Observable properties of non-axisymmetric galaxies

The analysis of triaxial, coaxial ellipsoids with different intrinsic axial ratios initiated in a previous paper is extended here, introducing an intrinsic distribution of light for each shell.The general properties of this model are studied, considering the analytical solutions for the projection along a line-of-sight in three theoretical cases: (i) dust-free systems; (ii) dusty systems; (iii) luminous gaseous shells. The first case is then extended in order to predict some observable consequences.The observed properties of both an exponential and a power-law luminosity profile are compared with those of triaxial and axisymmetric systems. In addition, the variation of the central surface brightness and of the isophotal flattening at a fixed level with respect to the inclination of the Galaxy are analyzed.     

Isolated and mildly interacting spiral galaxies: Rotation curves and metallicities

We present the study of long slit spectra in the region ofHα emission line of a sample of 111 spiral galaxies with recognizable and well defined spiral morphology and with a well determined environmental status, ranging from isolation to non-disruptive interaction with satellites or companions. The form and properties of the rotation curves (RC) are considered as a function of the isolation degree, morphological type, t, and luminosity. The line ratios are used to estimate the metallicity of all the detected HII regions, thus producing a composite metallicity profile for different types of spirals. We have found that isolated galaxies (ISO) tend to be of later types and lower luminosity than the interacting galaxies (INT). The outer parts of the RC of ISO tend to be flatter than in INT, but they show similar relations between global parameters. The scatter of the Tully-Fisher (TF) relation defined by ISO is significantly lower than that of INT. The [NII]/Hα ratios, used as a metallicity indicator, show a clear trend between Z and t, with earlier spirals showing higher ratios; this trend is tighter when instead of t the gradient of the inner RC, G, is used; no trend is found with the change in interaction status. The Z-gradient of the disks depends on the type, being almost flat for early spirals, and increasing for later types. The [NII]/Hα ratios measured for disk HII regions of INT are higher than for normal/ISO objects, even if all the galaxy families present similar distributions of Hα Equivalent Width. This revised version was published online in August 2006 with corrections to the Cover Date.     

An extended ultraviolet ring around the SB0 galaxy NGC 4262

We present Galaxy Ultraviolet Explorer (GALEX) satellite observations of the SB0 galaxy NGC 4262 where we detect an extended, outer ring studded with UV-bright knots surrounding the galaxy body. Such a structure, not visible at optical wavelengths, is coupled with a ring of atomic (HI) gas. We will show that both star-forming and HI rings surrounding this SB0 galaxy share the same radial distance from the galaxy center and spatial orientation. We also model the kinematics of the ring(s) and of the galaxy body. Their kinematics is not coupled with that of the galaxy stars. We suggest that NGC 4262 has undergone a major gas stripping event in the past that was the origin of the present “necklace” of UV-bright knots.     

Revisiting the formation history of the minor-axis dust lane galaxy NGC 1947

In this paper, we present a detailed study of the peculiar early-type galaxy NGC 1947. The main goal of this work is to constrain the dynamical status and the formation history of NGC 1947 by comparing the observed properties with the predictions derived from different galaxy formation scenarios. To this aim, we derived the photometric and kinematical properties of NGC 1947. Due to the presence of an extended dust lane, which crosses the galaxy centre along the photometric minor axis, we used near-infrared (NIR) images ( J and K bands) to derive an accurate analysis of the stellar light distribution. Optical images (in the V and R bands) are used to derive the colour profiles and colour maps to study the structure of the dust lane. The observed kinematics confirm the presence of two components with decoupled angular momentum: gas and dust rotate along the minor axis, while the rotation velocities of the stars are observed along the major axis. The complex structure observed in NGC 1947 supports the hypothesis that some kind of interactions happened in the evolution of this object. We analysed two alternatives: a merging process and an accretion event. We discussed how the observed properties strongly suggest that the decoupled ring of gas and dust has been accreted from outside.     

The UV window on counter rotating ETGs: insight from SPH simulations with chemo-photometric implementation

The Galaxy Evolution Explorer (GALEX) detected ultraviolet emission in about 50 % of multi-spin early-type galaxies (ETGs), suggesting the occurrence of a recent rejuvenation episode connected to the formation of these kinematical features. With the aim at investigating the complex evolutionary scenario leading to the formation of counter rotating ETGs (CR-ETGs) we use our Smooth Particle Hydrodynamic (SPH) code with chemo-photometric implementation. We discuss here the UV evolutionary path of two CR-ETGs, NGC 3593 and NGC 5173, concurrently best fitting their global observed properties, i.e., morphology, dynamics, as well as their total B-band absolute magnitude and spectral energy distribution (SED) extended over three orders of magnitude in wavelength. These simulations correspond to our predictions about the target evolution which we follow in the color-magnitude diagram (CMD), near-UV (NUV) versus r-band absolute magnitude, as a powerful diagnostic tool to emphasize rejuvenation episodes.     

Observable properties of non-axisymmetryc galaxies

We analyse the simple geometrical theory of the triaxial, coaxial ellipsoids with different intrinsic axial ratios, suggesting that some observed properties of the isophotes could be interpreted as resulting from a similar distribution of the stars. The general analytical solutions for the apparent ellipticity and the difference in position angle of the major axes between each projected shell are also applied to composite structures formed by two subsystems of different shape. In comparison with the observable structures we considered three cases: (i) completely triaxial shells; (ii) barred discs; (iii) prolate-like systems. Some geometrical tests applying to these systems are also suggested in order to bring a better under-standing of their spatial structure.     

Automatic colorimetric analyzer prototype for high frequency measurement of nutrients in seawater

This paper describes the characteristics of a prototype of a modular multiparametric analyzer (MicroMAC FAST MP3) for automatic monitoring of seawater and analytical methods for nutrients.The MicroMAC FAST reactor is an evolution of the basic LFA (Loop Flow Analysis) reactor. It has been conceived to assay ammonium, nitrate–nitrite and orthophosphate at low concentration in seawater samples. A sample analysis is 3–4 times faster than that obtainable with a standard LFA reactor. With respect to the previous analyzer a temperature control (30–52 °C) on the measurement cell has been added (only for modules NH₄ and PO₄), while the colorimeter and the related links for transporting the sample have been moved beyond the Loop and form a hydraulic-optical set almost completely independent from the main LFA. All the steps of a wet-chemical colorimetric analysis method are carried out in an analysis cycle sequentially. The hermetic closed Loop provides full protection against background interference, which is a basic requirement for stable trace analysis. At the start of a cycle the loop is washed and filled with sample. The sample color is measured for compensation. Small amounts of concentrated reagents are added and mixed with high intensity. This new technique allows the preparation of two products of reaction which can be introduced at intervals of 150 s in the measurement cell. The intensity of the color of the reaction product is measured on the colorimeter using a monochromatic light beam of specific wavelength. The statistical test shows that the results of automated and manual analyses agree for all the examined parameters. Precision of all three analyses is ≤ 4% RSD.Multiparametric online analyzer: it is possible to connect the analytical modules to a data logger with analogue and digital signals, in order to have online simultaneous analysis of the sample. A typical application is used during research at sea which vessel does not require an operator.