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Bright Side versus Dark Side of Star Formation: UV and IR Views

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.

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Bright Side versus Dark Side of Star Formation: UV and IR Views

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  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? Total SFR 1 population: IR surveys UV surveys Total SFR 2 populations: UV surveys IR surveys

  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 Martin et al. 2005, ApJL, GALEX Edition A(FUV)=1 • 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 <A(NUV)>=0.8+/-0.3 mag <A(FUV)>=1.1+/-0.3 mag FIR selected sample <A(NUV)>=2.1+/-1.0 mag <A(FUV)>=2.9+/-1.0 mag NUV FUV (Buat et al. 2005, ApJL, GALEX edition) Confirm pre-GALEX results

  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) IRAS galaxies (Heinis et al. 2004 A&A 424, L9)

  13. Comparisons of stellar mass distributions Mstars: 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 L • 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. • 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.

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

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

  18. Characteristics of IR quiet UV galaxiesdwarf galaxies oflow metallicity < ~1/10 solarmass: a few 10^8 -- 10^9UV 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 IR-quiet

  19. UV luminous galaxies (UVLG): z~0 LBGs(Heckman et al 05, ApJL GALEX edition) FUV Luminosity vs. Half-light Radius FUV Surface Brightness vs. Stellar Mass (L๏/kpc2) (L๏ kpc-2) Compact (kpc) Large (M๏) (L๏) • Nearby galaxies brighter than L_UV=2 1010 L(sun) with z<0.3 • 10-5 galaxy/Mpc3 (~100 times less dense than LBGs)

  20. Population ComparisonLarge UVLGs, Compact UVLGs, LBGs (Slide courtesy of Chris Martin) Log LUV Log rUV M* AUV Log b [O/H] 12 1.5 12 3 2 9 11 1 11 2 1 8.5 10 0.5 10 1 0 8 9 9 9 0 -1 7.5

  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 • 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. (Adelberger & Steidel 2001)

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

  24. Rest frame V-band luminosity and mass 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). LBG (Shapley et al 2001) SCUBA (Smail et al. 2004, ApJ 616, 71)

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

  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: GALEX ELAISE-N1_00 (~ 1 deg2) (inside SWIRE ELAISE-N1 ~ 9 deg2) restrictions: - within 1 deg circle of GALEX field - exclude the SWIRE gap Final area: 0.6 deg2 ELAIS-N1_00 NUV NUV sources: 8995 F3.6 sources: 19100 F24 sources: 2080 Matches f24/NUV: 1086 (52% of f24 srcs, 12% of NUV srcs) NUV ELAIS-N1, 24μ m

  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, <f24>=39 Jy 9.8 < log(L_FUV) < 10.2: 422 sources, <f24>=70Jy 10.2 < log(L_FUV) < 10.5: 95 sources, <f24>=107Jy 10.5 < log(L_FUV) < 10.8: 17 sources, <f24>=219Jy (212 sources)

  30. L_dust of z=0.6 UV galaxies:comparison with z=0 couterparts • <f24> --> < L(15m)> • 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. 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.) SEDs of the 160um source at z=0.6

  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. 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. SEDs of 70mm sources at z=0.6 ~ ~ 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 • 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. blue squares: z=0 pink points: z=0.6 f3.6=3.7Jy

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

  40. Evolution seen in IR and in UV:from z=0 to z=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.

  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, 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. ๏ ๏ ๏

  42. 5. The z~0 counterparts of LBGs are a population of compact luminous UV galaxies (UVLG). In terms of Ltot (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 LIR. 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. Summary (continue)

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

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