Observations of 115 GHz CO Emission Towards the Carina Nebula

1984 ◽  
Vol 5 (4) ◽  
pp. 552-557 ◽  
Author(s):  
J. B. Whiteoak ◽  
Robina E. Otrupcek
Keyword(s):  
Interstellar Medium ◽  
Radio Telescope ◽  
Molecular Clouds ◽  
Line Emission ◽  
Microwave Frequencies ◽  
Carina Nebula ◽  
Co Emission ◽  
Csiro Division

We have carried out a survey of the 115 GHz CO emission (J = 1→0 transition) towards the Carina nebula (NGC 3372) using the Epping 4 m radio telescope of the CSIRO Division of Radiophysics. Of all the molecules detected in the interstellar medium CO is perhaps the best tracer of molecular clouds. It is an abundant molecule (second only to H2) and its line emission at microwave frequencies occurs at relatively low excitation.

Observations of the 1→0 Transition of CO Towards Southern HII Regions

1982 ◽  
Vol 4 (4) ◽  
pp. 434-440 ◽  
Author(s):  
J. B. Whiteoak ◽  
Robina E. Otrupcek ◽  
C. J. Rennie
Keyword(s):  
Radio Telescope ◽  
Molecular Cloud ◽  
Milky Way ◽  
Line Emission ◽  
Hii Regions ◽  
Hii Region ◽  
Giant Molecular Cloud ◽  
Molecular Lines ◽  
Csiro Division

The 4-m radio telescope of the CSIRO Division of Radiophysics at Epping is being used to survey the line emission associated with the 1→0 transition of CO (rest frequency 115.271 GHz) in the southern Milky Way. The programme includes mapping the CO distribution across giant molecular-cloud/HII-region complexes. As a first stage the emission has been observed towards bright southern HII regions. These results will not only serve as a basis for future extensive mapping but will also provide data which is directly comparable with observations of other molecular lines that have been made towards the HII regions.

scholarly journals Structure of photodissociation fronts in star-forming regions revealed by Herschel observations of high-J CO emission lines

2018 ◽  
Vol 615 ◽  
pp. A129 ◽  
Author(s):  
C. Joblin ◽  
E. Bron ◽  
C. Pinto ◽  
P. Pilleri ◽  
F. Le Petit ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Massive Star ◽  
Line Emission ◽  
Massive Star Formation ◽  
Star Forming ◽  
Star Forming Regions ◽  
Key Species ◽  
Two Parameters ◽  
Co Emission

Context. In bright photodissociation regions (PDR) associated with massive star formation, the presence of dense “clumps” that are immersed in a less dense interclump medium is often proposed to explain the difficulty of models to account for the observed gas emission in high-excitation lines. Aims. We aim to present a comprehensive view of the modelling of the CO rotational ladder in PDRs, including the high-J lines that trace warm molecular gas at PDR interfaces. Methods. We observed the 12CO and 13CO ladders in two prototypical PDRs, the Orion Bar and NGC 7023 NW using the instruments onboard Herschel. We also considered line emission from key species in the gas cooling of PDRs (C+, O, and H2) and other tracers of PDR edges such as OH and CH+. All the intensities are collected from Herschel observations, the literature and the Spitzer archive and were analysed using the Meudon PDR code. Results. A grid of models was run to explore the parameter space of only two parameters: thermal gas pressure and a global scaling factor that corrects for approximations in the assumed geometry. We conclude that the emission in the high-J CO lines, which were observed up to Jup = 23 in the Orion Bar (Jup = 19 in NGC 7023), can only originate from small structures with typical thicknesses of a few 10−3 pc and at high thermal pressures (Pth ~ 108 K cm−3). Conclusions. Compiling data from the literature, we find that the gas thermal pressure increases with the intensity of the UV radiation field given by G0, following a trend in line with recent simulations of the photoevaporation of illuminated edges of molecular clouds. This relation can help to rationalise the analysis of high-J CO emission in massive star formation and provides an observational constraint for models which study stellar feedback on molecular clouds.

scholarly journals Major impact from a minor merger

2018 ◽  
Vol 615 ◽  
pp. A122 ◽  
Author(s):  
S. König ◽  
S. Aalto ◽  
S. Muller ◽  
J. S. Gallagher III ◽  
R. J. Beswick ◽  
...  
Keyword(s):  
Star Formation ◽  
Brightness Temperature ◽  
Central Region ◽  
Molecular Clouds ◽  
Molecular Gas ◽  
Transfer Model ◽  
Dense Gas ◽  
Giant Molecular Clouds ◽  
Minor Mergers ◽  
Co Emission

