arXiv subjects

V. Bonvin

Publications and source records attributed to V. Bonvin.

26 records · Page 2Linked to original sources

arXiv2018

COSMOGRAIL XVII: Time delays for the quadruply imaged quasar PG 1115+080

We present time-delay estimates for the quadruply imaged quasar PG 1115+080. Our resuls are based on almost daily observations for seven months at the ESO MPIA 2.2m telescope at La Silla Observatory, reaching a signal-to-noise ratio of about 1000 per quasar image. In addition, we re-analyse existing light curves from the literature that we complete with an additional three seasons of monitoring with the Mercator telescope at La Palma Observatory. When exploring the possible source of bias we consider the so-called microlensing time delay, a potential source of systematic error so far never directly accounted for in previous time-delay publications. In fifteen years of data on PG 1115+080, we find no strong evidence of microlensing time delay. Therefore not accounting for this effect, our time-delay estimates on the individual data sets are in good agreement with each other and with the literature. Combining the data sets, we obtain the most precise time-delay estimates to date on PG 1115+080, with Dt(AB) = 8.3+1.5-1.6 days (18.7% precision), Dt(AC) = 9.9+1.1-1.1 days (11.1%) and Dt(BC) = 18.8+1.6-1.6 days (8.5%). Turning these time delays into cosmological constraints is done in a companion paper that makes use of ground-based Adaptive Optics (AO) with the Keck telescope.

astro-ph.CO↗

arXiv2017

H0LiCOW VIII. A weak lensing measurement of the external convergence in the field of the lensed quasar HE$\,$0435$-$1223

We present a weak gravitational lensing measurement of the external convergence along the line of sight to the quadruply lensed quasar HE$\,$0435$-$1223. Using deep r-band images from Subaru-Suprime-Cam we observe galaxies down to a 3$σ$ limiting magnitude of $\sim 26$ mags resulting in a source galaxy density of 14 galaxies / arcmin$^2$ after redshift-based cuts. Using an inpainting technique and Multi-Scale Entropy filtering algorithm, we find that the region in close proximity to the lens has an estimated external convergence of $κ=-0.012^{+0.020}_{-0.013}$ and is hence marginally under-dense. We also rule out the presence of any halo with a mass greater than $M_{\rm vir}=1.6\times10^{14}h^{-1}M_\odot$ (68$\%$ confidence limit). Our results, consistent with previous studies of this lens, confirm that the intervening mass along the line of sight to HE$\,$0435$-$1223 does not affect significantly the cosmological results inferred from the time delay measurements of that specific object.

astro-ph.CO↗

arXiv2017

COSMOGRAIL XVI: Time delays for the quadruply imaged quasar DES J0408-5354 with high-cadence photometric monitoring

We present time-delay measurements for the new quadruply imaged quasar DES J0408-5354, the first quadruply imaged quasar found in the Dark Energy Survey (DES). Our result is made possible by implementing a new observational strategy using almost daily observations with the MPIA 2.2m telescope at La Silla observatory and deep exposures reaching a signal-to-noise ratio of about 1000 per quasar image. This data quality allows us to catch small photometric variations (a few mmag rms) of the quasar, acting on temporal scales much shorter than microlensing, hence making the time delay measurement very robust against microlensing. In only 7 months we measure very accurately one of the time delays in DES J0408-5354: Dt(AB) = -112.1 +- 2.1 days (1.8%) using only the MPIA 2.2m data. In combination with data taken with the 1.2m Euler Swiss telescope, we also measure two delays involving the D component of the system Dt(AD) = -155.5 +- 12.8 days (8.2%) and Dt(BD) = -42.4 +- 17.6 days (41%), where all the error bars include systematics. Turning these time delays into cosmological constraints will require deep HST imaging or ground-based Adaptive Optics (AO), and information on the velocity field of the lensing galaxy.

