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Register a new userJ1721$+$8842: a gravitationally lensed binary quasar with a proximate damped Lyman-$alpha$ absorber
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High-redshift binary quasars provide key insights into mergers and quasar activity, and are useful tools for probing the spatial kinematics and chemistry of galaxies along the line-of-sight. However, only three sub-10-kpc binaries have been confirmed above $z=1$. Gravitational lensing would provide a way to easily resolve such binaries, study them in higher resolution, and provide more sightlines, though the required alignment with a massive foreground galaxy is rare. Through image deconvolution of StanCam Nordic Optical Telescope (NOT) monitoring data, we reveal two further point sources in the known, $z approx 2.38$, quadruply lensed quasar (quad), J1721+8842. An ALFOSC/NOT long-slit spectrum shows that the brighter of these two sources is a quasar with $z = 2.369 pm 0.007$ based on the C III] line, while the C III] redshift of the quad is $z = 2.364 pm 0.003$. Lens modelling using point source positions rules out a single source model, favouring an isothermal lens mass profile with two quasar sources separated by $sim6.0$ kpc (0.73$^{prime prime}$) in projection. Given the resolving ability from lensing and current lensed quasar statistics, this discovery suggests a large population of undiscovered, unlensed sub-10-kpc binaries. We also analyse spectra of two images of the quad, showing narrow Ly$alpha$ emission within the trough of a proximate damped Ly$alpha$ absorber (PDLA). An apparent mismatch between the continuum and narrow line flux ratios provides a new potential tool for simultaneously studying microlensing and the quasar host galaxy. Signs of the PDLA are also seen in the second source, however a deeper spectrum is still required to confirm this. Thanks to the multiple lines-of-sight from lensing and two quasar sources, this system offers simultaneous sub-parsec and kpc-scale probes of a PDLA.
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Dual-Active Galactic Nuclei (AGN) are a natural consequence of the hierarchical structure formation scenario, and can provide an important test of various models for black hole growth. However, due to their rarity and difficulty to find at high redshift, very few confirmed dual-AGN are known at the epoch where galaxy formation peaks. Here we report the discovery of a gravitationally lensed dual-AGN system at redshift 2.37 comprising two optical/IR quasars separated by 6.5+/-0.6 kpc, and a third compact (R_eff = 0.45+/-0.02 kpc) red galaxy that is offset from one of the quasars by 1.7+/-0.1 kpc. From Very Large Array imaging at 3 GHz, we detect 600 and 340 pc-scale radio emission that is associated with both quasars. The 1.4 GHz luminosity densities of the radio sources are about 10^24.35 W / Hz, which is consistent with weak jets. However, the low brightness temperature of the emission is also consistent with star-formation at the level of 850 to 1150 M_sun / yr. Although this supports the scenario where the AGN and/or star-formation is being triggered through an ongoing triple-merger, a post-merger scenario where two black holes are recoiling is also possible, given that neither has a detected host galaxy.
We report on the discovery of a bright Lyman alpha blob associated with the z=3 quasar SDSSJ124020.91+145535.6 which is also coincident with strong damped Lyman alpha absorption from a foreground galaxy (a so-called proximate damped Lyman alpha system; PDLA). The one dimensional spectrum acquired by the Sloan Digital Sky Survey (SDSS) shows a broad Lyman alpha emission line with a FWHM ~ 500 km/s and a luminosity of L_{Lya} = 3.9e43 erg/s superposed on the trough of the PDLA. Mechanisms for powering this large Lyman alpha luminosity are discussed. We argue against emission from HII regions in the PDLA galaxy since this requires an excessive star-formation rate ~ 500 Msun/yr and would correspond to the largest Lyman alpha luminosity ever measured from a damped Lyman alpha system or starburst galaxy. We use a Monte Carlo radiative transfer simulation to investigate the possibility that the line emission is fluorescent recombination radiation from the PDLA galaxy powered by the ionizing flux of the quasar, but find that the predicted Lyman alpha flux is several orders of magnitude lower than observed. We conclude that the Lyman alpha emission is not associated with the PDLA galaxy at all, but instead is intrinsic to the quasars host and similar to the extended Lyman alpha fuzz which is detected around many AGN. PDLAs are natural coronagraphs that block their background quasar at Lyman alpha, and we discuss how systems similar to SDSSJ124020.91+145535.6 might be used to image the neutral hydrogen in the PDLA galaxy in silhouette against the screen of extended Lyman alpha emission from the background quasar.
