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B. J. Boyle

Publications and source records attributed to B. J. Boyle.

At least 19 recordsLinked to original sources
arXiv2007

Extending the infrared radio correlation

Co-addition of deep (rms about 30 microJy) 20 cm data obtained with the Australia Telescope Compact Array at the location of Spitzer Wide field survey (SWIRE) sources has yielded statistics of radio source counterparts to faint 24 micron sources in stacked images with rms < 1 microJy. We confirm that the infrared-radio correlation extends to f(24micron) = 100 microJy but with a significantly lower coefficient, f (20cm) = 0.039 f(24micron) (or q24 = 1.39) than hitherto reported. We postulate that this may be due to a change in the mean q24 value ratio for objects with f(24micron) < 1mJy.

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arXiv2006

The 2dF BL Lac Survey II

We report on our further analysis of the expanded and revised sample of potential BL Lac objects (the 2BL) optically identified from two catalogues of blue-selected (UV excess) point sources, the 2dF and 6dF QSO Redshift Surveys (2QZ and 6QZ). The 2BL comprises 52 objects with no apparent proper motion, over the magnitude range 16.0 < bj< 20.0. Follow-up high signal-to-noise spectra of 36 2BL objects and NIR imaging of 18 objects, together with data for 19 2BL objects found in the Sloan Digital Sky survey (SDSS), show 17 objects to be stellar, while a further 16 objects have evidence of weak, broad emission features, although for at least one of these the continuum level has clearly varied. Classification of three objects remains uncertain,with NIR results indicating a marked reduction in flux as compared to SDSS optical magnitudes. Seven objects have neither high signal-to-noise spectra nor NIR imaging. Deep radio observations of 26 2BL objects at the VLA resulted in only three further radio-detections, however none of the three is classed as a featureless continuum object. Seven 2BL objects with a radio detection are confirmed as candidate BL Lac objects while one extragalactic (z=0.494) continuum object is undetected at radio frequencies. One further radio-undetected object is also a potential BL Lac candidate. However it would appear that there is no significant population of radio-quiet BL Lac objects.

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arXiv2006

The evolution of host mass and black hole mass in QSOs from the 2dF QSO Redshift Survey

We investigate the relation between the mass of super-massive black holes (Mbh) in QSOs and the mass of the dark matter halos hosting them (Mdh). We measure the widths of broad emission lines (Mgii lambda 2798, Civ lambda 1549) from QSO composite spectra as a function of redshift. These widths are then used to determine virial black hole mass estimates. We compare our virial black hole mass estimates to dark matter halo masses for QSO hosts derived by Croom et al. (2005) based on measurements of QSO clustering. This enables us to trace the Mbh-Mdh relation over the redshift range z=0.5 to 2.5. We calculate the mean zero-point of the Mbh-Mdh relation to be Mbh=10^(8.4+/-0.2)Msun for an Mdh=10^(12.5)Msun. These data are then compared with several models connecting Mbh and Mdh as well as recent hydrodynamical simulations of galaxy evolution. We note that the flux limited nature of QSO samples can cause a Malmquist-type bias in the measured zero-point of the Mbh-Mdh relation. The magnitude of this bias depends on the scatter in the Mbh-Mdh relation, and we reevaluate the zero-point assuming three published values for this scatter. (abridged)

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arXiv2006

The Radial Velocity Experiment (RAVE): first data release

We present the first data release of the Radial Velocity Experiment (RAVE), an ambitious spectroscopic survey to measure radial velocities and stellar atmosphere parameters (temperature, metallicity, surface gravity) of up to one million stars using the 6dF multi-object spectrograph on the 1.2-m UK Schmidt Telescope of the Anglo-Australian Observatory (AAO). The RAVE program started in 2003, obtaining medium resolution spectra (median R=7,500) in the Ca-triplet region ($λλ$ 8,410--8,795 Å) for southern hemisphere stars drawn from the Tycho-2 and SuperCOSMOS catalogs, in the magnitude range 9<I<12. The first data release is described in this paper and contains radial velocities for 24,748 individual stars (25,274 measurements when including re-observations). Those data were obtained on 67 nights between 11 April 2003 to 03 April 2004. The total sky coverage within this data release is $\sim$4,760 square degrees. The average signal to noise ratio of the observed spectra is 29.5, and 80% of the radial velocities have uncertainties better than 3.4 km/s. Combining internal errors and zero-point errors, the mode is found to be 2 km/s. Repeat observations are used to assess the stability of our radial velocity solution, resulting in a variance of 2.8 km/s. We demonstrate that the radial velocities derived for the first data set do not show any systematic trend with color or signal to noise. The RAVE radial velocities are complemented in the data release with proper motions from Starnet 2.0, Tycho-2 and SuperCOSMOS, in addition to photometric data from the major optical and infrared catalogs (Tycho-2, USNO-B, DENIS and 2MASS). The data release can be accessed via the RAVE webpage: http://www.rave-survey.org.

