Outflow from Outer-arm Starburst in a Grazing Collision between Galaxies

Abstract

Gemini NIFS K-band spectra and ALMA 12 CO J = 1 → 0, HCO + , and 100 GHz continuum observations are used to study a bright starburst clump on an outer arm of the interacting galaxy NGC 2207. This clump emits 23% of the total 24 µm flux of the galaxy pair and has an optically-opaque dust cone extending out of its 170 pc core. The measured CO accounts for the dark cone extinction if almost all the gas and dust there is in front of the star clusters. An associated approaching CO outflow has v z ∼ 16 km s −1 , an estimated molecular mass 8 × 10 6 M , and rises to heights ∼ 0.9 kpc. A receding CO outflow on the far side with v z ∼ 28 km s −1 is less extensive. The observed star formation in the core over 10 Myr can supply the dark cone kinetic energy of roughly 2 × 10 52 ergs via supernovae and stellar winds. Other signs of intense activity are variable radio continuum, suggesting an embedded supernova or other outburst, X-ray emission possibly from an X-ray binary or intermediate mass black hole, depending on the extinction, and Brγ and He I lines with 82 km s −1 linewidths and fluxes consistent with excitation by embedded O-type stars. According to previous models, the retrograde encounter suffered by NGC 2207 caused loss of angular momentum. This compressed its outer disk. We suggest that the resulting inward crashing stream hit a massive H I clump on the pre-existing spiral arm and triggered the observed starburst.

Are all post-starbursts mergers? HST reveals hidden disturbances in the majority of PSBs

“…Galaxies outside of Group C appear to have unusual dust morphologies that lead to a disturbed appearance of the galaxies -e.g., D1 and D10. Disrupted dust morphology can be linked to a disturbed molecular gas and possible outflows (e.g., Obied et al 2016;Kaufman et al 2020).…”

“…There are many processes that could lead to a disturbed dust morphology and quenching of star formation that are not necessarily associated with mergers. For example, outflows from a starburst-or AGN-driven feedback could lead to the disruption of dust, dusty outflows and dust cones (e.g., Obied et al 2016;Kaufman et al 2020), while accreting AGNs are linked to nuclear dust spirals (e.g., Martini et al 2003). HST-SPOGs still contain large reservoirs of molecular gas and dust.…”

Hamilton's Object -- a clumpy galaxy straddling the gravitational caustic of a galaxy cluster : Constraints on dark matter clumping

“…Given the appearance of 𝐶7 on the edge of counterimage 𝐶 (Fig. 7), we conclude that this is a superstarburst region or a starburst clump in an outer arm of the galaxy, similar to an object in Abell S1063 at redshift 0.6 (Walth et al 2019) or the starburst clump in NGC2207 (Kaufman et al 2020) . Such kpc-sized starburst HII clumps are high redshift counterparts to actively star-forming clumps in nearby massive turbulent disk galaxies (Fisher et al 2016, Elmegreen et al 2021.…”