This is a brief note to
explain the photometry of sources given in this site. Non-spitzer data
has been culled from the literature and from our own hard drives. Some
general points:
- Conv: 1MJy/sr= 23.5uJy/asec
- Error Conv = pixel rms x Conv x Ap Conv x
sqrt(aperature area in pixels)
- Table of IRS/MIPS data at bottom of page
- all upper limits are 3 sigma
The '.dat' files
The second to last column
'D' contains a link to what data we have centrally. Clearly this is
very incomplete so if you have any data please let me know. The link is
a just an ascii file with the source name, redshift, filter code,
filter name, aperature radius (in asec), magnitude, error on the
magnitude,
flux (uJy), flux error and finally
(where needed) a reference code to the source of the photometry.
negative number = upper limit (3 sigma)
-99
= no
data (or data not converted to/from Jy/magnitudes)
64 for aperature = aperature equivalent to
64kpc (for K-band only)
The '.notes' files
The last column 'N' contains a link to a file with random notes on
background info on the sources, including the output of my IRAC
reduction code (see below).
The IRAC reduction
output
The images:
The bcds were mosaiced and resampled at half pixel size (0.61") to
improve resolution. The outlier rejection was optimised in the regions
of highest coverage (ie 4 exposures) in the centre of the maps. It is
clear where the coverage decreases as the noise goes up towards the
edge. The upshot is that there are cosmic ray hits near the edge of the
field. The bright ones should be obvious, but be warey of doing science
on sources away from the regions of good coverage. Occaisionally there
is stray light (mainly chans 1+2), but we have not removed them as it
has to be done by hand and is a pain. However if an interesting part of
the sky near your favourite source is affected, let me know and I'll
have a go at removing it. The files are found by following the
'RED' link. Also you may find a tarball of all IRAC fits images to date
in that directory and
here. A
tarball of name lists, sextractor files and the regions
file can be found
here.
The regions file:
For those who use ds9 there is a ds9 regions file with all 70 sources
here.
The photometry
After creation of the fits images we used Sextractor to extract the
fluxes. We ran sextractor twice: once allowing it find sources freely
and once using the aperatures from source detected in channel 1 (in
order to get fluxes of faint sources at longer wavelengths). The fluxes
where converted to uJy and we used an aperature of 7" diameter. For
each channel the code created the following outputs which are in each
'.notes' files:
aper corr = aperature
correction from in flight PSFs (from Mark Lacy)
RA
= RA of the source found in channel one*
dec
= dec of the source found in channel one*
distance = separation
of radio position and RA dec above, always less than 10"
free fluxes = fluxes from 1st iteration of SE
with no aperature restrictions (uJy)
2 sigma = 2
sigma limit in centre of field
1=upperlimit = flag where 1 = no detection 1st time with SE
4band fluxes = fluxes from aperatures defined by detection
in chan1 (uJy)
errors
= errors on these fluxes (uJy)
* this may not be the true radio galaxy in some cases where there are
mulitple counterparts, just the nearest to the given radio position.
The fluxes in both iterations of SE generally agreed as expected.
Sometimes a weak detection was made at longer wavelengths in the second
iteration and often in these cases I used the rms as calculated earlier
for the error as it was more realistic (ie higher) than the error given
by SE. Where no detection was made I have quoted a 2sigma upper limit.
The IRS reduction output
These consist of just two nodded exposures of the 16um
peak-up imager. Latents are removed for the few images affected. Median
of all images subtracted. Hotpixels replaced with median of each
individual. Two difference images created, i.e. A-B and B-A. Negative
spots (<-1x rms
) replaced
with +1x rms. Both images resampled by a factor 2/3rds and the average
of these is taken (i.e. pixels size decreases from 1.8" to 1.2").
Conversion e-/s to uJy (+ aperature correction for
3"/2.5pixels radius) is 1.33 x(2/3)^2 = 0.591, the 1.33 is from Harry
Teplitz. Error = rms x conv x sqrt(area of aperature) = rms x 0.591 x
sqrt(pi x 2.5^2) = rms x 2.62.
The MIPS reduction output
24um and 70um images resampled by factor 2 when
remosaicing with 24um being median filtered by a code by Mark and I.
160um images are just those from the pbcd pipeline.
Filter
|
Wavelength
|
Pixel (")
|
Conv to uJy
|
Aperature (")
|
Annulus (")
|
Aperature Correction
|
Image rms to uJy
|
IRS16
|
16um
|
1.2
|
0.591*
|
3
|
6-10
|
-
|
2.62
|
MIPS24
|
24um
|
1.25
|
36.71
|
13
|
20-32
|
1.167
|
790
|
MIPS70
|
70um
|
4.95
|
576
|
35
|
39-60
|
1.185
|
8550
|
MIPS160
|
160um
|
8
|
1500
|
48
|
56-72
|
1 (assumed)
|
15950
|
* including aperature correction
