Estimating Black Hole Masses in Active Galactic Nuclei Using the MgII 2800 Emission Line (original) (raw)
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Estimating Black Hole Masses in Active Galactic Nuclei Using the Mg II lambda2800 Emission Line
Astrophysical Journal, 2009
We investigate the relationship between the linewidths of broad Mg ii λ2800 and Hβ in active galactic nuclei (AGNs) to refine them as tools to estimate black hole (BH) masses. We perform a detailed spectral analysis of a large sample of AGNs at intermediate redshifts selected from the Sloan Digital Sky Survey, along with a smaller sample of archival ultraviolet spectra for nearby sources monitored with reverberation mapping (RM). Careful attention is devoted to accurate spectral decomposition, especially in the treatment of narrow-line blending and Fe ii contamination. We show that, contrary to popular belief, the velocity width of Mg ii tends to be smaller than that of Hβ, suggesting that the two species are not cospatial in the broad-line region. Using these findings and recently updated BH mass measurements from RM, we present a new calibration of the empirical prescriptions for estimating virial BH masses for AGNs using the broad Mg ii and Hβ lines. We show that the BH masses derived from our new formalisms show subtle but important differences compared to some of the mass estimators currently used in the literature.
ESTIMATING BLACK HOLE MASSES IN ACTIVE GALACTIC NUCLEI USING THE Mg II λ2800 EMISSION LINE
The Astrophysical Journal, 2009
We investigate the relationship between the linewidths of broad Mg II λ2800 and Hβ in active galactic nuclei (AGNs) to refine them as tools to estimate black hole (BH) masses. We perform a detailed spectral analysis of a large sample of AGNs at intermediate redshifts selected from the Sloan Digital Sky Survey, along with a smaller sample of archival ultraviolet spectra for nearby sources monitored with reverberation mapping (RM). Careful attention is devoted to accurate spectral decomposition, especially in the treatment of narrow-line blending and Fe II contamination. We show that, contrary to popular belief, the velocity width of Mg II tends to be smaller than that of Hβ, suggesting that the two species are not cospatial in the broad-line region. Using these findings and recently updated BH mass measurements from RM, we present a new calibration of the empirical prescriptions for estimating virial BH masses for AGNs using the broad Mg II and Hβ lines. We show that the BH masses derived from our new formalisms show subtle but important differences compared to some of the mass estimators currently used in the literature.
Comparing and Calibrating Black Hole Mass Estimators for Distant Active Galactic Nuclei
The Astrophysical Journal, 2008
Black hole mass (M BH ) is a fundamental property of active galactic nuclei (AGNs). In the distant universe, M BH is commonly estimated using the MgII, Hβ, or Hα emission line widths and the optical/UV continuum or line luminosities, as proxies for the characteristic velocity and size of the broad-line region. Although they all have a common calibration in the local universe, a number of different recipes are currently used in the literature. It is important to verify the relative accuracy and consistency of the recipes, as systematic changes could mimic evolutionary trends when comparing various samples. At z = 0.36, all three lines can be observed at optical wavelengths, providing a unique opportunity to compare different empirical recipes. We use spectra from the Keck Telescope and the Sloan Digital Sky Survey to compare M BH estimators for a sample of nineteen AGNs at this redshift. We compare popular recipes available from the literature, finding that M BH estimates can differ up to 0.38 ± 0.05 dex in the mean (or 0.13 ± 0.05 dex, if the same virial coefficient is adopted). Finally, we provide a set of 30 internally self consistent recipes for determining M BH from a variety of observables. The intrinsic scatter between cross-calibrated recipes is in the range 0.1 − 0.3 dex. This should be considered as a lower limit to the uncertainty of the M BH estimators.
