scholarly journals Investigation of chemical differentiation among the NGC 2264 cluster-forming clumps

2020 ◽  
Vol 493 (2) ◽  
pp. 2395-2409 ◽  
Author(s):  
Kotomi Taniguchi ◽  
Adele Plunkett ◽  
Eric Herbst ◽  
Kazuhito Dobashi ◽  
Tomomi Shimoikura ◽  
...  
Keyword(s):  
Column Density ◽  
Point Sources ◽  
Emission Lines ◽  
Filamentary Structure ◽  
Molecular Emission ◽  
Sky Survey ◽  
Integrated Intensity ◽  
Positive Correlations ◽  
Density Ratios ◽  
Massive Cluster

ABSTRACT We have carried out mapping observations of molecular emission lines of HC3N and CH3OH toward two massive cluster-forming clumps, NGC 2264-C and NGC 2264-D, using the Nobeyama 45-m radio telescope. We derive an I(HC3N)/I(CH3OH) integrated intensity ratio map, showing a higher value at clumps including 2MASS (Two Micron All Sky Survey) point sources at the northern part of NGC 2264-D. Possible interpretations of the I(HC3N)/I(CH3OH) ratio are discussed. We have also observed molecular emission lines from CCS and N2H+ toward five positions in each clump. We investigate the N(N2H+)/N(CCS) and N(N2H+)/N(HC3N) column density ratios among the ten positions in order to test whether they can be used as chemical evolutionary indicators in these clumps. The N(N2H+)/N(CCS) ratio shows a very high value toward a bright embedded IR source (IRS1), whereas the N(N2H+)/N(HC3N) ratio at IRS1 is comparable with those at the other positions. These results suggest that ultraviolet radiation affects the chemistry around IRS1. We find that there are positive correlations between these column density ratios and the excitation temperatures of N2H+, which implies the chemical evolution of clumps. These chemical evolutionary indicators likely reflect the combination of evolution along the filamentary structure and evolution of each clump.

scholarly journals A synergy of the velocity gradients technique and the probability density functions for identifying gravitational collapse in self-absorbing media

2021 ◽  
Vol 502 (2) ◽  
pp. 1768-1784
Author(s):  
Yue Hu ◽  
A Lazarian
Keyword(s):  
Magnetic Fields ◽  
Probability Density ◽  
Column Density ◽  
Mass Density ◽  
Probability Density Functions ◽  
Emission Lines ◽  
Density Functions ◽  
Star Forming ◽  
Velocity Gradients ◽  
Self Gravity

ABSTRACT The velocity gradients technique (VGT) and the probability density functions (PDFs) of mass density are tools to study turbulence, magnetic fields, and self-gravity in molecular clouds. However, self-absorption can significantly make the observed intensity different from the column density structures. In this work, we study the effects of self-absorption on the VGT and the intensity PDFs utilizing three synthetic emission lines of CO isotopologues 12CO (1–0), 13CO (1–0), and C18O (1–0). We confirm that the performance of VGT is insensitive to the radiative transfer effect. We numerically show the possibility of constructing 3D magnetic fields tomography through VGT. We find that the intensity PDFs change their shape from the pure lognormal to a distribution that exhibits a power-law tail depending on the optical depth for supersonic turbulence. We conclude the change of CO isotopologues’ intensity PDFs can be independent of self-gravity, which makes the intensity PDFs less reliable in identifying gravitational collapsing regions. We compute the intensity PDFs for a star-forming region NGC 1333 and find the change of intensity PDFs in observation agrees with our numerical results. The synergy of VGT and the column density PDFs confirms that the self-gravitating gas occupies a large volume in NGC 1333.

scholarly journals Modelling intergalactic low ionization metal absorption line systems near the epoch of reionization

2021 ◽  
Vol 502 (1) ◽  
pp. 888-903
Author(s):  
Teresita Suarez ◽  
Avery Meiksin
Keyword(s):  
Radiative Transfer ◽  
Numerical Simulations ◽  
Absorption Line ◽  
Column Density ◽  
Massive Star ◽  
Good Description ◽  
Chemical Abundances ◽  
Metal Absorption ◽  
Density Ratios ◽  
Galactic Haloes

ABSTRACT We interpret observations of intergalactic low ionization metal absorption systems at redshifts z ≳ 5 in terms of pressure-confined clouds. We find clouds confined by the expected pressure of galactic haloes with masses $11\lt \log M_h/h^{-1}\, \mathrm{M}_\odot \lt 12$ provide a good description of the column density ratios between low ionization metal absorbers. Some of the ratios, however, require extending conventional radiative transfer models of irradiated slabs to spherical (or cylindrical) clouds to allow for lines of sight passing outside the cores of the clouds. Moderate depletion of silicon on to dust grains is also indicated in some systems. The chemical abundances inferred span the range between solar and massive-star-dominated stellar populations as may arise in starburst galaxies. The typical H i column densities matching the data correspond to damped Ly α absorbers (DLAs) or sub-DLAs, with sizes of 40 pc to 3 kpc, gas masses 3.5 < log Mc/M⊙ < 8 and metallicites $0.001\!-\!0.01\, \mathrm{Z}_\odot$. Such systems continue to pose a challenge for galaxy-scale numerical simulations to reproduce.

