Contents
Images
Upload your image
DSS Images Other Images
Related articles
H I 21 cm Observations of the PG 1216+069 Sub-damped Lyα Absorber Field at z = 0.00632
The Westerbork Synthesis Radio Telescope finds a weak 21 cm lineemission feature at the coordinates (R.A., decl., velocity) of thesub-damped Lyα (DLA) absorber observed at zabs=0.00632in the spectrum of PG 1216+069. The emission feature, WSRT J121921+0639,lies within 30" of the quasar sight line, is detected at a 99.8% (3σ) confidence level, has MHI between 5 and15×106 Msolar, and has a velocity spreadbetween 20 and 60 km s-1. Other H I emitters in the fieldinclude VCC 297 at a projected distance of 86h-175 kpc and a previously unreported H I cloud,WSRT J121919+0624, at 112 h-175 kpc withMHI~3×108 Msolar. The opticallyidentified foreground galaxy that is closest to the quasar sight lineappears to be VCC 339 (~L*/25) at 29h-175 kpc with a velocity offset of 292 kms-1. A low surface brightness galaxy with the H I mass of thesub-DLA absorber WSRT J121921+0639 would likely have mB~17,and its diffuse optical emission would need to compete with the light ofboth the background QSO and a brighter foreground star ~10" from the QSOsight line.
| 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
| Are interactions the primary triggers of star formation in dwarf galaxies?
We investigate the assumption that the trigger of star formation indwarf galaxies is interactions with other galaxies, in the context of asearch for a `primary' trigger of a first generation of stars. This iscosmologically relevant because the galaxy formation process consistsnot only of the accumulation of gas in a gravitational potential wellbut also of the triggering of star formation in this gas mass, and alsobecause some high-z potentially primeval galaxy blocks look like nearbystar-forming dwarf galaxies. We review theoretical ideas proposed toaccount for the tidal interaction triggering mechanism and present aseries of observational tests of this assumption using published data.We also show results of a search in the vicinity of a composite sampleof 96 dwarf late-type galaxies for interaction candidates showing starformation. The small number of possible perturbing galaxies identifiedin the neighbourhood of our sample galaxies, along with similar findingsfrom other studies, supports the view that tidal interactions may not berelevant as primary triggers of star formation. We conclude thatinteractions between galaxies may explain some forms of star formationtriggering, perhaps in central regions of large galaxies, but they donot seem to be significant for dwarf galaxies and, by inference, forfirst-time galaxies forming at high redshifts. Intuitive reasoning,based on an analogy with stellar dynamics, shows that conditions forprimary star formation triggering may occur in gas masses oscillating ina dark-matter gravitational potential. We propose this mechanism as aplausible primary trigger scenario, which would be worth investigatingtheoretically.
| Globular Clusters as Candidates for Gravitational Lenses to Explain Quasar-Galaxy Associations
We argue that globular clusters (GCs) are good candidates forgravitational lenses in explaining quasar-galaxy associations. Thecatalog of associations (Bukhmastova 2001) compiled from the LEDAcatalog of galaxies (Paturel 1997) and from the catalog of quasars(Veron-Cetty and Veron 1998) is used. Based on the new catalog, we showthat one might expect an increased number of GCs around irregulargalaxies of types 9 and 10 from the hypothesis that distant compactsources are gravitationally lensed by GCs in the halos of foregroundgalaxies. The King model is used to determine the central surfacedensities of 135 GCs in the Milky Way. The distribution of GCs incentral surface density was found to be lognormal.
| Broad-band colours of Virgo cluster low surface brightness dwarf irregular galaxies
We present UBVRI images and surface photometry of a complete sample of29 low-luminosity dwarf irregular galaxies in the Virgo cluster, forwhich we derive central surface brightnesses, scalelengths, integratedmagnitudes and median colours. The colour distributions are discussed interms of radial surface brightness profiles, and colour gradients areinterpreted and compared with corresponding ones for lowsurface-brightness (LSB) spiral galaxies. By combining broad-band andnarrow-band filter observations, the past and current influences of thecluster environment on the evolution of LSB dwarf irregular galaxies isevaluated.
