1. Bright Side versus Dark Side of Star Formation: UV and IR Views C. Kevin Xu, IPAC, Caltech Veronique Buat, LAM, Marseille Collaborators: J. Iglesias-Paramo, T. Tekeuchi, M. Rowan-Robinson, GALEX team, SWIRE team

2. Question: Do UV and IR surveys see the two sides of SF of the same population, or SF of two different populations? UV surveys IR surveys UV surveys IR surveys Total SFR Total SFR 1 population: 2 populations:

3. Talk plan Local UV and IR galaxies: how much do they overlap? comparisons of IR/UV ratio, L_tot, Hubble type, mass, clustering UV LF of IR galaxies and IR LF of UV galaxies IR-quiet UV galaxies (low metallicity dwarfs) UVLGs and ULIRGs LBGs and SCUBA galaxies: UV and IR galaxies at z ~ 3 UV and IR galaxies at intermediate redshifts (0.5 < z < 0.7) --- early results from a GALEX/SWIRE comparison study evolution of attenuation in UV and IR selected galaxies evolution of stellar mass in UV and IR selected galaxies Summary

4. FIR-UV bivariate luminosity function of local UV+FIR galaxies A(FUV)=1 Martin et al. 2005, ApJL, GALEX Edition Saturation of L_UV at ~ 2 x10^10 L_sun bi-modality (of L_IR/L_UV ratio) Strong dependence of L_IR/L_UV (best A_FUV indicator) on L_tot =L_UV+L_IR.

5. L_tot LF of local UV+IR galaxies Martin et al. 2005, ApJL, GALEX Edition L_tot=L_FUV+L_60 Solid line -- log-normal fit Blue -- UV selected (GALEX src) Red -- IR selected (IRAS src) UV galaxies are absent in high L_tot (>10^11) end!

6. Local samples: IR selected versus UV selected (details in J. Iglesias’ talk) IR selected (126): f60 > 0.6 Jy UV selected (61): NUV < 16 mag UV: low L_60/L_FUV IR: high L_60/L_FUV

7. L_IR/L_FUV distributions of IR and UV selected galaxies Very different. The overlap between the two samples is ~ 30%. The mean ratio of IR galaxies is ~ 10 times higher than that of UV galaxies!

8. Mean attenuations from the Fdust/F(UV) ratio NUV selected sample =0.8+/-0.3 mag =1.1+/-0.3 mag FIR selected sample =2.1+/-1.0 mag =2.9+/-1.0 mag NUV FUV Confirm pre-GALEX results (Buat et al. 2005, ApJL, GALEX edition)

9. L_IR/L_FUV v.s. L_tot (`Adelberger plot’) Two populations are separated: IR: high L_tot, high L_IR/L_UV ratio UV: low L_tot, low L_IR/L_UV ratio Explanation: Consequence of selection effect on L_IR/L_UV ratio, and the strong correlation between the ratio and L_tot.

10. L_tot LFs of local UV and IR galaxies Using L_IR/L_UV ratio to convert to L_tot The L_tot of UV galaxies has a sharp cutoff at ~ 10^11 L_sun

11. Comparison of Hubble type distributions of local UV and IR galaxies Good overlap in the middle: both populations peak around ~ Sbc IR galaxies: excess of interacting galaxies (~ 30%) more early types (S0/Sa/Sb) UV galaxies: more late types (Sc/Sd/Ir/CB ~ 50%)

12. Comparison of correlation lengths UV (FOCA sources): r_0=3.2 (+0.8, -2.3) h -1 Mpc (Heinis et al. 2004) IR (IRAS sources): r_0=3.9+-1.8 h -1 Mpc (Strauss et al. 1992) UV galaxies seem to be less clustered than IR galaxies (confirmed by preliminary GALEX results) (FOCA result) (Heinis et al. 2004 A&A 424, L9) IRAS galaxies

13. Comparisons of stellar mass distributions M stars : estimated from L_K (Cole et al. 2001 calibration, H_0= 70 km s -1 Mpc -1 ). `Survival Tech.’ used. Good overlap between two populations: medians differ < 2, both are sub-M *. Though: IR: slightly tilted for more massive end UV: more galaxies with low mass (<10^10 L_sun).

