Abstract
We search Dark Energy Survey (DES) Year 3 imaging data for galaxy–galaxy strong gravitational lenses using convolutional neural networks. We generate 250 000 simulated lenses at redshifts > ...0.8 from which we create a data set for training the neural networks with realistic seeing, sky and shot noise. Using the simulations as a guide, we build a catalogue of 1.1 million DES sources with 1.8 < g − i < 5, 0.6 < g − r < 3, r_mag > 19, g_mag > 20, and i_mag > 18.2. We train two ensembles of neural networks on training sets consisting of simulated lenses, simulated non-lenses, and real sources. We use the neural networks to score images of each of the sources in our catalogue with a value from 0 to 1, and select those with scores greater than a chosen threshold for visual inspection, resulting in a candidate set of 7301 galaxies. During visual inspection, we rate 84 as ‘probably’ or ‘definitely’ lenses. Four of these are previously known lenses or lens candidates. We inspect a further 9428 candidates with a different score threshold, and identify four new candidates. We present 84 new strong lens candidates, selected after a few hours of visual inspection by astronomers. This catalogue contains a comparable number of high-redshift lenses to that predicted by simulations. Based on simulations, we estimate our sample to contain most discoverable lenses in this imaging and at this redshift range.
Abstract
Recent JWST/NIRCam imaging taken for the ultra-deep UNCOVER program reveals a very red dropout object at
z
phot
≃ 7.6, triply imaged by the galaxy cluster A2744 (
z
d
= 0.308). All three ...images are very compact, i.e., unresolved, with a delensed size upper limit of
r
e
≲ 35 pc. The images have apparent magnitudes of
m
F444W
∼ 25−26 AB, and the magnification-corrected absolute UV magnitude of the source is
M
UV,1450
= −16.81 ± 0.09. From the sum of observed fluxes and from a spectral energy distribution (SED) analysis, we obtain estimates of the bolometric luminosities of the source of
L
bol
≳ 10
43
erg s
−1
and
L
bol
∼ 10
44
–10
46
erg s
−1
, respectively. Based on its compact, point-like appearance, its position in color–color space, and the SED analysis, we tentatively conclude that this object is a UV-faint dust-obscured quasar-like object, i.e., an active galactic nucleus at high redshift. We also discuss other alternative origins for the object’s emission features, including a massive star cluster, Population III, supermassive, or dark stars, or a direct-collapse black hole. Although populations of red galaxies at similar photometric redshifts have been detected with JWST, this object is unique in that its high-redshift nature is corroborated geometrically by lensing, that it is unresolved despite being magnified—and thus intrinsically even more compact—and that it occupies notably distinct regions in both size–luminosity and color–color space. Planned UNCOVER JWST/NIRSpec observations, scheduled in Cycle 1, will enable a more detailed analysis of this object.
We report new high-quality galaxy-scale strong lens candidates found in the Kilo-Degree Survey data release 4 using machine learning. We have developed a new convolutional neural network (CNN) ...classifier to search for gravitational arcs, following the prescription by Petrillo et al. and using only r-band images. We have applied the CNN to two "predictive samples": a luminous red galaxy (LRG) and a "bright galaxy" (BG) sample (r < 21). We have found 286 new high-probability candidates, 133 from the LRG sample and 153 from the BG sample. We have ranked these candidates based on a value that combines the CNN likelihood of being a lens and the human score resulting from visual inspection (P-value), and here we present the highest 82 ranked candidates with P-values ≥0.5. All of these high-quality candidates have obvious arc or pointlike features around the central red defector. Moreover, we define the best 26 objects, all with P-values ≥0.7, as a "golden sample" of candidates. This sample is expected to contain very few false positives; thus, it is suitable for follow-up observations. The new lens candidates come partially from the more extended footprint adopted here with respect to the previous analyses and partially from a larger predictive sample (also including the BG sample). These results show that machine-learning tools are very promising for finding strong lenses in large surveys and more candidates can be found by enlarging the predictive samples beyond the standard assumption of LRGs. In the future, we plan to apply our CNN to the data from next-generation surveys such as the Large Synoptic Survey Telescope, Euclid, and the Chinese Space Station Optical Survey.
