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