# Browsing by Subject "general"

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Now showing items 1-6 of 6
• (2019)
Aims. We perform clustering measurements of 800 X-ray selected Chandra COSMOS Legacy (CCL) Type 2 active galactic nuclei (AGN) with known spectroscopic redshift to probe the halo mass dependence on AGN host galaxy properties, such as galaxy stellar mass M-star, star formation rate (SFR), and specific black hole accretion rate (BHAR; lambda(BHAR)) in the redshift range z;=;[0-3]. Methods. We split the sample of AGN with known spectroscopic redshits according to M-star, SFR and lambda(BHAR), while matching the distributions in terms of the other parameters, including redshift. We measured the projected two-point correlation function w(p)(r(p)) and modeled the clustering signal, for the different subsamples, with the two-halo term to derive the large-scale bias b and corresponding typical mass of the hosting halo. Results. We find no significant dependence of the large-scale bias and typical halo mass on galaxy stellar mass and specific BHAR for CCL Type 2 AGN at mean z;similar to;1, while a negative dependence on SFR is observed, i.e. lower SFR AGN reside in richer environment. Mock catalogs of AGN, matched to have the same X-ray luminosity, stellar mass, lambda(BHAR), and SFR of CCL Type 2 AGN, almost reproduce the observed M-star - M-h, lambda(BHAR) - M-h and SFR-M-h relations, when assuming a fraction of satellite AGN f(AGN)(sat) similar to 0.15fAGNsat similar to 0.15$f_{\mathrm{AGN}}{\mathrm{sat}} \sim 0.15$. This corresponds to a ratio of the probabilities of satellite to central AGN of being active Q;similar to;2. Mock matched normal galaxies follow a slightly steeper M-star - M-h relation, in which low mass mock galaxies reside in less massive halos than mock AGN of similar mass. Moreover, matched mock normal galaxies are less biased than mock AGN with similar specific BHAR and SFR, at least for Q > 1.
• (2021)
Context. The Mutual Impedance Probe (RPC-MIP) carried by the Rosetta spacecraft monitored both the plasma density and the electric field in the close environment of comet 67P/Churyumov-Gerasimenko (67P), as the instrument was operating alternatively in two main modes: active and passive. The active mode is used primarily to perform plasma density measurements, while the passive mode enables the instrument to work as a wave analyzer. Aims. We are reporting electric field emissions at the plasma frequency near comet 67P observed by RPC-MIP passive mode. The electric field emissions are related to Langmuir waves within the cometary ionized environment. In addition, this study gives feedback on the density measurement capability of RPC-MIP in the presence of cold electrons. Methods. We studied the occurrence rate of the electric field emissions as well as their dependence on solar wind structures like stream interaction regions (SIRs) and coronal mass ejections (CMEs). Results. We are showing that strong electric field emissions at the plasma frequency near 67P were present sporadically throughout the period when Rosetta was escorting the comet, without being continuous, as the occurrence rate is reported to be of about 1% of all the measured RPC-MIP passive spectra showing strong electric field emissions. The Langmuir wave activity monitored by RPC-MIP showed measurable enhancements during SIR or CME interactions and near perihelion. Conclusions. According to our results, Langmuir waves are a common feature at 67P during the passage of SIRs. Comparing the plasma frequency given by the RPC-MIP passive mode during Langmuir wave periods with the RPC-MIP active mode observations, we conclude that the measurement accuracy of RPC-MIP depends on the operational submode when the cold electron component dominates the electron density.
• (2021)
We present the results of a search for additional exoplanets in allmultiplanetary systems discovered to date, employing a logarithmic spacing between planets in our Solar System known as the Titius-Bode (TB) relation. We use theMarkov Chain Monte Carlo method and separately analyse 229 multiplanetary systems that house at least three or more confirmed planets. We find that the planets in similar to 53% of these systems adhere to a logarithmic spacing relation remarkably better than the Solar System planets. Using the TB relation, we predict the presence of 426 additional exoplanets in 229 multiplanetary systems, of which 197 candidates are discovered by interpolation and 229 by extrapolation. Altogether, 47 predicted planets are located within the habitable zone of their host stars, and 5 of the 47 planets have a maximum mass limit of 0.1-2 M-circle plus and a maximum radius lower than 1.25 R-circle plus. Our results and prediction of additional planets agree with previous studies' predictions; however, we improve the uncertainties in the orbital period measurement for the predicted planets significantly.
