Stellar population gradient in lenticular galaxies: NGC 1023, NGC 3115 and NGC 4203

Abstract

We investigate the stellar population content in the lenticular galaxies NGC 1023, NGC 3115 and NGC 4203 applying a population synthesis method based on a seven component spectral basis with different ages - 2.5*E⁶, 10*E⁶, 25*E⁶, 75*E⁶, 200*E⁶, 1.2*E⁹ and older than 10¹⁰ years, and metallicity in the range -1.3<= [Z/Z_sun] <=-0.2. This study employs two-dimensional STIS spectra in the range lambda lambda 2900-5700 Å, obtained from the Hubble Space Telescope public archives. We extracted one-dimensional spectra in adjacent windows 100 pc wide (projected distance) from the nuclear regions up to 300-400 pc. The largest contribution, both in lambda 5870 Å flux and mass fraction, comes from old stars (age >10¹⁰ years). We verified the possible existence of circumnuclear bursts (CNBs) in NGC 3115 and NGC 4203.