Marianne Vestergaard - Academia.edu (original) (raw)
Papers by Marianne Vestergaard
Bulletin of the American Astronomical Society, Dec 1, 1998
We report the discovery of X-ray emission from a radio knot at a projected distance of 25'' from ... more We report the discovery of X-ray emission from a radio knot at a projected distance of 25'' from the nucleus of the Seyfert galaxy, 3C 120. The data were obtained with the ROSAT High Resolution Imager (HRI). Optical upper limits for the knot preclude a simple power law extension of the radio spectrum and we calculate some of the physical parameters for thermal bremsstrahlung and synchrotron self Compton models. We conclude that no simple model is consistent with the data and suggest the existence of one or more small, non-thermal sources with flat spectra. The energy requirements for these would be modest and the features would not be discernable in previous radio maps.
... S. CoUin, F. Combes, and I. Shiosman Continuum and Emission Line Correlations in AGN Matthias... more ... S. CoUin, F. Combes, and I. Shiosman Continuum and Emission Line Correlations in AGN Matthias Dietrich, Fred Hamann Department of ... Athens, 011 45701, USA M. Vestergaard Department of Astronomy, The Ohio State University, 140 West 18th Ay., Columbus, OH 43210 ...
Astrophysics and Space Science Library, 2012
ABSTRACT How will quasar studies be pursued in the near future? Starting from a summary of past a... more ABSTRACT How will quasar studies be pursued in the near future? Starting from a summary of past achievement, we ask questions on expected instrumental and computational advancements that can shape quasar research in a foreseeable way. There is excitement due to the planned large new-generation telescopes, ground-based and in space. New surveys will lead to an order-of-magnitude increase of known quasars.
Astrophysical Journal, 2003
We examine rest-frame ultraviolet spectra of 70 high redshift quasars (z ≥ 3.5) to study the chem... more We examine rest-frame ultraviolet spectra of 70 high redshift quasars (z ≥ 3.5) to study the chemical enrichment history of the gas closely related to the quasars, and thereby estimate the epoch of first star formation. The fluxes of several ultraviolet emission lines were investigated within the framework of the most recent photoionization models to estimate the metallicity of the gas associated with the high-z quasars. Standard photoionization parameters and the assumption of secondary nitrogen enrichment indicate an average abundance of Z/Z ⊙ ≃ 4 to 5 in the line emitting gas. Assuming a time scale of τ evol ≃ 0.5 − 0.8 Gyrs for the chemical enrichment of the gas, the first major star formation for quasars with z ≃ 4 should have started at a redshift of z f ≃ 6 − 8, corresponding to an age of the universe of several 10 8 yrs (H o = 65 km s −1 Mpc −1 , Ω M = 0.3, Ω Λ = 0.7). We note that this also appears to be the era of re-ionization of the universe. Finally, there is some evidence for a positive luminosity -metallicity relation in this high redshift quasar sample. USA.
Astrophysics and Space Science Library, 2012
ABSTRACT Most of the questions in this chapter deal with sources that do not show the "c... more ABSTRACT Most of the questions in this chapter deal with sources that do not show the "classical" broad emission-line spectrum that characterizes the majority of known AGNs at high and low redshift. If that majority represents a "parent population" of AGNs, is the apparent absence of broad lines a result of obscuration, orientation, or different physical conditions? Can all of the subclasses be unified under the AGN umbrella? With the unification scheme set in place and assumed to be fundamentally correct, there are at least four overarching questions: do all type-2 AGNs possess an obscured broad-line region? Or how can we distinguishing type-2 AGNs without a broad-line region if they exist? Where is the low end of quasar activity? The least luminous AGNs are the so-called low-ionization nuclear emission-line regions (LINERs), but it is legitimate to ask if they are all true AGNs.
The Astrophysical Journal, 1999
We report the discovery of X-ray emission from a radio knot at a projected distance of 25 ′′ from... more We report the discovery of X-ray emission from a radio knot at a projected distance of 25 ′′ from the nucleus of the Seyfert galaxy, 3C 120. The data were obtained with the ROSAT High Resolution Imager (HRI). Optical upper limits for the knot preclude a simple power law extension of the radio spectrum and we calculate some of the physical parameters for thermal bremsstrahlung and synchrotron self-Compton models. We conclude that no simple model is consistent with the data but if the knot contains small regions with flat spectra, these could produce the observed X-rays (via synchrotron emission) without being detected at other wavebands.
