Quasars Probing Quasars IV: Joint Constraints on the Circumgalactic Medium from Absorption and Emission

We have constructed a sample of 29 close projected quasar pairs where the background quasar spectrum reveals absorption from optically thick HI gas associated with the foreground quasar. These unique sightlines allow us to study the quasar circumgalactic medium (CGM) in absorption and emission simultaneously, because the background quasar pinpoints large concentrations of gas where Ly-a emission, resulting from quasar-powered fluorescence, resonant Ly-a scattering, and/or cooling radiation, is expected. A sensitive slit-spectroscopic search (1-sigma limits of SB_Lya ~= 3e-18 erg/s/cm^2/arcsec^2) for diffuse Ly-a emission in the environments of the foreground quasars is conducted. We fail to detect large-scale ~ 100 kpc Ly-a emission, either at the location of the optically thick absorbers or in the foreground quasar halos, in all cases except a single system. We interpret these non-detections as evidence that the gas detected in absorption is shadowed from the quasar UV radiation due to obscuration effects, which are frequently invoked in unified models of AGN. Small-scale R_perp <~ 50 kpc extended Ly-a nebulosities are detected in 34% of our sample, which are likely the high-redshift analogs of the extended emission-line regions commonly observed around low-redshift (z < 0.5) quasars. We also detect a compact high rest-frame equivalent width (W_Lya > 50 A) Ly-alpha-emitter with luminosity L_Lya =2.1+-0.32e41 erg/s at small impact parameter R_perp=134 kpc from one foreground quasar, and argue that it is more likely to result from quasar-powered fluorescence, than simply be a star-forming galaxy clustered around the quasar. Our observations imply that much deeper integrations with upcoming integral-field spectrometers such as MUSE and KCWI will be able to routinely detect a diffuse Ly-a glow around bright quasars on scales R ~ 100 kpc and thus directly image the CGM. [abridged]Comment: 39 pages, 5 figures, 1 table, accepted by ApJ: http://adsabs.harvard.edu/abs/2013ApJ...766...58

He II Proximity Effect and the Lifetime of Quasars

The lifetime of quasars is fundamental for understanding the growth of supermassive black holes, and is an important ingredient in models of the reionization of the intergalactic medium. However, despite various attempts to determine quasar lifetimes, current estimates from a variety of methods are uncertain by orders of magnitude. This work combines cosmological hydrodynamical simulations and 1D radiative transfer to investigate the structure and evolution of the He II Ly$\alpha$ proximity zones around quasars at $z \simeq 3-4$. We show that the time evolution in the proximity zone can be described by a simple analytical model for the approach of the He II fraction $x_{\rm HeII}\left( t \right)$ to ionization equilibrium, and use this picture to illustrate how the transmission profile depends on the quasar lifetime, quasar UV luminosity, and the ionization state of helium in the ambient IGM (i.e. the average He II fraction, or equivalently the metagalactic He II ionizing background). A significant degeneracy exists between the lifetime and the average He II fraction, however the latter can be determined from measurements of the He II Ly$\alpha$ optical depth far from quasars, allowing the lifetime to be measured. We advocate stacking existing He II quasar spectra at $z\sim 3$, and show that the shape of this average proximity zone profile is sensitive to lifetimes as long as $\sim 30$ Myr. At higher redshift $z\sim 4$ where the He II fraction is poorly constrained, degeneracies will make it challenging to determine these parameters independently. Our analytical model for He II proximity zones should also provide a useful description of the properties of H I proximity zones around quasars at $z \simeq 6-7$.Comment: 26 pages, 18 figures, accepted to Ap

Quasars Probing Quasars IX. The Kinematics of the Circumgalactic Medium Surrounding z ~ 2 Quasars

