galaxy formation in the early universe
DESCRIPTION
Galaxy Formation in the Early Universe. (z≥7). Haojing Yan Center for Cosmology & AstroParticle Physics Ohio State University CCAPP Symposium 2009 October 14, 2009. - PowerPoint PPT PresentationTRANSCRIPT
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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)
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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)
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““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'
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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
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(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
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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
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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)
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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
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New Opportunity Offered by HST WFC3 New Opportunity Offered by HST WFC3 (UVIS + IR)(UVIS + IR)
May 14, 2009May 14, 2009
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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
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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
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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
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20 Galaxy Candidates at z 7
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15 Galaxy Candidates at z 8
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20 Galaxy Candidates at z 10
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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)
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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
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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
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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