The Astrophysical Journal, 2002
We report on the analysis of a large sample of 744 type 1 Active Galactic Nuclei, including quasa... more We report on the analysis of a large sample of 744 type 1 Active Galactic Nuclei, including quasars and Seyfert 1 galaxies across the redshift range from 0 z 5 and spanning nearly 6 orders of magnitude in continuum luminosity.
The Astrophysical Journal, 2005
We reinvestigate the relationship between the characteristic broad-line region size (R BLR ) and ... more We reinvestigate the relationship between the characteristic broad-line region size (R BLR ) and the Balmer emission-line, X-ray, UV, and optical continuum luminosities. Our study makes use of the best available determinations of R BLR for a large number of active galactic nuclei (AGNs) from Peterson et al. Using their determinations of R BLR for a large sample of AGNs and two different regression methods, we investigate the robustness of our correlation results as a function of data sub-sample and regression technique. Though small systematic differences were found depending on the method of analysis, our results are generally consistent. Assuming a power-law relation R BLR ∝ L α , we find the mean best-fitting α is about 0.67 ± 0.05 for the optical continuum and the broad Hβ luminosity, about 0.56 ± 0.05 for the UV continuum luminosity, and about 0.70 ± 0.14 for the X-ray luminosity. We also find an intrinsic scatter of ∼ 40% in these relations. The disagreement of our results with the theoretical expected slope of 0.5 indicates that the simple assumption of all AGNs having on average same ionization parameter, BLR density, column density, and ionizing spectral energy distribution, is not valid and there is likely some evolution of a few of these characteristics along the luminosity scale.
Astronomy and Astrophysics, 2006
Context. Scatter around the relationship between central black hole masses in active galactic nuc... more Context. Scatter around the relationship between central black hole masses in active galactic nuclei (AGNs) obtained by reverberation-mapping methods and host-galaxy bulge velocity dispersion indicates that the masses are uncertain typically by a factor of about three. Aims. In this paper, we try to identify the sources and systematics of this uncertainty. Methods. We characterize the broad Hβ emission-line profiles by the ratio of their full-width at half maximum (FWHM) to their line dispersion, i.e., the second moment of the line profile. We use this parameter to separate the reverberation-mapped AGNs into two populations, the first with narrower Hβ lines that tend to have relatively extended wings, and the second with broader lines that are relatively flat-topped. The first population is characterized by higher Eddington ratios than the second. Within each population, we calibrate the black-hole mass scale by comparison of the reverberation-based mass with that predicted by the bulge velocity dispersion. We also use the distribution of ratios of the reverberation-based mass to the velocity-dispersion mass prediction in a comparison with a "generalized thick disk" model in order to see if inclination can plausibly account for the observed distribution. Results. We find that the line dispersion is a less biased parameter in general than FWHM for black hole mass estimation, although we show that it is possible to empirically correct for the bias introduced by using FWHM to characterize the emissionline width. We also argue that inclination effects are apparent only in some small subset of the reverberation-based mass measurements; it is primarily the objects with the narrowest emission lines that seem to be most strongly affected. Conclusions. Our principal conclusion is that the Hβ profile is sensitive primarily to Eddington ratio, but that inclination effects play a role in some cases.
Astronomy and Astrophysics, 2003
We present observations of 11 high redshift quasars (3.9 < ∼ z < ∼ 5.0) observed with low spectra... more We present observations of 11 high redshift quasars (3.9 < ∼ z < ∼ 5.0) observed with low spectral resolution in the restframe ultraviolet using FORS 1 at the VLT UT 1. The emission-line fluxes of strong permitted and intercombination ultraviolet emission lines are measured to estimate the chemical composition of the line emitting gas. Comparisons to photoionization calculations indicate gas metallicities in the broad emission line region in the range of solar to several times solar. The average of the mean metallicity of each high-z quasar in this sample is Z/Z ⊙ = 4.3 ± 0.3. Assuming a chemical evolution time scale of τ evol ≃ 0.5 − 0.8 Gyrs, we derive a redshift of z f ≃ 6 to 8 for the onset of the first major star formation episode (H o = 65 km s −1 Mpc −1 , Ω M = 0.3, Ω Λ = 0.7), corresponding to an age of the universe of several 10 8 yrs at this epoch. We note that this epoch is also supposed to be the era of re-ionization of the universe.
