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Title: IMPACT OF SUPERNOVA AND COSMIC-RAY DRIVING ON THE SURFACE BRIGHTNESS OF THE GALACTIC HALO IN SOFT X-RAYS

Abstract

The halo of the Milky Way contains a hot plasma with a surface brightness in soft X-rays of the order 10{sup −12} erg cm{sup −2} s{sup −1} deg{sup −2}. The origin of this gas is unclear, but so far numerical models of galactic star formation have failed to reproduce such a large surface brightness by several orders of magnitude. In this paper, we analyze simulations of the turbulent, magnetized, multi-phase interstellar medium including thermal feedback by supernova explosions as well as cosmic-ray feedback. We include a time-dependent chemical network, self-shielding by gas and dust, and self-gravity. Pure thermal feedback alone is sufficient to produce the observed surface brightness, although it is very sensitive to the supernova rate. Cosmic rays suppress this sensitivity and reduce the surface brightness because they drive cooler outflows. Self-gravity has by far the largest effect because it accumulates the diffuse gas in the disk in dense clumps and filaments, so that supernovae exploding in voids can eject a large amount of hot gas into the halo. This can boost the surface brightness by several orders of magnitude. Although our simulations do not reach a steady state, all simulations produce surface brightness values of the same ordermore » of magnitude as the observations, with the exact value depending sensitively on the simulation parameters. We conclude that star formation feedback alone is sufficient to explain the origin of the hot halo gas, but measurements of the surface brightness alone do not provide useful diagnostics for the study of galactic star formation.« less

Authors:
; ; ;  [1];  [2];  [3]; ; ;  [4];  [5]
  1. Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, D-85748 Garching (Germany)
  2. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln (Germany)
  3. Astronomical Institute, Academy of Sciences of the Czech Republic, Bocni II 1401, 141 31 Prague (Czech Republic)
  4. Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany)
  5. School of Physics and Astronomy, Cardiff University, 5 The Parade, Cardiff CF24 3AA, Wales (United Kingdom)
Publication Date:
OSTI Identifier:
22518706
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 813; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BRIGHTNESS; COSMIC DUST; COSMIC RADIATION; FEEDBACK; FILAMENTS; GRAVITATION; HOT PLASMA; MILKY WAY; SENSITIVITY; SOFT X RADIATION; STAR EVOLUTION; SUPERNOVAE; TIME DEPENDENCE; X-RAY GALAXIES

