Showing papers on "Spiral galaxy published in 1985"
TL;DR: In this paper, a linear correlation was established between the far-infrared flux measured by IRAS and the nonthermal radio flux density (at 1.4 GHz) from disks of spiral galaxies.
Abstract: A tight, linear correlation is established between the far-infrared flux measured by IRAS and the nonthermal radio flux density (at 1.4 GHz) from disks of spiral galaxies. This correlation defines a ratio of infrared to radio fluxes that is characteristic of star formation activity. Galaxies with nuclear starbursts seem to follow the correlation. If the far-infrared is reradiated luminosity from young massive stars, then the supernova remnants alone account for less than 10 percent of the radio emission. These results indicate a close coupling between dust heating and cosmic-ray generation and confinement in a wide range of conditions.
915 citations
TL;DR: In this article, the major and minor-axis profiles given previously for 105 galaxies of all morphological types are decomposed into bulge and disk components, and three model-independent parameters which measure the mean surface brightness, scale radius, and degree of light concentration are derived.
Abstract: Major- and minor-axis profiles given previously for 105 galaxies of all morphological types are decomposed into bulge and disk components. In addition, three model-independent parameters which measure the mean surface brightness, scale radius, and degree of light concentration are derived. The best correlations are found between Hubble type, concentration, bulge/disk ratio, and mean surface brightness. Correlations between the individual bulge and disk parameters generally show large scatter. The properties of S0 galaxies are inconsistent with their having been formed from spiral galaxies via gas depletion; their properties are intermediate between those of ellipticals and spirals. Most elliptical galaxies probably do not form by the merging of disk galaxies. The difficulty of distinguishing between elliptical and S0 galaxies in some cases is emphasized.
359 citations
TL;DR: In this article, the available 21 cm line data in the literature for galaxies in nine clusters is combined with new high-sensitivity observations of 51 galaxies in five of the nine clusters in order to test for discriminating circumstances between those clusters which show H I deficiency among their spiral population and those which do not.
Abstract: The available 21 cm line data in the literature for galaxies in nine clusters is combined with new high-sensitivity observations of 51 galaxies in five of the nine clusters in order to test for discriminating circumstances between those clusters which show H I deficiency among their spiral population and those which do not. An H I deficiency for the complete cluster sample is derived employing a comparison sample of galaxies chosen from the Catalog of Isolated Galaxies. The deficiency and its radial dependence is summarized for each cluster and a composite. A comparison of the environments in different clusters leads to the conclusion that the occurrence of H I deficiency is correlated with the presence of a hot X-ray intracluster medium, and that an ongoing interaction process is active through the cores of X-ray clusters.
350 citations
TL;DR: In this article, the authors present results of spectrophotometry of the nuclei of 161 (mostly spiral) galaxies with bright companions, and emission-line imaging of 63 galaxies.
Abstract: We present results of spectrophotometry of the nuclei of 161 (mostly spiral) galaxies with bright companions, and emission-line imaging of 63 galaxies. The program includes a complete sample, unbiased as to morphological disturbance, and an Arp-atlas sample selected for visual evidence of tidal distortion. When compared to a similarly observed sample of isolated-spiral nuclei, both samples of interacting galaxies show significant excesses of nuclear emission. Both nonthermal (Seyfert) activity and nuclear star formation are enhanced, while low-ionization (LINER) nuclei are uncommon. The rate of nuclear star formation is significantly above average even in systems without noticeable tidal distortion in the outer disks, suggesting that the near-nuclear gas is only marginally stable in isolated galaxies. There is evidence that Seyfert nuclei are more frequent in very close pairs. Very disrupted systems possess significantly fewer Seyfert nuclei. These effects become more pronounced with increasing galaxy luminosity. Sizes of nuclear emission regions appear to be unchanged by interactions. The enhancement in nuclear star formation depends only weakly on pair separation over the range we have sampled. Our results suggest that nuclear phenomena are triggered by tidally induced influx of gas from the disk into the nuclear regions, rather than gas transfer between themore » galaxies.« less
292 citations
TL;DR: In this paper, a new gravitational lens system has been discovered which consists of a quasar at z = 1.695 nearly centered on a 15-mag spiral galaxy, 2237 + 0305, at Z = 0.0394.
