Deep far-IR surveys and source counts

G. Lagache Institut d’Astrophysique Spatiale

• 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

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

• 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

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

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

IR luminosity function evolution

Normal StarburstTotal LFLocal LF At high z, (U)LIRGs

dominate the energyproduction

Linked to the merger/interaction phases

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

15 m

850 m

24 m

170 m

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

Predictions for Herschel and ALMA

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

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.

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

• 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

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

The CIB fluctuations:

A « tool» for studying the source Clustering

Probe the LSS at high z

• 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)

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

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.)

• 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

• 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

Exemple of decorrelation

F(250) F(250) – F(100)

F(850) F(850) – F(250) – F(100)

F(1380) F(1380) – F(850)

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…

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)

• 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

• « 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