arXiv.org > astro-ph

Search for

(Help | Advanced search)

All papers Titles Authors Abstracts Full text

Astrophysics

---

astro-ph new abstracts, Mon, 30 Jan 06 01:00:09 GMT
0601618 -- 0601653 received

---

astro-ph/0601618 [abs, ps, pdf, other] :

Title: The Surface of 2003EL61 in the Near Infrared
Authors: C. A. Trujillo, M. E. Brown, K. M. Barkume, E. L. Schaller, D. L. Rabinowitz

We report the detection of crystalline water ice on the surface of 2003EL61. Reflectance spectra were collected from Gemini North telescope from 1.0 to 2.4 micron wavelength range, and from the Keck telescope across the 1.4 to 2.4 micron wavelength range. The signature of crystalline water ice is clear and obvious in all data collected. Like the surface of many outer solar system bodies, the surface of 2003EL61 is rich in crystalline water ice, which is energetically less favored than amorphous water ice at cold temperatures, suggesting resurfacing processes may be taking place. The near infrared color of the object is much bluer than a pure water ice model. Adding a near infrared blue component such as hydrogen cyanide or phyllosilicate clays improves the fit considerably, with hydrogen cyanide providing the greatest improvement. The addition of hydrated tholins and bitumens also improves the fit but is inconsistent with the neutral V-J reflectance of 2003EL61. A small decrease in reflectance beyond 2.3 micron may be attributable to cyanide salts. Overall, the reflected light from 2003 EL61 is best fit by a model of 2/3 to 4/5 pure crystalline water ice and 1/3 to 1/5 near infrared blue component such as hydrogen cyanide or kaolinite. The surface of 2003 EL61 is unlikely to be covered by significant amounts of dark material such as carbon black, as our pure ice models reproduce published albedo estimates derived from the spin state of 2003 EL61.

 

astro-ph/0601619 [abs, ps, pdf, other] :

Title: Sub-GeV flashes in $\gamma-$ray burst afterglows as probes of underlying bright UV flares
Authors: Yizhong Fan, Tsvi Piran

Bright optical and X-ray flares have been observed in many Gamma-ray Burst (GRB) afterglows. These flares have been attributed to late activity of the central engine. In most cases the peak energy is not known and it is possible and even likely that there is a significant far-ultraviolet component. These far-UV photons escape our detection because they are absorbed by the neutral hydrogen before reaching Earth. However, these photons cross the blast wave produced by the ejecta that have powered the initial GRB. They can be inverse Compton upscattered by hot electrons within this blast wave. This process will produce a strong sub-GeV flare that can be detected by the upcoming {\em Gamma-Ray Large Area Telescope} (GLAST) satellite. This signature can be used to probe the spectrum of the underlying far-ultraviolet flare. The extra cooling produced by this inverse Compton process can lower the X-ray emissivity of the forward shock and explain the unexpected low early X-ray flux seen in many GRBs.

 

astro-ph/0601620 [abs, ps, pdf, other] :

Title: XMM-Newton View of the z>0 Warm-Hot Intergalactic Medium Toward Markarian 421
Authors: Rik J. Williams (1), Smita Mathur (1), Fabrizio Nicastro (2,3,4), Martin Elvis (2) ((1) Department of Astronomy, The Ohio State University, (2) Harvard-Smithsonian Center for Astrophysics, (3) Instituto de Astronomia, UNAM, (4) OAR-INAF)
Comments: 10 pages, 2 figures, submitted to ApJ Letters

The recent detection with Chandra of two warm-hot intergalactic medium (WHIM) filaments toward Mrk 421 by Nicastro et al. provides, for the first time, a measurement of the "missing baryons" in the nearby universe. Since Mrk 421 is a bright X-ray source, it is also frequently observed by the XMM-Newton Reflection Grating Spectrometer (RGS) for calibration purposes. Using all available archived XMM observations of this source with small pointing offsets (<15"), we construct the highest-quality XMM grating spectrum of Mrk 421 to date with a net exposure time (excluding periods of high background flux) of 437 ks and ~15000 counts per resolution element at 21.6\AA, more than twice that of the Chandra spectrum. Despite the long exposure time neither of the two intervening absorption systems is seen, though the upper limits derived are fully consistent with the Chandra equivalent width measurements. This appears to result from (1) the larger number of narrow instrumental features caused by bad detector columns, (2) the degraded resolution of XMM/RGS as compared to the Chandra/LETG, and (3) fixed pattern noise at \lambda >~ 29\AA. The Chandra detection of the intervening WHIM systems is thus robust despite the RGS non-detection.

 

astro-ph/0601621 [abs, ps, pdf, other] :

Title: Observational Evidence for the Co-evolution of Galaxy Mergers, Quasars, and the Blue/Red Galaxy Transition
Authors: Philip F. Hopkins (1), Kevin Bundy (2), Lars Hernquist (1), Richard S. Ellis (2) ((1) Harvard/CfA, (2) Caltech)
Comments: 5 pages, 3 figures. Submitted to ApJ Letters

Observations indicate the mass above which ellipticals dominate the galaxy population increases with redshift over the range 0<z<2, implying that galaxies transition from the blue to red sequence in a manner consistent with 'cosmic downsizing.' Theories predict that mergers between gas-rich blue galaxies produce ellipticals, with an associated phase of bright quasar activity which expels and heats gas, terminating star formation, so that the remnant rapidly becomes red. If this is true, then the transition mass at a given redshift, where the red sequence is being built, should also correspond to the characteristic mass of both merging gas-rich galaxies and quasar hosts at that redshift. We compare observations of these quantities from 0<z<3, as well as theoretical models of mergers and associated quasar activity, and show that they indeed appear to be the same mass and evolve in the same manner over this range. We also provide new tests of this association, such as the AGN fraction peaking near the transition mass and the quasar host mass as a function of luminosity. Our results support the view that mergers and subsequent quasar activity drive the transition of galaxies from the blue to the red sequence.

 

astro-ph/0601622 [abs, ps, pdf, other] :

Title: Deducing the Lifetime of Short Gamma-Ray Burst Progenitors from Host Galaxy Demography
Authors: Zheng Zheng, Enrico Ramirez-Ruiz (IAS)
Comments: 4 pages, 3 figures, submitted to ApJL

The frequency of short gamma-ray bursts (GRBs) in galaxies of different spectral type is used here to constrain the lifetime of the progenitors. On average, early-type galaxies have their stars formed earlier than late-type galaxies, and this difference, together with the time delay between progenitor formation and short GRB outburst, leads to different burst rates in the two types of galaxies. Presently available data suggest, but not yet prove, that the short GRB rate in early-type galaxies may be higher than it is in late-type galaxies. This suggests that, unlike Type Ia supernovae, at least half of the short GRB progenitors that can outburst within a Hubble time have lifetimes greater than 10 Gyr. Models of the probability distribution of time delays, here parametrized as P(\tau)\propto \tau^n, with n>3/2 are favored. This apparent long time delay and the fact that early-type galaxies in clusters make a substantial contribution to the local stellar mass inventory can explain the observed preponderance of short GRBs in galaxy clusters.

