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XMM-Newton observations of the interacting galaxy pairs NGC 7771/0 and NGC 2342/1
We present XMM-Newton X-ray observations of the interacting galaxy pairsNGC 7771/7770 and NGC 2342/2341. In NGC 7771, for the first time we areable to resolve the X-ray emission into a bright central source plus twobright (LX > 1040 erg s-1)ultraluminous X-ray sources (ULXs) located either end of the bar. In thebright central source (LX~ 1041 ergs-1), the soft emission is well-modelled by a two-temperaturethermal plasma with kT= 0.4/0.7 keV. The hard emission is modelled witha flat absorbed power-law (Γ~ 1.7, NH~ 1022cm-2), and this together with a low-significance (1.7σ)~ 300 eV equivalent width emission line at ~6 keV are the firstindications that NGC 7771 may host a low-luminosity AGN. For the barULXs, a power-law fit to X-1 is improved at the 2.5σ level withthe addition of a thermal plasma component (kT~ 0.3 keV), while X-2 isimproved only at the 1.3σ level with the addition of a discblackbody component with Tin~ 0.2 keV. Both sources arevariable on short time-scales implying that their emission is dominatedby single accreting X-ray binaries (XRBs). The three remaining galaxies,NGC 7770, NGC 2342 and NGC 2341, have observed X-ray luminosities of0.2, 1.8 and 0.9 × 1041 erg s-1,respectively (0.3-10 keV). Their integrated spectra are alsowell-modelled by multi-temperature thermal plasma components with kT=0.2-0.7 keV, plus power-law continua with slopes of Γ= 1.8-2.3that are likely to represent the integrated emission of populations ofXRBs as observed in other nearby merger systems. A comparison with otherisolated, interacting and merging systems shows that all four galaxiesfollow the established correlations for starburst galaxies betweenX-ray, far-infrared and radio luminosities, demonstrating that theirX-ray outputs are dominated by their starburst components.
| Ultraviolet Emission from Stellar Populations within Tidal Tails: Catching the Youngest Galaxies in Formation?
New Galaxy Evolution Explorer (GALEX) observations have detectedsignificant far-UV (FUV; 1530 Å) and near-UV (NUV; 2310 Å)emission from stellar substructures within the tidal tails of fourongoing galaxy mergers. The UV-bright regions are optically faint andare coincident with H I density enhancements. FUV emission is detectedat any location where the H I surface density exceeds ~2Msolar pc-2, and it is often detected in theabsence of visible wavelength emission. UV luminosities of the brighterregions of the tidal tails imply masses of 106 to~109 Msolar in young stars in the tails, and H Iluminosities imply similar H I masses. UV-optical colors of the tidaltails indicate stellar populations as young as a few megayears, and inall cases ages under 400 Myr. Most of the young stars in the tailsformed in single bursts, rather than resulting from continuous starformation, and they formed in situ as the tails evolved. Star formationappears to be older near the parent galaxies and younger at increasingdistances from the parent galaxy. This could be because the starformation occurs progressively along the tails, or because the starformation has been inhibited near the galaxy/tail interface. Theyoungest stellar concentrations, usually near the ends of long tidaltails, have masses comparable to confirmed tidal dwarf galaxies and maybe newly forming galaxies undergoing their first burst of starformation.