We examine the kinematics of the gas in the environments of galaxies hosting quasars at $z\sim2$. We employ 148 projected quasar pairs to study the circumgalactic gas of the foreground quasars in absorption. The sample selects foreground quasars with precise redshift measurements, using emission-lines with precision $\lesssim300\,{\rm km\,s^{-1}}$ and average offsets from the systemic redshift $\lesssim|100\,{\rm km\,s^{-1}}|$. We stack the background quasar spectra at the foreground quasar's systemic redshift to study the mean absorption in \ion{C}{2}, \ion{C}{4}, and \ion{Mg}{2}. We find that the mean absorptions exhibit large velocity widths $\sigma_v\approx300\,{\rm km\,s^{-1}}$. Further, the mean absorptions appear to be asymmetric about the systemic redshifts. The mean absorption centroids exhibit small redshift relative to the systemic $\delta v\approx+200\,{\rm km\,s^{-1}}$, with large intrinsic scatter in the centroid velocities of the individual absorption systems. We find the observed widths are consistent with gas in gravitational motion and Hubble flow. However, while the observation of large widths alone does not require galactic-scale outflows, the observed offsets suggest that the gas is on average outflowing from the galaxy. The observed offsets also suggest that the ionizing radiation from the foreground quasars is anisotropic and/or intermittent.Comment: 13 pages, 9 figures, accepted to Ap

Quasars Probing Quasars VII. The Pinnacle of the Cool Circumgalactic Medium Surrounds Massive z~2 Galaxies

We survey the incidence and absorption strength of the metal-line transitions CII 1334 and CIV from the circumgalactic medium (CGM) surrounding z~2 quasars, which act as signposts for massive dark matter halos M_halo~10^12.5 Msun. On scales of the virial radius (Mvir~160kpc), we measure a high covering fraction fC=0.73+/-0.10 to strong CII absorption (rest equivalent width W1334>0.2A), implying a massive reservoir of cool (T~10^4K) metal enriched gas. We conservatively estimate a metal mass exceeding 10^8 Msun. We propose these metals trace enrichment of the incipient intragroup/intracluster medium that these halos eventually inhabit. This cool CGM around quasars is the pinnacle amongst galaxies observed at all epochs, as regards covering fraction and average equivalent width of HI Lya and low-ion metal absorption. We argue that the properties of this cool CGM primarily reflect the halo mass, and that other factors such as feedback, star-formation rate, and accretion from the intergalactic medium are secondary. We further estimate, that the CGM of massive, z~2 galaxies accounts for the majority of strong MgII absorption along random quasar sightlines. Lastly, we detect an excess of strong CIV absorption (W1548>0.3A) over random incidence to 1Mpc physical impact parameter and measure the quasar-CIV cross-correlation function: xi(r)=(r/r0)^-g with r0 = 7.5Mpc and g=1.7. Consistent with previous work on larger scales, we infer that this highly ionized CIV gas traces massive (10^12 Msun) halos.Comment: 27 pages, 16 figures; Re-submitted to ApJ following referee comments; Additional comments encouraged prior to publicatio

Early and Extended Helium Reionization Over More Than 600 Million Years of Cosmic Time

We measure the effective optical depth of HeII Ly\alpha\ absorption \tau$_\mathsf{eff,HeII}$ at 2.3<z<3.5 in 17 UV-transmitting quasars observed with UV spectrographs on the Hubble Space Telescope (HST). The median \tau$_\mathsf{eff,HeII}$ values increase gradually from 1.95 at z=2.7 to 5.17 at z=3.4, but with a strong sightline-to-sightline variance. Many $\simeq$35 comoving Mpc regions of the z>3 intergalactic medium (IGM) remain transmissive (\tau$_\mathsf{eff,HeII}$<4), and the gradual trend with redshift appears consistent with density evolution of a fully reionized IGM. These modest optical depths imply average HeII fractions of x$_\mathsf{HeII}$<0.01 and HeII ionizing photon mean free paths of $\simeq$50 comoving Mpc at z$\simeq$3.4, thus requiring that a substantial volume of the helium in the Universe was already doubly ionized at early times; this stands in conflict with current models of HeII reionization driven by luminous quasars. Along 10 sightlines we measure the coeval HI Ly\alpha\ effective optical depths, allowing us to study the density dependence of \tau$_\mathsf{eff,HeII}$ at z$\sim$3. We establish that the dependence of \tau$_\mathsf{eff,HeII}$ on increasing \tau$_\mathsf{eff,HI}$ is significantly shallower than expected from simple models of an IGM reionized in HeII. This requires higher HeII photoionization rates in overdense regions or underdense regions being not in photoionization equilibrium. Moreover, there are very large fluctuations in \tau$_\mathsf{eff,HeII}$ at all $\tau_\mathsf{eff,HI}$, which greatly exceed the expectations from these simple models. These data present a distinct challenge to scenarios of HeII reionization - an IGM where HeII appears to be predominantly ionized at z$\simeq$3.4, and with a radiation field strength that may be correlated with the density field, but exhibits large fluctuations at all densities.Comment: 31 pages, 15 figures; accepted to ApJ; systematic errors in the data corrected, conclusions unchange

