Ionized Gas Motions and the Structure of Feedback near a Forming Globular Cluster in NGC 5253

Abstract

We observed Brackett α 4.05µm emission towards the supernebula in NGC 5253 with NIRSPEC on Keck II in adaptive optics mode, NIRSPAO, to probe feedback from its exciting embedded super star cluster (SSC). NIRSPEC's Slit-Viewing Camera was simultaneously used to image the K-band continuum at ∼0. ′′ 1 resolution. We register the IR continuum with HST imaging, and find that the visible clusters are offset from the K-band peak, which coincides with the Br α peak of the supernebula and its associated molecular cloud. The spectra of the supernebula exhibit Br α emission with a strong, narrow core. The linewidths are 65-76 km s −1 , FWHM, comparable to those around individual ultra-compact Hii regions within our Galaxy. A weak, broad (FWHM≃150-175 km s −1 ) component is detected on the base of the line, which could trace a population of sources with high-velocity winds. The core velocity of Br α emission shifts by +13 km s −1 from NE to SW across the supernebula, possibly indicating a bipolar outflow from an embedded object, or linked to a foreground redshifted gas filament. The results can be explained if the supernebula comprises thousands of ionized wind regions around individual massive stars, stalled in their expansion due to critical radiative cooling and unable to merge to drive a coherent cluster wind. Based on the absence of an outflow with large mass loss, we conclude that feedback is currently ineffective at dispersing gas, and the SSC retains enriched material out of which it may continue to form stars.

Light element discontinuities suggest an early termination of star formation in the globular cluster NGC 6402 (M14)

“…He enhancements have also been detected (López-Sánchez et al 2007) but are so far unconfirmed ). Cohen et al (2018) showed that strong radiative cooling within the NGC 5253 supernebula region is likely stalling stellar winds and preventing the formation of significant cluster-scale outflow, which could enable prolonged star formation from chemically enriched gas. Even if the pollution sources are not exactly the same as those in early Universe massive clusters, the results from NGC 5253 indicate that enriched gas from massive stars can be produced quickly and retained for at least a few Myr within an extremely dense proto-cluster region 10 .…”

Two Thresholds for Globular Cluster Formation and the Common Occurrence of Massive Clusters in the Early Universe

“…The role of feedback in limiting the mass of a cluster is not clear. Ginsburg et al (2016) suggest that feedback has virtually no role and gas exhaustion stops star formation in the cluster, rather than gas expulsion (see also Girichidis et al 2012;Kruijssen 2012;Matzner 2017;Galván-Madrid et al 2017;Tsang & Milosavljević 2018;Silich & Tenorio-Tagle 2018;Cohen et al 2018;Ward & Kruijssen 2018). Also, there is no jump in the mass function of bound clusters at a mass of around 10 3 M ⊙ where ionization feedback suddenly increases as a result of the increasingly likely appearance of O-type stars (Vacca et al 1996).…”

On the early evolution of massive star clusters: the case of cloud D1 and its embedded cluster in NGC 5253

“…However, recent observations of nearby galaxies in infrared, millimeter and radio wavelengths revealed an obscured mode of star formation in such galaxies as SBS 0335-052 (Thuan et al 1999), He 2-10 (Vacca et al 2002), NGC 2366 (Oey et al 2017) and NGC 5253 (Turner et al 2015;Beck 2015;Turner et al 2017;Cohen et al 2018). The extension of the hidden star cluster phase is also required in some models of the multiple stellar generations formation in globular clusters (e.g.…”