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Star Formation Properties of a Large Sample of Irregular Galaxies
We present the results of Hα imaging of a large sample ofirregular galaxies. Our sample includes 94 galaxies with morphologicalclassifications of Im, 26 blue compact dwarfs (BCDs), and 20 Sm systems.The sample spans a large range in galactic parameters, includingintegrated absolute magnitude (MV of -9 to -19), averagesurface brightness (20-27 mag arcsec-2), current starformation activity (0-1.3 Msolar yr-1kpc-2), and relative gas content(0.02-5Msolar/LB). The Hα images were usedto measure the integrated star formation rates, determine the extents ofstar formation in the disks, and compare azimuthally averaged radialprofiles of current star formation to older starlight. The integratedstar formation rates of Im galaxies normalized to the physical size ofthe galaxy span a range of a factor of 104 with 10% Imgalaxies and one Sm system having no measurable star formation at thepresent time. The BCDs fall, on average, at the high star formation rateend of the range. We find no correlation between star formation activityand proximity to other cataloged galaxies. Two galaxies located in voidsare similar in properties to the Sm group in our sample. The H IIregions in these galaxies are most often found within the Holmbergradius RH, although in a few systems H II regions are tracedas far as 1.7RH. Similarly, most of the star formation isfound within three disk scale lengths RD, but in somegalaxies H II regions are traced as far as 6RD. A comparisonof Hα surface photometry with V-band surface photometry shows thatthe two approximately follow each other with radius in Sm galaxies, butin most BCDs there is an excess of Hα emission in the centers thatdrops with radius. In approximately half of the Im galaxies Hα andV correspond well, and in the rest there are small to large differencesin the relative rate of falloff with radius. The cases with stronggradients in the LHα/LV ratios and with highcentral star formation rate densities, which include most of the BCDs,require a significant fraction of their gas to migrate to the center inthe last gigayear. We discuss possible torques that could have causedthis without leaving an obvious signature, including dark matter barsand past interactions or mergers with small galaxies or H I clouds.There is now a substantial amount of evidence for these processes amongmany surveys of BCDs. We note that such gas migration will also increasethe local pressure and possibly enhance the formation of massive denseclusters but conclude that the star formation process itself does notappear to differ much among BCD, Im, and Sm types. In particular, thereis evidence in the distribution function for Hα surface brightnessthat the turbulent Mach numbers are all about the same in these systems.This follows from the Hα distribution functions corrected forexponential disk gradients, which are log-normal with a nearly constantdispersion. Thus, the influence of shock-triggered star formation isapparently no greater in BCDs than in Im and Sm types.
| The 1000 Brightest HIPASS Galaxies: H I Properties
We present the HIPASS Bright Galaxy Catalog (BGC), which contains the1000 H I brightest galaxies in the southern sky as obtained from the H IParkes All-Sky Survey (HIPASS). The selection of the brightest sourcesis based on their H I peak flux density (Speak>~116 mJy)as measured from the spatially integrated HIPASS spectrum. The derived HI masses range from ~107 to 4×1010Msolar. While the BGC (z<0.03) is complete inSpeak, only a subset of ~500 sources can be consideredcomplete in integrated H I flux density (FHI>~25 Jy kms-1). The HIPASS BGC contains a total of 158 new redshifts.These belong to 91 new sources for which no optical or infraredcounterparts have previously been cataloged, an additional 51 galaxiesfor which no redshifts were previously known, and 16 galaxies for whichthe cataloged optical velocities disagree. Of the 91 newly cataloged BGCsources, only four are definite H I clouds: while three are likelyMagellanic debris with velocities around 400 km s-1, one is atidal cloud associated with the NGC 2442 galaxy group. The remaining 87new BGC sources, the majority of which lie in the zone of avoidance,appear to be galaxies. We identified optical counterparts to all but oneof the 30 new galaxies at Galactic latitudes |b|>10deg.Therefore, the BGC yields no evidence for a population of``free-floating'' intergalactic H I clouds without associated opticalcounterparts. HIPASS provides a clear view of the local large-scalestructure. The dominant features in the sky distribution of the BGC arethe Supergalactic Plane and the Local Void. In addition, one can clearlysee the Centaurus Wall, which connects via the Hydra and Antlia Clustersto the Puppis Filament. Some previously hardly noticable galaxy groupsstand out quite distinctly in the H I sky distribution. Several newstructures, including some not behind the Milky Way, are seen for thefirst time.
