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Astrophysics

astro-ph new abstracts, Fri, 10 Mar 06 01:00:07 GMT
0603205 -- 0603250 received

astro-ph/0603205 [abs, ps, pdf, other] :

Title: A New Robust Low-Scatter X-ray Mass Indicator for Clusters of Galaxies
Authors: Andrey V. Kravtsov (1,2), Alexey Vikhlinin (3,4), Daisuke Nagai (5), ((1) U. Chicago; (2) KICP, EFI; (3) SAO, Harvard, (4) IKI, Moscow; (5) Caltech)
Comments: submitted to ApJ; 9 pages, 6 figures, uses emulateapj

We present comparison of X-ray proxies for the total cluster mass, including the spectral temperature (Tx), gas mass measured within r500 (Mg), and the new proxy, Yx, which is a simple product of Tx and Mg and is related to the total thermal energy of the ICM. We use mock Chandra images constructed for a sample of clusters simulated with the eulerian N-body+gasdynamics adaptive mesh refinement ART code in the concordance LCDM cosmology. The simulations achieve high spatial and mass resolution and include radiative cooling, star formation, and other processes accompanying galaxy formation. Our analysis shows that simulated clusters exhibit a high degree of regularity and tight correlations between the considered observables and total mass. The normalizations of the M-Tx, Mg-Tx, and M-Yx relations agree to better than 10-15% with the current observational measurements of these relations. Our results show that Yx is the best mass proxy with a remarkably low scatter of only ~5-7% in M500 for a fixed Yx, at both low and high redshifts and regardless of whether clusters are relaxed or not. In addition, we show that redshift evolution of the Yx-M500 relation is close to the self-similar prediction, which makes Yx a very attractive mass indicator for measurements of the cluster mass function from X-ray selected samples.

 

astro-ph/0603206 [abs, ps, pdf, other] :

Title: Cosmological Parameters and Cosmic Topology
Authors: M.J. Reboucas, J.S. Alcaniz
Comments: 6 pages, 3 figures, mn2e style

Geometry constrains but does not dictate the topology of the 3--dimensional space. In a locally spatially homogeneous and isotropic universe, however, the topology of its spatial section dictates its geometry. We show that, besides determining the geometry, the knowledge of the spatial topology through the circles--in--the--sky offers an effective way of setting constraints on the density parameters associated with dark matter ($\Omega_m$) and dark energy ($\Omega_{\Lambda}$). By assuming the Poincar\'e dodecahedral space as the circles--in--the--sky detectable topology of the spatial sections of the Universe, we re-analyze the constraints on the density parametric plane $\Omega_{m}$--$ \Omega_{\Lambda} $ from the current type Ia supenovae (SNe Ia) plus X-ray gas mass fraction data, and show that a circles--in--the sky detection of the dodecahedral space topology give rise to strong and complementary constraints on the region of the density parameter plane currently allowed by these observational data sets.

 

astro-ph/0603207 [abs, ps, pdf, other] :

Title: The XMM-Newton view of GRS1915+105 during a "plateau"
Authors: Andrea Martocchia (CESR, OAS), Giorgio Matt, Tomaso Belloni, Marco Feroci, Vladimir Karas, Gabriele Ponti
Comments: 5 pages, 3 figures, 1 table. Submitted
Journal-ref: Proceedings of the Albert Einstein Century International Conference, held in Paris, France, July 18-22, 2005 (2006) 000

Two XMM-Newton observations of the black-hole binary GRS1915+105 were triggered in 2004 (April 17 and 21), during a long "plateau" state of the source. We analyzed the data collected with EPIC-pn in Timing and Burst modes, respectively. No thermal disc emission is required by the data; the spectrum is well fitted by four components: a primary component (either a simple power law or thermal Comptonization) absorbed by cold matter with abundances different than those of standard ISM; reprocessing from an ionized disc; emission and absorption lines; and a soft X-ray excess around 1 keV. The latter is not confirmed by RGS (which were used in the second observation only); if real, the excess could be due to reflection from the optically thin, photoionized plasma of a disc wind, in which case it may provide a way to disentangle intrinsic from interstellar absorption. Indeed, the former is best traced by the higher abundances of heavier elements, while an independent estimate of the latter may be given by the value we get for the disc wind component only, which roughly coincides with what is found for lower-Z species.

 

astro-ph/0603208 [abs, ps, pdf, other] :

Title: The Cosmic Infrared Background Resolved by Spitzer. Contributions of Mid-Infrared Galaxies to the Far-Infrared Background
Authors: Herve Dole, Guilaine Lagache, Jean-Loup Puget, Karina I. Caputi, Nestor Fernandez-Conde, Emeric Le Floc'h, Casey Papovich, Pablo G. Perez-Gonzalez, George H. Rieke, Myra Blaylock
Comments: A&A, in press. 14 pages, 14 figures. Best resolution file: this http URL (2.3M)

Aims. We quantify the contributions of 24um galaxies to the Far-Infrared (FIR) Background at 70 and 160um. We provide new estimates of the Cosmic Infrared Background (CIB), and compare it with the Cosmic Optical Background (COB). Methods. Using Spitzer data at 24, 70 and 160um in three deep fields, we stacked more than 19000 MIPS 24um sources with S24>60uJy at 70 and 160um, and measured the resulting FIR flux densities. Results. This method allows a gain up to one order of magnitude in depth in the FIR. We find that the Mid-Infrared (MIR) 24um selected sources contribute to more than 70% of the CIB at 70 and 160um. This is the first direct measurement of the contribution of MIR-selected galaxies to the FIR CIB. Galaxies contributing the most to the total CIB are thus z~1 luminous infrared galaxies, which have intermediate stellar masses. We estimate that the CIB will be resolved at 0.9 mJy at 70 and 3 mJy at 160um. By combining the extrapolation of the 24um source counts below 60uJy, with 160/24 and 70/24 colors as measured with the stacking analysis, we obtain lower limits of 7.1+/-1.0 and 13.4+/-1.7 nW/m2/sr for the CIB at 70 and 160um, respectively. Conclusions. The MIPS surveys have resolved more than three quarters of the MIR and FIR CIB. By carefully integrating the Extragalactic Background Light (EBL) SED, we also find that the CIB has the same brightness as the COB, around 24 nW/m2/sr. The EBL is produced on average by 115 infrared photons for one visible photon. Finally, the galaxy formation and evolution processes emitted a brightness equivalent to 5% of the primordial electromagnetic background (CMB).

 

astro-ph/0603209 [abs, ps, pdf, other] :

Title: Galaxy Formation and Dark Matter
Authors: Joseph Silk
Comments: To be published in "The Invisible Universe: Dark Matter and Dark Energy", proceedings of the Third Aegean Summer School, Chios, 26 September-1 October, 2005

The challenge of dark matter may be addressed in two ways; by studying the confrontation of structure formation with observation and by direct and indirect searches. In this review, I will focus on those aspects of dark matter that are relevant for understanding galaxy formation, and describe the outlook for detecting the most elusive component, non-baryonic dark matter. Galaxy formation theory is driven by phenomenology and by numerical simulations of dark matter clustering under gravity. Once the complications of star formation are incorporated, the theory becomes so complex that the brute force approach of numerical simulations needs to be supplemented by incorporation of such astrophysical processes as feedback by supernovae and by active galactic nuclei. I present a few semi-analytical perspectives that may shed some insight into the nature of galaxy formation.

