Distribution and motions of atomic hydrogen in lenticular galaxies. X. The blue SO galaxy NGC 5102

We have mapped the blue gas-rich S0 galaxy NGC 5102 in the 21-cm HI line with a spatial resolution of 34'' x 37'' (DELTAalpha x DELTAdelta) and a velocity resolution of 12 km s-1. Optically NGC 5102 is a peculiar S0 galaxy, in the sense that it has unusually blue colours, and shows evidence for a burst of star formation a few times 10(8) years ago in its nucleus. Also the inner bulge and parts of its disk show signs of low-level star formation activity. It further has a 'supershell' of 1.7 kpc diameter seen in Halpha around its central regions, a unique feature for a lenticular galaxy.The HI distribution has a pronounced central depression of 1.9 kpc radius, and most of the HI is concentrated in a 3.6 kpc wide ring with an average radius of 3.7 kpc (= 0.7 R25), assuming a distance of 4 Mpc for NGC 5102. The maximum azimuthally averaged HI surface density in the ring is 1.4 M. pc-2, comparable to that found in other SO galaxies. The extent of the HI gas is not much larger than the optical de Vaucouleurs' radius (R25) of die galaxy, contrary to what is found in other gas-rich S0's, which often have large outer HI rings at R approximately 2 R25. The HI velocity field is quite regular, showing no evidence for large-scale deviations from circular rotation, and the HI is found to rotate in the plane of the stellar disk. The rotation curve is essentially flat at V(rot) approximately 95 km s-1 out to R = 6 kpc (1.1 R25). Assuming a simple spherical mass model, we find a total mass-to-light ratio M(T)/L(B)0 = 4.3 M./L. within R = 6 kpc.In contrast to other SO galaxies studied in this series of papers, both the HI mass/blue luminosity ratio and the radial HI distribution are similar to those in early-type spirals. The HI may be an old, ''smouldering'', disk or it may have been acquired through capture of a gas-rich smaller galaxy. The recent starburst in the nuclear region, which gave the galaxy its blue colour, may have been caused by partial radial collapse of the gas disk, or by infall of a gas-rich dwarf galaxy.</p

Cold gas accretion in galaxies

Evidence for the accretion of cold gas in galaxies has been rapidly accumulating in the past years. HI observations of galaxies and their environment have brought to light new facts and phenomena which are evidence of ongoing or recent accretion: 1) A large number of galaxies are accompanied by gas-rich dwarfs or are surrounded by HI cloud complexes, tails and filaments. It may be regarded as direct evidence of cold gas accretion in the local universe. It is probably the same kind of phenomenon of material infall as the stellar streams observed in the halos of our galaxy and M31. 2) Considerable amounts of extra-planar HI have been found in nearby spiral galaxies. While a large fraction of this gas is produced by galactic fountains, it is likely that a part of it is of extragalactic origin. 3) Spirals are known to have extended and warped outer layers of HI. It is not clear how these have formed, and how and for how long the warps can be sustained. Gas infall has been proposed as the origin. 4) The majority of galactic disks are lopsided in their morphology as well as in their kinematics. Also here recent accretion has been advocated as a possible cause. In our view, accretion takes place both through the arrival and merging of gas-rich satellites and through gas infall from the intergalactic medium (IGM). The infall may have observable effects on the disk such as bursts of star formation and lopsidedness. We infer a mean ``visible'' accretion rate of cold gas in galaxies of at least 0.2 Msol/yr. In order to reach the accretion rates needed to sustain the observed star formation (~1 Msol/yr), additional infall of large amounts of gas from the IGM seems to be required.Comment: To appear in Astronomy & Astrophysics Reviews. 34 pages. Full-resolution version available at http://www.astron.nl/~oosterlo/accretionRevie

Shape Variation in Aterian Tanged Tools and the Origins of Projectile Technology: A Morphometric Perspective on Stone Tool Function

BACKGROUND: Recent findings suggest that the North African Middle Stone Age technocomplex known as the Aterian is both much older than previously assumed, and certainly associated with fossils exhibiting anatomically modern human morphology and behavior. The Aterian is defined by the presence of 'tanged' or 'stemmed' tools, which have been widely assumed to be among the earliest projectile weapon tips. The present study systematically investigates morphological variation in a large sample of Aterian tools to test the hypothesis that these tools were hafted and/or used as projectile weapons. METHODOLOGY/PRINCIPAL FINDINGS: Both classical morphometrics and Elliptical Fourier Analysis of tool outlines are used to show that the shape variation in the sample exhibits size-dependent patterns consistent with a reduction of the tools from the tip down, with the tang remaining intact. Additionally, the process of reduction led to increasing side-to-side asymmetries as the tools got smaller. Finally, a comparison of shape-change trajectories between Aterian tools and Late Paleolithic arrowheads from the North German site of Stellmoor reveal significant differences in terms of the amount and location of the variation. CONCLUSIONS/SIGNIFICANCE: The patterns of size-dependent shape variation strongly support the functional hypothesis of Aterian tools as hafted knives or scrapers with alternating active edges, rather than as weapon tips. Nevertheless, the same morphological patterns are interpreted as one of the earliest evidences for a hafting modification, and for the successful combination of different raw materials (haft and stone tip) into one implement, in itself an important achievement in the evolution of hominin technologies

HI Velocity Fields and Rotation Curves

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