EDP Sciences
Free access
Volume 416, Number 3, March IV 2004
Page(s) L35 - L40
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20040065

A&A 416, L35-L40 (2004)
DOI: 10.1051/0004-6361:20040065


ISAAC/VLT observations of a lensed galaxy at z = 10.0

R. Pelló1, D. Schaerer2, 1, J. Richard1, J.-F. Le Borgne1 and J.-P. Kneib3, 1

1  Laboratoire d'Astrophysique, UMR 5572, Observatoire Midi-Pyrénées, 14 Avenue E. Belin, 31400 Toulouse, France
2  Observatoire de Genève, 51, Ch. des Maillettes, 1290 Sauverny, Switzerland
3  Caltech Astronomy, MC105-24, Pasadena, CA 91125, USA

(Received 20 January 2004 / Accepted 13 February 2004)

We report the first likely spectroscopic confirmation of a $z\sim 10.0$ galaxy from our ongoing search for distant galaxies with ISAAC/VLT. Galaxy candidates at  $z \ga 7$ are selected from ultra-deep JHKs images in the core of gravitational lensing clusters for which deep optical imaging is also available, including HST data. The object reported here, found behind Abell 1835, exhibits a faint emission line detected in the J band, leading to z=10.0 when identified as Ly $\alpha$, in excellent agreement with the photometric redshift determination. Redshifts z < 7 are very unlikely for various reasons we discuss. The object is located on the critical lines corresponding to  z=9 to 11. The magnification factor  $\mu$ ranges from 25 to 100. For this object we estimate ${\it SFR}({\rm Ly}\alpha) \sim (0.8{-}2.2)~M _{\odot}$ yr -1 and  ${\it SFR}({\rm UV}) \sim (47{-}75)~M _{\odot}$ yr -1, both uncorrected for lensing. The steep UV slope

indicates a young object with negligible dust extinction. SED fits with young low-metallicity stellar population models yield (adopting  $\mu=25$) a lensing corrected stellar mass of  $M_\star \sim 8 \times 10^6~M _{\odot}$, and luminosities of  $2 \times 10^{10}~L _{\odot}$, corresponding to a dark matter halo of a mass of typically $M_{\rm tot} \ga 5 \times 10^8~M _{\odot}$. In general our observations show that under excellent conditions and using strong gravitational lensing direct observations of galaxies close to the "dark ages" are feasible with ground-based 8-10 m class telescopes.

Key words: galaxies: high-redshift -- galaxies: evolution -- galaxies: starburst -- galaxies: active -- infrared: galaxies

Offprint request: R. Pelló, roser@ast.obs-mip.fr

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© ESO 2004