49 research outputs found
Velocity resolved [CII], [CI], and CO observations of the N159 star-forming region in the Large Magellanic Cloud: a complex velocity structure and variation of the column densities
The [CII]158um line is one of the dominant cooling lines in star-forming
active regions. The commonly assumed clumpy UV-penetrated cloud models predict
a [CII] line profile similar to that of CO. However, recent spectral-resolved
observations show that they are often very different, indicating a more complex
origin of the line emission including the dynamics of the source region. The
aim of our study is to investigate the physical properties of the star-forming
ISM in the Large Magellanic Cloud (LMC) by separating the origin of the
emission lines spatially and spectrally. In this paper, we focus on the
spectral characteristics and the origin of the emission lines, and the phases
of carbon-bearing species in the N159 star-forming region in the LMC. We mapped
a 4'x(3-4)' region in N159 in [CII]158um and [NII]205um with the GREAT on board
SOFIA, and in CO(3-2), (4-3), (6-5), 13CO(3-2), and [CI]3P1-3P0 and 3P2-3P1
with APEX. The emission of all transitions observed shows a large variation in
the line profiles across the map and between the different species. At most
positions the [CII] emission line profile is substantially wider than that of
CO and [CI]. We estimated the fraction of the [CII] integrated line emission
that cannot be fitted by the CO line profile to be 20%-50%. We derived the
relative contribution from C+, C, and CO to the column density in each velocity
bin. The contribution from C+ dominates the velocity range far from the
velocities traced by the dense molecular gas, and the region located between
the CO cores of N159 W and E. We estimate the contribution of the ionized gas
to the [CII] emission using the ratio to the [NII] emission to be < 19% to the
[CII] emission at its peak position, and <15% over the whole observed region.
Using the integrated line intensities, we present the spatial distribution of
I([CII])/I(FIR). (abridged for arXiv)Comment: 16 pages with 14 figures, accepted for publication in A&
L1599B: Cloud Envelope and C+ Emission in a Region of Moderately Enhanced Radiation Field
We study the effects of an asymmetric radiation field on the properties of a
molecular cloud envelope. We employ observations of carbon monoxide (12CO and
13CO), atomic carbon, ionized carbon, and atomic hydrogen to analyze the
chemical and physical properties of the core and envelope of L1599B, a
molecular cloud forming a portion of the ring at approximately 27 pc from the
star Lambda Ori. The O III star provides an asymmetric radiation field that
produces a moderate enhancement of the external radiation field. Observations
of the [CII] fine structure line with the GREAT instrument on SOFIA indicate a
significant enhanced emission on the side of the cloud facing the star, while
the [Ci], 12CO and 13CO J = 1-0 and 2-1, and 12CO J = 3-2 data from the PMO and
APEX telescopes suggest a relatively typical cloud interior. The atomic, ionic,
and molecular line centroid velocities track each other very closely, and
indicate that the cloud may be undergoing differential radial motion. The HI
data from the Arecibo GALFA survey and the SOFIA/GREAT [CII] data do not
suggest any systematic motion of the halo gas, relative to the dense central
portion of the cloud traced by 12CO and 13CO.Comment: 9 Figure
GREAT/SOFIA atmospheric calibration
The GREAT observations need frequency-selective calibration across the
passband for the residual atmospheric opacity at flight altitude. At these
altitudes the atmospheric opacity has both narrow and broad spectral features.
To determine the atmospheric transmission at high spectral resolution, GREAT
compares the observed atmospheric emission with atmospheric model predictions,
and therefore depends on the validity of the atmospheric models. We discusse
the problems identified in this comparison with respect to the observed data
and the models, and describe the strategy used to calibrate the science data
from GREAT/SOFIA during the first observing periods.Comment: 14 pages, 4 figure
A lambda=3 mm molecular line survey of NGC1068. Chemical signatures of an AGN environment
We aimed to study the molecular composition of the interstellar medium (ISM)
surrounding an Active Galactic Nucleus (AGN), by making an inventory of
molecular species and their abundances, as well as to establish a chemical
differentiation between starburst galaxies and AGN. We used the IRAM-30 m
telescope to observe the central 1.5-2 kpc region of NGC1068, covering the
frequencies between 86.2 GHz and 115.6 GHz. Using Boltzmann diagrams, we
calculated the column densities of the detected molecules. We used a chemical
model to reproduce the abundances found in the AGN, to determine the origin of
each detected species, and to test the influence of UV fields, cosmic rays, and
shocks on the ISM. We identified 24 different molecular species and
isotopologues, among which HC3N, SO, N2H+, CH3CN, NS, 13CN, and HN13C are
detected for the first time in NGC1068. We obtained the upper limits to the
isotopic ratios 12C/13C=49, 16O/18O=177 and 32S/34S=5. Our chemical models
suggest that the chemistry in the nucleus of NGC1068 is strongly influenced by
cosmic rays, although high values of both cosmic rays and far ultraviolet (FUV)
radiation fields also explain well the observations. The gas in the nucleus of
NGC1068 has a different chemical composition as compared to starburst galaxies.
