Abstract. High sensitivity (rms noise ∼ 0.5 mJy) 21-cm H i line observations were made of 33 galaxies in the Virgo cluster, using the refurbished Arecibo telescope, which resulted in the detection of 12 objects. These data, combined with the measurements available from the literature, provide the first set of H i data that is complete for all 355 late-type (Sa-Im-BCD) galaxies in the Virgo cluster with mp ≤ 18.0 mag. The Virgo cluster H i mass function (HIMF) that was derived for this optically selected galaxy sample is in agreement with the HIMF derived for the Virgo cluster from the blind HIJASS H i survey and is inconsistent with the Field HIMF. This indicates that both in this rich cluster and in the general field, neutral hydrogen is primarily associated with late-type galaxies, with marginal contributions from early-type galaxies and isolated H i clouds. The inconsistency between the cluster and the field HIMF derives primarily from the difference in the optical luminosity function of late-type galaxies in the two environments, combined with the HI deficiency that is known to occur in galaxies in rich clusters.

We present B-and R-band optical imaging and photometry, Hα narrow-band imaging, near-infrared H-band imaging, and H i 21-cm spectroscopy of the nearby (V h =407 km/s), Sd spiral galaxy UGC 7321. UGC 7321 exhibits a remarkably thin stellar disk with no discernible bulge component. The galaxy has a very diffuse, low surface brightness disk, which appears to suffer relatively little internal extinction in spite of its nearly edge-on geometry (i ≈88 • ). If seen face-on, UGC 7321 would have an observed central B-band surface brightness of only ∼23.4 mag arcsec −2 .The UGC 7321 disk shows significant B − R color gradients in both the radial and vertical directions: ∆(B − R) ≥0.80 magnitudes along the galaxy major axis, and ∆(B − R) as large as 0.45 magnitudes is observed parallel to the galaxy minor axis. These color gradients cannot be explained solely by dust and are indicative of changes in the mix of stellar ages and/or metallicity as a function of both radius and height above the galaxy plane. The outer regions of the UGC 7321 disk are too blue to be explained by low metallicity alone (B − R ≤ 0.6), and must be relatively young. However, the galaxy also contains stellar populations with B − R >1.1, indicating it is not a young or recently-formed galaxy.The disk of UGC 7321 is not a simple exponential, but exhibits a light excess at small radii, as well as distinct surface brightness zones. Despite its organized disk structure, many of the global properties of UGC 7321 (M B = −17.0; M HI =1.1×10 9 M ⊙ ;

High sensitivity 21-cm H i line observations with an rms noise level of ∼0.5 mJy were made of 35 spiral galaxies in the Coma Supercluster, using the refurbished Arecibo telescope, leading to detection of 25 objects. These data, combined with the measurements available in the literature, provide the set of H i data for 94% of all late-type galaxies in the Coma Supercluster with an apparent photographic magnitude m p ≤ 15.7 mag. We confirm that the typical scale of H i deficiency around the Coma cluster is 2 Mpc, i.e. one virial radius. Comparing the H i mass function (HIMF) of cluster with non-cluster members of the Coma Supercluster we detected a shortage of high H i mass galaxies among cluster members that can be attributed to the pattern of H i deficiency found in rich clusters.

We have carried out a fully sampled large area (4°× 8°) 21‐cm H i line survey of part of the Virgo cluster using the Jodrell Bank multibeam instrument. The survey has a sensitivity some three times better than the standard HIJASS (H i Jodrell All Sky Survey) and HIPASS (H i Parkes All Sky Survey) surveys. We detect 31 galaxies, 27 of which are well‐known cluster members. The four new detections have been confirmed in the HIPASS data and by follow‐up Jodrell Bank pointed observations. One object lies behind M86, but the other three have no obvious optical counterparts upon inspection of the digital sky survey fields. These three objects were mapped at Arecibo with a smaller 3.6‐arcmin half power beam width (HPBW) and a four times better sensitivity than the Jodrell Bank data, which allow an improved determination of the dimensions and location of two of the objects, but surprisingly failed to detect the third. The two objects are resolved by the Arecibo beam, giving them a size far larger than any optical images in the nearby field. To our mass limit of 5 × 107(Δv/50 km s−1) M⊙ and column density limit of 3 × 1018(Δv/50 km s−1) atom cm−2, these new detections represent only about 2 per cent of the cluster atomic hydrogen mass. Our observations indicate that the H i mass function of the cluster turns down at the low‐mass end, making it very different to the field galaxy H i mass function. This is quite different to the Virgo cluster optical luminosity function, which is much steeper than that in the general field. Many of the sample galaxies are relatively gas‐poor compared with H i selected samples of field galaxies, confirming the ‘anaemic spirals’ view of Virgo cluster late‐type galaxies. The velocity distribution of the H i detected galaxies is also very different to that of the cluster as a whole. There are relatively more high‐velocity galaxies in the H i sample, suggesting that they form part of a currently infalling population. The H i sample with optical identifications has a minimum H i column density cut‐off more than an order of magnitude above that expected from the sensitivity of the survey. This observed column density is above the normally expected level for star formation to occur. The two detections with no optical counterparts have very much lower column densities than that of the rest of the sample, below the star formation threshold.

