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

NGC 4470



Upload your image

DSS Images   Other Images

Related articles

The SAURON project - V. Integral-field emission-line kinematics of 48 elliptical and lenticular galaxies
We present the emission-line fluxes and kinematics of 48 representativeelliptical and lenticular galaxies obtained with our custom-builtintegral-field spectrograph, SAURON, operating on the William HerschelTelescope. Hβ, [OIII]λλ4959,5007 and[NI]λλ5198,5200 emission lines were measured using a newprocedure that simultaneously fits both the stellar spectrum and theemission lines. Using this technique we can detect emission lines downto an equivalent width of 0.1 Å set by the current limitations indescribing galaxy spectra with synthetic and real stellar templates,rather than by the quality of our spectra. Gas velocities and velocitydispersions are typically accurate to within 14 and 20 kms-1, respectively, and at worse to within 25 and 40 kms-1. The errors on the flux of the [OIII] and Hβ linesare on average 10 and 20 per cent, respectively, and never exceed 30 percent. Emission is clearly detected in 75 per cent of our samplegalaxies, and comes in a variety of resolved spatial distributions andkinematic behaviours. A mild dependence on the Hubble type and galacticenvironment is observed, with higher detection rates in lenticulargalaxies and field objects. More significant is the fact that only 55per cent of the galaxies in the Virgo cluster exhibit clearly detectedemission. The ionized-gas kinematics is rarely consistent with simplecoplanar circular motions. However, the gas almost never displayscompletely irregular kinematics, generally showing coherent motions withsmooth variations in angular momentum. In the majority of the cases, thegas kinematics is decoupled from the stellar kinematics, and in half ofthe objects this decoupling implies a recent acquisition of gaseousmaterial. Over the entire sample however, the distribution of the meanmisalignment values between stellar and gaseous angular momenta isinconsistent with a purely external origin. The distribution ofkinematic misalignment values is found to be strongly dependent on theapparent flattening and the level of rotational support of galaxies,with flatter, fast rotating objects hosting preferentially corotatinggaseous and stellar systems. In a third of the cases, the distributionand kinematics of the gas underscore the presence of non-axisymmetricperturbations of the gravitational potential. Consistent with previousstudies, the presence of dust features is always accompanied by gasemission while the converse is not always true. A considerable range ofvalues for the [OIII]/Hβ ratio is found both across the sample andwithin single galaxies. Despite the limitations of this ratio as anemission-line diagnostic, this finding suggests either that a variety ofmechanisms is responsible for the gas excitation in E and S0 galaxies orthat the metallicity of the interstellar material is quiteheterogeneous.

Low-Luminosity Active Galaxies and Their Central Black Holes
Central black hole masses for 117 spiral galaxies representingmorphological stages S0/a through Sc and taken from the largespectroscopic survey of Ho et al. are derived using Ks-banddata from the Two Micron All Sky Survey. Black hole masses are foundusing a calibrated black hole-Ks bulge luminosity relation,while bulge luminosities are measured by means of a two-dimensionalbulge-disk decomposition routine. The black hole masses are correlatedagainst a variety of parameters representing properties of the nucleusand host galaxy. Nuclear properties such as line width (FWHM [N II]), aswell as emission-line ratios (e.g., [O III]/Hβ, [O I]/Hα, [NII]/Hα, and [S II]/Hα), show a very high degree ofcorrelation with black hole mass. The excellent correlation with linewidth supports the view that the emission-line gas is in virialequilibrium with either the black hole or bulge potential. The very goodemission-line ratio correlations may indicate a change in ionizingcontinuum shape with black hole mass in the sense that more massiveblack holes generate harder spectra. Apart from theinclination-corrected rotational velocity, no excellent correlations arefound between black hole mass and host galaxy properties. Significantdifferences are found between the distributions of black hole masses inearly-, mid-, and late-type spiral galaxies (subsamples A, B, and C) inthe sense that early-type galaxies have preferentially larger centralblack holes, consistent with observations that Seyfert galaxies arefound preferentially in early-type systems. The line width distributionsshow a marked difference among subsamples A, B, and C in the sense thatearlier type galaxies have larger line widths. There are also cleardifferences in line ratios between subsamples A+B and C that likely arerelated to the level of ionization in the gas. Finally, aKs-band Simien & de Vaucouleurs diagram shows excellentagreement with the original B-band relation, although there is a largedispersion at a given morphological stage.

Ultraluminous X-Ray Sources in Nearby Galaxies from ROSAT High Resolution Imager Observations I. Data Analysis
X-ray observations have revealed in other galaxies a class ofextranuclear X-ray point sources with X-ray luminosities of1039-1041 ergs s-1, exceeding theEddington luminosity for stellar mass X-ray binaries. Theseultraluminous X-ray sources (ULXs) may be powered by intermediate-massblack holes of a few thousand Msolar or stellar mass blackholes with special radiation processes. In this paper, we present asurvey of ULXs in 313 nearby galaxies withD25>1' within 40 Mpc with 467 ROSAT HighResolution Imager (HRI) archival observations. The HRI observations arereduced with uniform procedures, refined by simulations that help definethe point source detection algorithm employed in this survey. A sampleof 562 extragalactic X-ray point sources withLX=1038-1043 ergs s-1 isextracted from 173 survey galaxies, including 106 ULX candidates withinthe D25 isophotes of 63 galaxies and 110 ULX candidatesbetween 1D25 and 2D25 of 64 galaxies, from which aclean sample of 109 ULXs is constructed to minimize the contaminationfrom foreground or background objects. The strong connection betweenULXs and star formation is confirmed based on the striking preference ofULXs to occur in late-type galaxies, especially in star-forming regionssuch as spiral arms. ULXs are variable on timescales over days to yearsand exhibit a variety of long term variability patterns. Theidentifications of ULXs in the clean sample show some ULXs identified assupernovae (remnants), H II regions/nebulae, or young massive stars instar-forming regions, and a few other ULXs identified as old globularclusters. In a subsequent paper, the statistic properties of the surveywill be studied to calculate the occurrence frequencies and luminosityfunctions for ULXs in different types of galaxies to shed light on thenature of these enigmatic sources.

