Transcript Stellar Feedback and Evolution of Milky Way

Stellar Feedback and
Hot Gaseous Halos of Galaxies
Q. Daniel Wang
IRAC 8 micro
K-band
ACIS diffuse 0.5-2 keV
University of Massachusetts, Amherst
Galaxy formation and evolution context
Toft et al. (2002)
The “overcooling” problem:
Too much condensation
to be consistent with
observations (e.g., White &
Rees 1978; Navarro & Steinmetz
1997)
The “missing” baryon problem
• Stars and the ISM accounts for 1/31/2 of the baryon expected from the
gravitational mass of a galaxy.
• Where is the remaining baryon
matter?
– In a hot gaseous galactic halo?
– Or having been pushed away?
• Both are related to the galactic energy
feedback!
Origins of the galactic feedback
• AGNs (jets)
• Nuclear starbursts:
– Radiation pressure
– Superwinds
• Gradual energy inputs
– Galactic disks: massive star formation
– Galactic bulges: Type Ia SNe.
X-ray absorption line spectroscopy:
adding depth into the map
4U1957+11
X-ray binary
AGN
X-ray binary
Wang et al. 05, Yao & Wang 05/06,
Yao et al. 06/07
ROSAT all-sky survey
in the ¾-keV band
Galactic global hot gas properties
• Structure:
– A thick Galactic disk with a scale height 1-2 kpc/f,
~ the values of OVI absorbers and free electrons
– Enhanced hot gas around the Galactic bulge
• 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 consistent with solar
But a large-scale hot gaseous halo is required to explain HVCs!
•Confinement
•Head-tail morphology
•OVI absorption
Hot gas in the M31 bulge
• L(0.5-2 keV) ~ 31038
erg/s
~1% of the SN mechanical
energy input!
• T ~ 0.3 keV
~10 times lower than
expected from Type Ia
heating and mass-loss
from evolved stars!
• Mental abundance ~
solar
inconsistent with the SN
enrichment!
IRAC 8 micro, K-band, 0.5-2 keV
Li & Wang (2007); Bogdan & Gilfanov 2008
Mass-loading from the nuclear spiral?
• Correlation of
diffuse X-ray with
the H emission
 evaporation via
thermal conduction?
• SMBH is not active
• No SF in the bulge
Li & Wang (2008)
H image with 0.5-2 keV contours
Feedback from disk-wide star formation
NGC 5775
• Scale height ~ 2 kpc +
more distant blubs.
• T1 ~ 106.3 K, T2 > 107.1 K
• Lx(diffuse) ~ 4x1039
erg/s
Red – H
Green – R-band
Blue – 0.3-1.5 keV
Li et al. (2008)
NGC 2841 (Sb)
• D=15 Mpc
• Vc = 317 km/s
• Lx ~ 7 x 1039 ergs/s
NW
SE
Red: optical
Blue: 0.3-1.5 keV diffuse emission
Wang et al 2008
NGC 4594 (Sa)
• Average T ~ 6 x 106 K
• Lx ~ 4 x 1039 erg/s, ~ 2% of Type Ia SN energy
• Not much cool gas to hide/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
Li et al. 2007
Observations vs. simulations
• X-ray-emitting gas in normal
massive disk galaxies:
– Disk – driven by massive
star formation
– Bulge – heated primarily
by Type-Ia SNe
Galaxy
Vc
NGC 4565 250
NGC 2613 304
NGC 5746 307
NGC 2841 317
NGC 4594 370
Simulations by Toft et al. (2003)
– Extent ~ a few kpc
– temperature ~ 0.3 keV
– A possible very hot
component (T > 107 K) is
poorly constrained
• Little evidence for X-ray
emission or absorption from
IGM accretion.
• No “overcooling” problem
• Instead, we have a missing
feedback problem!
Problems with the existing models
• Model for stellar feedback
– Typically with no consideration of the evolving galactic
environment
– Fixed outer boundary  unstable subsonic solution
– No additional mass-loading
– Such a superwind model fails: too low Lx, too high T, and too
steep surface brightness profile.
• Model for galaxy evolution via IGM accretion
– Typically with no stellar feedback
– If implemented, receipts are used, typically with an injection
of energy or momentum or in form of an assumed preheating.
– Predicted massive cooling hot gaseous halos are not
observed.
– But a large-scale, low-density hot gaseous halo is required to
explain HVCs around the MW.
1- and 2-D simulations of galaxy evolution
with the stellar feedback
• Both dark and baryon
matters trace each
other initially and
evolve with to a final
mass of 1012 Msun (see
also Birnboim & Dekel 03)
Density evolution; size of box = 1.5 Mpc
See the poster by Tang & Wang
Tang et al., Tang & Wang 2008
• A blastwave is initiated
by the SB (+AGN) and
maintained by the Type
Ia SN feedback +
stellar winds from
evolved stars.
• IGM is heated beyond
the virial radius, and
accretion can be
stopped.
Stellar feedback with mass-loading
z=1.4
z=0
z=0.5
• With mass-loading, the
wind can evolve into a
subsonic outflow.
• This outflow can be
stable and long-lasting 
higher Lx, lower T, and
more extended.
• Consistent with
observations of galactic
bulges and Lx/Lb
ellipticals!
• For massive ellipticals,
the outflow can be
completely stopped.
Galaxies such as the MW evolve in hot
bubbles of baryon deficit!
Total baryon
before the SB
Cosmological
baryon fraction
Total baryon
at present
Hot gas
• Explains the lack of
large-scale X-ray
halos.
• Bulge outflow drives
away the present
stellar feedback.
• Allows later
starbursts to
develop highvelocity superwinds.
3-D simulations of a galactic
bulge wind
• Adaptive mesh
refinement, down
to 6 pc
• Stellar mass
injection and
sporadic SNe,
following the
stellar light.
10x10x10 kpc3 box
density distribution
Tang et al. (2008)
• Sedov solution does apply for
individual SNRs
• Emission primarily from shells and
filaments.
• Fe-rich ejecta dominate the high-T
emission and are not well-mixed with
the ambient medium
• Consistent with the low metallicity
inferred from X-ray spectral
observations
3-D Effects
1-D
• Large dispersion 
Low
Res.
Log(T(K))
1-D
– enhanced emission at both
low and high temperatures
– Overall luminosity increase
by a factor of ~ 3.
– Low metallicity if modeled
with a 1-T plasma.
• Consistent with the 1-D
radial density and
temperature
distributions, except for
the center region.
Conclusions
• Diffuse hot gas is strongly concentrated toward
galactic disks/bulges (< 20 kpc) due to the feedback.
• But the bulk of the feedback is not detected and is
probably propagated into very hot (~107 K) halos.
• The feedback from a galactic bulge likely plays a key
role in galaxy evolution:
– Initial burst led to the heating and expansion of gas beyond
the virial radius
– Ongoing feedback keeps the gas from forming a cooling flow
and starves SMBHs
– Mass-loaded outflows account for diffuse X-ray emission
from galactic bulges.
– Condensation of the initial starburst material may account
for some HVCs.
Galaxies like ours reside in hot bubbles!
No overcooling or missing energy problem!