340 research outputs found
Behavioral-Independent Features of Complex Heartbeat Dynamics
We test whether the complexity of cardiac interbeat interval time series is
simply a consequence of the wide range of scales characterizing human behavior,
especially physical activity, by analyzing data taken from healthy adult
subjects under three conditions with controls: (i) a ``constant routine''
protocol where physical activity and postural changes are kept to a minimum,
(ii) sympathetic blockade, and (iii) parasympathetic blockade. We find that
when fluctuations in physical activity and other behavioral modifiers are
minimized, a remarkable level of complexity of heartbeat dynamics remains,
while for neuroautonomic blockade the multifractal complexity decreases.Comment: 4 pages with 6 eps figures. Latex file. For more details or for
downloading the PDF file of the published article see
http://polymer.bu.edu/~amaral/Heart.html and
http://polymer.bu.edu/~amaral/Multifractal.htm
Ammonia (J,K) = (1,1) to (4,4) and (6,6) inversion lines detected in the Seyfert 2 galaxy NGC 1068
We present the detection of the ammonia (NH3) (J,K) = (1,1) to (4,4) and
(6,6) inversion lines toward the prototypical Seyfert 2 galaxy NGC 1068, made
with the Green Bank Telescope (GBT). This is the first detection of ammonia in
a Seyfert galaxy. The ortho-to-para-NH3 abundance ratio suggests that the
molecule was formed in a warm medium of at least 20 K. For the NH3 column
density and fractional abundance, we find (1.09\pm0.23)\times10^14 cm^-2 and
(2.9\pm0.6)\times10^-8, respectively, from the inner 1.2 kpc of NGC 1068. The
kinetic temperature can be constrained to 80\pm20 K for the bulk of the
molecular gas, while some fraction has an even higher temperature of 140\pm30
K.Comment: 5 pages, 3 figures, accepted by A&
An Electron-Tracking Compton Telescope for a Survey of the Deep Universe by MeV gamma-rays
Photon imaging for MeV gammas has serious difficulties due to huge
backgrounds and unclearness in images, which are originated from incompleteness
in determining the physical parameters of Compton scattering in detection,
e.g., lack of the directional information of the recoil electrons. The recent
major mission/instrument in the MeV band, Compton Gamma Ray
Observatory/COMPTEL, which was Compton Camera (CC), detected mere
persistent sources. It is in stark contrast with 2000 sources in the GeV
band. Here we report the performance of an Electron-Tracking Compton Camera
(ETCC), and prove that it has a good potential to break through this stagnation
in MeV gamma-ray astronomy. The ETCC provides all the parameters of
Compton-scattering by measuring 3-D recoil electron tracks; then the Scatter
Plane Deviation (SPD) lost in CCs is recovered. The energy loss rate (dE/dx),
which CCs cannot measure, is also obtained, and is found to be indeed helpful
to reduce the background under conditions similar to space. Accordingly the
significance in gamma detection is improved severalfold. On the other hand, SPD
is essential to determine the point-spread function (PSF) quantitatively. The
SPD resolution is improved close to the theoretical limit for multiple
scattering of recoil electrons. With such a well-determined PSF, we demonstrate
for the first time that it is possible to provide reliable sensitivity in
Compton imaging without utilizing an optimization algorithm. As such, this
study highlights the fundamental weak-points of CCs. In contrast we demonstrate
the possibility of ETCC reaching the sensitivity below erg
cm s at 1 MeV.Comment: 19 pages, 12 figures, Accepted to the Astrophysical Journa
Large Silicon Abundance in Photodissociation Regions
We have made one-dimensional raster-scan observations of the rho Oph and
sigma Sco star-forming regions with two spectrometers (SWS and LWS) on board
the ISO. In the rho Oph region, [SiII] 35um, [OI] 63um, 146um, [CII] 158um, and
the H2 pure rotational transition lines S(0) to S(3) are detected, and the PDR
properties are derived as the radiation field scaled by the solar neighborhood
value G_0~30-500, the gas density n~250--2500 /cc, and the surface temperature
T~100-400 K. The ratio of [SiII] 35um to [OI] 146um indicates that silicon of
10--20% of the solar abundance must be in the gaseous form in the
photodissociation region (PDR), suggesting that efficient dust destruction is
undergoing even in the PDR and that part of silicon atoms may be contained in
volatile forms in dust grains. The [OI] 63um and [CII] 158um emissions are too
weak relative to [OI] 146um to be accounted for by standard PDR models. We
propose a simple model, in which overlapping PDR clouds along the line of sight
absorb the [OI] 63um and [CII] 158um emissions, and show that the proposed
model reproduces the observed line intensities fairly well. In the sigma Sco
region, we have detected 3 fine-structure lines, [OI] 63um, [NII] 122um, and
[CII] 158um, and derived that 30-80% of the [CII] emission comes from the
ionized gas. The upper limit of the [SiII] 35um is compatible with the solar
abundance relative to nitrogen and no useful constraint on the gaseous Si is
obtained for the sigma Sco region.Comment: 25 pages with 7 figures, accepted in Astrophysical Journa
SMA/PdBI multiple line observations of the nearby Seyfert2 galaxy NGC 1068: Shock related gas kinematics and heating in the central 100pc?
