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|Discovery of Water Maser Emission in Five AGNs and a Possible Correlation Between Water Maser and Nuclear 2-10 keV Luminosities|
We report the discovery of water maser emission in five active galacticnuclei (AGNs) with the 100 m Green Bank Telescope (GBT). The positionsof the newly discovered masers, measured with the VLA, are consistentwith the optical positions of the host nuclei to within 1 σ (0.3"radio and 1.3" optical) and most likely mark the locations of theembedded central engines. The spectra of three sources, 2MASXJ08362280+3327383, NGC 6264, and UGC 09618 NED02, display thecharacteristic spectral signature of emission from an edge-on accretiondisk with maximum orbital velocity of ~700, ~800, and ~1300 kms-1, respectively. We also present a GBT spectrum of apreviously known source, Mrk 0034, and interpret the narrow Dopplercomponents reported here as indirect evidence that the emissionoriginates in an edge-on accretion disk with orbital velocity of ~500 kms-1. We obtained a detection rate of 12% (5 out of 41) amongSeyfert 2 and LINER systems with 10,000 kms-1
|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 (220.127.116.11) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/941
|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.
|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.
|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.
|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.
|Rotation Curves and Velocity Measures for Spiral Galaxies in Pairs|
Rotation curves have been obtained for 76 spiral galaxies in pairs,including a geometrically selected subset from the Karachentsev catalogand a set of Seyfert galaxies with close companions. Derived parametersof the rotation curves and the galaxies light distributions are alsopresented. The rotation curves are classified broadly by shape, withspecial emphasis on kinematic disturbances and regions of solid-bodybehavior that may lead to bar development. Broadband images of thegalaxies allow assessments of their degree of symmetry or disturbance.These velocity slices afford an empirical basis for evaluating theaccuracy of radial velocity measures for spiral galaxies in pairs, andthe dynamically important radial velocity differences. Specifically, thedisagreement among several plausible ways of estimating the centralvelocity from these rotation data is used to estimate how closely any ofthese might approximate the nuclear or center-of-mass values. From sevenindicators of central velocity, the internal scatter is σ_vv_ = 34km s^-1^. Of these, the velocity weighted by Hα intensity alongthe slit shows a systematic offset of about 20 km s^-1^ with respect tothe others for the Karachentsev pairs, in the sense that this measure isredshifted with respect to the other indicators. This is in the sense(but not of the total magnitude) required to account for statisticalasymmetries in pair velocity differences. Individual scatter between thevelocity indicators taken pairwise ranges from σ = 20 to 52 km s^-1^. These results imply that emission-line data such as these cannotspecify the center of mass or nuclear redshift at a level more accuratethan this, even for arbitrarily precise velocity measurements, becauseit is not clear how the observed quantities relate to the desiredmeasurement in a physical sense. No useful predictor of which galaxieshave large or small scatter among velocity measures was found, exceptthat the scatter is small for the class of "nonrotating" galaxies withsmall overall velocity amplitudes. Projected separation, separationnormalized to disk scale length, and morphological disturbance do notcorrelate with the velocity scatter.
|Double galaxies - Redshift measurements, error analysis, and mean mass/luminosity ratio|
New radial velocities for 44 double galaxy systems are presented. Theratio k between the internal and external errors in the redshift data isestimated by comparing data from catalog galaxies with a sample fromWhite et al. (1983). This ratio is found to increase from 1.0 to 2.1from galaxies with strong emission lines to absorption-line objects. Thedisparity between the absolute and internal errors diminishes for theredshift differentials of pair components, because the individual errorsin the redshifts measured for the members of a given pair are observedto be positively correlated. The average value of k for the whole sampleis estimated by considering the values of the first four moments of themass/luminosity ratio as functions of k. The absolute error in theredshift differential is 1.4 times the internal error, bringing the meanratio of orbital mass to luminosity for 490 pairs into good agreementwith the values determined from the differential rotation of galaxies.
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