ABSTRACT
We have scanned 5000 deg2 of Southern Sky to search for strongly lensed quasars with five methods, all source oriented, but based on different assumptions and selection criteria. We present ...a list of high-grade candidates from each method (totalling 98 unique, new candidates), to facilitate follow-up spectroscopic campaigns, including two previously unknown quadruplets, WG 210014.9-445206.4 and WG 021416.37-210535.3. We analyse morphological searches based on Gaia multiplet detection and astrometric offsets, fibre-spectroscopic pre-selection, and X-ray and radio pre-selection. The performance and complementarity of the methods are evaluated on a common sample of known lenses in the Dark Energy Survey public Data Release 1 (DR1) footprint. We recovered in total 13 known lenses, of which 8 are quadruplets. Morphological and colour selection of objects, from the WISE andGaia-DR2 surveys, recovers most of those known lenses, but searches in the radio and X-ray cover regimes that are beyond the completeness of Gaia. Given the footprint, pre-selection, and depth limits, the current number of quads indicates that the union of these searches is complete, and the expected purity on high-grade candidates is ${\approx}60{{\ \rm per\ cent}}$. Ongoing, spectroscopic campaigns confirm this estimate.
Abstract
We revisit the claimed tension, or lack thereof, of measured values of the Hubble–Lemaître parameter H0 from cosmic microwave background (CMB) data and low-redshift indicators. Baryon ...acoustic oscillations (BAOs) rely on the scale of the sound horizon at recombination rs to convert angular measurements into angular-diameter distances, so fixing rs from CMB measurements already constrains H0. If departures from concordance cosmology are to be constrained, truly independent measurements of H0 are needed. We use the angular-diameter distances to three time-delay lenses from the H0LiCOW collaboration to calibrate the distance ladder, combine them with relative distances from supernovae ia and BAOs, leaving rs completely free, and provide the inferred coefficients (q0, j0, s0) in the polynomial expansion of H(z). We obtain H0rs = (9895 ± 161) km s−1 and H0 = (72 ± 7) km s−1 Mpc−1. Combined with H0 from H0LiCOW, then rs = (137 ± 4.5) Mpc is consistent with previous work and systematically lower than the CMB-inferred value. Our results are independent of the adopted cosmology, and removing supernovae with z < 0.1 has a negligible effect.
Abstract
Wide-field photometric surveys enable searches of rare yet interesting objects, such as strongly lensed quasars or quasars with a bright host galaxy. Past searches for lensed quasars based ...on their optical and near-infrared properties have relied on photometric cuts and spectroscopic preselection (as in the Sloan Quasar Lens Search), or neural networks applied to photometric samples. These methods rely on cuts in morphology and colours, with the risk of losing many interesting objects due to scatter in their population properties, restrictive training sets, systematic uncertainties in catalogue-based magnitudes and survey-to-survey photometric variations. Here, we explore the performance of a Gaussian mixture model to separate point-like quasars, quasars with an extended host and strongly lensed quasars using griz
psf and model magnitudes and WISE
W1, W2. The choice of optical magnitudes is due to their presence in all current and upcoming releases of wide-field surveys, whereas UV information is not always available. We then assess the contamination from blue galaxies and the role of additional features such as W3 magnitudes or psf-model terms as morphological information. As a demonstration, we conduct a search in a random 10 per cent of the SDSS footprint, and provide the catalogue of the 43 SDSS object with the highest ‘lens’ score in our selection that survive visual inspection, and are spectroscopically confirmed to host active nuclei. We inspect archival data and find images of 5/43 objects in the Hubble Legacy Archive, including two known lenses. The code and materials are available to facilitate follow-up.
Context. The matter sound horizon can be infered from the cosmic microwave background within the Standard Model. Independent direct measurements of the sound horizon are then a probe of possible ...deviations from the Standard Model. Aims. We aim at measuring the sound horizon rs from low-redshift indicators, which are completely independent of CMB inference. Methods. We used the measured product H(z)rs from baryon acoustic oscillations (BAO) together with supernovae Ia to constrain H(z)/H0 and time-delay lenses analysed by the H0LiCOW collaboration to anchor cosmological distances ( ∝ H0−1 ∝ H 0 − 1 $ {\propto}\ H_{0}^{-1} $ ). Additionally, we investigated the influence of adding a sample of quasars with higher redshift with standardisable UV-Xray luminosity distances. We adopted polynomial expansions in H(z) or in comoving distances so that our inference was completely independent of any cosmological model on which the expansion history might be based. Our measurements are independent of Cepheids and systematics from peculiar motions to within percent-level accuracy. Results. The inferred sound horizon rs varies between (133 ± 8) Mpc and (138 ± 5) Mpc across different models. The discrepancy with CMB measurements is robust against model choice. Statistical uncertainties are comparable to systematics. Conclusions. The combination of time-delay lenses, supernovae, and BAO yields a distance ladder that is independent of cosmology (and of Cepheid calibration) and a measurement of rs that is independent of the CMB. These cosmographic measurements are then a competitive test of the Standard Model, regardless of the hypotheses on which the cosmology is based.
Context.
Persistent tension between low-redshift observations and the cosmic microwave background radiation (CMB), in terms of two fundamental distance scales set by the sound horizon
r
d
and the ...Hubble constant
H
0
, suggests new physics beyond the Standard Model, departures from concordance cosmology, or residual systematics.
Aims.
The role of different probe combinations must be assessed, as well as of different physical models that can alter the expansion history of the Universe and the inferred cosmological parameters.
