scholarly journals Excitation Mechanism of Extended Emission-Line Regions in Active Galaxies

1997 ◽  
Vol 159 ◽  
pp. 386-389
Author(s):  
Ian Evans ◽  
Anuradha Koratkar ◽  
Mark Allen ◽  
Zlatan Tsvetanov ◽  
Michael Dopita
Keyword(s):  
Emission Line ◽  
Hubble Space Telescope ◽  
Optical Emission ◽  
Active Galaxies ◽  
Emission Lines ◽  
Uv Spectrophotometry ◽  
Excitation Mechanism ◽  
Space Telescope ◽  
Shock Models ◽  
Extended Emission

AbstractPhotoionization and shock models of the extended emissionline regions (EELRs) in active galaxies demonstrate that the optical emission lines alone are a poor discriminant of the excitation mechanism. Combining optical and UV data provides a discriminant between nuclear photoionization and autoionizing shock models. Hubble Space Telescope UV spectrophotometry of two Seyferts suggests that the EELRs in these objects are probably photoionized by the nucleus.

scholarly journals Galaxies with Binary Nuclei

2013 ◽  
Vol 9 (S304) ◽  
pp. 363-370
Author(s):  
Yervant Terzian ◽  
Edward Khachikian
Keyword(s):  
Hubble Space Telescope ◽  
Radio Galaxies ◽  
Active Galaxies ◽  
Emission Lines ◽  
Special Astrophysical Observatory ◽  
Host Galaxies ◽  
Strong Emission ◽  
Space Telescope ◽  
Byurakan Astrophysical Observatory ◽  
The Common

AbstractIt is known that among active galaxies (AG) with strong emission lines (UV-galaxies, Sy1 and Sy2, Markarian and Kazarian galaxies, radio-galaxies, QSOs host galaxies and so on) there is a large percentage of objects with double and multiple (or complex) nuclei. The common sizes of these nuclei are of the order of a few hundred parsecs or kiloparsecs. We shall discuss the results of morphological and spectroscopic observations of a number of “active galaxies” carried out with the 5m Palomar telescope, 2.6m telescope of Ambartsumian Byurakan Astrophysical Observatory, 6m telescope of Special Astrophysical Observatory in Russia, and newer Hubble Space Telescope data.

scholarly journals TheChandra,Hubble Space Telescope, and VLA View of the Circumnuclear Extended Emission in the Narrow Emission Line Galaxy NGC 2110

2006 ◽  
Vol 653 (2) ◽  
pp. 1121-1128 ◽  
Author(s):  
Daniel A. Evans ◽  
Julia C. Lee ◽  
Maria Kamenetska ◽  
Sarah C. Gallagher ◽  
Ralph P. Kraft ◽  
...  
Keyword(s):  
Emission Line ◽  
Hubble Space Telescope ◽  
Space Telescope ◽  
Line Galaxy ◽  
Extended Emission ◽  
Narrow Emission

scholarly journals Gaia-assisted discovery of a detached low-ionisation BAL quasar with very large ejection velocities

2020 ◽  
Vol 634 ◽  
pp. A111 ◽  
Author(s):  
J. P. U. Fynbo ◽  
P. Møller ◽  
K. E. Heintz ◽  
J. N. Burchett ◽  
L. Christensen ◽  
...  
Keyword(s):  
Emission Line ◽  
Absorption Line ◽  
Emission Lines ◽  
Broad Absorption ◽  
Broad Absorption Line ◽  
Red Edge ◽  
First Case ◽  
Bl Lac ◽  
Spatially Extended ◽  
Extended Emission

We report on the discovery of a peculiar broad absorption line (BAL) quasar identified in our Gaia-assisted survey of red quasars. The systemic redshift of this quasar was difficult to establish because of the absence of conspicuous emission lines. Based on deep and broad BAL troughs of at least Si IV, C IV, and Al III, a redshift of z = 2.41 was established under the assumption that the systemic redshift can be inferred from the red edge of the BAL troughs. However, we observe a weak and spatially extended emission line at 4450 Å that is most likely due to Lyman-α emission, which implies a systemic redshift of z = 2.66 if correctly identified. There is also evidence for the onset of Lyman-α forest absorption bluewards of 4450 Å and evidence for Hα emission in the K band consistent with a systemic redshift of z = 2.66. If this redshift is correct, the quasar is an extreme example of a detached low-ionisation BAL quasar. The BALs must originate from material moving with very large velocities ranging from 22 000 km s−1 to 40 000 km s−1. To our knowledge, this is the first case of a systemic-redshift measurement based on extended Lyman-α emission for a BAL quasar. This method could also be useful in cases of sufficiently distant BL Lac quasars without systemic-redshift information.

