Compact steep-spectrum and peaked-spectrum radio sources

O’Dea, C. P.; Saikia, D. J.

doi:10.1007/s00159-021-00131-w

Cited by 198 publications

(147 citation statements)

References 626 publications

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“…To investigate the skew towards flatter and inverted spectral indices shown in Figures 10 and 11, we compare the spectral index distributions for a sample of clearly resolved and unresolved components from the EMU-PS. The unresolved population contains radio cores and therefore includes flat-spectrum radio quasars (Urry & Padovani 1995) and peaked-spectrum sources (O'Dea & Saikia 2021). At the observing frequency of EMU-PS (ν ∼ 900 MHz), the radio spectra of Gigahertz Peaked-Spectrum sources tend to have shallow spectral index values as EMU-PS is observing close to their turnover frequency (O'Dea 1998).…”

Section: The Excess Of Flat Spectral Index Sourcesmentioning

confidence: 99%

The Evolutionary Map of the Universe pilot survey

Norris

Marvil

Collier

et al. 2021

Publ. Astron. Soc. Aust.

114

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We present the data and initial results from the first pilot survey of the Evolutionary Map of the Universe (EMU), observed at 944 MHz with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope. The survey covers $270 \,\mathrm{deg}^2$ of an area covered by the Dark Energy Survey, reaching a depth of 25–30 $\mu\mathrm{Jy\ beam}^{-1}$ rms at a spatial resolution of $\sim$ 11–18 arcsec, resulting in a catalogue of $\sim$ 220 000 sources, of which $\sim$ 180 000 are single-component sources. Here we present the catalogue of single-component sources, together with (where available) optical and infrared cross-identifications, classifications, and redshifts. This survey explores a new region of parameter space compared to previous surveys. Specifically, the EMU Pilot Survey has a high density of sources, and also a high sensitivity to low surface brightness emission. These properties result in the detection of types of sources that were rarely seen in or absent from previous surveys. We present some of these new results here.

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Section: The Excess Of Flat Spectral Index Sourcesmentioning

confidence: 99%

The Evolutionary Map of the Universe pilot survey

Norris

Marvil

Collier

et al. 2021

Publ. Astron. Soc. Aust.

114

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“…The life cycle of a radio galaxy is understood to start from a phase of morphologically compact radio emission with an absorbed or steep spectrum. Such sources are called compact steep spectrum (CSS) and gigahertz peaked spectrum (GPS) sources (O'Dea 1998;Fanti 2009;O'Dea & Saikia 2021). These sources show morphological similarities to large-scale radio sources, but with sizes of just a few kiloparsecs (similar to galactic scales), and they are thought to develop into large-scale radio galaxies.…”

