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Ýlgili Makaleler
Echelle Long-Slit Optical Spectroscopy of Evolved Stars
We present echelle long-slit optical spectra of a sample of objectsevolving off the asymptotic giant branch (AGB), most of them in thepreplanetary nebula (PPN) phase, obtained with the ESI and MIKEspectrographs at the 10 m Keck II and 6.5 m Magellan-I telescopes,respectively. The total wavelength range covered with ESI (MIKE) is~3900-10900 Å (~3600-7200 Å). In this paper, we focus ouranalysis mainly on the Hα profiles. Prominent Hα emission isdetected in half of the objects, most of which show broad Hα wings(with total widths of up to ~4000 km s-1). In the majority ofthe Hα-emission sources, fast, post-AGB winds are revealed byP-Cygni profiles. In ~37% of the objects Hα is observed inabsorption. In almost all cases, the absorption profile is partiallyfilled with emission, leading to complex, structured profiles that areinterpreted as an indication of incipient post-AGB mass loss. The restof the objects (~13%) are Hα nondetections. We investigatecorrelations between the Hα profile and different stellar andenvelope parameters. All sources in which Hα is seen mainly inabsorption have F-G type central stars, whereas sources with intenseHα emission span a larger range of spectral types from O to G,with a relative maximum around B, and also including very late C types.Shocks may be an important excitation/ionization agent of the closestellar surroundings for objects with late type central stars. Sourceswith pure emission or P Cygni Hα profiles have larger J-K colorexcess than objects with Hα mainly in absorption, which suggeststhe presence of warm dust near the star in the former. The two classesof profile sources also segregate in the IRAS color-color diagram in away that intense Hα-emitters have dust grains with a larger rangeof temperatures. Spectral classification of the central stars in oursample is presented. For a subsample (13 objects), the stellarluminosity has been derived from the analysis of the O I 7771-7775Å infrared triplet. The location in the HR diagram of most ofthese targets, which represent ~30% of the whole sample, is consistentwith relatively high final (and, presumably, initial) masses in therange Mf~0.6-0.9 Msolar (Mi~3-8Msolar).
| Investigating ChaMPlane X-Ray Sources in the Galactic Bulge with Magellan LDSS2 Spectra
We have carried out optical and X-ray spectral analyses on a sample of136 candidate optical counterparts of X-ray sources found in fiveGalactic bulge fields included in our Chandra Multiwavelength PlaneSurvey. We use a combination of optical spectral fitting and quantileX-ray analysis to obtain the hydrogen column density toward each object,and a three-dimensional dust model of the Galaxy to estimate the mostprobable distance in each case. We present the discovery of a populationof stellar coronal emission sources, likely consisting ofpre-main-sequence, young main-sequence, and main-sequence stars, as wellas a component of active binaries of RS CVn or BY Dra type. We identifyone candidate quiescent low-mass X-ray binary with a subgiant companion;we note that this object may also be an RS CVn system. We report thediscovery of three new X-ray-detected cataclysmic variables (CVs) in thedirection of the Galactic center (at distances <~2 kpc). This numberis in excess of predictions made with a simple CV model based on a localCV space density of <~10-5 pc-3, and a scaleheight ~200 pc. We discuss several possible reasons for this observedexcess.
| Meeting the Cool Neighbors. X. Ultracool Dwarfs from the 2MASS All-Sky Data Release
Using data from the 2 Micron All Sky Survey All-Sky Point SourceCatalogue, we have extended our census of nearby ultracool dwarfs tocover the full celestial sphere above Galactic latitude of 15°.Starting with an initial catalog of 2,139,484 sources, we have winnowedthe sample to 467 candidate late-type M or L dwarfs within 20 pc of theSun. Fifty-four of those sources already have spectroscopic observationsconfirming them as late-type dwarfs. We present optical spectroscopy of376 of the remaining 413 sources, and identify 44 as ultracool dwarfswith spectroscopic distances less than 20 pc. Twenty-five of the 37sources that lack optical data have near-infrared spectroscopy.Combining the present sample with our previous results and data from theliterature, we catalog 94 L dwarf systems within 20 pc. We discuss thedistribution of activity, as measured by Hα emission, in thisvolume-limited sample. We have coupled the present ultracool catalogwith data for stars in the northern 8 pc sample and recent (incomplete)statistics for T dwarfs to provide a snapshot of the current 20 pccensus as a function of spectral type.
| Intrinsic Absorption Properties in Active Galaxies Observed with the Far Ultraviolet Spectroscopic Explorer
In a continuing survey of active galactic nuclei observed by the FarUltraviolet Spectroscopic Explorer, we provide a deeper analysis ofintrinsic absorption features found in 35 objects. Our survey is forlow-redshift and moderate-luminosity objects, mostly Seyfert galaxies.We find a strong correlation between maximum radial velocity andluminosity. We also examine the relationships between equivalent width(EW), full width at half maximum, velocity, and continuum flux. Thecorrelation between velocity and luminosity has been explored previouslyby Laor & Brandt, but at a significantly higher redshift and heavilyweighted by broad absorption line quasars. We also have examined eachobject with multiple observations for variability in each of theaforementioned quantities, and have characterized the variation of EWwith the continuum flux. In our survey, we find that variability of O VIλλ1032, 1038 is less common than of the UV doublets of CIV and N V seen at longer wavelengths, because the O VI absorption isusually saturated. Lyman β absorption variability is more frequent.In a target-by-target examination we find that broad absorption line andnarrow absorption line absorbers are related in terms of maximum outflowvelocity and luminosity, and both can be exhibited in similar luminosityobjects. We also find one object that shows radial velocity change,seven objects that show equivalent width variability, and two objectsthat show either transverse velocity changes or a change in ionization.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by the Johns HopkinsUniversity under NASA contract NAS5-32985.
