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— Comparison of Abell 2261 critical curves for a source redshift of z s = 2 calculated from field redshifts. The image is overlaid on Figure 1 of Coe et al. (2012). Our model is constructed using galaxy redshifts to estimate halo membership, halo mass, and virial radius. Our model is augmented with some strong lensing-derived information; halo centroid, projected ellipticity, and position angle are taken from Coe et al. (2012), in which they are derived from the cluster image using the “mass follows light” technique (Zitrin et al. 2009b). Yellow bands mark the fiducial critical curves of our model and white dashed lines show the 1 σ confidence intervals on the position of the tangential critical curve. For comparison, we show the critical curves derived from strong lensing information alone (Coe et al. 2012). The critical curves derived from spectroscopy and the cluster image agree with those derived only from strong lensing information to within the error bars.
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Lines of sight with multiple projected cluster-scale gravitational lenses have high total masses and complex lens plane interactions that can boost the area of magnification, or étendue, making detection of faint background sources more likely than elsewhere. To identify these new "compound" cosmic telescopes, we have found directions in the sky wi...
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... Monte Carlo trials, including multiple intersections for individual trials if present. The 68% intervals in the distribution of radii for each ray define the positive and negative 1 σ contours of the location of the critical curve for that angle. We show the fiducial critical curve for Abell 2261 and the 1 σ confidence intervals on its location in Figure 9. The “fiducial” measurement uses a mass model with halo parameters exactly as measured, with no Monte Carlo variation. The critical curves derived from spectroscopy and the cluster image compare favorably to those derived from strong lensing information only, and agree to within the substantial error bars. The fiducial critical curve we construct is slightly larger than that from Coe et al. (2012), likely due to the smaller halo mass of 2 . 2 × 10 15 M calculated in that study, as compared to the value of 2 . 5 × 10 15 M we calculate. The Abell 2261 test firstly indicates that if halo centroid and ellipticity are measured under comparable assumptions (i.e., mass follows light), a model constructed from redshifts predicts critical curve locations close to those predicted by a model derived from strong lensing. Secondly, this test provides a check that NFW halo parameters are being treated correctly in our models of 0850 and 1306. Note that we currently treat halo centroid, ellipticity, and position angle somewhat differently for the 0850 and 1306 models (halo centroid is measured from the member galaxies, and we marginalize about halo ellipticity and position angle in the Monte Carlo trials). Constraining these halo parameters with the “mass follows light” assumption is a refinement upon our technique that could be performed with publicly available imaging and would further constrain the models shown in Figures 6 and 7. Multiply-imaged arcs are particularly valuable for constraining the mass distribution in multiple-cluster sys- tems, as they “pin down” the location of the critical curves for a source plane at a given redshift. We identify potential strongly-lensed arcs in both 0850 and 1306 in Figures 10 and 11 through visual inspection. We have identified a candidate multiply-imaged galaxy in beam 0850 in deep multi-band Subaru imaging of this field (see Figure 10) through the morphology and color information of the two components. The two adjacent components are both extended (with length-to-width ratio greater than 5), are individually tangential to the radial vector pointing to the center of the nearby massive cluster, are both V-dropouts with V − I > 2, and have similar spectral energy distributions (SEDs). The red V − R color in both components is highly suggestive of a Lyman break at z ∼ 5, but could potentially be the 4000 A Balmer break in a lower-redshift, dusty galaxy. Their great distance from the center of the cluster (55 ) suggests a large Einstein radius. Thus we proceed to estimate their photometric redshift to test whether this beam is a massive cluster-scale lens. To assess whether these dropout arcs 2 and 3 (Figures 10 and 12) are candidate multiply-imaged, we compare the SEDs and photometric redshifts for both. Due to the potential contamination of arc photometry from lower- redshift galaxies, we use GALFIT (Peng et al. 2002) to fit and remove adjacent galaxies before measuring photometry. We fit elliptical 2-D sersic profiles to three galaxies in the 15 × 15 region surrounding arcs 2 and 3. Resid- ual images for each band for arcs 2 and 3 are shown in Figure 12. We measure photometry on GALFIT residual images with elliptical apertures of axis ratio 2.8 and long axis 2 . 