8 research outputs found
On Measuring Chemical Abundances in Distant Galaxies Using Global Emission Line Spectra
The advent of 8--10 meter class telescopes enables direct measurement of the
chemical properties in the ionized gas of cosmologically--distant galaxies with
the same nebular analysis techniques used in local H II regions. We show that
spatially unresolved (i.e., global) emission line spectra can reliably indicate
the chemical properties of distant star-forming galaxies. However, standard
nebular chemical abundance measurement methods (those with a measured electron
temperature from [O III] lambda4363) may be subject to small systematic errors
when the observed volume includes a mixture of gas with diverse temperatures,
ionization parameters, and metallicities. To characterize these systematic
effects, we compare physical conditions derived from spectroscopy of individual
H II regions with results from global galaxy spectroscopy. We consider both
low-mass, metal poor galaxies with uniform abundances and larger galaxies with
internal chemical gradients. Well-established empirical calibrations using
strong-line ratios can serve as reliable (~0.2 dex) indicators of the overall
systemic oxygen abundance even when the signal-to-noise of the Hbeta and [O
III] emission lines is as low as 8:1. We present prescriptions, directed toward
high-redshift observers, for using global emission line spectra to trace the
chemical properties of star-forming galaxies in the distant universe.
[abridged]Comment: Accepted for Publication in the Astrophysical Journal; 34 pages, 10
figures, uses AASTeX and psfi
LSST Science Book, Version 2.0
A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo