Deep far-IR surveys and source counts
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Deep far-IR surveys and source counts
G. Lagache Institut d’Astrophysique Spatiale
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• Standard model of cosmological structure formation:– Very successful in the description of the formation of LSS
– Small adiabatic perturbations amplified by self gravity
– Linear development of the density perturbations modeled by well-known physics
• Description of the non-linear phase: (of the baryonic component)– More complicated
– Model the thermal balance (depends on the chemistry and hydrodynamics of the baryonic gas)
• Major numerical simulations (e.g. GalICS project, IAP)
• Main problems: « overcooling problem»
=> Observe small structures that are becoming non linear first
Galaxy formation
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Observations relevant to the problem of star and galaxy formation at high z:
– Cosmic Infrared-submm Background (CIB)see Hauser & Dwek 2001 for a review
– Power spectra of the unresolved background in the far-IRLagache & Puget 2000, Matsuhara et al. 2000, Miville-Deschênes et al. 2002
– Deep number counts of IR galaxies from mid-IR to mme.g. Dole et al. 2001, Serjeant et al. 2001, Elbaz et al. 2002, Scott et al. 2002,
Papovich et al. 2004, Dole et al. 2004….
– Identifications and multi-wavelength observations of IR galaxies
Status of IR-submm observations
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• Find discrepancies with present theories of structure formation• Plan future observations
Empirical models
• Basic inputs of empirical models:– Luminosity functions of a small number of populations of IR galaxies as a
function of z– Set of templates of SED
e.g. Devriendt & Guiderdoni 2000, Wang & Biermann 2000, Chary & Elbaz 2001, Dole et al. 2001, Franceschini 2001, Lagache et al. 2003, Malkan & Stecker 2001, Pearson 2001, Rowan-Robinson 2001, Takeuchi et al. 2001, Xu et al. 2001, Wang 2002, Chapman et al. 2003, …..
• Investigate the basic capabilities of the future missions:– Sensitivity– Resolving power to beat confusion– Capabilities to cover large enough areas to find rare distant sources
Status of empirical models in the IR
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The Model
• Features
– Phenomenological (backward evolution)
– Valid in the range: 5 m to 2 mm
– Fast, Portable, Available (http://www.ias.fr/PPERSO/glagache/act/gal_model.html)
– No source clustering
– Convenient tool to plan further observations
Lagache, Dole, Puget, 2003, MNRASLagache et al., 2004, APJSS
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Galaxy SEDs
Lagache, Dole, Puget, 2002, MNRAS
SEDs for Starburst Galaxies
1010 Lo
1011 Lo
5. 1011 Lo
3. 1012 Lo
Comparison of SEDs: Starburst & Normal
Galaxies
5. 1011 Lo
Normal
Starburst
Only two populations
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IR luminosity function evolution
Normal StarburstTotal LFLocal LF At high z, (U)LIRGs
dominate the energyproduction
Linked to the merger/interaction phases
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The Model• Features
– Phenomenological (backward evolution)
– Valid in the range: 5 m to 2 mm
– Fast, Portable, Available (http://www.ias.fr/PPERSO/glagache/act/gal_model.html)
– No source clustering
– Convenient tool to plan further observations
• Reproduces
– Source Counts, Galaxy redshift distributions, CIB SED– CIB Fluctuation levels, SPITZER confusion levels (Dole et al. 2003)
Lagache, Dole, Puget, 2003, MNRASLagache et al., 2004, APJSS
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15 m
850 m
24 m
170 m
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The Model• Features
– Phenomenological (backward evolution)
– Valid in the range: 5 m to 2 mm
– Fast, Portable, Available (http://www.ias.fr/PPERSO/glagache/act/gal_model.html)
– No source clustering
– Convenient tool to plan further observations
• Reproduces
– Source Counts, Galaxy redshift distributions, CIB SED
– CIB Fluctuation levels, SPITZER confusion levels
• One exemple of cosmological implications:
– The PAHs features remain prominent in the redshift band 0.5-2
– The IR energy output has to be dominated by ~2 1011 Lo to ~3 1012 Lo galaxies from z~0.5 to 2.
Lagache, Dole, Puget, 2003, MNRASLagache et al., 2004, APJSS
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Predictions for Herschel and ALMA
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Surface (m) Days 5inst (mJy) Smin (mJy) Nsources %CIB
20 Sq. Deg. 170 88 7.08 10.0 7322 49
625 Sq. Arcmin
110 67 0.89 1.26 1955 77
25 Sq. Arcmin 75 96 0.13 0.18 192 87
The Herschel/PACS cosmological surveys
• Designed surveys that could be done with PACS :
5inst = Slim
= Conf. limit
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Sq. deg 5inst 5conf 5tot Days Nsources %CIB400 100 mJy 28.2 103.9 18 4768 1
100 15.3 22.4 27.1 192 33451 6.7
8 7.5 22.4 23.6 64 3533 7.8
The Herschel/SPIRE cosmological surveys• Designed surveys that could be done with SPIRE (350 m):
__ 400 Sq. deg. (x2)- - 100 Sq. deg
z=1.0
z=0.7 z=2.5
z=0.5
100 Sq. deg.
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Herschel will…
– Give for the first time complete IR SEDs.• Combined with SPITZER: from 3.6 to 550 microns.
