GOODS-ALMA 2.0: Starbursts in the main sequence reveal compact star formation regulating galaxy evolution prequenching

Abstract

Compact star formation appears to be generally common in dusty star-forming galaxies (SFGs). However, its role in the framework set by the scaling relations in galaxy evolution remains to be understood. In this work we follow up on the galaxy sample from the GOODS-ALMA 2.0 survey, an ALMA blind survey at 1.1 mm covering a continuous area of 72.42 arcmin2 using two array configurations. We derived physical properties, such as star formation rates, gas fractions, depletion timescales, and dust temperatures for the galaxy sample built from the survey. There exists a subset of galaxies that exhibit starburst-like short depletion timescales, but they are located within the scatter of the so-called main sequence of SFGs. These are dubbed starbursts in the main sequence and display the most compact star formation and they are characterized by the shortest depletion timescales, lowest gas fractions, and highest dust temperatures of the galaxy sample, compared to typical SFGs at the same stellar mass and redshift. They are also very massive, accounting for ∼60% of the most massive galaxies in the sample (log(M*/M⊙) > 11.0). We find trends between the areas of the ongoing star formation regions and the derived physical properties for the sample, unveiling the role of compact star formation as a physical driver of these properties. Starbursts in the main sequence appear to be the extreme cases of these trends. We discuss possible scenarios of galaxy evolution to explain the results drawn from our galaxy sample. Our findings suggest that the star formation rate is sustained in SFGs by gas and star formation compression, keeping them within the main sequence even when their gas fractions are low and they are presumably on the way to quiescence.

Probing Cold Gas in a Massive, Compact Star-forming Galaxy at z = 6

“…While higher angular resolutions are required to precisely determine the causes of the high star formation efficiency in G09-83808, we attribute it to its internal properties, such as compactness and/or gravitational instabilities, that facilitate gas compression (see further discussion in Tsujita et al (2022), who found evidence of star-forming clumps within the rotating disk of this system). This is in line with recent results from Gómez-Guijarro et al (2022), who found that the most compact galaxies show the shortest depletion time and a starburst-like modes of star formation.…”

“…This is well aligned with the derived masses of massive quiescent galaxies discovered at high redshifts (e.g., Tanaka et al 2019;Marsan et al 2022;Valentino et al 2020;Santini et al 2021;Stevans et al 2021), which also show compact sizes similar to the size of our target. This hints at a progenitor-descendant scenario between these populations of galaxies, and support other results from the literature suggesting that compact galaxies with low gas fractions and short depletion times are likely in the latest stages of a starburst episode and on the verge of quenching (e.g., van Dokkum et al 2015;Spilker et al 2016a;Puglisi et al 2021;Gómez-Guijarro et al 2022;Ikarashi et al 2022).…”

“…While our target, G09-83808 lies around the scatter of the main sequence of star-forming galaxies at z ∼ 6 (see Figure 1), it shows properties that resemble those from local ULIRGs and other starbursts, including a compact (dust and gas) size of R circ = 0.6 ± 0.2 kpc (Section 3.1), a relatively high dust temperature (T d = 49 ± 3 K; Zavala et al 2018), a low α CO of < 2.5 M e K km s −1 pc 2 (Section 3.2), and a short depletion time (τ dep = 50 ± 20 Myr; Section 3.3.2). All this suggests that galaxies with starburst-like ISM properties and star formation modes could also be hidden within the main-sequence population (see also Gómez-Guijarro et al 2022).…”

“…Nevertheless, Tsujita et al (2022) showed, based on a sourceplane reconstruction of the [O III]88 μm and [N II]205 μm emission lines across different velocity channels, that this galaxy is well-modeled by a rotating disk with some compact star-forming clumps. It is thus likely that the high star formation efficiency of this galaxy, and its starburst-like properties are the consequence of gas compression induced by its compact size (e.g., Elbaz et al 2011;Gómez-Guijarro et al 2022).…”

Inferences on Relations between Distant Supermassive Black Holes and Their Hosts Complemented by the Galaxy Fundamental Plane

“…With substantial stellar mass in the disk component of their hosts, a process is required to redistribute the stars that already exist in the disk to the bulge. Also, a nonnegligible fraction of the bulge mass is likely built up in situ, as evident by recent Atacama Large Millimeter/submillimeter Array detections of centrally concentrated star formation in high-z galaxies and AGNs (e.g., Puglisi et al 2019;Gómez-Guijarro et al 2022). A picture is emerging in which the bulge needs to be further assembled for galaxies and their SMBHs to align with the local relation.…”