Determining AGN Black Hole Masses from Two-Dimensional Gas Kinematics

Determining AGN Black Hole Masses from Two-Dimensional Gas Kinematics

Determining AGN Black Hole Masses from Two-Dimensional Gas Kinematics

Erin K. S. Hicks – UCLA NNG 2005 Poster (page by page) Determining AGN Black Hole Masses from Two-Dimensional Gas Kinematics Erin K. S. Hicks & Matthew A. Malkan University of California, Los Angeles email: ehicks@astro.ucla.edu

Determining AGN Black Hole Masses from Two-Dimensional Gas Kinematics

Erin K. S. Hicks – UCLA NNG 2005 Poster (page by page) Poster Abstract We have measured two-dimensional nuclear gas kinematics of a sample of nine Seyfert 1 galaxies. The inner arcsecond of each AGN is well sampled with Keck NIRSPEC K-band spectroscopy obtained with adaptive optics and a 4'' slit at a high spatial resolution (0''.0185 pixel-1).

The typical point spread function has a full-width- half-maximum of 0''.1, which for our sample corresponds to 21 pc on average, with a range from 3 to 29 pc. The spectra contain many emission lines from molecular hydrogen and Brγ, as well as coronal lines. The gas velocity fields are measured to an accuracy of around 20 km s-1, and for two galaxies, NGC 3227 and NGC 7469, steep gradients of over 150 km s-1 are observed across the central arcsecond. The two-dimensional (2D) flux distributions of the line emitting gases are also mapped, with NGC 3227 showing an offset in molecular hydrogen of 0''.5 SE from the AGN, while Brγ is peaked at the AGN location.

The 2D gas kinematics are interpreted using dynamical models; these provide an estimate for the central mass in each AGN, presumably a supermassive black hole. The models assume a co-planar thin disk undergoing circular rotation, and they take into account the point spread function for each spectroscopic exposure (measured simultaneously using the slit viewing camera). Also included in the models are the emission line surface brightness distribution and the stellar gravitational field (estimated from HST NICMOS near-infrared images by separating the stellar light from the point source and assuming a constant stellar mass-to-light ratio).

Compared to most non-active spiral galaxies, both NGC 3227 and NGC 7469 appear to have higher stellar surface densities in the inner two arcseconds. Preliminary results indicate NGC 3227 has a black hole of 5 x 106 ≤ MBH ≤ 108 M, while NGC 7469 contains a black hole of 2.5x107 ≤ MBH ≤ 108 M, depending strongly on the stellar mass-to-light ratio. For both objects the steepness of the inner rotation curve can not be fit without a black hole.

Determining AGN Black Hole Masses from Two-Dimensional Gas Kinematics

Erin K. S. Hicks – UCLA NNG 2005 Poster (page by page) Observations Spectroscopy of the Seyfert 1 galaxies was obtained at the Keck II telescope using NIRSPEC (McLean et al. 1998, SPIE, 3354, 566) with adaptive optics (AO). The Seyfert nucleus was utilized as the guiding source for the AO system. Spectra of 1.9–2.4µm (roughly K-band) were obtained over 10 half-nights, each with a different slit position angle. See Fig. 1 for placement of the slits and total on-source exposure time for each object. The AO correction typically resulted in a strehl of around 0.3 and FWHM of 0''.1. See Fig. 2 for examples of the spectra obtained.

Indispensable to the project is the slit-viewing camera, SCAM, with a 0''.017 pixel scale and a field of view of 4''.4 x 4''.4. Images are taken approximately every minute throughout spectroscopic exposures, resulting in a very accurate determination of the PSF and the slit position as well as any drift of the slit throughout the spectroscopic exposure (typically < 1 pixel during 600 seconds). NGC 4151 4.1 hr 64 6'' pc/'' Galaxy Total Exp. Slit Placement NGC 3227 74 5.1 hr NGC 6814 101 0.9 hr Ark 120 613 1.9 hr NGC 5548 334 1.3 hr NGC 3516 172 1.8 hr NGC 4051 47 3.9 hr NGC 7469 318 3.1 hr NGC 4593 175 0.3 hr Fig 1.

