Title and Abstract for Dom’s talk:
AGN
accretion
disk
megamasers
Some
accretion
disks
surrounding
supermassive
black
holes
in
active
galactic
nuclei
(AGN)
are
observed
to
host
powerful
water
vapor
maser
emission.
These
astrophysical
masers
--
dubbed
"megamasers"
because
of
their
large
luminosities
relative
to
Galactic
counterparts
--
have
proven
to
be
unique
tools
for
studying
the
geometry
and
dynamics
of
AGN
accretion
disks
on
sub-parsec
scales,
where
the
black
hole
dominates
the
gravitational
potential.
The
masing
gas
parcels
act
as
test
particles
in
this
potential,
and
very
long
baseline
interferometric
(VLBI)
observations
reveal
that
they
exhibit
the
ordered,
Keplerian
motion
expected
for
orbits
about
a
point
mass.
By
combining
the
exquisite
angular
resolution
provided
by
VLBI
with
multi-year
spectral
monitoring
observations,
we
can
exploit
the
simple
dynamics
of
these
systems
to
break
the
mass-distance
degeneracy
and
make
precise
measurements
of
both
quantities.
In
this
talk
I'll
cover
some
background
on
AGN
disk
masers
before
presenting
recent
developments
in
the
world
of
maser
disk
modeling.
I'll
describe
our
application
of
these
improved
models
to
the
maser
systems
in
the
galaxies
NGC
4258
and
CGCG
074-064,
and
I'll
wrap
up
with
a
brief
discussion
of
the
resulting
constraints
on
the
Hubble
constant.