CO Multi-line Imaging of Nearby Galaxies (COMING): I. Physical properties of molecular gas in the barred spiral galaxy NGC 2903

Abstract

We present simultaneous mappings of J=1-0 emission of 12CO, 13CO, and C18O molecules toward the whole disk (8' x 5' or 20.8 kpc x 13.0 kpc) of the nearby barred spiral galaxy NGC 2903 with the Nobeyama Radio Observatory 45-m telescope at an effective angular resolution of 20" (or 870 pc). We detected 12CO(J=1-0) emission over the disk of NGC 2903. In addition, significant 13CO(J=1-0) emission was found at the center and bar-ends, whereas we could not detect any significant C18O(J=1-0) emission. In order to improve the signal-to-noise ratio of CO emission and to obtain accurate line ratios of 12CO(J=2-1)/12CO(J=1-0) ($R_{2-1/1-0}$) and 13CO(J=1-0)/12CO(J=1-0) ($R_{13/12}$), we performed the stacking analysis for our 12CO(J=1-0), 13CO(J=1-0), and archival 12CO(J=2-1) spectra with velocity-axis alignment in nine representative regions of NGC 2903. We successfully obtained the stacked spectra of the three CO lines, and could measure averaged $R_{2-1/1-0}$ and $R_{13/12}$ with high significance for all the regions. We found that both $R_{2-1/1-0}$ and $R_{13/12}$ differ according to the regions, which reflects the difference in the physical properties of molecular gas; i.e., density ($n_{{\mathrm{H}}_2}$) and kinetic temperature ($T_K$). We determined $n_{{\mathrm{H}}_2}$ and $T_K$ using $R_{2-1/1-0}$ and $R_{13/12}$ based on the large velocity gradient approximation. The derived $n_{{\mathrm{H}}_2}$ ranges from ~ 1000 cm${}^{-3}$ (in the bar, bar-ends, and spiral arms) to 3700 cm${}^{-3}$ (at the center) and the derived $T_K$ ranges from 10 K (in the bar and spiral arms) to 30 K (at the center). We examined the dependence of star formation efficiencies (SFEs) on $n_{{\mathrm{H}}_2}$ and $T_K$, and found the positive correlation between SFE and $n_{{\mathrm{H}}_2}$ with the correlation coefficient for the least-square power-law fit $R^2$ of 0.50. This suggests that molecular gas density governs the spatial variations in SFEs.

26 pages, 11 figures, 3 tables, accepted for publication in PASJ

References in corpus (8)

• High-Resolution Rotation Curves and Galaxy Mass Models from THINGS
• An H-alpha Imaging Survey of Galaxies in the Local 11 Mpc Volume
• The Abundance Properties of Nearby Late-Type Galaxies.I. The Data
• HCN Observations of Dense Star-Forming Gas in High Redshift Galaxies
• Sub-millimeter Observations of Giant Molecular Clouds in the Large Magellanic Cloud: Temperature and Density as Determined from J=3-2 and J=1-0 transitions of CO
• 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?
• Cumulative Oxygen Abundances of Spiral Galaxies

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