Completing H I observations of galaxies in the Virgo cluster
High sensitivity (rms noise ˜ 0.5 mJy) 21-cm H I line observationswere made of 33 galaxies in the Virgo cluster, using the refurbishedArecibo telescope, which resulted in the detection of 12 objects. Thesedata, combined with the measurements available from the literature,provide the first set of H I data that is complete for all 355 late-type(Sa-Im-BCD) galaxies in the Virgo cluster with mp ≤ 18.0mag. The Virgo cluster H I mass function (HIMF) that was derived forthis optically selected galaxy sample is in agreement with the HIMFderived for the Virgo cluster from the blind HIJASS H I survey and isinconsistent with the Field HIMF. This indicates that both in this richcluster and in the general field, neutral hydrogen is primarilyassociated with late-type galaxies, with marginal contributions fromearly-type galaxies and isolated H I clouds. The inconsistency betweenthe cluster and the field HIMF derives primarily from the difference inthe optical luminosity function of late-type galaxies in the twoenvironments, combined with the HI deficiency that is known to occur ingalaxies in rich clusters.Tables \ref{t1, \ref{sample_dat} and Appendix A are only available inelectronic form at http://www.edpsciences.org

Tracing the star formation history of cluster galaxies using the Hα/UV flux ratio
Since the Hα and UV fluxes from galaxies are sensitive to stellarpopulations of ages <107 and ≈ 108 yrrespectively, their ratio f(Hα)/f(UV) provides us with a tool tostudy the recent t ≤ 108 yr star formation history ofgalaxies, an exercise that we present here applied to 98 galaxies in 4nearby clusters (Virgo, Coma, Abell 1367 and Cancer). The observedf(Hα)/f(UV) ratio is ˜ a factor of two smaller than theexpected one as determined from population synthesis models assuming arealistic delayed, exponentially declining star formation history. Wediscuss various mechanisms that may have affected the observedf(Hα)/f(UV) ratio and we propose that the above discrepancy arisesfrom either the absorption of Lyman continuum photons by dust within thestar formation regions or from the occurrence of star formationepisodes. After splitting our sample into different subsamples accordingto evolutionary criteria we find that our reference sample of galaxiesunaffected by the cluster environment show an average value off(Hα)/f(UV) two times lower than the expected one. We argue thatthis difference must be mostly due to absorption of ≈45% of the Lymancontinuum photons within star forming regions. Galaxies with clear signsof an ongoing interaction show average values of f(Hα)/f(UV)slightly higher than the reference value, as expected if those objectshad SFR increased by a factor of ≃4. The accuracy of the currentUV and Hα photometry is not yet sufficient to clearly disentanglethe effect of interactions on the f(Hα)/f(UV) ratio, butsignificant observational improvements are shortly expected to resultfrom the GALEX mission.Tables 1-3 are only available in electronic form athttp://www.edpsciences.org

UV and FIR selected samples of galaxies in the local Universe. Dust extinction and star formation rates
We have built two samples of galaxies selected at 0.2 μm (hereafterUV) and 60 μm (hereafter FIR) covering a sky area of 35.36deg2. The UV selected sample contains 25 galaxies brighterthan AB0.2=17. All of them, but one elliptical, are detectedat 60 μm with a flux density larger or equal to 0.2 Jy. The UV countsare significantly lower than the Euclidean extrapolation towardsbrighter fluxes of previous determinations. The FIR selected samplecontains 42 galaxies brighter than f60=0.6 Jy. Except fourgalaxies, all of them have a UV counterpart at the limiting magnitudeAB0.2=20.3 mag. The mean extinction derived from the analysisof the FIR to UV flux ratio is ˜1 mag for the UV selected sample and˜2 mag for the FIR selected one. For each sample we compare severalindicators of the recent star formation rate (SFR) based on the FIRand/or the UV emissions. We find linear relationships with slopes closeto unity between the different SFR indicator, which means that, over thewhole converting offset. Various absolute calibrations for both samplesare discussed in this paper. A positive correlation between extinctionand SFR is found when both samples are considered together although witha considerable scatter. A similar result is obtained when using the SFRnormalized to the optical surface of the galaxies.Tables 3, 4 and Fig. 1 are only available in electronic form athttp://www.edpsciences.org