| Late-type dwarf irregular galaxies in the Virgo cluster - I. H alpha and red continuum data
We present H alpha and red continuum observations for a sample oflate-type low surface brightness (LSB) dwarf irregular galaxies,consisting of all the ImIV and V galaxies with m_B<= 17.2 in theVirgo cluster, and compare them with similar data for a representativesample of high surface brightness (HSB) dwarf irregular galaxies, alsoin the Virgo cluster. Line fluxes and equivalent widths are listed forindividual HII regions, and total H alpha emission is measured for theentire galaxy. Although significant line emission originates in the HIIregions that we have identified, it does not make up the entire H alphaoutput of all galaxies. For those objects in the LSB sample withHα emission, we find typical star formation rates (SFRs) from6.9x10^-3 to as high as 4.3x10^-2 M_solar yr^-1. This is, on average,one order of magnitude weaker than for HSB objects, although the SFRsoverlap. On average, ~2 HII regions are detected per LSB galaxy, for atotal of 38 HII regions among 17 galaxies with Hα emission. TheHII regions are smaller and fainter than in HSB galaxies in the sameVirgo cluster environment, have Hα line equivalent widths about 50per cent of those in HSBs, and cover similar fractions of the galaxies.When more than one HII region is present in a galaxy, we observe astrong intensity difference between the brightest and the secondbrightest HII regions. The line-emitting regions of LSB galaxies arepreferentially located at the periphery of the galaxy, while in HSBsthey tend to be central. The Hα line strength of an HII region iscorrelated with the red continuum light underneath the region; thisholds for both LSBs and HSBs. We do not identify fundamental differencesin the star formation properties of the LSB and HSB dwarf galaxies thatwe have studied, and we infer that these galaxies must be similar, withthe difference being the intensity of the present star formation burst.
| 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 (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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
| A catalogue of spatially resolved kinematics of galaxies: Bibliography
We present a catalogue of galaxies for which spatially resolved data ontheir internal kinematics have been published; there is no a priorirestriction regarding their morphological type. The catalogue lists thereferences to the articles where the data are published, as well as acoded description of these data: observed emission or absorption lines,velocity or velocity dispersion, radial profile or 2D field, positionangle. Tables 1, 2, and 3 are proposed in electronic form only, and areavailable from the CDS, via anonymous ftp to cdsarc.u-strasbg.fr (to130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| Arecibo H i Mapping of a Large Sample of Dwarf Irregular Galaxies
Neutral hydrogen mapping of 70 dwarf irregular (Sm, Im, and BCD)galaxies is reported, with position-velocity contour maps (and a fewcontour maps in R.A. and decl.) presented for those resolved by theArecibo beam. The galaxies were selected either from the Virgo ClusterCatalog, from similarly identified field galaxies, or from a distance-limited sample within the Arecibo declination range. We do not find anyisolated dwarfs with a larger H I to optical radius ratio than DDO 154;the "protogalaxy" H I 1225+01 of Giovanelli & Haynes continues to bea unique object among dwarfs that have been mapped in H I. For alldwarfs with significant rotation, we are able to determine the sense ofthe spin. For a number of better resolved dwarfs, we are able todetermine rotation curves, in most cases extending well beyond the lastmeasured point in available synthesis array maps. Correlations among theseveral measures of galaxy size and mass are studied; in a companionpaper we combine these data with those for the set of all availablemapped dwarf irregular galaxies and for mapped spirals spanning asimilar range of redshifts to investigate variations in Tully-Fisherrelations and in surface densities as functions of galaxy size andluminosity or mass.
