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A `super' star cluster grown old: the most massive star cluster in the Local Group
We independently redetermine the reddening and age of the globularcluster (GC) 037-B327 in M31 by comparing independently obtainedmulticolour photometry with theoretical stellar population synthesismodels. 037-B327 has long been known to have a very large reddeningvalue, which we confirm to be E(B - V) = 1.360 +/- 0.013, in goodagreement with the previous results. We redetermine its most likely ageat 12.4 +/- 3.2 Gyr.037-B327 is a prime example of an unusually bright early counterpart tothe ubiquitous `super' star clusters presently observed in mosthigh-intensity star-forming regions in the local Universe. In order tohave survived for a Hubble time, we conclude that its stellar initialmass function (IMF) cannot have been top-heavy. Using this constraint,and a variety of simple stellar population (SSP) models, we determine aphotometric mass of , somewhat depending on the SSP models used, themetallicity and age adopted and the IMF representation. This mass, andits relatively small uncertainties, makes this object the most massivestar cluster of any age in the Local Group. Assuming that thephotometric mass estimate thus derived is fairly close to its dynamicalmass, we predict that this GC has a (one-dimensional) velocitydispersion of the order of (72 +/- 13) km s-1. As a surviving`super' star cluster, this object is of prime importance for theoriesaimed at describing massive star cluster evolution.
| Massive Star Cluster Populations in Irregular Galaxies as Probable Younger Counterparts of Old Metal-rich Globular Cluster Populations in Spheroids
Peak metallicities of metal-rich populations of globular clusters(MRGCs) belonging to early-type galaxies and spheroidal subsystems ofspiral galaxies (spheroids) of different mass fall within the somewhatconservative -0.7<=[Fe/H]<=-0.3 range. Indeed, if possible ageeffects are taken into account, this metallicity range might becomesmaller. Irregular galaxies such as the Large Magellanic Cloud (LMC),with longer timescales of formation and lower star formation (SF)efficiency, do not contain old MRGCs with [Fe/H]>-1.0, but they areobserved to form populations of young/intermediate-age massive starclusters (MSCs) with masses exceeding 104 Msolar.Their formation is widely believed to be an accidental process fullydependent on external factors. From the analysis of available data onthe populations and their hosts, including intermediate-age populousstar clusters in the LMC, we find that their most probable meanmetallicities fall within -0.7<=[Fe/H]<=-0.3, as the peakmetallicities of MRGCs do, irrespective of signs of interaction.Moreover, both the disk giant metallicity distribution function (MDF) inthe LMC and the MDFs for old giants in the halos of massive spheroidsexhibit a significant increase toward [Fe/H]~-0.5. That is in agreementwith a correlation found between SF activity in galaxies and theirmetallicity. The formation of both the old MRGCs in spheroids and MSCpopulations in irregular galaxies probably occurs at approximately thesame stage of the host galaxies' chemical evolution and is related tothe essentially increased SF activity in the hosts around the samemetallicity that is achieved very early in massive spheroids, later inlower mass spheroids, and much later in irregular galaxies. Changes inthe interstellar dust, particularly in elemental abundances in dustgrains and in the mass distribution function of the grains, may be amongthe factors regulating star and MSC formation activity in galaxies.Strong interactions and mergers affecting the MSC formation presumablyplay an additional role, although they can substantially intensify theinternally regulated MSC formation process. Several implications of oursuggestions are briefly discussed.
