TY - JOUR
T1 - PHIBSS
T2 - Exploring the dependence of the CO–H2 conversion factor on total mass surface density at z < 1.5
AU - Carleton, Timothy
AU - Cooper, Michael C.
AU - Bolatto, Alberto D.
AU - Bournaud, Frederic
AU - Combes, Françoise
AU - Freundlich, Jonathan
AU - Garcia-Burillo, Santiago
AU - Genzel, Reinhard
AU - Neri, Roberto
AU - Tacconi, Linda J.
AU - Sandstrom, Karin M.
AU - Weiner, Benjamin J.
AU - Weiss, Axel
N1 - Funding Information:
We are grateful to the anonymous referee, whose comments significantly improved the clarity of this work. Support for this work was provided by NASA through grants (GO-12547 and AR-13242) from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. This work was also supported, in part, by NSF grant AST-1518257. TC and MCC thank the National Achievement Rewards for College Scientists (ARCS) Foundation and the International Space Science Institute (ISSI), respectively, for support of this work. The observations presented here would not have been possible without the diligence and sensitive new-generation receivers from the IRAM staff – for this, they have our highest admiration and thanks. We also thank the astronomers on duty and telescope operators for delivering consistently high-quality data to our team. Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation and the U.S. Department of Energy Office of Science. The SDSS-III website is http://www.sdss3.org/. SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, Harvard University, the Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York University, Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington and Yale University. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research made use of Astropy, a community-developed core PYTHON package for astronomy (Astropy Collaboration et al. 2013). Additionally, the PYTHON packages NumPy (Walt, Colbert & Varoquaux 2011), iPython (Pérez & Granger 2007), SciPy (Jones et al. 2001) and matplotlib (Hunter 2007) were utilized for the majority of our data analysis and presentation. This work has made use of the Rainbow Cosmological Surveys Database, which is operated by the Universidad Complutense de Madrid (UCM), partnered with the University of California Observatories at Santa Cruz (UCO/Lick, UCSC), as well as the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
Funding Information:
Support for this work was provided by NASA through grants (GO-12547 and AR-13242) from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. This work was also supported, in part, by NSF grant AST-1518257. TC and MCC thank the National Achievement Rewards for College Scientists (ARCS) Foundation and the International Space Science Institute (ISSI), respectively, for support of this work. The observations presented here would not have been possible without the diligence and sensitive new-generation receivers from the IRAM staff – for this, they have our highest admiration and thanks. We also thank the astronomers on duty and telescope operators for delivering consistently high-quality data to our team.
Funding Information:
Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation and the U.S. Department of Energy Office of Science. The SDSS-III website is http://www.sdss3.org/.
Publisher Copyright:
© 2017 The Authors.
PY - 2017/6/1
Y1 - 2017/6/1
N2 - We present an analysis of the relationship between the CO–H2 conversion factor (αCO) and total mass surface density (tot) in star-forming galaxies at z < 1.5. Our sample, which is drawn from the IRAM Plateau de Bure HIgh-z Blue Sequence Survey (PHIBSS) and the CO Legacy Database for GASS (COLD GASS), includes ‘normal’, massive star-forming galaxies that dominate the evolution of the cosmic star formation rate (SFR) at this epoch and probe the tot regime where the strongest variation in αCO is observed. We constrain αCO via existing CO observations, measurements of the SFR and an assumed molecular gas depletion time (tdep = Mgas/SFR) – the latter two of which establish the total molecular gas mass independent of the observed CO luminosity. For a broad range of adopted depletion times, we find that αCO is independent of total mass surface density, with little deviation from the canonical Milky Way value. This runs contrary to a scenario in which αCO decreases as surface density increases within the extended clouds of molecular gas that potentially fuel clumps of star formation in z ∼ 1 galaxies, similar to those observed in local ultra-luminous infrared galaxies. Instead, our results suggest that molecular gas, at both z ∼ 0 and z ∼ 1, is primarily in the form of self-gravitating molecular clouds. While CO observations suggest a factor of ∼3 reduction in the average molecular gas depletion time between z ∼ 0 and z ∼ 1, we find that, for typical galaxies, the structure of molecular gas and the process of star formation at z ∼ 1 is otherwise remarkably similar to that observed in local star-forming systems.
AB - We present an analysis of the relationship between the CO–H2 conversion factor (αCO) and total mass surface density (tot) in star-forming galaxies at z < 1.5. Our sample, which is drawn from the IRAM Plateau de Bure HIgh-z Blue Sequence Survey (PHIBSS) and the CO Legacy Database for GASS (COLD GASS), includes ‘normal’, massive star-forming galaxies that dominate the evolution of the cosmic star formation rate (SFR) at this epoch and probe the tot regime where the strongest variation in αCO is observed. We constrain αCO via existing CO observations, measurements of the SFR and an assumed molecular gas depletion time (tdep = Mgas/SFR) – the latter two of which establish the total molecular gas mass independent of the observed CO luminosity. For a broad range of adopted depletion times, we find that αCO is independent of total mass surface density, with little deviation from the canonical Milky Way value. This runs contrary to a scenario in which αCO decreases as surface density increases within the extended clouds of molecular gas that potentially fuel clumps of star formation in z ∼ 1 galaxies, similar to those observed in local ultra-luminous infrared galaxies. Instead, our results suggest that molecular gas, at both z ∼ 0 and z ∼ 1, is primarily in the form of self-gravitating molecular clouds. While CO observations suggest a factor of ∼3 reduction in the average molecular gas depletion time between z ∼ 0 and z ∼ 1, we find that, for typical galaxies, the structure of molecular gas and the process of star formation at z ∼ 1 is otherwise remarkably similar to that observed in local star-forming systems.
KW - Galaxies: ISM
KW - Galaxies: evolution
KW - Galaxies: formation
KW - Galaxies: high-redshift
KW - Galaxies: star formation
KW - ISM: molecules
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U2 - 10.1093/mnras/stx390
DO - 10.1093/mnras/stx390
M3 - Article
AN - SCOPUS:85019001824
SN - 0035-8711
VL - 467
SP - 4886
EP - 4901
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 4
ER -