 

astro-ph/0603210 [abs, ps, pdf, other] :

Title: High-frequency Quasi-Periodic Oscillations from GRS 1915+105 in its C state
Authors: T. Belloni (INAF-OABrera), P. Soleri (Univ. Amsterdam), P. Casella (Univ. Amsterdam), M. Mendez (SRON Utrecht), S. Migliari (UCSD)
Comments: 7 pages, 8 figures, accepted for publication on MNRAS

We report the results of a systematic timing analysis of RXTE observations of GRS 1915+105 when the source was in its variability class theta, characterized by alternating soft and hard states on a time scale of a few hundred seconds. The aim was to examine the high-frequency part of the power spectrum in order to confirm the hecto-Hertz Quasi-Periodic Oscillations (QPO) previously reported from observations from mixed variability behaviours. During the hard intervals (corresponding to state C in the classification of Belloni et al., 2000, A&A, 35, 271), we find a significant QPO at a frequency of ~170 Hz, although much broader (Q~2) than previously reported. No other significant peak is observed at frequencies >30 Hz. A time-resolved spectral analysis of selected observations shows that the hard intervals from class theta show a stronger and steeper (Gamma=2.8-3.0) power-law component than hard intervals from other classes. We discuss these results in the framework of hecto-Hertz QPOs reported from GRS 1915+105 and other black-hole binaries.

 

astro-ph/0603211 [abs, ps, pdf, other] :

Title: Simulations of relativistic collisionless shocks: shock structure and particle acceleration
Authors: Anatoly Spitkovsky (KIPAC, Stanford University)
Comments: 6 pages, invited talk at "Astrophysical Sources of High Energy Particles and Radiation," Torun, June 20 - 24, 2005
Journal-ref: AIP Conf. Proc. 801 (2005), 345-350

We discuss 3D simulations of relativistic collisionless shocks in electron-positron pair plasmas using the particle-in-cell (PIC) method. The shock structure is mainly controlled by the shock's magnetization ("sigma" parameter). We demonstrate how the structure of the shock varies as a function of sigma for perpendicular shocks. At low magnetizations the shock is mediated mainly by the Weibel instability which generates transient magnetic fields that can exceed the initial field. At larger magnetizations the shock is dominated by magnetic reflections. We demonstrate where the transition occurs and argue that it is impossible to have very low magnetization collisionless shocks in nature (in more than one spatial dimension). We further discuss the acceleration properties of these shocks, and show that higher magnetization perpendicular shocks do not efficiently accelerate nonthermal particles in 3D. Among other astrophysical applications, this may pose a restriction on the structure and composition of gamma-ray bursts and pulsar wind outflows.

 

astro-ph/0603212 [abs, ps, pdf, other] :

Title: Pulsar electrodynamics: a time-dependent view
Authors: Anatoly Spitkovsky (KIPAC, Stanford University)
Comments: 6 pages, invited talk at "Astrophysical Sources of High Energy Particles and Radiation," Torun, June 20 - 24, 2005
Journal-ref: AIP Conf. Proc. 801 (2005), 253-258

Pulsar spindown forms a reliable yet enigmatic prototype for the energy loss processes in many astrophysical objects including accretion disks and back holes. In this paper we review the physics of pulsar magnetospheres, concentrating on recent developments in force-free modeling of the magnetospheric structure. In particular, we discuss a new method for solving the equations of time-dependent force-free relativistic MHD in application to pulsars. This method allows to dynamically study the formation of the magnetosphere and its response to perturbations, opening a qualitatively new window on pulsar phenomena. Applications of the method to other magnetized rotators, such as magnetars and accretion disks, are also discussed.

 

astro-ph/0603213 [abs, ps, pdf, other] :

Title: Comments on "Dark matter: A phenomenological existence proof"
Authors: R. G. Vishwakarma
Comments: 5 pages

A recent paper by Ahluwalia-Khalilova (astro-ph/0601489) is examined where he claims that the standard FRW cosmology with a $\Lambda$ predicts existence of dark matter without invoking the data on galactic rotation curves and gravitational lensing. However, we find that his claims are not correct. He has already assumed (without realizing) in the very outset what he wants to prove.

 

astro-ph/0603214 [abs, ps, pdf, other] :

Title: On the Orbits and Masses of the Satellites of the Pluto-Charon System
Authors: Man Hoi Lee, S. J. Peale (UCSB)
Comments: 24 pages, including 11 figures; uses AASTeX; submitted to Icarus

(Abridged) The orbits of the recently discovered satellites of Pluto, S/2005 P2 and S/2005 P1, are significantly non-Keplerian, even if P2 and P1 have negligible masses, because the mass ratio of Charon-Pluto is ~0.1. We present an analytic theory with P2 and P1 treated as test particles. This analytic theory shows that the azimuthal periods of P2 and P1 are shorter than the Keplerian orbital periods and that the periapse and ascending node precess at nearly equal rates in opposite directions for P2 and P1. The deviation from Kepler's third law is already detected in the unperturbed Keplerian fit of Buie and coworkers. We also present direct numerical orbit integrations with different assumed masses for P2 and P1 within the ranges allowed by the albedo uncertainties. If the albedos are as high as that of Charon, the masses of P2 and P1 are sufficiently low that their orbits are well described by the analytic theory. There is at present no evidence that P2 has any significant epicyclic eccentricity. However, the orbit of P1 has a significant epicyclic eccentricity, and its prograde periapse precession with a period of 5300 days should be easily detectable. If the albedos are as low as that of comets, the large inferred masses induce significant variations in the epicyclic eccentricities and/or periapse longitudes on the 400-500-day timescales, due to the proximity of P2 and P1 to the 3:2 mean-motion commensurability. In fact, for the maximum inferred masses, P2 and P1 may be in the 3:2 mean-motion resonance, with the resonance variable involving the periapse longitude of P1 librating. Observations that sample the orbits of P2 and P1 well on the 400- 500-day timescales should provide strong constraints on the masses of P2 and P1 in the near future.

 

astro-ph/0603215 [abs, ps, pdf, other] :

Title: Chemical abundances for Hf 2-2, a planetary nebula with the strongest known heavy element recombination lines
Authors: X.-W. Liu, M. J. Barlow, Y. Zhang, R. J. Bastin, P. J. Storey
Comments: 12 pages, 5 figures, accepted for publication in the Monthly Notices of the Royal Astronomical Society

We present high quality optical spectroscopic observations of the planetary nebula (PN) Hf 2-2. The spectrum exhibits many prominent optical recombination lines (ORLs) from heavy element ions. Analysis of the H {\sc i} and He {\sc i} recombination spectrum yields an electron temperature of $\sim 900$ K, a factor of ten lower than given by the collisionally excited [O {\sc iii}] forbidden lines. The ionic abundances of heavy elements relative to hydrogen derived from ORLs are about a factor of 70 higher than those deduced from collisionally excited lines (CELs) from the same ions, the largest abundance discrepancy factor (adf) ever measured for a PN. By comparing the observed O {\sc ii} $\lambda$4089/$\lambda$4649 ORL ratio to theoretical value as a function of electron temperature, we show that the O {\sc ii} ORLs arise from ionized regions with an electron temperature of only $\sim 630$ K. The current observations thus provide the strongest evidence that the nebula contains another previously unknown component of cold, high metallicity gas, which is too cool to excite any significant optical or UV CELs and is thus invisible via such lines. The existence of such a plasma component in PNe provides a natural solution to the long-standing dichotomy between nebular plasma diagnostics and abundance determinations using CELs on the one hand and ORLs on the other.