Studying the Flux Density of Bright Active Galaxies at Different Spectral Bands

2019 ◽  
Vol 16 (1(Suppl.)) ◽  
pp. 0230
Author(s):  
Rashed Et al.
Keyword(s):  
Flux Density ◽  
Galactic Nuclei ◽  
Absolute Magnitude ◽  
Active Galaxies ◽  
X Ray ◽  
Spectral Bands ◽  
Sky Survey ◽  
Multi Wavelength ◽  
Statistical Studies ◽  
Density Ratios

Statistical studies are reported in this article for an active galactic nuclei sample of different type of active galaxies Seyferts 1, Seyferts 2, and Quasars. These sources have been selected from a Catalogue for bright X-ray galaxies. The name of this index is ROSAT Bright Source Catalogue (RBSC) and the NRAO VLA Sky Survey (NVSS). In this research, multi-wavelength observational bands Radio at 1.4 GHz, Optical at 4400 A0, and X-ray at energy 0.1-2.4 KeV have been adopted in this study. The behavior of flux density ratios has been studied ,  with respect to the absolute magnitude . Furthermore, the Seyfert1 and Seyfert 2 objects are combined in one group and the QSOs are collectest in another group. Also, it has been found that the ratios , are increasing towards fainter optical absolute magnitude especially in Quasars.

scholarly journals The frequency of gaseous debris discs around white dwarfs

2020 ◽  
Vol 493 (2) ◽  
pp. 2127-2139 ◽  
Author(s):  
Christopher J Manser ◽  
Boris T Gänsicke ◽  
Nicola Pietro Gentile Fusillo ◽  
Richard Ashley ◽  
Elmé Breedt ◽  
...  
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Signal To Noise Ratio ◽  
Infrared Emission ◽  
Sloan Digital Sky Survey ◽  
Emission Lines ◽  
Occurrence Rate ◽  
Limited Sample ◽  
Sky Survey ◽  
Gaseous Disc

ABSTRACT A total of 1–3 per cent of white dwarfs are orbited by planetary dusty debris detectable as infrared emission in excess above the white dwarf flux. In a rare subset of these systems, a gaseous disc component is also detected via emission lines of the Ca ii 8600 Å triplet, broadened by the Keplerian velocity of the disc. We present the first statistical study of the fraction of debris discs containing detectable amounts of gas in emission at white dwarfs within a magnitude and signal-to-noise ratio limited sample. We select 7705 single white dwarfs spectroscopically observed by the Sloan Digital Sky Survey (SDSS) and Gaia with magnitudes g ≤ 19. We identify five gaseous disc hosts, all of which have been previously discovered. We calculate the occurrence rate of a white dwarf hosting a debris disc detectable via Ca ii emission lines as $0.067\, \pm \, ^{0.042}_{0.025}$ per cent. This corresponds to an occurrence rate for a dusty debris disc to have an observable gaseous component in emission as 4 ± $_{2}^{4}$ per cent. Given that variability is a common feature of the emission profiles of gaseous debris discs, and the recent detection of a planetesimal orbiting within the disc of SDSS J122859.93+104032.9, we propose that gaseous components are tracers for the presence of planetesimals embedded in the discs and outline a qualitative model. We also present spectroscopy of the Ca ii triplet 8600 Å region for 20 white dwarfs hosting dusty debris discs in an attempt to identify gaseous emission. We do not detect any gaseous components in these 20 systems, consistent with the occurrence rate that we calculated.

scholarly journals Non-Local Origin of a Substantial Portion of the Soft X-Ray Background

1984 ◽  
Vol 81 ◽  
pp. 204-210
Author(s):  
George W. Clark
Keyword(s):  
Column Density ◽  
Angular Resolution ◽  
General Trend ◽  
Neutral Hydrogen ◽  
Substantial Portion ◽  
X Ray ◽  
Local Origin ◽  
Sky Survey ◽  
Non Local ◽  
X Ray Background

Comparison of the SAS-3 soft X-ray sky survey (F. Marshall and G. Clark 1984) with the 21-cm neutral hydrogen survey of Stark et al. (1984) confirms the well-known anticorrelation between the counting rates in the C-band (0.10-0.28 keV) and the column density of neutral hydrogen, and demonstrates that this anticorrelation is significant on all angular scales ranging from that of the general trend from the galactic equator to the poles down to the angular resolution of the detector (2°.7 FWHM). Included in this general anticorrelation are numerous instances of what appear to be soft X-ray “shadows” of nearby (100-300 pc) 21-cm features, and several bright X-ray regions coincident with “holes” in the ISM.

