Lens modelling of the strongly lensed Type Ia supernova iPTF16geu

ABSTRACT In 2016, the first strongly lensed Type Ia supernova (SN Ia), iPTF16geu, at redshift z = 0.409 with four resolved images arranged symmetrically around the lens galaxy at z = 0.2163, was discovered. Here, refined observations of iPTF16geu, including the time delay between images, are used to decrease uncertainties in the lens model, including the the slope of the projected surface density of the lens galaxy, Σ ∝ r1 − η, and to constrain the universal expansion rate H0. Imaging with Hubble Space Telescope provides an upper limit on the slope η, in slight tension with the steeper density profiles indicated by imaging with Keck after iPTF16geu had faded, potentially due to dust extinction not corrected for in host galaxy imaging. Since smaller η implies larger magnifications, we take advantage of the standard candle nature of SNe Ia constraining the image magnifications, to obtain an independent constraint of the slope. We find that a smooth lens density fails to explain the iPTF16geu fluxes, regardless of the slope, and additional substructure lensing is needed. The total probability for the smooth halo model combined with star microlensing to explain the iPTF16geu image fluxes is maximized at 12 per cent for η ∼ 1.8, in excellent agreement with Keck high-spatial-resolution data, and flatter than an isothermal halo. It also agrees perfectly with independent constraints on the slope from lens velocity dispersion measurements. Combining with the observed time delays between the images, we infer a lower bound on the Hubble constant, $H_0 \gtrsim 40\, {\rm km \ s^{-1} Mpc^{-1}}$, at 68.3 per cent confidence level.

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The Hubble Space Telescope Key Project to Measure the Hubble Constant

Symposium - International Astronomical Union ◽

10.1017/s007418090013205x ◽

1999 ◽

Vol 183 ◽

pp. 17-30 ◽

Cited By ~ 13

Author(s):

Wendy L. Freedman ◽

Jeremy R. Mould ◽

Robert C. Kennicutt ◽

Barry F. Madore

Keyword(s):

Hubble Space Telescope ◽

Hubble Constant ◽

Distance Scale ◽

General Assembly ◽

Host Galaxies ◽

Space Telescope ◽

Type Ia Supernova ◽

Type Ia ◽

Extragalactic Distance Scale

A Joint Discussion on the extragalactic distance scale and the Hubble constant took place fifteen years ago, at the 1982 XVIIIth General Assembly of the IAU, held in Patras, Greece. At that time, the newest applications of infrared photometers to Tully-Fisher measurements (Aaronson 1983) and Cepheid distances (Madore 1983) were reported. CCDs were just coming into use and had not yet been applied to extragalactic distance determinations; all of the extragalactic Cepheid distances were based on photographic Argelander (eye-estimated) photometry (Tammann and Sandage 1983 and references therein). No Cepheid distances to type Ia supernova-host galaxies were available.

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Spectroscopy of the first resolved strongly lensed Type Ia supernova iPTF16geu

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3829 ◽

2020 ◽

Author(s):

J Johansson ◽

A Goobar ◽

S H Price ◽

A Sagués Carracedo ◽

L Della Bruna ◽

...

Keyword(s):

Time Delay ◽

Hubble Space Telescope ◽

Signal To Noise Ratio ◽

Spectral Energy Distribution ◽

Compact Objects ◽

Light Curves ◽

Host Galaxy ◽

Spectral Energy ◽

Type Ia Supernova ◽

Type Ia

Abstract We report the results from spectroscopic observations of the multiple images of the strongly lensed Type Ia supernova (SN Ia), iPTF16geu, obtained with ground based telescopes and the Hubble Space Telescope (HST). From a single epoch of slitless spectroscopy with HST, we resolve spectra of individual lensed supernova images for the first time. This allows us to perform an independent measurement of the time-delay between the two brightest images, Δt = 1.4 ± 5.0 days, which is consistent with the time-delay measured from the light-curves. We also present measurements of narrow emission and absorption lines characterizing the interstellar medium in the SN Ia host galaxy at z = 0.4087, as well as in the foreground lensing galaxy at z = 0.2163. We detect strong Na id absorption in the host galaxy, indicating that iPTF16geu belongs to a subclass of SNe Ia displaying ”anomalously” large Na id column densities compared to dust extinction derived from light curves. For the lens galaxy, we refine the measurement of the velocity dispersion, σ = 129 ± 4 km s−1, which significantly constrains the lens model. We use ground-based spectroscopy, boosted by a factor ∼70 from lensing magnification, to study the properties of a high-z SN Ia with unprecedented signal-to-noise ratio. The spectral properties of the supernova, such as pseudo-Equivalent widths of several absorption features and velocities of the Si ii-line, indicate that iPTF16geu is a normal SN Ia. We do not detect any significant deviations of the SN spectral energy distribution from microlensing of the SN photosphere by stars and compact objects in the lensing galaxy.

