Nowadays it is well established that BCDs are mostly old systems, as the vast majority of them have an extended low-surface brightness (LSB) stellar host underlying their central starburst component. Detailed and systematic investigations of this old stellar population are indispensable for the understanding of the structure and evolution of these systems. Recently, we presented a two-dimensional fitting methodology in order to improve the extraction of the structural parameters of the LSB hosts. Here, we apply this new technique to fit a Sersic law in a sample of 28 BCGs. We analyse luminosities, sizes, surface brightness, colours and the Sersic index, n, of this galaxies and their possible correlations with the sizes and luminosities of the starburst, as well as with their HI mass. By using the HI line width, we also analyse the position of this galaxies in the Tully-Fisher relation. Moreover, we compare the distribution of the BCDs with that of early- and late-type galaxies in the diagrams built upon the Sersic parameters. While previous works claimed that dwarf BCGs are segregated from the other dwarfs in such diagrams, here we find that the dwarf systems in this sample occupy the same region as the other dwarf types. These results suggest that evolutionary connections between dwarf BCGs and the other dwarf classes cannot be ruled out.

Little is known about the content and distribution of dark matter in spiral galaxies. There is a degeneracy in the galaxy rotation curve decompositions, which allows a wide range of dark matter halo density profiles. To break this disk-halo degeneracy an independent measure of the mass surface density is needed. Here, the current status of the Disk Mass Project is presented. We are using two custom-built Integral Field Units to measure the vertical velocity dispersion of the stars in ~40 nearly face-on spiral galaxies. These stellar velocity dispersions provide a kinematic measurement of the stellar disk mass, which breaks the disk-halo degeneracy and makes it possible to determine the dark matter properties in spiral galaxies with unprecedented accuracy.

Until now, studies of local barred galaxies have primarily used small samples of a few hundred galaxies drawn from small volumes that may suffer from cosmic variance and small number statistics. We present the first study of several hundred barred disk galaxies drawn from the Sloan Digitized Sky Survey (SDSS). Our sample of ~3600 galaxies with Mg<-18.5 mag is drawn from the SDSS and covers the redshift range 0.01<z<0.03. Structural parameters for all objects have been determined by single component Sersic fits to 2-D images. We use a color cut in the color-magnitude diagram and the Sersic index n to identify ~2000 disk galaxies. We characterize bar and disk features in disk systems by fitting ellipses to the r-band images. We investigate the relationship between the bar and host galaxy properties. The study will also serve as a comparison z=0 point for high redshift studies of bars, which follow the evolution of barred galaxies over large look-back times. After excluding highly inclined (>60 degrees) systems we find the following results: (1) The optical r-band fraction of barred galaxies is ~48%-52%. (2) When galaxies are separated according to half light radius, or normalized half light radius, which is a measure of the bulge-to-disk (B/D) ratio, we find a sharp increase of the bar fraction from ~40% in galaxies with large B/D and visually appear bulge-dominated, to ~70% for galaxies that have small B/D and appear disk-dominated. A visual classification confirms that bars are more frequent (>70%) in disk galaxies with no bulge or a very low B/D, than in galaxies with prominent bulges (40%). (3) The optical r-band bar fraction rises for galaxies with bluer colors, lower masses, or fainter luminosities. This is expected from (2), given that disk-dominated galaxies are fainter, bluer, and less massive. (4) After applying the same cutoffs in magnitude, bar size, and bar ellipticity that studies out to z~1 apply to ensure a complete sample, adequate spatial resolution, and reliable bar identification, we obtain a bar fraction of 34%. This is comparable to the value of ~30% reported at z~0.2-1, implying that the optical bar fraction is fairly constant in bright galaxies out to z~1.

The growth of supermassive black holes (SMBHs) appears to be closely linked with the formation of spheroids. There is a pressing need to acquire better statistics on SMBH masses, since the existing samples are preferentially weighted toward early-type galaxies with very massive SMBHs. With this motivation we started a project aimed at measuring upper limits on the mass of the SMBHs that can be present in the center of all the nearby galaxies (D<100 Mpc) for which STIS/G750M spectra are available in the HST archive. These upper limits have been derived by modeling the central emission-line widths observed in the Hα region, over a central aperture of ~0.25”. Here we present our preliminary results for a subsample of 83 bulges.

