Abstract
ABSTRACTWe 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 a baryon fraction similar to the cosmological mean. By means of a 3D kinematic modelling fitting technique, we show that the H i 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 exponential disc scale length valid for dwarf galaxies with circular speeds ≲ 45 km s−1, 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.
Highlights
In the last five years there have been a significant number of studies aiming to detect and systematically characterize a population of lowC The Author(s) 2020
Along with Mancera Pina et al (2019b), we suggest that a scenario where feedback processes in our ultra-diffuse galaxies (UDGs) have been relatively weak and inefficient in ejecting gas out of their virial radii could explain their quiescent interstellar medium (ISM) and high baryon fractions
We present the 3D kinematic models of six dwarf gas-rich UDGs
Summary
Yun, Ho & Lo 1994; de Blok & Walter 2000; Fraternali et al 2002; Oosterloo, Fraternali & Sancisi 2007; Di Teodoro & Fraternali 2014), and allow us to estimate their rotation velocity, angular momentum and matter distribution, key ingredients to understand their formation and evolution (e.g. de Blok 1997; Verheijen 1997; Swaters 1999; Noordermeer 2006; Posti et al 2018b) Because of these key properties, that may reveal telltale clues about their origins, pursuing studies of UDGs from an H I perspective is potentially very interesting. On the other hand, Amorisco & Loeb (2016) suggested that the extended sizes of UDGs can be explained if they live in dark matter haloes with high spin parameter (see Rong et al 2017; Posti et al 2018a) While currently those seem to be the most popular ideas, more mechanisms have been proposed in the literature, as we discuss in detail later.
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