Quasar Quartet Embedded in Giant Nebula Reveals Rare Massive Structure in Distant Universe

All galaxies once passed through a hyperluminous quasar phase powered by accretion onto a supermassive black hole. But because these episodes are brief, quasars are rare objects typically separated by cosmological distances. In a survey for Lyman-alpha emission at redshift z ~ 2, we discovered a physical association of four quasars embedded in a giant nebula. Located within a substantial overdensity of galaxies, this system is probably the progenitor of a massive galaxy cluster. The chance probability of finding a quadruple quasar is estimated to be ~10^-7, implying a physical connection between Lyman-alpha nebulae and the locations of rare protoclusters. Our findings imply that the most massive structures in the distant universe have a tremendous supply (~ 10^11 solar masses) of cool dense (volume density ~1 cm^-3) gas, which is in conflict with current cosmological simulations.Comment: accepted for publication in Science. Main text: 11 pages, 4 figures; Supplementary Online Material: 52 pages, 10 figures, 6 table

LSST: a Complementary Probe of Dark Energy

The number of mass clusters and their distribution in redshift are very sensitive to the density of matter Omega_m and the equation of state of dark energy w. Using weak lens gravitational tomography one can detect clusters of dark matter, weigh them, image their projected mass distribution, and determine their 3-D location. The degeneracy curve in the Omega_m - w plane is nearly orthogonal to that from CMB or SN measurements. Thus, a combination of CMB data with weak lens tomography of clusters can yield precision measurements of Omega_m and w, independently of the SN observations. The Large Synoptic Survey Telescope (LSST) will repeatedly survey 30,000 square degrees of the sky in multiple wavelengths. LSST will create a 3-D tomographic assay of mass overdensities back to half the age of the universe by measuring the shear and color-redshift of billions of high redshift galaxies. By simultaneously measuring several functions of cosmic shear and mass cluster abundance, LSST will provide a number of independent constraints on the dark energy density and the equation of state.Comment: 9 pages, 6 figures, for Proc. 5th International UCLA Symposium on Sources and Detection of Dark Matter, Marina del Rey, February 2002, ed. D. Clin

Deep HeII and CIV Spectroscopy of a Giant Lyman alpha Nebula: Dense Compact Gas Clumps in the Circumgalactic Medium of a z~2 Quasar

The recent discovery by Cantalupo et al. (2014) of the largest (~500 kpc) and luminous Ly-alpha nebula associated with the quasar UM287 (z=2.279) poses a great challenge to our current understanding of the astrophysics of the halos hosting massive z~2 galaxies. Either an enormous reservoir of cool gas is required $M\simeq10^{12}$ $M_{\odot}$, exceeding the expected baryonic mass available, or one must invoke extreme gas clumping factors not present in high-resolution cosmological simulations. However, observations of Ly-alpha emission alone cannot distinguish between these two scenarios. We have obtained the deepest ever spectroscopic integrations in the HeII and CIV lines with the goal of detecting extended line emission, but detect neither line to a 3$\sigma$ limiting SB $\simeq10^{-18}$ erg/s/cm$^2$/arcsec$^2$. We construct models of the expected emission spectrum in the highly probable scenario that the nebula is powered by photoionization from the central hyper-luminous quasar. The non-detection of HeII implies that the nebular emission arises from a mass $M_{\rm c}\lesssim6.4\times10^{10}$ $M_{\odot}$ of cool gas on ~200 kpc scales, distributed in a population of remarkably dense ($n_{\rm H}\gtrsim3$ cm$^{-3}$) and compact ($R\lesssim20$ pc) clouds, which would clearly be unresolved by current cosmological simulations. Given the large gas motions suggested by the Ly-alpha line ($v\simeq$ 500 km/s), it is unclear how these clouds survive without being disrupted by hydrodynamic instabilities. Our study serves as a benchmark for future deep integrations with current and planned wide-field IFU such as MUSE, KCWI, and KMOS. Our work suggest that a $\simeq$ 10 hr exposure would likely detect ~10 rest-frame UV/optical emission lines, opening up the possibility of conducting detailed photoionization modeling to infer the physical state of gas in the CGM.Comment: 24 pages, 11 figures, submitted to Ap

