A near-infrared view of luminous quasars: black hole masses, outflows and hot dust

Supermassive black holes (BHs) and their host-galaxies are thought to evolve in tandem, with the energy output from the rapidly-accreting BH regulating star formation and the growth of the BH itself. The goal of better understanding this process has led to much work focussing on the properties of quasars at high redshifts, $z\gtrsim 2$, when cosmic star formation and BH accretion both peaked. At these redshifts, however, ground-based statistical studies of the quasar population generally have no access to the rest-frame optical spectral region, which is needed to measure H$\beta$-based BH masses and narrow line region outflow properties. The cornerstone of this thesis has been a new near-infrared spectroscopic catalogue providing rest-frame optical data on 434 luminous quasars at redshifts $1.5 \lesssim z \lesssim 4$. At high redshift, $z \gtrsim 2$, quasar BH masses are derived using the velocity-width of the CIV broad emission-line, based on the assumption that the observed velocity-widths arise from virial-induced motions. However, CIV exhibits significant asymmetric structure which suggests that the associated gas is not tracing virial motions. By combining near-infrared spectroscopic data (covering the hydrogen Balmer lines) with optical spectroscopy from SDSS (covering CIV), we have quantified the bias in CIV BH masses as a function of the CIV blueshift. CIV BH masses are shown to be over-estimated by almost an order of magnitude at the most extreme blueshifts. Using the monotonically increasing relationship between the CIV blueshift and the mass ratio BH(CIV)/BH(H$\alpha$) we derive an empirical correction to all CIV BH-masses. The correction depends only on the CIV line properties and therefore enables the derivation of un-biased virial BH mass estimates for the majority of high-luminosity, high-redshift, spectroscopically confirmed quasars. Quasars driving powerful outflows over galactic scales is a central tenet of galaxy evolution models involving 'quasar feedback' and significant resources have been devoted to searching for observational evidence of this phenomenon. We have used [OIII] emission to probe ionised gas extended over kilo-parsec scales in luminous $z\gtrsim2$ quasars. Broad [OIII] velocity-widths and asymmetric structure indicate that strong outflows are prevalent in this population. We estimate the kinetic power of the outflows to be up to a few percent of the quasar bolometric luminosity, which is similar to the efficiencies required in recent quasar-feedback models. [OIII] emission is very weak in quasars with large CIV blueshifts, suggesting that quasar-driven winds are capable of sweeping away gas extended over kilo-parsec scales in the host galaxies. Using data from a number of recent wide-field photometric surveys, we have built a parametric SED model that is able to reproduce the median optical to infrared colours of tens of thousands of AGN at redshifts $1 < z < 3$. In individual objects, we find significant variation in the near-infrared SED, which is dominated by emission from hot dust. We find that the hot dust abundance is strongly correlated with the strength of outflows in the quasar broad line region, suggesting that the hot dust may be in a wind emerging from the outer edges of the accretion disc.Supported by STF

Correcting CIV-Based Virial Black Hole Masses

The CIV broad emission line is visible in optical spectra to redshifts exceeding z~5. CIV has long been known to exhibit significant displacements to the blue and these `blueshifts' almost certainly signal the presence of strong outflows. As a consequence, single-epoch virial black hole (BH) mass estimates derived from CIV velocity-widths are known to be systematically biased compared to masses from the hydrogen Balmer lines. Using a large sample of 230 high-luminosity (log $L_{\rm Bol}$ = 45.5-48 erg/s), redshift 1.5<z<4.0 quasars with both CIV and Balmer line spectra, we have quantified the bias in CIV BH masses as a function of the CIV blueshift. CIV BH masses are shown to be a factor of five larger than the corresponding Balmer-line masses at CIV blueshifts of 3000 km/s and are over-estimated by almost an order of magnitude at the most extreme blueshifts, >5000 km/s. Using the monotonically increasing relationship between the CIV blueshift and the mass ratio BH(CIV)/BH(H$\alpha$) we derive an empirical correction to all CIV BH-masses. The scatter between the corrected CIV masses and the Balmer masses is 0.24 dex at low CIV blueshifts (~0 km/s) and just 0.10 dex at high blueshifts (~3000 km/s), compared to 0.40 dex before the correction. The correction depends only on the CIV line properties - i.e. full-width at half maximum and blueshift - and can therefore be applied to all quasars where CIV emission line properties have been measured, enabling the derivation of un-biased virial BH mass estimates for the majority of high-luminosity, high-redshift, spectroscopically confirmed quasars in the literature.Comment: Accepted for publication in MNRAS; fixed typo in CIV wavelengt