Overlay of slit positions on HST images of each Seyfert 1 galaxy in the sample. Each thin black line is a single slit position; thicker lines are overlapping slit positions. Also included are the total exposure time and a 1'' bar and corresponding distance in parsecs. See upper left for legend. Assumed Ho = 75 km s -1 Mpc-1 .

Determining AGN Black Hole Masses from Two-Dimensional Gas Kinematics

Erin K. S. Hicks – UCLA NNG 2005 Poster (page by page) Fig 2. Example nuclear spectra from a 0''.05 x 0''.04 aperture. Several H2 emission lines and Brγ are labeled. Also labeled are some stellar absorption features, most notably the CO bandheads at 2.3µm.

Determining AGN Black Hole Masses from Two-Dimensional Gas Kinematics

Erin K. S. Hicks – UCLA NNG 2005 Poster (page by page) Data Analysis The 2D kinematics are constructed from up to dozens of slit positions. The velocity of the gas, as well as the flux of the emission, is determined from a single Gaussian fit to the emission line profile. 2D maps were created for each object using all emission lines with at least a 3σ detection; for most objects this included two or more of the following: H2 1.9576, 2.1218, 2.2235, 2.2477, 2.4066, 2.4237, and Brγ 2.1661µm.

Example 2D velocity and flux distribution maps for NGC 3227 and NGC 7469 are shown in Figures 3 and 4, respectively.

Data reduction was done using IRAF. Following cosmic ray removal, the spectral images were rectified using the WMKONSPEC reduction package. Sky subtraction was done by differencing dithered pairs (2'' nod) of spectral images, and spectra were extracted and then wavelength calibrated using arc lamp spectra taken immediately following the spectroscopic exposure.

Determining AGN Black Hole Masses from Two-Dimensional Gas Kinematics

Erin K. S. Hicks – UCLA NNG 2005 Poster (page by page) Fig 3a Fig 3b Fig 3c Fig 3d Fig 3. 2D velocity of the central 1''.5 of NGC 3227 for (a) H2 2.1218 and (b) H2 2.4237. Both lines exhibit organized rotation.

Brγ and H2 2.4066 are also consistent with this rotation. (c) In NGC 3227 the distribution of Brγ is centrally concentrated while the peak of H2 is offset from the AGN by 0".5 SE. (d) The 2D flux distribution of the continuum from 2.14-2.15µm is, as expected, centrally concentrated.

Determining AGN Black Hole Masses from Two-Dimensional Gas Kinematics

Erin K. S. Hicks – UCLA NNG 2005 Poster (page by page) Fig 4. 2D velocity maps of the central 1''.5 of NGC 7469 for (a) H2 2.1218 and (b) H2 1.9576. The organized rotation of both lines is consistent, as is that of Brγ. (c) The Brγ and H2 flux distributions are both centrally concentrated. Fig 4c Fig 4b Fig 4a

Determining AGN Black Hole Masses from Two-Dimensional Gas Kinematics

Erin K. S. Hicks – UCLA NNG 2005 Poster (page by page) Emission too Weak to Measure Reliably Organized Gradient: 150 km s-1 in central arcsec No Velocity Gradient Measured No Velocity Gradient Measured Emission too Weak to Measure Reliably Organized Gradient: 100 km s-1 in central arcsec Organized Gradient: 100 km s-1 in central arcsec No Velocity Gradient Measured Organized Gradient: 150 km s-1 in central arcsec Nuclear Velocity Field H2 2.1218 H2 1.9576, H2 2.1218, H2 2.2235 H2 2.1218, H2 2.2014, H2 2.2235, H2 2.2477 H2 2.1218 H2 2.1218, H2 2.4066 H2 2.1218, Brγ 2.1661 H2 2.1218, Brγ 2.1661 H2 2.1218 H2 2.1218, Brγ 2.1661, H2 2.4066, H2 2.4237 Emission Lines Measured Ark 120 NGC 7469 NGC 6814 NGC 5548 NGC 4593 NGC 4151 NGC 4051 NGC 3516 NGC 3227 Object Summary of 2D Velocity Fields

