PEARLS: Discovery of Point-Source Features Within Galaxies in the North Ecliptic Pole Time Domain Field
arxiv(2024)
Abstract
The first public 0.9-4.4 μm NIRCam images of the North Ecliptic Pole
(NEP) Time Domain Field (TDF) uncovered many galaxies that display point-source
features in their cores as seen in the longer wavelength filters. We visually
identified a sample of 66 galaxies (∼1 galaxy per arcmin^2) with
point-like cores and fit their spectral energy distributions (SED)s using EAZY
and CIGALE to characterize the sample's active galactic nucleus (AGN) and host
galaxy parameters. Single-template fitting best fits 70% of the sample with
a Seyfert-blended SED. With CIGALE we compute the median fractional AGN
contribution to the 0.1-30.0 μm flux to be 0.30±0.06, and that 56%
of the 66 galaxies have star-formation rates in the starburst range whereas the
remainder are near the star-formation main sequence. There are Very Large Array
(VLA) 3 GHz detections for 24/66 galaxies, implying some combination of AGN
emission and vigorous star formation. We present a novel sample selection
procedure in tandem to the morphological sample selection based on objects'
light profiles at 4.4 μm. This procedure identifies a parameter space which
probes point-source features and automatically recovers our visual sample with
minimal contamination from both stars and brighter galaxies. This procedure may
be used in other extant and future NIRCam images to streamline the search for
galaxies with point-like cores. The morphological approach to recognizing AGN
is being resurrected by the James Webb Space Telescope (JWST) by virtue of its
superb angular resolution at infrared wavelengths.
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