There goes the neighbourhood: The extinction and distance of the dominant members of the IC 342/Maffei group of galaxies.

摘要

Two techniques for determining the Galactic extinction of heavily obscured galaxies are applied to the three dominant members of the highly reddened IC 342/Maffei group of galaxies, revealing these objects to be among the brightest galaxies in the Northern sky.;The first technique is applied to the giant elliptical Maffei 1 and involves the application of a well defined correlation between the Mg2 index and effective V-I colour for elliptical galaxies. The Galactic extinction for Maffei 1 is thereby determined using a measurement of the Mg2 index from spectra of the core of the galaxy. In combination with modern photometry and a revised velocity dispersion measured from high-resolution spectra, an I-band Fundamental Plane distance to this galaxy is determined for the first time.;The second technique is applied to the giant spirals Maffei 2 and IC 342. It involves a comparison of the dust-to-gas ratio in spirals of similar morphological type using observations of the Balmer decrement in extragalactic HII regions combined with measurements of azimuthally averaged HI column densities. Revised distances to these galaxies are obtained from the Tully-Fisher relation in the I-band.;Special attention to the determination of broadband reddening coefficients is used in this analysis to account for shifts in effective wavelengths, which can be significant for highly reddened galaxies. In addition, by restricting the distance analyses to the I-band, uncertainties are minimized in the photometric parameters owing to the extinction. The revised distances are consistent with what would be suspected for the Hubble Flow, making it highly unlikely that these galaxies interacted with the Local Group since the Big Bang, as has been previously hypothesized.