The process of tooth displacement in response to orthodontic forces is thought to be induced by the stresses and strains in the periodontium. The mechanical force on the tooth is transmitted to the alveolar bone through a layer of soft connective tissue, the periodontal ligament. Stress and/or strain distribution in this layer must be derived from mathematical models, such as the finite element method, because it cannot be measured directly in a non-destructive way. The material behaviour of the constituent tissues is required as an input for such a model. The purpose of this study was to determine the time-dependent mechanical behaviour of the periodontal ligament due to orthodontic loading of a tooth. Therefore, in vivo experiments were performed on beagle dogs. The experimental configuration was simulated in a finite element model to estimate the poroelastic material properties for the periodontal ligament. The experiments showed a two-step response: an instantaneous displacement of 14.10 +/- 3.21 microns within 4 s and a more gradual (creep) displacement reaching a maximum of 60.00 +/- 9.92 microns after 5 h. This response fitted excellently in the finite element model when 21 per cent of the ligament volume was assigned a permeability of 1.0 x 10(-14) m4/N s, the remaining 97 per cent was assigned a permeability of 2.5 x 10(-17) m4/N s. A tissue elastic modulus of 0.015 +/- 0.001 MPa was estimated. Our results indicate that fluid compartments within the periodontal ligament play an important role in the transmission and damping of forces acting on teeth.

We present the basic properties of three objects near the Galactic Plane-a large galaxy and two candidate globular clusters-discovered in the Two Micron All Sky Survey (2MASS) dataset. All were noted during spot-checks of the data during 2MASS quality assurance reviews. The galaxy is a late-type spiral galaxy (Sc-Sd), ~11 Mpc distant, at l = 236.82°, b = -1.86°. From its observed angular extent of 6.3' in the near infrared, we estimate an extinction-corrected optical diameter of ~9.5', making it larger than most Messier galaxies. The candidate globular clusters are ~2-3' in extent and are hidden optically behind foreground extinctions of A v ~18-21 mag at l ~ 10°, b ~ 0°. These chance discoveries were not the result of any kind of systematic search but they do hint at the wealth of obscured sources of all kinds, many previously unknown, that are in the 2MASS dataset.

Context. When a galaxy acquires material from the outside, it is likely that the resulting angular momentum of the accreted material is decoupled from that of the pre-existing galaxy. The presence of stars counter-rotating with respect to other stars and/or gas represents an extreme case of decoupling. Aims. NGC 5719, an almost edge-on Sab galaxy with a prominent skewed dust lane, shows a spectacular on-going interaction with its face-on Sbc companion NGC 5713. Observations of such interacting systems provide insight into the processes at work in assembling and reshaping galaxies. Methods. Studies were made of the distribution and kinematics of neutral hydrogen in the NGC 5719/13 galaxy pair and the ionised gas and stellar kinematics along the major axis of NGC 5719. Results. Two HI tidal bridges that loop around NGC 5719 and connect to NGC 5713, and two HI tidal tails departing westward from NGC 5713 were detected. There is a correspondence between the HI condensations and the location of clumps of young stars within and outside the disc of NGC 5719. The low-mass satellite PGC 135857 at the tip of the northern tail was detected in HI, and is likely a by-product of the interaction. The neutral and ionised hydrogen in the disc of NGC 5719 are counter-rotating with respect to the main stellar disc. The counter-rotating stellar disc contains about 20% of the stars in the system, and has the same radial extension as the main stellar disc. This is the first interacting system in which a counter-rotating stellar disc has been detected. Conclusions. The data support a scenario where HI from the large reservoir available in the galaxy's surroundings was accreted by NGC 5719 onto a retrograde orbit and subsequently fuelled the in situ formation of the counter-rotating stellar disc.

We study the distribution of orbital eccentricities of stars in thick disks generated by the heating of a pre-existing thin stellar disk through a minor merger (mass ratio 1:10), using N-body/SPH numerical simulations of interactions that span a range of gas fractions in the primary disk and initial orbital configurations. The resulting eccentricity distributions have an approximately triangular shape, with a peak at 0.2−0.35, and a relatively smooth decline towards higher values. Stars originally in the satellite galaxy tend to have higher eccentricities (on average from e = 0.45 to e = 0.75), which is in general agreement with the models of Sales and collaborators, although in detail we find fewer stars with extreme values and no evidence of their secondary peak around e = 0.8. The absence of this high-eccentricity feature results in a distribution that qualitatively matches the observations. Moreover, the increase in the orbital eccentricities of stars in the solar neighborhood with vertical distance from the Galactic mid-plane found by Dierickx and collaborators can be qualitatively reproduced by our models, but only if the satellite is accreted onto a direct orbit. We thus speculate that if minor mergers were the dominant means of forming the Milky Way thick disk, the primary mechanism should be merging with satellite(s) on direct orbits.