Contenidos
Imágenes
Subir su imagen
DSS Images Other Images
Artículos relacionados
Scale Heights of Non-Edge-on Spiral Galaxies
We present a method of calculating the scale height of non-edge-onspiral galaxies, together with a formula for errors. The method is basedon solving Poisson's equation for a logarithmic disturbance of matterdensity in spiral galaxies. We show that the spiral arms can not extendto inside the ``forbidden radius'' r0, due to the effect ofthe finite thickness of the disk. The method is tested by re-calculatingthe scale heights of 71 northern spiral galaxies previously calculatedby Ma, Peng & Gu. Our results differ from theirs by less than 9%. Wealso present the scale heights of a further 23 non-edge-on spiralgalaxies.
| The Structural Properties of Isolated Galaxies, Spiral-Spiral Pairs, and Mergers: The Robustness of Galaxy Morphology during Secular Evolution
We present a structural analysis of nearby galaxies in spiral-spiralpairs in optical BVRI bands and compare them with the structures ofisolated spiral galaxies and galaxies in ongoing mergers. We use thesecomparisons to determine how galaxy structure changes during galaxyinteractions and mergers. We analyze light concentration (C), asymmetry(A), and clumpiness (S) parameters, and use the projections of CASparameter space to compare these samples. We find that the CASparameters of paired galaxies are correlated with the projectedseparations of the pair. For the widest and closest pairs, the CASparameters tend to be similar to those of isolated and ongoing majormergers (e.g., ultraluminous infrared galaxies), respectively. Ourresults imply that galaxy morphology is a robust property that onlychanges significantly during a strong interaction or major merger. Thetypical timescale for this change in our paired sample, based ondynamical friction arguments, is short, τ~0.1-0.5 Gyr. We findaverage enhancement factors for the spiral-pair asymmetries andclumpiness values of ~2.2 and 1.5. The S parameter, which is related tostar formation (SF) activity, has a moderate level of enhancement,suggesting that this activity in modern spirals depends more on internalprocesses than on external conditions. We further test the statisticalcriterion for picking up interacting galaxies in an automated way byusing the A-S projection plane. The diversity of our spiral-pair samplein the CAS space suggests that structural/SF/morphological properties ofinteracting galaxies change abruptly only when the interaction becomesvery strong and the criteria given previously by Conselice for findinggalaxies involved in major mergers are effective.
| On the alignment between binary spiral galaxies
We show some significance against the null hypothesis of randominteractions of binary spiral galaxies, and in favour of the alternativethat more interactions than expected occur for axes either nearlyparallel (spins being parallel or anti-parallel) or nearly orthogonal.We discuss this in the context of similar prior studies, using adifferent statistical focus in such a way that we are able toincorporate additional data.
| Studies of Extragalactic Formaldehyde and Radio Recombination Lines
We present the most sensitive and extensive survey yet performed ofextragalactic H2CO 6 cm (4.829 GHz) emission/absorption.Sixty-two sources were observed with the C-band system of the AreciboTelescope to a 1 σ rms noise level of ~0.3 mJy. We report a newdetection of H2CO 6 cm absorption toward NGC 520 and theconfirmation of H2CO 6 cm absorption toward several sources.We report confirmation of H2CO 6 cm emission toward the OHmegamasers Arp 220, IC 860, and IRAS 15107+0724. At present these arethe only extragalactic H2CO 6 cm emitters independentlyconfirmed. A characterization of the properties of formaldehydeabsorbers and emitters based on infrared properties of the galaxies isdiscussed. We also conducted a simultaneous survey of the H110αhydrogen recombination line toward a sample of 53 objects. We report thedetection of H110α toward the giant extragalactic H II region NGC604 in M33.
