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Density of Active Galactic Nuclei at Various Redshifts

Faculty Mentor: Paul Wiita

Student: Walter Ingram

The goal of this project is to determine the density and fraction of Active Galactic Nuclei (AGN) in different redshift bins: we chose .01-.03 (close distance); .4-.5 (medium distance); and .7-.9 (far distance). By looking at random parts of the sky using the NASA Extragalactic Database (NED) we were able to obtain a survey of about 500 close objects, 250 medium objects and 150 far objects. By entering right ascension and declination coordinates into NED the search returns all objects within a 20-arc minute circle that have been found by various satellites and telescopes around the world. Each search can return anywhere from 0-10,000 results. However, most of these objects have not been thoroughly researched and do not have redshift determinations. By adding redshift to the search criteria we get results that are almost all previously studied objects that have been defined as Galaxies, Quasars, UV Excess, or Radio Excess.  We found that at the smallest redshift it is easiest to find objects; however, the odds of finding an AGN are very low.  At the medium and large redshifts finding objects takes more trials, but we find greater fractions of AGN. There are two main reasons for this: (1) there are more AGN’s in the past and the bigger the redshift the farther back in time we are looking;  (2) AGN’s are much more luminous and outshine other galaxies around them, so at farther distances we cannot see the dimmer galaxies but we can still see Quasars and Seyfert Galaxies. Our survey of randomly selected patches on the sky included less then 1% of the entire sky. To do this project more thoroughly one would expand the survey and look at more patches of the sky and make corrections for the selection effects that favor the detection of Quasars.

 

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