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HI content in galaxies in loose groups
Gas deficiency in cluster spirals is well known and ram-pressurestripping is considered the main gas removal mechanism. In some compactgroups too gas deficiency is reported. However, gas deficiency in loosegroups is not yet well established. Lower dispersion of the membervelocities and the lower density of the intragroup medium in small loosegroups favour tidal stripping as the main gas removal process in them.Recent releases of data from the HI Parkes All-Sky Survey (HIPASS) andcatalogues of nearby loose groups with associated diffuse X-ray emissionhave allowed us to test this notion. In this paper, we address thefollowing questions: (i) do galaxies in groups with diffuse X-rayemission statistically have lower gas content compared to the ones ingroups without diffuse X-ray emission? (ii) does HI deficiency vary withthe X-ray luminosity, LX, of the loose group in a systematicway? We find that (i) galaxies in groups with diffuse X-ray emission, onaverage, are HI deficient, and have lost more gas compared to those ingroups without X-ray emission; the latter are found not to havesignificant HI deficiency; (ii) no systematic dependence of the HIdeficiency with LX is found. Ram-pressure-assisted tidalstripping and evaporation by thermal conduction are the two possiblemechanisms to account for this excess gas loss.
| Primordial Helium Abundance: A Reanalysis of the Izotov-Thuan Spectroscopic Sample
A reanalysis is made for the helium abundance determination for theIzotov-Thuan spectroscopic sample of extragalactic H II regions. We findthat the effect of underlying stellar absorption of the He I lines,which is more important for metal-poor systems, affects significantlythe inferred primordial helium abundance Yp obtained in thezero-metallicity limit and the slope of linear extrapolation, dY/dZ.This brings Yp from 0.234+/-0.004 to 0.250+/-0.004 anddY/dZ=4.7+/-1.0 to 1.1+/-1.4. Conservatively, this indicates theimportance of the proper understanding of underlying stellar absorptionfor accurate determinations of the primordial helium abundance to theerror of δYp~=0.002-0.004.
| Balmer and Paschen Jump Temperature Determinations in Low-Metallicity Emission-Line Galaxies
We have used the Balmer and Paschen jumps to determine the temperaturesof the H+ zones of a total sample of 47 H II regions. TheBalmer jump was used on MMT spectrophotometric data of 22low-metallicity H II regions in 18 blue compact dwarf (BCD) galaxies andof one H II region in the spiral galaxy M101. The Paschen jump was usedon spectra of 24 H II emission-line galaxies selected from the DataRelease 3 of the Sloan Digital Sky Survey (SDSS). To derive thetemperatures, we have used a Monte Carlo technique varying the electrontemperature in the H+ zone, the extinction of the ionized gasand that of the stellar population, the relative contribution of theionized gas to the total emission, and the star formation history to fitthe spectral energy distribution of the galaxies. For the MMT spectra,the fit was done in the wavelength range 3200-5200 Å, whichincludes the Balmer discontinuity, and for the SDSS spectra, in thewavelength range 3900-9200 Å, which includes the Paschendiscontinuity. We find for our sample of H II regions that thetemperatures of the O2+ zones determined from thenebular-to-auroral line intensity ratio of doubly ionized oxygen [O III]λλ(4959+5007)/λ4363 do not differ, in a statisticalsense, from the temperatures of the H+ zones determined fromfitting the Balmer and Paschen jumps and the spectral energydistributions (SEDs). We cannot rule out small temperature differencesof the order of 3%-5%.
