Distribution Of Matter In Galaxies Research Articles

Gravity as Embedding Theory and the Distribution of Matter in Galaxies

Gravity as Embedding Theory and the Distribution of Matter in Galaxies

Rotation Curve Decompositions with Gaussian Processes: Taking into Account Data Correlations Leads to Unbiased Results

Correlations between velocity measurements in disk galaxy rotation curves are usually neglected when fitting dynamical models. Here I show how data correlations can be taken into account in rotation curve decompositions using Gaussian Processes. I find that marginalizing over correlation parameters proves critical to obtain unbiased estimates of the luminous and dark matter distributions in galaxies.

Developing a victorious strategy to the second strong gravitational lensing data challenge

ABSTRACT Strong lensing is a powerful probe of the matter distribution in galaxies and clusters and a relevant tool for cosmography. Analyses of strong gravitational lenses with deep learning have become a popular approach due to these astronomical objects’ rarity and image complexity. Next-generation surveys will provide more opportunities to derive science from these objects and an increasing data volume to be analysed. However, finding strong lenses is challenging, as their number densities are orders of magnitude below those of galaxies. Therefore, specific strong lensing search algorithms are required to discover the highest number of systems possible with high purity and low false alarm rate. The need for better algorithms has prompted the development of an open community data science competition named strong gravitational lensing challenge (SGLC). This work presents the deep learning strategies and methodology used to design the highest scoring algorithm in the second SGLC (II SGLC). We discuss the approach used for this data set, the choice of a suitable architecture, particularly the use of a network with two branches to work with images in different resolutions, and its optimization. We also discuss the detectability limit, the lessons learned, and prospects for defining a tailor-made architecture in a survey in contrast to a general one. Finally, we release the models and discuss the best choice to easily adapt the model to a data set representing a survey with a different instrument. This work helps to take a step towards efficient, adaptable, and accurate analyses of strong lenses with deep learning frameworks.

Using artificial intelligence and real galaxy images to constrain parameters in galaxy formation simulations

ABSTRACT Cosmological galaxy formation simulations are still limited by their spatial/mass resolution and cannot model from first principles some of the processes, like star formation, that are key in driving galaxy evolution. As a consequence they still rely on a set of ’effective parameters’ that try to capture the scales and the physical processes that cannot be directly resolved in the simulation. In this study, we show that it is possible to use Machine Learning techniques applied to real and simulated images of galaxies to discriminate between different values of these parameters by making use of the full information content of an astronomical image instead of collapsing it into a limited set of values like size, or stellar/ gas masses. In this work, we apply our method to the NIHAO simulations and the THINGS and VLA-ANGST observations of H i maps in nearby galaxies to test the ability of different values of the star formation density threshold n to reproduce observed H i maps. We show that observations indicate the need for a high value of n ≳ 80 cm−3 (although the numerical value is model-dependent), which has important consequences for the dark matter distribution in galaxies. Our study shows that with innovative methods it is possible to take full advantage of the information content of galaxy images and compare simulations and observations in an interpretable, non-parametric, and quantitative manner.

Possible Effects of the Fractal Distribution of Relic Wormholes

We discuss the possibility that the distribution of relic wormholes may possess fractal properties. Relic wormholes and their fractal distributions are predicted in a natural way by lattice quantum gravity models. This provides a new approach to some long standing problems. That is the nature of dark matter phenomena, the origin of Faber-Jackson and Tully-Fisher relations and the observed deficit of baryons. We derive corrections to the Newton’s potential caused by the presence of relic wormholes and show that the analysis of dark matter distribution in galaxies allows us to fix the parameters of the fractal distribution of wormholes.

