Main Beam Brightness Temperature Research Articles

Comparison of NH3 and 12CO, 13CO, C18O Molecular Lines in the Aquila Rift Cloud Complex

The observations of the Aquila Rift cloud complex at 23.708 and 115.271 GHz made using the Nanshan 26 m radio telescope and the 13.7 m millimeter-wavelength telescope are presented. We find that the CO(1 − 0) gas distribution is similar to the NH3 gas distribution in the Aquila Rift cloud complex. In some diffusion regions characterized by CO, we identified several dense clumps based on the distribution of detected ammonia molecular emission. Through the comparison of spectral line parameters for NH3, 13CO, and C18O, our study reveals that the line center velocities of the NH3, 13CO, and C18O lines are comparable and positively correlated, indicating that they originate from the same emission region. No significant correlation was identified for other parameters, including integrated intensity, line widths, main beam brightness temperature, as well as the column densities of NH3, 13CO, and C18O. The absolute difference in line-center velocities between the 13CO and NH3 lines is less than both the average line width of NH3 and that of 13CO. This suggests that there are no significant movements of NH3 clumps in relation to their envelopes. The velocity deviation is likely due to turbulent activity within the clumps.

Peering into the Milky Way by FAST: II. Ionized gas in the inner Galactic disk revealed by the piggyback line observations of the FAST GPPS survey

As one of the major components of the interstellar medium, the ionized gas in our Milky Way, especially the low-density diffuse component, has not been extensively observed in the radio band. The Galactic Plane Pulsar Snapshot (GPPS) survey covers the sky area within the Galactic latitude of $\pm10^\circ$ around the Galactic plane visible by the Five-hundred-meter Aperture Spherical radio Telescope (FAST), and the spectral line data are simultaneously recorded during the pulsar survey observations. With an integration time of 5 minutes for each beam, the GPPS survey project provides the most sensitive piggyback spectra for tens of radio recombination lines (RRLs) in the band of 1000$-$1500 MHz for H$n\alpha$, He$n\alpha$, C$n\alpha$, as well as H$n\beta$ and H$n\gamma$. We processed the spectral data of RRLs, and obtained a sensitive averaged H$n\alpha$ RRL map of a sky area of 88 square degrees in the inner Galaxy of 33$^\circ$ $\leqslant l \leqslant$ 55$^\circ$ and $|b| \leqslant$ 2.0$^\circ$. The final spectral data of the H$n\alpha$ RRLs have a spatial resolution of $\sim$3$^\prime$, a spectral resolution of 2.2 km s$^{-1}$, and a typical spectral rms noise of 0.25 mJy beam$^{-1}$ or 6.3 mK in main-beam brightness temperature. The new H$n\alpha$ RRL map shows complex structural features dominated by a number of HII regions and large extended diffuse ionized gas regions. We detect about 94% of the known HII regions and confirm 43 WISE HII regions in the observed sky area. Several large HII regions or star-forming complexes in the distant outer Galaxy are resolved in the map of H$n\alpha$ RRLs. Extended RRL features of the diffuse ionized gas are detected. The RRL data products of the GPPS survey will be published and updated at http://zmtt.bao.ac.cn/MilkyWayFAST/

ATLASGAL – Ammonia observations towards the southern Galactic plane

Context. The initial conditions of molecular clumps in which high-mass stars form are poorly understood. In particular, a more detailed study of the earliest evolutionary phases is needed. The APEX Telescope Large Area Survey of the whole inner Galactic disk at 870 μm, ATLASGAL, has therefore been conducted to discover high-mass star-forming regions at different evolutionary phases. Aims. We derive properties such as velocities, rotational temperatures, column densities, and abundances of a large sample of southern ATLASGAL clumps in the fourth quadrant. Methods. Using the Parkes telescope, we observed the NH3 (1, 1) to (3, 3) inversion transitions towards 354 dust clumps detected by ATLASGAL within a Galactic longitude range between 300° and 359° and a latitude within ± 1.5°. For a subsample of 289 sources, the N2H+ (1–0) line was measured with the Mopra telescope. Results. We measured a median NH3 (1, 1) line width of ~ 2 km s-1, rotational temperatures from 12 to 28 K with a mean of 18 K, and source-averaged NH3 abundances from 1.6 × 10-6 to 10-8. For a subsample with detected NH3 (2, 2) hyperfine components, we found that the commonly used method to compute the (2, 2) optical depth from the (1, 1) optical depth and the (2, 2) to (1, 1) main beam brightness temperature ratio leads to an underestimation of the rotational temperature and column density. A larger median virial parameter of ~ 1 is determined using the broader N2H+ line width than is estimated from the NH3 line width of ~ 0.5 with a general trend of a decreasing virial parameter with increasing gas mass. We obtain a rising NH3 (1, 1)/N2H+ line-width ratio with increasing rotational temperature. Conclusions. A comparison of NH3 line parameters of ATLASGAL clumps to cores in nearby molecular clouds reveals smaller velocity dispersions in low-mass than high-mass star-forming regions and a warmer surrounding of ATLASGAL clumps than the surrounding of low-mass cores. The NH3 (1, 1) inversion transition of 49% of the sources shows hyperfine structure anomalies. The intensity ratio of the outer hyperfine structure lines with a median of 1.27 ± 0.03 and a standard deviation of 0.45 is significantly higher than 1, while the intensity ratios of the inner satellites with a median of 0.9 ± 0.02 and standard deviation of 0.3 and the sum of the inner and outer hyperfine components with a median of 1.06 ± 0.02 and standard deviation of 0.37 are closer to 1.