8, elongated in the direction of the extension of each arc. We determine the sky background with annular elliptical apertures of axis ratio 2.8, inner radius 2 . 8, and outer radius 3 . 5. Photometric zeropoints are measured by comparing to SDSS photometry of unsaturated stars as described in Section 3.2. We obtain error bars for each band by performing aperture photometry with the same elliptical apertures on 50 non-overlapping blank regions in the 120 . × 120 . region surrounding the center of the beam, computing the 68% confidence intervals on the resulting flux distribution, and combining the result with the known zeropoint error for each band. The positive 68% confidence interval is quoted as the 1 σ upper limit for non-detections. These upper limits match those from the online Subaru Suprime-Cam Exposure Time Calcu- lator to within 0 . 3 magnitudes in all bands for photometric apertures of comparable area, assuming point sources and 0 . 7 seeing. Aperture photometry for 0850 arc candidates 2 and 3 is plotted in the top panel of Figure 13. Arcs 2 and 3 are not detected in the LBT/LUCI J-band image of 0850 at the 3 σ level, so we plot one-sigma upper limits, measured using the same photometric apertures as for the optical photometry. Excluding non-detections in the B and V -bands, the photometry of the two arcs matches to within 1 σ in all bands, suggesting that the two sources are multiple images of the same galaxy. To be bona-fide multiply-imaged arcs, sources 2 and 3 would need to be located near the critical curve; but their significant distance of 55 away from the central BCG suggests that they must also be at high redshift ( z > 2). Here, we use the public photometric redshift code BPZ (Benitez 2000) to estimate photometric redshifts for the two arcs independently. This template-fitting code uses a Bayesian approach with priors of redshift probability as a function of galaxy type and magnitude. For this analysis, we retain BPZ’s default priors, which are generated for objects with spectroscopic redshifts in the Hubble Deep Field and judged superior to a flat redshift prior (Benitez 2000). This is a conservative choice, as such priors reduce the probability of finding high-redshift solutions for bright sources, including sources made appar- ently bright by high magnification. In addition to BPZ’s eight template SEDs, we add the SED library distributed in the SDSS pipeline idlspec2d used to fit SDSS spectroscopic redshifts (Aihara et al. 2011). The set of SEDs includes single stellar models gridded over metallicity and age (ranging from 5 Myr to 5 Gyr), galaxy eigenspectra with emission lines, and star forming galaxy templates. We use the i and I c filters as separate constraints. The bottom panel of Figure 13 plots the resulting redshift probability distributions for both arcs. The most likely redshift is z = 5 . 03 for arc 2 and z = 5 . 04 for arc 3. The 1 σ confidence intervals are 4 . 84 < z < 5 . 13 for arc 2 and 4 . 90 < z < 5 . 08 for arc 3. BPZ calculates the odds that a given redshift solution is correct by in- tegrating the probability distribution p ( z | C, m ) within ...
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... Since we do not have redshifts for these sources, we corrected the flux densities of the sources by adopting estimated median redshifts of 1.5 based on previous 450 μm studies (e.g., Casey et al. 2013;Chen et al. 2013). We took our lens models from the LENSTOOL developers and Hubble Frontier Fields Archive (Liesenborgs et al. 2006;Jullo et al. 2007;Bradač et al. 2009;Jullo & Kneib 2009;Keeton 2010;Oguri 2010;Merten et al. 2011;Jauzac et al. 2012Jauzac et al. , 2014Zitrin et al. 2013;Ammons et al. 2014;Johnson et al. 2014;McCully et al. 2014;Mohammed et al. 2014;Richard et al. 2014;Diego et al. 2015;Grillo et al. 2015;Ishigaki et al. 2015;Hoag et al. 2016;Caminha et al. 2017;Lotz et al. 2017;Kawamata et al. 2018). ...
