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Conference summary

Catherine CesarskyESO

Moriond, March 2005

When UV meets infrared

• (and everything from gamma rays to radio)

• Do we see the same sources in UV and IR?

GALEX 24 micron MIPS

IRAC GOODS

Summary

1. By selection, UV galaxies and IR galaxies have very different characteristic IR/UV ratios (the means differ by a factor of 10). 2. The morphological and stellar mass distributions of the two populations have good overlaps (> 70%). IR galaxies tend to be more massive and earlier types, with an excess of interacting galaxies, and UV galaxies to be less massive and later types.3. UV galaxies are less clustered than IR galaxies.

4. Galaxies with the highest SFR (>100 M /yr, Ltot > 1012 L ),

are missed in the UV samples.5. A population of low metallicity (< 1/10 solar), low mass (<10^9 M ) dwarf UV galaxies (prototype I Zw 18) are `IR quiet’, with the IR/UV ratio ~ 0.3 or less. They occupy only a few percent of a UV selected sample.

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Moriond 2005VC

UV/mid-IR comparison of two LIRGsUV/mid-IR comparison of two LIRGs

Charmandaris, Le Floc’h, Mirabel, ApJ, 2004, 600, L15

At z~2: UV --> R-/I- band & ISO/CAM 7μm -> Spitzer/MIPS24.

The poor spatial at z~2 will result in blending of the emission from the unresolved interacting components. An increased scatter will thus be introduced in the observed optical to mid-IR colors of these galaxies, leading to a

systematic underestimation of their dust content.

7μm/UV ~ 800:10:35 7μm/UV ~ 330:160:190

Images: HST/STIS UV - Contours: ISOCAM 7μm

• Do we need UV to understand star formation?

• YES, at least in some cases (low obscuration)

Rest UV Traces Star Formation

Over Large Range of Specific Star Formation & SFR/Area

What gives???

gas ranges 20:1

gas 1.4 ranges 70:1

Milky Way

Luminous UV Galaxies

Low SurfaceBrightnessGalaxies

Early Type Gals

( )* *

** / age

M tM= =

Shortcut to SFH

• b-parameter vs. NUV-r color

– Obtain b from color alone– Works when no spectra are

available– Valuable for high z– Spread in x-direction due to

internal extinction

( )* *

** / age

M tM= =

NUV-r b

Rest UV Traces Star Formation

Over Large Range of Specific Star Formation

H and UV radial profiles Thilker, Meuer, et al

• Radial profile differences seen in other galaxies

• Not all galaxies show H deficit

•Star clusters as indicators/ demonstrators of star formation

• Do we need IR to understand star formation?

• YES, especially for the brightest galaxies

• Can the different star formation indicators be reconciled?

• Sometimes…

Ha/UV in SDSSTreyer, Johnson, et al.

• Ha/UV shows systematic trend

Higher LUV, Blue NUV-r

L(Ha)/L(UV)~Kennicutt

Low LUV, Red NUV-r

L(Ha)/L(UV) > Kennicutt

OII line & UV luminosities underestimate SFR values by factors 5 to 100 for starbursts & LIRGs !

SFRs as estimated by UV, [OII] & IR(Hammer et al, Venice 2003, proceedings, astro-

ph/0401246)

SFRSFRNUVNUV vs. SFR vs. SFR

dustdust

Quite good agreement on average but...Quite good agreement on average but...lo

FRdust (

log SFRNUV (Msun yr-1)

● At low values of At low values of AANUVNUV, the dust , the dust

emission emission underestimates the underestimates the total SFR because of total SFR because of the non negligible the non negligible NUV emission.NUV emission.● At high values of At high values of AANUVNUV, the NUV , the NUV

emission emission underestimates the underestimates the total SFR. total SFR. Problem with AProblem with ANUVNUV??

Two different trends are observed:Two different trends are observed:

log SFRNUV (Msun yr-1)

FRdust

Estimating extinctions and SFRs at z ~1

(Flores et al, 2004, A&A 415, 885)FORS2/ISAAC: 16 ISO galaxies, 0.4< z <1

- extinction corrected H SFRs are close to mid-IR estimates (Elbaz et al, 2002) for SFR < 150 MO/yr (i.e. below ULIRGs)

more robust SFR estimates

-luminous IR galaxies (not ULIRGs) dominates the cosmic star formation density at z~1 (confirmed by Spitzer, Le Floch et al, 2004)

less than 20% of the star formation density is coming from extremely dust enshrouded regions

•Deep IR surveys: do we understand what we see?

