The effect of environment on the formation and evolution of galaxies in the distant universe

Chuter, Robert W. (2011) The effect of environment on the formation and evolution of galaxies in the distant universe. PhD thesis, University of Nottingham.

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In this thesis I primarily use the UKIDSS Ultra-Deep Survey (UDS) to investigate the effect environment has on galaxies across the redshift range 0.25 < z < 3.25. The UDS is a K-selected survey so it does not suffer from the strong iases that affect optical surveys at high redshift (z > 1). The combination of a large contiguous area (0.77 deg2) and depth (KAB ∼24) allows us to study a range of environments up to a redshift of z ∼3. Due to the multiwavelength coverage we are able to obtain reliable photometric redshifts which are necessary for studies of environment. I utilise progressive releases of the UDS data to study the effect environment has on the rest frame (U-B) colour of galaxies. Using the U-B colour and absolute K-band magnitude I was able to divide our galaxies into red and blue and study their average environments. In this thesis I also employ data from the spaced based, GOODS NICMOS Survey (GNS) to help study the environments out to high redshift (z ∼3), in which I also study the colour-density relation.

The UDS project was recently enhanced by the addition of ∼3500 spectra of highredshift galaxies, obtained using the VIMOS and FORS2 instruments on the VLT. The data reduction and redshift determination for the VIMOS data is discussed and is exploited to improve the photometric redshifts for the study of environments in the DR8. The ∼1600 reliable spectra are utilised directly to investigate the effect that environment has on the spectral properties of galaxies.

We find that red galaxies are on average in denser environments than blue galaxies up to a redshift of z ∼2. The colour-density relation is strongest at the lowest redshifts studied (0.25 < z < 0.75) and gradually weakens out to redshift z ∼2 where it becomes almost flat. We also observe a distinct positive correlation between K-band luminosity and local density for galaxies between 1.25 < z < 2.75. This relation becomes strongest for the blue galaxies on the smallest scale studied (125kpc radius). Through studying the effect of environment on spectral features we have found evidence that galaxies between a redshift of 1.25 < z < 2.2 have significantly larger values of the C(29-33) index, in denser environments, indicating that older/more passive galaxies, even at this high redshift, reside in denser environments. The other indices similarly tend to indicate that older galaxies inhabit denser environments, whilst the environment has little effect on the properties of the blue galaxies. The spectra also indicate that one age determining index, C(29-33) is a very good indicator of colour for samples of galaxies at high redshift where the traditional measures such as the 4000°A break strength are difficult to obtain. This study of environments leads us to the final conclusion that although the stellar mass of a galaxy is clearly important in determining its evolution, its environment is also an important driver in a galaxy’s evolution. Disentangling the relative importance of these drivers (nature vs nurture) will be a major goal in the coming years.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Almaini, O.
Keywords: galaxies, galaxy formation, red shift, redshift
Subjects: Q Science > QB Astronomy
Faculties/Schools: UK Campuses > Faculty of Science > School of Physics and Astronomy
Item ID: 12366
Depositing User: EP, Services
Date Deposited: 16 Mar 2012 10:56
Last Modified: 13 Sep 2016 22:16

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