The extragalactic background light (EBL) is the cumulative radiation outside the Milky Way. The determination of its corresponding primary emitting sources as well as its total energy level across the entire electromagnetic spectrum has profound implications for both cosmology and galaxy formation. However, the detailed origin of the EBL at far-infrared wavelengths, particularly those close to the peak of the cosmic infrared background, remains unclear. Here we report the results of our ongoing SCUBA-2 450 μ m survey of 10 massive galaxy cluster fields. By exploiting the strong gravitational lensing offered by these clusters, we obtain significant counts down to an unprecedented depth of ∼0.1 mJy at this wavelength, about 10 times deeper than that reached by any other previous survey. The cumulative energy density based on the counts is 138.1 − 19.3 + 23.9 Jy deg ⁻² or 0.45 − 0.06 + 0.08 MJy sr ⁻¹ . Comparing our measurements to those made by the COBE and Planck satellites, we find that at this flux density level, the 450 μ m EBL is entirely resolved by our SCUBA-2 observations. Thus, we find for the first time that discrete sources produce fully to the 450 μ m EBL, and that about half of it comes from sources with sub-mJy flux densities. Our deep number counts provide strong constraints on galaxy formation models.
... (Jullo & Kneib 2009;Jauzac et al. 2012Jauzac et al. , 2014Richard et al. 2014), GLAFIC(Oguri 2010;Ishigaki et al. 2015;Kawamata et al. 2016Kawamata et al. , 2018, Sharon/Johnson(Johnson et al. 2014), and Keeton Keeton 2010;Ammons et al. 2014;McCully et al. 2014). For the free-form method, we choose Diego 6(Diego et al. 2015a(Diego et al. , 2015b(Diego et al. , 2016b(Diego et al. , 2016a(Diego et al. , 2018, GRALE(Liesenborgs et al. 2006;Sebesta et al. 2016), and Bradač(Bradač et al. 2005). ...
We present a new strong-lensing (SL) mass reconstruction of the six Hubble Frontier Fields (HFF) clusters with the MAximum-entropy ReconStruction ( MARS ) algorithm. MARS is a new free-form inversion method, which suppresses spurious small-scale fluctuations while achieving excellent convergence in positions of multiple images. For each HFF cluster, we obtain a model-independent mass distribution from the compilation of the self-consistent SL data in the literature. With 100–200 multiple images per cluster, we reconstruct solutions with small scatters of multiple images in both source (∼0.″02) and image planes (0.″05–0.″1), which are lower than the previous results by a factor of 5–10. An outstanding case is the MACS J0416.1-2403 mass reconstruction, which is based on the largest high-quality SL data set where all 236 multiple images/knots have spectroscopic redshifts. Although our solution is smooth on a large scale, it reveals group/galaxy-scale peaks where the substructures are required by the data. We find that in general, these mass peaks are in excellent spatial agreement with the member galaxies, although MARS never uses the galaxy distributions as priors. Our study corroborates the flexibility and accuracy of the MARS algorithm and demonstrates that MARS is a powerful tool in the JWST era, when a 2–3 times larger number of multiple image candidates become available for SL mass reconstruction, and self-consistency within the data set becomes a critical issue.
... Several independent teams produced numerous SL models for all six HFF clusters, which are all publicly available in the MAST archive. 3 In this study we restrict ourselves to models that are both available for all six clusters and are based on the full and most recent data sets available from the HFF program: CATS (Jauzac et al., 2014(Jauzac et al., , 2015Limousin et al., 2016;Lagattuta et al., 2017), Diego (Diego et al., 2015), GLAFIC (Kawamata et al., 2016, Keeton (Ammons et al., 2014;McCully et al., 2014), Sharon & Johnson (Johnson et al., 2014) and Williams (Grillo et al., 2015). We compute gravitational magnification factors at each galaxy's position and photometric redshift from the convergence κ and shear γ (cf. ...