•Probably, but…

EBL: optical vs IR

CIRB~ 1.5 OPT IGL

In local universe, about 30% bolometric light in IR; LIRGs, ULIRGs produce 2% of bolometric luminosity

However,distant universe is IR.

Due to LIRGs? How distant?

LW3z=0

Typical galaxyspectra

K-corrections

LW3 15

LW2 6.7

CIRB peak: 140 m

Individual galaxies peak: 60 to 100 m

Peak shifted to 140 m

if z=0.4 to 1.3 (<z>~0.85)

15 m 8 m

z=0.85 z=0

140 m 80 m

ISOCAM deep surveys in LW3 (12-18 m):

Ideal to detect redshifted PAH for z~0.85 (or in general at z<1.5)

Number Counts• Roughly in agreement with

ISOCAM results • Some confused ISOCAM

sources are resolved by Spitzer• The HDF-N pilot study is not an

unbiased survey• Marleau et al. (2004) find 24

m number counts peak at fainter flux than 15 m counts

• difference b/w 15 and 24 m counts is not the result of confusion of ISOCAM sources or systematic differences between the observatories

From the MIR ? From the MIR ?

Local universe : correlation MIR – LIR Local universe : correlation MIR – LIR (Elbaz et al, 2002)

correlation radio-MIR correlation radio-MIR (Codon 1992, Yun et al, 2001)

or radio is a tracer of LIRor radio is a tracer of LIR

MIR + local templates or correlations => FIR=> LIR => SFRMIR + local templates or correlations => FIR=> LIR => SFR Chary & Elbaz 2001 Kennicutt 1998Chary & Elbaz 2001 Kennicutt 1998

Dale & Helou, 2002 Dale & Helou, 2002 Lagache et et al, 2004Lagache et et al, 2004

…… ……....

M82(disque)

(Laurent et al. 2000)

15 m vs IRIR vs IRAS 12 mIR vs ISOCAM 15 m

24m Spitzer-MIPS

15m ISOCAM

SED of a LIRG at z=0.69 (LIR~10SED of a LIRG at z=0.69 (LIR~1011.111.1 L L,SFR~22 M,SFR~22 Myr-1)yr-1)

The PAH bump exists at z=0.7The PAH bump exists at z=0.7

50 % stars born z<1.5 (70 % universe age)36 % @ z<1 (57 %)67 % @ z<2 (76 %)

Proportion of present-day stars born in LIRGs > 50 %==> Common phase experienced by all/most galaxies...

LIRGs and cosmic star formation

General 24m differential counts (this work, Chary et al. 2004, Papovich et al. 2004)

Model predictions Model predictions SS2424/S/S1515 as a function of z, Sas a function of z, S2424Model predictions Model predictions SS2424/S/S1515 as a function of z, Sas a function of z, S2424

S > 2-3 mJyS > 2-3 mJy dominated by dominated by objects with Sobjects with S2424/S/S15152-2.52-2.5

S S 0.3 mJy 0.3 mJy dominated by dominated by objects with Sobjects with S2424/S/S15 15 1.51.5

S < 0.2-0.3 mJyS < 0.2-0.3 mJy dominated dominated by objects with Sby objects with S2424/S/S15 15 > 2-3 > 2-3 -> NEW POPULATION !-> NEW POPULATION !

S > 2-3 mJyS > 2-3 mJy dominated by dominated by objects with Sobjects with S2424/S/S15152-2.52-2.5

S S 0.3 mJy 0.3 mJy dominated by dominated by objects with Sobjects with S2424/S/S15 15 1.51.5

S < 0.2-0.3 mJyS < 0.2-0.3 mJy dominated dominated by objects with Sby objects with S2424/S/S15 15 > 2-3 > 2-3 -> NEW POPULATION !-> NEW POPULATION !

R-band mag versus Flux@24μm

Rencontres de Moriond, March 6-12th 2005

80% completeness limit at 24μm

VERY hard to be complete in the redshift identification at any 24μm flux, using VVDS/GOODS/COMBO-17

IR luminosities in the CDFS

2635 sourceswith redshifts

* Modest IR emitters at 0<z<0.5

* ULIRGs : quite rare at 0<z<1

* LIRGS: significant contribution at z>0.5

* More « normal » starbursts are not negligible neither

80% completeness limit

Star formation history at z<1

LIRGs/ULIRGs dominate beyond z~0.7

Chary & Elbaz 2001

Blain et al. 2002

Lagache et al. 2004

. . . . . .

_ _ _ _ _

ULIRGs

L >10 L .11

L <10 L .11

Compilation by Hopkins 2004

Moriond 2005VC

V. Lebouteiller – Moriond 2005

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