Proceedings of the International Astronomical Union, 2010
Reverberation mapping takes advantage of the presence of a time delay or lag, τ, between continuu... more Reverberation mapping takes advantage of the presence of a time delay or lag, τ, between continuum and emission line flux variations observed through spectroscopic monitoring campaigns to infer the radius of the broad-line region (BLR) and, subsequently, the central black hole mass in type 1 AGNs. We present results from a multi-month reverberation mapping campaign undertaken primarily at MDM Observatory with supporting observations from around the world. We measure BLR radii and black hole masses for six objects. The primary goal of this campaign was to obtain either new or improved Hβ reverberation lag measurements for several relatively low-luminosity AGNs. Using cross correlation techniques to measure the time delay between the mean optical continuum flux density around 5100 Å and the integrated Hβ flux, we determine the Hβ lags and black hole mass measurements listed in columns 2 and 3 of Table 1, respectively. Column 4 tells if this measurement is new, an improvement meant to replace a previous, less reliable measurement, or simply an additional measurement not used to replace a previous value. The complete results from this study are currently being prepared for publication. A subsequent velocity-resolved analysis of the Hβ response shows that three of the six primary targets demonstrate kinematic signatures (column 5) of infall, outflow, and non-radial virialized motions (see Denney et al. 2009).
The Astrophysical Journal, Jun 15, 2009
We identify a sample of 74 high-redshift quasars (z > 3) with weak emission lines from the Fifth ... more We identify a sample of 74 high-redshift quasars (z > 3) with weak emission lines from the Fifth Data Release of the Sloan Digital Sky Survey and present infrared, optical, and radio observations of a subsample of four objects at z > 4. These weak emission-line quasars (WLQs) constitute a prominent tail of the Lyα + N v equivalent width distribution, and we compare them to quasars with more typical emission-line properties and to low-redshift active galactic nuclei with weak/absent emission lines, namely BL Lac objects. We find that WLQs exhibit hot (T ~ 1000 K) thermal dust emission and have rest-frame 0.1-5 μm spectral energy distributions that are quite similar to those of normal quasars. The variability, polarization, and radio properties of WLQs are also different from those of BL Lacs, making continuum boosting by a relativistic jet an unlikely physical interpretation. The most probable scenario for WLQs involves broad-line region properties that are physically distinct from those of normal quasars.
We present Spitzer observations of thirteen z~6 quasars using the Infrared Array Camera (IRAC) an... more We present Spitzer observations of thirteen z~6 quasars using the Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS). All the quasars except SDSS J000552.34-000655.8 (SDSS J0005-0006) were detected with high S/N in the four IRAC channels and the MIPS 24um band, while SDSS J0005-0006 was marginally detected in the IRAC 8.0um band, and not detected in the MIPS 24um band. We find that most of these quasars have prominent emission from hot dust as evidenced by the observed 24um fluxes. Their spectral energy distributions (SEDs) are similar to those of low-redshift quasars at rest-frame 0.15-3.5 um, suggesting that accretion disks and hot-dust structures for these sources already have reached maturity. However, SDSS J0005-0006 has an unusual SED that lies significantly below low-redshift SED templates at rest-frame 1 and 3.5 um, and thus shows a strong near-IR (NIR) deficit and no hot-dust emission. Type I quasars with extremely small NIR-to-optical flux ratios like SDSS J0005-0006 are not found in low-redshift quasar samples, indicating that SDSS J0005-0006 has different dust properties at high redshift. We combine the Spitzer observations with X-ray, UV/optical, mm/submm and radio observations to determine bolometric luminosities for all the quasars. We find that the four quasars with central black-hole mass measurements have Eddington ratios of order unity.
Astrophys J, 2008
We investigate the relationship between black hole mass and bulge luminosity for AGNs with reverb... more We investigate the relationship between black hole mass and bulge luminosity for AGNs with reverberation-based black hole mass measurements and bulge luminosities from two-dimensional decompositions of Hubble Space Telescope host galaxy images. We find that the slope of the relationship for AGNs is 0.76-0.85 with an uncertainty of ~0.1, somewhat shallower than the M_BH \propto L^{1.0+/-0.1} relationship that has been fit to nearby quiescent galaxies with dynamical black hole mass measurements. This is somewhat perplexing, as the AGN black hole masses include an overall scaling factor that brings the AGN M_BH-sigma relationship into agreement with that of quiescent galaxies. We discuss biases that may be inherent to the AGN and quiescent galaxy samples and could cause the apparent inconsistency in the forms of their M_BH-L_bulge relationships.