| Properties of isolated disk galaxies
We present a new sample of northern isolated galaxies, which are definedby the physical criterion that they were not affected by other galaxiesin their evolution during the last few Gyr. To find them we used thelogarithmic ratio, f, between inner and tidal forces acting upon thecandidate galaxy by a possible perturber. The analysis of thedistribution of the f-values for the galaxies in the Coma cluster leadus to adopt the criterion f ≤ -4.5 for isolated galaxies. Thecandidates were chosen from the CfA catalog of galaxies within thevolume defined by cz ≤5000 km s-1, galactic latitudehigher than 40o and declination ≥-2.5o. Theselection of the sample, based on redshift values (when available),magnitudes and sizes of the candidate galaxies and possible perturberspresent in the same field is discussed. The final list of selectedisolated galaxies includes 203 objects from the initial 1706. The listcontains only truly isolated galaxies in the sense defined, but it is byno means complete, since all the galaxies with possible companions underthe f-criterion but with unknown redshift were discarded. We alsoselected a sample of perturbed galaxies comprised of all the diskgalaxies from the initial list with companions (with known redshift)satisfying f ≥ -2 and \Delta(cz) ≤500 km s-1; a totalof 130 objects. The statistical comparison of both samples showssignificant differences in morphology, sizes, masses, luminosities andcolor indices. Confirming previous results, we found that late spiral,Sc-type galaxies are, in particular, more frequent among isolatedgalaxies, whereas Lenticular galaxies are more abundant among perturbedgalaxies. Isolated systems appear to be smaller, less luminous and bluerthan interacting objects. We also found that bars are twice as frequentamong perturbed galaxies compared to isolated galaxies, in particularfor early Spirals and Lenticulars. The perturbed galaxies have higherLFIR/LB and Mmol/LB ratios,but the atomic gas content is similar for the two samples. The analysisof the luminosity-size and mass-luminosity relations shows similartrends for both families, the main difference being the almost totalabsence of big, bright and massive galaxies among the family of isolatedsystems, together with the almost total absence of small, faint and lowmass galaxies among the perturbed systems. All these aspects indicatethat the evolution induced by interactions with neighbors would proceedfrom late, small, faint and low mass Spirals to earlier, bigger, moreluminous and more massive spiral and lenticular galaxies, producing atthe same time a larger fraction of barred galaxies but preserving thesame relations between global parameters. The properties we found forour sample of isolated galaxies appear similar to those of high redshiftgalaxies, suggesting that the present-day isolated galaxies could bequietly evolved, unused building blocks surviving in low densityenvironments.Tables \ref{t1} and \ref{t2} are only available in electronic form athttp://www.edpsciences.org
| Tidally Triggered Star Formation in Close Pairs of Galaxies. II. Constraints on Burst Strengths and Ages
Galaxy-galaxy interactions rearrange the baryons in galaxies and triggersubstantial star formation; the aggregate effects of these interactionson the evolutionary histories of galaxies in the universe are poorlyunderstood. We combine B- and R-band photometry and optical spectroscopyto estimate the strengths and timescales of bursts of triggered starformation in the centers of 190 galaxies in pairs and compact groups.Based on an analysis of the measured colors and EW(Hα), wecharacterize the preexisting and triggered populations separately. Thebest-fitting burst scenarios assume stronger reddening corrections forline emission than for the continuum and continuous star formationlasting for >~100 Myr. The most realistic scenarios require aninitial mass function that is deficient in the highest mass stars. Thecolor of the preexisting stellar population is the most significantsource of uncertainty. Triggered star formation contributessubstantially (probably >~50%) to the R-band flux in the centralregions of several galaxies; tidal tails do not necessarily accompanythis star formation. Many of the galaxies in our sample have bluercenters than outskirts, suggesting that pre- or nonmerger interactionsmay lead to evolution along the Hubble sequence. These objects wouldappear blue and compact at higher redshifts; the older, redder outskirtsof the disks would be difficult to detect. Our data indicate thatgalaxies with larger separations on the sky contain weaker, and probablyolder, bursts of star formation on average. However, confirmation ofthese trends requires further constraints on the colors of the olderstellar populations and on the reddening for individual galaxies.
