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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). 3-D stellar feedback simulation. NGC 4697: X-ray intensity contours. Key questions to address.

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Feedback Observations and Simulations of Elliptical Galaxies

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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)

3-D stellar feedback simulation

NGC 4697: X-ray intensity contours

Key questions to address

  • Why do elliptical galaxies typically evolve passively?

     Understanding the cause of the bi-modality of galaxies

  • What 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)



Humphrey & Buote (2006)

O’Sullivan & Ponman (2004),Irwin et al (2001), Irwin (2008)

Observations of stellar feedback

Bregman et al (2004)

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

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 dispersion

    • Too steep radial X-ray intensity profile

    • Too high Temperature, fixed by the specific energy input

    • Too 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 spheroid

  • Adaptive mesh refinement, ~2 pc spatial resolution, using FLASH Hydrodynamic code

  • Continuous stellar mass injection and sporadic SNe

  • Initialized from established 1-D wind solution

Tang et al 2009

Tang & Wang 2009

10x10x10 kpc3 BoxDensity snapshot

3-D effects

Differential Emission Measure

  • 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.

Galactic wind model: limitation

  • A passive evolved galaxy inside a static halo

  • Gas-free initial condition

    Only reasonable for low-mass

  • For more massive galaxies

    • Hot gas may not be able to escape from the dark matter halo

    • IGM accretion needs to be considered

    • Hot 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

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

Subsonic Outflow: 3-D Simulations

  • 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 evolution

Tang & Wang in prep

3-D Subsonic Outflow Simulations: Results

1-D outflow model

3-D simulation

1-D wind model

Positive temperature gradient,mimicking a “cooling flow”!

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


  • Hot gas in (low- and intermediate mass) ellipticals is in outflows driven by Ia SNe and stellar mass loss

  • 1-D galactic wind model cannot explain observed diffuse X-ray emission

  • 3-D hot gas structures can significantly affect observational properties

  • Outflow dynamic state depends on galaxy history and environment

  • 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

Total baryon before the SB

Cosmological baryon fraction

Total baryon at present

Hot gas

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.

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

  • Mass, energy, and metal distributions

  • Comparison with observations

  • Effect on galaxy evolution

Tang & Wang 2005, 2009

Tang et al. 2009

Hot gas in the M31 bulge

  • L(0.5-2 keV) ~ 31038 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 ~ solar

    inconsistent with the SN enrichment!

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

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

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