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Astrophysics

astro-ph new abstracts, Tue, 28 Feb 06 01:00:11 GMT
0602548 -- 0602595 received

astro-ph/0602548 [abs, ps, pdf, other] :

Title: The Effect of Large-Scale Structure on the SDSS Galaxy Three-Point Correlation Function
Authors: R. C. Nichol (ICG Portsmouth), R. K. Sheth, Y. Suto, A. J. Gray, I. Kayo, R. H. Wechsler, F. Marin, G. Kulkarni, M. Blanton, A. J. Connolly, J. P. Gardner, B. Jain, C. J. Miller, A. W. Moore, A. Pope, J. Pun, D. Schneider, J. Schneider, A. Szalay, I. Szapudi, I. Zehavi, N. A. Bahcall, I. Csabai, J. Brinkmann
Comments: Accepted for publication in MNRAS

We present measurements of the normalised redshift-space three-point correlation function (Q_z) of galaxies from the Sloan Digital Sky Survey (SDSS) main galaxy sample. We have applied our "npt" algorithm to both a volume-limited (36738 galaxies) and magnitude-limited sample (134741 galaxies) of SDSS galaxies, and find consistent results between the two samples, thus confirming the weak luminosity dependence of Q_z recently seen by other authors. We compare our results to other Q_z measurements in the literature and find it to be consistent within the full jack-knife error estimates. However, we find these errors are significantly increased by the presence of the ``Sloan Great Wall'' (at z ~ 0.08) within these two SDSS datasets, which changes the 3-point correlation function (3PCF) by 70% on large scales (s>=10h^-1 Mpc). If we exclude this supercluster, our observed Q_z is in better agreement with that obtained from the 2dFGRS by other authors, thus demonstrating the sensitivity of these higher-order correlation functions to large-scale structures in the Universe. This analysis highlights that the SDSS datasets used here are not ``fair samples'' of the Universe for the estimation of higher-order clustering statistics and larger volumes are required. We study the shape-dependence of Q_z(s,q,theta) as one expects this measurement to depend on scale if the large scale structure in the Universe has grown via gravitational instability from Gaussian initial conditions. On small scales (s <= 6h^-1 Mpc), we see some evidence for shape-dependence in Q_z, but at present our measurements are consistent with a constant within the errors (Q_z ~ 0.75 +/- 0.05). On scales >10h^-1 Mpc, we see considerable shape-dependence in Q_z.

 

astro-ph/0602549 [abs, ps, pdf, other] :

Title: The relation between accretion rate and jet power in X-ray luminous elliptical galaxies
Authors: S.W. Allen (KIPAC, Stanford), R.J.H. Dunn, A.C. Fabian (IoA, Cambridge), G.B. Taylor (UNM), C.S. Reynolds (UMD)
Comments: Submitted for publication in MNRAS (Jan 2006). 10 pages, 5 figures

Using Chandra X-ray observations of 9 nearby, X-ray luminous ellipticals with good optical velocity dispersion measurements, we show that a tight correlation exists between the Bondi accretion rates calculated from the X-ray data and estimated black hole masses, and the power emerging from these systems in relativistic jets. The jet powers, inferred from the energies and timescales required to inflate the cavities observed in the surrounding X-ray emitting gas, can be related to the accretion rates by a power law model. A significant fraction (2.4^{+1.0}_{-0.7} per cent, for P_jet=10^{43} erg/s) of the energy associated with the rest mass of material entering the accretion radius emerges in the jets. Our results have significant implications for studies of accretion, jet formation and galaxy formation. The tight correlation between P_Bondi and P_jet suggests that the Bondi formulae provide a reasonable description of the accretion process, despite the likely presence of magnetic pressure and angular momentum in the accreting gas, and that the accretion flows are approximately stable over timescales of a few million years. Our results show that the black hole engines at the hearts of large elliptical galaxies and groups feed back sufficient energy to stem cooling and star formation, leading naturally to the observed exponential cut off at the bright end of the galaxy luminosity function.

