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.
ISM: molecules
galaxies: formation
galaxies: evolution
galaxies: starburst
galaxies: ISM
Författare
T. R. Greve
University College London (UCL)
I. Leonidaki
National Observatory of Athens
E. M. Xilouris
National Observatory of Athens
A. Weiss
Max-Planck-Gesellschaft
Z. Y. Zhang
European Southern Observatory (ESO)
Royal Observatory
P. van der Werf
Universiteit Leiden
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
Chinese Academy of Sciences
E. Gonzalez-Alfonso
Universidad de Alcala
A. I. Harris
University of Maryland
C. Henkel
King Abdulaziz University
Max-Planck-Gesellschaft
R. Meijerink
Universiteit Leiden
D. A. Naylor
University of Lethbridge
H. Smith
Harvard-Smithsonian Center for Astrophysics
M. Spaans
Rijksuniversiteit Groningen
G. J. Stacey
Cornell University
S. Veilleux
University of Maryland
F. Walter
Max-Planck-Gesellschaft
Astrophysical Journal
0004-637X (ISSN) 1538-4357 (eISSN)
Vol. 794 2 Art. no. 142- 142Ämneskategorier
Astronomi, astrofysik och kosmologi
Fundament
Grundläggande vetenskaper
DOI
10.1088/0004-637x/794/2/142