A 5° × 5° deep H i survey of the M81 group − II. H i distribution and kinematics of IC 2574 and HIJASS J1021+68

Abstract

We analyse the eastern region of a 5° × 5° deep H i survey of the M81 group containing the dwarf galaxy IC 2574 and the H i complex HIJASS J1021+68, located between the dwarf and the M81 system. The data show that IC 2574 has an extended H i envelope that connects to HIJASS J1021+68 in the form of a collection of small clouds, but no evident connection has been found between IC 2574 and the central members of the M81 group. We argue, based on the morphology of the clouds forming HIJASS J1021+68 and its velocity distribution, that the complex is not a dark galaxy as previously suggested, but is instead a complex of clouds either stripped from, or falling on to the primordial H i envelope of IC 2574. We also use the deep H i observations to map the extended H i envelope around IC 2574 and, using a 3D tilted-ring model, we derive the rotation curve of the galaxy to a larger extent than has been done before. Combining the obtained rotation curve to higher resolution curves from the literature, we constrain the galaxy’s dark matter halo parameters.

Uncertainties in Galaxy Rotation Curves

“…Some of the velocity residuals are large, but there is no telltale pattern in them to suggest a non-axisymmetry in the flow and allowing a bar/oval component to the flow made only a marginal improvement. Our best fit inclination and systemic velocity (Table 1) are in good agreement with the values obtained by Sorgho et al (2020) from their direct fits to their low resolution 3D data cube, but both differ significantly from the values given in table 2 of dB08, which are i = 53.3 • and 53.1 km s −1 . Also our rotation curve is in rough agreement with that reported by dB08 and better agreement with that derived from the lower resolution data by Sorgho et al (2020).…”

“…Our best fit inclination and systemic velocity (Table 1) are in good agreement with the values obtained by Sorgho et al (2020) from their direct fits to their low resolution 3D data cube, but both differ significantly from the values given in table 2 of dB08, which are i = 53.3 • and 53.1 km s −1 . Also our rotation curve is in rough agreement with that reported by dB08 and better agreement with that derived from the lower resolution data by Sorgho et al (2020). Our estimates of the uncertainties, which largely stem from an almost 10 • uncertainty in the fitted inclination (Table 1), are much greater than those suggested by the THINGS team.…”

“…This galaxy is a member of the M81 group and is surrounded by a number of substantial HI clouds Sorgho et al (2020). It is not well fitted by our axisymmetric model Figure A6.…”

Star formation in the nearby dwarf galaxy DDO 53: interplay between gas accretion and stellar feedback

“…All these galaxies are gas rich and reveal extended complexes of star formation with prominent feedback-driven superbubbles, and in most of them the long duration of star formation activity led to the creation of so called supergiant shells (SGS), having sizes up to 2 kpc, the interaction of which could be a driver of star formation propagation (Egorov et al 2017;Vasiliev et al 2020). H i observations revealed a presence of gaseous tidal tails or surrounding high velocity clouds around some of the mentioned galaxies thus indicating their interaction with the IGM in the M81 group (Ashley et al 2017;Sorgho et al 2019Sorgho et al , 2020.…”

A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE)

“…The origin of AGC 226178 and other almost dark galaxies has been discussed without obtaining definitive answers (Cannon et al 2015;Janowiecki et al 2015;Leisman et al 2017;Brunker et al 2019). Among the propositions for their origin are suggestions that dark galaxies are: disks of high angular momentum (spin) that are stable against star formation (Jimenez & Heavens 2020;Leisman et al 2017); galaxies with low star formation efficiency (Janowiecki et al 2015); galaxies that are gas stripped by or falling onto a companion galaxy (Sorgho et al 2020); or tidal debris, as in the cases of VIRGO-HI (Duc & Bournaud 2008;Boselli et al 2018a) and SECCO 1 (Beccari et al 2017) for example. Cannon et al (2015) classify their sample of almost dark candidates as either tidal debris or dwarf galaxies (as for AGC 226178).…”