Extended optical line emission associated with radio galaxies

1986 ◽  
Vol 64 (4) ◽  
pp. 392-397 ◽  
Author(s):  
Wil van Breugel
Keyword(s):  
Emission Line ◽  
Ambient Medium ◽  
Line Emission ◽  
Optical Emission ◽  
Radio Galaxies ◽  
General Properties ◽  
Extragalactic Jets ◽  
Optical Line

Observations of radio galaxies that have extended optical emission-line regions provide a new way of studying the interaction of extragalactic jets with their ambient medium. Their general properties are briefly reviewed and are illustrated using recent results on 4C 29.30 and Minkowski's Object.

scholarly journals High-Redshift Radio Galaxies

1995 ◽  
Vol 10 ◽  
pp. 543-546
Author(s):  
George Miley
Keyword(s):  
Galaxy Formation ◽  
High Redshift ◽  
Line Emission ◽  
Optical Emission ◽  
Delta Function ◽  
Radio Galaxies ◽  
Radio Continuum ◽  
Spatially Resolved ◽  
A Value ◽  
Optical Line

Radio galaxies are unique cosmological probes. As with radio-loud quasars, the presence of luminous radio continuum and optical line emission enable radio galaxies to be observed and recognized at large distances, up to z = 4.2. However, unlike the situation for most quasars, their optical emission can be spatially resolved from the ground and studied in detail.Progress in detecting distant radio galaxies has been rapid in recent years due to the use of CCDs and the exploitation of new selection criteria. Now, more than 60 radio galaxies are known with z > 2. More than half of these have been found by our group by concentrating on radio sources with the steepest spectra, most of these in a “Key Programme” of the European Southern Observatory. Although several people contributed to this Key Programme, most of the work was done by Huub Röttgering, who presented his Ph.D thesis in January and Rob van Ojik, who succeededhim. Redshifts of 1.5 to 4 correspond to a time when the Universe was 10% -20% of its present age. This was a crucial period in history when galaxy formation must have been rampant. It corresponds to the AGN era, a two-billion year “delta function” in the population evolution of luminous quasars and radio galaxies, when their space-density rose to a value several hundred times larger than the present density before the species mysteriously and suddenly became almost extinct.

scholarly journals Discovery of diffuse optical emission lines from the inner Galaxy: Evidence for LI(N)ER-like gas

2020 ◽  
Vol 6 (27) ◽  
pp. eaay9711 ◽  
Author(s):  
D. Krishnarao ◽  
R. A. Benjamin ◽  
L. M. Haffner
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Center ◽  
Line Emission ◽  
Galactic Nuclei ◽  
Optical Emission ◽  
Hydrogen Gas ◽  
Emission Lines ◽  
Neutral Gas ◽  
Optical Line ◽  
Tilted Disk

Optical emission lines are used to categorize galaxies into three groups according to their dominant central radiation source: active galactic nuclei, star formation, or low-ionization (nuclear) emission regions [LI(N)ERs] that may trace ionizing radiation from older stellar populations. Using the Wisconsin H-Alpha Mapper, we detect optical line emission in low-extinction windows within eight degrees of Galactic Center. The emission is associated with the 1.5-kiloparsec-radius “Tilted Disk” of neutral gas. We modify a model of this disk and find that the hydrogen gas observed is at least 48% ionized. The ratio [NII] λ6584 angstroms/Hα λ6563 angstroms increases from 0.3 to 2.5 with Galactocentric radius; [OIII] λ5007 angstroms and Hβ λ4861 angstroms are also sometimes detected. The line ratios for most Tilted Disk sightlines are characteristic of LI(N)ER galaxies.

scholarly journals Radio spectral index distribution of SDSS-FIRST sources across optical diagnostic diagrams

