The Herschel M 33 extended survey (HerM33es): PACS spectroscopy of the star-forming region BCLMP 302
Artikel i vetenskaplig tidskrift, 2011

Context. The emission line of [CII] at 158 mu m is one of the strongest cooling lines of the interstellar medium (ISM) in galaxies. Aims. Distinguishing the relative contributions of the different ISM phases to [CII] emission is a major objective of the HerM33es program, a Herschel key project to study the ISM in the nearby spiral galaxy M 33. Methods. Using PACS, we have mapped the emission of [CII] 158 mu m, [OI] 63 mu m, and other FIR lines in a 2' x 2' region of the northern spiral arm of M 33, centered on the HII region BCLMP302. At the peak of Ha emission, we observed in addition a velocity-resolved [CII] spectrum using HIFI. We use scatterplots to compare these data with PACS 160 mu m continuum maps, and with maps of CO and HI data, at a common resolution of 12 '' or 50 pc. Maps of Ha and 24 mu m emission observed with Spitzer are used to estimate the SFR. We created maps of the [CII] and [OI] 63 mu m emission and detected [NII] 122 mu m and [NIII] 57 mu m at individual positions. Results. The [CII] line observed with HIFI is significantly broader than that of CO, and slightly blue-shifted. In addition, there is little spatial correlation between [CII] observed with PACS and CO over the mapped region. There is even less spatial correlation between [CII] and the atomic gas traced by HI. Detailed comparison of the observed intensities towards the HII region with models of photo-ionization and photon-dominated regions, confirms that a significant fraction, 20-30%, of the observed [CII] emission stems from the ionized gas and not from the molecular cloud. The gas heating efficiency, using the ratio of [CII] to the TIR as a proxy, varies between 0.07 and 1.5%, with the largest variations found outside the HII region.


nearby galaxies


long-wavelength spectrometer

far-infrared spectroscopy



photon-dominated regions

photodissociation regions

HII regions


h-ii regions

photon-dominated region (PDR)

m emission

star formation

M 33



B. Mookerjea

Tata Institute of Fundamental Research

C. Kramer

Instituto de Radioastronomia Milimetrica

C. Buchbender

Instituto de Radioastronomia Milimetrica

M. Boquien

University of Massachusetts

S. Verley

Universidad de Granada

M. Relano

Universidad de Granada

G. Quintana-Lacaci

Instituto de Radioastronomia Milimetrica

Susanne Aalto

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

J. Braine

Laboratoire d'Astrophysique de Bordeaux

D. Calzetti

University of Massachusetts

F. Combes

CNRS Centre National de la Recherche Scientifique

S. G. Burillo

P. Gratier

Max Planck-institutet

C. Henkel

Max Planck-institutet

F. P. Israel

Universiteit Leiden

S. Lord


T. Nikola

Cornell University

M. Rollig

University of Cambridge Institute of Astronomy

Universität zu Köln

G. Stacey

Cornell University

F. Tabatabaei

Max Planck-institutet

F. F. S. van der Tak

Netherlands Institute for Space Research (SRON)

P. van der Werf

University of Edinburgh

Universiteit Leiden

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 532 art. no. A152- A152


Astronomi, astrofysik och kosmologi