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z > 6 Surveys Represent the Current Frontier

z > 6 Surveys Represent the Current Frontier. Motivation: census of earliest galaxies (z=6, =0.95 Gyr) - contribution of SF to cosmic reionization - constraints on early mass assembly - planning effective use of future facilities (ELTs, JWST)

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z > 6 Surveys Represent the Current Frontier

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  1. z > 6 Surveys Represent the Current Frontier • Motivation: • census of earliest galaxies (z=6, =0.95 Gyr)- contribution of SF to cosmic reionization - constraints on early mass assembly - planning effective use of future facilities (ELTs, JWST) • Developing complementary optical/IR techniques: • - Lyman break dropouts • - Ly emitters • - strong gravitational lensing by galaxy clusters

  2. Some Key Issues • How effective are the various high z selection methods? - L*(z=6)  i~26 where spectroscopy is hard - spectroscopic samples biased to include strong L - great reliance on photometric redshifts • Is there a decline in the UV luminosity density 3<z<6? - results are in some disagreement - differing trends in continuum drops & L emitters • Significant stellar masses for post-burst z~6 galaxies - how reliable are the stellar masses? - inconsistent with declining SF observed 6<z<10? - does this imply an early intense period of activity? - in conflict with hierarchical models?

  3. Continuum sources probed via dropout technique z-dropout Stanway et al (2003) Traditional dropout technique poorly-suited for z>6 galaxies: - significant contamination (cool stars, z~2 passive galaxies) - spectroscopic verification impractical below ~few L* i-drop volumes: UDF (2.6 104), GOODS-N/S (5.105), Subaru (106) Mpc3 flux limits: UDF z<28.5, GOODS z<25.6, Subaru z<25.4

  4. Reducing Contamination from z~2 Passive Galaxies Addition of a precise optical-infrared color (z - J) can, in addition to the (i - z) dropout cut, assist in rejecting z~2 passive galaxy contaminants. (Stanway et al 2004) (i – z) 5.7 < z < 6.5 z~2 passive galaxies This contamination is ~10% at z~25.6 but is negligible at UDF limit (z~28.5) (z – J)

  5. Contamination by cool Galactic dwarfs - more worrisome UDF z<25.6 (Stanway et al 2004) L dwarfs E/S0 HST half-light radius Rh more effective than broad-band colors Contamination at bright end (z<25.6) is significant (30-40%)

  6. ACS dropouts: Luminosity Dependent Evolution? z=3 Bouwens et al (2006, ~500 sources at z=6!!!) propose L-dependent evolution - decline in abundance over 3<z<6 mostly for luminous sources – finally hierarchical growth?? If correct, this affects z-dependent integrated SF density measures corrected to some fiducial luminosity

  7. Decline in UVover 3<z<6 has been controversial Giavalisco et al 2004 Bunker et al 2004 • Poisson errors fail to account for dispersion in claimed number of z~6 i-drops, because of varying ways of accounting for contamination plus cosmic variance (10% in GOODS; 40% in UDF) Bouwens et al 2005 Ap J 624, L5

  8. Results from Subaru • HST offers superior photometry & resolution (important for stellar contamination) but SuPrimeCam has much bigger field (each pointing = 2  GOODS-N+S) • Additional photometric bands developed to sort stellar contamination • Shioya et al (2005): used intermediate band filters @ 709nm, 826nm to estimate stellar contamination in z~5 and z~6 samples respectively • Shimasaku et al (2005) split z-band into two intermediate filters zB, zR - to measure UV continuum slope These studies confirm decline indicated via HST studies

  9. z~6 dropouts from Subaru • SDF dataset > 2  GOODS N+S; cosmic variance ~ 25% • Confirm 5 abundance drop from z~3 to 6 (c.f. Bunker et al, HST) • Luminosity dependent trends - more evolution in massive galaxies? • Remember: this is observed number not dust-corrected SFR

  10. A modest 60cm cooled telescope can see the most distant known objects and provide crucial data on their assembled stellar masses! IRAC camera has 4 channels at 3.6, 4.5, 5.8 and 8 m corresponding to 0.5-1m at z~7! The Spitzer Space Telescope Revolution • Egami et al (2005) - characterization of a lensed z~6.8 galaxy • Eyles et al (2005) - old stars at z~6 • Yan et al (2005) - masses at z~5 and z~6 • Mobasher et al (2005) - a galaxy > 1011 M at z~6?

  11. Spitzer detections of i-drops at z=6 #1 z=5.83 #3 z=5.78 Eyles et al (2005) MNRAS 364, 443 • 4 i-drops in GOODS-S confirmed spectroscopically at Keck • Ly  emission consistent with SFR > 6 M yr-1 • IRAC detections from GOODS Super-Deep Legacy Program

  12. Spectral Energy Distributions of i-drops #1 z=5.83 #3 z=5.78 VLT K VLT K Spitzer + Ly emission constrains present & past star formation Ages > 100 Myr, probable 250-650 Myr (but Universe is only 1 Gyr old!!! (7.5<zF<13.5) Stellar masses: 2-4 1010 M (>20% L*) Look at lines!!!!!

