426 research outputs found
A consistent measure of the merger histories of massive galaxies using close-pair statistics I:Major mergers at z <3.5
We use a large sample of galaxies constructed by combining the
UKIDSS UDS, VIDEO/CFHT-LS, UltraVISTA/COSMOS and GAMA survey regions to probe
the major merging histories of massive galaxies ()
at . We use a method adapted from that presented in
Lopez-Sanjuan et al. (2014) using the full photometric redshift probability
distributions, to measure pair of flux-limited, stellar
mass selected galaxy samples using close-pair statistics. The pair fraction is
found to weakly evolve as with no dependence on stellar
mass. We subsequently derive major merger for galaxies at and at a constant number density of
Mpc, and find rates a factor of 2-3 smaller than previous works,
although this depends strongly on the assumed merger timescale and likelihood
of a close-pair merging. Galaxies undergo approximately 0.5 major mergers at , accruing an additional 1-4 in the
process. Major merger accretion rate densities of
yr Mpc are found for number density selected
samples, indicating that direct progenitors of local massive
() galaxies have experienced a steady supply of
stellar mass via major mergers throughout their evolution. While pair fractions
are found to agree with those predicted by the Henriques et al. (2014)
semi-analytic model, the Illustris hydrodynamical simulation fails to
quantitatively reproduce derived merger rates. Furthermore, we find major
mergers become a comparable source of stellar mass growth compared to
star-formation at , but is 10-100 times smaller than the SFR density at
higher redshifts.Comment: 26 pages, 18 figures, accepted to MNRA
KiDS-450: testing extensions to the standard cosmological model
We test extensions to the standard cosmological model with weak gravitational
lensing tomography using 450 deg of imaging data from the Kilo Degree
Survey (KiDS). In these extended cosmologies, which include massive neutrinos,
nonzero curvature, evolving dark energy, modified gravity, and running of the
scalar spectral index, we also examine the discordance between KiDS and cosmic
microwave background measurements from Planck. The discordance between the two
datasets is largely unaffected by a more conservative treatment of the lensing
systematics and the removal of angular scales most sensitive to nonlinear
physics. The only extended cosmology that simultaneously alleviates the
discordance with Planck and is at least moderately favored by the data includes
evolving dark energy with a time-dependent equation of state (in the form of
the parameterization). In this model, the respective constraints agree at the level, and there
is `substantial concordance' between the KiDS and Planck datasets when
accounting for the full parameter space. Moreover, the Planck constraint on the
Hubble constant is wider than in LCDM and in agreement with the Riess et al.
(2016) direct measurement of . The dark energy model is moderately favored
as compared to LCDM when combining the KiDS and Planck measurements, and
remains moderately favored after including an informative prior on the Hubble
constant. In both of these scenarios, marginalized constraints in the
plane are discrepant with a cosmological constant at the level.
Moreover, KiDS constrains the sum of neutrino masses to 4.0 eV (95% CL), finds
no preference for time or scale dependent modifications to the metric
potentials, and is consistent with flatness and no running of the spectral
index. The analysis code is public at https://github.com/sjoudaki/kids450Comment: 22 pages, 16 figures, results unchanged, version accepted for
publication by MNRA
On the luminosity distance and the epoch of acceleration
Standard cosmological models based on general relativity (GR) with dark
energy predict that the Universe underwent a transition from decelerating to
accelerating expansion at a moderate redshift . Clearly, it
is of great interest to directly measure this transition in a model-independent
way, without the assumption that GR is the correct theory of gravity. We
explore to what extent supernova (SN) luminosity distance measurements provide
evidence for such a transition: we show that, contrary to intuition, the
well-known "turnover" in the SN distance residuals relative to an
empty (Milne) model does not give firm evidence for such a transition within
the redshift range spanned by SN data. The observed turnover in that diagram is
predominantly due to the negative curvature in the Milne model, {\em not} the
deceleration predicted by CDM and relatives. We show that there are
several advantages in plotting distance residuals against a flat,
non-accelerating model , and also remapping the axis to ; we outline a number of useful and intuitive properties of this
presentation. We conclude that there are significant complementarities between
SNe and baryon acoustic oscillations (BAOs): SNe offer high precision at low
