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ESA's PLATO mission aims the detection and characterization of terrestrial planets around solar-type stars as well as the study of host star properties. The noise-to-signal ratio (NSR) is the main performance parameter of the PLATO instrument, which consists of 24 Normal Cameras and 2 Fast Cameras. In order to justify, verify and breakdown NSR-relevant requirements the software simulator PINE was developed. PINE models the signal pathway from a target star to the digital output of a camera based on physical models and considers the major noise contributors. In this paper, the simulator's coarse mode is introduced which allows fast performance analyses on instrument level. The added value of PINE is illustrated by exemplary applications., Comment: 17 pages, 8 figures, 3 tables

PLATO (PLAnetary Transits and Oscillations of stars) is ESA's M3 mission designed to detect and characterise extrasolar planets and perform asteroseismic monitoring of a large number of stars. PLATO will detect small planets (down to <2 R_(Earth)) around bright stars (<11 mag), including terrestrial planets in the habitable zone of solar-like stars. With the complement of radial velocity observations from the ground, planets will be characterised for their radius, mass, and age with high accuracy (5 %, 10 %, 10 % for an Earth-Sun combination respectively). PLATO will provide us with a large-scale catalogue of well-characterised small planets up to intermediate orbital periods, relevant for a meaningful comparison to planet formation theories and to better understand planet evolution. It will make possible comparative exoplanetology to place our Solar System planets in a broader context. In parallel, PLATO will study (host) stars using asteroseismology, allowing us to determine the stellar properties with high accuracy, substantially enhancing our knowledge of stellar structure and evolution. The payload instrument consists of 26 cameras with 12cm aperture each. For at least four years, the mission will perform high-precision photometric measurements. Here we review the science objectives, present PLATO's target samples and fields, provide an overview of expected core science performance as well as a description of the instrument and the mission profile at the beginning of the serial production of the flight cameras. PLATO is scheduled for a launch date end 2026. This overview therefore provides a summary of the mission to the community in preparation of the upcoming operational phases.

We present Ly $\alpha$ imaging of 45 low redshift star-forming galaxies observed with the Hubble Space Telescope. The galaxies have been selected to have moderate to high star formation rates using far-ultraviolet (FUV) luminosity and \ha equivalent width criteria, but no constraints on Ly $\alpha$ luminosity. We employ a pixel stellar continuum fitting code to obtain accurate continuum subtracted Ly $\alpha$, H $\alpha$ and H $\beta$ maps. We find that Ly $\alpha$ is less concentrated than FUV and optical line emission in almost all galaxies with significant Ly $\alpha$ emission. We present global measurements of Ly $\alpha$ and other quantities measured in apertures designed to capture all of the Ly $\alpha$ emission. We then show how the escape fraction of Ly $\alpha$ relates to a number of other measured quantities (mass, metallicity, star formation, ionisation parameter, and extinction). We find that the escape fraction is strongly anti-correlated with nebular and stellar extinction, weakly anti-correlated with stellar mass, but no conclusive evidence for correlations with other quantities. We show that Ly $\alpha$ escape fractions are inconsistent with common dust extinction laws, and discuss how a combination of radiative transfer effects and clumpy dust models can help resolve the discrepancies. We present a star formation rate calibration based on Ly $\alpha$ luminosity, where the equivalent width of Ly $\alpha$ is used to correct for non-unity escape fraction, and show that this relation provides a reasonably accurate SFR estimate. We also show stacked growth curves of Ly $\alpha$ for the galaxies that can be used to find aperture loss fractions at a given physical radius., Comment: 48 pages, 21 figures, accepted for publication in The Astrophysical Journal Supplement Series. Multipanel figures for all 45 galaxies will be available in the online version of the published paper (and here: https://stockholmuniversity.box.com/s/ghvnvjyhxts64hpbqh90uwcj5dlczlhm ). Data products will be available as a MAST HLSP soon (placeholder DOI: 10.17909/pbe1-m743)

The Athena X-ray Integral Unit (X-IFU) is the high resolution X-ray spectrometer, studied since 2015 for flying in the mid-30s on the Athena space X-ray Observatory, a versatile observatory designed to address the Hot and Energetic Universe science theme, selected in November 2013 by the Survey Science Committee. Based on a large format array of Transition Edge Sensors (TES), it aims to provide spatially resolved X-ray spectroscopy, with a spectral resolution of 2.5 eV (up to 7 keV) over an hexagonal field of view of 5 arc minutes (equivalent diameter). The X-IFU entered its System Requirement Review (SRR) in June 2022, at about the same time when ESA called for an overall X-IFU redesign (including the X-IFU cryostat and the cooling chain), due to an unanticipated cost overrun of Athena. In this paper, after illustrating the breakthrough capabilities of the X-IFU, we describe the instrument as presented at its SRR, browsing through all the subsystems and associated requirements. We then show the instrument budgets, with a particular emphasis on the anticipated budgets of some of its key performance parameters. Finally we briefly discuss on the ongoing key technology demonstration activities, the calibration and the activities foreseen in the X-IFU Instrument Science Center, and touch on communication and outreach activities, the consortium organisation, and finally on the life cycle assessment of X-IFU aiming at minimising the environmental footprint, associated with the development of the instrument. Thanks to the studies conducted so far on X-IFU, it is expected that along the design-to-cost exercise requested by ESA, the X-IFU will maintain flagship capabilities in spatially resolved high resolution X-ray spectroscopy, enabling most of the original X-IFU related scientific objectives of the Athena mission to be retained. (abridged)., Comment: 48 pages, 29 figures, Accepted for publication in Experimental Astronomy with minor editing

