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Paper text:
brightest cluster galaxies ( bcgs ) are the brightest and most massive galaxies in the universe .
they form within galaxy clusters , and generally lie near the bottom of the cluster gravitational potential well .
they have unique properties , including extended light profiles , and they are brighter than the cluster luminosity function leads us to expect @xcite .
these properties differentiate them from other elliptical galaxies .
most bcgs can be readily identified in observations as a result of their brightness and dominance within a galaxy cluster .
additionally , n - body simulations can be carried out to create mock galaxy clusters , which also contain readily - identifiable bcgs .
these observed and simulated bcgs can be directly compared , and this allows us to test models that describe the growth of these bcgs - a task that is difficult to do with galaxies in general as a result of the large variety of different types of galaxies , with varying formation histories .    initially , there was considerable disagreement between the models and the observations , with models predicting a factor of three increase in the stellar mass of bcgs between @xmath1 and today ( * ? ? ? * hereafter referred to as dlb07 ) , and observations showing little growth over the same redshift interval ( see * ? ? ? * for example ) .
while more recent models @xcite and observations @xcite are now in better agreement with one another with both predicting or showing a doubling of the stellar mass since @xmath2 , there is still some disagreement as to when this growth occurs . in the semi - empirical model of @xcite ,
the stellar mass of bcgs continues to increase to the present day .
however , in the semi - analytic model of @xcite , the growth appears to stall after @xmath3 .
there is some observational support for the second model .
@xcite find that most of of the growth since @xmath4 occurs in the redshift range @xmath5 .
similarly , @xcite find no significant growth in the range @xmath6 , and @xcite , who explores the redshifts range @xmath7 , find an increase of between 2 and 14% .
in contrast to these results , @xcite find an increase of 50% between @xmath8 and @xmath9 , and @xcite find an increase of 35% between @xmath1 and the present day .
the aim of this study is to make a more detailed measurement of the growth of bcgs using new data that covers the redshift interval over which the growth appears to stall .
the paper is outlined as follows . 
[ sec : data ] describes the data used and the steps used to process them , and  [ sec : stelmasdet ] outlines how the stellar masses of the bcgs and clusters within the sample were determined .
the analysis of the data is carried out in  [ sec : analysis ] , and the discussion and conclusions are presented in  [ sec : discussion ] and  [ sec : conclusion ] respectively . throughout this paper
we use vega magnitudes , and assume a @xmath10cdm cosmology with @xmath11 , @xmath12 and @xmath13 .
we utilise a sample of 98 newly imaged galaxy clusters from the relics survey within this study .
the data were collected during 6 observing runs on three instruments over a period spanning from october 2013 to march 2015 .
the instruments utilised were the sofi camera on the new technology telescope at the eso la silla observatory in chile @xcite , whirc on the wiyn telescope at the kitt peak national observatory @xcite and liris on the william herschel telescope in la palma , spain .
the observing runs are summarised in table [ observingruns ] .
using a sample of 98 galaxy clusters recently imaged in the near infra - red with the eso ntt , wiyn and wht telescopes , supplemented with 33 clusters from the eso archive , we measure how the stellar mass of the most massive galaxies in the universe , namely brightest cluster galaxies ( bcg ) , increases with time . 
 most of the bcgs in this new sample lie in the redshift range @xmath0 , which has been noted in recent works to mark an epoch over which the growth in the stellar mass of bcgs stalls . from this sample of 132 clusters , 
 we create a subsample of 102 systems that includes only those clusters that have estimates of the cluster mass . 
 we combine the bcgs in this subsample with bcgs from the literature , and find that the growth in stellar mass of bcgs from 10 billion years ago to the present epoch is broadly consistent with recent semi - analytic and semi - empirical models . as in other recent studies , tentative evidence indicates that the stellar mass growth rate of bcgs may be slowing in the past 3.5 billion years . 
 further work in collecting larger samples , and in better comparing observations with theory using mock images is required if a more detailed comparison between the models and the data is to be made .    
 [ firstpage ]    galaxies : elliptical and lenticular , cd - galaxies : evolution - galaxies : clusters : general