Feedback in Elliptical Galaxies

Feedback in Elliptical Galaxies

A Thesis Prospectus PresentationDavid A. Riethmiller

March 16, 2009

What is an Elliptical Galaxy?

Smooth, round, no spiral arms

Really big ones at centers of clusters (not the ones I study)

Stars show little organized motion

Size ~ 10s of kpc

Temperature ~ below 1-2 keV

M87: Optical, 11’

chandra.harvard.edu/photo/m87/m87_optic.jpg

What is an Elliptical Galaxy?

X-Ray properties very different from optical

M87: X-Ray, 11’

chandra.harvard.edu/photo/m87/m87_xray.jpg

What is an Elliptical Galaxy?

Composite image

yellow = optical

red = radio

blue = x-ray

chandra.harvard.edu/photo/m87/m87_scale.jpg

Outline

• Goals of the Project

• History of X-Ray Observations and

Models

• Physics of Galactic X-Ray Emitting Gas

• Observational Constraints

• Basics of SPH Code

• Proposed Project

Goals of the Project

• Simulate cooling and feedback in elliptical galaxies.

• Discard models that fail to match observational constraints.

“Feedback is important. We don’t know what it is.”

History of X-Ray Observations and Models:

Einstein Observatory

• X-Ray universe poorly understood until Einstein launch in 1978

IPC FOV: 75’

1 arcmin resolution

heasarc.gsfc.nasa.gov

History of X-Ray Observations and Models: “Cooling Flow”

Fabian 1994

More prevalent on cluster scale

• Sinks and Sources

• Flow Dynamic

History of X-Ray Observations and Models: ROSAT

• ROSAT (Röntgen Satellite) launched in 1990

• same spatial resolution, improved spectral resolution

heasarc.gsfc.nasa.gov

History of X-Ray Observations and Models: Chandra

Chandra X-Ray Observatory launched in 1999.

http://chandra.harvard.edu/graphics/resources/illustrations/chandra_earth.jpg

• High spectral resolution

• High spatial resolution (narrow PSF)

• High sensitivityFOV 16.5’

chandra.harvard.edu

Physics of Galactic X-Ray Emitting Gas: Radiative

Cooling

http://proteus.pha.jhu.edu/dks/Code/Coolcurve_create/index.html

Bremsstrahlung

vs

Line Emission

Physics of Galactic X-Ray Emitting Gas: Runaway Cooling?

We don’t observe this.

Must be method of returning energy to gas to balance cooling.

Signature:

• very bright center

• steep drop in luminosity with increasing radius

Physics of Galactic X-Ray Emitting Gas: Feedback

Three main forms of feedback:

• Stellar Wind

• Supernova Feedback

• AGN activity

“Feedback is important. We don’t know what it is.”

Physics of Galactic X-Ray Emitting Gas: Compressive

Heating

If AGN not dominant, compressive heating may be important

• dW = -PdV

Efficiency depends on mass and temperature.

Isophotes

Diehl & Statler, 2008a

Observational Constraints: Hydrostatic?

If hydrostatic, expect hot gas isophotes to follow shape of stellar potential (at small radii).

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From Diehl & Statler, 2007

Observational Constraints: Asymmetry (I)

Diehl & Statler, 2008a

Quantify morphological asymmetry in

x-ray isophotes

Observational Constraints: Asymmetry (II)

Diehl & Statler, 2008a

Observational Constraints: Asymmetry (III)

Diehl & Statler, 2008a

Observational

Constraints: Gradients

Diehl & Statler (2008b)

4 types:

Observational Constraints: Gradients (I)

Diehl & Statler (2008b)

Observational Constraints: Gradients (II)

Diehl & Statler (2008b)

Central velocity dispersion:

Dispersion in stellar radial velocityσ 2 = V 2

Observational Constraints: Gradients (III)

Diehl & Statler (2008b)

