279 research outputs found
Cosmic Dynamics in the Chameleon Cosmology
We study in this paper chameleon cosmology applied to
Friedmann-Robertson-Walker space, which gives rise to the equation of state
(EoS) parameter larger than -1 in the past and less than -1 today, satisfying
current observations. We also study cosmological constraints on the model using
the time evolution of the cosmological redshift of distant sources which
directly probes the expansion history of the universe. Due to the evolution of
the universe's expansion rate, the model independent Cosmological Redshift
Drift (CRD)test is expected to experience a small, systematic drift as a
function of time. The model is supported by the observational data obtained
from the test.Comment: 16 pages, 9 figure
Galaxy and Mass Assembly (GAMA): Demonstrating the Power of WISE in the Study of Galaxy Groups to z \u3c 0.1
Combining high-fidelity group characterization from the Galaxy and Mass Assembly survey and source-tailored z \u3c 0.1 photometry from the Wide-Field Infrared Survey Explorer (WISE) survey, we present a comprehensive study of the properties of ungrouped galaxies, compared to 497 galaxy groups (4 †N FoF †20) as a function of stellar and halo mass. Ungrouped galaxies are largely unimodal in WISE color, the result of being dominated by star-forming, late-type galaxies. Grouped galaxies, however, show a clear bimodality in WISE color, which correlates strongly with stellar mass and morphology. We find evidence for an increasing early-type fraction, in stellar mass bins between 1010 M oË âČ M stellar âČ 1011 M oË, with increasing halo mass. Using ungrouped, late-type galaxies with star-forming colors (W2-W3 \u3e 3), we define a star-forming main sequence (SFMS), which we use to delineate systems that have moved below the sequence ( quenched for the purposes of this work). We find that with increasing halo mass, the relative number of late-type systems on the SFMS decreases, with a corresponding increase in early-type, quenched systems at high stellar mass (M stellar \u3e 1010.5 M oË), consistent with mass quenching. Group galaxies with masses M stellar \u3c 1010.5 M oË show evidence of quenching consistent with environmentally driven processes. The stellar mass distribution of late-type, quenched galaxies suggests that it may be an intermediate population as systems transition from being star-forming and late-type to the red sequence. Finally, we use the projected area of groups on the sky to extract groups that are (relatively) compact for their halo mass. Although these show a marginal increase in their proportion of high-mass and early-type galaxies compared to nominal groups, a clear increase in quenched fraction is not evident
Herschel-ATLAS/GAMA: A difference between star formation rates in strong-line and weak-line radio galaxies
We have constructed a sample of radio-loud objects with optical spectroscopy from the Galaxy and Mass Assembly (GAMA) project over the Herschel Astrophysical Terahertz Large Area Survey (Herschel-ATLAS) Phase 1 fields. Classifying the radio sources in terms of their optical spectra, we find that strong-emission-line sources ('high-excitation radio galaxies') have, on average, a factor of ~4 higher 250-ÎŒm Herschel luminosity than weak-line ('lowexcitation') radio galaxies and are also more luminous than magnitude-matched radio-quiet galaxies at the same redshift. Using all five H-ATLAS bands, we show that this difference in luminosity between the emission-line classes arises mostly from a difference in the average dust temperature; strong-emission-line sources tend to have comparable dust masses to, but higher dust temperatures than, radio galaxies with weak emission lines. We interpret this as showing that radio galaxies with strong nuclear emission lines are much more likely to be associated with star formation in their host galaxy, although there is certainly not a one-to-one relationship between star formation and strong-line active galactic nuclei (AGN) activity. The strong-line sources are estimated to have star formation rates at least a factor of 3-4 higher than those in the weak-line objects. Our conclusion is consistent with earlier work, generally carried out using much smaller samples, and reinforces the general picture of high-excitation radio galaxies as being located in lower-mass, less evolved host galaxies than their low-excitation counterparts.Peer reviewe
Large-scale structure in the Lyman-alpha forest II: analysis of a group of ten QSOs
The spatial distribution of Ly-alpha forest absorption systems towards ten
