Aims. The EROS-2 project was designed to test the hypothesis that massive compact halo objects (the so-called "machos") could be a major component of the dark matter halo of the Milky Way galaxy. To ...this end, EROS- 2 monitored over 6.7 years 33\times10 similar to stars in the Magellanic clouds for microlensing events caused by such objects. Methods. In this work, we use only a subsample of 7\times10 similar to bright stars spread over 84\,\rm deg arrow up of the LMC and 9\,\rm deg arrow up of the SMC. The strategy of using only bright stars helps to discriminate against background events due to variable stars and allows a simple determination of the effects of source confusion (blending). The use of a large solid angle makes the survey relatively insensitive to effects that could make the optical depth strongly direction dependent. Results. Using this sample of bright stars, only one candidate event was found, whereas similar to 39 events would have been expected if the Halo were entirely populated by objects of mass M\sim0.4 similar to M_{\odot}. Combined with the results of EROS-1, this implies that the optical depth toward the Large Magellanic Cloud ( LMC) due to such lenses is \tau<0.36\times10 (95% CL), corresponding to a fraction of the halo mass of less than 8%. This optical depth is considerably less than that measured by the MACHO collaboration in the central region of the LMC. More generally, machos in the mass range 0.6\times10 contains as a subset _\odot<M<15 similar to M_{\odot} are ruled out as the primary occupants of the Milky Way Halo.
We present the Data Release 9 Quasar (DR9Q) catalog from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey III. The catalog includes all BOSS objects that were ...targeted as quasar candidates during the survey, are spectrocopically confirmed as quasars via visual inspection, have luminosities Miz = 2 < −20.5 (in a ΛCDM cosmology with H0 = 70 km s-1 Mpc-1, ΩM = 0.3, and ΩΛ = 0.7) and either display at least one emission line with full width at half maximum (FWHM) larger than 500 km s-1 or, if not, have interesting/complex absorption features. It includes as well, known quasars (mostly from SDSS-I and II) that were reobserved by BOSS. This catalog contains 87 822 quasars (78 086 are new discoveries) detected over 3275 deg2 with robust identification and redshift measured by a combination of principal component eigenspectra newly derived from a training set of 8632 spectra from SDSS-DR7. The number of quasars with z > 2.15 (61 931) is ~2.8 times larger than the number of z > 2.15 quasars previously known. Redshifts and FWHMs are provided for the strongest emission lines (C iv, C iii, Mg ii). The catalog identifies 7533 broad absorption line quasars and gives their characteristics. For each object the catalog presents five-band (u, g, r, i, z) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method. The catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3600−10 500 Å at a spectral resolution in the range 1300 < R < 2500; the spectra can be retrieved from the SDSS Catalog Archive Server. We also provide a supplemental list of an additional 949 quasars that have been identified, among galaxy targets of the BOSS or among quasar targets after DR9 was frozen.
We use the VESPA algorithm and spectra from the Sloan Digital Sky Survey to investigate the star formation history of the host galaxies of 257 type Ia supernovae. We find 5σ evidence of a short-lived ...population of progenitors with lifetimes of less than 180 Myr, indicating a type Ia supernova channel arising from stars in the mass range ~3.5-8 $M_\odot$. As standardizeable candles, type Ia supernovae play an important role in determining the expansion history of the Universe, but to be useful for future cosmological surveys, the peak luminosity needs to be free of uncorrected systematic effects at the level of 1-2%. If the different progenitor routes lead to supernovae with even moderately small differences in properties, then these need to be corrected for separately, or they could lead to a systematic bias in future supernovae surveys, as the prompt route is likely to increase in importance at high redshift. VESPA analysis of hosts could be a valuable tool in this, by identifying which progenitor route is most likely.
We report a detection of the baryon acoustic oscillation (BAO) feature in the three-dimensional correlation function of the transmitted flux fraction in the Lyα forest of high-redshift quasars. The ...study uses 48 640 quasars in the redshift range 2.1 ≤ z ≤ 3.5 from the Baryon Oscillation Spectroscopic Survey (BOSS) of the third generation of the Sloan Digital Sky Survey (SDSS-III). At a mean redshift z = 2.3, we measure the monopole and quadrupole components of the correlation function for separations in the range 20 h-1 Mpc < r < 200 h-1 Mpc. A peak in the correlation function is seen at a separation equal to (1.01 ± 0.03) times the distance expected for the BAO peak within a concordance ΛCDM cosmology. This first detection of the BAO peak at high redshift, when the universe was strongly matter dominated, results in constraints on the angular diameter distance DA and the expansion rate H at z = 2.3 that, combined with priors on H0 and the baryon density, require the existence of dark energy. Combined with constraints derived from cosmic microwave background observations, this result implies H(z = 2.3) = (224 ± 8) km s-1 Mpc-1, indicating that the time derivative of the cosmological scale parameter ȧ = H(z = 2.3)/(1 + z) is significantly greater than that measured with BAO at z ~ 0.5. This demonstrates that the expansion was decelerating in the range 0.7 < z < 2.3, as expected from the matter domination during this epoch. Combined with measurements of H0, one sees the pattern of deceleration followed by acceleration characteristic of a dark-energy dominated universe.
