Persistent Link:
http://hdl.handle.net/10150/288720
Title:
Star forming regions and the IMF along the Hubble sequence
Author:
Bresolin, Fabio, 1966-
Issue Date:
1997
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
This thesis examines the properties of star forming regions in galaxies across the Hubble sequence. It focuses on the stellar populations of giant extragalactic H scII regions and OB associations, addressing in particular the question of Initial Mass Function (IMF) variations with metallicity and/or galaxy morphology. This work is composed of three main sections: (a) 3650-10,000 Å spectroscopy of nearly 100 H scII regions in 20 spiral galaxies (Sa through Sm). Two indicators of the ionizing cluster effective temperature (T ͙) are analyzed: the intensity of the He I λ5876 line, and the 'radiation softness' parameter η = (O⁺O⁺⁺)/(S⁺S⁺⁺). The interpretation of the data relies on CLOUDY photoionization models. A positive T ͙ gradient of 7000-8000 K is found between 2 Z(⊙) and 0.2 Z(⊙). The diagnostic diagrams and the T ͙ - metallicity relation are consistent with an upper mass limit of the IMF of ∼100 M(⊙) and an age of ∼1 Myr, irrespective of chemical abundance or Hubble type. (b) An investigation of extragalactic OB associations, based on Hubble Space Telescope images. The size distribution of the associations (found with an automated search algorithm) is similar in all galaxies examined, with a mean size around 80 pc. An indication is found that the average number of bright blue stars depends on the parent galaxy Hubble type. The upper stellar V luminosity function is comparable among galaxies, with slope d log N/dMᵥ=0.61±0.03. A few star cluster candidates are identified. (c) UBVR and Hα photometry of 266 H II regions in 10 spiral galaxies (Sa through Sd). The Hα equivalent width is independent of Hubble type. The continuum and Hα luminosity functions show similar trends, namely a steeper slope and a smaller characteristic luminosity for early-type galaxies. These results lead to the conclusion that changes in the properties of H II regions and associations along the Hubble sequence are most likely due to variations in the number of stars per star forming region and in the number of regions per unit area, rather than the mass function.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Physics, Astronomy and Astrophysics.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Astronomy
Degree Grantor:
University of Arizona
Advisor:
Kennicutt, Robert C.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleStar forming regions and the IMF along the Hubble sequenceen_US
dc.creatorBresolin, Fabio, 1966-en_US
dc.contributor.authorBresolin, Fabio, 1966-en_US
dc.date.issued1997en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThis thesis examines the properties of star forming regions in galaxies across the Hubble sequence. It focuses on the stellar populations of giant extragalactic H scII regions and OB associations, addressing in particular the question of Initial Mass Function (IMF) variations with metallicity and/or galaxy morphology. This work is composed of three main sections: (a) 3650-10,000 Å spectroscopy of nearly 100 H scII regions in 20 spiral galaxies (Sa through Sm). Two indicators of the ionizing cluster effective temperature (T ͙) are analyzed: the intensity of the He I λ5876 line, and the 'radiation softness' parameter η = (O⁺O⁺⁺)/(S⁺S⁺⁺). The interpretation of the data relies on CLOUDY photoionization models. A positive T ͙ gradient of 7000-8000 K is found between 2 Z(⊙) and 0.2 Z(⊙). The diagnostic diagrams and the T ͙ - metallicity relation are consistent with an upper mass limit of the IMF of ∼100 M(⊙) and an age of ∼1 Myr, irrespective of chemical abundance or Hubble type. (b) An investigation of extragalactic OB associations, based on Hubble Space Telescope images. The size distribution of the associations (found with an automated search algorithm) is similar in all galaxies examined, with a mean size around 80 pc. An indication is found that the average number of bright blue stars depends on the parent galaxy Hubble type. The upper stellar V luminosity function is comparable among galaxies, with slope d log N/dMᵥ=0.61±0.03. A few star cluster candidates are identified. (c) UBVR and Hα photometry of 266 H II regions in 10 spiral galaxies (Sa through Sd). The Hα equivalent width is independent of Hubble type. The continuum and Hα luminosity functions show similar trends, namely a steeper slope and a smaller characteristic luminosity for early-type galaxies. These results lead to the conclusion that changes in the properties of H II regions and associations along the Hubble sequence are most likely due to variations in the number of stars per star forming region and in the number of regions per unit area, rather than the mass function.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectPhysics, Astronomy and Astrophysics.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineAstronomyen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorKennicutt, Robert C.en_US
dc.identifier.proquest9806801en_US
dc.identifier.bibrecord.b37541377en_US
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