SAURON Project Research Articles

Guidance for ports: security and safety against physical, cyber and hybrid threats

The European Commission (EC) has funded the Scalable multidimensionAl sitUation awaReness sOlution for protectiNg european ports (SAURON) project to reduce the vulnerabilities of EU ports, as one of the main European critical infrastructures, and increase their systemic resilience in the face of a physical, cyber or combined cyber-physical threat. The goal of SAURON has been to provide a multidimensional yet installation-specific Situational Awareness platform to help port operators anticipate and withstand potential cyber, physical or combined threats to their businesses and to people. During the SAURON project port authorities and stakeholders stated that it would be very helpful to have generic guidance to help ports respond to the combined cyber-physical security threat. The goal of this paper is to help ports understand the hybrid cyber-physical security threat, and how to reduce port vulnerabilities, based on lessons from the SAURON project. The paper is structured in line with the International Ship and Port Facility Security (ISPS) Code Port Facility security assessment process, and relates port security planning based on the ISPS guidelines to insights and lessons from SAURON. This paper demonstrates the importance of understanding the interdependencies between the cyber and physical domains and improving security situational awareness when incidents (including deliberate attacks) cause cascading effects across these domains. Furthermore, the paper draws conclusions and makes recommendations to ports and policy makers to reduce the vulnerability of ports to hybrid cyber-physical attacks.

How Port Security has to evolve to address the Cyber-Physical Security Threat: lessons from the SAURON project

How Port Security has to evolve to address the Cyber-Physical Security Threat: lessons from the SAURON project

Dynamical Models and Anisotropy of the Velocity Dispersions in Elliptical Galaxies

Models for 12 elliptical galaxies are constructed based on the second-order tensor virial theorem. This method takes into account the spatial shape and structure of the internal density layers for each galaxy. New data for the surface brightness and isophote structure of the E galaxies derived from deep photometric observations are used. A system of equations is used to find the components of the gravitational-energy, rotational-energy, and velocity-dispersion tensors. This makes it possible to calculate the anisotropy index β of the velocity dispersion of each galaxy. The values for the entire sample lie in the range 0.012 ⩽ β ⩽ 0.246. It is shown that taking into account variations in the mass-to-light ratio M/L (for the stellar component) can reduce the value of β by roughly 20%. The results are compared with those from other studies. Our values of β for small E galaxies (rapid rotators) agree with those found in the ATLAS3D project based on Jeans anisotropy models. However, our models for giant E galaxies (slow rotators) taking into account the triaxial shape and realistic structure of the density layers provide a much better agreement with observations than the simple axially symmetrical models from the SAURON project.

The SAURON project - XXI. The spatially resolved UV-line strength relations of early-type galaxies

The unexpected rising flux of early-type galaxies at decreasing ultraviolet (UV) wavelengths is a long-standing mystery. One important observational constraint is the correlation between UV-optical colours and Mg2 line strengths found by Burstein et al. (1988). The simplest interpretation of this phenomenon is that the UV strength is related to the Mg line strength. Under this assumption, we expect galaxies with larger Mg gradients to have larger UV colour gradients. By combining UV imaging from GALEX, optical imaging from MDM and SAURON integral-field spectroscopy, we investigate the spatially-resolved relationships between UV colours and stellar population properties of 34 early-type galaxies from the SAURON survey sample. We find that galaxies with old stellar populations show tight correlations between the FUV colours (FUV-V and FUV-NUV) and the Mgb index, H{\beta} index and metallicity [Z/H]. The equivalent correlations for the Fe5015 index, {\alpha}-enhancement [{\alpha}/Fe] and age are present but weaker. We have also derived logarithmic internal radial colour, measured line strength and derived stellar population gradients for each galaxy and again found a strong dependence of the FUV-V and FUV-NUV colour gradients on both the Mg b line strength and the metallicity gradients for galaxies with old stellar populations. In particular, global gradients of Mg b and [Z/H] with respect to the UV colour across galaxies are consistent with their local gradients within galaxies, suggesting that the global correlations also hold locally. From a simple model based on multi-band colour fits of UV upturn and UV-weak galaxies, we have identified a plausible range of parameters that reproduces the observed radial colour profiles. In these models, the centers of elliptical galaxies, where the UV flux is strong, are enhanced in metals by roughly 60% compared to UV-weak regions.

