202 research outputs found

    A Thirty-Four Billion Solar Mass Black Hole in SMSS J2157-3602, the Most Luminous Known Quasar

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    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

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    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

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    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

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    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 z6.5z \gtrsim 6.5 Quasars with DES, VHS and unWISE Photometry

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    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 z7z\sim 7 quasars to the footprint of the Dark Energy Survey (DES) Data Release One (DR1), covering 5000\sim 5000 deg2^2 of new area. We select z7z\sim 7 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 (WISEWISE) images (unWISE). The inclusion of DES and unWISE photometry allows the search to reach \sim 1 magnitude fainter, comparing to our z6.5z \gtrsim 6.5 quasar survey in the northern sky (Wang et al. 2018). We report the initial discovery and spectroscopic confirmation of six new luminous quasars at z>6.4z>6.4, including an object at z=7.02z=7.02, the fourth quasar yet known at z>7z>7, from a small fraction of candidates observed thus far. Based on the recent measurement of z6.7z \sim 6.7 quasar luminosity function using the quasar sample from our survey in the northern sky, we estimate that there will be \gtrsim 55 quasars at z>6.5z > 6.5 at M1450<24.5M_{1450} < -24.5 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

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    Recent observations have suggested that the CIII]λ1907/1909\lambda1907/1909 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 (HST\it{HST}) 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 JABJ_{\rm{AB}} ranging from 24.10 -- 27.00 in our sample. For the brightest galaxy J132416.13+274411.6 in our sample (z = 5.70, JAB=24.10J_{\rm{AB}} = 24.10), which has a significantly higher signal to noise, we report a CIII] flux of 3.34±1.81×10183.34\pm1.81 \times 10^{-18} erg s1 cm2\mathrm{erg\ s^{-1}\ cm^{-2}}, which places a stringent 3-σ\rm\sigma upper limit of 5.43×10185.43\times 10^{-18} $\mathrm{erg\ s^{-1}\ cm^{-2}}onCIII]fluxand6.57A˚ ontheCIII]equivalentwidth.Usingthestackedimage,weputa3 on CIII] flux and 6.57 \AA\ on the CIII] equivalent width. Using the stacked image, we put a 3-\rm\sigmaupperlimitonthemeanCIII]fluxof upper limit on the mean CIII] flux of \mathrm{2.55\times10^{-18}\ erg\ s^{-1}\ cm^{-2}},anda3, and a 3-\rm\sigmaupperlimitonthemeanCIII]equivalentwidthof4.20A˚forthissampleofgalaxiesatz=5.70.CombinedwithstrongCIII]detectionreportedamonghighzgalaxiesintheliterature,ourobservationssuggestthattheequivalentwidthsofCIII]fromgalaxiesatz upper limit on the mean CIII] equivalent width of 4.20 {\AA} for this sample of galaxies at z = 5.70. Combined with strong CIII] detection reported among high-z galaxies in the literature, our observations suggest that the equivalent widths of CIII] from galaxies at z >$ 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 zz \sim 3.5 Quasars

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    We present new near-infrared (IR) observations of the Hβ λ4861\beta\ \lambda4861 and MgII λ2798\lambda2798 lines for 32 luminous quasars with 3.2<z<3.93.2<z<3.9 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 Hβ\beta FWHM, confirming itself as a good substitute for the Hβ\beta 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 (Hβ\beta and MgII). With simultaneous near-IR spectroscopy of the Hβ\beta 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 Hβ\beta line based black hole mass and Eddington ratio estimates, we find that the z3.5z\sim3.5 quasars in our sample have black hole masses 1.90×109MMBH1.37×1010M1.90\times10^{9} M_{\odot} \lesssim M_{\rm BH} \lesssim 1.37\times10^{10} M_{\odot}, with a median of 5.14×109M\sim 5.14\times10^{9} M_{\odot} and are accreting at Eddington ratios between 0.30 and 3.05, with a median of 1.12\sim1.12. Assuming a duty cycle of 1 and a seed black hole mass of 104M10^{4} M_{\odot}, we show that the z3.5z\sim3.5 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

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    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