The detection of Lyman-$\alpha$ emitting galaxies (LAEs) puts severe constraints on the reionization history. In this Paper we derive the properties of very high-$z$ LAEs predicted in the only two reionization scenarios shown in a previous Paper to be consistent with current data on 15 independent evolving global (or averaged) cosmic properties regarding luminous objects and the intergalactic medium and the optical depth to electron scattering of ionized hydrogen to CMB photons: one with a monotonic behavior, which is completed by $z=6$, as commonly considered, and another one with a non-monotonic behavior with two full ionization events at $z=6$ and $z=10$. We find that the Ly$\alpha$ luminosity functions of very high-$z$ LAEs are very distinct in those two scenarios. Thus, comparing these predictions to the observations that will soon be available thanks to new instruments such as the James Webb Space Telescope, it should be possible to unveil the right reionization scenario. In the meantime, we can compare the predicted redshift distribution and UV (or Lyman-$\alpha$) luminosities of very high-$z$ LAEs to those of the few objects already observed at $z>7.5$. By doing that we find that such data are in tension with the single reionization scenario, while they are fully compatible with the double reionization scenario., Comment: 16 pages, 10 figures, accepted for publication in The Astrophysical Journal. Minor changes included to match the published version

ESA's INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) was launched on 17 Oct 2002 at 06:41 CEST. Since then, it has been providing long, uninterrupted observations (up to about 47 hr, or 170 ksec, per satellite orbit of 2.7 days) with a large field-of-view (fully coded: 100 deg^2), msec time resolution, keV energy resolution, polarization measurements, as well as additional coverage in the optical. This is realized by two main instruments in the 15 keV to 10 MeV range, the spectrometer SPI (spectral resolution 3 keV at 1.8 MeV) and the imager IBIS (angular resolution 12 arcmin FWHM), complemented by X-ray (JEM-X; 3-35 keV) and optical (OMC; Johnson V-band) monitors. All instruments are co-aligned to simultaneously observe the target region. A particle radiation monitor (IREM) measures charged particle fluxes near the spacecraft. The Anti-coincidence subsystems of the main instruments are also efficient all-sky gamma-ray detectors, which provide omni-directional monitoring above ~75 keV. INTEGRAL can also rapidly (within a couple of hours) re-point and conduct Target of Opportunity observations. INTEGRAL has build an impressive legacy: e.g. discovery of >600 new high-energy sources; first-ever direct detection of 56Ni and 56Co radio-active decay lines from a Type Ia supernova; new insights on positron annihilation in the Galactic bulge and disk; pioneering gamma-ray polarization studies. INTEGRAL is also a successful in multi-messenger astronomy: INTEGRAL found the first prompt electromagnetic radiation in coincidence with a binary neutron star merger. More than 1750 papers based on INTEGRAL data have been published in refereed journals. Here we give a comprehensive update of the satellite status after more than 18 years of operations in a harsh space environment, and an account of the successful Ground Segment., Comment: 29 pages, 20 figures, accepted for publication in special issue of New Astronomy Reviews

We show herein that the population of star forming galaxies in the Bremer Deep Field (BDF) have enough ionising power to form two large ionised bubbles which could be in the process of merging into a large one with a volume of 14000 cMpc3. The sources identified in the BDF have been completed with a set of expected low luminosity sources at z $\approx$ 7. We have estimated the number of ionising photons per second produced by the different star forming galaxies in the BDF. This number has been compared with the number that would be required to ionise the bubbles around the two overdense regions. We have used, as reference, ionising emissivities derived from the AMIGA cosmological evolutionary model. We find that even using the most conservative estimates, with a Lyman continuum escape fraction of 10\% the two regions we have defined within the BDF would be reionised. Assuming more realistic estimates of the ionising photon production efficiency, both bubbles would be in the process of merging into a large reionised bubble, such as those that through percolation completed the reionisation of the universe by z = 6. The rather small values of the escape fraction required to reionise the BDF are compatible with the low fraction of faint Ly{\alpha} emitters identified in the BDF. Finally, we confirm that the low luminosity sources represent indeed the main contributors to the BDF ionising photon production., Comment: 8 pages, 2 figures

High mass X-ray binaries are among the brightest X-ray sources in the Milky Way, as well as in nearby Galaxies. Thanks to their highly variable emissions and complex phenomenology, they have attracted the interest of the high energy astrophysical community since the dawn of X-ray Astronomy. In more recent years, they have challenged our comprehension of physical processes in many more energy bands, ranging from the infrared to very high energies. In this review, we provide a broad but concise summary of the physical processes dominating the emission from high mass X-ray binaries across virtually the whole electromagnetic spectrum. These comprise the interaction of stellar winds with the high gravitational and magnetic fields of compact objects, the behaviour of matter under extreme magnetic and gravity conditions, and the perturbation of the massive star evolutionary processes by presence in a binary system. We highlight the role of the INTEGRAL mission in the discovery of many of the most interesting objects in the high mass X-ray binary class and its contribution in reviving the interest for these sources over the past two decades. We show how the INTEGRAL discoveries have not only contributed to significantly increase the number of high mass X-ray binaries known, thus advancing our understanding of the population as a whole, but also have opened new windows of investigation that stimulated the multi-wavelength approach nowadays common in most astrophysical research fields. We conclude the review by providing an overview of future facilities being planned from the X-ray to the very high energy domain that will hopefully help us in finding an answer to the many questions left open after more than 18 years of INTEGRAL scientific observations., Comment: 61 pages, 22 figures, 1 table, will be published in New Astronomy Reviews

