A Novel Method for Estimating the Ambient Medium Density Around Distant Radio Sources from Their Observed Radio Spectra

Abstract The dynamical evolution and radiative properties of luminous radio galaxies and quasars of the FR II type, are well understood. As a result, through the use of detailed modeling of the observed radio emission of such sources, one can estimate various physical parameters of the systems, including the density of the ambient medium into which the radio structure evolves. This, however, requires rather comprehensive observational information, i.e., sampling the broadband radio continua of the targets at several frequencies, and imaging their radio structures with high resolution. Such observations are, on the other hand, not always available, especially for high-redshift objects. Here, we analyze the best-fit values of the source physical parameters, derived from extensive modeling of the largest currently available sample of FR II radio sources, for which good-quality multiwavelength radio flux measurements could be collected. In the analyzed data set, we notice a significant and nonobvious correlation between the spectral index of the nonthermal radio emission continuum, and density of the ambient medium. We derive the corresponding correlation parameters, and quantify the intrinsic scatter by means of Bayesian analysis. We propose that the discovered correlation could be used as a cosmological tool to estimate the density of ambient medium for large samples of distant radio galaxies. Our method does not require any detailed modeling of individual sources, and relies on limited observational information, namely, the slope of the radio continuum between the rest-frame frequencies 0.4 and 5 GHz, possibly combined with the total linear size of the radio structure.

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A closer look at the deep radio sky: Multi-component radio sources at 3 GHz VLA-COSMOS

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832982 ◽

2019 ◽

Vol 627 ◽

pp. A142

Author(s):

E. Vardoulaki ◽

E. F. Jiménez Andrade ◽

A. Karim ◽

M. Novak ◽

S. K. Leslie ◽

...

Keyword(s):

Radio Emission ◽

Radio Continuum ◽

Continuum Emission ◽

High Angular Resolution ◽

Radio Sources ◽

Source Population ◽

Data Set ◽

Star Forming ◽

Large Project ◽

Automatic Code

Context. Given the unprecedented depth achieved in current large radio surveys, we are starting to probe populations of radio sources that have not been studied in the past. However, identifying and categorising these objects, differing in size, shape and physical properties, is becoming a more difficult task. Aims. In this data paper we present and characterise the multi-component radio sources identified in the VLA-COSMOS Large Project at 3 GHz (0.75 arcsec resolution, 2.3 μJy beam−1 rms), i.e. the radio sources which are composed of two or more radio blobs. Methods. The classification of objects into multi-components was done by visual inspection of 351 of the brightest and most extended blobs from a sample of 10,899 blobs identified by the automatic code BLOBCAT. For that purpose we used multi-wavelength information of the field, such as the 1.4 GHz VLA-COSMOS data and the Ultra Deep Survey with the VISTA telescope (UltraVISTA) stacked mosaic available for COSMOS. Results. We have identified 67 multi-component radio sources at 3 GHz: 58 sources with active galactic nucleus (AGN) powered radio emission and nine star-forming galaxies. We report eight new detections that were not observed by the VLA-COSMOS Large Project at 1.4 GHz, due to the slightly larger area coverage at 3 GHz. The increased spatial resolution of 0.75 arcsec has allowed us to resolve (and isolate) multiple emission peaks of 28 extended radio sources not identified in the 1.4 GHz VLA-COSMOS map. We report the multi-frequency flux densities (324 MHz, 325 MHz, 1.4 GHz & 3 GHz), star formation rates, and stellar masses of these objects. We find that multi-component objects at 3 GHz VLA-COSMOS inhabit mainly massive galaxies (> 1010.5 M⊙). The majority of the multi-component AGN lie below the main sequence of star-forming galaxies (SFGs), in the green valley and the quiescent region. Furthermore, we provide detailed descriptions of the objects and find that amongst the AGN there are two head-tail, ten core-lobe, nine wide-angle-tail (WAT), eight double-double or Z-/X-shaped, three bent-tail radio sources, and 26 symmetric sources, while amongst the SFGs we find the only star-forming ring seen in radio emission in COSMOS. Additionally, we report a large number (32 out of 58) of disturbed/bent multi-component AGN, 18 of which do not lie within X-ray groups in COSMOS (redshift range 0.08 ≤ z < 1.53). Conclusion. The high angular resolution and sensitivity of the 3 GHz VLA-COSMOS data set give us the opportunity to identify peculiar radio structures and sub-structures of multi-component objects, and relate them to physical phenomena such as AGN or star-forming galaxies. This study illustrates the complexity of the μJy radio-source population; at the sensitivity and resolution of 3 GHz VLA-COSMOS, the radio structures of AGN and SFG both emitting radio continuum emission, become comparable in the absence of clear, symmetrical jets. Thus, disentangling the AGN and SFG contributions using solely radio observations can be misleading in a number of cases. This has implications for future surveys, such as those done by square kilometre array (SKA) and precursors, which will identify hundreds of thousands of multi-component objects.

