PEARLS: Low Stellar Density Galaxies in the El Gordo Cluster Observed with JWST

Abstract

A full understanding of how unusually large "Ultra Diffuse Galaxies" (UDGs) fit into our conventional theory of dwarf galaxy formation remains elusive, despite the large number of objects identified locally. A natural extension of UDG research is the study of similar galaxies at higher redshift to establish how their properties may evolve over time. However, this has been a challenging task given how severely cosmological surface brightness dimming inhibits our ability to detect low-surface brightness galaxies at high-z. Here, we present a sample of low stellar surface density galaxies (LDGs) at moderate redshift, likely the progenitors of local UDGs, identified in deep near-IR JWST observations of the El Gordo cluster at z = 0.87. By stacking 8 NIRCAM filters, reach an apparent surface brightness sensitivity of 24.59 mag arcsec −2 , faint enough to be complete to the bright end of the LDG population. Our analysis identifies significant differences between this population and UDGs observed locally, including differences in their color and size distributions, which suggest that the UDG progenitors at high-z are bluer and more extended than UDGs at z = 0. This suggests that multiple mechanisms are responsible for UDG formation and that prolonged transformation of cluster dwarfs is not a primary UDG formation mechanism at high-z. Furthermore, we find a slight overabundance of LDGs in El Gordo, and, in contrast to findings in local clusters, our analysis does not show a deficit of LDGs in the center of El Gordo, implying that tidal destruction of LDGs is significant between z = 0.87 and z = 0.

Near-infrared characterization of ultra-diffuse galaxies in Abell 2744 by JWST/NIRISS imaging

“…The effective radius of the F200W imaging (Table 1) was used for the calculation of surface stellar mass densities. We find that the range of surface stellar mass density of the UDGs are in good agreement with the definition presented in Carleton et al (2023). In Carleton et al (2023), the possible progenitors of local cluster UDGs, referred to as low surface density galaxies, are defined by the effective radius and the surface stellar mass density.…”

“…We find that the range of surface stellar mass density of the UDGs are in good agreement with the definition presented in Carleton et al (2023). In Carleton et al (2023), the possible progenitors of local cluster UDGs, referred to as low surface density galaxies, are defined by the effective radius and the surface stellar mass density. The agreement implies that our UDG selection using the F200W filter is largely consistent with the physically motivated definition using the surface stellar mass density.…”

“…In addition to its sensitivity to faint light enabled by the large mirror, NIR imaging serves as an effective tracer of stellar mass distribution, given the stellar mass-to-light ratio is expected to be close to unity at these wavelengths (e.g., Bell & de Jong 2001). Carleton et al (2023) report a sample of possible progenitors of local cluster UDGs in the El Gordo cluster at 𝑧 = 0.87, identified from the stacked image of eight JWST/NIRCam filters.…”

Variation in optical and infrared properties of galaxies in relation to their surface brightness

“…( 1): where R e is the r-band half-light radius and M star is the stellar mass. Equation ( 1) is a widely used method in the literature to estimate Σ star for both LSBs and HSBs (e.g., Kauffmann et al 2003;Zhong et al 2010;Cortese et al 2012b;Grootes et al 2013;Boselli et al 2022;Carleton et al 2023). Although several other methods also exist to obtain Σ star , many of them provide similar values without changing the global properties of our sample.…”