scholarly journals Molecular Hydrogen in the High Redshift Damped Ly-α Systems:

2005 ◽  
Vol 13 ◽  
pp. 833-838
Author(s):  
R. Srianand ◽  
P. Petitjean ◽  
C. Ledoux ◽  
G. Ferland
Keyword(s):  
Fine Structure ◽  
Star Formation ◽  
Molecular Hydrogen ◽  
High Redshift ◽  
Simple Consequence ◽  
Preliminary Results ◽  
Physical Conditions ◽  
Lower Temperature ◽  
Fine Structure Lines ◽  
High Dust

AbstractThis review talk summarizes the main results obtained from the just completed survey of molecular hydrogen in damped Lyman-a systems (DLAs). Preliminary results based on modeling ionization conditions and chemical network is also presented. The presence of H2 and fine-structure lines of C 1 in 13-20% of DLAs allow one to investigate the physical conditions using the techniques that are commonly used in the studies of the Galactic ISM. It is shown that the DLAs with H2 trace regions with higher density, lower temperature, moderate to high dust depletion, and local star-formation. Absence of H2 in DLAs with moderate dust depletion could just be a simple consequence of lower densities in the systems.

scholarly journals AGN Spectra as Seen by the Infrared Space Observatory: First Results

1997 ◽  
Vol 159 ◽  
pp. 333-336
Author(s):  
D. Lutz ◽  
R. Genzel ◽  
E. Sturm ◽  
A.F.M. Moorwood ◽  
E. Oliva ◽  
...  
Keyword(s):  
Fine Structure ◽  
Short Wavelength ◽  
Molecular Hydrogen ◽  
Molecular Gas ◽  
Space Observatory ◽  
Infrared Space Observatory ◽  
First Results ◽  
External Galaxies ◽  
First Time ◽  
Fine Structure Lines

AbstractWe discuss 2.5–45 µm spectra of the Circinus galaxy and of Cen A, obtained with the Short Wavelength Spectrometer (SWS) on board the Infrared Space Observatory. The large number of detected ionic fine structure lines, observable also in visually obscured sources, provides strong constraints on the shape of the ionizing spectrum, which is found to exhibit a UV bump peaking at ~ 70 eV in the case of Circinus. Pure rotational emission of molecular hydrogen, directly probing warm molecular gas, can for the first time be detected in external galaxies.

scholarly journals The VLT-UVES survey for molecular hydrogen in high-redshift damped Lyman α systems: physical conditions in the neutral gas

2005 ◽  
Vol 362 (2) ◽  
pp. 549-568 ◽  
Author(s):  
Raghunathan Srianand ◽  
Patrick Petitjean ◽  
Cédric Ledoux ◽  
Gary Ferland ◽  
Gargi Shaw
Keyword(s):  
Molecular Hydrogen ◽  
High Redshift ◽  
Physical Conditions ◽  
Neutral Gas

scholarly journals The nature of molecular cloud boundary layers from SOFIA [O I] observations

2018 ◽  
Vol 617 ◽  
pp. A94 ◽  
Author(s):  
W. D. Langer ◽  
P. F. Goldsmith ◽  
J. L. Pineda ◽  
E. T. Chambers ◽  
K. Jacobs ◽  
...  
Keyword(s):  
Fine Structure ◽  
Boundary Layers ◽  
Molecular Clouds ◽  
High Spectral Resolution ◽  
Thermal Pressure ◽  
Physical Conditions ◽  
Upper Limits ◽  
Structure Line ◽  
Warm Ionized Medium ◽  
Fine Structure Lines

Context. Dense highly ionized boundary layers (IBLs) outside of the neutral Photon Dominated Regions (PDRs) have recently been detected via the 122 and 205 μm transitions of ionized nitrogen. These layers have higher densities than in the Warm Ionized Medium (WIM) but less than typically found in H II regions. Observations of [C II] emission, which is produced in both the PDR and IBL, do not fully define the characteristics of these sources. Observations of additional probes which just trace the PDRs, such as the fine structure lines of atomic oxygen, are needed derive their properties and distinguish among different models for [C II] and [N II] emissison. Aims. We derive the properties of the PDRs adjacent to dense highly ionized boundary layers of molecular clouds. Methods. We combine high-spectral resolution observations of the 63 μm [O I] fine structure line taken with the upGREAT HFA-band instrument on SOFIA with [C II] observations to constrain the physical conditions in the PDRs. The observations consist of samples along four lines of sight (LOS) towards the inner Galaxy containing several dense molecular clouds. We interpret the conditions in the PDRs using radiative transfer models for [C II] and [O I]. Results. We have a 3.5-σ detection of [O I] toward one source but only upper limits towards the others. We use the [O I] to [C II] ratio, or their upper limits, and the column density of C+ to estimate the thermal pressure, Pth, in these PDRs. In two LOS the thermal pressure is likely in the range 2–5 × 105 in units of K cm−3, with kinetic temperatures of order 75–100 K and H2 densities, n(H2) ~ 2–4 × 103 cm−3. For the other two sources, where the upper limits on [O I] to [C II] are larger, Pth ≲105 (K cm−3). We have also used PDR models that predict the [O I] to [C II] ratio, along with our observations of this ratio, to limit the intensity of the Far UV radiation field. Conclusions. The [C II] and [N II] emission with either weak, or without any, evidence of [O I] indicates that the source of dense highly ionized gas traced by [N II] most likely arises from the ionized boundary layers of clouds rather than from H II regions.

