NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-05-22 T03:43:43 PDT
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For refcode 2009A&A...493..453V:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
2009A&A...493..453V Star formation in M 33: multiwavelength signatures across the disk Verley, S.; Corbelli, E.; Giovanardi, C.; Hunt, L. K. Abstract. Aims. We use different tracers, such as H{alpha}, ultraviolet (UV), and infrared (IR) emissions at various wavelengths, to study the dust and star formation (SF) conditions throughout the disk of M 33. Methods: We derive the radial distribution of dust, of the old and young stellar population using Spitzer and GALEX data, complemented by ground-based optical data and available surveys of atomic and molecular gas. We separate the contribution of discrete sources to the IR brightness from the diffuse emission. Results: At 8 and 24 micron, discrete sources account for >~ 40% of the IR emission in the innermost 3 kpc, and for <~20% further out. We find that stochastic emission from very small grains in the diffuse interstellar medium accounts for only ~10% of the diffuse 24 micron emission, and that dusty circumstellar shells of unresolved, evolved AGB stars (carbon stars) are a viable alternative. The 8 micron profile suggests that PAH emission declines faster with radius than the dust continuum. In annular regions 0.24 kpc wide, we find a mean extinction value for the stellar continuum A_V_ ~ 0.25 mag with a weak dependence on radius, consistent with the shallow metallicity gradient observed. Dust opacity derived from the 160 micron emission decreases instead by a factor of 10 from the center to edge of the star forming disk. Conclusions: Using extinction corrected UV and H{alpha} maps we find the global SF rate in M 33 over the last 100 Myr to be 0.45+/- 0.10~M_o yr^-1^. Far-IR and total-IR luminosities can trace SF even though a high conversion factor is required to recover the effective rate. If carbon stars are powering the diffuse 24 micron emission in M 33, this can trace star formation 1 Gyr ago and provide a more complete view of the SF history of the galaxy. Today the SF rate declines radially with a scale length of ~2 kpc, longer than for the old stellar population, suggesting an inside-out growth of the disk. Key words: galaxies: individual: M 33, galaxies: ISM, galaxies: Local Group, galaxies: spiral
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