Home     Getting Started     To Survive in the Universe    
Inhabited Sky
    News@Sky     Astro Photo     The Collection     Forum     Blog New!     FAQ     Press     Login  

NGC 2444



Upload your image

DSS Images   Other Images

Related articles

Gas in early-type galaxies: cross-fuelling in late-type-early-type pairs?
We present 12CO (J= 1-0) and 12CO (J= 2-1)observations of eight early-type galaxies, forming part of a sample ofinteracting galaxies, each consisting of one late- and one early-typesystem. All of the early-type galaxies observed are undetected in CO tolow levels, allowing us to place tight constraints on their moleculargas content. Additionally, we present HI absorption data for one system.The implications for possible gas transfer from the late- to theearly-type galaxy during the interaction are discussed.

HI Tidal Tails, Bridges and Clouds
There is plenty of intergalactic H I gas without any obvious stellarcontent ranging from (1) extended gas envelopes around some normal andpeculiar galaxies, (2) tidal tails/bridges in interacting or merginggalaxy systems, (3) large-scale rings around early type galaxies, and(4) detached clouds at varying distances from associated galaxies, butthere are few or no isolated H I clouds.The HIPASS Bright Galaxy Catalog, which covers the whole southern sky,contains only one definite extragalactic H I cloud which is locatedclose to the galaxy NGC 2442 whereas it is sensitive to isolated H Iclouds with MHI > 106 × D2Mȯ. The space density of H I clouds is therefore about1/1000th that of galaxies with the same MHI.

A Minor-Merger Interpretation for NGC 1097's ``Jets''
We have conducted a deep search for neutral hydrogen gas associated withthe faint optical ``jets'' of NGC 1097 using the Very Large Array.Measurable H I would have been expected if the jets were tidal in origingiven their moderately blue optical and near-infrared colors. The jetsare free of H I emission to a limiting surface density(ΣHI) of 0.06 Msolar pc-2 (3σ) over a 1102 km s-1 velocity range. We also rule outextended H I emission down to 0.02 Msolar pc-2 (3σ, ΔV=45 km s-1) within a 4' FWHM aperturecentered on the right-angle turn in jet R1. We have detected an H Isource [MHI=(5.1+/-1.0)×106Msolar] coincident with a small edge-on spiral or irregulargalaxy (NGC 1097B) 12' southwest of NGC 1097, situated between two jets.Two other ~106 Msolar H I point sources in thefield are considered marginal detections. Neither are associated withthe optical jets.The jets' radio-X-ray spectral energy distribution is most consistentwith starlight. However, from their morphology, optical/near-infraredcolors, and lack of H I, we argue that the jets are not tidal tailsdrawn out of NGC 1097's disk or stars stripped from the ellipticalcompanion NGC 1097A. We also reject in situ star formation in ancientradio jets as this requires essentially 100% conversion of gas intostars on large scales. Instead, we conclude that the jets represent thecaptured remains of a disrupted dwarf galaxy that passed through theinner few kiloparsecs of NGC 1097's disk.We present N-body simulations of such an encounter that reproduce theessential features of NGC 1097's jets: A long and narrow ``X''-shapedmorphology centered near the spiral's nucleus, right-angle bends, and nodiscernible dwarf galaxy remnant. A series of jetlike distributions areformed, with the earliest appearing ~1.4 Gyr after impact. Well-definedX shapes form only when the more massive galaxy has a strong diskcomponent. Ram-pressure stripping of the dwarf's interstellar mediumwould be expected to occur while passing through NGC 1097's disk,accounting for the jets' lack of H I and H II. The remnants' (B-V) colorwould still agree with observations even after ~3 Gyr of passiveevolution, provided the cannibalized dwarf was low-metallicity anddominated by young stars at impact.

