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Register a new userJupiters Ammonia Distribution Derived from VLA Maps at 3--37 GHz
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We observed Jupiter four times over a full rotation (10 hrs) with the upgraded Karl G. Jansky Very Large Array (VLA) between December 2013 and December 2014. Preliminary results at 4-17 GHz were presented in de Pater et al. (2016); in the present paper we present the full data set at frequencies between 3 and 37 GHz. Major findings are: (i) the radio-hot belt at 8.5--11$^circ$N latitude, near the interface between the North Equatorial Belt (NEB) and the Equatorial Zone (EZ) is prominent at all frequencies (3--37 GHz). Its location coincides with the southern latitudes of the NEB (7--17$^{circ}$ N). (ii) Longitude-smeared maps reveal belts and zones at all frequencies at latitudes $lesssim |20^circ|$. The lowest brightness temperature is in the EZ near a latitude of 4$^circ$N, and the NEB has the highest brightness temperature near 11$^circ$N. The bright part of the NEB increases in latitudinal extent (spreads towards the north) with deceasing frequency, i.e., with depth into the atmosphere. In longitude-resolved maps, several belts, in particular in the southern hemisphere, are not continuous along the latitude line, but broken into small segments as if caused by an underlying wave. (iii) Model fits to longitude-smeared spectra are obtained at each latitude. These show a high NH$_3$ abundance (volume mixing ratio $sim 4 times 10^{-4}$) in the deep ($P>8-10$ bar) atmosphere, decreasing at higher altitudes due to cloud formation (e.g., in zones), or dynamics in combination with cloud condensation (belts). In the NEB ammonia gas is depleted down to at least the 20 bar level with an abundance of $1.75 times 10^{-4}$. (iv) Using the entire VLA dataset, we confirm that the planet is extremely dynamic in the upper layers of the atmosphere, at $P<$2--3 bar, i.e., at the altitudes where clouds form. [Abridged]
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Spatially resolved maps of Jupiters far-infrared 17-37 $mu$m hydrogen-helium collision-induced spectrum were acquired by the FORCAST instrument on the Stratospheric Observatory for Infrared Astronomy (SOFIA) in May 2014. Spectral scans in two grisms covered the broad S(0) and S(1) absorption lines, in addition to contextual imaging in eight broad-band filters (5-37 $mu$m) with spatial resolutions of 2-4. The spectra were inverted to map the zonal-mean temperature and para-H$_2$ distribution ($f_p$, the fraction of the para spin isomer with respect to the ortho spin isomer) in Jupiters upper troposphere (the 100-700 mbar range). We compared these to a reanalysis of Voyager-1 and -2 IRIS spectra covering the same spectral range. Para-H$_2$ increases from equator to pole, with low-$f_p$ air at the equator representing sub-equilibrium conditions (i.e., less para-H$_2$ than expected from thermal equilibration), and high-$f_p$ air and possible super-equilibrium at higher latitudes. In particular, we confirm the continued presence of a region of high-$f_p$ air at high northern latitudes discovered by Voyager/IRIS, and an asymmetry with generally higher $f_p$ in the north than in the south. We note that existing collision-induced absorption databases lack opacity from (H$_2$)$_2$ dimers, leading to under-prediction of the absorption near the S(0) and S(1) peaks. There appears to be no spatial correlation between para-H$_2$ and tropospheric ammonia, phosphine and cloud opacity derived from Voyager/IRIS at mid-infrared wavelengths (7-15 $mu$m). We note, however, that para-H$_2$ tracks the similar latitudinal distribution of aerosols within Jupiters upper tropospheric and stratospheric hazes observed in reflected sunlight, suggesting that catalysis of hydrogen equilibration within the hazes (and not the main clouds) may govern the equator-to-pole gradient. [Abridged]
As the SKA is expected to be operational in the next decade, investigations of the radio sky in the range of 100 MHz to 10 GHz have become important for simulations of the SKA observations. In determining physical properties of galaxies from radio data, the radio SED is often assumed to be described by a simple power law, usually with a spectral index of 0.7 for all sources. Even though radio SEDs have been shown to exhibit deviations from this assumption, both in differing spectral indices and complex spectral shapes, it is often presumed that their individual differences cancel out in large samples. We constructed the average radio SED of radio-excess active galactic nuclei (RxAGN), defined as those that exhibit a 3 $sigma$ radio luminosity excess with respect to the value expected only from contribution from star formation, out to z~4. We combined VLA observations of the COSMOS field at 1.4 GHz and 3 GHz with GMRT observations at 325 MHz and 610 MHz. To account for nondetections in the GMRT maps, we employed the survival analysis technique. We selected a sample of RxAGN out to z~4. We find that a sample of RxAGN can be described by a spectral index of $alpha_1=0.28pm0.03$ below the break frequency $ u_b=(4.1pm0.2)$ GHz and $alpha_2=1.16pm0.04$ above, while a simple power-law model yields a single spectral index of $alpha=0.64pm0.07$. By binning in 1.4 GHz radio luminosity and redshift, we find that the power-law spectral index, as well as broken power-law spectral indices, may increase for larger source sizes, while the power-law spectral index and lower-frequency (<4 GHz) broken power-law spectral index are additionally positively correlated with redshift.
