1. GIANT TO DWARF RATIO OF RED-SEQUENCE GALAXY CLUSTERS Abhishesh N Adhikari Mentor-Jim Annis Fermilab IPM / SDSS August 8, 2007

2. OUTLINE OF TALK Introduction to SDSS Introduction to SDSS The physics of my project: Giant to Dwarf Ratio in Red Galaxy Clusters The physics of my project: Giant to Dwarf Ratio in Red Galaxy Clusters MaxBCG: A cluster detection algorithm MaxBCG: A cluster detection algorithm My procedure and programming My procedure and programming Initial Results for the ratio and issues I had with it Initial Results for the ratio and issues I had with it Latest Results: Explanation and Conclusion Latest Results: Explanation and Conclusion Comparing my results with the rest of the scientific community Comparing my results with the rest of the scientific community Further Steps Further Steps

3. INTRODUCTION TO SDSS Sloan Digital Sky Survey is one of the most ambitious astronomical surveys ever undertaken Sloan Digital Sky Survey is one of the most ambitious astronomical surveys ever undertaken When complete, it will have mapped more than a 100 million objects and 25 percent of the sky When complete, it will have mapped more than a 100 million objects and 25 percent of the sky The SDSS red-shift limit for galaxies is 0.4 (a distance of a few billion light years) The SDSS red-shift limit for galaxies is 0.4 (a distance of a few billion light years) The survey releases all its data on the internet and constantly updates it The survey releases all its data on the internet and constantly updates it

4. GIANT TO DWARF RATIO OF RED GALAXY CLUSTERS Galaxy Galaxy Cluster: A group of galaxies that are gravitationally bounded Cluster: A group of galaxies that are gravitationally bounded Field Galaxies: Galaxies that are not a part of any cluster Field Galaxies: Galaxies that are not a part of any cluster Blue Galaxies: Blue, Star forming galaxies Blue Galaxies: Blue, Star forming galaxies Red Galaxies: Red, Very little star formation, bigger Red Galaxies: Red, Very little star formation, bigger Giant Galaxies: Bright galaxies Giant Galaxies: Bright galaxies Dwarf Galaxies: Faint galaxies Dwarf Galaxies: Faint galaxies

5. GIANT TO DWARF RATIO OF RED GALAXY CLUSTERS Luminosity Function of present day Red galaxy clusters (take note of the curve shape only) Luminosity Function of present day Red galaxy clusters (take note of the curve shape only)

6. GIANT TO DWARF RATIO OF RED GALAXY CLUSTERS Two theories regarding the evolution of red sequence galaxy clusters: Two theories regarding the evolution of red sequence galaxy clusters: 1) Red Galaxies form very early on and evolve very passively afterwards 1) Red Galaxies form very early on and evolve very passively afterwards 2) Red galaxies constantly evolve, and are formed from the merger of blue field galaxies 2) Red galaxies constantly evolve, and are formed from the merger of blue field galaxies

7. GIANT TO DWARF RATIO OF RED GALAXY CLUSTERS Theory 2 would mean an increase in giant to dwarf ratio at higher red-shifts Theory 2 would mean an increase in giant to dwarf ratio at higher red-shifts Theory 1 would mean a constant giant to dwarf ratio over time Theory 1 would mean a constant giant to dwarf ratio over time

8. GIANT TO DWARF RATIO OF RED GALAXY CLUSTERS Why is this important: Why is this important: Theory of evolution of galaxies Theory of evolution of galaxies Cosmological Parameters and the Large Scale Structure Cosmological Parameters and the Large Scale Structure Useful for other surveys Useful for other surveys

9. GIANT TO DWARF RATIO OF RED GALAXIES Only a handful of people have done investigation in this particular area, the reason being there has never been a huge cluster catalog. Only a handful of people have done investigation in this particular area, the reason being there has never been a huge cluster catalog. Nevertheless, a few people have tried to figure out if the ratio changes using a handful of clusters: Nevertheless, a few people have tried to figure out if the ratio changes using a handful of clusters: Stott et al. Compares 5 clusters Stott et al. Compares 5 clusters De Lucia et al. Compares 14 clusters De Lucia et al. Compares 14 clusters (Both conclude increasing giant to dwarf ratio at high red-shifts) Sloan Digital Sky Survey, with its huge database was ideal to conduct this research on a large number of clusters. Sloan Digital Sky Survey, with its huge database was ideal to conduct this research on a large number of clusters. But first, we needed an algorithm of detecting red cluster galaxies in the SDSS database But first, we needed an algorithm of detecting red cluster galaxies in the SDSS database

10. MaxBCG ALGORITHM A red-sequence galaxy cluster finding algorithm, described in Koester et al. A red-sequence galaxy cluster finding algorithm, described in Koester et al. Based on identifying the brightest galaxy that exists at a cluster’s center Based on identifying the brightest galaxy that exists at a cluster’s center Once the center is located, search for member red-sequence galaxies using the following criteria: Once the center is located, search for member red-sequence galaxies using the following criteria: A Standard Radius A Standard Radius Magnitude Cuts Magnitude Cuts Color Cuts (Getting just the red-sequence galaxies) Color Cuts (Getting just the red-sequence galaxies)

