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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 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
| Radio sources in the 2dF Galaxy Redshift Survey - II. Local radio luminosity functions for AGN and star-forming galaxies at 1.4 GHz
We have cross-matched the 1.4-GHz NRAO VLA Sky Survey (NVSS) with thefirst 210 fields observed in the 2dF Galaxy Redshift Survey (2dFGRS),covering an effective area of 325deg2 (about 20 per cent ofthe final 2dFGRS area). This yields a set of optical spectra of 912candidate NVSS counterparts, of which we identify 757 as genuine radioidentifications - the largest and most homogeneous set of radio sourcespectra ever obtained. The 2dFGRS radio sources span the redshift rangez=0.005 to 0.438, and are a mixture of active galaxies (60 per cent) andstar-forming galaxies (40 per cent). About 25 per cent of the 2dFGRSradio sources are spatially resolved by NVSS, and the sample includesthree giant radio galaxies with projected linear size greater than 1Mpc.The high quality of the 2dF spectra means we can usually distinguishunambiguously between AGN and star-forming galaxies. We make a newdetermination of the local radio luminosity function at 1.4GHz for bothactive and star-forming galaxies, and derive a local star formationdensity of 0.022+/-0.004Msolaryr-1Mpc-3(H0=50kms-1Mpc-1).
| Bar Galaxies and Their Environments
The prints of the Palomar Sky Survey, luminosity classifications, andradial velocities were used to assign all northern Shapley-Ames galaxiesto either (1) field, (2) group, or (3) cluster environments. Thisinformation for 930 galaxies shows no evidence for a dependence of barfrequency on galaxy environment. This suggests that the formation of abar in a disk galaxy is mainly determined by the properties of theparent galaxy, rather than by the characteristics of its environment.
| FLAIR II Spectroscopy of Two DENIS J Band Galaxy Samples
As a pilot survey for the forthcoming 6dF Galaxy Redshift Survey,spectroscopy of galaxies selected in the 1.2 micron J waveband with theDENIS imaging survey was performed atthe UKST using the FLAIR IImulti-object spectroscope. Sixty-nine galaxy redshifts were obtained ina high galactic latitude field and an additional 12 redshifts in a lowgalactic latitude (b=-17°), obscured field. This spectroscopicfollowup of NIR selected galaxies illustrates the feasibility ofobtaining redshifts with optical spectra on galaxies selected at muchlonger wavelengths. It validated a very preliminary algorithm forstar/galaxy separation for high galactic latitude DENIS objects, with99% reliability for J<13.9. The FLAIR redshifts are in excellentagreement with those, previously published, of 20 common galaxies.However, the redshift determinations presented here requiredsubstantially longer integration times to achieve 90% completeness thanexpected from previous optical surveys at comparable depth. This ismainly due to a degradation in overall fibre throughput due to knownproblems with ageing of the prism-cement-fibre interface with exposureto UV light. In comparison to our high galactic latitude field, our lowlatitude (high extinction) field required 2.5 times more exposure timefor less than 50% of successful redshift measurements. Among theJ≤13.9 galaxies with measured redshifts, only 37+/-6% displayemission lines, in comparison with 60% of emission line galaxies inoptical samples of comparable depth. These galaxies are, on average,half a magnitude bluer in B-J than galaxies of the same luminositywithout emission lines. We confirm a previous optically-based resultthat the fraction of galaxies with emission lines increases rapidly withdecreasing galaxy luminosity. The J band luminosity function isestimated. Our high latitude field displays a concentration of galaxiesat cz≃38000kms-1 suggesting a possible supercluster. Aradial velocity is reported for a galaxy lying near the projected centreof the Abell 1434 cluster of galaxies, for which no cluster redshift iscurrently available.
| 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.
| Galaxy coordinates. II. Accurate equatorial coordinates for 17298 galaxies
Using images of the Digitized Sky Survey we measured coodinates for17298 galaxies having poorly defined coordinates. As a control, wemeasured with the same method 1522 galaxies having accurate coordinates.The comparison with our own measurements shows that the accuracy of themethod is about 6 arcsec on each axis (RA and DEC).
| 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.