How did the first stars form? How did they assemble to galaxies? All elements heavier than hydrogen and helium, ‘metals’ that play crucial roles in the physics of star-formation, galaxy evolution and ultimately the formation of planets and life upon them, are formed in or by stars. And yet, many details of the formation of the very first galaxies, the build-up of stellar mass and chemical enrichment of the Universe, remain an open field of research. This field represents one of the major challenges of modern astronomy, in particular for the upcoming James Webb Space Telescope one of whose primary science goals will be observing first light and primordial galaxies. In an effort towards answering these questions and preparing for the JWST-era, my thesis work focuses on studying the physics of high-redshift galaxies at the frontier of observability and pushing the limits of the current instrumentation further towards the formation of the earliest stars and galaxies - The Cosmic Dawn.
... Several independent teams produced numerous SL models for all six HFF clusters, which are all publicly available in the MAST archive. 4 In this study we restrict ourselves to models that are both available for all six clusters and are based on the full and most recent data sets available from the HFF program: CATS (Jauzac et al. 2014(Jauzac et al. , 2015Limousin et al. 2016;Lagattuta et al. 2017), Diego (Diego et al. 2015), GLAFIC (Kawamata et al. 2016, Keeton (Ammons et al. 2014;McCully et al. 2014), Sharon & Johnson (Johnson et al. 2014) and Williams (Grillo et al. 2015). We compute gravitational magnification factors at each galaxy's position and photometric redshift from the convergence and shear maps provided by the SL modelling teams as, ...
We present new measurements of the very low-mass end of the galaxy stellar mass function (GSMF) at z ∼ 6 − 7 computed from a rest-frame ultraviolet selected sample of dropout galaxies. These galaxies lie behind the six Hubble Frontier Fields clusters and are all gravitationally magnified. Using deep Spitzer/IRAC and Hubble Space Telescope imaging, we derive stellar masses by fitting galaxy spectral energy distributions and explore the impact of different model assumptions and parameter degeneracies on the resulting GSMF. Our sample probes stellar masses down to M⋆ > 106 M⊙ and we find the z ∼ 6 − 7 GSMF to be best parametrized by a modified Schechter function which allows for a turnover at very low masses. Using a Monte-Carlo Markov Chain analysis of the GSMF, including accurate treatment of lensing uncertainties, we obtain a relatively steep low-mass end slope $\alpha \simeq -1.96_{-0.08}^{+0.09}$ and a turnover at $\log (M_T/\text{M}_{\odot })\simeq 7.10_{-0.56}^{+0.17}$ with a curvature of $\beta \simeq 1.00_{-0.73}^{+0.87}$ for our minimum assumption model with constant star-formation history (SFH) and low dust attenuation, AV ≤ 0.2. We find that the z ∼ 6 − 7 GSMF, in particular its very low-mass end, is significantly affected by the assumed functional form of the star formation history and the degeneracy between stellar mass and dust attenuation. For example, the low-mass end slope ranges from $\alpha \simeq -1.82_{-0.07}^{+0.08}$ for an exponentially rising SFH to $\alpha \simeq -2.34_{-0.10}^{+0.11}$ when allowing AV of up to 3.25. Future observations at longer wavelengths and higher angular resolution with the James Webb Space Telescope are required to break these degeneracies and to robustly constrain the stellar mass of galaxies on the extreme low-mass end of the GSMF.
... Several independent teams produced numerous SL models for all six HFF clusters, which are all publicly available in the MAST archive. 4 In this study we restrict ourselves to models that are both available for all six clusters and are based on the full and most recent data sets available from the HFF program: CATS (Jauzac et al. 2014(Jauzac et al. , 2015Limousin et al. 2016;Lagattuta et al. 2017), Diego (Diego et al. 2015), GLAFIC (Kawamata et al. 2016, Keeton (Ammons et al. 2014;McCully et al. 2014), Sharon & Johnson (Johnson et al. 2014) and Williams (Grillo et al. 2015). We compute gravitational magnification factors at each galaxy's position and photometric redshift from the convergence and shear maps provided by the SL modelling teams as, ...
