5,135 research outputs found
The Impact of Strong Gravitational Lensing on Observed Lyman-Break Galaxy Numbers at 4<z<8 in the GOODS and the XDF Blank Fields
Detection of Lyman-Break Galaxies (LBGs) at high-redshift can be affected by
gravitational lensing induced by foreground deflectors not only in galaxy
clusters, but also in blank fields. We quantify the impact of strong
magnification in the samples of , , , LBGs () observed in the XDF and GOODS/CANDELS fields, by investigating the
proximity of dropouts to foreground objects. We find that of bright
LBGs () by
foreground objects. This fraction decreases from at to
at . Since the observed fraction of strongly lensed
galaxies is a function of the shape of the luminosity function (LF), it can be
used to derive Schechter parameters, and , independently
from galaxy number counts. Our magnification bias analysis yields
Schechter-function parameters in close agreement with those determined from
galaxy counts albeit with larger uncertainties. Extrapolation of our analysis
to suggests that future surveys with JSWT, WFIRST and EUCLID
should find excess LBGs at the bright-end, even if there is an intrinsic
exponential cutoff of number counts. Finally, we highlight how the
magnification bias measurement near the detection limit can be used as probe of
the population of galaxies too faint to be detected. Preliminary results using
this novel idea suggest that the magnification bias at is not
as strong as expected if extends well below the current
detection limits in the XDF. At face value this implies a flattening of the LF
at . However, selection effects and completeness estimates
are difficult to quantify precisely. Thus, we do not rule out a steep LF
extending to .Comment: Submitted to ApJ on 18/12/201
Isolation and Characterisation of Genes Encoding Malate Synthesis and Transport Determinants in the Aluminum-Tolerant Australian Weeping-Grass (\u3cem\u3eMicrolaena Stipoides\u3c/em\u3e)
Acid soils cover some 40% of the Earth’s arable land where they represent a major limitation to plant production. Plant growth on acid soils is primarily limited due to aluminium (Al) solubilized by acidity into toxic Al3+ cations which will inhibit root growth resulting in poor uptake of water and nutrients. Many important pasture species lack sufficient Al tolerance within their germplasm to allow effective breeding for this character
Initial Hubble Diagram Results from the Nearby Supernova Factory
The use of Type Ia supernovae as distance indicators led to the discovery of
the accelerating expansion of the universe a decade ago. Now that large second
generation surveys have significantly increased the size and quality of the
high-redshift sample, the cosmological constraints are limited by the currently
available sample of ~50 cosmologically useful nearby supernovae. The Nearby
Supernova Factory addresses this problem by discovering nearby supernovae and
observing their spectrophotometric time development. Our data sample includes
over 2400 spectra from spectral timeseries of 185 supernovae. This talk
presents results from a portion of this sample including a Hubble diagram
(relative distance vs. redshift) and a description of some analyses using this
rich dataset.Comment: Short version of proceedings for ICHEP08, Philadelphia PA, July 2008;
see v1 for full-length versio
Iterative image reconstruction algorithms using wave-front intensity and phase variation,”
Iterative algorithms that reconstruct images from far-field x-ray diffraction data are plagued with convergence difficulties. An iterative image reconstruction algorithm is described that ameliorates these convergence difficulties through the use of diffraction data obtained with illumination modulated in both intensity and phase
Standardizing Type Ia Supernova Absolute Magnitudes Using Gaussian Process Data Regression
We present a novel class of models for Type Ia supernova time-evolving
spectral energy distributions (SED) and absolute magnitudes: they are each
modeled as stochastic functions described by Gaussian processes. The values of
the SED and absolute magnitudes are defined through well-defined regression
prescriptions, so that data directly inform the models. As a proof of concept,
we implement a model for synthetic photometry built from the spectrophotometric
time series from the Nearby Supernova Factory. Absolute magnitudes at peak
brightness are calibrated to 0.13 mag in the -band and to as low as 0.09 mag
in the blueshifted -band, where the dispersion includes
contributions from measurement uncertainties and peculiar velocities. The
methodology can be applied to spectrophotometric time series of supernovae that
span a range of redshifts to simultaneously standardize supernovae together
with fitting cosmological parameters.Comment: 47 pages, 15 figures, accepted for publication by Astrophysical
Journa
Nebular Spectra and Explosion Asymmetry of Type Ia Supernovae
The spectral signatures of asymmetry in Type Ia Supernova (SN Ia) explosions
are investigated, using a sample of late-time nebular spectra. First, a
kinematical model is constructed for SN Ia 2003hv, which can account for the
main features in its optical, Near-Infrared (NIR), and Mid-Infrared (Mid-IR)
late-time spectra. It is found that an asymmetric off-center model can explain
the observed characteristics of SN 2003hv. This model includes a relatively
