J/MNRAS/510/2228 ZTF DR1 light curves of SNe Type Ia (Dhawan+, 2022)
The Zwicky Transient Facility Type Ia supernova survey first data release
and results.
Dhawan S., Goobar A., Smith M., Johansson J., Rigault M., Nordin J.,
Biswas R., Goldstein D., Nugent P., Kim Y.-L., Miller A.A., Graham M.J.,
Medford M., Kasliwal M.M., Kulkarni S.R., Duev D.A., Bellm E., Rosnet P.,
Riddle R., Sollerman J.
<Mon. Not. R. Astron. Soc. 510, 2228-2241 (2022)>
=2022MNRAS.510.2228D 2022MNRAS.510.2228D (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Supernovae ; Transient ; Surveys ; Optical ;
Infrared ; Spectroscopy ; Photometry ; Positional data ;
Redshifts ; Spectral types
Keywords: surveys - supernovae: general - distance scale
Abstract:
Type Ia supernovae (SNe Ia) in the nearby Hubble flow are excellent
distance indicators in cosmology. The Zwicky Transient Facility (ZTF)
has observed a large sample of SNe from an untargeted, rolling survey,
reaching 20.8, 20.6, and 20.3 mag in g r, and i band, respectively.
With an FoV of 47 deg2, ZTF discovered > 3000 SNe Ia in a little
over 2.5 yr. Here, we report on the sample of 761 spectroscopically
classified SNe Ia from the first year of operations (DR1). The sample
has a median redshift zmed = 0.057, nearly a factor of 2 higher than
the current low-z sample. Our sample has a total of 934 spectra, of
which 632 were obtained with the robotic SEDm on Palomar P60. We
assess the potential for precision cosmology for a total of 305 SNe
with redshifts from host galaxy spectra. The sample is already
comparable in size to the entire combined literature low-z anchor
sample. The median first detection is 13.5 d before maximum light,
about 10 d earlier than the median in the literature. Furthermore, six
SNe from our sample are at DL < 80 Mpc, for which host galaxy
distances can be obtained in the JWST era, such that we have
calibrator and Hubble flow SNe observed with the same instrument. In
the entire duration of ZTF-I, we have observed nearly 50 SNe for which
we can obtain calibrator distances, key for per cent level distance
scale measurements.
Description:
In this paper, we present the data set from the first year of
operations and first results from the ZTF SN Ia survey. The ZTF SNe Ia
sample aims to anchor current and future high-z SN Ia sample for dark
energy studies, unlock the study of LSS in the nearby universe, and
measure H0 using a unique, self-consistent, calibrator and
Hubble-flow sample. With the anticipated deluge of well-observed
high-z SNe Ia from the Vera Rubin Observatory Legacy Survey of Space
and time (see The LSST Dark Energy Science Collaboration et al.
2018arXiv180901669T 2018arXiv180901669T, for the science requirements document), the
large, homogeneously measured, untargeted low-z sample of SNe Ia from
ZTF has the potential to be a definitive data set for cosmology in the
coming decade, (i.e see section Introduction).
The survey design and science objectives for ZTF are described in
detail in Bellm et al. (2019PASP..131a8002B 2019PASP..131a8002B, 2019PASP..131f8003B 2019PASP..131f8003B) and
Graham et al. (2019PASP..131g8001G 2019PASP..131g8001G). ZTF uses a 47 deg2 field with a
600 megapixel camera to scan the entire northern visible sky. ZTF in
phase-I of observations from 2018 March to 2020 November, operated a
unique survey strategy. The distribution of the SNe across the sky is
available which also presents a graphical overview of the DR1 survey,
including light-curve and spectral sampling. ZTF acheived these
observations in g,r, i optical/IR bands (i.e see sections 2.1 Survey
strategy, 2.2 The partnership survey and 2.3 Spectroscopy and sample
selection).
As explicited in the section 2.3 Spectroscopy and sample selection, we
focus on the sample of spectroscopically classified SNe Ia discovered
in 2018, i.e. the first year of operations for ZTF. For the complete
sample of 761 objects, we have obtained a total of 632 spectra with
the SED machine, which corresponds to 68 per cent of the total sample
of spectra. In our study (i.e see section 2.4 Host galaxy redshifts),
we want to infer the light-curve parameters for the SNe Ia in the DR1
sample and quantify the scatter in the Hubble residuals. The table1.dat
provide the observational informations of all observed SNe in the
first year. Hereafter, we process to data quality cuts giving birth to
a constrained 305 SNe Ia sample presented in the table2.dat with
associated zhelio SNe host galaxy.
