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Journal ArticleDOI

Monitoring of the optical and 2.5-11.7 mu m spectrum and mid-IR imaging of the Seyfert 1 galaxy Mrk 279 with ISO

01 Apr 2001-Vol. 369, Iss: 1, pp 57-64

AbstractMid-infrared images of the Seyfert 1 galaxy Mrk 279 obtained with the ISO satellite are presented together with the results of a one-year monitoring campaign of the 2.5-11.7 mum spectrum. Contemporaneous optical photometric and spectrophotometric observations are also presented. The galaxy appears as a point-like source at the resolution of the ISOCAM instrument (4-5 "). The 2.5-11.7 mum average spectrum of the nucleus in Mrk 279 shows a strong power law continuum with alpha = -0.80 +/- 0.05 (F nu proportional to nu (alpha)) and weak PAK emission features. The Mrk 279 spectral energy distribution shows a mid-IR bump, which extends from 2 to 15-20 mum The mid-IR bump is consistent with thermal emission from dust grains at a distance of greater than or similar to 100 It-d. No significant variations of the mid-IR flux have been detected during our observing campaign, consistent with the relatively low amplitude (similar to 10% rms) of the optical variability during the campaign. The time delay for H beta line emission in response to the optical continuum variations is tau = 16.7(-5.6)(+5.3), days, consistent with previous measurements.

Topics: Active galactic nucleus (53%), Luminous infrared galaxy (52%), Galaxy (51%), Quasar (50%)

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Citations
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Journal ArticleDOI
Abstract: We present improved black hole masses for 35 active galactic nuclei (AGNs) based on a complete and consistent reanalysis of broad emission-line reverberation-mapping data From objects with multiple line measurements, we find that the highest precision measure of the virial product cτΔV2/G, where τ is the emission-line lag relative to continuum variations and ΔV is the emission-line width, is obtained by using the cross-correlation function centroid (as opposed to the cross-correlation function peak) for the time delay and the line dispersion (as opposed to FWHM) for the line width and by measuring the line width in the variable part of the spectrum Accurate line-width measurement depends critically on avoiding contaminating features, in particular the narrow components of the emission lines We find that the precision (or random component of the error) of reverberation-based black hole mass measurements is typically around 30%, comparable to the precision attained in measurement of black hole masses in quiescent galaxies by gas or stellar dynamical methods Based on results presented in a companion paper by Onken et al, we provide a zero-point calibration for the reverberation-based black hole mass scale by using the relationship between black hole mass and host-galaxy bulge velocity dispersion The scatter around this relationship implies that the typical systematic uncertainties in reverberation-based black hole masses are smaller than a factor of 3 We present a preliminary version of a mass-luminosity relationship that is much better defined than any previous attempt Scatter about the mass-luminosity relationship for these AGNs appears to be real and could be correlated with either Eddington ratio or object inclination

1,756 citations


Cites methods from "Monitoring of the optical and 2.5-1..."

  • ...We examined two completely independent sets of data, one from theWise Observatory program in 1988 (Maoz et al. 1990) and one from an International AGN Watch project in 1996 (Santos-Lleó et al. 2001)....

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Journal ArticleDOI
Abstract: We present an updated and revised analysis of the relationship between the H{beta} broad-line region (BLR) radius and the luminosity of the active galactic nucleus (AGN). Specifically, we have carried out two-dimensional surface brightness decompositions of the host galaxies of nine new AGNs imaged with the Hubble Space Telescope Wide Field Camera 3. The surface brightness decompositions allow us to create ''AGN-free'' images of the galaxies, from which we measure the starlight contribution to the optical luminosity measured through the ground-based spectroscopic aperture. We also incorporate 20 new reverberation-mapping measurements of the H{beta} time lag, which is assumed to yield the average H{beta} BLR radius. The final sample includes 41 AGNs covering four orders of magnitude in luminosity. The additions and updates incorporated here primarily affect the low-luminosity end of the R{sub BLR}-L relationship. The best fit to the relationship using a Bayesian analysis finds a slope of {alpha}= 0.533{sup +0.035}{sub -0.033}, consistent with previous work and with simple photoionization arguments. Only two AGNs appear to be outliers from the relationship, but both of them have monitoring light curves that raise doubt regarding the accuracy of their reported time lags. The scatter around the relationship is found to be 0.19more » {+-} 0.02 dex, but would be decreased to 0.13 dex by the removal of these two suspect measurements. A large fraction of the remaining scatter in the relationship is likely due to the inaccurate distances to the AGN host galaxies. Our results help support the possibility that the R{sub BLR}-L relationship could potentially be used to turn the BLRs of AGNs into standardizable candles. This would allow the cosmological expansion of the universe to be probed by a separate population of objects, and over a larger range of redshifts.« less

