The sub-millimeter properties of broad absorption line quasars

We have carried out the first systematic survey of the sub-millimeter properties of broad absorption line (BAL) quasars. 30 BAL quasars drawn from a homogeneously selected sample from the Sloan Digital Sky Survey at redshifts 2<z<2.6 were observed with the SCUBA array at the JCMT to a typical rms sensitivity of 2.5 mJy. Eight quasars were detected at > 2 sigma significance, four of which are at > 3 sigma significance. The far-infrared luminosities of these quasars are > 10^{13} L_solar. There is no correlation of sub-millimeter flux with either the strength of the broad absorption feature or with absolute magnitude in our sample. We compare the sub-millimeter flux distribution of the BAL quasar sample with that of a sample of quasars which do not show BAL features in their optical spectra and find that the two are indistinguishable. BAL quasars do not have higher sub-millimeter luminosities than non-BAL quasars. These findings are consistent with the hypothesis that all quasars would contain a BAL if viewed along a certain line-of-sight. The data are inconsistent with a model in which the BAL phenomenon indicates a special evolutionary stage which co-incides with a large dust mass in the host galaxy and a high sub-millimeter luminosity. Our work provides constraints on alternative evolutionary explanations of BAL quasars.Comment: 8 pages, 2 figures, ApJ, in pres

The Faintness of the 158 um [CII] Transition in the z=6.42 Quasar SDSS J1148+5251

We report the non-detection of the [CII] 157.74 um transition in the z=6.42 quasar SDSS J1148+5251 after 37.5 hours of integration with the James Clerk Maxwell Telescope. This transition is the main cooling line of the star-forming interstellar medium, and usually the brightest FIR line in galaxies. Our observed RMS of 1.3 mK in the Ta* scale translates to L([CII])<2.6 x 10^9 Lsun. Using a recent estimate of the far-infrared continuum of this quasar, we derive for SDSS J1148+5251 L([CII])/L(FIR)<5 x 10^-4, a ratio similar to that observed in local ultra-luminous infrared galaxies but considerably smaller than what is typical in nearby normal and starburst galaxies. This indicates that the small L([CII])/L(FIR) ratio observed locally in luminous far-infrared objects also persists at the highest redshifts.Comment: Five pages, one figure, accepted by the Astrophysical Journal Letter

First results from the Canada-France High-z Quasar Survey: Constraints on the z=6 quasar luminosity function and the quasar contribution to reionization

We present preliminary results of a new quasar survey being undertaken with multi-colour optical imaging from the Canada-France-Hawaii Telescope. The current data consists of 3.83 sq. deg. of imaging in the i' and z' filters to a 10 sigma limit of z'<23.35. Near-infrared photometry of 24 candidate 5.7<z<6.4 quasars confirms them all to be low mass stars including two T dwarfs and four or five L dwarfs. Photometric estimates of the spectral type of the two T dwarfs are T3 and T6. We use the lack of high-redshift quasars in this survey volume to constrain the z=6 quasar luminosity function. For reasonable values of the break absolute magnitude M*_1450 and faint-end slope alpha, we determine that the bright-end slope beta>-3.2 at 95% confidence. We find that the comoving space-density of quasars brighter than M_1450=-23.5 declines by a factor >25 from z=2 to z=6, mirroring the decline observed for high-luminosity quasars. We consider the contribution of the quasar population to the ionizing photon density at z=6 and the implications for reionization. We show that the current constraints on the quasar population give an ionizing photon density <<30% that of the star-forming galaxy population. We conclude that active galactic nuclei make a negligible contribution to the reionization of hydrogen at z~6.Comment: 9 pages, 6 figures, ApJ, in pres

