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CALIFA, the Calar Alto Legacy Integral Field Area survey. I. Survey presentation
The final product of galaxy evolution through cosmic time is thepopulation of galaxies in the local universe. These galaxies are alsothose that can be studied in most detail, thus providing a stringentbenchmark for our understanding of galaxy evolution. Through the hugesuccess of spectroscopic single-fiber, statistical surveys of the LocalUniverse in the last decade, it has become clear, however, that anauthoritative observational description of galaxies will involvemeasuring their spatially resolved properties over their full opticalextent for a statistically significant sample. We present here the CalarAlto Legacy Integral Field Area (CALIFA) survey, which has been designedto provide a first step in this direction. We summarize the survey goalsand design, including sample selection and observational strategy. Wealso showcase the data taken during the first observing runs (June/July2010) and outline the reduction pipeline, quality control schemes andgeneral characteristics of the reduced data. This survey is obtainingspatially resolved spectroscopic information of a diameter selectedsample of ~600 galaxies in the Local Universe (0.005 < z < 0.03).CALIFA has been designed to allow the building of two-dimensional mapsof the following quantities: (a) stellar populations: ages andmetallicities; (b) ionized gas: distribution, excitation mechanism andchemical abundances; and (c) kinematic properties: both from stellar andionized gas components. CALIFA uses the PPAK integral field unit (IFU),with a hexagonal field-of-view of ~1.3⎕', with a 100% coveringfactor by adopting a three-pointing dithering scheme. The opticalwavelength range is covered from 3700 to 7000 Å, using twooverlapping setups (V500 and V1200), with different resolutions: R ~ 850and R ~ 1650, respectively. CALIFA is a legacy survey, intended for thecommunity. The reduced data will be released, once the quality has beenguaranteed. The analyzed data fulfillthe expectations of the originalobserving proposal, on the basis of a set of quality checks andexploratory analysis: (i) the final datacubes reach a 3? limitingsurface brightness depth of ~23.0 mag/arcsec2 for the V500grating data (~22.8 mag/arcsec2 for V1200); (ii) about ~70%of the covered field-of-view is above this 3? limit; (iii) thedata have a blue-to-red relative flux calibration within a few percentin most of the wavelength range; (iv) the absolute flux calibration isaccurate within ~8%with respect to SDSS; (v) the measured spectralresolution is ~85 km s-1 for V1200 (~150 km s-1for V500); (vi) the estimated accuracy of the wavelength calibration is~5 km s-1 for the V1200 data (~10 km s-1 for theV500 data); (vii) the aperture matched CALIFA and SDSS spectra arequalitatively and quantitatively similar. Finally, we show that we areable to carry out all measurements indicated above, recovering theproperties of the stellar populations, the ionized gas andthe kinematicsof both components. The associated maps illustrate the spatial variationof these parameters across the field, reemphasizing the redshiftdependence of single aperture spectroscopic measurements. We concludefrom this first look at the data that CALIFA will be an importantresource for archaeological studies of galaxies in the Local Universe.Based on observations collected at the Centro Astronómico HispanoAlemán (CAHA) at Calar Alto, operated jointly by theMax-Planck-Institut für Astronomie and the Instituto deAstrofísica de Andalucía (CSIC).
| Post common envelope binaries from SDSS. XII. The orbital period distribution
Context. The complexity of the common-envelope phase and of magneticstellar wind braking currently limits our understanding of close binaryevolution. Because of their intrinsically simple structure,observational population studies of white dwarf plus main sequence(WDMS) binaries can potentially test theoretical models and constraintheir parameters. Aims: The Sloan Digital Sky Survey (SDSS) hasprovided a large and homogeneously selected sample of WDMS binaries,which we characterise in terms of orbital and stellar parameters. Methods: We have obtained radial velocity information for 385 WDMSbinaries from follow-up spectroscopy and for an additional 861 systemsfrom the SDSS subspectra. Radial velocity variations identify 191 ofthese WDMS binaries as post common-envelope binaries (PCEBs). Orbitalperiods of 58 PCEBs were subsequently measured, predominantly fromtime-resolved spectroscopy, bringing the total number of SDSS PCEBs withorbital parameters to 79. Observational biases inherent to this PCEBsample were evaluated through extensive Monte Carlo simulations. Results: We find that 21-24% of all SDSS WDMS binaries have undergonecommon-envelope evolution, which is in good agreement with publishedbinary population models and high-resolution HST imaging of WDMSbinaries unresolved from the ground. The bias-corrected orbital perioddistribution of PCEBs ranges from 1.9 h to 4.3 d and approximatelyfollows a normal distribution in log (Porb), peaking at ~10.3h. There is no observational evidence for a significant population ofPCEBs with periods in the range of days to weeks. Conclusions:The large and homogeneous sample of SDSS WDMS binaries provides themeans to test fundamental predictions of binary population models, henceto observationally constrain the evolution of all close compactbinaries.Figures 3-6, Tables 1, 5 and Appendices are only available in electronicform at http://www.aanda.orgFullTables 3, 4, and 6 are only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/536/A43
| Optical and OH megamaser observations of the starburst galaxy IIZw 096
Using the Multi-Element Radio-Linked Interferometer Network (MERLIN), wehave acquired a high spatial resolution spectral image of the OHmegamaser (OHMM) in the nearby starburst 'galaxy' known as IIZw 096. Wehave also acquired optical B, V, R, I and H? images with the 1.5-mtelescope in San Pedro Mártir. By comparing the MERLINobservations with Hubble archive images, we are able to pinpoint thelocation of the OH maser emission in this object; the OHMM emissionseems to be associated with a faint and reddish, compact-round structure(a few hundred parsecs) off-centre of a merging system of galaxies. Fromthe colour and strong H? emission, this object is consistent withthe remains of the nucleus of a very perturbed galaxy in interaction.Assuming a Keplerian bounded system the mass necessary to produce avelocity range of ?200 km s-1 for the OHMM is of the orderof 109 M&sun;, which is consistent with a massiveblack hole. Consequently, although the OHMM was previously suspected tobe of starburst origin, our analysis suggests that an active galacticnucleus (AGN) could also be present in this merging system making it acomposite source. IIZw 096 is a nearby example which shows how highspatial resolution data of the OHMM emission region, and supportingoptical data, can be extremely helpful in determining the nature(starburst, AGN or composite) of such phenomenon.
