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This paper reports on the culmination of an NSF Scholarships in Science, Technology, Engineering and Mathematics (S-STEM) awarded to a two-year college located in a metro area with high rates of concentrated poverty and low levels of educational attainment. This two-year college is a minority-serving institution with curriculum to prepare students majoring in engineering to transfer and complete a baccalaureate degree at a four-year university. The Engineering Scholars Program (ESP) was established in fall 2019 to award students majoring in engineering annual scholarships of up to $6000, depending on financial need. In addition to supporting students through scholarships, the program engages scholars in professional development activities inclusive of academic seminars, extracurricular events, and undergraduate research opportunities in collaboration with the local four-year university. The program also established a mentorship structure with faculty mentors, student peer mentors, and academic advising. In addition to supporting scholars at the two-year college, the ESP provides support for a portion of cohorts that have transferred to the local four-year university and remained connected to the program. To date, the ESP has awarded a total of 131 semester long scholarships; 16 in year one (2019-2020), 28 in year two (2020-2021), 35 in year three (2021-2022), including six transfers, 38 in year four (2022-2023), including eight transfers, and 28 in year five (2023-2024), including 10 transfers. In year three, the ESP was awarded supplemental funding to support a larger portion of students and transfer cohorts; this helped reduce the financial burdens resulting from exacerbated financial needs due to the COVID-19 pandemic during years two and three of this project. This paper details the progress made towards the achievement of the program goals of creating a welcoming STEM climate at the two-year college, increasing the participation and persistence in engineering among economically disadvantaged students, and establishing transfer support to the local four-year university. Program evaluation findings have identified several opportunities for sustaining scholar transfer support outside of the financial support provided in the form of scholarships. These opportunities fell into two major themes: (1) peer-led transfer support inclusive of connecting transferred students and students preparing for transfer with emphasis on navigating different university structures, and (2) collaboration across engineering disciplines to develop and offer interdisciplinary undergraduate research and/or collaborative work on other projects. Furthermore, research findings from interviews with scholars provided additional context for taking action on program outcomes while also enhancing the understanding of how participation in a collaborative cohort experience can contribute to students’ membership within the STEM community and the construction of their own STEM identity. Although formal financial support sunsets during the final year of the ESP, program and research findings have identified programmatic elements that provide key support for students and can be sustained into the future. This paper reports on the program strategy for meeting the future needs of scholars at both the two-year college and the four-year transfer university. 

We present results from an optical search for Local Group dwarf galaxy candidates associated with the Ultra-Compact High Velocity Clouds (UCHVCs) discovered by the ALFALFA neutral hydrogen survey. The ALFALFA UCHVCs are isolated, compact Hiclouds with projected sizes, velocities, and estimated Himasses that suggest they may be nearby dwarf galaxies, but that have no clear counterpart in existing optical survey data. We observed 26 UCHVCs with the WIYN 3.5 m telescope and One Degree Imager (ODI) in two broadband filters and searched the images for resolved stars with properties that match those of stars in typical dwarf galaxies at distances <2.5 Mpc. We identify one promising dwarf galaxy candidate at a distance of ∼570 kpc associated with the UCHVC AGC 268071, and five other candidates that may deserve additional follow-up. We carry out a detailed analysis of ODI imaging of a UCHVC that is close in both projected distance and radial velocity to the outer-halo Milky Way globular cluster Pal 3. We also use our improved detection methods to reanalyze images of five UCHVCs that were found to have possible optical counterparts during the first phase of the project, and confirm the detection of a possible stellar counterpart to the UCHVC AGC 249525 at an estimated distance of ∼2 Mpc. We compare the optical and Hiproperties of the dwarf galaxy candidates to the results from recent theoretical simulations that model satellite galaxy populations in group environments, as well as to the observed properties of galaxies in and around the Local Group.