We use spectroscopic observations of the gravitationally lensed systems SDSS0924+0219(BC), Q1355-2257(AB), and SDSS1029+2623(BC) to analyze microlensing and dust extinction in the observed ...components. We detect chromatic microlensing effects in the continuum and microlensing in the broad emission line profiles of the systems SDSS0924+0219(BC) and Q1355-2257(AB). Using magnification maps to simulate microlensing and modeling the emitting region as a Gaussian intensity profile with size rs ∝ λp, we obtain the probability density functions for a logarithmic size prior to . In the case of SDSS0924+0219, we obtain lt-d (at 1 ), which is larger than the range of other estimates, and p = 0.8 0.2 (at 1 ), which is smaller than predicted by the thin disk theory, but still in agreement with previous results. In the case of Q1355-2257 we obtain (at 1 ) lt-d, which is also larger than the theoretical prediction, and p = 2.0 0.7, which is in agreement with the theory within errors. SDSS1029+2326 spectra show evidence of extinction, probably produced by a galaxy in the vicinity of image C. Fitting an extinction curve to the data we estimate ΔE ∼ 0.2 in agreement with previous results. We found no evidence of microlensing for this system.
For ultra compact objects, light rings and fundamental photon orbits (FPOs) play a pivotal role in the theoretical analysis of strong gravitational lensing effects, and of BH shadows in particular. ...In this short review, specific models are considered to illustrate how FPOs can be useful in order to understand some non-trivial gravitational lensing effects. This paper aims at briefly overviewing the theoretical foundations of these effects, touching also some of the related phenomenology, both in general relativity and alternative theories of gravity, hopefully providing some intuition and new insights for the underlying physics, which might be critical when testing the Kerr black hole hypothesis.
Abstract
Among known strongly lensed quasar systems, ∼25% have gravitational potentials sufficiently flat (and sources sufficiently well aligned) to produce four images rather than two. The projected ...flattening of the lensing galaxy and tides from neighboring galaxies both contribute to the potential’s quadrupole. Witt’s hyperbola and Wynne’s ellipse permit determination of the overall quadrupole from the positions of the quasar images. The position of the lensing galaxy resolves the distinct contributions of intrinsic ellipticity and tidal shear to that quadrupole. Among 31 quadruply lensed quasars systems with statistically significant decompositions, 15 are either reliably (2
σ
) or provisionally (1
σ
) shear-dominated and 11 are either reliably or provisionally ellipticity-dominated. For the remaining eight, the two effects make roughly equal contributions to the combined cross section (newly derived here) for quadruple lensing. This observational result is strongly at variance with the ellipticity-dominated forecast of Oguri & Marshall.
Abstract
Joint analyses of small-scale cosmological structure probes are relatively unexplored and promise to advance measurements of microphysical dark matter properties using heterogeneous data. ...Here, we present a multidimensional analysis of dark matter substructure using strong gravitational lenses and the Milky Way (MW) satellite galaxy population, accounting for degeneracies in model predictions and using covariances in the constraining power of these individual probes for the first time. We simultaneously infer the projected subhalo number density and the half-mode mass describing the suppression of the subhalo mass function in thermal relic warm dark matter (WDM),
M
hm
, using the semianalytic model
Galacticus
to connect the subhalo population inferred from MW satellite observations to the strong lensing host halo mass and redshift regime. Combining MW satellite and strong lensing posteriors in this parameter space yields
M
hm
< 10
7.0
M
⊙
(WDM particle mass
m
WDM
> 9.7 keV) at 95% confidence and disfavors
M
hm
= 10
7.4
M
⊙
(
m
WDM
= 7.4 keV) with a 20:1 marginal likelihood ratio, improving limits on
m
WDM
set by the two methods independently by ∼30%. These results are marginalized over the line-of-sight contribution to the strong lensing signal, the mass of the MW host halo, and the efficiency of subhalo disruption due to baryons and are robust to differences in the disruption efficiency between the MW and strong lensing regimes at the ∼10% level. This work paves the way for unified analyses of next-generation small-scale structure measurements covering a wide range of scales and redshifts.
