arXiv subjects

D. J. Lagattuta

Publications and source records attributed to D. J. Lagattuta.

13 recordsLinked to original sources

arXiv2026

Hedorah, the first yellow supergiant Kaiju star candidate at $z=3.7$ revealed by JWST behind AS1063

We present a new free-form lens model for the $z=0.348$ galaxy cluster AS1063, based on previously spectroscopically confirmed lensed galaxies and new JWST images from the GLIMPSE program. We use the ultra-deep JWST data to identify new counterimages for previously confirmed (spectroscopically) lensed systems. We use the full set of spectroscopically confirmed systems to derive a new lens model, which is later used to confirm many of the previous lensed system candidates and discover new lensed system candidates in the JWST images. We compute the geometric redshifts, time delays, and magnification for all counterimages (confirmed and not confirmed). Among the new systems, and based on photometry, we find a peculiar multiply lensed galaxy with a strong emission line at $\approx 4\, μ$m that likely corresponds to H$-β$ and/or OIII at $z\approx 7.5$. This galaxy could be a little-red-dot or an extreme emission line galaxy. We also identify a yellow supergiant lensed star candidate at $z\approx 3.7$. This star shows some similarities with previous Kaiju stars and we nickname it "Hedorah", in honor of the famous yellow-eyed Kaiju. Previous lensed stars at $z>0.1$ are either blue supergiants or red supergiants, making Hedorah the first yellow supergiant discovered beyond $z=0.1$ and confirming that, despite their rarity, they can also be found at these redshifts. Since many Cepheid stars are yellow supergiants, we consider the possibility that Hedorah could also be the first Cepheid discovered at cosmological distances, but we conclude that Hedorah is more likely a hypergiant yellow star approaching the end of its life. Alternatively, Hedorah could be a small group of stars, although this is less likely based on Hedorah's peculiar colors and additionally may require the more exotic fuzzy dark matter to help explain the lack of counterimage.

astro-ph.GA↗

arXiv2026

Non-spherical BUFFALOs: a weak lensing view of the Frontier Field clusters and associated systematics

Galaxy clusters are tracers of the large scale structures of the Universe, making the time evolution of their mass function dependent on key cosmological parameters, such as the cosmic matter density or the amplitude of density fluctuations $σ_8$. Accurate measurements of cluster's total masses are therefore essential, yet they can be challenging, particularly for clusters with complex morphologies, as simple mass profiles are often adopted to fit the measurements. In this work, we focus on the Frontier Fields galaxy clusters: a sample of six extremely massive systems, that, in most cases, exhibit highly complex mass distributions. The BUFFALO survey extended the Hubble Space Telescope observations for the Frontier Fields galaxy clusters, providing high-resolution multi-band imaging within a few Mpc. Combining this high-quality imaging dataset with ancillary spectroscopy, we produce weak-lensing catalogues with very high source densities, about 50 sources/arcmin$^2$. This allows us to robustly estimate the individual weak-lensing cluster masses and quantify the sensitivity of these measurements on different factors, such as the cluster centring, the uncertainty on the redshift distribution or the foreground contamination and boost factor correction. This provides a data-driven analysis of the different sources of systematics that can impact such measurements. We find that the largest sources of systematic bias arise for the most disturbed clusters, such as the multi-modal, merging galaxy cluster Abell 2744. This analysis sets a comprehensive framework for assessing the impact of systematics on the weak-lensing estimates of cluster masses, and in particular, in the case of unrelaxed clusters. This can play a key role in forthcoming cosmological analyses based on wide-field surveys such as Euclid and the Legacy Survey of Space and Time of the Rubin Observatory.