| The chemical composition of metal-poor emission-line galaxies in the Data Release 3 of the Sloan Digital Sky Survey
We have re-evaluated empirical expressions for the abundancedetermination of N, O, Ne, S, Cl, Ar and Fe taking into account thelatest atomic data and constructing an appropriate grid ofphotoionization models with state-of-the art model atmospheres. Usingthese expressions we have derived heavy element abundances in the ~310emission-line galaxies from the Data Release 3 of the Sloan Digital SkySurvey (SDSS) with an observed Hβ flux F(Hβ) >10-14 erg s-1 cm-2 and for which the [Oiii] λ4363 emission line was detected at least at a 2σlevel, allowing abundance determination by direct methods. The oxygenabundance 12 + log O/H of the SDSS galaxies lies in the range from ~7.1(Zȯ/30) to ~8.5 (0.7 Zȯ). The SDSSsample is merged with a sample of 109 blue compact dwarf (BCD) galaxieswith high quality spectra, which contains extremely low-metallicityobjects. We use the merged sample to study the abundance patterns oflow-metallicity emission-line galaxies. We find that extremelymetal-poor galaxies (12 + log O/H < 7.6, i.e. Z -1.6, implying that theyhave a different nature than the subsample of high-redshift dampedLyα systems with log N/O of ~-2.3 and that their ages are largerthan 100-300 Myr. We confirm the apparent increase in N/O withdecreasing EW(Hβ), already shown in previous studies, and explainit as the signature of gradual nitrogen ejection by massive stars fromthe most recent starburst.
| The Structure of the Underlying Stellar Host in Blue Compact Dwarf Galaxies
Nowadays it is well established that BCDs are mostly old systems, as thevast majority of them have an extended low-surface brightness (LSB)stellar host underlying their central starburst component. This hostgenerally extends several kpc from the star-forming (SF) regions, showsregular elliptical isophotes, and displays red colors indicative of anevolved stellar population Papaderos96a,Cairos01a,Cairos01b,Cairos03.
| The Second Byurakan Survey. General Catalogue
The Second Byurakan Survey (SBS) General Catalogue is presented. TheSBS, a continuation of the Markarian survey reaching fainter limitingmagnitudes, is the first survey which combines the search of galaxiesand QSOs. A total area of 991OS#square;degrees of the Northern sky wascovered with the use of three objective prisms in combination withSchott filters. The limited magnitude on the best plates reached B ~19.5.The General Catalogue consists of 3563 objects presented in two parts: aCatalogue of galaxies (1863 objects) and one of stellar objects (1700objects). The Catalogue of SBS AGN consists of 761 objects (155 SyG, 596QSOs, and 10 BLLac). Multi-wavelength data are presented for 1438 SBSobjects identified with X-ray, IRAS and FIRST sources.Spectrophotometric observations obtained over 26 years are available for3132 objects. Redshifts were measured for ~ 2100 extragalactic objects.Spectral classification is presented for ~ 2970 objects. The majority ofthe data is presented here for the first time. The Catalogue presentsnew large homogeneous deep representative complete samples of brightQSOs, AGNs, and faint UVX galaxies in the Northern sky. The SBS sampleis found to be complete at 70% for galaxies and ~ 85% for AGN/QSOs withB ≤ 17.5.
| High-Ionization Emission in Metal-deficient Blue Compact Dwarf Galaxies
Primordial stars are expected to be very massive and hot, producingcopious amounts of hard ionizing radiation. The best place to study hardionizing radiation in the local universe is in very metal-deficient bluecompact dwarf (BCD) galaxies. We have carried out a MMT spectroscopicsearch for [Ne V] λ3426 (ionization potential of 7.1 ryd), [Fe V]λ4227 (ionization potential of 4 ryd), and He II λ4686(ionization potential of 4 ryd) emission in a sample of 18 BCDs. We haveadded data from previous work and from the Data Release 3 of the SloanDigital Sky Survey. In total, we have assembled a BCD high-ionizationsample with [Ne V] emission in four galaxies, [Fe V] emission in 15galaxies, and He II emission in 465 galaxies. With this large sample, wehave reached the following conclusions. There is a general trend ofhigher [Ne V], [Fe V], and He II emission at lower metallicities.However, metallicity is not the only factor that controls the hardnessof the radiation. High-mass X-ray binaries and main-sequence stars areprobably excluded as the main sources of the very hard ionizingradiation responsible for [Ne V] emission. The most likely source of [NeV] emission is probably fast radiative shocks moving with velocities>~450 km s-1 through a dense interstellar medium with anelectron number density of several hundreds cm-3 andassociated with supernova explosions of the most massive stars. Thesehave masses of ~50-100 Msolar and are formed in very compactsuper-star clusters (SSCs). The softer ionizing radiation required forHe II emission is likely associated with less massive evolved starsand/or radiative shocks moving through a less dense interstellar medium.The observations reported here were obtained at the MMT Observatory, ajoint facility of the Smithsonian Institution and the University ofArizona.
