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[91.01] How much does a galaxy know about its neighbors? Mutual information between galaxies as a function of separation.

M. Masjedi, M.R. Blanton, D.W. Hogg (NYU), S. Roweis (Toronto)

In this work we test the hypothesis that blue galaxies tend to be in groups with other blue galaxies and red galaxies tend to be in groups with other red galaxies. The galaxies are taken from the SDSS spectroscopic sample; we look at their rest-frame color, luminosity, Sersic index and surface brightness. We find that galaxies selected to be in close pairs tend to be redder than galaxies selected randomly. Over and above this effect, knowing one galaxy's color in a pair implies information about the other galaxy's color. In pairs closer than 0.5 Mpc knowing one galaxy's color gives rise to an amount of information equal to 0.032±0.003 in units of bits about the other galaxy's color, and as we select pairs of greater separation this information diminishes, with no detectable mutual information at separations larger than 2 Mpc. Repeating the same analysis for luminosity, Sersic index and surface brightness we find that color is the only property which carries this information. This result agrees with previous work (Blanton, M. R. et al. astro-ph/0310453) suggesting that star formation rate is the galaxy property most closely tied to environment. This work was partially supported by NASA and the NSF.

The author(s) of this abstract have provided an email address for comments about the abstract: morad.masjedi@physics.nyu.edu

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Bulletin of the American Astronomical Society, 36 #2
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