VLT-XSHOOTER and Subaru-MOIRCS Spectroscopy of HUDF-YD3: No Evidence for Lyman-alpha Emission at z=8.55Reportar como inadecuado



 VLT-XSHOOTER and Subaru-MOIRCS Spectroscopy of HUDF-YD3: No Evidence for Lyman-alpha Emission at z=8.55


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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, 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 WFC3 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-alpha 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-sigma. The line emission also seems to be ruled out by the faintness of this object in recently extremely deep F105W Y-band HST-WFC3 imaging from HUDF12; the line would fall within this filter and such a galaxy should have been detected at YAB=28.6mag ~20 sigma rather than the marginal YAB~30mag 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-alpha line emission at z8 is real, meaning that the highest-redshift sources for which Lyman-alpha emission has been seen are at z=6.9-7.2. It is conceivable that Lyman-alpha 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 z7 galaxies will be needed to test this.



Autor: Andrew J. Bunker; Joseph Caruana; Stephen M. Wilkins; Elizabeth R. Stanway; Silvio Lorenzoni; Mark Lacy; Matt J. Jarvis; Samantha Hickey

Fuente: https://archive.org/



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