Week 1

Beginning to classify the sources

The first step in our project is to sort through the data and find the sources that are AGN. Looking at the SC4K data catalogue from the COSMOS survey we see that some sources are detected in the X-ray (258) and some are detected in the radio (121). We have 13 different slices of red-shift between z ~ 2 and z ~ 6.

This plot shows the data available, we are interested in the blue and green data detected in X-ray and radio respectively. As can be seen from the plot, there are more sources at lower red-shift, especially when looking at the radio data

We have decided to start with focusing on the X-ray data from the Chandra COSMOS legacy survey before moving on to the radio as the X-ray data is easier to work with and we have more sources in the X-ray. To find AGN we are looking for sources that have an X-ray luminosity of greater than or equal to 10^42 ergs^-1 within one standard error. To save time and reduce the chances of human error we are putting all of the sources through a python program which will tell us which of the sources are AGN.

Our coding lead, Ben spent the lab session writing and testing the program. The program was set up to change count rates to X-ray flux which is needed to find X-ray luminosity. Using TopCat, luminosity distance was calculated from red-shift which is going to be used along with X-ray flux to find the luminosity. As expected with any amount of programming, we ran into a few issues: there were unexpected steps and factor of 10 issues, meaning we left the lab without finding out which sources were definitely AGN and which weren’t.

The rest of us made a start on classifying galaxies based on their morphologies (their shape). We used the same classification scheme as the SHREDS team from last year’s group project for the sources. We added type ‘4’ as the category of sources where we saw nothing or found that the image is too distorted to draw any conclusions.

Examples of the different types of morphologies. Four members of the group assigned numbers to each of the sources and we took an average of the values to assign a source to a group.

This started as a bit of a filler exercise as practise for when the program was ready but we chose to classify all sources that are found in X-ray from the COSMOS survey since from just looking at the table of data with luminosities we think they may all be AGN. Using COSMOS Cutouts we downloaded 2” by 2” images of all the sources taken by the Hubble telescope. Most of the sources seem to be ‘compact’. Not all of the sources found in the X-ray from the SC4K catalogue are in the COSMOS Hubble coverage; the ones outside the field do not have images from Hubble. For the AGN we find outside of the field will try and classify them using X-ray data in ds9.

Chandra survey coverage is in green, sources outside the coverage that are in the SC4K catalogue are in red, these are the sources we have no X-ray data for so are not included in out research.
RA and DEC describe the position of the source in the sky (Right Ascension and Declination)

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