arXiv subjects

A. J. Hedge

Publications and source records attributed to A. J. Hedge.

4 recordsLinked to original sources

arXiv2026

Exploring biases in derived stellar parameters and the ionizing photon production efficiency

Constraining the timescale and manner in which the Epoch of Reionization (EoR) occurred is a major JWST science goal. However, any constraints on the stellar or ionizing parameters (xi ion) of galaxies in the EoR must contend with biases introduced by both the data and the models used. We explore three techniques that use spectroscopic and photometric data as well as three different spectral energy distribution (SED) fitting codes, each comprised of multiple star formation history, stellar population synthesis, dust, and photoionization prescriptions to determine their relative influence on stellar parameters and xi ion. We use z=3 EoR analog galaxies due to their reliable photometric coverage (improved physical constraints) in comparison to direct EoR sources and potential for direct Lyman Continuum escape research. For this population the median stellar mass can vary by over 0.6 dex and the SFR by more than 0.9 dex. Further, the xi ion can vary by over 1.1 dex for individual sources when comparing spectroscopic and photometric derivations, or by more than 0.5 dex when fitting SEDs with different models. As such, the choice of methodology can have significant consequences for the derived xi ion and the subsequent sources of reionization. We find that the presence of a redshift evolution for xi ion is dependent on the method adopted for its derivation, where a consistent method yields an evolutionary trend with redshift in extreme emitters while an indiscriminant selection of studies does not. The model, method and data dependence of the xi ion parameter is undeniable even for a homogeneous population.

astro-ph.GA↗

arXiv2025

The Centre of Attention: a Powerful Radio Galaxy Pinpoints a NIR-Dark Protocluster at z~3.9

We report the discovery of a $z\sim3.9$ protocluster identified from Atacama Large Millimetre/sub-millimetre Array Band 3 spectral scans of a bright radio source selected from the GaLactic and Extra-galactic All-sky Murchison Widefield Array (GLEAM) survey. Extended CO(4-3) and [CI](1-0) line emission was detected in GLEAM J005332$-$325630 confirming it to be a $z=3.879$ powerful radio galaxy with luminosity, $L_{500 MHz}=1.3\times10^{28}$ ${W Hz}^{-1}$. This source is part of a sample of candidate high redshift radio galaxies with bright radio fluxes, $S_{150MHz}>0.1$ Jy, but host galaxies with $K_s({AB})\gtrsim23$ mag. The molecular gas associated with the radio galaxy host has two kinematically separate components, likely in-falling and indicative of a recent interaction or merger with another galaxy. One 100-GHz continuum source $\sim120$ pkpc away is found to have both CO(4-3) and [CI](1-0) emission lines and a further five protocluster members are identified from CO(4-3) emission alone, all at similar redshift ($Δv<700$ km s$^{-1}$) and within a radius of $1.1^{\prime}$. Using photometry from the High Acuity Widefield K-band Imager $K_s$-band and the Dark Energy Survey $g, r, i, z$ and $Y$ bands, we find this protocluster harbours a rare, optically-dark, very massive $M_*\sim10^{12}$ ${M}_\odot$ galaxy. Comparisons with the TNG300 cosmological simulation puts this galaxy in a dark matter halo of $M_{DM}\sim3\times10^{13}$ ${M}_\odot$ which will evolve into a Coma-like DM halo ($M_{DM}\sim10^{15}$ ${M}_\odot$) by the present day.

astro-ph.GA↗

arXiv2024

A Jet-Induced Shock in a Young, Powerful Radio Galaxy at z=3.00

The bright radio source, GLEAM J091734-001243 (hereafter GLEAM J0917-0012), was previously selected as a candidate ultra-high redshift (z>5) radio galaxy due to its compact radio size and faint magnitude (K(AB)=22.7). Its redshift was not conclusively determined from follow-up millimetre and near-infrared spectroscopy. Here we present new HST WFC3 G141 grism observations which reveal several emission lines including [NeIII]3867, [NeV]3426 and an extended (~4.8 kpc), [OII]3727 line which confirm a redshift of 3.004+/-0.001. The extended component of the [OII]3727 line is co-spatial with one of two components seen at 2.276 GHz in high resolution (60x20 mas) Long Baseline Array data, reminiscent of the alignments seen in local compact radio galaxies. The BEAGLE stellar mass (~2x10^11 Msun) and radio luminosity (L_500MHz}~10^28 W Hz^-1) put GLEAM J0917-0012 within the distribution of the brightest high-redshift radio galaxies at similar redshifts. However, it is more compact than all of them. Modelling of the radio jet demonstrates that this is a young, ~50 kyr old, but powerful, 10^39 W, compact steep spectrum radio source. The weak constraint on the active galactic nucleus bolometric luminosity from the [NeV]3426 line combined with the modelled jet power tentatively implies a large black hole mass, >10^9 Msun, and a low, advection-dominated accretion rate, an Eddington ratio <0.03. The [NeV]3426/[NeIII]3867 vs [OII]3727/[NeIII]3867 line ratios are most easily explained by radiative shock models with precursor photoionisation. Hence, we infer that the line emission is directly caused by the shocks from the jet and that this radio source is one of the youngest and most powerful known at cosmic noon. We speculate that the star-formation in GLEAM J0917-0012 could be on its way to becoming quenched by the jet.

astro-ph.CO↗

arXiv2024

The GLEAMing of the first supermassive black holes: III. Radio sources with ultra-faint host galaxies

We present deep near-infrared $K_{\rm s}$-band imaging for 35 of the 53 sources from the high-redshift ($z > 2$) radio galaxy candidate sample defined in Broderick et al. (2022). These images were obtained using the High-Acuity Widefield $K$-band Imager (HAWK-I) on the Very Large Telescope. Host galaxies are detected for 27 of the sources, with $K_{\rm s} \approx 21.6$$-$$23.0$ mag (2$''$ diameter apertures; AB). The remaining eight targets are not detected to a median $3σ$ depth of $K_{\rm s} \approx 23.3$ mag ($2''$ diameter apertures). We examine the radio and near-infrared flux densities of the 35 sources, comparing them to the known $z > 3$ powerful radio galaxies with 500-MHz radio luminosities $L_{500\,{\rm MHz}} > 10^{27}$ W Hz$^{-1}$. By plotting 150-MHz flux density versus $K_{\rm s}$-band flux density, we find that, similar to the sources from the literature, these new targets have large radio to near-infrared flux density ratios, but extending the distribution to fainter flux densities. Five of the eight HAWK-I deep non-detections have a median $3σ$ lower limit of $K_{\rm s} \gtrsim 23.8$ mag ($1.5''$ diameter apertures); these five targets, along with a further source from Broderick et al. (2022) with a deep non-detection ($K_{\rm s} \gtrsim 23.7$ mag; $3σ$; $2''$ diameter aperture) in the Southern H-ATLAS Regions $K_{\rm s}$-band Survey, are considered candidates to be ultra-high-redshift ($z > 5$) radio galaxies. The extreme radio to near-infrared flux density ratios ($>10^5$) for these six sources are comparable to TN J0924$-$2201, GLEAM J0856$+$0223 and TGSS J1530$+$1049, the three known powerful radio galaxies at $z > 5$. For a selection of galaxy templates with different stellar masses, we show that $z \gtrsim 4.2$ is a plausible scenario for our ultra-high-redshift candidates if the stellar mass $M_{\rm *} \gtrsim 10^{10.5}\,{\rm M}_\odot$. [abridged]

astro-ph.GA↗