astro-ph.IM↗

arXiv2017

Models of the strongly lensed quasar DES J0408-5354

We present gravitational lens models of the multiply imaged quasar DES J0408-5354, recently discovered in the Dark Energy Survey (DES) footprint, with the aim of interpreting its remarkable quad-like configuration. We first model the DES single-epoch $grizY$ images as a superposition of a lens galaxy and four point-like objects, obtaining spectral energy distributions (SEDs) and relative positions for the objects. Three of the point sources (A,B,D) have SEDs compatible with the discovery quasar spectra, while the faintest point-like image (G2/C) shows significant reddening and a `grey' dimming of $\approx0.8$mag. In order to understand the lens configuration, we fit different models to the relative positions of A,B,D. Models with just a single deflector predict a fourth image at the location of G2/C but considerably brighter and bluer. The addition of a small satellite galaxy ($R_{\rm E}\approx0.2$") in the lens plane near the position of G2/C suppresses the flux of the fourth image and can explain both the reddening and grey dimming. All models predict a main deflector with Einstein radius between $1.7"$ and $2.0",$ velocity dispersion $267-280$km/s and enclosed mass $\approx 6\times10^{11}M_{\odot},$ even though higher resolution imaging data are needed to break residual degeneracies in model parameters. The longest time-delay (B-A) is estimated as $\approx 85$ (resp. $\approx125$) days by models with (resp. without) a perturber near G2/C. The configuration and predicted time-delays of J0408-5354 make it an excellent target for follow-up aimed at understanding the source quasar host galaxy and substructure in the lens, and measuring cosmological parameters. We also discuss some lessons learnt from J0408-5354 on lensed quasar finding strategies, due to its chromaticity and morphology.

astro-ph.GA↗

arXiv2017

H0LiCOW V. New COSMOGRAIL time delays of HE0435-1223: $H_0$ to 3.8% precision from strong lensing in a flat $Λ$CDM model

We present a new measurement of the Hubble Constant H0 and other cosmological parameters based on the joint analysis of three multiply-imaged quasar systems with measured gravitational time delays. First, we measure the time delay of HE0435-1223 from 13-year light curves obtained as part of the COSMOGRAIL project. Companion papers detail the modeling of the main deflectors and line of sight effects, and how these data are combined to determine the time-delay distance of HE 0435-1223. Crucially, the measurements are carried out blindly with respect to cosmological parameters in order to avoid confirmation bias. We then combine the time-delay distance of HE0435-1223 with previous measurements from systems B1608+656 and RXJ1131-1231 to create a Time Delay Strong Lensing probe (TDSL). In flat $Λ$CDM with free matter and energy density, we find $H_0$ = 71.9 +2.4 -3.0 km/s/Mpc and $Ω_Λ$ = 0.62 +0.24 -0.35 . This measurement is completely independent of, and in agreement with, the local distance ladder measurements of H0. We explore more general cosmological models combining TDSL with other probes, illustrating its power to break degeneracies inherent to other methods. The TDSL and Planck joint constraints are $H_0$ = 69.2 +1.4 -2.2 km/s/Mpc, $Ω_Λ$ = 0.70 +0.01 -0.01 and $Ω_k$ = 0.003 +0.004 -0.006 in open $Λ$CDM and $H_0$ = 79.0 +4.4 -4.2 km/s/Mpc, $Ω_{de}$ = 0.77 +0.02 -0.03 and $w$ = -1.38 +0.14 -0.16 in flat $w$CDM. Combined with Planck and Baryon Acoustic Oscillation data, when relaxing the constraints on the numbers of relativistic species we find $N_{eff}$ = 3.34 +0.21 -0.21 and when relaxing the total mass of neutrinos we find 0.182 eV. In an open $w$CDM in combination with Planck and CMB lensing we find $H_0$ = 77.9 +5.0 -4.2 km/s/Mpc, $Ω_{de}$ = 0.77 +0.03 -0.03, $Ω_k$ = -0.003 +0.004 -0.004 and $w$ = -1.37 +0.18 -0.23.

astro-ph.CO↗

arXiv2017

H0LiCOW II. Spectroscopic survey and galaxy-group identification of the strong gravitational lens system HE0435-1223