We report the discovery of a super-damped Lyman-alpha absorber at $z_{abs}=2.2068$ toward QSO Q1135-0010 in the Sloan Digital Sky Survey, and follow-up VLT UVES spectroscopy. Voigt profile fit to the DLA line indicates log $N_{rm H I} = 22.05 pm 0.1$. This is the second QSO DLA discovered to date with such high $N_{rm H I}$. We derive element abundances [Si/H] = $-1.10 pm 0.10$, [Zn/H] = $-1.06 pm 0.10$, [Cr/H] = $-1.55 pm 0.10$, [Ni/H] = $-1.60 pm 0.10$, [Fe/H] = $-1.76 pm 0.10$, [Ti/H] = $-1.69 pm 0.11$, [P/H] = $-0.93 pm 0.23$, and [Cu/H] = $-0.75 pm 0.14$. Our data indicate detection of Ly-$alpha$ emission in the DLA trough, implying a star formation rate of $sim$10 $M_{odot}$ yr$^{-1}$ in the absence of dust attenuation. C II$^{*} , lambda 1336$ absorption is also detected, suggesting SFR surface density $-2 < {rm log} , dot{psi_{*}} < 0$ $M_{odot}$ yr$^{-1}$ kpc$^{-2}$. We estimate electron density in the range $3.5 times 10^{-4}$ to 24.7 cm$^{-3}$ from C II$^{*}$/C II, and $sim$0.5-0.9 cm$^{-3}$ from Si II$^{*}$/Si II. Overall, this is a robustly star-forming, moderately enriched absorber, but with relatively low dust depletion. Fitting of the SDSS spectrum yields low reddening for Milky Way, LMC, or SMC extinction curves. No CO absorption is detected, and C I absorption is weak. The low dust and molecular content, reminiscent of some SMC sight-lines, may result from the lower metallicity, and a stronger radiation field (due to higher SFR). Finally, we compare this absorber with other QSO and GRB DLAs.
We present a detailed analysis of a red quasar at z=2.32 with an intervening damped Lyman-alpha absorber (DLA) at z=2.13. Using high quality data from the X-shooter spectrograph at ESO Very Large Telescope we find that the absorber has a metallicity consistent with Solar. We observe strong C I and H$_2$ absorption indicating a cold, dense absorbing medium. Partial coverage effects are observed in the C I lines, from which we infer a covering fraction of $27 pm 6$ % and a physical diameter of the cloud of 0.1 pc. From the covering fraction and size, we estimate the size of the background quasars broad line region. We search for emission from the DLA counterpart in optical and near-infrared imaging. No emission is observed in the optical data. However, we see tentative evidence for a counterpart in the H and K band images. The DLA shows high depletion (as probed by [Fe/Zn]=-1.22) indicating that significant amounts of dust must be present in the DLA. By fitting the spectrum with various dust reddened quasar templates we find a best-fitting amount of dust in the DLA of $A(V)_{rm DLA}=0.28 pm 0.01|_{rm stat} pm 0.07|_{rm sys}$. We conclude that dust in the DLA is causing the colours of this intrinsically very luminous background quasar to appear much redder than average quasars, thereby not fulfilling the criteria for quasar identification in the Sloan Digital Sky Survey. Such chemically enriched and dusty absorbers are thus underrepresented in current samples of DLAs.
Strong gravitational lensing provides a powerful probe of the physical properties of quasars and their host galaxies. A high fraction of the most luminous high-redshift quasars was predicted to be lensed due to magnification bias. However, no multiple imaged quasar was found at z>5 in previous surveys. We report the discovery of J043947.08+163415.7, a strongly lensed quasar at z=6.51, the first such object detected at the epoch of reionization, and the brightest quasar yet known at z>5. High-resolution HST imaging reveals a multiple imaged system with a maximum image separation theta ~ 0.2, best explained by a model of three quasar images lensed by a low luminosity galaxy at z~0.7, with a magnification factor of ~50. The existence of this source suggests that a significant population of strongly lensed, high redshift quasars could have been missed by previous surveys, as standard color selection techniques would fail when the quasar color is contaminated by the lensing galaxy.
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