Download X-ray observations of the hot CGM of nearby disk galaxies

X-ray observations of the hot CGM
of nearby disk galaxies
Q. Daniel Wang
University of Massachusetts
Key questions to be addressed:
1.  How does the X-ray emission of the CGM depend on
galaxy properties?
2.  Does the X-ray emission trace the accretion or
feedback of the galaxies?
3.  What is the emission mechanism?
4.  What might be the spatial distribution of the CGM?
X-ray observations
I.  Chandra survey of hot gas around disk galaxies
(led by Jiangtao Li)
II.  High-res spectroscopy of nearby starforming
galaxies, using XMM-Newton RGS data (Jiren Liu)
III.  X-ray absorption line spectroscopy (Yangsen Yao)
I. Chandra survey of disk galaxies:
imaging the CGM X-ray emission
Galaxy sample:
•  Highly-inclination angles (i > 60o)
•  D < 30 Mpc
•  Each with Chandra ACIS exposure > 10 kses
•  Size: 53, compared to < 10 in previous studies
Allowing for statistical analysis and
comparison with cosmological simulations.
Li & Wang 2012
Hot Gaseous Halo
Diffuse X-ray Emission: Examples
Lx vs. energy C feedback rate
Adding Type Ia SNe to the total energy input improves the
ESN-LX correlation for normal galaxies; Type Ia SNe
contribute 3%-93% of the input for our sample galaxies.
X-ray emission efficiency
(η=LX/ĖSN) vs. galaxy properties
η < a few %!
What determines the X-ray
radiation efficiency?
η is roughly proportional to
the mean surface density of
the galaxy mass (MTF/M*).
Enhanced soft X-ray emission:
NGC 4438 as an example
An interacting system within the Virgo cluster.
Good spatial correlation of the X-ray and Hα
emissions.
Color: Chandra 0.3-­‐2 keV Contour: Hα+[NII] Machacek, Jones & Forman (2004) Comparison with elliptical/S0 galaxies
SF disk galaxies tend to have higher Lx and T than
expected for elliptical or S0 galaxies.
Fe/O abundance ratio vs. galaxy type
•  Hot gas is Oxygen
enriched in late-type
galaxies, especially
for starburst ones.
Q1: How does the X-ray emission
depend on galaxy properties?
•  Lx is correlated primarily with the total mechanical
energy input rate and secondarily with the
compactness of galaxy mass.
•  Environmental effect is apparent, but difficult to
quantify.
•  Lx accounts for < a few % of the rate; the bulk of
the energy is most likely gone with galactic outflows.
•  Both Lx and T of the hot gas are typically higher
than expected for elliptical/S0 galaxies.
•  O is strongly enriched (relative to Fe) in late-type
galaxies.
Comparison with simulations
Simulations by Crain et al.
(2010)
Caveats of the comparison:
•  Simulated Lx is calculated
over a much larger regions
than those covered in the
observations.
•  Galaxy mass selection of
the simulated sample:
M* > 2 x 1010 Msun.
•  Observed galaxy sample is
far from uniformly
selected.
• 
• 
• 
There is little overlap in the Lx, M*, and SFR space
between the observed and simulated samples!
The simulation greatly under-produces Lx!
Q2: Does the X-ray emission trace the
accretion or feedback of the galaxies?
•  The observed X-ray emission is too concentrated
toward the disks, while the predicted scale of the
X-ray emitting CGM is substantially greater.
•  The emission is observed from low-mass galaxies for
which little hot CGM is expected from the accretion.
•  The X-ray-emitting gas is apparently enriched by
the stellar feedback of different types of galaxies.
Thus the emission most likely traces the feedback.
•  Such simulations may still miss important physical
processes in disk/halo interaction regions.
II. X-ray Emission Line Spectroscopy
Liu, Mao, & Wang 2011
r
i
Soft X-ray arises primarily from
the interplay between a
superwind and entrained cool
gas clouds.
f
Composite of optical (HST), infrared
(Spitzer), and X-ray (Chandra) images
The resonance line is found to be weaker than
the “forbidden”+”inter-recommbination” lines,
which is not expected for thermal emission.
Charge exchange origin of soft X-ray
line emission
•  Charge exchange (CX) nature of
comet X-ray emission is confirmed,
spectroscopically and temporally.
•  CX has a cross-section of ~10-15 cm-2
and occurs on scales of the mean free
path of hot ions at the interface.
•  PCX/Pth propto 1/ne2
Peter Beiersdorfer
ri
f
Color: Chandra 0.3-­‐2 keV Contour: Hα+[NII] Machacek, Jones & Forman (2004) RGS Survey of nearby active star
forming galaxies: examples Liu, Wang, Mao (2012)
M83
M51
r
i
f
r
Soria & Wu (2002)
i
f
(Credit: NASA/CXC/SAO/R.DiStefano et al.)
•  Little evidence for significant AGN activities
•  Soft X-ray are spatially correlated with star forming regions
•  fOVIII/fOVII ratios are similar to star bursts than AGNs
Antennae galaxy
r
i
f
Liu, Wang, & Mao (2012)
Optical (Yellow), X-ray (Blue), Infrared (Red)
Q3: What is the X-ray emission
mechanism?