We construct the average radio spectral energy distribution (SED) of highly star-forming galaxies (HSFGs) up to z~4. Infrared and radio luminosities are bound by a tight correlation that is defined by the so-called q parameter. This infrared-radio correlation provides the basis for the use of radio luminosity as a star-formation tracer. Recent stacking and survival analysis studies find q to be decreasing with increasing redshift. It was pointed out that a possible cause of the redshift trend could be the computation of rest-frame radio luminosity via a single power-law assumption of the star-forming galaxies (SFGs) SED.To test this, we constrained the shape of the radio SED of a sample of HSFGs. To achieve a broad rest-frame frequency range, we combined previously published VLA observations of the COSMOS field at 1.4 GHz and 3 GHz with unpublished GMRT observations at 325 MHz and 610 MHz by employing survival analysis to account for non-detections in the GMRT maps. We selected a sample of HSFGs in a broad redshift range (0.3<z<4,SFR>100M0/yr) and constructed the average radio SED. By fitting a broken power-law, we find that the spectral index changes from $alpha_1=0.42pm0.06$ below a rest-frame frequency of 4.3 GHz to $alpha_2=0.94pm0.06$ above 4.3 GHz. Our results are in line with previous low-redshift studies of HSFGs (SFR>10M0/yr) that show the SED of HSFGs to differ from the SED found for normal SFGs (SFR<10M0/yr). The difference is mainly in a steeper spectrum around 10 GHz, which could indicate a smaller fraction of thermal free-free emission. Finally, we also discuss the impact of applying this broken power-law SED in place of a simple power-law in K-corrections of HSFGs and a typical radio SED for normal SFGs drawn from the literature. We find that the shape of the radio SED is unlikely to be the root cause of the q-z trend in SFGs.
In this data paper we present and characterise the multi-component radio sources identified in the VLA-COSMOS Large Project at 3 GHz (0.75 arcsec resolution, 2.3 {mu}Jy/beam rms), i.e. the radio sources which are composed of two or more radio blobs.The classification of objects into multi-components was done by visual inspection of 351 of the brightest and most extended blobs from a sample of 10,899 blobs identified by the automatic code blobcat. For that purpose we used multi-wavelength information of the field, such as the 1.4-GHz VLA-COSMOS data and the UltraVISTA stacked mosaic available for COSMOS. We have identified 67 multi-component radio sources at 3 GHz: 58 sources with AGN powered radio emission and 9 star-forming galaxies. We report 8 new detections that were not observed by the VLA-COSMOS Large Project at 1.4 GHz, due to the slightly larger area coverage at 3 GHz. The increased spatial resolution of 0.75 arcsec has allowed us to resolve (and isolate) multiple emission peaks of 28 extended radio sources not identified in the 1.4-GHz VLA-COSMOS map. We report the multi-frequency flux densities (324 MHz, 325 MHz, 1.4 GHz & 3 GHz), star-formation-rates, and stellar masses of these objects. Multi-component objects at 3-GHz VLA-COSMOS inhabit mainly massive galaxies (>10^10.5 Msun). The majority of the multi-component AGN lie below the main-sequence of star-forming galaxies (SFGs), in the green valley and the quiescent region. We provide detailed description of the objects: amongst the AGN there are 2 head-tail, 10 core-lobe, 9 wide-angle-tail (WAT), 8 double-double or Z-/X-shaped, 3 bent-tail radio sources, and 26 symmetric sources, while amongst the SFGs we find the only star-forming ring seen in radio emission in COSMOS. We report a large number (32/58) of disturbed/bent multi-component AGN, 18 of which do not lie within X-ray groups in COSMOS (0.08 < z < 1.53). [abridged]
To better understand the influence of the activity cycle on the solar atmosphere, we report the time variation of the radius observed at 37 GHz ($lambda$=8.1 mm) obtained by the Metsahovi Radio Observatory (MRO) through Solar Cycles 22 to 24 (1989-2015). Almost 5800 maps were analyzed, however, due to instrumental setups changes the data set showed four distinct behaviors, which requested a normalisation process to allow the whole interval analysis. When the whole period was considered, the results showed a positive correlation index of 0.17 between the monthly means of the solar radius at 37 GHz and solar flux obtained at 10.7 cm (F10.7). This correlation index increased to 0.44, when only the data obtained during the last period without instrumental changes were considered (1999-2015). The solar radius correlation with the solar cycle agrees with the previous results obtained at mm/cm wavelengths (17 and 48 GHz), nevertheless, this result is the opposite of that reported at submillimetre wavelengths (212 and 405 GHz).
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