| From young massive star cluster to old globular: the LV-σ0 relationship as a diagnostic tool
We present a new analysis of the properties of the young massive starclusters (YMCs) forming profusely in intense starburst environments,which demonstrates that these objects are plausible progenitors of theold globular clusters (GCs) seen abundantly in the Local Group. Themethod is based on the tight relationship for old GCs between theirV-band luminosities, LV, and (central) velocity dispersions,σ0. We improve the significance of the relationship byincreasing the GC sample size and find that its functional form,LV/Lsolar~σ1.57+/-0.100(km s-1), is fully consistent with previous determinationsfor smaller Galactic and M31 GC samples. The tightness of therelationship for a GC sample drawn from environments as diverse as thosefound in the Local Group implies that its origin must be sought inintrinsic properties of the GC formation process itself. We evolve theluminosities of those YMCs in the local Universe which have velocitydispersion measurements to an age of 12 Gyr, adopting a variety ofinitial mass function (IMF) descriptions, and find that most YMCs willevolve to loci close to, or to slightly fainter luminosities than theimproved GC relationship. In the absence of significant externaldisturbances, this implies that these objects may potentially survive tobecome old GC-type objects over a Hubble time. The main advantage of ournew method is its simplicity. Whereas alternative methods, based ondynamical mass estimates, require one to obtain accurate size estimatesand to make further assumptions, the only observables required here arethe system's velocity dispersion and luminosity. The most importantfactor affecting the robustness of our conclusions is the adopted formof the IMF. We use the results of N-body simulations to confirm thatdynamical evolution of the clusters does not significantly alter ourconclusions about the likelihood of individual clusters surviving tolate times. Finally, we find that our youngest observed clusters areconsistent with having evolved from a relation of the form . Thisrelation may actually correspond to the origin of the GC fundamentalplane.
| Systematic uncertainties in the analysis of star cluster parameters based on broad-band imaging observations
High-resolution Hubble Space Telescope (HST) imaging observations ofstar cluster systems provide a very interesting and useful alternativeto spectroscopic studies for stellar population analyses with 8-m classtelescopes. Here, we assess the systematic uncertainties in (young)cluster age, mass and (to a lesser extent) extinction and metallicitydeterminations, based on broad-band imaging observations with the HST.Our aim here is to intercompare the results obtained using a variety ofcommonly used modelling techniques, specifically with respect to our ownextensively tested multidimensional approach. Any significantdifferences among the resulting parameters are due to the details of thevarious, independently developed, modelling techniques used, rather thanto the stellar population models themselves. Despite the modeluncertainties and the selection effects inherent to most methods used,we find that the peaks in the relative age and mass distributions of agiven young (<~109 yr) cluster system can be derivedrelatively robustly and consistently, to accuracies ofσt≡Δ<= 0.35 andσM≡Δ<=0.14, respectively, assuming Gaussian distributions in cluster ages andmasses for reasons of simplicity. The peaks in the relative massdistributions can be obtained with a higher degree of confidence thanthose in the relative age distributions, as exemplified by the smallerspread among the peak values of the mass distributions derived. Thisimplies that mass determinations are mostly insensitive to the approachadopted. We reiterate that as extensive a wavelength coverage aspossible is required to obtain robust and internally consistent age andmass estimates for the individual objects, with reasonableuncertainties. Finally, we conclude that the actual filter systems usedfor the observations should be used for constructing model colours,instead of using conversion equations, to achieve more accuratederivations of ages and masses.
| Young Super Star Clusters in the Starburst of M82: The Catalog
Recent results from the Hubble Space Telescope (HST) have resolvedstarbursts as collections of compact young stellar clusters. Here wepresent a photometric catalog of the young stellar clusters in thenuclear starburst of M82, observed with the HST WFPC2 in Hα(F656N) and in four optical broadband filters. We identify 197 youngsuper stellar clusters. The compactness and high density of the sourcesled us to develop specific techniques to measure their sizes. Strongextinction lanes divide the starburst into five different zones, and weprovide a catalog of young super star clusters for each of these. In thecatalog we include relative coordinates, radii, fluxes, luminosities,masses, equivalent widths, extinctions, and other parameters. Extinctionvalues have been derived from the broadband images. The radii rangebetween 3 and 9 pc, with a mean value of 5.7+/-1.4 pc, and a stellarmass between 104 and 106 Msolar. Theinferred masses and mean separation, comparable to the size of the superstar clusters, together with their high volume density, provide strongevidence for the key ingredients postulated by Tenorio-Tagle andcoworkers as required for the development of a supergalactic wind.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained from the data archive at the Space Telescope Science Institute.STScI is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555.