Methods.
We examined recently updated distance calibrations from Cepheids, gravitational lensing time-delay observations, and the tip of the red giant branch. Calibrating the baryon acoustic oscillations and type Ia supernovae with combinations of the distance indicators, we obtained a joint and self-consistent measurement of
H
0
and
r
d
at low redshift, independent of cosmological models and CMB inference. In an attempt to alleviate the tension between late-time and CMB-based measurements, we considered four extensions of the standard ΛCDM model.
Results.
The sound horizon from our different measurements is
r
d
= (137 ± 3
stat.
± 2
syst.
) Mpc based on absolute distance calibration from gravitational lensing and the cosmic distance ladder. Depending on the adopted distance indicators, the combined tension in
H
0
and
r
d
ranges between 2.3 and 5.1
σ
, and it is independent of changes to the low-redshift expansion history. We find that modifications of ΛCDM that change the physics after recombination fail to provide a solution to the problem, for the reason that they only resolve the tension in
H
0
, while the tension in
r
d
remains unchanged. Pre-recombination extensions (with early dark energy or the effective number of neutrinos
N
eff
= 3.24 ± 0.16) are allowed by the data, unless the calibration from Cepheids is included.
Conclusions.
Results from time-delay lenses are consistent with those from distance-ladder calibrations and point to a discrepancy between absolute distance scales measured from the CMB (assuming the standard cosmological model) and late-time observations. New proposals to resolve this tension should be examined with respect to reconciling not only the Hubble constant but also the sound horizon derived from the CMB and other cosmological probes.
Abstract
Strongly lensed active galactic nuclei (AGN) provide a unique opportunity to make progress in the study of the evolution of the correlation between the mass of supermassive black holes (
...$\mathcal {M}_{\rm BH}$
) and their host galaxy luminosity (L
host). We demonstrate the power of lensing by analysing two systems for which state-of-the-art lens modelling techniques have been applied to deep Hubble Space Telescope imaging data. We use (i) the reconstructed images to infer the total and bulge luminosity of the host and (ii) published broad-line spectroscopy to estimate
$\mathcal {M}_{\rm BH}$
using the so-called virial method. We then enlarge our sample with new calibration of previously published measurements to study the evolution of the correlation out to z ∼ 4.5. Consistent with previous work, we find that without taking into account passive luminosity evolution, the data points lie on the local relation. Once the passive luminosity evolution is taken into account, we find that black holes in the more distant Universe reside in less luminous galaxies than today. Fitting this offset as
$\mathcal {M}_{\rm BH}$
/L
host ∝ (1 + z)γ, and taking into account selection effects, we obtain γ = 0.6 ± 0.1 and 0.8 ± 0.1 for the case of
$\mathcal {M}_{\rm BH}$
–L
bulge and
$\mathcal {M}_{\rm BH}$
–L
total, respectively. To test for systematic uncertainties and selection effects we also consider a reduced sample that is homogeneous in data quality. We find consistent results but with considerably larger uncertainty due to the more limited sample size and redshift coverage (γ = 0.7 ± 0.4 and 0.2 ± 0.5 for
$\mathcal {M}_{\rm BH}$
–L
bulge and
$\mathcal {M}_{\rm BH}$
–L
total, respectively), highlighting the need to gather more high-quality data for high-redshift lensed quasar hosts. Our result is consistent with a scenario where the growth of the black hole predates that of the host galaxy.
Abstract
We present a Bayesian graph neural network (BGNN) that can estimate the weak lensing convergence (
κ
) from photometric measurements of galaxies along a given line of sight (LOS). The method ...is of particular interest in strong gravitational time-delay cosmography (TDC), where characterizing the “external convergence” (
κ
ext
) from the lens environment and LOS is necessary for precise Hubble constant (
H
0
) inference. Starting from a large-scale simulation with a
κ
resolution of ∼1′, we introduce fluctuations on galaxy–galaxy lensing scales of ∼1″ and extract random sight lines to train our BGNN. We then evaluate the model on test sets with varying degrees of overlap with the training distribution. For each test set of 1000 sight lines, the BGNN infers the individual
κ
posteriors, which we combine in a hierarchical Bayesian model to yield constraints on the hyperparameters governing the population. For a test field well sampled by the training set, the BGNN recovers the population mean of
κ
precisely and without bias (within the 2
σ
credible interval), resulting in a contribution to the
H
0
error budget well under 1%. In the tails of the training set with sparse samples, the BGNN, which can ingest all available information about each sight line, extracts a stronger
κ
signal compared to a simplified version of the traditional method based on matching galaxy number counts, which is limited by sample variance. Our hierarchical inference pipeline using BGNNs promises to improve the
κ
ext
characterization for precision TDC. The code is available as a public Python package,
Node to Joy
⏬
.
Abstract
We report the discovery of the quadruply lensed quasar SDSS J1433+6007 (RA = 14:33:22.8, Dec. = +60:07:13.44), mined in the SDSS DR12 photometric catalogues using a novel outlier-selection ...technique, without prior spectroscopic or ultraviolet excess information. Discovery data obtained at the Nordic Optical Telescope (La Palma) show nearly identical quasar spectra at zs = 2.737 ± 0.003 and four quasar images in a fold configuration, one of which sits on a blue arc, with maximum separation 3.6 arcsec. The deflector redshift is zl = 0.407 ± 0.002, from Keck-ESI spectra. We describe the selection procedure, discovery and follow-up, image positions and BVRi magnitudes, and first results and forecasts from lens model fit to the relative image positions.
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