The asymmetry in the azimuthal angle distribution of hadrons produced in unpolarized Semi-Inclusive Deep Inelastic Scattering (SIDIS) carries information on the intrinsic transverse momentum of the ...quark k → T and on the still unknown Boer-Mulders parton distribution function h 1 ⊥ . Using the data collected in 2016 and 2017 with 160 GeV/c muon beams scattering off a liquid hydrogen target, the COMPASS Collaboration is measuring the azimuthal asymmetries A UU cos ϕ h , A UU cos2 ϕ h and A LU sin ϕ h for charged hadrons. The preliminary results shown here confirm the strong kinematic dependencies observed in previous measurements conducted by COMPASS, HERMES and CLAS. The contribution from hadrons produced in the decay of vector mesons diffractively produced is also discussed.
ABSTRACT Galaxies that are being stripped of their gas can sometimes be recognized from their optical appearance. Extreme examples of stripped galaxies are the so-called "jellyfish galaxies" that ...exhibit tentacles of debris material with a characteristic jellyfish morphology. We have conducted the first systematic search for galaxies that are being stripped of their gas at low-z (z = 0.04−0.07) in different environments, selecting galaxies with varying degrees of morphological evidence for stripping. We have visually inspected B- and V-band images and identified 344 candidates in 71 galaxy clusters of the OMEGAWINGS+WINGS sample and 75 candidates in groups and lower mass structures in the PM2GC sample. We present the atlas of stripping candidates and a first analysis of their environment and their basic properties, such as morphologies, star formation rates and galaxy stellar masses. Candidates are found in all clusters and at all clustercentric radii, and their number does not correlate with the cluster velocity dispersion or X-ray luminosity LX. Interestingly, convincing cases of candidates are also found in groups and lower mass halos (1011−1014M ), although the physical mechanism at work needs to be securely identified. All the candidates are disky, have stellar masses ranging from log M/M < 9 to > 11.5 and the majority of them form stars at a rate that is on average a factor of 2 higher (2.5 ) compared to non-stripped galaxies of similar mass. The few post-starburst and passive candidates have weak stripping evidence. We conclude that disturbed morphologies suggestive of stripping phenomena are ubiquitous in clusters and could be present even in groups and low mass halos. Further studies will reveal the physics of the gas stripping and clarify the mechanisms at work.
We present a systematic analysis of X-ray archival data of all the 29 quasars (QSOs) at z> 5.5 observed so far with Chandra, XMM-Newton and Swift-XRT, including the most-distant quasar ever ...discovered, ULAS J1120+0641 (z = 7.08). This study allows us to place constraints on the mean spectral properties of the primordial population of luminous Type 1 (unobscured) quasars. Eighteen quasars are detected in the X-ray band, and we provide spectral-fitting results for their X-ray properties, while for the others we provide upper limits to their soft (0.5–2.0 keV) X-ray flux. We measured the power-law photon index and derived an upper limit to the column density for the five quasars (J1306+0356, J0100+2802, J1030+0524, J1148+5251, J1120+0641) with the best spectra (>30 net counts in the 0.5–7.0 keV energy range) and find that they are consistent with values from the literature and lower-redshift quasars. By stacking the spectra of ten quasars detected by Chandra in the redshift range 5.7 ≤ z ≤ 6.1 we find a mean X-ray power-law photon index of Γ = 1.92-0.27+0.28 and a neutral intrinsic absorption column density of NH ≤ 1023 cm-2. These results suggest that the X-ray spectral properties of luminous quasars have not evolved up to z ≈ 6. We also derived the optical-X-ray spectral slopes (αox) of our sample and combined them with those of previous works, confirming that αox strongly correlates with UV monochromatic luminosity at 2500 Å. These results strengthen the non-evolutionary scenario for the spectral properties of luminous active galactic nuclei (AGN).