| The Westerbork HI survey of spiral and irregular galaxies. III. HI observations of early-type disk galaxies
We present Hi observations of 68 early-type disk galaxies from the WHISPsurvey. They have morphological types between S0 and Sab and absoluteB-band magnitudes between -14 and -22. These galaxies form the massive,high surface-brightness extreme of the disk galaxy population, few ofwhich have been imaged in Hi before. The Hi properties of the galaxiesin our sample span a large range; the average values of MHI/LB and DH I/D25 are comparableto the ones found in later-type spirals, but the dispersions around themean are larger. No significant differences are found between the S0/S0aand the Sa/Sab galaxies. Our early-type disk galaxies follow the same Himass-diameter relation as later-type spiral galaxies, but theireffective Hi surface densities are slightly lower than those found inlater-type systems. In some galaxies, distinct rings of Hi emissioncoincide with regions of enhanced star formation, even though theaverage gas densities are far below the threshold of star formationderived by Kennicutt (1989, ApJ, 344, 685). Apparently, additionalmechanisms, as yet unknown, regulate star formation at low surfacedensities. Many of the galaxies in our sample have lopsided gasmorphologies; in most cases this can be linked to recent or ongoinginteractions or merger events. Asymmetries are rare in quiescentgalaxies. Kinematic lopsidedness is rare, both in interacting andisolated systems. In the appendix, we present an atlas of the Hiobservations: for all galaxies we show Hi surface density maps, globalprofiles, velocity fields and radial surface density profiles.
| Near-Infrared Integral Field Spectroscopy of Star-forming Galaxies
The Palomar Integral Field Spectrograph was used to probe a variety ofenvironments in nine nearby galaxies that span a range of morphologicaltypes, luminosities, metallicities, and infrared-to-blue ratios. For thefirst time, near-infrared spectroscopy was obtained for nuclear orbright H II regions in star-forming galaxies over two spatial dimensions(5.7"×10.0") in the [Fe II] (1.257 μm), [Fe II] (1.644 μm),Paβ (1.282 μm), H2 (2.122 μm), and Brγ(2.166 μm) transition lines. These data yield constraints on variouscharacteristics of the star-forming episodes in these regions, includingtheir strength, maturity, spatial variability, and extinction. The H IIregions stand out from the nuclei. Unlike observations of nuclearregions, H II region near-infrared observations do not show a spatialcoincidence of the line and continuum emission; the continuum and linemaps of H II regions usually show distinct and sometimes spatiallyseparated morphologies. Gauging from Paβ and Brγ equivalentwidths and luminosities, the H II regions have younger episodes of starformation than the nuclei and more intense radiation fields.Near-infrared line ratio diagnostics suggest that H II regions have``purer'' starbursting properties. The correlation between ionizingphoton density and mid-infrared color is consistent with the starformation activity level being higher for H II regions than for nuclei.And though the interpretation is complicated, on a purely empiricalbasis the H II regions show lower Fe1+ abundances than nucleiby an order of magnitude.
| A Study of the Distribution of Star-forming Regions in Luminous Infrared Galaxies by Means of Hα Imaging Observations
We performed Hα imaging observations of 22 luminous infraredgalaxies to investigate how the distribution of star-forming regions inthese galaxies is related to galaxy interactions. Based on correlationdiagrams between Hα flux and continuum emission for individualgalaxies, a sequence for the distribution of star-forming regions wasfound: very compact (~100 pc) nuclear starbursts with almost nostar-forming activity in the outer regions (type 1), dominant nuclearstarbursts <~1 kpc in size with a negligible contribution from theouter regions (type 2), nuclear starbursts >~1 kpc in size with asignificant contribution from the outer regions (type 3), and extendedstarbursts with relatively faint nuclei (type 4). These classes ofstar-forming regions were found to be strongly related to globalstar-forming properties, such as star formation efficiency, far-infraredcolor, and dust extinction. There was a clear tendency for the objectswith more compact distributions of star-forming regions to show a higherstar formation efficiency and hotter far-infrared color. An appreciablefraction of the sample objects were dominated by extended starbursts(type 4), which is unexpected in the standard scenario ofinteraction-induced starburst galaxies. We also found that thedistribution of star-forming regions was weakly but clearly related togalaxy morphology: severely disturbed objects had a more concentrateddistribution of star-forming regions. This suggests that the propertiesof galaxy interactions, such as dynamical phase and orbital parameters,play a more important role than the internal properties of progenitorgalaxies, such as dynamical structure or gas mass fraction. We alsodiscuss the evolution of the distribution of star-forming regions ininteracting galaxies.