Context. Minor mergers are important processes contributing significantly to how galaxies evolve across the age of the Universe. Their impact on the growth of supermassive black holes and star formation is profound – about half of the star formation activity in the local Universe is the result of minor mergers. Aims. The detailed study of dense molecular gas in galaxies provides an important test of the validity of the relation between star formation rate and HCN luminosity on different galactic scales – from whole galaxies to giant molecular clouds in their molecular gas-rich centers. Methods. We use observations of HCN and HCO+ 1−0 with NOEMA and of CO3−2 with the SMA to study the properties of the dense molecular gas in the Medusa merger (NGC 4194) at 1′′ resolution. In particular, we compare the distribution of these dense gas tracers with CO2−1 high-resolution maps in the Medusa merger. To characterize gas properties, we calculate the brightness temperature ratios between the three tracers and use them in conjunction with a non-local thermodynamic equilibrium (non-LTE) radiative line transfer model. Results. The gas represented by HCN and HCO+ 1−0, and CO3−2 does not occupy the same structures as the less dense gas associated with the lower-J CO emission. Interestingly, the only emission from dense gas is detected in a 200 pc region within the “Eye of the Medusa”, an asymmetric 500 pc off-nuclear concentration of molecular gas. Surprisingly, no HCN or HCO+ is detected for the extended starburst of the Medusa merger. Additionally, there are only small amounts of HCN or HCO+ associated with the active galactic nucleus. The CO3−2/2−1 brightness temperature ratio inside “the Eye” is ~2.5 – the highest ratio found so far – implying optically thin CO emission. The CO2−1/HCN 1−0 (~9.8) and CO2−1/HCO+ 1−0 (~7.9) ratios show that the dense gas filling factor must be relatively high in the central region, consistent with the elevated CO3−1/2−1 ratio. Conclusions. The line ratios reveal an extreme, fragmented molecular cloud population inside the Eye with large bulk temperatures (T > 300 K) and high gas densities (n(H2) > 104 cm-3). This is very different from the cool, self-gravitating structures of giant molecular clouds normally found in the disks of galaxies. The Eye of the Medusa is found at an interface between a large-scale minor axis inflow and the central region of the Medusa. Hence, the extreme conditions inside the Eye may be the result of the radiative and mechanical feedback from a deeply embedded, young and massive super star cluster formed due to the gas pile-up at the intersection. Alternatively, shocks from the inflowing gas entering the central region of the Medusa may be strong enough to shock and fragment the gas. For both scenarios, however, it appears that the HCN and HCO+ dense gas tracers are not probing star formation, but instead a post-starburst and/or shocked ISM that is too hot and fragmented to form newstars. Thus, caution is advised in taking the detection of emission from dense gas tracers as evidence of ongoing or imminent star formation.

scholarly journals Challenges and Techniques for Simulating Line Emission

Galaxies ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 100 ◽  
Author(s):  
Karen Olsen ◽  
Andrea Pallottini ◽  
Aida Wofford ◽  
Marios Chatzikos ◽  
Mitchell Revalski ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Emission Line ◽  
Line Emission ◽  
Emission Lines ◽  
Synthetic Spectra ◽  
Recent Advances ◽  
The Future ◽  
Important Quality ◽  
Circumgalactic Medium

Modeling emission lines from the millimeter to the UV and producing synthetic spectra is crucial for a good understanding of observations, yet it is an art filled with hazards. This is the proceedings of “Walking the Line”, a 3-day conference held in 2018 that brought together scientists working on different aspects of emission line simulations, in order to share knowledge and discuss the methodology. Emission lines across the spectrum from the millimeter to the UV were discussed, with most of the focus on the interstellar medium, but also some topics on the circumgalactic medium. The most important quality of a useful model is a good synergy with observations and experiments. Challenges in simulating line emission are identified, some of which are already being worked upon, and others that must be addressed in the future for models to agree with observations. Recent advances in several areas aiming at achieving that synergy are summarized here, from micro-physical to galactic and circum-galactic scale.

scholarly journals Molecular clouds photoevaporation and FIR line emission

2017 ◽  
pp. stx180 ◽  
Author(s):  
L. Vallini ◽  
A. Ferrara ◽  
A. Pallottini ◽  
S. Gallerani
Keyword(s):  
Molecular Clouds ◽  
Line Emission

Discussion session on star formation, molecular clouds and the interstellar medium

1994 ◽  
Vol 217 (1-2) ◽  
pp. 227-230
Author(s):  
Karen M. Strom ◽  
Lennart Nordh ◽  
Eli Dwek
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Molecular Clouds ◽  
Discussion Session

scholarly journals Understanding biases in measurements of molecular cloud kinematics using line emission