I will present a study of the molecular gas throughout the disk of M31. From observations with the IRAM 30meter telescope in the HCN and HCO⁺ lines we have deduced the distribution of the dense gas in the disk of the galaxy and its variation as a function of the galactocentric radius. We have focused on a segment of a spiral arm to compare ISM tracers (CO, HI), star formation tracers (Hα, 24 (µm) and the [CII] line emission from ISO observations. [CII] emission is an excellent tracer of star formation and by comparison with photo-dissociation region models we have estimated the quantity of HI that is the product of H₂ dissociation.

I will discuss an ongoing project of sensitive mapping of Local Group spiral galaxies in the CO(2-1) line with the IRAM 30-m antenna and the HERA multibeam receiver array, with a focus on the outer parts of spirals. The CO observations provide a wide-field view of the molecular gas at high angular resolution, such that individual molecular clouds can be identified. The CO data are of M33, NGC6822, and the outer part of the Milky Way. Further observations of the 13CO lines in M33 will be discussed to better understand the variation of cloud properties with galactocentric distance and galaxy type. In particular, the CO and ¹³CO lines have been detected in M33 out to beyond the R₂₅ radius, despite the low metallicity. This allows us to place constraints on the conversion factor between CO and H₂ and study the link between the atomic and molecular gas and regions of star formation.

We searched the HST Science Archive for the nuclei of elliptical galaxies with images obtained in different epochs, to detect the presence of far-ultraviolet variability. We found multi-epochs observations only for the elliptical galaxy NGC4278. It hosts a barely resolved nuclear source which increased its UV luminosity by a factor 4 between June 1994 and January 1995. The properties of the UV flare of NGC4278 are remarkably similar to the UV-bright nuclear transients discovered earlier in other low-luminosity AGNs. This supports the idea that UV flaring near the center of galaxies may be a common event and offers a way to search for black-hole-related activities in otherwise quiescent galaxies.

I present the physical properties of the nuclear star clusters in the centers of "bulged" late-type disks, and their relation with their host bulges and inner disks. I compare the scaling relations between nuclear and global properties in late-type disks with equivalent relationships at the early-type end of the Hubble sequence, and discuss the implications of our results for the formation of disk galaxies.

A still unresolved question about active galactic nuclei (AGN) is the determination of the mechanism responsible for the nuclear activity. It is important to understand what can force gas or other material to lose angular momentum and fall into the galaxy nucleus, activating and fuelling the supermassive black hole (SMBH). Many authors proposed a lot of different solutions: circumnuclear star clusters, bars, disks or nuclear spirals, interactions between galaxies, and mergers. All of these mechanisms generate a non-axysimmetrical potential which can trigger nuclear activity, but no one of these can give a complete explanation for all classes of AGN. This work is part of a larger project focused on the study of the possible causes of AGN triggering. Here we present preliminary results about morphological and photometric analysis of a sample of 35 nearby (z<0.035) and isolated or partially isolated Seyfert galaxies, observed through broad-band BVR filters at the 1.8-m Vatican Telescope and the 2.2-m ESO-La Silla Telescope. We analyzed photometric and morphological parameters and obtained bidimensional decomposition of luminosity profiles of these galaxies, using GALFIT software.

We observed a sample of three brightest cluster galaxies (BCGs), Abell1836-BCG, Abell2052-BCG, and Abell3565-BCG, with the Advanced Camera for Surveys (ACS) and the Imaging Spectrograph (STIS) on board the Hubble Space Telescope (HST). For each target galaxy we obtained high-resolution spectroscopy of the HΑ and [NII] emission lines at three slit positions, to measure the central ionized-gas kinematics. ACS images in three different filters (namely, F435W, F625W, and FR656N) have been used to determine the optical depth of the dust, stellar mass distribution near the nucleus, and intensity map. We present supermassive black hole (SBH) mass estimates for two galaxies which show regular rotation curves and strong central velocity gradients, and an upper limit on the SBH mass of the third one. For the SBHs of Abell1836-BCG (147.2 Mpc) and Abell3565-BCG (50.8 Mpc), we derived M_BH=5.8(+1.0/-0.8)x10⁹ solar masses and M_BH=1.7(+0.4/-0.5)x10⁹ solar masses at 1 sigma confidence level, respectively. Abell1836-BCG harbours the largest SBH mass to have been dinamically measured to-date. For the SBH of Abell2052-BCG (141.0 Mpc), we found MBH<8.7.x10⁹ solar masses.