686 citations


Journal ArticleDOI
Abstract: We analyze a sample of optical light curves for 100 quasars, 70 of which have black hole mass estimates. Our sample is the largest and broadest used yet for modeling quasar variability. The sources in our sample have z < 2.8, 1042 λL λ(5100 A) 1046, and 106 M BH/M ☉ 1010. We model the light curves as a continuous time stochastic process, providing a natural means of estimating the characteristic timescale and amplitude of quasar variations. We employ a Bayesian approach to estimate the characteristic timescale and amplitude of flux variations; our approach is not affected by biases introduced from discrete sampling effects. We find that the characteristic timescales strongly correlate with black hole mass and luminosity, and are consistent with disk orbital or thermal timescales. In addition, the amplitude of short-timescale variations is significantly anticorrelated with black hole mass and luminosity. We interpret the optical flux fluctuations as resulting from thermal fluctuations that are driven by an underlying stochastic process, such as a turbulent magnetic field. In addition, the intranight variations in optical flux implied by our empirical model are 0.02 mag, consistent with current microvariability observations of radio-quiet quasars. Our stochastic model is therefore able to unify both long- and short-timescale optical variations in radio-quiet quasars as resulting from the same underlying process, while radio-loud quasars have an additional variability component that operates on timescales 1 day.

661 citations


Journal ArticleDOI
Abstract: We present high-resolution Hubble Space Telescope images of all 35 active galactic nuclei (AGNs) with optical reverberation-mapping results, which we have modeled to create a nucleus-free image of each AGN host galaxy. From the nucleus-free images, we determine the host-galaxy contribution to ground-based spectroscopic luminosity measurements at 5100 A. After correcting the luminosities of the AGNs for the contribution from starlight, we re-examine the Hβ R BLR-L relationship. Our best fit for the relationship gives a power-law slope of 0.52 with a range of 0.45-0.59 allowed by the uncertainties. This is consistent with our previous findings, and thus still consistent with the naive assumption that all AGNs are simply luminosity-scaled versions of each other. We discuss various consistency checks relating to the galaxy modeling and starlight contributions, as well as possible systematic errors in the current set of reverberation measurements from which we determine the form of the R BLR-L relationship.

613 citations


Cites result from "Monitoring of the optical and 2.5-1..."

  • ...We include here only the results for Mrk 279 reported by Santos-Lleó et al. (2001)....

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Journal ArticleDOI
Abstract: We have obtained high-resolution images of the central regions of 14 reverberation-mapped active galactic nuclei (AGNs) using the Hubble Space Telescope Advanced Camera for Surveys High Resolution Camera to account for host-galaxy starlight contamination of measured AGN luminosities. We measure the host-galaxy starlight contribution to the continuum luminosity at 5100 ? through the typical ground-based slit position and geometry used in the reverberation-mapping campaigns. We find that removing the starlight contribution results in a significant correction to the luminosity of each AGN both for lower luminosity sources, as expected, but also for the higher luminosity sources such as the PG quasars. After accounting for the host galaxy starlight, we revisit the well-known broad-line region radius-luminosity relationship for nearby AGNs. We find the power-law slope of the relationship for the H? line to be 0.518 ? 0.039, shallower than what was previously reported and consistent with the slope of 0.5 expected from the naive theoretical assumption that all AGNs have, on average, the same ionizing spectrum and the same ionization parameter and gas density in the H? line-emitting region.

463 citations


References
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Journal ArticleDOI
Abstract: A method for measuring correlation functions without interpolating in the temporal domain is proposed which provides an assumption-free representation of the correlation measured in the data and allows meaningful error estimates. Physical interpretation of the cross-correlation function of two series believed to be related by a convolution is shown to require knowledge of the input function's fluctuation power spectrum. Application of the method to two systems reveals no correlation for the optical data of Akn 120, but a strong correlation for the UV data of NGC 4151, placing bounds of between 1.2 and 20 light days on the size of the line-emitting region.

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Journal ArticleDOI
Abstract: Variations in the strengths of the central photoionization source in a quasar or Seyfert galaxy will generate variations in the strengths and profiles of the emission lines. These ''reverberations'' in the emission lines will lag behind the continuum variations due to light travel time effects. A procedure is described for analyzing a time series of measurements of both the continuum and the lines. This procedure permits direct verification of the assumed causal connection of the lines to the continuum. We demonstrate that if the emission line region has a high degree of symmetry, then it is possible to invert the time-dependent line profiles and obtain the phase space distribution of the emission-line gas: i.e., its emissivity and the moments of its velocity distributions as functions of position. The cases of spherical and disk symmetry are considered in detail; the case of a straight jet, which may be relevent to correlated optical and radio variations, is discussed briefly. Explicit calculations of expected line variations have been carried out for several simple models. We suggest that with recently developed instrumentation it should now be possible to apply this technique to Seyfert galaxies. Long term, highly accurate observations will be required for themore » application to quasars.« less

950 citations


"Monitoring of the optical and 2.5-1..." refers methods in this paper

  • ...Reverberation-mapping techniques (Blandford & McKee 1982) have been used extensively to map the BLR in several AGN, on scales of light days to light months, notably by the International AGN Watch1 consortium (Alloin et al. 1994)....

