Emily Moravec

Radio continuum surveys provide samples of active galactic nuclei (AGN) and star forming galaxies (SFGs) to high redshifts, free of biases due to dust obscuration. However, radio detected sources require multiwavelength counterparts to understand their intrinsic properties (e.g. redshift, stellar mass) and to study the evolution of star formation and AGN activity. In this work, we present host galaxy counterparts for the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey continuum Data Release 1 in regions with the best ancillary data (totalling 7.5 sq. deg). We combine statistical cross-matching and visual inspection to identify $K_s$-band selected host galaxies, and additionally combine multiple radio components into single physical objects, where needed. This results in a combined radio catalogue of $\sim$66 000 sources, with host counterparts and redshifts identified for $\sim$95 per cent of sources in the COSMOS field, $\sim$91 per cent in XMM-LSS and $\sim$90 per cent in CDFS-DEEP. This includes a significant fraction of sources with spectroscopic redshifts within the COSMOS field ($\sim$50 per cent), with $\sim$30 and $\sim$20 per cent in the XMM-LSS and CDFS-DEEP fields, respectively. Using the cross-matched catalogue, we make an initial identification of radio-excess and SFGs based on comparisons of the radio luminosities to host star formation rates. Using this split as a proxy for radio loud AGN or SFGs, we present expectations for the redshift distributions of these sources, finding broad agreement with those from deep radio luminosity functions and simulated catalogues.

The Massive and Distant Clusters of Wide-field Infrared Survey Explorer (WISE) Survey 2 (MaDCoWS2) is a WISE-selected catalog of galaxy clusters at 0.1 < z < 2 covering an effective area of >6000 deg ² . In this paper, we derive splashback radii for this cluster ensemble from galaxy density profiles and constrain the mass threshold of the survey as a function of redshift. We use MaDCoWS2 cluster candidates at 0.4 ≤ z ≤ 1.65 divided into subsamples with different Poissonian signal-to-noise ratios (S/N _P s) and redshifts, cross correlated with galaxies from the CatWISE2020 catalog, to obtain average surface density profiles. We perform a Markov Chain Monte Carlo analysis to derive parameter estimates for theoretical models consisting of orbiting and infalling terms. A distinct splashback feature is detected in all subsamples. The measured splashback radii span from 0.8 9 − 0.02 + 0.02 h − 1 cMpc ( 0.6 1 − 0.02 + 0.02 h − 1 pMpc) at z ¯ = 0.45 to 1.2 7 − 0.05 + 0.05 h − 1 cMpc ( 0.5 3 − 0.04 + 0.04 h − 1 pMpc) at z ¯ = 1.54 . We also find that the splashback radii increase with S/N _P at fixed redshift. The resultant splashback radii constrain the redshift dependence of the mass of MaDCoWS2 clusters at fixed S/N _P . We calculate M _200m from the radii using a relation based on a cosmological simulation. MaDCoWS2 M _200m values derived from the simulation-based relation are lower than the expected values based on weak-lensing observations. More robust mass constraints will come from calibrating splashback radii derived from galaxy density profiles with weak-lensing shear profiles from facilities such as Euclid, the Vera C. Rubin Observatory, and the Nancy Grace Roman Space Telescope.

The splashback radius, the radius of the apocenter of the first orbit of infalling material, is a measurable quantity marking the boundary between a galaxy cluster and its infalling region. We report detections of splashback radii in total light stacks, i.e., image stacks centered on the cores of galaxy clusters. Our analysis uses Wide-field Infrared Survey Explorer (WISE) W1 and W2 images of 83,345 candidate clusters at 0.5 ≲ z ≲ 1.9 from the Massive and Distant Clusters of WISE Survey 2 (MaDCoWS2). The clusters are organized in stacks by redshift and signal-to-noise (S/N) ratios. We adopt a statistical approach, using 1000 bootstrap realizations to determine the median projected splashback radius and its confidence interval in a given bin. We compare our splashback radii with the measurements made by K. Thongkham et al. on a similar sample of MaDCoWS2 clusters using galaxy-cluster cross-correlation and find that they are consistent, although our method yields larger error bars. Our main systematic error is the accuracy of the background subtraction, but its impact remains small: the consistency of K. Thongkham et al. and our results suggests that neither method suffers from large systematics. The sensitivity of total light stacking to the contribution of faint galaxies can be advantageous to locate splashback radii when only the brightest galaxies are detected in individual images, such as at high redshifts. We present a potential application of this new technique to probe the evolution of the stellar mass in cluster infalling regions.

Several new galaxy-galaxy strong gravitational lenses have been detected in the early release observations (ERO) from Euclid . The all-sky survey is expected to find 170 000 new systems, which are expected to greatly enhancing studies of dark matter and dark energy, and to constrain the cosmological parameters better. As a first step, we visually inspect all galaxies in one of the ERO fields (Perseus) to identify candidate strong-lensing systems and compared them to the predictions from convolutional neural networks (CNNs). The entire ERO dataset is too large for an expert visual inspection, however. In this paper, we therefore extend the CNN analysis to the whole ERO dataset and use different CNN architectures and methods. Using five CNN architectures, we identified 8469 strong gravitational lens candidates from I _E -band cutouts of 13 Euclid ERO fields and narrowed them down to 97 through visual inspection. The sample includes 14 grade A and 31 grade B candidates. We present the spectroscopic confirmation of a strong gravitational lensing candidate, EUCL J081705.61+702348.8. The foreground lensing galaxy, an early-type system at z = 0.335, and the background source, a star-forming galaxy at z = 1.475 with [O II ] emission, are both identified. The lens modelling with the Euclid strong lens modelling pipeline revealed two distinct arcs in a lensing configuration, with an Einstein radius of 1.″18 ± 0.″03. This confirms the lensing nature of the system. These findings demonstrate that CNN-based candidate selection followed by visual inspection provides an effective approach for identifying strong lenses in Euclid data. They also highlight areas for improvement in future large-scale implementations.

It has previously been found that the galaxy cluster environment can affect the fueling and evolution of active galactic nuclei (AGN). This work examines the effect of the merging cluster environment on the properties of radio AGN by comparing the radio morphology of cluster members in a sample of four merging and eight relaxed galaxy clusters at low redshift (z < 0.2). Using 144 MHz data from the LOFAR Two-meter Sky Survey and Zooniverse, we classify the radio morphology of the radio-detected cluster members using the following morphology classes: compact, compact extended, extended, jetted, and disturbed. We find that the merging cluster environment has a statistically significant, higher population proportion of disturbed (bent and head tail) sources, indicating that the merging environment can affect the morphology of cluster radio AGN. We also investigate the number of AGN that are detected in the radio data only and the number that are detected in both the radio and optical data in mergers and nonmergers. We find that the merging cluster environment has a higher population proportion of AGN that are identified only as radio AGN compared to AGN that are identified as both radio and optical AGN. Overall, we find that the merging environment affects certain radio AGN (disturbed and only radio-identified AGN), but not all.