Aquarius iPhone Application

The Office of the CIO at JPL has developed an iPhone application for the Aquarius/SAC-D mission. The application includes specific information about the science and purpose of the Aquarius satellite and also features daily mission news updates pulled from sources at Goddard Space Flight Center as well as Twitter. The application includes a media and data tab section. The media section displays images from the observatory, viewing construction up to the launch and also includes various videos and recorded diaries from the Aquarius Project Manager. The data tab highlights many of the factors that affect the Earth s ocean and the water cycle. The application leverages the iPhone s accelerometer to move the Aquarius Satellite over the Earth, revealing these factors. Lastly, this application features a countdown timer to the satellite s launch, which is currently counting the days since launch. This application was highly successful in promoting the Aquarius Mission and educating the public about how ocean salinity is paramount to understanding the Earth

Bound and unbound substructures in Galaxy-scale Dark Matter haloes

We analyse the coarse-grained phase-space structure of the six Galaxy-scale dark matter haloes of the Aquarius Project using a state-of-the-art 6D substructure finder. Within r_50, we find that about 35% of the mass is in identifiable substructures, predominantly tidal streams, but including about 14% in self-bound subhaloes. The slope of the differential substructure mass function is close to -2, which should be compared to around -1.9 for the population of self-bound subhaloes. Near r_50 about 60% of the mass is in substructures, with about 30% in self-bound subhaloes. The inner 35 kpc of the highest resolution simulation has only 0.5% of its mass in self-bound subhaloes, but 3.3% in detected substructure, again primarily tidal streams. The densest tidal streams near the solar position have a 3-D mass density about 1% of the local mean, and populate the high velocity tail of the velocity distribution.Comment: Submitted to MNRAS on 12/10/2010, 11 pages, 10 figure

The Orbital Ellipticity of Satellite Galaxies and the Mass of the Milky Way

We use simulations of Milky Way-sized dark matter haloes from the Aquarius Project to investigate the orbits of substructure haloes likely, according to a semi-analytic galaxy formation model, to host luminous satellites. These tend to populate the most massive subhaloes and are on more radial orbits than the majority of subhaloes found within the halo virial radius. One reason for this (mild) kinematic bias is that many low-mass subhaloes have apocentres that exceed the virial radius of the main host; they are thus excluded from subhalo samples identified within the virial boundary, reducing the number of subhalos on radial orbits. Two other factors contributing to the difference in orbital shape between dark and luminous subhaloes are their dynamical evolution after infall, which affects more markedly low-mass (dark) subhaloes, and a weak dependence of ellipticity on the redshift of first infall. The ellipticity distribution of luminous satellites exhibits little halo-to-halo scatter and it may therefore be compared fruitfully with that of Milky Way satellites. Since the latter depends sensitively on the total mass of the Milky Way we can use the predicted distribution of satellite ellipticities to place constraints on this important parameter. Using the latest estimates of position and velocity of dwarfs compiled from the literature, we find that the most likely Milky Way mass lies in the range $6 \times 10^{11} M_{\odot} < M_{200} < 3.1 \times 10^{12} M_{\odot}$, with a best fit value of $M_{200} = 1.1 \times 10^{12} M_{\odot}$. This value is consistent with Milky Way mass estimates based on dynamical tracers or the timing argument.Comment: 10 pages, 9 figures, Accepted by MNRA

Stellar Disks in Aquarius Dark Matter Haloes

We investigate the gravitational interactions between live stellar disks and their dark matter halos, using LCDM haloes similar in mass to that of the Milky Way taken from the Aquarius Project. We introduce the stellar disks by first allowing the haloes to respond to the influence of a growing rigid disk potential from z = 1.3 to z = 1.0. The rigid potential is then replaced with star particles which evolve self-consistently with the dark matter particles until z = 0.0. Regardless of the initial orientation of the disk, the inner parts of the haloes contract and change from prolate to oblate as the disk grows to its full size. When the disk normal is initially aligned with the major axis of the halo at z=1.3, the length of the major axis contracts and becomes the minor axis by z=1.0. Six out of the eight disks in our main set of simulations form bars, and five of the six bars experience a buckling instability that results in a sudden jump in the vertical stellar velocity dispersion and an accompanying drop in the m=2 Fourier amplitude of the disk surface density. The bars are not destroyed by the buckling but continue to grow until the present day. Bars are largely absent when the disk mass is reduced by a factor of two or more; the relative disk-to-halo mass is therefore a primary factor in bar formation and evolution. A subset of the disks is warped at the outskirts and contains prominent non-coplanar material with a ring-like structure. Many disks reorient by large angles between z=1 and z=0, following a coherent reorientation of their inner haloes. Larger reorientations produce more strongly warped disks, suggesting a tight link between the two phenomena. The origins of bars and warps appear independent: some disks with strong bars show no disturbances at the outskirts, while the disks with the weakest bars show severe warps.Comment: 19 pages, 13 figures, accepted MNRAS; fixed compatibility problem in figures 8,

