We present a kinematic study of the outer regions (R_25<R<2 R_25) of 17 edge-on disk galaxies. Using deep long-slit spectroscopy (flux sensitivity a few 10^-19 erg s^-1 cm^-2 arcsec^-2), we search for H-alpha emission, which must be emitted at these flux levels by any accumulation of hydrogen due to the presence of the extragalactic UV background and any other, local source of UV flux. We present results from the individual galaxy spectra and a stacked composite. We detect H-alpha in many cases well beyond R_25 and sometimes as far as 2 R_25. The combination of sensitivity, spatial resolution, and kinematic resolution of this technique thus provides a powerful complement to 21-cm observations. Kinematics in the outer disk are generally disk-like (flat rotation curves, small velocity dispersions) at all radii, and there is no evidence for a change in the velocity dispersion with radius. We place strong limits, few percent, on the existence of counter-rotating gas out to 1.5 R_25. These results suggest that thin disks extend well beyond R_25; however, we also find a few puzzling anomalies. In ESO 323-G033 we find two emission regions that have velocities close to the systemic velocity rather than the expected rotation velocity. These low relative velocities are unlikely to be simply due to projection effects and so suggest that these regions are not on disk-plane, circular orbits. In MCG-01-31-002 we find emission from gas with a large velocity dispersion that is co-rotating with the inner disk.
Asymmetries in the distribution of light and neutral hydrogen are often observed in spiral galaxies. Here, attention is drawn to the presence of large-scale asymmetries in their kinematics. Two examples of kinematically lopsided galaxies are presented and discussed. The shape of the rotation curve --rising more steeply on one side of the galaxy than on the other-- is the signature of the kinematic lopsidedness. It is shown that kinematic lopsidedness may be related to lopsidedness in the potential, and that even a mild perturbation in the latter can produce significant kinematical effects. Pro…
We present major and minor-axis kinematics of stars and ionized gas as well as narrow and broad-band surface photometry of the Sa spiral NGC 2855. In the nuclear regions of this unbarred and apparently undisturbed spiral galaxy the gas is rotating perpendicularly to the galaxy disk. We suggest that this kinematically-decoupled component is the signature of an acquisition process in the history of this galaxy.
We present a study of the observable spectral manifestations associated with spiral shocks within quiescent accretion disks and compare them with observations of the dwarf nova U Geminorum. Our results indicate that the orbital behaviour of the hydrogen emission line profile in the spectrum of U Gem can be reproduced via a simple model of the accretion disk with two symmetrically located spiral shocks with the spiral angle theta about 60 degrees. This provides for the first time convincing evidence for the existence of spiral shocks in the accretion disk of a cataclysmic variable in quiescence…
A comlex structure of nuclear disks of normal spiral galaxies was illustrated on the example of five galaxies, observed at 6m telescope. A problem of gravitational stability of nuclear disks is shortly discussed.
We present a study of the kinematics of the ionised gas in the nearby spiral galaxy NGC 2403 using deep long-slit spectra obtained with the 4.2-m William Herschel Telescope. The data show the presence of a halo component of ionised gas that is rotating more slowly than the gas in the disk. The kinematics of this ionised halo gas is similar to that of the neutral halo gas. On small scales, broad line profiles (up to 300 km/s wide) indicate regions of fast outflows of ionised gas. We discuss these new results in the context of galactic fountain models.
