117,518 research outputs found
Kinematic properties of early type galaxy halos using planetary nebulae
No full textWe studied the kinematics of the halo of a sample of 16 early type galaxies out to 5-10 effective radii using Planetary Nebulae (PNe) as kinematic tracers (Coccato et al. 2009)
On the relation between circular velocity and central velocity dispersion in high and low surface brightness galaxies
No full textIn order to investigate the correlation between the circular velocity V_c and the central velocity dispersion of the spheroidal component σ_c, we analyzed these quantities for a sample of 40 high surface brightness (HSB) disk galaxies, eight giant low surface brightness (LSB) spiral galaxies, and 24 elliptical galaxies characterized by flat rotation curves. Galaxies have been selected to have a velocity gradient =0.35 R_25. We used these data to better define the previous V_c-σ_c correlation for spiral galaxies (which turned out to be HSB) and elliptical galaxies, especially at the lower end of the σ_c values. We find that the V_c-σ_c relation is described by a linear law out to velocity dispersions as low as σ_c~50 km/s, while in previous works a power law was adopted for galaxies with σ_c>80 km/s. Elliptical galaxies with V_c based on dynamical models or directly derived from the H I rotation curves follow the same relation as the HSB galaxies in the V_c-σ_c plane. On the other hand, the LSB galaxies follow a different relation, since most of them show either higher V_c or lower σ_c with respect to the HSB galaxies. This argues against the relevance of baryon collapse to the radial density profile of the dark matter halos of LSB galaxies. Moreover, if the V_c-σ_c relation is equivalent to one between the mass of the dark matter halo and that of the supermassive black hole, then these results suggest that the LSB galaxies host a supermassive black hole (SMBH) with a smaller mass compared to HSB galaxies with an equal dark matter halo. On the other hand, if the fundamental correlation of SMBH mass is with the halo circular velocity, then LSB galaxies should have larger black hole masses for a given bulge dispersion. Elliptical galaxies with V_c derived from H I data and LSB galaxies were not considered in previous studies
The search for inner polar disks with integral field spectroscopy: the case of NGC 2855 and NGC 7049
No full textContext: The presence of non-circular and off-plane gas motion is frequently observed in the inner regions of disk galaxies. Aims: With integral-field spectroscopy we have measured the surface-brightness distribution and kinematics of the ionized gas in NGC 2855 and NGC 7049. These two early-type spiral galaxies were selected as possibly hosting a kinematically-decoupled gaseous component in orthogonal rotation with respect to the galaxy disk. Methods: We have modeled the ionized-gas kinematics and distribution of both galaxies assuming that the gaseous component is distributed either on two orthogonally-rotating disks or in a single and strongly warped disk. Results: In both galaxies the velocity field and distribution of the inner gas are consistent with the presence of an inner polar disk. In NGC 2855 it correponds to the innermost and strongly warped portion of the main disk. In NGC 7049 it is a central and geometrically-decoupled disk, which is nested in the main disk
The counter-rotating stellar core of NGC 4494
No full textContext. Kinematically decoupled cores (KDCs) are often found in the centers of early-type galaxies. Aims. We aim to investigate the kinematics, structure, and stellar populations of the KDC residing in the early-type galaxy NGC 4494 to understand its formation. Methods. We used long-slit spectroscopic data obtained with the FORS2 instrument on the VLT to measure the stellar kinematics and stellar populations. We performed a spectroscopic decomposition to disentangle the properties of the KDC from those of the host galaxy and construct models of the observed rotation curve. Results. The rotation curve is characterized by two symmetric dips at |R| = 6, where the rotation velocity drops to zero. Contrary to previous studies that explained the decoupled structure as a rapidly co-rotating disk, our analysis clearly shows that it is a counter-rotating component. A counter-rotating core is indeed needed to reproduce the observed dip in the velocity curve. The properties of the stellar populations of the decoupled core and the main galaxy are very similar: old stars (12-13 Gyr) with slightly super-solar metallicities (0-<-[Z/H]< 0.15 dex) and α-enhanced (0-<-[α/Fe]< 0.15 dex). Conclusions. Our results indicate that the counter-rotating component is a disk of about 1 kpc in diameter that is obscured by dust in the central 0.12 kpc. The properties of its stellar populations suggest that it formed from the same material as the main stellar body of the host galaxy. This could have happened via internal processes such as the precession of a pre-existing rotating core, or, alternatively, via gas accretion in retrograde orbits followed by star formation. In the latter scenario, the accretion event occurred almost simultaneously with the formation of the galaxy, using material that had the same composition as the gas from which the stars in the main body of the galaxy were formed
The deposition from the Cross in the church of Saint-Germain-en-Laye (France): A masterpiece of Romanesque sculpture? Materials characterization to solve a 20th c. mystery