The implementation of large field imagers on 4 metre telescopes has enabled comprehensive surveys of the stellar contents of spiral galaxies in nearby groups. Efforts to study the radial distribution of stars of various evolutionary types in a large sample of galaxies are of interest, as the results provide insights into disk evolution. We are using the CFHT MegaCam to probe the bright stellar contents in nearby spiral galaxies. In the current presentation, the radial distributions and properties of bright main sequence stars and supergiants in NGC 247, NGC 2403, and NGC 3031 are discussed. Stars that formed within the past few tens of millions of years are traced out to distances of 7 or more disk scale lengths in each galaxy.

One of the major goals of near-field cosmology is to determine the physical sequence of events involved in the formation of the Galactic disk during the epoch of dissipation. The disk’s dissipative formation and subsequent dynamical evolution means most of its dynamical information is lost. Any dynamical probing of the disk can only provide information up until the epoch of last dissipation or dynamical scattering event. However the chemical information survives. If star-forming aggregates can preserve a unique chemical signature within their stellar members, we can use the method of chemical tagging to associate individual disk stars to a common formation event. Detailed chemical abundance patterns offer the possibility to reconstruct now dispersed stellar aggregates of the protogalactic disk and so improve our basic understanding of the disk formation process. I will present recent abundance analyses of several open clusters and moving groups which are the likely left-overs of the star-forming aggregates of the disk, and discuss their implications for extensive use of the chemical tagging technique.

We report some results of a spectrophotometric study of a sample of nearby Active Galactic Nuclei (AGN) observed using Integral Field Spectroscopy. Aim of the project is to derive and to compare the physical properties of the circumnuclear and extranuclear regions of galaxies hosting an AGN. The Multi Pupil Fiber Spectrograph (MPFS) mounted at the Russian 6 m telescope, which takes simultaneously 240 spectra at low or intermediate spectral resolution of a 16x15 arcsec field has been used for the observations. Two-dimensional maps of diagnostic emssion line ratios have allowed to investigate in detail the nature of the ionization processes acting in these regions. Contour maps of the velocity field of the stellar and of the gaseous component have been used as tools for extracting information on the origin of the resolved emitting regions located around the AGN.

Clues to the early formation of the Milky Way disk are preserved within the detailed stellar abundances of its most metal-poor stars. Only a few metal-poor disk stars with [Fe/H] < -1 have been analyzed for their abundances until now. We have observed a large sample (> 75 stars, most since May) of metal-poor disk stars isolated from the catalog of the RAdial Velocity Experiment (RAVE). While the analysis is ongoing, we have confirmed that a significant metal-poor disk population with an alpha-element enhancement slightly greater than the local stellar halo. This suggests an early and rapid formation for these stars.

We have analyzed the radial scales, central surface brightnesses, and colors of 400 disks of various types of galaxies. For ten galaxies, the brightness decrease and the central disk brightness were obtained via a two-dimensional decomposition of the UBVRIJHK photometric images into bulge and disk componens. We used published disk parameters for 392 of the galaxies. The central surface brightness μ(0) and linear disk scale length h vary smoothly along the Hubble sequence of galaxies within a rather narrow interval. The disks of relatively early-type galaxies display higher central surface brightnesses in K, higher central surface densities, higher central mass-to-luminosity ratios M/L(B), smaller sizes (relative to the diameter of the galaxy), redder integrated colors, and redder central colors. The color gradient normalized to the radius of the galaxy and the blue central surface brightness µ(0,B) of the disk, are both independent of the galaxy type. The radial disk scales in different photometric bands differ less in early-type than in late-type galaxies. The ratio of linear disk scales measured in different photometric bands increases with the isophote ellipticity e of the disk (the inclination of the galaxy); however, the range of the ratio values for each e value exceeds the range of variations of scale length ratio over e. The disks in S0 galaxies have more homogeneous parameters than those in spiral galaxies. This may be due to the lower linear age and metallicity gradients of their stellar populations, as well as the lower amounts of dust in the disks of S0 galaxies. However, no sharp boundary in the properties of disks in lenticular, spiral, and irregular galaxies has been found, all the parameters vary smoothly along the Hubble sequence. A correlation between the central disk surface brightness and the total luminosity of the galaxy is observed. We also consider the influence of dust on the photometric parameters of the disks.