 

astro-ph/0601623 [abs, ps, pdf, other] :

Title: The magnetic field and confined wind of the O star $\theta^1$~Orionis~C
Authors: G.A. Wade, A.W. Fullerton, J.-F. Donati, J.D. Landstreet, P. Petit, S. Strasser

In this paper we confirm the presence of a globally-ordered, kG-strength magnetic field in the photosphere of the young O star $\theta^1$~Orionis~C, and examine the properties of its optical line profile variations. A new series of high-resolution MuSiCoS Stokes $V$ and $I$ spectra has been acquired which samples approximately uniformly the rotational cycle of $\theta^1$~Orionis~C. Using the Least-Squares Deconvolution (LSD) multiline technique, we have succeeded in detecting variable Stokes $V$ Zeeman signatures associated with the LSD mean line profile. These signatures have been modeled to determine the magnetic field geometry. We have furthermore examined the profi le variations of lines formed in both the wind and photosphere using dynamic spectra. Based on spectrum synthesis fitting of the LSD profiles, we determine that the polar strength of the magnetic dipole component is $1150 \la B_{\rm d}\la 1800$~G and that the magnetic obliquity is $27\degr \la \beta \la 68\degr$, assuming $i=45\pm 20\degr$. The best-fit values for $i=45\degr$ are $B_{\rm d} = 1300 \pm 150 (1\sigma)$~G and $\beta = 50\degr \pm 6\degr (1\sigma)$. Our data confirm the previous detection of a magnetic field in this star, and furthermore demonstrate the sinusoidal variability of the longitudinal field and accurately determine the phases and intensities of the magnetic extrema. The analysis of ``photospheric'' and ``wind'' line profile variations supports previous reports of the optical spectroscopic characteristics, and provides evidence for infall of material within the magnetic equatorial plane.

 

astro-ph/0601624 [abs, ps, pdf, other] :

Title: Investigation of the magnetic field characteristics of Herbig Ae/Be stars: Discovery of the pre-main sequence progenitors of the magnetic Ap/Bp stars
Authors: G.A. Wade, D. Drouin, S. Bagnulo, J.D. Landstreet, E. Mason, J. Silvester, E. Alecian, T. Bohm, J.-C. Bouret, C. Catala, J.-F. Donati, C. Folsom, K. Bale

We are investigating the magnetic characteristics of pre-main sequence Herbig Ae/Be stars, with the aim of (1) understanding the origin and evolution of magnetism in intermediate-mass stars, and (2) exploring the influence of magnetic fields on accretion, rotation and mass-loss at the early stages of evolution of A, B and O stars. We have begun by conducting 2 large surveys of Herbig Ae/Be stars, searching for direct evidence of photospheric magnetic fields via the longitudinal Zeeman effect. From observations obtained using FORS1 at the ESO-VLT and ESPaDOnS at the Canada-France-Hawaii Telescope, we report the confirmed detection of magnetic fields in 4 pre-main sequence A- and B-type stars, and the apparent (but as yet unconfirmed) detection of fields in 2 other such stars. We do not confirm the detection of magnetic fields in several stars reported by other authors to be magnetic: HD 139614, HD 144432 or HD 31649. One of the most evolved stars in the detected sample, HD 72106A, shows clear evidence of strong photospheric chemical peculiarity, whereas many of the other (less evolved) stars do not. The magnetic fields that we detect appear to have surface intensities of order 1 kG, seem to be structured on global scales, and appear in about 10% of the stars studied. Based on these properties, these magnetic stars appear to be pre-main sequence progenitors of the magnetic Ap/Bp stars.

 

astro-ph/0601625 [abs, ps, pdf, other] :

Title: Magnetic properties of intermediate-mass stars
Authors: G.A. Wade

Magnetic fields play an important role in producing and modifying the photospheric chemical peculiarities of intermediate-mass main sequence stars. This article discusses the basic theory and methods of measurement used to detect and characterise stellar magnetic fields, and reviews our current knowledge of selected characteristics of magnetic fields in intermediate-mass stars.

 

astro-ph/0601626 [abs, ps, pdf, other] :

Title: Magnetic Fields in Starburst Galaxies and The Origin of the FIR-Radio Correlation
Authors: Todd A. Thompson, Eliot Quataert, Eli Waxman, Norman Murray, Crystal L. Martin
Comments: 13 pages, emulateapj, 4 figures, 3 tables, submitted to ApJ

We estimate minimum energy magnetic fields (B_min) for a sample of galaxies with measured gas surface densities, spanning from normal spirals to starbursts. We show that the ratio of the minimum energy magnetic pressure to the total pressure in the ISM decreases substantially with increasing surface density; for Arp 220 this ratio is ~10^-4. Therefore, if the minimum energy estimate is applicable, magnetic fields in starbursts are dynamically weak compared to gravity, in contrast to normal spiral galaxies. We argue, however, that rapid cooling of relativistic electrons in starbursts invalidates the minimum energy estimate. We critically assess a number of independent constraints on the magnetic field strength in starbursts. In particular, we argue that the existence of the FIR-radio correlation implies that the synchrotron cooling timescale for cosmic ray electrons is much shorter than their escape time from the galactic disk; this in turn implies that the true magnetic field in starbursts is significantly larger than B_min. The strongest argument against such large fields is that one might expect starbursts to have steep radio spectra indicative of strong synchrotron cooling, which is not observed. We show, however, that ionization and bremsstrahlung losses can flatten the nonthermal spectra of starburst galaxies even in the presence of rapid cooling, providing much better agreement with observed spectra. We further demonstrate that ionization and bremsstrahlung losses are likely to be important in shaping the radio spectra of most starbursts at GHz frequencies, thereby preserving the linearity of the FIR-radio correlation. We thus conclude that magnetic fields in starbursts are significantly larger than B_min. We highlight several observations that can test this conclusion.

