photometric redshifts of objects in b0218+357 field sanhita joshi angles workshop, crete 07/04/2005
TRANSCRIPT
Photometric Redshifts of objects in B0218+357 field
Sanhita Joshi
ANGLES Workshop, Crete
07/04/2005
What do we know about 0218+357
• 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 – 0.944 (Lawrence et al)
Galaxy – 0.685 (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