J/ApJ/936/72 HaloSat survey of the Galactic CGM (Bluem+, 2022)
Widespread detection of two components in the hot circumgalactic medium
of the Milky Way.
Bluem J., Kaaret P., Kuntz K.D., Jahoda K., Koutroumpa D., Hodges-Kluck E.,
Fuller C.A., LaRocca D.M., Zajczyk A.
<Astrophys. J. 936, 72 (2022)>
=2022ApJ...936...72B 2022ApJ...936...72B (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; X-ray sources ; Interstellar medium ; Surveys
Keywords: Galaxy: halo - ISM: structure - X-rays: diffuse background -
X-rays: ISM
Abstract:
Surrounding the Milky Way (MW) is the circumgalactic medium (CGM), an
extended reservoir of hot gas that has significant implications for
the evolution of the MW. We used the HaloSat all-sky survey to study
the CGM's soft X-ray emission in order to better define its
distribution and structure. We extend a previous HaloSat study of the
southern CGM (Galactic latitude b←30°) to include the northern
CGM (b>30°) and find evidence that at least two hot gas model
components at different temperatures are required to produce the
observed emission. The cooler component has a typical temperature of
kT∼0.18keV, while the hotter component has a typical temperature of
kT∼0.7keV. The emission measure in both the warm and hot components
has a wide range ∼0.005-0.03, ∼0.0005-0.004cm-6*pc respectively),
indicating that the CGM is clumpy. A patch of relatively consistent
CGM was found in the north, allowing for the CGM spectrum to be
studied in finer detail using a stacked spectrum. The stacked spectrum
is well described with a model including two hot gas components at
temperatures of kT=0.166±0.005keV and kT=0.69+0.04-0.05keV. As
an alternative to adding a hot component, a neon-enhanced
single-temperature model of the CGM was also tested and found to have
worse fit statistics and poor residuals.
Description:
The table contains the thermal plasma emission measure and temperature
for the warm and hot components of the HaloSat Galactic CGM fields.
Also included is the equivalent OVII and OVIII line emission for each
component.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
cgmcat.dat 308 156 Observation details and spectral fit results
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Byte-by-byte Description of file: cgmcat.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- ID HaloSat field ID, hsNNNN (ID)
8- 14 F7.3 deg GLON Galctic longitude (GLON)
16- 22 F7.3 deg GLAT Galctic latitude (GLAT)
24- 29 I6 s ExpTime Exposure time (EXPOS)
31- 34 F4.2 --- Chi2 Reduced chi2 of fit (CHI)
36- 42 F7.5 pc/cm6 EMW Emission measure of warm component (EM_W)
44- 55 E12.6 pc/cm6 E_EMW EM of warm component upper error (90% CI)
(EMWerr_U)
57 A1 --- --- [-]
58- 68 E11.6 pc/cm6 e_EMW EM of warm component lower error (90% CI)
(EMWerr_L)
70- 75 F6.4 keV kTW Temperature of warm component (kT_W)
77- 81 F5.3 keV E_kTW Warm temperature upper error (90% CI)
(kTWerr_U)
83 A1 --- --- [-]
84- 88 F5.3 keV e_kTW Warm temperature lower error (90% CI)
(kTWerr_L)
90-101 E12.6 pc/cm6 EMH Emission measure of hot component (EM_H)
103-114 E12.6 pc/cm6 E_EMH EM of hot component upper error (90% CI)
(EMHerr_U)
116 A1 --- --- [-]
117-127 E11.6 pc/cm6 e_EMH EM of hot component lower error (90% CI)
(EMHerr_L)
129-133 F5.3 keV kTH Temperature of hot component (kT_H) (1)
135-139 F5.3 keV E_kTH Hot temperature upper error (90% CI)
(kTHerr_U) (1)
141 A1 --- --- [-]
142-146 F5.3 keV e_kTH Hot temperature lower error (90% CI)
(kTHerr_L) (1)
148-153 F6.3 ph/cm2/s/sr OVIIW OVII line strength of warm component
(OVII_W) (2)
155-159 F5.3 ph/cm2/s/sr e_OVIIW OVII strength of warm component error
(90% CI) (OVIIWerr) (2)
161-166 F6.3 ph/cm2/s/sr OVIIIW OVIII line strength of warm component
(OVIII_W) (2)
168-172 F5.3 ph/cm2/s/sr e_OVIIIW OVIII strength of warm component error
(90% CI) (OVIIIWerr) (2)
174-179 F6.3 ph/cm2/s/sr O887W OVIII + unresolved OVII line strength,
warm (O887_W) (2)
181-185 F5.3 ph/cm2/s/sr e_O887W OVIII + unres OVII line error, warm
(90% CI) (O887Werr) (2)
187-193 F7.5 ph/cm2/s/sr OVIIH OVII line strength of hot component
(OVII_H) (2)
195-206 E12.6 ph/cm2/s/sr e_OVIIH OVII strength of hot component error
(90% CI) (OVIIHerr) (2)
208-213 F6.4 ph/cm2/s/sr OVIIIH OVIII line strength of hot component
(OVIII_H) (2)
215-220 F6.4 ph/cm2/s/sr e_OVIIIH OVIII strength of hot component error
(90% CI) (OVIIIHerr) (2)
222-227 F6.4 ph/cm2/s/sr O887H OVIII + unresolved OVII line strength,
hot (O887_H) (2)
229-234 F6.4 ph/cm2/s/sr e_O887H OVIII + unres OVII line error, hot
(90% CI) (O887Herr) (2)
236-241 F6.3 ph/cm2/s/sr OVIIT Total OVII line strength (OVII_T) (2)
243-247 F5.3 ph/cm2/s/sr e_OVIIT Total OVII line strength error (90% CI)
(OVIITerr) (2)
249-254 F6.3 ph/cm2/s/sr OVIIIT Total OVIII line strength (OVIII_T) (2)
256-260 F5.3 ph/cm2/s/sr e_OVIIIT Total OVIII line strength error (90% CI)
(OVIIITerr) (2)
262-267 F6.3 ph/cm2/s/sr O887T OVIII + unresolved OVII line strength,
total (O887_T) (2)
269-273 F5.3 ph/cm2/s/sr e_O887T OVIII + unres OVII line error, total
(90% CI) (O887Terr) (2)
275-286 E12.6 pc/cm6 LHBEM Emission measure of the LHB (LHB_EM)
288-293 F6.4 10+22cm-2 nH TBabs nH parameter (nH)
295-300 F6.4 ph/cm2/s a561 SWCX gauss norm at 0.561 keV (a561)
302-308 F7.5 ph/cm2/s a654 SWCX gauss norm at 0.654 keV (a654)
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Note (1): Fields with kTH=0.7keV and errors of 0 had that temperature fixed
during fitting.
Note (2): Emission in OVII and OVIII is calculated from the best-fit CGM
temperature and emission measure as the sum of each of these lists
of lines as [element, ion, upper level, lower level] energy.
OVII:
[8,7,2,1] 0.561keV
[8,7,5,1] 0.569keV
[8,7,7,1] 0.574keV
OVIII:
[8,8,3,1] 0.653keV
[8,8,4,1] 0.654keV
O887:
[8,8,3,1] 0.653keV
[8,8,4,1] 0.654keV
[8,7,13,1] 0.666keV
All values are reported in line units (LU, photons cm-2 s-1 sr-1).
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Acknowledgements:
Jesse Bluem, jesse-bluem(at)uiowa.edu
(End) Patricia Vannier [CDS] 04-Jul-2022