scholarly journals Infrared Radiation from Compact Objects

1972 ◽  
Vol 44 ◽  
pp. 163-163
Author(s):  
G. Neugebauer
Keyword(s):  
Power Law ◽  
Infrared Radiation ◽  
Optical Emission ◽  
Seyfert Galaxies ◽  
Compact Objects ◽  
Infrared Excess ◽  
Large Variability ◽  
Infrared Observations ◽  
Ngc 1068 ◽  
To Come

Current infrared observations of Seyfert galaxies, QSOs, and compact galaxies in the lists of Markarian and Zwicky have been reviewed. The bright Seyfert galaxies generally show similar infrared excesses at the longer wavelengths accessible from the ground. Only NGC 1068 has been observed, by F. J. Low, in the 100μ region; if the spectral distributions of all Seyfert galaxies are similar to that of NGC 1068, the intrinsic luminosities vary from 1 to 100 × 1044 erg s−1. Measurements by Kleinmann and Low, Gillett and Stein, Pacholczyk, and Penston and Neugebauer at 10 and 2μ apparently confirm variability of NGC 1068 and NGC 4151 on a time scale too short to allow the infrared radiation to come predominantly from dust shells.The published infrared observations of QSOs have been limited to wavelengths shorter than 3.5μ except for 3C 273. The energy distributions either show a power law fall-off, a flat spectrum, or a combination of these two. Those four QSOs which show large variability all have steep power law spectra. If one accepts that the distance of QSOs are cosmological, the extrapolated luminosity at 2μ of several QSOs exceeds that of 3C 273. The integrated luminosity of 3C 273 depends critically on the spectrum in the unobserved 10–1000μ region, but is probably in the range 1047 to 1048 erg s−1.The infrared observations of the compact Markarian and Zwicky objects show a correlation between the infrared excess and the broad optical emission lines. Presumably the infrared can be used to differentiate between the stellar and non-thermal components of the radiation from these objects.

scholarly journals Infrared Observations of Radio Galaxies

1982 ◽  
Vol 97 ◽  
pp. 239-246
Author(s):  
George H. Rieke
Keyword(s):  
Thermal Emission ◽  
Optical Emission ◽  
Seyfert Galaxies ◽  
Radio Sources ◽  
Extragalactic Radio Source ◽  
Extragalactic Source ◽  
Infrared Observations ◽  
Infrared Studies ◽  
Complete Identification ◽  
Ultraviolet Photons

For technical reasons, infrared studies of active galaxies have lagged far behind optical and radio ones. This is unfortunate, since entirely new aspects of these sources are often revealed in the infrared. The extreme efficiency of dust at degrading ultraviolet photons into cool thermal emission frequently makes the luminosity of an extragalactic source inaccessible to optical and radio astronomers. At the same time, the effects of dust on optical emission line ratios and continuum shapes can be profound. The complete identification of samples of radio sources will require infrared observations to supplement the optical techniques now generally employed, and the extreme properties of the sources bright in the infrared can provide new insights to conditions in extragalactic nonthermal sources. To illustrate these points, I will discuss three cases: 1.) galaxies undergoing a powerful burst of star formation, 2.) intermediate type Seyfert galaxies, and 3.) an extreme infrared identification of an extragalactic radio source.

scholarly journals X-Ray Properties of Extragalactic Compact Objects

1984 ◽  
Vol 110 ◽  
pp. 85-94
Author(s):  
G. Zamorani
Keyword(s):  
Optical Emission ◽  
Seyfert Galaxies ◽  
Compact Objects ◽  
Relative Importance ◽  
Bl Lac Objects ◽  
X Ray ◽  
Working Definition ◽  
The Subject ◽  
Definition Of ◽  
5 Ghz

The compact objects which are the subject of this talk are essentially quasars and Seyfert galaxies; I will only briefly mention a couple of results about BL Lac objects. Before describing the X-ray properties of these objects, it is useful to introduce a “working” definition of radio-quiet and radio-loud quasars: I will call radio-loud quasars all the objects which have been detected at radio frequencies and have a spectral index between radio (5 GHz) and optical frequencies (2500 A) greater than 0.35 (Zamorani et al. 1981); all the other objects will be considered radio-quiet. Note that this definition is independent of distance and is a function only of the relative importance of radio and optical emission.

scholarly journals Attempts to Detect Neutral Hydrogen in Compact Objects

1972 ◽  
Vol 44 ◽  
pp. 259-263
Author(s):  
William A. Dent
Keyword(s):  
Column Density ◽  
Neutral Hydrogen ◽  
Seyfert Galaxies ◽  
Compact Objects ◽  
Upper Limits ◽  
Ngc 1068 ◽  
Stellar Sources ◽  
Ngc 1275 ◽  
3C 120

