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1. "Almost Darks": HI Mapping and Optical Analysis

   Singer, Quinton; Ball, Catie; 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 VLA HI imaging of the "Almost Dark" galaxies AGC 227982, AGC 268363, and AGC 219533. 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. These three HI-rich objects harbor some of the most extreme levels of suppressed star formation amongst the isolated sources in the ALFALFA catalog. Our new multi-configuration, high angular (~20") and spectral (1.7 km/s) resolution HI observations produce spatially resolved column density and velocity distribution moment maps. We compare these images to Sloan Digitized Sky Survey (SDSS) optical images. By localizing the HI gas, we identify previously unknown optical components (offset from the ALFALFA pointing center) for AGC 227982 and AGC 268363, and confirm the association with a very low surface brightness stellar counterpart for AGC 219533. Baryonic masses are derived from VLA flux integral values and ALFALFA distance estimates, giving answers consistent with those derived from ALFALFA fluxes. All three sources appear to have fairly regular HI morphologies and show evidence of ordered rotation.Support for this work was provided by NSF grant 1211683 to JMC at Macalester College. 

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2. 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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3. Targeted HI Line Observations of Low Mass Galaxies in the Pisces-Perseus Supercluster: Results for the Declination Strip 30° < Dec < 32°

   Kumagai, Samuel F. (January 2019, American Astronomical Society, AAS Meeting)

   The Arecibo Pisces-Perseus Supercluster Survey (APPSS) is an observing project undertaken by the Undergraduate ALFALFA Team that aims to detect HI in galaxies in the Pisces-Perseus neighborhood and analyze the dynamics and the properties of the galaxies. The galaxies targeted in APPSS are suspected from their optical properties (color, morphology, surface brightness) to lie in the Pisces-Perseus Supercluster (PPS) but are below the detection threshold of the ALFALFA blind HI survey. Here we present results for galaxies targeted in a strip across the PPS region in declination from 30o to 32o. This region is along the main filament of the supercluster and includes objects such as the Pisces Cluster. The data was recorded by the L-Band Wide receiver of the Arecibo Observatory. Data reduction was done using routines derived for the APPSS in IDL. After baselining the spectra and sifting out radio interference, we fit either a gaussian or two-horned profile to their 21-centimeter line to measure the HI line flux density, velocity, and velocity width. From these parameters we calculate distances, hydrogen gas mass, and rotational velocities. As expected, the galaxies analyzed in this slice of declination have consistently lower mass than the ALFALFA detections thus extending the sampling of galaxies within the PPS. The combined ALFALFA and APPSS HI line detections will be used for future applications of the Baryonic Tully-Fisher Relation in this region. This research has been supported by NSF grant NSF/AST-1714828 to M.P. Haynes and by the Brinson Foundation for the Arecibo Pisces-Perseus Supercluster Survey (APPSS). 

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4. The Arecibo Pisces-Perseus Supercluster Survey: Characteristics of the APPSS Galaxy Population

   Montalvo, B.; Haynes, M. P.; Team, Undergraduate Alfalfa (January 2020, American Astronomical Society meeting)

   The Arecibo Pisces-Perseus Supercluster Survey(APPSS) aims to measure the infall and mass density along the PPS filament using red-shift independent distances obtained from the Baryonic Tully-Fisher Relation (BTFR). We will combine photometric data from the Sloan Digital Sky Survey with HI line spectroscopy obtained with the Arecibo telescope to derive BTFR distances and peculiar velocities over the PPS volume and its immediate foreground and background. To supplement the ALFALFA detections in the PPS volume, we have conducted new HI line observations with the Arecibo L-band Wide receiver system of blue, low surface brightness galaxies identified by their photometric properties in the Sloan Digital Sky Survey (SDSS). These targets are predicted to lie in the PPS volume but with HI masses of 8.0 < log HI mass < 9.0, putting them below the ALFALFA detection limit at that distance. We compare a preliminary sample of 634 galaxies detected as part from the APPSS survey with the main ALFALFA survey and other public catalogs of local galaxies, confirming that the new APPSS HI line detections are rotation-dominated, HI bearing galaxies with low stellar mass. Nearly all are star-forming, bluer, and of lower surface brightness, extinction and metallicity than optically selected samples. Preliminary BTFRs were calculated for both APPSS and ALFALFA galaxies and compared with BTFRs of simulated galaxies similar to those found in APPSS and ALFALFA using simulations such as IllustrisTNG (see poster by J. Borden). This work has been supported by NSF/AST-1714828 and the Brinson Foundation. 

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5. A Candidate Dark Matter Deficient Dwarf Galaxy in the Fornax Cluster Identified through Overluminous Star Clusters

   https://doi.org/10.3847/2515-5172/ad7112  

   Romanowsky, Aaron_J; Cabrera, Enrique; Janssens, Steven_R (August 2024, Research Notes of the AAS)

   Abstract Two low surface brightness (LSB) dwarf galaxies were identified recently as having little or no dark matter (DM), provoking widespread interest in their formation histories. These galaxies also host populous systems of star clusters that are on average larger and more luminous than typical globular clusters (GCs). We report an initial attempt to identify new candidate DM-deficient dwarfs via their unusual GC systems. Using a large catalog of LSB galaxies from the Dark Energy Survey, we inspect their Dark Energy Camera Legacy Survey (DECaLS) imaging and identify FCC 224 as a candidate found on the outskirts of the Fornax cluster. We analyze the GC system using DECaLS and archival Hubble Space Telescope WFPC2 imaging, and find an apparent population of overluminous GCs. More detailed follow-up of FCC 224 is in progress. 

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