The Lagrange planetary equations are used to study to secular evolution of a small, eccentric satellite that orbits within a narrow gap in a broad, self-gravitating planetary ring. These equations show that the satellite's secular perturbations of the ring will excite a very long-wavelength spiral density wave that propagates away from the gap's outer edge. The amplitude of these waves, as well as their dispersion relation, are derived here. That dispersion relation reveals that a planetary ring can sustain two types of density waves: long waves that, in Saturn's A ring, would have wavelengths of order 100 km, and short waves that tend to be very nonlinear and are expected to quickly damp. The excitation of these waves also transports angular momentum from the ring to the satellite in a way that damps the satellite's eccentricity e, which also tends to reduce the amplitude of subsequent waves. The rate of eccentricity damping due to this wave action is then compared to the rates at which the satellite's Lindblad and corotation resonances alter the satellite's e. These results are then applied to the gap-embedded Saturnian satellites Pan and Daphnis, and the long-term stability of their eccentricities is assessed.
The secular perturbations exerted by an inclined satellite orbiting in a gap in a broad planetary ring tends to excite the inclinations of the nearby ring particles, and the ring's self-gravity can allow that disturbance to propagate away in the form of a spiral bending wave. The amplitude of this spiral bending wave is determined, as well as the wavelength, which shrinks as the waves propagate outwards due to the effects of the central planet's oblateness. The excitation of these bending waves also damps the satellite's inclination I. This secular I damping is also compared to the inclination…
Simulations and observations of galactic bars suggest they do not commonly evolve into bulges, although it is possible that the earliest bars formed bulges long ago, when galaxies were smaller, denser, and had more gas. The most highly evolved of today's bars may become lenses over a Hubble time. Most galaxies in the early Universe are extremely clumpy, with 10^8-10^9 Msun blue clumps that resemble in color and magnitude the isolated field objects nearby. The presence of blue and irregular bars at high redshift suggests that some bars formed primarily in the gas phase accompanied by giant star…
We combine deep optical and IR photometry for 326 spiral galaxies from two recent galaxy samples and report that the surface brightness profiles of late-type spirals are best fit by two exponentials. Moreover, the ratio of bulge and disk scale lengths takes on a restricted range of values and is uncorrelated with Hubble type. This suggests a scale-free Hubble sequence for late-type spirals. Careful numerical simulations ensure that our results are not affected by seeing or resolution effects. Many of these galaxies show spiral structure continuing into the central regions with a previously und…
It is now a well established fact that galaxies undergo significant morphological transformation during their lifetimes, manifesting as an evolution along the Hubble sequence from the late to the early Hubble types. The physical processes commonly believed to be responsible for this observed evolution trend, i.e. the major and minor mergers, as well as gas accretion under a barred potential, though demonstrated applicability to selected types of galaxies, on the whole have failed to reproduce the most important statistical and internal properties of galaxies. The secular evolution mechanism re…
The physical phenomena contributing to the galaxy growth can be tested all the way to z= 1. Galaxy mass, extinction, star formation and gas metal abundance can be measured in a robust way, as well as the distribution of the galaxy morphologies. I discuss here the observational methods and their accuracy. Physical quantities can be evaluated with uncertainties much lower than 0.3 dex, if they are based on 2 sets of independent measurements. For example, at a given IMF, the star formation rate is well estimated by combining flux measurements of the extinction corrected Balmer line and of the mid…
Except in the most extreme cases of nuclear activity, either starbursts or AGN, it is difficult to find observationnally a close link between the dynamics and the activity. Theoretically however, the necessary step to fuel the gas to the center, is that gravity torques are created through a non-axisymmetric pattern, either bar and/or spiral, triggered or not by a tidal interaction. We describe the sequence of processes for a typical evolution cycle for a spiral galaxy, and the possible efficient feedback mechanisms. The various morphologies and dynamical states of spiral galaxies are interpret…
