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Figure 35. Portions of the ISIS spectrum showing the OI, OI*, OI**,
SiII, SiII* and SII lines. It is clearly visible that there are four
discrete velocity components, with velocity differences of up to
~500 km s -1 .
measurement of the neutral hydrogen column density and
the metal content from weak, unsaturated singly-ionised
sulphur (S II) lines, a metallicity of [S/H] = –0.84 ± 0.10, or
~0.14 times solar metallicity, was derived. This is in fact
one of the highest metallicities measured from absorption
lines at redshift around 4. From the very high column
densities for the forbidden singly-ionised silicon (Si II*),
and neutral oxygen (O I* and O I**) lines, the researchers
infer very high densities in the system, significantly larger
than 10 4 cm -3 .
The high-resolution spectra also allow the astronomers to
study the kinematics of the absorption systems. Several
different, discrete velocity systems can be distinguished,
with velocities of up to 500 km s -1 . Most surprisingly
however, was the tentative detection of molecular
hydrogen in the ISIS spectrum. This is the very first
detection of molecular lines in an optical GRB afterglow
spectrum. Especially remarkable is the fact that this
possible detection has been achieved with a 4-metre
telescope, proving that medium size telescopes can
compete when response times are short.
U AND B NUMBER COUNTS FROM THE
GOYA SURVEY
The Galaxy Origins and Young Assembly (GOYA) survey is
designed to study the formation and evolution of galaxies
with the aim of learning about the epoch and the
Figure 36. Observations of the GOYA Survey in the GWS region
over a DSS image. The 28 HST WFPC2 pointings defining the
GWS in F606W and F814W are shown in gray, while J and Ks
WHT INGRID fields are shown in white. The GWS runs diagonally
across the wide 45'×45' field marked in black, which corresponds
to the INT WFC field (U and B data). Numbers in black indicate
positions and orientations of the four chips of WFC (figure from
Eliche-Moral et al., 2006, ApJ, 639, 644).
mechanisms by which galaxies assembled the bulk of their
stars and acquired their present structure and dynamics.
For this, a near-infrared/optical observational program
using some of the most powerful ground-based telescopes
and public data is being conducted to map 0.5 square
degrees of high-latitude sky. As the main scientific
motivation behind the design of EMIR (a NIR cryogenic
multi-slit spectrograph for the 10.4m GTC at Observatorio
del Roque de los Muchachos), GOYA emphasizes the use
of near-infrared observations, which sample the optical
rest-frame spectrum of galaxies at very high redshifts.
The GOYA photometric survey is a multicolour survey in
six broadband filters (U, B, V, I, J, K s
) with target depths of
U=B=V=I=26 and J=K=22 (AB magnitudes). Its principal
aim is to generate a galaxy database for sample selection
and characterisation for subsequent NIR spectroscopy
with EMIR.
The U and B imaging came from observations carried out
with the INT Wide Field Camera and covers the Groth-
Westphal Strip (GWS). The GOYA Survey has also
reduced and analysed data over this field in NIR filters from
WHT INGRID (J and Ks) and in visible filters from HST
WFPC2 (F606W and F814W). Originally, the GWS field
40 • ING BIENNIAL R EPORT 2006–2007