C IV emission-line properties and systematic trends in quasar black hole mass estimates

Black hole masses are crucial to understanding the physics of the connection between quasars and their host galaxies and measuring cosmic black hole-growth. At high redshift, z ≳ 2.1, black hole masses are normally derived using the velocity width of the C IV λ λ1548, 1550 broad emission line, based on the assumption that the observed velocity widths arise from virial-induced motions. In many quasars, the C IV emission line exhibits significant blue asymmetries (`blueshifts') with the line centroid displaced by up to thousands of km s-1 to the blue. These blueshifts almost certainly signal the presence of strong outflows, most likely originating in a disc wind. We have obtained near-infrared spectra, including the Hα λ6565 emission line, for 19 luminous (LBol = 46.5-47.5 erg s-1) Sloan Digital Sky Survey quasars, at redshifts 2 &lt; z &lt; 2.7, with C IV emission lines spanning the full range of blueshifts present in the population. A strong correlation between C IV velocity width and blueshift is found and, at large blueshifts, &gt;2000 km s-1, the velocity widths appear to be dominated by non-virial motions. Black hole masses, based on the full width at half-maximum of the C IV emission line, can be overestimated by a factor of 5 at large blueshifts. A larger sample of quasar spectra with both C IV and H β, or Hα, emission lines will allow quantitative corrections to C IV-based black hole masses as a function of blueshift to be derived. We find that quasars with large C IV blueshifts possess high Eddington luminosity ratios and that the fraction of high-blueshift quasars in a flux-limited sample is enhanced by a factor of approximately 4 relative to a sample limited by black hole mass

[O III] Emission line properties in a new sample of heavily reddened quasars at z > 2

International audienceWe present VLT-SINFONI near infra-red spectra of 26 new heavily reddened quasar candidates selected from the UKIDSS-LAS, VISTA VHS, and VIKING imaging surveys. This new sample extends our reddened quasar search to both brighter and fainter luminosities. 25 of the 26 candidates are confirmed to be broad line quasars with redshifts 0.7 bol ≈ 1047 erg s-1 and z > 2. We present the first comparison of the [O III] line properties in high luminosity reddened quasars to a large sample of 111 unobscured quasars in the same luminosity and redshift range. Broad wings extending to velocities of 2500 km s-1 are seen in the [O III] emission line profiles of our reddened quasars, suggesting that strong outflows are affecting the ionized gas kinematics. However, we find no significant difference between the kinematics of the [O III] emission in reddened and unobscured quasars when the two samples are matched in luminosity and redshift. Our results are consistent with a model where quasar-driven outflows persist for some time after the obscuring dust has been cleared from along the line of sight. Assuming the amount of ionized gas in reddened and unobscured quasars is similar, we use the equivalent width distribution of the [O III] emission to constrain the location of the obscuring dust in our reddened quasars. We find that the dust is most likely to be located on galactic scales, outside the [O III] emitting region

[O iii] Emission line properties in a new sample of heavily reddened quasars at z &gt; 2