astro-ph.CO↗

arXiv2025

Euclid Quick Data Release (Q1): VIS processing and data products

This paper describes the VIS Processing Function (VIS PF) of the Euclid ground segment pipeline, which processes and calibrates raw data from the VIS camera. We present the algorithms used in each processing element, along with a description of the on-orbit performance of VIS PF, based on Performance Verification (PV) and Q1 data. We demonstrate that the principal performance metrics (image quality, astrometric accuracy, photometric calibration) are within pre-launch specifications. The image-to-image photometric scatter is less than $0.8\%$, and absolute astrometric accuracy compared to Gaia is $5$ mas Image quality is stable over all Q1 images with a full width at half maximum (FWHM) of $0.\!^{\prime\prime}16$. The stacked images (combining four nominal and two short exposures) reach $I_\mathrm{E} = 25.6$ ($10σ$, measured as the variance of $1.\!^{\prime\prime}3$ diameter apertures). We also describe quality control metrics provided with each image, and an appendix provides a detailed description of the provided data products. The excellent quality of these images demonstrates the immense potential of Euclid VIS data for weak lensing. VIS data, covering most of the extragalactic sky, will provide a lasting high-resolution atlas of the Universe.

astro-ph.IM↗

arXiv2020

MUSE observations towards the lensing cluster A2744: Intersection between the LBG and LAE populations at z $\sim$ 3-7

We present a study of the intersection between the populations of star forming galaxies (SFGs) selected as either Lyman break galaxies (LBGs) or Lyman-alpha emitters (LAEs) in the redshift range 2.9 - 6.7, within the same volume of universe sampled by the Multi-Unit Spectroscopic Explorer (MUSE) behind the Hubble Frontier Fields lensing cluster A2744. We define three samples of star-forming galaxies: LBG galaxies with an LAE counterpart (92 galaxies), LBG galaxies without LAE counterpart (408 galaxies) and LAE galaxies without an LBG counterpart (46 galaxies). All these galaxies are intrinsically faint due to the lensing nature of the sample (Muv $\ge$ -20.5). The fraction of LAEs among all selected SFGs increases with redshift up to z $\sim$ 6 and decreases for higher redshifts. The evolution of LAE/LBG populations with UV magnitude and Lya luminosity shows that the LAE selection is able to identify intrinsically UV faint galaxies with Muv $\ge$ -15 that are typically missed in the deepest lensing photometric surveys. The LBG population seems to fairly represent the total population of SFGs down to Muv$\sim$-15. Galaxies with Muv$<-17$ tend to have SFRLya$<$SFRuv, whereas the opposite trend is observed within our sample for faint galaxies with Muv$>-17$, including galaxies only detected by their Lya emission, with a large scatter. These trends, previously observed in other samples of SFGs at high-$z$, are seen here for very faint Muv$\sim -15$ galaxies, much fainter than in previous studies. There is no clear evidence, based on the present results, for an intrinsic difference on the properties of the two populations selected as LBG and/or LAE. The observed trends could be explained by a combination of several facts, like the existence of different star-formation regimes, the dust content, the relative distribution and morphology of dust and stars, or the stellar populations

astro-ph.GA↗

arXiv2020

SHARP -- VI. Evidence for CO (1-0) molecular gas extended on kpc-scales in AGN star forming galaxies at high redshift

We present a study of the stellar host galaxy, CO (1$-$0) molecular gas distribution and AGN emission on 50 to 500 pc-scales of the gravitationally lensed dust-obscured AGN MG J0751+2716 and JVAS B1938+666 at redshifts 3.200 and 2.059, respectively. By correcting for the lensing distortion using a grid-based lens modelling technique, we spatially locate the different emitting regions in the source plane for the first time. Both AGN host galaxies have 300 to 500 pc-scale size and surface brightness consistent with a bulge/pseudo-bulge, and 2 kpc-scale AGN radio jets that are embedded in extended molecular gas reservoirs that are 5 to 20 kpc in size. The CO (1$-$0) velocity fields show structures possibly associated with discs (elongated velocity gradients) and interacting objects (off-axis velocity components). There is evidence for a decrement in the CO (1$-$0) surface brightness at the location of the host galaxy, which may indicate radiative feedback from the AGN, or offset star formation.We find CO-H$_2$ conversion factors of around $α_{\rm CO} = 1.5\pm0.5$ (K km s$^{-1}$ pc$^2$)$^{-1}$, molecular gas masses of $> 3\times10^{10}$ M$_{\odot}$, dynamical masses of $\sim 10^{11}$ M$_{\odot}$ and gas fractions of around 60 per cent. The intrinsic CO line luminosities are comparable to those of unobscured AGN and dusty star-forming galaxies at similar redshifts, but the infrared luminosities are lower, suggesting that the targets are less efficient at forming stars. Therefore, they may belong to the AGN feedback phase predicted by galaxy formation models, because they are not efficiently forming stars considering their large amount of molecular gas.

