18 research outputs found
Measurement of Galactic Logarithmic Spiral Arm Pitch Angle Using Two-Dimensional Fast Fourier Transform Decomposition
A logarithmic spiral is a prominent feature appearing in a majority of
observed galaxies. This feature has long been associated with the traditional
Hubble classification scheme, but historical quotes of pitch angle of spiral
galaxies have been almost exclusively qualitative. We have developed a
methodology, utilizing two-dimensional fast Fourier transformations of images
of spiral galaxies, in order to isolate and measure the pitch angles of their
spiral arms. Our technique provides a quantitative way to measure this
morphological feature. This will allow comparison of spiral galaxy pitch angle
to other galactic parameters and test spiral arm genesis theories. In this
work, we detail our image processing and analysis of spiral galaxy images and
discuss the robustness of our analysis techniques.Comment: 23 pages, 22 figures, and 3 Tables; published in ApJS 199, 33
http://iopscience.iop.org/0067-0049/199/2/33/; software available for
download at http://dafix.uark.edu/~ages/downloads.html and
http://astro.host.ualr.edu/2DFFT
On the Link Between Central Black Holes, Bar Dynamics, and Dark Matter Halos in Spiral Galaxies
The discovery of a relationship between supermassive black hole (SMBH) mass
and spiral arm pitch angle (P) is evidence that SMBHs are tied to the overall
secular evolution of a galaxy. The discovery of SMBHs in late-type galaxies
with little or no bulge suggests that an underlying correlation between the
dark matter halo concentration and SMBH mass (MBH) exists, rather than between
the bulge mass and MBH. In this paper we measure P using a two-dimensional fast
fourier transform and estimate the bar pattern speeds of 40 barred spiral
galaxies from the Carnegie-Irvine Galaxy Survey. The pattern speeds were
derived by estimating the gravitational potentials of our galaxies from Ks-band
images and using them to produce dynamical simulation models. The pattern
speeds allow us to identify those galaxies with low central dark halo
densities, or fast rotating bars, while P provides an estimate of MBH. We find
that a wide range of MBH exists in galaxies with low central dark matter halo
densities, which appears to support other theoretical results. We also find
that galaxies with low central dark halo densities appear to follow more
predictable trends in P versus de Vaucouleurs morphological type (T) and bar
strength versus T than barred galaxies in general. The empirical relationship
between MBH and total gravitational mass of a galaxy (Mtot) allows us to
predict the minimum Mtot that will be observationally measured of our fast bar
galaxies. These predictions will be investigated in a subsequent paper.Comment: 17 pages, 1 table, 11 figures, accepted for publication in MNRA
Absolute Properties Of The Eclipsing Binary Star Im Persei
IM Per is a detached A7 eccentric eclipsing binary star. We have obtained extensive measurements of the light curve (28,225 differential magnitude observations) and radial velocity curve (81 spectroscopic observations) which allow us to fit orbits and determine the absolute properties of the components very accurately: masses of 1.7831 ± 0.0094 and 1.7741 ± 0.0097 solar masses, and radii of 2.409 ± 0.018 and 2.366 ± 0.017 solar radii. The orbital period is 2.25422694(15) days and the eccentricity is 0.0473(26). A faint third component was detected in the analysis of the light curves, and also directly observed in the spectra. The observed rate of apsidal motion is consistent with theory (U = 151.4 ± 8.4 year). We determine a distance to the system of 566 ± 46 pc