Abstract: A new gravitational lens system has been discovered which consists of a quasar at z = 1.695 nearly centered on a 15-mag spiral galaxy, 2237 + 0305, at z = 0.0394. At 2 arcsec resolution, only a single optical image of the quasar is visible; its centroid is located within approximately 0.3 arcsec of the center of the galaxy. 'Snapshot' observations at the VLA yielded no detectable radio radiation, placing an upper limit of about 0.5 mJy on the combined flux density of the galaxy and quasar at a wavelength of 6 cm. A simple gravitational lens model that accounts for these observations is discussed.
282 citations
TL;DR: In this paper, the authors derived an expression for the induced changes in the phase-space distribution function, finding them to be second order in the perturbing potential, and of the form of a diffusion in phase space.
Abstract: The dynamical structure of a galactic disk is changed by fluctuations in its gravitational potential field. The orbits of stars are deflected, changing the velocity dispersion and angular-momentum distribution. We derive an expression for the induced changes in the phase-space distribution function, finding them to be second order in the perturbing potential, and of the form of a diffusion in phase space. We evaluate our result for a model transient spiral. The radial-velocity dispersion of the stars increases in response to a steady sequence of perturbations as t/sup 1/2/, for low velocity stars, declining towards t/sup 1/5/ as the radial excursions of stars become large in comparison to the spatial wavelength of the spirals. The waves also transport angular momentum, allowing the disk to become more centrally concentrated. In equilibrium the wave amplitude is controlled by the rate of dynamical cooling in the disk, and, inasmuch as the gas also gives rise to star formation, the heating time scale may be similar to the galactic star-formation time scale. Spiral waves may then rearrange the structure of the disk, as stars form out of the gas. Our predictions are in good agreement with the age/velocity-dispersion relation observed in our N-body experiments,more » and we conclude that recurrent transient spirals naturally account for that observed for the solar neighborhood stars.« less
161 citations
TL;DR: In this article, the results of the rechercheche de noyaux galactiques actifs parmi les galaxies en interaction were presented, on a spectrophotometriquement dans le domaine 4700-7100 A.
Abstract: On presente les resultats de la recherche de noyaux galactiques actifs parmi les galaxies en interaction. On a observe spectrophotometriquement dans le domaine 4700-7100 A, un echantillon de galaxies asymetriques et en interaction. Les resultats sont compares aux donnees d'observations d'un echantillon de galaxies isolees
153 citations
TL;DR: In this paper, a strong correlation is found between the FIR and extended 21 cm continuum flux, implying that the fraction of massive stars formed is independent of the star formation rate, which is a strong indicator of the current rate of star formation.
Abstract: CO emission has been detected from 20 of 21 bright radio spirals with strong extended nuclear sources, including the most distant (NGC 7674) and the most luminous (IC 4553 = Arp 220, NGC 6240) galaxies yet detected in CO. All of these galaxies are rich in molecular gas, with M total(H2) = 3 x 10 to the 8th - 2 x 10 to the 10th solar masses. IRAS observations show that they have a strong far-infrared (FIR) excess, with L(FIR)/L(B) approximately equal to 1-35 and L(FIR) (40-400 microns) approximately equal to 10 to the 10th - 10 to the 12th L solar masses. The primary luminosity source for these radio cores appears to be star formation in molecular clouds. A strong correlation is found between the FIR and extended 21 cm continuum flux, implying that the fraction of massive stars formed is independent of the star formation rate. The ratio L(FIR)/M(H2) provides a measure of the current rate of star formation, which is found to be a factor 3-20 larger in these galaxies than for the ensemble of molecular clouds in the Milky Way. At these rates their molecular gas will be depleted in about 10 to the 8th yr.
