Stellar Feedback and Galactic Outflow
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Transcript Stellar Feedback and Galactic Outflow
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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) ~ 31038
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