Contents
Images
Upload your image
DSS Images Other Images
Related articles
HI in extremely metal deficient galaxies - III. Giant Metrewave Radio Telescope observations of blue compact galaxy HS 0822+3542
We present the results of Giant Metrewave Radio Telescope HI 21-cm lineobservations of the extremely metal deficient (XMD) blue compact galaxy(BCG) HS 0822+3542. HS 0822+3542 is the smallest known XMD galaxy; fromHubble Space Telescope (HST) imaging, it has been suggested that itactually consists of two still smaller (~100 pc sized) ultra-compactdwarfs that are in the process of merging. The brighter of these twoputative ultra-compact dwarfs has an ocular appearance, similar to thatseen in galaxies that have suffered a penetrating encounter with asmaller companion. From our HI imaging, we find that the gasdistribution and kinematics in this object are similar to that of otherlow-mass galaxies, albeit with some evidence for tidal disturbance. Onthe other hand, the HI emission has an angular size ~25 times largerthan that of the putative ultra-compact dwarfs. The optical emission isalso offset from the centre of the HI emission. HS 0822+3542 is locatedin the nearby Lynx-Cancer void, but has a nearby companion low surfacebrightness dwarf galaxy SAO 0822+3545. In light of all this, we alsoconsider a scenario where the optical emission from HS 0822+3542 comesnot from two merging ultra-compact dwarfs but from multiple star-formingregions in a tidally disturbed galaxy. In this model, the ocularappearance of the brighter star-forming region could be the result oftriggered star formation.
| Gas distribution, kinematics and star formation in faint dwarf galaxies
We compare the gas distribution, kinematics and the current starformation in a sample of 10 very faint (-13.37 < MB <-9.55) dwarf galaxies. For five of these galaxies we present fresh,high-sensitivity, Giant Metrewave Radio Telescope HI 21-cm observations.We find that the large-scale HI distribution in the galaxies istypically irregular and clumpy, with the peak gas density rarelyoccurring at the geometric centre. We also find that the velocity fieldsfor all the galaxies have an ordered component, although in general, thepatterns seen do not fit that expected from a rotating disc. For all ourgalaxies we construct maps of the HI column density at a constant linearresolution of ~300 pc; this forms an excellent data set to check for thepresence of a threshold column density for star formation. We find thatwhile current star formation (as traced by Hα emission) isconfined to regions with relatively large [NHI > (0.4-1.7)× 1021cm-2] HI column density, themorphology of the Hα emission is in general not correlated withthat of the high HI column density gas. Thus, while high column densitygas may be necessary for star formation, in this sample at least, it isnot sufficient to ensure that star formation does in fact occur. Weexamine the line profiles of the HI emission, but do not find a simplerelation between regions with complex line profiles and those withongoing star formation. Our sample includes examples of regions wherethere is ongoing star formation, but the profiles are well fitted by asingle Gaussian, as well as regions where there is no star formation butthe line profiles are complex. Finally, we examine the very fine scale(~20-100 pc) distribution of the HI gas, and find that at these scalesthe emission exhibits a variety of shell-like, clumpy and filamentaryfeatures. The Hα emission is sometimes associated withhigh-density HI clumps, sometimes the Hα emission lies inside ahigh-density shell, and sometimes there is no correspondence between theHα emission and the HI clumps. In summary, the interplay betweenstar formation and gas density in these galaxies does not seem to showthe simple large-scale patterns observed in brighter galaxies.
| Massive HI clouds with no optical counterparts as high-density regions of intragroup HI rings and arcs
We present a new scenario in which massive intragroup HI clouds are thehigh-density parts of large HI rings/arcs formed by dynamicalinteraction between galaxy groups and gas-rich, low surface brightness(LSB) galaxies with extended gas discs. Our hydrodynamical simulationsdemonstrate that the group tidal field is very efficient at strippingthe outer HI gas of the disc if the gaseous disc of the LSB galaxyextends 2-5 times further than the stellar disc. We find that a massive,extended `leading stream' orbiting the centre of the group can form outof the stripped outer HI envelope, while the severely shrunken LSBgalaxy, whose stellar disc remains unaffected, continues on its path.The result is a relatively isolated, massive HI cloud with a ring- orarc-like shape, a very inhomogeneous density distribution(NHI~ 1.0 × 1017-1.1 × 1020atomcm-2), and, initially, no stellar content. Only thehigh-density peaks of the simulated intragroup HI ring/arc can bedetected in many current HI observations. These will appear asrelatively isolated `HI islands' near the group centre. We also findthat star formation can occur within the ring/arc, if the total gas masswithin the intragroup ring/arc is very large (~4 × 109Msolar). We discuss these results in terms of existingobservations of intragroup gas (e.g. the Leo Ring and HIPASS J0731-69)and intergalactic HII regions.
