Deep 1.4-GHz observations of diffuse polarized emission

Polarized diffuse emission observations at 1.4 GHz in a high Galactic latitude area of the Northern celestial hemisphere are presented. The  3.2 × 3.2 deg²  field, centred at  RA = 10^h58^m, Dec. =+42°18' (B1950)  , has Galactic coordinates   l ∼ 172°, b ∼+63°  and is located in the region selected as northern target of the Balloon-borne Radiometers for Sky Polarization Observations experiment. Observations have been performed with the Effelsberg 100-m telescope. We find that the angular power spectra of the E and B modes have slopes of  β _E =−1.79 ± 0.13  and  β _B =−1.74 ± 0.12  , respectively. Because of the very high Galactic latitude and the smooth emission, a weak Faraday rotation action is expected, which allows both a fair extrapolation to cosmic microwave background polarization (CMBP) frequencies and an estimate of the contamination by the Galactic synchrotron emission. We extrapolate the E -mode spectrum up to 32 GHz and confirm the possibility to safely detect the CMBP E -mode signal in the Ka band found in another low-emission region. Extrapolated up to 90 GHz, the Galactic synchrotron B mode looks to compete with the cosmic signal only for models with a tensor-to-scalar perturbation power ratio   T / S < 0.001  , which is even lower than the T / S value of 0.01 found to be accessible in the only other high Galactic latitude area investigated to date. This suggests that values as low as   T / S = 0.01  might be accessed at high Galactic latitudes. Such low-emission values can allow a significant redshift of the best frequency to detect the CMBP B mode, also reducing the contamination by Galactic dust, and opening interesting perspectives to investigate inflation models.     

The Arecibo Galaxy Environment Survey – II. A H i view of the Abell cluster 1367 and its outskirts

We present 21 cm H  i line observations of 5 × 1 deg² centred on the local Abell cluster 1367 obtained as part of the Arecibo Galaxy Environment Survey. One hundred sources are detected (79 new H  i measurements and 50 new redshifts), more than half belonging to the cluster core and its infalling region. Combining the H  i data with Sloan Digital Sky Survey (SDSS) optical imaging, we show that our H  i selected sample follows scaling relations similar to the ones usually observed in optically selected samples. Interestingly, all galaxies in our sample appear to have nearly the same baryon fraction independently of their size, surface brightness and luminosity. The most striking difference between H  i and optically selected samples resides in their large-scale distribution: whereas optical and X-ray observations trace the cluster core very well, in H  i there is almost no evidence of the presence of the cluster. Some implications on the determination of the cluster luminosity function and H  i distribution for samples selected at different wavelength are also discussed.     

5个CSS源50cm VLBI观测数据的再处理

本文给出了全球VLBI网50cm数据成图再处理的部分结果.样本包括5个CSS射电源:3C43、3C138、3C186、3C216和3C237.为了便于比较,同时给出了二次成图处理后的图象.通过对这些源的形态描述,并且通过与其它波段高分辨率图的对照,核实了再处理图上各子源的位置,这些低频观测细节,对更好地了解CSS源的本质无疑是十分有益的。     

A textbook case of bow shock entrainment in a YSO outflow

Near-infrared images in H₂ line emission and submillimetre maps in CO J  = 3–2 emission illustrate the remarkable association between a molecular bow shock and the redshifted molecular outflow lobe in W75N. The flow lobe fits perfectly into the wake of the bow, as one would expect if the lobe represented swept-up gas. Indeed, these observations strongly support the 'bow shock' entrainment scenario for molecular outflows driven by young stars.   The characteristics of the bow shock and CO outflow lobe are compared with those of numerical simulations of jet-driven flows. These models successfully reproduce the bulge and limb-brightening in the CO outflow, although the model H₂ bow exhibits more structure extending back along the flow axis. We also find that the size of the flow, the high mass fraction in the flow at low outflow velocities (low γ values) and the high CO/H₂ luminosity ratio indicate that the system is evolved. We also predict a correlation, in evolved systems, between outflow age and the CO/H₂ luminosity ratio.     

The LMC supernova (SN 1987 A) as a probe for the outcome of stellar collapse

Implications from the available information on the supernova SN 1987 A are discussed for the supernova models. We derive an upper bound of 10–25 eV for the neutrino rest mass.     

The role of AGN in the colour transformation of galaxies at redshifts z≈ 1

We explore the role of active galactic nuclei (AGN) in establishing and/or maintaining the bimodal colour distribution of galaxies by quenching their star formation and hence, causing their transition from the blue to the red cloud. Important tests for this scenario include (i) the X-ray properties of galaxies in the transition zone between the two clouds and (ii) the incidence of AGN in post-starbursts, i.e. systems observed shortly after (<1 Gyr) the termination of their star formation. We perform these tests by combining deep Chandra observations with multiwavelength data from the All-wavelength Extended Groth strip International Survey (AEGIS). Stacking the X-ray photons at the positions of galaxies  (0.4 < z < 0.9)  not individually detected at X-ray wavelengths suggests a population of obscured AGN among sources in the transition zone and in the red cloud. Their mean X-ray and mid-infrared (IR) properties are consistent with moderately obscured low-luminosity AGN, Compton thick sources or a mix of both. Morphologies show that major mergers are unlikely to drive the evolution of this population but minor interactions may play a role. The incidence of obscured AGN in the red cloud (both direct detections and stacking results) suggests that black hole (BH) accretion outlives the termination of the star formation. This is also supported by our finding that post-starburst galaxies at z ≈ 0.8 and AGN are associated, in agreement with recent results at low z . A large fraction of post-starbursts and red cloud galaxies show evidence for at least moderate levels of AGN obscuration. This implies that if AGN outflows cause the colour transformation of galaxies, then some nuclear gas and dust clouds either remain unaffected or relax to the central galaxy regions after quenching their star formation.     

Anisotropic Beam Model for the Spectral Observations of Radio Burst Fine Structures on 1998 April 15

A fine structure consisting of three almost equidistant frequency bands was observed in the high frequency part of a solar burst on 1998 April 15 by the spectrometer of Beijing Astronomical Observatory in the range 2.6-3.8GHz. A model for this event based on beam-anisotropic instability in the solar corona is presented. Longitudinal plasma waves are excited at cyclotron resonance and then transformed into radio emission at their second harmonic.The model is in accordance with the observations if we suppose a magnetic field strength in the region of emission generation of about 200G.     

Some results of solar radio emission observations at the Siberian Solar Radio Telescope

This paper gives the main characteristics of the Siberian Solar Radio Telescope as well as some results derived by investigating the s-component sources and radio bursts on the Sun using the SSRT.     

Large molecules in the envelope surrounding IRC+10216

A new chemical model of the circumstellar envelope surrounding the carbon-rich star IRC+10216 is developed that includes carbon-containing molecules with up to 23 carbon atoms. The model consists of 3851 reactions involving 407 gas-phase species. Sizeable abundances of a variety of large molecules including carbon clusters, unsaturated hydrocarbons and cyanopolyynes have been calculated. Negative molecular ions of chemical formulae and C _n H (7 n 23) exist in considerable abundance, with peak concentrations at distances from the central star somewhat greater than their neutral counterparts. The negative ions might be detected in radio emission, or even in the optical absorption of background field stars. The calculated radial distributions of the carbon-chain C _n H radicals are looked at carefully and compared with interferometric observations.