Time-dependent radio sources in the star-forming region Cepheus A (east)

1991 ◽  
Vol 383 ◽  
pp. 280 ◽  
Author(s):  
V. A. Hughes
Keyword(s):  
Time Dependent ◽  
Radio Sources ◽  
Star Forming ◽  
Cepheus A

The Nature of the Radio Sources within the Cepheus A Star-forming Region

1996 ◽  
Vol 459 ◽  
pp. 193 ◽  
Author(s):  
Guido Garay ◽  
Solange Ramirez ◽  
Luis F. Rodriguez ◽  
Salvador Curiel ◽  
Jose M. Torrelles
Keyword(s):  
Radio Sources ◽  
Star Forming ◽  
Cepheus A

scholarly journals Two Types of Jet in Cepheus A

1998 ◽  
Vol 164 ◽  
pp. 345-346
Author(s):  
V. A. Hughes
Keyword(s):  
Young Star ◽  
Time Dependent ◽  
Star Forming ◽  
Cepheus A

AbstractThe young star forming region, Cepheus A, has been monitored since 1981, and shows four new types of time-dependent events. Two of these are briefly described.

scholarly journals VLBA+GBT observations of the COSMOS field and radio source counts at 1.4 GHz

2018 ◽  
Vol 616 ◽  
pp. A128 ◽  
Author(s):  
N. Herrera Ruiz ◽  
E. Middelberg ◽  
A. Deller ◽  
V. Smolčić ◽  
R. P. Norris ◽  
...  
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
Lower Limit ◽  
High Sensitivity ◽  
Host Galaxy ◽  
Radio Sources ◽  
Source Population ◽  
Star Forming ◽  
Brightness Temperatures ◽  
Long Baseline

We present very long baseline interferometry (VLBI) observations of 179 radio sources in the COSMOS field with extremely high sensitivity using the Green Bank Telescope (GBT) together with the Very Long Baseline Array (VLBA) (VLBA+GBT) at 1.4 GHz, to explore the faint radio population in the flux density regime of tens of μJy. Here, the identification of active galactic nuclei (AGN) is based on the VLBI detection of the source, meaning that it is independent of X-ray or infrared properties. The milli-arcsecond resolution provided by the VLBI technique implies that the detected sources must be compact and have large brightness temperatures, and therefore they are most likely AGN (when the host galaxy is located at z ≥ 0.1). On the other hand, this technique only allows us to positively identify when a radio-active AGN is present, in other words, we cannot affirm that there is no AGN when the source is not detected. For this reason, the number of identified AGN using VLBI should be always treated as a lower limit. We present a catalogue containing the 35 radio sources detected with the VLBA+GBT, ten of which were not previously detected using only the VLBA. We have constructed the radio source counts at 1.4 GHz using the samples of the VLBA and VLBA+GBT detected sources of the COSMOS field to determine a lower limit for the AGN contribution to the faint radio source population. We found an AGN contribution of >40−75% at flux density levels between 150 μJy and 1 mJy. This flux density range is characterised by the upturn of the Euclidean-normalised radio source counts, which implies a contribution of a new population. This result supports the idea that the sub-mJy radio population is composed of a significant fraction of radio-emitting AGN, rather than solely by star-forming galaxies, in agreement with previous studies.

Time Dependent Energy Supply in Radio Sources and Morphology of Radio Lobes

1982 ◽  
pp. 51-52
Author(s):  
W. A. Christiansen ◽  
A. G. Pacholczyk ◽  
John S. Scott
Keyword(s):  
Energy Supply ◽  
Time Dependent ◽  
Radio Sources

scholarly journals Time Dependent Energy Supply in Radio Sources and Morphology of Radio Lobes

1982 ◽  
Vol 97 ◽  
pp. 51-52
Author(s):  
W. A. Christiansen ◽  
A. G. Pacholczyk ◽  
John S. Scott
Keyword(s):  
Energy Supply ◽  
Morphological Features ◽  
Time Dependent ◽  
Radio Sources ◽  
Low Density ◽  
Background Medium ◽  
Radio Jets ◽  
Parent Galaxy

The fact that radio jets, which are often one-sided, are nevertheless associated with extended lobes of nearly equal luminosity indicates when analyzed in detail (1) that the energy supply by the nuclear engine to the lobes is strongly time-dependent. Time dependent ejection from the nucleus of a parent galaxy produces low density channels which are ploughed in the background medium by the passage of intermittently ejected radio emitting plasmons (2), (3), (4) and (5). An analysis of the dynamics of radio emitting plasmons in such channels leads to unique morphological features consistent with observations of both narrow jets (resulting from splashback or reflections from the channel ends) and conical lobes (resulting from slower hydrodynamic deceleration).

scholarly journals Ultraviolet spectra of star-forming galaxies with time-dependent dust obscuration

2003 ◽  
Vol 212 ◽  
pp. 734-735
Author(s):  
Lucimara P. Martins ◽  
Claus Leitherer ◽  
Daniela Calzetti
Keyword(s):  
Stellar Wind ◽  
Time Dependent ◽  
New Technique ◽  
New Approach ◽  
Star Forming ◽  
Ultraviolet Spectra

We present a new approach to probe the properties of the most massive, ionizing stars with respect to the less massive, non-ionizing stars. The new technique utilizes stellar-wind lines, instead of the previously employed nebular lines. This allows us to probe the timescale of the dust dispersal in a very young obscured starburst from purely stellar diagnostics.

scholarly journals VSOP, A Space VLBI Programme

1990 ◽  
Vol 123 ◽  
pp. 263-269
Author(s):  
H. Hirabayashi
Keyword(s):  
Active Galactic Nuclei ◽  
Phase Transfer ◽  
Galactic Nuclei ◽  
Satellite Orbit ◽  
Radio Sources ◽  
Space Observatory ◽  
Stellar Objects ◽  
Radio Observatory ◽  
Star Forming ◽  
Star Forming Regions

AbstractVSOP, VLBI Space Observatory Programme, is an approved space VLBI programme of ISAS for the study of very compact radio sources with the synthesized aperture of 30,000 km diameter, by connecting an orbiting radio observatory with ground radiotelescopes. The VSOP satellite carrying 10 m antenna with 1.6, 5, and 22 GHz band receivers will be launched in early 1995 by M-V rocket of ISAS into an eccentric orbit with 20,000 km in apogee height. The tracking network will be formed for the satellite orbit determination, phase transfer and IF down-link. VSOP aims imaging capability with best resolution of 0.0001 arc second in 22 GHz band. Imaging of active galactic nuclei, star forming regions and stellar objects, and radioastrometry are main scientific targets.

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

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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