scholarly journals The Interstellar Gas in the Line of Sight to ϵ Canis Majoris

1996 ◽  
Vol 152 ◽  
pp. 299-299
Author(s):  
C. Gry ◽  
L. Lemonon ◽  
A. Vidal-Madjar ◽  
M. Lemoine ◽  
R. Ferlet
Keyword(s):  
Interstellar Medium ◽  
Hubble Space Telescope ◽  
Line Of Sight ◽  
Interstellar Gas ◽  
Local Bubble ◽  
Gas Density ◽  
Neutral Gas ◽  
Turbulence Velocity ◽  
Main Components ◽  
Local Cloud

We analyse Hubble Space Telescope GHRS observations of the interstellar medium in the direction to ϵ CMa, the strongest EUV source in the sky located 200 pc away in a region deficient in neutral gas. We show that the neutral gas density is the lowest yet measured in a galactic sight-line. The line of sight contains three main components among which the Local Cloud, and we derive their column densities, their velocity their temperature and their turbulence velocity. We discuss the ionization of the Local Cloud and we show that we detect the conductive interface between diffuse local cloud and the hot local bubble.

The Line of Sight of ϵ Canis Majoris: Depletion and Extent of the Local Cloud

1997 ◽  
Vol 166 ◽  
pp. 161-164
Author(s):  
Cécile Gry ◽  
Olivier Dupin
Keyword(s):  
High Resolution ◽  
Column Density ◽  
Uv Spectra ◽  
Line Of Sight ◽  
Gas Density ◽  
Neutral Gas ◽  
Local Cloud

AbstractWith new high resolution UV spectra of ϵ CMa we show that the gas column density in this sight-line is less than 4 1017 cm−2, that the neutral gas density is less than 10−5 cm−3 after the first 3 parsecs, and that the Local Cloud seems to be almost undepleted and to extend to no more than 0.6 pc in this direction.

Diffuse Ionized Gas in the β CMa Tunnel

1997 ◽  
Vol 166 ◽  
pp. 173-176
Author(s):  
Olivier Dupin ◽  
Cécile Gry
Keyword(s):  
Interstellar Medium ◽  
Low Density ◽  
Ionized Gas ◽  
Local Bubble ◽  
Diffuse Ionized Gas ◽  
Main Components ◽  
Collisional Ionization ◽  
Dust Grain

AbstractWe present HST observations of the interstellar medium toward the star β CMa known to be located in a low density extension of the Local Bubble. Most of the matter in the sight-line is ionized and clumped in two main components. One of them, as well as one of the components detected toward ϵ CMa, is mostly ionized and only slightly depleted. Their ionization ratios are compatible with collisional ionization at T~25 000 K. These clouds could have been ionized by shocks related to the Local Bubble creation and also responsible of some dust grain sputtering.

scholarly journals Atomic and Ionized Microstructures in the Diffuse Interstellar Medium

2018 ◽  
Vol 56 (1) ◽  
pp. 489-540 ◽  
Author(s):  
Snežana Stanimirović ◽  
Ellen G. Zweibel
Keyword(s):  
Interstellar Medium ◽  
Supernova Remnants ◽  
Spatial Scales ◽  
Physical Processes ◽  
Interstellar Gas ◽  
Local Bubble ◽  
Turbulent Dissipation ◽  
Atomic Structures ◽  
Discrete Structures ◽  
Turbulent Cascade

It has been known for half a century that the interstellar medium (ISM) of our Galaxy is structured on scales as small as a few hundred kilometers, more than 10 orders of magnitude smaller than typical ISM structures and energy input scales. In this review we focus on neutral and ionized structures on spatial scales of a few to ∼104AU, which appear to be highly overpressured, as these have the most important role in the dynamics and energy balance of interstellar gas: the tiny scale atomic structures (TSASs) and extreme scattering events (ESEs) as the most overpressured example of the tiny scale ionized structures (TSISs). We review observational results and highlight key physical processes at AU scales. We present evidence for and against microstructures as part of a universal turbulent cascade and as discrete structures, and we review their association with supernova remnants, the Local Bubble, and bright stars. We suggest a number of observational and theoretical programs that could clarify the nature of AU structures. TSAS and TSIS probe spatial scales in the range of what is expected for turbulent dissipation scales and are therefore of key importance for constraining exotic and not-well-understood physical processes that have implications for many areas of astrophysics. The emerging picture is one in which a magnetized, turbulent cascade, driven hard by a local energy source and acting jointly with phenomena such as thermal instability, is the source of these microstructures.

