1,879 research outputs found
Millimeter Interferometric HCN(1-0) and HCO+(1-0) Observations of Luminous Infrared Galaxies
We present the results on millimeter interferometric observations of four
luminous infrared galaxies (LIRGs), Arp 220, Mrk 231, IRAS 08572+3915, and VV
114, and one Wolf-Rayet galaxy, He 2-10, using the Nobeyama Millimeter Array
(NMA). Both the HCN(1-0) and HCO+(1-0) molecular lines were observed
simultaneously and their brightness-temperature ratios were derived.
High-quality infrared L-band (2.8-4.1 micron) spectra were also obtained for
the four LIRGs to better constrain their energy sources deeply buried in dust
and molecular gas. When combined with other LIRGs we have previously observed
with NMA, the final sample comprised nine LIRGs (12 LIRGs' nuclei) with
available interferometric HCN(1-0) and HCO+(1-0) data-sufficient to investigate
the overall trend in comparison with known AGNs and starburst galaxies. We
found that LIRGs with luminous buried AGN signatures at other wavelengths tend
to show high HCN(1-0)/HCO+(1-0) brightness-temperature ratios as seen in
AGN-dominated galaxies, while the Wolf-Rayet galaxy He 2-10 displays a small
ratio. An enhanced HCN abundance in the interstellar gas surrounding a strongly
X-ray-emitting AGN, as predicted by some chemical calculations, is a natural
explanation of our results.Comment: 43 pages, 11 figures, accepted for publication in Astronomical
Journal. Higher resolution version is available at
http://optik2.mtk.nao.ac.jp/~imanishi/Paper/HCN2/HCN2.pd
HCN to HCO^+ Millimeter Line Diagnostics of AGN Molecular Torus I : Radiative Transfer Modeling
We explore millimeter line diagnostics of an obscuring molecular torus
modeled by a hydrodynamic simulation with three-dimensional nonLTE radiative
transfer calculations. Based on the results of high-resolution hydrodynamic
simulation of the molecular torus around an AGN, we calculate intensities of
HCN and HCO^{+} rotational lines as two representative high density tracers.
The three-dimensional radiative transfer calculations shed light on a
complicated excitation state in the inhomogeneous torus, even though a
spatially uniform chemical structure is assumed. Our results suggest that HCN
must be much more abundant than HCO^{+} in order to obtain a high ratio
() observed in some of the nearby galaxies. There is a
remarkable dispersion in the relation between integrated intensity and column
density, indicative of possible shortcomings of HCN(1-0) and HCO^{+}(1-0) lines
as high density tracers. The internal structures of the inhomogeneous molecular
torus down to subparsec scale in external galaxies will be revealed by the
forthcoming Atacama Large Millimeter/submillimeter Array (ALMA). The
three-dimensional radiative transfer calculations of molecular lines with
high-resolution hydrodynamic simulation prove to be a powerful tool to provide
a physical basis for molecular line diagnostics of the central regions of
external galaxies.Comment: 29 pages, 13 figures, Accepted for publication in ApJ, For high
resolution figures see http://alma.mtk.nao.ac.jp/~masako/MS72533v2.pd
The nature of the fluorescent iron line in V 1486 Ori
The fluorescent 6.4 keV iron line provides information on cool material in
the vicinity of hard X-ray sources as well as on the characteristics of the
X-ray sources themselves. First discovered in the X-ray spectra of the flaring
Sun, X-ray binaries and active galactic nuclei (AGN), the fluorescent line was
also observed in a number of stellar X-ray sources. The young stellar object
(YSO) V1486 Ori was observed in the framework of the Chandra Ultra Deep Project
(COUP) as the source COUP 331. We investigate its spectrum, with emphasis on
the strength and time variability of the fluorescent iron K-alpha line, derive
and analyze the light curve of COUP 331 and proceed with a time-resolved
spectral analysis of the observation. The light curve of V 1486 Ori shows two
major flares, the first one lasting for (approx) 20 ks with a peak X-ray
luminosity of 2.6*10^{32} erg/s (dereddened in the 1-10 keV band) and the
second one -- only partially observed -- for >60 ks with an average X-ray
luminosity of 2.4*10^{31} erg/s (dereddened). The spectrum of the first flare
is very well described by an absorbed thermal model at high temperature, with a
pronounced 6.7 keV iron line complex, but without any fluorescent K-alpha line.