A near-infrared relationship for estimating black hole masses in active galactic nuclei
Monthly Notices of the Royal Astronomical Society, 2013
Black hole masses for samples of active galactic nuclei (AGN) are currently estimated from single-epoch optical spectra using scaling relations anchored in reverberation mapping results. In particular, the two quantities needed for calculating black hole masses, namely, the velocity and the radial distance of the orbiting gas are derived from the widths of the Balmer hydrogen broad emission lines and the optical continuum luminosity, respectively. We have recently presented a near-infrared (near-IR) relationship for estimating AGN black hole masses based on the widths of the Paschen hydrogen broad emission lines and the total 1 µm continuum luminosity. The near-IR offers several advantages over the optical: it suffers less from dust extinction, the AGN continuum is observed only weakly contaminated by the host galaxy and the strongest Paschen broad emission lines Paα and Paβ are unblended. Here we improve the calibration of the near-IR black hole mass relationship by increasing the sample from 14 to 23 reverberation-mapped AGN using additional spectroscopy obtained with the Gemini Near-Infrared Spectrograph (GNIRS). The additional sample improves the number statistics in particular at the high luminosity end.
On the Systematic Bias in the Estimation of Black Hole Masses in Active Galactic Nuclei
2012
In this report, we find the M BH estimated from the formalism of Wang et al. (2009)[1] are more consistent with those from the M BH -σ * relation than those from previous single-epoch mass estimators, using a large sample of AGNs. Furthermore, we examine the differences between the line widths of Hβ and Mg II in detail by comparing their line profiles. The flux around the line core and that in the wing of both Hβ and Mg II show an opposite variation tendency, which indicates the BLR is multi-componential. The contribution of the wing makes the FWHM deviate from σ line , and thus bias the M BH estimated from previous single-epoch mass estimators. Thus the correction on the formalism suggested by Wang et al. (2009)[1] is crucial to M BH estimation. Quasars, Galactic nuclei, Masses, Statistical and correlative studies of properties PACS: 98.54.Aj, 98.62.Js, 98.62.Ck, 98.62.Ve
THE IMPORTANCE OF BROAD EMISSION LINE WIDTHS IN SINGLE-EPOCH BLACK HOLE MASS ESTIMATES
The Astrophysical Journal, 2012
Estimates of the mass of super-massive black holes (BHs) in distant active galactic nuclei (AGNs) can be obtained efficiently only through single-epoch (SE) spectra, using a combination of their broad emission line widths and continuum luminosities. Yet the reliability and accuracy of the method and the resulting mass estimates, M BH , remain uncertain. A recent study by Croom using a sample of Sloan Digital Sky Survey, 2dF QSO Redshift Survey, and 2dF-SDSS LRG and QSO Survey quasars suggests that line widths contribute little information about the BH mass in these SE estimates and can be replaced by a constant value without significant loss of accuracy. In this Letter, we use a sample of nearby reverberation-mapped AGNs to show that this conclusion is not universally applicable. We use the bulge luminosity (L Bulge ) of these local objects to test how well the known M BH -L Bulge correlation is recovered when using randomly assigned line widths instead of the measured ones to estimate M BH . We find that line widths provide significant information about M BH , and that for this sample, the line width information is just as significant as that provided by the continuum luminosities. We discuss the effects of observational biases upon the analysis of Croom and suggest that the results can probably be explained as a bias of flux-limited, shallow quasar samples.
2017
We provide an updated calibration of C IV λ1549 broad emission line-based single-epoch (SE) black hole (BH) mass estimators for active galactic nuclei (AGNs) using new data for six reverberation-mapped AGNs at redshift z = 0.005 − 0.028 with BH masses (bolometric luminosities) in the range 106.5–107.5 M (1041.7– 1043.8 erg s−1). New rest-frame UV-to-optical spectra covering 1150–5700 Å for the six AGNs were obtained with the Hubble Space Telescope (HST). Multi-component spectral decompositions of the HST spectra were used to measure SE emission-line widths for the C IV, Mg II, and Hβ lines as well as continuum luminosities in the spectral region around each line. We combine the new data with similar measurements for a previous archival sample of 25 AGNs to derive the most consistent and accurate calibrations of the C IV-based SE BH mass estimators against the Hβ reverberation-based masses, using three different measures of broad-line width: full-width at half maximum (FWHM), line di...
