Stellar Distributions and NIR Colours of Normal Galaxies

We discuss some results of a morphological study of edge-on galaxies, based on optical and especially near-infrared surface photometry. We find that the vertical surface brightness distributions of galaxies are fitted very well by exponential profiles, much better than by isothermal distributions. We find that in general the vertical scale height increases when going outward. This increase is strong for early-type spiral galaxies and very small for late types. We argue that it can be due to the presence of thick discs with scale lengths larger than the galaxy's main disc. Finally we discuss the colour-magnitude relation in I-K for spiral galaxies. We find that it is a tight relation, for which the scatter is similar to the observational uncertainties, with a steeper slope than for elliptical galaxies.Comment: Invited review, to appear in "Extragalactic Astronomy in the Infrared", eds. G.A. Mamon, Trinh Xuan Thuan, and J. Tran Thanh Van, Editions Frontieres, Gif-sur-Yvette. LaTeX2e, 10 pages, 6 postscript figures and moriond.sty included. See also ftp://kapteyn.astro.rug.nl/peletier/lesarcs.ps.g

IAU Symposium 241 - Stellar Populations as Building Blocks of Galaxies

Stellar populations, building blocks of galaxies, are direct tracers of the star formation history, the chemical enrichment and the assembly of galaxies in the Universe. They therfore allow us to understand how galaxies formed and evolved. This last decade has witnessed a revolution in our observations of galaxies; with larger telescopes and new instruments we are not only able to look deeper in the Universe, we can also study nearby galaxies with greater detail. The fact that now is becoming possible to resolve stars up to the distance of Virgo Cluster allows us to rigorously compare and calibrate the analysis of the integrated light with resolved stellar populations. These Proceedings report the considerable progress made in recent years in this topic. Theorists and observers, researchers of resolved and unresolved stellar populations, discussed the ingredients of stellar population models, and rigorously compared them to new data, forcing theorists to develop more refined models and methods to derive the physical parameters of the stellar populations. New results from the Milky Way, the Local Group, and nearby and distant galaxies were presented.Comment: This is the table of contents of the upcoming proceedings of IAU Symposium 241. The book will appear in September, from Cambridge University Press, and will also be available electronically at http://www.journals.cambridge.org/action/displayJournal?jid=IA

Near-Infrared Surface Photometry of Bulges and Disks of Spiral Galaxies. The Data

We present optical and near-infrared (NIR) surface brightness and colour profiles,in bands ranging from U to K, for the disk and bulge components of a complete sample of 30 nearby S0 to Sbc galaxies with inclinations larger than 50 degrees. We describe in detail the observations and the determination of colour parameters. Calibrated monochromatic and real-colour images are presented, as well as colour index maps. This data set, tailored for the study of the population characteristics of galaxy bulges, provides useful information on the colours of inner disks as well. In related papers, we have used them to quantify colour gradients in bulges, and age differentials between bulge and inner disk.Comment: 18 pages Latex with 2 postscript figures. Accepted for New Astronomy. This is an electronic paper; a complete preprint, including all of the tables and figures can be found at ftp://www.astro.rug.nl/peletier/newast/newast.htm

Spiral galaxy distance indicators based on near-infrared photometry

We compare two methods of distance determination to spiral galaxies using optical/near-infrared (NIR) observations, the (I-K) versus M_K colour - absolute magnitude (CM) relation and the I and K-band Tully-Fisher relation (TFR). Dust-free colours and NIR absolute magnitudes greatly enhance the usefulness of the NIR CM relation as a distance indicator for moderately to highly inclined_spiral_ galaxies_in the field_ (inclinations between ~ 80 and 90 deg); by avoiding contamination by dust the scatter in the CM relation is significantly reduced, compared to similar galaxy samples published previously. The CM relation can be used to determine distances to field spiral galaxies with M_K > -25.5, to at least M_K ~ -20. Our results, supplemented with previously published observations for which we can - to some degree - control the effects of extinction, are consistent with a universal nature of the CM relation for field spiral galaxies. High-resolution observations done with the Hubble Space Telescope can provide a powerful tool to calibrate the relation and extend the useful distance range by more than a factor of 2 compared to ground-based observations. The intrinsic scatter in the NIR CM relation in the absolute K-band magnitudes is ~0.5 mag, yielding a lower limit to the accuracy of distance determinations on the order of 25%. Although we find an unusually low scatter in the TFR (probably a statistical accident), a typical scatter in the TFR would yield distances to our sample galaxies with uncertainties of only about 15%. However, one of the main advantages of the use of the NIR CM relation is that_we only need photometric data_ to obtain distance estimates; use of the TFR requires additional kinematic data, although it can be used to significantly greater distances.Comment: 12 pages, incl. 5 postscript files, LaTeX, accepted for publication in MNRA

Kinematic Properties and Dark Matter Fraction of Virgo Dwarf Early-Type Galaxies

What happens to dwarf galaxies as they enter the cluster potential well is one of the main unknowns in studies of galaxy evolution. Several evidence suggests that late-type galaxies enter the cluster and are transformed to dwarf early-type galaxies (dEs). We study the Virgo cluster to understand which mechanisms are involved in this transformation. We find that the dEs in the outer parts of Virgo have rotation curves with shapes and amplitudes similar to late-type galaxies of the same luminosity. These dEs are rotationally supported, have disky isophotes, and younger ages than those dEs in the center of Virgo, which are pressure supported, often have boxy isophotes and are older. Ram pressure stripping, thus, explains the properties of the dEs located in the outskirts of Virgo. However, the dEs in the central cluster regions, which have lost their angular momentum, must have suffered a more violent transformation. A combination of ram pressure stripping and harassment is not enough to remove the rotation and the spiral/disky structures of these galaxies. We find that on the the Faber-Jackson and the Fundamental Plane relations dEs deviate from the trends of massive elliptical galaxies towards the position of dark matter dominated systems such as the dwarf spheroidal satellites of the Milky Way and M31. Both, rotationally and pressure supported dEs, however, populate the same region in these diagrams. This indicates that dEs have a non-negligible dark matter fraction within their half light radius.Comment: Proceeding of the XXVIII IAU General Assembly, Special Session 3: Galaxy Evolution through Secular Processes. Edts: R. Buta and D. Pfennige