Seeding Supermassive Black Holes with Self-interacting Dark Matter: A Unified Scenario with Baryons

Abstract Observations show that supermassive black holes (SMBHs) with a mass of ∼109 M ⊙ exist when the universe is just 6% of its current age. We propose a scenario where a self-interacting dark matter halo experiences gravothermal instability and its central region collapses into a seed black hole. The presence of baryons in protogalaxies could significantly accelerate the gravothermal evolution of the halo and shorten collapse timescales. The central halo could dissipate its angular momentum remnant via viscosity induced by the self-interactions. The host halo must be on high tails of density fluctuations, implying that high-z SMBHs are expected to be rare in this scenario. We further derive conditions for triggering general relativistic instability of the collapsed region. Our results indicate that self-interacting dark matter can provide a unified explanation for diverse dark matter distributions in galaxies today and the origin of SMBHs at redshifts z ∼ 6–7.

Disk galaxies and their dark halos as self-organized patterns

Galaxies are built by complex physical processes with significant inherent stochasticity. It is therefore surprising that the inferred dark matter distributions in galaxies are correlated with the observed baryon distributions leading to various ‘Baryon-Halo conspiracies’. The fact that no dark matter candidate has been definitively identified invites a search for alternative explanations for such correlations and we present an approach motivated by the behaviors of self organized patterns. We propose a nonlocal relativistic Lagrangian theory for a ‘pattern field’ which acts as an ‘effective dark matter’, built on the idea that defects in this pattern field couple to the baryonic matter distribution.The model applies to rotation supported systems and, for them, we compute galactic rotation curves, obtain a radial acceleration relation with two branches, and deduce the Freeman limit for central surface brightness.

Dark matter distribution in the Galactic dwarf spheroidal galaxies

The Galactic dwarf spheroidal (dSph) galaxies are excellent laboratories to shed light on fundamental properties of dark matter. In particular, the dSphs are promising targets for the indirect searches for particle dark matter. In order to set robust constraints on properties of dark matter particles, revealing dark matter distributions in these galaxies is of crucial importance. However, there are various non-negligible systematic uncertainties on the estimate of dark matter distributions in these galaxies. Therefore, it is necessary to address the development of dynamical models considering the effects of these systematic uncertainties. In this talk, we will introduce our constructed dynamical models taking into account these uncertainties and present the inferred dark matter profiles in the classical dSphs using their current kinematic data. In addition, as an intriguing result, we will show that some of dSphs favor cusped dark halo rather than cored one even considering a mass-anisotropy degeneracy. Using these dark matter profiles, we will revisit the core-cusp problem and discuss a possible link between the inner slope of their dark halos and the star formation history.

Tracing the Dynamical Mass in Galaxy Disks Using H i Velocity Dispersion and Its Implications for the Dark Matter Distribution in Galaxies

Abstract We present a method to derive the dynamical mass of face-on galaxy disks using their neutral hydrogen (H i) velocity dispersion (σ H i ). We have applied the method to nearby, gas-rich galaxies that have extended H i gas disks and have low inclinations. The galaxy sample includes four large disk galaxies, NGC 628, NGC 6496, NGC 3184, and NGC 4214, and three dwarf galaxies, DDO 46, DDO 63, and DDO 187. We have used archival H i data from The H i Nearby Galaxy Survey (THINGS) and the LITTLE THINGS survey to derive the H i gas distributions and Spitzer mid-infrared images to determine the stellar disk mass distributions. We examine the disk dynamical and baryonic mass ratios in the extreme outer disks where there is H i gas but no visible stellar disk. We find that for the large galaxies, the disk dynamical and H i gas mass surface densities are comparable in the outer disks. But in the smaller dwarf galaxies, for which the total H i gas mass dominates the baryonic mass, i.e., M(H i) ≥ M(stars), the disk dynamical mass is much larger than the baryonic mass. For these galaxies, there must either be a very low-luminosity stellar disk which provides the vertical support for the H i gas disk or there is halo dark matter associated with their disks, which is possible if the halo has an oblate shape so that the inner part of the dark matter halo is concentrated around the disk. Our results are important for explaining the equilibrium of H i disks in the absence of stellar disks and is especially important for gas-rich, dwarf galaxies that appear to have significant dark matter masses associated with their disks.