We compare both the Milky Way and M31 galaxies to local external disk galaxies within the same mass range, using their relative locations in the planes formed by V_flat versus M_K (the Tully-Fisher relation), j_disk (angular momentum) and the average Fe abundance of stars in the galaxy outskirts. We find, for all relationships, that the MW is systematically offset by 1 sigma, showing a significant deficiency in stellar mass, in angular momentum, in disk radius and [Fe/H] in the stars in its outskirts at a given V_flat. On the basis of their location in the M_K, V_flat, and R_d volume, the fraction of spirals like the MW is 7±1%, while M31 appears to be a “typical” spiral. Our Galaxy appears to have escaped any significant merger over the last 10-11 Gyr which may explain why it is deficient by a factor 2 to 3 in stellar mass, angular momentum and outskirts metallicity and then, unrepresentative of the typical spiral. As with M31, most local spirals show evidence for a history shaped mainly by relatively recent merging. We conclude that the standard scenario of secular evolution driven by the accretion of gas and disk instabilities is generally unable to reproduce the properties of most (if not all) spiral galaxies.

We discuss the long-standing problem of the limit on the accretion rate onto a black hole. To understand observed spectral features of supercritical accretion flows (accretion above the classical Eddington limit) in ultraluminous X-ray sources (ULXs), we calculate spectral energy distributions of such highly-accreting stellar mass black holes surrounded by an accretion disk and an extended atmosphere. The underlying data are taken from 2-dimensional radiation hydrodynamic simulations (Ohsuga et al. 2005). Continuum features like the peak intensity of thermal emission around 1 keV are analyzed for various orientations of the observer relative to the accretion disk. We find that mild relativistic beaming effects become important for face-on seen systems and that spectral diagnostic tools like e.g. total luminosity and effective temperatures differ considerably for edge-on and face-on seen systems. We also investigate line emission features of the iron K line complex, finding that line shapes and line emission and absorption ratios reflect the observer's orientation just as well as continuum features. From the advent of high-resolution and high-sensitivity X-ray telescopes, we expect to be able to deduce details about the accretion process like central black hole masses and accretion rates in ULXs by comparing observed continuum and line emission spectra with our theoretical predictions. From our analysis, we hope to shed new light on the open question of intermediate mass black holes or stellar mass black holes as central objects in ULXs.

Most of our understanding of dark matter halos comes from the assumption that the mass-to-light ratio of spiral disks is constant. The best way to test this assumption is to determine the disk mass surface density directly by measuring the velocity dispersion in the direction perpendicular to the plane of face-on spiral galaxies. We have been using planetary nebulae as test particles in M33 and five other nearby but more face-on spirals: M74, M83, M94, M101, and IC 342. Our results indicate that the mass-to-light ratio actually increases in the outer regions. We discuss the implications of our findings.

A recent data analysis of the far-infrared map of the Galaxy and the Magellanic Clouds has shown that there is a tight correlation between two far-infrared (FIR) colors: the 60 µm-100 µm and 100 µm-140 µm colors. This FIR color relation called “main correlation” can be interpreted as indicative of a sequence of various interstellar radiation fields with common FIR optical properties. We analyze this main correlation by using a FIR spectral energy distribution (SED) model and constrain the FIR emissivity of grains. Then, we apply this constraint to nearby galaxies, finding that the FIR colors of nearby galaxies are also consistent with the main correlation. In this sense, the main correlation derived from the Galaxy and the Magellanic Clouds is “universal”. We also analyze the structure of the Galactic disk based on our analysis, and estimate the star formation rate of the Galaxy and nearby galactic disks.

