Deep far-IR surveys and
source counts
G. Lagache
Institut d’Astrophysique Spatiale
Galaxy formation
• 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
Status of IR-submm observations
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-IR
Lagache & Puget 2000, Matsuhara et al. 2000, Miville-Deschênes et al. 2002
– Deep number counts of IR galaxies from mid-IR to mm
e.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 empirical models in the IR
• 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
The Model
• Features
– Phenomenological (backward evolution)
– Valid in the range: 5 mm 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, MNRAS
Lagache et al., 2004, APJSS
Galaxy SEDs
SEDs for Starburst Galaxies
3. 1012 Lo
5. 1011 Lo
1011 Lo
1010 Lo
Comparison of SEDs:
Starburst & Normal Galaxies
5.
1011 Lo
Normal
Starburst
Only two populations
Lagache, Dole, Puget, 2002, MNRAS
IR luminosity function evolution
Normal
Starburst
Total LF
Local LF
At high z, (U)LIRGs
dominate the energy
production
Linked to the merger/
interaction phases
The Model
• Features
– Phenomenological (backward evolution)
– Valid in the range: 5 mm 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, MNRAS
Lagache et al., 2004, APJSS
15 mm
24 mm
170 mm
850 mm
The Model
• Features
– Phenomenological (backward evolution)
– Valid in the range: 5 mm 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, MNRAS
Lagache et al., 2004, APJSS
Predictions for Herschel and ALMA
The Herschel/PACS cosmological surveys
• Designed surveys that could be done with PACS :
Surface
l (mm) Days
5sinst (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
5sinst = Slim
= Conf. limit
The Herschel/SPIRE cosmological surveys
• Designed surveys that could be done with SPIRE (350 mm):
Sq. deg 5sinst
5sconf
5stot
Days
Nsources %CIB
400
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
100 Sq. deg.
__
400 Sq. deg. (x2)
- - 100 Sq. deg
z=1.0
z=0.7
z=0.5
z=2.5
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
ALMA capabilities for surveys at 230 GHz
• Large area survey:
– GOAL: Find 3 1011 Lo galaxies at z~5
– 1 Deg2, 5s = 0.1 mJy (50% of CIB)
– 138 days (30 000 sources)
• A deeper survey:
– GOAL: 80% of the CIB
– 10 arcmin2, 5s=0.02 mJy
– 96 days (200 sources)
• A total of ~8 months (without including overheads)
So what?
• Future surveys: (SPITZER), Herschel, Planck
• For l>150 mm: 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 and
constraints on the clustering of IR galaxies:
=> Studying the CIB fluctuations
The CIB fluctuations:
A « tool» for studying the source
Clustering
Probe the LSS at high z
The CIB and its fluctuations (l>100 mm)
•
•
•
•
•
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, 170mm
(Miville-Deschênes et al. 2003, Lagache &Puget 2000, Matsuhara et al. 2000)
Cirrus/CIB power spectra at 550 mm
Cirrus (NHI=1, 2, 3 1020 at/cm2)
IR gal clustering
IR gal Poisson
(Slim=103.9 mJy)
FIRBACK 170 mm: constraint on b
- IR emissivities: j/j = b (/)dark matter
- FIRBACK observations => b≤0.6
(N. Fernandez et al.)
b=3
b=0.6
Poissonian (from the model)
Diamonds: FIRBACK observations
Fluctuations of the CIB
• Longer l probe to higher z
• CIB fluctuation maps (l~100 mm => 1 mm)
– IRAS (IRIS, Miville-Deschênes & Lagache, 2004), SPIRE, Planck/HFI
• Waveband decorrelation
=> « Invert » fluctuation maps l / z
• Clustering in function of z
• Seems very easy!!
Fluctuations of the CIB
• Longer l probe to higher z
• CIB fluctuation maps (l~100 mm => 1 mm)
– IRAS/IRIS, SPIRE, Planck/HFI
• Waveband decorrelation
=> « Invert » fluctuation maps l / z
• Clustering in function of z
• Seems very easy!!
Exemple of decorrelation
F(250)
F(850)
F(1380)
F(250) – F(100)
F(850) – F(250) – F(100)
F(1380) – F(850)
Panchromatic IR Sky
Simulated sky: 5 squares degrees
MIPS 24 mm
MIPS 70 mm
MIPS 160 mm
Dole, Lagache, Puget, 2003, ApJ
Towards including the correlations…
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
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)
ALMA capabilities for surveys at 850 GHz
• Large area survey: (3 1011Lo objects)
– 1 Deg2, 5s = 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
Main unresolved problem in gal. formation
• « 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.