Hintze Centre for Astrophysical Surveys

Abstract:

We present the discovery of radio emission from the Be/X-ray binary A0538−66 with the Australian Square Kilometre Array Pathfinder, and results from a subsequent weekly monitoring campaign with the MeerKAT radio telescope. A0538−66, located in the Large Magellanic Cloud, hosts a neutron star with a short spin period ( ms) in a highly eccentric -d orbit . Its rare episodes of super-Eddington accretion, rapid optical and X-ray flares, and other peculiar properties make it an interesting system among high-mass X-ray binaries. Our MeerKAT data reveal that it is also one of the most radio-luminous neutron star X-ray binaries observed to date, reaching (at 1.28 GHz), with radio emission that appears to be orbitally modulated. We consider several possible mechanisms for the radio emission, and place A0538−66 in context by comparing it to similar systems.

Abstract:

Context. It is well known that star-forming galaxies (SFGs) exhibit a tight correlation between their radio and infrared emissions, commonly referred to as the infrared-radio correlation (IRRC). Recent empirical studies have reported a dependence of the IRRC on the galaxy stellar mass, in which more massive galaxies tend to show lower infrared-to-radio ratios ( q IR ) with respect to less massive galaxies. One possible, yet unexplored, explanation is a residual contamination of the radio emission from active galactic nuclei (AGNs), not captured through “radio-excess” diagnostics. Aims. To investigate this hypothesis, we aim to statistically quantify the contribution of AGN emission to the radio luminosities of SFGs located within the scatter of the IRRC. Methods. Our Very Large Baseline Array (VLBA) AGN-sCAN program has targeted 500 galaxies that follow the q IR distribution of the IRRC, i.e., with no prior evidence for radio-excess AGN emission based on low-resolution (∼arcsec) VLA radio imaging. Our VLBA 1.4 GHz observations reach a 5 σ sensitivity limit of 25 μJy/beam, corresponding to a radio-brightness temperature of T b  ∼ 10 5 K. This classification serves as a robust AGN diagnostic, regardless of the host galaxy’s star formation rate. Results. We detect four VLBA sources in the deepest regions, which are also the faintest VLBI-detected AGNs in SFGs to date. The effective AGN detection rate is 9%, when considering a control sample matched in mass and sensitivity, which is in good agreement with the extrapolation of previous radio AGN number counts. Despite the non-negligible AGN flux contamination (∼30%) in our individual VLBA detections, we find that the peak of the q IR distribution is completely unaffected by this correction. Although we cannot rule out a high incidence of radio-silent AGNs at (sub)μJy levels among the VLBA non-detections, we derive a conservative upper limit of < 0.1 dex of their cumulative impact on the q IR distribution. We conclude that residual AGN contamination from non-radio-excess AGNs is unlikely to be the primary driver of the M ★ – dependent IRRC.

Abstract:

Molecular gas is crucial to understanding star formation and galaxy evolution, but the giant molecular clouds (GMCs) of early-type galaxies (ETGs) have rarely been studied. Here, we present analyses of the spatially resolved GMCs of the lenticular galaxy NGC 1387, exploiting high spatial resolution ( or 14 pc) CO(2-1) line observations from the Atacama Large Millimeter/submillimeter Array. We identify 1285 individual GMCs and measure the fundamental properties (radius, velocity dispersion, and molecular gas mass) of each with a modified version of the CPROPStoo package. Unusually for an ETG, the GMCs of NGC 1387 follow scaling relations very similar to those of the Milky Way disc and Local Group galaxy clouds, and most are virialized. GMCs with large masses and radii and/or small galactocentric distances have their angular momenta aligned with the large-scale galactic rotation, while other GMCs do not. These results show that ETGs have more diversified GMC properties than previously thought. We discuss potential reasons for such diversity, and viewing-angle dependency is a plausible candidate.

Abstract:

Context . Many applications in transient science, gravitational wave follow-up, and galaxy population studies require all-sky galaxy catalogs with reliable distances, extents, and stellar masses. However, existing catalogs often lack completeness beyond ~100 Mpc, suffer from stellar contamination, or do not provide homogeneous stellar mass estimates and size information. Aims . Our goal is to build a high-purity, high-completeness, all-sky galaxy catalog out to 2000 Mpc, specifically designed to support time-domain and multi-messenger astrophysics. Methods . We combined major galaxy catalogs and deep imaging surveys – including the Legacy Surveys, Pan-STARRS, DELVE, and SDSS – and added spectroscopic, photometric, and redshift-independent distances. We cleaned the sample using the Gaia catalog to remove stars and visually inspected all ambiguous cases below 100 Mpc through a classification platform that gathered 27 000 expert votes. Stellar masses were estimated using optical and mid-infrared profile-fit photometry, and we improved the accuracy of photometric distances by combining multiple independent estimates. Results . The resulting catalog, REGALADE, includes nearly 80 million galaxies with distances under 2000 Mpc. It provides stellar masses for 88% of the sample and ellipse fits for 80%. REGALADE is more than 90% complete for galaxies contributing 50% of the total r -band luminosity out to 360 Mpc. In science tests, it recovers 60% more known supernova hosts, doubles the number of low-luminosity transient hosts, and identifies more reliable hosts for ultraluminous and hyper-luminous X-ray sources. Conclusions . REGALADE is one of the most complete and reliable all-sky galaxy catalog to date for the nearby Universe, built for real-world applications in transient and multi-messenger astrophysics. The full dataset, visual classifications, and code will be released to support broad community use.