119 research outputs found
A parsec-scale flow associated with the IRAS 16547-4247 radio jet
IRAS 16547-4247 is the most luminous (6.2 x 10^4 Lsun) embedded young stellar
object known to harbor a thermal radio jet. We report the discovery using
VLT-ISAAC of a chain of H_2 2.12 um emission knots that trace a collimated flow
extending over 1.5 pc. The alignment of the H_2 flow and the central location
of the radio jet implies that these phenomena are intimately linked. We have
also detected using TIMMI2 an isolated, unresolved 12 um infrared source
towards the radio jet . Our findings affirm that IRAS 16547-4247 is excited by
a single O-type star that is driving a collimated jet. We argue that the
accretion mechanism which produces jets in low-mass star formation also
operates in the higher mass regime.Comment: Accepted for publication in ApJL, 10 pages, 2 figure
Spiral structure in the outer galactic disk, I: the third galactic quadrant
We combine optical and radio observations to trace the spiral structure in the third quadrant of the Milky Way. The optical observations consist of a large sample of young open clusters and associations, whereas the radio observations consist of a survey of nearby and distant clouds observed in CO. Both the optical and radio samples are the largest ones thus far presented in the literature. We use this unique material to analyze the behavior of interstellar extinction and to trace the detailed structure of the third Galactic quadrant (TGQ).We find that the outer (Cygnus) grand design spiral arm is traced by stellar and CO components, while the Perseus arm is traced solely by CO and is possibly being disrupted by the crossing of the Local (Orion) arm. The Local arm is traced by CO and young stars toward l ¼ 240 and extends for over 8 kpc along the line of sight reaching the outer arm. Finally, we characterize the Galactic warp and compare the geometries implied by the young stellar and CO components.Fil: Vazquez, Ruben Angel. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: May, Jorge. Universidad de Chile; ChileFil: Carraro, Giovanni. European Southern Observatory; ChileFil: Bronfman, Leonardo. Universidad de Chile; ChileFil: Moitinho, Andre. Universidad de Lisboa; PortugalFil: Baume, Gustavo Luis. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentin
Physical characteristics of G331.5-0.1: The luminous central region of a Giant Molecular Cloud
We report molecular line and dust continuum observations toward the high-mass
star forming region G331.5-0.1, one of the most luminous regions of massive
star-formation in the Milky Way, located at the tangent region of the Norma
spiral arm, at a distance of 7.5 kpc. Molecular emission was mapped toward the
G331.5-0.1 GMC in the CO (J=1-0) and C18O (J=1-0) lines with NANTEN, while its
central region was mapped in CS (J=2-1 and J=5-4) with SEST, and in CS (J=7-6)
and 13CO (J=3-2) with ASTE. Continuum emission mapped at 1.2 mm with SIMBA and
at 0.87 mm with LABOCA reveal the presence of six compact and luminous dust
clumps, making this source one of the most densely populated central regions of
a GMC in the Galaxy. The dust clumps are associated with molecular gas and they
have the following average properties: size of 1.6 pc, mass of 3.2x10^3 Msun,
molecular hydrogen density of 3.7x10^4 cm^{-3}, dust temperature of 32 K, and
integrated luminosity of 5.7x10^5 Lsun, consistent with values found toward
other massive star forming dust clumps. The CS and 13CO spectra show the
presence of two velocity components: a high-velocity component at ~ -89 km
s^{-1}, seen toward four of the clumps, and a low-velocity component at ~ -101
km s^{-1} seen toward the other two clumps. Radio continuum emission is present
toward four of the molecular clumps, with spectral index estimated for two of
them of 0.8+-0.2 and 1.2+-0.2. A high-velocity molecular outflow is found at
the center of the brightest clump, with a line width of 26 km s^{-1} (FWHM) in
CS (J=7-6). Observations of SiO (J=7-6 and J=8-7), and SO (J_K=8_8-7_7 and
J_K=8_7-7_6) lines provide estimates of the gas rotational temperature toward
this outflow >120 K and >75 K, respectively.Comment: 34 pages, 20 figures, 11 tables, Accepted for Publication in The
Astrophysical Journa
G345.45+1.50: An expanding ring-like structure with massive star formation
Ring-like structures in the ISM are commonly associated with high-mass stars.
Kinematic studies of large structures in GMCs toward these ring-like structures
may help us to understand how massive stars form. The origin and properties of
the ring-like structure G345.45+1.50 is investigated through observations of
the 13CO(3-2) line. The aim of the observations is to determine the kinematics
in the region and to compare physical characteristics estimated from gas
emission with those previously determined using dust continuum emission. The
13CO(3-2) line was mapped toward the whole ring using the APEX telescope. The
ring is found to be expanding with a velocity of 1.0 km/s, containing a total
mass of 6.9e3 Msun, which agrees well with that determined using 1.2 mm dust
continuum emission. An expansion timescale of 3e6 yr and a total energy of 7e46
erg are estimated. The origin of the ring might have been a supernova
explosion, since a 35.5 cm source, J165920-400424, is located at the center of
the ring without an infrared counterpart. The ring is fragmented, and 104
clumps were identified with diameters of between 0.3 and 1.6 pc, masses of
between 2.3 and 7.5e2 Msun, and densities of between 1.0e2 and 1.0e4 cm^-3. At
least 18% of the clumps are forming stars, as is shown in infrared images.
