Properties of the interstellar medium in distant star-forming galaxies

Galaxies assemble theirs stellar mass mostly in long timescales at a moderate rate although stochastic episodes can trigger a starburst pushing the star formation rate to extreme values for short time. The evolution of galaxies then ends with the quenching of star-formation well below the average values, possibly because of the activity of the central black hole, capable of injecting large amount of energy into the galaxy interstellar medium via outflows. Understanding the details of galaxy growth, the modes in which stars are formed within galaxies and how galaxies are quenched are still hotly debated topics and studying the properties of star-forming galaxies and the connection with the activity of the central black hole can shed light on the different mechanisms shaping galaxies across cosmic time. Star-formation episodes, black hole and outflow activity in galaxies are mainly constrained through observations in the UV-optical regime but this wavelength range is heavily affected by dust obscu- ration. As such, modeling the effect of dust on the galaxy spectrum is essential. This Thesis uses near-IR spectroscopic observations to study dusty star-forming galaxies at 0.7 ≤ z ≤ 2.5 to analyze their dust attenuation properties and investigate their ionized gas features. The sample analyzed in this work includes galaxies representative of the average star-forming population at high redshift, starburst galaxies forming stars at an exceptional rate as well as galaxies hosting an active galactic nucleus (AGN). For a sample of 79 Herschel-selected “normal” galaxies at 0.7 z 1.5 I use HST slitless spec- troscopy in the near-IR to study the attenuation on the Hα emission line. I study the Hα dust attenua- tion as a function of integrated parameters (i.e. M⋆ , S FRFIR and continuum dust attenuation) derived via spectral energy distribution fitting of the high-quality, ancillary photometric coverage from UV to far-IR. I show that the Hα emission line and the continuum are attenuated by a similar amount, unlike in the local Universe. Furthermore, I show that the Hα attenuation grows with stellar mass and this trend deviates from the local relation towards higher values of dust attenuation. Both results hint an evolution of dust attenuation properties with redshift and galaxy parameters. I also analyze the near-IR spectra of twelve starburst galaxies at z ∼ 1.6 using fiber spectroscopy from FMOS at Subaru. I measure the metal content showing that z ∼ 1.6 starbursts are metal rich, suggesting a rapid enrichment and/or a negligible role of major pristine gas inflow from the cosmic web in enhancing the star-formation. I also show tentative indications of larger density than “normal” star-forming galaxies as well as a larger ionization parameter. Most importantly, I demonstrate that the effects of dust are dramatic in this class of objects. From a comparison between dust attenuation indicators, I show in fact that ∼ 90% of star-formation is buried in heavily obscured cores so that rest-frame optical wavelengths do not provide a complete overview of starburst sources. I discuss the implications of these findings for the interpretation of distant dusty starbursts. I provide a toy model to describe the dust attenuation and distribution in these objects, warning that the metal content and interstellar medium (ISM) conditions of the most star-forming regions remain unconstrained. To better understand the connection between black hole accretion and star-forming activity, I present a preliminary study of the AGN-dominated sources among starburst galaxies at z ∼ 1.6. I use FMOS near-IR spectra to constrain their dust attenuation, finding indications that it is lower than in the star-forming parent sample. I discuss the detection of a blue-shifted component in the [OIII]5007 emission observed in the near-IR spectrum of these AGN-starbursts at z ∼ 1.6 indicating the presence of outflowing material. Furthermore, a visual inspection of the morphology reveals that AGN reside in interacting pairs more compact than star-formation dominated starbusts. If confirmed, all these preliminary results would provide strong support to the idea that AGN are cleaning their environment from dust after a buried star-formation dominated phase, a picture theorized since 30 years but not yet firmly proved. Finally, I introduce Integral Field Spectroscopic techniques in the context of the SUPER survey, an ongoing large program with SINFONI designed to unveil the role of the AGN in the life-cycle of z ∼ 2 star-forming host galaxies. IFS observations are key to add the geometrical information to the study of outflows as well as star-formation processes I present the scientific analysis on a test case from preliminary SUPER observations, to discuss the potential of SUPER observations in obtaining a complete overview of the AGN-driven outflow physics, its link with the AGN and galaxy properties and its impact on the life of the latter. Overall, this Thesis demonstrates that spectroscopic techniques are a powerful tool for constraining the properties of high-z dusty star-forming galaxies. This work also stresses the importance of a parallel, careful study of the multi-wavelength SED of galaxies spanning the electromagnetic spec- trum from the UV to the far-IR. The results presented through this work have been possible thanks to the use of multi-wavelength techniques, the ultimate approach to tackle open problems in Galaxy Evolution studies.Le galassie assemblano la loro massa stellare per lo più in tempi lunghi a un ritmo moderato, sebbene episodi stocastici possano innescare una esplosione di stelle che spinge il tasso di formazione delle stelle a valori estremi per un breve periodo di tempo. L'evoluzione delle galassie termina infine con l'estinzione della formazione stellare ben al di sotto dei valori medi, probabilmente a causa dell'attività del buco nero centrale, in grado di iniettare grandi quantità di energia nel mezzo interstellare della galassia attraverso potenti venti, detti outflow. Capire i dettagli della crescita della galassia, i modi in cui le stelle si formano all'interno delle galassie e il modo in cui le galassie si estinguono sono argomenti ancora dibattuti e studiare le proprietà delle galassie che formano le stelle e la connessione con l'attività del buco nero centrale può far luce su i diversi meccanismi che modellano le galassie nel tempo cosmico. Gli episodi di formazione stellare, il buco nero e l'attività di outflow nelle galassie sono principalmente studiati tramiteosservazioni nel regime ottico-UV, ma questo intervallo di lunghezze d'onda è fortemente influenzato dall'oscuramento della polvere. Pertanto, è essenziale modellare l'effetto della polvere sullo spettro della galassia. Questa tesi utilizza osservazioni spettroscopiche near-IR per studiare galassie ricche di polvere e con un elevato tasso di formazione stellare a 0,7 ≤ z ≤ 2,5 per analizzare le loro proprietà di attenuazione della polvere e indagare le caratteristiche del gas ionizzato contenuto in esse. Il campione analizzato in questo lavoro include galassie rappresentative della popolazione media di galassie, galassie "starburst:, che formano stelle con tassi molto piu elevati rispetto alla popolazione media e galassie che ospitano un nucleo galattico attivo (AGN). Per un campione di 79 galassie "normali" selezionate da osservazioni del telescopio Herschel a 0,7<z