Ultraviolet through far-infrared spatially resolved analysis of the recent star formation in M81 (NGC 3031)
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2006
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Abstract
The recent star formation (SF) in the early-type spiral galaxy M81 is characterized using imaging observations from the far-ultraviolet to the far-infrared. We compare these data with models of the stellar, gas, and dust emission for subgalactic regions. Our results suggest the existence of a diffuse dust emission not directly linked to the recent star formation. We find a radial decrease of the dust temperature and dust mass density, and in the attenuation of the stellar light. The IR emission in M81 can be modeled with three components: (1) cold dust with a temperature <T_c> = 18 ± 2 K, concentrated near the H II regions but also presenting a diffuse distribution; (2) warm dust with <T_w> = 53 ± 7 K, directly linked with the H II regions; and (3) aromatic molecules, with diffuse morphology peaking around the H II regions. We derive several relationships to obtain total IR luminosities from IR monochromatic fluxes, and we compare five different star formation rate (SFR) estimators for H II regions in M81 and M51: the UV, Hα, and three estimators based on Spitzer data. We find that the Hα luminosity absorbed by dust correlates tightly with the 24 μm emission. The correlation with the total IR luminosity is not as good. Important variations from galaxy to galaxy are found when estimating the total SFR with the 24 μm or the total IR emission alone. The most reliable estimations of the total SFRs are obtained by combining the Hα emission (or the UV) and an IR luminosity (especially the 24 μm emission), which probe the unobscured and obscured SF, respectively. For the entire M81 galaxy, about 50% of the total SF is obscured by dust. The percentage of obscured SF ranges from 60% in the inner regions of the galaxy to 30% in the outer zones.
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© 2006. The American Astronomical Society. All rights reserved. Artículo firmado por 16 autores. We thank an anonymous referee for her/his useful comments. Support for this work was provided by NASA through contract 1255094 issued by JPL/Caltech. This work is part of SINGS, the Spitzer Infrared Nearby Galaxies Survey, one of the Spitzer Space Telescope Legacy Science Programs, and was supported by the JPL, Caltech, contract 1224667. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, Caltech under NASA contract 1407. GALEX is a NASA Small Explorer launched in 2003 April. We gratefully acknowledge NASA’s support for construction, operation, and scientific analysis of the GALEX mission. This research has made use of the NASA/ IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. P. G. P.-G. and A. G. de P. also wish to acknowledge support from the Spanish Programa Nacional de Astronomía y Astrofísica under grant AYA 2004-01676.