Recent studies of the radial abundance distribution among stellar populations in the Galactic disk have shown a change in the abundance trend at galactocentric distance R_gc~10 kpc, as first noted by Twarog et al. (1997). Here the gradient in [Fe/H] with distance appears to vanish, with abundances of stars at greater distances dropping to [Fe/H]~-0.5, independent of galactocentric distance. Also, [α/Fe]>0 for R_gc>10 kpc (Yong et al. 2005). This implies that the outer disk has undergone a different star formation history than the inner disk. However, abundances of many more stars at R_gc ~9-12 kpc must be determined to characterize the nature of the transition from inner to outer disk. We have initiated a survey of a large sample of open clusters in this region using multi-object spectrographs on the WIYN 3.5-m, CTIO 4-m and MMT 6.5-m telescopes. We present preliminary results of this survey.

It is well known that galaxies contain dust and that viewing them from different angles will led to differing measurements of their properties. That is why it is so important to deal with the intrinsic properties of galaxies, those that do not depend on inclination angle. We show how to determine the intrinsic properties of galaxies statistically with a large data set like the SDSS. We then show how many measurements of disk galaxy properties change when one considers the intrinsic properties instead of the observed properties.

Our IDS/ISOCAM sample comprises a complete, 60 μm selected sample of 56 galaxies in the North Ecliptic Polar Region (NEPR), a subsample of the original 98 IRAS Deep Survey (IDS) fields (Hacking & Houck 1987). We exploited our ISOCAM observations of the IRAS Deep Survey (IDS) fields, to correct the 60 µm fluxes for confusion effects and observational biases. In della Valle et al. (2006), we presented spectroscopic and optical observations of candidate identifications of our ISOCAM sources. Thanks to our ISOCAM and optical/near-IR observations, our sample, which provides a direct link between the IRAS and ISO surveys, and the forthcoming deeper Spitzer Space Telescope and Akari cosmological surveys, is one of the far-IR selected complete samples with the larger spectral coverage. Mazzei et al. (2007) analyzed the far-IR properties of such a sample. Here we present the optical properties of such galaxies which turn out to be disk like systems. Diagnostic diagrams, based on suitable line intensity ratios, place them among the starburst class of galaxies.

A variety of formation scenarios was proposed to explain the diversity of properties observed in bulges. Studying their intrinsic shape can help in constraining the dominant mechanism at the epochs of their assembly. The structural parameters of a magnitude-limited sample of 148 unbarred S0-Sb galaxies were derived in order to study the correlations between bulges and disks as well as the probability distribution function (PDF) of the intrinsic equatorial ellipticity of bulges. It is presented a new fitting algorithm (GASP-2D) to perform the two-dimensional photometric decomposition of galaxy surface-brightness distribution. This was assumed to be the sum of the contribution of a bulge and disk component characterized by elliptical and concentric isophotes with constant (but possibly different) ellipticity and position angles. Bulge and disk parameters of the sample galaxies were derived from the J-band images which were available in the Two Micron All Sky Survey. The PDF of the equatorial ellipticity of the bulges was derived from the distribution of the observed ellipticities of bulges and misalignments between bulges and disks. Strong correlations between the bulge and disk parameters were found. About 80% of bulges in unbarred lenticular and early-to-intermediate spiral galaxies are not oblate but triaxial ellipsoids. Their mean axial ratio in the equatorial plane is <B/A> = 0.85. There is not significant dependence of their PDF on morphology, light concentration, and luminosity. The interplay between bulge and disk parameters favors scenarios in which bulges assembled from mergers and/or grew over long times through disk secular evolution. But all these mechanisms have to be tested against the derived distribution of bulge intrinsic ellipticities.

Bars play a vital role in the evolution of disk galaxies. Their presence is recognized as one of the most important internal factor on the evolution of these galaxies. Bars are responsible for the redistribution of the angular momentum of the baryonic and dark matter components, driving their dynamical, morphological and chemical evolution through secular processes. However, even if many bar galaxies at low redshift have been studied in details, a crucial piece of information is still missing, such as a statistical study of their properties and a robust estimation of the algorithm errors. Lately, large galaxy surveys as SDSS provides the opportunity for studying very large and complete samples of galaxies. We study a volume limited sample of galaxies which cover the redshift range 0.01<z <0.04 with magnitudes M_r<-20 drawn from the Sloan Digital Sky Survey (SDSS-DR5). By using two independent methods to identify and characterize the bars, we investigate the relationship between the bar and host galaxy properties in a statistical way. Both method were extensively tested through simulations with mock galaxies detecting possible bias in the results and estimating reliable errors from the algorithm. Our aim is to put strong constraints on the barred galaxy fraction and to characterize bars and their host galaxies in the local universe. Our results will shed light on the impact of bars on their host galaxy and constrain secular evolution scenarios.

