BULGES, BARS, AND DISCS IN THE NEARBY UNIVERSE.

An Anchor for High-Redshift Studies.

BULGES.It is now commonly accepted that bulges come in two flavours: classical and pseudobulges. The importance of understanding the demography of bulge types is clear since different formation mechanisms have been proposed to explain this dichotomy. Simulations predict that classical bulges form before the disc, via galaxy mergers (Kauffmann et al. 1993), dissipative collapse (Eggen et al. 1962) or coalescence of gas clumps in primordial discs (Bournaud et al. 2007). On the other hand, the formation of pseudobulges is driven by instabilities acting within the galactic disc (Kormendy & Kennicutt 2004). In the past I have tackled this problem using different approaches: studying the bulge scaling relations in the NIR (Méndez-Abreu et al. 2008), by exploring different diagnostics to separate bulge types (Méndez-Abreu et al. 2008) or by linking the three-dimensional shape of bulges with its type (Méndez-Abreu et al. 2010, Mendez-Abreu et al 2015). In Méndez-Abreu et al. (2014), we moved forward showing that different bulge types coexisting in the same galaxy are common in the Universe.

BARS AND DISCS. Bars represent the perfect hub for understanding galaxy evolution. Sitting in a middle point between the external disc and the central bulge, their evolution is mainly regulated by the disc properties but in turn they act as the main internal driver of pseudobulge formation (Athanassoula et al. 2005). Therefore, characterizing the properties of bars is crucial to gain new insights on bulge and disc evolution. During the last years I have studied the properties of bar structures in different environments: from the field (Aguerri, Méndez-Abreu et al. 2009) to clusters of galaxies (Méndez-Abreu et al. 2010; Méndez-Abreu et al. 2012). We firstly demonstrated that galaxy mass is the main driver of bar formation and the bimodal role of environment on bar formation. These results have confirmed previous hints on the mass dependent population of cold discs (Sanchez-Janssen, Méndez-Abreu et al. 2010).

COSMIC EVOLUTION OF BULGES, BARS, AND DISCS: In-situ evolution.

BULGES. The fossil approach described before has historically provided important information about bulge formation and evolution. However, a more complete view can only be achieved by studying the properties of galaxies distant enough in look-back time to reveal their in-situ. In particular, studying the demography of bulge types with cosmic time will provided new insights on the influence of merger vs secular processes on bulge formation. Recently, I started a project to study the properties of high-redshift bulges and their relation with those in the nearby Universe. This project has now become the building block of the Ph.D. thesis of Josh Argyle, that I am supervising at the University of St. Andrews. We have created a new code (MOGAL) to create libraries of mock galaxies at different redshifts including cosmological effects associated with: different spatial resolution sampling, surface-brightness dimming, K-correction, and colour evolution. The analysis of these libraries has been crucial to choose a suitable high-redshift sample to be compared with low-redshift.

BARS AND DISCS. Unlike discs, our current knowledge of the redshift evolution of bar properties is currently limited to a few number of works (Sheth et al. 2008). However, recent numerical simulations have found a characteristic epoch of bar formation, namely redshift z~0.8–1, which agrees well with bar fraction measurements at these redshifts. Furthermore, this seems to be also the epoch at which today’s spirals acquire their disc-dominated morphology (Krajlic et al. 2012). In Pérez et al. (2012) we studied the bar dynamical properties of galaxies until z~0.8. We found that bars always end close to the corotation radius, therefore implying that dark matter haloes central densities are not high enough to slow down them at any time. Recently, in Aguerri, Méndez-Abreu et al. (2015) we found similar results in the local Universe using a sample of barred galaxies in CALIFA. All these results suggest that the dynamical evolution of bars is less strong than predicted by numerical simulation therefore imposing new constraints on bar formation models. On the other hand, as part as the Ph.D. project of my student Rodrigo Hinojosa-Goñi, we have studied the photometric properties of the host galaxy in a sample of starburst galaxies until redshift z~1. We found that they are well described by an exponential profile indicating the presence of previously formed discs at those redshifts (paper in prep.).