AAS 205th Meeting, 9-13 January 2005
Session 122 HI and Galactic Disks
Oral, Wednesday, January 12, 2005, 10:00-11:30am, Pacific Salon 1

Previous   |   Session 122   |   Next

[122.05] The opacity of spiral disks from counts of distant galaxies.

B. W. Holwerda (STSCI/Kapteyn Institute), R. A. Gonzalez (Centro de Radiastronom\'{i}a y Astrof\'{i}sica, UNAM), R. J. Allen (STScI), P. C. van der Kruit (Kapteyn Institute)

The numbers of distant galaxies seen in an HST image of a spiral galaxy is an indication of the average extinction by dust in the disk. This number of distant galaxies has to be calibrated for crowding effects and for this the ``Synthetic Field Method'' (SFM, Gonzalez et al. 1998) was developed. Synthetic fields are the science field with a dimmed Hubble Deep Field added. From the relation between the dimming and the number of synthetic galaxies, the average extinction in the science field can be derived.

32 HST/WFPC2 fields were analysed and from the numbers of distant galaxies an average radial extinction profile for spiral disks was constructed, for the whole sample, arm and disk regions and different Hubble types. When the average radial extinction profile is compared to the HI surface density profile, an estimate of the average gas-to-dust ratio as a function of radius can be obtained. The effects of the phase of the hydrogen and metallicity gradient in disks are discussed. The average radial extinction profile is compared to the light distribution of spiral disks. The relation between typical radii of light and dust and the relation between surface brightness and extinction is also explored.

Combining the detailed images of dust emission from the Spitzer space telescope with the extinction measurements from counts in HST images could offer insight into the relative prominence of cold dust and possibly the dust geometry in the disk. Future work on dust extinction using the wealth of new imaging in the HST archive is briefly discussed.

This research was supported by funding from STSCI, the Director's Discretionary Research Fund and the Kapteyn Institute.

The author(s) of this abstract have provided an email address for comments about the abstract: holwerda@stsci.edu

Previous   |   Session 122   |   Next

Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.