Molecular gas observations of the reddened quasar 3C 318

3C 318 is a z=1.574 radio-loud quasar. The small physical size of its radio jets indicate that these jets were triggered relatively recently. In addition to the ultraviolet continuum emission being reddened by dust, detections with IRAS and SCUBA show it to have an exceptionally high far-infrared luminosity. We present CO(2-1) observations of 3C 318 made with the IRAM Plateau de Bure Interferometer. We detect CO(2-1) emission with a FWHM=200 km/s at a signal-to-noise ratio of 5.4. There is evidence for positional (~ 20 kpc) and velocity (~ -400 km/s) offsets between the molecular gas and the quasar which may be due to the quasar experiencing a major merger. The mass of molecular gas inferred from our observations is M_{H_2}=(3.0 +/- 0.6) x 10^{10} M_sun. This molecular gas mass is comparable to that in sub-mm-selected galaxies at similar redshifts. The large molecular gas mass is consistent with the primary source of heating for the cool dust in this quasar to be massive star formation with a star formation rate of 1700 M_sun/yr and a gas depletion timescale of 20 Myr. Our observations support the idea that star formation episodes and jet triggering can be synchronised.Comment: 4 pages, 3 b/w figures, AJ, in pres

The SCUBA 8-mJy survey - II: Multiwavelength analysis of bright sub-mm sources

We present the results of a multi-wavelength study of the 19 most significant sub-mm sources detected in the SCUBA 8-mJy survey. As described in Scott et al. (2001), this survey covers ~260 arcmin^2 using the sub-millimetre camera SCUBA, to a limiting source detection limit S(850um) ~ 8 mJy. One advantage of this relatively bright flux-density limit is that accurate astrometric positions are potentially achievable for every source using existing radio and/or mm-wave interferometers. However, an associated advantage is that SED-based redshift constraints should be more powerful than in fainter sub-mm surveys. Here we therefore exploit the parallel SCUBA 450um data, in combination with existing radio and ISO data at longer and shorter wavelengths to set constraints on the redshift of each source. We also analyse new and existing optical and near-infrared imaging of our SCUBA survey fields to select potential identifications consistent with these constraints. Our derived SED-based redshift constraints, and the lack of statistically significant associations with even moderately bright galaxies allow us to conclude that all 19 sources lie at z > 1, and at least half of them apparently lie at z > 2.Comment: 14 pages (including 30 figures and 4 tables) accepted by MNRAS. Figure 1 and 2 and a higher quality version of the full paper are available at http://astro.ic.ac.uk/~mfox

Ionization near-zones associated with quasars at z ~ 6

We analyze the size evolution of HII regions around 27 quasars between z=5.7 to 6.4 ('quasar near-zones' or NZ). We include more sources than previous studies, and we use more accurate redshifts for the host galaxies, with 8 CO molecular line redshifts and 9 MgII redshifts. We confirm the trend for an increase in NZ size with decreasing redshift, with the luminosity normalized proper size evolving as: R_{NZ,corrected} = (7.4 \pm 0.3) - (8.0 \pm 1.1) \times (z-6) Mpc. While derivation of the absolute neutral fraction remains difficult with this technique, the evolution of the NZ sizes suggests a decrease in the neutral fraction of intergalactic hydrogen by a factor ~ 9.4 from z=6.4 to 5.7, in its simplest interpretation. Alternatively, recent numerical simulations suggest that this rapid increase in near-zone size from z=6.4 to 5.7 is due to the rapid increase in the background photo-ionization rate at the end of the percolation or overlap phase, when the average mean free path of ionizing photons increases dramatically. In either case, the results are consistent with the idea that z ~ 6 to 7 corresponds to the tail end of cosmic reionization. The scatter in the normalized NZ sizes is larger than expected simply from measurement errors, and likely reflects intrinsic differences in the quasars or their environments. We find that the near-zone sizes increase with quasar UV luminosity, as expected for photo-ionization dominated by quasar radiation.Comment: 16 pages, aas format, 4 figures, to appear in the ApJ letter

Six more quasars at redshift 6 discovered by the Canada-France High-z Quasar Survey