2020 ◽  
Vol 498 (2) ◽  
pp. 2440-2455
Author(s):  
Yuxuan (宇轩) Yuan (原) ◽  
Mark R Krumholz ◽  
Blakesley Burkhart
Keyword(s):  
Magnetic Field ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Velocity Dispersion ◽  
Signal To Noise Ratio ◽  
Line Emission ◽  
Molecular Line ◽  
Velocity Dispersions ◽  
Cloud Kinematics ◽  
Measurement Biases

ABSTRACT Molecular line observations using a variety of tracers are often used to investigate the kinematic structure of molecular clouds. However, measurements of cloud velocity dispersions with different lines, even in the same region, often yield inconsistent results. The reasons for this disagreement are not entirely clear, since molecular line observations are subject to a number of biases. In this paper, we untangle and investigate various factors that drive linewidth measurement biases by constructing synthetic position–position–velocity cubes for a variety of tracers from a suite of self-gravitating magnetohydrodynamic simulations of molecular clouds. We compare linewidths derived from synthetic observations of these data cubes to the true values in the simulations. We find that differences in linewidth as measured by different tracers are driven by a combination of density-dependent excitation, whereby tracers that are sensitive to higher densities sample smaller regions with smaller velocity dispersions, opacity broadening, especially for highly optically thick tracers such as CO, and finite resolution and sensitivity, which suppress the wings of emission lines. We find that, at fixed signal-to-noise ratio, three commonly used tracers, the J = 4 → 3 line of CO, the J = 1 → 0 line of C18O, and the (1,1) inversion transition of NH3, generally offer the best compromise between these competing biases, and produce estimates of the velocity dispersion that reflect the true kinematics of a molecular cloud to an accuracy of $\approx 10{{\ \rm per\ cent}}$ regardless of the cloud magnetic field strengths, evolutionary state, or orientations of the line of sight relative to the magnetic field. Tracers excited primarily in gas denser than that traced by NH3 tend to underestimate the true velocity dispersion by $\approx 20{{\ \rm per\ cent}}$ on average, while low-density tracers that are highly optically thick tend to have biases of comparable size in the opposite direction.

scholarly journals INTERSTELLAR MEDIUM AND DECAMETER RADIO SPECTROSCOPY

2021 ◽  
Vol 26 (4) ◽  
pp. 314-325
Author(s):  
S. V. Stepkin ◽  
◽  
O. O. Konovalenko ◽  
Y. V. Vasylkivskyi ◽  
D. V. Mukha ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Radio Telescope ◽  
Radio Astronomy ◽  
Low Frequency ◽  
Spectral Lines ◽  
Physical Parameters ◽  
Recombination Mechanism ◽  
Radio Recombination Lines ◽  
Radio Spectroscopy ◽  
Correlation Spectrum

Purpose: The analytical review of the main results of research in the new direction of the low-frequency radio astronomy, the interstellar medium radio spectroscopy at decameter waves, which had led to astrophysical discovery, recording of the radio recombination lines in absorption for highly excited states of interstellar carbon atoms (more than 600). Design/methodology/approach: The UTR-2 world-largest broadband radio telescope of decameter waves optimally connected with the digital correlation spectrum analyzers has been used. Continuous modernization of antenna system and devices allowed increasing the analysis band from 100 kHzto 24 MHz and a number of channels from 32 to 8192. The radio telescope and receiving equipment with appropriate software allowed to have a long efficient integration time enough for a large line series simultaneously with high resolution, noise immunity and relative sensitivity. Findings: A new type of interstellar spectral lines has been discovered and studied, the interstellar carbon radio recombination lines in absorption for the record high excited atoms with principal quantum numbers greater than 1000. The line parameters (intensity, shape, width, radial velocity) and their relation ship with the interstellar medium physical parameters have been determined. The temperature of line forming regions is about 100 K, the electron concentration up to 0.1 cm–3 and the size of a line forming region is about 10 pc. For the first time, radio recombination lines were observed in absorption. They have significant broadening and are amplified by the dielectronic-like recombination mechanism and are also the lowest frequency lines in atomic spectroscopy. Conclusions: The detected low-frequency carbon radio recombination lines and their observations have become a new highly effective tool for the cold partially ionized interstellar plasma diagnostics. Using them allows obtaining the information which is not available with the other astrophysical methods. For almost half a century of their research, a large amount of hardware-methodical and astrophysical results have been obtained including a record number of Galaxy objects, where there levant lines have been recorded. The domestic achievements have stimulated many theoretical and experimental studies in other countries, but the scientific achievements of Ukrainian scientists prove the best prospects for further development of this very important area of astronomical science. Key words: low-frequency radio astronomy; radio telescope; interstellar medium; radio recombination lines; carbon; hydrogen; spectral analyzer

Sign in / Sign up

Export Citation Format

Share Document