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Chandra Observations of the Interacting NGC 4410 Galaxy Group
We present high-resolution X-ray imaging data from the ACIS-S instrumenton the Chandra telescope of the nearby interacting galaxy group NGC4410. Four galaxies in the inner portion of this group are clearlydetected by Chandra, including the peculiar low-luminosity radio galaxyNGC 4410A. In addition to a nuclear point source, NGC 4410A containsdiffuse X-ray emission, including an X-ray ridge extending out to about12" (6 kpc) to the northwest of the nucleus. This ridge is coincidentwith an arc of optical emission-line gas, which has previously beenshown to have optical line ratios consistent with shock ionization. Thisstructure may be due to an expanding superbubble of hot gas caused bysupernovae and stellar winds or by the active nucleus. The Chandraobservations also show four or five possible compact ultraluminous X-ray(ULX) sources (LX>=1039 ergs s-1)associated with NGC 4410A. At least one of these candidate ULXs appearsto have a radio counterpart, suggesting that it may be due to an X-raybinary with a stellar-mass black hole, rather than an intermediate-massblack hole. In addition, a faint diffuse intragroup X-ray component hasbeen detected between the galaxies (LX~1041 ergss-1). This supports the hypothesis that the NGC 4410 group isin the process of evolving via mergers from a spiral-dominated group(which typically has no X-ray-emitting intragroup gas) to anelliptical-dominated group (which often has a substantial intragroupmedium).
| The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| Star Formation in the radio galaxy NGC 4410A
The NGC 4410 group of galaxies provides us with a rare opportunity tostudy a nearby (97 h-175 Mpc) example of a radiogalaxy (NGC 4410A) embedded in an extended X-ray source, with evidencefor star formation that can be readily spatially distinguished fromregions dominated by the active galactic nucleus and shocks. We presentbroadband and narrowband optical images, along with optical and IUEultraviolet spectroscopy, for the radio galaxy NGC 4410A and itscompanion, NGC 4410B. Our Hα+[N II] images reveal six luminous HII regions (LHα~1040 ergs s-1)distributed in an arc near NGC 4410A. Partially completing the ring is aprominent stellar loop containing diffuse ionized gas. This filamentarygas, in contrast to the H II regions, shows spectroscopic signatures ofshock ionization. The star formation in this system may have beentriggered by a collision or interaction between the two galaxies,perhaps by an expanding density wave, as in classical models of ringgalaxies. Alternatively, the star formation may have been induced by theimpact of a radio jet on the interstellar matter. Extended Lyα isdetected in the ultraviolet IUE spectrum. The ultraviolet continuum,which is presumably radiated by the nucleus of NGC 4410A, is notextended. NGC 4410A appears to be interacting with its neighbors in theNGC 4410 group and could be an example of a spiral galaxy transforminginto an elliptical.
| Compact groups in the UZC galaxy sample
Applying an automatic neighbour search algorithm to the 3D UZC galaxycatalogue (Falco et al. \cite{Falco}) we have identified 291 compactgroups (CGs) with radial velocity between 1000 and 10 000 kms-1. The sample is analysed to investigate whether Tripletsdisplay kinematical and morphological characteristics similar to higherorder CGs (Multiplets). It is found that Triplets constitute lowvelocity dispersion structures, have a gas-rich galaxy population andare typically retrieved in sparse environments. Conversely Multipletsshow higher velocity dispersion, include few gas-rich members and aregenerally embedded structures. Evidence hence emerges indicating thatTriplets and Multiplets, though sharing a common scale, correspond todifferent galaxy systems. Triplets are typically field structures whilstMultiplets are mainly subclumps (either temporarily projected orcollapsing) within larger structures. Simulations show that selectioneffects can only partially account for differences, but significantcontamination of Triplets by field galaxy interlopers could eventuallyinduce the observed dependences on multiplicity. Tables 1 and 2 are onlyavailable in electronic at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/391/35
| Interstellar Gas in the NGC 4410 Galaxy Group
We present new radio continuum, 21 cm H I, and 2.6 mm CO data for thepeculiar radio galaxy NGC 4410A and its companion NGC 4410B and comparewith available optical and X-ray maps. Our radio continuum maps show anasymmetric double-lobed structure, with a high surface brightness lobeextending 3.6′ (~100 kpc) to the southeast and a 6.2′(~180 kpc) low surface brightness feature in the northwest. Moleculargas is abundant in NGC 4410A, withMH2~4×109 Msolar(using the standard Galactic conversion factor) but is undetected in NGC4410B. H I is less abundant, with MHI~109Msolar for the pair. Our H I map shows a3×108 Msolar H I tail extending 1.7′(50 kpc) to the southeast of the pair, coincident with a faint opticaltail and partially overlapping with the southeastern radio lobe. The H Itail is anticoincident with a 2' (56 kpc) long X-ray structure alignedwith a stellar bridge that connects the pair to a third galaxy. If thisX-ray emission is associated with the group, we infer(3-8)×108 Msolar of hot gas in this feature.This may be either intracluster gas or shocked gas associated with thebridge. Our detection of abundant interstellar gas in this pair,including an H I-rich tidal tail near the southeastern