750 research outputs found
A Thirty-Four Billion Solar Mass Black Hole in SMSS J2157-3602, the Most Luminous Known Quasar
From near-infrared spectroscopic measurements of the MgII emission line
doublet, we estimate the black hole (BH) mass of the quasar, SMSS
J215728.21-360215.1, as being (3.4 +/- 0.6) x 10^10 M_sun and refine the
redshift of the quasar to be z=4.692. SMSS J2157 is the most luminous known
quasar, with a 3000A luminosity of (4.7 +/- 0.5) x 10^47 erg/s and an estimated
bolometric luminosity of 1.6 x 10^48 erg/s, yet its Eddington ratio is only
~0.4. Thus, the high luminosity of this quasar is a consequence of its
extremely large BH -- one of the most massive BHs at z > 4.Comment: 7 pages, 3 figures. Accepted for publication in MNRA
A Survey for High-redshift Gravitationally Lensed Quasars and Close Quasars Pairs. I. the Discoveries of an Intermediately-lensed Quasar and a Kpc-scale Quasar Pair at
We present the first results from a new survey for high-redshift
gravitationally lensed quasars and close quasar pairs. We carry
out candidate selection based on the colors and shapes of objects in public
imaging surveys, then conduct follow-up observations to confirm the nature of
high-priority candidates. In this paper, we report the discoveries of
J0025--0145 () which we identify as an {intermediately-lensed quasar,
and J2329--0522 () which is a kpc-scale close quasar pair. The {\em
Hubble Space Telescope (HST)} image of J0025--0145 shows a foreground lensing
galaxy located 0\farcs6 away from the quasar. However, J0025--0145 does not
exhibit multiple lensed images of the quasar, and we identify J0025--0145 as an
intermediate lensing system (a lensing system that is not multiply imaged but
has a significant magnification). The spectrum of J0025--0145 implies an
extreme Eddington ratio if the quasar luminosity is intrinsic, which could be
explained by a large lensing magnification. The {\em HST} image of J0025--0145
also indicates a tentative detection of the quasar host galaxy in rest-frame
UV, illustrating the power of lensing magnification and distortion in studies
of high-redshift quasar host galaxies. J2329--0522 consists of two resolved
components with significantly different spectral properties, and a lack of
lensing galaxy detection under sub-arcsecond seeing. We identify it as a close
quasar pair, which is the highest confirmed kpc-scale quasar pair to date. We
also report four lensed quasars and quasar pairs at , and discuss
possible improvements to our survey strategy.Comment: 23 pages, 10 figures, 6 tables. Accepted by the Astronomical Journa
Spectroscopy of broad absorption line quasars at -- I: evidence for quasar winds shaping broad/narrow emission line regions
We present an observational study of 22 broad absorption line quasars (BAL
QSOs) at based on optical/near-IR spectroscopy, aiming
to investigate quasar winds and their effects. The near-IR spectroscopy covers
the \hb\ and/or \mgii\ broad emission lines (BELs) for these quasars, allowing
us to estimate their central black hole (BH) masses in a robust way. We found
that our BAL QSOs on average do not have a higher Eddington ratio than that
from non-BAL QSOs matched in redshift and/or luminosity. In a subset consisting
of seven strong BAL QSOs possessing sub-relativistic BAL outflows, we see the
prevalence of large \civ-BEL blueshift (3100 km s) and weak \oiii\
emission (particularly the narrow \oiii5007 component), indicative of
nuclear outflows affecting the narrow emission-line (NEL) regions. In another
subset consisting of thirteen BAL QSOs having simultaneous observations of
\mgii\ and \hb, we found a strong correlation between 3000~\AA\ and 5000~\AA\
monochromatic luminosity, consistent with that from non-BAL QSOs matched in
redshift and luminosity; however, there is no correlation between \mgii\ and
\hb\ in FWHM, likely due to nuclear outflows influencing the BEL regions. Our
spectroscopic investigations offer strong evidence that the presence of nuclear
outflows plays an important role in shaping the BEL/NEL regions of these
quasars and possibly, regulating the growth of central supermassive black holes
(SMBHs). We propose that BEL blueshift and BAL could be different
manifestations of the same outflow system viewed at different sightlines and/or
phases.Comment: 13 pages, 10 figures. Accepted for publication in Ap
Exploring Reionization-Era Quasars IV: Discovery of Six New Quasars with DES, VHS and unWISE Photometry
This is the fourth paper in a series of publications aiming at discovering
quasars at the epoch of reionization. In this paper, we expand our search for
quasars to the footprint of the Dark Energy Survey (DES) Data Release
One (DR1), covering deg of new area. We select quasar
candidates using deep optical, near-infrared (near-IR) and mid-IR photometric
data from the DES DR1, the VISTA Hemisphere Survey (VHS), the VISTA Kilo-degree
Infrared Galaxy (VIKING) survey, the UKIRT InfraRed Deep Sky Surveys -- Large
Area Survey (ULAS) and the unblurred coadds from the Wide-field Infrared Survey
Explore () images (unWISE). The inclusion of DES and unWISE photometry
allows the search to reach 1 magnitude fainter, comparing to our quasar survey in the northern sky (Wang et al. 2018). We report
the initial discovery and spectroscopic confirmation of six new luminous
quasars at , including an object at , the fourth quasar yet
known at , from a small fraction of candidates observed thus far. Based on
the recent measurement of quasar luminosity function using the
quasar sample from our survey in the northern sky, we estimate that there will
be 55 quasars at at in the full DES
footprint.Comment: 8 pages, 3 figures, submitted to A
An ultra-luminous quasar with a twelve-billion-solar-mass black hole at redshift 6.30
So far, roughly 40 quasars with redshifts greater than z=6 have been
discovered. Each quasar contains a black hole with a mass of about one billion
