Tidal debris from high-velocity collisions as fake dark galaxies: A numerical model of VirgoHI21

High speed collisions, although current in clusters of galaxies, have long been neglected, as they are believed to cause little damages to galaxies, except when they are repeated, a process called harassment. In fact, they are able to produce faint but extended gaseous tails. Such low-mass, starless, tidal debris may become detached and appear as free floating clouds in the very deep HI surveys that are currently being carried out. We show in this paper that these debris possess the same apparent properties as the so-called "Dark Galaxies", objects originally detected in HI, with no optical counterpart, and presumably dark matter dominated. We present a numerical model of the prototype of such Dark Galaxies - VirgoHI21 -, that is able to reproduce its main characteristics: the one-sided tail linking it to the spiral galaxy NGC 4254, the absence of stars, and above all the reversal of the velocity gradient along the tail originally attributed to rotation motions caused by a massive dark matter halo and which we find to be consistent with simple streaming motions plus projection effects. According to our numerical simulations, this tidal debris was expelled 750 Myr ago during a fly-by at 1100 km/s of NGC 4254 by a massive companion which should now lie at a projected distance of about 400 kpc. A candidate for the intruder is discussed. The existence of galaxies that have never been able to form stars had already been challenged based on theoretical and observational grounds. Tidal collisions, in particular those occurring at high speed, provide a much more simple explanation for the origin of such putative Dark Galaxies.Comment: 13 pages, 6 figures, accepted for publication in Ap

The angular momentum of two collided rarefied preplanetesimals and the formation of binaries

This paper studies the mean angular momentum associated with the collision of two celestial objects in the earliest stages of planet formation. Of primary concern is the scenario of two rarefied preplanetesimals (RPPs) in circular heliocentric orbits. The theoretical results are used to develop models of binary or multiple system formation from RPPs, and explain the observation that a greater fraction of binaries originated farther from the Sun. At the stage of RPPs, small-body satellites can form in two ways: a merger between RPPs can have two centers of contraction, or the formation of satellites from a disc around the primary or the secondary. Formation of the disc can be caused by that the angular momentum of the RPP formed by the merger is greater than the critical angular momentum for a solid body. One or several satellites of the primary (moving mainly in low-eccentricity orbits) can be formed from this disc at any separation less than the Hill radius. The first scenario can explain a system such as 2001 QW322 where the two components have similar masses but are separated by a great distance. In general, any values for the eccentricity and inclination of the mutual orbit are possible. Among discovered binaries, the observed angular momenta are smaller than the typical angular momenta expected for identical RPPs having the same total mass as the discovered binary and encountering each other in circular heliocentric orbits. This suggests that the population of RPPs underwent some contraction before mergers became common.Comment: 12 pages, Monthly Notices of Royal Astron. Society, in pres

Quasi-Resonant Theory of Tidal Interactions

When a spinning system experiences a transient gravitational encounter with an external perturber, a quasi-resonance occurs if the spin frequency of the victim matches the peak orbital frequency of the perturber. Such encounters are responsible for the formation of long tails and bridges of stars during galaxy collisions. For high-speed encounters, the resulting velocity perturbations can be described within the impulse approximation. The traditional impulse approximation, however, does not distinguish between prograde and retrograde encounters, and therefore completely misses the resonant response. Here, using perturbation theory, we compute the effects of quasi-resonant phenomena on stars orbiting within a disk. Explicit expressions are derived for the velocity and energy change to the stars induced by tidal forces from an external gravitational perturber passing either on a straight line or parabolic orbit. Comparisons with numerical restricted three-body calculations illustrate the applicability of our analysis.Comment: 22 pages, 13 figures, ApJ submitted, numerical routines for evaluation of special functions and analytical results are provided upon reques

Spectrometric method to detect exoplanets as another test to verify the invariance of the velocity of light

Hypothetical influences of variability of light velocity due to the parameters of the source of radiation, for the results of spectral measurements of stars to search for exoplanets are considered. Accounting accelerations of stars relative to the barycenter of the star - a planet (the planets) was carried out. The dependence of the velocity of light from the barycentric radial velocity and barycentric radial acceleration component of the star should lead to a substantial increase (up to degree of magnitude) semi-major axes of orbits detected candidate to extrasolar planets. Consequently, the correct comparison of the results of spectral method with results of other well-known modern methods of detecting extrasolar planets can regard the results obtained in this paper as a reliable test for testing the invariance of the velocity of light.Comment: 11 pages, 5 figure