 

astro-ph/0601627 [abs, ps, pdf, other] :

Title: A Chandra Catalog of X-ray Sources in the Central 150 pc of the Galaxy
Authors: M. P. Muno (UCLA), F. E. Bauer (Columbia), R. M. Bandyopadhyay (U Florida), Q. D. Wang (UMass Amherst)
Comments: 16 pages, incl. 9 figures, 3 in color. Submitted to ApJ. An electronic catalog of X-ray point sources is located at this http URL . A high-resolution version of figure 1 will be available when the manuscript is published

We present the catalog of X-ray sources detected in a shallow Chandra survey of the inner 2 by 0.8 degrees of the Galaxy, and in two deeper observations of the Radio Arches and Sgr B2. The catalog contains 1352 objects that are highly-absorbed (N_H > 4e22 cm^-2 and are therefore likely to lie near the Galactic center (D~8 kpc), and 549 less-absorbed sources that lie within <6 kc of Earth. Based on the inferred luminosities of the X-ray sources and the expected numbers of various classes of objects, we suggest that the sources with L_X < 1e33 erg/s that comprise ~90% of the catalog are cataclysmic variables, and that the ~100 brighter objects are accreting neutron stars and black holes, young isolated pulsars, and Wolf-Rayet and O stars in colliding-wind binaries. We find that the spatial distribution of X-ray sources matches that of the old stellar population observed in the infrared, which supports our suggestion that most of the X-ray sources are old cataclysmic variables. However, we find that there is an apparent excess of ~10 bright sources in the Radio Arches region. That region is already known to be the site of recent star formation, so we suggest that the bright sources in this region are young high-mass X-ray binaries, pulsars, or WR/O star binaries. We briefly discuss some astrophysical questions that this catalog can be used to address.

 

astro-ph/0601628 [abs, ps, pdf, other] :

Title: The Sloan Lens ACS Survey. III - The Structure and Formation of Early-type Galaxies and their Evolution since z~1
Authors: L.V.E. Koopmans (Kapteyn Astronomical Institute), T.Treu (UCSB), A. S. Bolton (CfA), S. Burles (MIT), L. A. Moustakas (JPL)
Comments: 19 pages, 5 figures, 1 table; submitted to ApJ, including referee's comments

(Abridged) We present a joint gravitational lensing and stellar dynamical analysis of fifteen massive field early-type galaxies, selected from the Sloan Lens (SLACS) Survey. The following numerical results are found: (i) A joint-likelihood gives an average logarithmic density slope for the total mass density of 2.01 (+0.02/-0.03) (68 perecnt C.L). inside the Einstein radius. (ii) The average position-angle difference between the light distribution and the total mass distribution is found to be 0+-3 degrees, setting an upper limit of <= 0.035 on the average external shear. (iii) The average projected dark-matter mass fraction is inferred to be 0.25+-0.06 inside R_E, using the stellar mass-to-light ratios derived from the Fundamental Plane as priors. (iv) Combined with results from the LSD Survey, we find no significant evolution of the total density slope inside one effective radius: a linear fit gives d\gamma'/dz = 0.23+-0.16 (1-sigma) for the range z=0.08-1.01. The small scatter and absence of significant evolution in the inner density slopes suggest a collisional scenario where gas and dark matter strongly couple during galaxy formation, leading to a total mass distribution that rapidly converge to dynamical isothermality.

 

astro-ph/0601629 [abs, ps, pdf, other] :

Title: Low radiative efficiency accretion at work in active galactic nuclei: the nuclear spectral energy distribution of NGC4565
Authors: M. Chiaberge, R. Gilli, F.D. Macchetto, W.B. Sparks
Comments: 6 pages, 6 figures, submitted to the Astrophysical Journal

We derive the spectral energy distribution (SED) of the nucleus of the Seyfert galaxy NGC4565. The nuclear source is substantially unabsorbed. The absorption we find from Chandra data is N_H=2.5 x 10^21 cm^-2 is consistent with that produced by material in the galactic disk of the host galaxy. HST images show a nuclear unresolved source in all of the available observations, from the near-IR H band to the optical U band. The SED is completely different from all other Seyfert galaxies, as it appears basically ``flat'' in the IR-optical region, with a small drop-off in the U-band. The extremely low Eddington ratio L_o/L_Edd and the location of the object in diagnostic planes for low luminosity AGNs indicate that the radiation we observe is most likely produced in a radiative inefficient accretion disk. This would make NGC4565 the first AGN in which an ADAF-like process is directly observed in the optical. We find that the relatively high [OIII] flux observed from the ground cannot be all produced in the nucleus. Therefore, an extended NLR must exist in this object. This may imply that the nuclear source has recently ``turned-off'', switching from a high-efficiency accretion regime to the present low-efficiency state.

 

astro-ph/0601630 [abs, ps, pdf, other] :

Title: Hosts of Type II Quasars: an HST Study
Authors: Nadia L. Zakamska (1), Michael A. Strauss (2), Julian H. Krolik (3), Susan E. Ridgway (3), Gary D. Schmidt (4), Paul S. Smith (4), Lei Hao (5), Timothy M. Heckman (3), Donald P. Schneider (6) (1 - IAS, 2 - Princeton, 3 - Johns Hopkins, 4 - UArizona, 5 - Cornell, 6 - Penn State)
Comments: 6 pages including 2 color figures; proceedings of the 'QSO host galaxies: evolution and environment' conference, Leiden, August 2005

Type II quasars are luminous Active Galactic Nuclei whose centers are obscured by large amounts of gas and dust. In this contribution we present 3-band HST images of nine type II quasars with redshifts 0.25<z<0.4 selected from the Sloan Digital Sky Survey based on their emission line properties. The intrinsic luminosities of these quasars are thought to be in the range -24>M_B>-26, but optical obscuration implies that host galaxies can be studied unencumbered by bright nuclei. Each object has been imaged in three filters (`red', `green' and `blue') placed between the strong emission lines. The spectacular, high quality images reveal a wealth of details about the structure of the host galaxies and their environments. Most galaxies in the sample are ellipticals, but strong deviations from de Vaucouleurs profiles are found, especially in the blue band. We argue that most of these deviations are due to the light from the nucleus scattered off interstellar material in the host galaxy. This scattered component can make a significant contribution to the broad-band flux and complicates the analysis of the colors of the stellar populations in the host galaxy. This extended component can be difficult to notice in unobscured luminous quasars and may bias the results of host galaxy studies.

