532 research outputs found
Determining dust temperatures and masses in the Herschel era: The importance of observations longward of 200 micron
Context. The properties of the dust grains (e.g., temperature and mass) can be derived from fitting far-IR SEDs (≥100 μm). Only with SPIRE on Herschel has it been possible to get high spatial resolution at 200 to 500 μm that is beyond the peak (~160 μm) of dust emission in most galaxies.
Aims. We investigate the differences in the fitted dust temperatures and masses determined using only 200 μm data (new SPIRE observations) to determine how important having >200 μm data is for deriving these dust properties.
Methods. We fit the 100 to 350 μm observations of the Large Magellanic Cloud (LMC) point-by-point with a model that consists of a single temperature and fixed emissivity law. The data used are existing observations at 100 and 160 μm (from IRAS and Spitzer) and new SPIRE observations of 1/4 of the LMC observed for the HERITAGE key project as part of the Herschel science demonstration phase.
Results. The dust temperatures and masses computed using only 100 and 160 μm data can differ by up to 10% and 36%, respectively, from those that also include the SPIRE 250 & 350 μm data. We find that an emissivity law proportional to λ^(−1.5) minimizes the 100–350 μm fractional residuals. We find that the emission at 500 μm is ~10% higher than expected from extrapolating the fits made at shorter wavelengths. We find the fractional 500 μm excess is weakly anti-correlated with MIPS 24 μm flux and the total gas surface density. This argues against a flux calibration
error as the origin of the 500 μm excess. Our results do not allow us to distinguish between a systematic variation in the wavelength dependent emissivity law or a population of very cold dust only detectable at λ ≥ 500 μm for the origin of the 500 μm excess
Cold dust clumps in dynamically hot gas
Aims. We present clumps of dust emission from Herschel observations of the Large Magellanic Cloud (LMC) and their physical and statistical
properties. We catalog cloud features seen in the dust emission from Herschel observations of the LMC, the Magellanic type irregular galaxy
closest to the Milky Way, and compare these features with Hi catalogs from the ATCA+Parkes Hi survey.
Methods. Using an automated cloud-finding algorithm, we identify clouds and clumps of dust emission and examine the cumulative mass distribution
of the detected dust clouds. The mass of cold dust is determined from physical parameters that we derive by performing spectral energy distribution
fits to 250, 350, and 500 μm emission from SPIRE observations using dust grain size distributions for graphite/silicate in low-metallicity
extragalactic environments.
Results. The dust cloud mass spectrum follows a power law distribution with an exponent of γ = −1.8 for clumps larger than 4 × 10^2 M_⊙ and is
similar to the Hi mass distribution. This is expected from the theory of ISM structure in the vicinity of star formation
Long-Wavelength Excesses in Two Highly Obscured High-Mass X-Ray Binaries: IGR J16318–4848 and GX 301–2
We present evidence for excess long-wavelength emission from two high-mass X-ray binaries, IGR J16318-4848 and GX 301-2, that show enormous obscuration (N_H ≃ 10^(23)-10^(24) cm^(-2)) in their X-ray spectra. Using archival near- and mid-infrared data, we show that the spectral energy distributions of IGR J16318-4848 and GX 301-2 are substantially higher in the mid-infrared than their expected stellar emission. We successfully fit the excesses with ~1000 K blackbodies, which suggests that they are due to warm circumstellar dust that also gives rise to the X-ray absorption. However, we need further observations to constrain the detailed properties of the excesses. This discovery highlights the importance of mid-infrared observations for understanding highly obscured X-ray binaries
Detection of Far-Infrared Water Vapor, Hydroxyl, and Carbon Monoxide Emissions from the Supernova Remnant 3C 391
We report the detection of shock-excited far-infrared emission of H2O, OH,
and CO from the supernova remnant 3C 391, using the ISO Long-Wavelength
Spectrometer. This is the first detection of thermal H2O and OH emission from a
supernova remnant. For two other remnants, W~28 and W~44, CO emission was
detected but OH was only detected in absorption. The observed H2O and OH
emission lines arise from levels within ~400 K of the ground state, consistent
with collisional excitation in warm, dense gas created after the passage of the
shock front through the dense clumps in the pre-shock cloud. The post-shock gas
we observe has a density ~2x10^5 cm^{-3} and temperature 100-1000 K, and the
relative abundances of CO:OH:H2O in the emitting region are 100:1:7 for a
temperature of 200 K. The presence of a significant column of warm H2O suggests
that the chemistry has been significantly changed by the shock. The existence
of significant column densities of both OH and H2O, which is at odds with
models for non-dissociative shocks into dense gas, could be due to
photodissociation of H2O or a mix of fast and slow shocks through regions with
different pre-shock density.Comment: AASTeX manuscript and 4 postscript figure