 

astro-ph/0602550 [abs, ps, pdf, other] :

Title: An Exploratory Chandra Survey of a Well-Defined Sample of 35 Large Bright Quasar Survey Broad Absorption Line Quasars
Authors: S.C. Gallagher (UCLA), W.N. Brandt, G. Chartas (Penn State), R. Priddey (Hertfordshire), G.P. Garmire (Penn State), R.M. Sambruna (GSFC)
Comments: 21 pages, uses emulateapj, 11 figures (3 color), ApJ accepted

We present 4-7 ks Chandra observations of 35 Broad Absorption Line (BAL) quasars from the Large Bright Quasar Survey, the largest sample of sensitive, 0.5-8.0 keV X-ray observations of this class of quasars to date. The limited ranges in both redshift (z=1.42-2.90) and UV luminosity (a factor of ~12) of the sample also make it relatively uniform. Of 35 targets, 27 are detected for a detection fraction of 77%, and we confirm previous studies that find BAL quasars to be generally X-ray weak. Five of the eight non-detections are known low-ionization BAL quasars, confirming reports of extreme X-ray weakness in this subset (~10% of optically selected BAL quasars). Those BAL quasars with the hardest X-ray spectra are also the X-ray weakest, consistent with the interpretation that intrinsic absorption is the primary cause of X-ray weakness in this class of quasars as a whole. Furthermore, the observed trend is not consistent with simple neutral absorption, supporting findings from spectroscopic observations of individual targets that BAL quasars typically exhibit complex X-ray absorption (e.g., partially covering or ionized absorbers). In sum, high-ionization BAL quasars are typically neither intrinsically X-ray weak nor suffer from Compton-thick absorption. In general, we find no evidence for correlations between X-ray weakness and UV absorption-line properties, with the exception of a likely correlation between the maximum outflow velocity of CIV absorption and the magnitude of X-ray weakness. We discuss the implications of our results for disk-wind models of BAL outflows in quasars. (abridged)

 

astro-ph/0602551 [abs, ps, pdf, other] :

Title: Short-lived Nuclei in the Early Solar System: Possible AGB Sources
Authors: G. J. Wasserburg, M. Busso, R. Gallino, K. M. Nollett
Comments: 92 pages, 14 figure files, in press at Nuclear Physics A

(Abridged) We review abundances of short-lived nuclides in the early solar system (ESS) and the methods used to determine them. We compare them to the inventory for a uniform galactic production model. Within a factor of two, observed abundances of several isotopes are compatible with this model. I-129 is an exception, with an ESS inventory much lower than expected. The isotopes Pd-107, Fe-60, Ca-41, Cl-36, Al-26, and Be-10 require late addition to the solar nebula. Be-10 is the product of particle irradiation of the solar system as probably is Cl-36. Late injection by a supernova (SN) cannot be responsible for most short-lived nuclei without excessively producing Mn-53; it can be the source of Mn-53 and maybe Fe-60. If a late SN is responsible for these two nuclei, it still cannot make Pd-107 and other isotopes. We emphasize an AGB star as a source of nuclei, including Fe-60 and explore this possibility with new stellar models. A dilution factor of about 4e-3 gives reasonable amounts of many nuclei. We discuss the role of irradiation for Al-26, Cl-36 and Ca-41. Conflict between scenarios is emphasized as well as the absence of a global interpretation for the existing data. Abundances of actinides indicate a quiescent interval of about 1e8 years for actinide group production in order to explain the data on Pu-244 and new bounds on Cm-247. This interval is not compatible with Hf-182 data, so a separate type of r-process is needed for at least the actinides, distinct from the two types previously identified. The apparent coincidence of the I-129 and trans-actinide time scales suggests that the last actinide contribution was from an r-process that produced actinides without fission recycling so that the yields at Ba and below were governed by fission.

 

astro-ph/0602552 [abs, ps, pdf, other] :

Title: Tentative Discovery of a New Supernova Remnant in Cepheus: Unveiling an Elusive Shell in the Spitzer Galactic First Look Survey
Authors: Patrick W. Morris, Susan Stolovy, Stefanie Wachter, Alberto Noriega-Crespo, Thomas G. Pannuti, D.W. Hoard
Comments: 11 pages; accepted for publication in Astrophysical Journal Letters