| Unveiling the Nature of the Low Surface Brightness Stellar Host in Blue Compact Dwarf Galaxies
In order to characterize the low surface brightness component in bluecompact dwarf galaxies, we determine their structural parameters foreight objects by fitting a Sérsic law to their B, V, and R lightprofiles. We restrict the fit to the outer regions, excluding thestarburst emission with the help of color and Hα maps. We discussthe problems and the uncertainties involved in fitting the Sérsicmodel, in particular the limited surface brightness interval and thesky-subtraction errors. We show that by carefully selecting the fittedradial range and by performing consistency checks on the fits in thedifferent bands we can derive reliable structural parameters. Allgalaxies but one show very good agreement on the Sérsicparameters in the three bands. Six of these galaxies have Sérsicindexes n very close to 1, while the other two have n~2.5.We compare the distribution of the BCDs with that of dI, dE, and LSBgalaxies in the diagrams built upon the Sérsic parameters. Whileprevious works claimed that BCDs are segregated from the other dwarfs insuch diagrams, here we find that six BCDs occupy the same region as theother dwarf types, while two galaxies have larger n, smallerRe, and brighter μ0. These results indicatethat evolutionary connections between BCDs and the other dwarf classescannot be ruled out.
| Comparison of Star Clusters With and Without Wolf-Rayet Stars in Wolf-Rayet Galaxies
We compare the properties of young star clusters with and withoutWolf-Rayet (W-R) stars in W-R galaxies using optical, near-infraredimagery and optical spectroscopy. Our work identifies the clusters withW-R stars in these galaxies for the first time. With this information,comparisons of clusters with and without W-R stars are now possible,enabling us to understand the chemical and morphological impact ofmassive stars on their environment and to constrain the parameters formodeling these systems. We find that clusters with W-R stars (W-Rclusters) are systematically younger, bluer clusters. Knowing this agedifference between the two cluster sets, we use an evolutionary scenarioto interpret their other properties. Young clusters, typically W-Rclusters, have a Strömgren sphere-like gas configuration. They alsotend to have H-K colors redder than those of theoretical models. Weinterpret the H-K excess as a combination of thermal emission from hotdust, nebular emission, and molecular emission. Older clusters,typically clusters without W-R stars, have ionized gas in a superbubbleconfiguration caused by the prolonged influence of stellar winds andsupernovae. The H-K excess is generally absent for these clusters. Thenitrogen-to-oxygen abundance ratio (N/O) does not appear to increase asa function of age over the first 10 Myr. Systems without W-R stars doappear to have a significant, elevated N/O over systems with W-R starsin the metallicity range 12+log(O/H)=7.7-7.9. For the entire metallicityrange in our sample, this finding is only marginally significant. Weconcur with previous studies, which find no correlation between thesulfur-to-oxygen abundance ratio and metallicity.
| 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.
| A Fresh View of Henize 2-10 with VLT NAOS-CONICA
We present high-resolution observations of Henize 2-10 in Ks(2.2 μm), L' (3.8 μm), and M' (4.8 μm) bands. These allow us,for the first time, to track accurately the structures at the heart ofthe galaxy from the optical to the radio. All radio knots previouslyobserved can now be associated with L'- and Ks-emittingregions. This implies a revision of their physical nature. Instead ofhighly extinguished ultradense H II regions, we propose that two of thefive radio knots are either supernova remnants or normal H II regions,while the remaining three are bona fide ultradense H II regions,although less obscured than previously thought.Based on observations made at the ESO VLT, under programs 71.B-0492 and270.B-5011.