We present the discovery of seven quasars at z>5.7, selected from ~2000 deg^2 of multicolor imagi... more We present the discovery of seven quasars at z>5.7, selected from ~2000 deg^2 of multicolor imaging data of the Sloan Digital Sky Survey (SDSS). The new quasars have redshifts z from 5.79 to 6.13. Five are selected as part of a complete flux-limited sample in the SDSS Northern Galactic Cap; two have larger photometric errors and are not part of the complete sample. One of the new quasars, SDSS J1335+3533 (z=5.93), exhibits no emission lines; the 3-sigma limit on the rest-frame equivalent width of Ly alpha+NV line is 5 A. It is the highest redshift lineless quasar known, and could be a gravitational lensed galaxy, a BL Lac object or a new type of quasar. Two new z>6 quasars, SDSS 1250+3130 (z=6.13) and SDSS J1137+3549 (z=6.01), show deep Gunn-Peterson absorption gaps in Ly alpha. These gaps are narrower the complete Gunn-Peterson absorption troughs observed among quasars at z>6.2 and do not have complete Ly beta absorption.
I will present the black hole mass function (BHMF) of broad line quasars in the SDSS DR3. We empl... more I will present the black hole mass function (BHMF) of broad line quasars in the SDSS DR3. We employ a powerful Bayesian statistical technique that corrects for incompleteness and the statistical uncertainty in the mass estimates. We find evidence that the most massive black hole appeared as quasars earlier in the universe, and that most quasars are not radiating at or near the Eddington limit. I will also present constraints on the quasar lifetime and maximum black hole mass, derived from the mass functions.
We calibrate reverberation-based black hole masses in active galactic nuclei (AGNs) by using the ... more We calibrate reverberation-based black hole masses in active galactic nuclei (AGNs) by using the correlation between black hole mass, M, and bulge/spheroid stellar velocity dispersion, sigma. We use new measurements of sigma for 6 AGNs and published velocity dispersions for 10 others, in conjunction with improved reverberation mapping results, to determine the scaling factor required to bring reverberation-based black hole masses into agreement with the quiescent galaxy M-sigma relationship. The scatter in the AGN black hole masses is found to be less than a factor of 3. The current observational uncertainties preclude use of the scaling factor to discriminate between broad-line region models.
Spitzer Proposal, Sep 1, 2004
We propose to obtain high S/N Spitzer photometry of a flux-limited sample of thirteen luminous qu... more We propose to obtain high S/N Spitzer photometry of a flux-limited sample of thirteen luminous quasars at 5.7 < z < 6.4 selected from the Sloan Digital Sky Survey. They are the thirteen most distant quasars known to date, near the end of the cosmic reionization epoch. The Spitzer observations will be carried out in all the IRAC bands, the MIPS 24 micron band, and for the brightest sources, in the MIPS 70 micron band. These observations will provide the first high S/N Spitzer measurement of luminous objects at z>6, and establish the basic infrared characteristics of the most distant quasars. The Spitzer observations sample the rest-frame near to mid-IR, a wavelength range that has never been probed before at this redshift, where the radiation begins to be dominated by hot dust in the quasar environment and where the SED might peak. High quality X-ray, optical/near-IR, sub-millimeter and radio observations of this sample have either been acquired or planned. Combined with measurements in other wavelengths, the Spitzer data will allow us to measure the bolometric luminosity of z~6 quasars and to estimate the accretion rate and efficiency of the earliest billion solar mass black holes in the universe. Comparing with low-redshift samples, including the Spitzer GTO sample at 0 < z < 5, we will study the evolution of quasar SEDs to the first billion years of cosmic history, constraining physical models of the highest-redshift quasars. Finally, combining with sub-millimeter and radio molecular gas observations, we will study dust properties in the quasar environment and the AGN/starburst connection in the earliest massive galaxies.
Bulletin of the American Astronomical Society, Dec 1, 2007
I will discuss recent work on using the X-ray and optical properties of a sample of 318 radio-qui... more I will discuss recent work on using the X-ray and optical properties of a sample of 318 radio-quiet quasars to investigate the dependence quasar accretion disk structure on black hole mass and accretion rate. Specifically, we studied the dependence of the ratio of quasar optical flux to X-ray flux on black hole mass and Eddington ratio, as well as the dependence of the X-ray spectral slope on black hole mass and Eddington ratio. We find evidence that quasars emit a smaller fraction of their bolometric luminosity in the X-rays as black hole mass and accretion rate increase. In addition, we find evidence that the X-ray spectral slope displays a non-monotonic dependence on black hole mass and accretion rate. I will discuss our results within the context of accretion models with comptonizing corona, and discuss the implications for quasar feedback. This work was supported in part by NSF grant AST03-07384.