We have discovered an axially symmetric, well-defined shell of material in the constellation of Cepheus, based on imaging acquired as part of the Galactic First Look Survey with the Spitzer Space Telescope. The 86'' x 75'' object exhibits brightened limbs on the minor axis, and is clearly visible at 24 microns, but is not detected in the 3.6, 4.5, 5.8, 8.0, 70, or 160 micron images. Followup with 7.5 - 40 micron spectroscopy reveals the shell to be composed entirely of ionized gas, and that the 24 micron imaging traces solely [O IV] 25.89 micron emission. The spectrum also exhibits weaker [Ne III], [S III], and very weak [Ne V] emission. No emission from warm dust is detected. Spectral cuts through the center of the shell and at the northern limb are highly consistent with each other. The progenitor is not readily identified, but with scaling arguments and comparison to well-known examples of evolved stellar objects, we find the observations to be most straightforward to interpret in terms of a young supernova remnant located at a distance of at least 10 kpc, some 400 pc above the Galactic disk. If confirmed, this would be the first SNR discovered initially at infrared wavelengths.

 

astro-ph/0602553 [abs, ps, pdf, other] :

Title: A high resolution UV absorption spectrum of supernova ejecta in SN1006
Authors: Andrew J. S. Hamilton (JILA, U. Colorado), Robert A. Fesen (Dartmouth), William P. Blair (JHU)
Comments: 9 pages, 5 embedded postscript figs

We report a high resolution, far-ultraviolet, STIS E140M spectrum of the strong, broad Si II, III, and IV features produced by the ejecta of SN1006 seen in absorption against the background Schweizer-Middleditch star. The spectrum confirms the extreme sharpness of the red edge of the redshifted Si II 1260 A feature, supporting the idea that this edge represents the location of the reverse shock moving into the freely expanding ejecta. The expansion velocity of ejecta at the reverse shock is measured to be 7026 +-3(relative) +-10(absolute) km/s. If the shock model is correct, then the expansion velocity should be decreasing at the observable rate of 2.7 +-0.1 km/s per year. The pre-shock velocity, post-shock velocity, and post-shock velocity dispersion are all measured from the Si II 1260 A feature, and consistency of these velocities with the shock jump conditions implies that there is little or no electron heating in this fast (2680 km/s) Si-rich shock.

 

astro-ph/0602554 [abs, ps, pdf, other] :

Title: Powerful High Velocity-Dispersion Molecular Hydrogen Associated with an Intergalactic Shock Wave in Stephan's Quintet
Authors: P. N. Appleton, K. C. Xu, W. Reach, M. A. Dopita, Y. Gao, N. Lu, C. C. Popescu, J. W. Sulentic, R. J. Tuffs, M. S. Yun
Comments: 4 pages, 4 figures and 1 table

We present the discovery of strong mid-infrared emission lines of molecular hydrogen of apparently high velocity dispersion (~870 km/s) originating from a group-wide shock wave in Stephan's Quintet. These Spitzer Space Telescope observations reveal emission lines of molecular hydrogen and little else. this is the first time an almost pure H_2 line spectrum has been seen in an extragalactic object. Along with the absence of PAH features and very low excitation ionized gas tracers, the spectra resemble shocked gas seen in Galactic supernova remnants, but on a vast scale. The molecular emission extends over 24 kpc along the X-ray emitting shock-front, but has ten times the surface luminosity as the soft X-rays, and about one-third the surface luminosity of the IR continuum. We suggest that the powerful H_2 emission is generated by the shock wave caused when a high-velocity intruder galaxy collides with filaments of gas in the galaxy group. Our observations suggest a close connection between galaxy-scale shock-waves and strong broad H_2 emission lines, like those seen in the spectra of Ultraluminous Infrared Galaxies where high-speed collisions between galaxy disks are common.

 

astro-ph/0602555 [abs, ps, pdf, other] :

Title: Probing Multiple Sight Lines through the SN 1006 Remnant by UV Absorption Spectroscopy
Authors: P. Frank Winkler (Middlebury), Knox S. Long (STScI), Andrew J. S. Hamilton (JILA, U. Colorado), Robert A. Fesen (Dartmouth)
Comments: 26 pages, 8 postscript figures
Journal-ref: ApJ 624, 189-197 (2005)

