Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
StarCAT: A Catalog of Space Telescope Imaging Spectrograph Ultraviolet Echelle Spectra of Stars
StarCAT is a catalog of high resolution ultraviolet spectra of objectsclassified as "stars," recorded by Space Telescope Imaging Spectrograph(STIS) during its initial seven years of operations (1997-2004). StarCATis based on 3184 echelle observations of 545 distinct targets, with atotal exposure duration of 5.2 Ms. For many of the objects, broadultraviolet coverage has been achieved by splicing echellegrams taken intwo or more FUV (1150-1700 Å) and/or NUV (1600-3100 Å)settings. In cases of multiple pointings on conspicuously variablesources, spectra were separated into independent epochs. Otherwise,different epochs were combined to enhance the signal-to-noise ratio(S/N). A post-facto correction to the {\sf calstis} pipeline data setscompensated for subtle wavelength distortions identified in a previousstudy of the STIS calibration lamps. An internal "fluxing" procedureyielded coherent spectral energy distributions (SEDs) for objects withbroadly overlapping wavelength coverage. The best StarCAT materialachieves 300 m s-1 internal velocity precision;absolute accuracy at the 1 km s-1 level; photometricaccuracy of order 4%; and relative flux precision several times better(limited mainly by knowledge of SEDs of UV standard stars). WhileStarCAT represents a milestone in the large-scale post-processing ofSTIS echellegrams, a number of potential improvements in the underlying"final" pipeline are identified.
| Subaru FOCAS Spectroscopic Observations of High-Redshift Supernovae
We present spectra of high-redshift supernovae (SNe) that were takenwith the Subaru low-resolution optical spectrograph, FOCAS. These SNewere found in SN surveys with Suprime-Cam on Subaru, the CFH12k cameraon the Canada-France-Hawaii Telescope, and the Advanced Camera forSurveys on the Hubble Space Telescope. These SN surveys specificallytargeted z > 1 Type Ia supernovae (SNe Ia). From the spectra of 39candidates, we obtained redshifts for 32 candidates andspectroscopically identified 7 active candidates as probable SNe Ia,including one at z = 1.35, which is the most distant SN Ia to bespectroscopically confirmed with a ground-based telescope. An additional4 candidates were identified as likely SNe Ia from thespectrophotometric properties of their host galaxies. Seven candidatesare not SNe Ia, either being SNe of another type or active galacticnuclei. When SNe Ia were observed within one week of the maximum light,we found that we could spectroscopically identify most of them up to z =1.1. Beyond this redshift, very few candidates were spectroscopicallyidentified as SNe Ia. The current generation of super red-sensitive,fringe-free CCDs will push this redshift limit higher.
| 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.
| The WHIQII Survey: Metallicities and Spectroscopic Properties of Luminous Compact Blue Galaxies
As part of the WIYN High Image Quality Indiana-Irvine (WHIQII) survey,we present 123 spectra of faint emission-line galaxies, selected tofocus on intermediate redshift (0.4 lsim z lsim 0.8) galaxies with bluecolors that appear physically compact on the sky. The sample includes 15true Luminous Compact Blue Galaxies (LCBGs) and an additional 27slightly less extreme emission-line systems. These galaxies represent ahighly evolving class that may play an important role in the decline ofstar formation since z ~ 1, but their exact nature and evolutionarypathways remain a mystery. Here, we use emission lines to determinemetallicities and ionization parameters, constraining their intrinsicproperties and state of star formation. Some LCBG metallicities areconsistent with a "bursting dwarf" scenario, while a substantialfraction of others are not, further confirming that LCBGs are a highlyheterogeneous population but are broadly consistent with theintermediate redshift field. In agreement with previous studies, weobserve overall evolution in the luminosity-metallicity relation atintermediate redshift. Our sample, and particularly the LCBGs, occupiesa region in the empirical R 23-O 32 plane thatdiffers from luminous local galaxies and is more consistent with dwarfirregulars at the present epoch, suggesting that cosmic "downsizing" isobservable in even the most fundamental parameters that describe starformation. These properties for our sample are also generally consistentwith lying between local galaxies and those at high redshift, asexpected by this scenario. Surprisingly, our sample exhibits nodetectable correlation between compactness and metallicity, stronglysuggesting that at these epochs of rapid star formation, the morphologyof compact star-forming galaxies is largely transient.
| A Type IIn Supernova with Coronal Lines in the Low-Metallicity Compact Dwarf Galaxy J1320+2155
We report the discovery of a Type IIn supernova (SN) in thelow-metallicity dwarf galaxy J1320+2155, with an oxygen abundance 12 +log O/H = 8.0 ± 0.2. This finding is based on Sloan Digital SkySurvey (SDSS; 2008 February) and 3.5 m Apache Point Observatory (2009February) spectra taken one year apart, and on the observations that:the H? and H? emission lines show broad componentscorresponding to gas expansion velocities of ~1600 kms-1 the Balmer decrement is exceedingly high: theH?/H? flux ratio, being more than 30, implies a very denseenvironment (>107 cm-3) and the H?broad luminosity decreases slowly, by only a factor of ~1.8 over thecourse of a year, typical of the slow luminosity evolution of a Type IInSN. Several weak coronal lines of [Fe VII] and [Fe X] are also seen inthe SDSS spectrum, implying ionization of the pre-shock circumstellarmedium by shock-induced X-ray emission. The galaxy J1320+2155 is thefirst dwarf system ever to be discovered with a Type IIn SN exhibitingcoronal lines in its spectrum.
| The Sloan Bright Arcs Survey: Four Strongly Lensed Galaxies with Redshift > 2
We report the discovery of four very bright, strongly lensed galaxiesfound via systematic searches for arcs in Sloan Digital Sky Survey DataRelease 5 and 6. These were followed up with spectroscopy and imagingdata from the Astrophysical Research Consortium 3.5 m telescope atApache Point Observatory and found to have redshift z > 2.0. Withisophotal magnitudes r = 19.2-20.4 and 3'' diameter magnitudes r =20.0-20.6, these systems are some of the brightest and highest surfacebrightness lensed galaxies known in this redshift range. In addition tothe magnitudes and redshifts, we present estimates of the Einsteinradii, which range from 5farcs0 to 12farcs7, and use those to derive theenclosed masses of the lensing galaxies.
