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Exploring Type Ia Supernova Systematics: the Host Galaxy Bias and Intrinsic Variability

Hand, Jared (2023) Exploring Type Ia Supernova Systematics: the Host Galaxy Bias and Intrinsic Variability. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Type Ia supernovae are bright transient events with similar peak brightness.
Once calibrated and standardized, type Ia supernova samples become powerful cosmological probes, especially for measuring dark energy and the universe’s accelerating expansion.
Rising tensions between independent measurements in an era of precision cosmology underscores the importance of accounting for systematic errors in analyses.
This is particularly true for type Ia supernova cosmology, where observations are fit to empirical models in place of elusive theoretical alternatives.
Additional concerning systematics include those arising from redshift dependence of the underlying supernova population.

This dissertation explores two topics in type Ia supernova systematics.
The established type Ia supernova host galaxy bias, where intrinsically brighter type Ia supernovae prefer less massive, younger hosts, alongside its potential dependence on observation methods and fitting techniques, is studied in chapter two.
Various host galaxy stellar mass and specific star formation rates samples are estimated from photometry or spectroscopy using different galaxy property fitting software, from which different estimates of the host bias are calculated and then compared.
No evidence is found that the choice in method or technique influences the host bias, let alone being the source of it.

The dissertation’s third chapter introduces a new physics-agnostic empirical model which provides more detailed exploration of phase-independent flux variation than that afforded by ubiquitous comparable models, such as SALT2.
It is demonstrated that there is sufficient signal-to-noise in available data sets to constrain models beyond the commonly used two parameter empirical model.
The results also indicate that intrinsic flux variation can be misidentified as dust-like, highlighting the difficulty estimated dust properties of type Ia supernovae.
For the second project, more work is needed to better separate dust-like flux variation from intrinsic variability, and to analyze the model’s standardization performance for cosmology applications.

Both topics studied advance our understanding of supernova cosmology systematics while stressing nuance in exploring sources of and solutions to these errors.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Hand, Jaredjsh89@pitt.edujsh890000-0001-7260-4274
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairWood-Vasey, William Michaelwmwv@pitt.eduwmwv0000-0001-7113-1233
Committee MemberBezanson, Rachelrachel.bezanson@pitt.edurab2500000-0001-5063-8254
Committee MemberBoudreau, Josephboudreau@pitt.eduboudreau
Committee MemberHillier, Desmond Johnhillier@pitt.eduhillier0000-0001-5094-8017
Committee MemberMandelbaum, Rachelrmandelb@andrew.cmu.edu0000-0003-2271-1527
Date: 6 September 2023
Date Type: Publication
Defense Date: 26 June 2023
Approval Date: 6 September 2023
Submission Date: 20 July 2023
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 183
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Physics
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: supernova, cosmology
Date Deposited: 06 Sep 2023 16:03
Last Modified: 06 Sep 2023 16:03


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