feedback in elliptical galaxies a thesis prospectus presentation david a. riethmiller march 16, 2009
TRANSCRIPT
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Feedback in Elliptical Galaxies
A Thesis Prospectus PresentationDavid A. Riethmiller
March 16, 2009
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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
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What is an Elliptical Galaxy?
X-Ray properties very different from optical
M87: X-Ray, 11’
chandra.harvard.edu/photo/m87/m87_xray.jpg
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What is an Elliptical Galaxy?
Composite image
yellow = optical
red = radio
blue = x-ray
chandra.harvard.edu/photo/m87/m87_scale.jpg
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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
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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.”
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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
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History of X-Ray Observations and Models: “Cooling Flow”
Fabian 1994
More prevalent on cluster scale
• Sinks and Sources
• Flow Dynamic
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History of X-Ray Observations and Models: ROSAT
• ROSAT (Röntgen Satellite) launched in 1990
• same spatial resolution, improved spectral resolution
heasarc.gsfc.nasa.gov
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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
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Physics of Galactic X-Ray Emitting Gas: Radiative
Cooling
http://proteus.pha.jhu.edu/dks/Code/Coolcurve_create/index.html
Bremsstrahlung
vs
Line Emission
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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
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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.”
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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.
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Isophotes
Diehl & Statler, 2008a
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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
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Observational Constraints: Asymmetry (I)
Diehl & Statler, 2008a
Quantify morphological asymmetry in
x-ray isophotes
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Observational Constraints: Asymmetry (II)
Diehl & Statler, 2008a
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Observational Constraints: Asymmetry (III)
Diehl & Statler, 2008a
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Observational
Constraints: Gradients
Diehl & Statler (2008b)
4 types:
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Observational Constraints: Gradients (I)
Diehl & Statler (2008b)
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Observational Constraints: Gradients (II)
Diehl & Statler (2008b)
Central velocity dispersion:
Dispersion in stellar radial velocityσ 2 = V 2
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Observational Constraints: Gradients (III)
Diehl & Statler (2008b)
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Observational Constraints: XGFP
X-Ray Gas Fundamental Plane
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Face-on
Edge-on
Diehl & Statler 2005
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Observational Constraints: AGN Scenarios I
Scenario 1
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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
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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
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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:
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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)
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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
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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
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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)
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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
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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
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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
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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)
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Physics of Galactic X-Ray Emitting Gas:
• Sinks and Sources
• Flow Dynamic
http://www.gemini.edu/index.php?q=node/276
Inflow