I discuss SAURON integral field observations of a sample of 42 spirals, ranging in type from Sa to Sd. Using 2-dimensional maps of the stellar velocity, velocity dispersion, and absorption line strength, it is now much easier to understand the nature of nearby galactic bulges, and the relations with the inner disk. The observations show that spiral galaxies contain at least 2 components: one (or more) thin, disc-like component, often containing recent star formation, and another, elliptical-like component, consisting of old stars and rotating more slowly, dominating the light above the plane. If one defines a bulge to be the component responsible for the light in excess of the outer exponential disc, then many Sa-bulges are dominated by a thin, disk-like component containing recent star formation.

Interstellar extinction remains a serious obstacle for the observation of stars in the Milky Way, and for interpreting these observations in terms of Galactic structure. As the extinction suffered in the NIR is roughly an order of magnitude lower than in the visible, recent infrared surveys provide a superb tool to probe further into the densest parts of the Galaxy, namely the Galactic plane. We use the Stellar Population Synthesis Model of the Galaxy, developed in Besancon, along with the Two Micron All Sky Survey to constrain the Galactic structure of the external disc, and in particular the warp. The warp parameters such as its slope at positive and negative longitudes are adjusted by comparing 2MASS star counts with the simulated ones from the Galactic model. In order to properly interpret the observations, the simulated stars are reddened using a three dimensional extinction map. We find that the warp is asymmetric and we compare our results to other recent estimations.

Investigating the transition from atomic to molecular gas in galactic outskirts is crucial for the understanding of star formation and thus the evolution of galactic disks throughout all epochs of galaxy formation. M33 is a late-type spiral in the Local Group and is ideal for a detailed case study as its metallicity and size resemble that of galaxies at z~2 while its close distance (0.84 Mpc) allows us to resolve individual giant molecular clouds. We present unique high sensitivity mapping of the CO(2-1) line with HERA at the IRAM 30-m telescope which covers the transition from the atomic outskirts to the inner part of the disk dominated by molecular gas. By comparison of our data with HI and HΑ emission we find that the star forming efficiency in M33 is clearly enhanced as compared to large local disk galaxies. The enhancement is similar to that found in intermediate-redshift galaxies. Our analysis points to a relation between HI and H2 in the outer parts of the disk that cannot easily be explained by a simple mid plane pressure induced atomic to molecular transition. Apart from an in depth analysis of the relation between molecular gas and HI, our high sensitivity observations allow also to identify particular local entities which are important to understand the variety of processes which have to be taken into account to model the physics of the interstellar medium in M33. Such structures are isolated molecular clouds which have no HI counterpart and previously unknown molecular bubble structures which indicate that dynamics can locally be dominated by individual star forming events.

The mostly applied separation technique of the two components of the radio continuum emission, free-free (thermal) and synchrotron (non-thermal) emission, is based on a constant non-thermal spectral index. However, this assumption does not lead to a reliable thermal/non-thermal distribution in high resolution studies where variations of the non-thermal spectral index are expected. For example, it is not possible to investigate the existing energy loss processes of the relativistic electrons within a galaxy. For the first time, we decompose the radio continuum emission from M33 (NGC598), the nearest late-type spiral galaxy, using a method based on a template of free-free emission. This galaxy, which is nearly face on, is ideal to study the variations of the non-thermal spectral index from star forming regions in spiral arms to interarm regions and outer galactic parts. With the high sensitivity and resolution Multiband Imaging Photometer Spitzer data at 70, and 160 μm, we obtain the distribution of dust optical depth at the HΑ wavelength. This leads to an HΑ map corrected for extinction (our free-free template) providing the thermal maps at 3.6 and 20 cm. Subtracting these thermal maps from the recently observed maps at 3.6 cm (Effelsberg telescope) and 20 cm (Very Large Array + Effelsberg telescopes) gives the corresponding non-thermal maps. The non-thermal spectral index map determined from the 3.6 and 20 cm non-thermal maps shows flatter non-thermal spectrum in star forming regions than in interarm regions and outer parts of the galaxy. Other important results of this study are presented as follows: a) The distribution of the dust extinction is more or less similar to that of the 160 μm emission. We find a shallow radial gradient of the mean extinction in rings of 0.5 kpc width in the galactic plane. b) The contribution of the spiral arms and star forming regions in the non-thermal emission is more pronounced at 3.6 cm than at 20 cm. c) The thermal emission is slightly more concentrated in the southern than in the northern half of the galaxy.