| Homogenization of the Stellar Population along Late-Type Spiral Galaxies
We present a study of the broadband UBV color profiles for 257 Sbcbarred and nonbarred galaxies, using photoelectric aperture photometrydata from the literature. Using robust statistical methods, we haveestimated the color gradients of the galaxies, as well as the total andbulge mean colors. A comparative photometric study using CCD images wasdone. In our sample, the color gradients are negative (reddish inward)in approximately 59% of the objects, are almost null in 27%, and arepositive in 14%, considering only the face-on galaxies, which representapproximately 51% of the sample. The results do not change, essentially,when we include the edge-on galaxies. As a consequence of this study wehave also found that barred galaxies are overrepresented among theobjects having null or positive gradients, indicating that bars act as amechanism of homogenization of the stellar population. This effect ismore evident in the U-B color index, although it can also be detected inthe B-V color. A correlation between the total and bulge colors wasfound that is a consequence of an underlying correlation between thecolors of bulges and disks found by other authors. Moreover, the meantotal color is the same irrespective of the gradient regime, whilebulges are bluer in galaxies with null or positive gradients, whichindicates an increase of the star formation rate in the central regionsof these objects. We have also made a quantitative evaluation of theamount of extinction in the center of these galaxies. This was doneusing the Wide Field Planetary Camera 2 (WFPC2) and the Near InfraredCamera and Multi-Object Spectrometer (NICMOS) Hubble Space Telescope(HST) archival data, as well as CCD B, V, and I images. We show thatalthough the extinction in the V-band can reach values up to 2 mag inthe central region, it is unlikely that dust plays a fundamental role inglobal color gradients. We found no correlation between color and O/Habundance gradients. This result could suggest that the color gradientsare more sensitive to the age rather than to the metallicity of thestellar population. However, the absence of this correlation may becaused by dust extinction. We discuss this result by considering apicture in which bars are a relatively fast, recurrent phenomenon. Theseresults are not compatible with a pure classical monolithic scenario forbulge and disk formation. On the contrary, they favor a scenario inwhich both these components are evolving in a correlated process inwhich stellar bars play a crucial role. Based partly on observationsmade at the Pico dos Dias Observatory (PDO/LNA-CNPq), Brazil.
| BVRI surface photometry of (S+S) binary galaxies I. The data
We present multicolour broad band (BVRI) photometry for a sample of 33spiral-spiral (S+S) binary galaxies drawn from the KarachentsevCatalogue of Isolated Pairs of Galaxies (KPG). The data is part of ajoint observational programme devoted to systematic photometric study ofone of the most complete and homogeneous pair samples available in theliterature. We present azimuthally averaged colour and surfacebrightness profiles, colour index (B-I) maps, B band and sharp/filteredB band images as well as integrated magnitudes, magnitudes at differentcircular apertures and integrated colours for each pair. Internal andexternal data comparisons show consistency within the estimated errors.Two thirds of the sample have total aperture parameters homogeneouslyderived for the first time. After reevaluating morphology for all thepairs, we find a change in Hubble type for 24 galaxies compared to theoriginal POSS classifications. More than half of our pairs showmorphological concordance which could explain, in part, the strongcorrelation in the (B-V) colour indices (Holmberg Effect) between paircomponents. We find a tendency for barred galaxies to show grand designmorphologies and flat colour profiles. The measurements will be used ina series of forthcoming papers where we try to identify and isolate themain structural and photometric properties of disk galaxies at differentstages of interaction. Table A.1 is only available in electronic form atthe CDS via anonymous ftp cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/379/54 and Tables 2-4 arealso available in electronic form at the CDS. Full Fig. 5 is onlyavailable in electronic form at the http://www.edpsciences.org Based ondata obtained at the 2.1 m telescope of the Observatorio Guillermo Haroat Cananea, Sonora, México, operated by the Instituto Nacional deAstrofísica, Optica y Electrónica.