We present a structural analysis of nearby galaxies in spiral-spiral pairs in optical BVRI bands and compare with the structures of isolated spiral galaxies and galaxies in ongoing mergers. We use these comparisons to determine how galaxy structure changes during galaxy interactions and mergers. We analyze light concentration (C), asymmetry (A), and clumpiness (S) parameters, and use the projections of CAS parameter space to compare these samples. We find that the CAS parameters of paired galaxies are correlated with the projected separations of the pair. For the widest and closest pairs, the …
In the solar-neighbourhood, older stars have larger random velocities than younger ones. It is argued that the increase in velocity dispersion with time is predominantly a gradual process rather than one induced by discrete events such as minor mergers. Ephemeral spiral arms seem to be the fundamental drivers of disk heating, although scattering by giant molecular clouds plays an important moderating role. In addition to heating the disk, spiral arms cause stars' guiding centres to diffuse radially. The speed of this diffusion is currently controversial. Data from the Hipparcos satellite has m…
It is found that a previously thought-to-be well established result of density wave theory, that there is no interaction between a quasi-stationary spiral density wave and the basic state (i.e. the axisymmetric part) of the galactic disk, is in fact false. When solved as a nonlinear and globally self-consistent problem, the presence of non-axisymmetric patterns such as spirals or bars is shown to lead to significant interaction of the basic state and the density wave, with the net result being the simultaneous acquirement of a quasi-steady wave amplitude and the secular redistribution of disk …
We have done a robust statistical study of the behaviour of color profiles for 257 Sbc galaxies, having determined (B-V) and (U-B) color gradients, as well as color indices of bulges and disks separately. Applying a bidimensional decomposition technique to model the brightness profiles of bulges and disks, we obtained characteristic structural parameters for 39 galaxies. Among the main results obtained, we point out: 65% of the galaxies have negative color gradients (reddish inward), 25% have no gradients, and 10% show positive gradients; galaxies that show no color gradients tend to be barred…
In this paper, I mention a few processes which may play a role in the evolution of the central regions of galaxies. In this context, I briefly discuss some issues regarding the formation of bulges in spirals, the role of supermassive black holes, and the importance of nuclear density waves.
(Abridged) A robust analysis of galaxy structural parameters, based on the modeling of bulge and disk brightnesses in the BVRH bandpasses, is presented for 121 face-on and moderately inclined late-type spirals. Each surface brightness (SB) profile is decomposed into a sum of a generalized Sersic bulge and an exponential disk. The reliability and limitations of our bulge-to-disk (B/D) decompositions are tested with extensive simulations of galaxy brightness profiles (1D) and images (2D). Galaxy types are divided into 3 classes according to their SB profile shapes; Freeman Type-I and Type-II, an…
We have observed the nearby spiral galaxy NGC6503 using Chandra. Seven discrete sources associated with the galaxy have been found, one of them coincident with its Liner-starburst nucleus. One of the sources corresponds to a ULX with Lx >~ 10e39 ergs/s. Previous ROSAT observations of the galaxy show that this source has varied by at least a factor 3 in the last 6 years. No evidence is found for strong diffuse emission in the nuclear region or the presence of a low luminosity AGN.
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…
I present a brief review of some of the mid-infrared properties of interacting galaxies as these were revealed using observations from the Infrared Space Observatory and Spitzer Space Telescope over the last decade. The variation of the infrared spectral energy distribution in interacting galaxies can be used as an extinction free tracer not only of the location of the star formation activity but also of the physical mechanism dominating their energy production.
