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Far-Ultraviolet and X-Ray Observations of VV 114: Feedback in a Local Analog to Lyman Break Galaxies
We have analyzed Far Ultraviolet Spectroscopic Explorer (FUSE),XMM-Newton, and Chandra observations of VV 114, a local galaxy mergerwith strong similarities to typical high-redshift Lyman break galaxies(LBGs). Diffuse thermal X-ray emission encompassing VV 114 has beenobserved by Chandra and XMM-Newton. This region of hot (kT~0.59 keV) gashas an enhanced α/Fe element ratio relative to solar abundancesand follows the same relations as typical starbursts between itsproperties (luminosity, size, and temperature) and those of thestarburst galaxy (star formation rate, dust temperature, and galaxymass). These results are consistent with the X-ray gas having beenproduced by shocks driven by a galactic superwind. The FUSE observationsof VV 114 show strong, broad interstellar absorption lines with apronounced blueshifted component (similar to what is seen in LBGs). Thisimplies an outflow of material moving at ~300-400 km s-1relative to VV 114. The properties of the strong O VI absorption lineare consistent with radiative cooling at the interface between the hotoutrushing gas seen in X-rays and the cooler material seen in the otheroutflowing ions in the FUSE data. We show that the wind in VV 114 has not created a ``tunnel'' that enables more than a small fraction(
| The Second Kiso Survey for ultraviolet-excess galaxies. V.
The catalogue list and the identification chart of ultraviolet(UV)-excess galaxies, which have been detected on two or three-colorKiso Schmidt plates, are presented for 10 Schmidt fields. Catalogued are127 objects, down to the photographic magnitude ~17.5 in the sky area ofsome 300 square degrees. The number of KUGs detected in this paper ismuch smaller than that of the high galactic area, and the total numberof KUGs newly detected in the second survey reaches up to 1,954.
| High-Density Molecular Gas in the Infrared-bright Galaxy System VV 114
The new high-resolution CO (3-2) interferometric map of the IR-brightinteracting galaxy system VV 114 observed with the Submillimeter Arrayreveals a substantial amount of warm and dense gas in the IR-bright butoptically obscured galaxy, VV 114E, and the overlap region connectingthe two nuclei. A 1.8×1.4 kpc concentration of CO (3-2) emittinggas with a total mass of 4×109 Msolarcoincides with the peaks of near-IR, mid-IR, and radio continuumemission found previously by others, identifying the dense fuel for theactive galactic nucleus and/or the starburst activity there. ExtensiveCO (2-1) emission is also detected, revealing detailed distribution andkinematics that are consistent with the earlier CO (1-0) results. Thewidely distributed molecular gas traced in CO (2-1) and the distributeddiscrete peaks of CO (3-2) emission suggest that a spatially extendedintense starbursts may contribute significantly to its large IRluminosity. These new observations further support the notion that VV114 is approaching its final stage of merger, when a violent centralinflow of gas triggers intense starburst activity possibly boosting theIR luminosity above the ultraluminous threshold.
| Missing Massive Stars in Starbursts: Stellar Temperature Diagnostics and the Initial Mass Function
Determining the properties of starbursts requires spectral diagnosticsof their ultraviolet radiation fields, to test whether very massivestars are present. We test several such diagnostics, using new models ofline ratio behavior combining CLOUDY, Starburst99, and up-to-datespectral atlases. For six galaxies we obtain new measurements of He I1.7 μm/Br10, a difficult to measure but physically simple (andtherefore reliable) diagnostic. We obtain new measurements of He I 2.06μm/Brγ in five galaxies. We find that He I 2.06 μm/Brγand [O III]/Hβ are generally unreliable diagnostics in starbursts.The heteronuclear and homonuclear mid-infrared line ratios (notably [NeIII] 15.6 μm/[Ne II] 12.8 μm) consistently agree with each otherand with He I 1.7 μm/Br10 this argues that the mid-infrared lineratios are reliable diagnostics of spectral hardness. In a sample of 27starbursts, [Ne III]/[Ne II] is significantly lower than modelpredictions for a Salpeter initial mass function (IMF) extending to 100Msolar. Plausible model alterations strengthen thisconclusion. By contrast, the low-mass and low-metallicity galaxies II Zw40 and NGC 5253 show relatively high neon line ratios, compatible with aSalpeter slope extending to at least ~40-60 Msolar. Onesolution for the low neon line ratios in the high-metallicity starburstswould be that they are deficient in >~40 Msolar starscompared to a Salpeter IMF. An alternative explanation, which we prefer,is that massive stars in high-metallicity starbursts spend much of theirlives embedded within ultracompact H II regions that prevent the near-and mid-infrared nebular lines from forming and escaping. Thishypothesis has important consequences for starburst modeling andinterpretation.