Study of the interacting system NGC 6845

We present optical spectroscopy, B, V, R and I CCD photometry and VLA neutral hydrogen observations of the interacting quartet NGC 6845, also know as Klemola 30. NGC 6845 A, the dominant component, sports a broad and bright tidal bridge and a faint tidal tail, which bifurcate. The tidal bridge has a (B-I) color bluer than that of NGC 6845 A inner disk. Five strong condensations, identified as HII regions brighter than the brightest in our Galaxy, are found along the tidal bridge, with the two most luminous located at the bridge tip. Two giant HII regions, comparable to 30 Dor, are located where the tidal bridge and the tidal tail joint the disk of NGC 6845 A. Since the age of the HII regions are 3-8 Myr, star formation has been occurring along the tidal bridge and the tidal arm well after they had begun to be torn apart (>= 100 Myr). Satoh model fitting to the rotation curve of the A component reveals a kinematical mass of 4.4(+-1.2)E11 M_sun, inside the central 12 kpc (H_0=75 km/s/Mpc). The HI emission shows two components, a more massive one that belongs to NGC 6845 A, and a second one associated to NGC 6845 B. We do not detect gas associated to galaxies C and D. The total amount of HI is 1.4E10 M_sun, five time the HI content of the Milky Way. The HI kinematics indicates an amount of dark matter associated to the A component two times higher than the mass inside its central 12 kpc. The group kinematics indicates an M/L ~ 43(+-2) or M/L ~ 66(+-2) (solar units), according to two different prescriptions for the internal absorption correction. In spite of this difference, both values furnish similar group mass (~1E13 M_sun). Although preliminary results on N-Body simulations indicate that either B or C might well create a tidal feature like the bridge of the A component, the collision with B appears to be more favourable.Comment: 24 pages, 11 JPEG figures, uses aastex.cls and natbib.sty (included). To appear in the June/1999 issue of the Astronomical Journa

Multi-wavelength Study of Young Massive Star Clusters in the Interacting Galaxy ARP 24

We made a multi-wavelength study of young massive star clusters (YSCs) in the interacting galaxy ARP 24, using the optical and ultraviolet images from Hubble Space Telescope (HST), Sloan Digital Sky Survey, and Galaxy Evolution Explorer; the mid-infrared images from Spitzer Space Telescope; and the narrow-band Ha image and optical spectra from the NAOC 2.16m telescope. Based on the HST images, we found that the brightest infrared knot in ARP 24 is associated with a complex of five young massive star clusters, within a region of ~ 0.95" radius (127pc) in size. The ages and masses of the star clusters in this complex and other regions were estimated using HST broadband photometries and the Starburst99 synthesis models. The star clusters in this complex are very young (within ages of ~ 3-5 Myr) and massive (masses of ~ 10^5 Msun). The ionization parameter and metallicity of the complex were estimated using the emission line ratios, and the star formation rates were calculated using monochromatic 24um, FUV, and Ha line luminosities. We speculate that ARP 24 may formed by a retrograde fly-by encounter indicated by its one-armed appearance and fan-like structure, and the formation of the YSCs in this galaxy is triggered by the interaction. The clusters in the YSC complex may formed in a single giant molecular cloud simultaneously. From the ultraviolet to mid-infrared spectral energy distributions, we found that the region of the YSC complex is relatively bluer in optical and has higher 24um dust emission relative to the starlight and 8um emission. This warm infrared color may due to strong UV radiation field or other mechanisms (e.g., shocks) within this region which may destroy the Polycyclic Aromatic Hydrocarbons and enhance the small grain emission at 24um.Comment: 33 pages, 9 figures, accepted for publication in A

Tides in colliding galaxies

Long tails and streams of stars are the most noticeable upshots of galaxy collisions. Their origin as gravitational, tidal, disturbances has however been recognized only less than fifty years ago and more than ten years after their first observations. This Review describes how the idea of galactic tides emerged, in particular thanks to the advances in numerical simulations, from the first ones that included tens of particles to the most sophisticated ones with tens of millions of them and state-of-the-art hydrodynamical prescriptions. Theoretical aspects pertaining to the formation of tidal tails are then presented. The third part of the review turns to observations and underlines the need for collecting deep multi-wavelength data to tackle the variety of physical processes exhibited by collisional debris. Tidal tails are not just stellar structures, but turn out to contain all the components usually found in galactic disks, in particular atomic / molecular gas and dust. They host star-forming complexes and are able to form star-clusters or even second-generation dwarf galaxies. The final part of the review discusses what tidal tails can tell us (or not) about the structure and content of present-day galaxies, including their dark components, and explains how tidal tails may be used to probe the past evolution of galaxies and their mass assembly history. On-going deep wide-field surveys disclose many new low-surface brightness structures in the nearby Universe, offering great opportunities for attempting galactic archeology with tidal tails.Comment: 46 pages, 13 figures, Review to be published in "Tidal effects in Astronomy and Astrophysics", Lecture Notes in Physics. Comments are most welcom

ASSESSMENT OF THE BOROZDKOVY ELEMENTS OF WATERING OF SUNFLOWER ON THE CISCAUCASIAN CARBONATE CHERNOZEM OF THE STEPPE ZONE OF KBR

Basic elements of superficial watering on furrows in a steppe zone of the Central part of the North Caucasus on the carbonate chernozem of long irrigation are studied. Parameters of dependence of field norm on length of an irrigation furrow and a specific stream of water, productivity on watering for a shift of a polivalshchik, energy consumption at the studied elements of borozdkovy watering and frequency rate of irrigation are determined. It is revealed that at biases 0,025-0,030 speed of current of water don’t lead to manifestation of washout of the soil to negative level. The maximum irrigation norm about 1100-1300 m3 of hectare are reached when watering on the furrow length 200-300 m the productivity of sunflower is in direct dependence on irrigating norm and varies from 22 to 32 c/hectare. The maximum efficiency of sunflower is formed in a head piece of the sector of the irrigated site.</jats:p