Dissecting quasars with the J-PAS narrow-band photometric survey

2019 ◽  
Vol 15 (S356) ◽  
pp. 12-16
Author(s):  
Silvia Bonoli ◽  
Giorgio Calderone ◽  
Raul Abramo ◽  
Jailson Alcaniz ◽  
Narciso Benitez ◽  
...  
Keyword(s):  
Emission Line ◽  
Wavelength Range ◽  
Software Package ◽  
Narrow Band ◽  
Active Galaxies ◽  
Emission Lines ◽  
Low Resolution ◽  
Strong Emission ◽  
Optical Wavelength ◽  
Quasar Spectra

AbstractThe J-PAS survey will soon start observing thousands of square degrees of the Northern Sky with its unique set of 56 narrow band filters covering the entire optical wavelength range, providing, effectively, a low resolution spectra for every object detected. Active galaxies and quasars, thanks to their strong emission lines, can be easily identified and characterized with J-PAS data. A variety of studies can be performed, from IFU-like analysis of local AGN, to clustering of high-z quasars. We also expect to be able to extract intrinsic physical quasar properties from the J-PAS pseudo-spectra, including continuum slope and emission line luminosities. Here we show the first attempts of using the QSFit software package to derive the properties for 22 quasars at 0.8 < z < 2 observed by the miniJPAS survey, the first deg2 of J-PAS data obtained with an interim camera. Results are compared with the ones obtained by applying the same software to SDSS quasar spectra.

scholarly journals Hubble Space Telescope observations of Europa in and out of eclipse

2010 ◽  
Vol 9 (4) ◽  
pp. 265-271 ◽  
Author(s):  
W.B. Sparks ◽  
M. McGrath ◽  
K. Hand ◽  
H.C. Ford ◽  
P. Geissler ◽  
...  
Keyword(s):  
Hubble Space Telescope ◽  
Broad Band ◽  
Line Emission ◽  
Optical Emission ◽  
High Energy ◽  
High Energy Particle ◽  
Wide Field ◽  
Particle Radiation ◽  
Space Telescope ◽  
Solar Blind

AbstractEuropa is a prime target for astrobiology and has been prioritized as the next target for a National Aeronautics and Space Administration flagship mission. It is important, therefore, that we advance our understanding of Europa, its ocean and physical environment as much as possible. Here, we describe observations of Europa obtained during its orbital eclipse by Jupiter using the Hubble Space Telescope. We obtained Advanced Camera for Surveys Solar Blind Channel far ultraviolet low-resolution spectra that show oxygen line emission both in and out of eclipse. We also used the Wide-Field and Planetary Camera-2 and searched for broad-band optical emission from fluorescence of the surface material, arising from the very high level of incident energetic particle radiation on ices and potentially organic substances. The high-energy particle radiation at the surface of Europa is extremely intense and is responsible for the production of a tenuous oxygen atmosphere and associated FUV line emission. Approximately 50% of the oxygen emission lasts at least a few hours into the eclipse. We discuss the detection limits of the optical emission, which allow us to estimate the fraction of incident energy reradiated at optical wavelengths, through electron-excited emission, Cherenkov radiation in the ice and fluorescent processes.

scholarly journals UV Monochromatic Imaging of the Protoplanetary Nebula Hen 3-1475 Using HST STIS

Galaxies ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 141
Author(s):  
Xuan Fang ◽  
Martín Guerrero ◽  
Ana Castro ◽  
Jesús Toalá ◽  
Bruce Balick ◽  
...  
Keyword(s):  
Hubble Space Telescope ◽  
Critical Role ◽  
Planetary Nebulae ◽  
Emission Lines ◽  
Comparison Analysis ◽  
Space Telescope ◽  
Monochromatic Imaging ◽  
Protoplanetary Nebula ◽  
Low Dispersion ◽  
Negative Gradient

Collimated outflows and jets play a critical role in shaping planetary nebulae (PNe), especially in the brief transition from a spherical AGB envelope to an aspherical PN, which is called the protoplanetary nebula (pPN) phase. We present UV observations of Hen 3-1475, a bipolar pPN with fast, highly collimated jets, obtained with STIS on board the Hubble Space Telescope (HST). The deep, low-dispersion spectroscopy enabled monochromatic imaging of Hen 3-1475 in different UV nebular emission lines; this is the first of such attempt ever conducted for a pPN. The northwest inner knot (NW1) is resolved into four components in Mg ii λ 2800. Through comparison analysis with the HST optical narrowband images obtained 6 yr earlier, we found that these components of NW1 hardly move, despite of a negative gradient of high radial velocities, from −1550 km s - 1 on the innermost component to ∼−300 km s - 1 on the outermost. These NW1 knot components might thus be quasi-stationary shocks near the tip of the conical outflow of Hen 3-1475.