This paper presents a survey of X-ray-selected active galactic nuclei (AGNs) with optical spectroscopic follow-up in a ∼ 18 deg2 area of the equatorial XMM-XXL north field. A sample of 8445 ...point-like X-ray sources detected by XMM–Newton above a limiting flux of
$F_{\rm 0.5{\rm -}10\, keV} > 10^{-15} \rm \,erg\, cm^{-2}\, s^{-1}$
was matched to optical (Sloan Digital Sky Survey, SDSS) and infrared (IR; WISE) counterparts. We followed up 3042 sources brighter than r = 22.5 mag with the SDSS Baryon Oscillation Spectroscopic Survey (BOSS) spectrograph. The spectra yielded a reliable redshift measurement for 2578 AGNs in the redshift range z = 0.02–5.0, with 0.5-2 keV luminosities ranging from 1039-1046 erg s− 1. This is currently the largest published spectroscopic sample of X-ray-selected AGNs in a contiguous area. The BOSS spectra of AGN candidates show a distribution of optical line widths which is clearly bimodal, allowing an efficient separation between broad- and narrow-emission line AGNs. The former dominate our sample (70 per cent) due to the relatively bright X-ray flux limit and the optical BOSS magnitude limit. We classify the narrow-emission line objects (22 per cent of the full sample) using standard optical emission line diagnostics: the majority have line ratios indicating the dominant source of ionization is the AGN. A small number (8 per cent of the full sample) exhibit the typical narrow line ratios of star-forming galaxies, or only have absorption lines in their spectra. We term the latter two classes ‘elusive’ AGN, which would not be easy to identify correctly without their X-ray emission. We also compare X-ray (XMM–Newton), optical colour (SDSS) and and IR (WISE) AGN selections in this field. X-ray observations reveal, by far, the largest number of AGN. The overlap between the selections, which is a strong function of the imaging depth in a given band, is also remarkably small. We show using spectral stacking that a large fraction of the X-ray AGNs would not be selectable via optical or IR colours due to host galaxy contamination. A substantial fraction of AGN may therefore be missed by these longer wavelength selection methods.
We report the discovery in the Sloan Digital Sky Survey (SDSS) and the SDSS-III Baryon Oscillation Spectroscopic Survey of 17 broad absorption line (BAL) quasars with high-ionization troughs that ...include absorption redshifted relative to the quasar rest frame. The redshifted troughs extend to velocities up to v 12 000 km s−1 and the trough widths exceed 3000 km s−1 in all but one case. Approximately 1 in 1000 BAL quasars with blueshifted C iv absorption also has redshifted C iv absorption; objects with C iv absorption present only at redshifted velocities are roughly four times rarer. In more than half of our objects, redshifted absorption is seen in C ii or Al iii as well as C iv, making low-ionization absorption at least 10 times more common among BAL quasars with redshifted troughs than among standard BAL quasars. However, the C iv absorption equivalent widths in our objects are on average smaller than those of standard BAL quasars with low-ionization absorption.
We consider several possible ways of generating redshifted absorption. The two most likely possibilities may be at work simultaneously, in the same objects or in different ones. Rotationally dominated outflows seen against a quasar's extended continuum source can produce redshifted and blueshifted absorption, but variability consistent with this scenario is seen in only one of the four objects with multiple spectra. The infall of relatively dense and low-ionization gas to radii as small as 400 Schwarzschild radii can in principle explain the observed range of trough profiles, but current models do not easily explain the origin and survival of such gas. Whatever the origin(s) of the absorbing gas in these objects, it must be located at small radii to explain its large redshifted velocities, and thus offers a novel probe of the inner regions of quasars.
Context. R Coronae Borealis stars (RCB) are a rare type of evolved carbon-rich supergiant stars that are increasingly thought to result from the merger of two white dwarfs, called the Double ...degenerate scenario. This scenario is also studied as a source, at higher mass, of type Ia Supernovae (SnIa) explosions. Therefore a better understanding of RCBs composition would help to constrain simulations of such events. Aims. We searched for and studied RCB stars in the EROS Magellanic Clouds database. We also extended our research to DY Per type stars (DYPers) that are expected to be cooler RCBs ($T \sim 3500$ K) and much more numerous than their hotter counterparts. With the aim of studying possible evolutionary connections between RCBs and DYPers, and also ordinary carbon stars, we compared their publically available broad band photometry in the optical, near, and mid-infrared. Methods. The light curves of ~70 millions stars, monitored for 6.7 years (from July 1996 to February 2003), have been analysed to search for the main signature of RCBs and DYPers: a large (up to 9 mag) drop in luminosity. Carbon stars with fading episodes were also found by inspecting numerous light curves of objects that presented an infrared excess in the 2MASS and Spitzer- SAGE and S3MC databases. Follow-up optical spectroscopy was used to confirm each photometric candidate found. Results. We have discovered and confirmed 6 new Magellanic Cloud RCB stars and 7 new DYPers, but also listed new candidates: 3 RCBs and 14 DYPers. Optical and infrared colour magnitude diagrams that give new insights into these two sets of stars are discussed. We estimated a range of Magellanic RCB shell temperatures between 360 and 600 K. Conclusions. We confirm the wide range of absolute luminosity known for RCB stars, $M_V \sim -5.2$ to –2.6. Our study further shows that mid-infrared surveys are ideal to search for RCB stars, since they have thinner and cooler circumstellar shells than classical post-AGB stars. In addition, by increasing the number of known DYPers by ~400%, we have been able to shed light on the similarities in the spectral energy distribution between DYPers and ordinary carbon stars. We also observed that DYPer circumstellar shells are fainter and hotter than those of RCBs. This suggests that DYPers may simply be ordinary carbon stars with ejection events, but more abundance analysis is necessary to give a status on a possible evolutionnary connexion between RCBs and DYPers.
