90 research outputs found
Deconvolving the Wedge: Maximum-Likelihood Power Spectra via Spherical-Wave Visibility Modeling
Direct detection of the Epoch of Reionization (EoR) via the red-shifted 21-cm
line will have unprecedented implications on the study of structure formation
in the infant Universe. To fulfill this promise, current and future 21-cm
experiments need to detect this weak EoR signal in the presence of foregrounds
that are several orders of magnitude larger. This requires extreme noise
control and improved wide-field high dynamic-range imaging techniques. We
propose a new imaging method based on a maximum likelihood framework which
solves for the interferometric equation directly on the sphere, or equivalently
in the -domain. The method uses the one-to-one relation between spherical
waves and spherical harmonics (SpH). It consistently handles signals from the
entire sky, and does not require a -term correction. The spherical-harmonics
coefficients represent the sky-brightness distribution and the visibilities in
the -domain, and provide a direct estimate of the spatial power spectrum.
Using these spectrally-smooth SpH coefficients, bright foregrounds can be
removed from the signal, including their side-lobe noise, which is one of the
limiting factors in high dynamics range wide-field imaging. Chromatic effects
causing the so-called "wedge" are effectively eliminated (i.e. deconvolved) in
the cylindrical () power spectrum, compared to a
power spectrum computed directly from the images of the foreground visibilities
where the wedge is clearly present. We illustrate our method using simulated
LOFAR observations, finding an excellent reconstruction of the input EoR signal
with minimal bias.Comment: 13 pages, 8 figures. Replaced to match accepted MNRAS version; few
typos corrected & textual clarification added (no changes to results
Reionization and cosmic dawn astrophysics from the Square Kilometre Array:impact of observing strategies
Interferometry of the cosmic 21-cm signal is set to revolutionize our understanding of the epoch of reionization (EoR) and the cosmic dawn (CD). The culmination of ongoing efforts will be the upcoming Square Kilometre Array (SKA), which will provide tomography of the 21-cm signal from the first billion years of our Universe. Using a galaxy formation model informed by high-z luminosity functions, here we forecast the accuracy with which the first phase of SKA-low (SKA1-low) can constrain the properties of the unseen galaxies driving the astrophysics of the EoR and CD. We consider three observing strategies: (i) deep (1000 h on a single field); (ii) medium-deep (100 h on 10 independent fields); and (iii) shallow (10 h on 100 independent fields). Using the 21-cm power spectrum as a summary statistic, and conservatively only using the 21-cm signal above the foreground wedge, we predict that all three observing strategies should recover astrophysical parameters to a fractional precision of 3c0.1-10 per cent. The reionization history is recovered to an uncertainty of \u394z 7e 0.1 (1\u3c3 ) for the bulk of its duration. The medium-deep strategy, balancing thermal noise against cosmic variance, results in the tightest constraints, slightly outperforming the deep strategy. The shallow observational strategy performs the worst, with up to an 3c10-60 per cent increase in the recovered uncertainty. We note, however, that non-Gaussian summary statistics, tomography, as well as unbiased foreground removal would likely favour the deep strategy
The Sloan Lens ACS Survey. I. A Large Spectroscopically Selected Sample of Massive Early-Type Lens Galaxies
The Sloan Lens ACS (SLACS) Survey is an efficient Hubble Space Telescope
Snapshot imaging survey for new galaxy-scale strong gravitational lenses. The
targeted lens candidates are selected spectroscopically from within the Sloan
Digital Sky Survey (SDSS) database of galaxy spectra for having multiple
nebular emission lines at a redshift significantly higher than that of the SDSS
target galaxy. In this paper, we present a catalog of 19 newly discovered
gravitational lenses, along with 9 other observed candidate systems that are
either possible lenses, non-lenses, or non-detections. The survey efficiency is
thus >=68%. We also present Gemini and Magellan IFU data for 9 of the SLACS
targets, which further support the lensing interpretation. A new method for the
effective subtraction of foreground galaxy images to reveal faint background
features is presented. We show that the SLACS lens galaxies have colors and
ellipticities typical of the spectroscopic parent sample from which they are
drawn (SDSS luminous red galaxies and quiescent main-sample galaxies), but are
somewhat brighter and more centrally concentrated. Several explanations for the
latter bias are suggested. The SLACS survey provides the first statistically
significant and homogeneously selected sample of bright early-type lens
galaxies, furnishing a powerful probe of the structure of early-type galaxies
within the half-light radius. The high confirmation rate of lenses in the SLACS
survey suggests consideration of spectroscopic lens discovery as an explicit
