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HST imaging of the brightest z~8-9 galaxies from UltraVISTA: the extreme bright end of the UV luminosity function

Stefanon, Mauro and Labbé, Ivo and Bouwens, Rychard J. and Brammer, Gabriel B. and Oesch, Pascal and Franx, Marijn and Fynbo, Johan P. U. and Milvang-Jensen, Bo and Muzzin, Adam and Illingworth, Garth D. and Le Fèvre, Olivier and Caputi, Karina I. and Holwerda, Benne W. and McCracken, Henry J. and Smit, Renske and Magee, Dan (2017) HST imaging of the brightest z~8-9 galaxies from UltraVISTA: the extreme bright end of the UV luminosity function. . (Submitted)

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We report on the discovery of three especially bright candidate zphot & 8 galaxies. Five sources were targeted for follow-up with HST/WFC3, selected from a larger sample of 16 bright (24.8 . H . 25.5 mag) candidate z & 8 LBGs identified over the 1.6 degrees2 of the COSMOS/UltraVISTA field. These were identified as Y and J dropouts by leveraging the deep (Y -to-KS ∼ 25.6 − 25.2 mag, 5σ) NIR data from the UltraVISTA DR3 release, deep ground based optical imaging from the CFHTLS and Subaru Suprime Cam programs and Spitzer/IRAC mosaics combining observations from the SMUVS and SPLASH programs. Through the refined spectral energy distributions, which now also include new HyperSuprime Cam g, r, i, z, and Y band data, we confirm that 3/5 galaxies have robust zphot ∼ 8.0−8.7, consistent with the initial selection. The remaining 2/5 galaxies have a nominal zphot ∼ 2. However, if we use the HST data alone, these objects have increased probability of being at z ∼ 9. Furthermore, we measure mean UV continuum slopes β = −1.97±0.23 for the three z ∼ 8−9 galaxies, marginally bluer than similarly luminous z ∼ 4−6 in CANDELS but consistent with previous measurements of similarly luminous galaxies at z ∼ 7. The circularized effective radius for our brightest source is 0.9 ± 0.2 kpc, similar to previous measurements for a bright z ∼ 11 galaxy and bright z ∼ 7 galaxies. Finally, using the 1/Vmax formalism, we estimate for the first time the volume density of the extreme bright (MUV . −22 mag) end of the z ∼ 8 UV LF from actual detection of sources, as opposed to current upper limits from non-detections. Despite this exceptional result, the still large statistical uncertainties do not allow us to discriminate between a Schechter and a double power-law form.

Item Type:Report or Paper (Discussion Paper)
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URLURL TypeDescription Paper
McCracken, Henry J.0000-0002-9489-7765
Record Number:CaltechAUTHORS:20170628-104503624
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:78644
Deposited By: Joy Painter
Deposited On:28 Jun 2017 17:57
Last Modified:28 Sep 2017 22:09

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