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1. The Enigmatic ALFALFA (Almost) Dark Galaxy AGC 229101

   Leisman, Lukas; Pagel, Hannah; Ball, Catherine; Rhode, Katherine; Salzer, John; Janesh, William; Cannon, John M.; Haynes, Martha P.; Józsa, Gyula; Adams, Elizabeth; et al (January 2019, American Astronomical Society, AAS Meeting)

   We present deep HI and optical imaging of AGC 229101, an enigmatic and potentially unique source detected in the ALFALFA survey. Though it has an HI mass >109 solar masses, it is not detected in SDSS imaging, and has a very narrow HI line width. Deep follow up imaging with pODI on the WIYN 3.5m at KPNO detects a very blue, very low surface brightness optical counterpart with a stellar mass <107 solar masses, giving a gas fraction of MHI/M* in excess of 200. Low resolution WSRT HI imaging and higher resolution VLA B-array imaging reveal that AGC 229101 appears to consist of two connected HI components, with the optical counterpart associated with the peak column density in the northern component. The two components have approximately equal mass and radii, and together stretch over >80 kpc as projected on the sky. We compare the properties of AGC 229101 to other extreme HI-rich sources, and demonstrate that its properties appear to be unique relative to others sources in ALFALFA. We discuss potential explanations, including a tidal encounter between neighboring sources, a merger of two independent, almost dark sources, and gas in-fall along a filament. 

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2. ALFALFA Harvest: HI Imaging of Candidate Local Group Dwarf Galaxies

   Paine, S.; Bralts-Kelly, L.; Adams, E.; Cannon, J.; Giovanelli, R.; Haynes, M.; Janesh, W.; Janowiecki, S.; Oosterloo, T.; Rhode, K.; et al (January 2020, American Astronomical Society meeting)

   The ALFALFA blind extragalactic survey has populated the faint end of the neutral hydrogen (HI) mass function with statistical confidence for the first time. Of particular interest is a subset of the ALFALFA detections, termed "ultra-compact high-velocity clouds" (UCHVCs). These systems, if located within ~1 Mpc, would populate the lowest-mass end of the HI mass function. Subsequent optical imaging has revealed that some of these UCHVCs harbor associated (though sparse) stellar populations, revealing that they may be some of the most extreme galaxies known in the Local Volume, with optical properties akin to ultra-faint dwarf galaxies but with significant neutral gas reservoirs. In this campaign, we investigate the neutral hydrogen properties of six UCHVC candidate galaxies using deep VLA HI spectral line imaging. A companion poster (Bralts-Kelly et al.) presents 3D kinematic modeling of selected sources. Here, we show the imaging products and discuss the morphological and kinematic properties of the six chosen sources: AGC 198606, AGC 215417, AGC219656, AGC 249525, AGC 258237, and AGC 268069. 

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3. VLA+WSRT HI Imaging of Two "Almost Dark" Galaxies

   Ball, Catie; Singer, Quinton; Cannon, John M.; Leisman, Luke; Haynes, Martha P.; Adams, Elizabeth A.; Bernal Neira, David; Giovanelli, Riccardo; Hallenbeck, Gregory L.; Janesh, William; et al (January 2017, American Astronomical Society ... meeting)

   We present sensitive HI imaging of the "Almost Dark" galaxies AGC229385 and AGC229101. Selected from the ALFALFA survey, "Almost Dark" galaxies have significant HI reservoirs but lack an obvious stellar counterpart in survey-depth ground-based optical imaging. Deeper ground- and space-based imaging reveals very low surface brightness optical counterparts in both systems. The resulting M_HI/L_B ratios are among the highest ever measured for individual galaxies. Here we combine VLA and WSRT imaging of these two systems, allowing us to preserve surface brightness sensitivity while working at high angular resolution. The resulting maps of HI mass surface density, velocity field, and velocity dispersion are compared to deep optical and ultraviolet imaging. In both systems the highest column density HI gas is clumpy and resolved into multiple components. In the case of AGC229385, the kinematics are inconsistent with a simple rotating disk and may be the result of either an infall episode or an interaction between two HI-rich disks.Support for this work was provided by NSF grant 1211683 to JMC at Macalester College. 

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4. HI-Bearing Ultra-Diffuse Galaxies: VLA Imaging of AGC 749290 and AGC 238764

   Gault, Lexi; Leisman, Lukas (January 2019, American Astronomical Society, AAS Meeting)

   Ultra-diffuse galaxies (UDGs) are galaxies with a very low optical surface brightness; they have very few stars for their given radius. Since UDGs are thus difficult to study in visible light, we observe radio emission from neutral hydrogen gas (HI) in these galaxies. Here we present observations of the HI gas in the UDGs AGC 749290 and AGC 238764. Initially selected from a sample of Ultra-Diffuse Galaxies detected in the ALFALFA survey, these sources were imaged as a part of a follow up program using the Jansky Very Large Array (VLA) in both C and D configurations. We reduce the data using the CASA software suite, removing radio interference, applying calibration, and creating images. From these data we obtain spectra and maps of the galaxies' HI distribution and radial velocities. We find that both sources show ordered gas distributions and rotation, and that the HI gas extends well beyond the already extended optical emission. Further, we estimate inclinations and plot these sources on the Baryonic Tully-Fisher relation, providing tentative evidence that these sources are rotating too slowly for their given mass. This work has been supported by NSF grant AST-1637339. 

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5. Using Very Large Array Data to Image the Ultra-Diffuse Galaxy AGC 749251

   Reiter, Kameron; Leisman, Lukas (January 2019, American Astronomical Society, AAS Meeting)

   Ultra-diffuse galaxies (UDGs) have generated significant interest in recent years, as their stars appear too spread out relative to typical galaxies, and because some UDGs appear to have more than typical amounts of dark matter. The ALFALFA Survey has detected a number of UDGs in the field that are rich with neutral hydrogen (HI). We use the Karl G. Jansky Very Large Array (VLA) to image one of these HI-rich UDG, AGC 749251. We manually remove radio frequency interference, and reduce it using standard procedures in CASA. From the resulting data cubes we created 2D maps (moment 0 maps) and maps of the radial velocities of the HI gas. We find that the HI in AGC 749251 shows reasonably ordered morphology and rotation, and extends beyond the already extended optical emission. We estimate the source's inclination and rotation velocity, constraining the source's dark matter content. We also compare our results to other, non-ultra diffuse galaxies, and suggest that the rotation velocity seems low compared with other sources of similar mass. This work has been supported by NSF grant AST-1637339. 

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