Kinematics of dwarf galaxies in gas-rich groups, and the survival and detectability of tidal dwarf galaxies

Abstract

We present DEIMOS multi-object spectroscopy (MOS) of 22 star-forming dwarf galaxies located in four gas-rich groups, including six newly-discovered dwarfs. Two of the galaxies are strong tidal dwarf galaxy (TDG) candidates based on our luminosity-metallicity relation definition. We model the rotation curves of these galaxies. Our sample shows low mass-to-light ratios (M/L=0.73±0.39M /L ) as expected for young, star-forming dwarfs. One of the galaxies in our sample has an apparently strongly-falling rotation curve, reaching zero rotational velocity outside the turnover radius of r turn = 1.2r e . This may be 1) a polar ring galaxy, with a tilted bar within a face-on disk; 2) a kinematic warp. These scenarios are indistinguishable with our current data due to limitations of slit alignment inherent to MOS-mode observations. We consider whether TDGs can be detected based on their tidal radius, beyond which tidal stripping removes kinematic tracers such as Hα emission. When the tidal radius is less than about twice the turnover radius, the expected falling rotation curve cannot be reliably measured. This is problematic for as much as half of our sample, and indeed more generally, galaxies in groups like these. Further to this, the Hα light that remains must be sufficiently bright to be detected; this is only the case for three (14%) galaxies in our sample. We conclude that the falling rotation curves expected of tidal dwarf galaxies are intrinsically difficult to detect.

Environmental processing of galaxies in H i-rich groups

“…Moreover, Sweet et al (2016) observed 22 star-forming dwarf galaxies in four Choir groups with DEIMOS multi-object spectroscopy and analysed the galaxy kinematics, finding two new tidal dwarf galaxy candidates: J1051-17:g11 and J1403-06:g1. The rotation curves of the observed dwarf galaxies are disturbed due to recent interactions (Sweet et al 2016). Moreover, they found that as much as half of the sample may be affected by the tidal interactions with neighbouring galaxies.…”

Star–Gas Misalignment in Galaxies. I. The Properties of Galaxies from the Horizon-AGN Simulation and Comparisons to SAMI

“…However, earlier observations have found that some galaxies have highly misaligned rotations between stars and gas (e.g., Ulrich 1975;Rubin et al 1992). Moreover, long-slit observations have revealed that galaxies can be misaligned regardless of their mass or morphology (e.g., Bertola et al 1992;Kuijken et al 1996;Kannappan & Fabricant 2001;Sweet et al 2016). Recently, the advent of integral field spectroscopy (IFS) observations has revealed more detailed kinematic properties of misaligned galaxies (e.g., Sarzi et al 2006;Coccato et al 2011Coccato et al , 2015Davis et al 2011;Barrera-Ballesteros et al 2014Serra et al 2014;Krajnović et al 2015;Jin et al 2016;Katkov et al 2016;Bryant et al 2019).…”

“…As stars form from gas, stars and gas of a galaxy are naturally expected to share the same or similar spin orientation, assuming the overall angular momentum is conserved. However, spectral observations have found that some galaxies have different axes of rotation be-tween stars and gases (e.g., Ulrich 1975;Bertola et al 1992;Rubin et al 1992;Kuijken et al 1996;Kannappan & Fabricant 2001;Sweet et al 2016). Moreover, recent integral field spectroscopy (IFS) observations confirmed the presence of misaligned galaxies regardless of the shape and environment (e.g., Sarzi et al 2006;Coccato et al 2011Coccato et al , 2015Davis et al 2011;Serra et al 2014;Barrera-Ballesteros et al 2014Krajnović et al 2015;Katkov et al 2016;Jin et al 2016;Bryant et al 2019).…”

Angular momentum of z ∼ 1.5 galaxies and their local analogues with adaptive optics

“…(i) Long-slit spectroscopy, such as in RF12, can suffer from misalignment between the kinematic and photometric major axes. The 2D nature of IFS means that the kinematic major axis need not be known a priori (Sweet et al 2016).…”