ISAAC Spectroscopy Overview

ISAAC Spectroscopy of a gravitationally magnified galaxyat z=2.72

Isaac Spectroscopy

Overview

Low-resolution spectroscopy in the H band of MS1512-cB58

MS1512-cB58 was serendipitously discovered by Yee et al. (1996, AJ, 111,1783) in the course of the CNOC cluster survey. It lies in the field ofthe z=0.36 cluster MS1512+36, and its redshift was derived from a dozenstrong absorption lines in the rest frame UV (Ellingson et al. 1996, ApJ, 466, L71). Most interestingly, this galaxy is gravitationally lensed and amplified by a factor of about40. Its near-IR magnitudes are J=19.12, H=18.42, K'=17.83, i.e. theobject is exceptionally bright for its redshift.Therefore, it offers a unique opportunity to get a high S/Ninfrared spectrum of a high redshift galaxy, with important lines suchas H_alpha (at the edge of the K band) and H_gamma (within the H band)being uncontaminated by atmospheric emission/absorption.The detection of such lines would allow a more reliable determination of thestar formation rates, compared to other indicators such as [O II] andthe UV continuum. More importantly, the profile of such lines - ifpresent - may provide hints on the mass of this high-redshift galaxy.ISAAC is the first instrument that offers this opportunity, and the unusuallylarge amplification factor makes it an attractive target for the VLT, in spite of the large zenithal distance at which it can be observed from Paranal.


 MS1512-cB58: RA(2000)= 15 14 22.25, DEC(2000)=+36 36 25.46