EDP Sciences

Vol. 614
In section 4. Extragalactic astronomy

Constraints on submicrojansky radio number counts based on evolving VLA-COSMOS luminosity functions

by M. Novak, V. Smolcic, E. Schinnerer, G. Zamorani, I. Delvecchio, M. Bondi, and J. Delhaize A&A 614, A47


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Radio emission in galaxies at frequencies below 30 GHz is mostly synchrotron radiation from cosmic electrons gyrating in magnetic fields. The electrons are accelerated by supernovae in star forming (SF) galaxies, and by an accreting supermassive black hole (SMBH) in active galactic nuclei (AGN). Comparison with other wavelengths, such as optical, IR, or X-ray, is necessary to disentangle the two possibilities. This paper presents the results of the Large Program COSMOS-3GHz with the VLA. The total radio luminosity function (LF) since z~5.7 has been derived for the radio selected sample of 7826 galaxies with robust optical/near-infrared (NIR) counterparts. The populations of SF galaxies and AGN are separated on the basis of presence or absence of a radio excess with respect to the star-formation rates (SFRs) derived from the infrared (IR) emission. The redshift dependent pure luminosity evolution (PLE) model fitted to the data with an MCMC algorithm is in very good agreement with the previously published VLA-COSMOS LFs. Different models of evolving LFs are able to reproduce the observed radio sky brightness, despite relying on extrapolations toward the faint end. The results imply that no new radio emitting galaxy population is present below 1 microJy. Selecting galaxies with radio flux densities between 0.1 and 10 microJy will yield a starforming galaxy in 90-95% of the cases with a large percentage of these galaxies existing around a redshift of z ~ 2, thus providing useful constraints for planned surveys with the Square Kilometer Array (SKA) and its precursors.

Vol. 614
In section 4. Extragalactic astronomy

ALMA observations of AGN fuelling. The case of PKS B1718–649

by F. M. Maccagni, R. Morganti, T. A. Oosterloo, J. B. R. Oonk, and B. H. C. Emonts A&A 614, A42


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Active galaxy nuclei (AGN) are fueled by cold gas falling into the center, and the energy released by their activity can produce some feedback to eject gas, and moderate accretion and growth of the black hole. These complex processes can be traced through observations of the cold gas, under the atomic (HI) or molecular form of either the warm through near-infrared H2 lines or cold through the millimetric CO lines. The authors present ALMA observations of the CO (2–1) line in the spiral galaxy NGC 6328, which hosts a radio AGN, PKSB1718–649. The CO line gas in the disk of the galaxy (15kpc) is warped, a possible sign of interaction. While the outer parts follow the north-south orientation of the galaxy major axis, in the inner parts the gas abruptly changes orientation and forms a circumnuclear disk of radius 700pc, whose major axis is perpendicular to that of the outer disk. This structure is characteristic of a kinematically decoupled core (KDC). Together with the centered CO emission, ALMA reveals a CO absorption in front of the continuum source, at red-shifted velocities by 365km/s with respect to the systemic velocity. This absorbing CO gas could trace molecular clouds falling onto the central super-massive black hole. The physical conditions of molecular clouds in the a circumnuclear disk are in good agreement with the predictions for the conditions of the gas when cold chaotic accretion triggers an active galactic nucleus.

Vol. 613
In section 10. Planets and planetary systems

The nature of the TRAPPIST-1 exoplanets

by S. Grimm, B.-O. Demory, M. Gillon, et al. A&A 613, A68


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Using time-transit variations and a genetic algorithm, Grimm et al. improve the uncertainties on the internal densities of the TRAPPIST planets by a factor of between five and eight. These results will help shed light on the compositions of these planets and eventually on the formation of this system.

Vol. 611
In section 9. The Sun

Chromospheric heating during flux emergence in the solar atmosphere

by J. Leenaarts, J. de la Cruz Rodriguez, S. Danilovic, G. Scharmer, and M. Carlsson A&A 611, A28


This study shows the clear correspondence between the emission seen in the solar chromosphere during the emergence of magnetic flux and the strength of the horizontal magnetic field in the low chromosphere. This is direct confirmation of the major role the magnetic field and currents that are induced during the flux emergence play in energizing the chromosphere.

Vol. 611
In section 4. Extragalactic astronomy

Jekyll & Hyde: quiescence and extreme obscuration in a pair of massive galaxies 1.5 Gyr after the Big Bang

by C. Schreiber, I. Labbé, K. Glazebrook, et al. A&A 611, A22


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It is possible to observe galaxies at very high redshifts (more than seven) with ALMA, but these are bright star forming galaxies; here the authors have searched for the most remote quiescent galaxy, at z=3.717. They discovered that the sub-millimeter emission of this object comes in fact from a companion galaxy, 3.2kpc away, which is dusty and star forming. The quiescent galaxy (Jekyll) has another face (Hyde), which has a strong [C II]158micron line, confirming the physical association of the two objects (their redshift difference is 550 km/s). Only Jekyll is detected in the Hubble images, meaning that Hyde is completely obscured by dust. SED fitting of multi-wavelength emission of both galaxies shows that Jekyll was fully quenched at least 200 Myr ago while Hyde harbors moderate star formation with an SFR ~120Msun/yr, or has also been quenched, as Jekyll has. The two objects have similar mass, compactness, environment, and star formation history, so the authors argue that Jekyll and Hyde can be seen as two stages of the same quenching process, and provide a unique laboratory to study this poorly understood phenomenon.

Vol. 611
In section 6. Interstellar and circumstellar matter

Large Interstellar Polarisation Survey. II. UV/optical study of cloud-to-cloud variations of dust in the diffuse ISM

by R. Siebenmorgen, N.V. Voshchinnikov, S. Bagnulo, et al. A&A 611, A5


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The variance of magnetic field strengths and structures is a fundamental issue in the structure of the diffuse interstellar medium. Although Zeeman measurements and infrared polarization provide a picture of the dense phase, the translucent medium remains elusive. This study is a comprehensive survey of approximately 50 lines of sight, using very high resolution UV and optical spectroscopy (resonance transitions for velocity and density information) and optical polarization measurements to decompose the contributors along the lines of sight. In the majority of cases, the contributors are composite and clouds can be separated in velocity and extinction contributions. A substantial fraction, however, are single clouds (about 15% of the sample). Unsurprisingly, the polarization is more randomized with more line-of-sight contributors, but the exceptional detail also makes this study a warning regarding interpretation of single-direction measurements of dust properties.