EDP Sciences

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.

Vol. 610
In section 1. Letters to the Editor

Sub-arcsecond imaging of Arp299-A at 150 MHz with LOFAR: Evidence for a starburst-driven outflow

by N. Ramírez-Olivencia, E. Varenius, M. Pérez-Torres, et al. A&A 610, L18


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Starbursts in merging galaxies can provide spectacular outflows, due to supernovae feedback. The starburst in the Arp 299 pair of colliding galaxies is here shown to provide a huge outflow, of about 5kpc in length, perpendicular to one of the disks. The outflow is remarkable in the high-resolution (0.4 arcsec) image at 150 MHz obtained with the International Low Frequency Array (LOFAR) Telescope. The filamentary outflowing structure accounts for almost 40% of the extended emission of the entire galaxy system. The structure coincides with the ionized gas outflow imaged with HST/NICMOS in the [FeII] and H2 2 mumicron lines. The outflow is also confirmed through Na I D spectra. The low-luminosity AGN in this galaxy would be insufficient to drive this outflow, contrary to the powerful and compact nuclear starburst. The outflow corresponds to 10-60 Mo/yr at a velocity 400-800km/s. This work shows that subarcsecond imaging with LOFAR might be an excellent new tool with which to unveil outflows in the central regions of local luminous infrared galaxies.

Vol. 610
In section 6. Interstellar and circumstellar matter

An ALMA study of the Orion Integral Filament. I. Evidence for fibers in a massive cloud

by A. Hacar, M. Tafalla, J. Forbrich, et al. A&A 610, A77


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The authors combined two new ALMA Cycle 3 mosaics with previous IRAM 30m observations to produce a high-dynamic range N2H+ (1-0) emission map of the Orion integral filament that traces its high-density material and velocity structure down to scales of 0.009 pc (approx. 2000 au). From the analysis of the gas kinematics, the authors identify a total of 55 dense fibers in the central region of the Orion filament. These fibers are characterized by transonic internal motions, lengths of ∼ 0.15 pc, and masses per-unit-length close to those expected in hydrostatic equilibrium. The fibers form a dense bundle with multiple hub-like associations. Within this complex network, the fibers show a compact radial emission profile with a median FWHM of 0.035 pc, systematically narrower than the previously proposed universal 0.1 pc filament width. These observations suggest strong similarities between the internal substructure of this massive filament and previously studied lower-mass objects. In particular, the fibers show identical dynamic properties in both low- and high-mass regions. While their origin remains under debate, the formation of transonic fibers appears to be an inherent property of the interstellar medium turbulence and an essential ingredient of the star formation process in both low- and high-mass regions.

Vol. 610
In section 1. Letters to the Editor

Discovery of a dual AGN at z~3.3 with 20 kpc separation

by B. Husemann, G. Worseck, F. Arrigoni Battaia, and T. Shanks A&A 610, L7


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In the standard CDM cosmological model, galaxies form through mergers in a hierarchical scenario. Since each galaxy nucleus hosts a super massive black hole, a large number of dual AGN, with separations of a few kpc, is expected. However they have been elusive up to now. Thanks to MUSE on the VLT, the authors report the detection of one of the closest pairs of AGN known at z > 3. The object, dubbed Jil, meaning “neighbor” in the Klingon language (Star Trek universe) is a narrow-line emitter within the 120kpc-wide Ly-alpha nebula of the luminous radio-quiet QSO LBQS 0302-0019 at z = 3.3. Jill emits several high ionization narrow emission lines (HeII, CIV, CIII) and is only 20 kpc away from the QSO in projection. Emission-line diagnostics confirm that the source is likely powered by photoionization of an obscured AGN three orders of magnitude fainter than the QSO.