Abstract: Understanding the nature of high-redshift dusty galaxies, the ancestors of most galaxies today, requires a comprehensive view of their interstellar medium (ISM) and molecular complexity. However, the molecular ISM at high redshifts is commonly studied using only a few species beyond CO, limiting our understanding. In this talk, I will present the results of deep 3 mm spectral line surveys using the NOrthern Extended Millimeter Array (NOEMA) targeting two lensed dusty galaxies observed when the Universe was less than 1.8 Gyr old: APM 08279+5255, a quasar at redshift z = 3.911, and NCv1.143, a z = 3.565 starburst galaxy. The spectral line surveys cover both galaxies' rest-frame frequencies from about 330 to 550 GHz. We report the detection of 38 and 25 emission lines in APM 08279+5255 and NCv1.143, respectively. The transitions originate from 17 species, namely CO, 13CO, C18O, CN, CCH, HCN, HCO+, HNC, CS, C34S, H2O, H3O+, NO, N2H+, CH, cC3H2, as well as the vibrationally excited HCN (HCN-VIB lines) and neutral carbon (fine-structure [CI] line). The spectra reveal the chemical richness and the complexity of the physical properties of the ISM. From these rich toolsets of molecular lines, we begin now to have a clearer picture of star formation, AGN, fueling and feedback, and structural formation of these galaxies, of which I will show some during this talk. Such deep spectral line surveys open a new window to study the physical and chemical properties of the ISM and the radiation field of galaxies in the early Universe.

Bio: Dr. Yangchen Tao is currently a postdoc at the Department of Space, Earth and Environment of the Chalmers University of Technology since November 2021. Previously, he was an European Southern Observatory (ESO) Fellow in Chile with duties at ALMA.  His research interests mainly focus on observing extragalactic objects via submm/mm windows. He primarily studies the molecular gas and dust contents in galaxies from the local to the high-redshift Universe. He is especially interested in water (a unique diagnostic tool of the interstellar medium). Besides being an active reviewer for journals like A&A, ApJ, PASJ, etc., he has also served as an external panel reviewer for telescopes, including HST, JWST and JCMT, as well as for funding organisations, including STFC (UK). He was also a selection committee member for the ESO (Chile) Fellow and ALMA Fellow at JAO.