14. L_tot v.s. mass L_IR/L_UV v.s. mass UV galaxies of lowest mass (< 10^10) have lowest L_tot and IR/UV most massive IR galaxies (>10^12) are not galaxies with highest L_tot brightest IR galaxies (~ ULIRGs) have mass ~ M * for given mass, UV galaxies have lower L_tot and IR/UV ratio than IR galaxies

15. 60  m LF of UV galaxies FUV LF of IR galaxies UV galaxies substantially under- represent galaxies of L_IR > 10^11 L_sun (LIGs). ULIRGs (L_IR > 10^12) are completely absent in UV sample. IR galaxies can fully account for all UV galaxies of L_UV > 10^9 (L * ~ 4 10^9). some fainter UV galaxies (L_UV < 10^9) could be missing in IR sample. L

16. IR-quiet UV galaxies I Zw 18: prototype metallicity = 1/50 solar (lowest known) (from NED, Hubble Heritage Gallery image) low mass (star+gas): ~ 2 10^8 M_sun distance=15 Mpc L(FUV)=2.5 10^8 not detected in FIR: L_dust/L_FUV < 0.25

17. SBS0335-052 another prototype IR- quiet UV galaxy: metallicity = 1/35 solar (2nd lowest) (Houck et al. 2004, ApJS, Spitzer edition) undetected by IRAS, but detected by both ISO and Spitzer: very different IR SED from normal galaxies M82 mass (star+gas) ~ 2 10^9 M_sun distance=58.3 Mpc L(FUV) ~ 10^9 L_dust/L_FUV ~ 0.4

18. Characteristics of IR quiet UV galaxies dwarf galaxies of low metallicity < ~1/10 solar mass: a few 10^8 -- 10^9 UV lum: a few 10^8 -- 10^9 (~ 10 times < L * of FUV, not z~0 LBG) L_dust/L_FUV ~0.3 (~ a few % of UV galaxies) IR-quiet

19. UV luminous galaxies (UVLG): z~0 LBGs (Heckman et al 05, ApJL GALEX edition) Nearby galaxies brighter than L_UV=2 10 10 L(sun) with z<0.3 10 -5 galaxy/Mpc 3 (~100 times less dense than LBGs) (kpc) FUV Luminosity vs. Half-light Radius (L ๏ /kpc2) (L ๏ ) (L ๏ kpc -2 ) FUV Surface Brightness vs. Stellar Mass (M ๏ ) Compact Large

20. Population Comparison Large UVLGs, Compact UVLGs, LBGs (Slide courtesy of Chris Martin) 12 11 10 9 Log L UV 1.5 1 0.5 9 Log r UV 12 11 10 9 M*M* 3 2 1 0 A UV 2 1 0 Log b 9 8.5 8 7.5 [O/H]

21. A_FUV vs. SFR plot of UVLGs: comparison with ULIRGs and others UVLGs occupy the bright end of UV population, but still they have L_tot cutoff at ~ 2 10^11. Their attenuation (IR/UV ratio) spans the same range as that of major UV population. None of UVLGs is as bright as ULIRGs (>10^12). /LIRGs

22. LBGs and SCUBA galaxies: UVLGs and ULIRGs at z~3 (Adelberger & Steidel 2001) Blue dots: LBG galaxies. L_dust/L_1600 estimated using UV slope (very uncertain). Red squares: SCUBA galaxies (radio pre- selected) studied in Chapman et al. 2004. The overlap between the two populations is small: only 1 LBG detected by SCUBA (Chapman et al. 2000). Only 1 red square (SCUBA) has IR/UV < 100.

23. SCUBA galaxies: HST ACS images overlaid by radio contours (Chapman et al. 2004, ApJ 611, 732) Extended UV emission outside the radio/FIR emission region: unobscured UV light. 3”

24. Rest frame V-band luminosity and mass (Smail et al. 2004, ApJ 616, 71) LBG (Shapley et al 2001) SCUBA SCUBA galaxies: stellar mass (estimated from rest V-band lum.) plus gas mass ~ 5 10^10 M_sun, (Spitzer measurements of rest frame K may be ~2 times higher). A few times (~1.5 mag) more massive than LBGs (green curve).

