• DOI:10.1051/0004-6361/201423847
• Corpus ID: 53537685

Spatially resolved physical conditions of molecular gas and potential star formation tracers in M 83, revealed by the Herschel SPIRE FTS

@article{Wu2015SpatiallyRP,
  title={Spatially resolved physical conditions of molecular gas and potential star formation tracers in M 83, revealed by the Herschel SPIRE FTS},
  author={Ronin Wu and Suzanne C. Madden and Fr{\'e}d{\'e}ric Galliano and Christine D. Wilson and Julia Kamenetzky and Min-Young Lee and Maximilien R. P. Schirm and Sacha Hony and Vianney Lebouteiller and Luigi Spinoglio and Diane Cormier and Jason Glenn and Philip Richard Maloney and Miguel Pereira-Santaella and Aur'elie R'emy-Ruyer and Maarten Baes and A. Boselli and Fr{\'e}d{\'e}ric Bournaud and Ilse de Looze and Thomas M. Hughes and Pasquale Panuzzo and Naseem Rangwala},
  journal={Astronomy and Astrophysics},
  year={2015},
  volume={575}
}

• R. Wu, S. Madden, +19 authors N. Rangwala
• Published 5 December 2014
• Physics
• Astronomy and Astrophysics

We investigate the physical properties of the molecular and ionized gas, and their relationship to the star formation and dust properties in M 83, based on submillimeter imaging spectroscopy from within the central 3.5′ (~4 kpc in diameter) around the starburst nucleus. The observations use the Fourier Transform Spectrometer (FTS) of the Spectral and Photometric Imaging REceiver (SPIRE) onboard the Herschel Space Observatory. The newly observed spectral lines include [CI] 370 μm, [CI] 609 μm, [NII] 205 μm, and CO transitions from J = 4−3 to J = 13−12. Combined with previously observed J = 1−0 to J = 3−2 transitions, the CO spectral line energy distributions are translated to spatially resolved physical parameters, column density of CO, N(CO), and molecular gas thermal pressure, Pth, with a non-local thermal equilibrium (non-LTE) radiative transfer model, RADEX. Our results show that there is a relationship between the spatially resolved intensities of [NII] 205 μm and the surface density of the star formation rate (SFR), ΣSFR. This relation, when compared to integrated properties of ultra-luminous infrared galaxies (ULIRGs), exhibits a different slope, because the [NII] 205 μm distribution is more extended than the SFR. The spatially resolved [CI] 370 μm, on the other hand, shows a generally linear relationship with ΣSFR and can potentially be a good SFR tracer. Compared with the dust properties derived from broad-band images, we find a positive trend between the emissivity of CO in the J = 1−0 transition with the average intensity of interstellar radiation field (ISRF), ⟨ U ⟩. This trend implies a decrease in the CO-to-H2 conversion factor, XCO, when ⟨ U ⟩ increases. We estimate the gas-to-dust mass ratios to be 77 ± 33 within the central 2 kpc and 93 ± 19 within the central 4 kpc of M 83, which implies a Galactic dust-to-metal mass ratio within the observed region of M 83. The estimated gas-depletion time for the M 83 nucleus is 1.13 ± 0.6 Gyr, which is shorter than the values for nearby spiral galaxies found in the literature (~2.35 Gyr), most likely due to the young nuclear starbursts. A linear relationship between Pth and the radiation pressure generated by ⟨ U ⟩, Prad, is found to be Pth ≈ 30 Prad, which signals that the ISRF alone is insufficient to sustain the observed CO transitions. The spatial distribution of Pth reveals a pressure gradient, which coincides with the observed propagationof starburst activities and the alignment of (possibly background) radio sources. We discover that the off-centered (from the optical nucleus) peak of the molecular gas volume density coincides well with a minimum in the relative aromatic feature strength, indicating a possible destruction of their carriers. We conclude that the observed CO transitions are most likely associated with mechanical heating processes that are directly or indirectly related to very recent nuclear starbursts.