| Gemini GMOS spectroscopy of HeII nebulae in M 33
We have carried out a narrow-band survey of the Local Group galaxy, M33, in the HeII ?4686 emission line, to identify HeII nebulae inthis galaxy. With spectroscopic follow-up observations, we confirm threeof seven candidate objects, including identification of two new HeIInebulae, BCLMP651, HBW673. We also obtain spectra of associated ionizingstars for all the HII regions, identifying two new WN stars. Wedemonstrate that the ionizing source for the known HeII nebula, MA 1, isconsistent with being the early-type WN star MC8 (M 33-WR14), bycarrying out a combined stellar and nebular analysis of MC8 and MA 1. Wewere unable to identify the helium ionizing sources for HBW 673 andBCLMP 651, which do not appear to be Wolf-Rayet stars. According to the[OIII]?5007/H? vs. [NII]?6584/H? diagnosticdiagram, excitation mechanisms apart from hot stellar continuum areneeded to account for the nebular emission in HBW 673, which appears tohave no stellar source at all.
| Identification of blue high proper motion objects in the Tycho-2 and 2MASS catalogues using Virtual Observatory tools
Aims: With available Virtual Observatory tools, we looked for newbright blue high proper motion objects in the entire sky: white dwarfs,hot subdwarfs, runaway OB stars, and early-type stars in nearby youngmoving groups. Methods: We performed an all-sky cross-matchbetween the optical Tycho-2 and near-infrared 2MASS catalogues withAladin, and selected objects with proper motions ? > 50 masyr-1 and colours VT - Ks < -0.5 magwith TOPCAT. We also collected multi-wavelength photometry, constructedthe spectral energy distributions and estimated effective temperaturesfrom fits to atmospheric models with VOSA for the most interestingtargets. Results: We assembled a sample of 32 bright blue highproper motion objects, including ten sdO/B subdwarfs, nine DA whitedwarfs, five young early-type stars (two of which are runaway stars),two blue horizontal branch stars, one star with poor information, andfive objects reported for the first time in this work. These last fiveobjects have magnitudes BT ? 11.0-11.6 mag, effectivetemperatures Teff ? 24 000-30 000 K, and are located inthe region of known white dwarfs and hot subdwarfs in a reduced propermotion-colour diagram. We confirmed the hot subdwarf nature of one ofthe new objects, Albus 5, with public far-ultraviolet spectroscopic dataobtained with FUSE.
| On the Origins of the High-latitude H? Background
The diffuse high-latitude H? background is widely believed to bepredominantly the result of in situ recombination of ionized hydrogen inthe warm interstellar medium of the Galaxy. Instead, we show that both asubstantial fraction of the diffuse high-latitude H? intensity inregions dominated by Galactic cirrus dust and much of the variance inthe high-latitude H? background are the result of scattering byinterstellar dust of H? photons originating elsewhere in theGalaxy. We provide an empirical relation, which relates the expectedscattered H? intensity to the IRAS 100 ?m diffuse backgroundintensity, applicable to about 81% of the entire sky. The assumptioncommonly made in reductions of cosmic microwave background observations,namely that the observed all-sky map of diffuse H? light is asuitable template for Galactic free-free foreground emission, is foundto be in need of reexamination.
| Spectral Variability of Romano's Star
We combine archival spectral observations of the LBV star V532 (Romano'sstar) together with existing photometric data in the B band.Spectroscopic data cover 15 years of observations (from 1992 to 2007).We show that the object in maximum of brightness behaves as an emissionline supergiant while in minimum V532 moves along the sequence of lateWN stars. In this sense, the object behaves similarly to the well-knownLuminous Blue Variable (LBV) stars AG Car and R127, but is somewhathotter at the minima. We identify about 100 spectral lines in the3700-7300Å range. As of today, our spectroscopy is the mostcomprehensive for this object. The velocity of the wind is derived usingthe He I triplet lines (360±30 km s(-1) ). Physical parameters ofthe nebula around V532 are estimated.