 

astro-ph/0603216 [abs, ps, pdf, other] :

Title: Automated Editing of Radio Interferometer Data with Pieflag
Authors: E. Middelberg
Comments: 6 pages, 5 figures, requires apj.bst, accepted for publication in Publications of the Astronomical Society of Australia

Editing of radio interferometer data, a process commonly known as ``flagging'', can be laborious and time-consuming. One quickly tends to flag more data than actually required, sacrificing sensitivity and image fidelity in the process. I describe a program, Pieflag, which can analyse radio interferometer data to filter out measurements which are likely to be affected by interference. Pieflag uses two algorithms to allow for data sets which are either dominated by receiver noise or by source structure. Together, the algorithms detect essentially all affected data whilst the amount of data which is not affected by interference but falsely marked as such is kept to a minimum. The sections marked by Pieflag are very similar to what would be deemed affected by the observer in a visual inspection of the data. Pieflag displays its results concisely and allows the user to add and remove flags interactively. It is written in Python, is easy to install and use, and has a variety of options to adjust its algorithms to a particular observing situation. I describe how Pieflag works and illustrate its effect using data from typical observations.

 

astro-ph/0603217 [abs, ps, pdf, other] :

Title: Accurate photometric redshifts for the CFHT Legacy Survey calibrated using the VIMOS VLT Deep Survey
Authors: O. Ilbert, S. Arnouts, H.J. McCracken, M. Bolzonella, E. Bertin, O. Le Fevre, Y. Mellier, G. Zamorani, R. Pello, A. Iovino, L. Tresse, D. Bottini, B. Garilli, V. Le Brun, D. Maccagni, J.P. Picat, R. Scaramella, M. Scodeggio, G. Vettolani, A. Zanichelli, C. Adami, S. Bardelli, A. Cappi, S. Charlot, P. Ciliegi, T. Contini, O. Cucciati, S. Foucaud, P. Franzetti, I. Gavignaud, L. Guzzo, B. Marano, C. Marinoni, A. Mazure, B. Meneux, R. Merighi, S. Paltani, A. Pollo, L. Pozzetti, M. Radovich, E. Zucca, M. Bondi, A. Bongiorno, G. Busarello, S. De La Torre, L. Gregorini, F. Lamareille, G. Mathez, P. Merluzzi, V. Ripepi, D. Rizzo, D. Vergani
Comments: 19 pages, 17 figures, submitted to A&A. The photometric redshifts described in this paper will be made publicly available from 1st may 2006 at this http URL and this http URL

We present photometric redshifts for an uniquely large and deep sample of 522286 objects with i'_{AB}<25 in the Canada-France Legacy Survey ``Deep Survey'' fields, which cover a total effective area of 3.2 deg^2. We use 3241 spectroscopic redshifts with 0<z<5 from the VIMOS VLT Deep Survey as a calibration to derive these photometric redshifts. We devise a robust calibration method which removes systematic trends in the photometric redshifts and significantly reduces the fraction of catastrophic errors. We use our unique spectroscopic sample to present a detailed assessment of the robustness of the photometric redshift sample. For a sample selected at i'_{AB}<24, we reach a redshift accuracy of \sigma_{\Delta z/(1+z)}=0.037 with \eta=3.7% of catastrophic error. The reliability of our photometric redshifts is lower for fainter objects: we find \sigma_{\Delta z/(1+z)}=0.029, 0.043 and \eta=1.7%, 5.4% for samples selected at i'_{AB}=17.5-22.5 and 22.5-24 respectively. We find that the photometric redshifts of starburst galaxies in our sample are less reliable: although these galaxies represent only 18% of the spectroscopic sample they are responsible for 54% of the catastrophic errors. We find an excellent agreement between the photometric and the VVDS spectroscopic redshift distributions at i'_{AB}<24. Finally, we compare the redshift distributions of i' selected galaxies on the four CFHTLS deep fields, showing that cosmic variance is already present on fields of 0.8 deg^2.

 

astro-ph/0603218 [abs, ps, pdf, other] :

Title: Star Formation in QSO Host Galaxies
Authors: Gabriela Canalizo, Alan Stockton, Michael S. Brotherton, Mark Lacy
Comments: 8 pages, 5 figures, invited review for "QSO Host Galaxies: Evolution and Environment", held at the Lorentz Center, Universiteit Leiden, August, 2005

Many of the conditions that are necessary for starbursts appear to be important in the triggering of QSOs. However, it is still debatable whether starbursts are ubiquitously present in galaxies harboring QSOs. In this paper we review our current knowledge from observations of the role of starbursts in different types of QSOs. Post-starburst stellar populations are potentially present in the majority of QSO hosts. QSOs with far-infrared colors similar to those of ultraluminous infrared galaxies invariably reside in merging galaxies that have interaction-induced starbursts of a few hundred Myr or less. Similar, but dramatically more luminous post-starburst populations are found in the recently discovered class of QSOs known as post-starburst QSOs, or Q+A's. Both of these classes, however, comprise only a small fraction (10-15%) of the total QSO population. The so-called "red" QSOs generally suffer from strong extinction at optical wavelengths, making them ideal candidates for the study of hosts. Their stellar populations typically show a post-starburst component as well, though with a larger range of ages. Finally, optical "classical" QSO hosts show traces of major star formation episodes (typically involving >10% of the mass of the stellar component) in the more distant past (1-2 Gyr). These starbursts appear to be linked to past merger events. It remains to be determined whether these mergers were also responsible for triggering the QSO activity that we observe today.

 

astro-ph/0603219 [abs, ps, pdf, other] :

Title: HD 98618: A Star Closely Resembling our Sun
Authors: Jorge Melendez (1,2), Katie Dodds-Eden (1), Jose A. Robles (1) (1) RSAA/Mt Stromlo Observatory (Australia), (2) Caltech (USA), UNMSM (Peru)
Comments: ApJ letters, in press

Despite the observational effort carried out in the last few decades, no perfect solar twin has been found to date. An important milestone was achieved a decade ago by Porto de Mello & da Silva, who showed that 18 Sco is almost a solar twin. In the present work, we use extremely high resolution (R = 10^5) high S/N Keck HIRES spectra to carry out a differential analysis of sixteen solar twin candidates. We show that HD 98618 is the second closest solar twin, and that the fundamental parameters of both HD 98618 and 18 Sco are very similar (within a few percent) to the host star of our solar system, including the likelihood of hosting a terrestrial planet within their habitable zone. We suggest that these stars should be given top priority in exoplanet and SETI surveys.

 

astro-ph/0603220 [abs, ps, pdf, other] :

Title: The Possibly Remnant Massive Outflow in G5.89-0.39: I - Observations and Initial MHD Simulations
Authors: P.D. Klaassen, R. Plume, R. Ouyed, A.M. von Benda-Beckmann, J. Di Francesco
Comments: 27 Pages, 9 Figures, Accepted to ApJ. For full (High) resolution figures, please see this http URL

We have obtained maps of the large scale outflow associated with the UCHII regionG5.89-0.39 in CO and 13CO (J=3-2), SiO (J=8-7,J=5-4), SO2 (13(2,12)-13(1,13)) and H13CO+(J=4-3). From these maps we have been able to determine the mass (3.3 M_sun), momentum (96 M_sun km/s), energy (3.5x10^{46} erg), mechanical luminosity (141 L_sun), and mass loss rate (~1x10^{-3}M_sun/yr) in the large scale outflow. The observationally derived parameters were used toguide 3D magnetohydrodynamic models of the jet entrained outflow. Through the combination of observations and simulations, we suggest that the large scale outflowmay be inclined by approximately 45 deg to the line of sight, and that the jet entraining the observed molecular outflow may have been active for as little as 1000 years, half the kinematic age of the outflow.

