The Amleth Nebula is an emission nebula located in the Cardassian Union. The entire Amleth system is located with it.
Prior to 2318, Kotan Pa'Dar had told his family he was studying the Amleth Nebula, although the nebula had been studied extensively prior to that year. (DS9 novel: Day of the Vipers)
In 2372, Skrain Dukat suggested that the Klingon bird-of-prey he and Kira Nerys were tracking might attempt an assault on Amleth Prime, although Kira pointed out the emissions from the nebula would render their cloaking device useless. (DS9 episode: "Return to Grace")