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

NGC 1522



Upload your image

DSS Images   Other Images

Related articles

A Survey of O VI, C III, and H I in Highly Ionized High-Velocity Clouds
We present a Far Ultraviolet Spectroscopic Explorer survey of highlyionized high-velocity clouds (HVCs) in 66 extragalactic sight lines with(S/N)1030>8. We search the spectra for high-velocity (100km s-1<|vLSR|<400 km s-1) O VIabsorption and find a total of 63 absorbers, 16 with 21 cm emitting H Icounterparts and 47 ``highly ionized'' absorbers without 21 cm emission.The highly ionized HVC population is characterized by =38+/-10 km s-1 and =13.83+/-0.36, with negative-velocity clouds generally found atl<180deg and positive-velocity clouds found atl>180deg. Eleven of these highly ionized HVCs arepositive-velocity wings (broad O VI features extending asymmetrically tovelocities of up to 300 km s-1). We find that 81% (30 of 37)of highly ionized HVCs have clear accompanying C III absorption, and 76%(29 of 38) have accompanying H I absorption in the Lyman series. Wepresent the first (O VI selected) sample of C III and H I absorptionline HVCs and find =30+/-8 km s-1,logNa(C III) ranges from <12.5 to >14.4, =22+/-5 km s-1, and log Na(H I) ranges from<14.7 to >16.9. The lower average width of the high-velocity H Iabsorbers implies the H I lines arise in a separate, lower temperaturephase than the O VI. The ratio Na(C III)/Na(O VI)is generally constant with velocity in highly ionized HVCs, suggestingthat at least some C III resides in the same gas as the O VI.Collisional ionization equilibrium models with solar abundances canexplain the O VI/C III ratios for temperatures near1.7×105 K; nonequilibrium models with the O VI ``frozenin'' at lower temperatures are also possible. Photoionization models arenot viable since they underpredict O VI by several orders of magnitude.The presence of associated C III and H I strongly suggests the highlyionized HVCs are not formed in the hotter plasma that gives rise to OVII and O VIII X-ray absorption. We find that the shape of the O VIpositive-velocity wing profiles is well reproduced by a radiativelycooling, vertical outflow moving with ballistic dynamics, withT0=106 K, n0~2×10-3cm-3, and v0~250 km s-1. However, theoutflow has to be patchy and out of ionization equilibrium to explainthe sky distribution and the simultaneous presence of O VI, C III, and HI. We found that a spherical outflow can produce high-velocity O VIcomponents (as opposed to the wings), showing that the possible range ofoutflow model results is too broad to conclusively identify whether ornot an outflow has left its signature in the data. An alternative model,supported by the similar multiphase structure and similar O VIproperties of highly ionized and 21 cm HVCs, is one where the highlyionized HVCs represent the low N(H I) tail of the HVC population, withthe O VI formed at the interfaces around the embedded H I cores.Although we cannot rule out the possibility that some highly ionizedHVCs exist in the Local Group or beyond, we favor a Galactic origin.This is based on the recent evidence that both H I HVCs and themillion-degree gas detected in X-ray absorption are Galactic phenomena.Since the highly ionized HVCs appear to trace the interface betweenthese two Galactic phases, it follows that highly ionized HVCs areGalactic themselves. However, the nondetection of high-velocity O VI inhalo star spectra implies that any Galactic high-velocity O VI exists atz distances beyond a few kpc.

A wide-field HI study of the NGC 1566 group
We report on neutral hydrogen observations of a ~ 5.5 × 5.5deg2 field around the NGC 1566 galaxy group with themultibeam narrow-band system on the 64-m Parkes Telescope. We detected13 HI sources in the field, including two galaxies not previously knownto be members of the group, bringing the total number of confirmedgalaxies in this group to 26. Each of the HI galaxies can be associatedwith an optically catalogued galaxy. No `intergalactic HI clouds' werefound to an HI mass limit of ~3.5 ×108Msolar. We have estimated the expected HIcontent of the late-type galaxies in this group and find that the totaldetected HI is consistent with our expectations. However, while noglobal HI deficiency is inferred for this group, two galaxies exhibitindividual HI deficiencies. Further observations are needed to determinethe gas removal mechanisms in these galaxies.

