Connecting Compact Star-forming and Extended Star-forming Galaxies at Low Redshift: Implications for Galaxy Compaction and Quenching

Abstract

Previous findings show that the existence of dense cores or bulges is the prerequisite for quenching a galaxy, leading to a proposed two-step quenching scenario: compaction and quenching. In this scenario, galaxies first grow their cores to a stellar mass surface density threshold and subsequently quenching occurs, suggesting that galaxies evolve from extended star-forming galaxies (eS-FGs), through compact star-forming galaxies (cSFGs), to quenched population. In this work, we aim at examining the possible evolutionary link between eSFGs and cSFGs by identifying the trends in star formation rate (SFR), gas-phase metallicity and HI content, since one would naturally expect that galaxies evolve along the track of cold gas consumption and metal enhancement. We select a volumelimited sample of 15,933 galaxies with stellar mass above 10 9.5 M ⊙ and redshift of 0.02 < z < 0.05 from the NASA-Sloan-Atlas catalog within the ALFALFA footprint. The cSFGs on average exhibit similar or slightly higher SFRs of ∼0.06 dex and significantly higher gas-phase metallicity (up to 0.2 dex at low mass) with respect to the eSFGs, while the cSFGs dominate the galaxy population of the most intense star formation activities. More importantly, overall the median HI content and gas depletion time of cSFGs are about half of eSFGs. Our result supports the compaction and quenching scenario that galaxies evolve and grow their cores along the track of cold gas consumption and metal enhancement. The environments of eSFGs and cSFGs are indistinguishable, suggesting that the compaction process is independent of any environmental effects at least for low-redshift universe.5 This definition of compact SF galaxies differs from previous works, where compact is an absolute term to identify the smallest galaxies (e.g. van Dokkum et al. 2015). 6 http://www.nsatlas.org/ 7

Linking compact dwarf starburst galaxies in the RESOLVE survey to downsized blue nuggets

“…Detailed studies (Östlin et al 2004;Marquart et al 2007;Cumming et al 2008;Östlin et al 2015) of BCGs in the local universe have shown that these objects regularly exhibit irregular kinematics and secondary dynamical components akin to those we see in §4.2.3, consistent with merger formation, although some BCGs are also observed to have companions (Östlin et al 2004;Cumming et al 2008). For galaxies above M * ∼ 10 9.5 M however, merger-driven compaction in z ∼ 0 galaxies appears closely tied to quenching by gas depletion (Wang et al 2018). Consistent with this picture, low-z blue E/S0s show declining evidence for disk rebuilding in the mass range M * ∼ 10 9.5−10.5 M and seem to form almost entirely via quenching mergers at higher masses (Kannappan et al 2009;Schawinski et al 2009).…”

“…Relative to the original high-z blue nuggets reported in Barro et al (2013), the Fang et al (2013) objects are generally less massive, less compact, and less vigorously star-forming. More recently, Wang et al (2018) have described a population of compact star-forming galaxies with M * 10 9.5 M at z 0.05 that appear to be in the midst of quenching to form red nuggets, based on evidence of depressed gas content. At still lower stellar masses, the observational analysis of van der Wel et al (2014) suggests that the fraction of prolate galaxies with M * 10 9.5 M , i.e., potential blue nuggets in the regime of self-regulated evolution by cyclic fueling, decreases dramatically from z = 2 to z = 0 but is non-vanishing at z = 0.…”

The SAMI Galaxy Survey: satellite galaxies undergo little structural change during their quenching phase

“…In recent years, several works have proposed a scenario in which a rapid increase in the central galaxy density truncates star formation: i.e., galaxies grow their inner core and then quench (a process sometimes referred to as 'compaction'; e.g., Cheung et al 2012;Fang et al 2013;Woo et al 2015;Zolotov et al 2015;Tacchella et al 2016;Wang et al 2018). While originally motivated by studies of central galaxies (e.g., Cheung et al 2012;Fang et al 2013), compaction has also been suggested as a viable quenching path for satellite galaxies (e.g., Wang et al 2018).…”

The Variability of Star Formation Rate in Galaxies: II. Power Spectrum Distribution on the Main Sequence

“…This could reproduce the observed relation between the gas depletion times (either τ dep or τ dep,eff ) and the observed dispersion of Σ SFR from galaxy to galaxy. In addition, the dynamical gasregulator model can qualitatively explain the observed dependence of the SFMS on stellar mass and stellar surface density (Wang et al 2018a;Davies et al 2019;.…”

“…The scatter of the SFMS depends on both the stellar mass and structural properties of galaxies. Wang et al (2018a) found that the scatter of the SFMS depends strongly on the structure of galaxies, with more compact galaxies enci.wang@phys.ethz.ch 1 Department of Physics, ETH Zurich, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich, Switzerland showing a larger range of sSFR. By using different SFR measurements, including Hα, UV and infrared emission, Davies et al (2019) found that the scatter of the SFMS increases with increasing stellar mass at stellar masses greater than 10 9.2 M .…”