Hot, Entrained Gas in the 5-arcmin-long X-ray Jet of the Nearby Spiral Galaxy NGC 4258

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Session 80 -- AGN and Jets
Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[80.07] Hot, Entrained Gas in the 5-arcmin-long X-ray Jet of the Nearby Spiral Galaxy NGC 4258

G.Cecil, C.DePree (UNC-CH), A.S.Wilson (STScI)

The famous, large-scale, bisymmetric ``braided" jets are found to emit most of the X-rays from this nearby SABbc LINER/Seyfert galaxy. After removing wobble-related errors of up to $\pm$6$^{\prime\prime}$ in our 27 ksec ROSAT HRI image, we find that the SE branch of the jet is spatially unresolved across its width along much of its 2.5-arcmin length. The NW branch is more diffuse, and fainter X-ray emission is present throughout much of the more extensive, trailing (in the sense of galactic rotation) radio ``plateaus". The energy spectrum of the jet from a 4 ksec ROSAT PSPC exposure is quite noisy, but the best fit is provided by a Raymond-Smith plasma with T $\approx$ 0.2 keV, $\log(N_H)\approx$ 20.3 cm$^{-2}$, and integrated X-ray luminosity of $2.2\times10^{40}$ ergs~s$^{-1}$ in the 0.1:2.4 keV band. Shocks with velocities $200-400$ km s$^{-1}$ (depending on the physical state of the pre-shock gas) produce this temperature. The gaseous excitation and radial velocities derived from our optical, emission-line spectra of the jets (Cecil, Wilson, \& Tully 1992 ApJ, 390, 365) are also consistent with these shock speeds, provided that the gas flows along intrinsically helical paths in the region of kinematic braiding near the nucleus. Observed and modeled X-ray luminosities agree if the average ambient gas density is similar to that inferred from the H~I. This component is plausibly gas that has become entrained as the jets scrape along complexes of dense molecular clouds, known to be adjacent to the jet in the gas-rich disk of this barred galaxy. The major deficiency of our current spectral model is that it produces too few photons above 0.6 keV, suggesting the presence of a hard component from the jets themselves. Finally, we will also discuss newly acquired optical long-slit and Fabry-Perot spectra that constrain the excitation mechanism of the optical gas.

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