Palomar/Las Campanas Imaging Atlas of Blue Compact Dwarf Galaxies. II. Surface Photometry and the Properties of the Underlying Stellar Population
We present the results from an analysis of surface photometry of B, R,and Hα images of a total of 114 nearby galaxies(vhelio<4000 km s-1) drawn from the Palomar/LasCampanas Imaging Atlas of blue compact dwarf (BCD) galaxies. Surfacebrightness and color profiles for the complete sample have beenobtained. We determine the exponential and Sérsic profiles thatbest fit the surface brightness distribution of the underlying stellarpopulation detected in these galaxies. We also compute the (B-R) colorand total absolute magnitude of the underlying stellar population andcompared them to the integrated properties of the galaxies in thesample. Our analysis shows that the (B-R) color of the underlyingpopulation is systematically redder than the integrated color, except inthose galaxies where the integrated colors are strongly contaminated byline and nebular-continuum emission. We also find that galaxies withrelatively red underlying stellar populations [typically (B-R)>=1mag] show structural properties compatible with those of dwarfelliptical galaxies (i.e., a smooth light distribution, fainterextrapolated central surface brightness, and larger scale lengths thanBCD galaxies with blue underlying stellar populations). At least ~15% ofthe galaxies in the sample are compatible with being dwarf elliptical(dE) galaxies experiencing a burst of star formation. For the remainingBCD galaxies in the sample we do not find any correlation between therecent star formation activity and their structural differences withrespect to other types of dwarf galaxies.

Optimization of Starburst99 for Intermediate-Age and Old Stellar Populations
We have incorporated the latest release of the Padova models into theevolutionary synthesis code Starburst99. The Padova tracks were extendedto include the full asymptotic giant branch (AGB) evolution until thefinal thermal pulse over the mass range 0.9-5 Msolar. Withthis addition, Starburst99 accounts for all stellar phases thatcontribute to the integrated light of a stellar population witharbitrary age from the extreme-ultraviolet to the near-infrared. AGBstars are important for ages between 0.1 and 2 Gyr, with theircontribution increasing at longer wavelengths. We investigatesimilarities and differences between the model predictions by the Genevaand the Padova tracks. The differences are particularly pronounced atages >1 Gyr, when incompleteness sets in for the Geneva models. Wealso perform detailed comparisons with the predictions of other majorsynthesis codes and find excellent agreement. Our synthesized opticalcolors are compared to observations of old, intermediate-age, and youngpopulations. Excellent agreement is found for the old globular clustersystem of NGC 5128 and for old and intermediate-age clusters in NGC4038/4039. In contrast, the models fail for red supergiant-dominatedpopulations with subsolar abundances. This failure can be traced back toincorrect red supergiant parameters in the stellar evolutionary tracks.Our models and the synthesis code are publicly available as version 5.0of Starburst99 at http://www.stsci.edu/science/starburst99.

Catalog of Double Nucleus Disk Galaxies
We have compiled a catalog of disk galaxies that have a double nucleus,through systematic examination of existing catalogs and publications.The Catalog of Double Nucleus Disk Galaxies includes 107 objects,together with their basic data. The aim of the catalog is to provide amore systematic and homogeneous basis for the study of the relevance ofgalaxy interactions and minor mergers in the formation of these doublenuclei. We have also investigated possible correlations betweengeometric and photometric parameters of the double nuclei and their hostgalaxies. The preliminary results indicate the presence of severalsignificant correlations that should be considered in any theoreticalscenario describing minor mergers and disk galaxy evolution.

Palomar/Las Campanas Imaging Atlas of Blue Compact Dwarf Galaxies. I. Images and Integrated Photometry
We present B, R, and Hα images for a total of 114 nearby galaxies(vhelio<4000 km s-1) that, with exception ofnine objects, are classified as blue compact dwarfs (BCDs). BRintegrated magnitudes, Hα fluxes and Hα equivalent widthsfor all the objects in the sample are presented. A new set ofquantitative, observational criteria for a galaxy to be classified as aBCD is proposed. These criteria include a limit on the K-band luminosity(i.e., stellar mass; MK>-21 mag), peak surface brightness(μB,peak<22 mag arcsec-2), and color at thepeak surface brightness(μB,peak-μR,peak<~1). Hα emissionis detected in all but three sample galaxies. Typical color, absolutemagnitude, and Hα luminosity are (B-R)=0.7+/-0.3 mag,MB=-16.1+/-1.4 mag, and log (LHα)=40.0+/-0.6(ergs s-1). Galaxies morphologically classified as nE and iEBCDs within our sample show lower Hα equivalent widths and reddercolors, on average, than the iI- and i0-type BCDs. For most of thegalaxies the presence of an evolved stellar population is required toexplain their observed properties; only the most metal-poor BCDs (e.g.,I Zw 18, Tol 65) are still compatible with a pure, young burst. Theflux-calibrated and WCS-compliant images in this Atlas are individuallyavailable through the NASA/IPAC Extragalactic Database (NED) imageserver and collectively through a dedicated Web page.

