We present a forecast analysis on the feasibility of measuring the cosmological parameters with a large number of galaxy-galaxy scale strong gravitational lensing systems. Future wide area surveys ...are expected to discover and measure the properties of more than 10 000 strong lensing systems. We develop a hierarchical model that can simultaneously constrain the lens population and cosmological parameters by combining Einstein radius measurements with stellar dynamical mass estimates for every lens. Marginalizing over the lens density profiles and stellar orbital anisotropies, we find that \(w\) can be constrained to a precision of \(0.11\) with 10 000 galaxy-galaxy lens systems, which would be better than any existing single-probe constraint. We test our method on 161 existing lenses, finding \(w=-0.96\pm0.46\). We also show how to mitigate against the potential systematic of redshift evolution in the mean lens density profile of the population.
We explore the mid-infrared (mid-IR) through ultraviolet (UV) spectral energy distributions (SEDs) of 119,652 luminous type 1 quasars with 0:064 < z < 5:46 using mid-IR data from Spitzer and WISE , ...near-infrared data from 2MASS and UKIDSS, optical data from SDSS and UV data from GALEX. The mean SED requires a bolometric correction of BC2500-A = 2:75 ± 0:40 using the integrated light from 1 μm2 keV. We investigate the mean SED dependence on various parameters, particularly the UV luminosity for quasars with 0:5 special character omitted z special character omitted 3. Low-luminosity SEDs exhibit a bluer far-UV spectral slope, a redder optical continuum, and less hot dust. Our work suggests that lower-luminosity quasars may require an extra continuum component in the unseen extreme-UV that is weak in high-luminosity quasars. As such, we consider four possible models and explore the resulting BCs. Taking a subset of ∼ 35, 000 uniformly selected quasars we explore their extinction/reddening in order to better understand their intrinsic SEDs. Using optical-UV photometry, we isolate outliers in the color distribution and find them well described by an SMC-like reddening law. A hierarchical Bayesian model was used to find distributions of powerlaw indices and E(B – V) consistent with both the broad absorption line (BAL) and non-BAL samples. 2.5% (13%) of the non-BAL (BAL) sample are shown to be consistent with E(B – V) > 0:1 and 0.1% (1.3%) with E(B – V) > 0:2. Simulations show both populations of quasars are intrinsically bluer than the mean composite, with a mean spectral index (αλ) of -1.79 (-1.83). The emission and absorption-line properties of both samples showed that quasars with intrinsically red continua have weaker Balmer lines and stronger ionizing spectral lines, the latter indicating a harder continuum in the extreme-UV. Applying corrections for associated dust, we better determine the intrinsic SEDs and true BCs for our uniformly selected subsample. The SEDs with the most dust extinction are intrinsically brighter and showed more dust emission near ∼ 10 μm than the SEDs with less extinction. The bluer SEDs have more hot dust emission and higher BCs, consistent with having hotter accretions disks and/or being viewed closer to edge-on. Mean SEDs were also made based on the black hole mass (M BH) and the Eddington fraction (L/LEdd). Quasars with large L/LEdd and/or large MBH have more hot dust and a bluer optical continua, both consistent with a hotter accretion disk.
The standardizable nature of gravitationally lensed Type Ia supernovae (glSNe Ia) makes them an attractive target for time delay cosmography, since a source with known luminosity breaks the mass ...sheet degeneracy. It is known that microlensing by stars in the lensing galaxy can add significant stochastic uncertainty to the unlensed luminosity which is often much larger than the intrinsic scatter of the Ia population. In this work, we show how the temporal microlensing variations as the supernova disc expands can be used to improve the standardization of glSNe Ia. We find that SNe are standardizable if they do not cross caustics as they expand. We estimate that this will be the case for \(\approx\)6 doubly imaged systems and \(\approx\)0.3 quadruply imaged systems per year in LSST. At the end of the ten year LSST survey, these systems should enable us to test for systematics in \(H_0\) due to the mass sheet degeneracy at the \(1.00^{+0.07}_{-0.06}\)\% level, or \(1.8\pm0.2\)\% if we can only extract time delays from the third of systems with counter images brighter than \(i=24\) mag.
Strong gravitationally lensed supernovae (glSNe) are a powerful probe to obtain a measure of the expansion rate of the Universe, but they are also extremely rare. To date, only two glSNe with ...multiple images strongly lensed by galaxies have been found, but their short time delays make them unsuitable for cosmography. Here, we simulate a realistic catalogue of lensed supernovae and study the characteristics of the population of detectable systems for different surveys. Compared to previous studies, our simulations also account for the effect of microlensing and its impact on the glSNe yields. We show that the properties of glSNe in shallow surveys (such as the Zwicky Transient Facility; ZTF) are determined by the need for large magnifications, which favours systems of four images with short time delays and low image separations. This picture is consistent with the properties of iPTF16geu and SN Zwicky, but is not representative of the population found in deeper surveys, which are limited by the volume of the Universe that is strongly lensed. For deeper surveys, such as the Legacy Survey of Space and Time (LSST), glSNe show longer time delays and greater angular separations, and the inclusion of microlensing results in 8\(\%\) of glSNe becoming demagnified under the detection threshold. In the 10 years of the survey LSST should be able to find \(\approx\) 180 systems, of which 70 will be suited for cosmography enabling a \(\approx\) 1.2\(\%\) precision \(H_0\) measurement with LSST glSNe.
