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The Link between Star Formation and Accretion in LINERs: A Comparison with Other Active Galactic Nucleus Subclasses
We present archival high-resolution X-ray imaging observations of 25nearby LINERs observed by ACIS on board Chandra. This sample builds onour previously published proprietary and archival X-ray observations andincludes the complete set of LINERs with published black hole masses andFIR luminosities that have been observed by Chandra. Of the 82 LINERsobserved by Chandra, 41 (50%) display hard nuclear cores consistent withan AGN. The nuclear 2-10 keV luminosities of these AGN-LINERs range from~2×1038 to ~1×1044 ergss-1. Reinforcing our previous work, we find a significantcorrelation between the Eddington ratio,Lbol/LEdd, and the FIR luminosity,LFIR, as well as the IR brightness ratio,LFIR/LB, in the host galaxy of AGN-LINERs thatextends over 7 orders of magnitude in Lbol/LEdd.Combining our AGN-LINER sample with galaxies from other AGN subclasses,we find that this correlation is reinforced in a sample of 129 AGNs,extending over almost 9 orders of magnitude inLbol/LEdd. Using archival and previously publishedobservations of the 6.2 μm PAH feature from ISO, we find that it isunlikely that dust heating by the AGN dominates the FIR luminosity inour sample of AGNs. Our results may therefore imply a fundamental linkbetween the mass accretion rate (M˙), as measured by the Eddingtonratio, and the star formation rate (SFR), as measured by the FIRluminosity. Apart from the overall correlation, we find that thedifferent AGN subclasses occupy distinct regions in the LFIRand Lbol/LEdd plane. Assuming a constant radiativeefficiency for accretion, our results may imply a variation in theSFR/M˙ ratio as a function of AGN activity level, a result that mayhave significant consequences for our understanding of galaxy formationand black hole growth.
| Active and Star-forming Galaxies and Their Supernovae
To investigate the extent to which nuclear starbursts or other nuclearactivity may be connected with enhanced star formation activity in thehost galaxy, we perform a statistical investigation of supernovae (SNe)discovered in host galaxies from four samples: the Markarian galaxiessample, the Second Byurakan Survey (SBS) sample, the north Galactic pole(NGP) sample of active or star-forming galaxies, and the NGP sample ofnormal galaxies. Forty-seven SNe in 41 Mrk galaxies, 10 SNe in six SBSgalaxies, 29 SNe in 26 NGP active or star-forming galaxies, and 29 SNein 26 NGP normal galaxies have been studied. We find that the rate ofSNe, particularly core-collapse (Types Ib/c and II) SNe, is higher inactive or star-forming galaxies in comparison with normal galaxies.Active or star-forming host galaxies of SNe are generally of latermorphological type and have lower luminosity and smaller linear sizethan normal host galaxies of SNe. The radial distribution of SNe inactive and star-forming galaxies shows a higher concentration toward thecenter of the active host galaxy than is the case for normal hostgalaxies, and this effect is more pronounced for core-collapse SNe.Ib/c-type SNe have been discovered only in active and star-forminggalaxies of our samples. About 78% of these SNe are associated with H IIregions or are located very close to the nuclear regions of these activegalaxies, which are in turn hosting AGNs or starburst nuclei. Besidesthese new results, our study also supports the conclusions of severalother earlier papers. We find that Type Ia SNe occur in all galaxytypes, whereas core-collapse SNe of Types Ib/c and II are found only inspiral and irregular galaxies. The radial distribution of Type Ib SNe intheir host galaxies is more centrally concentrated than that of Type IIand Ia SNe. The radial distances of Types Ib/c and II SNe, from thenuclei of their host galaxies, is larger for barred spiral hosts.Core-collapse SNe are concentrated in spiral arms and are often close toor in the H II regions, whereas Type Ia SNe show only a looseassociation with spiral arms and no clear association with H II regions.
| MERLIN observations of Stephan's Quintet
We present MERLIN L-band images of the compact galaxy group, Stephan'sQuintet (SQ). The Seyfert 2 galaxy, NGC 7319, the brightest member ofthe compact group, is seen to have a triple radio structure typical ofmany extra-galactic radio sources that have a flat spectrum core and twosteep spectrum lobes with hot spots. The two lobes are asymmetricallydistributed on opposite sides of the core along the minor axis of thegalaxy. Ultraviolet (UV) emission revealed in a high-resolution channel(HRC)/ACS Hubble Space Telescope (HST) image is strongly aligned withthe radio plasma and we interpret the intense star formation in the coreand north lobe as an event induced by the collision of the north radiojet with over-dense ambient material. In addition, a remapping ofarchive Very Large Array (VLA) L-band observations reveals more extendedemission along the major axis of the galaxy, which is aligned with theoptical axis. Images formed from the combined MERLIN and archive VLAdata reveal more detailed structure of the two lobes and hot spots.