| The star cluster population of M 51. II. Age distribution and relations among the derived parameters
We use archival Hubble Space Telescope observations of broad-band imagesfrom the ultraviolet (F255W-filter) through the near infrared (NICMOSF160W-filter) to study the star cluster population of the interactingspiral galaxy M 51. We obtain age, mass, extinction, and effectiveradius estimates for 1152 star clusters in a region of ~7.3 × 8.1kpc centered on the nucleus and extending into the outer spiral arms. Inthis paper we present the data set and exploit it to determine the agedistribution and relationships among the fundamental parameters (i.e.age, mass, effective radius). We show the critical dependence of the agedistribution on the sample selection, and confirm that using a constantmass cut-off, above which the sample is complete for the entire agerange of interest, is essential. In particular, in this sample we arecomplete only for masses above 5×104~Mȯ for the last 1 Gyr. Using this datasetwe find: i) that the cluster formation rate seems to have had a largeincrease ~50-70 Myr ago, which is coincident with the suggested secondpassage of its companion, NGC 5195; ii) a large number of extremelyyoung (<10 Myr) star clusters, which we interpret as a population ofunbound clusters of which a large majority will disrupt within the next~10 Myr; and iii) that the distribution of cluster sizes can be wellapproximated by a power-law with exponent, -η = -2.2 ± 0.2,which is very similar to that of Galactic globular clusters, indicatingthat cluster disruption is largely independent of cluster radius. Inaddition, we have used this dataset to search for correlations among thederived parameters. In particular, we do not find any strong trendsbetween the age and mass, mass and effective radius, nor between thegalactocentric distance and effective radius. There is, however, astrong correlation between the age of a cluster and its extinction, withyounger clusters being more heavily reddened than older clusters.
| Star cluster formation and evolution in the dwarf starburst galaxy NGC 1569
We analyse multiwavelength Hubble Space Telescope (HST) observations ofa large number of star clusters in the nearby (post-)starburst dwarfgalaxy NGC 1569. Their spectral energy distributions (SEDs) cover atleast the wavelength range from U to I in equivalent HST filters, inmost cases supplemented by near-infrared data. Using our most up-to-dateevolutionary synthesis models of the Göttingen GALEV code wedetermine ages, metallicities, extinction values and masses for eachindividual cluster robustly and independently. We confirm the youth ofmost of these objects. The majority were formed in a very intensestarburst starting around 25 Myr ago. While there are two prominent`super star clusters' present in this galaxy, with masses of (5-16)×105 Msolar, almost all remaining clustersare significantly less massive than an average Milky Way globularcluster, and are generally consistent with open cluster-type objects. Wedetermine the cluster mass function from individual cluster massesderived by scaling the model SEDs of known mass to the observed clusterSEDs for each individual cluster. We find signs of a change in thecluster mass function as the burst proceeds, which we attribute to thespecial conditions of star cluster formation in this starburst dwarfgalaxy environment.
