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|The K Luminosity-Metallicity Relation for Dwarf Galaxies and the Tidal Dwarf Galaxies in the Tails of HCG 31|
We determine a K-band luminosity-metallicity (L-Z) relation for dwarfirregular galaxies over a large range of magnitudes,-20.5
|The evolution of HCG 31: Optical and high-resolution HI study|
Here we present the results of our new optical imaging and spectroscopicstudy and the analysis of new high-resolution HI images of the HicksonCompact Group HCG 31. Taking advantage of the improved sensitivity andangular resolution of the new optical and HI images, we have identifiedan extensive complex of stellar and HI tidal features and theirkinematics. Our HI study show that H31A and C are not an advanced mergersince their velocity fields can be still separated and have almostorthogonal orientations. All of the current sites of ongoing activestar formation are shown to be associated with the highest columndensity peaks traced in HI. A new companion A0500-0434 located 240 kpcsouth of the group center is also discovered in HI. A detailed scenariofor the tidal interactions involved and the origins of the individualtidal features are constructed using the morphology and kinematics ofthe tidal features. The derived dynamical mass for the entire group isabout 2× 1011 Mȯ, which is a few timeslarger than the sum of the masses of the individual group galaxies. Theultimate fate of the group is that HCG 31 is probably on its way to forma single HI cloud group containing all galaxies.Based on observations made with the VLA operated by the National RadioAstronomy Observatory (the National Radio Astronomy Observatory is afacility of the National Science Foundation operated under cooperativeagreement by Associated Universities, Inc.) and on data taken usingALFOSC, which is owned by the Instituto de Astrofísica deAndalucía (IAA) and operated at the Nordic Optical Telescopeunder agreement between IAA and the NBIfA of the AstronomicalObservatory of Copenhagen.
|Chemical Properties and Kinematics of Blue Compact Dwarf Galaxies|
|Massive Star Formation and Tidal Structures in HCG 31|
We present new broadband optical and near-infrared CCD imaging togetherwith deep optical intermediate-resolution spectroscopy of the HicksonCompact Group 31. We analyze the morphology and colors of the stellarpopulations of the galaxies, as well as the kinematics, physicalconditions, and chemical composition of the ionized gas in order to geta more complete view on the origin and evolution of the system. Weestimate the ages of the most recent star formation bursts of thesystem, finding an excellent consistency among the values obtained withdifferent indicators and starburst models. We find that member F hoststhe youngest starburst of the group, showing a substantial population ofWolf-Rayet stars. The chemical abundances are fairly similar in all themembers of the group despite their very different absolute magnitudes.We argue that the use of traditional metallicity-luminosity relationsbased on the absolute B-magnitude is not appropriate for dwarf starburstgalaxies, because their luminosity is dominated by the transientcontribution of the starburst to the blue luminosity. We think thatmembers E and F of the group are candidate tidal dwarf galaxies becauseof their high metallicity, their kinematics, and the absence ofunderlying old stellar populations. Finally, we propose that HCG 31 issuffering several almost simultaneous interaction processes. The mostrelevant of these processes are (1) the merging of members A and C,which would have produced two optical tidal tails, and (2) a fly-byencounter between G and the A+C complex, which would have produced an HI tidal tail from the stripping of the external gas of A+C, from whichmembers F and E have originated.ID="FN1"> 1Based on observations made with several telescopesoperated on the islands of La Palma and Tenerife by the Isaac NewtonGroup of Telescopes, Nordic Optical Telescope and Instituto deAstrofísica de Canarias in the Spanish observatories of Roque deLos Muchachos and Teide of the Instituto de Astrofísica deCanarias.
|Physical Properties of the Stellar Population and the Gas in BCD Galaxies|
|The PDS versus Markarian starburst galaxies: comparing strong and weak IRAS emitter at 12 and 25 μm in the nearby Universe|
The characteristics of the starburst galaxies from the Pico dos Diassurvey (PDS) are compared with those of the nearby ultraviolet (UV)bright Markarian starburst galaxies, having the same limit in redshift(vh < 7500 km s-1) and absolute B magnitude(MB < -18). An important difference is found: theMarkarian galaxies are generally undetected at 12 and 25 μm in IRAS.This is consistent with the UV excess shown by these galaxies andsuggests that the youngest star-forming regions dominating thesegalaxies are relatively free of dust.The far-infrared selection criteria for the PDS are shown to introduce astrong bias towards massive (luminous) and large size late-type spiralgalaxies. This is contrary to the Markarian galaxies, which are found tobe remarkably rich in smaller size early-type galaxies. These resultssuggest that only late-type spirals with a large and massive disc arestrong emitters at 12 and 25 μm in IRAS in the nearby Universe.The Markarian and PDS starburst galaxies are shown to share the sameenvironment. This rules out an explanation of the differences observedin terms of external parameters. These differences may be explained byassuming two different levels of evolution, the Markarian being lessevolved than the PDS galaxies. This interpretation is fully consistentwith the disc formation hypothesis proposed by Coziol et al. to explainthe special properties of the Markarian SBNG.