 

astro-ph/0601631 [abs, ps, pdf, other] :

Title: On the feedback from super stellar clusters. I. The structure of giant HII regions and HII galaxies
Authors: G. Tenorio-Tagle, C. Munoz-Tunon, E. Perez, S. Silich, E. Telles
Comments: 28 pages, 10 figures, accepted for publication in the ApJ. Animated version of the models can be found at this http URL}eperez/ssc/ssc.html

We review the structural properties of giant extragalactic HII regions and HII galaxies based on 2D hydrodynamic calculations, and propose an evolutionary sequence that accounts for their observed detailed structure. The model assumes a massive and young stellar cluster surrounded by a large collection of clouds. These are thus exposed to the most important star-formation feedback mechanisms: photoionization and the cluster wind. The models show how the two feedback mechanisms compete in the disruption of clouds and lead to two different hydrodynamic solutions: The storage of clouds into a long lasting ragged shell that inhibits the expansion of the thermalized wind, and the steady filtering of the shocked wind gas through channels carved within the cloud stratum. Both solutions are claimed to be concurrently at work in giant HII regions and HII galaxies, causing their detailed inner structure. This includes multiple large-scale shells, filled with an X-ray emitting gas, that evolve to finally merge with each other, giving the appearance of shells within shells. The models also show how the inner filamentary structure of the giant superbubbles is largely enhanced with matter ablated from clouds and how cloud ablation proceeds within the original cloud stratum. The calculations point at the initial contrast density between the cloud and the intercloud media as the factor that defines which of the two feedback mechanisms becomes dominant throughout the evolution. Animated version of the models can be found at this http URL}eperez/ssc/ssc.html.

 

astro-ph/0601632 [abs, ps, pdf, other] :

Title: Observations of Magnetic Fields and Relativistic Beaming in Four Quasar Jets
Authors: D.A. Schwartz (1), H.L. Marshall (2), J.E.J. Lovell (3), D.W. Murphy (4), G.V. Bicknell (5), M. Birkinshaw (1,6), J. Gelbord (2), M. Georganopoulos (7,8), L. Godfrey (3,5), D.L. Jauncey (3), E.S. Perlman (7), D. M. Worrall (1,6) ((1) Harvard-Smithsonian Center for Astrophysics, (2) Kavli Institute MIT, (3) CSIRO Australia Telescope National Facility (4) Jet Propulsion Laboratory, (5) Australian National University, (6) University of Bristol, (7) University of Maryland-Baltimore County, (8) Goddard Space Flight Center)
Comments: Accepted for Publication in the Astrophysical Journal, Part I

We discuss the physical properties of four quasar jets imaged with the Chandra X-ray Observatory in the course of a survey for X-ray emission from radio jets. These objects have sufficient counts to study their spatially resolved properties, even in the 5 ks survey observations. We have acquired Australia Telescope Compact Array data with resolution matching Chandra. We have searched for optical emission with Magellan, with sub-arcsecond resolution. The radio to X-ray spectral energy distribution for most of the individual regions indicates against synchrotron radiation from a single-component electron spectrum. We therefore explore the consequences of assuming that the X-ray emission is the result of inverse Compton scattering on the cosmic microwave background. If particles and magnetic fields are near minimum energy density in the jet rest frames, then the emitting regions must be relativistically beamed, even at distances of order 500 kpc from the quasar. We estimate the magnetic field strengths, relativistic Doppler factors, and kinetic energy flux as a function of distance from the quasar core for two or three distinct regions along each jet. We develop, for the first time, estimates in the uncertainties in these parameters, recognizing that they are dominated by our assumptions in applying the standard synchrotron minimum energy conditions. The kinetic power is comparable with, or exceeds, the quasar radiative luminosity, implying that the jets are a significant factor in the energetics of the accretion process powering the central black hole. The measured radiative efficiencies of the jets are of order 10^(-4).

 

astro-ph/0601633 [abs, ps, pdf, other] :

Title: Spectacular Spitzer images of the Trifid Nebula: Protostars in a young, massive-star-forming region
Authors: J. Rho, W. T. Reach (Spitzer Science Center/CalTech), B. Lefloch (Laboratoire d'Astrophysique, Observatoire de Grenoble), G. Fazio (Harvard-Smithsonian Center for Astrophysics)
Comments: Accepted for publication in ApJ. Full resolution images are available at this http URL

Spitzer IRAC and MIPS images of the Trifid Nebula (M20) reveal its spectacular appearance in infrared light, highlighting the nebula's special evolutionary stage. The images feature recently-formed massive protostars and numerous young stellar objects, and a single O star that illuminates the surrounding molecular cloud from which it formed, and unveil large-scale, filamentary dark clouds. The hot dust grains show contrasting infrared colors in shells, arcs, bow-shocks and dark cores. Multiple protostars are detected in the infrared, within the cold dust cores of TC3 and TC4, which were previously defined as Class 0. The cold dust continuum cores of TC1 and TC2 contain only one protostar each. The Spitzer color-color diagram allowed us to identify ~160 young stellar objects and classify them into different evolutionary stages. The diagram also revealed a unique group of YSOs which are bright at 24 micron but have the spectral energy distribution peaking at 5-8 micron. Despite expectation that Class 0 sources would be "starless" cores, the Spitzer images, with unprecedented sensitivity, uncover mid-infrared emission from these Class 0 protostars. The mid-infrared detections of Class 0 protostars show that the emission escapes the dense, cold envelope of young protostars. The mid-infrared emission of the protostars can be fit by two temperatures of 150 and 400 K; the hot core region is probably optically thin in the mid-infrared regime, and the size of hot core is much smaller than that of the cold envelope. The presence of multiple protostars within the cold cores of Class 0 objects implies that clustering occurs at this early stage of star formation. The TC3 cluster shows that the most massive star is located at the center of the cluster and at the bottom of the gravitational-potential well.

 

astro-ph/0601634 [abs, ps, pdf, other] :

Title: Spatial Correlation Function of the Chandra Selected Active Galactic Nuclei
Authors: Y. Yang (UMCP, NASA/GSFC) R. F. Mushotzky (NASA/GSFC) A. J. Barger (U. Wisc.) L. L. Cowie (IfA, U. Hawaii)
Comments: ApJ accepted

