369 research outputs found
Design and construction of the IMACS-IFU, a 2000-element integral field unit
The IMACS-IFU is an Integral Field Unit built for the IMACS spectrograph at
the Magellan-I-Telescope at Las Campanas Observatory. It consists of two
rectangular fields of 5 by 7 arcseconds, separated by roughly one arcminute.
With a total number of 2000 spatial elements it is the second largest
fiber-lenslet based IFU worldwide, working in a wavelength range between 400
and 900 nm. Due to the equally sized fields classical background subtraction,
beam switching and shuffling are possible observation techniques. One
particular design challenge was the single, half a metre long curved slit in
combination with a non telecentric output. Besides the construction some
preliminary results are described.Comment: 10 pages, 7 figures, 1 table. Proceedings for SPIE poster 5492-175 of
SPIE Symposium "Astronomical Telescopes and Instrumentation", June 2004,
Glasgo
A faint galaxy redshift survey to B=24
Using the multislit LDSS-2 spectrograph on the {\it William Herschel
Telescope} we have completed a redshift survey in the magnitude range which has produced 73 redshifts representing a 73\% complete sample
uniformly-selected from four deep fields at high Galactic latitude. The survey
extends out to and includes the highest redshift galaxy () yet
discovered in a field sample. The median redshift, \zmed=0.46, and form of
the redshift distribution constitute compelling evidence against simple
luminosity evolution as an explanation of the large excess of faint galaxies
(2--4 no-evolution) seen in this magnitude range. Rather we
identify the excess population as blue objects with and \,
luminosities similar to local galaxies indicating a dramatic decrease in
the density of such objects over the last Hubble time, confirming the trends
found in brighter redshift surveys. We also find a marked absence of {\it very}
low redshift galaxies (0.1) at faint limits, severely constraining any
significant steepening of the local field galaxy luminosity function at low
luminosities.Comment: uuencoded compressed postscript. The preprint are also available at
URL http://www.ast.cam.ac.uk/preprint/PrePrint.htm
Modelling the application of integrated photonic spectrographs to astronomy
One of the well-known problems of producing instruments for Extremely Large
Telescopes is that their size (and hence cost) scales rapidly with telescope
aperture. To try to break this relation alternative new technologies have been
proposed, such as the use of the Integrated Photonic Spectrograph (IPS). Due to
their diffraction limited nature the IPS is claimed to defeat the harsh scaling
law applying to conventional instruments. The problem with astronomical
applications is that unlike conventional photonics, they are not usually fed by
diffraction limited sources. This means in order to retain throughput and
spatial information the IPS will require multiple Arrayed Waveguide Gratings
(AWGs) and a photonic lantern. We investigate the implications of these extra
components on the size of the instrument. We also investigate the potential
size advantage of using an IPS as opposed to conventional monolithic optics. To
do this, we have constructed toy models of IPS and conventional image sliced
spectrographs to calculate the relative instrument sizes and their requirements
in terms of numbers of detector pixels. Using these models we can quantify the
relative size/cost advantage for different types of instrument, by varying
different parameters e.g. multiplex gain and spectral resolution. This is
accompanied by an assessment of the uncertainties in these predictions, which
may prove crucial for the planning of future instrumentation for
highly-multiplexed spectroscopy.Comment: 11 pages, 11 figures, SPIE Astronomical Telescopes and
Instrumentatio
Spectroscopy of arcs in the rich cluster Abell 963
Spectra are presented for portions of the two arcs observed close to the dominant cD galaxy in the rich cluster Abell 963 (z = 0.206). The spectrum of the northern arc displays a strong emission line at 6600 Å which is seen along the entire arc. The feature cannot be understood unless the redshift is greater than that of the cluster, the most likely interpretation being [O II] 3727 Å at z = 0.771. The southern arc is considerably fainter and its spectrum shows no obvious features. However, new CCD photometry is consistent with a near-constant blue color ( B – R ~ 0.3) along both arcs, supporting the suggestion that they arise from the gravitationally lensed light of a background object. The optical and infrared color is consistent with a spiral galaxy undergoing strong star formation at this redshift. We discuss briefly the implication of this result, and the possible role lensing surveys may play in the study of high-redshift galaxies
Coupling starlight into single-mode photonic crystal fiber using a field lens.
We determine the coupling characteristics of a large mode area (LMA) photonic crystal, single-mode fiber when fed with an on-axis field lens used to place an image of the telescope exit pupil at the fiber input. The maximum field of view is found to be approximately the same as that of feeding the fiber directly with the telescope PSF in the image plane. However, the field lens feed can be used to provide a flat, maximised coupling response over the entire visible-NIR which is not possible using either the highly wavelength dependent direct feed coupling to the LMA fiber or the attenuation spectrum limited step index fiber cases
Further redshifts of 1-Jy radio sources
We have firm redshifts for a further 12 faint radio source identifications from the ‘1-Jy’ complete radio-selected sample, two of which are galaxies with redshifts z > 1.5. Another object has a provisional redshift that requires confirmation. Five of these identifications had previously been classified as QSOs on the basis of their optical morphology. Our spectroscopy shows that of these, one is definitely a galaxy and two have characteristics intermediate between those of ‘normal’ radio galaxies and those of ‘normal’ quasars, for instance broad Balmer emission but an extended optical image. Two of the eight identifications previously classified as galaxies have similar ‘intermediate’ properties. The remaining identifications have low-excitation narrow emission-line systems of the type seen in other 1-Jy radio sources by Allington-Smith et al. We confirm that the 1-Jy emission lines are a factor 2 weaker than those of 3C galaxies in the same redshift interval
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