  News sharing on social networks reveals how information disseminates among
users. This process, constrained by user preferences and social ties, plays a
key role in the formation of public opinion. In this work we study news sharing
of main Argentinian media outlets in Twitter, using bipartite news-user
networks, in order to understand if the emergence of affinity groups is driven
by the underlying political polarization. We compare the results between an
electoral and non-electoral year and between a set of politically active users
and a control group. We found that users' behavior produces well differentiated
communities of news articles identified by a unique distribution of media
outlets in all analyzed datasets. In particular, these communities split into
two groups which reflect the dominant ideological polarization in Argentina. We
also found that users form two well differentiated groups identified by their
preferences in media outlets consumption. These two groups of media outlets
display a bias towards the two main political parties that rule the political
life in Argentina. These results reveal consistently that ideological
polarization is the main driving force shaping the Argentinian news sharing in
Twitter.