We investigate the energy sources of the infrared (IR) emission and their relation to the radio continuum emission at various spatial scales within the Scd galaxy M33. We use the data at the Spitzer wavelengths of 24, 70, and 160 μm, as well as recent radio continuum maps at 3.6 cm and 20 cm observed with the 100-m Effelsberg telescope and VLA, respectively. We use the wavelet transform of these maps to a) separate the diffuse emission components from compact sources, b) compare the emission at different wavelengths, and c) study the radio-IR correlation at various spatial scales. An HΑ map serves as a tracer of the star forming regions and as an indicator of the thermal radio emission. The bright HII regions affect the wavelet spectra causing dominant small scales or decreasing trends towards the larger scales. The dominant scale of the 70 μm emission is larger than that of the 24 μm emission, while the 160 μm emission shows a smooth wavelet spectrum. The radio and HΑ maps are well correlated with all 3 MIPS maps, although their correlations with the 160 μm map are weaker. After subtracting the bright HII regions, the 24 and 70 μm maps show weaker correlations with the 20 cm map than with the 3.6 cm map at most scales. We also find a strong correlation between the 3.6 cm and HΑ emission at all scales. Comparing the results with and without the bright HII regions, we conclude that the IR emission is influenced by young, massive stars increasingly with decreasing wavelength from 160 to 24 μm. The radio-IR correlations indicate that the warm dust-thermal radio correlation is stronger than the cold dust-non-thermal radio correlation at scales smaller than 4 kpc. A perfect 3.6 cm-HΑ correlation implies that extinction has no significant effect on HΑ emitting structures.

To investigate the mid and far IR emission of M33, we reduced IRAC and MIPS Spitzer images. We compared the photometric results on three samples of discrete known type sources (HII regions, supernovae remnants and planetary nebulae) with theoretical diagnostic diagrams. We generated a catalogue of 24 μm sources and inferred their nature in light of the observational and theoretical colours of the known type sources. We estimated the star formation rate in M33 both globally and locally, from the IR emission and from the HΑ emission line. The colours of the typical IR emissions of HII regions, supernovae remnants and planetary nebulae are continuous between the different samples, with overlapping regions in the diagnostic diagrams. The comparison between the model results and the colours of HII regions indicates a dusty envelope at relatively high temperatures, of order 600 K. The derived TIR luminosity function is very similar to the HII luminosity function observed in the Milky Way and in other late type spirals. Even though our completeness limit is 10³⁸ ergs s^-1 in low density regions we are able to detect sources, one order of magnitude fainter than this, corresponding to the faintest possible HII region. The total IR emission within the first 5 kpc of M33 is 10⁹ L(Sun) and the far IR luminosity is about 5.8 x 10⁸ L(Sun). The discrete sources account for about one third of the 24 μm emission while the rest is diffuse. From the IR emission, we derive a star formation rate for the inner disk equal to 0.2 M(Sun) yr^-1, consistent with the star formation rate obtained from the HΑ emission.

We use the COBE/DIRBE (1.2, 2.2, 60, 100, 140, and 240 (µm) maps and the COBE/FIRAS spectra (for the wavelength range 100-1000 µm) to constrain a model for the spatial distribution of the dust, the stars and the gas in the Milky Way. By assuming exponential axisymmetric distributions for the dust and the stars and by performing the corresponding radiative transfer calculations we reproduce the FIR and NIR maps of the Milky Way. Similar distributions for the atomic and molecular hydrogen in the disk are used (with an inner cut off radius for the atomic Hydrogen) to fit the gas data. The star formation rate as a function of the Galactic radius is derived from the FIR emission and is well in agreement with existing estimates from various star formation tracers. The gas surface density is plotted against the star formation rate density and an “intrinsic” Galactic Schmidt law is derived with excellent agreement with the “external” Schmidt law found for spiral galaxies. The Milky Way is found to consume ~1% and ~10% of its gas in the outer and inner regions respectively (for a period of 0.1 Gyr) for making stars. The dust-induced B-V colour excess observed in various directions and distances (up to ~6.5 kpc) to well-studied Cepheid stars is compared with the model predictions showing a good agreement. The simple assumption of exponential distributions of stars and dust in the Galaxy is found to be quite instructive and adequate in modelling all the available data sets from 0.45 µm (B-band) to 1000 µm.

