Jesse van de Sande

Our Galaxy is by far the best studied in the Universe, and it has long been regarded as a benchmark for understanding galaxy evolution. However, the Milky Way is only one galaxy, and it is crucial to link Galactic and extra-galactic research to understand the formation and evolution of disk galaxies. Currently, it is difficult to compare galactic and extra-galactic observations directly: Galactic studies focus on individual stars, while extra-galactic are derived from integrated light. We present a novel approach to generate an integral field spectrograph (IFS) data cube of the Milky Way using theoretical models and catalogues of Galactic populations. This enables a direct comparison of the Galaxy with external systems to identify key signatures of formation processes, such as the detailed chemodynamic structure of disks, the velocity dispersion profile, the radial and vertical age gradients, and the mass fraction of the [ α /Fe]-rich versus [ α /Fe]-poor populations.

We present evidence that the Hector Galaxy Survey galaxy C901005481609968 ( z _cl = 0.0553), which exhibits spatially extended LINER-like emission in optical integral-field spectroscopy (IFS), hosts a low-luminosity active galactic nucleus (LLAGN) that contributes substantially to its ionization budget. Although the galaxy is not selected as an AGN by mid-infrared AGN color criteria, archival Chandra data reveal a compact nuclear X-ray source with log L X ≈ 41.46 erg s ⁻¹ , supporting the presence of an LLAGN. Spatially resolved emission-line diagnostics show LINER-like line ratios across most spaxels with S/N ≥ 3, while spatially resolved τ maps ( τ ≡ Q _pAGB / Q _req ) indicate a widespread photon deficit ( log τ < 0 over most of the mapped region), even under the most optimistic pAGB normalizations, the nuclear region remains at τ < 1. Line-ratio–kinematic tests find no evidence for shock-dominated excitation as the primary driver of the extended emission, although a localized or subdominant shock contribution cannot be ruled out with the present data. We use this galaxy as a pilot case because the combination of Hector IFS and an independent nuclear X-ray constraint provides a stringent validation of the spatially resolved photon-budget framework. Our results indicate that evolved stellar populations alone cannot account for the observed emission, that an additional nuclear ionizing source is required at least in the inner region, and that a weak LLAGN likely contributes to the ionizing budget, particularly in the inner region. Our results demonstrate that extended LINER-like emission can conceal a substantial LLAGN contribution even when traditional optical and infrared AGN indicators are weak and that spatially resolved photon-budget tests combined with X-ray constraints can effectively reveal such hidden activity.

We present high-resolution (0 . ″ 94 ≈ 55 pc) Atacama Large Millimeter/submillimeter Array (ALMA) CO(2–1) and ¹³ CO(2–1) observations of the highly inclined ( i ∼ 87 . ° 5 ) galaxy NGC 4565 covering out to galactocentric radius R _gal ≳ ± 17 kpc. The combination of sensitivity and resolution enables the detection of CO emission well into the H i -dominated outer disk while isolating individual molecular clouds across the full extent of the galaxy. Although often described as an edge-on Milky Way analog, the molecular gas profile of NGC 4565 has a central gap that is more similar to M31. The ¹³ CO/ ¹² CO ratio remains consistent at 0.086 ± 0.009 from R _gal = 5–13 kpc. Based on fits to position–velocity slices, the molecular disk remains thin, with an FWHM scale height of 79.1 ± 1.6 pc measured from the vertical intensity profile with little evidence for vertical flaring. Molecular clouds in NGC 4565 show sizes, linewidths, and surface densities consistent with those found in similar environments in PHANGS-ALMA galaxies and in M31. We identify a prominent star-forming complex on the ring—an overdensity of molecular gas we term the “East Ring Pileup.” This feature hosts a compact, multiwavelength-bright region, which we call “the Jewel.” Effects of galaxy inclination on molecular cloud radius, velocity dispersion, surface density, and virial parameter appear as second-order effects that are strongest in velocity dispersion. At this resolution, GMCs are preferentially aligned with the disk of the galaxy and horizontally elongated by a factor of ∼2.

