1. Ultraviolet and far-infrared observations of galaxies: 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

2. The GALEX surveys P.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 deg 2 « 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

3. GALEX sky coverage 10/02/2006

4. 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 sample Second 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

5. L TIR /L FUV (i.e. dust attenuation) versus L bol 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 10 9 <L< 5 10 10 L sun 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 L bol 4 mag 2 mag 0.5 mag A(FUV) L TIR : 8-1000 µm, L FUV :. L A(FUV) is calculated as a function of log(L TIR /L FUV ) using the calibration of Buat et al 2005 (TIR+FUV)

6. L TIR /L FUV (i.e. dust attenuation) versus M star at z=0: A shallow increase of L TIR /L FUV when M star increases

7. Theoretical models show that the F dust /F UV flux ratio is a robust tracer of the dust attenuation A(NUV) mag Various geometries/dust properties Gordon et al. 2000 Various star formation histories Buat et al 05 ApJL special issue (GALEX)

8. The « IRX-ß » in galactic disks IRX: L dust /L UV ( sometimes L FIR(40-120 µm) /L UV ), 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

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

10. Models predict dispersed relations between  and the attenuation (Witt & Gordon 2000) A shell distribution and no bump (SMC) are necessary to reproduce the starburst distribution with these models

11. The complexity of the IRX-ß plot is confirmed by the first GALEX results (Buat et al. 05 ApJL GALEX special issue, also 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

12. A result already suggested by pre-GALEX works but with smaller statistics Bell, 2002, normal galaxies Goldader et al. 2002, ULIRGs

13. « IRX-ß » relation for radial profiles in galaxies « IRX-ß » relation for radial profiles in galaxies 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 »

14. SINGS sample (Dale et al. 06) SINGS sample (Dale et al. 06) From Cortese et al. 06

15. 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…

16. 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 Log(L dust /L FUV ) b= sfr0/ Kong et al 2004 Dust attenuation curve from Charlot & Fall (2000)

17. 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 d S is the distance from the starburts line

18. An important issue/advantage: the GALEX NUV band overlaps the bump at 2175 Å of the MW extinction curve MW extinction curves Starburst attenuation curve LMC ext. curve SMC ext. curve From Calzetti 2001 FUV NUV

19. GRASIL models with various scenarii of dust attenuation GRASIL models with various scenarii of dust attenuation Panuzzo et al. 07,MNRAS 375, 640 A modified GRASIL model: age dependent extinction AND molecular clouds (t<t esc ) and young stars (t<t thin ) concentrated in the galactic plane (small scale height). A MW extinction curve is found consistent with the F TIR /F FUV vs FUV-NUV color: the age- dependent extinction reduces the presence of the 2175 A bump Starburst line

20. The role of the albedo The 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

21. Best models: SMC (Witt & Gordon 2000) albedo ~ct LMC (Weingartner & Draine 2001) albedo (like in GRASIL models) The role of the albedo (2) Screen configuration Calzetti law UV selection FIR selection models XOXO

22. 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)

23. An empirical modeling An empirical modeling Burgarella, 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( )=  +A bump exp( -( - mean ) 2 /  2 ) mean = 2175 Å &  = 200 Å -2<  <-0.25 & 0<A bump <500 Range of values covering « classical » extinction and attenuation curves Bayesian method

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

25. Aperture effects in the IRX-ß relation for starbursts- Seibert et al. In prep. Original IUE/IRAS data Galex/IRAS data ~30 IUE starbursts observed by GALEX IUE aperture: 10x20 arsec 2 Galaxy size: 1 arcmin or more Shift of the galaxies to redder colors and lower F dust /F fuv ratios when integrated fluxes from GALEX are used

26. GALEX spectroscopy: may help at understanding dust obscuration processes Rosa-Gonzales et al. On-going work…

27. GALEX spectroscopy of 2 galaxies observed by SPITZER FUV NUV 24 µm 70 µm 160 µm B V Z=0.075 CDFS We subtract a dust-free model(instantaneous starburst or continuous SF) to the observed spectrum  dust attenuation curve

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

30. High z studies: SPITZER/MIPS & GALEX MIPS-GTO/GALEX: CDFS (deep fields ~0.25 deg 2 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 SWIRE/GALEX sample from z=0.2 to z=0.7 cf Jorge’s talk

31. =3.82  0.1 mag =3.36  0.1 mag The distributions of L TIR /L FUV 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 (L TIR >10 11 L sun ) at z=0.7 as compared to a complete sample of LIRGs at z=0 Buat et al. A&A in press/ astroph0703014

32. 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

33. Final comments about on going and future works 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…