solar masses (). The existence of such black holes when the
Universe was less than 1 billion years old presents substantial challenges to
theories of the formation and growth of black holes and the coevolution of
black holes and galaxies. Here we report the discovery of an ultra-luminous
quasar, SDSS J010013.02+280225.8, at redshift z=6.30. It has an optical and
near-infrared luminosity a few times greater than those of previously known z>6
quasars. On the basis of the deep absorption trough on the blue side of the Ly
emission line in the spectrum, we estimate the proper size of the
ionized proximity zone associated with the quasar to be 26 million light years,
larger than found with other z>6.1 quasars with lower luminosities. We estimate
(on the basis of a near-infrared spectrum) that the black hole has a mass of
, which is consistent with the derived by assuming an Eddington-limited accretion rate.Comment: 24 pages, 4 figures plus 4 extended data figures, published in Nature
on 26 February 201
Quasar Photometric Redshifts and Candidate Selection: A New Algorithm Based on Optical and Mid-Infrared Photometric Data
We present a new algorithm to estimate quasar photometric redshifts
(photo-s), by considering the asymmetries in the relative flux distributions
of quasars. The relative flux models are built with multivariate Skew-t
distributions in the multi-dimensional space of relative fluxes as a function
of redshift and magnitude. For 151,392 quasars in the SDSS, we achieve a
photo- accuracy, defined as the fraction of quasars with the difference
between the photo- and the spectroscopic redshift , within 0.1, of 74%. Combining the WISE W1 and W2 infrared
data with the SDSS data, the photo- accuracy is enhanced to 87%. Using the
Pan-STARRS1 or DECaLS photometry with WISE W1 and W2 data, the photo-
accuracies are 79% and 72%, respectively. The prior probabilities as a function
of magnitude for quasars, stars and galaxies are calculated respectively based
on (1) the quasar luminosity function; (2) the Milky Way synthetic simulation
with the Besan\c{c}on model; (3) the Bayesian Galaxy Photometric Redshift
estimation. The relative fluxes of stars are obtained with the Padova
isochrones, and the relative fluxes of galaxies are modeled through galaxy
templates. We test our classification method to select quasars using the DECaLS
, , , and WISE W1 and W2 photometry. The quasar selection completeness
is higher than 70% for a wide redshift range , and a wide magnitude
range mag. Our photo- regression and classification method has
the potential to extend to future surveys. The photo- code will be publicly
available.Comment: 22 pages, 17 figure, accepted by AJ. The code is available at
https://doi.org/10.5281/zenodo.101440
Constraining the Gravitational Lensing of Quasars from their Proximity Zones
Since their discovery twenty years ago, the observed luminosity function of
quasars has been suspected to be biased by gravitational lensing.
Apart from the recent discovery of UHS J0439+1634 at , no other
strongly lensed quasar has been conclusively identified. The
hyperluminous quasar SDSS J0100+2802, believed to host a
supermassive black hole of , has recently been claimed to
be lensed by a factor of , which would negate both its extreme
luminosity and black hole mass. However, its Ly-transparent proximity
zone is the largest known at , suggesting an intrinsically extreme
ionizing luminosity. Here we show that the lensing hypothesis of
quasars can be quantitatively constrained by their proximity zones. We first
show that our proximity zone analysis can recover the strongly lensed nature of
UHS J0439+1634, with an estimated magnification
at 68% (95%) credibility that is
consistent with previously published lensing models. We then show that the
large proximity zone of SDSS J0100+2802 rules out lensing magnifications of
at 95% probability, and conclusively rule out the proposed
scenario. Future proximity zone analyses of existing quasar samples
have the potential to identify promising strongly lensed candidates, constrain
the distribution of quasar lensing, and improve our knowledge of
the shape of the intrinsic quasar luminosity function.Comment: 8 pages, 4 figure
Discovery of 21 New Changing-look AGNs in Northern Sky
The rare case of changing-look (CL) AGNs, with the appearance or
disappearance of broad Balmer emission lines within a few years, challenges our
understanding of the AGN unified model. We present a sample of 21 new CL AGNs
at , which doubles the number of such objects known to date. These
new CL AGNs were discovered by several ways, from (1) repeat spectra in the
SDSS, (2) repeat spectra in the Large Sky Area Multi-Object Fiber Spectroscopic
Telescope (LAMOST) and SDSS, and (3) photometric variability and new
spectroscopic observations. We use the photometric data from surveys, including
the SDSS imaging survey, the Pan-STARRS1, the DESI Legacy imaging survey, the
Wide-field Infrared Survey Explorer (WISE), the Catalina Real-time Transient
Survey, and the Palomar Transient Factory. The estimated upper limits of
transition timescale of the CL AGNs in this sample spans from 0.9 to 13 years
in the rest frame. The continuum flux in the optical and mid-infrared becomes
brighter when the CL AGNs turn on, or vice versa. Variations of more than 0.2
mag in band were detected in 15 CL AGNs during the transition. The optical
and mid-infrared variability is not consistent with the scenario of variable
obscuration in 10 CL AGNs at more than confidence level. We confirm a
bluer-when-brighter trend in the optical. However, the mid-infrared WISE colors
become redder when the objects become brighter in the band,
possibly due to a stronger hot dust contribution in the band when the AGN
activity becomes stronger. The physical mechanism of type transition is
important for understanding the evolution of AGNs.Comment: Accepted for publication in Ap
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