12CO(J=3→2) detections in bulges of low surface brightness galaxies with APEX

AbstractUsing the APEX sub-millimeter telescope we have detected for the first time the CO rotational transition 12CO(J=3→2) in two of five low surface brightness galaxies. For galaxies with positive detection, the emission is detected in their bulges, with measured gas velocity dispersion of about 80 km/s and observed main-beam brightness temperature TM B ~ 10 mK. Using a standard CO to H2 conversion factor, we are able to estimate molecular gas masses for LSBs with positive detections, and upper limits for those LSBs with negative detections. Assuming a higher gas temperature for the generation of the 12CO(J=3→2) line compared to that for the 12CO(J=1→0) one, results suggest that a warm molecular gas component is present in bulges, indicating a radiation field preventing the formation of large cooler amounts of molecular gas, compared to high surface brightness galaxies with higher metallicity and likely more dust.

Detection of CS emission towards Cygnus OB2 No. 12

Aims.The CS (J = 2-1) line was searched at locations with brightest 13CO (J=1-0) emissions in the region in front of the star Cyg OB2 No. 12. Methods.The observations were made with the 20-m millimeter wave telescope at Onsala using a 1024-channel autocorrelator with a resolution of 50 kHz (0.14 km s-1). Results.The line was detected only in one position (core B) with main beam brightness temperature $T_{\rm MB} = 0.15(2)$ K at $v_{\rm LSR} = 11.4(1)$ km s-1. Conclusions.The line excitation analysis suggests that core B could be a Bok globule in consideration of its morphology, chemistry and physical conditions.

A spectral survey of the Orion Nebula from 455–507 GHz

The results of a submillimetre wavelength spectral line survey between 455.1-507.4 GHz of the Orion-KL hot cloud core are reported. A total of 254 lines were detected to a main beam brightness temperature sensitivity Tmb 1-3 K. The detected lines are identified as being associated with 30 dierent molecular species or their isotopomeric variants. The strongest line detected was the J= 4-3 transition of the CO molecule. Apart from abundant diatomic rotors such as CO and CS, the spectrum is dominated by SO, SO2 and CH3OH and large organic molecules such as (CH3)2O, CH3CN, C2H3CN, C2H5CN and HCOOCH3 which make up72% of the total number of lines; unidentified lines 13%; and other lines the remaining 15% of the total. Rotational temperatures and column densities derived using standard rotation diagram analysis techniques were found to range from 70-300 K, and 10 14 -10 17 cm 2 respectively.

A Line Survey of Orion‐KL from 607 to 725 GHz

With the Caltech Submillimeter Telescope, we have performed an unbiased line survey of Orion-KL in the frequency range 607-725 GHz. We were able to identify lines down to a threshold of 1-2 K in main beam brightness temperature units, and we found 1064 spectral features consisting of 2032 lines, partially blended. Apart from the abundant diatomic rotors such as CO, CS, SO, the spectrum is dominated by CH3OH and SO2, both in terms of numbers of lines and integrated flux. The number of unidentified lines is 155 or 14%. We also report the tentative identification of the new molecule SiH in our data. For some complex organic molecules, we find rotation temperatures and column densities which are much higher than those found in earlier studies. It is likely the cause of this is a significant contribution from a very compact, hot component of the Orion molecular cloud core which was not visible in lower frequency surveys.

