Cosmological constant and the fate of the DDM theory

We investigate the impact of the non-zero cosmological constant on the classical decaying dark matter theory developed by the late Dennis Sciama. In particular, we concentrate on the change in relevant values of cosmological parameters in comparison to the high-precision estimates given by Sciama (1997). It is shown that the appropriate changes in resulting parameter values are such to make the DDM concept less plausible. This is in complete agreement with recently reported observational results detrimental to this theory.Comment: 4 pages, 2 eps figures, uses AA latex styl

MOND vs. Newtonian dynamics in early-type galaxies. The case of NGC 4649 (M60)

Context: Regarding the significant interest in both dark matter and the application of MOND to early-type galaxies, we investigate the MOND theory by comparing its predictions, for models of constant mass-to-light ratio, with observational data of the early-type galaxy NGC 4649. Aims: We study whether measurements for NGC 3379 and NGC 1399 are typical of early-type systems and we test the assumption of a Newtonian constant M/L ratio underlying most of the published models. Methods: We employ the globular clusters of NGC 4649 as a mass tracer. The Jeans equation is calculated for both MOND and constant mass-to-light ratio assumptions. Spherical symmetry is assumed and the calculations are performed for both isotropic and anisotropic cases. Results: We found that both Jeans models with the assumption of a constant mass-to-light ratio and different MOND models provide good agreement with the observed values of the velocity dispersion. The most accurate fits of the velocity dispersion were obtained for the mass-to-light ratio in the B-band, which was equal to 7, implying that there is no need for significant amounts of dark matter in the outer parts (beyond 3 effective radii) of this galaxy. We also found that tangential anisotropies are most likely present in NGC 4649.Comment: 6 pages, 4 figure

Dark matter in early-type galaxies: dynamical modelling of IC1459, IC3370, NGC3379 and NGC4105

We analyse long-slit spectra of four early-type galaxies which extend from ~1 to ~3 effective radii: IC1459, IC3370, NGC3379 and NGC4105. We have extracted the full line-of-sight velocity distribution (in the case of NGC3379 we also used data from the literature) which we model using the two-integral approach. Using two-integral modelling we find no strong evidence for dark haloes, but the fits suggest that three-integral modelling is necessary. We also find that the inferred constant mass-to-light ratio in all four cases is typical for early-type galaxies. Finally, we also discuss the constraints on the mass-to-light ratio which can be obtained using X-ray haloes in the case of IC1459, NGC3379 and NGC4105 and compare the estimated values with the predictions from the dynamical modelling.Comment: 42 pages, 18 figures, accepted for publication in MNRA

Measuring the non-thermal pressure in early type galaxy atmospheres: A comparison of X-ray and optical potential profiles in M87 and NGC1399

We compare the gravitational potential profiles of the elliptical galaxies NGC 4486 (M87) and NGC 1399 (the central galaxy in the Fornax cluster) derived from X-ray and optical data. This comparison suggests that the combined contribution of cosmic rays, magnetic fields and micro-turbulence to the pressure is ~10% of the gas thermal pressure in the cores of NGC 1399 and M87, although the uncertainties in our model assumptions (e.g., spherical symmetry) are sufficiently large that the contribution could be consistent with zero. In the absence of any other form of non-thermal pressure support, these upper bounds translate into upper limits on the magnetic field of ~10-20 muG at a distance of 1'-2' from the centers of NGC1399 and M87. We show that these results are consistent with the current paradigm of cool cluster cores, based on the assumption that AGN activity regulates the thermal state of the gas by injecting energy into the intra-cluster medium. The limit of ~10-20% on the energy density in the form of relativistic protons applies not only to the current state of the gas, but essentially to the entire history of the intra-cluster medium, provided that cosmic ray protons evolve adiabatically and that their spatial diffusion is suppressed.Comment: Accepted for MNRAS. 19 pages; 14 figures; expanded version in response to comments from the refere

On the Correlations between Galaxy Properties and Supermassive Black Hole Mass

We use a large sample of upper limits and accurate estimates of supermassive black holes masses coupled with libraries of host galaxy velocity dispersions, rotational velocities and photometric parameters extracted from Sloan Digital Sky Survey i-band images to establish correlations between the SMBH and host galaxy parameters. We test whether the mass of the black hole, MBH, is fundamentally driven by either local or global galaxy properties. We explore correlations between MBH and stellar velocity dispersion sigma, bulge luminosity, bulge mass Sersic index, bulge mean effective surface brightness, luminosity of the galaxy, galaxy stellar mass, maximum circular velocity Vc, galaxy dynamical and effective masses. We verify the tightness of the MBH-sigma relation and find that correlations with other galaxy parameters do not yield tighter trends. We do not find differences in the MBH-sigma relation of barred and unbarred galaxies. The MBH-sigma relation of pseudo-bulges is also coarser and has a different slope than that involving classical bulges. The MBH-bulge mass is not as tight as the MBH-sigma relation, despite the bulge mass proving to be a better proxy of MBH than bulge luminosity. We find a rather poor correlation between MBH and Sersic index suggesting that MBH is not related to the bulge light concentration. The correlations between MBH and galaxy luminosity or mass are not a marked improvement over the MBH sigma relation. If Vc is a proxy for the dark matter halo mass, the large scatter of the MBH-Vc relation then suggests that MBH is more coupled to the baryonic rather than the dark matter. We have tested the need for a third parameter in the MBH scaling relations, through various linear correlations with bulge and galaxy parameters, only to confirm that the fundamental plane of the SMBH is mainly driven by sigma, with a small tilt due to the effective radius. (Abridged)Comment: 32 pages, 18 figures, 6 tables, accepted for publication in MNRA

