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

TL;DR

This study presents multi-wavelength observations of a tadpole-shaped nebula in Cygnus, revealing its molecular composition, structure, and the influence of nearby stellar radiation and winds shaping its morphology.

Contribution

It provides detailed imaging and analysis of the Tadpole nebula and surrounding structures, highlighting the effects of ultraviolet radiation and ram pressure in shaping molecular cores.

Findings

The Tadpole nebula is predominantly molecular with over 3.7 solar masses.

Nearby tadpole-shaped objects share a common orientation, indicating a shared formation process.

Ripples in the tail suggest instabilities at wind-medium interfaces.

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.