25. Corrlations lengths of SCUBA galaxies and LBGs (Blain et al. 2004, ApJ 611, 725) SCUBA LBGs SCUBA galaxies: r_0=6.9+-2.1 h -1 Mpc Significantly larger than that of LBGs (~ 3 -- 4 h -1 Mpc)

26. UV and IR galaxies at intermediate redshifts (z ~ 0.6) --- early results of a GALEX/SWIRE comparison study Why z=0.6? close to the peak of cosmic SF suggested by some ISO and SDSS fossil studies for z ~ 1 or larger, NUV is affected by rest frame Ly  emission/absorption (K-correction for L_UV very uncertain) at z~0.6: NUV ( 2300A) ---> rest frame FUV (1500A) MIPS 24  m ---> rest frame 15  m (L_IR indicator) IRAC 3.6  m ---> rest frame K band (stellar mass indicator)

27. Field: NUV sources: 8995 F3.6 sources: 19100 F24 sources: 2080 Matches f24/NUV: 1086 (52% of f24 srcs, 12% of NUV srcs) GALEX ELAISE-N1_00 (~ 1 deg 2 ) (inside SWIRE ELAISE-N1 ~ 9 deg 2 ) restrictions: - within 1 deg circle of GALEX field - exclude the SWIRE gap Final area: 0.6 deg 2 ELAIS-N1_00 NUV ELAIS-N1, 24μ m NUV

28. Sample selection of 0.5<z<0.7 galaxies redshifts: photo-z catalog of ELAIS-N1 (ugriz + IRAC, by Rowan-Robinson) GALEX sources: 1124 (NUV < 24) MIPS sources: 396 (F24 > 0.2mJy) NUV/F24 matches: 159 ( 40% of F24 src, but only 14% of NUV src!!). F24 ~ 0.2mJy, z~0.6 --> L_dust ~ 10^11 L_sun NUV ~ 24, z~0.6 --> L_FUV~ 10^9.5 L_sun ~ ~

29. Mean f24 flux of z=0.6 UV sources from stacking Stacked f24 image of UV sources in bin 9.4 < log(L_FUV) < 9.8 9.4 < log(L_FUV) < 9.8: 212 sources, =39  Jy 9.8 < log(L_FUV) < 10.2: 422 sources, =70  Jy 10.2 < log(L_FUV) < 10.5: 95 sources, =107  Jy 10.5 < log(L_FUV) < 10.8: 17 sources, =219  Jy (212 sources)

30. L_dust of z=0.6 UV galaxies: comparison with z=0 couterparts --> in rest frame L_dust = 11.1 x L(15  m) (Chary & Elbaz 2001, Elbaz et al. 2002) Error bar estimated from fraction of F24 > 0.2mJy In the 2 fainter L_UV bins, the means of z=0.6 and z=0 galaxies are close to each other, both are a factor of few below the SWIRE detection limit.

31. Comparison of mean L_dust/L_FUV ratios of z=0.6 and z=0 UV galaxies for galaxies of L_FUV < 10^10.2 L_sun, the IR/UV ratio does not show any evolution from z=0 to z=0.6. for brighter galaxies of L_FUV > 10^10.2 L_sun, there seems to be a negative evolution in the sense that z=0.6 galaxies have lower ratios.

32. SEDs of the 160um source at z=0.6 However, is the extrapolation from L(15  m) to L_dust reliable??? Need to check the SEDs of z=0.6 sources which are also detected in MIPS 70  m band and 160  m band. Only 1 z=0.6 source in 24  m sample (395 sources) is also detected in both 70  m and 160  m band. It is a ULIRG with an SED close to that Arp220! (M82 SED is closer to Elbaz calib.)

