scholarly journals Nature of the DLA towards Q 0528−250: High pressure and strong UV field revealed by excitation of C i, H2, and Si ii

2020 ◽  
Vol 497 (2) ◽  
pp. 1946-1956 ◽  
Author(s):  
S A Balashev ◽  
C Ledoux ◽  
P Noterdaeme ◽  
R Srianand ◽  
P Petitjean ◽  
...  
Keyword(s):  
Fine Structure ◽  
Relative Velocity ◽  
Energy Levels ◽  
Line Of Sight ◽  
Host Galaxy ◽  
Neutral Medium ◽  
Kinetic Temperature ◽  
Thermal Pressure ◽  
Physical Conditions ◽  
Companion Galaxy

ABSTRACT We present the detection of excited fine-structure energy levels of singly ionized silicon and neutral carbon associated with the proximate damped Lyman-α system at zabs = 2.811 towards Q 0528−250. This absorber has an apparent relative velocity that is inconsistent with the Hubble flow indicating motion along the line-of-sight towards the quasar, i.e. zabs > zem. We measure the metallicity of the system to be [Zn/H] = −0.68 ± 0.02. Using the relative populations of the fine-structure levels of Si ii and C i, as well as the populations of H2 rotational levels, we constrain the physical conditions of the gas. We derive hydrogen number densities of $n_{\rm H}=190^{+70}_{-50}$ cm−3 and $260^{+30}_{-20}$ cm−3 in two velocity components where both C i and H2 are detected. Taking into account the kinetic temperature in each component, ∼150 K, we infer high values of thermal pressure in the cold neutral medium probed by the observations. The strengths of the UV field in Draine’s unit are $I_{\rm UV} = 10^{+5}_{-3}$ and $14^{+3}_{-3}$ in each of these two components, respectively. Such enhanced UV fluxes and thermal pressure compared to intervening DLAs are likely due to the proximity of the quasar. The typical size of the absorber is ∼104 au. Assuming the UV flux is dominated by the quasar, we constrain the distance between the quasar and the absorber to be ∼150−200 kpc. This favours a scenario where the absorption occurs in a companion galaxy located in the group where the quasar-host galaxy resides. This is in line with studies in emission that revealed the presence of several galaxies around the quasar.

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 Helical Structure in an Eruptive Prominence Related to a CME (SUMER, CDS, LASCO)

1998 ◽  
Vol 167 ◽  
pp. 318-321
Author(s):  
T.A. Kucera ◽  
A.I. Poland ◽  
J.E. Wiik ◽  
B. Schmieder ◽  
G. Simnett
Keyword(s):  
Fine Structure ◽  
Structure Analysis ◽  
Doppler Shift ◽  
Large Scale ◽  
Helical Structure ◽  
Line Of Sight ◽  
Eruptive Prominence ◽  
Physical Conditions ◽  
Multiple Components ◽  
Large Dispersion

AbstractSOHO (SUMER/CDS) observed an eruptive prominence on May 1,1996, associated with a CME observed by LASCO. We investigate the physical conditions of this prominence in order to quantify velocity, temperature, and density. SUMER spectra in Si IV and O IV lines are used to obtain Doppler-shift images of the prominence. The prominence shows large-scale red and blueshifted regions, revealing a large helical structure with a global twist. In addition, fine structure analysis shows multiple components in the line profile, suggesting integration of many threads along the line-of-sight with a large dispersion of velocities (±50 km s−1).

scholarly journals THz Observations of the Cool Neutral Medium

2012 ◽  
Vol 8 (S288) ◽  
pp. 135-138
Author(s):  
John M. Dickey
Keyword(s):  
Column Density ◽  
Far Infrared ◽  
Neutral Medium ◽  
Spectral Structure ◽  
Kinetic Temperature ◽  
Far Infrared Spectroscopy ◽  
Dome A ◽  
Physical Conditions ◽  
Low Latitudes ◽  
Atomic Phase

AbstractThe astrophysical drivers for far-infrared spectroscopy of the Galactic interstellar medium using a 15m class telescope on Dome A are compelling. For the diffuse, atomic phase, the most important lines in the far-IR spectrum are OIat 63μm and CIIat 158μm. These are the dominant cooling lines of the cool, neutral medium, and they show rich spectral structure in Herschel observations at low latitudes. But theory predicts that they should both be highly sub-thermal in excitation, so that the level populations are not in equilibrium with the kinetic temperature of the gas. A large single dish telescope or an interferometer may be able to study the absorption and emission to determine the optical depth and column density of atoms and the physical conditions in the emission regions. Comparison of Herschel CIIspectra with 21-cm absorption spectra indicates that a significant fraction of the 158μm flux may be coming from the atomic rather than the molecular phase.

