arXiv subjects

Madeline Marshall

Publications and source records attributed to Madeline Marshall.

4 recordsLinked to original sources

arXiv2026

The Lifetimes of High-redshift Quasars Suggest Magnetic Disk Support

It has recently been suggested that a variety of data on active galactic nuclei (AGN) can be explained if AGN disks are supported against gravitational fragmentation by magnetic fields that are advected into the disk from the surrounding galaxy. Here we derive the maximum timescales over which accretion onto a black hole (BH) powering an AGN can be maintained at a given rate, both with and without magnetic disk support. We then compare these timescales to the lifetimes of episodes of sustained luminous accretion that are inferred from measurements of the photoionized proximity zones around high-redshift quasars. While some of the shortest inferred quasar lifetimes are consistent with pure gas pressure support, we find that some additional magnetic support is likely required to explain the longest inferred quasar lifetimes of > 10$^4$ yr. For these longest-lived AGN, we find that magnetic pressure in their disks can be up to a hundred times higher than the gas pressure. In addition, the lack of inferred quasar lifetimes that are definitively > 10$^6$ yr is consistent with gas pressure and advected magnetic fields being the principal sources of disk support. This adds to the body of evidence that magnetic fields play an important role in sustaining the rapid growth of supermassive BHs in the early universe.

astro-ph.GA↗

arXiv2026

Alpha Cygni Variables as Seen from the Transiting Exoplanet Survey Satellite

The Alpha Cygni (ACYG) variables are blue-white supergiants which display low-amplitude brightness variations of around 0.1 magnitude. The prototype Deneb shows quasi-periodic variations of around 12 days, interrupted by intervals of erratic variability, and occasionally large excursions in amplitude. To gain insight on the behavior of these variables, we examined 27-day light curves from the Transiting Exoplanet Survey Satellite (TESS) for 75 ACYG variables south of the ecliptic plane which are being revisited by TESS in 2025-2026. We use the web-based TESS Extractor app for screening TESS light curves. We identified ten stars with similarities to Deneb that may be good candidates for ground-based monitoring. We approximated the location of these stars on the Hertzsprung-Russell diagram, and find most lie below the Luminous Blue Variables, are cooler than the beta Cephei variables, and are hotter than the RV Tauri stars. We also compare light curves processed with several different pipelines available on the Mikulski Archive for Space Telescopes (MAST) and comment on their utility for ACYG stars.

astro-ph.SR↗

arXiv2025

The Distribution of Quenched Galaxies in the Massive z = 0.87 Galaxy Cluster El Gordo

El Gordo (ACT-CL J0102$-$4915) is a massive galaxy cluster with two major mass components at redshift $z=0.87$. Using SED fitting results from JWST/NIRCam photometry, the fraction of quenched galaxies in this cluster was measured in two bins of stellar mass: $9<\log{({M_*}/\mathrm{M}_{\odot})}<10$ and $10\leq\log{({M_*}/\mathrm{M}_{\odot})}<12$. While there is no correlation between the quenched fraction and angular separation from the cluster's overall center of mass, there is a correlation between the quenched fraction and angular separation from the center of the nearest of the two mass components for the less-massive galaxies. This suggests that environmental quenching processes are in place at $z\sim1$, and that dwarf galaxies are more affected by those processes than massive galaxies.

astro-ph.GA↗

arXiv2025

GA-NIFS: an extended [OIII] halo around the sub-Eddington quasar J1342+0928 at z=7.54

The James Webb Space Telescope (\textit{JWST}) opened a new observational window on the primordial Universe. Here we present new JWST NIRSpec integral field spectroscopy (IFS) observations of the $z=7.54$ quasar ULAS J1342+0928 obtained as part of the Galaxy Assembly with NIRSpec IFS (GA-NIFS) GTO programme. The new data-set obtained with both the prism ($R\sim100$) and the high-resolution grating ($R\sim2700$) allow for a complete description of the quasar emission from the rest-frame UV to optical bands. The low-resolution data reveal the presence of [\ion{O}{iii}] emission on $\sim$7 kpc scales, well above the typical galaxy size at this redshift, likely associated with a past outflow event. Additionally, the high-resolution observations show a more energetic ionised outflow on nuclear scales ($\lesssim 0.6$ kpc). The total ionised mass outflow rate ranges between 50 and 300 $\rm M_{\odot} \, yr^{-1}$ where the significant spread is mostly due to the lack of tight constraints on the electron density. This range overlaps in part with the star formation rate range (85--545 $\rm M_{\odot} \, yr^{-1}$), implying that the nuclear outflow could ultimately lead to an early star formation quenching. By employing an accretion disc modelling, for the first time on \textit{JWST} data, we manage to robustly estimate the black hole mass and the bolometric luminosity, $\rm \log(M_{BH}/(M_{\odot}))=9.2\pm 0.2$ and $\rm \log(L_{bol}/(erg \, s^{-1}))=46.8\pm 0.1$, respectively. We derive an Eddington ratio of $\rm \lambda_{Edd}\sim 0.4$, challenging the paradigm of widespread super-Eddington accretion in quasars at the epoch of reionisation.

astro-ph.GA↗