scholarly journals Origin of hydrogen fluoride emission in the Orion Bar

2019 ◽  
Vol 631 ◽  
pp. A117 ◽  
Author(s):  
Ü. Kavak ◽  
F. F. S. van der Tak ◽  
A. G. G. M. Tielens ◽  
R. F. Shipman
Keyword(s):  
Hydrogen Fluoride ◽  
Galactic Nuclei ◽  
Ionization Front ◽  
Molecular Gas ◽  
Thermal Excitation ◽  
Small Contribution ◽  
Non Local ◽  
Density Map ◽  
Orion Trapezium ◽  
Fluoride Emission

Context. The hydrogen fluoride (HF) molecule is seen in absorption in the interstellar medium (ISM) along many lines of sight. Surprisingly, it is observed in emission toward the Orion Bar, which is an interface between the ionized region around the Orion Trapezium stars and the Orion molecular cloud. Aims. We aim to understand the origin of HF emission in the Orion Bar by comparing its spatial distribution with other tracers. We examine three mechanisms to explain the HF emission: thermal excitation, radiative dust pumping, and chemical pumping. Methods. We used a Herschel/HIFI strip map of the HF J = 1 → 0 line, covering 0.5′ by 1.5′ that is oriented perpendicular to the Orion Bar. We used the RADEX non-local thermodynamic equilibrium (non-LTE) code to construct the HF column density map. We use the Meudon PDR code to explain the morphology of HF. Results. The bulk of the HF emission at 10 km s−1 emerges from the CO-dark molecular gas that separates the ionization front from the molecular gas that is deeper in the Orion Bar. The excitation of HF is caused mainly by collisions with H2 at a density of 105 cm−3 together with a small contribution of electrons in the interclump gas of the Orion Bar. Infrared pumping and chemical pumping are not important. Conclusions. We conclude that the HF J = 1 → 0 line traces CO-dark molecular gas. Similarly, bright photodissociation regions associated with massive star formation may be responsible for the HF emission observed toward active galactic nuclei.

scholarly journals SDSS J211852.96−073227.5: The first non-local, interacting, late-type intermediate Seyfert galaxy with relativistic jets

2020 ◽  
Vol 636 ◽  
pp. L12 ◽  
Author(s):  
E. Järvelä ◽  
M. Berton ◽  
S. Ciroi ◽  
E. Congiu ◽  
A. Lähteenmäki ◽  
...  
Keyword(s):  
Near Infrared ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Seyfert Galaxy ◽  
Late Type ◽  
Host Galaxies ◽  
Relativistic Jets ◽  
Galaxy Interactions ◽  
Non Local ◽  
First Time

It has been often suggested that a tangible relation exists between relativistic jets in active galactic nuclei (AGN) and the morphology of their host galaxies. In particular, relativistic jets may commonly be related to merging events. Here we present for the first time a detailed spectroscopic and morphological analysis of a Seyfert galaxy, SDSS J211852.96−073227.5, at z = 0.26. This source has previously been classified as a gamma-ray emitting narrow-line Seyfert 1 galaxy. We re-observed it with the 6.5 m Clay Telescope and these new, high-quality spectroscopic data have revealed that it is actually an intermediate-type Seyfert galaxy. Furthermore, the results of modelling the Ks-band near-infrared images obtained with the 6.5 m Baade Telescope indicate that the AGN is hosted by a late-type galaxy in an interacting system, strengthening the suggested connection between galaxy interactions and relativistic jets.

scholarly journals Gas Dynamics and Active Phenomena in Galactic Nuclei: M100 and M94

1996 ◽  
Vol 157 ◽  
pp. 247-249
Author(s):  
Kazushi Sakamoto ◽  
Takeo Minezaki ◽  
Keiichi Wada ◽  
Sachiko Okumura ◽  
Yukiyasu Kobayashi
Keyword(s):  
Gravitational Potential ◽  
Gas Dynamics ◽  
Molecular Clouds ◽  
Galactic Nuclei ◽  
Trace Gas ◽  
Molecular Gas ◽  
Barred Galaxies ◽  
Nir Imaging ◽  
Oval Distortion

Since molecular gas fuels AGNs and molecular clouds form stars, understanding of molecular gas dynamics is a key to the understanding of active phenomena (such as starbursts and AGNs) in galactic nuclei. To study gas dynamics in weakly barred galaxies, we made CO interferometry (to trace gas) and NIR imaging (to trace stars) toward two nearby SAB galaxies M100 and M94. Each galaxy has a small stellar nuclear bar and also has an outer bar or oval distortion, thus suitable for the study of gas dynamics in a barred gravitational potential. Observations were made using Nobeyama Millimeter Array (NMA) and the IRcamera PICNIC installed at the ISAS 1.3 m telescope.

scholarly journals A Helical Magnetic Field Model of the Jets

1987 ◽  
Vol 115 ◽  
pp. 381-383
Author(s):  
T. Maruyama ◽  
M. Fujimoto
Keyword(s):  
Magnetic Field ◽  
Active Galactic Nuclei ◽  
Lorentz Force ◽  
Field Model ◽  
Galactic Nuclei ◽  
Molecular Gas ◽  
Magnetic Field Model ◽  
Helical Magnetic Field ◽  
Jet Axis

A hydromagnetic model is presented for the bipolar flow of molecular gas from newborn stars and for the radio jet emerging out of active galactic nuclei. We assume a tightly-twisted helical magnetic field in the jet, which can collimate and accelerate the gas along the jet axis. The Lorentz force is also shown to rotate the gas around it.