 

We present the discovery of the most distant OH megamaser (OHM) to be observed in the main lines, using data from the MeerKAT International Giga-Hertz Tiered Extragalactic Exploration (MIGHTEE) survey. At a newly measured redshift of z = 0.7092, the system has strong emission in both the 1665 MHz (L ≈ 2500 L⊙) and 1667 MHz (L ≈ 4.5 × 104 L⊙) transitions, with both narrow and broad components. We interpret the broad line as a high-velocity-dispersion component of the 1667 MHz transition, with velocity v ∼ 330 km s−1 with respect to the systemic velocity. The host galaxy has a stellar mass of M⋆ = 2.95 × 1010 M⊙ and a star formation rate of SFR = 371 M⊙ yr−1, placing it ∼1.5 dex above the main sequence for star-forming galaxies at this redshift, and can be classified as an ultraluminous infrared galaxy. Alongside the optical imaging data, which exhibit evidence for a tidal tail, this suggests that the OHM arises from a system that is currently undergoing a merger, which is stimulating star formation and providing the necessary conditions for pumping the OH molecule to saturation. The OHM is likely to be lensed, with a magnification factor of ∼2.5, and perhaps more if the maser emitting region is compact and suitably offset relative to the centroid of its host galaxy’s optical light. This discovery demonstrates that spectral line mapping with the new generation of radio interferometers may provide important information on the cosmic merger history of galaxies.

 

ABSTRACT We present new H i interferometric observations of the gas-rich ultra-diffuse galaxy AGC 114905, which previous work, based on low-resolution data, identified as an outlier of the baryonic Tully–Fisher relation. The new observations, at a spatial resolution ∼2.5 times higher than before, reveal a regular H i disc rotating at about 23 km s−1. Our kinematic parameters, recovered with a robust 3D kinematic modelling fitting technique, show that the flat part of the rotation curve is reached. Intriguingly, the rotation curve can be explained almost entirely by the baryonic mass distribution alone. We show that a standard cold dark matter halo that follows the concentration–halo mass relation fails to reproduce the amplitude of the rotation curve by a large margin. Only a halo with an extremely (and arguably unfeasible) low concentration reaches agreement with the data. We also find that the rotation curve of AGC 114905 deviates strongly from the predictions of modified Newtonian dynamics. The inclination of the galaxy, which is measured independently from our modelling, remains the largest uncertainty in our analysis, but the associated errors are not large enough to reconcile the galaxy with the expectations of cold dark matter or modified Newtonian dynamics. 

Abstract The ratio of baryonic-to-dark matter in present-day galaxies constrains galaxy formation theories and can be determined empirically via the baryonic Tully–Fisher relation (BTFR), which compares a galaxy’s baryonic mass ( M bary ) to its maximum rotation velocity ( V max ). The BTFR is well determined at M bary > 10 8 M ⊙ , but poorly constrained at lower masses due to small samples and the challenges of measuring rotation velocities in this regime. For 25 galaxies with high-quality data and M bary ≲ 10 8 M ⊙ , we estimate M bary from infrared and H i observations and V max from the H i gas rotation. Many of the V max values are lower limits because the velocities are still rising at the edge of the detected H i disks ( R max ); consequently, most of our sample has lower velocities than expected from extrapolations of the BTFR at higher masses. To estimate V max , we map each galaxy to a dark matter halo assuming density profiles with and without cores. In contrast to noncored profiles, we find the cored profile rotation curves are still rising at R max values, similar to the data. When we compare the V max values derived from the cored density profiles to our M bary measurements, we find a turndown of the BTFR at low masses that is consistent with Λ cold dark matter predictions and implies baryon fractions of 1%–10% of the cosmic value. Although we are limited by the sample size and assumptions inherent in mapping measured rotational velocities to theoretical rotation curves, our results suggest that galaxy formation efficiency drops at masses below M bary ∼ 10 8 M ⊙ , corresponding to M 200 ∼ 10 10 M ⊙ . 