Determining AGN Black Hole Masses from Two-Dimensional Gas Kinematics

Erin K. S. Hicks – UCLA NNG 2005 Poster (page by page) Modeling Dynamical models have been created assuming a co-planar thin gas disk undergoing circular rotation. The gravitational potential is assumed to be created by both the stellar gravitational field, which is determined from the separation of the AGN and stellar light in HST F160W images (see below), and a point source mass, presumably a supermassive black hole. The model velocity field is then synthetically observed using the same parameters used for the actual observations. This includes the point spread function for each spectroscopic exposure and the emission line surface brightness distribution.

See the handouts for more details. Free parameters in the model are the black hole mass (MBH), the H-band mass-to-light ratio (M/L), and the disk inclination and position angle of its major axis.

Preliminary results indicate that for NGC 3227 a black hole of 5x106 ≤ MBH ≤ 108 M is favored for 0.5 ≤ M/L ≤ 1.0. For NGC 7469, a black hole of 2.5x107 ≤ MBH ≤ 108 M is favored, again dependent on the M/L. For both objects, an unreasonably high M/L (~1.5) must be used to fit the data with no black hole. The mass estimate for NGC 3227 is consistent with that based on reverberation mapping, which gives MBH = 4.2 ± 2.1x107 M, while for NGC 7469 reverberation mapping gives a slightly lower estimate of MBH = 1.2 ± 0.1x107 M. Figures 6 and 7 give more detailed modeling results.

Determining AGN Black Hole Masses from Two-Dimensional Gas Kinematics

Erin K.

S. Hicks – UCLA NNG 2005 Poster (page by page) Stellar Gravitational Field Separation of the stellar light from the point source was done by fitting a Sérsic function plus a point source to HST NICMOS H-band images. The strip brightness method (Moriondo et al. 1998, AA, 339, 409) was used to deproject the fitted stellar distribution. An assumed constant M/L in the range 0.1-1.5 H-band units (Bell & de Jong 2001, ApJ, 550, 221) was then used to determine the stellar mass distribution. As a check on this method, a scaled Tiny Tim PSF was subtracted from the images to determine the minimum amount of stellar light that is acceptable.

See Fig. 5 for the fits, deprojections, and resulting velocity fields for NGC 3227. Compared to most non-active spiral galaxies (Scarlata et al. 2004, ApJ, 128, 1124, Seigar et al. 2002, AJ, 123, 184), both NGC 3227 and NGC 7469 appear to have higher stellar surface densities in the inner two arcseconds.

Fig 5. (a) Sérsic (n=3) plus point source fit to the NICMOS F160W image of NGC 3227. (b) Stellar density after deprojection. Each of the Sérsic fits and the remaining stellar light after PSF subtraction are shown for both the maximum and minimum allowable star light. The n=2 and n=3 Sérsic fits are the best fits to the data. (c) The resulting intrinsic velocities in the plane of the disk assuming a disk inclination of i = 56o and mass-to-light ratio (H-band) = 0.5. Fig. 5a Observed Surface Brightness Fig. 5b Deprojected 3D Stellar Density Fig. 5c Velocity Field

Erin K.

S. Hicks – UCLA NNG 2005 Poster (page by page) NGC 3227 All three H2 lines and Brγ have similar rotation patterns, with a major axis PA=130o, in contrast to the PA of 158o seen at greater radii. The 2D map reveals a velocity field that is generally in organized circular rotation, but with many reproducible smaller scale “wiggles” in the curve indicating that gas motion is not purely circular in a thin disk. Fig 6. (a) Delta Chi-Squared of the best fit model and H2 2.1218 2D velocity field, which has PA=130o and i=56o . The best fit MBH ranges from 5x106 to 108 M, depending on the M/L. (b) Data along a single slit position (angle=100o , offset=0''.09) with Sérsic n=3 stellar models with MBH = 0, 107 , and 108 M.

Fig 6b Fig 6a Mass estimate of 5x106 ≤ MBH ≤ 108 M is favored for 0.5 ≤ M/L ≤ 1.0.

