Hydrogen emission-line spectra in quasars and active galactic nuclei

Journal Article · Tue Aug 01 04:00:00 EDT 1978 · Astrophys. J., Suppl. Ser.; (United States)

DOI:https://doi.org/10.1086/190538· OSTI ID:6638412

Krolik, J H; McKee, C F

This paper presents a detailed analysis of the strengths of hydrogen emission lines emitted by a gas cloud for a wide range of density (N/sub e/< or =10/sup 13/cm/sup -3/), temperature (10/sup 4/ K< or =T< or approx. =3 x 10/sup 4/ K), and ionization (10/sup -6/< or approx. = neutral fraction < or approx. =1), with an emphasis on the conditions thought to occur in quasars and Seyfert nuclei. Level populations as a function of principal quantum number n and angular momentum l are numerically calculated for n< or =12 using all important known physical processes, including the effects of intense radio and infrared background radiation. The intensity of the line radiation inside the cloud, assumed to be a homogeneous slab, is obtained by means of the escape probability formalism. We find that an intense nonionizing bacground and/or a high electron density brings the levels into thermal equilibrium at lower values of n than without the background; this increases the intensities of lines such as H7 and P7 by up to a factor of 2, but it does not significantly affect lines from n< or =5. Collisional excitation from the n=2 state and finite optical depth in the Balmer lines account for the line intensities seen in many Seyferts. For the quasar 3C 273, which has a remarkably low observed L..cap alpha../H..beta.. ratio but a normal P..cap alpha../H..beta.. ratio, we propose that the density is high enough (N/sub e/approx. =10/sup 10/cm/sup -3/) and the Lyman ..cap alpha.. ootical depth large enough that collisional de-excitation of L..cap alpha.. is important as well.

• Research Organization: University of California, Berkeley
• OSTI ID: 6638412
• Journal Information: Astrophys. J., Suppl. Ser.; (United States), Journal Name: Astrophys. J., Suppl. Ser.; (United States) Vol. 37:4; ISSN APJSA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics &amp; Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BALMER LINES
COLLISIONS
COSMIC GASES
COSMIC RADIO SOURCES
CRYOGENIC FLUIDS
ELEMENTS
EMISSION SPECTRA
ENERGY-LEVEL DENSITY
ENERGY-LEVEL TRANSITIONS
EXCITATION
FLUIDS
FUNCTIONS
GALAXIES
GASES
HYDROGEN
IONIZATION
NONMETALS
QUANTUM NUMBERS
QUASARS
RECOMBINATION
SEYFERT GALAXIES
SPECTRA
SPECTRAL FUNCTIONS