Molecular and Ionic shocks in the Supernova Remnant 3C391
New observations of the supernova remnant 3C391 are in the H2 2.12 micron and
[Fe II] 1.64 micron narrow-band filters at the Palomar 200-inch telescope, and
in the 5-15 micron CVF on ISOCAM. Shocked H2 emission was detected from the
region 3C391:BML, where broad millimeter CO and CS lines had previously been
detected. A new H2 clump was confirmed to have broad CO emission, demonstrating
that the near-infrared H2 images can trace previously undetected molecular
shocks. The [Fe II] emission has a significantly different distribution, being
brightest in the bright radio bar, at the interface between the supernova
remnant and the giant molecular cloud, and following filaments in the radio
shell. The near-infrared [Fe II] and the mid-infrared 12-18 micron filter
images are the first images to reveal the radiative shell of 3C391. The
mid-infrared spectrum is dominated by bright ionic lines and H2 S(2) through
S(7). There are no aromatic hydrocarbons associated with the shocks, nor is
their any mid-infrared continuum, suggesting that macromolecules and very small
grains are destroyed. Comparing 3C391 to the better-studied IC443, both
remnants have molecular- and ionic-dominated regions; for 3C391, the
ionic-dominated region is the interface into the giant molecular cloud, showing
that the main bodies of giant molecular clouds contain significant regions with
densities 100 to 1000/cm^3 and a small filling factor with higher-density. The
molecular shocked region resolves into 16 clumps of H2 emission, with some
fainter diffuse emission but with no associated near-infrared continuum
sources. One of the clumps is coincident with a previously-detected OH 1720 MHz
maser. These clumps are interpreted as a cluster of pre-stellar, dense
molecular cores that are presently being shocked by the supernova blast wave
Discovery of Broad Molecular lines and of Shocked Molecular Hydrogen from the Supernova Remnant G357.7+0.3: HHSMT, APEX, Spitzer and SOFIA Observations
We report a discovery of shocked gas from the supernova remnant (SNR)
G357.7+0.3. Our millimeter and submillimeter observations reveal broad
molecular lines of CO(2-1), CO(3-2), CO(4-3), 13CO (2-1) and 13CO (3-2), HCO^+
and HCN using HHSMT, Arizona 12-Meter Telescope, APEX and MOPRA Telescope. The
widths of the broad lines are 15-30 kms, and the detection of such broad lines
is unambiguous, dynamic evidence showing that the SNR G357.7+0.3 is interacting
with molecular clouds. The broad lines appear in extended regions (>4.5'x5').
We also present detection of shocked H2 emission in mid-infrared but lacking
ionic lines using the Spitzer IRS observations to map a few arcmin area. The H2
excitation diagram shows a best-fit with a two-temperature LTE model with the
temperatures of ~200 and 660 K. We observed [C II] at 158um and high-J
CO(11-10) with the GREAT on SOFIA. The GREAT spectrum of [C II], a 3 sigma
detection, shows a broad line profile with a width of 15.7 km/s that is similar
to those of broad CO molecular lines. The line width of [C~II] implies that
ionic lines can come from a low-velocity C-shock. Comparison of H2 emission
with shock models shows that a combination of two C-shock models is favored
over a combination of C- and J-shocks or a single shock. We estimate the CO
density, column density, and temperature using a RADEX model. The best-fit
model with n(H2) = 1.7x10^{4} cm^{-3}, N(CO) = 5.6x10^{16} cm^{-2}, and T = 75
K can reproduce the observed millimeter CO brightnesses.Comment: 19 pages, 22 figure
Shock processing of interstellar dust and polycyclic aromatic hydrocarbons in the supernova remnant N132D
We observed the oxygen-rich Large Magellanic Cloud (LMC) supernova remnant
N132D (SNR 0525-69.6), using all instruments onboard the Spitzer Space
Telescope, IRS, IRAC, and MIPS (Infrared Spectrograph, Infrared Array Camera,
Multiband Imaging Photometer for Spitzer). The 5-40 micron IRS spectra toward
the southeastern shell of the remnant show a steeply rising continuum with
[NeIII] and [OIV] as well as PAH emission. We also present the spectrum of a
fast moving ejecta knot, previously detected at optical wavelengths, which is
dominated by strong [NeIII] and [OIV] emission lines. We interpret the
continuum as thermal emission from swept-up, shock-heated dust grains in the
expanding shell of N132D, which is clearly visible in the MIPS 24 micron image.
A 15-20 micron emission hump appears superposed on the dust continuum, and we
attribute this to PAH C-C-C bending modes. We also detect the well-known 11.3
micron PAH C-H bending feature, and find the integrated strength of the 15-20
micron hump about a factor of seven stronger than the 11.3 micron band in the
shell of the remnant. IRAC 3-9 micron images do not show clear evidence of
large-scale, shell-like emission from the remnant, partly due to confusion with
the ambient ISM material. However, we identified several knots of shocked
interstellar gas based on their distinct infrared colors. We discuss the bright
infrared continuum and the polycyclic aromatic hydrocarbon features with
respect to dust processing in young supernova remnants.Comment: Accepted by Ap
- …