Galaxy evolution is in transition from an early universe dominated by hierarchical clustering to a future dominated by secular processes. These result from interactions involving collective phenomena such as bars, oval disks, spiral structure, and triaxial dark halos. This paper summarizes a review by Kormendy & Kennicutt (2004) using, in part, illustrations of different galaxies. In simulations, bars rearrange disk gas into outer rings, inner rings, and galactic centers, where high gas densities feed starbursts. Consistent with this picture, many barred and oval galaxies have dense central co…
We use data from the BIMA Survey of Nearby Galaxies (SONG) to investigate the relationship between ellipticity and central mass concentration in barred spirals. Existing simulations predict that bar ellipticity decreases as inflowing mass driven by the bar accumulates in the central regions, ultimately destroying the bar. Using the ratio of the bulge mass to the mass within the bar radius as an estimate of the central mass concentration, we obtain dynamical mass estimates from SONG CO 1-0 rotation curve data. We find an inverse correlation between bar ellipticity and central mass concentration…
Chandra is revolutionising our understanding of the X-ray emission from spiral galaxies. Before Chandra, detailed extragalactic studies were limited to Local Group galaxies. We are now able to obtain detailed inventories of sources in galaxies outside the Local Group, allowing population studies for the first time. In this review I will first discuss some intriguing observations of globular cluster sources in M31, then move outside the Local Group and summarise the observational properties of sources in several spiral galaxies (both bulge dominated and disk dominated). The X-ray colors and var…
In current $Λ$CDM galaxy formation scenarios, at least three physical phenomena could contribute to the mass assembly: monolithic collapse, hierarchical mergers and more quiescent external gas accretion, with secular evolution. The three processes are described, and their successes and problems are reviewed. It is shown that monolithic collapse is likely to be quite restricted to sub-components of galaxies, while the two main scenarii, hierarchical merging and secular evolution, might have comparable roles, depending on environment. Evidences are reviewed for the important role of gas accretio…
We present evidence for cosmological gas accretion onto spiral galaxies in the local universe. The accretion is seen through its effects on the dynamics of the extra-planar neutral gas. The accretion rates that we estimate for two nearby spiral galaxies are of the order of their star formation rates. Our model shows that most of the extra-planar gas is produced by supernova feedback (galactic fountain) and only 10-20 % comes from accretion. The accreting material must have low specific angular momentum about the disc's spin axis, although the magnitude of the specific angular-momentum vector c…
The data from a CO(1 - 0) mapping survey of 40 nearby spiral galaxies performed with the Nobeyama 45-m telescope are presented. The criteria of the sample selection were (1) RC3 morphological type in the range Sa to Scd, (2) distance less than 25 Mpc, (3) inclination angle less than 79deg (RC3), (4) flux at 100 um higher than ~ 10 Jy, (5) spiral structure is not destroyed by interaction. The maps of CO cover most of the optical disk of the galaxies. We investigated the influence of bar on the distribution of molecular gas in spiral galaxies using these data. We confirmed that the degree of cen…
We report subarcsecond-resolution VLA imaging of the centers of four nearby spiral galaxies: IC 342, Maffei II, NGC 2903, and NGC 6946. In each galaxy, 7 - 12 compact radio continuum sources were identified within the central 15" x 15". Slightly over half of the compact sources appear to be HII regions with flat or positive spectral indices (alpha >~ -0.1). The HII regions with rising spectra are optically thick at centimeter wavelengths, and thus dense (n_i ~ 10^4 cm^(-3)) and young. The largest of these HII regions require the excitation of 500 - 800 O stars, within regions of only few parse…
We present an analysis of the molecular gas distributions in the 29 barred and 15 unbarred spirals in BIMA SONG. For CO-bright galaxies, we confirm the conclusion by Sakamoto et al. (1999b) that barred spirals have higher molecular gas concentrations in the central kiloparsec. The SONG sample also includes 27 galaxies below the CO brightness limit used by Sakamoto et al. Even in these CO-faint galaxies we show that high central gas concentrations are more common in barred galaxies, consistent with radial inflow driven by the bar. However, there is a significant population of early-type (Sa--Sb…
This Supplementary Information provides details about the spectral extraction (crowding issues and the removal of nebular lines), a discussion about the distance to M33, a model for the O-star wind and the measurement of the true photospheric X-ray eclipse width Theta, and details about ellipsoidal modelling. It also contains five related figures, one related table, and additional references.