| The ISOPHOT 170 μm Serendipity Survey II. The catalog of optically identified galaxies%
The ISOPHOT Serendipity Sky Survey strip-scanning measurements covering≈15% of the far-infrared (FIR) sky at 170 μm were searched forcompact sources associated with optically identified galaxies. CompactSerendipity Survey sources with a high signal-to-noise ratio in at leasttwo ISOPHOT C200 detector pixels were selected that have a positionalassociation with a galaxy identification in the NED and/or Simbaddatabases and a galaxy counterpart visible on the Digitized Sky Surveyplates. A catalog with 170 μm fluxes for more than 1900 galaxies hasbeen established, 200 of which were measured several times. The faintest170 μm fluxes reach values just below 0.5 Jy, while the brightest,already somewhat extended galaxies have fluxes up to ≈600 Jy. For thevast majority of listed galaxies, the 170 μm fluxes were measured forthe first time. While most of the galaxies are spirals, about 70 of thesources are classified as ellipticals or lenticulars. This is the onlycurrently available large-scale galaxy catalog containing a sufficientnumber of sources with 170 μm fluxes to allow further statisticalstudies of various FIR properties.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.Members of the Consortium on the ISOPHOT Serendipity Survey (CISS) areMPIA Heidelberg, ESA ISO SOC Villafranca, AIP Potsdam, IPAC Pasadena,Imperial College London.Full Table 4 and Table 6 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/39
| Emission-Line Spectroscopy of H II Regions in Irregular and Blue Compact Dwarf Galaxies
We present reddenings and abundances of 189 H II regions measured from203 emission-line spectra in a sample of 65 irregular (Im), blue compactdwarf (BCD), and Sm galaxies. In most of these spectra we measure [OIII] lambda5007, Hβ, [N II] lambda6584, and [S II]lambdalambda6717, 6731; in 24 spectra we measure [O II] lambda3727 andin five we measure [O III] lambda4363. The internal reddenings of thegalaxies are used to determine whether redder irregular galaxies arealso dustier than bluer irregulars. We find that the range in opticalbroadband colors among Im galaxies is most likely dominated bydifferences in the contributions of the massive star population or theeffects of abundances, while the range in colors of BCDs does showevidence consistent with a contribution from dustiness. We use theabundances to confirm that our sample of BCD galaxies, selected to becomparable to Im systems in other global properties, are also comparablein abundances and, hence, evolutionary status. Finally, we explorerelationships between abundances and other global galactic propertiesand find few convincing correlations. However, bluer galaxies tend to bemore metal-poor. There is a slight trend of higher relative gas contentwith lower abundances among the BCD sample, but not in the Im sample.The difference could be due to a difference in gas distributions and thefraction of total gas that is actively participating in the chemicalevolution of the galaxy. In addition, our BCD, but not our Im, sample ofgalaxies are consistent by themselves with the galacticluminosity-metallicity relationship determined by others, but the Imsample is consistent with the general trend seen over a large baselinewhen combined with spiral galaxies. However, the scatter is large.