We present new measurements of the very low-mass end of the galaxy stellar mass function (GSMF) at $z\sim6-7$ computed from a rest-frame ultraviolet selected sample of dropout galaxies. These galaxies lie behind the six Hubble Frontier Fields clusters and are all gravitationally magnified. Using deep Spitzer/IRAC and Hubble Space Telescope imaging, we derive stellar masses by fitting galaxy spectral energy distributions and explore the impact of different model assumptions and parameter degeneracies on the resulting GSMF. Our sample probes stellar masses down to $M_{\star}>10^{6}\,\text{M}_{\odot}$ and we find the $z\sim6-7$ GSMF to be best parametrized by a modified Schechter function which allows for a turnover at very low masses. Using a Monte-Carlo Markov Chain analysis of the GSMF, including accurate treatment of lensing uncertainties, we obtain a relatively steep low-mass end slope $\alpha\simeq-1.96_{-0.08}^{+0.09}$ and a turnover at $\log(M_T/\text{M}_{\odot})\simeq7.10_{-0.56}^{+0.17}$ with a curvature of $\beta\simeq1.00_{-0.73}^{+0.87}$ for our minimum assumption model with constant star-formation history (SFH) and low dust attenuation, $A_V\leq0.2$. We find that the $z\sim6-7$ GSMF, in particular its very low-mass end, is significantly affected by the assumed functional form of the star formation history and the degeneracy between stellar mass and dust attenuation. For example, the low-mass end slope ranges from $\alpha\simeq-1.82_{-0.07}^{+0.08}$ for an exponentially rising SFH to $\alpha\simeq-2.34_{-0.10}^{+0.11}$ when allowing $A_V$ of up to 3.25. Future observations at longer wavelengths and higher angular resolution with the James Webb Space Telescope are required to break these degeneracies and to robustly constrain the stellar mass of galaxies on the extreme low-mass end of the GSMF.
... Sluse et al. 2017) and WFI 2033-4723(Sluse et al. 2019), which is based on the group-finding algorithms ofWilman et al. (2005) andAmmons et al. (2014).Wilson et al. (2016) uses a similar method, the results of which were used in the analysis of the H0LiCOW lens PG 1115 + 080(Chen et al. 2019). We summarize the method here, and refer interested readers toSluse et al. (2017) for a more complete description and explanation of parameter choices in this algorithm. ...
In time-delay cosmography, three of the key ingredients are (1) determining the velocity dispersion of the lensing galaxy, (2) identifying galaxies and groups along the line of sight with sufficient proximity and mass to be included in the mass model, and (3) estimating the external convergence κext from less massive structures that are not included in the mass model. We present results on all three of these ingredients for two time-delay lensed quad quasar systems, DES J0408–5354 and WGD 2038–4008 . We use the Gemini, Magellan, and VLT telescopes to obtain spectra to both measure the stellar velocity dispersions of the main lensing galaxies and to identify the line-of-sight galaxies in these systems. Next, we identify 10 groups in DES J0408–5354 and two groups in WGD 2038–4008 using a group-finding algorithm. We then identify the most significant galaxy and galaxy-group perturbers using the ‘flexion shift’ criterion. We determine the probability distribution function of the external convergence κext for both of these systems based on our spectroscopy and on the DES-only multiband wide-field observations. Using weighted galaxy counts, calibrated based on the Millennium Simulation, we find that DES J0408–5354 is located in a significantly underdense environment, leading to a tight (width $\sim 3{{\ \rm per\ cent}}$), negative-value κext distribution. On the other hand, WGD 2038–4008 is located in an environment of close to unit density, and its low source redshift results in a much tighter κext of $\sim 1{{\ \rm per\ cent}}$, as long as no external shear constraints are imposed.