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The ATESP 5 GHz radio survey

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834288 ◽

2018 ◽

Vol 621 ◽

pp. A19

Author(s):

R. Ricci ◽

I. Prandoni ◽

H. R. De Ruiter ◽

P. Parma

Keyword(s):

High Resolution ◽

Radio Emission ◽

Radio Galaxies ◽

Host Galaxy ◽

Radio Sources ◽

Early Type ◽

Host Galaxies ◽

Star Forming ◽

Open Questions ◽

5 Ghz

Aims. It is now established that the faint radio population is a mixture of star-forming galaxies and faint active galactic nuclei (AGNs), with the former dominating below S1.4 GHz ∼ 100μJy and the latter at larger flux densities. The faint radio AGN component can itself be separated into two main classes, mainly based on the host-galaxy properties: sources associated with red/early-type galaxies (like radio galaxies) are the dominant class down to ∼100 μJy; quasar/Seyfert–like sources contribute an additional 10–20%. One of the major open questions regarding faint radio AGNs is the physical process responsible for their radio emission. This work aims at investigating this issue, with particular respect to the AGN component associated with red/early-type galaxies. Such AGNs show, on average, flatter radio spectra than radio galaxies and are mostly compact (≤30 kpc in size). Various scenarios have been proposed to explain their radio emission. For instance they could be core/core-jet dominated radio galaxies, low-power BL Lacertae, or advection-dominated accretion flow (ADAF) systems. Methods. We used the Australia Telescope Compact Array (ATCA) to extend a previous follow-up multi-frequency campaign to 38 and 94 GHz. This campaign focuses on a sample of 28 faint radio sources associated with early-type galaxies extracted from the ATESP 5 GHz survey. Such data, together with those already at hand, are used to perform radio spectral and variability analyses. Both analyses can help us to disentangle between core- and jet-dominated sources, as well as to verify the presence of ADAF/ADAF+jet systems. Additional high-resolution observations at 38 GHz were carried out to characterise the radio morphology of these sources on kiloparsec scales. Results. Most of the sources (25/28) were detected at 38 GHz, while only one (ATESP5J224547−400324) of the twelve sources observed at 94 GHz was detected. From the analysis of the radio spectra we confirmed our previous findings that pure ADAF models can be ruled out. Only eight out of the 28 sources were detected in the 38-GHz high-resolution (0.6 arcsec) radio images and of those eight only one showed a tentative core-jet structure. Putting together spectral, variability, luminosity, and linear size information we conclude that different kinds of sources compose our AGN sample: (a) luminous and large (≥100 kpc) classical radio galaxies (∼18% of the sample); (b) compact (confined within their host galaxies), low-luminosity, power-law (jet-dominated) sources (∼46% of the sample); and (c) compact, flat (or peaked) spectrum, presumably core-dominated, radio sources (∼36% of the sample). Variability is indeed preferentially associated with the latter.

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VLBI Cores in a Sample of Radio Galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900133996 ◽

1988 ◽

Vol 129 ◽

pp. 75-76

Author(s):

G. Comoretto ◽

L. Feretti ◽

G. Giovannini

Keyword(s):

Statistical Study ◽

Dynamic Range ◽

Total Sample ◽

Radio Galaxies ◽

Log P ◽

Complete Sample ◽

Radio Structure ◽

First Results ◽

5 Ghz ◽

Radio Power

We present the first results of a statistical study of the milliarcsec structure in a complete sample of radio galaxies. We have selected from the B2 and 3CR samples of galaxies the sources which present, at the VLA or WSRT angular resolution, an unresolved core with a flux density at 5 GHz Sc ≥ 100 mJy. The total sample consists of 30 radio galaxies, 17 from the B2 and 13 from the 3CR catalog. This complete sample covers a range of total radio power at 408 MHz log P = 23.5 – 26.5 W/Hz (low-intermediate luminosity). The radio structure of these sources on the arcsec-arcmin scale is well known, thanks to good dynamic range VLA and/or WSRT maps; a large variety of structures is present in the sample, from classical doubles to head-tail sources; flat, inverted and steep spectrum cores are also present.