|Is HCG 31 undergoing a merger or a fly-by interaction?|
We present Fabry-Perot and multi-object spectroscopy of the galaxies inHickson compact group 31 (HCG 31). Based upon our Hα data cubes,galaxies A and C are a single entity, showing no discontinuity in theirkinematics. Kinematically, galaxy E is probably a component of the A+Ccomplex; otherwise it is a recently detached fragment. Galaxy F appears,both kinematically and chemically, to have formed from material tidallyremoved from the A+C complex. Galaxies B and G are kinematicallydistinct from this complex. Galaxy Q also has a radial velocitycompatible with group membership. Galaxies A, B, C, and F have nearlyidentical oxygen abundances, despite spanning a luminosity range of 5mag. Galaxy B's oxygen abundance is normal for its luminosity, whilegalaxy F's abundance is that expected given its origin as a tidalfragment of the A+C complex. The oxygen abundances in galaxies A and Care also understandable if the A+C complex is a late-type spiralsuffering strong gas inflow and star formation as a result of a tidalinteraction. Given the kinematics of both the galaxies and the H I gas,the oxygen abundances, and the position of galaxy G, we propose that aninteraction of galaxy G with the A+C complex, rather than a merger ofgalaxies A and C, is a more complete explanation for the tidal featuresand other properties of HCG 31. In this case, the A+C complex need notbe a merger in progress, though this is not ruled out.
|Infrared Space Observatory Observations of Hickson Compact Group 31 with the Central Wolf-Rayet Galaxy NGC 1741|
Hickson Compact Group (HCG) 31, consisting of the Wolf-Rayet galaxy NGC1741 and its irregular dwarf companions, was observed using the InfraredSpace Observatory. The deconvolved ISOCAM maps of the galaxies using the7.7 and 14.3 μm (LW6 and LW3) filters are presented, along withISOPHOT spectrometry of the central starburst region of NGC 1741 and thenucleus of galaxy HCG 31A. Strong mid-IR emission was detected from thecentral burst in NGC 1741, along with strong polycyclic aromatichydrocarbon (PAH) features and a blend of features, including [S IV] at10.5 μm. The 14.3/6.75 μm flux ratio, for which the 6.75 μmflux was synthesized from the PHT-S spectrum, and 14.3/7.7 μm fluxratio suggest that the central burst within NGC 1741 may be movingtoward the poststarburst phase. Diagnostic tools including the ratio ofthe integrated PAH luminosity to the 40-120 μm infrared luminosityand the far-infrared colors reveal that despite the high surfacebrightness of the nucleus, the properties of NGC 1741 can be explainedin terms of a starburst and do not require the presence of an activegalactic nucleus. The Tycho catalog star Tyc 04758 466 1, withmV=11.3 and spectral type F6, was detected at 7.7 and 14.3μm.
|Multiband Analysis of a Sample of Blue Compact Dwarf Galaxies. II. Spatially Resolved and Integrated Photometry|
This is the second in a series of papers devoted to the study of asample of 28 blue compact dwarf galaxies (BCDs). In the first paper, wepresented the broadband observations in B, V, R, and I. Deep contourmaps, surface-brightness profiles, and color profiles were used toanalyze and discuss their morphology and structure. Here, we present newU-band and Hα observations. We compute isophotal and asymptoticmagnitudes of the sample galaxies and total Hα fluxes. Comparisonwith previous works is done to assess the quality of the data availablefor BCDs. Finally, we produce an atlas of detailed color and Hαmaps, the first systematic atlas of this kind published so far. The highquality of the data allows us to identify the different star-formingknots in the maps and to discriminate between them and the regions wherestar formation activity has already ceased. We supplement the atlas witha morphological description of each galaxy and group the galaxies infour classes according to the distribution of their star-formingregions.