| Star Formation in H I-selected Galaxies. II. H II Region Properties
A sample of 69 galaxies with radial velocities less than 2500 kms-1 was selected from the H I Parkes All Sky Survey (HIPASS)to deduce details about star formation in nearby disk galaxies selectedwith no bias to optical surface brightness selection effects. Broadband(B and R) and narrowband (Hα) images were obtained for all ofthese objects. More than half of the sample galaxies are late-type,dwarf disks (mostly Sc and Sm galaxies). We have measured the propertiesof the H II regions on Hα continuum-subtracted images, using theHIIphot package developed by Thilker et al. All but one of the galaxiescontained at least one detectable H II region. Examination of theproperties of the H II regions in each galaxy revealed that thebrightest regions in higher surface brightness galaxies tend to be moreluminous than those in lower surface brightness galaxies. A higherfraction (referred to as the diffuse fraction) of the Hα emissionfrom lower surface brightness galaxies comes from diffuse ionized gas. HII region luminosity functions (LFs) co-added according to surfacebrightness show that the shapes of the LFs for the lowest surfacebrightness galaxies are different from those for typical spiralgalaxies. This discrepancy could be caused by the lowest surfacebrightness galaxies having somewhat episodic star formation or by themforming a relatively larger fraction of their stars outside of dense,massive molecular clouds. In general, the results imply that theconditions under which star formation occurs in lower surface brightnessgalaxies are different than in more typical, higher surface brightnessspiral galaxies.
| Star Formation in H I-Selected Galaxies. I. Sample Characteristics
A sample of 69 galaxies with radial velocities of less than 2500 kms-1 was selected from the H I Parkes All-Sky Survey (HIPASS)and imaged in broadband B and R and narrowband Hα, to deducedetails about star formation in nearby disk galaxies while avoidingsurface brightness selection effects. The sample is dominated bylate-type, dwarf disks (mostly Sc and Sm galaxies) with exponential diskscale lengths of ~1-5 kpc. The HIPASS galaxies, on average, have lowerstar formation rates (SFRs), are bluer, and have lower surfacebrightness than an optically selected sample. H II regions were detectedin all but one of the galaxies. Many galaxies had as few as two to fiveH II regions. The galaxies' Hα equivalent widths, colors, and SFRsper unit of H I mass are best explained by young mean ages (~3-5 Gyr,according to Schmidt-law models) with star formation histories in whichthe SFRs were higher in the past. Comparison of the surface brightnesscoverage of the HIPASS galaxies with that of an optically selectedsample shows that such a sample may miss ~10% of the local galaxy numberdensity and could possibly miss as much as 3%-4% of the SFR density. Theamount lower surface brightness galaxies contribute to the totalluminosity density may be insignificant, but this conclusion is somewhatdependent on how the fluxes of these objects are determined.
| Australia Telescope Compact Array H I observations of the NGC 6845 galaxy group
We present the results of Australia Telescope Compact Array (ATCA) HIline and 20-cm radio continuum observations of the galaxy quartet NGC6845. The HI emission extends over all four galaxies but can only beassociated clearly with the two spiral galaxies, NGC 6845A and B, whichshow signs of strong tidal interaction. We derive a total HI mass of atleast 1.8 × 1010 Msolar, most of which isassociated with NGC 6845A, the largest galaxy of the group. Weinvestigate the tidal interaction between NGC 6845A and B by studyingthe kinematics of distinct HI components and their relation to the knownHII regions. No HI emission is detected from the two lenticulargalaxies, NGC 6845C and D. A previously uncatalogued dwarf galaxy, ATCAJ2001-4659, was detected 4.4 arcmin NE from NGC 6845B and has an HI massof ~5 × 108 Msolar. No HI bridge is visiblebetween the group and its newly detected companion. Extended 20-cm radiocontinuum emission is detected in NGC 6845A and B as well as in thetidal bridge between the two galaxies. We derive star formation rates of15-40 Msolar yr-1.
| ATCA HI observations of the peculiar galaxy IC 2554
ATCA HI and radio continuum observations of the peculiar southern galaxyIC 2554 and its surroundings reveal typical signatures of an interactinggalaxy group. We detected a large HI cloud between IC 2554 and theelliptical galaxy NGC 3136B. The gas dynamics in IC 2554 itself, whichis sometimes described as a colliding pair, are surprisingly regular,whereas NGC 3136B was not detected. The HI cloud, which emerges from IC2554 as a large arc-shaped plume, has a size of ~30 kpc, larger thanthat of IC 2554. The total HI mass of the IC 2554 system is ~2 ×109 Msolar, one-third of which resides in the HIcloud. It is possible that tidal interaction between IC 2554 and NGC3136B caused this spectacular HI cloud, but the possibility of IC 2554being a merger remnant is also discussed. We also detected HI gas in thenearby galaxies ESO 092-G009 and RKK 1959 and an associated HI cloud,ATCA J1006-6710. Together they have an HI mass of ~4.6 ×108 Msolar. Another new HI source, ATCAJ1007-6659, with an HI mass of only ~2.2 × 107Msolar was detected roughly between IC 2554 and ESO 092-G009and corresponds to a face-on low surface brightness dwarf galaxy. Starformation is evident only in the galaxy IC 2554 with a rate of ~4Msolar yr-1.
