The role of mergers in triggering AGNs and starbursts
Silva Bustamante, Andrea.
Abstract: In this thesis I present three studies aiming at understanding the role of mergers and environment in triggering active galaxies and starbursts. First, I describe a study of the star formation properties of a sample of galaxy mergers at 0.3 < z < 2.5 with galaxy nuclei separations of 3-15 kpc and identi- fied in the CANDELS/3D-HST surveys by using a recent method to select mergers (Chapt... read moreer 2). The sample of mergers lie at the interface between early-stage merg- ers selected in close galaxy pairs and post-merger galaxies which present disturbed morphologies. The star formation properties of the 168 merging systems identified with this method are compared with those of non-merging galaxies (Chapter 3). We find no significant difference in the star formation activity when galaxies with masses log(M/M⊙) > 10 are compared. However, at lower masses, a higher fraction of star-bursting galaxies is found in the merging systems compared to non-merging systems at the same stellar mass. We also find that the members in the merger with lower masses are more affected by the interaction, since they present higher specific star formation rates compared to the higher mass galaxy in the system. Second, I present preliminary results in a study of the incidence of AGNs in galaxy mergers (Chapter 4). We use a subsample of mergers found in Chapter 3 (mergers in the COSMOS field) and cross-match with the Chandra COSMOS- Legacy Survey in order to search for X-ray selected AGNs in this sample. We find that the total fraction of AGNs in mergers is higher (∼15%) than in non-merging galaxies (∼5%). However, no trend in the fraction of AGNs as a function of redshift and nuclei projected separation is found with this small sample (60 merging galax- ies out of which 9 have AGNs). These preliminary results suggest that merging has an impact in the triggering of AGNs. More conclusive results will be found as more ii merger samples are included from the other four CANDELS fields and by selecting AGNs based on radio and MIR observations. In Chapter 5, I present a study of the environments of 49 hyper-luminous, heav- ily obscured, z ∼ 2 quasars observed at 870 μm with the Atacama Large Millimeter- submillimeter Array. We find that 17 of the 49 sources present additional galaxies (23 sources) within the primary beam. Source counts were calculated for these field and found that they are 10 times higher than expectations for unbiased fields, in- dicative of heavily obscured quasars preferentially inhabiting over-dense regions. Finally, I present the conclusions and future directions (Chapter 6).
Thesis (Ph.D.)--Tufts University, 2018.
Submitted to the Dept. of Physics.
Advisors: Anna Sajina, and Danilo Marchesini.
Committee: Ken Olum, Cristian Staii, and Alberto Fernandez-Soto.
Keyword: Astronomy.read less