QSOs has been analysed to search for large-scale structure over the redshift
range 2.2 < z < 3.4. The QSOs form a closely spaced group on the sky and are
concentrated within a 1 deg^2 field. We have employed a technique based on the
first and second moments of the transmission probability density function which
is capable of identifying and assessing the significance of regions of over- or
underdense Ly-alpha absorption. We find evidence for large-scale structure in
the distribution of Ly-alpha forest absorption at the > 99 per cent confidence
level. In individual spectra we find overdense Ly-alpha absorption on scales of
up to 1200 km s^-1. There is also strong evidence for correlated absorption
across line of sight pairs separated by < 3 h^-1 proper Mpc (q_0 = 0.5). For
larger separations the cross-correlation signal becomes progressively less
significant.Comment: 15 pages, LaTeX, 6 Postscript figures, accepted for publication in
MNRA
The VIRMOS deep imaging survey II: CFH12K BVRI optical data for the 0226-04 deep field
(abridged) In this paper we describe in detail the reduction, preparation and
reliability of the photometric catalogues which comprise the 1.2 deg^2
CFH12K-VIRMOS deep field. The survey reaches a limiting magnitude of BAB~26.5,
VAB~26.2, RAB~25.9 IAB~25.0 and contains 90,729 extended sources in the
magnitude range 18.0<IAB<24.0. We demonstrate our catalogues are free from
systematic biases and are complete and reliable down these limits. We estimate
that the upper limit on bin-to-bin systematic photometric errors for the I-
limited sample is ~10% in this magnitude range. We estimate that 68% of the
catalogues sources have absolute per co-ordinate astrometric uncertainties less
than ~0.38" and ~0.32" (alpha,delta). Our internal (filter-to-filter) per
co-ordinate astrometric uncertainties are 0.08" and 0.08" (alpha,delta). We
quantify the completeness of our survey in the joint space defined by object
total magnitude and peak surface brightness. Finally, we present numerous
comparisons between our catalogues and published literature data: galaxy and
star counts, galaxy and stellar colours, and the clustering of both point-like
and extended populations. In all cases our measurements are in excellent
agreement with literature data to IAB<24.0. This combination of depth and areal
coverage makes this multi-colour catalogue a solid foundation to select
galaxies for follow-up spectroscopy with VIMOS on the ESO-VLT and a unique
database to study the formation and evolution of the faint galaxy population to
z~1 and beyond.Comment: 18 pages, 23 figures, accepted for publication in A&
Galaxy And Mass Assembly (GAMA)
The GAMA survey aims to deliver 250,000 optical spectra (3--7Ang resolution)
over 250 sq. degrees to spectroscopic limits of r_{AB} <19.8 and K_{AB}<17.0
mag. Complementary imaging will be provided by GALEX, VST, UKIRT, VISTA,
HERSCHEL and ASKAP to comparable flux levels leading to a definitive
multi-wavelength galaxy database. The data will be used to study all aspects of
cosmic structures on 1kpc to 1Mpc scales spanning all environments and out to a
redshift limit of z ~ 0.4. Key science drivers include the measurement of: the
halo mass function via group velocity dispersions; the stellar, HI, and
baryonic mass functions; galaxy component mass-size relations; the recent
merger and star-formation rates by mass, types and environment. Detailed
modeling of the spectra, broad SEDs, and spatial distributions should provide
individual star formation histories, ages, bulge-disc decompositions and
stellar bulge, stellar disc, dust disc, neutral HI gas and total dynamical
masses for a significant subset of the sample (~100k) spanning both the giant
and dwarf galaxy populations. The survey commenced March 2008 with 50k spectra
obtained in 21 clear nights using the Anglo Australian Observatory's new
multi-fibre-fed bench-mounted dual-beam spectroscopic system (AAOmega).Comment: Invited talk at IAU 254 (The Galaxy Disk in Cosmological Context,
Copenhagen), 6 pages, 5 figures, high quality PDF version available at
http://www.eso.org/~jliske/gama
Chameleonic Generalized Brans--Dicke model and late-time acceleration
In this paper we consider Chameleonic Generalized Brans--Dicke Cosmology in
the framework of FRW universes. The bouncing solution and phantom crossing is
investigated for the model. Two independent cosmological tests: Cosmological
Redshift Drift (CRD) and distance modulus are applied to test the model with
the observation.Comment: 20 pages, 15 figures, to be published in Astrophys. Space Sci. (2011