| Extended LY alpha -absorbing Halos around Nearby Galaxies
In order to establish the Lyα absorption cross section ofpresent-day galaxies, we have identified 38 galaxies with z = 0-0.08that lie within 40-500 h^-1^ kpc of the line of sight to a QSO observedwith the Faint Object Spectrograph aboard the Hubble Space Telescope(HST). Including three galaxies in the field of 3C 273 investigated byprevious authors, we find that nine of 41 galaxies have associatedLyα absorption. If the identified Lyα absorption systems aregenuinely associated with the galaxies, then the covering factor of gasaround galaxies remains roughly constant at ~40% between 100 and 300h^-1^ kpc. Beyond 300 h^-1^ kpc, the incidence of absorption dropssharply. We conclude that (1) nearby galaxies do not possessLyα-absorbing halos beyond 300 h^-1^ kpc in radius and (2) thecovering factor of present-day galaxies between 50 and 300 h^-1^ kpc is44% at an equivalent width limit of W >= 0.3 A. For the nine galaxieswith associated Lyα absorption lines, differences in the galaxiessystemic velocities and the velocity of the absorption line, {DELTA}v,range over +/- 300 km s^-1^, consistent with the distribution found atredshifts > 0.1 by Lanzetta et al. and Le Brun, Bergeron, &Boisse. Values of {DELTA}v spanning several hundred km s^-1^ areprobably real for some of the QSO-galaxy pairs, however, and do notsimply arise from errors in measuring cz_gal_ or cz_abs_. This suggeststhat the absorbing clouds are kinematically tied to the galaxy disks andthat the distribution of {DELTA}v may arise because of the effects ofgalaxy inclination. We find no evidence for a correlation betweenLyα equivalent width and galaxy line-of-sight separation, whichweakens the argument that the identified galaxies are directlyassociated with the Lyα lines. Also, we find that absorption doesnot arise only from bright galaxies, since there are several examples inwhich low-luminosity galaxies apparently cause absorption. Yet we showthat the absorbing halos around galaxies cannot be independent of galaxyluminosity because if all low- redshift galaxies were surrounded byextended halos, the number of Lyα absorption systems found in HSTspectra would be much larger than has recently been determined. Thisresult leads us to question whether the galaxies are actuallyresponsible for the Lyα absorption lines or whether theassociation in redshift is fortuitous. Our results support the picturesuggested by others that Lyα lines arise in filaments or sheetsthat connect and contain the overdense regions that galaxies inhabit.This conclusion, however, remains at odds with the results of Lanzettaet al., who find that Lyα systems are more intimately linked withgalaxies. It may be, therefore, that we are seeing an evolution of theway in which Ly& lines associate with galaxies over the last fewbillion years. We suggest that at least some of the Lyα cloudsthat are not associated with galaxies at z ~ 0.5 have been slowlymerging with galaxies over time, creating larger but less uniform gasdistributions around the galaxies we see today.
| 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.
| Criticism of Lake's analysis of the rotation curves of dwarf spirals
This paper disputes the presence of a disparity found by Lake (1989)between the predictions of MOND and the observed rotation curves of five(out of the total six observed) dwarf spirals. Lake reported that theobserved rotation velocities of DDO 154, NGC 3109, VCC 381, IC 1613, andDDO 125 were smaller than the velocities predicted by MOND by factors ofabout 1.2, 1.3, 1.5, 2, and 1.8. It is shown that, in each case, errorsin the adopted distances and/or inclinations can fully account for theobserved disparities between the theory and measurements.
| Testing modifications of gravity
Milgrom's (1983) non-Newtonian theory that dark matter is caused by achange in the law of gravity at low accelerations (10 to the -8th cm/sqs), is tested. Six dwarf galaxies with low accelerations are modeled,showing that Milgrom's theory fails for these galaxies. It is found thatbecause these systems have large H I mass/luminosity ratios thenon-Newtonian theory cannot be fitted by arbitrarily lowering themass-to-light ratio of the stellar component.
| The mass distribution and the law of gravity in the Local Group dwarf irregular galaxy IC 1613
Results are presented on the H I spectral-line distribution and velocityfield of the Local Group dwarf galaxy IC 1613, which were obtained usingVLA of the NRAO. The rotation curve of IC 1613 was determined, andNewtonian and non-Newtonian mass models were built. It was found thatthe H I is lumpy in the inner parts, but H I contours in the outer partsof the galaxy are smooth. The velocity field is regular, and the line ofnodes is coincident with the major axis of the gas distribution. Therotation curve of IC 1613 shows evidence of dark matter in the outerparts. However, the maximum density of a dark halo that can be toleratedis an order of magnitude lower than that needed to explain the velocitydispersions of the extreme dwarf spheroidals.
