Galactic Conformity via Small-Scale Clustering in Simulations and Surveys
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CitationBray, Aaron David Dakin. 2016. Galactic Conformity via Small-Scale Clustering in Simulations and Surveys. Doctoral dissertation, Harvard University, Graduate School of Arts & Sciences.
AbstractData from recent galaxy surveys reveal that, even at fixed stellar mass, quiescent galaxies are preferentially found around other red galaxies, an observation referred to as galactic conformity. This detection may offer important clues toward a fuller understanding of galaxy formation and evolution. While dark matter halo mass is thought to be the dominant reason that star-forming galaxies are eventually quenched, galaxy conformity suggests that additional physics or environmental factors could be required. This has important implications for modeling large-scale surveys and understanding cosmology from small-scale clustering.
We present an analysis of galactic conformity in the Illustris Suite of cosmological hydro simulations. We find that a strong galactic conformity signal is present out to r = 3 Mpc and that a smaller signal is present to r = 10 Mpc for the lowest mass galaxies in our sample. The red fraction is higher around red galaxies than around blue galaxies in bins of either stellar mass or halo mass. We show that this galactic conformity is matched by a dark matter halo conformity in which older halos are preferentially located nearby other older halos. We connect the two types of conformity with a semi-empirical model that connect stellar mass and color with dark matter halos, and we study how using different galaxy properties in our model affects the resultant galactic conformity signal. We discuss the implications of these results for interpreting similar signals in observations.
We show the results of a small-scale clustering investigation from the PRIMUS redshift survey. We use spectroscopic-photometric cross-correlations to calculate local galaxy overdensities as function of galaxy properties from 0.2 < z < 1. We present the luminosity and color dependencies of galaxy clustering as a function of physical scale. We show that there exists a luminosity-dependence for both red and blue galaxies, but that they differ in shape, with red galaxies showing non-monotonic behavior as a function of luminosity while blue galaxies are reasonably fit with a power-law. We discuss these results in light of physics of galaxy evolution.
We then extend our PRIMUS small-scale clustering study to incorporate an exploration of galactic conformity. We now select photometric galaxies by their inferred stellar mass and color, and we use the quotient of the relative overdensities calculated from the clustering amplitude to define a quiescent fraction around each PRIMUS galaxy. We present study this quiescent fraction as a function of primary mass, secondary mass, and redshift. We show that, at 0.2 < z < 0.6, there exists a galactic conformity signal out to r ≈ 1 Mpc, at least for lower mass primary galaxies. We also show that there exists a strong mass dependence in our lowest redshift bin. In our highest redshift bin, we show that the signal is weaker than at lower redshift. We explain our results in the context of both the current observational and theoretical literature.
Citable link to this pagehttp://nrs.harvard.edu/urn-3:HUL.InstRepos:33493538
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