arXiv subjects

Anthony Taylor

Publications and source records attributed to Anthony Taylor.

5 recordsLinked to original sources

arXiv2026

Star Formation and Nebular Attenuation from Pa$α$, Br$α$, and Br$β$ in Massive Dust-obscured Galaxies at Cosmic Noon using JWST

Near-infrared hydrogen recombination lines can provide robust star-formation rates if the effects of dust attenuation continue to diminish towards longer wavelengths. To quantify near-infrared attenuation and ultimately measure accurate star-formation rates (SFRs) at the height of cosmic star-formation, we present Pa$α$, Br$α$, and Br$β$ detections in $27$ luminous infrared galaxies at $z\sim 1-2$, including pure star-forming galaxies as well as dust-obscure Active Galactic Nuclei (AGN). Using combined spectra from the JWST MIRI (Mid-Infrared Instrument) LRS (Low Resolution Spectrometer) and the Spitzer Space Telescope IRS we quantify the star formation rates of our sample using a sub-sample of 13 galaxies detected in Pa$α$ emission ($1.87\, μ$m), 14 galaxies detected in Br$α$ ($4.05\, μ$m), and 12 galaxies detected in Br$β$ ($2.63\, μ$m). By combining multiple near-infrared recombination lines in individual galaxies we calculate nebular attenuation, finding $A_λ\sim3$ mag at $\sim2\,μ$m and $A_λ\sim1$ mag at $\sim4\,μ$m. Nebular lines trace the SFR on $\sim 10$ Myr timescales, which we compare to the total infrared luminosity ($L_{\rm IR}$) which probes the star formation over the last $\sim 100$ Myr. SFRs measured from $L_{\rm IR}$ using common conversions are systematically higher than the SFRs derived from attenuation-corrected nebular line measurements by a factor of $\sim2.5$. This could be indicative of a declining or static star formation history with a past burst or systematic effects on $\rm SFR_{\rm IR}$ such as dust heating from evolved stellar populations, and/or an active galactic nucleus.

astro-ph.GA↗

arXiv2026

Unified modelling of broad and narrow optical-UV emission lines from massive black holes: interpreting high-redshift JWST observations

JWST is uncovering a large population of active galactic nuclei (AGN) at high redshift, motivating the extension of models calibrated on local sources to a broader range of physical conditions. We present a consistent suite of broad- and narrow-line photoionisation models based on ionising spectra that vary with black-hole mass and Eddington ratio, spanning sub- to super-Eddington accretion. For the broad-line region (BLR), we investigate the detectability of low-mass accreting black holes. At z=6, broad Hα may be detectable down to $M_{BH}\approx10^{5.7} M\odot$ for a BH accreting at the Eddington limit under favourable assumptions. We derive line-to-accretion-luminosity corrections, with hydrogen and helium recombination lines providing more robust tracers than metal lines. We also explore which changes in black-hole properties and BLR conditions can contribute to the large Hα equivalent widths, elevated Balmer decrements, and weak high-ionisation lines observed in some high-redshift sources, finding that variations in BLR structure can substantially modify the emergent spectrum. For the narrow-line region (NLR), Hα and [O III] λ5007 are among the most promising tracers of low-mass accreting black holes, probing $M_{BH}\approx10^{5.5} M\odot$ at the Eddington limit. Many classical diagnostic diagrams miss low-metallicity AGN; we identify alternative UV and optical diagnostics that more robustly separate AGN from Pop. II and Pop. III stellar photoionisation over the conditions explored. Nevertheless, NLR line ratios are driven primarily by metallicity and ionisation parameter, with only a weak dependence on black-hole mass and Eddington ratio. Looking ahead, these models are intended for Bayesian interpretation of JWST spectra and connection to cosmological simulations through physically motivated priors.

