218 research outputs found
[CI], [CII] and CO emission lines as a probe for alpha variations at low and high redshifts
The offsets between the radial velocities of the rotational transitions of
carbon monoxide and the fine structure transitions of neutral and singly
ionized carbon are used to test the hypothetical variation of the fine
structure constant, alpha. From the analysis of the [CI] and [CII] fine
structure lines and low J rotational lines of 12CO and 13CO, emitted by the
dark cloud L1599B in the Milky Way disk, we find no evidence for fractional
changes in alpha at the level of || < 3*10^-7. For the
neighbour galaxy M33 a stringent limit on Delta alpha/alpha is set from
observations of three HII zones in [CII] and CO emission lines: || < 4*10^-7. Five systems over the redshift interval z = 5.7-6.4,
showing CO J=6-5, J=7-6 and [CII] emission, yield a limit on || < 1.3*10^-5. Thus, a combination of the [CI], [CII], and CO
emission lines turns out to be a powerful tool for probing the stability of the
fundamental physical constants over a wide range of redshifts not accessible to
optical spectral measurements.Comment: 10 pages, 3 figures, 5 tables. Accepted for publication in MNRA
C^+ distribution around S1 in rho Ophiuchi
We analyze a [C II] 158 micron map obtained with the L2 GREAT receiver on
SOFIA of the emission/reflection nebula illuminated by the early B star S1 in
the rho-OphA cloud core. This data set has been complemented with maps of
CO(3-2), 13CO(3-2) and C18O(3-2), observed as a part of the JCMT Gould Belt
Survey, with archival HCO^+(4-3) JCMT data, as well as with [O I] 63 and 145
micron imaging with Herschel/PACS. The [C II] emission is completely dominated
by the strong PDR emission from the nebula surrounding S1 expanding into the
dense Oph A molecular cloud west and south of S1. The [C II] emission is
significantly blue shifted relative to the CO spectra and also relative to the
systemic velocity, particularly in the northwestern part of the nebula. The [C
II] lines are broader towards the center of the S1 nebula and narrower towards
the PDR shell. The [C II] lines are strongly self-absorbed over an extended
region in the S1 PDR. Based on the strength of the [13C II] F = 2-1 hyperfine
component, [C II] is significantly optically thick over most of the nebula. CO
and 13CO(3-2) spectra are strongly self-absorbed, while C18O(3-2) is single
peaked and centered in the middle of the self-absorption. We have used a simple
two-layer LTE model to characterize the background and foreground cloud
contributing to the [C II] emission. From this analysis we estimate the
extinction due to the foreground cloud to be ~9.9 mag, which is slightly less
than the reddening estimated towards S1. Since some of the hot gas in the PDR
is not traced by low J CO emission, this result appears quite plausible. Using
a plane parallel PDR model with the observed [OI(145)]/[C II] brightness ratio
and an estimated FUV intensity of 3100-5000 G0 suggests that the density of the
[C II] emitting gas is ~3-4x10^3 cm^-3.Comment: Accepted for publication in Astronomy & Astrophysic
Opening the Treasure Chest in Carina
We have mapped the G287.84-0.82 cometary globule (with the Treasure Chest
cluster embedded in it) in the South Pillars region of Carina (i) in [CII],
63micron [OI], and CO(11-10) using upGREAT on SOFIA and (ii) in J=2-1
transitions of CO, 13CO, C18O and J=3-2 transitions of H2CO using the APEX
telescope in Chile. We probe the morphology, kinematics, and physical
conditions of the molecular gas and the photon dominated regions (PDRs) in
G287.84-0.82. The [CII] and [OI] emission suggest that the overall structure of
the pillar (with red-shifted photo evaporating tails) is consistent with the
effect of FUV radiation and winds from eta-Car and O stars in Trumpler 16. The
gas in the head of the pillar is strongly influenced by the embedded cluster,
whose brightest member is an O9.5V star, CPD-59 2661. The emission of the [CII]
and [OI] lines peak at a position close to the embedded star, while all other
tracers peak at another position lying to the north-east consistent with gas
being compressed by the expanding PDR created by the embedded cluster. The
molecular gas inside the globule is probed with the J=2-1 transitions of CO and
isotopologues as well as H2CO, and analyzed using a non-LTE model
(escape-probability approach), while we use PDR models to derive the physical
conditions of the PDR. We identify at least two PDR gas components; the diffuse
part (~10^4 cm^-3) is traced by [CII], while the dense (n~ 2-8x10^5 cm^-3) part
is traced by [CII], [OI], CO(11-10). Using the F=2-1 transition of [13CII]
detected at 50 positions in the region, we derive optical depths (0.9-5),
excitation temperatures of [CII] (80-255 K), and N(C+) of 0.3-1x10^19 cm^-2.
