VSOP, A Space VLBI Programme

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.

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Multiwavelength analysis of OH Megamaser galaxies: The case of IRAS11506-3851

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320004317 ◽

2020 ◽

Vol 15 (S359) ◽

pp. 347-349

Author(s):

Carpes P. Hekatelyne ◽

Thaisa Storchi-Bergmann

Keyword(s):

Active Galactic Nuclei ◽

Hubble Space Telescope ◽

Galactic Nuclei ◽

Large Array ◽

Very Large Array ◽

Star Forming ◽

Star Forming Regions ◽

Field Unit ◽

Mixed Transition ◽

Integral Field

AbstractWe present Multi-Object Spectrograph (GMOS) Integral Field Unit (IFU), Hubble Space Telescope (HST) and Very Large Array (VLA) observations of the inner kpc of the OH Megamaser galaxy IRAS 11506-3851. In this work we discuss the kinematics and excitation of the gas as well as its radio emission. The HST images reveal an isolated spiral galaxy and the combination with the GMOS-IFU flux distributions allowed us to identify a partial ring of star-forming regions surrounding the nucleus with a radius of ≍500 pc. The emission-line ratios and excitation map reveal that the region inside the ring present mixed/transition excitation between those of Starbursts and Active Galactic Nuclei (AGN), while regions along the ring are excited by Starbursts. We suggest that we are probing a buried or fading AGN that could be both exciting the gas and originating an outflow.

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The ATLAS 9.0 GHz survey of the extended Chandra Deep Field South: the faint 9.0 GHz radio population

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3187 ◽

2019 ◽

Vol 491 (3) ◽

pp. 3395-3410 ◽

Cited By ~ 1

Author(s):

M T Huynh ◽

N Seymour ◽

R P Norris ◽

T Galvin

Keyword(s):

Radio Emission ◽

Active Galactic Nuclei ◽

Radio Source ◽

Galactic Nuclei ◽

Radio Galaxies ◽

Significant Fraction ◽

Radio Sources ◽

Star Forming ◽

Source Populations ◽

Compact Array

ABSTRACT We present a new image of the 9.0 GHz radio emission from the extended Chandra Deep Field South. A total of 181 h of integration with the Australia Telescope Compact Array has resulted in a 0.276 deg2 image with a median sensitivity of ∼20 µJy beam−1 rms, for a synthesized beam of 4.0 × 1.3 arcsec. We present a catalogue of the 9.0 GHz radio sources, identifying 70 source components and 55 individual radio galaxies. Source counts derived from this sample are consistent with those reported in the literature. The observed source counts are also generally consistent with the source counts from simulations of the faint radio population. Using the wealth of multiwavelength data available for this region, we classify the faint 9 GHz population and find that 91 per cent are radio-loud active galactic nuclei (AGNs), 7 per cent are radio-quiet AGNs, and 2 per cent are star-forming galaxies. The 9.0 GHz radio sources were matched to 5.5 and 1.4 GHz sources in the literature and we find a significant fraction of flat or inverted spectrum sources, with 36 per cent of the 9 GHz sources having $\alpha _{5.5\,\mathrm{ GHz}}^{9.0\,\mathrm{ GHz}}$ > −0.3 (for S ∝ να). This flat or inverted population is not well reproduced by current simulations of radio source populations.

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Deep LOFAR 150 MHz imaging of the Boötes field: Unveiling the faint low-frequency sky

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833677 ◽

2018 ◽

Vol 620 ◽

pp. A74 ◽

Cited By ~ 6

Author(s):

E. Retana-Montenegro ◽

H. J. A. Röttgering ◽

T. W. Shimwell ◽

R. J. van Weeren ◽

I. Prandoni ◽

...

Keyword(s):