Made-to-measure galaxy models - II. Elliptical and lenticular galaxies

We take a sample of 24 elliptical and lenticular galaxies previously analysed by the SAURON project using three-integral dynamical models created with Schwarzschild's method, and re-analyse them using the made-to-measure (M2M) method of dynamical modelling. We obtain good agreement between the two methods in determining the dynamical mass-to-light (M/L) ratios for the galaxies with over 80% of ratios differing by < 10% and over 95% differing by < 20%. We show that (M/L)_M2M is approximately equal to (M/L)_Sch. For the global velocity dispersion anisotropy parameter delta, we find similar values but with fewer of the made-to-measure models tangentially anisotropic by comparison with their SAURON Schwarzschild counterparts. Our investigation is the largest comparative application of the made-to-measure method to date.

The SAURON project - XX. The Spitzer [3.6] − [4.5] colour in early-type galaxies: colours, colour gradients and inverted scaling relations

We investigate the [3.6] - [4.5] Spitzer-IRAC colour behaviour of the early-type galaxies of the SAURON survey, a representative sample of 48 nearby ellipticals and lenticulars. We investigate how this colour, which is unaffected by dust extinction, can be used to constrain the stellar populations in these galaxies. We find a tight relation between the [3.6]-[4.5] colour and effective velocity dispersion, a good mass-indicator in early-type galaxies. Contrary to other colours in the optical and near-infrared, we find that the colours become bluer for larger galaxies. The relations are tighter when using the colour inside r_e, rather than the much smaller r_e/8 aperture, due to the presence of young populations in the central regions. We also obtain strong correlations between the [3.6]-[4.5] colour and 3 strong absorption lines (H beta, Mg b and Fe 5015). Comparing our data with the models of Marigo et al., which show that more metal rich galaxies are bluer, we can explain our results in a way consistent with results from the optical, by stating that larger galaxies are more metal rich. The blueing is caused by a strong CO absorption band, whose line strength increases strongly with decreasing temperature and which covers a considerable fraction of the 4.5 micron filter. In galaxies that contain a compact radio source, the [3.6]-[4.5] colour is generally slightly redder than in the other galaxies, indicating small amounts of either hot dust, non-thermal emission, or young stars near the center. We find that the large majority of the galaxies show redder colours with increasing radius. abbreviated...

The SAURON project - XIX. Optical and near-infrared scaling relations of nearby elliptical, lenticular and Sa galaxies

We present ground-based MDM Observatory V-band and Spitzer/InfraRed Array Camera 3.6-m-band photometric observations of the 72 representative galaxies of the SAURON survey. Galaxies in our sample probe the elliptical E, lenticular S0 and spiral Sa populations in the nearby Universe, both in field and cluster environments. We perform aperture photometry to derive homogeneous structural quantities. In combination with the SAURON stellar velocity dispersion measured within an effective radius (σe), this allows us to explore the location of our galaxies in the colour–magnitude, colour–σe, Kormendy, Faber–Jackson and Fundamental Plane scaling relations. We investigate the dependence of these relations on our recent kinematical classification of early-type galaxies (i.e. slow/fast rotators) and the stellar populations. Slow rotator and fast rotator E/S0 galaxies do not populate distinct locations in the scaling relations, although slow rotators display a smaller intrinsic scatter. We find that Sa galaxies deviate from the colour–magnitude and colour–σe relations due to the presence of dust, while the E/S0 galaxies define tight relations. Surprisingly, extremely young objects do not display the bluest (V−[3.6]) colours in our sample, as is usually the case in optical colours. This can be understood in the context of the large contribution of thermally pulsing asymptotic giant branch stars to the infrared, even for young populations, resulting in a very tight (V−[3.6])–σe relation that in turn allows us to define a strong correlation between metallicity and σe. Many Sa galaxies appear to follow the Fundamental Plane defined by E/S0 galaxies. Galaxies that appear offset from the relations correspond mostly to objects with extremely young populations, with signs of ongoing, extended star formation. We correct for this effect in the Fundamental Plane, by replacing luminosity with stellar mass using an estimate of the stellar mass-to-light ratio, so that all galaxies are part of a tight, single relation. The new estimated coefficients are consistent in both photometric bands and suggest that differences in stellar populations account for about half of the observed tilt with respect to the virial prediction. After these corrections, the slow rotator family shows almost no intrinsic scatter around the best-fitting Fundamental Plane. The use of a velocity dispersion within a small aperture (e.g. Re/8) in the Fundamental Plane results in an increase of around 15 per cent in the intrinsic scatter and an average 10 per cent decrease in the tilt away from the virial relation.