The Caterpillar Project: A Large Suite of Milky Way Sized Halos

We present the largest number of Milky Way sized dark matter halos simulated at very high mass ($\sim$$10^4$ M$_\odot$/particle) and temporal resolution ($\sim$5 Myrs/snapshot) done to date, quadrupling what is currently available in the literature. This initial suite consists of the first 24 halos of the $Caterpillar$ $Project$ (www.caterpillarproject.org) whose project goal of 60 - 70 halos will be made public when complete. We resolve $\sim$20,000 gravitationally bound subhalos within the virial radius of each host halo. Over the ranges set by our spatial resolution our convergence is excellent and improvements were made upon current state-of-the-art halo finders to better identify substructure at such high resolutions (e.g., on average we recover $\sim$4 subhalos in each host halo above 10$^8$ M$_\odot$ which would have otherwise not been found using conventional methods). For our relaxed halos, the inner profiles are reasonably fit by Einasto profiles ($\alpha$ = 0.169 $\pm$ 0.023) though this depends on the relaxed nature and assembly history of a given halo. Averaging over all halos, the substructure mass fraction is $f_{m,subs} = 0.121 \pm 0.041$, and mass function slope is d$N$/d$M\propto M^{-1.88 \pm 0.10}$ though we find scatter in the normalizations for fixed halo mass due to more concentrated hosts having less subhalos at fixed subhalo mass. There are no biases stemming from Lagrangian volume selection as all Lagrangian volume types are included in our sample. Our detailed contamination study of 264 low resolution halos has resulted in obtaining very large and unprecedented, high-resolution regions around our host halos for our target resolution (sphere of radius $\sim$$1.4 \pm 0.4$ Mpc) allowing for accurate studies of low mass dwarf galaxies at large galactocentric radii and the very first stellar systems at high redshift ($z \geq$ 10).Comment: 19 pages; 14 figures; 6 tables; Received September 3, 2015; Accepted November 15, 2015; Published February 2, 201

SubHaloes going Notts: The SubHalo-Finder Comparison Project

We present a detailed comparison of the substructure properties of a single Milky Way sized dark matter halo from the Aquarius suite at five different resolutions, as identified by a variety of different (sub-)halo finders for simulations of cosmic structure formation. These finders span a wide range of techniques and methodologies to extract and quantify substructures within a larger non-homogeneous background density (e.g. a host halo). This includes real-space, phase-space, velocity-space and time- space based finders, as well as finders employing a Voronoi tessellation, friends-of-friends techniques, or refined meshes as the starting point for locating substructure.A common post-processing pipeline was used to uniformly analyse the particle lists provided by each finder. We extract quantitative and comparable measures for the subhaloes, primarily focusing on mass and the peak of the rotation curve for this particular study. We find that all of the finders agree extremely well on the presence and location of substructure and even for properties relating to the inner part part of the subhalo (e.g. the maximum value of the rotation curve). For properties that rely on particles near the outer edge of the subhalo the agreement is at around the 20 per cent level. We find that basic properties (mass, maximum circular velocity) of a subhalo can be reliably recovered if the subhalo contains more than 100 particles although its presence can be reliably inferred for a lower particle number limit of 20. We finally note that the logarithmic slope of the subhalo cumulative number count is remarkably consistent and <1 for all the finders that reached high resolution. If correct, this would indicate that the larger and more massive, respectively, substructures are the most dynamically interesting and that higher levels of the (sub-)subhalo hierarchy become progressively less important.Comment: 16 pages, 7 figures, 2 tables, Accepted for MNRA

The Effect of Environment on Milky Way-mass galaxies in a Constrained Simulation of the Local Group

In this letter we present, for the first time, a study of star formation rate, gas fraction and galaxy morphology of a constrained simulation of the Milky Way (MW) and Andromeda (M31) galaxies, compared to other MW-mass galaxies. By combining with unconstrained simulations we cover a sufficient volume to compare these galaxies environmental densities ranging from the field to that of the Local Group (LG). This is particularly relevant as it has been shown that, quite generally, galaxy properties depend intimately upon their environment, most prominently when galaxies in clusters are compared to those in the field. For galaxies in loose groups such as the LG, however, environmental effects have been less clear. We consider the galaxy's environmental density in spheres of 1200 kpc (comoving) and find that whilst environment does not appear to directly affect morphology, there is a positive trend with star formation rates. This enhancement in star formation occurs systematically for galaxies in higher density environments, regardless whether they are part of the LG or in filaments. Our simulations suggest that the richer environment at Mpc-scales may help replenish the star-forming gas, allowing higher specific star formation rates in galaxies such as the MW.Comment: 6 pages, 4 figures, accepted to ApJ