Active Galactic Nuclei ◽

Angular Resolution ◽

Low Frequency ◽

Galactic Nuclei ◽

Radio Sources ◽

Low Frequencies ◽

Star Forming ◽

Radio Imaging ◽

Deep Survey ◽

Systematic Effects

We have conducted a deep survey (with a central rms of 55 μJy) with the LOw Frequency ARray (LOFAR) at 120–168 MHz of the Boötes field, with an angular resolution of 3.98″ × 6.45″, and obtained a sample of 10 091 radio sources (5σ limit) over an area of 20 deg2. The astrometry and flux scale accuracy of our source catalog is investigated. The resolution bias, incompleteness and other systematic effects that could affect our source counts are discussed and accounted for. The derived 150 MHz source counts present a flattening below sub-mJy flux densities, that is in agreement with previous results from high- and low- frequency surveys. This flattening has been argued to be due to an increasing contribution of star-forming galaxies and faint active galactic nuclei. Additionally, we use our observations to evaluate the contribution of cosmic variance to the scatter in source counts measurements. The latter is achieved by dividing our Boötes mosaic into 10 non-overlapping circular sectors, each one with an approximate area of 2 deg2. The counts in each sector are computed in the same way as done for the entire mosaic. By comparing the induced scatter with that of counts obtained from depth observations scaled to 150 MHz, we find that the 1σ scatter due to cosmic variance is larger than the Poissonian errors of the source counts, and it may explain the dispersion from previously reported depth source counts at flux densities S < 1 mJy. This work demonstrates the feasibility of achieving deep radio imaging at low-frequencies with LOFAR.

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CHILES VERDES: Radio Variability at an Unprecedented Depth and Cadence in the COSMOS Field

The Astrophysical Journal ◽

10.3847/1538-4357/ac2239 ◽

2021 ◽

Vol 923 (1) ◽

pp. 31

Author(s):

Sumit K. Sarbadhicary ◽

Evangelia Tremou ◽

Adam J. Stewart ◽

Laura Chomiuk ◽

Charee Peters ◽

...

Keyword(s):

Active Galactic Nuclei ◽

Flux Density ◽

Galactic Nuclei ◽

Density Variation ◽

Time Variable ◽

Host Galaxy ◽

Radio Sources ◽

Star Forming ◽

Lower Variability ◽

Cross Matching

Abstract Although it is well established that some extragalactic radio sources are time-variable, the properties of this radio variability, and its connection with host galaxy properties, remain to be explored—particularly for faint sources. Here we present an analysis of radio variable sources from the CHILES Variable and Explosive Radio Dynamic Evolution Survey (CHILES VERDES)—a partner project of the 1.4 GHz COSMOS H i Large Extragalactic Survey. CHILES VERDES provides an unprecedented combination of survey depth, duration, and cadence, with 960 hr of 1–2 GHz continuum VLA data obtained over 209 epochs between 2013 and 2019 in a 0.44 deg2 section of the well-studied extragalactic deep field, COSMOS. We identified 18 moderate-variability sources (showing 10%–30% flux density variation) and 40 lower-variability sources (2%–10% flux density variation). They are mainly active galactic nuclei (AGNs) with radio luminosities in the range of 1022–1027 W Hz−1, based on cross-matching with COSMOS multiwavelength catalogs. The moderate-variability sources span redshifts z = 0.22–1.56, have mostly flat radio spectra (α > −0.5), and vary on timescales ranging from days to years. The lower-variability sources have similar properties, but generally have higher radio luminosities than the moderate-variability sources, extending to z = 2.8, and have steeper radio spectra (α < −0.5). No star-forming galaxy showed statistically significant variability in our analysis. The observed variability likely originates from scintillation on short (∼week) timescales, and Doppler-boosted intrinsic AGN variability on long (month–year) timescales.

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Quasi Stellar Objects and Active Galactic Nuclei

International Astronomical Union Colloquium ◽

10.1017/s0252921100107043 ◽

1984 ◽

Vol 78 ◽

pp. 443-456

Author(s):

C. Barbieri

Keyword(s):

Active Galactic Nuclei ◽

High Redshift ◽

Galactic Nuclei ◽

Radio Sources ◽

Physical Processes ◽

Stellar Objects ◽

Sky Survey ◽

Quasi Stellar Objects ◽

The One

The role of the Schmidt telescopes in the discovery of the Quasi Stellar Objects and of the Active Galactic Nuclei, and in the understanding of their properties was and continues to be of the greatest importance. Thousands of Radio-Sources have been quickly associated to their optical counterparts thanks to the worldwide availability of the Palomar Observatory Sky Survey plates and charts and more recently of the films of the ESO B Survey. Other thousands of QSOs and AGNs devoid of radio emission are found by the large Schmidts nowaday in operation. This wealth of data give fundamental cosmological knowledge and insight in the physical processes occuring in these objects. I'll concentrate in this Review on two specific topics, namely on the discovery techniques and on the study of the optical variability. To both subjects, the 67/92 cm Schmidt telescope here at Asiago has made significant contributions. The first topic is treated in several excellent papers, such as the one by M. Smith (1978) and the one by P. Veron (1983); the material presented in the second part is largely new. In the following, I'll use rather loosely the terms QSOs and AGNs to designate a variety of objects including Quasars (those QSOs in catalogs of Radio-Sources), high-redshift compact galaxies with emission lines, BL LACset similia.

