5,949 research outputs found
Planetary nebulae in the elliptical galaxy NGC 821: kinematics and distance determination
Using a slitless spectroscopy method with the 8.2 m Subaru telescope and its
FOCAS Cassegrain spectrograph, we have increased the number of planetary nebula
(PN) detections and PN velocity measurements in the flattened elliptical galaxy
NGC 821. A comparison with the detections reported previously by the Planetary
Nebula Spectrograph (PN.S) group indicates that we have confirmed most of their
detections. The velocities measured by the two groups, using different
telescopes, spectrographs and slitless techniques, are in good agreement. We
have built a combined sample of 167 PNs and have confirmed the keplerian
decline of the line-of-sight velocity dispersion reported previously. We also
confirm misaligned rotation from the combined sample. A dark matter halo may
exist around this galaxy, but it is not needed to keep the PN velocities below
the local escape velocity as calculated from the visible mass. We have measured
the m(5007) magnitudes of 145 PNs and produced a statistically complete sample
of 40 PNs in NGC 821. The resulting PN luminosity function (PNLF) was used to
estimate a distance modulus of 31.4 mag, equivalent to 19 Mpc. We also
estimated the PN formation rate. NGC 821 becomes the most distant galaxy with a
PNLF distance determination. The PNLF distance modulus is smaller than the
surface brightness fluctuation (SBF) distance modulus by 0.4 mag. Our kinematic
information permits to rule out the idea that a shorter PNLF distance could be
produced by the contamination of the PNLF by background galaxies with emission
lines redshifted into the on-band filter transmission curve.Comment: Accepted for publication in ApJ; 16 figure
On the lack of stellar bars in Coma dwarf galaxies
We present a study of the bar fraction in the Coma cluster galaxies based on
a sample of ~190 galaxies selected from the SDSS-DR6 and observed with the
Hubble Space Telescope (HST) Advanced Camera for Survey (ACS). The
unprecedented resolution of the HST-ACS images allows us to explore the
presence of bars, detected by visual classification, throughout a luminosity
range of 9 mag (-23 < M_r < -14), permitting us to study the poor known region
of dwarf galaxies. We find that bars are hosted by galaxies in a tight range of
both luminosities (-22 < M_r < -17) and masses (10^9 < M*/Msun < 10^11). In
addition, we find that the bar fraction does not vary significantly when going
from the center to the cluster outskirts, implying that cluster environment
plays a second-order role in bar formation/evolution. The shape of the bar
fraction distribution with respect to both luminosity and mass is well matched
by the luminosity distribution of disk galaxies in Coma, indicating that bars
are good tracers of cold stellar disks.Comment: 2 pages, 1 figure, to appear in the proceedings of the conference "A
Universe of Dwarf Galaxies" (Lyon, June 14-18, 2010
Random Surfaces that Suppress Single Scattering
We present a method for generating numerically a one-dimensional random
surface, defined by the equation x_3 = \zx, that suppresses single-scattering
processes in the scattering of light from it within a specified range of
scattering angles. Rigorous numerical calculations of the scattering of light
from surfaces generated by this approach show that the single-scattering
contribution to the mean scattered intensity is indeed suppressed within that
range of angles.Comment: 3 pagers (Latex), 3 figure
Absorption and Direct Processes in Chaotic Wave Scattering
Recent results on the scattering of waves by chaotic systems with losses and
direct processes are discussed. We start by showing the results without direct
processes nor absorption. We then discuss systems with direct processes and
lossy systems separately. Finally the discussion of systems with both direct
processes and loses is given. We will see how the regimes of strong and weak
absorption are modified by the presence of the direct processes.Comment: 8 pages, 4 figures, Condensed Matter Physics (IV Mexican Meeting on
Mathematical and Experimental Physics), Edited by M. Martinez-Mares and J. A.
Moreno-Raz
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