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Bentz M.C.,University of California at Irvine | Horne K.,University of St. Andrews | Barth A.J.,University of California at Irvine | Bennert V.N.,University of California at Santa Barbara | And 8 more authors.
Astrophysical Journal Letters | Year: 2010

We present velocity-delay maps for optical Hi, Hei, and He ii recombination lines in Arp 151, recovered by fitting a reverberation model to spectrophotometric monitoring data using the maximum-entropy method. Hi response is detected over the range 0-15 days, with the response confined within the virial envelope. The Balmer-line maps have similarmorphologies but exhibit radial stratification, with progressively longer delays for Hγ to Hβ to Hα. The He i and He ii response is confined within 1-2 days. There is a deficit of prompt response in the Balmer-line cores but strong prompt response in the red wings. Comparison with simple models identifies two classes that reproduce these features: free-falling gas and a half-illuminated disk with a hot spot at small radius on the receding lune. Symmetrically illuminated models with gas orbiting in an inclined disk or an isotropic distribution of randomly inclined circular orbits can reproduce the virial structure but not the observed asymmetry. Radial outflows are also largely ruled out by the observed asymmetry. A warped-disk geometry provides a physically plausible mechanism for the asymmetric illumination and hot spot features. Simple estimates show that a disk in the broad-line region of Arp 151 could be unstable to warping induced by radiation pressure. Our results demonstrate the potential power of detailed modeling combined with monitoring campaigns at higher cadence to characterize the gas kinematics and physical processes that give rise to the broad emission lines in active galactic nuclei. © 2010. The American Astronomical Society. All rights reserved. Source


Wang X.,University of California at Berkeley | Wang X.,Tsinghua University | Filippenko A.V.,University of California at Berkeley | Ganeshalingam M.,University of California at Berkeley | And 11 more authors.
Astrophysical Journal Letters | Year: 2010

We study the observables of 158 relatively normal Type Ia supernovae (SNe Ia) by dividing them into two groups in terms of the expansion velocity inferred from the absorption minimum of the Si II λ6355 line in their spectra near B-band maximum brightness. One group ("Normal") consists of normal SNe Ia populating a narrow strip in the Si II velocity distribution, with an average expansion velocity 〈v〉 = 10, 600 400 kms-1 near B maximum; the other group ("HV") consists of objects with higher velocities, v ≳ 11, 800 km s-1. Compared with the Normal group, the HV one shows a narrower distribution in both the peak luminosity and the luminosity decline rate Δm 15. In particular, their B-V colors at maximum brightness are found to be on average redder by ∼ 0.1 mag, suggesting that they either are associated with dusty environments or have intrinsically red B-V colors. The HV SNe Ia are also found to prefer a lower extinction ratio RV ≈ 1.6 (versus ∼ 2.4 for the Normal ones). Applying such an absorption-correction dichotomy to SNe Ia of these two groups remarkably reduces the dispersion in their peak luminosity from 0.178 mag to only 0.125 mag. © 2009 The American Astronomical Society. Source


Park D.,Seoul National University | Woo J.-H.,Seoul National University | Treu T.,University of California at Santa Barbara | Barth A.J.,University of California at Irvine | And 9 more authors.
Astrophysical Journal | Year: 2012

We investigate the calibration and uncertainties of black hole (BH) mass estimates based on the single-epoch (SE) method, using homogeneous and high-quality multi-epoch spectra obtained by the Lick Active Galactic Nucleus (AGN) Monitoring Project for nine local Seyfert 1 galaxies with BH masses <108 M ⊙. By decomposing the spectra into their AGNs and stellar components, we study the variability of the SE Hβ line width (full width at half-maximum intensity, FWHMHβ or dispersion, σHβ) and of the AGN continuum luminosity at 5100 (L 5100). From the distribution of the "virial products" (∞ FWHMHβ 2 L 0.5 5100 or σHβ 2 L 0.5 5100) measured from SE spectra, we estimate the uncertainty due to the combined variability as 0.05dex (12%). This is subdominant with respect to the total uncertainty in SE mass estimates, which is dominated by uncertainties in the size-luminosity relation and virial coefficient, and is estimated to be ∼0.46dex (factor of ∼3). By comparing the Hβ line profile of the SE, mean, and root-mean-square (rms) spectra, we find that the Hβ line is broader in the mean (and SE) spectra than in the rms spectra by ∼0.1dex (25%) for our sample with FWHMHβ <3000kms-1. This result is at variance with larger mass BHs where the difference is typically found to be much less than 0.1dex. To correct for this systematic difference of the Hβ line profile, we introduce a line-width dependent virial factor, resulting in a recalibration of SE BH mass estimators for low-mass AGNs. © 2012. The American Astronomical Society. All rights reserved. Source


