TY - JOUR
T1 - The Low-Luminosity End of the Radius-Luminosity Relationship for Active Galactic Nuclei
AU - Bentz, Misty C.
AU - Denney, K.
AU - Grier, C.J.
AU - Barth, Aaron J.
AU - Peterson, B. M.
AU - Vestergaard, M.
PY - 2014/1/1
Y1 - 2014/1/1
N2 - We present an updated and revised analysis of the relationship between
the Hβ broad-line region (BLR) radius and the luminosity of the
active galactic nucleus (AGN). Specifically, we have carried out
two-dimensional surface brightness decompositions of the host galaxies
of nine new AGNs imaged with the Hubble Space Telescope Wide Field
Camera 3. The surface brightness decompositions allow us to create
"AGN-free" images of the galaxies, from which we measure the starlight
contribution to the optical luminosity measured through the ground-based
spectroscopic aperture. We also incorporate 20 new reverberation-mapping
measurements of the Hβ time lag, which is assumed to yield the
average Hβ BLR radius. The final sample includes 41 AGNs covering
four orders of magnitude in luminosity. The additions and updates
incorporated here primarily affect the low-luminosity end of the R-L
relationship. The best fit to the relationship using a Bayesian analysis
finds a slope of α = 0.533^{+0.035}_{-0.033}, consistent with
previous work and with simple photoionization arguments. Only two AGNs
appear to be outliers from the relationship, but both of them have
monitoring light curves that raise doubt regarding the accuracy of their
reported time lags. The scatter around the relationship is found to be
0.19 ± 0.02 dex, but would be decreased to 0.13 dex by the
removal of these two suspect measurements. A large fraction of the
remaining scatter in the relationship is likely due to the inaccurate
distances to the AGN host galaxies. Our results help support the
possibility that the R-L relationship could potentially be used to turn
the BLRs of AGNs into standardizable candles. This would allow the
cosmological expansion of the universe to be probed by a separate
population of objects, and over a larger range of redshifts.
AB - We present an updated and revised analysis of the relationship between
the Hβ broad-line region (BLR) radius and the luminosity of the
active galactic nucleus (AGN). Specifically, we have carried out
two-dimensional surface brightness decompositions of the host galaxies
of nine new AGNs imaged with the Hubble Space Telescope Wide Field
Camera 3. The surface brightness decompositions allow us to create
"AGN-free" images of the galaxies, from which we measure the starlight
contribution to the optical luminosity measured through the ground-based
spectroscopic aperture. We also incorporate 20 new reverberation-mapping
measurements of the Hβ time lag, which is assumed to yield the
average Hβ BLR radius. The final sample includes 41 AGNs covering
four orders of magnitude in luminosity. The additions and updates
incorporated here primarily affect the low-luminosity end of the R-L
relationship. The best fit to the relationship using a Bayesian analysis
finds a slope of α = 0.533^{+0.035}_{-0.033}, consistent with
previous work and with simple photoionization arguments. Only two AGNs
appear to be outliers from the relationship, but both of them have
monitoring light curves that raise doubt regarding the accuracy of their
reported time lags. The scatter around the relationship is found to be
0.19 ± 0.02 dex, but would be decreased to 0.13 dex by the
removal of these two suspect measurements. A large fraction of the
remaining scatter in the relationship is likely due to the inaccurate
distances to the AGN host galaxies. Our results help support the
possibility that the R-L relationship could potentially be used to turn
the BLRs of AGNs into standardizable candles. This would allow the
cosmological expansion of the universe to be probed by a separate
population of objects, and over a larger range of redshifts.
M3 - Journal article
VL - 223
JO - American Astronomical Society, AAS Meeting #229
JF - American Astronomical Society, AAS Meeting #229
ER -