Medium Deep Survey

WFPC2 HST Gravitational Lens Image Creator

The main parameters that change the lens configuration are the (X,Y) offsets of Source and the Lens Mass axis ratio. The Critical radius governs the scale of the deflection. It is the Einstein ring radius for zero offsets and lens mass axis ratio equal to unity.

Change any of the parameters below and click to
Parameter/Object unit The Lens. Central
Elliptical galaxy
The Source. QSO or
galaxy being lensed
I Magnitude mag.
Half-light radius arc-seconds
Axis ratio  
Orientation degrees
Light Profile index
(V-I) color mag.
(B-V) colormag.
X offset arc-seconds *
Y offset arc-seconds *
Gravitational Lens Potential
Critical radius arc-seconds
Lens Mass axis ratio  
Profile Softening (alpha)
Core/Critical Radius ratio (beta)
Cosmic Shear(gamma)
Cosmic Shear Direction degrees
Mass wrt light orientation degrees *
velocity dispersion km/s
RedShift km/s/Mpc

Observation PSF convolve Bleed CCD charge Photon Noise
Lens Potential Model KSB - SIE WMS - SSS NFW - CDM
Compute Critical Radius Velocity Dispersion  

Cosmological Constants.
Hubble Constant Omega_matter Omega_lambda

HST WFPC2 Observation
Exposure/Filter unit I F814W (Red) V F606W (Green) B F450W (Blue)
Total Exposure time Seconds
Number of Exposures  
Mean Sky Background DN
HST image URL .jpg

An ImageMap with the Caustic/Cut which can be clicked will be generated to change source location interactively.

To compare the simulation side by side with a HST WFPC2 image of a lens candidate, create an image (.jpg or .gif) of a 6.4 arcsecond (64 WFC pixels) square region, and specify a URL to it.
The specified comparison image, the simulated image and the corresponding caustic/cut image would be in the image stack on right and maybe blinked in a javascript enabled browser.

The table below gives an array of links which model each of six candidates in each of the six potentials models used to compute gravitational lens configurations in
Knudson, A., Ratnatunga, K. U. & Griffiths, R. E.
Investigation of Gravittional Lens Mass Models
2001 A. J. 122 103-112 .
Clicking on the acronym will simulate that maximum likelihood model fitted to that lens.

HST UMDS Lens Comment Gravitational Lens Potential Model
14176+5226 u26x8 0009 Quadruple - Confirmed SIE SIG SML NIE SSS NFW
12531-2914 urz00 0035 Quadruple SIE SIG SML NIE SSS NFW
01247+0352 uci10 0034 Double SIE SIG SML NIE SSS NFW
15433+5352 uvd01 0014 Arc+One - On Caustic SIE SIG SML NIE SSS NFW
16309+8230 urg01 0010 Arc - Mild Lens SIE SIG SML NIE SSS NFW
12368+6212 uhdfk 0056 Distortion - Weak Lens SIE SIG SML NIE SSS NFW

The potential model acronyms are described below.
SIE Singular Isothermal Ellipsoid.
Korman, Schneider & Bartelmann 1994 A&A 284, 285.
SIG Same as SIE with the orientation of the lens mass is constrained to be the same as the light of lens galaxy by including an external shear term.
SML Same as SIE with the axis ratio and the orientation of the lens mass is constrained to be the same as the light of lens galaxy by including an external shear term.
NIE Isothermal Ellipsoid with a core radius.
Korman, Schneider & Bartelmann 1994 A&A 284, 285.
SSS Singular Spherical model with a softness parameter, with an external shear term.
Witt, Mao & Schechter 1995 ApJ 443, 18
NFW Spherical mass model from CDM simulations with an external shear term.
Navarro, Frenk, & White 1995 MNRAS 275, 720

The table below gives similar links which will start with the maximum likelihood model fitted using the simple SIE - singular isothermal elliptical lens potential, to the other four gravitational lens candidates published in
Ratnatunga, K. U., Griffiths, R. E. & Ostrander, E. J. 1999,
The Top Ten List of Gravitational Lens Candidates from the HST Medium Deep Survey
A. J. 117 2010-2013. astro-ph/9802100.

HST UMDS Lens Comment Gravitational Lens Potential Model
14164+5215 u26xi 0017 Double SIE
01248+0351 uci10 0050 Double - edgeon Disk SIE
16302+8230 urg01 0042 Almost Ring ? SIE
18078+4600 uqc00 0029 Arc - galaxy group SIE

The deflection from gravitational lens used in the simulation is defined by the critical radius which is the directly observed quantity. It can be related to the potential of the lensing galaxy mass, redshifts of the lens and source, and cosmological constants. The true effective potential which depends also on the projection of the mass distribution to the line-of-sight is at best only known statistically.

Compute either the effective velocity dispersion corresponding to the input critical radius, or the critical radius coresponding to the input observed or estimated velocity dispersion.

Although it is OK to change, it is logical to keep without loss of generality the parameters flagged with * at their default zero value.
The profile index for elliptical scale free models can only take values
0.25 (Bulge-like) or 1 (Disk-like) or 2 (Gaussian)

The simulated WFPC2 images are 64 pixel square with 0.1 arc second pixels.
They have been combined into a color jpg image using the same automated f77 algorithm used for CMU/STScI/NASA Press Release 99-18 of 13 May 1999.
The transformation is non-linear and designed to highlight faint components.

The temporary image files are named with the time of creation to avoid a cache copy being displayed. They are deleted by a cron task within 1 to 2 hours. The cgi driver has been written in f77 using the same subroutines used for the gravitational lens image analysis. Each computation takes under a second on the Athlon 700MHz Linux server.

Comments: E-mail Kavan Ratnatunga