arXiv subjects

Loraine Sandoval Ascencio

Publications and source records attributed to Loraine Sandoval Ascencio.

5 recordsLinked to original sources

arXiv2026

SMUDGes Below the Surface: Clusters Confirm the Diversity of Low-Surface-Brightness Galaxies

We use spatially resolved Keck Cosmic Web Imager spectroscopy to study high-surface-brightness stellar components and internal kinematics in 44 low-surface-brightness galaxies from the SMUDGes survey, including 30 ultradiffuse galaxies, spanning the red sequence, green valley, and blue cloud regions of the galaxy color-magnitude diagram. Although these galaxies appear largely smooth in survey imaging, we detect at least one cluster candidate in every galaxy. We identify clusters with nebular emission lines in 24 galaxies. They are common in blue-cloud galaxies but rare in red sequence galaxies. We identify three nuclear star cluster candidates, one of which shows nebular emission lines. Among clusters without nebular emission lines, bluer galaxies tend to have brighter cluster luminosity functions, suggesting the presence of young or intermediate-age clusters in addition to old globular clusters. This age diversity may complicate the use of photometrically selected globular cluster populations as tracers of total halo mass. We measure rotation velocities for 17 galaxies using the clusters with nebular emission lines and for 12 using diffuse stellar light. Within 0.5 effective radii, the inferred dynamical mass generally exceeds the stellar mass, although the inferred dark matter contribution varies by an order of magnitude. The variety in properties for this sample of ultradiffuse galaxies and low-surface-brightness dwarfs suggests that no single formation mechanism explains the population of low-surface-brightness galaxies.

astro-ph.GA↗

arXiv2026

Systematically Measuring Ultra-Diffuse Galaxies. IX. A Gyr in the Life of Nearby Low Surface Brightness Galaxies

We augment the published optical photometry of ultra-diffuse galaxy candidates in the SMUDGes catalog with UV and IR measurements to investigate the recent ($<1$ Gyr) star formation history of 966 galaxies. We find that 1) we classify star forming, post-starforming, and quenched galaxies with a precision that is comparable to that of spectroscopic studies, 2) the star forming systems are sub-normally efficient and would not have formed their current stellar mass at their current star formation rate over a Hubble time, 3) the sample is biased against more strongly star forming systems by the central surface brightness criterion of ultra-diffuse galaxies, 4) for galaxies that are not quenched, the timescale of star formation episodes in this sample is typically $\lesssim$ 1 Gyr, 5) post-starburst galaxies in the sample tend to be of lower stellar mass and star forming galaxies of higher stellar mass, suggesting that the star forming behavior of these galaxies does depend on mass, and 6) there is a marginal indication, with caveats, that star formation episodes increase galaxy size, as measured by the half-light radius, by about 8\%. In addition to providing a statistically-sized sample with which to explore the star formation behavior of these galaxies, this study also provides a way to select galaxies with specific recent star formation histories for spectroscopic follow-up.

astro-ph.GA↗

arXiv2025

Caught in the Act of Quenching? -- A Population of Post-Starburst Ultra-Diffuse Galaxies

We report the discovery of post-starburst ultra-diffuse galaxies (UDGs), identified through spectroscopic analysis with KCWI at the Keck II Telescope. Our analysis is based on a sample of 44 candidate UDGs selected from the Systematically Measuring Ultra-Diffuse Galaxies (SMUDGes) program. Our measured spectroscopic redshifts reveal $\sim 85\%$ of the entire KCWI sample exhibit large physical sizes ($R_{e} \gtrsim 1~{\rm kpc}$) and low surface brightnesses ($24 \lesssim μ_{0,g} \lesssim 25$ mag arcsec$^{-2}$) which categorize them as UDGs. We find $20\%$ of the confirmed UDG population contain post-starburst (or K+A) features, characterized by minimal to no emission in H$β$ indicative of quenched star formation and a predominant presence of spectral A-type stars. In surveying the local environments of the post-starburst UDGs, we find that nearly half are isolated systems, which is unusual given that isolated UDGs are most commonly found to be star-forming. Two of these systems reside $2-3~R_{\rm vir}$ away from potential nearby massive hosts ($M_{\star} >10^{10}~\mathrm{M}_{\odot}$), indicating the absence of environmental influence. These post-starburst UDGs may represent systems experiencing star formation feedback such that a recent burst may lead to (at least temporary) quenching. Overall, our results highlight the potentially diverse quenching pathways of UDGs in the local Universe.

astro-ph.GA↗

arXiv2025

The Dynamics of Infall and Accretion Shocks in the Outer Disk

High-spatial-resolution observations of disks around young stars suggest planetary systems begin forming early, during the protostellar phase (< 1 Myr) when stars accrete most of their mass via infall from the surrounding cloud. During this era shocks are expected to be ubiquitous around the gaseous accretion disk due to supersonic infall that strikes the disk. We investigate the role of shocks using a theoretical and modeling framework we call the shock twist-angle Keplerian (STAK) disk, connecting the disk and infalling envelope gas via a shock using general physical principles. Briefly, at the shock, energy is dissipated while angular momentum is conserved, so that the infalling gas must change direction sharply, yielding a bend or twist in the streamlines. The model's pre-shock gas follows free-fall parabolic trajectories, while the post-shock gas is on lower-energy, elliptical orbits. We construct synthetic observations and find that the deviations from circular Keplerian orbits are detectable in Doppler-shifted molecular spectral lines using radio interferometers such as ALMA. Specifically, the STAK model leads to line emission intensity and velocity-moment maps that are asymmetric and offset with respect to the disk structure traced by the dust continuum. We examine archival ALMA data for the class 0/I protostar L1527 and find the C$^{18}$O velocity moment map has features resembling the disk plus envelope emission that naturally arise when the two are connected by a shock. Thus, spectral line observations having sub-km/s spectral resolution and angular resolution sufficient to fully resolve the disk can reveal protostars' envelope-disk shocks.

astro-ph.EP↗

arXiv2025

A Closer Look at an Unusual Ultra-Diffuse Galaxy

We present a spectroscopic study of the ``Disco Ball'' (SMDG0038365-064207), a rotationally-supported, red-sequence, ultra-diffuse galaxy (UDG) with a nuclear star cluster (NSC), multiple stellar clusters, and active star-forming regions using data obtained with KCWI on the Keck II Telescope. We calculate that the galaxy hosts $34\pm11$ ``globular" clusters. Kinematic measurements confirm rotation with a peak rotational velocity of at least 53km s$^{-1}$ and a dynamical mass within $r_{\rm e}$ of at least $10^{9.3 \pm 0.2}M_{\odot}$. Our dynamical estimates of the halo mass are consistent with that obtained using the number of globular clusters and together suggest $M_{\rm h}=10^{11.1\pm0.2}M_{\odot}$. The NSC may exhibit signatures of weak AGN activity. Our findings challenge two common assumptions: (1) clusters in some UDGs may be younger than generally assumed, and thus more luminous than standard globular clusters (GCs), affecting GC counts and the derived GC luminosity function in these UDGs, and (2) quiescent UDGs can be rotationally supported, making kinematic measurements viewing-angle dependent in such cases. The Disco Ball, while unremarkable in mass, size, projected structural properties, or color, reveals surprising complexity, highlighting the need for detailed studies of more UDGs.

astro-ph.GA↗