4,077 research outputs found
Imaging density disturbances in water with 41.3 attosecond time resolution
We show that the momentum flexibility of inelastic x-ray scattering may be
exploited to invert its loss function, alowing real time imaging of density
disturbances in a medium. We show the disturbance arising from a point source
in liquid water, with a resolution of 41.3 attoseconds (
sec) and 1.27 ( cm). This result is used to
determine the structure of the electron cloud around a photoexcited molecule in
solution, as well as the wake generated in water by a 9 MeV gold ion. We draw
an analogy with pump-probe techniques and suggest that energy-loss scattering
may be applied more generally to the study of attosecond phenomena.Comment: 4 pages, 4 color figure
On the Nodal Count Statistics for Separable Systems in any Dimension
We consider the statistics of the number of nodal domains aka nodal counts
for eigenfunctions of separable wave equations in arbitrary dimension. We give
an explicit expression for the limiting distribution of normalised nodal counts
and analyse some of its universal properties. Our results are illustrated by
detailed discussion of simple examples and numerical nodal count distributions.Comment: 21 pages, 4 figure
Searching for molecular outflows in Hyper-Luminous Infrared Galaxies
We present constraints on the molecular outflows in a sample of five
Hyper-Luminous Infrared Galaxies using Herschel observations of the OH doublet
at 119 {\mu}m. We have detected the OH doublet in three cases: one purely in
emission and two purely in absorption. The observed emission profile has a
significant blueshifted wing suggesting the possibility of tracing an outflow.
Out of the two absorption profiles, one seems to be consistent with the
systemic velocity while the other clearly indicates the presence of a molecular
outflow whose maximum velocity is about ~1500 km/s. Our analysis shows that
this system is in general agreement with previous results on Ultra-luminous
Infrared Galaxies and QSOs, whose outflow velocities do not seem to correlate
with stellar masses or starburst luminosities (star formation rates). Instead
the galaxy outflow likely arises from an embedded AGN.Comment: Accepted for publication in MNRAS. 13 pages, 11 figures, 4 table
The [CII] 158 um Line Deficit in Ultraluminous Infrared Galaxies Revisited
We present a study of the [CII] 157.74 um fine-structure line in a sample of
15 ultraluminous infrared (IR) galaxies (L_IR>10^12 Lsun; ULIRGs) using the
Long Wavelength Spectrometer (LWS) on the Infrared Space Observatory (ISO). We
confirm the observed order of magnitude deficit (compared to normal and
starburst galaxies) in the strength of the [CII] line relative to the far-IR
dust continuum emission found in our initial report (Luhman et al. 1998), but
here with a sample that is twice as large. This result suggests that the
deficit is a general phenomenon affecting 4/5 ULIRGs. We present an analysis
using observations of generally acknowledged photodissociation region (PDR)
tracers ([CII], [OI] 63 and 145 um, and FIR continuum emission), which suggests
that a high UV flux G_o incident on a moderate density n PDR could explain the
deficit. However, comparisons with other ULIRG observations, including CO
(1-0), [CI] (1-0), and 6.2 um polycyclic aromatic hydrocarbon (PAH) emission,
suggest that high G_o/n PDRs alone cannot produce a self-consistent solution
that is compatible with all of the observations. We propose that non-PDR
contributions to the FIR continuum can explain the apparent [CII] deficiency.
