arXiv subjects

Aaron Watkins

Publications and source records attributed to Aaron Watkins.

6 recordsLinked to original sources

arXiv2026

An overview of stray light findings and interpretation during on-sky commissioning of LSSTCam

Wide-field telescopes are intrinsically difficult to shield from unwanted stray and scattered light, while the search to identify sources of contaminating light is frequently a challenging task. The Vera C.~Rubin Observatory, which achieved its first photon with the LSST Camera (LSSTCam) on April 15, 2025, will initiate a revolutionary era for the study of dark matter, dark energy, the transient sky, the Solar System, and the Milky Way. LSSTCam will provide near seeing-limited images of the sky in six bands ($u,g,r,i,z,y$) over a $3.^\circ 5$-diameter field of view, and over the course of a decade, it will execute the Legacy Survey of Space and Time (LSST). This work provides an overview of the dedicated stray and scattered light test campaign that has been undertaken since the start of Rubin commissioning. In particular, we highlight the processes used to characterize, model, and mitigate stray light present in LSSTCam images. The Rubin commissioning team created a series of testing and analysis tools to track stray light artifacts from their initial discovery through reproduction with timely observations, simulation using ray tracing to identify opto-mechanical origins, and finally devising corrective actions. The complex stray light features encountered by Rubin provide a wealth of experience for the future wide-field and extremely wide-field observatories. This work covers the many stages of a long journey that started with conceiving an innovative and challenging optical design, followed by the engineering and system engineering efforts to build it, to finally delivering an optimized and revolutionary cutting-edge facility.

astro-ph.IM↗

arXiv2025

The dwarf stellar mass function in different environments and the lack of a generic missing dwarfs problem in {\Lambda}CDM

We combine deep photometric data in the COSMOS and XMM-LSS fields with high-resolution cosmological hydrodynamical simulations to explore two key questions: (1) how does the galaxy stellar mass function, particularly in the dwarf (Mstar < 10^9.5 MSun ) regime, vary with environment, defined as distance from the large-scale structure (LSS) traced by nodes and filaments in the cosmic web? (2) is there a generic 'missing dwarfs' problem in LambdaCDM predictions when all environments - and not just satellites around Milky Way like galaxies - are considered? The depth of the observational data used here enables us to construct complete, unbiased samples of galaxies, down to Mstar ~ 10^7 MSun and out to z ~ 0.4. Strong environmental differences are found for the galaxy stellar mass function when considering distance from LSS. As we move closer to LSS, the dwarf mass function becomes progressively flatter and the knee of the mass function shifts to larger stellar masses, both of which result in a higher ratio of massive to dwarf galaxies. While the stellar mass functions from the three simulations (NewHorizon, TNG50 and FIREbox) considered here do not completely agree across the dwarf regime, there is no evidence of a generic missing dwarfs problem in the context of LambdaCDM, akin to the results of recent work that demonstrates that there is no missing satellites problem around Galactic analogues.

astro-ph.GA↗

arXiv2025

2D light distributions of dwarf galaxies -- key tests of the implementation of physical processes in simulations

Cosmological simulations provide much of the theoretical framework within which we interpret extragalactic observations. However, even if a given simulation reproduces the integrated properties of galaxies well, it may not reproduce the detailed structures of individual galaxies. Comparisons between the 2D light distributions of simulated and observed galaxies -- particularly in the dwarf regime, where key processes like tidal perturbations and baryonic feedback most strongly influence galaxy structure -- thus provide an additional valuable test of the simulation's efficacy. We compare scaling relations derived from mock observations of simulated galaxies, drawn from the two largest halos in the high-resolution NewHorizon cosmological simulation, with galaxies in the Fornax cluster. While Fornax is significantly more massive than either group, it is the lowest-mass cluster in the local Universe, and contains a well-studied population of spatially resolved dwarfs, hence serves as a useful benchmark. Per unit stellar mass, NewHorizon dwarfs are systematically larger in half-light radius, much fainter in surface brightness, and bluer in colour than their Fornax counterparts, albeit with similar light profile shapes. We discuss potential reasons for these discrepancies, including environmental effects, baryonic feedback, resolution, or couplings of these factors. As observations of dwarfs outside of the local Universe become more plentiful through on-going or up-coming surveys such as Euclid and LSST, 2D comparisons such as these, where properties are measured in the same way across both simulations and observations, can place strong constraints on processes that alter the spatial distribution of baryons in galaxies.

