Deep Observations of the GOODS-North Field from the e-MERGE Survey

Access to files

•   FULL-TEXT.PDF (pdf)

Abstract

The Great Observatories Origins Deep Survey North (GOODS-N) field, first surveyed by the HST, has been observed across numerous wavebands revealing populations of both Star Forming Galaxies (SFG) and Active Galactic Nuclei (AGN) over wide ranges of luminosities. It has been surmised that the evolution in the star forming population appears to diverge from that in the AGN population leading to a domination of SFGs at low flux densities. The number of starbursts can only be disentangled from the entire population if each source can be classified individually, which usually requires high angular resolution imaging. This is the motivation behind the e-MERLIN Galaxy Evolution survey, e-MERGE, which expands the depth of high resolution radio imaging in the GOODS-N field to increase the number of potentially classifiable sources. By use of wide-field imaging techniques, including a new high-speed mapping tool, together with a new semi-empirical primary beam-shape model for the e-MERLIN array, a deep wide-field high-resolution map is derived. This is the widest and deepest contiguous imaging yet obtained from e-MERLIN and JVLA observations, and yet contains less than 25% of the e-MERLIN data so far observed. The majority of the objects are shown to exhibit extended structure, and the angular size distribution place the median size around 1.2 arcsec, peaking between 0.5 and 0.7 arcsec. Automated algorithms are utilised to facilitate a new probabilistic classification tool based on multi-parameter correlations. 248 sources could be classified using the tool, each deriving a probability of AGN or SFG rather than forcing a binary category. Linear sizes of star-formation dominated sources are determined to lie in a range of 4 - 11 kpc, within the optical extent of galaxies. Differential source counting based on probabilistic classifications reveals that an increase in the luminosity evolution of SFGs is likely, although an apparent upturn in AGN may also exist to some lesser degree at low flux densities. The thesis establishes a clear roadmap for the remainder of the e-MERGE survey and a path to determine the star formation rate history of the Universe.

Layman's Abstract

The spectacular Hubble Deep Field (HDF) image, first captured in the late 1990s by the Hubble Space Telescope, resolves thousands of galaxies, each a collection of hundreds of billions of stars, spread across billions of light years and provides evidence for the evolution of galaxies over cosmic timescales. This thesis documents the creation of a radio equivalent image of the HDF (known as the Great Observatories Origins Deep Survey North field) using the United Kingdom’s upgraded high resolution e-MERLIN ‘interferometer’ array of optical fibre linked radio telescopes, of which Jodrell Bank Observatory plays a central role. Observations from another radio telescope array in the United States (the Karl G. Jansky Very Large Array) is utilised to complement e-MERLIN observations. The resulting picture emerging is the deepest (i.e. farthest) high resolution radio image of the region to date and provides a unique view of its galaxies, since radio waves can pass unhindered through intermediate gas and dust. In particular the e-MERLIN observations allow us to discriminate between the two main emission processes powering them, with cosmological implications. An introduction to the astrophysics involved in measuring the two broad types of galaxies is presented, as well as an overview of radio astronomy using interferometer array techniques. It concludes with a taste of things to come from the e-MERGE project.

Keyword(s)

AGN; GOODS-North; HDF-N; Hubble Deep Field; Primary Beam; SFG; Star-formation history; Wide Field Imaging; e-MERGE; e-MERLIN

Bibliographic metadata

Institutional metadata

Record metadata