Erin K. S. Hicks – UCLA NNG 2005 Poster (page by page) NGC 7469 Both H2 lines and Brγ have similar rotation patterns, with a major axis PA=128o, consistent with that based on the motion of CO gas in the inner 3'' (Davies, R. I. et al. 2004, ApJ, 602, 148). Rotation curves are consistent with Davies et al. who measured H2 with the same instrumental setup at two position angles (33o and 128o) centered on the galaxy. Fig 7. (a) Delta Chi-Squared of the best fit model and H2 2.1218 2D velocity field, which has PA=128o and i=45o .

The best fit MBH ranges from 2.5x107 to 108 M, depending on the M/L. (b) Data along a single slit position (angle=-30o , offset=0''.09) with Sérsic n=2 stellar models with MBH = 0, 5x107 , and 5x108 M.

Fig 7b Fig 7a Mass estimate of 2.5x107 ≤ MBH ≤ 108 M is favored for 0.5 ≤ M/L ≤ 1.0.

Abstract We have measured two-dimensional nuclear gas kinematics of a sample of nine Seyfert 1 galaxies. The inner arcsecond of each AGN is well sampled with Keck NIRSPEC K-band spectroscopy obtained with adaptive optics and a 4'' slit at a high spatial resolutio n (0''.0185 pixel-1). The typical point spread function has a full-width-half-maximum of 0''.1, which for our sample corresponds to 21 pc on average, with a range from 3 to 29 pc. The spectra contain many emission lines from molecular hydrogen and Brγ, as well as coronal lines.

The gas velocity fields are measured to an accuracy of around 20 km s-1, and for two galaxies, NGC 3227 and NGC 7469, steep gradients of over 150 km s-1 are observed across the central arcsecond. The two-dimensional (2D) flux d istributions of the line emitting gases are also mapped, with NGC 3227 showing an offset in molecular hydrogen of 0''.5 SE from the AGN, while Brγ is peaked at the AGN location. The 2D gas kinematics are interpreted using dynamical models; these provide an estimate for the central mass in each AGN, presumably a supermassive black hole. The models assume a co-planar thin disk undergoing circular rotation, and they take into account the point spread function for each spectroscopic exposure (measured simul taneously using the slit viewing camera).

Also included in the models are the emission line surface brightness distribution and the stellar gravitational field (estimated from HST NICMOS near-infrared images by separating the stellar light from the point source and assuming a constant stellar mass-to-light ratio). Compared to most non-active spiral galaxies, both NGC 3227 and NGC 7469 appear to have higher stellar surface densities in the inner two arcseconds. Preliminary results indicate NGC 3227 has a black hole of 5 x 106 ≤ MBH ≤ 108 M, while NGC 7469 contains a black hole of 2.5x107 ≤ MBH ≤ 108 M, depending strongly on the stellar mass-to-light ratio.

For both objects the steepness of the inner rotation curve can not be fit without a black hole. Determining AGN Black Hole Masses from Two-Dimensional Gas Kinematics Observations Spectroscopy of the Seyfert 1 galaxies was obtained at the Keck II telescope using NIRSPEC (McLean et al. 1998, SPIE, 3354, 566) with adaptive optics (AO). The Seyfert nucleus was utilized as the guiding source for the AO system. Spectra of 1.9–2.4µm (roughly K-band) were obtained over 10 half-nights, each with a different slit position angle. See Fig. 1 for placement of the slits and total on- source exposure time for each object.

The AO correction typically resulted in a strehl of around 0.3 and FWHM of 0''.1. See Fig. 2 for examples of the spectra obtained. Indispensable to the project is the slit-viewing camera, SCAM, with a 0''.017 pixel scale and a field of view of 4''.4 x 4''.4. Images are taken approximately every minute throughout spectroscopic exposures, resulting in a very accurate determination of the PSF and the slit position as well as any drift of the slit throughout the spectroscopic exposure (typically < 1 pixel during 600 seconds). Data Analysis The 2D kinematics are constructed from up to dozens of slit positions.

