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Register a new userUltra-luminous quasars at redshift $z>4.5$ from SkyMapper
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The most luminous quasars at high redshift harbour the fastest-growing and most massive black holes in the early Universe. They are exceedingly rare and hard to find. Here, we present our search for the most luminous quasars in the redshift range from $z=4.5$ to $5$ using data from SkyMapper, Gaia and WISE. We use colours to select likely high-redshift quasars and reduce the stellar contamination of the candidate set with parallax and proper motion data. In $sim$12,500~deg$^2$ of Southern sky, we find 92 candidates brighter than $R_p=18.2$. Spectroscopic follow-up has revealed 21 quasars at $zge 4$ (16 of which are within $z=[4.5,5]$), as well as several red quasars, BAL quasars and objects with unusual spectra, which we tentatively label OFeLoBALQSOs at redshifts of $zapprox 1$ to $2$. This work lifts the number of known bright $zge 4.5$ quasars in the Southern hemisphere from 10 to 26 and brings the total number of quasars known at $R_p<18.2$ and $zge 4.5$ to 42.
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We search for ultra-luminous QSOs at high redshift using photometry from the SkyMapper Southern Survey DR3, in combination with 2MASS, VHS DR6, VIKING DR5, AllWISE, and CatWISE2020, as well as parallaxes and proper motions from Gaia DR2 and eDR3. We report 119 newly discovered Southern QSOs, of which 97 with -29 < M_145 < -27 and 4 < z < 5.5 are found an effective search area of 14,120 deg^2. In combination with already known QSOs, we construct a sample that is >90% complete for M_145 < -27.5 at z=4.4 and for M_145 < -28 at z=5.4. This Southern sample has a surface density that is over 3 times higher than in previous searches in the Northern hemisphere, which is only partly due to a more inclusive selection. We derive the bright end of the QSO luminosity function at restframe 145nm and measure its slope as $beta approx -3.84$ at z~5. We also present the first z~5 QSO luminosity function at restframe 300nm.
Significant clustering around the rarest luminous quasars is a feature predicted by dark matter theory combined with number density matching arguments. However, this expectation is not reflected by observations of quasars residing in a diverse range of environments. Here, we assess the tension in the diverse clustering of visible $i$-band dropout galaxies around luminous $zsim6$ quasars. Our approach uses a simple empirical method to derive the median luminosity to halo mass relation, $L_{c}(M_{h})$ for both quasars and galaxies under the assumption of log-normal luminosity scatter, $Sigma_{Q}$ and $Sigma_{G}$. We show that higher $Sigma_{Q}$ reduces the average halo mass hosting a quasar of a given luminosity, thus introducing at least a partial reversion to the mean in the number count distribution of nearby Lyman-Break galaxies. We generate a large sample of mock Hubble Space Telescope fields-of-view centred across rare $zsim6$ quasars by resampling pencil beams traced through the dark matter component of the BlueTides cosmological simulation. We find that diverse quasar environments are expected for $Sigma_{Q}>0.4$, consistent with numerous observations and theoretical studies. However, we note that the average number of galaxies around the central quasar is primarily driven by galaxy evolutionary processes in neighbouring halos, as embodied by our parameter $Sigma_{G}$, instead of a difference in the large scale structure around the central quasar host, embodied by $Sigma_{Q}$. We conclude that models with $Sigma_{G}>0.3$ are consistent with current observational constraints on high-z quasars, and that such a value is comparable to the scatter estimated from hydrodynamical simulations of galaxy formation.
We present Reverberation Mapping (RM) results for 17 high-redshift, high-luminosity quasars with good quality R-band and emission line light curves. We are able to measure statistically significant lags for Ly_alpha (11 objects), SiIV (5 objects), CIV (11 objects), and CIII] (2 objects). Using our results and previous lag determinations taken from the literature, we present an updated CIV radius--luminosity relation and provide for the first time radius--luminosity relations for Ly_alpha, SiIV and CIII]. While in all cases the slope of the correlations are statistically significant, the zero points are poorly constrained because of the lack of data at the low luminosity end. We find that the emissivity weighted distance from the central source of the Ly_alpha, SiIV and CIII] line emitting regions are all similar, which corresponds to about half that of the H_beta region. We also find that 3/17 of our sources show an unexpected behavior in some emission lines, two in the Ly_alpha light curve and one in the SiIV light curve, in that they do not seem to follow the variability of the UV continuum. Finally, we compute RM black hole masses for those quasars with highly significant lag measurements and compare them with CIV single--epoch (SE) mass determinations. We find that the RM-based black hole mass determinations seem smaller than those found using SE calibrations.
