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The ALMA Spectroscopic Survey in the HUDF: CO Excitation and Atomic Carbon in Star-Forming Galaxies at $z=1-3$ | | Leindert A. Boogaard
; Paul van der Werf
; Axel Weiß
; Gergö Popping
; Roberto Decarli
; Fabian Walter
; Manuel Aravena
; Rychard Bouwens
; Dominik Riechers
; Jorge González-López
; Ian Smail Chris Carilli
; Melanie Kaasinen
; Emanuele Daddi
; Pierre Cox
; Tanio Díaz-Santos
; Hanae Inami
; Paulo C. Cortes
; Jeff Wagg
; | | Date: |
9 Sep 2020 | | 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 VLA 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 six [C I] 3P_1 -> 3P_0 and 3P_2 -> 3P_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 (L_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 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. | | Source: | arXiv, 2009.04348 | | Services: | Forum | Review | PDF | Favorites | |
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