Strong magnetic spiral pattern in a ringed galaxy NGC4736
Krzysztof T. Chyzy, Ronald J. Buta
备注：
2 pages, 1 figure, To appear in the proceedings of IAU Symposium 245, "Formation and Evolution of Galaxy Bulges," M. Bureau, E. Athanassoula, and B. Barbuy, eds
We present high sensitivity radio polarimetric (VLA) observations of a galaxy with strong orbital resonances - NGC4736. The total radio intensity at 8.4GHz covers smoothly the whole galaxy bulge and reveals a distinct ring of radio emission closely related to the ring morphology visible in infrared, CO and Halpha emission. However, the magnetic field reveals a very coherent spiral pattern. The magnetic field vectors are crossing the inner starbursting ring, the dust lanes within the ring and other rather circularly shaped features visible in other gas traces. Either the magnetic field uncovers the pattern of gas motions not seen in other spectral ranges, or the spiral magnetic field is of a pure dynamo origin, ignoring the ringed morphology of the galaxy.
The intriguing nearly face-on southern ringed spiral galaxy NGC 4622, the first galaxy definitively shown to have leading spiral structure, is revisited in this paper with new images from the Hubble Space Telescope's WFPC2, together with ground-based optical and near-IR imaging, and a Fabry-Perot H-alpha velocity field. The data provide new information on the disk/bulge/halo mix, rotation curve, star formation in the galaxy, and the sense of winding of its prominent spiral arms. Previously, we suggested that the weaker, inner single arm most likely has the leading sense, based on a numerical s…
Surface photometry and a 21cm HI line spectrum of the giant double-ringed galaxy ESO 474-G26 are presented. The morphology of this system is unique among the 30,000 galaxies with >B15. Two almost orthogonal optical rings with diameters of 60 and 40 kpc surround the central body (assuming H0=70 km/s/Mpc). The outer one is an equatorial ring, while the inner ring lies in a nearly polar plane. The rings have blue optical colors typical of late-type spirals. Both appear to be rotating around the central galaxy, so that this system can be considered as a kinematically confirmed polar ring galaxy. I…
We present CO(1-0) and CO(2-1) maps of the LINER galaxy NGC7217, obtained with the IRAM interferometer, at 2.4"x1.9" and 1.2"x0.8" resolution respectively. The nuclear ring (at r=12"=0.8kpc) dominates the CO maps, and has a remarkable sharp surface density gradient at its inner edge. The latter is the site of the stellar/Halpha ring, while the CO emission ring extends farther or is broader (500-600pc). This means that the star formation has been more intense toward the inner edge of the CO ring, in a thin layer, just at the location of the high gas density gradient. In the CO(2-1) map, a centr…
Outer rings are located at the greatest distance from the galaxy center of any feature resonant with a bar. Because of their large scale, their morphology is sensitive to the distribution of the dark matter in the galaxy. We introduce here how study of these rings can constrain the mass-to-light ratio of the bar, and so the percentage of dark matter in the center of these galaxies. We compare periodic orbits integrated in the ringed galaxy NGC 6782 near the outer Lindblad resonance to the shape of the outer ring. The non-axisymmetric component of the potential resulting from the bar is derived…
We have made observations of the \ion{H}{1} in the southern ringed barred spiral galaxies NGC~1433 and NGC~6300 with the Australia Telescope Compact Array (ATCA), the main goal being to test the resonance theory for the origin of these rings. NGC~1433 is the prototypical ringed barred spiral, and displays distinct \ion{H}{1}~counterparts to its nuclear ring, inner ring, outer pseudoring, and plume-like features. The $L_{4}$ and $L_{5}$ regions at corotation, as well as the bar itself, are relatively devoid of neutral atomic hydrogen. By associating the inner ring of NGC~1433 with the inner sec…
We present CO(1-0) and CO(2-1) maps of the Seyfert galaxy NGC 7217, obtained with the IRAM interferometer, at 3" and 1.5" resolution respectively. The nuclear ring (at r=12"=0.8kpc) is predominant in the CO maps, with a remarkable surface density gradient between the depleted region inside the ring and the inner border of the ring. The CO nuclear ring is significantly broader (500-600pc) than the dust lane ring. The CO(2-1)/CO(1-0) ratio is around 1, typical of optically thick gas with high density. The overall morphology of the ring is quite circular, with no evidence of non-circular velociti…
