Contents
Images
Upload your image
DSS Images Other Images
Related articles
Small-Scale Systems of Galaxies. I. Photometric and Spectroscopic Properties of Members
This paper is the first of a series addressed to the investigation ofgalaxy formation/evolution in small-scale systems of galaxies (SSSGs),which are located in low-density cosmic environments. Our algorithm forSSSG selection includes galaxy systems of two or more galaxies lyingwithin Δcz<=1000 km s-1 and a 200h-1100 kpc radius volume. We present the analysisof the photometric and spectroscopic properties of 19 member galaxiesbelonging to a sample of 11 SSSGs. In the μe-replane early-type members may be considered ``ordinary,'' rather than``bright,'' galaxies, with a significant fraction of galaxies having adisk or disky isophotes. We do not detect fine structure or signaturesof recent interaction events in the early-type galaxy population, apicture also confirmed by the spectroscopy. At odds with these findingsare several spiral members with open arm configurations, as expected ininteracting systems. At the same time, emission lines in the spectra ofspiral members fall in the H II regions regime. None of the objectsdisplays unambiguous indications of nuclear activity, although fourspiral nuclei could be ascribed to the class of Seyferts. The starformation rate seems enhanced over the average expected in spiralgalaxies only for poorer SSSGs in particular pairs (<=50Msolar yr-1) but without being in the range ofstarburst systems.Based on observations obtained at the European Southern Observatory, LaSilla, Chile (program No. 57.B-036).
| The nature of elongated ellipticals
We have analyzed the isophotal shapes of a sample of 63 elongatedelliptical galaxies, previously classified E4, 5, 6 or 7. We sorted themaccording to their isophotal class, defined by the type of deviationsfrom perfectly elliptical isophotal contours. These deviations areexpected to appear clearly, because of the very favorable orientation ofthese galaxies. We find the following results, after exclusion of 6non-elliptical galaxies: A large percentage (56%) of elongated E's aredisky objects with pointed isophotes, while only 35% have either boxy orirregular isophotes, in equal proportions, and the remaining 6 galaxies(10%) are diffucult to classify. Furthermore, 38% of disky Es's alsoshow slightly boxy spheroids. In almost all the galaxies of the sample,there is an angular range where the deviations are of the disk-type. Thefour galaxies not showing this effect are among the roundest ones in thesample, which suggests that projection effects hide detailed structuresof this kind in many ellipticals. The correlations already reported inthe literature between isophotal class and radio, X-ray emission andkinematical behavior are confirmed. In particular, there is a clear-cutcorrelation between velocity anisotropy and isophotal shape. The mostelongated Hubble types tend to be disky E's. Boxy/irregular E's rarelyexceed ellipticities of 0.45 while the maximum ellipticity of half ofthe disky Es's exceeds this value. These results confirm the dichotomyof E's, which fall roughly into two classes, disky and boxy/irregularellipticals. They also show a physical continuity between disky E's andSO's and suggest that the Hubble types are strongly correlated withdisk-to-bulge ratios throughout the Hubble sequence, even at itsearly-type end (round E's), for which the disk is hidden by orientationeffects Galaxies escaping the correlations are the boxy/irregular Es's,resulting probably from strong merging processes.
| General study of group membership. II - Determination of nearby groups
We present a whole sky catalog of nearby groups of galaxies taken fromthe Lyon-Meudon Extragalactic Database. From the 78,000 objects in thedatabase, we extracted a sample of 6392 galaxies, complete up to thelimiting apparent magnitude B0 = 14.0. Moreover, in order to considersolely the galaxies of the local universe, all the selected galaxieshave a known recession velocity smaller than 5500 km/s. Two methods wereused in group construction: a Huchra-Geller (1982) derived percolationmethod and a Tully (1980) derived hierarchical method. Each method gaveus one catalog. These were then compared and synthesized to obtain asingle catalog containing the most reliable groups. There are 485 groupsof a least three members in the final catalog.
| Isophotal shapes of early-type galaxies. I - Elongated ellipticals
Forty-three very elongated elliptical galaxies were observed in directB, V, R CCD imaging with the 2-m telescope of Pic-du-Midi Observatoryand with the Canada-France-Hawaii telescope in fairly good seeingconditions. Five galaxies do not show an elliptical structure: threeclearly show spiral features and one is a dumbbell. The 38 othergalaxies were analyzed with an isophote-fitting procedure which allowsone to derive the deviations from pure ellipses in terms of thecoefficients of a Fourier series. The geometrical parameters of these 38elongated ellipticals are presented, with brief comments on theirpeculiarities.
| Observations of galaxies in groups at 102 MHz
Observations of 325 galaxies in groups were carried out at a frequencyof 102 MHz via the scintillation method. Radio emission was found in 42of these components. Eleven of these have a meridional component.
| H I observations of elliptical galaxies
Results are presented for 21-cm observations of 38 early-type galaxies,mostly ellipticals, performed with the 305-m Arecibo telescope with anefficiency corresponding roughly to 6 K/Jy. Six of the galaxies weredetected, including only one 'normal' elliptical, NGC 4278. The resultsindicate that elliptical galaxies as a class contain very little neutralhydrogen, that some of the galaxies observed contain less than 1 part in10,000 of their total mass in the form of neutral gas, and that thepresent gas content of an early-type galaxy is not related to theexpected amount of mass lost over the history of the galaxy. Individualresults are evaluated separately for the six galaxies detected in H I:NGC 3226-3227 (E2p, Sap), NGC 4278 (E1), NGC 7013 (S0/a), NGC 7332 (S0),NGC 7625 (Sa), and NGC 7742 (Sb). It is concluded that star formation isprobably not taking place in ellipticals, that NGC 3226 and 7332 maycontain gas due to accretion from their spiral neighbors, and thatellipticals may contain much of their mass in an extended halo of verylow surface brightness.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