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Pumping of H2O Megamasers

Highlights of Astronomy ◽

10.1017/s1539299600019298 ◽

1998 ◽

Vol 11 (2) ◽

pp. 960-963

Author(s):

Moshe Elitzur

Keyword(s):

Active Galactic Nuclei ◽

Galactic Nuclei ◽

Broad Line ◽

X Ray ◽

Star Forming ◽

Broad Line Region ◽

Star Forming Regions ◽

Disk Rotation ◽

Line Region ◽

Pump Mechanism

AbstractStrong H2O maser emission is detected from active galactic nuclei (AGN) as well as Galactic objects such as star-forming regions and late-type stars. In spite of the widely different luminosities of the different masers, a common pump mechanism seems adequate: neutral collisions at densities of ˜ 108-1010 cm-3 and temperatures of ˜ 250-500 K. The different properties of the various masers can be attributed to geometry. Although disk rotation controls the AGN maser geometry it does not directly determine the dimensions. X-ray radiation and spiral shocks have been suggested as the heating sources of H2O megamasers. Both are capable of explaining the observations, and the radiative scenario seems best understood in terms of chance alignment of standard broad-line-region clouds. It is not yet clear whether these different proposals produce distinct maser signatures.

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Constraining photoionization models with a reprojected optical diagnostic diagram

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3259 ◽

2020 ◽

Vol 499 (4) ◽

pp. 5749-5764 ◽

Cited By ~ 1

Author(s):

Xihan Ji ◽

Renbin Yan

Keyword(s):

Star Formation ◽

Active Galactic Nuclei ◽

Galactic Nuclei ◽

Theoretical Models ◽

Line Ratio ◽

Star Forming ◽

Optical Diagnostic ◽

Diagnostic Diagram ◽

Upper Limits ◽

Nitrogen Abundance

ABSTRACT Optical diagnostic diagrams are powerful tools to separate different ionizing sources in galaxies. However, the model-constraining power of the most widely used diagrams is very limited and challenging to visualize. In addition, there have always been classification inconsistencies between diagrams based on different line ratios, and ambiguities between regions purely ionized by active galactic nuclei (AGNs) and composite regions. We present a simple reprojection of the 3D line ratio space composed of [N ii]λ6583/H α, [S ii]λλ6716, 6731/H α, and [O iii]λ5007/H β, which reveals its model-constraining power and removes the ambiguity for the true composite objects. It highlights the discrepancy between many theoretical models and the data loci. With this reprojection, we can put strong constraints on the photoionization models and the secondary nitrogen abundance prescription. We find that a single nitrogen prescription cannot fit both the star-forming locus and AGN locus simultaneously, with the latter requiring higher N/O ratios. The true composite regions stand separately from both models. We can compute the fractional AGN contributions for the composite regions, and define demarcations with specific upper limits on contamination from AGN or star formation. When the discrepancy about nitrogen prescriptions gets resolved in the future, it would also be possible to make robust metallicity measurements for composite regions and AGNs.

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The GLEAM 4-Jy Sample: The brightest radio-sources in the southern sky

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320003476 ◽

2019 ◽

Vol 15 (S356) ◽

pp. 375-375

Author(s):

Sarah White

Keyword(s):

Radio Emission ◽

Active Galactic Nuclei ◽

Visual Inspection ◽

Low Frequency ◽

Galactic Nuclei ◽

Radio Sources ◽

Relativistic Jets ◽

The Galaxy ◽

Murchison Widefield Array ◽

Past Activity

AbstractLow-frequency radio emission allows powerful active galactic nuclei (AGN) to be selected in a way that is unaffected by dust obscuration and orientation of the jet axis. It also reveals past activity (e.g. radio lobes) that may not be evident at higher frequencies. Currently, there are too few “radio-loud” galaxies for robust studies in terms of redshift-evolution and/or environment. Hence our use of new observations from the Murchison Widefield Array (the SKA-Low precursor), over the southern sky, to construct the GLEAM 4-Jy Sample (1,860 sources at S151MHz > 4 Jy). This sample is dominated by AGN and is 10 times larger than the heavily relied-upon 3CRR sample (173 sources at S178MHz > 10 Jy) of the northern hemisphere. In order to understand how AGN influence their surroundings and the way galaxies evolve, we first need to correctly identify the galaxy hosting the radio emission. This has now been completed for the GLEAM 4-Jy Sample – through repeated visual inspection and extensive checks against the literature – forming a valuable, legacy dataset for investigating relativistic jets and their interplay with the environment.

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