Thanks to the described pipeline in the section 2.5 Photometry
pipeline, we generated light curves for our SNe Ia sample, access to
these LCs are in the folder lcs and the table2b.dat shows all studied
SNe with LC file path. Finally, as exposed in the section 3 Analysis
and results, we fit all LCs with a fitting algorithm SALT2 (Guy et al.
2007A&A...466...11G 2007A&A...466...11G, see section 3.1 Light-curve fitting) in order to
obtain relations between luminosity, light-curve shape and colour for
measuring accurate SNe Ia distances. Output SALT2 fit parameters for
SNe in our sample are given the table3.dat.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 108 729 The SNe Ia in the complete Year 1 sample
table2.dat 150 305 *Heliocentric frame redshift for our SN Ia host
galaxy sample
table2b.dat 134 761 The light curves of SNe Ia in the complete
Year 1 sample
table3.dat 164 305 Output SALT2 fit parameters for SNe in our
sample along with the CMB frame redshift
lcs/* . 305 The individual SNe Ia light curves
(with file names Name.dat)
--------------------------------------------------------------------------------
Note on table2.dat: We restrict the sample to SNe with sufficient data around
and before maximum light from the alert pipeline. This is required to have a
robust initial estimate of the time of maximum for creating custom reference
and difference images to perform forced photometry (see Section 2.5 Photometry
pipeline for details). The final sample with these constraints has 305 SNe Ia.
--------------------------------------------------------------------------------
See also:
V/154 : Sloan Digital Sky Surveys (SDSS), Release 16 (DR16)
(Ahumada+, 2020)
J/ApJ/895/32 : Zwicky Transient Facility BTS. I. (Fremling+, 2020)
J/ApJ/886/152 : ZTF early observations of Type Ia SNe. I. LCs (Yao+, 2019)
J/ApJ/859/101 : The supernovae Ia Pantheon sample (Scolnic+, 2018)
https://github.com/ZwickyTransientFacility/ztfcosmodr : Data used in this study
https://ned.ipac.caltech.edu/ : NED database
https://github.com/zuds-survey/zuds-pipeline : Photometry pipeline for LCs
https://sncosmo.readthedocs.io/en/v2.1.x/ : Python SNe tools library
https://github.com/astrobarn/spextractor : Spectroscopic gaussian fitting code
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- Name SNe name given by ZTF (Name)
14- 22 A9 --- IAU IAU name for SNe (IAU Name)
24- 34 F11.7 deg RAdeg Right ascension (J2000) (RA)
36- 46 F11.7 deg DEdeg Declination (J2000) (Dec)
48- 62 A15 --- Class Object SN Ia classification with the ZTF SED
machine (Classification)
64- 73 A10 "Y:M:D" Obs First observation date (Obs Date)
75- 85 A11 --- Inst Spectroscopic instrument name (Instrument)
87- 97 A11 --- R Instrumental resolution range (Resolution)
99-108 A10 "Y:M:D" Spec Date of the first spectroscopic observation
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- Name SNe name given by ZTF (Name)
14- 33 F20.18 --- zhost SNe Ia host galaxy heliocentric
redshift (zhelio) (1)
35- 53 F19.15 deg RAdeg Right ascension of the SNe (J2000) (RA)
55- 75 F21.17 deg DEdeg Declination of the SNe (J2000) (Dec)
77-132 A56 --- FileName Name of the light curve files path
in ZTF data
134-150 A17 --- FileName2 Name of the light curve files
in subdirectory lcs
--------------------------------------------------------------------------------
Note (1): We compile the SN Ia host galaxy redshifts here. A large fraction of
these host galaxy redshifts are obtained from the Sloan Digital Sky
Survey (SDSS) 16th data release (Ahumada et al. 2020ApJS..249....3A 2020ApJS..249....3A,
Cat. V/154). For SNe Ia that do not have a redshift for the host
galaxy in SDSS, we obtain the redshift from the NASA Extragalactic
Database (NED, https://ned.ipac.caltech.edu/).
