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Finding Signatures of the Youngest Starbursts

Chip Kobulnicky·Kelsey E. Johnson
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Abstract

Embedded massive starclusters have recently been identified in several nearby galaxies by means of the radio-wave thermal bremsstrahlung emission from their surrounding HII regions. Energy requirements imply that these optically-obscured starclusters contain 500-1000 O-type stars, making them similar to the ``super starclusters'' observed in many dwarf starbursts and mergers. Based on their high free-free optical depth and visual extinctions of A_V>>10 mag., these massive ``ultra-dense'' HII regions (UDHIIs) are distinct signatures of the youngest, most compact super starclusters. UDHII regions may represent the earliest stages of globular cluster formation. We review the properties of presently-known UDHIIs, and we outline a pictoral evolutionary taxonomy for massive cluster formation which is analogous to the more familiar evolutionary sequence for individual stars.

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Chip Kobulnicky, Kelsey E. Johnson. 2000-11-22. Finding Signatures of the Youngest Starbursts. https://arxiv.org/abs/astro-ph/0011409

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