Master Thesis Defence: André Endrup Hartwigsen

Abstract:

Observing and classifying galaxies at high redshift is paramount to understanding the formation and evolution of the universe. This thesis aims to find and characterize Ly-man break galaxies at z > 7, probing the early universe at the Epoch of Reionization. This is accomplished with preliminary access to the COSMOS2020 catalog, using new observations from the VISTA telescope. UltraVISTA is a very deep imaging survey, totalling observations spanning over 6 years, containing 4 broadband  lters (Y , J, H and Ks) and one narrowband filter NB118 at 1:18 µm. COSMOS2020 (Weaver et al., subm) combines these in a multi-wavelength photometric and photo-z catalogue, including numerous of the deepest surveys of the 2 deg² COSMOS  field to date. The narrowband filter NB118 is placed within the FWHM of broadband  filter J, sources with excess flux (emission lines) can be identified in the narrowband filter. This enables the search for strong emitters such as [OII] at redshift 2.2, [OIII] and Hb around redshift 1.4, Ha at redshift 0.8 and Lyaat redshift 8.8. In this work the focus is on searching for Lyman break galaxies with Lya narrowband excess at z~   8.75. Candidates are selected by requiring flux blueward of the Lya line to be consistent with zero, and inferring strict criteria for narrowband excess. No sources were found with satisfactory NB118 significance. A galaxy with substantial potential (J3) at zphot = 8.8 +/- 0.6 was found, currently with narrowband excess indicating a Lya line, but additional observation time will be required to be statistically significant. COSMOS2020 uses a wide range of deep broadband  filters to create an izYJHKs chi mean detection image. This does not include NB118, and it is therefore inherently interesting to use NB118 as detection image in contrast. This yielded 114 potential new sources not previously in the COSMOS2020 catalogue. With a handful of these presenting very good candidates to be real emission line galaxies. Finally a search for lensed-, blended- and critically failed photometric redshift fit-galaxies was completed. Here sources with a photometric redshift within 2ó of the a major emission line in the NB118  lter are excluded, and the remaining galaxies are selected for narrowband excess and significance. This resulted in the detection of emission lines outside the search range and blended sources but no obvious lensed object. A bright r < 21.5 mag galaxy with complex morphology was selected and sent as observation proposal to the NOT telescope on La Palma. Spectroscopy of Hb, Hy, Ha, and two [OIII] lines visible in the otherwise at spectrum, revealed a likely low metallicity irregular galaxy at redshift z = 0.101 21 +/- 0.000 02 corresponding to a He I emission line, causing the observed narrowband excess at 10 830 A.

Supervisor: Johan Peter Uldall Fynbo, NBI

Censor: Maximilian David Stritzinger, AU