Radio continuum spectra of galaxies in the Virgo cluster region
New radio continuum observations of galaxies in the Virgo cluster regionat 4.85, 8.6, and 10.55 GHz are presented. These observations arecombined with existing measurements at 1.4 and 0.325 GHz. The sampleincludes 81 galaxies where spectra with more than two frequencies couldbe derived. Galaxies that show a radio-FIR excess exhibit centralactivity (HII, LINER, AGN). The four Virgo galaxies with the highestabsolute radio excess are found within 2° of the centerof the cluster. Galaxies showing flat radio spectra also host activecenters. There is no clear trend between the spectral index and thegalaxy's distance to the cluster center.Figure 3 is only available in electronic form athttp://www.edpsciences.orgTable 3 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/1

Spectrophotometry of galaxies in the Virgo cluster. II. The data
Drift-scan mode (3600-6800 Å) spectra with 500

Companions of Bright Barred Shapley-Ames Galaxies
Companion galaxy environment for a subset of 78 bright and nearby barredgalaxies from the Shapley-Ames Catalog is presented. Among the spiralbarred galaxies, there are Seyfert galaxies, galaxies with circumnuclearstructures, galaxies not associated with any large-scale galaxy cloudstructure, galaxies with peculiar disk morphology (crooked arms), andgalaxies with normal disk morphology; the list includes all Hubbletypes. The companion galaxy list includes the number of companiongalaxies within 20 diameters, their Hubble type, and projectedseparation distance. In addition, the companion environment was searchedfor four known active spiral galaxies, three of them are Seyfertgalaxies, namely, NGC 1068, NGC 1097, and NGC 5548, and one is astarburst galaxy, M82. Among the results obtained, it is noted that theonly spiral barred galaxy classified as Seyfert 1 in our list has nocompanions within a projected distance of 20 diameters; six out of 10Seyfert 2 bar galaxies have no companions within 10 diameters, six outof 10 Seyfert 2 galaxies have one or more companions at projectedseparation distances between 10 and 20 diameters; six out of 12 galaxieswith circumnuclear structures have two or more companions within 20diameters.

Star formation rate in galaxies from UV, IR, and Hα estimators
Infrared (IR) luminosity of galaxies originating from dust thermalemission can be used as an indicator of the star formation rate (SFR).Inoue et al. (\cite{inoue00}, IHK) have derived a formula for theconversion from dust IR luminosity to SFR by using the following threequantities: the fraction of Lyman continuum luminosity absorbed by gas(f), the fraction of UV luminosity absorbed by dust (epsilon ), and thefraction of dust heating from old (ga 108 yr) stellarpopulations (eta ). We develop a method to estimate those threequantities based on the idea that the various way of SFR estimates fromultraviolet (UV) luminosity (2000 Å luminosity), Hαluminosity, and dust IR luminosity should return the same SFR. Afterapplying our method to samples of galaxies, the following results areobtained in our framework. First, our method is applied to a sample ofstar-forming galaxies, finding that f ~ 0.6, epsilon ~ 0.5, and eta ~0.4 as representative values. Next, we apply the method to a starburstsample, which shows larger extinction than the star-forming galaxysample. With the aid of f, epsilon , and eta , we are able to estimatereliable SFRs from UV and/or IR luminosities. Moreover, the Hαluminosity, if the Hα extinction is corrected by using the Balmerdecrement, is suitable for a statistical analysis of SFR, because thesame {correction factor for the Lyman continuum extinction (i.e. 1/f)}is applicable to both normal and starburst galaxies over all the rangeof SFR. The metallicity dependence of f and epsilon is also tested:Only the latter proves to have a correlation with metallicity. As anextension of our result, the local (z=0) comoving density of SFR can beestimated with our dust extinction corrections. We show that all UV,Hα , and IR comoving luminosity densities at z=0 give a consistentSFR per comoving volume ( ~ 3x 10-2h M_sun yr-1Mpc-3). Useful formulae for SFR estimate are listed.Tables 1 and 2, and Appendix A are only available in electronic form athttp://www.edpsciences.org

A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr ( or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5

Spectrophotometry of Galaxies in the Virgo Cluster. I. The Star Formation History
As a result of an extensive observational campaign targeting the VirgoCluster, we obtained integrated (drift-scan mode) optical spectra andmultiwavelength (UV, U, B, V, H) photometry for 124 and 330 galaxies,respectively, spanning the whole Hubble sequence, and withmp<=16(Mp<=-15). These data were combined toobtain galaxy Spectral Energy Distributions (SEDs) extending from 2000to 22000 Å. By fitting these SEDs with synthetic ones derivedusing Bruzual & Charlot population synthesis models we try toconstrain observationally the star formation history (SFH) of galaxiesin the rich cluster of galaxies nearest to us. Assuming a Salpeter IMFand an analytical form for the SFH, the fit free parameters are the age(T) of the star formation event, its characteristic timescale (τ),and the initial metallicity (Z). In this work we test the (simplistic)case in which all galaxies have a common age T=13 Gyr, exploring a SFHwith ``delayed'' exponential form (which we call ``a la Sandage''), thusallowing for an increasing SFR with time. This SFH is consistent withthe full range of observed SEDs, provided that the characteristictimescale τ is let free to vary between 0.1 (quasi-instantaneousburst) and 25 Gyr (increasing SFR) and Z between 1/50 and 2.5 Zsolar.Elliptical galaxies (including dEs) are best fitted with shorttimescales (τ~3 Gyr) and metallicity varying between 1/5 and Zsolar.The model metallicity is found to increase as a function of H-bandluminosity. Spiral galaxies require that both τ and metallicitycorrelate with H-band luminosity: low-mass Im+BCD have subsolar Z andτ>=10 Gyr, whereas giant spirals have solar metallicities andτ~3 Gyr, consistent with elliptical galaxies. Moreover, we find thatthe SFH of spiral galaxies in the Virgo Cluster depends upon thepresence at their interior of fresh gas capable of sustaining the starformation. In fact, the residuals of the τ vs. LHrelation depend significantly on the H I content. H I deficient galaxieshave shorter (up to a factor of 4) τ (truncated SFH) than spiralswith normal H I content. Based on observations collected at theObservatoire de Haute Provence (OHP) (France), operated by the CNRS,France, and at the European Southern Observatory (Chile) (programme66.B-0026).

