Alireza Rafiee | Towson University (original) (raw)

Papers by Alireza Rafiee

The Astrophysical Journal, 2009

estimated an average radiative efficiency of 30%-35% for quasars at moderate redshift. We find th... more estimated an average radiative efficiency of 30%-35% for quasars at moderate redshift. We find that their method is not independent of quasar lifetimes and thus that quasars do not necessarily have such high efficiencies. Nonetheless, it is possible to derive interrelated constraints on quasar lifetimes, Eddington ratios, and radiative efficiencies of supermassive black holes. We derive such constraints using a statistically complete sample of quasars with black hole mass estimates from broad Mg II, made both with and without the radiation pressure correction of . We conclude that for quasars with L/L Edd 0.02, lifetimes can range from 140 to 750 Myr for Schwarzschild black holes. Coupled with observed black hole masses, quasar lifetimes of ≤140 Myr would imply that radiatively inefficient accretion or BH mergers must be important in the accretion history of quasars. Given reasonable assumptions about the quasar population, if the average quasar lifetime is < 1 Gyr, and if radiatively inefficient accretion is unimportant, then not many BHs with Eddington ratio < 0.2 can be rapidly spinning.

The Astrophysical Journal Supplement Series, 2011

We present Mg ii -based black hole mass estimates for 27,602 quasars with rest-frame UV spectra a... more We present Mg ii -based black hole mass estimates for 27,602 quasars with rest-frame UV spectra available in the Sloan Digital Sky Survey Data Release Three. This estimation is possible due to the existence of an empirical correlation between the radius of the broad line region and the continuum luminosity at 3000 Angstroms. We regenerate this correlation by applying our measurement method to UV spectra of low-redshift quasars in the HST/IUE databases which have corresponding reverberation mapping estimates of the H β broad line region's radius. Our mass estimation method uses the line dispersion rather than the full width at half maximum of the low-ionization Mg ii emission line. We measure Mg ii line dispersions for quasars whose spectra have been reconstructed using the most significant eigenspectra produced through Principal Component Analysis. We have tested the reliability of using reconstructed spectra in black hole mass estimation using a Monte Carlo simulation and by comparing the results from original and reconstructed Data Release Three spectra. We show that using reconstructed spectra not only makes bias-free mass estimation possible for quasars with low spectroscopic signal-to-noise ratio, but also reduces the intrinsic scatter of the distribution of the black hole masses to lower than 0.15 dex.

Wang et al. (2006) estimated a high average radiative efficiency of 30% to 35% for quasars (activ... more Wang et al. (2006) estimated a high average radiative efficiency of 30% to 35% for quasars (actively accreting black holes) at moderate redshift, strongly suggesting that all supermassive black holes are rotating very rapidly. Their method for determining radiative efficiencies has two advantages: it deals with changes in quantities rather than absolutes and it is independent of obscured sources. However, we have investigated the reliability of the assumptions made by Wang et al. and have found that their method is not independent of quasar lifetimes. Nonetheless, given constraints on quasar lifetimes, their method can be used to constrain quasar radiative efficiencies and black hole spins. Conversely, the range of radiative efficiencies possible for the full range of black hole spins can be used to constrain the average lifetimes of quasars (assuming that luminous quasars are not powered by radiatively inefficient accretion flows). We will present interrelated constraints on quasar lifetimes, Eddington ratios and radiative efficiencies (black hole spins) from a statistically complete sample of SDSS quasars with black hole mass estimates from Mg II. PBH and AR are supported in part by NSERC.

The Astrophysical Journal, 2007

We present observations of probable line-of-sight acceleration of a broad absorption trough of C ... more We present observations of probable line-of-sight acceleration of a broad absorption trough of C IV in the quasar SDSS J024221.87+004912.6. We also discuss how the velocity overlap of two other outflowing systems in the same object constrains the properties of the outflows. The Si IV doublet in each system has one unblended transition and one transition which overlaps with absorption from the other system. The residual flux in the overlapping trough is well fit by the product of the residual fluxes in the unblended troughs. For these optically thick systems to yield such a result, at least one of them must consist of individual subunits rather than being a single structure with velocity-dependent coverage of the source. If these subunits are identical, opaque, spherical clouds, we estimate the cloud radius to be r ≃ 3.9 × 10 15 cm. If they are identical, opaque, linear filaments, we estimate their width to be w ≃ 6.5 × 10 14 cm. These subunits are observed to cover the Mg II broad emission line region of the quasar, at which distance from the black hole the above filament width is equal to the predicted scale height of the outer atmosphere of a thin accretion disk. Insofar as that scale height is a natural size scale for structures originating in an accretion disk, these observations are evidence that the accretion disk can be a source of quasar absorption systems. Based on data from ESO program 075.B-0190(A).