X-ray radiation from accreting compact objects is an important part of stellar feedback. The metal-poor galaxy ESO 338-4 has experienced vigorous starburst during the last 40 Myr and contains some of the most massive super star clusters in the nearby Universe. Given its starburst age and its star-formation rate, ESO 338-4 is one of the most efficient nearby manufactures of neutron stars and black holes, hence providing an excellent laboratory for feedback studies. We compared X-ray images and spectra obtained by XMM-Newton and Chandra telescopes with integral field spectroscopic VLT MUSE observations in the optical to constrain the nature of strong X-ray emitters. X-ray observations uncover three ultraluminous X-ray sources (ULXs) in ESO 338-4. The brightest among them, ESO 338~X-1, has X-ray luminosity in excess of 10^{40} erg/s. We speculate that ESO 338-4 is powered by accretion on an intermediate-mass (~300Msun) black hole. We show that X-ray radiation from ULXs and hot superbubbles strongly contributes to HeII ionization and general stellar feedback in this template starburst galaxy., Comment: A&A, in press

The X-ray Integral Field Unit (X-IFU) is the high resolution X-ray spectrometer of the ESA Athena X-ray observatory. Over a field of view of 5' equivalent diameter, it will deliver X-ray spectra from 0.2 to 12 keV with a spectral resolution of 2.5 eV up to 7 keV on ~5 arcsecond pixels. The X-IFU is based on a large format array of super-conducting molybdenum-gold Transition Edge Sensors cooled at about 90 mK, each coupled with an absorber made of gold and bismuth with a pitch of 249 microns. A cryogenic anti-coincidence detector located underneath the prime TES array enables the non X-ray background to be reduced. A bath temperature of about 50 mK is obtained by a series of mechanical coolers combining 15K Pulse Tubes, 4K and 2K Joule-Thomson coolers which pre-cool a sub Kelvin cooler made of a 3He sorption cooler coupled with an Adiabatic Demagnetization Refrigerator. Frequency domain multiplexing enables to read out 40 pixels in one single channel. A photon interacting with an absorber leads to a current pulse, amplified by the readout electronics and whose shape is reconstructed on board to recover its energy with high accuracy. The defocusing capability offered by the Athena movable mirror assembly enables the X-IFU to observe the brightest X-ray sources of the sky (up to Crab-like intensities) by spreading the telescope point spread function over hundreds of pixels. Thus the X-IFU delivers low pile-up, high throughput (>50%), and typically 10 eV spectral resolution at 1 Crab intensities, i.e. a factor of 10 or more better than Silicon based X-ray detectors. In this paper, the current X-IFU baseline is presented, together with an assessment of its anticipated performance in terms of spectral resolution, background, and count rate capability. The X-IFU baseline configuration will be subject to a preliminary requirement review that is scheduled at the end of 2018., Comment: 15 pages, 5 figures, to appear in Proc. SPIE Astronomical Telescopes and Instrumentation, Austin 2018

We examine the dust geometry and Ly{\alpha} scattering in the galaxies of the Lyman Alpha Reference Sample (LARS), a set of 14 nearby (0.02 < $z$ < 0.2) Ly{\alpha} emitting and starbursting systems with Hubble Space Telescope Ly{\alpha}, H{\alpha}, and H{\beta} imaging. We find that the global dust properties determined by line ratios are consistent with other studies, with some of the LARS galaxies exhibiting clumpy dust media while others of them show significantly lower Ly{\alpha} emission compared to their Balmer decrement. With the LARS imaging, we present Ly{\alpha}/H{\alpha} and H{\alpha}/H{\beta} maps with spatial resolutions as low as $\sim$ 40 pc, and use these data to show that in most galaxies, the dust geometry is best modeled by three distinct regions: a central core where dust acts as a screen, an annulus where dust is distributed in clumps, and an outer envelope where Ly{\alpha} photons only scatter. We show that the dust that affects the escape of Ly{\alpha} is more restricted to the galaxies' central regions, while the larger Ly{\alpha} halos are generated by scattering at large radii. We present an empirical modeling technique to quantify how much Ly{\alpha} scatters in the halo, and find that this "characteristic" scattering distance correlates with the measured size of the Ly{\alpha} halo. We note that there exists a slight anti-correlation between the scattering distance of Ly{\alpha} and global dust properties., Comment: 32 pages, 51 figures, accepted to ApJ

We combine observational data on a dozen independent cosmic properties at high-$z$ with the information on reionization drawn from the spectra of distant luminous sources and the cosmic microwave background (CMB) to constrain the interconnected evolution of galaxies and the intergalactic medium since the dark ages. The only acceptable solutions are concentrated in two narrow sets. In one of them reionization proceeds in two phases: a first one driven by Population III stars, completed at $z\sim 10$, and after a short recombination period a second one driven by normal galaxies, completed at $z\sim 6$. In the other set both kinds of sources work in parallel until full reionization at $z\sim 6$. The best solution with double reionization gives excellent fits to all the observed cosmic histories, but the CMB optical depth is 3-$\sigma$ larger than the recent estimate from the Planck data. Alternatively, the best solution with single reionization gives less good fits to the observed star formation rate density and cold gas mass density histories, but the CMB optical depth is consistent with that estimate. We make several predictions, testable with future observations, that should discriminate between the two reionization scenarios. As a byproduct our models provide a natural explanation to some characteristic features of the cosmic properties at high-$z$, as well as to the origin of globular clusters., Comment: 25 pages, 13 figures. Accepted for publication in ApJ. Minor typos corrected