Bulletin of the American Astronomical Society, Dec 1, 1998
We report the discovery of X-ray emission from a radio knot at a projected distance of 25'' from ... more We report the discovery of X-ray emission from a radio knot at a projected distance of 25'' from the nucleus of the Seyfert galaxy, 3C 120. The data were obtained with the ROSAT High Resolution Imager (HRI). Optical upper limits for the knot preclude a simple power law extension of the radio spectrum and we calculate some of the physical parameters for thermal bremsstrahlung and synchrotron self Compton models. We conclude that no simple model is consistent with the data and suggest the existence of one or more small, non-thermal sources with flat spectra. The energy requirements for these would be modest and the features would not be discernable in previous radio maps.
... S. CoUin, F. Combes, and I. Shiosman Continuum and Emission Line Correlations in AGN Matthias... more ... S. CoUin, F. Combes, and I. Shiosman Continuum and Emission Line Correlations in AGN Matthias Dietrich, Fred Hamann Department of ... Athens, 011 45701, USA M. Vestergaard Department of Astronomy, The Ohio State University, 140 West 18th Ay., Columbus, OH 43210 ...
Astrophysics and Space Science Library, 2012
ABSTRACT How will quasar studies be pursued in the near future? Starting from a summary of past a... more ABSTRACT How will quasar studies be pursued in the near future? Starting from a summary of past achievement, we ask questions on expected instrumental and computational advancements that can shape quasar research in a foreseeable way. There is excitement due to the planned large new-generation telescopes, ground-based and in space. New surveys will lead to an order-of-magnitude increase of known quasars.
Astrophysical Journal, 2003
We examine rest-frame ultraviolet spectra of 70 high redshift quasars (z ≥ 3.5) to study the chem... more We examine rest-frame ultraviolet spectra of 70 high redshift quasars (z ≥ 3.5) to study the chemical enrichment history of the gas closely related to the quasars, and thereby estimate the epoch of first star formation. The fluxes of several ultraviolet emission lines were investigated within the framework of the most recent photoionization models to estimate the metallicity of the gas associated with the high-z quasars. Standard photoionization parameters and the assumption of secondary nitrogen enrichment indicate an average abundance of Z/Z ⊙ ≃ 4 to 5 in the line emitting gas. Assuming a time scale of τ evol ≃ 0.5 − 0.8 Gyrs for the chemical enrichment of the gas, the first major star formation for quasars with z ≃ 4 should have started at a redshift of z f ≃ 6 − 8, corresponding to an age of the universe of several 10 8 yrs (H o = 65 km s −1 Mpc −1 , Ω M = 0.3, Ω Λ = 0.7). We note that this also appears to be the era of re-ionization of the universe. Finally, there is some evidence for a positive luminosity -metallicity relation in this high redshift quasar sample. USA.
Astrophysics and Space Science Library, 2012
ABSTRACT Most of the questions in this chapter deal with sources that do not show the "c... more ABSTRACT Most of the questions in this chapter deal with sources that do not show the "classical" broad emission-line spectrum that characterizes the majority of known AGNs at high and low redshift. If that majority represents a "parent population" of AGNs, is the apparent absence of broad lines a result of obscuration, orientation, or different physical conditions? Can all of the subclasses be unified under the AGN umbrella? With the unification scheme set in place and assumed to be fundamentally correct, there are at least four overarching questions: do all type-2 AGNs possess an obscured broad-line region? Or how can we distinguishing type-2 AGNs without a broad-line region if they exist? Where is the low end of quasar activity? The least luminous AGNs are the so-called low-ionization nuclear emission-line regions (LINERs), but it is legitimate to ask if they are all true AGNs.
The Astrophysical Journal, 1999
We report the discovery of X-ray emission from a radio knot at a projected distance of 25 ′′ from... more We report the discovery of X-ray emission from a radio knot at a projected distance of 25 ′′ from the nucleus of the Seyfert galaxy, 3C 120. The data were obtained with the ROSAT High Resolution Imager (HRI). Optical upper limits for the knot preclude a simple power law extension of the radio spectrum and we calculate some of the physical parameters for thermal bremsstrahlung and synchrotron self-Compton models. We conclude that no simple model is consistent with the data but if the knot contains small regions with flat spectra, these could produce the observed X-rays (via synchrotron emission) without being detected at other wavebands.