118 citations
106 citations
TL;DR: In this paper, a high-resolution 2 cm map of the nuclear region of the spiral galaxy NGC 253 is analyzed, and the alignment of the knots at position angle 44 deg + or - 1 deg is studied.
Abstract: A high-resolution 2 cm map of the nuclear region of the spiral galaxy NGC 253 is analyzed. The size, position angle, flux density, and brightness temperature for compact radio sources in NGC 253 are described. The central core and radio knots of NGC 253 are examined. It is observed that the central radio source has a brightness temperature of 90,000 K and is surrounded by knots of 0.1 arcsec with spectral indices of -0.3 and brightness temperatures of a few thousand degrees. The alignment of the knots at position angle 44 deg + or - 1 deg is studied. The relationship between the nuclear structure orientation and the nuclear activity is discussed. 35 references.
106 citations
TL;DR: A survey of a large number of sources shows that a strong microwave spectral line appears in emission in cold dust clouds, in absorption in the direction of the Galactic center, and exhibits complex profiles toward H II regions.
Abstract: The discovery of a strong microwave (1.6 cm-wavelength) spectral line, the carrier of which is common and widespread throughout the Galaxy is reported. A survey of a large number of sources shows that the line appears in emission in cold dust clouds, in absorption in the direction of the Galactic center, and exhibits complex profiles toward H II regions. Toward Cas A and distant H II regions, intervening 'spiral arm' clouds produce absorption. For almost all cases, the absorption features show a striking 1:1 radial velocity correspondence with those seen, e.g., in H2CO spectra of the same objects. The data indicate that the line arises between low-lying energy states of a rather polar molecule. Recent work by Thaddeus, Vrtilek, and Gottlieb (1985) incorporating the present data, shows that the line in question is the 1(10)-1(01) transition of the small hydrocarbon ring C3H2.
TL;DR: In this article, self-consistent N-body experiments have been performed for a galactic disk containing both stars and a dissipative gas component, where the gas is treated with a simple sticky particle scheme, which maintains the gas at a low velocity dispersion and results in continuous dynamical cooling of the disk.
Abstract: Self-consistent N-body experiments have been performed for a galactic disk containing both stars and a dissipative gas component. The gas is treated with a simple sticky particle scheme, which maintains the gas at a low velocity dispersion and results in continuous dynamical cooling of the disk. The disks exhibit dramatic activity, with both the stars and the gas showing large-scale spiral structure. The gas arms generally overlie the stellar arms but are much narrower and show structure on smaller scales than the stars. The number of spiral arms m is found to be strongly correlated with the fraction of the total mass in the disk f, such that m is approximately equal to 1/f, as expected from swing amplification theory. A population of disk stars with a large velocity dispersion (Qroughly-equal2.5) is shown to be so ''stiff'' that is effectively in the halo, as far as spiral activity is concerned. The gas loses angular momentum to the stars, resulting in a slow inward radial flow on a time scale of about 100 revolutions.
TL;DR: In this article, the authors developed equations which express relatively well determined parameters characterizing the internal properties of all the mass models invoked in a sampling of spiral galaxy cases, and the numerical values thus obtained constitute benchmarks, relative to which theories of the missing mass problem can be tested.
Abstract: In the present consideration of the missing mass problem, equations are developed which express relatively well determined parameters characterizing the internal properties of all the mass models invoked in a sampling of spiral galaxy cases. The numerical values thus obtained constitute benchmarks, relative to which theories of spiral galaxy formation can be tested. Simple regularities are noted to be exhibited by the unseen matter in the spiral galaxy sample. Attention is given to the possibility that both the visible and invisible matter are baryonic. 23 references.
TL;DR: A preliminary analysis of a high-resolution CO survey of the galactic disk is presented in this article, which can detect and measure essentially all molecular clouds and cloud components in the inner Galaxy with size greater than 10 pc.
