Euclid

Abstract:

The Oxford-Dartmouth Thirty Degree Survey (ODTS) is a deep, wide, multiband imaging survey designed to cover a total of 30 deg² in BV Ri′Z, with a subset of U- and K-band data, in four separate fields of 5-10 deg² centred at 00:18:24 +34:52, 09:09:45 +40:50, 13:40:00 +02:30 and 16:39:30 +45:24. Observations have been made using the Wide Field Camera on the 2.5-m Isaac Newton Telescope (INT) in La Palma to average limiting depths (5σ Vega, aperture magnitudes) of U = 24.8, B = 25.6, V = 25.0, R = 24.6 and i′ = 23.5, with observations taken in ideal conditions reaching the target depths of U = 25.3, B = 26.2, V = 25.7, R = 25.4 and i′ = 24.6. The INT Z-band data were found to be severely effected by fringing and, consequently, are now being obtained at the MDM observatory in Arizona. A complementary K-band survey has also been carried out at MDM, reaching an average depth of K5σ ≈ 18.5. At present, approximately 23 deg² of the ODTS have been observed, with 3.5 deg² of the K-band survey completed. This paper details the survey goals, field selection, observation strategy and data reduction procedure, focusing on the photometric calibration and catalogue construction. Preliminary photometric redshifts have been obtained for a subsample of the objects with R ≤ 23. These results are presented alongside a brief description of the photo-metric redshift determination technique used. The median redshift of the survey is estimated to be z ≈ 0.7 from a combination of the ODTS photometric redshifts and comparison with the redshift distributions of other surveys. Finally, galaxy number counts for the ODTS are presented which are found to be in excellent agreement with previous studies.

Abstract:

We review the current status of QSO clustering measurements, particular with respect to their relevance in understanding AGN physics. Measurements based on the 2dF QSO Redshift Survey (2QZ) find a scale length for QSO clustering of s_0=5.76(+0.17-0.27) h-1 Mpc at a redshift ~1.5, very similar to low redshift galaxies. There is no evidence of evolution in the clustering of QSOs from z~0.5 to z~2.2. This lack of evolution and low clustering amplitude suggests a short life time for AGN activity of the order ~10^6-10^7 years. Large surveys such at the 2QZ and SDSS also allow the the study of QSO environments in 3D for the first time (at least at low redshift), early results from this work seem to show no difference between the environments of QSOs and normal galaxies. Future studies e.g. measuring clustering as a function of black hole mass, and deep QSO surveys should provide further insight into the formation and evolution of AGN.

Abstract:

We present results of a Gemini adaptive optics (AO) imaging program to investigate the host galaxies of typical QSOs at z ∼ 2. Our aim is to study the host galaxies of typical L*QSO QSOs at the epoch of peak QSO and star formation activity. The large database of faint QSOs provided by the Two-Degree Field QSO Redshift Survey allows us to select a sample of QSOs at z = 1.75-2.5 that have nearby (<12″ separation) bright stars suitable for use as AO guide stars. We have observed a sample of nine QSOs. The images of these sources have AO-corrected FWHM of between 0″.11 and 0″.25. We use multiple observations of point-spread function (PSF) calibration star pairs to quantify any uncertainty in the PSF. We then factored these uncertainties into our modeling of the QSO plus host galaxy. In only one case did we convincingly detect a host (2QZ J133311.4+001949, at z = 1.93). This host galaxy has K = 18.5 ± 0.2 mag with a half-light radius Re = 0″.55 ± 0″.1 equivalent to ∼3L*gal, assuming a simple passively evolving model. From detailed simulations of our host galaxy modeling process, we find that for four of our targets we should be sensitive to host galaxies that are equivalent to ∼2L*gal (passively evolved). Our nondetections therefore place tight constraints on the properties of L*QSO QSO host galaxies, which can be no brighter (after allowing for passive evolution) than the host galaxies of L*QSO active galactic nuclei at low redshift, although the QSOs themselves are a factor of ∼50 brighter. This implies that either the fueling efficiency is much greater at high redshift or that more massive black holes are active at high redshift.