| Outflows and Massive Stars in the Protocluster IRAS 05358+3543
We present new near-IR H2, CO J = 2-1, and CO J = 3-2observations to study outflows in the massive star-forming region IRAS05358+3543. The Canada-France-Hawaii Telescope H2 images andJames Clerk Maxwell Telescope CO data cubes of the IRAS 05358 regionreveal several new outflows, most of which emerge from the dense clusterof submillimeter cores associated with the Sh 2-233IR NE cluster to thenortheast of IRAS 05358. We used Apache Point Observatory JHK spectra todetermine line-of-sight velocities of the outflowing material. Analysisof archival Very Large Array cm continuum data and previously publishedvery long baseline interferometry observations reveal a massive starbinary as a probable source of one or two of the outflows. We haveidentified probable sources for six outflows and candidate counterflowsfor seven out of a total of 11 seen to be originating from the IRAS05358 clusters. We classify the clumps within Sh 2-233IR NE as an earlyprotocluster and Sh 2-233IR SW as a young cluster, and conclude that theoutflow energy injection rate approximately matches the turbulent decayrate in Sh 2-233IR NE.
| Large Area Survey for z = 7 Galaxies in SDF and GOODS-N: Implications for Galaxy Formation and Cosmic Reionization
We present results of our large area survey for z'-band dropout galaxiesat z = 7 in a 1568 arcmin2 sky area covering the SDF andGOODS-N fields. Combining our ultra-deep Subaru/Suprime-Cam z'- andy-band (?eff = 1 ?m) images with legacy data ofSubaru and Hubble Space Telescope, we have identified 22 brightz-dropout galaxies down to y = 26, one of which has a spectroscopicredshift of z = 6.96 determined from Ly? emission. The z = 7luminosity function yields the best-fit Schechter parameters of phi* =0.69+2.62 -0.55 ×10-3 Mpc-3, M*UV =-20.10 ± 0.76 mag, and ? = -1.72 ± 0.65,and indicates a decrease from z = 6 at a >95% confidence level. Thisdecrease is beyond the cosmic variance in our two fields, which isestimated to be a factor of lsim2. We have found that the cosmic starformation rate density drops from the peak at z = 2-3 to z = 7 roughlyby a factor of ~10 but not larger than ~100. A comparison with thereionization models suggests either that the universe could not betotally ionized by only galaxies at z = 7, or more likely thatproperties of galaxies at z = 7 are different from those at lowredshifts having, e.g., a larger escape fraction (gsim0.2), a lowermetallicity, and/or a flatter initial mass function. Our SDF z-dropoutgalaxies appear to form 60 Mpc long filamentary structures, and the z =6.96 galaxy with Ly? emission is located at the center of anoverdense region consisting of four UV bright dropout candidates, whichmight suggest an existence of a well-developed ionized bubble at z = 7.Based on data obtained with the Subaru Telescope, the NASA/ESA HubbleSpace Telescope (HST), and Spitzer Space Telescope. The Subaru Telescopeis operated by the National Astronomical Observatory of Japan. HST isoperated by the Association of Universities for Research in Astronomy(AURA), Inc., under NASA contract NAS5-26555. The Spitzer SpaceTelescope is operated by the Jet Propulsion Laboratory, CaliforniaInstitute of Technology under a contract with NASA.
| Astrometry with the Hubble Space Telescope: Trigonometric Parallaxes of Planetary Nebula Nuclei NGC 6853, NGC 7293, Abell 31, and DeHt 5
We present absolute parallaxes and relative proper motions for thecentral stars of the planetary nebulae NGC 6853 (The Dumbbell), NGC 7293(The Helix), Abell 31, and DeHt 5. This paper details our reduction andanalysis using DeHt 5 as an example. We obtain these planetary nebulanuclei (PNNi) parallaxes with astrometric data from Fine GuidanceSensors FGS 1r and FGS 3, white-light interferometers on the HubbleSpace Telescope. Proper motions, spectral classifications andVJHKT2M and DDO51 photometry of the stars comprising theastrometric reference frames provide spectrophotometric estimates ofreference star absolute parallaxes. Introducing these into our model asobservations with error, we determine absolute parallaxes for each PNN.Weighted averaging with previous independent parallax measurementsyields an average parallax precision, ??/? = 5%.Derived distances are: d NGC 6853 = 405+28-25 pc, d NGC 7293 = 216+14-12 pc, d Abell 31 = 621+91-70 pc, and d DeHt 5 = 345+19-17 pc. These PNNi distances are all smaller thanpreviously derived from spectroscopic analyses of the central stars. Toobtain absolute magnitudes from these distances requires estimates ofinterstellar extinction. We average extinction measurements culled fromthe literature, from reddening based on PNNi intrinsic colors derivedfrom model SEDs, and an assumption that each PNN experiences the samerate of extinction as a function of distance as do the reference starsnearest (in angular separation) to each central star. We also applyLutz-Kelker bias corrections. The absolute magnitudes and effectivetemperatures permit estimates of PNNi radii through both theStefan-Boltzmann relation and Eddington fluxes. Comparing absolutemagnitudes with post-AGB models provides mass estimates. Masses clusteraround 0.57 {\cal M}_{\odot }, close to the peak of the white dwarf massdistribution. Adding a few more PNNi with well-determined distances andmasses, we compare all the PNNi with cooler white dwarfs of similarmass, and confirm, as expected, that PNNi have larger radii than whitedwarfs that have reached their final cooling tracks.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, Inc., underNASA contract NAS5-26555.
