Dense CO in Mrk 71-A: Superwind Suppressed in a Young Super Star Cluster

Abstract

We report the detection of CO(J = 2 − 1) coincident with the super star cluster (SSC) Mrk 71-A in the nearby Green Pea analog galaxy, NGC 2366. Our NOEMA observations reveal a compact, ∼ 7 pc, molecular cloud whose mass (10 5 M ) is similar to that of the SSC, consistent with a high star-formation efficiency, on the order of 0.5. There are two, spatially distinct components separated by 11 km s −1 . If expanding, these could be due to momentumdriven, stellar wind feedback. Alternatively, we may be seeing the remnant infalling, colliding clouds responsible for triggering the SSC formation. The kinematics are also consistent with a virialized system. These extreme, highdensity, star-forming conditions inhibit energy-driven feedback; the co-spatial existence of a massive, molecular cloud with the SSC supports this scenario, and we quantitatively confirm that any wind-driven feedback in Mrk 71-A is momentum-driven, rather than energy-driven. Since Mrk 71-A is a candidate Lyman continuum emitter, this implies that energy-driven superwinds may not be a necessary condition for the escape of ionizing radiation. In addition, the detection of the nebular continuum emission yields an accurate astrometric position for the Mrk 71-A. We also detect four other massive, molecular clouds in this giant star-forming complex.

Multiple populations in globular clusters: New insights from chemical evolution and horizontal-branch models

“…In our recent chemical evolution models ( we have released that constraint and assume that SN ejecta escape (undergo blowout) without expelling the ambient gas. This is predicted by recent hydrodynamic simulations with more realistic treatment on the proto-GC environment (Tenorio-Tagle et al 2015; Silich & Tenorio-Tagle 2018), which is also supported by some observations (Turner et al 2017;Oey et al 2017). So in our model, chemical evolution is dictated by both WMS anf AGB.…”

Neutral Gas Properties and Lyα Escape in Extreme Green Pea Galaxies∗

“…While mechanical feedback may operate in some cases, other mechanisms are required to produce low covering fractions in the galaxies with low velocities. Potential candidates include radiative feedback, as suggested by Jaskot et al (2017) and Oey et al (2017), or a two-stage starburst. Ionizing photon escape may be optimized in some GPs at young ages 1 − 5 Myr after the starburst, where mechanical feedback may not strongly influence the ISM.…”

“…A different scenario may produce low covering fractions at low velocity in extreme GPs. For example, Oey et al (2017) find suppressed superwinds in the super star-cluster Mrk 71-A, a GP analog and LCE candidate likely dominated by radiative feedback. On the other hand, that system also shows a two-stage starburst with an older and younger component of ages < 3 − 5 Myr and 1 Myr respectively (Micheva et al 2017).…”

Extremely weak CO emission in IZw 18

“…Solomon & Vanden Bout (2005). The CO emission tends to reside in clumps of a few parsecs at low metallicity (Rubio et al 2015;Oey et al 2017;Schruba et al 2017;Shi et al 2020), which is much smaller than the beam size of our observation, hence we do not expect significant missing diffuse emission.…”

“…Therefore it is still unclear whether it is feasible to use [C ii] to trace H 2 gas. Substantial efforts have been made to search for the molecular gas in metal-poor galaxies (Rubio et al 2015;Oey et al 2017;Schruba et al 2017;Elmegreen et al 2018); nevertheless, among the galaxies below 10% Z , only Sextans B (7% Z ) has a robust CO detection (Shi et al 2016(Shi et al , 2020. The impact of low metal abundance on star formation requires further exploration of the most metal-poor galaxies.…”