science goal of future spectroscopic galaxy surveys (abridged).Comment: ApJ, in press. 20 pages, numerous figures, uses emulateapj. Replaced
to include full-resolution spectro figures. Version with full-resolution
imaging figures available at
http://www.cfa.harvard.edu/~abolton/slacs1_hires.pdf (PDF) or at
http://www.cfa.harvard.edu/~abolton/slacs1_hires.ps.gz (PS). Additional SLACS
survey info at http://www.slacs.or
SHARP -- VII. New constraints on the dark matter free-streaming properties and substructure abundance from gravitationally lensed quasars
We present an analysis of seven strongly gravitationally lensed quasars and
the corresponding constraints on the properties of dark matter. Our results are
derived by modelling the lensed image positions and flux-ratios using a
combination of smooth macro models and a population of low-mass haloes within
the mass range 10^6 to 10^9 Msun. Our lens models explicitly include
higher-order complexity in the form of stellar discs and luminous satellites,
as well as low-mass haloes located along the observed lines of sight for the
first time. Assuming a Cold Dark Matter (CDM) cosmology, we infer an average
total mass fraction in substructure of f_sub = 0.012^{+0.007}_{-0.004} (68 per
cent confidence limits), which is in agreement with the predictions from CDM
hydrodynamical simulations to within 1 sigma. This result is closer to the
predictions than those from previous studies that did not include line-of-sight
haloes. Under the assumption of a thermal relic dark matter model, we derive a
lower limit on the particle relic mass of m th > 5.58 keV (95 per cent
confidence limits), which is consistent with a value of m_th > 5.3 keV from the
recent analysis of the Ly-alpha forest. We also identify two main sources of
possible systematic errors and conclude that deeper investigations in the
complex structure of lens galaxies as well as the size of the background
sources should be a priority for this field.Comment: 14 pages, 7 figures, accepted for publication in MNRA
Two-dimensional kinematics of SLACS lenses: I. Phase-space analysis of the early-type galaxy SDSS J2321-097 at z=0.1
We present the first results of a combined VLT VIMOS integral-field unit and
Hubble Space Telescope (HST)/ACS study of the early-type lens galaxy SDSS
J2321-097 at z=0.0819, extending kinematic studies to a look-back time of 1
Gyr. This system, discovered in the Sloan Lens ACS Survey (SLACS), has been
observed as part of a VLT Large Programme with the goal of obtaining
two-dimensional stellar kinematics of 17 early-type galaxies to z~0.35 and Keck
spectroscopy of an additional dozen lens systems. Bayesian modelling of both
the surface brightness distribution of the lensed source and the
two-dimensional measurements of velocity and velocity dispersion has allowed
us, under the only assumptions of axisymmetry and a two-integral stellar
distribution function (DF) for the lens galaxy, to dissect this galaxy in three
dimensions and break the classical mass--anisotropy, mass-sheet and
inclination--oblateness degeneracies. Our main results are that the galaxy (i)
has a total density profile well described by a single power-law rho propto
r^{-gamma'} with gamma'=2.06^{+0.03}_{-0.06}; (ii) is a very slow rotator
(specific stellar angular momentum parameter lambda_R = 0.075); (iii) shows
only mild anisotropy (delta ~ 0.15); and (iv) has a dark matter contribution of
~30 per cent inside the effective radius. Our first results from this large
combined imaging and spectroscopic effort with the VLT, Keck and HST show that
the structure of massive early-type galaxies beyond the local Universe can now
be studied in great detail using the combination of stellar kinematics and
gravitational lensing. Extending these studies to look-back times where
evolutionary effects become measurable holds great promise for the
understanding of formation and evolution of early-type galaxies.Comment: 16 pages, 12 figures; accepted for publication in MNRAS; corrected
typo
H0LiCOW III. Quantifying the effect of mass along the line of sight to the gravitational lens HE 0435-1223 through weighted galaxy counts
Based on spectroscopy and multiband wide-field observations of the
gravitationally lensed quasar HE 0435-1223, we determine the probability
distribution function of the external convergence for
this system. We measure the under/overdensity of the line of sight towards the
lens system and compare it to the average line of sight throughout the
universe, determined by using the CFHTLenS as a control field. Aiming to
constrain as tightly as possible, we determine
under/overdensities using various combinations of relevant informative weighing
schemes for the galaxy counts, such as projected distance to the lens,
redshift, and stellar mass. We then convert the measured under/overdensities
into a distribution, using ray-tracing through the
Millennium Simulation. We explore several limiting magnitudes and apertures,
and account for systematic and statistical uncertainties relevant to the
quality of the observational data, which we further test through simulations.
