Galaxy formation and evolution

Abstract:

The relationship between the already formed stellar mass in a galaxy and the gas reservoir of neutral atomic hydrogen, is a key element in our understanding of how gas is turned into stars in galaxy haloes. In this paper, we measure the relation based on a stellar-mass selected sample at and the MeerKAT International GHz Tiered Extragalactic Exploration-H i Data Release 1 spectral data. Using a powerful Bayesian stacking technique, for the first time we are also able to measure the underlying bivariate distribution of H i mass and stellar mass of galaxies with M, finding that an asymmetric underlying H i distribution is strongly preferred by our complete samples. We define the concepts of the average of the logarithmic H i mass, , and the logarithmic average of the H i mass, , and find that the difference between and can be as large as 0.5 dex for the preferred asymmetric H i distribution. We observe shallow slopes in the underlying scaling relations, suggesting the presence of an upper H i mass limit beyond which a galaxy can no longer retain further H i gas. From our bivariate distribution we also infer the H i mass function at this redshift and find tentative evidence for a decrease of 2–10 times in the comoving space density of the most H i massive galaxies up to .

Abstract:

ABSTRACT Broad-band mid-infrared (MIR) imaging with high-spatial resolution is useful to study extended dust structures in the circumnuclear regions of nearby active galactic nuclei. However, broad-band imaging filters cannot distinguish dust continuum emission from emission lines, and so accounting for the emission line contamination becomes crucial in studying extended dust in these environments. This paper uses Cycle 1 MIR imaging from the James Webb Space Telescope's Mid-Infrared Instrument (JWST/MIRI) and spectroscopy from the Medium-Resolution Spectrometer (JWST/MRS) for 11 local Seyfert galaxies, as part of the Galactic Activity, Torus and Outflow Survey (GATOS). Three of the objects (NGC 3081, NGC 5728, and NGC 7172) exist in both data sets, allowing direct measurement of the line emission using the spectroscopy for these objects. We find that extended MIR emission persists on scales of 100 s of parsecs after the removal of contamination from emission lines. Further, the line contamination levels vary greatly between objects (from 5 per cent to 30 per cent in the F1000W filter), and across filters, so cannot be generalized across a sample and must be carefully treated for each object and band. We also test methods to estimate the line contamination when only MRS spectroscopy or MIRI imaging is available, using pre-JWST ancillary data. We find that these methods estimate the contamination within 10 percentage points. This paper serves as a useful guide for methods to quantify and mitigate for emission line contamination in MIRI broad-band imaging.

Abstract:

We present the PHANGS-MUSE/HST-H α nebulae catalogue, comprising 5177 spatially resolved nebulae across 19 nearby star-forming galaxies ( D < 20 Mpc), based on high-resolution H α imaging from HST, homogenised to a fixed (10 pc) physical resolution and sensitivity. Combined with MUSE integral field spectroscopy, this enables robust classification of 4882 H  II regions and the separation of planetary nebulae and supernova remnants. We derive electron densities for 2544 H  II regions using [S  II ] diagnostics and adopt direct or representative electron temperatures for consistent physical characterisation. Nebular sizes are measured using circularised radii and intensity-weighted second moments, yielding a median radius of approximately 20 pc and extending down to (sub-)parsec (deconvolved) radii. A structural complexity score is introduced via hierarchical segmentation to trace substructure, highlighting that around a third of the regions are H  II complexes containing several individual clusters and bubbles, with an increased fraction of these regions in galactic centres. A luminosity–size relation, calibrated using the resolved HST sample, is applied to 30 790 MUSE nebulae, allowing the recovery of nebular sizes down to ~1 pc and providing statistical completeness beyond the HST detection limit. Comparisons with classical Strömgren radii indicate that observed sizes are systematically larger, corresponding to typical volume filling factors with a median of ϵ ~ 0.22 (10th–90th percentile 0.06–0.78), with larger regions exhibiting progressively lower values. We associate 3349 H  II regions with stellar populations from the PHANGS-HST association catalogue, finding median ages of ~3 Myr and typical stellar masses of around 10 4 –10 5 M ⊙ , supporting the link between ionised nebular and young stellar populations. We also assess the impact of diffuse ionised gas on emission-line diagnostics and after removing confirmed supernova remnants, find no strong variation in line ratios with nebular resolution, indicating minimal systematic bias in the MUSE catalogue. This dataset establishes a detailed, spatially resolved connection between nebular structure and ionising sources, and provides a benchmark for future studies of feedback, DIG contributions, and star formation regulation in the ISM, especially in combination with matched high-resolution observations. The full catalogue is made publicly available in machine-readable format.