scholarly journals X-shooter observations of strong H2-bearing DLAs at high redshift

2019 ◽  
Vol 490 (2) ◽  
pp. 2668-2678 ◽  
Author(s):  
S A Balashev ◽  
V V Klimenko ◽  
P Noterdaeme ◽  
J-K Krogager ◽  
D A Varshalovich ◽  
...  
Keyword(s):  
Signal To Noise Ratio ◽  
High Redshift ◽  
Energy Levels ◽  
Metal Species ◽  
Kinetic Temperature ◽  
Chemical Enrichment ◽  
Physical Conditions ◽  
Very Large Telescope ◽  
Analytical Expressions ◽  
Selection Of

ABSTRACT We present results from spectroscopic observations with X-shooter at the Very Large Telescope of seven H2-bearing damped Lyman-α systems (DLAs) at high redshifts (zabs ∼ 2.5–3). These DLAs were originally selected from the presence of strong H2 lines directly seen at the DLA redshift in low-resolution low signal-to-noise ratio SDSS spectra. We confirm the detection of molecular hydrogen in all of them. We measure the column densities of H i, H2 in various rotational levels, and metal species, and associated dust extinction. The metallicities, obtained from undepleted species, are in the range log Z = −0.8 to −0.2. We discuss the chemical enrichment in these clouds and compare their properties with that of other molecular-rich systems selected by other means. In particular, we show that three different methods of pre-selection of H2-bearing DLAs in the SDSS have their own biases but complement each other mostly in terms of chemical enrichment. We use the rotational excitation of H2 molecules together with the fine-structure energy levels of neutral carbon to constrain the physical conditions in the gas with the help of numerical modelling as well as analytical expressions for the surface density at which atomic to molecular conversion happens. We find that the H2-bearing medium revealed by the studied DLAs has typical values for the kinetic temperature, hydrogen density, and UV radiation field of T ∼ 100 K, nH ∼ 100 cm−3, and IUV , respectively, about twice the intensity of the Draine field. Detailed studies combining different selections should therefore bring important clues to understand the H i-H2 transition at high redshift.

scholarly journals Reference wavelengths of Si ii, C ii, Fe i, and Ni ii for quasar absorption spectroscopy

2020 ◽  
Author(s):  
Gillian Nave ◽  
Christian Clear
Keyword(s):  
Silicon Carbide ◽  
Fourier Transform ◽  
Fine Structure ◽  
Energy Levels ◽  
Structure Constant ◽  
Fine Structure Constant ◽  
Line Of Sight ◽  
Order Of Magnitude ◽  
Better Than ◽  
Ft Spectroscopy

Abstract Wavelengths of absorption lines in the spectra of galaxies along the line-of-sight to distant quasars can be used to probe the variablility of the fine structure constant, α, at high redshifts, provided that the laboratory wavelengths are known to better than 6 parts in 108, corresponding to a radial velocity of ≈ 20 ms−1. For several lines of Si ii, C ii, Fe i, and Ni ii, previously published wavelengths are inadequate for this purpose. Improved wavelengths for these lines were derived by re-analyzing archival Fourier transform (FT) spectra of iron hollow cathode lamps (HCL) and a silicon carbide Penning discharge lamp, and with new spectra of nickel HCLs. By re-optimizing the energy levels of Fe i, the absolute uncertainty of 13 resonance lines has been reduced by over a factor of 2. A similar analysis for Si ii gives improved values for 45 lines with wavelength uncertainties over an order of magnitude smaller than previous measurements. Improved wavelengths for 8 lines of Ni ii were measured and Ritz wavelengths from optimized energy levels determined for an additional 3 lines at shorter wavelengths. Three lines of C ii near 135 nm were observed using FT spectroscopy and the wavelengths confirm previous measurements.

scholarly journals The ultra-violet spectrum of magnesium hydride. 1.—The band at λ 2430

1929 ◽  
Vol 122 (790) ◽  
pp. 442-455 ◽  
Keyword(s):  
Fine Structure ◽  
General Structure ◽  
Energy Levels ◽  
Visible Region ◽  
Ultra Violet ◽  
Present Theory ◽  
Magnesium Hydride ◽  
Electronic Energy ◽  
Band Spectra ◽  
Electronic Energy Levels