We propose a theory to explain the formation of both spirals and rings in barred galaxies using a common dynamical framework. It is based on the orbital motion driven by the unstable equilibrium points of the rotating bar potential. Thus, spirals, rings and pseudo-rings are related to the invariant manifolds associated to the periodic orbits around these equilibrium points. We examine the parameter space of three barred galaxy models and discuss the formation of the different morphological structures according to the properties of the bar model. We also study the influence of the shape of the …
We analyze the gas kinematics and star formation properties of the nearby RSab galaxy NGC 4736 using interferometric and single-dish CO(1-0) data and previously published Halpha and HI data. The CO morphology is dominated by a central molecular bar and tightly wound spiral arms associated with a bright ring of star formation. Strong HI emission is also found in the ring, but HI is absent from the central regions. Comparison of the HI and Halpha distributions suggests that HI in the ring is primarily dissociated H$_2$. Modeling of the CO kinematics reveals gas motion in elliptical orbits around…
M94 (NGC 4736) is investigated using images from the Ultraviolet Imaging Telescope (FUV-band), Hubble Space Telescope (NUV-band), Kitt Peak 0.9-m telescope (H-alpha, R, and I bands), and Palomar 5-m telescope (B-band), along with spectra from the International Ultraviolet Explorer and Lick 1-m telescopes. The wide-field UIT image shows FUV emission from (a) an elongated nucleus, (b) a diffuse inner disk, where H-alpha is observed in absorption, (c) a bright inner ring of H II regions at the perimeter of the inner disk (R = 48 arcsec. = 1.1 kpc), and (d) two 500-pc size knots of hot stars exter…
In this and in a previous paper (Romero-Gomez et al. 2006) we propose a theory to explain the formation of both spirals and rings in barred galaxies using a common dynamical framework. It is based on the orbital motion driven by the unstable equilibrium points of the rotating bar potential. Thus, spirals, rings and pseudo-rings are related to the invariant manifolds associated to the periodic orbits around these equilibrium points. We examine the parameter space of three barred galaxy models and discuss the formation of the different morphological structures according to the properties of the …
We report the discovery of a coherent magnetic spiral structure within the nearby ringed Sab galaxy NGC 4736. High sensitivity radio polarimetric data obtained with the VLA at 8.46GHz and 4.86GHz show a distinct ring of total radio emission precisely corresponding to the bright inner pseudoring visible in other wavelengths. However, unlike the total radio emission, the polarized radio emission reveals a clear pattern of ordered magnetic field of spiral shape, emerging from the galactic centre. The magnetic vectors do not follow the tightly-wrapped spiral arms that characterize the inner pseudo…
Among 330 normal spirals of types Sa-Sc the fraction of objects exhibiting ``ring'', ``intermediate'' and ``spiral'' arm varieties does not correlated with environment. A similar conclusion appears to apply to the arm varieties of 123 barred spirals of types SBa-SBc. It is concluded that, among the northern Shapley-Ames galaxies, the distinction between the spiral and ring varieties of spiral arms is, within the accuracy of presently available data, independent of galaxy environment. This result suggests that the detailed morphology of spiral arms depends primarily on parent galaxy characteris…
The environmental dependencies of the characteristics of spiral galaxy rotation curves are studied in this work. We use our large, homogeneously collected sample of 510 cluster spiral galaxy rotation curves to test the claim that the shape of a galaxy's rotation curve strongly depends on its location within the cluster, and thus presumably on the strength of the local intracluster medium and on the frequency and strength of tidal interactions with the cluster and cluster galaxies. Our data do not corroborate such a scenario, consistent with the fact that Tully-Fisher residuals are independent …
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 best-fitting B, R, I and K-band (Sersic R^(1/n) bulge + exponential disk) model parameters for the de Jong & van der Kruit (1994) sample of 86 spiral galaxies are made electronically available. This sample covers all spiral galaxy types and provides the largest homogeneous set of structural parameters for spiral galaxies modeled with an R^(1/n) bulge.