We present some preliminary results from new Chandra and XMM-Newton X-ray observations of the nearby barred spiral galaxy NGC1672. It shows dramatic nuclear and extra-nuclear star formation activity, including starburst regions located near each end of its strong bar, both of which host ultraluminous X-ray sources (ULXs). With the new high-spatial-resolution Chandra imaging, we show for the first time that NGC1672 possesses a faint ($L(X)~10^39 erg/s), hard central X-ray source surrounded by an X-ray bright circumnuclear starburst ring that dominates the X-ray emission in the region. The centr…
We have measured the intrinsic disk ellipticity for 7 nearby, nearly face-on spiral galaxies by combining Densepak integral-field spectroscopy with I-band imaging from the WIYN telescope. Initially assuming an axisymmetric model, we determine kinematic inclinations and position angles from H-alpha velocity fields, and photometric axis ratios and position angles from imaging data. We interpret the observed disparities between kinematic and photometric disk parameters in terms of an intrinsic non-zero ellipticity. The mean ellipticity of our sample is 0.05. If the majority of disk galaxies have …
We have done a robust statistical analysis of UBV color profiles of 257 Sbc barred and unbarred galaxies. We found that there is an excess of barred galaxies among the objects with null or positive (bluish inward) color gradients, which seems to indicate that bars act as a mechanism of homogenization of the stellar population along galaxies. Moreover, the relationship found between total and bulge colors shows that, in the process of homogenization, the stellar population of bulges are getting bluer, whereas the total color of galaxies remains the same. These characteristics are expected in a …
AIMS. To check whether the polar angle distribution of QSOs around nearby spiral galaxies is isotropic or not. METHODS. A statistical analysis of the polar angle distribution of large samples of QSOs from the SDSS survey and Monte Carlo simulations to calculate their significance are carried out. RESULTS. There is a clear excess of QSOs near the minor axis with respect to the major axis of nearby edge-on spiral galaxies, significant at a level 3.5-sigma up to angular distances of 3 deg. (or ~1.7 Mpc) from the centre of each galaxy. The significance is increased to 3.9-sigma with the z>0.5 QSOs…
Galaxy disks evolve through angular momentum transfers between sub-components, like gas, stars, or dark matter halos, through non axi-symmetric instabilities. The speed of this evolution is boosted in presence of a large fraction of cold and dissipative gas component. When the visible matter dominates over the whole disk, angular momentum is exchanged between gas and stars only. The gas is driven towards the center by bars, stalled transiently in resonance rings, and driven further by embedded bars, which it contributes to destroy. From a small-scale molecular torus, the gas can then inflow fr…
Today we have numerous evidences that spirals evolve dynamically through various secular or episodic processes, such as bar formation and destruction, bulge growth and mergers, sometimes over much shorter periods than the standard galaxy age of 10-15 Gyr. This, coupled to the known properties of the Hubble sequence, leads to a unique sense of evolution: from Sm to Sa. Linking this to the known mass components provides new indications on the nature of dark matter in galaxies. The existence of large amounts of yet undetected dark gas appears as the most natural option. Bounds on the amount of da…
During the course of a search for compact, isolated gas clouds moving with anomalous velocities in or near our own Galaxy (Braun and Burton 1998 A&A, in press), we have discovered, in the data of the Leiden/Dwingeloo survey (Hartmann and Burton 1997, Atlas of Galactic Neutral Hydrogen, CUP) of Galactic hydrogen, the HI signature of a large galaxy, moving at a recession velocity of 282 km/s, with respect to our Galaxy. Deep multicolor and spectroscopic optical observations show the presence of star formation in scattered HII regions; radio HI synthesis interferometry confirms that the galaxy is…
We have conducted a study of optical and HI properties of spiral galaxies (size, luminosity, H-alpha flux distribution, circular velocity, HI gas mass) to explore the role of gas stripping as a driver of morphological evolution in clusters. We find a strong correlation between the spiral and S0 fractions within clusters, and the spiral fraction scales tightly with cluster X-ray gas luminosity. We explore young star formation and identify spirals that are (1) asymmetric, with truncated H-alpha emission and HI gas reservoirs on the leading edge of the disk, on a first pass through the dense intr…
We are conducting a search for supermassive black holes (SMBHs) with masses below 10^7 M_sun by looking for signs of extremely low-level nuclear activity in nearby galaxies that are not known to be AGNs. Our survey has the following characteristics: (a) X-ray selection using the Chandra X-ray Observatory, since x-rays are a ubiquitous feature of AGNs; (b) Emphasis on late-type spiral and dwarf galaxies, as the galaxies most likely to have low-mass SMBHs; (c) Use of multiwavelength data to verify the source is an AGN; and (d) Use of the highest angular resolution available for observations in x…
