Namely, the excitation temperature ranges from 3. The highest optical depths with This gradient of T kin 8. The corresponding spectra are depicted in Fig. For DoP1 , two possible detections of the ammonia emission are shown at the bottom panels, but the noise is high and the identification of the NH 3 1, 1 line is not certain.
A list of 37 targets from our dataset with undetected NH 3 emission is presented in Table 2. Columns 3 and 7 give the noise level per channel width of 0. In the fields of some targets we found the following objects:.
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We have used the Effelsberg m telescope to observe the NH 3 1, 1 and 2, 2 spectral lines in high-density molecular cores. The targets were preliminarily selected from the CO and 13 CO survey of the Aquila rift cloud complex carried out with the Delingha m telescope. We mapped a larger area for sources where ammonia emission was detected to delineate the spatial distribution of NH 3. The NH 3 sources in our sample represent diverse populations of molecular clouds from isolated and homogeneous starless cores with suppressed turbulence to star formation regions with complex intrinsic motion and gas density fluctuations.
The masses of the starless cores do not exceed a solar mass and are typically 0.
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It also has a high ratio of the turbulent to thermal velocity. Two isolated star-forming cores, Ka05 and DoP2 , were observed. For the former core, we estimated a sub-solar mass and thus confirm that Ka05 is a low-mass protostellar source. The most intense ammonia emission was observed toward four clouds with complex gas density and velocity structures that harbor numerous YSOs: Each of them consists of a number of clumps with different angular sizes.
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Only one cloud — DoP12 — where the bulk motions dispersion has a comparable to the ammonia linewidths. The internal bulk motions in the other three clouds are less pronounced and show lower dispersions than the NH 3 linewidths. In the former object, the splitting is most probably caused by bipolar molecular outflows observed in other molecular lines. This object has been observed in ammonia lines with the Effelsberg telescope three decades ago.
We compared these observations with the current spectra and found velocity shifts at some positions that correspond to an acceleration of the gas flow of km s -1 yr The measured kinetic temperatures lie between 9 K and 12 K for the starless and isolated star-forming sources, except for the fast rotator DoP7 , where T kin ranges between 12 K and 15 K.
An increased value of T kin in this case may be due to magnetic energy dissipation since magnetic and non-thermal energy densities may be nearly equal in DoP7: However, to what extent the magnetic energy dissipation contributes to the gas heating requires additional investigations. For the complex filamentary dark clouds, T kin varies between 9 K and 18 K and strongly fluctuates from point to point.
We found no simple relationship between gas density and kinetic temperature. High-density condensations in the filamentary dark clouds have a broad range of temperatures, most probably determined by radiation from embedded stars and dust. We thank the staff of the Effelsberg m telescope for the assistance in observations and acknowledge the help of Benjamin Winkel in preliminary data reduction.
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We also thank the anonymous referee and Malcolm Walmsley for suggestions that led to substantial improvements of the paper. We acknowledge Dima Shalybkov for valuable comments. Table 2 Molecular cores toward Aquila targets without detected NH 3 emission in the 1, 1 and 2, 2 inversion transitions. We give a consistent summary of the basic formulae relevant to the study of cold molecular cores. The recorded NH 3 spectra were first converted into the T MB scale and a baseline was removed from each of them.
The baseline was typically linear in the range covered by the ammonia hyperfine hf structure lines, but occasionally it was quadratic. After that the spectra of the same offset were co-added with weights inversely proportional to the mean variance of the noise per channel, rms -2 , estimated from the channels without emission.
The values of these parameters are given in, e. For some molecular cores we observe two-component NH 3 profiles. Given the estimate of the amplitude , the excitation temperature T ex can be calculated from Eq. For emission lines, the radiation temperature within the line is higher than the 2. At gas densities higher than the critical density 5 and for optically thin lines, the local density of line photons is negligible compared to the background radiation field, and the lower metastable states in NH 3 are mainly populated via collisions with molecular hydrogen 6 , i.
This means that the regime of low collisional excitation does not dominate. With this we can restrict the unknown filling factor for an unresolved source in the interval A. The second temperature, which describes the NH 3 population, is the rotational temperature T rot , which characterizes the population of energy levels with different J,K.
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As mentioned above, the population of the lower metastable inversion doublets is determined by collisions with H 2 and, thus, is regulated by the kinetic temperature T kin. The population ratio between the 1, 1 and 2, 2 states is defined as A. Substituting these numerical values in Eq. Substituting and from A. The value of A for the inversion transition 1, 1 is 1. However, the gas density calculated using Eq. Given a fractional NH 3 abundance, an upper bound on the gas density may be estimated from the deduced N NH assuming that the ammonia emission traces the real distribution of the gas density 7.
If the source is unresolved, its diameter d and the beam filling factor are related as A. The highest gas density is obtained at the smallest diameter,: If the source is resolved, i. To conclude, we note that if T kin varies slowly within an ammonia clump, the NH 3 column density can be deduced from the 1, 1 line alone assuming the same average T kin in the core as in the outskirts of a cloud. This allows us to extend the radial gas distribution to zones with unobservable 2, 2 emission Morgan et al. The observed spectra of the NH 3 1, 1 and 2, 2 transitions detected at the peak positions of ammonia emission toward each core are shown in Figs.
The measured physical parameters are listed in Tables B. The distributions of the physical parameters for the three most abundant cores are presented in Figs. The channel spacing is 0. The red curves show the fit of a single-component Gaussian model to the original data. The residuals between the observed and model spectra are shown in black. The red curves show the fit of a single-component Gaussian model to the NH 3 1, 1 original data and the upper limit on NH 3 2, 2. The ammonia spectra have a double structure.
The upper panels show the high-resolution spectra channel spacing 0. Two NH 3 components are marked by ticks and labeled by letters A and B in the upper panels. The corresponding spectral resolutions are 0.
The red curves show the fit of a single-component two upper panels and a double-component three lower panels Gaussian model to the original NH 3 data. Two components of the NH 3 emission are marked by ticks and labeled by letters A and B. The corresponding numerical values are listed in Table B. Molecular cores toward Aquila targets without detected NH 3 emission in the 1, 1 and 2, 2 inversion transitions.
Observed parameters of the NH 3 1, 1 and 2, 2 lines and calculated model parameters for DoP6. Observed parameters of the NH 3 1, 1 and 2, 2 lines and calculated model parameters for DoP Observed parameters of the NH 3 1, 1 and 2, 2 lines and calculated model parameters for SS3. NH 3 1, 1 intensity grey contours and radial velocity color map structure in the source DoP Ammonia 1, 1 and 2, 2 spectra blue toward the source Ka In the future, computers write books specifically for you, and learn to use them as weapons of control.
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