We present the 2-D photometric decomposition of the Virgo galaxy IC3328. The analysis of the global light distribution of this morphologically classified nucleated dwarf elliptical galaxy (dE1,N) reveals a tightly wound, bi-symmetric spiral structure with a diameter of 4.5 kpc, precisely centered on the nucleus of the dwarf. The amplitude of the spiral is only three percent of the dwarf's surface brightness making it the faintest and smallest spiral ever found in a galaxy. In terms of pitch angle and arm winding the spiral is similar to the intermediate-type galaxy M51, but it lacks the dust a…
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.
The spiral pattern of the Galaxy identified by analyzing the kinematics of young stars within 3 kpc of the Sun is Fourier decomposed into spiral harmonics. The spiral pattern of the Galaxy is shown to be representable as a superposition of trailing and leading waves with interarm distances of 1.8(+/-0.4) kpc and 4(+/-2) kpc, respectively. Shock waves are probably present only in the portions of the trailing spiral pattern where it crosses the crest of the leading wave. The small interarm distance of the trailing spiral wave (1.8 kpc) can be explained by its evolution - by the decrease in the i…
We present the near-infrared and optical properties of the peculiar galaxy ESO 235-G58, which resembles a late-type ringed barred spiral seen close to face-on. However, the apparent bar of ESO 235-G58 is in reality an edge-on disk galaxy of relatively low luminosity. We have analyzed the light and color distributions of ESO 235-G58 in the NIR and optical bands and compared them with the typical properties observed for other morphological galaxy types, including polar ring galaxies. Similar properties are observed for ESO 235-G58, polar ring galaxies, and spiral galaxies, which leads us to conc…
Observations with the Hubble Space Telescope reveal an irregular network of dust spiral arms in the nuclear region of the interacting disk galaxy NGC 2207. The spirals extend from ~50 pc to ~300 pc in galactocentric radius, with a projected width of ~20 pc. Radiative transfer calculations determine the gas properties of the spirals and the inner disk, and imply a factor of ~4 local gas compression in the spirals. The gas is not strongly self-gravitating, nor is there a nuclear bar, so the spirals could not have formed by the usual mechanisms applied to main galaxy disks. Instead, they may resu…
Hot gaseous haloes surrounding galaxies and extending well beyond the distribution of stars are a ubiquitous prediction of galaxy formation scenarios. The haloes are believed to consist of gravitationally trapped gas with a temperature of millions of Kelvin. The existence of such hot haloes around massive elliptical galaxies has been established through their X-ray emission. While gas out-flowing from starburst spiral galaxies has been detected, searches for hot haloes around normal, quiescent spiral galaxies have so far failed, casting doubts on the fundamental physics in galaxy formation mod…
We present new Hubble Space Telescope images of the gravitational lens PKS 1830-211, which allow us to characterize the lens galaxy and update the determination of the Hubble constant from this system. The I-band image shows that the lens galaxy is a face-on spiral galaxy with clearly delineated spiral arms. The southwestern image of the background quasar passes through one of the spiral arms, explaining the previous detections of large quantities of molecular gas and dust in front of this image. The lens galaxy photometry is consistent with the Tully-Fisher relation, suggesting the lens galax…
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…
Using a variety of parameters of local galaxy density, we have examined the effects of the environmental density on the presence of bar structures in spiral galaxies of various morphological types. For an extensive sample of nearby galaxies, listed in the ``Nearby Galaxies Catalogue'' (Tully, 1988a), we have found that the spirals characterized by a high local density tend to be barred if they are early-type and early-type if they are barred (at the significance level of $\sim$3 sigma), confirming some earlier suggestion of low statistical significance. This fact, which is observed substantial…
This is the second of two papers based on a systematic multi-wavelength (X, B, H, 12$μ$m, FIR, 6cm) statistical analysis of the {\it Einstein Observatory Galaxy Catalog} sample of 234 `normal' S0/a-Irr galaxies. This sample is representative of spiral galaxies (Paper I), and its wide wavelength coverage provides a unique opportunity for a systematic exploration of the relations among different emission bands, that can give novel insight on the different emission processes and their relation to galaxian components, as a function of galaxy morphology.