scholarly journals The Thermal Pressure of the Interstellar Medium Derived from Cloud Shadows in the Extreme Ultraviolet

1997 ◽  
Vol 166 ◽  
pp. 61-64 ◽  
Author(s):  
Thomas W. Berghöfer ◽  
Stuart Bowyer ◽  
Richard Lieu ◽  
Jens Knude
Keyword(s):  
Interstellar Medium ◽  
Extreme Ultraviolet ◽  
Optical Data ◽  
Interstellar Gas ◽  
Thermal Pressure ◽  
Deep Survey ◽  
X Ray Background ◽  
Almost All ◽  
New Evidence ◽  
Local Cloud

AbstractWe have used the Deep Survey telescope of EUVE to investigate shadows in the diffuse EUV/Soft X-ray background cast by clouds in the interstellar medium. We confirm the existence of a shadow previously reported, and provide evidence for two new shadows. We used IRAS data to identify the clouds producing these shadows and to determine their optical depth to EUV radiation. The EUV-absorbing clouds are optically thick in the EUV, and all EUV emission detected in the direction of these shadows must be produced from material in front of the clouds. We obtained new optical data to determine the distance to these clouds. We use a new differential cloud technique to obtain the pressure of the interstellar medium. These results do not depend on any zero level calibration of the data. Our results provide evidence that the pressure of the hot interstellar gas is the same in three different directions in the local interstellar medium, and is at least 8 times higher than derived for the local cloud surrounding our Sun. This provides new evidence for large thermal pressure imbalances in the local ISM, and directly contradicts the basic assumption of thermal pressure equilibrium used in almost all present models of the interstellar medium.

scholarly journals The Interstellar Abundance of Lead: Experimental Oscillator Strengths for Pb ii λ1203 and λ1433 and New Detections of Pb ii in the Interstellar Medium

2015 ◽  
Vol 11 (A29A) ◽  
Author(s):  
A. M. Ritchey ◽  
N. Heidarian ◽  
R. E. Irving ◽  
S. R. Federman ◽  
D. G. Ellis ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Hubble Space Telescope ◽  
Oscillator Strengths ◽  
Interstellar Gas ◽  
Lifetime Measurements ◽  
Space Telescope ◽  
Interstellar Grains ◽  
Imaging Spectrograph ◽  
Theoretical Results ◽  
Beam Foil

AbstractWe present the first experimentally determined oscillator strengths for the Pb ii transitions at 1203.6 Å and 1433.9 Å, obtained from lifetime measurements made using beam-foil techniques. We also present new detections of these lines in the interstellar medium from an analysis of archival spectra acquired by the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope. Our observations of the Pb ii λ1203 line represent the first detection of this transition in interstellar gas. Our experimental f-values for the Pb ii λ1203 and λ1433 transitions are consistent with recent theoretical results, including our own relativistic calculations, but are significantly smaller than previous values based on older calculations. Our new f-value for Pb ii λ1433 (0.321 ± 0.034) yields an increase in the interstellar abundance of Pb of 0.43 dex over estimates based on the f-value listed by Morton. With our revised f-values, and with our new detections of Pb ii λ1203 and λ1433, we find that the depletion of Pb onto interstellar grains is not nearly as severe as previously thought, and is very similar to the depletions seen for elements such as Zn and Sn, which have similar condensation temperatures.

scholarly journals The Interstellar Medium in Star Burst Galaxies

1987 ◽  
Vol 115 ◽  
pp. 614-614
Author(s):  
R. Genzel ◽  
J. B. Lugten ◽  
M. K. Crawford ◽  
D. M. Watson
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Line Emission ◽  
Far Infrared ◽  
High Rate ◽  
Interstellar Gas ◽  
Infrared Observations ◽  
Bolometric Luminosity ◽  
Neutral Gas ◽  
Molecular Lines

We report far-infrared observations of [0 I], [C II] and [O III] fine structure emission lines toward the nuclei of M82 and 7 other galaxies with a high rate of star formation. The far-infrared line emission is bright, contains about 0.5% of the bolometric luminosity in the central 60″, and is spatially concentrated toward the nuclei. In these galaxies between 10 and 30% of the interstellar gas near the nuclei is contained in a warm, atomic component. This atomic gas is probably located at the UV photodissociated surfaces of molecular clouds. The neutral gas in M82 has a temperature of ∼ 200 K, hydrogen density of ∼ 3 × 104 cm−3 and is very clumpy, indicating that the interstellar medium in this star burst galaxy is very different from that in the disk of our own galaxy. We discuss the implications of the infrared observations for the interpretation of mm molecular lines and for star formation at the nuclei of star burst galaxies.