|Multiband Analysis of a Sample of Blue Compact Dwarf Galaxies. I. Surface Brightness Distribution, Morphology, and Structural Parameters|
Broadband observations in B, V, R, and I have been performed for asample of 28 galaxies cataloged as blue compact dwarf galaxies (BCDs).Our deep imaging, reaching surface brightness levels of a few percent ofthe sky brightness, has allowed the detection of underlying emission orlow surface brightness features for a substantial fraction of thesample. In this paper we present the first results of the program: deepcontour maps in the B band, surface brightness profiles, and colorprofiles for all the galaxies. The information derived for this sampleof galaxies has allowed us to analyze the morphology and the structuralcomponents of BCDs. Over 70% of the galaxies show complex profiles thatpreclude fitting by a single standard law, with extra structure at highto intermediate intensity levels. In 21 galaxies of the sample, anunderlying low surface brightness component has been detected.
|Multiband Analysis of a Sample of Blue Compact Dwarf Galaxies|
We present preliminary results of the surface photometry of a sample ofblue compact dwarf galaxies (BCDGs). A total of 28 galaxies have beenobserved in the BVRI bands. From these data the contour maps and surfacebrightness distributions in each band have been built. Contour maps andsurface profiles of the 22 galaxies already analysed are presented,together with preliminary conclusions regarding their morphology andstructural components.
|Where is the neutral atomic gas in Hickson groups?|
We have analyzed the total HI contents of 72 Hickson compact groups ofgalaxies (HCGs) and the detailed spatial distributions and kinematics ofHI within a subset of 16 groups using the high angular resolutionobservations obtained with the VLA in order to investigate a possibleevolutionary scenario for these densest systems in the present daygalaxy hierarchy. For the more homogeneous subsample of 48 groups, wefound a mean HI deficiency of Def_HI = 0.40 +/- 0.07, which correspondsto 40% of the expected HI for the optical luminosities and morphologicaltypes of the member galaxies. The individual galaxies show largerdegrees of deficiency than the groups globally, Def_HI = 0.62 +/- 0.09(24% of the expected HI), due in most cases to efficient gas strippingfrom individual galaxies into the group environment visible in the VLAmaps. The degree of deficiency is found to be similar to the centralgalaxies of Virgo and Coma cluster, and Coma I group, in spite of thesignificantly different characteristics (number of galaxies, velocitydispersion) of these environments. It does not seem plausible that asignificant amount of extended HI has been missed by the observations.Hence phase transformation of the atomic gas should explain the HIdeficiency. The groups richer in early type galaxies or more compactwith larger velocity dispersions show a weak tendency to be more HIdeficient. The detection rate of HCGs at X-ray wavelengths is larger forHI deficient groups, although the hot gas distribution and hence itsorigin is only known for a few cases. In the evolutionary scenario wepropose, the amount of detected HI would decrease further withevolution, by continuous tidal stripping and/or heating. The H_2 contentalso tends to be lower than expected for the galaxies in HI deficientgroups, this may suggest that the HI stripping by frequent tidalinteraction breaks the balance between the disruption of molecularclouds by star formation and the replenishment from the ambient HI. Thiswork is partially based on observations made with the VLA operated bythe National Radio Astronomy Observatory, a facility of the NationalScience Foundation operated under cooperative agreement by AssociatedUniversities, Inc., ALFOSC, which is owned by the Instituto deAstrofísica de Andalucía (IAA, CSIC) and operated at theNordic Optical Telescope (NOT) under agreement between IAA and the NBIfAof the Astronomical Observatory of Copenhagen, and 1.5 m telescope ofthe Observatorio de Sierra Nevada, Granada, Spain, which is operated bythe IAA (CSIC).
|Recent Star Formation in Several Galaxies of the Tidally Disturbed System HCG 31|
High-resolution (0.7" to 0.8") Hα images of the Hickson CompactGroup 31 (HCG 31) obtained with the WIYN telescope are used inconjunction with broadband optical images from the Hubble SpaceTelescope (HST) to examine the star formation history and properties ofthe component galaxies. The high spatial resolution of the WIYNtelescope has allowed us to identify a large number of starburst regionsfrom their Hα emission, which traces the recent star birthactivity. The HST images of galaxies E and F reveal more detail withinthe starburst regions in which we have identified numerous super starclusters (SSCs). Photometry of these starburst regions and SSCs in theHα and optical images indicates that there has been a substantialamount of star formation throughout HGC 31 over the past 10 Myr. TheHα equivalent widths suggest activity within the group as recentlyas a few megayears ago. There is evidence that galaxy F, the youngestmember of the group, is possibly undergoing its initial episode of starformation, as no underlying stellar population has yet been detected.
