of large-scale dynamics, and the environment in which galaxies live. In this paper, we present the first results from a follow-up of CALIFA survey galaxies with observations of molecular gas obtained with the APEX telescope. Together with the EDGE-CARMA observations, we collected 12 CO observations that cover approximately one effective radius in 472 CALIFA galaxies. We observe that the deficit of galaxy star formation with respect to the star formation main sequence (SFMS) increases with the absence of molecular gas and with a reduced efficiency of conversion of molecular gas into stars, which is in line with the results of other integrated studies. However, by dividing the sample into galaxies dominated by star formation and galaxies quenched in their centres (as indicated by the average value of the Hα equivalent width), we find that this deficit increases sharply once a certain level of gas consumption is reached, indicating that different mechanisms drive separation from the SFMS in star-forming and quenched galaxies. Our results indicate that differences in the amount of molecular gas at a fixed stellar mass are the primary drivers for the dispersion in the SFMS, and the most likely explanation for the start of star formation quenching. However, once a galaxy is quenched, changes in star formation efficiency drive how much a retired galaxy differs in its star formation rate from star-forming ones of similar masses. In other words, once a paucity of molecular gas has significantly reduced star formation, changes in the star formation efficiency are what drives a galaxy deeper into the red cloud, hence retiring it.

ALMaQUEST -- VII: Star Formation Scaling Relations of Green Valley Galaxies

“…Our results suggest that the suppressed star formation in GV galaxies does not always require a strong depletion in molecular gas. This is in line with some previous global studies that found that SFE is correlated with sSFR or the distance from the MS in the low sSFR regime (i.e., transitioning and retired galaxies) (e.g., Colombo et al 2020;Lin et al 2020).…”

“…Many global studies of molecular gas contents have investigated the dependence of the distance from the star-forming main sequence on the gas fraction or SFE (e.g. Huang & Kauffmann 2014;Scoville et al 2016;Bolatto et al 2017;Saintonge et al 2017;Tacconi et al 2018;Colombo et al 2020;Lin et al 2020;Piotrowska et al 2020). While the relative importance between the gas supply and star formation efficiency is still controversial depending on the choice of the gas tracer and the range of the star formation rate sampled (e.g., within or outside the SFMS), it becomes clear that both the gas fraction and SFE contribute to the change in sSFR to a certain level.…”

EDGE-CALIFA survey: Self-regulation of Star formation at kpc scales

“…31 by Bolatto et al (2013). Following Colombo et al (2020), we assume that the total density in our regions is dominated by Σ * (Σ total ∼ Σ * ), also that the Giant Molecular Cloud (GMC) molecular gas surface density in units of 100 M pc −2 is equal to one. The ionized gas metallicity is obtained by using the strong-lines calibrator derived by Marino et al (2013):…”

MASCOT: an ESO–ARO legacy survey of molecular gas in nearby SDSS-MaNGA galaxies – I. First data release, and global and resolved relations between H2 and stellar content

“…The observed relations are similar and consistent with other studies in the literature. For example, Colombo et al ( 2020 ) carried out a large CO(1-0) surv e y of 472 galaxies selected from the CALIFA surv e y with the APEX telescope and the CARMA array. The CALIFA CO sample is of lower redshift than the MaNGA CO observations presented here.…”

“…Compared with MASCOT, the CALIFA-APEX observations target galaxies at lower redshift (0.005 < z < 0.03) and pro vide less co v erage. The first set of combined CARMA and APEX observations of CALIFA galaxies comprises 472 sources (Colombo et al 2020 ). The APEX CO(2-1) beam co v ers the galaxies roughly out to 1 R eff .…”