| The 1.0 Megaparsec Galaxy Pair Sample in Low-Density Regions
Using complete redshift catalogs, we have compiled a list of galaxypairs based solely on a pair's projected separation, rp, andvelocity difference, ΔV. We have made high-velocity precision H Iobservations of each galaxy in the sample and have reported these in theliterature. Due to the nature of the redshift catalogs, we are able toquantitatively evaluate the effects of isolation and number density ofsurrounding galaxies on each pair in the sample. For the close galaxypairs (rp<100 kpc), the degree of isolation (a measure ofthe number of near neighbors) has little effect on the median ΔV.This median is about 55 km s-1 for the 25 close pairs (ifmedium-density close pairs are omitted ΔV is even smaller, but thedifference is not statistically significant). The effect of isolation isstrong for the entire sample of galaxy pairs with separations as largeas 1.0 Mpc. For these larger separation pairs, relaxation of strictisolation requirements introduces small groups into the sample, whichdramatically increases the median ΔV. We find little evidence ofan increase in the median ΔV with decreasing rp, norwith increasing total luminosity. For our isolated pairs in low-densityregions, the overall median ΔV is only 30 km s-1. Forsimilar separations and isolation criteria, galaxy satellites withlarger luminosity ratios (i.e., less dynamical friction) in higherdensity regions have ΔV approximately twice as large. Weconjecture that our orbits are highly eccentric, so that the indirecteffect of dynamical friction leads to predominantly small ΔV.However, the halos of our galaxies may also be of low density (althoughhighly extended).
| 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.
| Box- and peanut-shaped bulges. I. Statistics
We present a classification for bulges of a complete sample of ~ 1350edge-on disk galaxies derived from the RC3 (Third Reference Catalogue ofBright Galaxies, de Vaucouleurs et al. \cite{rc3}). A visualclassification of the bulges using the Digitized Sky Survey (DSS) inthree types of b/p bulges or as an elliptical type is presented andsupported by CCD images. NIR observations reveal that dust extinctiondoes almost not influence the shape of bulges. There is no substantialdifference between the shape of bulges in the optical and in the NIR.Our analysis reveals that 45% of all bulges are box- and peanut-shaped(b/p). The frequency of b/p bulges for all morphological types from S0to Sd is > 40%. In particular, this is for the first time that such alarge frequency of b/p bulges is reported for galaxies as late as Sd.The fraction of the observed b/p bulges is large enough to explain theb/p bulges by bars. Partly based on observations collected at ESO/LaSilla (Chile), DSAZ/Calar Alto (Spain), and Lowell Observatory/Flagstaff(AZ/U.S.A.). Tables 6 and 7 are only available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Box- and peanut-shaped bulges. II. NIR observations
We have observed 60 edge-on galaxies in the NIR in order to study thestellar distribution in galaxies with box/peanut-shaped bulges. The muchsmaller amount of dust extinction at these wavelengths allows us toidentify in almost all target galaxies with box/peanut-shaped bulges anadditional thin, central component in cuts parallel to the major axis.This structure can be identified with a bar. The length of thisstructure scaled by the length of the bulge correlates with themorphologically classified shape of the bulge. This newly establishedcorrelation is therefore mainly interpreted as the projection of the barat different aspect angles. Galaxies with peanut bulges have a bar seennearly edge-on and the ratio of bar length to thickness, 14 +/- 4, canbe directly measured for the first time. In addition, the correlation ofthe boxiness of bulges with the bar strength indicates that the barcharacteristic could partly explain differences in the bulge shape.Furthermore, a new size relation between the box/peanut structure andthe central bulge is found. Our observations are discussed in comparisonto a N-body simulation for barred galaxies (Pfenniger & Friedli\cite{pfe}). We conclude that the inner region of barred disk galaxiesare build up by three distinct components: the spheroidal bulge, a thinbar, and a b/p structure most likely representing the thick part of thebar. Based on observations collected at ESO/La Silla (61.A-0143),DSAZ/Calar Alto, and TIRGO/Gornergrat.}
| 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 Subarcsecond-Resolution Near-Infrared Study of Seyfert and ``Normal'' Galaxies. I. Imaging Data
We present new high-resolution near-infrared observations in the J, H,and K bands, obtained to study the properties of Seyfert host galaxies.The data set consists of images in the three bands of practically theentire CfA sample of Seyfert galaxies, and K-band images of a controlsample of nonactive, ``normal,'' galaxies, matched to the Seyfert samplein the distribution of type and inclination. The spatial resolution andsampling of the new images is a factor of 2 better than previouslypublished K-band data. In this paper, we present the data in the form ofprofiles of surface brightness and color, ellipticity and major axisposition angle, as well as gray-scale maps of surface brightness in H orK and both J-H and H-K colors. We compare our surface brightness andcolor profiles with the literature and find good agreement. Our data arediscussed in detail in three subsequent publications, where we analyzethe morphologies of Seyfert and normal hosts, quantify the strength ofnonaxisymmetric features in disks and their relationship to nuclearactivity, address the question of bar fraction in Seyferts and normalgalaxies, and analyze the color information in the framework of emissionmechanisms in Seyfert 1's and 2's and in nonactive galaxies.
| Groups of galaxies. III. Some empirical characteristics.
