arXiv subjects

Michael Gabe

Publications and source records attributed to Michael Gabe.

2 recordsLinked to original sources

arXiv2026

Combining Rubin and Roman photometry and its implications for photometric redshift estimation

We perform a joint Roman--Rubin photometry analysis using the LSST Science Pipelines (LSP) on simulated images, by using the Roman F158 band as the reference band and applying forced photometry on the other bands. We find that the LSP CModel photometry for Roman bands is on average unbiased, but with a bright-end systematic uncertainty floor of 7-8%. The pgauss photometry as part of the Metadetection weak-lensing shape measurement pipeline also exhibits a similar floor despite a substantially different flux-bias behavior. However, this systematic uncertainty floor becomes negligible for the color residuals and both algorithms recover unbiased colors for Roman as well as Rubin. We also show that not accounting for correlated pixel noise in Roman IMCOM coadded images results in underestimation of flux errors by a factor of ~4. Based on the measured photometry, we build a machine-learning algorithm that maps the true galaxy properties to empirical flux errors, providing a convenient method to reproduce realistic photometry errors without having to rerun expensive image simulations and photometry pipelines. We apply this empirical error model to a new mock galaxy catalog with improved realism to investigate the impact of different survey depths and configurations on photometric redshift (photo-z) estimation performance. We find that 1) Rubin survey depth significantly impacts the photo-$z$ precision, 2) additional systematic uncertainties on photometry could significantly degrade the photo-z performance especially towards high redshifts, therefore eroding the Roman--Rubin synergy, and 3) Roman photometry becomes important above z~1.5 while adding Rubin photometry to that of Roman improves photo-z performance across all redshifts. Our results provide a foundation for understanding how realistic uncertainties in galaxy photometry may propagate into the Roman--Rubin synergy in photo-z analyses.

astro-ph.IM↗

arXiv2026

Robust Photometry for Roman High-Latitude Imaging Survey Cosmology Using Roman and Rubin Imaging

Accurate and precise photometry is essential for Roman cosmology because it affects photometric-redshift performance, galaxy and cluster selection, tomographic binning, and redshift-distribution characterization. Achieving robust photometry is challenging because Roman's depth leads to substantial source blending, particularly in joint Roman--Rubin analyses, where the two surveys have different spatial resolutions. In this work, we develop and validate slimfarmer, a model-fitting photometry pipeline designed for Roman High-Latitude Imaging Survey (HLIS) cosmological analyses. Building on The Farmer, slimfarmer introduces treatments of the correlated noise present in Roman images and of astronomical shot noise, together with model-fitting configurations tuned for Roman imaging. We validate the pipeline using Roman coadded simulated images and perform forced photometry on matched Rubin image simulations. We find that slimfarmer recovers galaxy colors with the mode of the color residuals within 20 millimag for Roman-based colors and within 70 millimag for Rubin-based colors. Properly accounting for correlated noise is essential for uncertainty quantification, as photometric uncertainties are otherwise underestimated by up to a factor of ~3. We also find that applying multi-object fitting consistently to both Roman and Rubin imaging substantially mitigates blending-induced color systematics. In crowded regions, single-object fitting produces environment-dependent color biases of up to ~0.5 mag, leading to environment-dependent degradation of photometric-redshift performance. Together, these results establish slimfarmer as a prototype photometric pipeline for Roman HLIS cosmology applications and identify the correlated-noise corrections, astronomical shot-noise treatment, and joint Roman--Rubin multi-object fitting required for robust photometric-redshift characterization.

astro-ph.IM↗