We report on the direct observation of an extended X-ray jet in the
z
= 6.1 radio-loud active galactic nucleus PSO J030947.49+271757.31 from a deep
Chandra
X-ray observation (128 ksec). This ...detection represents the most distant kiloparsec-scale off-nuclear emission resolved in X-rays to date. The angular distance of the emission is ∼4″ (corresponding to ∼20 kpc at
z
= 6.1), along the same direction of the jet observed at parsec scales in previous VLBA high-resolution radio observations. Moreover, the 0.5–7.0 keV isophotes coincide with the extended radio emission as imaged by the VLA Sky Survey at 3 GHz. The rest-frame 2–10 keV luminosity of the extended component is
L
2 − 10
keV = 5.9 × 10
44
erg s
−1
, about 8% of the core: this makes it one of the most luminous jets resolved in X-rays so far. Through spectral energy distribution modelling we find that this emission can be explained by the inverse Compton interaction with the photons of the cosmic microwave background, assuming that the jet’s physical parameters are similar to those in the local Universe. At the same time, we find that the radiation produced by a putative population of high-energy electrons through the synchrotron process observed at low redshift is quenched at high redshift, hence becoming negligible.
We investigate the mid-infrared (mid-IR) properties of the largest (42 objects) sample of radio-loud narrow-line Seyfert 1 (RL NLS1) collected to date, using data from the Wide-field Infrared Survey ...Explorer. We analyse the mid-IR colours of these objects and compare them to what is expected from different combinations of AGN and galaxy templates. We find that, in general, the host galaxy emission gives an important contribution to the observed mid-IR flux in particular at the longest wavelengths (W3, at 12 μm, and W4, at 22 μm). In about half of the sources (22 objects), we observe a very red mid-IR colour (W4 − W3 > 2.5) that can be explained only using a starburst galaxy template (M82). Using the 22 μm luminosities, corrected for the AGN contribution, we have then estimated the star formation rate (SFR) for 20 of these ‘red’ RL NLS1, finding values ranging from 10 to 500 M⊙ yr−1. For the RL NLS1 showing bluer colours, instead, we cannot exclude the presence of a star-forming (SF) host galaxy although, on average, we expect a lower SFR. Studying the radio (1.4 GHz) to mid-IR (22 μm) flux ratios of the RL NLS1 in the sample, we found that in ∼10 objects the SF activity could represent the most important component also at radio frequencies, in addition (or in alternative) to the relativistic jet. We conclude that both the mid-IR and the radio emission of RL NLS1 are a mixture of different components, including the relativistic jet, the dusty torus and an intense SF activity.
ABSTRACT
Different works have recently found an increase of the average X-ray-to-radio luminosity ratio with redshift in the blazar population. We evaluate here whether the inverse Compton ...interaction between the relativistic electrons within the jet and the photons of the cosmic microwave background (IC/CMB) can explain this trend. Moreover, we test whether the IC/CMB model can also be at the origin of the different space density evolutions found in X-ray and radio-selected blazar samples. By considering the best statistically complete samples of blazars selected in the radio or in the X-ray band and covering a large range of redshift (0.5 ≲ z ≲ 5.5), we evaluate the expected impact of the CMB on the observed X-ray emission on each sample and then we compare these predictions with the observations. We find that this model can satisfactorily explain both the observed trend of the X-ray-to-radio luminosity ratios with redshift and the different cosmological evolutions derived from the radio and X-ray band. Finally, we discuss how currently on-going X-ray missions, like extended ROentgen Survey with an Imaging Telescope Array, could help to further constrain the observed evolution at even higher redshifts (up to z ∼ 6–7).