Abstract: A preliminary analysis of a new high-resolution CO survey of the galactic disk is presented, which can detect and measure essentially all molecular clouds and cloud components in the inner Galaxy with size greater than 10 pc. In the region of l between 20 and 50 deg approximately 2000 emission centers are identified. Two populations which separate according to temperature are found. The disk population of cold molecular cores contains about three-quarters of the total number of cores, is not confined to any large-scale pattern in longitude-velocity space, and must be widespread in the Galaxy both in and out of spiral arms. The spiral arm population of warm molecular cores contains about one-quarter of the population with one-half of the emission and is very closely associated with radio H II regions. Between longitudes 20 and 50 deg their radial distribution shows two peaks at R = 5 and 7.5 kpc. The warm molecular cloud cores have a nonaxisymmetric galactic distribution, occur in clusters, and are confined to restricted regions and patterns in longitude-velocity space and in the galactic disk. 20 references.
TL;DR: In this article, the Owens Valley millimeter-wave interferometer was used to synthesize a beam 7.6 arc sec by 5.4 arc sec for NGC 6946 in the 2.6 mm line of CO.
Abstract: The bright, nearby galaxy NGC 6946 in the 2.6 mm line of CO has been observed with the Owens Valley Millimeter-Wave Interferometer, synthesizing a beam 7.6 arc sec by 5.4 arc sec. The molecular gas in the central 1.5 kpc of the galaxy is confined to a bar of extent of approximately 2700 pc by 550 pc, which is centered on the nucleus and connects two dust lanes in the innermost spiral arms. The molecular bar is the likely source of the star formation activity suggested by optical and infrared studies in the nucleus of NGC 6946. 34 references.
TL;DR: Etude de la courbe de lumiere definitive de cette supernova, membre de M31, d'apres une nouvelle reduction de 40 etoiles de comparaison dans le systeme V et des observations recentes as discussed by the authors.
Abstract: Etude de la courbe de lumiere definitive de cette supernova, membre de M31, d'apres une nouvelle reduction de 40 etoiles de comparaison dans le systeme V et des observations recentes
TL;DR: In this article, a program d'observations des luminosites, couleurs et contenus en gaz des galaxies spirales dans les amas.
Abstract: On presente les resultats d'un programme d'observations des luminosites, couleurs et contenus en gaz des galaxies spirales dans les amas. Les donnees ont ete utilisees pour reviser l'echelle des distances utilisant la relation de Tully-Fisher infrarouge
TL;DR: The results of a spectroscopic study of 38 objects in the field of the very rich, concentrated cluster Cl 0024+1654 at a redshift of z = 0.391 were presented in this paper.
Abstract: We present the results of a spectroscopic study of 38 objects in the field of the very rich, concentrated cluster Cl 0024+1654 at a redshift of z = 0.391. All of the red galaxies and 14 of the 22 blue objects are found to be cluster members. The spectra of the blue cluster members are very similar to those of low-redshift spirals, suggesting that these distant galaxies are also undergoing protracted periods of star formnation. These data support Butcher and Oemler's suggestion that this cluster provides evidence for evolution of the blue population of clusters, to the extent that no low-redshift, concentrated cluster is known to have such a large population of blue galaxies. Three of the blue cluster members have spectra typical of active galactic nuclei, which lends support to the proposal of Dressler and Gunn that such activity was much more common only 4--5 x 10/sup 9/ yr ago. On the other hand, no '' starburst'' galaxies like those in the 3C 295 cluster have been found. We describe a technique for finding emission-line galaxies at a known redshift by imaging through a narrow-band filter centered on redshifted (OII) lambda3727 and demonstrate that this procedure detects (OII) emissionmore » at a level consistent with our spectroscopic measurements. With this technique, we have found other examples of blue galaxies with (OII) emission, and the strongest of these was confirmed to be an AGN by subsequent spectroscopic measurement. This method is extremely efficient because it covers the entire field at once and will be particularly valuable for work on higher redshift clusters where even multislit spectroscopy is difficult at the present time.« less
TL;DR: In this article, the spectral properties of a bright stellar object near the nucleus of the spiral galaxy NGC4618 reveal strong, very broad emission lines similar to those in quasars but having the wrong relative wavelengths.
