{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/21485"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/21485","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Cosmological hydrodynamic simulations of the Lyman-alpha forest","abstract":"Several three dimensional, multi-species, cosmological hydrodynamic simulations of the formation and evolution of Ly$\\alpha$ forest absorbers were performed in three CDM-like cosmological models: the standard CDM model (SCDM), the flat CDM model with a nonzero cosmological constant ($\\Lambda$CDM) and the open CDM model (OCDM). Synthetic spectra along random lines-of-sight were generated and analyzed by using a powerful spectrum analysis method designed to mimic observational data reduction. The SCDM model was studied in great detail and found to be in excellent agreement with observations in: the slope and shape of the column density distribution, the value and distribution of the Doppler parameter and the equivalent width, the evolution of line density, effective opacity and flux decrement, etc. A number of sensitive tests were devised to compare and contrast different cosmological models, and it is found that both the SCDM and the $\\Lambda$CDM models agree with observations quite well, while the OCDM model fails to match most of the observational data satisfactorily. It is discovered that the low column density (log $N\\sb{HI}\\ \\simeq$ 13.3 and log $N\\sb{HeII}\\ \\simeq$ 14.5) H sc I and He sc II Ly$\\alpha$ absorbers which are optically-thin at the line center ($\\tau\\sb0 <$ 1) actually originate from density fluctuations in the underdense regions--cosmic minivoids, which have lower temperature than is allowed by thermal equilibrium, expand faster than the cosmic expansion, and contain a significant percentage of baryons previously thought to be in the diffuse form. A new picture of IGM is established with a continuous spectrum of clumpiness: from the traditional high column density Ly$\\alpha$ clouds, to intermediate column density Ly$\\alpha$ sheets and filaments, to a new class of absorbers--Ly$\\alpha$ voids--the under-brushes in the Ly$\\alpha$ forest.","abstract_html":"Several three dimensional, multi-species, cosmological hydrodynamic simulations of the formation and evolution of Ly<span class=\"etd-inline-math\">&alpha;</span> forest absorbers were performed in three CDM-like cosmological models: the standard CDM model (SCDM), the flat CDM model with a nonzero cosmological constant ($\\Lambda$CDM) and the open CDM model (OCDM). Synthetic spectra along random lines-of-sight were generated and analyzed by using a powerful spectrum analysis method designed to mimic observational data reduction. The SCDM model was studied in great detail and found to be in excellent agreement with observations in: the slope and shape of the column density distribution, the value and distribution of the Doppler parameter and the equivalent width, the evolution of line density, effective opacity and flux decrement, etc. A number of sensitive tests were devised to compare and contrast different cosmological models, and it is found that both the SCDM and the $\\Lambda$CDM models agree with observations quite well, while the OCDM model fails to match most of the observational data satisfactorily. It is discovered that the low column density (log <span class=\"etd-inline-math\">N\\sb{HI} \\simeq</span> 13.3 and log <span class=\"etd-inline-math\">N\\sb{HeII} \\simeq</span> 14.5) H sc I and He sc II Ly<span class=\"etd-inline-math\">&alpha;</span> absorbers which are optically-thin at the line center ($\\tau\\sb0 &lt;$ 1) actually originate from density fluctuations in the underdense regions--cosmic minivoids, which have lower temperature than is allowed by thermal equilibrium, expand faster than the cosmic expansion, and contain a significant percentage of baryons previously thought to be in the diffuse form. A new picture of IGM is established with a continuous spectrum of clumpiness: from the traditional high column density Ly<span class=\"etd-inline-math\">&alpha;</span> clouds, to intermediate column density Ly<span class=\"etd-inline-math\">&alpha;</span> sheets and filaments, to a new class of absorbers--Ly<span class=\"etd-inline-math\">&alpha;</span> voids--the under-brushes in the Ly<span class=\"etd-inline-math\">&alpha;</span> forest.","abstract_has_math":true,"creators":["Zhang, Yu"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Astronomy","degree_department":null,"school":null,"contributors":["Norman, Michael L."],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2011,"date_issued":"2011-05-07T13:09:58Z","date_published":"2011-05-07T13:09:58Z","updated_at":"2026-07-22T22:25:18Z","subjects":["Physics, Astronomy and Astrophysics"],"languages":["eng"],"rights":["Copyright 1996 Zhang, Yu"],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["9780591199840","AAI9712502","(UMI)AAI9712502"],"render_values":[{"text":"9780591199840","href":null,"code":true},{"text":"AAI9712502","href":null,"code":true},{"text":"(UMI)AAI9712502","href":null,"code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/2142/21485","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Norman, Michael L."]