astro-ph.GA↗

arXiv2024

Bright Star Subtraction Pipeline for LSST: Phase one report

We present the phase one report of the Bright Star Subtraction (BSS) pipeline for the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST). This pipeline is designed to create an extended PSF model by utilizing observed stars, followed by subtracting this model from the bright stars present in LSST data. Running the pipeline on Hyper Suprime-Cam (HSC) data shows a correlation between the shape of the extended PSF model and the position of the detector within the camera's focal plane. Specifically, detectors positioned closer to the focal plane's edge exhibit reduced circular symmetry in the extended PSF model. To mitigate this effect, we present an algorithm that enables users to account for the location dependency of the model. Our analysis also indicates that the choice of normalization annulus is crucial for modeling the extended PSF. Smaller annuli can exclude stars due to overlap with saturated regions, while larger annuli may compromise data quality because of lower signal-to-noise ratios. This makes finding the optimal annulus size a challenging but essential task for the BSS pipeline. Applying the BSS pipeline to HSC exposures allows for the subtraction of, on average, 100 to 700 stars brighter than 12th magnitude measured in g-band across a full exposure, with a full HSC exposure comprising ~100 detectors.

astro-ph.IM↗

arXiv2024

Bright Star Subtraction Pipeline for LSST: Progress Review

We present the Bright Star Subtraction (BSS) pipeline for the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST). This pipeline generates an extended PSF model using observed stars and subtracts the model from the bright stars in LSST data. When testing the pipeline on Hyper Suprime-Cam (HSC) data, we find that the shape of the extended PSF model depends on the location of the detector on the camera's focal plane. The closer a detector is to the edge of the focal plane, the less the extended PSF model is circularly symmetric. We introduce an algorithm that allows the user to consider the location dependency of the model.

astro-ph.IM↗

arXiv2016

The Burrell Schmidt Deep Virgo Survey: Tidal Debris, Galaxy Halos, and Diffuse Intracluster Light in the Virgo Cluster

We present a deep imaging survey of the Virgo Cluster, designed to study the connection between cluster galaxies and Virgo's diffuse intracluster light (ICL). Our observations span roughly 16 square degrees and reach a 3-sigma depth of mu(B)=29.5 and mu(V)=28.5 mag/arcsec^2. At these depths, the limiting systematic uncertainties are astrophysical: scattered starlight from foreground Galactic dust, and variations in faint background sources. The dust-scattered starlight is well-traced by deep far-infrared imaging, making it distinguishable from true Virgo diffuse light. Our imaging maps the Virgo core around M87 and the adjacent M86/M84 region, in subcluster B around M49, and in the more distant W' cloud around NGC 4365. Most of the detected ICL is found in the Virgo core and within the W' cloud, with little evidence for extensive ICL in subcluster B. The large amount of diffuse light seen in the infalling W' cloud likely illustrates the importance of the group environment for generating ICL. The bulk of the detected ICL is fairly red (B-V=0.7-0.9), indicative of old stellar populations. We estimate a total Virgo ICL fraction of 7-15%, somewhat smaller than expected for massive, evolved clusters, suggesting that Virgo is still growing its ICL component. We trace M87's extremely boxy halo out to ~ 150 kpc, and show that the current stripping rate of low luminosity galaxies is insufficient to have built M87's outer halo over a Hubble time. Finally, we identify another large ultra-diffuse galaxy in Virgo, likely in the process of being shredded by the cluster tidal field.

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