The CO(3-2)/CO(1-0) luminosity line ratio in nearby star-forming galaxies and AGN from xCOLD GASS, BASS and SLUGS. (arXiv:1912.01026v1 [astro-ph.GA])

The CO(3-2)/CO(1-0) luminosity line ratio in nearby star-forming galaxies and AGN from xCOLD GASS, BASS and SLUGS. (arXiv:1912.01026v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Lamperti_I/0/1/0/all/0/1">Isabella Lamperti</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Saintonge_A/0/1/0/all/0/1">Am&#xe9;lie Saintonge</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Koss_M/0/1/0/all/0/1">Michael Koss</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Viti_S/0/1/0/all/0/1">Serena Viti</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wilson_C/0/1/0/all/0/1">Christine D. Wilson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+He_H/0/1/0/all/0/1">Hao He</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shimizu_T/0/1/0/all/0/1">T. Taro Shimizu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Greve_T/0/1/0/all/0/1">Thomas R. Greve</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mushotzky_R/0/1/0/all/0/1">Richard Mushotzky</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Treister_E/0/1/0/all/0/1">Ezequiel Treister</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kramer_C/0/1/0/all/0/1">Carsten Kramer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sanders_D/0/1/0/all/0/1">David Sanders</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Schawinski_K/0/1/0/all/0/1">Kevin Schawinski</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tacconi_L/0/1/0/all/0/1">Linda J. Tacconi</a>

We study the r31=L’CO(3-2)/L’CO(1-0) luminosity line ratio in a sample of
nearby (z < 0.05) galaxies: 25 star-forming galaxies (SFGs) from the xCOLD GASS survey, 36 hard X-ray selected AGN host galaxies from BASS and 37 infrared luminous galaxies from SLUGS. We find a trend for r31 to increase with star-formation efficiency (SFE). We model r31 using the UCL-PDR code and find that the gas density is the main parameter responsible for variation of r31, while the interstellar radiation field and cosmic ray ionization rate play only a minor role. We interpret these results to indicate a relation between SFE and gas density. We do not find a difference in the r31 value of SFGs and AGN host galaxies, when the galaxies are matched in SSFR (= 0.52 +/- 0.04 for SFGs
and = 0.53 +/- 0.06 for AGN hosts). According to the results of UCL-PDR
models, the X-rays can contribute to the enhancement of the CO line ratio, but
only for strong X-ray fluxes and for high gas density (nH > 10$^4$ cm-3). We
find a mild tightening of the Kennicutt-Schmidt relation when we use the
molecular gas mass surface density traced by CO(3-2) (Pearson correlation
coefficient R=0.83), instead of the molecular gas mass surface density traced
by CO(1-0) (R=0.78), but the increase in correlation is not statistically
significant (p-value=0.06). This suggests that the CO(3-2) line can be reliably
used to study the relation between SFR and molecular gas for normal SFGs at
high redshift, and to compare it with studies of low-redshift galaxies, as is
common practice.

We study the r31=L’CO(3-2)/L’CO(1-0) luminosity line ratio in a sample of
nearby (z < 0.05) galaxies: 25 star-forming galaxies (SFGs) from the xCOLD GASS
survey, 36 hard X-ray selected AGN host galaxies from BASS and 37 infrared
luminous galaxies from SLUGS. We find a trend for r31 to increase with
star-formation efficiency (SFE). We model r31 using the UCL-PDR code and find
that the gas density is the main parameter responsible for variation of r31,
while the interstellar radiation field and cosmic ray ionization rate play only
a minor role. We interpret these results to indicate a relation between SFE and
gas density. We do not find a difference in the r31 value of SFGs and AGN host
galaxies, when the galaxies are matched in SSFR (<r31>= 0.52 +/- 0.04 for SFGs
and <r31> = 0.53 +/- 0.06 for AGN hosts). According to the results of UCL-PDR
models, the X-rays can contribute to the enhancement of the CO line ratio, but
only for strong X-ray fluxes and for high gas density (nH > 10$^4$ cm-3). We
find a mild tightening of the Kennicutt-Schmidt relation when we use the
molecular gas mass surface density traced by CO(3-2) (Pearson correlation
coefficient R=0.83), instead of the molecular gas mass surface density traced
by CO(1-0) (R=0.78), but the increase in correlation is not statistically
significant (p-value=0.06). This suggests that the CO(3-2) line can be reliably
used to study the relation between SFR and molecular gas for normal SFGs at
high redshift, and to compare it with studies of low-redshift galaxies, as is
common practice.

http://arxiv.org/icons/sfx.gif

Comments are closed.