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Title: | The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: CO Excitation and Atomic Carbon in Star-forming Galaxies at z = 1-3 | Authors: | Boogaard, Leindert A. van der Werf, Paul Weiss, Axel Popping, Gergö DECARLI, ROBERTO Walter, Fabian Aravena, Manuel Bouwens, Rychard Riechers, Dominik González-López, Jorge Smail, Ian Carilli, Chris Kaasinen, Melanie Daddi, Emanuele Cox, Pierre Díaz-Santos, Tanio Inami, Hanae Cortes, Paulo C. Wagg, Jeff |
Issue Date: | 2020 | Journal: | THE ASTROPHYSICAL JOURNAL | Number: | 902 | Issue: | 2 | First Page: | 109 | 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 $J\to J-1$ transitions with J = 1 up to 8 (and an additional 21 upper limits, up to J = 10) and 6 $[{\rm{C}}\,{\rm\small{I}}]$ ${}^{3}{P}_{1}{\to }^{3}\,{P}_{0}$ and ${}^{3}{P}_{2}{\to }^{3}\,{P}_{1}$ transitions (and 12 upper limits). The CO(2-1) and CO(3-2)-selected galaxies, at $\langle z\rangle =1.2$ 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 ( ${L}_{\mathrm{IR}}$ -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 $\langle z\rangle =1.2$ . We use stacking and Large Velocity Gradient models to measure and predict the average CO ladders at z < 2 and z ≥ 2, finding ${r}_{21}=0.75\pm 0.11$ and ${r}_{31}=0.77\pm 0.14$ , 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 $(1.9\pm 0.4)\times {10}^{-5}$ , comparable to the Milky Way and main-sequence galaxies at similar redshifts, and fairly high densities (≥10<SUP>4</SUP> cm<SUP>-3</SUP>), 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. | URI: | http://hdl.handle.net/20.500.12386/31001 | URL: | https://iopscience.iop.org/article/10.3847/1538-4357/abb82f | ISSN: | 0004-637X | DOI: | 10.3847/1538-4357/abb82f | Bibcode ADS: | 2020ApJ...902..109B | Fulltext: | reserved |
Appears in Collections: | 1.01 Articoli in rivista |
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