• Fill the « far-IR desert » (between 160-850 microns)
– Resolve the peak of the CIB
- NOT probe the CIB at long wavelengths
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• Large area survey:– GOAL: Find 3 1011 Lo galaxies at z~5
– 1 Deg2, 5 = 0.1 mJy (50% of CIB)
– 138 days (30 000 sources)
• A deeper survey:– GOAL: 80% of the CIB
– 10 arcmin2, 5=0.02 mJy
– 96 days (200 sources)
• A total of ~8 months (without including overheads)
ALMA capabilities for surveys at 230 GHz
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So what?• Future surveys: (SPITZER), Herschel, Planck• For >150 m: confusion-limited
- Resolved CIB: <10% (~50% for SCUBA/MAMBO blank surveys)
- Brightest contributors - Clustering of IR galaxies?
ALMA:- Reveal, in the high-z galaxies, the astrophysical processes at work- Problem: find these high-z objects (>8 months in the final config)
Informations on the underlying population andconstraints on the clustering of IR galaxies:
=> Studying the CIB fluctuations
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The CIB fluctuations:
A « tool» for studying the source Clustering
Probe the LSS at high z
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• Same sources (shape of the counts)• You probe the fluctuations = you probe the CIB • P(D) analysis: number count distribution• Statistical informations on the SEDs• Clustering:
– On large angular scales: linear clustering bias of far-IR galaxies in dark matter halos
– On smaller angular scales: non-linear clustering within a dark matter halo
• Problem: detecting them! (Component separation)
• Detection of the shot noise at 60, 100, 170m (Miville-Deschênes et al. 2003, Lagache &Puget 2000, Matsuhara et al. 2000)
The CIB and its fluctuations (>100 m)
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Cirrus/CIB power spectra at 550 m
IR gal Poisson
(Slim=103.9 mJy)
Cirrus (NHI=1, 2, 3 1020 at/cm2)
IR gal clustering
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FIRBACK 170 m: constraint on b
b=3
Diamonds: FIRBACK observations
b=0.6
Poissonian (from the model)
- IR emissivities: - IR emissivities: jj//j j = = bb ( (//))dark matterdark matter
- FIRBACK observations => bFIRBACK observations => b≤0.6≤0.6 (N. Fernandez et al.)(N. Fernandez et al.)
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• Longer probe to higher z• CIB fluctuation maps (100 m => 1 mm)
– IRAS (IRIS, Miville-Deschênes & Lagache, 2004), SPIRE, Planck/HFI
• Waveband decorrelation => « Invert » fluctuation maps / z
• Clustering in function of z
• Seems very easy!!
Fluctuations of the CIB
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• Longer probe to higher z• CIB fluctuation maps (00 m => 1 mm)
– IRAS/IRIS, SPIRE, Planck/HFI
• Waveband decorrelation => « Invert » fluctuation maps / z
• Clustering in function of z
• Seems very easy!!
Fluctuations of the CIB
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Exemple of decorrelation
F(250) F(250) – F(100)
F(850) F(850) – F(250) – F(100)
F(1380) F(1380) – F(850)
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Panchromatic IR Sky
MIPS 24 m MIPS 70 m MIPS 160 m
Simulated sky: 5 squares degrees
Dole, Lagache, Puget, 2003, ApJ
Towards including the correlations…
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Conclusions
- Dust emission and extinction: Key processes at high-z => Large IR/submm/mm surveys
- In the Far-IR/Submm: current and planned surveys are and will be confusion-limited
- Except for ALMA (but need time…)
-Before ALMA: Study the clustering using the CIB anisotropies with Planck/HFI and Herschel/SPIRE
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Herschel follow-up observations
– PACS: no problem for source identification
– SPIRE: use band merging technique (as for SPITZER) when PACS data are available to extract sources
– In areas where we have only SPIRE data :
• Build an « extreme source sample »
• Use the same technique as for the SCUBA/MAMBO sources: interferometry
• Problem: about 3000 sources with z>3
(and about 9000 with z>2)
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• Large area survey: (3 1011Lo objects)– 1 Deg2, 5 = 0.21 mJy– Need 4289 years !!
=> The L=3 1011 Lo objects will not be found at 350 microns
(5 observation days for ONE source 3 1011 Lo at z~5)
The 850 GHz is not suited for cosmological surveys
ALMA capabilities for surveys at 850 GHz
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• « overcooling problem»– The fraction of the predicted baryonic mass that fragment and
form stars is clearly larger than what is observed
– The mass distribution of galaxies should also contain more dwarf galaxies than it does
– The baryonic gas collapses to the center of the potential well loosing its angular momentum to the non dissipative dark mater component.
Main unresolved problem in gal. formation