Browsing by Author "Wilkins, Stephen M."
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Item Constraining the bright-end of the UV luminosity function for z ~ 7-9 galaxies: results from CANDELS/GOODS-South(OUP, 2013) Lorenzoni, Silvio; Bunker, Andrew J.; Wilkins, Stephen M.; Caruana, Joseph; Stanway, Elizabeth R.; Jarvis, MattThe recent Hubble Space Telescope near-infrared imaging with the Wide-Field Camera #3 (WFC3) of the GOODS-South field in the CANDELS program covering nearly 100 arcmin2, along with already existing Advanced Camera for Surveys optical data, makes possible the search for bright galaxy candidates at redshift z ~ 7 − 9 using the Lyman-break technique. We present the first analysis of z′-drop z ~ 7 candidate galaxies in this area, finding 19 objects. We also analyse Y -drops at z ~ 8, trebling the number of bright (HAB < 27mag) Y -drops from our previous work, and compare our results with those of other groups based on the same data. The bright high redshift galaxy candidates we find serve to better constrain the bright end of the luminosity function at those redshift, and may also be more amenable to spectroscopic confirmation than the fainter ones presented in various previous work on the smaller fields (the Hubble Ultra Deep Field and the WFC3 Early Release Science observations). We also look at the agreement with previous luminosity functions derived from WFC3 dropout counts, finding a generally good agreement, except for the luminosity function of Yan et al. (2010) at z ~ 8, which is strongly ruled out.Item VLT/XSHOOTER & Subaru/MOIRCS spectroscopy of HUDF-YD3: No evidence for Lyman-alpha emission at z=8.55(Oxford University Press, 2013) Bunker, Andrew J.; Caruana, Joseph; Wilkins, Stephen M.; Jarvis, MattWe present spectroscopic observations with VLT/XSHOOTER and Subaru/MOIRCS of a relatively bright Y -band drop-out galaxy in the Hubble Ultra Deep Field, first selected by Bunker et al. (2010), McLure et al. (2010) and Bouwens et al. (2010) to be a likely z ≈ 8 − 9 galaxy on the basis of its colours in the HST ACS and WFC 3 images. This galaxy, HUDF.YD3 (also known as UDFy-38135539) has been targetted for VLT/SINFONI integral field spectroscopy by Lehnert et al. (2010), who published a candidate Lyman-α emission line at z = 8.55 from this source. In our independent spectroscopy using two different infrared spectrographs (5 hours with VLT/XSHOOTER and 11 hours with Subaru/MOIRCS) we are unable to reproduce this line. We do not detect any emission line at the spectral and spatial location reported in Lehnert et al. (2010), despite the expected signal in our combined MOIRCS & XSHOOTER data being 5 σ. The line emission also seems to be ruled out by the faintness of this object in recently extremely deep F105W (Y -band) HST/WFC 3 imaging from HUDF12; the line would fall within this filter and such a galaxy should have been detected at YAB = 28.6 mag ( ∼ 20σ) rather than the marginal YAB ≈ 30 mag observed in the Y -band image, > 3 times fainter than would be expected if the emission lie was real. Hence it appears highly unlikely that the reported Lyman-α line emission at z > 8 is real, meaning that the highest-redshift sources for which Lyman-α emission has been seen are at z = 6.9 − 7.2. It is conceivable that Lyman-α does not escape galaxies at higher redshifts, where the Gunn-Peterson absorption renders the Universe optically thick to this line. However, deeper spectroscopy on a larger sample of candidate z > 7 galaxies will be needed to test this.