2019 ◽  
Vol 630 ◽  
pp. A83 ◽  
Author(s):  
Michal Zajaček ◽  
Gerold Busch ◽  
Mónica Valencia-S. ◽  
Andreas Eckart ◽  
Silke Britzen ◽  
...  
Keyword(s):  
Black Holes ◽  
Emission Line ◽  
Spectral Index ◽  
Line Emission ◽  
Optical Emission ◽  
Supermassive Black Holes ◽  
Emission Region ◽  
Optical Diagnostic ◽  
Liner Galaxies ◽  
Ionization Ratio

Context. The empirical relations between supermassive black holes and their host spheroids point towards the crucial role of galactic nuclei in affecting the properties of their hosts. A detailed understanding of how the activity of a galactic nucleus regulates the growth of its host is still missing. Aims. To understand the activity and the types of accretion of supermassive black holes in different hosts, it is essential to study the radio-optical properties of a large sample of extragalactic sources. In particular, we aim to study the radio spectral index trends across the optical emission line diagnostic diagrams to search for potential (anti)correlations. Methods. To this goal, we combined flux densities from the radio FIRST survey at 1.4 GHz (with the flux density range 10 mJy ≤ F1.4 ≤ 100 mJy) for 396 SDSS sources at intermediate redshift (0.04 ≤ z ≤ 0.4) with the Effelsberg radiotelescope measurements at 4.85 GHz and 10.45 GHz. The information about the optical emission-line ratios is obtained from the SDSS-DR7 catalogue. Results. Using the Effelsberg data, we were able to infer the two-point radio spectral index distributions for star-forming galaxies, composite galaxies (with a combined contribution to the line emission from the star formation and AGN activity), Seyferts, and low ionization narrow emission region (LINER) galaxies. Conclusions. While studying the distribution of steep, flat, and inverted sources across optical diagnostic diagrams, we found three distinct classes of radio emitters for our sample: (i) sources with a steep radio index, high ionization ratio, and high radio loudness, (ii) sources with a flat radio index, lower ionization ratio, and intermediate radio loudness, (iii) sources with an inverted radio index, low ionization ratio, and low radio loudness. The classes (i), (ii), and (iii) cluster mainly along the transition from Seyfert to LINER sources in the optical diagnostic (Baldwin, Phillips & Telervich; BPT) diagram. We interpret these groups as a result of the recurrent nuclear-jet activity.

scholarly journals Peculiar emission line spectra of core extremely red BOSS quasars at z∼2–3: orientation and/or evolution?

2020 ◽  
Vol 634 ◽  
pp. A116 ◽  
Author(s):  
M. Villar Martín ◽  
M. Perna ◽  
A. Humphrey ◽  
N. Castro Rodríguez ◽  
L. Binette ◽  
...  
Keyword(s):  
Emission Line ◽  
Near Infrared ◽  
Outer Part ◽  
Line Emission ◽  
Optical Emission ◽  
Broad Line ◽  
Broad Line Region ◽  
Line Region ◽  
Evolutionary Phase

Context. Core extremely red quasars (core ERQ) have been proposed to represent an intermediate evolutionary phase in which a heavily obscured quasar blows out the circumnuclear interstellar medium with very energetic outflows before it becomes an optical quasar. Aims. We investigate whether the properties of core ERQ fit the AGN orientation-based unification scenario. Methods. We revised the general UV and optical emission line properties of core ERQ in the context of the orientation-based scenario. We used diagnostic diagrams based on UV emission line ratios and UV-to-optical line kinematic information to compare the physical and kinematic gas properties of core ERQ with those of other luminous narrow- and broad-line AGN. In particular, we provide a revised comparison of the [OIII] kinematics in 21 core ERQ (20 from Perrotta et al. 2019, MNRAS, 488, 4126 and SDSS J171420.38+414815.7, based on GTC EMIR near-infrared spectroscopy) with other samples of quasars with matching luminosity with the aim of evaluating whether core ERQ host the most extreme [OIII] outflows. Results. The UV line ratios suggest that the physical properties (e.g., density and metallicity) of the ionised gas in core ERQ are similar to those observed in the broad-line region of blue nitrogen-loud quasars. The [OIII] outflow velocities of core ERQ are on average consistent with those of very luminous blue type 1 quasars, although extreme outflows are much more frequent in core ERQ. These similarities can be explained in the context of the AGN unification model under the assumption that core ERQ are viewed with an intermediate orientation between type 2 (edge-on) and type 1 (face-on) quasars. Conclusions. We propose that core ERQ are very luminous but otherwise normal quasars viewed at an intermediate orientation. This orientation allows a direct view of the outer part of the large broad-line region from which core ERQ UV line emission originates; the extreme [OIII] outflow velocities are instead a consequence of the very high luminosity of core ERQ.