Not Available
| 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 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| The thicknesses and inclinations of 71 northern spiral galaxies
This paper presents the thicknesses and inclinations (i.e., the anglebetween the galactic plane and the tangent plane) of 71 northern spiralgalaxies. The method for measuring the thickness has been proposed byPeng. It is based on the solution of Poisson's equation for alogarithmic disturbance of density. The inclination is determined byassuming that the pattern of spiral structure is a logarithmic spiral.We find that the thickness is correlated with color and with theH_α+[NII] equivalent width.
| 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.
| Hubble constant from sosie galaxies and HIPPARCOS geometrical calibration
New distances, larger than previous ones, have been obtained for M 31and M 81 based on the geometrical zero-point of the CepheidPeriod-luminosity relation provided by the HIPPARCOS satellite. Bycombining them with independent determinations we define reasonableranges for the distances of these important calibrating galaxies. Onthis basis, we determine the Hubble constant from the method of sosies(look-alike) galaxies, galaxies having the same characteristics than thecalibrators. The method is quite secure because it is purelydifferential and it does not depend on any assumption (apart from thenatural one that two sosies galaxies have similar absoluteluminosities). Nevertheless, the Malmquist bias has to be taken intoaccount. The observations behave exactly as predicted from theanalytical formulation of the bias. Thus, rejecting galaxies which areaffected by the Malmquist bias we derive the Hubble constant: H_o = 60+/- 10 (external) km.s^{-1}.Mpc^{-1} If we strictly use the calibrationobtained with HIPPARCOS and if the bias found in the Period-LuminosityRelation is considered, the Hubble constant is smaller than this (~ 55km.s(-1}.Mpc({-1)) ). This gives arguments in favour of thelong-distance scale. We briefly discuss possible improvements aiming atstill reducing the uncertainty.
| Galaxy Pairs, Redshift Catalogs, and the Cosmic Peculiar Velocity
We discuss pairs of spiral galaxies with projected separations r_p_ranging from very wide (r_p_ ~ 1.0 Mpc) to very small (r_p_ <~ 75kpc). Single-dish H I data for the wide pairs and H I aperture synthesisas well as CCD images for the close pairs were presented in earlierpapers. From pairs (regardless of isolation criteria) in redshiftcatalogs, we find that the kinematics of spiral-spiral pairs inlow-density regions is qualitatively different from that in high-densityregions. The velocity distribution function f({DELTA}V) in low-densityregions has two components: (i) a narrow component (which is related toisolated pairs) with a very small rms value σ_v,n_ of the"one-dimensional random cosmic peculiar velocity" δν, and (ii)a broad, slowly decreasing component (which is related to pairs in loosegroups) with a large rms value of the "one-dimensional random cosmicpeculiar velocity" σnu,b_. Thus, we confirm that thedistribution of the "one- dimensional cosmic peculiar velocity"{DELTA}ν is not Gaussian and its rms value σ_V_ varies withenvironment. The median {DELTA}V_med_ of the absolute value of thevelocity difference of isolated wide pairs is ~30 km s^-1^, considerablysmaller than all estimates of σ_v_. This small {DELTA}V_med_suggests that the pairs are on low total energy, almost radial orbits,and it is also a constraint on cosmological models of structureformation. We find some circumstantial evidence for a negativecorrelation between the peculiar velocity δν and thedifferential Hubble flow velocity {DELTA}V_H_ which would be the casefor bound orbits near the maximum separation (" turnaround ``) at thecurrent epoch. If future larger samples (e.g., the CfA2 and the SSRS2surveys) confirm this, then a total galaxy mass ~10^12^ M_sun_ isimplied. All the six close pairs for which we have detailed H I andoptical CCD images show some signs of interaction, even though theselection criteria were specifically independent of known morphologicalpeculiarities. For three of the six pairs there is good evidence for thepairs also being on high eccentricity, low total energy orbits, andthere is some evidence that the impact parameter for one pair is ~1 diskradius. The median velocity difference {DELTA}V_med_ of the close pairssample is also ~30 km s^-1^. This small value of {DELTA}V_med_ isprobably an indirect effect of dynamical friction.
