31 research outputs found
The 3-Dimensional Distribution of Dust in NGC 891
We produce three-dimensional Monte-Carlo radiative transfer models of the
edge-on spiral galaxy NGC 891, a fast-rotating galaxy thought to be an analogue
to the Milky Way. The models contain realistic spiral arms and a fractal
distribution of clumpy dust. We fit our models to Hubble Space Telescope images
corresponding to the B and I bands, using shapelet analysis and a genetic
algorithm to generate 30 statistically best-fitting models. These models have a
strong preference for spirality and clumpiness, with average face-on
attenuation decreasing from 0.24(0.16) to 0.03(0.03) mag in the B(I) band
between 0.5 and 2 radial scale-lengths. Most of the attenuation comes from
small high-density clumps with low (<10%) filling factors. The fraction of dust
in clumps is broadly consistent with results from fitting NGC 891's spectral
energy distribution. Because of scattering effects and the intermixed nature of
the dust and starlight, attenuation is smaller and less wavelength-dependent
than the integrated dust column-density. Our clumpy models typically have
higher attenuation at low inclinations than previous radiative transfer models
using smooth distributions of stars and dust, but similar attenuation at
inclinations above 70 degrees. At all inclinations most clumpy models have less
attenuation than expected from previous estimates based on minimizing scatter
in the Tully-Fisher relation. Mass-to-light ratios are higher and the intrinsic
scatter in the Tully-Fisher relation is larger than previously expected for
galaxies similar to NGC 891. The attenuation curve changes as a function of
inclination, with R_(B,B-I)=A_(B)/E(B-I) increasing by ~0.75 from face-on to
near-edge-on orientations.Comment: 26 pages, 18 figures, accepted for publication in Ap
The 3-Dimensional Structure of NGC 891 and M51
We investigate the three-dimensional structure of the nearby edge-on spiral
galaxy NGC 891 using 3D Monte Carlo radiative transfer models, with realistic
spiral structure and fractally clumped dust. Using the spiral and clumpiness
parameters found from recently completed scattered light models we produce
lower resolution SED models which reproduce the global UV-to-FIR SED of NGC
891. Our models contain a color gradient across the major axis of the galaxy -
similar to what is seen in images of the NGC 891. With minor adjustment our SED
models are able to match the majority of M51's SED, a similar galaxy at a near
face-on different inclination.Comment: 3 pages, 1 figure. To appear in the Conference Proceedings of IAU
Symposium No. 284: The Spectral Energy Distribution of Galaxies, R.J. Tuffs &
C.C. Popescu, ed
The DiskMass Survey. IV. The Dark-Matter-Dominated Galaxy UGC 463
We present a detailed and unique mass budget for the high-surface-brightness
galaxy UGC 463, showing it is dominated by dark matter (DM) at radii beyond one
scale length (h_R) and has a baryonic-to-DM mass ratio of approximately 1:3
within 4.2 h_R. Assuming a constant scale height (h_z, calculated via an
empirical oblateness relation), we calculate dynamical disk mass surface
densities from stellar kinematics, which provide vertical velocity dispersions
after correcting for the shape of the stellar velocity ellipsoid (measured to
have sigma_theta/sigma_R=1.04 +/- 0.22 and sigma_z/sigma_R=0.48 +/- 0.09). We
isolate the stellar mass surface density by accounting for all gas mass
components and find an average K-band mass-to-light ratio of 0.22 +/- 0.09
(ran) ^{+0.16}_{-0.15} (sys) M_{sun}/L_{sun}^{K}; Zibetti et al. and Bell et
al. predict, respectively, 0.56 and 3.6 times our dynamical value based on
stellar-population-synthesis modeling. The baryonic matter is submaximal by a
factor of ~3 in mass and the baryonic-to-total circular-speed ratio is
0.61^{+0.07}_{-0.09} (ran) ^{+0.12}_{-0.18} (sys) at 2.2 h_R; however, the disk
is globally stable with a multi-component stability that decreases
asymptotically with radius to Q~2. We directly calculate the circular speed of
the DM halo by subtracting the baryonic contribution to the total circular
speed; the result is equally well described by either a Navarro-Frenk-White
halo or a pseudo-isothermal sphere. The volume density is dominated by DM at
heights of |z|>1.6 h_z for radii of R > h_R. As is shown in follow-up papers,
UGC 463 is just one example among nearly all galaxies we have observed that
contradict the hypothesis that high-surface-brightness spiral galaxies have
maximal disks.Comment: accepted for publication in ApJ (36 pages, 20 figures, 9 tables
A millisecond pulsar in a stellar triple system
Gravitationally bound three-body systems have been studied for hundreds of
years and are common in our Galaxy. They show complex orbital interactions,
which can constrain the compositions, masses, and interior structures of the
bodies and test theories of gravity, if sufficiently precise measurements are
available. A triple system containing a radio pulsar could provide such
measurements, but the only previously known such system, B1620-26 (with a
millisecond pulsar, a white dwarf, and a planetary-mass object in an orbit of
several decades), shows only weak interactions. Here we report precision timing
and multi-wavelength observations of PSR J0337+1715, a millisecond pulsar in a
hierarchical triple system with two other stars. Strong gravitational
interactions are apparent and provide the masses of the pulsar (1.4378(13)
Msun, where Msun is the solar mass and the parentheses contain the uncertainty
in the final decimal places) and the two white dwarf companions (0.19751(15)
Msun and 0.4101(3) Msun), as well as the inclinations of the orbits (both
approximately 39.2 degrees). The unexpectedly coplanar and nearly circular
orbits indicate a complex and exotic evolutionary past that differs from those
of known stellar systems. The gravitational field of the outer white dwarf
strongly accelerates the inner binary containing the neutron star, and the
system will thus provide an ideal laboratory in which to test the strong
equivalence principle of general relativity.Comment: 17 pages, 3 figures, 1 table. Published online by Nature on 5 Jan
2014. Extremely minor differences with published version may exis
The Infrared Light Curve of SN 2011fe in M101 and the Distance to M101
We present near infra-red light curves of supernova (SN) 2011fe in M101,
including 34 epochs in H band starting fourteen days before maximum brightness
in the B-band. The light curve data were obtained with the WIYN High-Resolution
Infrared Camera (WHIRC). When the data are calibrated using templates of other
Type Ia SNe, we derive an apparent H-band magnitude at the epoch of B-band
maximum of 10.85 \pm 0.04. This implies a distance modulus for M101 that ranges
from 28.86 to 29.17 mag, depending on which absolute calibration for Type Ia
SNe is used.Comment: 9 pages, 3 figures, emulateapj style, accepted for publication in The
Astrophysical Journa