Detection of He++ ion in the star-forming ring of the Cartwheel using MUSE data and ionizing mechanisms
Mayya, Y.D.; Plat, A.; Gomez-Gonzalez, V.M.A.; Zaragoza-Cardiel, J.; Charlot, S.; Bruzual, G.
We here report the detection of the nebular HeII4686 line in 32 HII
regions in the metal-poor collisional ring galaxy Cartwheel using the
Multi-Unit Spectroscopic Explorer (MUSE) dataset. The measured
I(HeII4686)/I(Hbeta) ratio varies from 0.004 to 0.07, with a mean value
of 0.010+/-0.003. Ten of these 32 HII regions are coincident with the
location of an Ultra Luminous X-ray (ULX) source. We used the flux
ratios of important diagnostic lines and results of photoionization by
Simple Stellar Populations (SSPs) to investigate the likely physical
mechanisms responsible for the ionization of He+. We find that the
majority of the regions (27) are consistent with photoionization by star
clusters in their Wolf-Rayet (WR) phase with initial ionization
parameter -3.5