The multiwaveband spectrum of MCG-6-30-15 clearly shows a large IR bump.
If this infrared bump is interpreted as the thermal emission from dust
grains, the corresponding grain temperature is 
. The fact
that the 
fluxes describe an approximate Rayleigh-Jeans
form shows that dust cooler than 
cannot contribute much to
the observed emission. However, the relatively flat 
spectrum shows that there are probably hotter dust components. Here we
investigate whether this IR bump can be understood as thermal emission from
a dusty warm absorber.
Following the work of Barvainis (1987), we calculate the mass of dust
required to produce the 
flux observed in MCG-6-30-15.
Assuming graphite grains with a radius of 
, a density of
and temperature of 
, we estimate that
of dust is required to produce the flux.
Furthermore, assuming a standard gas-to-dust mass ratio of 200, the
corresponding mass of associated gas is 
. If, instead, we
consider a grain temperature of 
, the increased dust emissivity
lowers the dust mass requirement to 
with a corresponding gas mass
of 
.
The mass of the outer (dusty) warm absorber can be independently estimated from simple arguments using the X-ray data. Approximating as a thin, uniform, spherical shell, the mass of ionized plasma is
where 
is the radial distance of the absorbing region,
is the column density and 
is the
covering fraction of the material as seen from the central source (i.e. the
`global' covering fraction). In MCG-6-30-15, we must have 
in order to heat the dust to 
. The
ASCA data directly constrain the column density to be 
.
Thus, we have
with only remaining unconstrained. This is somewhat less than
the mass derived in the previous paragraph, especially when it is noted
that there are arguments suggesting 
(see Reynolds 1997
and Section 5.)
The disagreement between these two mass estimates is not unexpected. We would only expect agreement if most of the warm/hot dust emission originated from grains in a warm absorber which approximated a uniform spherical shell. Realistically, a rather more complicated geometry would be expected. In particular, large quantities of warm/hot grain emission would be expected from dusty gas associated with the irradiated inner edge of the putative dusty molecular torus. Indeed, it may be artificial to consider the outer warm absorber and the torus as distinct and separate entities - the outer warm absorber may well be an optically-thin, outflowing extension of the standard (optically-thick) cold torus.