| The IRAS Revised Bright Galaxy Sample
IRAS flux densities, redshifts, and infrared luminosities are reportedfor all sources identified in the IRAS Revised Bright Galaxy Sample(RBGS), a complete flux-limited survey of all extragalactic objects withtotal 60 μm flux density greater than 5.24 Jy, covering the entiresky surveyed by IRAS at Galactic latitudes |b|>5°. The RBGS includes629 objects, with median and mean sample redshifts of 0.0082 and 0.0126,respectively, and a maximum redshift of 0.0876. The RBGS supersedes theprevious two-part IRAS Bright Galaxy Samples(BGS1+BGS2), which were compiled before the final(Pass 3) calibration of the IRAS Level 1 Archive in 1990 May. The RBGSalso makes use of more accurate and consistent automated methods tomeasure the flux of objects with extended emission. The RBGS contains 39objects that were not present in the BGS1+BGS2,and 28 objects from the BGS1+BGS2 have beendropped from RBGS because their revised 60 μm flux densities are notgreater than 5.24 Jy. Comparison of revised flux measurements forsources in both surveys shows that most flux differences are in therange ~5%-25%, although some faint sources at 12 and 25 μm differ byas much as a factor of 2. Basic properties of the RBGS sources aresummarized, including estimated total infrared luminosities, as well asupdates to cross identifications with sources from optical galaxycatalogs established using the NASA/IPAC Extragalactic Database. Inaddition, an atlas of images from the Digitized Sky Survey with overlaysof the IRAS position uncertainty ellipse and annotated scale bars isprovided for ease in visualizing the optical morphology in context withthe angular and metric size of each object. The revised bolometricinfrared luminosity function, φ(Lir), forinfrared-bright galaxies in the local universe remains best fit by adouble power law, φ(L)~Lα, withα=-0.6(+/-0.1) and α=-2.2(+/-0.1) below and above the``characteristic'' infrared luminosityL*ir~1010.5Lsolar,respectively. A companion paper provides IRAS High Resolution (HIRES)processing of over 100 RBGS sources where improved spatial resolutionoften provides better IRAS source positions or allows for deconvolutionof close galaxy pairs.
| A Search for H2O Maser Emission in Southern Active Galactic Nuclei and Star-forming Galaxies: Discovery of a Maser in the Edge-on Galaxy IRAS F01063-8034
We report the cumulative results of five surveys for H2Omaser emission at 1.35 cm wavelength in 131 active galactic nuclei(AGNs) and star-forming galaxies, conducted at the Parkes Observatorybetween 1993 and 1998. We detected one new maser, in the edge-on galaxyIRAS F01063-8034, which exhibits a single ~0.1 Jy spectral feature at4282+/-6 km s-1 (heliocentric) with an unusually large54+/-16 km s-1 half-power full width. The centroid velocityof the emission increased to 4319.6+/-0.6 km s-1 (38+/-2 kms-1 width) over the 13 days between discovery andconfirmation of the detection. A similarly broad-line width and largechange in velocity has been noted for the maser in NGC 1052, wherein jetactivity excites the emission. Neither optical spectroscopy,radio-infrared correlations, nor infrared colors provide compellingevidence of unusual activity in the nucleus of IRAS F01063-8034. Sincethe galaxy appears to be outwardly normal at optical and infraredwavelengths, detection of an H2O maser therein is unique. Themaser emission is evidence that the galaxy harbors an AGN that isprobably obscured by the edge-on galactic disk. The detection highlightsthe possibility that undetected AGNs could be hidden in other relativelynearby galaxies. No other maser emission features have been identifiedat velocities between 3084 and 6181 km s-1.