Results from kinematic observations of the central regions of spiral galaxies are reviewed, with particular emphasis on starburst and AGN hosts. While morphological studies lead to important insight, a more complete understanding of the physical processes that drive the evolution of the central regions can be achieved with measurements of the kinematics of gas and stars. Here, a variety of observational techniques at different wavelengths is critically discussed, and specific areas of interest are highlighted, such as inflow in barred galaxies and the origin of nuclear spiral arms. A brief dis…
Observations at high spectral and temporal resolution are presented of the dwarf nova EX Dra in outburst. The disk seen in the He I line reconstructed by Doppler tomography shows a clear two-armed spiral pattern pointing to spiral shocks in the disk. The Balmer and He II maps also give evidence for the presence of spirals. The eclipse as seen in the red continuum indicates a disk radius of 0.31 times the orbital separation, which might be large enough to explain the observed spiral shocks through excitation by the tidal field of the secondary. The eclipse in the Balmer line profiles, well reso…
An improved linear stability theory of small-amplitude oscillations of a self-gravitating, infinitesimally thin gaseous disk of spiral galaxies has been developed. It was shown that in the differentially rotating disks for nonaxisymmetric perturbations Toomre's modified hydrodynamical simulations to test the validity of the modified local criterion.
We study the ionizing sources in spiral galaxies and examine in more detail our Galaxy. Using Taylor & Cordes (1993) model we analyze the electron density in different parts of the Galaxy, and emphasize the still unsolved problems. Finally, we compare the intensities of H$α$ emission in disk and halo.
The Halpha gas kinematics of twenty-one representative barred spiral galaxies belonging to the BHaBAR sample is presented. The galaxies were observed with FaNTOmM, a Fabry-Perot integral-field spectrometer, on three different telescopes. The 3D data cubes were processed through a robust pipeline with the aim of providing the most homogeneous and accurate dataset possible useful for further analysis. The data cubes were spatially binned to a constant signal-to-noise ratio, typically around 7. Maps of the monochromatic Halpha emission line and of the velocity field were generated and the kinemat…
A single merger scenario for making galaxies such as NGC 4550 possessing equal coplanar counter-rotating stellar disks is investigated by collisionless N-body technique. The scenario is successful in producing an axisymmetric disk made of two almost equal counter-rotating populations. The final disk shows a clear bimodal line profile in the outer part, which demonstrates that disk-disk mergers do not always produce ellipticals.
Using 2D nonlinear simulations, we study the generation and nonlinear evolution of spiral structure in a star-forming multi-component gravitating disk. We confirm in agreement with previous studies the destabilizing role of a cold gaseous component and extend this conclusion for multi-component star-forming disks exchanging mass and momentum between its components. We show that the spiral structure growing on a non-stationary multi-phase background reaches its saturation in a similar manner like the one-component disks. The spiral structure survives even if most of the gas is transformed into …
We present a relationship between spiral arm pitch angle (a measure of the tightness of spiral structure) and the mass of supermassive black holes (BHs) in the nuclei of disk galaxies. We argue that this relationship is expected through a combination of other relationships, whose existence has already been demonstrated. The recent discovery of AGN in bulgeless disk galaxies suggests that halo concentration or virial mass may be one of the determining factors in BH mass. Taken together with the result that mass concentration seems to determine spiral arm pitch angle, one would expect a relation…
We present for the first time a two-dimensional velocity field of the central region of the grand-design spiral galaxy NGC 5248, at 0.9 arcsec spatial resolution. The H-alpha velocity field is dominated by circular rotation. While no systematic streaming motions are seen in the area of the nuclear grand-design spiral or the circumnuclear ring, the amplitude of residual velocities, after subtracting a model circular velocity field, reaches 20 km/s in projection. The rotation curve levels out at around 140 km/s, after a well-resolved and rather shallow rise. We have generated an analytical model…