33. F24 image of the f160 source at z=0.6 The green circle: 160  m beam (40”) An isolated, clean source (no confusion).

34. SEDs of  m sources at z=0.6 Other 4 z=0.6 sources are detected in 70  m, but not in 160  m: 2 have log(L_dust) < 12 and M82 like SEDs. 2 have log(L_dust) >12 and SEDs closer to Arp220. ~ ~ Conclusion: SEDs span a wide range.

35. effect of different calibrations When Arp220 SED is used in converting L(15  m) to L_dust, the mean IR/UV ratio of z=0.6 UV galaxies in 2 bright bins (log(L_FUV)>10.2) is in good agreement with that of z=0 galaxies. Consistent with no evolution in the ratio!

36. L_dust/L_FUV ratio of z=0.6 IR galaxies Elbaz calibration mean ratios derived from both stacking and ‘survival tech.’ (consistent with each other). mean ratios of z=0.6 galaxies in all lum. bins are consistent with those of z=0 galaxies in the same bins.

37. Effect of Arp220 calibration The arp220 calib. shifts the points along the IR/UV vs. L_dust correlation line, so does not change the result that the IR/UV ratio for given L_dust does not have any significant evolution.

38. Stellar mass of given L_FUV: comparison of z=0.6 and z=0 UV galaxies pink points: z=0.6 blue squares: z=0 Stellar mass: estimated from f3.6 (rest frame K). SWIRE sensitivity limit of 3.6  m band (the green line). The stellar mass of z=0.6 galaxies of given L_FUV is about ~2 times less than that of their z=0 counter- parts. f3.6=3.7  Jy

39. Stellar mass v.s. L_dust: comparison of z=0.6 and z=0 IR galaxies red points: z=0.6 No evidence for evolution in stellar mass of IR selected galaxies.

40. z  (dust) (L 0 Mpc -3 )  (FUV) (L 0 Mpc -3 )  (dust)/  (FUV) A(FUV) (mag) 0.066 10 7 1.8 10 7 3.3 1.2 0.530 10 7 4.1 10 7 7.4 1.9 0.750 10 7 7.7 10 7 6.5 1.8 196 10 7 6.9 10 7 13.9 2.1  (dust): ~ (1+z) 4, Spitzer results of Le Floch et al. (2005).  (FUV): Schiminovich et al. 2005 (ApJL, GALEX Edition). Both IR and UV have luminosity evolution --> at high z galaxies on average are more luminous, therefore with higher attenuation. Evolution seen in IR and in UV: from z=0 to z=1

41. 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, L tot > 10 12 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. ๏ ๏ ๏

42. Summary (continue) 5. The z~0 counterparts of LBGs are a population of compact luminous UV galaxies (UVLG). In terms of L tot (SFR), UVLGs are more than 10 times fainter than ULIRGs. 6. LBGs and SCUBA galaxies (UV and IR selected galaxies at z~3) do not overlap with each other very much. SCUBA galaxies have significantly higher SFR, higher attenuation, higher stellar mass, and higher correlation length than LBGs. 7. At intermediate redshifts of z~0.6, UV selected galaxies show moderate evolution in stellar mass in the sense that for a given luminosity, galaxies at z=0.6 have stellar mass ~2 times less than their z=0 counterparts. No evidence for any evolution in the IR/UV ratio (attenuation) for UV galaxies. For IR (24  m) selected galaxies at z~0.6, no evidence is found for evolution of either the stellar mass or the IR/UV ratio for given L IR. 8. Both  IR and  UV evolve significantly from z=0 to z=1, and the ratio   IR /  UV increases by ~ 4. This is consistent with the scenario that high z galaxies are more luminous therefore with higher attenuation.

43. Star formation history measured in diff. wavebands 1) They have the same trend (rising from z=0 to z ~1, then becoming relatively flat). 2) IR (ISO, IRAS, SCUBA) and rest frame UV (blue symbols and yellow shade) measurements agree with each other within a factor of ~2!! Schiminovich et al. 2005

44. I Zw 18 does have dust: Balmer decrement (  ) study (Cannon et la. 2001) found dust in regions delineated by the boxes in the  image, covering only parts of the bubble-like star formation regions: blow-away of dust? (Cannon et al. 2002, ApJ. 595, 931) HST  image