The Astrophysical Journal, 2002
We report on the analysis of a large sample of 744 type 1 Active Galactic Nuclei, including quasa... more We report on the analysis of a large sample of 744 type 1 Active Galactic Nuclei, including quasars and Seyfert 1 galaxies across the redshift range from 0 z 5 and spanning nearly 6 orders of magnitude in continuum luminosity.
The Astrophysical Journal, 2005
We reinvestigate the relationship between the characteristic broad-line region size (R BLR ) and ... more We reinvestigate the relationship between the characteristic broad-line region size (R BLR ) and the Balmer emission-line, X-ray, UV, and optical continuum luminosities. Our study makes use of the best available determinations of R BLR for a large number of active galactic nuclei (AGNs) from Peterson et al. Using their determinations of R BLR for a large sample of AGNs and two different regression methods, we investigate the robustness of our correlation results as a function of data sub-sample and regression technique. Though small systematic differences were found depending on the method of analysis, our results are generally consistent. Assuming a power-law relation R BLR ∝ L α , we find the mean best-fitting α is about 0.67 ± 0.05 for the optical continuum and the broad Hβ luminosity, about 0.56 ± 0.05 for the UV continuum luminosity, and about 0.70 ± 0.14 for the X-ray luminosity. We also find an intrinsic scatter of ∼ 40% in these relations. The disagreement of our results with the theoretical expected slope of 0.5 indicates that the simple assumption of all AGNs having on average same ionization parameter, BLR density, column density, and ionizing spectral energy distribution, is not valid and there is likely some evolution of a few of these characteristics along the luminosity scale.
Astronomy and Astrophysics, 2006
Context. Scatter around the relationship between central black hole masses in active galactic nuc... more Context. Scatter around the relationship between central black hole masses in active galactic nuclei (AGNs) obtained by reverberation-mapping methods and host-galaxy bulge velocity dispersion indicates that the masses are uncertain typically by a factor of about three. Aims. In this paper, we try to identify the sources and systematics of this uncertainty. Methods. We characterize the broad Hβ emission-line profiles by the ratio of their full-width at half maximum (FWHM) to their line dispersion, i.e., the second moment of the line profile. We use this parameter to separate the reverberation-mapped AGNs into two populations, the first with narrower Hβ lines that tend to have relatively extended wings, and the second with broader lines that are relatively flat-topped. The first population is characterized by higher Eddington ratios than the second. Within each population, we calibrate the black-hole mass scale by comparison of the reverberation-based mass with that predicted by the bulge velocity dispersion. We also use the distribution of ratios of the reverberation-based mass to the velocity-dispersion mass prediction in a comparison with a "generalized thick disk" model in order to see if inclination can plausibly account for the observed distribution. Results. We find that the line dispersion is a less biased parameter in general than FWHM for black hole mass estimation, although we show that it is possible to empirically correct for the bias introduced by using FWHM to characterize the emissionline width. We also argue that inclination effects are apparent only in some small subset of the reverberation-based mass measurements; it is primarily the objects with the narrowest emission lines that seem to be most strongly affected. Conclusions. Our principal conclusion is that the Hβ profile is sensitive primarily to Eddington ratio, but that inclination effects play a role in some cases.
Astronomy and Astrophysics, 2003
We present observations of 11 high redshift quasars (3.9 < ∼ z < ∼ 5.0) observed with low spectra... more We present observations of 11 high redshift quasars (3.9 < ∼ z < ∼ 5.0) observed with low spectral resolution in the restframe ultraviolet using FORS 1 at the VLT UT 1. The emission-line fluxes of strong permitted and intercombination ultraviolet emission lines are measured to estimate the chemical composition of the line emitting gas. Comparisons to photoionization calculations indicate gas metallicities in the broad emission line region in the range of solar to several times solar. The average of the mean metallicity of each high-z quasar in this sample is Z/Z ⊙ = 4.3 ± 0.3. Assuming a chemical evolution time scale of τ evol ≃ 0.5 − 0.8 Gyrs, we derive a redshift of z f ≃ 6 to 8 for the onset of the first major star formation episode (H o = 65 km s −1 Mpc −1 , Ω M = 0.3, Ω Λ = 0.7), corresponding to an age of the universe of several 10 8 yrs at this epoch. We note that this epoch is also supposed to be the era of re-ionization of the universe.
