Dark Matter In Spiral Galaxies Research Articles

Distribution of Baryonic and Dark Matter in Spiral Galaxies

In the present paper, the distributions of baryonic and dark matter are derived for 24 northern sky spiral galaxies. The baryonic mass surface density profile is derived, and the component of the galaxies' observed rotation due to the baryons (stars and gas) is computed. Thus, the baryonic rotation curve of each sampled galaxy is separated from the observed rotation curve given in data base (Stapehane Courteau).

Collapsed Dark Matter Structures.

The distributions of dark matter and baryons in the Universe are known to be very different: The dark matter resides in extended halos, while a significant fraction of the baryons have radiated away much of their initial energy and fallen deep into the potential wells. This difference in morphology leads to the widely held conclusion that dark matter cannot cool and collapse on any scale. We revisit this assumption and show that a simple model where dark matter is charged under a "dark electromagnetism" can allow dark matter to form gravitationally collapsed objects with characteristic mass scales much smaller than that of a Milky-Way-type galaxy. Though the majority of the dark matter in spiral galaxies would remain in the halo, such a model opens the possibility that galaxies and their associated dark matter play host to a significant number of collapsed substructures. The observational signatures of such structures are not well explored but potentially interesting.

Nonlocal Newtonian cosmology

We explore some of the cosmological implications of the recent classical nonlocal generalization of Einstein’s theory of gravitation in which nonlocality is due to the gravitational memory of past events. In the Newtonian regime of this theory, the nonlocal character of gravity simulates dark matter in spiral galaxies and clusters of galaxies. However, dark matter is considered indispensable as well for structure formation in standard models of cosmology. Can nonlocal gravity solve the problem of structure formation without recourse to dark matter? Here we make a beginning in this direction by extending nonlocal gravity in the Newtonian regime to the cosmological domain. The nonlocal analog of the Zel’dovich solution is formulated and the consequences of the resulting nonlocal Zel’dovich model are investigated in detail.

Plasma dark matter direct detection

Dark matter in spiral galaxies like the Milky Way may take the form of a dark plasma. Hidden sector dark matter charged under an unbroken U(1)′ gauge interaction provides a simple and well defined particle physics model realising this possibility. The assumed U(1)′ neutrality of the Universe then implies (at least) two oppositely charged dark matter components with self-interactions mediated via a massless “dark photon” (the U(1)′ gauge boson). In addition to nuclear recoils such dark matter can give rise to keV electron recoils in direct detection experiments. In this context, the detailed physical properties of the dark matter plasma interacting with the Earth is required. This is a complex system, which is here modelled as a fluid governed by the magnetohydrodynamic equations. These equations are numerically solved for some illustrative examples, and implications for direct detection experiments discussed. In particular, the analysis presented here leaves open the intriguing possibility that the DAMA annual modulation signal is due primarily to electron recoils (or even a combination of electron recoils and nuclear recoils). The importance of diurnal modulation (in addition to annual modulation) as a means of probing this kind of dark matter is also emphasised.

Galaxy rotation curves inf(R,ϕ)gravity

We investigate the possibility of explaining theoretically the galaxy rotation curves by a gravitational potential in total absence of dark matter. To this aim an analytic fourth-order theory of gravity, nonminimally coupled with a massive scalar field, is considered. Specifically, the interaction term is given by an analytic function $f(R,\ensuremath{\phi})$, where $R$ is the Ricci scalar and $\ensuremath{\phi}$ is the scalar field. The gravitational potential is generated by a pointlike source and compared with the so-called Sanders's potential that can be exactly reproduced in this case. This result means that the problem of dark matter in spiral galaxies could be fully addressed by revising general relativity at galactic scales and requiring further gravitational degrees of freedom instead of new material components that have not been found up to now.

