1,009 research outputs found
Spikes in the SED and Ripples in the Outskirts of Galaxies
We describe a new method that allows us to quantitatively characterize
galactic satellites from analysis of disturbances in outer gas disks, without
requiring knowledge of their optical light. We have demonstrated the validity
of this method, which we call Tidal Analysis, by applying it to local spirals
with known optical companions, including M51 and NGC 1512. These galaxies span
the range from having a low mass companion (~ one-hundredth the mass of the
primary galaxy) to a fairly massive companion (~ one-third the mass of the
primary galaxy). This approach has broad implications for many areas of
astrophysics - for the indirect detection of dark matter (or dark-matter
dominated dwarf galaxies), and for galaxy evolution in its use as a decipher of
the dynamical impact of satellites on galactic disks. Here, we present some
preliminary results on the emergent SEDs and images, calculated along the time
sequence of these dynamical simulations using the 3-D self-consistent Monte
Carlo radiative transfer code RADISHE. We explore star formation prescriptions
and how they affect the emergent SEDs and images. Our goal is to identify SED
colors that are primarily affected by the galaxy's interaction history, and not
significantly affected by the choice of star formation prescription. If
successful, we may be able to utilize the emergent UV-IR SED of the primary
galaxy to understand its recent interaction history.Comment: 7 pages, 4 figures, proceedings of invited talk at IAU Symposium No.
284, The Spectral Energy Distribution of Galaxie
Tidal Imprints of a Dark Sub-Halo on the Outskirts of the Milky Way II. Perturber Azimuth
We extend our analysis of the observed disturbances on the outskirts of the
HI disk of the Milky Way. We employ the additional constraints of the phase of
the modes of the observed HI image and asymmetry in the radial velocity field
to derive the azimuth of the perturber inferred to be responsible for the
disturbances in the HI disk. We carry out a modal analysis of the phase of the
disturbances in the HI image and in SPH simulations of a Milky Way-like galaxy
tidally interacting with dark perturbers, the relative offset of which we
utilize to derive the perturber azimuth. To make a direct connection with
observations, we express our results in sun-centered coordinates, predicting
that the perturber responsible for the observed disturbances is between -50
\la l \la -10. We show explicitly that the phase of the disturbances in the
outskirts of simulated galaxies at the time that best fits the Fourier
amplitudes, our primary metric for the azimuth determination, is relatively
insensitive to the equation of state. Our calculations here represent our
continuing efforts to develop the "Tidal Analysis" method of Chakrabarti \&
Blitz (2009; CB09). CB09 employed SPH simulations to examine tidal interactions
between perturbing dark sub-halos and the Milky Way. They found that the
amplitudes of the Fourier modes of the observed planar disturbances are
best-fit by a perturbing dark sub-halo with mass one-hundredth that of the
Milky Way, and a pericentric approach distance of . The
overarching goal of this work is to attempt to outline an alternate procedure
to optical studies for characterizing and potentially discovering dwarf
galaxies -- whereby one can approximately infer the azimuthal location of a
perturber, its mass and pericentric distance (CB09) from analysis of its tidal
gravitational imprints on the HI disk of the primary galaxy.Comment: submitted to ApJ; 12 pages; higher resolution figures can be found
at: http://astro.berkeley.edu/~sukanya/perturbersubmit.pd
Complete breakdown of the Debye model of rotational relaxation near the isotropic-nematic phase boundary: Effects of intermolecular correlations in orientational dynamics
The Debye-Stokes-Einstein (DSE) model of rotational diffusion predicts that
the rotational correlation times vary as , where
is the rank of the orientational correlation function (given in terms of the
Legendre polynomial of rank ). One often finds significant deviation from
this prediction, in either direction. In supercooled molecular liquids where
the ratio falls considerably below three (the Debye limit),
one usually invokes a jump diffusion model to explain the approach of the ratio
to unity. Here we show in a computer simulation study of a
standard model system for thermotropic liquid crystals that this ratio becomes
much less than unity as the isotropic-nematic phase boundary is approached from
the isotropic side. Simultaneously, the ratio (where is
the shear viscosity of the liquid) becomes {\it much larger} than hydrodynamic
value near the I-N transition. We have also analyzed the break down of the
Debye model of rotational diffusion in ratios of higher order rotational
correlation times. We show that the break down of the DSE model is due to the
growth of orientational pair correlation and provide a mode coupling theory
analysis to explain the results.Comment: Submitted to Physical Review
Accretion Flow Properties of EXO 1846-031 During its Multi-Peaked Outburst After Long Quiescence
We study the recent outburst of the black hole candidate EXO 1846-031 which
went into an outburst in 2019 after almost 34 years in quiescence. We use
archival data from Swift/XRT, MAXI/GSC, NICER/XTI and NuSTAR/FPM
satellites/instruments to study the evolution of the spectral and temporal
properties of the source during the outburst. Low energy X-ray flux of the
outburst shows multiple peaks making it a multipeak outburst. Evolving type-C
quasi-periodic oscillations (QPOs) are observed in the NICER data in the hard,
hard intermediate and soft intermediate states. We use the physical Two
Component Advective Flow (TCAF) model to analyze the combined spectra of
multiple satellite instruments. According to the TCAF model, the accreting
matter is divided into Keplerian and sub-Keplerian parts, and the variation in
the observed spectra in different spectral states arises out of the variable
contributions of these two types of accreting matter in the total accretion
rate. Studying the evolution of the accretion rates and other properties of the
accretion flow obtained from the spectral analysis, we show how the multiple
peaks in the outburst flux arises out of discontinuous supply and different
radial velocities of two types of accreting matter from the pile-up radius. We
detect an Fe emission line at keV in the hard and the intermediate
states in the NICER spectra. We determine the probable mass of the black hole
to be from the spectral analysis with the TCAF
model. We also estimate viscous time scale of the source in this outburst to be
days from the peak difference of the Keplerian and sub-Keplerian mass
accretion rates.Comment: 15 pages, 8 Figures, 2 Tables (In Communication ApJ
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