We measure the CO-to-H2conversion factor (
We present a measurement of the intrinsic space density of intermediate-redshift (
- NSF-PAR ID:
- 10377481
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astronomical Journal
- Volume:
- 164
- Issue:
- 5
- ISSN:
- 0004-6256
- Format(s):
- Medium: X Size: Article No. 222
- Size(s):
- ["Article No. 222"]
- Sponsoring Org:
- National Science Foundation
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Abstract α CO) in 37 galaxies at 2 kpc resolution, using the dust surface density inferred from far-infrared emission as a tracer of the gas surface density and assuming a constant dust-to-metal ratio. In total, we have ∼790 and ∼610 independent measurements ofα COfor CO (2–1) and (1–0), respectively. The mean values forα CO (2–1)andα CO (1–0)are and , respectively. The CO-intensity-weighted mean is 5.69 forα CO (2–1)and 3.33 forα CO (1–0). We examine howα COscales with several physical quantities, e.g., the star formation rate (SFR), stellar mass, and dust-mass-weighted average interstellar radiation field strength ( ). Among them, , ΣSFR, and the integrated CO intensity (W CO) have the strongest anticorrelation with spatially resolvedα CO. We provide linear regression results toα COfor all quantities tested. At galaxy-integrated scales, we observe significant correlations betweenα COandW CO, metallicity, , and ΣSFR. We also find thatα COin each galaxy decreases with the stellar mass surface density (Σ⋆) in high-surface-density regions (Σ⋆≥ 100M ⊙pc−2), following the power-law relations and . The power-law index is insensitive to the assumed dust-to-metal ratio. We interpret the decrease inα COwith increasing Σ⋆as a result of higher velocity dispersion compared to isolated, self-gravitating clouds due to the additional gravitational force from stellar sources, which leads to the reduction inα CO. The decrease inα COat high Σ⋆is important for accurately assessing molecular gas content and star formation efficiency in the centers of galaxies, which bridge “Milky Way–like” to “starburst-like” conversion factors. -
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