The connection between Lyman-alpha absorption in low-redshift quasars and intervening galaxies
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Transcript of The connection between Lyman-alpha absorption in low-redshift quasars and intervening galaxies
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The connection between Lyman-alpha absorption in low-redshift quasars
and intervening galaxies
Alizera Aghaee, Begona Ascaso Angles, Ryan Houghton, Yuri Bialetski
Johen Liske
Tutor:
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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
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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
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What sort of data do we need ?
Large homogeneous spectroscopic database
of low-redshift QSO’s
Large homogeneousdatabase of
galaxies
Sloan Digital Sky Survey HST, Faint Object Spectrograph (FOS)
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1. RAW data
2. Reduced data
We can use …
3. Analysed (higher-level) data
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Go to the Archive …
… and get High-Level data !!!
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Method Overview
1. Search for homogenous archive of QSOs• Online archive of HST (FOS) QSO spectra
compiled by Bechtold et al. 2002
2. Search for large galaxy database• SDSS
3. Analyse & Cross-correlate absorbers and galaxies
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Quasar archive
1. Locate
2. Download
3. Select useful data
4. Summarize properties• Table of Quasar properties• Table of ‘clean’ Ly-a absorption
properties
335
273
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Galaxy archive
1.Locate which quasars positions in SDSS
2.Search for spectral observations taken ‘near’ these positions (SQL search)
• 2o x 2o bounding box
• Galaxies ONLY!
3.Extract galaxy properties from SDSS database
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Analysis and Cross-correlation
1.For each quasar calculate distance between each galaxy and each Lyman Alpha absorber (to find nearest neighbour galaxy)
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Can’t be related
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Conclusions
1. We found 6 galaxies which are likely to be associated with Lyman Alpha absorbers
2. For these six: EW ~ r -0.64 ± 0.1 (consistent with literature)
3. Relation holds up to r ~ 1 Mpc !!
4. However 4 of our pair are derived from one quasar spectrum (Q1226+0219) which is also used in Penton et al.
5. We need wider, deeper galaxy surveys to match the depth of the quasar archive (SDSS not finished)
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Summary
1. Compiled list of ‘clean’ Ly-a absorption lines in QSO spectra
2. Locate galaxies near QSO coordinates and extract their properties
3. Cross correlate and analyse: • Find nearest galaxy to each Ly-a absorption line• Study correlation between absorber and galaxy
properties
4. EW ~ r -0.64 ± 0.1