We present the spatial correlation function analysis of non-stellar X-ray point sources in the Chandra Large Area Synoptic X-ray Survey of Lockman Hole Northwest (CLASXS). Our 9 ACIS-I fields cover a contiguous solid angle of 0.4 deg^2 and reach a depth of 3x10^-15 c.g.s in the 2-8 keV band. We supplement our analysis with data from the Chandra Deep Field North (CDFN). The addition of this field allows better probe of the correlation function at small scales. A total of 233 and 252 sources with spectroscopic information are used in the study of the CLASXS and CDFN fields respectively. We calculate both redshift-space and projected correlation functions in comoving coordinates, averaged over the redshift range of 0.1<z<3.0, for both CLASXS and CDFN fields for a standard cosmology with \Omega_{\Lambda} = 0.73, \Omega_{M} = 0.27, and H_0 = 0.71. The correlation function for the CLASXS field over scales of 3 Mpc <s< 200 Mpc can be modeled as a power-law of the form \xi(s) = (s/s_0)^{-\gamma}, with \gamma = 1.6^{+0.4}_{-0.3} and s_0 = 8.0^{+1.4}_{-1.5} Mpc. The redshift-space correlation function for CDFN on scales of 1 Mpc$<s<$~100 Mpc is found to have a similar correlation length $s_0 = 8.55^{+0.75}_{-0.74}$ Mpc, but a shallower slope ($\gamma = 1.3 \pm 0.1$). The real-space correlation functions derived from the projected correlation functions, are found to be $r_0 = 8.1^{+1.2}_{-2.2}$ Mpc, and $\gamma = 2.1 \pm 0.5$ for the CLASXS field, and $r_0 = 5.8^{+1.0}_{-1.5}$ Mpc, $\gamma = 1.38^{+0.12}_{-0.14}$ for the CDFN field. By comparing the real- and redshift-space correlation functions in the combined CLASXS and CDFN samples, we are able to estimate the redshift distortion parameter $\beta = 0.4 \pm 0.2$ at an effective redshift $z = 0.94$.(abridged)

 

astro-ph/0601635 [abs, ps, pdf, other] :

Title: Equations of General Relativistic Radiation Hydrodynamics from Tensor Formalism
Authors: Myeong-Gu Park (Kyungpook National University, KOREA)
Comments: 7 pages, no figure

Radiation interacts with matter via exchange of energy and momentum. When matter is moving with relativistic velocity or when the background spacetime is strongly curved, rigorous relativistic treatment of hydrodynamics and radiative transfer is required. Here, we derive fully general relativistic radiation hydrodynamic equations from covariant tensor formalism. The equations are easier to understand compared to previous comoving frame-based equations, and can be applied to any three-dimensional problems. Current derivation is applicable to any spacetime geometry or metric, but we limit the geometry specifically to Schwarzschild spacetime in this work and explicitly show how the hydrodynamic and radiation moment equations are derived. Some important aspects of relativistic radiation hydrodynamics, for example, the distinction between radiation moments defined in different frames, are discussed as well as one reasonable form of Eddington factor that closes the radiation moment equations.

 

astro-ph/0601636 [abs, ps, pdf, other] :

Title: First Attempt at Spectroscopic Detection of Gravity Modes in a Long-Period Pulsating Subdwarf B Star -- PG 1627+017
Authors: B.-Q. For, E.M. Green, D. O'Donoghue, L.L. Kiss, S.K. Randall, G. Fontaine, A.P. Jacob, S.J. O'Toole, E.A. Hyde, T.R. Bedding
Comments: 39 pages, 9 figures, 4 tables, ApJ accepted. See postscript for full abtract

In the first spectroscopic campaign for a PG 1716 variable (or long-period pulsating subdwarf B star), we succeeded in detecting velocity variations due to g-mode pulsations at a level of 1.0-1.5 km/s.The observations were obtained during 40 nights on 2-m class telescopes in Arizona, South Africa,and Australia. The target,PG1627+017, is one of the brightest and largest amplitude stars in its class.It is also the visible component of a post-common envelope binary.Our final radial velocity data set includes 84 hours of time-series spectroscopy over a time baseline of 53 days. Our derived radial velocity amplitude spectrum, after subtracting the orbital motion, shows three potential pulsational modes 3-4 sigma above the mean noise level, at 7201.0s,7014.6s and 7037.3s.Only one of the features is statistically likely to be real,but all three are tantalizingly close to, or a one day alias of, the three strongest periodicities found in the concurrent photometric campaign. We further attempted to detect pulsational variations in the Balmer line amplitudes. The single detected periodicity of 7209 s, although weak, is consistent with theoretical expectations as a function of wavelength.Furthermore, it allows us to rule out a degree index of l= 3 or l= 5 for that mode. Given the extreme weakness of g-mode pulsations in these stars,we conclude that anything beyond simply detecting their presence will require larger telescopes,higher efficiency spectral monitoring over longer time baselines,improved longitude coverage, and increased radial velocity precision.

 

astro-ph/0601637 [abs, ps, pdf, other] :

Title: ELT requirements for future observations of the Intergalactic Medium
Authors: Tom Theuns (ICC, Durham University and Dept of Physics, Antwerp University), Raghunathan Srianand (IUCAA)
Comments: proceedings IAU 232 "Extremely Large Telescopes", eds Whitelock, Leibundgut and Dennefeld, comments welcome

We summarise the science cases for an ELT that were presented in the parallel session on the intergalactic medium, and the open discussion that followed the formal presentations. Observations of the IGM with an ELT provides tremendous potential for dramatic improvements in current programmes in a very wide variety of subjects. These range from fundamental physics (expansion of the Universe, nature of the dark matter, variation of physical constants), cosmology (geometry of the Universe, large-scale structure), reionisation (ionisation state of the IGM at high redshift>6, to more traditional astronomy, such as the interactions between galaxies and the IGM (metal enrichment, galactic winds and other forms of feedback), and the study of the interstellar medium in high redshift galaxies through molecules. The requirements on ELTs and their instruments for fulfilling this potential are discussed.

 

astro-ph/0601638 [abs, ps, pdf, other] :

Title: Tracing the Mass-Assembly History of Galaxies with Deep Surveys
Authors: Georg Feulner (1,2), Armin Gabasch (1,2), Yuliana Goranova (1,2), Ulrich Hopp (1,2), Ralf Bender (1,2) ((1) Universitaets-Sternwarte Muenchen, (2) Max-Planck-Institut fuer extraterrestrische Physik, Garching)
Comments: 3 pages, 2 figures; contribution to the proceedings of the conference on "Relativistic Astrophysics and Cosmology - Einstein's Legacy" held in Munich, Germany, November 7-11 2005; to be published in the ESO Astrophysics Symposia (Springer)

We use the optical and near-infrared galaxy samples from the Munich Near-Infrared Cluster Survey (MUNICS), the FORS Deep Field (FDF) and GOODS-S to probe the stellar mass assembly history of field galaxies out to z ~ 5. Combining information on the galaxies' stellar mass with their star-formation rate and the age of the stellar population, we can draw important conclusions on the assembly of the most massive galaxies in the universe: These objects contain the oldest stellar populations at all redshifts probed. Furthermore, we show that with increasing redshift the contribution of star-formation to the mass assembly for massive galaxies increases dramatically, reaching the era of their formation at z ~ 2 and beyond. These findings can be interpreted as evidence for an early epoch of star formation in the most massive galaxies in the universe.