We present supermassive black hole mass estimates for quasars with rest-frame UV spectra availabl... more We present supermassive black hole mass estimates for quasars with rest-frame UV spectra available in the Sloan Digital Sky Survey database. We use the line dispersion rather than the full width at half maximum of the low-ionization MgII emission line and an empirical correlation between the radius of the broad line region and the continuum luminosity at 3000 Angstroms. This empirical correlation is generated from UV spectra of low-redshift quasars in the HST/IUE databases which have corresponding reverberation mapping estimates of the broad line region's radius. The main algorithm of the line dispersion measurement is based on fitting a power-law continuum and an FeII emission template to the quasar spectra around the MgII line. Despite the fact that the fitting is sensitive to the accuracy of the quasar's redshift, the results are consistent with previous studies of MgII for quasars in our sample. We will use our sample to study the black hole mass function and its evolution, as well as correlations (or lack thereof) between black hole masses and other quasar properties.

Monthly Notices of the Royal Astronomical Society, 2011

We report that the reported sub-Eddington boundary in the quasar massluminosity plane (a departur... more We report that the reported sub-Eddington boundary in the quasar massluminosity plane (a departure from the Eddington luminosity limit for the highest quasar black hole masses at a given redshift) is an artifact due to biases in black hole mass measurements. The sub-Eddington boundary was initially found by Steinhardt & Elvis (2010a) using the FWHM-based black hole mass catalogue of Shen et al. (2008). However, the significance of the boundary is reduced when the FWHM-based mass-scaling relationship is recalibrated following Wang et al. and using the most updated reverberation mapping estimates of black hole masses. Furthermore, this boundary is not seen using mass estimates based on the line dispersion of the same quasars' Mg ii emission lines. Thus, the initial report of the sub-Eddington boundary was due to biases in estimating masses using the FWHM of a fit of one or two Gaussians to quasar Mg ii emission lines. We provide evidence that using the line dispersion of the Mg ii line produces less biased black hole mass estimates.

The Astrophysical Journal, 2009

estimated an average radiative efficiency of 30%-35% for quasars at moderate redshift. We find th... more estimated an average radiative efficiency of 30%-35% for quasars at moderate redshift. We find that their method is not independent of quasar lifetimes and thus that quasars do not necessarily have such high efficiencies. Nonetheless, it is possible to derive interrelated constraints on quasar lifetimes, Eddington ratios, and radiative efficiencies of supermassive black holes. We derive such constraints using a statistically complete sample of quasars with black hole mass estimates from broad Mg II, made both with and without the radiation pressure correction of . We conclude that for quasars with L/L Edd 0.02, lifetimes can range from 140 to 750 Myr for Schwarzschild black holes. Coupled with observed black hole masses, quasar lifetimes of ≤140 Myr would imply that radiatively inefficient accretion or BH mergers must be important in the accretion history of quasars. Given reasonable assumptions about the quasar population, if the average quasar lifetime is < 1 Gyr, and if radiatively inefficient accretion is unimportant, then not many BHs with Eddington ratio < 0.2 can be rapidly spinning.

The Astrophysical Journal Supplement Series, 2011

We present Mg ii -based black hole mass estimates for 27,602 quasars with rest-frame UV spectra a... more We present Mg ii -based black hole mass estimates for 27,602 quasars with rest-frame UV spectra available in the Sloan Digital Sky Survey Data Release Three. This estimation is possible due to the existence of an empirical correlation between the radius of the broad line region and the continuum luminosity at 3000 Angstroms. We regenerate this correlation by applying our measurement method to UV spectra of low-redshift quasars in the HST/IUE databases which have corresponding reverberation mapping estimates of the H β broad line region's radius. Our mass estimation method uses the line dispersion rather than the full width at half maximum of the low-ionization Mg ii emission line. We measure Mg ii line dispersions for quasars whose spectra have been reconstructed using the most significant eigenspectra produced through Principal Component Analysis. We have tested the reliability of using reconstructed spectra in black hole mass estimation using a Monte Carlo simulation and by comparing the results from original and reconstructed Data Release Three spectra. We show that using reconstructed spectra not only makes bias-free mass estimation possible for quasars with low spectroscopic signal-to-noise ratio, but also reduces the intrinsic scatter of the distribution of the black hole masses to lower than 0.15 dex.