We present high angular resolution (0.5-2.0") observations of the mm
continuum and the 12CO(J=3-2), 13CO(J=3-2), 13CO(J=2-1), C18O(J=2-1),
HCN(J=3-2), HCO+(J=4-3) and HCO+(J=3-2) line emission in the circumnuclear disk
(r=100pc) of the proto-typical Seyfert type-2 galaxy NGC1068, carried out with
the Submillimeter Array. We further include in our analysis new 13CO(J=1-0) and
improved 12CO(J=2-1) observations of NGC1068 at high angular resolution
(1.0-2.0") and sensitivity, conducted with the IRAM Plateau de Bure
Interferometer. Based on the complex dynamics of the molecular gas emission
indicating non-circular motions in the central ~100pc, we propose a scenario in
which part of the molecular gas in the circumnuclear disk of NGC1068 is
radially blown outwards as a result of shocks. This shock scenario is further
supported by quite warm (Tkin>=200K) and dense (nH2=10^4cm^-3) gas constrained
from the observed molecular line ratios. The HCN abundance in the circumnuclear
disk is found to be [HCN]/[12CO]=10^-3.5. This is slightly higher than the
abundances derived for galactic and extragalactic starforming/starbursting
regions. This results lends further support to X-ray enhanced HCN formation in
the circumnuclear disk of NGC1068, as suggested by earlier studies. The HCO+
abundance ([HCO+]/[12CO]=10^-5) appears to be somewhat lower than that of
galactic and extragalactic starforming/starbursting regions. When trying to fit
the cm to mm continuum emission by different thermal and non-thermal processes,
it appears that electron-scattered synchrotron emission yields the best results
while thermal free-free emission seems to over-predict the mm continuum
emission.Comment: accepted for publication by ApJ; 35pages, 22 figures and 6 tables (at
the end of the file); 3 figures have been decreased in quality to match size
limi
Parsec-scale dust emission from the polar region in the type 2 nucleus of NGC 424
Advancements in infrared IR open up the possibility to spatially resolve AGN
on the parsec-scale level and study the circumnuclear dust distribution,
commonly referred to as the "dust torus", that is held responsible for the type
1/type 2 dichotomy of AGN. We used the mid-IR beam combiner MIDI together with
the 8m telescopes at the VLTI to observe the nucleus of the Seyfert 2 galaxy
NGC 424, achieving an almost complete coverage of the uv-plane accessible by
the available telescope configurations. We detect extended mid-IR emission with
a relatively baseline- and model-independent mid-IR half-light radius of (2.0
\pm 0.2) pc \times (1.5 \pm 0.3) pc (averaged over the 8-13 {\mu}m wavelength
range). The extended mid-IR source shows an increasing size with wavelength.
The orientation of the major axis in position angle -27deg is closely aligned
with the system axis as set by optical polarization observations. Torus models
typically favor extension along the mid-plane at mid-IR wavelengths instead.
Therefore, we conclude that the majority of the pc-scale mid-IR emission
(>~60%) in this type 2 AGN originates from optically-thin dust in the polar
region of the AGN, a scenario consistent with the near- to far-IR SED. We
suggest that a radiatively-driven dusty wind, possibly launched in a puffed-up
region of the inner hot part of the torus, is responsible for the polar dust.
