75 research outputs found
Spatially Resolved Spectroscopy of Starburst and Post-Starburst Galaxies in The Rich z~0.55 Cluster CL0016+16
We have used the Low Resolution Imaging Spectrograph (LRIS) on the W.M. Keck
I telescope to obtain spatially resolved spectroscopy of a small sample of six
post-starburst and three dusty-starburst galaxies in the rich cluster CL0016+16
at z=0.55. We use this to measure radial profiles of the Hdelta and OII3727
lines which are diagnostic probes of the mechanisms that give rise to the
abrupt changes in star-formation rates in these galaxies. In the post-starburst
sample we are unable to detect any radial gradients in the Hdelta line
equivalent width - although one galaxy exhibits a gradient from one side of the
galaxy to the other. The absence of Hdelta gradients in these galaxies is
consistent with their production via interaction with the intra-cluster medium,
however, our limited spatial sampling prevents us from drawing robust
conclusions. All members of the sample have early type morphologies, typical of
post-starburst galaxies in general, but lack the high incidence of tidal tails
and disturbances seen in local field samples. This argues against a merger
origin and adds weight to a scenario where truncation by the intra-cluster
medium is at work. The post-starburst spectral signature is consistent over the
radial extent probed with no evidence of OII3727 emission and strong Hdelta
absorption at all radii i.e. the post-starburst classification is not an
aperture effect. In contrast the dusty-starburst sample shows a tendency for a
central concentration of OII3727 emission. This is most straightforwardly
interpreted as the consequence of a central starburst. However, other
possibilities exist such as a non-uniform dust distribution (which is expected
in such galaxies) and/or a non-uniform starburst age distribution. The sample
exhibit late type and irregular morphologies.Comment: accepted for publication in PAS
The HI gas content of galaxies around Abell 370, a galaxy cluster at z = 0.37
We used observations from the Giant Metrewave Radio Telescope to measure the
atomic hydrogen gas content of 324 galaxies around the galaxy cluster Abell 370
at a redshift of z = 0.37 (a look-back time of ~4 billion years). The HI 21-cm
emission from these galaxies was measured by coadding their signals using
precise optical redshifts obtained with the Anglo-Australian Telescope. The
average HI mass measured for all 324 galaxies is (6.6 +- 3.5)x10^9 solar
masses, while the average HI mass measured for the 105 optically blue galaxies
is (19.0 +- 6.5)x10^9 solar masses. The significant quantities of gas found
around Abell 370, suggest that there has been substantial evolution in the gas
content of galaxy clusters since redshift z = 0.37. The total amount of HI gas
found around Abell 370 is up to ~8 times more than that seen around the Coma
cluster, a nearby galaxy cluster of similar size. Despite this higher gas
content, Abell 370 shows the same trend as nearby clusters, that galaxies close
to the cluster core have lower HI gas content than galaxies further away. The
Abell 370 galaxies have HI mass to optical light ratios similar to local galaxy
samples and have the same correlation between their star formation rate and HI
mass as found in nearby galaxies. The average star formation rate derived from
[OII] emission and from de-redshifted 1.4 GHz radio continuum for the Abell 370
galaxies also follows the correlation found in the local universe. The large
amounts of HI gas found around the cluster can easily be consumed by the
observed star formation rate in the galaxies over the ~4 billion years (from z
= 0.37) to the present day.Comment: accepted by MNRA
The Large Area Radio Galaxy Evolution Spectroscopic Survey (LARGESS): survey design, data catalogue and GAMA/WiggleZ spectroscopy
© 2016 The Authors. We present the Large Area Radio Galaxy Evolution Spectroscopic Survey (LARGESS), a spectroscopic catalogue of radio sources designed to include the full range of radio AGN populations out to redshift z ~ 0.8. The catalogue covers ~800 deg 2 of sky, and provides optical identifications for 19 179 radio sources from the 1.4 GHz Faint Images of the Radio Sky at Twenty-cm (FIRST) survey down to an optical magnitude limit of i mod < 20.5 in Sloan Digital Sky Survey (SDSS) images. Both galaxies and point-like objects are included, and no colour cuts are applied. In collaboration with the WiggleZ and Galaxy And Mass Assembly (GAMA) spectroscopic survey teams, we have obtained new spectra for over 5000 objects in the LARGESS sample. Combining these new spectra with data from earlier surveys provides spectroscopic data for 12 329 radio sources in the survey area, of which 10 856 have reliable redshifts. 85 per cent of the LARGESS spectroscopic sample are radio AGN (median redshift z = 0.44), and 15 per cent are nearby star-forming galaxies (median z = 0.08). Low-excitation radio galaxies (LERGs) comprise the majority (83 per cent) of LARGESS radio AGN at z < 0.8, with 12 per cent being high-excitation radio galaxies (HERGs) and 5 per cent radioloud QSOs. Unlike the more homogeneous LERG and QSO sub-populations, HERGs are a heterogeneous class of objects with relatively blue optical colours and a wide dispersion in mid-infrared colours. This is consistent with a picture in which most HERGs are hosted by galaxies with recent or ongoing star formation as well as a classical accretion disc