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arXiv2005

The 2dF QSO Redshift Survey - XV. Correlation analysis of redshift-Space distortions

We analyse the redshift-space (z-space) distortions of QSO clustering in the 2dF QSO Redshift Survey (2QZ). To interpret the z-space correlation function, xi(sigma,pi), we require an accurate model for the QSO real-space correlation function, xi(r). Although a single power-law xi(r) model fits the projected correlation function (wp(sigma)) at small scales, it implies somewhat too shallow a slope for both wp(sigma) and the z-space correlation function, xi(s), at larger scales > 20 h^(-1) Mpc. Motivated by the form for xi(r) seen in the 2dF Galaxy Redshift Survey (2dFGRS) and in standard LCDM predictions, we use a double power-law model for xi(r) which gives a good fit to xi(s) and wp(sigma). The model is parametrized by a slope of gamma=1.45 for 1<r<10 h^(-1) Mpc and gamma=2.30 for 10<r<40 h^(-1) Mpc. As found for 2dFGRS, the value of beta determined from the ratio of xi(s)/xi(r) depends sensitively on the form of xi(r) assumed. With our double power-law form for xi(r), we measure beta(z=1.4)=0.32(+0.09)(-0.11). Assuming the same model for xi(r) we then analyse the z-space distortions in the 2QZ xi(sigma,pi) and put constraints on the values of Omega m and beta(z=1.4), using an improved version of the method of Hoyle et al. The constraints we derive are Omega m=0.35(+0.19)(-0.13), beta(z=1.4)=0.50(+0.13)(-0.15), in agreement with our xi(s)/ξ(r) results at the ~1 sigma level.

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arXiv2005

200 Mpc Sized Structure in the 2dF QSO Redshift Survey

The completed 2dF QSO Redshift (2QZ) Survey has been used to search for extreme large-scale cosmological structure (around 200 Mpc) over the redshift range 0 100Mpc are in the linear or only weakly non-linear regime and do not represent collapsed non-linear structures. We compare the measurements with the expectation of a standard LCDM model by measuring the variance of counts in cells and find that, provided the distribution of QSOs on large scales exhibits a mild bias with respect to the distribution of dark matter, the observed fluctuations are found to be in good agreement with the model. There is no evidence on such scales for any extreme structures that might require, for example, departures from the assumption of Gaussian initial perturbations. Thus the power-spectrum derived from the 2QZ Survey appears to provide a complete description of the distribution of QSOs. The amount of bias and its redshift dependence that is required is consistent with that found from studying the clustering of 2QZ QSOs on 10 Mpc scales, and may be adequately described by an approximately redshift-invariant power spectrum with normalisation sigma_8=1.0 corresponding to a bias at z=0 of b=1.1 rising to b=2 at the survey's mean redshift z=1.5.

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arXiv2005

On Statistical Lensing and the Anti-Correlation Between 2dF QSOs and Foreground Galaxies

We cross-correlate APM and SDSS galaxies with background QSOs from the 2dF QSO Redshift Survey, and detect a significant (2.8sigma) anti-correlation. The lack of a signal between 2dF stars and our galaxy samples suggests the anti-correlation is not due to a systematic error. The possibility that dust in the foreground galaxies could produce the anti-correlation is marginally rejected, at the 2sigma level through consideration of QSO colours. It is possible that dust that obscures QSOs without reddening them, or preferentially discards reddened QSOs from the 2QZ sample, could produce such an anti-correlation, however, such models are at odds with the positive QSO-galaxy correlations found at bright magnitudes by other authors. Our detection of a galaxy-QSO anti-correlation is consistent with statistical lensing theory. When combined with earlier results that have reported a positive galaxy-QSO correlation, a consistent, compelling picture emerges that spans faint and bright QSO samples showing positive or negative correlations according to the QSO N(m) slope. We find that galaxies are highly anti-biased on small scales. We consider two models that use different descriptions of the lensing matter and find they yield consistent predictions for the strength of galaxy bias on 0.1Mpc/h scales of b~0.1 (for LCDM). Whilst the slope of our power-law fit to the QSO-galaxy cross-correlation does not rule out linear bias, when we compare our measurement of b on 100 kpc/h scales to independent methods that determine b~1 on Mpc/h scales, we conclude that bias, on these small scales, is scale-dependent. These results indicate more mass, at least on the 100 kpc/h scales probed, than predicted by simple LCDM biasing prescriptions, and can thus constrain halo occupation models of the galaxy distribution.

