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Register a new userThe WISSH Quasars Project III. X-ray properties of hyper-luminous quasars
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We perform a survey of the X-ray properties of 41 objects from the WISE/SDSS selected Hyper-luminous (WISSH) quasars sample, composed by 86 broad-line quasars (QSOs) with bolometric luminosity $L_{Bol}geq 2times 10^{47},erg, s^{-1}$, at z~2-4. All but 3 QSOs show unabsorbed 2-10 keV luminosities $L_{2-10}geq10^{45} ,erg ,s^{-1}$. Thanks to their extreme radiative output across the Mid-IR-to-X-ray range, WISSH QSOs offer the opportunity to significantly extend and validate the existing relations involving $L_{2-10}$. We study $L_{2-10}$ as a function of (i) X-ray-to-Optical (X/O) flux ratio, (ii) mid-IR luminosity ($L_{MIR}$), (iii) $L_{Bol}$ as well as (iv) $alpha_{OX}$ vs. the 2500$mathring{A}$ luminosity. We find that WISSH QSOs show very low X/O(<0.1) compared to typical AGN values; $L_{2-10}/L_{MIR}$ ratios significantly smaller than those derived for AGN with lower luminosity; large X-ray bolometric corrections $k_{rm Bol,X}sim$ 100-1000; and steep $-2<alpha_{OX}<-1.7$. These results lead to a scenario where the X-ray emission of hyper-luminous quasars is relatively weaker compared to lower-luminosity AGN. Models predict that such an X-ray weakness can be relevant for the acceleration of powerful high-ionization emission line-driven winds, commonly detected in the UV spectra of WISSH QSOs, which can in turn perturb the X-ray corona and weaken its emission. Accordingly, hyper-luminous QSOs represent the ideal laboratory to study the link between the AGN energy output and wind acceleration. Additionally, WISSH QSOs show very large BH masses ($log[M_{rm BH}/M_{odot}]$>9.5). This enables a more robust modeling of the $Gamma-M_{BH}$ relation by increasing the statistics at high masses. We derive a flatter $Gamma$ dependence than previously found over the broad range 5 <$log(M_{rm BH}/M_{odot})$ < 11.
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Studying the coupling between the energy output produced by the central quasar and the host galaxy is fundamental to fully understand galaxy evolution. Quasar feedback is indeed supposed to dramatically affect the galaxy properties by depositing large amounts of energy and momentum into the ISM. In order to gain further insights on this process, we study the SEDs of sources at the brightest end of the quasar luminosity function, for which the feedback mechanism is supposed to be at its maximum. We model the rest-frame UV-to-FIR SEDs of 16 WISE-SDSS Selected Hyper-luminous (WISSH) quasars at 1.8 < z < 4.6 disentangling the different emission components and deriving physical parameters of both the nuclear component and the host galaxy. We also use a radiative transfer code to account for the contribution of the quasar-related emission to the FIR fluxes. Most SEDs are well described by a standard combination of accretion disk+torus and cold dust emission. However, about 30% of them require an additional emission component in the NIR, with temperatures peaking at 750K, which indicates the presence of a hotter dust component in these powerful quasars. We measure extreme values of both AGN bolometric luminosity (LBOL > 10^47 erg/s) and SFR (up to 2000 Msun/yr). A new relation between quasar and star-formation luminosity is derived (LSF propto LQSO^(0.73)) by combining several Herschel-detected quasar samples from z=0 to 4. Future observations will be crucial to measure the molecular gas content in these systems, probe the impact between quasar-driven outflows and on-going star-formation, and reveal the presence of merger signatures in their host galaxies.
We present an ALMA high-resolution observation of the 840 um continuum and [CII] line emission in the WISE-SDSS selected hyper-luminous (WISSH) QSO J1015+0020 at z~4.4. Our analysis reveals an exceptional overdensity of [CII]-emitting companions with a very small (<150 km/s) velocity shift with respect to the QSO redshift. We report the discovery of the closest companion observed so far in submillimetre observations of high-z QSOs. It is only 2.2 kpc distant and merging with J1015+0020, while two other [CII] emitters are found at 8 and 17 kpc. Two strong continuum emitters are also detected at <3.5 arcsec. They are likely associated to the same overdense structure of J1015+0020, as they exceed by a factor of 100 the number of expected sources, considering the Log(N)-Log(S) at 850 um. The host galaxy of J1015+0020 shows a SFR of about 100 Msun/yr while the total SFR of the QSO and its companion galaxies is a factor of 10 higher, indicating that substantial stellar mass assembly at early epochs may have taken place in the QSO satellites. For J1015+0020 we compute a SMBH mass MBH~6E9 Msun and a dynamical mass Mdyn~4E10 Msun . This translates into an extreme ratio Mdyn/MBH~7. The total stellar mass of the QSO host galaxy plus the [CII] emitters already exceeds 1E11 Msun at z~4.4. These sources will likely merge and develop into a giant galaxy of 1.3E12 Msun. Under the assumption of constant mass or Eddington accretion rate equal to the observed values, we find that the growth timescale of the host galaxy is comparable or even shorter than that inferred for the SMBH.
