69 research outputs found
The SCUBA Bright Quasar Survey II: unveiling the quasar epoch at submillimetre wavelengths
We present results of the first systematic search for submillimetre continuum emission from z=2, radio-quiet, optically-luminous quasars, using the SCUBA/JCMT. We have observed a homogeneous sample of 57 quasars in the redshift range 1.54) redshift. The target sensitivity of the survey (3sigma=10mJy at 850um) was chosen to enable efficient identification of bright submm sources, suitable for detailed follow-up. 9 targets are detected, with fluxes in the range 7-17mJy. Although there is a suggestion of variation of submm detectability between z=2 and z=4, this is consistent with the K-correction of a characteristic far-infrared spectrum. Additionally, the weighted mean fluxes of non-detections at z=2 and z>4 are comparable
Early GRB Optical and Infrared Afterglow Observations with the 2-m Robotic Liverpool Telescope
We present the first optical observations of a Gamma Ray Burst (GRB)
afterglow using the 2-m robotic Liverpool Telescope (LT), which is owned and
operated by Liverpool John Moores University and situated on La Palma. We
briefly discuss the capabilities of LT and its suitability for rapid follow-up
observations of early optical and infrared GRB light curves. In particular, the
combination of aperture, site, instrumentation and rapid response (robotic
over-ride mode aided by telescope's rapid slew and fully-opening enclosure)
makes the LT ideal for investigating the nature of short bursts, optically-dark
bursts, and GRB blast-wave physics in general. We briefly describe the LT's key
position in the RoboNet-1.0 network of robotic telescopes. We present the LT
observations of GRB041006 and use its gamma-ray properties to predict the time
of the break in optical light curve, a prediction consistent with the
observations.Comment: 4 pages, 1 figure, accepted for publication in Il nuovo cimento (4th
Workshop Gamma-Ray Bursts in the Afterglow Era, Rome, 18-22 October 2004
The first Swift X-ray Flash: The faint afterglow of XRF 050215B
We present the discovery of XRF 050215B and its afterglow. The burst was
detected by the Swift BAT during the check-out phase and observations with the
X-ray telescope began approximately 30 minutes after the burst. These
observations found a faint, slowly fading X-ray afterglow near the centre of
the error box as reported by the BAT. Infrared data, obtained at UKIRT after 10
hours also revealed a very faint K-band afterglow. The afterglow appear unusual
since it is very faint, especially in the infrared with K>20 only 9 hours post
burst. The X-ray and infrared lightcurves exhibit a slow, monotonic decay with
alpha=0.8 and no evidence for steepening associated with the jet break to 10
days post burst. We discuss possible explanations for the faintness and slow
decay in the context of present models for the production of X-ray Flashes.Comment: 8 pages, 5 figures, accepted for publication in Ap
Thermal Emission from Warm Dust in the Most Distant Quasars
We report new continuum observations of fourteen z~6 quasars at 250 GHz and
fourteen quasars at 1.4 GHz. We summarize all recent millimeter and radio
observations of the sample of the thirty-three quasars known with
5.71<=z<=6.43, and present a study of the rest frame far-infrared (FIR)
properties of this sample. These quasars were observed with the Max Plank
Millimeter Bolometer Array (MAMBO) at 250 GHz with mJy sensitivity, and 30% of
them were detected. We also recover the average 250 GHz flux density of the
MAMBO undetected sources at 4 sigma, by stacking the on-source measurements.
The derived mean radio-to-UV spectral energy distributions (SEDs) of the full
sample and the 250 GHz non-detections show no significant difference from that
of lower-redshift optical quasars. Obvious FIR excesses are seen in the
individual SEDs of the strong 250 GHz detections, with FIR-to-radio emission
ratios consistent with that of typical star forming galaxies. Most 250
GHz-detected sources follow the L_{FIR}--L_{bol} relationship derived from a
sample of local IR luminous quasars (L_{IR}>10^{12}L_{\odot}), while the
average L_{FIR}/L_{bol} ratio of the non-detections is consistent with that of
the optically-selected PG quasars. The MAMBO detections also tend to have
weaker Ly\alpha emission than the non-detected sources. We discuss possible FIR
dust heating sources, and critically assess the possibility of active star
formation in the host galaxies of the z~6 quasars. The average star formation
rate of the MAMBO non-detections is likely to be less than a few hundred
M_{\odot} yr^{-1}, but in the strong detections, the host galaxy star formation
is probably at a rate of \gtrsim10^{3} M_{\odot} yr^{-1}, which dominates the
FIR dust heating.Comment: 32 pages with 6 figures; ApJ, in press; Added references; Corrected
typo
Herschel-ATLAS: the far-infrared properties and star-formation rates of broad absorption line quasi-stellar objects
We have used data from the Herschel-ATLAS at 250, 350 and 500 \mu m to
determine the far-infrared (FIR) properties of 50 Broad Absorption Line Quasars
(BAL QSOs). Our sample contains 49 high-ionization BAL QSOs (HiBALs) and 1
low-ionization BAL QSO (LoBAL) which are compared against a sample of 329
non-BAL QSOs. These samples are matched over the redshift range 1.5 \leq z <
2.3 and in absolute i-band magnitude over the range -28 \leq M_{i} \leq -24. Of
these, 3 BAL QSOs (HiBALs) and 27 non-BAL QSOs are detected at the > 5 sigma
level. We calculate star-formation rates (SFR) for our individually detected
HiBAL QSOs and the non-detected LoBAL QSO as well as average SFRs for the BAL
and non-BAL QSO samples based on stacking the Herschel data. We find no
difference between the HiBAL and non-BAL QSO samples in the FIR, even when
separated based on differing BAL QSO classifications. Using Mrk 231 as a
template, the weighted mean SFR is estimated to be \approx240\pm21 M_{\odot}
yr^{-1} for the full sample, although this figure should be treated as an upper
limit if AGN-heated dust makes a contribution to the FIR emission. Despite