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arXiv2005

Radio-quiet objects in the 2QZ survey

Co-addition of blank-field FIRST data at the location of over 8000 QSOs in the 2QZ survey has yielded statistical detections of radio quiet QSOs with median flux levels of 20-40microJy. We show that the total radio flux of radio-quiet QSOs in the 2QZ is consistent with a smooth extrapolation of the 2QZ radio-loud QSO number-flux distribution based on the slope of the relation flattening near the FIRST flux limit. However, we are unable to distinguish a smooth extrapolation of the luminosity function to faint levels from a bimodal luminosity function with a break close to or below the FIRST radio detection limit. We also demonstrate that the redshift dependence of the median radio-to-optical spectral index for these radio quiet QSOs is consistent with that obtained for individual radio-loud 2QZ QSOs detected by FIRST.

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arXiv2004

The 2dF QSO Redshift Survey - XIV. Structure and evolution from the two-point correlation function

We present a clustering analysis of QSOs using over 20000 objects from the final catalogue of the 2dF QSO Redshift Survey (2QZ), measuring the z-space correlation function, xi(s). When averaged over the range 0.3<z<2.2 we find that xi(s) is flat on small scales, steepening on scales above ~25h-1Mpc. In a WMAP/2dF cosmology we find a best fit power law with s_0=5.48+0.42-0.48h-1Mpc and gamma=1.20+-0.10 on scales s=1-25h-1Mpc. A CDM model assuming WMAP/2dF cosmological parameters is a good description of the QSO xi(s) after accounting for non-linear clustering and z-space distortions, and a linear bias of b_qso(z=1.35)=2.02+-0.07. We subdivide the 2QZ into 10 redshift intervals from z=0.53 to 2.48 and find a significant increase in clustering amplitude at high redshift in the WMAP/2dF cosmology. We derive the bias of the QSOs which is a strong function of redshift with b_qso(z=0.53)=1.13+-0.18 and b_qso(z=2.48)=4.24+-0.53. We use these bias values to derive the mean dark matter halo (DMH) mass occupied by the QSOs. At all redshifts 2QZ QSOs inhabit approximately the same mass DMHs with M_DH=(3.0+-1.6)x10^12h-1M_sun, which is close to the characteristic mass in the Press-Schechter mass function, M*, at z=0. If the relation between black hole (BH) mass and M_DH or host velocity dispersion does not evolve, then we find that the accretion efficiency (L/L_edd) for L* QSOs is approximately constant with redshift. Thus the fading of the QSO population from z~2 to 0 appears to be due to less massive BHs being active at low redshift. We apply different methods to estimate, t_qso, the active lifetime of QSOs and constrain this to be in the range 4x10^6-6x10^8 years at z~2. (Abridged).

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arXiv2004

2QZJ215454.3-305654: a radio-quiet BL Lac object or lineless QSO?

High signal-to-noise spectroscopy has established a redshift of z=0.494 for the source 2QZJ215454.3-305654, originally selected from the 2dF/6dF QSO Redshift Surveys as one of 45 candidate BL Lac objects displaying a featureless continuum at optical wavelengths. Radio observations using the Australia Telescope Compact Array at 1.4 GHz place a 3σupper limit on the object's radio flux density of approx 0.14mJy. The radio-to-optical flux ratio of this object is thus more than 7 times lower than the lowest such ratio observed in BL Lac objects. While the optical properties of 2QZJ215454.3-305654 are consistent with a BL Lac identification, the lack of radio and/or X-ray emission is not. It is uncertain whether this object is an AGN dominated by optical continuum emission from an accretion disk, or is similar to a BL Lac object with optical nonthermal emission from a relativistic jet.

