SwitchWare: Accelerating Network Evolution (White Paper)

We propose the development of a set of software technologies ( SwitchWare ) which will enable rapid development and deployment of new network services. The key insight is that by making the basic network service selectable on a per user (or even per packet) basis, the need for formal standardization is eliminated. Additionally, by making the basic network service programmable, the deployment times, today constrained by capital funding limitations, are tremendously reduced (to the order of software distribution times). Finally, by constructing an advanced, robust programming environment, even the service development time can be reduced. A SwitchWare switch consists of input and output ports controlled by a software-programmable element; programs are contained in sequences of messages sent to the SwitchWare switch\u27s input ports, which interpret the messages as programs. We call these Switchlets . This accelerates the pace of network evolution, as evolving user needs can be immediately reflected in the network infrastructure. Immediate reconfigurability enhances the adaptability of the network infrastructure in the face of unexpected situations. We call a network built from SwitchWare switches an active network

Variation in Emission and Absorption Lines and Continuum Flux by Orbital Phase in Vela X-1

High resolution spectral studies were undertaken at orbital phases 0, 0.25 and 0.5 on the high-mass X-ray binary (HMXB) Vela X-1 using archival Chandra data. We present (a) the first detailed analysis of the multiple strong narrow emission lines present in phase 0.5 (b) an analysis of the absorption of the continuum in phase 0.5, and (c) the first detection of narrow emission and absorption lines in phase 0.25. Multiple fluorescent and H-and He-like emission lines in the band 1.6 - 20 Angstrom in eclipse are partially obscured at phase 0.25 by the X-ray continuum. The phase 0.25 spectrum displays 3 triplets, 2 with a blue-shifted resonance (r) line in absorption and the intercombination (i) and forbidden (f) lines in emission, and shows in absorption other blue-shifted lines seen in emission in eclipse. At phase 0.5 the soft X-ray continuum diminishes revealing an "eclipse-like" spectrum, however line flux values are around 13-fold those in eclipse. We conclude the narrow emission lines in Vela X-1 become apparent when the continuum is blocked from line of sight, either by eclipse or by scattering and/or absorption from a wake or cloud. The H-and He-like lines arise in warm photoionised regions in the stellar wind, while the fluorescent lines (including a Ni K alpha line) are produced in cooler clumps of gas outside these regions. Absorption of the 5-13 Angstrom continuum at phase 0.5 may be caused by an accretion wake comprised of dense stagnant photoionized plasma inside a Stromgren zone. Multiple fluorescent emission lines may be a common feature of the supergiant category of HMXBs.Comment: 29 pages, 7 figures, accepted for publication in the Astronomical Journa

X-ray Variability in the Young Massive Triple theta2 Ori A

Massive stars rarely show intrinsic X-ray variability. The only O-stars credited to be intrinsically variable are theta1 Ori C due to effects from magnetic confinement of its wind, and theta2 Ori A suspected of similar activity. Early Chandra observations have shown that the most massive star system in the Orion Trapezium Cluster, theta2 Ori A, shows rapid variability on time scales of hours. We determine X-ray fluxes and find that the star shows very strong variability over the last 5 years. We observed a second large X-ray outburst in November 2004 with the high resolution transmission grating spectrometer on-board Chandra. In the low state X-ray emissivities indicate temperatures well above 25 MK. In the high state we find an extended emissivity distribution with high emissivities in the range from 3 MK to over 100 MK. The outburst event in stellar terms is one of the most powerful ever observed and the most energetic one in the ONC with a lower total energy limit of 1.5x10^37 ergs. The line diagnostics show that under the assumption that the line emitting regions in the low states are as close as within 1 -- 2 stellar radii from the O-star's photosphere, whereas the hard states suggest a distance of 3 -- 5 stellar radii. The two outbursts are very close to the periastron passage of the stars. We argue that the high X-ray states are possibly the result of reconnection events from magnetic interactions of the primary and secondary stars of the spectroscopic binary. Effects from wind collisions seem unlikely for this system. The low state emissivity and R-ratios strengthen the predicament that the X-ray emission is enhanced by magnetic confinement of the primary wind. We also detect Fe fluorescence indicative of the existence of substantial amounts of neutral Fe in the vicinity of the X-ray emission.Comment: 11 pages, 8 figures, accepted for publication in The Astrophysical Main Journa

High-Resolution Chandra X-Ray Imaging And Spectroscopy Of The Sigma Orionis Cluster

