Clumpiness of the interstellar medium in the central parsec of the Galaxy from H2 flux extinction correlation. (arXiv:1811.04965v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Ciurlo_A/0/1/0/all/0/1">Anna Ciurlo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Paumard_T/0/1/0/all/0/1">Thibaut Paumard</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rouan_D/0/1/0/all/0/1">Daniel Rouan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Clenet_Y/0/1/0/all/0/1">Yann Clenet</a>
The central parsec of the Galaxy contains a young star cluster embedded in a
complex interstellar medium. The latter mainly consists of a torus of dense
clumps and streams of molecular gas (the circumnuclear disk, CND) enclosing
streamers of ionized gas (the Minispiral). In this complex environment,
knowledge of the local extinction that locally affects each feature is crucial
to properly study and disentangle them. We previously studied molecular gas in
this region and inferred an extinction map from two H2 lines. Extinction
appears to be correlated with the dereddened flux in several contiguous areas
in the field of view. Here, we discuss the origin of this local correlation. We
model the observed effect with a simple radiative transfer model. H2 emission
arises from the surfaces of clumps (i.e., shells) that are exposed to the
ambient ultraviolet (UV) radiation field. We consider the shell at the surface
of an emitting clump. The shell has a varying optical depth and a screen of
dust in front of it. The optical depth varies from one line of sight to
another, either because of varying extinction coefficient from the shell of one
clump to that of another or because of a varying number of identical clumps on
the line of sight. In both scenarios, the model accurately reproduces the
dependence of molecular gas emission and extinction. The reason for this
correlation is that, in the central parsec, the molecular gas is mixed
everywhere with dust that locally affects the observed gas emission. In
addition, there is extinction due to foreground (screen) dust. This analysis
favors a scenario where the central parsec is filled with clumps of dust and
molecular gas. Separating foreground from local extinction allows for a probe
for local conditions (H2 is mixed with dust) and can also constrain the
three-dimensional (3D) position of objects under study.
The central parsec of the Galaxy contains a young star cluster embedded in a
complex interstellar medium. The latter mainly consists of a torus of dense
clumps and streams of molecular gas (the circumnuclear disk, CND) enclosing
streamers of ionized gas (the Minispiral). In this complex environment,
knowledge of the local extinction that locally affects each feature is crucial
to properly study and disentangle them. We previously studied molecular gas in
this region and inferred an extinction map from two H2 lines. Extinction
appears to be correlated with the dereddened flux in several contiguous areas
in the field of view. Here, we discuss the origin of this local correlation. We
model the observed effect with a simple radiative transfer model. H2 emission
arises from the surfaces of clumps (i.e., shells) that are exposed to the
ambient ultraviolet (UV) radiation field. We consider the shell at the surface
of an emitting clump. The shell has a varying optical depth and a screen of
dust in front of it. The optical depth varies from one line of sight to
another, either because of varying extinction coefficient from the shell of one
clump to that of another or because of a varying number of identical clumps on
the line of sight. In both scenarios, the model accurately reproduces the
dependence of molecular gas emission and extinction. The reason for this
correlation is that, in the central parsec, the molecular gas is mixed
everywhere with dust that locally affects the observed gas emission. In
addition, there is extinction due to foreground (screen) dust. This analysis
favors a scenario where the central parsec is filled with clumps of dust and
molecular gas. Separating foreground from local extinction allows for a probe
for local conditions (H2 is mixed with dust) and can also constrain the
three-dimensional (3D) position of objects under study.
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