Stellar populations in spiral bulges are investigated using the Lick system of spectral indices .
Long-slit spectroscopic observations of line-strengths and kinematics made along the minor axes of four spiral bulges are reported .
Comparisons are made between central line-strengths in spiral bulges and those in other morphological types ( elliptical , spheroidal ( Sph ) and S0 ) .
The bulges investigated are found to have central line-strengths comparable with those of single stellar populations of approximately solar abundance or above .
Negative radial gradients are observed in line-strengths , similar to those exhibited by elliptical galaxies .
The bulge data are also consistent with correlations between Mg _ { 2 } , Mg _ { 2 } gradient and central velocity dispersion observed in elliptical galaxies .
In contrast to elliptical galaxies , central line-strengths lie within the loci defining the range of < Fe > and Mg _ { 2 } achieved by Worthey ’ s [ Worthey 1994 ] solar abundance ratio , single stellar populations ( SSPs ) .
The implication of solar abundance ratios indicates significant differences in the star formation histories of spiral bulges and elliptical galaxies .
A “ single zone with in-fall ” model of galactic chemical evolution , using Worthey ’ s [ Worthey 1994 ] SSPs , is used to constrain the possible star formation histories of our sample .
We show that the < Fe > , Mg _ { 2 } and H { \beta } line-strengths observed in these bulges can not be reproduced using primordial collapse models of formation but can be reproduced by models with extended in-fall of gas and star formation ( 2-17 Gyr ) in the region modelled .
One galaxy ( NGC 5689 ) shows a central population with a luminosity weighted average age of \sim 5 Gyr , supporting the idea of extended star formation .
Kinematic substructure , possibly associated with a central spike in metallicity , is observed at the centre of the Sa galaxy NGC 3623 .