Citation Formats

Peters, Thomas, Girichidis, Philipp, Gatto, Andrea, Naab, Thorsten, Walch, Stefanie, Wünsch, Richard, Glover, Simon C. O., Klessen, Ralf S., Baczynski, Christian, and Clark, Paul C., E-mail: tpeters@mpa-garching.mpg.de. IMPACT OF SUPERNOVA AND COSMIC-RAY DRIVING ON THE SURFACE BRIGHTNESS OF THE GALACTIC HALO IN SOFT X-RAYS. United States: N. p., 2015. Web. doi:10.1088/2041-8205/813/2/L27.
Peters, Thomas, Girichidis, Philipp, Gatto, Andrea, Naab, Thorsten, Walch, Stefanie, Wünsch, Richard, Glover, Simon C. O., Klessen, Ralf S., Baczynski, Christian, & Clark, Paul C., E-mail: tpeters@mpa-garching.mpg.de. IMPACT OF SUPERNOVA AND COSMIC-RAY DRIVING ON THE SURFACE BRIGHTNESS OF THE GALACTIC HALO IN SOFT X-RAYS. United States. doi:10.1088/2041-8205/813/2/L27.
Peters, Thomas, Girichidis, Philipp, Gatto, Andrea, Naab, Thorsten, Walch, Stefanie, Wünsch, Richard, Glover, Simon C. O., Klessen, Ralf S., Baczynski, Christian, and Clark, Paul C., E-mail: tpeters@mpa-garching.mpg.de. Tue . "IMPACT OF SUPERNOVA AND COSMIC-RAY DRIVING ON THE SURFACE BRIGHTNESS OF THE GALACTIC HALO IN SOFT X-RAYS". United States. doi:10.1088/2041-8205/813/2/L27.
@article{osti_22518706,
title = {IMPACT OF SUPERNOVA AND COSMIC-RAY DRIVING ON THE SURFACE BRIGHTNESS OF THE GALACTIC HALO IN SOFT X-RAYS},
author = {Peters, Thomas and Girichidis, Philipp and Gatto, Andrea and Naab, Thorsten and Walch, Stefanie and Wünsch, Richard and Glover, Simon C. O. and Klessen, Ralf S. and Baczynski, Christian and Clark, Paul C., E-mail: tpeters@mpa-garching.mpg.de},
abstractNote = {The halo of the Milky Way contains a hot plasma with a surface brightness in soft X-rays of the order 10{sup −12} erg cm{sup −2} s{sup −1} deg{sup −2}. The origin of this gas is unclear, but so far numerical models of galactic star formation have failed to reproduce such a large surface brightness by several orders of magnitude. In this paper, we analyze simulations of the turbulent, magnetized, multi-phase interstellar medium including thermal feedback by supernova explosions as well as cosmic-ray feedback. We include a time-dependent chemical network, self-shielding by gas and dust, and self-gravity. Pure thermal feedback alone is sufficient to produce the observed surface brightness, although it is very sensitive to the supernova rate. Cosmic rays suppress this sensitivity and reduce the surface brightness because they drive cooler outflows. Self-gravity has by far the largest effect because it accumulates the diffuse gas in the disk in dense clumps and filaments, so that supernovae exploding in voids can eject a large amount of hot gas into the halo. This can boost the surface brightness by several orders of magnitude. Although our simulations do not reach a steady state, all simulations produce surface brightness values of the same order of magnitude as the observations, with the exact value depending sensitively on the simulation parameters. We conclude that star formation feedback alone is sufficient to explain the origin of the hot halo gas, but measurements of the surface brightness alone do not provide useful diagnostics for the study of galactic star formation.},
doi = {10.1088/2041-8205/813/2/L27},
journal = {Astrophysical Journal Letters},
number = 2,
volume = 813,
place = {United States},
year = {Tue Nov 10 00:00:00 EST 2015},
month = {Tue Nov 10 00:00:00 EST 2015}
}
  • We present measurements of the Galactic halo's X-ray emission for 110 XMM-Newton sight lines selected to minimize contamination from solar wind charge exchange emission. We detect emission from few million degree gas on {approx}4/5 of our sight lines. The temperature is fairly uniform (median = 2.22 Multiplication-Sign 10{sup 6} K, interquartile range = 0.63 Multiplication-Sign 10{sup 6} K), while the emission measure and intrinsic 0.5-2.0 keV surface brightness vary by over an order of magnitude ({approx}(0.4-7) Multiplication-Sign 10{sup -3} cm{sup -6} pc and {approx}(0.5-7) Multiplication-Sign 10{sup -12} erg cm{sup -2} s{sup -1} deg{sup -2}, respectively, with median detections of 1.9more » Multiplication-Sign 10{sup -3} cm{sup -6} pc and 1.5 Multiplication-Sign 10{sup -12} erg cm{sup -2} s{sup -1} deg{sup -2}, respectively). The high-latitude sky contains a patchy distribution of few million degree gas. This gas exhibits a general increase in emission measure toward the inner Galaxy in the southern Galactic hemisphere. However, there is no tendency for our observed emission measures to decrease with increasing Galactic latitude, contrary to what is expected for a disk-like halo morphology. The measured temperatures, brightnesses, and spatial distributions of the gas can be used to place constraints on models for the dominant heating sources of the halo. We provide some discussion of such heating sources, but defer comparisons between the observations and detailed models to a later paper.« less
  • The mass of the Crab Nebula pulsar is determined to be 2 M/sub sun/ by solving a complete set of equations for nebular brightness and dynamics; the star's dipole moment of inertia obtains for the nearly incompressible star. The theoretical optical brightness agrees in detail with sufficient data to allow for a priori prediction of X-ray brightness. The theory is predicated in terms of a simple magnetic dipolar radiating neutron star and basic postulates.
  • We have observed Kepler's supernova remnant (SNR) with the imaging instruments on board the Einstein Observatory. The 0.15-4.5 keV flux incident on the Earth is 1.2 x 10/sup -10/ ergs cm/sup -2/ s/sup -1/; the flux corrected for interstellar absorption is 3.4 x 10/sup -10/ ergs cm/sup -2/ s/sup -1/ (L/sub x/ = 1.0 x 10/sup 36/ ergs s/sup -1/ at D = 5 kpc) if the absorbing column density is N/sub H/ = 2.8 x 10/sup 21/ cm/sup -2/. The remnant is circular and shows a strong shell which is at least 5 times brighter in the north thanmore » in the south. The X-ray observations do not unambiguously determine whether the remnant is in the adiabatic or the free expansion phase. If the remnant is in the adiabatic phase, the density of the interstellar medium (ISM) (/sup 1/2/) surrounding Kepler's SNR must be about 5 cm/sup -3/. If the remnant is in the free expansion phase, where most of the emission arises from shock-heated ejecta, the ISM density must still be relatively high, n/sub i/> or approx. =0.1 cm/sup -3/. Even if the ISM is very inhomogeneous, with very many small, dense clouds, we show that the mean density of the ISM must be greater than approx.0.1 cm/sup -3/. In any case, the density of the x-ray emitting gas must be high (/sup 1/2/ > or approx. =10 cm/sup -3/), and the temperature must be fairly low (T/sub e/< or approx. =2 x 10/sup 7/ K). The relatively high ISM density which is required is surprising in view of Kepler's distance above the galactic plane, approx.600 pc. Possibly the ISM around Kepler's SNR and around other type i SNRs is dominated by the mass lost from the presupernova star.« less