We report evidence for nuclear stellar disks in 3 early-type spirals, namely NGC 1425, NGC 3898 and NGC 4698, revealed by WFPC2/F606W images out of a sample of 38 spiral galaxies, selected from the Hubble Space Telescope Data Archive. Adopting the photometric method introduced by Scorza & Bender we derived their central surface brightness and scalelength by assuming them to be infinitesimally thin exponential disks. No nuclear disk was found in barred galaxies or galaxies of Hubble type later than Sb. The external origin of the disk in NGC 4698 is strongly suggested by its orthogonal geometric…
This paper presents some new statistical correlations between the properties of disks and spiral arms with some physical properties of galaxies. Our results show that the thickness of spiral disks tend to diminish along the Hubble sequence in the sense that disks of Sc galaxies are 40% thinner than disks of Sab-Sb galaxies. Moreover, the thinner disks tend also to be bluer. We also find that there exists a correlation between HI linewidths and arm pattern within each Hubble type, which suggests that the arm shape is partially determined by the mass of a galaxy. Total mass luminosity ratios and…
Gravitational lensing is a potentially important probe of spiral galaxy structure, but only a few cases of lensing by spiral galaxies are known. We present Hubble Space Telescope and Magellan observations of the two-image quasar PMN J2004-1349, revealing that the lens galaxy is a spiral galaxy. One of the quasar images passes through a spiral arm of the galaxy and suffers 3 magnitudes of V-band extinction. Using simple lens models, we show that the mass quadrupole is well-aligned with the observed galaxy disk. A more detailed model with components representing the bulge and disk gives a bulge-…
The analysis of a sample of 30 isolated spiral galaxies with and without an AGN results in active and control galaxies having similar bulge and disk properties (since both samples are selected to match in morphological and bar classification, they have similar bar percentages). Secondary bars seem also to be indistinguishable. The central kinematics (both stellar and gas) are also studied in order to put some constraints on the processes required to fuel AGNs. Together with previous results, this points to AGNs being an episode of the life of galaxies, providing that the fuel is available and …
It is generally believed that major galaxy mergers with mass ratios in the range 1:1-3:1 result in remnants that have properties similar to elliptical galaxies, and minor mergers below 10:1 result in disturbed spiral galaxies. The intermediate range of mass ratios 4:1-10:1 has not been studied so far. Using N-body simulations, we show that such mergers can result in very peculiar systems, that have the morphology of a disk galaxy with an exponential profile, but whose kinematics is closer to that of elliptical systems. These objects are similar to those recently observed by Jog & Chitre (2002)…
We derive the disk masses of 18 spiral galaxies of different luminosity and Hubble Type, both by mass modelling their rotation curves and by fitting their SED with spectro-photometric models. The good agreement of the estimates obtained from these two different methods allows us to quantify the reliability of their performance and to derive very accurate stellar mass-to-light ratio vs color (and stellar mass) relationships.
A spiral galaxy partially ovelapping a more distant elliptical offers an unique opportunity to measure the dust extinction in the foreground spiral. From the Sloan Digital Sky Survey DR4 spectroscopic sample, we selected 83 occulting galaxy pairs and measured disk opacity over the redshift range z = 0.0-0.2 with the goal to determine the recent evolution of disk dust opacity. The enrichment of the ISM changes over the lifetime of a disk and it is reasonable to expect the dust extinction properties of spiral disks as a whole to change over their lifetime. When they do, the change will affect ou…
With 2D hydrodynamical simulations of disks perturbed externally by stars, brown dwarfs or planets we investigate possible scenarios that can account for the spiral structure in circumstellar disks. We consider two scenarios, spiral structure driven by an external bound planet or low mass star and that excited by a previous stellar close encounter or flyby. We find that both scenarios produce morphology similar to that observed in the outer disks of HD 141569A and HD 100546; moderately open 2-armed outer spiral structure. The outer two-armed spiral structure observed in the disk of HD 141569A …
We find that the quiescent accretion disk of U Gem has a complicated structure. Along to the bright spot originating in the region of interaction between the stream and the disk particles, there are also explicit indications of spiral shocks. The Doppler map and the variations of the peak separation of the emission lines are indicative.
