Multi-object spectroscopy field configuration by simulated annealing

Abstract

Multi‐object spectroscopy (MOS) instruments, such as the Two‐degree Field (2dF) facility of the Anglo‐Australian Observatory (AAO), have facilitated large‐scale redshift surveys. Yet despite their acclaim, instrument design has been suspected of introducing subtle selection effects into surveys. Investigation into these selection effects has been overshadowed by instrument complexity. We identify the field configuration algorithm (FCA) used to select targets for observation as mainly responsible for such effects. An FCA can imprint artificial structure on observed target distributions, which may accrue over large angular scales, potentially to the detriment of statistical analyses applied to such surveys. We present here a new FCA developed for 2dF that is based on simulated annealing (SA), a generic method commonly used to solve constrained optimization problems. We generate synthetic fields and utilize mock 2dF volumes to contrast the behaviour of previous strategies with the SA FCA. The angular two‐point correlation function and other sensitive techniques reveal that the new FCA achieves unprecedented sampling uniformity and target yield with improved target priority handling and observational flexibility over current FCAs. The SA FCA is generic enough to be used by current 2dF‐like and potentially next‐generation MOS instruments with little modification.

Multi-fibre optical spectroscopy of low-mass stars and brown dwarfs in Upper Scorpius

“…AAOmega has a two degree field-of-view which is sampled by 400 fibres that feed a two-armed spectrograph. The projected diameter on the sky of each fibre is 2 arcsec and their minimum separation is 30 arcsec (Miszalski et al 2006). On the red arm we have employed the 385R grating to cover the wavelength range 5700−8800 Å (the exact coverage depends slightly on the position of the fibre on the spectrograph slit) at a resolution of R ∼ 1350.…”

Binary planetary nebulae nuclei towards the Galactic bulge

“…In most fields a few hundred sky targets were included to assist subtraction of the variable sky background. Prior to observation fibres were assigned to selected positions using the simulated annealing field configuration algorithm (Miszalski et al 2006). The relatively low target densities per field (∼20−70 PNe) enabled ∼200 sky targets and uncatalogued Hα emitters to be allocated, although the latter were given lower priority than catalogued PNe.…”

An Efficient Approach to Obtaining Large Numbers of Distant Supernova Host Galaxy Redshifts

“…If a sufficient number of hot DA white dwarfs can be found within the supernova search fields, then an alternative and perhaps more precise method of calibrating SNe Ia fluxes would become available. These objects were given the highest priority (priority six) as we wanted to make sure that they were all allocated a fibre by the automated fibre allocation software (Miszalski et al 2006). At the other end of the mass scale, the number density and clustering of galaxy clusters and the evolution of these properties with redshift depend on the properties of dark energy and can therefore be used to constrain it.…”

“…If the separation between a given pair of supernova hosts is smaller than the minimum permitted fibre separation, then both hosts cannot be observed at the same time. The allocation of fibres to targets is then done on the basis of this requirement, the number of available fibres and target priorities (Miszalski et al 2006).…”