Ultraviolet and far-infrared observations of Ultraviolet and far-infrared observations of galaxies: constraints on dust attenuationgalaxies: constraints on dust attenuation

V. Buat, J. Iglesias-Paramo, D. Burgarella, A. Inoue, P. Panuzzo, T. Takeuchi

Tracing dust in spiral galaxies:radiative transfer studies in the dawn of a new generation of observing facilities-

Gent 14-16 may 2007

The GALEX surveysThe GALEX surveysP.I: C. Martin, Caltech, participation of CNES/ LAMP.I: C. Martin, Caltech, participation of CNES/ LAM

GALEX satellite, launch: Avril 2003, still observing Imaging mode at 1530 Å (FUV) and 2315 Å (NUV), spatial

resolution ~5 arcsec, FOV~1 deg2

• « All Sky » Shallow Imaging Survey @ 20-21ABmag/14000 fields• Medium Imaging Survey @ 23 ABmag/1200 fields• Deep Imaging Surveys @ 25.5 ABmag/150 fields • Nearby Galaxies Survey: ~1000 galaxies

Slitless spectroscopy in the FUV and NUV bands

X-correlations with surveys at other wavelengths

GALEX sky coverage 10/02/2006GALEX sky coverage 10/02/2006

FIR (60µm) SELECTED SAMPLE • IRAS(PSCZ) / GALEX AIS: UV photometry of each IRAS source 94% detected in FUV-1530A (FUV< 20.5 AB mag) 93% of the sources detected in H (2MASS) stellar masses all the galaxies have a known distance (radial velocity)FUV SELECTED SAMPLE• GALEX (FUV(1530A) / IRAS(FSC) 83% detected at 60 microns 89% of the sources detected in H (2MASS) stellar masses 91% of the galaxies have a known distance (radial velocity)

First samples (Buat et al. 05): ~100 sources in each sampleSecond samples (Buat et al. 06) ~750 sources in each sample

Unfortunately the overlap with SDSS is very small: 20% of the FOV

Z=0 samples and related studies

LTIR/LFUV (i.e. dust attenuation) versus Lbol young stars

(Buat et al. 06, ApJS in press, astroph 0609738)

A general increase of the dust attenuation with the luminosity

(SFR of the galaxies).

Similar trends for different selections for intermediate

luminosities 109<L< 5 1010Lsun but

•For bright IR selected galaxies: a monotonic increase

•For bright UV selected galaxies: some hint for a lower dust attenuation than for IR galaxies of the same Lbol

4 mag

2 mag

0.5 mag

A(F

UV

)

•LTIR : 8-1000 µm, LFUV : . L

•A(FUV) is calculated as a function of log(LTIR/LFUV) using the calibration of Buat et al 2005

(TIR+FUV)

LTIR/LFUV (i.e. dust attenuation) versus Mstar at z=0:

A shallow increase of LTIR/LFUV when Mstar increases

Theoretical modelsTheoretical models show that show that the the FFdustdust/F/FUVUV flux ratio is a robust tracer flux ratio is a robust tracer

of the dust attenuationof the dust attenuation

A(N

UV

) m

ag

Various geometries/dust propertiesGordon et al. 2000

Various star formation histories Buat et al 05 ApJL special issue (GALEX)

The « IRX-ß » in galactic disks

IRX: Ldust/LUV ( sometimes LFIR(40-120 µm)/LUV), a quantitative tracer of dust obscuration

ß: slope of the UV continuum with f() , estimated from the FUV-NUV color for

GALEX data,

ß is expected to be constant after more than 10 Myr of active star formation, any

departure is attributed to a wavelength dependent dust attenuation

A tight relation is found for starburst galaxies (Meurer et al. 99) from IUE and IRAS data

We will focus on studies based on integrated fluxes or data averaged over large disk areas

Meurer et al. 99, starburst galaxies observed by IUE and IRAS

Models predict dispersed relations between Models predict dispersed relations between and the attenuationand the attenuation

((Witt & Gordon 2000Witt & Gordon 2000))

