J/A+A/707/A91 ZTF SN Ia DR2 follow-up (Alburai+, 2026)
ZTF SN Ia DR2 follow-up:
Characterization of subluminous Type Ia supernovae in the ZTF DR2 full sample.
Alburai A., Galbany L., Burgaz U., Dimitriadis G., Johansson J., Smith M.,
Sanfeliu R., Guerra S., Mueller-Bravo T., Goobar A., Dhawan S., Kim Y.-L.,
Nordin J., Townsend A., Sollerman J., Ginolin M., Rigault M., Terwel J.H.,
Smith R., Wold A., Chen T.X., Jegou du Laz T.
<Astron. Astrophys. 707, A91 (2026)>
=2026A&A...707A..91A 2026A&A...707A..91A (SIMBAD/NED BibCode)
ADC_Keywords: Supernovae ; Photometry ; Optical ; Spectroscopy
Keywords: supernovae: general
Abstract:
The Zwicky Transient Facility Data Release 2 (ZTF DR2) includes a
total of 3628 Type Ia supernovae (SNe Ia), providing the largest and
most complete sample of spectroscopically confirmed SNe Ia at low
redshift to date. In this paper, we present a photometric and
spectroscopic analysis of 124 subluminous SNe Ia, the largest sample
of spectroscopically classified subluminous type Ia supernova observed
with a single instrument, comprising 87 91bg-like, 12 86G-like, 18
04gs-like, and 7 02es-like events. We complement the published DR2
SALT2 light-curve parameters with new parameters obtained using
template-based fits from SNooPy. Expansion velocities and
pseudo-equivalent widths pEW of key spectral features are measured
using Spextractor, and spectral averages are constructed for each
subluminous subtype, binned by phase. We also analyze the host galaxy
environments, both global and local, in terms of g-z color, stellar
mass, and directional light radius dDLR. We find that all subluminous
SNe∼Ia (except the 02es-like subtype) are intrinsically red. This is
evident by separating extrinsic from intrinsic color components. Since
SALT2 is not trained on subluminous SNe Ia, it compensates for their
redder colors by inflating the c parameter, thus extending the
luminosity- width relation to negative values of x1. As expected, all
subluminous SNe Ia fall within the Cool region of the Branch et al.
(2006PASP..118..560B 2006PASP..118..560B) diagram, with the exception of 02es-like events,
which show lower SiII 5972 pEW values. All subluminous subtypes tend
to occur in more massive, redder host galaxies, and in the reddest
local environments within their stellar mass bins. Notably, 91bg- and
86G-like SNe Ia explode at significantly larger normalized
galactocentric distances. Finally, we identify the $pEW$ of the
blended TiII+ SiII+MgII absorption feature at 4300Å, along with
sBV, as robust and sufficient indicators for subclassifying
subluminous SNe Ia.
Description:
This sample includes spectral measurements of velocity and
pseudo-equivalent widths (pEW), as well as photometric for subluminous
SNe Ia detected in the ZTF SN Ia DR2 full sample. It contains a data
for 124 SNe Ia.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 148 124 SN Ia light-curve parameters
tablea2.dat 133 124 Spectroscopic properties of all 124 SNe in
the initial sample
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See also:
J/A+A/694/A9 : Spectral Measurements of ZTF SN Ia DR2 (Burgaz+, 2025)
J/A+A/694/A10 : ZTF SN Ia DR2 (Dimitriadis+, 2025)
J/A+A/694/A11 : SN 2020alm spectrum (Terwel+, 2025)
J/A+A/694/A12 : ZTF SN Ia DR2. Secondary maximum in Type Ia SN
(Deckers+, 2025)
J/A+A/695/A264 : ZTF SN Ia DR2. SiII6355 high-velocity comp. (Harvey+, 2025)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- ZTF ZTF Name
15- 22 A8 --- IAU IAU Name
25- 32 F8.2 d MJDB SALT2 time of maximum B brightness
35- 39 F5.3 d e_MJDB SALT2 time of maximum B brightness error
42- 46 F5.2 mag Bmax SALT2 maximum B brightness
49- 53 F5.3 mag e_Bmax SALT2 maximum B brightness error
56- 60 F5.2 --- x1 SALT2 x1 stretch parameter
63- 67 F5.3 --- e_x1 SALT2 x1 stretch parameter error
70- 75 F6.3 mag c SALT2 color parameter
78- 82 F5.3 mag e_c SALT2 color parameter error
85- 92 F8.2 d MJDG ?=- SNooPy time of maximum G brightness
95- 98 F4.2 d e_MJDG ?=- SNooPy time of maximum G brightness error
101-106 F6.3 mag Gmax ?=- SNooPy maximum G brightness
108-112 F5.3 mag e_Gmax ?=- SNooPy maximum G brightness error
115-119 F5.3 --- sBV ?=- Reddest point in the B-V color curve
normalized by 30 days, sBV=(tmax/30days)
122-126 F5.3 --- e_sBV ?=- Reddest point in the B-V color curve
normalized by 30 days, sBV=(tmax/30days)
error
129-134 F6.3 mag E(B-V) ?=- Extinction E(B-V)
137-141 F5.3 mag e_E(B-V) ?=- Extinction E(B-V) error
144-148 A5 --- Source Source from which the values of the time of
maximum light are obtained
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Byte-by-byte Description of file: tablea2.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- ZTF ZTF name
15- 22 A8 --- IAU IAU name
25- 40 A16 --- subtype Spectroscopic classification
42- 48 F7.3 d Phase Spectral phase
50- 55 F6.3 10+3lm/s V SiII λ6355 velocity
57- 61 F5.3 10+3lm/s e_V SiII λ6355 velocity error
63- 69 F7.3 0.1nm pEWSiII6355 SiII λ6355 pseudo-equivalent width
71- 75 F5.3 0.1nm e_pEWSiII6355 SiII λ6355 pseudo-equivalent
width error
77- 83 F7.3 0.1nm pEWSiII5972 ? SiII λ5972 pseudo-equivalent
width
86- 90 F5.3 0.1nm e_pEWSiII5972 ? SiII λ5972 pseudo-equivalent
width error
92- 98 F7.3 0.1nm pEWMgII4000 ? MgII λ4000 pseudo-equivalent
width
100-104 F5.3 0.1nm e_pEWMgII4000 ? MgII λ4000 pseudo-equivalent
width error
106-112 F7.3 0.1nm pEWOI7774 ? OI λ7774 pseudo-equivalent width
114-118 F5.3 0.1nm e_pEWOI7774 ? OI λ7774 pseudo-equivalent
width error
120-126 F7.3 0.1nm pEWCaIINIR ? CaII NIR pseudo-equivalent width
128-133 F6.3 0.1nm e_pEWCaIINIR ? CaII NIR pseudo-equivalent width error
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Acknowledgements:
Alaa Alburai, alburai(at)ice.csic.es
(End) Patricia Vannier [CDS] 27-Dec-2025