The SAURON project - XVIII. The integrated UV-line-strength relations of early-type galaxies

Using far (FUV) and near (NUV) ultraviolet photometry from guest investigator programmes on the Galaxy Evolution Explorer (GALEX) satellite, optical photometry from the MDM Observatory and optical integral-field spectroscopy from SAURON, we explore the UV-linestrength relations of the 48 nearby early-type galaxies in the SAURON sample. Identical apertures are used for all quantities, avoiding aperture mismatch. We show that galaxies with purely old stellar populations show well-defined correlations of the integrated FUV-V and FUV-NUV colours with the integrated Mgb and Hbeta absorption linestrength indices, strongest for FUV-NUV. Correlations with the NUV-V colour, Fe5015 index and stellar velocity dispersion are much weaker. These correlations put stringent constraints on the origin of the UV-upturn phenomenon in early-type galaxies, and highlight its dependence on age and metallicity. In particular, despite recent debate, we recover the negative correlation between FUV-V colour and Mg linestrength originally publicised by Burstein et al. (1988), which we refer to as the "Burstein relation", suggesting a positive dependence of the UV-upturn on metallicity. We argue that the scatter in the correlations is real, and present mild evidence that a strong UV excess is preferentially present in slow-rotating galaxies. We also demonstrate that most outliers in the correlations are galaxies with current or recent star formation, some at very low levels. We believe that this sensitivity to weak star formation, afforded by the deep and varied data available for the SAURON sample, explains why our results are occasionally at odds with other recent but shallower surveys. This is supported by the analysis of a large, carefully-crafted sample of more distant early-type galaxies from the Sloan Digital Sky Survey (SDSS), more easily comparable with current and future large surveys.

The Fundamental Plane of Early-Type Galaxies

We report recent results from the photometric follow-up study we are conducting in the context of the SAURON project. We use ground-based MDM V -band and Spitzer/IRAC 3.6 μm imaging to characterise our sample of E, S0 and Sa galaxies photometrically. Combined with SAURON integral-field spectroscopic observations, this information allows us to explore and understand the location of these galaxies on the Fundamental Plane relation, providing an important diagnostic tool to study their formation and evolution.

The non-evolving internal structure of early-type galaxies: the case study SDSS J0728+3835 at z= 0.206

We study the internal dynamical structure of the early-type lens galaxy SDSS J0728+3835 at z = 0.206. The analysis is based on two-dimensional kinematic maps extending out to 1.7 effective radii obtained from Keck spectroscopy, on lensing geometry and on stellar mass estimates obtained from multiband Hubble Space Telescope imaging. The data are modelled under the assumptions of axial symmetry supported by a two-integral distribution function (DF), by applying the combined gravitational lensing and stellar dynamics code CAULDRON, and yielding high-quality constraints for an early-type galaxy at cosmological redshifts. Modelling the total density profile as a power-law of the form rho_tot ~ 1/r^{gamma}, we find that it is nearly isothermal (logarithmic slope gamma = 2.08^{+0.04}_{-0.02}), and quite flattened (axial ratio q = 0.60^{+0.08}_{-0.03}). The galaxy is mildly anisotropic (delta = 0.08 +/- 0.02) and shows a fair amount of rotational support, in particular towards the outer regions. We determine a dark matter fraction lower limit of 28 per cent within the effective radius. The stellar contribution to the total mass distribution is close to maximal for a Chabrier initial mass function (IMF), whereas for a Salpeter IMF the stellar mass exceeds the total mass within the galaxy inner regions. We find that the combination of a NFW dark matter halo with the maximally rescaled luminous profile provides a remarkably good fit to the total mass distribution over a broad radial range. Our results confirm and expand the findings of the SLACS survey for early-type galaxies of comparable velocity dispersion (sigma_SDSS = 214 +/- 11 km/s). The internal structure of J0728 is consistent with that of local early-type galaxies of comparable velocity dispersion as measured by the SAURON project, suggesting lack of evolution in the past two billion years.

