2,035 research outputs found
Measuring H0 from the 6dF Galaxy Survey and future low-redshift surveys
Baryon acoustic oscillations (BAO) at low redshift provide a precise and
largely model-independent way to measure the Hubble constant, H0. The 6dF
Galaxy Survey measurement of the BAO scale gives a value of H0 = 67 +/- 3.2
km/s/Mpc, achieving a 1-sigma precision of 5%. With improved analysis
techniques, the planned WALLABY (HI) and TAIPAN (optical) redshift surveys are
predicted to measure H0 to 1-3% precision.Comment: Proceedings of IAU Symposium 289, "Advancing the Physics of Cosmic
Distances", Richard de Grijs & Giuseppe Bono (eds), 2012, 4p
The peculiar motions of early-type galaxies in two distant regions - II. The spectroscopic data
We present the spectroscopic data for the galaxies studied in the EFAR
project, which is designed to measure the properties and peculiar motions of
early-type galaxies in two distant regions. We have obtained 1319 spectra of
714 early-type galaxies over 33 observing runs on 10 different telescopes. We
describe the observations and data reductions used to measure redshifts,
velocity dispersions and the Mgb and Mg2 Lick linestrength indices. Detailed
simulations and intercomparison of the large number of repeat observations lead
to reliable error estimates for all quantities. The measurements from different
observing runs are calibrated to a common zeropoint or scale before being
combined, yielding a total of 706 redshifts, 676 velocity dispersions, 676 Mgb
linestrengths and 582 Mg2 linestrengths. The median estimated errors in the
combined measurements are dcz=20 km/s, dsigma/sigma=9.1%, dMgb/Mgb=7.2% and
dMg2=0.015 mag. Comparison of our measurements with published datasets shows no
systematic errors in the redshifts or velocity dispersions and only small
zeropoint corrections to bring our linestrengths onto the standard Lick system.
We have assigned galaxies to physical clusters by examining the line-of-sight
velocity distributions based on EFAR and ZCAT redshifts, together with the
projected distributions on the sky. We derive mean redshifts and velocity
dispersions for these clusters, which will be used in estimating distances and
peculiar velocities and to test for trends in the galaxy population with
cluster mass. The spectroscopic parameters presented here for 706 galaxies
combine high quality data, uniform reduction and measurement procedures, and
detailed error analysis. They form the largest single set of velocity
dispersions and linestrengths for early-type galaxies published to date.Comment: 27 pages, 18 figures, accepted by MNRA
The Peculiar Motions of Early-Type Galaxies in Two Distant Regions VI: The Maximum Likelihood Gaussian Algorithm
The EFAR project is designed to measure the properties and peculiar motions
of early-type galaxies in two distant regions. Here we describe the maximum
likelihood algorithm we developed to investigate the correlations between the
parameters of the EFAR database. One-, two-, and three-dimensional gaussian
models are constructed to determine the mean value and intrinsic spread of the
parameters, and the slopes and intrinsic parallel and orthogonal spread of the
Mgb'-Mg2, Mg2-sigma, Mgb'-sigma relations, and the Fundamental Plane. In the
latter case, the cluster peculiar velocities are also determined. We show that
this method is superior to ``canonical'' approaches of least-squares type,
which give biased slopes and biased peculiar velocities. We test the algorithm
with Monte Carlo simulations of mock EFAR catalogues and derive the systematic
and random errors on the estimated parameters. We find that random errors are
always dominant. We estimate the influence of systematic errors due to the way
clusters were selected and the hard limits and uncertainties in the selection
function parameters for the galaxies. We explore the influence of uniform
distributions in the Fundamental Plane parameters and the errors. We conclude
that the mean peculiar motions of the EFAR clusters can be determined reliably.
In particular, the placement of the two EFAR sample regions relative to the
Lauer and Postman dipole allows us to strongly constrain the amplitude of the
bulk motion in this direction.Comment: 43 pages, 19 figures, accepted for publication in MNRA
Internal Kinematics of Distant Field Galaxies: I. Emission Line Widths for a Complete Sample of Faint Blue Galaxies at <z>=0.25
We present measurements of the OII(3727) emission line width for a complete
sample of 24 blue field galaxies (21.25=0.25, obtained
with the AUTOFIB fibre spectrograph on the Anglo-Australian Telescope. Most
emission lines are spectrally resolved, yet all have dispersions sigma<100km/s.
