Spiral Galaxies Research Papers - Academia.edu (original) (raw)

- by
- •
- Magnetic field, Spiral Galaxies, Large Scale
- by Piet van der Kruit
- •
- Physics, Quantum Mechanics, Dust (Astronomy & Astrophysics), Astrophysics

We report the first detailed X-ray and optical observations of the medium-distant cluster A33 obtained with the Beppo-SAX satellite and with the UH 2.2m and Keck II telescopes at Mauna Kea. The information deduced from X-ray and optical imaging and spectroscopic data allowed us to identify the X-ray source 1SAXJ0027.2-1930 as the X-ray counterpart of the A33 cluster. The faint, F 2−10 keV ≈ 2.4 × 10 −13 erg s −1 cm −2 , X-ray source 1SAXJ0027.2-1930, ∼ 2 arcmin away from the optical position of the cluster as given in the Abell catalogue, is identified with the central region of A33. Based on six cluster galaxy redshifts, we determine the redshift of A33, z = 0.2409; this is lower than the value derived by Leir and . The source X-ray luminosity, L 2−10 keV = 7.7 × 10 43 erg s −1 , and intracluster gas temperature, T = 2.9 keV, make this cluster interesting for cosmological studies of the cluster L X − T relation at intermediate redshifts. Two other X-ray sources in the A33 field are identified. An AGN at z=0.2274, and an M-type star, whose emission are blended to form an extended X-ray emission ∼ 4 arcmin north of the A33 cluster. A third possibly point-like X-ray source detected ∼ 3 arcmin north-west of A33 lies close to a spiral galaxy at z=0.2863 and to an elliptical galaxy at the same redshift as the cluster.

- by Isabella M. Gioia
- •
- Organic Chemistry, Intergalactic Medium, Galaxy Clusters, Optical Imaging

We carry out an objective classification of four samples of spiral galaxies having extended rotation curves beyond the optical radius. A multivariate statistical analysis (viz., principal component analysis [PCA]) shows that about 96% of the total variation is due to two components, one being the combination of absolute blue magnitude and maximum rotational velocity beyond the optical region and the other being the central density of the halo. On the basis of PCA a fundamental plane has been constructed that reduces the scatter in the Tully-Fisher relation up to a maximum of 16%. A multiple stepwise regression analysis of the variation of the overall shape of the rotation curves shows that it is mainly determined by the central surface brightness, while the shape purely in the outer part of the galaxy (beyond the optical radius) is mainly determined by the size of the galactic disk.

We study the evolution of disk galaxies within the frame of the cold dark matter (CDM) cosmologies. The hydrodynamics of a centrifugally supported gaseous disk and the growth of a stellar disk is calculated in detail taking into account the energy balance of the ISM and the gravitational instabilities that concern gas and stars. The halo density profile is derived from the primordial cosmological conditions and its gravitational contraction produced by the disk is included. Several features of the spiral galaxies at different redshifts are predicted, and the main factors which influence on these features are found. A strong evidence is provided that the Tully-Fisher (TF) relation is an imprint of the primordial cosmological conditions.

- by Vladimir Avila-Reese
- •
- Galaxy evolution, Energy Balance, Spiral Galaxies, Cold Dark Matter
- by za null
- •
- Mathematical Sciences, Physical sciences, Space Time, Spiral Galaxies

We use a series of ray-tracing experiments to determine the magnification distribution of high-redshift sources by gravitational lensing. We determine empirically the relation between magnification and redshift, for various cosmological models. We then use this relation to estimate the effect of lensing on the determination of the cosmological parameters from observations of high-z supernovae. We found that, for supernovae at redshifts z < 1.8, the effect of lensing is negligible compared to the intrinsic uncertainty in the measurements. Using mock data in the range 1.8 < z < 8, we show that the effect of lensing can become significant. Hence, if a population of very-high-z supernovae was ever discovered, it would be crucial to fully understand the effect of lensing, before these SNe could be used to constrain cosmological models. We show that the distance moduli m−M for an open CDM universe and a ΛCDM universe are comparable at z > 2. Therefore if supernovae up to these redshifts were ever discovered, it is still the ones in the range 0.3 < z < 1 that would distinguish these two models.

- by Thomas H. Puzia
- •
- Star Formation, Morphology, Galaxy Clusters, Models

We present V −band surface photometry and major-axis kinematics of stars and ionized gas of three early-type spiral galaxies, namely NGC 772, NGC 3898 and NGC 7782. For each galaxy we present a self-consistent Jeans model for the stellar kinematics, adopting the light distribution of bulge and disc derived by means of a twodimensional parametric photometric decomposition. This allowed us to investigate the presence of non-circular gas motions, and derive the mass distribution of luminous and dark matter in these objects.

The ACS Nearby Galaxy Survey Treasury (ANGST) is a large Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) treasury program to obtain resolved stellar photometry for a volume-limited sample of galaxies out to 4 Mpc. As part of this program, we have obtained deep ACS imaging of a field in the outer disk of the large spiral galaxy M81. The field contains the outskirts of a spiral arm as well as an area containing no current star formation. Our imaging results in a colormagnitude diagram (CMD) reaching to m F 814W = 28.8 and m F 606W = 29.5, one magnitude fainter than the red clump. Through detailed modeling of the full CMD, we quantify the age and metallicity distribution of the stellar populations contained in the field. The mean metallicity in the field is −1 < [M/H] < 0 and only a small fraction of stars have ages < ∼ 1 Gyr. The results show that most of the stars in this outer disk field were formed by z ∼ 1 and that the arm structure at this radius has a lifetime of > ∼ 100 Myr. We discuss the measured evolution of the M81 disk in the context of surveys of high-redshift disk galaxies and deep stellar photometry of other nearby galaxies. All of these indicate that massive spiral disks are mostly formed by z∼1 and that they have experienced rapid metal enrichment.