scholarly journals Electrons in the supernova-driven interstellar medium

2020 ◽  
Vol 644 ◽  
pp. A156
Author(s):  
Miguel A. de Avillez ◽  
Gervásio J. Anela ◽  
Ashish Asgekar ◽  
Dieter Breitschwerdt ◽  
Dominic H. F. M. Schnitzeler
Keyword(s):  
Interstellar Medium ◽  
Adaptive Mesh Refinement ◽  
Electron Distribution ◽  
Mesh Refinement ◽  
Adaptive Mesh ◽  
Vantage Point ◽  
Line Of Sight ◽  
Interstellar Gas ◽  
Volume Analysis ◽  
Dispersion Measures

Context. Interstellar gas is in a highly turbulent dynamic state driven by successive supernova explosions and stellar winds, while its electron distribution is determined by microscopic processes such as ionization and recombination. In order to understand the properties of the electrons in the interstellar medium (ISM) it is necessary to follow numerically the nonlinear spatial and temporal evolution of the gas, its ionization structure, and its emission properties. Aims. We study the time evolution of the electrons in the ISM and how line of sight observations compare to volume analysis of the simulated medium populated with atoms and ions of the ten most abundant species. In particular, we make quantitative predictions about the occupation fractions and averaged densities of electrons, the dispersion measures, and their vantage point dependence. Methods. We carried out state-of-the-art adaptive mesh refinement simulations of the supernova-driven interstellar gas tracing the evolution of 112 ions and atoms of H, He, C, N, O, Ne, Mg, Si, S, and Fe and their emissivities in a time-dependent fashion. The gas is followed with the magnetohydrodynamical adaptive mesh refinement parallel code coupled with the Collisional + Photo Ionization Plasma Emission Software to trace the ionic structure and radiative emission of the plasma. Results. We show that more than 60% of the electrons are in thermally unstable regimes: about 50% at 200 < T ≤ 103.9 K and 14% at 104.2 < T ≤ 105.5 K. The probability density functions for the electron distribution in different temperature regimes is rather broad, also a result of turbulence in the ISM. Comparing the calculated dispersion measures along different lines of sight to observation, we find a very good agreement. They increase linearly for distances greater than 300 pc from the observer at an average rate of 27 cm−3 pc per kpc. The dispersion regarding the average dispersion measures does not decrease with distance along the line of sight, pointing to a high clumpiness of the electrons and of the turbulent ISM. The mean electron density in the Galactic midplane derived from the volume analysis varies between 0.029 and 0.031 cm−3, while that derived from the dispersion measures, varies between 0.0264 and 0.03 cm−3 depending on the vantage point and on the time averaged period. These variations can be as high as 8.3% between vantage points.

scholarly journals 2D kinematics of massive stars near the Galactic Centre

2020 ◽  
Vol 500 (3) ◽  
pp. 3213-3239
Author(s):  
Mattia Libralato ◽  
Daniel J Lennon ◽  
Andrea Bellini ◽  
Roeland van der Marel ◽  
Simon J Clark ◽  
...  
Keyword(s):  
Moving Objects ◽  
Hubble Space Telescope ◽  
Massive Stars ◽  
Line Of Sight ◽  
Galactic Centre ◽  
Harsh Environment ◽  
Proper Motions ◽  
Sgr A ◽  
Better Than ◽  
Rule Out

ABSTRACT The presence of massive stars (MSs) in the region close to the Galactic Centre (GC) poses several questions about their origin. The harsh environment of the GC favours specific formation scenarios, each of which should imprint characteristic kinematic features on the MSs. We present a 2D kinematic analysis of MSs in a GC region surrounding Sgr A* based on high-precision proper motions obtained with the Hubble Space Telescope. Thanks to a careful data reduction, well-measured bright stars in our proper-motion catalogues have errors better than 0.5 mas yr−1. We discuss the absolute motion of the MSs in the field and their motion relative to Sgr A*, the Arches, and the Quintuplet. For the majority of the MSs, we rule out any distance further than 3–4 kpc from Sgr A* using only kinematic arguments. If their membership to the GC is confirmed, most of the isolated MSs are likely not associated with either the Arches or Quintuplet clusters or Sgr A*. Only a few MSs have proper motions, suggesting that they are likely members of the Arches cluster, in agreement with previous spectroscopic results. Line-of-sight radial velocities and distances are required to shed further light on the origin of most of these massive objects. We also present an analysis of other fast-moving objects in the GC region, finding no clear excess of high-velocity escaping stars. We make our astro-photometric catalogues publicly available.

