arXiv subjects

N. S. Loaring

Publications and source records attributed to N. S. Loaring.

29 records · Page 2Linked to original sources

arXiv2002

X-ray and optical properties of X-ray sources in the 13hr XMM-Newton/Chandra deep survey

The 13hr XMM-Newton/Chandra deep survey is the first of two extremely deep XMM-Newton fields observed by the XMM-OM consortium. A 120 ks Chandra mosaic, covering 0.2 square degrees, provides sensitive, confusion-free point source detection with sub-arcsecond positions, while the 200 ks XMM-Newton observation provides high quality X-ray spectroscopy over the same sky area. We have optical spectroscopic identifications for 70 X-ray sources. Of these, 42 are broad emission-line AGN with a wide range of redshifts. The optical counterparts of a further 23 sources are narrow emission line galaxies and absorption line galaxies. These 23 sources all lie at z < 1 and typically have lower X-ray luminosities than the broad-line AGN. About half of them show significant X-ray absorption and are almost certainly intrinsically absorbed AGN. However some of them have unabsorbed, AGN-like, power-law components in their X-ray spectra, but do not show broad emission lines in their optical spectra. These sources may be weak, unobscured AGN in bright galaxies and their existence at low redshifts could be a consequence of the strong cosmological evolution of AGN characteristic luminosities.

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arXiv2002

The correlation of line strength with luminosity and redshift from composite QSO spectra

We have generated a series of composite QSO spectra using over 22000 individual low resolution (~8A) QSO spectra obtained from the 2dF (18.25<bj<20.85) and 6dF (16<bj<18.25) QSO Redshift Surveys. The large size of the catalogue has enabled us to construct composite spectra in narrow redshift (dz=0.25) and absolute magnitude (dMb=0.5) bins. The median number of QSOs in each composite is ~200, yielding typical S/N of ~100. For a given redshift interval, the composite spectra cover a factor of over 25 in luminosity. Using the composite spectra we have measured the equivalent widths (EWs) of the major broad and narrow emission lines, and the CaII K absorption feature due to the host galaxy of the AGN. Assuming a fixed host galaxy spectral energy distribution (SED), the correlation between CaII K EW and luminosity implies Lgal proportional to Lqso**{0.42+-0.05}. We find strong anti-correlations with luminosity for the EWs of [OII] and [NeV]. These provide hints to the general fading of the NLR in high luminosity sources which we attribute to the NLR dimensions becoming larger than the host galaxy. If average AGN host galaxies have SEDs similar to average galaxies, then the observed narrow [OII] emission could be solely due to the host galaxy at low luminosities (M_B~-20). We measure highly significant Baldwin effects for most broad emission lines (CIV, CIII], MgII, Hbeta, Hgamma) and show that they are predominantly due to correlations with luminosity, not redshift. We find that the Hbeta and Hgamma Balmer lines show an inverse Baldwin effect and are positively correlated with luminosity, unlike the broad UV lines. We postulate that this previously unknown effect is due to a luminosity dependent change in the the ratio of disk to non-disk continuum components (abridged).

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arXiv2002

Clustering in the 2dF QSO Redshift Survey

We present clustering results from the 2dF QSO Redshift Survey (2QZ) which currently contains over 20,000 QSOs at z<3. The two-point correlation function of QSOs averaged over the entire survey ( ~1.5) is found to be similar to that of local galaxies. When sub-dividing the sample as a function of redshift, we find that for an Einstein-de Sitter universe QSO clustering is constant (in comoving coordinates) over the entire redshift range probed by the 2QZ, while in a universe with Omega_0=0.3 and Lambda_0=0.7 there is a marginal increase in clustering with redshift. Sub-dividing the 2QZ on the basis of apparent magnitude we find only a slight difference between the clustering of QSOs of different apparent brightness, with the brightest QSOs having marginally stronger clustering. We have made a first measurement of the redshift space distortion of QSO clustering, with the goal of determining the value of cosmological parameters (in partcular Lambda_0) from geometric distortions. The current data do not allow us to discriminate between models, however, in combination with constraints from the evolution of mass clustering we find Omega_0=1-Lambda_0=0.23 +0.44-0.13 and beta(z~1.4)=0.39 +0.18-0.17. The full 2QZ data set will provide further cosmological constraints.

