2,081 research outputs found
Submillimeter Imaging of NGC 891 with SHARC
The advent of submillimeter wavelength array cameras operating on large
ground-based telescopes is revolutionizing imaging at these wavelengths,
enabling high-resolution submillimeter surveys of dust emission in star-forming
regions and galaxies. Here we present a recent 350 micron image of the edge-on
galaxy NGC 891, which was obtained with the Submillimeter High Angular
Resolution Camera (SHARC) at the Caltech Submillimeter Observatory (CSO). We
find that high resolution submillimeter data is a vital complement to shorter
wavelength satellite data, which enables a reliable separation of the cold dust
component seen at millimeter wavelengths from the warmer component which
dominates the far-infrared (FIR) luminosity.Comment: 4 pages LaTeX, 2 EPS figures, with PASPconf.sty; to appear in
"Astrophysics with Infrared Surveys: A Prelude to SIRTF
CH^+(1â0) and ^(13)CH^+(1â0) absorption lines in the direction of massive star-forming regions
We report the detection of the ground-state rotational transition of the methylidyne cation CH^+ and its isotopologue ^(13)CH^+ toward the remote
massive star-forming regions W33A, W49N, and W51 with the HIFI instrument onboard the Herschel satellite. Both lines are seen only in
absorption against the dust continuum emission of the star-forming regions. The CH^+ absorption is saturated over almost the entire velocity
ranges sampled by the lines-of-sight that include gas associated with the star-forming regions (SFR) and Galactic foreground material. The CH^+
column densities are inferred from the optically thin components. A lower limit of the isotopic ratio [^(12)CH^+]/[^(13)CH^+] > 35.5 is derived from
the absorptions of foreground material toward W49N. The column density ratio, N(CH^+)/N(HCO^+), is found to vary by at least a factor 10,
between 4 and >40, in the Galactic foreground material. Line-of-sight ^(12)CH^+ average abundances relative to total hydrogen are estimated. Their
average value, N(CH^+)/N_H > 2.6 Ă 10^(â8), is higher than that observed in the solar neighborhood and confirms the high abundances of CH^+ in
the Galactic interstellar medium. We compare this result to the predictions of turbulent dissipation regions (TDR) models and find that these high
abundances can be reproduced for the inner Galaxy conditions. It is remarkable that the range of predicted N(CH^+)/N(HCO^+) ratios, from 1 to
~50, is comparable to that observed
Interstellar CH absorption in the diffuse interstellar medium along the sight-lines to G10.6â0.4 (W31C), W49N, and W51
We report the detection of the ground state N, J = 1, 3/2 â 1, 1/2 doublet of the methylidyne radical CH at ~532 GHz and ~536 GHz with
the Herschel/HIFI instrument along the sight-line to the massive star-forming regions G10.6â0.4 (W31C), W49N, and W51. While the molecular
cores associated with these massive star-forming regions show emission lines, clouds in the diffuse interstellar medium are detected in absorption
against the strong submillimeter background. The combination of hyperfine structure with emission and absorption results in complex profiles,
with overlap of the different hyperfine components. The opacities of most of the CH absorption features are linearly correlated with those of CCH,
CN, and HCO^+ in the same velocity intervals. In specific narrow velocity intervals, the opacities of CN and HCO^+ deviate from the mean trends,
giving rise to more opaque absorption features. We propose that CCH can be used as another tracer of the molecular gas in the absence of better
tracers, with [CCH]/[H_2] ~3.2 ± 1.1 Ă 10^(â8). The observed [CN]/[CH], [CCH]/[CH] abundance ratios suggest that the bulk of the diffuse matter
along the lines of sight has gas densities n_H = n(H) + 2n(H_2) ranging between 100 and 1000 cm^(â3)
Excitation and abundance of C_3 in star forming cores: Herschel/HIFI observations of the sight-lines to W31C and W49N
We present spectrally resolved observations of triatomic carbon (C_3) in several ro-vibrational transitions between the vibrational ground state and
the low-energy Îœ_2 bending mode at frequencies between 1654â1897 GHz along the sight-lines to the submillimeter continuum sources W31C
and W49N, using Herschelâs HIFI instrument. We detect C_3 in absorption arising from the warm envelope surrounding the hot core, as indicated
by the velocity peak position and shape of the line profile. The sensitivity does not allow to detect C_3 absorption due to diffuse foreground clouds.
