Papers by Bradley Peterson
arXiv (Cornell University), Oct 29, 2002
We present a progress report on a project whose goal is to improve both the precision and accurac... more We present a progress report on a project whose goal is to improve both the precision and accuracy of reverberation-based blackhole masses. Reverberation masses appear to be accurate to a factor of about three, and the black-hole mass/bulge velocity dispersion (M-σ) relationship appears to be the same in active and quiescent galaxies.
arXiv (Cornell University), Feb 3, 2015
We present host stellar velocity dispersion measurements for a sample of 88 broad-line quasars at... more We present host stellar velocity dispersion measurements for a sample of 88 broad-line quasars at 0.1 < z < 1 (46 at z > 0.6) from the Sloan Digital Sky Survey Reverberation Mapping (SDSS-RM) project. High signalto-noise ratio coadded spectra (average S/N ≈ 30 per 69 km s −1 pixel) from SDSS-RM allowed decomposition of the host and quasar spectra, and measurements of the host stellar velocity dispersions and black hole (BH) masses using the single-epoch (SE) virial method. The large sample size and dynamic range in luminosity (L 5100 = 10 43.2−44.7 erg s −1) lead to the first clear detection of a correlation between SE virial BH mass and host stellar velocity dispersion far beyond the local universe. However, the observed correlation is significantly flatter than the local relation, suggesting that there are selection biases in high-z luminosity-threshold quasar samples for such studies. Our uniform sample and analysis enable an investigation of the redshift evolution of the M • − σ * relation relatively free of caveats by comparing different samples/analyses at disjoint redshifts. We do not observe evolution of the M • − σ * relation in our sample up to z ∼ 1, but there is an indication that the relation flattens towards higher redshifts. Coupled with the increasing threshold luminosity with redshift in our sample, this again suggests certain selection biases are at work, and simple simulations demonstrate that a constant M • − σ * relation is favored to z ∼ 1. Our results highlight the scientific potential of deep coadded spectroscopy from quasar monitoring programs, and offer a new path to probe the co-evolution of BHs and galaxies at earlier times.
Monthly Notices of the Royal Astronomical Society, Aug 5, 2021
Reverberation mapping is a robust method to measure the masses of supermassive black holes outsid... more Reverberation mapping is a robust method to measure the masses of supermassive black holes outside of the local Universe. Measurements of the radius-luminosity (R−L) relation using the Mg II emission line are critical for determining these masses near the peak of quasar activity at z ≈ 1−2, and for calibrating secondary mass estimators based on Mg II that can be applied to large samples with only single-epoch spectroscopy. We present the first nine Mg II lags from our 5-yr Australian Dark Energy Survey reverberation mapping programme, which substantially improves the number and quality of Mg II lag measurements. As the Mg II feature is somewhat blended with iron emission, we model and subtract both the continuum and iron contamination from the multiepoch spectra before analysing the Mg II line. We also develop a new method of quantifying correlated spectroscopic calibration errors based on our numerous, contemporaneous observations of F-stars. The lag measurements for seven of our nine sources are consistent with both the H β and Mg II R−L relations reported by previous studies. Our simulations verify the lag reliability of our nine measurements, and we estimate that the median false positive rate of the lag measurements is 4 per cent.
Astronomy and Astrophysics, 1995
With the aim of better understanding the physical processes that produce the continuous emission ... more With the aim of better understanding the physical processes that produce the continuous emission in active galactic nuclei (AGNs), a snapshot of the overall continuous energy distribution of NGC 3783, from "y-ray to radio wavelengths, has been obtained within the framework of the World Astronomy Days. The data collected in this campaign are from GRO, ROSAT, Voyager 2, IUE, HST, ESO, CTIO, SAAO and the (DARA/NASA/SERC), Voyager (NASA), HST (NASAJESA) and IUE (NASA/ESA/SERC) spacecraft and at ESO (La Silla), CTIO. SAAO. and VLA the observed AGN spectral energy distribution, we find values for the accretion disc innermost temperature, accretion rate, and 294 D. Alloin et al.: Emission of the active galactic nucleus in NGC 3783 black hole mass, with some differences that depend on whether or not we extrapolate the high-energy power law up to infrared wavelengths.