The total mass of the globule is ~1000 Msun, about half of which is traced by
[CII]. The dense PDR gas has a thermal pressure of 10^7-10^8 K cm^-3, which is
similar to the values observed in other regions.Comment: Accepted for publication in Astronomy and Astrophysics (abstract
slightly abridged
The Carbon content in the Galactic CygnusX/DR21 star forming region
Observations of Carbon bearing species are among the most important
diagnostic probes of ongoing star formation. CO is a surrogate for H and is
found in the vicinity of star formation sites. There, [CI] emission is thought
to outline the dense molecular cores and extend into the lower density regions,
where the impinging interstellar UV radiation field plays a critical role for
the dissociation and ionization processes. Emission of ionized carbon ([CII])
is found to be even more extended than [CI] and is linking up with the ionized
medium. These different tracers emphasize the importance of multi-wavelength
studies to draw a coherent picture of the processes driving and driven by high
mass star formation. Until now, large scale surveys were only done with low
resolution, such as the COBE full sky survey, or were biased to a few selected
bright sources (e.g. Yamamoto et al. 2001, Schneider et al. 2003). A broader
basis of unbiased, high-resolution observations of [CI], CO, and [CII] may play
a key role to probe the material processed by UV radiation.Comment: 4 pages, 4 figure, to appear in "Proceedings of the 4th
Cologne-Bonn-Zermatt-Symposium", ed. S. Pfalzner, C. Kramer, C. Straubmeier,
and A. Heithausen (Springer Verlag
CII, CI, and CO in the massive star forming region W3 Main
We have used the KOSMA 3m telescope to map the core 7'x5' of the Galactic
massive star forming region W3Main in the two fine structure lines of atomic
carbon and four mid-J transitions of CO and 13CO. In combination with a map of
singly ionized carbon (Howe et al. 1991), and FIR fine structure line data
observed by ISO/LWS at the center position, these data sets allow to study in
detail the physical structure of the photon dominated cloud interface regions
(PDRs) where the occurance of carbon changes from CII to CI, and to CO.Comment: 4 pages, 4 figures, to appear in "Proceedings of the 4th
Cologne-Bonn-Zermatt-Symposium, The dense interstellar medium in galaxies",
eds. S. Pfalzner, C. Kramer, C. Straubmeier, and A. Heithausen (Springer
Verlag
High Spectral and Spatial Resolution Observations of the PDR Emission in the NGC2023 Reflection Nebula with SOFIA and APEX
We have mapped the NGC 2023 reflection nebula in [CII] and CO(11--10) with
the heterodyne receiver GREAT on SOFIA and obtained slightly smaller maps in
13CO(3--2), CO(3--2), CO(4--3), CO(6--5), and CO(7--6) with APEX in Chile. We
use these data to probe the morphology, kinematics, and physical conditions of
the C II region, which is ionized by FUV radiation from the B2 star HD37903.