The SAURON project - XV. Modes of star formation in early-type galaxies and the evolution of the red sequence

We combine SAURON integral field data of a representative sample of local early-type, red sequence galaxies with Spitzer/Infrared Array Camera imaging in order to investigate the presence of trace star formation in these systems. With the Spitzer data, we identify galaxies hosting low-level star formation, as traced by polycyclic aromatic hydrocarbon emission, with measured star formation rates that compare well to those estimated from other tracers. This star formation proceeds according to established scaling relations with molecular gas content, in surface density regimes characteristic of disc galaxies and circumnuclear starbursts. We find that star formation in early-type galaxies happens exclusively in fast-rotating systems and occurs in two distinct modes. In the first, star formation is a diffuse process, corresponding to widespread young stellar populations and high molecular gas content. The equal presence of co- and counter-rotating components in these systems strongly implies an external origin for the star-forming gas, and we argue that these star formation events may be the final stages of (mostly minor) mergers that build up the bulges of red sequence lenticulars. In the second mode of star formation, the process is concentrated into well-defined disc or ring morphologies, outside of which the host galaxies exhibit uniformly evolved stellar populations. This implies that these star formation events represent rejuvenations within previously quiescent stellar systems. Evidence for earlier star formation events similar to these in all fast-rotating early-type galaxies suggests that this mode of star formation may be common to all such galaxies, with a duty cycle of roughly 1/10, and likely contributes to the embedded, corotating inner stellar discs ubiquitous in this population.

The SAURON project - XVI. On the sources of ionization for the gas in elliptical and lenticular galaxies

Following our study on the incidence, morphology and kinematics of the ionised gas in early-type galaxies we now address the question of what is powering the observed nebular emission. To constrain the likely sources of gas excitation, we resort to a variety of ancillary data, draw from complementary information on the gas kinematics, stellar populations and galactic potential from the SAURON data, and use the SAURON-specific diagnostic diagram juxtaposing the [OIII]/Hb and [NI]/Hb line ratios. We find a tight correlation between the stellar surface brightness and the flux of the Hb recombination line across our sample, which points to a diffuse and old stellar source as the main contributor of ionising photons in early-type galaxies, with post-asymptotic giant branch (pAGB) stars being still the best candidate based on ionising-balance arguments. Other ionising sources such as a central AGN, OB-stars, shocks or the interaction between the hot and warm phases of the interestellar medium are found to play only a limited or localised role in powering the diffuse nebular emission observed in our sample galaxies. These results lead us to investigate the relative importance of stellar and AGN photoionisation in explaining the ionised-gas emission observed in early-type galaxies by the Sloan Digital Sky Survey (SDSS). By simulating how our sample galaxies would appear if placed at further distance and targeted by the SDSS, we conclude that only in very few, if any, of the SDSS early-type galaxies that display modest values for the equivalent width of the [OIII] line (less than ~2.4\AA) and LINER-like [OIII]/Hb values, the nebular emission is truly powered by an AGN.

