The SCUBA Bright Quasar Survey (SBQS): 850micron observations of the z>4 sample

We present initial results of a new, systematic search for massive star-formation in the host galaxies of the most luminous and probably most massive z>=4 radio-quiet quasars (M(B) 10^13Lsun). A total of 38 z>=4 radio-quiet quasars have been observed at the JCMT using SCUBA at 850microns: 8 were detected (>3sigma) with S(850microns)>~ 10mJy (submillimetre-loud). The new detections almost triple the number of optically selected, submillimetre-loud z>~4 radio-quiet quasars known to date. We include a detailed description of how our quasar sample is defined in terms of radio and optical properties. There is no strong evidence for trends in either detectability or 850microns flux with absolute magnitude, M(B). We find that the weighted mean flux of the undetected sources is 2.0 +/- 0.6mJy, consistent with an earlier estimate of \~3mJy based on more sensitive observations of a sample z>~4 radio-quiet quasars (McMahon et al., 1999). This corresponds to an inferred starformation rate of \~1000Msun/yr, similar to Arp220. The typical starformation timescale for the submillimetre-bright sources is ~1Gyr, 10 times longer than the typical accretion-driven e-folding timescale of ~5x10^7 years. Our 850micron detection of the z=4.4 quasar PSS J1048+4407 when analysed in conjunction with 1.2mm single-dish and interferometric observations suggests that this source is resolved on angular scales of 1-2" (6-12 kpc). In addition, we present a new optical spectrum of this source, identifying it as a broad absorption line (BAL) quasar. The new redshift is outside that covered in a recent CO line search by Guilloteau et al., (1999), highlighting the need for accurate redshifts for the obervation and interpretation of high-redshift line studies.Comment: 16 pages, 11 figures. Accepted by Monthly Notices of the Royal Astronomical Societ

Short gamma-ray bursts from SGR giant flares and neutron star mergers: two populations are better than one

‘The definitive version is available at www.blackwell-synergy.com.’ Copyright Blackwell Publishing. DOI: 10.1111/j.1365-2966.2009.14610.xThere is increasing evidence of a local population of short duration gamma-ray bursts (sGRB), but it remains to be seen whether this is a separate population to higher redshift bursts. Here we choose plausible luminosity functions (LFs) for both neutron star binary mergers and giant flares from soft gamma repeaters (SGR), and combined with theoretical and observed Galactic intrinsic rates we examine whether a single progenitor model can reproduce both the overall Burst and Transient Source Experiment (BATSE) sGRB number counts and a local population, or whether a dual progenitor population is required. Though there are large uncertainties in the intrinsic rates, we find that at least a bimodal LF consisting of lower and higher luminosity populations is required to reproduce both the overall BATSE sGRB number counts and a local burst distribution. Furthermore, the best-fitting parameters of the lower luminosity population agree well with the known properties of SGR giant flares, and the predicted numbers are sufficient to account for previous estimates of the local sGRB population.Peer reviewe

Submillimetre observations of z > 6 quasars

Peer reviewe

Two populations are better than one: Short gamma-ray bursts from SGR giant flares and NS-NS mergers

With a peak luminosity of ~ 1047 erg s-1 the December 27th 2004 giant flare from SGR1806-20 would have been visible by BATSE (the Burst and Transient Source Experiment) out to ≈50 Mpc. It is thus plausible that some fraction of the short duration Gamma-Ray Bursts (sGRBs) in the BATSE catalogue were due to extragalactic magnetar giant flares. According to the most widely accepted current models, the remaining BATSE sGRBs were most likely produced by compact object (neutron star-neutron star or neutron star-black hole) mergers with intrinsically higher luminosities [1]. Previously, by examining correlations on the sky between BATSE sGRBs and galaxies within 155 Mpc, we placed limits on the proportion of nearby sGRBs [3]. Here, we examine the redshift distribution of sGRBs produced by assuming both one and two populations of progenitor with separate Luminosity Functions (LFs). Using the local Galactic SGR giant flare rate and theoretical NS-NS merger rates evolved according to well-known Star Formation Rate parameterisations, we constrain the predicted distributions by BATSE sGRB overall number counts. We show that only a dual population consisting of both SGR giant flares and NS-NS mergers can reproduce the likely local distribution of sGRBs as well as the overall number counts. In addition, the best fit LF parameters of both sub-populations are in good agreement with observed luminosities

How common are long gamma-ray bursts in the local Universe?

The two closest gamma-ray bursts so far detected (GRBs 980425 and 060218) were both under-luminous, spectrally soft, long-duration bursts with smooth, single-peaked light curves. Only of the order of 100 GRBs have measured redshifts, and there are, for example, 2704 GRBs in the BATSE (Burst and Transient Source Experiment) catalogue alone. It is therefore plausible that other nearby GRBs have been observed but not identified as being relatively nearby. Here we search for statistical correlations between BATSE long-duration GRBs and galaxy samples with recession velocities v <= 11 000 km s(-1) (z = 0.0367, approximate to 155 Mpc) selected from two catalogues of nearby galaxies. We also examine the correlations using burst subsamples restricted to those with properties similar to the two known nearby bursts. Our results show correlation of the entire long-GRB sample to remain consistent with zero out to the highest radii considered whereas a subsample selected to be low fluence, spectrally soft, with smooth single-peaked light curves (177 bursts), demonstrates increased correlation with galaxies within approximate to 155 Mpc. The measured correlation (28 +/- 16 per cent of the sample) suggests that BATSE observed between two and nine long-duration GRBs per year similar to, and from within similar distances to, GRBs 980425 and 060218. This implies an observed local rate density (to BATSE limits) of 700 +/- 360 Gpc(-3) yr(-1) within 155 Mpc

Quasars as probes of the submillimetre cosmos at z > 5 - I. Preliminary SCUBA photometry --

The definitive version is available at www.blackwell-synergy.com '.--Copyright Blackwell PublishingPeer reviewe