astro-ph.GA↗

arXiv2018

SHARP - V. Modelling gravitationally-lensed radio arcs imaged with global VLBI observations

We present milliarcsecond (mas) angular resolution observations of the gravitationally lensed radio source MG J0751+2716 (at z=3.2) obtained with global Very Long Baseline Interferometry (VLBI) at 1.65 GHz. The background object is highly resolved in the tangential and radial directions, showing evidence of both compact and extended structure across several gravitational arcs that are 200 to 600~mas in size. By identifying compact sub-components in the multiple images, we constrain the mass distribution of the foreground z=0.35 gravitational lens using analytic models for the main deflector [power-law elliptical mass model; $ρ(r) \propto r^{-γ}$, where $γ=2$ corresponds to isothermal] and for the members of the galaxy group. Moreover, our mass models with and without the group find an inner mass-density slope steeper than isothermal for the main lensing galaxy, with $γ_1 = 2.08 \pm 0.02$ and $γ_2 = 2.16 \pm 0.02$ at the 4.2$σ$ level and 6.8$σ$ level, respectively, at the Einstein radius ($b_1 = 0.4025 \pm 0.0008$ and $b_2 = 0.307 \pm 0.002$ arcsec, respectively). We find randomly distributed image position residuals of about 3 mas, which are much larger that the measurement errors ($40$ $μ$as on average). This suggests that at the mas level, the assumption of a smooth mass distribution fails, requiring additional structure in the model. However, given the environment of the lensing galaxy, it is not clear whether this extra mass is in the form of sub-haloes within the lens or along the line of sight, or from a more complex halo for the galaxy group.

astro-ph.GA↗

arXiv2018

Searching for supernovae in the multiply-imaged galaxies behind the gravitational telescope A370

Strong lensing by massive galaxy clusters can provide magnification of the flux and even multiple images of the galaxies that lie behind them. This phenomenon facilitates observations of high-redshift supernovae (SNe), that would otherwise remain undetected. Type Ia supernovae (SNe Ia) detections are of particular interest because of their standard brightness, since they can be used to improve either cluster lensing models or cosmological parameter measurements. We present a ground-based, near-infrared search for lensed SNe behind the galaxy cluster Abell 370. Our survey was based on 15 epochs of J-band observations with the HAWK-I instrument on the Very Large Telescope (VLT). We use Hubble Space Telescope (HST) photometry to infer the global properties of the multiply-imaged galaxies. Using a recently published lensing model of Abell 370, we also present the predicted magnifications and time delays between the images. In our survey, we did not discover any live SNe from the 13 lensed galaxies with 47 multiple images behind Abell 370. This is consistent with the expectation of $0.09\pm0.02$ SNe calculated based on the measured star formation rate. We compare the expectations of discovering strongly lensed SNe in our survey and that performed with HST during the Hubble Frontier Fields (HFF) programme. We also show the expectations of search campaigns that can be conducted with future facilities, such as the James Webb Space Telescope (JWST) or the Wide-Field Infrared Survey Telescope (WFIRST). We show that the NIRCam instrument aboard the JWST will be sensitive to most SN multiple images in the strongly lensed galaxies and thus will be able to measure their time delays if observations are scheduled accordingly.

astro-ph.GA↗

arXiv2017

OzDES multifibre spectroscopy for the Dark Energy Survey: Three year results and first data release