| A Bias in Optical Observations of High-Redshift Luminous Infrared Galaxies
We present evidence for the dramatically different morphology betweenthe rest-frame UV and 7 μm mid-IR emission of VV 114 and Arp 299, twonearby (z~0) violently interacting luminous infrared galaxies (LIRGs).Nearly all LIRGs are interacting systems, and it is currently acceptedthat they dominate the IR emission at z>1. LIRGs located at z=1-2could easily be detected as unresolved sources in deep optical/near-IRground-based surveys as well as in upcoming 24 μm surveys with theSpace Infrared Telescope Facility. We demonstrate that the spatialresolution of these surveys will result in blending of the emission fromunresolved interacting components. An increased scatter will thus beintroduced in the observed optical-to-mid-IR colors of these galaxies,leading to a systematic underestimation of their dust content.
| The gas content of peculiar galaxies: Strongly interacting systems
A study of the gas content in 1038 interacting galaxies, essentiallyselected from Arp, Arp & Madore, Vorontsov-Velyaminov catalogues andsome of the published literature, is presented here. The data on theinterstellar medium have been extracted from a number of sources in theliterature and compared with a sample of 1916 normal galaxies. The meanvalues for each of the different ISM tracers (FIR, 21 cm, CO lines,X-ray) have been estimated by means of survival analysis techniques, inorder to take into account the presence of upper limits. From the datait appears that interacting galaxies have a higher gas content thannormal ones. Galaxies classified as ellipticals have both a dust and gascontent one order of magnitude higher than normal. Spirals have in mostpart a normal dust and HI content but an higher molecular gas mass. TheX-ray luminosity also appears higher than that of normal galaxies ofsame morphological type, both including or excluding AGNs. We consideredthe alternative possibilities that the molecular gas excess may derivefrom the existence of tidal torques which produce gas infall from thesurrounding regions or from a different metallicity which affects the Xconversion factor between the observed CO line luminosity and the H_2calculated mass. According to our tests, it appears that interactinggalaxies possess a higher molecular mass than normal galaxies but with asimilar star formation efficiency.Table 1 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/422/941
| Dust-to-gas ratios in the starburst regions of luminous infrared galaxies
We investigate the properties of dust and dust-to-gas ratios in variousstarburst regions of luminous infrared galaxies (LIGs). We refer to thesample of seven LIGs recently observed in the mid-infrared by Soifer etal. using the Keck Telescope with spatial resolution approaching thediffraction limit. These seven objects are among the closest LIGs andhave been classified as starburst galaxies from optical spectroscopy.Our goal consists in modelling the continuum spectral energydistribution of each galaxy, particularly in the infrared range. Modelsare further constrained by observed emission-line ratios in the opticalrange. Multicloud models consistently account for the coupled effects ofshock, photoionization by hot stars and diffuse secondary radiation fromthe shock-heated gas. Emission from clouds in the neighbourhood ofevolved starbursts and with high shock velocities (~500 kms-1) explains both the bremsstrahlung and reradiation fromdust in the mid-infrared. Clouds with lower velocity (100 kms-1), which correspond to younger starbursts, also contributeto both line and continuum spectra. Both low- and high-velocity cloudsare thus present in nearly all the sample galaxies. For all thegalaxies, an old stellar population is revealed by blackbody emission inthe optical/near-infrared range. Dust-to-gas ratios vary in differentregions of individual galaxies.