| The Nuclear Gas Dynamics and Star Formation of Markarian 231
We report adaptive optics H- and K-band spectroscopy of the inner fewarcseconds of the luminous merger/ultraluminous infrared galaxy(ULIRG)/QSO Mrk 231, at spatial resolutions as small as 0.085". For thefirst time we have been able to resolve the active star-forming regionclose to the active galactic nucleus (AGN) using stellar absorptionfeatures, finding that its luminosity profile is well represented by anexponential function with a disk scale length 0.18"-0.24" (150-200 pc),and implying that the stars exist in a disk rather than a spheroid. Thestars in this region are also young (10-100 Myr), and it therefore seemslikely that they have formed in situ in the gas disk, which itselfresulted from the merger. The value of the stellar velocity dispersion(~100 km s-1 rather than the usual few times 10 kms-1 in large-scale disks) is a result of the large masssurface density of the disk. The stars in this region have a combinedmass of at least 1.6×109 Msolar, and accountfor 25%-40% of the bolometric luminosity of the entire galaxy. At ourspatial resolution the stellar light in the core is diluted by more thana factor of 10 even in the H band by continuum emission from hot dustaround the AGN. We have detected the 2.12 μm 1-0 S(1) H2and 1.64 μm [Fe II] lines out to radii exceeding 0.5". The kinematicsfor the two lines are very similar to each other as well as to thestellar kinematics, and broadly consistent with the nearly face-onrotating disk reported in the literature and based on interferometric CO1-0 and CO 2-1 measurements of the cold gas. However, they suggest amore complex situation in which the inner 0.2"-0.3" (200 pc) is warpedout of its original disk plane. Such a scenario is supported by theprojected shape of the nuclear stellar disk, the major axis of which issignificantly offset from the nominal direction, and by the pronouncedshift on very small scales in the direction of the radio jet axis, whichhas been reported in the literature.The near-infrared data presented herein were obtained at the W. M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California, andthe National Aeronautics and Space Administration. The Observatory wasmade possible by the generous financial support of the W. M. KeckFoundation.
| An IRAS High Resolution Image Restoration (HIRES) Atlas of All Interacting Galaxies in the IRAS Revised Bright Galaxy Sample
The importance of far-infrared observations for our understanding ofextreme activity in interacting and merging galaxies has beenillustrated by many studies. Even though two decades have passed sinceits launch, the most complete all-sky survey to date from which far-IRselected galaxy samples can be chosen is still that of the InfraredAstronomical Satellite (IRAS). However, the spatial resolution of theIRAS all-sky survey is insufficient to resolve the emission fromindividual galaxies in most interacting galaxy pairs, and hence previousstudies of their far-IR properties have had to concentrate either onglobal system properties or on the properties of very widely separatedand weakly interacting pairs. Using the HIRES image reconstructiontechnique, it is possible to achieve a spatial resolution ranging from30" to 1.5m (depending on wavelength and detector coverage), whichis a fourfold improvement over the normal resolution of IRAS. This issufficient to resolve the far-IR emission from the individual galaxiesin many interacting systems detected by IRAS, which is very importantfor meaningful comparisons with single, isolated galaxies. We presenthigh-resolution 12, 25, 60, and 100 μm images of 106 interactinggalaxy systems contained in the IRAS Revised Bright Galaxy Sample (RBGS,Sanders et al.), a complete sample of all galaxies having a 60 μmflux density greater than 5.24 Jy. These systems were selected to haveat least two distinguishable galaxies separated by less than threeaverage galactic diameters, and thus we have excluded very widelyseparated systems and very advanced mergers. Additionally, some systemshave been included that are more than three galactic diameters apart,yet have separations less than 4' and are thus likely to suffer fromconfusion in the RBGS. The new complete survey has the same propertiesas the prototype survey of Surace et al. We find no increased tendencyfor infrared-bright galaxies to be associated with other infrared-brightgalaxies among the widely separated pairs studied here. We find smallenhancements in far-IR activity in multiple galaxy systems relative toRBGS noninteracting galaxies with the same blue luminosity distribution.We also find no differences in infrared activity (as measured byinfrared color and luminosity) between late- and early-type spiralgalaxies.
| Nuclear star formation in NGC 6240
We have made use of archival HST BVIJH photometry to constrain thenature of the three discrete sources, A1, A2 and B1, identified in thedouble nucleus of NGC 6240. STARBURST99 models have been fitted to theobserved colours, under the assumption, first, that these sources can betreated as star clusters (i.e. single, instantaneous episodes of starformation), and subsequently as star-forming regions (i.e. characterisedby continuous star formation). For both scenarios, we estimate ages asyoung as 4 million years, integrated masses ranging between 7 ×106 Mȯ (B1) and 109Mȯ (A1) and a rate of 1 supernova per year, which,together with the stellar winds, sustains a galactic wind of 44Mȯ yr-1. In the case of continuous starformation, a star-formation rate has been derived for A1 as high as 270Mȯ yr-1, similar to what is observed for warmUltraluminous Infrared Galaxies (ULIRGs) with a double nucleus. The A1source is characterised by a mass density of about 1200Mȯ pc-3 which resembles the CO molecular massdensity measured in cold ULIRGs and the stellar density determined in``elliptical core'' galaxies. This, together with the recent discoveryof a supermassive binary black hole in the double nucleus of NGC 6240,might indicate that the ongoing merger could shape the galaxy into acore elliptical.