H II Regions in Ring Galaxies
We carried out H alpha +[N II] emission line imaging survey of a sampleof nine ring galaxies in order to map the distribution of H II regionsin them. H II regions are detected in all the nine galaxies, with amajority of the H II regions confined to the ring. In four of the samplegalaxies, we detect relatively faint intra-ring H alpha emission. Theintra-ring/total flux fraction is 0.20-0.30 in three cases (Arp141, 291,and 143) and 0.45 in the fourth (NGC2793). The utility of these galaxieswith intra-ring H alpha emission for the determination of abundancegradients is discussed.

Mid-Infrared and CO Observations of the Infrared/X-Ray Luminous Seyfert 1 Galaxy NGC 985: The Making or Breaking of a ULIRG?
We describe Infrared Space Observatory (ISO)1 and BIMA observations of the z=0.04 Seyfert 1ring galaxy NGC 985 which suggest close parallels with some quasar hostgalaxies. NGC 985 contains two closely spaced nuclei embedded in anR1/4-law stellar bulge and an outer ring, evidence of anongoing merger. The system contains ~1.8×1010Msolar of highly disturbed molecular gas which lies in anasymmetric barlike structure with the peak in observed CO columndensities significantly offset from the compact double nucleus. Incontrast to this, the ISO observations show strong dust emissioncentered on the active galactic nucleus (AGN), located in one of the twonuclei. Fainter CO, mid-infrared (MIR), and radio continuum emissionprovides a glimpse of the complexities of star formation in the outerring. An analysis of the kinematics of the main CO emission revealsevidence for two dynamically distinct molecular components within NGC985. The first is a set of isolated supergiant molecular clouds (SGMCs)which are concentrated within 9-10 kpc of the active nucleus. Althoughrandomly distributed about the center, the clouds may form part of aclumpy highly disturbed disk which may be either just forming arounddouble nucleus (the making of an ultraluminous infrared galaxy [ULIRG])or alternatively in the process of being disrupted, perhaps as a resultof a powerful nuclear outflow (the breaking of a ULIRG). A second majorconcentration of CO lies offset from the double nucleus in a dynamicallycoherent ridge of emission in which powerful star formation isoccurring. We tentatively associate CO emission with two out of six UVabsorption lines seen in the blue wing of the very broad Lyαemission. Such an association would imply a complex interrelationshipbetween the nuclear CO cloud population in colliding systems andAGN-driven winds.

GHASP: A 3-D Survey of Spiral and Irregular Galaxies at Hα
Not Available

A catalogue and analysis of X-ray luminosities of early-type galaxies
We present a catalogue of X-ray luminosities for 401 early-typegalaxies, of which 136 are based on newly analysed ROSAT PSPC pointedobservations. The remaining luminosities are taken from the literatureand converted to a common energy band, spectral model and distancescale. Using this sample we fit the LX:LB relationfor early-type galaxies and find a best-fit slope for the catalogue of~2.2. We demonstrate the influence of group-dominant galaxies on the fitand present evidence that the relation is not well modelled by a singlepower-law fit. We also derive estimates of the contribution to galaxyX-ray luminosities from discrete-sources and conclude that they provideLdscr/LB~=29.5ergs-1LBsolar-1. Wecompare this result with luminosities from our catalogue. Lastly, weexamine the influence of environment on galaxy X-ray luminosity and onthe form of the LX:LB relation. We conclude thatalthough environment undoubtedly affects the X-ray properties ofindividual galaxies, particularly those in the centres of groups andclusters, it does not change the nature of whole populations.

Star-formation in ring galaxies: Multi-band observations
Not Available

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.

Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.

