Radiation, winds, and jets from the active nucleus of a massive galaxy can interact with its interstellar medium, and this can lead to ejection or heating of the gas. This terminates star formation in the galaxy and stifles accretion onto the black hole. Such active galactic nuclei (AGN) feedback can account for the observed proportionality between the central black hole and the host galaxy mass. Direct observational evidence for the radiative or quasar mode of feedback, which occurs when AGN are very luminous, has been difficult to obtain but is accumulating from a few exceptional objects. Feedback from the kinetic or radio mode, which uses the mechanical energy of radio-emitting jets often seen when AGN are operating at a lower level, is common in massive elliptical galaxies. This mode is well observed directly through X-ray observations of the central galaxies of cool core clusters in the form of bubbles in the hot surrounding medium. The energy flow, which is roughly continuous, heats the hot intraclu...

Observational Evidence of Active Galactic Nuclei Feedback

We compile black hole (BH) masses for ~60,000 quasars in the redshift range 0.1 z 4.5 included in the Fifth Data Release of the Sloan Digital Sky Survey, using virial BH mass estimators based on the Hβ, Mg II, and C IV emission lines. Within our sample, the widths of the three lines follow lognormal distributions, with means and dispersions that do not depend strongly on luminosity or redshift. The Mg II- and Hβ-estimated BH masses are consistent with one another, but there is a positive bias between the C IV- and Mg II-estimated BH masses correlated with the C IV-Mg II blueshift, suggesting that the C IV estimator is more severely affected by a disk wind. If the underlying BH mass distribution decreases with mass and the Eddington ratio distribution at fixed true BH mass has nonzero width, we show that the measured virial BH mass and Eddington ratio distributions within finite luminosity bins are subject to Malmquist bias. We present a model that reproduces the observed virial mass distribution, quasar luminosity function, and line width distribution of our sample; it has an underlying BH mass distribution dN/dlog M ∝ M−2.6 and a lognormal true Eddington ratio distribution at fixed true mass with dispersion 0.4 dex and mean dependent on BH mass. In this model, the observed virial mass (Eddington ratio) distribution for the SDSS sample is biased high (low) by ~0.6 dex within finite luminosity bins. Finally, we compare virial BH masses of radio and broad absorption line quasars with ordinary quasars matched in redshift and luminosity.

Biases in Virial Black Hole Masses: An SDSS Perspective

We propose a ‘two-stage’ model for the effects of feedback from a bright quasar on the cold gas in a galaxy. It is difficult for winds or other forms of feedback from near the accretion disc to directly impact (let alone blow out of the galaxy) dense molecular clouds at ∼kpc. However, if such feedback can drive a weak wind or outflow in the hot, diffuse interstellar medium (a relatively ‘easy’ task), then in the wake of such an outflow passing over a cold cloud, a combination of instabilities and simple pressure gradients will drive the cloud material to effectively expand in the direction perpendicular to the incident outflow. This shredding/expansion (and the corresponding decrease in density) may alone be enough to substantially suppress star formation in the host. Moreover, such expansion, by even a relatively small factor, dramatically increases the effective cross-section of the cloud material and makes it much more susceptible to both ionization and momentum coupling from absorption of the incident quasar radiation field. We show that even a moderate effect of this nature can dramatically alter the ability of clouds at large radii to be fully ionized and driven into a secondary outflow by radiation pressure. Since the amount of momentum and volume which can be ionized by observed quasar radiation field is more than sufficient to affect the entire cold gas supply once it has been altered in this manner (and the ‘initial’ feedback need only initiate a moderate wind in the low-density hot gas), this reduces by an order of magnitude the required energy budget for feedback to affect a host galaxy. Instead of ∼5 per cent of the radiated energy (∼100 per cent momentum) needed if the initial feedback must directly heat or ‘blow out’ the galactic gas, if only ∼0.5 per cent of the luminosity (∼10 per cent momentum) can couple to drive the initial hot outflow, this mechanism could be efficient. This amounts to hot gas outflow rates from near the accretion disc of only ∼5–10 per cent of the black hole accretion rate.

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Quasar feedback: more bang for your buck

We develop and test a model for the cosmological role of mergers in the formation and quenching of red, early-type galaxies. By combining theoretically well-constrained halo and subhalo mass functions as a function of redshift and environment with empirical halo occupation models, we predict the distribution of mergers as a function of redshift, environment, and physical galaxy properties. Making the simple Ansatz that star formation is quenched after a gas-rich, spheroid-forming major merger, we demonstrate that this naturally predicts the turnover in the efficiency of star formation and baryon fractions in galaxies at ~ -->L* (without any parameters tuned to this value), as well as the observed mass functions and mass density of red galaxies as a function of redshift, the formation times of early-type galaxies as a function of mass, and the fraction of quenched galaxies as a function of galaxy and halo mass, environment, and redshift. Comparing our model to a variety of semianalytic models in which quenching is primarily driven by halo mass considerations or secular/disk instabilities, we demonstrate that our model makes unique and robust qualitative predictions for a number of observables, including the bivariate red fraction as a function of galaxy and halo mass, the density of passive galaxies at high redshifts, the emergence/evolution of the color-morphology-density relations at high redshift, and the fraction of disky/boxy (or cusp/core) spheroids as a function of mass. In each case, the observations favor a model in which some mechanism quenches future star formation after a major merger builds a massive spheroid. Models where quenching is dominated by a halo mass threshold fail to match the behavior of the bivariate red fractions, predict too low a density of passive galaxies at high redshift, and overpredict by an order of magnitude the mass of the transition from disky to boxy ellipticals. Models driven by secular disk instabilities also qualitatively disagree with the bivariate red fractions, fail to predict the observed evolution in the color-density relations, and predict order-of-magnitude incorrect distributions of kinematic types in early-type galaxies. We make specific predictions for how future observations, for example, quantifying the red fraction as a function of galaxy mass, halo mass, environment, or redshift, can break the degeneracies between a number of different assumptions adopted in present galaxy formation models. We discuss a variety of physical possibilities for this quenching and propose a mixed scenario in which traditional quenching in hot, quasi-static massive halos is supplemented by the strong shocks and feedback energy input associated with a major merger (e.g., tidal shocks, starburst-driven winds, and quasar feedback), which temporarily suppress cooling and establish the conditions of a dynamically hot halo in the central regions of the host, even in low-mass halos (below the traditional threshold for accretion shocks).

