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

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.

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.

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 ASYMMETRIES OF AGN JETS IN INHOMOGENEOUS MEDIA

2014 ◽  
Vol 28 ◽  
pp. 1460192
Author(s):  
VOLKER GAIBLER
Keyword(s):  
Interstellar Medium ◽  
Active Galactic Nuclei ◽  
High Redshift ◽  
Galactic Nuclei ◽  
Inhomogeneous Media ◽  
Host Galaxy ◽  
Radio Sources ◽  
Propagation Models ◽  
Hydrodynamical Simulations

Considerable asymmetries in jets from active galactic nuclei (AGN) and associated double radio sources can be caused by an inhomogeneous interstellar medium of the host galaxy. These asymmetries can easily be estimated by 1D propagation models, but hydrodynamical simulations have shown that the actual asymmetries can be considerably larger. With a set of smaller-scale hydrodynamical simulations we examine these asymmetries, and find they are typically a factor of ~ 3 larger than in 1D models. We conclude that, at high redshift, large asymmetries in radio sources are expected in gas-rich galaxies with a clumpy interstellar medium.

scholarly journals Host galaxy properties and environment of obscured and unobscured X-ray selected active galactic nuclei in the COSMOS survey

2020 ◽  
Vol 494 (1) ◽  
pp. 1189-1202 ◽  
Author(s):  
C Bornancini ◽  
D García Lambas
Keyword(s):  
Active Galactic Nuclei ◽  
Formation Rate ◽  
Control Sample ◽  
Galactic Nuclei ◽  
Local Environment ◽  
Spectroscopic Properties ◽  
Stellar Mass ◽  
Host Galaxy ◽  
X Ray ◽  
Star Forming

ABSTRACT We analyse different photometric and spectroscopic properties of active galactic nuclei (AGNs) and quasars (QSOs) selected by their mid-IR power-law and X-ray emission from the COSMOS survey. We use a set of star-forming galaxies as a control sample to compare with the results. We have considered samples of obscured (HR &gt; −0.2) and unobscured (HR &lt; −0.2) sources including AGNs with LX &lt; 1044 erg s−1, as well as QSOs (LX &gt; 1044 erg s−1) with 1.4 ≤ z ≤ 2.5. We also study the typical environment of these samples, by assessing neighbouring galaxy number density and neighbour properties such as colour, stellar mass, and star formation rate. We find that the UV/optical and mid-infrared colour distribution of the different AGN types differ significantly. Also, we obtain most of AGNs and QSOs to be more compact when compared to the sample of SF galaxies. In general we find that the stellar mass distribution of the different AGN sample are similar, obtaining only a difference of $\Delta \overline{\mathrm{log}M}=0.3$ dex (M⊙) between unobscured and obscured QSOs. Obscured and unobscured AGNs and QSOs reside in different local environment at small (rp &lt; 100 kpc) scales. Our results support previous findings where AGN type correlates with environment. These differences and those found in AGN host properties cast out the simplest unified model in which obscuration is purely an orientation effect.

scholarly journals Host galaxy properties of changing-look AGNs revealed in the MaNGA survey

2020 ◽  
Vol 498 (3) ◽  
pp. 3985-3994
Author(s):  
Xiaoling Yu ◽  
Yong Shi ◽  
Yanmei Chen ◽  
Jianhang Chen ◽  
Songlin Li ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Main Sequence ◽  
Galactic Nuclei ◽  
Axial Ratio ◽  
Emission Lines ◽  
Host Galaxy ◽  
Type I ◽  
Host Galaxies ◽  
Star Forming ◽  
Nearby Galaxies

ABSTRACT Changing-look active galactic nuclei (CL-AGNs) are a subset of AGNs in which the broad Balmer emission lines appear or disappear within a few years. We use the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey to identify five CL-AGNs. The 2D photometric and kinematic maps reveal common features as well as some unusual properties of CL-AGN hosts as compared to the AGN hosts in general. All MaNGA CL-AGNs reside in the star-forming main sequence, similar to MaNGA non-changing-look AGNs (NCL-AGNs). The $80 \pm 16{{\ \rm per\ cent}}$ of our CL-AGNs do possess pseudo-bulge features, and follow the overall NCL-AGN MBH–σ* relationship. The kinematic measurements indicate that they have similar distributions in the plane of angular momentum versus galaxy ellipticity. MaNGA CL-AGNs, however, show a higher, but not statistically significant ($20 \pm 16{{\ \rm per\ cent}}$) fraction of counter-rotating features compared to that ($1.84 \pm 0.61{{\ \rm per\ cent}}$) in general star formation population. In addition, MaNGA CL-AGNs favour more face-on (axial ratio &gt; 0.7) than that of type I NCL-AGNs. These results suggest that host galaxies could play a role in the CL-AGN phenomenon.

scholarly journals AGN types and unification model

2019 ◽  
Vol 15 (S356) ◽  
pp. 29-43
Author(s):  
Luigi Spinoglio ◽  
Juan Antonio Fernández-Ontiveros
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Physical Object ◽  
Host Galaxy ◽  
Star Forming ◽  
Star Formation Activity ◽  
Frequency Monitoring

AbstractThe motivation of the “unified model” is to explain the main properties of the large zoo of active galactic nuclei with a single physical object. The discovery of broad permitted lines in the polarized spectrum of type 2 Seyfert galaxies in the mid 80’s led to the idea of an obscuring torus, whose orientation with respect to our line of sight was the reason of the different optical spectra. However, after many years of observations with different techniques, including IR and mm interferometry, the resulting properties of the observed dust structures differ from the torus model that would be needed to explain the type 1 vs type 2 dichotomy. Moreover, in the last years, multi-frequency monitoring of active galactic nuclei has shown an increasing number of transitions from one type to the other one, which cannot be explained in terms of the simple orientation of the dusty structure surrounding the active galactic nucleus (AGN). The interrelations between the AGN and the host galaxy, as also shown in the Magorrian relation, suggest that the evolution of the host galaxy may also have an important role in the observed manifestation of the nuclei. As an example, the observed delay between the maximum star formation activity and the onset of the AGN activity, and the higher occurrence of type 2 nuclei in star forming galaxies, have suggested the possible evolutionary path from, e.g., H II → AGN2 → AGN1. In the next years the models of unification need to also consider this observational framework and not only simple orientation effects.

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

2019 ◽  
Vol 491 (3) ◽  
pp. 3395-3410 ◽  
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 $\alpha _{5.5\,\mathrm{ GHz}}^{9.0\,\mathrm{ GHz}}$ &gt; −0.3 (for S ∝ να). This flat or inverted population is not well reproduced by current simulations of radio source populations.

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

2018 ◽  
Vol 620 ◽  
pp. A74 ◽  
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.

scholarly journals Constraining photoionization models with a reprojected optical diagnostic diagram

2020 ◽  
Vol 499 (4) ◽  
pp. 5749-5764 ◽  
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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