We use radiative transfer to study the growth of ionized regions around the brightest, z=8 quasars in a large cosmological hydrodynamic simulation that includes black hole growth and feedback (the MassiveBlack simulation). We find that in the presence of the quasar s the comoving HII bubble radii reach 10 Mpc/h after 20 My while with the stellar component alone the HII bubbles are smaller by at least an order of magnitude. Our calculations show that several features are not captured within an analytical growth model of Stromgren spheres. The X-ray photons from hard quasar spectra drive a smooth transition from fully neutral to partially neutral in the ionization front. However the transition from partially neutral to fully ionized is significantly more complex. We measure the distance to the edge of bubbles as a function of angle and use the standard deviation of these distances as a diagnostic of the isotropy of ionized regions. We find that the overlapping of nearby ionized regions from clustered halos not only increases the anisotropy, but also is the main mechanism which allows the outer radius to grow. We therefore predict that quasar ionized bubbles at this early stage in the reionization process should be both significantly larger and more irregularly shaped than bubbles around star forming galaxies. Before the star formation rate increases and the Universe fully reionizes, quasar bubbles will form the most striking and recognizable features in 21cm maps.
We examine recent high-precision measurements of small-scale quasar clustering (at $z\sim0.5-2$ on scales of $\sim25~\mathrm{kpc/h}$) from the SDSS in the context of the MassiveBlackII (MBII) cosmological hydrodynamic simulation and conditional luminosity function (CLF) modeling. At these high luminosities ($g < 20.85$ quasars), the MBII simulation volume ($100~\mathrm{cMpc}/h$ comoving boxsize) has only 3 quasar pairs at distances of $1-4$ Mpc. The black-hole masses for the pairs range between $M_{bh}\sim1-3\times 10^{9}~M_{\odot}/h$ and the quasar hosts are haloes of $M_h\sim1-3\times10^{14}…
We examine multiple AGN systems (triples and quadruples, in particular) in the \texttt{MassiveBlackII} simulation over a redshift range of $0.06\lesssim z \lesssim 4$. We identify AGN systems (with bolometric luminosity $L_{\mathrm{bol}}>10^{42}~\mathrm{ergs/sec}$) at different scales~(defined by the maximum distance between member AGNs) to determine the AGN multiplicity functions. This is defined as the volume/ surface density of AGN systems per unit \textit{richness} $R$, the number of AGNs in a system. We find that gravitationally bound multiple AGN systems tend to populate scales of $\less…
The conditions within the ionization front of a quasar during reionization (T ~ 30,000 K, neutral hydrogen fraction ~ 0.5) are ideal for producing Lyman-alpha emission via collisional excitation of hydrogen atoms. Observations of this emission, which could subtend >10 arcmin$^2$ on the sky, would definitively demonstrate the presence of a neutral intergalactic medium at the observed epoch, placing valuable constraints on the progress of reionization. We find that the expected Lyman-alpha surface brightness is significantly weaker than previously determined and may be impossible to observe with…
The larger-than-expected scatter in the opacity of the Ly$α$ forest suggests that the metagalactic ionizing background is strongly fluctuating at $z > 5.5$. Models for ionizing background fluctuations predict a strong positive bias on large scales, so the environments of massive $>10^{12}\,{\rm M}_\odot$ dark matter halos, e.g. $z\sim6$ quasar hosts, would be ideal laboratories to constrain the sources of ionizing photons. While the quasars themselves should overwhelm any plausible ionizing photon contribution from neighboring galaxies, proximate damped Ly$α$ absorbers (DLAs) have recently bee…
BLR Physical Conditions in Extreme Population A Quasars: a Method to Estimate Central Black Hole Mass at High Redshift
我们描述了一种方法，用于确定的物理条件在宽线区域的一个显着的子样本的Seyfert-1核和类星体。基于类星体紫外光谱中的中（Al III 1860，Si III 1892）和高（CIV 1549，Si IV 1397）电离线的几个诊断比率被用来约束发射气体的密度，电离和金属性。我们将该方法应用于两个极端的人口A类星体-原型NLSy 1 I Zw 1和高Z\NLSy 1-like对象，SDSS J120144.36+011611.6。我们发现了明确的物理条件：低电离（电离参数$< 10^{-2}$），高密度（10 $^{12} - 10^{13}$ cm^{-3}）和显着的金属富集。电离参数和密度可以独立地推导出每个源的不确定性，总是小于$\pm 0.3$的对数。我们用乘积密度乘以电离参数来估计宽线区半径和维里黑洞质量。基于本文描述的“光电离”分析的黑洞质量估计可能比从半径-光度相关性导出的更准确。
The Eddington ratio is a key parameter that governs the diversity of quasar properties. It can be scaled with a strong anti-correlation between optical Fe II and [O III] emission. In search of such indicators in the far-UV band, the HST far-UV spectra of 150 low-redshift quasars are analyzed in combination with their optical SDSS counterparts. The strength of Fe II+Fe III 1123 emission is significantly correlated with that of optical Fe II. A moderate correlation may also exist between Fe II 1071 and optical Fe II. The finding opens the possibility that far-UV Fe II emission may serve as a new…