We investigate the relation between star formation rates ($dot{M}_{s}$) and AGN properties in optically selected type 1 quasars at $2<z<3$ using data from Herschel and the SDSS. We find that $dot{rm{M}}_s$ remains approximately constant with redshift, at $300pm100~rm{M}_{odot}$yr$^{-1}$. Conversely, $dot{rm{M}}_s$ increases with AGN luminosity, up to a maximum of $sim600~rm{M}_{odot}$yr$^{-1}$, and with CIV FWHM. In context with previous results, this is consistent with a relation between $dot{rm{M}}_s$ and black hole accretion rate ($dot{rm{M}}_{bh}$) existing in only parts of the $z-dot{rm{M}}_{s}-dot{rm{M}}_{bh}$ plane, dependent on the free gas fraction, the trigger for activity, and the processes that may quench star formation. The relations between $dot{rm{M}}_s$ and both AGN luminosity and CIV FWHM are consistent with star formation rates in quasars scaling with black hole mass, though we cannot rule out a separate relation with black hole accretion rate. Star formation rates are observed to decline with increasing CIV equivalent width. This decline can be partially explained via the Baldwin effect, but may have an additional contribution from one or more of three factors; $M_i$ is not a linear tracer of L$_{2500}$, the Baldwin effect changes form at high AGN luminosities, and high CIV EW values signpost a change in the relation between $dot{rm{M}}_s$ and $dot{rm{M}}_{bh}$. Finally, there is no strong relation between $dot{rm{M}}_s$ and Eddington ratio, or the asymmetry of the CIV line. The former suggests that star formation rates do not scale with how efficiently the black hole is accreting, while the latter is consistent with CIV asymmetries arising from orientation effects.
We perform a systematic study of outflow in the narrow-line region (NLR) of active galactic nuclei (AGNs) at $zsim0.4-0.8$ basing upon a large sample of $sim900$ quasars at $zsim 0.4-0.8$. The sample is extracted from the Sloan Digital Sky Survey by mainly requiring 1) the g-band magnitude is brighter than 19 magnitude; and 2) the [OIII]$lambda5007$ emission line has a signal-to-noise ration larger than 30. Profiles of multiple emission lines are modeled by a sum of several Gaussian functions. The spectral analysis allows us to identify 1) a prevalence of both [OIII]$lambda5007$ line blue asymmetry and bulk velocity blueshift of both [NeIII]$lambda3869$ and [NeV]$lambda3426$ lines, when the [ion{O}{2}]$lambda3727$ line is used as a reference. The velocity offset of [ion{O}{3}]$lambda5007$ line is, however, distributed around zero value, except for a few outliers. 2) not only the significant [OIII]$lambda5007$ line asymmetry, but also the large bulk velocity offsets of [NeIII]$lambda3869$ and [NeV]$lambda3426$ emission lines tend to occur in the objects with high $L/L_{mathrm{Edd}}$, which is considerably consistent with the conclusions based on local AGNs. With three $M_{mathrm{BH}}$ estimation methods, the significance level of the trend is found to be better than $2.9sigma$, $3.2sigma$ and $1.8sigma$ for [OIII], [NeIII] and [NeV], respectively. rm After excluding the role of radio jets, the revealed dependence of NLR gas outflow on $L/L_{mathrm{Edd}}$ allows us to argue that the pressure caused by the wind/radiation launched/emitted from central supermassive black hole is the most likely origin of the outflow in these distant quasars, which implies that the outflow in luminous AGNs up to $zsim1$ have the same origin.
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