Making Galaxies Red and Dead Without Feedback

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Making Normal Galaxies in a Cosmological Setting
Making Galaxies Red and Dead Without Feedback
T.Naab, P. Johansson, K. Nagamine, G.Efstathiou,
RY Cen and J.P.O.
Cambridge, 8 May 2008
Princeton, 27 Feb 2009 jpo
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Cosmological SimulationStart with WMAP CBR Sky
Hinshaw et al 2008
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WMAP Spectrum of Cosmic Perturbations
(Amplitude)2
(Aplitude)2
Spherical Harmonic
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I believe, with a perfect faith
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Cosmic Structure Formation(cartoon version)
Recombination
Nucleosynthesis
linear perturbation theory
nonlinear simulations
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Computing the Universe locally, growth of
perturbations computed classically numerical
hydro required to reach the current epoch

• Transformation to co-moving coordinates xr/a(t)
• Co-moving cube, periodic boundary conditions
• Lbox gtgtlnl

Lbox
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Physics Input Included

• Newtonian gravity.
• Standard equations of hydrodynamics.
• Atomic physicsadiabatic, cooling, heating,
  non-equilibrium ionization.
• Radiative transfer global average, shielding of
  sinks, distribution of sources.
• Heuristic treatment of star-formation.
• --------------------------------------------------
  
• Maxwells equations in MHD form.

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Physics Input Missing(important on galactic
scales)

• Cosmic ray pressure and heating.
• Dust grain physics (depletion, absorption and
  catalyzation).
• Magnetic field generation.
• Multiphase media.

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Star Formation Algorithm

• Consider gas that is dense, cooling and
  collapsing.
• Make stellar particle
• DM const x DMgas x dt/Max(Tcool,Tdyn).
• (cf R. Kennicutt and M. Kuchner)
• Label particle with position, mass, metallicity
  and epoch.
• Give particle velocity of gas and follow dynamics
  as if dark matter particle.
• Allow output of mass, energy and radiation from
  each particle consistent with a star-cluster of
  same mass and age feedback.

C 0.05
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Global Simulations
(better mass resolution)
Naab et al (2007)
(better spatial resolution)
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Choice of parameters (free or otherwise)

• Cosmological parameters
• Determined by observational constraints such as
  WMAP, SDSS etc
• Star-Formation algorithm
• Results nearly independent of algorithm so long
  as cooling gas made into stars (in agreement w
  observation)
• Metallicity
• Yield determined by match to cluster IGM
• THAT IS ALL THERE IS

But what about feedback ?
(but feedback is necessary and does cause some
moderate variance NB digression -gt)
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Bubbles blown by super-winds from forming
galaxies heat the ambient medium and retard
subsequent gas infall Cen et al 2004, Dave
(feedback important for IGM, but relatively
unimportant for galaxy properties)
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Feedback Increases Number of Small Mass Galaxies
and Reduces Number of High Mass Galaxies.
(effects largely compensate and produce little
net change in SF rate)
high feedback
no feedback
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Star Formation history Nagamine et al (2005)
TVD Hydro vs Data
SPH Hydro SAM vs Data
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Butcher-Oemler or Gunn-Dressler effect
Blanton, M. Cen, R. Ostriker, J. P. Strauss,
M. A. Tegmark, M. ApJ.531, 1 (2000) TVD Hydro
Simulation In clusters, the fall off in star
formation since z1 is much more rapid than in
the field. Cause is simply C2x gt V2 gal,esc
Effect of hot gas in suppressing GF
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Results of Global Simulations

• Reasonably good results on epoch of galaxy
  formation mass distribution of galaxies.
• Reasonably good on spatial distribution of
  galaxies and environmental effects (eg early red
  and dead in clusters).
• Good treatment of the IGM.
• Essentially no information re internal structure
  of galaxies.

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Individual Galaxy Simulations

• Find and isolate objects of interest in large
  box.
• Add small scale power to region(s) of interest.
• Nest within bigger and bigger boxes (but smaller
  than the total volume) and add intermediate scale
  power (for tidal forces).
• Repeat simulation at higher spatial, temporal and
  mass resolution in smaller regions.
• Go back to step (2) with still higher
  resolution and repeat steps (3) and (4) to
  convergence.

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Hydro Codes

• SPH (eg Springel Hernquist, Weinberg Katz
  etc)
• Advantage good spatial resolution, community
  standard.
• Disadvantages poor mass resolution, too much
  viscosity, and cooling instabilities.
• AMR (eg Norman Bryan, Klypin,Tessier etc )
• Advantage more accurate hydro.
• Disadvantage technically very costly to resolve
  many regions simultaneously (communication).