| 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.
| FUSE Observations of Interstellar and Intergalactic Absorption toward the X-Ray-bright BL Lacertae Object Markarian 421
High-quality Far Ultraviolet Spectroscopic Explorer (FUSE) observationsat 20 km s-1 resolution of interstellar and intergalacticabsorption from 910 to 1187 Å are presented for the X-ray-brightBL Lac object Mrk 421. These observations are supplemented with FUSEdata for the distant halo stars BD +38°2182 and HD 93521 near theMrk 421 line of sight, in order to obtain information about the distanceto absorbing structures in the Milky Way toward Mrk 421. The FUSE ISMobservations provide measures of absorption by O VI and many otherspecies commonly found in warm neutral and warm ionized gas, including HI, C II, C III, O I, N I, N II, Fe II, and Fe III. In this study weconsider the O VI absorption between -140 and 165 km s-1 andits relationship to the lower ionization absorption and strongabsorption produced by O VII and O VIII at X-ray wavelengths. The O VIabsorption extending from -140 to 60 km s-1 is associatedwith strong low-ionization gas absorption and originates in the Galacticthick disk/halo. This O VI appears to be produced by a combination ofprocesses, including conductive interfaces between warm and hot gas andpossibly cooling Galactic fountain gas and hot halo gas bubbles. The OVI absorption extending from 60 to 165 km s-1 has unusualionization properties in that there is very little associatedlow-ionization absorption, with the exception of C III. This absorptionis not observed toward the two halo stars, implying that it occurs ingas more distant than 3.5 kpc from the Galactic disk. Over the 60-165 kms-1 velocity range, O VI and C III absorption have the samekinematic behavior. The ratio N(OVI)/N(CIII)=10+/-3 over the 60-120 kms-1 velocity range. Given the association of O VI with C III,it is unlikely that the high-velocity O VI coexists with the hotter gasresponsible for the O VII and O VIII absorption. The O VI positivevelocity absorption wing might be tracing cooler gas entrained in a hotGalactic fountain outflow. The O VII and O VIII absorption observed byChandra and XMM-Newton may trace the hot gas in a highly extended (~100kpc) Galactic corona or hot gas in the Local Group. The low resolutionof the current X-ray observations (~750-900 km s-1) and thekinematical complexity of the O VI absorption along typical lines ofsight through the Milky Way halo make it difficult to clearly associatethe O VI absorption with that produced by O VII and O VIII. A search formetal lines associated with the Lyα absorber at z=0.01, which issituated in a galactic void, was unsuccessful.
| Dust properties of UV bright galaxies at z ~ 2
We investigate the properties of the extinction curve in the rest-frameUV for a sample of 34 UV-luminous galaxies at 2 < z < 2.5,selected from the FORS Deep Field (FDF) spectroscopic survey. A newparametric description of the rest-frame UV spectral energy distributionis adopted; its sensitivity to properties of the stellar populations orof dust attenuation is established with the use of models. The latterare computed by combining composite stellar population models andcalculations of radiative transfer of the stellar and scatteredradiation through the dusty interstellar medium (ISM) for a dust/starsconfiguration describing dust attenuation in local starbursts. In thefavoured configuration the stars are enveloped by a shell with atwo-phase, clumpy, dusty ISM. The distribution of the z 2UV-luminous FDF galaxies in several diagnostic diagrams shows that theirextinction curves range between those typical of the Small and LargeMagellanic Clouds (SMC and LMC, respectively). For the majority ofstrongly reddened objects having a UV continuum slope β > -0.4 asignificant 2175 Å absorption feature (or "UV bump") is inferred,indicating an LMC-like extinction curve. On the other hand, the UVcontinua of the least reddened objects are mostly consistent withSMC-like extinction curves, lacking a significant UV bump, as for thesample of local starbursts investigated by Calzetti and collaborators.Furthermore, the most opaque (β 0) and, thus (for ourmodels), dustiest UV-luminous FDF galaxies tend to be among the mostmetal-rich, most massive, and largest systems at z 2, indicating< Z > 0.5 {-} 1 Zȯ, < Mstars> 6 × 1010 Mȯ, and 4 kpc, respectively. The presence of the UVbump does not seem to depend on the total metallicity, as given by theequivalent width (EW) of the C IV doublet. Conversely, it seems to beassociated with a large average EW of the six most prominentinterstellar low-ionisation absorption lines falling in the FORSspectra. The average EW of these saturated lines offers a proxy for theISM topology. We interpret these results as the evidence for adifference in the properties of the dusty ISM among the most evolvedUV-luminous, massive galaxies at z 2.