The Three-dimensional Structure of the Virgo Cluster Region from Tully-Fisher and H I Data
The distances and H I contents of 161 spiral galaxies in the region ofthe Virgo cluster are used to gain insight into the complicatedstructure of this galaxy system. Special attention has been paid to theinvestigation of the suggestion presented in an earlier work that someperipheral Virgo groups may contain strongly gas-deficient spiralgalaxies. The three-dimensional galaxy distribution has been inferredfrom quality distance estimates obtained by averaging distance modulibased on the Tully-Fisher relationship taken from eight published datasets previously homogenized, resulting in a relation with a dispersionof 0.41 mag. Previous findings that the spiral distribution issubstantially more elongated along the line of sight than in the planeof the sky are confirmed by the current data. In addition, an importanteast-west disparity in this effect has been detected. The overallwidth-to-depth ratio of the Virgo cluster region is about 1:4, with themost distant objects concentrated in the western half. The filamentarystructure of the spiral population and its orientation are alsoreflected by the H I-deficient objects alone. The H I deficiency patternshows a central enhancement extending from ~16 to 22 Mpc inline-of-sight distance; most of this enhancement arises from galaxiesthat belong to the Virgo cluster proper. However, significant gasdeficiencies are also detected outside the main body of the cluster in aprobable group of galaxies at line-of-sight distances ~25-30 Mpc, lyingin the region dominated by the southern edge of the M49 subcluster andclouds W' and W, as well as in various foreground galaxies. In the Virgoregion, the H I content of the galaxies then is not a straightforwardindicator of cluster membership.

Hα surface photometry of galaxies in the Virgo cluster. IV. The current star formation in nearby clusters of galaxies
Hα +[NII] imaging observations of 369 late-type (spiral) galaxiesin the Virgo cluster and in the Coma/A1367 supercluster are analyzed,covering 3 rich nearby clusters (A1367, Coma and Virgo) and nearlyisolated galaxies in the Great-Wall. They constitute an opticallyselected sample (mp<16.0) observed with ~ 60 %completeness. These observations provide us with the current(T<107 yrs) star formation properties of galaxies that westudy as a function of the clustercentric projected distances (Theta ).The expected decrease of the star formation rate (SFR), as traced by theHα EW, with decreasing Theta is found only when galaxies brighterthan Mp ~ -19.5 are considered. Fainter objects show no orreverse trends. We also include in our analysis Near Infrared data,providing information on the old (T>109 yrs) stars. Puttogether, the young and the old stellar indicators give the ratio ofcurrently formed stars over the stars formed in the past, or``birthrate'' parameter b. For the considered galaxies we also determinethe ``global gas content'' combining HI with CO observations. We definethe ``gas deficiency'' parameter as the logarithmic difference betweenthe gas content of isolated galaxies of a given Hubble type and themeasured gas content. For the isolated objects we find that b decreaseswith increasing NIR luminosity. In other words less massive galaxies arecurrently forming stars at a higher rate than their giant counterpartswhich experienced most of their star formation activity at earliercosmological epochs. The gas-deficient objects, primarily members of theVirgo cluster, have a birthrate significantly lower than the isolatedobjects with normal gas content and of similar NIR luminosity. Thisindicates that the current star formation is regulated by the gaseouscontent of spirals. Whatever mechanism (most plausibly ram-pressurestripping) is responsible for the pattern of gas deficiency observed inspiral galaxies members of rich clusters, it also produces the observedquenching of the current star formation. A significant fraction of gas``healthy'' (i.e. with a gas deficiency parameter less than 0.4) andcurrently star forming galaxies is unexpectedly found projected near thecenter of the Virgo cluster. Their average Tully-Fisher distance isfound approximately one magnitude further away (muo = 31.77)than the distance of their gas-deficient counterparts (muo =30.85), suggesting that the gas healthy objects belong to a cloudprojected onto the cluster center, but in fact lying a few Mpc behindVirgo, thus unaffected by the dense IGM of the cluster. Based onobservations taken at the Observatorio Astronómico Nacional(Mexico), the OHP (France), Calar Alto and NOT (Spain) observatories.Table \ref{tab4} is only available in electronic form athttp://www.edpsciences.org

