Searching for Dark Galaxies Via Their Distorted Companions in the SDSS
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Date
2013-05
Authors
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Publisher
The Ohio State University
Abstract
In the past several years, astronomers have become increasingly interested in
the possible existence of so-called “dark galaxies”, dark matter halos of galaxyorder
mass which emit little to no visible light. As it is difficult to observe
these galaxies directly, an alternative method used for detection of dark galaxies
involves measuring their influence on observable luminous galaxies through
gravitational interactions. Galaxies which have experienced interactions with
other galaxies of comparable mass are known to be subject to a number of observable
effects, including an increased star formation rate (SFR) and an asymmetrical
shape. Hence, galaxies that display above-average asymmetry or signs of star
formation are more likely to have undergone interactions in the past than those
that do not. Further, if there is not visible companion nearby with which such a
galaxy could have interacted, it is possible that a dark galaxy exists in the
vicinity. In our research, we focus on a sample of 14,226 spiral galaxies, both
edge-on and face-on, over a redshift range 0.02<z<0.06, examining them for
different types of evidence of asymmetry by implementing a “distortion index” D
based on available pipeline data from the Sloan Digital Sky Survey (SDSS). We then
further separate these galaxies based on the presence and separation distance of
similar-magnitude companions on a plane-of-the-sky coordinate grid. Based on
available merger timescale predictions, we check for companions at a distance of up
to 1 megaparsec, and give special attention to galaxies with “close” companions
less than 140 kiloparsecs away. We find that the percentage of distorted galaxies
by region is inconclusive, as our sample contains too few isolated galaxies to
distinctively identify a difference in distortion percentages.
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Keywords
Astronomy, Dark Galaxies, SDSS, Sloan Digital Sky Survey, Data Mining