Determining Central Black Hole Masses in Distant Active Galaxies
The Astrophysical Journal, 2002
An empirical relationship, of particular interest for studies of high-redshift active galactic nuclei (AGNs) and quasars, between the masses of their central black holes and rest-frame ultraviolet (UV) parameters measured in single-epoch AGN spectra is presented. This relationship is calibrated to recently measured reverberation masses of low-redshift AGNs and quasars. An empirical relationship between single-epoch rest-frame optical spectrophotometric measurements and the central masses is also presented. The UV relationship allows reasonable estimates of the central masses to be made for high-redshift AGNs and quasars for which these masses cannot be directly or easily measured by the techniques applicable to the lower luminosity, nearby AGNs. The central mass obtained by this method can be estimated to within a factor of $3 for most objects. This is reasonable given the intrinsic uncertainty of a factor of less than 2 in the primary methods used to measure the central masses of nearby inactive and active galaxies, namely, resolved gas and stellar kinematics in the underlying host galaxy and reverberation-mapping techniques. The UV relationship holds good potential for being a powerful tool for studying black hole demographics at high redshift as well as statistically studying the fundamental properties of AGNs. The broad-line region size-luminosity relationship is key to the calibrations presented here. The fact that its intrinsic scatter is also the main source of uncertainty in the calibrations stresses the need for better observational constraints to be placed on this relationship. The empirically calibrated relationships presented here will be applied to quasar samples in forthcoming work.
New Estimators of Black Hole Mass in Active Galactic Nuclei with Hydrogen Paschen Lines
The Astrophysical Journal, 2010
More than 50% of Active Galactic Nuclei (AGNs) are suspected to be red and affected by dustobscuration. Meanwhile, popular spectral diagnostics of AGNs are based on optical or ultraviolet light, making the dust obscuration as a primary concern for understanding the general nature of AGNs and supermassive black holes residing in them. To provide with a method of investigating properties of the dusty AGNs, we derive new black hole (BH) mass estimators based on velocity widths and luminosities of Near Infrared (NIR) hydrogen emission lines such as Pα and Pβ, and also investigate the line ratios of these Hydrogen lines. To derive the BH mass (M BH ) estimators, we used a sample of 37 unobscured Type-1 AGNs with a M BH range of 10 6.8 -10 9.4 M ⊙ , where M BH come from either reverberation mapping method or single-epoch measurement method using Balmer lines. Our work shows that M BH can be estimated from the Paschen line luminosities and the velocity widths to the accuracy of 0.18 -0.24 dex (rms scatter). We also show that the mean line ratios of the Paschen lines and the Balmer lines are Hα Pα ≃ 9.00, Hβ Pα ≃ 2.70, which are consistent with a Case B recombination under a typical AGN broad line region environment. These ratios can be used as reference points when estimating the amount of dust extinction over the broad line region (BLR) for red AGNs. We expect the future application of the new BH mass estimators on red, dusty AGNs to provide a fresh view of obscured AGNs.
The Astrophysical Journal
We provide an updated calibration of C IV λ1549 broad emission line-based single-epoch (SE) black hole (BH) mass estimators for active galactic nuclei (AGNs) using new data for six reverberation-mapped AGNs at redshift z = 0.005 − 0.028 with BH masses (bolometric luminosities) in the range 10 6.5-10 7.5 M (10 41.7-10 43.8 erg s −1). New rest-frame UV-to-optical spectra covering 1150-5700 Å for the six AGNs were obtained with the Hubble Space Telescope (HST). Multi-component spectral decompositions of the HST spectra were used to measure SE emission-line widths for the C IV, Mg II, and Hβ lines as well as continuum luminosities in the spectral region around each line. We combine the new data with similar measurements for a previous archival sample of 25 AGNs to derive the most consistent and accurate calibrations of the C IV-based SE BH mass estimators against the Hβ reverberation-based masses, using three different measures of broad-line width: full-width at half maximum (FWHM), line dispersion (σ line) and mean absolute deviation (MAD). The newly expanded sample at redshift z = 0.005 − 0.234 covers a dynamic range in BH mass (bolometric luminosity) of log M BH /M = 6.5 − 9.1 (log L bol /erg s −1 = 41.7 − 46.9), and we derive the new C IV-based mass estimators using a Bayesian linear regression analysis over this range. We generally recommend the use of σ line or MAD rather than FWHM to obtain a less biased velocity measurement of the C IV emission line, because its narrowline component contribution is difficult to decompose from the broad-line profile.