arXiv subjects

Wout M. Goesaert

Publications and source records attributed to Wout M. Goesaert.

4 recordsLinked to original sources

arXiv2026

Jeans Dynamical Constraints on the IMF in Massive Quiescent Galaxies at $z\sim0.7$ from JWST/NIRSpec

We present dynamical masses for nine massive quiescent galaxies at $z\sim0.7$ from the JWST-IMFERNO program, measured from ultra-deep ($\sim32$hr), spatially resolved NIRSpec/MSA spectroscopy combined with NIRCam imaging. The most massive of these galaxies have previously been found to have a bottom-heavy initial mass function (IMF), based on measurements of dwarf-sensitive absorption features. Here, we examine whether the stellar masses inferred for these IMFs are consistent with the dynamical masses of these galaxies. We derive the dynamical masses by including Jeans Anisotropic Modelling within a forward-modelling framework that accounts for instrumental optics, source morphology, and geometric effects. We compare the resulting dynamical masses to the stellar masses for different IMF assumptions. A Milky Way IMF produces physically plausible dynamical-to-stellar mass ratios but implies central dark matter fractions ($f_{\rm DM,1R_e}=0.54\pm0.06$) that are a factor $\sim2$ higher compared to local ETGs and simulations. When uniformly applying the IMF that was measured from absorption features, the mean dark matter fraction becomes low ($f_{\rm DM,1R_e}=0.02\pm0.18$), and the stellar masses exceed the dynamical mass at $2σ$ significance for two out of seven galaxies in the sample. When we adopt the measured IMF only in the central $R_e$ and use a MW IMF in the outskirts, we find realistic dark matter fractions ($f_{\rm DM,1R_e}=0.28\pm0.12$) and consistent dynamical masses. These results support a scenario where the cores of the most massive quiescent galaxies at $z\sim0.7$ had a bottom-heavy IMF, similar to those observed in the centres of local early-type galaxies. Our results are consistent with an inside-out growth scenario, in which size and mass growth of massive galaxies proceeds after quenching through minor mergers, leaving the bottom-heavy cores mostly intact.

astro-ph.GA↗

arXiv2026

Hidden mass in early galaxies revealed by bottom-heavy initial mass functions

James Webb Space Telescope (JWST) observations have revealed that massive galaxies formed and evolved faster than predicted by galaxy formation models, with many having already assembled a large mass in stars approximately 12 billion years ago. However, masses of distant galaxies are uncertain, as they assume a distribution of stellar birth masses (the initial mass function (IMF)) similar to that in the Milky Way. Specifically, the contribution from low-mass stars, which make up the bulk of stellar mass, is not directly observed, but inferred based on an extrapolation of the Milky Way IMF. Here, we provide robust constraints on the low-mass IMF beyond the local Universe from full-spectrum models. Using ultra-deep spectra of nine massive quiescent galaxies at redshift $z$ $\approx0.7$ from the JWST Initial Mass Function of Early Red NIRSpec Objects program, extended to bluer wavelengths with deep Very Large Telescope Large Early Galaxy Astrophysics Census spectra, we find that the most massive galaxies have excess low-mass stars. Remarkably, our oldest galaxy (formation redshift $z_{\rm form} > 5$) has the most bottom-heavy IMF. This galaxy may be a descendant of JWST's 'impossibly early' galaxies, implying that the latter may have had similarly bottom-heavy IMFs increasing their masses by a factor of approximately $4\pm1$. Our findings may thus amplify the tension with galaxy formation models.

astro-ph.GA↗

arXiv2025

Torus feeding and outflow launching in the active nucleus of the Circinus galaxy

Context: Most active galactic nuclei (AGN) are believed to be surrounded by a dusty molecular torus on the parsec scale which is often embedded within a larger circumnuclear disk (CND). AGN are fuelled by the inward transport of material through these structures and can launch multi-phase outflows that influence the host galaxy through AGN feedback. Aims: We use the Circinus Galaxy as a nearby laboratory to investigate the physical mechanisms responsible for feeding the torus and launching a multi-phase outflow in this Seyfert-type AGN, as these mechanisms remain poorly understood. Methods: We analysed observations from the Atacama Large Millimeter/submillimeter Array of the Circinus nucleus at angular resolutions down to 13 mas (0.25 pc). We traced dust and the ionised outflow using 86-665 GHz continuum emission, and studied the morphology and kinematics of the molecular gas. Results: We find that the Circinus CND hosts molecular and dusty spiral arms, two of which connect directly to the torus. We detect inward mass transport along these structures and argue that the non-axisymmetric potential generated by these arms is the mechanism responsible for fuelling the torus. We estimate a feeding rate of 0.3-7.5 M$_{\odot}$yr$^{-1}$, implying that over 88% of the inflowing material is expelled in a multi-phase outflow before reaching the accretion disk. The inferred torus feeding time scale (120 kyr - 2.7 Myr) suggests that variability in AGN activity may be driven by changes in torus feeding. On parsec scales, the ionised outflow is traced by optically thin free-free emission. The outflow is stratified, with a slightly wider opening angle in the molecular phase than in the dusty and ionised components. The ionised outflow is launched or collimated by a warped accretion disk at a radius of r ~ 0.16 pc, and its geometry requires an anisotropic launching mechanism.

astro-ph.GA↗

arXiv2023

Easy method to establish the dispersion relation of capillary waves on water jets

A simple, intuitive, and low-cost setup for generating and measuring capillary waves is presented enabling a precise determination of the dispersion relation for a cylindrical water jet. By setting the phase velocity and measuring the wavelength of capillary waves directly, this method provides an intuitive way for students to understand the dispersion relation of a cylindrical water jet. The setup produced measurements of wavelength versus phase velocity over a broader range of values than earlier work. The resulting data are generally consistent with earlier results but show an error of up to 15\% at both the higher and the lower end of the measured range of wavelengths compared to the theoretical dispersion relation of cylindrical water jets. For the shorter wavelengths, the deviation is in the opposite direction from that of earlier work.

physics.flu-dyn↗