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Chandra observations of the interacting galaxies NGC 3395/3396 (Arp 270)
In this paper we present the results of a 20-ks high-resolution ChandraX-ray observation of the peculiar galaxy pair NGC 3395/3396, a system ata very early stage of merging, and less evolved than the famous Antennaeand Mice merging systems. Previously unpublished ROSAT High-ResolutionImager data are also presented. The point-source population and the hotdiffuse gas in this system are investigated and compared with othermerging galaxy pairs.16 X-ray point sources are detected in Arp 270, seven of which areclassified as ultraluminous X-ray sources (ULXs, LX>=1039 erg s-1). From spectral fits and the age ofthe system it seems likely that these are predominantly high-mass X-raybinaries. The diffuse gas emits at a global temperature of ~0.5 keV,consistent with temperatures observed in other interacting systems, andwe see no evidence of the starburst-driven hot gaseous outflows seen inmore evolved systems such as The Mice and The Antennae. It is likelythat these features are absent from Arp 270 as the gas has hadinsufficient time to break out of the galaxy discs. 32 per cent of theluminosity of Arp 270 arises from the diffuse gas in the system, this islow when compared with later stage merging systems and gives furthercredence that this is an early-stage merger.Comparing the ULX population of Arp 270 to other merging systems, wederive a relationship between the star formation rate of the system,indicated by LFIR, and the number [N(ULX)] and luminosity(LULX) of its ULX population. We find N(ULX)~L0.18FIR andLULX~L0.54FIR. These relationships,coupled with the relation of the point-source X-ray luminosity(LXP) to LK and LFIR+UV (Colbert et al.2003), indicate that the ULX sources in an interacting system havecontributions from both the old and young stellar populations.
| Shock-induced star formation in a model of the Mice
Star formation plays an important role in the fate of interactinggalaxies. To date, most galactic simulations including star formationhave used a density-dependent star formation rule designed toapproximate a Schmidt law. Here, I present a new star formation rulewhich is governed by the local rate of energy dissipation in shocks. Thenew and old rules are compared using self-consistent simulations of NGC4676; shock-induced star formation provides a better match to theobservations of this system.
| Stellar populations and star cluster formation in interacting galaxies with the Advanced Camera for Surveys
Pixel-by-pixel colour-magnitude and colour-colour diagrams-based on asubset of the Hubble Space Telescope Advanced Camera for Surveys EarlyRelease Observations-provide a powerful technique to explore and deducethe star and star cluster formation histories of the Mice and the Tadpole interactinggalaxies. In each interacting system we find some 40 bright young starclusters (20<~F606W(mag)<~25, with a characteristic mass of~3×106 Msolar), which are spatiallycoincident with blue regions of active star formation in their tidaltails and spiral arms. We estimate that the main events triggering theformation of these clusters occurred ~(1.5-2.0)×108 yrago. We show that star cluster formation is a major mode of starformation in galaxy interactions, with >~35% of the active starformation in encounters occurring in star clusters. This is the firsttime that young star clusters have been detected along the tidal tailsin interacting galaxies. The tidal tail of the Tadpole system isdominated by blue star forming regions, which occupy some 60% of thetotal area covered by the tail and contribute ~70% of the total flux inthe F475W filter (decreasing to ~40% in F814W). The remaining pixels inthe tail have colours consistent with those of the main disk. Thetidally triggered burst of star formation in the Mice is of similarstrength in both interacting galaxies, but it has affected onlyrelatively small, spatially coherent areas.
| Chandra observations of the Mice
Presented here are high spatial and spectral resolution Chandra X-rayobservations of the famous interacting galaxy pair, the Mice, a systemsimilar to, though less evolved than, the well-known Antennae galaxies.Previously unpublished ROSAT High Resolution Imager data of the systemare also presented.Starburst-driven galactic winds outflowing along the minor axis of bothgalaxies (but particularly the northern one) are observed, and spectraland spatial properties, and energetics are presented. That such aphenomenon can occur in such a rapidly evolving and turbulent system issurprising, and this is the first time that the very beginning - theonset, of starburst-driven hot gaseous outflow in a full-blown disc-discmerger has been seen.Point-source emission is seen at the galaxy nuclei, and within theinteraction-induced tidal tails. Further point-source emission isassociated with the galactic bar in the southern system. A comparison ofthe source X-ray luminosity function and of the diffuse emissionproperties is made with the Antennae and other galaxies, and evidence ofa more rapid evolution of the source population than the diffusecomponent is found. No evidence for variability is found between theChandra and previous observations.