We present results for the first three years of OzDES, a six-year programme to obtain redshifts for objects in the Dark Energy Survey (DES) supernova fields using the 2dF fibre positioner and AAOmega spectrograph on the Anglo-Australian Telescope. OzDES is a multi-object spectroscopic survey targeting multiple types of targets at multiple epochs over a multi-year baseline, and is one of the first multi-object spectroscopic surveys to dynamically include transients into the target list soon after their discovery. At the end of three years, OzDES has spectroscopically confirmed almost 100 supernovae, and has measured redshifts for 17,000 objects, including the redshifts of 2,566 supernova hosts. We examine how our ability to measure redshifts for targets of various types depends on signal-to-noise, magnitude, and exposure time, finding that our redshift success rate increases significantly at a signal-to-noise of 2 to 3 per 1-Angstrom bin. We also find that the change in signal-to-noise with exposure time closely matches the Poisson limit for stacked exposures as long as 10 hours. We use these results to predict the redshift yield of the full OzDES survey, as well as the potential yields of future surveys on other facilities such as the 4m Multi-Object Spectroscopic Telescope (4MOST), the Subaru Prime Focus Spectrograph (PFS), and the Maunakea Spectroscopic Explorer (MSE). This work marks the first OzDES data release, comprising 14,693 redshifts. OzDES is on target to obtain over a yield of approximately 5,700 supernova host-galaxy redshifts.

astro-ph.CO↗

arXiv2017

SHARP - IV. An apparent flux ratio anomaly resolved by the edge-on disc in B0712+472

Flux ratio anomalies in quasar lenses can be attributed to dark matter substructure surrounding the lensing galaxy and, thus, used to constrain the substructure mass fraction. Previous applications of this approach infer a substructure abundance that potentially in tension with the predictions of a $Λ$CDM cosmology. However, the assumption that all flux ratio anomalies are due to substructure is a strong one, and alternative explanations have not been fully investigated. Here, we use new high-resolution near-IR Keck~II adaptive optics imaging for the lens system CLASS B0712+472 to perform pixel-based lens modelling for this system and, in combination with new VLBA radio observations, show that the inclusion of the disc in the lens model can explain the flux ratio anomalies without the need for dark matter substructures. The projected disc mass comprises 16% of the total lensing mass within the Einstein radius and the total disc mass is $1.79 \times 10^{10} M_{sun}$. The case of B0712+472 adds to the evidence that not all flux ratio anomalies are due to dark subhaloes, and highlights the importance of taking the effects of baryonic structures more fully into account in order to obtain an accurate measure of the substructure mass fraction.

astro-ph.GA↗

arXiv2016

MUSE observations of the lensing cluster Abell 1689

We present the results obtained with MUSE on the core of the lensing cluster A1689. Integral-field observations with MUSE provide a unique view of the central region, allowing us to conduct a complete census on both cluster galaxies and lensed background sources, identified based on their spectral features without preselection. We investigate the multiple-image configuration for all known sources in the field. Previous to our survey, 28 different lensed galaxies displaying 46 multiple images were known in the MUSE field of view, most of them based on photometric redshifts and lensing considerations. Among them, we spectroscopically confirm 12 images based on their emission-lines, corresponding to 7 different lensed galaxies between z = 0.95 and 5.0. In addition, 14 new galaxies have been spectroscopically identified in this area, with redshifts ranging between 0.8 and 6.2. All background sources within the MUSE field of view correspond to multiple-imaged systems lensed by A1689. 17 sources in total are found at z > 3 based on their Lyman-alpha emission, with Lyman-alpha luminosities ranging between 40.5 < log(Lyα) < 42.5 after correction for magnification. This sample is particularly sensitive to the slope of the LF toward the faintest-end. The density of sources obtained in this survey is consistent with a steep value of α < -1.5, although this result still needs further investigation. These results illustrate the efficiency of MUSE in the characterization of lensing clusters on one hand, and the study of faint and distant populations of galaxies on the other hand. In particular, our current survey of lensing clusters should provide a unique census of sources responsible for the reionization in a representative volume at z ~ 4-7.

