arXiv subjects

L. R. Jones

Publications and source records attributed to L. R. Jones.

42 records · Page 3Linked to original sources

arXiv1997

Cluster Evolution in the Wide Angle ROSAT Pointed Survey (WARPS)

A new flux limited catalogue of low luminosity (Lx <= 10^44 erg/s) X-ray galaxy clusters and groups covering a redshift range of z~0.1 to z~0.7 has been produced from the WARPS project. We present the number counts of this low luminosity population at high redshifts (z>0.3). The results are consistent with an unevolving population which does not exhibit the evolution seen in the higher luminosity cluster population. These observations can be qualitatively described by self-similarly evolving dark matter and preheated IGM models of X-ray cluster gas, with a power law index for the spectrum of matter density fluctuations n >= -1.

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arXiv1996

X-ray QSO evolution from a very deep ROSAT survey

In the deepest optically identified X-ray survey yet performed, we have identified 32 X-ray selected QSOs to a flux limit of 2x10^{-15} erg cm^{-2} s^{-1} (0.5-2 keV). The survey, performed with the ROSAT PSPC, has 89% spectroscopic completeness. The QSO log(N)-log(S) relation is found to have a break to a flat slope at faint fluxes. The surface density of QSOs at the survey limit is 230+/-40 per square degree, the largest so far of any QSO survey. We have used this survey to measure the QSO X-ray luminosity function at low luminosities (Lx<10^{44.5} erg s^{-1}) and high redshifts (1<z<2.5). The highest redshift QSO in the survey has z=3.4. Combined with the QSOs from the Einstein EMSS at bright fluxes, we find pure luminosity evolution of the form Lx proportional to (1+z)^{3.0(+0.2,-0.3)} is an adequate description of the evolution of the X-ray luminosity function at low redshifts. A redshift cutoff in the evolution is required at z=1.4 ^{+0.4}_{-0.17} (for qo=0.5). We discuss the form of this evolution, its dependence on the model assumed and the errors on the derived parameters. We show that most previous X-ray surveys, including the EMSS, are consistent with a power law luminosity evolution index of 3.0. The contribution of QSOs to the 1-2 keV cosmic X-ray background is found to be between 31% and 51%.

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arXiv1996

The WARPS X-ray survey of galaxies, groups and clusters I: Method and first results

We have embarked on a survey of ROSAT PSPC archival data with the aim of detecting all significant surface brightness enhancements due to sources in the innermost 15 arcmin of the PSPC field of view (0.5-2.0 keV). This project is part of the Wide Angle ROSAT Pointed Survey (WARPS) and is designed primarily to measure the low luminosity, high redshift, X-ray luminosity function of galaxy clusters and groups. The approach we have chosen for source detection [Voronoi Tessellation and Percolation (VTP)] represents a significant advance over conventional methods and is particularly suited for the detection and accurate quantification of extended and/or low surface brightness emission. In an extensive optical follow-up programme we are identifying galaxies, groups and clusters at redshifts ranging from z~0.1 to z~0.7. We present first results for an initial 17.2 deg^2 at detected fluxes > 3.5 x 10^-14 erg s^-1 cm^-2. We find the sky density of extended objects to be in the range 2.8 to 4.0 (+- 0.4) deg^-2. A comparison with a point source detection algorithm demonstrates that our VTP approach typically finds 1-2 more objects deg^-2 to this detected flux limit. The surface brightness limit of the WARPS cluster survey is ~1x10^-15 erg sec^-1 cm^-2 arcmin^-2, approximately 6 times lower than the EMSS. The WARPS LogN-LogS shows a significant excess over previous measurements for S > 8 x 10^-14 erg sec^-1 cm^-2.

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arXiv1996

ROSAT PSPC spectra of X-ray selected Narrow Emission Line Galaxies

We analyse the ROSAT PSPC spectrum of 19 X-ray selected Narrow Emission Line Galaxies (NELGs) discovered during the optical identification of sources in the ROSAT UK Deep Survey. Their properties are compared to those of broad line Active Galactic Nuclei (AGN) in the same sample. Counts in three spectral bands have been extracted for all the sources, and have been fitted with a power-law model assuming the Galactic value for NH. The average slope of NELGs is α=0.45+-0.09, whilst for the AGN it is α=0.96+-0.03. The power-law model is a good fit for ~90% of NELGs and ~75% of AGN. Recent work shows that the fractional surface density of NELGs increases with respect to AGN at faint fluxes. Thus they are expected to be an important component of the residual soft (<2 keV) X--ray background. The slope of the X--ray background (α~0.4, 1-10 keV) is harder than that of AGN (α~1) but our results show that it is consistent with the summed spectrum of the NELGs in the deep survey (α~0.4). This may finally reconcile the spectrum of the background with the properties of the sources that constitute it.

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arXiv1995

The WARPS survey for faint Clusters of Galaxies

The WARPS cluster survey is based on the ROSAT PSPC archive of pointed observations. It includes extended X-ray sources, detected with the Voronoi Tessellation and Percolation algorithm (VTP), and point-like X-ray sources with non-stellar optical counterparts. It is designed to minimize selection effects whilst covering a large area of sky. The aims of the survey are to (a) measure the low luminosity (<10^44 ergs^-1), high redshift (z>0.2) X-ray luminosity function of clusters and groups, and (b) investigate cluster morphologies and unusual systems (e.g. merging clusters). In an initial 13 sq deg (66 fields) we have found 22 extended X-ray sources with detected flux >7x10^-14 erg cm^-2s^-1 (0.5-2.0keV) and sizes of 1 to 5 arcmin. Optically they range from a single bright nearby galaxy which has been resolved, an Abell cluster which is revealed to have two (probably merging) components and groups and clusters of galaxies at estimated redshifts beyond z=0.4.

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arXiv1995

Faint Extended X-ray Sources: A new Large Area Survey

We have searched for extended X-ray sources in the ROSAT PSPC archive using the Voronoi Tesslation and Percolation algorithm (VTP). This algorithm detects all significant sources regardless of shape or size, and is particularly suited to finding low surface brightness extended sources which could be missed or wrongly interpreted by other algorithms. In an initial 13 sq deg (66 fields) we have found 22 sources with detected flux $>$7x10$^{-14}$ erg cm$^{-2}$ s$^{-1}$ (0.5-2 keV) and sizes of 1 to 5 arcmin. Optically, they range from a single bright nearby galaxy which has been resolved, an Abell cluster which is revealed to have two (probably merging) components, and groups and clusters of galaxies at estimated redshifts beyond z$=$0.4. This work is part of an ongoing survey with the aims of (a) measuring the low luminosity ($<$10$^{44}$ erg s$^{-1}$), high redshift (z$>$0.2) X-ray luminosity function of clusters, and (b) investigating cluster morphologies and unusual systems (eg `fossil' groups).

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