| Massive star formation in Wolf-Rayet galaxies. II. Optical spectroscopy results
Aims. We have performed a comprehensive multiwavelength analysis of asample of 20 starburst galaxies that show the presence of a substantialpopulation of very young massive stars, most of them classified asWolf-Rayet (WR) galaxies. In this paper, the second of the series, wepresent the results of the analysis of long-slit intermediate-resolutionspectroscopy of star-formation bursts for 16 galaxies of our sample. Methods: We study the spatial localization of the WR stars in eachgalaxy. We analyze the excitation mechanism and derive the reddeningcoefficient, physical conditions, and chemical abundances of the ionizedgas. We study the kinematics of the ionized gas to check therotation/turbulence pattern of each system. When possible, tentativeestimates of the Keplerian mass of the galaxies are calculated.Results: Aperture effects and the exact positioning of the slit onto theWR-rich bursts seem to play a fundamental role in their detection. Wecheck that the ages of the last star-forming burst estimated usingoptical spectra agree with those derived from Hα imagery. Ouranalysis shows that a substantial fraction of the galaxies exhibitevidence of perturbed kinematics. With respect to the results found inindividual galaxies, we remark the detection of objects with differentmetallicity and decoupled kinematics in Haro 15 and Mkn 1199, thedetection of tidal streams in IRAS 08208+2816, Tol 9, and perhaps in SBS1319+579, and the development of a merging process in both SBS 0926+606A and Tol 1457-262. Conclusions: All of these results - incombination with those obtained in Paper I - reinforce the hypothesisthat interactions with or between dwarf objects is a very importantmechanism in triggering massive-star formation in starburst galaxies,especially in dwarf ones. It must be highlighted that only deep and verydetailed observations - as presented in this paper - can provide clearevidences that these subtle interaction processes are taking place.Based on observations made with NOT (Nordic Optical Telescope), INT(Isaac Newton Telescope) and WHT (William Herschel Telescope) operatedon the island of La Palma jointly by Denmark, Finland, Iceland, Norwayand Sweden (NOT) or the Isaac Newton Group (INT, WHT) in the SpanishObservatorio del Roque de Los Muchachos of the Instituto deAstrofísica de Canarias.Table 1 and Figs. 1-4, 6-10, 12, 13, 15-30, 32-35 and Appendix are onlyavailable in electronic form at http://www.aanda.org
| Ly? blobs like company: the discovery of a candidate 100kpc Ly? blob near to a radio galaxy with a giant Ly? halo B3J2330+3927 at z = 3.1
We present the discovery of a candidate of giant radio-quiet Ly?blob (RQLAB) in a large-scale structure around a high-redshift radiogalaxy (HzRG) lying in a giant Ly? halo B3J2330+3927 at redshift z= 3.087. We obtained narrow- and broad-band imaging around B3J2330+3927with Subaru/Suprime-Cam to search for Ly? emitters (LAEs) andabsorbers (LAAs) at redshift z = 3.09 +/- 0.03. We detected candidate127 LAEs and 26 LAAs in the field of view of 31 ×24arcmin2 (58 × 44 comoving Mpc). We found thatB3J2330+3927 is surrounded by a 130kpc Ly? halo and a large-scale(~60 × 20 comoving Mpc) filamentary structure. The large-scalestructure contains one prominent local density peak with an overdensityof greater than 5, which is 8arcmin (15 comoving Mpc) away fromB3J2330+3927. In this peak, we discovered a candidate 100kpc RQLAB. Theexistence of both types of Ly? nebulae in the same large-scalestructure suggests that giant Ly? nebulae need special large-scaleenvironments to form. On smaller scales, however, the location ofB3J2330+3927 is not a significant local density peak in this structure,in contrast to the RQLAB. There are two possible interpretations of thedifference of the local environments of these two Ly? nebulae.First, RQLAB may need a prominent (? ~ 5) density peak of galaxiesto form through intense starbursts due to frequent galaxyinteractions/mergers and/or continuous gas accretion in an overdenseenvironment. On the other hand, Ly? halo around HzRG may notalways need a prominent density peak to form if the surroundingLy? halo is mainly powered by its radio and active galacticnucleus activities. Alternatively, both RQLAB and Ly? halo aroundHzRG may need prominent density peaks to form but we could notcompletely trace the density of galaxies because we missed evolved anddusty galaxies in this survey.Based on data collected at Subaru Telescope, which is operated by theNational Astronomical Observatory of Japan.E-mail: yuichi.matsuda@durham.ac.uk
| First-Year Sloan Digital Sky Survey-II Supernova Results: Hubble Diagram and Cosmological Parameters
We present measurements of the Hubble diagram for 103 Type Ia supernovae(SNe) with redshifts 0.04 < z < 0.42, discovered during the firstseason (Fall 2005) of the Sloan Digital Sky Survey-II (SDSS-II)Supernova Survey. These data fill in the redshift "desert" between low-and high-redshift SN Ia surveys. Within the framework of the MLCS2K2light-curve fitting method, we use the SDSS-II SN sample to infer themean reddening parameter for host galaxies, RV = 2.18± 0.14stat ± 0.48syst, and find thatthe intrinsic distribution of host-galaxy extinction is well fitted byan exponential function, P(AV ) = exp(-AV/τV), with τV = 0.334 ± 0.088 mag.We combine the SDSS-II measurements with new distance estimates forpublished SN data from the ESSENCE survey, the Supernova Legacy Survey(SNLS), the Hubble Space Telescope (HST), and a compilation of Nearby SNIa measurements. A new feature in our analysis is the use of detailedMonte Carlo simulations of all surveys to account for selection biases,including those from spectroscopic targeting. Combining the SN Hubblediagram with measurements of baryon acoustic oscillations from the SDSSLuminous Red Galaxy sample and with cosmic microwave backgroundtemperature anisotropy measurements from the Wilkinson MicrowaveAnisotropy Probe, we estimate the cosmological parameters w andΩM, assuming a spatially flat cosmological model(FwCDM) with constant dark energy equation of state parameter, w. Wealso consider constraints upon ΩM andΩΛ for a cosmological constant model(ΛCDM) with w = -1 and non-zero spatial curvature. For theFwCDM model and the combined sample of 288 SNe Ia, we find w =-0.76 ± 0.07(stat) ± 0.11(syst), ΩM= 0.307 ± 0.019(stat) ± 0.023(syst) using MLCS2K2 and w =-0.96 ± 0.06(stat) ± 0.12(syst), ΩM= 0.265 ± 0.016(stat) ± 0.025(syst) using the SALT-IIfitter. We trace the discrepancy between these results to a differencein the rest-frame UV model combined with a different luminositycorrection from color variations; these differences mostly affect thedistance estimates for the SNLS and HST SNe. We present detaileddiscussions of systematic errors for both light-curve methods and findthat they both show data-model discrepancies in rest-frame U band. Forthe SALT-II approach, we also see strong evidence forredshift-dependence of the color-luminosity parameter (β).Restricting the analysis to the 136 SNe Ia in the Nearby+SDSS-IIsamples, we find much better agreement between the two analysis methodsbut with larger uncertainties: w = -0.92 ±0.13(stat)+0.10 -0.33(syst) for MLCS2K2 andw = -0.92 ± 0.11(stat)+0.07-0.15 (syst) for SALT-II.
