Distance Limits on the Bright X‐Ray Emission toward the Galactic Center: Evidence for a Very Hot Interstellar Medium in the Galactic X‐Ray Bulge

The Milky Way’s Kiloparsec‐Scale Wind: A Hybrid Cosmic‐Ray and Thermally Driven Outflow

“…8 Applying these general models to the wind, the resulting matrix of emissivity per emission measure versus temperature for each band is then interpolated to calculate the emissivity at each point in the wind model. We find that the newer APEC-derived models yield a maximum of 50% more emission in the M band (the combined ROSAT R45 band) than the Raymond & Smith (1977) derived models of Almy et al (2000) near T ¼ 4 ; 10 6 K, but the differences are only on the order of 20% near T ¼ 2 ; 10 6 K. The emission measure is calculated by simply summing n 2 e Ál along lines of sight through the wind model. This model emission is then corrected for absorption by applying (as a foreground absorption screen) the N H data of Dickey & Lockman (1990) for each line of sight.…”

“…Later, Almy et al (2000) used intervening absorption to show that at least half of the central, enhanced X-ray emission lies more than 2 kpc from the Sun (see Park et al 1997Park et al , 1998; Yao & Wang (2007) also constrained the emission to most likely lie at the Galactic center. Since that measurement was made in the Galactic plane, where the absorption is strongest, it was inferred that most of the emission observed at higher latitudes lies beyond that 2 kpc distance.…”

“…Since that measurement was made in the Galactic plane, where the absorption is strongest, it was inferred that most of the emission observed at higher latitudes lies beyond that 2 kpc distance. Almy et al (2000) also improved on previous modeling efforts: their work presents a model of the emission due to a static polytropic gas (with ¼ 5/3) and, very importantly, includes the effects of known background components, such as the stellar background, the extragalactic background, and an additional isotropic background (to fit high-latitude emission). For comparison, their model had a central temperature of T 0 ¼ 8:2 ; 10 6 K, a central electron density of n e ¼ 1:1 ; 10 À2 cm…”

Multiwavelength features of Fermi bubbles as signatures of a Galactic wind

“…An enhancement in the diffuse soft X-ray emission in the longitude range −20 • l 35 • with an emission scale height (in the southern hemisphere) of b ∼ −17 • suggests a large-scale flow of gas out of the disc (Snowden et al 1995;Everett et al 2008). This emission was modelled by Snowden et al (1995) with a mid plane gas density ne ∼ 3.5 × 10 −3 cm −3 and temperature T ∼ 4×10 6 K. Observations by Almy et al (2000) proved that at least half of the central emission comes from more than 2 kpc from the Sun, and most likely lies near the Galactic centre (see also, Park et al (1997); Yao & Wang (2007)). Almy et al (2000) took into account other components (stellar, extragalactic), and improved the model density and temperature to ne ∼ 10 −2 cm −3 and T ∼ 8.2 × 10 6 K. Interestingly, this emission was predicted from a model of cosmic ray driven Galactic outflow by Breitschwerdt & Schmutzler (1994).…”

“…This emission was modelled by Snowden et al (1995) with a mid plane gas density ne ∼ 3.5 × 10 −3 cm −3 and temperature T ∼ 4×10 6 K. Observations by Almy et al (2000) proved that at least half of the central emission comes from more than 2 kpc from the Sun, and most likely lies near the Galactic centre (see also, Park et al (1997); Yao & Wang (2007)). Almy et al (2000) took into account other components (stellar, extragalactic), and improved the model density and temperature to ne ∼ 10 −2 cm −3 and T ∼ 8.2 × 10 6 K. Interestingly, this emission was predicted from a model of cosmic ray driven Galactic outflow by Breitschwerdt & Schmutzler (1994). In fact, using mid-infrared (8.3µm) and ROSAT (1.5keV) observations, Bland-Hawthorn & Cohen (2003) first showed the existence of a biconical Galactic outflow.…”