5,327 research outputs found
Unveiling the nature of bright z ~ 7 galaxies with the Hubble Space Telescope
We present new Hubble Space Telescope/Wide Field Camera 3 imaging of 25
extremely luminous (-23.2 < M_ UV < -21.2) Lyman-break galaxies (LBGs) at z ~
7. The sample was initially selected from 1.65 deg^2 of ground-based imaging in
the UltraVISTA/COSMOS and UDS/SXDS fields, and includes the extreme Lyman-alpha
emitters, `Himiko' and `CR7'. A deconfusion analysis of the deep Spitzer
photometry available suggests that these galaxies exhibit strong rest-frame
optical nebular emission lines (EW_0(H_beta + [OIII]) > 600A). We find that
irregular, multiple-component morphologies suggestive of clumpy or merging
systems are common (f_multi > 0.4) in bright z ~ 7 galaxies, and ubiquitous at
the very bright end (M_UV < -22.5). The galaxies have half-light radii in the
range r_1/2 ~ 0.5-3 kpc. The size measurements provide the first determination
of the size-luminosity relation at z ~ 7 that extends to M_UV ~ -23. We find
the relation to be steep with r_1/2 ~ L^1/2. Excluding clumpy, multi-component
galaxies however, we find a shallower relation that implies an increased
star-formation rate surface density in bright LBGs. Using the new, independent,
HST/WFC3 data we confirm that the rest-frame UV luminosity function at z ~ 7
favours a power-law decline at the bright-end, compared to an exponential
Schechter function drop-off. Finally, these results have important implications
for the Euclid mission, which we predict will detect > 1000 similarly bright
galaxies at z ~ 7. Our new HST imaging suggests that the vast majority of these
galaxies will be spatially resolved by Euclid, mitigating concerns over dwarf
star contamination.Comment: 26 pages, 11 figures and 5 tables. Updated to match MNRAS accepted
versio
Orientation of biological cells using plane-polarized Gaussian beam optical tweezers
Optical tweezers are widely used for the manipulation of cells and their
internal structures. However, the degree of manipulation possible is limited by
poor control over the orientation of trapped cells. We show that it is possible
to controllably align or rotate disc shaped cells - chloroplasts of Spinacia
oleracea - in a plane polarised Gaussian beam trap, using optical torques
resulting predominantly from circular polarisation induced in the transmitted
beam by the non-spherical shape of the cells.Comment: 9 pages, 6 figure
A Combined EIS-NVSS Survey Of Radio Sources (CENSORS) III: Spectroscopic observations
The Combined EIS-NVSS Survey Of Radio Sources (CENSORS) is a 1.4GHz radio
survey selected from the NRAO VLA Sky Survey (NVSS) and complete to a
flux-density of 7.2mJy. It targets the ESO Imaging Survey (EIS) Patch D, which
is a 3 by 2 square degree field centred on 09 51 36.0, -21 00 00 (J2000). This
paper presents the results of spectroscopic observations of 143 of the 150
CENSORS sources. The primary motivation for these observations is to achieve
sufficient spectroscopic completeness so that the sample may be used to
investigate the evolution of radio sources.
The observations result in secure spectroscopic redshifts for 63% of the
sample and likely redshifts (based on a single emission line, for example) for
a further 8%. Following the identification of the quasars and star-forming
galaxies in the CENSORS sample, estimated redshifts are calculated for the
remainder of the sample via the K-z relation for radio galaxies. Comparison of
the redshift distribution of the CENSORS radio sources to distributions
predicted by the various radio luminosity function evolution models of Dunlop &
Peacock 1990, results in no good match. This demonstrates that this sample can
be used to expand upon previous work in that field.Comment: Accepted for publication in MNRAS. This version has some reduced
resolution figures and 13 associated gif files. A version with all figures
incorporated (at full resolution) is available at
http://www.roe.ac.uk/~pnb/papers/censors_spectro.pd
Morphology and Redshifts of Extremely Red Galaxies in the GOODS/CDFS deep ISAAC field
We present the photometric redshift distribution of a sample of 198 Extremely
Red Galaxies (ERGs) with Ks3.92 (Vega), selected by Roche et al.