Section: Introductionmentioning

confidence: 99%

Unmasking the history of 3C 293 with LOFAR sub-arcsecond imaging

Kukreti

Morganti

Shimwell

et al. 2022

A&A

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Active galactic nuclei (AGNs) show episodic activity, which can be evident in galaxies that exhibit restarted radio jets. These restarted jets can interact with their environment, leaving signatures on the radio spectral energy distribution. Tracing these signatures is a powerful way to explore the life of radio galaxies. This requires resolved spectral index measurements over a broad frequency range including low frequencies. We present such a study for the radio galaxy 3C 293, which has long been thought to be a restarted galaxy on the basis of its radio morphology. Using the International LOFAR telescope (ILT) we probed spatial scales as fine as ∼0.2 at 144 MHz, and to constrain the spectrum we combined these data with Multi-Element Radio Linked Interferometer Network (MERLIN) and Very Large Array (VLA) archival data at frequencies up to 8.4 GHz that have a comparable resolution. In the inner lobes (∼2 kpc), we detect the presence of a spectral turnover that peaks at ∼225 MHz and is most likely caused by free-free absorption from the rich surrounding medium. We confirm that these inner lobes are part of a jet-dominated young radio source (spectral age 0.17 Myr), which is strongly interacting with the rich interstellar medium (ISM) of the host galaxy. The diffuse emission surrounding these lobes on scales of up to ∼4.5 kpc shows steeper spectral indices (∆α ∼ 0.2-0.5, S ∝ ν −α ) and a spectral age of 0.27 Myr. The outer lobes (extending up to ∼100 kpc) have a spectral index of α ∼ 0.6-0.8 from 144-4850 MHz with a remarkably uniform spatial distribution and only mild spectral curvature (∆α 0.2). We propose that intermittent fuelling and jet flow disruptions are powering the mechanisms that keep the spectral index in the outer lobes from steepening and maintain the spatial uniformity of the spectral index. Overall, it appears that 3C 293 has gone through multiple (two to three) epochs of activity. This study adds 3C 293 to the new sub-group of restarted galaxies with short interruption time periods. This is the first time a spatially resolved study has been performed that simultaneously studies a young source as well as the older outer lobes at such low frequencies. This illustrates the potential of the International LOFAR telescope to expand such studies to a larger sample of radio galaxies.

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“…During the first stages of nuclear activity, called the gigahertz-peaked spectrum (GPS) and compact steep spectrum (CSS) sources, the radio jets have sizes smaller than a few kiloparsecs and reside within the interstellar medium of the host galaxy. Their radio spectra have convex shapes with peak emission frequency inversely proportional to the source size (Fanti et al 1990;Orienti & Dallacasa 2014;O'Dea & Saikia 2021). If the jets are free to expand further, to the intergalactic medium, the source evolves into Fanaroff-Riley type I (FRI) or type II (FRII) morphology (Fanaroff & Riley 1974), reaching sizes of a few hundred kiloparsecs.…”

Section: Introductionmentioning

confidence: 99%

Caltech-NRAO Stripe 82 Survey (CNSS). V. AGNs That Transitioned to Radio-loud State

Wołowska¹,

Kunert-Bajraszewska²,

Mooley

et al. 2021

ApJ

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A recent multiyear Caltech-NRAO Stripe 82 Survey revealed a group of objects that appeared as new radio sources after >5-20 yr of absence. They are transient phenomena with respect to the Faint Images of the Radio Sky at Twenty Centimeters survey and constitute the first unbiased sample of renewed radio activity. Here we present a follow-up, radio, optical, and X-ray study of them. The group consists of 12 sources, both quasars and galaxies with wide redshift (0.04 < z < 1.7) and luminosity ( < > -L 22 log W Hz 24.5Their radio properties in the first phase of activity, namely the convex spectra and compact morphology, allow them all to be classified as gigahertz-peaked spectrum (GPS) sources. We conclude that the spectral changes are a consequence of the evolution of newly born radio jets. Our observations show that over the next few years of activity the GPS galaxies keep the convex shape of the spectrum, while GPS quasars rapidly transform into flatspectrum sources, which may result in them not being recognized as young sources. The wide range of bolometric luminosities, black hole masses, and jet powers among the transient sources indicates even greater population diversity in the group of young radio objects. We also suggest that small changes of the accretion disk luminosity (accretion rate) may be sufficient to ignite low-power radio activity that evolves on the scale of decades. Unified Astronomy Thesaurus concepts: Active galaxies (17); AGN host galaxies (2017); Radio galaxies (1343); Quasars (1319); Radio loud quasars (1349); Radio quiet quasars (1354); Supermassive black holes (1663); Active galactic nuclei (16); Galaxy evolution (594)

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Compact steep-spectrum and peaked-spectrum radio sources

Cited by 198 publications

References 626 publications

The Evolutionary Map of the Universe pilot survey

The Evolutionary Map of the Universe pilot survey

Unmasking the history of 3C 293 with LOFAR sub-arcsecond imaging

Caltech-NRAO Stripe 82 Survey (CNSS). V. AGNs That Transitioned to Radio-loud State

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