Absorption-line spectroscopy is an effective probe for cold ejecta within an SNR, provided that suitable background UV sources can be identified. For the SN 1006 remnant we have identified four such sources, in addition to the much-studied Schweitzer-Middleditch (SM) star. We have used STIS on HST to obtain UV spectra of all four sources, to study "core samples" of the SN 1006 interior. The line of sight closest to the center of the SNR shell, passing only 2.0 arcmin away, is to a V = 19.5 QSO at z = 1.026. Its spectrum shows broad Fe II absorption lines, asymmetric with red wings broader than blue. The similarity of these profiles to those seen in the SM star, which is 2.8 arcmin from the center in the opposite direction, confirms the existence of a bulge on the far side of SN 1006. The Fe II equivalent widths in the QSO spectrum are ~ 50% greater than in the SM star, suggesting that somewhat more iron may be present within SN 1006 than studies of the SM star alone have indicated, but this is still far short of what most SNIa models require. The absorption spectrum against a brighter z = 0.337 QSO seen at 57% of the shell radius shows broad silicon absorption lines but no iron other than narrow, probably interstellar lines. The cold iron expanding in this direction must be confined within v <~ 5200 km/s, also consistent with a high-velocity bulge on the far side only. The broad silicon lines indicate that the silicon layer has expanded beyond this point, and that it has probably been heated by a reverse shock. Finally, the spectra of two ~ A0V stars near the southern shell rim show no broad or unusually strong absorption lines, suggesting that the low-ionization ejecta are confined within 83% of the shell radius, at least at the azimuths of these background sources.

 

astro-ph/0602556 [abs, ps, pdf, other] :

Title: The intensity contrast of solar photospheric faculae and network elements II. Evolution over the rising phase of solar cycle 23
Authors: Ada Ortiz, Vicente Domingo, Blai Sanahuja
Comments: 11 pages, 6 figures, A&A in press

We studied the radiative properties of small magnetic elements (active region faculae and the network) during the rising phase of solar cycle 23 from 1996 to 2001, determining their contrasts as a function of heliocentric angle, magnetogram signal, and the solar cycle phase. We combined near-simultaneous full disk images of the line-of-sight magnetic field and photospheric continuum intensity provided by the MDI instrument on board the SOHO spacecraft. Sorting the magnetogram signal into different ranges allowed us to distinguish between the contrast of different magnetic structures. We find that the contrast center-to-limb variation (CLV) of these small magnetic elements is independent of time with a 10% precision, when measured during the rising phase of solar cycle 23. A 2-dimensional empirical expression for the contrast of photospheric features as a function of both the position on the disk and the averaged magnetic field strength was determined, showing its validity through the studied time period. A study of the relationship between magnetogram signal and the peak contrasts shows that the intrinsic contrast (maximum contrast per unit of magnetic flux) of network flux tubes is higher than that of active region faculae during the solar cycle.

 

astro-ph/0602557 [abs, ps, pdf, other] :

Title: The 2:1 resonant exoplanetary system orbiting HD73526
Authors: C.G. Tinney, R. Paul Butler, Geoffrey W. Marcy, Hugh R.A. Jones, Gregory Laughlin, Brad D. Carter, Jeremy A. Bailey, Simon O'Toole
Comments: To appear in The Astrophysical Journal

We report the detection of a second exoplanet orbiting the G6V dwarf HD73526. This second planet has an orbital period of 377 d, putting it in a 2:1 resonance with the previously known exoplanet, the orbital period for which is updated to 188d. Dynamical modeling of the combined system allows solution for a self-consistent set of orbital elements for both components. HD73526 is the fourth exoplanetary system (of a total of 18 systems with 2 or more components currently known) to have components detected in 2:1 resonance. Finding such a large fraction of multiple planets (more than 20 per cent) in 2:1 resonance strongly suggests that orbital migration, halted by stabilisation in a trapping resonance, plays an important role in the evolution of exoplanets in multiple planet systems.

 

astro-ph/0602558 [abs, ps, pdf, other] :

Title: Luminosity dependent study of the High Mass X-ray Binary Pulsar 4U~0114+65 with ASCA
Authors: U. Mukherjee, B. Paul
Comments: 14 pages, 4 figures and 2 tables. Accepted in Journal of Astrophysics and Astronomy

Here we report the spectral characteristics of the high and low states of the pulsar 4U~0114+65 and examine the change in the parameters of the spectral model. A power law and a photoelectric absorption by material along the line of sight together with a high energy cut-off suffice to describe the continuum spectrum in both the states. A fluorescence iron line at $\sim$6.4 keV is present in the high as well as in the low state, though it is less intense in the latter. The photon index, cut-off energy and e-folding energy values hardly show any discernible change over the states. We compare these spectral characteristics as observed with ASCA to that with other satellites. We also compare the spectral characteristics of 4U~0114+650 with other X-ray sources which show intensity variation at different time scales.

