Westra, Everhardus Antonius Metske
Description
Narrowband surveys are a well-established tool for finding star-forming
galaxies at different epochs. This thesis presents the Wide Field Imager
Lyman Alpha Search (WFILAS), a survey originally designed to find
Lyman-a (Lya) emission-line galaxies at redshift z~5.7, and subsequently
utilised to find Hydrogen-a (Ha) emitting galaxies at redshift z~0.24.
The survey covers three 0.25 sq. deg. fields each observed in three
narrowband filters, an intermediate band filter (encompassing all
narrowband...[Show more] filters), and two broadband filters.
A sample of seven luminous Lya-emitting galaxies was identified (Lya
luminosity greater than or equal to 1.8e43 ergs), complementing existing
surveys by further constraining the bright end of the Lya luminosity
function. Three candidates identified in one of the three fields, the
well-studied Chandra Deep Field South, were grouped together, supporting
claims of an overdensity at this redshift by other groups.
Two of the seven candidate Lya emitting galaxies have been confirmed
through spectroscopy, one of which is the most luminous at this redshift
to date. The spectra of both objects displayed the asymmetric line
profiles common in Lya at these redshifts. Furthermore, tentative
evidence of a second Lya component, redward of the Lya line was found.
Additional high-resolution imaging showed that both objects were unresolved.
Spectroscopic follow-up was used to determine the fraction of
Ha-emitting galaxies in two of the fields from a total sample of 707
candidate emission line galaxies. This yielded two independent Ha
luminosity functions and star formation densities at z ~ 0.24 following
corrections for extinction, imaging and spectroscopic incompleteness.
These values were found to agree with those of other recent surveys
within the limits of uncertainty. A detailed error analysis found that
both cosmic variance and differences in selection criteria remain the
dominant sources of uncertainty between various Ha luminosity functions
at z smaller than or equal to 0.4. While the star formation rates were
consistent with the typical field galaxy densities probed by the fields,
a tentative increase in star formation rate per galaxy with increasing
density of star forming galaxies was found. This observation supports
galaxy formation scenarios in which galaxy-galaxy interactions are
triggers for star formation.
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