We reanalyze the mid-infrared (5-40 $μ$m) Spitzer spectra of 86 low-redshift ($z < 0.5$) Palomar-Green quasars to investigate the nature of polycyclic aromatic hydrocarbon (PAH) emission and its utility as a star formation rate (SFR) indicator for the host galaxies of luminous active galactic nuclei (AGNs). We decompose the spectra with our recently developed template-fitting technique to measure PAH fluxes and upper limits, which we interpret using mock spectra that simulate the effects of AGN dilution. While luminous quasars can severely dilute and affect the detectability of emission lines,…
Neutral Helium multiplets, HeI*3189,3889,10830 are very useful diagnostics to the geometry and physical conditions of the absorbing gas in quasars. So far only a handful of HeI* detections have been reported. Using a newly developed method, we detected HeI*3889 absorption line in 101 sources of a well-defined sample of 285 MgII BAL quasars selected from the SDSS DR5. This has increased the number of HeI* BAL quasars by more than one order of magnitude. We further detected HeI*3189 in 50% (52/101) quasars in the sample. The detection fraction of HeI* BALs in MgII BAL quasars is about 35% as a w…
The inter-line comparison between high- and low-ionization emission lines has yielded a wealth of information on the quasar broad line region (BLR) structure and dynamics, including perhaps the earliest unambiguous evidence in favor of a disk + wind structure in radio-quiet quasars. We carried out an analysis of the CIV 1549 and Hbeta line profiles of 28 Hamburg-ESO high luminosity quasars and of 48 low-z, low luminosity sources in order to test whether the high-ionization line CIV 1549 width could be correlated with Hbeta and be used as a virial broadening estimator. We analyze intermediate- …
We have used spectra of 181 projected quasar pairs at separations $\le 1.5$ arcmins from the Sloan Digital Sky-Survey Data Release 12 in the redshift range of 2.5 to 3.5 to probe the proximity regions of the foreground quasars. We study the proximity effect both in the longitudinal as well as in the transverse directions, by carrying out a comparison of the \lya absorption lines originating from the vicinity of quasars to those originating from the general inter-galactic medium at the same redshift. We found an enhancement in the transmitted flux within 4 Mpc to the quasar in the longitudinal …
We present the variability study of broad absorption lines (BALs) in a uniformly radio-selected sample of 28 BAL quasars using the archival data from the FIRST Bright Quasar Survey (FBQS) and the Sloan Digital Sky Survey (SDSS), as well as those obtained by ourselves, covering time scales $\sim 1-10$ years in the quasar's rest-frame. To our surprise, 5 quasars showing strong variations are all belong to a special subclass of overlapping iron low ionization BAL (OFeLoBAL) quasars, however, other 4 non-overlapping FeLoBALs (non-OFeLoBALs) are invariable except one case with weak optical depth ch…
Over the past 15 years, examples of exotic radio-quiet quasars with intrinsically weak or absent broad emission line regions (BELRs) have emerged from large-scale spectroscopic sky surveys. Here, we present spectroscopy of seven such weak emission line quasars (WLQs) at moderate redshifts (z=1.4-1.7) using the X-shooter spectrograph, which provides simultaneous optical and near-infrared spectroscopy covering the rest-frame ultraviolet through optical. These new observations effectively double the number of WLQs with spectroscopy in the optical rest-frame, and they allow us to compare the stren…
We investigate the impact of quasars on the ionization of the surrounding intergalactic medium (IGM) with the radiative transfer code \texttt{CRASH4}, now accounting for X-rays and secondary electrons. After comparing with analytic solutions, we post-process a cosmic volume ($ \approx 1.5\times 10^4$ Mpc$^3 h^{-3}$) containing a ULAS J1120+0641-like quasar (QSO) hosted by a $5 \times 10^{11} {\rm M}_\odot h^{-1}$ dark matter (DM) halo. We find that: (i) the average HII region ($R\sim3.2$~pMpc in a lifetime $t_f = 10^7$~yrs) is mainly set by UV flux, in agreement with semi-analytic scaling rela…
We study the dramatic decrease in iron absorption strength in the iron low-ionization broad absorption line quasar SDSS J084133.15+200525.8. We report on the continued weakening of absorption in the prototype of this class of variable broad absorption line quasar, FBQS J140806.2+305448. We also report a third example of this class, SDSS J123103.70+392903.6; unlike the other two examples, it has undergone an increase in observed continuum brightness (at 3000~Å rest-frame) as well as a decrease in iron absorption strength. These changes could be caused by absorber transverse motion or by ionizat…