We present results of a 90 ks Chandra X-ray observation of the young sigma Orionis cluster ( age similar to 3 Myr) obtained with the HETGS. We use the high-resolution grating spectrum and moderate-resolution CCD spectrum of the massive central star sigma Ori AB (O9.5 V + B0.5 V) to test wind shock theories of X-ray emission and also analyze the high spatial resolution zero-order ACIS-S image of the central cluster region. Chandra detected 42 X-ray sources on the primary CCD (ACIS-S3). All but five have near-IR or optical counterparts and about one-fourth are variable. Notable high-mass stellar detections are sigma Ori AB, the magnetic B star sigma Ori E, and the B5 V binary HD 37525. Most of the other detections have properties consistent with lower mass K- or M-type stars. We present the first X-ray spectrum of the unusual infrared source IRS 1, located approximate to 3 \u27\u27 north of sigma Ori AB. Its X-ray properties and elongated mid-IR morphology suggest that it is an embedded low-mass T Tauri star whose disk/envelope is being photoevaporated by sigma Ori AB. We focus on the radiative wind shock interpretation of the soft luminous X-ray emission from sigma Ori AB, but also consider possible alternatives including magnetically confined wind shocks and colliding wind shocks. Its emission lines show no significant asymmetries or centroid shifts and are moderately broadened to HWHM approximate to 264 km s(-1), or one-fourth the terminal wind speed. Forbidden lines in He-like ions are formally undetected, implying strong UV suppression. The Mg XI triplet forms in the wind acceleration zone within one stellar radius above the surface. These X-ray properties are consistent in several respects with the predictions of radiative wind shock theory for an optically thin wind, but explaining the narrow line widths presents a challenge to the theory

Ly-alpha Emission-Line Galaxies at z = 3.1 in the Extended Chandra Deep Field South

We describe the results of an extremely deep, 0.28 deg^2 survey for z = 3.1 Ly-alpha emission-line galaxies in the Extended Chandra Deep Field South. By using a narrow-band 5000 Anstrom filter and complementary broadband photometry from the MUSYC survey, we identify a statistically complete sample of 162 galaxies with monochromatic fluxes brighter than 1.5 x 10^-17 ergs cm^-2 s^-1 and observers frame equivalent widths greater than 80 Angstroms. We show that the equivalent width distribution of these objects follows an exponential with a rest-frame scale length of w_0 = 76 +/- 10 Angstroms. In addition, we show that in the emission line, the luminosity function of Ly-alpha galaxies has a faint-end power-law slope of alpha = -1.49 +/- 0.4, a bright-end cutoff of log L^* = 42.64 +/- 0.2, and a space density above our detection thresholds of 1.46 +/- 0.12 x 10^-3 h70^3 galaxies Mpc^-3. Finally, by comparing the emission-line and continuum properties of the LAEs, we show that the star-formation rates derived from Ly-alpha are ~3 times lower than those inferred from the rest-frame UV continuum. We use this offset to deduce the existence of a small amount of internal extinction within the host galaxies. This extinction, coupled with the lack of extremely-high equivalent width emitters, argues that these galaxies are not primordial Pop III objects, though they are young and relatively chemically unevolved.Comment: 45 pages, 15 figures, accepted for publication in the Astrophysical Journa

Chandra spectroscopy of the hot star beta Crucis and the discovery of a pre-main-sequence companion

In order to test the O star wind-shock scenario for X-ray production in less luminous stars with weaker winds, we made a pointed 74 ks observation of the nearby early B giant, beta Cru (B0.5 III), with the Chandra HETGS. We find that the X-ray spectrum is quite soft, with a dominant thermal component near 3 million K, and that the emission lines are resolved but quite narrow, with half-widths of 150 km/s. The forbidden-to-intercombination line ratios of Ne IX and Mg XI indicate that the hot plasma is distributed in the wind, rather than confined near the photosphere. It is difficult to understand the X-ray data in the context of the standard wind-shock paradigm for OB stars, primarily because of the narrow lines, but also because of the high X-ray production efficiency. A scenario in which the bulk of the outer wind is shock heated is broadly consistent with the data, but not very well motivated theoretically. It is possible that magnetic channeling could explain the X-ray properties, although no field has been detected on beta Cru. We detected periodic variability in the hard (hnu > 1 keV) X-rays, modulated on the known optical period of 4.58 hours, which is the period of the primary beta Cep pulsation mode for this star. We also have detected, for the first time, an apparent companion to beta Cru at a projected separation of 4 arcsec. This companion was likely never seen in optical images because of the presumed very high contrast between it and beta Cru in the optical. However, the brightness contrast in the X-ray is only 3:1, which is consistent with the companion being an X-ray active low-mass pre-main-sequence star. The companion's X-ray spectrum is relatively hard and variable, as would be expected from a post T Tauri star.Comment: Accepted for publication in MNRAS; 19 pages, 15 figures, some in color; version with higher-resolution figures available at http://astro.swarthmore.edu/~cohen/papers/bcru_mnras2008.pd

Metal enrichment processes

There are many processes that can transport gas from the galaxies to their environment and enrich the environment in this way with metals. These metal enrichment processes have a large influence on the evolution of both the galaxies and their environment. Various processes can contribute to the gas transfer: ram-pressure stripping, galactic winds, AGN outflows, galaxy-galaxy interactions and others. We review their observational evidence, corresponding simulations, their efficiencies, and their time scales as far as they are known to date. It seems that all processes can contribute to the enrichment. There is not a single process that always dominates the enrichment, because the efficiencies of the processes vary strongly with galaxy and environmental properties.Comment: 18 pages, 8 figures, accepted for publication in Space Science Reviews, special issue "Clusters of galaxies: beyond the thermal view", Editor J.S. Kaastra, Chapter 17; work done by an international team at the International Space Science Institute (ISSI), Bern, organised by J.S. Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke