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arXiv2002

The 2dF QSO Redshift Survey - IX. A measurement of the luminosity dependence of QSO clustering

In this Paper we present a clustering analysis of QSOs as a function of luminosity over the redshift range z=0.3-2.9. We use a sample of 10566 QSOs taken from the preliminary data release catalogue of the 2dF QSO Redshift Survey (2QZ). We analyse QSO clustering as a function of apparent magnitude. The strong luminosity evolution of QSOs means that this is approximately equivalent to analysing the data as a function of absolute magnitude relative to M* over the redshift range that the 2QZ probes. Over the relatively narrow range in apparent magnitude of the 2QZ we find no significant (>2sigma) variation in the strength of clustering, however, there is marginal evidence for QSOs with brighter apparent magnitudes having a stronger clustering amplitude. QSOs with 18.25<bj<19.80 show a correlation scale length s_0=5.50+-0.79h-1Mpc in an Einstein-de Sitter (EdS) universe and s_0=8.37+-1.17h-1Mpc in a universe with omega_0=0.3 and lambda_0=0.7 (Lambda), while the best fit values for the full magnitude interval (18.25<bj<20.85) over the same spatial scales are s_0=4.29+-0.30h-1Mpc (EdS) and s_0=6.35+-0.45h-1Mpc (Lambda). We can therefore determine that the bias of the brightest sub-sample is a factor 1.22+-0.15 (EdS) or 1.24+-0.15 (Lambda) larger than that of the full data set. An increase in clustering with luminosity, if confirmed, would be in qualitative agreement with models in which the luminosity of a QSO is correlated to the mass of the dark halo in which it resides, implying that the mass of the host plays at least some part in determining a QSO's formation and evolution. These models predict that the clustering in brighter QSO data sets, such as Sloan Digital Sky Survey QSO sample or the bright extension of the 2QZ should show a higher clustering amplitude than the 2QZ.

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arXiv2002

The 2dF BL Lac Survey

We have optically identified a sample of 56 featureless continuum objects without significant proper motion from the 2dF QSO Redshift Survey (2QZ). The steep number--magnitude relation of the sample, $n(\bj) \propto 10^{0.7\bj}$, is similar to that derived for QSOs in the 2QZ and inconsistent with any population of Galactic objects. Follow up high resolution, high signal-to-noise, spectroscopy of five randomly selected objects confirms the featureless nature of these sources. Assuming the objects in the sample to be largely featureless AGN, and using the QSO evolution model derived for the 2QZ, we predict the median redshift of the sample to be $z=1.1$. This model also reproduces the observed number-magnitude relation of the sample using a renormalisation of the QSO luminosity function, $Φ^* = Φ^*_{\rm \sc qso}/66 \simeq 1.65 \times 10^{-8} $mag$^{-1}$Mpc$^{-3}$. Only $\sim$20 per cent of the objects have a radio flux density of $S_{1.4}>3 $mJy, and further VLA observations at 8.4 GHz place a $5σ$ limit of $S_{8.4} < 0.2$mJy on the bulk of the sample. We postulate that these objects could form a population of radio-weak AGN with weak or absent emission lines, whose optical spectra are indistinguishable from those of BL Lac objects.

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arXiv2001

The 2dF QSO Redshift Survey - VI. Measuring Lambda and Beta from Redshift-space Distortions in the Power Spectrum

