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ALMA [C i]3 P 1-3 P 0 Observations of NGC 6240: A Puzzling Molecular Outflow, and the Role of Outflows in the Global α CO Factor of (U)LIRGs

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cam.issuedOnline2018-08-20
cam.orpheus.successThu Jan 30 10:54:37 GMT 2020 - The item has an open VoR version.
dc.contributor.authorCicone, C
dc.contributor.authorSevergnini, P
dc.contributor.authorPapadopoulos, PP
dc.contributor.authorMaiolino, R
dc.contributor.authorFeruglio, C
dc.contributor.authorTreister, E
dc.contributor.authorPrivon, GC
dc.contributor.authorZhang, ZY
dc.contributor.authorCeca, RD
dc.contributor.authorFiore, F
dc.contributor.authorSchawinski, K
dc.contributor.authorWagg, J
dc.contributor.orcidCicone, C [0000-0003-0522-6941]
dc.contributor.orcidTreister, E [0000-0001-7568-6412]
dc.contributor.orcidPrivon, GC [0000-0003-3474-1125]
dc.contributor.orcidSchawinski, K [0000-0001-5464-0888]
dc.date.accessioned2018-10-03T04:44:02Z
dc.date.available2018-10-03T04:44:02Z
dc.date.issued2018
dc.description.abstractWe present ALMA and ACA [CI]$^{3}P_{1}-^{3}P_{0}$ ([CI](1-0)) observations of NGC6240, which we combine with ALMA CO(2-1) and IRAM PdBI CO(1-0) data to study the physical properties of the massive molecular (H$_2$) outflow. We discover that the receding and approaching sides of the H$_2$ outflow, aligned east-west, exceed 10 kpc in their total extent. High resolution ($0.24"$) [CI](1-0) line images surprisingly reveal that the outflow emission peaks between the two AGNs, rather than on either of the two, and that it dominates the velocity field in this nuclear region. We combine the [CI](1-0) and CO(1-0) data to constrain the CO-to-H$_2$ conversion factor ($\alpha_{\rm CO}$) in the outflow, which is on average $2.1\pm1.2~\rm M_{\odot} (K~km~s^{-1}~pc^2)^{-1}$. We estimate that $60\pm20$ % of the total H$_2$ gas reservoir of NGC6240 is entrained in the outflow, for a resulting mass-loss rate of $\dot{M}_{\rm out}=2500\pm1200~M_{\odot}~yr^{-1}$ $\equiv 50\pm30$ SFR. This energetics rules out a solely star formation-driven wind, but the puzzling morphology challenges a classic radiative-mode AGN feedback scenario. For the quiescent gas we compute $\langle\alpha_{\rm CO}\rangle = 3.2\pm1.8~\rm M_{\odot} (K~km~s^{-1}~pc^2)^{-1}$, which is at least twice the value commonly employed for (U)LIRGs. We observe a tentative trend of increasing $r_{21}\equiv L^{\prime}_{\rm CO(2-1)}/L^{\prime}_{\rm CO(1-0)}$ ratios with velocity dispersion and measure $r_{21}>1$ in the outflow, whereas $r_{21}\simeq1$ in the quiescent gas. We propose that molecular outflows are the location of the warmer, strongly unbound phase that partially reduces the opacity of the CO lines in (U)LIRGs, hence driving down their global $\alpha_{\rm CO}$ and increasing their $r_{21}$ values.
dc.description.sponsorshipERC Advanced Grant 695671 "QUENCH" STFC ST/M001172/1
dc.identifier.doi10.17863/CAM.30407
dc.identifier.eissn1538-4357
dc.identifier.issn0004-637X
dc.identifier.urihttps://www.repository.cam.ac.uk/handle/1810/283044
dc.language.isoeng
dc.publisherAmerican Astronomical Society
dc.publisher.urlhttp://dx.doi.org/10.3847/1538-4357/aad32a
dc.subjectgalaxies: active
dc.subjectgalaxies: evolution
dc.subjectgalaxies: individual (NGC 6240)
dc.subjectgalaxies: ISM
dc.subjectsubmillimeter: ISM
dc.titleALMA [C i]<sup>3</sup> P <inf>1</inf>-<sup>3</sup> P <inf>0</inf> Observations of NGC 6240: A Puzzling Molecular Outflow, and the Role of Outflows in the Global α <inf>CO</inf> Factor of (U)LIRGs
dc.typeArticle
dcterms.dateAccepted2018-07-16
prism.endingPage18
prism.issueIdentifier2
prism.publicationDate2018
prism.publicationNameAstrophysical Journal
prism.startingPage1
prism.volume863
pubs.funder-project-idScience and Technology Facilities Council (ST/M001172/1)
pubs.funder-project-idEuropean Research Council (695671)
rioxxterms.licenseref.startdate2018-01-01
rioxxterms.licenseref.urihttp://www.rioxx.net/licenses/all-rights-reserved
rioxxterms.typeJournal Article/Review
rioxxterms.versionofrecord10.3847/1538-4357/aad32a

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