| Photometric calibration of the Supernova Legacy Survey fields
Aims: We present the photometric calibration of the Supernova LegacySurvey (SNLS) fields. The SNLS aims at measuring the distances to SNe Iaat (0.3 < z < 1) using MegaCam, the 1 deg2 imager onthe Canada-France-Hawaii Telescope (CFHT). The uncertainty affecting thephotometric calibration of the survey dominates the systematicuncertainty of the key measurement of the survey, namely the dark energyequation of state. The photometric calibration of the SNLS requiresobtaining a uniform response across the imager, calibrating the sciencefield stars in each survey band (SDSS-like ugriz bands) with respect tostandards with known flux in the same bands, and binding the calibrationto the UBVRI Landolt standards used to calibrate the nearby SNe from theliterature necessary to produce cosmological constraints. Methods: The spatial non-uniformities of the imager photometricresponse are mapped using dithered observations of dense stellar fields.Photometric zero-points against Landolt standards are obtained. Thelinearity of the instrument is studied. Results: We show that theimager filters and photometric response are not uniform and publishcorrection maps. We present models of the effective passbands of theinstrument as a function of the position on the focal plane. We define anatural magnitude system for MegaCam. We show that the systematicsaffecting the magnitude-to-flux relations can be reduced if we use thespectrophotometric standard star BD +17 4708 instead of Vega as afundamental flux standard. We publish ugriz catalogs of tertiarystandards for all the SNLS fields.Based on observations obtained with MegaPrime/MegaCam, a joint projectof CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT)which is operated by the National Research Council (NRC) of Canada, theInstitut National des Sciences de l'Univers of the Centre National de laRecherche Scientifique (CNRS) of France, and the University of Hawaii.This work is based in part on data products produced at the CanadianAstronomy Data Centre as part of the Canada-France-Hawaii TelescopeLegacy Survey, a collaborative project of NRC and CNRS. Tables 13-22 andD.1-D.3 are also available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/506/999
| Galaxy Zoo: `Hanny's Voorwerp', a quasar light echo?
We report the discovery of an unusual object near the spiral galaxyIC2497, discovered by visual inspection of the Sloan Digital Sky Survey(SDSS) as part of the Galaxy Zoo project. The object, known as Hanny'sVoorwerp, is bright in the SDSS g band due to unusually strong[OIII]4959, 5007 emission lines. We present the results of the firsttargeted observations of the object in the optical, ultraviolet andX-ray, which show that the object contains highly ionized gas. Althoughthe line ratios are similar to extended emission-line regions nearluminous active galactic nucleus (AGN), the source of this ionization isnot apparent. The emission-line properties, and lack of X-ray emissionfrom IC2497, suggest either a highly obscured AGN with a novel geometryarranged to allow photoionization of the object but not the galaxy's owncircumnuclear gas, or, as we argue, the first detection of a quasarlight echo. In this case, either the luminosity of the central sourcehas decreased dramatically or else the obscuration in the system hasincreased within 105yr. This object may thus represent thefirst direct probe of quasar history on these time-scales.This publication has been made possible by the participation of morethan 100000 volunteers in the Galaxy Zoo project. Their contributionsare individually acknowledged athttp://www.galaxyzoo.org/Volunteers.aspxE-mail: cjl@astro.ox.ac.uk ‡Visiting Astronomer, Kitt Peak National Observatory, National OpticalAstronomy Observatory, which is operated by the Association ofUniversities for Research in Astronomy (AURA) under cooperativeagreement with the National Science Foundation.
| Host Galaxies of Luminous Type 2 Quasars at z ~ 0.5
We present deep Gemini GMOS optical spectroscopy of nine luminousquasars at redshifts z ~ 0.5, drawn from the Sloan Digital Sky Surveytype 2 quasar sample. Our targets were selected to have high intrinsicluminosities (MV < -26 mag) as indicated by the [OIII] ?5007 Å emission-line luminosity (L [OIII]). Our sample has a median black hole mass of~108.8 M sun inferred assuming the local MBH-?* relation and a median Eddington ratioof ~0.7, using stellar velocity dispersions ?* measuredfrom the G band. We estimate the contamination of the stellar continuumfrom scattered quasar light based on the strength of broad H?, andprovide an empirical calibration of the contamination as a function of L[O III]; the scattered-light fraction is ~30% of L5100 for objects with L [O III] = 109.5L sun. Population synthesis indicates that youngpoststarburst populations (<0.1 Gyr) are prevalent in luminous type 2quasars, in addition to a relatively old population (>1 Gyr) whichdominates the stellar mass. Broad emission complexes around He II?4686 Å with luminosities up to 108.3 Lsun are unambiguously detected in three out of the ninetargets, indicative of Wolf-Rayet (WR) populations. Population synthesisshows that ~5 Myr poststarburst populations contribute substantially tothe luminosities (>50% of L 5100) of all three objectswith WR detections. We find two objects with double cores and four withclose companions. Our results may suggest that luminous type 2 quasarstrace an early stage of galaxy interaction, perhaps responsible for boththe quasar and the starburst activity.Based, in part, on observations obtained at the Gemini Observatory,which is operated by the Association of Universities for Research inAstronomy, Inc., under a cooperative agreement with the NSF on behalf ofthe Gemini partnership: the National Science Foundation (United States),the Science and Technology Facilities Council (United Kingdom), theNational Research Council (Canada), CONICYT (Chile), the AustralianResearch Council (Australia), Ministério da Ciência eTecnologia (Brazil), and Ministerio de Ciencia, Tecnología eInnovación Productiva (Argentina).
