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Galaxy Formation in the Early Universe

Galaxy Formation in the Early Universe. (z≥7). Haojing Yan Center for Cosmology & AstroParticle Physics Ohio State University CCAPP Symposium 2009 October 14, 2009.

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Galaxy Formation in the Early Universe

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  1. Galaxy Formation in the Early Universe (z≥7) Haojing YanCenter for Cosmology & AstroParticle PhysicsOhio State UniversityCCAPP Symposium 2009October 14, 2009

  2. Based on our recent paper submitted to Astrophysical Journal (see arXiv:0910.0077)“Galaxy Formation in the Reionization Epoch as Hinted by Wide Field Camera 3 Observations of the Hubble Ultra Deep Field”Collaborators:Rogier Windhorst (Arizona State University)Nimish Hathi (UC Riverside)Seth Cohen (Arizona State University)Russell Ryan (UC Davis) Robert O’Connell (University of Virginia) Patrick McCarthy (Carnegie Observatories)

  3. “Dropout” Search for High-z Galaxies i' z' • Line-of-sight neutral H absorption (Lyman limit + Lyforest) creates strong Lyman-break signature in SEDs of galaxies at z3 (Steidel & Hamilton 1992)

  4. Result from ACS HUDF:galaxy luminosity function at z  6 has a very step faint-end slope  = -1.8— -1.9 108 i’-dropouts (z~6 galaxy candidates) to ~ 30 mag in the Hubble Ultra Deep Field taken by the Advanced Camera for Surveys (Yan & Windhorst 2004b; ApJ, 612, L93)

  5. (Universal) Schechter Formalism of Luminosity Function of Galaxies Luminosity domain Absolute magnitude domain Apparent magnitude domain Cumulative surface density (credit: Binggeli)

  6. Why it’s a big deal:Low-luminosity Galaxies Could Be Major Contributors of Ionizing Photons at z  6 Cumulative contribution from galaxies (with different LF faint-end slopes) • Complete Gunn-Peterson trough detected in SDSS quasar spectra only at z6.3 and beyond: universe still fully ionized until looking-back to z6.3 • “Normal” star-forming galaxies can do the job at z6 as their LF is step enough • Q: Could they be the major source of Reionization? Critical Value Let’s push to higher redshifts and find out! Yan & Windhorst 2004a; ApJ, 600, L1

  7. Dropout selection using HST NICMOS+ACS in field — Yan & Windhorst (2004b) in HUDF — Bouwens & Illingworth (2006), Bouwens et al. (2008) using archival NICMOS data (including HUDF) Dropout selection using HST NICMOS+ACS around clusters (gravitational lensing) — Bradley et al. (2008): the best z~7 candidate (zph=7.4) Direct Slit-spectrosopy around clusters — Stark et al. (2007): 6 possible Lya-emitter at z~8.5-10.4 Ground-based Lya-emitter search — Iye et al. (2006): z=6.96 (Record holder) Moderate Success (up to 2008)

  8. All observations seem to suggest a decreasing number density of galaxies at higher redshifts (dimmer M* and lower *) But more active star-forming activities (reads: more star-forming galaxies) at higher redshifts are needed to explain: — Reionization — “Matured”, high-mass galaxies observed at z~6 Disturbing Results

  9. New Opportunity Offered by HST WFC3 (UVIS + IR) May 14, 2009

  10. Deepest Optical Deepest Optical + Deepest NIR HUDF WFC3,  4.7 arcmin2  29 mag from 0.9—1.7m (36% more data to come next year) HST Cycle-17 GO 11563, PI: G. Illigworth HUDF ACS,  11 arcmin2  30-31 mag from 0.4—0.9m

  11. Data taken Aug. 26 - Sept. 6, released to public mid-night Sept. 9 Two papers from the GO team appeared at arXiv on Sept. 10: — Oesch et al. (0909.1806): 16 candidates at z~7 — Bouwens et al. (0909.1803): 5 candidates at z~8 Two more papers appeared on Sept. 14: — Bunker et al. (0909.2255): 10 candidates at z~7 and (didn’t even mention in their abstract) 7 at z~8 — McClure et al. (0909.2437): 4 additional candidates (w.r.t. Oesch + Bouwens) at z>7 Fast Papers! Reiterating the same thing: decreasing SFR at higher redshifts

  12. Starting from zero photon (and zero character) at mid-night Sept. 9, doing a better data reduction/analysis to take full advantage of these precious data — reducing data from scratch (rather than relying on pipeline) — using in-flight calibration files (rather than ground-test files) — extra treatment to remove instrumental signatures — extreme care in alignment while mosaicking We were able to perform a much more complete search at the faintest level (but did not go beyond what data allow), and to push to the highest redshift possible; paper submitted Oct. 1 We decided that SCIENCE could be done differently …

  13. 20 Galaxy Candidates at z  7

  14. 15 Galaxy Candidates at z  8

  15. 20 Galaxy Candidates at z  10

  16. LF & GSFRD @ Very High-z Cumulative Surface Density LUV SFR Extrapolate to M  -15.0 mag (AB  32 mag)  Volume Global Star Formation Rate Density to AB~29 mag (observed) (Data points at z<6 taken from compilation of Hopkins & Beacom 2006)

  17. While totally unexpected, this result could solve many (every?) problems • Not a problem in producing high-mass galaxies at z~6 • Not a problem in producing reionization photons

  18. (In)direct Supporting Evidence from GRB-based SFRD Estimate Kistler et al. (arXiv:0906:0590) GRB 090423 @ z=8.26 Salvaterra et al. (arXiv:0906.1578) Tanvir et al. (arXiv:0906.1577)

  19. After careful analysis, the deepest IR data reveal a large number of galaxy candidates at z  7, 8 and 10 Earlier estimate of z  7 galaxy luminosity function consistent with new data, but a sudden, strong change in LF seems inevitable at z  8 and beyond Star-formation Rate Density could rise sharply from z>7 to z  10  First direct evidence that the Universe must be actively forming galaxies in the reionization epoch Summary

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