scholarly journals How Are Red and Blue Quasars Different? The Radio Properties

Galaxies ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 107
Author(s):  
Victoria A. Fawcett ◽  
David M. Alexander ◽  
David J. Rosario ◽  
Lizelke Klindt
Keyword(s):  
Radio Emission ◽  
Blue Emission ◽  
Accretion Disc ◽  
Small Scale ◽  
Direct Connection ◽  
Radio Flux ◽  
Frequency Range ◽  
Optical Wavelengths ◽  
Parent Sample ◽  
Rule Out

A non-negligible fraction of quasars are red at optical wavelengths, indicating (in the majority of cases) that the accretion disc is obscured by a column of dust which extinguishes the shorter-wavelength blue emission. In this paper, we summarize recent work by our group, where we find fundamental differences in the radio properties of SDSS optically-selected red quasars. We also present new analyses, using a consistent color-selected quasar parent sample matched to four radio surveys (FIRST, VLA Stripe 82, VLA COSMOS 3 GHz, and LoTSS DR1) across a frequency range 144 MHz–3 GHz and four orders of magnitude in radio flux. We show that red quasars have enhanced small-scale radio emission (∼kpc) that peaks around the radio-quiet threshold (defined as the ratio of 1.4 GHz luminosity to 6 μm luminosity) across the four radio samples. Exploring the potential mechanisms behind this enhancement, we rule out star-formation and propose either small-scale synchrotron jets, frustrated jets, or dusty winds interacting with the interstellar medium; the latter two scenarios would provide a more direct connection between opacity (dust; gas) and the production of the radio emission. In our future study, using new multi-band uGMRT data, we aim to robustly distinguish between these scenarios.

scholarly journals How Are Red and Blue Quasars Different? The Radio Properties

2021 ◽  
Author(s):  
Victoria Anne Fawcett ◽  
David Alexander ◽  
David Rosario ◽  
Lizelke Klindt
Keyword(s):  
Radio Emission ◽  
Blue Emission ◽  
Accretion Disc ◽  
Small Scale ◽  
Viewing Angle ◽  
Radio Flux ◽  
Frequency Range ◽  
Optical Wavelengths ◽  
Parent Sample ◽  
Rule Out

A non-negligible fraction of quasars are red at optical wavelengths, indicating (in the vast majority of cases) that the accretion disc is obscured by a column of dust which extinguishes the shorter-wavelength blue emission. In this paper we summarise recent work by our group, where we find fundamental differences in the radio properties of SDSS optically selected red quasars. We also present new analyses, using a consistent colour-selected quasar parent sample matched to four radio surveys (FIRST, VLA Stripe 82, VLA COSMOS 3 GHz and LoTSS DR1) across a frequency range 150 MHz-3 GHz and four orders of magnitude in radio flux. We show this enhancement is driven by systems with small-scale radio emission (∼kpc) and peaks around the radio-quiet threshold (defined as the ratio of 1.4 GHz luminosity to 6μm luminosity) across the four radio samples. Exploring the potential mechanisms behind this enhancement, we rule out star-formation and propose either small-scale jets or dusty winds interacting with the interstellar medium; this will be tested in detail using new multi-band uGMRT data. Overall our results cannot be explained with a simple viewing angle hypothesis, and so may point towards red quasars representing a key phase in the evolution of galaxies.

scholarly journals Constraints on magnetospheric radio emission from Y dwarfs

2019 ◽  
Vol 487 (2) ◽  
pp. 1994-2004 ◽  
Author(s):  
Melodie M Kao ◽  
Gregg Hallinan ◽  
J Sebastian Pineda
Keyword(s):  
Radio Emission ◽  
Large Scale ◽  
Empirical Relationship ◽  
Frequency Range ◽  
Noise Levels ◽  
Brown Dwarf ◽  
Very Large Array ◽  
Hα Emission ◽  
Larger Sample ◽  
Rule Out

