Probing the cold and warm molecular gas in the Whirlpool Galaxy: Herschel SPIRE-FTS Observations of the central region of M51 (NGC 5194)
arXiv:1707.01973 · doi:10.1093/mnras/stx1554
Abstract
We present Herschel SPIRE-FTS intermediate-sampled mapping observations of the central ~8 kpc (~150") of M51, with a spatial resolution of 40". We detect 4 12CO transitions (J=4-3 to J=7-6) and the CI 3P2-3P1 and 3P1-3P0 transitions. We supplement these observations with ground based observations of 12CO J=1-0 to J=3-2 and perform a two-component non-LTE analysis. We find that the molecular gas in the nucleus and centre regions has a cool component (T_kin~10-20 K) with a moderate but poorly constrained density (n(H2)~10^3-10^6 cm^-3), as well as significant molecular gas in a warmer (T_kin~300-3000 K), lower density (n(H2)~10^1.6-10^2.5 cm^-3) component. We compare our CO line ratios and calculated densities along with ratios of CO to total infrared luminosity to a grid of photon dominated region (PDR) models and find that the cold molecular gas likely resides in PDRs with a field strength of G_o~10^2. The warm component likely requires an additional source of mechanical heating, from supernovae and stellar winds or possibly shocks produced in the strong spiral density wave. When compared to similar two-component models of other star-forming galaxies published as part of the Very Nearby Galaxies Survey (Arp 220, M82 and NGC 4038/39), M51 has the lowest density for the warm component, while having a warm gas mass fraction that is comparable to those of Arp 220 and M82, and significantly higher than that of NGC 4038/39.
21 pages; accepted to MNRAS
References in corpus (13)
- The ACS Nearby Galaxy Survey Treasury
- Dynamically Driven Evolution of the Interstellar Medium in M51
- A complete 12CO 2-1 map of M51 with HERA: I. Radial averages of CO, HI, and radio continuum
- High-Resolution Radio Continuum Measurements of the Nuclear Disks of Arp 220
- A Survey of the Molecular ISM Properties of Nearby Galaxies using the Herschel FTS
- Calibration of the Herschel SPIRE Fourier Transform Spectrometer
- Diagnostics of the molecular component of PDRs with mechanical heating. II: line intensities and ratios
- Spatially resolved physical conditions of molecular gas and potential star formation tracers in M83, revealed by the Herschel SPIRE FTS
- On the dichotomy of Seyfert 2 galaxies: intrinsic differences and evolution
- Long-term observations of Uranus and Neptune at 90 GHz with the IRAM 30m telescope - (1985 -- 2005)
- Astrochemical Correlations in Molecular Clouds
- Imaging galactic diffuse gas: Bright, turbulent CO surrounding the line of sight to NRAO150
- Warm Molecular Gas in M51: Mapping the Excitation Temperature and Mass of H_2 with the Spitzer Infrared Spectrograph