| A Search for Core-Collapse Supernova Progenitors in Hubble Space Telescope Images
Identifying the massive progenitor stars that give rise to core-collapsesupernovae (SNe) is one of the main pursuits of supernova and stellarevolution studies. Using ground-based images of recent, nearby SNeobtained primarily with the Katzman Automatic Imaging Telescope,astrometry from the Two Micron All Sky Survey, and archival images fromthe Hubble Space Telescope, we have attempted the direct identificationof the progenitors of 16 Type II and Type Ib/c SNe. We may haveidentified the progenitors of the Type II SNe 1999br in NGC 4900, 1999evin NGC 4274, and 2001du in NGC 1365 as supergiant stars withM0V~-6 mag in all three cases. We may have alsoidentified the progenitors of the Type Ib SNe 2001B in IC 391 and 2001isin NGC 1961 as very luminous supergiants withM0V~-8 to -9 mag, and possibly the progenitor ofthe Type Ic SN 1999bu in NGC 3786 as a supergiant withM0V~-7.5 mag. Additionally, we have recovered atlate times SNe 1999dn in NGC 7714, 2000C in NGC 2415, and 2000ew in NGC3810, although none of these had detectable progenitors on pre-supernovaimages. In fact, for the remaining SNe only limits can be placed on theabsolute magnitude and color (when available) of the progenitor. Thedetected Type II progenitors and limits are consistent with redsupergiants as progenitor stars, although possibly not as red as we hadexpected. Our results for the Type Ib/c SNe do not strongly constraineither Wolf-Rayet stars or massive interacting binary systems asprogenitors. Based on observations made with the NASA/ESA Hubble SpaceTelescope, obtained from the data archive of the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy (AURA), Inc., under NASA contract NAS 5-26555.
| On the formation of star clusters in the merger NGC 6240
We identified star clusters in archived Hubble Space Telescope/WideField Planetary Camera 2 (HST/WFPC2) images of the merger andultraluminous infrared galaxy NGC 6240, with the aim of investigatingwhether star cluster properties (luminosity, age and mass) in such anextreme environment differ from those of clusters in less luminousstarburst galaxies. We found 54 star clusters in all of the F450W, F547Mand F814W exposures, of which 41 are located in the main body of NGC6240 and 13 are located in the galactic tails. Given that only twocolours are available to derive two independent variables (clusterreddening and age), we adopted an ad hoc procedure to derive clusterparameters statistically under the assumption that the clustermetallicity is like that in the Large Magellanic Cloud. The colours ofeach cluster are fitted to STARBURST99 models of fixed mass and variableages and reddenings. All cluster reddening and age solutions withχ2 < 1 are considered to be consistent with the data.Masses are derived by scaling the luminosity of the models withbest-fitting χ2 < 1 by the observed V luminosity,after correction for reddening and distance. Therefore, each cluster isdescribed by a range of reddening values, ages and masses; for each ofthese parameters, we derive probability functions. Thus we infer thatthe most probable age of the observed clusters is between 5 and 13 Myrand their most probable mass is about (1-2) × 105Msolar. A low probability exists for clusters as massive as108 Msolar, as well as for the trend that the meancluster mass increases towards the double nuclei of NGC 6240. Comparisonwith star clusters in starburst galaxies seems to point to more massiveclusters being formed in more massive galaxies and gas-rich mergers,while the overall cluster mass distribution might be relativelyindependent of the details of the associated starburst where dense,massive clusters preferentially form.
