2,018 research outputs found
A submillimetre survey of the star-formation history of radio galaxies
We present the results of the first major systematic submillimetre survey of
radio galaxies spanning the redshift range 1 < z < 5. The primary aim of this
work is to elucidate the star-formation history of this sub-class of elliptical
galaxies by tracing the cosmological evolution of dust mass. Using SCUBA on the
JCMT we have obtained 850-micron photometry of 47 radio galaxies to a
consistent rms depth of 1 mJy, and have detected dust emission in 14 cases. The
radio galaxy targets have been selected from a series of low-frequency radio
surveys of increasing depth (3CRR, 6CE, etc), in order to allow us to separate
the effects of increasing redshift and increasing radio power on submillimetre
luminosity. Although the dynamic range of our study is inevitably small, we
find clear evidence that the typical submillimetre luminosity (and hence dust
mass) of a powerful radio galaxy is a strongly increasing function of redshift;
the detection rate rises from 15 per cent at z 2.5,
and the average submillimetre luminosity rises as (1+z)^3 out to z~4. Moreover
our extensive sample allows us to argue that this behaviour is not driven by
underlying correlations with other radio galaxy properties such as radio power,
radio spectral index, or radio source size/age. Although radio selection may
introduce other more subtle biases, the redshift distribution of our detected
objects is in fact consistent with the most recent estimates of the redshift
distribution of comparably bright submillimetre sources discovered in blank
field surveys. The evolution of submillimetre luminosity found here for radio
galaxies may thus be representative of massive ellipticals in general.Comment: 31 pages - 10 figures in main text, 3 pages of figures in appendix.
This revised version has been re-structured, but the analysis and conclusions
have not changed. Accepted for publication in MNRA
The Evolution of the Stellar Hosts of Radio Galaxies
We present new near-infrared images of z>0.8 radio galaxies from the
flux-limited 7C-III sample of radio sources for which we have recently obtained
almost complete spectroscopic redshifts. The 7C objects have radio luminosities
about 20 times fainter than 3C radio galaxies at a given redshift. The absolute
magnitudes of the underlying host galaxies and their scale sizes are only
weakly dependent on radio luminosity. Radio galaxy hosts at z~2 are
significantly brighter than the hosts of radio-quiet quasars at similar
redshifts and the model AGN hosts of Kauffmann & Haehnelt (2000). There is no
evidence for strong evolution in scale size, which shows a large scatter at all
redshifts. The hosts brighten significantly with redshift, consistent with the
passive evolution of a stellar population that formed at z>~3. This scenario is
consistent with studies of host galaxy morphology and submillimeter continuum
emission, both of which show strong evolution at z>~2.5. The lack of a strong
``redshift cutoff'' in the radio luminosity function to z>4 suggests that the
formation epoch of the radio galaxy host population lasts >~1Gyr from z>~5 to
z~3. We suggest these facts are best explained by models in which the most
massive galaxies and their associated AGN form early due to high baryon
densities in the centres of their dark matter haloes.Comment: To appear in A
Sensitive Limits on the Water Abundance in Cold Low Mass Molecular Cores
We present SWAS observations of water vapor in two cold star-less clouds, B68
and Core D in rho Ophiuchus. Sensitive non-detections of the 1(10)-1(01)
transition of o-H2O are reported for each source. Both molecular cores have
been previously examined by detailed observations that have characterized the
physical structure. Using these rather well defined physical properties and a
Monte-Carlo radiation transfer model we have removed one of the largest
uncertainties from the abundance calculation and set the lowest water abundance
limit to date in cold low-mass molecular cores. These limits are < 3 x 10^{-8}
(relative to H2) and < 8 x 10^{-9} in B68 and rho Oph D, respectively. Such low
abundances confirm the general lack of ortho-water vapor in cold (T < 20 K)
cores. Provided that the ortho/para ratio of water is not near zero, these
limits are well below theoretical predictions and appear to support the
suggestion that most of the water in dense low-mass cores is frozen onto the
surfaces of cold dust grains.Comment: 12 pages, 3 figures, accepted by Astrophysical Journal Letter
What Powers the Compact Radio Emission in Nearby Elliptical and S0 Galaxies?