| Small-spatial-scale variations of nebular properties and the abundance discrepancy in three Galactic HII regions
We present the results of long-slit spectroscopy in several slitpositions that cover different morphological structures of the centralparts of three bright Galactic HII regions: M8, M17 and NGC 7635. Westudy the spatial distributions of a large number of nebular parameters,such as the extinction coefficient, line fluxes, physical conditions andionic abundances at the maximum spatial resolution attainable with ourinstrumentation. Particularly, our goal is to study the behaviour of theabundance discrepancy factor of O2+ [ADF(O2+)],defined as the logarithmic difference of the O2+ abundancesderived from collisionally excited and recombination lines. We find thatADF(O2+) remains fairly constant along the slit positions ofM8 and M17. For NGC 7635, we only detect the OII recombination lines inthe integrated spectrum along the whole slit, where ADF(O2+)reaches a remarkably high value of about 0.59 dex. We compare ourresults with previous results obtained for the Orion Nebula. We findmuch evidence to suggest the presence of a candidate Herbig-Haro objectin M8.Based on observations made with the 4.2-m William Herschel Telescope(WHT) operated on the island of La Palma by the Isaac Newton Group inthe Spanish Observatorio del Roque de los Muchachos of the Instituto deAstrofísica de Canarias.E-mail: amd@iac.es
| SAO RAS 6-m telescope spectroscopic observations of globular clusters in nearby galaxies
We present the results of medium-resolution spectroscopy of 28 globularclusters (GCs) in six nearby galaxies of different luminosities andmorphological types, situated in M33 (15 objects), M31 (three), IC10(four), UGCA86 (four), Holmberg IX (one) and DDO71 (one) obtained at theSpecial Astrophysical Observatory 6-m telescope. Measurements of Lickabsorption line indices and comparison with Simple Stellar Populationmodels enabled us to obtain their spectroscopic ages, metallicities and?-element to Fe abundance ratios. We found that all old- andintermediate-age GCs in our sample have low metallicities [Z/H] <~-0. 8dex. Metal-rich clusters are young and are preferentially found ingalaxies more massive than ~ 109 Msolar. The leastmassive dwarfs of our sample, DDO71 and Holmberg IX, host one massiveintermediate-age and one massive young metal-poor GC, respectively.[?/Fe] abundance ratios tend to be enhanced but closer to solarvalues for dwarf galaxies compared to GCs in more massive galaxies. Weanalyse the age-metallicity relation for GCs in our sample and othersfrom the literature, and find that (1) there is a general trend for GCsin low surface brightness dwarf galaxies to be more metal-poor at agiven age than GCs in more massive galaxies; (2) the GC metallicityspread is wider for more massive galaxies and (3) intermediate-age GCsin early-type dwarf galaxies are more metal-rich at any given age thanthose in irregular galaxies of similar luminosity.
| PINGS: the PPAK IFS Nearby Galaxies Survey
We present the PPAK Integral Field Spectroscopy (IFS) Nearby GalaxiesSurvey (PINGS), a two-dimensional spectroscopic mosaicking of 17 nearbydisc galaxies in the optical wavelength range. This project representsthe first attempt to obtain continuous coverage spectra of the wholesurface of a galaxy in the nearby Universe. The final data set comprisesmore than 50000 individual spectra, covering in total an observed areaof nearly 80 arcmin2. The observations will be supplementedwith broad-band and narrow-band imaging for those objects withoutpublicly available images in order to maximize the scientific andarchival values of the data set. In this paper we describe the mainastrophysical issues to be addressed by the PINGS project, present thegalaxy sample and explain the observing strategy, the data reductionprocess and all uncertainties involved. Additionally, we give somescientific highlights extracted from the first analysis of the PINGSsample. A companion paper will report on the first results obtained forNGC 628: the largest IFS survey on a single galaxy.Based on observations collected at the Centro Astronómico HispanoAlemán (CAHA) at Calar Alto, operated jointly by the Max-PlanckInstitut für Astronomie and the Instituto de Astrofísica deAndalucía (CSIC).E-mail: frosales@ast.cam.ac.uk
| Neutral Gas Outflows and Inflows in Infrared-faint Seyfert Galaxies
Previous studies of the Na I D interstellar absorption line doublet haveshown that galactic winds occur in most galaxies with high infraredluminosities. However, in infrared-bright composite systems where astarburst coexists with an active galactic nucleus (AGN), it is unclearwhether the starburst, the AGN, or both are driving the outflows. Thepresent paper describes the results from a search for outflows in 35infrared-faint Seyferts with 109.9< L IR/Lsun < 1011, or, equivalently, star formationrates (SFRs) of ~0.4-9 M sun yr-1, toattempt to isolate the source of the outflow. We find that the outflowdetection rates for the infrared-faint Seyfert 1s (6%) and Seyfert 2s(18%) are lower than previously reported for infrared-luminous Seyfert1s (50%) and Seyfert 2s (45%). The outflow kinematics of infrared-faintand infrared-bright Seyfert 2 galaxies resemble those of starburstgalaxies, while the outflow velocities in Seyfert 1 galaxies aresignificantly larger. Taken together, these results suggest that the AGNdoes not play a significant role in driving the outflows in mostinfrared-faint and infrared-bright systems, except the high-velocityoutflows seen in Seyfert 1 galaxies. Another striking result of thisstudy is the high rate of detection of inflows in infrared-faintgalaxies (39% of Seyfert 1s, 35% of Seyfert 2s), significantly largerthan in infrared-luminous Seyferts (15%). This inflow may becontributing to the feeding of the AGN in these galaxies, andpotentially provides more than enough material to power the observednuclear activity over typical AGN lifetimes.