DISENTANGLING BARYONS AND DARK MATTER IN THE SPIRAL GRAVITATIONAL LENS B1933+503

Measuring the relative mass contributions of luminous and dark matter in spiral galaxies is important for understanding their formation and evolution. The combination of a galaxy rotation curve and strong lensing is a powerful way to break the disk-halo degeneracy that is inherent in each of the methods individually. We present an analysis of the 10-image radio spiral lens B1933+503 at z_l=0.755, incorporating (1) new global VLBI observations, (2) new adaptive-optics assisted K-band imaging, (3) new spectroscopic observations for the lens galaxy rotation curve and the source redshift. We construct a three-dimensionally axisymmetric mass distribution with 3 components: an exponential profile for the disk, a point mass for the bulge, and an NFW profile for the halo. The mass model is simultaneously fitted to the kinematics and the lensing data. The NFW halo needs to be oblate with a flattening of a/c=0.33^{+0.07}_{-0.05} to be consistent with the radio data. This suggests that baryons are effective at making the halos oblate near the center. The lensing and kinematics analysis probe the inner ~10 kpc of the galaxy, and we obtain a lower limit on the halo scale radius of 16 kpc (95% CI). The dark matter mass fraction inside a sphere with a radius of 2.2 disk scale lengths is f_{DM,2.2}=0.43^{+0.10}_{-0.09}. The contribution of the disk to the total circular velocity at 2.2 disk scale lengths is 0.76^{+0.05}_{-0.06}, suggesting that the disk is marginally submaximal. The stellar mass of the disk from our modeling is log_{10}(M_{*}/M_{sun}) = 11.06^{+0.09}_{-0.11} assuming that the cold gas contributes ~20% to the total disk mass. In comparison to the stellar masses estimated from stellar population synthesis models, the stellar initial mass function of Chabrier is preferred to that of Salpeter by a probability factor of 7.2.

A new integral representation for reconstructing the density distribution of matter in the discs of spiral galaxies using the rotation velocity curve in it

In this paper we propose a new method for reconstructing the surface density of matter in flat disks of spiral galaxies. The surface density is expressed through observational rotation velocity curves of visible matter in the disks of spiral galaxies. The new method is not based on quadrature of special functions. The found solution is used for processing and analysis of observational data from several spiral galaxies. The new method can be used to more accurately estimate the amount of dark matter in spiral galaxies.

A Study of General Education Astronomy Students’ Understandings of Cosmology. Part I. Development and Validation of Four Conceptual Cosmology Surveys

This is the first in a series of five articles describing a national study of general education astronomy students’ conceptual and reasoning difficulties with cosmology. In this paper, we describe the process by which we designed four new surveys to assess general education astronomy students’ conceptual cosmology knowledge. These surveys focused on the expansion and evolution of the universe, the Big Bang, and the evidence for dark matter in spiral galaxies. We also present qualitative evidence for the validity of these surveys.

The structure of spiral galaxies: radial profiles in stellar mass-to-light ratio and the dark matter distribution

<i>Context. <i/>The colour and metallicity gradients observed in spiral galaxies suggest that the mass-to-light ratio (/<i>L<i/>) of the stellar disc is a function of radius. This is indeed predicted by chemo-photometric models of galactic discs.<i>Aims. <i/>We investigate the distribution of luminous and dark matter in spiral galaxies, taking into account the radial dependence of the stellar /<i>L<i/>, which is usually assumed to be constant in studies of the mass structure.<i>Methods. <i/>From earlier chemo-photometric models and in agreement with the observed radial profiles of galaxy colours, we derive the typical average /<i>L<i/> profile of the stellar discs of spiral galaxies. We computed the corresponding variable mass-to-light (VML) stellar surface density profile and then the VML disc contribution to the circular velocity. We used the latter, combined with a well-studied dark matter velocity profile, to mass model co-added rotation curves.<i>Results. <i/>By investigating rotation curves in the framework of VML stellar discs, we confirm the scenario obtained with the constant /<i>L<i/> assumption: a dark matter halo with a shallow core, an inner baryon-dominated region, and a larger proportion of dark matter in smaller objects. However, the resulting size of the the dark halo core and of the inner baryon dominance region are somewhat smaller. The stronger role that VML discs have in the innermost regions is important for constraining the galaxy mass structure in both <i>Λ<i/> Cold Dark Matter and MOND scenarios.