ABSTRACT
We present the selection of high-redshift (z ≳ 5.7) radio-loud (RL) quasi-stellar object (QSO) candidates from the combination of the radio Rapid ASKAP Continuum Survey (RACS; at 888 MHz) ...and the optical/near-infrared Dark Energy Survey (DES). In particular, we selected six candidates brighter than $S_{\rm 888\, MHz}\gt 1$ mJy beam−1 and mag(zDES) < 21.3 using the dropout technique (in the i-band). From this sample, we were able to confirm the high-z nature (z ∼ 6.1) of two sources, which are now among the highest redshift RL QSOs currently known. Based on our Gemini-South/GMOS observations, neither object shows a prominent Ly α emission line. This suggests that both sources are likely to be weak emission-line QSOs hosting radio jets and would therefore further strengthen the potential increase of the fraction of weak emission-line QSOs recently found in the literature. However, further multiwavelength observations are needed to constrain the properties of these QSOs and of their relativistic jets. From the discovery of these two sources, we estimated the space density of RL QSOs in the redshift range 5.9 < z < 6.4 to be 0.13$^{+0.18}_{-0.09}$ and found it to be consistent with the expectations based on our current knowledge of the blazar population up to z ∼ 5.
The space density of z > 4 blazars Caccianiga, A; Moretti, A; Belladitta, S ...
Monthly notices of the Royal Astronomical Society,
03/2019, Letnik:
484, Številka:
1
Journal Article
The cerebellum has demonstrated a critical role during adaptation in motor learning. However, the extent to which it can contribute to the skill acquisition of complex real-world tasks remains ...unclear. One particularly challenging application in terms of motor activities is robotic surgery, which requires surgeons to complete complex multidimensional visuomotor tasks through a remotely operated robot. Given the need for high skill proficiency and the lack of haptic feedback, there is a pressing need for understanding and improving skill development. We investigated the effect of cerebellar transcranial direct current stimulation applied during the execution of a robotic surgery training task. Study participants received either real or sham stimulation while performing a needle driving task in a virtual (simulated) and a real-world (actual surgical robot) setting. We found that cerebellar stimulation significantly improved performance compared to sham stimulation at fast (more demanding) execution speeds in both virtual and real-world training settings. Furthermore, participants that received cerebellar stimulation more effectively transferred the skills they acquired during virtual training to the real world. Our findings underline the potential of non-invasive brain stimulation to enhance skill learning and transfer in real-world relevant tasks and, more broadly, its potential for improving complex motor learning.
We present the first results of a radio survey of 79 narrow-line Seyfert 1 (NLS1) carried out with the Karl G. Jansky Very Large Array (JVLA) at 5 GHz in A configuration aimed at studying the radio ...properties of these sources. We report the detection of extended emission in one object: Mrk 783. This is intriguing, since the radio-loudness parameter R of this object is close to the threshold between radio-quiet and radio-loud active galactic nuclei (AGN). The galaxy is one of the few NLS1 showing such an extended emission at z < 0.1. The radio emission is divided into a compact core component and an extended component, observed on both sides of the nucleus and extending from 14 kpc southeast to 12 kpc northwest. There is no sign of a collimated jet and the shape of the extended component is similar to those of some Seyfert galaxies. The properties of the emission are compatible with a relic produced by the intermittent activity cycle of the AGN.
Context. Obscuration in high-redshift quasi-stellar objects (QSOs) has a profound impact on our understanding of the evolution of supermassive black holes across cosmic time. An accurate ...quantification of its relevance is therefore mandatory. Aims. We present a study aimed at evaluating the importance of obscuration in high-redshift jetted QSOs, that is, active nuclei characterised by the presence of powerful relativistic jets. Methods. We compared the observed number of radio-detected QSOs at different radio flux density limits with the value predicted by the beaming model on the basis of the number of oriented sources (blazars). Any significant deficit between observations and predictions of radio-detected QSOs can be caused by the presence of obscuration along large angles from the jet direction. We applied this approach to two sizeable samples characterised by the same optical limit (mag = 21) but with significantly different radio density limits (30 mJy and 1 mJy, respectively) and containing a total of 87 independent radio-loud 4 ≤ z ≤ 6.8 QSOs, 31 of which are classified as blazars. Results. We found generally good agreement between the numbers predicted by the model and those actually observed, with only a marginal discrepancy at ∼0.5 mJy that could be caused by the sample’s lack of completeness. We concluded that we have no evidence of obscuration within angles 10–20° from the relativistic jet direction. We also discuss how the ongoing deep wide-angle radio surveys will be instrumental to testing the presence of obscuration at much larger angles, up to 30–35°. Finally, we suggest that, depending on the actual fraction of obscured QSOs, relativistic jets could be much more common at high redshifts compared to what is usually observed in the local Universe.
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