X-ray and UV spectroscopy of Galactic diffuse hot gas along the LMC X--3 sight line

TL;DR

This study uses Suzaku X-ray spectra to analyze the hot gas around the LMC X-3 sight line, revealing a non-isothermal, extended Galactic hot gas component with specific temperature, density, and scale height estimates.

Contribution

It provides the first joint analysis of emission and absorption data to characterize the spatial and thermal structure of Galactic hot gas along this sight line.

Findings

Detected OVII, OVIII, and NeIX emission lines indicating hot plasma.

Estimated gas temperature and density at the Galactic plane.

Characterized the scale heights of hot gas and explained OVI absorption and emission.

Abstract

We present Suzaku spectra of X-ray emission in the fields just off the LMC X-3 sight line. OVII, OVIII, and NeIX emission lines are clearly detected, suggesting the presence of an optically thin thermal plasma with an average temperature of 2.4E6. This temperature is significantly higher than that inferred from existing X-ray absorption line data obtained with Chandra grating observations of LMC X-3, strongly suggesting that the gas is not isothermal. We then jointly analyze these data to characterize the spatial and temperature distributions of the gas. Assuming a vertical exponential Galactic disk model, we estimate the gas temperature and density at the Galactic plane and their scale heights as 3.6(2.9, 4.7)E6 K and 1.4(0.3, 3.4)E-3 cm^{-3} and 1.4(0.2, 5.2) kpc and $2.8(1.0, 6.4)$ kpc, respectively. This characterization can account for all the \ovi line absorption, as observed in a FUSE spectrum of LMC X-3, but only predicts less than one tenth of the OVI line emission intensity typically detected at high Galactic latitudes. The bulk of the OVI emission most likely arises at interfaces between cool and hot gases.