•  Spectroscopy shows that a substantial fraction
of the diffuse soft X-ray emission appears to
arise from the CX.
•  Such an interface mechanism naturally explains
the enhanced X-ray emission in the immediate
vicinity of galactic disks and the spatial
correlation between X-ray and cool gas tracers.
•  CX measurements can potentially provide a
powerful tool for probing the thermal, chemical,
and kinematical properties of the hot plasma
and its interplay with cool gas.
X-ray Absorption Line Spectroscopy:
Add Depth to the Map
4U1957+11
AGN
X-ray binary
ROSAT all-sky survey
in the ¾-keV band
X-ray absorption line spectroscopy is powerful!
Mrk 421
•  Tracing all K transitions of metals
à all three phases of the ISM.
•  Not affected by photo-electric
absorptionà unbiased
measurements of the global ISM.
•  Multiple lines à EW, as well as
velocity centroid, velocity
dispersion, gas temperature, and/
or relative metal abundance.
•  Multiple sightlines --> differential
hot plasma properties
•  Joint-fit of absorption and
emission data --> pathlength and
density
Wang et al. 05, Yao & Wang 05/06, Yao
et al. 06/07/08/09/10
LMC X-3 Sightline as an example of
X-ray absorption line spectroscopy
•  BH X-ray binary undergoing
Roche lobe accretion
•  Away from the LMC main body
•  50 kpc away
•  Vs = +310 km/s
•  The line centroids of the OVI
and OVII lines are consistent
with their Galactic origin.
•  NOVII ~ 1.9 x 1016 atoms/cm2,
similar to those seen in AGN
spectra!
•  T ~ 1.3 x 106 K
•  b ~ 79 km/s
Wang et al. 2005
Galactic global hot plasma properties
•  Thermal property:
–  mean T ~ 106.3 K toward the inner region
– 
~ 106.1 K at solar neighborhood
•  Velocity dispersion from ~200 km/s to 80 km/s
•  Abundance ratios ~ solar
•  Structure:
–  A thick Galactic disk with a scale height of ~ a few kpc,
~ the values of OVI absorbers and free electrons
–  Enhanced hot gas around the Galactic bulge
–  95% upper limit: NOVII~ 3 x1015 cm-2
for r > 10 kpc
~ 1 x1015 cm-2 for r > 50 kpc
No evidence for a large-scale X-ray-emitting/absorbing halo!
No evidence for X-ray line absorption by hot
plasma in intervening groups of galaxies
• Sightline: PKS 2115-304
• Total exposure: 1 Ms
• Selected galaxies: < 500 kpc
projected distance.
Blue lines: Galactic absorption
Vertical red bars: expected group absorption line positions
Yao, QDW, Tripp, et al. (2010)
Stacking of absorption line spectra according
to intervening galaxy/group redshifts
With an effective exposure:
~ 10 Ms, no absorption is
detected!
•  NOVII < 1015 cm-2, or < 1/10
of the column density
observed around the
Milky Way.
•  Groups typically contain
little gas at T~105.3-106.3 K,
unless the Oxygen
abundance is << 1/10
solar.
Q4: What is the spatial
distribution of the CGM?
•  X-ray absorption line spectroscopy allows for
the tomography of the spatial, thermal,
chemical, and kinetic properties of diffuse hot
plasma in and around the Galaxy.
•  The missing baryon matter of galaxies is
apparently not in their immediate vicinity and
is likely dispersed on scales greater than
galaxy groups (> 1 Mpc).
How to make progress?
•  Need to detect the emission on large scales ß
staking of existing data; eROSITA all sky survey; and
more sensitive X-ray absorption line observations.
•  Better spectral data ß deeper observations with
Chandra/XMM-Newton/Suzaku, as well as Astro-H.
•  Need complete samples for comparison with
simulations ß eROSITA and dedicated large surveys
with existing X-ray telescopes.
•  Theory/simulations should predict the absorption
column of various key lines, temperature, kinematics,
and morphology, as well as Lx; dedicated modeling of
the interfaces; spectral models of CX.
•  Multi-wavelengths: e.g., radio and far-UV
Continuum HAlos in Nearby Galaxies – an EVLA
Survey (CHANG-ES; PI: Judy Irwin)pes
Selec0on of 35 edge-­‐on galaxies with inclina0on > 75◦ δ  > -­‐25◦ 1.4 GHz fluxes > 20 mJy 4’ ≤ D25 ≤ 15’, Comple0on of the (> 400 hrs) data taking by fall, 2012; two wide bands centered at 1.5 and 6 GHz and in B, C & D arrays, all 4 Stokes. 153 hours of GBT 0me in the upcoming cycle. CHANG-ES: Determining the role of
cosmic-ray/magnetic field in regulating
outflows
Based on a 2-hr C-array 1.5 GHz JVLA test
observation (Irwin et al. 2012).