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Register a new userImprints of the super-Eddington accretion on the quasar clustering
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Taira Oogi
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Super-Eddington mass accretion has been suggested as an efficient mechanism to grow supermassive black holes (SMBHs). We investigate the imprint left by the radiative efficiency of the super-Eddington accretion process on the clustering of quasars using a new semi-analytic model of galaxy and quasar formation based on large-volume cosmological $N$-body simulations. Our model includes a simple model for the radiative efficiency of a quasar, which imitates the effect of photon trapping for a high mass accretion rate. We find that the model of radiative efficiency affects the relation between the quasar luminosity and the quasar host halo mass. The quasar host halo mass has only weak dependence on quasar luminosity when there is no upper limit for quasar luminosity. On the other hand, it has significant dependence on quasar luminosity when the quasar luminosity is limited by its Eddington luminosity. In the latter case, the quasar bias also depends on the quasar luminosity, and the quasar bias of bright quasars is in agreement with observations. Our results suggest that the quasar clustering studies can provide a constraint on the accretion disc model.
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Gravitational microlensing by the stellar population of lensing galaxies provides an important opportunity to spatially resolve the accretion disk structure in strongly lensed quasars. Some of the objects (like Einsteins cross) are reasonably consistent with the predictions of the standard accretion disk model. In other cases, the size of the emitting region is larger than predicted by the standard thin disk theory and practically independent on wavelength. This may be interpreted as an observational manifestation of an optically-thick scattering envelope possibly related to super-Eddington accretion with outflows.
We use a statistical sample of galaxy clusters from a large cosmological $N$-body$+$hydrodynamics simulation to examine the relation between morphology, or shape, of the X-ray emitting intracluster medium (ICM) and the mass accretion history of the galaxy clusters. We find that the mass accretion rate (MAR) of a cluster is correlated with the ellipticity of the ICM. The correlation is largely driven by material accreted in the last $sim 4.5$~Gyr, indicating a characteristic time-scale for relaxation of cluster gas. Furthermore, we find that the ellipticity of the outer regions ($Rsim R_{rm 500c}$) of the ICM is correlated with the overall MAR of clusters, while ellipticity of the inner regions ($lesssim 0.5 R_{rm 500c}$) is sensitive to recent major mergers with mass ratios of $geq 1:3$. Finally, we examine the impact of variations in cluster mass accretion history on the X-ray observable-mass scaling relations. We show that there is a {it continuous/} anti-correlation between the residuals in the $T_x-M$ relation and cluster MARs, within which merging and relaxed clusters occupy extremes of the distribution rather than form two peaks in a bi-modal distribution, as was often assumed previously. Our results indicate the systematic uncertainties in the X-ray observable-mass relations can be mitigated by using the information encoded in the apparent ICM ellipticity.
We present a systematic X-ray and multiwavelength study of a sample of 47 active galactic nuclei (AGNs) with reverberation-mapping measurements. This sample includes 21 super-Eddington accreting AGNs and 26 sub-Eddington accreting AGNs. Using high-state observations with simultaneous X-ray and UV/optical measurements, we investigate whether super-Eddington accreting AGNs exhibit different accretion disk-corona connections compared to sub-Eddington accreting AGNs. We find tight correlations between the X-ray-to-UV/optical spectral slope parameter ($alpha_{rm OX}$) and the monochromatic luminosity at $2500~r{A}$ ($L_{rm 2500~r{A}}$) for both the super- and sub-Eddington subsamples. The best-fit $alpha_{rm OX}-L_{rm 2500~r{A}}$ relations are consistent overall, indicating that super-Eddington accreting AGNs are not particularly X-ray weak in general compared to sub-Eddington accreting AGNs. We find dependences of $alpha_{rm OX}$ on both the Eddington ratio ($L_{rm Bol}/L_{rm Edd}$) and black hole mass ($M_{rm BH}$) parameters for our full sample. A multi-variate linear regression analysis yields $alpha_{rm OX}=-0.13 {rm log}(L_{rm Bol}/L_{rm Edd})-0.10 {rm log}M_{rm BH}-0.69$, with a scatter similar to that of the $alpha_{rm OX}-L_{rm 2500~r{A}}$ relation. The hard (rest-frame $>2rm ~keV$) X-ray photon index ($Gamma$) is strongly correlated with $L_{rm Bol}/L_{rm Edd}$ for the full sample and the super-Eddington subsample, but these two parameters are not significantly correlated for the sub-Eddington subsample. A fraction of super-Eddington accreting AGNs show strong X-ray variability, probably due to small-scale gas absorption, and we highlight the importance of employing high-state (intrinsic) X-ray radiation to study the accretion disk-corona connections in AGNs.
Owing to the advent of large area photometric surveys, the possibility to use broad band photometric data, instead of spectra, to measure the size of the broad line region of active galactic nuclei, has raised a large interest. We describe here a new method using time-delay lensed quasars where one or several images are affected by microlensing due to stars in the lensing galaxy. Because microlensing decreases (or increases) the flux of the continuum compared to the broad line region, it changes the contrast between these two emission components. We show that this effect can be used to effectively disentangle the intrinsic variability of those two regions, offering the opportunity to perform reverberation mapping based on single band photometric data. Based on simulated light curves generated using a damped random walk model of quasar variability, we show that measurement of the size of the broad line region can be achieved using this method, provided one spectrum has been obtained independently during the monitoring. This method is complementary to photometric reverberation mapping and could also be extended to multi-band data. Because the effect described above produces a variability pattern in difference light curves between pairs of lensed images which is correlated with the time-lagged continuum variability, it can potentially produce systematic errors in measurement of time delays between pairs of lensed images. Simple simulations indicate that time-delay measurement techniques which use a sufficiently flexible model for the extrinsic variability are not affected by this effect and produce accurate time delays.
Super-Eddington accretion onto massive black hole seeds may be commonplace in the early Universe, where the conditions exist for rapid accretion. Direct collapse black holes are often invoked as a possible solution to the observation of super massive black holes (SMBHs) in the pre-reionisation Universe. We investigate here how feedback, mainly in the form of bipolar jets, from super-Eddington accreting seed black holes will affect their subsequent growth. We find that, nearly independent of the mass loading of the bipolar jets, the violent outflows generated by the jets evacuate a region of approximately 0.1 pc surrounding the black hole seed. However, the jet outflows are unable to break free of the halo and their impact is limited to the immediate vicinity of the black hole. The outflows suppress any accretion for approximately a dynamical time. The gas then cools, recombines and falls back to the centre where high accretion rates are again observed. The overall effect is to create an effective accretion rate with values of between 0.1 and 0.5 times the Eddington rate. If this episodic accretion rate is maintained for order 500 million years then the black hole will increase in mass by a factor of between 3 and 300 but far short of the factor of $10^4$ required for the seeds to become the SMBHs observed at $z>6$. Therefore, direct collapse black holes born into atomic cooling haloes and which experience strong negative mechanical feedback will require external influences (e.g. rapid major mergers with other haloes) to promote efficient accretion and reach SMBH masses within a few hundred million years.
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