Measuring star formation with resolved observations: the test case of M 33
Journal article, 2015
Context. Measuring star formation on a local scale is important to constrain star formation laws. It is not clear yet, however, whether and how the measure of star formation is affected by the spatial scale at which a galaxy is observed. Aims. We wish to understand the impact of the resolution on the determination of the spatially resolved star formation rate (SFR) and other directly associated physical parameters such as the attenuation. Methods. We carried out a multi-scale, pixel-by-pixel study of the nearby galaxy M33. Assembling FUV, H alpha, 8 mu m, 24 mu m, 70 mu m, and 100 mu m maps, we have systematically compared the emission in individual bands with various SFR estimators from a resolution of 33 pc to 2084 pc. Results. There are strong, scale-dependent, discrepancies of up to a factor 3 between monochromatic SFR estimators and H alpha + 24 mu m. The scaling factors between individual IR bands and the SFR show a strong dependence on the spatial scale and on the intensity of star formation. Finally, strong variations of the differential reddening between the nebular emission and the stellar continuum are seen, depending on the specific SFR (sSFR) and on the resolution. At the finest spatial scales, there is little differential reddening at high sSFR. The differential reddening increases with decreasing sSFR. At the coarsest spatial scales the differential reddening is compatible with the canonical value found for starburst galaxies. Conclusions. Our results confirm that monochromatic estimators of the SFR are unreliable at scales smaller than 1 kpc. Furthermore, the extension of local calibrations to high-redshift galaxies presents non-trivial challenges because the properties of these systems may be poorly known.
galaxies: ISM
galaxies: star formation
galaxies: individual: M 33
Author
M. Boquien
Laboratoire d'Astrophysique de Marseille
University of Cambridge
D. Calzetti
University of Massachusetts
Susanne Aalto
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
A. Boselli
Laboratoire d'Astrophysique de Marseille
J. Braine
Laboratoire d'Astrophysique de Bordeaux
V. Buat
Laboratoire d'Astrophysique de Marseille
F. Combes
Centre national de la recherche scientifique (CNRS)
F. P. Israel
Leiden University
C. Kramer
Institut de Radioastronomie Millimétrique (IRAM)
S. Lord
California Institute of Technology (Caltech)
M. Relano
Universidad de Granada
E. Rosolowsky
University of Alberta
G. Stacey
Cornell University
F. Tabatabaei
Max Planck Society
F. F. S. van der Tak
Netherlands Institute for Space Research (SRON)
University of Groningen
P. van der Werf
Leiden University
S. Verley
Universidad de Granada
M. Xilouris
National Observatory of Athens
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 578 A8Subject Categories
Fusion, Plasma and Space Physics
DOI
10.1051/0004-6361/201423518