| Star cluster formation and evolution in nearby starburst galaxies - II. Initial conditions
We use the ages, masses and metallicities of the rich young star clustersystems in the nearby starburst galaxies NGC 3310 and 6745 to derivetheir cluster formation histories and subsequent evolution. We furtherexpand our analysis of the systematic uncertainties involved in the useof broad-band observations to derive these parameters (Paper I) byexamining the effects of a priori assumptions on the individual clustermetallicities. The age (and metallicity) distributions of both theclusters in the circumnuclear ring in NGC 3310 and of those outside thering are statistically indistinguishable, but there is a clear andsignificant excess of higher-mass clusters in the ring compared to thenon-ring cluster sample. It is likely that the physical conditions inthe starburst ring may be conducive for the formation of higher-massstar clusters, on average, than in the relatively more quiescentenvironment of the main galactic disc. For the NGC6745 cluster system wederive a median age of ~10 Myr. NGC6745 contains a significantpopulation of high-mass `super star clusters', with masses in the range6.5 <~ log(Mcl/Msolar) <~ 8.0. Thisdetection supports the scenario that such objects form preferentially inthe extreme environments of interacting galaxies. The age of the clusterpopulations in both NGC3310 and 6745 is significantly lower than theirrespective characteristic cluster disruption time-scales, respectivelylog(tdis4/yr) = 8.05 and 7.75, for 104Msolar clusters. This allows us to obtain an independentestimate of the initial cluster mass function slope, α=2.04(+/-0.23)+0.13-0.43 for NGC3310, and1.96(+/-0.15) +/- 0.19 for NGC6745, respectively, for massesMcl>~ 105 Msolar andMcl>~ 4 × 105 Msolar. Thesemass function slopes are consistent with those of other young starcluster systems in interacting and starburst 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.
| Classifications of the Host Galaxies of Supernovae
Classifications on the DDO system are given for the host galaxies of 177supernovae (SNe) that have been discovered since 1997 during the courseof the Lick Observatory Supernova Search with the Katzman AutomaticImaging Telescope. Whereas SNe Ia occur in all galaxy types, it isfound, at a high level of statistical confidence, that SNe Ib, Ic, andII are strongly concentrated in late-type galaxies. However, attentionis drawn to a possible exception provided by SN 2001I. This SN IInoccurred in the E2 galaxy UGC 2836, which was not expected to harbor amassive young supernova progenitor.
| Supernovae
IAUC 7193 available at Central Bureau for Astronomical Telegrams.
| Supernova 1999bx in NGC 6745
IAUC 7162 available at Central Bureau for Astronomical Telegrams.
| Supernova 1999bx in NGC 6745
IAUC 7156 available at Central Bureau for Astronomical Telegrams.
| Supernova 1999bx in UGC 11391
IAUC 7154 available at Central Bureau for Astronomical Telegrams.
| Molecular Gas in Strongly Interacting Galaxies. I. CO (1-0) Observations
We present observations of the CO (1-0) line in 80 interacting galaxiesas part of a program to study the role of interactions and mergers intriggering starbursts. The sample, which only includes obviouslyinteracting pairs of galaxies, is the largest such sample observed inCO. The observations were carried out at the NRAO 12 m and IRAM 30 mtelescopes. CO emission was detected in 56 galaxies (of which 32 are newdetections), corresponding to a detection rate of 70%. Because mostgalaxies are slightly larger than the telescope beam, correction factorswere applied to include CO emission outside the beam. The correctionfactors were derived by fitting a Gaussian function or an exponential CObrightness distribution to galaxies with multiple pointings and byassuming an exponential model for galaxies with single pointing. Wecompared the global CO fluxes of 10 galaxies observed by us at bothtelescopes. We also compared the measured fluxes for another 10 galaxiesobserved by us with those by other authors using the NRAO 12 m and FCRAO14 m telescopes. These comparisons provide an estimate of the accuracyof our derived global fluxes, which is ~40%. Mapping observations of twoclose pairs of galaxies, UGC 594 (NGC 317) and UGC 11175 (NGC 6621), arealso presented. In subsequent papers we will report the statisticalanalyses of the molecular properties in our sample galaxies and makecomparisons between isolated spirals and interacting galaxies.
