VLT/XSHOOTER and Subaru/MOIRCS spectroscopy of HUDF.YD3: no evidence for Lyman emission at z = 8.55

Bunker, Andrew J, Caruana, Joseph, Wilkins, Stephen M, Stanway, Elizabeth R, Lorenzoni, Silvio, Lacy, Mark, Jarvis, Matt J and Hickey, Samantha (2013) VLT/XSHOOTER and Subaru/MOIRCS spectroscopy of HUDF.YD3: no evidence for Lyman emission at z = 8.55. Monthly Notices of the Royal Astronomical Society, 430 (4). pp. 3314-3319. ISSN 0035-8711

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We present spectroscopic observations with VLT/XSHOOTER and Subaru/MOIRCS of a relatively bright Y-band drop-out galaxy in the Hubble Ultra Deep Field (HUDF), first selected by Bunker et al., McLure et al. and Bouwens et al. to be a likely z ≈ 8–9 galaxy on the basis of its colours in the Hubble Space Telescope (HST) Advanced Camera for Surveys and Wide Field Camera 3 images. This galaxy, HUDF.YD3 (also known as UDFy-38135539), has been targetted for VLT/SINFONI integral field spectroscopy by Lehnert et al., 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 h with VLT/XSHOOTER and 11 h 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., despite the expected signal in our combined MOIRCS and XSHOOTER data being 5σ. 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 line 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.

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 09:32
Last Modified: 07 Mar 2017 07:23
URI: http://srodev.sussex.ac.uk/id/eprint/44493

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