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Register a new userCO observations toward HI-rich Ultra Diffuse Galaxies
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We present CO observations toward a sample of six HI-rich Ultra-diffuse galaxies (UDGs) as well as one UDG (VLSB-A) in the Virgo Cluster with the IRAM 30-m telescope. CO 1-0 is marginally detected at 4sigma level in AGC122966, as the first detection of CO emission in UDGs. We estimate upper limits of molecular mass in other galaxies from the non-detection of CO lines. These upper limits and the marginal CO detection in AGC122966 indicate low mass ratios between molecular and atomic gas masses. With the star formation efficiency derived from the molecular gas, we suggest that the inefficiency of star formation in such HI-rich UDGs is likely caused by the low efficiency in converting molecules from atomic gas, instead of low efficiency in forming stars from molecular gas.
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We study the gas kinematics of a sample of six isolated gas-rich low surface brightness galaxies, of the class called ultra-diffuse galaxies (UDGs). These galaxies have recently been shown to be outliers from the baryonic Tully-Fisher relation (BTFR), as they rotate much slower than expected given their baryonic mass, and to have baryon fractions similar to the cosmological mean. By means of a 3D kinematic modelling fitting technique, we show that the HI in our UDGs is distributed in thin regularly rotating discs and we determine their rotation velocity and gas velocity dispersion. We revisit the BTFR adding galaxies from other studies. We find a previously unknown trend between the deviation from the BTFR and the disc scale length valid for dwarf galaxies with circular speeds < 45 km/s, with our UDGs being at the extreme end. Based on our findings, we suggest that the high baryon fractions of our UDGs may originate due to the fact that they have experienced weak stellar feedback, likely due to their low star formation rate surface densities, and as a result they did not eject significant amounts of gas out of their discs. At the same time, we find indications that our UDGs may have higher-than-average stellar specific angular momentum, which can explain their large optical scale lengths.
We present resolved HI and CO observations of three galaxies from the HIghMass sample, a sample of HI-massive ($M_{HI} > 10^{10} M_odot$), gas-rich ($M_{HI}$ in top $5%$ for their $M_*$) galaxies identified in the ALFALFA survey. Despite their high gas fractions, these are not low surface brightness galaxies, and have typical specific star formation rates (SFR$/M_*$) for their stellar masses. The three galaxies have normal star formation rates for their HI masses, but unusually short star formation efficiency scale lengths, indicating that the star formation bottleneck in these galaxies is in the conversion of HI to H$_2$, not in converting H$_2$ to stars. In addition, their dark matter spin parameters ($lambda$) are above average, but not exceptionally high, suggesting that their star formation has been suppressed over cosmic time but are now becoming active, in agreement with prior H$alpha$ observations.
Ultra-diffuse galaxies have generated significant interest due to their large optical extents and low optical surface brightnesses, which challenge galaxy formation models. Here we present resolved synthesis observations of 12 HI-bearing ultra-diffuse galaxies (HUDs) from the Karl G. Jansky Very Large Array (VLA), as well as deep optical imaging from the WIYN 3.5-meter telescope at Kitt Peak National Observatory. We present the data processing and images, including total intensity HI maps and HI velocity fields. The HUDs show ordered gas distributions and evidence of rotation, important prerequisites for the detailed kinematic models in Mancera Pi~na et al. (2019b). We compare the HI and stellar alignment and extent, and find the HI extends beyond the already extended stellar component and that the HI disk is often misaligned with respect to the stellar one, emphasizing the importance of caution when approaching inclination measurements for these extreme sources. We explore the HI mass-diameter scaling relation, and find that although the HUDs have diffuse stellar populations, they fall along the relation, with typical global HI surface densities. This resolved sample forms an important basis for more detailed study of the HI distribution in this extreme extragalactic population.
We report on the first resolved HI observations of two blue ultra-diffuse galaxies (UDGs)using the Giant Metrewave Radio Telescope (GMRT). These observations add to the sofar limited number of UDGs with resolved HI data. The targets are from contrasting non-cluster environments: UDG-B1 is projected in the outskirts of Hickson Compact Group 25 and Secco-dI-2 (SdI-2) is an isolated UDG. These UDGs also have contrasting effective radii with Re of 3.7 kpc (similar to the Milky Way) and 1.3 kpc respectively. SdI-2 has an unusually large MHI/M* ratio =28.9, confirming a previous single dish HI observation. Both galaxies display HI morphological and kinematic signatures consistent with a recent tidal interaction, which is also supported by observations from other wavelengths, including optical spectroscopy. Within the limits of the observations resolution, our analysis indicates that SdI-2 is dark matter-dominated within its HI radius and this is also likely to be the case for UDG-B1. Our study highlights the importance of high spatial and spectral resolution HI observations for the study of the dark matter properties of UDGs.
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