Monthly Notices of the Royal Astronomical Society
Mrk 590 is a known changing-look active galactic nuclei (AGNs) which almost turned off in 2012, a... more Mrk 590 is a known changing-look active galactic nuclei (AGNs) which almost turned off in 2012, and then in 2017 partially re-ignited into a repeat flaring state, unusual for an AGN. Our Swift observations since 2013 allow us to characterize the accretion-generated emission and its reprocessing in the central engine of a changing-look AGN. The X-ray and UV variability amplitudes are higher than those typically observed in ‘steady-state’ AGN at similar moderate accretion rates; instead, the variability is similar to that of highly accreting AGN. The unusually strong X-ray to UV correlation suggests that the UV-emitting region is directly illuminated by X-ray outbursts. We find evidence that the X-rays are reprocessed by two UV components, with the dominant one at ∼3 d and a faint additional reprocessor at near-zero lag. However, we exclude a significant contribution from diffuse broad line region continuum, known to contribute for bonafide AGN. A near-zero lag is expected for a stand...
Astronomy & Astrophysics, 2021
Using VLTI/GRAVITY and SINFONI data, we investigate the subparsec gas and dust structure around t... more Using VLTI/GRAVITY and SINFONI data, we investigate the subparsec gas and dust structure around the nearby type 1 active galactic nucleus (AGN) hosted by NGC 3783. The K-band coverage of GRAVITY uniquely allows simultaneous analysis of the size and kinematics of the broad line region (BLR), the size and structure of the near-infrared(near-IR)-continuum-emitting hot dust, and the size of the coronal line region (CLR). We find the BLR, probed through broad Brγ emission, to be well described by a rotating, thick disc with a radial distribution of clouds peaking in the inner region. In our BLR model, the physical mean radius of 16 light-days is nearly twice the ten-day time-lag that would be measured, which closely matches the ten-day time-lag that has been measured by reverberation mapping. We measure a hot dust full-width at half-maximum (FWHM) size of 0.74 mas (0.14 pc) and further reconstruct an image of the hot dust, which reveals a faint (5% of the total flux) offset cloud that we...
Monthly Notices of the Royal Astronomical Society, 2020
Using a month-long X-ray light curve from RXTE/PCA and 1.5 month-long UV continuum light curves f... more Using a month-long X-ray light curve from RXTE/PCA and 1.5 month-long UV continuum light curves from IUE spectra in 1220–1970 Å, we performed a detailed time-lag study of the Seyfert 1 galaxy NGC 7469. Our cross-correlation analysis confirms previous results showing that the X-rays are delayed relative to the UV continuum at 1315 Å by 3.49 ± 0.22 d, which is possibly caused by either propagating fluctuation or variable Comptonization. However, if variations slower than 5 d are removed from the X-ray light curve, the UV variations then lag behind the X-ray variations by 0.37 ± 0.14 d, consistent with reprocessing of the X-rays by a surrounding accretion disc. A very similar reverberation delay is observed between Swift/XRT X-ray and Swift/UVOT UVW2, U light curves. Continuum light curves extracted from the Swift/GRISM spectra show delays with respect to X-rays consistent with reverberation. Separating the UV continuum variations faster and slower than 5 d, the slow variations at 1825...
Astronomy & Astrophysics, 2020
We use VLTI/GRAVITY near-infrared interferometry measurements of eight bright type 1 AGN to study... more We use VLTI/GRAVITY near-infrared interferometry measurements of eight bright type 1 AGN to study the size and structure of hot dust that is heated by the central engine. We partially resolve each source, and report Gaussian full width at half-maximum sizes in the range 0.3−0.8 mas. In all but one object, we find no evidence for significant elongation or asymmetry (closure phases ≲1°). The narrow range of measured angular sizes is expected given the similar optical flux of our targets, and implies an increasing effective physical radius with bolometric luminosity, as found from previous reverberation and interferometry measurements. The measured sizes for Seyfert galaxies are systematically larger than for the two quasars in our sample when measured relative to the previously reported R ∼ L1/2 relationship, which is explained by emission at the sublimation radius. This could be evidence of an evolving near-infrared emission region structure as a function of central luminosity.
Astronomy & Astrophysics, 2020
We present near-infrared interferometric data on the Seyfert 2 galaxy NGC 1068, obtained with the... more We present near-infrared interferometric data on the Seyfert 2 galaxy NGC 1068, obtained with the GRAVITY instrument on the European Southern Observatory Very Large Telescope Interferometer. The extensive baseline coverage from 5 to 60 Mλ allowed us to reconstruct a continuum image of the nucleus with an unrivaled 0.2 pc resolution in the K-band. We find a thin ring-like structure of emission with a radius r = 0.24 ± 0.03 pc, inclination i = 70 ± 5°, position angle PA = −50 ± 4°, and h/r < 0.14, which we associate with the dust sublimation region. The observed morphology is inconsistent with the expected signatures of a geometrically and optically thick torus. Instead, the infrared emission shows a striking resemblance to the 22 GHz maser disc, which suggests they share a common region of origin. The near-infrared spectral energy distribution indicates a bolometric luminosity of (0.4–4.7) × 1045 erg s−1, behind a large AK ≈ 5.5 (AV ≈ 90) screen of extinction that also appears to...
