The Radio Spectrum Across Three Tailed Radio Galaxies

1984 ◽

Vol 5 (4) ◽

pp. 516-529 ◽

Cited By ~ 17

Author(s):

O. B. Slee ◽

J. E. Reynolds

Keyword(s):

Radio Galaxies ◽

High Energy ◽

Radio Spectrum ◽

Radio Sources ◽

Clusters Of Galaxies ◽

Detailed Review ◽

X Ray ◽

High Energy Electrons ◽

Spectrum Radio ◽

Inverse Compton

It is well established (e.g. Slee et al. 1983) that radio galaxies near the centres of rich clusters of galaxies tend to have steeper radio spectra than field radio galaxies. The fact that the sources with the steepest spectra occur in clusters that are highly luminous X-ray emitters has generally been interpreted in terms of the confining influence of a hot (~108 K), relatively dense (10-2 to 10-3 electrons cm-3) intra-cluster gas; the confined relativistic plasma then preferentially loses its high-energy electrons through synchrotron and inverse Compton losses, resulting in a steepening of the radio spectrum. A more detailed review of the evidence for this process is given by Robertson (1983).

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uGMRT HI 21-cm absorption observations of two extremely inverted spectrum sources

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038923 ◽

2020 ◽

Vol 643 ◽

pp. A174

Author(s):

Mukul Mhaskey ◽

Surajit Paul ◽

Neeraj Gupta ◽

Dipanjan Mukherjee ◽

Gopal-Krishna

Keyword(s):

Optical Depth ◽

Column Density ◽

Radio Galaxies ◽

Radio Spectrum ◽

Absorption Feature ◽

Radio Sources ◽

Spin Temperature ◽

Inverted Spectrum ◽

Spectrum Radio ◽

Thick Part

We report the detection of HI 21-cm absorption in a member of the rare and recently discovered class of compact radio sources: extremely inverted spectrum extragalactic radio sources (EISERS). The EISERS conceivably form a special subclass of the inverted spectrum radio galaxies since the spectral index of the optically thick part of the spectrum for these sources crosses the synchrotron self-absorption limit of α = +2.5 (S(ν) ∝ να). We searched for HI absorption in two EISERS using the recently upgraded Giant Metrewave Radio Telescope (uGMRT) and detected an absorption feature in one of them. The strong associated HI absorption detected against the source J1209−2032 (z = 0.4040) implies an optical depth of 0.178 ± 0.02, corresponding to an HI column density of 34.8 ± 2.9 × 1020 cm−2, for an assumed HI spin temperature of 100 K and covering factor of 1. This is among the highest known optical depth and HI column densities found for compact radio sources of peaked spectrum type and supports the free-free absorption model for the steeply inverted radio spectrum of this source. For the other source, J1549+5038 (z = 2.171), no HI absorption was detected in our observations.

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Radio Observations of Moderately Compact Steep Spectrum Sources

Symposium - International Astronomical Union ◽

10.1017/s0074180900141920 ◽

1989 ◽

Vol 134 ◽

pp. 537-538

Author(s):

Chidi Akujor ◽

I.W.A. Browne ◽

P.N. Wilkinson

Keyword(s):

Radio Galaxies ◽

Radio Spectrum ◽

List Type ◽

Type Number ◽

Radio Observations ◽

Radio Structure ◽

Clear Cut ◽

Wide Range ◽

Compact Sources

It is now common practice for objects with a steep radio spectrum and compact radio structure to be lumped together and called compact steep spectrum (CSS) sources (Peacock and Wall, 1982; van Breugel, 1984 Fanti et al. 1985). This rather arbitrary categorisation results in the class containing sources with a wide range of structures, from core-jet or complex (e.g. 3C147,3C48), small classical doubles (e.g. 3C237, 3C241), to VLBI compact doubles (e.g. CTD93; Phillips and Mutel, 1982). Some of the questions we are asking include: (a)Are compact sources intrinsically small, or do they appear small because they are seen in projection?(b)Why are structures in compact radio galaxies and compact radio quasars different? Wilkinson et al. (1984) and Spencer et al (1988, in preparation)have shown that there appears to be a ‘clear-cut’ difference in morphology between quasar CSS and galaxy CSS, with quasars showing more distortions while galaxies tend to be doubles. But is this trend present even in their slightly more-extended counterparts?

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The low-frequency properties of FR 0 radio galaxies

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936254 ◽

2019 ◽

Vol 631 ◽

pp. A176 ◽

Cited By ~ 3

Author(s):

A. Capetti ◽

R. D. Baldi ◽

M. Brienza ◽

R. Morganti ◽

G. Giovannini

Keyword(s):

Large Population ◽

Low Frequency ◽

Radio Galaxies ◽

Radio Spectrum ◽

Radio Sources ◽

High Frequencies ◽

Sky Survey ◽

5 Ghz ◽

Frequency Properties ◽

Extended Emission

Using the alternative data release of the TIFR GMRT Sky Survey (TGSS), we studied the low-frequency properties of FR 0 radio galaxies, the large population of compact radio sources associated with red massive early-type galaxies revealed by surveys at 1.4 GHz. We considered TGSS observations from FR0CAT, a sample formed by 104 FR 0s at z < 0.05: all but one of them are covered by the TGSS, and 43 of them are detected above a 5σ limit of 17.5 mJy. No extended emission has been detected around the FR 0s, corresponding to a luminosity limit of ≲4 × 1023 W Hz−1 over an area of 100 kpc × 100 kpc. All but eight FR 0s have a flat or inverted spectral shape (α < 0.5) between 150 MHz and 1.4 GHz: this spectral behavior confirms the general paucity of optically thin extended emission within the TGSS beam, as is expected for their compact 1.4 GHz morphology. Data at 5 GHz were used to build their radio spectra, which are also generally flat at higher frequencies. By focusing on a sub-sample of FR 0s with flux density > 50 mJy at 1.4 GHz, we found that ∼75% of them have a convex spectrum, but with a smaller curvature than the more powerful gigahertz peaked-spectrum sources (GPS). The typical FR 0s radio spectrum is better described by a gradual steepening toward high frequencies, rather than to a transition from an optically-thick to an optically-thin regime, possibly observed in only ∼15% of the sample.