Hα surface photometry of galaxies in the Virgo cluster. II. Observations with the OHP and Calar Alto 1.2 m telescopes
We present Hα line imaging observations of 122 galaxies obtainedwith the 1.20 m telescopes of the Observatoire de Haute Provence (OHP)and of Calar Alto. The observed galaxies are mostly Virgo clustermembers (95), along with 10 objects in the Coma/A1367 supercluster, 6 inthe clusters A2197 and A2199, and 11 nearby galaxies taken as fillers.Hα +[NII] fluxes and equivalent widths, as well as images of allthe detected targets, are presented. Based on observations taken at theObservatoire de Haute Provence (OHP) (France), operated by the FrenchCNRS, and Calar Alto Observatory (Spain), operated by theMax-Planck-Institut für Astronomie (Heidelberg) jointly with theSpanish National Commission for Astronomy. Figure 1 is only available inelectronic form at http://www.edpsciences.org

Molecular gas in normal late-type galaxies
We present 12CO(J=1-0) line observations of 22 low-luminosityspiral galaxies in the Virgo cluster. These data, together with 244others available in the literature, allow us to build a large samplethat we use to study the molecular gas properties of galaxies spanning alarge range of morphological types and luminosities and belonging todifferent environments (clusters - field). The molecular gas content ofthe target galaxies is estimated using a luminosity-dependent X =N(H_2)/I(CO) conversion factor that has been calibrated on a sample ofnearby galaxies. X spans from ~ 1020 mol cm-2 (Kkm s-1)-1 in giant spirals to ~ 1021mol cm-2 (K km s-1)-1 in dwarfirregulars. The value of the X conversion factor is found consistentwith a value derived independently from dust masses estimated from FIRfluxes, with a metallicity-dependent dust to gas ratio. Therelationships between X and the UV radiation field (as traced by theHα +[NII]EW), the metallicity and the H band luminosity areanalysed. We show that the molecular gas contained in molecular cloudsor complexes is of the order of 15% of the total gas on average whateverthe luminosity or the Hubble type of the galaxies. We discuss therelation between the star formation rate and the molecular gas contentand estimate the average star formation efficiency of late-typegalaxies. Based on observations made with the 12-m National RadioAstronomical Observatory, Kitt Peak, Arizona.

Star formation and dust extinction in nearby star-forming and starburst galaxies
We study the star formation rate and dust extinction properties of asample of nearby star-forming galaxies as derived from Hα and UV (~ 2000 Å) observations and we compare them to those of a sample ofstarburst galaxies. The dust extinction in Hα is estimated fromthe Balmer decrement and the extinction in UV using the FIR to UV fluxratio or the attenuation law for starburst galaxies of Calzetti et al.(\cite{calzetti5}). The Hα and UV emissions are stronglycorrelated with a very low scatter for the star-forming objects and witha much higher scatter for the starburst galaxies. The Hα to UVflux ratio is found to be larger by a factor ~ 2 for the starburstgalaxies. We compare both samples with a purely UV selected sample ofgalaxies and we conclude that the mean Hα and UV properties ofnearby star-forming galaxies are more representative of UV-selectedgalaxies than starburst galaxies. We emphasize that the Hα to UVflux ratio is strongly dependent on the dust extinction: the positivecorrelation found between FHα/FUV andFFIR/FUV vanishes when the Hα and UV fluxare corrected for dust extinction. The Hα to UV flux ratiosconverted into star formation rate and combined with the Balmerdecrement measurements are tentatively used to estimate the dustextinction in UV.

An Ultraviolet/Optical Atlas of Bright Galaxies
We present wide-field imagery and photometry of 43 selected nearbygalaxies of all morphological types at ultraviolet and opticalwavelengths. The ultraviolet (UV) images, in two broad bands at 1500 and2500 Å, were obtained using the Ultraviolet Imaging Telescope(UIT) during the Astro-1 Spacelab mission. The UV images have ~3"resolution, and the comparison sets of ground-based CCD images (in oneor more of B, V, R, and Hα) have pixel scales and fields of viewclosely matching the UV frames. The atlas consists of multiband imagesand plots of UV/optical surface brightness and color profiles. Otherassociated parameters, such as integrated photometry and half-lightradii, are tabulated. In an appendix, we discuss the sensitivity ofdifferent wavebands to a galaxy's star formation history in the form of``history weighting functions'' and emphasize the importance of UVobservations as probes of evolution during the past 10-1000 Myr. We findthat UV galaxy morphologies are usually significantly different fromvisible band morphologies as a consequence of spatially inhomogeneousstellar populations. Differences are quite pronounced for systems in themiddle range of Hubble types, Sa through Sc, but less so for ellipticalsor late-type disks. Normal ellipticals and large spiral bulges arefainter and more compact in the UV. However, they typically exhibitsmooth UV profiles with far-UV/optical color gradients which are largerthan any at optical/IR wavelengths. The far-UV light in these cases isprobably produced by extreme horizontal branch stars and theirdescendants in the dominant, low-mass, metal-rich population. The coolstars in the large bulges of Sa and Sb spirals fade in the UV while hotOB stars in their disks brighten, such that their Hubble classificationsbecome significantly later. In the far-UV, early-type spirals oftenappear as peculiar, ringlike systems. In some spiral disks, UV-brightstructures closely outline the spiral pattern; in others, the disks canbe much more fragmented and chaotic than at optical wavelengths.Contributions by bright active galactic nuclei (AGNs) to the integratedUV light in our sample range from less than 10% to nearly 100%. A numberof systems have unusual UV-bright structures in their inner disks,including rings, compact knots, and starburst nuclei, which could easilydominate the UV light in high-redshift analogs. A significant butvariable fraction of the far-UV light in spiral disks is diffuse ratherthan closely concentrated to star-forming regions. Dust in normal spiraldisks does not control UV morphologies, even in some highly inclineddisk systems. The heaviest extinction is apparently confined to thinlayers and the immediate vicinity of young H II complexes; the UV lightemerges from thicker star distributions, regions evacuated of dust byphotodestruction or winds, or by virtue of strong dust clumpiness. Onlyin cases where the dust layers are disturbed does dust appear to be amajor factor in UV morphology. The UV-bright plume of M82 indicates thatdust scattering of UV photons can be important in some cases. In acompanion paper, we discuss far-UV data from the Astro-2 mission andoptical comparisons for another 35 galaxies, emphasizing face-onspirals.