| The IRAS Revised Bright Galaxy Sample
IRAS flux densities, redshifts, and infrared luminosities are reportedfor all sources identified in the IRAS Revised Bright Galaxy Sample(RBGS), a complete flux-limited survey of all extragalactic objects withtotal 60 μm flux density greater than 5.24 Jy, covering the entiresky surveyed by IRAS at Galactic latitudes |b|>5°. The RBGS includes629 objects, with median and mean sample redshifts of 0.0082 and 0.0126,respectively, and a maximum redshift of 0.0876. The RBGS supersedes theprevious two-part IRAS Bright Galaxy Samples(BGS1+BGS2), which were compiled before the final(Pass 3) calibration of the IRAS Level 1 Archive in 1990 May. The RBGSalso makes use of more accurate and consistent automated methods tomeasure the flux of objects with extended emission. The RBGS contains 39objects that were not present in the BGS1+BGS2,and 28 objects from the BGS1+BGS2 have beendropped from RBGS because their revised 60 μm flux densities are notgreater than 5.24 Jy. Comparison of revised flux measurements forsources in both surveys shows that most flux differences are in therange ~5%-25%, although some faint sources at 12 and 25 μm differ byas much as a factor of 2. Basic properties of the RBGS sources aresummarized, including estimated total infrared luminosities, as well asupdates to cross identifications with sources from optical galaxycatalogs established using the NASA/IPAC Extragalactic Database. Inaddition, an atlas of images from the Digitized Sky Survey with overlaysof the IRAS position uncertainty ellipse and annotated scale bars isprovided for ease in visualizing the optical morphology in context withthe angular and metric size of each object. The revised bolometricinfrared luminosity function, φ(Lir), forinfrared-bright galaxies in the local universe remains best fit by adouble power law, φ(L)~Lα, withα=-0.6(+/-0.1) and α=-2.2(+/-0.1) below and above the``characteristic'' infrared luminosityL*ir~1010.5Lsolar,respectively. A companion paper provides IRAS High Resolution (HIRES)processing of over 100 RBGS sources where improved spatial resolutionoften provides better IRAS source positions or allows for deconvolutionof close galaxy pairs.
| Extended mid-infrared emission from VV 114: Probing the birth of a ULIRG
We present our 5-16 mu m spectro-imaging observations of VV114, an infrared luminous early-stage merger of two galaxiesVV 114E and VV 114W, taken with the ISOCAM camera on-board the InfraredSpace Observatory. We find that only 40% of the mid-infrared (MIR) fluxis associated with a compact nuclear region of VV 114E, while the restof the emission originates from a rather diffuse component extended overseveral kpc in the regions between VV 114E and VV 114W. This is in starkcontrast with the very compact MIR starbursts usually seen in luminousand ultraluminous infrared galaxies. A secondary peak of MIR emission isassociated with an extra-nuclear star forming region of VV 114W whichdisplays the largest Hα equivalent width in the whole system.Comparing our data with the distribution of the molecular gas and colddust, as well as with radio observations, it becomes evident that theconversion of molecular gas into stars can be triggered over large areasat the very first stages of an interaction. This extended star formationalong with the extreme nuclear starburst observed in VV 114E can easilylead to the heating of dust grains found in the tidally disturbed disksof the progenitor galaxies and subsequently traced via their MIRemission. The presence of a very strong continuum at the 5-6.5 mu mrange in the spectrum of VV 114E indicates that an enshrouded activegalactic nucleus (AGN) may contribute to ~ 40% of its MIR flux. Wefinally note that the relative variations in the UV to radio spectralproperties between VV 114E and VV 114W provide evidence that theextinction-corrected star formation rate of similar objects at high z,such as those detected in optical deep surveys, cannot be accuratelyderived from their rest-frame UV properties. Based on observations withthe ISO satellite, an ESA project with instruments funded by ESA MemberStates (especially the PI countries: France, Germany, the Netherlandsand the United Kingdom) and with the participation of ISAS and NASA.
