Photometric Redshifts of objects in B field Sanhita Joshi ANGLES Workshop, Crete 07/04/2005
What do we know about Double image, with Einstein Ring with radius 334 mas (Patnaik et al) Time delay of 10.5 ± 0.4 days (Biggs et al) Redshifts: Quasar – (Lawrence et al) Galaxy – (Browne et al) Galaxy position: (255±6, 119 ± 4) mas to A. –LENSCLEAN (Wucknitz et al) –With HST images (York et al) Hubble Constant: 73 ± 8 km/s-Mpc (York et al)
Need more work on 0218? The result can be (im)proved ! Any other object assisting lensing? – Redshifts of objects in field of view – 3D mapping of these objects Time delay
How to find photo-z For good enough accuracy, need data in 5 bands Wavelength range: –UBVRI from Keck – JK from UKIRT Fluxes compared with standard templates, using code HyperZ
Photometric Calibration Magnitudes should be corrected for –Zero point of the instrument – Atmospheric extinction (small) –Galactic extinction (small) Used a standard star for photometric calibration of J and K data
Why ‘Photometric’ Redshift Less time consuming Accuracy in z up to 0.1, which is sufficient for the purpose Objects with z > 1.0 can be neglected
Model spectrum and SED fits The spectra don’t fit to the model!
Sources of Error Sky was not photometric during Keck observations Some other systematic errors
What I will find ? Redshifts for objects in 0218 field (Non) – presence of any cluster assisting lensing