Galaxy collisions.
Theories of how galaxies, the fundamental constituents of large-scalestructure, form and evolve have undergone a dramatic paradigm shift inthe last few decades. Earlier views were of rapid, early collapse andformation of basic structures, followed by slow evolution of the stellarpopulations and steady buildup of the chemical elements. Currenttheories emphasize hierarchical buildup via recurrent collisions andmergers, separated by long periods of relaxation and secularrestructuring. Thus, collisions between galaxies are now seen as aprimary process in their evolution. This article begins with a briefhistory; we then tour parts of the vast array of collisional forms thathave been discovered to date. Many examples are provided to illustratehow detailed numerical models and multiwaveband observations haveallowed the general chronological sequence of collisional morphologiesto be deciphered, and how these forms are produced by the processes oftidal kinematics, hypersonic gas dynamics, collective dynamical frictionand violent relaxation. Galaxy collisions may trigger the formation of alarge fraction of all the stars ever formed, and play a key role infueling active galactic nuclei. Current understanding of the processesinvolved is reviewed. The last decade has seen exciting new discoveriesabout how collisions are orchestrated by their environment, howcollisional processes depend on environment, and how these environmentsdepend on redshift or cosmological time.

Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.

A 180 Kiloparsec Tidal Tail in the Luminous Infrared Merger ARP 299
We present VLA H I observations and University of Hawaii 88 inch (2.2 m)deep optical B- and R-band observations of the IR-luminous merger Arp299 (=NGC 3690+IC 694). These data reveal a gas-rich (M_HI=3.3x10^9M_solar) optically faint (mu_B>~27 mag arcsec^-2, mu_R>~26 magarcsec^-2) tidal tail with a length of over 180 kpc. The size of thistidal feature necessitates an old interaction age for the merger(>~750 Myr since first periapse), which is currently experiencing avery young starburst (<~20 Myr). The observations reveal a mostremarkable structure within the tidal tail: it appears to be composed oftwo parallel filaments separated by approximately 20 kpc. One of thefilaments is gas-rich with little if any starlight, while the other isgas-poor. We believe that this bifurcation results from a warped disk inone of the progenitors. The quantities and kinematics of the tidal H Isuggest that Arp 299 results from the collision of a retrograde Sab-Sbgalaxy (IC 694) and a prograde Sbc-Sc galaxy (NGC 3690) that occurred750 Myr ago and will merge into a single object in roughly 60 Myr. Wesuggest that the present IR-luminous phase in this system is due in partto the retrograde spin of IC 694. Finally, we discuss the apparent lackof tidal dwarf galaxies within the tail.

Surface Brightness Gradients Produced by the Ring Waves of Star Formation
We compute surface brightness profiles of galactic disks for outwardlypropagating waves of star formation with a view to investigating thestellar populations in ring galaxies. We consider two mechanisms thatcan create outwardly propagating star-forming rings in a purely gaseousdisk: a self-induced wave and a density wave. We show that the surfacebrightness profiles produced by both scenarios of ring formation aresimilar and are strongly sensitive to the velocity of the wave. Theresults of our computations are compared with the observationalquantities sensitive to the young and old stellar populations in thering galaxies A0035-335 (the Cartwheel Galaxy) and VII Zw 466. The bestfit to the observed radial H alpha surface brightness distribution inthe Cartwheel Galaxy is obtained for a wave velocity of about 90 km s-1.The red continuum brightness of the ring can be fully explained by theevolving stars present in the trailing part of the wave. However, thered continuum brightness in regions internal to the ring indicates thatthe wave of star formation propagates in a preexisting stellar disk inthe Cartwheel. The H alpha and K-band surface brightness profiles in VIIZw 466 match very well the values expected from stellar populationsproduced by a wave of star formation propagating in a purely gaseousdisk. We conclude that VII Zw 466 is probably experiencing the firstevent of star formation in the disk.

Catalogue of HI maps of galaxies. I.
A catalogue is presented of galaxies having large-scale observations inthe HI line. This catalogue collects from the literature the informationthat characterizes the observations in the 21-cm line and the way thatthese data were presented by means of maps, graphics and tables, forshowing the distribution and kinematics of the gas. It containsfurthermore a measure of the HI extension that is detected at the levelof the maximum sensitivity reached in the observations. This catalogueis intended as a guide for references on the HI maps published in theliterature from 1953 to 1995 and is the basis for the analysis of thedata presented in Paper II. The catalogue is only available inelectronic form at the CDS via anonymous ftp orhttp://cdsweb.u-strasbg.fr/Abstract.html

Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.

