The large scale distribution of PAHs in the Galaxy
M. Giard, J. M. Lamarre, F. Pajot, G. Serra;
AaA, 1994, 286, 203
ABSTRACT:AROME, concerning the general emission of the Galaxy at 3.3{mu}m : continuum and emission feature.
Maps of the galactic plane are presented for
galactic longitudes -60deg< LII < 60deg and latitudes -5deg< BII < 5deg.
The
continuum shows the exponential disk plus bulge stellar distributions, and the
feature shows the thin dust disk.
We show that, at large scale, the variations
of the 3.3{mu}m-feature/100{mu}m and 12{mu}m/100{mu}m ratios can be
interpreted in terms of extinction along the line of sight.
We derive the following
generic galactic dust colors for the diffuse medium:
{DELTA}{lambda.epsilon_lambda_}(3.3{mu}m-feature)/{lambda.epsilon_lambda_}(100) = 2.5+/-0.4 10^-3^, and
{lambda.epsilon_lambda_}(12)/{lambda.epsilon_lambda_}(100) = 0.31+/-0.03.
We show that there is no evidence for large scale
variations of these colors, neither with the galactocentric distance, nor with
the nature of the gas in which the emitting dust is located, neutral or
molecular.
This is interpreted as a strong argument in favor of a universal galactic
mixture of dust grains.
We show that the value of the 12/100 ratio can only be
explained with a dust model including large molecules a few Angstroems size.
The
observation of the 3.3{mu}m feature indicates that a significant fraction of these
molecules may be Polycyclic Aromatic Hydrocarbons (PAHs).
In this hypothesis,
our results imply a homogeneous mixing of the PAHs into the general
interstellar medium and a mass abundance of 3 to 8 % of the cosmic carbon.
We show that
these observational facts are marginally compatible with the hypothesis of
mass-losing carbon stars being the main sites of PAH production in the Galaxy.
We
suggest that direct formation of PAHs in interstellar clouds may also occur.
KEYWORDS: galaxy: structure, ism: general, ism: molecular, ism dust: extinction, infrared: ism: lines and bands
PERSOKEY:milky way, ,
CODE: giard94