Methods and constraints for the correction of the error beam pick-up in single dish radio observations

The beam pattern of a single dish radio telescope is given by the main beam and additional components at larger angles, usually called error beam or stray pattern. The latter have relatively small peak amplitudes (typ. below -25 dB), depending on the rms surface error of the primary reflector. However, because of their large angular extent, they are sensitive to extended sources, and a significant fraction of the observed intensity can result from error beam pick-up. For (sub-)mm observations suffering from error beam pick-up we introduce a new temperature scale for the corrected data, the corrected main beam brightness temperature T mb,c , which provides a better approximation to the intensity detected by the main beam than the commonly used antenna temperature and main beam brightness temperature . We consider two different correction methods. The first method uses complementary observations obtained with a smaller telescope. Smeared to the angular resolution of the error beam pattern they provide an estimate of the error beam pick-up in the observations of the large telescope. For the second method, the error beam pick-up is de-convolved from the observed map in Fourier space. The requirements for both correction methods and their advantages and limitations are discussed in detail. Both correction methods require additional observations, unless the full spatial extent of the emission is observed. We find that the de-convolution method is attractive for the correction of fully sampled maps with an angular extent much larger than the error beam pattern. For smaller maps and more sparsely sampled observations, the subtraction method is favorable, because the additional observations with a small telescope are less time consuming.

The Apparent Sizes of the 62–61E‐Type Methanol Masers in OMC‐1

The 62-61 E transition of CH3OH has been observed toward the Orion KL region with an angular resolution of 007 and frequency resolution of 12 kHz (0.15 km s-1) at two epochs, 1 year apart. The observations have a sensitivity of 1 Jy beam-1 (corresponding to a main beam brightness temperature of 4 × 105 K). Only the brightest masers previously measured with 3'' resolution are detected; these are resolved into several bright features. The brightness temperatures of the detected masers range from 2 × 106 to 3 × 107 K, with apparent sizes in the range 22-56 AU.

Erratum - Hot Gas in the Nucleus of M82 - 12CO/ and 13CO/ J=3-2 Observations

view Abstract Citations (3) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Erratum - Hot Gas in the Nucleus of M82 - 12CO/ and 13CO/ J=3-2 Observations Tuner, J. L. ; Martin, R. N. ; Ho, P. T. P. Abstract We report observations of the J = 3-2 transitions of ^12^CO and ^13^CO in the starburst galaxy M82. We have detected and mapped the ^12^CO J = 3-2 transition in the nuclear region at 22" resolution. The high main beam brightness temperature of the line, 6.4 K, when compared to the J = 1-0 and J = 2-1 intensities, requires a hot (T_k_ >~ 40 K), moderately optically thin gas. We place a lower limit of ~ 15 off the I_CO_/I__^13^CO_, implying that τ_32_ <~ 6 and τ_10_ < 1 for this warm component. There are ~ 10^8^ M_sun_of warm molecular gas within a radius of 360 pc of M82. The low optical depths and high densities required to excite the J = 3-2 transition may imply sheetlike or filamentary clumping. The pressure in the molecular gas is high, nT ~ 10^6^ - 10^7^ cm^-3^ K. The unusually high pressure and filamentary nature of the interstellar medium in M82 are probably related to winds and shocks originating in the starburst. Publication: The Astrophysical Journal Pub Date: February 1991 DOI: 10.1086/169664 Bibcode: 1991ApJ...367..677T full text sources ADS | data products NED (1) Related Materials (1) Original Paper: 1990ApJ...351..418T

Hot gas in the nucleus of M82 - (C-12)O and (C-13)O J = 3-2 observations

view Abstract Citations (19) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hot gas in the nucleus of M 82 : 12CO and 13CO J=3-2 observations. Turner, Jean L. ; Martin, Robert N. ; Ho, Paul T. P. Abstract Observations of the J = 3-2 transitions of (C-12)O and (C-13)O in the starburst galaxy M82 are reported. The (C-12)O J = 3-2 transition in the nuclear region is detected and mapped at 22-arcsec resolution. The high main beam brightness temperature of the line, 6.4 K, when compared to the J = 1-0 and J = 2-1 intensities, requires a hot moderately optically thin gas. There are about 10 to the 8th solar masses of warm molecular gas within a radius of 360 pc of M82. The low optical depths and high densities required to excite the J = 3-2 transition may imply sheetlike or filamentary clumping. Publication: The Astrophysical Journal Pub Date: March 1990 DOI: 10.1086/168477 Bibcode: 1990ApJ...351..418T Keywords: Galactic Nuclei; Interstellar Gas; Starburst Galaxies; Carbon Monoxide; Early Stars; Star Formation; Astrophysics full text sources ADS | data products SIMBAD (1) NED (1) Related Materials (1) Erratum: 1991ApJ...367..677T