| A comparative study of morphological classifications of APM galaxies
We investigate the consistency of visual morphological classificationsof galaxies by comparing classifications for 831 galaxies from sixindependent observers. The galaxies were classified on laser print copyimages or on computer screen using scans made with the Automated PlateMeasuring (APM) machine. Classifications are compared using the RevisedHubble numerical type index T. We find that individual observers agreewith one another with rms combined dispersions of between 1.3 and 2.3type units, typically about 1.8 units. The dispersions tend to decreaseslightly with increasing angular diameter and, in some cases, withincreasing axial ratio (b/a). The agreement between independentobservers is reasonably good but the scatter is non-negligible. In spiteof the scatter, the Revised Hubble T system can be used to train anautomated galaxy classifier, e.g. an artificial neural network, tohandle the large number of galaxy images that are being compiled in theAPM and other surveys.
| 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.
| CCD calibration of the magnitude scale for the SSRS2 sample: The equatorial region
In this paper we continue our investigation on the isophotal nature,accuracy, and uniformity of the magnitude system adopted in the SouthernSky Redshift Survey extension (SSRS2). Extending our earlier work, weexamine galaxies in the equatorial region, primarily in the declinationrange delta greater than or equal to -17.5 deg and less than or equal to0 deg, over a large range of right ascension, covering the southern andnorthern Galactic caps. For this purpose, we have obtained CCD isophotalmagnitudes in the B and R bands for 265 galaxies of differentmorphological types. Using the larger sample we confirm our earlierclaim that the mSSRS2 magnitudes are very nearly themagnitude measured within the isophote muB = 26 mag/sqarcsec, with a dispersion of about 0.30 mag. The relative zero-pointoffset between our mSSRS2 magnitudes and the CCD photometryis -0.02 mag from all data we have obtained. However, we detect avariation of the zero-point across different regions of the sky of +/-0.10 mag for regions at large angular separations. We also estimate thatthe zero-point offset between the mSSRS2 and Zwicky systemsis relatively small (approximately 0.10 mag), which should allow us tocombine the data from the SSRS2 and the CfA2 Redshift Survey.
| General study of group membership. II - Determination of nearby groups
We present a whole sky catalog of nearby groups of galaxies taken fromthe Lyon-Meudon Extragalactic Database. From the 78,000 objects in thedatabase, we extracted a sample of 6392 galaxies, complete up to thelimiting apparent magnitude B0 = 14.0. Moreover, in order to considersolely the galaxies of the local universe, all the selected galaxieshave a known recession velocity smaller than 5500 km/s. Two methods wereused in group construction: a Huchra-Geller (1982) derived percolationmethod and a Tully (1980) derived hierarchical method. Each method gaveus one catalog. These were then compared and synthesized to obtain asingle catalog containing the most reliable groups. There are 485 groupsof a least three members in the final catalog.
| Galaxies possibly resembling M82-type galaxies
A list of 298 galaxies with possible features of M82 galaxies ispresented. This list contains those Irr II candidates whose images onPalomar photographs shown no trace of dust although the objects are redand suspected to be peculiar.
| A self-regulated star formation rate as a function of global galactic parameters
A sample of active dwarf galaxies and a sample of Sc and irregulargalaxies are analyzed based on the assumption that the stellar formationrate is self-regulated in such a way that it maintains the criticalpressure P(max) near the gas pressure P(g) of the interstellar medium,where P(max) is the pressure of the marginal state of stability for thetransition warm gas to small clouds. The stellar formation rate Psi(PP)consistent with the condition P(max) = P(g), can be expressed as asimple analytical function of global galactic parameters. When it isassumed that the dust temperature, the gas metallicity, and the galacticdiameter remain constant, it is found that Psi(PP) is reduced to the lawof Schmidt with an exponent value of 1.43. Specifically, for the Galaxy,it is fond that Psi(PP) = about 10 solar masses/yr, which is reasonablyconsistent with previous values.
| Revised supernova rates in Shapley-Ames galaxies
Observations of 855 Shapley Ames galaxies made from November 1, 1980 toOctober 31, 1988, together with improved supernova luminosities, havebeen used to derive the frequency of supernovae of different types, andthe results are presented in tables. From a uniform database of 24supernovae discovered, the following SN rates are found, expressed in SNper century per 10 to the 10th L(B)(solar): SN Ia, 0.3; SN Ib, 0.3; andSN II, 1.0. The present data confirm the relatively high frequency of SNII in late-type galaxies that has been found by many previousinvestigators.
