ROSAT Roentgen Satellite. Chandra X-ray Observatory

Transcription

1 ROSAT Roentgen Satellite Joint facility: US, Germany, UK Operated All-sky survey + pointed observations Chandra X-ray Observatory US Mission Operating 1999 present Pointed observations

2 How do you focus X-rays? Wolter X-ray telescope What is the collecting area (the size) of the telescope? How can we improve the collecting area?

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4 ROSAT Instrumentation Position Sensitive Proportional Counter (PSPC) 20 resolution, 2 degree FOV Energy range kev Effective area ~ 240 cm 2 at 1 kev Conducted all-sky survey Also did pointed observations High Resolution Imager (HRI) 5 resolution, 38 FOV Effective area ~ 80 cm 2 at 1 kev Pointed observations

5 Chandra Instrumentation Advanced CCD Imaging Spectrometer (ACIS) Imaging: 2 spatial resolution, ten 8 x8 CCDs Moderate resolution spectroscopy Energy range kev Effective area ~ 600 cm 2 at 1 kev High Resolution Camera (HRC) 0.4 resolution, 30 FOV Effective area ~ 200 cm 2 at 1 kev High Energy Transmission Grating (HETG) E/ΔE = kev Low Energy Transmission Grating (LETG) Optimized for low energy ( kev) spectroscopy

6 Chandra vs ROSAT: The Crab Nebula Optical image

7 Chandra vs ROSAT: The Crab Nebula

8 But how do you detect X-rays? Proportional Counters (ROSAT PSPC) Pass X-rays into a gas-filled chamber X-ray enters chamber, ionizes an atom (primary electron) Primary electrons can have enough energy to ionize other atoms (secondary electrons) Electrons accelerate towards anode wire, ionizing more atoms ( gas gain ~ 2-3 orders of magnitude) Multiple anode wires give positional sensitivity Energy information comes from signal strength Limited by gas supply Scintillation Detectors For X-ray energies > 50 kev, the gas density needed to stop an X-ray becomes prohibitive Scintillation detectors use solid crystal (NaI or CsI for example) which emits light upon absorption of a photon Detect photons using a photomultiplier tube

9 Microchannel plates (Chandra HRC) Material with many pores/channels, with a voltage applied. X-ray hits side of channel, kicks out electron Electron accelerates, kicks out more electrons Signal measured for each channel Long life-time (no gas supply issues) Good spatial resolution, poor energy resolution X-ray CCDs (Chandra ACIS) Conceptually like optical CCDs Optical photon produces 1 electron, X-ray photon produces many Optical CCDs integrate to build up charge X-ray CCDs can be read out fast, so charge tells you energy of X-ray

10 The Sloan Digital Sky Survey Dedicated 2.5m telescope at Apache Point, NM Main Survey ( Legacy ) operated , through Data Release 7 (DR7) Additional projects since then: SEGUE, BOSS, APOGEE, MARVELS (DR12) Imaging: Multiband ugriz, median seeing ~ s exposure time by scanning gives g lim = 22.2 ~ 1% photometric uncertainty 14,500 square degrees 208M galaxies, 260M stars Fiber spectroscopy: R ~ 2000 spectra from Å Redshift accuracy ~ 30 km/s Galaxies (r<17.77) and Quasars (i<19.1 or 20.2) ~ 2.4M galaxy spectra, 0.5M quasar spectra, 0.85M stellar spectra

11 SDSS Data Products Calibrated Images and Spectra: Quick look format Reduced fits files Data Products (Imaging): Magnitudes, colors For galaxies: size, structural information, photo-z Data Products (Spectra): Redshift/velocity Line indices Spectral classification Catalogs, for example: Luminous Red Galaxies Quasar catalog White dwarf catalog Moving objects

12 The ROSAT Brightest Cluster Sample (Ebeling et al 1998) Flux limited catalog of bright X-ray clusters (N=206)

13 Picking Clusters 1: Sky position: must be on SDSS footprint. (N ~ 159)

14 Picking Clusters 2: Cluster properties: we want massive clusters. (N = 111) Vikhlinin et al (2006) M 500 M 2500 M N = mass contained within a radius with an density of N times the average density of the universe. kt > 4 kev

15 Picking Clusters 3. Distance: We want them to fit on ACIS field of view (array of 8 x8 CCDs). z>0.035 We want to understand their optical morphology and nuclear spectra. (SDSS imaging resolution ~ 1 and fiber diameter ~ 3 ) z D A (Mpc) 1 Mpc (arcmin) 1 arcsec (kpc) z<0.075 N = 14

16 Picking Clusters so far. SDSS footprint kt > 4 kev < z < What s the next criterion? Chandra ACIS pointings!

17 Final Cluster Targets Cluster RA (deg) Dec (deg) Redshift Abell Abell Abell Notes: Cluster redshifts are approximate; you should refine these estimates using the SDSS data. When calculating intrinsic properties (physical sizes, luminosities, etc) remember that at these distances you must use the cosmologically correct luminosity distance (D L ) and angular size distance (D A ) to do the calculations.