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lenticular ( s0 ) galaxies are often seen as an endpoint in the evolution of spiral galaxies since they display the same discy morphologies as spirals , but contain older stellar populations . in order to transform a spiral into an s0 , the star - formation in the disc must be truncated and the bulge luminosity enhanced @xcite . therefore , to understand how these two phenomena occur , we need to study the individual star - formation histories of the bulges and discs
a sample of 21 s0s from the virgo cluster were used in this study , with b - band magnitudes in the range of @xmath0 to @xmath1 and inclinations above 40 degrees to reduce contamination from misclassified ellipticals .
a long - slit spectrum was obtained along the major axis of each galaxy using gemini - gmos with typical exposure times of .
the reduced spectra were decomposed using the spectroscopic bulge 
disc decomposition technique of @xcite , in which light profile of the galaxy in each wavelength bin was separated into bulge and disc components by fitting a srsic bulge plus exponential disc model . having found the best fit and obtained the decomposition parameters for each wavelength bin , the total light from each component was then calculated by integration , and plotted against wavelength to create two one - dimensional spectra representing purely the bulge and disc light .    the ages , metallicities and mgb/@xmath2fe@xmath3 ratios of the bulges and discs were measured using the strengths of the absorption features in the decomposed spectra .
it can be seen in fig .
[ fig : johnston_fig1 ] that the bulges contain systematically younger and more metal rich stellar populations than their associated discs , suggesting that a final star - formation event occurred in the bulge region during the transformation .
additionally , a comparison of the mgb/@xmath2fe@xmath3 ratios for the bulges and discs , also shown in fig .
[ fig : johnston_fig1 ] , reveals a correlation , indicating that their star - formation histories are linked .
fe@xmath3 ratios for the bulges and discs .
errors are shown on the right of each plot . ]
we find that during the transformation from a spiral to an s0 , gas is stripped from the disc gently enough that no significant amounts of star formation were triggered there . at some point ,
a final star - formation event occurs in the bulge region , resulting in younger , more metal rich stellar populations there .
the most likely origin of the gas that fuelled this star formation is from the associated disc , which appears to be true from the clear correlation in the chemical enrichment of the the bulges and discs .
together , these results present a scenario for the transformation of spirals to s0s in which gas is stripped gently from the disc , while the residual gas is channelled in towards the centre of the galaxy .
eventually , this gas induces a final episode of star formation within the bulge , which uses up all the remaining gas and boosts the luminosity of the bulge relative to the disc .
the whole galaxy then fades to an s0 .
clearly , further information on the transformation can be obtained if the decomposition was carried out in two dimensions using integral field unit ( ifu ) data .
the up - coming ifu mapping of nearby galaxies at apo ( manga , bundy et  al , submitted to apj ) survey in sdss - iv promises the resolution and wide field of view that will answer the remaining questions about how the bulge and disc star - formation histories are linked .
ej acknowledges support from the stfc , the iau and the ras .
by studying the individual star - formation histories of the bulges and discs of lenticular ( s0 ) galaxies , it is possible to build up a sequence of events that leads to the cessation of star formation and the consequent transformation from the progenitor spiral . in order to separate the bulge and disc stellar populations 
 , we spectroscopically decomposed long - slit spectra of virgo cluster s0s into bulge and disc components . 
 analysis of the decomposed spectra shows that the most recent star formation activity in these galaxies occurred within the bulge regions , having been fuelled by residual gas from the disc . 
 these results point towards a scenario where the star formation in the discs of spiral galaxies are quenched , followed by a final episode of star formation in the central regions from the gas that has been funnelled inwards through the disc .