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  1. Abstract

    We present theoretical expectations for infall toward supercluster-scale cosmological filaments, motivated by the Arecibo Pisces–Perseus Supercluster Survey (APPSS) to map the velocity field around the Pisces–Perseus Supercluster (PPS) filament. We use a minimum spanning tree applied to dark matter halos the size of galaxy clusters to identify 236 large filaments within the Millennium simulation. Stacking the filaments along their principal axes, we determine a well-defined, sharp-peaked velocity profile function that can be expressed in terms of the maximum infall rateVmaxand the distanceρmaxbetween the location of maximum infall and the principal axis of the filament. This simple, two-parameter functional form is surprisingly universal across a wide range of linear mass densities.Vmaxis positively correlated with the halo mass per length along the filament, andρmaxis negatively correlated with the degree to which the halos are concentrated along the principal axis. We also assess an alternative, single-parameter method usingV25, the infall rate at a distance of 25 Mpc from the axis of the filament. Filaments similar to the PPS haveVmax=612±116 km s−1,ρmax=8.9±2.1Mpc, andV25= 329 ± 68 km s−1. We create mock observations to model uncertainties associated with viewing angle, lack of three-dimensional velocity information, limited sample size, and distance uncertainties. Our results suggest that it would be especially useful to measure infall for a larger sample of filaments to test our predictions for the shape of the infall profile and the relationships among infall rates and filament properties.

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  2. 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. 
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  3. Abstract Virgo is the nearest galaxy cluster; it is thus ideal for studies of galaxy evolution in dense environments in the local universe. It is embedded in a complex filamentary network of galaxies and groups, which represents the skeleton of the large-scale Laniakea supercluster. Here we assemble a comprehensive catalog of galaxies extending up to ∼12 virial radii in projection from Virgo to revisit the cosmic-web structure around it. This work is the foundation of a series of papers that will investigate the multiwavelength properties of galaxies in the cosmic web around Virgo. We match spectroscopically confirmed sources from several databases and surveys including HyperLeda, NASA Sloan Atlas, NASA/IPAC Extragalactic Database, and ALFALFA. The sample consists of ∼7000 galaxies. By exploiting a tomographic approach, we identify 13 filaments, spanning several megaparsecs in length. Long >17 h –1 Mpc filaments, tend to be thin (<1 h –1 Mpc in radius) and with a low-density contrast (<5), while shorter filaments show a larger scatter in their structural properties. Overall, we find that filaments are a transitioning environment between the field and cluster in terms of local densities, galaxy morphologies, and fraction of barred galaxies. Denser filaments have a higher fraction of early-type galaxies, suggesting that the morphology–density relation is already in place in the filaments, before galaxies fall into the cluster itself. We release the full catalog of galaxies around Virgo and their associated properties. 
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  4. 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. 
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    We present an HI-optical catalog of ~ 30,000 galaxies based on the 100% complete Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) survey combined with data from the Sloan Digital Sky Survey (SDSS). Our goal is to facilitate public use of the completed ALFALFA catalog by providing carefully determined matches to SDSS counterparts, including matches for ~ 10,000 galaxies that do not have SDSS spectra. These identifications can provide a basis for further cross-matching with other surveys using SDSS photometric IDs as a reference point. We derive absolute magnitudes and stellar masses for each galaxy using optical colors combined with an internal reddening correction designed for small- and intermediate-mass galaxies with active star formation. We also provide measures of stellar masses and star formation rates based on infrared and/or ultraviolet photometry for galaxies that are detected by the Wide-field Infrared Survey Explorer (WISE) and/or the Galaxy Evolution Explorer (GALEX). Finally, we compare the galaxy population in the ALFALFA-SDSS sample with the populations in several other publicly-available galaxy catalogs, and confirm that ALFALFA galaxies typically have lower masses and bluer colors. 
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    The Arecibo Pisces-Perseus Supercluster Survey (APPSS) aims to observationally measure the dark matter mass density of Pisces-Perseus by detecting the peculiar velocities of galaxies falling onto the supercluster. To do this, APPSS will measure galaxies' distances using the Baryonic Tully Fisher Relation (BTFR), which relates a galaxy's baryonic mass and rotational velocity. Recovering the signature of infall as robustly as possible requires a careful choice of rotational velocity measurement, as the use of various velocity definitions changes the scatter and systematics of the relation. We introduce and compare multiple automated methods for measuring a galaxy's rotational velocity using its unresolved line profile. The velocities discussed include global HI profile width measures commonly reported in large surveys, velocity widths derived from best-fit parametrizations to profiles, and velocity widths derived using more novel methods including the spectral line's curve of growth and neural network-derived velocities which incorporate information about the profile's width and shape. We compare these velocity measures by finding best-fit BTFR relations for two samples of galaxies - the SPARC sample and a selected sample of gas-dominated ALFALFA galaxies (Papastergis et al. 2016). With these best-fit BTFRs, we compare intrinsic scatters and residual correlations with source properties to investigate how velocity choice affects the absolute and systematic uncertainties of BTFR-derived galaxy distances. This research is supported by NSF/AST-1714828 and the Brinson Foundation. 
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    We present our work on constructing a template Baryonic Tully-Fisher Relation (BTFR) from galaxies in the local universe that have primary distances. We utilize HI 21 cm line data from the complete Arecibo Legacy Fast ALFA (ALFALFA) survey and the digital HI archive from Springob et al. 2005; we also use photometry from the Sloan Digital Sky Survey (SDSS) and the NASA Sloan Atlas (NSA) MANGA v1_0_2 database; lastly, we have also made use of the Extragalactic Distance Database (EDD) for identifying galaxies with primary distances. After cross-matching the galaxies in these catalogues, we identify some 144 galaxies which meet our requirements for having all the necessary HI and photometry data, having primary distances, residing within 30 Mpc, and having low enough uncertainties to be considered reliable data points. An important trait of this data set is the prominence of low-mass, low-luminosity dwarves. Notably, we find the values for the slope, intercept and intrinsic scatter of the relation to be around 2.3, 4.8, and 0.4, respectively. Further, while unresolved velocity widths have historically produced shallower slopes, and while the BTFR has been shown to have a higher intrinsic scatter for low-mass galaxies, these precedents are not enough to explain the deviation of our data from the “standard” values of the BTFR. This work therefore raises several questions about why this discrepancy exists, how it can be resolved, and what we can learn from it. The authors would like to acknowledge the support of NSF/AST-1714828 and the Brinson Foundation. 
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    We present a method for estimating the amount of matter in large-scale (approximately 50 Mpc) filaments using the surrounding velocity infall pattern, based on 242 filaments in the Millennium simulation. We identify filaments using a minimal spanning tree to link large groups and clusters, and find the axis of each filament using a weighted principle component analysis. We improve our previous determination of a typical infall velocity profile by rescaling the profile for each filament by the distance where the infall speed reaches a maximum. We use the resulting average profile to determine a two-parameter piecewise function that can be used to estimate the maximum infall speed and location for individual filaments. Finally, we present the correlation between the maximum infall speed and the mass of the filament. These results will be used as part of the Arecibo Pisces-Perseus Supercluster Survey (APPSS), a project to map the infall pattern around the Pisces-Perseus Supercluster filament. This work is supported by NSF grant AST-1637339. 
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