A Model of f (R) Gravity as an Alternative for Dark Matter in Spiral Galaxies

In this paper we study consistent solutions of spherically symmetric space in metric f(R) gravity theory. Here we inversely obtain a generic action from metric solutions that describe flat rotation curves in spiral galaxies without dark matter. Then we show that obtained solutions are in conformity with Tully-Fisher relation and modified Newtonian dynamics, which are two strong constraints in justification of flat rotation curves in spiral galaxies.

Results of a Search for Cold Flows of Dark Matter Axions

Theoretical arguments predict that the distribution of cold dark matter in spiral galaxies has peaks in velocity space associated with nonthermalized flows of dark matter particles. We searched for the corresponding peaks in the spectrum of microwave photons from axion to photon conversion in a cavity detector for dark matter axions. We found none and place limits on the density of any local flow of axions as a function of the flow velocity dispersion over the axion mass range 1.98 to 2.17 microeV.

Detecting cold H2globules in the outer Galactic disc by microlensing towards the Maffei 1 elliptical

A candidate source of dark matter in spiral galaxies is cold molecular hydrogen globules with a condensed central core and a disc-like space distribution probably similar to that of neutral hydrogen. This paper shows that the H2 cores are sufficiently compact and massive to be detected by microlensing in the outer Galactic disc and that the Maffei 1 elliptical galaxy, at a distance of 3 Mpc and Galactic latitude , offers an ideal target for such an experiment. The microlensing optical depth of H2 cores along the line of sight to this galaxy is estimated to if most of the dark mass in the Milky Way resides in such cores, and the typical event timescale to 1 day. Detection rates are computed both in the classical and pixel lensing approaches in the I- and K-bands, and for a representative selection of existing observing facilities. In the more efficient pixel lensing case, two 10-h observing runs, separated in time by at least several days, should yield of the order of 10 positive detections at the level using ground-based 8 m-class telescopes in the K-band or the Hubble Space Telescope ACS camera in the I-band, and the corresponding fraction of events with timescale measurable to an accuracy better than amounts to about and respectively for these observing alternatives.

The cored distribution of dark matter in spiral galaxies

We present the Hi data for 5 spiral galaxies that, along with their Hα rotation curves, are used to derive the distribution of dark matter within these objects. A new method for extracting rotation curves from Hi data cubes is presented; this takes into account the existence of a warp and minimises projection effects. The rotation curves obtained are tested by taking them as input to construct model data cubes that are compared to the observed ones: the agreement is excellent. On the contrary, the model data cubes built using rotation curves obtained with standard methods, such as the first-moment analysis, fail the test. The Hi rotation curves agree well with the Hα data, where they coexist. Moreover, the combined Hα + Hi rotation curves are smooth, symmetric and extended to large radii. The rotation curves are decomposed into stellar, gaseous and dark matter contributions and the inferred density distribution is compared to various mass distributions: dark haloes with a central density core, � Cold Dark Matter (�CDM) haloes (NFW, Moore profiles), Hi scaling and MOND. The observations point to haloes with con

Cores vs. Cusps: Dark Matter Density Profiles in Spirals

We use photometric, Hα and Hi data to investigate the distribution of dark matter in spiral galaxies. A new technique for deriving the Hi rotation curve is presented. the final combined Hα+Hi rotation curves are symmetric, well resolved and extend to large radii. We perform the rotation curve decomposition into the luminous and dark matter contributions. the observations are confronted with different models of the dark matter distribution, including core-dominated and cusp-dominated halos as well as less conventional possibilities. the best agreement with the observations is found for the core-dominated halos.

Alternative approach to the galactic dark matter problem

We discuss scenarios in which the galactic dark matter in spiral galaxies is described by a long range coherent field which settles in a stationary configuration that might account for the features of the galactic rotation curves. The simplest possibility is to consider scalar fields, so we discuss in particular, two mechanisms that would account for the settlement of the scalar field in a non-trivial configuration in the absence of a direct coupling of the field with ordinary matter: topological defects, and spontaneous scalarization.