| A Catalog of H I-Selected Galaxies from the South Celestial Cap Region of Sky
The first deep catalog of the H I Parkes All Sky Survey (HIPASS) ispresented, covering the south celestial cap (SCC) region. The SCC areais ~2400 deg2 and covers δ<-62°. The average rmsnoise for the survey is 13 mJy beam-1. Five hundredthirty-six galaxies have been cataloged according to their neutralhydrogen content, including 114 galaxies that have no previous catalogedoptical counterpart. This is the largest sample of galaxies from a blindH I survey to date. Most galaxies in optically unobscured regions of skyhave a visible optical counterpart; however, there is a small populationof low-velocity H I clouds without visible optical counterparts whoseorigins and significance are unclear. The rms accuracy of the HIPASSpositions is found to be 1.9′. The H I mass range of galaxiesdetected is from ~106 to ~1011 Msolar.There are a large number of late-type spiral galaxies in the SCC sample(66%), compared with 30% for optically selected galaxies from the sameregion in the NASA Extragalactic Database. The average ratio of H I massto B luminosity of the sample increases according to optical type, from1.8 Msolar/Lsolar for early types to 3.2Msolar/Lsolar for late-type galaxies. The HI-detected galaxies tend to follow the large-scale structure traced bygalaxies found in optical surveys. From the number of galaxies detectedin this region of sky, we predict the full HIPASS catalog will contain~5000 galaxies, to a peak flux density limit of ~39 mJy (3 σ),although this may be a conservative estimate as two large voids arepresent in the region. The H I mass function for this catalog ispresented in a subsequent paper.
| Local velocity field from sosie galaxies. I. The Peebles' model
Pratton et al. (1997) showed that the velocity field around clusterscould generate an apparent distortion that appears as tangentialstructures or radial filaments. In the present paper we determine theparameters of the Peebles' model (1976) describing infall of galaxiesonto clusters with the aim of testing quantitatively the amplitude ofthis distortion. The distances are determined from the concept of sosiegalaxies (Paturel 1984) using 21 calibrators for which the distanceswere recently calculated from two independent Cepheid calibrations. Weuse both B and I-band magnitudes. The Spaenhauer diagram method is usedto correct for the Malmquist bias. We give the equations for theconstruction of this diagram. We analyze the apparent Hubble constant indifferent regions around Virgo and obtain simultaneously the Local Groupinfall and the unperturbed Hubble constant. We found:[VLG-infall = 208 ± 9 km s-1] [\log H =1.82 ± 0.04 (H ≈ 66 ± 6 km s-1Mpc-1).] The front side and backside infalls can be seenaround Virgo and Fornax. In the direction of Virgo the comparison ismade with the Peebles' model. We obtain: [vinfall} =CVirgo/r0.9 ± 0.2] withCVirgo=2800 for Virgo and CFornax=1350 for Fornax,with the adopted units (km s-1 and Mpc). We obtain thefollowing mean distance moduli: [μVirgo=31.3 ± 0.2(r=18 Mpc )] [μFornax=31.7 ± 0.3 (r=22 Mpc). ] Allthese quantities form an accurate and coherent system. Full Table 2 isonly available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/57
| Parkes H I observations of galaxies behind the southern Milky Way. I. The Hydra/Antlia region (l~ 266o to 296o)
As part of our program to map the large-scale distribution of galaxiesbehind the Milky Way, we used the Parkes 210 ft (64 m) radio telescopefor pointed \normalsize H \footnotesize I observations of a sample oflow surface-brightness (due to heavy obscuration) spiral galaxiesselected from the deep optical Zone of Avoidance (ZOA) galaxy catalog inthe Hydra/Antlia region (Kraan-Korteweg \cite{Kraan-2000a}). Searching asimultaneous velocity range of either 300 to 5500 km s-1 or300 to 10 500 km s-1 to an rms level of typically 2-4 m Jyresulted in detections in 61 of the 139 pointings, leading to a total of66 detections (an additional detection was made in a reference position,and two other pointings revealed two and four independent signalsrespectively). Except for 2 strong \normalsize H \footnotesize Iemitters identified in the shallow Zone of Avoidance \normalsize H\footnotesize I survey (Henning et al. \cite{Henning}), all \normalsizeH \footnotesize I detections are new. An analysis of the properties ofthe observed and detected galaxies prove that pointed \normalsize H\footnotesize I observations of highly obscured galaxies allow thetracing of a population of nearby, intrinsically large and bright spiralgalaxies that otherwise would not be recovered. The new data identifieda previously unrecognized nearby group at l ~ 287. o5, b ~-9. o5, V ~ 1700 km s-1, the continuation of theHydra/Antlia filament on the opposite side of the Galactic plane, andhelped to delimit a distinct void in the ZOA centered at 2000 kms-1. Tables 1 and 2 are also available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/391/887
| 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.