 

astro-ph/0603221 [abs, ps, pdf, other] :

Title: Star Formation in the Northern Cloud Complex of NGC 2264
Authors: Abigail S. Hedden (1), Christopher K. Walker (1), Christopher E. Groppi (1), Harold M. Butner (2) ((1) Steward Observatory, (2) Joint Astronomy Centre)
Comments: 28 pages including 6 figures, to be published in ApJ 01 July 2006, v645, 1 issue

We have made continuum and spectral line observations of several outflow sources in the Mon OB1 dark cloud (NGC 2264) using the Heinrich Hertz Telescope (HHT) and ARO 12m millimeter-wave telescope. This study explores the kinematics and outflow energetics of the young stellar systems observed and assesses the impact star formation is having on the surrounding cloud environment. Our data set incorporates 12CO(3-2), 13CO(3-2), and 12CO(1-0) observations of outflows associated with the sources IRAS 06382+1017 and IRAS 06381+1039, known as IRAS 25 and 27, respectively, in the northern cloud complex. Complementary 870 micron continuum maps were made with the HHT 19 channel bolometer array. Our results indicate that there is a weak (approximately less than 0.5%) coupling between outflow kinetic energy and turbulent energy of the cloud. An analysis of the energy balance in the IRAS 25 and 27 cores suggests they are maintaining their dynamical integrity except where outflowing material directly interacts with the core, such as along the outflow axes.

 

astro-ph/0603222 [abs, ps, pdf, other] :

Title: The extinction curve of long gamma-ray burst host galaxies: Are they two different types?
Authors: Shilun Chen, Aigen Li, Daming Wei
Comments: 13 pages, 3 figures. submitted to ApJL

We present the extinction curves of long gamma ray burst (GRB) host galaxies (here after GRB hosts) utilizing the extinction feature of the optical afterglow of gamma ray bursts. The extinction curve of a galaxy is essential to understanding its dust and gas properties which in return will help us to reveal the origin of GRBs. We find out that the shape of the extinction curves may be divided into two clusters and are different from that of Milky Way (MW), Large and Small Magellanic Clouds (LMC and SMC). Fitting the extinction curve with the silicate-graphite model yields that in some GRB hosts (referred as Type-I) the dust size is small and their distribution is smooth and graphite content is extremely low; in some other GRB hosts (referred as Type-II) the dust distribution index and graphite content is similar to LMC but characteristic size is larger than that of LMC. In GRB hosts the dust size parameters cover a rather large range and the graphite content are low. The results may imply that GRB hosts are of young galaxies. Due to the different dust properties, it is possible that the progenitors or the explosion mechanism may be also different for this two groups of GRBs.

 

astro-ph/0603223 [abs, ps, pdf, other] :

Title: Numerical Studies of Diffusive Shock Acceleration at Spherical Shocks
Authors: Hyesung Kang, T. W. Jones
Comments: 23 pages, 7 figures, accepted by Astroparticle Physics

We have developed a cosmic ray (CR) shock code in one dimensional spherical geometry with which the particle distribution, the gas flow and their nonlinear interaction can be followed numerically in a frame comoving with an expanding shock. In order to accommodate a very wide dynamic range of diffusion length scales in the CR shock problem, we have incorporated subzone shock tracking and adaptive mesh refinement techniques. We find the spatial grid resolution required for numerical convergence is less stringent in this code compared to typical, fixed-grid Eulerian codes. The improved convergence behavior derives from maintaining the shock discontinuity inside the same grid zone in the comoving code. That feature improves numerical estimates of the compression rate experienced by CRs crossing the subshock compared to codes that allow the subshock to drift on the grid. Using this code with a Bohm-like diffusion model we have calculated the CR acceleration and the nonlinear feedback at supernova remnant shocks during the Sedov-Taylor stage. Similarly to plane-parallel shocks, with an adopted thermal leakage injection model, about 10^{-3} of the particles that pass through the shock and up to 60 % of the explosion energy are transferred to the CR component. These results are in good agreement with previous nonlinear spherical CR shock calculations of Berezhko and collaborators.

 

astro-ph/0603224 [abs, ps, pdf, other] :

Title: The Evidence for a Binary origin of the Young Planetary Nebula HB 12
Authors: Chih Hao Hsia, Wing Huen Ip, Jin Zeng Li
Comments: 9 pages, 11 figures, Accepted for publication in AJ

The young planetary nebulae play an important role in stellar evolution when intermediate- to low-mass stars (0.8 $\sim$ 8 M$_\odot$) evolve from the proto-planetary nebulae phase to the planetary nebulae phase. Many young planetary nebulae display distinct bipolar structures as they evolve away from the proto-planetary nebulae phase. One possible cause of their bipolarity could be due to a binary origin of its energy source. Here we report our detailed investigation of the young planetary nebula, Hubble 12, which is well-known for its extended hourglass-like envelope. We present evidence with time-series photometric observations the existence of an eclipsing binary at the center of Hubble 12. Low-resolution spectra of the central source show, on the other hand, absorption features such as CN, G-band & Mg b${\arcsec}$, which can be suggestive of a low-mass nature of the secondary component.

 

astro-ph/0603225 [abs, ps, pdf, other] :

Title: AGB star intershell abundances inferred from analyses of extremely hot H-deficient post-AGB stars
Authors: K. Werner, D. Jahn, T. Rauch, E. Reiff, F. Herwig, J.W. Kruk
Comments: To appear in Proceedings of The VIII Torino Workshop on Nucleosynthesis in AGB stars: Constraints on AGB Nucleosynthesis from Observations, edited by C. Abia and I. Dominguez

The hydrogen-deficiency in extremely hot post-AGB stars of spectral class PG1159 is probably caused by a (very) late helium-shell flash or a AGB final thermal pulse that consumes the hydrogen envelope, exposing the usually-hidden intershell region. Thus, the photospheric element abundances of these stars allow to draw conclusions about details of nuclear burning and mixing processes in the precursor AGB stars. We compare predicted element abundances to those determined by quantitative spectral analyses performed with advanced non-LTE model atmospheres. A good qualitative and quantitative agreement is found for many species (He, C, N, O, Ne, F, Si) but discrepancies for others (P, S, Fe) point at shortcomings in stellar evolution models for AGB stars.

 

astro-ph/0603226 [abs, ps, pdf, other] :

Title: Non-Friedmann cosmology for the Local Universe, significance of the universal Hubble constant and short-distance indicators of dark energy
Authors: Arthur D. Chernin, Pekka Teerikorpi, Yurij V. Baryshev
Comments: 10 pages, 1 figure, submitted to A&A

Basing on the increasing evidence for the cosmological relevance of the local Hubble flow, we consider a simple analytical cosmological model for the Local Universe. This is a non-Friedmann model with a non-uniform static space-time. The major dynamical factor controlling the local expansion is the antigravity produced by the omnipresent and permanent dark energy of the cosmic vacuum (or the cosmological constant). The antigravity dominates at distances larger than 1-2 Mpc from the center of the Local Group. The model gives a natural explanation of the two key quantitative characteristics of the local expansion flow, which are the local Hubble constant and the velocity dispersion of the flow. The observed kinematical similarity of the local and global flows of expansion is clarified by the model. We demonstrate analytically the efficiency of the vacuum cooling mechanism that allows one to see the Hubble flow so close to the Local Group. Special significance is argued for the 'universal Hubble constant' H_V, depending only on the vacuum density (H_V \approx 60 km/s/Mpc). The model makes a number of testable predictions. It also shows unexpectedly that it is the dwarf galaxies of the local flow with the shortest distances and lowest redshifts that may be the most sensitive indicators of dark energy in our neighborhood.