Simulations of Collisions between Two Gas-rich Galaxy Disks with Heating and Cooling
Particle hydrodynamics (SPH) simulations are presented of directcollisions between two model galaxies, most consisting of a rigid haloand a gas disk. Local self-gravity is also computed in the gas. Thecompanion galaxy in these simulations is about one-third of the mass ofthe primary, and its disk is half the size. An adiabatic equation ofstate is combined with simple approximations for the effects ofradiative cooling and local heating due to young star activity, whichallows a continuous range of thermal phases to develop. These terms andmultiple phases have not generally been included in galaxy collisionsimulations to date. Their effects are assessed in part by repeatingruns with an isothermal equation of state and comparing the results. Onemodel with a star plus gas disk is also included for comparison. Thesemodels are most relevant to interactions involving low surfacebrightness, or other late-type galaxies with extensive gas disks,including the precursors to well-known ring galaxies like the Cartwheeland VII Zw 466. In the simulations, the companion impact is slightly offcenter in the target disk, as is probably the case in these systems. Inall cases, clear ring waves develop in the primary despite thedisruption of parts of the disk by impact shocks. The gas density in thedisk of the primary is initialized to values slightly below thegravitational instability threshold throughout, and the ring wavesinduce star formation in all the heating and cooling models. Thestructure of the waves and other interaction morphologies are found tobe quite similar on large scales in both isothermal and heating/coolingcases, despite the fact that at certain stages large quantities of gasare heated above the initial temperature in the latter. On a finerscale, there are clear differences, including the fact that starformation heating in ring waves increases the vertical scale height ofthe primary gas disk and delays spoke development. The companion disk islargely disrupted in most of these simulations, and a substantial massof gas is splashed out into a bridge connecting the two potentialcenters. The companion disk reforms by accreting gas out of the bridge,though generally in a different plane than its initial one. There isalso a good deal of infall back onto the primary disk. Although heatedby impact, the gas in the bridge cools rapidly. However, kinematicexpansion prevents it from reaching threshold density, and there is nostar formation heating there. A comparison run with a diskless companionproduced no significant bridge, so in this type of collision the bridgeis primarily a hydrodynamic phenomenon. The amount of material pushedout into the splash bridge and how much of it comes from each galaxydepends on the relative orientation of the disks at impact. Thisorientation also affects how much bridge material accretes onto eachgalaxy. The onset of accretion is initially delayed but then acceleratesto a peak and declines thereafter in both galaxies. The infall isspatially asymmetric and is primarily located in well-defined streams.Most of the accreted gas ends up in the central regions of the modelgalaxies, but only after spiraling around the center and passing throughone or more shocks. Accretion heating is substantial, and is shown toinhibit or delay global star formation enhancements. The thermal effectsof the impact between galaxies are short-lived, but the models predictthat accretion and young star heating effect the global thermal phasebalance for a much longer period. The magnitude and duration of theseeffects also depend on the relative orientation of the disks at impact.Thus, the postcollision Hubble type of the companion is a sensitivefunction of initial orientation.

