An Etymological Dictionary of Astronomy and Astrophysics
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1) General: Drop of liquid; small round mass (e.g. wax); spot of color.
2) Astro.: A relatively → small, → unresolved source lying toward a much larger structure. → high-excitation blob.

From M.E. bubelen "to bubble."

Žig "drop," probably from žohidan "to drop," variant of cakidan "to drop."

A rare class of → H II regions in the → Magellanic Clouds. In contrast to the typical H II regions of the Magellanic Clouds, which are extended structures (sizes of several arc minutes corresponding to more than 50 pc, powered by a large number of exciting stars), HEBs are very dense and small regions (~ 4" to 10" in diameter corresponding to ~ 1-3 pc). They have a higher degree of → excitation ([O III] 5007Å /Hβ) with respect to the typical H II regions, and are, in general, heavily affected by local → dust. They are powered by a relatively smaller number of → massive stars.

→ high; → excitation; → blob.

A gigantic cloud of → hydrogen hydrogen gas emitting the → Lyman alpha line identified in → high redshift, → narrow band → surveys. LABs can span hundreds of thousands of → light-years that is larger than galaxies. Normally, Lyman alpha emission is in the ultraviolet part of the spectrum, but Lyman alpha blobs are so distant, their light is redshifted to (longer) optical wavelengths. The most important questions in LAB studies remain unanswered: how are they formed and what maintains their power? One of the largest LABs known is SSA22-LAB-01 (z = 3.1). Embedded in the core of a huge → cluster of galaxies in the early stages of formation, it was the very first such object to be discovered (in 2000) and is located so far away that its light has taken about 11.5 billion years to reach us. Recent observations of SSA22-LAB-01 using → ALMA shows two galaxies at the core of this object and they are undergoing a burst of → star formation that is lighting up their surroundings. These large galaxies are in turn at the centre of a swarm of smaller ones in what appears to be an early phase in the formation of a massive cluster of galaxies (see J. E. Geach et al. 2016, arXiv:1608.02941).

→ Lyman; → alpha; → blob.