Q. Daniel Wang

University of Massachusetts, Amherst

Stellar Feedback and Evolutionof Milky Way-like Galaxies

IRAC 8 microK-bandACIS diffuse 0.5-2 keV

Galaxy formation and evolution context

The “overcooling” problem:

Too much condensation to be consistent with observations (e.g., White & Rees 1978; Navarro & Steinmetz 1997)

Toft et al. (2002)

The “missing” baryon problem

• Stars and the ISM accounts for 1/3-1/2 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.

Outline• X-ray absorption line

spectroscopy of hot gas in and around the MW.

• X-ray imaging of nearby “normal” galaxies

• Hydro-simulations of stellar feedback and galaxy evolution.

Pre-Chandra View of the hot gas

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:

adding depth into the map

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

4U1957+11

X-ray absorption line spectroscopy is powerful !

Fe XVII K

• Tracing all K transitions of metals all three phases of the ISM.

• Not affected by photo-electric absorption unbiased measurements of the global ISM.

Yao & Wang 2006, Yao et al. 2006, Futamoto et al 2004

LETG+HETG spectrum of LMXB X1820-303

Spectroscopic diagnostics

Assuming solar abundances and CIE

One line (e.g., OVII K) velocity centroid and EW constraints on the column density, depending on assumed b and T

Two lines of different ionization states (OVII and OVIII K) T

Two lines of the same state (K and K) b

Lines from different species abundance fa

OVI

OVIIIOVII

Ne IX

Ne VIII

Ne X

Yao & Wang 2005

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

LMC X-3 as a distance marker

• BH X-ray binary, typically in a high/soft state

• 50 kpc away

• Vs = +310 km/s

• Away from the LMC main body

H image

Wang, Yao, Tripp, et al. 2005

LMC X-3: absorption linesOVII

Ne IX The EWs are about the same as those seen in AGN spectra!

Galactic global hot gas properties

• Structure:– 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

• 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!

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

• Scale height ~ 2 kpc + more distant blubs.

• Lx(diffuse) ~ 4x1039 erg/s

• T1 ~ 106.3 K, T2 > 107.1 K

Li, J. et al. (2008)

NGC 5775

M83Soria & Wu (2002)

Much work is yet to be done to determine the differential properties of the hot gas.

M31

0.5-1 keV1-2 keV2-8 keV

IRAC 8 microK-band0.5-2 keV

Li & Wang 2007

Lx~2x1038 erg/s, only ~1% of the Type Ia SN energy input

Mass-loading from the nuclear spiral?

• SMBH is not active• No SF in the bulge• Photo-ionization

probably due to PAGB stars

• Correlation of diffuse X-ray with the H emission

evaporation via thermal conduction?

H image with 0.5-2 keV contours

Li et al. 2007

• 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

NGC 4594 (Sa)

Summary for 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, although a possible very hot component (T > 107 K) is poorly constrained.

Observations vs. simulations

Little evidence for X-ray emission or absorption from IGM accretion.No “overcooling” problem?

Simulations by Toft et al. (2003)

Galaxy Vc

NGC 4565 250

NGC 2613 304

NGC 5746 307

NGC 2841 317

NGC 4594 370

The missing energy and large LX/LK dispersion problems of low-mass

ellipticals• Observed LX is < 10%

of the energy inputs.• Galactic wind model

fails:– Predict too small LX

with little dispersion– Too high T, fixed by the

specific energy input– Too steep radial surface

intensity profile.

David et al (2006)

AGN

SNe

Problems with the existing models

• Model of the stellar feedback– Typically with no consideration of the evolving galactic

environment – Fixed outer boundary unstable subsonic solution– No additional mass-loading

• Model of galaxy evolution via IGM accretion– Typically with no stellar feedback (e.g., BirnBoim, Dekel, &

Neistein 07)

– 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-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, Lu, & Mo 2008

1-D Simulations of galaxy formation with the stellar

feedback• A blastwave, initiated

by the SB, is maintained by the Type Ia SN feedback.

• The IGM is heated beyond the virial radius.

• The accretion can be stopped.

• The bulge wind can be shocked at a large radius.

z=1.4

z=0.5

z=0

Dependence on the specific energy of the feedback

• If the mass-loading is important, the wind may then have evolved into a subsonic outflow.

• This outflow can be stable and long-lasting higher Lx, lower T, and more extended profile.

• Consistent with observations!

z=1.4

z=0.5

z=0

Galaxies such as the MW evolve in hot bubbles of baryon deficit!

• Explains the lack of large-scale X-ray halos.

• Bulge wind drives away the present stellar feedback.

Hot gas

Total baryon before the SB

Total baryon at present

Cosmological baryon fraction

2-D simulations of the feedback in M31

• Qualitatively consistent with the 1-D results

• Instabilities at the contact discontinuities formation of HVCs?

An ellipsoid bulge (q=0.6),a disk, and an NFW halo Tang & Wang (2008)

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

• Emission primarily from shells and filaments.

• Fe-rich ejecta dominate the high-T emission

• Not well-mixed with the ambient medium

3-D Effects• Large dispersion

– 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.

Log(T(K))

Low

Res.

1-D

1-D

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.

Galaxies like ours reside in hot bubbles!

No overcooling or missing energy problem!