Summary: Galactic hot ISM

• No significant X-ray absorption beyond the LMC (~< 1019 cm-2, assuming the solar abundance)

• A thick Galactic disk with a scale height 1-2 kpc, ~ the values of OVI absorbers and free electrons

• O abundance ~ solar or higher• Mean T ~ 106.3+-0.2 K, ~ 106.1 K at solar neighborhood• Large nonthermal v dispersion, especially at the GC• High volume filling factor (> 0.8) within |z| < 1 kpc

Missing Energy” and “Over-cooling” Problems in Galaxies

and Possible Solutions

The Overcooling Problem

Toft et al. (2002) Muller & Bullock (2004)Toft et al. (2002) Muller & Bullock (2004)

External Perspective: NGC 3556 (Sc)

Red – optical

Green – 0.3-1.5 keV band

Blue – 1.5-7 keV band

•Active star forming

•Hot gas scale height ~ 2 kpc

•Lx ~ 1% of SN mech. Energy input

Wang et al. 2004

NGC 2841 (Sb)

Red: optical

Blue: 0.3-1.5 keV diffuse emission

Correlation with SF

NGC 4565 (Sb)

William McLaughlin (ARGO Cooperative Observatory)

Red – optical

Green – 0.3-1.5 keV band

Blue – 1.5-7 keV band

Wang (2004)

Very low specific SFR

No sign for any outflows from the disk in radio and optical

NGC 4594 (Sa)

Red: optical

Green: 0.3-1.5 keV

Blue: 1.5-7 keV

H ring

NGC 4594:X-ray

spectraPoint source

Inner bulge

Outer bulge

disk

•Average T ~ 6 x 106 K

•Strong Fe –L complex

Lx ~ 4 x 1039 erg/s, or ~ 2% of the energy input from Type Ia SNe alone

Not much cool gas to hide or 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 4631

Galaxy formation simulations vs. observations

Toft et al. (2003)

NGC 4565

NGC 4594

NGC 4594

NGC 4565

Correlation with mass

No evidence for large-scale X-ray-emitting galactic halos

Li et al. (2006)

Summary: Nearby galaxies• Good News

– 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

• Bad news– Missing stellar feedback, at least in early-type spirals. – Little evidence for X-ray emission or absorption from

IGM accretion --- maybe good news for solving the over-cooling problem.

Are these problems related?

Feedback

• Radiation• AGNs• Supernovae

– Core-collapsed SNe– Type 1a

Bulge wind model• Spherical, steady, and adiabatic • NFW Dark matter halo + stellar bulge• Energy and mass input follows the

stellar light distribution• CIE plasma emission• Implemented in XSPEC for both

projected spectral and radial surface brightness analyses

Li & Wang 2006

Data vs model

Consistent with the expected total mass loss and SN rates as well as the Fe abundance of ~ 4 x solar!

The best-fit model density and temperature profiles of the bulge

wind

3-D hydro simulations• Goals

– To characterize the density, temperature, and metal abundance structures, the heating and cooling processes, and the kinematics of the HISM

– To calibrate the 1-D model• Hydro simulations with metal particle tracers

– Parallel, adaptive mesh refinement FLASH code– Whole galactic bulge simulation with the finest

refinement in one octant down to 6 pc– Stellar mass injection and SNe, following stellar

light– Realistic gravitational potential of the bulge and

the dark matter halo

Galactic bulge simulation: density

• 3x3x3 kpc3 box• SN rate ~ 4x10-4 /yr• Mass injection rate

~0.03 Msun/yr• Logarithmic scale • Statistical steady

state• ~ adiabatic

Tang et al. 2005

ROSAT X-ray All-sky Survey

Red – 1/4 keV band

Green – 3/4 keV band

Blue – 1.5 keV band

Conclusions and implications

• Large inhomogeneity is expected– particularly in the hot Fe distribution– enhanced emission at both low and high

temperatures (compared to the 1-D solution)

• SNe generate waves in the HISM– Energy not dissipated locally or in swept-up

shells– Maybe eventually damped by cool gas or in

the galactic hot halo– Galactic wind not necessary– Possible solution to the over-cooling

problem of galaxy formation

Galactic bulge simulation: Fe• Fe-rich ejecta

dominate the high-T emission

• Not well-mixed with the ambient medium

• May cool too fast to be mixed with the global hot ISM

Non-uniformity effects

Log(T(K))

Low Res.

High

Res.

1-D

1-D