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- Espada, D., et al.
(författare)
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Disentangling the Circumnuclear Environs of Centaurus A. II. On the Nature of the Broad Absorption Line
- 2010
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Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 720:1, s. 666-678
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Tidskriftsartikel (refereegranskat)abstract
- We report on atomic gas (H I) and molecular gas (as traced by CO(2-1)) redshifted absorption features toward the nuclear regions of the closest powerful radio galaxy, Centaurus A (NGC 5128). Our H I observations using the Very Long Baseline Array allow us to discern with unprecedented sub-parsec resolution H I absorption profiles toward different positions along the 21 cm continuum jet in the inner 0farcs3 (or 5.4 pc). In addition, our CO(2-1) data obtained with the Submillimeter Array probe the bulk of the absorbing molecular gas with little contamination by emission, which was not possible with previous CO single-dish observations. We shed light on the physical properties of the gas in the line of sight with these data, emphasizing the still open debate about the nature of the gas that produces the broad absorption line (~55 km s–1). First, the broad H I line is more prominent toward the central and brightest 21 cm continuum component than toward a region along the jet at a distance ~20 mas (or 0.4 pc) further from the nucleus. This indicates that the broad absorption line arises from gas located close to the nucleus, rather than from diffuse and more distant gas. Second, the different velocity components detected in the CO(2-1) absorption spectrum match well with other molecular lines, such as those of HCO+(1-0), except the broad absorption line that is detected in HCO+(1-0) (and most likely related to that of the H I). Dissociation of molecular hydrogen due to the active galactic nucleus seems to be efficient at distances r lsim 10 pc, which might contribute to the depth of the broad H I and molecular lines.
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- Lucatelli, Geferson, et al.
(författare)
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The PARADIGM project I: a multiscale radio morphological analysis of local U/LIRGS
- 2024
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 529:4, s. 4468-4499
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Tidskriftsartikel (refereegranskat)abstract
- Disentangling the radio flux contribution from star formation (SF) and active-galactic-nuclei (AGNs) activity is a long-standing problem in extragalactic astronomy, since at frequencies of 10 GHz, both processes emit synchrotron radiation. We present in this work the general objectives of the PARADIGM (PAnchromatic high-Resolution Analysis of DIstant Galaxy Mergers) project, a multi-instrument concept to explore SF and mass assembly of galaxies. We introduce two novel general approaches for a detailed multiscale study of the radio emission in local (ultra) luminous infrared galaxies (U/LIRGs). In this work, we use archival interferometric data from the Very Large Array (VLA) centred at ∼6 GHz (C band) and present new observations from the e-Multi-Element Radio-Linked Interferometer Network (e-MERLIN) for UGC 5101, VV 705, VV 250, and UGC 8696. Using our image decomposition methods, we robustly disentangle the radio emission into distinct components by combining information from the two interferometric arrays. We use e-MERLIN as a probe of the core-compact radio emission (AGN or starburst) at ∼20 pc scales, and as a probe of nuclear diffuse emission, at scales ∼100-200 pc. With VLA, we characterize the source morphology and the flux density on scales from ∼200 pc up to and above 1 kpc. As a result, we find deconvolved and convolved sizes for nuclear regions from ∼10 to ∼200 pc. At larger scales, we find sizes of 1.5-2 kpc for diffuse structures (with effective sizes of ∼300-400 pc). We demonstrate that the radio emission from nuclear extended structures (∼100 pc) can dominate over core-compact components, providing a significant fraction of the total multiscale SF output. We establish a multiscale radio tracer for SF by combining information from different instruments. Consequently, this work sets a starting point to potentially correct for overestimations of AGN fractions and underestimates of SF activity.
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- Parra Barraza, Rodrigo, 1974, et al.
(författare)
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COLA. III. RADIO DETECTION OF ACTIVE GALACTIC NUCLEUS IN COMPACT MODERATE LUMINOSITY INFRARED GALAXIES
- 2010
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Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 720:1, s. 555-568
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Tidskriftsartikel (refereegranskat)abstract
- We present results from 4.8 GHz Very Large Array (VLA) and global very long baseline interferometry (VLBI) observations of the northern half of the moderate FIR luminosity (median L-IR = 10(11.01) L-circle dot) COLA sample of star-forming galaxies. VLBI sources are detected in a high fraction (20/90) of the galaxies observed. The radio luminosities of these cores (similar to 10(21) W Hz(-1)) are too large to be explained by radio supernovae or supernova remnants and we argue that they are instead powered by active galactic nuclei (AGNs). These sub-parsec scale radio cores are preferentially detected toward galaxies whose VLA maps show bright 100-500 parsec scale nuclear radio components. Since these latter structures tightly follow the FIR to radio-continuum correlation for star formation, we conclude that the AGN-powered VLBI sources are associated with compact nuclear starburst environments. The implications for possible starburst-AGN connections are discussed. The detected VLBI sources have a relatively narrow range of radio luminosity consistent with models in which intense compact Eddington-limited starbursts regulate the gas supply onto a central supermassive black hole. The high incidence of AGN radio cores in compact starbursts suggests little or no delay between the starburst phase and the onset of AGN activity.
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- van Langevelde, H. J., et al.
(författare)
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The Synergy between VLBI and Gaia astrometry
- 2018
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Ingår i: Proceedings of Science. - 1824-8039. ; 344
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Konferensbidrag (refereegranskat)abstract
- With the publication of Gaia DR2, 1.3 billion stars now have public parallax and proper motion measurements. In this contribution, we compare the results for sources that have both optical and radio measurements, focusing on circumstellar masers. For these large, variable and bright AGB stars, the VLBI astrometry results can be more robust. Moreover, there are a number of applications where VLBI astrometry provides unique data for studying stellar populations and Galactic structure. The BeSSel project not only provides parallax and proper motions at much larger distances than Gaia can reach, but it also uniquely samples the spiral arms of the Galaxy. The evolved stars in the BAaDE sample can potentially constrain the dynamics and stellar content of the inner bulge and bar of the Milky Way, not reachable in the optical.
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