| On the detectability of Lyα emission in star forming galaxies. The role of dust
Context: Lyman-alpha (Lyα) radiation is now widely used toinvestigate the galaxy formation and evolution in the high redshiftuniverse. However, without a rigorous understanding of the processesregulating the Lyα escape fraction, physical interpretations ofhigh-z observations remain questionable. Aims: We examine six nearbystar forming galaxies to disentangle the role of the dust from otherparameters such as gas kinematics, geometry, and ISM morphology in theobscuration of Lyα. Thereby, we attempt to understand theLyα escape physics and infer the implications for high-redshiftstudies. Methods: We use HST/ACS imaging to producecontinuum-subtracted Lyα maps, and ground-based observations(ESO/NTT and NOT) to map the Hα emission and the extinction E(B-V)in the gas phase derived from the Balmer decrement Hα/Hβ. Results: When large outflows are present, the Lyα emission doesnot appear to be correlated with the dust content, confirming the roleof the Hi kinematics in the escape of Lyα photons. In the case ofa dense, static Hi covering, we observe a damped absorption with anegative correlation between Lyα and E(B-V). We found that theLyα escape fraction does not exceed 10% in all our galaxies and ismostly about 3% or below. Finally, because of the radiative transfercomplexity of the Lyα line, star formation rate based on Lyαluminosity is underestimated with respect to that derived from UVluminosity. Simple reddening correction does not reconcileSFR(Lyα) with the total star formation rate. Conclusions: Thedust is not necessarily the main Lyα escape regulatory factor. ISMkinematics and geometry may play a more significant role. The failure ofsimple dust correction to recover the intrinsic Lyα/Hα ratioor the total star formation rate should prompt us to be more cautiouswhen interpreting high-z observations and related properties, such asSFRs based on Lyα alone. To this end, we propose a more realisticcalibration for SFR(Lyα), which accounts for dust attenuation andresonant scattering effects via the Lyα escape fraction.This work was supported by the Centre National d'Études Spatiales(CNES). It is based on observations made with the NASA/ESA Hubble SpaceTelescope, obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy,Incorporated under NASA contract NAS 5-26555. These observations areassociated with programs #GO 9470 and #GO 10575.Based on observations made with ESO Telescopes at the La SillaObservatories under programme IDs 073.B-0785 and 70.B-0639.A part of data presented here have been taken using ALFOSC, which isowned by the Instituto de Astrofisica de Andalucia (IAA) and operated atthe Nordic Optical Telescope under agreement between IAA and the NBIfAFGof the Astronomical Observatory of Copenhagen.
| Luminosity-metallicity relation for dIrr galaxies in the near-infrared
Context: The luminosity-metallicity relation is one of the fundamentalconstraints in the study of galaxy evolution; yet none of the relationsavailable today has been universally accepted by the community. Aims:The present work is a first step to collect homogeneous abundances andnear-infrared (NIR) luminosities for a sample of dwarf irregular (dIrr)galaxies, located in nearby groups. The use of NIR luminosities isintended to provide a better proxy to mass than the blue luminositiescommonly used in the literature; in addition, selecting group membersreduces the impact of uncertain distances. Accurate abundances arederived to assess the galaxy metallicity. Methods: Optical spectra arecollected for H II regions in the dIrrs, allowing the determination ofoxygen abundances by means of the temperature-sensitive method. For eachdIrr galaxy H-band imaging is performed and the total magnitudes aremeasured via surface photometry. Results: This high-quality databaseallows us to build a well-defined luminosity-metallicity relation in therange -13≥ MH≥-20. The scatter around its linear fit isreduced to 0.11 dex, the lowest of all relations currently available.There might exist a difference between the relation for dIrrs and therelation for giant galaxies, although a firm conclusion should awaitdirect abundance determinations for a significant sample of massivegalaxies. Conclusions: This new dataset provides an improvedluminosity-metallicity relation, based on a standard NIR band, for dwarfstar-forming galaxies. The relation can now be compared with someconfidence to the predictions of models of galaxy evolution. Excitingfollow-ups of this work are (a) exploring groups with higher densities,(b) exploring nearby galaxy clusters to probe environmental effects onthe luminosity-metallicity relation, and (c) deriving direct oxygenabundances in the central regions of star-forming giant galaxies, tosettle the question of a possible dichotomy between the chemicalevolution of dwarfs and that of massive galaxies.Based on datacollected at the European Southern Observatory, La Silla, Chile,Proposal N. 70.B-0424(A,B); based on observations made at Lick (UCO)Observatory; based on observations made with the William HerschelTelescope operated on the island of La Palma by the Isaac Newton Groupin the Spanish Observatorio del Roque de los Muchachos of the Institutode Astrofísica de Canarias.
| Long-Term Variability in the Optical Spectrum of the Seyfert Galaxy NGC 2992
New spectra of NGC 2992 from the Cerro Tololo Inter-American Observatoryshow that this nearby active galactic nucleus changed its typeclassification to a Seyfert 2 in 2006. It was originally classified as aSeyfert 1.9, and has been previously seen as a Seyfert 1.5 with strongbroad Hα emission. A comparison of the reddening and equivalenthydrogen column density derived for the narrow-line region from thesenew data with those previously calculated for different regions closerto the nucleus shows them to be very similar, and suggests that thesedifferent regions are all being absorbed by the same opacity source, alarge 100 pc scale dust lane running across the nucleus. However,obscuration by dust in this lane is probably not responsible forclassification changes which occur in only a few years. It is morelikely that NGC 2992's observed variations are due to a highly variableionizing continuum. We therefore conclude that, although NGC 2992 wasoriginally identified as a Seyfert 1.9, this was not because of anoblique viewing angle through the atmosphere of a central dusty torus,but because its active nucleus was identified when it was in alow-continuum state.