- by Andrew Dolphin and +2
- •
- Star Formation, High Redshift Universe, Spiral Galaxies, Star formation History

We present near-infrared spectroscopy and Hubble Space Telescope (HST) imaging of ERO J003707+0909.5, the brightest of three gravitationally-lensed images of an Extremely Red Object (ERO) at z = 1.6, in the field of the massive cluster A 68 (z = 0.255). We exploit the superlative resolution of our HST data and the enhanced spatial resolution and sensitivity afforded by the lens amplification to reconstruct the source-plane properties of this ERO. Our morphological and photometric analysis reveals that ERO J003707 is an L ⋆ early-type disk-galaxy and we estimate that ∼ 10 per cent of EROs with (R − K) ≥ 5.3 and K ≤ 21 may have similar properties. The unique association of passive EROs with elliptical galaxies therefore appears to be too simplistic. We speculate on the evolution of ERO J003707: if gas continues to cool onto this galaxy in the manner predicted by hierarchical galaxy formation models, then by the present day, ERO J003707 could evolve into a very luminous spiral galaxy.

- by Harald Ebeling
- •
- Thermodynamics, Organic Chemistry, Astrophysical Plasma, Dark Matter

We revisit the question of the ionization of the diffuse medium in late-type galaxies, by studying NGC 891, the prototype of edge-on spiral galaxies. The most important challenge for the models considered so far was the observed increase of [O III]/Hβ, [O II]/Hβ and [N II]/Hα with increasing distance to the galactic plane. We propose a scenario based on the expected population of massive OB stars and hot low-mass evolved stars (HOLMES) in this galaxy to explain this observational fact. In the framework of this scenario we construct a finely meshed grid of photoionization models. For each value of the galactic altitude z we look for the models which simultaneously fit the observed values of the [O III]/Hβ, [O II]/Hβ and [N II]/Hα ratios. For each value of z we find a range of solutions which depends on the value of the oxygen abundance. The models which fit the observations indicate a systematic decrease of the electron density with increasing z. They become dominated by the HOLMES with increasing z only when restricting to solar oxygen abundance models, which argues that the metallicity above the galactic plane should be close to solar. They also indicate that N/O increases with increasing z.

- by Christophe Morisset
- •
- Interstellar Medium, HII Regions, Electron Density, Spiral Galaxies

- by Giuseppe Bertin
- •
- Mathematical Sciences, Physical sciences, Spiral Galaxies

We use Herschel Space Observatory data to place observational constraints on the peak and Rayleigh-Jeans slope of dust emission observed at 70-500 µm in the nearby spiral galaxy M81. We find that the ratios of wave bands between 160 and 500 µm are primarily dependent on radius but that the ratio of 70 to 160 µm emission shows no clear dependence on surface brightness or radius. These results along with analyses of the spectral energy distributions imply that the 160-500 µm emission traces 15-30 K dust heated by evolved stars in the bulge and disc whereas the 70 µm emission includes dust heated by the active galactic nucleus and young stars in star forming regions.

The SFI++ consists of ~5000 spiral galaxies which have measurements suitable for the application of the I-band Tully-Fisher (TF) relation. This sample builds on the SCI and SFI samples published in the 1990s but includes significant amounts of new data as well as improved methods for parameter determination. We derive a new I-band TF relation from a subset of this sample which consists of 807 galaxies in the fields of 31 nearby clusters and groups. This sample constitutes the largest ever available for the calibration of the TF template and extends the range of line-widths over which the template is reliably measured. Careful accounting is made of observational and sample biases such as incompleteness, finite cluster size, galaxy morphology and environment. We find evidence for a type-dependent TF slope which is shallower for early type than for late type spirals. The line-of-sight cluster peculiar velocity dispersion is measured for the sample of 31 clusters. This value is directly related to the spectrum of initial density fluctuations and thus provides an independent verification of the best fit WMAP cosmology and an estimate of Omega^0.6 sigma_8 = 0.52+/-0.06. We also provide an independent measure of the TF zeropoint using 17 galaxies in the SFI++ sample for which Cepheid distances are available. In combination with the ``basket of clusters'' template relation these calibrator galaxies provide a measure of H0 = 74+/-2 (random) +/-6 (systematic) km/s/Mpc.

- by Karen Masters
- •
- Organic Chemistry, Astrophysical Plasma, Galaxy Clusters, Cosmology

We present absorption line-strength maps for a sample of 18 Sb-Sd galaxies observed using the integral-field spectrograph SAURON operating at the William Herschel Telescope on La Palma, as part of a project devoted to the investigation of the kinematics and stellar populations of late-type spirals, a relatively unexplored field. The SAURON spectral range allows the measurement of the Lick/IDS indices Hβ, Fe5015 and Mgb, which can be used to estimate the stellar population parameters. We present here the two-dimensional line-strength maps for each galaxy. From the maps, we learn that late-type spiral galaxies tend to have high Hβ and low Fe5015 and Mgb values, and that the Hβ index has often a positive gradient over the field, while the metal indices peak in the central region. We investigate the relations between the central line-strength indices and their correlations with morphological type and central velocity dispersion, and compare the observed behaviour with that for ellipticals, lenticulars and early-type spirals from the SAURON survey. We find that our galaxies lie below the Mg -σ relation determined for elliptical galaxies and that the indices show a clear trend with morphological type. From the line-strength maps we calculate age, metallicity and abundance ratio maps via a comparison with model predictions; we discuss the results from a one-SSP (Single Stellar Population) approach and from a two-SSP approach, considering the galaxy as a superposition of an old (≈ 13 Gyr) and a younger (age 5 Gyr) population. We confirm that late-type galaxies are generally younger and more metal poor than ellipticals and have abundance ratios closer to solar values. We also explore a continuous star formation scenario, and try to recover the star formation history using the evolutionary models of , assuming constant or exponentially declining star formation rate (SFR). In this last case, fixing the galaxy age to 10 Gyr, we find a correlation between the e-folding time-scale τ of the starburst and the central velocity dispersion, in the sense that more massive galaxies tend to have shorter τ , suggesting that the star formation happened long ago and has now basically ended, while for smaller objects with larger values of τ it is still active now.

