Galactic Archaeology: Mining the Fossil Record of Disk Galaxies

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Galactic ArchaeologyMining the Fossil Record of
Disk Galaxies
Brad Gibson
University of Central LancashireJeremiah
Horrocks Institute for Astrophysics
Supercomputing
Stephanie Courty, Chris Brook, Patricia
Sanchez-Blazquez, Greg StinsonElisa House,
Gareth Few, Simon RichardRomain Teyssier,
Daisuke Kawata, Hugo Martel
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Preston The Jeremiah Horrocks Institute

• ?40 staff students
• Galactic Archaeology Group est 2006 recent
  permanent appointments (besides me)
  Debattista, Popescu, Stinson, 4th in neg. 3-4
  PDRAs Brook, Sanchez-Blazquez, Courty

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The Family Tree
Brad Gibson
2nd Cousins, Twice Removed!
?
Paul HIckson
James Gunn
John Norris
Mike Bessell
Guido Munch
Alex Rodgers
Leonard Searle
Chandrasekhar
Richard Woolley
Ralph Fowler
Eddington
Archibald Hill
Robert Herman
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Disk Galaxy Formation 101
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Galactic ArchaeologyMining the Fossil Record of
Disk Galaxies
Observations
Structure
Chemistry
Kinematics
Modeling
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Galactic ArchaeologyMining the Fossil Record of
Disk Galaxies
Structure
Chemistry
Kinematics

• DM vs stars vs gas
• gradients (vertical and radial)
• bulge-to-disk ratios
• abundance patterns
• thick vs thin disks
• stellar populations
• warps, lopsidedness
• disk heating
• radial migration

• anomalous velocity clouds
• age-metallicity relation
• metallicity distribution functions
• isotopic patterns
• streams and debris
• gas infall and mass assembly
• star formation histories
• dust
• scaling relations

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Galactic Archaeology 5 Questions for Today

• How do you construct chemodynamical models of
  galaxies?
• Should I avoid SPH when simulating galaxies?
• Do stars in the disk move around much during
  their life?
• What are high velocity clouds?
• What does the future hold?

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Constructing Chemodynamical Models? SPH
Kawata Gibson (2003ab20042005)
Parent Low-Resolution Cosmological Dark Matter
Simulation (100kpc scales)
Re-simulate Region of Interest with Increased
Particle numbers (Resolution) Baryonic Physics
(sub-kpc scales)
B-band
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Particles vs Grids

• Two common approaches employed to solve Poissons
  equation (andtherefore determine the
  gravitational potential)
• direct particle-particle summation (eg. Tree
  codes, GADGET, PKDGRAV/Gasoline, GCD, etc)
• numerically integrate by introducing mesh upon
  which to define density, and employ FFTs
  introduce finer meshes in regions of
  high-density (eg. Enzo, AMIGA, ART, RAMSES, etc)

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Constructing Models? AMR
Sanchez-Blazquez, Gibson, Courty Brook (2009)

• parent cosmological dark matter simulation
• select halo randomly
• zoom-style re-simulation w/8 more levels
  w/baryonic physics (res 200pc 104-5 M?)
• analyse

We may not be the first, but were the first with
a gridcode (to z0, anyways) cf. Sommer-Larsen
et al (2003) Abadi et al (2003) Governato
et al (2004,2007) Robertson et al (2004)
Okamoto et al (2005) Bailin et al (2005)
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Particles vs Grids Differences Do Exist! ?
redundancy/sanity checks are important

• Gas Mass Fraction
• Entropy Profile
• Ram Pressure Stripping

• factor of 10 scatter
• mesh codes sit systematically high, well
  within virial radius

Frenk et al (1999) OShea et al (2005) Agertz
et al (2007)
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Particles vs Grids Differences Do Exist! ?
redundancy/sanity checks are important

• Gas Mass Fraction
• Entropy Profile
• Ram Pressure Stripping

• 50 scatter
• Mesh codes sit systematically high, well
  within virial radius

Frenk et al (1999) OShea et al (2005) Agertz
et al (2007)
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A Fundamental Problem for SPH?
Agertz et al (2007)
Gasoline
SPH and AMR simulations of a gas cloud moving
sub-sonically through ahot halo (101 ?
contrast) SPH in its standardimplementation
does apoor job of capturingshocks and K-H,
R-T,R-M instabiities
SPH
Gadget
Enzo
Flash
AMR
ART
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A Fundamental Problem for SPH?

• Should we trust SPH-based simulations?