• (2020)
In an effort to better understand the formation of galaxy groups, we examine the kinematics of a large sample of spectroscopically confirmed X-ray galaxy groups in the Cosmic Evolution Survey with a high sampling of galaxy group members up to z & x2004;=& x2004;1. We compare our results with predictions from the cosmological hydrodynamical simulation of HORIZON-AGN. Using a phase-space analysis of dynamics of groups with halo masses of M-200c & x2004;similar to & x2004;10(12.6) - 10(14.50)& x2006;M-circle dot, we show that the brightest group galaxies (BGG) in low mass galaxy groups (M-200c & x2004;<& x2004;2 x 10(13)& x2006;M-circle dot) have larger proper motions relative to the group velocity dispersion than high mass groups. The dispersion in the ratio of the BGG proper velocity to the velocity dispersion of the group, sigma(BGG)/sigma(group), is on average 1.48 +/- 0.13 for low mass groups and 1.01 +/- 0.09 for high mass groups. A comparative analysis of the HORIZON-AGN simulation reveals a similar increase in the spread of peculiar velocities of BGGs with decreasing group mass, though consistency in the amplitude, shape, and mode of the BGG peculiar velocity distribution is only achieved for high mass groups. The groups hosting a BGG with a large peculiar velocity are more likely to be offset from the L-x - sigma(v) relation; this is probably because the peculiar motion of the BGG is influenced by the accretion of new members.
• (2022)
Context. The role of large-scale magnetic fields in the evolution of star-forming regions remains elusive. Its investigation requires the observational characterization of well-constrained molecular clouds. The Monoceros OB 1 molecular cloud is a large complex containing several structures that have been shown to be engaged in an active interaction and to have a rich star formation history. However, the magnetic fields in this region have only been studied on small scales. Aims. We study the large-scale magnetic field structure and its interplay with the gas dynamics in the Monoceros OB 1 east molecular cloud. Methods. We combined observations of dust polarized emission from the Planck telescope and CO molecular line emission observations from the Taeduk Radio Astronomy Observatory 14-metre telescope. We calculated the strength of the plane-of-sky magnetic field using a modified Chandrasekhar-Fermi method and estimated the mass-over-flux ratios in different regions of the cloud. We used the comparison of the velocity and intensity gradients of the molecular line observations with the polarimetric observations to trace dynamically active regions. Results. The molecular complex shows an ordered large-scale plane-of-sky magnetic field structure. In the northern part, it is mostly orientated along the filamentary structures, while the southern part shows at least two regions with distinct magnetic field orientations. Our analysis reveals a shock region in the northern part right between two filamentary clouds that, in previous studies, were suggested to be involved in a collision. The magnetic properties of the north-main and north-eastern filaments suggest that these filaments once formed a single one, and that the magnetic field evolved together with the material and did not undergo major changes during the evolution of the cloud. In the southern part, we find that either the magnetic field guides the accretion of interstellar matter towards the cloud or it is dragged by the matter falling towards the main cloud. Conclusions. The large-scale magnetic field in the Monoceros OB 1 east molecular cloud is tightly connected to the global structure of the complex. In the northern part, it seems to serve a dynamically important role by possibly providing support against gravity in the direction perpendicular to the field and to the filament. In the southern part, it is probably the most influential factor governing the morphological structure by guiding possible gas inflow. A study of the whole Monoceros OB 1 molecular complex at large scales is necessary to form a global picture of the formation and evolution of the Monoceros OB 1 east cloud and the role of the magnetic field in this process.
• (2022)