The X-ray Integral Field Unit (X-IFU) on board the Advanced Telescope for High-ENergy Astrophysics (Athena) will provide spatially resolved high-resolution X-ray spectroscopy from 0.2 to 12 keV, with 5 arc second pixels over a field of view of 5 arc minute equivalent diameter and a spectral resolution of 2.5 eV up to 7 keV. In this paper, we first review the core scientific objectives of Athena, driving the main performance parameters of the X-IFU, namely the spectral resolution, the field of view, the effective area, the count rate capabilities, the instrumental background. We also illustrate the breakthrough potential of the X-IFU for some observatory science goals. Then we briefly describe the X-IFU design as defined at the time of the mission consolidation review concluded in May 2016, and report on its predicted performance. Finally, we discuss some options to improve the instrument performance while not increasing its complexity and resource demands (e.g. count rate capability, spectral resolution). The X-IFU will be provided by an international consortium led by France, The Netherlands and Italy, with further ESA member state contributions from Belgium, Finland, Germany, Poland, Spain, Switzerland and two international partners from the United States and Japan., Comment: 41 pages, 18 Figures

While numerical simulations suggest that the strength of the Lyman alpha (Lya) line of star-forming disk galaxies strongly depends on the inclination at which they are observed (i.e. from edge-on to face-on, we expect to see a change from an attenuated Lya line to a strong Lya emission line), recent observations with the Hubble space telescope (HST) have highlighted few low-redshift highly inclined (edge-on) disk galaxies that breaks this trend. We aim to understand how a strong Lya emission line is able to escape from one of those inclined disk galaxies, named Mrk1486 (z=0.0338). For that purpose we used a large set of HST imaging and spectroscopic data to investigate both the ISM structure and the dominant source of Lya radiation inside Mrk1486. Moreover, we used a 3D Monte Carlo Lya radiation transfer code to study the radiative transfer of Lya and UV continuum photons inside a 3D geometry of neutral hydrogen (HI) and dust that models the ISM structure at the galaxy center. The analysis of IFU Halpha spectroscopic data of Mrk1486 indicates the presence of two bipolar galactic winds of HI gas above and bellow the disk plane of Mrk1486. Furthermore, comparing different diagnostic diagrams (such as [OIII]5007/Hbeta versus [OI]6300/Halpha) to photo- and shock-ionization models, we find that the Lya production of Mrk1486 is dominated by photoionization inside the galaxy disk. From this perspective, our numerical simulations succeed in reproducing the strength and spectral shape of the observed Lya line of Mrk1486 by assuming a scenario in which the Lya photons are produced inside the disk, travel along the galactic winds and scatter on cool HI materials toward the observer. As bipolar galactic winds are ubiquitous in star-forming disk galaxies, this mechanism may explain the origin of strong Lya emission lines recently observed from highly inclined galaxies at high-redshift., Comment: 25 pages, 22 figures, accepted for publication in A&A

We present integral field spectroscopic observations with the Potsdam Multi Aperture Spectrophotometer of all 14 galaxies in the $z\sim 0.1$ Lyman Alpha Reference Sample (LARS). We produce 2D line of sight velocity maps and velocity dispersion maps from the Balmer $\alpha$ (H$\alpha$) emission in our data cubes. These maps trace the spectral and spatial properties of the LARS galaxies' intrinsic Ly$\alpha$ radiation field. We show our kinematic maps spatially registered onto the Hubble Space Telescope H$\alpha$ and Lyman $\alpha$ (Ly$\alpha$) images. Only for individual galaxies a causal connection between spatially resolved H$\alpha$ kinematics and Ly$\alpha$ photometry can be conjectured. However, no general trend can be established for the whole sample. Furthermore, we compute non-parametric global kinematical statistics -- intrinsic velocity dispersion $\sigma_0$, shearing velocity $v_\mathrm{shear}$, and the $v_\mathrm{shear}/\sigma_0$ ratio -- from our kinematic maps. In general LARS galaxies are characterised by high intrinsic velocity dispersions (54\,km\,s$^{-1}$ median) and low shearing velocities (65\,km\,s$^{-1}$ median). $v_\mathrm{shear}/\sigma_0$ values range from 0.5 to 3.2 with an average of 1.5. Noteworthy, five galaxies of the sample are dispersion dominated systems with $v_\mathrm{shear}/\sigma_0 <1$ and are thus kinematically similar to turbulent star forming galaxies seen at high redshift. When linking our kinematical statistics to the global LARS Ly$\alpha$ properties, we find that dispersion dominated systems show higher Ly$\alpha$ equivalent widths and higher Ly$\alpha$ escape fractions than systems with $v_\mathrm{shear}/\sigma_0 > 1$. Our result indicates that turbulence in actively star-forming systems is causally connected to interstellar medium conditions that favour an escape of Ly$\alpha$ radiation., Comment: 26 pages, 15 figures, accepted for publication in A&A

