Haylee N. Archer

We present the Local Group L-Band Survey, a Karl G. Jansky Very Large Array (VLA) survey producing the highest-quality 21 cm and 1–2 GHz radio continuum images to date, for the six VLA-accessible, star-forming, Local Group galaxies. Leveraging the VLA’s spectral multiplexing power, we simultaneously survey the 21 cm line at high 0.4 km s⁻¹ velocity resolution, the 1–2 GHz polarized continuum, and four OH lines. For the massive spiral M31, the dwarf spiral M33, and the dwarf irregular galaxies NGC 6822, IC 10, IC 1613, and the Wolf–Lundmark–Melotte Galaxy, we use all four VLA configurations and the Green Bank Telescope to reach angular resolutions of 20 cm⁻² column density sensitivity, and even sharper views (D ≲ 1 Mpc) reveals a sharp, resolved view of the atomic gas, including 21 cm absorption, and continuum emission from supernova remnants and H ii regions. These data sets can be used to test theories of the abundance and formation of cold clouds, the driving and dissipation of interstellar turbulence, and the impact of feedback from massive stars and supernovae. Here, we describe the survey design and execution, scientific motivation, data processing, and quality assurance. We provide a first look at and publicly release the wide-field 21 cm H i data products for M31, M33, and four dwarf irregular targets in the survey, which represent some of the highest-physical-resolution 21 cm observations of any external galaxies beyond the LMC and SMC.

We investigate the stellar populations and molecular gas properties of a star-forming region within the dwarf irregular (dIrr) galaxy Wolf–Lundmark–Mellote (WLM). Low-metallicity dIrrs like WLM offer a valuable window into star formation in environments that are unlike those of larger, metal-rich galaxies such as the Milky Way. In these conditions, carbon monoxide (CO), typically used to trace molecular clouds, is more easily photodissociated by ultraviolet (UV) radiation, leading to a larger fraction of CO-dark molecular gas, where H₂ exists without detectable CO emission, or CO-dark gas in the form of cold H i. Understanding the molecular gas content and the stellar populations in these star-forming regions provides important information about the role of CO-bright and CO-dark gas in forming stars. Using Hubble Space Telescope imaging across five Wide Field Camera 3 UVIS bands and CO observations from the Atacama Large Millimeter Array, we examine stellar populations within and outside CO cores and the photodissociation region. Our findings indicate similar physical characteristics such as age and mass across the different environments. Assuming 2% of molecular gas is converted to stars, we estimate the molecular gas content and determine that CO-dark gas constitutes a large fraction of the molecular reservoir in WLM. These results are consistent with molecular gas estimates using a previous dust-derived CO-to-H₂ conversion factor (α _CO) for WLM. These findings highlight the critical role of CO-dark gas in low-metallicity star formation.

We investigate the stellar populations and molecular gas properties of a star-forming region within the dwarf irregular (dIrr) galaxy WLM. Low-metallicity dIrrs like WLM offer a valuable window into star formation in environments that are unlike those of larger, metal-rich galaxies such as the Milky Way. In these conditions, carbon monoxide (CO), typically used to trace molecular clouds, is more easily photodissociated by ultraviolet (UV) radiation, leading to a larger fraction of CO-dark molecular gas, where H$_2$ exists without detectable CO emission, or CO-dark gas in the form of cold HI. Understanding the molecular gas content and the stellar populations in these star-forming regions provides important information about the role of CO-bright and CO-dark gas in forming stars.

