1,781 research outputs found
Gravitationally lensed quasars in Gaia: I. Resolving small-separation lenses
Gaia’s exceptional resolution (FWHM ~ 0.1 arcsec) allows identification and cataloguing of the multiple images of gravitationally lensed quasars. We investigate a sample of 49 known lensed quasars in the Sloan Digital Sky Survey (SDSS) footprint, with image separations less than 2 arcsec, and find that eight are detected with multiple components in the first Gaia data release. In the case of the 41 single Gaia detections, we generally are able to distinguish these lensed quasars from single quasars when comparing Gaia flux and position measurements to those of Pan-STARRS and SDSS. This is because the multiple images of these lensed quasars are typically blended in ground-based imaging and therefore the total flux and a flux-weighted centroid are measured, which can differ significantly from the fluxes and centroids of the individual components detected by Gaia. We compare the fluxes through an empirical fit of Pan-STARRS griz photometry to the wide optical Gaia bandpass values using a sample of isolated quasars. The positional offsets are calculated from a recalibrated astrometric SDSS catalogue. Applying flux and centroid difference criteria to spectroscopically confirmed quasars, we discover four new sub-arcsecond-separation lensed quasar candidates which have two distinct components of similar colour in archival Canada–France–Hawaii Telescope or Hyper Suprime Cam data. Our method based on single Gaia detections can be used to identify the ~1400 lensed quasars with image separation above 0.5 arcsec, expected to have only one image bright enough to be detected by Gaia
The compact, ∼1 kpc host galaxy of a quasar at a redshift of 7.1
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the [C ii] fine-structure line and the underlying far-infrared (FIR) dust continuum emission in J1120+0641, the most distant quasar currently known (). We also present observations targeting the CO(2–1), CO(7–6), and [C i] 369 μm lines in the same source obtained at the Very Large Array and Plateau de Bure Interferometer. We find a [C ii] line flux of Jy and a continuum flux density of mJy beam−1, consistent with previous unresolved measurements. No other source is detected in continuum or [C ii] emission in the field covered by ALMA (~ 25''). At the resolution of our ALMA observations (0farcs23, or 1.2 kpc, a factor of ~70 smaller beam area compared to previous measurements), we find that the majority of the emission is very compact: a high fraction (~80%) of the total line and continuum flux is associated with a region 1–1.5 kpc in diameter. The remaining ~20% of the emission is distributed over a larger area with radius lesssim4 kpc. The [C ii] emission does not exhibit ordered motion on kiloparsec scales: applying the virial theorem yields an upper limit on the dynamical mass of the host galaxy of , only ~20 × higher than the central black hole (BH). The other targeted lines (CO(2–1), CO(7–6), and [C i]) are not detected, but the limits of the line ratios with respect to the [C ii] emission imply that the heating in the quasar host is dominated by star formation, and not by the accreting BH. The star formation rate (SFR) implied by the FIR continuum is 105–340 , with a resulting SFR surface density of ~100–350 kpc−2, well below the value for Eddington-accretion-limited star formation
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Heavily reddened z ~ 2 Type 1 quasars - II. H α star formation constraints from SINFONI IFU observations
We use near infrared integral field unit (IFU) spectroscopy to search for
H emission associated with star formation in a sample of 28 heavily
reddened (0.5-1.9), hyperluminous
(47-48) broad-line quasars at 1.4-2.7.
Sixteen of the 28 quasars show evidence for star formation with an average
extinction-corrected star formation rate (SFR) of 32070Myr.
A stacked spectrum of the detections shows weak [NII], consistent with star
formation as the origin of the narrow H emission. The star-forming
regions are spatially unresolved in 11 of the 16 detections and constrained to
lie within 6kpc of the quasar emission. In the five resolved detections
we find the star-forming regions are extended on scales of 8kpc around
the quasar emission. The prevalence of high SFRs is consistent with the
identification of the heavily reddened quasar population as representing a
transitional phase from apparent `starburst galaxies' to optically-luminous
quasars. Upper limits are determined for 10 quasars in which star formation is
undetected. In two of the quasars the SFR is constrained to be relatively
modest, 50Myr, but significantly higher levels of star
formation could be present in the other eight quasars. The combination of the
16 strong star formation detections and the eight high SFR limits means that
high levels of star formation may be present in the majority of the sample.