Lynden-Bell & Kalnajs (1972) presented a useful formula for computing the long-range torque between spiral arms and the disk at large. The derivation uses second-order perturbation theory and assumes that the perturbation slowly grows over a very long time: the time-asymptotic limit. This formula has been widely used to predict the angular momentum transport between spiral arms and stellar bars between disks and dark-matter halos. However, this paper shows that the LBK time-asymptotic limit is not appropriate because the characteristic evolution time for galaxies is too close to the relevant d…
We present a statistical analysis of the largest X-ray survey of nearby spiral galaxies in which diffuse emission has been separated from discrete source contributions. Regression and rank-order correlation analyses are used to compare X-ray properties such as total, source and diffuse luminosities, and diffuse emission temperature, with a variety of physical and multi-wavelength properties, such as galaxy mass, type and activity, and optical and infrared luminosity. The results are discussed in terms of the way in which hot gas and discrete X-ray sources scale with the mass and activity of ga…
We report subarcsecond-resolution VLA imaging of four nearby spiral galaxies: IC 342, Maffei II, NGC 2903, and NGC 6946. In each galaxy, compact radio continuum sources are identified in the central ~ 15" x 15" region. These compact sources are responsible for 20 - 30 % of the total emission from the central kpc of the host galaxies at 2 cm, but only ~ 5 - 10 % at 6 cm. More than half of the compact sources appear to be HII regions. The HII regions with rising spectra must be fairly dense (n_i ~ 10^4 cm^(-3)) and are presumably very young. The largest of these HII regions require the excitatio…
We study the morphology-radius (MR-) and morphology-density (MD-) relations for a sample of about 850 galaxies (with M <= -19.5) in 23 clusters from the ENACS (ESO Nearby Abell Cluster Survey). On the basis of their radial distributions we must distinguish: 1. brightest ellipticals (with M < -22), 2. late spirals, and 3. the ensemble of less bright ellipticals, S0 galaxies and early spirals. The latter have indistinguishable distributions of projected radial distance R. The brightest ellipticals are most centrally concentrated, the late spirals are almost absent from the central regions and th…
In this review, I highlight a number of recent surveys of molecular gas in nearby spiral galaxies. Through such surveys, more complete observations of the distribution and kinematics of molecular gas have become available for galaxies with a wider range of properties (e.g., brightness, Hubble type, strength of spiral or bar structure). These studies show the promise of both interferometers and single-dish telescopes in advancing our general understanding of molecular gas in spiral galaxies. In particular, I highlight the contributions of the recent BIMA Survey of Nearby Galaxies (SONG).
(Abridged) We present a detailed study of the relation between circumnuclear dust morphology, host galaxy properties, and nuclear activity in nearby galaxies. We use our sample of 123 nearby galaxies with visible--near-infrared colormaps from the Hubble Space Telescope to create well-matched, "paired" samples of 28 active and 28 inactive galaxies, as well as 19 barred and 19 unbarred galaxies, that have the same host galaxy properties. Comparison of the barred and unbarred galaxies shows that grand design nuclear dust spirals are only found in galaxies with a large-scale bar. Tightly wound nuc…
Narrow-band H-alpha+[NII] and broadband R images and surface photometry are presented for a sample of 29 bright (M_B < -18) isolated S0-Scd galaxies within a distance of 48 Mpc. These galaxies are among the most isolated nearby spiral galaxies of their Hubble classifications as determined from the Nearby Galaxies Catalog (Tully 1987a).
Ionized gas and stellar kinematics have been measured along the major axes of seventeen nearby spiral galaxies of intermediate to late morphological type. We discuss the properties of each sample galaxy distinguishing between those characterized by regular or peculiar kinematics. In most of the observed galaxies ionized gas rotates more rapidly than stars and have a lower velocity dispersion, as is to be expected if the gas is confined in the disc and supported by rotation while the stars are mostly supported by dynamical pressure. In a few objects, gas and stars show almost the same rotationa…
We have conducted a study of optical and HI properties of spiral galaxies (size, luminosity, H-alpha flux distribution, circular velocity, HI gas mass) to investigate causes (e.g., nature versus nurture) for variation within the cluster environment. We find HI deficient cluster galaxies to be offset in Fundamental Plane space, with disk scale lengths decreased by a factor of 25%. This may be a relic of early galaxy formation, caused by the disk coalescing out of a smaller, denser halo (e.g., higher concentration index) or by truncation of the hot gas envelope due to the enhanced local density …
We explore the secular dynamical evolution of an N-body model of M31 in the presence of a population of 100 dark matter satellites over 10 Gyr. The satellite population has structural and kinematic characteristics modelled to follow the predictions of Lambda-CDM cosmological simulations. Vertical disk heating is a small effect despite many interactions with the satellite population with only a 20% increase in vertical velocity dispersion sigma_z and the disk scale height z_d at the equivalent solar radius R = 2.5R_d . However, the stellar disk is noticeably flared after 10 Gyr with z_d nearly …