| 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.
| A Hubble Space Telescope WFPC2 Investigation of the Nuclear Morphology in the Toomre Sequence of Merging Galaxies
We report on the properties of nuclear regions in the Toomre sequence ofmerging galaxies, based on imaging data gathered with the Hubble SpaceTelescope WFPC2 camera. We have imaged the 11 systems in the proposedevolutionary merger sequence in the F555W and F814W broadband filters,and in Hα+[N II] narrowband filters. The broadband morphology ofthe nuclear regions varies from nonnucleated starburst clumps throughdust-covered nuclei to a nucleated morphology. There is no unambiguoustrend in the morphology with merger stage. The emission-line morphologyis extended beyond the nucleus in most cases, but centrally concentrated(within 1 kpc) emission-line gas can be seen in the four latest-stagemerger systems. We have quantified the intrinsic luminosity densitiesand colors within the inner 100 pc and 1 kpc of each identified nucleus.We find little evidence for a clear trend in nuclear properties alongthe merger sequence other than a suggestive rise in the nuclearluminosity density in the most evolved members of the sequence. The lackof clear trends in nuclear properties is likely due both to the effectsof obscuration and geometry, as well as the physical variety of galaxiesincluded in the Toomre sequence.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555. These observations are associated with proposal8669.
| Hα surface photometry of galaxies in the Virgo cluster. IV. The current star formation in nearby clusters of galaxies
Hα +[NII] imaging observations of 369 late-type (spiral) galaxiesin the Virgo cluster and in the Coma/A1367 supercluster are analyzed,covering 3 rich nearby clusters (A1367, Coma and Virgo) and nearlyisolated galaxies in the Great-Wall. They constitute an opticallyselected sample (mp<16.0) observed with ~ 60 %completeness. These observations provide us with the current(T<107 yrs) star formation properties of galaxies that westudy as a function of the clustercentric projected distances (Theta ).The expected decrease of the star formation rate (SFR), as traced by theHα EW, with decreasing Theta is found only when galaxies brighterthan Mp ~ -19.5 are considered. Fainter objects show no orreverse trends. We also include in our analysis Near Infrared data,providing information on the old (T>109 yrs) stars. Puttogether, the young and the old stellar indicators give the ratio ofcurrently formed stars over the stars formed in the past, or``birthrate'' parameter b. For the considered galaxies we also determinethe ``global gas content'' combining HI with CO observations. We definethe ``gas deficiency'' parameter as the logarithmic difference betweenthe gas content of isolated galaxies of a given Hubble type and themeasured gas content. For the isolated objects we find that b decreaseswith increasing NIR luminosity. In other words less massive galaxies arecurrently forming stars at a higher rate than their giant counterpartswhich experienced most of their star formation activity at earliercosmological epochs. The gas-deficient objects, primarily members of theVirgo cluster, have a birthrate significantly lower than the isolatedobjects with normal gas content and of similar NIR luminosity. Thisindicates that the current star formation is regulated by the gaseouscontent of spirals. Whatever mechanism (most plausibly ram-pressurestripping) is responsible for the pattern of gas deficiency observed inspiral galaxies members of rich clusters, it also produces the observedquenching of the current star formation. A significant fraction of gas``healthy'' (i.e. with a gas deficiency parameter less than 0.4) andcurrently star forming galaxies is unexpectedly found projected near thecenter of the Virgo cluster. Their average Tully-Fisher distance isfound approximately one magnitude further away (muo = 31.77)than the distance of their gas-deficient counterparts (muo =30.85), suggesting that the gas healthy objects belong to a cloudprojected onto the cluster center, but in fact lying a few Mpc behindVirgo, thus unaffected by the dense IGM of the cluster. Based onobservations taken at the Observatorio Astronómico Nacional(Mexico), the OHP (France), Calar Alto and NOT (Spain) observatories.Table \ref{tab4} is only available in electronic form athttp://www.edpsciences.org
| Hα surface photometry of galaxies in the Virgo cluster I. Observations with the San Pedro Martir 2.1 m telescope
Hα imaging observations of 125 galaxies obtained with the 2.1 mtelescope of the San Pedro Martir Observatory (SPM) (Baja California,Mexico) are presented. The observed galaxies are mostly Virgo clustermembers (77), with 36 objects in the Coma/A1367 supercluster and 12 inthe clusters A2197 and A2199 taken as fillers. Hα +[NII] fluxesand equivalent widths, as well as images of the detected targets arepresented. The observatory of San Pedro Martir (Mexico) belongs to theObservatorio Astronómico Nacional, UNAM. Figure 4 is onlyavailable in electronic form at http://www.edpsciences.org
