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XMM-Newton Observation of an X-Ray Trail between the Spiral Galaxy NGC 6872 and the Central Elliptical Galaxy NGC 6876 in the Pavo Group
We present XMM-Newton observations of a trail of enhanced X-ray emissionextending along the full 8.7 arcmin ×4' region betweenthe large spiral galaxy NGC 6872 and the dominant elliptical galaxy NGC6876 in the Pavo group, the first known X-ray trail associated with aspiral galaxy in a poor galaxy group and, with a projected length of 90kpc, one of the longest known X-ray trails. The X-ray surface brightnessin the trail region is roughly constant beyond ~20 kpc of NGC 6876 inthe direction of the spiral galaxy. The trail is hotter (~1 keV) thanthe undisturbed Pavo IGM (~0.5 keV) and has low metal abundances (0.2Zsolar). The 0.5-2 keV luminosity of the trail, measuredusing a 67×90 kpc rectangular region, is 6.6×1040ergs s-1. We compare the properties of gas in the trail tothe spectral properties of gas in the spiral galaxy NGC 6872 and in theelliptical galaxy NGC 6876 to constrain its origin. We suggest that theX-ray trail is either IGM gas gravitationally focused into a Bondi-Hoylewake, a thermal mixture of ~60% Pavo IGM gas with ~40% galaxy gas thathas been removed from the spiral galaxy NGC 6872 by turbulent viscousstripping, or both, due to the spiral galaxy's supersonic motion atangle ξ~40deg with respect to the plane of the sky,through the densest region of the Pavo IGM. Assumingξ=40deg and a filling factor η in a cylindrical volumewith radius 33 kpc and projected length 90 kpc, the mean electrondensity and total hot gas mass in the trail are1×10-3η-1/2 cm-3 and1.1×1010η1/2 Msolar,respectively.
| The star cluster population in the tidal tails of NGC 6872
We present a photometric analysis of the rich star cluster population inthe tidal tails of NGC 6872. We find star clusters with ages between1-100 Myr distributed in the tidal tails, while the tails themselveshave an age of less than 150 Myr. Most of the young massive(104 ≤ M/Mȯ ≤ 107)clusters are found in the outer regions of the galactic disk or thetidal tails. The mass distribution of the cluster population can be welldescribed by a power-law of the form N(m) ∝ m-α,where α = 1.85 ± 0.11, in very good agreement with otheryoung cluster populations found in a variety of different environments.We estimate the star formation rate for three separate regions of thegalaxy, and find that the eastern tail is forming stars at ~2 times therate of the western tail and ~5 times the rate of the main body of thegalaxy. By comparing our observations with published N-body models ofthe fate of material in tidal tails in a galaxy cluster potential, wesee that many of these young clusters will be lost into theintergalactic medium. We speculate that this mechanism may also be atwork in larger galaxy clusters such as Fornax, and suggest that theso-called ultra-compact dwarf galaxies could be the most massive starclusters that have formed in the tidal tails of an ancient galacticmerger.
| Stars and Gas in the Large Interacting Galaxy NGC 6872
The luminous barred galaxy NGC 6872 is one of the largest spiralgalaxies known. Star formation occurs all along the arms, which extendover more than 100 kpc. The galaxy experiences tidal perturbations fromthe nearby companion IC 4970 passing by on a low-inclination, progradeorbit. We have mapped the large-scale distribution and kinematics of theatomic gas (HI) in the NGC 6872/IC 4970 system and carried out N-bodysimulations with stars and gas. HI is absent from the central region; onthe other hand, large gas concentrations are found at the tip of thetidal arms, spatially coincident with the blue stellar clusters and withthe peaks of the Hα distribution. We use that remarkable system toinvestigate the evolution of gas and stars in a close progradeencounter, examine the influence of a dark matter halo on the length ofthe tidal tails, and test models of collisionally induced starformation.
