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Title: Molecular Gas Properties and CO-to-H 2 Conversion Factors in the Central Kiloparsec of NGC 3351
Abstract The CO-to-H 2 conversion factor ( α CO ) is critical to studying molecular gas and star formation in galaxies. The value of α CO has been found to vary within and between galaxies, but the specific environmental conditions that cause these variations are not fully understood. Previous observations on ~kiloparsec scales revealed low values of α CO in the centers of some barred spiral galaxies, including NGC 3351. We present new Atacama Large Millimeter/submillimeter Array Band 3, 6, and 7 observations of 12 CO, 13 CO, and C 18 O lines on 100 pc scales in the inner ∼2 kpc of NGC 3351. Using multiline radiative transfer modeling and a Bayesian likelihood analysis, we infer the H 2 density, kinetic temperature, CO column density per line width, and CO isotopologue abundances on a pixel-by-pixel basis. Our modeling implies the existence of a dominant gas component with a density of 2–3 × 10 3 cm −3 in the central ∼1 kpc and a high temperature of 30–60 K near the nucleus and near the contact points that connect to the bar-driven inflows. Assuming a CO/H 2 abundance of 3 × 10 −4 , our analysis yields α CO ∼ 0.5–2.0 M ⊙ (K km s −1 pc 2 ) −1 with a decreasing trend with galactocentric radius in the central ∼1 kpc. The inflows show a substantially lower α CO ≲ 0.1 M ⊙ (K km s −1 pc 2 ) −1 , likely due to lower optical depths caused by turbulence or shear in the inflows. Over the whole region, this gives an intensity-weighted α CO of ∼1.5 M ⊙ (K km s −1 pc 2 ) −1 , which is similar to previous dust-modeling-based results at kiloparsec scales. This suggests that low α CO on kiloparsec scales in the centers of some barred galaxies may be due to the contribution of low-optical-depth CO emission in bar-driven inflows.  more » « less
Award ID(s):
2108081
NSF-PAR ID:
10338721
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;
Date Published:
Journal Name:
The Astrophysical Journal
Volume:
925
Issue:
1
ISSN:
0004-637X
Page Range / eLocation ID:
72
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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