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The connection between Lyman-alpha absorption in low-redshift quasars and intervening galaxies

The connection between Lyman-alpha absorption in low-redshift quasars and intervening galaxies. Johen Liske. Tutor:. Alizera Aghaee, Begona Ascaso Angles, Ryan Houghton, Yuri Bialetski. What are quasars ?. The first quasar (3C273) was discovered in 1963

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The connection between Lyman-alpha absorption in low-redshift quasars and intervening galaxies

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  1. The connection between Lyman-alpha absorption in low-redshift quasars and intervening galaxies Johen Liske Tutor: Alizera Aghaee, Begona Ascaso Angles, Ryan Houghton, Yuri Bialetski

  2. What are quasars ? • The first quasar (3C273) was discovered in 1963 • Quasars are small, compact, powerful and extremely remote objects • Observed luminosity is approximately 10 - 1000 times that of a normal galaxy

  3. Lyman Alpha Absorption • Quasars emit strongly in the Lyman alpha • We observe the spectrum shifted to longer wavelengths • Light is absorbed by gas located between us and the quasar

  4. What sort of data do we need ? Large homogeneous spectroscopicdatabase of low-redshift QSO’s Large homogeneous database of galaxies HST, Faint Object Spectrograph (FOS) Sloan Digital Sky Survey

  5. What are the options?

  6. We can use … 1. RAW data 2. Reduced data 3. Analysed (higher-level) data

  7. Go to the Archive … … and get High-Level data !!!

  8. Method Overview • Search for homogenous archive of QSOs • Online archive of HST (FOS) QSO spectra compiled by Bechtold et al. 2002 • Search for large galaxy database • SDSS • Analyse & Cross-correlate absorbers and galaxies

  9. Quasar archive • Locate • Download • Select useful data • Summarize properties • Table of Quasar properties • Table of ‘clean’ Ly-a absorption properties 335 273

  10. Galaxy archive 58 • Locate which quasars positions in SDSS • Search for spectral observations taken ‘near’ these positions (SQL search) • 2o x 2o bounding box • Galaxies ONLY! • Extract galaxy properties from SDSS database

  11. Analysis and Cross-correlation • For each quasar calculate distance between each galaxy and each Lyman Alpha absorber (to find nearest neighbour galaxy)

  12. Can’t be related

  13. Conclusions • We found 6 galaxies which are likely to be associated with Lyman Alpha absorbers • For these six: EW ~ r -0.64 ± 0.1 (consistent with literature) • Relation holds up to r  ~ 1 Mpc !! • However 4 of our pair are derived from one quasar spectrum (Q1226+0219) which is also used in Penton et al. • We need wider, deeper galaxy surveys to match the depth of the quasar archive (SDSS not finished)

  14. Summary • Compiled list of ‘clean’ Ly-a absorption lines in QSO spectra • Locate galaxies near QSO coordinates and extract their properties • Cross correlate and analyse: • Find nearest galaxy to each Ly-a absorption line • Study correlation between absorber and galaxy properties • EW ~ r -0.64 ± 0.1

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