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

Abstract

We investigate the stellar population content in the lenticular galaxies NGC1023, NGC3115 and NGC4203 applying a population synthesis method based on a seven component spectral basis with different ages – 2.5 × 106, 10× 106, 25× 106, 75× 106, 200 × 106,1 .2 × 109 and older than 1010 years, and metallicity in the range −1.3 ≤ [Z/Z ] ≤− 0.2. This study employs two-dimensional STIS spectra in the range λλ2900–5700 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 λ5870Å flux and mass fraction, comes from old stars (age > 1010 years). We verified the possible existence of circumnuclear bursts (CNBs) in NGC3115 and NGC4203.