Gas and dust cooling along the major axis of M33 (HerM33es) ISO/LWS C II observations
Artikel i vetenskaplig tidskrift, 2013

Aims. We aim to better understand the heating of gas by observing the prominent gas cooling line [C II] at 158 mu m in the low-metallicity environment of the Local Group spiral galaxy M33 on scales of 280 pc. In particular, we describe the variation of the photoelectric heating efficiency with the galactic environment. Methods. In this study, we present [C II] observations along the major axis of M33 using the Infrared Space Observatory in combination with Herschel continuum maps, IRAM 30m CO 2-1, and VLA H I data to study the variation in velocity integrated intensities. The ratio of [C II] emission over the far-infrared continuum is used as a proxy for the heating efficiency, and models of photon-dominated regions are used to study the local physical densities, far-ultraviolet radiation fields, and average column densities of the molecular clouds. Results. The heating efficiency stays constant at 0.8% in the inner 4.5 kpc radius of the galaxy, where it increases to reach values of similar to 3% in the outskirts at about a 6 kpc radial distance. The rise of efficiency is explained in the framework of PDR models by lowered volume densities and FUV fields for optical extinctions of only a few magnitudes at constant metallicity. For the significant fraction of Hi emission stemming from PDRs and for typical pressures found in the Galactic cold neutral medium (CNM) traced by Hi emission, the CNM contributes similar to 15% to the observed [C II] emission in the inner 2 kpc radius of M33. The CNM contribution remains largely undetermined in the south, while positions between radial distances of 2 and 7.3 kpc in the north of M33 show a contribution of similar to 40% +/- 20%.

ISM: structure evolution

galaxies: ISM

photon-dominated region (PDR)


C. Kramer

Instituto de Radioastronomia Milimetrica

J. Abreu-Vicente

Instituto de Radioastronomia Milimetrica

S. G. Burillo

Observatorio Astronomico Nacional

M. Relano

Universidad de Granada

Susanne Aalto

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

M. Boquien

Laboratoire d'Astrophysique de Marseille

J. Braine

Laboratoire d'Astrophysique de Bordeaux

C. Buchbender

Instituto de Radioastronomia Milimetrica

P. Gratier

Laboratoire d'Astrophysique de Bordeaux

Institut de RadioAstronomie Millimetrique (IRAM)

F. P. Israel

Universiteit Leiden

T. Nikola

Cornell University

M. Rollig

Universität zu Köln

S. Verley

Universidad de Granada

P. van der Werf

Universiteit Leiden

E. M. Xilouris

National Observatory of Athens

Astronomy and Astrophysics

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

Vol. 553 A114


Astronomi, astrofysik och kosmologi