| Tidally Triggered Star Formation in Close Pairs of Galaxies. II. Constraints on Burst Strengths and Ages
Galaxy-galaxy interactions rearrange the baryons in galaxies and triggersubstantial star formation; the aggregate effects of these interactionson the evolutionary histories of galaxies in the universe are poorlyunderstood. We combine B- and R-band photometry and optical spectroscopyto estimate the strengths and timescales of bursts of triggered starformation in the centers of 190 galaxies in pairs and compact groups.Based on an analysis of the measured colors and EW(Hα), wecharacterize the preexisting and triggered populations separately. Thebest-fitting burst scenarios assume stronger reddening corrections forline emission than for the continuum and continuous star formationlasting for >~100 Myr. The most realistic scenarios require aninitial mass function that is deficient in the highest mass stars. Thecolor of the preexisting stellar population is the most significantsource of uncertainty. Triggered star formation contributessubstantially (probably >~50%) to the R-band flux in the centralregions of several galaxies; tidal tails do not necessarily accompanythis star formation. Many of the galaxies in our sample have bluercenters than outskirts, suggesting that pre- or nonmerger interactionsmay lead to evolution along the Hubble sequence. These objects wouldappear blue and compact at higher redshifts; the older, redder outskirtsof the disks would be difficult to detect. Our data indicate thatgalaxies with larger separations on the sky contain weaker, and probablyolder, bursts of star formation on average. However, confirmation ofthese trends requires further constraints on the colors of the olderstellar populations and on the reddening for individual galaxies.
| Physical Coupling of Kazarian Galaxies with Surrounding Galaxies
Results from a statistical study of Kazarian galaxies and the objectssurrounding them are presented. It is shown that: (1) the sample ofKazarian galaxies up to 16m.0 is complete. (2) Roughly 35.7% of theKazarian galaxies are members of clusters, 14.0% of groups, and 13.6% ofbinary systems, while 36.7% are single galaxies. (3) Of the 580 Kazariangalaxies, roughly 61.2% are infrared, 8.8% radio, and 2.8% x-raysources. (4) The relative numbers of Kazarian galaxies for completesamples of I, R, and X in the different groups are systematically higherthan the corresponding numbers for samples of all Kazarian galaxies.
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| 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.
| 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
| Thermal Infrared 3-5 Micron Colors of Obscured and Unobscured Active Galactic Nuclei
Thermal infrared photometry in the L and M' bands and L-M' colors oftype 1 and type 2 active galactic nuclei (AGNs) are presented. Aftercombining our observations with photometric data at similar wavelengthstaken from the literature, we find that the excess of L-M' colors oftype 2 AGNs (37 sources, 50 data points) relative to type 1 AGNs (27sources, 36 data points), due to dust extinction, is statisticallydetectable but very small. We next investigate the L-M' colors of type 2AGNs by separating less dust obscured type 2 AGNs and highly dustobscured type 2 AGNs. In both cases, the L-M' colors are similar to theintrinsic L-M' color of unobscured AGNs, and the L-M' color excess ofthe latter highly dust obscured type 2 AGNs, due to dust extinction, ismuch smaller than that expected from the Galactic dust extinction curve.Contamination from starbursts and the time lag of flux variation areunlikely to explain this small L-M' color excess, which is bestexplained if the dust extinction curve in the close vicinity of AGNs isfairly flat at 3-5 μm, as a result of a size increase of theabsorbing dust grains through coagulation.
| The Structure of Infrared-luminous Galaxies at 100 Microns
We have observed 22 galaxies at 100 μm with the Kuiper AirborneObservatory in order to determine the angular size of their FIR-emittingregions. This one-dimensional array data constitutes the highest spatialresolution ever achieved on luminous galaxies in the far-infrared. Mostof these galaxies are very luminous far-infrared sources, withLFIR>1011 Lsolar. We clearlyresolved six of these galaxies at 100 μm and have some evidence forextension in seven others. Those galaxies that we have resolved can havelittle of their 100 μm flux directly emitted by a pointlike activegalactic nucleus. Dust heated to ~40 K by recent bursts of nonnuclearstar formation provides the best explanation for their extreme FIRluminosity. In a few cases, heating of an extended region by a compactcentral source is also a plausible option.
