EXPLORING THE LOW-MASS END OF THEM_BH-σ_*RELATION WITH ACTIVE GALAXIES

Abstract

We present new measurements of stellar velocity dispersions, using spectra obtained with the Keck Echellette Spectrograph and Imager (ESI) and the Magellan Echellette (MagE), for 76 Seyfert 1 galaxies from the recent catalogue of Greene & Ho. These objects were selected from the Sloan Digital Sky Survey (SDSS) to have estimated black hole (BH) masses below 2 × 10 6 M ⊙ . Combining our results with previous ESI observations of similar objects, we obtain an expanded sample of 93 galaxies and examine the relation between BH mass and velocity dispersion (the M BH − σ * relation) for active galaxies with low BH masses. The low-mass active galaxies tend to follow the extrapolation of the M BH −σ * relation of inactive galaxies. Including results for active galaxies of higher BH mass from the literature, we find a zero point α = 7.68 ± 0.08 and slope of β = 3.32 ± 0.22 for the M BH − σ * relation [in the form log M BH = α + β log(σ * /200 km s −1 )], with intrinsic scatter of 0.46 ± 0.03 dex. This result is consistent, within the -2uncertainties, with the slope of the M BH − σ * relation for reverberation-mapped active galaxies with BH masses from 10 6 to 10 9 M ⊙ . For the subset of our sample having morphological information from Hubble Space Telescope images, we examine the slope of the M BH − σ * relation separately for subsamples of barred and unbarred host galaxies, and find no significant evidence for a difference in slope. We do find a mild offset between low-inclination and high-inclination disk galaxies, such that more highly inclined galaxies tend to have larger σ * at a given value of BH mass, presumably due to the contribution of disk rotation within the spectroscopic aperture. We also find that the velocity dispersion of the ionized gas, measured from narrow emission lines including [N II] λ6583Å, [S II] λλ6716, 6731ÅÅ, and the core of [O III] λ5007Å (with the blue-shifted wing removed), trace the stellar velocity dispersion well for this large sample of low-mass Seyfert 1 galaxies.

The Host Galaxies of Low-Mass Black Holes

“…The M BH -σ * relation of this sample is discussed in more detail in Xiao et al (2011) while the M BH -L bulge relation is discussed in a companion paper (Jiang et al 2011). In that paper, we find that the tight scaling relations between BH mass and bulge luminosity found for massive classical bulges do not exist for the pseudobulges that we have shown are the hosts of low-mass BHs.…”

“…The data were taken at Keck with ESI and at Magellan with MagE. The measurements are based on direct-pixel fitting of broadened stellar templates to the galaxy spectra (Barth et al 2005;Xiao et al 2011). For the remaining objects, we do not have direct stellar velocity dispersion measurements.…”

“…At Keck we employed a slit of 0. 75 while at Magellan we used a 1 slit (Barth et al 2005;Xiao et al 2011). If the bulge size is smaller than the slit size and the bulge is much fainter than the disk component, then the observed σ * will be contaminated by light from the disk.…”

“…We use our photometric fits to divide the sample with σ * measurements into three equal inclination bins containing 10 galaxies each. Extrapolating the Faber-Jackson relation of classical bulges defined by the sample from Gültekin et al (2009) to low luminosities, we calculate a predicted velocity dispersion σ predict from (Xiao et al 2011) while gray open circles have velocity dispersions from [S ii] line widths in SDSS spectra (Greene & Ho 2007b). We also highlight galaxies with no extended disk (red triangles) and those with low disk contamination (black solid circles; see Section 6.2.1 for details).…”

“…The virial masses we use in this paper are calculated according to the above formula with the Hα luminosity and FWHM based either on the SDSS spectrum or a higher-resolution spectrum from the Echelle Spectrograph and Imager (ESI) on Keck (Sheinis et al 2002) or the Magellan Echellette Spectrograph (MagE; Marshall et al 2008). The spectra are presented in Xiao et al (2011).…”