CO(2-1)/CO(1-0) line ratio on $\sim$100 parsec scale in the nearby barred galaxy NGC1300

Abstract

CO(2-1) emission is often used as a tracer of the giant molecular clouds (GMCs) as an alternative to CO(1-0) emission in recent years. Therefore, understanding the environmental dependence of the line ratio of CO(2-1)/CO(1-0), $R_{21}$, on GMC scale is important to accurately estimate the mass of the GMCs. We thus measured the $R_{21}$ in the strongly barred galaxy NGC1300, where star formation activity strongly depends on galactic structure, on $\sim 100$ pc scale. CO images were obtained from ALMA and Nobeyama 45-m telescope. The resultant typical $R_{21}$ in NGC1300 is $0.57\pm 0.06$. We find environmental variations in $R_{21}$; it is the highest in the bar-end region ($0.72\pm 0.08$), followed by arm ($0.60\pm 0.07$) and bar regions ($0.50\pm 0.06$). GMCs with H$\alpha$ emission show a systematically higher ratio ($0.67\pm 0.07$) than those without H$\alpha$ ($0.47\pm 0.05$). In the bar region, where massive star formation is suppressed, H$\alpha$ emission is not associated with most GMCs, resulting in the lowest $R_{21}$. These results raise a possibility that properties of GMCs derived from CO(2-1) observations with the assumption of a constant $R_{21}$ are different from those derived from CO(1-0) observations. Furthermore, we find the $R_{21}$ measured on kpc scale tends to be lower than that of the GMCs probably due to the presence of an extended diffuse molecular gas in NGC1300.

18 pages, 14 figures, accepted for publication in ApJ

References in corpus (26)

• xCOLD GASS: the complete IRAM-30m legacy survey of molecular gas for galaxy evolution studies
• Physical properties of molecular clouds for the entire Milky Way disk
• Bias-free Measurement of Giant Molecular Cloud Properties
• The lifecycle of molecular clouds in nearby star-forming disc galaxies
• Fast and inefficient star formation due to short-lived molecular clouds and rapid feedback
• Do cloud-cloud collisions trigger high-mass star formation? I. Small cloud collisions
• Giant Molecular Cloud Catalogues for PHANGS-ALMA: Methods and Initial Results
• The interplay between a galactic bar and a supermassive black hole: nuclear fueling in a sub-parsec resolution galaxy simulation
• Revealing the physical properties of molecular gas in Orion with a large scale survey in J=2-1 lines of 12CO, 13CO and C18O
• New Constraints on the ${}^{12}$CO(2-1)/(1-0) Line Ratio Across Nearby Disc Galaxies
• Molecular Gas in the Low Metallicity, Star Forming Dwarf IC 10
• A Portrait of Cold Gas in Galaxies at 60pc Resolution and a Simple Method to Test Hypotheses That Link Small-Scale ISM Structure to Galaxy-Scale Processes
• Giant Molecular Clouds in M31: I - Molecular Cloud Properties
• Giant Molecular Clouds in the Early-Type Galaxy NGC4526
• CO Multi-line Imaging of Nearby Galaxies (COMING). IX. ${}^{12}$CO($J$=2-1)/${}^{12}$CO($J$=1-0) line ratio on kiloparsec scales
• Environmental dependence of star formation induced by cloud collisions in a barred galaxy
• Interpreting the sub-linear Kennicutt-Schmidt relationship: The case for diffuse molecular gas
• The headlight cloud in NGC 628: An extreme giant molecular cloud in a typical galaxy disk
• Dense molecular gas properties on 100 pc scales across the disc of NGC 3627
• CO Multi-line Imaging of Nearby Galaxies (COMING): I. Physical properties of molecular gas in the barred spiral galaxy NGC 2903
• A large amount of diffuse molecular gases in the bar of the strongly barred galaxy NGC1300: Cause of the low star formation efficiency
• Spatially extended and high-velocity dispersion molecular component in spiral galaxies: single-dish vs. interferometric observations
• Stacking Analysis of 12CO and 13CO Spectra of NGC3627: Existence of non-optically thick 12CO emission?
• Properties of giant molecular clouds in the strongly barred galaxy NGC1300
• Connection among environment, cloud-cloud collision speed, and star formation activity in the strongly barred galaxy NGC1300
• A 3 mm Spectral Line Survey toward the Barred Spiral Galaxy NGC 3627