13CO(J=1-0) On-the-fly Mapping of the Giant HII Region NGC 604: Variation in Molecular Gas Density and Temperature due to Sequential Star Formation

Abstract

We present 13CO(J=1-0) line emission observations with the Nobeyama 45-m telescope toward the giant HII region NGC 604 in the spiral galaxy M 33. We detected 13CO(J=1-0) line emission in 3 major giant molecular clouds (GMCs) labeled as GMC-A, B, and C beginning at the north. We derived two line intensity ratios, 13CO(J=1-0)/12CO(J =1-0), R13/12, and 12CO(J=3-2)/12CO(J =1-0), R31, for each GMC at an angular resolution of 25" (100 pc). Averaged values of R13/12 and R31 are 0.06 and 0.31 within the whole GMC-A, 0.11 and 0.67 within the whole GMC-B, and 0.05 and 0.36 within the whole GMC-C, respectively. In addition, we obtained R13/12=0.09\pm0.02 and R31=0.76\pm0.06 at the 12CO(J=1-0) peak position of the GMC-B. Under the Large Velocity Gradient approximation, we determined gas density of 2.8 \times10^3 cm^-3 and kinetic temperature of 33+9-5 K at the 12CO(J=1-0) peak position of the GMC-B. Moreover, we determined 2.5 \times10^3 cm^-3 and 25\pm2 K as averaged values within the whole GMC-B. We concluded that dense molecular gas is formed everywhere in the GMC-B because derived gas density not only at the peak position of the GMC but also averaged over the whole GMC exceeds 10^3 cm^-3. On the other hand, kinetic temperature averaged over the whole GM-B, 25 K, is significantly lower than that at the peak position, 33 K. This is because HII regions are lopsided to the northern part of the GMC-B, thus OB stars can heat only the northern part, including the 12CO(J=1-0) peak position, of this GMC.

16 pages, 7 figures, PASJ in press

References in corpus (6)

• Keck HIRES Spectroscopy of Extragalactic HII Regions: C and O Abundances from Recombination Lines
• Breakdown of Kennicutt-Schmidt Law at GMC Scales in M33
• 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
• Dense Clumps in Giant Molecular Clouds in the Large Magellanic Cloud: Density and Temperature Derived from ${}^{13}$CO($J=3-2$) Observations
• NRO M33 All Disk Survey of Giant Molecular Clouds (NRO MAGiC): I. HI to H_2 Transition
• Aperture Synthesis Observations of CO, HCN, and 89GHz Continuum Emission toward NGC 604 in M 33: Sequential Star Formation Induced by Supergiant Hii region

Cited by in corpus (7)

• GMC Evolutions in the Nearby Spiral Galaxy M33
• CO Multi-line Imaging of Nearby Galaxies (COMING): I. Physical properties of molecular gas in the barred spiral galaxy NGC 2903
• CO Multi-line Imaging of Nearby Galaxies (COMING). III. Dynamical effect on molecular gas density and star formation in the barred spiral galaxy NGC 4303
• ALMA Observations of Giant Molecular Clouds in M33. II. Triggered High-mass Star Formation by Multiple Gas Colliding Events at the NGC 604 Complex
• SMA Observations of Extended $\mathrm{CO}(\mathrm{J}=2-1)$ Emission in Interacting Galaxy NGC 3627
• NRO M33 All-Disk Survey of Giant Molecular Clouds (NRO MAGiC): II. Dense Gas Formation within Giant Molecular Clouds in M33
• ALMA ${}^{13}\mathrm{CO}$(J=1-0) Observations of NGC 604 in M33: Physical Properties of Molecular Clouds