Local Galaxies


Galaxies in the Local Universe are a privileged window for the modern observational cosmology. Thanks to their vicinity, today multi-wavelength observations map a so wide wealth of morphological, kinematical, structural details, unconceivable for distant galaxies, able to feed, proof/disproof theories about their formation and evolution. Furthermore, local galaxies inhabit widely different environments, from which their evolution itself is influenced, from rich cluster, to groups, to scarcely populated regions. A comparative investigation allows to avoid large biases on galaxy evolutionary studies.

A large number of research programs developed at OAPd are devoted to the study of local galaxies, from both an observational and a theoretical point of view. Observational programs are performed both applying to top ranked ground based instrument (VLT, LBT...) and to space facilities (XMM, Chandra, HST ) and mining data bases either generated by large ground based observational endeavors (e.g. SDSS) or heritage of recent/on-going space missions (HST, GALEX, Spitzer, XMM, Chandra ...). The evolved nature of local galaxies requires a special  archeological approach that makes use of a constant effort of comparison with theory for a correct interpretation of observations. Theoretical and computational programs rely on the usage of the most advanced available computational facilities (supercomputers at CINECA and all around Europe), and are aimed to perform high-resolution simulations of star formation, galaxy evolution and galaxy interactions.

Many observational and theoretical studies focus on Early-Type galaxies (E + S0s, ETGs). Although ETGs are historically considered as a unique class of galaxies, Ellipticals are thought to be the fossil evidence of the galaxy evolution driven by merging episodes, while S0s are considered the result of secular evolution, likely due a progressive to gas depletion. At OAPd we attempt to understand the evolution of ETGs studying their spectral energy distribution (SED) from the far UV (GALEX), to optical and NIR (VLT X-shooter) up to Mid Infrared (Spitzer). We devised a new MIR galaxy spectral classification which separates passively evolving from still active (star forming and/or AGN-like) ETGs, using the properties of their interstellar medium (ISM). In MIR the ISM presents ionic and molecular emissions as well as emission from Polycyclic Aromatic Hydrocarbon (PAH) complexes. We are investigating transition classes, showing H2 emission lines and anomalous PAH emissions ratios, suggesting that these represent phases of the ISM evolution during an accretion episode. In this framework, we are extending the MIR spectral classification to all ETGs in the Revised Shapley Ames catalogue having a high S/N Spitzer-IRS observation.

We are studying ETGs and late-type galaxies in very poor and loose environments, the natural complement of the nearby galaxy rich Virgo Cluster. We are characterizing such poor environments, showing a different fraction of ETGs, using Far UV vs. optical Color Magnitude Diagrams. Far UV (GALEX) and optical (SDSS) observations combined with 2D Fabry-Perot kinematic observations are used to identify morphological and kinematical signatures of interaction and/or other mechanisms which may induce galaxy evolution within a specific environment. Galaxy SEDs are investigated to derive the evolutionary history of prototypical galaxies from comparison with cosmological chemo-photometric SPH simulations. X-ray observations (XMM, SWIFT) of ETGs in low density environments, especially in groups, are also obtained to investigate the evolution of the hot gas component, quite relevant in ellipticals, both in the galaxy and in the group.

The role of minor mergers and accretion episodes in rejuvenating ETG galaxies is also studied by means of N-body smoothed particle hydrodynamics (SPH) and adaptive mesh refinement (AMR) simulations. These simulations adopt some the best available N-body codes (gasoline, GADGET, RAMSES) together with the most updated recipes for cooling, star formation rate and feedback from massive stars, in order to investigate the evolution of gas and stars during and after any merger event.



Figure: Color composite image (left panel GALEX; right panel SDSS) of the interacting pair NGC 3447/3447A in LGG 225. The strongly interacting is modifying the galaxy original structure and inducing a star formation rate of about 2 solar masses per year.





Local galaxies: past studies

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