Polarization in Lines—a New Method for Measuring Black Hole Masses in Active Galaxies

Here we give an observational method for measurements of the equatorial scattering region radius using variability in the polarized broad lines in Type 1 active galactic nuclei (AGNs). The polarization in broad lines of Type 1 AGNs is mostly caused by equatorial scattering, where specific features allow one to separate its contribution from the total polarized flux. We propose to monitor variability in the polarized line flux and find the time lag between the nonpolarized continuum and polarized broad line variability. The distance to the scattering screen can then be determined from the time delay.The method was, for the first time, applied to the observations of the Type 1 AGN Mrk 6, and we found that the size of the scattering region in this AGN is around 100 light days. That is significantly smaller than the dusty region size estimated by the infrared interferometric observations and also larger than known broad line region (BLR) size. This indicates that the scattering region lies between the BLR and the dusty region and could be used as a probe of the dust sublimation radius.

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“…• The direct estimates of R sc will increase the accuracy of mass estimations (Afanasiev & Popović 2015).…”

Section: Discussionmentioning

confidence: 99%

Measuring the AGN Sublimation Radius with a New Approach: Reverberation Mapping of Broad Line Polarization

Shablovinskaya

Afanasiev

2020

ApJ

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“…where V i is the rotational velocity of emitting gas, M BH is the BH mass and R i is the distance from the center of the disk; G is the gravitational constant and θ is the angle between the disc and the plane of scattering (Afanasiev & Popović 2015). R i can be connected with the corresponding polarization angle ϕ i as R i = R sc tan ϕ i , where R sc is the distance from the center to the SR (Fig.…”

Section: Ap15 Methodsmentioning

confidence: 99%

AGN black hole mass estimates using polarization in broad emission lines

Savić

Goosmann

Popović

et al. 2018

A&A

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Context. The innermost regions in active galactic nuclei (AGNs) were not being spatially resolved so far but spectropolarimetry can provide us insight about their hidden physics and the geometry. From spectropolarimetric observations in broad emission lines and assuming equatorial scattering as a dominant polarization mechanism, it is possible to estimate the mass of supermassive black holes (SMBHs) residing in the AGN center. Aims. We explore the possibilities and limits and put constraints on the usage of the method for determining SMBH masses using polarization in broad emission lines by providing more in-depth theoretical modeling. Methods. We use the Monte Carlo radiative transfer code stokes for exploring polarization properties of Type 1 AGNs. We model equatorial scattering using flared-disk geometry for a set of different SMBH masses assuming Thomson scattering. In addition to the Keplerian motion which is assumed to be dominant in the broad line region (BLR), we also consider cases of additional radial inflows and vertical outflows. Results. We model the profiles of polarization plane position angle ϕ, degree of polarization and total unpolarized line for different BLR geometries and different SMBH masses. Our modeling confirms that the method can be widely used for Type-1 AGNs when viewing inclinations are between 25• and 45• . We show that the distance between the BLR and scattering region (SR) has a significant impact on the mass estimates and the best mass estimates are when the SR is situated at the distance 1.5-2.5 times larger than the outer BLR radius. Conclusions. Our models show that if Keplerian motion can be traced through the polarized line profile, then the direct estimation of the mass of the SMBH can be performed. When radial inflows or vertical outflows are present in the BLR, this method can still be applied if velocities of the inflow/outflow are less than 500 km s −1 . We also find that models for NGC 4051, NGC 4151, 3C 273 and PG0844+349 are in good agreements with observations.

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“…The method is described in more details in Afanasiev & Popović (2015). We used the fact that in the case of equatorial scattering, the polarization angle (ϕ i ) is connected with the distance (R i ) of an emitting cloud (see Fig.…”

Section: Polarization Methods For Smbh Measurementsmentioning

confidence: 99%

“…We used the fact that in the case of equatorial scattering, the polarization angle (ϕ i ) is connected with the distance (R i ) of an emitting cloud (see Fig. 1 in Afanasiev & Popović 2015) as…”

Section: Polarization Methods For Smbh Measurementsmentioning

confidence: 99%

“…G is the gravitational constant and the virial factor f depends on the BLR inclination and geometry which are unknown and, consequently there is a problem to accurately determine the virial factor (Peterson 2014). On the other side, the polarization in the broad lines can be very useful for investigation of the nature of the BLR (Smith et al 2002(Smith et al , 2004(Smith et al , 2005Afanasiev et al 2014;Afanasiev & Popović 2015. The polarization in the broad lines, especially the polarization angle (ϕ) that shows horizontal S shape across the broad line profile, which indicates a dominant Keplerian-like motion in the BLR, and dominant equatorial scattering as a polarization mechanism in the broad lines (see Afanasiev & Popović 2015).…”

Section: Introductionmentioning

confidence: 99%

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Black hole mass measurements in AGN: Polarization in broad emission lines

Afanasiev

Savic

2018

Proc. IAU

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We present a new method for supermassive black hole (SMBH) mass measurements in Type 1 active galactic nuclei (AGN) using polarization angle across broad lines. This method gives measured masses which are in a good agreement with reverberation estimates. Additionally, we explore the possibilities and limits of this method using the STOKES radiative transfer code taking a dominant Keplerian motion in the broad line region (BLR). We found that this method can be used for the direct SMBH mass estimation in the cases when in addition to the Kepler motion, radial inflows or vertical outflows are present in the BLR. Some advantages of the method are discussed.

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Polarization in Lines—a New Method for Measuring Black Hole Masses in Active Galaxies

Cited by 38 publications

References 15 publications

Measuring the AGN Sublimation Radius with a New Approach: Reverberation Mapping of Broad Line Polarization

Measuring the AGN Sublimation Radius with a New Approach: Reverberation Mapping of Broad Line Polarization

AGN black hole mass estimates using polarization in broad emission lines

Black hole mass measurements in AGN: Polarization in broad emission lines

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