| IRAS observations of a large sample of normal irregular galaxies
IRAS 12, 25, 60, and 100 micron data are presented for a sample of Irrgalaxies which span a large range in star-formation activity. It isfound that the dwarf, giant, and amorphous Irr's generally have similarIR properties. The typical L(IR)/L(H-alpha) ratios of most classes ofIrr's, except for many of the luminous blue galaxies, are low comparedwith those of spiral galaxies and are consistent with the Irr's beingrelatively transparent systems without large amounts of optically hiddenstar formation. Compared with spiral galaxies, the Irr's have similarL(IR)/L(B) ratios, warmer S(100)/S(60) ratios, cooler S(25)/S(12)ratios, and lower dust-to-H I gas mass ratios. The temperature,dust-to-H I gas mass ratios, and L(IR)/L(B) ratios do not correlate withthe metallicity of the ionized gas of the Irr's. A correlation betweenthe IR fluxes and both the H-alpha and the blue stellar fluxes is foundfor the Irr's.
| A model of spiral-galaxy evolution. I - Galaxy morphology and star formation rate
The suggestion by Sandage (1986), that the change of star-formation ratewith time is a signature of each Hubble type, is discussed and verifiedon a large set of data. The nonlinear phase-coupling model of Shore etal. (1986), proposed for the evolution of galaxies with disk and halocomponents, is here adopted to follow the star-formation history inspiral galaxies. The effects of both stimulated and spontaneous starformation are included. A simple hypothesis on the connection betweenthe spiral wave amplitude and the cloud phase is sufficient to generatea continuous series of star-formation histories, which may correspond tothe sequence of Hubble types.
| The supernova rate in Shapley-Ames galaxies
A visual search for SNs in 748 Shapley-Ames galaxies during the 5-yearperiod from November 1, 1980 to October 31, 1985 has yielded SN rates of0.3h-squared, 0.4h-squared, and 1.1h-squared for objects of types Ia,Ib, and II, respectively. These data are judged to imply that Tammann's(1974, 1982) SN rates are probably too high by a factor of about 3. Fora Galactic luminosity of 2 x 10 to the 10th solar L(B), the predicted SNrates in the Milky Way system are 0.6h-squared, 0.8h-squared, and2.2h-squared/century, respectively, for the three aforementioned types.
| Colors and the evolution of amorphous galaxies
UBVRI and H-alpha photometric observations are presented for 16amorphous galaxies and a comparison sample of Magellanic irregular (Im)and Sc spiral galaxies. These data are analyzed in terms ofstar-formation rates and histories in amorphous galaxies. Amorphousgalaxies have mean global colors and star-formation rates per unit areathat are similar to those in giant Im systems, despite differences inspatial distributions of star-forming centers in these two galacticstructural classes. Amorphous galaxies differ from giant Im systems inhaving somewhat wider scatter in relationships between B - V and U - Bcolors, and between U - B and L(H-alpha)/L(B). This scatter isinterpreted as resulting from rapid variations in star-formation ratesduring the recent past, which could be a natural consequence of theconcentration of star-forming activity into centrally located,supergiant young stellar complexes in many amorphous galaxies. While theunusual spatial distribution and intensity of star formation in someamorphous galaxies is due to interactions with other galaxies, severalamorphous galaxies are relatively isolated and thus the processes mustbe internal. The ultimate evolutionary fate of rapidly evolvingamorphous galaxies remains unknown.
| H I observations of galaxies in between the Local and the Hydra/Centaurus superclusters
H I observations obtained with the 300-ft NRAO and 100-m Effelsbergradio telescopes in 1984-1985 are reported for 440 galaxies, ofmorphological types S0/a or later and diameter at least 2 arcmin in thecatalog of de Vaucouleurs et al., 1976, from the region between theLocal and Hya/Cen superclusters. The data are compiled in tables alongwith published data on 310 galaxies to form a data base for studies offilamentary structures in the intercluster region. More than 50 percentof the galaxies are detected in H I, and the redshift distribution isfound to be consistent with the existence of filaments.
| 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.