| A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
A study of gas-phase element abundances reported in the literature for17 different elements sampled over 243 sight lines in the local part ofour Galaxy reveals that the depletions into solid form (dust grains) areextremely well characterized by trends that employ only three kinds ofparameters. One is an index that describes the overall level ofdepletion applicable to the gas in any particular sight line, and theother two represent linear coefficients that describe how to derive eachelement's depletion from this sight-line parameter. The information fromthis study reveals the relative proportions of different elements thatare incorporated into dust at different stages of grain growth. Anextremely simple scheme is proposed for deriving the dust contents andmetallicities of absorption-line systems that are seen in the spectra ofdistant quasars or the optical afterglows of gamma-ray bursts. Contraryto presently accepted thinking, the elements sulfur and krypton appearto show measurable changes in their depletions as the general levels ofdepletions of other elements increase, although more data are needed toascertain whether or not these findings are truly compelling. Nitrogenappears to show no such increase. The incorporation of oxygen into solidform in the densest gas regions far exceeds the amounts that can takethe form of silicates or metallic oxides; this conclusion is based ondifferential measurements of depletion and thus is unaffected byuncertainties in the solar abundance reference scale.Based in large part on published observations from (1) the NASA/ESAHubble Space Telescope obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS 5-26555, (2) theFar Ultraviolet Spectroscopic Explorer (FUSE) mission operated by JohnsHopkins University, supported by NASA contract NAS5-32985, and (3) TheCopernicus satellite, supported by NASA grant NAGW-77 to PrincetonUniversity.
| Discovery of a Very Bright, Strongly Lensed z = 2 Galaxy in the SDSS DR5
We report on the discovery of a very bright z = 2.00 star-forming galaxythat is strongly lensed by a foreground z = 0.422 luminous red galaxy(LRG), SDSS J120602.09+514229.5. This system, nicknamed the "Clone," wasfound in a systematic search for bright arcs lensed by LRGs andbrightest cluster galaxies in the Sloan Digital Sky Survey Data Release5 sample. Follow-up observations on the Subaru 8.2 m telescope on MaunaKea and the Astrophysical Research Consortium 3.5 m telescope at ApachePoint Observatory confirmed the lensing nature of this system. A simplelens model for the system, assuming a singular isothermal ellipsoid massdistribution, yields an Einstein radius of ?Ein = 3.82± 0farcs03 or 14.8 ± 0.1 h -1 kpc at thelens redshift. The total projected mass enclosed within the Einsteinradius is 2.10 ± 0.03 × 1012 h-1 M sun, and the magnification factor forthe source galaxy is 27 ± 1. Combining the lens model with ourgVriz photometry, we find a (unlensed) star formation rate (SFR) for thesource galaxy of 32 h -1 M sunyr-1, adopting a fiducial constant SFR model with anage of 100 Myr and E(B - V) = 0.25. With an apparent magnitude ofr = 19.8, this system is among the very brightest lensed z >= 2galaxies, and provides an excellent opportunity to pursue detailedstudies of the physical properties of an individual high-redshiftstar-forming galaxy.
| An Analysis of the Shapes of Interstellar Extinction Curves. VI. The Near-IR Extinction Law
We combine new observations from the Hubble Space Telescope's AdvancedCamera of Survey with existing data to investigate the wavelengthdependence of near-IR (NIR) extinction. Previous studies suggest a powerlaw form for NIR extinction, with a "universal" value of the exponent,although some recent observations indicate that significant sightline-to-sight line variability may exist. We show that a power-law modelfor the NIR extinction provides an excellent fit to most extinctioncurves, but that the value of the power, β, varies significantlyfrom sight line to sight line. Therefore, it seems that a "universal NIRextinction law" is not possible. Instead, we find that as βdecreases, R(V) ≡ A(V)/E(B – V) tends to increase,suggesting that NIR extinction curves which have been considered"peculiar" may, in fact, be typical for different R(V) values. We showthat the power-law parameters can depend on the wavelength interval usedto derive them, with the β increasing as longer wavelengths areincluded. This result implies that extrapolating power-law fits todetermine R(V) is unreliable. To avoid this problem, we adopt adifferent functional form for NIR extinction. This new form mimics apower law whose exponent increases with wavelength, has only two freeparameters, can fit all of our curves over a longer wavelength baselineand to higher precision, and produces R(V) values which are consistentwith independent estimates and commonly used methods for estimatingR(V). Furthermore, unlike the power-law model, it gives R(V)s that areindependent of the wavelength interval used to derive them. It alsosuggests that the relation R(V) = -1.36 \frac{E(K-V)}{E(B-V)} - 0.79 canestimate R(V) to ±0.12. Finally, we use model extinction curvesto show that our extinction curves are in accord with theoreticalexpectations, and demonstrate how large samples of observationalquantities can provide useful constraints on the grain properties.