 

astro-ph/0603227 [abs, ps, pdf, other] :

Title: M-type giants as optical counterparts of X-ray sources 4U 1700+24 and 4U 1954+319
Authors: N. Masetti, M. Orlandini, E. Palazzi, L. Amati, F. Frontera
Comments: 6 pages, 3 figures, 2 tables, accepted for publication on A&A, main journal

We observed with Chandra two peculiar galactic X-ray sources, 4U 1700+24 and 4U 1954+319, which are suspected to have a M-type giant star as optical counterpart, in order to get an high-precision astrometric position for both of them. The peculiarity of these sources lies in the fact that these are the only two cases among low-mass X-ray binaries (LMXBs), besides the confirmed case of GX 1+4, for which the companion can possibly be a M-type giant. We found that in both cases the field M-type giant star is indeed the counterpart of these X-ray sources. We also determined the distance to 4U 1954+319 to be about 1.7 kpc. This result suggests that a number of faint (L_X around 10^32-10^34 erg s-1) Galactic X-ray sources are `symbiotic X-ray binaries', that is, wide-orbit LMXBs composed of a compact object, most likely a neutron star, accreting from the wind of a M-type giant.

 

astro-ph/0603228 [abs, ps, pdf, other] :

Title: Early ComeOn+ Adaptive Optics Observation of GQ Lup and its Substellar Companion
Authors: Markus Janson, Wolfgang Brandner, Thomas Henning, Hans Zinnecker
Comments: 8 pages, 4 figures, accepted for publication in A&A

An analysis of adaptive optics K-band imaging data of GQ Lup acquired in 1994 by the first generation adaptive optics system ComeOn+ at the ESO 3.6m optical telescope in La Silla is presented. The data reveal a likely candidate for the low-mass companion recently reported in the literature. An a posteriori detection in the 11 year old data would provide a useful astrometric data point for the very long period (~1000 yr) orbit of the GQ Lup system. However, the data is severely contaminated by speckle noise at the given projected separation, which decreases the confidence of the detection. Still, from the data we can conclude that GQ Lup B is not an unrelated background source, but instead a physical companion to GQ Lup A. We present here the reduction and analysis of the ComeOn+ images, as well as the results. We also discuss the nature of the companion based on data and models available in the scientific literature and examine claims made regarding the classification of the object as a planet.

 

astro-ph/0603229 [abs, ps, pdf, other] :

Title: On Multipolar Analytical Potentials for Galaxies
Authors: D. Vogt, P. S. Letelier
Journal-ref: Publ. Astron. Soc. Japan 57, 871-875, 2005 December 25

We present analytical potential-density pairs in three dimensions for the gravitational field of galaxies, obtained by thickening the multipolar expansion up to the quadrupole term. These may be interpreted as generalizations of the Miyamoto and Nagai potential-density pairs. With a suitable restriction on the possible values of the multipole moments, the density distributions are positive and monotone decreasing functions of the radial and axial coordinates.

 

astro-ph/0603230 [abs, ps, pdf, other] :

Title: Triggered star formation in Bright-Rimmed Clouds: The Eagle Nebula revisited
Authors: J. Miao, G.J. White, R.P. Nelson, M.A. Thompson, L.K. Morgan
Comments: 13 pages, accepted by MNRAS

A three dimensional Smoothed Particle Hydrodynamical (SPH) model has been extended to study the radiative driven implosion effect of massive stars on the dynamical evolutions of surrounding molecular clouds. The new elements in the upgraded code are the inclusion of Lyman continuum in the incident radiation flux and the treatment of hydrogen ionisation process; introducing ionisation heating & recombination cooling effects; and adding a proper description of the magnetic and turbulent pressures to the internal pressure of the molecular cloud. The application of this newly developed model to the structure of the middle Eagle Nebula finger suggests that the shock induced by the ionising radiation at the front side of the head precedes an ionisation front moving towards the center of the core, and that the core at the fingertip is at transition stage evolving toward a state of induced star formation. The dynamical evolution of the velocity field of the simulated cloud structure is discussed to illustrate the role of the self-gravity and the different cloud morphologies which appear at different stages in the evolutionary process of the cloud. The modelled gas evaporation rate is consistent with that of current other models and the density, temperature and chemical profiles are agreement with the observed values. The relative lifetimes of different simulated cloud morphologies suggests a possible answer to the question of why more bright-rimmed clouds are observed to possess a flat-core than an elongated-core morphology. [Abridged]

 

astro-ph/0603231 [abs, ps, pdf, other] :

Title: Orientation dependency of broad-line widths in quasars and consequences for black-hole mass estimation
Authors: Matt J. Jarvis (1), Ross J. McLure (2) ((1) Oxford, (2) Edinburgh)
Comments: 7 pages, 3 figures, accepted for publication in MNRAS

In this paper we report new evidence that measurements of the broad-line widths in quasars are dependent on the source orientation, consistent with the idea that the broad-line region is flattened or disc-like. This reinforces the view derived from radio-selected samples, where the radio-core dominance has been used as a measure of orientation. The results presented here show a highly significant (>99.95%) correlation between radio spectral index (which we use as a proxy for source orientation) and broad-line width derived from the H-beta and MgII emission lines. This is the first time that this type of study has used quasars derived from a large optically selected quasar sample, where the radio-loud quasars (RLQs) and radio-quiet quasars (RQQs) have indistinguishable distributions in redshift, bolometric luminosity and colour, and therefore overcomes any biases which may be present in only selecting via radio emission. We find that the mean FWHM for the flat-spectrum radio-loud quasars (FSQs) to be <FWHM(FSQ)>= 4990 +/- 536km/s, which differs significant from the mean FWHM of the steep-spectrum radio-loud quasars (SSQs), where <FWHM(SSQ)>=6464 +/- 506km/s. We also find that the distribution in FWHM for the FSQs is indistinguishable from that of the radio-quiet quasars (RQQs), where <FWHM(RQQ)>= 4831 +/-25km/s. Considering other observational results in the literature we interpret this result in the context of a significant fraction of the FSQs being derived from the underlying RQQ population which have their radio flux Doppler boosted above the RLQ/RQQ divide. Under the assumption of a disc-like broad-line region we find no evidence for a difference in the average line-of-sight angle for RQQs and RLQs, implying that the difference is due to black-hole mass. (abridged)

 

astro-ph/0603232 [abs, ps, pdf, other] :

Title: Integral-field studies of the high-redshift Universe
Authors: Matt J. Jarvis (1), Caroline van Breuekeln (1), Bram P. Venemans (2,3), Richard J. Wilman (4) ((1) Oxford, (2) Leiden, (3) IoA, (4) Durham)
Comments: From proceedings of Euro3D Spectroscopy annual RTN network meeting (ed. J. Walsh). 5 pages, accepted for publication in Astron. Nachr

We present results from a new method of exploring the distant Universe. We use 3-D spectroscopy to sample a large cosmological volume at a time when the Universe was less than 3 billion years old to investigate the evolution of star-formation activity. Within this study we also discovered a high redshift type-II quasar which would not have been identified with imaging studies alone. This highlights the crucial role that integral-field spectroscopy may play in surveying the distant Universe in the future.

 

astro-ph/0603233 [abs, ps, pdf, other] :

Title: The Fragmentation of Cores and the Initial Binary Population
Authors: S. P. Goodwin (1), P. Kroupa (2), A. Goodman (3), A. Burkert (4) (1. Sheffield; 2. Bonn; 3. CfA; 4. Munich)
Comments: 16 pages, 6 figures. To appear in 'Protostars and Planets V'. Includes proto.cls style file. Figures degraded in quality, full version available by anonymous ftp (ftp:astro.shef.ac.uk, pub/spg/GoodwinPPV.pdf.gz)

Almost all young stars are found in multiple systems. This suggests that protostellar cores almost always fragment into multiple objects. The observed properties of multiple systems such as their separation distribution and mass ratios provide strong constraints on star formation theories. We review the observed properties of young and old multiple systems and find that the multiplicity of stars changes. Such an evolution is probably due to (a) the dynamical decay of small-N systems and/or (b) the destruction of multiple systems within dense clusters. We review simulations of the fragmentation of rotating and turbulent molecular cores. Such models almost always produce multiple systems, however the properties of those systems do not match observations at all well. Magnetic fields appear to supress fragmentation, prehaps suggesting that they are not dynamically important in the formation of multiple systems. We finish by discussing possible reasons why theory fails to match observation, and the future prospects for this field.