radio lobe,suggests that the observed distortions in this lobe may have been causedby the interstellar medium in this system. The gravitational interactionof the two galaxies and the subsequent motion of the interstellar mediumin the system relative to the jet may have produced sufficient rampressure to bend and distort the radio jet. An alternative hypothesis isthat the jet was distorted by ram pressure due to an intraclustermedium, although the small radial velocity of NGC 4410A relative to thegroup and the lack of diffuse X-ray emission in the group makes thisless likely unless the group is not virialized or is in the process ofmerging with another group. Using our VLA data, we also searched for H Icounterparts to the other 10 known members of the NGC 4410 group and COfrom three other galaxies in the inner group. In our velocity range of6690-7850 km s-1, we detected six other galaxies above our HI sensitivity limits of 2×108 Msolar for theinner group and 4×108 Msolar for the outergroup. The total H I in the group is 1.4×1010Msolar, 80% of which arises from four galaxies in the outergroup. Three of these galaxies (VCC 822, VCC 831, and VCC 847) arespirals with MHI/LB ratios typical of fieldgalaxies, while FGC 170A appears to be a gas-rich dwarf galaxy(MB~-18, MHI~3×109Msolar). In the inner group, the SBa galaxy NGC 4410D (VCC934) was detected in H I and CO (MHI~5×108Msolar and MH2~8×108Msolar) and has a 1' (28 kpc) long H I tail that pointstoward the nearby disk galaxy NGC 4410F. NGC 4410F was also detected inH I (MHI~4×108 Msolar). Thegalaxies in the inner group appear to be somewhat deficient in H Icompared to their blue luminosities, suggesting phase changes driven bygalaxy-galaxy or galaxy-intracluster medium encounters.
| Far infrared and Ultraviolet emissions of individual galaxies at z=0: selection effects on the estimate of the dust extinction
We have cross-correlated Far Infrared (IRAS) and UV (FOCA) observationsof galaxies to construct a sample of FIR selected galaxies with a UVobservation at 0.2 mu m. The FIR and UV properties of this sample arecompared to the mean properties of the local Universe deduced from theluminosity distributions at both wavelengths. Almost all the galaxies ofour sample have a FIR to UV flux ratio larger than the ratio of the FIRand UV luminosity densities, this effect becoming worse as the galaxiesbecome brighter: the increase of the UV (0.2 mu m) extinction is about0.5 mag per decade of FIR (60 mu m) luminosity. Quantitative starformation rates are estimated by adding the contribution of the FIR andUV emissions. They are found consistent with the corrections forextinction deduced from the FIR to UV flux ratio. A total localvolume-average star formation rate is calculated by summing thecontribution of the FIR and UV wavelengths bands. Each band contributesfor an almost similar amount to the total star formation rate with rhoSFR = 0.03 +/- 0.01 h * Msun/yr/Mpc3 at z=0. Thisis equivalent to a global extinction of 0.75 mag to apply to the localluminosity density at 0.2 mu m. The trend of a larger FIR to UV fluxratio for a larger FIR luminosity found for our sample of nearbygalaxies is extended and amplified toward the very large FIRluminosities when we consider the galaxies detected by ISOCAM in a CFRSfield and the Ultra Luminous Infrared Galaxies at low and high redshift.A UV extinction is tentatively estimated for these objects.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| Optical identifications of the IRAS faint sources in the Virgo cluster area.
This paper presents a study on the deep optical identifications of 369IRAS faint sources in a 102 square degree area centered on the Virgocluster. We obtained the positions and magnitudes of candidates fromfour UK Schmidt Telescope IIIa-J direct plates. 89 (24%) are identifiedas stars and 276 (75%) as galaxies. There are 4 (1%) empty fields to theplate limit of B=~22. The infrared-optical database for 193 FSC-onlysources is given. Most of the IRAS galaxy sources are spirals. There are83 IRAS galaxy sources being regarded as the cluster members by Binggeliet al. (1985). In our sample, a correlation between the luminosity ratioL_IR_/L_B_ and the infrared flux ratio F(100μm)/F(60μm) isevident. For the member galaxies, a weak correlation between L_IR_/L_B_and L_IR_ is also found.
| The kinematics of dense clusters of galaxies. I - The data
We have measured redshifts in the fields of the 31 R greater than 1Abell clusters with z of 0.02-0.05 and absolute b exp II above 30 deg.At least ten of the fields are severely contaminated by superimposedvelocity peaks. We derive the mean velocities and velocity dispersionsof the 25 dense peaks in the sample. The abundance of peaks, 6.6 x 10exp -6 h-cubed Mpc exp -3, is consistent with the mean number density ofR above 1 Abell clusters. The range of velocity dispersions is 304-1346km/s. The median dispersion is 718 km/s. The subset of eight systemswith cD galaxies has a median velocity dispersion of 792 km/s, close tothat of non-cD systems (626 km/s). When these data are combined with 16cD cluster velocity dispersions from our previous study (Zabludoff etal., 1990, or ZHG) and Dunn (1991), eight of 25 cD galaxies havepeculiar motions larger than half the cluster velocity dispersions.These findings further support the conclusions of Beers and Geller(1983), ZHG, and Dunn (1991), who argue that cD galaxies do not lie inthe global kinematic center, but in local potential minima. If so,systems with speeding cD's are probably a guide to substructure indynamically evolving systems.