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The effects of peculiar velocities in SN Ia environments on the local H0 measurement

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3456 ◽

2020 ◽

Vol 500 (3) ◽

pp. 3728-3742

Author(s):

Thomas M Sedgwick ◽

Chris A Collins ◽

Ivan K Baldry ◽

Philip A James

Keyword(s):

Hubble Constant ◽

Density Parameter ◽

Host Galaxies ◽

Peculiar Velocities ◽

Standard Candle ◽

Modern Cosmology ◽

Type Ia ◽

The Difference ◽

Ia Supernovae ◽

Distance Indicators

ABSTRACT The discrepancy between estimates of the Hubble constant (H0) measured from local (z ≲ 0.1) scales and from scales of the sound horizon is a crucial problem in modern cosmology. Peculiar velocities (vpec) of standard candle distance indicators can systematically affect local H0 measurements. We here use 2MRS galaxies to measure the local galaxy density field, finding a notable z < 0.05 underdensity in the SGC-6dFGS region of 27 ± 2 per cent. However, no strong evidence for a ‘Local Void’ pertaining to the full 2MRS sky coverage is found. Galaxy densities are used to measure a density parameter, Δϕ+−, which we introduce as a proxy for vpec that quantifies density gradients along a supernova (SN) line of sight. Δϕ+− is found to correlate with local H0 estimates from 88 Pantheon Type Ia supernovae (SNe Ia; 0.02 < z < 0.05). Density structures on scales of ∼50 Mpc are found to correlate strongest with H0 estimates in both the observational data and in mock data from the MDPL2-Galacticus simulation. Using trends of H0 with Δϕ+−, we can correct for the effects of density structure on local H0 estimates, even in the presence of biased vpec. However, the difference in the inferred H0 estimate with and without the peculiar velocity correction is limited to < 0.1 per cent. We conclude that accounting for environmentally induced peculiar velocities of SN Ia host galaxies does not resolve the tension between local and CMB-derived H0 estimates.

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Ultralong-period Cepheids: a possible primary distance indicator?

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312021552 ◽

2012 ◽

Vol 8 (S289) ◽

pp. 282-286 ◽

Cited By ~ 2

Author(s):

G. Fiorentino ◽

F. Annibali ◽

G. Clementini ◽

R. Contreras Ramos ◽

M. Marconi ◽

...

Keyword(s):

Spiral Galaxies ◽

Hubble Space Telescope ◽

Hubble Constant ◽

Variable Stars ◽

Evolutionary Status ◽

Stellar Systems ◽

Classical Cepheids ◽

Type Ia ◽

Distance Indicator ◽

Crucial Test

AbstractWe present a project that aims to provide a complete theoretical and observational framework for an as yet unexplored class of variable stars, the ultralong-period Cepheids (P longer than 80–100 days). Given their very high luminosities (MV up to −7 mag), with the Hubble Space Telescope we will be able to observe them easily in stellar systems located at large distances (~ 100 Mpc). This limit will be further increased, out to the Hubble flow (~ 350 Mpc), using future ground-based facilities such as the European Extremely Large Telescope. The nature of their pulsation is as yet unclear, as is their evolutionary status, which seems different from the central helium-burning phase generally associated with classical Cepheids. These objects have been found to cover a very large metallicity range, from [Fe/H] ~ −2 dex to solar values, and they are located in heterogeneous stellar systems, from dwarf to spiral galaxies. Once completely characterized, they could provide a crucial test, since they have been found in all Type Ia supernova host spiral galaxies that have been monitored for variability over long periods and that currently offer sound constraints on the estimated value of the Hubble constant.

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