We present imaging and spectroscopic observations for six quasars at z>5.9 discovered by the Canada-France High-z Quasar Survey (CFHQS). The CFHQS contains sub-surveys with a range of flux and area combinations to sample a wide range of quasar luminosities at z~6. The new quasars have luminosities 10 to 75 times lower than the most luminous SDSS quasars at this redshift. The least luminous quasar, CFHQS J0216-0455 at z=6.01, has absolute magnitude M_1450=-22.21, well below the likely break in the luminosity function. This quasar is not detected in a deep XMM-Newton survey showing that optical selection is still a very efficient tool for finding high redshift quasars.Comment: 7 pages, 4 figures, AJ, in pres

Redshifts and Neutral Hydrogen Observations of Compact Symmetric Objects in the COINS Sample

Compact Symmetric Objects (CSOs) are young radio galaxies whose jet axes lie close to the plane of the sky, and whose appearance is therefore not dominated by relativistic beaming effects. The small linear sizes of CSOs make them valuable for studies of both the evolution of radio galaxies and testing unified schemes for active galactic nuclei (AGN). A parsec-scale region of gas surrounding the central engine is predicted by both accretion and obscuration scenarios. Working surfaces, or ``hot spots,'' and the radio jets of CSOs are close enough to the central engines that this circumnuclear gas can be seen in absorption. The CSOs Observed in the Northern Sky (COINS) sample is comprised of 52 CSO candidates identified in three VLBI surveys. Of these, 27 have now been confirmed as CSOs. Optical redshifts are available in the literature for 28 of the CSO candidates, and HI absorption has been detected toward four. We present new optical spectroscopic redshifts for three of the candidates and summarize the current status of optical identifications. We further report on the discovery of HI in absorption towards the CSO J1816+3457 and summarize the results of neutral hydrogen absorption studies of the sources in this sample.Comment: 12 pages, Accepted for publication in Ap

MESMER: MeerKAT Search for Molecules in the Epoch of Reionization

[Abridged] Observations of molecular gas at all redshifts are critical for measuring the cosmic evolution in molecular gas density and understanding the star-formation history of the Universe. The 12CO molecule (J=1-0 transition = 115.27 GHz) is the best proxy for extragalactic H2, which is the gas reservoir from which star formation occurs, and has been detected out to z~6. Typically, redshifted high-J lines are observed at mm-wavelengths, the most commonly targeted systems exhibiting high SFRs (e.g. submm galaxies), and far-IR-bright QSOs. While the most luminous objects are the most readily observed, detections of more typical galaxies with modest SFRs are essential for completing the picture. ALMA will be revolutionary in terms of increasing the detection rate and pushing the sensitivity limit down to include such galaxies, however the limited FoV when observing at such high frequencies makes it difficult to use ALMA for studies of the large-scale structure traced out by molecular gas in galaxies. This article introduces a strategy for a systematic search for molecular gas during the EoR (z~7 and above), capitalizing on the fact that the J=1-0 transition of 12CO enters the upper bands of cm-wave instruments at high-z. The FoV advantage gained by observing at such frequencies, coupled with modern broadband correlators allows significant cosmological volumes to be probed on reasonable timescales. In this article we present an overview of our future observing programme which has been awarded 6,500 hours as one of the Large Survey Projects for MeerKAT, the forthcoming South African SKA pathfinder instrument. Its large FoV and correlator bandwidth, and high-sensitivity provide unprecedented survey speed for such work. An existing astrophysical simulation is coupled with instrumental considerations to demonstrate the feasibility of such observations and predict detection rates.Comment: 7 pages, 4 figures, to appear in the proceedings of "Astronomy with megastructures: Joint science with the E-ELT and SKA", 10-14 May 2010, Crete, Greece (Eds: Isobel Hook, Dimitra Rigopoulou, Steve Rawlings and Aris Karastergiou

The coincidence and angular clustering of Chandra and SCUBA sources

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