| A 1.425 GHz Atlas of the IRAS Bright Galaxy Sample, Part II
Galaxies with δ >= -45^deg^ and |b| >= 10^deg^ in the IRASBright Galaxy Sample, Part II, were observed at 1.425 GHz by the VeryLarge Array in its B, CnB, C, DnC, and D configurations. An atlas ofradio contour maps and a table listing the principal radio sourceparameters (position, flux density, angular size) are given. This atlasof 187 galaxies supplements the 1.49 GHz atlas of 313 galaxies in therevised Bright Galaxy Sample, Part I. Together, they are complete forextragalactic sources stronger than S = 5.24Jy at λ = 60 micronsin the area |b| > 10^deg^, δ > -45^deg^. To the extent thatthe far-infrared and radio brightness distributions overlap, these radiomaps provide the most accurate positions and high-resolution images ofthe brightest extragalactic far-infrared sources.
| Large-Scale Structure at Low Galactic Latitude
We have extended the CfA Redshift Survey to low galactic latitudes toinvestigate the relation between the Great Wall in the North GalacticCap and the Perseus-Pisces chain in the South Galactic Cap. We presentredshifts for 2020 galaxies in the Catalogue of Galaxies and of Clustersof Galaxies (Zwicky et al. 1961-68, CGCG) in the following regions: 4^h^<= α <= 8^h^, 17^h^ <= α <= 20^h^, 0^deg^ <=δ <= 45^deg^. In these regions, the redshift catalogue includes1664 galaxies with B(0) <= 15.5 (of which 820 are newly measured) andis 97% complete. We also include redshifts for an additional 356galaxies in these regions with B(O) > 15.5; of these, 148 werepreviously unmeasured. The CGCG samples the galaxy distribution down tob_II_ = 10^deg^. In this paper, we discuss the acquisition and reductionof the spectra, and we examine the qualitative features of the redshiftdistribution. The Great Wall and the Perseus-Pisces chain are not simplyconnected across the Zone of Avoidance. These structures, which at firstappear to be coherent on scales of ~100 h^-1^ Mpc or more, actually formthe boundaries of neighboring voids of considerably smaller scale,approximately 50h^-1^ Mpc. The structures delineated by ouroptically-selected sample are qualitatively similar to those detected bythe far-infrared-selected IRAS 1.2 Jansky Survey (Fisher et al. 1995).Although the IRAS survey probes more deeply into the Zone of Avoidance,our optically-selected survey provides better sampling of structures atb_II_ >= 10^deg^.
| The IRAS Bright Galaxy Survey - Part II: Extension to Southern Declinations (delta ~< -30), and Low Galactic Latitudes (f<|b|
Complete IRAS Observations and redshifts are reported for all sourcesidentified in the IRAS Bright Galaxy Survey-Part II (hereafter referredto as BGS_2_). Source positions, radial velocities, optical magnitudes,and total flux densities, peak flux densities, and spatial extents at12, 25, and 100 ,microns are reported for 288 sources having 60 micronflux densities > 5.24 Jy, the completeness limit of the originalBright Galaxy Survey [Soifer et al., AJ, 98,766(1989)], hereafterreferred to as BGS_1_. These new data represent the extension of theIRAS Bright Galaxy Survey to southern declinations,δ<~-30^deg^, and low Galactic latitudes,5^deg^<|b|<30^deg^. Although the sky coverage of the BGS_2_ (~19935 deg^2^) is 37% larger than the sky coverage of the BGS_1_, thenumber of sources is 8% smaller due primarily to large scale structurein the local distribution of galaxies. Otherwise, the sources in theBGS_2_ show similar relationships between number counts and flux densityas observed for the 313 sources in the BGS_1_. The BGS_2_ along with theearlier BGS, represents the best sample currently available for definingthe infrared properties of galaxies in the local (z <~ 0.1) Universe.