Aims. The EROS-2 project has been designed to search for microlensing events towards any dense stellar field. The densest parts of the Galactic spiral arms have been monitored to maximize the ...microlensing signal expected from the stars of the Galactic disk and bulge. Methods. 12.9 million stars have been monitored during 7 seasons towards 4 directions in the Galactic plane, away from the Galactic center. Results. A total of 27 microlensing event candidates have been found. Estimates of the optical depths from the 22 best events are provided. A first order interpretation shows that simple Galactic models with a standard disk and an elongated bulge are in agreement with our observations. We find that the average microlensing optical depth towards the complete EROS-cataloged stars of the spiral arms is $\bar{\tau}$ = 0.51±.13$\times$10-6, a number that is stable when the selection criteria are moderately varied. As the EROS catalog is almost complete up to IC = 18.5, the optical depth estimated for the sub-sample of bright target stars with $I_C < 18.5$ ($\bar{\tau}$ = 0.39±.11$\times$10-6) is easier to interpret. Conclusions. The set of microlensing events that we have observed is consistent with a simple Galactic model. A more precise interpretation would require either a better knowledge of the distance distribution of the target stars, or a simulation based on a Galactic model. For this purpose, we define and discuss the concept of optical depth for a given catalog or for a limiting magnitude.
We present the first results from an ongoing survey for damped Lyman-α systems (DLAs) in the spectra of z > 2 quasars observed in the course of the Baryon Oscillation Spectroscopic Survey (BOSS), ...which is part of the Sloan Digital Sky Survey (SDSS) III. Our full (non-statistical) sample, based on Data Release 9, comprises 12 081 systems with log N(H i) ≥ 20, out of which 6839 have log N(H i) ≥ 20.3. This is the largest DLA sample ever compiled, superseding that from SDSS-II by a factor of seven. Using a statistical sub-sample and estimating systematics from realistic mock data, we probe the N(H i) distribution at ⟨z⟩ = 2.5. Contrary to what is generally believed, the distribution extends beyond 1022 cm-2 with a moderate slope of index ≈−3.5. This result matches the opacity-corrected distribution observed at z = 0 surprisingly well. The cosmological mass density of neutral gas in DLAs is found to be \hbox{$\omegagdla \approx 10^{-3}$}ΩgDLA≈10-3, evolving only mildly over the past 12 billion years.
Context. Rare types of variable stars may provide unique insight into short-lived stages of stellar evolution. The systematic monitoring of millions of stars and advanced light curve analysis ...techniques of microlensing surveys make them ideal for discovering such rare variable stars. One example is the R Coronae Borealis (RCB) stars, a rare type of evolved carbon-rich supergiant. Aims. We have conducted a systematic search of the EROS-2 database for the Galactic catalogue Bulge and spiral arms to find Galactic RCB stars. Methods. The light curves of ~100 million stars, monitored for 6.7 years (from July 1996 to February 2003), have been analysed to search for the main signature of RCB stars, large and rapid drops in luminosity. Follow-up spectroscopy has been used to confirm the photometric candidates. Results. We have discovered 14 new RCB stars, all in the direction of the Galactic Bulge, bringing the total number of confirmed Galactic RCB stars to about 51. Conclusions. After reddening correction, the colours and absolute magnitudes of at least 9 of the stars are similar to those of Magellanic RCB stars. This suggests that these stars are in fact located in the Galactic Bulge, making them the first RCB stars discovered in the Bulge. The localisation of the 5 remaining RCBs is more uncertain: 4 are either located behind the Bulge at an estimated maximum distance of 14 kpc or have an unusual thick circumstellar shell; the other is a DY Per RCB which may be located in the Bulge, even if it is fainter than the known Magellanic DY Per. From the small scale height found using the 9 new Bulge RCBs, $61<h^{\rm RCB}_{\rm Bulge}<246$ pc (95% C.L.), we conclude that the RCB stars follow a disk-like distribution inside the Bulge.
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