A principle of corresponding states for two-component, self-gravitating fluids

Macrogases are defined as two-component, large-scale celestial objects where the subsystems interact only via gravitation. The macrogas equation of state is formulated and compared to the van der Waals (VDW) equation of state for ordinary gases. By analogy, it is assumed that real macroisothermal curves in macrogases occur as real isothermal curves in ordinary gases, where a phase transition (vapour-liquid observed in ordinary gases and gas-stars assumed in macrogases) takes place along a horizontal line in the macrovolume-macropressure (O, Xv, Xp) plane. The intersections between real and theoretical (deduced from the equation of state) macroisothermal curves, make two regions of equal surface as for ordinary gases obeying the VDW equation of state. A numerical algorithm is developed for determining the following points of a selected theoretical macroisothermal curve on the (O, Xv, Xp) plane: the three intersections with the related real macroisothermal curve, and the two extremum points (one maximum and one minimum). Different kinds of macrogases are studied in detail: UU, where U density profiles are flat, to be conceived as a simple guidance case; HH, where H density profiles obey the Hernquist (1990) law, which satisfactorily fits the observed spheroidal components of galaxies; HN/NH, where N density profiles obey the Navarro-Frenk-White (1995, 1996, 1997) law, which satisfactorily fits the simulated nonbaryonic dark matter haloes. A different trend is shown by theoretical macroisothermal curves on the (O/XV/Xp) plane, according to whether density profiles are sufficiently mild (UU) or sufficiently steep (HH, HN/NH). In the former alternative, no critical macroisothermal curve exists, below or above which the trend is monotonous. In the latter alternative, a critical macroisothermal curve exists, as shown by VDW gases, where the critical point may be defined as the horizontal inflexion point. In any case, by analogy with VDW gases, the first quadrant of the (O, Xv, Xp) plane may be divided into three parts: (i) The G region, where only gas exists; (ii) The S region, where only stars exist; (iii) The GS region, where both gas and stars, exist. With regard to HH and HN/NH macrogases, an application is made to a subsample (N = 16) of elliptical galaxies extracted from larger samples (N = 25, N = 48) of early type galaxies investi?gated within the SAURON project (Cappellari et al. 2006, 2007). Under the simplifying assumption of universal mass ratio of the two subsystems, m, different models character?ized by different scaled truncation radii, i.e. concentrations, ?i, ?j, are considered and the related position of sample objects on the (O, Xv, Xp) plane is determined. Macrogases fitting to elliptical galaxies are expected to lie within the S region or slightly outside the boundary between the S and the GS region at most. Accordingly, models where sample objects lie outside the S region and far from its boundary, or cannot be positioned on the (O/XV/Xp) plane, are rejected. For each macrogas, twenty models are considered for different values of (?i, ?j, m), namely ?i, ?j = 5, 10, 20, + ? (?i, ?j, both either finite or infinite), and m = 10, 20. Acceptable models are (10, 10, 20), (10, 20, 20), (20, 10, 20), (20, 20, 20), for HH macrogases, and (10, 5, 10), (10, 10, 20), (20, 10, 20), for HN/NH macrogases. Tipically, fast rotators are found to lie within the S region, while slow rotators are close (from both sides) to the boundary between the S and the GS region. The net effect of the uncertainty affecting observed quantities, on the position of sample objects on the (O, Xv, Xp) plane, is also investigated. Finally, a principle of corresponding states is formulated for macrogases with assigned density profiles and scaled truncation radii.

Elliptical galaxies: Rotationally distorted, after all

On the basis of earlier investigations on homeoidally striated Mac Laurin spheroids and Jacobi ellipsoids (Caimmi and Marmo 2005, Caimmi 2006a, 2007), different sequences of configurations are defined and represented in the ellipticity-rotation plane, (O??2v). The rotation parameter, ?2v, is defined as the ratio, Erot=Eres, of kinetic energy related to the mean tangential equatorial velocity component, M(v?)2/2, to kinetic energy related to tangential equatorial component velocity dispersion, M?2 ??/2, and residual motions, M(?2 ww + ?2 33)=2. Without loss of generality (above a threshold in ellipticity values), the analysis is restricted to systems with isotropic stress tensor, which may be considered as adjoint configurations to any assigned homeoidally striated density profile with anisotropic stress tensor, different angular momentum, and equal remaining parameters. The description of configurations in the (O??2v) plane is extended in two respects, namely (a) from equilibrium to nonequilibrium figures, where the virial equations hold with additional kinetic energy, and (b) from real to imaginary rotation, where the effect is elongating instead of flattening, with respect to the rotation axis. An application is made to a subsample (N = 16) of elliptical galaxies extracted from richer samples (N = 25, N = 48) of early type galaxies investigated within the SAURON project (Cappellari et al. 2006, 2007). Sample objects are idealized as homeoidally striated MacLaurin spheroids and Jacobi ellipsoids, and their position in the (O??2v) plane is inferred from observations following a procedure outlined in an earlier paper (Caimmi 2009b). The position of related adjoint configurations with isotropic stress tensor is also determined. With a single exception (NGC 3379), slow rotators are characterized by low ellipticities (0 ? ? &lt; 0.2), low anisotropy parameters (0 ? ? &lt; 0.15), and low rotation parameters (0 ? ?2v &lt; 0.15), while fast rotators show large ellipticities (0.2 ? ? &lt; 0.65), large anisotropy parameters (0.15 ? ? &lt; 0.35), and large rotation parameters (0.15 ? ?2v &lt; 0.5). An alternative kinematic classification with respect to earlier attempts (Emsellem et al. 2007) requires larger samples for providing additional support to the above mentioned results. A possible interpretation of slow rotators as nonrotating at all and elongated due to negative anisotropy parameters, instead of flattened due to positive anisotropy parameters, is exploited. Finally, the elliptical side of the Hubble morphological sequence is interpreted as a sequence of equilibrium (adjoint) configurations where the ellipticity is an increasing function of the rotation parameter, slow rotators correspond to early classes (E0-E2 in the oblate limit and E2-E0 in the prolate limit) and fast rotators to late classes (E3-E6). In this view, boundaries are rotationally distorted regardless of angular momentum and stress tensor, where rotation has to be intended as due to additional kinetic energy of tangential equatorial velocity components, with respect to spherical configurations with isotropic stress tensor.