Previous studies conclusively show that pencil-and-paper lecture-tutorials (LTs) are incredibly effective at increasing student engagement and learning gains on a variety of topics when compared to traditional lecture. LTs in astronomy are post-lecture activities developed with the intention of helping students engage with conceptual and reasoning difficulties around a specific topic with the end goal of them developing a more expert-like understanding of astrophysical concepts. To date, all astronomy LTs have been developed for undergraduate courses taught in-person. Increases in online course enrollments and the COVID-19 pandemic further highlighted the need for additional interactive, research-based, curricular materials designed for online classrooms. To this end, we developed and assessed the efficacy of an innovative, interactive LT designed to teach planet formation in asynchronous, online, introductory astronomy courses for undergraduates. We utilized the Planet Formation Concept Inventory to compare learning outcomes between courses that implemented the new online, interactive LT, and those that used either a lecture-only approach or utilized a standard pencil-and-paper LT on the same topic. Overall, learning gains from the standard pencil-and-paper LT were statistically indistinguishable from the in-person implementation of the online LT and both of these conditions outperformed the lecture-only condition. However, when implemented asynchronously, learning gains from the online LT were lower and not significantly above the lecture-only condition. While improvements can be made to improve the online LT in the future, the current discipline ideas still outperform traditional lecture, and can be used as a tool to teach planet formation effectively.

PEARLSDG was previously reported as an isolated dwarf galaxy with a TRGB distance of 30 Mpc. New data show this to not be the case. We report a new spectroscopic redshift of 0.02809, which argues for an association with a group of galaxies at ∼124 Mpc.

Wolf–Lundmark–Melotte (WLM) is a Local Group dwarf irregular (dIrr) galaxy with a metallicity 13% of solar. At 1 Mpc, the relative isolation of WLM provides a unique opportunity to investigate the internal mechanisms of star formation at low metallicities. The earliest stages of star formation in larger spirals occur in embedded clusters within molecular clouds, but dIrrs lack the dust, heavy metals, and organized structure of spirals believed necessary to collapse the molecular clouds into stars. Despite actively forming stars, the early stages of star formation in dIrrs is not well understood. We examine the relationship between early star formation and molecular clouds at low metallicities. We utilize ALMA-detected CO cores, JWST near-infrared (NIR) images (F090W, F150W, F250M, and F430M), and GALEX far-ultraviolet (FUV) images of WLM to trace molecular clouds, early star formation, and longer star formation timescales respectively. We compare clumps of NIR-bright sources (referred to as objects) categorized into three types based on their proximity to FUV sources and CO cores. We find objects, independent of their location, have similar colors and magnitudes and no discernible difference in temperature. However, we find that objects near CO have higher masses than objects away from CO, independent of proximity to FUV. Additionally, objects near CO are coincident with Spitzer 8 μm sources at a higher frequency than objects elsewhere in WLM. This suggests objects near CO may be embedded star clusters at an earlier stage of star formation, but accurate age estimates for all objects are required for confirmation.

A wealth of observations have long suggested that the vast majority of isolated classical dwarf galaxies (M _* = 10⁷–10⁹ M _⊙) are currently star forming. However, recent observations of the large abundance of “ultra-diffuse galaxies” beyond the reach of previous large spectroscopic surveys suggest that our understanding of the dwarf galaxy population may be incomplete. Here we report the serendipitous discovery of an isolated quiescent dwarf galaxy in the nearby Universe, which was imaged as part of the JWST PEARLS Guaranteed Time Observation program. Remarkably, individual red-giant branch stars are visible in this near-IR imaging, suggesting a distance of 30 ± 4 Mpc, and a wealth of archival photometry point to an sSFR of 2 × 10⁻¹¹ yr⁻¹ and star formation rate of 4 × 10⁻⁴ M _⊙ yr⁻¹. Spectra obtained with the Lowell Discovery Telescope find a recessional velocity consistent with the Hubble Flow and >1500 km s⁻¹ separated from the nearest massive galaxy in Sloan Digital Sky Survey suggesting that this galaxy was either quenched from internal mechanisms or had a very high-velocity (≳1000 km s⁻¹) interaction with a nearby massive galaxy in the past. This analysis highlights the possibility that many nearby quiescent dwarf galaxies are waiting to be discovered and that JWST has the potential to resolve them.