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Stellar populations in LIRGs and post-Starburst QSOs : the case of the LIRG NGC 2623

Clara Cortijo (Instituto de Astrofísica de Andalucía, Granada)

Most up to date numerical simulations show that major gas-rich mergers, like those ongoing in (U)LIRGs, induce radial gas inflows to the nuclear regions where it generates massive star formation and black hole accretion. Subsequently, feedback from the active galactic nucleus (AGN) removes the gas and dust and quenches star formation and black hole activity (Di Matteo et al. 2005). The final stage of the merger, once the system has relaxed is the formation of an elliptical galaxy (Kormendy & Sanders 1992, Barnes & Hernquist 1996).

The merger-driven evolution between LIRGs and QSOs was originally proposed by Sanders et al. (1988), and has nowadays plenty observational evidences, including the discovery of transition objects in the evolutionary path, like the post-Starbursts QSOs (Brotherton et al. 1999).

The goal of my PhD is to determine and compare the stellar population properties, star formation histories and ionization structure of two small samples of LIRGs and post-SBs QSOs in order to look for additional evidences of their evolutionary link.

For this purpose I am analysing high-resolution HST broadband imaging data and IFS data from PMAS@CAHA and VIMOS@VLT.

Using Starlight code (Cid Fernandes et al. 2005) and stellar populations synthesis models (González Delgado et al. 2005 and Vazdekis et al. 2010) we fit the optical spectral continuum in the data cubes to derive the stellar population properties.

In this talk I will expose the main motivations of our work and the methodology we are applying. As a case of study I will show the results we are obtaining for the local merging LIRG NGC2623.

This system is dominated by a post-starburst population with ages between 100 Myr – 2 Gyr. There is also a younger stellar population of less than 30 Myr contributing to 40-50% of the nuclear light, but which represents less than 1% of its total stellar mass.

As the IFS provides us with spatially resolved spectral information, we are able to compare the differences in the SP properties along the whole extension of the system.

Currently, we are comparing some of our observational results with Galmer database simulations (Di Matteo et al.). The final goal is to understand the dynamical merger process that could have led to a system like NGC2623 and to be able to make predictions about its future evolution.