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2b.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- Name SNe name given by ZTF (Name)
14- 33 F20.18 --- zhost SNe Ia host galaxy heliocentric redshift
(zhelio) (1)
35- 45 F11.7 deg RAdeg Right ascension of the SNe (J2000) (RA)
47- 57 F11.7 deg DEdeg Declination of the SNe (J2000) (Dec)
59- 73 A15 --- Class Object SN Ia classfifcation (Classification)
75-130 A56 --- FileName Name of the light curve files path
132-134 A3 --- Flag [Yes No] Indicates if the SNe pass the data
quality test mentionned for the table2.dat
--------------------------------------------------------------------------------
Note (1): We compile the SN Ia host galaxy redshifts here. A large fraction of
these host galaxy redshifts are obtained from the Sloan Digital Sky
Survey (SDSS) 16th data release (Ahumada et al. 2020ApJS..249....3A 2020ApJS..249....3A,
Cat. V/154). For SNe Ia that do not have a redshift for the host
galaxy in SDSS, we obtain the redshift from the NASA Extragalactic
Database (NED, https://ned.ipac.caltech.edu/).
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- Name SNe name given by ZTF (ZTFName)
14- 33 F20.18 --- zCMB SNe Ia host galaxy redshift in CMB rest
frame (zCMB) (1)
35- 52 F18.15 mag Bmag Observed apparent magnitude in B-band AB mag
system (mb) (2)
54- 75 F22.18 mag e_Bmag Mean error of Bmag (emb)
77- 97 F21.18 --- x1 The x1 SALT2 output parameter (x1) (2)
99-119 F21.18 --- e_x1 Mean error of x1 (ex1)
121-143 F23.20 --- c The c SALT2 output parameter (c) (2)
145-164 F20.18 --- e_c Mean error of c (ec)
--------------------------------------------------------------------------------
Note (1): We convert the heliocentric redshifts to CMB frame using the standard
conversion formula and the dipole velocity and position of the CMB
from Fixsen et al. (1996ApJ...473..576F 1996ApJ...473..576F), (i.e see section 3.4.2
Hubble residuals).
Note (2): To be used for cosmology, SNe Ia need to be standardized, using
relations between their luminosity and the light-curve shape and
colour, for measuring accurate distances (see Leibundgut &
Sullivan 2018SSRv..214...57L 2018SSRv..214...57L, for a review of how SNe Ia are used in
cosmology). Currently, the most widely used light-curve fitting (light
curves generated using the pipeline described in section 2.5
Photometry pipeline) algorithm is the Spectral Adaptive Lightcurve
Template 2 (SALT2; Guy et al. 2007A&A...466...11G 2007A&A...466...11G), based on the SALT
method (Guy et al. 2005A&A...443..781G 2005A&A...443..781G) and we use this in our
analysis (i.e see section 3.1 Light-curve fitting). The SALT2 model
assumes a parametrization from Tripp as written in the equation 1 of
this 2.5 section(1998A&A...331..815T 1998A&A...331..815T) including mb, x1 and c.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: lcs/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 F15.7 d JD The Julian date time of the recorded image
(time)
17- 20 A4 --- Band [p48g p48r p48i] The ZTF photometry band
used to record the image (band) (1)
22- 46 F25.19 mag SNemag The SNe apparent AB magnitude in the
dedicated band from aperture photometry at
the SN position as explained in the section
2.5 Photometry pipeline and in the
Appendix A (flux)
48- 66 F19.15 mag e_SNemag Mean uncertainty of the SNemag (flux_err)
68- 85 F18.15 mag zpmag Zero point magnitude (zp) (2)
87- 92 F6.1 --- Flag [0.0/2050.0] Light curves flag value (flags)
(3)
94- 95 A2 --- Sys [ab] The magnitude systems used to register
the zero-point (zpsys)
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Note (1): The ZTF Observing System delivers efficient, high-cadence,
wide-field-of-view, multi-band optical imagery for time-domain
astrophysics analysis. It is installed on the 48 inch Samuel Oschin
Telescope (Schmidt-type) at the Palomar Observatory delivering
photometry images in the g, r and i bands.
Note (2): We use the photutilsastropy package (Bradley et al.
2019zndo...3450769E) for performing aperture photometry at the SN
position, determined from the alert photometry provided by IPAC.
For each epoch, the zero-point (used to calibrate to the standard
magnitude system) is derived from a combination of the nightly
zero-point and aperture correction provided by IPAC (see Masci et
al. 2019PASP..131a8003M 2019PASP..131a8003M, for details), (i.e refer to section 2.5
Photometry pipeline and in the Appendix A).
Note (3): This particular flage takes four possible values as 0.0, 2.0, 2048.0
and 2050.0 (∼82 per cent of this flag is 2050.0).
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 04-Nov-2024