| Molecular gas in compact galaxies
New observations of eleven compact galaxies in the 12CO J =2{-}1 and J = 3{-}2 transitions are presented. From these observationsand literature data accurate line ratios in matched beams have beenconstructed, allowing the modelling of physical parameters. Matching asingle gas component to observed line ratios tends to produce physicallyunrealistic results, and is often not possible at all. Much betterresults are obtained by modelling two distinct gas components. In mostobserved galaxies, the molecular gas is warm (Tk = 50{-}150K) and at least partially dense (n(H2) ≥ 3000cm-3). Most of the gas-phase carbon in these galaxies is inatomic form; only a small fraction ( 5%) is in carbon monoxide.Beam-averaged CO column densities are low (of the order of1016 cm-2). However, molecular hydrogen columndensities are high (of the order of 1022 cm-2)confirming large CO-to- H2 conversion factors (typically X =1021{-}1022 cm-2/ {K kms-1}) found for low-metallicity environments by othermethods. From CO spectroscopy, three different types of molecularenvironment may be distinguished in compact galaxies. Type I (highrotational and isotopic ratios) corresponds to hot and dense molecularclouds dominated by star-forming regions. Type II has lower ratios,similar to the mean found for infrared-luminous galaxies in general, andcorresponds to environments engaged in, but not dominated by,star-forming activity. Type III, characterized by low 12CO(2-1)/(1-0) ratios, corresponds to mostly inactive environments ofrelatively low density.
| Spectroscopic study of blue compact galaxies. V. Oxygen abundance and the metallicity-luminosity relation
This is the fifth paper in a series studying the stellar components,star formation histories, star formation rates and metallicities of ablue compact galaxy (BCG) sample. Based on our high-quality ground-basedspectroscopic observations, we have determined the electrontemperatures, electron densities, nitrogen abundances and oxygenabundances for 72 star-forming BCGs in our sample, using differentoxygen abundance indicators. The oxygen abundance covers the range 7.15< 12 + log (O/H)< 9.0, and nitrogen is found to be mostly aproduct of secondary nucleosynthesis for 12 + log (O/H)>8.2 andapparently a product of primary nucleosynthesis for 12 + log (O/H)<8.2. To assess the possible systematic differences among differentoxygen abundance indicators, we have compared oxygen abundances of BCGsobtained with the Te method, R23 method, P method,N2 method and O3N2 method. The oxygen abundances derived from theTe method are systematically lower by 0.1-0.25 dex than thosederived from the strong line empirical abundance indicators, consistentwith previous studies based on region samples. We confirm the existenceof the metallicity-luminosity relation in BCGs over a large range ofabundances and luminosities. Our sample of galaxies shows that the slopeof the metallicity-luminosity relation for the luminous galaxies(~-0.05) is slightly shallower than that for the dwarf galaxies(~-0.17). An offset was found in the metallicity-luminosity relation ofthe local galaxies and that of the intermediate redshift galaxies. Itshows that the metallicity-luminosity relation for the emission linegalaxies at high redshift is displaced to lower abundances, higherluminosities, or both.
