P. A. Shaver

The ROSAT-ESO flux limited X-ray (REFLEX) galaxy cluster survey. I. The construction of the cluster sample ?

We discuss the construction of an X-ray flux-limited sample of galaxy clusters, the REFLEX survey catalogue, to be used for cosmological studies. This cluster identication and redshift survey was conducted in the frame of an ESO key programme and is based on candidates selected from the southern part of the ROSAT All-Sky Survey (RASS). For the rst cluster candidate selection from a flux-limited RASS source list, we make use of optical data from the COSMOS digital catalogue produced from the scans of the UK-Schmidt plates. To ensure homogeneity of the sample construction process, this selection is based only on this one well-dened optical data base. The nature of the candidates selected in this process is subsequently checked by a more detailed evaluation of the X-ray and optical source properties and available literature data. The nal identication and the redshift is then based on optical spectroscopic follow-up observations. In this paper we document the process by which the primary cluster candidate catalogue is constructed prior to the optical follow-up observations. We describe the reanalysis of the RASS source catalogue which enables us to impose a proper flux limit cut to the X-ray source list without introducing a severe bias against extended sources. We discuss the correlation of the X-ray and optical (COSMOS) data to nd galaxy density enhancements at the RASS X-ray source positions and the further evaluation of the nature of these cluster candidates. Based also on the results of the follow-up observations we provide a statistical analysis of the completeness and contamination of the nal cluster sample and show results on the cluster number counts. The nal sample of identied X-ray clusters reaches a flux limit of 3 10 12 erg s 1 cm 2 in the 0.1{2.4 keV band and comprises 452 clusters in an area of 4.24 ster. The results imply a completeness of the REFLEX cluster sample well in excess of 90%. We also derive for the rst time an upper limit of less than 9% for the number of clusters which may feature a dominant contribution to the X-ray emission from AGN. This accuracy is sucient for the use of this cluster sample for cosmological tests.

Cosmic dynamics in the era of Extremely Large Telescopes

The redshifts of all cosmologically distant sources are expected to experience a small, systematic drift as a function of time due to the evolution of the Universes expansion rate. A measurement of this effect would represent a direct and entirely model-independent determination of the expansion history of the Universe over a redshift range that is inaccessible to other methods. Here we investigate the impact of the next generation of Extremely Large Telescopes on the feasibility of detecting and characterising the cosmological redshift drift. We consider the Lyman alpha forest in the redshift range 2 < z < 5 and other absorption lines in the spectra of high redshift QSOs as the most suitable targets for a redshift drift experiment. Assuming photon-noise limited observations and using extensive Monte Carlo simulations we determine the accuracy to which the redshift drift can be measured from the Ly alpha forest as a function of signal-to-noise and redshift. Based on this relation and using the brightness and redshift distributions of known QSOs we find that a 42-m telescope is capable of unambiguously detecting the redshift drift over a period of ~20 yr using 4000 h of observing time. Such an experiment would provide independent evidence for the existence of dark energy without assuming spatial flatness, using any other cosmological constraints or making any other astrophysical assumption.

The Parkes quarter-Jansky flat-spectrum sample: III. Space density and evolution of QSOs

We analyze the Parkes quarter-Jansky flat-spectrum sample of QSOs in terms of space density, including the redshift distribution, the radio luminosity function, and the evidence for a redshift cutoff. With regard to the luminosity function, we note the strong evolution in space density from the present day to epochs corresponding to redshifts ∼1. We draw attention to a selection effect due to spread in spectral shape that may have misled other investigators to consider the apparent similarities in shape of luminosity functions in different redshift shells as evidence for luminosity evolution. To examine the evolution at redshifts beyond 3, we develop a model-independent method based on the Vmax test using each object to predict expectation densities beyond z = 3. With this we show that a diminution in space density at z > 3 is present at a significance level >4σ. We identify a severe bias in such determinations from using flux-density measurements at epochs significantly later than that of the finding survey. The form of the diminution is estimated, and is shown to be very similar to that found for QSOs selected in X-ray and optical wavebands. The diminution is also compared with the current estimates of star-formation evolution, with less conclusive results. In summary we suggest that the reionization epoch is little influenced by powerful flat-spectrum QSOs, and that dust obscuration does not play a major role in our view of the QSO population selected at radio, optical or X-ray wavelengths.

