Chemically distinct nuclei and circumnuclear rings in lenticular galaxies NGC 4429 and NGC 7013^*

¹ Sternberg Astronomical Institute, University Av. 13, Moscow 119899, Russia
² Isaac Newton Institute of Chile, Moscow Branch
³ UK Astronomy Data Centre, Guest Investigator
⁴ Special Astrophysical Observatory, Nizhnij Arkhyz 369167, Russia

Corresponding author: O. K. Sil'chenko, olga@sai.msu.su

Received: 12 September 2001
Accepted: 13 December 2001

Abstract

The central regions of the regular lenticular galaxies NGC 4429 and NGC 7013 have been studied with the Multi-Pupil Field (Fiber) Spectrograph (MPFS) of the 6 m telescope of the Special Astrophysical Observatory RAS (Nizhnij Arkhyz, Russia) in two spectral ranges, the blue one including the strong absorption lines and and the red one including the emission lines Hα and []λ6583. We confirm the presence of the chemically distinct nucleus in NGC 7013 reported earlier. Besides this unresolved (in the magnesium index) structure, we have found a ring of younger stellar populations than those in the nucleus and in the bulge; the radius of this ring is about 6´´ (400 pc). A similar ring, distinguished by high magnesium- and iron-index values and bordered by Hα emission at its inner edge, with a radius of 6´´ (500 pc), is found in NGC 4429. We try to relate the ringed structure of the chemically decoupled cores in these galaxies with past, now dissolved, large-scale bars whose remnants are now seen in NGC 4429 and NGC 7013 as lenses between the bulges and global disks. An analysis of the gas and star kinematics in the centers of the galaxies has revealed the presence of an inclined circumnuclear disk in NGC 7013 and the existence of minibar in NGC 4429.