| H i observations of interacting galaxy pair NGC 4038/9
We present the results of new radio interferometer Hi line observationsfor the merging galaxy pair NGC 4038/9 (`The Antennae'), obtained usingthe Australia Telescope Compact Array. The results improve substantiallywith respect to those of van der Hulst and show in detail the twomerging galactic discs and the two tidal tails produced by theirinteraction. The small edge-on spiral dwarf galaxy ESO 572-G045 is alsoseen near the tip of the southern tail, but distinct from it. It showsno signs of tidal interaction. The northern tidal tail of the Antennaeshows no Hi connection to the discs and has an extension towards thewest. The southern tidal tail is continuous, with a prominent Hiconcentration at its tip, roughly at the location of the tidal dwarfgalaxy observed optically by Mirabel, Dottori & Lutz. Clear velocitystructure is seen along the tidal tails and in the galactic discs. Radiocontinuum images at 20 and 13cm are also presented, showing the discs indetail.
| Molecular Gas in Optically Selected Mergers
We have mapped the 2.6 mm CO J=1-->0 emission in three opticallyselected ``Toomre sequence'' mergers (NGC 520, NGC 3921, NGC 4676). Themolecular gas distribution is well resolved by the observations. For NGC520 and NGC 4676A, the nuclear gas concentrations form a disklike or aringlike structure, and the gas kinematics are regular and consistentwith simple rotation. Discrete molecular gas complexes are found alongthe stellar bar in NGC 4676B, and the gas kinematics is consistent withthe disk rotation traced in Hα. The molecular gas distribution inNGC 3921 is asymmetric about the stellar remnant, and both thedistribution and kinematics suggest that the molecular gas has notsettled into the center of the remnant. Molecular gas clouds aredetected outside the central regions of NGC 3921 and NGC 4676, and theymay be associated with the tidal tails and bridges mapped in H I.Departures from the canonical scenario for a merger involving two largespiral galaxies are found in all three Toomre sequence mergers studied.Our data suggest that one of the progenitor disks in NGC 520 and NGC3921 was relatively gas-poor. A detailed comparison of these opticallyselected mergers and more luminous IR-selected mergers is deferred to aseparate paper.
| Cold gas and star formation in a merging galaxy sequence
We explore the evolution of the cold gas (molecular and neutralhydrogen) and star formation activity during galaxy interactions, usinga merging galaxy sequence comprising both pre- and post-mergercandidates. Data for this study come from the literature, but aresupplemented by some new radio observations presented here. First, weconfirm that the ratio of far-infrared luminosity to molecular hydrogenmass (LFIRM(H2); star formation efficiency)increases close to nuclear coalescence. After the merging of the twonuclei there is evidence that the star formation efficiency declinesagain to values typical of ellipticals. This trend can be attributed toM(H2) depletion arising from interaction induced starformation. However, there is significant scatter, likely to arise fromdifferences in the interaction details (e.g., disc-to-bulge ratio,geometry) of individual systems. Secondly, we find that the centralmolecular hydrogen surface density, ΣH2,increases close to the final stages of the merging of the two nuclei.Such a trend, indicating gas inflows caused by gravitationalinstabilities during the interaction, is also predicted by numericalsimulations. Furthermore, there is evidence for a decreasing fraction ofcold gas mass from early interacting systems to merger remnants,attributed to neutral hydrogen conversion into other forms (e.g., stars,hot gas) and molecular hydrogen depletion resulting from ongoing starformation. The evolution of the total-radio to blue-band luminosityratio, reflecting the total (disc and nucleus) star formation activity,is also investigated. Although this ratio is on average higher than thatfor isolated spirals, we find a marginal increase along the mergingsequence, attributed to the relative insensitivity of disc starformation to interactions. However, a similar result is also obtainedfor the nuclear radio emission, although galaxy interactions arebelieved to significantly affect the activity (star formation, AGN) inthe central galaxy regions. Nevertheless, the nuclear-radio to blue-bandluminosity ratio is significantly elevated compared with that forisolated spirals. Finally, we find that the FIR-radio flux ratiodistribution of interacting galaxies is consistent with star formationbeing the main energizing source.