Abstract
The first deep field images from the James Webb Space Telescope (JWST) of the galaxy cluster SMACS J0723.3-7327 reveal a wealth of new lensed images at uncharted infrared wavelengths, with ...unprecedented depth and resolution. Here we securely identify 14 new sets of multiply imaged galaxies totaling 42 images, adding to the five sets of bright and multiply imaged galaxies already known from Hubble Space Telescope data. We find examples of arcs crossing critical curves, allowing detailed community follow-up, such as JWST spectroscopy for precise redshift determinations, and measurements of the chemical abundances and of the detailed internal gas dynamics of very distant, young galaxies. One such arc contains a pair of compact knots that are magnified by a factor of hundreds, and features a microlensed transient. We also detect an Einstein cross candidate only visible thanks to JWST’s superb resolution. Our parametric lens model is available through the following link (
https://www.dropbox.com/sh/gwup2lvks0jsqe5/AAC2RRSKce0aX-lIFCc9vhBXa?dl=0
) and will be regularly updated using additional spectroscopic redshifts. The model is constrained by 16 of these sets of multiply imaged galaxies, three of which have spectroscopic redshifts, and reproduces the multiple images to better than an rms of 0.″5, allowing for accurate magnification estimates of high-redshift galaxies. The intracluster light extends beyond the cluster members, exhibiting large-scale features that suggest a significant past dynamical disturbance. This work represents a first taste of the enhanced power JWST will have for lensing-related science.
Abstract
Since their discovery 20 years ago, the observed luminosity function of
z
≳ 6 quasars has been suspected to be biased by gravitational lensing. Apart from the recent discovery of ...UHS J0439+1634 at
z
≈ 6.52, no other strongly lensed
z
≳ 6 quasar has been conclusively identified. The hyperluminous
z
≈ 6.33 quasar SDSS J0100+2802, believed to host a supermassive black hole of ∼10
10
M
⊙
, has recently been claimed to be lensed by a factor of ∼450, which would negate both its extreme luminosity and black hole mass. However, its Ly
α
-transparent proximity zone is the largest known at
z
> 6, suggesting an intrinsically extreme ionizing luminosity. Here we show that the lensing hypothesis of
z
≳ 6 quasars can be quantitatively constrained by their proximity zones. We first show that our proximity zone analysis can recover the strongly lensed nature of UHS J0439+1634, with an estimated magnification
at 68% (95%) credibility that is consistent with previously published lensing models. We then show that the large proximity zone of SDSS J0100+2802 rules out lensing magnifications of
μ
> 4.9 at 95% probability, and conclusively rule out the proposed
μ
> 100 scenario. Future proximity zone analyses of existing
z
≳ 6 quasar samples have the potential to identify promising strongly lensed candidates, constrain the distribution of
z
≳ 6 quasar lensing, and improve our knowledge of the shape of the intrinsic quasar luminosity function.
Abstract
Einstein’s theory of general relativity (GR) has been precisely tested on solar system scales, but extragalactic tests are still poorly performed. In this work, we use a newly compiled ...sample of galaxy-scale strong gravitational lenses to test the validity of GR on kiloparsec scales. In order to solve the circularity problem caused by the presumption of a specific cosmological model based on GR, we employ the distance sum rule in the Friedmann–Lemaître–Robertson–Walker metric to directly estimate the parameterized post-Newtonian (PPN) parameter
γ
PPN
and the cosmic curvature Ω
k
by combining observations of strong lensing and Type Ia supernovae. This is the first simultaneous measurement of
γ
PPN
and Ω
k
without any assumptions about the contents of the universe or the theory of gravity. Our results show that
γ
PPN
=
1.11
−
0.09
+
0.11
and
Ω
k
=
0.48
−
0.71
+
1.09
, indicating a strong degeneracy between the two quantities. The measured
γ
PPN
, which is consistent with the prediction of 1 from GR, provides a precise extragalactic test of GR with a fractional accuracy better than 9.0%. If a prior of the spatial flatness (i.e., Ω
k
= 0) is adopted, the PPN parameter constraint can be further improved to
γ
PPN
=
1.07
−
0.07
+
0.07
, representing a precision of 6.5%. On the other hand, in the framework of GR (i.e.,
γ
PPN
= 1), our results are still marginally compatible with zero curvature (
Ω
k
=
−
0.12
−
0.36
+
0.48
), supporting no significant deviation from a flat universe.
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