astro-ph.GA↗

arXiv2026

Significant Evidence of an AGN Contribution in GHZ2 at z = 12.34

GHZ2 is among the highest-redshift galaxies discovered to date, exhibiting a spectrum rich with prominent emission lines in the rest-frame ultraviolet (UV) and optical. These features raise critical questions about the mechanism powering this nebular emission, in particular the extremely strong C IV1548 emission (rest-frame EW = 45 Angstrom). Here we aim to quantify the AGN contribution within this system using the BEAGLE-AGN tool to simultaneously fit the spectrum and photometry of GHZ2. We consider a range of models with and without AGN components, allowing us to disentangle the stellar and AGN contribution of GHZ2 for the first time. We conclude that a partial contribution by an AGN is significantly favored based on the Bayes factor comparison to models without an AGN component, measuring an AGN contribution of 54$^{+1}_{-1}$% and 26$^{+4}_{-2}$% for the C IV$λ$1548 and C III]$λ$1908 emission lines, respectively. We obtain an estimate for the black hole mass using the accretion luminosity ($L_{acc}$) from the best fit BEAGLE-AGN model, computing a value of log$_{10}$(M$_{BH}$/M$_{\odot}$) = 7.20$^{+0.04}_{-0.04}$, for an Eddington ratio of $η$ = 0.5 (with a systematic uncertainty of $\sim$1 dex). The inferred black hole mass to stellar mass ratio is 0.05$^{+0.02}_{-0.02}$, consistent with other high redshift AGN systems. If the black hole interpretation is confirmed, GHZ2 would represent the most distant black hole identified to date, making it an ideal laboratory to study AGN growth and their role in shaping high-redshift galactic evolution.

astro-ph.GA↗

arXiv2026

A Rapid Evolution in the Observed Mbh/M* Relation at z > 3 Revealed via Spectro-photometric SED-Modeling

Spectroscopic observations from JWST have uncovered a plethora of active galactic nuclei (AGN) at z > 4 with black hole (BH) mass (Mbh) to stellar mass (M*) ratios significantly above the local relation when using standard virial mass scaling relations. However, M* estimates of AGN may be inaccurate due to limitations in spectral energy distribution (SED) fitting codes, exemplified by a lack of physically-motivated AGN line emission models. Here, we fit NIRSpec/PRISM spectra of 39 galaxies at z ~ 3.5-7 selected as broad-line AGN from the CEERS and RUBIES surveys. Applying kinematic decompositions from NIRSpec/G395M spectra, we fit their continuum and narrow-component line fluxes using the BEAGLE-AGN SED fitting tool. While limitations of BEAGLE-AGN make it difficult to model little red dots (LRDs), we find that M* estimates of non-LRDs are, surprisingly, only modestly impacted by the inclusion or not of AGN narrow-line region (NLR) and continuum emission model components. We further find that non-LRD AGN at z < 3.5 are consistent with the local Mbh/M* relation while those at z > 4.5 display elevated ratios. While we cannot rule out observational biases or systematic uncertainties as partial causes, this transition over just ~500 Myr is driven entirely by changes in M* rather than an evolving Mbh distribution. These findings are consistent with models in which rapid BH growth results in elevated Mbh/M* ratios at early times, with a swift late-time assembly of host galaxies returning sources to the local relation at z < 4.

astro-ph.GA↗

arXiv2026

Thermal Structure and Chemical Enrichment of the North and South Polar Spurs: Supersolar N/O and Ne/O in the X-ray Plasma

The North Polar Spur (NPS) is a prominent diffuse X-ray feature whose origin has remained uncertain for decades. Using a uniform analysis of archival \textit{Suzaku} and \textit{XMM--Newton} data with new \textit{Chandra} observations, we constrain its thermal and chemical properties. The NPS emission is fully absorbed by the neutral interstellar medium, demonstrating that the plasma lies beyond the Galactic disk and is not a local supernova remnant or nearby superbubble. The spectra require a two-temperature model with a warm--hot component ($kT \approx 0.2$ keV) and a hotter component ($kT = 0.4$--$0.5$ keV), with emission measures of $(41.8 \pm 4.9) \times 10^{-3}$ and $(12.9 \pm 2.2) \times 10^{-3} \mathrm{cm^{-6}~pc}$, respectively. A key result is the detection of super-solar abundance ratios in the warm--hot phase, with N/O $= 3.6 \pm 0.3$ and Ne/O $= 1.9 \pm 0.1$ solar. A Suzaku observation of the outer South Polar Spur (SPS) shows similar absorption, temperatures, and enhanced abundances (N/O $= 2.9 \pm 0.4$, Ne/O $= 1.6 \pm 0.2$), though with lower emission measures. The similar super-solar abundance ratios suggest a common enrichment history. These properties are consistent with those measured along other sightlines through the X-ray--bright shells of the Galactic bubbles. Together, these results support that the NPS and SPS trace opposite limbs of the Galactic bubbles. The chemical properties suggest a strong contribution from stellar feedback in shaping the Galactic bubbles.

astro-ph.HE↗