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01 Jun 1988
TL;DR: It is shown that physical interpretation of active galactic nuclei cross-correlation functions requires knowledge of the input function's fluctuation power spectrum, involves model-dependence in the form of symmetry assumptions, and must take into account intrinsic scale bias.
Abstract: A method of measuring correlation functions without interpolating in the temporal domain, the discrete correlation function, is introduced. It provides an assumption-free representation of the correlation measured in the data, and allows meaningful error estimates. This method does not produce spurious correlations at zero lag due to correlated errors. It is shown that physical interpretation of active galactic nuclei cross-correlation functions requires knowledge of the input function's fluctuation power spectrum, involves model-dependence in the form of symmetry assumptions, and must take into account intrinsic scale bias. This technique was used to find a correlation in published IUE data for NGC 4151, which indicates that the broad C IV feature emanates from a shell 15 to 75 light-days in radius, assuming spherical symmetry.

787 citations


"Monitoring of the optical and 2.5-1..." refers methods in this paper

  • ...We used both the interpolation method of Gaskell & Sparke (1986) and the discretecorrelation function (DCF) method of Edelson & Krolik (1988), in both cases employing the specific implementation described by White & Peterson (1994)....

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Journal ArticleDOI
Abstract: Continuum observations from ~0.3 nm to 6 cm (10^(9.7)-10^(18) Hz) are presented for 109 bright quasars from the Palomar-Green (PG) survey. Two-thirds of the quasars have been detected in the infrared at wavelengths between 10 and 100 μm. All of the PG quasars appear to emit the bulk of their luminosity (typically more than 90%) between 3 nm and 300 μm (10^(12)-10^(17) Hz). The total luminosity at wavelengths longer than 1 μm is typically 20%-40% of that at wavelengths shortward of 1 μm. The gross shape of the energy distributions between 3 nm and 300 μm is remarkably similar for all the quasars except the flat-spectrum radio-loud quasars like 3C 273 and can plausibly be fitted by two broad components of thermal emission. In this interpretation the emission in the spectral range ~ 10 nm to 0.3 μm, the "big blue bump," is dominated by 10,00-100,000 K thermal emission from an accretion disk. The emission between 2 μm and 1 mm, the "infrared bump," is made up of reradiation from dust in a distorted disk extending from 0.1 pc to more than 1 kpc. The fairly small range in the relative sizes of the bumps suggests that the covering factor in most of the PG quasars is similar. There is no obvious connection between the strengths of the blue and infrared peaks and whether or not the quasar is radio quiet or radio loud. The mass of infrared emitting dust is estimated to be ~0.01 M_☉ at 2 μm and ~ 10^5 M_☉ at 60 μm. The radiation from 0.5 μm is thermal emission from the portion of the disk between 0.1 and 1 pc, illuminated primarily by the clouds of the broad-line region. The radiation from 5 μm to 1 mm is reradiation from a warped disk at distances greater than 1 pc from the central source, which is heated directly by radiation from the central source. Optically thin atomic emission (free-free and partially thermalized lines and bound-free) from gas within 1 pc of the central source, whose dust has sublimated, probably contributes to the flux from 0.5 to 2 μm. We believe that there is no convincing evidence for energetically significant nonthermal radiation in the wavelength range 3 nm to 300 μm in the continua of the radio-quiet and steep-spectrum radio-loud PG quasars.

642 citations


"Monitoring of the optical and 2.5-1..." refers background in this paper

  • ...The presence of a universal inflection point near 1.2µm in the spectral energy distribution of radio-quiet AGN’s strongly suggests that the bulk of the near IR flux arises from dust thermal emission (e.g., Barvainis 1987; Sanders et al. 1989)....

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Journal ArticleDOI
Abstract: It is shown here that thermal radiation by dust can reproduce the overall shape of the bump seen in the near-infrared continua of many QSOs and AGN. A simple model in which dust grains are heated by the primary nuclear optical/ultraviolet continuum produces the required emission at short wavelengths. The model naturally explains the onset of the bump at about 2 microns. This wavelength corresponds to the optically thin emission peak for the hottest possible grains, i.e., graphite grains at their evaporation temperature near 1500 K. Emission longward of 2 microns is due to cooler grains farther from the central source. 33 references.

609 citations


"Monitoring of the optical and 2.5-1..." refers background in this paper

  • ...The presence of a universal inflection point near 1.2µm in the spectral energy distribution of radio-quiet AGN’s strongly suggests that the bulk of the near IR flux arises from dust thermal emission (e.g., Barvainis 1987; Sanders et al. 1989)....

    [...]


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