 

astro-ph/0602559 [abs, ps, pdf, other] :

Title: Variable Quasi Periodic Oscillations during an outburst of the transient X-ray pulsar XTE J1858+034
Authors: U. Mukherjee, S. Bapna, H. Raichur, B. Paul, S. N. A. Jaaffrey
Comments: 17 pages, 8 figures and 1 table. Accepted in Journal of Astrophysics and Astronomy

We have investigated the Quasi Periodic Oscillation (QPO) properties of the transient accreting X-ray pulsar XTE J1858+034 during the second outburst of this source in April-May 2004. We have used observations made with the Proportional Counter Array (PCA) of the Rossi X-ray Timing Explorer (RXTE) during May 14-18 2004, in the declining phase of the outburst. We detected the presence of low frequency QPOs in the frequency range of 140--185 mHz in all the RXTE-PCA observations. We report evolution of the QPO parameters with the time, X-ray flux, and X-ray photon energy. Though a correlation between the QPO centroid frequency and the instantaneous X-ray flux is not very clear from the data, we point out that the QPO frequency and the one day averaged X-ray flux decreased with time during these observations. We have obtained a clear energy dependence of the RMS variation in the QPOs, increasing from about 3% at 3 keV to 6% at 25 keV. The X-ray pulse profile is a single peaked sinusoidal, with pulse fraction increasing from 20% at 3 keV to 45% at 30 keV. We found that, similar to the previous outburst, the energy spectrum is well fitted with a model consisting of a cut-off power law along with an iron emission line.

 

astro-ph/0602560 [abs, ps, pdf, other] :

Title: LOFAR views of cosmic reionization
Authors: M. Valdes, B. Ciardi, A. Ferrara, M. Johnston-Hollitt, H. Rottgering
Comments: 6 pages, 3 figures

We use numerical simulations of cosmic reionization and radiative processes related to the HI 21 cm emission line to produce synthetic radio maps as seen by LOFAR, a new radio telescope currently under construction that will operate at low radio frequencies. Two different scenarios, in which the end of reionization occurs early (z approx 13) or late (z approx 8) depending on the Initial Mass Function (IMF) of the first stars and ionizing photon escape fraction, have been explored. For each of these models we produce synthetic HI 21 cm emission maps by convolving the simulation outputs with the LOFAR sampling function in the frequency range 76-140 MHz. If reionization occurs late, LOFAR will be able to detect individual HI structures on arcmin scales, emitting at a brightness temperature of approx 35 mK as a 3-sigma signal in about 1000 hours of observing time. In the case of early reionization, the detection would be unlikely, due to decreased sensitivity and increased sky temperatures. These results assume that ionospheric, interference and foreground issues are fully under control.

 

astro-ph/0602561 [abs, ps, pdf, other] :

Title: Physical origin of X-ray flares following GRBs
Authors: Bing Zhang (UNLV)
Comments: 6 pages, 2 figure, uses aipproc.cls; to appear in ``16th Annual October Astrophysics Conference in Maryland", eds. S. Holt, N. Gehrels and J. Nousek, AIP Conf.Procs

One of the major achievements of Swift is the discovery of the erratic X-ray flares harboring nearly half of gamma-ray bursts (GRBs), both for long-duration and short-duration categories, and both for traditional hard GRBs and soft X-ray flashes (XRFs). Here I review the arguments in support of the suggestion that they are powered by reactivation of the GRB central engine, and that the emission site is typically ``internal'', i.e. at a distance within the forward shock front. The curvature effect that characterizes the decaying lightcurve slope during the fading phase of the flares provides an important clue. I will then discuss several suggestions to re-start the GRB central engine and comment on how future observations may help to unveil the physical origin of X-ray flares.