| New insights to the photometric structure of Blue Compact Dwarf Galaxies from deep near-infrared studies. II. The sample of northern BCDs
This paper is part of a series of publications which present asystematic study of Blue Compact Dwarf (BCD) Galaxies in the nearinfrared (NIR). Compared to the visible light, NIR data allow a betterseparation of the starburst emission from the light distribution of theold stellar low-surface brightness (LSB) host galaxy. We analyze deepNIR broad band images of a sample of 11 BCDs, observed with the CalarAlto 3.6 m telescope. This work enlarges the samples presented inpreceding papers of this study (Noeske et al. \cite{Noeske2003},A&A, 410, 481; Cairós et al. \cite{c03a}, ApJ, 593, 312) byBCDs of the most common morphological type, displaying a regularelliptical LSB host galaxy. The data presented here allow the detectionand quantitative study of the extended stellar LSB host galaxy in allsample BCDs. The NIR surface brightness profiles (SBPs) of the LSB hostgalaxies agree at large galactocentric radii with those from opticalstudies, showing also an exponential intensity decrease and compatiblescale lengths. Similar to Noeske et al. (\cite{Noeske2003}), we findcentrally flattening exponential (type V) SBPs of the host galaxy forseveral BCDs. Such SBPs remain mostly undetected in optical bands, dueto the comparatively stronger starburst emission at these wavelengths.We apply a modified exponential distribution to decompose andquantitatively analyze SBPs of LSB hosts with a type V intensitydistribution. We present the results of the surface photometry and thedecomposition of SBPs, and discuss individual objects with respect tomorphological details of their star-forming regions.Table 2 is also available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/ cgi-bin/ qcat?J/A+A/429/115Figures 2 to 11 are only available in electronic form athttp://www.edpsciences.orgGerman-Spanish Astronomical Center, Calar Alto, operated by theMax-Planck-Institute for Astronomy, Heidelberg, jointly with the SpanishNational Commission for Astronomy.
| Structural parameters of nearby emission-line galaxies
We present the results of an investigation on the main structuralproperties derived from VRI and Hα surface photometry of galaxieshosting nuclear emission-line regions [including Seyfert 1, Seyfert 2,low-ionization nuclear emission region (LINER) and starburst galaxies]as compared with normal galaxies. Our original sample comprises 22active galaxies, four starbursts and one normal galaxy and has beenextended with several samples obtained from the literature. Bulge anddisc parameters, along with the bulge-to-disc luminosity ratio, havebeen derived applying an iterative procedure. The resulting parametershave been combined with additional data in order to reach astatistically significant sample. We find some differences in the bulgedistribution across the different nuclear types that could implyfamilies of bulges with different physical properties. Bulge and disccharacteristic colours have been defined and derived for our sample andcompared with a control sample of early-type objects. The resultssuggest that bulge and disc stellar populations are comparable in normaland active galaxies.
| Principal component analysis of International Ultraviolet Explorer galaxy spectra
We analyse the UV spectral energy distribution of a sample of normalgalaxies listed in the International Ultraviolet Explorer (IUE) NewlyExtracted Spectra (INES) Guide No. 2 - Normal Galaxies using a principalcomponent analysis. The sample consists of the IUE short-wavelength (SW)spectra of the central regions of 118 galaxies, where the IUE apertureincluded more than 1 per cent of the galaxy size. The principalcomponents are associated with the main components observed in theultraviolet (UV) spectra of galaxies. The first component, accountingfor the largest source of diversity, may be associated with the UVcontinuum emission. The second component represents the UV contributionof an underlying evolved stellar population. The third component issensitive to the amount of activity in the central regions of galaxiesand measures the strength of star-formation events.In all the samples analysed here, the principal component representativeof star-forming activity accounts for a significant percentage of thevariance. The fractional contribution to the spectral energydistribution (SED) by the evolved stars and by the young population aresimilar.Projecting the SEDs on to their eigenspectra, we find that none of thecoefficients of the principal components can outline an internalcorrelation or can correlate with the optical morphological types. In asubsample of 43 galaxies, consisting of almost only compact and BCDgalaxies, the third principal component defines a sequence related tothe degree of starburst activity of the galaxy.
