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Session 67 - ISM in Galaxies.
Display session, Wednesday, January 15
We present a method to determine dust masses of disk galaxies that is an alternative to using far-infrared fluxes to determine dust masses. An accurate assessment of the dust mass of external galaxies can be used to measure the importance of extinction in disk galaxies and to compare the gas to dust ratio in these galaxies to our own, which would aid in our understanding of the ISM in external galaxies. This method is more accurate than the commonly used method based on far-IR fluxes because it is independent of dust temperature, does not suffer from inadequate spatial resolution, and is free of the uncertainty associated with the wavelength dependence of the dust emissivity. The method relies on a global relationship between color excesses and the optical depth needed to produce specific color excesses in realistic dust-star geometries. These optical depths are then integrated over the face of the disk to yield a dust mass for the system. Thus a dust mass can be determined from a high resolution color excess map of a galaxy. In order to calibrate this method effectively, we have used a Monte Carlo radiative transfer model of disk galaxies. The model is a complete, three dimensional representation of a disk galaxy that takes into account both absorption and scattering of the stellar radiation by dust. V-K color profiles from the model with either a homogeneous or two-phase clumpy dust distribution were used to create relationships between color excess and optical depth for each dust distribution. We find that for a specific V-K color excess, the optical depth in the clumpy dust distribution is approximately twice that needed for the homogeneous dust distribution. This method was applied to images of actual disk galaxies. We will present the results of the dust masses as well as gas to dust ratios of these galaxies. This research has been supported by NASA under the LTSA grants NAGW-3168 and NAG 5-3367 to the University of Toledo.
Program listing for Wednesday