When the 2dF QSO Redshift Survey (2QZ) is complete, a powerful geometric test for the cosmological constant will be available. By comparing the clustering along and across the line of sight and modelling the effects of peculiar velocities and bulk motions in redshift space, geometric distortions, which occur if the wrong cosmology is assumed, can be detected. In this paper we investigate the effect of geometric and redshift-space distortions in the power spectrum parallel and perpendicular to the observer's line of sight. Ballinger et al. developed a model to estimate the cosmological constant, $Λ$, and the important parameter $β\approx Ω_m^{0.6}/b$ from these distortions. We apply this model to a detailed simulation of the final 25k 2QZ, produced using the Virgo Consortium's huge {\it Hubble Volume} N-body $Λ$-CDM light cone simulation. We confirm the conclusions of Ballinger et al.; the shape of the redshift-space and geometric distortions are very similar. When all the uncertainties are taken into account we find that only a joint $Λ- β$ constraint is possible. By combining this result with a second constraint based on mass clustering evolution, however, we can make significant progress. We predict that this method should allow us to constrain $β$ to approximately $\pm0.1$, and $Ω_{m}$ to $\pm0.25$ using the final catalogue. We apply the method to the 2QZ catalogue of 10000 QSOs and find that this incomplete catalogue marginally favours a $Λ$ cosmology.

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arXiv2001

The 2dF QSO Redshift Survey - VIII. Absorption systems in the 10k catalogue

We examine the highest S/N spectra from the 2QZ 10k release and identify over 100 new low-ionisation heavy element absorbers; DLA candidates suitable for higher resolution follow-up observations. These absorption systems map the spatial distribution of high-z metals in exactly the same volumes that the foreground 2QZ QSOs themselves sample and hence the 2QZ gives us the unique opportunity to directly compare the two tracers of large scale structure. We examine the cross-correlation of the two populations to see how they are relatively clustered, and, by considering the colour of the QSOs, detect a small amount of dust in these metal systems.

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arXiv2001

The 2dF QSO Redshift Survey - II. Structure and evolution at high redshift

We present a clustering analysis of QSOs over the redshift range z=0.3-2.9. We use a sample of 10558 QSOs taken from the preliminary catalogue of the 2dF QSO Redshift Survey (2QZ). The two-point redshift-space correlation function of QSOs is shown to follow a power law on scales s~1-35h-1Mpc. Fitting a power law to QSO clustering averaged over the redshift interval 0.3 99 per cent confidence level). A redshift dependent bias is required to reconcile QSO clustering observations with theory. A simple biasing model, in which QSOs have cosmologically long lifetimes (or alternatively form in peaks above a constant threshold in the density field) is acceptable in an EdS cosmology, but is only marginally acceptable if Omega_0=0.3 and lambda_0=0.7. Biasing models which assume QSOs form over a range in redshift, based on the Press-Schechter formalism are approximately consistent with QSO clustering evolution (abridged).

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arXiv2001

The 2dF QSO Redshift Survey - V. The 10k catalogue

We present a catalogue comprising over 10000 QSOs covering an effective area of 289.6 sq. degrees, based on spectroscopic observations with the 2-degree Field instrument at the Anglo-Australian Telescope. This catalogue forms the first release of the 2-degree Field QSO Redshift Survey. QSO candidates with 18.25<b_J<20.85 were obtained from a single homogeneous colour-selected catalogue based on APM measurements of UK Schmidt photographic material. The final catalogue will contain approximately 25000 QSOs and will be released to the public at the end of 2002, one year after the observational phase is concluded.

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arXiv2001

First Results from the 2dF QSO redshift survey

We present some initial results from the 2dF QSO redshift survey. The aim of the survey is to produce an optically-selected catalogue of 25000 QSOs over the redshift range 0<z<3 using the 2-degree field at the Anglo-Australian Telescope.

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arXiv1998

The 2dF QSO Redshift Survey

We present preliminary results from the 2-degree Field (2dF) QSO Redshift Survey currently under way at the Anglo-Australian Telescope. This survey aims to determine the redshifts of >25000 QSOs over a redshift range of 0.3<z<3.0 with the primary goal of investigating large-scale structure in the Universe to high redshift and at very large scales (~1000h-1Mpc). We describe the photometric procedure used to select QSO candidates for spectroscopic observation. We then describe results from our first 2dF observations, which have so far measured the redshifts for over 1000 QSOs. We already find a significant detection of clustering and have also found one close pair of QSOs (separation 17'') which are gravitational lens candidates. To keep up to date with the current progress of the survey see: http://msowww.anu.edu.au/~rsmith/QSO_Survey/qso_surv.html

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