39 research outputs found
SuperMALT: Physical and Chemical Properties of Massive and Dense Clumps
The SuperMALT survey is observing 76 MALT90 clumps at different evolutionary
stages (from pre-stellar or quiescent to HII) in high excitation molecular
lines and key isotopomers using the Apex 12m telescope with an angular
resolution of 20" and a velocity resolution of 0.1 km/s. The aim of
this survey is to determine the physical, chemical, and kinematical properties
of the gas within clumps as they evolve. Here we report some preliminary
results based on observations of the =3-2 \& 4-3 lines of HNC, HCN, HCO,
NH and of the =3-2 line of the isotopologue HCO. We find
that the morphologies and line profiles vary with the evolutionary stage of the
clumps. The average line width increases from quiescent to HII clumps while
line ratios show hint of chemical differences among the various evolutionary
stages.Comment: 7 pages, 6 figures, Astrochemistry VII: IAU Symposium No. 33
The Carina Nebula and Gum 31 molecular complex: II. The distribution of the atomic gas revealed in unprecedented detail
We report high spatial resolution observations of the HI 21cm line in the
Carina Nebula and the Gum 31 region obtained with the Australia Telescope
Compact Array. The observations covered 12 deg centred on , achieving an angular resolution of 35
arcseconds. The HI map revealed complex filamentary structures across a wide
range of velocities. Several "bubbles" are clearly identified in the Carina
Nebula Complex, produced by the impact of the massive star clusters located in
this region. An HI absorption profile obtained towards the strong extragalactic
radio source PMN J1032--5917 showed the distribution of the cold component of
the atomic gas along the Galactic disk, with the Sagittarius-Carina and Perseus
spiral arms clearly distinguishable. Preliminary calculations of the optical
depth and spin temperatures of the cold atomic gas show that the HI line is
opaque ( 2) at several velocities in the Sagittarius-Carina
spiral arm. The spin temperature is K in the regions with the highest
optical depth, although this value might be lower for the saturated components.
The atomic mass budget of Gum 31 is of the total gas mass. HI self
absorption features have molecular counterparts and good spatial correlation
with the regions of cold dust as traced by the infrared maps. We suggest that
in Gum 31 regions of cold temperature and high density are where the atomic to
molecular gas phase transition is likely to be occurring.Comment: 20 pages, 1 table, 16 Figures, Accepted for Publication in the
Monthly Notices of the Royal Astronomical Society Journa
A multiwavelength study of young massive star forming regions: II. The dust environment
We present observations of 1.2-mm dust continuum emission, made with the
Swedish ESO Submillimeter Telescope, towards eighteen luminous IRAS point
sources, all with colors typical of compact HII regions and associated with
CS(2-1) emission, thought to be representative of young massive star forming
regions. Emission was detected toward all the IRAS objects. We find that the
1.2-mm sources associated with them have distinct physical parameters, namely
sizes of 0.4 pc, dust temperatures of 30 K, masses of 2x10^3 Msun, column
densities of 3x10^23 cm^-2, and densities of 4x10^5 cm^-3. We refer to these
dust structures as massive and dense cores. Most of the 1.2-mm sources show
single-peaked structures, several of which exhibit a bright compact peak
surrounded by a weaker extended envelope. The observed radial intensity
profiles of sources with this type of morphology are well fitted with power-law
intensity profiles with power-law indices in the range 1.0-1.7. This result
indicates that massive and dense cores are centrally condensed, having radial
density profiles with power-law indices in the range 1.5-2.2. We also find that
the UC HII regions detected with ATCA towards the IRAS sources investigated
here (Paper I) are usually projected at the peak position of the 1.2-mm dust
continuum emission, suggesting that massive stars are formed at the center of
the centrally condensed massive and dense cores.Comment: 6 figures, accepted by Ap
Characterizing [C II] Line Emission In Massive Star Forming Clumps
Because the 157.74 micron [C II] line is the dominant coolant of star-forming
regions, it is often used to infer the global star-formation rates of galaxies.
By characterizing the [C II] and far-infrared emission from nearby Galactic
star-forming molecular clumps, it is possible to determine whether
extragalactic [C II] emission arises from a large ensemble of such clumps, and
whether [C II] is indeed a robust indicator of global star formation. We
describe [C II] and far-infrared observations using the FIFI-LS instrument on
the SOFIA airborne observatory toward four dense, high-mass, Milky Way clumps.
