Astrophysics of Galaxies (astro-ph.GA)

Abstract: We present MeerKAT L-band (886-1682 MHz) observations of the extended radio structure of the peculiar galaxy pair PKS 2130-538 known as the "Dancing Ghosts". The complex of bending and possibly interacting jets and lobes originate from two Active Galactic Nuclei hosts in the Abell 3785 galaxy cluster, one of which is the brightest cluster galaxy. The radio properties of the PKS 2130-538 flux density, spectral index and polarization - are typical for large, bent-tail galaxies. We also investigate a number of thin extended low surface brightness filaments originating from the lobes. Southeast from the Dancing Ghosts, we detect a region of low surface brightness emission that has no clear origin. While it could originate from the Abell 3785 radio halo, we investigate the possibility that it is a radio relic or emission associated with the two PKS 2130-538 hosts. We find no evidence of interaction between the two PKS 2130-538 hosts.

Abstract: In this second communication we continue our analysis of the turbulence in the Huygens Region of the Orion Nebula (M 42). We calculate the associated transverse structure functions up to order 8-th and find that the higher-order transverse structure functions are almost proportional to the second-order transverse structure function: we find that after proper normalisation, the higher-order transverse structure functions only differ by very small deviations from the second-order transverse structure function in a sub-interval of the inertial range. We demonstrate that this implies that the turbulence in the Huygens Region is quasi-log-homogeneous, or to a better degree of approximation, binomially weighted log-homogeneous in the statistical sense, this implies that there is some type of invariant statistical structure in the velocity field of the Huygens Region. We also obtain and analyse the power-spectrum of the turbulent field and find that it displays a large tail that follows very approximately two power-laws, one of the form $E(k)\propto k^{-2.7}$ for the initial side of the tail, and one of the form $E(k)\propto k^{-1}$ for the end of the tail. We find that the power-law with exponent $\beta\sim -2.7$ corresponds to spatial scales of 0.0301--0.6450 pc. We find that the exponent of the first power-law $\beta\sim -2.7$ is related to the exponent $\alpha_2$ of the second-order structure function in the inertial range. We interpret the second power-law with exponent $\beta \sim -1$ as an indicator of viscous-dissipative processes occurring at scales of $\delta r=1$--5 pixels which correspond to spatial scales of 0.00043--0.00215 pc.

Abstract: Age-metallicity relation for the Galactic disc is a crucial tool and to constrain the Galactic chemical evolution models. We investigate the age-metallicity relation of the Galactic disc using the red giant branch stars in the Solar neighbourhood. The data cover the Galactocentric radius of $7\leq R_{\rm gc} (\rm kpc) \leq9.5$, but extends up to 4 kpc in height from the Galactic plane. We use kinematic age derived from highly precise astrometric data of Gaia Data Release 2 and element abundance ratios from high-resolution spectroscopic data of APOGEE-2 catalogues. We apply a two-component Gaussian mixture model to chemically separate the programme stars into thin and thick disc populations. The stars in each population are grouped into different distance intervals from the Galactic plane. The mean metal abundances and velocity dispersions of the stars in the groups were calculated and the kinematic ages were determined from their kinematic parameters. We found a steep relation for the thin disc with -0.057$\pm$0.007 dex Gyr$^{-1}$, and even a steeper value of -0.103$\pm$0.009 dex Gyr$^{-1}$ for the thick disc. These age-metallicity relations along with the prominent differences in age, metallicity, and kinematic behaviours seen from the data, clearly show it is important to consider the distinct formation scenarios of the Galactic disc components in modelling the Milky Way.