stellar feedback and galaxy evolution
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Q. Daniel Wang
University of Massachusetts
Stellar Feedback and Galaxy Evolution
IRAC 8 microK-bandACIS diffuse 0.5-2 keV
Galaxy formation and evolution context
Toft et al. (2002); Muller & Bullock (2004)
The missing baryon problem
• Observed baryon mass in stars and the ISM accounts for 1/3-1/2 of what is 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!
Forms of the galactic feedback
• AGNs (jets)• Nuclear starbursts or superwinds• Gradual energy inputs
– Galactic disks: massive star formation– Galactic bulges: Type Ia SNe.
Karovska et al. 2002
AGN feedback• Centaurus A:
– D=3.5 Mpc– Nearest radio-bright AGN– Lx(AGN) ~ 1042 erg/s– Lx(diffuse) ~ 5x1038
erg/s
• The total mechanical energy output is not clear.
• Most nearby galaxies do not contain AGNs!
Starburst feedback
Starbursts typically occur in low-mass gas-rich galaxies in the present Universe.
optical0.5-2 keV2-8 keV
Feedback in normal galaxies: our Galaxy
X-ray binaryROSAT ¾-keV Diffuse Background Map: ~50% of the background is thermal and local (z < 0.01)The rest is mostly from faint AGNs (McCammon et al. 2002)
X-ray absorption line spectroscopy
X-ray binaryROSAT all-sky
survey in the ¾-keV band
X-ray binaryAGN Wang et al. 05, Yao & Wang
05/06, Yao et al. 06/07
LMXB X1820-303
Fe XVII K
In the GC NGC 6624– l, b = 2o.8, -8o
– Distance = 7.6 kpc 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 2006, Yao et al. 2006
LETG+HETG spectrum
X-ray absorption line spectroscopy along the X1820-303 sightline:
Results• Hot gas accounts for ~ 6% of the total O column
density
• Mean temperature T = 106.34 K
• O abundance: – 0.3 (0.2-0.6) solar in neutral atomic gas
– 2.0 (0.8-3.6) solar in ionized gas
• Hot Ne/O =1.4(0.9-2.1) solar (90% confidence)
• Hot Fe/Ne = 0.9(0.4-2.0) solar
• Velocity dispersion 255 (165–369) km/s
Mrk 421 (Yao & Wang 2006)
OVI 1032 A
•Joint-fit with the absorption lines with the OVII and OVIII line emission (McCammon et al. 2002)
•Model: n=n0e-z/hn; T=T0e-z/hT
n=n0(T/T0), =hT/hn, L=hn/sin
b
Galactic global hot gas properties
• Non-isothermal: – 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• Consistent with solar abundance ratios• A thick Galactic disk with a scale height 1-2 kpc, ~ the values of OVI absorbers and free electrons • Enhanced hot gas around the Galactic bulge• No evidence for a large-scale (r ~ 102 kpc) X-ray-
emitting/absorbing halo with an upper limit of NH~1 x1019 cm-2
• But a large-scale hot halo is required to explain HVCs: confinement and OVI line absorption!
Feedback from disk-wide star formation
Diffuse X-ray emission compared with HST/ACS images:
Red – HGreen – Optical R-bandBlue – 0.3-1.5 keV
• Lx(diffuse) ~ 4x1039 erg/s
• T1 ~ 106.3 K, T2 > 107.1 K• Scale height ~ 2 kpc +
more distant blubs.
Li et al. (2008)
NGC 5775
M83
Soria & Wu (2002)
Li et al. 2007
Extraplanar hot gas seen in nearby galaxies
• 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
• No evidence for large-scale X-ray-emitting galactic halos
Observations vs. simulations
• Little evidence for X-ray emission or absorption from IGM accretion.No “overcooling” problem?
• Missing stellar energy feedback, at least in early-type spirals. Where does the energy go?
Simulations by Toft et al. (2003)
Galaxy Vc
NGC 4565 250
NGC 2613 304
NGC 5746 307
NGC 2841 317
NGC 4594 370
1-D Simulations of galaxy formation with the stellar feedback
• Evolution of both dark and baryon matters (with the final mass 1012 Msun)
• Initial bulge formation (5x1010 Msun) starburst shock-heating and expanding of gas
• Later Type Ia SNe bulge wind/outflow, maintaining a low-density high-T halo, preventing a cooling flow
Tang & Wang 2007
1-D Simulations of galaxy formation with the stellar
feedback• Both dark and baryon matters
evolve (with the final mass 1012 Msun)
• A blastwave is initiated by the SB (forming a 5x1010 Msun
bulge) and maintained by the Type Ia SN feedback.
• The IGM is heated beyond the virial radius
• The accretion can be stopped and the shocked hot gas expands
• The resultant low density allows the bulge wind.
• The wind can be shocked at a large radius.
z=1.4
z=0.5
z=0
1-D Simulations of galaxy formation with the stellar
feedback• If the specific energy of the
feedback is reduced (e.g., because of mass-loading of the bulge wind), the wind has then evolved into a subsonic outflow.
• This outflow can be stable and long-lasting
• Consistent with observations of low Lx/LB galaxies (relative higher Lx, lower T, and more extended than those predicted by a supersonic wind.
z=1.4
z=0.5
z=0
Evolution of Baryons around galaxies
• Galaxies such as the MW evolves in a hot bubble with a deficit of baryon matter
• This bubble explains the lack of large-scale X-ray halos.
• Bulge wind removes the present stellar feedback.
• Results are sensitive to the initial burst and to the bulge/halo mass ratio
Hot gas
Total baryon before the SB
Total baryon at present
Cosmological baryon fraction
2-D simulations of galactic flows in M31
An ellipsoid bulge (q=0.6), a disk, and an NFW halo
SNu=0.06 SNu=0.12
3-D simulations of a galactic bulge wind
• Energy not dissipated locally • Most of the energy is in the
bulk motion and in waves
• Parallel, adaptive mesh refinement FLASH code
• Finest refinement in one octant down to 6 pc
• Stellar mass injection and SNe, following stellar light
• SN rate ~ 4x10-4 /yr• Mass injection rate ~0.1
Msun/yr)
10x10x10 kpc3 box
density distribution
Conclusions• Diffuse X-ray-emitting gas is strongly concentrated
toward galactic disks and bulges (< 20 kpc).• Heating is mostly due to SNe. But the bulk of their
energy is not detected in X-ray near galactic bulges/disks and is probably propagated into the halos.
• Feedback from a galactic bulge likely plays a key role in galaxy evolution: – Initial burst heating and expansion of gas beyond the
virial radius– Ongoing Type Ia SNe keeping the gas from forming a
cooling flow
• Low n and high T are characteristics of the gaseous halos
• Mass-loaded subsonic outflows account for diffuse X-ray emission from galactic bulges
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