| Post common envelope binaries from SDSS. II: Identification of 9 close binaries with VLT/FORS2
Context: Post common envelope binaries (PCEBs) consisting of a whitedwarf and a main sequence star are ideal systems to use to calibratecurrent theories of angular momentum loss in close compact binary stars.The potential held by PCEBs for further development of close binaryevolution could so far not be exploited due to the small number of knownsystems and the inhomogeneity of the sample. The Sloan Digital SkySurvey is changing this scene dramatically, as it is very efficient inidentifying white dwarf/main sequence (WDMS) binaries, including bothwide systems whose stellar components evolve like single stars and -more interesting in the context of close binary evolution - PCEBs. Aims: We pursue a large-scale follow-up survey to identify andcharacterise the PCEBs among the WDMS binaries that have been found withSDSS. We use a two-step strategy with the identification of PCEBs amongWDMS binaries in the first phase and orbital period determinations inthe second phase. Here we present first results of our ESO-VLT/FORS2pilot study that targets the identification of the PCEBs among thefainter (≳18.5) SDSS WDMS binaries. Methods: From published SDSScatalogues we selected 26 WDMS binaries to be observed withESO-VLT/FORS2 in service mode. The design of the observations was to gettwo spectra per object separated by at least one night. We used the NaIλλ8183.27, 8194.81 doublet to measure radial velocityvariations of our targets and a spectral decomposition/fitting techniqueto determine the white dwarf effective temperatures and surfacegravities, masses, and secondary star spectral types for all WDMSbinaries in our sample. Results: Among the 26 observed WDMS binaries,we find 9 strong PCEB candidates showing clear (≥3σ) radialvelocity variations, and we estimate the fraction of PCEBs among SDSSWDMS binaries to be ~35±12%. We find indications of a dependenceof the relative number of PCEBs among SDSS WDMS binaries on the spectraltype of the secondary star. These results are subject to small numberstatistics and need to be confirmed by additional observations. UsingMagellan-Clay/LDSS3, we measured the orbital periods of two PCEBcandidates, SDSS J1047+0523 and SDSS J1414-0132, to be 9.17 h and 17.48h, respectively. Conclusions: This pilot study demonstrates that oursurvey is highly efficient in identifying PCEBs among the SDSS WDMSbinaries, and it will indeed provide the observational parameters thatare needed to constrain the theoretical models of close binaryevolution.Based on observations collected at the European Southern Observatory,Paranal, Chile under programme ID 078.D-0719. This paper includes datagathered with the 6.5m Magellan Telescopes located at Las CampanasObservatory, Chile.
| Reionization and Galaxy Evolution Probed by z = 7 Lyα Emitters
We have performed narrowband NB973 (bandwidth 200 Å centered at9755 Å) imaging of the Subaru Deep Field (SDF) and found two z=7Lyα emitter (LAE) candidates down to NB973 =24.9. Carrying outdeep follow-up spectroscopy, we identified one of them as a real z=6.96LAE. This has established a new redshift record, showing that galaxyformation was in progress just 750 Myr after the big bang. Meanwhile,the Lyα line luminosity function of LAEs is known to decline fromz=5.7 to 6.6 in the SDF; L* at z=6.6 is 40%-60% that atz=5.7. We also confirm that the number density of z=7 LAEs is only 17%of the density at z=6.6 comparing the latest SDF LAE samples. Thisseries of significant decreases in LAE density with increasing redshiftcould be the result of galaxy evolution during these epochs. However,using the UV continuum luminosity functions of LAEs and Lyman breakgalaxies, and a LAE evolution model based on hierarchical clustering, wefind that galaxy evolution alone cannot entirely explain the decrease indensity. This extra density deficit might reflect the attenuation of theLyα photons from LAEs by the neutral hydrogen possibly left at thelast stage of cosmic reionization at z~6-7.Based on data collected at Subaru Telescope, which is operated byNational Astronomical Observatory of Japan.
| Optical Spectroscopy of Type ia Supernovae
We present 432 low-dispersion optical spectra of 32 Type Ia supernovae(SNe Ia) that also have well-calibrated light curves. The coverageranges from 6 epochs to 36 epochs of spectroscopy. Most of the data wereobtained with the 1.5 m Tillinghast telescope at the F. L. WhippleObservatory with typical wavelength coverage of 3700-7400 Å and aresolution of ~7 Å. The earliest spectra are 13 days before B-bandmaximum; two-thirds of the SNe were observed before maximum brightness.Coverage for some SNe continues almost to the nebular phase. Theconsistency of the method of observation and the technique of reductionmakes this an ideal data set for studying the spectroscopic diversity ofSNe Ia.Based in part on observations obtained at the F. L. Whipple Observatory,which is operated by the Smithsonian Astrophysical Observatory, and theMMT Observatory, a joint facility of the Smithsonian Institution and theUniversity of Arizona.
| Faint super-soft X-ray sources in XMM-Newton Large Magellanic Cloud fields
Aims. We report the discovery of three faint, super-soft X-ray sourcesin LMC fields observed with XMM-Newton. Methods: We analyse the threenew sources together with RX J0537.7-7034 and RX J0507.1-6743, bothknown since ROSAT. Results: We identify XMMU J050803.1-684017 with theLMC planetary nebula LHA 120-N 102 = LMC SMP 29. The EPIC-pn spectrum ofXMMU J050803.1-684017 can be fitted with a blackbody spectrum with aneffective temperature of ~(26-51) eV and a bolometric luminosity of(0.1-30)×1036 erg s-1, depending on theassumed absorption. The source is consistent with the nucleus of aplanetary nebula. The EPIC-pn spectrum of XMMU J052530.5-671501 ischaracterized by a blackbody temperature of ~(38-120) eV, a best-fitbolometric luminosity of ~3×1037 erg s-1 andabsorbing LMC column of˜8+2-8×1021cm-2. This most likely highly-absorbed super-soft sourceresembles the LMC super-soft source CAL 87. The EPIC-pn spectrum of XMMUJ052215.0-701658 yields a blackbody temperature of ~(24-83) eV, butthere are only about 40 source counts and the spectral parameters of thesource are not well constrained. We observe RX J0537.7-7034 with EPIC-pnto be about a factor of 15 fainter compared to the ROSAT observation 11years earlier. RX J0507.1-6743 is observed as an absorbed super-softsource by XMM-Newton and the improved X-ray position coincides with aMACHO star which is consistent with a symbiotic star.
