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|Australia Telescope Compact Array H I observations of the NGC 6845 galaxy group|
We present the results of Australia Telescope Compact Array (ATCA) HIline and 20-cm radio continuum observations of the galaxy quartet NGC6845. The HI emission extends over all four galaxies but can only beassociated clearly with the two spiral galaxies, NGC 6845A and B, whichshow signs of strong tidal interaction. We derive a total HI mass of atleast 1.8 × 1010 Msolar, most of which isassociated with NGC 6845A, the largest galaxy of the group. Weinvestigate the tidal interaction between NGC 6845A and B by studyingthe kinematics of distinct HI components and their relation to the knownHII regions. No HI emission is detected from the two lenticulargalaxies, NGC 6845C and D. A previously uncatalogued dwarf galaxy, ATCAJ2001-4659, was detected 4.4 arcmin NE from NGC 6845B and has an HI massof ~5 × 108 Msolar. No HI bridge is visiblebetween the group and its newly detected companion. Extended 20-cm radiocontinuum emission is detected in NGC 6845A and B as well as in thetidal bridge between the two galaxies. We derive star formation rates of15-40 Msolar yr-1.
|FAUST observations in the Fourth Galactic Quadrant*|
We analyse UV observations with FAUST of four sky fields in the generaldirection of the Fourth Galactic Quadrant, in which we detect 777 UVsources. This is ~50 per cent more than detected originally by Bowyer etal. We discuss the source detection process and the identification of UVsources with optical counterparts. For the first time in this project weuse ground-based objective-prism information for two of the fields, toselect the best-matching optical objects with which to identify the UVsources. Using this, and correlations with existing catalogues, wepresent reliable identifications for ~75 per cent of the sources. Mostof the remaining sources have assigned optical counterparts but, lackingadditional information, we offer only plausible identifications. Wediscuss the types of objects found, and compare the observed populationwith predictions of our UV Galaxy model.
|Southern Isolated Galaxy Triplets|
Seventy-six isolated triple systems of galaxies with declinatiosnδ<-3° were selected using ESO/SERC and POSS-I sky surveydata. The equatorial coordinates, configuration types, angular sizes,component angular separations, component morphological types, totalmagnitudes, and other parameters are reported for each triplet.Radial-velocity estimates are available for all components in 33 of the76 triplets. The median values of the main dynamicalparametersradial-velocity dispersion, mean harmonic radius,absolute magnitudes of member galaxies, and mass-to-luminosityratiosare similar to those obtained earlier for 83 isolatedtriple systems with δ>-3°.
|Formation of a Tidal Dwarf Galaxy in the Interacting System Arp 245 (NGC 2992/93)|
Among the various phenomena observed in interacting galaxies is theejection due to tidal forces of stellar and gaseous material into theintergalactic medium and its subsequent rearranging which can lead tothe formation of self-gravitating tidal dwarf galaxies (TDGs). Weinvestigate this process with a detailed multiwavelength study of theinteracting system Arp 245 and a numerical model of the collisioncomputed with a Tree-SPH code. Our observations consist ofoptical/near-infrared broadband imaging, Hα imaging, opticalspectroscopy, H I VLA cartography and CO line mapping. The system,composed of the two spiral galaxies NGC 2992 and NGC 2993, is observedat an early stage of the interaction, about 100 Myr afterperigalacticon, though at a time when tidal tails have alreadydeveloped. The VLA observations disclose a third partner to theinteraction: an edge-on, flat galaxy, FGC 0938, which looks strikinglyundisturbed and might just be falling toward the NGC 2992/93 system. OurH I map shows prominent counterparts to the optical tails. Whereas thestellar and gaseous components of the plume that originates from NGC2992 match, the stellar and H I tails emanating from NGC 2993 have adifferent morphology. In particular, the H I forms a ring, a featurethat has been successfully reproduced by our numerical simulations. TheH I emission in the system as a whole peaks at the tip of the NGC 2992tail where a gas reservoir of about 109 Msolar, about 60% ofthe H I toward NGC 2992, coincides with a star-forming opticalcondensation, A245N. The latter tidal object exhibits properties rangingbetween those of dwarf irregular galaxies (structural parameters, gascontent, star formation rate) and those of spiral disks (metallicity,star formation efficiency, stellar population). Although it is likely,based on our analysis of the H I and model data cube, that A245N mightbecome an independent dwarf galaxy, the dynamical evidence is still opento debate. Prompted by the questions raised for this particular object,we discuss some issues related to the definition and identification ofTDGs and highlight some specific conditions which seem required to formthem. Finally, we outline what is needed in terms of future numericalsimulations in order to further our understanding of these objects.
