CO Excitation and its Connection to Star Formation at 200 pc in NGC 1365

Abstract

We report high resolution 2" ~ 200 pc mappings of the central region of the nearby barred spiral galaxy NGC 1365 in the CO(1--0) and CO(2--1) emission lines. The 2--1/1--0 ratio of integrated intensities shows a large scatter (0.15) with a median value of 0.67. We also calculate the ratio of velocity dispersions and peak temperatures and find that in most cases the velocity dispersion ratio is close to unity and thus the peak temperature ratio is comparable to the integrated intensity ratio. This result indicates that both CO(1--0) and CO(2--1) lines trace similar components of molecular gas, with their integrated intensity (or peak temperature) ratios reflecting the gas density and/or temperature. Similar to recent kpc scale studies, these ratios show a positive correlation with a star formation rate indicator (here we use an extinction-corrected H-alpha map), suggesting that molecular gas associated with recent star formation is denser and/or warmer. We also find that some CO spectra show two peaks owing to complicated kinematics, and such two components likely trace molecular gas at different conditions. This result demonstrates the importance of spectral fitting to measure integrated intensities and their ratios more accurately.

13 pages, 7 figures, 2 tables. accepted to ApJ

References in corpus (21)

• xCOLD GASS: the complete IRAM-30m legacy survey of molecular gas for galaxy evolution studies
• Bias-free Measurement of Giant Molecular Cloud Properties
• The PHANGS-MUSE survey -- Probing the chemo-dynamical evolution of disc galaxies
• Stellar structures, molecular gas, and star formation across the PHANGS sample of nearby galaxies
• 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
• Low-J CO Line Ratios From Single Dish CO Mapping Surveys and PHANGS-ALMA
• AUTO-MULTITHRESH: A General Purpose Automasking Algorithm
• The environmental dependence of the X_CO conversion factor
• CO Multi-line Imaging of Nearby Galaxies (COMING). IX. ${}^{12}$CO($J$=2-1)/${}^{12}$CO($J$=1-0) line ratio on kiloparsec scales
• Using CO line ratios to trace the physical properties of molecular clouds
• Photodissociation Region Diagnostics Across Galactic Environments
• Detection of CO Hotspots Associated with Young Clusters in the Southern Starburst Galaxy NGC 1365
• The headlight cloud in NGC 628: An extreme giant molecular cloud in a typical galaxy disk
• 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
• Near-infrared observations of star formation and gas flows in the NUGA galaxy NGC 1365
• The Nuclear Region of NGC1365: Star Formation, Negative Feedback, and Outflow Structure
• Total Power Map to Visibilities (TP2VIS): Joint Deconvolution of ALMA 12m, 7m, and Total Power Array Data
• Molecular gas and star formation within 12 strong galactic bars observed with IRAM-30m
• CO(2-1)/CO(1-0) line ratio on $\sim$100 parsec scale in the nearby barred galaxy NGC1300

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• JWST Observations of Starbursts: Relations between PAH features and CO clouds in the starburst galaxy M 82
• The Arizona Molecular ISM Survey with the SMT: Variations in the CO(2-1)/CO(1-0) Line Ratio Across the Galaxy Population
• ALMA FACTS. II. Large Scale Variations in the 12CO(J=2-1) to 12CO(J=1-0) Line Ratio in Nearby Galaxies
• Quantitative analysis of the molecular gas morphology in nearby disk galaxies
• Molecular Clouds at the Edge of the Galaxy I. Variation of CO J=2-1/1-0 Line Ratio
• Surveying the Whirlpool at Arcseconds with NOEMA (SWAN): III. ${}^{13}$CO/C${}^{18}$O ratio variations across the M51 galaxy