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Abstract:

Stellar bars are elongated structures in disk galaxies that can torque and funnel gas inward, influencing galaxy evolution. While strong bars are known to induce rapid inflow, the impact of weaker bars remains less certain. We collected spectroscopic data using the Isaac Newton Telescope to analyze 18 nearby galaxies (strongly barred, weakly barred, and unbarred) drawn from Galaxy Zoo DESI. We obtained spatial profiles of equivalent width (EW) and ionized gas velocity dispersion by fitting Gaussian profiles to the Hα emission line. Strongly barred galaxies exhibit a distinctive three-peaked EW[Hα] structure, consistent with inward funneling of gas. Weakly barred systems lack this pattern, which suggests limited inflow. Velocity dispersion distributions further distinguish the bar types, with strongly barred galaxies showing significantly higher values than weakly barred and unbarred systems. These results suggest that strong bars drive gas inflow, while weak bars exert a limited dynamical influence.

Abstract:

We measure the seeing-deconvolved gas-phase metallicity gradients of 70 star-forming galaxies at from the MAGPI survey and investigate their relationship with galaxy properties to understand the mechanisms that influence the distribution of metals and shape the evolution of the galaxies. We use a Bayesian modelling technique, blobby3d, which accounts for seeing effects (beam smearing) and can model the substructures of the flux distribution. The median metallicity gradient of our sample is dex kpc−1. Among the galaxies in our sample, 32.9 per cent have negative metallicity gradients (2 significance), 10.0 per cent have positive gradients and 57.1 per cent have flat gradients. The – relation of the MAGPI galaxies generally agrees with theoretical predictions, where a combination of stellar feedback, gas transport, and accretion shapes the metallicity profile, with the dominant processes varying with galaxy mass. We find a positive correlation between and gas velocity dispersion (), indicating that stronger gas turbulence is associated with flatter or inverted metallicity gradients, likely due to enhanced gas mixing. Additionally, smaller galaxies tend to have flatter or positive gradients, suggesting that metal dilution by gas accretion or removal via feedback-driven winds may outweigh metal enrichment in small galaxies.

Abstract:

Kilonovae are the scientifically rich—but observationally elusive—optical transient phenomena associated with compact binary mergers. Only a handful of events have been discovered to date, all through multiwavelength (gamma-ray) and multimessenger (gravitational-wave) signals. Given their scarcity, it is important to maximise the discovery possibility of new kilonova events. To this end, we present our follow-up observations of the gravitational-wave signal S250818k—a plausible binary neutron star merger at a distance of 237 ± 62 Mpc. Pan-STARRS tiled 286 and 318 deg2 (32% and 34% of the 90% sky localisation region) within 3 and 7 days of the GW signal, respectively. ATLAS covered 65% of the sky map within 3 days, but with lower sensitivity. These observations uncovered 47 new transients; however, none were deemed to be linked to S250818k. We undertook an expansive follow-up campaign of AT2025ulz, the purported counterpart to S250818k. The griz-band light curve, combined with our redshift measurement (z = 0.0849 ± 0.0003), all indicate that SN2025ulz is a type IIb supernova and thus not the counterpart to S250818k. We rule out the presence of an AT2017gfo-like kilonova within ≈27% of the distance posterior sampled by our Pan-STARRS pointings (≈9.1% across the total 90% 3D sky localisation). We demonstrate that early observations are optimal for probing the distance posterior of the 3D gravitational-wave sky map, and that SN2025ulz was a plausible kilonova candidate for ≲5 days, before ultimately being ruled out.