| LO Pegasi: an investigation of multiband optical polarization
We present BVR polarimetric study of the cool active star LO Pegasi (LOPeg) for the first time. LO Peg was found to be highly polarized amongthe cool active stars. Our observations yield average values ofpolarization in LO Peg: PB = 0.387 +/- 0.004 per cent,θB = 88° +/- 1° PV = 0.351 +/-0.004 per cent, θV = 91° +/- 1° andPR = 0.335 +/- 0.003 per cent, θR = 91°+/- 1°. Both the degree of polarization and the position angle arefound to be variable. The semi-amplitude of the polarization variabilityin B, V and R bands is found to be 0.18 +/- 0.02, 0.13 +/- 0.01 and 0.10+/- 0.02 per cent, respectively. We suggest that the levels ofpolarization observed in LO Peg could be the result of scattering of ananisotropic stellar radiation field by an optically thin circumstellarenvelope or scattering of the stellar radiation by prominence-likestructures.
| New faint optical spectrophotometric standards: hot white dwarfs from the Sloan Digital Sky Survey
The spectral energy distributions for pure-hydrogen (DA) hot whitedwarfs can be accurately predicted by model atmospheres. This makes itpossible to define spectrophotometric calibrators by scaling thetheoretical spectral shapes with broad-band photometric observations - astrategy successfully exploited for the spectrographs onboard the HubbleSpace Telescope (HST) using three primary DA standards. Absolute fluxesfor non-DA secondary standards, introduced to increase the density ofcalibrators in the sky, need to be referred to the primary standards,but a far better solution would be to employ a network of DA starsscattered throughout the sky. We search for blue objects in the sixthdata release of the Sloan Digital Sky Survey (SDSS) and fit DA modelfluxes to identify suitable candidates. Reddening needs to be consideredin the analysis of many of these stars. We propose a list of ninepure-hydrogen white dwarfs with absolute fluxes with estimateduncertainties below 3 per cent, including four objects with estimatederrors <2 per cent, as candidates for spectrophotometric standards inthe range 14 < g < 18, and provide model-based fluxes scaled tomatch the SDSS broad-band fluxes for each. We apply the same method tothe three HST DA standards, linking the zero point of their absolutefluxes to ugr magnitudes transformed from photometry obtained with theUS Naval Observatory 1-m telescope. For these stars, we estimateuncertainties of <1 per cent in the optical, finding good consistencywith the fluxes adopted for HST calibration.
| Properties of the ionized gas in HH 202 - II. Results from echelle spectrophotometry with Ultraviolet Visual Echelle Spectrograph
We present results of deep echelle spectrophotometry of the brightestknot of the Herbig-Haro object HH 202 in the Orion Nebula - HH 202-S -using the Ultraviolet Visual Echelle Spectrograph in the spectral rangefrom 3100 to 10400 Å. The high spectral resolution of theobservations has permitted to separate the component associated with theambient gas from that associated with the gas flow. We derive electrondensities and temperatures from different diagnostics for bothcomponents, as well as the chemical abundances of several ions andelements from collisionally excited lines, including the firstdeterminations of Ca+ and Cr+ abundances in theOrion Nebula. We also calculate the He+, C2+,O+ and O2+ abundances from recombination lines.The difference between the O2+ abundances determined fromcollisionally excited and recombination lines - the so-called abundancediscrepancy factor - is 0.35 and 0.11 dex for the shock and nebularcomponents, respectively. Assuming that the abundance discrepancy isproduced by spatial variations in the electron temperature, we derivevalues of the temperature fluctuation parameter, t2, of 0.050and 0.016 for the shock and nebular components, respectively.Interestingly, we obtain almost coincident t2 values for bothcomponents from the analysis of the intensity ratios of HeI lines. Wefind significant departures from case B predictions in the Balmer andPaschen flux ratios of lines of high principal quantum number n. Weanalyse the ionization structure of HH 202-S, finding enough evidence toconclude that the flow of HH 202-S has compressed the ambient gas insidethe nebula trapping the ionization front. We measure a strong increaseof the total abundances of nickel and iron in the shock component, theabundance pattern and the results of photoionization models for bothcomponents are consistent with the partial destruction of dust after thepassage of the shock wave in HH 202-S.Based on observations collected at the European Southern Observatory,Chile, proposal number ESO 70.C-0008(A).E-mail: amd@iac.es
| A Photoionized Nebula Surrounding and Variable Optical Continuum Emission from the Ultraluminous X-Ray Source in NGC 5408
We obtained optical spectra of the counterpart of the ultraluminousX-ray source NGC 5408 X-1 using the FORS spectrograph on the Very LargeTelescope. The spectra show strong high-excitation emission lines, He II?4686 and [Ne V] ?3426, indicative of X-rayphotoionization. Using the measured X-ray spectrum as input to aphotoionization model, we calculated the relation between the He II andX-ray luminosities and found that the He II flux implies a lower boundon the X-ray luminosity of 3 × 1039 ergs-1. The [Ne V] flux requires a similar X-rayluminosity. After subtraction of the nebular emission, the continuumappears to have a power-law form with a spectral slope of-2.0+0.1 -0.2. This is similar tolow-mass X-ray binaries where the optical spectra are dominated byreprocessing of X-rays in the outer accretion disk. In one observation,the continuum, He II ?4686, and [Ne V] ?3426 fluxes areabout 30% lower than in the other five observations. This implies thatpart of the line emission originates within 1 lt-day of the compactobject. Fitting the optical continuum emission and archival X-ray datato an irradiated disk model, we find that (6.5 ± 0.7) ×10-3 of the total bolometric luminosity is thermalizedin the outer accretion disk. This is consistent with values found forstellar-mass X-ray binaries and larger than expected in models ofsuper-Eddington accretion flows. We find no evidence for absorptionlines that would permit measurement of the radial velocity of thecompanion star.Based on observations collected at the European Organisation forAstronomical Research in the Southern Hemisphere, Chile (ESO Programme69.A-0123(A)).