Stellar population gradients in the cores of nearby field E+A galaxies
We have selected a sample of local E+A galaxies from the Sloan Digital Sky
Survey (SDSS) Data Release 7 for follow up integral field spectroscopy with the
Wide Field Spectrograph (WiFeS) on the ANU 2.3-m telescope. The sample was
selected using the Halpha line in place of the [OII]3727 line as the indicator
of on-going star formation (or lack thereof). This allowed us to select a lower
redshift sample of galaxies than available in the literature since the
[OII]3727 falls off the blue end of the wavelength coverage in the SDSS for the
very lowest redshift objects. This low redshift selection means that the
galaxies have a large angular to physical scale which allows us to resolve the
central ~1kpc region of the galaxies; the region where stellar population
gradients are expected. Such observations have been difficult to make using
other higher redshift samples because even at redshifts z~0.1 the angular to
physical scale is similar to the resolution provided by ground based seeing.
Our integral field spectroscopy has enabled us to make the first robust
detections of Balmer line gradients in the centres of E+A galaxies. Six out of
our sample of seven, and all the galaxies with regular morphologies, are
observed to have compact and centrally-concentrated Balmer line absorption.
This is evidence for compact young cores and stellar population gradients which
are predicted from models of mergers and tidal interactions which funnel gas
into the galaxy core. Given the generally isolated nature of our sample this
argues for the galaxies being seen in the late stage of a merger where the
progenitors have already coalesced.Comment: accepted to MNRA
The HI content of star-forming galaxies at z = 0.24
We use observations from the Giant Metrewave Radio Telescope (GMRT) to
measure the atomic hydrogen gas content of star-forming galaxies at z = 0.24
(i.e. a look-backtime of ~3 Gyr). The sample of galaxies studied were selected
from Halpha-emitting field galaxies detected in a narrow-band imaging survey
with the Subaru Telescope. The Anglo-Australian Telescope was used to obtain
precise optical redshifts for these galaxies. We then coadded the HI 21 cm
emission signal for all the galaxies within the GMRT spectral line data cube.
From the coadded signal of 121 galaxies, we measure an average atomic
hydrogen gas mass of (2.26 +- 0.90)*10^9 solar masses. We translate this HI
signal into a cosmic density of neutral gas at z = 0.24 of Omega_gas = (0.91 +-
0.42)*10^-3. This is the current highest redshift at which Omega_gas has been
constrained from 21 cm emission and our value is consistent with that estimated
from damped Lyman-alpha systems around this redshift. We also find that the
correlations between the Halpha luminosity and the radio continuum luminosity
and between the star formation rate and the HI gas content in star-forming
galaxies at z = 0.24 are consistent with the correlations found at z = 0. These
two results suggest that the star formation mechanisms in field galaxies ~3 Gyr
ago were not substantially different from the present, even though the star
formation rate is 3 times higher.Comment: 11 pages, contains 9 figures and 1 table. Accepted for publishing in
MNRAS 2007 January 22. Received 2007 January 22; in original form 2006
November 3
The WiggleZ Dark Energy Survey: high-resolution kinematics of luminous star-forming galaxies
We report evidence of ordered orbital motion in luminous star-forming galaxies at z~ 1.3. We present integral field spectroscopy (IFS) observations, performed with the OH Suppressing InfraRed Imaging Spectrograph (OSIRIS) system, assisted by laser guide star adaptive optics on the Keck telescope, of 13 star-forming galaxies selected from the WiggleZ Dark Energy Survey. Selected via ultraviolet and [Oii] emission, the large volume of the WiggleZ survey allows the selection of sources which have comparable intrinsic luminosity and stellar mass to IFS samples at z > 2. Multiple 1-2kpc size subcomponents of emission, or 'clumps', are detected within the Hα spatial emission which extends over 6-10kpc in four galaxies, resolved compact emission (r 100kms-1) in the most compact sources. This unique data set reveals that the most luminous star-forming galaxies at z > 1 are gaseous unstable discs indicating that a different mode of star formation could be feeding gas to galaxies at z > 1, and lending support to theories of cold dense gas flows from the intergalactic medium
The WiggleZ Dark Energy Survey: Star-formation in UV-luminous galaxies from their luminosity functions
We present the ultraviolet (UV) luminosity function of galaxies from the
GALEX Medium Imaging Survey with measured spectroscopic redshifts from the
first data release of the WiggleZ Dark Energy Survey. This sample selects
galaxies with high star formation rates: at 0.6 < z < 0.9 the median star
formation rate is at the upper 95th percentile of optically-selected (r<22.5)
galaxies and the sample contains about 50 per cent of all NUV < 22.8, 0.6 < z <
0.9 starburst galaxies within the volume sampled.
