2006ApJ...643..112L -
Astrophys. J., 643, 112-119 (2006/May-3)
Evidence for line broadening by electron scattering in the broad-line region of NGC 4395.
LAOR A.
Abstract (from CDS):
A high-quality Keck spectrum of the Hα line in NGC 4395 reveals symmetric exponential wings, fv∝e–v/σ, with σ≃500 km/s. The wings extend out to ≳2500 km/s from the line core, and down to a flux density of ≲10–3 of the peak flux density. Numerical and analytic calculations indicate that exponential wings are expected for optically thin, isotropic, thermal electron scattering. Such scattering produces exponential wings with σ≃1.1σe(lnτ–1e)0.45, where σe is the electron velocity dispersion, and τeis the electron-scattering optical depth. The Hα wings in NGC 4395 are well fit by an electron-scattering model with τe=0.34 and an electron temperature Te=1.1x104 K. Such conditions are produced in photoionized gas with an ionization parameter U≃0.3, as expected in the broad-line region (BLR). Similar analysis of the [O III] λ5007 line yields τe<0.01, consistent with the lower ionization in the narrow-line region. If the electron-scattering interpretation is correct, there should be a tight correlation between τeand the ionizing flux on timescales shorter than the BLR dynamical time, or ∼1 week for NGC 4395. In contrast, the value of σ should remain nearly constant on these timescales. Such wings may be discernible in other objects with unusually narrow Balmer lines, and they can provide a useful direct probe of Teand τein the BLR.
Abstract Copyright:
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Journal keyword(s):
Galaxies: Active - Galaxies: Individual: NGC Number: NGC 4395 - Galaxies: Seyfert - Galaxies: Quasars: Emission Lines
Simbad objects:
2
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