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HI Stacking: Past, Present and Future

HI Stacking: Past, Present and Future. Philip Lah. HI Pathfinder Workshop Perth, February 2-4, 2011. HI Stacking. C oadding the HI 21-cm emission from distant galaxies using the galaxies’ known optical positions and redshifts n oise decreases √ N galaxies stacked. HI Stacking.

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HI Stacking: Past, Present and Future

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  1. HI Stacking: Past, Present and Future Philip Lah HI Pathfinder Workshop Perth, February 2-4, 2011

  2. HI Stacking Coadding the HI 21-cm emission from distant galaxies using the galaxies’ known optical positions and redshiftsnoise decreases √N galaxies stacked

  3. HI Stacking Coadding the HI 21-cm emission from distant galaxies using the galaxies’ known optical positions and redshiftsnoise decreases √N galaxies stacked

  4. Past

  5. HI Stacking

  6. HI Stacking

  7. HI Stacking

  8. HI Stacking

  9. The HI Gas Density of the Universe

  10. HI Gas Density Evolution

  11. HI Gas Density Evolution Noterdaeme et al. 2009 & Prochaska et al. 2005 DLAs Lah et al. 2007 coadded HI 21cm Rao et al. 2006 DLAs from MgII absorption Zwaan et al. 2005 HIPASS HI 21cm

  12. HI Gas Density Evolution Lah et al. 2007 coadded HI 21cm

  13. HI Stacking

  14. HI Stacking

  15. HI Stacking

  16. HI Gas Density Evolution

  17. HI Gas Density Evolution Chang et al. 2010 HI emission cross-correlation

  18. Hydrogen 21-cm Intensity Mapping at Redshift 0.8 • ΩHI = (5.5 ± 1.5) × 10-4× (1/rb) • b is the bias factor, the HI to optical galaxy relationship • r is the stochasticity, the distribution of galaxies, how random is it • theoretical constraints put rb in the range 0.5 to 2

  19. Hydrogen 21-cm Intensity Mapping at Redshift 0.8 • ΩHI = (5.5 ± 1.5) × 10-4× (1/rb) • b is the bias factor, the HI to optical galaxy relationship • r is the stochasticity, the distribution of galaxies, how random is it • theoretical constraints put rb in the range 0.5 to 2

  20. Hydrogen 21-cm Intensity Mapping at Redshift 0.8 • ΩHI = (5.5 ± 1.5) × 10-4× (1/rb) • b is the bias factor, the HI to optical galaxy relationship • r is the stochasticity, the distribution of galaxies, how random is it • theoretical constraints put rb in the range 0.5 to 2

  21. HI Gas Density Evolution Chang et al. 2010 HI emission cross-correlation Effect of systematic uncertainty in ‘rb’ term (0.5 to 2)

  22. HI Stacking

  23. Present

  24. Challenges Encountered When HI Stacking

  25. The Telescope Primary Beamand the Galaxy Spatial Distribution

  26. Telescope Gain GMRT Primary Beam Abell 370 galaxies

  27. Telescope Gain GMRT Primary Beam Abell 370 galaxies 50% beam level 10% beam level use a weighted average

  28. Galaxy Size and the Telescope Synthesis Beam

  29. HI Galaxy Size

  30. HI Galaxy Size 20 kpc HI mass ~109M with cosmological correction uncorrected R2 law

  31. HI Galaxy Size GMRT synthesis beam FWHM

  32. HI Galaxy Size ASKAP synthesis beam FWHM GMRT synthesis beam FWHM

  33. HI Galaxy Size WSRT synthesis beam FWHM ASKAP synthesis beam FWHM GMRT synthesis beam FWHM 100 kpc HI mass ~ 31010 M

  34. HI Galaxy Size Beam Confusion – problem mainly with companion galaxies and in outskirts of clusters

  35. HI Velocity Width and Optical Selection

  36. HI velocity width face on disk galaxy HI flux velocity edge on disk galaxy HI flux velocity

  37. HI Velocity Width y • Assuming a random distribution of disk orientations: • 13% of disk galaxies will have inclinations < 30° (face on) • 50% of disk galaxies will have inclinations > 60° (edge on) face on disk galaxies x z  z y edge on disk galaxies x

  38. HI Velocity Width HI selected galaxies biased towards face on – higher peak flux

  39. HI Velocity Width optical selection less effected by inclination bias edge on systems – higher optical surface brightness

  40. The End Result The coadded HI velocity width of an optically selected sample of galaxies will be larger than the coadded HI velocity width of a HI selected sample of similar galaxies → the HI flux of coadded optical samples will be spread over more frequency channels

  41. Optical Redshift Error additionally the coadded HI velocity width of an optically selected sample of galaxies will be further broadened by the random error in the optical redshift

  42. Future

  43. HI coadding with SKA Pathfinders

  44. EVLA &zCOSMOS

  45. EVLA z= 0 to 0.4

  46. EVLA EVLAbeam FWHM at 1000 MHz HI z = 0.42 45 arcmin EVLAbeam 10% level at 1000 MHz HI z = 0.42 82 arcmin z= 0 to 0.4

  47. EVLA ~65 per cent of zCOSMOS galaxies are star-forming, blue, disk-dominate galaxies (Mignoli et al.2008) nz = 1723

  48. EVLA

  49. EVLA Examining volume spanned by zCOSMOS survey

  50. EVLA Examining volume spanned in a redshift bin

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