 

astro-ph/0601639 [abs, ps, pdf, other] :

Title: The stellar populations of E and S0 galaxies as seen with SAURON
Authors: H. Kuntschner, E. Emsellem, R. Bacon, M. Bureau, M. Cappellari, R. L. Davies, P. T. de~Zeeuw, J. Falcon-Barroso, D. Krajnovic, R. M. McDermid, R. F. Peletier, M. Sarzi
Comments: 5 pages, 4 figures, to appear in "Science Perspectives for 3D Spectroscopy", eds. M. Kissler-Patig, M. M. Roth and J. R. Walsh, ESO Astrophysics Symposia

We present selected results from integral-field spectroscopy of 48 early-type galaxies observed as part of the SAURON survey. Maps of the Hbeta, Fe5015, Mgb and Fe5270 indices in the Lick/IDS system were derived for each of the survey galaxies. The metal line strength maps show generally negative gradients with increasing radius roughly consistent with the morphology of the light profiles. Remarkable deviations from this general trend exist, particularly the Mgb isoindex contours appear to be flatter than the isophotes of the surface brightness for about 40% of our galaxies without significant dust features. Generally these galaxies exhibit significant rotation. We infer from this that the fast-rotating component features a higher metallicity and/or an increased Mg/Fe ratio as compared to the galaxy as a whole. We also use the line strengths maps to compute average values integrated over circular apertures of one effective radius, and derive luminosity weighted ages and metallicities. The lenticular galaxies show a wide range in age and metallicity estimates, while elliptical galaxies tend to occupy regions of older stellar populations.

 

astro-ph/0601640 [abs, ps, pdf, other] :

Title: An HLLC Solver for Relativistic Flows -- II. Magnetohydrodynamics
Authors: A. Mignone, G. Bodo
Comments: 17 pages, 12 figures

An approximate Riemann solver for the equations of relativistic magnetohydrodynamics (RMHD) is derived. The HLLC solver, originally developed by Toro, Spruce and Spears, generalizes the algorithm described in a previous paper (Mignone & Bodo 2004) to the case where magnetic fields are present. The solution to the Riemann problem is approximated by two constant states bounded by two fast shocks and separated by a tangential wave. The scheme is Jacobian-free, in the sense that it avoids the expensive characteristic decomposition of the RMHD equations and it improves over the HLL scheme by restoring the missing contact wave.
Multidimensional integration proceeds via the single step, corner transport upwind (CTU) method of Colella, combined with the contrained tranport (CT) algorithm to preserve divergence-free magnetic fields. The resulting numerical scheme is simple to implement, efficient and suitable for a general equation of state. The robustness of the new algorithm is validated against one and two dimensional numerical test problems.

 

astro-ph/0601641 [abs, ps, pdf, other] :

Title: INTEGRAL observations of the Crab pulsar
Authors: T.Mineo, C.Ferrigno, L.Foschini, A.Segreto, G.Cusumano, G.Malaguti, G.Di Cocco, C.Labanti
Comments: 10 pages, 7 figures, accepted by Astronomy and Astrophysics

The paper presents the timing and spectral analysis of several observations of the Crab pulsar performed with INTEGRAL in the energy range 3-500 keV. All these observations, when summed together provide a high statistics data set which can be used for accurate phase resolved spectroscopy. A detailed study of the pulsed emission at different phase intervals is performed. The spectral distribution changes with phase showing a characteristic reverse S shape of the photon index. Moreover the spectrum softens with energy, in each phase interval, and this behavior is adequately modeled over the whole energy range 3-500 keV with a single curved law with a slope variable with Log(E), confirming the BeppoSAX results on the curvature of the pulsed emission. The bending parameter of the log-parabolic model is compatible with a single value of 0.14+/-0.02 over all phase intervals. Results are discussed within the three-dimensional outer gap model.

 

astro-ph/0601642 [abs, ps, pdf, other] :

Title: Smoothed Particle Hydrodynamics coupled with Radiation Transfer
Authors: Hajime Susa
Comments: 19pages, 10figures, PASJ accepted

We have been constructed a brand-new radiation hydrodynamics solver based upon Smoothed Particle Hydrodynamics (SPH), which works on parallel computer system. The code is designed to investigate the formation and evolution of the first generation objects at $z \gtrsim 10$, where the radiative feedback from various sources play important roles. The code can compute the fraction of chemical species e, H$^+$, H,
H$^-$, H$_2$, and H$_2^+$ by fully implicit time integration. It also can deal with multiple sources of ionizing radiation, as well as the radiation at Lyman-Werner band. We compare the results for a few test calculations with the results of one dimensional simulations, in which we find good agreements with each other.
We also evaluate the speedup by parallelization, that is found to be almost ideal, as far as the number of sources is comparable to the number of processors.

 

astro-ph/0601643 [abs, ps, pdf, other] :

Title: Radial velocity measurements of B stars in the Scorpius-Centaurus association
Authors: E. Jilinski, S. Daflon, K.Cunha, R. de la Reza
Comments: accepted for publication in A&A

We derive single-epoch radial velocities for a sample of 56 B-type stars members of the subgroups Upper Scorpius, Upper Centaurus Lupus and Lower Centaurus Crux of the nearby Sco-Cen OB association. The radial velocity measurements were obtained by means of high-resolution echelle spectra via analysis of individual lines. The internal accuracy obtained in the measurements is estimated to be typically 2-3 km/s, but depends on the projected rotational velocity of the target. Radial velocity measurements taken for 2-3 epochs for the targets HD120307, HD142990 and HD139365 are variable and confirm that they are spectroscopic binaries, as previously identified in the literature. Spectral lines from two stellar components are resolved in the observed spectra of target stars HD133242, HD133955 and HD143018, identifying them as spectroscopic binaries.