An Einstein X-Ray Survey of Optically Selected Galaxies. I. Data
We present the results of a complete Einstein imaging proportionalcounter X-ray survey of optically selected galaxies from theShapley-Ames Catalog, the Uppsala General Catalogue, and the EuropeanSouthern Observatory Catalog. Well-defined optical criteria are used toselect the galaxies, and X-ray fluxes are measured at the opticallydefined positions. The result is a comprehensive list of X-ray detectionand upper limit measurements for 1018 galaxies. Of these, 827 haveeither independent distance estimates or radial velocities. Associatedoptical, redshift, and distance data have been assembled for thesegalaxies, and their distances come from a combination of directlypredicted distances and those predicted from the Faber-Burstein GreatAttractor/Virgocentric infall model. The accuracy of the X-ray fluxeshas been checked in three different ways; all are consistent with thederived X-ray fluxes being of <=0.1 dex accuracy. In particular,there is agreement with previously published X-ray fluxes for galaxiesin common with a 1991 study by Roberts et al. and a 1992 study byFabbiano et al. The data presented here will be used in further studiesto characterize the X-ray output of galaxies of various morphologicaltypes and thus to enable the determination of the major sourcescontributing to the X-ray emission from galaxies.

The Detection of Massive Molecular Complexes in the Ring Galaxy System ARP 143
We have imaged the kiloparsec-scale distribution of 12CO( J=1--0 )emission in the ring galaxy system Arp 143 (NGC 2444/2445) using theOVRO millimeter array. We find two giant molecular complexes in the ringcomponent (NGC 2445) and a bright central source. The ring complexesrepresent 20%--60% of the detected M _{{H}2} , depending onthe relative ICO- N_{{H}2} for the ring and nucleus. Theirindividual H2 masses and surface densities ( Sigma _{{H}2} )exceed typical spiral arm giant molecular clouds and associationsregardless of the conversion factor. Both are associated with a 6 kpcridge of peak Sigma H I and massive star formation activity. Halpha imaging shows a patchy ring of H II regions situated along theouter edge of the H I ring. The kinematics of the H I ring show clearsigns of expansion. A simple rotating-expanding ring model (V_{{exp}}=118+/-30 {km} {s}^{-1} ) fits the data reasonably well, whichimplies a ring age of 60+/-15 Myr. NGC 2445's ring is able to form verylarge molecular complexes promptly in a metal-poor ISM and triggermassive star formation. Nearly 80% of the detected 12CO(1--0) fluxoriginates in a resolved central source that is slightly offset from NGC2445's starburst nucleus. We find an ordered velocity field in thiscomponent. Assuming an inclined disk, we argue that it is dynamicallystable. The central Sigma _{{H}2} (9 x 10 Msolar pc-2)significantly exceeds Sigma _{{H}2} values commonly found innormal spirals but is much smaller than values derived in similar sizedregions of IR-luminous galaxies. The nuclear H2 may be the result of aprevious encounter with NGC 2444. 12CO(1--0) emission in ring galaxiesmay be dominated by the nucleus, which could bias the interpretation ofsingle-dish measurements.

Collisional Ring Galaxies
We review the current state of knowledge of both the observational andtheoretical nature of collisional ring galaxies. Ring galaxies representa class of colliding galaxy in which nearly symmetrical density wavesare driven into a disk as a result of an almost bulls-eye collision withanother galaxy. Since the basic dynamics of the collision is now quitewell understood, the ring galaxies can be used as a form of cosmicperturbation "experiment" to explore various properties of galacticdisks. For example, as the density wave expands into the disk, ittriggers the birth of large numbers of massive stars. This provides uswith an opportunity to study the evolution of stars and star clusters inthe wake of the ring. We review the now extensive observations of ringgalaxies from the early photographic measurements to recent infrared,radio and optical studies. We also present a simple analytical treatmentof the ring-making collisions and compare them to recent N-body andgas-dynamical models. The importance of ring galaxies lies in theirrelative simplicity compared with other colliding systems and thepossibility that low-angular momentum collisions might have been morecommon in the past.

Classification of colliding galaxies
Not Available

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^.

Photoelectric UBV Photometry of 179 Bright Galaxies
This paper presents photoelectric UBV multiaperture photometry of 179bright galaxies that was used to compute total magnitudes and colorindices published in the Third Reference Catalog of Bright Galaxies(RC3). The observations were made at the McDonald Observatory from 1983December to 1986 September with an Amperex 56-DVP photometer attached tothe 0.76 and 0.91 m telescopes. The observations can also be used tocalibrate CCD images.

