Far-infrared-radio relations in clusters and groups at intermediate redshift

Abstract

In this thesis, we present a multi-wavelength analysis of star-forming galaxies to shed new light on the evolution of the far-IR-radio relations in intermediate redshift (0.3 < z < 0.6) galaxy clusters and galaxy groups. The far-infrared (far-IR) emission from galaxies is dominated by thermal dust emission. The radio emission at 1.4 GHz is predominantly produced by non-thermal synchrotron radiation. The underlying mechanisms, which drive the far-IR-radio correlation, are believed to arise from massive star formation. A number of studies have investigated the relationship as a function of redshift in the field and have found no evolution out to at least z _ 2, however few works have been done in galaxy clusters. In nearby clusters, the median logarithmic ratio of the far-IR to radio luminosity is qFIR = 2.07_0.74, which is lower than the value found in the field, and there is an indication of an enhancement of radio emission relative to the far-IR emission. Understanding the properties of the far-IR-radio correlation in a sample of distant and massive cluster and groups plays an important role in understanding the physical processes in these systems. We have derived total infrared luminosities for a sample of cluster, group, and field galaxies through an empirical relation based on Spitzer MIPS 24 _m photometry. The radio flux densities were measured from deep Very Large Array 1.4 GHz radio continuum observations. We have studied the properties of the far-IR-radio correlation of galaxies at intermediate redshift clusters by comparing the relationship of these galaxies to that of low redshift clusters. We have also examined the properties of the galaxies showing radio excess to determine the extent that galaxy type or environment may explain the radio excess in galaxy clusters. We find that the ratio of far-IR to radio luminosity for galaxies in an intermediate redshift cluster to be qFIR = 1.72_0.63. This value is comparable to that measured in low redshift clusters. A higher fraction of galaxies in clusters show an excess in their radio fluxes when compared to low redshift clusters, and corroborates previous evidence of a cluster enhancement of radio excess sources at this earlier epoch as well. We have also investigated the properties of the far-IR-radio correlation for a sample of galaxy groups in the COSMOS field. We find a lower percentage of radio-excess sources in groups as compared to clusters. This provides preliminary evidence that the number of radioexcess sources may depend on galaxy environment. We also find that a larger fraction of radio-excess sources in clusters are red sequence galaxies.