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تسجيل مستخدم جديدA Local Baseline of the Black Hole Mass Scaling Relations for Active Galaxies. I. Methodology and Results of Pilot Study
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Vardha Nicola Bennert
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We present high-quality Keck/LRIS longslit spectroscopy of a pilot sample of 25 local active galaxies selected from the SDSS (0.02<z<0.1; MBH>10^7 M_sun) to study the relations between black hole mass (MBH) and host-galaxy properties. We determine stellar kinematics of the host galaxy, deriving stellar-velocity dispersion profiles and rotation curves from three spectral regions (including CaH&K, MgIb triplet, and CaII triplet). In addition, we perform surface photometry on SDSS images, using a newly developed code for joint multi-band analysis. BH masses are estimated from the width of the Hbeta emission line and the host-galaxy free 5100A AGN luminosity. Combining results from spectroscopy and imaging allows us to study four MBH scaling relations: MBH-sigma, MBH-L(sph), MBH-M(sph,*), MBH-M(sph,dyn). We find the following results. First, stellar-velocity dispersions determined from aperture spectra (e.g. SDSS fiber spectra or unresolved data from distant galaxies) can be biased, depending on aperture size, AGN contamination, and host-galaxy morphology. However, such a bias cannot explain the offset seen in the MBH-sigma relation at higher redshifts. Second, while the CaT region is the cleanest to determine stellar-velocity dispersions, both the MgIb region, corrected for FeII emission, and the CaHK region, although often swamped by the AGN powerlaw continuum and emission lines, can give results accurate to within a few percent. Third, the MBH scaling relations of our pilot sample agree in slope and scatter with those of other local active and inactive galaxies. In the next papers of the series we will quantify the scaling relations, exploiting the full sample of ~100 objects.
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We create a baseline of the black hole (BH) mass (MBH) - stellar-velocity dispersion (sigma) relation for active galaxies, using a sample of 66 local (0.02<z<0.09) Seyfert-1 galaxies, selected from the Sloan Digital Sky Survey (SDSS). Analysis of SDS
S images yields AGN luminosities free of host-galaxy contamination and morphological classification. 51/66 galaxies have spiral morphology. 28 bulges have Sersic index n<2 and are considered candidate pseudo bulges, with eight being definite pseudo bulges based on multiple classification criteria met. Only 4/66 galaxies show sign of interaction/merging. High signal-to-noise ratio Keck spectra provide the width of the broad Hbeta emission line free of FeII emission and stellar absorption. AGN luminosity and Hbeta line widths are used to estimate MBH. The Keck-based spatially-resolved kinematics is used to determine stellar-velocity dispersion within the spheroid effective radius. We find that sigma can vary on average by up to 40% across definitions commonly used in the literature, emphasizing the importance of using self-consistent definitions in comparisons and evolutionary studies. The MBH-sigma relation for our Seyfert-1 galaxies has the same intercept and scatter as that of reverberation-mapped AGNs as well as quiescent galaxies, consistent with the hypothesis that our single epoch MBH estimator and sample selection do not introduce significant biases. Barred galaxies, merging galaxies, and those hosting pseudo bulges do not represent outliers in the MBH-sigma relation. This is in contrast with previous work, although no firm conclusion can be drawn due to the small sample size and limited resolution of the SDSS images.
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