On the Injection Spectrum of Relativistic Electrons in High-Redshift Radio Galaxies

Gopal-Krishna, . .; Mhaskey, Mukul; Mangalam, A.

doi:10.1088/0004-637x/744/1/31

Cited by 8 publications

(5 citation statements)

References 64 publications

(75 reference statements)

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“…However, the k-correction mechanism has been disputed owing to the remarkable linearity and the lack of evidence for a spectral curvature in wide band radio spectrum of high redshift radio galaxies (Chambers et al 1990;Klamer et al 2006Klamer et al , 2007. Gopal-Krishna et al (2012) however argue that since the steepness of the spectral index anti-correlates with the spectral curvature (Mangalam & Gopal-Krishna 1995), the spectral steepening becomes negligible for sources with steep spectra (α 1GHz ≤ −1.2, also reflected in Klamer et al (2006)). k-correction being insufficient to explain the observed z − α relation, alternative effects have been proposed.…”

Section: Hotspot Spectral Indicesmentioning

confidence: 91%

A VLA–GMRT look at 11 powerful FRiiquasars

Vaddi

Kharb

Daly

et al. 2018

Monthly Notices of the Royal Astronomical Society

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We present results from 1.4 and 5 GHz observations at matched resolution with the Karl G. Jansky Very Large Array (VLA) of 11 powerful 3C FR II quasars. We examine the 11 quasars along with a sample of 13 narrow-line FR II radio galaxies and find that radio-loud unification largely holds but environmental effects cannot be ignored. The radio core prominence, largest linear size, and axial ratio parameter values indicate that quasars are at relatively smaller angles compared to the radio galaxies and thus probe orientation. Lack of correlation between statistical orientation indicators such as misalignment angle and radio core prominence, and larger lobe distortions in quasars compared to radio galaxies suggest that intrinsic/environment effects are also at play. Some of 150 MHz observations with the TGSS-GMRT reveal peculiar lobe morphologies in these FR II sources, suggesting complex past lives and possibly restarted AGN activity. Using the total 150 MHz flux density we estimate the timeaveraged jet kinetic power in these sources and this ranges from (1 − 38) × 10 45 erg s −1 , with 3C 470 having the highest jet kinetic power.

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Section: Hotspot Spectral Indicesmentioning

confidence: 91%

A VLA–GMRT look at 11 powerful FRiiquasars

Vaddi

Kharb

Daly

et al. 2018

Monthly Notices of the Royal Astronomical Society

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“…The hotspots along with the lobes therefore remain in the high-pressure medium for a prolonged duration. A reduction in the velocity will result in the production of electrons with steeper energy distribution (Kirk & Schneider 1987;Mangalam & Gopal-Krishna 1995;Klamer et al 2006;Gopal-Krishna et al 2012).…”

Section: Pdzα Parameters Of Grgsmentioning

confidence: 99%

Search and analysis of giant radio galaxies with associated nuclei (SAGAN)

Dabhade

Mahato

Bagchi

et al. 2020

A&A

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We present the first results of a project called SAGAN, which is dedicated solely to the studies of relatively rare megaparsec-scale radio galaxies in the Universe, called giant radio galaxies (GRGs). We have identified 162 new GRGs primarily from the NRAO VLA Sky Survey with sizes ranging from ∼0.71 Mpc to ∼2.82 Mpc in the redshift range of ∼0.03−0.95, of which 23 are hosted by quasars (giant radio quasars). As part of the project SAGAN, we have created a database of all known GRGs, the GRG catalogue, from the literature (including our new sample); it includes 820 sources. For the first time, we present the multi-wavelength properties of the largest sample of GRGs. This provides new insights into their nature. Our results establish that the distributions of the radio spectral index and the black hole mass of GRGs do not differ from the corresponding distributions of normal-sized radio galaxies (RGs). However, GRGs have a lower Eddington ratio than RGs. Using the mid-infrared data, we classified GRGs in terms of their accretion mode: either a high-power radiatively efficient high-excitation state, or a radiatively inefficient low-excitation state. This enabled us to compare key physical properties of their active galactic nuclei, such as the black hole mass, spin, Eddington ratio, jet kinetic power, total radio power, magnetic field, and size. We find that GRGs in high-excitation state statistically have larger sizes, stronger radio power, jet kinetic power, and higher Eddington ratio than those in low-excitation state. Our analysis reveals a strong correlation between the black hole Eddington ratio and the scaled jet kinetic power, which suggests a disc-jet coupling. Our environmental study reveals that ∼10% of all GRGs may reside at the centres of galaxy clusters, in a denser galactic environment, while the majority appears to reside in a sparse environment. The probability of finding the brightest cluster galaxy as a GRG is quite low and even lower for high-mass clusters. We present new results for GRGs that range from black hole mass to large-scale environment properties. We discuss their formation and growth scenarios, highlighting the key physical factors that cause them to reach their gigantic size.

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“…As a result, the advance of their hot spots is slowed down, giving rise to a steep energy spectrum of the relativistic electrons accelerated there via the firstorder Fermi process, which causes an ultra-steep straight synchrotron radio spectrum ab initio (Athreya & Kapahi 1998;Klamer et al 2006;Bicknell et al 1997). This potentially attractive theoretical scenario would, however, need further substantiation, particularly in view of the empirical study presented by Gopal-Krishna et al (2012), which found no correlation of the particle injection spectral index with rotation measure for powerful double radio sources.…”

Section: Introductionmentioning

confidence: 99%

GMRT observations of extragalactic radio sources with steeply inverted spectra

Mhaskey

Gopal-Krishna

Dabhade

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We report quasi-simultaneous GMRT observations of seven extragalactic radio sources at 150, 325, 610 and 1400 MHz, in an attempt to accurately define their radio continuum spectra, particularly at frequencies below the observed spectral turnover. We had previously identified these sources as candidates for a sharply inverted integrated radio spectrum whose slope is close to, or even exceeds α c = +2.5, the theoretical limit due to synchrotron self-absorption (SSA) in a source of incoherent synchrotron radiation arising from relativistic particles with the canonical (i.e., power-law) energy distribution. We find that four out of the seven candidates have an inverted radio spectrum with a slope close to or exceeding +2.0, while the critical spectral slope α c is exceeded in at least one case. These sources, together with another one or two reported in very recent literature, may well be the archetypes of an extremely rare class, from the standpoint of violation of the SSA limit in compact extragalactic radio sources. However, the alternative possibility that free-free absorption is responsible for their ultra-sharp spectral turnover cannot yet be discounted.

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On the Injection Spectrum of Relativistic Electrons in High-Redshift Radio Galaxies

Cited by 8 publications

References 64 publications

A VLA–GMRT look at 11 powerful FRiiquasars

A VLA–GMRT look at 11 powerful FRiiquasars

Search and analysis of giant radio galaxies with associated nuclei (SAGAN)

GMRT observations of extragalactic radio sources with steeply inverted spectra

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