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ATTRICI v1.1 – counterfactual climate for impact attribution
Attribution in its general definition aims to quantify drivers of change in a system. According to IPCC Working Group II (WGII) a change in a natural, human or managed system is attributed to climate change by quantifying the difference between the observed state of the system and a counterfactual baseline that characterizes the system's behavior in the absence of climate change, where “climate change refers to any long-term trend in climate, irrespective of its cause” (IPCC, 2014). Impact attribution following this definition remains a challenge because the counterfactual baseline, which characterizes the system behavior in the hypothetical absence of climate change, cannot be observed. Process-based and empirical impact models can fill this gap as they allow us to simulate the counterfactual climate impact baseline. In those simulations, the models are forced by observed direct (human) drivers such as land use changes, changes in water or agricultural management but a counterfactual climate without long-term changes. We here present ATTRICI (ATTRIbuting Climate Impacts), an approach to construct the required counterfactual stationary climate data from observational (factual) climate data. Our method identifies the long-term shifts in the considered daily climate variables that are correlated to global mean temperature change assuming a smooth annual cycle of the associated scaling coefficients for each day of the year. The produced counterfactual climate datasets are used as forcing data within the impact attribution setup of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP3a). Our method preserves the internal variability of the observed data in the sense that factual and counterfactual data for a given day have the same rank in their respective statistical distributions. The associated impact model simulations allow for quantifying the contribution of climate change to observed long-term changes in impact indicators and for quantifying the contribution of the observed trend in climate to the magnitude of individual impact events. Attribution of climate impacts to anthropogenic forcing would need an additional step separating anthropogenic climate forcing from other sources of climate trends, which is not covered by our method
Dark matter halos of massive elliptical galaxies at are well described by the Navarro-Frenk-White profile
We investigate the internal structure of elliptical galaxies at
from a joint lensing-dynamics analysis. We model Hubble Space Telescope images
of a sample of 23 galaxy-galaxy lenses selected from the Sloan Lens ACS (SLACS)
survey. Whereas the original SLACS analysis estimated the logarithmic slopes by
combining the kinematics with the imaging data, we estimate the logarithmic
slopes only from the imaging data. We find that the distribution of the
lensing-only logarithmic slopes has a median and intrinsic
scatter , consistent with the original SLACS analysis. We
combine the lensing constraints with the stellar kinematics and weak lensing
measurements, and constrain the amount of adiabatic contraction in the dark
matter (DM) halos. We find that the DM halos are well described by a standard
Navarro-Frenk-White halo with no contraction on average for both of a constant
stellar mass-to-light ratio () model and a stellar gradient model.
For the gradient model, we find that most galaxies are consistent with no
gradient. Comparison of our inferred stellar masses with those obtained
from the stellar population synthesis method supports a heavy initial mass
function (IMF) such as the Salpeter IMF. We discuss our results in the context
of previous observations and simulations, and argue that our result is
consistent with a scenario in which active galactic nucleus feedback
counteracts the baryonic-cooling-driven contraction in the DM halos.Comment: 26 pages, 19 figures, 3 tables. This version: accepted to MNRA
Pushing the Limits of Detectability: Mixed Dark Matter from Strong Gravitational Lenses
One of the frontiers for advancing what is known about dark matter lies in
using strong gravitational lenses to characterize the population of the
smallest dark matter halos. There is a large volume of information in strong
gravitational lens images -- the question we seek to answer is to what extent
we can refine this information. To this end, we forecast the detectability of a
mixed warm and cold dark matter scenario using the anomalous flux ratio method
from strong gravitational lensed images. The halo mass function of the mixed
dark matter scenario is suppressed relative to cold dark matter but still
predicts numerous low-mass dark matter halos relative to warm dark matter.
Since the strong lens signal is a convolution over a range of dark matter halo
masses and since the signal is sensitive to the specific configuration of dark
matter halos, not just the halo mass function, degeneracies between different
forms of suppression in the halo mass function, relative to cold dark matter,
can arise. We find that, with a set of lenses with different configurations of
the main deflector and hence different sensitivities to different mass ranges
of the halo mass function, the different forms of suppression of the halo mass
function between the warm dark matter model and the mixed dark matter model can
be distinguished with lenses with Bayesian odds of 29.4:1.Comment: 8 pages, 7 figure
Testing the Evolution of the Correlations between Supermassive Black Holes and their Host Galaxies using Eight Strongly Lensed Quasars
One of the main challenges in using high redshift active galactic nuclei to
study the correlations between the mass of the supermassive Black Hole (MBH)
and the properties of their active host galaxies is instrumental resolution.
Strong lensing magnification effectively increases instrumental resolution and
thus helps to address this challenge. In this work, we study eight strongly
lensed active galactic nuclei (AGN) with deep Hubble Space Telescope imaging,
using the lens modelling code Lenstronomy to reconstruct the image of the
source. Using the reconstructed brightness of the host galaxy, we infer the
host galaxy stellar mass based on stellar population models. MBH are estimated
from broad emission lines using standard methods. Our results are in good
agreement with recent work based on non-lensed AGN, demonstrating the potential
of using strongly lensed AGNs to extend the study of the correlations to higher
redshifts. At the moment, the sample size of lensed AGN is small and thus they
provide mostly a consistency check on systematic errors related to resolution
for the non-lensed AGN. However, the number of known lensed AGN is expected to
increase dramatically in the next few years, through dedicated searches in
ground and space based wide field surveys, and they may become a key diagnostic
of black hole and galaxy co-evolution.Comment: 12 pages, 4 figures, 3 tables. MNRAS in press. Comments welcom
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