| Extremely Luminous Supernova 2006gy at Late Phase: Detection of Optical Emission from Supernova
Supernova (SN) 2006gy is an extremely luminous Type IIn SN characterizedby the bright peak magnitude MR ~-22 mag and itslong duration. The mechanism giving rise to its huge luminosity is stillunclear. We performed optical spectroscopy and photometry of SN 2006gyat late time, ~400 days after the explosion, with the Subaru/FOCAS in agood seeing condition. We carefully extracted the SN component, althoughthere is an ambiguity because of the contamination by bright nucleus ofthe host galaxy. We found that the SN faded by ~3 mag from ~200 to~400 days after the explosion (i.e., by ~5 mag from peak to ~400days) in R band. The overall light curve is marginally consistent withthe 56Ni heating model, although the flattening around 200days suggests the optical flux declined more steeply between ~200 and~400 days. The late time spectrum was quite peculiar among all types ofSNe. It showed many intermediate width (~2000 km s-1FWHM) emission lines, e.g., [Fe II], [Ca II], and Ca II. The absence ofthe broad [O I] 6300, 6364 line and weakness of [Fe II] and [Ca II]lines compared with Ca II IR triplet would be explained by a moderatelyhigh electron density in the line emitting region. This high-densityassumption seems to be consistent with the large amount of ejecta andlow expansion velocity of SN 2006gy. The Hα line luminosity was assmall as ~1× 1039 erg s-1, beingcomparable with those of normal Type II SNe at similar epochs. Ourobservation indicates that the strong circumstellar medium interactionhad almost finished by ~400 days. If the late time optical flux ispurely powered by radioactive decay, at least M(56Ni) ~ 3 Msun should be produced at the SN explosion. In the late phasespectrum, there were several unusual emission lines at7400 Å-8800 Å and some of them might be due to Tior Ni synthesized at the explosion.Based on data collected at Subaru telescope, which is operated by theNational Astronomical Observatory of Japan (NAOJ).
| The Reddening Toward Cassiopeia A's Supernova: Constraining the 56Ni Yield
We present new reddening measurements toward the young supernova remnantCassiopeia A using two techniques not previously applied to this object.Our observations of the near-infrared [Fe II] 1.257 ?m and 1.644?m lines show the extinction to be highly variable across theremnant, increasing toward the west and the south, consistent withprevious radio and X-ray observations. While the absolute value ofAV as determined by the [Fe II] lines is uncertain dueto conflicting calculations and observations of their intrinsic fluxratio, parts of the remnant without previous optical measurements showcomparatively higher reddening. We find AV = 6.2 ± 0.6from the broadband shape of the infrared synchrotron emission of a knotwithin 13'' of the expansion center. Given this reddening, the apparentfaintness of the nascent supernova, and iron mass constraints from X-rayobservations, we estimate an ejected mass of 56Ni of0.058-0.16 M sun. Taken with ?-ray observations of the44Ti decay chain, this nickel mass is broadly consistent withthe solar 44Ca/56Fe ratio.
| The Optical Structure of the Starburst Galaxy M82. I. Dynamics of the Disk and Inner-Wind
We present Gemini-North GMOS-IFU observations of the central starburstclumps and inner wind of M82, together with WIYN DensePak IFUobservations of the inner 2 × 0.9 kpc of the disk. These cover theemission lines of H?, [N II], [S II], and [S III] at a spectralresolution of 45-80 km s-1. The high signal-to-noise ofthe data is sufficient to accurately decompose the emission lineprofiles into multiple narrow components (FWHM ~ 30-130 kms-1) superimposed on a broad (FWHM ~ 150-350 kms-1) feature. This paper is the first of a seriesexamining the optical structure of M82's disk and inner wind; here wefocus on the ionized gaseous and stellar dynamics and present maps ofthe relevant emission line properties. Our observations show thationized gas in the starburst core of M82 is dynamically complex withmany overlapping expanding structures located at different radii.Localised line splitting of up to 100 km s-1 in thenarrow component is associated with expanding shells of compressed,cool, photoionized gas at the roots of the superwind outflow. We havebeen able to associate some of this inner-wind gas with a distinctoutflow channel characterised by its dynamics and gas density patterns,and we discuss the consequences of this discovery in terms of thedeveloping wind outflow. The broad optical emission line component isobserved to become increasingly important moving outward along theoutflow channel, and in general with increasing height above/below theplane. Following our recent work on the origins of this component, weassociate it with turbulent gas in wind-clump interface layers and hencesites of mass loading, meaning that the turbulent mixing of cooler gasinto the outflowing hot gas must become increasingly important withheight, and provides powerful direct evidence for the existence ofmass-loading over a large, spatially extended area reaching far into theinner wind. We discuss the consequences and implications of this. Weconfirm that the rotation axis of the ionized emission-line gas isoffset from the stellar rotation axis and the photometric major axis by~12°, not only within the nuclear regions but over the whole inner 2kpc of the disk. This attests to the perturbations introduced from M82'spast interactions within the M81 group. Finally, finding a turn-over inthe stellar and ionized gas rotation curves on both sides of the galaxyindicates that our sight line, in places, extends at least half waythrough disk, and conflicts with the high levels of obscuration usuallyassociated with the nuclear regions of M82.Based on observations with the Gemini and WIYN telescopes.
| The Polarimetric and Photometric Variability of HH 30
We have obtained ground-based photopolarimetry of the young stellarobject HH 30 over the course of one year. Our observations reveal thepresence of a dominant periodic modulation of the polarization with aperiod of 7.49 ± 0.04 days or one of the aliases of this periodclose to 1 day. There are also suggestions of a weak periodic modulationin the photometry with the same period but a phase displaced by onequarter of a period. These results are in agreement with the lighthousemodel for HH 30, in which a beam or shadow from a central source sweepsacross the disk. Our observations by themselves appear to be consistentwith both of the mechanisms that have been proposed for thelighthouse—asymmetric accretion hot spots on the star or orbitingclumps or voids in the disk—and provide strong quantitativeconstraints for future models.