Single-armed, stationary density waves can propagate in very weakly self-gravitating gas disks dominated by a central mass. Examples include circumstellar disks of protostars and molecular disks in galactic nuclei. We explore the linear and nonlinear dynamics of such waves. Variational methods yield nonlinear versions of the dispersion relation, angular momentum flux, and propagation velocity in the tight-winding limit. The pitch angle increases with amplitude until the tight-winding approximation breaks down. We also find a series of nonlinear logarithmic spirals which is exact in the limit o…
Investigation of gaseous and stellar kinematics and of broad-band VRI and narrow-band H-alpha and [NII]6583 images is performed for the central part (R < 4 kpc) of the regular spiral galaxy NGC 2841. We have found emission-line splitting at R < 20" and three-component LOSVD for the stars in the radius range 6" - 100". Morphological analysis reveals strong narrow shock fronts close to the major axis in the radius range of 30" - 50", a turn of the isophote major axis by 5 degrees and strongly negative Fourier coefficient a4 (boxy isophotes) in the radius range of 15" - 33". In principle, all the…
We present the results of two-dimensional numerical simulations of stellar galactic disks, aimed at studying the non-linear coupling between bar and spiral waves and modes, in disks with realistically peaked rotation profiles. The power spectrum analysis of the perturbed density in the disk, for azimuthal numbers ranging from m=0 to m=4, shows an unambiguous signature of non-linear coupling between the bar and spiral waves, or between spiral waves only, with a very sharp selection of the frequencies which optimize the coupling efficiency. It turns out that non-linear coupling can be quite effi…
We discuss the distribution and kinematics of neutral hydrogen in the halos of spiral galaxies. We focus in particular on new results obtained for the nearby Sc galaxy NGC 2403 which have revealed the presence of extended HI emission (here referred to as the `beard') at anomalous velocities with respect to the `cold' HI disk. Modeling shows that this component has a mass of about 1/10 of the total HI mass and is probably located in the halo region. Its kinematics differs from that of the thin HI disk: it rotates more slowly and shows radial inflow. The origin of this anomalous gas component is…
We present a method, based on the kinematic analysis of the Galactic disk stars, to clarify whether the internal motions of the stellar system in spiral arms follow those expected in the density wave theory. The method relies on the comparison with the linear relation between the phases of spatial positions and epicyclic motions of stars, as drawn from the theory. The application of the method to the 78 Galactic Cepheids near the Sun, for which accurate proper motions are available from the {\it Hipparcos} Catalogue, has revealed that these Cepheids hold no correlation between both phases, the…
We present observational evidence for a galaxy `Type' dependence to the location of a spiral galaxy's disk parameters in the mu_0-log(h) (central disk surface-brightness - disk scale-length) plane. With a sample of ~40 Low Surface Brightness galaxies (both bulge- and disk-dominated) and ~80 High Surface Brightness galaxies, the early-type disk galaxies (<=Sc) tend to define a bright envelope in the mu_0-log(h) plane, while the late-type (>=Scd) spiral galaxies have, in general, smaller and fainter disks. Below the defining surface brightness threshold for a Low Surface Brightness galaxy (i.e. …
The circumstellar dust disk of the Herbig Ae star AB Aur has been found to exhibit complex spiral-like structures in the near-IR image obtained with the Subaru Telescope. We present maps of the disk in both 12CO (3-2) and dust continuum at 345 GHz with the SMA at an angular resolution of 1.0"x0.7" (144AU x 100AU). The continuum emission traces a dust disk with a central depression and a maximum overall dimension of 450AU (FWHM). This dust disk exhibits several distinct peaks that appear to coincide with bright features in the near-IR image, in particular the brightest inner spiral arm. The CO …
We explore how the growth rate of spiral disks can be measured via analyses of the scatter in the Tully-Fisher (TF) relation of local and intermediate redshift galaxies. As an initial step, we show it is possible to construct a low-dispersion TF relation for nearly face-on, nearby spirals. We find these spiral disks are non-circular, (a mean ellipticity of 6%), which accounts for about 0.1 mag of the intrinsic scatter in the nearby TF relation of even the most ``normal'' looking spirals. If this ellipticity is induced by matter accretion, we expect to find greater disk ellipticity or disturban…
The stability of self-similar power-law disks to non-axially symmetrical disturbances of zero frequency (omega = 0) is discussed. It is established that marginally unstable modes either have (omega = 0) or consist of continua with modes of all frequencies becoming unstable together. A careful study of all modes close to omega = 0 yields a remarkable conclusion.
