On the Clustering of Compact Galaxy Pairs in Dark Matter Haloes
Yiran Wang and Robert J. Brunner
We analyze the clustering of photometrically selected galaxy pairs by using the halo-occupation distribution (HOD) model. We select galaxy pairs in three volume limited samples: 0.0<z≤0.30.0<z≤0.3, Mr <−19.0Mr <−19.0, 0.0<z≤0.30.0<z≤0.3, Mr <−19.5Mr <−19.5, and 0.3<z≤0.40.3<z≤0.4, Mr <−19.5Mr <−19.5. These samples are cut from our clean galaxy sample that we generated from the Sloan Digital Sky Survey (SDSS), Data Release 7 (DR7). We measure the two-point auto-correlation functions, ω(θ)ω(θ), for galaxies and galaxy pairs and develop an HOD to model their clustering. Our results are successfully fit by these HOD models, and we see the separation of “1-halo” and “2-halo” clustering terms for both single galaxies and galaxy pairs. Our clustering measurements and HOD model fits for the single galaxy samples are consistent with previous results. We find that the galaxy pairs generally have larger clustering amplitudes than single galaxies, and the quantities computed during the HOD fitting, e.g., effective mass, MeffMeff, and linear bias, bgbg, are also larger for galaxy pairs. We find that the central fractions for galaxy pairs are significantly higher than for single galaxies, which confirms that galaxy pairs are formed at the center of more massive dark matter haloes. We also model the clustering dependence of the galaxy pair correlation function on redshift, galaxy type, and luminosity. We find early-early pairs cluster more strongly than late-late pairs, that bright galaxy pairs cluster more strongly than dim galaxy pairs, and that the clustering does not depend on the luminosity contrast between the two galaxies in the compact group.