An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.

A multiparametric analysis of the Einstein sample of early-type galaxies. 1: Luminosity and ISM parameters
We have conducted bivariate and multivariate statistical analysis ofdata measuring the luminosity and interstellar medium of the Einsteinsample of early-type galaxies (presented by Fabbiano, Kim, &Trinchieri 1992). We find a strong nonlinear correlation betweenLB and LX, with a power-law slope of 1.8 +/- 0.1,steepening to 2.0 +/- if we do not consider the Local Group dwarfgalaxies M32 and NGC 205. Considering only galaxies with logLX less than or equal to 40.5, we instead find a slope of 1.0+/- 0.2 (with or without the Local Group dwarfs). Although E and S0galaxies have consistent slopes for their LB-LXrelationships, the mean values of the distribution functions of bothLX and LX/LB for the S0 galaxies arelower than those for the E galaxies at the 2.8 sigma and 3.5 sigmalevels, respectively. We find clear evidence for a correlation betweenLX and the X-ray color C21, defined by Kim,Fabbiano, & Trinchieri (1992b), which indicates that X-rayluminosity is correlated with the spectral shape below 1 keV in thesense that low-LX systems have relatively large contributionsfrom a soft component compared with high-LX systems. We findevidence from our analysis of the 12 micron IRAS data for our samplethat our S0 sample has excess 12 micron emission compared with the Esample, scaled by their optical luminosities. This may be due toemission from dust heated in star-forming regions in S0 disks. Thisinterpretation is reinforced by the existence of a strongL12-L100 correlation for our S0 sample that is notfound for the E galaxies, and by an analysis of optical-IR colors. Wefind steep slopes for power-law relationships between radio luminosityand optical, X-ray, and far-IR (FIR) properties. This last point arguesthat the presence of an FIR-emitting interstellar medium (ISM) inearly-type galaxies is coupled to their ability to generate nonthermalradio continuum, as previously argued by, e.g., Walsh et al. (1989). Wealso find that, for a given L100, galaxies with largerLX/LB tend to be stronger nonthermal radiosources, as originally suggested by Kim & Fabbiano (1990). We notethat, while LB is most strongly correlated withL6, the total radio luminosity, both LX andLX/LB are more strongly correlated with L6CO, the core radio luminosity. These points support the argument(proposed by Fabbiano, Gioia, & Trinchieri 1989) that radio cores inearly-type galaxies are fueled by the hot ISM.

The detection of molecular gas in the ring galaxy ARP 143
We have used the NRAO 12 m telescope to map the inner 10 kpc of NGC2445, the ring galaxy in Arp 143, in CO-12(J = 1-0). Emission is peakednear the ring galaxy nucleus, but we find evidence for an additionalasymmetric and extended CO component. This extended CO distribution isconsistent with an approximately 8 kpc diameter crescent-shaped ring ofmolecular gas, similar to the one seen in H I, accounting forapproximately half of the total CO flux. Assuming this distribution, wederive a total H2 mass for NGC 2445 of 0.4-2.4 x 1010 solarmass, depending on whether a Galactic or low-metallicity LargeMagellanic Cloud (LMC) conversion factor is used, and an H2/H I massratio between 0.9 and 5. The ring is experiencing low rates of massivestar formation despite very high gas column densities. We find that thegas surface density exceeds the critical threshold for star formationthroughout the ring, even without a possible contribution from asignificant molecular component. The absence of vigorous star formationis most simply understood in terms of its youth (approximately 30 Myr):massive stars have not had time to form in large numbers. Our resultssupport the interpretation that NGC 2445 is a nascent ring galaxy, seenprior to its ring starburst phase.