... galaxy-group identification, we employed the same algorithm used in the spectroscopic analysis of the fields of H0LiCOW lenses HE 0435−1223(Sluse et al. 2017) and WFI 2033−4723(Sluse et al. 2019), which is based on the group-finding algorithms ofWilman et al. (2005) andAmmons et al. (2014).Wilson et al. (2016) uses a similar method, the results of which were used in the analysis of the H0LiCOW lens PG 1115+080(Chen et al. 2019) ...
In time-delay cosmography, three of the key ingredients are 1) determining the velocity dispersion of the lensing galaxy, 2) identifying galaxies and groups along the line of sight with sufficient proximity and mass to be included in the mass model, and 3) estimating the external convergence $\kappa_\mathrm{ext}$ from less massive structures that are not included in the mass model. We present results on all three of these ingredients for two time-delay lensed quasar systems, DES J0408-5354 and WGD 2038-4008. We use the Gemini, Magellan and VLT telescopes to obtain spectra to both measure the stellar velocity dispersions of the main lensing galaxies and to identify the line-of-sight galaxies in these systems. Next, we identify 10 groups in DES J0408-5354 and 2 groups in WGD 2038-4008using a group-finding algorithm. We then identify the most significant galaxy and galaxy-group perturbers using the "flexion shift" criterion. We determine the probability distribution function of the external convergence $\kappa_\mathrm{ext}$ for both of these systems based on our spectroscopy and on the DES-only multiband wide-field observations. Using weighted galaxy counts, calibrated based on the Millennium Simulation, we find that DES J0408-5354 is located in a significantly underdense environment, leading to a tight (width $\sim3\%$), negative-value $\kappa_\mathrm{ext}$ distribution. On the other hand, WGD 2038-4008 is located in an environment of close to unit density, and its low source redshift results in a much tighter $\kappa_\mathrm{ext}$ of $\sim1\%$, as long as no external shear constraints are imposed.
... this cluster field belongs to the 200 most massive lines of sight in the SDSS . Ammons et al. (2013) have studied this field with Hectospec at the MMT (formerly Multiple Mirror Telescope) on Mt. Hopkins, Arizona. ...
... There is another LRG at a spectroscopic redshift of z = 0.563 in the field. Ammons et al. (2013) do not find evidence for the presence of a third group at this redshift, though this could be due to the limited depth of their spectroscopic sample. Ammons et al. (2013) also use six-band B, V, R c , I c , i , z Subaru/Suprime-Cam data to search for strong lensing features. ...
... Ammons et al. (2013) do not find evidence for the presence of a third group at this redshift, though this could be due to the limited depth of their spectroscopic sample. Ammons et al. (2013) also use six-band B, V, R c , I c , i , z Subaru/Suprime-Cam data to search for strong lensing features. They have found a candidate multiply imaged source at a photometric redshift of z = 5.03 +0.21 −0.17 . ...
We present results from the Wendelstein Weak Lensing (WWL) pathfinder project, in which we have observed three intermediate-redshift Planck clusters of galaxies with the new 30 arcmin × 30 arcmin wide field imager at the 2 m Fraunhofer Telescope at Wendelstein Observatory. We investigate the presence of biases in our shear catalogues and estimate their impact on our weak lensing mass estimates. The overall calibration uncertainty depends on the cluster redshift and is below 8.1–16 per cent for z ≈ 0.27–0.77. It will decrease with improvements on the background sample selection and the multiplicative shear bias calibration. We present the first weak lensing mass estimates for PSZ1 G109.88+27.94 and PSZ1 G139.61+24.20, two Sunyaev-Zeldovich (SZ)-selected cluster candidates. Based on Wendelstein colours and SDSS (Sloan Digital Sky Survey) photometry, we find that the redshift of PSZ1 G109.88+27.94 has to be corrected to z ≈ 0.77. We investigate the influence of line-of-sight structures on the weak lensing mass estimates and find upper limits for two groups in each of the fields of PSZ1 G109.88+27.94 and PSZ1 G186.98+38.66. We compare our results to SZ and dynamical mass estimates from the literature, and in the case of PSZ1 G186.98+38.66 to previous weak lensing mass estimates. We conclude that our pathfinder project demonstrates that weak lensing cluster masses can be accurately measured with the 2 m Fraunhofer Telescope.
