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Dark Molecular Gas in Simulations of z - 0 Disk Galaxies

Li, Qi; Narayanan, Desika; Dave, Romeel; Krumholz, Mark

Description

The H2 mass of molecular clouds has traditionally been traced by the CO(J = 1−0) rotational transition line. This said, CO is relatively easily photodissociated and can also be destroyed by cosmic rays, thus rendering some fraction of molecular gas to be "CO-dark." We investigate the amount and physical properties of CO-dark gas in two z ~ 0 disk galaxies and develop predictions for the expected intensities of promising alternative tracers ([C i] 609 μm and [C ii] 158 μm emission). We do this...[Show more]

dc.contributor.authorLi, Qi
dc.contributor.authorNarayanan, Desika
dc.contributor.authorDave, Romeel
dc.contributor.authorKrumholz, Mark
dc.date.accessioned2019-12-09T04:48:23Z
dc.date.available2019-12-09T04:48:23Z
dc.identifier.issn0004-637X
dc.identifier.urihttp://hdl.handle.net/1885/188702
dc.description.abstractThe H2 mass of molecular clouds has traditionally been traced by the CO(J = 1−0) rotational transition line. This said, CO is relatively easily photodissociated and can also be destroyed by cosmic rays, thus rendering some fraction of molecular gas to be "CO-dark." We investigate the amount and physical properties of CO-dark gas in two z ~ 0 disk galaxies and develop predictions for the expected intensities of promising alternative tracers ([C i] 609 μm and [C ii] 158 μm emission). We do this by combining cosmological zoom simulations of disk galaxies with thermal-radiative-chemical equilibrium interstellar medium (ISM) calculations to model the predicted H i and H2 abundances and CO (J = 1−0), [C i] 609 μm, and [C ii] 158 μm emission properties. Our model treats the ISM as a collection of radially stratified clouds whose properties are dictated by their volume and column densities, the gas-phase metallicity, and the interstellar radiation field (ISRF) and CR ionization rates. Our main results follow. Adopting an observationally motivated definition of CO-dark gas, i.e., H2 gas with W CO < 0.1 K km s−1, we find that a significant amount (gsim50%) of the total H2 mass lies in CO-dark gas, most of which is diffuse gas, poorly shielded due to low dust column density. The CO-dark molecular gas tends to be dominated by [C ii], though [C i] also serves as a bright tracer of the dark gas in many instances. At the same time, [C ii] also tends to trace neutral atomic gas. As a result, when we quantify the conversion factors for the three carbon-based tracers of molecular gas, we find that [C i] suffers the least contamination from diffuse atomic gas and is relatively insensitive to secondary parameters.
dc.description.sponsorshipQ.L. was funded by NSF grant AST-1724864. D.N. acknowledges funding from NSF grants AST-1724864 and AST-1715206 and HST AR-13906.001 from the Space Telescope Science Institute. M.R.K. acknowledges support from the Australian Research Council’s Discovery Projects funding scheme, grant DP160100695.
dc.format.mimetypeapplication/pdf
dc.language.isoen_AU
dc.publisherIOP Publishing
dc.rights© 2018 The American Astronomical Society.
dc.sourceThe Astrophysical Journal
dc.subjectastrochemistry
dc.subjectgalaxies: ISM
dc.subjectISM: molecules
dc.subjectmethods: numerical
dc.titleDark Molecular Gas in Simulations of z - 0 Disk Galaxies
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume869
dcterms.dateAccepted2018-10-25
dc.date.issued2018-12-13
local.identifier.absfor020103 - Cosmology and Extragalactic Astronomy
local.identifier.ariespublicationu3102795xPUB140
local.publisher.urlhttps://iopscience.iop.org/
local.type.statusPublished Version
local.contributor.affiliationLi, Qi, University of Florida
local.contributor.affiliationNarayanan, Desika, University of Florida
local.contributor.affiliationDave, Romeel, University of the Western Cape
local.contributor.affiliationKrumholz, Mark, College of Science, ANU
dc.relationhttp://purl.org/au-research/grants/arc/DP160100695
local.bibliographicCitation.issue73
local.bibliographicCitation.startpage1
local.bibliographicCitation.lastpage14
local.identifier.doi10.3847/1538-4357/aaec77
local.identifier.absseo970102 - Expanding Knowledge in the Physical Sciences
dc.date.updated2019-07-28T08:17:56Z
local.identifier.scopusID2-s2.0-85058449807
dcterms.accessRightsOpen Access
dc.provenancehttp://sherpa.ac.uk/romeo/issn/0004-637X/..."author can archive publisher's version/PDF" from SHERPA/RoMEO site (as at 9/12/19)
CollectionsANU Research Publications

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