The system of bands in the visible region of the emission spectrum of magnesium hydride is now well known. The bands with heads at λλ 5622, 5211, 4845 were first measured by Prof. A. Fowler, who arranged many of the strongest lines in empirical series for identification with absorption lines in the spectra of sun-spots. Later, Heurlinger rearranged these series in the now familiar form of P, Q and R branches, and considered them, with the OH group, as typical of doublet systems in his classification of the fine structure of bands. More recently, W. W. Watson and P. Rudnick have remeasured these bands, using the second order of a 21-foot concave grating, and have carried out a further investigation of the fine structure in the light of the present theory of band spectra. Their detection of an isotope effect of the right order of magnitude, considered with the general structure of the system, and the experimental work on the production of the spectrum, seems conclusive in assigning these bands to the diatomic molecule MgH. The ultra-violet spectrum of magnesium hydride is not so well known. The band at λ 2430 and the series of double lines in the region λ 2940 to λ 3100, which were recorded by Prof. Fowler in 1909 as accompanying the group of bands in the visible region, appear to have undergone no further investigation. In view of the important part played by hydride band spectra in the correlation of molecular and atomic electronic energy levels, it was thought that a study of these features might prove of interest in yielding further information on the energy states of the MgH molecule. The present paper deals with observations on the band at λ 2430; details of an investigation of the other features of the ultra-violet spectrum will be given in a later communication.

scholarly journals Constraining physical conditions for the PDR of Trumpler 14 in the Carina Nebula

2018 ◽  
Vol 618 ◽  
pp. A53 ◽  
Author(s):  
Ronin Wu ◽  
Emeric Bron ◽  
Takashi Onaka ◽  
Franck Le Petit ◽  
Frédéric Galliano ◽  
...  
Keyword(s):  
Uv Radiation ◽  
Massive Stars ◽  
Local Heating ◽  
Spectral Lines ◽  
Ionization Front ◽  
Thermal Pressure ◽  
Line Energy ◽  
Physical Conditions ◽  
Radiation Fields ◽  
Carina Nebula

We investigate the physical conditions of the CO gas, based on the submillimeter imaging spectroscopy from a 2′ × 7′ (1.5 × 5 pc2) area near the young star cluster, Trumpler 14 of the Carina Nebula. The observations presented in this work are taken with the Fourier Transform Spectrometer (FTS) of the Spectral and Photometric Imaging REceiver (SPIRE) onboard the Herschel Space Observatory. The newly observed spectral lines include [CI] 370 μm [CI] 609 μm, and CO transitions from J = 4−3 to J = 13−12. Our field of view covers the edge of a cavity carved by Trumpler 14 about 1 Myr ago and marks the transition from H ii regions to photo-dissociation regions. The observed CO intensities are the most prominent at the northwest region, Car I-E. With the state-of-the-art Meudon PDR code, we successfully derive the physical conditions, which include the thermal pressure (P) and the scaling factor of radiation fields (GUV), from the observed CO spectral line energy distributions (SLEDs) in the observed region. The derived GUV values generally show excellent agreement with the UV radiation fields created by nearby OB-stars and thus confirm that the main excitation source of the observed CO emission is the UV-photons provided by the massive stars. The derived thermal pressure is in the range 0.5−3 × 108 K cm-3 with the highest values found along the ionization front in Car I-E region facing Trumpler 14, hinting that the cloud structure is similar to the recent observations of the Orion Bar. We also note a discrepancy at a local position (<0.17 × 0.17 pc2) between the photo-dissociation region (PDR) modeling result and the UV radiation fields estimated from nearby massive stars, which requires further investigation on nearby objects that could contribute to local heating, including outflow. Comparing the derived thermal pressure with the radiation fields, we report the first observationally derived and spatially resolved P ~ 2 × 104 GUV relationship. As direct comparisons of the modeling results to the observed 13CO, [O I] 63 μm, and [C II] 158 μm intensities are not straightforward, we urge the reader to be cautious when constraining the physical conditions of PDRs with combinations of 12CO, 13CO, [C I], [O I] 63 μm, and [C II] 158 μm observations.

Dust-reddened Quasars

1996 ◽  
Vol 13 (2) ◽  
pp. 183-184 ◽  
Author(s):  
M. J. Drinkwater ◽  
R. L. Webster ◽  
P. J. Francis ◽  
T. Wiklind ◽  
F. Combes
Keyword(s):  
Molecular Clouds ◽  
Physical State ◽  
Absorption Lines ◽  
Line Of Sight ◽  
Host Galaxy ◽  
Molecular Gas ◽  
Molecular Absorption

We have recently discovered evidence for a population of radio-loud quasars that is reddened by dust. The dust is either along the line of sight to the quasars or is associated with the quasars. In the latter case the dust may be in molecular clouds in the quasar’s host galaxy, or in a molecular torus around the nucleus. We are planning to use 3 mm observations to search for molecular absorption lines (CO and HCO+) associated with dust at the redshift of these quasars. If any absorption systems are detected we will be able to deduce detailed information about the physical state of the molecular gas, hopefully showing which of the proposed locations of the dust is most likely.

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