| Near-Infrared Line Imaging of the Circumnuclear Starburst Ring in NGC 7771
We present high spatial resolution near-infrared broadband JHK imagesand, for the first time, Brγ 2.1661 μm and H2 1-0S(1) 2.122 μm emission-line images of the circumnuclear star-formingring (major axis diameter 7''=2 kpc) in the starburst galaxyNGC 7771. These data are used to investigate the morphology andextinction of the starburst ring and to study its star-formingproperties and history by comparing the observed quantities with anevolutionary population synthesis model. The clumpy morphology of NGC7771 varies strongly with wavelength, as a result of the combination ofextinction (for which we derive an average value of AV=2.8),emission from hot dust and red supergiants, and several stellargenerations in the ring. Also, the ellipticity and the position angle ofthe ring depend on the wavelength. The starburst ring in NGC 7771exhibits small Brγ equivalent widths. Assuming a constant starformation model with Mu=100 Msolar results in verylong lifetimes of the star-forming regions (up to 1 Gyr), indisagreement with the clumpy near-infrared morphology and the observedradio spectral index of NGC 7771. This situation is only slightlyremedied by assuming a reduced upper mass cutoff (Mu=30Msolar), resulting in ages between 8 and 180 Myr. We preferan instantaneous star formation model with Mu=100Msolar, which can explain the derived Brγ equivalentwidths if a single starburst occurred 6-7 Myr ago. The main excitationmechanism of the molecular gas, based on the observed S(1)/Brγratio, appears to be excitation by UV radiation from hot young stars. Wederive M~=1900 Msolar for the mass of the excitedH2.
| Optical Spectral Signatures of Dusty Starburst Galaxies
We analyze the optical spectral properties of the complete sample ofVery Luminous Infrared Galaxies presented by Wu et al., and we find ahigh fraction (~50%) of spectra showing both a strong Hδ line inabsorption and relatively modest [O II] emission [e(a) spectra]. Thee(a) signature has been proposed as an efficient method to identifydusty starburst galaxies, and we study the star formation activity andthe nature of these galaxies, as well as the effects of dust on theirobserved properties. We examine their emission-line characteristics, inparticular their [O II]/Hα ratio, and we find this to be greatlyaffected by reddening. A search for AGN spectral signatures reveals thatthe e(a) galaxies are typically H II/LINER galaxies. We compare the starformation rates derived from the FIR luminosities with the estimatesbased on the Hα line and find that the values obtained from theoptical emission lines are a factor of 10-70 (Hα) and 20-140 ([OII]) lower than the FIR estimates (50-300 Msolaryr-1). We then study the morphological properties of the e(a)galaxies, looking for a near companion or signs of a merger/interaction.In order to explore the evolution of the e(a) population, we present anoverview of the available observations of e(a) galaxies in differentenvironments both at low and high redshift. Finally, we discuss the roleof dust in determining the e(a) spectral properties and we propose ascenario of selective obscuration in which the extinction decreases withthe stellar age.
