Hot Gaseous Halos of Disk Galaxies

Q. Daniel Wang

University of Massachusetts

The galaxy evolution context

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

The “overcooling” problem:

Too much condensation to be consistent with observations

ROSAT X-ray All-sky ¾-keV Diffuse Background Map

X-ray binary~50% of the background is thermal and local (z < 0.01)The rest is mostly from AGNs (McCammon et al. 2002)

New Tool: Chandra

CCD:

•Resolution res. ~ 1”

•Spectral Res. E/E ~ 20

Grating:

•Spectral Res. ~ 500 km/s

Absorption Sight Lines

X-ray binaryROSAT all-sky

survey in the ¾-keV band

X-ray binaryAGN

LMXB X1820-303

Fe XVII K

• In 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

Absorption line diagnostics

Assuming CIE and solar abundances

I()=Ic() exp[-()]

()NHfafi(T)flu(,0,b)

b=(2kT/mi+2)1/2

Accounting for linesaturation and

multiple line detections

Yao & Wang 2005

OVI

OVIIIOVII

Ne IX

Ne VIII

Ne X

X1820-303: Results• Hot gas accounts for ~ 6% of the total O column

density

• Mean temperature LogT(k) = 6.34 (6.29-6.41)

• O abundance: – 0.3 (0.2-0.6) solar in neutral atomic gas

– 2.0 (0.8-3.6) solar in ionized gas

• Ne/O =1.4(0.9-2.1) solar (90% confidence)

• 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

LMC X-3 as a distance marker

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

• Roche lobe accretion• 50 kpc away

• Vs = +310 km/s

• Away from the LMC main body

H image Wang et al. 2005

LMC X-3: absorption linesOVII

Ne IX

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

Global distribution modelsCombining all the sight lines together:• Disk model

nH = 5.0x10-3 cm-3 exp[-|z|/1.1 kpc]

Total NH~1.6 x1019 cm-2

• Sphere modelnH = 6.1x10-2 cm-3 exp[-R/2.7 kpc]

~3 x 10-3 cm-3 at the Sun

Total NH~6.1 x1019 cm-2

MH~7.5x108 Msun

X-ray absorption is primarily around the Galactic disk and the bulge within a few kpc!

Yao & Wang (2005)

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 • No evidence for a large-scale (r ~ 102 kpc) X-

ray-emitting/absorbing halo

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 energy

Wang et al. 2004

NGC 2841 (Sb)

Red: optical

Blue: 0.3-1.5 keV diffuse emission

• D=15 Mpc• Low SF rate

• Lx ~ 7 x 1039 ergs/s

Wang 2006

NGC 4565 (Sb)

William McLaughlin (ARGO Cooperative Observatory)

Red – optical

Green – 0.3-1.5 keV band

Blue – 1.5-7 keV band

Wang (2006)

Very low specific SFR

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

NGC 4594 (Sa)

Red: near-IR

Green: 0.3-1.5 keV

Blue: 1.5-7 keV

H ring

Li et al. 2006

NGC 4594Point 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 from evolving stars ~ 1.3 Msun/yr

•Each Type Ia SN 0.7 Msun Fe

NGC 4631

XMM/Newton observation of NGC 2613

(Sb, D=26 Mpc, Vc=304 km/s)

0.5-2 keV band; Li et al. (2006)

Similar results from NGC 5746 (Vc=250 km/s, Petersen et al. 2005)

Toft et al.

Stellar light

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?

Toft et al. (2003)

NGC 4565NGC 4594

NGC 2613

Galactic bulge Wind Scenario3-D simulation:• 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

Galactic bulge simulation: Density dist.

3x3x3 kpc3 box

density distribution

Galactic bulge simulation: Metal dist.• Ejecta dominate the high-

T emission• Not well-mixed with the

ambient medium• Probably cool too fast to

be mixed with the medium

SN ejecta

Comparison with the 1-D solution

• The average radial density and temperature distributions are similar to the 1-D model.

• Large dispersion, particularly in the hot Fe distribution– enhanced emission at

both low and high temperatures

Log(T(K))

Low Res.

High

Res.

1-D

Where is the energy?

• Radiative cooling is not important in the bulge region, consistent with the observation

• Energy not dissipated locally

• Most of the energy is in the bulk motion and in waves

The fate of the energy

• Maybe eventually damped by cooling gas in the galactic hot halo.

• Galactic wind not necessary, depending the galaxy mass and IGM environment.

• Interaction with the infalling IGM a possible solution to the over-cooling problem.

kpc

1-D modeling: Present hot gas distribution

Free infall of the IGM

Virial shock

Gas dropping out

Zg=0

Zg=0.03

•For Milky-Way size galaxy

•Assuming Collisional Ionization Eq.

Tang et al. 2006

Evolution of the accreted IGM: hot vs. cool

• Following approx mass accretion history for a galaxy similar to the Milky Way

• No pre-heating• Multi-phase assumes a

power law distribution (z=0-2 solar)

Single z=0.1

Multi-z, avg=0.1

Single z=0.0

Conclusions• Diffuse X-ray-emitting gas is strongly concentrated

toward galactic disks and bulges. No X-ray evidence for large-scale halos on scales > ~ 20 kpc.

• Heating is most due to SNe. But the bulk of their energy is not detected and is probably propagated into the halo, balancing the cooling.

• Metallicity inhomogneity in the IGM naturally leads to its selective cooling in galactic halosHigh velocity clouds OVI absorbers, etc. Low metallicity and high T the radiatively inefficient hot

halo.