Galaxies located in the environment or on the line of sight towards gravitational lenses can significantly affect lensing observables, and can lead to systematic errors on the measurement of $H_0$ from the time-delay technique. We present the results of a systematic spectroscopic identification of the galaxies in the field of view of the lensed quasar HE0435-1223, using the W. M. Keck, Gemini and ESO-Very Large telescopes. Our new catalog triples the number of known galaxy redshifts in the vicinity of the lens, expanding to 102 the number of measured redshifts for galaxies separated by less than 3 arcmin from the lens. We complement our catalog with literature data to gather redshifts up to 15 arcmin from the lens, and search for galaxy groups or clusters projected towards HE0435-1223. We confirm that the lens is a member of a small group that includes at least 12 galaxies, and find 8 other group candidates near the line of sight of the lens. The flexion shift, namely the shift of lensed images produced by high order perturbation of the lens potential, is calculated for each galaxy/group and used to identify which objects produce the largest perturbation of the lens potential. This analysis demonstrates that i) at most three of the five brightest galaxies projected within 12 arcsec of the lens need to be explicitly used in the lens models, and ii) the groups can be treated in the lens model as an external tidal field (shear) contribution.

astro-ph.CO↗

arXiv2017

H0LiCOW I. $H_0$ Lenses in COSMOGRAIL's Wellspring: Program Overview

Strong gravitational lens systems with time delays between the multiple images allow measurements of time-delay distances, which are primarily sensitive to the Hubble constant that is key to probing dark energy, neutrino physics, and the spatial curvature of the Universe, as well as discovering new physics. We present H0LiCOW ($H_0$ Lenses in COSMOGRAIL's Wellspring), a program that aims to measure $H_0$ with $<3.5\%$ uncertainty from five lens systems (B1608+656, RXJ1131-1231, HE0435-1223, WFI2033-4723 and HE1104-1805). We have been acquiring (1) time delays through COSMOGRAIL and Very Large Array monitoring, (2) high-resolution Hubble Space Telescope imaging for the lens mass modeling, (3) wide-field imaging and spectroscopy to characterize the lens environment, and (4) moderate-resolution spectroscopy to obtain the stellar velocity dispersion of the lenses for mass modeling. In cosmological models with one-parameter extension to flat $Λ$CDM, we expect to measure $H_0$ to $<3.5\%$ in most models, spatial curvature $Ω_{\rm k}$ to 0.004, $w$ to 0.14, and the effective number of neutrino species to 0.2 (1$σ$ uncertainties) when combined with current CMB experiments. These are, respectively, a factor of $\sim15$, $\sim2$, and $\sim1.5$ tighter than CMB alone. Our data set will further enable us to study the stellar initial mass function of the lens galaxies, and the co-evolution of supermassive black holes and their host galaxies. This program will provide a foundation for extracting cosmological distances from the hundreds of time-delay lenses that are expected to be discovered in current and future surveys.

astro-ph.CO↗

arXiv2016

COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses XV. Assessing the achievability and precision of time-delay measurements

COSMOGRAIL is a long-term photometric monitoring of gravitationally lensed QSOs aimed at implementing Refsdal's time-delay method to measure cosmological parameters, in particular H0. Given long and well sampled light curves of strongly lensed QSOs, time-delay measurements require numerical techniques whose quality must be assessed. To this end, and also in view of future monitoring programs or surveys such as the LSST, a blind signal processing competition named Time Delay Challenge 1 (TDC1) was held in 2014. The aim of the present paper, which is based on the simulated light curves from the TDC1, is double. First, we test the performance of the time-delay measurement techniques currently used in COSMOGRAIL. Second, we analyse the quantity and quality of the harvest of time delays obtained from the TDC1 simulations. To achieve these goals, we first discover time delays through a careful inspection of the light curves via a dedicated visual interface. Our measurement algorithms can then be applied to the data in an automated way. We show that our techniques have no significant biases, and yield adequate uncertainty estimates resulting in reduced chi2 values between 0.5 and 1.0. We provide estimates for the number and precision of time-delay measurements that can be expected from future time-delay monitoring campaigns as a function of the photometric signal-to-noise ratio and of the true time delay. We make our blind measurements on the TDC1 data publicly available

astro-ph.IM↗