11 research outputs found
Deep Imaging of AXJ2019+112: The Luminosity of a ``Dark Cluster''
We detect a distant cluster of galaxies centered on the QSO lens and luminous
X-ray source AXJ2019+112, a.k.a. ``The Dark Cluster'' (Hattori et al 1997).
Using deep V,I Keck images and wide-field K_s imaging from the NTT, a tight red
sequence of galaxies is identified within a radius of 0.2 h^{-1} Mpc of the
known z=1.01 elliptical lensing galaxy. The sequence, which includes the
central elliptical galaxy, has a slope in good agreement with the model
predictions of Kodama et al (1998) for z~1. We estimate the integrated
rest-frame luminosity of the cluster to be L_V > 3.2 x 10^{11}h^{-2}L_{\sun}
(after accounting for significant extinction at the low latitude of this
field), more than an order of magnitude higher than previous estimates. The
central region of the cluster is deconvolved using the technique of Magain,
Courbin & Sohy (1998), revealing a thick central arc coincident with an
extended radio source. All the observed lensing features are readily explained
by differential magnification of a radio loud AGN by a shallow elliptical
potential. The QSO must lie just outside the diamond caustic, producing two
images, and the arc is a highly magnified image formed from a region close to
the center of the host galaxy, projecting inside the caustic. The
mass--to--light ratio within an aperture of 0.4 h ^{-1} Mpc is M_x/L_V=
224^{+112}_{-78}h(M/L_V)_{\sun}, using the X-ray temperature. The strong lens
model yields a compatible value, M/L_V= 372^{+94}_{-94}h(M/L_V)_{\sun}, whereas
an independent weak lensing analysis sets an upper limit of M/L_V <520
h(M/L_V)_{\sun}, typical of massive clusters.Comment: AAS Latex format, 24 pages, 9 figures. Fig 1a,b available at
http://astro.berkeley.edu/~benitezn/cluster.html . Submitted to ApJ on August
15t
GREAT3 results I: systematic errors in shear estimation and the impact of real galaxy morphology
We present first results from the third GRavitational lEnsing Accuracy
Testing (GREAT3) challenge, the third in a sequence of challenges for testing
methods of inferring weak gravitational lensing shear distortions from
simulated galaxy images. GREAT3 was divided into experiments to test three
specific questions, and included simulated space- and ground-based data with
constant or cosmologically-varying shear fields. The simplest (control)
experiment included parametric galaxies with a realistic distribution of
signal-to-noise, size, and ellipticity, and a complex point spread function
(PSF). The other experiments tested the additional impact of realistic galaxy
morphology, multiple exposure imaging, and the uncertainty about a
spatially-varying PSF; the last two questions will be explored in Paper II. The
24 participating teams competed to estimate lensing shears to within systematic
error tolerances for upcoming Stage-IV dark energy surveys, making 1525
submissions overall. GREAT3 saw considerable variety and innovation in the
types of methods applied. Several teams now meet or exceed the targets in many
of the tests conducted (to within the statistical errors). We conclude that the
presence of realistic galaxy morphology in simulations changes shear
calibration biases by per cent for a wide range of methods. Other
effects such as truncation biases due to finite galaxy postage stamps, and the
impact of galaxy type as measured by the S\'{e}rsic index, are quantified for
the first time. Our results generalize previous studies regarding sensitivities
to galaxy size and signal-to-noise, and to PSF properties such as seeing and
defocus. Almost all methods' results support the simple model in which additive
shear biases depend linearly on PSF ellipticity.Comment: 32 pages + 15 pages of technical appendices; 28 figures; submitted to
MNRAS; latest version has minor updates in presentation of 4 figures, no
changes in content or conclusion
GREAT3 results - I. Systematic errors in shear estimation and the impact of real galaxy morphology
We present first results from the third GRavitational lEnsing Accuracy Testing (GREAT3) challenge, the third in a sequence of challenges for testing methods of inferring weak gravitational lensing shear distortions from simulated galaxy images. GREAT3 was divided into experiments to test three specific questions, and included simulated space- and ground-based data with constant or cosmologically varying shear fields. The simplest (control) experiment included parametric galaxies with a realistic distribution of signal-to-noise, size, and ellipticity, and a complex point spread function (PSF). The other experiments tested the additional impact of realistic galaxy morphology, multiple exposure imaging, and the uncertainty about a spatially varying PSF; the last two questions will be explored in Paper II. The 24 participating teams competed to estimate lensing shears