Star Formation Relations and CO-Spectral Line Energy Distributions Across the J-Ladder and Redshift
Artikel i vetenskaplig tidskrift, 2014

We present FIR [50-300 mu m]-CO luminosity relations (i.e., log L-FIR = alpha log L'(CO) + beta) 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 InfraredGalaxies (LIRGs; LIR[8-1000 mu m] > 10(11) L-circle dot) 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., a similar or equal to 1) for J = 1-0 up to J = 5-4, with a nearly constant normalization (beta similar to 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 (similar to 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.

galaxies: starburst

galaxies: formation

galaxies: evolution

galaxies: ISM

ISM: molecules


T. R. Greve

University College London (UCL)

I. Leonidaki

National Observatory of Athens

E. M. Xilouris

National Observatory of Athens

A. Weiss

Max Planck-institutet

Z. Y. Zhang

Royal Observatory

European Southern Observatory (ESO)

P. van der Werf

Leiden University

Susanne Aalto

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

L. Armus

Spitzer Science Center

T. Diaz-Santos

Spitzer Science Center

A. S. Evans

University of Virginia

National Radio Astronomy Observatory

J. Fischer

Naval Research Laboratory

Y. Gao

Purple Mountain Observatory Chinese Academy of Sciences

E. Gonzalez-Alfonso

Universidad de Alcala

A. I. Harris

University of Maryland

C. Henkel

Max Planck-institutet

King Abdulaziz University

R. Meijerink

Leiden University

D. A. Naylor

University of Lethbridge

H. Smith

Harvard-Smithsonian Center for Astrophysics

M. Spaans

University of Groningen, Kapteyn Astronomical Institute

G. J. Stacey

Cornell University

S. Veilleux

University of Maryland

F. Walter

Max Planck-institutet

Astrophysical Journal

0004-637X (ISSN) 1538-4357 (eISSN)

Vol. 794 Art. no. 142- 142


Astronomi, astrofysik och kosmologi


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