Identifying Active Galactic Nuclei at z ∼ 3 from the HETDEX Survey Using Machine Learning

Tardugno Poleo, Valentina; Finkelstein, Steven L.; Leung, Gene; Mentuch Cooper, Erin; Gebhardt, Karl; Farrow, Daniel J.; Gawiser, Eric; Zeimann, Greg; Schneider, Donald P.; Morabito, Leah; Mock, Daniel; Liu, Chenxu

Abstract

We used data from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) to study the incidence of AGN in continuum-selected galaxies at z ∼ 3. From optical and infrared imaging in the 24 deg2 Spitzer HETDEX Exploratory Large Area survey, we constructed a sample of photometric-redshift selected z ∼ 3 galaxies. We extracted HETDEX spectra at the position of 716 of these sources and used machine-learning methods to identify those which exhibited AGN-like features. The dimensionality of the spectra was reduced using an autoencoder, and the latent space was visualized through t-distributed stochastic neighbor embedding. Gaussian mixture models were employed to cluster the encoded data and a labeled data set was used to label each cluster as either AGN, stars, high-redshift galaxies, or low-redshift galaxies. Our photometric redshift (photoz) sample was labeled with an estimated 92% overall accuracy, an AGN accuracy of 83%, and an AGN contamination of 5%. The number of identified AGN was used to measure an AGN fraction for different magnitude bins. The ultraviolet (UV) absolute magnitude where the AGN fraction reaches 50% is M UV = −23.8. When combined with results in the literature, our measurements of AGN fraction imply that the bright end of the galaxy luminosity function exhibits a power law rather than exponential decline, with a relatively shallow faint-end slope for the z ∼ 3 AGN luminosity function.

Citation

Tardugno Poleo, V., Finkelstein, S. L., Leung, G., Mentuch Cooper, E., Gebhardt, K., Farrow, D. J., …Liu, C. (2023). Identifying Active Galactic Nuclei at z ∼ 3 from the HETDEX Survey Using Machine Learning. Astronomical Journal, 165(4), Article 153. https://doi.org/10.3847/1538-3881/acba92

• Journal Article Type: Article
• Acceptance Date: Feb 7, 2023
• Online Publication Date: Mar 10, 2023
• Publication Date: Apr 1, 2023
• Deposit Date: Apr 17, 2024
• Publicly Available Date: Apr 23, 2024
• Journal: Astronomical Journal
• Print ISSN: 0004-6256
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 165
• Issue: 4
• Article Number: 153
• DOI: https://doi.org/10.3847/1538-3881/acba92
• Public URL: https://hull-repository.worktribe.com/output/4626508