| Global physical conditions of the interstellar medium in nearby galaxies
Far-infrared spectra (43-197 mu m) of 34 nearby galaxies obtained by theLong Wavelength Spectrometer (LWS) aboard the Infrared Space Observatory(ISO) were analyzed to investigate the general properties ofinterstellar matter in galaxies. The present sample includes not onlynormal galaxies but also starbursts and active galactic nuclei (AGNs).Far-infrared forbidden lines, such as [C Ii]158 mu m, [O I]63 mu m, [NIi]122 mu m, and [O Iii]88 mu m, were detected in most of the samplegalaxies. [O I]145 mu m line was detected in 13 galaxies. The linefluxes of [C Ii]158 mu m and [N Ii]122 mu m relative to the totalfar-infrared flux (FIR) decrease as the far-infrared color becomesbluer, while the ratio of the [O I]63 mu m flux to FIR does not show asystematic trend with the color. The [O Iii]88 mu m to FIR ratio shows alarge scatter with a weak trend of increase with the color. AGNs do notshow any distinguishable trend from normal and starburst galaxies in thefar-infrared spectra, suggesting that the far-infrared emission ismainly driven by star-formation activities even in AGNs. We estimate thephysical conditions of photodissociation regions (PDRs) in the samplegalaxies, such as the far-ultraviolet radiation field intensityG0 and the gas density n by assuming that all the observed [OI]63 mu m and far-infrared continuum emissions come from PDRs.Comparison with PDR models indicates that G0 ranges from102-104 and n ~ 102-104cm-3. The present results also suggest that n variesproportionally with G0. The ratio of [C Ii] 158 mu m to CO(J=1-0) line emission supports the linear increase in n withG0. We estimate that about a half of [C Ii]158 mu m emissionoriginates from PDRs and attribute the rest to the emission as comingfrom low-density diffuse ionized gas. The estimated intensity of [CIi]158 mu m from the ionized gas is compatible with the observedintensity of [N Ii]122 mu m if both lines come from the same diffuseionized gas. The present analysis suggests that the decrease in [CIi]158 mu m/FIR with the far-infrared color may not be accounted for bythe decrease in the photoelectric heating efficiency owing to theincrease in positive charges of dust grains because a measure of theefficiency, G0/n, is found to stay constant with thefar-infrared color. Instead the decrease can be interpreted in terms ofeither the increase in the collisional de-excitation of the [C Ii]transition due to the increase in the gas density or the decrease in theionized component relative to the far-infrared intensity suggested bythe decrease in [N Ii]122 mu m/FIR. Based on the present analysis, wederive average relations of the far-infrared color with G0and n in galaxies, which can be applied to the investigation ofinterstellar matter in distant galaxies. Based on observations with ISO,an ESA project with instruments funded by ESA Member States (especiallythe PI countries: France, Germany, The Netherlands and the UK) and withthe participation of ISAS and NASA.
| The impact of bars on the mid-infrared dust emission of spiral galaxies: global and circumnuclear properties
We study the mid-infrared properties of a sample of 69 nearby spiralgalaxies, selected to avoid Seyfert activity contributing a significantfraction of the central energetics, or strong tidal interaction, and tohave normal infrared luminosities. These observations were obtained withISOCAM, which provides an angular resolution of the order of 10arcsec(half-power diameter of the point spread function) and low-resolutionspectro-imaging information. Between 5 and 18 mu m, we mainly observetwo dust phases, aromatic infrared bands and very small grains, both outof thermal equilibrium. On this sample, we show that the globalF15/F_7 colors of galaxies are very uniform, the onlyincrease being found in early-type strongly barred galaxies, consistentwith previous IRAS studies. The F15/F_7 excesses areunambiguously due to galactic central regions where bar-inducedstarbursts occur. However, the existence of strongly barred early-typegalaxies with normal circumnuclear colors indicates that therelationship between a distortion of the gravitational potential and acentral starburst is not straightforward. As the physical processes atwork in central regions are in principle identical in barred andunbarred galaxies, and since this is where the mid-infrared activity ismainly located, we investigate the mid-infrared circumnuclear propertiesof all the galaxies in our sample. We show how surface brightnesses andcolors are related to both the available molecular gas content and themean age of stellar populations contributing to dust heating. Therefore,the star formation history in galactic central regions can beconstrained by their position in a color-surface brightness mid-infrareddiagram. Based on observations with ISO, an ESA project with instrumentsfunded by ESA Member States (especially the PI countries: France,Germany, the Netherlands and the UK) and with the participation of ISASand NASA.