| The H I distribution and kinematics in four low-luminosity elliptical galaxies
The neutral hydrogen distribution in four low-luminosity ellipticalgalaxies was imaged using the VLA, and B and V CCD images were obtainedto determine their luminosity profiles. The brighter two of thesegalaxies, NGC 5666 and NGC 3265, show gapped disks, a feature typical ofthe H I distribution in the few bright early-type galaxies mapped todate. The gas in NGC 5666 extends to nearly 20 times the half-lightradius, making it an ideal probe for the presence of dark matter. Thefainter two galaxies, UGC 7354 and A1230 + 09, have centrallyconcentrated gas distributions, but the H I again extends to twice theHolmberg radius. The velocity distributions in the galaxies show more orless regular rotation, NGC 5666 being remarkably regular for anelliptical galaxy. In all cases, the large radial extent of the gas iscompelling evidence against its origin being stellar mass loss from theluminous stellar figure.
| A VLA 20 CM survey of poor groups of galaxies
The paper reports on VLA 20 cm observations of an extensive sample ofgalaxies in 139 poor groups. These groups, composed of galaxies down tothe limit of the Zwicky et al. (CGCG) catalog, were chosen using apercolation algorithm set at a high surface-density threshold.Approximately 50 percent of the groups have measured redshifts. Thesegroups were surveyed using a 'snapshot' mode of the VLA with aresolution of about 13 arcsec. Analysis of the resulting radio andoptical properties reveals that the presence of a nearby companiongalaxy has an important role in generating radio emission in a galaxy.CCD observations of two radio-loud, disturbed galaxies with companionsare presented and are used to discuss models of radio-source production.Nine tailed radio galaxies are found in the poor groups, which is muchmore than had been expected from previous work on rich clusters and fromtheoretical models. The paper discusses previous statistical biases andproposes a method for bending head-tail sources in poor groups. From theconfinement of extended radio features associated with tailed sources,the presence of a substantial intracluster medium that should radiatesignificantly at soft-X-ray energies is predicted.
| UBV colors of Virgo cluster irregular galaxies
Photoelectric UBV aperture photometry is presented for 65 dwarfirregular and morphologically related types of galaxies that areprobable Virgo cluster members. Virgo cluster Irr galaxies cover a widerrange in color than typical samples of field Irr systems, primarily dueto the presence of unusually red Im galaxies in Virgo. The extremelyblue 'blue compact dwarf' and the red amorphous galaxies in Virgo alsostand out on a UBV color-color plot, but the majority of Virgo Irrs areundistinguished in terms of UBV colors. Statistical correlations arefound between colors and location within the cluster. Red Irrs often arein elliptical galaxy rich, dense areas of the cluster, while the blueIrrs roughly follow the spiral distribution pattern. Thus a connectionexists between environment and the properties of Irrs. Simplestatistical tests for ongoing stripping as the source of red Irrs,however, yields null results.
| NGC 4410a/b - A strong radio source associated with interacting galaxies
The tidally interacting pair of galaxies NGC 4410a/b is in a group ofgalaxies. Two members of the group form with NGC 4410 a chain linked bybridges of diffuse, but knotty, optical emission. The radio sourceassociated with NGC 4410 is studied in detail with aid of observationsdone with the Very Large Array. The source has a radio luminosity (7 x10 to the 40th erg/s) comparable to low luminosity radio galaxies and itis very asymmetric with respect to NGC 4410. Its size is much largerthan the optical size of NGC 4410. Some features, if not all, of theradio source are probably related to the interaction.
| Studies of the Virgo Cluster. II - A catalog of 2096 galaxies in the Virgo Cluster area.
The present catalog of 2096 galaxies within an area of about 140 sq degapproximately centered on the Virgo cluster should be an essentiallycomplete listing of all certain and possible cluster members,independent of morphological type. Cluster membership is essentiallydecided by galaxy morphology; for giants and the rare class of highsurface brightness dwarfs, membership rests on velocity data. While 1277of the catalog entries are considered members of the Virgo cluster, 574are possible members and 245 appear to be background Zwicky galaxies.Major-to-minor axis ratios are given for all galaxies brighter than B(T)= 18, as well as for many fainter ones.
| Middle-ultraviolet photometry of Virgo cluster galaxies
Photographic photometry of Virgo cluster galaxies has been performed ina wavelength band extending from 1620-3200 A using sounding rockettechniques. The observational results are middle ultraviolet magnitudes,U2421, or faint limits for U2421, for 201 galaxies within 5.5 arcmin ofthe cluster center. A strong negative correlation is found between U2421- V and V for all observed S0 galaxies and a similar but weakercorrelation for the observed ellipticals. No such correlation is foundfor spiral galaxies regardless of their projection angles on the sky.The measured colors are generally compatible with colors computed frompreviously generated composite spectra.
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