The X-ray spectrum of the second flare is characterized by even higher
temperatures (>= 10 keV) without any detectable 6.7 keV Fe XXV feature, but
with a very strong fluorescent iron K-alpha line appearing predominantly in the
20 ks rise phase of the flare. Preliminary model calculations indicate that
photoionization is unlikely to account for the entire fluorescent emission
during the rise phase.Comment: 4 pages, letter, accepted for publication in A&
Vibrationally excited HC3N in NGC 4418
We investigate the molecular gas properties of the deeply obscured luminous
infrared galaxy NGC 4418. We address the excitation of the complex molecule
HC3N to determine whether its unusually luminous emission is related to the
nature of the buried nuclear source. We use IRAM 30m and JCMT observations of
rotational and vibrational lines of HC3N to model the excitation of the
molecule by means of rotational diagrams. We report the first confirmed
extragalactic detection of vibrational lines of HC3N. We detect 6 different
rotational transitions ranging from J=10-9 to J=30-29 in the ground vibrational
state and obtain a tentative detection of the J=38-37 line. We also detect 7
rotational transitions of the vibrationally excited states v6 and v7, with
angular momenta ranging from J=10-9 to 28-27. The energies of the upper states
of the observed transitions range from 20 to 850 K. In the optically thin
regime, we find that the rotational transitions of the vibrational ground state
can be fitted for two temperatures, 30 K and 260 K, while the vibrationally
excited levels can be fitted for a rotational temperature of 90 K and a
vibrational temperature of 500 K. In the inner 300 pc of NGC 4418, we estimate
a high HC3N abundance, of the order of 10^-7. The excitation of the HC3N
molecule responds strongly to the intense radiation field and the presence of
warm, dense gas and dust at the center of NGC 4418. The intense HC3N line
emission is a result of both high abundances and excitation. The properties of
the HC3N emitting gas are similar to those found for hot cores in Sgr B2, which
implies that the nucleus (< 300 pc) of NGC 4418 is reminiscent of a hot core.
The potential presence of a compact, hot component (T=500 K) is also discussed
A survey for Fe 6.4 keV emission in young stellar objects in rho Oph: the strong fluorescence from Elias 29
We report the results of a search for 6.4 keV Fe fluorescent emission in
Young Stellar Objects (YSOs) with measured accretion luminosities in the rho
Oph cloud, using all existing chandra and XMM-Newton observations of the
region. A total of nine such YSOs have X-ray data with sufficiently high S/N
for the 6.4 keV line to be potentially detected if present. A positive
detection of the Fe 6.4 keV line is reported for one object, Elias 29, in both
the XMM-Newton and the chandra data. The 6.4 keV line is detected in Elias 29
both during quiescent and flaring emission, unlikely all previously reported
detections of 6.4 keV Fe fluorescence in YSOs which were made during intense
flaring. The observed equivalent width of the fluorescent line is large, at
W_alpha approx 140 eV, ruling out fluorescence from diffuse circumstellar
material. It is also larger than expected for simple reflection from a
solar-composition photosphere or circumstellar disk, but it is compatible with
being due to fluorescence from a centrally illuminated circumstellar disk. The
X-ray spectrum of Elias 29 is also peculiar in terms of its high (ionized) Fe
abundance, as evident from the very intense Fe xxv 6.7 keV line emission; we
speculate on the possible mechanism leading to the observed high abundance.Comment: Accepted by A&
Subaru Spectroscopy and Spectral Modeling of Cygnus A
We present high angular resolution (0.5) MIR spectra
of the powerful radio galaxy, Cygnus A, obtained with the Subaru telescope. The
overall shape of the spectra agree with previous high angular resolution MIR
observations, as well as previous Spitzer spectra. Our spectra, both on and off
nucleus, show a deep silicate absorption feature. The absorption feature can be
modeled with a blackbody obscured by cold dust or a clumpy torus. The deep
silicate feature is best fit by a simple model of a screened blackbody,
suggesting foreground absorption plays a significant, if not dominant role, in
shaping the spectrum of Cygnus A. This foreground absorption prevents a clear
view of the central engine and surrounding torus, making it difficult to
quantify the extent the torus attributes to the obscuration of the central
engine, but does not eliminate the need for a torus in Cygnus A
ALMA polarimetry measures magnetically aligned dust grains in the torus of NGC 1068
The obscuring structure surrounding active galactic nuclei (AGN) can be
explained as a dust and gas flow cycle that fundamentally connects the AGN with
their host galaxies. This structure is believed to be associated with dusty
winds driven by radiation pressure. However, the role of magnetic fields, which
are invoked in almost all models for accretion onto a supermassive black hole
and outflows, is not thoroughly studied. Here we report the first detection of
polarized thermal emission by means of magnetically aligned dust grains in the
dusty torus of NGC 1068 using ALMA Cycle 4 polarimetric dust continuum
observations (, pc; 348.5 GHz, m). The polarized torus
has an asymmetric variation across the equatorial axis with a peak polarization
of \% and position angle of (B-vector) at
pc east from the core. We compute synthetic polarimetric observations of
magnetically aligned dust grains assuming a toroidal magnetic field and
homogeneous grain alignment. We conclude that the measured 860 m continuum
polarization arises from magnetically aligned dust grains in an optically thin
region of the torus. The asymmetric polarization across the equatorial axis of
the torus arises from 1) an inhomogeneous optical depth, and 2) a variation of
the velocity dispersion, i.e. variation of the magnetic field turbulence at
sub-pc scales, from the eastern to the western region of the torus. These
observations and modeling constrain the torus properties beyond spectral energy
distribution results. This study strongly supports that magnetic fields up to a
few pc contribute to the accretion flow onto the active nuclei.Comment: 19 pages, 11 figures (Accepted for Publication to ApJ
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