A survey of 329 nearby galaxies (redshift z < 0.045) has been conducted to study the distribution of mass and light within spiral galaxies over a range of environments. The 18 observed clusters and groups span a range of richness, density, and X-ray temperature, and are supplemented by a set of 30 isolated field galaxies. Optical spectroscopy taken with the 200-inch Hale Telescope provides separately resolved H-alpha and [NII] major axis rotation curves for the complete set of galaxies, which are analyzed to yield velocity widths and profile shapes, extents and gradients. HI line profiles prov…
It is an observational fact that bulges of spiral galaxies contain a high fraction of old and metal-rich stars. Following this observational fact, we have investigated colors of 21 bulges hosted by a selected sample of high surface brightness spirals and low surface brightness galaxies observed in B and R optical bands and in J and Ks near-IR bands. Using structural parameters derived from these observations we obtain evidence that bulges could be formed by pure disk evolution (secular evolution), in agreement with the suggestion by some authors. The color profiles, especially the near-IR ones…
Within the hierarchical framework for galaxy formation, merging and tidal interactions are expected to shape large galaxies to this day. While major mergers are quite rare at present, minor mergers and satellite disruptions - which result in stellar streams - should be common, and are indeed seen in both the Milky Way and the Andromeda Galaxy. As a pilot study, we have carried out ultra-deep, wide-field imaging of some spiral galaxies in the Local Volume, which has revealed external views of such stellar tidal streams at unprecedented detail, with data taken at small robotic telescopes (0.1-0.…
(Abridged) We have compared H-alpha and far ultraviolet (FUV) images of 10 nearby spirals, with the goal of understanding the contribution of field OB stars to the ionization of the diffuse ionized gas (DIG) in spiral galaxies. The FUV images were obtained by the Ultraviolet Imaging Telescope (UIT) and the H-alpha images were obtained using various ground-based telescopes. In all of the galaxies, the F_H-alpha/F_UIT flux ratio is lower in the DIG than in the HII regions. This is likely an indication that the mean spectral type for OB stars in the field is later than that in HII regions. Compar…
We observed several nearby face-on spiral galaxies with the ROSAT PSPC to study their 0.1-2.0 keV diffuse emission. After the exclusion of resolved discrete sources, there is unresolved X-ray emission in all the galaxies observed. Since this emission is a combination of diffuse emission and a contribution from unresolved point sources, it represents an upper limit to the truly diffuse soft X-ray emission. The derived upper limits on the diffuse emission can be interpreted in terms of upper limits to the average intensity of a putative hot halo. They can also be used to derived limits to the to…
A model that computes the secular evolution of a gravitating disk-planet system is developed. The disk is treated as a set of gravitating rings, with the rings'/planets' time-evolution governed by the classical Laplace-Lagrange solution for secular evolution but modified to account for the disk's finite thickness h. This system's Lagrange planetary equations yield a particular class of spiral wave solutions, usually denoted as apsidal density waves and nodal bending waves. There are two varieties of apsidal waves:long waves and short waves. Planets typically launch long density waves at the di…
We investigate the relations among the stellar continuum-subtracted 8 micron polycyclic aromatic hydrocarbon (PAH 8 micron) emission, 24 micron hot dust emission, and 160 micron cold dust emission in fifteen nearby face-on spiral galaxies in the Spitzer Infrared Nearby Galaxies Survey sample. The relation between PAH 8 and 24 micron emission measured in ~2 kpc regions is found to exhibit a significant amount of scatter, and strong spatial variations are observed in the (PAH 8 micron)/24 micron surface brightness ratio. In particular, the (PAH 8 micron)/24 micron surface brightness ratio is obs…
We present an exploratory survey of the central regions of the nearby spiral galaxies Dwingeloo 1 and Dwingeloo 2 made in the CO J=2->1 line at 230GHz using the James Clerk Maxwell Telescope. In Dwingeloo 1, which is probably the nearest grand-design barred spiral, the CO emission was sampled along a cross with its major axis aligned with the bar. The CO emission is an order of magnitude weaker (peak Tmb=~70mK) than in its neighbours IC 342 and Maffei 2 and appears to be confined to the nucleus, bar, and spiral arms. In Dwingeloo 2, a small system quite likely to be a companion of Dw1, a 3-sig…
We present first results from an HST/ACS imaging survey of stars and star clusters in five nearby spiral galaxies. This contribution concentrates on NGC 1313, a highly distorted late-type barred spiral. We compare the field star and cluster formation histories in our three ACS pointings for this galaxy. In one pointing, both the cluster and field star age distributions show clear evidence for a ramp-up in the star formation rate about 100 Myrs ago.