We analyze the structural and dynamical properties of disk-like objects formed in fully consistent cosmological simulations which include inefficient star formation. Comparison with data of similar observable properties of spiral galaxies gives satisfactory agreement, in contrast with previous findings using other codes. This suggests that the stellar formation implementation used has allowed the formation of disks as well as guaranteed their stability.
Dust extinction can be determined from the number of distant field galaxies seen through a spiral disk. To calibrate this number for the crowding and confusion introduced by the foreground image, Gonzalez et al.(1998) and Holwerda et al. (2005) developed the ``Synthetic Field Method'' (SFM), which analyses synthetic fields constructed by adding various deep exposures of unobstructed background fields to the candidate foreground galaxy field. The advantage of the SFM is that it gives the average opacity for area of galaxy disk without assumptions about either the distribution of absorbers or of…
We present a kinematic model of the neutral-hydrogen in the spiral galaxy of the lens system PKS1830-211, based on a Multi Element Radio-Linked Interferometer (MERLIN) 1.4-GHz radio map and the integrated and redshifted 21-cm hydrogen absorption-line profile as measured with the Westerbork Synthesis Radio Telescope (WSRT). Degeneracies in the models do not allow a unique determination of the kinematic center and forthcoming deeper Hubble Space Telescope observations with the Advanced Camera for Surveys (ACS) are required to break this degeneracy. Even so, we measure the inclination of the hydr…
We analyze formation of grand-design two-arm spiral structure in the nuclear regions of disk galaxies. Such morphology has been recently detected in a number of objects using high-resolution near-infrared observations. Motivated by the observed (1) continuity between the nuclear and kpc-scale spiral structures, and by (2) low arm-interarm contrast, we apply the density wave theory to explain the basic properties of the spiral nuclear morphology. In particular, we address the mechanism for the formation, maintenance and the detailed shape of nuclear spirals. We find, that the latter depends mos…
We present H-alpha velocity fields for a sample of nearly face--on spiral galaxies observed with DensePak on the WIYN telescope. We combine kinematic inclinations and position angles measured from these data with photometric inclinations and position angles measured from I-band images to show that spiral disks are intrinsically non-circular.
We investigate colors and mass-to-light ratios ($M/L$s) of the bulges and disks for 28 nearby spiral galaxies with various morphological types of Sab to Scd, using images in optical and near-infrared ($V$, $I$, and $J$) bands and published rotation curves. It is shown that the observed colors and $M/L$s generally agree with the galaxy formation model with an exponentially declining star formation rate and shallow slope (ex. Scalo) initial mass function (IMF) for both the bulges and the disks. We find that the bulge $M/L$ is generally higher than the disk $M/L$ and that the galaxies with larger…
The scaling relations between rotation velocity, size and luminosity form a benchmark test for any theory of disk galaxy formation. We confront recent theoretical models of disk formation to a recent large compilation of such scaling relations. We stress the importance of achieving a fair comparison between models and observations.
To investigate the stability properties of polar disks we performed two-dimensional hydrodynamical simulations for flat polytropic gaseous self-gravitating disks which were perturbed by a central S0-like component. Our disk was constructed to resemble that of the proto-typical galaxy NGC 4650A. This central perturbation induces initially a stationary two-armed tightly-wound leading spiral in the polar disk. For a hot disk (Toomre parameter Q>1.7), the structure does not change over the simulation time of 4.5 Gyr. In case of colder disks, the self-gravity of the spiral becomes dominant, it deco…
We present a grid of 440 spectro-photometric models for simulating spiral and irregular galaxies. They have been consistently calculated with evolutionary synthesis models which use as input the information proceeding from chemical evolution models. The model predictions are spectral energy distributions, brightness and color profiles and radial distributions of spectral absorption stellar indices which are in agreement with observations.