We present high-resolution far-UV spectroscopy of the 14 galaxies of the Lyman Alpha Reference Sample; a sample of strongly star-forming galaxies at low redshifts ($0.028 < z < 0.18$). We compare the derived properties to global properties derived from multi band imaging and 21 cm HI interferometry and single dish observations, as well as archival optical SDSS spectra. Besides the Lyman $\alpha$ line, the spectra contain a number of metal absorption features allowing us to probe the kinematics of the neutral ISM and evaluate the optical depth and and covering fraction of the neutral medium as a function of line-of-sight velocity. Furthermore, we show how this, in combination with precise determination of systemic velocity and good Ly$\alpha$ spectra, can be used to distinguish a model in which separate clumps together fully cover the background source, from the "picket fence" model named by Heckman et al. (2011). We find that no one single effect dominates in governing Ly$\alpha$ radiative transfer and escape. Ly$\alpha$ escape in our sample coincides with a maximum velocity-binned covering fraction of $\lesssim 0.9$ and bulk outflow velocities of $\gtrsim 50$ km s$^{-1}$, although a number of galaxies show these characteristics and yet little or no Ly$\alpha$ escape. We find that Ly$\alpha$ peak velocities, where available, are not consistent with a strong backscattered component, but rather with a simpler model of an intrinsic emission line overlaid by a blueshifted absorption profile from the outflowing wind. Finally, we find a strong anticorrelation between H$\alpha$ equivalent width and maximum velocity-binned covering factor, and propose a heuristic explanatory model., Comment: 28 pages, 19 figures, 5 tables

The Lyman-alpha reference sample (LARS) is a program with the Hubble Space Telescope (HST) that provides a sample of local universe laboratory galaxies in which to study the astrophysics of the visibility and strength of the Lyman-alpha (Lya) line of hydrogen. This article presents an overview of the survey, its selection function and HST imaging observations. The sample was selected from the GALEX+SDSS catalogue at z=0.028-0.19, in order to allow Lya to be captured with combinations of long pass filters in the Solar Blind Channel (SBC) of HST/ACS. In addition, LARS utilises Halpha and Hbeta narrow, and U, B, i broad-band imaging with ACS and WFC3. In order to study galaxies in which large numbers of Lya photons are produced we demanded an Halpha equivalent width > 100{\AA}. The sample of 14 galaxies covers far UV (FUV) luminosities that overlaps with those of high-z Lya emitters and Lyman Break Galaxies (LBGs). We present the reduction steps used to obtain the Lya images, including our LARS eXtraction software (LaXs) which utilises pixel-by-pixel spectral synthesis fitting to subtract the continuum at Lya. We demonstrate that the use of SBC long pass filters dramatically increase the signal to noise compared to the nominal Lya filter in SBC. To exemplify, we present results for Mrk 259. This irregular galaxy shows extended but strongly asymmetric Lya emission. Spectroscopy from HST/COS show a moderate outflow in the neutral ISM and an asymmetric Lya profile. Radiative transfer modeling is able to reproduce the Lya line profile, confirming the presence of an outflow. The integrated photometry provides a Lya luminosity of 1.3E42 erg/s an equivalent width W(Lya) =45{\AA} and a FUV absolute magnitude -19.2. Mrk 259 would hence be detectable in high-z Lya and LBG surveys. The total Lya escape fraction is 12%, similar to that observed at z>4. (shortened), Comment: To appear in ApJ

We present the search for eclipsing binaries with a pulsating component in the first catalogue of optically variable sources observed by OMC/INTEGRAL, which contains photometric data for more than 1000 eclipsing binaries. Five objects were found and a detailed analysis of one of them, DY Aqr, has been performed. Photometric and spectroscopic observations of DY Aqr were obtained to analyse the binary system and the pulsational characteristics of the primary component. By applying the binary modelling software phoebe to the OMC and ground-based photometric light curves, and to the radial velocity curve obtained using echelle high-resolution spectroscopy, the physical parameters of the system have been determined. Frequency analysis of the residual data has been performed using Fourier techniques to identify pulsational frequencies. We have built a grid of theoretical models to classify spectroscopically the primary component as an A7.5V star (plus or minus one spectral subtype). The best orbital fit was obtained for a semi-detached system configuration. According to the binary modelling, the primary component has Teff = 7625+-125 K and log g = 4.1+-0.1 and the secondary component has Teff = 3800+-200 K and log g = 3.3+-0.1, although it is too faint to isolate its spectral features. From the analysis of the residuals we have found a main pulsation frequency at 23.37 c/d, which is typical of a delta Scuti star. In the O-C diagram no evidence of orbital period changes over the last 8 years has been found., Comment: 12 pages, 10 figures. Accepted for publication in MNRAS

We report upon new results regarding the Lya output of galaxies, derived from the Lyman alpha Reference Sample (LARS), focusing on Hubble Space Telescope imaging. For 14 galaxies we present intensity images in Lya, Halpha, and UV, and maps of Halpha/Hbeta, Lya equivalent width (EW), and Lya/Halpha. We present Lya and UV light profiles and show they are well-fitted by S\'ersic profiles, but Lya profiles show indices systematically lower than those of the UV (n approx 1-2 instead of >~4). This reveals a general lack of the central concentration in Lya that is ubiquitous in the UV. Photometric growth curves increase more slowly for Lya than the FUV, showing that small apertures may underestimate the EW. For most galaxies, however, flux and EW curves flatten by radii ~10 kpc, suggesting that if placed at high-z, only a few of our galaxies would suffer from large flux losses. We compute global properties of the sample in large apertures, and show total luminosities to be independent of all other quantities. Normalized Lya throughput, however, shows significant correlations: escape is found to be higher in galaxies of lower star formation rate, dust content, mass, and several quantities that suggest harder ionizing continuum and lower metallicity. Eight galaxies could be selected as high-z Lya emitters, based upon their luminosity and EW. We discuss the results in the context of high-z Lya and UV samples. A few galaxies have EWs above 50 AA, and one shows f_escLya of 80%; such objects have not previously been reported at low-z., Comment: Submitted to ApJ and corrected for first iteration of referee report