We present deep optical imaging and photometry of four objects classified as “Almost-Dark” galaxies in the Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) survey because of their gas-rich nature and extremely faint or missing optical emission in existing catalogs. They have Himasses of 10⁷–10⁹M_⊙and distances of ∼9–100 Mpc. Observations with the WIYN 3.5 m telescope and One Degree Imager reveal faint stellar components with central surface brightnesses of ∼24–25$\mathrm{mag}{\mathrm{arcsec}}^{-2}$in thegband. We also present the results of Hisynthesis observations with the Westerbork Synthesis Radio Telescope. These Almost-Dark galaxies have been identified as possible tidal dwarf galaxies (TDGs) based on their proximity to one or more massive galaxies. We demonstrate that AGC 229398 and AGC 333576 likely have the low dark matter content and large effective radii representative of TDGs. They are located much farther from their progenitors than previously studied TDGs, suggesting they are older and more evolved. AGC 219369 is likely dark matter dominated, while AGC 123216 has a dark matter content that is unusually high for a TDG, but low for a normal dwarf galaxy. We consider possible mechanisms for the formation of the TDG candidates such as a traditional major merger scenario and gas ejection from a high-velocity flyby. Blind Hisurveys like ALFALFA enable the detection of gas-rich, optically faint TDGs that can be overlooked in other surveys, thereby providing a more complete census of the low-mass galaxy population and an opportunity to study TDGs at a more advanced stage of their life cycle.

 

Abstract We use panoramic optical spectroscopy obtained with the Very Large Telescope/MUSE to investigate the nature of five candidate extremely isolated low-mass star-forming regions (Blue Candidates; hereafter, BCs) toward the Virgo cluster of galaxies. Four of the five (BC1, BC3, BC4, and BC5) are found to host several H ii regions and to have radial velocities fully compatible with being part of the Virgo cluster. All the confirmed candidates have mean metallicity significantly in excess of that expected from their stellar mass, indicating that they originated from gas stripped from larger galaxies. In summary, these four candidates share the properties of the prototype system SECCO 1, suggesting the possible emergence of a new class of stellar systems, intimately linked to the complex duty cycle of gas within clusters of galaxies. A thorough discussion of the nature and evolution of these objects is presented in a companion paper, where the results obtained here from the MUSE data are complemented with Hubble Space Telescope (optical) and Very Large Array (H i ) observations. 

Abstract We present results from deep H i and optical imaging of AGC 229101, an unusual H i source detected at v helio =7116 km s −1 in the Arecibo Legacy Fast ALFA (ALFALFA) blind H i survey. Initially classified as a candidate “dark” source because it lacks a clear optical counterpart in Sloan Digital Sky Survey (SDSS) or Digitized Sky Survey 2 (DSS2) imaging, AGC 229101 has 10 9.31±0.05 M ⊙ of H i , but an H i line width of only 43 ± 9 km s −1 . Low-resolution Westerbork Synthesis Radio Telescope (WSRT) imaging and higher-resolution Very Large Array (VLA) B-array imaging show that the source is significantly elongated, stretching over a projected length of ∼80 kpc. The H i imaging resolves the source into two parts of roughly equal mass. WIYN partially populated One Degree Imager (pODI) optical imaging reveals a faint, blue optical counterpart coincident with the northern portion of the H i . The peak surface brightness of the optical source is only μ g ∼ 26.6 mag arcsec −2 , well below the typical cutoff that defines the isophotal edge of a galaxy, and its estimated stellar mass is only 10 7.32±0.33 M ⊙ , yielding an overall neutral gas-to-stellar mass ratio of M / M * = 98 − 52 + 111 . We demonstrate the extreme nature of this object by comparing its properties with those of other H i -rich sources in ALFALFA and the literature. We also explore potential scenarios that might explain the existence of AGC 229101, including a tidal encounter with neighboring objects and a merger of two dark H i clouds.