- by Katia Ganda and +1
- •
- Star Formation, Galaxy Formation and Evolution, Spiral Galaxies, Star formation History

We have performed an X-ray study of the nearby barred spiral galaxy NGC 1672, primarily to ascertain the effect of the bar on its nuclear activity. We use both Chandra and XMM-Newton observations to investigate its X-ray properties, together with supporting high-resolution optical imaging data from the Hubble Space Telescope (HST), infrared imaging from the Spitzer Space Telescope, and ATCA ground-based radio data. We detect 28 X-ray sources within the D 25 area of the galaxy, many of which correlate spatially with starformation in the bar and spiral arms, while two are identified as background galaxies in the HST images. Nine of the X-ray sources are ULXs, with the three brightest (L X > 5 × 10 39 erg s −1 ) located at the ends of the bar. With the spatial resolution of Chandra, we are able to show for the first time that NGC 1672 possesses a hard (Γ ∼ 1.5) nuclear X-ray source with a 2-10 keV luminosity of 4 × 10 38 erg s −1 . This is surrounded by an X-ray bright circumnuclear star-forming ring, comprised of point sources and hot gas, which dominates the 2-10 keV emission in the central region of the galaxy. The spatially resolved multiwavelength photometry indicates that the nuclear source is a low-luminosity AGN (LLAGN), but with star formation activity close to the central black hole. A high-resolution multiwavelength survey is required to fully assess the impact of both large-scale bars and smaller-scale phenomena such as nuclear bars, rings and nuclear spirals on the fueling of LLAGN.

- by B. Koribalski
- •
- Organic Chemistry, Astrophysical Plasma, Star Formation, Optical Imaging

The new information-theoretic Process Physics has shown that space is a quantum foam system with gravity being, in effect, an inhomogeneous in-flow of the quantum foam into matter. The theory predicts that absolute motion with respect to this system should be observable, and it is shown here that absolute motion has been detected in at least seven experiments. As well

We discuss the importance of very metal-poor stars to develop an understanding of the nature of the first stars that formed in the Universe and the nucleosynthesis events associated with them, as well as to refine models of galaxy formation, in particular for large spiral galaxies such as the Milky Way. After briefly reviewing the history of the search for

- by Timothy Beers
- •
- Carbon, Evolution, Galaxy Formation and Evolution, Dust (Astronomy & Astrophysics)

We present specific Star Formation Rate (sSFR) radial profiles for a sample of 161 relatively face-on spiral galaxies from the GALEX Atlas of Nearby Galaxies. The sSFR profiles are derived from GALEX & 2MASS (FUV−K) color profiles after a proper SFR calibration of the UV luminosity and K-band mass-to-light ratio are adopted. The (FUV−K) profiles were first corrected for foreground Galactic extinction and later for internal extinction using the ratio of the totalinfrared (TIR) to FUV emission. For those objects where TIR-to-FUV-ratio radial profiles were not available, the (FUV−NUV) color profiles as a measure of the UV slope. The sSFR radial gradients derived from these profiles allow us to quantify the inside-out scenario for the growth of spiral disks for the first time in the local Universe.

- by Jesus Gallego and +1
- •
- Organic Chemistry, Astrophysical Plasma, Infrared, Spiral Galaxies

We study the stellar response in a spectrum of potentials describing the barred spiral galaxy NGC 1300. These potentials have been presented in a previous paper and correspond to three different assumptions as regards the geometry of the galaxy. For each potential we consider a wide range of Ω p pattern speed values. Our goal is to discover the geometries and the Ω p supporting specific morphological features of NGC 1300. For this purpose we use the method of response models. In order to compare the images of NGC 1300 with the density maps of our models, we define a new index which is a generalization of the Hausdorff distance. This index helps us to find out quantitatively which cases reproduce specific features of NGC 1300 in an objective way. Furthermore, we construct alternative models following a Schwarzschild type technique. By this method we vary the weights of the various energy levels, and thus the orbital contribution of each energy, in order to minimize the differences between the response density and that deduced from the surface density of the galaxy, under certain assumptions. We find that the models corresponding to Ω p ≈ 16km s −1 kpc −1 and Ω p ≈ 22km s −1 kpc −1 are able to reproduce efficiently certain morphological features of NGC 1300, with each one having its advantages and drawbacks.