The [CII] emission traces an ellipsoidal shell-like region at a position angle
of ~ -50 deg, and is surrounded by a hot molecular shell. In the southeast,
where the C II region expands into a dense, clumpy molecular cloud ridge, we
see narrow and strong line emission from high-J CO lines, which comes from a
thin, hot molecular shell surrounding the [CII] emission. The [CII] lines are
broader and show photo evaporating gas flowing into the C II region. Based on
the strength of the [13CII] F=2--1 line, the [CII] line appears to be somewhat
optically thick over most of the nebula with an optical depth of a few. We
model the physical conditions of the surrounding molecular cloud and the PDR
emission using both RADEX and simple PDR models. The temperature of the CO
emitting PDR shell is ~ 90 -- 120 K, with densities of 10^5 -- 10^6 cm^-3, as
deduced from RADEX modeling. Our PDR modeling indicates that the PDR layer
where [CII] emission dominates has somewhat lower densities, 10^4 to a few
times 10^5 cm^-3Comment: Accepted by A&
Probing the massive star forming environment - a multiwavelength investigation of the filamentary IRDC G333.73+0.37
We present a multiwavelength study of the filamentary infrared dark cloud
(IRDC) G333.73+0.37. The region contains two distinct mid-infrared sources S1
and S2 connected by dark lanes of gas and dust. Cold dust emission from the
IRDC is detected at seven wavelength bands and we have identified 10 high
density clumps in the region. The physical properties of the clumps such as
temperature: 14.3-22.3 K and mass: 87-1530 M_sun are determined by fitting a
modified blackbody to the spectral energy distribution of each clump between
160 micron and 1.2 mm. The total mass of the IRDC is estimated to be $~4700
M_sun. The molecular line emission towards S1 reveals signatures of
protostellar activity. Low frequency radio emission at 1300 and 610 MHz is
detected towards S1 (shell-like) and S2 (compact morphology), confirming the
presence of newly formed massive stars in the IRDC. Photometric analysis of
near and mid-infrared point sources unveil the young stellar object population
associated with the cloud. Fragmentation analysis indicates that the filament
is supercritical. We observe a velocity gradient along the filament, that is
likely to be associated with accretion flows within the filament rather than
rotation. Based on various age estimates obtained for objects in different
evolutionary stages, we attempt to set a limit to the current age of this
cloud.Comment: 26 pages, 20 figures, accepted by Ap
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
Far and mid infrared observations of two ultracompact H II regions and one compact CO clump
Two ultracompact H II regions (IRAS 19181+1349 and 20178+4046) and one
compact molecular clump (20286+4105) have been observed at far infrared
wavelengths using the TIFR 1 m balloon-borne telescope and at mid infrared
wavelengths using ISO. Far infrared observations have been made simultaneously
in two bands with effective wavelengths of ~ 150 and ~ 210 micron, using liquid
3He cooled bolometer arrays. ISO observations have been made in seven spectral
bands using the ISOCAM instrument; four of these bands cover the emission from
Polycyclic Aromatic Hydrocarbon (PAH) molecules. In addition, IRAS survey data
for these sources in the four IRAS bands have been processed using the HIRES
routine. In the high resolution mid infrared maps as well as far infrared maps
multiple embedded energy sources have been resolved. There are structural
similarities between the images in the mid infrared and the large scale maps in
the far infrared bands, despite very different angular resolutions of the two.
Dust temperature and optical depth (tau_150 um) maps have also been generated
using the data from balloon-borne observations. Spectral energy distributions
(SEDs) for these sources have been constructed by combining the data from all
these observations. Radiation transfer calculations have been made to
understand these SEDs. Parameters for the dust envelopes in these sources have
been derived by fitting the observed SEDs. In particular, it has been found
that radial density distribution for three sources is diffrent. Whereas in the
case of IRAS 20178+4046, a steep distribution of the form r^-2 is favoured, for
IRAS 20286+4105 it is r^-1 and for IRAS 19181+1349 it the uniform distribution
(r^0). Line ratios for PAH bands have generally been found to be similar to
those for other compact H II regions but different from general H II regions.Comment: To appear in Astronomy & Astrophysics; (19 pages including 14 Figures
and 6 Tables
The structure of hot gas in Cepheus B
By observing radiation-affected gas in the Cepheus B molecular cloud we probe
whether the sequential star formation in this source is triggered by the
radiation from newly formed stars. We used the dual band receiver GREAT onboard
SOFIA to map [C II] and CO 13--12 and 11--10 in Cep B and compared the spatial
distribution and the spectral profiles with complementary ground-based data of
low- transitions of CO isotopes, atomic carbon, and the radio continuum. The
interaction of the radiation from the neighboring OB association creates a
large photon-dominated region (PDR) at the surface of the molecular cloud
traced through the photoevaporation of C^+. Bright internal PDRs of hot gas are
created around the embedded young stars, where we detect evidence of the
compression of material and local velocity changes; however, on the global
scale we find no indications that the dense molecular material is dynamically
affected.Comment: Accepted for publication in A&A (SOFIA/GREAT special issue
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