| 21 centimeter line width distances of cluster galaxies and the value of H0
Locally calibrated blue and infrared Tully-Fisher (TF) relations areapplied to an 82 percent complete sample of 81 Sab-Sm galaxies which arebona fide members of the Virgo Cluster. A nearly unbiased Virgo modulusof 31.60 + or - 0.15 can be derived in perfect agreement withindependent recent determinations. It is shown that the blue TF andinfrared TF relations give almost identical distance moduli from anyselected Virgo subsample. The intrinsic scatter about the two TFrelations is 0.7 mag, considerably larger than the observed scatter inthe UMa Cluster and in 10 more distant clusters. Distance determinationof these clusters therefore can be achieved only by fitting the upperenvelopes of their TF relations onto the blue and infrared upperenvelopes of the Virgo Cluster. The resulting distances define a linearexpansion law with a small scatter. The present cluster data require H0= 56.6 + or - 0.9 km/s/Mpc.
| H I detection survey of a complete magnitude-limited sample of dwarf irregular galaxies in the Virgo Cluster area
New single-beam Arecibo H I observations of 298 late-type galaxies inthe Virgo Cluster drawn mostly from the new catalog of Binggeli,Sandage, and Tammann (1985) are presented. Two hundred seventeen ofthese constitute a magnitude-limited 'complete sample' of such galaxies,types Sdm through Im and BCD. Sixty-one percent of this 'completesample' was detected, greatly enhancing the store of redshifts and H Imasses for such galaxies in the Virgo Cluster. For detected galaxies,heliocentric velocities, 50 percent profile widths, and single-beamfluxes are presented. For those that escaped detection, upper limits arecomputed to the flux appropriate to the redshift range (-600 to +3000km/s).
| UBV colors of Virgo cluster irregular galaxies
Photoelectric UBV aperture photometry is presented for 65 dwarfirregular and morphologically related types of galaxies that areprobable Virgo cluster members. Virgo cluster Irr galaxies cover a widerrange in color than typical samples of field Irr systems, primarily dueto the presence of unusually red Im galaxies in Virgo. The extremelyblue 'blue compact dwarf' and the red amorphous galaxies in Virgo alsostand out on a UBV color-color plot, but the majority of Virgo Irrs areundistinguished in terms of UBV colors. Statistical correlations arefound between colors and location within the cluster. Red Irrs often arein elliptical galaxy rich, dense areas of the cluster, while the blueIrrs roughly follow the spiral distribution pattern. Thus a connectionexists between environment and the properties of Irrs. Simplestatistical tests for ongoing stripping as the source of red Irrs,however, yields null results.
| Studies of the Virgo Cluster. II - A catalog of 2096 galaxies in the Virgo Cluster area.
The present catalog of 2096 galaxies within an area of about 140 sq degapproximately centered on the Virgo cluster should be an essentiallycomplete listing of all certain and possible cluster members,independent of morphological type. Cluster membership is essentiallydecided by galaxy morphology; for giants and the rare class of highsurface brightness dwarfs, membership rests on velocity data. While 1277of the catalog entries are considered members of the Virgo cluster, 574are possible members and 245 appear to be background Zwicky galaxies.Major-to-minor axis ratios are given for all galaxies brighter than B(T)= 18, as well as for many fainter ones.
| A catalog of dwarf galaxies in Virgo
A catalog listing the location, apparent angular diameter, type,estimated central light concentration, and estimated brightness of 846dwarf galaxies in a 200-deg-sq region in Virgo is presented. Thegalaxies comprise 634 ellipticals, 137 IC-3475-type galaxies, 73 dwarfspirals and irregulars, and two objects which are jets of normalgalaxies, and were found on nine long-exposure IIIa-J-emulsion platesmade with the 1.2-m-Schmidt telescope at Palomar Observatory from 1971to 1976. Concordances to other catalogs, tables of additionalparameters, maps, graphs, and photographs are provided. The projecteddistributions of normal and dwarf galaxies and the dependence ofapparent luminosity on central light concentration are discussed. It isfound that dwarf ellipticals and IC-3475-type galaxies are probablemembers of the Virgo cluster, while dwarf spirals and possibly dwarfirregulars are not.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
