The Highly Flattened Dark Matter Halo of NGC 4244

In a previous paper (Olling 1995, \aj, 110, 591; astro-ph/9505002) a method was developed to determine the shapes of dark matter halos of spiral galaxies from an accurate determination of the rotation curve, the flaring of the gas layer and the velocity dispersion in the HI. Here this method is applied to the almost edge-on Scd galaxy NGC 4244 for which the necessary parameters are determined in the accompanying paper (AJ, Aug. 1996; astro-ph/9605110). The observed flaring of the HI beyond the optical disk puts significant constraints on the shape of the dark matter halo, which are almost independent of the stellar mass-to-light ratio. NGC 4244's dark matter halo is found to be highly flattened with a shortest-to-longest axis ratio of 0.2 (-0.1)(+0.3). If the dark matter is disk-like, the data presented in this paper imply that the vertical velocity dispersion of the dark matter must be 10% - 30% larger than the measured tangential dispersion in the HI. Alternatively, the measured flaring curve is consistent with a round halo if the gaseous velocity dispersion ellipsoid is anisotropic. In that case the vertical dispersion of the gas is 50 - 70% of the measured tangential velocity dispersion.Comment: 16 pages LaTeX, uses aaspptwo style (357kByte). Includes 3 figures. Complete paper, is also available at http://www.astro.soton.ac.uk/~olling/PrePrints/Paper_03/ or via anonymous ftp at ftp.astro.soton.ac.uk, cd pub/olling/Paper_03 To be published in the Aug. 1996 issue of the Astronomical Journa

CERTCOST News

The EU research project, CERTCOST, has issued the first digital CERTCOST newsletter. Despite the fact that organic certification and its costs might be a somewhat dry subject from a consumer’s point of view, we intend to present the results in a eatable manner. The International Center for Research in Organic Food Systems, ICROFS, is responsible for dissemination of the CERTCOST project

ICROFS news 1/2009 - newsletter from ICROFS

News and research dissemination from ICROF

Organic for the future

Organic research and innovation moves the organic food sector from a niche to a general reference model for sustainable agriculture. Europe faces major challenges to conserve biodiversity, secure soil, and promote animal welfare and there is an urgent need to ensure global food security. Organic food and farming paves the way to meet these challenges; but to succeed a further development of organic food and farming is key

Accurate Extra-Galactic Distances and Dark Energy: Anchoring the Distance Scale with Rotational Parallaxes

We investigate how the uncertainty on the Hubble constant (H_0) affects the uncertainty in the Equation of State (EOS) of Dark Energy and the total density of the Universe (Omega_tot). We use the approximate relations between the cosmological parameters [Spergel etal (2007)] and use error-propagation to estimate the effects of improving the CMB parameters and H_0 on the EOS of Dark Energy (DE). First we assume that the additional data does not improve significantly, but decrease the error on H_0 by a factor <~10. Second, we allow improved additional data but current H_0 errors (i.e., the DE Task Force case). In the 1st scenario, improvements of the CMB parameters hardly change the accuracy of the EOS and Omega_tot, unless H_0 can be measured with an accuracy of a few %. We find that a combination of moderate improvements for both H_0 and other data significantly constrains the evolution of dark energy, but at a reduced cost. We review several methods (and their strengths and weaknesses) that might yield extra-galactic distances with errors of about 1%. We review: the Velocity Field method, two Maser methods, two Light Echo techniques, the Binary Star method, and the Rotational Parallax (RP) technique. Because these methods substantially rely on geometry rather than astrophysics or cosmology, their results are quite robust. We focus on the advantages of the RP technique which can provide single-step, bias-free distances to nearby spirals. These distances can be used to improve the zero-point for other methods which in turn allow for a much improved H_0 errors. Achieving an accuracy of ~2% in the distances to M31, M33 and the LMC by the RP method requires proper motions from future astrometric missions (SIM, GAIA and OBSS, or the SKA).Comment: 20 pages, 2 figures. Minor changes. Now includes a review of methods capable of achieving unbiased 1% extra-galactic distances. MNRAS: Accepted for publicatio

Luminous and Dark Matter in the Milky Way

(Abridged) Axisymmetric models of the Milky Way exhibit strong interrelations between the Galactic constants (R_0 and T_0), the stellar columndensity (S_*) and the shape of the dark matter (DM) halo. Here we present analytical relations that can be used to investigate the effects of the uncertain gaseous velocity dispersion on the HI flaring constraints. The contribution of cosmic rays and magnetic fields to the pressure gradients is small. A significantly flattened dark matter halo is only possible if R_0 <~ 6.8 kpc. If R_0 is larger than ~7 kpc, or T_0 >~ 170 km/s, we can rule out two DM candidates that require a highly flattened DM halo: 1) decaying massive neutrinos; and 2) a disk of cold molecular hydrogen. It is only possible to construct self-consistent models of the Galaxy based on the IAU-recommended values for the Galactic constants in the unlikely case that the the stellar columndensity is smaller than ~18 M_sun/pc^2. If we assume that the halo is oblate and S_* = 35 +/- 5 M_sun/pc^2, R_0 <~ 8 kpc and T_0 <~ 200 km/s. Combining the best kinematical and star-count estimates of S_*, we conclude that: 25 <~ S_* <~ 45 M_sun/pc^2. Kuijken & Gilmore's (1991) determination of the columndensity of matter with |z|<=1.1 kpc is robust and valid over a wide range of Galactic constants. Our mass models show that the DM density in the Galactic centre is uncertain by a factor 1000. In the Solar neighbourhood we find: rho_DM ~0.42 GeV/c^2/cm^3 or (11 +/- 5) mM_sun/pc^3 -- roughly 15% of rho_tot.Comment: Accepted for publication in MNRA

Refining the Oort and Galactic constants

The local stellar kinematics of the Milky Way offer a useful tool for studying the rotation curve of the Galaxy. These kinematics -- usually parameterized by the Oort constants A and B -- depend on the local gradient of the rotation curve as well as its absolute value (Theta_0), and the Sun's distance to the Galactic center (R_0). The density of interstellar gas in the Milky Way is shown to vary non-monotonically with radius, and so contributes significantly to the local gradient of the rotation curve. We have therefore calculated mass models for the Milky Way that include this component, and have derived the corresponding radial variation in the Oort constants. Between 0.9R_0 and 1.2R_0, the Oort functions, A(R) and B(R), differ significantly from the general Theta/R dependence. Various previously-inexplicable observations are shown to be consistent with these predictions. These models can explain the 40% difference between the values for 2 A R_0 derived from radial velocity data originating in the inner and outer Galaxy. They also go some way toward explaining the different shapes of the velocity ellipsoids of giant and dwarf stars in the solar neighbourhood. However, a consistent picture only emerges if one adopts small values of R_0 = 7.1 +/- 0.4 kpc and Theta_0 = 184 +/- 8 km/s. With these Galactic constants, the Milky Way's rotation curve declines slowly in the outer Galaxy; V_rot(20 kpc) = 166 kms. Our low value for R_0 agrees well with the only direct determination (7.2 +/- 0.7 kpc, Reid 1993). Using these Galactic constants, we find that the proper motion of Sgr A^* is consistent with the observational constraints. The radial velocities and proper motions of our best fit model are entirely consistent with the radial velocities of Cepheids and the Hipparcos measurements of their proper motions.Comment: 11 pages, LaTeX, including 5 figures, using mn and epsf style files. Accepted for publication in MNRA