We study possible systematic effects on the values of the cosmological parameters measured through strong lensing analyses of the Hubble Frontier Field galaxy cluster MACS J1149.5+2223. We use the ...observed positions of a large set of spectroscopically selected multiple images, including those of supernova "Refsdal" with their published time delays. Starting from our reference model in a flat ΛCDM cosmology, published in Grillo et al. (2018), we confirm the relevance of the longest measurable time delay, between SX and S1, and an approximately linear relation between its value and that of H0. We perform true blind tests by considering a range of time delays around its original estimate of 345 10 days, as an accurate measurement of this time delay is still not known at the time of analysis and writing. We investigate separately the impact of a constant sheet of mass at the cluster redshift, of a power-law profile for the mass density of the cluster main halo and of some scatter in the cluster member scaling relations. Remarkably, we find that these systematic effects do not introduce a significant bias on the inferred values of H0 and m and that the statistical uncertainties dominate the total error budget: a 3% uncertainty on the time delay of image SX translates into approximately 6% and 40% (including both statistical and systematic 1 ) uncertainties for H0 and m, respectively. Furthermore, our model accurately reproduces the extended surface brightness distribution of the supernova host. We also present the interesting possibility of measuring the value of the equation-of-state parameter w of the dark energy density, currently with a 30% uncertainty.
Abstract
The observed lensed fraction of high-redshift quasars (∼0.2%) is significantly lower than previous theoretical predictions (≳4%). We revisit the lensed fraction of high-redshift quasars ...predicted by theoretical models, where we adopt recent measurements of galaxy velocity dispersion functions (VDFs) and explore a wide range of quasar luminosity function (QLF) parameters. We use both analytical methods and mock catalogs, which give consistent results. For ordinary QLF parameters and the depth of current high-redshift quasar surveys (
m
z
≲ 22), our model suggests a multiply imaged fraction of
F
multi
∼ 0.4%–0.8%. The predicted lensed fraction is ∼1%–6% for the brightest
z
s
∼ 6 quasars (
m
z
≲ 19), depending on the QLF. The systematic uncertainties of the predicted lensed fraction in previous models can be as large as 2–4 times and are dominated by the VDF. Applying VDFs from recent measurements decreases the predicted lensed fraction and relieves the tension between observations and theoretical models. Given the depth of current imaging surveys, there are ∼15 lensed quasars at
z
s
> 5.5 detectable over the sky. Upcoming sky surveys like the Legacy Survey of Space and Time survey and the Euclid survey will find several tens of lensed quasars at this redshift range.
Abstract
The gravitationally lensed star WHL 0137–LS, nicknamed Earendel, was identified with a photometric redshift
z
phot
= 6.2 ± 0.1 based on images taken with the Hubble Space Telescope. Here we ...present James Webb Space Telescope (JWST) Near Infrared Camera images of Earendel in eight filters spanning 0.8–5.0
μ
m. In these higher-resolution images, Earendel remains a single unresolved point source on the lensing critical curve, increasing the lower limit on the lensing magnification to
μ
> 4000 and restricting the source plane radius further to
r
< 0.02 pc, or ∼4000 au. These new observations strengthen the conclusion that Earendel is best explained by an individual star or multiple star system and support the previous photometric redshift estimate. Fitting grids of stellar spectra to our photometry yields a stellar temperature of
T
eff
≃ 13,000–16,000 K, assuming the light is dominated by a single star. The delensed bolometric luminosity in this case ranges from
log
(
L
)
=
5.8
to 6.6
L
⊙
, which is in the range where one expects luminous blue variable stars. Follow-up observations, including JWST NIRSpec scheduled for late 2022, are needed to further unravel the nature of this object, which presents a unique opportunity to study massive stars in the first billion years of the universe.