An attempt was made to detect the redshifted Hi line in absorption in the quasi-stellar sources 3C 273 and 1510 - 08 and in the N-galaxies 3C 120 and 3C 371. The Seyfert galaxies NGC 1068 and NGC 1275 were also searched for Hi in absorption as well as in emission. Although no lines were detected, it was possible to place upper limits on the column density of Hi in all these objects, as well as upper limits on the mass of Hi in the Seyfert galaxies observed.

scholarly journals Subarcsecond-Scale Optical and Radio Structure Correlations in Seyfert Galaxies

1994 ◽  
Vol 159 ◽  
pp. 455-455
Author(s):  
R.W. Pogge ◽  
M.M. Derobertis
Keyword(s):  
Optical Emission ◽  
Detailed Comparison ◽  
Seyfert Galaxies ◽  
Radio Continuum ◽  
Radio Structure ◽  
Structure Correlations ◽  
Radio Lobe ◽  
Extended Radio ◽  
Ngc 1068 ◽  
Basic Features

An unanswered question in the study of Seyferts is the nature of the relationship between the extended radio-continuum and optical emission-line gas. Detailed comparison is difficult as most Seyferts have radio structure on sub-arcsecond scales, while most optical imaging is on 1–2″ scales. Despite this, some basic features have emerged. Extended radio and optical emission regions are generally aligned in projection, but the overall optical emission extends to much greater galactocentric radii. Pedlar et al. (1989) and Whittle et al. (1986) have reported a tendency for optical emission knots to lie behind the radio lobes, interpreted in terms of the “cooling length” of gas heated by a radiative bowshock driven into the ISM by a jet. In NGC 1068 (Cecil et al. 1990) and M51 (Cecil 1988), however, ambient gas appears to be piling up ahead of a radio lobe at the terminus of the radio jet.

scholarly journals Optical/infrared observations of RV Tauri stars

1987 ◽  
Vol 122 ◽  
pp. 537-540
Author(s):  
M. J. Goldsmith ◽  
A. Evans ◽  
J. S. Albinson ◽  
M. F. Bode
Keyword(s):  
Dust Formation ◽  
Infrared Excess ◽  
Infrared Observations ◽  
Dust Shells ◽  
Discernible Difference

Optical/infrared observations of RV Tauri stars obtained at SAAO have allowed the natures of the dust shells around stars with infrared excess to be investigated. The data suggest that dust formation occurs sporadically and that some stars have multiple shells. There is no photometrically discernible difference between carbon- and oxygen-rich stars or their dust shells. There is some evidence that stars with higher metallicity have more dust.

scholarly journals Exploring the inner parsecs of active galactic nuclei using near-infrared high resolution polarimetric simulations with MontAGN

2018 ◽  
Vol 612 ◽  
pp. A69 ◽  
Author(s):  
L. Grosset ◽  
D. Rouan ◽  
D. Gratadour ◽  
D. Pelat ◽  
J. Orkisz ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Optical Depth ◽  
Near Infrared ◽  
Galactic Nuclei ◽  
Constant Density ◽  
Characteristic Model ◽  
Infrared Observations ◽  
Current Estimation ◽  
Direct Light ◽  
Ngc 1068

Aims. In this paper we aim to constrain the properties of dust structures in the central first parsecs of active galactic nuclei (AGN). Our goal is to study the required optical depth and composition of different dusty and ionised structures. Methods. We developed a radiative transfer code called Monte Carlo for Active Galactic Nuclei (MontAGN), which is optimised for polarimetric observations in the infrared. With both this code and STOKES, designed to be relevant from the hard X-ray band to near-infrared wavelengths, we investigate the polarisation emerging from a characteristic model of the AGN environment. For this purpose, we compare predictions of our models with previous infrared observations of NGC 1068, and try to reproduce several key polarisation patterns revealed by polarisation mapping. Results. We constrain the required dust structures and their densities. More precisely, we find that the electron density inside the ionisation cone is about 2.0 × 109 m−3. With structures constituted of spherical grains of constant density, we also highlight that the torus should be thicker than 20 in term of K-band optical depth to block direct light from the centre. It should also have a stratification in density: a less dense outer rim with an optical depth at 2.2 μm typically between 0.8 and 4 for observing the double scattering effect previously proposed. Conclusions. We bring constraints on the dust structures in the inner parsecs of an AGN model supposed to describe NGC 1068. When compared to observations, this leads to an optical depth of at least 20 in the Ks band for the torus of NGC 1068, corresponding to τV ≈ 170, which is within the range of current estimation based on observations. In the future, we will improve our study by including non-uniform dust structures and aligned elongated grains to constrain other possible interpretations of the observations.

scholarly journals Constraining Soft and Hard X-Ray Irradiation in Ultraluminous X-Ray Sources