Quantitative Morphology of Galaxies Observed in the Ultraviolet
We present a quantitative study of the far-ultraviolet (FUV) and opticalmorphology in 32 nearby galaxies and estimate the ``morphologicalk-correction'' expected if these objects were observed unevolved at highredshift. Using the common indices of central concentration (C) androtational asymmetry (A) to quantify morphology, we considerindependently two phenomena that give rise to this k-correction.Bandshifting, the decrease in the rest-frame wavelength of lightobserved through optical filters, is explored by measuring these indicesin several passbands for each galaxy, and it is found to be the primarydriver of changes in C and A. In general, the optical trend found fordecreasing C and increasing A when going to shorter wavelengths extendsto the FUV. However, the patchy nature of recent star formation inlate-type galaxies, which is accentuated in the FUV, results in poorquantitative correspondence between morphologies determined in theoptical and FUV. We then artificially redshift our FUV images into theHubble Deep Field (HDF) filters to simulate various cosmologicaldistance effects, such as surface brightness dimming and loss of spatialresolution. Hubble types of many galaxies in our sample are not readilyidentifiable at redshifts beyond z~1, and the galaxies themselves aredifficult to detect beyond z~3. Because only features of the highestsurface brightness remain visible at cosmological distances, the changein C and A between simulated high-z galaxies and their unredshiftedcounterparts depends on whether their irregular features are primarilybright or faint. Our simulations suggest that k-corrections alone areindeed capable of producing the peculiar morphologies observed at highredshift; for example, several spiral galaxies have C and A indicestypical of irregular or peculiar HDF objects viewed at z>=2. Webriefly discuss some elements of a scheme to classify rest-frame UVimages, mergers, protogalaxies, and other objects for which classicalHubble types do not adequately encompass the existing morphology.

A ROSAT High Resolution Imager survey of bright nearby galaxies
We use the extensive public archive of ROSAT High Resolution Imager(HRI) observations to carry out a statistical investigation of the X-rayproperties of nearby galaxies. Specifically we focus on the sample of486 bright (BT<=12.5) northern galaxies studied by Ho,Filippenko and Sargent (HFS) in the context of their exploration of theoptical spectroscopic properties of nearby galactic nuclei. Over 20percent of HFS galaxies are encompassed in ROSAT HRI fields of reasonable(>=10ks) exposure. The X-ray sources detected within the opticalextent of each galaxy are categorized as either nuclear or non-nuclear,depending on whether the source is positioned within or outside a25-arcsec radius circle centred on the optical nucleus. A nuclear X-raysource is detected in over 70per cent of the galaxies harbouring eithera Seyfert or LINER nucleus, compared with a detection rate of only~40per cent in less active systems. The correlation of the Hαluminosity with nuclear X-ray luminosity previously observed in QSOs andbright Seyfert 1 galaxies appears to extend down into the regime ofultra-low luminosity(LX~1038-1040ergs-1) activegalactic nuclei (AGN). The inferred accretion rates for this sample oflow-luminosity AGN are significantly sub-Eddington. In total, 142non-nuclear sources were detected. In combination with published datafor M31, this leads to a luminosity distribution (normalized to anoptical blue luminosity of 1010Lsolar) for thediscrete X-ray source population in spiral galaxies of the formdN/dL38 = (1.0 ± 0.2)L-1.838where L38 is the X-ray luminosity in units of1038ergs-1. The implied LXLBratio is ~1.1×1039ergs-1(1010Lsolar)-1. The nature ofthe substantial number of `superluminous' non-nuclear objects detectedin the survey is discussed.

The Nature of Composite LINER/H II Galaxies as Revealed from High-Resolution VLA Observations
A sample of 37 nearby galaxies displaying composite LINER/H II and pureH II spectra was observed with the VLA in an investigation of the natureof their weak radio emission. The resulting radio contour maps overlaidon optical galaxy images are presented here, together with an extensiveliterature list and discussion of the individual galaxies. Radiomorphological data permit assessment of the ``classical active galacticnucleus (AGN)'' contribution to the global activity observed in these``transition'' LINER galaxies. One in five of the latter objects displayclear AGN characteristics: these occur exclusively in bulge-dominatedhosts.

1.65 ^mum (H-band) surface photometry of galaxies. IV. observations of 170 galaxies with the Calar Alto 2.2 m telescope
We present near-infrared (H band) surface photometry of 170 galaxies,obtained in 1997 using the Calar Alto 2.2 m telescope equipped with theNICMOS3 camera MAGIC. The majority of our targets are selected amongbright members of the Virgo cluster, however galaxies in the A262 andCancer clusters and in the Coma/A1367 supercluster are also included.This data set is aimed at complementing the NIR survey in the Virgocluster discussed in \cite[Boselli et al. (1997)]{B97} and in the ComaSupercluster, presented in Papers I, II and III of this series.Magnitudes at the optical radius, total magnitudes, isophotal radii andlight concentration indices are derivedTables 1 and 2 (full version) are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/Abstract.html.Based on observations taken at the Calar Alto Observatory, operated bythe Max-Planck-Institut für Astronomie (Heidelberg) jointly withthe Spanish National Commission for Astronomy.