| Multifrequency observations of the interacting galaxy NGC 4922 (UCM 1259 + 2934)
We present new multifrequency observations (X-ray ROSAT HRI, optical rGunn--Thuan and near-infrared J and K imaging, and optical spectroscopy)of the interacting galaxy pair UCM 1259 + 2934 (NGC 4922A + B). Thesedata are used to study the origin of the extended soft X-ray emissionand the star formation history of the northern component of theinteracting system. The southern component (NGC 4922S) shows no signs ofactivity, with an optical spectrum consistent with that of an ellipticalgalaxy, which is also supported by its morphology. The northerncomponent (NGC 4922N) shows evidence of composite activity; the nuclearoptical line ratios are intermediate between those of a LINER and aSeyfert 2 galaxy. Its circumnuclear regions resemble a normal H iiregion. NGC 4922N can be classified as a transition object, in the sensethat its optical emission lines may be produced by both a non-stellarcontinuum and hot stars. The ROSAT HRI observation shows extended softX-ray emission which appears to peak close to the nucleus of NGC 4922N,with luminosity L_X(0.1--2.4 keV)=(2.6--4.3)x10^41 erg s^-1, dependingon the parameters of the adopted model. The extended nature of thesource rules out a situation in which most of the X-ray emissionoriginates from an active nucleus. The most likely mechanism responsiblefor the extended soft X-ray emission is star formation activity viasupernova remnants and/or massive X-ray binaries (MXRBs) formed in aburst of star formation that occurred about 7x10^6 yr ago, plus alarge-scale supernova-driven wind. Based on the far-infrared versusX-ray correlations for high-flux IRAS galaxies, we can conclude that thesoft X-ray emission is arising from both galaxies in the system, thoughdominated by the northern component. An evolutionary synthesis model isused to investigate the star formation history of NGC 4922N. From theextinction-corrected r-J and J-K colours we argue that between 0.1 and 1per cent of the total stellar mass of the galaxy was formed during thelast episode of star formation. The star formation rate (SFR) of thenorthern component, 6<=SFR<=35 M_solar yr^-1 as inferred from theHα and far-infrared luminosities, is higher than typical SFRs ofisolated galaxies. Such a high SFR could result from an episode of starformation triggered by interaction with the southern component.
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| The Luminous Starburst Ring in NGC 7771: Sequential Star Formation?
Only two of the 20 highly luminous starburst galaxies analyzed by Smithet al. exhibit circumnuclear rings of star formation. These galaxiesprovide a link between ~10^11 L_solar luminosity class systems andclassical, less-luminous ringed systems. In this paper, we report thediscovery of a near-infrared counterpart to the 1.6 kpc diameter nuclearring of radio emission in NGC 7771 (UGC 12815). The ring contains ~10radio-bright clumps and ~10 near-infrared-bright clumps. A displacementbetween the peaks of the radio and the near-infrared emission indicatesthe presence of multiple generations of star formation. The estimatedthermal emission from each radio source is equivalent to that of ~35,000O6 stars. Each near-infrared-bright knot contains ~5000 red supergiants,on average. In the case that the radio-bright knots are 4 Myr old andthe near-infrared-bright knots are ~10 Myr old, each knot ischaracterized by a stellar mass of 10^7 M_solar, and the impliedtime-averaged star formation rate is ~40 M_solar yr^-1. Severalsimilarities are found between the properties of this system and otherringed and nonringed starbursts. Morphological differences between NGC7771 and the starburst+Seyfert 1 galaxy NGC 7469 (UGC 12332) suggestthat NGC 7771 may not be old enough to fuel an active galactic nucleus(AGN), or may not be capable of fueling an AGN. Alternatively, thedifferences may be unrelated to the presence or absence of an AGN andmay simply reflect the possibility that star formation in rings isepisodic.
