We report molecular line observations, made with ASTE and SEST, and dust continuum observations at 0.87 mm, made with APEX, towards the cold dust core G305.136+0.068. The molecular observations show that the core is isolated and roughly circularly sy
mmetric and imply that it has a mass of $1.1times10^3~M_odot$. A simultaneous model fitting of the spectra observed in four transitions of CS, using a non-LTE radiative transfer code, indicates that the core is centrally condensed, with the density decreasing with radius as $r^{-1.8}$, and that the turbulent velocity increases towards the center. The dust observations also indicate that the core is highly centrally condensed and that the average column density is 1.1 g cm$^{-2}$, value slightly above the theoretical threshold required for the formation of high mass stars. A fit to the spectral energy distribution of the emission from the core indicates a dust temperature of $17pm2$ K, confirming that the core is cold. Spitzer images show that the core is seen in silhouette from 3.6 to 24.0 $mu$m and that is surrounded by an envelope of emission, presumably tracing an externally excited photo-dissociated region. We found two embedded sources within a region of 20 centered at the peak of the core, one of which is young, has a luminosity of $66~L_odot$ and is accreting mass with a high accretion rate, of $sim1times10^{-4}~M_odot$ yr$^{-1}$. We suggest that this object corresponds to the seed of a high mass protostar still in the process of formation. The present observations support the hypothesis that G305.136+0.068 is a massive and dense cold core in an early stage of evolution, in which the formation of a high mass star has just started.
We report the detection, made using ALMA, of the 92 GHz continuum and hydrogen recombination lines (HRLs) H40$alpha$, H42$alpha$, and H50$beta$ emission toward the ionized wind associated with the high-mass young stellar object G345.4938+01.4677. Thi
s is the luminous central dominating source located in the massive and dense molecular clump associated with IRAS 16562$-$3959. The HRLs exhibit Voigt profiles, a strong signature of Stark broadening. We successfully reproduce the observed continuum and HRLs simultaneously using a simple model of a slow ionized wind in local thermodynamic equilibrium, with no need a high-velocity component. The Lorentzian line wings imply electron densities of $5times10^7$ cm$^{-3}$ on average. In addition, we detect SO and SO$_2$ emission arising from a compact ($sim3000$ AU) molecular core associated with the central young star. The molecular core exhibits a velocity gradient perpendicular to the jet-axis, which we interpret as evidence of rotation. The set of observations toward G345.4938+01.4677 are consistent with it being a young high-mass star associated with a slow photo-ionized wind.
We are carrying out multi-frequency radio continuum observations, using the Australia Telescope Compact Array, to systematically search for collimated ionized jets towards high-mass young stellar objects (HMYSOs). Here we report observations at 1.4,
2.4, 4.8 and 8.6 GHz, made with angular resolutions of about 7, 4, 2, and 1 arcsec, respectively, towards six objects of a sample of 33 southern HMYSOs thought to be in very early stages of evolution. The objects in the sample were selected from radio and infrared catalogs by having positive radio spectral indices and being luminous (L_bol > 20,000 L_sun), but underluminous in radio emission compared to that expected from its bolometric luminosity. This criteria makes the radio sources good candidates for being ionized jets. As part of this systematic search, two ionized jets have been discovered: one previously published and the other reported here. The rest of the observed candidates correspond to three hypercompact hii regions and two ultracompact hii regions. The two jets discovered are associated with two of the most luminous (70,000 and 100,000 Lsun) HMYSOs known to harbor this type of objects, showing that the phenomena of collimated ionized winds appears in the formation process of stars at least up to masses of ~ 20 M_sun and provides strong evidence for a disk-mediated accretion scenario for the formation of high-mass stars. From the incidence of jets in our sample, we estimate that the jet phase in high-mass protostars lasts for 40,000 yr.
We present high angular and spectral resolution HI 21~cm line observations toward the cometary-shaped compact HII region G213.880-11.837 in the GGD~14 complex.The kinematics and morphology of the photodissociated region, traced by the HI line emissio
n, reveal that the neutral gas is part of an expanding flow. The kinematics of the HI gas along the major axis of G213.880-11.837 shows that the emission is very extended toward the SE direction, reaching LSR radial velocities in the tail of about 14 km/s. The ambient LSR radial velocity of the molecular gas is 11.5 km/s, which suggests a champagne flow of the HI gas. This is the second (after G111.61+0.37) cometary HII/HI region known.