11. MaxBCG ALGORITHM: Color Cuts It has been observed that red sequence cluster galaxies inhabit a tight sequence in the color-magnitude diagram. This is called the E/S0 ridgeline. It has been observed that red sequence cluster galaxies inhabit a tight sequence in the color-magnitude diagram. This is called the E/S0 ridgeline. In MaxBCG color cuts, you select galaxies whose colors are within 2 sigma of the central color value of the ridgeline, where sigma is: In MaxBCG color cuts, you select galaxies whose colors are within 2 sigma of the central color value of the ridgeline, where sigma is:

12. MaxBCG ALGORITHM Koester had already performed the algorithm earlier on the SDSS database, and he had a list of centers (about 14000). Koester had already performed the algorithm earlier on the SDSS database, and he had a list of centers (about 14000). But his magnitude limits weren’t faint enough for us to be able to use in our project But his magnitude limits weren’t faint enough for us to be able to use in our project I also did not have access to any of his codes he used for the algorithm I also did not have access to any of his codes he used for the algorithm

13. MY PROCEDURE Study the theory behind the algorithm to understand how exactly it is supposed to work. Study the theory behind the algorithm to understand how exactly it is supposed to work. Then convert the algorithm to programming codes so that I could do something useful with it. Then convert the algorithm to programming codes so that I could do something useful with it. Extract all the cluster centers from the MaxBCG catalog (using TCL) Extract all the cluster centers from the MaxBCG catalog (using TCL) Use those centers and the required cuts to do a search in the SDSS database ( using SQL) to get a members catalog for the clusters Use those centers and the required cuts to do a search in the SDSS database ( using SQL) to get a members catalog for the clusters Count the number of galaxies in each of the clusters, find the required ratios and analyze Count the number of galaxies in each of the clusters, find the required ratios and analyze

14. INITIAL RESULTS AND ISSUES This was my initial result for giant to dwarf ratio vs red-shift This was my initial result for giant to dwarf ratio vs red-shift

15. INITIAL RESULTS AND ISSUES This was quite an unexpected result, and it seemed that something was going wrong This was quite an unexpected result, and it seemed that something was going wrong

16. INITIAL RESULTS AND ISSUES I re-assessed all of my procedures, and figured out that my problem existed in the color cuts. I created color-magnitude diagrams for some of my clusters I re-assessed all of my procedures, and figured out that my problem existed in the color cuts. I created color-magnitude diagrams for some of my clusters

17. COLOR MAGNITUDE DIAGRAMS I should not have ignored the slope in the color-magnitude diagram

18. COLOR MAGNITUDE DIAGRAMS The error in the colors seemed to be way too high for higher redshifts

19. COLOR MAGNITUDE DIAGRAMS

20. At higher red-shifts, objects are further away, and hence they appear fainter At higher red-shifts, objects are further away, and hence they appear fainter The fainter the object appears on the telescope, its photometric precision gets less accurate The fainter the object appears on the telescope, its photometric precision gets less accurate Looking at the graph, we can’t trust the data for red-shift more than about 0.2 Looking at the graph, we can’t trust the data for red-shift more than about 0.2

21. NEW RESULTS After making the adjustment for the slope, and understanding that I can’t trust the data for red-shift range 0.2-0.3, I plotted the graph and got the following result After making the adjustment for the slope, and understanding that I can’t trust the data for red-shift range 0.2-0.3, I plotted the graph and got the following result

22. MY CONCLUSION So ignoring data for red-shift range 0.2-0.3, and only looking at the range of 0.1 to 0.2, I came to the conclusion that there is no significant change in the giant to dwarf ratio of red galaxies in clusters at different red-shifts. So ignoring data for red-shift range 0.2-0.3, and only looking at the range of 0.1 to 0.2, I came to the conclusion that there is no significant change in the giant to dwarf ratio of red galaxies in clusters at different red-shifts.

23. COMPARING MY RESULTS WITH OTHER PEOPLE Strength Strength My data is very precise. I use 14000 clusters as opposed to 10 or 20 by others My data is very precise. I use 14000 clusters as opposed to 10 or 20 by others Weakness Weakness My red-shift range is small (0.1 to 0.2) compared to De Lucia whose clusters range from 0.02 to 0.7 My red-shift range is small (0.1 to 0.2) compared to De Lucia whose clusters range from 0.02 to 0.7

24. FURTHER STEPS Background subtraction Background subtraction Modifying MaxBCG algorithm to make it more efficient for my project Modifying MaxBCG algorithm to make it more efficient for my project A better way of selecting galaxies at higher red-shifts ( 0.2 to 0.3) A better way of selecting galaxies at higher red-shifts ( 0.2 to 0.3) Analyzing clusters with red-shifts higher than the SDSS range ( >0.4 ) Analyzing clusters with red-shifts higher than the SDSS range ( >0.4 ) Extensive theoretical analysis of the explanation and consequences of my results Extensive theoretical analysis of the explanation and consequences of my results

25. QUESTIONS???