to within systematic error tolerances for upcoming Stage-IV dark energy surveys, making 1525 submissions overall. GREAT3 saw considerable variety and innovation in the types of methods applied. Several teams now meet or exceed the targets in many of the tests conducted (to within the statistical errors). We conclude that the presence of realistic galaxy morphology in simulations changes shear calibration biases by ∼1percent for a wide range of methods. Other effects such as truncation biases due to finite galaxy postage stamps, and the impact of galaxy type as measured by the Sérsic index, are quantified for the first time. Our results generalize previous studies regarding sensitivities to galaxy size and signal-to-noise, and to PSF properties such as seeing and defocus. Almost all methods' results support the simple model in which additive shear biases depend linearly on PSF ellipticit
Constraining the microlensing effect on time delays with a new time-delay prediction model in measurements
International audienceTime-delay strong lensing provides a unique way to directly measure the Hubble constant (H_0). The precision of the H_0 measurement depends on the uncertainties in the time-delay measurements, the mass distribution of the main deflector(s), and the mass distribution along the line of sight. Tie & Kochanek have proposed a new microlensing effect on time delays based on differential magnification of the coherent accretion disc variability of the lensed quasar. If real, this effect could significantly broaden the uncertainty on the time-delay measurements by up to 30 per cent for lens systems such as PG 1115+080, which have relatively short time delays and monitoring over several different epochs. In this paper we develop a new technique that uses the cosmological time-delay ratios and simulated microlensing maps within a Bayesian framework in order to limit the allowed combinations of microlensing delays and thus to lessen the uncertainties due to the proposed effect. We show that, under the assumption of Tie & Kochanek, the uncertainty on the time-delay distance (DΔt, which is proportional to 1/H0) of the short time-delay (∼18 d) lens, PG 1115+080, increases from ∼7 per cent to ∼10 per cent by simultaneously fitting the three time-delay measurements from the three different data sets across 20 yr, while in the case of the long time-delay (∼90 d) lens, the microlensing effect on time delays is negligible as the uncertainty on DΔt of RXJ 1131−1231 only increases from ∼2.5 per cent to ∼2.6 per cent
GREAT3 results - I. Systematic errors in shear estimation and the impact of real galaxy morphology
ISSN:0035-8711ISSN:1365-2966ISSN:1365-871
Cosmology Intertwined : A Review of the Particle Physics, Astrophysics, and Cosmology Associated with the Cosmological Tensions and Anomalies
Contribution to Snowmass 2021. 224 pages, 27 figures. Accepted for publication in JHEApPeer reviewe
Cosmology Intertwined: A Review of the Particle Physics, Astrophysics, and Cosmology Associated with the Cosmological Tensions and Anomalies
In this paper we will list a few important goals that need to be addressed in
the next decade, also taking into account the current discordances between the
different cosmological probes, such as the disagreement in the value of the
Hubble constant , the -- tension, and other less
statistically significant anomalies. While these discordances can still be in
part the result of systematic errors, their persistence after several years of
accurate analysis strongly hints at cracks in the standard cosmological
scenario and the necessity for new physics or generalisations beyond the
standard model. In this paper, we focus on the tension between
the {\it Planck} CMB estimate of the Hubble constant and the SH0ES
collaboration measurements. After showing the evaluations made from
different teams using different methods and geometric calibrations, we list a
few interesting new physics models that could alleviate this tension and
discuss how the next decade's experiments will be crucial. Moreover, we focus
on the tension of the {\it Planck} CMB data with weak lensing measurements and
redshift surveys, about the value of the matter energy density , and
the amplitude or rate of the growth of structure (). We
list a few interesting models proposed for alleviating this tension, and we
discuss the importance of trying to fit a full array of data with a single
model and not just one parameter at a time. Additionally, we present a wide
range of other less discussed anomalies at a statistical significance level
lower than the -- tensions which may also constitute hints towards
new physics, and we discuss possible generic theoretical approaches that can
collectively explain the non-standard nature of these signals.[Abridged]Comment: Contribution to Snowmass 2021. 224 pages, 27 figures. Accepted for
publication in JHEA