|Study of MCLeish's Interacting Object|
We discuss the morphology, kinematics, and physical conditions of theemitting gas of the interacting system IRAS 20048-6621. We present aswell numerical simulations of this interacting system, discovered byDavid McLeish in 1946. The main galaxy (McL A) is an edge-on spiralgalaxy with highly distorted NW side. On this side is also located McLB, the perturber galaxy. We determined a distance of 151 Mpc (h=0.75)and a diameter of 70 kpc for McL A. It presents a bright nucleus withbroad red emission lines (~500 km s-1). McL A has far-IRcolor indexes closely comparable to NGC 3628, one the few nearby edge-ongalaxies which is a bright infrared emitter. Nevertheless, McL A is moreluminous (in these bands) than any of the edge-on galaxies in the sampleof bright infrared galaxies of Young et al. (1988). The two sides of McLA rotation curve are remarkably different. The N-body model that bestreproduces McL A kinematical and morphological data (Kuijken &Dubinski 1995) gives a total mass 7x1011 Msolarfor McL A. Numerical simulations with the TREESPH code closely reproducethe morphology and radial velocity observations. The best scenario forthis system is that of a prograde encounter between McL A and B, withMcL B's orbit 35 deg tilted with respect to the spiral disk of McL A anda perigalactic distance of 17.6 kpc. The derived mass ratio is McL B/McLA~1/26. In the last 5x108 yr the perturber has crossed themain galaxy disk twice, in between it crossed the perigalacticon.According to our simulations, the emitting gas present in McL B has notbeen stripped out from the McL A disk, so that leads us to conclude thatMcL B is an irregular or small spiral galaxy.
|The QDOT all-sky IRAS galaxy redshift survey|
We describe the construction of the QDOT survey, which is publiclyavailable from an anonymous FTP account. The catalogue consists ofinfrared properties and redshifts of an all-sky sample of 2387 IRASgalaxies brighter than the IRAS PSC 60-μm completeness limit(S_60>0.6Jy), sparsely sampled at a rate of one-in-six. At |b|>10deg, after removing a small number of Galactic sources, the redshiftcompleteness is better than 98per cent (2086/2127). New redshifts for1401 IRAS sources were obtained to complete the catalogue; themeasurement and reduction of these are described, and the new redshiftstabulated here. We also tabulate all sources at |b|>10 deg with noredshift so far, and sources with conflicting alternative redshiftseither from our own work, or from published velocities. A list of 95ultraluminous galaxies (i.e. with L_60μm>10^12 L_solar) is alsoprovided. Of these, ~20per cent are AGN of some kind; the broad-lineobjects typically show strong Feii emission. Since the publication ofthe first QDOT papers, there have been several hundred velocity changes:some velocities are new, some QDOT velocities have been replaced by moreaccurate values, and some errors have been corrected. We also present anew analysis of the accuracy and linearity of IRAS 60-μm fluxes. Wefind that the flux uncertainties are well described by a combination of0.05-Jy fixed size uncertainty and 8per cent fractional uncertainty.This is not enough to cause the large Malmquist-type errors in the rateof evolution postulated by Fisher et al. We do, however, find marginalevidence for non-linearity in the PSC 60-μm flux scale, in the sensethat faint sources may have fluxes overestimated by about 5per centcompared with bright sources. We update some of the previous scientificanalyses to assess the changes. The main new results are as follows. (1)The luminosity function is very well determined overall but is uncertainby a factor of several at the very highest luminosities(L_60μm>5x10^12L_solar), as this is where the remainingunidentified objects are almost certainly concentrated. (2) Thebest-fitting rate of evolution is somewhat lower than our previousestimate; expressed as pure density evolution with density varying as(1+z)^p, we find p=5.6+/-2.3. Making a rough correction for the possible(but very uncertain) non-linearity of fluxes, we find p=4.5+/-2.3. (3)The dipole amplitude decreases a little, and the implied value of thedensity parameter, assuming that IRAS galaxies trace the mass, isΩ=0.9(+0.45, -0.25). (4) Finally, the estimate of density varianceon large scales changes negligibly, still indicating a significantdiscrepancy from the predictions of simple cold dark matter cosmogonies.
