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Quasar Environments at z ~ 4

Garcia Vergara, Cristina

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Abstract

In the standard picture of structure formation, the first massive galaxies form in the highest peaks of the density field, which are the cores of massive proto-clusters. Such structures must be exceedingly rare, and thus hard to find. Luminous quasars (QSOs) at z ~ 4 are the most strongly clustered population in the Universe and this large auto-correlation demands that they reside in massive dark matter halos, associated with large overdensities of galaxies. This imply a strong QSO-galaxy cross-correlation for luminous QSOs at z ~ 4. In order to put the first observational constrain on the QSO-galaxy clustering properties, I present the measurement of the cross-correlation function between QSOs and both Lyman break galaxies (LBGs) and Lyman alpha emitters (LAEs) at z ~ 4. I present VLT/FORS1 observations of 6 luminous QSOs fields. Using a novel narrow band filter technique I select LBGs associated with each quasar in a narrow redshift range of Δz ~ 0.2. I measure the QSO-LBG cross correlation function on scales of 0.1 < R < 10 h-1 Mpc (comoving), which is well fitted by a power law form with a correlation length r0 = 9.91+3.28-1.79 h-1 Mpc and a slope gamma = 2.05+0.20-0.46. This is in agreement with the theoretical expected clustering computed from the individual QSO and LBGs auto-correlation, assuming a linear bias model. I also measure the auto-correlation of LBGs in the QSO fields, which shows a stronger clustering in comparison with LBGs in random fields. The new technique used for the detection of LBGs is efficient in selecting them in a thin redshift slice, but this shows important shortcomings whereby this result should be carefully considered. Additionally, I present VLT/FORS2 observations of 14 luminous QSO fields, designed to search for LAEs in their environments. I find that QSOs and LAEs are not correlated at z ~ 4, and the mean LAEs number density in our fields is consistent with the expected number density in random fields. This could mean either that the QSO auto-correlation length at z ~ 4 is overestimated, or that LAEs preferentially avoid QSO environments on ≲10 Mpc h-1 scales.

Item Type: Dissertation
Supervisor: Hennawi, Dr. Joseph F.
Date of thesis defense: 25 May 2016
Date Deposited: 29 Jun 2016 07:35
Date: 2016
Faculties / Institutes: The Faculty of Physics and Astronomy > Dekanat der Fakultät für Physik und Astronomie
Service facilities > Max-Planck-Institute allgemein > MPI for Astronomy
Subjects: 520 Astronomy and allied sciences
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