| The Iron Abundance in Galactic Planetary Nebulae
We constrain the iron abundance in a sample of 33 low-ionizationGalactic planetary nebulae (PNe) using [Fe III] lines andcorrecting for the contribution of higher ionization states withionization correction factors that take into account uncertainties inthe atomic data. We find very low iron abundances in all the objects,suggesting that more than 90% of their iron atoms are condensed ontodust grains. This number is based on the solar iron abundance andimplies a lower limit on the dust-to-gas mass ratio, solely due to iron,of M dust/M gas >= 1.3 ×10–3 for our sample. The depletion factors of differentPNe cover about two orders of magnitude, probably reflecting differencesin the formation, growth, or destruction of their dust grains. However,we do not find any systematic difference between the gaseous ironabundances calculated for C-rich and O-rich PNe, suggesting similar irondepletion efficiencies in both environments. The iron abundances of oursample PNe are similar to those derived following the same procedure fora group of 10 Galactic H II regions. These high depletion factorsargue for high depletion efficiencies of refractory elements onto dustgrains both in molecular clouds and asymptotic giant branch stars, andlow dust destruction efficiencies both in interstellar and circumstellarionized gas.Partly based on observations made with the 2.1 m telescope atObservatorio Astronómico Nacional, San Pedro Mártir,Mexico.
| An evolved donor star in the long-period cataclysmic variable HS 0218+3229
Context: We present time-resolved spectroscopy and photometry of HS0218+3229, a new long-period cataclysmic variable discovered within theHamburg Quasar Survey. It is one of the few systems that allow adynamical measurement of the masses of the stellar components. Aims: We combine the analysis of time-resolved optical spectroscopyand R-band photometry with the aim of measuring the mass of the whitedwarf and the donor star and the orbital inclination. Methods:Cross-correlation of the spectra with K-type dwarf templates is used toderive the radial velocity curve of the donor star. An optimalsubtraction of the broadened templates is performed to measure therotational broadening and constrain the spectral type of the donor.Finally, an ellipsoidal model is fitted to the R-band light curve toobtain constraints upon the orbital inclination of the binary system. Results: The orbital period of HS 0218+3229 is found to be0.297229661 ± 0.000000001 d (7.13351186 ± 0.00000002 h),and the amplitude of the donor's radial velocity curve is K2= 162.4 ± 1.4 km~s-1. Modelling the ellipsoidal lightcurves gives an orbital inclination in the range i = 59° ±3°. A rotational broadening between 82.4 ± 1.2km~s-1 and 89.4 ± 1.3 km~s-1 is found whenassuming zero and continuum limb darkening, respectively. The secondarystar has most likely a spectral type K5 and contributes ~80-85% to theR-band light. Our analysis yields a mass ratio of 0.52 < q < 0.65,a white dwarf mass of 0.44 < M1 (M_ȯ) < 0.65, anda donor star mass of 0.23 < M2 (M_ȯ) < 0.44. Conclusions: We find that the donor star in HS 0218+3229 issignificantly undermassive for its spectral type. It is therefore verylikely that it has undergone nuclear evolution prior to the onset ofmass transfer.
| The NEWFIRM Medium-Band Survey: Filter Definitions and First Results
Deep near-infrared imaging surveys allow us to select and study distantgalaxies in the rest-frame optical, and have transformed ourunderstanding of the early Universe. As the vast majority of K- orIRAC-selected galaxies are too faint for spectroscopy, theinterpretation of these surveys relies almost exclusively on photometricredshifts determined from fitting templates to the broadband photometry.The best-achieved accuracy of these redshifts,Dz/(1+z)?0.06?z/(1 + z) ? 0.06 at z>1.5, issufficient for determining the broad characteristics of the galaxypopulation but not for measuring accurate rest-frame colors, stellarpopulation parameters, or the local galaxy density. We have started anear-infrared imaging survey with the NEWFIRM camera on the Kitt Peak4-m telescope to greatly improve the accuracy of photometric redshiftsin the range 1.5?z?3.5. The survey uses five medium-bandwidthfilters, which provide crude "spectra" over the wavelength range 1-1.8?m for all objects in the 27.6'×27.6'NEWFIRM field. In this first paper, we illustrate the technique byshowing medium-band NEWFIRM photometry of several galaxies at1.71.5 in the COSMOS andAEGIS fields. The filter set also enables efficient selection of exoticobjects such as high-redshift quasars, galaxies dominated by emissionlines, and very cool brown dwarfs; we show that late T and candidate Ydwarfs could be identified using only two of the filters.
| Subaru and Keck Observations of the Peculiar Type Ia Supernova 2006GZ at Late Phases
Recently, a few peculiar Type Ia supernovae (SNe Ia) that showexceptionally large peak luminosity have been discovered. Theirluminosity requires more than 1 M sun of 56Ni tobe ejected during the explosion, suggesting that they might haveoriginated from super-Chandrasekhar mass white dwarfs. However, thenature of these objects is not yet well understood. In particular, nodata have been taken at late phases, about one year after the explosion.We report on Subaru and Keck optical spectroscopic and photometricobservations of the SN Ia 2006gz, which had been classified as being oneof these "overluminous" SNe Ia. The late-time behavior is distinctlydifferent from that of normal SNe Ia, reinforcing the argument that SN2006gz belongs to a different subclass than normal SNe Ia. However, thepeculiar features found at late times are not readily connected to alarge amount of 56Ni; the SN is faint, and it lacks [Fe II]and [Fe III] emissions. If the bulk of the radioactive energy escapesthe SN ejecta as visual light, as is the case in normal SNe Ia, the massof 56Ni does not exceed ~0.3 M sun. We discussseveral possibilities to remedy the problem. With the limitedobservations, however, we are unable to conclusively identify whichprocess is responsible. An interesting possibility is that the bulk ofthe emission might be shifted to longer wavelengths, unlike the case inother SNe Ia, which might be related to dense C-rich regions asindicated by the early-phase data. Alternatively, it might be the casethat SN 2006gz, though peculiar, was actually not substantiallyoverluminous at early times.Based on data collected at the Subaru Telescope (operated by theNational Astronomical Observatory of Japan) and the W. M. KeckObservatory (operated as a scientific partnership among the CaliforniaInstitute of Technology, the University of California, and NASA;supported by the W. M. Keck Foundation).
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
Catàlegs i designacions:
|
INHABITED SKY