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High Resolution Simulation of Massive Galaxy
Formation Naab, Johannson, Ostriker and Eftsatiou
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Input

• Dark Matter Simulation (AP3M 50 h-1Mpc)
• Pick isolated halos ( 1012 Msolar)
• Re-simulate at higher resolution with gas (SPH
  and GADGET-2)
• Standard star-formation algorithm
• Standard cooling
• No feedback

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Questions

• Convergence how do results change with
  resolution improvement?
• Is feedback necessary to make an early formed
  red and dead galaxy?
• Are the paradigms monolithic collapse,
  merger, dry or wet accretion useful,
  relevant?
• What is the physics that matters?
• What is the expected evolution of an elliptical?
• How to test the picture presented?

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Detailed Hydro Simulations (N,J,OE 2007ApJ,
658,710)
Convergence to low and to a flat rotation curve
at high resolution
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In Situ Star Formation
Convergence to stellar system formed very early
which quickly becomes red and dead.
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Gas Properties
Gas, at all radii, becomes hotter with time
despite fact that the cooling timelt the Hubble
time! Why?
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Accreted Stellar Mass
Accreted stellar mass, 45 of total is added late
( z lt 1.5), and at larger radii.
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Half-Light Radii of In-situ and Accreted Stars
A Normal Elliptical fits Sersic
Profile (detailed kinematics ok as well)
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Size Evolution
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Profile Evolution
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Dark Matter Evolution
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Physics

• Gas is steadily being heated by in-falling new
  gas ( -PdV and Tds) and by dynamical friction
  from infalling lumps of DM and stars (dynamical
  friction) via viscosity.
• These effects not included in SAM, but equal -
  quantitatively - feedback used by the SAM
  schemes.
• Of course feedback really exists and must be
  complementary to effects listed above.
• Dynamical Friction due to in-falling stellar
  lumps is very important for evolution of the
  stellar and DM components.

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Astronomy

• Two phase growth. First in situ star-formation
  from in-falling cold gas, and then accretion of
  stellar lumps.
• DM initially increases in density (adiabatic
  contraction) and then decreases (dynamical
  friction)
• Metal rich component in center from in-situ
  star-formation and metal poor component in
  outskirts due to stellar infall of old and small
  systems.
• Stellar system grows in size with time and
  central velocity dispersion actually declines
  with time

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What have we learned?

• High resolution needed 107 particles.
• For massive systems the three papers of 1977
  (Binney, Silk and Rees Ostriker) appear to
  point to the correct physics
• Cooling time of gas becomes longer than the
  dynamical time and star formation ceases. Systems
  live in hot bubbles and then grow by accretion of
  smaller stellar systems.

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Intermediate Mass Systems ie Normal Spirals

• Where ? Filaments - not clusters or voids.
• When? Slowly - bulge, then disc and halo.
• How? Not understood and complicated (ie cannot
  simulate), but at least four phases/components
• Bulges formed like early ellipticals, smaller
  scale models of same dissipational collapse
• Discs form slowly from inflowing cold gas
  streams
• Accretion of satellites adds metal poor stars to
  halo and gas to disc
• Dynamical evolution can produce bars, thick
  discs, globular cluster in-fall and destruction
  etc.

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Technical Issues that make this a VERY hard
problem

• Very high mass space and time resolution is
  needed, since discs are so thin and relaxation in
  them is so easy to produce (spuriously).
• Since things happen slowly, one must have a
  reasonably good model of star formation (ie if it
  is short compared to T0 , one can get it wrong
  and it matters little).
• Since thin discs are fragile, both feedback and
  dynamical effects can strongly alter the
  evolution
• Etc, etc, etc - a difficult problem.

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Many papers with beautiful work Examples include
Simulations of Galaxy Formation in a ? Cold
Dark Matter Universe. I. Dynamical and
Photometric Properties of a Simulated Disk
Galaxy II. The Fine Structure of Simulated
Galactic Disks by Abadi, Mario G. Navarro,
Julio F. Steinmetz, Matthias Eke, Vincent R.
Ap.J591,499 (2003) 597, 21
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But
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Many other good papers, but typically suffer from
same problem, of too bulge dominated and too high
a rotation curve, with a recent excellent summary
of the issues
The formation of disk galaxies in computer
simulations Mayer, L. Governato, F. Kaufmann,
T.( astroph0801.3845v ) We review the progress
made by numerical simulations carried out on
large parallel supercomputers. Recent progress
stems from a combination of increased resolution
and improved treatment of the astrophysical
processes modeled in the simulations, such as the
phenomenological description of the interstellar
medium and of the process of star formation. High
mass and spatial resolution is a necessary
condition in order to obtain large disks
comparable with observed spiral galaxies avoiding
spurious dissipation of angular momentum. A
realistic model of the star formation history.
gas-to-stars ratio and the morphology of the
stellar and gaseous component is instead
controlled by the phenomenological description of
the non-gravitational energy budget in the
galaxy. We show that simulations of gas collapse
within cold dark matter halos including a
phenomenological description of supernovae
blast-waves allow to obtain stellar disks with
nearly exponential surface density profiles as
those observed in real disk galaxies,
counteracting the tendency of gas collapsing in
such halos to form cuspy baryonic profiles.
However, the ab-initio formation of a realistic
rotationally supported disk galaxy with a pure
exponential disk in a fully cosmological
simulation is still an open problem.
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However, see solution

