Galaxy Formation Galaxy Formation in the Early Universein the Early UniverseGalaxy Formation Galaxy Formation

in the Early Universein the Early Universe

Haojing YanCenter for Cosmology & AstroParticle Physics

Ohio State University

CCAPP Symposium 2009October 14, 2009

Haojing YanCenter for Cosmology & AstroParticle Physics

Ohio State University

CCAPP Symposium 2009October 14, 2009

(z≥7)(z≥7)

Based on our recent paper Based on our recent paper submitted to Astrophysical Journal submitted to Astrophysical Journal (see arXiv:0910.0077)(see arXiv:0910.0077)

“Galaxy Formation in the “Galaxy Formation in the Reionization EpochReionization Epoch as Hinted by as Hinted by Wide Field Camera 3Wide Field Camera 3 Observations of the Observations of the Hubble Ultra Deep FieldHubble Ultra Deep Field””

CollaboratorsCollaborators:

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 Dropout” Search for High-z GalaxiesGalaxies

• Line-of-sight neutral H absorption (Lyman limit + Lyforest) creates strong Lyman-break signature in SEDs of galaxies at z3 (Steidel & Hamilton 1992)

i'i' z'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 (Universal) Schechter Formalism of Luminosity Function of of Luminosity Function of

GalaxiesGalaxiesLuminosity 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 z6.3 and beyond: universe still fully ionized until looking-back to z6.3

• “Normal” star-forming galaxies can do the job at z6 as their LF is step enough

• Q: Could they be the major source of ReReionization?

Let’s push to higher redshiftsand find out!Yan & Windhorst 2004a; ApJ, 600, L1

Moderate Success (up to Moderate Success (up to 2008)2008)• Dropout selection using HST Dropout selection using HST NICMOSNICMOS++ACS ACS in fieldin field

— Yan & Windhorst (2004b) in HUDF

— Bouwens & Illingworth (2006), Bouwens et al. (2008) using archival NICMOS data (including HUDF)

• Dropout selection using HST Dropout selection using HST NICMOSNICMOS++ACS ACS around around clusters (gravitational lensing)clusters (gravitational lensing)

— Bradley et al. (2008): the best z~7 candidate (zph=7.4)

• Direct Slit-spectrosopy around clustersDirect Slit-spectrosopy around clusters

— Stark et al. (2007): 6 possible Lya-emitter at z~8.5-10.4

• Ground-based Lya-emitter searchGround-based Lya-emitter search

— Iye et al. (2006): z=6.96 (Record holder)

Disturbing ResultsDisturbing 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 New Opportunity Offered by HST WFC3 (UVIS + IR)(UVIS + IR)

May 14, 2009May 14, 2009

Deepest Optical + Deepest Deepest Optical + Deepest NIRNIR

HUDF ACS, HUDF ACS, 11 arcmin 11 arcmin22

30-31 mag from 0.4—0.930-31 mag from 0.4—0.9mm

HUDF WFC3, HUDF WFC3, 4.74.7 arcmin arcmin22

29 mag from 0.9—1.729 mag from 0.9—1.7mm(36% more data to come next year)(36% more data to come next year)HST Cycle-17 GO 11563, PI: G. IlligworthHST Cycle-17 GO 11563, PI: G. Illigworth

Deepest Deepest OpticalOptical

Fast Papers!• Data taken Aug. 26 - Sept. 6, released to public mid-Data taken Aug. 26 - Sept. 6, released to public mid-night Sept. 9night Sept. 9

• Two papers from the GO team appeared at arXiv on Sept. Two papers from the GO team appeared at arXiv on Sept. 10:10:

— 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: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

Reiterating the same thing: decreasing SFR at higher redshiftsReiterating the same thing: decreasing SFR at higher redshifts

We decided that SCIENCE could be We decided that SCIENCE could be done differently …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 & GSFRD @ Very High-zLF & GSFRD @ Very High-z

CumulativeCumulativeSurfaceSurfaceDensityDensity

Global StarGlobal StarFormationFormation

Rate DensityRate Density

to AB~29 magto AB~29 mag(observed)(observed)

Extrapolate toExtrapolate toM M -15.0 mag -15.0 mag(AB (AB 32 mag) 32 mag)

LLUVUV

SFRSFRVolumeVolume

(Data points at z<6 taken from compilation of Hopkins & Beacom 2006)

While totally unexpected, this While totally unexpected, this result could solve many (every?) result could solve many (every?)

problemsproblems

• Not a problem in producing reionization photons

• Not a problem in producing high-mass galaxies at z~6

Salvaterra et al. (arXiv:0906.1578)Salvaterra et al. (arXiv:0906.1578) Tanvir et al. (arXiv:0906.1577)Tanvir et al. (arXiv:0906.1577)

GRB 090423GRB 090423@ z=8.26@ z=8.26

Kistler et al. (arXiv:0906:0590)Kistler et al. (arXiv:0906:0590)

(In)direct Supporting Evidence from GRB-based (In)direct Supporting Evidence from GRB-based SFRD EstimateSFRD Estimate

SummarySummary

• 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