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VLBI Morphology of GHz-Peaked Spectrum Radio Galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900176107 ◽

1994 ◽

Vol 159 ◽

pp. 425-425

Author(s):

D. Dallacasa ◽

C. Fanti ◽

R. Fanti

Keyword(s):

Radio Galaxies ◽

Radio Sources ◽

Complete Sample ◽

Spectrum Radio ◽

5 Ghz

GHz-Peaked Spectrum (GPS) radio sources are intrinsically small (< 1 kpc) and unbeamed objects. The galaxies considered here (0316+161, 0404+768, 0428+205, 1323+321, 1358+624, 1819+39, 1829+29) have been selected from the Peacock and Wall (1981) catalogue, and belong to a complete sample of Compact Steep-Spectrum (CSS) radio sources (Fanti et al., 1990). Their radio spectra show a turnover which could be explained in terms of synchrotron self-absorption. It occurs at frequencies ranging from about 100 MHz to 5 GHz and for this reason they do not appear in the 3CR catalogue.

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Observations of Straight-angle Tailed Radio Galaxies in Rich Clusters of Galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900081067 ◽

1996 ◽

Vol 175 ◽

pp. 349-350

Author(s):

Aileen A. O'Donoghue ◽

Jean A. Eilek ◽

Frazer N. Owen

Keyword(s):

Spectral Index ◽

Radio Galaxies ◽

Radio Sources ◽

Clusters Of Galaxies ◽

Data Set ◽

Dynamical Properties

We have begun VLA observations of straight-angle tailed radio sources (SATs) at 1.5 and 4.8 GHz (L and C band) to achieve one arcsecond resolution at each frequency. This will provide a SAT data set similar to the O'Donoghue, Owen, and Eilek (1990) WAT data set with both total intensity and spectral index information. We will use these data to examine morphological and dynamical properties of straight-tailed radio sources in clusters of galaxies.

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Radio Emission from High Redshift Galaxies: VLA Observations of the Hubble Deep Field

Symposium - International Astronomical Union ◽

10.1017/s007418090012902x ◽

1998 ◽

Vol 179 ◽

pp. 356-357

Author(s):

E.A. Richards

Keyword(s):

Radio Emission ◽

Small Area ◽

High Redshift ◽

Radio Galaxies ◽

Radio Sources ◽

High Redshift Galaxies ◽

Area 5 ◽

Moderate Power ◽

Galaxy Populations ◽

Hubble Deep Field

To study galaxy populations and their evolution at the highest possible redshifts, a small area of the sky, the Hubble Deep Field (HDF) was imaged to an unprecedented sensitivity of R = 29.5 (Williams et al. 1996). As a complement to the HST observations, we have used the VLA at 8 GHz to image an area 5.′4 in diameter (FWHM) centered on the HDF to an rms sensitivity of 2 μJy. With a radio resolution of about 3″, we have 33 sources above 9.5 μJy, seven in the 4 arcmin2 HDF field of which six have clear optical IDs. There are an additional 12 IDs in the HST flanking fields. The optical counterparts of the radio sources are a mixture of ellipticals, spirals, and irregulars, consistent with earlier surveys of comparable depth (Windhorst et al. 1995). With a median redshift <z> ∼ 1, the radio galaxies we are sampling are somewhat more distant than the classical starbursting galaxies which dominate less sensitive radio surveys. Our HDF identifications are predominately with post-starburst galaxies, moderate power AGN, and blue irregulars (Fomalont et al. 1996).

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Radio emission during the formation of stellar clusters in M 33

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037555 ◽

2020 ◽

Vol 639 ◽

pp. A27

Author(s):

Edvige Corbelli ◽

Jonathan Braine ◽

Fatemeh S. Tabatabaei

Keyword(s):

