arXiv subjects

Kathryn A. Harris

Publications and source records attributed to Kathryn A. Harris.

4 recordsLinked to original sources

arXiv2017

Quantifying the Origin and Distribution of Intracluster Light in a Fornax-like Cluster

Using a cosmological $N$-body simulation, we investigate the origin and distribution of stars in the intracluster light (ICL) of a Fornax-like cluster. In a dark matter only simulation we identify a halo which, at $z=0$, has $M_200 \simeq 4.1 \times 10^{13}M_{sun}$ and $r_{200} = 700kpc$, and replace infalling subhalos with models that include spheroid and disc components. As they fall into the cluster, the stars in some of these galaxies are stripped from their hosts, and form the ICL. We consider the separate contributions to the ICL from stars which originate in the haloes and the discs of the galaxies. We find that disc ICL stars are more centrally concentrated than halo ICL stars. The majority of the disc ICL stars are associated with one initially disc-dominated galaxy that falls to the centre of the cluster and is heavily disrupted, producing part of the cD galaxy. At radial distances greater than 200kpc, well beyond the stellar envelope of the cD galaxy, stars formerly from the stellar haloes of galaxies dominate the ICL. Therefore at large distances, the ICL population is dominated by older stars.

astro-ph.GA↗

arXiv2013

Evidence of Increased UV FeII Emission in Quasars in Candidate Overdense Regions

We present evidence for a skewed distribution of UV FeII emission in quasars within candidate overdense regions spanning spatial scales of ~ 50 Mpc at 1.11 < z < 1.67, compared to quasars in field environments at comparable redshifts. The overdense regions have an excess of high equivalent width sources (W2400 > 42 Å), and a dearth of low equivalent width sources. There are various possible explanations for this effect, including dust, Lyαfluorescence, microturbulence, and iron abundance. We find that the most plausible of these is enhanced iron abundance in the overdense regions, consistent with an enhanced star formation rate in the overdense regions compared to the field.

astro-ph.CO↗

arXiv2012

A structure in the early universe at z ~ 1.3 that exceeds the homogeneity scale of the R-W concordance cosmology

A Large Quasar Group (LQG) of particularly large size and high membership has been identified in the DR7QSO catalogue of the Sloan Digital Sky Survey. It has characteristic size (volume^1/3) ~ 500 Mpc (proper size, present epoch), longest dimension ~ 1240 Mpc, membership of 73 quasars, and mean redshift = 1.27. In terms of both size and membership it is the most extreme LQG found in the DR7QSO catalogue for the redshift range 1.0 <= z <= 1.8 of our current investigation. Its location on the sky is ~ 8.8 deg north (~ 615 Mpc projected) of the Clowes & Campusano LQG at the same redshift, = 1.28, which is itself one of the more extreme examples. Their boundaries approach to within ~ 2 deg (~ 140 Mpc projected). This new, huge LQG appears to be the largest structure currently known in the early universe. Its size suggests incompatibility with the Yadav et al. scale of homogeneity for the concordance cosmology, and thus challenges the assumption of the cosmological principle.

astro-ph.CO↗

arXiv2012

The Cluster and Large Scale Environments of Quasars at z<0.9

In this thesis, I present an investigation into the environments of quasars with respect to galaxy clusters, and environment evolution with redshift and luminosity. The orientation of the quasar with respect to the major axis of the closest cluster was calculated, introducing new information to previous work. The aim of this work was i.) to study the large scale environment over a large redshift range, ii.) to study the evolution as well as any change in environment with quasar luminosity and redshift, and iii.) to study the orientation of a quasar with respect to a galaxy cluster. There is a deficit of quasars lying close to cluster centres for 0.4<z<0.8, indicating a preference for less dense environments, in agreement with previous work. These is no change with redshift (over 0<z<1.2) in the positions of the quasars as a function of absolute quasar magnitude, nor preferred orientation between the quasar and the cluster major axis for bright or faint quasars. Spectra of a selection of 680 star forming galaxies, red galaxies, and AGN were taken, and used to study the environments of quasars with respect to star-forming galaxies and galaxy clusters. The objects were classified (33 classed as AGN), and star formation rates calculated. Three AGN and 10 star forming galaxies lie at the same redshift (z=0.29) as three galaxy clusters. The three galaxy clusters have the same orientation angle and may be part of a filament along with the star forming galaxies and AGN. A number of high redshift quasars showed evidence of ultra-strong UV FeII emission in their spectra in the direction of three LQGs in the redshift range 1.1<z<1.6, including the Clowes-Campusano Large Quasar Group (CCLQG). Though there has been no previous indication that the LQG environment is unique, the high level of iron emission may indicate a difference in environment.

astro-ph.CO↗