| Exploring interstellar titanium and deuterium abundances and other correlations
Aims. The origin of the observed variability of the gas-phase D/H ratioin the local interstellar medium is still debated, and in particular therole of deuterium depletion onto dust grains. Here we extend the studyof the relationship between deuterium and titanium, a refractory speciesand tracer of elemental depletion, and explore other relationships. Methods: We have acquired high resolution spectra for nine early-typestars using the VLT/UVES spectrograph, and detected the absorption linesof interstellar TiII. Using a weighted orthogonal distance regression(ODR) code and a special method to treat non symmetric errors, wecompare the TiII columns with the corresponding HI, DI and also OIcolumns. In parallel we perform the same comparisons for available FeIIdata. Results: We find a significant correlation between TiII/HI andD/H in our data set, and, when combined with published results, weconfirm and better constrain the previously established trends andextend the trends to low HI columns. We exclude uncertainties in HI andOI columns as the main contributor to the derived metals-deuteriumcorrelations by showing that the TiII/HI ratio is positively correlatedwith DI/OI. We find a similar correlation between FeII/HI and DI/OI. TheTiII gradients are similar or slightly smaller than for FeII, while onewould expect larger variations on the basis of the higher condensationtemperature of titanium. However we argue that ionisation effectsintroduce biases that affect iron and not titanium and may explain thegradient similarity. We find a less significant negative correlationbetween the TiII/DI ratio and the hydrogen column, possibly a sign ofdifferent evaporation of D and metals according to the cloud properties.More TiII absorption data along very low H column lines-of-sight wouldbe useful to improve the correlation statistics.Based on observations taken with the Ultraviolet and Visual EchelleSpectrograph (UVES) on the Very Large Telescope (VLT) Unit 2 (Kueyen) atParanal, Chile, operated by ESO.
| Small-Scale Behavior of the Physical Conditions and the Abundance Discrepancy in the Orion Nebula
We present the results of long-slit spectroscopy, in several positions,of the Orion Nebula. Our goal is to study the spatial distributions of alarge number of nebular quantities, including line fluxes, physicalconditions, and ionic abundances, at a spatial resolution of about 1".In particular, we have compared the O++ abundance determinedfrom collisionally excited and recombination lines in 671 individualone-dimensional spectra covering different morphological zones of thenebula. We find that protoplanetary disks (proplyds) show prominentspikes of Te([N II), which is probably produced bycollisional deexcitation due to the high electron densities found inthese objects. Herbig-Haro objects show also relatively high values ofTe([N II), but these are probably produced by local heatingdue to shocks. We also find that the spatial distribution of the purerecombination O II and [O III] lines is fairly similar. The abundancediscrepancy factor (ADF) of O++ remains rather constant alongthe slit positions, except in some particular small areas of the nebula,such as at the locations of the most conspicuous Herbig-Haro objects.There is also an apparent slight increase of the ADF in the inner 40"around θ1 Ori C. We find a negative radial gradient ofTe([O III) and Te([N II) in the nebula, based onthe projected distance from θ1 Ori C. In addition, theADF of O++ seems to increase very slightly with the electrontemperature. Finally, we estimate the value of the mean-square electrontemperature fluctuation, the so-called t2 parameter. Ourresults indicate that the hypothetical thermal inhomogeneities, if theyexist, should be smaller than our spatial resolution element.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.
| High-redshift blazar identification for Swift J1656.3-3302
We report on the high-redshift blazar identification of a new gamma-raysource, Swift J1656.3-3302, detected with the BAT imager onboard theSwift satellite and the IBIS instrument on the INTEGRAL satellite.Follow-up optical spectroscopy has allowed us to identify thecounterpart as an R˜ 19 mag source that shows broad Lyman-α,Si iv, He ii, C iv, and C iii] emission lines at redshift z = 2.40± 0.01. Spectral evolution is observed in X-rays when theINTEGRAL/IBIS data are compared to the Swift/BAT results, with thespectrum steepening when the source gets fainter. The 0.7-200 keV X-raycontinuum, observed with Swift/XRT and INTEGRAL/IBIS, shows the powerlaw shape typical of radio loud (broad emission line) active galacticnuclei (with a photon index Γ ˜ 1.6) and a hint of spectralcurvature below ~2 keV, possibly due to intrinsic absorption(NH ˜ 7× 10 22 cm-2) localto the source. Alternatively, a slope change (Δ Γ ˜ 1)around 2.7 keV can describe the X-ray spectrum equally well. At thisredshift, the observed 20-100 keV luminosity of the source is~1048 erg s-1 (assuming isotropic emission),making Swift J1656.3-3302 one of the most X-ray luminous blazars. Thissource is yet another example of a distant gamma-ray loud quasardiscovered above 20 keV. It is also the farthest object, among thepreviously unidentified INTEGRAL sources, whose nature has beendetermined a posteriori through optical spectroscopy.Partly based on X-ray observations with INTEGRAL, an ESA project withinstruments and science data centre funded by ESA member states(especially the PI countries: Denmark, France, Germany, Italy,Switzerland, Spain), Czech Republic and Poland, and with theparticipation of Russia and the USA, and on optical observationscollected at ESO (La Silla, Chile) under programme 079.A-0171(A).