Mirror Magnetic Field and Its Impact on Dark Matter Distribution in Galaxies

We obtain the value of the mirror magnetic field during different stages of cosmological evolution. We consider the magnetic field generation in the radiation-dominated era and the post-recombination epoch. We also estimate its galactic low-scale value in the process of dynamo amplification. We discuss a possible effect of the mirror magnetic field on the mirror matter distribution in a galaxy. The model can be generalized by assuming the existence of kinetic mixing between ordinary and mirror particles.

Theory of Dark Matter and Dark Energy

In this article, we propose a new model of dark matter. According to this new model, dark matter is a substance, that is a new physical element not constituted of classical particles, called dark substance and filling the Universe. Assuming some very simple physical properties to this dark substance, we theoretically justify the flat rotation curve of galaxies and the baryonic Tully-Fisher’s law. We then study according to our new theory of dark matter  the different possible distributions of dark matter in galaxies and in galaxy clusters, and the velocities of galaxies in galaxy clusters.
 
 Then using the new model of dark matter we are naturally led to propose a new geometrical model of Universe, finite, that is different from all geometrical models proposed by the Standard Cosmological Model (SCM). Despite that our Theory of dark matter is compatible with the SCM, we then expose a new Cosmological model based on this new geometrical form of the Universe and on the interpretation of the CMB Rest Frame (CRF), that has not physical interpretation on the SCM and that we will call local Cosmological frame. We then propose 2 possible mathematical models of expansion inside the new Cosmological model. The 1st mathematical model is based on General Relativity as the SCM and gives the same theoretical predictions of distances and of the Hubble’s constant as the SCM. The 2nd mathematical model of expansion of the Universe is mathematically much simpler than the mathematical model of expansion used in the SCM, but we will see that its theoretical predictions are in agreement with astronomical observations. Moreover, this 2nd mathematical model of expansion does not need to introduce the existence of a dark energy contrary to the mathematical model of expansion of the SCM. To end we study the evolution of the temperature of dark substance in the Universe and we make appear the existence of a dark energy, due to our model of dark matter.

Lensed: a code for the forward reconstruction of lenses and sources from strong lensing observations

Robust modelling of strong lensing systems is fundamental to exploit the information they contain about the distribution of matter in galaxies and clusters. In this work, we present lensed, a new code which performs forward parametric modelling of strong lenses. lensed takes advantage of a massively parallel ray-tracing kernel to perform the necessary calculations on a modern graphics processing unit (GPU). This makes the precise rendering of the background lensed sources much faster, and allows the simultaneous optimization of tens of parameters for the selected model. With a single run, the code is able to obtain the full posterior probability distribution for the lens light, the mass distribution and the background source at the same time. lensed is first tested on mock images which reproduce realistic space-based observations of lensing systems. In this way, we show that it is able to recover unbiased estimates of the lens parameters, even when the sources do not follow exactly the assumed model. Then, we apply it to a subsample of the Sloan Lens ACS Survey lenses, in order to demonstrate its use on real data. The results generally agree with the literature, and highlight the flexibility and robustness of the algorithm.

Modern Gravitational Lens Cosmology for Introductory Physics and Astronomy Students

Recent and exciting discoveries in astronomy and cosmology have inspired many high school students to learn about these fields. A particularly fascinating consequence of general relativity at the forefront of modern cosmology research is gravitational lensing, the bending of light rays that pass near massive objects. Gravitational lensing enables high-precision mapping of dark matter distributions in galaxies and galaxy clusters, provides insight into large-scale cosmic structure of the universe, aids in the search for exo-planets, and may offer valuable insight toward understanding the evolution of dark energy. In this article we describe a gravitational lensing lab and associated lecture/discussion material that was highly successful, according to student feedback. The gravitational lens unit was developed as part of a two-week summer enrichment class for junior and senior high school students. With minor modifications, this lab can be used within a traditional classroom looking to incorporate topics of modern physics (such as in a unit on optics).