scholarly journals Face-on SS 433 Stars as a Possible New Type of Extragalactic X-Ray Sources

2001 ◽  
Vol 205 ◽  
pp. 268-269 ◽  
Author(s):  
S. Fabrika ◽  
A. Mescheryakov
Keyword(s):  
X Rays ◽  
Relativistic Jets ◽  
Expected Frequency ◽  
X Ray ◽  
Ss 433 ◽  
Sky Survey ◽  
Supercritical Accretion ◽  
The Face ◽  
New Type ◽  
Positive Correlations

The object SS433 is a well-known source of relativistic jets, which are formed in supercritical accretion disk. It is very probable that the disk has polar channels and their radiation is collimated (the photo-cones). A face-on SS433 object can appear as ultra-bright and highly variable X-ray source, Lx ˜ 1040 − 1042 erg/s. We discuss the properties of these hypothetical objects and their frequency expected in galaxies. We describe a search for such objects using the ROSAT All Sky Survey and RC3 catalog of galaxies. Among the total 418 positive correlations we find that 142 sources in S and Irr galaxies are unknown as AGNs. Nuclear sources among them still contain many AGNs. Non-nuclear (offset) sources are rather hard, their X-ray luminosities are 1039 − 1041 erg/s. Their observed frequency is about 4–5% per galaxy, that is in agreement with expected frequency of the face-on SS 433 stars. The only way to recognize such stars is their expected violent variability in X rays.

scholarly journals Quasi-stellar objects acting as potential strong gravitational lenses in the SDSS-III BOSS survey

2019 ◽  
Vol 625 ◽  
pp. A56 ◽  
Author(s):  
Romain A. Meyer ◽  
Timothée Delubac ◽  
Jean-Paul Kneib ◽  
Frédéric Courbin
Keyword(s):  
Emission Line ◽  
Sloan Digital Sky Survey ◽  
Emission Lines ◽  
Gravitational Lenses ◽  
Stellar Objects ◽  
Sky Survey ◽  
Quasi Stellar Objects ◽  
Unique Approach ◽  
Algorithmic Search ◽  
Emission Line Galaxies

We present a sample of 12 quasi-stellar objects (QSOs) that potentially act as strong gravitational lenses on background emission line galaxies (ELG) or Lyman-α emitters (LAEs) selected through a systematic search of the 297 301 QSOs in the Sloan Digital Sky Survey (SDSS)-III Data Release 12. Candidates were identified by looking for compound spectra, where emission lines at a redshift larger than that of the quasar can be identified in the residuals after a QSO spectral template is subtracted from the observed spectra. The narrow diameter of BOSS fibers (2″) then ensures that the object responsible for the additional emission lines must lie close to the line of sight of the QSO and hence provides a high probability of lensing. Among the 12 candidates identified, nine have definite evidence for the presence of a background ELG identified by at least four higher-redshift nebular emission lines. The remaining three probable candidates present a strong asymmetrical emission line attributed to a background Lyman-α emitter (LAE). The QSO-ELG (QSO-LAE) lens candidates have QSO lens redshifts in the range 0.24 ≲ zQSO ≲ 0.66 (0.75 ≲ zQSO ≲ 1.23 ) and background galaxy redshifts in the range 0.48 ≲ zS, ELG ≲ 0.94 (2.17 ≲ zS, LAE ≲ 4.48). We show that the algorithmic search is complete at > 90% for QSO-ELG systems, whereas it falls at 40−60% for QSO-LAE, depending on the redshift of the source. Upon confirmation of the lensing nature of the systems, this sample may quadruple the number of known QSOs acting as strong lenses. We have determined the completeness of our search, which allows future studies to compute lensing probabilities of galaxies by QSOs and differentiate between different QSO models. Future imaging of the full sample and lens modelling offers a unique approach to study and constrain key properties of QSOs.

scholarly journals How the power spectrum of dust continuum images may hide the presence of a characteristic filament width

2019 ◽  
Vol 626 ◽  
pp. A76 ◽  
Author(s):  
A. Roy ◽  
Ph. André ◽  
D. Arzoumanian ◽  
M.-A. Miville-Deschênes ◽  
V. Könyves ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Numerical Experiments ◽  
Column Density ◽  
Power Spectra ◽  
Density Profiles ◽  
Filamentary Structure ◽  
Interstellar Clouds ◽  
Scale Free ◽  
Free Behavior ◽  
Area Filling

