Doctoral Thesis Old

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Tracing galaxies over the past 8 billion years, we found a correlation between their star formation activity and stellar mass (Noeske et al., 2007, Schreiber et al. 2015). This “main sequence” of star-formation suggests that galaxies evolved through a steady and self-regulated mode of star-formation, sustained by the accretion of cold gas along the cosmic web. Variations of the gas accretion rate on a Gyr timescale and internal gas transport can affect the star formation rate, leading to the apparent 0.3 dex dispersion of the main sequence (Tacchella et al., 2016). To constrain the mechanisms that cause the shape and dispersion of the main-sequence requires detailed observations of large and comprehensive samples of galaxies.
PhD project: We will constrain the star formation, dust content and temperature, and the gas content of several ten thousands of low redshift (z<0.4) galaxies. This requires a careful modelling of the far-infrared spectral energy distribution using the largest optical-to-submillimeter dataset available, the GAMA/H-ATLAS survey (Driver et al. 2016), employing innovative statistical methods (e.g., stacking). We will investigate variations of the dust and gas properties across and along the main-sequence and compare those with theoretical expectations. Combined with size measurements from GAMA, we will study the so called Schmidt-Kennicutt relation across and along the main-sequence, obtaining constraints on the physical conditions of star-formation within these galaxies. We will also explore the effects of large-scale cosmic environment on these relations. 
Literature: Driver et al. 2016, MNRAS, 455, 3911; Magnelli et al. 2014, A&A, 561, 86; Noeske et al., 2007, ApJ 660, 43; chreiber et al., 2015, A&A, 575, 74; Tacchella et al., 2016, MNRAS 457, 2790


Among the most pressing questions in galaxy evolution studies is how the total stellar mass assembled over cosmic time. Our understanding of the regulating cause of star formation in galaxies is poor, but over the past years a picture emerged in which the build-up of new stars is tightly related to the existing stellar mass (e.g. Karim et al. 2011, Magnelli et al. 2014, Schreiber et al. 2015). This suggests that a self-regulated gas-exchange of galaxies with their respective haloes relates to the small-scale, highly inefficient process of star formation (e.g., Bouché et al., 2010; Lilly et al., 2013; Peng et al., 2014; Rathaus et al. 2016). Given the hierarchical, violent assembly of the large-scale dark matter component of the Universe, this link is surprising and needs concrete observational evidence. A future confirmation or falsification of this gas-regulator model relies on better measurements of the gas content of galaxies across cosmic time.
PhD project: We will measure the gas content, gas surface density, and star formation surface density in representative samples of star forming galaxies across cosmic time. The gas content of galaxies is measured using deep and wide area millimeter “surveys” provided by the ALMA archive. Their star forming sizes will be inferred from our 3 GHz, 0.7 arcsec resolution radio continuum survey of the COSMOS field, extending results from Jimenez et al. (in prep.) towards low mass galaxies, using innovative statistical methods (e.g., stacking). By combining the gas and size measurements, we can measure for the first time the Schmidt-Kennicutt relation and its evolution across cosmic time. We will then explore the effects of the galaxy environment on the gas content of galaxies, which was suggested to be separable from the star formation-mass link (e.g. Peng et al. 2010).
This project is to be conducted within the Cologne-Bonn collaborative research center CRC 956, and in close collaboration with our international colleagues E. Schinnerer, D. Liu, V. Smolcic.
Literature: Bouché et al., ApJ 718, 1001, 2010; Karim et al. 2011, ApJ, 730, 61; Lilly et al., 2013, ApJ 772, 119; Magnelli et al. 2014, A&A, 561, 86; Peng et al., 2014, MNRAS 438, 262; Rathaus et al., 2016, MNRAS 458, 3168


We will investigate the physical, chemical and dynamical conditions of the star forming gas in high-redshift quasars and far-infrared selected starburst galaxies, and follow how this relates to the processes that shape galaxies and govern the formation of stars in the early universe. For this we will conduct high angular resolution imaging of CO, [CII], [NII] and continuum emission of redshift 2 to 7 quasars, using the IRAM PdBI, JVLA, and ALMA (Swinbank et al. 2012, Riechers et al. 2013, Decarli et al., 2017). We will search for new samples of high-redshift 4 to 6 far-infrared-selected galaxies, applying a blind [CII] line detection method to the ALMA archive. With high angular resolution follow-up of their [CII] line emission with ALMA/NOEMA, together with available observations (Jimenez-Andrade et al. 2018), we will study their dynamics and the gas conditions in which their intense star-formation occurred. We will compare [CII] observations of far-infrared selected galaxies and quasars, and in the long term plan blind spectral surveys of [CII] for the earliest star forming galaxies using ALMA and CCAT-prime, for which we shall define the first survey observations. We will identify and quantify the potential of far-infrared fine structure lines to provide new diagnostics that constrain physical parameters, such as average densities and temperatures in the star forming interstellar medium on sub-kpc scales.
This project is expected to be conducted within the Cologne-Bonn collaborative research center CRC 956, and in close collaboration with our international colleagues F. Walter, C. Carilli, A. Omont, R. Wang, V. Smolcic, X. Fan, et al. 
Literature:  Decarli et al., 2017, Nature, 545, 457; Swinbank et al. 2012, MNRAS, 427, 1066; Riechers et al. 2013, Nature, 496, 329; Jimenez-Andrade et al. 2018, A&A, 615, 25