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arXiv2004

The 2dF QSO Redshift Survey - XII. The spectroscopic catalogue and luminosity function

We present the final catalogue of the 2dF QSO Redshift Survey (2QZ), based on Anglo-Australian Telescope 2dF spectroscopic observations of 44576 colour-selected (u b_J r) objects with 18.25<b_J<20.85 selected from APM scans of UK Schmidt Telescope (UKST) photographic plates. The 2QZ comprises 23338 QSOs, 12292 galactic stars (including 2071 white dwarfs) and 4558 compact narrow-emission-line galaxies. We obtained a reliable spectroscopic identification for 86 per cent of objects observed with 2dF. We also report on the 6dF QSO Redshift Survey (6QZ), based on UKST 6dF observations of 1564 brighter 16<b_J<18.25 sources selected from the same photographic input catalogue. In total, we identified 322 QSOs spectroscopically in the 6QZ. The completed 2QZ is, by more than a factor 50, the largest homogeneous QSO catalogue ever constructed at these faint limits (b_J<20.85) and high QSO surface densities (35 QSOs deg^-2). As such it represents an important resource in the study of the Universe at moderate-to-high redshifts. As an example of the results possible with the 2QZ, we also present our most recent analysis of the optical QSO luminosity function and its cosmological evolution with redshift. For a flat, Omega_m=0.3 and Omega_lam=0.7, Universe, we find that a double power law with luminosity evolution that is exponential in look-back time, t, of the form L*(z) exp(6.15t), equivalent to an e-folding time of 2Gyr, provides an acceptable fit to the redshift dependence of the QSO luminosity function over the range 0.4 < z < 2.1 and M_bJ<-22.5. Evolution described by a quadratic in redshift is also an acceptable fit, with L*(z)~10^(1.39z-0.29z^2).

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arXiv2003

The XMM-Newton/2dF survey - II. The nature of X-ray faint optically bright X-ray sources

In this paper we investigate the properties of low X-ray-to-optical flux ratio sources detected in a wide area (2.5deg^2) shallow (f(0.5-8keV)~10e-14cgs) XMM-Newton survey. We find a total of 26 sources (5% of the total X-ray selected population) with log f_X/f_{opt}<-0.9 to the above flux limit. Optical spectroscopy is available for 20 of these low X-ray-to-optical flux ratio objects. Most of them are found to be associated with Galactic stars (total of 8) and broad line AGNs (total of 8).We also find two sources with optical spectra showing absorption and/or narrow emission lines and X-ray/optical properties suggesting AGN activity. Another two sources are found to be associated with low redshift galaxies with narrow emission line optical spectra, X-ray luminosities L_X(0.5-8keV)~10e41cgs and logf_X/f_opt ~ -2 suggesting `normal' star-forming galaxies. Despite the small number statistics the sky density of `normal' X-ray selected star-forming galaxies at the flux limit of the present sample is low consistent with previous ROSAT HRI deep surveys. Also, the number density estimated here is in good agreement with both the logN-logS of `normal' galaxies in the Chandra Deep Field North (extrapolated to bright fluxes) and model predictions based on the X-ray luminosity function of local star-forming galaxies.

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arXiv2003

The 2dF QSO Redshift Survey - XIII. A Measurement of Lambda from the QSO Power Spectrum

We report on measurements of the cosmological constant, Lambda, and the redshift space distortion parameter beta=Omega_m^0.6/b, based on an analysis of the QSO power spectrum parallel and perpendicular to the observer's line of sight, from the final catalogue of the 2dF QSO Redshift Survey. We derive a joint Lambda - beta constraint from the geometric and redshift-space distortions in the power spectrum. By combining this result with a second constraint based on mass clustering evolution, we break this degeneracy and obtain strong constraints on both parameters. Assuming a flat cosmology and a Lambda cosmology r(z) function to convert from redshift into comoving distance, we find best fit values of Omega_Lambda=0.71^{+0.09}_{-0.17} and beta(z~1.4)=0.45^{+0.09}_{-0.11}. Assuming instead an EdS cosmology r(z) we find that the best fit model obtained, with Omega_Lambda=0.64^{+0.11}_{-0.16} and beta(z~1.4)=0.40^{+0.09}_{-0.09}, is consistent with the Lambda r(z) results, and inconsistent with a Lambda=0 flat cosmology at over 95 per cent confidence.

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arXiv2003

Possible arcminute-separation gravitational lensed QSOs in the 2dF QSO survey

We report the possible discovery of multiple gravitationally-lensed images of QSOs with angular separations on arcminute scales. The QSOs were selected from the completed 2dF QSO survey as having redshifts and optical colours which are statistically consistent. In this paper we present higher-quality optical spectra of the candidates and discuss the likelihood of their genuinely being systems lensed by massive clusters of galaxies. From a comparison of the spectra it appears that up to six pairs of QSOs may be lensed multiple images, although the true number may be less than that and further observations should be undertaken to amass more evidence and to detect the lensing clusters. Two of the candidates may be associated with low redshift clusters of galaxies.