| 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
| A catalog of galaxies behind the Southern Milky Way . I. The Hydra/Antlia extension (l~ 266or - 296or)
A deep optical galaxy search in the southern Milky Way - aimed atreducing the width of the Zone of Avoidance - revealed 3279 galaxycandidates above the diameter limit of D >~ 0.2', of which only 112(3.4%) were previously catalogued. The surveyed region (266o<~ \ell <~ 296o and -10o <~ b <~+8o) lies in the extension of the Hydra and Antlia clusters -where a supercluster is suspected - and in the approximate direction ofthe dipole anisotropy in the Cosmic Microwave Background radiation. Herewe present the optical properties of the unveiled galaxies such aspositions, diameters, magnitudes, morphological types, including adetailed discussion on the quality of these data and the completenesslimits as a function of the foreground dust extinction. For 127 of the227 positional matches in the IRAS PSC, a reliable cross-identificationcould be found. Several distinct overdensities and filaments of galaxiescan be identified that are apparently uncorrelated with the Galacticforeground extinction hence the probable signature of extragalacticlarge-scale structures. This catalog constitutes the first part in aseries of five equally conducted optical searches for galaxies in thesouthern Milky Way (245o <~ \ell <~ 350o).With these surveys, the entire Zone of Avoidance will have been coveredby means of visual inspection. The catalogs build the basis for variousspectroscopic and photometric follow-up programs which eventually willallow a thorough analyse of the galaxy distribution in redshift spaceand the peculiar velocity fields within the Zone of Avoidance, as wellan an improved understanding of the Galactic foreground extinction.Tables 1 and 2 are available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| ^13CO (J=1-0) Depression in Luminous Starburst Mergers, Revisited
It is known that merging galaxies with luminous starbursts and highfar-infrared luminosities tend to have higher R_1-0=^12CO (J=1-0)/^13CO(J=1-0) integrated line intensity ratios (R_1-0~=20-50) than normalspiral galaxies (R_1-0~=5-15). Comparing far-infrared luminosities[L(FIR)] with those of ^12CO (J=1-0) and ^13CO (J=1-0) for a sample ofnormal and starburst galaxies, Taniguchi & Ohyama found that theobserved high R_1-0 values for the luminous starburst mergers areattributed to their lower (by a factor of 3 on average) ^13CO lineintensities. They suggested the following two possibilities: in theluminous starburst mergers (1) ^13CO is underabundant with respect to^12CO, or (2) exitation and/or optical depth effects are responsible forthe change in R_1-0. In this paper, we investigate the secondpossibility, using higher transition data of both ^12CO and ^13COemission lines. Applying the same method proposed by Taniguchi &Ohyama to both ^12CO (J=2-1) and ^13CO (J=2-1), we find that ^13CO(J=2-1) is also depressed with respect to ^12CO (J=2-1). This suggeststhat the ^13CO gas may be underabundant in the high-R_1-0 starburstmergers, although we cannot rule out the possibility that excitation andoptical depth effects are still affecting R_2-1, for example, as aresult of the large velocity widths in the CO emission lines. Additionalobservations of both ^12CO and ^13CO lines at J>=3 are required tobetter constrain the conditions of the molecular gas in luminousstarburst galaxies.
| Transitional YSOs: candidates from flat-spectrum IRAS sources
We are searching for Young Stellar Objects (YSOs) near the boundarybetween protostars and pre-main-sequence objects, what we termTransitional YSOs. We have identified a sample of 125 objects ascandidate transitional YSOs on the basis of IRAS colors and the opticalappearance on POSS plates. We have obtained optical and near-IR imagingof 82 objects accessible from the Northern Hemisphere and optical imagesof 62 sources accessible from the South. We also created deconvolved 60mu m IRAS images of all sources. We have classified the objects on thebasis of their morphology in the optical and near-IR images. We findthat the majority of our objects are associated with star-formingregions, confirming our expectation that the bulk of these objects areYSOs. Of the 125 objects, 28 have a variety of characteristics verysimilar to other transitional YSOs, while another 22 show some of thesecharacteristics. Furthermore we have found seven objects to be goodcandidates for members of the Herbig Ae/Be stellar group, of which threeare newly identified as such. We have placed a set of images for each ofthe objects in the archives of the Centre de Données astronomiquede Strasbourg (CDS). Based on observations collected at the EuropeanSouthern Observatory, La Silla, Chile.
| ^13CO (J = 1-0) Depression in Luminous Starburst Mergers
It is known that the class of luminous starburst galaxies tends to havehigher R=^12CO (J=1-0)/^13CO (J=1-0) integrated line intensity ratios(R>20) than normal spiral galaxies (R~10). Since most previousstudies investigated only R, it remains uncertain whether the luminousstarburst galaxies are overabundant in ^12CO or underabundant in ^13CO.Here we propose a new observational test to examine this problem. Ournew test is to compare far-infrared luminosities [L(FIR)] with those of^12CO and ^13CO [L(^12CO) and L(^13CO), respectively]. It is shown thatthere is a very tight correlation between L(^12CO) and L(FIR), as foundin many previous studies. However, we find that the ^13CO luminositiesof the high-R galaxies are lower by a factor of 3 on average than thoseexpected from the correlation for the remaining galaxies with ordinary Rvalues. Therefore, we conclude that the observed high R values for theluminous starburst galaxies are attributed to their lower ^13CO lineintensities.
| 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.