| 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.
| Galaxies with f12 > f25
We have compiled a sample of galaxies whose flux density is higher at 12microns (f12) than at 25 microns (f25). It is argued thatf12 >f25effectively selects quiescent galaxies which are less active ininfrared, radio, and optical bands than other types of normal galaxies.Moreover galaxies withf12 >f25 do not exhibit the well-knownrelations that normal galaxies show between far-infrared parameters, forexample, the negative correlation betweenf12/f25 andf60/f100. Thesegalaxies also show different far-infrared and radio properties. In ouropinion this sample of quiescent galaxies is suitable for use as acontrol sample when properties of more active galaxies are discussed. Itmay also be used in modeling galaxies with active star formation or anactive nucleus.
| Dynamics of Binary Galaxies. III. Details of the Close Pairs
In a previous paper [Chengalur et al. ApJ, 107, 1984(1994)] H Isynthesis data and CCD images were presented for an objectively chosensample of six close spiral-spiral galaxy pairs. In this paper we presenta detailed analysis of the data. Although the presence of tidal featureswas not an explicit selection criterion, five of our six pairs showtidal tails and bridges. The remaining pair also shows signs ofinteraction: both galaxies in the pair have disturbed velocity fieldsand one of the two galaxies has a central concentration of molecular gasand is undergoing a starburst. The morphology of three of the six pairsimplies that the galaxies are on high eccentricity, low total energyorbits, and for one of these pairs there is some evidence that theimpact parameter is as small as ~1 disk radius. For the remaining threepairs the tidal features are not as pronounced, and the observations donot yield as much information on the orbit. However, even for thesepairs, the observed morphology is consistent with the galaxies being onslow, small impact parameter orbits, provided the galaxies are at arelatively early phase of the orbit, i.e., prior to the first closeencounter. We also find weak evidence for preferential alignment in thepairs (with the lack of preferential alignment being ruled out at the97% level), in the sense that the major axis of a galaxy tends to pointtoward the companion galaxy. This sample of close pairs is complementedby a larger sample of wide pairs (Chengalur et al. 1993). The medianvelocity difference {DELTA}V of the sample of close pairs in low-densityregions is not much different from that for the wide pairs sample, inparticular, there is no evidence for positive energy impacts. The effectof dynamical friction on infall velocities is controversial and will bediscussed in the following paper [Chengalur et al., in preparation(1995)] which combines the data on close and wide pairs.
| 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 spatial distribution of supernovae in paired and interacting galaxies
In order to investigate the location of supernovae (SNe) in paired andinteracting galaxies, the 54 supernovae discovered up to May 1993 in 14Isolated Pairs of Galaxies and the 32 Interacting Systems were taken asa sample and studied. The whole sample of SNe, as well as a subsampleformed of type II, and Ib SNe, whose progenitors are young massivestars, do not appear in any one particluar direction with respect to thecompanion. On paired and interacting galaxies, the radial distributionof type Ib and II SNe peaks more toward the galaxy centers than it doesin isolated galaxies, indicating an enhanced Star Formation Rate (SFR)around the nuclei and in the inner disks. The distribution of SNIaappear similar in both samples, confirming that their progenitors arenot the same as those of SNII and IB. The SN rates are related to galaxyluminosity and, as expected, the discovery of SNe is twice more frequentin the brighter galaxy of the pair than in fainter ones. We did not findany relation between the locations of SNe in parent galaxies, the totalStar Formation activity and the kinematics of paired and interactinggalaxies.