- by P. Patsis
- •
- Dynamics, Models, Kinematics, Spectrum

In a series of papers we study the stellar dynamics of the grand design barred-spiral galaxy NGC 1300. In the first paper of this series we estimate the gravitational potential and we give it in a form suitable to be used in dynamical studies. The estimation is done directly from near-infrared observations. Since the 3D distribution of the luminous matter is unknown, we construct three different general models for the potential corresponding to three different assumptions for the geometry of the system, representing limiting cases. A pure 2D disc, a cylindrical geometry (thick disc) and a third case, where a spherical geometry is assumed to apply for the major part of the bar. For the potential of the disc component on the galactic plane a Fourier decomposition method is used, that allows us to express it as a sum of trigonometric terms. Both even and odd components are considered, so that the estimated potential accounts also for the observed asymmetries in the morphology. For the amplitudes of the trigonometric terms a smoothed cubic interpolation scheme is used. The total potential in each model may include two additional terms (Plummer spheres) representing a central mass concentration and a dark halo component, respectively. In all examined models, the relative force perturbation points to a strongly nonlinear gravitational field, which ranges from 0.45 to 0.8 of the axisymmetric background with the pure 2D being the most nonlinear one. The force perturbation in each model is found being robust to small changes of the required parameter values. We present the topological distributions of the stable and unstable Lagrangian points as a function of the pattern speed (Ω p ). The topological distribution found deviates in several cases from the classical paradigm with two stable Lagrangian points at the sides of the bar and two unstable ones close to the ends of the bar. In all three models there is a range of Ω p values, where we find multiple stationary points whose stability affects the overall dynamics of the system.

- by Preben Grosboel
- •
- Morphology, Stellar Dynamics, Near Infrared, Models

We study the spectroscopic properties and environments of red (or passive) spiral galaxies found by the Galaxy Zoo project. By carefully selecting face-on, disk dominated spirals we construct a sample of truly passive disks (i.e. they are not dust reddened spirals, nor are they dominated by old stellar populations in a bulge). As such, our red spirals represent an interesting set of possible transition objects between normal blue spiral galaxies and red early types, making up ∼ 6% of late-type spirals. We use optical images and spectra from SDSS to investigate the physical processes which could have turned these objects red without disturbing their morphology. We find red spirals preferentially in intermediate density regimes. However there are no obvious correlations between red spiral properties and environment suggesting that environment alone is not sufficient to determine if a galaxy will become a red spiral. Red spirals are a very small fraction of all spirals at low masses (M ⋆ < 10 10 M ⊙ ), but are a significant fraction of the spiral population at large stellar masses showing that massive galaxies are red independent of morphology. We confirm that as expected, red spirals have older stellar populations and less recent star formation than the main spiral population. While the presence of spiral arms suggests that major star formation cannot have ceased long ago (not more than a few Gyrs), we show that these are also not recent post-starburst objects (having had no significant star formation in the last Gyr), so star formation must have ceased gradually. Intriguingly, red spirals are roughly four times as likely than the normal spiral population to host optically identified Seyfert/LINER (at a given stellar mass and even accounting for low luminosity lines hidden by star formation), with most of the difference coming from objects with LINER-like emission. We also find a curiously large optical bar fraction in the red spirals (70 ± 5% verses 27 ± 5% in blue spirals) suggesting that the cessation of star formation and bar instabilities in spirals are strongly correlated. We conclude by discussing the possible origins of these red spirals. We suggest they may represent the very oldest spiral galaxies which have already used up their reserves of gas -probably aided by strangulation or starvation, and perhaps also by the effect of bar instabilities moving material around in the disk. We provide an online table listing our full sample of red spirals along with the normal/blue spirals used for comparison.

- by Steven Bamford
- •
- Star Formation, Galaxy Formation and Evolution, Optical Imaging, Spiral Galaxies

We present first results from Galaxy Zoo 2, the second phase of the highly successful Galaxy Zoo project (www.galaxyzoo.org). Using a volume-limited sample of 13665 disk galaxies (0.01 < z < 0.06 and M r < −19.38), we study the fraction of galaxies with bars as a function of global galaxy properties like colour, luminosity and bulge prominence. Overall, 29.4 ± 0.5% of galaxies in our sample have a bar, in excellent agreement with previous visually-classified samples of galaxies (although this overall fraction is lower than measured by automated bar-finding methods). We see a clear increase in the bar fraction with redder (g − r) colours, decreased luminosity and in galaxies with more prominent bulges, to the extent that over half of the red, bulge-dominated, disk galaxies in our sample possess a bar. We see evidence for a colour bi-modality for our sample of disk galaxies, with a "red sequence" that is both bulge and bar-dominated, and a "blue cloud" which has little, or no, evidence for a (classical) bulge or bar. These results are consistent with similar trends for barred galaxies seen recently both locally and at higher redshift, and with early studies using the RC3. We discuss these results in the context of internal (secular) galaxy evolution scenarios and the possible links to the formation of bars and bulges in disk galaxies.

- by Steven Bamford
- •
- Galaxy Formation and Evolution, Galaxy evolution, Spiral Galaxies

Rotation information for spiral galaxies can be obtained through the observation of different spectral lines. While the Halpha(6563 A) line is often used for galaxies with low to moderate redshifts, it is redshifted into the near-infrared at z>0.4. This is why most high redshift surveys rely on the [OII](3727 A) line. Using a sample of 32 spiral galaxies at 0.155 < z < 0.25 observed simultaneously in both Halpha and [OII] with the Hale 200 inch telescope, the relation between velocity widths extracted from these two spectral lines is investigated, and we conclude that Halpha derived velocities can be reliably compared to high z [OII] measurements. The sample of galaxies is then used along with VIMOS-VLT Deep Survey observations to perform the angular diameter - redshift test to find constraints on cosmological parameters. The test makes it possible to discriminate between various cosmological models, given the upper limit of disc size evolution at the maximum redshift of the data set, no matter what the evolutionary scenario is.

- by Karen Masters
- •
- Near Infrared, High Redshift Universe, Spiral Galaxies, Sloan Digital Sky Survey

We present the HI observations of 94 flat spiral galaxies from RFGC (the Revised Flat Galaxy Catalog) and 14 galaxies from 2MFGC (the 2MASS selected Flat Galaxy Catalog) performed with the 100-m radio telescope in Effelsberg (Germany). HI fluxes, heliocentric radial velocities, and HI line widths are given for 65 detected galaxies. We present a mosaic of HI profiles.