The z-structure of disk galaxies towards the galaxy planes

We present a detailed study of a statistically complete sample of highly inclined disk galaxies in the near-infrared K' band. Since the K'-band light is relatively insensitive to contamination by galactic dust, we have been able to follow the vertical light distributions all the way down to the galaxy planes. The mean levels for the sharpness of the K'-band luminosity peaks indicate that the vertical luminosity distributions are more peaked than expected for the intermediate sech(z) distribution, but rounder than exponential. Since projection of not completely edge-on galaxies onto the plane of the sky causes vertical luminosity profiles to become rounder, we have performed simulations that show that it is possible that all our galaxies can have intrinsically exponential vertical surface brightness distributions. We find that the profile shape is independent of galaxy type, and varies little with position along the major axis. The fact that we observe this in all our sample galaxies indicates that the formation process of the galaxy disks perpendicular to the galaxy planes is a process intrinsic to the disks themselves.Comment: 23 pages, LaTeX, includes 12 figures, accepted for publication in Astronomy and Astrophysics. Fig. 1 will be sent on reques

A monolithic collapse origin for the thin/thick disc structure of ESO 243-49

ESO 243-49 is a high-mass (circular velocity $v_{\rm c}\approx200\,{\rm km\,s^{-1}}$) edge-on S0 galaxy in the Abell 2877 cluster at a distance of $\sim95\,{\rm Mpc}$. To elucidate the origin of its thick disc, we use MUSE science verification data to study its kinematics and stellar populations. The thick disc emits $\sim80\%$ of the light at heights in excess of $3.5^{\prime\prime}$ ($1.6\,{\rm kpc}$). The rotation velocities of its stars lag by $30-40\,{\rm km\,s^{-1}}$ compared to those in the thin disc, which is compatible with the asymmetric drift. The thick disc is found to be more metal-poor than the thin disc, but both discs have old ages. We suggest an internal origin for the thick disc stars in high-mass galaxies. We propose that the thick disc formed either ${\rm a)}$ first in a turbulent phase with a high star formation rate and that a thin disc formed shortly afterwards, or ${\rm b)}$ because of the dynamical heating of a thin pre-existing component. Either way, the star formation in ESO 243-49 was quenched just a few Gyrs after the galaxy was born and the formation of a thin and a thick disc must have occurred before the galaxy stopped forming stars. The formation of the discs was so fast that it could be described as a monolithic collapse where several generations of stars formed in a rapid succession.Comment: Accepted for publication in A&A. The reduced data-cube as well as the data necessary to build the kinematic and stellar population maps are available at https://etsin.avointiede.fi/dataset/urn-nbn-fi-csc-kata2016092414291163237

The Stellar Populations of Pixels and Frames

Derived from first physical principles, a few simple rules are presented that can help in both the planning and interpretation of CCD and IR-array camera observations of resolvable stellar populations. These rules concern the overall size of the population sampled by a frame as measured by its total luminosity, and allow to estimate the number of stars (in all evolutionary stages) that are included in the frame. The total luminosity sampled by each pixel (or resolution element) allows instead to estimate to which depth meaningful stellar photometry can be safely attempted, and below which crowding makes it impossible. Simple relations give also the number of pixels (resolution elements) in the frame that will contain an unresolved blend of two stars of any kind. It is shown that the number of such blends increases quadratically with both the surface brightness of the target, as well as with the angular size of the pixel (or resolution element). A series of examples are presented illustrating how the rules are practically used in concrete observational situations. Application of these tools to existing photometric data for the inner parts of the bulge of M31, M32 and NGC 147 indicates that no solid evidence has yet emerged for the presence of a significant intermediate age population in these objects.Comment: 28 pages, LaTeX file using aasms4.sty, 2 postscript figures To appear on: The Astronomical Journa

On microscopic origins of generalized gradient structures

Classical gradient systems have a linear relation between rates and driving forces. In generalized gradient systems we allow for arbitrary relations derived from general non-quadratic dissipation potentials. This paper describes two natural origins for these structures. A first microscopic origin of generalized gradient structures is given by the theory of large-deviation principles. While Markovian diffusion processes lead to classical gradient structures, Poissonian jump processes give rise to cosh-type dissipation potentials. A second origin arises via a new form of convergence, that we call EDP-convergence. Even when starting with classical gradient systems, where the dissipation potential is a quadratic functional of the rate, we may obtain a generalized gradient system in the evolutionary $\Gamma$-limit. As examples we treat (i) the limit of a diffusion equation having a thin layer of low diffusivity, which leads to a membrane model, and (ii) the limit of diffusion over a high barrier, which gives a reaction-diffusion system.Comment: Keywords: Generalized gradient structure, gradient system, evolutionary \Gamma-convergence, energy-dissipation principle, variational evolution, relative entropy, large-deviation principl