Non-equilibrium ionization effects are important in cosmological hydrodynamical simulations but are computationally expensive. We study the effect of non-equilibrium ionization evolution and UV ionizing background (UVB) generated with different quasar spectral energy distribution (SED) on the derived physical conditions of the intergalactic medium (IGM) at $2\leq z \leq 6$ using our post-processing tool 'Code for Ionization and Temperature Evolution' (CITE). CITE produces results matching well with self-consistent simulations more efficiently. The HeII reionization progresses more rapidly in n…
In this paper, we present an intercomparison study of two quasars, SDSS J145618.32+340037.2 and SDSS J215331.50-025514.1, which have proximate damped Lya systems (PDLAs) with residual flux upon the Lya absorption trough. Though they both have residual flux as luminous as $10^{43}erg/s$, their PDLAs are quite different in, e.g., HI column density, metal line absorption strength, high-ionization absorption lines as well as residual flux strength. For J1456, the HI column density is $20.6\pm0.2$, with za=2.3138, nearly identical to the quasar redshift (z=2.3142) determined from the [OIII] emissio…
Quasars accreting matter at very high rates (known as extreme Population A [xA] or super-Eddington accreting massive black holes) provide a new class of distance indicators covering cosmic epochs from the present-day Universe up to less than 1 Gyr from the Big Bang. The very high accretion rate makes it possible that massive black holes hosted in xA quasars radiate at a stable, extreme luminosity-to-mass ratio. This in turns translates into stable physical and dynamical conditions of the mildly ionized gas in the quasar low-ionization line emitting region. In this contribution, we analyze the …
We study quasar proximity zones in the redshift range $5.77 \leq z \leq 6.54$ by homogeneously analyzing $34$ medium resolution spectra, encompassing both archival and newly obtained data, and exploiting recently updated systemic redshift and magnitude measurements. Whereas previous studies found strong evolution of proximity zone sizes with redshift, and argued that this provides evidence for a rapidly evolving intergalactic medium (IGM) neutral fraction during reionization, we measure a much shallower trend $\propto(1+z)^{-1.44}$. We compare our measured proximity zone sizes to predictions f…
We analyze relative abundances and ionization conditions in a strong absorption system at z=6.84, seen in the spectrum of the z=7.54 background quasar ULAS J134208.10+092838.61. Singly ionized C, Si, Fe, Mg, and Al measurements are consistent with a warm neutral medium that is metal-poor but not chemically pristine. Firm non-detections of C IV and Si IV imply that any warm ionized phase of the IGM or CGM has not yet been enriched past the ultra-metal-poor regime (<0.001Z_{solar}), unlike lower redshift DLAs where these lines are nearly ubiquitous. Relative abundances of the heavy elements 794 …
We report the discovery of excess broad band absorption near 2250 A (EBBA) in the spectra of seven broad absorption line (BAL) quasars. By comparing with the statistical results from the control quasar sample, the significance for the detections are all above the > 4σ level, with five above > 5σ. The detections have also been verified by several other independent methods. The EBBAs present broader and weaker bumps at smaller wavenumbers than the Milky Way, and similar to the Large Magellanic Cloud. The EBBA bump may be related to the 2175 A bump seen in the Local Group and may be a counterpart…
The intense radiation emitted by luminous quasars dramatically alters the ionization state of their surrounding IGM. This so-called proximity effect extends out to tens of Mpc, and manifests as large coherent regions of enhanced Lyman-$α$ (Ly$α$) forest transmission in absorption spectra of background sightlines. Here we present a novel method based on Ly$α$ forest tomography, which is capable of mapping these quasar `light echoes' in three dimensions. Using a dense grid (10-100) of faint ($m_r\approx24.7\,\mathrm{mag}$) background galaxies as absorption probes, one can measure the ionization …
The duration of quasar accretion episodes is a key quantity for distinguishing between models for the formation and growth of supermassive black holes, the evolution of quasars, and their potential feedback effects on their host galaxies. However, this critical timescale, often referred to as the quasar lifetime, is still uncertain by orders of magnitude ($t_{\rm Q} \simeq 0.01\,{\rm Myr} - 1\,{\rm Gyr}$). Absorption spectra of quasars exhibiting transmission in the He II Ly$α$ forest provide a unique opportunity to make precise measurements of the quasar lifetime. Indeed, the size of a quasar…
FeLoBAL Outflow Variability Constraints from Multi-Year Observations
宽吸收线流出流的物理性质和动力学行为是理解星系中心与其宿主之间联系的关键主题。FeLoBALs（与低电离Fe II BALs的存在有关）是一类特殊的类星体流出物，约占BAL人口的1%。凭借其大的柱密度和明显的外流动力学光度，FeLoBALs似乎是非常强大的，是星系演化反馈的强有力的候选人。我们对12个发射红移在0.69和1.93之间的FeLoBAL类星体进行了变异性研究，这些类星体在类星体的休息框架中跨越了每周和多年的时间尺度。我们在我们的四个对象中检测到低电离物质（Fe II，Mg II）的吸收线变化，我们建立了一个有代表性的上限，吸收体与超大质量黑洞（SMBH）的距离约为20秒差距。我们的目标是了解产生可变性的机制（例如电离变化或气体穿过我们的视线），并对流出的位置，结构和动能施加新的约束。