| Molecular hydrogen in the central regions of southern infrared galaxies
An extensive set of molecular hydrogen observations of centers ofsouthern infrared galaxies is presented. Our data are combined withpublished infrared and radio observations to investigate therelationship between nuclear and circumnuclear activity. We convert theobservational data to absolute luminosities, by applying the knowndistances. The resulting dataset covers several decades in luminosityfor the various parameters, which observe fairly tight correlations. Theparameters of our (power law) fits are, at the level of accuracyachieved, not dependent on the type of nuclear activity: while thedataset comprises a mixture of alleged Seyfert, Liner & starburstgalaxies, single fits match the complete sample well enough. Inparticular, non-thermal nuclei (AGN) present in some of the galaxies inthe current sample, do not stand out in the parameters we investigated.The absence of a significant dependence on the nuclear type isconsistent with the idea that the ever present starbursts energeticallydominate a possible `AGN in a dusty environment'-component in mostgalaxy nuclei with infrared excesses. The size of the H_2 emittingregion is found to be proportional to the square root of the 21 cm radiocontinuum luminosity. The excitation of the circumnuclear H_2 isdominated by shocks. If the H_2 extent marks the size of an inner cavityin the dense molecular material surrounding a galaxy nucleus and theradio luminosity is proportional to the mechanical luminosity of(circum)nuclear winds. This result then indicates that the cavity sizeoccurs at constant pressure in the sample galaxies, in accordance withthe superwind model by Heckman et al. (1990) [ApJS, 74, 833]. Ourresults, together with those obtained by others, thus suggest thatluminosities and size scales of excited gas associated with activenuclei are dominated by the mechanical energy input. Given thedifficulties of uniquely establishing the presence of an AGN, we cannotexclude that (a large fraction of the) infrared luminous galaxiesprocure part of their radiated energy through accretion onto a massivedark object.
| Redshift Distribution of Galaxies in the Southern Milky Way Region 210 degrees < L < 360 degrees and B < 15 degrees
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..107..521V&db_key=AST
| A CO survey of galaxies with the SEST and the 20-m Onsala telescope.
A large survey of galaxies in the J=1-0 CO line, performed during1985-1988 using the 15-m SEST and the 20-m millimetre wave telescope ofOnsala Space Observatory, is presented. The HPBW of the telescopes are44" and 33" at 115GHz, respectively. The central positions of 168galaxies were observed and 101 of these were detected in the CO line.More than 20% of these are new detections. Maps of some of the galaxiesare also presented.
| The IRAS Bright Galaxy Survey - Part II: Extension to Southern Declinations (delta ~< -30), and Low Galactic Latitudes (f<|b|
Complete IRAS Observations and redshifts are reported for all sourcesidentified in the IRAS Bright Galaxy Survey-Part II (hereafter referredto as BGS_2_). Source positions, radial velocities, optical magnitudes,and total flux densities, peak flux densities, and spatial extents at12, 25, and 100 ,microns are reported for 288 sources having 60 micronflux densities > 5.24 Jy, the completeness limit of the originalBright Galaxy Survey [Soifer et al., AJ, 98,766(1989)], hereafterreferred to as BGS_1_. These new data represent the extension of theIRAS Bright Galaxy Survey to southern declinations,δ<~-30^deg^, and low Galactic latitudes,5^deg^<|b|<30^deg^. Although the sky coverage of the BGS_2_ (~19935 deg^2^) is 37% larger than the sky coverage of the BGS_1_, thenumber of sources is 8% smaller due primarily to large scale structurein the local distribution of galaxies. Otherwise, the sources in theBGS_2_ show similar relationships between number counts and flux densityas observed for the 313 sources in the BGS_1_. The BGS_2_ along with theearlier BGS, represents the best sample currently available for definingthe infrared properties of galaxies in the local (z <~ 0.1) Universe.
| 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.