| Dynamics of binary galaxies. 2: Close pairs
As part of a comprehensive study of binary galaxies, broadband opticalCharge Coupled Device (CCD) images and high resolution H I maps arepresented for six close pairs of spiral galaxies. A previous paperChengalur, et al., (1993) presented the results of a study of binarygalaxies with wide separations. The current sample of close pairs waschosen from the Center for Astrophysics (CfA) redshift catalog usingselection criteria that were objective and completely independent of anypreviously known morphological peculiarities. Nonetheless, all thegalaxies show some sign of interaction, implying that the selectioncriteria were sufficiently well tailored to choose physically associatedparis. All the galaxies show kinematical disturbances and haveasymmetric rotation curves. Tidal tails and bridges are clearly detectedfor some, and two pairs have a large common H I envelope. This common HI envelope also shows a large scale radial velocity gradient and givesthe impression of being in rotation about a single kinematical axis.There is relatively good agreement between the optical and H I images,with similar tidal features being seen in both. The H I features,however, extend to a much larger galactocentric radius than thecorresponding optical features. In at least one case, however, thestellar disk appears relatively normal, while the H I disk appearsdisturbed even towards the center of the galaxy. The systematic velocitydifference for the galaxy pairs has been measured quite accuratelyeither from the integrated H I spectral profile, or from a global fit tothe galaxy velocity fields. The median velocity difference for the sixgalaxy pairs is very small, approximately 20 km/s. Detailed analysis ofthe data will be presented in a separate paper.
| Galaxy structures in the Hercules region
216 redshifts have been obtained in a region of 981 sq deg south of theHercules supercluster. 172 of these redshifts are of galaxies withmpg less than or equal to 15.1, 110 of which had no previousvelocity measurement. 44 new redshifts are of galaxies fainter thanmpg = 15.1. With these new data we have been able to define asample in a vast region (approximately 1700 sq deg) around Herculeslimited to mpg less than or equal to 15.1 with a velocitycompleteness of 81.5%. 189 galaxies have been morphologically classifiedso that all galaxies in the sample with known velocity now also haveknown morphology. The magnitude limited sample, including 556 galaxies,is then used to identify and describe galaxy structures in the region.We find that the overdense volume is small, that its overall appearanceis that of a coral branch floating in a sea of nothing and that earlyand late type galaxies defined different structures.
| The dynamics and structure of the S0 galaxy NGC 7332
Spectroscopic and photometric observations of the edge-on S0 galaxy NGC7332 are presented. The spectra show the galaxy to possess a rapidlycounter-rotating extended gas disk as detected from both (O III) 5007 Aand H alpha emission. Multiple slit orientations at a variety ofposition angles clearly show the decoupling of the angular momentabetween the stellar and gaseous components. The gas is distributedasymmetrically and displays noncircular motions indicating that it hasnot reached equilibrium. These observations are strong evidence insupport of an accretion process having occurred in NGC 7332. Broad R andB band CCD images show the boxy isophotes that NGC 7332 has long beenknown to possess while offset spectra taken parallel to the major andminor axes display the cylindrical rotation common to galaxies withbox-shaped bulges. The bulge of NGC 7332 is well described by anr1/4-law on both the major and minor axes while the outerdisk is exponential. The B-R color of the disk is uniform; the onlyindication of a trend to blue colors is a Delta(B-Rc)/Deltalog r= -0.04 +/- 0.01 gradient seen perpendicular to the bulge and disk.There exists a 10 sec long region of nearly constant surface brightnessalong the major axis between the bulge and disk components. Not likelydue to absorbing material, the relation of this feature to the alreadycomplicated structure of the galaxy is considered.