Proceedings of the International Astronomical Union, 2010
Reverberation mapping takes advantage of the presence of a time delay or lag, τ, between continuu... more Reverberation mapping takes advantage of the presence of a time delay or lag, τ, between continuum and emission line flux variations observed through spectroscopic monitoring campaigns to infer the radius of the broad-line region (BLR) and, subsequently, the central black hole mass in type 1 AGNs. We present results from a multi-month reverberation mapping campaign undertaken primarily at MDM Observatory with supporting observations from around the world. We measure BLR radii and black hole masses for six objects. The primary goal of this campaign was to obtain either new or improved Hβ reverberation lag measurements for several relatively low-luminosity AGNs. Using cross correlation techniques to measure the time delay between the mean optical continuum flux density around 5100 Å and the integrated Hβ flux, we determine the Hβ lags and black hole mass measurements listed in columns 2 and 3 of Table 1, respectively. Column 4 tells if this measurement is new, an improvement meant to replace a previous, less reliable measurement, or simply an additional measurement not used to replace a previous value. The complete results from this study are currently being prepared for publication. A subsequent velocity-resolved analysis of the Hβ response shows that three of the six primary targets demonstrate kinematic signatures (column 5) of infall, outflow, and non-radial virialized motions (see Denney et al. 2009).
The Astrophysical Journal, Jun 15, 2009
We identify a sample of 74 high-redshift quasars (z > 3) with weak emission lines from the Fifth ... more We identify a sample of 74 high-redshift quasars (z > 3) with weak emission lines from the Fifth Data Release of the Sloan Digital Sky Survey and present infrared, optical, and radio observations of a subsample of four objects at z > 4. These weak emission-line quasars (WLQs) constitute a prominent tail of the Lyα + N v equivalent width distribution, and we compare them to quasars with more typical emission-line properties and to low-redshift active galactic nuclei with weak/absent emission lines, namely BL Lac objects. We find that WLQs exhibit hot (T ~ 1000 K) thermal dust emission and have rest-frame 0.1-5 μm spectral energy distributions that are quite similar to those of normal quasars. The variability, polarization, and radio properties of WLQs are also different from those of BL Lacs, making continuum boosting by a relativistic jet an unlikely physical interpretation. The most probable scenario for WLQs involves broad-line region properties that are physically distinct from those of normal quasars.
We present Spitzer observations of thirteen z~6 quasars using the Infrared Array Camera (IRAC) an... more We present Spitzer observations of thirteen z~6 quasars using the Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS). All the quasars except SDSS J000552.34-000655.8 (SDSS J0005-0006) were detected with high S/N in the four IRAC channels and the MIPS 24um band, while SDSS J0005-0006 was marginally detected in the IRAC 8.0um band, and not detected in the MIPS 24um band. We find that most of these quasars have prominent emission from hot dust as evidenced by the observed 24um fluxes. Their spectral energy distributions (SEDs) are similar to those of low-redshift quasars at rest-frame 0.15-3.5 um, suggesting that accretion disks and hot-dust structures for these sources already have reached maturity. However, SDSS J0005-0006 has an unusual SED that lies significantly below low-redshift SED templates at rest-frame 1 and 3.5 um, and thus shows a strong near-IR (NIR) deficit and no hot-dust emission. Type I quasars with extremely small NIR-to-optical flux ratios like SDSS J0005-0006 are not found in low-redshift quasar samples, indicating that SDSS J0005-0006 has different dust properties at high redshift. We combine the Spitzer observations with X-ray, UV/optical, mm/submm and radio observations to determine bolometric luminosities for all the quasars. We find that the four quasars with central black-hole mass measurements have Eddington ratios of order unity.
Astrophys J, 2008
We investigate the relationship between black hole mass and bulge luminosity for AGNs with reverb... more We investigate the relationship between black hole mass and bulge luminosity for AGNs with reverberation-based black hole mass measurements and bulge luminosities from two-dimensional decompositions of Hubble Space Telescope host galaxy images. We find that the slope of the relationship for AGNs is 0.76-0.85 with an uncertainty of ~0.1, somewhat shallower than the M_BH \propto L^{1.0+/-0.1} relationship that has been fit to nearby quiescent galaxies with dynamical black hole mass measurements. This is somewhat perplexing, as the AGN black hole masses include an overall scaling factor that brings the AGN M_BH-sigma relationship into agreement with that of quiescent galaxies. We discuss biases that may be inherent to the AGN and quiescent galaxy samples and could cause the apparent inconsistency in the forms of their M_BH-L_bulge relationships.