Proceedings of Narrow-Line Seyfert 1 Galaxies and their place in the Universe — PoS(NLS1), 2011
We have completed observations for a 125-night reverberation mapping campaign to measure new or i... more We have completed observations for a 125-night reverberation mapping campaign to measure new or improved black hole masses in six AGNs. From these observations we can further constrain broad line region kinematics and improve the observed relation between the radius of the BLR and the AGN luminosity (the R− L relation), which allows us to accurately estimate black hole masses for large samples of AGNs. High-quality reverberation mapping datasets are difficult to obtain, as well-spaced observations over long timescales are required. Some reverberation campaigns in the past have not yielded satisfactory results due to inadequate time sampling; this campaign is part of a larger effort to improve the reverberation mapping database.
Monthly Notices of the Royal Astronomical Society, 2019
Optical changing-look Active Galactic Nuclei (AGN) are a class of sources that change type within... more Optical changing-look Active Galactic Nuclei (AGN) are a class of sources that change type within a short timescale of years or decades. This change is characterized by the appearance or disappearance of broad emission lines, often associated with dramatic AGN continuum flux changes that are orders of magnitude larger than those expected from typical AGN variability. In this work we study for the first time the host galaxy of a changing-look AGN, Mrk 590, using high spatial resolution optical and near-infrared observations. We discover that after ∼10 yr absence, the optical broad emission lines of Mrk 590 have reappeared. The AGN optical continuum flux however is still ∼10 times lower than that observed during the most luminous state in the 1990s. The host galaxy shows a 4.5 kpc radius star-forming ring with knots of ionized and cold molecular gas emission. Extended ionized and warm molecular gas emission is detected in the nucleus, indicating that there is a reservoir of gas as close as 60 pc from the black hole. We observe a nuclear gas spiral between radii r ∼ 0.5 and 2 kpc, which has been suggested as a dynamical mechanism able to drive the necessary gas to fuel AGN. We also discover blue-shifted and high velocity dispersion [O III] emission out to a radius of 1 kpc, tracing a nuclear gas outflow. The gas dynamics in Mrk 590 suggest a complex balance between gas inflow and outflow in the nucleus of the galaxy.
The Astrophysical Journal, 2018
Mrk 590 was originally classified as a Seyfert 1 galaxy, but then it underwent dramatic changes: ... more Mrk 590 was originally classified as a Seyfert 1 galaxy, but then it underwent dramatic changes: the nuclear luminosity dropped by over two orders of magnitude and the broad emission lines all but disappeared from the optical spectrum. Here we present followup observations to the original discovery and characterization of this "changing look" active galactic nucleus (AGN). The new Chandra and HST observations from 2014 show that Mrk 590 is awakening, changing its appearance again. While the source continues to be in a low state, its soft excess has re-emerged, though not to the previous level. The UV continuum is brighter by more than a factor of two and the broad Mg ii emission line is present, indicating that the ionizing continuum is also brightening. These observations suggest
Monthly Notices of the Royal Astronomical Society, 2018
We report the results of intensive X-ray, UV, and optical monitoring of the Seyfert 1 galaxy NGC ... more We report the results of intensive X-ray, UV, and optical monitoring of the Seyfert 1 galaxy NGC 4593 with Swift. There is no intrinsic flux-related spectral change in any variable component with small apparent variations being due to contamination by a constant hard (reflection) component in the X-rays and the red host galaxy in the UV/optical. Relative to the shortest wavelength band, UVW2, the lags of the other UV/optical bands mostly agree with the predictions of reprocessing of high energy emission by an accretion disc. The U-band lag is, however, larger than expected, probably because of reprocessed Balmer continuum emission from the distant broad line region (BLR). The UVW2 band is well correlated with the X-rays but lags by ∼6× more than expected if the UVW2 results only from reprocessing of X-rays by the disc. However, if the light curves are filtered to remove variations on timescales >5 d, the lag approaches the expectation from disc reprocessing. MEMECHO analysis shows that direct X-rays can be the driver of most of the UV/optical variations if the response functions have tails up to 10 d, from BLR reprocessing, together with strong peaks at short lag (<1 d) from disc reprocessing. For the 5 AGN monitored so far, the observed UVW2 to V-band lags are < ∼ 2 of disc reprocessing expectations and vary little between AGN. However, the X-ray to UVW2 lags greatly exceed disc reprocessing expectations and differ between AGN. The two most absorbed AGN have the largest excesses, so absorption and scattering may affect these lags, but there is no simple relationship between excess and absorption.
