Warm dust and aromatic bands as quantitative probes of star-formation activity
Abstract
We combine samples of spiral galaxies and starburst systems observed with ISOCAM on board ISO to investigate the reliability of mid-infrared dust emission as a quantitative tracer of star formation activity. The total sample covers very diverse galactic environments and probes a much wider dynamic range in star formation rate density than previous similar studies. We find that both the monochromatic 15 μm continuum and the 5-8.5 µm emission constitute excellent indicators of the star formation rate as quantified by the Lyman continuum luminosity L_(Lye), within specified validity limits which are different for the two tracers. Normalized to projected surface area, the 15 μm continuum luminosity Σ_(15 µm,ct) is directly proportional to Σ_(Lyc) over several orders of magnitude. Two regimes are distinguished from the relative offsets in the observed relationship: the proportionality factor increases by a factor of ≈5 between quiescent disks in spiral galaxies, and moderate to extreme star-forming environments in circumnuclear regions of spirals and in starburst systems. The transition occurs near Σ_(Lyc) ~ 10^2 L⊙ pc^(-2) and is interpreted as due to very small dust grains starting to dominate the emission at 15 μm over aromatic species above this threshold. The 5-8.5 µm luminosity per unit projected area is also directly proportional to the Lyman continuum luminosity, with a single conversion factor from the most quiescent objects included in the sample up to Σ_(Lyc) ~ 10^4 L⊙ pc^(-2), where the relationship then flattens. The turnover is attributed to depletion of aromatic band carriers in the harsher conditions prevailing in extreme starburst environments. The observed relationships provide empirical calibrations useful for estimating star formation rates from mid-infrared observations, much less affected by extinction than optical and near-infrared tracers in deeply embedded H II regions and obscured starbursts, as well as for theoretical predictions from evolutionary synthesis models.
Additional Information
© 2004 ESO. Article published by EDP Sciences. Received 2 January 2004; Accepted 23 February 2004; Published online 03 May 2004. Based on observations with ISO, an ESA project with instruments funded by ESA member states (especially the PI countries: France, Germany, The Netherlands, and the UK), and with participation of ISAS and NASA. Our referee, Dr. D.A. Dale, is gratefully thanked for his swiftness and help in improving the dicussion flow. It is a pleasure to thank all the persons who made some of the data used here available to us or publicly (and who are named in Table 3). V.C. would like to acknowledge the support of JPL contract 960803. This research 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. The ISOCAM data presented in this paper were analyzed using and adapting the CIA package, a joint development by the ESA Astrophysics Division and the ISOCAM Consortium (led by the PI C. Cesarsky, Direction des Sciences de la Matière, CEA, France).Attached Files
Published - aa0002-04.pdf
Accepted Version - 0402388.pdf
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Additional details
- Eprint ID
- 84798
- Resolver ID
- CaltechAUTHORS:20180212-161317515
- 960803
- JPL
- NASA/JPL/Caltech
- Created
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2018-02-13Created from EPrint's datestamp field
- Updated
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2021-11-15Created from EPrint's last_modified field