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A 20/20 vision of Reionization and Galaxy formation

A 20/20 vision of Reionization and Galaxy formation. Sangeeta Malhotra School of Earth and Space Exploration Arizona State University. Why Reionization?. As a watermark for galaxy-formation: 10 ionizing photons per Baryon produced by galaxies. Why Reionization?.

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A 20/20 vision of Reionization and Galaxy formation

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  1. A 20/20 vision of Reionization and Galaxy formation Sangeeta Malhotra School of Earth and Space Exploration Arizona State University.

  2. Why Reionization? • As a watermark for galaxy-formation: • 10 ionizing photons per Baryon produced by galaxies.

  3. Why Reionization? • Thermal history of the universe requires it: • Expansion and adiabatic cooling implies recombination of the IGM at z ~ 1100. • Transmission of UV light from nearby quasars requires a largely ionized IGM at z ~ 0 (indeed, up to z ~ 6). • Reionization sources: • Stars- likely • First stars- possible • AGN- currently disfavored • Studying the history of reionization sheds light on the history of early star formation.

  4. Two methods of identifying High redshift galaxies Lyman-break galaxies Lyman- galaxies

  5. Slitless spectroscopy

  6. If you were to look at high redshift (z > 6) galaxies with your naked eyes. This is what they would look like:

  7. To see galaxies in the Era of reionization, we need to 1. Go to the infra red.

  8. 2.Go faint

  9. OH forest from the ground

  10. 3. Have high spatial resolution Extrapolation to z~10 Ferguson et al. 2004

  11. 4. Have wide-field surveys Ouchi et al 05 LSS at z = 5.7

  12. 5. Get Spectra to get rid of foreground objects

  13. Malhotra et al. 2005, Pirzkal et al. 2007.

  14. Luminosity function of z~6 galaxies: slope of the faint end - whether or not there are sufficient photons to do the reionization? (Bunker et al. 04, Yan & Windhorst 04, Malhotra 05) Does the number of galaxies go up at z > 6 (Bouwens & Illingworth 2006, Stark et al. 2007) Stark et al. 07 Things to argue about: Bouwens & Illingworth 2006

  15. Masses of old stars on z~6 galaxies: Low mass, young ages for Lyman- galaxies. (Pirzkal et al. 2007) Massive LBGs: Mobasher et al. 06, Wiklind et al 07, Egami et al. 2005

  16. When was reionization? • Z~6 from Gunn-Peterson effect • Z~11 from WMAP3 • Z > 6.5 from Lyman- galaxies • Z ? From 21 cm tomography

  17. The Lyman-Test Neutral IGM Continuum Photons To Youngstarburst Observer Lyman- photons (Miralda-Escude 1998; Miralda-Escude & Rees 1998; Haiman & Spaans 1999; Loeb & Rybicki 1999)

  18. Comparing the Tests

  19. Reionization Test Malhotra & Rhoads 2004, ApJ Letters617, L5; See also Stern et al 2005; Haiman & Cen 2005; Kashikawa et al 2006 • We constructed Ly-α luminosity functions at z=5.7 and z=6.5 from a variety of surveys (including work from LALA, Hu et al, Kodaira et al, Taniguchi et al, Santos et al, Ajiki et al, Tran et al, Martin & Sawicki.)

  20. Lyman-α Luminosity Functions • Luminosity function fits for three faint-end slopes. • z = 6.5 plot shows two null hypotheses: • z = 5.7 LF, or • z = 5.7 LF reduced by a factor of 3 in luminosity to approximate IGM absorption. • No evidence for neutral IGM! Malhotra & Rhoads 2004, ApJ Letters617, L5

  21. The volume test:(Malhotra & Rhoads, 2006) Suppose each Lyman- emitter is visible because of a local Stromgren sphere, created by neighboring undetected dwarf galaxies, hidden AGNs, decaying dark matter, tooth fairies … • We know the space density of Lyman- galaxies at z=6.5  > 1x10-4 cMpc-3 (Taniguchi et al. 2005) • Place each one in a ionized bubble of the smallest size to enable escape of half of the line flux in an otherwise neutral medium • [V(I)] > 4/3(RssMpc)3 • Get a filling factor: f = n V. • The required volume ionized fraction is then roughly 1 - exp(-f). • Correlations modify the higher order terms.

  22. Ly- Luminosity Functions Revisited • Kashikawa et al (2006) and Shimasaku et al (2006) have revisited the LyA luminosity functions at z=6.5 and z=5.7. • Find apparent bright end evolution. Interpretation: • Neutral IGM? But: LF shape change not as expected • True LF evolution (Dijkstra et al 2007)? • Field to field variations?

  23. Kashikawa et al see some evolution (2006) • They see evolution at the bright end of the luminosity function: 3sigma, 2sigma if you take into account large scale clustering seen at z=3. • Not significant if clustering becomes stronger as expected theoretically (Dijkstra, Wyithe, Haiman 2006)

  24. Ly- Luminosity Functions Revisited The z=5.7 LF from Shimasaku et al is the highest yet observed. If we compared z=6.5 from K06 to any other z=5.7 LF, the difference would be smaller... Field to field variations?

  25. New questions that we have not yet asked • Morphology: HST has shown fairly compact (but not point like) morphology, Morphology in the line different from continuum: radiative transfer • Slope of the Faint end of the luminosity function: dwarfs • Blobs: cold accretion of gas in galaxies that are forming: can we see that? • Spectral Energy Distribution of galaxies: know little about the continuum properties • Spectra: physical properties, extinction, metallicities, SF history. • Go to higher redshift and look for signatures of reionization, manifested as attenuation of Ly-a line.

  26. Cold accretion flows

  27. Mapping Ionized and Neutral Gas with Lyman Alpha Galaxies • A control sample of Lyman break selected galaxies will be useful (green dots, below).

  28. 9 square-degrees of grism observationsshould yield about 1-4x105galaxies between z = 7-13, with redshifts Should be capable of detecting large scale structure

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