| Radio Identifications of Extragalactic IRAS Sources
Extragalactic sources detected at λ= 60 microns were selectedfrom the IRAS Faint Source Catalog, Version 2 by the criterion S_60microns_ >= S_12_ microns. They were identified by positioncoincidence with radio sources stronger than 25 mJy at 4.85 GHz in the6.0 sr declination band 0^deg^ < δ < +75^deg^ (excluding the0.05 sr region 12^h^40^m^< α < 14^h^40^m^, 0^deg^<+5^deg^) and with radio sources stronger than 80 mJy in the 3.4 sr areao^h^ <α < 2o^h^, -40^deg^ < δ < 0^deg^ (plus theregion 12^h^40^m^ < α < 14^h^40^m^, 0^deg^<δ<+5^deg^). Fields containing new candidate identifications weremapped by the VLA at 4.86 GHz with about 15" FWHM resolution. Difficultcases were confirmed or rejected with the aid of accurate (σ ~ 1")radio and optical positions. The final sample of 354 identifications in{OMEGA} = 9.4 sr is reliable and large enough to contain statisticallyuseful numbers of radio-loud FIR galaxies and quasars. The logarithmicFIR radio flux ratio parameter q can be used to distinguish radiosources powered by "starbursts" from those powered by "monsters."Starbursts and normal spiral galaxies in a λ = 60 micronflux-limited sample have a narrow (σ_q_ = 0.14 +/- 0.01) qdistribution with mean = 2.74 +/- 0.01, and none have "warm"FIR spectra [α(25 microns, 60 microns) < 1.5]. The absence ofradio- quiet (but not completely silent) blazars indicates that nearlyall blazars become optically thin at frequencies v<~100 GHz.Nonthermal sources with steep FIR/optical spectra and dusty-embeddedsources visible only at FIR and radio wavelengths must be very rare.
| Hydroxyl in galaxies. I - Surveys with the NRAO 300 FT telescope
Results are presented of a search for 1667- and 1665-MHz mainline OHtransitions for 321 galaxies, which were observed during four separatesessions at the NRAO 300-ft telescope in the period 1984-1987. Threedetections of OH megamasers are reported, as well as detections of threenew OH absorption sources. The observational sample contains sourcesfrom a variety of catalogs and represents different criteria. Theresults for the whole sample confirm that FIR luminosity and colorcriteria used for these surveys are indeed optimized for findingmegamasers. The results also confirm that detecting distant highluminosity OH megamasers is considerably more successful than findingnearby weak masers.
| UGC galaxies stronger than 25 mJy at 4.85 GHz
UGC galaxies in the declination band +5 to +75 deg were identified byposition coincidence with radio sources stronger than 25 mJy on theGreen Bank 4.85 GHz sky maps. Candidate identifications were confirmedor rejected with the aid of published aperture-synthesis maps and new4.86 GHz VLA maps having 15 or 18 arcsec resolution, resulting in asample of 347 nearby radio galaxies plus five new quasar-galaxy pairs.The radio energy sources in UGC galaxies were classified as 'starbursts'or 'monsters' on the basis of their infrared-radio flux ratios, infraredspectral indices, and radio morphologies. The rms scatter in thelogarithmic infrared-radio ratio q is not more than 0.16 for starburstgalaxies selected at 4.85 GHz. Radio spectral indices were obtained fornearly all of the UGC galaxies, and S0 galaxies account for adisproportionate share of the compact flat-spectrum (alpha less than0.5) radio sources. The extended radio jets and lobes produced bymonsters are preferentially, but not exclusively, aligned within about30 deg of the optical minor axes of their host galaxies. The tendencytoward minor-axis ejection appears to be independent of radio-sourcesize and is strongest for elliptical galaxies.
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