The Physical Nature of Lyman Alpha Emitting Galaxies at z=3.1

We selected 40 candidate Lyman Alpha Emitting galaxies (LAEs) at z ~=3.1 with observed frame equivalent widths >150A and inferred emission line fluxes >2.5x10^-17 ergs/cm^2/s from deep narrow-band and broad-band MUSYC images of the Extended Chandra Deep Field South. Covering 992 sq. arcmin, this is the largest ``blank field'' surveyed for LAEs at z ~3, allowing an improved estimate of the space density of this population of 3+-1x10^-4 h_70^3/Mpc^3. Spectroscopic follow-up of 23 candidates yielded 18 redshifts, all at z ~=3.1. Over 80% of the LAEs are dimmer in continuum magnitude than the typical Lyman break galaxy spectroscopic limit of R= 25.5 (AB), with a median continuum magnitude R ~=27 and very blue continuum colors, (V-z) ~=0. Over 80% of the LAEs have the right UVR colors to be selected as Lyman break galaxies, but only 10% also have R<=25.5. Stacking the UBVRIzJK fluxes reveals that LAEs have stellar masses ~=5x10^8 h_70^-2 M_sun and minimal dust extinction, A_V < ~ 0.1. Inferred star formation rates are ~=6 h_70^-2 M_sun/yr, yielding a cosmic star formation rate density of 2x10^-3 h_70 M_sun/yr/Mpc^3. None of our LAE candidates show evidence for rest-frame emission line equivalent widths EW_rest>240A which might imply a non-standard IMF. One candidate is detected by Chandra, implying an AGN fraction of 2+-2% for LAE candidate samples. In summary, LAEs at z ~ 3 have rapid star formation, low stellar mass, little dust obscuration and no evidence for a substantial AGN component.Comment: ApJ Letters, in press, very minor revisions to match accepted version, 4 pages with 2 color figure

PHANGS-JWST First Results: A combined HST and JWST analysis of the nuclear star cluster in NGC 628

We combine archival HST and new JWST imaging data, covering the ultraviolet to mid-infrared regime, to morphologically analyze the nuclear star cluster (NSC) of NGC 628, a grand-design spiral galaxy. The cluster is located in a 200 pc x 400 pc cavity, lacking both dust and gas. We find roughly constant values for the effective radius (r_eff ~ 5 pc) and ellipticity ({\epsilon} ~ 0.05), while the S\'ersic index (n) and position angle (PA) drop from n ~ 3 to ~ 2 and PA ~ 130{\deg} to 90{\deg}, respectively. In the mid-infrared, r_eff ~ 12pc, {\epsilon} ~ 0.4, and n ~ 1-1.5, with the same PA ~ 90{\deg}. The NSC has a stellar mass of log10 (M_nsc / M_Sun) = 7.06 +- 0.31, as derived through B-V, confirmed when using multi-wavelength data, and in agreement with the literature value. Fitting the spectral energy distribution, excluding the mid-infrared data, yields a main stellar population's age of (8 +- 3) Gyr with a metallicity of Z = 0.012 +- 0.006. There is no indication of any significant star formation over the last few Gyr. Whether gas and dust were dynamically kept out or evacuated from the central cavity remains unclear. The best-fit suggests an excess of flux in the mid-infrared bands, with further indications that the center of the mid-infrared structure is displaced with respect to the optical center of the NSC. We discuss five potential scenarios, none of them fully explaining both the observed photometry and structure.Comment: 26 pages, 10 figures, 6 tables. Accepted for publication by ApJ

The Hard X-ray Luminosity of OB Star Populations: Implications for the Contribution of Star Formation to the Cosmic X-ray Background

We present an empirical analysis of the integrated X-ray luminosity arising from populations of OB stars. In particular, we utilize results from the All-Sky Monitor on RXTE, along with archival data from previous missions, to assess the mean integrated output of X-rays in the 2-10 keV band from accreting early-type binaries within 3 kpc of the Sun. Using a recent OB star census of the Solar neighborhood, we then calculate the specific X-ray luminosity per O star from accretion-powered systems. We also assess the contribution to the total X-ray luminosity of an OB population from associated T Tauri stars, stellar winds, and supernovae. We repeat this exercise for the major Local Group galaxies, concluding that the total X-ray luminosity per O star spans a broad range from 2 to 20e34 erg/s. Contrary to previous results, we do not find a consistent trend with metallicity; in fact, the specific luminosities for M31 and the SMC are equal, despite having metallicities which differ by an order of magnitude. In light of these results, we assess the fraction of the observed 2-10 keV emission from starburst galaxies that arises directly from their OB star populations, concluding that, while binaries can explain most of the hard X-ray emission in many local starbursts, a significant additional component or components must be present in some systems. A discussion of the nature of this additional emission, along with its implications for the contribution of starbursts to the cosmic X-ray background, concludes our report.Comment: aastex, 30 pages including 2 tables and 1 figure. To appear in Ap