Quiescent Galaxies 1.5 Billion Years after the Big Bang and Their Progenitors

Abstract

We report two secure (z = 3.775, 4.012) and one tentative (z ≈ 3.767) spectroscopic confirmations of massive and quiescent galaxies close to their quenching epoch through K-band observations with Keck/MOSFIRE and VLT/X-Shooter. The stellar continuum emission, the absence of strong nebular emission lines and the lack of significant far-infrared detections confirm the passive nature of these objects, disfavoring the alternative solution of low-redshift dusty star-forming interlopers. We derive stellar masses of log(M /M ) ∼ 11 and ongoing star formation rates placing these galaxies 1 − 2 dex below the main sequence at their redshifts. The adopted parametrization of the star formation history suggests that these sources experienced a strong ( SFR ∼ 1200 − 3500 M yr −1 ) and short (∼ 50 Myr) burst of star formation, peaking ∼ 150 − 500 Myr before the time of observation, all properties reminiscent of the characteristics of sub-millimeter galaxies (SMGs) at z > 4. We investigate this connection by comparing the comoving number densities and the properties of these two populations. We find a fair agreement only with the deepest sub-mm surveys detecting not only the most extreme 2 Valentino et al.starbursts, but also more normal galaxies. We support these findings by further exploring the Illustris-TNG cosmological simulation, retrieving populations of both fully quenched massive galaxies at z ∼ 3 − 4 and SMGs at z ∼ 4 − 5, with number densities and properties in broad agreement with the observations at z ∼ 3, but in increasing tension at higher redshift. Nevertheless, as suggested by the observations, not all the progenitors of quiescent galaxies at these redshifts shine as bright SMGs in their past and, similarly, not all bright SMGs quench by z ∼ 3, both fractions depending on the threshold assumed to define the SMGs themselves. This cautions against the blind application of the assumption of a univocal connection between the two populations at high redshift.

The Typical Massive Quiescent Galaxy at z ∼ 3 is a Post-starburst

“…Despite the uncertainties, our data at z∼3 seems to disfavor the steep (1+z) 4−5 trend inferred from z = 0 to 1.5-2, suggesting a flattening in the M mol /M evolution (or equivalently, of the sSFR). The published SFR [O II] for z > 3 galaxies with a clear spectral break in Schreiber et al (2018) and Valentino et al (2020) also seem to support this trend.…”

“…Our SFR thus converts into M mol =(1.5±0.6)×10 10 M , hence f mol ∼ 9 ± 4%. We compare it to CO or dust-continuum-based gas fractions and upper limits (converted to Salpeter) for quiescent and post-starburst galaxies: Davis et al (2014) and Saintonge et al (2011) for local massive PEGs; Sargent et al (2015), Bezanson et al (2019), Spilker et al (2018), Zavala et al (2019), Rudnick et al (2017), Suess et al (2017), Spilker et al (2018), Hayashi et al (2018), Gobat et al (2018) for intermediate-z quiescent galaxies; Schreiber et al (2018) and Valentino et al (2020) for z∼3-4 galaxies. Despite the uncertainties, our data at z∼3 seems to disfavor the steep (1+z) 4−5 trend inferred from z = 0 to 1.5-2, suggesting a flattening in the M mol /M evolution (or equivalently, of the sSFR).…”

ALMA Deep Field in SSA22

“…We also placed ADF22.A2 in the context of galaxy evolution across the cosmic time. Recently an increasing number of quiescent galaxies has been identified at z ∼ 3−4 (e.g., Schreiber et al 2018;Tanaka et al 2019;Valentino et al 2020). These findings invoke the prevalent galaxy populations which experience an active star-forming phase at higher redshifts.…”

The GOGREEN survey: post-infall environmental quenching fails to predict the observed age difference between quiescent field and cluster galaxies at z > 1

“…Evidence of quenched populations of massive galaxies at this epoch is growing (e.g. Glazebrook et al 2017;Schreiber et al 2018a;Tanaka et al 2019;Forrest et al 2020;Tanaka et al 2020;Valentino et al 2020, Forrest et al 2020bsubmitted, Mc-Conachie et al 2020;in prep). Environmental quenching must still play a role, but it may only become dominant at z<1.…”