The ROSAT-ESO Flux-Limited X-ray (REFLEX) galaxy cluster survey — II. The spatial correlation function

We report the results of the spatial two-point correlation functioncc(r) for the new X- ray galaxy cluster survey REFLEX, which comprises of 452 X-ray selected clusters (449 with redshifts) detected by the ROSAT satellite during the ROSAT All-Sky-Survey (RASS). The REFLEX cluster sample is flux limited to 3 × 10 12 erg s 1 cm 2 in the ROSAT energy band (0.1 − 2.4 keV) and spans 3 decades in X-ray luminosity (10 42 −10 45 h 2 erg s 1 ), containing galaxy groups and rich clusters out to a redshift z ≤ 0.3. Covering a contiguous area of 4.24 sr REFLEX is the largest X-ray cluster sample to date for which spatial clustering has been analysed. Correlation studies using clusters selected on the basis of their X-ray emission are particularly interesting as they are largely free from the projection biases inherent to optical studies. For the entire flux-limited sample we find that the correlation length (the scale at which the correlation amplitude passes through unity) r0 ≃ 20h 1 Mpc. For example, if a power-law fit is made to �(r) over the range 4 − 40h 1 Mpc then r0 = 18.8 ± 0.9. An indication of the robustness of this result comes from the high degree of isotropy seen in the clustering pattern on scales close to the correlation length. On larger scalescc(r) deviates from a power-law, crossing zero at ≃ 45h 1 Mpc. From an examination of 5 volume-limited cluster sub-samples we find no significant trend of r0 with limiting X-ray luminosity. A comparison with recent model predictions for the clustering properties of X-ray flux-limited samples, indicates that Cold Dark Matter models with the matter density m = 1 fail to produce sufficient clustering to account for the data, while m ≃ 0.3 models provide an excellent fit.

The ROSAT-ESO Flux-Limited X-ray (REFLEX) Galaxy Cluster Survey. IV. The X-ray luminosity function

The X-ray galaxy cluster sample from the REFLEX Cluster Survey, which covers the X-ray brightest galaxy clusters detected in the ROSAT All-Sky Survey in the southern sky, is used to construct the X-ray luminosity function of clusters in the local universe. With 452 clusters detected above an X-ray flux limit of 3 × 10-12 ergs s-1 cm-2 in 4.24 sr of the sky, this sample is the most comprehensive X-ray cluster sample with a well-documented selection function, providing the best current census of the local X-ray galaxy cluster population. In this paper we discuss the construction of the luminosity function and the effects of flux measurement errors and of variations with sample region, and we compare the results with those from previous surveys.

Detection of CO (4-3), CO (9-8), and Dust Emission in the Broad Absorption Line Quasar APM 08279+5255 at a Redshift of 3.9

With the IRAM interferometer, we detected the lines of CO (4-3) and CO (9-8) from the recently discovered broad absorption line quasar APM 08279+5255. The molecular lines are at a redshift of 3.911, which we take to be the true cosmological redshift of the quasars host galaxy. This means that the quasar emission lines at z=3.87 are blueshifted by a kinematic component of -2500 km s−1 and, along with the broad absorption lines, are probably emitted in the quasars wind or jet, moving toward us. The CO line ratios suggest that the molecular gas is at a temperature of ~200 K, at a density of ~4000 cm−3. We also detected the dust emission at 94 and 214 GHz (with emitted wavelengths of 650 and 290 μm). The spectral index of the millimeter/submillimeter continuum is 3.2, indicating that the dust emission is optically thin in this part of the spectrum. The extremely high CO and dust luminosities suggest magnification by gravitational lensing. Using the optical extent and our limit on the size of the CO region, we estimate a magnification of 7-30 for the CO lines and the far-IR continuum and 14-60 for the optical/UV. In this interpretation, the molecular gas and dust are in a nuclear disk of radius 90-270 pc around the quasar. The quasar is 25-100 times stronger than, but otherwise resembles, the nucleus of Mrk 231.

A spectroscopic study of UM 673 A and B - On the size of Lyman-alpha clouds

A study of the Lyα forest spectra (2 A resolution) obtained for the A and B images of the gravitationally lensed high-redshift quasar UM 673 is presented. Higher resolution data of the brightest (A) image are also presented. In the 2 A resolution spectra, all the absorption lines detected at 5 σ in the spectrum of the fainter B image are present in the A image; however, two anticoincidences are found, i.e., two lines in A which do not have a counterpart in B at more than a 3 σ confidence level. Given the fact that corresponding Lyα lines in the spectra of A and B have their equivalent widths well correlated, this proves that both light beams actually cross the same clouds

