Evolution and Extend of Disk Opacity

Details Evolution and Extend of Disk Opacity Evolution and Extend of Disk Opacity

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.9311h&link_type=abstract

American Astronomical Society, AAS Meeting #211, #93.11; Bulletin of the American Astronomical Society, Vol. 39, p.891

Astronomy and Astrophysics

Astronomy

1

Scientific paper

The opacity of a spiral disk due to dust absorption influences every measurement we make of it in the UV and optical. Two separate techniques directly measure the total absorption by dust in the disk: calibrated distant galaxy counts and overlapping galaxy pairs. The main results from both so far are a semi-transparent disk with more opaque arms and a relation between surface brightness and disk opacity.
In the Spitzer era, SED models of spiral disks add a new perspective on the role of dust in spiral disks. Combined with the overall opacity from galaxy counts, we can derive a typical optical depth and size of the dusty ISM clouds: 0.4 and 60 pc. respectively. Current work on galaxy counts focuses on the HST/ACS mosaics of M51, M101 and M81.
Occulting galaxies offer the possibility of probing the history of disk opacity from higher redhift overlapping galaxy pairs. Evolution in disk opacity could influence distance measurements (e.g., SN1a lightcurves, Tully-Fisher relation). Star-formation was an order of magnitude more at z 1 and hence we can expect typical disk opacity to change dramatically over the redshift range since.
Here we present first results from spectroscopically selected occulting pairs in the SDSS and the HST/ACS observations of the Extended Growth Strip. The SDSS redshift range is limited but does offer a first insight into recent disk opacity evolution as well as a reference for higher redshift measurements.
The two techniques achieve complementary goals: the calibrated counts limit the radial extent of dusty ISM and the occulting galaxy pairs the evolution of disk opacity since z 1.

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