| Gas emission spectrum in the Irr galaxy IC 10
Observations of the dwarf Irr galaxy IC 10 have been performed at the6-m Special Astrophysical Observatory telescope with the SCORPIO focalreducer in the mode of a slit spectrograph. The ionized-gas emissionspectrum in the region of intense current star formation has beeninvestigated. The relative oxygen, N+, and S+abundances in about twenty H II regions and the synchrotron superbubblehave been estimated. The galaxy-averaged oxygen abundance is 12 +log(O/H) = 8.17 ± 0.35 and the metallicity is Z = 0.18 ±0.14 Z &sun;. The metallicity found by comparing diagnosticdiagrams with photoionization models is shown to be less reliable thanits estimate based on strong oxygen lines.
| Low-ionization pairs of knots in planetary nebulae: physical properties and excitation
We obtained optical long-slit spectra of four planetary nebulae (PNe)with low-ionization pair of knots, namely He 1-1, IC 2149, KjPn 8 andNGC 7662.These data allow us to derive the physical parameters and excitation ofthe pairs of knots, and those of higher ionization inner components ofthe nebulae, separately.Our results are as follows. (1) The electron temperatures of the knotsare within the range 9500-14500 K, similar to the temperatures of thehigher ionization rims/shells. (2) Typical knots' densities are 500-2000cm-3. (3) Empirical densities of the inner rims/shells arehigher than those of the pairs of knots, by up to a factor of 10.Theoretical predictions, at variance with the empirical results, suggestthat knots should be denser than the inner regions, by at least a factorof 10. (4) Empirical and theoretical density contrasts can be reconciledif we assume that at least 90 per cent of the knots' gas is neutral(likely composed of dust and molecules). (5) By using the new Raga etal. shock modelling and diagnostic diagrams appropriated for spatiallyresolved PNe, we suggest that high-velocity shocked knots travelling inthe photoionized outer regions of PNe can explain the emission of thepairs of knots analysed in this paper.
| Keck HIRES Spectroscopy of Extragalactic H II Regions: C and O Abundances from Recombination Lines
We present very deep spectrophotometry of 14 bright extragalacticH II regions belonging to spiral, irregular, and blue compactgalaxies. The data for 13 objects were taken with the High ResolutionEchelle Spectrometer on the Keck I telescope. We have measured C IIrecombination lines in 10 of the objects and O II recombinationlines in eight of them. We have determined electron temperatures fromline ratios of several ions, especially those of low ionizationpotential. We have found a rather tight linear empirical relationbetween T e([N II]) and T e([O III]). Wehave found that O II lines give always larger abundances than[O III] lines. Moreover, the difference of both O++abundance determinations—the so-called abundance discrepancyfactor—is very similar in all the objects, with a mean value of0.26 ± 0.09 dex, independent of the properties of the H IIregion and of the parent galaxy. Using the observed recombination lines,we have determined the O, C, and C/O radial abundance gradients forthree spiral galaxies: M33, M101, and NGC 2403, finding that C abundancegradients are always steeper than those of O, producing negative C/Ogradients across the galactic disks. This result is similar to thatfound in the Milky Way and has important implications for chemicalevolution models and the nucleosynthesis of C.Most of the data presented herein were obtained at the W.M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California and theNational Aeronautics and Space Administration. The Observatory was madepossible by the generous financial support of the W.M. Keck Foundation.Part of the observations were made with the 4.2 m William HerschelTelescope (WHT), operated on the island of La Palma by the Isaac NewtonGroup in the Spanish Observatorio del Roque de los Muchachos of theInstituto de Astrofísica de Canarias.
| Extended Red Emission in High Galactic Latitude Interstellar Clouds
We report initial results from an optical imaging survey of opticallythin high Galactic latitude clouds, which is designed to study thesurface brightness, structure, and spectral energy distribution of theseobjects. The primary aim of this paper is to study the extended redemission (ERE) that has been reported at high Galactic latitudes inearlier investigations and which is attributed to ultraviolet-excitedphotoluminescence of an as yet unidentified component of interstellardust. We conduct this ongoing survey with remotely operated, fast, shortfocal length (0.5 m) telescopes equipped with absolutely calibrated CCDcameras yielding a field of view of2deg×3deg. The telescopes are located at NewMexico Skies at 7300 ft (2225 m) altitude near Mayhill, New Mexico. Theoptical surface brightness of our objects is typically a few percent ofthe brightness of the dark night sky, implying that the cloud SEDs mustbe deduced from differential surface brightness photometry in differentfilter bands. We find strong evidence for dust emission in the form of abroad (>~1000 Å FWHM) ERE band with peak emission near 600 nmwavelength and peak intensity of ~5×10-9 ergscm-2 s-1 Å-1 sr-1 inoptically thin clouds. This amounts to about 30% of the total opticalsurface brightness of these clouds, the remainder being consistent withexpectations for dust-scattered light.
