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

By J. Everett, E. Zweibel, R. Benjamin, D. McCammon, L. Rocks, J. Gallagher III. 2007

231 citations recorded by the source corpus.

We apply a wind model, driven by combined cosmic-ray and thermal-gas pressure, to the Milky Way, and show that the observed Galactic diffuse soft X-ray emission can be better explained by a wind than by previous static gas models. We find that cosmic-ray pressure is essential to driving the observed wind. Having thus defined a “best-fit” model for a Galactic wind, we explore variations in the base parameters and show how the wind’s properties vary with changes in gas pressure, cosmic-ray pressure, and density. We demonstrate the importance of cosmic rays in launching winds, and the effect cosmic rays have on wind dynamics. In addition, this model adds support to the hypothesis of Breitschwerdt and collaborators that such a wind may help to explain the relatively small gradient observed in γ-ray emission as a function of galactocentric radius.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/d55f4c978d95aafce9c2d177fd8b6209b8f05ae2

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Citations in the corpus

THE PHYSICS OF THE FAR-INFRARED–RADIO CORRELATION. I. CALORIMETRY, CONSPIRACY, AND IMPLICATIONS (2009, methodology): “The new wind speeds are v = 175 km s−1 in the Σg = 0.01 g cm −2 model (comparable to the Everett et al. 2008 wind), and v = 600 km s−1 in the starbursts.”
Cosmic ray transport in the Galaxy: A review (2017, background): “Most important, a Galactic wind may affect the propagation of CRs Ptuskin et al. (1997); Recchia et al. (2016), and in turn CRs may contribute to launching such winds (Ipavich, 1975; Breitschwerdt et al., 1991; Everett et al., 2008).”
GIANT GAMMA-RAY BUBBLES FROM FERMI-LAT: ACTIVE GALACTIC NUCLEUS ACTIVITY OR BIPOLAR GALACTIC WIND? (2010, background): “Everett et al. (2008, 2010) compared the synchrotron and soft X-ray emission from large-scale galactic wind models to ROSAT and Haslam 408 MHz maps.”
Theoretical Challenges in Galaxy Formation (2016, background): “Nevertheless, recent ROSAT observations of the Milky Way show extended, soft X-ray emission, which is best explained with a kpc-scale wind for which the cosmic ray pressure may be essential (Everett et al. 2008).”
SIMULATIONS OF DISK GALAXIES WITH COSMIC RAY DRIVEN GALACTIC WINDS (2013, background): “Theoretical models of dynamical haloes in which CRs diffuse and are advected out in a galactic wind predict steady, supersonic galaxy-scale outflows driven by a combination of CR and thermal pressure (Breitschwerdt et al. 1991; Everett et al. 2008).”
DEVELOPMENT OF THE MODEL OF GALACTIC INTERSTELLAR EMISSION FOR STANDARD POINT-SOURCE ANALYSIS OF FERMI LARGE AREA TELESCOPE DATA (2016, background): “Convection in the form of Galactic winds is supported by X-ray (Everett et al. 2008) and radio (McClure-Griffiths et al. 2013) observations.”
Cosmic-ray propagation with DRAGON2: I. numerical solver and astrophysical ingredients (2016, background): “, [120]), as described by the following functional form:”
Cosmic ray driven outflows in global galaxy disc models (2013, methodology): “Subsequent work has enhanced this simple model to include effects in the disc–halo interface, slightly modified magnetic field geometries, disc rotation/magnetic tension and more sophisticated damping mechanisms (Breitschwerdt et al. 1993; Zirakashvili et al. 1996; Everett et al. 2008).”
Galactic winds driven by cosmic ray streaming (2012, unknown): “Similarly, an outflow from the Milky Way driven by CRs explains the observed synchrotron emission as well as the diffuse soft Xray emission towards the Galactic bulge region much better than a static atmosphere model (Everett et al. 2008; Everett, Schiller & Zweibel 2010).”
The Vertical Structure of Warm Ionised Gas in the Milky Way (2008, background): “At z ≈ 5 − 10 kpc, the ambient pressure in the Galactic halo isP/k ≈ 1000 − 2000 K cm−3 (Shull & Slavin 1994; Sternberg et al. 2002; Everett et al. 2008).”