tentative claims in the literature, we do not find a dependence of {\sc C\,iv}
equivalent width on FIR emission, suggesting that the strength of any outflow
in these objects is not linked to their FIR output. These results strongly
suggest that BAL QSOs (more specifically HiBALs) can be accommodated within a
simple AGN unified scheme in which our line-of-sight to the nucleus intersects
outflowing material. Models in which HiBALs are caught towards the end of a
period of enhanced spheroid and black-hole growth, during which a wind
terminates the star-formation activity, are not supported by the observed FIR
properties.Comment: 11 pages, 4 figures, 4 tables. Accepted for publication in MNRA
Short gamma-ray bursts from SGR giant flares and neutron star mergers: two populations are better than one
âThe definitive version is available at www.blackwell-synergy.com.â 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
X-ray and optical properties of Broad Absorption Line Quasars in the Canada-France-Hawaii Telescope Legacy Survey
We study the X-ray and optical properties of 16 Broad Absorption Line (BAL)
quasars detected in about 3 degree square region common to the wide synoptic
(W-1) component of the Canada-France-HawaiiTelescope Legacy Survey (CFHTLS) and
the XMM Large Scale Structure survey (XMM-LSS). The BAL fraction is found to be
10% in full sample, 7% for the optical colour selected QSOs and as high as 33%
if we consider QSOs selected from their IR colours. The X-ray detected non-BAL
and BAL quasars have a mean observed X-ray-to-optical spectral slope of -1.47
+/- 0.13 and -1.66 +/- 0.17 respectively. We also find that the BAL QSOs have
alpha_ox systematically smaller than what is expected from the relationship
between optical luminosity and alpha_ox as derived from our sample. Based on
this, we show, as already reported in the literature for quasars with high
optical luminosities, our new sample of BAL QSOs have X-ray luminosity a factor
of three smaller than what has been found for non-BAL QSOs with similar optical
luminosities. Comparison of hardness ratio of the BAL and non-BAL QSOs suggests
a possible soft X-ray weakness of BAL QSOs. Combining our sample, of relatively
fainter QSOs, with others from the literature we show that larger balnicity
index (BI) and maximum velocity (V_max) of the C IV absorption are correlated
with steeper X-ray to optical spectral index. We argue that this is most likely
a consequence of the existence of a lower envelope in the distribution of BI
(or V_max) values versus optical luminosity. Our results thus show that the
previously known X-ray weakness of BAL QSOs extends to lower optical
luminosities as well.Comment: 12 pages, 12 figures, 3 tables, accepted for publication in MNRA
CO emission and associated HI absorption from a massive gas reservoir surrounding the z=3 radio galaxy B3 J2330+3927
We present results of a comprehensive multi-frequency study of the radio
galaxy B3 J2330+3927. The 1.9" wide radio source, consisting of 3 components,
is bracketed by 2 objects in our Keck K-band image. Optical and near-IR Keck
spectroscopy of these two objects yield z=3.087+-0.004. The brightest (K=18.8)
object has a standard type II AGN spectrum, and is the most likely location of
the AGN, which implies a one-sided jet radio morphology. Deep 113 GHz
observations with the IRAM Plateau de Bure Interferometer reveal CO J=4-3
emission, which peaks at the position of the AGN. The CO line is offset by 500
km/s from the systemic redshift of the AGN, but corresponds very closely to the
velocity shift of an associated HI absorber seen in Lya. This strongly suggests
that both originate from the same gas reservoir surrounding the AGN host
galaxy. Simultaneous 230 GHz interferometer observations find a ~3x lower
integrated flux density when compared to single dish 250 GHz observations with
MAMBO at the IRAM 30m telescope. This can be interpreted as spatially resolved
thermal dust emission at scales of 0.5" to 6". Finally, we present a tau <1.3%
limit to the HI 21 cm absorption against the radio source, which represents the
seventh non-detection out of 8 z>2 radio galaxies observed to date with the
WSRT. We present mass estimates for the atomic, neutral, and ionized hydrogen,
and for the dust, ranging from M(HI)=2x10^7 M_Sun derived from the associated
HI absorber in Lya up to M(H_2)=7x10^{10} M_Sun derived from the CO emission.
This indicates that the host galaxy is surrounded by a massive reservoir of gas
and dust. The K-band companion objects may be concentrations within this
reservoir, which will eventually merge with the central galaxy hosting the AGN.Comment: 16 Pages, including 11 PostScript figures. Accepted for publication
in Astronomy & Astrophysic
A supernova origin for dust in a high-redshift quasar
Interstellar dust plays a crucial role in the evolution of the Universe by
assisting the formation of molecules, by triggering the formation of the first
low-mass stars, and by absorbing stellar ultraviolet-optical light and
subsequently re-emitting it at infrared/millimetre wavelengths. Dust is thought
to be produced predominantly in the envelopes of evolved (age >1 Gyr), low-mass
stars. This picture has, however, recently been brought into question by the
discovery of large masses of dust in the host galaxies of quasars at redshift
z>6, when the age of the Universe was less than 1 Gyr. Theoretical studies,
corroborated by observations of nearby supernova remnants, have suggested that
supernovae provide a fast and efficient dust formation environment in the early
Universe. Here we report infrared observations of a quasar at redshift 6.2,
which are used to obtain directly its dust extinction curve. We then show that
such a curve is in excellent agreement with supernova dust models. This result
demonstrates a supernova origin for dust in this high-redshift quasar, from
which we infer that most of the dust at high redshifts has probably the same
origin.Comment: To Appear in Nature, September 30, 200
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