 

astro-ph/0603234 [abs, ps, pdf, other] :

Title: Cosmological Acceleration and Gravitational Collapse
Authors: Pantelis S. Apostolopoulos, Nikolaos Brouzakis, Nikolaos Tetradis, Eleftheria Tzavara
Comments: 20 pages, 8 figures

The acceleration parameter defined through the local volume expansion is negative for a pressureless, irrotational fluid with positive energy density. In the presence of inhomogeneities or anisotropies the volume expansion rate results from averaging over various directions. On the other hand, the nature of the expansion deduced through the observation of light from a certain source in the sky is specific to the direction to that source. If there are preferred directions in the underlying geometry one can define several expansion parameters. We provide such definitions for the case of the Tolman-Bondi metric. We then examine the effect of a localized inhomogeneity on the surrounding cosmological fluid. Our framework is similar in spirit to the model of spherical collapse. For an observer in the vicinity of a central overdensity, the perceived local evolution is consistent with acceleration along the radial direction, and deceleration perpendicularly to it. A negative mass leads to deceleration along the radial direction, and acceleration perpendicularly to it. If the observer is located at the center of an overdensity the null geodesics are radial. The form of the luminosity distance as a function of the redshift is consistent with acceleration for a certain range of redshifts.

 

astro-ph/0603235 [abs, ps, pdf, other] :

Title: Diffusive Migration of Low-Mass Proto-planets in Turbulent Disks
Authors: Eric T. Johnson (Princeton), Jeremy Goodman (Princeton), Kristen Menou (Columbia)
Comments: 31 pages, 7 figures, submitted to ApJ

Torque fluctuations due to magnetorotational turbulence in proto-planetary disks may greatly influence the migration patterns and survival probabilities of nascent planets. Provided that the turbulence is a stationary stochastic process with finite amplitude and correlation time, the resulting diffusive migration can be described with a Fokker-Planck equation, which we reduce to an advection-diffusion equation. We calibrate the coefficients with existing turbulent-disk simulations and mean-migration estimates, and solve the equation both analytically and numerically. Diffusion tends to dominate over advection for planets of low-mass and those in the outer regions of proto-planetary disks, whether they are described by the Minimum Mass Solar Nebula (MMSN) or by T-Tauri alpha disks. Diffusion systematically reduces the lifetime of most planets, yet it allows a declining fraction of them to survive for extended periods of time at large radii. Mean planet lifetimes can even be formally infinite (e.g. in an infinite steady MMSN), though median lifetimes are always finite. Surviving planets may linger near specific radii where the combined effects of advection and diffusion are minimized, or at large radii, depending on model specifics. The stochastic nature of migration in turbulent disks challenges deterministic planet formation scenarios and suggests instead that a wide variety of planetary outcomes are possible from similar initial conditions. This would contribute to the diversity of (extrasolar) planetary systems.

 

astro-ph/0603236 [abs, ps, pdf, other] :

Title: The Relic Neutrino Backround from the First Stars
Authors: Keith A. Olive, Pearl Sandick
Comments: 19 pages, 15 figures, Summary of talk given at the IIIrd International Workshop on: NO-VE "Neutrino Oscillations in Venice", Venice Italy, February 2006

We consider the relic neutrino background produced by Population III stars coupled with a normal mode of star formation at lower redshift. The computation is performed in the framework of hierarchical structure formation and is based on cosmic star formation histories constrained to reproduce the observed star formation rate at redshift z \la 6, the observed chemical abundances in damped Lyman alpha absorbers and in the intergalactic medium, and to allow for an early reionization of the Universe at z ~ 10-20. We consider both a burst and non-burst model for Population III star formation. We find that although the high redshift burst of Population III stars does lead to an appreciable flux of neutrinos at relatively low energy (E_\nu \approx 1 MeV), the observable neutrino flux is dominated by the normal mode of star formation. We also find that predicted fluxes are at the present level of the SuperK limit. As a consequence, the supernova relic neutrino background has a direct impact on models of chemical evolution and/or supernova dynamics.

 

astro-ph/0603237 [abs, ps, pdf, other] :

Title: Impact of dark matter decays and annihilations on reionzation
Authors: M. Mapelli (1), A. Ferrara (1), E. Pierpaoli (2), ((1) SISSA, (2) Caltech)
Comments: 6 pages, 5 figures, submitted to MNRAS

One of the possible methods to distinguish among various dark matter candidates is to study the effects of dark matter decays. We consider four different dark matter candidates (light dark matter, gravitinos, neutralinos and sterile neutrinos), for each of them deriving the decaying/annihilation rate, the influence on reionization, matter temperature and CMB spectra. We find that light dark matter particles (1-10 MeV) and sterile neutrinos (2-7 keV) can be sources of partial early reionization (z<~100). However, their integrated contribution to Thomson optical depth is small (<~0.01). Finally, they can significantly affect the behavior of matter temperature. On the contrary, effects of heavy dark matter candidates (gravitinos and neutralinos) on reionization and heating are minimal. All the considered dark matter particles have completely negligible effects on the CMB spectra.

 

astro-ph/0603238 [abs, ps, pdf, other] :

Title: The Origins and Evolutionary Status of B Stars Found Far From the Galactic Plane II: Kinematics and Full Sample Analysis
Authors: J. C. Martin
Comments: 59 pages including 14 Figures, 12 Tables; Accepted for publication in the Astronomical Journal

This paper continues the analysis of faint high latitude B stars from Martin (2004). Here we analyze the kinematics of the stars and combine them with the abundance information from the first paper to classify each one. The sample contains 31 Population I runaways, fifteen old evolved stars (including five BHB stars, three post-HB stars, a pulsating helium dwarf, and six stars of ambiguous classification), one F-dwarf, and two stars which do not easily fit in one of the other categories. No star in the sample unambiguously shows the characteristics of a young massive star formed in situ in the halo. The two unclassified stars are probably extreme Population I runaways. The low binary frequency and rotational velocity distribution of the Population I runaways imply that most were ejected from dense star clusters by DES (dynamic ejection scenario). However we remain puzzled by the lack of runaway Be stars. We also confirm that PB 166 and HIP 41979 are both nearby solar-metallicity BHB stars.

 

astro-ph/0603239 [abs, ps, pdf, other] :

Title: Hubble Space Telescope Near-Infrared Snapshot Survey of 3CR radio source counterparts at low redshift
Authors: Juan P. Madrid, Marco Chiaberge, David Floyd, William B. Sparks, (STScI), Duccio Macchetto (STScI, ESA), George K. Miley (Leiden Observatory), David Axon (Rochester Institute of Technology), Alessandro Capetti (Torino Observatory), Christopher P. O'Dea, Stefi Baum (Rochester Institute of Technology), Eric Perlman (University of Maryland BC), Alice Quillen (University of Rochester)
Comments: Submitted to ApJS, this version incorporates referee comments; 77 bitmapped figures

We present newly acquired images of the near-infrared counterpart of 3CR radio sources. All the sources were selected to have a redshift of less than 0.3 to allow us to obtain the highest spatial resolution. The observations were carried out as a snapshot program using the Near-Infrared Camera and Multiobject Spectrograph (NICMOS) on-board the Hubble Space Telescope (HST). In this paper we describe 69 radio galaxies observed for the first time with NICMOS during HST cycle 13. All the objects presented here are elliptical galaxies. However, each of them has unique characteristics such as close companions, dust lanes, unresolved nuclei, arc-like features, globular clusters and jets clearly visible from the images or with basic galaxy subtraction.