A shell distribution and no bump (SMC) are necessary to reproduce the starburst distribution with these models

The complexity of the IRX-ß plot is The complexity of the IRX-ß plot is confirmed by the first GALEX results confirmed by the first GALEX results

(Buat et al. 05 ApJL GALEX special issue, also (Buat et al. 05 ApJL GALEX special issue, also Seibert et al. 05)Seibert et al. 05)

(~slope with f() )

The galaxies do not follow the starburst relation (solid line, Meurer et al. 99) UV selected galaxies under the line, FIR selected galaxies also above the line

A result already suggested by pre-GALEX A result already suggested by pre-GALEX works but with smaller statisticsworks but with smaller statistics

Bell, 2002, normal galaxies

Goldader et al. 2002, ULIRGs

« IRX-ß » relation for radial profiles in « IRX-ß » relation for radial profiles in galaxiesgalaxies

Boissier et al. 2007 ApJS GALEX special issue astroph/0609071

• Radial profiles for large late-type galaxies with GALEX+IRAS data: again under the « starburst line »

SINGS sample SINGS sample (Dale et al. 06)(Dale et al. 06)

From Cortese et al. 06

How to interpret these results?How to interpret these results?The main parameters at work in the IRX-ß plot:• The star formation history• The dust attenuation: dust characteristics+geometry• The IMF (not discussed here)• Aperture mismatch between UV (IUE) and IR (IRAS)

data for starbursts.• Lots of works about the IRX-ß diagnostic: E.g. Calzetti et al. 05, Boissier et al. 07. Gil de Paz et al. 07, Dale et al. 06, Panuzzo

et al. 07, Inoue et al. 06, Burgarella et al. 05, Kong et al. 04, Bell 02, Cortese et al. 06 etc…

My presentation is obviously not exhaustive and probably biased…

Different star formation histories can lead to some dispersion and may explain the locus of galaxies below the

starburst curve (Kong et al 04)

-2 -1 0 1

L

og(L

du

st/L

FU

V)

b= sfr0/<sfr>Kong et al 2004

Dust attenuation curve from Charlot & Fall (2000)

Only a very weak trend (if any) is observed between the distance to the starburst line and the

birthrate parameter

Panuzzo et al. 2006, UV selection Cortese et al. 06, Virgo galaxies

dS isthe distance from the starburts line

An important An important issue/advantage:issue/advantage:

the GALEX NUV band the GALEX NUV band overlaps the bump at overlaps the bump at 2175 2175 Å of the MW Å of the MW extinction curveextinction curve

MW extinction curves

Starburst attenuation curve

LMC ext. curve

SMC ext. curve

From Calzetti 2001

FUV NUV

GRASIL models with various scenarii of dust attenuationGRASIL models with various scenarii of dust attenuationPanuzzo et al. 07,MNRAS 375, 640

•A modified GRASIL model: age dependent extinction AND molecular clouds (t<tesc) and young stars (t<tthin) concentrated in the galactic plane (small scale height). A MW extinction curve is found consistent with the FTIR/FFUV vs FUV-NUV color: the age-dependent extinction reduces the presence of the 2175 A bump

Starburst line

The role of the albedoThe role of the albedo

Inoue et al. 2006, MNRAS 370, 380 •Young stars (<10 Myr) :clumpy distribution, Molecular Clouds

•10-300Myr old stars: smooth dist, clumpy medium, h(stars)<h(dust))

•>300Myr stars: smooth dist, smooth medium, h(stars)>h(dust)

•Exponential SFR, e folding rate: 5 Gyr

Data from Buat et al 05:

UV selection & FIR selection

& Models

•Best models: SMC (Witt & Gordon 2000) albedo ~ct

•LMC (Weingartner & Draine 2001) albedo

(like in GRASIL models)

The role of the albedoThe role of the albedo(2) (2)

Screen configuration

Calzetti law

UV selection

FIR selection

models

XO

The role of albedo (3):The role of albedo (3):Derived attenuation curves

The amplitude of the bump and the attenuation law flattens

when extinction Also found in other studies

(models and data)