| The Overdense Environment of a Large Lyα Nebula at z ~ 2.7
Large nebulae (>~50 kpc) emitting strongly in Lyα (also knownas Lyα ``blobs'') are likely signposts of ongoing massive galaxyformation. The relative rarity of these sources and their discovery inwell-studied galaxy overdensities suggest that they may be associatedwith regions of high galaxy density. One of the largest Lyαnebulae, discovered at a redshift of z~2.7 via its strong mid-infraredemission, provides an unbiased test of this association. We have carriedout a deep intermediate-band imaging survey for Lyα-emittinggalaxies (LAEs) within a 30' × 26' field of view around thisLyα nebula. This is the first study of the environment of aLyα nebula found without a priori knowledge of its surroundings.We find that the nebula is located in an overdense region, at least 20× 50 h-170 comoving Mpc in size, showing afactor of ~3 LAE number density enhancement relative to the edge of thefield. Given the predicted number of such overdensities, we rule out thepossibility of a chance coincidence at the <~1% level. This study, inconjunction with previous work, provides strong confirmation of theassociation between the largest Lyα nebulae and overdense regionsof the universe.Based on data collected at Subaru Telescope, which is operated by theNational Astronomical Observatory of Japan.Based in part on observations obtained at Kitt Peak NationalObservatory, a division of the National Optical Astronomy Observatory,which is operated by the Association of Universities for Research inAstronomy, Inc., under cooperative agreement with the National ScienceFoundation.
| M1-78: a nitrogen-rich Galactic compact H II region beyond the Perseus arm
Context: There is considerable controversy surrounding the nature ofM1-78, a compact nebula located beyond the Perseus arm. It was firstclassified as a planetary nebula and is nowadays generally considered tobe a compact H II region. Aims: To investigate the nature of M1-78further, we present a detailed spectroscopic study of M1-78 in theoptical and near-infrared. Methods: We obtained long-slit,intermediate-resolution, optical spectroscopy with the ISIS spectrographmounted on the William Herschel Telescope (WHT) at Roque de losMuchachos Observatory (La Palma, Spain). As a complement, we obtainedlong-slit, intermediate-resolution, near-infrared spectra using LIRIS,the near-infrared imager/spectrographer also installed at the WHT.Results: M1-78 is a high-density nebula with substantial physicaldifferences between its two main morphological zones: a bright arc inthe SW and a blob of emission in the NE. Specifically, the blob in theNE has a higher electron temperature (13 400 K) and visual extinction(about 9 mag) than the SW arc. The most important result, however, isthe confirmation of a nitrogen enrichment in M1-78. This enrichment isstronger at the location of the NE blob and is correlated with adefficiency in the O abundance and a (dubious) He enrichment. Such anabundance pattern is typical of ejecta nebulae around evolved massivestars such as Wolf-Rayet and Luminous Blue Variable stars. The spatialvariations in the physical conditions and chemical abundances and thepresence of more than one possible ionizing source indicate, however,that M1-78 is better described as a combination of a compact H II region+ ejecta. This is confirmed by the He I 2.112 μm/Brγ lineratio, which indicates a hot (T_eff ⪆ 40 000 K) O star in the SWarc. Finally, we detect H2 emission that extends over a large(~30´´) area around the ionized nebula. Analysis of thenear-infrared H2 lines indicates that the excitation mechanism is UVfluorescence.
| Ionized and neutral gas in the peculiar star/cluster complex in NGC 6946
The characteristics of ionized and H I gas in the peculiar star/clustercomplex in NGC 6946, obtained with the 6-m telescope (BTA) SpecialAstrophysical Observatory Russian Academy of Sciences (RAS), the GeminiNorth telescope, and the Westerbork Synthesis Radio Telescope, arepresented. The complex is unusual as hosting a super star cluster, themost massive known in an apparently non-interacting giant galaxy. Itcontains a number of smaller clusters and is bordered by a sharpC-shaped rim. We found that the complex is additionally unusual inhaving peculiar gas kinematics. The velocity field of the ionized gasreveals a deep oval minimum, ~300 pc in size, centred 7 arcsec east ofthe supercluster. The Vr of the ionized gas in the dip centreis 100 km s-1 lower than in its surroundings, and emissionlines within the dip appear to be shock-excited. This dip is near thecentre of an H I hole and a semi-ring of H II regions. The H I (and lesscertainly, H II) velocity fields reveal expansion, with the velocityreaching ~30 km s-1 at a distance about 300 pc from thecentre of expansion, which is near the deep minimum position. Thesuperstar cluster is at the western rim of the minimum. The sharpwestern rim of the whole complex is plausibly a manifestation of aregular dust arc along the complex edge. Different hypotheses about thecomplex and the Vr depression's origins are discussed,including a high-velocity HI cloud/dark minihalo impact, a blue compactdwarf galaxy merging, and a gas outflow due to release of energy fromthe supercluster stars.