| New optical spectra and general discussion on the nature of ULXs
We present optical spectroscopic observations of three Ultra LuminousX-ray sources (ULXs). Two of them are very close to the active galaxyNGC 720 and the other is near NGC 1073. The two around NGC 720 turn outto be quasars at z= 2.216 and z= 0.959, the one near NGC 1073 seems tobe associated to an HII region at the redshift of NGC 1073. Weconcentrate our analysis on the two quasars and analyze them inconjunction with a set of 22 additional X-ray sources close to nearbygalaxies which also fit the criteria of ULXs and which also have beenidentified as quasars of medium to high redshift. This sample shows anunusually large fraction of rare BL Lac type objects. The high redshiftsof these ULXs and their close proximity to their low redshift,supposedly parent galaxies is a surprising result in the light ofstandard models. We describe the main properties of each of theseobjects and their parent galaxy, and briefly discuss possibleinterpretations.
| Seyfert galaxies in UZC-Compact Groups
We present results concerning the occurrence of Seyfert galaxies in anew automatically selected sample of nearby Compact Groups of galaxies(UZC-CGs). Seventeen Seyferts are found, constituting 3% of theUZC-CG galaxy population. CGs hosting and non-hosting a Seyfert memberexhibit no significant differences, except that a relevant number of Sy2is found in unusual CGs, all presenting large velocity dispersion(σ>400 km s-1), many neighbours and a high number ofellipticals. We also find that the fraction of Seyferts in CGs is 3times as large as that among UZC-single-galaxies, and results from anexcess of Sy2s. CG-Seyferts are not more likely than other CG galaxiesto present major interaction patterns, nor to display a bar. Our resultsindirectly support the minor-merging fueling mechanism.
| Radio continuum spectra of galaxies in the Virgo cluster region
New radio continuum observations of galaxies in the Virgo cluster regionat 4.85, 8.6, and 10.55 GHz are presented. These observations arecombined with existing measurements at 1.4 and 0.325 GHz. The sampleincludes 81 galaxies where spectra with more than two frequencies couldbe derived. Galaxies that show a radio-FIR excess exhibit centralactivity (HII, LINER, AGN). The four Virgo galaxies with the highestabsolute radio excess are found within 2° of the centerof the cluster. Galaxies showing flat radio spectra also host activecenters. There is no clear trend between the spectral index and thegalaxy's distance to the cluster center.Figure 3 is only available in electronic form athttp://www.edpsciences.orgTable 3 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/1
| Radio emission from AGN detected by the VLA FIRST survey
Using the most recent (April 2003) version of the VLA FIRST survey radiocatalog, we have searched for radio emission from >2800 AGN takenfrom the most recent (2001) version of the Veron-Cetty and Veron AGNcatalog. These AGN lie in the 9033 square degrees of sky alreadycovered by the VLA FIRST survey. Our work has resulted in positivedetection of radio emission from 775 AGN of which 214 are new detectionsat radio wavelengths.Tables 3 and 4 are 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/cgi-bin/qcat?J/A+A/416/35
| 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.
| Chandra Observations of the Interacting NGC 4410 Galaxy Group
We present high-resolution X-ray imaging data from the ACIS-S instrumenton the Chandra telescope of the nearby interacting galaxy group NGC4410. Four galaxies in the inner portion of this group are clearlydetected by Chandra, including the peculiar low-luminosity radio galaxyNGC 4410A. In addition to a nuclear point source, NGC 4410A containsdiffuse X-ray emission, including an X-ray ridge extending out to about12" (6 kpc) to the northwest of the nucleus. This ridge is coincidentwith an arc of optical emission-line gas, which has previously beenshown to have optical line ratios consistent with shock ionization. Thisstructure may be due to an expanding superbubble of hot gas caused bysupernovae and stellar winds or by the active nucleus. The Chandraobservations also show four or five possible compact ultraluminous X-ray(ULX) sources (LX>=1039 ergs s-1)associated with NGC 4410A. At least one of these candidate ULXs appearsto have a radio counterpart, suggesting that it may be due to an X-raybinary with a stellar-mass black hole, rather than an intermediate-massblack hole. In addition, a faint diffuse intragroup X-ray component hasbeen detected between the galaxies (LX~1041 ergss-1). This supports the hypothesis that the NGC 4410 group isin the process of evolving via mergers from a spiral-dominated group(which typically has no X-ray-emitting intragroup gas) to anelliptical-dominated group (which often has a substantial intragroupmedium).