1.65 μm (H-band) surface photometry of galaxies. V. Profile decomposition of 1157 galaxies
We present near-infrared H-band (1.65 μm) surface brightness profiledecomposition for 1157 galaxies in five nearby clusters of galaxies:Coma, A1367, Virgo, A262 and Cancer, and in the bridge between Coma andA1367 in the ``Great Wall". The optically selected (mpg≤16.0) sample is representative of all Hubble types, from E to Irr+BCD,except dE and of significantly different environments, spanning fromisolated regions to rich clusters of galaxies. We model the surfacebrightness profiles with a de Vaucouleurs r1/4 law (dV), withan exponential disk law (E), or with a combination of the two (B+D).From the fitted quantities we derive the H band effective surfacebrightness (μe) and radius (re) of each component, theasymptotic magnitude HT and the light concentration indexC31. We find that: i) Less than 50% of the Ellipticalgalaxies have pure dV profiles. The majority of E to Sb galaxies is bestrepresented by a B+D profile. All Scd to BCD galaxies have pureexponential profiles. ii) The type of decomposition is a strong functionof the total H band luminosity (mass), independent of the Hubbleclassification: the fraction of pure exponential decompositionsdecreases with increasing luminosity, that of B+D increases withluminosity. Pure dV profiles are absent in the low luminosity rangeLH<1010 L\odot and become dominantabove 1011 L\odot . Based on observations taken atTIRGO, Gornergrat, Switzerland (operated by CAISMI-CNR, Arcetri,Firenze, Italy) and at the Calar Alto Observatory (operated by theMax-Planck-Institut für Astronomie (Heidelberg) jointly with theSpanish National Commission for Astronomy). Table 2 and Figs. 2, 3, 4are available in their entirety only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/Abstract.html

The QDOT all-sky IRAS galaxy redshift survey
We describe the construction of the QDOT survey, which is publiclyavailable from an anonymous FTP account. The catalogue consists ofinfrared properties and redshifts of an all-sky sample of 2387 IRASgalaxies brighter than the IRAS PSC 60-μm completeness limit(S_60>0.6Jy), sparsely sampled at a rate of one-in-six. At |b|>10deg, after removing a small number of Galactic sources, the redshiftcompleteness is better than 98per cent (2086/2127). New redshifts for1401 IRAS sources were obtained to complete the catalogue; themeasurement and reduction of these are described, and the new redshiftstabulated here. We also tabulate all sources at |b|>10 deg with noredshift so far, and sources with conflicting alternative redshiftseither from our own work, or from published velocities. A list of 95ultraluminous galaxies (i.e. with L_60μm>10^12 L_solar) is alsoprovided. Of these, ~20per cent are AGN of some kind; the broad-lineobjects typically show strong Feii emission. Since the publication ofthe first QDOT papers, there have been several hundred velocity changes:some velocities are new, some QDOT velocities have been replaced by moreaccurate values, and some errors have been corrected. We also present anew analysis of the accuracy and linearity of IRAS 60-μm fluxes. Wefind that the flux uncertainties are well described by a combination of0.05-Jy fixed size uncertainty and 8per cent fractional uncertainty.This is not enough to cause the large Malmquist-type errors in the rateof evolution postulated by Fisher et al. We do, however, find marginalevidence for non-linearity in the PSC 60-μm flux scale, in the sensethat faint sources may have fluxes overestimated by about 5per centcompared with bright sources. We update some of the previous scientificanalyses to assess the changes. The main new results are as follows. (1)The luminosity function is very well determined overall but is uncertainby a factor of several at the very highest luminosities(L_60μm>5x10^12L_solar), as this is where the remainingunidentified objects are almost certainly concentrated. (2) Thebest-fitting rate of evolution is somewhat lower than our previousestimate; expressed as pure density evolution with density varying as(1+z)^p, we find p=5.6+/-2.3. Making a rough correction for the possible(but very uncertain) non-linearity of fluxes, we find p=4.5+/-2.3. (3)The dipole amplitude decreases a little, and the implied value of thedensity parameter, assuming that IRAS galaxies trace the mass, isΩ=0.9(+0.45, -0.25). (4) Finally, the estimate of density varianceon large scales changes negligibly, still indicating a significantdiscrepancy from the predictions of simple cold dark matter cosmogonies.