| The Southern Sky Redshift Survey
We report redshifts, magnitudes, and morphological classifications for5369 galaxies with m_B <= 15.5 and for 57 galaxies fainter than thislimit, in two regions covering a total of 1.70 sr in the southerncelestial hemisphere. The galaxy catalog is drawn primarily from thelist of nonstellar objects identified in the Hubble Space TelescopeGuide Star Catalog (GSC). The galaxies have positions accurate to ~1"and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes(m_SSRS2) from the relation between instrumental GSC magnitudes and thephotometry by Lauberts & Valentijn. From a comparison with CCDphotometry, we find that our system is homogeneous across the sky andcorresponds to magnitudes measured at the isophotal level ~26 magarcsec^-2. The precision of the radial velocities is ~40 km s^-1, andthe redshift survey is more than 99% complete to the m_SSRS2 = 15.5 maglimit. This sample is in the direction opposite that of the CfA2; incombination the two surveys provide an important database for studies ofthe properties of galaxies and their large-scale distribution in thenearby universe. Based on observations obtained at Cerro TololoInter-American Observatory, National Optical Astronomy Observatories,operated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation;Complejo Astronomico El Leoncito, operated under agreement between theConsejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; the European Southern Observatory, LaSilla, Chile, partially under the bilateral ESO-ObservatórioNacional agreement; Fred Lawrence Whipple Observatory;Laboratório Nacional de Astrofísica, Brazil; and the SouthAfrican Astronomical Observatory.
| 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.
| Asymmetry in high-precision global H I profiles of isolated spiral galaxies
New high-SNR 21 cm H I line profiles have been obtained for 104 galaxieswith the Green Bank 43 m telescope. The primary sample is composed ofisolated spirals with no known optical companions within a 1 radius anda median ratio of optical diameter to beamwidth of 0.17. An effort wasmade to ensure linearity of baseline fitting and precise flux densitycalibration to better than 5 percent. Two quantitative measures ofasymmetry are applied to assess the occurrence of lopsidedness in theglobal H I profiles. In agreement with previous estimates, half thegalaxies show significant H I profile asymmetries. The lopsidednesscannot be explained by pointing offsets but, rather, must result fromnoncircular motions, confusion with unidentified companions within thetelescope beam, or true distortions in the H I distribution.
| 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.
| Corrections and additions to the third reference catalogue of bright galaxies
List of corrections and additions to the Third Reference Catalogue ofBright Galaxies (RC3) are given. The corrected version of the catalogue(RC3.9b), dated April 1994, is currently available through the nationaldata centers.
| ROSAT X-ray survey of an area 10 degrees square around the active radio galaxy Centaurus A
Diffuse X-ray material extends in an irregular, broad filament for morethan 5 degrees north east of the giant radio elliptical, NGC 5128 (CenA). In the opposite direction the X-ray extension is clearly traced forabout 2 degrees, making an overall line of X-rays of greater than 7degon the sky originating from Cen A. The direction of this line coincidesalmost exactly with the direction of the X-ray jet, and its associatedradio jet, in the interior of Cen A. At a slightly different angle,within the accuracy of measurement along the X-ray counter jet, isencountered the radio and X-ray galaxy NGC 5090. Its presence in theX-ray ejection from Cen A supports the precedent from other associationsthat NGC 5090 is physically associated with Cen A. In the hardest X-raysthere is some indication that the radio lobes from Cen A are edgebrightened. Positions and known identifications of sources in the fieldare given. Some preliminary estimates of the properties of thisextensive X-ray material which has apparently been ejected from thisactive galaxy are given.
| Global properties of dwarf galaxies II. Colours and luminosities
We have used a previously determined sample of 278 dwarf galaxies formost of which B magnitudes, optical colours, HI fluxes and IRASflux-densities are known, in order to derive luminosities, colours andsurface brightnesses. Dwarf galaxy properties are compared to those of acontrol sample of 228 larger spiral galaxies. The dwarf galaxies have onaverage higher 60/100μm flux ratios and lower 12/25μm flux ratiosthan the spiral galaxies, indicating that the contribution of `cirrus'to the infrared emission from dwarf galaxies is relativelyinsignificant. In the dwarf galaxies, the 60/100μm flux ratioincreases with increasing optical blueness; spiral galaxies show theopposite. Dwarf galaxies with a low optical surface brightness have low100μm/HI ratios, but the converse is not true. Galaxies with high100μm/HI ratios (indicative of high dust-to-gas ratios) also havehigh FIR/B ratios as well as high 60/100μm flux-density ratios.Although this is true for both spiral and dwarf galaxies, at given100μm/HI ratios the dwarf galaxies have both a lower FIR/B ratio anda higher 60/100μm flux-density ratio. This result is of importance inthe interpretation of FIR/B - 60/100μm diagrams in terms of starformation activity.