... This is important since it now becomes clear that, with the current depth and lensing models, we will not be able to put robust constraints on the UV LF shape beyond such magnitude limit. It is noteworthy that despite significant differences in the survey volume between the models, the luminosity functions Figure 5. Source plane reconstruction for MACS1149 cluster using four different lensing models (Richard et al. 2014a;Jauzac et al. 2016;Johnson et al. 2014;Ammons et al. 2014;Diego et al. 2016) for which deflection maps were submitted to the HFF lensing project. The mass models affect not only the magnification maps but also the total surface area in the source plane and the spatial distribution of the sources when lensed back to the image plane. ...
With the Hubble Frontier Fields program, gravitational lensing has provided a powerful way to extend the study of the ultraviolet luminosity function (LF) of galaxies at $z \sim 6$ down to unprecedented magnitude limits. At the same time, significant discrepancies between different studies were found at the very faint end of the LF. In an attempt to understand such disagreements, we present a comprehensive assessment of the uncertainties associated with the lensing models and the size distribution of galaxies. We use end-to-end simulations from the source plane to the final LF that account for all lensing effects and systematic uncertainties by comparing several mass models. In addition to the size distribution, the choice of lens model leads to large differences at magnitudes fainter than $M_{UV} = -15~$ AB mag, where the magnification factor becomes highly uncertain. We perform MCMC simulations that include all these uncertainties at the individual galaxy level to compute the final LF, allowing, in particular, a crossover between magnitude bins. The best LF fit, using a modified Schechter function that allows for a turnover at faint magnitudes, gives a faint-end slope of $\alpha = -2.01_{-0.14}^{+0.12}$, a curvature parameter of $\beta = 0.48_{-0.25}^{+0.49}$, and a turnover magnitude of $M_{T} = -14.93_{-0.52}^{+0.61}$. Most importantly our procedure shows that robust constraints on the LF at magnitudes fainter than $M_{UV} = -15~$ AB remain unrealistic. More accurate lens modeling and future observations of lensing clusters with the James Webb Space Telescope can reliably extend the UV LF to fainter magnitudes.
... The galaxies to be used are determined automatically according to the luminosity function of the galaxies in the sample and for different redshift bins. In doing so, EasyCritics combines the lens modelling approach described by Zitrin et al. (2009) and the arc-free analysis by Zitrin et al. (2012b) with the LRG-based lens detection by Wong et al. (2013) and Ammons et al. (2014). Having at hands much larger data sats, the mathematical approach and numerical implementation had to be changed in order to achieve higher computational performances. ...
We present EasyCritics, an algorithm to detect strongly-lensing groups and clusters in wide-field surveys without relying on a direct recognition of arcs. EasyCritics assumes that light traces mass and predicts the most likely locations of critical curves from the observed fluxes of luminous red early-type galaxies in the line of sight. The positions, redshifts and fluxes of these galaxies constrain the idealized gravitational lensing potential as a function of source redshift up to five free parameters, which are calibrated on few known lenses. From the lensing potential, EasyCritics derives the critical curves for a given, representative source redshift. EasyCritics is highly parallelized, uses fast Fourier methods and, optionally, GPU acceleration in order to process large datasets efficiently. The search of a $\smash{1 \, \mathrm{deg}^2}$ field of view requires less than 1 minute on a modern quad-core CPU, when using a pixel resolution of $0.25"/\mathrm{px}$. In this first part of a paper series on EasyCritics, we describe the main underlying concepts and present a first demonstration on data from the Canada-France-Hawaii-Telescope Lensing survey. We show that EasyCritics is able to identify known group- and cluster-scale lenses, including a cluster with two giant arc candidates that were previously missed by automated arc detectors. An additional null test on a candidate-free $\smash{1 \, \mathrm{deg}^2}$ field yields zero group- or cluster scale detections.
