Evidence for Line Broadening by Electron Scattering in the Broad Line Region of NGC 4395

Abstract

A high quality Keck spectrum of the Halpha line in NGC 4395 reveals symmetric exponential wings, fv\propto e^{-v/sigma}, with sigma~500km/s. The wings extend out to >2500km/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 sigma=1.1sigma_e(ln tau_e^-1)^0.45, where sigma_e is the electron velocity dispersion, and tau_e is the electron scattering optical depth. The Halpha wings in NGC 4395 are well fit by an electron scattering model with tau_e=0.34, and an electron temperature T_e=1.1x10^4K. 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] 5007 line yields tau_e<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 tau_e and the ionizing flux on time scales shorter than the BLR dynamical time, or ~1 week for NGC 4395. In contrast, the value of sigma should remain nearly constant on these time scales. Such wings may be discernible in other objects with unusually narrow Balmer lines, and they can provide a useful direct probe of T_e and tau_e in the BLR.

arXiv comment8 pages, accepted for publication in The Astrophysical Journal

References in corpus (16)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• The Relationship Between Luminosity and Broad-Line Region Size in Active Galactic Nuclei
• ESI, a new Keck Observatory echellette spectrograph and imager
• Multiwavelength Monitoring of the Dwarf Seyfert 1 Galaxy NGC 4395. I. A Reverberation-Based Measurement of the Black Hole Mass
• Supermassive Black Holes in Active Galactic Nuclei. I. The Consistency of Black Hole Masses in Quiescent and Active Galaxies
• Evidence for Supermassive Black Holes in Active Galactic Nuclei from Emission-Line Reverberation
• POX 52: A Dwarf Seyfert 1 Galaxy With An Intermediate-Mass Black Hole
• On Quasar Masses and Quasar Host Galaxies
• Dynamics of Broad-Emission Line Region in NGC 5548: Hydromagnetic Wind Model versus Observations
• Polarized Broad-Line Emission from Low-Luminosity Active Galactic Nuclei
• The Nuclear Spectral Energy Distribution of NGC 4395, The Least Luminous Type 1 Seyfert Galaxy
• Cepheids and Long Period Variables in NGC 4395
• Physical Conditions in the Emission Line Gas in the Extremely Low Luminosity Seyfert Nucleus of NGC 4395
• Is the Broad-Line Region Clumped or Smooth? Constraints from the H alpha Profile in NGC 4395, the Least Luminous Seyfert 1 Galaxy
• The UV-Optical Albedo of Broad Emission Line Clouds
• Polarization Structures in the Thomson-Scattered Emission Lines in Active Galactic Nuclei

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