[abridged] Among the different observational techniques used to select high-redshift galaxies, the hydrogen recombination line Lyman-alpha (Lya) is of particular interest as it gives access to the measurement of cosmological quantities such as the star formation rate of distant galaxy populations. However, the interpretation of this line and the calibration of such observables is still subject to serious uncertainties. Therefore, it important to understand under what conditions the Lya line can be used as a reliable star formation diagnostic tool. We use a sample of 24 Lya emitters at z ~ 0.3 with an optical spectroscopic follow-up to calculate the Lya escape fraction and its dependency upon different physical properties. We also examine the reliability of Lya as a star formation rate indicator. We combine these observations with a compilation of Lya emitters selected at z = 0 - 0.3 to assemble a larger sample. The Lya escape fraction depends clearly on the dust extinction following the relation fesc(Lya) = C(Lya) x 10^(-0.4 E(B-V) k(Lya)), but with a shallower slope than previously reported, with k(Lya) ~ 6.67 and C(Lya) = 0.22. However, the correlation does not follow the expected curve for a simple dust attenuation. We explore the various mechanisms than lead to fesc(Lya) values above the continuum extinction curve, i.e. to an enhancement of the Lya output. We also observe that the strength of Lya and the escape fraction appear unrelated to the galaxy metallicity. Regarding the reliability of Lya as a star formation rate (SFR) indicator, we show that the deviation of SFR(Lya) from the true SFR (as traced by the UV continuum) is a function of the observed SFR(UV), which can be seen as the decrease of fesc(Lya) with increasing UV luminosity. Moreover, we observe a redshift-dependence of this relationship revealing the underlying evolution of fesc(Lya) with redshift., Comment: 17 pages. Accepted for publication

We report on new imaging observations of the Lyman alpha emission line (Lya), performed with the Hubble Space Telescope, that comprise the backbone of the Lyman alpha Reference Sample (LARS). We present images of 14 starburst galaxies at redshifts 0.028 < z < 0.18 in continuum-subtracted Lya, Halpha, and the far ultraviolet continuum. We show that Lya is emitted on scales that systematically exceed those of the massive stellar population and recombination nebulae: as measured by the Petrosian 20 percent radius, RP20, Lya radii are larger than those of Halpha by factors ranging from 1 to 3.6, with an average of 2.4. The average ratio of Lya-to-FUV radii is 2.9. This suggests that much of the Lya light is pushed to large radii by resonance scattering. Defining the "Relative Petrosian Extension" of Lya compared to Halpha, \xi_ext = RP20_Lya / RP20_Ha, we find \xi_ext to be uncorrelated with total Lya luminosity. However \xi_ext is strongly correlated with quantities that scale with dust content, in the sense that a low dust abundance is a necessary requirement (although not the only one) in order to spread Lya photons throughout the interstellar medium and drive a large extended Lya halo., Comment: Published in ApJ Letters ~~ 6 pages using emulateapj, 4 figures ~~ Higher-resolution, larger, nicer jpeg versions of Figures 1 and 2 can be found here: http://xayes.org/pub/press_lars.html

OMC-VAR is the first catalogue of variable sources observed by the Optical Monitoring Camera (OMC) on board INTEGRAL. It includes photometry and variability data for more than 5000 sources of very different nature. In order to study the multi-wavelength similarities and differences of the engines powering AGN and X-ray binaries, especially those powered by a black hole, we have searched for counterparts in several high-energy and infrared catalogues, including the 4th IBIS/ISGRI soft gamma-ray survey catalogue, the XMM-Newton Serendipitous Source catalogue, the 2MASS All-Sky catalogue of Point Sources, the 2MASS Extended Source Catalog and the WISE All-Sky Data Release. Preliminary multiwavelength results for the IBIS counterparts are presented and discussed., Comment: Proceedings of "An INTEGRAL view of the high-energy sky (the first 10 years)" the 9th INTEGRAL Workshop, October 15-19, 2012, Paris, France, in Proceedings of Science (INTEGRAL 2012), Eds. A. Goldwurm, F. Lebrun and C. Winkler, (http://pos.sissa.it/cgi-bin/reader/conf.cgi? confid=176), id 087

The Ly-alpha emission line has been proven a powerful tool by which to study evolving galaxies at the highest redshifts. However, in order to use Lya as a physical probe of galaxies, it becomes vital to know the Lya escape fraction (fescLya). Unfortunately, due to the resonant nature of Lya, fescLya may vary unpredictably and requires empirical measurement. Here we compile Lya luminosity functions between redshift z=0 and 8 and, combined with H-alpha and ultraviolet data, assess how fescLya evolves with redshift. We find a strong upwards evolution in fescLya over the range z=0.3-6, which is well-fit by the power-law fescLya \propto (1+z)^\xi, with \xi =(2.57_-0.12^+0.19). This predicts that fescLya should reach unity at z=11.1. By comparing fescLya and E(B-V) in individual galaxies we derive an empirical relationship between fescLya and E(B-V), which includes resonance scattering and can explain the redshift evolution of fescLya between z=0 and 6 purely as a function of the evolution in the dust content of galaxies. Beyond z~6.5, fescLya drops more substantially; an effect attributed to either ionizing photon leakage, or an increase in the neutral gas fraction of the intergalactic medium. While distinguishing between those two scenarios may be extremely challenging, by framing the problem this way we remove the uncertainty of the halo mass from Lya-based tests of reionization. We finally derive a new method by which to estimate the dust content of galaxies based purely upon the observed Lya and UV LFs. These data are characterized by an exponential with an e-folding redshift of ~3.5., Comment: Accepted by the Astrophysical Journal. 14 pages in emulateapj template with 4 figures