Spatially resolved stellar populations of massive quiescent galaxies at cosmic noon provide powerful insights into star-formation quenching and stellar mass assembly mechanisms. Previous photometric studies have revealed that the cores of these galaxies are redder than their outskirts. However, spectroscopy is needed to break the age-metallicity degeneracy and uncover the driver of these colour gradients. In this work, we derive the age and elemental abundance gradients for eight distant (1.2 ≲ z ≲ 2.2), massive (10.3 ≲ log( M _* /M _⊙ )≲11.1) quiescent galaxies by fitting full-spectrum models to ultra-deep NIRSpec-MSA spectroscopy from the JWST -SUSPENSE survey. We find that these galaxies have negative age and flat [Fe/H] gradients as well as tentative indications of positive [Mg/H] and [Mg/Fe] gradients. These results suggest that galaxy cores are older and perhaps also Mg deficient compared to galaxy outskirts. The age gradients may indicate inside-out quenching, while Mg-deficient cores could suggest rapid gas expulsion as the central quenching mechanism. Thus, galaxy cores may have formed faster and quenched more efficiently than their outskirts. In this scenario, however, our [Fe/H] and [Mg/Fe] gradients are still puzzling, and further investigation is required to understand the nature of [Mg/H] gradients in massive quiescent galaxies at these redshifts. Our results contrast with those of lower-redshift studies, which find flat age and [Mg/Fe] gradients and negative metallicity gradients. Additionally, we find a positive trend between age gradients and rotational support and marginal trends between [Fe/H] gradients and galaxy velocity dispersions and ages. We discuss our findings in the context of galaxy growth scenarios, including minor mergers and progenitor bias. With this work, we present the first stellar population gradients from NIRSpec-MSA spectroscopy in the current largest sample of distant quiescent galaxies.

We present early science results from the Multiphase Astrophysics to Unveil the Virgo Environment (MAUVE) program, which targets 40 Virgo Cluster galaxies to investigate the effect of environment on the interstellar medium (ISM) at ∼100 pc scales. From 12 galaxies in the MAUVE–Multi Unit Spectroscopic Explorer (MUSE) early sample, we find systematically elevated line ratios compared to Physics at High Angular resolution in Nearby GalaxieS (PHANGS)–MUSE field disks, with higher medians of [N ii ]/H α (0.75 versus 0.50), [S ii ]/H α (0.57 versus 0.49), and [O iii ]/H β (1.04 versus 0.68). Spatially resolved Baldwin–Phillips–Terlevich diagrams show 74% of MAUVE spaxels ionized by sources other than H ii regions versus 61% in the field, and we find these ionization differences to be closely coupled to broadened kinematics. In all, 44% of MAUVE spaxels exceed H α σ _LOS = 40 km s ⁻¹ (versus 26% in the field), driven mainly by non-star-forming gas with σ _LOS between 40 and 80 km s ⁻¹ , consistent with enhanced contribution of diffuse ionized gas (DIG). A subdominant tail of 5% of spaxels at σ _LOS > 100 km s ⁻¹ , largely absent in PHANGS–MUSE (1%), points to shocks or turbulent mixing layers from intracluster interactions. Our results show that environmental quenching primarily suppresses star formation, unveiling DIG as the dominant ionized component in cluster disks. The elevated line ratios and broadened kinematics observed in the MAUVE sample reflect the physical state of the ISM in the absence of vigorous star formation, rather than widespread direct environmental excitation. The observed shock-like emission provides an additional, secondary contribution likely driven by active interactions with the intracluster medium.

We examine to what extent the galaxy spin parameter proxy (λ_R) is affected by bar formation and how it is related to the strong and weak classifications of stellar bars. By creating mock observations of a simulated galaxy, we show that the emergence of a stellar bar can cause mass-weighted λ_R to decrease by up to 16 %, depending on the bar’s orientation. This decrease can be exaggerated if there is a burst of star formation due to the bar driving gas to the center of the galaxy. We use the SAMI galaxy survey to show that weakly barred galaxies have statistically significant younger average stellar populations, higher galaxy spin proxy and higher specific star formation rates compared to strongly barred galaxies within one effective radius. If we consider galaxies with average light-weighted stellar population age less than 3 Gyr within one effective radius, we still find weakly barred galaxies to have a higher galaxy spin proxy than strongly barred galaxies. Based on these trends found from the SAMI galaxy survey, we suggest weakly barred galaxies are rapidly forming, similar to the bar formation process seen in simulations, while strongly barred galaxies are undergoing slower (secular) evolution.