The Stacked Lyman-Alpha Emission Profile from the Circum-Galactic Medium of z~2 Quasars

In the context of the FLASHLIGHT survey, we obtained deep narrow band images of 15 $z\sim2$ quasars with GMOS on Gemini-South in an effort to measure Ly$\alpha$ emission from circum- and inter-galactic gas on scales of hundreds of kpc from the central quasar. We do not detect bright giant Ly$\alpha$ nebulae (SB~10$^{-17}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ at distances >50 kpc) around any of our sources, although we routinely ($\simeq47$%) detect smaller scale <50 kpc Ly$\alpha$ emission at this SB level emerging from either the extended narrow emission line regions powered by the quasars or by star-formation in their host galaxies. We stack our 15 deep images to study the average extended Ly$\alpha$ surface brightness profile around $z\sim2$ quasars, carefully PSF-subtracting the unresolved emission component and paying close attention to sources of systematic error. Our analysis, which achieves an unprecedented depth, reveals a surface brightness of SB$_{\rm Ly\alpha}\sim10^{-19}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ at $\sim200$ kpc, with a $2.3\sigma$ detection of Ly$\alpha$ emission at SB$_{\rm Ly\alpha}=(5.5\pm3.1)\times10^{-20}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ within an annulus spanning 50 kpc <R< 500 kpc from the quasars. Assuming this Ly$\alpha$ emission is powered by fluorescence from highly ionized gas illuminated by the bright central quasar, we deduce an average volume density of $n_{\rm H}=0.6\times10^{-2}$ cm$^{-3}$ on these large scales. Our results are in broad agreement with the densities suggested by cosmological hydrodynamical simulations of massive ($M\simeq10^{12.5}M_\odot$) quasar hosts, however they indicate that the typical quasars at these redshifts are surrounded by gas that is a factor of ~100 times less dense than the (~1 cm$^{-3}$) gas responsible for the giant bright Ly$\alpha$ nebulae around quasars recently discovered by our group.Comment: 22 pages, 13 figures, 1 table, submitted to Ap

Observational Constraints on the Self Interacting Dark Matter Scenario and the Growth of Supermassive Black Holes

We consider the consequences of SIDM for a velocity dependent cross section per unit mass. Accretion of SIDM onto seed black holes can produce supermassive black holes that are too large for certain combinations of parameters,which is used to obtain a new constraint on the dark matter interaction. Constraints due to other considerations are presented and previous ones are generalized. The black hole constraint is extremely sensitive to the slope \alpha, of the inner density profile of dark halos. For the most probable value of \alpha=1.3, there exists a narrow range in parameter space, such that all constraints are satisfied. However, the adiabatic compression of the dark halo by baryons as they cool and contract in normal galaxies yields a steeper cusp, \alpha=1.7. This gives a tighter constraint, which would exclude SIDM as a possible solution to the purported problems with CDM in the absence of other dynamical processes. Nevertheless, SIDM with parameters consistent with this stronger constraint, can explain the ubiquity of supermassive black holes in the centers of galaxies. A ``best fit'' model is presented which reproduces the supermassive black hole masses and their observed correlations with the velocity dispersion of the host bulges. Specifically, the fourth power dependence of black hole mass on velocity dispersion is a direct consequence of the power spectrum having an index of n=-2. Although the dark matter collision rates for this model are too small to directly remedy problems with CDM, mergers between dark halos harboring supermassive black holes at high redshift could ameliorate the cuspy halo problem. This scenario also explains the lack of comparable supermassive black holes in bulgeless galaxies like M33