Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userDense and warm molecular gas in the envelopes and outflows of southern low-mass protostars
98
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Observations of dense molecular gas lie at the basis of our understanding of the density and temperature structure of protostellar envelopes and molecular outflows. We aim to characterize the properties of the protostellar envelope, molecular outflow and surrounding cloud, through observations of high excitation molecular lines within a sample of 16 southern sources presumed to be embedded YSOs. Observations of submillimeter lines of CO, HCO+ and their isotopologues, both single spectra and small maps were taken with the FLASH and APEX-2a instruments mounted on APEX to trace the gas around the sources. The HARP-B instrument on the JCMT was used to map IRAS 15398-3359 in these lines. HCO+ mapping probes the presence of dense centrally condensed gas, a characteristic of protostellar envelopes. The rare isotopologues C18O and H13CO+ are also included to determine the optical depth, column density, and source velocity. The combination of multiple CO transitions, such as 3-2, 4-3 and 7-6, allows to constrain outflow properties, in particular the temperature. Archival submillimeter continuum data are used to determine envelope masses. Eleven of the sixteen sources have associated warm and/or dense quiescent as characteristic of protostellar envelopes, or an associated outflow. Using the strength and degree of concentration of the HCO+ 4-3 and CO 4-3 lines as a diagnostic, five sources classified as Class I based on their spectral energy distributions are found not to be embedded YSOs. The C18O 3-2 lines show that for none of the sources, foreground cloud layers are present. Strong molecular outflows are found around six sources, .. (continued in paper)
rate research
Read More
We performed 12CO(1-0), 13CO(1-0), and HCN(1-0) single-dish observations (beam size ~14-18) toward nearby starburst and non-starburst galaxies using the Nobeyama 45 m telescope. The 13CO(1-0) and HCN(1-0) emissions were detected from all the seven starburst galaxies, with the intensities of both lines being similar (i.e., the ratios are around unity). On the other hand, for case of the non-starburst galaxies, the 13CO(1-0) emission was detected from all three galaxies, while the HCN(1-0) emission was weakly or not detected in past observations. This result indicates that the HCN/13CO intensity ratios are significantly larger (~1.15+-0.32) in the starburst galaxy samples than the non-starburst galaxy samples (<0.31+-0.14). The large-velocity-gradient model suggests that the molecular gas in the starburst galaxies have warmer and denser conditions than that in the non-starburst galaxies, and the photon-dominated-region model suggests that the denser molecular gas is irradiated by stronger interstellar radiation field in the starburst galaxies than that in the non-starburst galaxies. In addition, HCN/13CO in our sample galaxies exhibit strong correlations with the IRAS 25 micron flux ratios. It is a well established fact that there exists a strong correlation between dense molecular gas and star formation activities, but our results suggest that molecular gas temperature is also an important parameter.
We use PACS and SPIRE continuum data at 160 um, 250 um, 350 um, and 500 um from the Herschel Gould Belt Survey to sample seven clumps in Perseus: B1, B1-E, B5, IC348, L1448, L1455, and NGC1333. Additionally, we identify and characterize the embedded Class 0 protostars using detections of compact Herschel sources at 70 um as well as archival Spitzer catalogues and SCUBA 850 um photometric data. We identify 28 candidate Class 0 protostars, four of which are newly discovered sources not identified with Spitzer. We find that the star formation efficiency of clumps, as traced by Class 0 protostars, correlates strongly with the flatness of their respective column density distributions at high values. This correlation suggests that the fraction of high column density material in a clump reflects only its youngest protostellar population rather than its entire source population. We propose that feedback from either the formation or evolution of protostars changes the local density structure of clumps.