The Lyman-alpha (Lya) emission line is the primary observational signature of star-forming galaxies at the highest redshifts, and has enabled the compilation of large samples of galaxies with which to study cosmic evolution. The resonant nature of the line, however, means that Lya photons scatter in the neutral interstellar medium of their host galaxies, and their sensitivity to absorption by interstellar dust may therefore be enhanced greatly. This implies that the Lya luminosity may be significantly reduced, or even completely suppressed. Hitherto, no unbiased empirical test of the escaping fraction (f_esc) of Lya photons has been performed at high redshifts. Here we report that the average fesc from star-forming galaxies at redshift z = 2.2 is just 5 per cent by performing a blind narrowband survey in Lya and Ha. This implies that numerous conclusions based on Lya-selected samples will require upwards revision by an order of magnitude and we provide a benchmark for this revision. We demonstrate that almost 90 per cent of star-forming galaxies emit insufficient Lya to be detected by standard selection criteria. Both samples show an anti-correlation of fesc with dust content, and we show that Lya- and Ha-selection recovers populations that differ substantially in dust content and fesc., Comment: Letter to Nature, in press. Under terms of the press embargo, authors may not converse with the media before publication. 24 pages, 5 images, Supplementary Information included

The Lyman-alpha (Lya) recombination line is a fundamental tool for galaxy evolution studies and modern observational cosmology. However, subsequent interpretations are still prone to a number of uncertainties. Besides numerical efforts, empirical data are urgently needed for a better understanding of Lya escape process. We empirically estimate the Lyman-alpha escape fraction fesc(Lya) in a statistically significant sample of z ~ 0 - 0.3 galaxies in order to calibrate high-redshift Lyman-alpha observations. An optical spectroscopic follow-up of a sub-sample of 24 Lyman-alpha emitters (LAEs) detected by GALEX at z ~ 0.2-0.3, combined with a UV-optical sample of local starbursts, both with matched apertures, allow us to quantify the dust extinction through Balmer lines, and to estimate the Lyman-alpha escape fraction from the Halpha flux corrected for extinction in the framework of the recombination theory. The global escape fraction of Lyman-alpha radiation spans nearly the entire range of values, from 0.5 to 100 %, and fesc(Lya) clearly decreases with increasing nebular dust extinction E(B-V). Several objects show fesc(Lya) greater than fesc(continuum) which may be an observational evidence for clumpy ISM geometry or for an aspherical ISM. Selection biases and aperture size effects may still prevail between z ~ 0.2-0.3 LAEs and local starbursts, which may explain the difference observed for fesc(Lya)., Comment: 4 pages, 2 figures, accepted for publication in Astronomy and Astrophysics

Lyman-alpha is now widely used to investigate the galaxy formation and evolution in the high redshift universe. However, without a rigorous understanding of the processes which regulate the Lya escape fraction, physical interpretations of high-z observations remain questionable. We examine six nearby star-forming galaxies to disentangle the role of the dust from other parameters such as gas kinematics, geometry and ISM morphology in the obscuration of Ly-alpha. Thereby we aim to understand the Ly-a escape physics and infer the implications for high-redshift studies. We use HST/ACS to produce continuum-subtracted Lya maps, and ground-based observations (ESO/NTT and NOT) to map the Halpha emission and the extinction E(B-V) in the gas phase derived from the Balmer decrement Halpha/Hbeta. When large outflows are present, the Lya emission appears not to correlate with the dust content, confirming the role of the HI kinematics in the escape of Lya photons. In the case of a dense, static HI covering, we observe a damped absorption with a declining relationship between Lya and E(B-V). We found that the Lya escape fraction does not exceed 10% in all our galaxies and is mostly about 3% or below. Finally, because of the radiative transfer complexity of the Lya line, star formation rate based on Lya luminosity is underestimated with respect to that derived from UV luminosity. The failure of simple dust correction to recover the intrinsic Lya/Ha ratio or the total star formation rate should prompt us to be more cautious when interpreting high-z observations and related properties, such as SFRs based on Lya alone. To this end we propose a more realistic calibration for SFR(Lya) which accounts for dust attenuation and resonant scattering effects via the Lya escape fraction., Comment: Accepted for publication in A&A, 19 pages, 15 figures

We present reduced and calibrated high resolution Lyman-alpha (Lya) images for a sample of 6 local star forming galaxies. Targets were selected to represent a range in luminosity and metallicity and to include both known Lya emitters and non-emitters. Far ultraviolet imaging was carried out with the Solar Blind Channel of the ACS on HST in the F122M (Lya on-line) and F140LP (continuum) filters. The resulting Lya images are the product of careful modeling of both the stellar and nebular continua, facilitated by supporting HST imaging in Ha and 5 continuum bands, combined with Starburst99 evolutionary synthesis models, and prescriptions for dust extinction on the continuum. In all, the resulting morphologies in Lya, Ha, and UV-continuum are qualitatively very different and we show that the bulk of Lya emerges in a diffuse component resulting from resonant scattering events. Lya escape fractions, computed from integrated Ha luminosities and recombination theory, are found never to exceed 14%. Internal dust extinction is estimated in each pixel and used to correct Lya fluxes. However, the extinction corrections are far too small (factors from 2.6 to infinity) to reconcile the global Lya luminosities with recombination theory. Surprisingly, when comparing the global equivalent widths of Lya and Ha, the two quantities appear anti-correlated, which may be due to the evolution of mechanical feedback. This calls for caution in the interpretation of Lya observations. The images presented have a physical resolution 3 orders of magnitude better than attainable at high-z from the ground with current instrumentation and our images may therefore serve as useful templates for comparing with observations and modeling of primeval galaxy formation. We therefore provide the reduced Lya, Ha, and continuum images to the community., Comment: Accepted by the Astronomical Journal. See also http://ttt.astro.su.se/projects/Lyman-alpha/