in 50.4 sq. arcmin of the Chandra Deep Field South (CDFS). The sample has been
obtained using ISAAC-VLT and ACS-HST GOODS public data. We also show the
results of a morphological study of the 72 brightest ERGs in the z band (z<25,
AB).Comment: 2 pages, 2 figures. To appear in the proceedings of the ESO/USM/MPE
Workshop "Multiwavelength Mapping of Galaxy Formation and Evolution", Venice,
October 13-16, 200
The Evolution of 3CR Radio Galaxies from z=1
We present the results of a comprehensive re-analysis of the images of a
virtually complete sample of 28 powerful 3CR radio galaxies with redshifts
0.6<z<1.8 from the HST archive. Using a two-dimensional modelling technique we
have derived scalelengths and absolute magnitudes for a total of 16 3CR
galaxies with a median redshift of z=0.8. Our results confirm the basic
conclusions of Best, Longair & R\"{o}ttgering (1997, 1998) in that we also find
z=1 3CR galaxies to be massive, well-evolved ellipticals, whose infrared
emission is dominated by starlight. However, we in fact find that the
scalelength distribution of 3CR galaxies at z \simeq 1 is completely
indistinguishable from that derived for their low-redshift counterparts from
our own recently-completed HST study of AGN hosts at z \simeq 0.2. There is
thus no evidence that 3CR radio galaxies at z \simeq 1 are dynamically
different from 3CR galaxies at low redshift. Moreover, for a 10-object
sub-sample we have determined the galaxy parameters with sufficient accuracy to
demonstrate, for the first time, that the z \simeq 1 3CR galaxies follow a
Kormendy relation which is indistinguishable from that displayed by
low-redshift ellipticals if one allows for purely passive evolution. The
implied rather modest level of passive evolution since z \simeq 1 is consistent
with that predicted from spectrophotometric models provided one assumes a high
formation redshift (z \ge 4) within a low-density Universe. We conclude that
there is no convincing evidence for significant dynamical evolution among 3CR
galaxies in the redshift interval 0<z<1, and that simple passive evolution
remains an acceptable interpretation of the K-z relation for powerful radio
galaxies.Comment: 10 pages, 5 figures, minor changes, accepted for publication in MNRA
F stars, metallicity, and the ages of red galaxies at z > 1
We explore whether the rest-frame near-UV spectral region, observable in
high-redshift galaxies via optical spectroscopy, contains sufficient
information to allow the degeneracy between age and metallicity to be lifted.
We do this by testing the ability of evolutionary synthesis models to reclaim
the correct metallicity when fitted to the near-UV spectra of F stars of known
(sub-solar and super-solar) metallicity. F stars are of particular interest
because the rest-frame near-UV spectra of the oldest known elliptical galaxies
at z > 1 appear to be dominated by F stars near to the main-sequence turnoff.
We find that, in the case of the F stars, where the HST ultraviolet spectra
have high signal:noise, model-fitting with metallicity allowed to vary as a
free parameter is rather successful at deriving the correct metallicity. As a
result, the estimated turnoff ages of these stars yielded by the model fitting
are well constrained. Encouraged by this we have fitted these same variable-
metallicity models to the deep, optical spectra of the z \simeq 1.5 mJy radio
galaxies 53W091 and 53W069 obtained with the Keck telescope. While the
age-metallicity degeneracy is not so easily lifted for these galaxies, we find
that even when metallicity is allowed as a free parameter, the best estimates
of their ages are still \geq 3 Gyr, with ages younger than 2 Gyr now strongly
excluded. Furthermore, we find that a search of the entire parameter space of
metallicity and star formation history using MOPED (Heavens et al., 2000) leads
to the same conclusion. Our results therefore continue to argue strongly
against an Einstein-de Sitter universe, and favour a lambda-dominated universe
in which star formation in at least these particular elliptical galaxies was
completed somewhere in the redshift range z = 3 - 5.Comment: 10 pages, LaTeX, uses MNRAS style file, incorporates 14 postscript
figures, submitted to MNRAS. Changes include: inclusion of single stellar
atmosphere model fits; more rigorous calculation of confidence regions; some
re-structurin
OC009—An Assessment Of The Accuracy Of Horizon Scanning Predictions Of Medicine Use In The Scottish National Health Service
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