| The escape of Lyman photons from a young starburst: the case of Haro11†
Lyman α (Lyα) is one of the dominant tools used to probe thestar-forming galaxy population at high redshift (z). However,astrophysical interpretations of data drawn from Lyα alone hingeon the Lyα escape fraction which, due to the complex radiativetransport, may vary greatly. Here, we map the Lyα emission fromthe local luminous blue compact galaxy Haro11, a known emitter ofLyα and the only known candidate for low-z Lyman continuumemission. To aid in the interpretation, we perform a detailedultraviolet and optical multiwavelength analysis and model the stellarpopulation, dust distribution, ionizing photon budget, and star-clusterpopulation. We use archival X-ray observations to further constrainproperties of the starburst and estimate the neutral hydrogen columndensity.The Lyα morphology is found to be largely symmetric around asingle young star-forming knot and is strongly decoupled from otherwavelengths. From general surface photometry, only very slightcorrelation is found between Lyα and Hα, E(B - V), and theage of the stellar population. Only around the central Lyα brightcluster do we find the Lyα/Hα ratio at values predicted bythe recombination theory. The total Lyα escape fraction is foundto be just 3 per cent. We compute that ~90 per cent of the Lyαphotons that escape do so after undergoing multiple resonance scatteringevents, masking their point of origin. This leads to a largely symmetricdistribution and, by increasing the distance that photons must travel toescape, decreases the escape probability significantly. While dust mustultimately be responsible for the destruction of Lyα, it plays alittle role in governing the observed morphology, which is regulatedmore by interstellar medium kinematics and geometry. We find tentativeevidence for local Lyα equivalent width in the immediate vicinityof star clusters being a function of cluster age, consistent withhydrodynamic studies. We estimate the intrinsic production of ionizingphotons and put further constraints of ~9 per cent on the escapingfraction of photons at 900Å.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Incorporated,under NASA contract NAS 5-26555. These observations are associated withprogrammes #GO9470 and #GO10575.Based on observations made with ESO Telescopes at the La SillaObservatories under programme ID 073.B-0785. ‡E-mail: matthew@astro.su.se
| Spectroscopic follow-up of a cluster candidate at z = 1.45
We have obtained deep optical spectroscopic data of the highest-redshiftcluster candidate (z ~ 1.4, CVB13) selected by Van Breukelen et al. in aphotometric optical/infrared catalogue of the Subaru XMM-Newton DeepField. The data, which comprise 104 targeted galaxies, were taken withthe DEep Imaging Multi-Object Spectrograph on the Keck 2 telescope andyielded 31 secure redshifts in the range 1.25 < z < 1.54 within a7 × 4-arcmin2 field centred on CVB13. Instead of onemassive cluster at z = 1.4, we find evidence for three projectedstructures at z = 1.40,1.45 and 1.48. The most statistically robust ofthese structures, at z = 1.454, has six spectroscopically confirmedgalaxies. Its total mass is estimated at>~1014Msolar and it may therefore be termed acluster. There is an X-ray source at the cluster position which ismarginally spatially resolved but whose X-ray spectrum is too hard to bethermal cluster emission. Its origin could be the summed X-ray emissionfrom active galaxies in, and projected on to, the cluster.Serendipitously, we have discovered a cluster at z = 1.28 with a mass of>~1014Msolar at the same position on the sky,comprising six spectroscopically confirmed cluster galaxies and at leastone additional radio source. The selection of CVB13 for the clustercatalogue was evidently aided by the superposition of other, presumablylower mass, structures, whereas the single cluster at z = 1.28 containedtoo few galaxies to be isolated by the same algorithm. Given thecomplicated nature of such structures, caution must be employed whenmeasuring the mass function of putative high-redshift clusters withphotometric techniques alone.
| Hα Tail, Intracluster H II Regions, and Star Formation: ESO 137-001 in Abell 3627
We present the discovery of a 40 kpc Hα tail and at least 29emission-line objects downstream of a star-forming galaxy, ESO 137-001,in the rich, nearby cluster A3627. The galaxy is known to possess adramatic 70 kpc X-ray tail. The detected Hα tail coincidespositionally with the X-ray tail. The Hα emission in the galaxy issharply truncated on the front and the sides near the nucleus,indicating significant ram pressure stripping. ESO 137-001 is thus thefirst cluster late-type galaxy known unambiguously to have both an X-raytail and an Hα tail. The emission-line objects are all distributeddownstream of the galaxy, with projected distances of up to 39 kpc fromthe galaxy. From the analysis on the Hαoff frame andthe estimate of the background emission-line objects, we conclude thatit is very likely that all 29 emission-line objects are H II regions inA3627. The high surface number density and luminosities of these H IIregions (up to 1040 ergs s-1) dwarf the previouslyknown examples of isolated H II regions in clusters. We suggest thatstar formation may proceed in the stripped ISM in both the galactic haloand intracluster space. The total mass of formed stars in the strippedISM of ESO 137-001 may approach several times 107Msolar. Therefore, stripping of the ISM not only contributesto the ICM, but also adds to the intracluster stellar light throughsubsequent star formation. The data also imply that ESO 137-001 is in anactive stage of transformation accompanied by the buildup of a centralbulge and depletion of the ISM.