Abstract
We present a new high-precision, JWST-based, strong-lensing model for the galaxy cluster Abell 2744 at
z
= 0.3072. By combining the deep, high-resolution JWST imaging from the Grism Lens ...Amplified Survey from Space–JWST and Ultradeep NIRSpec and NIRCam Observations before the Epoch of Reionization programs and a Director’s Discretionary Time program, with newly obtained Very Large Telescope/Multi Unit Spectroscopic Explorer (MUSE) data, we identify 32 multiple images from 11 background sources lensed by two external subclusters at distances of ∼160″ from the main cluster. The new MUSE observations enable the first spectroscopic confirmation of a multiple-image system in the external clumps. Moreover, the reanalysis of the spectrophotometric archival and JWST data yields 27 additional multiple images in the main cluster. The new lens model is constrained by 149 multiple images (∼66% more than in our previous model) covering an extended redshift range between 1.03 and 9.76. The subhalo mass component of the cluster includes 177 member galaxies down to
m
F160W
= 21, of which 163 are spectroscopically confirmed. Internal velocity dispersions are measured for 85 members. The new lens model is characterized by a remarkably low scatter between the predicted and observed positions of the multiple images (0.″43). This precision is unprecedented given the large multiple-image sample, the complexity of the cluster mass distribution, and the large modeled area. The improved precision and resolution of the cluster total mass distribution provides a robust magnification map over a ∼30 arcmin
2
area, which is critical for inferring the intrinsic physical properties of the highly magnified, high-
z
sources. The lens model and the new MUSE redshift catalog are released with this publication.
ABSTRACT
Gravitational time delays provide a powerful one-step measurement of H0, independent of all other probes. One key ingredient in time-delay cosmography are high-accuracy lens models. Those ...are currently expensive to obtain, both, in terms of computing and investigator time (105–106 CPU hours and ∼0.5–1 yr, respectively). Major improvements in modelling speed are therefore necessary to exploit the large number of lenses that are forecast to be discovered over the current decade. In order to bypass this roadblock, we develop an automated modelling pipeline and apply it to a sample of 31 lens systems, observed by the Hubble Space Telescope in multiple bands. Our automated pipeline can derive models for 30/31 lenses with few hours of human time and <100 CPU hours of computing time for a typical system. For each lens, we provide measurements of key parameters and predictions of magnification as well as time delays for the multiple images. We characterize the cosmography-readiness of our models using the stability of differences in the Fermat potential (proportional to time delay) with respect to modelling choices. We find that for 10/30 lenses, our models are cosmography or nearly cosmography grade (<3 per cent and 3–5 per cent variations). For 6/30 lenses, the models are close to cosmography grade (5–10 per cent). These results utilize informative priors and will need to be confirmed by further analysis. However, they are also likely to improve by extending the pipeline modelling sequence and options. In conclusion, we show that uniform cosmography grade modelling of large strong lens samples is within reach.
Abstract
We present bright C
ii
158
μ
m line detections from a strongly magnified and multiply imaged (
μ
∼ 20–160) sub–
L
*
(
M
UV
=
−
19.75
−
0.44
+
0.55
) Lyman-break galaxy (LBG) at
z
= 6.0719 ± ...0.0004, drawn from the ALMA Lensing Cluster Survey (ALCS). Emission lines are identified at 268.7 GHz at ≥8
σ
exactly at the positions of two multiple images of the LBG, behind the massive galaxy cluster RXCJ0600−2007. Our lens models, updated with the latest spectroscopy from VLT/MUSE, indicate that a sub region of the LBG crosses the caustic, and is lensed into a long (∼6″) arc with a local magnification of
μ
∼ 160, for which the C
ii
line is also significantly detected. The source plane reconstruction resolves the interstellar medium (ISM) structure, showing that the C
ii
line is co-spatial with the rest-frame UV continuum at a scale of ∼300 pc. The C
ii
line properties suggest that the LBG is a rotation-dominated system, whose velocity gradient explains a slight difference in redshifts between the whole LBG and its sub-region. The star formation rate (SFR)–
L
CII
relations, for whole and sub-regions of the LBG, are consistent with those of local galaxies. We evaluate the lower limit of the faint-end of the C
ii
luminosity function at
z
= 6, finding it to be consistent with predictions from semi-analytical models and from the local SFR–
L
CII
relation with a SFR function at
z
= 6. These results imply that the local SFR–
L
CII
relation is universal for a wide range of scales, including the spatially resolved ISM, the whole region of the galaxy, and the cosmic scale, even in the epoch of reionization.
