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Finding z  6.5 galaxies with HST’s WFC3 and their implication on reionization

Finding z  6.5 galaxies with HST’s WFC3 and their implication on reionization. Mark Richardson. “Possible Low-Z starz in High-z z’-drop galaziez”. Outline. WFC3 in the IR LBGs Data Results SFR Shechter (Luminosity) Function Reionization. Note.

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Finding z  6.5 galaxies with HST’s WFC3 and their implication on reionization

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  1. Finding z  6.5 galaxies with HST’s WFC3 and their implication on reionization Mark Richardson

  2. “Possible Low-Z starz in High-z z’-drop galaziez”

  3. Outline • WFC3 in the IR • LBGs • Data • Results • SFR • Shechter (Luminosity) Function • Reionization

  4. Note • Paper 1  Probing ~ L* Lyman-Break Galaxies at z~7 in GOODS-South with WFC3 on HST • Paper 2  The Contribution of High Redshift Galaxies to Cosmic Reionization: New Results from Deep WFC3 Imaging of the Hubble Ultra Deep Field

  5. Hubble • Two previous detectors on Hubble used in these texts: ACS & NICMOS • ACS: Large detecting area, UV to NIR (~0.85μ), efficient • NICMOS: Small FOV, NIR (up to ~1.6μ) http://www.edcheung.com/job/sm4/wfpc/wfpc.htm

  6. Hubble • WFC3: Installed May 2009, Larger FOV than NICMOS, smaller FOV than ACS; same spectral range as NICMOS • Used Y,J,H bands with WFC3, although Paper 1 used Y(0.98μm) whereas Paper 2 used Y(1.05μm). • Note (in μm): • ACS • B = 0.435 • V = 0.606 • i ~ 0.740 • Z = 0.850 • NICMOS • Y ~ 1. • J ~ 1.25 • H ~ 1.6 • WFC3 • Y = 0.98 or 1.05 • J = 1.25 • H = 1.60

  7. http://www.stsci.edu/hst/proposing/documents/primer/Ch_49.html#1924814http://www.stsci.edu/hst/proposing/documents/primer/Ch_49.html#1924814

  8. Transmission efficiency for relevant filters

  9. High Redshift Observations • How do we find high-z objects? • Lyman-alpha emission (narrow band) • Lyman-break (broad band) • Gamma-Ray bursts (GR observatories) • Lyman-Break Galaxies: • Cue: Mark meet Board … • 3 Filters at low-z vs. 2 Filters at high-z

  10. Lyman break Galaxies • So for high-z (z > 5) galaxies: • No detection below filter with 1216A(1+z): Let’s call this a ‘UV detection’ • Detections in and above filter with 1216A(1+z) • Expect bluer colours in filters above 1216A(1+z) than most other sources.

  11. Data • Selection Criteria: • Paper I: z-Y>0.8 • Paper II: z-Y>1.3 • T-L dwarf & Low-z rejection Criteria • Paper I: Y-J~< 1.0 • Paper II: z-Y ~>3.6(Y-J)-0.8 OR >2 • Low-z rejection Criteria • No UV detections

  12. | | | | | | | | | | | | | | | | | |

  13. Results • Paper I: • Considered FOV of GOODS-South: 20 arcmin2 • 148 objects: 55 spurious, 79 have detections in B and V, 8 in i, 6 in z • 8 in i are likely z~6 galaxies (some previously confirmed) • 6 in z are likely z~7 galaxies. Further supported since objects not in MIPS 24μm (corresponds to ~3μm if z~7 correct)

  14. Results • Paper II: • Considered FOV of HUDF: 4.18 arcmin2 • 110 objects: 35 spurious, 55 have detections in B and V, 8 in i, 12 in z • 8 in i are likely z~6 galaxies (some previously confirmed) • 10 in z are likely z~7 galaxies. One in z is likely a transient object (compare with NICMOS), another is likely a T or L dwarf.

  15. Determining UV flux & SFR • For z=7, LUV can be determined from Y • Madau et al. 98 show that after enough time the equilibrium: LUV = const*SFR is reached • Paper I: SFRs in the range of 5-10 Mo/yr • Paper II: SFRs in the range of 1- 4 Mo/yr with one object having a SFR of 8Mo/yr --> Total SFR in field = 29.6 Mo/yr • Assumptions???

  16. Schechter Function • We wish to describe the number density of galaxies with luminosity between L and L+dL: • Parameters: z~7 • Φ* = 0.0011 Mpc-3 • α = -1.73 • MUV* = -19.8

  17. Reionization • Cosmological history: recombination, reionization, today • Possible sources of reionization: • AGN -- likely not: densities too low • Star formation early in the Universe • But evidence of Luminosity function evolution seems to contradict this.

  18. Reionization • Madau et al 98 give the necessary SFR density to provide reionization: ρSFR = (0.005Mo yr-1 Mpc-3/fesc)([1+z]/8)3(Ωbh702/0.0457)(C/5) • Considering Paper II, with a FOV of 4.2 arcmin2 and a z-range of 6.7-8.8, the 29.6 Mo/yr observed are taking place in a volume of ~18000Mpc giving a SFR density of ~ 0.0017Mo yr-1 Mpc -3 • Considering the assumptions that go into this a value of 0.0035-0.004 Mo yr-1 Mpc-3 is more likely (if not higher)

  19. Results • Thus the observed UV flux is too low to account for reionization by factors of a few. • Possible resolution: fesc is very high, or faint end slope of Luminosity function is much steeper than given before. • Two last possible solutions: low metallicity or top-heavy IMF

  20. Extra results • Z~8 results (y-drops)

  21. Sources • Wilkens, Stephen M. et al, Probing ~L* Lyman-break Galaxies at z ~ 7 in GOODS-South with WFC3 on HST, arXiv: 0910.1098v3, Dec 2009 • Bunker, Andrew J. et al, The Contribution of high Redshift Galaxies to Cosmic Reionization: New Results from Deep WFC3 Imaging of the Hubble Ultra Deep Field, arXiv:0909.2255v3, Dec 2009 • Luminosity Function lecture from Phil Armitage, university of Colorado in Boulder, http://jila.colorado.edu/~pja/astr3830/index.html • http://www.astro.ku.dk/~jfynbo/LBG.html • WFC3 info: http://www.edcheung.com/job/sm4/wfpc/wfpc.htm • WFC3 vs ACS: http://www.stsci.edu/hst/proposing/documents/primer/Ch_49.html#1924814 • ACS filters: http://adcam.pha.jhu.edu/instrument/filters/ • GRB: Wikipedia

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