Aims. According to coevolutionary scenarios, nuclear activity and star formation play relevant roles in the early stages of galaxy formation. We aim at identifying them in high redshift galaxies by exploiting high-resolution and sensitivity X-ray and millimetre-wavelength data to confirm the presence or absence of star formation and nuclear activity and their relative role in shaping their SEDs and contributing to their energy budget. Methods. In the current paper we present the data, model and analysis in the X-ray and mm bands for two strongly lensed galaxies, SDP.9 (HATLAS J090740.0-004200) and SDP.11 (HATLAS J091043.1-000322) that we selected in the Herschel-ATLAS catalogues as having an excess emission in the mid-IR regime at redshift > ∼ 1.5, suggesting the presence of a nuclear activity in the early stages of galaxy formation. We observed both of them with Chandra ACIS-S in the X-ray regime and analyzed the high resolution mm data available in the ALMA Science Archive for SDP9, and, by combining the information available in mm, optical and X-ray bands we reconstructed the source morphology.Results. Both the targets were detected in the X-ray, strongly indicating the presence of highly obscured nuclear activity. ALMA observations for SDP9 for continuum and CO(6-5) spectral line with high resolution (0.02arcsec corresponding to ∼ 65 pc at galaxy distance) allowed us to estimate the lensed galaxy redshift to a better accuracy than pre-ALMA estimates (1.5753±0.0003) and to model the emission of the optical, millimetric, and X-ray band emission for this galaxy. We demonstrated that the X-ray emission is generated in the nuclear environment and it strongly support the presence of nuclear activity in this object. On the basis of the X-ray data, we attempted an estimate of the BH properties in these galaxies. Conclusions. By taking advantage of the lensing magnification we identified weak nuclear activity associated with high-z galaxies with large star formation rates, useful to extend the investigation of the relationship between star formation and nuclear activity to two intrinsically less luminous, high-z star forming galaxies than was possible so far. Given our results only for two objects, they solely cannot constrain the evolutionary models, but provide us with interesting hints and set an observational path towards addressing the role of star formation and nuclear activity in forming galaxies.
Proxima Centauri, our closest stellar neighbour, is a low-mass M5 dwarf orbiting in a triple system. An Earth-mass planet with an 11 day period has been discovered around this star. The star's mass has been estimated only indirectly using a mass-luminosity relation, meaning that large uncertainties affect our knowledge of its properties. To refine the mass estimate, an independent method has been proposed: gravitational microlensing. By taking advantage of the close passage of Proxima Cen in front of two background stars, it is possible to measure the astrometric shift caused by the microlensing effect due to these close encounters and estimate the gravitational mass of the lens (Proxima Cen). Microlensing events occurred in 2014 and 2016 with impact parameters, the closest approach of Proxima Cen to the background star, of 1. 6 ± 0. 1 and 0. 5 ± 0. 1, respectively. Accurate measurements of the positions of the background stars during the last two years have been obtained with HST/WFC3, and with VLT/SPHERE from the ground. The SPHERE campaign started on March 2015, and continued for more than two years, covering 9 epochs. The parameters of Proxima Centauri's motion on the sky, along with the pixel scale, true North, and centering of the instrument detector were readjusted for each epoch using the background stars visible in the IRDIS field of view. The experiment has been successful and the astrometric shift caused by the microlensing effect has been measured for the second event in 2016. We used this measurement to derive a mass of 0.150 +0.062 −0.051 (an error of ∼ 40%) M for Proxima Centauri acting as a lens. This is the first and the only currently possible measurement of the gravitational mass of Proxima Centauri.
The star formation rate density (SFRD) history of the universe is well constrained up to redshift z ∼ 2. At earlier cosmic epochs, the picture has been largely inferred from UV-selected galaxies (e.g., Lyman-break galaxies; LBGs). However, the inferred star formation rates of LBGs strongly depend on the assumed dust extinction correction, which is not well constrained at high z, while observations in the radio domain are not affected by this issue. In this work we measure the SFRD from a 1.4 GHz selected sample of ∼600 galaxies in the GOODS-N field up to redshift ∼3.5. We take into account the contribution of active galactic nuclei from the infrared-radio correlation. We measure the radio luminosity function, fitted with a modified Schechter function, and derive the SFRD. The cosmic SFRD shows an increase up to z ∼ 2 and then an almost flat plateau up to z ∼ 3.5. Our SFRD is in agreement with those from other far-IR/radio surveys and a factor 2 higher than those from LBG samples. We also estimate that galaxies lacking a counterpart in the HST/WFC3 H-band (H-dark) make up ∼25% of the ϕ-integrated SFRD relative to the full sample at z ∼ 3.2, and up to 58% relative to LBG samples.
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