Combining GBT and VLA data

CASA Issues• GBT spectra (fully reduced, calibrated spectra) currently unable to

load into CASA– NRAO’s Bob Garwood working on program to convert SDFITS file into

scantable that CASA can read– Bob is working the program into his schedule, so no definitive time on

when it will be completed• CASA has new spherical Bessel function for gridding (imaging) GBT

data– waiting for above to be complete before testing can commence

• CASA’s current task ‘imregrid’ is producing checkerboard pattern in GBT data– likely due to large GBT pixels (3.5’/side) being re-gridded to match teeny

tiny VLA pixels (~7”/side), causing an artificial “edge-effect”– Helpdesk ticket submitted and NRAO is working on correcting problem

Flux measurements

• GBT flux:– converted K to Jy/bm using:

• GBT flux produced = 10.91 Jy/bm compared to 1.085 Jy/bm from VLA CLEAN channel (see Feather notes) – Does this make sense???

Weighting Function for Feather

FFT of GBT and VLA center pixel profile

Feathered image• The LT GBT + VLA data look like this:

Combined in Image Domain• GBT + VLA data look like this for M81/M82 group using AIPS:

Other data combination methods

• Image domain• Using GBT as model for CLEAN:

Other data combination methods

• Combining in uv-plane???– Convolving VLA data with GBT beam – then

combine – then run CLEAN (multi-scale??) on combined data