| Starburst Galaxies. III. Properties of a Radio-selected Sample
We have analyzed the properties of the 20 most radio-luminous UGCstarburst galaxies from Condon, Frayer, & Broderick. Near-infraredimages, spectra, and optical rotation curves were presented in Smith etal. In this paper, we use these data and published radio data to assessthe stellar populations, dust contents, ionizing conditions, anddynamics of the starbursts. Certain properties of the star formationoccurring in these galaxies differ from those observed locally. Theinfrared excesses (IREs) are lower than and span a narrower range ofvalues than those of Galactic H II regions. The starbursts appear toproduce a higher proportion of ionizing photons than most Galactic H IIregions. Consequently, the initial mass functions (IMFs) of thestarbursts may be more strongly biased toward high-mass star formation.The starbursts may also contain fewer old H II regions than the MilkyWay. Furthermore, the starburst IRE is likely to be influenced by thepresence of large reservoirs of gas that absorb a larger fraction of theLyman continuum photons. The OB stellar and far-infrared luminositiesimply that the upper mass range of the starburst IMF (M > 10 Mȯ)is characterized by a slope of 2.7 +/- 0.2. The starburst IMF thus bearsa strong similarity to that observed in Magellanic OB associations.Optical line ratios indicate that a range of excitation conditions arepresent. We conclude that the near-infrared light from many of thestarbursts is dominated by a heavily obscured mixture of emission fromevolved red stars and young blue stars with small contributions (~5%)from thermal gas and hot dust, under the assumptions that a Galactic orSMC extinction law can be applied to these systems and that the truereddening curve follows one of the models currently existing in theliterature. In some cases, larger amounts of emission from blue stars orhot dust may be required to explain the observed near-infrared colors.The amount of dust emission exceeds that predicted from comparisons withGalactic H II regions. The near-infrared colors of some of the systemsmay also be influenced by the presence of a low-luminosity activegalactic nucleus (AGN). Emission from blue stars and hot dust, ifpresent, dilutes the observed CO index. The activity in the redder, moreluminous systems is strongly peaked. The galaxies hosting the starburstsexhibit a wide range of morphological and star-forming properties. Whileall of the host galaxies are interacting systems, the nuclearseparations of the interacting nuclei range from <1 kpc to >1 Mpc.The dynamical behavior ranges from relaxed to strongly perturbed. Theoff-nuclear regions of the galaxies are sites of active star formationand are characterized by a range of excitation conditions. Spatiallyextended LINER emission is consistent with shock excitation produced bysuperwinds or galaxy-galaxy collisions. Violent star formation activityoccurs over a larger physical scale in the most active starbursts.Systems containing mergers and widely separated nuclei possess similarcolors and luminosities. The burst properties are most likely regulatedby the internal structures of the interacting galaxies and not theseparations of the interacting galaxies.
| A statistical study of the spectra of very luminous IRAS galaxies. II. Spectral and environmental analysis
Spectroscopic observations of a sample of 73 very luminous IRAS galaxies(log(LIR/Lsun)>=11.5 for H0=50 km\s(-1) ; Mpc(-1) ,q0=0.5) from the 2 Jy redshift surveycatalogue were carried out using the 2.16 m telescope at the BeijingAstronomical Observatory. The observational data, including the opticalimages (extracted from Digital Sky Survey) and spectra for thesegalaxies, are presented in Paper I \cite[(Wu et al. 1998)]{wu98}. Inthis paper, we give the spectral and morphological classifications forthese very luminous IRAS galaxies (VLIRGs). We show that about 60% ofVLIRGs exhibit AGN-like spectra (Seyfert 1s, Seyfert 2s, LINER-likegalaxies). This fraction goes up to 82% for the ultraluminous IRASgalaxies (ULIRGs) subsample (Log(LIR/Lsun) >=12.0). 56% of the VLIRGs show strong interaction or merging signatures;this fraction rises to 91% for the ULIRGs. These statistical resultsstrongly suggest that interaction triggers nuclear activities andenhances the infrared luminosity. We find that LINER and a mixture typewhich have optical properties of both HII galaxies and LINERs could beat the transition stage from infrared luminous HII galaxies to AGNs;their main energy production is from starbursts as well as AGNs. Bothinfrared luminosities and Hα equivalent widths increasedramatically as nuclear separations between VLIRGs and their nearestneighbors decrease. There is little doubt that strong starbursts happenin the nuclei of VLIRGs. Assuming class 0 as advanced merger, weconstruct a simple merger sequence, from morphological classes 1 to 4(with near or far companions), to class 5 and 6 (interacting pairs andmergers) and then to class 0 (isolated galaxies). Along this sequence,VLIRGs evolve from HII galaxies to AGNs. Table 1 is only available atthe CDS via anonymous ftp 130.79.128.5 or http://cdsweb.u-strasbg.fr
| 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.
