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Star Formation Relations and CO Spectral Line Energy Distributions across the J-ladder and Redshift

Greve, T. R. and Leonidaki, I. and Xilouris, E. M. and Weiß, A. and Zhang, Z.-Y. and van der Werf, P. and Aalto, S. and Armus, L. and Díaz-Santos, T. and Evans, A. S. and Fischer, J. and Gao, Y. and González-Alfonso, E. and Harris, A. and Henkel, C. and Meijerink, R. and Naylor, D. A. and Smith, H. A. and Spaans, M. and Stacey, G. J. and Veilleux, S. and Walter, F. (2014) Star Formation Relations and CO Spectral Line Energy Distributions across the J-ladder and Redshift. Astrophysical Journal, 794 (2). Art. No. 142. ISSN 0004-637X.

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We present FIR [50-300 μm]–CO luminosity relations (i.e., log L_FIR = α log L’_co + β) for the full CO rotational ladder from J = 1-0 up to J = 13-12 for a sample of 62 local (z ≤ 0.1) (Ultra) Luminous Infrared Galaxies (LIRGs; L_(IR[8-1000 μm]) > 10^(11) L ☉) using data from Herschel SPIRE-FTS and ground-based telescopes. We extend our sample to high redshifts (z > 1) by including 35 submillimeter selected dusty star forming galaxies from the literature with robust CO observations, and sufficiently well-sampled FIR/submillimeter spectral energy distributions (SEDs), so that accurate FIR luminosities can be determined. The addition of luminous starbursts at high redshifts enlarge the range of the FIR–CO luminosity relations toward the high-IR-luminosity end, while also significantly increasing the small amount of mid-J/high-J CO line data (J = 5-4 and higher) that was available prior to Herschel. This new data set (both in terms of IR luminosity and J-ladder) reveals linear FIR–CO luminosity relations (i.e., α 1) for J = 1-0 up to J = 5-4, with a nearly constant normalization (β ~ 2). In the simplest physical scenario, this is expected from the (also) linear FIR–(molecular line) relations recently found for the dense gas tracer lines (HCN and CS), as long as the dense gas mass fraction does not vary strongly within our (merger/starburst)-dominated sample. However, from J = 6-5 and up to the J = 13-12 transition, we find an increasingly sublinear slope and higher normalization constant with increasing J. We argue that these are caused by a warm (~100 K) and dense (>10^4 cm^(–3)) gas component whose thermal state is unlikely to be maintained by star-formation-powered far-UV radiation fields (and thus is no longer directly tied to the star formation rate). We suggest that mechanical heating (e.g., supernova-driven turbulence and shocks), and not cosmic rays, is the more likely source of energy for this component. The global CO spectral line energy distributions, which remain highly excited from J = 6-5 up to J = 13-12, are found to be a generic feature of the (U)LIRGs in our sample, and further support the presence of this gas component.

Item Type:Article
Related URLs:
URLURL TypeDescription
van der Werf, P.0000-0001-5434-5942
Díaz-Santos, T.0000-0003-0699-6083
Veilleux, S.0000-0002-3158-6820
Walter, F.0000-0003-4793-7880
Additional Information:© 2014 The American Astronomical Society. Received 2014 May 8; Accepted 2014 July 15; Published 2014 October 2. The authors gratefully acknowledge financial support under the “DeMoGas” project. The project DeMoGas is implemented under the “ARISTEIA” Action of the “Operational Programme Education and Lifelong Learning.” The project is co-funded by the European Social Fund (ESF) and National Resources. T.R.G. acknowledges support from an STFC Advanced Fellowship. T.R.G. was also supported by Chinese Academy of Sciences Fellowship for Young International Scientists (grant no. 2012y1ja0006). Z.Y.Z. acknowledges support from the European Research Council (ERC) in the form of Advanced Grant,cosmicism. We are indebted to P. P. Papadopoulos for extensive discussions and comments on the paper (He ho’okele wa’a no ka la ’ino). Basic research in infrared astronomy at the Naval Research Laboratory is funded by the Office of Naval Research. J.F. also acknowledges support from the NHSC/JPL. The research presented here 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. Finally, we would like to thank the anonymous referee for a useful and constructive referee report that helped improve the paper.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
European Social FundUNSPECIFIED
Science and Technology Facilities Council (STFC)UNSPECIFIED
Chinese Academy of Sciences2012y1ja0006
European Research Council (ERC)cosmicism
Office of Naval Research (ONR)UNSPECIFIED
Subject Keywords:galaxies: evolution; galaxies: formation; galaxies: ISM; galaxies: starburst; ISM: molecules
Record Number:CaltechAUTHORS:20141114-123844898
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Official Citation:Star Formation Relations and CO Spectral Line Energy Distributions across the J-ladder and Redshift T. R. Greve et al. 2014 ApJ 794 142
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51780
Deposited By: Joanne McCole
Deposited On:14 Nov 2014 22:36
Last Modified:25 Oct 2017 19:29

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