No full textDating and authenticating stone-sculpted works of art is a challenging aspect of cultural heritage studies. In fact, it is often possible to provenance the rock, by comparison of petrological, mineralogical and geochemical data, but no dating of the sculpture can be obtained. Also, stylistic observations need to be considered with care. However, in the case of mastic incrustation sculptures, the applied polychromy can support dating studies, based on pigments and binders. In the church of Saint-Germain-en-Laye, a haut-relief representing the Deposition from the Cross is exposed. The calcareous slab is decorated with red and black mastics. It resembles closely the Deposition from the Cross in the transept of Parma Cathedral, dated 1178 and “signed” by Benedictus Antelami. However, the St-Germain Deposition appeared in 1994, when it was donated to the parish by the descendants of Julien Auguste Duperrier, marble worker and collector of Italian antiquities. His last trip to Italy took place in 1924. No information is available on his deal, neither on the transport means arranged, nor on the sculpture itself (author, contractor, date, etc.). Art historical and historical considerations propose either a 12th or 19th–20th c. context for the creation of the sculpture. Chemical analyses of the pigments and binders are therefore proposed to clarify the dating the work of art. Microscopic samples are characterized by a multi-analytical approach: vibrational spectroscopies and X-ray powder diffraction are used to characterize the rock and the polychrome mastic. The rock is identified as a micritic limestone, and shows sulphation issues. Through Raman scattering measurements, the pigments were identified: carbon in the black mastic, and a mixture of red lead and a modern synthetic pigment (PR49:1) in the red areas. This information sheds new light on the chronology and manufacture of the Deposition from the Cross of Saint-Germain-en-Laye. These results allow for a better definition of further lines of research, and to finally propose an authorship for the sculpture
Disentangling the kinematics and stellar populations of counter-rotating stellar discs in galaxies
No full textSpectroscopic VIMOS/IFU observations are presented for three galaxies known to host two stellar counter-rotating discs of comparable sizes. For the first time both the kinematics and stellar population properties of the two counter-rotating discs in the observed galaxies were separated and measured. The secondary, less massive, stellar component rotates in the same direction as the ionised gas and is on average younger and less metal-rich than the main galaxy disc. These results support the scenario of gas accretion followed by star formation as the origin for large counter-rotating stellar discs in galaxies, and set an upper limit of 44% to those formed by binary galaxy mergers
Integral field spectroscopy of NGC 2855 and NGC 7049
No full textWe present the ionized gas bidimensional velocity field of two spiral galaxies (NGC 2855 and NGC 7049) which show an S-distortion of the isovelocities. We performed models of the velocity field in order to investigate the possible presence of an inner polar disk which generate such a kinematic behaviour, or the presence of a strong internal warp of the gaseous disk. The decomposition of the surface brightness map of NGC 7049 seems to indicate the presence of an orthogonal decoupled component, while the case of NGC 2855 seems to be better explained in terms of a strong central warp of the gaseous disk
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The difference in age of the two counter-rotating stellar disks of the spiral galaxy NGC 4138
No full textContext. Galaxies accrete material from the environment through acquisitions and mergers. These processes contribute to the galaxy assembly and leave their fingerprints on the galactic morphology, internal kinematics of gas and stars, and stellar populations. Aims: The Sa spiral NGC 4138 is known to host two counter-rotating stellar disks, with the ionized gas co-rotating with one of them. We measured the kinematics and properties of the two counter-rotating stellar populations to constrain their formation scenario. Methods: A spectroscopic decomposition of the observed major-axis spectrum was performed to disentangle the relative contribution of the two counter-rotating stellar and one ionized-gas components. The line-strength indices of the two counter-rotating stellar components were measured and modeled with single stellar population models that account for the α/Fe overabundance. Results: The counter-rotating stellar population is younger, marginally more metal poor, and more α-enhanced than the main stellar component. The younger stellar component is also associated with a star-forming ring. Conclusions: The different properties of the counter-rotating stellar components of NGC 4138 rule out the idea that they formed because of bar dissolution. Our findings support the results of numerical simulations in which the counter-rotating component assembled from gas accreted on retrograde orbits from the environment or from the retrograde merging with a gas-rich dwarf galaxy
Dating the formation of the counter-rotating stellar disc in the spiral galaxy NGC 5719 by disentangling its stellar populations
No full textWe present the results of the VLT/VIMOS integral-field spectroscopic observations of the inner 28 × 28 arcsec^2 (3.1 × 3.1 kpc^2) of the interacting spiral NGC 5719, which is known to host two cospatial counter-rotating stellar discs. At each position in the field of view, the observed galaxy spectrum is decomposed into the contributions of the spectra of two stellar and one ionized-gas components. We measure the kinematics and the line strengths of the Lick indices of the two stellar counter-rotating components. We model the data of each stellar component with single stellar population models that account for the α/Fe overabundance. We also derive the distribution and kinematics of the ionized-gas disc, that is associated with the younger, less rich in metals, more α-enhanced, and less luminous stellar component. They are both counter rotating with respect the main stellar body of the galaxy. These findings prove the scenario where gas was accreted first by NGC 5719 on to a retrograde orbit from the large reservoir available in its neighbourhoods as a result of the interaction with its companion NGC 5713, and subsequently fuelled the in situ formation of the counter-rotating stellar disc
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