[ABRIDGED] We are undertaking an imaging study of local star-forming galaxies in the Lyman-alpha (Lya) emission line using the Solar Blind Channel (SBC) of the ACS onboard the HST. Observations have been obtained in Lya and H-alpha (Ha) and 6 continuum filters between ~1500AA and the I-band. Previously (Hayes et al 2005) we demonstrated that the production of Lya line-only images in the SBC-only data-set is non-trivial and that supporting data is a requirement. We here develop various methods of continuum subtraction and assess their relative performance using a variety of spectral energy distributions (SED) as input. We conclude that simple assumptions about the behavior of the ultraviolet continuum consistently lead to results that are wildly erroneous, and determine that an SED fitting approach is essential. Moreover, a single component stellar or stellar+nebular spectrum is not always sufficient for realistic template SEDs and, in order to successfully recover the input observables, care must be taken to control contributions of nebular gas and underlying stellar populations. Independent measurements of the metallicity must first be obtained, but details of the initial mass function play only a small role. We identify the need to bin together pixels in our data to obtain signal-to-noise (S/N) of ~10 in each band before processing. At S/N=10 we can recover Lya fluxes accurate to ~30% for Lya lines with intrinsic equivalent width [W(Lya)] of 10AA. This accuracy improves to ~10% for W(Lya)=100AA. We describe the image processing applied to the observations presented in \"Ostlin et al. (2009) and the associated data-release. We also present simulations for an observing strategy for an alternative low-redshift SBC Lya imaging campaign using adjacent combinations of long-pass filters at slightly higher redshift., Comment: Accepted by the Astronomical Journal

(Abridged) Lyman-alpha (Lya) is a dominant probe of the galaxy population at high-z. However, interpretation of data drawn from Lya alone hinges on the Lya escape fraction which, due to the complex radiative transport, may vary greatly. Here we map the Lya emission from local starburst Haro 11, a Lya emitter and the only known candidate for low-z Lyman continuum emission (LyC). To aid in the interpretation we perform a detailed multi-wavelength analysis and model the stellar population, dust distribution, ionising photon budget, and star-cluster population. We use archival X-ray observations to further constrain properties of the starburst and estimate the HI column density. The Lya morphology is found to be strongly decoupled from stellar and nebular (H-alpha) morphologies. General surface photometry finds only very slight correlation between Lya and H-halpha, E(B-V), and stellar age. Only around the central Lya-bright cluster do we find the Lya/Ha ratio at values predicted by recombination theory. The total Lya escape fraction is found to be just 3%. We compute that ~90% of the Lya photons that escape do so after undergoing multiple resonance scattering events, masking their point of origin. This leads to a largely symmetric distribution and, by increasing the distance that photons must travel to escape, decreases the escape probability significantly. While dust must ultimately be responsible for the destruction of Lya, it plays little role in governing the observed morphology, which is regulated more by ISM kinematics and geometry. We find tentative evidence for local Lya equivalent width in the immediate vicinity of star-clusters being a function of cluster age, consistent with hydrodynamic studies. We estimate the ionising photon production and further constrain the escape fraction at 900 AA to <~9% ., Comment: In press for MNRAS. 18 pages, 9 figures. Version with full resolution images to be found at http://www.astro.su.se/~matthew/english/papers/hayes_lya_haro11_hires.pdf

Wolf-Rayet stars have been detected in a large number of galaxies experiencing intense bursts of star formation. All stars initially more massive than a certain, metallicity-dependent, value are believed to experience the Wolf-Rayet phase at the end of their evolution, just before collapsing in supernova explosion. The detection of Wolf-Rayet stars puts therefore important constraints on the evolutionary status of starbursts, the properties of their Initial Mass Functions and their star formation regime. In this contribution we review the properties of galaxies hosting Wolf-Rayet stars, with special emphasis on the factors that determine their presence and evolution, as well as their impact on the surrounding medium., Comment: Contribution to the Proceedings of the JENAM 99 conference "The interplay between massive stars and the ISM", held in Toulouse in September 7-11, 1999. 10 pages, 5 figures. Requires elsart.cls latex macro

We have analyzed new and archival IUE observations of narrow-line Seyfert 1 galaxies (NLS1) in order to revise the ultraviolet (UV) properties of this sub-group of Active Galactic Nuclei (AGN). We have found broad wings in the strongest UV emission lines, ruling out the hypothesis that there is no broad line emission region in this type of objects. Since the similarities in spectral energy distributions from the far-infrared (FIR) to the soft X rays in both narrow-line and broad-line Seyfert 1 galaxies do not suggest that the nuclei of NLS1 are hidden from a direct view, we discuss the possibility that the line emitting material in NLS1 is optically thin., Comment: Accepted for publication in Astron. Astrophys. Main Journal, 10 pages, LaTeX with epsf and l-aa macros, including 2 postscript figures