Five of the 24 sample members have OII doublet line flux ratios which imply gas
densities in excess of 100 cm^-3. The line emission in these galaxies may be
dominated by an active nucleus and the galaxies have been eliminated from the
subsequent analysis. The remaining 19 linewidths are too large by a factor of
two (7sigma significance) to be attributed to turbulent motions within an
individual star forming region, and therefore most likely reflect the orbital
motion of ionized gas in the galaxy. We use Fabry--Perot observations of nearby
galaxies to construct simulated datasets that mimic our observational setup at
z=0.25; these allow us to compute the expected distribution of (observable)
linewidths sigma_v for a galaxy of a given ``true'' (optical) rotation speed
v_c. These simulations include the effects of random viewing angles, clumpy
line emission, finite fibre aperture, and internal dust extinction on the
emission line profile. We assume a linewidth--luminosity--colour relation: ln[
v_c(M_B,B-R) ] = ln[v_c(-19,1)] - eta*(M_B+10) + zeta*[(B-R)-1] and determine
the range of parameters consistent with our data. We find a mean rotation speed
of v_c(-19,1)=66+-8km/s (68% confidence limits) for the distant galaxies with
M_B=-19 and B-R=1, with a magnitude dependence for v_c of eta=0.07+-0.08, and a
colour dependence of zeta =0.28+-0.25. Through comparison with several local
samples we show that this value of v_c(-19,1) is significantly lower than the
optical rotation speed of present-day galaxies with the same absolute magnitudeComment: TeX Text and Tables, no Figures. Compressed and uuencoded PS file of
the complete paper (43 pages including 9 figures) available at
http://zwicky.as.arizona.edu/~rix/; submitted to MNRA
The spectral characteristics of the 2dFGRS-NVSS galaxies
We have analysed the 2dF spectra of a sample of galaxies common to the 2dF
galaxy redshift survey (2dFGRS, Colless 1999) and the NRAO VLA sky survey
(NVSS, Condon et al. 1998). Our sample comprises 88 galaxies selected by Sadler
et al. (1999) from 30 2dFGRS fields observed in 1998. In this paper we discuss
how this and future, much larger, samples of 2dFGRS-NVSS galaxies can be
interpreted via analysis of those galaxies with strong narrow emission lines.
Using diagnostic line ratio measurements we confirm the majority of the eyeball
classifications of Sadler et al. (1999), although many galaxies show evidence
of being `composite' galaxies - a mixture of AGN plus starburst components.Comment: 11 pages, 5 figures, accepted for publication in PAS
Measurement of Star-Formation Rate from H-alpha in field galaxies at z=1
We report the results of J-band infrared spectroscopy of a sample of 13 z=1
field galaxies drawn from the Canada-France Redshift Survey, targeting galaxies
whose redshifts place the rest frame H-alpha line emission from HII regions in
between the bright night sky OH lines. As a result we detect emission down to a
flux limit of ~10^{-16} ergs cm^{-2} s^{-1} corresponding to a luminosity limit
of ~10^{41} ergs at this redshift for a H_0=50 km s^{-1} Mpc,^{-1} q_0=0.5
cosmology. From these luminosities we derive estimates of the star-formation
rates in these galaxies which are independent of previous estimates based upon
their rest-frame ultraviolet (2800A) luminosity. The mean star-formation rate
at z=1, from this sample, is found to be at least three times as high as the
ultraviolet estimates. The standard dust extinction in these galaxies is
inferred to be A_V=0.5-1.0 mags, comparable to local field galaxies, suggesting
that the bulk of star-formation is not heavily obscured unless one uses greyer
extinction laws. Star-forming galaxies have the bluest colours and a
preponderance of disturbed/interacting morphologies. We also investigate the
effects of particular star-formation histories, in particular the role of
bursts vs continuous star-formation in changing the detailed distribution of UV
to H-alpha emission. Generally we find that models dominated by short,
overlapping, bursts at typically 0.2 Gyr intervals provide a better model for
the data than a constant rate of star-formation. The star-formation history of
the Universe from Balmer lines is compiled and found to be typically 2--3\times
higher than that inferred from the UV {\em at all redshifts}. It can not yet be
clearly established whether the star-formation rate falls off or remains
constant at high-redshift.Comment: 15 pages including 8 figures. MNRAS in pres
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