Wang et al. (2006) estimated a high average radiative efficiency of 30% to 35% for quasars (activ... more Wang et al. (2006) estimated a high average radiative efficiency of 30% to 35% for quasars (actively accreting black holes) at moderate redshift, strongly suggesting that all supermassive black holes are rotating very rapidly. Their method for determining radiative efficiencies has two advantages: it deals with changes in quantities rather than absolutes and it is independent of obscured sources. However, we have investigated the reliability of the assumptions made by Wang et al. and have found that their method is not independent of quasar lifetimes. Nonetheless, given constraints on quasar lifetimes, their method can be used to constrain quasar radiative efficiencies and black hole spins. Conversely, the range of radiative efficiencies possible for the full range of black hole spins can be used to constrain the average lifetimes of quasars (assuming that luminous quasars are not powered by radiatively inefficient accretion flows). We will present interrelated constraints on quasar lifetimes, Eddington ratios and radiative efficiencies (black hole spins) from a statistically complete sample of SDSS quasars with black hole mass estimates from Mg II. PBH and AR are supported in part by NSERC.

The Astrophysical Journal, 2007

We present observations of probable line-of-sight acceleration of a broad absorption trough of C ... more We present observations of probable line-of-sight acceleration of a broad absorption trough of C IV in the quasar SDSS J024221.87+004912.6. We also discuss how the velocity overlap of two other outflowing systems in the same object constrains the properties of the outflows. The Si IV doublet in each system has one unblended transition and one transition which overlaps with absorption from the other system. The residual flux in the overlapping trough is well fit by the product of the residual fluxes in the unblended troughs. For these optically thick systems to yield such a result, at least one of them must consist of individual subunits rather than being a single structure with velocity-dependent coverage of the source. If these subunits are identical, opaque, spherical clouds, we estimate the cloud radius to be r ≃ 3.9 × 10 15 cm. If they are identical, opaque, linear filaments, we estimate their width to be w ≃ 6.5 × 10 14 cm. These subunits are observed to cover the Mg II broad emission line region of the quasar, at which distance from the black hole the above filament width is equal to the predicted scale height of the outer atmosphere of a thin accretion disk. Insofar as that scale height is a natural size scale for structures originating in an accretion disk, these observations are evidence that the accretion disk can be a source of quasar absorption systems. Based on data from ESO program 075.B-0190(A).

We present supermassive black hole mass estimates for quasars with rest-frame UV spectra availabl... more We present supermassive black hole mass estimates for quasars with rest-frame UV spectra available in the Sloan Digital Sky Survey database. We use the line dispersion rather than the full width at half maximum of the low-ionization MgII emission line and an empirical correlation between the radius of the broad line region and the continuum luminosity at 3000 Angstroms. This empirical correlation is generated from UV spectra of low-redshift quasars in the HST/IUE databases which have corresponding reverberation mapping estimates of the broad line region's radius. The main algorithm of the line dispersion measurement is based on fitting a power-law continuum and an FeII emission template to the quasar spectra around the MgII line. Despite the fact that the fitting is sensitive to the accuracy of the quasar's redshift, the results are consistent with previous studies of MgII for quasars in our sample. We will use our sample to study the black hole mass function and its evolution, as well as correlations (or lack thereof) between black hole masses and other quasar properties.

Monthly Notices of the Royal Astronomical Society, 2011

We report that the reported sub-Eddington boundary in the quasar massluminosity plane (a departur... more We report that the reported sub-Eddington boundary in the quasar massluminosity plane (a departure from the Eddington luminosity limit for the highest quasar black hole masses at a given redshift) is an artifact due to biases in black hole mass measurements. The sub-Eddington boundary was initially found by Steinhardt & Elvis (2010a) using the FWHM-based black hole mass catalogue of Shen et al. (2008). However, the significance of the boundary is reduced when the FWHM-based mass-scaling relationship is recalibrated following Wang et al. and using the most updated reverberation mapping estimates of black hole masses. Furthermore, this boundary is not seen using mass estimates based on the line dispersion of the same quasars' Mg ii emission lines. Thus, the initial report of the sub-Eddington boundary was due to biases in estimating masses using the FWHM of a fit of one or two Gaussians to quasar Mg ii emission lines. We provide evidence that using the line dispersion of the Mg ii line produces less biased black hole mass estimates.