We present molecular line observations, made with angular resolutions of ~20, toward the filamentary infrared dark cloud G34.43+0.24 using the APEX [CO(3-2), 13CO(3-2), C18O(3-2) and CS(7-6) transitions], Nobeyama 45 m [CS(2-1), SiO(2-1), C34S(2-1),
HCO+(1-0), H13CO+(1-0) and CH3OH(2-1) transitions], and SEST [CS(2-1) and C18O(2-1) transitions] telescopes. We find that the spatial distribution of the molecular emission is similar to that of the dust continuum emission observed with 11 resolution showing a filamentary structure and four cores. The cores have local thermodynamic equilibrium masses ranging from 3.3x10^2 - 1.5x10^3 solar masses and virial masses from 1.1x10^3 - 1.5x10^3 solar masses, molecular hydrogen densities between 1.8x10^4 and 3.9x10^5 cm^{-3}, and column densities >2.0x10^{22} cm^{-2}; values characteristics of massive star forming cores. The 13CO(3-2) profile observed toward the most massive core reveals a blue profile indicating that the core is undergoing large-scale inward motion with an average infall velocity of 1.3 km/s and a mass infall rate of 1.8x10^{-3} solar masses per year. We report the discovery of a molecular outflow toward the northernmost core thought to be in a very early stage of evolution. We also detect the presence of high velocity gas toward each of the other three cores, giving support to the hypothesis that the excess 4.5 $mu$ emission (green fuzzies) detected toward these cores is due to shocked gas. The molecular outflows are massive and energetic, with masses ranging from 25 -- 80 solar masses, momentum 2.3 - 6.9x10^2 Msun km/s, and kinetic energies 1.1 - 3.6x10^3 Msun km^2 s^{-2}; indicating that they are driven by luminous, high-mass young stellar objects.
We report molecular line and dust continuum observations, made with the SEST telescope, towards four young high-mass star forming regions associated with highly luminous (L> 6x10^5 Lsun) IRAS sources (15290-5546, 15502-5302, 15567-5236 and 16060-5146
). Molecular emission was mapped in lines of CS (J=2-1, 3-2 and 5-4), SiO (J=2-1 and 3-2), CH3OH (Jk=3k-2k and 2k-1k), and C34S (J=3-2). In addition, single spectra at the peak position were taken in the CO, 13CO and C18O (J=1-0) lines. We find that the luminous star forming regions are associated with molecular gas and dust structures with radii of typically 0.5 pc, masses of ~5x10^3 Msun, column densities of ~5x10^{23} cm^{-2}, molecular hydrogen densities of typically ~2x10^5 cm^{-3} and dust temperatures of ~40 K. The 1.2 mm dust continuum observations further indicate that the cores are centrally condensed, having radial density profiles with power-law indices in the range 1.6-1.9. We find that under these conditions dynamical friction by the gas plays an important role in the migration of high-mass stars towards the central core region, providing an explanation for the observed stellar mass segregation within the cores.
We present mid-infrared (MIR) observations, made with the TIMMI2 camera on the ESO 3.6 m telescope, toward 14 young massive star-forming regions. All regions were imaged in the N band, and nine in the Q band, with an angular resolution of ~ 1 arcsec.
Typically, the regions exhibit a single or two compact sources (with sizes in the range 0.008-0.18 pc) plus extended diffuse emission. The Spitzer-Galactic Legacy Infrared Mid-Plane Survey Extraordinaire images of these regions show much more extended emission than that seen by TIMMI2, and this is attributed to polycyclic aromatic hydrocarbon (PAH) bands. For the MIR sources associated with radio continuum radiation (Paper I) there is a close morphological correspondence between the two emissions, suggesting that the ionized gas (radio source) and hot dust (MIR source) coexist inside the H II region. We found five MIR compact sources which are not associated with radio continuum emission, and are thus prime candidates for hosting young massive protostars. In particular, objects IRAS 14593-5852 II (only detected at 17.7 microns) and 17008-4040 I are likely to be genuine O-type protostellar objects. We also present TIMMI2 N-band spectra of eight sources, all of which are dominated by a prominent silicate absorption feature (~ 9.7 microns). From these data we estimate column densities in the range (7-17)x10^22 cm^-2, in good agreement with those derived from the 1.2 mm data (Paper II). Seven sources show bright [Ne II] line emission, as expected from ionized gas regions. Only IRAS 123830-6128 shows detectable PAH emission at 8.6 and 11.3 microns.
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 t
o 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.