Context. Herschel observations of interstellar clouds support a paradigm for star formation in which molecular filaments play a central role. One of the foundations of this paradigm is the finding, based on detailed studies of the transverse column density profiles observed with Herschel, that nearby molecular filaments share a common inner width of ∼0.1 pc. The existence of a characteristic filament width has been recently questioned, however, on the grounds that it seems inconsistent with the scale-free nature of the power spectrum of interstellar cloud images. Aims. In an effort to clarify the origin of this apparent discrepancy, we examined the power spectra of the Herschel/SPIRE 250 μm images of the Polaris, Aquila, and Taurus–L1495 clouds in detail and performed a number of simple numerical experiments by injecting synthetic filaments in both the Herschel images and synthetic background images. Methods. We constructed several populations of synthetic filaments of 0.1 pc width with realistic area filling factors (Afil) and distributions of column density contrasts (δc). After adding synthetic filaments to the original Herschel images, we recomputed the image power spectra and compared the results with the original, essentially scale-free power spectra. We used the χ2variance of the residuals between the best power-law fit and the output power spectrum in each simulation as a diagnostic of the presence (or absence) of a significant departure from a scale-free power spectrum. Results. We find that χ2variance depends primarily on the combined parameter δ22 Afil. According to our numerical experiments, a significant departure from a scale-free behavior and thus the presence of a characteristic filament width become detectable in the power spectrum when δ22 Afil ⪆ 0.1 for synthetic filaments with Gaussian profiles and δ22 Afil ⪆ 0.4 for synthetic filaments with Plummer-like density profiles. Analysis of the real Herschel 250 μm data suggests that δ22 Afil is ∼0.01 in the case of the Polaris cloud and ∼0.016 in the Aquila cloud, significantly below the fiducial detection limit of δ22 Afil ∼ 0.1 in both cases. In both clouds, the observed filament contrasts and area filling factors are such that the filamentary structure contributes only ∼1/5 of the power in the image power spectrum at angular frequencies where an effect of the characteristic filament width is expected. Conclusions. We conclude that the essentially scale-free power spectra of Herschel images remain consistent with the existence of a characteristic filament width ∼0.1 pc and do not invalidate the conclusions drawn from studies of the filament profiles.

scholarly journals Spectral Characteristics of the 2dFGRS–NVSS Galaxies

2000 ◽  
Vol 17 (3) ◽  
pp. 234-240 ◽  
Author(s):  
C. A. Jackson ◽  
D. M. Londish
Keyword(s):  
Spectral Characteristics ◽  
Line Ratio ◽  
Emission Lines ◽  
Sky Survey ◽  
Show Evidence ◽  
Redshift Survey ◽  
Galaxy Redshift ◽  
Narrow Emission

AbstractWe have analysed the 2dF spectra of a sample of galaxies common to the 2dF Galaxy Redshift Survey (2dFGRS, Colless 1999) and the NRAO VLA Sky Survey (NVSS, Condon et al. 1998). Our sample comprises 88 galaxies selected by Sadler et al. (1999) from 30 2dFGRS fields observed in 1998. In this paper we discuss how this and future, much larger, samples of 2dFGRS–NVSS galaxies can be interpreted via analysis of those galaxies with strong narrow emission lines. Using diagnostic line ratio measurements, we confirm the majority of the eyeball classifications of Sadler et al. (1999), although many galaxies show evidence of being ‘composite’ galaxies—mixtures of AGN plus starburst components.

X-ray fine structure of dense plasma in a co-axial accelerator

1972 ◽  
Vol 8 (1) ◽  
pp. 7-20 ◽  
Author(s):  
W. H. Bostick ◽  
V. Nardi ◽  
W. Prior
Keyword(s):  
Dense Plasma ◽  
Point Sources ◽  
X Rays ◽  
Axial Region ◽  
Metal Vapour ◽  
Filamentary Structure ◽  
X Ray ◽  
Hard Radiation ◽  
Cylindrical Region ◽  
Coaxial Accelerator

The intensity of X-ray sources in a focused deuterium plasma produced by a coaxial accelerator has been analysed as a function of position, X-ray energy and time of emission. The X-ray source in the axial region can be resolved (by micro- densitometer readings on X-ray pinhole camera films) as a sequence of small sources (linear dimension ∼ 0.1–0.3 mm) of hard radiation ≳ 2 ke V inside a more diffused source (cylindrical region of 1–4mm diameter) of softer X-rays. In each discharge the point sources are distributed for the most part in the general axial region of the discharge and two or more sources with different radial positions can be frequently observed for one specific value of the axial co-ordinate. Images of localized X-ray sources are also observed in the off-axis halo region. Multiple repinching of the axial plasma column or emission from metal-vapour clouds (by anode bombardment) can be ruled out in this experiment (hollow central electrode, or anode, radius 3·4 cm). The source multiplicity can be related to a complex (filamentary) structure of the plasma.

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