The 3D structure of the Virgo cluster from H-band Fundamental Plane and Tully-Fisher distance determinations
We undertook a surface photometry survey of 200 galaxies in the Virgocluster (complete to B<14.0 mag) carried out in the near-infrared(NIR) H band. Combining velocity dispersion measurements from theliterature with new spectroscopic data for 11 galaxies, we derivedistances of 59 early-type galaxies using the Fundamental Plane (FP)method. The distances of another 75 late-type galaxies are determinedusing the Tully-Fisher (TF) method. For this purpose we use the maximumrotational velocity, as derived from HI spectra from the literature,complemented with new Hα rotation curves of eight highlyHI-deficient galaxies. The zero-points of the FP and TF templaterelations are calibrated assuming the distance modulus of Virgomu_0=31.0, as determined with the Cepheids method. Using these 134distance determinations (with individual uncertainties of 0.35 mag (TF)and 0.45 mag (FP)) we find that the distance of cluster A, associatedwith M87, is mu_0=30.84 +/- 0.06. Cluster B, offset to the south, isfound at mu_0=31.84 +/- 0.10. This subcluster is falling on to A atabout 750 km s^-1. Clouds W and M are at twice the distance of A.Galaxies on the north-west and south-east of the main cluster A belongto two clouds composed almost exclusively of spiral galaxies withdistances consistent with A, but with significantly different velocitydistributions, suggesting that they are falling on to cluster A atapproximately 770 km s^-1 from the far side and at 200 km s^-1 from thenear side respectively. The mass of Virgo inferred from the peculiarmotions induced on its vicinity is consistent with the virialexpectation.

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.

On the local radio luminosity function of galaxies. I. The Virgo cluster
We cross-correlate the galaxies brighter than m_B=18 in the Virgocluster with the radio sources in the NVSS survey (1.4 GHz), resultingin 180 radio-optical identifications. We determine the radio luminosityfunction of the Virgo galaxies, separately for the early- andlate-types. Late-type galaxies develop radio sources with a probabilityproportional to their optical luminosity. In fact their radio/optical(R_B) distribution is gaussian, centered at log R_B ~ -0.5, i.e. theradio luminosity is ~ 0.3 of the optical one. The probability oflate-type galaxies to develop radio sources is almost independent oftheir detailed Hubble type, except for Sa (and S0+S0a) which are afactor of ~ 5 less frequent than later types at any R_B. Giantelliptical galaxies feed ``monster" radio sources with a probabilitystrongly increasing with mass. However the frequency of fainter radiosources is progressively less sensitive on the system mass. The faintestgiant E galaxies (M_B=-17) have a probability of feeding low power radiosources similar to that of dwarf E galaxies as faint as M_B=-13. Table~1is only available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/Abstract.html

A Complete Redshift Survey to the Zwicky Catalog Limit in a 2^h X 15 deg Region around 3C 273
We compile 1113 redshifts (648 new measurements, 465 from theliterature) for Zwicky catalog galaxies in the region (-3.5d <= delta<= 8.5d, 11h5 <= alpha <= 13h5). We include redshifts for 114component objects in 78 Zwicky catalog multiplets. The redshift surveyin this region is 99.5% complete to the Zwicky catalog limit, m_Zw =15.7. It is 99.9% complete to m_Zw = 15.5, the CfA Redshift Survey(CfA2) magnitude limit. The survey region is adjacent to the northernportion of CfA2, overlaps the northernmost slice of the Las CampanasRedshift Survey, includes the southern extent of the Virgo Cluster, andis roughly centered on the QSO 3C 273. As in other portions of theZwicky catalog, bright and faint galaxies trace the same large-scalestructure.

The Virgo Cluster Distance from 21 Centimeter Line Widths
The distance of the Virgo cluster is derived in the B band from the 21cm line width-absolute magnitude relation. This relation is calibratedusing 18 spirals with Cepheid distances, mainly from the Hubble SpaceTelescope. The calibration is applied to a complete sample ofnonpeculiar spirals with i > 45 deg lying within the optical (n = 49)or X-ray (n = 35) contour of the cluster, resulting in a mean clusterdistance of (m - M)0 = 31.58 +/- 0.24 mag (external error), or 20.7 +/-2.4 Mpc. The mean distance of subcluster A is 0.46 +/- 0.18 mag smallerthan that of subcluster B, but the individual distances of the membersof the two substructures show considerable overlap. Cluster spirals with30 deg < i < 45 deg yield distances almost as good as those ofmore inclined galaxies. H I-truncated galaxies are overluminous by 0.8mag at a given line width. The distance modulus is corrected by -0.07mag for the fact that cluster members have lower H I surface fluxes andare redder in (B-I) at a given line width than the (field) calibrators.Different sources for the B magnitudes and line widths have littleeffect on the resulting distance. Different precepts for the internalabsorption correction change the result by no more than +/-0.17 mag. Theindividual distances of the cluster members do not show any dependenceon recession velocity, inclination, Hubble type, or line width. Thedependence on apparent magnitude reflects the considerable depth effectof the cluster. The adopted distance is in good agreement withindependent distance determinations of the cluster. Combining thecluster distance with the corrected cluster velocity of 1142 +/- 61 kms-1 gives H0 = 55 +/- 7 km s-1 Mpc-1 (external error). If the Virgocluster distance is inserted into the tight Hubble diagram of clustersout to 11,000 km s-1 using relative distances to the Virgo cluster, oneobtains a global value of H0 = 57 +/- 7 km s-1 Mpc-1.

Groups of galaxies. III. Some empirical characteristics.
Not Available

Submit a new article

Related links

  • - No Links Found -
Submit a new link

Member of following groups:

Observation and Astrometry data

Right ascension:12h29m37.80s
Aparent dimensions:1.288′ × 0.891′

Catalogs and designations:
Proper Names   (Edit)
NGC 2000.0NGC 4470
J/AJ/90/1681VCC 1205

→ Request more catalogs and designations from VizieR