Nuclear star-forming structures and the starburst-active galactic nucleus connection in barred spirals: NGC 3351 and NGC 4303

Publication date: 
Main author: 
Colina L.
IAA authors: 
Alberdi A.
Colina L., Vargas M.L.G., Mas-Hesse J.M., Alberdi A., Krabbe A.
Astrophysical Journal
Publication type: 
A high-resolution Hubble Space Telescope WFPC2 F218W UV image of the barred spiral NGC 4303 (classified as a LINER-type active galactic nucleus [AGN]) reveals for the first time the existence of a nuclear spiral structure of massive star-forming regions all the way down to the UV-bright unresolved core (size ≤ 8 pc) of an active galaxy. The spiral structure, as traced by the UV-bright star-forming regions, has an outer radius of 225 pc and widens as the distance from the core increases. The UV luminosity of NGC 4303 is dominated by the massive star-forming regions, and the unresolved LINER-type core contributes only 16% of the integrated UV luminosity. The nature of the UV-bright LINER-type core - stellar cluster or pure AGN - is still unknown. In contrast to NGC 4303, the UV F218W image of the non-AGN barred galaxy NGC 3351 shows a nuclear star-forming ring of 315 pc (semimajor axis) with a faint core. In the ring, the star formation is arranged in clumps of about 60-85 pc in diameter. Each clump consists of a few compact UV-bright clusters embedded in a more diffuse component. The integrated IUE spectrum of NGC 3351 shows the presence of Si IV 1400 Å and C IV 1550 A absorption lines, typical features of young, 4-5 Myr old, massive star clusters. The presence of ring and spiral star-forming structures in the nuclear regions of these two barred spirals supports the bar-induced gas-fueling scenario by which bars accumulate gas in the nuclear regions of galaxies, produce nuclear star-forming rings (NGC 3351), and might eventually generate or feed an AGN (NGC 4303). © 1997. The American Astronomical Society. All rights reserved.
Galaxies: active; Galaxies: nuclei; Galaxies: spiral galaxies: starburst galaxies: star clusters; Ultraviolet: galaxies