Integrated photoelectric magnitudes and color indices of bright galaxies in the Johnson UBV system
The photoelectric total magnitudes and color indices published in theThird Reference Catalogue of Bright Galaxies (RC3) are based on ananalysis of approximately equals 26,000 B, 25,000 B-V, and 17,000 U-Bmultiaperture measurements available up to mid 1987 from nearly 350sources. This paper provides the full details of the analysis andestimates of internal and external errors in the parameters. Thederivation of the parameters is based on techniques described by theVaucouleurs & Corwin (1977) whereby photoelectric multiaperture dataare fitted by mean Hubble-type-dependent curves which describe theintegral of the B-band flux and the typical B-V and U-B integrated colorgradients. A sophisticated analysis of the residuals of thesemeasurements from the curves was made to allow for the random andsystematic errors that effect such data. The result is a homogeneous setof total magnitudes BTA total colors(B-V)T and (U-B)T, and effective colors(B-V)e and (U-B)e for more than 3000 brightgalaxies in RC3.

The morphology of faint galaxies in Medium Deep Survey images using WFPC2
First results from Hubble Space Telescope (HST) Medium Deep Surveyimages taken with Wide Field/Planetary Camera-2 (WFPC2) demonstrate thatgalaxy classifications can be reliably performed to magnitudes I814approximately less than 22.0 in the F815W band. Published spectroscopicsurveys to this depth indicate a mean redshift of bar-z approximately0.5. We have classified over 200 galaxies in nine WFPC2 fields accordingto a basic morphological scheme. The majority of these faint galaxiesappear to be similar to regular Hubble-sequence examples observed at lowredshift. To the precision of our classification scheme, the relativeproportion of spheroidal and disk systems of normal appearance is asexpected from nearby samples, indicating that the bulk of the localgalaxy population was in place at half the Hubble time. However, themost intriguing result is the relatively high proportion (approximately40%) of objects which are in some way anomalous, and which may be ofrelevance in understanding the origin of the familiar excess populationof faint galaxies established by others. These diverse objects includeapparently interacting pairs whose multiple structure is only revealedwith HST's angular resolution, galaxies with superluminous star-formingregions, diffuse low surface brightness galaxies of various forms, andcompact galaxies. These anomalous galaxies contribute a substantialfraction of the excess counts at our limiting magnitude, and may provideinsights into the 'faint blue galaxy' problem.

A search for CO (1-0) emission from the tidal structures of interacting and merging galaxies
We have used the National Radio Astronomy Observatory (NRAO) 12 mtelescope to search for CO (J = 1 - 0) emission from the tidal tails ofsix merging or interacting galaxies. Although these plumes are H I-richand several contain star forming regions, they are undetected in CO tolow levels. The lack of strong CO emission from these plumes inconjunction with the presence of massive star formation is reminiscentof the situation in dwarf irregular galaxies, and the CO/H I limits areconsistent with those of dwarfs. The low CO brightness of these plumesmay be due either to a low proportion of molecular gas, or to a highN(H2)/ICO conversion factor.

A quasi-steady state cosmological model with creation of matter
A universe is envisioned in which there was a major creation episodewhen the mean universal density was about 10 to the -27 g/cu cm.Explicit equations are given for the creation of matter; in acosmological approximation, these equations lead to expressions for thetime-dependence of the cosmological scale factor S(t), but do notentail, as big bang cosmology does, that S(t) tend to zero at somefinite time t. The equations therefore possess a universality that isabsent from big bang cosmology. Creation occurs when certainconservation equations involving the gradient of a scalar field C(i) aresatisfied.

Submit a new article

Related links

  • - No Links Found -
Submit a new link

Member of following groups:

Observation and Astrometry data

Right ascension:07h46m53.00s
Aparent dimensions:1.148′ × 0.708′

Catalogs and designations:
Proper Names   (Edit)
NGC 2000.0NGC 2444

→ Request more catalogs and designations from VizieR