A Cosmological Framework for the Co-Evolution of Quasars, Supermassive Black Holes, and Elliptical Galaxies: II. Formation of Red Ellipticals

We present a catalog of 5039 broad absorption line (BAL) quasars (QSOs) in the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) QSO catalog that have absorption troughs covering a continuous velocity range ≥2000 km s–1. We have fitted ultraviolet (UV) continua and line emission in each case, enabling us to report common diagnostics of BAL strengths and velocities in the range –25, 000 to 0 km s–1 for Si IV λ1400, C IV λ1549, Al III λ1857, and Mg II λ2799. We calculate these diagnostics using the spectrum listed in the DR5 QSO catalog, and also for spectra from additional SDSS observing epochs when available. In cases where BAL QSOs have been observed with Chandra or XMM-Newton, we report the X-ray monochromatic luminosities of these sources. We confirm and extend previous findings that BAL QSOs are more strongly reddened in the rest-frame UV than non-BAL QSOs, and that BAL QSOs are relatively X-ray weak compared to non-BAL QSOs. The observed BAL fraction is dependent on the spectral signal-to-noise ratio (S/N); for higher S/N sources, we find an observed BAL fraction of ≈ 15%. BAL QSOs show a similar Baldwin effect as for non-BAL QSOs, in that their C IV emission equivalent widths decrease with increasing continuum luminosity. However, BAL QSOs have weaker C IV emission in general than do non-BAL QSOs. Sources with higher UV luminosities are more likely to have higher-velocity outflows, and the BAL outflow velocity and UV absorption strength are correlated with relative X-ray weakness. These results are in qualitative agreement with models that depend on strong X-ray absorption to shield the outflow from overionization and enable radiative acceleration. In a scenario in which BAL trough shapes are primarily determined by outflow geometry, observed differences in Si IV and C IV trough shapes would suggest that some outflows have ion-dependent structure.

https://iopscience.iop.org/article/10.1088/0004-637X/692/1/758/pdf

A catalog of broad absorption line quasars in Sloan digital sky survey data release 5

We have investigated a sample of 5088 quasars from the Sloan Digital Sky Survey Second Data Release in order to determine how the frequency and properties of broad absorptions lines (BALs) depend on black hole mass, bolometric luminosity, Eddington fraction (L/LEdd), and spectral slope. We focus only on high-ionization BALs and find a number of significant results. While quasars accreting near the Eddington limit are more likely to show BALs than lower L/LEdd systems, BALs are present in quasars accreting at only a few percent Eddington. We find a stronger effect with bolometric luminosity, such that the most luminous quasars are more likely to show BALs. There is an additional effect, previously known, that BAL quasars are redder on average than unabsorbed quasars. The strongest effects involving the quasar physical properties and BAL properties are related to terminal outflow velocity. Maximum observed outflow velocities increase with both the bolometric luminosity and the blueness of the spectral slope, suggesting that the ultraviolet luminosity to a great extent determines the acceleration. These results support the idea of outflow acceleration via ultraviolet line scattering. Subject headings: quasars: general — quasars: absorption lines — quasars: fundamental parameters

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Outflows and the Physical Properties of Quasars

We have investigated a sample of 5088 quasars from the Sloan Digital Sky Survey Second Data Release in order to determine how the frequency and properties of broad absorptions lines (BALs) depend on black hole mass, bolometric luminosity, Eddington fraction (L/L_Edd), and spectral slope. We focus only on high-ionization BALs and find a number of significant results. While quasars accreting near the Eddington limit are more likely to show BALs than lower $L/L_{Edd}$ systems, BALs are present in quasars accreting at only a few percent Eddington. We find a stronger effect with bolometric luminosity, such that the most luminous quasars are more likely to show BALs. There is an additional effect, previously known, that BAL quasars are redder on average than unabsorbed quasars. The strongest effects involving the quasar physical properties and BAL properties are related to terminal outflow velocity. Maximum observed outflow velocities increase with both the bolometric luminosity and the blueness of the spectral slope, suggesting that the ultraviolet luminosity to a great extent determines the acceleration. These results support the idea of outflow acceleration via ultraviolet line scattering.

Brian Scoggins

Papers

Outflows and the Physical Properties of Quasars

Outflows and the Physical Properties of Quasars