|On the Influence of the Environment on the Star Formation Rates of a Sample of Galaxies in Nearby Compact Groups|
We present the results of a study of the star formation rates (SFRs) ofa sample of disk galaxies in nearby compact groups compared with theSFRs of a sample of field galaxies. For this purpose, Hαluminosities and equivalent widths were derived for the galaxies of oursample. A direct comparison of the equivalent widths and Hαluminosities, normalized to the B luminosities and estimated area of thegalaxies of both samples, yields the result that the median values ofthese quantities are almost identical for both samples, although thedistributions for the compact-group sample are broader around the meanvalue than was found in the field galaxy sample. This result can beexplained by assuming that although interactions between galaxies incompact groups can alter the SFRs, the median value of the normalizedSFRs is preserved, being almost indistinguishable from the correspondingvalue for field galaxies. Measuring the global L_Hα/L_B of thegroups, including early-type galaxies, we find that most of the groupsthat show the highest level of L_Hα/L_B with respect to a set ofsynthetic groups built out of field galaxies show tidal features in atleast one of their members. Finally, we have explored the relationshipbetween the ratio L_Hα/L_B and several relevant dynamicalparameters of the groups: velocity dispersion, crossing time, radius,and the mass-to-luminosity ratio, finding no clear correlation. Thissuggests that the exact dynamical state of a group does not control theSFR of the group as a whole. Our results are compatible with a scenariofor compact groups of galaxies in which the dark matter of the group isarranged in a common halo, therefore preventing a fast collapse of thegalaxies.
|The Very Young Starburst Merger System NGC 1741|
We use Hubble Space Telescope (HST) Faint Object Camera (FOC)ultraviolet (UV) and WFPC2 optical images in conjunction with UVspectroscopic observations taken with the Goddard High ResolutionSpectrograph to examine the star formation history and properties of theinteracting galaxy system NGC 1741 in the Hickson Compact Group 31. Thehigh spatial resolution afforded by HST has allowed us to identify alarge number of starburst knots, or ``super-star clusters'' (SSCs), inthe starburst regions of this system. Photometry of these SSCs in the UVand optical bands indicates that most of these objects have ages of afew Myr, with a few up to ~100 Myr, and masses between 10^4 and 10^6M_solar. The estimated age is confirmed by a spectral synthesis analysisof one knot for which we have obtained a UV spectrum. The V-bandluminosity function of the SSCs is well represented by a power lawphi(L)~L^-alpha with an index of -1.85, with no evidence of a turnoverbrighter than the completeness limit. These properties are in goodagreement with those found for SSCs in other starburst galaxies. Ourresults support the suggestion that some of these SSCs may be extremelyyoung globular clusters formed in a relatively recent starburst episodethat has been triggered by a merger event.
|Atlas of H alpha Emission of a Sample of Nearby Hickson Compact Groups of Galaxies|
H alpha and adjacent continuum images are presented for a sample ofnearby groups of galaxies extracted from the Atlas of Compact Groups ofGalaxies. Also, more detailed H alpha maps of the most remarkablegalaxies are shown in this paper. A short description of the H alphaemission for each of the galaxies with accordant redshift is presentedtogether with a morphological classification of the accordant galaxiesin the sample. A large fraction of ellipticals and lenticulars weredetected in H alpha . Also, clear signs of interactions were found inseven of the groups, but in only in three of them was H alpha emissiondetected along the tidal features. Candidates of dwarf galaxies werefound at the tips of the tidal tails developed during the interactionsin these three groups.