| Star formation in active dwarf galaxies
Star formation and the ISM in active dwarf galaxies are studied based ondata from the IRAS Point Source Catalog. The dwarf galaxies that showevidence of recent energetic star formation are generally also strongfar-infrared emitters; thus, active current star formation is associatedwith a history of energetic star formation. A fraction of the galaxiesconsidered here have a star formation rate that is significantly greaterthan the average rate in the recent past. Available gas is beingconsumed as efficiently in the presently active dwarfs as in the MilkyWay. A primary difference between galaxies that are energeticallyforming stars and those that are not is the difference in gas mass, aswell as the efficiency of star formation. The most important process maybe the assembly of large amounts of gaseous material.
| UBV colors of Virgo cluster irregular galaxies
Photoelectric UBV aperture photometry is presented for 65 dwarfirregular and morphologically related types of galaxies that areprobable Virgo cluster members. Virgo cluster Irr galaxies cover a widerrange in color than typical samples of field Irr systems, primarily dueto the presence of unusually red Im galaxies in Virgo. The extremelyblue 'blue compact dwarf' and the red amorphous galaxies in Virgo alsostand out on a UBV color-color plot, but the majority of Virgo Irrs areundistinguished in terms of UBV colors. Statistical correlations arefound between colors and location within the cluster. Red Irrs often arein elliptical galaxy rich, dense areas of the cluster, while the blueIrrs roughly follow the spiral distribution pattern. Thus a connectionexists between environment and the properties of Irrs. Simplestatistical tests for ongoing stripping as the source of red Irrs,however, yields null results.
| 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 formation histories of irregular galaxies
The star formation histories of a selection of irregular and spiralgalaxies are analyzed using three parameters for sampling the starformation rate in different epochs: galaxy mass; blue luminosity; andLyman continuum photon fluxes derived from Hz luminosities. It is foundthat for most irregular galaxies these parameters are consistent with anearly constant SFR and a Salpeter initial mass function over thelifetimes of the galaxies. The spiral and high-mass irregular galaxiesappear to have had a constant SFR over the past few billion years butalso have high total mass indicating either an early phase of intensestar formation or the presence of dark matter. Global bursts of starformation among irregular galaxies appear to be rare. The constant SFRhistory implies that the simple classical model in which star formationis proportional to gas density in a closed system cannot be correct forirregular galaxies. Some alternative models for constant global SFRs arediscussed.
| Study of a complete sample of galaxies. I - UBV aperture photometry
UBV photometry was performed over the period September 1979-February1984 on 320 galaxies in the Revised Shapely-Ames catalog of galaxies(1981). The galaxies chosen had radial velocities under 3000 km/sec,declinations of no more than +20 deg and absolute magnitudes of at most-21.0. V, B-V and U-B data are provided for all the objects, along withdata for other galaxies which were either Seyfert galaxies or had astarburst nucleus.
| Gas kinematics and the structure of extragalactic giant and supergiant H II regions
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983ApJ...274..141G&db_key=AST
| Global properties of irregular galaxies
Optical and radio observations of global properties are presented for asample of noninteracting irregular galaxies and some companion objects.The data consist of intermediate-band filter photometry, large aperturespectrophotometry, small aperture spectrophotometry of individual H IIregions, and H I 21 cm telescope observations. The galaxies are found tobe generally blue, and may not show the classical two-peaked H I 21 cmprofile. There is no correlation between the SFR and global gas orabundance parameters, which implies that local, rather than globalcharacteristics govern the star formation process. Metallicities aregenerally low, comparable to the Magellanic Clouds, and there areabsorption features characteristic of cool stars in the spectraregardless of the strength of the SFR in the observed region.Observations appear to agree best with the gas infall model.
| Local properties of star-forming regions in irregular galaxies
The physical processes which control star formation histories andevolution in noninteracting irregular galaxies are investigated in thestar-forming region properties of a sample of 15 irregulars activelyengaged in star formation. H II region kinematics, sizes anddistributions are obtained from H-alpha velocity profiles taken fromhigh dispersion echelle spectra and from b, y, I and H-alpha bandpassesof a video camera. The young star-forming regions are found to dominatethe light at all optical wavelengths, and the observed colors are redderthan predicted from most theoretical population models of young systems.Young galaxies with high star formation rates would therefore not beexpected to be very blue. Although there is no compelling evidence forit, star formation propagation due to mechanical energy returned byyoung stars is considered as a possible star formation history mechanismin irregular galaxies.
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