The Distribution of Mass in (Disk) Galaxies: Maximal or Not?

AbstractThe relative distribution of matter in galaxies ought to be one of the most definitive predictions of galaxy formation models yet its validation is challenged by numerous observational, theoretical, and operational challenges. All galaxies are believed to be dominated by an invisible matter component in their outskirts. A debate has however been blazing for the last two decades regarding the relative fraction of baryons and dark matter in the inner parts of galaxies: whether galaxies are centrally dominated by baryons (“maximal disk”) is of issue. Some of those debates have been misconstrued on account of operational confusion, such as dark matter fractions being measured and compared at different radii. All galaxies are typically baryon-dominated (maximal) at the center and dark-matter dominated (sub-maximal) in their outskirts; for low-mass galaxies (Vtot ≲ 200 km s− 1), the mass of the dark halo equals the stellar mass at least within 2 disk scale lengths, the transition occurs at larger effective radii for more massive galaxies. An ultimate goal for galaxy structure studies is to achieve accurate data-model comparisons for the relative fractions of baryonic to total matter at any radius.

A new model of dark matter distribution in galaxies

In the absence of the physical understanding of the phenomenon, different empirical laws have been used as approximation for distribution of dark matter in galaxies and clusters of galaxies. We suggest a new profile which is not empirical in nature, but motivated with the physical idea that what we call dark matter is essentially the gravitational polarization of the quantum vacuum (containing virtual gravitational dipoles) by the immersed baryonic matter. It is very important to include this new profile in forthcoming studies of dark matter halos and to reveal how well it performs in comparison with empirical profiles. A good agreement of the profile with observational findings would be the first sign of unexpected gravitational properties of the quantum vacuum.

Kinematic Modeling of Distant Galaxies

Abstract Evolution of galaxies is one of the most actual topics in astrophysics. Among the most important factors determining the evolution are two galactic components which are difficult or even impossible to detect optically: the gaseous disks and the dark matter halo. We use deep Hubble Space Telescope images to construct a two-component (bulge + disk) model for stellar matter distribution of galaxies. Properties of the galactic components are derived using a three-dimensional galaxy modeling software, which also estimates disk thickness and inclination angle. We add a gas disk and a dark matter halo and use hydrodynamical equations to calculate gas rotation and dispersion profiles in the resultant gravitational potential. We compare the kinematic profiles with the Team Keck Redshift Survey observations. In this pilot study, two galaxies are analyzed deriving parameters for their stellar components; both galaxies are found to be disk-dominated. Using the kinematical model, the gas mass and stellar mass ratio in the disk are estimated.

COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses

(abridged) Gravitationally lensed quasars can be used as powerful cosmological and astrophysical probes. We can (i) infer the Hubble constant based on the time-delay technique, (ii) unveil substructures along the l.o.s. toward distant galaxies, and (iii) compare the shape and the slope of baryons and dark matter distributions in galaxies. To reach these goals, we need high-accuracy astrometry and morphology measurements of the lens. In this work, we first present new astrometry for 11 lenses with measured time delays. Using MCS deconvolution on NIC2 HST images, we reached an astrometric accuracy of about 1-2.5 mas and an accurate shape measurement of the lens galaxy. Second, we combined these measurements with those of 14 other systems to present new mass models of these lenses. This led to the following results: 1) In 4 double-image quasars, we show that the influence of the lens environment on the time delay can easily be quantified and modeled, hence putting these lenses with high priority for time-delay determination. 2) For quadruple-image quasars, the difficulty often encountered in reproducing the image positions to milli-arcsec accuracy (astrometric anomaly) is overcome by explicitly including the nearest visible galaxy in the model. However, one anomalous system (J1131-1231) does not show any luminous perturber in its vicinity, and three others (WFI2026-4536, WFI2033-4723, and B2045+265) have problematic modeling. These 4 systems are the best candidates for a pertubation by a dark matter substructure. 3) We find a significant correlation between the PA of the light and of the mass distributions in lensing galaxies. In contrast with other studies, we find that the ellipticity of the light and of the mass also correlate well, suggesting that the overall spatial distribution of matter is not very different from the baryon distribution in the inner \sim 5 kpc of lensing galaxies.