 

astro-ph/0602562 [abs, ps, pdf, other] :

Title: Spot patterns and differential rotation in the eclipsing pre-CV binary,V471 Tau
Authors: G. A. J. Hussain, C. Allende Prieto, S. H. Saar, M. D. Still
Comments: 12 pages, 9 figures, accepted by MNRAS

We present surface spot maps of the K2V primary star in the pre-cataclysmic variable binary system, V471 Tau. The spot maps show the presence of large high latitude spots located at the sub-white dwarf longitude region. By tracking the relative movement of spot groups over the course of four nights (eight rotation cycles), we measure the surface differential rotation rate of the system.Our results reveal that the star is rotating rigidly with a surface shear rate, dOmega = 1.6 +/- 6 mrad/d. The single active star AB Dor has a similar spectral type, rotation period, and activity level as the K star in V471 Tau but displays much stronger surface shear (46 < dOmega < 58 mrad/d). Our results suggest that tidal locking may inhibit differential rotation; this reduced shear, however, does not affect the overall magnetic activity levels in active K dwarfs.

 

astro-ph/0602563 [abs, ps, pdf, other] :

Title: Prediction of Supersoft X-ray Phase during the 2006 Outburst of RS Ophiuchi
Authors: Izumi Hachisu (Univ. of Tokyo), Mariko Kato (Keio Univ.)
Comments: 13 pages including 4 figures, submitted to ApJL

RS Ophiuchi is one of the well-observed recurrent novae and also a candidate progenitor of Type Ia supernovae. It has undergone the sixth recorded outburst on 12 February 2006. Detection of supersoft X-ray phases of novae will provide a firm confirmation of hydrogen shell-burning on the white dwarf and its turn-on/turn-off dates strongly constrain a mass range of the white dwarf, which clarify whether or not RS Oph becomes a Type Ia supernova. For a timely detection of its supersoft X-ray phase, we have calculated outburst evolution of RS Oph based on the optically thick wind theory, and predicted the days of supersoft X-ray phase for its 2006 outburst: it will most probably start on day 80-90 and continue until day 110-120 after the optical maximum. Its duration is so short as only a month or so. We strongly recommend multiple observations during April, May, and June of 2006 to detect turn-on and turn-off times of the supersoft X-ray phase.

 

astro-ph/0602564 [abs, ps, pdf, other] :

Title: The dust disk dynamics in week-nonlinear regime
Authors: Victor M. Zhuravlev, Alexander V. Patrushev
Comments: 12 pages,1 figure

We investigate the problem of self-gravitating dust disk dynamics in a static state taking into account nonlinear effects. For this purpose Schrodinger-type equation including the mass conservation law is used for the whole description of hydrodynamic flows of self-gravitating dust. We have shown a purely hydrodynamic mechanism of ring formation in the radial direction by taking into account nonlinearity in the lowest order of expansion parameter, which determines an order of magnitude of flow.

 

astro-ph/0602565 [abs, ps, pdf, other] :

Title: The asymmetric structure of the Galactic halo
Authors: Y. Xu, L. C. Deng, J. Y. Hu
Comments: 17 pages, 7 figures, 5 tables, MNRAS accepted

Using the stellar photometry catalogue based on the latest data release (DR4) of the Sloan Digital Sky Survey (SDSS), a study of the Galactic structure using star counts is carried out for selected areas of the sky. The sample areas are selected along a circle at a Galactic latitude of +60$^\circ$, and 10 strips of high Galactic latitude along different longitudes. Direct statistics of the data show that the surface densities of $\ell$ from $180^{\circ}$ to $360^{\circ}$ are systematically higher than those of $\ell$ from $0^{\circ}$ to $180^{\circ}$, defining a region of overdensity (in the direction of Virgo) and another one of underdensity (in the direction of Ursa Major) with respect to an axisymmetric model. It is shown by comparing the results from star counts in the $(g-r)$ colour that the density deviations are due to an asymmetry of the stellar density in the halo. Theoretical models for the surface density profile are built and star counts are performed using a triaxial halo of which the parameters are constrained by observational data. Two possible reasons for the asymmetric structure are discussed.

 

astro-ph/0602566 [abs, ps, pdf, other] :

Title: Suppressing cluster cooling flows by multiple AGN activity
Authors: Adi Nusser, Joseph Silk, Arif Babul

We apply a spherically symmetric one-dimensional hydrodynamical code to study the heating of the inter-cluster medium (ICM) by AGN activity in cluster galaxies. The AGNs drive bubbles into the ICM and the resulting heating is assumed to be self-regulating. Bubbles affect the ICM in three distinct ways. Firstly, immediately after injection, bubbles expand in situ until they reach pressure equilibrium with the ICM. During this expansion, they heat the ICM by means of weak shocks. Secondly, buoyancy is resisted by viscous or turbulent drag which can also heat the ICM. Thirdly and less importantly, as the bubbles rise by buoyancy, they expand and do adiabatic work which shortens the cooling time in the ICM. The resulting feedback adds considerably to previous estimates of mechanical energy input based only on the observed thermal energy content of x-ray cavities, and suffices to suppress cluster cooling flows. Our self-regulating scenario predicts that there should be enhanced AGN activity of galaxies inside cooling regions compared to galaxies in the outer parts of the cluster. This prediction remains to be confirmed or refuted by observations.