Constraints on the CMB temperature redshift dependence from SZ and distance measurements
The relation between redshift and the CMB temperature,
is a key prediction of standard cosmology, but is violated in many non-standard
models. Constraining possible deviations to this law is an effective way to
test the CDM paradigm and search for hints of new physics. We present
state-of-the-art constraints, using both direct and indirect measurements. In
particular, we point out that in models where photons can be created or
destroyed, not only does the temperature-redshift relation change, but so does
the distance duality relation, and these departures from the standard behaviour
are related, providing us with an opportunity to improve constraints. We show
that current datasets limit possible deviations of the form
to be up to a redshift
. We also discuss how, with the next generation of space and
ground-based experiments, these constraints can be improved by more than one
order of magnitude.Comment: 27 pages, 11 figure
Galaxy And Mass Assembly (GAMA): the 0.013 < z < 0.1 cosmic spectral energy distribution from 0.1 m to 1 mm
We use the Galaxy And Mass Assembly survey (GAMA) I data set combined with GALEX, Sloan Digital Sky Survey (SDSS) and UKIRT Infrared Deep Sky Survey (UKIDSS) imaging to construct the low-redshift (z < 0.1) galaxy luminosity functions in FUV, NUV, ugriz and YJHK bands from within a single well-constrained volume of 3.4 Ă 105 (Mpcâhâ1)3. The derived luminosity distributions are normalized to the SDSS data release 7 (DR7) main survey to reduce the estimated cosmic variance to the 5âper cent level. The data are used to construct the cosmic spectral energy distribution (CSED) from 0.1 to 2.1 ÎŒm free from any wavelength-dependent cosmic variance for both the elliptical and non-elliptical populations. The two populations exhibit dramatically different CSEDs as expected for a predominantly old and young population, respectively. Using the Driver et al. prescription for the azimuthally averaged photon escape fraction, the non-ellipticals are corrected for the impact of dust attenuation and the combined CSED constructed. The final results show that the Universe is currently generating (1.8 ± 0.3) Ă 1035âh W Mpcâ3 of which (1.2 ± 0.1) Ă 1035âh W Mpcâ3 is directly released into the inter-galactic medium and (0.6 ± 0.1) Ă 1035âh W Mpcâ3 is reprocessed and reradiated by dust in the far-IR. Using the GAMA data and our dust model we predict the mid- and far-IR emission which agrees remarkably well with available data. We therefore provide a robust description of the pre- and post-dust attenuated energy output of the nearby Universe from 0.1 ÎŒm to 0.6âmm. The largest uncertainty in this measurement lies in the mid- and far-IR bands stemming from the dust attenuation correction and its currently poorly constrained dependence on environment, stellar mass and morphology
A Catalogue of M51 type Galaxy Associations
A catalog of 232 apparently interacting galaxy pairs of the M51 class is
presented. Catalog members were identified from visual inspection of mult-band
images in the IRSA archive. The major findings in the compilation of this
catalog are (1) A surprisingly low number of the main galaxies in M51 systems
are early type spirals and barred spirals. (2) Over 70% of the main galaxies in
M51 systems are 2-armed spirals. (3) Some systems that were classified as M51
types in previous studies are not M51 types as defined in this catalog. There
were a number of systems previously classified as M51 systems for which the
companion is identified as an HII region within the main galaxy or a foreground
star within the Milky Way. (4) It was found that only 18% of the M51 type
companions have redshift measurements in the literature. There is a significant
need for spectroscopic study of the companions in order to improve the value of
the catalog as a sample for studying the effects of M51 type interaction on
galaxy dynamics, morphology, and star formation. Further spectroscopy will also
help constrain the statistics of possible chance projections between foreground
and background galaxies in this catalog. The catalog also contains over 430
additional systems which are classified as "possible M51" systems. The reasons
for classifying certain systems as possible M51 systems are discussed.Comment: 19 pages including 6 figures and tables 3-8, Tables 1 and 2 are found
at http://www.jorcat.com, Accepted for publication in Astrophysics and Space
Scienc
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