2012A&A...548A..22M -
Astronomy and Astrophysics, volume 548A, 22-22 (2012/12-1)
Dust temperature and CO -> H2 conversion factor variations in the SFR-M* plane.
MAGNELLI B., SAINTONGE A., LUTZ D., TACCONI L.J., BERTA S., BOURNAUD F., CHARMANDARIS V., DANNERBAUER H., ELBAZ D., FOERSTER-SCHREIBER N.M., GRACIA-CARPIO J., IVISON R., MAIOLINO R., NORDON R., POPESSO P., RODIGHIERO G., SANTINI P. and WUYTS S.
Abstract (from CDS):
Deep Herschel PACS/SPIRE imaging and
12CO(2-1) line luminosities from the IRAM Plateau de Bure Interferometer are combined for a sample of 17 galaxies at z>1 from the GOODS-N field. The sample includes galaxies both on and above the main sequence (MS) traced by star-forming galaxies in the SFR-M
* plane. The far-infrared data are used to derive dust masses, M
dust, following the Draine & Li (
2007ApJ...657..810D) models. Combined with an empirical prescription for the dependence of the gas-to-dust ratio on metallicity (δ
GDR(µ
0)), the CO luminosities and M
dust values are used to derive for each galaxy the CO-to-H
2 conversion factor, α
CO. Like in the local Universe, the value of α
CO is a factor of ∼5 smaller in starbursts compared to normal star-forming galaxies (SFGs). We additionally uncover a relation between α
CO and dust temperature (T
dust; α
CO decreasing with increasing T
dust) as obtained from modified blackbody fits to the far-infrared data. While the absolute normalization of the α
CO(T
dust) relation is uncertain, the global trend is robust against possible systematic biases in the determination of M
dust, δ
GDR(µ
0) or metallicity. Although we cannot formally distinguish between a step and a smooth evolution of α
CO with the dust temperature, we can unambiguously conclude that in galaxies of near-solar metallicity, a critical value of T
dust=30K can be used to determine whether the appropriate α
CO is closer to the ``starburst'' value (1.0M
☉/(K.km/s/pc2), when T
dust>30K) or closer to the Galactic value (4.35M
☉/(K.km/s/pc2), when T
dust<30K). This indicator has the great advantage of being less subjective than visual morphological classifications of mergers/SFGs, which can be difficult at high z because of the clumpy nature of SFGs. Using T
dust to select the appropriate α
CO is also more indicative of ISM conditions than a fixed L
IR criterion. In the absence of far-infrared data, the offset of a galaxy from the star formation main sequence (i.e., Δlog(SSFR)
MS=log[SSFR(galaxy)/SSFR
MS(M
*,z)]) can be used to identify galaxies requiring the use of an α
CO conversion factor lower than the Galactic value (i.e., when Δlog(SSFR)
MS>0.3dex).
Abstract Copyright:
∼
Journal keyword(s):
galaxies: evolution - infrared: galaxies - galaxies: starburst
Nomenclature:
Table 1: [MSL2012] PEP JHHMMSS+DDMMSS N=9
CDS comments:
HDF 242 and HDF 169 are respectively NAME SMM J123707.2+621408 and NAME SMM J123635+621237 in Simbad.
Simbad objects:
21
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