Cluster Cosmology » running stellar locus on VLT

h1. Wiki

This can be divided into 3 steps

h2. Step 1 run modelfitting photometry

you can find the scripts at /big/users/shantanu/VLTmfp/catalogs/runmfp_b.sh (for b band and so on)

note that since initial catalogs will be uncalibrated , use -mag_zeropoint for b,I and z bands.

The zeropoints for HST bands is :

F606W 26.493mag, F814W 25.947mag.

the sextractor param file used in the scripts is 

/big/des_home/stable/etc/sex.param_sersic

you can edit to remove params you don't need.

h2. Step 2 Produce a matched catalog across all 4 bands

This is the most tedious step.  Unfortunately you cannot run sextractor in dual image mode

since coadds are of different size.

The way I did it was to run a modified version of a code 

used in DESDM called coadd_grabmatches. I first ran it to match R vs I band and then used

that match catalog to match against z band and so on.

A code to do this is at /home/moon/shantanu/desdm/devel/ImageProc/trunk/src/coadd_grabmatches_singleband.c

There is one line in the code (below # 266) which needs to be changed depending upon number of coluns

in input catalog.

Once this is done you need to make a file with the matched magnitudes in all four bands

(its possible to automate this script with some effort so that it does not need to be changed)

h3. Step 3 Doing the stellar locus

One you have the catalogs all you need to do is to do a fit by eye or quantitative to SED fits provided by Joerg.

Here is my 2nd order polynomial  curve fit done to these relations

1) b-R vs R-I

b -R = -0.2904*x^2+1.319x +0.2941

(where x=R-I)

2) R-I vs I -z

R-I = -1.016*x^2+ 3.532*x +0.1294

where x=I-z

3) b-R vs I-z

R-I = -2.20378*x^2+ 3.96368*x +0.386878

You can either use (1) & (2) or (2)  & (3) to get the zeropoints.

I did the plotting in ROOT, but probably it can be done in any software.

h4. Step 4 Rerun sextractor with the new zeropoints

Same as (1) but use the new zeropoints now.

h3. Direct calibration of I-band

Joerg pointed out that I band can be directly calibrated using

I_BESS = a0 + a1 * F814W + a2 * (F606W - F814W)

with

a0 = -1.009

a1 =  1.067

a2 = -0.001

!{width: 10%}Izeropoint.png!

This allows us to get direct calibration of I-zeropoint= 28.37+/- 0.02 (where error = sigma of fit/sqrt(no of points))

We then recalibrated (b-R) vs (R-I)

!{width: 10%}plotslrfit.png!

Also a histogram wrt stellar locus

!{width: 10%}slrhisto.png!

the zeropoint for b band = 26.88 +/- 0.02

z band 28.02 +/- 0.012

h1. Results for other clusters

h2. SPT-CLJ0102-4915

I band zero-point = 28.52 +/- 0.0137

b band zp = 26.87 +/- 0.016

z band zp = 28.21 +/- 0.015 (I-0.31)

h2. SPT-CLJ0533-5005

I band  = 28.52 +/- 0.0123

b band= 26.69 +/- 0.014

z band = (I-z+0.4) = 28.12 +/- 0.006

h3. SPT-CLJ0559-5249

I-band 28.32 +/- 0.005

b band 27.2 +/- 0.023

z band (I-z+0.44) 27.88 +/- 0.0147

h3. SPT-CLJ2331-5051

I-band  28.32 +/- 0.012

b-band 27.07 +/- 0.017

z-band  I-z+0.42   27.9 +/- 0.013

h4. SPT-CLJ2337-5942

I-band 28.38 +/- 0.0123

b band 27.05 +/- 0.0198

z (I-z+0.37)  28.01 +/- 0.0076

h4. SPT-CLJ2341-5119

I-band 28.38 +/- 0.0096

 b-band           27.09 +/- 0.021

z band (I-z+0.39) 27.99 +/- 0.013

h4. SPT-CLJ2342-5411

I-band 28.3 +/- 0.017

b band 27.07  +/- 0.021

z band  27.91 +/- 0.007 

h4. SPT-CLJ2359-5009

I-band  28.41 +/- 0.0088

b-band 26.92 +/- 0.023

z-band  I-z+0.39     28.02 +/- 0.01

Jan 17 update:

Joerg provided a new relation I_BESS - F814W = -0.052 + 0.0095 * (F606W - F814W) only valid for

only valid for (F606W - F814W) < 1.7.

h2. Jan 19

h2. SPT-CLJ000-5748

I :  27.86 +/- 0.0129

b (b-r+2.37)  27.37 +- 0.045

z (I-z+0.56) 27.3 +/- 0.017

h2. SPT-CLJ0102-4915

I : 27.89 +/- 0.014

b : 27.47 +/- 0.0317

z : (I-z+0.51)  27.38 +/- 0.022

h2. SPT-CLJ0205-5829

I 27.81 +/- 0.0155

b 27.52 +/- 0.032

z (I -z + 0.55)    27.26 +/ - 0.02

h2. SPT-CLJ0533-5005

I : 27.8 +/- 0.0196

b  27.44  +/- 0.024 

z  (I-z + 0.62)  27.18 +/- 0.02

h2. SPT-CLJ0559-5009 

(same as 0533-5005)

I:   27.8 +/- 0.0174

b  27.52 +/- 0.0276

z  (I-z+0.62) 27.18 +/- 0.0223

h2. SPT-CLJ2331-5051

I : 27.83 +/- 0.0085

b  27.54  +/- 0.0194

z     (I-z+0.61)    27.22      +/- 0.0174

Inon reports some problems with the calibrated catalog. (seems fine after fixing this)

SD: errors seem a bit larger

h2. SPT-CLJ2337-5942

I   27.81 +/- 0.008 

b  27.565    +/- 0.0139

z   (I-z+0.55)     27.26          +/- 0.0105

h2. SPT-CLJ2341-5119

I  27.81+/- 0.0109

b 27.6 +/- 0.0241

z  (I-z + 0.565) 27.245 +/- 0.0154

h2. SPT-CLJ2040-5726

I  27.8  +/- 0.0162

b 27.46         +/- 0.0215

z  (I-z + 0.5)   27.3 +/- 0.0297 (large asymmetric tail in SLR histogram) 

h2. SPT-CLJ0615-5746

I : 27.7 +/- 0.0155

b  27.54        +/-  0.0234 (a slight asymmetric tail)

z (I-z+0.65) 27.05  +/- 0.01669

h2. SPT-CLJ0546-5345

I  27.79 +/- 0.0155

b 27.41  +/- 0.0283

z (I-z+0.62)  27.17  +/- 0.0197

h2.  SPT-CLJ2342-5411

I 27.79 +/- 0.011

b  27.49  +/- 0.021

z  (I-z+0.57)  27.22 +/- 0.0147

h2. SPT-CLJ2106-5844

I 27.74 +/- 0.0179

b  27.49   +/- 0.023

z  (I-z+0.49)  27.25 +/- 0.0218

March 2013

zeropoints re-calculated after cataloging in dual image mode with euclid style reductions

I 27.74 +/- 0.007

b 27.49 +/- 0.011

z (I-z+1.1) 26.64 +/- 0.022 -> WRONG (see below)

October 2013 Update : the z-band zeropoints from March were wrong. The new zeropoints are same as in January

z  (I-z+0.49)  27.25 +/- 0.0074

h2. SPT-CLJ2359-5009

I 27.79 +/- 0.0056

b 27.53 +/- 0.0272

z (I-z+0.57) 27.22 +/- 0.0146