Star-forming, rotating spheroidal galaxies in the GAMA and SAMI surveys

• Published in: Monthly Notices of the Royal Astronomical Society
• Main Authors: Moffett, Amanda, Phillipps, Steven, Robotham, Aaron, Driver, Simon, Bremer, Malcolm
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2019
• Subjects: galaxies: fundamental parameters; galaxies: structure; galaxies: dwarf; surveys; sami
• Online Access: https://hdl.handle.net/1983/1e4f3bf7-57aa-40ea-bd77-eb3252d042d5; https://research-information.bris.ac.uk/en/publications/1e4f3bf7-57aa-40ea-bd77-eb3252d042d5; https://doi.org/10.1093/mnras/stz2237; https://research-information.bris.ac.uk/ws/files/204901309/LBS_2ndrevisv1.pdf

The Galaxy And Mass Assembly (GAMA) survey has morphologically identified a class of “Little Blue Spheroid” (LBS) galaxies whose relationship to other classes of galaxies we now examine in detail. Considering a sample of 868 LBSs, we find that such galaxies display similar but not identical colours, specific star formation rates, stellar population ages, mass-to-light ratios, and metallicities to Sd-Irr galaxies. We also find that LBSs typically occupy environments of even lower density than those of Sd-Irr galaxies, where ∼65% of LBS galaxies live in isolation. Using deep, highresolution imaging from VST KiDS and the new Bayesian, two-dimensional galaxy profile modeling code PROFIT, we further examine the detailed structure of LBSs and find that their S´ersic indices, sizes, and axial ratios are compatible with those of low-mass elliptical galaxies. We then examine SAMI Galaxy survey integral field emission line kinematics for a subset of 62 LBSs and find that the majority (42) of these galaxies display ordered rotation with the remainder displaying disturbed/non-ordered dynamics. Finally, we consider potential evolutionary scenarios for a population with this unusual combination of properties, concluding that LBSs are likely formed by a mixture of merger and accretion processes still recently active in low-redshift dwarf populations. We also infer that if LBS-like galaxies were subjected to quenching in a rich environment, they would plausibly resemble cluster dwarf ellipticals.