scholarly journals High resolution observations of BD +30 3639 − A young PN

1997 ◽  
Vol 180 ◽  
pp. 99-99
Author(s):  
M. Bryce ◽  
G. Mellema
Keyword(s):  
Hubble Space Telescope ◽  
Optical Emission ◽  
Closed Shell ◽  
Detailed Comparison ◽  
Central Star ◽  
Emission Lines ◽  
Radio Image ◽  
Spatially Resolved ◽  
True Shape ◽  
Spatially Extended

Sub-arcsecond resolution radio and optical images of the young planetary nebula BD +30 3639 look superficially very similar, showing a pronounced box-shaped bright nebular shell. However, a detailed comparison at high spatial resolution reveals several regions where the optical emission is obscured by localised dusty regions. The highest resolution radio image to date of this PN, a 6 cm map obtained by combining MERLIN and VLA observations (Bryce et al, 1996) has been compared to the highest resolution optical Hβ image from the Hubble Space Telescope (obtained by J.P. Harrington and collaborators) to reveal the differences in emission which are probably due in the main to dust obscuration at optical wavelengths (Bryce et al, 1996 & Arnaud, Borkowski & Harrington, 1996). New 6 km s–1 resolution, spatially resolved spectra of optical emission lines, obtained using the Utrecht echelle spectrometer on the 4.2 m William Herschell Telescope, show that this nebula is bright in the low ionisation emission lines of [N II] 6548 + 6584 å and also appears to be more spatially extended than in the fainter, high ionisation [O III] 5007 å emission. The velocity ellipse observed from a long slit oriented north-south was found to be tilted, indicating an inclined, elliptical morphology rather than a simple, radially expanding spherical shell and the gaps in the velocity ellipse observed with an east-west slit suggest that the true shape is probably an open ring-like structure rather than a closed shell. A deep exposure of the [N II] 6584 å emission line appears to show a collimated, accelerating flow in an eastward direction away from the central star and extending well beyond the main bright nebular ring. It was also observed in the Hydrogen and [Nii] 6548 å emission lines. The H2 1–0 S(1) image of BD +30 3639 by Graham et al (1993) also shows a feature to the east of the main nebular ring. This may well be related to faint halo structures detected by Harrington and collaborators from their HST images (private communication).

A step further on the physical, kinematic and excitation properties of PNe

2018 ◽  
Vol 14 (S343) ◽  
pp. 409-410
Author(s):  
Denise Rocha Gonçalves ◽  
Stavros Akras
Keyword(s):  
Central Star ◽  
The Other ◽  
Emission Lines ◽  
Formation Processes ◽  
Excitation Mechanism ◽  
Electron Densities ◽  
Chemical Abundances ◽  
Shock Models ◽  
Intense Emission

AbstractPNe are known to be photoionized objects. However they also have low-ionization structures (LIS) with different excitation behavior. We are only now starting to answer why most LIS have lower electron densities than the PN shells hosting them, and whether or not their intense emission in low-ionization lines is the key to their main excitation mechanism. Can LIS line ratios, chemical abundances and kinematics enlight the interplay between the different excitation and formation processes in PNe? Based on the spectra of five PNe with LIS and using new diagnostic diagrams from shock models, we demonstrate that LIS’s main excitation is due to shocks, whereas the other components are mainly photoionized. We propose new diagnostic diagrams involving a few emission lines ([N II], [O III], [S II]) and fshocks/f*, where fshocks and f* are the ionization photon fluxes due to the shocks and to the central star ionizing continuum, respectively.

scholarly journals New Models for Massive Star Populations in Young Starbursts: Summary of the Models and Applications

1999 ◽  
Vol 186 ◽  
pp. 285-285
Author(s):  
Daniel Schaerer ◽  
William D. Vacca
Keyword(s):  
Emission Line ◽  
Stellar Evolution ◽  
Massive Star ◽  
Optical Emission ◽  
Emission Lines ◽  
Evolutionary Synthesis ◽  
Stellar Spectra ◽  
New Models ◽  
Helium Emission ◽  
Line Strengths

Using the latest stellar evolution models, theoretical stellar spectra, and a compilation of observed emission line strengths from Wolf-Rayet (WR) stars, we have constructed evolutionary synthesis models for young starbursts (Schaerer & Vacca 1997; see also Schaerer 1996). We provide detailed predictions of UV and optical emission line strengths for both the WR stellar lines and the major nebular hydrogen and helium emission lines, as a function of several input parameters related to the starburst episode.

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