John Blakeslee
Science Highlights
GMOS clocks the speed of gas reverberating in the vicinity
of an intermediate-mass black hole in a bulgeless dwarf
galaxy; the GPI Exoplanet Survey issues its interim report
on the divergent demographics of giant planets and brown
dwarfs around young nearby stars; and integral field
spectroscopy from the MASSIVE Survey reveals startling
diversity in the kinematical profiles of 20 heavyweight
galaxies.
Reverberations from an Intermediate-mass Black Hole
in a Bulgeless Dwarf
For some, the term “reverberation mapping” might suggest the idea of pinpointing the lo-
cations of the various garage bands in the neighborhood (all with their amplifiers turned
way up) based on the distribution and intensity of the vibrations emanating from one’s
walls and window panes. But in actuality, it denotes a powerful technique for determin-
ing the masses of the black holes embedded within the active galactic nuclei (AGNs) at
the centers of many galaxies. Interestingly, the two phenomena are not entirely dissimilar.
Like the perfect guitar riff, reverberation mapping requires precise timing and can be quite
challenging to execute in practice. In addition, the virtue of both lies in their conceptual
simplicity.
Reverberation mapping works by applying the familiar virial theorem to the broad line re-
gion (BLR) of an AGN. Assuming that the motion of the gas in the BLR is primarily influenced
by the central black hole, the mass of the black hole M BH will be proportional to σ 2 R, where σ
is the velocity dispersion determined from the Doppler width of a broad emission line and
R is the characteristic radius of the BLR. The radius is determined from the delay time τ be-
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GeminiFocus
July 2019