| Global properties of dwarf galaxies. I. Galaxy sample and IRAS infrared flux-densities
We have selected a sample of 278 dwarf galaxies for which at least Bmagnitudes and preferably also optical colour information are available.For those galaxies that have no previously published IRAS fluxes, wehave used the IRAS database to extract fluxes or upper limits tosensitivity levels significantly better than those of the IRAS PointSource Catalog. New IRAS data include 79 galaxies detected in at leastone band, and 66 galaxies with good upper limits. In total, about 60% ofall dwarf galaxies in the sample now have been detected at 60/100μm.
| Composition and Morphology of Five Dwarf Irregular Galaxies
We present deep B, R, and I broadband images of five dwarf irregulargalaxies: DDO 11, DDO 214, NGC 7292, UGC 12060 and Mrk 59. The differentmorphologies we observe at each wavelength, as well as the overall colordifferences, are the result of the stellar populations and star-forminghistories of the galaxies. The CCD data were obtained at the WyomingInfrared Observatory.
| The morphological catalogue of galaxies equatorial survey
We present 865 redshifts of galaxies located in the equatorial stripdelta between -17.5 deg and -2.5 deg in the right ascension rangebetween 20 h and 5 h. Redshifts have been obtained for the completesample of all 833 galaxies in the Morphological Catalog of Galaxies withmagnitudes brighter than m = 14.5 (corresponding approximately tom(Zwicky) = 15.0). This sample also includes three galaxies from othersources with more reliable magnitudes, satisfying this limit, and 29fainter galaxies, usually companions of the galaxies in the magnitudelimited sample. Our maps of a very large volume of nearby spacedemonstrate a variety of coherent large scale structures which includelarge voids, 20-50/h Mpc in diameter and large walls at least 70/h Mpcacross.
| Composition and Morphology of Three Dwarf Irregular Galaxies
We have obtained deep B, R, and I broadband images of three dwarfirregular galaxies: DDO 11, DDO 214, and NGC 7292. The differentmorphologies we observe at each wavelength as well as the overall colordifferences are the results of the stellar populations and star-forminghistories of the galaxies. The CCD data were obtained at the WyomingInfrared Observatory.
| Star formation in spiral galaxies. I - H-alpha observations
This paper presents large-aperture photometric measurements of H-alpha +forbidden N II emission line strengths in 110 spiral galaxies. Thesegalaxies represent three different samples of objects: (1) low surfacebrightness spiral galaxies; (2) galaxies of extreme arm classifications(flocculent versus grand design); and (3) galaxies with measured (B -H)colors which have been used to study the color-absolute magnituderelation for spiral galaxies. Details of the observations are given, anda comparison is made with previous work. Future papers will use thisdata to study the star-formation rates in the various samples.
| Properties of H II region populations in galaxies. I - The first-ranked H II regions
H-alpha photometry of the brightest H II regions in 95 nearby spiral andirregular galaxies has been analyzed in order to study the dependence ofthe H II region populations on the properties of their parent galaxies.It is found that the brightest H II regions in Magellanic irregulargalaxies are about 50 times brighter than those in early-type spirals ofthe same absolute magnitude. It is suggested that this difference is dueto both an increase in the numbers of H II regions in late-type galaxiesand a physical change in the characteristic sizes of the star-formingregions.
| Uncertainties in 21 centimeter redshifts. I - Data
High-precision data on the 21-cm redshifts, profile widths, and shapesfor 625 galaxies are presented. Each galaxy is listed in across-identification and morphology table. High-resolution spectra arealso given for each galaxy. Internal redshift consistency is roughly 1km/s for galaxies for which the S/N is above 15. No systematic effectshave been found which might influence the observed redshift quantizationat 72.5 km/s or its submultiples.
