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Finding z 6.5 galaxies with HSTs WFC3 and their implication on reionization Mark Richardson Slide 2 Possible Low-Z starz in High-z z-drop galaziez Slide 3 Outline WFC3 in the IR LBGs Data Results SFR Shechter (Luminosity) Function Reionization Slide 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 Slide 5 Hubble Two previous detectors on Hubble used in these texts: ACS & NICMOS ACS: Large detecting area, UV to NIR (~0.85), efficient NICMOS: Small FOV, NIR (up to ~1.6) http://www.edcheung.com/job/sm4/wfpc/wfpc.htm Slide 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(0.98m) whereas Paper 2 used Y(1.05m). Note (in m): 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 Slide 7 http://www.stsci.edu/hst/proposing/documents/primer/Ch_49.html#1924814 Slide 8 Transmission efficiency for relevant filters Slide 9 Slide 10 Slide 11 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 Slide 12 Lyman break Galaxies So for high-z (z > 5) galaxies: No detection below filter with 1216A(1+z): Lets 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. Slide 13 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 Slide 14 |||||||||||||||||||||||||||||||||||| Slide 15 Results Paper I: Considered FOV of GOODS-South: 20 arcmin 2 148 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 24m (corresponds to ~3m if z~7 correct) Slide 16 Slide 17 Results Paper II: Considered FOV of HUDF: 4.18 arcmin 2 110 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. Slide 18 Slide 19 Slide 20 Determining UV flux & SFR For z=7, L UV can be determined from Y Madau et al. 98 show that after enough time the equilibrium: L UV = const*SFR is reached Paper I: SFRs in the range of 5-10 M o /yr Paper II: SFRs in the range of 1- 4 M o /yr with one object having a SFR of 8M o /yr --> Total SFR in field = 29.6 M o /yr Assumptions??? Slide 21 Schechter Function We wish to describe the number density of galaxies with luminosity between L and L+dL: Parameters: z~7 * = 0.0011 Mpc -3 = -1.73 M UV * = -19.8 Slide 22 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. Slide 23 Reionization Madau et al 98 give the necessary SFR density to provide reionization: SFR = (0.005M o yr -1 Mpc -3 /f esc )([1+z]/8) 3 ( b h 70 2 /0.0457)(C/5) Considering Paper II, with a FOV of 4.2 arcmin 2 and a z-range of 6.7-8.8, the 29.6 M o /yr observed are taking place in a volume of ~18000Mpc giving a SFR density of ~ 0.0017M o yr -1 Mpc -3 Considering the assumptions that go into this a value of 0.0035- 0.004 M o yr -1 Mpc -3 is more likely (if not higher) Slide 24 Results Thus the observed UV flux is too low to account for reionization by factors of a few. Possible resolution: f esc 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 Slide 25 Extra results Z~8 results (y-drops) Slide 26 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://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.htmhttp://www.edcheung.com/job/sm4/wfpc/wfpc.htm WFC3 vs ACS: http://www.stsci.edu/hst/proposing/documents/primer/Ch_49.html#1924814http://www.stsci.edu/hst/proposing/documents/primer/Ch_49.html#1924814 ACS filters: http://adcam.pha.jhu.edu/instrument/filters/http://adcam.pha.jhu.edu/instrument/filters/ GRB: Wikipedia