An empirical modelingAn empirical modelingBurgarella, Buat & Iglesias-Paramo 05, MNRAS, 360, 1413

•Populations synthesis models (PEGASE 2) with an exponential SFR+ burst

•An empirical law for dust attenuation with two parameters: a slope and a (gaussian) bump

K()=+Abump exp( -(-mean )2/2)

mean = 2175 Å & = 200 Å

-2<<-0.25 & 0<Abump<500

Range of values covering « classical » extinction and attenuation curves

•Bayesian method

An empirical modeling (2)An empirical modeling (2)Burgarella et al; 05Burgarella et al; 05

Aperture effects in the IRX-ß relation for Aperture effects in the IRX-ß relation for starbursts- Seibert et al. In prep.starbursts- Seibert et al. In prep.

Original IUE/IRAS data

Galex/IRAS data

~30 IUE starbursts observed by GALEX

IUE aperture: 10x20 arsec2

Galaxy size: 1 arcmin or moreShift of the galaxies to redder

colors and lower Fdust/Ffuv

ratios when integrated fluxes from GALEX are used

GALEX spectroscopy: may help at GALEX spectroscopy: may help at understanding dust obscuration processesunderstanding dust obscuration processes

Rosa-Gonzales et al.

On-going work…

GALEX spectroscopy of 2 galaxies observed by GALEX spectroscopy of 2 galaxies observed by SPITZERSPITZER

FUV NUV 24 µm

70 µm 160 µmB

V

Z=0.075

CDFS

We subtract a dust-free model(instantaneous starburst or continuous SF) to the observed

spectrum dust attenuation curve

Evolution with redshift:Evolution with redshift:IR and UV luminosity densities increase with z but IR and UV luminosity densities increase with z but

at a different rate: we must understand whyat a different rate: we must understand why

Each wavelength range measures a fraction of the Star Formation in the Universe and their relative contribution evolves with z

Takeuchi, Buat & Burgarella 05

Spitzer 24 m

Galex

High z studies:

SPITZER/MIPS & GALEX

MIPS-GTO/GALEX: CDFS (deep fields ~0.25 deg2 in common)

1. Selection at 24 µm of 190 LIRGs at z~ 0.7

83% detected in NUV (2300 A)--> FUV (1500 A) rest-frame

2. Selection of 420 Lyman Break Galaxies at z~1 from GALEX

FUV-NUV>2, Xcorrelation with Combo-17 and ESO Imaging Survey

25% detected at 24 µm

1. SWIRE/GALEX sample from z=0.2 to z=0.7 cf Jorge’s talk

<A(FUV)>=3.82 0.1 mag <A(FUV)>=3.36 0.1 mag

The distributions of LTIR/LFUV are found different (confidence level

larger than 95%): the mean dust attenuation decreases by 0.4 mag

LIRGs z=0

FUV emission of Luminous InfraRed Galaxies (LTIR>1011Lsun) at z=0.7 as compared to a complete sample of LIRGs at z=0

Buat et al. A&A in press/ astroph0703014

GALEX/MIPS-GTO: IR emission of LBGs at z~1

A lower (~1 mag) dust attenuation than for the FUV selection at z~0

Burgarella et al. A&A submitted

Fully consistent with the results of Reddy et al.

05 for an optical-NIR selection of galaxies at z~2

Final comments about on going and future Final comments about on going and future worksworks

Lots of other works not presented here: metallicities, gas densities, Balmer lines, studies of dust attenuation not based on IR data

Future work:At z=0• SPITZER/GALEX data on resolved galaxies will be used to explore the IRX-ß relation, especially for starburst galaxies accepted archival proposal (Madore, Boissier, Buat et al.)

•GALEX spectroscopy on a larger sample of galaxies: ~10 very edge-on nearby galaxies & galaxies to be extracted from deep spectroscopic fields

At z>0•Analysis of the CDFS-GOODS field with UV and IR selected samples at z=0.7: Buat et al. in prep

•SWIRE/GALEX analysis: Jorge’s talk…