The SAURON project - XII. Kinematic substructures in early-type galaxies: evidence for discs in fast rotators

We analysed two-dimensional maps of 48 early-type galaxies obtained with the SAURON and OASIS integral-field spectrographs using kinemetry, a gene ralisation of surface photometry to the higher order moments of the line-of-sight velocity distribution (LOSVD). The maps analysed include: reconstructed image, mean velocity, velocity dispersion, h3 and h4 GaussHermite moments. Kinemetry is a good method to recognise structures otherwise missed by using surface photometry, such as embedded disks and kinematic sub-components. In the SAURON sample, we find that 31% of early-type galaxies are sin gle component systems. 91% of the multi-components systems have two kinematic subcomponents, the rest having three. In addition, 29% of galaxies have kinematically decoupled components, nuclear components with significant kinematic twists. We differentiate betwee n slow and fast rotators using velocity maps only and find that fast rotating galaxies contain disks with a large range in mass fractions to the main body. Specifically, we find that the velo city maps of fast rotators closely resemble those of inclined disks, except in the transition r egions between kinematic subcomponents. This deviation is measured with the kinemetric k5/k1 ratio, which is large and noisy in slow rotators and about 2% in fast rotators. In terms of E/S0 classification, this means that 74% of Es and 92% of S0s have components with disk-like kinematics. We suggest that differences in k5/k1 values for the fast and slow rotators arise from their differ ent intrinsic structure which is reflected on the velocity maps. For the majority of fa st rotators, the kinematic axial ratios are equal to or less than their photometric axial rati os, contrary to what is predicted with isotropic Jeans models viewed at different inclinations. T he position angles of fast rotators are constant, while they vary abruptly in slow rotators. Velocity dispersion maps of face-on galaxies have shapes similar to the distribution of light. Veloci ty dispersion maps of the edge-on fast rotators and all slow rotators show differences which can only be partially explained with isotropic models and, in the case of fast rotators, often req uire additional cold components. We constructed local (bin-by-bin) h3 V/σ and h4 V/σ diagrams from SAURON observations. We confirm the classical anti-correlation of h3 and V/σ, but we also find that h3 is almost zero in some objects or even weakly correlated with V/σ. The distribution of h4 for fast and slow rotators is mildly positive on average. In general, fast rot ators contain flattened components characterised by a disk-like rotation. The difference betw een slow and fast rotators is traceable throughout all moments of the LOSVD, with evidence for different intrinsic shapes and orbital contents and, hence, likely different evolutionary paths.

The SAURON project - XI. Stellar populations from absorption-line strength maps of 24 early-type spirals