Galaxy Zoo: Clump Scout is a web-based citizen science project designed to identify and spatially locate giant star forming clumps in galaxies that were imaged by the Sloan Digital Sky Survey Legacy ...Survey. We present a statistically driven software framework that is designed to aggregate two-dimensional annotations of clump locations provided by multiple independent Galaxy Zoo: Clump Scout volunteers and generate a consensus label that identifies the locations of probable clumps within each galaxy. The statistical model our framework is based on allows us to assign false-positive probabilities to each of the clumps we identify, to estimate the skill levels of each of the volunteers who contribute to Galaxy Zoo: Clump Scout and also to quantitatively assess the reliability of the consensus labels that are derived for each subject. We apply our framework to a dataset containing 3,561,454 two-dimensional points, which constitute 1,739,259 annotations of 85,286 distinct subjects provided by 20,999 volunteers. Using this dataset, we identify 128,100 potential clumps distributed among 44,126 galaxies. This dataset can be used to study the prevalence and demographics of giant star forming clumps in low-redshift galaxies. The code for our aggregation software framework is publicly available at: https://github.com/ou-astrophysics/BoxAggregator
Spiral structure is ubiquitous in the Universe, and the pitch angle of arms in spiral galaxies provide an important observable in efforts to discriminate between different mechanisms of spiral arm ...formation and evolution. In this paper, we present a hierarchical Bayesian approach to galaxy pitch angle determination, using spiral arm data obtained through the Galaxy Builder citizen science project. We present a new approach to deal with the large variations in pitch angle between different arms in a single galaxy, which obtains full posterior distributions on parameters. We make use of our pitch angles to examine previously reported links between bulge and bar strength and pitch angle, finding no correlation in our data (with a caveat that we use observational proxies for both bulge size and bar strength which differ from other work). We test a recent model for spiral arm winding, which predicts uniformity of the cotangent of pitch angle between some unknown upper and lower limits, finding our observations are consistent with this model of transient and recurrent spiral pitch angle as long as the pitch angle at which most winding spirals dissipate or disappear is larger than 10 degrees.
Multi-component modelling of galaxies is a valuable tool in the effort to quantitatively understand galaxy evolution, yet the use of the technique is plagued by issues of convergence, model selection ...and parameter degeneracies. These issues limit its application over large samples to the simplest models, with complex models being applied only to very small samples. We attempt to resolve this dilemma of "quantity or quality" by developing a novel framework, built inside the Zooniverse citizen science platform, to enable the crowdsourcing of model creation for Sloan Digitial Sky Survey galaxies. We have applied the method, including a final algorithmic optimisation step, on a test sample of 198 galaxies, and examine the robustness of this new method. We also compare it to automated fitting pipelines, demonstrating that it is possible to consistently recover accurate models that either show good agreement with, or improve on, prior work. We conclude that citizen science is a promising technique for modelling images of complex galaxies, and release our catalogue of models.
The exact nature of the arms of spiral galaxies is still an open question. It has been widely assumed that spiral arms in galaxies with two distinct symmetrical arms are the products of density waves ...that propagate around the disk, with the spiral arms being visibly enhanced by the star formation that is triggered as the passing wave compresses gas in the galaxy disk. Such a persistent wave would propagate with an approximately constant angular speed, its pattern speed Op. The quasi-stationary density wave theory can be tested by measuring this quantity and showing that it does not vary with radius in the galaxy. Unfortunately, this measurement is difficult because Op is only indirectly connected to observables such as the stellar rotation speed. Here, we use the detailed information on stellar populations of the grand-design spiral galaxy UGC 3825, extracted from spectral mapping, to measure the offset between young stars of a known age and the spiral arm in which they formed, allowing the first direct measure of Op at a range of radii. The offset in this galaxy is found to be as expected for a pattern speed that varies little with radius, indicating consistency with a quasi-stationary density wave, and lending credence to this new method.
We present Galaxy Zoo DECaLS: detailed visual morphological classifications for Dark Energy Camera Legacy Survey images of galaxies within the SDSS DR8 footprint. Deeper DECaLS images (r=23.6 vs. ...r=22.2 from SDSS) reveal spiral arms, weak bars, and tidal features not previously visible in SDSS imaging. To best exploit the greater depth of DECaLS images, volunteers select from a new set of answers designed to improve our sensitivity to mergers and bars. Galaxy Zoo volunteers provide 7.5 million individual classifications over 314,000 galaxies. 140,000 galaxies receive at least 30 classifications, sufficient to accurately measure detailed morphology like bars, and the remainder receive approximately 5. All classifications are used to train an ensemble of Bayesian convolutional neural networks (a state-of-the-art deep learning method) to predict posteriors for the detailed morphology of all 314,000 galaxies. When measured against confident volunteer classifications, the networks are approximately 99% accurate on every question. Morphology is a fundamental feature of every galaxy; our human and machine classifications are an accurate and detailed resource for understanding how galaxies evolve.
SkyPy is an open-source Python package for simulating the astrophysical sky.
It comprises a library of physical and empirical models across a range of
observables and a command-line script to run ...end-to-end simulations. The
library provides functions that sample realisations of sources and their
associated properties from probability distributions. Simulation pipelines are
constructed from these models using a YAML-based configuration syntax, while
task scheduling and data dependencies are handled internally and the modular
design allows users to interface with external software. SkyPy is developed and
maintained by a diverse community of domain experts with a focus on software
sustainability and interoperability. By fostering development, it provides a
framework for correlated simulations of a range of cosmological probes
including galaxy populations, large scale structure, the cosmic microwave
background, supernovae and gravitational waves.
Version 0.4 implements functions that model various properties of galaxies
including luminosity functions, redshift distributions and optical photometry
from spectral energy distribution templates. Future releases will provide
additional modules, for example, to simulate populations of dark matter halos
and model the galaxy-halo connection, making use of existing software packages
from the astrophysics community where appropriate.