Greene J.E.,Princeton University | Hood C.E.,University of California at Irvine | Barth A.J.,University of California at Irvine | Bennert V.N.,University of California at Santa Barbara | And 7 more authors.
Astrophysical Journal | Year: 2010

It is now possible to estimate black hole (BH) masses across cosmic time, using broad emission lines in active galaxies. This technique informs our views of how galaxies and their central BHs coevolve. Unfortunately, there are many outstanding uncertainties associated with these "virial" mass estimates. One of these comes from using the accretion luminosity to infer a size for the broad-line region (BLR). Incorporating the new sample of low-luminosity active galaxies from our recent monitoring campaign at Lick Observatory, we recalibrate the radius-luminosity relation with tracers of the accretion luminosity other than the optical continuum. We find that the radius of the BLR scales as the square root of the X-ray and Hβ luminosities, in agreement with recent optical studies. On the other hand, the scaling appears to be marginally steeper with narrow-line luminosities. This is consistent with a previously observed decrease in the ratio of narrow-line to X-ray luminosity with increasing total luminosity. The radius of the BLR correlates most tightly with Hβ luminosity, while the X-ray and narrow-line relations both have comparable scatter of a factor of 2. These correlations provide useful alternative virial BH masses in objects with no detectable optical/UV continuum emission, such as high-redshift galaxies with broad emission lines, radio-loud objects, or local active galaxies with galaxy-dominated continua. © 2010. The American Astronomical Society. Source


Woo J.-H.,Seoul National University | Woo J.-H.,University of California at Los Angeles | Treu T.,University of California at Santa Barbara | Barth A.J.,University of California at Irvine | And 13 more authors.
Astrophysical Journal | Year: 2010

To investigate the black hole mass versus stellar velocity dispersion (MBH-σ*) relation of active galaxies, we measured the velocity dispersions of a sample of local Seyfert 1 galaxies, for which we have recently determined black hole masses using reverberation mapping. For most objects, stellar velocity dispersions were measured from high signal-to-noise ratio optical spectra centered on the Ca II triplet region (∼ 8500 Å), obtained at the Keck, Palomar, and Lick Observatories. For two objects, in which the Ca II triplet region was contaminated by nuclear emission, the measurement was based on high-quality H-band spectra obtained with the OH-Suppressing Infrared Imaging Spectrograph at the Keck-II telescope. Combining our new measurements with data from the literature, we assemble a sample of 24 active galaxies with stellar velocity dispersions and reverberation-based black hole mass measurements in the range of black hole mass 106 < MBH/M⊙ < 109. We use this sample to obtain reverberation-mapping constraints on the slope and intrinsic scatter of the MBH-σ* relation of active galaxies. Assuming a constant virial coefficient f for the reverberation-mapping black hole masses, we find a slope β = 3.55 ± 0.60 and the intrinsic scatter σint = 0.43 ± 0.08 dex in the relation log(MBH/M⊙) = α + β log(σ*/200kms-1), which are consistent with those found for quiescent galaxies. We derive an updated value of the virial coefficient f by finding the value which places the reverberation masses in best agreement with the MBH-σ* relation of quiescent galaxies; using the quiescent MBH-σ* relation determined by Gültekin etal., we find log f = 0.72 +0.09 -0.10 with an intrinsic scatter of 0.44 ± 0.07 dex. No strong correlations between f and parameters connected to the physics of accretion (such as the Eddington ratio or line-shape measurements) are found. The uncertainty of the virial coefficient remains one of the main sources of the uncertainty in black hole mass determinations using reverberation mapping, and therefore also in single-epoch spectroscopic estimates of black hole masses in active galaxies. © 2010 The American Astronomical Society. Source

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