Recent observations from Herschel allow the identification of important mechanisms responsible for the heating of gas surrounding low-mass protostars and its subsequent cooling in the far-infrared (FIR). Shocks are routinely invoked to reproduce some properties of the far-IR spectra, but standard models fail to reproduce the emission from key molecules, e.g. H$_2$O. Here, we present the Herschel-PACS far-IR spectroscopy of 90 embedded low-mass protostars (Class 0/I). The Herschel-PACS spectral maps covering $sim55-210$ $mu$m with a field-of-view of $sim$50 are used to quantify the gas excitation conditions and spatial extent using rotational transitions of H$_{2}$O, high-$J$ CO, and OH, as well as [O I] and [C II]. We confirm that a warm ($sim$300 K) CO reservoir is ubiquitous and that a hotter component ($760pm170$ K) is frequently detected around protostars. The line emission is extended beyond $sim$1000 AU spatial scales in 40/90 objects, typically in molecular tracers in Class 0 and atomic tracers in Class I objects. High-velocity emission ($gtrsim90$ km s$^{-1}$) is detected in only 10 sources in the [O I] line, suggesting that the bulk of [O I] arises from gas that is moving slower than typical jets. Line flux ratios show an excellent agreement with models of $C$-shocks illuminated by UV photons for pre-shock densities of $sim$$10^5$ cm$^{-3}$ and UV fields 0.1-10 times the interstellar value. The far-IR molecular and atomic lines are a unique diagnostic of feedback from UV emission and shocks in envelopes of deeply embedded protostars.
We present the results of the observations of the (J,K)=(1,1) and the (J,K)=(2,2) inversion transitions of the NH3 molecule toward a large sample of 40 regions with molecular or optical outflows, using the 37 m radio telescope of the Haystack Observatory. We detected NH3 emission in 27 of the observed regions, which we mapped in 25 of them. Additionally, we searched for the 6{16}-5{23} H2O maser line toward six regions, detecting H2O maser emission in two of them, HH265 and AFGL 5173. We estimate the physical parameters of the regions mapped in NH3 and analyze for each particular region the distribution of high density gas and its relationship with the presence of young stellar objects. From the global analysis of our data we find that in general the highest values of the line width are obtained for the regions with the highest values of mass and kinetic temperature. We also found a correlation between the nonthermal line width and the bolometric luminosity of the sources, and between the mass of the core and the bolometric luminosity. We confirm with a larger sample of regions the conclusion of Anglada et al. (1997) that the NH3 line emission is more intense toward molecular outflow sources than toward sources with optical outflow, suggesting a possible evolutionary scheme in which young stellar objects associated with molecular outflows progressively lose their neighboring high-density gas, weakening both the NH3 emission and the molecular outflow in the process, and making optical jets more easily detectable as the total amount of gas decreases.
Aims. Young stars interact vigorously with their surroundings, as evident from the highly rotationally excited CO (up to Eup=4000 K) and H2O emission (up to 600 K) detected by the Herschel Space Observatory in embedded low-mass protostars. Our aim is to construct a model that reproduces the observations quantitatively, to investigate the origin of the emission, and to use the lines as probes of the various heating mechanisms. Methods. The model consists of a spherical envelope with a bipolar outflow cavity. Three heating mechanisms are considered: passive heating by the protostellar luminosity, UV irradiation of the outflow cavity walls, and C-type shocks along the cavity walls. Line fluxes are calculated for CO and H2O and compared to Herschel data and complementary ground-based data for the protostars NGC1333 IRAS2A, HH 46 and DK Cha. The three sources are selected to span a range of evolutionary phases and physical characteristics. Results. The passively heated gas in the envelope accounts for 3-10% of the CO luminosity summed over all rotational lines up to J=40-39; it is best probed by low-J CO isotopologue lines such as C18O 2-1 and 3-2. The UV-heated gas and the C-type shocks, probed by 12CO 10-9 and higher-J lines, contribute 20-80% each. The model fits show a tentative evolutionary trend: the CO emission is dominated by shocks in the youngest source and by UV-heated gas in the oldest one. This trend is mainly driven by the lower envelope density in more evolved sources. The total H2O line luminosity in all cases is dominated by shocks (>99%). The exact percentages for both species are uncertain by at least a factor of 2 due to uncertainties in the gas temperature as function of the incident UV flux. However, on a qualitative level, both UV-heated gas and C-type shocks are needed to reproduce the emission in far-infrared rotational lines of CO and H2O.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