Here we report the detection, in Halpha emission, of a radial corrugation in the velocity field of the spiral galaxy NGC 5427. The central velocity of the Halpha line displays coherent, wavy-like variations in the vicinity of the spiral arms. The spectra along three different arm segments show that the maximum amplitude of the sinusoidal line variations are displaced some 500 pc from the central part of the spiral arms. The peak blueshifted velocities appear some 500 pc upstream the arm, whereas the peak redshifted velocities are located some 500 pc downstream the arm. This kinematical behavio…
Using the B-I color index in the radial photometry of M51, applied to defined azimuthal sectors, we reveals asymmetries in the shape of the density pattern of the galactic arms. The anomalous shape is present only in the side close to the companion and not in the far side. Two more non-interacting check-spirals do not show similar behaviour. The anomalous sawtooth-like shape is similar to that produced by a progressive wave propagating in a preexisting density pattern. In this hypothesis we have to conclude that the galaxy M51 could be a spiral galaxy formerly, i.e. before the encounter with t…
We have detected diffuse soft X-ray emission (0.4-1 keV) from the disk of the spiral galaxy NGC 2403 with Chandra. This diffuse emission (with a total luminosity of 2.1 x 10^38 erg/s and a gas temperature of 2-8 x 10^6 K) is well separated from the numerous bright point sources. NGC 2403 is a luminous spiral galaxy with a high rate of star formation. Recent HI observations have revealed an extended HI halo with anomalous velocities and a general inflow towards the central regions of the galaxy. This result and the present detection of a diffuse, hot X-ray emitting gas point at a very active di…
The velocity field of the nearly face-on galaxy NGC 3631, derived from observations in the H alpha line and the HI radio line, is analysed to study perturbations related to the spiral structure of the galaxy. We confirm our previous conclusion that the line-of-sight velocity field gives evidence of the wave nature of the observed two-armed spiral structure. Fourier analysis of the observed velocity field is used to determine the location of corotation of the spiral structure of this galaxy, and the radius of corotation R_c is found to be about 42 arcsec, or 3.2 kpc. The vector velocity field o…
We present new results from our comprehensive comparative survey of two massive, intermediate redshift galaxy clusters, Cl0024+17 (z=0.39) and MS0451-03 (z=0.54). We identify and study several key classes of `transition objects' whose stellar populations or dynamical states indicate a recent or ongoing change in morphology and star formation rate. For the first time, we have been able to conclusively identify spiral galaxies in the process of transforming into S0 galaxies. This has been accomplished by locating both spirals whose star formation is being quenched as well as their eventual succe…
Spiral arm modulation in NGC 4062 (an optical flocculent) is detected for the first time; the Fourier spectra of NGC 4062 and NGC 5248 (a classic grand design in optical images) are almost identical.
