A Catalog of Ultra-Compact High Velocity Clouds From the Alfalfa Survey: Local Group Galaxy Candidates?

Adams, Elizabeth A. K.; Giovanelli, Riccardo; Haynes, Martha P.

doi:10.1088/0004-637x/768/1/77

Cited by 90 publications

(121 citation statements)

References 92 publications

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“…They are basically smaller versions, by roughly a factor 10, of the clouds of the CHVC model of Braun & Burton (1999). However, the clouds as proposed by Giovanelli et al (2010) and Adams et al (2013) are consistent with the theoretical models of, e.g., Sternberg et al (2002). They would also be small enough to have escaped detection in existing searches for dark H i clouds in nearby groups of galaxies.…”

Section: Local Group Minihalosupporting

confidence: 72%

Is GBT 1355+5439 a dark galaxy?

Oosterloo

Heald

Blok

2013

A&A

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We present H i imaging of GBT 1355+5439 performed with the Westerbork Synthesis Radio Telescope. This is a dark H i object recently discovered close to the nearby galaxy M101. We find GBT 1355+5439 to be an H i cloud 5 × 3 arcmin in size. The total H i image and the kinematics show that the cloud consists of condensations that have small (∼10 km s −1 ) motions with respect to each other. The column densities of the H i are low; the observed peak value is 7.1 × 10 19 cm −2 . The velocity field shows a mild velocity gradient over the body of GBT 1355+5439, possibly due to rotation, but it may also indicate large-scale radial motions. Although our data are limited in sensitivity, at all positions the H i velocity dispersion is higher than 5 km s −1 and no narrow, cold, H i component is seen. Because its distance is not known, we considered various possibilities for the nature of GBT 1355+5439. Both the scenarios that it is a tidal remnant near M101 and that it is a dark dwarf companion of M101 meet difficulties. Neither do the data fit the properties of known compact high-velocity clouds in the Galactic halo exactly, but we cannot entirely exclude this option and deeper observations are required. We also considered the possibility that GBT 1355+5439 is a gas-rich dark minihalo in the outer regions of the Local Group. Interestingly, it would then have similar properties as the clouds of a proposed Local Group population recently found in the ALFALFA survey. In this case, the H i mass of GBT 1355+5439 would be about a few times 10 5 M , its size about 1 kpc, and the dynamical mass M dyn > 5 × 10 7 M . However, if GBT 1355+5439 is a dark Local Group object, the internal kinematics of the H i appears to be different from that of gas-dominated, almost dark galaxies of similar size.

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Section: Local Group Minihalosupporting

confidence: 72%

Is GBT 1355+5439 a dark galaxy?

Oosterloo

Heald

Blok

2013

A&A

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“…1 (Bellazzini et al 2015a, B15a, hereafter) is a survey aimed at searching for stellar counterparts of Ultra Compact High Velocity Clouds (UCHVC) of neutral hydrogen that have been recently proposed by different teams as candidate mini-halos residing in the Local Group or its surroundings (D < ∼ 3.0 Mpc; Adams et al 2013;Saul et al 2012, ALFALFA and GALFA-Hi surveys, respectively). The only way to confirm the nature of UCHVCs as small gas-rich dwarf galaxies is to identify a concomitant stellar population that can allow to constrain the distance to the system.…”

Section: Seccomentioning

confidence: 99%

A very dark stellar system lost in Virgo: kinematics and metallicity of SECCO 1 with MUSE

Beccari

Bellazzini

Magrini

et al. 2016

Mon. Not. R. Astron. Soc.

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We present the results of VLT-MUSE integral field spectroscopy of SECCO 1, a faint, star-forming stellar system recently discovered as the stellar counterpart of an Ultra Compact High Velocity Cloud (HVC274.68+74.0), very likely residing within a substructure of the Virgo cluster of galaxies. We have obtained the radial velocity of a total of 38 individual compact sources identified as Hii regions in the main and secondary body of the system, and derived the metallicity for 18 of them. We provide the first direct demonstration that the two stellar bodies of SECCO 1 are physically associated and that their velocities match the Hi velocities. The metallicity is quite uniform over the whole system, with a dispersion lower than the uncertainty on individual metallicity estimates. The mean abundance, 12 + log(O/H) = 8.44, is much higher than the typical values for local dwarf galaxies of similar stellar mass. This strongly suggests that the SECCO 1 stars were born from a pre-enriched gas cloud, possibly stripped from a larger galaxy. Using archival HST images we derive a total stellar mass of 1.6 × 10 5 M for SECCO 1, confirming that it has a very high Hi to stellar mass ratio for a dwarf galaxy, M Hi /M * ∼ 100. The star formation rate, derived from the H α flux is a factor of more than 10 higher than in typical dwarf galaxies of similar luminosity.

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“…These systems can broadly be categorized as "ultra compact high velocity clouds" (UCHVCs; Adams et al 2013) and "Almost Dark" galaxy candidates Janowiecki et al 2015). Further comparisons of all of the SHIELD-class galaxies with members of these ALFALFA subsamples promise to populate the continuum of sources at the lowest and most extreme masses.…”

Section: Discussionmentioning

confidence: 99%

Shield: Neutral Gas Kinematics and Dynamics

McNichols

Teich

Nims³

et al. 2016

ApJ

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We present kinematic analyses of the 12 galaxies in the "Survey of H I in Extremely Low-mass Dwarfs" (SHIELD). We use multi-configuration interferometric observations of the H I 21 cm emission line from the Karl G. Jansky Very Large Array (VLA) 22 to produce image cubes at a variety of spatial and spectral resolutions. Both two-and three-dimensional fitting techniques are employed in an attempt to derive inclination-corrected rotation curves for each galaxy. In most cases, the comparable magnitudes of velocity dispersion and projected rotation result in degeneracies that prohibit unambiguous circular velocity solutions. We thus make spatially resolved position-velocity cuts, corrected for inclination using the stellar components, to estimate the circular rotation velocities. We find v circ  30 km s −1 for the entire survey population. Baryonic masses are calculated using singledish H I fluxes from Arecibo and stellar masses derived from HST and Spitzer imaging. Comparison is made with total dynamical masses estimated from the position-velocity analysis. The SHIELD galaxies are then placed on the baryonic Tully-Fisher relation. There exists an empirical threshold rotational velocity, Vrot < 15 km s −1 , below which current observations cannot differentiate coherent rotation from pressure support. The SHIELD galaxies are representative of an important population of galaxies whose properties cannot be described by current models of rotationally dominated galaxy dynamics.

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A Catalog of Ultra-Compact High Velocity Clouds From the Alfalfa Survey: Local Group Galaxy Candidates?

Cited by 90 publications

References 92 publications

Is GBT 1355+5439 a dark galaxy?

Is GBT 1355+5439 a dark galaxy?

A very dark stellar system lost in Virgo: kinematics and metallicity of SECCO 1 with MUSE

Shield: Neutral Gas Kinematics and Dynamics

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