| An X-ray halo in the ``hot-spot'' galaxy NGC 2903
In this paper we present ROSAT PSPC and HRI observations of the``hot-spot'' galaxy NGC 2903. This isolated system strikingly reveals asoft extended X-ray feature reaching in north-west direction up to aprojected distance of 5.2 kpc from the center into the halo. Theresidual X-ray emission in the disk reveals the same extension as theHα disk. No eastern counterpart of the western X-ray haloemission has been detected. The luminosity of the extraplanar X-ray gasis several 1038 erg s-1, comparable to X-ray halosin other starburst galaxies. It has a plasma temperature of about 0.2keV. The estimated star formation rate derived from X-rays and Hαresults in 1-2 M_sun yr-1. Since galactic superwinds, giantkpc-scale galactic outflows, seem to be a common phenomenon observed ina number of edge-on galaxies, especially in the X-ray regime, and areproduced by excess star-formation activity, the existence of hot halogas as found in NGC 2903 can be attributed to events such as centralstarbursts. That such a starburst has taken place in NGC 2903 must beproven. The detection of hot gas above galaxy disks also withintermediate inclination, however, encounters the difficulty ofdiscriminating between that contribution from disk and active nuclearregion.
| Faint light in clusters of galaxies
Not Available
| Star Formation in the radio galaxy NGC 4410A
The NGC 4410 group of galaxies provides us with a rare opportunity tostudy a nearby (97 h-175 Mpc) example of a radiogalaxy (NGC 4410A) embedded in an extended X-ray source, with evidencefor star formation that can be readily spatially distinguished fromregions dominated by the active galactic nucleus and shocks. We presentbroadband and narrowband optical images, along with optical and IUEultraviolet spectroscopy, for the radio galaxy NGC 4410A and itscompanion, NGC 4410B. Our Hα+[N II] images reveal six luminous HII regions (LHα~1040 ergs s-1)distributed in an arc near NGC 4410A. Partially completing the ring is aprominent stellar loop containing diffuse ionized gas. This filamentarygas, in contrast to the H II regions, shows spectroscopic signatures ofshock ionization. The star formation in this system may have beentriggered by a collision or interaction between the two galaxies,perhaps by an expanding density wave, as in classical models of ringgalaxies. Alternatively, the star formation may have been induced by theimpact of a radio jet on the interstellar matter. Extended Lyα isdetected in the ultraviolet IUE spectrum. The ultraviolet continuum,which is presumably radiated by the nucleus of NGC 4410A, is notextended. NGC 4410A appears to be interacting with its neighbors in theNGC 4410 group and could be an example of a spiral galaxy transforminginto an elliptical.
| Compact groups in the UZC galaxy sample
Applying an automatic neighbour search algorithm to the 3D UZC galaxycatalogue (Falco et al. \cite{Falco}) we have identified 291 compactgroups (CGs) with radial velocity between 1000 and 10 000 kms-1. The sample is analysed to investigate whether Tripletsdisplay kinematical and morphological characteristics similar to higherorder CGs (Multiplets). It is found that Triplets constitute lowvelocity dispersion structures, have a gas-rich galaxy population andare typically retrieved in sparse environments. Conversely Multipletsshow higher velocity dispersion, include few gas-rich members and aregenerally embedded structures. Evidence hence emerges indicating thatTriplets and Multiplets, though sharing a common scale, correspond todifferent galaxy systems. Triplets are typically field structures whilstMultiplets are mainly subclumps (either temporarily projected orcollapsing) within larger structures. Simulations show that selectioneffects can only partially account for differences, but significantcontamination of Triplets by field galaxy interlopers could eventuallyinduce the observed dependences on multiplicity. Tables 1 and 2 are onlyavailable in electronic at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/391/35
| The Interstellar Medium and the Intergalactic Medium
Here we present a summary of the first discussion session on theinterstellar and intergalactic medium.
