scholarly journals Probe of the Nearby Interstellar Medium by the Vacant Line of Sight to β CMa

1984 ◽  
Vol 81 ◽  
pp. 80-83 ◽  
Author(s):  
C. Gry ◽  
D.G. York ◽  
A. Vidal-Madjar
Keyword(s):  
Interstellar Medium ◽  
Line Of Sight ◽  
The Sun ◽  
Ionization State ◽  
Ionization Equilibrium ◽  
Hii Region

AbstractThe line of sight to βCMa has been probed by Copernicus observations. This particular line of sight is remarkable for the low mean densities. We find n̄H ∼ .002 cm-3. However we can distinguish two separate regions:1) A local nearby HI region extends over a few parsecs from the sun with a density of the order of 0.1 cm-3 and a temperature of 11000 to 12500 K.2) An HII region lies somewhere beyond the HI region and is spread over about 60pc. Its total hydrogen mean density is of the same order as the HI region, i.e. of ∼0.1 cm-3 and it contains only elements in low ionization state. All the data are coherent with the picture of a cloud in ionization equilibrium at T ∼ 23 000° K.

scholarly journals Is There a Polarization Horizon?

Galaxies ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 129 ◽  
Author(s):  
Alex Hill
Keyword(s):  
Interstellar Medium ◽  
Density Distribution ◽  
High Frequency ◽  
Electron Density Distribution ◽  
Low Frequency ◽  
Line Of Sight ◽  
Low Frequencies ◽  
Hii Region ◽  
Warm Ionized Medium ◽  
Spiral Arm

Modern radio spectrometers make measurement of polarized intensity as a function of Faraday depth possible. I investigate the effect of depolarization along a model line of sight. I model sightlines with two components informed by observations: a warm ionized medium with a lognormal electron density distribution and a narrow, denser component simulating a spiral arm or Hii region, all with synchrotron-emitting gas mixed in. I then calculate the polarized intensity from 300–1800 MHz and calculate the resulting Faraday depth spectrum. The idealized synthetic observations show far more Faraday complexity than is observed in Global Magneto-Ionic Medium Survey observations. In a model with a very nearby Hii region observed at low frequencies, most of the effects of a “depolarization wall” are evident: the Hii region depolarizes background emission, and less (but not zero) information from beyond the Hii region reaches the observer. In other cases, the effects are not so clear, as significant amounts of information reach the observer even through significant depolarization, and it is not clear that low-frequency observations sample largely different volumes of the interstellar medium than high-frequency observations. The observed Faraday depth can be randomized such that it does not always have any correlation with the true Faraday depth.

scholarly journals Deuterium Abundance in the Local Interstellar Medium

1984 ◽  
Vol 81 ◽  
pp. 84-88
Author(s):  
R. Ferlet ◽  
C. Gry ◽  
A. Vidal-Madjar
Keyword(s):  
Interstellar Medium ◽  
Present Situation ◽  
Line Of Sight ◽  
Interstellar Space ◽  
The Sun ◽  
Local Interstellar Medium ◽  
The One

AbstractWe underline the present situation of deuterium abundance evaluation in interstellar space and show that it should be < 10-5. Studiing in more detail the λ Sco line of sight and having observed two Nal interstellar components toward that star, we can show that the D/H evaluation made toward λ Sco is in fact related to the local interstellar medium (less than 10 pc from the sun). Because this evaluation is also < 10-5 it is in stricking contrast with the one made toward α Aur (D/H > 1.8 10-5 ) confirming the fact that the deuterium abundance in the local interstellar medium varies by at least a factor of two over few parsecs.

scholarly journals Simulating the interstellar medium of galaxies with radiative transfer, non-equilibrium thermochemistry, and dust

2020 ◽  
Vol 499 (4) ◽  
pp. 5732-5748 ◽  
Author(s):  
Rahul Kannan ◽  
Federico Marinacci ◽  
Mark Vogelsberger ◽  
Laura V Sales ◽  
Paul Torrey ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Galaxy Formation ◽  
State Of The Art ◽  
Complex Function ◽  
Ionization State ◽  
Radiation Fields ◽  
Stellar Feedback ◽  
Wide Range ◽  
Dust Distribution ◽  
Non Equilibrium

ABSTRACT We present a novel framework to self-consistently model the effects of radiation fields, dust physics, and molecular chemistry (H2) in the interstellar medium (ISM) of galaxies. The model combines a state-of-the-art radiation hydrodynamics module with a H  and He  non-equilibrium thermochemistry module that accounts for H2 coupled to an empirical dust formation and destruction model, all integrated into the new stellar feedback framework SMUGGLE. We test this model on high-resolution isolated Milky-Way (MW) simulations. We show that the effect of radiation feedback on galactic star formation rates is quite modest in low gas surface density galaxies like the MW. The multiphase structure of the ISM, however, is highly dependent on the strength of the interstellar radiation field. We are also able to predict the distribution of H2, that allow us to match the molecular Kennicutt–Schmidt (KS) relation, without calibrating for it. We show that the dust distribution is a complex function of density, temperature, and ionization state of the gas. Our model is also able to match the observed dust temperature distribution in the ISM. Our state-of-the-art model is well-suited for performing next-generation cosmological galaxy formation simulations, which will be able to predict a wide range of resolved (∼10 pc) properties of galaxies.