- by S. Mitronova
- •
- Radial Velocity, Spiral Galaxies, Radio Telescope

Abstract: The analysis of chess motifs and motifs of space exploration in Bend Sinister, Speak, Memory, and Lance, under¬ taken in this essay, allows us to expand our understanding of Nabokov’s “metaphysical storyline” as well as re¬interpret the concept of “knight’s move” the writer borrowed from one of the founders of Russian Formalism Victor Shklovsky. In all three works, the hero or the narrator consider the possibility of escaping a tor¬turous fate either by moving away from harm through the inter¬ planetary space or by undertaking an interstellar journey for the sake of achieving a “transcendental” goal of overcoming death and reaching life everlasting. The possibility of their escape into the otherworld by means of a metaphysical shift, a dramatic plot twist, and a chivalric exploit is encoded in Nabokov’s play on the homonymic overlap of the words “knight” (as in chess) and “knight” (as a hero of medieval romances). In the first part of the essay, the death of Krug in Bend Sinister is explored as a break¬ through in a chess game as well as a flight from the circles of hell, encapsulated in the name of the hero, into the author’s reality encoded in the trope of a spiral galaxy. Further, the novel’s auto¬ biographical subtext and ontological structure are compared to Nabokov’s image of the interstellar¬-scale love for his wife and son in Speak, Memory. This comparative study ends with the re¬eval-uation of Lance’s journey to another planet in the context of Na¬bokov’s “spiral” dialectics and Mikhail Bakhtin’s ideas about the chronotope of a chivalric narrative. Аннотация: Исследование космических и шахматных моти¬вов в романе «Под знаком незаконнорожденных», автобиографии «Другие берега» и рассказе «Ланс», предпринятое в данной ра¬боте, позволяет расширить наше представление о «метафизиче¬ском сюжете» В.В. Набокова, а также придать новое толкование заимствованному им у В.Б. Шкловского понятию «ход коня». В каждом из трех произведений герой или повествователь либо размышляют о возможности избежать мучительной участи по¬ средством перемещения в межпланетном пространстве, либо совершают космическое путешествие ради достижения «транс-цедентальной» цели преодоления смерти бессмертием. Возмож¬ность перехода ими в иную реальность с помощью сюжетно¬ метафизического сдвига и подвига, подобного рыцарскому, скрыта в обыгрывании писателем омонимического совпадения английских слов «knight» (шахматный конь) и «knight» (рыцарь). В первой части работы рассматривается смерть Круга в «Под зна¬ком незаконнорожденных» как прорыв в шахматной игре и, одновременно, бегство из воплощенных в имени героя кругов ада в инобытие автора, символом которого является спиральная галактика. Далее, автобиографический контекст романа и его онтологическая структура сопоставляются с развиваемой в «Дру¬гих берегах» мыслью о космическом масштабе любви автора к близким. Сравнительный анализ завершается переосмыслени¬ем путешествия Ланса на другую планету в свете набоковской «спиральной» диалектики и идей М.М. Бахтина о хронотопе рыцарского романа.

- by Olga Voronina
- •
- Chretien de Troyes, Metaphysics of Time, Vladimir Nabokov, Mikhail Bakhtin

We study the Kennicutt-Schmidt star formation law and efficiency in the gaseous disk of the isolated galaxy CIG 96 (NGC 864), with special emphasis on its unusually large atomic gas (H i) disk (r H i /r 25 = 3.5, r 25 = 1. 85). We present deep Galaxy Evolution Explorer near-and far-UV observations, used as a recent star formation tracer, and we compare them with new, high-resolution (16 or 1.6 kpc) Very Large Array H i observations. The UV and H i maps show good spatial correlation outside the inner 1 , where the H i phase dominates over H 2 . Star-forming regions in the extended gaseous disk are mainly located along the enhanced H i emission within two (relatively) symmetric, giant gaseous spiral arm-like features, which emulate an H i pseudo-ring at r 3 . Inside this structure, two smaller gaseous spiral arms extend from the northeast and southwest of the optical disk and connect to the previously mentioned H i pseudo-ring. Interestingly, we find that the (atomic) Kennicutt-Schmidt power-law index systematically decreases with radius, from N 3.0 ± 0.3 in the inner disk (0. 8-1. 7) to N = 1.6 ± 0.5 in the outskirts of the gaseous disk (3. 3-4. 2). Although the star formation efficiency (SFE), the star formation rate per unit of gas, decreases with radius where the H i component dominates as is common in galaxies, we find that there is a break of the correlation at r = 1.5r 25 . At radii 1.5r 25 < r < 3.5r 25 , mostly within the H i pseudo-ring structure, regions exist whose SFE remains nearly constant, SFE 10 −11 yr −1 . We discuss possible mechanisms that might be triggering the star formation in the outskirts of this galaxy, and we suggest that the constant SFE for such large radii (r > 2r 25 ) and at such low surface densities might be a common characteristic in extended UV disk galaxies.

- by José Sabater Montes
- •
- Organic Chemistry, Astrophysical Plasma, Star Formation, Galaxy evolution

Using both the Arecibo 305m and the Nançay decimetric 100-m class radio telescopes, we have observed the H i line of 116 Low Surface Brightness (LSB) galaxies from the Bothun et al. 1985 subset of LSB galaxies in the Uppsala General Catalog. The observations had a detection rate of 70%, resulting in the new determination of H i properties for 81 galaxies. Surprisingly, roughly half of the detected objects (38) have MHI ≥ 10 10 M⊙, placing them into the category of massive LSB galaxies. As previously only ∼18 of these 'Malin 1 cousins' were known, our results have more than tripled the number of these fascinating and enigmatic systems known. Combining our results with previous studies done on the Bothun et al. catalog results in a well-defined catalog of H i properties of 526 LSB galaxies ranging in redshift space from 0 ≤ z ≤ 0.1. With this catalog in hand, we have been able to explore the parameter space occupied by LSB galaxies more completely than has been previously possible. In agreement with previous studies, our results show LSB galaxies with some of the most extreme properties of disk galaxies, including MHI /LB ratios often exceeding 10 M⊙/L⊙,B.