| The metallicity gradient of M 33: chemical abundances of H ii regions
Context: We present spectroscopic observations of a sample of 72emission-line objects, including mainly H ii regions, in the spiralgalaxy M 33. Spectra were obtained with the multi-object, wide fieldspectrograph AF2/WYFFOS at the 4.2 m WHT telescope. Line intensities,extinction, and electron density were determined for the whole sample ofobjects. Aims: The aim of the present work was to derive chemicaland physical parameters of a set of H ii regions, and from them themetallicity gradient. Methods: Electron temperatures and chemicalabundances were derived for the 14 H ii regions where both [O ii] and [Oiii] emission line fluxes were measured, including the electrontemperature sensitive emission line [O iii] 436.3 nm and in a few cases[N ii] 575.5 nm. The ionization correction factor (ICF) method was usedto derive the total chemical abundances. Results: The presence ofabundance gradients was inferred from the radial behaviour of severalemission-line ratios, and accurately measured from chemical abundancesdirectly derived in 14 H ii regions. The oxygen abundances of our H iiregions, located in the radial region from ~2 to ~7.2 kpc, gave anoxygen gradient -0.054±0.011 dex kpc-1 Conclusions: The overall oxygen gradient for M 33 obtained using oursand previous oxygen determinations in a large number of H ii regionswith direct electron temperature determination as well as abundance inyoung stars presented a two slope shape: -0.19 dex kpc-1 forthe central regions (R < 3 kpc), and -0.038 dex kpc-1 forthe outer regions (R ? 3 kpc).Based on observations obtained at the 4.2 m WHT telescope operated onthe island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de Los Muchachos of the Instituto de Astrofisicade Canarias. Tables 1-4 are only available in electronic form athttp://www.aanda.org
| Propagating Star Formation in the Collisional Ring Galaxy Arp 10
Propagating star formation in a collisional ring galaxy Arp 10 isinvestigated by a complex approach, which includes the broadband andnarrowband photometry, long-slit spectroscopy, and scanning Fabry-Perotspectroscopy. The ionized gas velocity field obtained with best spatialresolution to date indicates a nonisotropic expansion of the outer ringwith a maximum velocity 110 km s-1. Strong vertical andnoncircular motions are also seen in the vicinity of the inner ring. Ourkinematic data suggest that Arp 10 has a small inclinationi=22deg and high total mass (1012Msolar within a 50 kpc radius). The abundance of oxygen12+log(O/H) in both star-forming rings is about 8.6. The analysis ofspectral indices provides an estimate on the propagation velocities ofboth rings and metallicity of the precollision stellar population. Asmall ``knot'' near the nucleus of Arp 10 is unambiguously identified asthe ``intruder.'' The intruder spectrum suggests that it was a spiralgalaxy before the collision, and its present mass amounts to at leastone-fourth of the total mass of Arp 10. We use a simplifiedtwo-dimensional hydrodynamic modeling of galaxy collisions to test acollisional origin of Arp 10. The sizes of the inner and outer rings,maximum expansion velocity of the outer ring, and radial profile of thegas circular velocity can be reproduced by a near-central collision withthe intruder galaxy, which occurred approximately 85 Myr ago. Weacknowledge that an apparent crescent-shaped distribution of Hαemission in the outer ring is caused by a star formation threshold inthe gas disk of Arp 10.
| The Oxygen Abundance in the Inner H II Regions of M101: Implications for the Calibration of Strong-Line Metallicity Indicators
I present deep spectroscopy of four H II regions in the inner,metal-rich zone of the spiral galaxy M101 obtained with the LRISspectrograph at the Keck telescope. From the analysis of thecollisionally excited lines in two of the target H II regions, H1013 andH493, I have obtained oxygen abundances 12+log(O/H)=8.52 and12+log(O/H)=8.74, respectively. These measurements extend thedetermination of the oxygen abundance gradient of M101 via the directmethod to only 3 kpc from the center. The intensity of the C IIλ4267 line in H1013 leads to a carbon abundance 12+log(C/H)=8.66,corresponding to nearly twice the solar value. From a comparison of thecontinuum temperature derived from the Balmer discontinuity, T(Bac)=5000K, and the line temperature derived from [O III]λ4363/λ5007, T[O III]=7700 K, an average temperatureT0=5500 K and a mean square temperature fluctuationt2=0.06 have been derived. Accounting for the spatialinhomogeneity in temperature raises the oxygen abundance obtained fromthe oxygen auroral lines to 12+log(O/H)=8.93. These findings arediscussed in the context of the calibration of strong-line metallicityindicators, in particular of the upper branch of R23. Thereis no evidence for the strong abundance biases arising from temperaturegradients predicted theoretically for metal-rich H II regions.The data presented herein were obtained at the W. M. Keck Observatory,which is operated as a scientific partnership among the CaliforniaInstitute of Technology, the University of California, and the NationalAeronautics and Space Administration. The Observatory was made possibleby the generous financial support of the W. M. Keck Foundation.
