arXiv subjects

Carys J. E. Gilbert

Publications and source records attributed to Carys J. E. Gilbert.

3 recordsLinked to original sources

arXiv2026

A New Hope for AGN SED Fitting: X-Ray Spectral Analysis of 12MGS AGN with the C2PO-Torus Model

In this paper, we present the results of comprehensive, broadband X-ray spectral analysis of a subsample of 43 mid-Infrared (IR) selected star-forming active galactic nuclei (AGN). We analysed archival NuSTAR, Chandra, and XMM-Newton data, and present the first pointed X-ray observation of IRASF03450+0055. We introduce a new physically-based X-ray spectral model, C2PO-Torus, based on a two-phase clumpy torus geometry. It is designed to provide constraints on physical parameters of the torus that can be directly linked to the parameters of the AGN model SKIRTOR. This model will allow us to exploit the synergies between the X-ray and IR regimes, place stronger constraints on the torus properties, and improve spectral energy distribution (SED) fitting by providing priors for the SKIRTOR parameters. We compare the results from the C2PO-Torus fitting to those obtained from traditional models, finding that it is an extremely effective tool for fitting a wide variety of X-ray spectra. We observe that our sample closely follows the established L_[OIII] - L_X AGN relation, while presenting an IR and Radio excess with respect to the L_X - L_12micron and L_X - L_1.4GHz AGN relations at low luminosities. We believe that this excess is due to contamination from star formation related emission. We anticipate that the C2PO-Torus model will aid substantially in completing full-spectrum SED fitting of this sample, allowing us to properly disentangle the different emission components of these objects, which are local analogues of AGN at Cosmic Noon.

astro-ph.GA↗

arXiv2026

Beyond the Dot: an LRD-like nucleus at the Heart of an IR-Bright Galaxy and its implications for high-redshift LRDs

Little Red Dots (LRDs) are compact, red sources discovered by JWST at high redshift ($z \gtrsim 4$), marked by distinctive 'V-shaped' spectral energy distributions (SEDs) and often interpreted as rapidly accreting Active Galactic Nuclei (AGNs). Their true nature remains unclear, however, and their evolutionary connection to their lower-redshift counterparts is still poorly constrained. Thus, we present WISEA J123635.56+621424.2, here dubbed {\it the Saguaro}, a $z=2.0145$ galaxy in GOODS-North, as a possible analog of high-redshift LRDs and a potential missing link in their evolutionary path toward lower-redshift systems. It features a compact LRD-like nucleus surrounded by a face-on spiral host. Its connection to LRDs includes that: (1) its nuclear spectrum shows a clear `V-shaped'' SED; and (2) when redshifted to $z=7$, surface-brightness dimming makes the host undetectable, thus mimicking an LRD. This suggests that high-redshift LRDs may be embedded in extended hosts. To test this, we stack rest-frame UV images of 99 photometrically selected LRDs, revealing faint, diffuse emission. Stacking in redshift bins reveals mild radial growth, consistent with the expected galaxy size evolution. A simple analytic model confirms that surface-brightness dimming alone can explain their compact appearance. Lastly, we show that {\it the Saguaro} is not unique by describing similar objects from the literature at $z\lesssim3.5$. Taken together, our results support a scenario in which LRDs may not be a distinct population, but could instead be the visible nuclei of galaxies undergoing a short-lived, perhaps AGN-dominated, evolutionary phase, with their compact, red appearance driven largely by observational biases.

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arXiv2026

Filling the Gap in Cluster Evolution: JWST's Glimpse into a Young, Star-Forming Cluster at Cosmic Noon

We present a detailed study of HUDFJ0332.4-2746.6 (HUDF46), a $z \approx 1.84$ overdensity in the Hubble Ultra Deep Field, previously identified with HST as a proto-cluster. JWST/NIRISS spectroscopy expands its confirmed membership from 18 to 37 galaxies, while deep HST/ACS, JWST/NIRCam, and JWST/MIRI imaging provide a comprehensive multiwavelength view from the rest-frame UV to the mid-infrared. This dataset probes the population across three dex in stellar mass ($M_\bigstar \approx 10^{7.5\text{--}10.5}\,M_\odot$), delivering the first direct view of a young cluster down to such low-$M_\bigstar$ at $z\gtrsim1$. Assuming virialization, we derive a velocity dispersion of $σ\approx 670\pm 91\,\mathrm{km\,s^{-1}}$ and a halo mass of $M_{200} \approx (1.2\pm0.2) \times 10^{14}\,M_\odot$, in agreement with X-ray constraints from deep {\it Chandra} data. Despite residing in a massive halo likely in the hot-halo regime, the population is overwhelmingly star-forming, with no established red sequence and no extended X-ray emission from a hot intracluster medium. HUDF46 members have stellar and structural properties nearly indistinguishable from coeval field galaxies, and the structure hosts only one AGN candidate, found in its brightest galaxy, which lies at the cluster center. Overall, HUDF46 appears to be in a transitional phase prior to the onset of environmental quenching, making its galaxy population a key benchmark for tracing the processes that will later build a passive population and shape the assembly of massive clusters at later cosmic times.

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