| H I line observations of luminous infrared galaxy mergers
A total of 19 luminous infrared galaxy mergers, with LIR>~ 2 1011 Lsun, for H0=75 kms-1 Mpc-1, have been observed in the H I line atNançay and four of them were observed at Arecibo as well. Ofthese 19, ten had not been observed before. Six were clearly detected,one of which for the first time. The objective was to statisticallysample the H I gas mass in luminous infrared mergers along a starburstmerger sequence where the molecular CO gas content is already known. Wealso searched the literature for H I data and compared these with ourobservations.
| Massive Star Formation and Evolution in Starburst Galaxies: Mid-infrared Spectroscopy with the ISO Short Wavelength Spectrometer
We present new Infrared Space Observatory Short Wavelength Spectrometerdata for a sample of 27 starburst galaxies, and with these data weexamine the issues of formation and evolution of the most massive starsin starburst galaxies. Using starburst models which incorporate timeevolution, new stellar atmosphere models for massive stars, and astarburst model geometry derived from observations of the prototypicalstarburst M82, we model the integrated mid-infrared line ratio [NeIII](15.6 μm)/[Ne II](12.8 μm). This line ratio is sensitive tothe hardness of the stellar energy distribution and therefore to themost massive stars present. We conclude from our models, withconsideration of recent determinations of the stellar census in local,high-mass star-forming regions, that the [Ne III]/[Ne II] ratios wemeasure are consistent with the formation of massive (~50-100Msolar) stars in most starbursts. In this framework, the lownebular excitation inferred from the measured line ratios can beattributed to aging effects. By including estimates of the ratio ofinfrared-to-Lyman continuum luminosity for the galaxies in our sample,we further find that most starbursts are relatively short-lived(106-107 yr), only a few O star lifetimes. Wediscuss a possible cause of such short events: the effectiveness ofstellar winds and supernovae in destroying the starburst environment.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, theNetherlands, and the United Kingdom) and with the participation of ISASand NASA. The SWS is a joint project of SRON and MPE.
| VV 114, a high infrared luminosity interacting galaxy system
VV 114 is a nearby example of a far-infrared (FIR) bright, highluminosity (LFIR greater than 1011 solarluminosity) interacting galaxy pair. At a redshift of z = 0.02 itprovides an opportunity to study such interacting galaxies at afavorable spatial scale (390 pc/arcsec). This paper presents new highresolution near-infrared (1.25 to 3.7 micrometer) and visible images,and visible spectra of VV 114. A picture emerges of a system withwidespread massive star formation throughout both interacting galaxies.The brighter visible galaxy (VV 114W) shows H II region-like emission inboth visual spectra and near-infrared colors, with no more than twomagnitudes of visual extinction. The brightest peak of infrared andradio emission (VV 114E) has extreme near-infrared colors and is locatedat a minimum of visible emission. This indicates a large concentrationof dust in the nucleus of VV 114E that is nearly entirely obscuring amajor luminosity source in this system.
| Less probable IRR II candidateas
The paper presents a list of 89 less probable Irr candidates in whichthe presence of dust is suspected. In a commentary to this list, theshape of the galaxies is described and their location in relation toneighboring background galaxies is noted.
| An extragalactic database. I - The Catalogue of Principal Galaxies
The Catalogue of Principal Galaxies is described, which lists equatorialcoordinates (for the equinoxes 1950 and 2000) and cross-identificationsfor 73,197 galaxies. The 40,932 coordinates have standard deviationssmaller than 10 arcsec. A total of 131,601 names from the 38 most commonsources are listed. In addition, mean data for each object are givenwhen available: 49,102 morphological descriptions, 52,954 apparent majorand minor axes, 67,116 apparent magnitudes, 20,046 radial velocities and24,361 position angles. This information was used for facilitatingproper identification. Finally, distribution options are explained.
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