Leading spiral arms are a rare phenomenon. We present here one of the very few convincing candidates of spiral arms opening counter-intuitively in the same direction as the galaxy disk is rotating. This detection in a luminous IR galaxy (LIRG) IRAS 18293-3134 is based on near infrared (NIR) adaptive optics imaging with the Very Large Telescope and long-slit NIR spectroscopy with the Anglo-Australian Telescope. We discuss the orientation of the galaxy based on imaging and derive rotation curves from both emission and absorption features in the spectrum. The galaxy is strongly star-forming and h…
CCD observations in V, I and H$_α$ for NGC 3389 are used to present photometry of 61 HII regions. Their $α$ and $δ$ positions, diameters and their absolute luminosities have been determined. The luminosity and size distribution functions of the HII regions in NGC 3389 are discussed.
We have analyzed high velocity resolution HI synthesis observations of the nearly face-on Sc galaxy NGC 1232. The neutral gas distribution extends well beyond the optical extent of the galaxy. As expected, local peaks in the HI column density are associated with the spiral arms. Further, the HI column density drops precipitously near the center of the galaxy. Closed contours in the velocity field suggest either that the system is warped, or that the rotation curve declines. The velocity dispersion is approximately constant throughout the system, with a median value of 9.9 +/- 1.8 km/s. When co…
A scalar potential model (SPM) was developed from considerations of galaxy clusters and of redshift. The SPM is applied to HI rotation curves (RCs) and RC asymmetry of spiral galaxies. The resulting model adds the force of a scalar potential of the host galaxy and of neighboring galaxies to the Newtonian rotation velocity equation. The RC is partitioned radially into regions. The form of the equation for each parameter of each region is the same with differing proportionality constants. Integer values of each equation are determined empirically for each galaxy. Among the sample galaxies, the g…
Aims. Falomo et al. (2005) discovered a disk-like galaxy at ~ 1.2 arcsec from the QSO Q0045-3337 by means of ESO VLT adaptive optics. They estimated a galaxy Einstein radius (for a point mass) of comparable size, thus pointing up the existence of a new, rare, spiral lens candidate, despite no evident image splitting. Here we discuss the possible lensing effect of the galaxy in some more detail. Methods. We performed two dimensional surface photometry on the VLT image of the galaxy, confirming its spiral nature. We then verified if simple mass models, partially constrained by observational data…
We present the results of a Hubble Space Telescope and ground-based optical and near-infrared study to identify progenitors of spirals and ellipticals at z > 1. We identify these systems through photometric and spectroscopic redshifts, deep K-band imaging, stellar mass measurements, and high resolution imaging. The major modes of galaxy formation, including major mergers, minor mergers, and accretion of intergalactic gas, and their relative contributions towards building up the stellar masses of galaxies, can now be directly measured using these data.
We present neutral hydrogen observations of the nearby edge-on spiral galaxy NGC891 which show extended extra-planar emission up to distances of 15 kpc from the plane. 3D modeling of the galaxy shows that this emission comes from halo gas rotating more slowly than the gas in the disk.We derive the rotation curves of the gas above the plane and find a gradient in rotation velocity of -15 km/s/kpc. We also present preliminary results of a galactic fountain model applied to NGC891.
We have obtained ground-based I, J and K band images of the spiral galaxy, Messier 74 (NGC 628). This galaxy has been shown to possess a circumnuclear ring of star formation from both near-infrared spectroscopy of CO absorption and sub-millimetre imaging of CO emission. Circumnuclear rings of star formation are believed to exist only as a result of a bar potential. In this paper we show evidence for a weak oval distortion in the centre of M74. We use the results of Combes & Gerin (1985) to suggest that this weak oval potential is responsible for the circumnuclear ring of star formation observe…
New high resolution, high sensitivity WSRT HI synthesis observations of the spiral galaxy NGC 3631 are presented. In the total atomic hydrogen map, the spiral arms are well distinguished from the interarm regions, while the sensitivity allows detection of HI in all but a few isolated regions of the areas between the spiral arms. Most of the atomic hydrogen is located within the optical disc, but the HI extends to some 1.5R_opt. The HI follows the spiral arms, and streaming motions of up to ~15 kms (projected) can be identified from the velocity field. Assuming a constant inclination angle of 1…
We examine the present-day galaxy disk colors and star formation rates (SFRs) in the semi-analytic model of Cole et al. (2000). We find that the fiducial model is a good match to Kennicutt's (1998) observed global star formation law, the color-based metallicity-magnitude correlation and the colors of low-luminosity galaxies. The main limitation of the model, from the point of view of present-day spirals, is that the optical colors of the disks of very luminous spiral galaxies are too blue, even after accounting for the effects of dust.