Artificial vacuumlayers througherroneouspressur
e forcesdue to incorrectdensity calculationsat
density gradients
Agertz et al (2007)
Basically, low-density SPH particles near to
high-density regions suffer asymmetric pressure
forces, due to asymmetric density within the
kernel
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Galactic ArchaeologyMining the Fossil Record of
Disk Galaxies
Brad Gibson
University of Central Lancashire
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Explosive Welding
Brad Gibson
University of Central Lancashire
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All is not lost for SPH Explosive Welding
Explosive force brings the surfaces togetherat a
collision front front velocity ltcs so thatshock
wave precedes the bond pressuresexceed yield
strength ? plastic deformation
Generate Kelvin-Helmholtz and Richtmyer-Meshkov
(impulsive-acceleration limit of the
Rayleigh-Taylor) instabilities which activate
Karman vortices
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Explosive Welding SPH Simulations
SPH simulations of subsonic shocks and captured
Richtmyer-Meshkov (Rayleigh-Taylor)
instabilities (31 ? contrast)
Tanaka (2008)
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Astrophysics SPH MkII
Introduction of artificial thermal conductivity
term rectifies lack of treatment of contact
discontinuities in standard SPH (21 ? contrast)
Rich literature with successfulvariants of
traditional SPH Balsara (1994) Owen et al
(19961998) Maron Howes (2003)
Price (2008)
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Astrophysics SPH MkII - GCD
Kawata, Okamoto, Cen Gibson (2009)
3d KHI Testw/GCD andPrice (2008)artificial
conductivityterm (GCD ? our
cosmological chemodyamical N-body / SPH
code)
(cluster entropy problem also fixed)
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Astrophysics SPH MkII - GCD
Kawata, Okamoto, Cen Gibson (2009)
3d KHI Testw/GCD andPrice (2008)artificial
conductivityterm (GCD ? our
cosmological chemodyamical N-body / SPH
code)
(cluster entropy problem also fixed)
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Galactic ArchaeologyMining the Fossil Record of
Disk Galaxies
Brad Gibson
University of Central LancashireJeremiah
Horrocks Institute for Astrophysics
Supercomputing
Stephanie Courty, Chris Brook, Patricia
Sanchez-Blazquez, Greg StinsonElisa House,
Gareth Few, Simon RichardRomain Teyssier,
Daisuke Kawata, Hugo Martel
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What We Found (or are finding)

• Basic Characteristics
• Disk Kinematics
• Disk Chemistry
• Disk Edges
• Accretion History
• Future Directions

Data looking for exploitation please send
suggestions.
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Basic Characteristics
B/D?0.3 ??0.02 fast rotating galaxy occupying
a low-spin halo
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Comparing Star Formation Histories
cf. Bailin et al (2005) cosmological disk
(GCD w/Abadi et al (2003) ICs) Brook et
al (2004) semi- cosmological disk (both SPH)
(Bailin)
(Brook)
cf. Fenner, Murphy Gibson (2005)semi-numerical
MW model
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Metallicities
Gas
60 kpc
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Disk Kinematics Disk Heating the Thick Disk
House, Brook, BKG (2009)
(AMR)
(AMR)
Holmberg et al (2007)
Thick disk?
Quillen Garnett (2001)
Q Born hot or did they get heated?
A Born cold and they were heated.
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Disk Kinematics Disk Heating the Thick Disk
House, Brook, BKG (2009)
Recall Stars are born cold and subsequently
heated.
(AMR)
(AMR)
Numerical effects may still be a problem
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Disk Edges Gas
BKG et al (2009), if I have to
Lopsided HI gas disk with truncation nearR19kpc
and NHI2x1019 cm-2 cf. THINGS (nice
agreement)
N(HII)
N(HI)
Extended ionised disk cf. Bland-Hawthorn et al
(1997)
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Disk Edges Stars / Radial Migration
Sanchez-Blazquez, BKG, Courty Brook (2009) cf
Roskar et al (2008ab)
.. but.. radial migration does occur
Bandpass / HeightIndependent Breaks
U-shaped age behaviourreflected in colour
gradientsdifferential star formation ininner
vs outer disk (cf. Roskar)
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Disk Edges Stars / Radial Migration
Sanchez-Blazquez, BKG, Courty (2009) cf Roskar
et al (2008ab)
Break in the pure exponential stellarsurface
brightness profile due to decrease in the star
formation per surface area, itself produced by
adecrease in the gas volume densitydue to a
warping of the gas disc.
Ratio of surface mass to gas volume density
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Disk Edges Stars / Radial Migration
Sanchez-Blazquez, BKG, Courty (2009) cf Roskar
et al (2008ab)
Colour profiles as a function of a redshift
Predicted (open) vs Observed (filled) Evolution
of Disk Size Surface Brightness
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Radial Migration the Age-Metallicity Relation
Sanchez-Blazquez, BKG, Courty (2009) cf Roskar
et al (2008ab)
Solar Neighbourhood AMRfrom RAMSES Disk
Simulation
AMR in the absence of migration
Radial migration produces flattening and
increased scatter in the AMR, consistent with
that observed.
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Gas Accretion History
Courty, BKG, et al. (2009) cf Dekel et al
(2008), Ocvirk et al (2008)
1 ? 0.5 M?/yr of gas flux at R30 kpc
cf. Fenner et al (2005)semi-numerical MW model
Is there any evidence of this infall?
2 ? 1 M?/yr of vertical gas flux at z6 kpc
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Accretion, HVCs, and the Missing Satellites?
Wakker (2001)
Local GroupAnti-barycentre
Local GroupBarycentre

