%0 Generic %1 hayes2012peculiar %A Hayes, Matthew %A Laporte, Nicolas %A Pello, Roser %A Schaerer, Daniel %A Borgne, Jean-Francois Le %D 2012 %K interlopers lbg low-z %T A peculiar galaxy appears at redshift 11: properties of a moderate redshift interloper %U http://arxiv.org/abs/1205.6815 %X Laporte et al. (2011) reported a very high redshift galaxy candidate: a lensed J-band dropout (A2667-J1). J1 has a photometric redshift of z=9.6-12, the probability density function for which permits no low or intermediate z solution. We here report new spectroscopic observations of this galaxy with VLT/XShooter, which show clear OIII5007AA, Ly-alpha, H-alpha, and H-beta emission and place the galaxy firmly at z=2.082. The oxygen lines contribute only ~25% to the H-band flux, and do not significantly affect the dropout selection of J1. After correcting the broadband fluxes for line emission, we identify two roughly equally plausible natures for A2667-J1: either it is young heavily reddened starburst, or a maximally old system with a very pronounced 4000AA break, upon which a minor secondary burst of star formation is superimposed. Fits show that to make a 3 sigma detection of this object in the B-band (V-band), imaging of depth AB=30.2 (29.5) would be required - despite the relatively bright NIR magnitude, we would need optical data of equivalent depth to the Hubble Ultra Deep Field to rule out the mid-z solution on purely photometric grounds. Assuming that this stellar population can be scaled to the NIR magnitudes of recent HST/WFC3 IR-selected galaxies, we conclude that infeasibly deep optical data AB~32 would be required for the same level of security. There is a population of galaxies at z~2 with continuum colours alone that mimic those of our z=7-12 candidates.

@misc{hayes2012peculiar, abstract = {Laporte et al. (2011) reported a very high redshift galaxy candidate: a lensed J-band dropout (A2667-J1). J1 has a photometric redshift of z=9.6-12, the probability density function for which permits no low or intermediate z solution. We here report new spectroscopic observations of this galaxy with VLT/XShooter, which show clear [OIII]5007AA, Ly-alpha, H-alpha, and H-beta emission and place the galaxy firmly at z=2.082. The oxygen lines contribute only ~25% to the H-band flux, and do not significantly affect the dropout selection of J1. After correcting the broadband fluxes for line emission, we identify two roughly equally plausible natures for A2667-J1: either it is young heavily reddened starburst, or a maximally old system with a very pronounced 4000AA break, upon which a minor secondary burst of star formation is superimposed. Fits show that to make a 3 sigma detection of this object in the B-band (V-band), imaging of depth AB=30.2 (29.5) would be required - despite the relatively bright NIR magnitude, we would need optical data of equivalent depth to the Hubble Ultra Deep Field to rule out the mid-z solution on purely photometric grounds. Assuming that this stellar population can be scaled to the NIR magnitudes of recent HST/WFC3 IR-selected galaxies, we conclude that infeasibly deep optical data AB~32 would be required for the same level of security. There is a population of galaxies at z~2 with continuum colours alone that mimic those of our z=7-12 candidates.}, added-at = {2012-06-01T03:59:48.000+0200}, author = {Hayes, Matthew and Laporte, Nicolas and Pello, Roser and Schaerer, Daniel and Borgne, Jean-Francois Le}, biburl = {https://www.bibsonomy.org/bibtex/2951a95cee1d76fa101fea8a2f1725906/miki}, description = {[1205.6815] A peculiar galaxy appears at redshift 11: properties of a moderate redshift interloper}, interhash = {942a712aee7992df729d84ec97c4eba1}, intrahash = {951a95cee1d76fa101fea8a2f1725906}, keywords = {interlopers lbg low-z}, note = {cite arxiv:1205.6815Comment: Accepted by Monthly Notices. 5 pages, 2 figures}, timestamp = {2012-06-01T03:59:48.000+0200}, title = {A peculiar galaxy appears at redshift 11: properties of a moderate redshift interloper}, url = {http://arxiv.org/abs/1205.6815}, year = 2012 }