scholarly journals Reconciling escape fractions and observed line emission in Lyman-continuum-leaking galaxies

2020 ◽  
Vol 644 ◽  
pp. A21
Author(s):  
L. Ramambason ◽  
D. Schaerer ◽  
G. Stasińska ◽  
Y. I. Izotov ◽  
N. G. Guseva ◽  
...  
Keyword(s):  
Emission Line ◽  
Column Density ◽  
Line Emission ◽  
Optical Emission ◽  
Emission Lines ◽  
Zone Model ◽  
High Hydrogen ◽  
Lyman Continuum ◽  
Hydrogen Column Density ◽  
Photoionization Model

Context. Finding and elucidating the properties of Lyman-continuum(LyC)-emitting galaxies is an important step in improving our understanding of cosmic reionization. Aims. Although the z ∼ 0.3 − 0.4 LyC emitters found recently show strong optical emission lines, no consistent quantitative photoionization model taking into account the escape of ionizing photons and inhomogenous interstellar medium (ISM) geometry of these galaxies has yet been constructed. Furthermore, it is unclear to what extent these emission lines can be used to distinguish LyC emitters. Methods. To address these questions we construct one- and two-zone photoionization models accounting for the observed LyC escape, which we compare to the observed emission line measurements. The main diagnostics used include lines of [O III], [O II], and [O I] plus sulfur lines ([S II], [S III]) and a nitrogen line ([N II]), which probe regions of different ionization in the ISM. Results. We find that single (one-zone) density-bounded photoionization models cannot reproduce the emission lines of the LyC leakers, as pointed out by earlier studies, because they systematically underpredict the lines of species of low ionization potential, such as [O I] and [S II]. Introducing a two-zone model, with differing ionization parameter and a variable covering fraction and where one of the zones is density-bounded, we show that the observed emission line ratios of the LyC emitters are well reproduced. Furthermore, our model yields LyC escape fractions, which are in fair agreement with the observations and independent measurements. The [O I] λ6300 excess, which is observed in some LyC leakers, can be naturally explained in this model, for example by emission from low-ionization and low-filling-factor gas. LyC emitters with a high escape fraction (fesc ≳ 38%) are deficient both in [O I] λ6300 and in [S II] λλ6716,6731. We also confirm that a [S II] λλ6716,6731 deficiency can be used to select LyC emitter candidates, as suggested earlier. Finally, we find indications for a possible dichotomy in terms of escape mechanisms for LyC photons between galaxies with relatively low (fesc ≲ 10%) and higher escape fractions. Conclusions. We conclude that two-zone photoionization models are sufficient and required to explain the observed emission line properties of z ∼ 0.3 − 0.4 LyC emitters. This is in agreement with UV absorption line studies, which also show the co-existence of regions with high hydrogen column density (i.e., no escape of ionizing photons) and density-bounded or very low column density regions responsible for the observed escape of LyC radiation. These simple but consistent models provide a first step towards the use of optical emission lines and their ratios as quantitative diagnostics of LyC escape from galaxies.

