Galaxy number count by using Optical images

1. Galaxy number count by using Optical images 潘國全(Pan Kuo-Chuan) Supervisor：川崎涉(Kawasaki Wataru)

2. Outline • I. Galaxy number count and probing the cosmological parameters • The data we used • Optical data reduction and calibration • Result

3. Galaxy number count and probing the cosmological parameters

4. Introduction • There are many methods to probe the cosmological parameters. • Number counting of faint galaxies is one of the most • fundamental observational test to determine the cosmological • density parameter, because it depends on the geometry of the • universe. • The spectrum of normal galaxies usually have a peak at optical • light, so we used the optical images to count galaxies.

5. Introduction to cosmological parameters • The Friedmann equations describing the space and • time by considering the homogeneous and isotropic • universe, which is given as :

6. Hubble constant, Density parameter Deceleration parameter Curvature parameter Λ parameter • We can define some cosmological parameter of • Friedmann cosmological models. Picture from : http://www.astr.ua.edu/white/mug/cluster/clusters.html

7. Why this depend on the cosmological parameter? Galaxy number count • The galaxy count data are obtained by counting up all images of • galaxies on a finite area of the sky. Let n(mλ,z)dmλdz be the • number of galaxies between mλ and mλ + dmλ and between z • and z + dz, then we have :

8. Assume Depend on cosmological parameters Ya! START

10. Subaru The Data we used Picture from: http://www.naoj.org/index.html

11. Instruments of Subaru Telescope • Infrared Camera and Spectrograph (IRCS) • Coronagraphic Imager with Adaptive Optics (CIAO) • Cooled Mid Infrared Camera and Spectrometer (COMICS) • Faint Object Camera And Spectrograph (FOCAS) • Subaru Prime Focus Camera (Suprime-Cam) • High Dispersion Spectrograpgh (HDS) • OH Airglow Suppression Spectrograph (OHS) • Adaptive Optics (AO)

12. Very unique instrument Subaru Prime Focus Camera (Suprime-Cam) • Suprime-Cam is one instrument of Subaru Telescope • which has 10 CCDs, and each have 2048*4096pixels The field of view is 34’x27’ Picture from: http://www.naoj.org/index.html

13. Picture from: http://www.naoj.org/index.html

14. Obs. Date : Apr.27 2003 • Observed Region • Passband : i ’ (SDSS) • Exposure time: 6x6min α：10h56m45s δ：-3°37’46” Data information

15. Optical Data Reduction and Calibration

16. Idea of getting the true objects value • It has 2048*4096 pixels in each CCD and we take it as a matrix then we say that the photon count of the Pixelij is Iij . Picture from: http://www.naoj.org/index.html

17. But the value we want is not the raw CCD pixels’ count, it depends on many conditions . Iij = ( Oij + Sij ) x Eij +Bij Iij = The observed value Oij = The object value Sij = The sky light value Eij = Efficiency Bij =Bias of CCDs So, the object value = ( (Iij-Bij )/ Eij ) - Sij

18. Estimate the Efficiency • If we give the same intensity for each pixels.

20. After subtracting the sky light we can • combine the 10CCDs images to be one image

21. Calibration • From now, we only have the electron counts of • each pixel, but we need the magnitude of each • object. • we get the relationship between apparent • magnitude and electron count of objects using • the standard star : • Make a catalog of all the objects in CCD image

22. Separating the stars and galaxies Peak flux/area

23. Peak flux/area

24. But the weather is bad for different exposures, so we also choose one exposure image to do the number count Peak flux/area

25. Result: Galaxy number count

26. Galaxy number counts

27. Compare with the theoretical number count lines

29. Problem • The seeing of data is bad. • We can not separate the faint galaxies and stars. • For different exposure time the data is not • consistent with theoretical line. • Main reason • Weather changed in different • exposure so there have some • systematic error.

30. Summary • Galaxy number count is one way to probe the cosmological • parameters. • We used some optical image data from Suprime-Cam on • Subaru Telescope. • With some optical data reduction we get the galaxy number • count and consistent with the theoretical model, but not • enough deep due to poor quality data. • If we had better seeing, we could reach to deeper magnitude • to fix the cosmological density parameter.

31. References • Galactic Evolution and Cosmology : Probing the Cosmological Deceleration Parameter (ApJ 326:1 1988) • Unavoidable selection effects in the analysis of faint galaxies in the Hubble deep field (ApJ540:81 2000) • http://www.naoj.org/