The EDGE-CALIFA survey: The role of spiral arms and bars in driving central molecular gas concentrations

Kavli Affiliate: Luis C. Ho

| First 5 Authors: Si-Yue Yu, Veselina Kalinova, Dario Colombo, Alberto D. Bolatto, Tony Wong

| Summary:

Shocks and torques produced by non-axisymmetric structures such as spiral
arms and bars may transport gas to galaxy central regions. We test this
hypothesis by studying the dependence of concentration of CO luminosity
($C_{CO}$), molecular gas ($C_{mol}$), and star formation rate ($C_{SFR}$) in
central $sim$ 2 kpc on the $strength$ of non-axisymmetric disk structure using
a sample of 57 disk galaxies selected from the EDGE-CALIFA survey. $C_{mol}$ is
calculated using a CO-to-H$_2$ conversion factor that decreases with higher
metallicity and higher stellar surface density. We find that $C_{mol}$ is
systematically 0.22 dex lower than $C_{CO}$. We confirm that high $C_{mol}$ and
strong non-axisymmetric disk structure are more common in barred galaxies than
in unbarred galaxies. However, we find that spiral arms also increase
$C_{mol}$. We show that there is a good correlation between $C_{mol}$ and the
$strength$ of non-axisymmetric structure (which can be due to a bar, spiral
arms, or both). This suggests that the stronger the bars and spirals, the more
efficient the galaxy is at transporting cold gas to its center. Despite the
small subsample size, $C_{mol}$ of the four Seyferts are not significantly
reduced compared to inactive galaxies of similar disk structure, implying that
the AGN feedback in Seyferts may not notably affect the molecular gas
distribution in the central $sim$2kpc. We find that $C_{SFR}$ tightly
correlates with $C_{mol}$ in both unbarred and barred galaxies. Likewise,
elevated $C_{SFR}$ is found in galaxies with strong disk structure. Our results
suggest that the disk structure, either spirals or bars, can transport gas to
the central regions, with higher inflow rates corresponding to stronger
structure, and consequently boost central star formation. Both spirals and bars
play, therefore, an essential role in the secular evolution of disk galaxies.

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