  13. Independent z~6 UDF Spitzer analysis Confirms high stellar masses and prominent Balmer breaks 3 sources at z=5.9, Yan et al Ap J 634, 109 (2005)

  14. Spitzer detection of a resolved J-drop in UDF Criterion: (J – H)AB > 1.3 plus no detection in combined ACS While prominent detection in all 4 IRAC bands JD2: strong K/3.6m break  potential high mass z~7 source Mobasher et al (2005) Ap J 635, 832

  15. High mass, two breaks, but not confirmed spectroscopically– risk of foregroundMobasher et al (2005) STARBURST99: z=6.6;EB-V =0.0; Z=0.02, zF>9 BC03: z=6.5; EB-V =0.0; Z=0.004, zF>9 Stellar Mass: 2-7  1011 M dependent on AGN contamination

  16. Uncertainty in Redshift and Stellar Mass ~ 25% chance of being z~2.5

  17. Abundance of massive galaxies at z~6 with CDM in terms of their implied halo masses, assuming • Scalo IMF • SF efficiency 20% • Find a 1013 M halo in the tiny UDF is a problem! Abundance of Massive Galaxies at z~6: A Crisis? z = 5.8 Mobasher et al z = 15 Yan et al Eyles et al Barkana & Loeb (2005)

  18. Summary • Great progress using v,i,z,J-band drop outs to probe abundance of SF galaxies from 3<z<10: Bouwens et al discuss the properties of 506 I-band dropouts to z~29.5! • In practice, these samples are contaminated by foreground stars, z~2 galaxies etc to an extent which remains controversial. We are unlikely to resolve this definitively with spectroscopy until era of ELTs. • Comoving SF rate declines from z~3 to z~6 (and probably beyond) • Contribution of lower luminosity systems less clear • Spitzer’s IRAC can detect large numbers of z~5-6 galaxies and it seems many have high masses (one spectacularly so!) and signatures of mature stellar populations - implies earlier activity • Reconciling mature galaxies at z~6 with little evidence for SF systems with 7<z<10 may turn out to be a very interesting result

  19. Strong lensing & the hi-z Universe From curiosity associated with verification of General Relativity to practical tool for cosmologists Zwicky (1937) predicted its utility

  20. Lensed pair dropout behind Abell2218: SED Implies Established Stellar Population @ z~7 Key parameters: SFR = 2.6 M yr-1 Mstar~ 5-10 108 M z ~ 6.8  0.1 age 40 – 450 Myr (7 < zF < 12) Age > e-folding SF time more luminous during active phase? (Egami et al 2005) Several groups are now surveying more lensing clusters - Given small search area, such sources may be very common

  21. z > 6 Lyman  Surveys Origin: ionizing flux absorbed by H gas  Ly photons Lyman alpha emission: n=21, E=10.2eV, 1216Å Efficient: as much as 6-7% of young galaxy light may emerge in L depending on IMF, metallicity etc. 1 M yr-1 = 1.5 1042 ergs sec-1 (Kennicutt 1998)(no dust, normal IMF) Complementary techniques: - narrow band imaging techniques (f< 10-17 cgs, L< 5. 1042 cgs, SFR~3 M yr-1, V~2. 105 Mpc3) at z=6 - lensed spectra (f< 3.10-19, L< 1041, SFR~0.1 M yr-1, V <50 Mpc3)

  22. Panoramic Imaging Camera on Subaru Suprime-Cam Megacam Can survey distant Universe for Lyman alpha emitters by constructing narrow-band filters and comparing with signal in suitably-chosen broad-band filters

  23. Large Scale Structure @ z=5.7 via 515 Ly emitters Ouchi et al 2005 Ap J 620 L1

  24. Narrow bands in `quiet’ windows in night sky spectrum Airglow spectrum z(L) = 4.7 5.7 6.6 6.9 Requires panoramic imaging as z range is small

  25. Selection & spectroscopic verification of interlopers Compare signal in nb filter with broad-band signal using Subaru 5007Å 3727Å Spectroscopic follow-up of candidates with Keck 1216Å Hu et al (2003) z=5.7 survey

  26. Example: Ly Emitters at z=6.5 spectra • Very distant Subaru Ly emitters: • z=6.541, W = 130, SFR=9 • z=6.578, W= 330, SFR=5 • Kodaira et al (2003) PASJ 55, 17

  27. z=5.7 Ly Luminosity Function Comprehensive Subaru nb survey of 725 arcmin2 89 candidates 28/39 spec. confirmed <EW> ~230 Å - normal stellar popn. Malhotra & Rhoads 2004 Shimasaku et al astro-ph/0602614

  28. Ly Emitters at z~6.6 (Taniguchi et al 2005) Two color criteria: (z - NB921) > 1.0 and(i - z) > 1.3 Yields 58 candidates Spectra confirm 9-14 out of 20 (45-70%) • Two key results: • L emitters less significant than dropouts as contributors to SFR at z~6.6 • Yet an increasing fraction with increasing redshift (less evolution from z~3-6 than dropouts)

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