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Near-infrared Emission Lines in Starburst Galaxies at 0.5 < z < 0.9: Discovery of a Merger Sequence of Extreme Obscurations

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cam.issuedOnline2018-08-01
dc.contributor.authorCalabrò, A
dc.contributor.authorDaddi, E
dc.contributor.authorCassata, P
dc.contributor.authorOnodera, M
dc.contributor.authorGobat, R
dc.contributor.authorPuglisi, A
dc.contributor.authorJin, S
dc.contributor.authorLiu, D
dc.contributor.authorAmorín, R
dc.contributor.authorArimoto, N
dc.contributor.authorBoquien, M
dc.contributor.authorCarraro, R
dc.contributor.authorElbaz, D
dc.contributor.authorIbar, E
dc.contributor.authorJuneau, S
dc.contributor.authorMannucci, F
dc.contributor.authorMéndez Hernánez, H
dc.contributor.authorOliva, E
dc.contributor.authorRodighiero, G
dc.contributor.authorValentino, F
dc.contributor.authorZanella, A
dc.contributor.orcidCalabrò, A [0000-0003-2536-1614]
dc.contributor.orcidDaddi, E [0000-0002-3331-9590]
dc.contributor.orcidCassata, P [0000-0002-6716-4400]
dc.contributor.orcidOnodera, M [0000-0003-3228-7264]
dc.contributor.orcidGobat, R [0000-0003-0121-6113]
dc.contributor.orcidPuglisi, A [0000-0001-9369-1805]
dc.contributor.orcidJin, S [0000-0002-8412-7951]
dc.contributor.orcidAmorín, R [0000-0001-5758-1000]
dc.contributor.orcidBoquien, M [0000-0003-0946-6176]
dc.contributor.orcidCarraro, R [0000-0002-6089-1947]
dc.contributor.orcidElbaz, D [0000-0002-7631-647X]
dc.contributor.orcidJuneau, S [0000-0002-0000-2394]
dc.contributor.orcidRodighiero, G [0000-0002-9415-2296]
dc.contributor.orcidValentino, F [0000-0001-6477-4011]
dc.contributor.orcidZanella, A [0000-0001-8600-7008]
dc.date.accessioned2018-11-01T14:03:27Z
dc.date.available2018-11-01T14:03:27Z
dc.date.issued2018
dc.description.abstractWe obtained optical/near-IR rest-frame Magellan FIRE spectra (including Pa$\beta$ and Pa$\gamma$) of 25 starburst galaxies at 0.5<z<0.9, with average star formation rates (SFR) x7 above the Main Sequence (MS). We find that Paschen-to-Balmer line ratios saturate around a constant value corresponding to $A_{\rm V}\sim$2-3 mag, while line to IR luminosity ratios suggest a large range of more extreme obscurations and appear to be uncorrelated to the former. This behavior is not consistent with standard attenuation laws derived for local and distant galaxies, while being remarkably consistent with observations of starburst cores in which young stars and dust are homogeneously mixed. This model implies $A_{\rm V}=$2-30 mag attenuation to the center of starburst cores, with a median of ~9 mag (a factor of 4000). X-ray hardness ratios for 6 AGNs in our sample and column densities derived from observed dust masses and radio sizes independently confirm this level of attenuation. In these conditions observed optical/near-IR emission comes from surface regions, while inner starburst cores are invisible. We thus attribute the high [NII]/H$\alpha$ ratios to widespread shocks from accretion, turbulence and dynamic disturbances rather than to AGNs. The large range of optical depths demonstrates that substantial diversity is present within the starburst population, possibly connected to different merger phases or progenitor properties. The majority of our targets are, in fact, morphologically classified as mergers. We argue that the extreme obscuration provides in itself smoking gun evidence of their merger origin, and a powerful tool for identifying mergers at even higher redshifts.
dc.identifier.doi10.17863/CAM.31894
dc.identifier.eissn2041-8213
dc.identifier.issn2041-8205
dc.identifier.urihttps://www.repository.cam.ac.uk/handle/1810/284519
dc.language.isoeng
dc.publisherAmerican Astronomical Society
dc.publisher.urlhttp://dx.doi.org/10.3847/2041-8213/aad33e
dc.subjectdust
dc.subjectextinction
dc.subjectgalaxies: evolution
dc.subjectgalaxies: high-redshift
dc.subjectgalaxies: ISM
dc.subjectgalaxies: starburst
dc.subjectinfrared: galaxies
dc.titleNear-infrared Emission Lines in Starburst Galaxies at 0.5 &lt; z &lt; 0.9: Discovery of a Merger Sequence of Extreme Obscurations
dc.typeArticle
prism.issueIdentifier2
prism.publicationDate2018
prism.publicationNameAstrophysical Journal Letters
prism.volume862
pubs.funder-project-idEuropean Research Council (695671)
rioxxterms.licenseref.startdate2018-08-01
rioxxterms.licenseref.urihttp://www.rioxx.net/licenses/all-rights-reserved
rioxxterms.typeJournal Article/Review
rioxxterms.versionAM
rioxxterms.versionofrecord10.3847/2041-8213/aad33e

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