Here, unusually high G_o and/or n physical conditions in ULIRGs as compared to
those in normal and starburst galaxies are not required to explain the [CII]
deficit. Dust-bounded photoionization regions, which generate much of the FIR
emission but do not contribute significant [CII] emission, offer one possible
physical origin for this additional non-PDR component. Such environments may
also contribute to the observed suppression of FIR fine-structure emission from
ionized gas and PAHs, as well as the warmer FIR colors found in ULIRGs. The
implications for observations at higher redshifts are also revisited.Comment: to be published in The Astrophysical Journal, 58 page
An infrared study of the double nucleus in NGC3256
We present new resolved near and mid-IR imaging and N-band spectroscopy of
the two nuclei in the merger system NGCA3256, the most IR luminous galaxy in
the nearby universe. The results from the SED fit to the data are consistent
with previous estimates of the amount of obscuration towards the nuclei and the
nuclear star formation rates. However, we also find substantial differences in
the infrared emission from the two nuclei which cannot be explained by
obscuration alone. We conclude that the northern nucleus requires an additional
component of warm dust in order to explain its properties. This suggests that
local starforming conditions can vary significantly within the environment of a
single system.Comment: Accepted for publication (MNRAS
Upper bounds on the first eigenvalue for a diffusion operator via Bakry-\'{E}mery Ricci curvature II
Let be a symmetric diffusion operator
with an invariant measure on a complete Riemannian
manifold. In this paper we prove Li-Yau gradient estimates for weighted
elliptic equations on the complete manifold with
and -dimensional Bakry-\'{E}mery Ricci curvature bounded below by some
negative constant. Based on this, we give an upper bound on the first
eigenvalue of the diffusion operator on this kind manifold, and thereby
generalize a Cheng's result on the Laplacian case (Math. Z., 143 (1975)
289-297).Comment: Final version. The original proof of Theorem 2.1 using Li-Yau
gradient estimate method has been moved to the appendix. The new proof is
simple and direc
Counterrotating Nuclear Disks in Arp 220
The ultraluminous infrared galaxy Arp 220 has been observed at 0.5"
resolution in CO(2-1) and 1 mm continuum using the newly expanded Owens Valley
Millimeter Array. The CO and continuum peaks at the double nuclei and the
surrounding molecular gas disk are clearly resolved. We find steep velocity
gradients across each nucleus (dV ~ 500 km/s within r= 0.3") whose directions
are not aligned with each other and with that of the outer gas disk. We
conclude that the double nuclei have their own gas disks (r ~ 100 pc). They are
counterrotating with respect to each other and embedded in the outer gas disk
(r ~ 1 kpc) rotating around the dynamical center of the system. The masses of
each nucleus are M_dyn > 2* 10^9 M_sun based on the CO kinematics. Although
there is no evidence of an old stellar population in the optical or near
infrared spectroscopy of the nuclei (probably due to the much brighter young
population), it seems likely that these nuclei were 'seeded' from the
pre-merger nuclei in view of their counterrotating gas kinematics. The gas
disks probably constitute a significant fraction (~ 50 %) of the mass in each
nucleus. The CO and continuum brightness temperatures imply that the nuclear
gas disks have high area filling factors (~ 0.5-1) and have extremely high
visual extinctions (Av ~ 1000 mag). The molecular gas must be hot (>= 40 K) and
dense (>= 10^4-5 cm^-3), given the large mass and small scale-height of the
nuclear disks. The continuum data suggest that the large luminosity (be it
starburst or AGN) must originate within 100 pc of the two nuclear gas disks
which were presumably formed through concentration of gas from the progenitor
outer galaxy disks.Comment: 20 pages, 5 figures. Accepted for publication in The Astrophysical
Journa
Angle-dependence of the Hall effect in HgBa2CaCu2O6 thin films
Superconducting compounds of the family Hg-Ba-Ca-Cu-O have been the subject
of intense study since the current record-holder for the highest critical
temperature of a superconductor belongs to this class of materials. Thin films
of the compound with two adjacent copper-oxide layers and a critical
temperature of about 120 K were prepared by a two-step process that consists of
the pulsed-laser deposition of precursor films and the subsequent annealing in
mercury-vapor atmosphere. Like some other high-temperature superconductors,
Hg-Ba-Ca-Cu-O exhibits a specific anomaly of the Hall effect, a double-sign
change of the Hall coefficient close to the superconducting transition. We have
investigated this phenomenon by measurements of the Hall effect at different
angles between the magnetic field direction and the crystallographic c-axis.
