High Resolution X-Ray Spectroscopy of the Local Hot Gas Along the 3c 273 Sightline

Abstract

X-ray observations of highly ionized metal absorption lines at z = 0 provide critical information of the hot gas distribution in and around the Milky Way. We present a study of more than ten-year Chandra and XMM-Newton observations of 3C 273, one of the brightest extragalactic X-ray sources. Compared with previous work, We obtain much tighter constraints of the physical properties of the X-ray absorber. We also find a large, non-thermal velocity at ∼ 100−150 km s −1 is the main reason for the higher line equivalent width when compared with other sightlines. Using joint analysis with X-ray emission and ultraviolet observations, we derive a size of 5 -15 kpc and a temperature of (1.5-1.8)×10 6 K for the X-ray absorber. The 3C 273 sightline passes through a number of Galactic structures, including the radio Loop I, IV, the North Polar Spur, and the neighborhood of the newly discovered "Fermi bubbles". We argue that the X-ray absorber is unlikely associated with the nearby radio Loop I and IV; however, the non-thermal velocity can be naturally explained as the result of the expansion of the "Fermi bubbles". Our data implies an shock-expansion velocity of 200 − 300 km s −1 . Our study indicates a likely complex environment for the production of the Galactic X-ray absorbers along different sightlines, and highlights the significance of probing galactic feedback with high resolution X-ray spectroscopy.

Clues to the origin of Fermi bubbles from O viii/O vii line ratio

“…• , +60 • ), also suggests a shock velocity of ≈ 200-300 km s −1 (Fang & Jiang 2014). These suggest a star formation driven or a low luminosity AGNW driven origin for the FBs (since the stronger AGNW would produce a stronger shock with M 1).…”

A Hadronic Model of the Fermi Bubbles: Cosmic-Rays in a Galactic Breeze

“…The current picture seems to indicate that cosmic-rays (CR) and hot gas are conveyed out from the GC region into the halo within a Galactocentric outflow. As for the velocity of this outflow, values of ∼ 300 km/s have been suggested in the region close to the Galactic disk (within ∼ a couple of kiloparsecs), from the weakness of the X-ray features associated with the edge of the bubbles [6,10,11,12]. At distances ∼ 4 kpc and ∼ 9 kpc away of the Galactic plane, observations of high velocity clouds suggest velocities of about ∼ 150 km/s, cf.…”

“…[17]) and observational (e.g. [11]) grounds, we adopt a constant gas density within the Bubbles at the level 3 × 10 −3 cm −3 . A γ-ray density map and a comparison of the γ-ray bubble-edge profile with Fermi data are shown in Fig.…”

Cosmic rays in a galactic breeze

“…Relatively mild velocities ∼ 300 km s −1 are suggested to be present in the outflow region close to the disk (∼ 1 − 2 kpc) by the weakness of the X-ray features associated with the bubble edges [6,[10][11][12]. The observation of high velocity clouds in regions consistent with the bubble's location [5], motivate outflow velocities of ∼ 150 km s −1 at distances of ∼ 4 kpc and ∼ 9 kpc away of the Galactic plane.…”

“…As motivated on theoretical grounds by [37], and on observational grounds by [11], we adopt a constant gas density within the bubble region at the level 3 × 10 −3 cm −3 . A γ-ray density map and a comparison of the γ-ray bubble-edge profile with Fermi measurement [38] are shown in Fig.…”