Line transfer through clumpy, large-scale outflows: Ly α absorption and haloes around star-forming galaxies

We present constrained radiative transfer calculations of Lyα photons propagating through clumpy, dusty, large-scale outflows, and explore whether we can quantitatively explain the Lyα haloes that have been observed around Lyman break galaxies. We construct phenomenological models of large-scale outflows which consist of cold clumps that are in pressure equilibrium with a constant-velocity hot wind. First, we consider models in which the cold clumps are distributed symmetrically around the galaxy and in which the clumps undergo a continuous acceleration in its ‘circumgalactic' medium (CGM). We constrain the properties of the cold clumps (radius, velocity, H i column density and number density) by matching the observed Lyα absorption strength of the CGM in the spectra of background galaxies. We then insert a Lyα source in the centre of this clumpy outflow, which consists of 105-106 clumps, and compute observable properties of the scattered Lyα photons. In these models, the scattered radiation forms haloes that are significantly more concentrated than observed. In order to simultaneously reproduce the observed Lyα absorption line strengths and the Lyα haloes, we require - preferably bipolar - outflows in which the clumps decelerate after their initial acceleration. This deceleration is predicted naturally in ‘momentum-driven' wind models of clumpy outflows. In models that simultaneously fit the absorption and emission-line data, the predicted linear polarization is ∼30-40 per cent at a surface brightness contour of S = 10−18 erg s−1 cm−2 arcsec−2. Our work illustrates clearly that Lyα emission-line haloes around star-forming galaxies provide valuable constraints on the cold gas distribution and kinematics in their CGM, and that these constraints complement those obtained from absorption-line studies alon

X-Ray Emission-Line Profile Modeling Of O Stars: Fitting A Spherically Symmetric Analytic Wind-Shock Model To The Chandra Spectrum Of Zeta Puppis

X-ray emission-line profiles provide the most direct insight into the dynamics and spatial distribution of the hot, X-ray-emitting plasma above the surfaces of OB stars. The O supergiant zeta Puppis shows broad, blueshifted, and asymmetric line profiles, generally consistent with the wind-shock picture of OB star X-ray production. We model the profiles of eight lines in the Chandra HETGS spectrum of this prototypical hot star. The fitted lines indicate that the plasma is distributed throughout the wind starting close to the photosphere, that there is significantly less attenuation of the X-rays by the overlying wind than is generally supposed, and that there is not a strong trend in wind absorption with wavelength

Analysis Of Doppler-Broadened X-Ray Emission Line Profiles From Hot Stars

We show how X-ray emission arising within an accelerating, expanding medium that also contains a source of continuum absorption generates line profiles of a characteristic shape. A simple, spherical wind model based on this picture provides good fits to the Chandra HETGS spectrum of the prototypical O star, Zeta Pup. We discuss the model, the fitting procedure and the determination of confidence limits on the model parameters, and our initial results for this star. The derived fit parameters are consistent with a generic wind-shock scenario for Zeta Pup, but there are several surprising aspects of the results, including a lower-than-expected mean wind optical depth and a nearly complete lack of wavelength dependence of the results

Feedback from Clustered Sources During Reionization

The reionization history of the intergalactic medium (IGM) at high redshift (z > 6) was likely strongly shaped by several global feedback processes. Because the earliest ionizing sources formed at the locations of the rare density peaks, their spatial distribution was strongly clustered. Here we demonstrate that this clustering significantly boosts the impact of feedback processes operating at high redshift. We build a semi-analytical model to include feedback and clustering simultaneously, and apply this model to the suppression of star-formation in minihalos due to photoionization. The model is built on the excursion-set-based formalism of Furlanetto, Zaldarriaga and Hernquist (2004), which incorporates the clustering of ionizing sources, and which we here extend to include suppression of star formation in minihalos. We find that clustering increases the mean HII bubble size by a factor of several, and it dramatically increases the fraction of minihalos that are suppressed, by a factor of up to 60 relative to a randomly distributed population. This enhanced suppression can significantly reduce the electron scattering optical depth, as required by the three-year data from the Wilkinson Microwave Anisotropy Probe (WMAP). We argue that source clustering is likely to similarly boost the importance of a variety of other feedback mechanisms.Comment: submitted to ApJ, 9 emulateapj pages with 7 figure

