Feedback Observations and Simulations of Elliptical Galaxies

– Daniel Wang, Shikui Tang, Yu Lu, Houjun Mo (UMASS)

– Mordecai Mac-Low (AMNH)

– Ryan Joung (Princeton)

– Zhiyuan Li (CfA)

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

Key questions to addressWhy do elliptical galaxies typically

evolve passively? Understanding the cause of the bi-

modality of galaxiesWhat is the role of stellar feedback?

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

Energy input from Ia SNe with a rate ~ 0.2 /1010LB☉/100yr

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

Observations of stellar feedback

Large scattering of LX for galaxies with the same LB or LK

Observed Lx is <10% of the energy inputs

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

David et al (2006)

AGN

SNe

Observations of stellar feedback

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

Bregman et al (2004)

Humphrey & Buote (2006)

O’Sullivan & Ponman (2004),

Irwin et al (2001), Irwin

(2008)

Galactic wind?

The overall dynamic may be described by a 1-D wind model

But it is inconsistent with observations:Too small Lx (by a factor > 10) with little

dispersionToo steep radial X-ray intensity profileToo high Temperature, fixed by the specific energy

inputToo high Fe abundance of hot gas

Can 3-D effects alleviate these discrepancies?X-ray emission is sensitive to the structure in

density, temperature, and metal distributions

Galactic wind: 3-D simulations

5 x 1010 Msun spheroidAdaptive mesh

refinement, ~2 pc spatial resolution, using FLASH Hydrodynamic code

Continuous stellar mass injection and sporadic SNe

Initialized from established 1-D wind solution

10x10x10 kpc3 BoxDensity snapshot

Tang et al 2009Tang & Wang 2009

3-D effects

Broad density and temperature distributions low metallicity if

modeled with a 1- or 2-T plasma, even assuming uniform solar metallicity.

Overall luminosity increase by a factor of ~ 3.

Differential Emission Measure

Galactic wind model: limitation

A passive evolved galaxy inside a static halo

Gas-free initial conditionOnly reasonable for low-mass

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 evolution

Outflow and galaxy formation: 1-D simulations

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

Initial bulge formation (5x1010 M☉) 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

The bulge wind can be shocked at a large radius.

Tang et al 2009b

z=1.4

z=0.5

z=0

Outflow dynamics: dependence on the interplay between

the feedback and the galactic environment

For a weak feedback, 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, as indicated by the observations

3-D simulation starting from a 1-D outflow initial condition

Luminosity boosted by a factor of ~5

The predicted gas temperature and Fe abundance are closer to the observed.

SN ejecta evolutionTang & 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

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

outflows driven by Ia SNe and stellar mass loss1-D galactic wind model cannot explain observed diffuse

X-ray emission3-D hot gas structures can significantly affect

observational propertiesOutflow dynamic state depends on galaxy history and

environmentStellar 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

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

3-D hydrodynamic simulations of hot gas in and around Galactic

bulges

•Mass, energy, and metal distributions •Comparison with observations

•Effect on galaxy evolutionTang & Wang 2005, 2009

Tang et al. 2009

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