redshifts and give good constraints on the net {\em amount} of acceleration
since , but are weak at constraining ; while radial BAO
measurements are probably superior for placing direct constraints on .Comment: Latex, 13 pages, 7 figures. Accepted by MNRAS. For the busy reader,
Figs 4 and 6 are the main result
Planck 2015 results. V. LFI calibration
We present a description of the pipeline used to calibrate the Planck Low Frequency Instrument (LFI) timelines into thermodynamic temperatures for the Planck 2015 data release, covering four years of uninterrupted operations. As in the 2013 data release, our calibrator is provided by the spin-synchronous modulation of the cosmic microwave background dipole, but we now use the orbital component, rather than adopting the Wilkinson Microwave Anisotropy Probe (WMAP) solar dipole. This allows our 2015 LFI analysis to provide an independent Solar dipole estimate, which is in excellent agreement with that of HFI and within 1σ (0.3% in amplitude) of the WMAP value. This 0.3% shift in the peak-to-peak dipole temperature from WMAP and a general overhaul of the iterative calibration code increases the overall level of the LFI maps by 0.45% (30 GHz), 0.64% (44 GHz), and 0.82% (70 GHz) in temperature with respect to the 2013 Planck data release, thus reducing the discrepancy with the power spectrum measured by WMAP. We estimate that the LFI calibration uncertainty is now at the level of 0.20% for the 70 GHz map, 0.26% for the 44 GHz map, and 0.35% for the 30 GHz map. We provide a detailed description of the impact of all the changes implemented in the calibration since the previous data release
Planck 2015 results. VI. LFI mapmaking
This paper describes the mapmaking procedure applied to Planck Low Frequency Instrument (LFI) data. The mapmaking step takes as input the calibrated timelines and pointing information. The main products are sky maps of I, Q, and U Stokes components. For the first time, we present polarization maps at LFI frequencies. The mapmaking algorithm is based on a destriping technique, which is enhanced with a noise prior. The Galactic region is masked to reduce errors arising from bandpass mismatch and high signal gradients. We apply horn-uniform radiometer weights to reduce the effects of beam-shape mismatch. The algorithm is the same as used for the 2013 release, apart from small changes in parameter settings. We validate the procedure through simulations. Special emphasis is put on the control of systematics, which is particularly important for accurate polarization analysis. We also produce low-resolution versions of the maps and corresponding noise covariance matrices. These serve as input in later analysis steps and parameter estimation. The noise covariance matrices are validated through noise Monte Carlo simulations. The residual noise in the map products is characterized through analysis of half-ring maps, noise covariance matrices, and simulations
Planck 2013 results. IX. HFI spectral response
The Planck High Frequency Instrument (HFI) spectral response was determined
through a series of ground based tests conducted with the HFI focal plane in a
cryogenic environment prior to launch. The main goal of the spectral
transmission tests was to measure the relative spectral response (including
out-of-band signal rejection) of all HFI detectors. This was determined by
measuring the output of a continuously scanned Fourier transform spectrometer
coupled with all HFI detectors. As there is no on-board spectrometer within
HFI, the ground-based spectral response experiments provide the definitive data
set for the relative spectral calibration of the HFI. The spectral response of
the HFI is used in Planck data analysis and component separation, this includes
extraction of CO emission observed within Planck bands, dust emission,
Sunyaev-Zeldovich sources, and intensity to polarization leakage. The HFI
spectral response data have also been used to provide unit conversion and
colour correction analysis tools. Verifications of the HFI spectral response
data are provided through comparisons with photometric HFI flight data. This
validation includes use of HFI zodiacal emission observations to demonstrate
out-of-band spectral signal rejection better than 10^8. The accuracy of the HFI
relative spectral response data is verified through comparison with
complementary flight-data based unit conversion coefficients and colour
correction coefficients. These coefficients include those based upon HFI
observations of CO, dust, and Sunyaev-Zeldovich emission. General agreement is
observed between the ground-based spectral characterization of HFI and
corresponding in-flight observations, within the quoted uncertainty of each;
explanations are provided for any discrepancies.Comment: 27 pages, 28 figures, one of the papers associated with the 2013
Planck data releas
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