Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...465...96n&link_type=abstract
Astrophysical Journal v.465, p.96
Astronomy and Astrophysics
Astronomy
160
Galaxies: Kinematics And Dynamics, Galaxies: Seyfert, Radio Continuum: Galaxies
Scientific paper
We have used measurements of the nuclear stellar velocity dispersion, σ_*_, for a large sample of Seyfert galaxies to investigate the role played by the nuclear gravitational potential in defining the properties of active galaxies. We address four basic questions. First, do Seyferts have unusual nuclear stellar dynamical properties compared to those of normal galaxies? Second, what are the relative contributions of gravitational and nongravitational forces creating the velocity field of the nuclear emission-line gas? Third, how do the emission-line and radio luminosities in the narrow-line region (NLR) depend on the bulge potential? Fourth, in what way are the properties of Seyfert galaxies related to those of radio galaxies? We find that Seyferts define a tight correlation between σ_*_ and bulge absolute magnitude, similar to the Faber-Jackson relation for normal spiral bulges. We infer from this that Seyfert bulges are kinematically normal. The Seyfert relation is, however, offset to higher bulge luminosities, which we interpret as evidence for a lower mean mass- to-light ratio. Either Seyferts have experienced higher than average star formation or they avoid systems with older stellar populations. We analyze the relations between σ_*_ and both galaxy rotation and galaxy absolute magnitude, finding similar relations to those of normal spirals. This also supports a normal kinematic relation between bulges and disks in Seyferts. A moderately strong correlation between σ_*_ and [O III] profile width suggests that gravitational motion plays an important role in the NLR velocity field. The correlation is weaker with [O III] base and wing widths, although the interpretation of this is not yet clear. The remaining real scatter on the relations indicates the importance of other factors. In particular, objects with kiloparsec-scale linear radio sources can have significantly broader [O III] lines, confirming that interaction with an expanding radio source can accelerate the NLR gas. We also find that Seyferts that are tidally distorted have broader [O III] lines. The kinematic relations do not depend on galaxy inclination or Seyfert class, suggesting that the NLR gas is confined neither to the plane of the galaxy nor to the plane of an inner obscuring disk. We find moderately strong correlations between [O III] luminosity and σ_*_ and between radio luminosity and σ_*_, confirming the importance of the bulge potential in determining the overall NLR luminosity. More massive bulges may have more massive black holes, provide more fuel through stellar mass loss, allow larger emitting regions, and/or have higher pressures and emissivities. We included radio galaxies in our analysis of the correlation between radio luminosity and bulge mass. Using total radio luminosity, the radio galaxies and Seyferts show little connection. However, when the core luminosities of radio galaxies are used, the two groups form a single continuous steep relation spanning 6 mag in M_bul_. There is some evidence that at a given bulge mass, more "jetlike" sources (Seyferts with linear morphology, and cores of FR II radio galaxies) are more luminous than the less "jetlike" sources (Seyferts without linear morphology, and cores of FR I radio galaxies). Finally, the radio galaxies fall on the same Faber-Jackson relation as the Seyferts, offset from the normal galaxy relation. Thus, we see both unity and continuity between the properties of Seyfert galaxies and radio galaxies. In particular, we can understand the separation of radio-quiet and radio- loud objects into spirals and ellipticals as a direct manifestation of a more fundamental dependence of galactic scale radio luminosity on bulge mass.
Nelson Charles H.
Whittle Mark
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