We present VLT-SINFONI near infra-red spectra of 26 new heavily reddened quasar candidates selected from the UKIDSS-LAS, VISTA VHS, and VIKING imaging surveys. This new sample extends our reddened quasar search to both brighter and fainter luminosities. 25 of the 26 candidates are confirmed to be broad line quasars with redshifts 0.7 &lt; z &lt; 2.6 and dust extinctions 0.5 &lt; E(B − V) &lt; 3.0. Combining with previously identified samples, we study the H α, H β, and [O III] emission line properties in 22 heavily reddened quasars with Lbol ≈ 1047 erg s−1 and z &gt; 2. We present the first comparison of the [O III] line properties in high luminosity reddened quasars to a large sample of 111 unobscured quasars in the same luminosity and redshift range. Broad wings extending to velocities of 2500 km s−1 are seen in the [O III] emission line profiles of our reddened quasars, suggesting that strong outflows are affecting the ionized gas kinematics. However, we find no significant difference between the kinematics of the [O III] emission in reddened and unobscured quasars when the two samples are matched in luminosity and redshift. Our results are consistent with a model where quasar-driven outflows persist for some time after the obscuring dust has been cleared from along the line of sight. Assuming the amount of ionized gas in reddened and unobscured quasars is similar, we use the equivalent width distribution of the [O III] emission to constrain the location of the obscuring dust in our reddened quasars. We find that the dust is most likely to be located on galactic scales, outside the [O III] emitting region

Kinematics of C iv and [O iii] emission in luminous high-redshift quasars

We characterize ionized gas outflows using a large sample of ≃330 high-luminosity [45.5 &lt; log(Lbol/erg s−1) &lt; 49.0], high-redshift (1.5 ≲ z ≲ 4.0) quasars via their [O III]λλ4960,5008 emission. The median velocity width of the [O III] emission line is 1540 kms−1, increasing with increasing quasar luminosity. Broad, blue-shifted wings are seen in the [O III] profiles of ≃42 per cent of the sample. Rest-frame ultraviolet spectra with well-characterized C IVλ1550 emission-line properties are available for more than 210 quasars, allowing an investigation of the relationship between the broad-line region (BLR) and narrow-line region (NLR) emission properties. The [O III] blueshift is correlated with C IV blueshift, even when the dependence of both quantities on quasar luminosity has been taken into account. A strong anticorrelation between the [O III] equivalent width (EW) and C IV blueshift also exists. Furthermore, [O III] is very weak, with EW &lt; 1 Å  in ≃10 per cent of the sample, a factor of 10 higher compared to quasars at lower luminosities and redshifts. If the [O III] emission originates in an extended NLR, the observations suggest that quasar-driven winds are capable of influencing the host-galaxy environment out to kilo-parsec scales. The mean kinetic power of the ionized gas outflows is then 1044.7 erg s−1, which is ≃0.15 per cent of the bolometric luminosity of the quasar. These outflow efficiencies are broadly consistent with those invoked in current active galactic nuclei feedback models

C iv emission-line properties and systematic trends in quasar black hole mass estimates

Black-hole masses are crucial to understanding the physics of the connection between quasars and their host galaxies and measuring cosmic black hole-growth. At high redshift, z > 2.1, black hole masses are normally derived using the velocity-width of the CIV broad emission line, based on the assumption that the observed velocity-widths arise from virial-induced motions. In many quasars, the CIV-emission line exhibits significant blue asymmetries (`blueshifts') with the line centroid displaced by up to thousands of km/s to the blue. These blueshifts almost certainly signal the presence of strong outflows, most likely originating in a disc wind. We have obtained near-infrared spectra, including the H$\alpha$ emission line, for 19 luminous ($L_{Bol}$ = 46.5-47.5 erg/s) Sloan Digital Sky Survey quasars, at redshifts 2 < z < 2.7, with CIV emission lines spanning the full-range of blueshifts present in the population. A strong correlation between CIV-velocity width and blueshift is found and, at large blueshifts, > 2000 km/s, the velocity-widths appear to be dominated by non-virial motions. Black-hole masses, based on the full width at half maximum of the CIV-emission line, can be overestimated by a factor of five at large blueshifts. A larger sample of quasar spectra with both CIV and H$\beta$, or H$\alpha$, emission lines will allow quantitative corrections to CIV-based black-hole masses as a function of blueshift to be derived. We find that quasars with large CIV blueshifts possess high Eddington luminosity ratios and that the fraction of high-blueshift quasars in a flux-limited sample is enhanced by a factor of approximately four relative to a sample limited by black hole mass.Comment: Accepted for publication in MNRAS (21 pages, 11 figures, 4 tables