| A Catalog of H I-Selected Galaxies from the South Celestial Cap Region of Sky
The first deep catalog of the H I Parkes All Sky Survey (HIPASS) ispresented, covering the south celestial cap (SCC) region. The SCC areais ~2400 deg2 and covers δ<-62°. The average rmsnoise for the survey is 13 mJy beam-1. Five hundredthirty-six galaxies have been cataloged according to their neutralhydrogen content, including 114 galaxies that have no previous catalogedoptical counterpart. This is the largest sample of galaxies from a blindH I survey to date. Most galaxies in optically unobscured regions of skyhave a visible optical counterpart; however, there is a small populationof low-velocity H I clouds without visible optical counterparts whoseorigins and significance are unclear. The rms accuracy of the HIPASSpositions is found to be 1.9′. The H I mass range of galaxiesdetected is from ~106 to ~1011 Msolar.There are a large number of late-type spiral galaxies in the SCC sample(66%), compared with 30% for optically selected galaxies from the sameregion in the NASA Extragalactic Database. The average ratio of H I massto B luminosity of the sample increases according to optical type, from1.8 Msolar/Lsolar for early types to 3.2Msolar/Lsolar for late-type galaxies. The HI-detected galaxies tend to follow the large-scale structure traced bygalaxies found in optical surveys. From the number of galaxies detectedin this region of sky, we predict the full HIPASS catalog will contain~5000 galaxies, to a peak flux density limit of ~39 mJy (3 σ),although this may be a conservative estimate as two large voids arepresent in the region. The H I mass function for this catalog ispresented in a subsequent paper.
| HIPASS Detection of an Intergalactic Gas Cloud in the NGC 2442 Group
We report the discovery from the H I Parkes All-Sky Survey (HIPASS) of agas cloud associated with the asymmetric spiral galaxy NGC 2442. Thisobject, designated HIPASS J0731-69, contains ~109Msolar of H I, or nearly one-third as much atomic gas as NGC2442 itself. No optical counterpart to any part of HIPASS J0731-69 hasyet been identified, consistent with the gas being diffuse and itsstreamlike kinematics. If the gas in HIPASS J0731-69 was once part ofNGC 2442, then it was most likely a fairly recent tidal encounter with amoderately massive companion that tore it loose, although thepossibility of ram-pressure stripping cannot be ruled out. Thisdiscovery highlights the potential of the HIPASS data for yielding newclues to the nature of some of the best-known galaxies in the localuniverse.
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| CO and HI in a southern sample of interacting galaxies. I. The data
Using SEST, the Parkes antenna and the Australia Telescope CompactArray, we have made a survey of the ^12CO(1-0) and HI emission of anoptically-selected sample of ~60 southern interacting and merginggalaxies. In this paper we present the data and determine global massesof neutral gas (in molecular and atomic form) for the observed galaxies.We have detected HI in 26 systems and found that these galaxies haveless than 15% of their gas in molecular form. Figure 3 in its entirelyis only available in electronic form at CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 2.1 μm images of the evolved stellar disk and the morphological classification of spiral galaxies
Near-infrared images confirm that the Hubble classification of spiralgalaxies does not constrain the morphology of their stellar PopulationII disk, since galaxies on opposite ends of the spiral sequence candisplay remarkably similar evolved disk morphologies. Thus, the gasdominated Population I component determines the types (a, b, c),decoupled from the Population II. The underlying mass distributionsobserved in the infrared are exceptionally regular, suggesting thatlarge scale spiral structure is principally intrinsic, as argued by themodal theory. Moreover, single arms, bisymmetric arms, lopsidednessand/or bars dominate the old stellar disk. The absence of infraredmultiple-armed structure is attributed to the efficiency of InnerLindblad Resonance absorption in the evolved Population II disk. Theseobservations support a coherent framework for galaxy classificationbased on three parameters: stellar disk "temperature", gas content andactive disk mass.
| Modeling the Spatial Distribution of Star Formation in Interacting Disk Galaxies
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993ApJ...418...82M&db_key=AST
| A study of a complete sample of interacting galaxies. I - Presentation of the sample and the UBVRIJHK photometry
An investigation is presented on what effects galaxy-galaxy interactionhas on the properties of the involved galaxies. A magnitude limitedsample of interacting galaxies is presented, together with a controlsample of isolated galaxies. The Cousins UBVRI and Johnson JHKphotometry of all galaxies included in the samples is also presented.
| Redshifts of galaxies in some southern groups and clusters
A table of redshifts for 67 galaxies in southern groups and clusters ispresented. The galaxies are found in or near Sersic 40/6, A496, Klemola44, 2354-35, Klemola 2, Pavo, Sersic 149/5, Sersic 149/10, 2355-35,0001-36, 0003-35, and 0007-36.
| A catalogue of early-type galaxies with emission lines
Spectroscopic and photometric data on 289 early-type galaxies (E and S0)with optical emission lines are presented and possible correlationsamong properties of the galaxies in the sample are investigated. Theoccurrence of phenomena as radio emission, presence of neutral hydrogenand dust shows an increase in comparison with the occurrence of the samephenomena in these morphological classes as a whole. There is noevidence of a relationship between apparent shape and presence ofionized gas in the central regions.
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