Observational Constraints: XGFP

X-Ray Gas Fundamental Plane

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Face-on

Edge-on

Diehl & Statler 2005

Observational Constraints: AGN Scenarios I

Scenario 1

Observational Constraints: AGN Scenarios II

Scenario 2:

• AGN heating only dominant in very bright x-ray galaxies

• Negative gradients in dimmer galaxies indicate prevalence of feedback from compressive heating or supernovaeScenario 3:

• AGN activity may be cyclic, and observed temperature gradients are simply various snapshots in time

Basics of SPH Code

• Lagrangian hydrodynamics method (Monoghan 1992)

• Fluid elements represented as individual particles carrying fluid attributes

• Spatial derivatives computed by analytical differentiation of interpolation formulae

• Momentum and energy equations become ODEs, interpreted easily in themodynamical and mechanical terms

Basics of SPH Code: Kernel

AI (r)= A( ′r )W(r - ′r ,h)d ′r∫

A(r) expressed in terms of its values at a set of disordered points, so integral interpolant is

W(r,h): integration kernel

volume element dr’

h: smoothing length (defines resolution of simulation)But the numerical code

requires a discrete function, so we approximate:

Proposed Project: Work to Date

Implemented routines into SPH code for:

• application of external gravitational field

• application of external pressure

• application of cooling function based on tabulated list of cooling rates

Also wrote several IDL scripts designed to analyze output data of SPH code.

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Snapshot

x (kpc)

y

(kpc

)

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Hydrostatic Check

g * rho

-dP / dr

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Pressure (r)

r (kpc)

Pressure

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Radial Accelertion

r (kpc)

a(r) (kpc /

myr2)

Proposed Project: Work to Date (I)

Ran test of a simplistic T1/2 cooling function

• “Can of gas” simulation

• self gravity and hydrostatic pressure disabled

• Bremsstrahlung-only cooling enabled (no line emission)

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Proposed Project: Objectives

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From Wiersma et al., 2009

Implement more complex cooling functions into SPH

• Sutherland & Dopita 1993

• Cloudy (Ferland et al., 1998)

• Mappings III (Groves et al., 2008)

• Gnat & Sternberg 2007

Cooling

Proposed Project: Objectives (I)

“Feedback is important. We don’t know what it is.”

Stellar wind models (Thacker and Couchman, 2000):

1) Energy Smoothing

2) Single Particle Feedback

3) Temperature Smoothing

Proposed Project: Objectives (II)

After matching simpler feedback models, we graduate to newer prescriptions.

Feedback properties to investigate:

• Can be injected sporadically

• Can model both thermal and mechanical energy

• AGN / SMBH (Ciotti & Ostriker 2007)

• Grow SMBH? (Lagos et. al 2008)

Proposed Project: Constraints on Simulation

Simulation must preserve observational constraints:

• Gas disturbed from hydrostatic at small radii

• Asymmetry correlations

• Temperature gradient correlations

• X-Ray Gas Fundamental Plane

Summary

• Project will simulate a range of feedback and cooling combinations with Smoothed Particle Hydrodynamics

• Rule out combinations which fail to match observational constraints

SPH code compiled in parallel on the Coyote supercomputer at Los Alamos National Laboratory

Also secured time on several Teragrid supercomputing facilities.

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Extra Slide 1: Alternate Initial Conditions

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Diehl et al. 2009

Extra Slide 2: SPH Initial Conditions

Initial Conditions

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Taken from Diehl et al. 2009. (Colors are simply for a better 3-D understanding.)

Weighted Voronoi Tesselations (WVT)

• Begin with configuration according to particle probability distribution P(r) h(r)-3 dV for smoothing length h and volume dV

Extra Slide 3: Theoretical Cooling Function

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History of X-Ray Observations and Models: “Cooling Flow”

http://www.nasa.gov/centers/marshall/images/content/98568main_a1795_xray_m.jpg

Abel 1795

(Chandra ACIS)

Physics of Galactic X-Ray Emitting Gas:

• Sinks and Sources

• Flow Dynamic

http://www.gemini.edu/index.php?q=node/276

Inflow