},{"key":"dc:creator","label":"Author","values":["Zhang, Yu"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2011-05-07T13:09:58Z","10000-01-01","1996"]},{"key":"dc:type","label":"Dc Type","values":["text"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Astronomy"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Physics, Astronomy and Astrophysics"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 1996 Zhang, Yu"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["9780591199840","AAI9712502","(UMI)AAI9712502","http://hdl.handle.net/2142/21485"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Several three dimensional, multi-species, cosmological hydrodynamic simulations of the formation and evolution of Ly$\\alpha$ forest absorbers were performed in three CDM-like cosmological models: the standard CDM model (SCDM), the flat CDM model with a nonzero cosmological constant ($\\Lambda$CDM) and the open CDM model (OCDM). Synthetic spectra along random lines-of-sight were generated and analyzed by using a powerful spectrum analysis method designed to mimic observational data reduction. The SCDM model was studied in great detail and found to be in excellent agreement with observations in: the slope and shape of the column density distribution, the value and distribution of the Doppler parameter and the equivalent width, the evolution of line density, effective opacity and flux decrement, etc. A number of sensitive tests were devised to compare and contrast different cosmological models, and it is found that both the SCDM and the $\\Lambda$CDM models agree with observations quite well, while the OCDM model fails to match most of the observational data satisfactorily. It is discovered that the low column density (log $N\\sb{HI}\\ \\simeq$ 13.3 and log $N\\sb{HeII}\\ \\simeq$ 14.5) H sc I and He sc II Ly$\\alpha$ absorbers which are optically-thin at the line center ($\\tau\\sb0 <$ 1) actually originate from density fluctuations in the underdense regions--cosmic minivoids, which have lower temperature than is allowed by thermal equilibrium, expand faster than the cosmic expansion, and contain a significant percentage of baryons previously thought to be in the diffuse form. A new picture of IGM is established with a continuous spectrum of clumpiness: from the traditional high column density Ly$\\alpha$ clouds, to intermediate column density Ly$\\alpha$ sheets and filaments, to a new class of absorbers--Ly$\\alpha$ voids--the under-brushes in the Ly$\\alpha$ forest.","Made available in DSpace on 2011-05-07T13:09:58Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9712502.pdf: 7321110 bytes, checksum: da1cac88166df6e2b874ac02798a5f61 (MD5) Previous issue date: 1996","Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T14:51:06Z Item is restricted indefinitely.","Restriction data tranferred 2014-07-01T11:23:25-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission","ETDs are only available to UIUC Users without author permission","U of I Only"]},{"key":"dc:title","label":"Title","values":["Cosmological hydrodynamic simulations of the Lyman-alpha forest"]}]}],"canonical_facts":{"dc:contributor":["Norman, Michael L."],"dc:creator":["Zhang, Yu"],"dc:date":["2011-05-07T13:09:58Z","10000-01-01","1996"],"dc:description":["Several three dimensional, multi-species, cosmological hydrodynamic simulations of the formation and evolution of Ly$\\alpha$ forest absorbers were performed in three CDM-like cosmological models: the standard CDM model (SCDM), the flat CDM model with a nonzero cosmological constant ($\\Lambda$CDM) and the open CDM model (OCDM). Synthetic spectra along random lines-of-sight were generated and analyzed by using a powerful spectrum analysis method designed to mimic observational data reduction. The SCDM model was studied in great detail and found to be in excellent agreement with observations in: the slope and shape of the column density distribution, the value and distribution of the Doppler parameter and the equivalent width, the evolution of line density, effective opacity and flux decrement, etc. A number of sensitive tests were devised to compare and contrast different cosmological models, and it is found that both the SCDM and the $\\Lambda$CDM models agree with observations quite well, while the OCDM model fails to match most of the observational data satisfactorily. It is discovered that the low column density (log $N\\sb{HI}\\ \\simeq$ 13.3 and log $N\\sb{HeII}\\ \\simeq$ 14.5) H sc I and He sc II Ly$\\alpha$ absorbers which are optically-thin at the line center ($\\tau\\sb0 <$ 1) actually originate from density fluctuations in the underdense regions--cosmic minivoids, which have lower temperature than is allowed by thermal equilibrium, expand faster than the cosmic expansion, and contain a significant percentage of baryons previously thought to be in the diffuse form. A new picture of IGM is established with a continuous spectrum of clumpiness: from the traditional high column density Ly$\\alpha$ clouds, to intermediate column density Ly$\\alpha$ sheets and filaments, to a new class of absorbers--Ly$\\alpha$ voids--the under-brushes in the Ly$\\alpha$ forest.","Made available in DSpace on 2011-05-07T13:09:58Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9712502.pdf: 7321110 bytes, checksum: da1cac88166df6e2b874ac02798a5f61 (MD5) Previous issue date: 1996","Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T14:51:06Z Item is restricted indefinitely.","Restriction data tranferred 2014-07-01T11:23:25-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission","ETDs are only available to UIUC Users without author permission","U of I Only"],"dc:identifier":["9780591199840","AAI9712502","(UMI)AAI9712502","http://hdl.handle.net/2142/21485"],"dc:language":["eng"],"dc:rights":["Copyright 1996 Zhang, Yu"],"dc:subject":["Physics, Astronomy and Astrophysics"],"dc:title":["Cosmological hydrodynamic simulations of the Lyman-alpha forest"],"dc:type":["text"],"thesis:degree_discipline":["Astronomy"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."],"thesis:institution_name":["University of Illinois at Urbana-Champaign"]},"updated_at":"2026-07-22T22:25:18Z"}