The velocity of the gas, as well as the flux of the emission, is determined from a single Gaussian fit to the emission line profile. 2D maps were created for each object using all emission lines with at least a 3σ detection; for most objects this included two or more of the following: H2 1.9576, 2.1218, 2.2235, 2.2477, 2.4066, 2.4237, and Brγ 2.1661µm. Example 2D velocity and flux distribution maps for NGC 3227 and NGC 7469 are shown in Figures 3 and 4, respectively.

Data reduction was done using IRAF. Following cosmic ray removal, the spectral images were rectified using the WMKONSPEC reduction package. Sky subtraction was done by differencing dithered pairs (2'' nod) of spectral images, and spectra were extracted and then wavelength calibrated using arc lamp spectra taken immediately following the spectroscopic exposure. Emission too Weak to Measure Reliably Organized Gradient: 150 km s-1 in central arcsec No Velocity Gradient Measured No Velocity Gradient Measured Emission too Weak to Measure Reliably Organized Gradient: 100 km s-1 in central arcsec Organized Gradient: 100 km s-1 in central arcsec No Velocity Gradient Measured Organized Gradient: 150 km s-1 in central arcsec Nuclear Velocity Field H2 2.1218 H2 1.9576, H2 2.1218, H2 2.2235 H2 2.1218, H2 2.2014, H2 2.2235, H2 2.2477 H2 2.1218 H2 2.1218, H2 2.4066 H2 2.1218, Brγ 2.1661 H2 2.1218, Brγ 2.1661 H2 2.1218 H2 2.1218, Brγ 2.1661, H2 2.4066, H2 2.4237 Emission Lines Measured Ark 120 NGC 7469 NGC 6814 NGC 5548 NGC 4593 NGC 4151 NGC 4051 NGC 3516 NGC 3227 Object Modeling Dynamical models have been created assuming a co-planar thin gas disk undergoing circular rotation.

The gravitational potential is assumed to be created by both the stellar gravitational field, which is determined from the separation of the AGN and stellar light in HST F160W images (see below), and a point source mass, presumably a supermassive black hole. The model velocity field is then synthetically observed using the same parameters used for the actual observations. This includes the point spread function for each spectroscopic exposure and the emission line surface brightness distribution. See the handouts for more details. Free parameters in the model are the black hole mass (MBH), the H-band mass-to-light ratio (M/L), and the disk inclination and position angle of its major axis.

Preliminary results indicate that for NGC 3227 a black hole of 5x106 ≤ MBH ≤ 108 M is favored for 0.5 ≤ M/L ≤ 1.0. For NGC 7469, a black hole of 2.5x107 ≤ MBH ≤ 108 M is favored, again dependent on the M/L. For both objects, an unreasonably high M/L (~1.5) must be used to fit the data with no black hole. The mass estimate for NGC 3227 is consistent with that based on reverberation mapping, which gives MBH = 4.2 ± 2.1x107 M, while for NGC 7469 reverberation mapping gives a slightly lower estimate of MBH = 1.2 ± 0.1x107 M. Figures 6 and 7 give more detailed modeling results. Stellar Gravitational Field Separation of the stellar light from the point source was done by fitting a Sérsic function plus a point source to HST NICMOS H-band images.

The strip brightness method (Moriondo et al. 1998, AA, 339, 409) was used to deproject the fitted stellar distribution. An assumed constant M/L in the range 0.1-1.5 H-band units (Bell & de Jong 2001, ApJ, 550, 221) was then used to determine the stellar mass distribution. As a check on this method, a scaled Tiny Tim PSF was subtracted from the images to determine the minimum amount of stellar light that is acceptable. See Fig. 5 for the fits, deprojections, and resulting velocity fields for NGC 3227. Compared to most non-active spiral galaxies (Scarlata et al. 2004, ApJ, 128, 1124, Seigar et al.

