Lyman Continuum Emission from Active Galactic Nuclei at 2.3 ≲ z ≲ 3.7 in the UVCANDELS Fields

Abstract

We present the results of our search for Lyman continuum (LyC)-emitting (weak) active galactic nuclei (AGN) at redshifts 2.3 ≲ z ≲ 4.9 from Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) F275W observations in the Ultraviolet Imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (UVCANDELS) fields. We also include LyC emission from AGN using HST WFC3 F225W, F275W, and F336W imaging found in Early Release Science (ERS) and Hubble Deep UV Legacy Survey data. We performed exhaustive queries of the Vizier database to locate AGN with high-quality spectroscopic redshifts. In total, we found 51 AGN that met our criteria within the UVCANDELS and ERS footprints. Out of these 51, we find 12 AGN that had ≥4σ detected LyC flux in the WFC3/UVIS images. Using a wide variety of space-based plus ground-based data, ranging from X-ray to radio wavelengths, we fit the multiwavelength photometric data of each AGN to a CIGALE spectral energy distribution (SED) using AGN models and correlate various SED parameters to the LyC flux. Kolmogorov–Smirnov tests of the SED parameter distributions for the LyC-detected and nondetected AGN showed they are likely not distinct samples. However, we find that the X-ray luminosity, star formation onset age, and disk luminosity show strong correlations relative to their emitted LyC flux. We also find strong correlations of the LyC flux to several dust parameters, i.e., polar and toroidal dust emission and 6 μm luminosity, and anticorrelations with metallicity and A FUV. We simulate the LyC escape fraction (f esc) using the CIGALE and intergalactic medium transmission models for the LyC-detected AGN and find an average f esc ≃ 18%, weighted by uncertainties. We stack the LyC fluxes of subsamples of AGN according to the wavelength continuum region in which they are detected and find no significant distinctions in their LyC emission, although our submillimeter-detected F336W sample (3.15 < z < 3.71) shows the brightest stacked LyC flux. These findings indicate that LyC production and escape in AGN are more complicated than the simple assumption of thermal emission and a 100% escape fraction. Further testing of AGN models with larger samples than presented here is needed.

TREASUREHUNT: Transients and Variability Discovered with HST in the JWST North Ecliptic Pole Time-domain Field

“…Assumptions 2 and 3 are simplified, as some AGNs will be hidden at rest-frame UV-visible wavelengths by surrounding dust. This fraction could be as large as 2/3 of all AGNs, if we use the ∼30% average Lyman continuum escape fraction of weak AGNs (Smith et al 2018(Smith et al , 2020(Smith et al , 2024 as a proxy for the fraction of AGNs with direct unobscured sight lines to the observer. Figure 8(c) implies an average SED age of ∼10 8 yr (∼100 Myr) for the parent population, although the spread in age is wide (0.01-10 Gyr).…”

UVCANDELS: The Role of Dust on the Stellar Mass–Size Relation of Disk Galaxies at 0.5 ≤ z ≤ 3.0

“…Galaxy properties in the UV are particularly important as the rest-frame UV probes ongoing star formation. As such, UVCANDELS has already been used to explore the properties of clumpy galaxies (Martin et al 2023;Sattari et al 2023), the star formation burstiness of galaxies by comparing their UV and Hα emission (Mehta et al 2023), the environmental dependence of quenching processes (Kuschel et al 2023), Lyman continuum emission from active galactic nuclei (Smith et al 2024) and star-forming galaxies (Wang et al 2023), the UV luminosity function (Sun et al 2023), and the UV spectral slope of star-forming galaxies (Morales et al 2024). The UVCANDELS data also provide the unique opportunity to investigate the properties of galaxies in already very well studied fields with a wealth of ancillary data.…”