Multi-Wavelength Continuum Emission of AGN, 1994
The Astrophysical Journal, 2009
We present the first results from a high sampling rate, multi-month reverberation mapping campaig... more We present the first results from a high sampling rate, multi-month reverberation mapping campaign undertaken primarily at MDM Observatory with
arXiv (Cornell University), Sep 19, 2011
I review how AGN black hole masses are calculated from emission-line reverberation-mapping data, ... more I review how AGN black hole masses are calculated from emission-line reverberation-mapping data, with particular attention to both assumptions and caveats. I discuss the empirical relationship between AGN luminosity and broad-line region radius that underpins the indirect methods by which most AGN masses are estimated. I also discuss how line widths are characterized in this method and illustrate how different ways of measuring the line-widths can lead to systematic errors in the mass scale. I discuss specific implications for NLS1 galaxies and consider whether the NLS1 phenomenon is better explained by source inclination or by Eddington rate, and conclude that there is evidence that both of these effects are contributing factors and that at least the high-Eddington rate NLS1s are physically similar to some high-luminosity quasars.
The Astrophysical Journal, 2015
Recent intensive Swift monitoring of the Seyfert 1 galaxy NGC 5548 yielded 282 usable epochs over... more Recent intensive Swift monitoring of the Seyfert 1 galaxy NGC 5548 yielded 282 usable epochs over 125 days across six UV/optical bands and the X-rays. This is the densest extended AGN UV/optical continuum sampling ever obtained, with a mean sampling rate <0.5-day. Approximately daily HST UV sampling was also obtained. The UV/optical light curves show strong correlations (r max = 0.57 − 0.90) and the clearest measurement to date of interband lags. These lags are well-fit by a τ ∝ λ 4/3 wavelength dependence, with a normalization that indicates an unexpectedly large disk radius of ∼ 0.35 ± 0.05 lt-day at 1367Å, assuming a simple face-on model. The U-band shows a marginally larger lag than expected from the fit and surrounding bands, which could be due to Balmer continuum emission from the broad-line region as suggested by Korista and Goad. The UV/X-ray correlation is weaker (r max < 0.45) and less consistent over time. This indicates that while Swift is beginning to measure UV/optical lags in general agreement with accretion disk theory (although the derived size is larger than predicted), the relationship with X-ray variability is less well understood. Combining this accretion disk size estimate with those from quasar microlensing studies suggests that AGN disk sizes scale approximately linearly with central black hole mass over a wide range of masses.
The Astrophysical Journal, 2015
We present results from a fifteen-month campaign of high-cadence (∼3 days) mid-infrared Spitzer a... more We present results from a fifteen-month campaign of high-cadence (∼3 days) mid-infrared Spitzer and optical (B and V) monitoring of the Seyfert 1 galaxy NGC 6418, with the objective of determining the characteristic size of the dusty torus in this active galactic nucleus (AGN). We find that the 3.6 µm and 4.5 µm flux variations lag behind those of the optical continuum by 37.2 +2.4 −2.2 days and 47.1 +3.1 −3.1 days, respectively. We report a cross-correlation time lag between the 4.5 µm and 3.6 µm flux of 13.9 +0.5 −0.1 days. The lags indicate that the dust emitting at 3.6 µm and 4.5 µm is located at a distance ≈ 1 light-month (≈ 0.03 pc) from the source of the AGN UV-optical continuum. The reverberation radii are consistent with the inferred lower limit to the sublimation radius for pure graphite grains at 1800 K, but smaller by a factor of ∼ 2 than the corresponding lower limit for silicate grains; this is similar to what has been found for near-infrared (K-band) lags in other AGN. The 3.6 and 4.5 µm reverberation radii fall above the K-band τ ∝ L 0.5 size-luminosity relationship by factors 2.7 and 3.4, respectively, while the 4.5 µm reverberation radius is only 27% larger than the 3.6 µm radius. This is broadly consistent with clumpy torus models, in which individual optically thick clouds emit strongly over a broad wavelength range.
The Encyclopedia of Astronomy and Astrophysics
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Papers by Bradley Peterson