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Title: THE ORIGIN OF THE HOT GAS IN THE GALACTIC HALO: TESTING GALACTIC FOUNTAIN MODELS' X-RAY EMISSION

Abstract

We test the X-ray emission predictions of galactic fountain models against XMM-Newton measurements of the emission from the Milky Way's hot halo. These measurements are from 110 sight lines, spanning the full range of Galactic longitudes. We find that a magnetohydrodynamical simulation of a supernova-driven interstellar medium, which features a flow of hot gas from the disk to the halo, reproduces the temperature but significantly underpredicts the 0.5-2.0 keV surface brightness of the halo (by two orders of magnitude, if we compare the median predicted and observed values). This is true for versions of the model with and without an interstellar magnetic field. We consider different reasons for the discrepancy between the model predictions and the observations. We find that taking into account overionization in cooled halo plasma, which could in principle boost the predicted X-ray emission, is unlikely in practice to bring the predictions in line with the observations. We also find that including thermal conduction, which would tend to increase the surface brightnesses of interfaces between hot and cold gas, would not overcome the surface brightness shortfall. However, charge exchange emission from such interfaces, not included in the current model, may be significant. The faintness of the modelmore » may also be due to the lack of cosmic ray driving, meaning that the model may underestimate the amount of material transported from the disk to the halo. In addition, an extended hot halo of accreted material may be important, by supplying hot electrons that could boost the emission of the material driven out from the disk. Additional model predictions are needed to test the relative importance of these processes in explaining the observed halo emission.« less

Authors:
;  [1];  [2];  [3];  [4]
  1. Department of Physics and Astronomy, University of Georgia, Athens, GA 30602 (United States)
  2. School of Natural Science, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulju-gun, Ulsan 689-798 (Korea, Republic of)
  3. CSIRO Astronomy and Space Science, Marsfield, NSW (Australia)
  4. Department of Astrophysics, American Museum of Natural History, 79th Street at Central Park West, New York, NY 10024 (United States)
Publication Date:
OSTI Identifier:
22522114
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 800; 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; CHARGE EXCHANGE; COMPARATIVE EVALUATIONS; INTERSTELLAR MAGNETIC FIELDS; INTERSTELLAR SPACE; KEV RANGE; MILKY WAY; PHOTON EMISSION; PLASMA; STAR ACCRETION; SURFACES; THERMAL CONDUCTION; X RADIATION

Citation Formats

Henley, David B., Shelton, Robin L., Kwak, Kyujin, Hill, Alex S., and Mac Low, Mordecai-Mark, E-mail: dbh@physast.uga.edu. THE ORIGIN OF THE HOT GAS IN THE GALACTIC HALO: TESTING GALACTIC FOUNTAIN MODELS' X-RAY EMISSION. United States: N. p., 2015. Web. doi:10.1088/0004-637X/800/2/102.
Henley, David B., Shelton, Robin L., Kwak, Kyujin, Hill, Alex S., & Mac Low, Mordecai-Mark, E-mail: dbh@physast.uga.edu. THE ORIGIN OF THE HOT GAS IN THE GALACTIC HALO: TESTING GALACTIC FOUNTAIN MODELS' X-RAY EMISSION. United States. doi:10.1088/0004-637X/800/2/102.
Henley, David B., Shelton, Robin L., Kwak, Kyujin, Hill, Alex S., and Mac Low, Mordecai-Mark, E-mail: dbh@physast.uga.edu. Fri . "THE ORIGIN OF THE HOT GAS IN THE GALACTIC HALO: TESTING GALACTIC FOUNTAIN MODELS' X-RAY EMISSION". United States. doi:10.1088/0004-637X/800/2/102.
@article{osti_22522114,
title = {THE ORIGIN OF THE HOT GAS IN THE GALACTIC HALO: TESTING GALACTIC FOUNTAIN MODELS' X-RAY EMISSION},
author = {Henley, David B. and Shelton, Robin L. and Kwak, Kyujin and Hill, Alex S. and Mac Low, Mordecai-Mark, E-mail: dbh@physast.uga.edu},
abstractNote = {We test the X-ray emission predictions of galactic fountain models against XMM-Newton measurements of the emission from the Milky Way's hot halo. These measurements are from 110 sight lines, spanning the full range of Galactic longitudes. We find that a magnetohydrodynamical simulation of a supernova-driven interstellar medium, which features a flow of hot gas from the disk to the halo, reproduces the temperature but significantly underpredicts the 0.5-2.0 keV surface brightness of the halo (by two orders of magnitude, if we compare the median predicted and observed values). This is true for versions of the model with and without an interstellar magnetic field. We consider different reasons for the discrepancy between the model predictions and the observations. We find that taking into account overionization in cooled halo plasma, which could in principle boost the predicted X-ray emission, is unlikely in practice to bring the predictions in line with the observations. We also find that including thermal conduction, which would tend to increase the surface brightnesses of interfaces between hot and cold gas, would not overcome the surface brightness shortfall. However, charge exchange emission from such interfaces, not included in the current model, may be significant. The faintness of the model may also be due to the lack of cosmic ray driving, meaning that the model may underestimate the amount of material transported from the disk to the halo. In addition, an extended hot halo of accreted material may be important, by supplying hot electrons that could boost the emission of the material driven out from the disk. Additional model predictions are needed to test the relative importance of these processes in explaining the observed halo emission.},
doi = {10.1088/0004-637X/800/2/102},
journal = {Astrophysical Journal},
number = 2,
volume = 800,
place = {United States},
year = {Fri Feb 20 00:00:00 EST 2015},
month = {Fri Feb 20 00:00:00 EST 2015}
}