We have carried out the wind analysis of six A-type supergiants in NGC 300. The derived Wind Momentum-Luminosity Relationship is compared with that of Galactic and M31 blue supergiants and with theoretical models.
The presence of unseen halos of ``dark matter'' has long been inferred from the high rotation speeds of gas and stars in the outer parts of spiral galaxies$^{1}$. The volume density of this dark matter decreases less quickly from the galactic center than does that of the luminous mass (such as that in stars), meaning that the dark matter dominates the mass far from the center$^{1,2}$. While searching for faint starlight away from the plane of the edge-on disk galaxy \gal$^{3}$, we have found that the galaxy is surrounded by a faint luminous halo. The intensity of light from this halo falls les…
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…
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 …
We investigate the effects of the gravitomagnetic corrections to the usual gravitational lens quantities for a specific lensing mass distribution modelled after spiral galaxies. An exponential disk is embedded into two different spherical halo models where disk and haloes parameters are fixed according to the observed mass to light ratios, galaxy magnitudes and rotation curves. The general expressions for the lensing deflection angle are given also taking into account the orientation of the galaxy disk plane with respect to the lens plane. It is found that the gravitomagnetic term changes the …
Deep Effelsberg HI spectra of the one-armed, bright Virgo cluster spiral galaxy NGC 4254 are presented.Five different positions were observed in the 21 cm HI line with the Effelsberg 100-m telescope: one in the center and 4 located one HPBW to the NE, NW, SW, and SE, respectively, from the galaxy center. The spectra are compared to existing deep VLA observations, and the single dish and interferometric HI data are used to constrain a dynamical model which includes the effects of ram pressure. The peculiar, one-armed spiral pattern of NGC 4254 and its distorted and kinematically perturbed atomi…
Recently, it has been shown that a correlation exists between the rate of shear and the spiral arm pitch angle in disk galaxies. The rate of shear depends upon the shape of the rotation curve, which is dependent upon the mass distribution in spiral galaxies. Here, we present an imporoved correlation between shear rate and spiral arm pitch angle, by increasing the sample size. We also use an adiabatic infall code to show that the rate of shear is most strongly correlated with the central mass concentration, c_m. The spin parameter, $λ$, and the fraction of baryons that cool, F, cause scatter in…
We simulated the behavior of interstellar gas clouds in a companion galaxy during a gas-dynamical interaction with the halo and disk of a spiral galaxy. By ram pressure, the gas clouds are stripped from the companion, and accreted to ward the disk of the spiral galaxy. If the companion's orbit is retrograde with respect to the rotation of the spiral galaxy, infalling clouds hit the nuclear region. Angular momentum transfer causes disruption of the inner gaseous disk, and makes a void of interstellar gas in the bulge. If the companion's orbit is either prograde or polar, infalling clouds are ac…
The results of $H_α$ and [NII]$λ6583$ observations of the spiral galaxy NGC 1084 at the SAO 6m telescope with a Fabry-Perot interferometer are presented. The complex structure of the emission line profile has revealed the presence of giant star formation regions (``spur'') in the NE part of the galaxy. In this region the $H_α$ line shows two distinct components, with line-of-sight velocity differences of $\pm(100-150)\km$. The first component corresponds to normal circular rotation. The second velocity component may be a signature of non-circular motions of the ionized gas in shock wave fronts…