The most luminous galaxies in our sample (-21.0>M_NUV>-22.5) evolve very
rapidly with a number density declining as (1+z)^{5\pm 1} from redshift z = 0.9
to z = 0.6. These starburst galaxies (M_NUV<-21 is approximately a star
formation rate of 30 \msuny) contribute about 1 per cent of cosmic star
formation over the redshift range z=0.6 to z=0.9. The star formation rate
density of these very luminous galaxies evolves rapidly, as (1+z)^{4\pm 1}.
Such a rapid evolution implies the majority of star formation in these large
galaxies must have occurred before z = 0.9.
We measure the UV luminosity function in 0.05 redshift intervals spanning
0.1<z<0.9, and provide analytic fits to the results. At all redshifts greater
than z=0.55 we find that the bright end of the luminosity function is not well
described by a pure Schechter function due to an excess of very luminous
(M_NUV<-22) galaxies. These luminosity functions can be used to create a radial
selection function for the WiggleZ survey or test models of galaxy formation
and evolution. Here we test the AGN feedback model in Scannapieco et al.
(2005), and find that this AGN feedback model requires AGN feedback efficiency
to vary with one or more of the following: stellar mass, star formation rate
and redshift.Comment: 27 pages; 13 pages without appendices. 22 figures; 11 figures in the
main tex
The WiggleZ Dark Energy Survey: improved distance measurements to z = 1 with reconstruction of the baryonic acoustic feature
We present significant improvements in cosmic distance measurements from the WiggleZ Dark Energy Survey, achieved by applying the reconstruction of the baryonic acoustic feature technique. We show using both data and simulations that the reconstruction technique can often be effective despite patchiness of the survey, significant edge effects and shot-noise. We investigate three redshift bins in the redshift range 0.2 < z < 1, and in all three find improvement after reconstruction in the detection of the baryonic acoustic feature and its usage as a standard ruler. We measure model-independent distance measures DV(rsfid/rs) of 1716 ± 83, 2221 ± 101, 2516 ± 86 Mpc (68 perâcent CL) at effective redshifts z = 0.44, 0.6, 0.73, respectively, where DV is the volume-averaged distance, and rs is the sound horizon at the end of the baryon drag epoch. These significantly improved 4.8, 4.5 and 3.4 per cent accuracy measurements are equivalent to those expected from surveys with up to 2.5 times the volume of WiggleZ without reconstruction applied. These measurements are fully consistent with cosmologies allowed by the analyses of the Planck Collaboration and the Sloan Digital Sky Survey. We provide the DV(rsfid/rs) posterior probability distributions and their covariances. When combining these measurements with temperature fluctuations measurements of Planck, the polarization of Wilkinson Microwave Anisotropy Probe 9, and the 6dF Galaxy Survey baryonic acoustic feature, we do not detect deviations from a flat Î cold dark matter (ÎCDM) model. Assuming this model, we constrain the current expansion rate to Hâ = 67.15 ± 0.98 km sâ»ÂčMpcâ»Âč. Allowing the equation of state of dark energy to vary, we obtain wDE = â1.080 ± 0.135. When assuming a curved ÎCDM model we obtain a curvature value of ΩK = â0.0043 ± 0.0047
- âŠ