high density, Fe-rich region which displays a large velocity off-set, and a
relatively low density, extended 56Ni-rich region which is more spherically
distributed. The high density region consists of the inner stable Fe-Ni region
and outer 56Ni-rich region. Such a distribution may be the result of a
delayed-detonation explosion, in which the first deflagration produces the
global asymmetry in the innermost ejecta, while the subsequent detonation can
lead to the bulk spherical symmetry. This configuration, if viewed from the
direction of the off-set, can consistently explain the blueshift in some of the
emission lines and virtually no observed shift in other lines in SN 2003hv. For
this model, we then explore the effects of different viewing angles and the
implications for SNe Ia in general. The model predicts that a variation of the
central wavelength, depending on the viewing angle, should be seen in some
lines (e.g., [Ni II]7378), while the strongest lines (e.g., [Fe III] blend at
4700A) will not show this effect. By examining optical nebular spectra of 12
SNe Ia, we have found that such a variation indeed exists. We suggest that the
global asymmetry in the innermost ejecta, as likely imprint of the deflagration
flame propagation, is a generic feature of SNe Ia (abridged).Comment: 14 pages, 11 figures, 4 tables. Accepted for publication in the
Astrophysical Journal. Minor correction
Distance to the Active Galaxy NGC 6951 via the Type Ia Supernova 2000E
CCD-photometry and low-resolution spectroscopy of the bright supernova SN
2000E in NGC 6951 are presented. Both the light curve extending up to 150 days
past maximum and the spectra obtained at 1 month past maximum confirm that SN
2000E is of Type Ia. The reddening of SN 2000E is determined as
E(B-V)=0.36+/-0.15, its error is mainly due to uncertainties in the predicted
SN (B-V) colour at late epochs. The V(RI)_C light curves are analyzed with the
Multi-Colour Light Curve Shape (MLCS) method. The shape of the late light curve
suggests that SN 2000E was overluminous by about 0.5 mag at maximum comparing
with a fiducial SN Ia. This results in an updated distance of 33+/-8 Mpc of NGC
6951 (corrected for interstellar absorption). The SN-based distance modulus is
larger by about +0.7 mag than the previous Tully-Fisher estimates. However,
possible systematic errors due to ambiguities in the reddening determination
and estimates of the maximum luminosity of SN 2000E may plague the present
distance measurement.Comment: 9 p., 5 figs, accepted for publication in A&A. A reference correcte
Host Galaxy Properties and Hubble Residuals of Type Ia Supernovae from the Nearby Supernova Factory
We examine the relationship between Type Ia Supernova (SN Ia) Hubble
residuals and the properties of their host galaxies using a sample of 115 SNe
Ia from the Nearby Supernova Factory (SNfactory). We use host galaxy stellar
masses and specific star-formation rates fitted from photometry for all hosts,
as well as gas-phase metallicities for a subset of 69 star-forming (non-AGN)
hosts, to show that the SN Ia Hubble residuals correlate with each of these
host properties. With these data we find new evidence for a correlation between
SN Ia intrinsic color and host metallicity. When we combine our data with those
of other published SN Ia surveys, we find the difference between mean SN Ia
brightnesses in low and high mass hosts is 0.077 +- 0.014 mag. When viewed in
narrow (0.2 dex) bins of host stellar mass, the data reveal apparent plateaus
of Hubble residuals at high and low host masses with a rapid transition over a
short mass range (9.8 <= log(M_*/M_Sun) <= 10.4). Although metallicity has been
a favored interpretation for the origin of the Hubble residual trend with host
mass, we illustrate how dust in star-forming galaxies and mean SN Ia progenitor
age both evolve along the galaxy mass sequence, thereby presenting equally
viable explanations for some or all of the observed SN Ia host bias.Comment: 20 pages, 11 figures, accepted for publication in Ap
Host Galaxies of Type Ia Supernovae from the Nearby Supernova Factory
We present photometric and spectroscopic observations of galaxies hosting
Type Ia supernovae (SNe Ia) observed by the Nearby Supernova Factory
(SNfactory). Combining GALEX UV data with optical and near infrared photometry,
we employ stellar population synthesis techniques to measure SN Ia host galaxy
stellar masses, star-formation rates (SFRs), and reddening due to dust. We
reinforce the key role of GALEX UV data in deriving accurate estimates of
galaxy SFRs and dust extinction. Optical spectra of SN Ia host galaxies are
fitted simultaneously for their stellar continua and emission lines fluxes,
from which we derive high precision redshifts, gas-phase metallicities, and
Halpha-based SFRs. With these data we show that SN Ia host galaxies present
tight agreement with the fiducial galaxy mass-metallicity relation from SDSS
for stellar masses log(M_*/M_Sun)>8.5 where the relation is well-defined. The
star-formation activity of SN Ia host galaxies is consistent with a sample of
comparable SDSS field galaxies, though this comparison is limited by systematic
uncertainties in SFR measurements. Our analysis indicates that SN Ia host
galaxies are, on average, typical representatives of normal field galaxies.Comment: 25 pages, 13 figures, accepted for publication in Ap
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