 

astro-ph/0603240 [abs, ps, pdf, other] :

Title: The dipole of the luminosity distance: a direct measure of H(z)
Authors: Camille Bonvin, Ruth Durrer, Martin Kunz (University of Geneva)
Comments: 4 pages, 4 figures

We show that the dipole of the luminosity distance is a useful observational tool which allows to determine the Hubble parameter as function of the redshift, H(z). We determine the number of supernovae needed to achieve a given precision for H(z) and to distinguish between different models for dark energy. We test our method on a sample of nearby supernovae and find H(z=0)=74 km/s/Mpc

 

astro-ph/0603241 [abs, ps, pdf, other] :

Title: Diffuse Ionized Gas in irregular galaxies:I- GR 8 and ESO 245-G05
Authors: A. M. Hidalgo-Gamez (Instituto de Astronomia, UNAM)
Comments: Accepted by AJ. Figure 1 can be downloaded from this http URL

We have studied the spectral characteristics of the Diffuse Ionized Gas in two irregular galaxies with low metallicities and intermediate Star Formation Rates: ESO 245-G05 and Gr 8. The [OIII]/Hbeta in these galaxies is higher than in the DIG of spiral galaxies but not as high as in other irregular galaxies previously studied, such as IC 10 and NGC 6822. The [NII]/Halpha and [SII]/Halpha ratios have very small values, indicating the absence of shocks as the ionization source for this gas. This ionization can be explained in both galaxies with photon leakage from the HII regions as the only source. The percentage of photons escaped from the HII regions is small in ESO 245-G05, of only 35%, but varies from 35% up to 60% in Gr 8. We also investigated if the differences found between spiral and irregular galaxies in the [OIII]/Hbeta and the [NII]/Halpha ratio are due to differences in the metal content between these types of galaxies. Although the number of galaxies studied is not very large, it can be concluded that the [OIII]/Hbeta is not related with the oxygen content, while the situation is more ambiguous for the [NII]/Halpha ratio.

 

astro-ph/0603242 [abs, ps, pdf, other] :

Title: The distribution of current helicity at the solar surface at the beginning of the solar cycle
Authors: D. Sokoloff, S.D. Bao, N. Kleeorin, K. Kuzanyan, D. Moss, I. Rogachevskii, D. Tomin, H. Zhang
Comments: 7 pages, 5 figures, an.cls, Astron. Nachr., submitted

A fraction of solar active regions are observed to have current helicity of a sign that contradicts the polarity law for magnetic helicity; this law corresponds to the well-known Hale polarity law for sunspots. A significant excess of active regions with the "wrong" sign of helicity is seen to occur just at the beginning of the cycle. We compare these observations with predictions from a dynamo model based on principles of helicity conservation, discussed by Zhang et al. (2006). This model seems capable of explaining only a fraction of the regions with the wrong sign of the helicity. We attribute the remaining excess to additional current helicity production from the twisting of rising magnetic flux tubes, as suggested by Choudhuri et al. (2004). We estimate the relative contributions of this effect and that connected with the model based on magnetic helicity conservation.

 

astro-ph/0603243 [abs, ps, pdf, other] :

Title: The ZEPLIN-III dark matter detector: performance study using an end-to-end simulation tool
Authors: H. M. Araujo, D. Yu. Akimov, G. J. Alner, A. Bewick, C. Bungau, B. Camanzi, M. J. Carson, V. Chepel, H. Chagani, D. Davidge, J. C. Davies, E. Daw, J. Dawson, T. Durkin, B. Edwards, T. Gamble, C. Ghag, R. Hollingworth, A. S. Howard, W. G. Jones, M. Joshi, J. Kirkpatrick, A. Kovalenko, V. A. Kudryavtsev, V. N. Lebedenko, T. Lawson, J. D. Lewin, P. Lightfoot, A. Lindote, I. Liubarsky, M. I. Lopes, R. Luscher, P. Majewski, K. Mavrokoridis, J. McMillan, B. Morgan, D. Muna, A. S. Murphy, F. Neves, G. Nicklin, S. Paling, J. Pinto da Cunha, R. Preece, J. J. Quenby, M. Robinson, C. Silva, V. N. Solovov, N. J. T. Smith, P. F. Smith, N. J. C. Spooner, V. Stekhanov, T. J. Sumner, D. R. Tovey, C. Thorne, E. Tziaferi, R. J. Walker
Comments: Submitted to Astroparticle Physics

We present results from a GEANT4-based Monte Carlo tool for end-to-end simulations of the ZEPLIN-III dark matter experiment. ZEPLIN-III is a two-phase detector which measures both the scintillation light and the ionisation charge generated in liquid xenon by interacting particles and radiation. The software models the instrument response to radioactive backgrounds and calibration sources, including the generation, ray-tracing and detection of the primary and secondary scintillations in liquid and gaseous xenon, and subsequent processing by data acquisition electronics. A flexible user interface allows easy modification of detector parameters at run time. Realistic datasets can be produced to help with data analysis, an example of which is the position reconstruction algorithm developed from simulated data. We present a range of simulation results confirming the original design sensitivity of a few times $10^{-8}$ pb to the WIMP-nucleon cross-section.

 

astro-ph/0603244 [abs, ps, pdf, other] :

Title: The Physical Nature of Lyman Alpha Emitting Galaxies at z=3.1
Authors: Eric Gawiser, Pieter G. van Dokkum, Caryl Gronwall, Robin Ciardullo, Guillermo Blanc, Francisco J. Castander, John Feldmeier, Harold Francke, Marijn Franx, Lutz Haberzettl, David Herrera, Thomas Hickey, Leopoldo Infante, Paulina Lira, Jose Maza, Ryan Quadri, Alexander Richardson, Kevin Schawinski, Mischa Schirmer, Edward N. Taylor, Ezequiel Treister, C. Megan Urry, Shanil N. Virani, for the MUSYC Collaboration
Comments: submitted to ApJ Letters, revised version after referee's comments, 4 pages with 2 color figures

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 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.

 

astro-ph/0603245 [abs, ps, pdf, other] :

Title: MUSYC: A Deep Square Degree Survey of the Formation and Evolution of Galaxies and Supermassive Black Holes
Authors: Eric Gawiser, for the MUSYC Collaboration
Comments: 4 pages, to appear in "From Z-Machines to ALMA: (Sub)millimeter Spectroscopy of Galaxies"

The Multiwavelength Survey by Yale-Chile (MUSYC) is optimized for the study of galaxies at z=3, AGN demographics, and Galactic structure. MUSYC consists of deep optical (UBVRIz') and near-infrared (JHK) imaging of four fields on the sky covering 1.2 square degrees to AB limiting depths of U,B,V,R=26 and K=22. Our optical catalog contains 277,341 objects detected in BVR images with median seeing of 0.9''. Satellite coverage of our fields includes Chandra, XMM, GALEX, HST-ACS, and Spitzer, with the Extended Chandra Deep Field South imaged at all of these wavelengths plus the radio, making it the premier multiwavelength field on the sky. Detailed follow-up spectroscopy is being performed with VLT+VIMOS, Magellan+IMACS and Gemini+GNIRS. MUSYC provides ideal supporting data for surveys with Z-Machines and rich target lists for spectroscopy with ALMA. We are conducting a census of protogalaxies at redshift three (Lyman break galaxies, Lyman-alpha emitters, Distant red galaxies, Sub-millimeter galaxies and AGN) in order to separate physical properties from selection effects. We discuss measurements of the dark matter halo masses and halo occupation numbers of these populations and of the total cosmic star formation rate at z=3. MUSYC publications and data releases are available at this http URL .