Aims. With the goal of providing constraints on the nature of the progenitors of core-collapse (CC) supernovae (SNe), we compare their radial distribution within their spiral host galaxies with the distributions of stars and ionized gas in spiral disks. Methods. SNe positions are taken from the Asiago catalog for a well-defined sample of 224 SNe within 204 host galaxies. The SN radial distances are estimated from the deprojected separations from the host galaxy nuclei, and normalized both to the 25th mag arcsec-2 blue-band isophotal radius and (for the first time) to the statistically-estimated disk scale length. Results. The normalized radial distribution of all CCSNe is consistent with an exponential law, as previously found, with a possible depletion of CCSNe within one-fifth of the isophotal radius (less significant with scale-length normalization). There are no signs of truncation of the exponential distribution of CCSNe out to 7 disk scale lengths. The scale length of the dist...

We study the phenomenological implications of the classical limit of the "stringy" commutation

- by Djordje Minic and +1
- •
- High Energy Physics, Spiral Galaxies, Classical Limit, Rotation Curve

We report the discovery, from the H I Parkes All-Sky Survey (HIPASS), of a gas cloud associated with the asymmetric spiral galaxy NGC 2442. This object, designated HIPASS J0731-69, contains ∼ 10 9 M ⊙ of H I, or nearly one-third as much atomic gas as NGC 2442 itself. No optical counterpart to any part of HIPASS J0731-69 has yet been identified, consistent with the gas being diffuse, and with its stream-like kinematics. If the gas in HIPASS J0731-69 was once part of NGC 2442, then it was most likely a fairly recent tidal encounter with a moderately massive companion which tore it loose, although the possibility of ram-pressure stripping cannot be ruled out. This discovery highlights the potential of the HIPASS data for yielding new clues to the nature of some of the best-known galaxies in the local universe.

- by David Malin and +2
- •
- Organic Chemistry, Astrophysical Plasma, Intergalactic Medium, Spiral Galaxies

Accurate surface photometry of five spiral galaxies (NGC 3223, NGC 5085, NGC 5247, NGC 5861 and NGC 7083) in visual and near-infrared bands is presented. All galaxies show grand design spiral structure in K ′ although several have a flocculent appearance on blue images suggesting that stellar and gaseous disks are decoupled. The decomposition of the K ′ maps in axisymmetric components suggests that both a spherical bulge and a flat exponential disk are required to explain the light distribution in the bulge regions. The central disk has a short scale length and sky projection parameters similar to the main disk. The scale length of the main exponential disk measured in the interarm region is consistently smaller than the value determined from the arms for three of the galaxies. Weak oval distortions were found in three galaxies while only one was classified as such. The galaxies with oval distortions have less concentrated and fainter bulges than those in the two galaxies without such ovals.

The structure and velocity curve of a spiral galaxy is described in terms of a constant Cartan torsion (spinning space-time) using Einstein Cartan Evans (ECE) unified field theory. In the central bulge region gravitational attraction predominates, i.e. the Riemann curvature predominates. In the spiral arms the Cartan torsion predominates. It is shown that the structure of the spiral arms is a hyperbolic spiral due to the underlying constant spinning of spacetime. In this generally covariant unified field theory dark matter does not exist and is replaced by Cartan torsion, missing from the Einstein Hilbert field theory of gravitation and its weak field limit, Newtonian dynamics.

- by Myron Evans
- •
- Field Theory, Dark Matter, Unified Field Theory, Space Time

Modified Newtonian Dynamics (MOND) has been shown to be able to fit spiral galaxy rotation curves as well as giving a theoretical foundation for empirically determined scaling relations, such as the Tully -Fisher law, without the need for a dark matter halo. As a complementary analysis, one should investigate whether MOND can also reproduce the dynamics of early -type galaxies (ETGs) without dark matter. As a first step, we here show that MOND can indeed fit the observed central velocity dispersion σ 0 of a large sample of ETGs assuming a simple MOND interpolating functions and constant anisotropy. We also show that, under some assumptions on the luminosity dependence of the Sersic n parameter and the stellar M/L ratio, MOND predicts a fundamental plane for ETGs : a log -linear relation among the effective radius R ef f , σ 0 and the mean effective intensity I e . However, we predict a tilt between the observed and the MOND fundamental planes.

- by Crescenzo Tortora
- •
- Dark Matter, Kinematics and Dynamics, Spiral Galaxies, Fundamental plane

We present an analysis of the spatial orientations of 1315 galaxies in 10 Abell clusters of BM type II-III (type II-III in the Bautz-Morgan system). It is found that the spin-vector orientations of the galaxies in six clusters (Abell 168, 426, 1035(Abell 168, 426, , 1227(Abell 168, 426, , 1367(Abell 168, 426, and 1904 tend to lie parallel to the Local Supercluster (LSC) plane. The spin-vector projections of galaxies in six clusters (Abell 168, 1020(Abell 168, , 1035(Abell 168, , 1227(Abell 168, , 1904(Abell 168, and 1920 are found to be oriented perpendicular with respect to the direction of the LSC centre. Three clusters (Abell 1920(Abell , 2255(Abell and 2256 show a bimodal orientation: spin vectors tend to be oriented both parallel and perpendicular to the LSC plane. No dependence of radial velocity, distance and cluster magnitude on galaxy orientation is noticed. In a comparison with previous work, we noticed that the anisotropy might increase from early-type (BM type I) to late-type (BM types II-III and III) clusters. We notice a vanishing angular momentum for the less massive galaxy clusters (richness class 0). A significant alignment of the angular momenta of galaxies for massive clusters, e.g. the core of the Shapley Supercluster (richness class 4, M > 10 15 M ), is found.

