Starbursting Nuclei in Old Dwarf Galaxies

• Published in: Astrophysical journal. Letters Vol. 898; no. 2; p. L47
• Main Authors: Paudel, Sanjaya, Yoon, Suk-Jin
• Format: Journal Article
• Language: English
• Published: Austin The American Astronomical Society 01.08.2020; IOP Publishing
• Subjects: Dwarf galaxies; Early-type galaxies; Emission lines; Nucleated dwarf galaxies; Nuclei; Sky surveys (astronomy); Space telescopes; Spectroscopy; Star formation; Stars & galaxies; Stellar mass; Stellar populations; Virgo Cluster
• ISSN: 2041-8205; 2041-8213
• DOI: 10.3847/2041-8213/aba6ed

Nuclei of early-type dwarf galaxies (dEs) are usually younger than the galaxy main body, and this discrepancy in age has been a puzzle. To explore the origin of young nuclei in dEs, we study a sample of dEs having compact star-forming blobs that are visually similar to dEs' nuclei but by far bluer. We find that (1) the compact star-forming blobs have a typical stellar mass of one percent of the host galaxy stellar mass; (2) some of the blobs are positioned slightly off from the center of the galaxies; (3) the H equivalent width measured from the publicly available Sloan Digital Sky Survey fiber spectroscopy shows their formation ages being an order of few megayear; (4) their emission line metallicities, 12 + log(O/H), are as high as the solar value, while the underlying galaxies have the typical stellar populations of dEs, i.e., log(Z/Z ) ∼ −0.8. Based on the results, we argue that the central star-forming blobs can provide a caught-in-the-act view of nuclei formation in dEs, and discuss possible formation mechanisms of young nuclei in old dEs. We particularly propose that these off-centered compact star-forming regions may act as seeds of nuclei as proposed in the "wet migration" scenario of Guillard et al.