 

astro-ph/0603246 [abs, ps, pdf, other] :

Title: The origin of cold fronts in the cores of relaxed galaxy clusters
Authors: Yago Ascasibar, Maxim Markevitch
Comments: 31 pages (emulateapj), 23 figures. Submitted to ApJ

[Abridged] Chandra X-ray observations revealed the presence of cold fronts -- sharp contact discontinuities between gas regions with different temperatures and densities -- in the centers of many, if not most, relaxed clusters with cool cores. We use high-resolution simulations of idealized cluster mergers to address the origin of such fronts. We find that these cold fronts are due to sloshing of the cool gas in the central gravitational potential well, which is easily set off by any minor merger and can persist for gigayears. The only necessary condition for their formation is a steep entropy drop in the gas peak. Most interestingly, the fronts form even if the infalling subcluster has no gas during core passage. If the subhalo had a nonzero impact parameter, the cool gas acquires angular momentum while offset from the center, and does not fall back radially. The resulting cold fronts combine into a characteristic spiral pattern, which initially does not represent any coherent spiraling motion, but evolves into a spiral inflow. There is little visible disturbance outside the cool core in such a merger. The picture is qualitatively different if the subcluster contains gas during core passage. Then the dominant agents are the shock front and stripped gas from the subcluster, which decouple most or all of the cool central gas of the main cluster from the dark matter peak via a "ram-pressure slingshot". Such a merger creates global disturbance in the ICM readily visible in the X-ray image long after the first core passage. We conclude that cold fronts at the centers of such exceptionally relaxed clusters as A2029 or A1795, often spiral or concentric-arc in shape, are probably caused by encounters with small subhalos stripped of all their gas at the early infall stages.

 

astro-ph/0603247 [abs, ps, pdf, other] :

Title: Reduction of Cosmological Data for the Detection of Time-varying Dark Energy Density
Authors: Jason Dick, Lloyd Knox, Mike Chu
Comments: 10 pages, 9 figures

We present a method for reducing cosmological data to constraints on the amplitudes of modes of the dark energy density as a function of redshift. The modes are chosen so that 1) one of them has constant density and 2) the others are non-zero only if there is time-variation in the dark energy density and 3) the amplitude errors for the time-varying modes are uncorrelated with each other. We apply our method to various combinations of CMB data, baryon acoustic oscillation data Eisenstein et. al. (2005), the Riess et. al. (2004) 'Gold' supernova data set, and the Supernova Legacy Survey data set Astier et. al. (2005). We find no significant evidence for a time-varying dark energy density or for non-zero mean curvature.

 

astro-ph/0603248 [abs, ps, pdf, other] :

Title: Probing the Coevolution of Supermassive Black Holes and Galaxies Using Gravitationally Lensed Quasar Hosts
Authors: C. Y. Peng (1), C. D. Impey (2), H.-W. Rix (3), C. S. Kochanek (4), C. R. Keeton (5), E. E. Falco (6), J. Lehar (7), B. A. McLeod (5) ((1) Space Telescope Science Institute, (2) Steward Observatory, University of Arizona, (4) Ohio State University, (5) Rutgers University, (6) Harvard-Smithsonian Center for Astrophysics, (7) CombinatoRx)
Comments: ApJ submitted. 23 pages, 11 figures, 4 tables

In the present-day universe, supermassive black hole masses (MBH) appear to be strongly correlated with their galaxy's bulge luminosity, among other properties. In this study, we explore the analogous relationship between MBH, derived using the virial method, and the stellar R-band bulge luminosity (Lr) or stellar bulge mass (M*) at epochs of 1 < z < 4.5 using a sample of 31 gravitationally lensed AGNs and 20 non-lensed AGNs. At redshifts z > 1.7 (10--12 Gyrs ago), we find that the observed MBH--Lr relation is nearly the same (to within ~0.3 mag) as it is today. When the observed Lr are corrected for luminosity evolution, this means that the black holes grew in mass faster than their hosts, with the MBH/M* mass ratio being a factor of > 4(+2)(-1) times larger at z > 1.7 than it is today. By the redshift range 1 < z < 1.7 (8--10 Gyrs ago), the MBH/M* ratio is only 1.3--2 times higher than today. Combining the results, we conclude that the ratio MBH/M* rises with look-back time, although it may saturate at ~6 times the local value. Scenarios in which moderately luminous quasar hosts at z>1.7 were fully formed bulges that passively faded to the present epoch are ruled out.

 

astro-ph/0603249 [abs, ps, pdf, other] :

Title: "Propeller" Regime of Disk Accretion to Rapidly Rotating Stars
Authors: G.V. Ustyugova, A.V. Koldoba, M.M. Romanova, R.V.E. Lovelace
Comments: 19 pages, 16 figures, ApJ (accepted), see animation at this http URL

We present results of axisymmetic magnetohydrodynamic simulations of the interaction of a rapidly-rotating, magnetized star with an accretion disk. The disk is considered to have a finite viscosity and magnetic diffusivity. The main parameters of the system are the star's angular velocity and magnetic moment, and the disk's viscosity, diffusivity. We focus on the "propeller" regime where the inner radius of the disk is larger than the corotation radius. Two types of magnetohydrodynamic flows have been found as a result of simulations: "weak" and "strong" propellers. The strong propeller is characterized by a powerful disk wind and a collimated magnetically dominated outflow or jet from the star. The weak propeller have only weak outflows. We investigated the time-averaged characteristics of the interaction between the main elements of the system, the star, the disk, the wind from the disk, and the jet. Rates of exchange of mass and angular momentum between the elements of the system are derived as a function of the main parameters. The propeller mechanism may be responsible for the fast spinning-down of the classical T Tauri stars in the initial stages of their evolution, and for the spinning-down of accreting millisecond pulsars.

 

astro-ph/0603250 [abs, ps, pdf, other] :

Title: Early supersymmetric cold dark matter substructure
Authors: Juerg Diemand, Michael Kuhlen, Piero Madau (UC Santa Cruz)
Comments: 12 pages, 10 figures, submitted to ApJ. A version with high-resolution figures is available at this http URL

Earth-mass dark matter microhalos may be the first objects to collapse and virialize in the early universe. Their ability to survive the hierarchical clustering process as substructure in the larger halos that form subsequently has implications for direct and indirect dark matter detection experiments. We present here the large N-body simulation of early substructure in a supersymmetric cold dark matter (SUSY-CDM) scenario characterized by an exponential cutoff in the matter power spectrum at M_c=10^{-6} Msun. The simulation resolves a 0.014 Msun parent SUSY halo at z=75 with 12 million particles within its virial radius. On these scales the effective index of the power spectrum approaches -3, a range of mass scales collapse almost simultaneously, and the formation history of the early SUSY host appears very different from that of a low-redshift massive halo. Compared to a z=0 galaxy cluster with similar concentration parameter, substructure within our SUSY host is less evident both in phase-space and in physical space, and it is less resistant against tidal stripping and disruption. As the scale factor of the universe increases by a factor of 1.3, we find that between 20 and 40 percent of well-resolved SUSY substructure is destroyed, compared to only about 1 percent in the low-redshift cluster. Despite the lower contrast and higher disruption probability, SUSY substructure is just as abundant as in z=0 galaxy clusters, i.e. the substructure normalized mass and circular velocity functions are very similar. The dark matter self-annihilation gamma-ray signal from resolved sub-microhalos is comparable to the spherically-averaged SUSY host signal, and should be included in estimates of the cosmological extragalactic gamma-ray background.(ABRIDGED)