From the column densities of the rotational levels in the vibrational ground state probed by the absorption we derive a rotation temperature (T_(rot))
of ~50â70 K, which is a good measure of the kinetic temperature of the absorbing gas, as radiative transitions within the vibrational ground state
are forbidden. It is also in good agreement with the dust temperatures for W31C and W49N. Applying the partition function correction based on
the derived T_(rot), we get column densities N(C_3) ~ 7â9 Ă 10^(14) cm^(â2) and abundance x(C_3) ~ 10^(â8) with respect to H_2. For W31C, using a radiative
transfer model including far-infrared pumping by the dust continuum and a temperature gradient within the source along the line of sight we find
that a model with x(C_3) = 10^(â8), T_(kin) = 30â50 K, N(C_3) = 1.5 Ă 10^(15) cm^(â2) fits the observations reasonably well and provides parameters in very
good agreement with the simple excitation analysis
Compact Q-balls and Q-shells in a scalar electrodynamics
We investigate spherically symmetric non topological solitons in
electrodynamics with a scalar field self interaction U ~|\psi| taken from the
complex signum-Gordon model. We find Q-balls for small absolute values of the
total electric charge Q, and Q-shells when |Q| is large enough. In both cases
the charge density exactly vanishes outside certain compact region in the three
dimensional space. The dependence of the total energy E of small Q-balls on the
total electric charge has the form E ~ |Q|^(5/6), while in the case of very
large Q-shells E ~ |Q|^(7/6).Comment: 21 pages, 7 figure
Herschel/HIFI discovery of interstellar chloronium (H_2Cl^+)
We report the first detection of chloronium, H_2Cl^+, in the interstellar medium, using the HIFI instrument aboard the Herschel Space Observatory.
The 2_(12)â1_(01) lines of ortho-H^(35)_2 Cl^+ and ortho-H^(37)_2 Cl^+ are detected in absorption towards NGC 6334I, and the 1_(11)â0_(00) transition of para-H^(35)_2 Cl^+ is
detected in absorption towards NGC 6334I and Sgr B2(S). The H_2Cl^+ column densities are compared to those of the chemically-related species
HCl. The derived HCl/H_2Cl^+ column density ratios, ~1â10, are within the range predicted by models of diffuse and dense photon dominated
regions (PDRs). However, the observed H_2Cl^+ column densities, in excess of 10^(13) cm^(â2), are significantly higher than the model predictions. Our
observations demonstrate the outstanding spectroscopic capabilities of HIFI for detecting new interstellar molecules and providing key constraints
for astrochemical models
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High-Frequency Measurements Of The Spectrum Of Sagittarius A*
We report near-simultaneous interferometric measurements of the spectrum of Sagittarius A* over the 5-354 GHz range and single-dish observations that have yielded the first detection of Sgr A* at 850 GHz. We confirm that Sgr A*'s spectrum rises more steeply at short millimeter wavelengths than at centimeter wavelengths, leading to a near-millimeter/submillimeter excess that dominates its luminosity. Below 900 GHz, Sgr A*'s observed luminosity is 70 +/- 30 L.. A new upper limit to Sgr A*'s 24.3 mu m flux, together with a compilation of other extant IR data, imply a far-infrared spectral turnover, which can result from either an intrinsic synchrotron cutoff or excess extinction near Sgr A*. If the former applies, Sgr A*'s total synchrotron luminosity is <10(3) L., while in the latter case it is <3 x 10(4) L. if spherical symmetry also applies.NSF AST96-15025, AST96-13717Astronom
Detection of interstellar oxidaniumyl: Abundant H_2O^+ towards the star-forming regions DR21, Sgr B2, and NGC6334
Aims. We identify a prominent absorption feature at 1115 GHz, detected in first HIFI spectra towards high-mass star-forming regions, and interpret its astrophysical origin.
Methods. The characteristic hyperfine pattern of the H_2O^+ ground-state rotational transition, and the lack of other known low-energy transitions in this frequency range, identifies the feature as H_2O^+ absorption against the dust continuum background and allows us to derive the velocity profile of the absorbing gas. By comparing this velocity profile with velocity profiles of other tracers in the DR21 star-forming region, we constrain the frequency of the transition and the conditions for its formation.
Results. In DR21, the velocity distribution of H_2O^+ matches that of the [C_(II)] line at 158 ÎŒm and of OH cm-wave absorption, both stemming from the hot and dense clump surfaces facing the H_(II)-region and dynamically affected by the blister outflow. Diffuse foreground gas dominates the absorption towards Sgr B2. The integrated intensity of the absorption line allows us to derive lower limits to the H_2O^+ column density of 7.2 Ă 10^(12) cm^(â2) in NGC 6334, 2.3 Ă 10^(13) cm^(â2) in DR21, and 1.1 Ă 10^(15) cm^(â2) in Sgr B2
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