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We present an analysis of the orientations of 1433 galaxies found in the region 15h 48m ≤α(2000) ≤ 19h 28m , −68°≤δ(2000) ≤−62° . In this region we investigated three Abell clusters (S0794, S0797, S0805) of richness Class 0 and the Triangulum Australis cluster. Our aim is to examine non-random effects in galaxy orientations in clusters. In addition, we classified the investigated galaxies into subsamples on the basis of their axial ratio, major diameter and morphology. The spin vector orientations of total galaxies in the investigated region is found to be random. No preferred orientation is found in the clusters. We could not note any morphological dependence of the galaxy orientations in our samples. No preferred orientations can be seen for the spiral galaxies. The morphologically unidentified galaxies, galaxies having major diameters of <47 arcsec, and the nearly edge-on galaxies ( b / a < 0.5, 0.4 < b / a ≤ 0.5) show anisotropy: spin vectors of galaxies tend to be oriented perpendicular to the Local Supercluster plane and spin vector projections tend to point radially with respect to the Virgo cluster centre. 相似文献
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Roland Jesseit Michele Cappellari Thorsten Naab Eric Emsellem Andreas Burkert 《Monthly notices of the Royal Astronomical Society》2009,397(3):1202-1214
We use two-dimensional kinematic maps of simulated binary disc mergers to investigate the λR -parameter, which is a luminosity-weighted measure of projected angular momentum per unit mass. This parameter was introduced to subdivide the SAURON sample of early-type galaxies in so-called fast λR > 0.1 and slow rotators λR < 0.1 . Tests on merger remnants reveal that λR is a robust indicator of the true angular momentum content in elliptical galaxies. We find the same range of λR values in our merger remnants as in the SAURON galaxies. The merger mass ratio is decisive in transforming fast rotators into slow rotators in a single binary merger, the latter being created mostly in an equal-mass merger. Slow rotators have a λR which does not vary with projection. The confusion rate with face-on fast rotators is very small. Mergers with a gas component form slow rotators with smaller ellipticities than collisionless merger remnants have, and are in much better agreement with the SAURON slow rotators. Remergers of merger remnants are slow rotators, but tend to have too high ellipticities. Fast rotators maintain the angular momentum content from the progenitor disc galaxy if merger mass ratio is high. Some SAURON galaxies have values of λ R as high as our progenitor disc galaxies. 相似文献
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L. Cortese A. Boselli P. Franzetti R. Decarli G. Gavazzi S. Boissier V. Buat 《Monthly notices of the Royal Astronomical Society》2008,386(2):1157-1168
We investigate the dependence of the total-IR (TIR) to ultraviolet (UV) luminosity ratio method for calculating the UV dust attenuation A (UV) from the age of the underlying stellar populations by using a library of spectral energy distributions for galaxies with different star formation histories. Our analysis confirms that the TIR/UV versus A (UV) relation varies significantly with the age of the underlying stellar population: that is, for the same TIR/UV ratio, systems with low specific star formation rate (SSFR) suffer a lower UV attenuation than starbursts. Using a sample of nearby field and cluster spiral galaxies, we show that the use of a standard (i.e. age-independent) TIR/UV versus A (UV) relation leads to a systematic overestimate up to 2 mag of the amount of UV dust attenuation suffered by objects with low SSFR and in particular H i -deficient star-forming cluster galaxies. This result points out that the age-independent TIR/UV versus A (UV) relation cannot be used to study the UV properties of large samples of galaxies including low star-forming systems and passive spirals. Therefore, we give some simple empirical relations from which the UV attenuation can be estimated taking into account its dependence on the age of the stellar populations, providing a less biased view of UV properties of galaxies. 相似文献
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I. Trujillo A. Asensio Ramos J. A. Rubiño-Martín Alister W. Graham J. A. L. Aguerri J. Cepa C. M. Gutiérrez 《Monthly notices of the Royal Astronomical Society》2002,333(3):510-516
We have investigated the structural and dynamical properties of triaxial stellar systems whose surface brightness profiles follow the r 1/ n luminosity law – extending the analysis by Ciotti, who explored the properties of spherical r 1/ n systems. A new analytical expression that accurately reproduces the spatial (i.e., deprojected) luminosity density profiles (error less than 0.1 per cent) is presented for detailed modelling of the Sérsic family of luminosity profiles. We evaluate both the symmetric and the non-axisymmetric components of the gravitational potential and force, and compute the torques as a function of position. For a given triaxiality, stellar systems with smaller values of n have a greater non-axisymmetric gravitational field component . We also explore the strength of the non-axisymmetric forces produced by bulges with differing n and triaxiality on systems having a range of bulge-to-disc ratios. The increasing disc-to-bulge ratio with increasing galaxy type (decreasing n ) is found to greatly reduce the amplitude of the non-axisymmetric terms, and therefore reduce the possibility that triaxial bulges in late-type systems may be the mechanism or perturbation for non-symmetric structures in the disc.