|Study of the Interacting System NGC 6845|
We present optical spectroscopy, B, V, R, and I CCD photometry, and VLAneutral hydrogen observations of the interacting quartet NGC 6845, alsoknow as Klemola 30. NGC 6845 A, the dominant component, sports a broadand bright tidal bridge and a faint tidal tail, which bifurcates. Thetidal bridge has a B-I color bluer than that of the inner disk of NGC6845 A. Five strong condensations, identified as H II regions brighterthan the brightest one known in our Galaxy, are found along the tidalbridge, with the two most luminous located at the bridge tip. Two giantH II regions, comparable to 30 Dor, are located where the tidal bridgeand the tidal tail join the disk of NGC 6845 A. Since the age of the HII regions is 3-8 Myr, star formation continued to occur along the tidalbridge and in the tidal arm well after they began to be torn apart(>=100 Myr). Satoh model fitting to the optical rotation curve of theA component reveals a kinematical mass of (4.4+/-1.2)x10^11 M_solar,inside the central 12 kpc (H_0=75 km s^-1 Mpc^-1). The H I emissionconsist of two components, a more massive one that belongs to NGC 6845 Aand a second one associated with NGC 6845 B. We do not detect gasassociated with galaxies C and D. The total amount of H I is 1.4x10^10M_solar, 5 time higher than the H I content of the Milky Way. The H Ikinematics indicates an amount of dark matter associated with the Acomponent 2 times higher than the mass inside its central 12 kpc. Thegroup kinematics indicates M/L~43(+/-2)(M/L)_solar orM/L~66(+/-2)(M/L)_solar, according to two different prescriptions forthe internal absorption correction. In spite of this large difference,both values furnish a similar group mass (~1x10^13 M_solar). Althoughpreliminary results on N-body simulations indicate that either B or Cmight well create a tidal feature like the bridge of the A component,the collision with B appears to be more favorable.
|Galaxies with f12 > f25|
We have compiled a sample of galaxies whose flux density is higher at 12microns (f12) than at 25 microns (f25). It is argued thatf12 >f25effectively selects quiescent galaxies which are less active ininfrared, radio, and optical bands than other types of normal galaxies.Moreover galaxies withf12 >f25 do not exhibit the well-knownrelations that normal galaxies show between far-infrared parameters, forexample, the negative correlation betweenf12/f25 andf60/f100. Thesegalaxies also show different far-infrared and radio properties. In ouropinion this sample of quiescent galaxies is suitable for use as acontrol sample when properties of more active galaxies are discussed. Itmay also be used in modeling galaxies with active star formation or anactive nucleus.
|The extended 12 micron galaxy sample|
We have selected an all-sky (absolute value of b greater than or equalto 25 deg) 12 micron flux-limited sample of 893 galaxies from the IRASFaint Source Catalog, Version 2 (FSC-2). We have obtained accurate totalfluxes in the IRAS wavebands by using the ADDSCAN procedure for allobjects with FSC-2 12 micron fluxes greater than 0.15 Jy and increasingflux densities from 12 to 60 microns, and defined the sample by imposinga survey limit of 0.22 Jy on the total 12 micron flux. Its completenessis verified, by means of the classical log N - log S andV/Vmax tests, down to 0.30 Jy, below which we have measuredthe incompleteness down to the survey limit, using the log N - log Splot, for our statistical analysis. We have obtained redshifts (mostlyfrom catalogs) for virtually all (98.4%) the galaxies in the sample.Using existing catalogs of active galaxies, we defined a subsample of118 objects consisting of 53 Seyfert 1s and quasars, 63 Seyfert 2s, andtwo blazars (approximately 13% of the full sample), which is the largestunbiased sample of Seyfert galaxies ever assembled. Since the 12 micronflux has been shown to be about one-fifth of the bolometric flux forSeyfert galaxies and quasars, the subsample of Seyferts (includingquasars and blazars) is complete not only to 0.30 Jy at 12 microns butalso with respect to a bolometric flux limit of approximately 2.0 x10-10 ergs/s/sq cm. The average value of V/Vmaxfor the full sample, corrected for incompleteness at low fluxes, is 0.51+/- 0.04, expected for a complete sample of uniformly distributedgalaxies, while the value for the Seyfert galaxy subsample is 0.46 +/-0.10. We have derived 12 microns and far-infrared luminosity functionsfor the AGNs, as well as for the entire sample. We extracted from oursample a complete subsample of 235 galaxies flux-limited (8.3 Jy) at 60microns. The 60 micron luminosity function computed for this subsampleis in satisfactory agreement with the ones derived from the brightgalaxy sample (BGS) and the deep high-galactic latitude sample, bothselected at 60 microns.
|Southern Sky Redshift Survey - The catalog|
The catalog of radial velocities for galaxies which comprise thediameter-limited sample of the Southern Sky Redshift Survey ispresented. It consolidates the data of observations carried out at theLas Campanas Observatory, Observatorio Nacional, and South AfricanAstronomical Observatory. The criteria used for the sample selection aredescribed, as well as the observational procedures and the techniqueutilized to obtain the final radial velocities. The intercomparisonbetween radial velocity measurements from different telescopes indicatesthat the final data base is fairly homogeneous with a typical error ofabout 40 km/s. The sample is at present 90 percent complete, and themissing galaxies are predominantly objects with very low surfacebrightness for which it is very difficult to obtain optical redshifts.
|Southern Galaxy Catalogue.|
|A List of Peculiar Galaxies, Interacting Pairs, Groups and Clusters South of Declination -43°|
The coordinates, dimensions and short descriptions of 186 objects aregiven after a search of the Maksutov plate collection in theObservatorio AstronÃ³mico, Universidad de Chile, Santiago
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