Modelling galactic spectra: I - A dynamical model for NGC3258

In this paper we present a method to analyse absorption line spectra of a galaxy designed to determine the stellar dynamics and the stellar populations by a direct fit to the spectra. This paper is the first one to report on the application of the method to data. The modelling results in the knowledge of distribution functions that are sums of basis functions. The practical implementation of the method is discussed and a new type of basis functions is introduced. With this method, a dynamical model for NGC 3258 is constructed. This galaxy can be successfully modelled with a potential containing 30% dark matter within 1r_e with a mass of 1.6x10^11 M_o. The total mass within 2r_e is estimated as 5x10^11 M_o, containing 63% dark matter. The model is isotropic in the centre, is radially anisotropic between 0.2 and 2 kpc (0.88 r_e) and becomes tangentially anisotropic further on. The photometry reveals the presence of a dust disk near the centre

The dynamics of S0 galaxies and their Tully-Fisher relation

This paper investigates the detailed dynamical properties of a relatively homogeneous sample of disc-dominated S0 galaxies, with a view to understanding their formation, evolution and structure. By using high signal-to-noise ratio long-slit spectra of edge-on systems, we have been able to reconstruct the complete line-of-sight velocity distributions of stars along the galaxies' major axes. From these data, we have derived both model distribution functions (the phase density of their stars) and the approximate form of their gravitational potentials. The derived distribution functions are all consistent with these galaxies being simple disc systems, with no evidence for a complex formation history. Essentially no correlation is found between the characteristic mass scale-lengths and the photometric scale-lengths in these galaxies, suggesting that they are dark-matter dominated even in their inner parts. Similarly, no correlation is found between the mass scale-lengths and asymptotic rotation speed, implying a wide range of dark matter halo properties. By comparing their asymptotic rotation speeds with their absolute magnitudes, we find that these S0 galaxies are systematically offset from the Tully-Fisher relation for later-type galaxies. The offset in luminosity is what one would expect if star formation had been suddenly switched off a few Gyrs ago, consistent with a simple picture in which these S0s were created from ordinary later-type spirals which were stripped of their star-forming ISM when they encountered a dense cluster environment.Comment: 8 pages, 16 figures, accepted by MNRA

Radial kinematics of brightest cluster galaxies

This is the first of a series of papers devoted to the investigation of a large sample of brightest cluster galaxies (BCGs), their kinematic and stellar population properties, and the relationships between those and the properties of the cluster. We have obtained high signal-to-noise ratio, long-slit spectra of these galaxies with Gemini and William Herschel Telescope with the primary purpose of investigating their stellar population properties. This paper describes the selection methods and criteria used to compile a new sample of galaxies, concentrating on BCGs previously classified as containing a halo (cD galaxies), together with the observations and data reduction. Here, we present the full sample of galaxies, and the measurement and interpretation of the radial velocity and velocity dispersion profiles of 41 BCGs. We find clear rotation curves for a number of these giant galaxies. In particular, we find rapid rotation (>100 km s−1) for two BCGs, NGC 6034 and 7768, indicating that it is unlikely that they formed through dissipationless mergers. Velocity substructure in the form of kinematically decoupled cores is detected in 12 galaxies, and we find five galaxies with velocity dispersion increasing with radius. The amount of rotation, the velocity substructure and the position of BCGs on the anisotropy–luminosity diagram are very similar to those of ‘ordinary’ giant ellipticals in high-density environments

Line-of-sight velocity distributions of 53 early-type galaxies


55 long-slit spectra of 53 early-type galaxies were observed at La Silla/ESO and reduced using standard methods. The line-of-sight velocity distributions (LOSVDs) were measured using the fourier quotient method and the fourier fitting method as described by van der Marel et al. (1993). 32% of the examined galaxies contain kinematically decoupled stellar omponents, the size of these cores was 0.40 ± 0.28 kpc, in each case the core was smaller than 1 kpc. Analysis of the kinematics reveals in 49% of the sample galaxies the signature of a stellar disk component, in 15% this is uncertain. There is evidence that the phenomenon of kinematically decoupled components is present in the whole class of early-type galaxies. Several correlations between photometric and kinematic parameters like the $(v/\sigma)^*$ vs. ϵ diagram, the anisotropy – luminosity correlation or κ-space were as well examined using measurement results for spectroscopic data and photometric data out of literature. It is also shown that those sample galaxies with kinematically decoupled components are more likely to be found in groups of high density, strengthening the assumption that such components are remnants of merging events.

Isolated ellipticals and their globular cluster systems

The globular cluster (GC) systems of isolated elliptical galaxies have only recently begun to be studied in detail, and may exhibit morphological connections to the evolutionary histories of their hosts. Here we present the first in a series of wide-field analyses of the GC systems of the isolated ellipticals – Washington C and R photometry of NGC 3585 and NGC 5812 down to R ~ 24 mag. The GC systems are characterised, with each system displaying both the “Universal” blue peak at (C − R) ~ 1.3, and a red peak, but each with differing strengths. The total number of GCs in each system, and their specific frequencies, are estimated. The GC colours and specific frequencies are highly indicative that the host galaxy environment plays a role in shaping its GC system. We produce, and subtract, accurate models of each galaxy, revealing interesting underlying features, including the first definitive evidence that NGC 5812 is interacting with a dwarf companion galaxy. From the galaxy models we also determine surface brightness and colour profiles. Both colour profiles appear quite flat and with (C − R) ~ 1.7 and we discuss the apparent youth of NGC 3585 in the context of this work

Nearby early-type galaxies with ionized gas. I. Line-strength indices of the underlying stellar population

With the aim of building a data-set of spectral properties of well studied early-type galaxies showing emission lines, we present intermediate resolution spectra of 50 galaxies in the nearby Universe. The sample, which covers several of the E and S0 morphological sub-classes, is biased toward objects that might be expected to have ongoing and recent star formation, at least in small amounts, because of the presence of the emission lines. The emission are expected to come from the combination of active galactic nuclei and star formation regions within the galaxies. Sample galaxies are located in environments corresponding to a broad range of local galaxy densities, although predominantly in low density environments. Our long-slit spectra cover the 3700 - 7250 A wavelength range with a spectral resolution of about 7.6 A at 5550 A. The specific aim of this paper, and our first step on the investigation, is to map the underlying galaxy stellar population by measuring, along the slit, positioned along the galaxy major axis, line--strength indices at several, homogeneous galacto-centric distances. For each object we extracted 7 luminosity weighted apertures corrected for the galaxy ellipticity and 4 gradients and we measured 25 line-strength indices. The paper introduces the sample, presents the observations, describes the data reduction procedures, the extraction of apertures and gradients, the determination and correction of the line--strength indices, the procedure adopted to transform them into the Lick-IDS System and the procedures adopted for the emission correction. We finally discuss the comparisons between our dataset and line-strength indices available in the literature