Star formation relations and co spectral line energy distributions across the J-ladder and redshift

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Greve, T. R.
Leonidaki, I.
Xilouris, E.M.
Weiss, A.
Zhang, Z.-Y.
van der Werf, P.
Aalto, S.
Armus, L.
Diaz-Santos, T.
Evans, A.S.
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American Astronomical Society
We present FIR[50-300 um]-CO luminosity relations (i.e., log Lfir = a log L’co + B) 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; lIR[8-1000um > 10^11 Lo) using data from Herschel SPIRE-FTS and ground-based telescopes. We extend our sample to high redshifts (z > 1) by including 35 (sub)-millimeter selected dusty star forming galaxies from the literature with robust CO observations, and sufficiently well-sampled FIR/sub-millimeter spectral energy distributions (SEDs) so that accurate FIR luminosities can be deduced. The addition of luminous starbursts at high redshifts enlarge the range of the FIR-CO luminosity relations towards 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. The new data-set (both in terms of IR luminosity and J-ladder) reveals linear FIR-CO luminosity relations (i.e., a ~= 1) for J = 1 – 0 up to J = 5 – 4, with a nearly constant normalization (B ~ 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 sub-linear slope (~ 100K) and dense (> 104 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 most likely source of energy for this component. The global CO spectral line energy distributions (SLEDs), 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 of the presence of this gas component.
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Galaxies , Low-redshift , High-redshift , Galaxies -- Formation , Galaxies -- Evolution , Starbursts , Lines
Greve, T.R., Leonidaki, I., Xilouris, E.M., Weiss, A., Zhang, Z.-Y., van der Werf, P., ... Walter, F. (2014). Star formation relations and co spectral line energy distributions across the J-ladder and redshift. Astrophysical Journal, 794(2). Retrieved from