Mass-luminosity distribution and physical conditions of ionized gas in NGC 4575

Photographic photometry and spectroscopic observations of NGC 4575 suggest it to be a galaxy of reduced dimensionsD×d=14.4×13.5 kpc and of high luminosityM=–20.7. The rotation curve was also determined. Assuming a model of three homogeneous similar spheroids, we derived the density and mass distribution, and their total mass was found to be _T =2.33 × 10¹⁰.The mass luminosity ratio does not vary withinr=24, indicating that the stellar composition is similar within it, and the ratio _T / _T 1 suggests that this object contains a high proportion of young stars. From the emission lines it is found that the electronic density Ne100 cm^–3 is relatively low in the HII regions. The abundance ratiosN(N)/N(S) andN(N)/N(H) for the nucleus and two emission regions were also derived.     

Chain of galaxies in centaurus

Further photometric and spectroscopic observations of a chain of galaxies in Centaurus are presented and discussed.     

Mass-luminosity ratio in NGC 5236

The mass-to-light ratio in NGC 5236 was studied in terms of four spheroids. The resulting values are quite small and increasing from the centre outwards, suggesting that Population I stars are rather uniformly distributed over its body with a certain concentration towards the central region.     

Radial variations of line ratios across NGC 5236

The ionized gas in NGC 5236 was studied by spectroscopic means. The radial behaviour of the line ratios [Nii]/[Sii], H/[Sii] suggest a real nitrogen overabundance in the central regions of that galaxy.     

Natural and human-induced environmental changes in Eastern Europe during the Holocene: a multi-proxy palaeolimnological study of a small Latvian lake in a humid temperate zone

This study uses the Holocene lake sediment of Lake ?ū?i (Latvia, Vidzeme Heights) for environmental reconstruction with multi-proxy records including lithology, computerised axial tomography scan, grain-size analysis, geochemistry, diatoms and macrofossils, supported by AMS radiocarbon dating. Numerical analyses (PCA; CONISS) reveal three main phases in the development of the lake. Response to the Lateglacial–Holocene transition in Lake ?ū?i took place around 11,300 cal. BP. Organogenic sedimentation started with distinctive 5-cm-thick peat layer and was followed by lacustrine sedimentation of carbonaceous gyttja. Several findings of the peat layer with similar dated age and position at different absolute altitudes indicate that lake basin was formed by glaciokarstic processes. In the Early Holocene (until around 8,500 cal. BP), the lake was shallow and holomictic, surrounded by unstable catchment with erosion and inflow events. Predominance of diatom species of Cyclotella and Tabellaria, large numbers of respiratory horns of phantom midge pupae (Chaoboridae), high Fe/Mn ratio, as well as the presence of laminated sediments indicates the transition to a dimictic and oligo-mesotrophic lake conditions with high water level, anoxia in the near-bottom and stable catchment in the Middle Holocene (8,500–2,000 cal. BP). This contrasts with many hydrologically sensitive lakes in Northern and Eastern Europe in which the water level fell several meters during this period. During the Late Holocene (from 2,000 cal. BP to the present), the lithological and biotic variables reveal major changes, such as the increase in erosion (coarser grain-size fraction) and eutrophication [diatoms Aulacoseira ambigua (Grun.) Sim., Stephanodiscus spp., Cyclostephanos dubius (Fricke) Round]. Characteristics of lake-catchment system during the Late Holocene reflect anthropogenic signal superimposed on the natural forcing factors. To date, the Late Quaternary palaeolimnological reconstructions using lake sediment has been limited in the Baltic region. Therefore, findings from Lake ?ū?i provide important information about environmental and climatic changes that took place in this part of Eastern Europe. This study shows that the relative importance of climate and local factors has varied over the time and it is essential to consider the lake basin topography, catchment size and land cover as potential dominant forcing factors for changes in sedimentary signal.     

Interferometric study of NGC 7793

Results of H interferometric observations of NGC 7793 are reported. This galaxy contains about 93 HII regions and a general emission background. Its radial velocity is 215 km s^–1.The total mass is low, 2–3×10⁹ solar masses, as well as the average density; the meanM/L is 0.4 suggesting a high proportion of young objects.     

Internal motions in NGC 55

The kinematics of the central zones of NGC 55 is discussed on the basis of interferometric observations. The emission regions have radial velocities well differentiated showing also a significant gradient and coinciding in general with those obtained in 21 cm. The exception consisting of an emission complex of high velocity is interpreted as moving towards the centre of the galaxy indicating flux of material along the bar.     

Interferometric study of NGC 1313

The kinematics and structure of NGC 1313 are discussed on the basis of interferometric observations. Several uniformly rotating components, a total mass of 2×10¹⁰ solar masses, and deviations from pure circular movement of an amplitude of almost 20 km s^–1 are found.     

The nitrogen abundance in NGC 55

The purpose of this paper is to propose an interpretation for the line spectrum of NGC 55, whose most remarkable feature is the absence of the generally noticeable 6584[Nii]. From the physical conditions of the ionized gas responsible of the observed emission, we infer that the N(N)/N(O) abundance ratio is significantly smaller than usual, probably reflecting a nitrogen underabundance in a medium of temperatures 9100 K and densities 500 cm^–3.     

Physical conditions of ionized gas and mass-luminosity distribution in NGC 7793

The physical state of ionized gas in NGC 7793 was studied by spectroscopical means: the electronic temperature isT _e10⁴K while the electronic density ranges fromN _e1400 cm^–3 in the nucleus toN _e1000 cm^–3 in the emission regions. There are also indications of an excess of nitrogen in the nucleus. TheM/L ratio suggests for NGC 7793, a high proportion of young objects quite uniformly distributed over its body, with a slight concentration towards the nuclear region.