Shocked and Scorched: The Tail of a Tadpole in an Interstellar Pond

Abstract

We report multi-wavelength observations of the far-infrared source IRAS 20324+4057, including high-resolution optical imaging with HST, and ground-based near-infrared, millimeter-wave and radio observations. These data show an extended, limb-brightened, tadpole-shaped nebula with a bright, compact, cometary nebula located inside the tadpole head. Our molecular line observations indicate that the Tadpole is predominantly molecular, with a total gas mass exceeding 3.7 Msun. Our radio continuum imaging, and archival Spitzer IRAC images, show the presence of additional tadpole-shaped objects in the vicinity of IRAS 20324+4057 that share a common E-W head-tail orientation: we propose that these structures are small, dense molecular cores that originated in the Cygnus cloud and are now being (i) photoevaporated by the ultraviolet radiation field of the Cyg OB2 No. 8 cluster located to the North-West, and (ii) shaped by ram pressure of a distant wind source or sources located to the West, blowing ablated and photoevaporated material from their heads eastwards. The ripples in the tail of the Tadpole are interpreted in terms of instabilities at the interface between the ambient wind and the dense medium of the former.

(accepted by the Astrophysical Journal)

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• The Kelvin-Helmholtz instability in Orion: a source of turbulence and chemical mixing
• Are Large, Cometary-Shaped Proplyds really (free-floating) EGGs?
• Probing X-ray photoevaporative winds through their interaction with ionising radiation in cluster environments: the case for X-ray proplyds
• Illuminating a tadpole's metamorphosis II: observing the on-going transformation with ALMA
• The Kelvin-Helmholtz instability in the Orion nebula: The effect of radiation pressure
• Irradiated Interfaces in the Ara OB1, Carina, Eagle Nebula, and Cyg OB2 Massive Star Formation Regions
• Radio observations of evaporating objects in the Cygnus OB2 region
• Shock waves in Interstellar Cloud-Cloud and Wind-Cloud Collisions