We present the discovery of seven quasars at z>5.7, selected from ~2000 deg^2 of multicolor imagi... more We present the discovery of seven quasars at z>5.7, selected from ~2000 deg^2 of multicolor imaging data of the Sloan Digital Sky Survey (SDSS). The new quasars have redshifts z from 5.79 to 6.13. Five are selected as part of a complete flux-limited sample in the SDSS Northern Galactic Cap; two have larger photometric errors and are not part of the complete sample. One of the new quasars, SDSS J1335+3533 (z=5.93), exhibits no emission lines; the 3-sigma limit on the rest-frame equivalent width of Ly alpha+NV line is 5 A. It is the highest redshift lineless quasar known, and could be a gravitational lensed galaxy, a BL Lac object or a new type of quasar. Two new z>6 quasars, SDSS 1250+3130 (z=6.13) and SDSS J1137+3549 (z=6.01), show deep Gunn-Peterson absorption gaps in Ly alpha. These gaps are narrower the complete Gunn-Peterson absorption troughs observed among quasars at z>6.2 and do not have complete Ly beta absorption.
I will present the black hole mass function (BHMF) of broad line quasars in the SDSS DR3. We empl... more I will present the black hole mass function (BHMF) of broad line quasars in the SDSS DR3. We employ a powerful Bayesian statistical technique that corrects for incompleteness and the statistical uncertainty in the mass estimates. We find evidence that the most massive black hole appeared as quasars earlier in the universe, and that most quasars are not radiating at or near the Eddington limit. I will also present constraints on the quasar lifetime and maximum black hole mass, derived from the mass functions.
We calibrate reverberation-based black hole masses in active galactic nuclei (AGNs) by using the ... more We calibrate reverberation-based black hole masses in active galactic nuclei (AGNs) by using the correlation between black hole mass, M, and bulge/spheroid stellar velocity dispersion, sigma. We use new measurements of sigma for 6 AGNs and published velocity dispersions for 10 others, in conjunction with improved reverberation mapping results, to determine the scaling factor required to bring reverberation-based black hole masses into agreement with the quiescent galaxy M-sigma relationship. The scatter in the AGN black hole masses is found to be less than a factor of 3. The current observational uncertainties preclude use of the scaling factor to discriminate between broad-line region models.
Spitzer Proposal, Sep 1, 2004
We propose to obtain high S/N Spitzer photometry of a flux-limited sample of thirteen luminous qu... more We propose to obtain high S/N Spitzer photometry of a flux-limited sample of thirteen luminous quasars at 5.7 < z < 6.4 selected from the Sloan Digital Sky Survey. They are the thirteen most distant quasars known to date, near the end of the cosmic reionization epoch. The Spitzer observations will be carried out in all the IRAC bands, the MIPS 24 micron band, and for the brightest sources, in the MIPS 70 micron band. These observations will provide the first high S/N Spitzer measurement of luminous objects at z>6, and establish the basic infrared characteristics of the most distant quasars. The Spitzer observations sample the rest-frame near to mid-IR, a wavelength range that has never been probed before at this redshift, where the radiation begins to be dominated by hot dust in the quasar environment and where the SED might peak. High quality X-ray, optical/near-IR, sub-millimeter and radio observations of this sample have either been acquired or planned. Combined with measurements in other wavelengths, the Spitzer data will allow us to measure the bolometric luminosity of z~6 quasars and to estimate the accretion rate and efficiency of the earliest billion solar mass black holes in the universe. Comparing with low-redshift samples, including the Spitzer GTO sample at 0 < z < 5, we will study the evolution of quasar SEDs to the first billion years of cosmic history, constraining physical models of the highest-redshift quasars. Finally, combining with sub-millimeter and radio molecular gas observations, we will study dust properties in the quasar environment and the AGN/starburst connection in the earliest massive galaxies.
Bulletin of the American Astronomical Society, Dec 1, 2007
I will discuss recent work on using the X-ray and optical properties of a sample of 318 radio-qui... more I will discuss recent work on using the X-ray and optical properties of a sample of 318 radio-quiet quasars to investigate the dependence quasar accretion disk structure on black hole mass and accretion rate. Specifically, we studied the dependence of the ratio of quasar optical flux to X-ray flux on black hole mass and Eddington ratio, as well as the dependence of the X-ray spectral slope on black hole mass and Eddington ratio. We find evidence that quasars emit a smaller fraction of their bolometric luminosity in the X-rays as black hole mass and accretion rate increase. In addition, we find evidence that the X-ray spectral slope displays a non-monotonic dependence on black hole mass and accretion rate. I will discuss our results within the context of accretion models with comptonizing corona, and discuss the implications for quasar feedback. This work was supported in part by NSF grant AST03-07384.