| The Aspherical Properties of the Energetic Type Ic SN 2002ap as Inferred from Its Nebular Spectra
The nebular spectra of the broad-lined, Type Ic SN 2002ap are studied bymeans of synthetic spectra. Two different modeling techniques areemployed. In one technique, the SN ejecta are treated as a single zone,while in the other a density and abundance distribution in velocity isused from an explosion model. In both cases, heating caused byγ-ray and positron deposition is computed (in the latter caseusing a Monte Carlo technique to describe the propagation ofγ-rays and positrons), as is cooling via forbidden-line emission.The results are compared, and although general agreement is found, thestratified models are shown to reproduce the observed line profiles muchmore accurately than the single-zone model. The explosion produced ~0.1Msolar of 56Ni. The distribution in velocity ofthe various elements is in agreement with that obtained from theearly-time models, which indicated an ejected mass of ~2.5Msolar with a kinetic energy of 4×1051 erg.Nebular spectroscopy confirms that most of the ejected mass (~1.2Msolar) was oxygen. The presence of an oxygen-rich innercore, combined with that of 56Ni at high velocities asdeduced from early-time models, suggests that the explosion wasasymmetric, especially in the inner part.Based in part on data obtained at the Subaru Telescope, which isoperated by the National Astronomical Observatory of Japan (NAOJ). Alsobased in part on data obtained at the University of California's LickObservatory.
| The early spectral evolution of SN 2004dt
Aims.We study the optical spectroscopic properties of Type Ia Supernova(SN Ia) 2004dt, focusing our attention on the early epochs. Methods:Observation triggered soon after the SN 2004dt discovery allowed us toobtain a spectrophotometric coverage from day -10 to almost one year(~353 days) after the B band maximum. Observations carried out on analmost daily basis allowed us a good sampling of the fast spectroscopicevolution of SN 2004dt in the early stages. To obtain this result,low-resolution, long-slit spectroscopy was obtained using a number offacilities. Results: This supernova, which in some absorption lines ofits early spectra showed the highest degree of polarization evermeasured in any SN Ia, has a complex velocity structure in the outerlayers of its ejecta. Unburnt oxygen is present, moving at velocities ashigh as ~16 700 km s-1, with some intermediate-mass elements(Mg, Si, Ca) moving equally fast. Modeling of the spectra based onstandard density profiles of the ejecta fails to reproduce the observedfeatures, whereas enhancing the density of outer layers significantlyimproves the fit. Our analysis indicates the presence of clumps ofhigh-velocity, intermediate-mass elements in the outermost layers, whichis also suggested by the spectropolarimetric data.
| CPD -20 1123 (Albus 1) Is a Bright He-B Subdwarf
Based on photometric and astrometric data it has been proposed thatAlbus 1 (also known as CPD -20 1123) might be a hot white dwarf similarto G191-B2B or, alternatively, a hot subdwarf. We obtained a series ofoptical spectra showing that CPD -20 1123 is a bright He-B subdwarf. Weanalyzed the H I Balmer and He I line spectra and measuredTeff = 19,800 +/- 400 K, logg=4.55+/-0.10, andlogN(He)/N(H)=0.15+/-0.15. This peculiar object belongs to a family ofevolved helium-rich stars that may be the products of double-degeneratemergers, or, alternatively, the products of post horizontal- orgiant-branch evolution.
| The Galactic deuterium abundance and dust depletion: insights from an expanded Ti/H sample
The primordial abundance of deuterium (D/H) yields a measure of thedensity of baryons in the Universe and is an important complement todeterminations from cosmic microwave background (CMB) experiments.Indeed, the current small samples of high-redshift D/H measurements fromquasar absorption line studies are in excellent agreement withCMB-derived values. Conversely, absorption line measurements of theGalactic D/H ratio in almost 50 stellar sightlines show a puzzlinglylarge scatter outside the local bubble which is difficult to explainsimply by astration from the primordial value. The currently favouredexplanation for these large variations is that D is differentiallydepleted relative to H in some parts of the local interstellar medium(ISM). Here, we test this scenario by studying the correlation betweenD/H and the abundance of titanium, one of the most refractory elementsreadily observed in the ISM. Previous work by Prochaska, Tripp &Howk found tentative evidence for a correlation between Ti/H and D/Hbased on seven sightlines. Here we almost triple the number of previousTi measurements and include several sightlines with very high or low D/Hthat are critical for quantifying any correlations with D/H. With ourlarger sample, we confirm a correlation between Ti/H and D/H at the 97per cent confidence level. However, the magnitude of this dependence isdifficult to reconcile with a simple model of dust depletion for tworeasons. First, contrary to what is expected from local depletion rates,the gradient of the highly refractory Ti is much shallower than thatobserved for Fe and Si. Secondly, we do not observe the establishedtight, steep correlation between [Ti/H] and the mean volume density ofhydrogen. Therefore, whilst dust remains a plausible explanation for thelocal D/H variations, the abundances of at least some of the refractoryelements do not provide unanimous support for this scenario. We alsoargue that the correlations of [Si/H], [Fe/H] and [Ti/H] with D/H areinconsistent with a simple infall model of low-metallicity gas withapproximately solar abundances as the dominant cause for D variations.Based on observations made with ESO Telescopes at the ParanalObservatories under programme ID 076.C-0503(A).E-mail: sarae@uvic.ca
| Kinematical studies of the low-mass X-ray binary GRMus (XB1254-690)
We present simultaneous high-resolution optical spectroscopy and X-raydata of the X-ray binary system GRMus (XB1254-690), obtained over a fullrange of orbital phases. The X-ray observations are used to re-establishthe orbital ephemeris for this source. The optical data include thefirst spectroscopic detection of the donor star in this system throughthe use of the Doppler Tomography technique on the Bowen fluorescenceblend (~4630-4650 Å). In combination with an estimate for theorbital parameters of the compact object using the wings of the HeIIλ4686 emission line, dynamical mass constraints of 1.20 <=MX/Msolar <= 2.64 for the neutron star and 0.45<= M2/Msolar <= 0.85 for the companion arederived.