scholarly journals Unbound Close Stellar Encounters in the Solar Neighborhood

2022 ◽  
Vol 163 (2) ◽  
pp. 44
Author(s):  
Bradley M. S. Hansen
Keyword(s):  
Spectral Type ◽  
Main Sequence ◽  
Radial Distance ◽  
Solar Neighborhood ◽  
Limiting Factors ◽  
Line Of Sight ◽  
The Sun ◽  
Finite Set ◽  
Host Stars ◽  
Migration Event

Abstract We present a catalog of unbound stellar pairs, within 100 pc of the Sun, that are undergoing close, hyperbolic, encounters. The data are drawn from the GAIA EDR3 catalog, and the limiting factors are errors in the radial distance and unknown velocities along the line of sight. Such stellar pairs have been suggested to be possible events associated with the migration of technological civilizations between stars. As such, this sample may represent a finite set of targets for a SETI search based on this hypothesis. Our catalog contains a total of 132 close passage events, featuring stars from across the entire main sequence, with 16 pairs featuring at least one main-sequence star of spectral type between K1 and F3. Many of these stars are also in binaries, so that we isolate eight single stars as the most likely candidates to search for an ongoing migration event—HD 87978, HD 92577, HD 50669, HD 44006, HD 80790, LSPM J2126+5338, LSPM J0646+1829 and HD 192486. Among host stars of known planets, the stars GJ 433 and HR 858 are the best candidates.

scholarly journals Limits to Ionization-parameter Mapping as a Diagnostic of Hii Region Optical Depth

2021 ◽  
Vol 923 (1) ◽  
pp. 78
Author(s):  
Amit N. Sawant ◽  
Eric W. Pellegrini ◽  
M. S. Oey ◽  
Jesús López-Hernández ◽  
Genoveva Micheva
Keyword(s):  
Optical Depth ◽  
Strong Dependence ◽  
Light Flux ◽  
Emission Lines ◽  
Ionization State ◽  
Hii Region ◽  
Parameter Mapping ◽  
Ionization Structure ◽  
The Galaxy ◽  
Ionization Parameter

Abstract We employ ionization-parameter mapping (IPM) to infer the optical depth of H ii regions in the northern half of M33. We construct [O iii]λ5007/[O ii]λ3727 and [O iii]λ5007/[S ii]λ6724 ratio maps from narrowband images continuum-subtracted in this way, from which we classify the H ii regions by optical depth to ionizing radiation, based on their ionization structure. This method works relatively well in the low-metallicity regime, 12 + log ( O / H ) ≤ 8.4 , where [O iii]λ λ4959, 5007 is strong. However, at higher metallicities, the method breaks down due to the strong dependence of the [O iii]λ λ4959, 5007 emission lines on the nebular temperature. Thus, although O++ may be present in metal-rich H ii regions, these commonly used emission lines do not serve as a useful indicator of its presence, and hence the O ionization state. In addition, IPM as a diagnostic of optical depth is limited by spatial resolution. We also report a region of highly excited [O iii] extending over an area ∼1 kpc across and [O iii]λ5007 luminosity of 4.9 ± 1.5 × 1038 erg s−1, which is several times higher than the ionizing budget of any potential sources in this portion of the galaxy. Finally, this work introduces a new method for continuum subtraction of narrowband images based on the dispersion of pixels around the mode of the diffuse-light flux distribution. In addition to M33, we demonstrate the method on C iii]λ1909 imaging of Haro 11, ESO 338-IG004, and Mrk 71.

scholarly journals ISM simulations: an overview of models

2012 ◽  
Vol 10 (H16) ◽  
pp. 606-608 ◽  
Author(s):  
M. A. de Avillez ◽  
D. Breitschwerdt ◽  
A. Asgekar ◽  
E. Spitoni
Keyword(s):  
Dynamical System ◽  
Interstellar Medium ◽  
Dynamical Evolution ◽  
Dynamic Processes ◽  
Ionization Equilibrium ◽  
Collisional Ionization

AbstractUntil recently the dynamical evolution of the interstellar medium (ISM) was simulated using collisional ionization equilibrium (CIE) conditions. However, the ISM is a dynamical system, in which the plasma is naturally driven out of equilibrium due to atomic and dynamic processes operating on different timescales. A step forward in the field comprises a multi-fluid approach taking into account the joint thermal and dynamical evolutions of the ISM gas.

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