Radio Emission ◽

Molecular Cloud ◽

Molecular Clouds ◽

Supernova Remnants ◽

Line Emission ◽

Radio Continuum ◽

Stellar Clusters ◽

Nonthermal Radio ◽

Early Formation ◽

5 Ghz

Aims. We investigate thermal and nonthermal radio emission associated with the early formation and evolution phases of young stellar clusters (YSCs) selected by their mid-infrared (MIR) emission at 24 μm in M 33. We consider regions in their early formation period, which are compact and totally embedded in the molecular cloud, and in the more evolved and exposed phase. Methods. Thanks to recent radio continuum surveys between 1.4 and 6.3 GHz we are able to find radio source counterparts to more than 300 star forming regions of M 33. We identify the thermal free–free component for YSCs and their associated molecular complexes using the Hα line emission. Results. A cross-correlation of MIR and radio continuum is established from bright to very faint sources, with the MIR-to-radio emission ratio that shows a slow radial decline throughout the M 33 disk. We confirm the nature of candidate embedded sources by recovering the associated faint radio continuum luminosities. By selecting exposed YSCs with reliable Hα flux, we establish and discuss the tight relation between Hα and the total radio continuum at 5 GHz over four orders of magnitude. This holds for individual YSCs as well as for the giant molecular clouds hosting them, and allows us to calibrate the radio continuum–star formation rate relation at small scales. On average, about half of the radio emission at 5 GHz in YSCs is nonthermal with large scatter. For exposed but compact YSCs and their molecular clouds, the nonthermal radio continuum fraction increases with source brightness, while for large HII regions the nonthermal fraction is lower and shows no clear trend. This has been found for YSCs with and without identified supernova remnants and underlines the possible role of massive stars in triggering particle acceleration through winds and shocks: these particles diffuse throughout the native molecular cloud prior to cloud dispersal.

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Radio Continuum Spectra of Planetary Nebulae

Galaxies ◽

10.3390/galaxies7010006 ◽

2018 ◽

Vol 7 (1) ◽

pp. 6

Author(s):

Marcin Hajduk ◽

Peter van Hoof ◽

Karolina Sniadkowska ◽

Andrzej Krankowski ◽

Leszek Błaszkiewicz ◽

...

Keyword(s):

Radio Emission ◽

Planetary Nebulae ◽

Radio Continuum ◽

Continuum Emission ◽

Physical Parameters ◽

Spectral Indices ◽

Homogeneous Sphere ◽

Spherical Morphology ◽

Competing Models ◽

Source Of Information

Radio continuum emission of planetary nebulae is a rich source of information about their structure and physical parameters. Although radio emission is well studied, planetary nebulae show higher spectral indices than expected for homogeneous sphere. A few competing models exist in the literature to explain this discrepancy. We propose that it is related to non-spherical morphology of most of planetary nebulae.

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Radio-optical Identification of Very-Steep Spectrum Radio Sources from the UTR-2 Catalogue

Symposium - International Astronomical Union ◽

10.1017/s0074180900168949 ◽

2002 ◽

Vol 199 ◽

pp. 217-218 ◽

Cited By ~ 1

Author(s):

H. Andernach ◽

O.V. Verkhodanov ◽

N.V. Verkhodanova

Keyword(s):

Radio Source ◽

High Redshift ◽

Radio Galaxies ◽

Image Databases ◽

Radio Continuum ◽

Radio Sources ◽

Optical Identification ◽

X Ray ◽

Spectrum Radio

We used radio source catalogues accessible from the CATS database to establish radio continuum spectra for decametric radio sources in the UTR-2 catalogue. In an attempt to find further candidates for high-redshift radio galaxies, we searched the FIRST and NVSS surveys for counterparts of a sample of UTR sources with ultra-steep radio spectra (USS, α ≤ −1.2, S ∼ vα). We derived accurate positions and sizes for 23 of these USS sources. The search for optical counterparts from the APM (object) and DSS (image) databases, as well as infrared and X—ray identifications of these UTR sources are in progress.

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Large-scale environment of FR 0 radio galaxies

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935962 ◽

2020 ◽

Vol 633 ◽

pp. A161 ◽

Cited By ~ 4

Author(s):

A. Capetti ◽

F. Massaro ◽

R. D. Baldi

Keyword(s):

Radio Emission ◽

Large Scale ◽

Large Fraction ◽

Radio Galaxies ◽

Radio Sources ◽

Early Type ◽

Extended Radio ◽

Significant Difference ◽

Two Populations ◽

Jet Power

We explore the properties of the large-scale environment of the sources in the Faranoff-Riley class 0 catalog (FR0CAT). This sample includes 104 compact radio sources that are associated with nearby (z < 0.05) early-type galaxies. Using various estimators, we find that FR 0s are located in regions with higher than the average number of galaxies. The average galaxies density around FR 0s is a factor two lower with respect to FR I radio galaxies. This latter difference is driven by the large fraction (63%) of FR 0s that are located in groups formed by fewer than 15 galaxies. FR Is rarely (17%) inhabit an environment like this. In addition to the lack of substantial extended radio emission that defines the FR 0 class, this is the first significant difference between the properties of these two populations of low-power radio galaxies. We interpret the differences in environment between FR 0s and FR Is as due to an evolutionary link between local galaxies density, black hole spin, jet power, and extended radio emission.

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