The dark and baryonic matter content of low surface brightness disk galaxies

We present mass models of a sample of 19 low surface brightness (LSB) galaxies and compare the properties of their constituent mass components with those of a sample of high surface brightness (HSB) galaxies.We find that LSB galaxies are dark matter dominated. Their halo parameters are only slightly affected by assumptions on stellar mass-to-light ratios. Comparing LSB and HSB galaxies we find that mass models derived using the maximum disk hypothesis result in the disks of LSB galaxies having systematically higher stellar mass-to-light ratios than HSB galaxies of similar rotation velocity. This is inconsistent with all other available evidence on the evolution of LSB galaxies. We argue therefore that the maximum disk hypothesis does not provide a representative description of the LSB galaxies and their evolution. Mass models with stellar mass-to-light ratios determined by the colors and stellar velocity dispersions of galactic disks imply that LSB galaxies have dark matter halos that are more extended and less dense than those of HSB galaxies. Surface brightness is thus related to the halo properties. LSB galaxies are slowly evolving, low density and dark matter dominated galaxies.Comment: 23 pages Latex, 12 postscript figures, uses mn.sty. Accepted for publication in MNRA

Two Dimensional Velocity Fields of Low Surface Brightness Galaxies

We present high resolution two dimensional velocity fields from integral field spectroscopy along with derived rotation curves for nine low surface brightness galaxies. This is a positive step forward in terms of both data quality and number of objects studied. We fit NFW and pseudo-isothermal halo models to the observations. We find that the pseudo-isothermal halo better represents the data in most cases than the NFW halo, as the resulting concentrations are lower than would be expected for LCDM.Comment: 2 pages, 1 figure, to appear in the XXIst IAP Colloquium "Mass Profiles and Shapes of Cosmological Structures", Paris 4-9 July 2005, (Eds.) G. Mamon, F. Combes, C. Deffayet, B. Fort, (EDP Sciences

Mass Density Profiles of LSB Galaxies

We derive the mass density profiles of dark matter halos that are implied by high spatial resolution rotation curves of low surface brightness galaxies. We find that at small radii, the mass density distribution is dominated by a nearly constant density core with a core radius of a few kpc. For rho(r) ~ r^a, the distribution of inner slopes a is strongly peaked around a = -0.2. This is significantly shallower than the cuspy a < -1 halos found in CDM simulations. While the observed distribution of alpha does have a tail towards such extreme values, the derived value of alpha is found to depend on the spatial resolution of the rotation curves: a ~ -1 is found only for the least well resolved galaxies. Even for these galaxies, our data are also consistent with constant density cores (a = 0) of modest (~ 1 kpc) core radius, which can give the illusion of steep cusps when insufficiently resolved. Consequently, there is no clear evidence for a cuspy halo in any of the low surface brightness galaxies observed.Comment: To be published in ApJ Letters. 6 pages. Uses aastex and emulateapj5.sty Typo in Eq 1 fixe

The Pricing of Housing and Mortgage Services for First-Time Versus Repeat Homebuyers

This study examines efficiency in the pricing of housing and mortgage services across first-time and repeat homebuyers. A logit model is used to test a number of variables for significant differences across first-time buyers and repeat buyers for a sample of brokered real estate sales. The results show that the housing market is somewhat less than completely efficient in providing its services. The logit results for the adjustable-rate mortgage segment show that first-time homebuyers are more likely to be associated with a higher sale price per square foot and higher discount points than repeat buyers. The results show that first-time homebuyers tend to be younger and have less household income than repeat homebuyers. For the full sample of data, the results show that higher sale price/square foot ratios and lower downpayment/sale price ratios are more likely to be associated with first-time homebuyers. For the fixed-rate mortgage segment of the data, the only distinguishing variables are downpayment/sale price and buyer age (both lower for first-time homebuyers). Type of buyer cannot be distinguished by sale price/square foot, contract interest rate, discount points, and other variables. For the adjustable-rate mortgage segment of the data, type of buyer can be distinguished by sale sprice/square foot (higher for first-time buyers), downpayment/sale price (lower for first-time buyers), and discount points (higher for first-time buyers).

Gas Mass Fractions and the Evolution of Spiral Galaxies

We show that the gas mass fraction of spiral galaxies is strongly correlated with luminosity and surface brightness. It is not correlated with linear size. Gas fraction varies with luminosity and surface brightness at the same rate, indicating evolution at fixed size. Dim galaxies are clearly less evolved than bright ones, having consumed only $\sim 1/2$ of their gas. This resolves the gas consumption paradox, since there exist many galaxies with large gas reservoirs. These gas rich galaxies must have formed the bulk of their stellar populations in the last half of a Hubble time. The existence of such immature galaxies at $z = 0$ indicates that either galaxy formation is a lengthy or even ongoing process, or the onset of significant star formation can be delayed for arbitrary periods in tenuous gas disks.Comment: Accepted for publication in the Astrophysical Journal. 18 pages AASLaTeX + 9 figure

A Multi-Criteria Model for Corporate Property Evaluation

A critical concern for corporations pursuing geographical expansion strategies involves property evaluation. In order for expansion to be successful, corporations must identify cities and properties that offer a good fit with the firm's corporate strategy. Unfortunately, little has been written to aid corporations in making complex property selection decisions. This paper presents a model that combines the concepts of strategic management, the management science technique of goal programming, and micro computer technology to provide managers with a more effective and efficient method for evaluation property and making selection decisions.

On the Nature of MeV-blazars

Broad-band spectra of the FSRQ (flat-spectrum-radio quasars) detected in the high energy gamma-ray band imply that there may be two types of such objects: those with steep gamma-ray spectra, hereafter called MeV-blazars, and those with flat gamma-ray spectra, GeV-blazars. We demonstrate that this difference can be explained in the context of the ERC (external-radiation-Compton) model using the same electron injection function. A satisfactory unification is reachable, provided that: (a) spectra of GeV-blazars are produced by internal shocks formed at the distances where cooling of relativistic electrons in a jet is dominated by Comptonization of broad emission lines, whereas spectra of MeV-blazars are produced at the distances where cooling of relativistic electrons is dominated by Comptonization of near-IR radiation from hot dust; (b) electrons are accelerated via a two step process and their injection function takes the form of a double power-law, with the break corresponding to the threshold energy for the diffusive shock acceleration. Direct predictions of our model are that, on average, variability time scales of the MeV-blazars should be longer than variability time scales of the GeV-blazars, and that both types of the blazar phenomenon can appear in the same object.Comment: Accepted for publication in the Astrophysical Journa

Milky Way Mass Models and MOND

Using the Tuorla-Heidelberg model for the mass distribution of the Milky Way, I determine the rotation curve predicted by MOND. The result is in good agreement with the observed terminal velocities interior to the solar radius and with estimates of the Galaxy's rotation curve exterior thereto. There are no fit parameters: given the mass distribution, MOND provides a good match to the rotation curve. The Tuorla-Heidelberg model does allow for a variety of exponential scale lengths; MOND prefers short scale lengths in the range 2.0 to 2.5 kpc. The favored value of scale length depends somewhat on the choice of interpolation function. There is some preference for the `simple' interpolation function as found by Famaey & Binney. I introduce an interpolation function that shares the advantages of the simple function on galaxy scales while having a much smaller impact in the solar system. I also solve the inverse problem, inferring the surface mass density distribution of the Milky Way from the terminal velocities. The result is a Galaxy with `bumps and wiggles' in both its luminosity profile and rotation curve that are reminiscent of those frequently observed in external galaxies.Comment: Accepted for publication in the Astrophysical Journal. 31 pages including 8 figures and 3 table