Photometric classification and redshift estimation of LSST Supernovae

Journal Article · 19 April 2018 · Monthly Notices of the Royal Astronomical Society

DOI: https://doi.org/10.1093/mnras/sty965 · OSTI ID:1439475

Dai, Mi  ^[1]; Kuhlmann, Steve ^[2]; Wang, Yun ^[3]; Kovacs, Eve ^[2]

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1. Rutgers University, Piscataway, NJ (United States)
2. Argonne National Laboratory (ANL), Argonne, IL (United States)
3. California Institute of Technology (CalTech), Pasadena, CA (United States)

Supernova (SN) classification and redshift estimation using photometric data only have become very important for the Large Synoptic Survey Telescope (LSST), given the large number of SNe that LSST will observe and the impossibility of spectroscopically following up all the SNe. We investigate the performance of an SN classifier that uses SN colours to classify LSST SNe with the Random Forest classification algorithm. Our classifier results in an area-under-the-curve of 0.98 which represents excellent classification. We are able to obtain a photometric SN sample containing 99 percent SNe Ia by choosing a probability threshold. We estimate the photometric redshifts (photo-z) of SNe in our sample by fitting the SN light curves using the SALT2 model with nested sampling. We obtain a mean bias ($$\langle$$z_phot - z_spec$$\rangle$$) of 0.012 with σ($$\frac{zphot-zspec}{1+zspec}$$)=0.0294 σ(zphot-zspec1+zspec)=0.0294 without using a host-galaxy photo-z prior, and a mean bias ($$\langle$$z_phot - z_spec$$\rangle$$) of 0.0017 with σ($$\frac{zphot-zspec}{1+zspec}$$)=0.0116 using a host-galaxy photo-z prior. Assuming a flat ΛCDM model with Ω_m = 0.3, we obtain Ω_m of 0.305 ± 0.008 (statistical errors only), using the simulated LSST sample of photometric SNe Ia (with intrinsic scatter σ_int = 0.11) derived using our methodology without using host-galaxy photo-z prior. Our method will help boost the power of SNe from the LSST as cosmological probes.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC02-06CH11357
• OSTI ID: 1439475
• Journal Information: Monthly Notices of the Royal Astronomical Society, Journal Name: Monthly Notices of the Royal Astronomical Society Journal Issue: 3 Vol. 477; ISSN 0035-8711
• Publisher: Oxford University PressCopyright Statement
• Country of Publication: United States
• Language: English