Morphological Evolution of Distant Galaxies from Adaptive Optics Imaging

et al. 2005

A&A

Abstract. In this paper we present the approach we have used to determine and account for the anisoplanatic point spread function (PSF) in deep adaptive optics (AO) images for the Survey of a Wide Area with NACO (SWAN) at the ESO VLT. The survey comprises adaptive optics observations in the K s band totaling ∼30 arcmin 2 , assembled from 42 discrete fields centered on different bright stars suitable for AO guiding. We develop a parametric model of the PSF variations across the field of view in order to build an accurate model PSF for every galaxy detected in each of the fields. We show that this approach is particularly convenient, as it uses only easily available data and makes no uncertain assumptions about the stability of the isoplanatic angle during any given night. The model was tested using simulated galaxy profiles to check its performance in terms of recovering the correct morphological parameters; we find that the results are reliable up to K s ∼ 20.5 (K AB ∼ 22.3) in a typical SWAN field. Finally, the model obtained was used to derive the first results from five SWAN fields, and to obtain the AO morphology of 55 galaxies brighter than K s = 20. These preliminary results demonstrate the unique power of AO observations to derive the details of faint galaxy morphologies and to study galaxy evolution.

Section: First Results From Five Deep Science Fieldssupporting

confidence: 77%

Accounting for the anisoplanatic point spread function in deep wide-field adaptive optics images

Cresci

et al. 2005

A&A

“…Although the advantages of near-IR AO observations for studying how galaxies form and evolve in the early universe are clear, until now there have been only a few attempts using natural guide stars (NGS; see e.g., Larkin et al 2000;Glassman et al 2002;Steinbring et al 2004;Minowa et al 2005), due to the very small number of known extragalactic sources lying at distances ∆θ < ∼ 30 from bright (V < ∼ 13) stars needed to correct the wavefront for AO guiding, and to the problems arising from the anisoplanaticism of the PSF in AO observations. The prospects for AO cosmology will undoubtedly improve with the widespread adoption of laser guide star (LGS) systems, since these impose less stringent requirements on the brightness of stars used for tip-tilt correction (e.g., Melbourne et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Galaxy morphology and evolution from SWAN adaptive optics imaging

Cresci¹,

et al. 2006

A&A

We present the results from adaptive optics (AO) assisted imaging in the K s band of an area of 15 arcmin 2 for SWAN (Survey of a Wide Area with NACO). We derive the high resolution near-IR morphology of ∼400 galaxies up to K s ∼ 23.5 in the first 21 SWAN fields around bright guide stars, carefully taking into account the survey selection effects and using an accurate treatment of the anisoplanatic AO PSF. The detected galaxies are sorted into two morphological classes according to their Sérsic index. The extracted morphological properties and number counts of the galaxies are compared with the predictions of different galaxy formation and evolution models, both for the whole galaxy population and separately for late-type and early-type galaxies. This is one of the first times such a comparison has been done in the near-IR, as AO observations and accurate PSF modeling are needed to obtain reliable morphological classification of faint field galaxies at these wavelengths. For early-type galaxies we find that a pure luminosity evolution model, without evidence for relevant number and size evolution, better reproduces the observed properties of our K s -selected sample than current semi-analytic models based on the hierarchical picture of galaxy formation. In particular, we find that the observed flattening of elliptical galaxy counts at K s ∼ 20 is quantitatively in good agreement with the prediction of the pure luminosity evolution model that was calculated prior to the observation. For late-type galaxies, while both models are able to reproduce the number counts, we find some hints of a possible size growth. These results demonstrate the unique power of AO observations to derive high resolution details of faint galaxies' morphology in the near-IR and drive studies of galaxy evolution.

“…In order to conduct cosmological studies with the present generation of AO technology (e.g., Larkin et al 2000;Davies et al 2001;Glassman et al 2002;Davies et al 2003), it is necessary to identify distant galaxies in the vicinity of bright guide stars. Unfortunately, most existing surveys either avoid bright stars (e.g., the Hubble Deep Field), or like DENIS and 2MASS (Epchtein et al 1997;Skrutskie et al 1997) are too shallow to detect very many targets at cosmological distances.…”

Section: Introductionmentioning

confidence: 99%

Galaxies in southern bright star fields

Lehnert

et al. 2003

A&A

Abstract. As a prerequisite for cosmological studies using adaptive optics techniques, we have begun to identify and characterize faint sources in the vicinity of bright stars at high Galactic latitudes. The initial phase of this work has been a program of K s imaging conducted with SOFI at the ESO NTT. From observations of 42 southern fields evenly divided between the spring and autumn skies, we have identified 391 additional stars and 1589 galaxies lying at separations ∆θ ≤ 60 from candidate guide stars in the magnitude range 9.0 ≤ R ≤ 12.4. When analyzed as a "discrete deep field" with 131 arcmin 2 area, our dataset gives galaxy number counts that agree with those derived previously over the range 16 ≤ K s < 20.5. This consistency indicates that in the aggregate, our fields should be suitable for future statistical studies. We provide our source catalogue as a resource for users of large telescopes in the southern hemisphere.