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

Based on our recent paper submitted to Astrophysical Journal (see arXiv: ) “Galaxy Formation in the Reionization Epoch as Hinted by Wide Field Camera 3 Observations of the Hubble Ultra Deep Field” Collaborators Based on our recent paper submitted to Astrophysical Journal (see arXiv: ) “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)

“Dropout” Search for High-z Galaxies 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) i'z'

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) Result from ACS HUDF: Result from ACS HUDF: galaxy luminosity function at z  6 has a very step faint-end slope  = -1.8— -1.9

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

Cumulative contribution from galaxies (with different LF faint-end slopes) Critical Value Why it’s a big deal: Why it’s a big deal: Low-luminosity Galaxies Could Be Major Contributors of Ionizing Photons at z  6 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 Re Q: Could they be the major source of Reionization? Let’s push to higher redshifts and find out! Yan & Windhorst 2004a; ApJ, 600, L1

Moderate Success (up to 2008) Dropout selection using HST NICMOS+ACS in field 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) Dropout selection using HST NICMOS+ACS around clusters (gravitational lensing) — Bradley et al. (2008): the best z~7 candidate (z ph =7.4) Direct Slit-spectrosopy around clusters Direct Slit-spectrosopy around clusters — Stark et al. (2007): 6 possible Lya-emitter at z~ Ground-based Lya-emitter search Ground-based Lya-emitter search — Iye et al. (2006): z=6.96 (Record holder)

Disturbing Results 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

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

Deepest Optical + Deepest NIR HUDF ACS,  11 arcmin 2  mag from 0.4—0.9  m HUDF WFC3,  4.7 arcmin 2  29 mag from 0.9—1.7  m (36% more data to come next year) HST Cycle-17 GO 11563, PI: G. Illigworth Deepest Optical

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

We decided that SCIENCE could be done differently … 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

20 Galaxy Candidates at z  7

15 Galaxy Candidates at z  8

20 Galaxy Candidates at z  10

LF & Very High-z CumulativeSurfaceDensity Global Star Formation Rate Density to AB~29 mag (observed) Extrapolate to M  mag (AB  32 mag) L UV SFR Volume (Data points at z<6 taken from compilation of Hopkins & Beacom 2006)

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

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

Summary 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