| Probable Association of T Tauri Stars with the L 1014 Dense Core
Using the Wide Field Grism Spectrograph 2 (WFGS2), we carried outslit-less spectroscopy, g'r'i' photometry, and slit spectroscopy on theL 1014 dense core. We detected three H? emission-line stars. Weinterpret one as being a weak-line T Tauri star (WTTS) and the others asclassical T Tauri stars (CTTS). Since their g'-i' colors and/orclassified spectral types are consistent with those of T Tauri stars andtwo of them show less extinction than the cloud, these three stars arelikely to be T Tauri stars associated with L 1014. Adopting an age rangefor T Tauri stars, 1-10Myr, the color-magnitude diagram suggests adistance of ˜ 400-900 pc, rather than the previously assumeddistance, 200pc. This could strongly affect the mass estimate of L1014-IRS, which is thought to be either a very young protostar orproto-brown dwarf.
| Seventeen new very low-mass members in Taurus. The brown dwarf deficit revisited
Recent studies of the substellar population in the Taurus cloud haverevealed a deficit of brown dwarfs compared to the Trapezium clusterpopulation. However, these works have concentrated on the higheststellar density regions of the Taurus cloud. We have performed a largescale optical survey of this region, covering a total area of ?28deg^2, and encompassing the densest parts of the cloud as well as theirsurroundings, down to a mass detection limit of 15 M_J. We present theoptical spectroscopic follow-up observations of 97 photometricallyselected potential new low-mass Taurus members, of which 27 are stronglate-M spectral type (SpT ? M4V) candidates. Our spectroscopic surveyis 87% complete down to i'=20 for spectral types later than M4V, whichcorresponds to a mass completeness limit of 30 MJ for ages?10 Myr and Av ? 4. We derive spectral types, visual absorptionand luminosity class estimates and discuss our criteria to assess Taurusmembership. These observations reveal 5 new VLM Taurus members and 12new BDs. Two of the new VLM sources and four of the new substellarmembers exhibit accretion/outflow signatures similar to higher massclassical T Tauri stars. From levels of H? emission we derive afraction of accreting sources of 42% in the substellar Tauruspopulation. Combining our observations with previously publishedresults, we derive an updated substellar to stellar ratio in Taurus ofR_ss=0.23 ± 0.05. This ratio now appears consistent with thevalue previously derived in the Trapezium cluster under similarassumptions of 0.26 ± 0.04. We find indications that the relativenumbers of BDs with respect to stars is decreased by a factor 2 in thecentral regions of the aggregates with respect to the more distributedpopulation. Our findings are best explained in the context of theembryo-ejection model where brown dwarfs originate from dynamicalinteractions in small N unstable multiple systems.
| The Subdwarf Database: Released
The work on the Subdwarf Database, presented at the previous meeting,has been completed, and the tool is now publicly available. The firstrelease contains data from close to 240 different literature sources,but more still awaits entry. The database interface includes advancedsearch capabilities in coordinate, magnitude and color space. Outputtables can be generated in HTML with hyperlinks to automaticallygenerated finding charts, the Aladin viewer and a detailed data sheetthat displays all registered data for each target, including physicaldata such as temperature, gravity and helium abundance, together with afinding chart. Search results can be visualized automatically asinteractive position, magnitude or color diagrams.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| Group, field and isolated early-type galaxies - I. Observations and nuclear data
This is the first paper of a series on the investigation of stellarpopulation properties and galaxy evolution of an observationallyhomogeneous sample of early-type galaxies in groups, field and isolatedgalaxies.Here we present high signal-to-noise ratio (S/N) long-slit spectroscopyof 86 nearby elliptical and S0 galaxies. Eight of them are isolated,selected according to a rigorous criterion, which guarantees a genuinelow-density subsample. The present survey has the advantage of coveringa larger wavelength range than normally found in the literature, whichincludes [OIII]λ5007 and Hα, both lines important foremission correction. Among the 86 galaxies with S/N >= 15 (perresolution element, for re/8 central aperture), 57 have theirHβ-index corrected for emission (the average correction is 0.190Åin Hβ) and 42 galaxies reveal [OIII]λ5007 emission,of which 16 also show obvious Hα emission. Most of the galaxies inthe sample do not show obvious signs of disturbances nor tidal featuresin the morphologies, although 11 belong to the Arp catalogue of peculiargalaxies; only three of them (NGC 750, 751 and 3226) seem to be stronglyinteracting. We present the measurement of 25 central line-strengthindices calibrated to the Lick/IDS system. Kinematic information isobtained for the sample. We analyse the line-strength index versusvelocity dispersion relations for our sample of mainly low-densityenvironment galaxies, and compare the slope of the relations withcluster galaxies from the literature. Our main findings are that theindex-σ0 relations presented for low-density regionsare not significantly different from those of cluster E/S0s. The slopeof the index-σ0 relations does not seem to change forearly-type galaxies of different environmental densities, but thescatter of the relations seems larger for group, field and isolatedgalaxies than for cluster galaxies.