The 1 to 2.5 mu broad band emission of Blue Compact Dwarf Galaxies
We present J, H and K surface photometry of 12 Blue Compact DwarfGalaxies (BCDGs) selected from the southern sample (Doublier et al.\cite{doublieretal99a}). A systematic excess of light in the K band withrespect to the other bands in the visible and the near infrared isobserved, indicating, since nebular emission is negligible, that astellar population of red giants dominates the global flux from thegalaxy. Moreover, comparisons of the metallicity-color relations ofBCDGs and globular clusters show very little differences, indicatingthat BCDGs are most probably old, in the cosmological sense, systems.Local colors of the star forming regions show that these regions areindeed very young and possibly coeval across the galaxy when severalstarburst locations exist. At least 4 BCDGs (UM 465A and B, Haro 14 andTololo 0610-378) show evidence of the presence of young red supergiantstars. The light distributions in the J, H and K bands are generallyconsistent with those in the optical, the differences are discussed. Weconfirm that our optical photometric classification remains valid in thenear infrared. Thus, the global light distribution in the galaxy is anintrinsic property of the host galaxy independent of the presence of thestarburst. Based on observations made at 2.2~m Danish telescope in LaSilla, operated by the European Southern Observatory.

FAUST observations in the Fourth Galactic Quadrant*
We analyse UV observations with FAUST of four sky fields in the generaldirection of the Fourth Galactic Quadrant, in which we detect 777 UVsources. This is ~50 per cent more than detected originally by Bowyer etal. We discuss the source detection process and the identification of UVsources with optical counterparts. For the first time in this project weuse ground-based objective-prism information for two of the fields, toselect the best-matching optical objects with which to identify the UVsources. Using this, and correlations with existing catalogues, wepresent reliable identifications for ~75 per cent of the sources. Mostof the remaining sources have assigned optical counterparts but, lackingadditional information, we offer only plausible identifications. Wediscuss the types of objects found, and compare the observed populationwith predictions of our UV Galaxy model.

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.

Multi-spectral study of a new sample of Blue Compact Dwarf Galaxies. II. B and R surface photometry of 22 southern objects
We present the results of surface photometry on a new sample of BlueCompact Dwarf galaxies (BCDGs), in continuation to a previous paper(Doublier et al. 1997, hereafter Paper I). The 22 galaxies (plus twocompanions) discussed in the present paper have been selected in theSouthern Hemisphere, from several lists. An atlas containing isophotalmaps, surface brightnesses and B-R color profiles of the sample isgiven, together with the tables containing the photometric parameters.The results are consistent with those obtained in Paper I for objectsselected from the Byurakan Surveys in the Northern hemisphere.Similarly, we find about one fourth of the BCDGs showing a dominantr(1/4) brightness distribution component, one fourth of the BCDG showinga dominant exponential surface brightness profile, and about half ofthem show composite brightness distributions. Integrated properties,colors, mean surface brightnesses and luminosity-radius relations areinvestigated and discussed for the objects presented in this paper andPaper I. We found that r(1/4) BCDGs tend to show a different behaviourcompared to the exponential BCDGs, with respect to colors, compactnessand luminosity-radius relations. We also include a brief study of thesurroundings of the galaxies, where we find several candidatecompanions. Based on observations collected at the 1.54 m DanishTelscope at the European Southern observatory (La Silla, Chile).

A Comparison of the Intrinsic Shapes of Two Different Types of Dwarf Galaxies: Blue Compact Dwarfs and Dwarf Ellipticals
We measure the apparent shapes for a sample of 62 blue compact dwarfgalaxies (BCDs) and compare them with the apparent shapes for a sampleof 80 dwarf elliptical galaxies (dEs). The BCDs are flatter, on average,than the dEs, but the difference is only marginally significant. We thenuse both nonparametric and parametric techniques to determine possibledistributions of intrinsic shapes for the BCDs. The hypothesis that BCDsare oblate spheroids can be ruled out with a high confidence level(>99%), but the hypothesis that they are prolate spheroids cannot beexcluded. The apparent shapes of BCDs are totally consistent with thehypothesis that they are triaxial ellipsoids. If the intrinsic axisratios beta and gamma are distributed according to a Gaussian with meansbeta 0 and gamma 0 and standard deviation sigma , we find that thebest-fitting distribution for BCDs has ( beta 0, gamma 0, sigma ) =(0.66, 0.55, 0.16), while that for dEs has ( beta 0, gamma 0, sigma ) =(0.85, 0.64, 0.24). Our results are consistent with the hypothesis thatBCDs have a close evolutionary relation with dEs.

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.

H II Galaxies versus Photoionization Models for Evolving Starbursts
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..107..661S&db_key=AST

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.