Higher spatial resolution data, of multiple emission lines, will allow us to
better understand the interplay between star formation and Active Galactic
Nucleus (AGN) activity in these transitioning quasars.The authors thank the Science and Technology Facilities Council (STFC) via the Consolidated Grant awarded to the Institute of Astronomy, Cambridge. SA-Z acknowledges the support from Peterhouse, Cambridge, and the Institute of Astronomy, Cambridge. The narrow-band imaging study is based on observations made with ESO Telescopes at the La Sill a Paranal Observatory under programme ID: 290.A-5062. The IFU study is based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme IDs:383.A-0573 (PI:McMahon) and 091.A-0341 (PI:Banerji).This is the author accepted manuscript. The final version is available from Oxford University Press via http://dx.doi.org/10.1093/mnras/stw68
A new bright z = 6.82 quasar discovered with VISTA: VHS J0411-0907
We present the discovery of a new quasar discovered with the
near-IR VISTA Hemisphere Survey (VHS) which has been spectroscopically
confirmed by the ESO New Technology Telescope (NTT) and the Magellan telescope.
This quasar has been selected by spectral energy distribution (SED)
classification using near infrared data from VISTA, optical data from
Pan-STARRS, and mid-IR data from WISE. The SED classification algorithm is used
to statistically rank two classes; foreground Galactic low-mass stars and high
redshift quasars, prior to spectroscopic observation. Forced photometry on
Pan-STARRS pixels for VHS J0411-0907 allows to improve the SED classification
reduced- and photometric redshift. VHS J0411-0907 (, mag, mag) has the brightest J-band continuum magnitude of
the nine known quasars at and is currently the highest redshift
quasar detected in the Pan-STARRS survey. This quasar has one of the lowest
black hole mass ()
and the highest Eddington ratio () of the known quasars at
. The high Eddington ratio indicates that some very high- quasars are
undergoing super Eddington accretion. We also present coefficients of the best
polynomials fits for colours vs spectral type on the Pan-STARRS, VISTA and WISE
system for MLT dwarfs and present a forecast for the expected numbers of
quasars at
Using New Submillimetre Surveys to Identify the Evolutionary Status of High-z Galaxies
This paper describes a key submillimetre survey which we are currently
conducting to address some of the outstanding questions in cosmology - how, at
what epoch and over what period of time did massive galaxies form at high
redshift? A summary of the technical feasibility of future submillimetre
observations with new ground-based, airborne and satellite telescopes is also
presented.Comment: 6 pages, 3 postscript figures, LaTex uses Kluwer book style file
crckapb10.sty, to appear in "Observational Cosmology with the New Radio
Surveys", 13-15 January 1997, Puerto de la Cruz, Tenerife, M.Bremer,
N.Jackson, I.Perez-Fournon (eds.), Kluwe
Gravitationally lensed quasars in Gaia - II. Discoveryof 24 lensed quasars
We report the discovery, spectroscopic confirmation and preliminary
characterisation of 24 gravitationally lensed quasars identified using Gaia
observations. Candidates were selected in the Pan-STARRS footprint with
quasar-like WISE colours or as photometric quasars from SDSS, requiring either
multiple detections in Gaia or a single Gaia detection near a morphological
galaxy. The Pan-STARRS grizY images were modelled for the most promising
candidates and 60 candidate systems were followed up with the William Herschel
Telescope. 13 of the lenses were discovered as Gaia multiples and 10 as single
Gaia detections near galaxies. We also discover 1 lens identified through a
quasar emission line in an SDSS galaxy spectrum. The lenses have median image
separation 2.13 arcsec and the source redshifts range from 1.06 to 3.36. 4
systems are quadruply-imaged and 20 are doubly-imaged. Deep CFHT data reveal an
Einstein ring in one double system. We also report 12 quasar pairs, 10 of which
have components at the same redshift and require further follow-up to rule out
the lensing hypothesis. We compare the properties of these lenses and other
known lenses recovered by our search method to a complete sample of simulated
lenses to show the lenses we are missing are mainly those with small
separations and higher source redshifts. The initial Gaia data release only
catalogues all images of ~ 30% of known bright lensed quasars, however the
improved completeness of Gaia data release 2 will help find all bright lensed
quasars on the sky
The Discovery of Gas-Rich, Dusty Starbursts in Luminous Reddened Quasars at with ALMA