- by B. Aryal
- •
- Galaxy Formation and Evolution, Galaxy Clusters, Galaxy evolution, Radial Velocity

We simulate the growth of large-scale structure, for 3 different cosmological models, an Einstein-de Sitter model (density parameter Ω 0 = 1), an open model (Ω 0 = 0.2) and a flat model with nonzero cosmological constant (Ω 0 = 0.2, cosmological constant λ 0 = 0.8), using a cosmological N-body code (P 3 M) with 64 3 dark matter particles in a comoving cubic volume of present comoving size 128 Mpc. The calculations start at z = 24 and end at z = 0. We use the results of these simulations to generate distributions of galaxies at the present (z = 0), as follows: Using a Monte-Carlo method based on the present distribution of dark matter, we located ∼ 40000 galaxies in the computational volume. We then ascribe to each galaxy a morphological type based on the local number density of galaxies in order to reproduce the observed morphology-density relation. The resulting galaxy distributions are similar to the observed ones, with most ellipticals concentrated in the densest regions, and most spirals concentrated in lowdensity regions. By "tying" each galaxy to its nearest dark matter particle, we can trace the trajectory of that galaxy back in time, by simply looking at the location of that dark matter particle at earlier time-slices provided by the N-body code. This enables us to reconstruct the distribution of galaxies at high redshift, and the trajectory of each galaxy from its formation epoch to the present.

- by Hugo Martel
- •
- Organic Chemistry, Astrophysical Plasma, Morphological evolution, Dark Matter

We analyze the observed properties of nested and single stellar bar systems in disk galaxies. The 112 galaxies in our sample comprise the largest matched Seyfert vs. non-Seyfert galaxy sample of nearby galaxies with complete near-infrared or optical imaging sensitive to lengthscales ranging from tens of pc to tens of kpc. The presence of bars is deduced by fitting ellipses to isophotes in HST H-band images up to 10 ′′ radius, and in ground-based near-infrared and optical images outside the H-band images. This is a conservative approach that is likely to result in an underestimate of the true bar fraction. We find that a significant fraction of the sample galaxies, 17% ± 4%, has more than one bar, and that 28% ± 5% of barred galaxies have nested bars. The bar fractions appear to be stable according to reasonable changes in our adopted bar criteria. For the nested bars, we detect a clear division in length between the large-scale (primary) bars and small-scale (secondary) bars, both in absolute and normalized (to the size of the galaxy) length. We argue that this bimodal distribution can be understood within the framework of disk resonances, specifically the inner Lindblad resonances (ILRs), which are located where the gravitational potential of the innermost galaxy switches effectively from 3D to 2D. This conclusion is further strengthened by the observed distribution of the sizes of nuclear rings which are dynamically associated with the ILRs. While primary bars are found to correlate with the host galaxy sizes, no such correlation is observed for the secondary bars. Moreover, we find that secondary bars differ morphologically from single bars. Our matched Seyfert and non-Seyfert samples show a statistically significant excess of bars among the Seyfert galaxies at practically all lengthscales. We confirm our previous results that bars are more abundant in Seyfert hosts than in non-Seyferts, and that Seyfert galaxies always show a preponderance of "thick" bars compared to the bars in non-Seyfert galaxies. Finally, no correlation is observed between the presence of a bar and that of companion galaxies, even relatively bright ones. Overall, since star formation and dust extinction can be significant even in the H-band, the stellar dynamics of the central kiloparsec cannot always be revealed reliably by the use of near-infrared surface photometry alone.

- by I. Shlosman
- •
- Organic Chemistry, Astrophysical Plasma, Near Infrared, Optical Imaging

Galaxies in clusters and groups moving through the intracluster or intragroup medium (abbreviated ICM for both) are expected to lose at least a part of their interstellar medium (ISM) by the ram pressure they experience. We perform high resolution 2D hydrodynamical simulations of face-on ram pressure stripping (RPS) of disk galaxies to compile a comprehensive parameter study varying galaxy properties (mass, vertical structure of the gas disk) and covering a large range of ICM conditions, reaching from high density environments like in cluster centres to low density environments typical for cluster outskirts or groups. We find that the ICM-ISM interaction proceeds in three phases: firstly the instantaneous stripping phase, secondly the dynamic intermediate phase, thirdly the quasi-stable continuous viscous stripping phase. In the first phase (time scale 20 to 200 Myr) the outer part of the gas disk is displaced but only partially unbound. In the second phase (10 times as long as the first phase) a part of the displaced gas falls back (about 10% of the initial gas mass) despite the constant ICM wind, but most displaced gas is now unbound. In the third phase the galaxy continues to lose gas at a rate of about 1 M ⊙ yr −1 by turbulent viscous stripping. We find that the stripping efficiency depends slightly on the Mach number of the flow, however, the main parameter is the ram pressure. The stripping efficiency does not depend on the vertical structure and thickness of the gas disk. We discuss uncertainties in the classic estimate of the stripping radius of Gunn & Gott (1972), which compares the ram pressure to the gravitational restoring force. In addition, we adapt the estimate used by Mori & Burkert (2000) for spherical galaxies, namely the comparison of the central pressure with ram pressure. We find that the latter estimate predicts the radius and mass of the gas disk remaining at the end of the second phase very well, and better than the Gunn & Gott (1972) criterion. From our simulations we conclude that gas disks of galaxies in high density environments are heavily truncated or even completely stripped, but also the gas disks of galaxies in low density environments are disturbed by the flow and back-falling material, so that they should also be pre-processed.