THE VERY LARGE ARRAY SURVEY OF THE CHANDRA DEEP FIELD SOUTH. IV. SOURCE POPULATION

We present a detailed analysis of 256 radio sources from our deep (flux density limit of 42 μJy at the field center at 1.4 GHz) Chandra Deep Field South 1.4 and 5 GHz VLA survey. The radio population is studied by using a wealth of multiwavelength information in the radio, optical, and X-ray bands. The availability of redshifts for ~80% of the sources in our complete sample allows us to derive reliable luminosity estimates for the majority of the objects. X-ray data, including upper limits, for all our sources turn out to be a key factor in establishing the nature of faint radio sources. Due to the faint optical levels probed by this study, we have uncovered a population of distant active galactic nuclei (AGNs) systematically missing from many previous studies of sub-millijansky radio source identifications. We find that, while the well-known flattening of the radio number counts below 1 mJy is mostly due to star-forming galaxies, these sources and AGNs make up an approximately equal fraction of the sub-millijansky sky, contrary to some previous results. The AGNs include radio galaxies, mostly of the low-power, Fanaroff-Riley I type, and a significant radio-quiet component, which amounts to approximately one fifth of the total sample. The ratio of radio-to-optical luminosity depends more on radio luminosity, rather than being due to optical absorption.

The VLA Survey of the Chandra Deep Field-South. I. Overview and the Radio Data

We report 20 and 6 cm VLA deep observations of the CDF-S including the Extended CDF-S. We discuss the radio properties of 266 cataloged radio sources, of which 198 are above a 20 cm completeness level reaching down to 43 μJy at the center of the field. Survey observations made at 6 cm over a more limited region cover the original CDF-S to a comparable level of sensitivity as the 20 cm observations. Of 266 cataloged radio sources, 52 have X-ray counterparts in the CDF-S and a further 37 have counterparts in the E-CDF-S area not covered by the 1 Ms exposure. Using a wide range of material, we have found optical or infrared counterparts for 254 radio sources, of which 186 have either spectroscopic or photometric redshifts. Three radio sources have no apparent counterpart at any other wavelength. Measurements of the 20 cm radio flux density at the position of each CDF-S X-ray source detected a further 30 radio sources above a conservative 3 σ detection limit. X-ray and submillimeter observations have been traditionally used as a measure of AGN and star formation activity, respectively. These new observations probe the faint end of both the star formation and radio galaxy/AGN population, as well as the connection between the formation and evolution of stars and SMBHs. Both of the corresponding gravitational and nuclear fusion driven energy sources can lead to radio synchrotron emission. AGN and radio galaxies dominate at high flux densities. Although emission from star formation becomes more prominent at the microjansky levels reached by deep radio surveys, even for the weakest sources, we still find an apparent significant contribution from low-luminosity AGN as well as from star formation.

The ROSAT-ESO Flux-Limited X-Ray (REFLEX) galaxy cluster survey III. The power spectrum ?

We present a measure of the power spectrum on scales from 15 to 800h 1 Mpc using the ROSAT- ESO Flux-Limited X-Ray (REFLEX) galaxy cluster catalogue. The REFLEX survey provides a sample of the 452 X-ray brightest southern clusters of galaxies with the nominal flux limit S =3 : 01 0 12 erg s 1 cm 2 for the ROSAT energy band (0:1 2:4) keV. Several tests are performed showing no signicant incompletenesses of the REFLEX clusters with X-ray luminosities brighter than 10 43 erg s 1 up to scales of about 800h 1 Mpc. They also indicate that cosmic variance might be more important than previous studies suggest. We regard this as a warning not to draw general cosmological conclusions from cluster samples with a size smaller than REFLEX. Power spectra, P (k), of comoving cluster number densities are estimated for flux- and volume-limited subsamples. The most important result is the detection of a broad maximum within the comoving wavenum- ber range 0:022 k 0:030h Mpc 1 . The data suggest an increase of the power spectral amplitude with X-ray luminosity. Compared to optically selected cluster samples the REFLEX P (k) is flatter for wavenumbers k 0:05h Mpc 1 thus shifting the maximum of P (k) to larger scales. The smooth maximum is not consis- tent with the narrow peak detected at k =0 :05h Mpc 1 using the Abell/ACO richness0 data. In the range 0:02 k 0:4h Mpc 1 general agreement is found between the slope of the REFLEX P (k) and those obtained with optically selected galaxies. A semi-analytic description of the biased nonlinear power spectrum in redshift space gives the best agreement for low-density Cold Dark Matter models with or without a cosmological constant.