Recent ground-based photometric investigations suggest that central regions of late-type spirals are closely coupled to the inner disk and probably formed via secular evolution. Evidence presented in support of this model includes the predominance of exponential bulges, the correlation of bulge and disk scale lengths, blueness of the bulge and small differences between bulge and central disk colors, detection of spiral structure into the core, and rapid rotation. Recent HST observations show that our own bulge and that of M31, M32, and M33 probably harbor both an old and intermediate-age popul…
I discuss anew how arguments about the internal dynamics of galactic disks set constraints on the otherwise ambiguous decomposition of the rotation curves of spiral galaxies into the contributions by the various constituents of the galaxies. Analyzing the two sample galaxies NGC 3198 and NGC 2985 I conclude from the multiplicities of the spiral arms and the values of the Q disk stability parameters that the disks of both galaxies are `maximum disks'.
Dust emission in the far-infrared (FIR) characterizes the temperature and quantity of interstellar dust in a spiral disk. The three Spitzer/MIPS bands are well suited to measuring the gradient in temperature and the total optical depth in the disk of a spiral galaxy. Another way to estimate the quantity of dust in a spiral disk is the "Synthetic Field Method" (SFM, Gonzalez et al. 1998), which uses the number of distant field galaxies seen through the disk of the nearby spiral. The optical depth estimated from this method can be compared to the values derived from the FIR emission. Since the t…
We study bisymmetric modes of angular wavenumber 2 for flat stellar disks in potentials with smooth cores. Stars either all circulate in the same direction or a small fraction may counter-rotate. The bisymmetric modes are unstable unless there is a sufficiently large external halo or bulge. We find two modes for each disk: a more central fundamental mode and a more extensive and more spiral (trailing) secondary mode. The fundamental mode is particularly sensitive to the orbital population in the central part of the disk. Depending on that population, it varies from a small compact bar to a tra…
We have measured the distribution of intrinsic ellipticities for a sample of 28 relatively face-on spiral disks. We combine H-alpha velocity fields and R and I-band images to determine differences between kinematic and photometric inclination and position angles, from which we estimate intrinsic ellipticities of galaxy disks. Our findings suggest disks have a log-normal distribution of ellipticities (mean epsilon =0.06) and span a range from epsilon= 0 (circular) to epsilon=0.2. We are also able to construct a tight Tully-Fisher relation for our face-on sample. We use this to assess the contri…
We explore the relative importance of the stellar mass density as compared to the inner dark halo, using the observed gas kinematics throughout the disk of the spiral galaxy NGC 4254 (Messier 99). We perform hydrodynamical simulations of the gas flow for a sequence of gravitational potentials in which we vary the stellar disk contribution to the total potential. This stellar portion of the potential was derived empirically from color corrected K-band photometry reflecting the spiral arms in the stellar mass, while the halo was modelled as an isothermal sphere. The simulated gas density and the…
Gravitational lensing of a quasar by a spiral galaxy should often be accompanied by damped Lyman-alpha absorption and dust extinction due to the intervening gaseous disk. In nearly edge-on configurations, the surface mass density of the gas and stars in the disk could by itself split the quasar image and contribute significantly to the overall lensing cross section. We calculate the lensing probability of a disk+halo mass model for spiral galaxies, including cosmic evolution of the lens parameters. A considerable fraction of the lens systems contains two images with sub-arcsecond separation, s…
The young star velocity field is analysed by means of a galactic model which takes into account solar motion, differential galactic rotation and spiral arm kinematics. We use two samples of Hipparcos data, one containing O- and B-type stars and another one composed of Cepheid variable stars. The robustness of our method is tested through careful kinematic simulations. Our results show a galactic rotation curve with a classical value of $A$ Oort constant for the O and B star sample ($A^{\mathrm{OB}} =$ 13.7-13.8 km s$^{-1}$ kpc $^{-1}$) and a higher value for Cepheids ($A^{\mathrm{Cep}} =$ 14.9…