The results concerning the upper part of the transition, where the first sign
change occurs, are discussed in terms of the renormalized fluctuation model for
the Hall conductivity, adapted through the field rescaling procedure in order
to take into account the arbitrary orientation of the magnetic field.Comment: to be published in Phys. Rev.
Interferometric Observations of the Nuclear Region of Arp220 at Submillimeter Wavelengths
We report the first submillimeter interferometric observations of an
ultraluminous infrared galaxy. We observed Arp220 in the CO J=3-2 line and
342GHz continuum with the single baseline CSO-JCMT interferometer consisting of
the Caltech Submillimeter Observatory (CSO) and the James Clerk Maxwell
Telescope (JCMT). Models were fit to the measured visibilities to constrain the
structure of the source. The morphologies of the CO J=3-2 line and 342GHz
continuum emission are similar to those seen in published maps at 230 and
110GHz. We clearly detect a binary source separated by about 1 arcsec in the
east-west direction in the 342GHz continuum. The CO J=3-2 visibility
amplitudes, however, indicate a more complicated structure, with evidence for a
compact binary at some velocities and rather more extended structure at others.
Less than 30% of the total CO J=3-2 emission is detected by the interferometer,
which implies the presence of significant quantities of extended gas. We also
obtained single-dish CO J=2-1, CO J=3-2 and HCN J=4-3 spectra. The HCN J=4-3
spectrum, unlike the CO spectra, is dominated by a single redshifted peak. The
HCN J=4-3/CO J=3-2, HCN J=4-3/HCN J=1-0 and CO J=3-2/2-1 line ratios are larger
in the redshifted (eastern) source, which suggests that the two sources may
have different physical conditions. This result might be explained by the
presence of an intense starburst that has begun to deplete or disperse the
densest gas in the western source, while the eastern source harbors undispersed
high density gas.Comment: 17 pages, 9 figures, 4 Tables. accepted by Ap
Spitzer/IRS Observations of Seyfert 1.8s and 1.9s: A Comparison with Seyfert 1s and Seyfert 2s
We present Spitzer Space Telescope mid-infrared spectra of 12 Seyfert 1.8 and
1.9 galaxies over the 5-38 um region. We compare the spectral characteristics
of this sample to those of 58 Seyfert 1 and Seyfert 2 galaxies from the Spitzer
archives. An analysis of the spectral shapes, the silicate 10 um feature and
the emission line fluxes have enabled us to characterize the mid-IR properties
of Seyfert 1.8/1.9s. We find that the equivalent widths of the 10 um silicate
feature are generally weak in all Seyfert galaxies, as previously reported by
several studies. The few Seyfert galaxies in this sample that show deep 10 um
silicate absorption features are highly inclined and/or merging galaxies. It is
likely that these absorption features originate primarily in the dusty
interstellar medium of the host galaxy rather than in a dusty torus on parsec
scales close to the central engine. We find that the equivalent width of the
polycyclic aromatic hydrocarbon (PAH) band at 6.2 um correlates strongly with
the 20-30 um spectral index. Either of these quantities are good indicators of
the amount of starburst contribution to the mid-IR spectra. The spectra of
Seyfert 1.8 and 1.9s are dominated by these starburst features, similar to most
Seyfert 2s. They show strong PAH bands and a strong red continuum toward 30 um.
The strengths of the high-ionization forbidden narrow emission lines [O IV]
25.89 um, [Ne III] 15.56 um and [Ne V] 14.32 um relative to [Ne II] 12.81 um
are weaker in Seyfert 1.8/1.9s and Seyfert 2s as compared to Seyfert 1s. The
weakness of high-ionization lines in Seyfert 1.8-1.9s is suggestive of
intrinsically weak active galactic nuclei (AGN) continua, and/or stronger star
formation activity leading to enhanced [Ne II]. We discuss the implications of
these observational results in the context of the Unified Model of AGN.Comment: 36 pages, 4 tables, 6 figures, Accepted for publication in The
Astrophysical Journal, December 200
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