The Local Group dwarf Leo T: H i on the brink of star formation

Ryan-Weber, E. V.; Begum, Ayesha; Oosterloo, Thomas; Pal, Sabyasachi; Irwin, M. J.; Belokurov, V.; Evans, N. W.; Zucker, D. B.

doi:10.1111/j.1365-2966.2007.12734.x

Cited by 135 publications

(165 citation statements)

References 26 publications

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“…However, in the regions where the column density is above this value, the spectra show, in addition, a narrower component with a dispersion of about 4 km s −1 . This two-phase character of the ISM is seen in many dwarf galaxies (Young & Lo 1996Begum et al 2006;Ryan-Weber et al 2008).…”

Section: Neutral Hydrogenmentioning

confidence: 87%

An optical and H i study of the dwarf Local Group galaxy VV124 = UGC4879

Bellazzini

Beccari

Oosterloo

et al. 2011

A&A

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We present a detailed study of the dwarf galaxy VV124 (UGC4879), recently recognized as a remarkably isolated member of the Local Group. We have obtained deep (r 26.5) wide-field (23 × 23 ) g,r photometry of individual stars with the LBC camera at the Large Binocular Telescope under sub-arcsec seeing conditions. The color-magnitude diagram suggests that the stellar content of the galaxy is dominated by an old, metal-poor population, with a significant metallicity spread. A very clean detection of the RGB tip allows us to derive an accurate distance of D = 1.3 ± 0.1 Mpc. Combining surface photometry with star counts, we are able to trace the surface brightness profile of VV124 out to ∼5 1.9 kpc radius (where μ r 30 mag/arcsec 2 ), showing that it is much more extended than previously believed. Moreover, the surface density map reveals the presence of two symmetric flattened wings emanating from the central elongated spheroid and aligned with its major axis, resembling a stellar disk seen nearly edge-on. We also present H i observations obtained with the Westerbork Synthesis Radio Telescope (WSRT), the first ever of this object. A total amount of 10 6 M of H i gas is detected in VV124. Compared to the total luminosity, this gives a value of M HI /L V = 0.11, which is particularly low for isolated Local Group dwarfs. The spatial distribution of the gas does not correlate with the observed stellar wings. The systemic velocity of the H i in the region superposed to the stellar main body of the galaxy is V h = −25 km s −1 . The velocity field shows substructures typical of galaxies of this size but no sign of rotation. The H i spectra indicates the presence of a two-phase interstellar medium, again typical of many dwarf galaxies.

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Section: Neutral Hydrogenmentioning

confidence: 87%

An optical and H i study of the dwarf Local Group galaxy VV124 = UGC4879

Bellazzini

Beccari

Oosterloo

et al. 2011

A&A

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“…This has indeed been the case for the most compact cloud identified in the survey: Giovanelli et al (2013) and Rhode et al (2013) reveal that this cloud embeds a faint (M V −9.4), low surface brightness (µ V 24.5 mag/arcsec 2 ), star-forming galaxy at a distance of D 1.7 Mpc, Leo P (McQuinn et al 2013). Leo P has a structure, as well as gas and stellar content, that is very similar to Leo T, another recently discovered dwarf galaxy (Irwin et al 2007), which, quoting Ryan-Weber et al (2008) ". .…”

Section: Introductionmentioning

confidence: 99%

The StEllar Counterparts of COmpact high velocity clouds (SECCO) survey

Bellazzini

Beccari

Battaglia

et al. 2015

A&A

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We present an imaging survey that searches for the stellar counterparts of recently discovered ultra-compact high-velocity H  clouds (UCHVC). It has been proposed that these clouds are candidate mini-haloes in the Local Group and its surroundings within a distance range of 0.25-2.0 Mpc. Using the Large Binocular Telescope we obtained wide-field ( 23 × 23 ) g-and r-band images of the twenty-five most promising and most compact clouds amongst the fifty-nine that have been identified. Careful visual inspection of all the images does not reveal any stellar counterpart that even slightly resembles Leo P, the only local dwarf galaxy that was found as a counterpart to a previously detected high-velocity cloud. Only a possible distant (D > 3.0 Mpc) counterpart to HVC274.68+74.70-123 has been identified in our images. The point source photometry in the central 17.3 × 7.7 chips reaches r ≤ 26.5 and is expected to contain most of the stellar counterparts to the UCHVCs. However, no obvious stellar overdensity is detected in any of our fields, in marked contrast to our comparison Leo P field, in which the dwarf galaxy is detected at a >30σ-significance level. Only HVC352.45+59.06+263 may be associated with a weak over-density, whose nature cannot be ascertained with our data. Sensitivity tests show that our survey would have detected any dwarf galaxy dominated by an old stellar population, with an integrated absolute magnitude of M V ≤ −8.0 and a half-light radius of r h ≤ 300 pc that lies within 1.5 Mpc of us, thereby confirming that it is unlikely that the observed UCHVCs are associated with the stellar counterparts typical of known Local Group dwarf galaxies.

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“…One useful comparison is with very small, almost dark, H idominated galaxies such as Leo T (Ryan-Weber et al 2008) and Leo P ). The size, gas content, and dynamical mass of these galaxies are very similar to that of GBT 1355, if it is assumed to be at 1 Mpc.…”

Section: Local Group Minihalomentioning

confidence: 99%

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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The Local Group dwarf Leo T: H i on the brink of star formation

Cited by 135 publications

References 26 publications

An optical and H i study of the dwarf Local Group galaxy VV124 = UGC4879

An optical and H i study of the dwarf Local Group galaxy VV124 = UGC4879

The StEllar Counterparts of COmpact high velocity clouds (SECCO) survey

Is GBT 1355+5439 a dark galaxy?

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