Predictions for surveys with HERSCHEL from a CDM model of galaxy evolution

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Predictions for surveys with HERSCHEL from a CDM
model of galaxy evolution

• Cedric Lacey
• Durham University

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Collaborators on theoretical models

• Galaxy formation models
• Carlton Baugh Durham
• Shaun Cole Durham
• Carlos Frenk Durham
• Andrew Benson Oxford
• Dust Modelling
• Alessandro Bressan Padova
• Gian Luigi Granato Padova
• Laura Silva Trieste

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Galaxy formation in the CDM model key physical
processes

• Assembly of dark matter halos
• Shock-heating and radiative cooling of gas within
  halos
• Star formation and feedback
• Production of heavy elements
• Galaxy mergers

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Galaxy formation made simple

• gas cools to make disks
• halos merge
• galaxies merge by dynamical friction
• major mergers make galactic spheroids from disks
• mergers trigger starbursts
• spheroids can grow new disks

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Modelling the stars dust

• dust in diffuse medium and molecular clouds
• stars form in clouds and leak out
• stellar emission from population synthesis
• radiative transfer of starlight through dust
  distribution
• heating of dust grains -gt dust temperature
  distribution

GRASIL code Silva etal 1998, Granato etal 2000
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More details of dust modelling

• Physical model for dust grains, chosen to
  reproduce local ISM extinction law
• Mixture of graphite silicate grains, with
  distribution of grain sizes
• Includes PAHs (polycyclic aromatic hydrocarbons)

• Assume dust/gas proportional to gas metallicity
• Optical depth for dust depends on both dust mass
  and galaxy radius
• these both predicted by galaxy formation model

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Model for radio emission

• Free-free radiation from HII regions ionized by
  young stars

• Synchrotron radiation from relativistic
  electrons accelerated in supernova remnants
  assume const frac of SN energy radiated

(Bressan, Silva Granato 2002)
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Example Model SED (1)

• unextincted starlight
• ( radio)

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Example Model SED (2)

• starlight with dust extinction

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Example Model SED (3)

• starlight with dust extinction
• emission from diffuse dust

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Example Model SED (4)

• starlight with dust extinction
• emission from diffuse dust molecular clouds

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Example Model SED (5)

• starlight with dust extinction
• emission from diffuse dust molecular clouds
• total

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SEDs from dust model comparison with
observations

• model predicts galaxy spectrum from far-UV to
  sub-mm
• accurately reproduces observed SEDs for nearby
  normal and starburst galaxies

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Important features of galaxy formation model

• Star formation timescale in quiescent disks

• disks more gas-rich at high z
• mergers more gas-rich at high-z

• Bursts triggered by minor and major mergers
• Top-heavy IMF in bursts

Cole etal 2000 Granato etal 2000 Baugh etal 2004
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Cosmic star formation history
total
quiescent
quiescent
bursts
bursts
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Present-day galaxy luminosity functions in
optical near-IR
B-band
K-band
total
total
no dust
quiescent
no dust
quiescent
bursts
bursts
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Present day luminosity functions in far-UV
far-IR
Far-UV (2000 A) Far-IR (60
mm)
total
total
no dust
bursts
bursts
quiescent
quiescent
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Sub-mm source counts
850 mm

• model predicts
• at observed fluxes, counts dominated by galaxies
  with ongoing burst of star formation triggered by
  galaxy merger
• at very faint fluxes, dominated by quiescent disks

total
total
bursts
bursts
quiescent
quiescent
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Redshift distribution of sub-mm sources

• model predicts median z2 for S(850)1-10 mJy
• consistent with observational constraints (e.g.
  Chapman etal 2003, z(median)2.4 at S5mJy)

total
bursts
quiescent
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Galaxy luminosity function in rest-frame UV at z3
Lyman-break galaxies

• Lyman-break galaxies dominated by ongoing bursts
• dust extinction has huge effect on predicted
  luminosity function
• most of UV radiation emitted by stars is
  absorbed by dust

no dust
bursts
total
quiescent
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Predictions for HERSCHEL
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Sensitivities in different bands
Diffraction limit 40 beams per source,
galaxies only
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PACS 60-90 mu
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PACS 90-130 mu
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PACS 130-210 mu
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SPIRE 250 mu
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SPIRE 350 mu
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SPIRE 500 mu
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Comparison with SPITZER 24 70 mu
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Comparison with ASTRO-F
N60 50-75 mu
N170 150-200 mu
WIDE S 50-110 mu
WIDE L 110-200 mu
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Evolution of bolometric (8-1000 mu) LF
Z0
Z2
Z4
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Cumulative fraction of bolometric (8-1000 mu)
luminosity gtL
Z0
Z2
Z4
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Bolometric (8-1000 mu) luminosity vs S(75mu)
Z0.5
Z1
Z2
Z3
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Bolometric (8-1000 mu) luminosity vs S(250mu)
Z0.5
Z1
Z2
Z3
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Bolometric (8-1000 mu) luminosity vs S(500mu)
Z0.5
Z1
Z2
Z3
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Bolometric (8-1000 mu) luminosity vs S(24mu)
Z0.5
Z1
Z2
Z3
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Bolometric (8-1000 mu) luminosity vs S(850mu)
Z0.5
Z1
Z2
Z3
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SFR vs S(250mu)
Z0.5
Z1
Z2
Z3
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Stellar mass vs S(250mu)
Z0.5
Z1
Z2
Z3
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Flux in other bands vs S(250 mu) _at_ z0.5
75mu
500mu 24mu
850mu
1.4GHz I
band
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Flux in other bands vs S(250 mu) _at_ z1
75mu
500mu 24mu
850mu
1.4GHz I
band
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Flux in other bands vs S(250 mu) _at_ z2
75mu
500mu 24mu
850mu
1.4GHz I
band