Abstract
A simple, novice-friendly scheme for classifying the image configurations of quadruply lensed quasars is proposed. With only six classes, it is intentionally coarse grained. It focuses on ...the kitelikeness and circularity of these configurations, or the absence thereof. Other features are deliberately ignored, their importance to professional astronomers notwithstanding. Readers are invited to test drive the scheme on a sample of 12 quadruply lensed quasar systems. The theoretical underpinnings of the scheme are described in a technical appendix.
Abstract
With the imaging and characterization of the horizon-scale images of M87* and Sgr A* by the Event Horizon Telescope (EHT), it has become possible to resolve the near-horizon region of ...astrophysical black holes. As a result, there has been considerable interest in the implications of the measurement of the shadow size, i.e., the asymptotic photon ring. We explore the general implications of such a measurement, identifying what is and, more importantly, is not constrained by such measurements, with applications to EHT and future instruments. We consider a general spherically symmetric metric, which effectively applies for a polar observer (appropriate for M87*) in the slow rotation limit. We propose a nonperturbative, nonparametric spacetime-domain characterization of shadow size and related measurements that makes explicit the nature and power (or lack thereof) of shadow-size-based constraints, and facilitates comparisons among observations and targets.
Abstract
The dominant uncertainty in the current measurement of the Hubble constant (
H
0
) with strong gravitational lensing time delays is attributed to uncertainties in the mass profiles of the ...main deflector galaxies. Strongly lensed supernovae (glSNe) can provide, in addition to measurable time delays, lensing magnification constraints when knowledge about the unlensed apparent brightness of the explosion is imposed. We present a hierarchical Bayesian framework to combine a data set of SNe that are not strongly lensed and a data set of strongly lensed SNe with measured time delays. We jointly constrain (i)
H
0
using the time delays as an absolute distance indicator, (ii) the lens model profiles using the magnification ratio of lensed and unlensed fluxes on the population level, and (iii) the unlensed apparent magnitude distribution of the SN population and the redshift–luminosity relation of the relative expansion history of the universe. We apply our joint inference framework on a future expected data set of glSNe and forecast that a sample of 144 glSNe of Type Ia with well-measured time series and imaging data will measure
H
0
to 1.5%. We discuss strategies to mitigate systematics associated with using absolute flux measurements of glSNe to constrain the mass density profiles. Using the magnification of SN images is a promising and complementary alternative to using stellar kinematics. Future surveys, such as the Rubin and Roman observatories, will be able to discover the necessary number of glSNe, and with additional follow-up observations, this methodology will provide precise constraints on mass profiles and
H
0
.
Abstract
As the interferometers detecting gravitational waves are upgraded, improving their sensitivity, the probability of observing strong lensing increases. Once a detection is made, it will be ...critical to gain as much information as possible about the lensing object from these observations. In this work, we present a methodology to rapidly perform model selection between differing mass density profiles for strongly lensed gravitational-wave signals, using the results of the fast strong-lensing analysis pipeline GOLUM. We demonstrate the validity of this methodology using some illustrative examples adopting the idealized singular isothermal sphere and point-mass lens models. We take several simulated lensed signals, analyze them with GOLUM, and subject them to our methodology to recover both the model and its parameters. To demonstrate the methodology’s stability, we show how the result varies with the number of samples used for a subset of these injections. In addition to the analysis of simulations, we also apply our methodology to the gravitational-wave event pair GW191230–LGW200104, two events with similar frequency evolutions and sky locations, which was analyzed in detail as a potential lensing candidate but ultimately discarded when considering the full population and the uncertain nature of the second event. We find a preference for the singular isothermal sphere model over the point mass, though our posteriors are much wider than for the lensed injections, in line with the expectations for a nonlensed event. The methodology developed in this work is made available as part of the
Gravelamps
software package.
PDF