scholarly journals THE CENTRAL MOLECULAR GAS STRUCTURE IN LINERS WITH LOW-LUMINOSITY ACTIVE GALACTIC NUCLEI: EVIDENCE FOR GRADUAL DISAPPEARANCE OF THE TORUS

2012 ◽  
Vol 763 (1) ◽  
pp. L1 ◽  
Author(s):  
F. Müller-Sánchez ◽  
M. A. Prieto ◽  
M. Mezcua ◽  
R. I. Davies ◽  
M. A. Malkan ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Molecular Gas ◽  
Gradual Disappearance

scholarly journals 5.11. Dense molecular gas in nearby galaxies

1998 ◽  
Vol 184 ◽  
pp. 231-233 ◽  
Author(s):  
Y. Gao ◽  
P.M. Solomon
Keyword(s):  
Dipole Moment ◽  
Surface Brightness ◽  
Galactic Nuclei ◽  
Molecular Gas ◽  
Galactic Disks ◽  
Central Regions ◽  
Nearby Galaxies ◽  
Gas Properties

HCN, one of the most abundant high dipole-moment molecules (traces molecular gas at densities ≳ 3 × 104 cm−3 whereas CO traces at ∼ 500 cm−3), has only been detected in ∼ 25 galaxies, primarily towards the galactic nuclei (Solomon et al. 1992; Nguyen-Q-Rieu et al. 1992; Helfer & Blitz 1993; Aalto et al. 1995). Dense molecular gas properties in “normal” galactic disks, as compared to the centers of “normal” spirals, starbursts, and luminous IR galaxies are not clear. As part of a large HCN survey in 60 galaxies (Gao 1996; Gao & Solomon 1997), we present here HCN observations in central regions of a few nearby galaxies. HCN was mapped at least along the major axes in the inner disks to determine the total HCN luminosity, the distribution with radius of HCN emission, and of the surface brightness ratio of SBR ≡ IHCN/ICO.

scholarly journals 5.13. High-density-and-temperature circumnuclear molecular torus in M51

1998 ◽  
Vol 184 ◽  
pp. 237-238
Author(s):  
S. Matsushita ◽  
K. Kohno ◽  
B. Vila-Vilaro ◽  
R. Kawabe ◽  
T. Tosaki
Keyword(s):  
Active Galactic Nuclei ◽  
Molecular Clouds ◽  
Galactic Nuclei ◽  
Active Galaxies ◽  
High Density ◽  
Molecular Gas ◽  
Physical Conditions

It is very important to know the physical conditions of circumnuclear molecular gas in order to understand the nature of Active Galactic Nuclei (AGN), since the circumnuclear molecular gas in active galaxies might be directly affected by or is affecting the activity of nucleus. To investigate the physical conditions of the molecular clouds in detail, multi-line observations with millimeter arrays are essential.

Macromolecular phasing with SHELXE

2002 ◽  
Vol 217 (12) ◽  
Author(s):  
G. M. Sheldrick
Keyword(s):  
Electron Density ◽  
Heavy Atom ◽  
Small Contribution ◽  
Initial Electron ◽  
Density Map ◽  
Electron Density Map

AbstractSHELXE was designed to provide a simple, fast and robust route from substructure sites found by the program SHELXD to an initial electron density map, if possible with an indication as to which heavy-atom enantiomorph is correct. This should be understood as a small contribution to

A Discussion on solar studies with special reference to space observations - Abundance of iron in the photosphere

1971 ◽  
Vol 270 (1202) ◽  
pp. 23-28 ◽  
Keyword(s):  
Temperature Distribution ◽  
Absorption Coefficient ◽  
Thermodynamic Equilibrium ◽  
Local Thermodynamic Equilibrium ◽  
Thermal Excitation ◽  
Solar Photosphere ◽  
Continuous Absorption ◽  
Non Local ◽  
Atomic States ◽  
Lower Chromosphere

About ten years ago astrophysics was haunted by a nightmare called non-local thermodynamic equilibrium (n.l.t.e.). Some astrophysicists, notably Pecker (1959) and R .N . Thomas, began to doubt whether the well-known formulae for thermal excitation and ionization could be applied with sufficient accuracy to, for example, the solar photosphere. If that contention had been true, it would have meant that all solar abundance determinations were affected by large errors. On the other hand, it would have been a hopeless enterprise to develop a purely statistical theory for the distribution of the atomic states, for example, of neutral iron under the influence of the complicated field of radiation in the photosphere together with all sorts of collisions. After preliminary studies (Unsold 1962) had made it probable that in reality deviations from local thermodynamic equilibrium (l.t.e) were quite negligible in the photosphere and the lower chromosphere (but probably not so in the higher chromosphere and certainly not in the corona), Holweger (1967) proceeded to construct an empirical model of the solar photosphere (and lower chromosphere) in l.t.e. Since it was known (Pagel 1959; Unsold 1962; Lambert & Pagel 1968) that the negative hydrogen ion in any case conformed to the laws of l.t.e., the continuous spectrum and its centre limb variation could be used for obtaining the temperature distribution T(r0) for about 0.05 < t0 < 2. Just extrapolating this temperature distribution towards smaller r 0—as many authors have done would lead to very serious errors. So T ( t0) out to t0 10-6 was obtained using the observed intensities within strong lines, where the line absorption coefficient is much larger than the continuous absorption coefficient.

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