Using Host Galaxy Photometric Redshifts to Improve Cosmological Constraints with Type Ia Supernovae in the LSST Era
Mitra A. Kessler R. More S. Hlozek R.
1 February 2023Institute of Physics
Astrophysical Journal
2023#944Issue 2
We perform a rigorous cosmology analysis on simulated Type Ia supernovae (SNe Ia) and evaluate the improvement from including photometric host galaxy redshifts compared to using only the “z spec” subset with spectroscopic redshifts from the host or SN. We use the Deep Drilling Fields (∼50 deg2) from the Photometric LSST Astronomical Time-Series Classification Challenge (PLAsTiCC) in combination with a low-z sample based on Data Challenge2. The analysis includes light-curve fitting to standardize the SN brightness, a high-statistics simulation to obtain a bias-corrected Hubble diagram, a statistical+systematics covariance matrix including calibration and photo-z uncertainties, and cosmology fitting with a prior from the cosmic microwave background. Compared to using the z spec subset, including events with SN+host photo-z results in (i) more precise distances for z > 0.5, (ii) a Hubble diagram that extends 0.3 further in redshift, and (iii) a 50% increase in the Dark Energy Task Force figure of merit (FoM) based on the w 0 w a CDM model. Analyzing 25 simulated data samples, the average bias on w 0 and w a is consistent with zero. The host photo-z systematic of 0.01 reduces FoM by only 2% because (i) most z < 0.5 events are in the z spec subset, (ii) the combined SN+host photo-z has ×2 smaller bias, and (iii) the anticorrelation between fitted redshift and color self-corrects distance errors. To prepare for analyzing real data, the next SN Ia cosmology analysis with photo-zs should include non-SN Ia contamination and host galaxy misassociations.
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The Inter-University Centre for Astronomy and Astrophysics (IUCAA), Post Bag 4, Ganeshkhind, Pune, 411007, India
Energetic Cosmos Laboratory, Nazarbayev University, Nur-Sultan, 010000, Kazakhstan
Kazakh-British Technical University, Almaty, Kazakhstan
Kavli Institute for Cosmological Physics, University of Chicago, Chicago, 60637, IL, United States
Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, 60637, IL, United States
University of Toronto, 27 King’s College Circle, Toronto, M5S, ON, Canada
The Inter-University Centre for Astronomy and Astrophysics (IUCAA)
Energetic Cosmos Laboratory
Kazakh-British Technical University
Kavli Institute for Cosmological Physics
Department of Astronomy and Astrophysics
University of Toronto
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