Hyperluminous quasars ($L_{rm bol}gtrsim 10^{47}$ erg s$^{-1}$) are ideal laboratories to study the interaction and impact of extreme radiative field and the most powerful winds in the AGN nuclear regions. They typically exhibit low coronal X-ray luminosity ($L_{rm X}$) compared to the UV and MIR radiative outputs ($L_{rm UV}$ and $L_{rm MIR}$) with a non-negligible fraction of them reporting even $sim$1 dex weaker $L_{rm X}$ compared to the prediction of the well established $L_{rm X}$-$L_{rm UV}$ and $L_{rm X}$-$L_{rm MIR}$ relations followed by the bulk of the AGN population. We report in our WISE/SDSS-selected Hyperluminous (WISSH) $z=2-4$ broad-line quasar sample, the discovery of a dependence between the intrinsic 2-10 keV luminosity ($L_{rm 2-10}$) and the blueshifted velocity of the CIV emission line ($v_{rm CIV}$) indicative of accretion disc winds. In particular, sources with fastest winds ($v_{rm CIV}gtrsim 3000~rm km s^{-1}$) possess $sim$0.5-1 dex lower $L_{rm 2-10}$ than sources with negligible $v_{rm CIV}$. No similar dependence is found on $L_{rm UV}$, $L_{rm MIR}$, $L_{rm bol}$, photon index and absorption column density. We interpret these findings in the context of accretion disc wind models. Both magnetohydrodynamic and line-driven models can qualitatively explain the reported relations as a consequence of X-ray shielding from the inner wind regions. In case of line-driven winds, the launch of fast winds is favoured by a reduced X-ray emission, and we speculate that these winds may play a role in directly limiting the coronal hard X-ray production.
During the last years, Ly$alpha$ nebulae have been routinely detected around high-z, radio-quiet quasars (RQQs) thanks to the advent of sensitive integral field spectrographs. Constraining the physical properties of the Ly$alpha$ nebulae is crucial for a full understanding of the circum-galactic medium (CGM), which is a venue of feeding and feedback processes. The most luminous quasars are privileged test-beds to study these processes, given their large ionizing fluxes and dense CGM environments in which they are expected to be embedded. We aim at characterizing the rest-frame UV emission lines in the CGM around a hyper-luminous, broad emission line, RQQ at z~3.6, that exhibits powerful outflows at both nuclear and host galaxy scales. We analyze VLT/MUSE observations of the quasar J1538+08 and perform a search for extended UV emission lines to characterize its morphology, emissivity, kinematics and metal content. We report the discovery of a very luminous ($sim2 times10^{44}~erg~s^{-1}$), giant Ly$alpha$ nebula and a likely associated extended CIV nebula. The Ly$alpha$ nebula emission exhibits moderate blueshift compared with the quasar systemic redshift and large average velocity dispersion ($sigma_{v}$ ~700 $km~s^{-1}$) across the nebula, while the CIV nebula shows $sigma_{v}$~$350~km~s^{-1}$. The Ly$alpha$ line profile exhibits a significant asymmetry towards negative velocity values at 20-30 kpc south of the quasar and is well parameterized by two Gaussian components: a narrow ($sigma$~$470~km~s^{-1}$) systemic one plus a broad ($sigma$~1200 $km~s^{-1}$), blueshifted (~1500 $km~s^{-1}$) one. Our analysis of the MUSE observation of J1538+08 reveals metal-enriched CGM around this hyper-luminous quasar and our detection of blueshifted emission in the line profile of the Ly$alpha$ nebula suggests that powerful nuclear outflows can propagate through the CGM over tens of kpc.
The clustering of active galactic nuclei (AGN) sheds light on their typical large (Mpc-scale) environments, which can constrain the growth and evolution of supermassive black holes. Here we measure the clustering of luminous X-ray-selected AGN in the Stripe 82X and XMM-XXL-North surveys around the peak epoch of black hole growth, in order to investigate the dependence of luminosity on large-scale AGN environment. We compute the auto-correlation function of AGN in two luminosity bins, $10^{43}leq L_X<10^{44.5}$ erg s$^{-1}$ at $zsim 0.8$ and $L_Xgeq 10^{44.5}$ erg s$^{-1}$ at $zsim 1.8$, and calculate the AGN bias taking into account the redshift distribution of the sources using three different methods. Our results show that while the less luminous sample has an inferred typical halo mass that is smaller than for the more luminous AGN, the host halo mass may be less dependent on luminosity than suggested in previous work. Focusing on the luminous sample, we calculate a typical host halo mass of $sim 10^{13}$ M$_{odot}~h^{-1}$, which is similar to previous measurements of moderate-luminosity X-ray AGN and significantly larger than the values found for optical quasars of similar luminosities and redshifts. We suggest that the clustering differences between different AGN selection techniques are dominated by selection biases, and not due to a dependence on AGN luminosity. We discuss the limitations of inferring AGN triggering mechanisms from halo masses derived by large-scale bias.
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