We present absorption line strength maps of a sample of 24 representative early-type spiral galaxies, mostly of type Sa, obtained as part of the SAURON survey of nearby galaxies using our custom-built integral-field spectrograph. Using high- quality spectra, spatially binned to a constant signal-to-noise, we measure several key age, metallicity and abundance ratio sensitive indices from the Lick/IDS system over a contiguous two-dimensional field including bulge and inner disc. We present maps of Hβ, Fe 5015, and Mgb, for each galaxy. We find that Sa galaxies on the average have slightly smaller Mg b and Fe 5015 line strengths than ellipticals and S0s, and higher Hβ values, but with a much larger scatter. The absorption line maps show that many galaxies contain some younger populations (6 1 Gyr), distributed in small or large inner discs, or in circu mnuclear star forming rings. In many cases these young stars are formed in circumnuclear mini-starbursts, which are dominating the light in the centres of some of the early-type spir als. These mini-starburst cause a considerable scatter in index-index diagrams such as Mg b ‐ Hβ and Mgb ‐ Fe 5015, more than is measured for early-type galaxies. We find that the cen tral regions of Sa galaxies display a wide range in ages, even within the galaxies. We find that the central regions of early-type spirals are often dusty, with a good correlation between the presence of young central stellar populations and a significant amount of dust extinction. 50% of the sample show velocity dispersion drops in their centres. All of the galaxies of our sample lie on or below the Mg b ‐ σ relation for elliptical galaxies in the Coma cluster, and above the Hβ absorption line ‐ σ relation for elliptical galaxies. If those relations are considered to be relations for the oldest local galaxies we see that our sample of spirals has a considerable scatter in age, with the largest scatter at the lowest σ. This is in disagreement with highly inclined samples, in which generally only old stellar populations are found in the central regions. The discrepancy between our sample and highly inclined samples, and the presence of so many stellar velocity dispersion dips, i.e., so-called σ-drops, in these spiral galaxies with large bulges (type Sa) can be understood if the central regions of Sa galaxies contain at least 2 components: a thin, disc-like component, often containing recent star formation, and another, elliptical-like component, consisting of old stars and rot ating more slowly, dominating the light above the plane. These components together form the photometrically defined bulge, in the same way as the thin and the thick disc co-exist in the solar neighbourhood. In this picture, consistent with the current literature, part of the bulge, t he thicker component, formed a very long time ago. Later, stars continued to form in the central r egions of the disc, rejuvenating in this way the bulge through dynamical processes. This picture is able to explain in a natural way the heterogeneous stellar populations and star formation characteristics that we are seeing in detailed observations of early-type spiral galaxies.

The SAURON project — II. Sample and early results

Early results are reported from the SAURON survey of the kinematics and stellar populations of a representative sample of nearby E, S0 and Sa galaxies. The survey is aimed at determining the intrinsic shape of the galaxies, their orbital structure, the mass-to-light ratio as a function of radius, the age and metallicity of the stellar populations, and the frequency of kinematically decoupled cores and nuclear black holes. The construction of the representative sample is described, and its properties are illustrated. A comparison with long-slit spectroscopic data establishes that the SAURON measurements are comparable to, or better than, the highest-quality determinations. Comparisons are presented for NGC 3384 and 4365, where stellar velocities and velocity dispersions are determined to a precision of 6 km s−1, and the h3 and h4 parameters of the line-of-sight velocity distribution to a precision of better than 0.02. Extraction of accurate gas emission-line intensities, velocities and linewidths from the data cubes is illustrated for NGC 5813. Comparisons with published line strengths for NGC 3384 and 5813 reveal uncertainties of ≲0.1 Å on the measurements of the Hβ, Mg b and Fe5270 indices. Integral-field mapping uniquely connects measurements of the kinematics and stellar populations to the galaxy morphology. The maps presented here illustrate the rich stellar kinematics, gaseous kinematics, and line-strength distributions of early-type galaxies. The results include the discovery of a thin, edge-on, disc in NGC 3623, confirm the axisymmetric shape of the central region of M32, illustrate the LINER nucleus and surrounding counter-rotating star-forming ring in NGC 7742, and suggest a uniform stellar population in the decoupled core galaxy NGC 5813.

Probing the Formation and Evolution of early-type galaxies: the SAURON project

We are conducting a systematic study of a carefully selected sampleof nearby E/S0 galaxies and Sa bulges using the unique panoramic integral-fieldspectrograph SAURON, mounted at the WHT. The goal of the SAURON projectis to fully map the gaseous/stellar kinematics and the stellar populations of a representative sample of 80 early-type galaxies up to 1 Re,probing different environments (clusters, field). These data, used in combination with existing ground-based and HST observations, and fed to the theoretical machinery we have developed, will allow to determine theintrinsic dynamical structure of the galaxies. We will also measure the masses of central black holes, relate the internal dynamics to the ageand metallicity of the stellar populations, and establish the historyof metal enrichment as a function of Hubble type and environment. Some brief results on two targets observed during the SAURON campaign will serve as an illustration of the unique and high quality data we are currently gathering.