1. Far-infrared properties of UV selected galaxies from z=4 to z=1.5: unveiling obscured star formation Véronique Buat & Sebastien Heinis With the contribution of Laure Ciesla Based on HerMES/SPIRE data in the COSMOS field Heinis, Buat et al. 2013 From Exoplanets to Distant Galaxies: SPICA’s New Window on the Cool Universe 18-21 june 2013-University of Tokyo, Japan

2. Elbaz’s lectures (david.elbaz3.free.fr/coursJ1.html), adapted from Devriendt+99 Visible InfraredmmUV wavelength intensity dust Both UV and IR are related to recent star formation They are anti-correlated because of dust attenuation IR selected objects are usually obscured with a low residual emission in UV Conversely: we expect a UV selection to be dominated by IR faint sources Only few words about the physical link between UV and IR emissions

3. We perform a UV rest-frame selection in the COSMOS field @ z=1.5, 3 & 4 Based on photometric redshifts (Ilbert+13) Down to u, r, i ≈ 26 ABmag

4. What do we find within HerMES/ SPIRE images? Almost nothing……. Z = 1.5

5. Stacking per bin of L FUV L IR measured by fitting Dale & Helou (2002) templates on SPIRE data A FUV = f(L IR /L FUV ) (Buat+05)  LIRGs and sub-LIRGs

6. Stacking per bin of M * (again on the UV selection) Z=1.5 Z=3 Z=4

7. Stacking per bin of (L FUV,M * ) Dust attenuation increases with M * for a given L FUV Dust attenuation decreases with L FUV for a given M * The dispersion in dust attenuation decreases with L FUV See also Burgarella+06, Buat+09,12

8. A recipe to derive L IR /L FUV =IRX Heinis+13, very close to be submitted IRX=log(L IR /L FUV )=IRX 0 (L FUV )+0.72*log(M * /10 10.35 ) @z=1.5 & 3

9. SFR versus M * : a well defined ‘Main Sequence’ for star-forming galaxies SFR= SFR 0 M * 0.7  slope< 1 see also Noeske+07, Oliver+10, Whitaker+12 slope~1 found by Elbaz+07, Daddi+07, Wuyts+11 (from Kennicutt, 98) Z=1.5 Z=3 Z=4

10. Specific SFR (sSFR=SFR/M * ) : very active galaxies at z =3 & 4, a challenge for the models  sSFR(z,M * )  high redshift galaxies (z~2.5-4) stay only around 1 Gyr on the Main Sequence, this time increasing with decreasing redshift

11. What can we do with SPICA? Herschel was unable to detect individual galaxies selected in UV at z >= 1.5 (less than 1% of the galaxies directly detected)  Studies based on a stacking technics: average trends only, no or little dispersion measured We must increase the number of individual detections if we want to discuss the variety of physical properties of individual galaxies

12. Individual detections with SPICA? Dale & Helou 02 templates α=2 α=1.5 Assuming 50 µJy @ 70 µm

13. How many galaxies in the COSMOS field? z=1.5 9419 galaxies/deg 2 z=3 3162 galaxies/deg 2 Assuming a Dale & Helou template with α = 2 As a function of L FUV

14. How many galaxies could be detected in the COSMOS field? z=1.5 9731 galaxies/deg 2 z=3 3493 galaxies/deg 2 z=4 952 galaxies/deg 2 As a function of M *

15. Which template to measure L IR ? What do we learn from Herschel? Z=0 Z=1.5 Ciesla+13, in prep.

16. The determination of L IR with a single monochromatic measurement might lead to large uncertainties Several bands might be very useful to constrain the SED Still some work to be made to refine SEDs…… Ciesla+13, in preparation

17. Conclusions To measure the dust emission of UV bright high redshift galaxies is challenging HERSCHEL was not able to detect them individually at z ≥1.5 Deep photometric observations with SPICA @ λ≈70 μm will allow direct detections of several thousands of galaxies per deg 2 also observed in optical (UV rest-frame) Coordinated deep surveys with SPICA instruments (SAFARI-MCS-FPF) would provide full SEDs of these galaxies, allowing physical analyses.

18. Stacking per bin of M * (again on the UV selection)

19. Stacking per bin of L FUV L IR measured by fitting Dale & Helou (2002) templates on SPIRE data A FUV = f(L IR /L FUV ) (Buat+05)  LIRGs and sub-LIRGs