| The Neutral Hydrogen Distribution in Merging Galaxies: Differences between Stellar and Gaseous Tidal Morphologies
As part of several H I synthesis-mapping studies of merging galaxies, wehave mapped the tidal gas in the three disk-disk merger systems Arp 157(NGC 520), Arp 220, and Arp 299 (NGC 3690). These systems differ fromthe majority of the mergers mapped in H I in that their stellar andgaseous tidal features do not coincide. In particular, they exhibitlarge stellar tidal features with little if any accompanying neutral gasand large gas-rich tidal features with little if any accompanyingstarlight. On smaller scales, there are striking anticorrelations inwhich the gaseous and stellar tidal features appear to cross. We exploreseveral possible causes for these differences, including dustobscuration, ram pressure stripping, and ionization effects. No singleexplanation can account for all of the observed differences. The factthat each of these systems shows evidence for a starburst-drivensuperwind expanding in the direction of the most strikinganticorrelations leads us to suggest that the superwind is primarilyresponsible for the observed differences, either by sweeping thefeatures clear of gas via ram pressure or by excavating a clearsightline toward the starburst and allowing UV photons to ionize regionsof the tails. If this suggestion is correct, only systems hosting agalactic superwind and experiencing a high-inclination encountergeometry (such that tidal gas is lifted high above the starburstregions) should exhibit such extreme differences between their H I andoptical tidal morphologies.
| Box- and peanut-shaped bulges. I. Statistics
We present a classification for bulges of a complete sample of ~ 1350edge-on disk galaxies derived from the RC3 (Third Reference Catalogue ofBright Galaxies, de Vaucouleurs et al. \cite{rc3}). A visualclassification of the bulges using the Digitized Sky Survey (DSS) inthree types of b/p bulges or as an elliptical type is presented andsupported by CCD images. NIR observations reveal that dust extinctiondoes almost not influence the shape of bulges. There is no substantialdifference between the shape of bulges in the optical and in the NIR.Our analysis reveals that 45% of all bulges are box- and peanut-shaped(b/p). The frequency of b/p bulges for all morphological types from S0to Sd is > 40%. In particular, this is for the first time that such alarge frequency of b/p bulges is reported for galaxies as late as Sd.The fraction of the observed b/p bulges is large enough to explain theb/p bulges by bars. Partly based on observations collected at ESO/LaSilla (Chile), DSAZ/Calar Alto (Spain), and Lowell Observatory/Flagstaff(AZ/U.S.A.). Tables 6 and 7 are only available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| Nearby Active and Starburst Galaxies as Seen with ISOCAM
We present a set of spectral characteristics distinguishing opticallyselected active galactic nuclei (AGNs) from starbursts in the mid-IR. InAGN spectra, the Unidentified Infrared Bands (UIBs) are not detectedwhich is probably due to the destruction of their carriers by the UV-Xradiation field. In addition, a non-negligible continuum below 10 μmcommonly associated with emission from very hot dust is exclusivelypresent in AGNs. On the contrary, starburst spectra present clearlydetected UIBs with a faint underlying continuum between 5-10 μm.Based on these features, we build a mid-IR diagnostic diagram toidentify emission induced by the AGN and that associated with the starformation activity. This diagnostic based on the mid-IR continuum andthe UIB intensity allows us to estimate the relative importance of thethree components (HII regions, photo-dissociation regions (PDRs), andAGN) contained in the integrated mid-IR emission of galaxies. Ourdiagnostic diagram can be applied to reveal the presence of veryobscured active nuclei behind large columns of dust.
| Galaxy coordinates. II. Accurate equatorial coordinates for 17298 galaxies
Using images of the Digitized Sky Survey we measured coodinates for17298 galaxies having poorly defined coordinates. As a control, wemeasured with the same method 1522 galaxies having accurate coordinates.The comparison with our own measurements shows that the accuracy of themethod is about 6 arcsec on each axis (RA and DEC).