The opacity of a spiral disk due to dust absorption influences every measurement we make of it in the UV and optical. Two separate techniques directly measure the total absorption by dust in the disk: calibrated distant galaxy counts and overlapping galaxy pairs. The main results from both so far are a semi-transparent disk with more opaque arms, and a relation between surface brightness and disk opacity. In the Spitzer era, SED models of spiral disks add a new perspective on the role of dust in spiral disks. Combined with the overall opacity from galaxy counts, they yield a typical optical de…
In this dissertation, I describe theoretical and numerical studies that address the three-dimensional behavior of spiral shocks in protoplanetary disks and the controversial topic of gas giant formation by disk instability. For this work, I discuss characteristics of gravitational instabilities (GIs) in bursting and asymptotic phase disks; outline a theory for the three-dimensional structure of spiral shocks, called shock bores, for isothermal and adiabatic gases; consider convection as a source of cooling for protoplanetary disks; investigate the effects of opacity on disk cooling; use multip…
Nonlinear solutions for the large-scale flow of interstellar gas in the presence of a spiral gravitational field have received considerable attention because this model allows to explain a lot of observations for galaxy disks. However this investigations were forced to limit by numerable analysis of the problem because of its nonlinearity. In this paper we wish to carry out the analytical expression which allows us to describe the super sonic nonlinear interstellar gas flow in rapidly rotating galaxy disk which is made by the spiral density wave. One of characteristic parameters of theory is t…
Spheroidal components of spiral galaxies have been considered the only dynamically important component in gravitational lensing studies thus far. Here we point out that including the disk component can have a significant effect, depending on the disk inclination, on a variety of lensing properties that are relevant to present studies and future surveys. As an example, we look at the multiple image system B1600+434, recently identified as being lensed by a spiral galaxy. We find that including the disk component one can understand the fairly large image separation as being due to the inclinatio…
When astronomers study the dark matter halos of spiral galaxies, they normally assume that the disk mass-to-light ratio is *constant*. We describe a method of analyzing the kinematics of planetary nebulae (PNe) in nearby face-on spiral galaxies to test this assumption. Since the restoring force for stellar motions perpendicular to the galactic disk is proportional to the disk mass surface density, measurements of the vertical velocity dispersion can be used to produce an independent measure of the total amount of matter in the disk. Our steps are: (1) to identify a population of PNe by imaging…
The rotation curves for a sample of 67 spiral galaxies observed by Marquez et al(2002) have been used as input for the multiphase chemicale volution model. By using N[II]/Halpha as estimator of the oxygen abundance, we constraint the possible models for each galaxy. We may, then, predict the time evolution of these galaxies and the present time radial distribution for gas, stars and star formation surface densities and elemental abundances.
The major axis and ellipse-fit intensity profiles of spiral galaxies larger than 0.3'' in the Hubble Space Telescope Ultra Deep Field (UDF) are generally exponential, whereas the major axis profiles in irregular disk galaxies, called clump-clusters in our previous studies, are clearly not. Here we show that the deprojected positions of star-forming clumps in both galaxy types are exponential, as are the deprojected luminosity profiles of the total emissions from these clumps. These exponentials are the same for both types when normalized to the outer isophotal radii. The results imply that clu…
We investigate how significant the spiral structure is on calculations concerning radiative transfer in dusty spiral galaxies seen edge-on. The widely adopted exponential disk model (i.e. both the stars and the dust are distributed exponentially in the radial direction and also perpendicular to the plane of the disk) is now subject to a detailed comparison with a realistic model that includes spiral structure for the stars and the dust in the disk. In particular, model images of galaxies with logarithmic spiral arms are constructed, such that the azimuthally averaged disk is exponential in rad…
Long-slit optical spectra along the major axis of spiral galaxies constitute a main source of information concerning the kinematics of galaxies. In highly inclined spiral galaxies the long-slit spectrum is distorted by dust, which obscures the innermost parts of the galaxy and eliminates the relevant kinematic information. This effect however may provide information concerning the amount and the spatial distribution of dust. Here I review previous attempts to quantify the internal extinction of spiral galaxies using kinematic information and I discuss the relevant theoretical models. Finally I…