| The Photometric Properties of Box / Peanut Galactic Bulges
Optical and near-IR photometry is presented for a sample of 14 edge-ongalaxies displaying `box/peanut' bulge structure. The observedluminosity distributions are modelled using a 2D non-linear,least-squares minimization scheme, and the resulting `best-fitting'model combinations subtracted from the observational data to study thedeviations from the imposed models. In all cases, the models usedunderestimate the observed luminosity in the region of the box/peanutdistortions by typically 5-15 percent of the luminosity of the bulge asa whole in the same regions (rising to ~60 per cent in some cases). Thisluminosity excess appears greater in later type galaxies - whilst thebulges in such systems are small, the box/peanut components contain alarger fraction of the total luminosity of the old stellar populations.The evidence for colour gradients within the bulge components iscontradictory: two systems show clear evidence of a blueing with radiusand Z-height, but in four out of seven cases there is no significantgradient in those regions clearly dominated by the stellar components.Taken together with the similar lack of evidence for low surfacebrightness arcs, shells, filaments, etc. in the present sample, thebox/peanuts do not appear to be the result of recent merger/accretionevents. Moreover, isophote twists with respect to the major axes areunambiguously detected in only two out of nine galaxies, supporting aprevious assertion that box/peanut bulges do not possess a significantdegree of triaxiality. The Z-height of the maximum excess flux withinthe derived (model - data) residual maps has been measured at severalradii (R). This turnover height (Z_peak_) accurately determines theposition of the box/peanut distortions at each radius. Z_peak_ variescontinuously with R in all galaxies, whilst Z_peak_/R fallsmonotonically with R. Both results are contrary to a recent theoreticalanalysis of the orbital families thought to be present within box/peanutbulges (such a study predicting that the zero-velocity curve increaseslinearly with radius, i.e. that Z_peak_/R is constant with R). This maysuggest that the orbits normally used to describe this morphology areinappropriate or, more likely, that each bulge possesses several suchorbital families and that their relative contributions vary withgalactocentric distance. If box/peanuts are the result of the presenceof a bar, regular/periodic orbits appear favoured at the expense of morechaotic orbits. However, the typical radii of the most extremebox/peanut isophotal distortions are larger than those of the inferredinner Lindblad resonances in typical barred potentials. Contrary toprevious expectations, it is clear that photometry alone can be used toplace valuable constraints on a theoretical understanding of thisstructure.
| The extended 12 micron galaxy sample
We have selected an all-sky (absolute value of b greater than or equalto 25 deg) 12 micron flux-limited sample of 893 galaxies from the IRASFaint Source Catalog, Version 2 (FSC-2). We have obtained accurate totalfluxes in the IRAS wavebands by using the ADDSCAN procedure for allobjects with FSC-2 12 micron fluxes greater than 0.15 Jy and increasingflux densities from 12 to 60 microns, and defined the sample by imposinga survey limit of 0.22 Jy on the total 12 micron flux. Its completenessis verified, by means of the classical log N - log S andV/Vmax tests, down to 0.30 Jy, below which we have measuredthe incompleteness down to the survey limit, using the log N - log Splot, for our statistical analysis. We have obtained redshifts (mostlyfrom catalogs) for virtually all (98.4%) the galaxies in the sample.Using existing catalogs of active galaxies, we defined a subsample of118 objects consisting of 53 Seyfert 1s and quasars, 63 Seyfert 2s, andtwo blazars (approximately 13% of the full sample), which is the largestunbiased sample of Seyfert galaxies ever assembled. Since the 12 micronflux has been shown to be about one-fifth of the bolometric flux forSeyfert galaxies and quasars, the subsample of Seyferts (includingquasars and blazars) is complete not only to 0.30 Jy at 12 microns butalso with respect to a bolometric flux limit of approximately 2.0 x10-10 ergs/s/sq cm. The average value of V/Vmaxfor the full sample, corrected for incompleteness at low fluxes, is 0.51+/- 0.04, expected for a complete sample of uniformly distributedgalaxies, while the value for the Seyfert galaxy subsample is 0.46 +/-0.10. We have derived 12 microns and far-infrared luminosity functionsfor the AGNs, as well as for the entire sample. We extracted from oursample a complete subsample of 235 galaxies flux-limited (8.3 Jy) at 60microns. The 60 micron luminosity function computed for this subsampleis in satisfactory agreement with the ones derived from the brightgalaxy sample (BGS) and the deep high-galactic latitude sample, bothselected at 60 microns.
|
Enviar un nuevo artículo
Enlaces relacionados
- - No se han encontrado enlaces -
En viar un nuevo enlace
Miembro de los siguientes grupos:
|
Datos observacionales y astrométricos
Catálogos y designaciones:
|
