The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: CO Excitation and Atomic Carbon in Star-forming Galaxies at z=1-3

Boogaard, Leindert A.; van der Werf, Paul; Weiss, Axel; Popping, Gergoe; Decarli, Roberto; Walter, Fabian; Aravena, Manuel; Bouwens, Rychard; Riechers, Dominik; Gonzalez-Lopez, Jorge; Smail, Ian; Carilli, Chris; Kaasinen, Melanie; Daddi, Emanuele; Cox, Pierre; et. al.

Abstract

We investigate the CO excitation and interstellar medium (ISM) conditions in a cold gas mass-selected sample of 22 star-forming galaxies at z = 0.46-3.60, observed as part of the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS). Combined with Very Large Array follow-up observations, we detect a total of 34 CO J -> J - 1 transitions with J.=.1 up to 8 (and an additional 21 upper limits, up to J = 10) and 6 [C I] P-3(1) -> P-3(0) and P-3(2) -> P-3(1) transitions (and 12 upper limits). The CO(2-1) and CO(3-2)-selected galaxies, at < z > = 1.2 and 2.5, respectively, exhibit a range in excitation in their mid-J.=.4, 5 and high-J.=.7, 8 lines, on average lower than (LIR-brighter) BzK-color- and submillimeter-selected galaxies at similar redshifts. The former implies that a warm ISM component is not necessarily prevalent in gas mass-selected galaxies at < z > = 1.2. We use stacking and Large Velocity Gradient models to measure and predict the average CO ladders at z < 2 and z >= 2, finding r(21) = 0.75 +/- 0.11 and r(31) = 0.77 +/- 0.14, respectively. From the models, we infer that the galaxies at z >= 2 have intrinsically higher excitation than those at z<2. This fits a picture in which the global excitation is driven by an increase in the star formation rate surface density of galaxies with redshift. We derive a neutral atomic carbon abundance of (1.9 +/- 0.4) x 10(-5), comparable to the Milky Way and main-sequence galaxies at similar redshifts, and fairly high densities (>= 10(4) cm(-3)), consistent with the low-J CO excitation. Our results imply a decrease in the cosmic molecular gas mass density at z >= 2 compared to previous ASPECS measurements.

Más información

Título según WOS: The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: CO Excitation and Atomic Carbon in Star-forming Galaxies at z=1-3
Título de la Revista: ASTROPHYSICAL JOURNAL
Volumen: 902
Número: 2
Editorial: IOP PUBLISHING LTD
Fecha de publicación: 2020
DOI:

10.3847/1538-4357/ABB82F

Notas: ISI