Abstract As a pilot study of magnetism in Y dwarfs, we have observed the three known infrared variable Y dwarfs WISE J085510.83−071442.5, WISE J140518.40+553421.4, and WISEP J173835.53+273258.9 with the NSF’s Karl G. Jansky Very Large Array in the 4–8 GHz frequency range. The aim was to investigate the presence of non-bursting quiescent radio emission as a proxy for highly circularly polarized radio emission associated with large-scale auroral currents. Measurements of magnetic fields on Y dwarfs may be possible by observing auroral radio emission, and such measurements are essential for constraining fully convective magnetic dynamo models. We do not detect any pulsed or quiescent radio emission, down to rms noise levels of 7.2 µJy for WISE J085510.83−071442.5, 2.2 µJy for WISE J140518.40+553421.4, and 3.2 µJy for WISEP J173835.53+273258.9. The fractional detection rate of radio emission from T dwarfs is ∼10 per cent suggesting that a much larger sample of deep observations of Y dwarfs is needed to rule out radio emission in the Y dwarf population. We discuss a framework that uses an empirical relationship between the auroral tracer Hα emission and quiescent radio emission to identify brown-dwarf auroral candidates. Finally, we discuss the implications that Y dwarf radio detections and non-detections can have for developing a picture of brown dwarf magnetism and auroral activity.

Radio cyclotron emission from extra-solar planets

2008 ◽  
Vol 4 (S253) ◽  
pp. 456-458
Author(s):  
Alexis Smith ◽  
Andrew Cameron ◽  
Jane Greaves ◽  
Moira Jardine ◽  
Glen Langston ◽  
...  
Keyword(s):  
Radio Emission ◽  
Flux Density ◽  
Radio Flux ◽  
Frequency Range ◽  
Upper Limit ◽  
Cyclotron Emission

AbstractWe present results from an attempt to detect radio emission from the interaction between a transiting extra-solar planet and its host star. We determine a new upper limit of 47 mJy on the radio flux density from HD 189733b, in the frequency range 327–347 MHz.

scholarly journals Jupiter's Radiation Belts and Upper Atmosphere

1974 ◽  
Vol 65 ◽  
pp. 375-383
Author(s):  
Joseph J. Degioanni ◽  
John R. Dickel
Keyword(s):  
Radio Emission ◽  
Radiation Belts ◽  
Upper Atmosphere ◽  
Mixing Ratio ◽  
Frequency Range ◽  
Emission Data ◽  
High Energies ◽  
Isotropic Distribution ◽  
Relativistic Particles ◽  
Flat Distribution

Models of Jupiter's radiation belts have been constructed to determine the distribution of particles and their energies which will produce the observed decimetric radio emission. Data on the spectrum and the variation of emission with Jovian longitude have been used to show that the relativistic particles have a nearly isotropic distribution with high energies (of order 100 MeV) within 2 Jovian radii and a very flat distribution in the equatorial plane of low energy particles further out in the magnetosphere.Subtraction of the emission predicted by this model from the total radio emission shows that the thermal contribution in the frequency range between 3000 and 10000 MHz is somewhat less than had been previously expected. (The brightness temperature of the planetary disk is 180 K at 3000 MHz, for example.) This suggests that the ammonia mixing ratio in Jupiter's upper atmosphere may be as high as 0.002.

The 1983 Liege Earthquake: Damage Distribution and Site Effects

1990 ◽  
Vol 6 (4) ◽  
pp. 713-737 ◽  
Author(s):  
D. Jongmans ◽  
M. Campillo
Keyword(s):  
Site Effects ◽  
Large Scale ◽  
Site Response ◽  
Dominant Frequency ◽  
Small Scale ◽  
Eastern United States ◽  
Frequency Range ◽  
Damage Distribution ◽  
Damage Data ◽  
The City

On November 8, 1983, a moderate magnitude (Ml=4.9) earthquake struck Liege (Belgium). A damage study has shown that site effects at different scales have played an important role in amplifying ground motion. On a large scale, the damage distribution has been determined by the presence of a large Carboniferous syncline beneath the city as shown by 2D numerical modeling. On a small scale, the main damage concentrations can be correlated with local superficial deposits which have amplified ground motions in the frequency range of buildings. A geophysical survey was carried out to measure the shear wave velocity of the different formations. Site response computations were made at numerous sites in order to estimate the possible amplification and to compare the results with the damage. It was shown that the spectral amplifications computed in the dominant frequency range of the buildings are consistent with the damage data. In very affected areas, 1D amplifications of 4 to 6 were obtained and in some cases 2D effects may have occurred. The Liege earthquake, taking place in the intraplate region of Northwestern Europe, presents a significant interest to other similar areas as the eastern United States.