We present ALMA observations of cold dust and molecular gas in four high-luminosity, heavily reddened (A mag) Type 1 quasars at with virial MM, to test whether dusty, massive quasars represent the evolutionary link between submillimetre bright galaxies (SMGs) and unobscured quasars. All four quasars are detected in both the dust continuum and in the CO(3-2) line. The mean dust mass is 610M assuming a typical high redshift quasar spectral energy distribution (T=41K, =1.95 or T=47K, =1.6). The implied star formation rates are very high - 1000 M yr in all cases. Gas masses estimated from the CO line luminosities cover 1-5()M and the gas depletion timescales are very short - Myr. A range of gas-to-dust ratios is observed in the sample. We resolve the molecular gas in one quasar - ULASJ23150143 () - which shows a strong velocity gradient over 20 kpc. The velocity field is consistent with a rotationally supported gas disk but other scenarios, e.g. mergers, cannot be ruled out at the current resolution of these data. In another quasar - ULASJ1234+0907 () - we detected molecular line emission from two millimetre bright galaxies within 200 kpc of the quasar, suggesting that this quasar resides in a significant over-density. The high detection rate of both cold dust and molecular gas in these sources, suggests that reddened quasars could correspond to an early phase in massive galaxy formation associated with large gas reservoirs and significant star formation.MB acknowledges funding from the UK Science and Technology Facilities Council (STFC) via an Ernest Rutherford Fellowship. GJ is grateful for support from NRAO through the Grote Reber Doctoral Fellowship Program. RGM and PCH acknowledge funding from STFC via the Institute of Astronomy, Cambridge Consolidated Grant. SA-Z acknowledges support from Peterhouse, Cambridge
Molecular Gas in Three z ∼ 7 Quasar Host Galaxies
We present ALMA band 3 observations of the CO(6-5), CO(7-6), and [C i] 369 μm emission lines in three of the highest-redshift quasar host galaxies at . These measurements constitute the highest-redshift CO detections to date. The target quasars have previously been detected in [C ii] 158 μm emission and the underlying FIR dust continuum. We detect (spatially unresolved, at a resolution of > 2″, or ≈14 kpc) CO emission in all three quasar hosts. In two sources, we detect the continuum emission around 400 μm (rest-frame), and in one source we detect [C i] at low significance. We derive molecular gas reservoirs of (1-3) T10 10 in the quasar hosts, i.e., approximately only 10 times the mass of their central supermassive black holes. The extrapolated [C ii]-to-CO(1-0) luminosity ratio is 2500-4200, consistent with measurement s in galaxies at lower redshift. The detection of the [C i] line in one quasar host galaxy and the limit on the [C i] emission in the other two hosts enables a first characterization of the physical properties of the interstellar medium in z ∼ 7 quasar hosts. In the sources, the derived global CO/[C ii] /[C i] line ratios are consistent with expectations from photodissociation regions, but not X-ray-dominated regions. This suggest that quantities derived from the molecular gas and dust emission are related to ongoing star-formation activity in the quasar hosts, providing further evidence that the quasar hosts studied here harbor intense starbursts in addition to their active nucleus
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Constraining the nature of two Lyα emitters detected by ALMA at z = 4.7
We report optical VLT FORS2 spectroscopy of the two Ly-alpha emitters (LAEs)
companions to the quasi-stellar object (QSO) - sub-millimetre galaxy (SMG)
system BRI1202-0725 at z = 4.7, which have recently been detected in the
[CII]158um line by the Atacama Large Millimetre/Sub-millimetre Array (ALMA). We
detect Ly-alpha emission from both sources and so confirm that these Ly-alpha
emitter candidates are physically associated with the BRI1202- 0725 system. We
also report the lack of detection of any high ionisation emission lines (N V,
Si IV, C IV and He II) and find that these systems are likely not photoionised
by the quasar, leaving in situ star formation as the main powering source of
these LAEs. We also find that both LAEs have Ly-alpha emission much broader
(1300 km/s) than the [CII] emission and broader than most LAEs. In addition,
both LAEs have roughly symmetric Ly-alpha profiles implying that both systems
are within the HII sphere produced by the quasar. This is the first time that
the proximity zone of a quasar is probed by exploiting nearby Ly-alpha
emitters. We discuss the observational properties of these galaxies in the
context of recent galaxy formation models.This work was co-funded under the Marie Curie Actions of the European Commission (FP7-COFUND).This is the final published version, which originally appeared in MNRAS and is available at http://mnras.oxfordjournals.org/content/439/2/2096
The discovery of a five-image lensed quasar at z = 3.34 using PanSTARRS1 and Gaia
We report the discovery, spectroscopic confirmation, and mass modelling of
the gravitationally lensed quasar system PS J0630-1201. The lens was discovered
by matching a photometric quasar catalogue compiled from Pan-STARRS and WISE
photometry to the Gaia DR1 catalogue, exploiting the high spatial resolution of
the latter (FWHM 0.1") to identify the three brightest components of the
lens. Follow-up spectroscopic observations with the WHT confirm the multiple
objects are quasars at redshift . Further follow-up with Keck AO
high-resolution imaging reveals that the system is composed of two lensing
galaxies and the quasar is lensed into a 2.8" separation four-image cusp
configuration with a fifth image clearly visible, and a 1.0" arc due to the
lensed quasar host galaxy. The system is well-modelled with two singular
isothermal ellipsoids, reproducing the position of the fifth image. We discuss
future prospects for measuring time delays between the images and constraining
any offset between mass and light using the faintly detected Einstein arcs
associated with the quasar host galaxy
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