| Faint Features of Interacting Galaxies Revealed by the Digital Coaddition of 13 Tech-Pan Films of the Virgo Cluster
We have digitally coadded APM scans of 13 Kodak TechPan films of the SEregion of the Virgo Cluster of galaxies. The ~6.2°×6.2°field of the R-band films combined with the resolution of ~2 arcsecpixel^- results in data-file sizes of about 222 MBytes. The 13 scannedfilms have been aligned, coadded, corrected for vignetting effects andcleaned of stellar features. To illustrate the astrophysical uses ofthis technique, we present high-contrast images of a sample ofinteracting galaxies in the field. Several very faint features (but veryclearly seen in the coadded array) - such as the interaction between IC3481, IC 3481A and IC 3483, and NGC 4410A and B and IC 790 - have beenpresented with clarity for the first time.
| New Observations of Extra-Disk Molecular Gas in Interacting Galaxy Systems, Including a Two-Component System in Stephan's Quintet
We present new CO (1-0) observations of 11 extragalactic tails andbridges in nine interacting galaxy systems, almost doubling the numberof such features with sensitive CO measurements. Eight of these 11features were undetected in CO to very low CO/H I limits, with the mostextreme case being the NGC 7714/5 bridge. This bridge contains luminousH II regions and has a very high H I column density(1.6×1021 cm-2 in the 55" CO beam), yet wasundetected in CO to rms T*R=2.4 mK. The H I columndensity is higher than standard H2 and CO self-shieldinglimits for solar-metallicity gas, suggesting that the gas in this bridgeis metal-poor and has an enhancedNH2/ICO ratio compared with theGalactic value. Only one of the 11 features in our sample wasunambiguously detected in CO, a luminous H I-rich star formation regionnear an optical tail in the compact group Stephan's Quintet. We detectCO at two widely separated velocities in this feature, at ~6000 and~6700 km s-1. Both of these components have H I and Hαcounterparts. These velocities correspond to those of galaxies in thegroup, suggesting that this gas is material that has been removed fromtwo galaxies in the group. The CO/H I/Hα ratios for bothcomponents are similar to global values for spiral galaxies.
| Hot halo gas in the Virgo cluster galaxy NGC 4569
We have observed the Virgo cluster spiral NGC 4569 in X-rays with ROSAT(0.1-2.4 keV) and in the optical. From the PSPC image one candistinguish different components, like the dominant source in thenuclear region, the galactic disk, and a diffuse soft component extendedto the west. This latter one coincides with a giant Hα structure.In both spectral ranges the structure reaches up to 9 kpc out of thedisk. This coincidence, the soft X-ray energy distribution, and theexistence of a central starburst in NGC 4569 let us conclude that theX-ray gas traces a large scale outflow from accumulating supernovaexplosions and stellar winds in the galactic center. The resultingphysical properties of this X-ray halo are comparable to those derivedfrom X-ray halos in edge-on galaxies, like e.g. NGC 253. We also discussthe influence of the intracluster medium on the observed X-ray andHα morphology. The spectral 0.1-2.4 keV distribution of thecentral source and the X-ray-to-Hα luminosity ratio favour asupermassive star cluster at the very compact core rather than anaccretion-powered active nucleus in agreement with the absence of a hardcompact X-ray source in the ASCA band. The nearby Magellanic dwarfgalaxy IC 3583 at a projected distance of only 30 kpc reveals anunresolved X-ray point source, several blue knots in the optical, and anarrow Hα spur, pointing toward NGC 4569, detected also in the Bband image. This is an indication for ongoing star formation also in IC3583. Some interaction with NGC 4569 will be discussed although therelative radial velocity between both objects of about 1300 kms-1 makes it rather unlikely.