SIMULATION OF RADIO SIGNALS FROM 1-10 TeV AIR SHOWERS USING EGSNRC

2006 ◽  
Vol 21 (supp01) ◽  
pp. 65-69 ◽  
Author(s):  
R. Engel ◽  
N. N. Kalmykov ◽  
A. A. Konstantinov
Keyword(s):  
Monte Carlo ◽  
Radio Emission ◽  
Monte Carlo Simulations ◽  
Frequency Spectrum ◽  
Radial Dependence ◽  
Frequency Range ◽  
Air Showers ◽  
Shower Development ◽  
Radio Signals ◽  
The Individual

Cherenkov and geosynchrotron radiation are considered as two fundamental mechanisms of the radio emission generated by extensive air showers (EAS). The code EGSnrc is used for Monte-Carlo simulations of the individual shower development. Calculations of the radial dependence and frequency spectrum of the emitted radiation are performed for the LOPES experiment frequency range.

scholarly journals Radio emission from Sgr A*: pulsar transits through the accretion disc

2017 ◽  
Vol 468 (1) ◽  
pp. L26-L30 ◽  
Author(s):  
I. M. Christie ◽  
M. Petropoulou ◽  
P. Mimica ◽  
D. Giannios
Keyword(s):  
Radio Emission ◽  
Accretion Disc ◽  
Sgr A

The Pitch Angles of Electrons in Jupiter’s Radiation Belt

1976 ◽  
Vol 3 (1) ◽  
pp. 53-55 ◽  
Author(s):  
J. A. Roberts
Keyword(s):  
Radio Emission ◽  
Pitch Angle ◽  
Radiation Belt ◽  
Synchrotron Emission ◽  
Angle Distribution ◽  
Space Probe ◽  
Frequency Range ◽  
Pitch Angle Distribution ◽  
5 Ghz ◽  
Apparent Conflict

The radio emission from Jupiter in the frequency range from ∽ 50 MHz to ∽ 5 GHz is mainly synchrotron emission from electrons in the intense radiation belt which surrounds Jupiter out to several planetary radii. Information about the pitch angles of these electrons can be derived both from the radio observations and from the Pioneer space probe observations. In this communication we discuss the pitch angle distribution inferred from the radio data and the apparent conflict with the Pioneer data.

scholarly journals On the Nature of Radio Emission of Late-Type Giants

1989 ◽  
Vol 106 ◽  
pp. 383-383
Author(s):  
G.M. Rudnitskij
Keyword(s):  
Radio Emission ◽  
Front Surface ◽  
Stellar Atmosphere ◽  
Variable Stars ◽  
Radio Continuum ◽  
Radio Flux ◽  
Cyclotron Maser ◽  
Thermal Radio Emission ◽  
Circumstellar Gas ◽  
Period Variable

Long-period variable stars (LPV's) are considered. Pulsations of the surface of such a star result in formation in the stellar atmosphere of a shock wave in each cycle of the star's variability, ionizing the circumstellar gas which, recombining, gives rise to emissions in optical lines hydrogen and metals. I show the recombining layer behind the shock front to be optically thick in the free-free continuum at the radio wavelengths as short as 1 cm. At the gas temperatures behind the front T = 20000 K, the radio flux density at 1 cm from the front surface at a distance of a few hundred parsees will be several or several tens of mjy. So far, the only positive result of searches for LPVS’ radio continuum is the detection of radio flux from R Aql, obtained at different epochs by several authors. In October 1978 R Aql showed radio emission of 5.3 mjy at 14.9 GHz (Bowers and Kundu, 1979), and in August 1985 - 0.54 mjy at the same frequency (Drake et al.. 1987); these figures are consistent with our model. Besides that, R Aql experienced stronger radio flares at longer wavelengths, up to a few hundred mjy (Woodsworth and Hughes, 1973; Estalella et al.. 1983); these cannot be explained by thermal radio emission and require a nonthermal mechanism (synchrotron or cyclotron maser).

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