The apparent shapes of spiral galaxies in the 2-Micron All Sky Survey Large Galaxy Atlas are used to constrain the intrinsic shape of their disks. When the distribution of apparent axis ratios is estimated using a nonparametric kernel method, the shape distribution is inconsistent with axisymmetry at the 90% confidence level in the B band and at the 99% confidence level in the K band. If spirals are subdivided by Hubble type, the late-type spirals (Sc and later) are consistent with axisymmetry, while the earlier spirals are strongly inconsistent with axisymmetry. The distribution of disk ellip…
We present 21-cm line observations of the spiral galaxy NGC 4559, made with the Westerbork Synthesis Radio Telescope. We have used them to study the HI distribution and kinematics, the relative amount and distribution of luminous and dark matter in this galaxy and, in particular, the presence of extra-planar gas. Our data do reveal the presence of such a component, in the form of a thick disk, with a mass of 5.9 x 10^8 Mo (one tenth of the total HI mass) and a mean rotation velocity 25-50 km/s lower than that of the thin disk. The extra-planar gas may be the result of galactic fountains but ac…
We report the discovery of two symmetric spiral arms in the near-infrared (NIR) images of the starburst galaxy M82. The spiral arms are recovered when an axi-symmetric exponential disk is subtracted from the NIR images. The arms emerge from the ends of the NIR bar and can be traced up to three disk scalelengths. The winding of the arms is consistent with an m=2 logarithmic spiral mode of pitch angle 14 degrees. The arms are bluer than the disk in spite of their detection on the NIR images. If the northern side of the galaxy is nearer to us, as is normally assumed, the observed sense of rotatio…
We have observed the emission-line kinematics and photometry of a southern triplet of galaxies. The triplet contains a giant spiral galaxy AM 1934-563 which optical structure resembles a polar-ring galaxy: distorted spiral disk, seen almost edge-on, and a faint large-scale (45 kpc in diameter) warped structure, inclined by 60^o-70^o with respect to the disk major axis. The triplet shows relatively small velocity dispersion (69 km/s) and a large crossing time (0.17 in units of the Hubble time). The disk of AM 1934-563 demonstrates optical colors typical for an early-type spirals, strong radial …
With the aim of studying the nonlinear stellar and gaseous response to the gravitational potential of a galaxy such as the Milky Way, we have modeled 3D galactic spiral arms as a superposition of inhomogeneous oblate spheroids and added their contribution to an axisymmetric model of the Galactic mass distribution. Three spiral loci are proposed here, based in different sets of observations. A comparison of our model with a tight-winding approximation shows that the self-gravitation of the whole spiral pattern is important in the middle and outer galactic regions. As a first step to full 3D cal…
Deep Chandra exposures reveal the presence of diffuse X-ray emission with a luminosity of 1.3x10^{39} ergs s^{-1} from the spiral galaxy NGC 3184. This appears to be truly diffuse thermal emission distinct from the low-luminosity LMXB emission. While the unresolved emission from older LMXBs is more uniformly distributed across the galaxy, the diffuse X-ray emission is concentrated in areas of younger stellar populations and star forming regions. The surface brightness of the diffuse emission over the spiral arms is five times greater than in off-arm regions, and eight times brighter in H II re…
We examined offsets between HII regions and molecular clouds belonging to spiral arms of a late type spiral galaxy NGC 4254 (M99). We used a high resolution CO(1-0) image obtained by Nobeyama Millimeter Array (NMA) and an H-alpha image. We derived angular offsets (theta) in the galactic disk, and found that these offsets show a linear dependence on the angular rotation velocity of gas (Omega_G). This linear relation can be expressed by an equation: theta =(Omega_G - Omega_P) * t_{H-alpha}, where Omega_P and t_{H-alpha} are constant. Here, Omega_P corresponds to the pattern speed of spiral arms…
[Abridged]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, j_disk, 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+/…
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.