This paper presents a spatially resolved kinematic study of the jellyfish galaxy JO201, one of the most spectacular cases of ram-pressure stripping (RPS) in the GAs Stripping Phenomena in galaxies ...with MUSE (GASP) survey. By studying the environment of JO201, we find that it is moving through the dense intracluster medium of Abell 85 at supersonic speeds along our line of sight, and that it is likely accompanied by a small group of galaxies. Given the density of the intracluster medium and the galaxy's mass, projected position, and velocity within the cluster, we estimate that JO201 must so far have lost ∼50% of its gas during infall via RPS. The MUSE data indeed reveal a smooth stellar disk accompanied by large projected tails of ionized ( ) gas, composed of kinematically cold (velocity dispersion <40 km s−1) star-forming knots and very warm (>100 km s−1) diffuse emission, that extend out to at least from the galaxy center. The ionized -emitting gas in the disk rotates with the stars out to ∼6 kpc; but, in the disk outskirts, it becomes increasingly redshifted with respect to the (undisturbed) stellar disk. The observed disturbances are consistent with the presence of gas trailing behind the stellar component resulting from intense face-on RPS along the line of sight. Our kinematic analysis is consistent with the estimated fraction of lost gas and reveals that stripping of the disk happens outside-in, causing shock heating and gas compression in the stripped tails.
The first blazar observed at z > 6 Belladitta, S.; Moretti, A.; Caccianiga, A. ...
Astronomy and astrophysics (Berlin),
03/2020, Letnik:
635
Journal Article
Recenzirano
Odprti dostop
We present the discovery of PSO J030947.49+271757.31, the radio brightest (23.7 mJy at 1.4 GHz) active galactic nucleus (AGN) at
z
> 6.0. It was selected by cross-matching the NRAO VLA Sky Survey ...and the Panoramic Survey Telescope and Rapid Response System PS1 databases and its high-
z
nature was confirmed by a dedicated spectroscopic observation at the Large Binocular Telescope. A pointed
Neil Gehrels Swift
Observatory XRT observation allowed us to measure a flux of ∼3.4 × 10
−14
erg s
−1
cm
−2
in the 0.5–10 keV energy band, which also makes this object the X-ray brightest AGN ever observed at
z
> 6.0. Its flat radio spectrum (
α
νr
< 0.5), very high radio loudness (
R
> 10
3
), and strong X-ray emission, compared to the optical, support the hypothesis of the blazar nature of this source. Assuming that this is the only blazar at this redshift in the surveyed area of sky, we derive a space density of blazars at
z
∼ 6 and with
M
1450 Å
< −25.1 of 5.5
+11.2
−4.6
× 10
−3
Gpc
−3
. From this number, and assuming a reasonable value of the bulk velocity of the jet (Γ = 10), we can also infer a space density of the entire radio-loud AGN population at
z
∼ 6 with the same optical/UV absolute magnitude of 1.10
+2.53
−0.91
Gpc
−3
. Larger samples of blazars will be necessary to better constrain these estimates.
We report the 888 MHz radio detection in the Rapid ASKAP Continuum Survey (RACS) of VIK J2318−3113, a
z
= 6.44 quasar. Its radio luminosity (1.2 × 10
26
W Hz
−1
at 5 GHz) compared to the optical ...luminosity (1.8 × 10
24
W Hz
−1
at 4400 Å) makes it the most distant radio-loud quasar observed so far, with a radio loudness
R
∼ 70 (
R
=
L
5 GHz
/
L
4400 Å
). Moreover, the high bolometric luminosity of the source (
L
bol
= 7.4 × 10
46
erg s
−1
) suggests the presence of a supermassive black hole with a high mass (≳6 × 10
8
M
⊙
) at a time when the Universe was younger than a billion years. Combining the new radio data from RACS with previous ASKAP observations at the same frequency, we found that the flux density of the source may have varied by a factor of ∼2, which could suggest the presence of a relativistic jet oriented towards the line of sight, that is, a blazar nature. However, currently available radio data do not allow us to firmly characterise the orientation of the source. Further radio and X-ray observations are needed.
