TY - JOUR
T1 - The quest for the dynamical signature of accretion disks in active galactic nuclei
AU - Eracleous, M.
N1 - Funding Information:
I am grateful to Jules Halpern, Andrea Gilbert, and Jeff Newman for a critical reading of the manuscript. I also thank the two anonymous refereesa nd the editor, Bill Welsh, for helpful comments and suggestions. This work is supported by NASA through the Hubble Fellowship grant HF-01068.01-94A awarded by the the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA under contract NAS 5-26255.
PY - 1998
Y1 - 1998
N2 - The most direct, dynamical evidence for the presence of accretion disks in the central engines of active galaxies comes from observations of very broad, double-peaked emission lines. These "exotic" line profiles are found preferentially in radio-loud AGNs; they occur in about 10% of such objects. Their hosts share a number of common spectral properties which can be understood consistently in the context of a physical model for line-emitting disks. Very recent UV spectroscopy of double-peaked emitters with the HST provides very strong additional evidence for an accretion disk origin of the double-peaked Balmer lines. Variability of the line profiles is an independent and complementary approach for assessing the applicability of disk models to double-peaked emission lines. Moreover, once an accretion disk origin is established, the variability of the line profiles will provide a wealth of information on the structure and dynamics of the disk (much like in cataclysmic variables). The dynamical time in the line-emitting part of the disk is expected to be about six months, which is much longer than the light crossing time. Thus the slow variations of the line profiles over time scales of a few years can be used to test models for the dynamical behaviour of the disk. These models include spiral waves in the disk, elliptical disks, supermassive binary black holes, and interactions of the disk with stars or gas clouds in its vicinity. Tests can be carried out using spectra of double-peaked emission lines with high signal-to-noise ratio taken every few months and spanning a baseline of several years.
AB - The most direct, dynamical evidence for the presence of accretion disks in the central engines of active galaxies comes from observations of very broad, double-peaked emission lines. These "exotic" line profiles are found preferentially in radio-loud AGNs; they occur in about 10% of such objects. Their hosts share a number of common spectral properties which can be understood consistently in the context of a physical model for line-emitting disks. Very recent UV spectroscopy of double-peaked emitters with the HST provides very strong additional evidence for an accretion disk origin of the double-peaked Balmer lines. Variability of the line profiles is an independent and complementary approach for assessing the applicability of disk models to double-peaked emission lines. Moreover, once an accretion disk origin is established, the variability of the line profiles will provide a wealth of information on the structure and dynamics of the disk (much like in cataclysmic variables). The dynamical time in the line-emitting part of the disk is expected to be about six months, which is much longer than the light crossing time. Thus the slow variations of the line profiles over time scales of a few years can be used to test models for the dynamical behaviour of the disk. These models include spiral waves in the disk, elliptical disks, supermassive binary black holes, and interactions of the disk with stars or gas clouds in its vicinity. Tests can be carried out using spectra of double-peaked emission lines with high signal-to-noise ratio taken every few months and spanning a baseline of several years.
UR - http://www.scopus.com/inward/record.url?scp=0002227411&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0002227411&partnerID=8YFLogxK
U2 - 10.1016/S0273-1177(97)00612-1
DO - 10.1016/S0273-1177(97)00612-1
M3 - Article
AN - SCOPUS:0002227411
SN - 0273-1177
VL - 21
SP - 33
EP - 45
JO - Advances in Space Research
JF - Advances in Space Research
IS - 1-2
ER -