The distinct physical processes dominating galaxy nuclei (e.g. C-shocks, UV
fields, X-rays, cosmic rays) leave clear imprints in the chemistry of the gas,
which allow to characterise the nucleus activity by its molecular abundances.Comment: 16 pages, 6 figures, 7 tables. Accepted for publication in Astronomy
and Astrophysic
Lambda = 3 mm line survey of nearby active galaxies
We used the IRAM 30m telescope to observe the frequency range [86-116]GHz
towards the central regions of the starburst galaxies M83, M82, and NGC253, the
AGNs M51, NGC1068, and NGC7469, and the ULIRGs Arp220 and Mrk231. Assuming LTE
conditions, we calculated the column densities of 27 molecules and 10
isotopologues. Among others, we report the first tentative detections of
CH3CHO, HNCO, and NS in M82 and, for the first time in the extragalactic
medium, HC5N in NGC253. Halpha recombination lines were only found in M82 and
NGC253. Vibrationally excited lines of HC3N were only detected in Arp220.
CH3CCH emission is only seen in the starburst-dominated galaxies. By comparison
of the fractional abundances among the galaxies, we looked for the molecules
that are best suited to characterise the chemistry of starbursts, AGNs and
ULIRGs, as well as the differences among galaxies within the same group.Comment: 24 pages, 6 figures, 12 tables. Accepted for publication in Astronomy
and Astrophysic
Molecular gas in the immediate vicinity of Sgr A* seen with ALMA
We report serendipitous detections of line emission with ALMA in band 3, 6,
and 7 in the central parsec of the Galactic center at an up to now highest
resolution (<0.7''). Among the highlights are the very first and highly
resolved images of sub-mm molecular emission of CS, H13CO+, HC3N, SiO, SO, C2H,
and CH3OH in the immediate vicinity (~1'' in projection) of Sgr A* and in the
circumnuclear disk (CND). The central association (CA) of molecular clouds
shows three times higher CS/X (X: any other observed molecule) luminosity
ratios than the CND suggesting a combination of higher excitation - by a
temperature gradient and/or IR-pumping - and abundance enhancement due to UV-
and/or X-ray emission. We conclude that the CA is closer to the center than the
CND is and could be an infalling clump consisting of denser cloud cores
embedded in diffuse gas. Moreover, we identified further regions in and outside
the CND that are ideally suited for future studies in the scope of hot/cold
core and extreme PDR/XDR chemistry and consequent star formation in the central
few parsecs
Characterizing the transition from diffuse atomic to dense molecular clouds in the Magellanic clouds with [CII], [CI], and CO
We present and analyze deep Herschel/HIFI observations of the [CII] 158um,
[CI] 609um, and [CI] 370um lines towards 54 lines-of-sight (LOS) in the Large
and Small Magellanic clouds. These observations are used to determine the
physical conditions of the line--emitting gas, which we use to study the
transition from atomic to molecular gas and from C^+ to C^0 to CO in their low
metallicity environments. We trace gas with molecular fractions in the range
0.1<f(H2)<1, between those in the diffuse H2 gas detected by UV absorption
(f(H2)<0.2) and well shielded regions in which hydrogen is essentially
completely molecular. The C^0 and CO column densities are only measurable in
regions with molecular fractions f(H2)>0.45 in both the LMC and SMC. Ionized
carbon is the dominant gas-phase form of this element that is associated with
molecular gas, with C^0 and CO representing a small fraction, implying that
most (89% in the LMC and 77% in the SMC) of the molecular gas in our sample is
CO-dark H2. The mean X_CO conversion factors in our LMC and SMC sample are
larger than the value typically found in the Milky Way. When applying a
correction based on the filling factor of the CO emission, we find that the
values of X_CO in the LMC and SMC are closer to that in the Milky Way. The
observed [CII] intensity in our sample represents about 1% of the total
far-infrared intensity from the LOSs observed in both Magellanic Clouds.Comment: 32 pages, 21 figures, Accepted to Ap