Abstract: Optical spectra of a bright stellar object near the nucleus of the spiral galaxy NGC4618 reveal strong, very broad emission lines similar to those in quasars but having the wrong relative wavelengths. Although lines of hydrogen and helium are absent, the most prominent features can be attributed to neutral atoms of oxygen, sodium, and magnesium at the redshift of NGC4618. The object is almost certainly a supernova whose highly unusual spectrum may be indicative of a fundamentally new subclass.
TL;DR: The most luminous H2O maser source yet reported, ∼500 L0, in the galaxy NGC3079 was detected in this article, which is also an indication of star formation activity.
Abstract: The 616–523 transition of water vapour at 22.235080 GHz has been found in our Galaxy to be associated with regions of young star formation1,2. H2O maser emission was detected initially in an external galaxy by Churchwell et al.3. To extend the range of detected properties of ‘star burst’ galaxies (galaxies showing an enhanced star formation from their optical spectra) we undertook an initial survey for H2O maser emission in this type of galaxy, but with negative results. Here we report on the subsequent extension of this survey to spiral galaxies displaying continuum radio emission, which is also an indication of star formation activity. We have detected the most luminous H2O maser source yet reported, ∼500 L0, in the galaxy NGC3079. OH absorption was also detected in this galaxy and we suggest that maser amplification of the nuclear radio source causes the observable H2O emission.
TL;DR: The influence of X-ray heating on the evolution and eventual structure of the ISM in a luminous active galaxy is studied in this paper, where conditions for runaway Xray heating are outlined, and the appropriate heating rates for Xray heated winds are estimated.
Abstract: The influence of X-ray heating on the evolution and eventual structure of the ISM in a luminous active galaxy is studied. The conditions for runaway X-ray heating are outlined, and the appropriate heating rates for X-ray heated winds are estimated. The parameters which govern these winds from active spiral galaxies are discussed. The theory of Compton-heated winds by Begelman, McKee, and Shields (1983) is used to derive steady-state mass loss rates from opaque, irradiated disks in the gravitational potentials of typical spirals. These rates are compared with the accretion rates necessary to power the activity in the nucleus and with the rate at which mass can be replenished by stellar evolutionary processes in the disk. The time required to establish this steady state is estimated, and the evolution of an ISM similar to that of the Galaxy after a luminous quasar or Seyfert turns it on is described. 70 references.
TL;DR: In a recent survey of the 2.6 mm line of CO in the southern Milky Way, 37 molecular clouds were identified along the Carina arm from l = 282 deg to 336 deg with masses generally greater than 10 to the 5th solar mass as mentioned in this paper.
Abstract: From a new survey of the 2.6 mm line of CO in the southern Milky Way, 37 molecular clouds were identified along the Carina arm from l = 282 deg to 336 deg with masses generally greater than 10 to the 5th solar mass. The clouds lie approximately every 700 pc along a spiral segment that is nearly 25 kpc long and has a pitch of about 10 deg. The total mass of these clouds is 40 x 10 to the 6th solar mass, or rougly 1 x 10 to the 6th solar mass each on average. The abrupt tangent point in molecular clouds at l = 280 deg and the characteristic loop structure in the l-v diagram are unmistakable evidence of a CO spiral arm in Carina. This arm apparently connects with the northern hemisphere Sagittarius arm to form a single 10 deg spiral which extends more than two-thirds of the way around the Galaxy.
TL;DR: The galaxy M51 and its companion NGC 5195 were observed with the Einstein High-Resolution Imager (EHRI) with (0.2-4.0 keV) X-ray luminosities.
Abstract: The galaxy M51 and its companion NGC 5195 were observed with the Einstein High-Resolution Imager. The X-ray observations led to the detection of both galaxies with (0.2-4.0 keV) X-ray luminosities of 3.0 x 10 to the 40th ergs/s and 2.1 x 10 to the 39th ergs/s respectively. M51 and its companion are compared to other spiral and irregular galaxies observed in X-rays, and the various components of the X-ray emission of M51 (i.e., nucleus, point sources, and unresolved extended emission) are discussed. 69 references.