 

astro-ph/0601644 [abs, ps, pdf, other] :

Title: INTEGRAL survey of the Cassiopeia region in hard X rays
Authors: P.R. den Hartog (1), W. Hermsen (1,2), L. Kuiper (1), J. Vink (3,1), J.J.M. in 't Zand (1,3), W. Collmar (4) ((1) SRON Netherlands Institute for Space Research (2) University of Amsterdam (3) University of Utrecht (4) MPE)
Comments: 16 pages, 13 figures, accepted for publication in A&A

We report on the results of a deep 1.6 Ms INTEGRAL observation of the Cassiopeia region performed from December 2003 to February 2004. Eleven sources were detected with the imager IBIS-ISGRI at energies above 20 keV, including three new hard X-ray sources. Most remarkable is the discovery of hard X-ray emission from the anomalous X-ray pulsar 4U 0142+61, which shows emission up to \~150 keV with a very hard power-law spectrum with photon index Gamma = 0.73 +/- 0.17. We derived flux upper limits for energies between 0.75 MeV and 30 MeV using archival data from the Compton telescope COMPTEL. In order to reconcile the very hard spectrum of 4U 0142+61 measured by INTEGRAL with the COMPTEL upper limits, the spectrum has to bend or break between ~75 keV and ~750 keV. 1E 2259+586, another anomalous X-ray pulsar in this region, was not detected. INTEGRAL and COMPTEL upper limits are provided. The new INTEGRAL sources are IGR J00370+6122 and IGR J00234+6144. IGR J00370+6122 is a new supergiant X-ray binary with an orbital period of 15.665 +/- 0.006 days, derived from RXTE All-Sky Monitor data. Archival BeppoSAX Wide-Field Camera data yielded four more detections. IGR J00234+6144 still requires a proper identification. Other sources for which INTEGRAL results are presented are high-mass X-ray binaries 2S 0114+650, Gamma~Cas, RX J0146.9+6121 and 4U 2206+54, intermediate polar V709 Cas and 1ES 0033+595, an AGN of the BL-Lac type. For each of these sources the hard X-ray spectra are fitted with different models and compared with earlier published results.

 

astro-ph/0601645 [abs, ps, pdf, other] :

Title: The Uncertainties in the 22Ne + alpha-capture Reaction Rates and the Production of the Heavy Magnesium Isotopes in Asymptotic Giant Branch Stars of Intermediate Mass
Authors: A. Karakas, M. Lugaro, M. Wiescher, J. Goerres, C. Ugalde
Comments: 38 pages, 10 figures, 6 tables, Accepted to ApJ

We present new rates for the 22Ne(alpha, n)25Mg and 22Ne(alpha,gamma)26Mg reactions, with uncertainties that have been considerably reduced compared to previous estimates, and we study how these new rates affect the production of the heavy magnesium isotopes in models of intermediate mass Asymptotic Giant Branch (AGB) stars of different initial compositions. All the models have deep third dredge-up, hot bottom burning and mass loss. Calculations have been performed using the two most commonly used estimates of the 22Ne + alpha rates as well as the new recommended rates, and with combinations of their upper and lower limits. The main result of the present study is that with the new rates, uncertainties on the production of isotopes from Mg to P coming from the 22Ne + alpha-capture rates have been considerably reduced. We have therefore removed one of the important sources of uncertainty to effect models of AGB stars. We have studied the effects of varying the mass-loss rate on nucleosynthesis and discuss other uncertainties related to the physics employed in the computation of stellar structure, such as the modeling of convection, the inclusion of a partial mixing zone and the definition of convective borders. These uncertainties are found to be much larger than those coming from 22Ne + alpha-capture rates, when using our new estimates. Much effort is needed to improve the situation for AGB models.

 

astro-ph/0601646 [abs, ps, pdf, other] :

Title: On the Decoherence of Primordial Fluctuations During Inflation
Authors: C.P. Burgess, R. Holman, D. Hoover
Comments: 31 pages, 1 figure

We study the process whereby quantum cosmological perturbations become classical within inflationary cosmology. By setting up a master-equation formulation we show how quantum coherence for super-Hubble modes can be destroyed by their coupling to the environment provided by sub-Hubble modes. We identify what features the sub-Hubble environment must have in order to decohere the longer wavelengths, and identify how the onset of decoherence (and how long it takes) depends on the properties of the sub-Hubble physics which forms the environment. Our results show that the decoherence process is largely insensitive to the details of the coupling between the sub- and super-Hubble scales. They also show how locality implies, quite generally, that the decohered density matrix at late times is diagonal in the field representation (as is implicitly assumed by extant calculations of inflationary density perturbations). Our calculations also imply that decoherence can arise even for couplings which are as weak as gravitational in strength.

 

astro-ph/0601647 [abs, ps, pdf, other] :

Title: Search for and investigation of new stellar clusters using the data from huge stellar catalogues
Authors: Sergey Koposov, Elena Glushkova, Ivan Zolotukhin
Comments: Proceedings of the 79th Annual Scientific Meeting of the Astronomische Gesellschaft, Cologne(Germany), September 2005
Journal-ref: Astron. Nachr. / AN 326, No. 7, 597 (2005)

We present new automatic methods of search for star clusters using the data available in new huge stellar catalogues. Using 2MASS catalogue we have discovered over ten new open clusters in the region of Galaxy anticenter and determined their physical parameters.

 

astro-ph/0601648 [abs, ps, pdf, other] :

Title: Dynamical Evolution of the TW Hya Association
Authors: R. de la Reza, E. Jilinski, V. G. Ortega
Comments: Accepted to Astronomical Journal

Using Galactic dynamics we have determined the age of the low mass post-T Tauri stars TW Hya Association (TWA). To do so we applied the method of Ortega et al.(2002, 2004) to five stars of the association with Hipparcos measured distances (TWA 1, TWA 4,TWA 9,TWA 11,TWA 19).The method is based on the calculation of the past 3D orbits of the stars. Of these stars only TWA 9 presents a quite different orbit so that it does not appear to be a dynamical member of TWA. The four remaining stars have a first maximum orbits' confinement at the age of -8.3 $\pm{0.8}$ Myr which is considered the dynamical age of TWA. This confinement fixes the probable 3D forming region of TWA with a mean radius of 14.5 pc. This region is related to the older subgroups of the Sco-Cen OB association, Lower Centaurus Crux (LCC) and Upper Centaurus Lupus (UCL), both with a mean age of about 18 Myr. This dynamical age of TWA and that of the $\beta$ Pic Moving Group (BPMG) with an age of 11 Myr, also discussed here, introduce a more precise temporal scale for studies of disks evolution and planetary formation around some stars of these associations. Using the retraced orbit of the runaway star HIP 82868 we examine the possibility that the formation of TWA was triggered by a supernova (SN) explosion. It is shown that for the four considered TWA stars, the expansion in volume is a factor of five since their origin to the present state. This is mainly due to the presently more distant star TWA 19.

