The Blue Compact Dwarf Galaxy VCC 848 Formed by Dwarf-Dwarf Merging: HI Gas, Star Formation and Numerical Simulations

Abstract

A clear link between a dwarf-dwarf merger event and enhanced star formation (SF) in the recent past was recently identified in the gas-dominated merger remnant VCC 848, offering by far the clearest view of a gas-rich late-stage dwarf-dwarf merger. We present a joint analysis of JVLA H i emission-line mapping, optical imaging and numerical simulations of VCC 848, in order to examine the impact of the merger on the stellar and gaseous distributions. VCC 848 has less than 30% of its H i gas concentrated within the central high-surface-brightness star-forming region, while the remaining H i is entrained in outlying tidal features. Particularly, a well-defined tidal arm reaches N (H i) comparable to the galaxy center but lacks SF. The molecular gas mass inferred from the current SF rate (SFR) dominates over the atomic gas mass in the central ∼ 1.5 kpc. VCC 848 is consistent with being a main-sequence starforming galaxy for its current stellar mass and SFR. The H ii region luminosity distribution largely agrees with that of normal dwarf irregulars with similar luminosities, except that the brightest H ii region is extraordinarily luminous. Our N -body/hydrodynamical simulations imply that VCC 848 is a merger between a gas-dominated primary progenitor and a gas-bearing star-dominated secondary. The progenitors had their first passage on a near-radial non-coplanar orbit more than 1 Gyr ago. The merger did not build up a core as compact as typical compact dwarfs with centralized starburst, which may be partly ascribed to the star-dominated nature of the secondary, and in a general sense, a negative stellar feedback following intense starbursts triggered at early stages of the merger.

The Smallest Scale of Hierarchy Survey (SSH). II. Extended star formation and bar-like features in the dwarf galaxy NGC 3741: recent merger or ongoing gas accretion?

“…Merger or interaction events can strongly impact the evolution of dwarf galaxies, affecting their morphology and kinematics, and providing a viable mechanism to trigger gas flows toward the inner galaxy regions and, possibly, the onset of a starburst (Bekki 2008;Stierwalt et al 2015;Carlin et al 2016;Privon et al 2017;Kado-Fong et al 2020). A number of individual dwarf-dwarf merger cases has been examined in the literature (Rich et al 2012;Martínez-Delgado et al 2012;Sand et al 2015;Belokurov & Koposov 2016;Amorisco, Evans & van de Ven 2014;Annibali et al 2016;Privon et al 2017;Makarova et al 2018;Johnston et al 2019;Kallivayalil et al 2018;Zhang et al 2020), but only a few systematic searches for dwarfs companions have been conducted so far (Stierwalt et al 2015;Higgs et al 2016;Carlin et al 2016;Paudel et al 2018;Annibali et al 2020;Kado-Fong et al 2020).…”