http://chandra.h
arvard.edu/phot
o/2007/m51/
Confronting Stellar Feedback Simulations with
Observations of Hot Gas in Elliptical Galaxies
NGC 4697: X-ray intensity contours
3-D stellar feedback simulation
Q. Daniel Wang, Shikui Tang, Yu Lu, Houjun Mo (UMass)
Mordecai Mac-Low (AMNH), Ryan Joung (Princeton)
Key questions to address
 Why do elliptical galaxies evolve passively?
 Understanding of the color bi-modality of galaxy
evolution
 What is the role of stellar feedback?
 Mass loss from evolved stars: ~ 0.2 M☉/1010LB☉/yr
 Energy input from Ia SNe: ~ 0.2 /1010LB☉/100yr + velocity
dispersion among stars
 Fe abundance ~Z*+5(MSN/0.7Msun)
 Specific temperature: kT ~ 1-2 kev
 traced by X-ray
Observations of stellar feedback
Humphrey & Buote (2006)
O’Sullivan & Ponman (2004),
Bregman et al (2004)
Irwin et al (2001), Irwin (2008)
 Both gas temperature and Fe abundance are
less than the expected.
Observations of stellar feedback
David et al (2006)
SNe
AGN
 Observed Lx is <10%
of the energy inputs
for low and
intermediate mass
ellipticals
 Large scattering in LX
for galaxies of same
stellar mass
 Mass of diffuse hot
gas ~ 106 – 107 M☉,
can be replenished
within 108 yrs
 Hardly any
accumulation of hot gas!
Gone with the wind?
 The overall dynamics of hot gas may be described
by a 1-D wind model (e.g., Ciotti et al. 1991)
 But it is inconsistent with the observations:
 Too high Temperature, fixed by the specific energy
input
 Too steep radial X-ray intensity profile
 Too small Lx (by a factor > 10) with little
dispersion
 Too high Fe abundance
 X-ray emission is sensitive to the structure in density,
temperature, and metal distributions.
Can 3-D effects alleviate these inconsistencies?
Galactic wind: 3-D simulations
 Initialized from a 1-D
solution for a 5 x 1010 Msun
spheroid
 Adaptive mesh
refinement  ~2 pc
spatial resolution
 Continuous and smooth
mass injection, following
stellar light
 Sporadic Sne in both
time and space
Tang, Wang, et al 2009a
Tang & Wang 2009
10x10x10 kpc3 Box
Density snapshot
3-D effects
Differential Emission Measure
Broad temperature
and density
distributions
 Lower metal
abundance if modeled
with a 1- or 2-T plasma
by a factor of 2-3
 X-ray measured
temperature is a
factor of ~2 lower
 Overall Lx is enhanced
by a factor of ~ 3.
Galactic wind model limitations
 Only reasonable for low-mass galaxies, where
wind materials can escape.
 For more massive galaxies
 Hot gas may not be able to escape from the dark
matter halo
 IGM accretion needs to be considered
 Hot gas properties thus depend on the
environment and galaxy history.
Feedback and galaxy formation:
1-D simulations
z=1.4
z=0.5
z=0
Tang, Wang, et al 2009b
 Evolution of both dark and
baryon matters (with the
final total mass of 1012 M☉)
 Initial spheroid formation
(5x1010 M☉)  starburst 
shock-heating and expanding
of surrounding gas
 Later Type Ia SNe 
wind/outflow, maintaining a
low-density, high-T gas halo
and preventing a cooling flow
 The wind can be shocked at
a large radius.
Dependence of outflow dynamics on the feedback
strength, galaxy mass, and environment
 For an intermediate mass
galaxy, the wind may have
evolved into a subsonic
outflow.
 This outflow can be stable
and long-lasting  higher
Lx and more extended
profile, as indicated by the
observations.
Subsonic Outflow: 3-D Simulations
 Starting from a 1-D
outflow simulation
 3-D Lx is a factor of
~5 higher
 Fe ejecta moves much
faster than stellar
mass-loss materials.
Fe abundance map
Tang & Wang in prep
3-D Subsonic Outflow Simulations: Results
1-D outflow model
3-D simulation
1-D wind model
3-D results
Positive temperature gradient, Positive Fe abundance
mimicking a “cooling flow”!
gradient, as observed in
central regions of
ellipticals
Conclusions
 Hot gas in (low- and intermediate mass) ellipticals is
likely in outflows (mostly subsonic) driven by Ia SNe
 1-D supersonic wind model cannot explain observed
diffuse X-ray emission
 3-D structures significantly affect X-ray measurements
(Lx, T, intensity profile, and Fe abundance)
 Stellar feedback can play a key role in galaxy evolution:
 Initial burst leads to the heating and expansion of gas beyond
the virial radius
 Ongoing feedback can keep the circum-galactic medium from
cooling and maintain a hot halo
 passive evolution of such galaxies.
Galaxies such as the MW evolves in hot
bubbles of baryon deficit!
• Explains the lack
of large-scale Xray halos.
• Bulge wind drives
away the present
stellar feedback.
Total
baryon
before
the SB
Cosmologi
cal baryon
fractionTotal
baryon
at
present
Hot
gas
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); Li, Wang, Wakker
(2009); Bogdan & Gilfanov 2008