| Seeing Galaxies through Thick and Thin. I. Optical Opacity Measures in Overlapping Galaxies
We describe the use of partially overlapping galaxies to provide directmeasurements of the effective absorption in galaxy disks, independent ofassumptions about internal disk structure. The nonoverlapping parts ofthe galaxies and symmetry considerations are used to reconstruct, viadifferential photometry, how much background galaxy light is lost inpassing through the foreground disks. Extensive catalog searches andfollow-up imaging yield ~15-25 nearby galaxy pairs suitable for varyingdegrees of our analysis; 11 of the best such examples are presentedhere. From these pairs, we find that interarm extinction is modest,declining from AB~1 mag at 0.3RB25 toessentially zero by RB25; the interarm dust has ascale length consistent with that of the disk starlight. In contrast,dust in spiral arms and resonance rings may be optically thick(AB>2) at virtually any radius. Some disks have flatterextinction curves than the Galaxy, with AB/AI~1.6this is probably the signature of clumpy dust distributions. Even thoughtypical spirals are not optically thick throughout their disks, wherethey are optically thick is correlated with where they are mostluminous: in spiral arms and inner disks. This correlation betweenabsorption and emission regions may account for their apparent surfacebrightness being only mildly dependent on inclination, erroneouslyindicating that spirals are generally optically thick. Taken as anensemble, the opacities of spiral galaxies may be just great enough tosignificantly affect QSO counts, though not enough to cause theirhigh-redshift cutoff. Based in part on archival observations with theNASA/ESA Hubble Space Telescope (HST) obtained at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy, Inc., under NASA contract NAS5-26555.
| Interstellar Gas in the NGC 4410 Galaxy Group
We present new radio continuum, 21 cm H I, and 2.6 mm CO data for thepeculiar radio galaxy NGC 4410A and its companion NGC 4410B and comparewith available optical and X-ray maps. Our radio continuum maps show anasymmetric double-lobed structure, with a high surface brightness lobeextending 3.6′ (~100 kpc) to the southeast and a 6.2′(~180 kpc) low surface brightness feature in the northwest. Moleculargas is abundant in NGC 4410A, withMH2~4×109 Msolar(using the standard Galactic conversion factor) but is undetected in NGC4410B. H I is less abundant, with MHI~109Msolar for the pair. Our H I map shows a3×108 Msolar H I tail extending 1.7′(50 kpc) to the southeast of the pair, coincident with a faint opticaltail and partially overlapping with the southeastern radio lobe. The H Itail is anticoincident with a 2' (56 kpc) long X-ray structure alignedwith a stellar bridge that connects the pair to a third galaxy. If thisX-ray emission is associated with the group, we infer(3-8)×108 Msolar of hot gas in this feature.This may be either intracluster gas or shocked gas associated with thebridge. Our detection of abundant interstellar gas in this pair,including an H I-rich tidal tail near the southeastern radio lobe,suggests that the observed distortions in this lobe may have been causedby the interstellar medium in this system. The gravitational interactionof the two galaxies and the subsequent motion of the interstellar mediumin the system relative to the jet may have produced sufficient rampressure to bend and distort the radio jet. An alternative hypothesis isthat the jet was distorted by ram pressure due to an intraclustermedium, although the small radial velocity of NGC 4410A relative to thegroup and the lack of diffuse X-ray emission in the group makes thisless likely unless the group is not virialized or is in the process ofmerging with another group. Using our VLA data, we also searched for H Icounterparts to the other 10 known members of the NGC 4410 group and COfrom three other galaxies in the inner group. In our velocity range of6690-7850 km s-1, we detected six other galaxies above our HI sensitivity limits of 2×108 Msolar for theinner group and 4×108 Msolar for the outergroup. The total H I in the group is 1.4×1010Msolar, 80% of which arises from four galaxies in the outergroup. Three of these galaxies (VCC 822, VCC 831, and VCC 847) arespirals with MHI/LB ratios typical of fieldgalaxies, while FGC 170A appears to be a gas-rich dwarf galaxy(MB~-18, MHI~3×109Msolar). In the inner group, the SBa galaxy NGC 4410D (VCC934) was detected in H I and CO (MHI~5×108Msolar and MH2~8×108Msolar) and has a 1' (28 kpc) long H I tail that pointstoward the nearby disk galaxy NGC 4410F. NGC 4410F was also detected inH I (MHI~4×108 Msolar). Thegalaxies in the inner group appear to be somewhat deficient in H Icompared to their blue luminosities, suggesting phase changes driven bygalaxy-galaxy or galaxy-intracluster medium encounters.
