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Investigating the Drivers of CO-to-H2 Conversion Factor Variations in Nearby Galaxy Centers

Published online by Cambridge University Press:  09 June 2023

Yu-Hsuan Teng Open the ORCID record for Yu-Hsuan Teng [Opens in a new window]  and
Karin Sandstrom
Yu-Hsuan Teng*
Affiliation:
University of California San Diego, 9500 Gilman Dr, La Jolla, CA 92093, USA
Karin Sandstrom
Affiliation:
University of California San Diego, 9500 Gilman Dr, La Jolla, CA 92093, USA
*
email: yuteng@ucsd.edu
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Abstract

The CO-to-H2 conversion factor (αCO) is crucial for accurate estimation of the amount and properties of molecular gas. However, αCO is known to vary with environmental conditions, and previous kpc-scale studies have revealed lower αCO in the centers of some barred galaxies, including NGC 3351, 3627, and 4321. We present ALMA Band 3, 6, and 7 observations toward the inner ∼2 kpc of these galaxies tracing 12CO, 13CO, and C18O lines at ∼100 pc resolution. We show that dynamical effects resulting from turbulence/shear can lead to substantially lower αCO in the bar-driven inflows of NGC 3351 due to lower optical depth. A clear, positive correlation between αCO and 12CO optical depth is seen in all three galaxy centers. We also find that the CO/13CO(2–1) ratio mainly traces the 12CO optical depth, and thus it may be a useful observable in predicting αCO variation in galaxy centers.

Keywords

Barred spiral galaxies (136)CO line emission (262)Galaxy nuclei (609)Molecular gas (1073)Star forming regions (1565)
Type
Contributed Paper
Information
Proceedings of the International Astronomical Union , Volume 17 , Symposium S373: Resolving the Rise and Fall of Star Formation in Galaxies , August 2021 , pp. 157 - 160
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Copyright
© The Author(s), 2023. Published by Cambridge University Press on behalf of International Astronomical Union

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