Polycyclic aromatic hydrocarbon emission toward the Galactic bulge
  We examine polycyclic aromatic hydrocarbon (PAH), dust and atomic/molecular
emission toward the Galactic bulge using Spitzer Space Telescope observations
of four fields: C32, C35, OGLE and NGC 6522. These fields are approximately
centered on (l, b) = (0.0{\deg}, 1.0{\deg}), (0.0{\deg}, -1.0{\deg}),
(0.4{\deg}, -2.1{\deg}) and (1.0{\deg}, -3.8{\deg}), respectively. Far-infrared
photometric observations complement the Spitzer/IRS spectroscopic data and are
used to construct spectral energy distributions. We find that the dust and PAH
emission are exceptionally similar between C32 and C35 overall, in part
explained due to their locations---they reside on or near boundaries of a 7
Myr-old Galactic outflow event and are partly shock-heated. Within the C32 and
C35 fields, we identify a region of elevated H{\alpha} emission that is
coincident with elevated fine-structure and [O IV] line emission and weak PAH
feature strengths. We are likely tracing a transition zone of the outflow into
the nascent environment. PAH abundances in these fields are slightly depressed
relative to typical ISM values. In the OGLE and NGC 6522 fields, we observe
weak features on a continuum dominated by zodiacal dust. SED fitting indicates
that thermal dust grains in C32 and C35 have comparable temperatures to those
of diffuse, high-latitude cirrus clouds. Little variability is detected in the
PAH properties between C32 and C35, indicating that a stable population of PAHs
dominates the overall spectral appearance. In fact, their PAH features are
exceptionally similar to that of the M82 superwind, emphasizing that we are
probing a local Galactic wind environment.
