http://chandra.harvard.

edu/photo/2007/m51/

Confronting Stellar Feedback Simulations with Observations of Hot Gas in Elliptical

Galaxies

Q. Daniel Wang, Shikui Tang, Yu Lu, Houjun Mo (UMass)

Mordecai Mac-Low (AMNH), Ryan Joung (Princeton)

NGC 4697: X-ray intensity contours 3-D stellar feedback simulation

Key questions to address

Why do elliptical galaxies evolve passively? Understanding of the color bi-modality of

galaxy evolutionWhat is the role of stellar feedback?

Mass loss from evolved stars: ~ 0.2 M☉/1010LB☉/yr

Energy input from Ia SNe: ~ 0.2 /1010LB☉/100yr + velocity dispersion among stars

Fe abundance ~Z*+5(MSN/0.7Msun)Specific temperature: kT ~ 1-2 kev traced by X-ray

Observations of stellar feedback

Both gas temperature and Fe abundance are less than the expected.

Bregman et al (2004)

Humphrey & Buote (2006)

O’Sullivan & Ponman (2004),

Irwin et al (2001), Irwin

(2008)

Observations of stellar feedback

Observed Lx is <10% of the energy inputs for low and intermediate mass ellipticals

Large scattering in LX for galaxies of same stellar mass

Mass of diffuse hot gas ~ 106 – 107 M☉,can be replenished within 108 yrs

Hardly any accumulation of hot gas!

David et al (2006)

AGN

SNe

Gone with the wind?

The overall dynamics of hot gas may be described by a 1-D wind model (e.g., Ciotti et al. 1991)

But it is inconsistent with the observations:Too high Temperature, fixed by the specific

energy inputToo steep radial X-ray intensity profileToo small Lx (by a factor > 10) with little

dispersionToo high Fe abundance

X-ray emission is sensitive to the structure in density, temperature, and metal distributions.

Can 3-D effects alleviate these inconsistencies?

Galactic wind: 3-D simulations

Initialized from a 1-D solution for a 5 x 1010 Msun spheroid

Adaptive mesh refinement ~2 pc spatial resolution

Continuous and smooth mass injection, following stellar light

Sporadic Sne in both time and space

10x10x10 kpc3 BoxDensity snapshot

Tang, Wang, et al 2009aTang & Wang 2009

3-D effects

Broad temperature and density distributions

Lower metal abundance if modeled with a 1- or 2-T plasma by a factor of 2-3

X-ray measured temperature is a factor of ~2 lower

Overall Lx is enhanced by a factor of ~ 3.

Differential Emission Measure

Galactic wind model limitations

Only reasonable for low-mass galaxies, where wind materials can escape.

For more massive galaxiesHot gas may not be able to escape from the

dark matter halo IGM accretion needs to be consideredHot gas properties thus depend on the

environment and galaxy history.

Feedback and galaxy formation: 1-D simulations

Evolution of both dark and baryon matters (with the final total mass of 1012 M☉)

Initial spheroid formation (5x1010 M☉) starburst shock-heating and expanding of surrounding gas

Later Type Ia SNe wind/outflow, maintaining a low-density, high-T gas halo and preventing a cooling flow

The wind can be shocked at a large radius.

Tang, Wang, et al 2009b

z=1.4

z=0.5

z=0

Dependence of outflow dynamics on the feedback strength, galaxy mass, and

environmentFor an intermediate mass

galaxy, the wind may have evolved into a subsonic outflow.

This outflow can be stable and long-lasting higher Lx and more extended profile, as indicated by the observations.

Starting from a 1-D outflow simulation

3-D Lx is a factor of ~5 higher

Fe ejecta moves much faster than stellar mass-loss materials.

Fe abundance mapTang & Wang in prep

Subsonic Outflow: 3-D Simulations

3-D Subsonic Outflow Simulations: Results

Positive temperature gradient,mimicking a “cooling flow”!

1-D wind model

1-D outflow model

3-D simulation

Positive Fe abundance gradient, as observed in central regions of ellipticals

3-D results

ConclusionsHot gas in (low- and intermediate mass) ellipticals is

likely in outflows (mostly subsonic) driven by Ia SNe1-D supersonic wind model cannot explain observed

diffuse X-ray emission3-D structures significantly affect X-ray

measurements (Lx, T, intensity profile, and Fe abundance)

Stellar feedback can play a key role in galaxy evolution: Initial burst leads to the heating and expansion of gas

beyond the virial radius Ongoing feedback can keep the circum-galactic medium

from cooling and maintain a hot halo passive evolution of such galaxies.

Galaxies such as the MW evolves 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

Hot gas in the M31 bulgeL(0.5-2 keV) ~ 31038

erg/s ~1% of the SN

mechanical energy input!

T ~ 0.3 keV~10 times lower than

expected from Type Ia heating and mass-loss from evolved stars!

Mental abundance ~ solarinconsistent with the SN

enrichment!

Li & Wang (2007); Li, Wang, Wakker (2009); Bogdan & Gilfanov 2008

IRAC 8 micro, K-band, 0.5-2 keV