• kinematics inconsistent with Galactic rotation
  (vLSR gt 100 km/s)
• large sky covering factor (gt40)
• 60 of HVC HI flux from Mag Stream (15 from
  Complex C)
• origin scenarios fountains, tidal debris,
  building blocks?
  (there are
  1000s of them)

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Direct Distances 2009 Scorecard
Nine HVC/Complexes with confirmed distances lt10
kpc
Mag Stream 5x108 M?Non-Mag Stream
1x107 M?
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What are they then?

• what they are not
• Local Group CDM substructures distributed on Mpc
  scales

• what they (likely) are
• by mass, 98 are associated with the
  Magellanic Stream and so many HVCs are
  clearly tidal debris
• outflow models Mag Stream consistent with bulk
  of the observational properties and/or
• infalling CDM substructures distributed on kpc
  scales and/or
• thermally-unstable clouds condensing out of the
  hot corona

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Galactic Archaeology 5 Questions for Today

• How do you construct chemodynamical models of
  galaxies?Run a low-resolution cosmological
  N-body (collisionless) simulationfind an
  interesting halo find all the particles in and
  around it tracethem all back to high-redshift
  split them and add gas turn on baryonic
  physics (hydrodynamics phenomenological star
  formationand feedback) re-run analyse
• Should I avoid SPH when simulating
  galaxies?Classical implementations of smoothing
  kernel do suffer from aninability to capture
  shocks and instabilities in regions of
  high-densitycontrast, due to strongly asymmetric
  particle distributions within thekernel
  hydrodynamics coupled to an adaptive mesh is less
  susceptiblenew treatments of artificial
  conductivity appear promising mesh-basedapproach
  es more robust in relation to metal diffusion
  (most SPH-basedsimulations provide meaningless
  information on abundance scatter)many (most?)
  problems (but not all) on galactic scales should
  be robust

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Galactic Archaeology 5 Questions for Today

• Do stars in the disk move around much during
  their life?Yes! Three processes are at play
  (1) secular heating from spiral arms, molecular
  clouds, etc, (2) impulsive heating from accretion
  events, (3) numerical heating (not physics,
  unfortunately!) we have not been able to
  ascertain the relative importance of each in
  oursimulations 60 of stars beyond the break
  formed in the innerdisk and were re-distributed
  this migration leads to a pure exponential in
  the mass density, but a break in the light
  profiles.
• What are high velocity clouds? First, they are
  not left-over building blocks from the formation
  of theLocal Group, dispersed on Mpc scales
  those with secure distancemeasures place them
  within ?10kpc their metallicities are
  sub-solar,but within ?0.5-0.8 dex of solar no
  evidence of their existence onMpc scales in
  nearby Local Group analogs likely a combination
  of(1) galactic fountain material (lower-velocity
  tail), (2) tidal debris(Magellanic Stream), (3)
  thermally-unstable clouds condensing outof a
  turbulent corona (support from UV ionisation
  studies)

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Galactic Archaeology 5 Questions for Today

• What does the future hold (lt5yr
  timeframe)?Statistical samples (30-40) of fully
  cosmological disks with both amesh- and
  particle-based approach (RAMSES, GASOLINE,
  GCD)at ?200pc and ?104 M? resolution dynamic
  range in mass, assembly history, environment,
  feedback, and AVAC, in order to betterexplore
  temporal evolution of scaling relations
  self-consistent dustyradiative transfer
  (interviewing in 2 weeks time) port GEtool
  toRAMSES and GASOLINE

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Galactic Archaeology
April 2007