scholarly journals The Orion Nebula in the Far-Infrared: High-J CO and fine-structure lines mapped by FIFI-LS/SOFIA

2015 ◽  
Vol 12 (S316) ◽  
pp. 153-154
Author(s):  
Randolf Klein ◽  
Leslie W. Looney ◽  
Erin Cox ◽  
Christian Fischer ◽  
Christof Iserlohe ◽  
...  
Keyword(s):  
Fine Structure ◽  
Far Infrared ◽  
Molecular Gas ◽  
Orion Nebula ◽  
Star Forming ◽  
Physical Conditions ◽  
Molecular Outflow ◽  
Integral Field ◽  
Fine Structure Lines ◽  
Co Observations

AbstractThe Orion Nebula is the closest massive star forming region allowing us to study the physical conditions in such a region with high spatial resolution. We used the far infrared integral-field spectrometer, FIFI-LS, on-board the airborne observatory SOFIA to study the atomic and molecular gas in the Orion Nebula at medium spectral resolution.The large maps obtained with FIFI-LS cover the nebula from the BN/KL-object to the bar in several fine structure lines. They allow us to study the conditions of the photon-dominated region and the interface to the molecular cloud with unprecedented detail.Another investigation targeted the molecular gas in the BN/KL region of the Orion Nebula, which is stirred up by a violent explosion about 500 years ago. The explosion drives a wide angled molecular outflow. We present maps of several high-J CO observations, allowing us to analyze the heated molecular gas.

scholarly journals Simulating High-Redshift Disk Galaxies: Applications to Long Duration Gamma-Ray Burst Hosts

2008 ◽  
Vol 4 (S254) ◽  
pp. 35-40
Author(s):  
Brant E. Robertson
Keyword(s):  
Star Formation ◽  
Molecular Hydrogen ◽  
Gamma Ray ◽  
High Redshift ◽  
Disk Galaxies ◽  
Host Galaxies ◽  
Long Duration ◽  
Low Mass ◽  
Hydrodynamical Simulations ◽  
The Impact

AbstractThe efficiency of star formation governs many observable properties of the cosmological galaxy population, yet many current models of galaxy formation largely ignore the important physics of star formation and the interstellar medium (ISM). Using hydrodynamical simulations of disk galaxies that include a treatment of the molecular ISM and star formation in molecular clouds (Robertson & Kravtsov 2008), we study the influence of star formation efficiency and molecular hydrogen abundance on the properties of high-redshift galaxy populations. In this work, we focus on a model of low-mass, star forming galaxies at 1 ≲ z ≲ 2 that may host long duration gamma-ray bursts (GRBs). Observations of GRB hosts have revealed a population of faint systems with star formation properties that often differ from Lyman-break galaxies (LBGs) and more luminous high-redshift field galaxies. Observed GRB sightlines are deficient in molecular hydrogen, but it is unclear to what degree this deficiency owes to intrinsic properties of the galaxy or the impact the GRB has on its environment. We find that hydrodynamical simulations of low-stellar mass systems at high-redshifts can reproduce the observed star formation rates and efficiencies of GRB host galaxies at redshifts 1 ≲ z ≲ 2. We show that the compact structure of low-mass high-redshift GRB hosts may lead to a molecular ISM fraction of a few tenths, well above that observed in individual GRB sightlines. However, the star formation rates of observed GRB host galaxies imply molecular gas masses of 108 – 109M⊙ similar to those produced in the simulations, and may therefore imply fairly large average H2 fractions in their ISM.

scholarly journals Bright-rimmed clouds with IRAS point sources: candidates for star formation by radiation-driven implosion

1991 ◽  
Vol 147 ◽  
pp. 498-499
Author(s):  
Koji Sugitani ◽  
Yasuo Fukui ◽  
Katsuo Ogura
Keyword(s):  
Star Formation ◽  
Hii Regions ◽  
Point Sources ◽  
Comprehensive Understanding ◽  
Preliminary Results ◽  
Physical Conditions ◽  
Potential Site

We present preliminary results of a survey of bright-rimmed clouds associated with IRAS point sources.Bright-rimmed globules associated with old HII regions have long been suspected as a potential site for star formation. Physical conditions of such clouds seem to well match to models of radiation-driven implosion, which have been studied as an effective process for induced star formation (e.g. Klein et al. 1985, Bertoldi 1989). Bright-rimmed globules associated with IRAS point sources are good candidates for the sites of induced star formation. Three well-established cases of radiation-driven implosions in bright-rimmed globules (Ori I-2, IC1396-n, and L1206) were reported (Sugitani et al. 1989). Similar examples were also reported in HH46/47 (Olberg et al. 1989) and in GN21.38.9 (Duvert et al. 1990). However, the samples are still not numerous enough to establish comprehensive understanding of star formation by such implosion process.

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