| Optical and infrared properties of V1647 Orionis during the 2003-2006 outburst. I. The reflection nebula
Aims.The recent outburst of the young eruptive star V1647Orionis has produced a spectacular appearance of a newreflection nebula in Orion (McNeil's nebula). Wepresent an optical/near infrared investigation of McNeil's nebula. Thisanalysis is aimed at determining the morphology, temporal evolution andnature of the nebula and its connection to the outburst. Methods: Weperformed multi epoch B, V, R_C, I_C, z_gunn, and KS imagingof McNeil's nebula and V1647 Ori as well as KS imagingpolarimetry. The multiband imaging allows us to reconstruct theextinction map inside the nebula. Through polarimetric observations weattempt to disentangle the emission from the nebula from that of theaccretion disk around V1647 Ori. We also attempt to resolve the smallspatial scale structure of the illuminating source. Results: The energydistribution and temporal evolution of McNeil's nebula mimic that of theilluminating source. The extinction map reveals a region of higherextinction in the direction of V1647 Ori. Excluding foregroundextinction, the optical extinction due to McNeil's nebula in thedirection of V1647 Ori is AV ~ 6.5 mag. The polarimetricmeasurement shows a compact high polarization emission around V1647 Ori.The percentage of KS band linear polarization goes from10-20%. The vectors are all well aligned with a position angle of90° ± 9° East of North. This may correspond to theorientation of a possible accretion disk around V1647 Ori. Thesefindings suggest that the appearance of McNeil's nebula is due toreflection of light by pre-existing material in the surroundings ofV1647 Ori. We also report on the discovery of a new candidate browndwarf or protostar in the vicinity of V1647 Ori as well as the presenceof clumpy structure within HH 22A.
| MMT Observations of New Extremely Metal-poor Emission-Line Galaxies in the Sloan Digital Sky Survey
We present 6.5 m MMT spectrophotometry of 20 H II regions in 13extremely metal-poor emission-line galaxies selected from Data Release 5of the Sloan Digital Sky Survey to have [O III]λ4959/Hβ<~1 and [N II] λ6583/Hβ<~0.05. Theelectron-temperature-sensitive emission line [O III] λ4363 isdetected in 13 H II regions, allowing a direct abundance determination.The oxygen abundance in the remaining H II regions is derived using asemiempirical method. The oxygen abundance of the galaxies in our sampleranges from 12+log(O/H)~7.1 to ~7.8, with 10 H II regions having anoxygen abundance lower than 7.5. The lowest oxygen abundances,7.14+/-0.03 and 7.13+/-0.07, are found in two H II regions of the bluecompact dwarf galaxy SDSS J0956+2849 (≡DDO 68), making it thesecond most metal-deficient emission-line galaxy known, after SBS0335-052W.
| A multi-wavelength study of z = 3.15 Lyman-α emitters in the GOODS South Field
Context: Lyα-emitters have proven to be excellent probes of faint,star-forming galaxies in the high redshift universe. However, althoughthe sample of known emitters is increasingly growing, their nature (e.g.stellar masses, ages, metallicities, star-formation rates) is stillpoorly constrained. Aims: We aim to study the nature ofLyα-emitters, to find the properties of a typicalLyα-emitting galaxy and to compare these properties with theproperties of other galaxies at similar redshift, in particularLyman-break galaxies. Methods: We have performed narrow-band imaging atthe VLT, focused on Lyα at redshift z ≈ 3.15, in the GOODS-Sfield. We have identified a sample of Lyα-emitting candidates, andwe have studied their Spectral Energy Distributions (SEDs). Results: Wefind that the emitters are best fit by an SED with low metallicity(Z/Zȯ = 0.005), low dust extinction (AV ≈ 0.26) andmedium stellar masses of approximately 109Mȯ. The age is not very well constrained. One object outof 24 appears to be a high redshift Lyα-emitting dusty starburstgalaxy. We find filamentary structure as traced by theLyα-emitters at the 4σ level. The rest-frame UV SED of thesegalaxies is very similar to that of Lyman Break Galaxies (LBGs) andcomply with the selection criteria for U-band drop-outs, except they areintrinsically fainter than the current limit for LBGs. Conclusions:Lyα-emitters are excellent probes of galaxies in the distantuniverse, and represent a class of star-forming, dust and AGN free,medium mass objects.Based on observations carried out at the European Southern Observatory(ESO) under prog. ID No. 70.A-0447, 274.A-5029 and LP168.A-0485.
| The Habitat Segregation between Lyman Break Galaxies and Lyα Emitters around a QSO at z ~ 5
We carried out a target survey for Lyman break galaxies (LBGs) andLyα emitters (LAEs) around QSO SDSS J0211-0009 at z=4.87. The deepand wide broadband and narrowband imaging simultaneously revealed theperspective structure of these two high-z populations. The LBGs withoutLyα emission form a filamentary structure including the QSO, whilethe LAEs are distributed around the QSO but avoid it within a distanceof ~4.5 Mpc. On the other hand, we serendipitously discovered aprotocluster with a significant concentration of LBGs and LAEs, where nostrongly UV ionizing source, such as a QSO or radio galaxy, is known toexist. In this cluster field, the two populations are spatiallycross-correlated with each other. The relative spatial distribution ofLAEs to LBGs in the QSO field is in stark contrast to that in thecluster field. We also found a weak trend showing that the number countsbased on Lyα and UV continuum fluxes of LAEs in the QSO field areslightly lower than in the cluster field, whereas the number counts ofLBGs are almost consistent with each other. The LAEs avoid the nearbyregion around the QSO where the local UV background radiation could be~100 times stronger than the average for the epoch. The clusteringsegregation between LBGs and LAEs seen in the QSO field could be due toeither enhanced early galaxy formation in an overdense environment,causing all the LAEs to evolve into LBGs, or local photoionization dueto the strong UV radiation from the QSO, effectively causing a deficitin low-mass galaxies like LAEs.Based on data collected with the Subaru Telescope, which is operated bythe National Astronomical Observatory of Japan.