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| Systematic Effects and a New Determination of the Primordial Abundance of 4He and dY/dZ from Observations of Blue Compact Galaxies
We use spectroscopic observations of a sample of 82 H II regions in 76blue compact galaxies to determine the primordial helium abundanceYp and the slope dY/dZ from the Y-O/H linear regression. Toimprove the accuracy of the dY/dZ measurement, we have included newspectrophotometric observations of 33 H II regions that span a largemetallicity range, with oxygen abundance 12+log(O/H) varying between7.43 and 8.30 (Zsolar/30<=Z<=Zsolar/4). Mostof the new galaxies were selected from the First Byurakan, theHamburg/SAO, and the University of Michigan objective prism surveys. Fora subsample of seven H II regions, we derive the He mass fraction takinginto account known systematic effects, including collisional andfluorescent enhancements of He I emission lines, collisional excitationof hydrogen emission, underlying stellar He I absorption, and thedifference between the temperatures Te(He II) in theHe+ zone and Te(O III) derived from thecollisionally excited [O III] lines. We find that the net result of allthe systematic effects combined is small, changing the He mass fractionby less than 0.6%. By extrapolating the Y versus O/H linear regressionto O/H=0 for seven H II regions of this subsample, we obtainYp=0.2421+/-0.0021 and dY/dO=5.7+/-1.8, which corresponds todY/dZ=3.7+/-1.2, assuming the oxygen mass fraction to be O=0.66Z. In theframework of the standard big bang nucleosynthesis theory, thisYp corresponds toΩbh2=0.012+0.003-0.002,where h is the Hubble constant in units of 100 km s-1Mpc-1. This is smaller at the 2 σ level than the valueobtained from recent deuterium abundance and microwave backgroundradiation measurements. The linear regression slope dY/dO=4.3+/-0.7(corresponding to dY/dZ=2.8+/-0.5) for the whole sample of 82 H IIregions is similar to that derived for the subsample of seven H IIregions, although it has a considerably smaller uncertainty.
| 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.
| Revealing the Young Starburst in Haro 3 with Radio and Infrared Imaging
The Wolf-Rayet galaxy Haro 3 (Mrk 35, NGC 3353) was observed at thenear-IR and radio wavelengths as part of an ongoing program to study theearliest stages of starbursts. These observations confirm that thecurrent episode of star formation is dominated by a single region(region A). While there are knots of recent (~10 Myr) star formationoutside of region A, the sources of ionizing radiation as observed inboth radio and Brγ observations are almost exclusively associatedwith region A. The derived ionizing flux implies a star formation rateof ~0.6 Msolar yr-1 localized within a radius of~0.1 kpc. A comparison with HST observations indicates that one or moreof the star clusters in region A are optically obscured. The starclusters in region A have ages at least as young as ~5 Myr, and possiblyas young as ~0.1 Myr. The star cluster that appears to be the youngestalso exhibits a near-IR excess in its colors, possibly indicating nataldust in very close proximity to the ionizing stars. The differencebetween optical- and radio-determined ionizing fluxes, as well as thenear-IR colors, indicates an average extinction value ofAV~2.5 in region A. The total stellar mass associated withthe current starburst in region A is inferred from both the near-IR andradio observations to be ~106 Msolar. The othermain stellar concentrations observed in the near-IR (regions B1 and B2)are somewhat older than region A, with ages ~8-10 Myr, and the near-IRobservations indicate they have stellar masses of~8×104 and ~2×104 Msolar,respectively.
| 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.