| A statistical study of the spectra of very luminous IRAS galaxies. I. Data
This paper presents the results of spectral observations for the largestcomplete sample of very luminous IRAS galaxies obtained to date. Thesample consists of those 73 objects for which log(L_IR/Lsun)>= 11.5 (H0=50;km; s(-1) Mpc(-1) , q0=0.5) andmag <= 15.5 , and was extracted from the 2 Jy IRAS redshift catalog.All the spectra were obtained using the 2.16 m telescope of BeijingAstronomical Observatory during the years 1994-1996. A total of 123galaxy spectra were obtained with spectral ranges of 4400;Angstroms to7100;Angstroms and 3500;Angstroms to 8100;Angstroms at resolutions of11.2;Angstroms and 9.3;Angstroms respectively. In addition to the 73spectra for sample galaxies, we also present spectra for ten non-samplegalaxies and a further 40 for the companions of sample galaxies. Thedata presented include nuclear spectrum and the parameters describingthe emission lines, absorption lines and continua as well as DSS imagesand environmental parameters. Table 1 is also available in electricform, Table 2-4 are only available in electronic form form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130. 79.128.5) or via http:cdsweb.u-strasbg.fr/Abstract.html. Figures 4 and 9 are published in theon-line version of A&A..
| A multiwavelength study of the starburst galaxy NGC 7771
We present a multiwavelength study of the interacting starburst galaxyNGC 7771, including new optical and ultraviolet spectra and a previouslyunpublished soft X-ray ROSAT image and spectrum. The FIR, radio, andX-ray fluxes suggest that a massive burst of star formation is currentlyin progress, but the small equivalent width of the Balmer emissionlines, the weak UV flux, the low abundance of ionized oxygen, and theshape of the optical spectrum lead us to conclude that there are few Ostars. This might normally suggest that star formation has ceased, butthe barred gravitational potential and large gas reserves of the galaxyimply that this should not be so, and we therefore consider otherexplanations. We argue that the observations cannot be due to effects ofgeometry, density-bounded nebulae, or dust within the nebulae, andconclude that a truncated IMF is required. The dwarf galaxy NGC 7770appears to be in the initial stages of a merger with NGC 7771, and theresulting tidal perturbations may have induced the apparent two-armedspiral pattern, and driven a substantial fraction of the disk gasinwards. The presence of a bulge in NGC 7771 may be moderating thestarburst so that, while still occurring on a large scale with asupernova rate of 0.8-1/yr, it is less violent and the IMF has arelatively low upper mass limit. We find that there is a cluster ofstars obscuring part of the starburst region, and we offer anexplanation of its origin.
| 21-cm line observations of galaxies from Kazarian's lists
The 21-cm neutral hydrogen line has been measured for the first time in39 non-Seyfert type galaxies from Kazarian list, with the Nancayradiotelescope. The line profiles, widths at 20% and 50% of the peakintensity, radial velocities as well as total fluxes are presented. Thevalues of radial velocity are in fairly good agreement with thoseobtained from optical spectra. The width values at 20% of the peak varyin wide range from 113 km s^{-1} (KAZ 579) to 608 km s^{-1} for KAZ 566.Nine of our objects remained undetected, whether their HI-flux was toofaint, the integration time too short, or the frequency sighted wrong.However, for part of them, there were positive hint of detection.Comments on individual objects are given. Tables 1 and 3 are onlyavailable in electronic form at CDS. Table 2 is also available inelectronic form at CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| Morphological classification of new galaxies with a UV excess
The results of a morphological classification of 580 galaxies with a UVexcess, included in the lists in [M. A. Kazarian, Astrofizika,15, 5(1979); ibid.,15, 193 (1979); M. A. Kazarian and É. S. Kazarian,ibid.,16, 17 (1980); ibid.,18, 512 (1982); ibid.,19, 213 (1983)], arepresented. For this we have developed a set of symbols, using the typesE, S, and Ir introduced by Hubble, as well as symbols introduced byother authors and us. This set enabled us to make the morphologicalclassification. Direct photographs obtained on the 2.6-m and 6-mtelescopes were used to classify 141 of the galaxies (over 24%), whilePalomar Atlas charts were used for the remaining 439 galaxies. Thesegalaxies were divided into two groups based on classificationconditions, and data on each group are given in Tables 1 and 2,respectively. The results for each group, given in Table 3, show thatwith the transition from early types, such as C and E, to later types,such as S and Ir, the relative number of galaxies going into one group(Table 1), in which the classification was based on direct photographs,increases in comparison with the number going into the other group(Table 2).
