A Multicolor CCD Survey for Quasars z > 3Nikhil Revankar, Dr. Julia Kennefick, Shelly Bursick

University of Arkansas, Arkansas Center for Space and Planetary Sciences

Cornell University, Department of Mathematics

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What are quasars and why should we study them?

Selection of Quasars and the SDSS

How does a multicolor survey work? Current Results

Future Work

Acknowledgements

B,V,R Filter Curves

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Figure 1: This illustration shows the accretion disk around a supermassive black hole. The powerful radiation we observe from quasars comes from matter and gas swirling around and falling into the black hole.

Quasars are small, high energy active cores of very distant galaxies.

Look like stars in the visible, but have higher energy outputs and are also highly red-shifted.

Their energy output comes from gigantic accretion disks surrounding supermassive black holes.

Since quasars have high red-shifts, studying them enables us to see the universe when it was young.

Studying their spectra allows us to probe the amount and nature of intervening material at high red-shifts.

Figure 2: This illustration shows the coverage area of the SDSS. It will cover approximately RA: 8h to 17h and dec: -10° to 80°.

My objective is to select three objects, classified by the Sloan Digital Sky Survey (SDSS) as quasars, and to confirm their classification via multicolor techniques. The three quasars I selected had red-shifts z=3.01, z=3.19, and z=3.4251.

These quasars represent a look-back time of ~11.5 billion years to ~12.1 billion years.The quasars had to be magnitude 18 or brighter due to telescope limitations.

About the SDSS: An ongoing survey that is trying to map a quarter of the entire sky. The survey will try to record the distance to 100,000 quasars. The SDSS had images and spectra for each of my quasars. I had to use the images from SDSS to detect the quasars in my own data.

Figure 3: Top- Filter curves for B, V, and R filter. The chart shows the efficiency of the various filters at different wavelengths. Middle- Spectrum of a star. Bottom- Spectrum of a quasar.

The NFO Webscope telescope, which is the telescope that was used for this project, has three filters (B,V,R). This gives us two usable colors, namely B-V and V-R.

By looking at the images above, we see that stars and quasars have very different spectrums in the wavelengths that the filters cover.

When we look at the two colors B-V and V-R we are essentially looking at two ratios: Fb/Fv and Fv/Fr. These ratios represent the flux (number of photons per unit area per unit time) in the various filters. The two ratios are sufficiently different in stars and quasars, so that when we plot B-V versus V-R, the quasars stand apart from the stellar locus.

For my project, I used apparent magnitudes so that B-V=Mb-Mv and V-R=Mv-Mr, is just the difference in apparent magnitudes in the various filters. These differences are once again dissimilar enough in stars and quasars so that pinpointing quasars in our plot is not difficult.

o Continue collecting data on z=3.4251 quasar in order to have a better defined stellar locus and separation. I also intend to use the same procedure used above for the z=3.01 and z=3.19 quasar.

o I have also started collecting data on a region of the sky that is not covered by the SDSS. The coordinates of this region lie around RA: 19h and dec: +58°. My hope is to identify possible quasar candidates by obtaining a well defined stellar locus, so that outliers can be pinpointed.

Figure 4: Image of z=3.4251 quasar with a B-filter. I stacked together 9 images to obtain the final image.

Figure 5: Same quasar, except this image is taken with a V-filter. The final image was obtained by stacking 10 images.

Figure 6: Image of the same quasar with a R-filter. This image was produced by combining 5 images.

Figure 7: I performed photometry on the above images to obtain the apparent magnitudes in the three filters. Next, I plotted the two colors, and the quasar stood apart from the general stellar locus, as expected.

Quasar z=3.4251

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Funding for the creation and distribution of the SDSS Archive has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Aeronautics and Space Administration, the National Science Foundation, the U.S. Department of Energy, the Japanese Monbukagakusho, and the Max Planck Society. The SDSS Web site is http://www.sdss.org/. I would also like to thank Brian for assisting me with my software questions, and a special thanks to Alison for helping me with the creation of various charts.