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Arcsecond Scale Polarization of BL Lac Objects

Symposium - International Astronomical Union ◽

10.1017/s0074180900080001 ◽

1996 ◽

Vol 175 ◽

pp. 55-56

Author(s):

C. Stanghellini ◽

P. Cassaro ◽

M. Bondi ◽

D. Dallacasa ◽

R. Della Ceca ◽

...

Keyword(s):

Galactic Nuclei ◽

Radio Galaxies ◽

Radio Spectrum ◽

Line Of Sight ◽

Parent Population ◽

Rapid Variability ◽

Bl Lac Objects ◽

Relativistic Jet ◽

Bl Lac ◽

Optical Continuum

BL Lac objects are an enigmatic class of active galactic nuclei. They are characterized by high luminosity, a flat radio spectrum that steepens at higher energies, relatively high optical and radio polarization, rapid variability and an optical continuum with weak or absent emission lines (see Urry and Padovani, 1995 for a recent review).These properties have been interpreted in terms of a relativistic jet closely aligned to the line of sight (Blandford and Rees, 1978, Ghisellini et al., 1993). This model, known as the beaming model, implies that there must be a so called “parent population” of radio sources intrinsically identical to BL Lac objects, but with the jets oriented at large angles to the line of sight. Browne (1983) was the first to propose the low luminosity FR I radio galaxies as the most likely candidates for the “parent population” of the core dominated BL Lac objects. An outcome of the beaming model is that all the properties not depending on orientation should be shared by the BL Lac objects and the FR I radio galaxies.

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The Relic Radio Source B2 0924+30

Symposium - International Astronomical Union ◽

10.1017/s0074180900081043 ◽

1996 ◽

Vol 175 ◽

pp. 345-346

Author(s):

U. Klein ◽

K.-H. Mack ◽

L. Gregorini ◽

P. Parma

Keyword(s):

Radio Source ◽

Rare Species ◽

Radio Galaxy ◽

Radio Galaxies ◽

Radio Spectrum ◽

Coherent Jet ◽

Double Radio Source ◽

Jet Structure

The double radio source B2 0924+30, associated with the luminous E/S0 galaxy IC2476, may be considered a prototypical genuine relic of a ‘dead’ radio galaxy as it seems to perfectly fulfill the following criteria: It has a rather steep overall radio spectrum (Ekers et al., 1981; Cordey, 1987). Its core luminosity is by far the lowest known so far (Giovannini et al., 1988). No coherent jet structure or other signs of activity are visible. Since only four possibly genuine relics of radio galaxies are known so far (Harris et al., 1993), a study of the archetypical source B2 0924+30 is of eminent importance for the understanding of this rare species of radio galaxies.

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The Radio Spectrum Across Three Tailed Radio Galaxies

Extragalactic Radio Sources ◽

10.1007/978-94-009-7781-5_10 ◽

1982 ◽

pp. 41-42

Author(s):

H. Andernach

Keyword(s):

Radio Galaxies ◽

Radio Spectrum

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Radio spectral properties and jet duty cycle in the restarted radio galaxy 3C388

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037457 ◽

2020 ◽

Vol 638 ◽

pp. A29

Author(s):

M. Brienza ◽

R. Morganti ◽

J. Harwood ◽

T. Duchet ◽

K. Rajpurohit ◽

...

Keyword(s):

Duty Cycle ◽

Radio Galaxy ◽

Low Frequency ◽

Radio Galaxies ◽

Radio Spectrum ◽

Frequency Range ◽

Very Large Array ◽

Spatially Resolved ◽

New Generation ◽

First Time

Context. Restarted radio galaxies represent a unique tool for investigating the duty cycle of the jet activity in active galactic nuclei (AGN). The radio galaxy 3C388 has long been claimed to be a peculiar example of an AGN with multi-epoch activity because it shows a very sharp discontinuity in the GHz spectral index distribution of its lobes. Aims. We present here for the first time a spatially resolved study of the radio spectrum of 3C388 down to MHz frequencies aimed at investigating the radiative age of the source and constraining its duty cycle. Methods. We used new low-frequency observations at 144 MHz performed with the Low Frequency Array and at 350 MHz performed with the Very Large Array that we combined with archival data at higher frequencies (614, 1400, and 4850 MHz). Results. We find that the spectral indices in the lower frequency range, 144−614 MHz, have flatter values (αlow ∼ 0.55−1.14) than those observed in the higher frequency range, 1400−4850 MHz, (αhigh ∼ 0.75−1.57), but they follow the same distribution across the lobes, with a systematic steepening towards the edges. However, the spectral shape throughout the source is not uniform and often deviates from standard models. This suggests that mixing of different particle populations occurs, although it remains difficult to understand whether this is caused by observational limitations (insufficient spatial resolution and/or projection effects) or by the intrinsic presence of multiple particle populations, which might be related to the two different outbursts. Conclusions. Using single-injection radiative models, we compute that the total source age is ≲80 Myr and that the duty cycle is about ton/ttot ∼ 60%, which is enough to prevent the intracluster medium from cooling, according to X-ray estimates. While to date the radio spectral distribution of 3C388 remains a rare case among radio galaxies, multi-frequency surveys performed with new-generation instruments will soon allow us to investigate whether more sources with the same characteristics exist.

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