arXiv subjects

Joanna Jałocha

Publications and source records attributed to Joanna Jałocha.

23 records · Page 2Linked to original sources

arXiv2011

Transverse gradients of azimuthal velocity in a global disk model of the Milky Way

In this paper, we aim to estimate the vertical gradients in the rotational velocity of the Galaxy. This is carried out in the framework of a global thin disc model approximation. The predicted gradient values coincide with the observed vertical fall-off in the rotation curve of the Galaxy. The gradient is estimated based on a statistical analysis of trajectories of test bodies in the gravitational field of the disc and in an analytical way using a quasi-circular orbit approximation. The agreement of the results with the gradient measurements is remarkable in view of other more complicated, non-gravitational mechanisms used for explaining the observed gradient values. Finally, we find that models with a significant spheroidal component give worse vertical gradient estimates than the simple disc model. In view of these results, we can surmise that, apart from the central spherical bulge and Galactic halo, the gross mass distribution in the Galaxy forms a flattened rather than spheroidal figure.

astro-ph.GA↗

arXiv2011

Vertical gradients of azimuthal velocity in a global thin disk model of spiral galaxies NGC 2403, NGC 4559, NGC 4302 and NGC 5775

We estimate the vertical gradient of rotational velocity for several spiral galaxies in the framework of a global thin-disc model, using the approximation of quasi-circular orbits. We obtain gradients having a broad range of values, in agreement with measurements, for galaxies with both low and high gradients. To model the gradient, it suffices to know the rotation curve only. We illustrate, using the example of galaxy NGC 4302 with particularly high gradients, that mass models of galactic rotation curves that assume a significant spheroidal mass component reduce the predicted gradient value, which may suggest that the mass distribution is dominated by a flattened disc-like component. We conclude that the value and behaviour of the vertical gradient in rotational velocity can be used to study the mass distribution in spiral galaxies.

astro-ph.GA↗

arXiv2011

Global disk model for galaxies NGC 1365, NGC 6946, NGC 7793, UGC 6446

Spiral galaxies are studied using a simple global disc model as a means for approximate determination of mass profiles. Based on rotation curves and the amount of gas (HI+He), we find global surface mass densities consistent with measurements and compare them with B-band surface brightness profiles. As a result we obtain mass-to-light ratio profiles. We give some arguments for why our approach is reliable and sometimes better than those assuming ad hoc the presence of a massive non-baryonic dark matter halo. Using this model, we study galaxies NGC 7793, 1365, 6946 and UGC 6446. Based on a rotation curve from The HI Nearby Galaxy Survey (THINGS) we also study galaxy NGC 4536 and compare the results with those we published elsewhere for the same galaxy.

astro-ph.GA↗

arXiv2010

SQM stars around pulsar PSR B1257+12

Following Wolszczan's landmark discovery of planets in orbit around pulsar PSR B1257+12 in 1991, over 300 planets in more than 200 planetary systems have been found. Therefore, the meaning of Wolszczan's discovery cannot be overestimated. In this paper we aim to convince the reader that the objects accompanying pulsar PSR B1257+12 are more exotic than thought so far. They might not be ordinary planets but dwarf strange quark stars, whereas the pulsar might be a quark star with standard mass, not a neutron star. If this was the case, it would indicate that strange quark matter is the ground state of matter.

astro-ph.EP↗

arXiv2008

On the axisymmetric thin disk model of flattened galaxies

Non-monotonic features of rotation curves, and also the related gravitational effects typical of thin disks -- like backward-reaction or amplification of rotation by negative surface density gradients -- which are characteristic imprints of disk-like mass distributions, are discussed in the axisymmetric thin disk model. The influence of the data cutoff in rotational velocity measurements on the determination of the mass distribution in flattened galaxies is studied. It has also been found that the baryonic matter distribution in the spiral galaxy NGC 5475, obtained in the axisymmetric thin disk approximation, accounts for the rotation curve of the galaxy. To obtain these results, the iteration method developed recently by the authors has been applied.

astro-ph↗