Dynamical constant mass-to-light ratio models of NGC 5128

Context. The existence and amount of dark matter in early-type galaxies remains a hotly debated topic. We study dynamical models of NGC 5128, which do not include dark matter, to test the predictions of different constant mass-to-light models. Aims. We use the measurements of the radial velocities of the planetary nebulae in NGC 5128 to test the predictions of Newtonian constant mass-to-light ratio models and we also extend our study to different MOND models. Methods. The planetary nebulae of NGC 5128 were used as a tracer of the galaxy's gravitational potential. The Jeans equation was calculated for both the Newtonian mass-follows-light and the MOND approaches. Spherical symmetry is assumed and the calculations are performed for both isotropic and anisotropic cases. Results. We solved the Jeans equation in spherical approximation and found that the isotropic Newtonian mass-follows-light models without dark matter may provide successful fits out to 6.4Re; to obtain a good fit in the outermost region (~ 10.7Re) one needs either dark matter or tangential anisotropies. Concerning MOND models we found that no isotropic MOND model without dark matter can provide a successful fit interior to ~ 6.4Re; for the anisotropic MOND models interior to ~40 arcmin only “standard” MOND model with tangential anisotropies can provide a successful fit of the observed velocity dispersion without the need of dark matter

Isotropic dynamical models of NGC 4472 (M 49)

Context. The existence of dark matter in some early-type galaxies is well-established. We address one such case and study dynamical models of NGC 4472 by means of using both Newtonian and MOdified Newtonian Dynamics (MOND) approaches with particular emphasis on the latter. Aims. We use the measurements of the radial velocities of globular clusters in NGC 4472 to test the predictions of dynamical models to fit a high and approximately constant value the velocity dispersion with radius for this galaxy. Methods. The globular clusters of NGC 4472 are used as a tracer of the galaxy’s gravitational potential. We calculate the Jeans equation for both the Newtonian (mass-follows-light and dark-matter models) and the MOND approaches assuming spherical symmetry and isotropic orbits. Results. We solve the isotropic Jeans equation for a spherical approximation and find, assuming a rotational velocity of 50 kms-1, that the isotropic Newtonian mass-follows-light models without dark matter cannot provide successful fits at radii larger than ~2 Re and that in the Newtonian approach dark matter is needed. Of the four different MOND models that we tested, two models can provide a successful fit to the velocity dispersion throughout the whole galaxy without assuming any anisotropy (again assuming a rotational velocity of 50 kms-1), thus showing that in the case of NGC 4472 MOND can describe the dynamics of a massive early-type galaxy with high values of velocity dispersion

The Newtonian and MOND dynamical models of NGC 5128: Investigation of the dark matter contribution

We study the well-known nearby early-type galaxy NGC 5128 (Centaurus A) and use the sample of its globular clusters to analyze its dynamics. We study both Newtonian and MOND models assuming three cases of orbital anisotropies: isotropic case, mildly tangentially anisotropic case and the radially anisotropic case based on the literature. We find that there are two regions with different values of the velocity dispersion: interior to ~ 3 effective radii the value of the velocity dispersion is approximately 150 km s−1 , whereas beyond ~ 3 effective radii its value increases to approximately 190 km s−1 , thus implying the increase of the total cumulative mass which is indicative of the existence of dark matter there in the Newtonian approach: the mass-to-light increases from M/LB = 7 in the inner regions to M/LB = 26 in the outer regions. We found that the Navarro-Frenk-White (NFW) model with dark halo provides good description of the dynamics of NGC 5128. Using three MOND models (standard, simple and toy), we find that they all provide good fits to the velocity dispersion of NGC 5128 and that no additional dark component is needed in MOND. [Projekat Ministarstva nauke Republike Srbije, br. 176021: Visible and Invisible Matter in Nearby Galaxies: Theory and Observations

Local elliptical galaxies: Some aspects of theory vs. observations

In this paper we analyze on, the sample of the local elliptical galaxies, some predictions of various cosmological theories. We start with the sample of ellipticals described in Samurović (2007b) and confront the established concentration parameters and mass-to-light ratios of these objects with various cosmological models, i.e. models given by Navarro, Frank and White (NFW) (1996, 1997) and Burkert (1995), respectively. We find that the bright galaxy (NGC 5846), for which the sum α + β is high, can be reasonably modelled by the NFW models. The Burkert model provides rather good predictions of the dark matter content at one effective radius. There is an indication that bright ellipticals (MB >˜ -21.0) are more dark matter dominated that the fainter ones (MB >˜ -21.0)

Phenomenological approach to the modelling of elliptical galaxies: The problem of the mass-to-light ratio

In this paper the problem of the phenomenological modelling of elliptical galaxies using various available observational data is presented. Recently, Tortora, Cardona and Piedipalumbo (2007) suggested a double power law expression for the global cumulative mass-to-light ratio of elliptical galaxies. We tested their expression on a sample of ellipticals for which we have the estimates of the mass-to-light ratio beyond ~ 3 effective radii, a region where dark matter is expected to play an important dynamical role. We found that, for all the galaxies in our sample, we have α + β > 0, but that this does not necessarily mean a high dark matter content. The galaxies with higher mass (and higher dark matter content) also have higher value of α+β. It was also shown that there is an indication that the galaxies with higher value of the effective radius also have higher dark matter content.