|Effects of Interaction-induced Activities in Hickson Compact Groups: CO and Far-Infrared Study|
A study of 2.6 mm CO J = 1 --> 0 and far-infrared (FIR) emission in adistance-limited (z < 0.03) complete sample of Hickson compact group(HCG) galaxies was conducted in order to examine the effects of theirunique environment on the interstellar medium of component galaxies andto search for a possible enhancement of star formation and nuclearactivity. Ubiquitous tidal interactions in these dense groups wouldpredict enhanced activities among the HCG galaxies compared to isolatedgalaxies. Instead, their CO and FIR properties (thus, "star formationefficiency") are surprisingly similar to isolated spirals. The CO datafor 80 HCG galaxies presented here (including 10 obtained from theliterature) indicate that the spirals globally show the same H2 contentas the isolated comparison sample, although 20% are deficient in COemission. Because of their large optical luminosity, low metallicity isnot likely the main cause for the low CO luminosity. The CO deficiencyappears linked with the group evolution, and gas exhaustion through paststar formation and removal of the external gas reserve by tidalstripping of the outer H I disk offer a possible explanation. The IRASdata for the entire redshift-limited complete sample of 161 HCG galaxieswere reanalyzed using ADDSCAN/SCANPI, improving the sensitivity by afactor of 3-5 over the existing Point Source Catalog (PSC) and resolvingbetter the contribution from individual galaxies. The new analysis ofthe IRAS data confirms the previous suggestion that FIR emission in HCGgalaxies is similar to isolated, Virgo Cluster, and weakly interactinggalaxies. Their H2 and FIR characteristics yield a star formationefficiency that is similar to that of these comparison samples. A factor2 enhancement in the 25-100 mu m flux ratio among the HCG spirals isfound, which suggests intense localized nuclear starburst activitysimilar to that of H II galaxies. A number of early-type galaxies inHCGs are detected in CO and FIR, lending further support to the ideathat tidal interactions and tidally induced evolution of the groups andmember galaxies are important in our sample.
|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.
|Recent Star Formation in Groups of Galaxies: HCG 31|
Broadband UBVRI and narrowband H alpha and continuum images have beenobtained for the Hickson compact group HCG 31 as part of an ongoingprogram devoted to the study of the star formation properties ofgalaxies in these groups. A spatially resolved analysis for the (U-B),(V-I), and (B-I) color maps has been performed, as well as for the Uband, H alpha luminosity, and H alpha equivalent width maps. Integratedluminosities in all the bands have been derived for all the galaxies inthe group. Our results show that all the galaxies appear to haveexperienced their most recent star formation episode less than 107 yearsago, in good agreement with previous values found in the literature.From the morphological point of view, three different kinds of starformation processes are taking place in the group: central starburstinduced by a strong interaction, star formation induced by stripping ofthe gas due to the presence of a medium of higher pressure, andformation of a dwarf galaxy at the tip of one of the tidal tails.Overall, the photometric properties of the central starburst in HCG 31are consistent with model predictions for the early stages of a mergerbetween late-type galaxies.
|Molecular Gas and Infrared Emission in HCG 31 and HCG 92 (Stephan's Quintet) and Tidal Interactions in Compact Group Environment|
We present the interferometric measurements of 2.6 mm CO (J = 1-->0)emission ( theta FWHM ~ 5") and the analysis of IRAS HIRES images of twoHickson compact groups HCG 31 and HCG 92 ("Stephan's Quintet"). Thefar-infrared (FIR) emission is concentrated to a single region in HCG 31while it is clearly extended and peaks near the group center in HCG 92.CO emission is weak in HCG 31, and the brightest peak occurs in theoverlap region between the galaxies A and C. CO emission is detectedonly in galaxy C (NGC 7319) in HCG 92, and the distribution is highlyasymmetric. No CO emission is detected in the interacting pair HCG 92 Band D (NGC 7318 A and B). Gas stripping and star formation by continuoustidal disruptions in compact group environment are discussed as possibleexplanations for the observed CO deficiency and peculiar molecular gasdistribution in HCG 31 and HCG 92.
|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.
|A multifrequency radio continuum and IRAS faint source survey of markarian galaxies|
Results are presented from a multifrequency radio continumm survey ofMarkarian galaxies (MRKs) and are supplemented by IRAS infrared datafrom the Faint Source Survey. Radio data are presented for 899 MRKsobserved at nu = 4.755 GHz with the National Radio Astronomy Observatory(NRAO)-Green Bank 300 foot (91 m) telescope, including nearly 88% ofthose objects in Markarian lists VI-XIV. In addition, 1.415 GHzmeasurements of 258 MRKs, over 30% of the MRKs accessible from theNational Aeronomy and Ionosphere Center (NAIC)-Arecibo, are reported.Radio continuum observations of smaller numbers of MRKs were made at10.63 GHz and at 23.1 GHz and are also presented. Infrared data from theIRAS Faint Source Survey (Ver. 2) are presented for 944 MRKs, withreasonably secure identifications extracted from the NASA/IPACExtragalactic Database. MRKs exhibit the same canonical infraredcharacteristics as those reported for various other galaxy samples, thatis well-known enhancement of the 25 micrometer/60 micrometer color ratioamong Seyfert MRKs, and a clear tendency for MRKs with warmer 60micrometer/100 micrometer colors to also possess cooler 12 micrometer/25micrometer colors. In addition, non-Seyfert are found to obey thewell-documented infrared/radio luminosity correlation, with the tightestcorrelation seen for starburst MRKs.