scholarly journals The prospects for observing [O iii] 52 micron emission from galaxies during the Epoch of Reionization

2021 ◽  
Vol 504 (1) ◽  
pp. 723-730
Author(s):  
Shengqi Yang ◽  
Adam Lidz ◽  
Gergö Popping
Keyword(s):  
Fine Structure ◽  
Interstellar Medium ◽  
Emission Line ◽  
Parameter Space ◽  
Gas Density ◽  
Star Forming ◽  
Upper Limits ◽  
Redshift Galaxies

ABSTRACT The [O iii] 88 $\mu$m fine-structure emission line has been detected into the Epoch of Reionization (EoR) from star-forming galaxies at redshifts 6 &lt; z ≲ 9 with ALMA. These measurements provide valuable information regarding the properties of the interstellar medium (ISM) in the highest redshift galaxies discovered thus far. The [O iii] 88 $\mu$m line observations leave, however, a degeneracy between the gas density and metallicity in these systems. Here, we quantify the prospects for breaking this degeneracy using future ALMA observations of the [O iii] 52 $\mu$m line. Among the current set of 10 [O iii] 88 $\mu$m emitters at 6 &lt; z ≲ 9, we forecast 52 $\mu$m detections (at 6σ) in SXDF-NB1006-2, B14-6566, J0217-0208, and J1211-0118 within on-source observing times of 2–10 h, provided their gas densities are larger than about nH ≳ 102–103 cm−3. Other targets generally require much longer integration times for a 6σ detection. Either successful detections of the 52 $\mu$m line or reliable upper limits will lead to significantly tighter constraints on ISM parameters. The forecasted improvements are as large as ∼3 dex in gas density and ∼1 dex in metallicity for some regions of parameter space. We suggest SXDF-NB1006-2 as a promising first target for 52 $\mu$m line measurements. We discuss how such measurements will help in understanding the mass–metallicity relationship during the EoR.

scholarly journals The interstellar medium in young supernova remnants: key to the production of cosmic X-rays and $\gamma $-rays

2021 ◽  
Vol 366 (6) ◽  
Author(s):  
Hidetoshi Sano ◽  
Yasuo Fukui
Keyword(s):  
Interstellar Medium ◽  
Supernova Remnants ◽  
Cosmic Ray ◽  
High Energy ◽  
X Rays ◽  
Interstellar Gas ◽  
High Energy Radiation ◽  
Dense Cores ◽  
The Relationship ◽  
Turbulent Velocity Field

AbstractWe review recent progress in elucidating the relationship between high-energy radiation and the interstellar medium (ISM) in young supernova remnants (SNRs) with ages of ∼2000 yr, focusing in particular on RX J1713.7−3946 and RCW 86. Both SNRs emit strong nonthermal X-rays and TeV $\gamma $ γ -rays, and they contain clumpy distributions of interstellar gas that includes both atomic and molecular hydrogen. We find that shock–cloud interactions provide a viable explanation for the spatial correlation between the X-rays and ISM. In these interactions, the supernova shocks hit the typically pc-scale dense cores, generating a highly turbulent velocity field that amplifies the magnetic field up to 0.1–1 mG. This amplification leads to enhanced nonthermal synchrotron emission around the clumps, whereas the cosmic-ray electrons do not penetrate the clumps. Accordingly, the nonthermal X-rays exhibit a spatial distribution similar to that of the ISM on the pc scale, while they are anticorrelated at sub-pc scales. These results predict that hadronic $\gamma $ γ -rays can be emitted from the dense cores, resulting in a spatial correspondence between the $\gamma $ γ -rays and the ISM. The current pc-scale resolution of $\gamma $ γ -ray observations is too low to resolve this correspondence. Future $\gamma $ γ -ray observations with the Cherenkov Telescope Array will be able to resolve the sub-pc-scale $\gamma $ γ -ray distribution and provide clues to the origin of these cosmic $\gamma $ γ -rays.

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