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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 421737.0, MPI für Astronomie / Publikationen_mpia
Warm molecular gas in M51: mapping the excitation temperature and mass of H2 with the Spitzer Infrared Spectrograph
Authors:Brunner, Gregory; Sheth, Kartik; Armus, Lee; Wolfire, Mark; Vogel, Stuart; Schinnerer, Eva; Helou, George; Dufour, Reginald; Smith, John-David; Dale, Daniel A.
Date of Publication (YYYY-MM-DD):2008
Title of Journal:The Astrophysical Journal
Journal Abbrev.:ApJ
Start Page:316
End Page:329
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:We have mapped the warm molecular gas traced by the H2 S(0)-H2 S(5) pure rotational mid-infrared emission lines over a radial strip across the nucleus and disk of M51 (NGC 5194) using the Infrared Spectrograph (IRS) on the Spitzer Space Telescope. The six H2 lines have markedly different emission distributions. We obtained the H2 temperature and surface density distributions by assuming a two-temperature model: a warm (T=100-300 K) phase traced by the low J [S(0)-S(2)] lines and a hot phase (T=400-1000 K) traced by the high J [S(2)-S(5)] lines. The lowest molecular gas temperatures are found within the spiral arms (T~155 K), while the highest temperatures are found in the inter-arm regions (T>700 K). The warm gas surface density reaches a maximum of 11 Msolar pc-2 in the northwest spiral arm, whereas the hot gas surface density peaks at 0.24 Msolar pc-2 at the nucleus. The spatial offset between the peaks in the different phases suggests that the warm phase is more efficiently heated by star formation activity and the hot phase is more efficiently heated by nuclear activity. The warm H2 is found in the dust lanes of M51 and is generally spatially coincident with the cold molecular gas traced by CO emission, consistent with excitation of the warm phase in dense photodissociation regions. The hot H2 is most prominent in the nuclear region. Here, the hot H2 coincides with [O IV] (25.89 mum) and X-ray emission indicating that shocks and/or X-rays are responsible for exciting this phase.
Free Keywords:Galaxies: Individual: Messier Number: M51; Galaxies: ISM; ISM: Molecules
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
Identifiers:URL:http://adsabs.harvard.edu/abs/2008ApJ...675..316B [ID No:1]
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