Our most robust estimate of has a median value
and a standard deviation of
. The measured corresponds to
uncertainty on the time delay distance, and hence the Hubble constant
inference from this system. The median value
is robust to (i.e. on ) regardless of the adopted
aperture radius, limiting magnitude and weighting scheme, as long as the latter
incorporates galaxy number counts, the projected distance to the main lens, and
a prior on the external shear obtained from mass modeling. The availability of
a well-constrained makes \hequad\ a valuable system for
measuring cosmological parameters using strong gravitational lens time delays.Comment: 24 pages, 17 figures, 6 tables. Submitted to MNRA
The internal structure and formation of early-type galaxies: the gravitational--lens system MG2016+112 at z=1.004
[Abridged] We combine our measurements of the velocity dispersion and the
surface brightness profile of the lens galaxy D in the system MG2016+112
(z=1.004) with constraints from gravitational lensing to study its internal
mass distribution. We find that: (i) dark matter accounts for >50% of the total
mass within the Einstein radius (99% CL), excluding at the 8-sigma level that
mass follows light inside the Einstein radius with a constant mass-to-light
ratio (M/L). (ii) the total mass distribution inside the Einstein radius is
well-described by a density profile ~r^-gamma' with an effective slope
gamma'=2.0+-0.1+-0.1, including random and systematic uncertainties. (iii) The
offset of galaxy D from the local Fundamental Plane independently constrains
the stellar M/L, and matches the range derived from our models, leading to a
more stringent lower limit of >60% on the fraction of dark matter within the
Einstein radius (99%CL).
Under the assumption of adiabatic contraction, the inner slope of the dark
matter halo before the baryons collapsed is gamma_i<1.4 (68 CL), marginally
consistent with the highest-resolution cold dark matter simulations that
indicate gamma_i~1.5. This might indicate that either adiabatic contraction is
a poor description of E/S0 formation or that additional processes play a role
as well. Indeed, the apparently isothermal density distribution inside the
Einstein radius, is not a natural outcome of adiabatic contraction models,
where it appears to be a mere coincidence. By contrast, we argue that
isothermality might be the result of a stronger coupling between luminous and
dark-matter, possibly the result of (incomplete) violent relaxation processes.