Many nearby early-type (elliptical and S0) galaxies contain weak
(milli-Jansky level) nuclear radio sources on scales a few hundred parsecs or
less. The origin of the radio emission, however, has remained unclear,
especially in volume-limited samples that select intrinsically less luminous
galaxies. Both active galactic nuclei and nuclear star formation have been
suggested as possible mechanisms for producing the radio emission. This paper
utilizes optical spectroscopic information to address this issue. A substantial
fraction of the early-type galaxies surveyed with the Very Large Array by
Wrobel & Heeschen (1991) exhibits detectable optical emission lines in their
nuclei down to very sensitive limits. Comparison of the observed radio
continuum power with that expected from the thermal gas traced by the optical
emission lines implies that the bulk of the radio emission is nonthermal. Both
the incidence and the strength of optical line emission correlate with the
radio power. At a fixed line luminosity, ellipticals have stronger radio cores
than S0s. The relation between radio power and line emission observed in this
sample is consistent with the low-luminosity extension of similar relations
seen in classical radio galaxies and luminous Seyfert nuclei. A plausible
interpretation of this result is that the weak nuclear sources in nearby
early-type galaxies are the low-luminosity counterparts of more powerful AGNs.
The spectroscopic evidence supports this picture. Most of the emission-line
objects are optically classified as Seyfert nuclei or low-ionization nuclear
emission-line regions (LINERs), the majority of which are likely to be
accretion-powered sources.Comment: LaTex, 16 pages including embedded figures. Accepted for publication
in the Astrophysical Journa
MESMER: MeerKAT Search for Molecules in the Epoch of Reionization
[Abridged] Observations of molecular gas at all redshifts are critical for
measuring the cosmic evolution in molecular gas density and understanding the
star-formation history of the Universe. The 12CO molecule (J=1-0 transition =
115.27 GHz) is the best proxy for extragalactic H2, which is the gas reservoir
from which star formation occurs, and has been detected out to z~6. Typically,
redshifted high-J lines are observed at mm-wavelengths, the most commonly
targeted systems exhibiting high SFRs (e.g. submm galaxies), and far-IR-bright
QSOs. While the most luminous objects are the most readily observed, detections
of more typical galaxies with modest SFRs are essential for completing the
picture. ALMA will be revolutionary in terms of increasing the detection rate
and pushing the sensitivity limit down to include such galaxies, however the
limited FoV when observing at such high frequencies makes it difficult to use
ALMA for studies of the large-scale structure traced out by molecular gas in
galaxies. This article introduces a strategy for a systematic search for
molecular gas during the EoR (z~7 and above), capitalizing on the fact that the
J=1-0 transition of 12CO enters the upper bands of cm-wave instruments at
high-z. The FoV advantage gained by observing at such frequencies, coupled with
modern broadband correlators allows significant cosmological volumes to be
probed on reasonable timescales. In this article we present an overview of our
future observing programme which has been awarded 6,500 hours as one of the
Large Survey Projects for MeerKAT, the forthcoming South African SKA pathfinder
instrument. Its large FoV and correlator bandwidth, and high-sensitivity
provide unprecedented survey speed for such work. An existing astrophysical
simulation is coupled with instrumental considerations to demonstrate the
feasibility of such observations and predict detection rates.Comment: 7 pages, 4 figures, to appear in the proceedings of "Astronomy with
megastructures: Joint science with the E-ELT and SKA", 10-14 May 2010, Crete,
Greece (Eds: Isobel Hook, Dimitra Rigopoulou, Steve Rawlings and Aris
Karastergiou
Performance of Sensitivity based NMPC Updates in Automotive Applications
In this work we consider a half car model which is subject to unknown but
measurable disturbances. To control this system, we impose a combination of
model predictive control without stabilizing terminal constraints or cost to
generate a nominal solution and sensitivity updates to handle the disturbances.
For this approach, stability of the resulting closed loop can be guaranteed
using a relaxed Lyapunov argument on the nominal system and Lipschitz
conditions on the open loop change of the optimal value function and the stage
costs. For the considered example, the proposed approach is realtime applicable
and corresponding results show significant performance improvements of the
updated solution with respect to comfort and handling properties.Comment: 6 pages, 2 figure
The inevitable youthfulness of known high-redshift radio galaxies
Radio galaxies can be seen out to very high redshifts, where in principle
they can serve as probes of the early evolution of the Universe. Here we show
that for any model of radio-galaxy evolution in which the luminosity decreases
with time after an initial rapid increase (that is, essentially all reasonable
models), all observable high-redshift radio-galaxies must be seen when the
lobes are less than 10^7 years old. This means that high-redshift radio
galaxies can be used as a high-time-resolution probe of evolution in the early
Universe. Moreover, this result helps to explain many observed trends of
radio-galaxy properties with redshift [(i) the `alignment effect' of optical
emission along radio-jet axes, (ii) the increased distortion in radio
structure, (iii) the decrease in physical sizes, (iv) the increase in radio
depolarisation, and (v) the increase in dust emission] without needing to
invoke explanations based on cosmology or strong evolution of the surrounding
intergalactic medium with cosmic time, thereby avoiding conflict with current
theories of structure formation.Comment: To appear in Nature. 4 pages, 2 colour figures available on request.
