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What do we know about the HISM?
Sun
For a review, see D. Cox (2005, ARAA)
ROSAT X-ray All-sky Survey
Red – 1/4 keV band
Green – 3/4 keV band
~50% of the ¾-keV background is thermal and
local (z < 0.01); rest is mostly from AGNs
Blue – 1.5 keV band
McCammon et al. 2002
What we do not know:
•
•
•
•
Overall spatial distribution
Filling factor
Physical and chemical states
Kinematics
• Heating, transporting, and cooling
• Effects on galaxy formation and
evolution
New Tool: Chandra
CCD
•resolution res. ~ 1”
•Spectral Res. E/E ~ 20
Grating
•Spectral Res. ~ 500 km/s
The Global Hot ISM: New Perspectives
Absorption
spectroscopy:
External views:
• Add the depth
• Measure the column
density, thus the mass
• Direct line diagnostics
• Independent of cool gas
absorption
• Global properties
• Relationship between
various components
• Dependence on galaxy
properties and
environment
Modeling of the SN-dominated hot ISM
• 1-D galactic bulge wind
• 3-D simulations
Detection of X-ray absorption lines:
Mrk 421; Nicastro et al. 2005
Mkn 421
LETG/HRC
LETG/ACIS
3C 273
Where is the
absorbing
gas located?
Wang & Yao 2005
LMC X-3 as a distance marker
• BH X-ray
binary, typically
in a high/soft
state
• Roche lobe
accretion
• 50 kpc away
• +310 km/s
• Away from the
LMC main body
H image
Obs. Of LMC X-3
•Chandra LETG: 100 ks.
•FUSE: 100 ks
•RXTE: 100 ks
Wang et al. 2005
LMC X-3: absorption lines
OVII
Ne IX
The EWs are about the same
as those seen in AGN spectra!
Absorption line diagnostics
OVII
OVIII
Ne IX
Ne VIII
OVI
Ne IX
Assuming CIE and solar abundances
I()=Ic() exp[-()]
()NHfafi(T)flu(,0,b)
b=(2kT/mi+2)1/2
accounting for line
saturation and
multiple
line detections
Yao & Wang 2005
Results from extragalactic sources
Source
Log[T(K)]
Log[NH(cm-2)]
PKS 2125-304
6.3(6.2-6.4)
19.8(19.5-20.3)
3C 273
6.3(6.1-6.4)
19.9(19.7-20.1)
MRK 421
6.2(6.1-6.3)
19.2(19.1-19.3)
LMC X-3
6.1(5.9-6.3)
19.6(19.4-19.8)
 No evidence for significant X-ray absorption
beyond the LMC!!!
LMXB 4U 1820-303:
A Galactic distance marker
• In GC NGC 6624
– Distance = 7.6; l, b = 2o.8, -8o
 tracing the global ISM
– 1 kpc away from the Galactic plane
 NHI
• Two radio pulsars in the GC
DM  Ne
• Chandra observations:
– 15 ks LETG (Futamoto et al. 2004)
– 21 ks HETG
Yao & Wang 2005
LETG+HETG spectrum
4U 1820-303: Results
• Hot gas accounts for ~ 6% of the total O
column density
• O abundance:
– 2.0 (0.8-3.6) solar in ionized gas
– 0.3 (0.2-0.6) solar in neutral atomic gas.
• Ne/O =1.4(0.9-2.1) solar
• Filling factor (relative to total ionized gas):
~0.95, if ph ~ pw
~0.8, if ph ~ 5pw as in the solar neighborhood
• LogT(k) = 6.34 (6.29-6.41)
• Velocity dispersion 255 (165–369) km/s
Temperature Dist.
d NH(T) = T dlogT
More Sources  Global HISM
distribution
• LMXBs with |b| > 2o
• S/N > 7 per bin at ~0.6 keV
• Excluding sources with identified
intrinsic emission/absorption features
• Ten LMXBs with 17 observations (6
with the LETG)
Yao & Wang 2005
Absorption Sight Lines
AGN
X-ray binary
No detection
ROSAT all-sky survey
in the ¾-keV band
Global distribution models
Disk model
•nH = 5.0(-1.8,+2.6)x10-3 cm-3
exp[-|z|/1.1(-0.5,+0.7) kpc]
•Total NH~1.6 x1019 cm-2
Sphere model
•nH = 6.1(-3.0,+3.6)x10-2 cm-3
exp[-R/2.7(-0.4,+0.8) kpc]
~3 x 10-3 cm-3 at the Sun
•Total NH~6.1 x1019 cm-2
•MH~7.5(2.5-16)x108 Msun
X-ray absorption is primarily around the Galactic disk within a few kpc!
Summary: Galactic hot ISM
• No significant X-ray absorption beyond the LMC
(~< 1019 cm-2, assuming the solar abundance)
• A thick Galactic disk with a scale height 1-2 kpc, ~
the values of OVI absorbers and free electrons
• O abundance ~ solar or higher
• Mean T ~ 106.3+-0.2 K, ~ 106.1 K at solar
neighborhood
• Large nonthermal v dispersion, especially at the GC
• High volume filling factor (> 0.8) within |z| < 1 kpc
External Perspective:
NGC 3556 (Sc)
•Active star forming
•Hot gas scale height
~ 2 kpc
•Lx ~ 1% of SN mech.