|Global properties of dwarf galaxies. I. Galaxy sample and IRAS infrared flux-densities|
We have selected a sample of 278 dwarf galaxies for which at least Bmagnitudes and preferably also optical colour information are available.For those galaxies that have no previously published IRAS fluxes, wehave used the IRAS database to extract fluxes or upper limits tosensitivity levels significantly better than those of the IRAS PointSource Catalog. New IRAS data include 79 galaxies detected in at leastone band, and 66 galaxies with good upper limits. In total, about 60% ofall dwarf galaxies in the sample now have been detected at 60/100μm.
|Global properties of dwarf galaxies II. Colours and luminosities|
We have used a previously determined sample of 278 dwarf galaxies formost of which B magnitudes, optical colours, HI fluxes and IRASflux-densities are known, in order to derive luminosities, colours andsurface brightnesses. Dwarf galaxy properties are compared to those of acontrol sample of 228 larger spiral galaxies. The dwarf galaxies have onaverage higher 60/100μm flux ratios and lower 12/25μm flux ratiosthan the spiral galaxies, indicating that the contribution of `cirrus'to the infrared emission from dwarf galaxies is relativelyinsignificant. In the dwarf galaxies, the 60/100μm flux ratioincreases with increasing optical blueness; spiral galaxies show theopposite. Dwarf galaxies with a low optical surface brightness have low100μm/HI ratios, but the converse is not true. Galaxies with high100μm/HI ratios (indicative of high dust-to-gas ratios) also havehigh FIR/B ratios as well as high 60/100μm flux-density ratios.Although this is true for both spiral and dwarf galaxies, at given100μm/HI ratios the dwarf galaxies have both a lower FIR/B ratio anda higher 60/100μm flux-density ratio. This result is of importance inthe interpretation of FIR/B - 60/100μm diagrams in terms of starformation activity.
|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.
|Pairing properties of Markarian starburst Galaxies|
The environmental parameters of 516 non-Seyfert Markarian galaxies werestudied in a redshift-bounded sample, supplemented by new spectra andredshift measures for possible companions, in order to evaluate theiroccurrence in galaxy pairs, defined through quantitative criteria. Itwas found that one-third of these galaxies occur in pairs (while only 6to 10 percent of optically-selected galaxies are known to be paired). Acomparison of various optical and IR properties of paired and nonpairedMarkarian galaxies showed no differences in the shape of the optical,far-IR, or H-alpha luminosity functions. It was found, however, that theMarkarian component is brighter than the other galaxy in each pair by0.66 magnitude in the mean at B.
|Optical properties and dynamics of galaxies in the Hickson compact groups|
The way in which galaxy properties in dense galaxy environments comparewith the properties isolated in the field is presently evaluated inlight of broadband R and H-alpha images, as well as H-alpha long-slitspectroscopy, for a set of galaxies (in 21 Hickson compact groups) whoseobserved velocity patterns range from too peculiar for rotation-curveformation, to abnormal, to normal. A surprisingly high correlation isnoted between absolute magnitude and (log) maximum rotation velocity,especially in the case of galaxies with normal rotation curves. Theseobservations support a model in which the compact-group galaxies haveonly recently accumulated from the general galaxy distribution, and inwhich tidal interactions are frequent and persisting.
|One galaxy from several - The Hickson compact group H31|
The compact group H31 was identified by Hickson in 1982; it consists offour galaxies in close proximity, at least two of which (A and C) areinteracting. Red and H-alpha frames and long-slit spectroscopy identifyat least three other close members of the group; an H I envelopeencloses all galaxies. Nuclear spectra of galaxies A and C show velocitypatterns characteristic of interacting galaxies as well as the broad4650 A feature indicative of W-R stars. These features reveal that largenumbers of massive stars formed more than 10 exp 6.5 yr ago. Otherobserved characteristics all suggest that H31 is in the process ofmerging to a single galaxy. H31 thus supports computations whichindicate that galaxies in compact groups merge to form a single remnant.
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