Also available at http://www-astro.physics.ox.ac.uk/~km
The Presence of Essential and Non-Essential Stratum Corneum Proteases: The Vital Need for Protease Inhibitors
Dry skin is one of the most important
concerns of consumers worldwide.
Despite huge efforts over several decades,
the personal care industry still
does not offer complete solutions that
satisfy the unmet needs of consumers
for moisturizing treatments. The
paucity of data for the underlying biochemical
problems in and the effects
of moisturizers on facial skin biology
and physiology may partly explain
this. Our recent color mapping studies
based on bio-instrumental evaluations
of skin capacitance and transepidermal
water loss have revealed the
complexity of facial skin. However,
the biomolecular reasons for these
subtle differences in the different
zones of the face are unknown so
far. As the maturation of the stratum
corneum is vital for skin moisturization
and optimal barrier function, we
believe that the protease / proteaseinhibitor
balance particularly of the
plasminogen system may be key in
these processes. Thus, our aim was
to develop a specific dual plasmin and
urokinase inhibitor for topical application
to barrier-impaired skin and
demonstrate its efficac
Tracing the Mass during Low-Mass Star Formation. II. Modelling the Submillimeter Emission from Pre-Protostellar Cores
We have modeled the emission from dust in pre-protostellar cores, including a
self-consistent calculation of the temperature distribution for each input
density distribution. Model density distributions include Bonnor-Ebert spheres
and power laws. The Bonnor-Ebert spheres fit the data well for all three cores
we have modeled. The dust temperatures decline to very low values (\Td \sim 7
K) in the centers of these cores, strongly affecting the dust emission.
Compared to earlier models that assume constant dust temperatures, our models
indicate higher central densities and smaller regions of relatively constant
density. Indeed, for L1544, a power-law density distribution, similar to that
of a singular, isothermal sphere, cannot be ruled out. For the three sources
modeled herein, there seems to be a sequence of increasing central
condensation, from L1512 to L1689B to L1544. The two denser cores, L1689B and
L1544, have spectroscopic evidence for contraction, suggesting an evolutionary
sequence for pre-protostellar cores.Comment: 22 pages, 9 figures, Ap. J. accepted, uses emulateapj5.st
HST NIR Snapshot Survey of 3CR Radio Source Counterparts II: An Atlas and Inventory of the Host Galaxies, Mergers and Companions
We present the second part of an H-band (1.6 microns) atlas of z<0.3 3CR
radio galaxies, using the Hubble Space Telescope Near Infrared Camera and
Multi-Object Spectrometer (HST NICMOS2). We present new imaging for 21 recently
acquired sources, and host galaxy modeling for the full sample of 101
(including 11 archival) -- an 87% completion rate. Two different modeling
techniques are applied, following those adopted by the galaxy morphology and
the quasar host galaxy communities. Results are compared, and found to be in
excellent agreement, although the former breaks down in the case of strongly
nucleated sources. Companion sources are tabulated, and the presence of
mergers, tidal features, dust disks and jets are catalogued. The tables form a
catalogue for those interested in the structural and morphological dust-free
host galaxy properties of the 3CR sample, and for comparison with morphological
studies of quiescent galaxies and quasar host galaxies. Host galaxy masses are
estimated, and found to typically lie at around 2*10^11 solar masses. In
general, the population is found to be consistent with the local population of
quiescent elliptical galaxies, but with a longer tail to low Sersic index,
mainly consisting of low-redshift (z<0.1) and low-radio-power (FR I) sources. A
few unusually disky FR II host galaxies are picked out for further discussion.
Nearby external sources are identified in the majority of our images, many of
which we argue are likely to be companion galaxies or merger remnants. The
reduced NICMOS data are now publicly available from our website
(http://archive.stsci.edu/prepds/3cr/)Comment: ApJS, 177, 148: Final version; includes revised figures 1, 15b, and
section 7.5 (and other minor changes from editing process. 65 pages, inc. 17
figure
- …