We present Director’s Discretionary Time multi-frequency observations obtained with the
Jansky
Very Large Array and the Very Long Baseline Array (VLBA) of the blazar PSO J030947.49+271757.31 ...(hereafter PSO J0309+27) at
z
= 6.10 ± 0.03. The milliarcsecond angular resolution of our VLBA observations at 1.5, 5, and 8.4 GHz unveils a bright one-sided jet extended for ∼500 parsecs in projection. This high-
z
radio-loud active galactic nucleus is resolved into multiple compact sub-components that are embedded in a more diffuse and faint radio emission that enshrouds them in a continuous jet structure. We directly derive limits on some physical parameters from observable quantities such as viewing angle and Lorentz and Doppler factors. If PSO J0309+27 is a genuine blazar, as suggested by its X-ray properties, then we find that its bulk Lorentz factor must be relatively low (lower than 5). This value would be in favour of a scenario currently proposed to reconcile the paucity of high-
z
blazars with current predictions. Nevertheless, we cannot exclude that PSO J0309+27 is seen under a larger viewing angle, which would imply that the X-ray emission must be enhanced, for example, by inverse Compton scattering with the cosmic microwave background. More stringent constraints on the bulk Lorentz factor in PSO J0309+27 and on these factors in the other high-
z
blazars are necessary to test whether their properties are intrinsically different from those of the low-
z
blazar population.
Context. The relation between a cosmological halo concentration and its mass (cMr) is a powerful tool to constrain cosmological models of halo formation and evolution. Aims. On the scale of galaxy ...clusters the cMr has so far been determined mostly with X-ray and gravitational lensing data. The use of independent techniques is helpful in assessing possible systematics. Here we provide one of the few determinations of the cMr by the dynamical analysis of the projected-phase-space distribution of cluster members. Methods. Based on the WINGS and OmegaWINGS data sets, we used the Jeans analysis with the MAMPOSSt technique to determine masses and concentrations for 49 nearby clusters, each of which has ≳60 spectroscopic members within the virial region, after removal of substructures. Results. Our cMr is in statistical agreement with theoretical predictions based on ΛCDM cosmological simulations. Our cMr is different from most previous observational determinations because of its flatter slope and lower normalization. It is however in agreement with two recent cMr obtained using the lensing technique on the CLASH and LoCuSS cluster data sets. Conclusions. The dynamical study of the projected-phase-space of cluster members is an independent and valid technique to determine the cMr of galaxy clusters. Our cMr shows no tension with theoretical predictions from ΛCDM cosmological simulations for low-redshift, massive galaxy clusters. In the future we will extend our analysis to galaxy systems of lower mass and at higher redshifts.
Context. Studies of the properties of low-redshift cluster galaxies suffer, in general, from small spatial coverage of the cluster area. WINGS, the most homogeneous and complete study of galaxies in ...dense environments to date, obtained spectroscopic redshifts for 48 clusters at a median redshift of 0.05, out to an average distance of approximately 0.5 cluster virial radii. The WINGS photometric survey was recently extended by the VST survey OmegaWINGS to cover the outskirts of a subset of the original cluster sample. Aims. In this work, we present the spectroscopic follow-up of 33 of the 46 clusters of galaxies observed with VST over 1 square degree. The aim of this spectroscopic survey is to enlarge the number of cluster members and study the galaxy characteristics and the cluster dynamical properties out to large radii, reaching the virial radius and beyond. Methods. We used the AAOmega spectrograph at AAT to obtain fiber-integrated spectra covering the wavelength region between 3800 and 9000 Å with a spectral resolution of 3.5−6 Å full width at half maximum (FWHM). Observations were performed using two different configurations and exposure times per cluster. We measured redshifts using both absorption and emission lines and used them to derive the cluster redshifts and velocity dispersions. Results. We present here the redshift measurements for 17 985 galaxies, 7497 of which turned out to be cluster members. The sample magnitude completeness is 80% at V = 20. Thanks to the observing strategy, the radial completeness turned out to be relatively constant (90%) within the AAOmega field of view. The success rate in measuring redshifts is 95%, at all radii. Conclusions. We provide redshifts for the full sample of galaxies in OmegaWINGS clusters together with updated and robust cluster redshift and velocity dispersions. These data, publicly accessible through the CDS and VO archives, will enable evolutionary and environmental studies of cluster properties, providing a local benchmark.
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