2021 ◽  
Vol 922 (2) ◽  
pp. 91
Author(s):  
Yanli Qiu ◽  
Hua Feng
Keyword(s):  
Optical Emission ◽  
Current Data ◽  
Compact Objects ◽  
X Rays ◽  
Optical Counterpart ◽  
X Ray ◽  
Outer Disk ◽  
Stringent Constraint ◽  
Supercritical Accretion ◽  
Key Questions

Abstract Most ultraluminous X-ray sources (ULXs) are argued to be powered by supercritical accretion onto compact objects. One of the key questions regarding these objects is whether or not the hard X-rays are geometrically beamed toward the symmetric axis. We propose testing the scenario using disk irradiation to see how much the outer accretion disk sees the central hard X-rays. We collect a sample of 11 bright ULXs with an identification of a unique optical counterpart, and model their optical fluxes considering two irradiating sources: soft X-rays from the photosphere of the optically thick wind driven by supercritical accretion, and if needed in addition, hard X-rays from the Comptonization component. Our results indicate that the soft X-ray irradiation can account for the optical emission in the majority of ULXs, and the fraction of hard X-rays reprocessed on the outer disk is constrained to be no more than ∼10−2 in general. Such an upper limit is well consistent with the irradiation fraction expected in the case of no beaming. Therefore, no stringent constraint on the beaming effect can be placed according to the current data quality.

A Study of the Seyfert Galaxy NGC 4151

1967 ◽  
Vol 1 (1) ◽  
pp. 7-7 ◽  
Author(s):  
J. B. Oke ◽  
Wallace L. W. Sargent
Keyword(s):  
Continuous Spectrum ◽  
Seyfert Galaxy ◽  
Seyfert Galaxies ◽  
Radio Galaxies ◽  
Emission Lines ◽  
Ngc 4151 ◽  
Broad Emission ◽  
Ngc 1068 ◽  
Stellar Sources ◽  
No Absorption

The small group of known Seyfert galaxies (Seyfert 1943) is of interest because it is clear that some violent activity is occurring in the nucleus, and some of the properties suggest a relationship with quasi-stellar sources. The spectrum of a Seyfert galaxy consists of strong, often very broad, emission lines superposed on a continuous spectrum which in some cases shows no absorption-line features. Two of the galaxies, NGC 1068 and 1275, are radio galaxies and the latter is known to be variable at radio frequencies (Dent 1966).

scholarly journals Survey of Milliarcsec Structure in Eight Seyfert Galaxies: Results on NGC 1068 and NGC 4151

1998 ◽  
Vol 164 ◽  
pp. 301-302 ◽  
Author(s):  
A. L. Roy ◽  
J. S. Ulvestad ◽  
E. J. M. Colbert ◽  
A. S. Wilson ◽  
R. P. Norris
Keyword(s):  
Spectral Index ◽  
Low Frequency ◽  
Seyfert Galaxies ◽  
Scale Structure ◽  
Scale Morphology ◽  
Ngc 4151 ◽  
Ngc 1068

AbstractWe are surveying eight nearby Seyfert galaxies (four Sy1s and four Sy2s) that have compact radio cores, using the VLBA. We are interested in parsec-scale morphology and low-frequency absorption effects, and so are observing four frequencies (1.6, 4.8, 8.4 and 15 GHz) to get spectral-index diagnostics. In this paper, we present results on two galaxies, NGC 1068 and NGC 4151. NGC 4151 shows a curved radio jet on the sub-parsec scale, with the smallest scale structure misaligned by 55° from the jet on scales of parsecs to hundreds of parsecs. NGC 1068 contains several components in the inner tens of parsecs, with those components showing a variety of absorption and resolution effects.

scholarly journals The Large-Scale Activity in NGC 1068

1989 ◽  
Vol 134 ◽  
pp. 343-344
Author(s):  
J. Bland ◽  
G. N. Cecil
Keyword(s):  
Large Scale ◽  
Physical State ◽  
Seyfert Galaxy ◽  
Optical Emission ◽  
Field Of View ◽  
Ionized Gas ◽  
Nuclear Activity ◽  
Fabry Perot ◽  
Ngc 1068 ◽  
Resolution Study

While NGC 1068 has received much attention in recent years, little is known of the large-scale dynamics and physical state of the ionized gas in this nearby Seyfert galaxy and, in particular, its connection with the nuclear activity. We have used the Hawaii Imaging Fabry-Perot Interferometer (HIFI) at the CFHT to obtain detailed spectrophotometry at 65 kms−1 resolution (FWHM) over the Hα and neighbouring [N II] lines. The final maps are derived from 100 000 fits to spectra taken at 0.4″ increments over a 200″ field-of-view. (A higher resolution study which concentrates on the circumnuclear, optical emission and its relation to the radio jet is presented at this conference by Cecil & Bland.)

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