We report the analysis of deep radio observations of the interacting galaxy system M51 from the Very Large Array, with the goal of understanding the nature of the population of compact radio sources in nearby spiral galaxies. We detect 107 compact radio sources, 64% of which have optical counterparts in a deep H$α$ Hubble Space Telescope image. Thirteen of the radio sources have X-ray counterparts from a {\em Chandra} observation of M51. We find that six of the associated H$α$ sources are young supernova remnants with resolved shells. Most of the SNRs exhibit steep radio continuum spectral ind…
We use available multifilter Hubble Space Telescope (HST) WFPC2 imaging of five (M81, M83, NGC 6946, M101, and M51) low inclination, nearby spiral galaxies to study ancient star cluster populations. M81 globular clusters (GC) have an intrinsic color distribution which is very similar to those in the Milky Way and M31, with ~40% of the clusters having colors expected for a metal-rich population. On the other hand, the GC system in M51 appears almost exclusively blue and metal poor. This lack of metal-rich GCs associated with the M51 bulge indicates that the bulge formation history of this Sbc g…
We identify nearby disk galaxies with optical structural parameters similar to those of intermediate-redshift compact blue galaxies. By comparing HI and optical emission-line widths, we show that the optical widths substantially underestimate the true kinematic widths of the local galaxies. By analogy, optical emission-line widths may underrepresent the masses of intermediate-z compact objects. For the nearby galaxies, the compact blue morphology is the result of tidally-triggered central star formation: we argue that interactions and minor mergers may cause apparently compact morphology at hi…
The first results of an observational programme aimed at mapping a sample of face--on spiral galaxies in the NIR are presented. This paper shows the surface photometry of the first ten galaxies in the sample. The data were taken in the broad band $J$ (1.2 $μ$m) and $K_{s}$ (2.2 $μ$m) filters. The sources were selected mainly according to their size and brightness in order to suit the characteristics of the CAIN 2D NIR camera on the 1.5 m Carlos Sánchez Telescope (Tenerife, Spain). The primary scientific goal is to provide a comprehensive and uniform database of the main structural and photomet…
We present K'(2.1 micron) observations of four nearby flocculent spirals, which clearly show low-level spiral structure and suggest that kiloparsec-scale spiral structure is more prevalent in flocculent spirals than previously supposed. In particular, the prototypical flocculent spiral NGC 5055 is shown to have regular, two-arm spiral structure to a radius of 4 kpc in the near infrared, with an arm-interarm contrast of 1.3. The spiral structure in all four galaxies is weaker than that in grand design galaxies. Taken in unbarred galaxies with no large, nearby companions, these data are consiste…
Deep surveys conducted during the past decades have shown that galaxies in the distant universe are generally of more irregular shapes, and are disky in appearance and in their star formation rate, compared to galaxies in similar environments in the nearby universe. Given that the merger rate between z=2 and the local universe is far from adequate to account for this observed morphological transformation rate, an internal mechanism for the morphological transformation of galaxies is to be sought, whose operation can be further aided by environmental factors. The secular evolution mechanism, es…
We present high resolution BV images of 12 edge-on spiral galaxies observed with the WIYN 3.5-m telescope. These images were obtained to search for extraplanar (|z| > 0.4 kpc) absorbing dust structures similar to those previously found in NGC 891 (Howk & Savage 1997). Our imaged galaxies include a sample of seven massive L_*-like spiral galaxies within D<25 Mpc that have inclinations i > 87 deg from the plane of the sky. We find that five of these seven systems show extraplanar dust, visible as highly-structured absorbing clouds against the background stellar light of the galaxies. The more pr…
I present recent observations and analyses of star cluster formation in a wide variety of environments -- from young star clusters and super star clusters in normal actively star-forming spirals and irregulars to starbursting dwarfs and spiral-spiral mergers. Star cluster formation in interacting galaxies can be restricted to central starburst region, extend over the entire body of the merger, or even all along extended tidal structures. I address methods and results for the determination of star cluster ages, metallicities, masses, and sizes and discuss the nature, possible lifetimes and futu…