| On the local radio luminosity function of galaxies. II. Environmental dependences among late-type galaxies
Using new extensive radio continuum surveys at 1.4 GHz (FIRST and NVSS),we derive the distribution of the radio/optical and radio/NIR luminosity(RLF) of late-type (Sa-Irr) galaxies (m_p<15.7) in 5 nearby clustersof galaxies: A262, Cancer, A1367, Coma and Virgo. With the aim ofdiscussing possible environmental dependences of the radio properties,we compare these results with those obtained for relatively isolatedobjects in the Coma supercluster. We find that the RLF of Cancer, A262and Virgo are consistent with that of isolated galaxies. Conversely weconfirm earlier claims that galaxies in A1367 and Coma have their radioemissivity enhanced by a factor ~ 5 with respect to isolated objects. Wediscuss this result in the framework of the dynamical pressure sufferedby galaxies in motion through the intra-cluster gas (ram-pressure). Wefind that the radio excess is statistically larger for galaxies in fasttransit motion. This is coherent with the idea that enhanced radiocontinuum activity is associated with magnetic field compression. TheX-ray luminosities and temperatures of Coma and A1367 imply that thesetwo clusters have significantly larger intracluster gas density than theremaining three studied ones, providing a clue for explaining the higherradio continuum luminosities of their galaxies. Multiple systems in theComa supercluster bridge (with projected separations smaller than 300kpc) have radio luminosities significantly larger than isolatedgalaxies. Table~1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html}
| Star formation in the northern component of the interacting NGC 4676 system (the Mice).
Not Available
| A catalogue of spatially resolved kinematics of galaxies: Bibliography
We present a catalogue of galaxies for which spatially resolved data ontheir internal kinematics have been published; there is no a priorirestriction regarding their morphological type. The catalogue lists thereferences to the articles where the data are published, as well as acoded description of these data: observed emission or absorption lines,velocity or velocity dispersion, radial profile or 2D field, positionangle. Tables 1, 2, and 3 are proposed in electronic form only, and areavailable from the CDS, via anonymous ftp to cdsarc.u-strasbg.fr (to130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| Simulation of large-scale gas structures formed in the interaction between galaxies. I. Method and preliminary results
Computer programs developed to study large-scale, transient gasstructures in galaxies are described and test results are given.Gas-dynamic quantities are determined on the basis of athree-dimensional algorithm using so-called "smoothed particlehydrodynamics" (SPH). Preliminary calculations were made to simulate theformation of a gas ring around a spheroidal galaxy when it absorbs alow-mass, gas-rich companion, as well due to gas accretion during theflyby of a spiral galaxy of comparable mass. The evolution of tidal gastails of disk galaxies is investigated.
| HI, HII, and R-Band Observations of a Galactic Merger Sequence
bWe present high-quality aperture synthesis observations of the neutralhydrogen distribution in a sample of five galactic systems believed tobe involved in progressive stages of merging: Arp 295, NGC 4676, NGC520, NGC 3921, and NGC 7252. This is the first time that the atomichydrogen in such a broad range of disk mergers has been imaged. Thesedata are supplemented by wide-field images taken through a narrowbandHα filter, and by deep (μ_R_ > 26.5 mag arcsec^-2^) R-bandsurface photometry. We identify several trends along the mergingsequence. In the early stages, large amounts of HI still exist withinthe galactic disks and star formation is widespread. The ionized gasemission often takes on the appearance of plumes and arcs emanating fromthe nuclear regions, which are presumably the sites ofinteraction-induced starbursts. In the final stages there is little ifany H I within the remnant bodies, and tidal material is seen movinginward. We conclude that as the merger rearranges the light profiles ofthe progenitor disk galaxies into r^1/4^ profiles, it leads to anefficient conversion of the atomic gas into other forms within the mainbodies of the merger remnants. This suggests that these remnants willevolve into elliptical galaxies in their atomic gas contents as well astheir photometric properties. However, the observations of NGC 520reveal an extensive rotating gaseous disk, suggesting that perhaps somemergers will not destroy the atomic gas disks of the progenitors. Themorphological similarity between the gaseous and stellar tails and thesmooth gas kinematics confirm that gravity plays the dominant role inproducing them. There are, however, some striking differences betweenthe faint gas and light distributions. H I mapping often reveals gaseousextension not at all apparent optically, and tidal features of differentoptical morphologies have different gas characteristics: Theedge-brightened tails are gas rich, while the featureless plumes andhalos are gas poor. Some of these features may be explained by thedifferent velocity dispersions of the gas and stars, some by differentgas contents in the progenitors, and some remain unexplained. Overall,large quantities of both gas and starlight (M_H I_ > 10^9^h^-2^M_sun_, L_R_ > 10^9^h^-2^ L_sun_) are seen at large radii (r > 50h^-1^ kpc). Since this material evolves on very long time scales, it mayleave observable signatures for many Gyr.