• Increase resolution to 107 mass elements.
• Add supernova feedback of types I and II
• Repeat (Quinn et al)

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Alternate approach put in cosmological context,
but model the components separately without
attempting hydro
A simple model for the evolution of disc
galaxies the Milky Way Naab, Thorsten
Ostriker, Jeremiah P. (MNRAS 366,8992006) A
simple model for the evolution of disc galaxies
is presented. We adopt three numbers from
observations of the Milky Way disc, Sd the local
surface mass density, rd the stellar scalelength,
Vc, the amplitude of the rotation curve, and
physically, the local Kennicutt star formation
prescription, standard chemical evolution
equations assuming a Salpeter initial mass
function and a model for spectral evolution of
stellar populations. We can determine the
detailed evolution of the model with only the
addition of standard cosmological scalings with
the time of the dimensional parameters. A
surprising wealth of detailed specifications
follows from this prescription including the
gaseous infall rate as a function of radius and
time, the distribution of stellar ages and
metallicities with time and radius, surface
brightness profiles at different wavelengths,
colors, etc.
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Same but better Schoenrich and Binney (astroph
0809.3006S)
Models of the chemical evolution of our Galaxy
are extended to include radial migration of stars
and flow of gas through the disc. The models
track the production of both iron and alpha
elements. A model is chosen that provides an
excellent fit to the metallicity distribution of
stars in the Geneva-Copenhagen survey (GCS) of
the solar neighbourhood, and an acceptable fit to
the local Hess diagram. The model provides a good
fit to the distribution of GCS stars in the
age-metallicity plane although this plane was not
used in the fitting process. Although this
model's star-formation rate is monotonic
declining, its disc naturally splits into an
alpha-enhanced thick disc and a normal thin disc.
In particular the model's distribution of stars
in the (O/Fe,Fe/H) plane resembles that of
Galactic stars in displaying a ridge line for
each disc. The thin-disc's ridge line is entirely
due to stellar migration and there is the
characteristic variation of stellar angular
momentum along it that has been noted by Haywood
in survey data. Radial mixing of stellar
populations with high sigma_z from inner regions
of the disc to the solar neighbourhood provides a
natural explanation of why measurements yield a
steeper increase of sigma_z with age than
predicted by theory. The metallicity gradient in
the ISM is predicted to be steeper than in
earlier models, but appears to be in good
agreement with data for both our Galaxy and
external galaxies. The absolute magnitude of the
disc is given as a function of time in several
photometric bands, and radial colour profiles are
plotted for representative times.
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What have we learned?

• Very high resolution (N 107) and SN feedback
  are both necessary.
• For lower mass systems cool gas accretion is
  important at late times (Weinberg, Katz Dekel,
  Birnboim).
• Cooling time of gas is shorter than the dynamical
  time and star formation continues via accretion
  of gas to discs which become the familiar spiral
  systems.

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Conclusions High Mass Systems

• High resolution SPH simulations without feedback
  produce normal, massive but small elliptical
  galaxies at early epochs.
• Accreted smaller systems add, over long times a
  lower metallicity stellar envelope.
• Physical basis for cutoff of star-formation is
  gravitational energy release of infalling matter
  acting through -PdV and Tds energy input to the
  gas (RO, 1973)
• Feedback from SN and AGN is a real phenomenon -
  but secondary and mainly important for clearing
  out gas at late times.

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Conclusions Lower Mass (predominantly spiral)
Systems

• Preliminary hydro simulations indicate cool gas
  accretes onto disks (around old bulges) and
  produces familiar spiral late forming galaxies.
• Physical basis for transition is cooling time vs
  in-fall time of gas. input to the gas.
• Dynamical evolution at late times is important.
• Major mergers at late times are relatively
  unimportant (would overly thicken discs if they
  occurred), but satellite accretion is significant.