During the late 60's and the beginning of the 70's it was discovered that many galaxies that were bright at optical wavelengths, were even brighter in the infrared (IR) range of the spectrum. All of these galaxies, regardless of the internal processes that generate their IR luminosity (whether it be star formation or AGN activity), showed more intense emission towards longer wavelengths with a maximum in the mid- and far-IR. However, it was not until the late 70's when it was confirmed that this radiation was due to ultraviolet and optical emission, which is absorbed, processed and re-emit at IR wavelengths by interstellar dust. This type of IR-bright objects caught the interest of the scientific community, and the first ground-based mid-IR photometric studies of large samples of galaxies with intense processes of star formation were carried out. It was also at this time that some works showed the role of interactions in triggering the star formation activity in the nuclei of IR-bright galaxies.

With the launch of the Infrared Astronomical Satellite (IRAS) in 1984, these systems were detected in large numbers and were classified based on their IR luminosities, basically in the so-called luminous and ultra-luminous IR galaxies (LIRGs and ULIRGs respectively). These systems are ten to hundred times more luminous than our own Galaxy but they are not very common in the local Universe and only represent a small amount of the total IR emission of the nearby Universe.

Nowadays the importance of LIRGs and ULIRGs in the grand scheme of galaxy evolution has been evinced by the IR luminosity functions in the local universe and at high-redshift. The Spitzer Space Telescope has provided new insights into not only local but also high-z (z>0.5) LIRGs and ULIRGs. Several cosmological surveys have demonstrated that the majority of IR-selected galaxies at z<1 are in the LIRG class and that ULIRGs make an important contribution to the IR galaxy population at 1Herschel Space Telescope.

Our group works in these topics as a partner in the Great Observatory All-sky LIRG Survey (GOALS) collaboration, a project that combines imaging and spectroscopic data from NASA's Spitzer, Hubble, Chandra, and GALEX space-borne observatories in a comprehensive study of over 200 of the most luminous infrared-selected galaxies in the local Universe. Our studies focus mainly on:

• A study the extended emission of a volume-limited sample of LIRGs drawn from the GOALS galaxy sample using high-sensitivity mid-IR spectroscopic data obtained with the Infrared Spectrograph (IRS) onboard Spitzer. Our goal is to determine the fraction and characteristics of the emission arising from the extended component (the disk) in these LIRGs. This will enable us to determine whether the high-redshift, higher-luminosity submillimeter galaxies (SMGs), which present very extended star-formation, could be the scaled-up luminosity examples of local LIRGs.

• Analysis of the physical properties of star-forming regions in local LIRGs, using high spatial resolution observations with Gemini/T-ReCS to determine whether their mid-IR emission (either from hot dust, from polycyclic aromatic hydrocarbons, or from emission lines) can be used to trace the star formation rate in these galaxies.

• Theoretical modeling of the total spectral energy distribution, from the UV to the far-infrared, using the detailed models of da Cunha et al. (2008).

• A. Psychogyios, V. Charmandaris, T. Diaz-Santos, L. Armus, S. Haan, J. Howell, E. Le Floc’h, S. M. Petty, and A. S. Evans "Morphological Classification of Local Luminous Infrared Galaxies", 2016, A&A, 591, 1
• L. Ciesla, V. Charmandaris, A. Georgakakis, E. Bernhard, P. D. Mitchell, V. Buat, D. Elbaz, E. LeFloc’h, C. G. Lacey, G. E. Magdis, and M. Xilouris, "Constraining the properties of AGN host galaxies with Spectral Energy Distribution modelling", 2015, A&Α, 576 10
• H. Inami, L. Armus, V. Charmandaris, B. Groves, L. Kewley, A. Petric, S. Stierwalt, T. Dıaz-Santos, J. Surace, J. Rich, S. Haan, J. Howell, A. Evans, J. Mazzarella, J. Marshall, P. Appleton, S. Lord, H. Spoon, D. Frayer, H. Matsuhara, S. Veilleux, "Mid-Infrared Atomic Fine-Structure Emission Line Spectra of Luminous Infrared Galaxies: Spitzer/IRS Spectra of the GOALS Sample", 2013, ApJ, 777, 156
• T. Diaz-Santos, L. Armus, V. Charmandaris, S. Stierwalt, E. Murphy, S. Haan, H. Inami, S. Malhotra, R. Meijerink, G. J. Stacey, A. Petric, A. Evans, S. Veilleux, P. van der Werf, S. Lord, N. Y. Lu, J. Howell, P.N. Appleton, J. Mazzarella, J. Surace, C. Bridge, Ben Chan, D. Frayer, K. Iwasawa, J. Melbourne, D. Sanders, B. Schulz, E. Sturm, and C.K. Xu., "Does [CII]157.7μm Emission Trace Current Star Formation in Luminous Infrared Galaxies? -- First Results from a Herschel/PACS Study of the GOALS Sample", 2013, ApJ, 774, 68
• S. Haan, J.A. Surace, L. Armus, A.S. Evans, J.H. Howell, J.M. Mazzarella, D.C. Kim, T. Vavilkin, H. Inami, D.B. Sanders, A. Petric, C.R. Bridge, J.L. Melbourne, V. Charmandaris, T. Diaz-Santos, E.J. Murphy, V. U, S. Stierwalt, J.A. Marshall, "The Nuclear Structure in Nearby Luminous Infrared Galaxies: HST NICMOS Imaging of the GOALS Sample", 2011, AJ, 141, 100
• A.O. Petric, L. Armus, J. Howell, B. Chan, J. Mazzarela, A.S. Evans, J.A. Surace, D. Sanders, P. Appleton, V. Charmandaris, T. Diaz-Santos, D. Frayer, S. Lord, S. Haan, H. Inami, K. Iwasawa, D. Kim, B. Madore, J. Marshall, H.W.W. Spoon, S. Stierwalt, E. Sturm, V. U, T. Vavilkin, S. Veilleux, "Mid-Infrared Diagnostics of Luminous Infrared Galaxies", 2011, ApJ, 730, 28
• E. da Cunha, V.Charmandaris, T. Dıaz-Santos, L. Armus, J. A. Marshall, and D. Elbaz, "Exploring the physical properties of local star-forming ULIRGs from the ultraviolet to the infrared", 2010, A&A, 523, A78
• T. Diaz-Santos, V. Charmandaris, A. O. Petric, L. Armus, J.H. Howell, E.J. Murphy, J.M. Mazzarella, S. Veilleux, G. Bothun, P.N. Appleton, A.S. Evans, H. Inami, S. Haan, J.A. Marshall, D.B. Sanders, S. Stierwalt, and J.A. Surace, "The Spatial Extent of (U)LIRGs in the mid-Infrared I: The Continuum Emission", 2010, ApJ, 723, 993