Energy input
Red – optical
Green – 0.3-1.5 keV band
Blue – 1.5-7 keV band
Wang et al. 2004
NGC 4565 (Sb)
Wang (2004)
Red – optical
Green – 0.3-1.5 keV band
Blue – 1.5-7 keV band
Very low specific SFR
William McLaughlin (ARGO Cooperative Observatory)
No sign for any outflows from the
disk in radio and optical
NGC 2841 (Sb)
Red: optical
Blue: 0.3-1.5 keV diffuse emission
NGC 4594 (Sa)
H ring
Red: optical
Green: 0.3-1.5 keV
Blue: 1.5-7 keV
disk
Inner
bulge
Outer
bulge
Point
source
NGC 4594:
X-ray spectra
•Average T ~ 6 x 106 K
•Strong Fe –L complex
•Lx ~ 4 x 1039 erg/s
NGC 4631
Missing stellar feedback in
early-type disk galaxies
• For NGC 4594, hot gas radiative
cooling rate ~ 2% of the energy
input from Type Ia SNe alone
• Not much cool gas to hide or
convert the SN energy
• Mass and metals are also missing!
– Mass input rate of evolved stars
~ 1.3 Msun/yr
– Each Type Ia SN  0.7 Msun Fe
Galaxy formation simulations
vs. observations
NGC 4594
NGC 4594
NGC 4565
NGC 4565
Toft et al. (2003)
Summary: Nearby galaxies
• Good News
– At least two components of diffuse hot gas:
• Disk – driven by massive star formation
• Bulge – heated primarily by Type-Ia SNe
– Characteristic extent and temperature similar
to the Galactic values
• Bad news
– Missing stellar feedback, at least in early-type
spirals.
– Little evidence for X-ray emission or absorption
from IGM accretion --- maybe good news for
solving the over-cooling problem.
Are these problems related?
Bulge wind model
• Spherical, steady, and adiabatic
• NFW Dark matter halo + stellar bulge
• Energy and mass input follows the
stellar light distribution
• CIE plasma emission
• Implemented in XSPEC for both
projected spectral and radial surface
brightness analyses
Li & Wang 2005
Data vs model
Consistent with the expected total mass loss and
SN rates as well as the Fe abundance of ~ 4 x solar!
The best-fit model density and
temperature profiles of the bulge wind
3-D hydro simulations
• Goals
– To characterize the density, temperature, and metal
abundance structures, the heating and cooling
processes, and the kinematics of the HISM
– To calibrate the 1-D model
• Hydro simulations with metal particle tracers
– Parallel, adaptive mesh refinement FLASH code
– Whole galactic bulge simulation with the finest
refinement in one octant down to 6 pc
– Stellar mass injection and SNe, following stellar light
– Realistic gravitational potential of the bulge and the
dark matter halo
Galactic bulge simulation: density
• 3x3x3 kpc3 box
• SN rate ~ 4x10-4 /yr
• Mass injection rate
~0.03 Msun/yr
• Logarithmic scale
• Statistical steady
state
• ~ adiabatic
Tang et al. 2005
Galactic bulge simulation: Fe
• Fe-rich ejecta
dominate the
high-T emission
• Not well-mixed
with the ambient
medium
• May cool too
fast to be mixed
with the global
hot ISM
Non-uniformity effects
High
Res.
1-D
Low
Res.
1-D
Log(T(K))
Conclusions and implications
• Large inhomogeneity is expected
– particularly in the hot Fe distribution
– enhanced emission at both low and high
temperatures (compared to the 1-D solution)
• SNe generate waves in the HISM
– Energy not dissipated locally or in swept-up
shells
– Maybe eventually damped by cool gas or in the
galactic hot halo
– Galactic wind not necessary
– Possible solution to the over-cooling problem of
galaxy formation
Acknowledgement
• Absorption line studies
– Y. Yao, T. Tripp, T.-T. Fang, …
• X-ray imaging of nearby galaxies
– T. Chevas, J. Irwin, Z. Li…
• 1-D and 3-D model and simulations
– Z. Li, S. Tang, M. Mac Low
Comparison with X-ray emission
Disk dist.
Observed
Uniform dist.
Consistency check: timescales
Radiative
cooling
O recom.
T/(dT/dt)
Fe recom.
Dependence on the
energy/mass input rate
Chandra Grating Instrument
Properties
FWHM ~ 5x102 km/s
Sample of normal disk galaxies
Galaxy
Name
Hubble
Type
D
(Mpc)
Incl. ang. Exp. Time
(ks)
(deg)
N4244
Sd/LSB
3.6
85
60
N4631
Sd
7.5
85
60
N3556
Sc
14.1
80
60
N4565
Sb
13.4
87
60
N4594
Sa
8.9
84
19
All with low Galactic foreground absorption (NH < 3 x 1020 cm-2)