astro-ph.GA↗

arXiv2016

SHARP - II. Mass structure in strong lenses is not necessarily dark matter substructure: A flux ratio anomaly from an edge-on disc

Gravitational lens flux-ratio anomalies provide a powerful technique for measuring dark matter substructure in distant galaxies. However, before using these flux-ratio anomalies to test galaxy formation models, it is imperative to ascertain that the given anomalies are indeed due to the presence of dark matter substructure and not due to some other component of the lensing galaxy halo or to propagation effects. Here we present the case of CLASS~B1555+375, which has a strong radio-wavelength flux-ratio anomaly. Our high-resolution near-infrared Keck~II adaptive optics imaging and archival Hubble Space Telescope data reveal the lensing galaxy in this system to have a clear edge-on disc component that crosses directly over the pair of images that exhibit the flux-ratio anomaly. We find that simple models that include the disc can reproduce the cm-wavelength flux-ratio anomaly without requiring additional dark matter substructure. Although further studies are required, our results suggest the assumption that all flux-ratio anomalies are due to a population of dark matter sub-haloes may be incorrect, and analyses that do not account for the full complexity of the lens macro-model may overestimate the substructure mass fraction in massive lensing galaxies.

astro-ph.CO↗

arXiv2012

SHARP - I. A high-resolution multi-band view of the infra-red Einstein ring of JVAS B1938+666

We present new mass models for the gravitational lens system B1938+666, using multi-wavelength data acquired from Keck adaptive optics (AO) and Hubble Space Telescope (HST) observations. These models are the first results from the Strong-lensing at High Angular Resolution Program (SHARP), a project designed to study known quadruple-image and Einstein ring lenses using high-resolution imaging, in order to probe their mass distributions in unprecedented detail. Here, we specifically highlight differences between AO- and HST-derived lens models, finding that -- at least when the lens and source galaxies are both bright and red, and the system has a high degree of circular symmetry -- AO-derived models place significantly tighter constraints on model parameters. Using this improved precision, we infer important physical properties about the B1938+666 system, including the mass density slope of the lensing galaxy (gamma = 2.045), the projected dark matter mass fraction within the Einstein radius (M_dark/M_lens = 0.55), and the total magnification factor of the source galaxy (~ 13). Additionally, we measure an upper-limit constraint on luminous substructure (M_V > 16.2), based on the non-detection of bright satellite galaxies in all data sets. Finally, we utilize the improved image resolution of the AO data to reveal the presence of faint arcs outside of the primary Einstein ring. The positions and orientations of these arcs raise the intriguing possibility that B1938+666 has a second source galaxy, located at a more distant redshift. However, future work is needed to verify this hypothesis.

astro-ph.CO↗

arXiv2012

Gravitational detection of a low-mass dark satellite at cosmological distance

The mass-function of dwarf satellite galaxies that are observed around Local Group galaxies substantially differs from simulations based on cold dark matter: the simulations predict many more dwarf galaxies than are seen. The Local Group, however, may be anomalous in this regard. A massive dark satellite in an early-type lens galaxy at z = 0.222 was recently found using a new method based on gravitational lensing, suggesting that the mass fraction contained in substructure could be higher than is predicted from simulations. The lack of very low mass detections, however, prohibited any constraint on their mass function. Here we report the presence of a 1.9 +/- 0.1 x 10^8 M_sun dark satellite in the Einstein-ring system JVAS B1938+666 at z = 0.881, where M_sun denotes solar mass. This satellite galaxy has a mass similar to the Sagittarius galaxy, which is a satellite of the Milky Way. We determine the logarithmic slope of the mass function for substructure beyond the local Universe to be alpha = 1.1^+0.6_-0.4, with an average mass-fraction of f = 3.3^+3.6_-1.8 %, by combining data on both of these recently discovered galaxies. Our results are consistent with the predictions from cold dark matter simulations at the 95 per cent confidence level, and therefore agree with the view that galaxies formed hierarchically in a Universe composed of cold dark matter.

astro-ph.CO↗