| Spectroscopic study of blue compact galaxies. IV. Star formation rates and gas depletion timescales
This is the fourth paper in a series studying star formation rates,stellar components, metallicities, and star formation histories of ablue compact galaxy (BCG) sample. Using Hα, [O II]λ3727,infrared (IR), radio (1.4 GHz) luminosities and neutral hydrogen (H I)gas masses, we estimated star formation rates and gas depletiontimescales of 72 star-forming BCGs. The star formation rates of the BCGsin our sample span nearly four orders of magnitude, from approximately10-2 to 102 Mȯ yr-1,with a median star formation rate of about 3 Mȯyr-1. The typical gas depletion timescale of BCGs is aboutone billion years. Star formation could be sustained at the currentlevel only on a timescale significantly lower than the age of theuniverse before their neutral gas reservoir is completely depleted. Toassess the possible systematic differences among different starformation rate indicators, we compared the star formation rates derivedfrom Hα, [O II]λ3727, IR, and radio luminosities, andinvestigated the effects from underlying stellar absorption and dustextinction. We found that subtracting underlying stellar absorption isvery important to calculate both dust extinction and star formation rateof galaxies. Otherwise, the intrinsic extinction will be overestimated,the star formation rates derived from [O II]λ3727 and Hαwill be underestimated (if the underlying stellar absorption and theinternal extinction were not corrected from the observed luminosity) oroverestimated (if an overestimated internal extinction were used forextinction correction). After both the underlying stellar absorption andthe dust extinction were corrected, a remarkably good correlationemerges among Hα, [O II]λ3727, IR and radio star formationrate indicators. Finally, we find a good correlation between themeasured star formation rate and the absolute blue magnitude,metallicity, interstellar extinction of BCGs. Our results indicate thatfaint, low-mass BCGs have lower star formation rates.Star formation rates and gas depletion timescales of BCGs are availablein electronic form at the 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/425/417
| Radio emission from AGN detected by the VLA FIRST survey
Using the most recent (April 2003) version of the VLA FIRST survey radiocatalog, we have searched for radio emission from >2800 AGN takenfrom the most recent (2001) version of the Veron-Cetty and Veron AGNcatalog. These AGN lie in the 9033 square degrees of sky alreadycovered by the VLA FIRST survey. Our work has resulted in positivedetection of radio emission from 775 AGN of which 214 are new detectionsat radio wavelengths.Tables 3 and 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/35
| Asteroid database
The development and significance of asteroid database are reviewed inthis paper. Some of online database of asteroid are presented andcompared briefly, including asteroid orbital elements database, asteroidphotometric database, asteroid infrared database, near earth asteroiddatabase and asteroid database. Ephemeris service based on asteroiddatabase is mentioned. The trend of development of asteroid database hasalso been discussed.
| The Outer Edges of Dwarf Irregular Galaxies: Stars and Gas
Workshop held in Flagstaff, AZ, on 2002 October 10-11. Proceedings areavailable on-line at http://www.lowell.edu/Workshops/Lowell02.
| The PDS versus Markarian starburst galaxies: comparing strong and weak IRAS emitter at 12 and 25 μm in the nearby Universe
The characteristics of the starburst galaxies from the Pico dos Diassurvey (PDS) are compared with those of the nearby ultraviolet (UV)bright Markarian starburst galaxies, having the same limit in redshift(vh < 7500 km s-1) and absolute B magnitude(MB < -18). An important difference is found: theMarkarian galaxies are generally undetected at 12 and 25 μm in IRAS.This is consistent with the UV excess shown by these galaxies andsuggests that the youngest star-forming regions dominating thesegalaxies are relatively free of dust.The far-infrared selection criteria for the PDS are shown to introduce astrong bias towards massive (luminous) and large size late-type spiralgalaxies. This is contrary to the Markarian galaxies, which are found tobe remarkably rich in smaller size early-type galaxies. These resultssuggest that only late-type spirals with a large and massive disc arestrong emitters at 12 and 25 μm in IRAS in the nearby Universe.The Markarian and PDS starburst galaxies are shown to share the sameenvironment. This rules out an explanation of the differences observedin terms of external parameters. These differences may be explained byassuming two different levels of evolution, the Markarian being lessevolved than the PDS galaxies. This interpretation is fully consistentwith the disc formation hypothesis proposed by Coziol et al. to explainthe special properties of the Markarian SBNG.
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