On the apparent coupling of neutral hydrogen and dark matter in spiral galaxies

We have studied a mass model for spiral galaxies in which the dark matter surface density is a scaled version of the observed HI surface density. Applying this mass model to a sample of 24 spiral galaxies with reliable rotation curves one obtains good fits for most galaxies. The scaling factors cluster around 7, after correction for the presence of primordial helium. But for several cases different, often larger, values are found. For galaxies that can not be fitted well the discrepancy occurs at large radii and results from a fairly rapid decline of the HI surface density in the outermost regions. Because of such imperfections and in view of possible selection effects it is not possible to conclude here that there is a real coupling between HI and dark matter in spiral galaxies.

A Universal Coupling Relation between Luminous and Dark Matter Surface Densities in Disk Rotating Galaxies

The mutual dynamical evolution of visible and dark matter in spiral galaxies may have resulted in some kind of coupling between the distributions of visible and dark matter today. This conjecture is empirically explored in the present paper, where rotation curves of 60 spiral galaxies and universal rota- tion curves are —tted using dark halo models with a distribution that depends on the luminous mass distribution. It is shown that the dark matter pro—les of any universal rotation curve can be decomposed into two components: (1) a main component, called ii coupled halo,ˇˇ and (2) a component having a gaslike distribution, negligible in bright galaxies, but of increasing signi—cance toward faint galaxies. Once the disk component (stars, gas, and gaslike component) is subtracted, the dark halo integrated surface densities, are in a plane (in log scale) where the fundamental parameters are p c , only and characterizes the relative importance of the dark halo to the disk mass. This is the coupled halo. In the case of an exponential disk, the coupled halo has a central pro—le of the form o P r~1 and a —at curve at The fact that the gaslike component decreases with luminosity suggests that it may r r opt . be transformed into stars, and therefore could be dark baryons, possibly cold gas in the disk. In these models, the baryonic fraction (stars, gas, and gaslike component) is almost a constant over a range of 5 mag, that is, D30% at 1.5 optical radii. The stellar fraction of baryonic matter increases with luminosity. The model predicts a large fraction of gaslike baryonic dark matter in faint spiral galaxies, i.e., in H I gasrich systems. The mass fraction of this gaslike component is negligible in a galaxy like the Milky Way, and reaches half the halo mass in the faint, low surface brightness galaxy DDO 154. Some —ne- tuning relations, which look mysterious in the context of isothermal halos, are deduced from the coupled halos. The Tully-Fisher relation results from the coupling relation between visible and dark matter surface densities and from the virial theorem. The empirical coupling relation can be used in simulations of the dynamical evolution of gas and stars plus dark matter subsystems to constrain the nature of the halo dark matter. If a form of halo dark matter complies with the coupling relation, it will —t rotation curves without —ne-tuning conspiracies. Subject headings: dark mattergalaxies: fundamental parameters ¨ galaxies: kinematics and dynamicsgravitation

Scalar fields as dark matter in spiral galaxies: comparison with experiments

We present an exact solution for a static and axially symmetric spacetime, which is obtained from a scalar-tensor theory that comes from unification theories. As an attempt to model the dark matter (DM) in spiral galaxies we find that an exponential scalar potential is enough to explain the rotation curves in such galaxies. We also present the fitting to the rotation curve of six spiral galaxies and we find an excellent agreement between observational data and the results of our model.

Scalar fields as dark matter in spiral galaxies: comparison with experiments

We present an exact solution for a static and axially symmetric spacetime, which is obtained from a scalar-tensor theory that comes from unification theories. As an attempt to model the dark matter (DM) in spiral galaxies we find that an exponential scalar potential is enough to explain the rotation curves in such galaxies. We also present the fitting to the rotation curve of six spiral galaxies and we find an excellent agreement between observational data and the results of our model.

Neutral hydrogen and dark matter in spiral galaxies

The first part presents a brief review of the main HI properties of isolated, normal spiral galaxies and of the phenomena which seem to characterize and dominate their internal metabolism. In the second part attention is drawn to all those processes, such as tidal interactions, accretion and mergers, that depend on the galaxy environment and may play a significant role in galaxy formation and evolution. In the third part the observational evidence for the dark matter component of spiral galaxies is discussed.