Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...303..673e&link_type=abstract
Astronomy and Astrophysics, v.303, p.673
Astronomy and Astrophysics
Astrophysics
21
Galaxies: Individual: M 104, Galaxies: Structure, Galaxies: Ism, Ism: Dust, Extinction, Scattering -
Scientific paper
We present high resolution ground based B, V, R_C_, I_C_ band images of the Sombrero Galaxy (M104), which enable us to build a spatial photometric model using the Multi-Gaussian Expansion technique. Assuming the dust is distributed in a series of concentric rings, we model the variation of the optical depth with radius in this galaxy. Discrepancies between this model and the observed absorption profiles perpendicular to the dust lane lead us to conclude that light scattering by dust grains has a crucial effect on the observed galactic properties. Using Monte Carlo simulations by Witt et al. (1992), we calculate an order of magnitude correction for the scattered light contribution. This is used to demonstrate that the observed attenuation integrated along the line of sight requires nearly twice the dust originally expected from models neglecting scattering effects. If the Sombrero had been viewed face-on, it would have appeared "dust free", although the face-on optical depth τ^0^_V_ reaches 0.8 mag and has a mean value of 0.3 for cylindrical radii between 100 and 200 arcseconds. We derive a total dust mass of about 3.2 d_18.5_10^7^ Msun_, which is probably a lower limit, although it is already 6 times higher than the dust mass predicted from the IRAS fluxes. We conclude that there must be a cold dust component (T_d_ < 20K) which is not detected by IRAS, but represents the major part (> 85%) of the total dust mass. We propose that the gas and dust rings observed in the Sombrero are due to the gravitational interaction of the interstellar medium with a now dissolved bar. This mechanism could also explain the possible presence of a central dark mass and the mild activity of the nucleus. This hypothesis may be tested by mapping the ionized gas in the central region.
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