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arXiv2003

The XMM-Newton/2dF survey I: X-ray properties of normal galaxies

This paper explores the X-ray properties of `normal' galaxies using a shallow XMM-Newton survey covering an area of ~1.5deg2. The X-ray survey overlaps with the 2dF Galaxy Redshift Survey. Compared with previous studies this has the advantage of high quality spectra and spectral classifications to bj=19.4. Moreover, sources with optical spectra revealing powerful AGNs can easily be discarded from the normal galaxy sample used here. In particular, we present stacking analysis results for 200 galaxies from the 2dFGRS at =0.1. We detect a strong signal for the whole sample (~6sigma) in the soft 0.5-2keV band corresponding to a flux of ~7*10^-16cgs and a luminosity of ~2*10^40cgs. A statistically significant signal is also detected for both the early and late galaxy sub-samples with X-ray luminosities of ~3*10^40 and ~5*10^39cgs respectively. In contrast, no signal is detected in the hard 2-8keV band for any of the above samples. The mean L_X/L_B ratio of the spiral galaxy sample is consistent with both local (<100Mpc) and distant (z~1) samples suggesting little or no evolution of the X-ray emission mechanisms relative to the optical. The 0.5-2keV XRB contribution of the spiral galaxy sub-sample at z~0.1 is estimated to be 0.4% in broad agreement with the XRB fractions estimated in previous studies.Assuming that star-forming galaxies evolve with redshift as (1+z)^{k} the present data combined with previous studies suggest k<3. The k values are constrained by the relatively low fraction of the soft X-ray background that remains unresolved by deep surveys (6-26%). The mean X-ray emissivity of spiral galaxies at z~0.1 is also estimated and is found to be consistent within the uncertainties with that of local HII galaxy samples.

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arXiv2003

Emission line widths and QSO black hole mass estimates from the 2dF QSO Redshift Survey

We have used composite spectra generated from more than 22000 QSOs observed in the course of the 2dF and 6dF QSO Redshift Surveys to investigate the relationship between the velocity width of emission lines and QSO luminosity. We find that the velocity width of the broad emission lines Hbeta, Hgamma, MgII, CIII] and CIV are correlated with the continuum luminosity, with a significance of more than 99 per cent. Of the major narrow emission lines ([OIII] 5007, [OII] 3727, NeIII 3870 and NeV 3426) only [OIII] exhibits a significant correlation between line width and luminosity. Assuming that the gas is moving in Keplerian orbits and that the radius of the broad line region is related to the QSO continuum luminosity, we use the velocity widths of the broad lines to derive average black hole masses for the QSOs contributing to the composite spectra. The resultant QSO mass-luminosity relationship is consistent with M ~ L^0.97+-0.16. We find that the correlation between line width and redshift, if present, must be weak, and only CIV shows significant evidence of evolution. This enables us to constrain the redshift evolution of the black hole mass-luminosity ratio to be ~(1+z)^beta with beta ~< 1, much less than the ~(1+z)^3 evolution seen in QSO luminosity evolution. Assuming that the motion of the broad line region gas is Keplerian and that its radius depends on the QSO luminosity, our models indicate that the observed weak redshift dependence is too small for the observed QSO luminosity function to be due to the evolution of a single long-lived population of sources.

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arXiv2003

Ghosts of the Milky Way: a search for topology in new quasar catalogues

We revisit the possibility that we inhabit a compact multi-connected flat, or nearly-flat, Universe. Analysis of COBE data has shown that, for such a case, the size of the fundamental domain must be a substantial fraction of the horizon size. Nevertheless, there could be several copies of the Universe within the horizon. If the Milky Way was once a quasar we might detect its `ghost' images. Using new large quasar catalogues we repeat the search by Fagundes & Wichoski for antipodal quasar pairs. By applying linear theory to account for the peculiar velocity of the local group, we are able to narrow the search radius to 134 arcsec. We find seven candidate antipodal quasar pairs within this search radius. However, a similar number would be expected by chance. We argue that, even with larger quasar catalogues, and more accurate values of the cosmological parameters, it is unlikely to be possible to identify putative ghost pairs unambiguously, because of the uncertainty of the correction for peculiar motion of the Milky Way.

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