| Molecular gas in starburst galaxies: line intensities and physical conditions
In a study of molecular gas in IR-bright galaxies, we have observed thecentral position in ^12^CO J=1-0, J=2-1; ^13^CO J=1-0, J=2-1; C^18^OJ=1-0 and HCN J=1-0 line emission. The sample (in total 32 galaxies)consists of starburst galaxies, interacting galaxies and two quiescentsystems. We find a mean ^12^CO 2-1/1-0 line ratio of 0.93+/-0.22, and amean ^13^CO 2-1/1-0 line ratio of 1.3+/-0.66. The mean ^12^CO/^13^CO 1-0ratio (=R(1-0)) is =~13+/-6 and for ^12^CO/^13^CO 2-1 it is =~13+/-5.The mean ^12^CO/HCN 1-0 ratio is =~16. The ^12^CO/C^18^O 1-0 intensityratio ranges from 20 to 140 in 6 galaxies. These values of ratios referto central positions corrected for effects of beam-size and source-size.A considerable fraction of the ^13^CO emission may be saturated andoriginate in dense cores of smaller volume filling factor than thesurrounding ^12^CO-emitting gas. High gas temperatures and turbulencework against large optical depths in the ^12^CO 1-0 line of the envelopegas. In contrast to what is usually assumed for the ^12^CO 1-0 line, weinfer moderate optical depths, τ=~1, for the dominant^12^CO-emitting structure. We have found that galaxies with largeintensity ratios of [C II] 158 μm to ^12^CO 1-0 also have ^12^CO2-1/1-0 ratios >=0.8, implying that the ^12^CO-emitting gas may beboth dense and hot enough to excite the [C II] 158 μm line, acharacteristic of warm (T_k_ > 100K), photon-dominated regions. Wehave not found a correlation between the intensity ratio, I(CO)/I(HCN),and disturbed morphology, far-infrared emission, or measures ofstar-forming activity in our sample of galaxies, in contrast to thefindings of Solomon et al. (1992). The ^12^CO/HCN intensity ratio isquite uniform over a sample of 11 interacting galaxies and mergers. HCNis not detected in the one isolated spiral in the sample. Furthermore,we have observed R(1-0) in off-centre positions in 6 galaxies: NGC 1808,NGC 3256, NGC 4038/39, NGC 5055, NGC 6221 and NGC 7552. Offset positionsin the ^12^CO/^13^CO 2-1 intensity ratio have been observed in 3galaxies: NGC 660, NGC 2146 and Arp 299. We suggest that galaxies thatdisplay significant variation in the ratio, such as the merger NGC 3256,have at least two populations of molecular cloud ensembles:high-pressure clouds in the centre and an extended disk-component ofmore quiescent clouds. The molecular gas in the centres of luminousmergers with large gas surface densities (>10^4^Mȯ/pc^2^) willbe highly turbulent. In general, we suggest that R(1-0) is a measure ofthe cloud environment: the extreme values R(1-0)>20 originate inturbulent, high-pressure gas in the centres of luminous mergers;intermediate ratios 10<~R(1-0)<~15 originate in the inner kpc ofmore normal starburst galaxies; small ratios R(1-0)=~6 are a signatureof a disk population of clouds. We address the notion that abundanceanomalies cause the elevated values of R(1-0) in luminous merginggalaxies. To some extent, this notion rests on the assumption ofτ>>1 in the ^12^CO 1-0 line. We demonstrate how thisassumption may be flawed and conclude that in order to measureabundances in the molecular medium, one must carefully model thephysical properties of the molecular gas. Although abundances may beunusual in extreme mergers, they are only one aspect of the propertiesof the molecular gas in these regions.
| Molecular gas in five southern active galaxies.
Not Available
| A search for IRAS galaxies behind the southern Milky Way
We systematically searched for IRAS galaxies with 60 micrometer fluxdensity larger than 0.6 Jy by using the UK Schmidt Infrared and IIIa-JAtlases in the Milky Way region (absolute value of b less than 15 deg)between l = 210 deg and 360 deg. We first selected about 4000 IRAS pointsources by using our far-infrared criteria, which are optimized for thesearch of IRAS galaxies behind the Milky Way region, and then inspectedvisually the optical counterparts of them on the Schmidt Atlas filmcopies. We found 966 IRAS sources associated with galaxy-like objects.The list of the objects is presented here with the IRAS source name,Galactic coordinates, IRAS flux densities, field number and emulsion ofthe Atlas, type and size of galaxy (-like) image, redshift,multiplicity, and cross-identification. Of these, 423 galaxies arealready cataloged in the Catalog of Galaxies and Quasars Observed in theIRAS Survey, and most of the remaining 543 galaxy candidates are newlyidentified in this search. Although the radial velocities are known foronly 387 galaxies, of which 60 were newly measured by us so far, weinferred the contamination by Galactic objects to be small from the goodcorrelation between the sky distributions of the newly identified galaxycandidates and the previously cataloged galaxies. In the regions wherethe Galactic molecular clouds dominate, almost all the sources were notidentified as galaxies. The detected galaxies are clustered in the threeregions around l = 240 deg, 280 deg, and 315 deg, where the projectednumber densities are higher than the whole-sky average of IRAS galaxiesof the same flux limit.
| IRAS LRS spectroscopy of galaxies
The study presents IRAS LRS data for 350 galaxies with pointlike IRASsources having either S(12) or S(25) not less than 1.5 Jy. Techniquesare presented which form the mean of an ensemble of LRS spectra, ll ofwhich are only of low signal-to-noise ratio, by quantitative evaluationof the significance of the individual spectra for each object ratherthan mere acceptance of the 'average spectrum' present in the completeLRS data base. Average LRS spectra for groups of galaxies with distinctoptical nuclear properties are formed. Average LRS spectra for severalcategories of objects are presented and interpreted. H II regiongalaxies show the polycyclic aromatic hydrocarbon spectrum of bands inemissions; type 2 Seyferts present a broad emission feature parking near16 microns; LINERs and galaxies without optical emission lines have LRSspectra that decline with wavelength, whereas type 1 Seyferts and WRgalaxies have red spectra suggestive of nonthermal emission processes.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