 

astro-ph/0601649 [abs, ps, pdf, other] :

Title: Near-infrared observations of water-ice in OH/IR stars
Authors: K. Justtanont, G. Olofsson, C. Dijkstra, A.W. Meyer
Comments: 10 pages, 6 figures : accepted for publication in A&A

A search for the near-infrared water-ice absorption band was made in a number of very red OH/IR stars which are known to exhibit the 10um silicate absorption. As a by-product, accurate positions of these highly reddened objects are obtained. We derived a dust mass loss rate for each object by modelling the spectral energy distribution and the gas mass loss rate by solving the equation of motion for the dust drag wind. The derived mass loss rates show a strong correlation with the silicate optical depth as well as that of the water-ice. The stars have a high mass loss rate (> 1.0E-4 Msun/yr) with an average gas-to-dust mass ratio of 110. In objects which show the 3.1um water-ice absorption, the near-IR slope is much steeper than those with no water-ice. Comparison between our calculated mass loss rates and those derived from OH and CO observations indicates that these stars have recently increased their mass loss rates.

 

astro-ph/0601650 [abs, ps, pdf, other] :

Title: A KOSMA 7 deg^2 13CO 2--1 & 12CO 3--2 survey of the Perseus cloud
Authors: K. Sun, C. Kramer, V. Ossenkopf, F. Bensch, J. Stutzki, M. Miller
Comments: 11 pages, 10 figures, accepted by A&A

Characterizing the spatial and velocity structure of molecular clouds is a first step towards a better understanding of interstellar turbulence and its link to star formation. We present observations and structure analysis results for a large-scale (~ 7.10 deg^2) 13CO J = 2--1 and 12 CO J = 3--2 survey towards the nearby Perseus molecular cloud observed with the KOSMA 3m telescope. We study the spatial structure of line-integrated and velocity channel maps, measuring the $\Delta$-variance as a function of size scale. We determine the spectral index $\beta$ of the corresponding power spectrum and study its variation across the cloud and across the lines. We find that the spectra of all CO line-integrated maps of the whole complex show the same index, $\beta$ ~ 3.1, for scales between about 0.2 and 3pc, independent of isotopomer and rotational transition. A complementary 2MASS map of optical extinction shows a noticeably smaller index of 2.6. In contrast to the overall region, the CO maps of individual subregions show a significant variation of $\beta$. The 12CO 3--2 data provide e.g. a spread of indices between 2.9 in L1455 and 3.5 in NGC1333. In general, active star forming regions show a larger power-law exponent. We find that the $\Delta$-variance spectra of individual velocity channel maps are very sensitive to optical depth effects clearly indicating self-absorption in the densest regions. When studying the dependence of the channel-map spectra as a function of the velocity channel width, the expected systematic increase of the spectral index with channel width is only detected in the blue line wings.This could be explained by a filamentary, pillar-like structure which is left at low velocities while the overall molecular gas is swept up by a supernova shock wave.

 

astro-ph/0601651 [abs, ps, pdf, other] :

Title: XMM-Newton observations of the brightest Ultraluminous X-ray sources
Authors: A-M. Stobbart, T. P. Roberts, J. Wilms
Comments: 17 pages, 3 figures, accepted for publication in MNRAS

We present an analysis of 13 of the best quality EPIC ULX datasets. We utilise the high signal-to-noise in these ULX spectra to investigate the best descriptions of their spectral shape in the 0.3-10 keV range. Simple models of an absorbed power-law or multicolour disc blackbody prove inadequate at describing the spectra. Better fits are found using a combination of these two components, with both variants of this model - a cool (0.2 keV) disc blackbody plus hard power-law continuum, and a soft power-law continuum plus a warm (1.7 keV) disc blackbody - providing good fits to 8/13 ULX spectra. However, by examining the data above 2 keV, we find evidence for curvature in the majority of datasets, inconsistent with the dominance of a power-law in this regime. The most successful empirical description of the spectra proved to be a combination of a cool (0.2 keV) classic blackbody spectrum, plus a warm disc blackbody (good fits to 10/13 ULX spectra). The best overall fits are provided by a physically self-consistent accretion disc plus Comptonised corona model (diskpn + eqpair), which fits acceptably to 11/13 ULXs. This model provides a physical explanation for the spectral curvature, namely that it originates in an optically-thick corona, though the accretion disc photons seeding this corona still originate in an apparently cool disc. We note similarities between this fit and models of Galactic black hole binaries at high accretion rates. We conclude that this analysis of the best spectral data for ULXs shows it to be plausible that the majority of the population are high accretion rate stellar-mass (perhaps up to 80-Msun) black holes, though we cannot categorically rule out the presence of larger, 1000-Msun intermediate-mass black holes (IMBHs) in individual sources with the current X-ray data.

 

astro-ph/0601652 [abs, ps, pdf, other] :

Title: MeV-GeV emission from neutron-loaded short gamma-ray burst jets
Authors: Soebur Razzaque, Peter Meszaros
Comments: 10 pages, 1 figure

Recent discovery of the afterglow emission from short gamma-ray bursts suggests that binary neutron star or black hole-neutron star binary mergers are the likely progenitors of these short bursts. The accretion of neutron star material and its subsequent ejection by the central engine implies a neutron-rich outflow. We consider here a neutron-rich relativistic jet model of short bursts, and investigate the high energy neutrino and photon emission as neutrons and protons decouple from each other. We find that upcoming neutrino telescopes are unlikley to detect the 50 GeV neutrinos expected in this model. For bursts at z~0.1, we find that GLAST and ground-based Cherenkov telescopes should be able to detect prompt 100 MeV and 100 GeV photon signatures, respectively, which may help test the neutron star merger progenitor identification.

 

astro-ph/0601653 [abs, ps, pdf, other] :

Title: The Warped HI Layer of the Outer Galaxy
Authors: Tom Voskes (1), W. Butler Burton (1 and 2) ((1) Leiden University Observatory, (2) National Radio Astronomy Observatory)
Comments: 44 pages, no figures. Version with figures available at this ftp URL . M.Sc. thesis prepared by Tom Voskes at the University of Leiden, under supervision of W.B. Burton

Using the Leiden/Dwingeloo Survey (Hartmann & Burton 1997) of the Galactic sky north of declination -30 degrees as the principal component of a composite data cube, the structure of the warped HI layer of the outer Galaxy was displayed by converting the data cube from heliocentric (l,b,v) coordinates to galactocentric (R,theta,z) coordinates. We masked out known high-velocity-cloud complexes that might otherwise have contaminated the resulting description of the warped layer. We considered analogous displays under controlled circumstances by using as input medium a simulation of the same complete (l,b,v) data cube corresponding to a modeled HI Galaxy of known morphology and kinematics. By varying this artificial input we were able to check our method of converting the data cube and to put constraints on the global parameters that have been used to explain different asymmetries in the heliocentric data.

 

---