Wind Signatures In The X-Ray Emission-Line Profiles Of The Late-O Supergiant Zeta Orionis

X-ray line-profile analysis has proved to be the most direct diagnostic of the kinematics and spatial distribution of the very hot plasma around O stars. The Doppler-broadened line profiles provide information about the velocity distribution of the hot plasma, while the wavelength-dependent attenuation across a line profile provides information about the absorption to the hot plasma, thus providing a strong constraint on its physical location. In this paper, we apply several analysis techniques to the emission lines in the Chandra High Energy Transmission Grating Spectrometer (HETGS) spectrum of the late-O supergiant zeta Ori (O9.7 Ib), including the fitting of a simple line-profile model. We show that there is distinct evidence for blueshifts and profile asymmetry, as well as broadening in the X-ray emission lines of zeta Ori. These are the observational hallmarks of a wind-shock X-ray source, and the results for zeta Ori are very similar to those for the earlier O star, zeta Pup, which we have previously shown to be well fit by the same wind-shock line-profile model. The more subtle effects on the line-profile morphologies in zeta Ori, as compared to zeta Pup, are consistent with the somewhat lower density wind in this later O supergiant. In both stars, the wind optical depths required to explain the mildly asymmetric X-ray line profiles imply reductions in the effective opacity of nearly an order of magnitude, which may be explained by some combination of mass-loss rate reduction and large-scale clumping, with its associated porosity-based effects on radiation transfer. In the context of the recent reanalysis of the helium-like line intensity ratios in both zeta Ori and zeta Pup, and also in light of recent work questioning the published mass-loss rates in OB stars, these new results indicate that the X-ray emission from zeta Ori can be understood within the framework of the standard wind-shock scenario for hot stars

Wind signatures in the X-ray emission line profiles of the late O supergiant ζ\zeta Orionis

X-ray line profile analysis has proved to be the most direct diagnostic of the kinematics and spatial distribution of the very hot plasma around O stars. In this paper we apply several analysis techniques to the emission lines in the Chandra HETGS spectrum of the late-O supergiant zeta Ori (O9.7 Ib), including the fitting of a simple line-profile model. We show that there is distinct evidence for blue shifts and profile asymmetry, as well as broadening in the X-ray emission lines of zeta Ori. These are the observational hallmarks of a wind-shock X-ray source, and the results for zeta Ori are very similar to those for the earlier O star, zeta Pup, which we have previously shown to be well-fit by the same wind-shock line-profile model. The more subtle effects on the line-profile morphologies in zeta Ori, as compared to zeta Pup, are consistent with the somewhat lower density wind in this later O supergiant. In both stars, the wind optical depths required to explain the mildly asymmetric X-ray line profiles imply reductions in the effective opacity of nearly an order of magnitude, which may be explained by some combination of mass-loss rate reduction and large-scale clumping, with its associated porosity-based effects on radiation transfer. In the context of the recent reanalysis of the helium-like line intensity ratios in both zeta Ori and zeta Pup, and also in light of recent work questioning the published mass-loss rates in OB stars, these new results indicate that the X-ray emission from zeta Ori can be understood within the framework of the standard wind-shock scenario for hot stars.Comment: MNRAS, accepted; 16 pages, 5 figure

X-Ray Emission Line Profile Modeling Of Hot Stars

The launch of high-spectral-resolution x-ray telescopes (Chandra, XMM) has provided a host of new spectralline diagnostics for the astrophysics community. In this paper we discuss Doppler-broadened emission line profiles from highly supersonic outflows of massive stars. These outflows, or winds, are driven by radiation pressure and carry a tremendous amount of kinetic energy, which can be converted to x rays by shock-heating even a small fraction of the wind plasma. The unshocked, cold wind is a source of continuum opacity to the x rays generated in the shock-heated portion of the wind. Thus the emergent line profiles are affected by transport through a two-component, moving, optically thick medium. While complicated, the interactions among these physical effects can provide quantitative information about the spatial distribution and velocity of the x-ray-emitting and absorbing plasma in stellar winds. We present quantitative models of both a spherically symmetric wind and a wind with hot plasma confined in an equatorial disk by a dipole magnetic field