| Stellar populations and star formation in irregular galaxies
A review and intercomparison is conducted of data on variousmorphologically-chosen groups of irregular galaxies in order tounderstand the underlying physical mechanisms that differentiate thesesystems. Particular attention is given to the observational clues to thestellar content, star-formation processes, and star-formation historiesof these galaxies, with an emphasis on the uncertainties and the manyunanswered questions.
| Irregular galaxies with extended H I emission
The NRAO 43-m telescope has been used to obtain H I 21-cm fluxes of alarge number of irregular galaxies integrated over a 21-arcmin beam,which can be used for determining total gas masses of these systems. Thedata are compared with fluxes obtained by Fisher and Tully (1975, 1981)with a 10-arcmin beam to identify those galaxies which may have extendedH I distributions relative to the optical sizes. Seven good candidatesystems are listed. The presence of extended H I in irregular galaxiesdoes not seem to correlate with basic global galaxian properties.
| Star-forming properties and histories of dwarf irregular galaxies - Down but not out
Spectroscopic and imaging data designed to study star formationprocesses in a sample of dwarf irregular (Irr) galaxies are presented.Although the low-surface brightness dwarf Irr's have much H I gas withwhich to form stars, the galaxy-wide star formation rates are low:typically about 10 to the -10th solar mass/yr/sq pc. The properties ofthe low-surface brightness dwarf Irr's are consistent with a constantstar formation rate equal to their current rate over approximately aHubble time. The typical star-forming regions in the dwarfs are onaverage smaller and less luminous than those in the giant Irr's,although the size distributions cover the same range, while similar togiant Irr's in many global parameters, the dwarfs have lower current andhistorical star formation rates per unit area. Dwarf Irr's have lowmetallicities relative to spirals, with typical nebular oxygenabundances falling between those of the LMC and SMC.
| Integrated magnitudes and mean colors of DDO dwarf galaxies in the UBV system. II - Distances, luminosities, and H I properties
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983AJ.....88..764D&db_key=AST
| Low surface brightness spiral galaxies. I - Neutral hydrogen content and location in the infrared Fisher-Tully diagram
Over the past three years, a survey of spiral galaxies characterized bydisks of unusually low surface brightness (LSB) has been conducted.These LSB spiral galaxies have luminosities in the range from -20 to -17(MB), and have projected central disk surface brightness valuesapproximately three times smaller, on average, than normal spirals inthe same luminosity range. Knowledge of the gas content of LSBs isimportant in connection with the study of processes which influence starformation, because the relative gas and stellar content of a galaxyprovides one indication of the degree to which star formation hasproceeded. Consequently, as a first step toward understanding of theconsidered systems, an H I survey of the available LSB sample wasconducted. The results of this survey are reported.
| Neutral hydrogen observations of DDO dwarf galaxies
All but 2 of the list of 243 David Dunlap Observatory (DDO) dwarf galaxycandidates have been observed in the H I 21-cm line with the NRAO 91 mand 43 m telescopes, and 179 have been detected. Among these, there areobjects which are particularly interesting because of their low surfacebrightness, including some systems which appear to be intrinsicallyreasonably big, and there are others of interest because they areintrinsically the smallest known extragalactic hydrogen-bearing systems.In this latter category are several new candidates for membership in theLocal Group. For all the detected systems, the radio observationsprovide redshifts, neutral hydrogen masses, and a total mass index. Thedistance independent hydrogen mass to luminosity ratio for the truedwarfs in the DDO sample indicates that they are relatively hydrogenrich with respect to large late type galaxies.
| Atlas of Peculiar Galaxies
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966ApJS...14....1A&db_key=AST
| Luminosity classifications of dwarf galaxies.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966AJ.....71..922V&db_key=AST
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