| Star formation in distant starburst galaxies
This paper discusses the stellar population content of distant (5 000 kms^{-1} <== V_R<=16 000 km s^{-1}) galaxies with enhancedstar-formation activity. Distinction is made between isolated galaxiesand galaxies morphologically disturbed, with clear signs of interactionsuch as mergers. In these galaxies the International UltravioletExplorer (M_BoxIUE) large aperture samples most of the galaxy's body.Consequently, the resulting integrated spectra arise primarily from bluestellar populations of different ages together with significantcontributions from intermediate and old age components, subject tovarying reddening amounts. Instead of analysing individual, usually lowSignal-to-Noise ratio (S/N) spectra, our approach is to coadd thespectra of objects with similar spectral properties in the UV,considering as well their properties in the visible/near-infraredranges. Consequently, the resulting high (S/N) template spectra containthe average properties of a rather uniform class of objects, andinformation on spectral features can now be analysed with moreprecision. Three groups have been found for the interacting galaxies,corresponding to a red, blue and very blue continuum. Isolated galaxieshave been separated into two groups, one with a flat/red continuum andthe other with a blue continuum. For comparison, we also include in thepresent analysis two groups of nearby disturbed galaxies. Stellarpopulations are analysed by means of a synthesis algorithm based on starcluster spectral components of different ages which fit the observedspectra both in terms of continuum distribution and spectral features.Flux fractions of the different age groups found in the synthesis havebeen transformed into mass fractions, allowing inferences on the starformation histories. Young stellar populations (age <500 Myr) are themain flux contributors, except for the groups with a red spectrum notdue to extinction, arising from the intermediate (age ~1 - 2 Gyr) andold age populations. We also study the reddening values and theextinction law: a Small Magellanic Cloud-like extinction law isappropriate for all cases. As compared to nearby galaxies with enhancedstar-formation, the distant starburst galaxy spectral groups exhibitlarger contributions from the intermediate and old age populations. Thiseffect is mainly accounted for by the larger spatial area sampled by theM_BoxIUE slit in the distant galaxies, including not only the entirebulge but also evolved disk populations. The present results provide aquantitative measure of the star-forming activity in interactinggalaxies, compared to isolated galaxies. Based upon data collected withthe International Ultraviolet Explorer (IUE) Satellite, supported byNASA, SERC and ESA.
| ROSAT X-ray observations of the interacting pair of galaxies NGC 4410: evidence for a central starburst
We present X-ray observations of the interacting pair of galaxies NGC4410a/b with the ROSAT HRI and PSPC. The ROSAT HRI images reveal apoint-like source corresponding to NGC 4410a and an X-ray halo,extending 10'' from the nucleus toward the southeast. The halo emissionaccounts for ~ 1/3 (LX = 1.3\tento{41} erg s(-1) in the0.1-2.4 keV ROSAT band) of the total X-ray emission detected from NGC4410a. The spectrum of the total X-ray emission from NGC 4410a can befitted at best with a two-component emission model, combining aRaymond-Smith spectrum with T = 10(7) K and a power-law spectrum (Gamma= 2.2). The fraction of the thermal component to the total flux withinthis model is 35%, supporting the results of the HRI observation. Thetotal unresolved X-ray luminosity detected with the PSPC amounts to4\tento{41} erg s(-1) in the ROSAT PSPC band (for D = 97 Mpc). Apreferable explanation might be the interaction between the two galaxiescausing a circumnuclear starburst around the active nucleus in thepeculiar late type Sab galaxy NGC 4410a. As a cumulative effect ofexploding stars a superbubble forms a bipolar outflow from the galacticdisk with an expansion time of ~ 8 Myr. The central source injectsmechanical energy at a constant rate of a few times 10(42) erg s(-1)into the superbubble. A HST WFPC2 image decovers that NGC 4410a is seenalmost face-on so that only the approaching outflow is visible. The HRIcontours reveal an elongation of this outflow indicative for a faintX-ray ridge below the detection limit (LX <= 1.4\tento{39}erg s(-1) ) toward the neighbouring galaxy NGC 4410b caused by its tidalinteraction. NGC 4410b houses only a faint X-ray source (LX<= 3.8\tento{39} erg s(-1) ).