A MICROLENSING MEASUREMENT OF DARK MATTER FRACTIONS IN THREE LENSING GALAXIES

Direct measurements of dark matter distributions in galaxies are currently only possible through the use of gravitational lensing observations. Combinations of lens modelling and stellar velocity dispersion measurements provide the best constraints on dark matter distributions in individual galaxies, however they can be quite complex. In this paper, we use observations and simulations of gravitational microlensing to measure the smooth (dark) matter mass fraction at the position of lensed images in three lens galaxies: MG 0414+0534, SDSS J0924+0219 and Q2237+0305. The first two systems consist of early-type lens galaxies, and both display a flux ratio anomaly in their close image pair. Anomalies such as these suggest a high smooth matter percentage is likely, and indeed we prefer ~50 per cent smooth matter in MG 0414+0534, and ~80 per cent in SDSS J0924+0219 at the projected locations of the lensed images. Q2237+0305 differs somewhat in that its lensed images lie in the central kiloparsec of the barred spiral lens galaxy, where we expect stars to dominate the mass distribution. In this system, we find a smooth matter percentage that is consistent with zero.

Dark Matter Halos: The Dynamical Basis of Effective Empirical Models

We investigate the dynamical basis of the classic empirical models (specifically, Sérsic-Einasto and generalized NFW) that are widely used to describe the distributions of collisionless matter in galaxies. We submit that such a basis is provided by ourα-profiles, shown to constitute solutions of the Jeans dynamical equilibrium with physical boundary conditions. We show how to set the parameters of the empirical in terms of the dynamical models; we find the empirical models, and specifically Sérsic-Einasto, to constitute a simple and close approximation to the dynamical models. Finally, we discuss how these provide a useful baseline for assessing the impact of the small-scale dynamics that may modulate the density slope in the central galaxy regions.

HIGH-RESOLUTION DARK MATTER DENSITY PROFILES OF THINGS DWARF GALAXIES: CORRECTING FOR NONCIRCULAR MOTIONS

We present a new method to remove the impact of random and small-scale noncircular motions from H I velocity fields in (dwarf) galaxies in order to better constrain the dark matter properties for these objects. This method extracts the circularly rotating velocity components from the H I data cube and condenses them into a so-called bulk velocity field. We derive high-resolution (~0.2 kpc) rotation curves of IC 2574 and NGC 2366 based on bulk velocity fields derived from The H I Nearby Galaxy Survey obtained at the Very Large Array. We compare the bulk velocity field rotation curves with those derived from the traditional intensity-weighted mean velocity fields and find significant differences. The bulk velocity field rotation curves are significantly less affected by noncircular motions and constrain the dark matter distribution in our galaxies, allowing us to address the discrepancy between the inferred and predicted dark matter distribution in galaxies (the cusp/core problem). Spitzer Infrared Nearby Galaxies Survey 3.6 μm data, which are largely unaffected by dust in these systems, as well as ancillary optical information, are used to separate the contribution of the baryons from the total matter content. Using stellar population synthesis models, assuming various sets of metallicity and star-formation histories, we compute stellar mass-to-light ratios for the 3.6 μm and 4.5 μm bands. Using our predicted value for the 3.6 μm stellar mass-to-light ratio, we find that the observed dark matter distributions of IC 2574 and NGC 2366 are inconsistent with the cusp-like dark matter halo predicted by Λ Cold Dark Matter models, even after corrections for noncircular motions. This result also holds for other assumptions about the stellar mass-to-light ratio. The distribution of dark matter within our sample galaxies is best described by models with a kpc-sized constant-density core.