Star-forming galaxies at z≈ 8-9 from Hubble Space Telescope/WFC3: implications for reionization

Lorenzoni, Silvio, Bunker, Andrew J, Wilkins, Stephen M, Stanway, Elizabeth R, Jarvis, Matt J and Caruana, Joseph (2011) Star-forming galaxies at z≈ 8-9 from Hubble Space Telescope/WFC3: implications for reionization. Monthly Notices of the Royal Astronomical Society, 414 (2). pp. 1455-1466. ISSN 0035-8711

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We present a search for galaxies at 7.6 < z < 9.8 using the latest Hubble Space Telescope/Wide Field Camera 3 (WFC3) near-infrared data, based on the Lyman-break technique. We search for galaxies which have large (Y−J) colours (the ‘Y-drops’) on account of the Lyman α forest absorption, and with (J−H) colours inconsistent with being low-redshift contaminants. We identify 24 candidates at redshift z≈ 8–9 (15 are robust and a further nine more marginal but consistent with being high redshift) over an area of ≈50 arcmin2. Previous searches for Y-drops with WFC3 have focused only on the Hubble Ultra Deep Field, and our larger survey (involving two other nearby deep fields and a wider area survey) has trebled the number of robust Y-drop candidates. For the first time, we have sufficient z≈ 8–9 galaxies to fit both φ* and M* of the UV Schechter luminosity function. There is evidence for evolution in this luminosity function from z= 6–7 to z= 8–9, in the sense that there are fewer UV-bright galaxies at z≈ 8–9, consistent with an evolution mainly in M*. The candidate z≈ 8–9 galaxies we detect have insufficient ionizing flux to reionize the Universe, and it is probable that galaxies below our detection limit provide a significant UV contribution. The faint-end slope, α, is not well constrained. However, adopting a similar faint-end slope to that determined at z= 3–6 (α=−1.7) and a Salpeter initial mass function (IMF), then the ionizing photon budget still falls short if fesc < 0.5, even integrating down to MUV=−8. A steeper faint-end slope or a low-metallicity population (or a top-heavy IMF) might still provide sufficient photons for star-forming galaxies to reionize the Universe, but confirmation of this might have to await the James Webb Space Telescope.

Item Type: Article
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Subjects: Q Science > QB Astronomy
Depositing User: Stephen Wilkins
Date Deposited: 26 Apr 2013 10:15
Last Modified: 03 Jul 2019 00:51

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