Using seeing-convolved r1/ n -bulge plus exponential-disc fits to the K -band data from a sample of 80 nearby disc galaxies, we probe the relations between galaxy type, Sérsic index n and the bulge-to-disc luminosity ratio. These relations are shown to be primarily a consequence of the relation between n and the total bulge luminosity. In the K band, the trend of decreasing bulge-to-disc luminosity ratio along the spiral Hubble sequence is predominantly, though not entirely, a consequence of the change in the total bulge luminosity; the trend between the total disc luminosity and Hubble type is much weaker. 相似文献
Using seeing-convolved r
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We examine the effects of cooling flows on the T X – L Bol relation for a sample of the most X-ray luminous ( L Bol > 1045 erg s−1 ) clusters of galaxies known. Using high-quality ASCA X-ray spectra and ROSAT images we explicitly account for the effects of cooling flows on the X-ray properties of the clusters and show that this reduces the previously noted dispersion in the T X – L Bol relationship. More importantly, the slope of the relationship is flattened from L Bol ∝ T 3 X to approximately L Bol ∝ T 2 X , in agreement with recent theoretical models which include the effects of shocks and pre-heating on the X-ray gas. We find no evidence for evolution in the T X – L Bol relation within z ∼ 0.3. Our results demonstrate that the effects of cooling flows must be accounted for before cosmological parameters can be determined from X-ray observations of clusters. The results presented here should provide a reliable basis for modelling the T X – L Bol relation at high X-ray luminosities. 相似文献
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H. Sugai R. I. Davies M. Ishii M. J. Ward 《Monthly notices of the Royal Astronomical Society》2000,317(2):447-452
We have obtained an H2 v =1–0 S(1) image of a merging galaxy system, NGC 6090, by using a Fabry–Perot imager. The H2 emission originates between the double nuclei of pre-merger galaxies, and exhibits an arc-like or ring-like structure almost connecting the double nuclei. This structure is similar to that suggested for Arp 220 from the velocity field measured by CO radio emission. The separation of the double nuclei in NGC 6090 is 5–6 arcsec, corresponding to a projected distance of 3–4 kpc. This is much larger than that of Arp 220 and suggests that the molecular gas distribution can form an organized shape between the nuclei, such as a ring, in a rather early phase of merging. 相似文献
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K. K. Knudsen P. P. van der Werf J.-P. Kneib 《Monthly notices of the Royal Astronomical Society》2008,384(4):1611-1626
We have conducted a submillimetre mapping survey of faint, gravitationally lensed sources, where we have targeted 12 galaxy clusters and additionally the New Technology Telescope (NTT) Deep Field. The total area surveyed is 71.5 arcmin2 in the image plane; correcting for gravitational lensing, the total area surveyed is 40 arcmin2 in the source plane for a typical source redshift z ≈ 2.5. In the deepest maps, an image plane depth of 1σ rms ∼0.8 mJy is reached. This survey is the largest survey to date to reach such depths. In total 59 sources were detected, including three multiply imaged sources. The gravitational lensing makes it possible to detect sources with flux density below the blank field confusion limit. The lensing-corrected fluxes range from 0.11 to 19 mJy. After correcting for multiplicity, there are 10 sources with fluxes <2 mJy of which seven have submJy fluxes, doubling the number of such sources known. Number counts are determined below the confusion limit. At 1 mJy, the integrated number count is ∼104 deg−2 , and at 0.5 mJy it is ∼2 × 104 deg−2 . Based on the number counts, at a source plan flux limit of 0.1 mJy, essentially all of the 850-μm background emission has been resolved. The dominant contribution (>50 per cent) to the integrated background arises from sources with fluxes S 850 between 0.4 and 2.5 mJy, while the bright sources S 850 > 6 mJy contribute only 10 per cent. 相似文献
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Andrew Harrison Phil Puxley Adrian Russell & Peter Brand 《Monthly notices of the Royal Astronomical Society》1998,297(2):624-632
We present measurements of several near-infrared emission lines from the nearby galaxy NGC 253. We have been able to measure four H2 lines across the circumnuclear starburst, from which we estimate the ortho- to para- ratio of excited H2 to be ∼2. This indicates that the bulk of the H2 emission arises from photodissociation regions (PDRs), rather than from shocks. This is the case across the entire region of active star formation.
As the H2 emission arises from PDRs, it is likely that the ratio of H2 to Brγ (the bright hydrogen recombination line) is a measure of the relative geometry of O and B stars and PDRs. Towards the nucleus of NGC 253 the geometry is deduced to be tightly clustered O and B stars in a few giant H II regions that are encompassed by PDRs. Away from the nuclear region, the geometry becomes that of PDRs bathed in a relatively diffuse ultraviolet radiation field.
The rotation curves of 1–0 S(1) and Brγ suggest that the ionized gas is tracing a kinetic system different from that of the molecular gas in NGC 253, particularly away from the nucleus. 相似文献
As the H
The rotation curves of 1–0 S(1) and Brγ suggest that the ionized gas is tracing a kinetic system different from that of the molecular gas in NGC 253, particularly away from the nucleus. 相似文献
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Russell J. Smith John R. Lucey Michael J. Hudson David J. Schlegel Roger L. Davies 《Monthly notices of the Royal Astronomical Society》2000,313(3):469-490
We present new spectroscopic data for 532 early-type galaxies, predominantly Abell cluster members with cz <12 000 km s−1 . We tabulate 919 individual measurements, from six observing runs, for recession velocity, cz , central velocity dispersion, σ , and magnesium line-strength indices, Mg2 and Mg b . The median estimated error, per measurement, in σ is 5 per cent. The Mg2 line-strength data have median errors of 0.009 mag. The observed scatter between repeat measurements is largely accounted for by photon-counting errors. These data will be employed in forthcoming papers, where they will form part of a merged and standardized catalogue of Fundamental Plane data for use in cluster distance estimates and peculiar velocity analyses. 相似文献
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Nicholas Scott Michele Cappellari Roger L. Davies R. Bacon P. T. de Zeeuw Eric Emsellem Jésus Falcón-Barroso Davor Krajnovi&#; Harald Kuntschner Richard M. McDermid Reynier F. Peletier Antonio Pipino Marc Sarzi Remco C. E. van den Bosch Glenn van de Ven † Eveline van Scherpenzeel 《Monthly notices of the Royal Astronomical Society》2009,398(4):1835-1857