- by G. Hensler
- •
- Interstellar Medium, Galaxy Formation and Evolution, Galaxy Clusters, High Resolution
- by Hiroshi Karoji
- •
- Multidisciplinary, Gravitational Lensing, Nature, Radio Galaxies

In previous work on galaxy clusters, several authors reported the discovery of an unusual population of galaxies, which have spiral morphologies, but do not show any star-formation activity. These galaxies are called "passive spirals", and have been interesting since it has been difficult to understand the existence of such galaxies. Using a volume-limited sample (0.05< z <0.1 and Mr * < −20.5; 25813 galaxies) of the Sloan Digital Sky Survey data, we found 73 (0.28±0.03%) passive spiral galaxies and studied their environments. It is found that passive spiral galaxies exist in a local galaxy density of 1-2 Mpc −2 and have a 1-10 cluster-centric virial radius. Thus, the origins of passive spiral galaxies are likely to be cluster-related. These characteristic environments coincide with a previously reported environment where the galaxy star-formation rate suddenly declines and the so-called morphology-density relation turns. It is likely that the same physical mechanism is responsible for all of these observational results. The existence of passive spiral galaxies suggests that a phys-1 ical mechanism that works calmly is preferred to dynamical origins such as major merger/interaction since such a mechanism would destroy the spiral-arm structures. Compared with the observed cluster galaxy evolution such as the Butcher-Oemler effect and the morphological Butcher-Oemler effect, passive spiral galaxies are likely to be a key galaxy population in transition between red, elliptical/S0 galaxies in lowredshift clusters and blue, spiral galaxies more numerous in higher-redshift clusters.

- by Jon Loveday
- •
- Star Formation, Galaxy Formation and Evolution, Galaxy Clusters, Clusters of Galaxies

Bars and spiral arms have played an important role as constraints on the dynamics and on the distribution of dark matter in the optical parts of disk galaxies. Dynamics linked to the dissipative nature of gas, and its transformation into stars provide clues that spiral galaxies are driven by dissipation close to a state of marginal stability with respect to the dynamics in the galaxy plane.

- by Daniel Pfenniger
- •
- Dark Matter, Spiral Galaxies

The methodology involved in deriving the Hubble Constant via the calibration of the corrected peak luminosities of Type Ia supernovae (SNe) is reviewed. We first present a re-analysis of the Calan-Tololo (C-T) and Center for Astrophysics (CfA) Type Ia SN surveys. Bivariate linear least squares and quadratic boot-strapped fits in peak apparent magnitude and light curve shape are employed to correct this heterogeneous sample of peak apparent magnitudes, resulting in an homogeneous (and excellent) secondary distance indicator: the so-called corrected peak luminosity. We next provide an empirical calibration for this corrected luminosity, using Cepheid-based distances for seven nearby spiral galaxies host to Type Ia SNe. Included in this sample is the spectroscopically peculiar SN 1991T (in NGC 4527), whose corrected peak luminosity is shown to be indistinguishable from that of so-called ``normal'' SNe. A robust value of the Hubble Constant is derived and shown to be H0=73+/-2(r)+/-7(s) km/s/Mpc.

- by CHRISTOPHER BRYAN BROOK .
- •
- Astrophysics, Task Assignment, Spiral Galaxies, Tully-Fisher Relation
- by Salvatore Capozziello
- •
- Gravitation, General Relativity, Dark Matter, Dark Energy
- by Salvatore Capozziello
- •
- Mathematical Physics, Quantum Physics, General Relativity, Dark Matter
- by Jakob Walcher
- •
- Interstellar Medium, Star Formation, Molecular Clouds, Ultraviolet

We present the preliminary results of our 5-configuration, 20-pointing mosaic with the Australia Telescope Compact Array of the neutral hydrogen in the nearby spiral galaxy NGC 6744. The bulk of the HI resides in a `ring' underlying the outer optical disk, with 2 HI spiral arms extending further out to almost 1.5 optical radii. The velocity field is fairly regular, apart from evidence for streaming motions along the HI arms, and the influence of the companion IB(s)m galaxy NGC 6744A. We associate a cloud of HI at a heliocentric velocity of 846 km s-1 with another companion object, ESO 104-g44. Our attempts to construct a mass model for NGC 6744 suffer from poor resolution in the inner disk, and the uncertainty in the total HI flux of NGC 6744. We anticipate that HIPASS observations will be crucial in resolving the latter issue.

- by Stuart Ryder
- •
- Spiral Galaxies, Velocity Field

In Greek, the word “nature” derives from the verb phyō, to come forth, to grow, to become. It is life independent of thought, and non-constructed. Aristotle calls physis “the coming-to-be what it is” (1960: 193a). Nature as physis contains both the movement of emergence and the specific growth, becoming and being, productivity and product. Growth in this context implies that withering and demise belong to it; genesis is always phthora, decay is integral to the act of coming-to-light. In pre-Socratic thought, the human being is seen as part of physis, which contains the human as a whole and in his/her individuality. The focus of the Roman words nasci and natura is, however, on being conceived and being born. Natura now means “native” and “inherent,” but is also defined in terms of the right of disposal, which influenced the formation of the modern term of object (cf. Picht 1998: 90). Nature as the quintessence of objects is nature as the sum of everything that is at our disposal in thought and action.

- by Carlos Castillo
- •
- Physical Chemistry, Pigmentation, Electrophysiology, Kinetics