Assuming that the clumps can be modeled as Bonnor-Ebert spheres, 13 clumps are
collapsing, and the rest of them are in hydrostatic equilibrium with an
external pressure with a median value of 4e4 K cm^-3. In the region, the
molecular outflow IRAS 16562-3959 is identified, with a velocity range of 38.4
km/s, total mass of 13 Msun, and kinematic energy of 7e45 erg. Finally, five
filamentary structures were found at the edge of the ring with an average size
of 3 pc, a width of 0.6 pc, a mass of 2e2 Msun, and a column density of 6e21
cm^-2
Chemistry of the High-Mass Protostellar Molecular Clump IRAS 16562-3959
We present molecular line observations of the high-mass molecular clump IRAS
165623959 taken at 3 mm using the Atacama Large Millimeter/submillimeter
Array (ALMA) at 1.\!\!^{\prime\prime}7 angular resolution ( pc spatial
resolution). This clump hosts the actively accreting high-mass young stellar
object (HMYSO) G345.4938+01.4677, associated with a hypercompact HII region. We
identify and analyze emission lines from 22 molecular species (encompassing 34
isomers) and classify them into two groups, depending on their spatial
distribution within the clump. One of these groups gathers shock tracers (e.g.,
SiO, SO, HNCO) and species formed in dust grains like methanol (CHOH),
ethenone or ketene (HCCO), and acetaldehyde (CHCHO). The second group
collects species resembling the dust continuum emission morphology and which
are formed mainly in the gas-phase, like hydrocarbons (CCH, c-CH,
CHCCH), cyanopolyynes (HCN and HCN) and cyanides (HCN and
CHCN). Emission from complex organic molecules (COMs) like CHOH,
propanenitrile (CHCHCN), and methoxymethane (CHOCH) arise from
gas in the vicinity of a hot molecular core ( K) associated with
the HMYSO. Other COMs such as propyne (CHCCH), acrylonitrile (CHCHCN),
and acetaldehyde seem to better trace warm ( K) dense gas. In
addition, deuterated ammonia (NHD) is detected mostly in the outskirts of
IRAS 165623959, associated with near-infrared dark globules, probably
gaseous remnants of the clump's prestellar phase. The spatial distribution of
molecules in IRAS 165623959 supports the view that in protostellar clumps,
chemical tracers associated with different evolutionary stages --- starless to
hot cores/HII regions --- exist coevally.Comment: 97 pages, Accepted in The Astrophysical Journal Supplement Series.
Journal file version have better quality figure
Observations and chemical modeling of the isotopologues of formaldehyde and the cations of formyl and protonated formaldehyde in the hot molecular core G331.512-0.103
In the interstellar cold gas, the chemistry of formaldehyde (HCO) can be
essential to explain the formation of complex organic molecules. On this
matter, the massive and energetic protostellar object G331 is still unexplored
and, hence, we carried out a comprehensive study of the isotopologues of
HCO and formyl cation (HCO), and of protonated formaldehyde
(HCOH) through the APEX observations in the spectral window
159-356~GHz. We employed observational and theoretical methods to derive
the physical properties of the molecular gas combining LTE and non-LTE
analyses. Formaldehyde was characterized via 35 lines of HCO, HCO,
HDCO and HCO. The formyl cation was detected via 8 lines of HCO,
HCO, HCO and HCO. Deuterium was clearly
detected via HDCO, whereas DCO remained undetected. HCOH was
detected through 3 clean lines. According to the radiative analysis,
formaldehyde appears to be embedded in a bulk gas with a wide range of
temperatures (20-90 K), while HCO and HCOH are primarily
associated with a colder gas ( 30 K). The reaction HCO+HCO HCOH + CO is crucial for the balance of the three species.
We used Nautilus gas-grain code to predict the evolution of their molecular
abundances relative to H which values at time scales 10 yr
matched with the observations in G331: [HCO] = (0.2-2) 10,
[HCO] = (0.5-4) 10 and [HCOH] = (0.2-2)
10. Based on the molecular evolution of HCO, HCO and
HCOH, we hypothesized about the young lifetime of G331, which is
consistent with the active gas-grain chemistry of massive protostellar objects.Comment: 24 pages, 8 figures, 8 tables. Accepted for publication in The
Astrophysical Journa
ALMA observations of the massive molecular outflow G331.512-0.103
The object of this study is one of the most energetic and luminous molecular
outflows known in the Galaxy, G331.512-0.103. Observations with ALMA Band 7
(350 GHz; 0.86 mm) reveal a very compact, extremely young bipolar outflow and a
more symmetric outflowing shocked shell surrounding a very small region of
ionized gas. The velocities of the bipolar outflow are about 70 km s^{-1} on
either side of the systemic velocity. The expansion velocity of the shocked
shell is ~24 km s^{-1}, implying a crossing time of about 2000 yrs. Along the
symmetry axis of the outflow, there is a velocity feature, which could be a
molecular "bullet" of high-velocity dense material. The source is one of the
youngest examples of massive molecular outflow found associated with a
high-mass star.Comment: 9 pages, 4 figures, 1 table, Accepted for publication in The
Astrophysical Journal Letters, small typos correcte
Spiral structure in the outer galactic disk. I. The third galactic quadrant
We combine optical and radio observations to trace the spiral structure in the third quadrant of the Milky Way. The optical observations consist of a large sample of young open clusters and associations, whereas the radio observations consist of a survey of nearby and distant clouds observed in CO. Both the optical and radio samples are the largest ones thus far presented in the literature. We use this unique material to analyze the behavior of interstellar extinction and to trace the detailed structure of the third Galactic quadrant (TGQ).We find that the outer (Cygnus) grand design spiral arm is traced by stellar and CO components, while the Perseus arm is traced solely by CO and is possibly being disrupted by the crossing of the Local (Orion) arm. The Local arm is traced by CO and young stars toward l = 240° and extends for over 8 kpc along the line of sight reaching the outer arm. Finally, we characterize the Galactic warp and compare the geometries implied by the young stellar and CO components.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat
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