Detection of Intracluster Globular Clusters in the First JWST Images of the Gravitational Lens Cluster SMACS J0723.3-7327 at z = 0.39

We present a survey of globular clusters (GCs) in the massive gravitational lens cluster SMACS J0723.3-7327 at $z=0.39$ based on the early released JWST/NIRCam images. In the color-magnitude diagrams of the point sources we find clearly a rich population of intracluster GCs that spread in a wide area of the cluster. Their ages, considering the cluster redshift, are younger than 9.5 Gyr. The F200W (AB) magnitudes of these GCs, $26.5<{F200W_0} <29.5$ mag, correspond to $-15.2<{M_{F200W}} <-12.2$ mag, showing that they belong to the brightest GCs (including ultracompact dwarfs). The spatial distributions of these GCs show a megaparsec-scale structure elongated along the major axis of the brightest cluster galaxy. In addition, they show a large number of substructures, some of which are consistent with the substructures seen in the map of diffuse intracluster light. The GC number density map is, in general, consistent with the dark matter mass density map based on the strong lensing analysis in the literature. The radial number density profile of the GCs in the outer region is steeper than the dark matter mass profile obtained from lensing models. These results are consistent with those for the GCs found in the deep HST images of Abell 2744, another massive cluster at $z=0.308$, and in simulated galaxy clusters. This shows that the intracluster GCs are an excellent independent tool to probe the dark matter distribution in galaxy clusters as well as to reveal the cluster assembly history in the JWST era.Comment: 25 pages, 12 figures, Accepted for publication in ApJ

Learning experiences and college access of American workers: Evidence from PIAAC

Using the U.S. data from the Program for the International Assessment of Adult Competencies (PIAAC), this study aims to explore how work-related learning experiences of working adults influence their sub-baccalaureate or baccalaureate degree-seeking in higher education institutions (HEIs). Given many jobs in the U.S. that require higher education credentials, we examined how formal and informal work-related learning experiences are associated with the college access of working adults who have a high school diploma. The multinomial logistic regression results show that work flexibility, distance learning, and private learning experience are positively related to working adults’ college access. Based on the findings, implications for policy and practice were discussed on how industry and organizations could support working adults’ learning opportunities in the workplace and HEIs

The Carnegie-Chicago Hubble Program: Discovery of the Most Distant Ultra-faint Dwarf Galaxy in the Local Universe

Ultra-faint dwarf galaxies (UFDs) are the faintest known galaxies and due to their incredibly low surface brightness, it is difficult to find them beyond the Local Group. We report a serendipitous discovery of an UFD, Fornax UFD1, in the outskirts of NGC 1316, a giant galaxy in the Fornax cluster. The new galaxy is located at a projected radius of 55 kpc in the south-east of NGC 1316. This UFD is found as a small group of resolved stars in the Hubble Space Telescope images of a halo field of NGC 1316, obtained as part of the Carnegie-Chicago Hubble Program. Resolved stars in this galaxy are consistent with being mostly metal-poor red giant branch (RGB) stars. Applying the tip of the RGB method to the mean magnitude of the two brightest RGB stars, we estimate the distance to this galaxy, 19.0 +- 1.3 Mpc. Fornax UFD1 is probably a member of the Fornax cluster. The color-magnitude diagram of these stars is matched by a 12 Gyr isochrone with low metallicity ([Fe/H] ~ -2.4). Total magnitude and effective radius of Fornax UFD1 are Mv ~ -7.6 +- 0.2 mag and r_eff = 146 +- 9 pc, which are similar to those of Virgo UFD1 that was discovered recently in the intracluster field of Virgo by Jang & Lee (2014).Fornax UFD1 is the most distant known UFD that is confirmed by resolved stars. This indicates that UFDs are ubiquitous and that more UFDs remain to be discovered in the Fornax cluster.Comment: 6 pages, 4 figures, 1 table, accepted for publication in ApJ Letter