Hence, we conclude that galaxy D appears already relaxed 8 Gyr ago.Comment: 8 pages, 4 figures, ApJ, in press, minor change
CASCO: Cosmological and AStrophysical parameters from Cosmological simulations and Observations -- I. Constraining physical processes in local star-forming galaxies
We compare the structural properties and dark matter content of star-forming
galaxies taken from the CAMELS cosmological simulations to the observed trends
derived from the SPARC sample in the stellar mass range , to provide constraints on the value of
cosmological and astrophysical (SN- and AGN-related) parameters. We consider
the size-, internal DM fraction-, internal DM mass- and total-stellar mass
relations for all the 1065 simulations from the IllustrisTNG, SIMBA and ASTRID
suites of CAMELS, and search for the parameters that minimize the
with respect to the observations. For the IllustrisTNG suite, we find the
following constraints for the cosmological parameters: , and , which are consistent within with the results
from the nine-year WMAP observations. SN feedback-related astrophysical
parameters, which describe the departure of outflow wind energy per unit star
formation rate and wind velocity from the reference IllustrisTNG simulations,
assume the following values: and
, respectively. Therefore, simulations
with a lower value of outflow wind energy per unit star formation rate with
respect to the reference illustrisTNG simulation better reproduce the
observations. Simulations based on SIMBA and ASTRID suites predict central dark
matter masses substantially larger than those observed in real galaxies, which
can be reconciled with observations only by requiring values of
inconsistent with cosmological constraints for SIMBA, or
simulations characterized by unrealistic galaxy mass distributions for ASTRID.Comment: 24 pages, 10 figures, 9 tables. Accepted by MNRAS for publication;
Added a reference to sec. 4.
SEAGLE--II: Constraints on feedback models in galaxy formation from massive early type strong lens galaxies
We use nine different galaxy formation scenarios in ten cosmological
simulation boxes from the EAGLE suite of {\Lambda}CDM hydrodynamical
simulations to assess the impact of feedback mechanisms in galaxy formation and
compare these to observed strong gravitational lenses. To compare observations
with simulations, we create strong lenses with >
with the appropriate resolution and noise level, and model them with an
elliptical power-law mass model to constrain their total mass density slope. We
also obtain the mass-size relation of the simulated lens-galaxy sample. We find
significant variation in the total mass density slope at the Einstein radius
and in the projected stellar mass-size relation, mainly due to different
implementations of stellar and AGN feedback. We find that for lens selected
galaxies, models with either too weak or too strong stellar and/or AGN feedback
fail to explain the distribution of observed mass-density slopes, with the
counter-intuitive trend that increasing the feedback steepens the mass density
slope around the Einstein radius ( 3-10 kpc). Models in which stellar
feedback becomes inefficient at high gas densities, or weaker AGN feedback with
a higher duty cycle, produce strong lenses with total mass density slopes close
to isothermal (i.e. -d log({\rho})/d log(r) 2.0) and slope
distributions statistically agreeing with observed strong lens galaxies in
SLACS and BELLS. Agreement is only slightly worse with the more heterogeneous
SL2S lens galaxy sample. Observations of strong-lens selected galaxies thus
appear to favor models with relatively weak feedback in massive galaxies.Comment: re-submitted to MNRAS, bug fixed, conclusions unchanged, updated
appendices and references, 23 pages, 10 Figures, 6 Table
H0LiCOW XII. Lens mass model of WFI2033-4723 and blind measurement of its time-delay distance and
We present the lens mass model of the quadruply-imaged gravitationally lensed
quasar WFI2033-4723, and perform a blind cosmographical analysis based on this
system. Our analysis combines (1) time-delay measurements from 14 years of data
obtained by the COSmological MOnitoring of GRAvItational Lenses (COSMOGRAIL)
collaboration, (2) high-resolution imaging,
(3) a measurement of the velocity dispersion of the lens galaxy based on
ESO-MUSE data, and (4) multi-band, wide-field imaging and spectroscopy
characterizing the lens environment. We account for all known sources of
systematics, including the influence of nearby perturbers and complex
line-of-sight structure, as well as the parametrization of the light and mass
profiles of the lensing galaxy. After unblinding, we determine the effective
time-delay distance to be , an average
precision of . This translates to a Hubble constant , assuming a flat CDM
cosmology with a uniform prior on in the range [0.05, 0.5].
This work is part of the Lenses in COSMOGRAIL's Wellspring (H0LiCOW)
collaboration, and the full time-delay cosmography results from a total of six
strongly lensed systems are presented in a companion paper (H0LiCOW XIII).Comment: Version accepted by MNRAS. 29 pages including appendix, 17 figures, 6
tables. arXiv admin note: text overlap with arXiv:1607.0140
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