207 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
Discovery of Eight z ~ 6 Quasars in the Sloan Digital Sky Survey Overlap Regions
We present the discovery of eight quasars at z~6 identified in the Sloan
Digital Sky Survey (SDSS) overlap regions. Individual SDSS imaging runs have
some overlap with each other, leading to repeat observations over an area
spanning >4000 deg^2 (more than 1/4 of the total footprint). These overlap
regions provide a unique dataset that allows us to select high-redshift quasars
more than 0.5 mag fainter in the z band than those found with the SDSS
single-epoch data. Our quasar candidates were first selected as i-band dropout
objects in the SDSS imaging database. We then carried out a series of follow-up
observations in the optical and near-IR to improve photometry, remove
contaminants, and identify quasars. The eight quasars reported here were
discovered in a pilot study utilizing the overlap regions at high galactic
latitude (|b|>30 deg). These quasars span a redshift range of 5.86<z<6.06 and a
flux range of 19.3<z_AB<20.6 mag. Five of them are fainter than z_AB=20 mag,
the typical magnitude limit of z~6 quasars used for the SDSS single-epoch
images. In addition, we recover eight previously known quasars at z~6 that are
located in the overlap regions. These results validate our procedure for
selecting quasar candidates from the overlap regions and confirming them with
follow-up observations, and provide guidance to a future systematic survey over
all SDSS imaging regions with repeat observations.Comment: AJ in press (8 pages
Close companions to two high-redshift quasars
We report the serendipitous discoveries of companion galaxies to two
high-redshift quasars. SDSS J025617.7+001904 is a z=4.79 quasar included in our
recent survey of faint quasars in the SDSS Stripe 82 region. The initial MMT
slit spectroscopy shows excess Lyman alpha emission extending well beyond the
quasar's light profile. Further imaging and spectroscopy with LBT/MODS1
confirms the presence of a bright galaxy (i_AB = 23.6) located 2arcsec (12 kpc
projected) from the quasar with strong Lyman alpha emission (EW_0 ~ 100Ang) at
the redshift of the quasar, as well as faint continuum. The second quasar,
CFHQS J005006.6+344522 (z=6.25), is included in our recent HST SNAP survey of
z~6 quasars searching for evidence of gravitational lensing. Deep imaging with
ACS and WFC3 confirms an optical dropout ~4.5 mag fainter than the quasar
(Y_AB=25) at a separation of 0.9 arcsec. The red i_775-Y_105 color of the
galaxy and its proximity to the quasar (5 kpc projected if at the quasar
redshift) strongly favor an association with the quasar. Although it is much
fainter than the quasar it is remarkably bright when compared to field galaxies
at this redshift, while showing no evidence for lensing. Both systems may
represent late-stage mergers of two massive galaxies, with the observed light
for one dominated by powerful ongoing star formation and for the other by rapid
black hole growth. Observations of close companions are rare; if major mergers
are primarily responsible for high-redshift quasar fueling then the phase when
progenitor galaxies can be observed as bright companions is relatively short.Comment: 13 pages, 12 figures, accepted for publication in A
A comparative study of a NiTi alloy subjected to uniaxial monotonic and cyclic loading-unloading in tension using digital image correlation: The grain size effect
The present digital image correlation study characterised the local axial and shear strain fields of a 56Ni-44Ti wt.% shape memory alloy with an average grain size of 100 μm, under uniaxial monotonic and cyclic loading-unloading in tension. To elucidate the grain size effect, the results were compared with a previous investigation of the same alloy with an average grain size of 10 μm. The maximum local axial strain rate signified the direction and extent of the localised transformation. The widened single inclined transformation band and multiple criss-crossing patterns assist in straightening the sample edge by releasing an in-plane moment instigated by local shear strains. Electron back-scattering diffraction analyses showed that the plastic strain within the B2 grains and the remnant B19′ variants account for the residual strains after unloading. Smaller grain sizes correspond to greater constraint from grain boundaries, higher interfacial energy and higher elastic strain energy barrier for transformation, and smaller intragranular heterogeneity of plastic deformation. This is reflected in the increases to the transformation start stress, stress level and stress-strain slope within the macroscopic stress plateau region and smaller complete transformation strain, super-elastic and residual strains upon unloading
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
Constraining C iii] Emission in a Sample of Five Luminous z = 5.7 Galaxies
Recent observations have suggested that the CIII] emission
lines could be alternative diagnostic lines for galaxies in the reionization
epoch. We use the F128N narrowband filter on the Hubble Space Telescope's
() Wide Field Camera 3 (WFC3) to search for CIII] emission in a
sample of five galaxies at z = 5.7 in the Subaru Deep Field and the
Subaru/XMM-Newton Deep Field. Using the F128N narrowband imaging, together with
the broadband imaging, we do not detect CIII] emission for the five galaxies
with ranging from 24.10 -- 27.00 in our sample. For the brightest
galaxy J132416.13+274411.6 in our sample (z = 5.70, ),
which has a significantly higher signal to noise, we report a CIII] flux of
, which places a
stringent 3- upper limit of $\mathrm{erg\
s^{-1}\ cm^{-2}}\rm\sigma\mathrm{2.55\times10^{-18}\ erg\ s^{-1}\ cm^{-2}}\rm\sigma>$ 5.70 exhibit a wide range
of distribution. Our strong limits on CIII] emission could be used as a guide
for future observations in the reionization epoch
Black Hole Mass Estimates and Rapid Growth of Supermassive Black Holes in Luminous 3.5 Quasars
We present new near-infrared (IR) observations of the H
and MgII lines for 32 luminous quasars with using the
Palomar Hale 200 inch telescope and the Large Binocular Telescope. We find that
the MgII Full Width at Half Maximum (FWHM) is well correlated with the H
FWHM, confirming itself as a good substitute for the H FWHM in the black
hole mass estimates. The continuum luminosity at 5100 \AA\ well correlates with
the continuum luminosity at 3000 \AA\ and the broad emission line luminosities
(H and MgII). With simultaneous near-IR spectroscopy of the H and
MgII lines to exclude the influences of flux variability, we are able to
evaluate the reliability of estimating black hole masses based on the MgII line
for high redshift quasars. With the reliable H line based black hole
mass and Eddington ratio estimates, we find that the quasars in our
sample have black hole masses , with a median of and are accreting at Eddington ratios between 0.30 and 3.05, with a
median of . Assuming a duty cycle of 1 and a seed black hole mass of
, we show that the quasars in this sample can grow
to their estimated black hole masses within the age of the Universe at their
redshifts.Comment: 38 pages, 6 figures, accepted for publication in Ap
Exploratory chandra observation of the ultraluminous quasar SDSS J010013.02+280225.8 at redshift 6.30
We report exploratory Chandra observations of the ultraluminous quasar SDSS J010013.02+280225.8 at redshift 6.30. The quasar is clearly detected by Chandra with a possible component of extended emission.Y.-L.A. thanks the support from NSFC grant Nos. 11273060,
11333008, and State Key Development Program for Basic
Research of China (Nos. 2013CB834900 and 2015CB857000).
F.W. and X.-B.W. thank the support from the NSFC grants
No.11373008 and 11533001, the Strategic Priority Research
Program “The Emergence of Cosmological Structures” of the
Chinese Academy of Sciences, grant No. XDB09000000, and
the National Key Basic Research Program of China
2014CB845700
- …