Deep fields around bright stars ( Galaxies around Stars )

Transcription

1 Deep fields around bright stars ( Galaxies around Stars ) Scientific context: the morphological evolution of faint field galaxies Near-IR observations ground-based observations with AO: PUEO/CFHT deep field observations NACO/VLT Science Verification phase: the Casertano Deep field Discussion and prospects for PUEO NUI

2 Scientific context Faint galaxies: general scheme for galaxy formation and evolution growth of structures by accretion and merging of sub-halos of dark matter star formation in the densest central regions The morphological evolution of galaxies segregation in the morphological evolution of galaxies with earlier formation of spheroids (z form > 3) the merging rate increases with redshift

3 Morphological distribution of the galaxies Impact of HST deep imaging 0.1 resolution in the visible (pixel size) 0.17 in the near-ir (H, diffraction limited) Ellipticals Spirals high redshift of formation. Regular increase of the mass by accretion of sub-entities Strong increase of the number of spirals and their surface brightness Irregulars Increase of their number with more and more disturbed morphologies + increase of the merging rate

4 Galaxies observed in the Northern and Southern Hubble Deep Fields (composite colors from blue, yellow and near-ir filters).

5 Near-IR ground-based observations with AO Interests The light emitted in the near-ir is dominated by old stellar populations and is more representative of the spheroidal population It is less sensitive to the shift of the rest frame wavelength (UV is observed in the optical) The average redshift of flux-limited samples is higher than in B. Practical points Need to center the fields around mag. stars! Best efficiency in K and H. 2 observational tests: PUEO/CFH and NACO/VLT

6 PUEO/CFHT deep field observations Selection of reference stars 13<R<14 (USNO catalog), as blue as possible (A-type). About 25% of the area nonoptimal (center+periphery) Number counts of field galaxies in K At K<20, 2-3 galaxies per PUEO field (35 x35 ). This means that statistically, some fields are empty!!!

7 Example of a 1h integration field (1) CFH12K Reference star: r=13.1 b=13.4 (USNO) PUEO Star ghost

8 Example of a 1h integration field (2) CFH12K Reference star: r=12.2 b=13.1 (USNO) PUEO Star ghost

9 Main limitations and difficulties The central reference star R=12 seems to be the max. brightness acceptable! A blue star is preferred for a lower occultation of the field in the near-ir Optical counter-parts partly blinded (star halo, saturated columns). Detection level limited by the size of the telescope Particularly true for extended objects small pixels = low S/N per pixel (limited by the sky background noise) Field availability, limited around bright stars only...

10 NACO/VLT Science Verification phase: the Casertano Deep field Reference star: r=12.1 b=13.9 (USNO) 5 hours integration in Ks + 5 hours in J Immediate release of the data NACO field 54 x ksec in F606W with HST/WFPC2

11 The Casertano deep field in 3 colors! J HST Star ghost Ks

12 The Casertano deep field in 3 colors! RJK true color image A large number of very promising sources!

13 Some detailed galaxies... Limiting magnitudes K ~ 22.0 (in 5 hours) Interacting systems Edge-on disk Very red objects

14 Discussion What could be the expected gain with a PUEO NUI? Seems difficult in the near-ir. Observations limited essentially by the size of the telescope. More promising in the far-red (I, z)... Resolution should be equivalent (or even better) to HST, but with a field size much smaller. PUEO NUI in I is equivalent in terms of resolution to NACO in H. Need to test deconvolution tools to test the gain in spatial sampling with AO systems (TBD...) The main limitation will still remain the bright reference star. Although this kind of programme cannot be leading science case, some specific observations could be realised in this mode.