Despite similar far-infrared luminosities, the [C II] to far-infrared
luminosity ratio, L([C II])/L(FIR) varies by a factor of at least 140 among
these four clumps. In particular, for AGAL313.576+0.324, no [C II] line
emission is detected despite a FIR luminosity of 24,000 L_sun.
AGAL313.576+0.324 lies a factor of more than 100 below the empirical
correlation curve between L([C II])/L(FIR) and S_\nu (63 micron)/S_\nu (158
micron) found for galaxies. AGAL313.576+0.324 may be in an early evolutionary
"protostellar" phase with insufficient ultraviolet flux to ionize carbon, or in
a deeply embedded ``hypercompact' H II region phase where dust attenuation of
UV flux limits the region of ionized carbon to undetectably small volumes.
Alternatively, its apparent lack of \cii\, emission may arise from deep
absorption of the \cii\, line against the 158 micron continuum, or
self-absorption of brighter line emission by foreground material, which might
cancel or diminish any emission within the FIFI-LS instrument's broad spectral
resolution element (~250 km/s
Infall Signatures in a Prestellar Core embedded in the High-Mass 70 m Dark IRDC G331.372-00.116
Using Galactic Plane surveys, we have selected a massive (1200 M),
cold (14 K) 3.6-70 m dark IRDC G331.372-00.116. This IRDC has the
potential to form high-mass stars and, given the absence of current star
formation signatures, it seems to represent the earliest stages of high-mass
star formation. We have mapped the whole IRDC with the Atacama Large
Millimeter/submillimeter Array (ALMA) at 1.1 and 1.3 mm in dust continuum and
line emission. The dust continuum reveals 22 cores distributed across the IRDC.
In this work, we analyze the physical properties of the most massive core,
ALMA1, which has no molecular outflows detected in the CO (2-1), SiO (5-4), and
HCO (3-2) lines. This core is relatively massive ( = 17.6 M),
subvirialized (virial parameter ), and is barely
affected by turbulence (transonic Mach number of 1.2). Using the HCO (3-2)
line, we find the first detection of infall signatures in a relatively massive,
prestellar core (ALMA1) with the potential to form a high-mass star. We
estimate an infall speed of 1.54 km s and a high accretion rate of 1.96
10 M yr. ALMA1 is rapidly collapsing, out of
virial equilibrium, more consistent with competitive accretion scenarios rather
than the turbulent core accretion model. On the other hand, ALMA1 has a mass
6 times larger than the clumps Jeans mass, being in an intermediate mass
regime ( 30 M), contrary to what both the
competitive accretion and turbulent core accretion theories predict.Comment: 13 Pages, 5 Figures, 3 Table
The ALMA Survey of 70 Dark High-mass Clumps in Early Stages (ASHES). II: Molecular Outflows in the Extreme Early Stages of Protocluster Formation
We present a study of outflows at extremely early stages of high-mass star
formation obtained from the ALMA Survey of 70 dark High-mass clumps
in Early Stages (ASHES). Twelve massive 3.670 dark prestellar
clump candidates were observed with the Atacama Large Millimeter/submillimeter
Array (ALMA) in Band 6. Forty-three outflows are identified toward 41 out of
301 dense cores using the CO and SiO emission lines, yielding a detection rate
of 14%. We discover 6 episodic molecular outflows associated with low- to
high-mass cores, indicating that episodic outflows (and therefore episodic
accretion) begin at extremely early stages of protostellar evolution for a
range of core masses. The time span between consecutive ejection events is much
smaller than those found in more evolved stages, which indicates that the
ejection episodicity timescale is likely not constant over time. The estimated
outflow dynamical timescale appears to increase with core masses, which likely
indicates that more massive cores have longer accretion timescales than less
massive cores. The lower accretion rates in these 70 dark objects
compared to the more evolved protostars indicate that the accretion rates
increase with time. The total outflow energy rate is smaller than the turbulent
energy dissipation rate, which suggests that outflow induced turbulence cannot
sustain the internal clump turbulence at the current epoch. We often detect
thermal SiO emission within these 70 dark clumps that is unrelated
to CO outflows. This SiO emission could be produced by collisions, intersection
flows, undetected protostars, or other motions.Comment: 32 pages, 9 figures, 4 tables, accepted for publication in Ap