Mikkel Theiss Kristensen Master's Defense

Title: Rare Emission-line Galaxies in the COSMOS Field

Supervisors: Johan Fynbo and Bo Milvang-Jensen

Censor: Knud Jepsen


Large scale surveys such as COSMOS are invaluable for observing galaxies across cosmic
time. Coupled with narrow band filters, surveys can be used to search for galaxies with emission lines at specific redshifts. The 4-meter VISTA telescope contributes to the COSMOS with an ultra-deep survey (UltraVISTA) with narrow-band imaging utilizing the NB118 filter centered at 11910 Å. This filter enables the search for a number of strong emission lines at z  2:2. For z > 2:2, a number of rarer emission lines can be found such as Mgii at redshift (z) = 3:3, Cii] at z = 4:1, and Ciii] at z = 5:2. Such emitters are rare. Combining the newest Y, NB118, and J images from UltraVISTA with the COSMOS2015 catalog containing precise photometric redshifts for more than half a million objects, the hope is to find a range of rare line emitters at high redshifts (z > 2:5). Candidates are selected if they shave narrow band excess. The method employed is evaluated in order to optimize the parameters for the present search. It is found that stricter detection parameters strongly influence the number of high redshift objects whereas selection parameters mostly affect the number of selected candidates rather than their redshifts. The 105 selected candidates, also called outliers, are found to have hzi = 3:08  0:62, although a large number have undesirable traits leaving only 34 for further for analysis with hzi = 3:35  0:56. Out of the 34 good outliers, 13 (~38%) are likely Mgii emitters. Up to 8 (~24%) more that may be Mgii emitters also but their nature is uncertain. 2( 6%) may be Cii] emitters and 1 (~3%) outlier is consistent with Ciii] (~3%). The remaining 10 (~29%) are possibly [Oii] emitters, although their narrow band excesses may be emission lines not considered.

Link to paper here >>