The proposed talk aims to give an overview over the observational knowledge on the nuclei of pure disk galaxies that was amassed over the last decade. The centers of 75% of bulgeless galaxies host a compact, massive star cluster at the center instead of a bulge. These clusters are thus a generic feature of pure disk galaxies. They are not only extremely dense, but also undergo repetitive bursts of new star formation. The fact that these clusters repetitively form stars, yet do not grow into bulges gives important constraints on the gas transport processes in the centers of pure disk galaxies. New data on gas velocity fields around the clusters will also be presented. This will allow us to measure the central potential of these galaxies and to understand why most of the galaxies form NCs, but some do not. Finally, I will also touch on the potential extension of relations (as found in earlier type galaxies) between the nucleus (black hole) and the overall galaxy properties (e.g. spheroid mass) to the smallest spheroid masses known as well as on the existence of AGN in the nuclei of pure disk galaxies.

We use 2D ionized gas and stellar line-of-sight kinematics to determine the stellar velocity ellipsoid for a subset of galaxies observed by the Disk Mass Survey. The derived ellipsoids provide physical constraints on the dynamical state of galactic disks - specifically their stability and heating mechanisms - and calibrates a surrogate method for estimating velocity dispersions in disks using only velocity centroids. We show recent observations in the low-surface brightness regime for which this surrogate method can be applied. Our approach to ellipsoid decomposition is the result of comparing various methods in an effort to determine the most robust measure of the axis ratios in different inclination regimes. We also take advantage of this over-determined problem to check for consistency between different dynamical assumptions. Finally, we compare our ellipsoid results to previous measurements, which rely less on the equation for asymmetric drift, and explore correlations of ellipsoid shape with physical disk parameters.

Edge-on spiral galaxies offer a unique perspective on disks. One can accurately determine the height distribution of stars and ISM and the line-of-sight integration allows for the study of faint structures. The Spitzer IRAC camera is an ideal instrument to study both the ISM and stellar structure on nearby galaxies; two of its channels trace the old stellar disk with little extinction and the 8 micron channel is dominated by the smallest grains (Polycyclic Aromatic Hydrocarbons, PAHs). Dalcanton et al (2004) probed the link between the appearance of dust lanes and the disk stability. In a sample of bulge-less disks they show how in massive disks the ISM collapses into the characteristic thin dust lane. Less massive disks are gravitationally stable and their dust morphology is fractured. The transition occurs at 120 km/s for bulgeless disks. Here I report on our results of our Spitzer/IRAC survey of nearby edge-on spirals and it's view on the disk stability.

We present results of a study of the stellar surface-brightness profiles of a complete sample of more than 100 S0 and early-type spiral galaxy disks, based on deep optical imaging. The profiles fall into three broad categories: pure exponential (Freeman Type I); profiles which steepen beyond a break radius (Freeman Type II, including so-called "truncations"); and profiles which are shallower beyond a break radius ("Type III" or "antitruncations"). We argue that most of the Type II profiles are related to the Outer Lindblad Resonances of bars; "truncations" due to star-formation thresholds appear to account for only a small fraction of the profiles. Type III profiles are primarily changes in the disk, not excess light from a spheroid or halo. Their presence is anti-correlated with bar strength: Type III profiles are most common in unbarred galaxies, and least common when the bar is strong. We also discuss environmental differences; in particular, the relative frequency of the different profiles differs significantly between the Virgo Cluster and the field.

By re-analyzing elemental abundances in Galactic PN, together with the best available distances, we determined metallicity gradients that are flatter than previously determined. These findings are not reconcilable with the flattening of metallicity gradients with time. We show how larger datasets and a better Galactic planetary nebula distance scale will improve this fundamental constraint to Galactic evolutionary models.