2002, AJ, 123, 184), both NGC 3227 and NGC 7469 appear to have higher stellar surface densities in the inner two arcseconds. Erin K. S. Hicks & Matthew A. Malkan - University of California, Los Angeles Email for Erin Hicks: ehicks@astro.ucla.edu Summary of 2D Velocity Fields Fig 1. Overlay of slit positions on HST images of each Seyfert 1 galaxy in the sample. Each thin black line is a single slit position; thicker lines are overlapping slit positions. Also included are the total exposure time and a 1'' bar and corresponding distance in parsecs. See upper left for legend. Assumed Ho = 75 km s -1 Mpc-1.

Fig 2. Example nuclear spectra from a 0''.05 x 0''.04 aperture. Several H2 emission lines and Brγ are labeled. Also labeled are some stellar absorption features, most notably the CO bandheads at 2.3µm. Fig 3. 2D velocity of the central 1''.5 of NGC 3227 for (a) H2 2.1218 and (b) H2 2.4237. Both lines exhibit organized rotation. Brγ and H2 2.4066 are also consistent with this rotation. (c) In NGC 3227 the distribution of Brγ is centrally concentrated while the peak of H2 is offset from the AGN by 0".5 SE. (d) The 2D flux distribution of the continuum from 2.14-2.15µm is, as expected, centrally concentrated.

Fig 4. 2D velocity maps of the central 1''.5 of NGC 7469 for (a) H2 2.1218 and (b) H2 1.9576. The organized rotation of both lines is consistent, as is that of Brγ. (c) The Brγ and H2 flux distributions are both centrally concentrated. Fig 5. (a) Sérsic (n=3) plus point source fit to the NICMOS F160W image of NGC 3227. (b) Stellar density after deprojection. Each of the Sérsic fits and the remaining stellar light after PSF subtraction are shown for both the maximum and minimum allowable star light. The n=2 and n=3 Sérsic fits are the best fits to the data. (c) The resulting intrinsic velocities in the plane of the disk assuming a disk inclination of i = 56o and mass-to-light ratio (H-band) = 0.5.

Fig 6. (a) Delta Chi-Squared of the best fit model and H2 2.1218 2D velocity field, which has PA=130o and i=56o. The best fit MBH ranges from 5x106 to 108 M, depending on the M/L. (b) Data along a single slit position (angle=100o, offset=0''.09) with Sérsic n=3 stellar models with MBH = 0 and the best fit masses of 2.5x107 to 108 M. NGC 3227 NGC 7469 All three H2 lines and Brγ have similar rotation patterns, with a major axis PA=130o, in contrast to the PA of 158o seen at greater radii. The 2D map reveals a velocity field that is generally in organized circular rotation, but with many reproducible smaller scale “wiggles” in the curve indicating that gas motion is not purely circular in a thin disk.

Both H2 lines and Brγ have similar rotation patterns, with a major axis PA=128o, consistent with that based on the motion of CO gas in the inner 3'' (Davies, R. I. et al. 2004, ApJ, 602, 148). Rotation curves are consistent with Davies et al. who measured H2 with the same instrumental setup at two position angles (33o and 128o) centered on the galaxy. NGC 4151 4.1 hr 64 6'' pc/'' Galaxy Total Exp. Slit Placement NGC 3227 74 5.1 hr 101 0.9 hr NGC 6814 Ark 120 613 1.9 hr NGC 5548 334 1.3 hr NGC 3516 172 1.8 hr NGC 4051 47 3.9 hr NGC 7469 318 3.1 hr NGC 4593 175 0.3 hr Fig. 5a Observed Surface Brightness Fig.

5b Deprojected 3D Stellar Density Fig. 5c Velocity Field Fig 3a Fig 3b Fig 3c Fig 3d Fig 4c Fig 4b Fig 4a Fig 7. (a) Delta Chi-Squared of the best fit model and H2 2.1218 2D velocity field, which has PA=128o and i=45o. The best fit MBH ranges from 2.5x107 to 108 M, depending on the M/L. (b) Data along a single slit position (angle=-30o, offset=0''.09) with Sérsic n=2 stellar models with MBH = 0 and the best fit masses of 5x107 to 108 M.

Fig 6b Fig 6a Fig 7b Fig 7a

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