Abstract
We present Herschel PACS observations of the [C II] 158 μm emission
line in a sample of 24 intermediate mass (9 <log
M*/M⊙ <10) and low metallicity (0.4 <
Z/Z⊙ <1.0) galaxies from the xCOLD GASS survey. In
combination with IRAM CO (1-0) measurements, we establish scaling
relations between integrated and molecular region L_{[C II]}/LCO
(1-0) ratios as a function of integrated galaxy properties. A
Bayesian analysis reveals that only two parameters, metallicity and
offset from the main sequence, Δ(MS), are needed to quantify
variations in the luminosity ratio; metallicity describes the total dust
content available to shield CO from UV radiation, while Δ(MS)
describes the strength of this radiation field. We connect the L_{[C
II]}/LCO (1-0) ratio to the CO-to-H2 conversion
factor and find a multivariate conversion function, which can be used up
to z ˜ 2.5. This function depends primarily on metallicity, with a
second-order dependence on Δ(MS). We apply this to the full xCOLD
GASS and PHIBSS1 surveys and investigate molecular gas scaling
relations. We find a flattening of the relation between gas mass
fraction and stellar mass at log M* <10.0. While the
molecular gas depletion time varies with sSFR, it is mostly independent
of mass, indicating that the low LCO/SFR ratios long observed
in low-mass galaxies are entirely due to photodissociation of CO and not
to an enhanced star formation efficiency.
Original language | English |
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Pages (from-to) | 4750-4766 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 470 |
Issue number | 4 |
DOIs | |
Publication status | Published - 22 Jun 2017 |
Keywords / Materials (for Non-textual outputs)
- surveys
- galaxies: evolution
- galaxies: fundamental parameters
- galaxies: ISM
- radio lines: galaxies