In this picture, the torus dominates the near-IR emission up to about 5 {\mu}m,
while the polar dust is the main contributor to the mid-IR flux. Our results of
NGC 424 are consistent with recent observations of the AGN in the Circinus
galaxy and resemble large-scale characteristics of other objects. If our
results reflect a general property of the AGN population, the current paradigm
for interpreting and modeling the IR emission of AGN have to be revised.
(abridged)Comment: 18 pages, 10 figures, 4 tables; accepted by ApJ (June 20
Herschel-PACS Observations of Far-IR CO Line Emission in NGC 1068: Highly Excited Molecular Gas in the Circumnuclear Disk
We report the detection of far-IR CO rotational emission from the
prototypical Seyfert 2 galaxy NGC 1068. Using Herschel-PACS, we have detected
11 transitions in the J_upper=14-30 (E_upper/k_B = 580-2565 K) range, all of
which are consistent with arising from within the central 10" (700 pc). The
detected transitions are modeled as arising from 2 different components: a
moderate excitation (ME) component close to the galaxy systemic velocity, and a
high excitation (HE) component that is blueshifted by ~80 km s^{-1}. We employ
a large velocity gradient (LVG) model and derive n_H2~10^{5.6} cm^{-3},
T_kin~170 K, and M_H2~10^{6.7} M_sun for the ME component, and n_H2~10^{6.4}
cm^{-3}, T_kin~570 K, and M_H2~10^{5.6} M_sun for the HE component, although
for both components the uncertainties in the density and mass are plus/minus
(0.6-0.9) dex. We compare the CO line profiles with those of other molecular
tracers observed at higher spatial and spectral resolution, and find that the
ME transitions are consistent with these lines arising in the ~200 pc diameter
ring of material traced by H_2 1-0 S(1) observations. The blueshift of the HE
lines may also be consistent with the bluest regions of this H_2 ring, but a
better kinematic match is found with a clump of infalling gas ~40 pc north of
the AGN. We discuss the prospects of placing the HE component near the AGN, and
conclude that while the moderate thermal pressure precludes an association with
the ~1 pc radius H_2O maser disk, the HE component could potentially be located
only a few parsecs more distant from the AGN, and might then provide the
N_H~10^{25} cm^{-2} column obscuring the nuclear hard X-rays. Finally, we also
report sensitive upper limits extending up to J_upper=50, which place
constraints on a previous model prediction for the CO emission from the X-ray
obscuring torus. [Abridged]Comment: 20 pages, 10 figures. Accepted for publication in Ap
Probing X-ray irradiation in the nucleus of NGC 1068 with observations of high-J lines of dense gas tracers
With the incorporation of high-J molecular lines, we aim to constrain the
physical conditions of the dense gas in the central region of the Seyfert 2
galaxy NGC 1068 and to determine signatures of the AGN or the starburst
contribution.
We used the James Clerk Maxwell Telescope to observe the J=4-3 transition of
HCN, HNC, and HCO+, as well as the CN N_J=2_{5/2}-1_{3/2} and
N_J=3_{5/2}-2_{5/2}, in NGC 1068.
We estimate the excitation conditions of HCN, HNC, and CN, based on the line
intensity ratios and radiative transfer models.
We find that the bulk emission of HCN, HNC, CN, and the high-J HCO+ emerge
from dense gas n(H_2)>=10^5 cm^-3). However, the low-J HCO+ lines (dominating
the HCO+ column density) trace less dense (n(H_2)<10^5 cm^-3) and colder
(T_K30 K) gas than
the other molecules.
The HCO+ J=4-3 line intensity, compared with the lower transition lines and
with the HCN J=4-3 line, support the influence of a local XDR environment. The
estimated N(CN)/N(HCN)~1-4 column density ratios are indicative of an XDR/AGN
environment with a possible contribution of grain-surface chemistry induced by
X-rays or shocks.Comment: Main text: 8 pages, 5 tables, 1 figure. Appendix: 7 pages, 1 table, 8
figures. Accepted for publication in A&
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