The ALMA Spectroscopic Survey in the HUDF: CO Luminosity Functions and the Molecular Gas Content of Galaxies through Cosmic History

Abstract

We use the results from the ALMA large program ASPECS, the spectroscopic survey in the Hubble Ultra Deep Field (HUDF), to constrain CO luminosity functions of galaxies and the resulting redshift evolution of ρ(H 2 ). The broad frequency range covered enables us to identify CO emission lines of different rotational transitions in the HUDF at z > 1. We find strong evidence that the CO luminosity function evolves with redshift, with the knee of the CO luminosity function decreasing in luminosity by an order of magnitude from ∼2 to the local universe. Based on Schechter fits, we estimate that

xGASS: H i Fueling of Star Formation in Disk-dominated Galaxies

“…In the more distant Universe, the phase of Hi might be less important, for the neutral gas seems to be dominated by the molecular phase (Tacconi et al 2013(Tacconi et al , 2018; but see also e.g. Cortese et al 2017;Decarli et al 2019). But in the local Universe, the conversion of Hi to H 2 is much less efficient and Hi is a significant component of the neutral gas (∼80% globally and 50% in the stellar disks for star-forming galaxies, Catinella et al 2018 and this paper).…”

The ALMA Spectroscopic Survey in the HUDF: Constraining Cumulative CO Emission at 1 ≲ z ≲ 4 with Power Spectrum Analysis of ASPECS LP Data from 84 to 115 GHz

“…13 There are, in total, 680 sources identified by MUSE that are available in the ASPECS LP areal and redshift coverage, and 415 of these lie within the cropped region used here for the power spectrum analysis; unless otherwise noted, we include all spec-z reported in the MUSE catalog. 14 Of these 415, 24 MUSE sources fall within the redshift interval and volume probed by CO(1-0) in ASPECS LP, and can be 10 Note that larger uncertainties on shot noise power derived from COLDz are largely due to differences in fitting the measured LFs: the authors in Riechers et al (2019) treated the faint-end slope of the LF as a free parameter, while Decarli et al (2019) kept it fixed during their fitting.…”

“…11 Decarli et al (2019) used the CO(3-2) LF measured at zcen = 2.6 to infer a CO(1-0) LF after accounting for CO excitation. The fiducial prescription to convert from CO(3-2) to CO(1-0) luminosities was based on Daddi et al (2015), but the authors there explored alternative lower and higher excitation scenarios, as well, finding that their results are qualitatively robust to the adopted CO line ratio.…”

“…Obtaining an unbiased and complete measure of the cold gas content and star formation activity of galaxies as functions of cosmic time provides insight into the underlying physical processes that regulate this evolution. With the cosmic star formation rate density (SFRD) well characterized out to z ∼ 3-4, and rest-frame UV observations setting constraints on the SFRD into the first billion years after the Big Bang (e.g., Madau & Dickinson (2014) for a review), there are ongoing efforts to complement this understanding with concurrent trends in the atomic (HI; e.g., Neeleman et al 2016) and molecular (H 2 ; e.g., Decarli et al 2019) gas history-particularly during the epoch of galaxy mass assembly at z ∼ 2, when cosmic star formation activity was approximately ten times higher than in the present epoch, and more than half of the stellar mass in the Universe was accumulated (Madau & Dickinson 2014).…”

The Experiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM)

“…EXCLAIM's IM measurements of two J lines at the same redshift will permit new diagnostics of the ISM environment. Additionally, EXCLAIM's measurements of the integrated emission will complement interferometric observations by the Atacama Large Millimeter/submillimeter Array (ALMA) 12 . In the Milky Way, [CI] emission can track molecular gas in regions where CO is photo-dissociated.…”