scholarly journals Dust and Ionized Gas in Active Radio Elliptical Galaxies

1990 ◽  
Vol 124 ◽  
pp. 431-435 ◽  
Author(s):  
D.A. Forbes ◽  
W.B. Sparks ◽  
F.D. Macchetto
Keyword(s):  
Emission Line ◽  
Strong Evidence ◽  
Line Emission ◽  
Elliptical Galaxies ◽  
Ionized Gas ◽  
Narrow Bandwidth ◽  
Optical Line ◽  
Excitation Mechanisms

AbstractWe present broad and narrow bandwidth imaging of three southern elliptical galaxies which have flat-spectrum active radio cores (NGC 1052, IC 1459 and NGC 6958). All three contain dust and extended low excitation optical line emission, particularly extensive in the case of NGC 1052 which has a large Hα + [Nil] luminosity. Both NGC 1052 and IC 1459 have a spiral morphology in emission-line images. All three display independent strong evidence that a merger or infall event has recently occurred, i.e., extensive and infalling HI gas in NGC 1052, a counter-rotating core in IC 1459 and Malin-Carter shells in NGC 6958. This infall event is the most likely origin for the emission-line gas and dust, and we a currently investigating possible excitation mechanisms (Sparks et al. 1990).

scholarly journals Why are some brightest cluster galaxies forming stars?

2007 ◽  
Vol 3 (S245) ◽  
pp. 185-188
Author(s):  
Christopher P. O'Dea ◽  
Alice Quillen ◽  
Nicholas Zufelt ◽  
Jaehong Park ◽  
Alastair Edge ◽  
...  
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Line Emission ◽  
Optical Emission ◽  
Infrared Emission ◽  
X Ray ◽  
Cluster Galaxies ◽  
Brightest Cluster Galaxies ◽  
First Results ◽  
Optical Line

AbstractWe present first results from an imaging survey with the Spitzer Space Telescope of 62 brightest cluster galaxies with optical line emission located in the cores of X-ray luminous clusters selected from the ROSAT All-Sky Survey. We find that 1/3 of these sources have signs of excess infrared emission; 22 objects of 62 are detected at 70 μm and 19 have 8 to 5.8 μm flux ratios above 0.98. The strength of the excess emission correlates with the luminosity of the optical emission lines. Excluding the four systems dominated by an AGN, the excess mid-infrared emission in the remaining brightest cluster galaxies is likely powered by star formation. We find a correlation between mass deposition rate from a cooling flow model for the X-ray emission and the star formation rate estimated from the infrared luminosity. The star formation rates are 1/10 to 1/100 of the mass deposition rates expected in the absence of heating suggesting that the re-heating of the ICM is generally very effective in reducing the amount of mass cooling from the hot phase.

scholarly journals MODELING THE SS 433 JET BENDS

2008 ◽  
Vol 17 (10) ◽  
pp. 1925-1930 ◽  
Author(s):  
H. L. MARSHALL ◽  
CLAUDE R. CANIZARES ◽  
NORBERT S. SCHULZ ◽  
SEBASTIAN HEINZ ◽  
TODD C. HILLWIG ◽  
...  
Keyword(s):  
Emission Measure ◽  
Line Emission ◽  
Optical Emission ◽  
Local Environment ◽  
Emission Lines ◽  
X Ray ◽  
Ss 433 ◽  
Jet Cooling ◽  
Doppler Shifts ◽  
Optical Line

We fit Chandra HETGS data obtained for the unusual X-ray binary SS 433. While line strengths and continuum levels hardly change, the jet Doppler shifts show aperiodic variations that probably result from shocks in interactions with the local environment. The X-ray and optical emission line regions are found to be related but not coincident as the optical line emission persists for days while the X-ray emission lines fade in less than 5000 s. The X-ray spectrum of the blueshifted jet shows over two dozen emission lines from plasma at a variety of temperatures. The emission measure distribution derived from the spectrum can be used to test jet cooling models.

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