| On the local radio luminosity function of galaxies. I. The Virgo cluster
We cross-correlate the galaxies brighter than m_B=18 in the Virgocluster with the radio sources in the NVSS survey (1.4 GHz), resultingin 180 radio-optical identifications. We determine the radio luminosityfunction of the Virgo galaxies, separately for the early- andlate-types. Late-type galaxies develop radio sources with a probabilityproportional to their optical luminosity. In fact their radio/optical(R_B) distribution is gaussian, centered at log R_B ~ -0.5, i.e. theradio luminosity is ~ 0.3 of the optical one. The probability oflate-type galaxies to develop radio sources is almost independent oftheir detailed Hubble type, except for Sa (and S0+S0a) which are afactor of ~ 5 less frequent than later types at any R_B. Giantelliptical galaxies feed ``monster" radio sources with a probabilitystrongly increasing with mass. However the frequency of fainter radiosources is progressively less sensitive on the system mass. The faintestgiant E galaxies (M_B=-17) have a probability of feeding low power radiosources similar to that of dwarf E galaxies as faint as M_B=-13. Table~1is only available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The MX Northern Abell Cluster Redshift Survey
The results from the COBE satellite show the existence of structure onscales ~10% or more of the horizon scale of the universe. Rich clustersof galaxies from the Abell/Abell, Corwin, & Olowin catalogs showevidence of structure on scales of 100 h-1 Mpc and hold the promise ofconfirming structure on the scale of the COBE results. An impediment tothat promise has been that redshift information has been unavailable fora large percentage of these clusters, so knowledge of theirthree-dimensional distribution has had large uncertainties. We have beenworking to greatly expand the sample of Abell clusters with reliableredshifts. Our approach in this effort, through the MX Northern AbellCluster Redshift Survey, has been to measure redshifts of at least 25galaxies in each of 95 R >= 1 Abell cluster fields with m10 <=16.8 and zero or one previously measured redshift. Of these 95 observedAbell clusters, 88 new cluster redshifts were obtained with an averageof nine cluster member galaxy redshifts per field. Two clusters werefound to be chance projections of galaxies along the line of sight,while five cluster observations did not provide enough galaxy redshiftsto make a positive identification. This work has resulted in a deeper,98% complete, and more reliable sample of three-dimensional positions ofrich Abell clusters in the northern hemisphere. The primary intent ofthis survey has been to produce a larger and more complete sample ofrich Abell clusters that can be used as tracers for large-scalestructure. Through analyses with tools such as the two-point correlationfunction, power spectrum, and velocity dispersions, this sample can beused to constrain theoretical models better for the formation ofstructure we see in the universe today.
| Groups of galaxies. III. Some empirical characteristics.
Not Available
| ROSAT X-ray observations of the interacting pair of galaxies NGC 4410.
Not Available
| Galaxies with a UV excess in which supernovae have been observed.
Not Available
| ROSAT X-RAY observations of the interacting pair of galaxies NGC 4410.
Not Available
| 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.
| The spatial distribution of supernovae in paired and interacting galaxies
In order to investigate the location of supernovae (SNe) in paired andinteracting galaxies, the 54 supernovae discovered up to May 1993 in 14Isolated Pairs of Galaxies and the 32 Interacting Systems were taken asa sample and studied. The whole sample of SNe, as well as a subsampleformed of type II, and Ib SNe, whose progenitors are young massivestars, do not appear in any one particluar direction with respect to thecompanion. On paired and interacting galaxies, the radial distributionof type Ib and II SNe peaks more toward the galaxy centers than it doesin isolated galaxies, indicating an enhanced Star Formation Rate (SFR)around the nuclei and in the inner disks. The distribution of SNIaappear similar in both samples, confirming that their progenitors arenot the same as those of SNII and IB. The SN rates are related to galaxyluminosity and, as expected, the discovery of SNe is twice more frequentin the brighter galaxy of the pair than in fainter ones. We did not findany relation between the locations of SNe in parent galaxies, the totalStar Formation activity and the kinematics of paired and interactinggalaxies.
| Interaction, star formation, and H I deficiency in E + S pairs
We use a sample of mixed morphology (ellictical + spiral) pairs ofgalaxies to make a new study of star formation enhancement in spiralgalaxies. The approach makes use of the fact that only the spiralcomponent in each pair is likely to be a significant source of (FIR) orH I emission. We find at least a twofold enhanced FIR emission fromabout one-half of the late-type components in close pairs. There isevidence that a typical burst duration may be as short as 2-3 x108 yr. The total H I masses of the spiral components arenear normal. Little or no H I depletion in star formation-enhancedgalaxies implies one or more of the following: (1) a bimodal IMF for theinteraction-induced starburst activity; (2) a duration for the activephase of enhanced star formation of no more than 1-2 x 109yr; or (3) a continuous source of gas replenishment. We find someevidence for an H I deficit in the currently most active star formingspiral. This argues for an transient phase change in up to 50% of theneutral gas during a burst event. We conclude that the InterstellarMatter (ISM) in our sample of pairs is clearly not predominantlymolecular gas.
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