Program Overview

 

We are using HST & Chandra to constrain the energetics of high-velocity gas flows in galaxies.
Such flows can be driven by wide-angle, galactic superwinds from a massive star- or AGN out-
burst, or by a collimated particle beam from an AGN.

 

Best constraints on flow energetics come from systems of ionized filaments because they can
have maximal contrast against unrelated background emission from prosaic processes in the
host galaxy. Depending on gas velocities, filaments with quite different density and

temperature — but perhaps comparable pressure — may be proximate, and resolving

displacement can constrain gas dynamics hence the ultimate power source.

 

Filaments often have uncertain gaseous excitation. Their morphology, hence volume filling fac-
tor h is also uncertain. h scales filament (ionized) masses, hence gas momentum and ener-
gies, so must be bound using filter images. We use HST & Chandra to obtain <0.“5 (10 pc)

resolution on nearby systems. Adjacent STIS slit placements map outflow gas motions with the
M-gratings, and UV emission-line fluxes with L-gratings constrain the dominant mechanism that
excites gas. We combine these datasets with ground-based, 3D spectra from Fabry-Perot (FP)
and Integral Field Spectrometers (IFS). The ground spectra have larger spatial-spectral cover-
age to complement our space data. This poster summarizes our work on filamentary outflows
in NGC 3079 and NGC 1068; we were supported by grants GO-7353 and GO-01700250 from
STScI & SAO.

 

Tightly Correlated X-ray/Ha Filaments in the Superbubble of NGC 3079 (astro-ph/0205508)

 

NGC 3079 hosts an AGN and shows much evidence that a powerful superwind has scoured
denser gas and dust from the circum-nuclear region (Cecil et al 2001, ApJ, 555, 338 & refs
therein, CBVF hereafter). Chandra now reveals (Fig. 1) a striking match of Ha and soft X-ray

filamentary systems.

 

With <1800 counts across the 14" (1.2 kpc) diameter superbubble in the available archival
dataset, we limited analysis to single-temperature models. Fig. 2 shows reasonable fits to both
the nucleus (kT = 0.55±0.1 keV, ½ solar metal abundance) and superbubble (0.75±0.1 keV,
15% solar metals). The nucleus also shows prominent a Fe complex at 6 keV that signifies an
obscured AGN. The soft X-ray gas in the superbubble has thermal and kinetic energies

2x1056 h0.5 & 5x1054h0.5 ergs, respectively.

 

Fig. 3 shows that X-rays are emitted by the walls of the radio counter- bubble that is obscured
at optical wavelengths by the galaxy ISM. Diffuse X-rays also occupy the “X” shaped volume
delineated by narrow Ha filaments centered on the nucleus. In CBVF we argued that these fila-
ments delineate the stand-off shock between superwind and galaxy ISM, now confirmed by
finding warm gas around the bubble.