| K 4-47: a planetary nebula excited by photons and shocks
K 4-47 is an unusual planetary nebula (PN) composed of a compacthigh-ionization core and a pair of low-ionization knots. Long-slitmedium-resolution spectra of the knots and core are analyzed in thispaper. Assuming photoionization from the central star, we have derivedphysical parameters for all the nebular components, and the ionizationcorrection factors (icf) chemical abundances of the core, which appearsimilar to Type I PNe for He and N/O but significantly deficient inoxygen. The nebula has been further modelled using both photoionization(CLOUDY) and shock (MAPPINGS) codes. From the photoionization modellingof the core, we find that both the strong auroral [OIII] 4363-Åand[NII] 5755-Åemission lines observed and the optical size of thecore cannot be accounted for if a homogeneous density is adopted. Wesuggest that a strong density stratification, matching the high-densitycore detected at radio wavelengths and the much lower density of theoptical core, might solve the problem. From the bow-shock modelling ofthe knots, on the other hand, we find that the chemistry of the knots isalso represented by Type I PN abundances, and that they would move withvelocities of 250-300kms-1.
| Two New Low Galactic D/H Measurements from the Far Ultraviolet Spectroscopic Explorer
We analyze interstellar absorption observed toward two subdwarf O stars,JL 9 and LS 1274, using spectra taken by the Far UltravioletSpectroscopic Explorer (FUSE). Column densities are measured for manyatomic and molecular species (H I, D I, C I, N I, O I, P II, Ar I, FeII, and H2), but our main focus is on measuring the D/Hratios for these extended lines of sight, as D/H is an importantdiagnostic for both cosmology and Galactic chemical evolution. We findD/H=(1.00+/-0.37)×10-5 toward JL 9 andD/H=(0.76+/-0.36)×10-5 toward LS 1274 (2 σuncertainties). With distances of 590+/-160 and 580+/-100 pc,respectively, these two lines of sight are currently among the longestGalactic lines of sight with measured D/H. With the addition of thesemeasurements, we see a significant tendency for longer Galactic lines ofsight to yield low D/H values, consistent with previous inferences aboutthe deuterium abundance from D/O and D/N measurements. Short lines ofsight with H I column densities of logN(HI)<19.2 suggest that thegas-phase D/H value within the Local Bubble is(D/H)LBg=(1.56+/-0.04)×10-5. However, thefour longest Galactic lines of sight with measured D/H, which haved>500 pc and logN(HI)>20.5, suggest a significantly lower valuefor the true local disk gas-phase D/H value,(D/H)LDg=(0.85+/-0.09)×10-5. Oneinterpretation of these results is that D is preferentially depletedonto dust grains relative to H and that longer lines of sight thatextend beyond the Local Bubble sample more depleted material. In thisscenario, the higher Local Bubble D/H ratio is actually a betterestimate than (D/H)LDg for the true local disk D/H,(D/H)LD. However, if (D/H)LDg is different from(D/H)LBg simply because of variable astration and incompleteinterstellar medium mixing, then (D/H)LD=(D/H)LDg.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer (FUSE), which is operated for NASA by JohnsHopkins University under NASA contract NAS5-32985.
| The Physical Parameters, Excitation, and Chemistry of the Rim, Jets, and Knots of the Planetary Nebula NGC 7009
We present long-slit optical spectra along the major axis of theplanetary nebula NGC 7009. These data allow us to discuss the physical,excitation, and chemical properties of all the morphological componentsof the nebula, including its remarkable systems of knots and jets. Themain results of this analysis are the following: (1) the electrontemperature throughout the nebula is remarkably constant,Te[OIII]=10,200 K; (2) the bright inner rim and inner pair ofknots have similar densities of Ne~6000 cm-3,whereas a much lower density of Ne~1500 cm-3 isderived for the outer knots as well as for the jets; (3) all the regions(rim, inner knots, jets, and outer knots) are mainly radiativelyexcited; and (4) there are no clear abundance changes across the nebulafor He, O, Ne, or S. There is marginal evidence for an overabundance ofnitrogen in the outer knots (ansae), but the inner ones (caps) and therim have similar N/H values that are at variance with previous results.Our data are compared with the predictions of theoretical models, fromwhich we conclude that the knots at the head of the jets are not matteraccumulated during the jet expansion through the circumstellar medium;nor can their origin be explained by the proposed hydrodynamic or MHDinteracting wind models for the formation of jets/ansae, since thedensities, as well as the main excitation mechanisms of the knots,disagree with model predictions.Based on observations obtained at the 2.5 m Isaac Newton Telescope (INT)of the European Northern Observatory and with the NASA/ESA Hubble SpaceTelescope, obtained at the Space Telescope Science Institute, which isoperated by AURA for NASA under contract NAS5-26555.
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
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