1FLAT: A Firmamento-based Catalog of Active Galactic Nuclei in Fermi-LAT High-Galactic-latitude gamma-ray Sources

We present a systematic reassessment of 5062 high-Galactic-latitude gamma-ray sources from the Fermi-Large Area Telescope (LAT) 4FGL-DR4 catalog using Firmamento, a web-based platform for multifrequency source discovery and analysis. Our goal is to provide an independent evaluation of LAT gamma-ray source associations using alternative spectral and spatial methods that integrate both recent and legacy survey data. The evaluation is further refined through human supervision of spectral energy distributions, source morphology, flux variability, and template-based comparisons. Firmamento confirms the 4FGL-DR4 and 4LAC-DR3 counterparts or unassociated sources in 4493 cases (88.8%), demonstrating the robustness of both approaches. Beyond this general agreement, we identify 421 new blazar counterparts among previously unassociated sources, thereby reducing the fraction of unidentified extragalactic Fermi-LAT sources from 25% to 17%. In addition, in 64 cases, we find alternative blazar associations, while in 49 instances, we do not confirm the 4FGL-DR4 association. For all confirmed blazar counterparts, we provide homogeneous estimates of synchrotron peak frequency and peak flux using machine learning and template-based methods. The results agree with 4LAC-DR3 values in most cases, though significant discrepancies appear for a few dozen sources, often due to improved X-ray coverage. The primary outcome of this work is the First Firmamento LAT AGN Table, made publicly available through the Firmamento platform (https://firmamento.nyuad.nyu.edu), where all related multiwavelength data and images are available. The project involved extensive manual validation and benefited from the active participation of graduate and undergraduate students, highlighting the platform's value for both research and education.