| The FCRAO Extragalactic CO Survey. I. The Data
Emission from the CO molecule at λ = 2.6 mm has been observed at1412 positions in 300 galaxies using the 14 m telescope of the FiveCollege Radio Astronomy Observatory (HPBW = 45"); these data comprisethe FCRAO Extragalactic CO Survey. In this paper we describe the galaxysample, present the data, and determine global CO fluxes and radialdistributions for the galaxies in the Survey. Future papers will dealwith the data analysis, both with regard to the global properties ofgalaxies and the radial distributions within them. CO emission wasdetected in 236 of the 300 Survey galaxies for an overall detection rateof 79%; among the 52 Sc galaxies in the Survey, the detection rate wasas high as 96%. most of the 193 galaxies observed in multiple positionsexhibit CO distributions which peak at the center. However, a smallnumber (10-primarily Sb galaxies) exhibit CO rings at 45" resolution,and a similar number (18-primarily Sc galaxies) have CO distributionswhich peak on one side of the center. We derive CO isophotal diametersfor 151 galaxies and find the mean ratio of CO to optical isophotaldiameters to be 0.5. We also find a trend along the Hubble sequence suchthat the mean ratio of CO to optical isophotal diameters is smallestamong the early-type spirals (SO/a, Sa, and Sab) and the mean ratioincreases for Sb, Sbc, and Sc galaxies, finally decreasing among thelater types. Comparison of the global fluxes we derive for the Surveygalaxies with independent measurements from the literature indicatesthat the global fluxes we derive are accurate to ~40%.
| Redshift Quantization - A Review
Not Available
| 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.
| An X-ray catalog and atlas of galaxies
An X-ray catalog and atlas of galaxies observed with the EinsteinObservatory imaging instruments (IPC and HRI) are presented. The catalogcomprises 493 galaxies, including targets of pointed observations, andRSA or RC2 galaxies serendipitously included in Einstein fields. A totalof 450 of these galaxies were imaged well within the instrumentalfields, resulting in 238 detections and 2123 sigma upper limits. Theother galaxies were either at the edge of the visible field of view orconfused with other X-ray sources. For these a rough measure of theirX-ray emission is also given. The atlas shows X-ray contour maps ofdetected galaxies superposed on optical photographs and givesazimuthally averaged surface brightness profiles of galaxies detectedwith a high signal-to-noise ratio.
| VLA observations of radio sources in interacting galaxy pairs in poor clusters
Observations of 16 radio sources in interacting galaxies in 14 poorclusters were made using the Very Large Array in the B configuration atlambda of 6 and 2 cm. These sources had been unresolved in earlierobservations at lambda of 21 cm, and were chosen as a sample todetermine which of three models for radio source formation actuallypertains in interacting galaxies. From the analysis of this sample, thestarburst model appears most successful, but the 'central monster' modelcould pertain in some cases.
| KISO survey for ultraviolet-excess galaxies. XIV.
The 14th list and identification charts of the UV-excess galaxiesdetected on the multicolor plates taken with the Kiso Schmidt telescopefor 10 survey fields are presented. In the sky area of some 300 sq deg,about 470 objects are cataloged down to the photographic magnitude ofabout 17.5.
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