| 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 ^12^CO(1-0) survey of spiral galaxies in the region of the Coma supercluster.
We present observations of the ^12^CO(J=1-0) line at 2.6mm of 65galaxies located in the Coma supercluster region: 33 actually belong tothe Coma supercluster while 32 are either foreground or backgroundobjects. These data have been obtained using the NRAO 12m telescope atKitt Peak (United States), and for four galaxies, using the IRAM 30mtelescope at Pico Veleta (Spain). Out of these 65 galaxies, 54 had neverbeen observed in the CO(1-0) line; 49 have been detected by us, of which37 are new detections. We give molecular gas masses deduced from the COline integrated intensities, and upper limits for the 16 undetectedobjects, computed with a Galactic conversion factorN(H_2_)=2.3x10^20^I(CO) and H_0_=75km/s/Mpc.
| Briefly noted: Irish astronomy (poem)
Not Available
| A Catalog of Stellar Velocity Dispersions. II. 1994 Update
A catalog of central velocity dispersion measurements is presented,current through 1993 September. The catalog includes 2474 measurementsof 1563 galaxies. A standard set of 86 galaxies is defined, consistingof galaxies with at least three reliable, concordant measurements. It issuggested that future studies observe some of these standard galaxies sothat different studies can be normalized to a consistent system. Allmeasurements are reduced to a normalized system using these standards.
| A search for CO (1-0) emission from the tidal structures of interacting and merging galaxies
We have used the National Radio Astronomy Observatory (NRAO) 12 mtelescope to search for CO (J = 1 - 0) emission from the tidal tails ofsix merging or interacting galaxies. Although these plumes are H I-richand several contain star forming regions, they are undetected in CO tolow levels. The lack of strong CO emission from these plumes inconjunction with the presence of massive star formation is reminiscentof the situation in dwarf irregular galaxies, and the CO/H I limits areconsistent with those of dwarfs. The low CO brightness of these plumesmay be due either to a low proportion of molecular gas, or to a highN(H2)/ICO conversion factor.
| A CCD survey of galaxies. II. Observations with the 2.1 M telescope at San Pedro Martir
As a part of a CCD survey of galaxies belonging or projected onto theComa and Hercules Superclusters and to the A262, Virgo and Cancerclusters, we present isophote maps and photometric profiles of 87galaxies (85 taken with the V, 25 with the B and 3 with the U Johnsonfilters). For the objects in common we compare our results with those inthe RC3.
| 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
| Effects of Interactions on the Nuclear Near Infrared Properties of Spiral Galaxies
Using JHKL photometric measures available in the literature, we havecompared the near-infrared colour indices and central luminosities ofsamples of relatively isolated spiral galaxies with LINER and H IIregion-like nuclei (hereafter called L and H) with corresponding samplesof interacting galaxies, in order to explore the effects of interactionson their near-infrared properties. We have found that the L galaxies andthe isolated H galaxies have, in general, normal near-infrared colourswhich are fully explainable in terms of emission from late-type evolvedstars. On the other hand, the sample of interacting H galaxies displays,on average, somewhat peculiar near-infrared colours (specifically,normal J - H colours, but redward H - K and, especially, K - Lexcesses), which very probably indicate the presence of thermal emissionfrom hot dust, presumably related to intense star formation activityinduced by the interactions. Furthermore, for the same galaxy samplethere is some evidence that the emission at λ ~ 2.2 microns issomewhat more centrally concentrated than that at shorter wavelengths.Interestingly, the L galaxies appear to have greater centralnear-infrared luminosities than the H galaxies, for the samemorphological-type interval.
| When galaxies go wrong.
Not Available
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