Will Saunders — Page 4

arXiv1995

The clustering of warm and cool IRAS galaxies

We use a series of statistical techniques to compare the clustering of samples of IRAS galaxies selected on the basis of their far-infrared emission temperature, to see whether a temperature-dependent effect, such as might be produced by interaction-induced star formation, could be responsible for the increase in clustering strength with redshift in the QDOT redshift survey that has been reported by several authors. The temperature-luminosity relation for IRAS galaxies means that warm and cool samples drawn from a flux-limited sample like QDOT will sample quite different volumes of space. To overcome this problem, and to distinguish truly temperature-dependent results from those depending directly on the volume of space sampled, we consider a pair of samples of warmer and cooler galaxies with matched redshift distributions, as well as pairs of samples selected using a simple temperature cut. ...(abstract shortened).... We conclude that that there may be a temperature-dependent component to the observed increase in the clustering strength of QDOT galaxies with redshift, but that it is less important than a sampling effect, which reflects the local cosmography, rather than the physical properties of the galaxies and their environment. We discuss the implications of this work for the use of IRAS galaxies as probes of large-scale structure and for models accounting for their far-infrared emission by interaction-induced star formation.

astro-ph↗

arXiv1994

The Clustering Properties of IRAS Galaxies

We investigate the clustering of galaxies in the QDOT redshift survey of IRAS galaxies. We find that the redshift space two-point correlation function is well approximated by a power-law of slope -1.11+\-0.09, with clustering length 3.87+\-0.32 Mpc/h out to pair separations of 25 Mpc\h. On scales larger than 40 Mpc/h, the correlation function is consistent with zero. The r.m.s. fluctuation in the count of QDOT galaxies above the Poisson level in spheres of radius 8 Mpc/h is σ_8^{IRAS}=0.58+\-0.14, showing that fluctuations in the distribution of IRAS galaxies on these scales are smaller than those of optical galaxies by a factor of about 0.65, with an uncertainty of 25%. We find no detectable difference between the correlation functions measured in redshift space and in real space, leading to a $2σ$ limit of b_{IRAS}/Ω^{0.6} >1.05, where b_{IRAS} is the bias factor for IRAS galaxies and Ωis the cosmological density parameter. The QDOT autocorrelation function calculated in concentric shells increases significantly with shell radius. This difference is more likely due to sampling fluctuations than to an increase of the clustering strength with galaxy luminosity, but the two effects are difficult to disentangle; our data allow at most an increase of \sim 20% in clustering strength for each decade in luminosity. For separations greater than \sim 3 Mpc/h, the cross-correlation function of Abell clusters (with Richness R\ge 1) and QDOT galaxies is well approximated by a power-law of slope -1.81+\-0.10, with clustering length 10.10+\-0.45 Mpc/h, and no significant signal beyond \gsim 50 Mpc\h. This cross-correlation depends only weakly on cluster richness.

astro-ph↗