Element abundances in H II galaxies
Data for 121 H II systems from the spectrophotometric catalog of H IIgalaxies (Terlevich et al. 1991) have been analyzed to determine theabundances of the most common chemical elements. The range of O/Hspanned by the data is from 0.5 to 0.03 the solar value. The rarity ofobjects in the sample with metallicities similar to that of I Zw 18could correspond to the claimed increasing probability to findlow-metallicity objects among intrinsically fainter systems. It isargued that the correction for ionization for Ne could be inadequate dueto the transformation of part of the O(2+) into O(+) in thehigh-ionization zone through charge transfer reactions. The apparentover-abundance of Ne found in low-excitation objects would then be justan artifact. When the analysis is restricted to high-excitation nebulae(O(2+)/O is greater than or equal to 0.9), we find a constant Ne/O =0.17 ratio, in agreement with the current ideas about thenucleosynthesis of those two elements. The N/O ratio, once the systemswith detected traces of the presence of shocks were discarded, was foundto be constant at the level 0.032. Thus, for those objects, N isessentially primary in origin. On the other hand, the greater Nabundances in higher metallicity systems would indicate that secondaryproduction is at work in them. Those mechanisms, however, are operativeonly when the metallicity is greater than some threshold value. The lastelement we have considered is helium. It is argued that none of theproposed ionization correction schemes works correctly, so only objectsfor which the amount of neutral He is seemingly negligible can beretained to determine He abundances. It is remarked that the selectionby effective temperature corresponds in fact to a selection bymetallicity. The lower envelope of the He abundances we find is about22%. We do not find any trend between the He content and the abundancesof other elements like O or N.

Southern Sky Redshift Survey - The catalog
The catalog of radial velocities for galaxies which comprise thediameter-limited sample of the Southern Sky Redshift Survey ispresented. It consolidates the data of observations carried out at theLas Campanas Observatory, Observatorio Nacional, and South AfricanAstronomical Observatory. The criteria used for the sample selection aredescribed, as well as the observational procedures and the techniqueutilized to obtain the final radial velocities. The intercomparisonbetween radial velocity measurements from different telescopes indicatesthat the final data base is fairly homogeneous with a typical error ofabout 40 km/s. The sample is at present 90 percent complete, and themissing galaxies are predominantly objects with very low surfacebrightness for which it is very difficult to obtain optical redshifts.

A catalog of southern groups of galaxies
A catalog of groups of galaxies identified in the southern Galactic capis presented. This catalog was constructed utilizing the group-findingalgorithm developed by Huchra and Geller (1982) to analyze galaxysamples with well-defined selection criteria and complete velocityinformation.

The Southern Supercluster
The Southern Supercluster is described using data compiled from fivecatalogs, reduced to a homogeneous system following RC2. In terms ofmass, luminosity, and mass-to-light ratio, the Southern Superclustercompares well with the Coma and Hercules superclusters, but is lessmassive than the Local Supercluster. It is shown that, even though theSouthern Supercluster is the nearest supercluster to the LocalSupercluster, it is well separated from the Local Supercluster. However,there is evidence of a tenuous stream of galaxies connecting theSouthern Supercluster with the Perseus Supercluster.

The components of mid- and far-infrared emission from S0 and early-type shell galaxies
The IRAS database has been used to study detections of about 150early-type elliptical and S0 galaxies exhibiting a shell structure. Nostrong evidence for the expected enhancement of either star formationrates or heating of the interstellar medium is found. It is suggestedthat for some of the sample galaxies either a contribution from warmdust surrounding evolved stars or emission from an active nucleus may besignificant.

Photometric and spectroscopic observations of 56 southern compact galaxies
UBVRI and UBVJHK multiaperture photometry results are presented for 56southern compact galaxies (CGs), together with basic properties for 35of these that were derived from spectroscopic and photometricobservations. CGs constitute a very heterogeneous group that ranges inabsolute magnitude from -16 to -23; their high surface brightness oftenmasks their morphological substructure. The present spectroscopy wascarried out at a dispersion varying from 114 to 244 A/mm.

Southern Galaxy Catalogue.
Not Available

A catalog of elliptical galaxies with shells
We present a catalog of 137 elliptical galaxies south of -17 deg declination which exhibit shell or ripple features at large distances from the galaxy or in the outer envelope. Some of these galaxies show similar features in the inner envelope when suitable high resolution plate material is examined. Very few of the galaxies are associated with radio sources. We discuss the environment of shell galaxies, and the proportion of ellipticals which have these features. It appears that about half of the galaxies with shells are isolated and most of the rest are members of small groups. We discuss several individual examples which appear to be typical of this class of galaxy, and others which probably illustrate an evolutionary sequence.

Submit a new article

Related links

  • - No Links Found -
Submit a new link

Member of following groups:

Observation and Astrometry data

Right ascension:04h06m07.70s
Aparent dimensions:1.23′ × 0.851′

Catalogs and designations:
Proper Names   (Edit)
NGC 2000.0NGC 1522

→ Request more catalogs and designations from VizieR