| The formation of S0 galaxies: evidence from globular clusters
Aims.We devise a simple experiment to test the theory that lenticular(S0) galaxies form from spirals whose star formation has been shut down.An individual galaxy's fading is measured using the globular clusterspecific frequency (S_N), defined as the number of globular clustersnormalised by the galaxy luminosity. This is compared with aspectroscopically-derived age estimate. Methods: We make NTT/EMMIlong-slit spectroscopic observations of 11 S0 galaxies at z < 0.006.We measure the absorption-line indices, Hδ, Hγ, Mgb, Fe5270and Fe5335 within the central r_e/8. By inverting single-stellarpopulation models, luminosity-weighted mean ages, metallicities andα-element abundance ratios are derived. We estimate the amount offading a galaxy has undergone by comparing each galaxy's SNwith its deviation from the mean spiral S_N. Results: Galaxies withhigher SN have older stellar populations. Moreover, we findthat the zero-point and amount of fading is consistent with a scenariowhere lenticulars are formed by the quenching of star formation inspiral galaxies. Our data also rule out any formation method for S0swhich creates a large number of new globular clusters. We confirm thatprevious results showing a relationship between SN and colorare driven by the SN -Age relation. Five galaxies showdetectable Hβ, [O iii], Hα or [N ii] emission lines. However,only in the two youngest galaxies is this emission unambiguously fromstar formation. Conclusions: Our results are consistent with the theorythat S0 galaxies are formed when gas in normal spirals is removed,possibly as a result of a change in environment. The on-going starformation in the youngest galaxies hints that the timescale of quenchingis ≲1 Gyr. We speculate, therefore, that the truncation of starformation is a rather gentle process unlikely to involve a rapid burstof star formation.
| ESC and KAIT observations of the transitional Type Ia SN 2004eo
We present optical and infrared observations of the unusual Type Iasupernova (SN) 2004eo. The light curves and spectra closely resemblethose of the prototypical SN 1992A, and the luminosity at maximum(MB = -19.08) is close to the average for a Type Ia supernova(SN Ia). However, the ejected 56Ni mass derived by modellingthe bolometric light curve (about 0.45Msolar) lies near thelower limit of the 56Ni mass distribution observed in normalSNe Ia. Accordingly, SN 2004eo shows a relatively rapid post-maximumdecline in the light curve [Δm15(B)true =1.46], small expansion velocities in the ejecta and a depth ratio SiIIλ5972/SiII λ6355 similar to that of SN 1992A. The physicalproperties of SN 2004eo cause it to fall very close to the boundarybetween the faint, low-velocity gradient and high-velocity gradientsubgroups proposed by Benetti et al. Similar behaviour is seen in a fewother SNe Ia. Thus, there may in fact exist a few SNe Ia withintermediate physical properties.
| Metal-Enriched Gaseous Halos around Distant Radio Galaxies: Clues to Feedback in Galaxy Formation
We present the results of an optical and near-IR spectroscopic study ofgiant nebular emission-line halos associated with three z>3 radiogalaxies, 4C 41.17, 4C 60.07, and B2 0902+34. Previous deep narrowbandLyα imaging revealed complex morphologies with sizes up to 100kpc, possibly connected to outflows and AGN feedback from the centralregions. The outer regions of these halos show quiet kinematics withtypical velocity dispersions of a few hundred km s-1 andvelocity shears that can mostly be interpreted as being due to rotation.The inner regions show shocked cocoons of gas closely associated withthe radio lobes. These display disturbed kinematics and have expansionvelocities and/or velocity dispersions >1000 km s-1. Thecore region is chemically evolved, and we also find spectroscopicevidence for the ejection of enriched material in 4C 41.17 up to adistance of ~60 kpc along the radio axis. The dynamical structurestraced in the Lyα line are, in most cases, closely echoed in thecarbon and oxygen lines. This shows that the Lyα line is producedin a highly clumped medium of small filling factor and can therefore beused as a tracer of the dynamics of high-redshift radio galaxies(HzRGs). We conclude that these HzRGs are undergoing a final jet-inducedphase of star formation with ejection of most of their interstellarmedium before becoming ``red and dead'' elliptical galaxies.Based on observations at the W. M. Keck Observatory, which is operatedas a scientific partnership among the University of California, theCalifornia Institute of Technology, and the National Aeronautics andSpace Administration. The Observatory was made possible by the generousfinancial support of the W. M. Keck Foundation.
| The strong transformation of spiral galaxies infalling into massive clusters at z ~ 0.2
We describe two peculiar galaxies falling into the massive galaxyclusters Abell1689 (z ~ 0.18) and Abell2667 (z ~ 0.23), respectively.Hubble Space Telescope (HST) images show extraordinary trails composedof bright blue knots (-16.5 < M < -11.5mag) and stellar streamsassociated with each of these systems. Combining optical, near- andmid-infrared and radio observations we prove that while both galaxiesshow similar extended trails of star-forming knots, their recent starformation histories are different. One (~L*) is experiencing a strongburst of star formation, appearing as a rare example of a luminousinfrared cluster galaxy. In comparison, the other (~0.1L*) has recentlyceased its star formation activity. Our model suggests that themorphologies and star formation in these galaxies have been influencedby the combined action of tidal interaction (likely with the clusterpotential) and of ram pressure with the intracluster medium (ICM). Theseresults can be used to gain more insights to the origin of S0s, dwarfand ultracompact dwarf (UCD) cluster galaxies.
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