 

astro-ph/0602567 [abs, ps, pdf, other] :

Title: CCD photometric search for peculiar stars in open clusters. VII. Berkeley 11, Berkeley 94, Haffner 15, Lynga 1, NGC 6031, NGC 6405, NGC 6834 and Ruprecht 130
Authors: E. Paunzen, M. Netopil, I.Kh. Iliev, H.M. Maitzen, A. Claret, O.I. Pintado

The detection of magnetic chemically peculiar (CP2) stars in open clusters of the Milky Way can be used to study the influence of different galactic environments on the (non-)presence of peculiarities, which has to be taken into account in stellar evolution models. Furthermore it is still unknown if the CP2 phenomenon evolves, i.e. does the strength of the peculiarity feature at 5200A, increase or decrease with age. We have observed eight young to intermediate age open clusters in the Delta a photometric system. This intermediate band photometric system samples the depth of the 5200A, flux depression by comparing the flux at the center with the adjacent regions having bandwidths of 110A, to 230A. The Delta a photometric system is most suitable to detect CP2 stars with high efficiency, but is also capable of detecting a small percentage of non-magnetic CP objects. Also, the groups of (metal-weak) lambda Bootis, as well as classical Be/shell stars, can be successfully investigated. This photometric system allows one to determine the age, reddening and distance modulus by fitting isochrones. Among the presented sample of eight galactic clusters, we have detected twenty three CP2, eight Be/Ae and eight metal-weak stars. Another six objects show a peculiar behaviour which is most probably due to a non-membership,variability or duplicity. Fitting isochrones to Delta a photometry yields estimates of the age, reddening and distance that are in excellent agreement with published values.

 

astro-ph/0602568 [abs, ps, pdf, other] :

Title: Generation of Shocked Hot Plasma Region in Black Hole Magnetosphere
Authors: Keigo Fukumura, Masaaki Takahashi, Sachiko Tsuruta
Comments: 35 pages, 18 b/w figures, submitted to ApJ, Corrected in v2: Incorrect Greek letters in figure labels fixed

We study magnetohydrodynamic (MHD) standing shocks in ingoing plasmas in a black hole (BH) magnetosphere. Fast and intermediate shock formation is explored in Kerr geometry. We find that low or high latitude standing MHD shocks are both possible, creating a very hot plasma region near the event horizon. Shocked downstream plasmas become substantially hot or magnetized depending on model parameters. We also investigate the effects of the poloidal magnetic field and the BH spin on the properties of shocks and show that both effects can significantly affect the characteristics of MHD shocks. A speculation for a possible connection between the global BH magnetosphere and the resulting shocks is presented in the framework of a simple disk-corona model. MHD shock formation can be a plausible mechanism for high energy radiation which illuminates the underlying accretion disk, relevant for the cause of the observed iron fluorescence in accretion-powered active galactic nuclei (AGNs).

 

astro-ph/0602569 [abs, ps, pdf, other] :

Title: A Spectroscopic Survey of Faint Quasars in the SDSS Deep Stripe: I. Preliminary Results from the Co-added Catalog
Authors: L. Jiang, X. Fan, R. J. Cool, D. J. Eisenstein, I. Zehavi, G. T. Richards, R. Scranton, D. Johnston, M. A. Strauss, D. P. Schneider, J. Brinkmann
Comments: 25 pages, 13 figures, accepted for publication in AJ

In this paper we present the first results of a deep spectroscopic survey of faint quasars in the Sloan Digital Sky Survey (SDSS) Southern Survey, a deep survey carried out by repeatedly imaging a 270 deg^2 area. Quasar candidates were selected from the deep data with good completeness over 0<z<5, and 2 to 3 magnitudes fainter than the SDSS main survey. Spectroscopic follow-up was carried out on the 6.5m MMT with Hectospec. The preliminary sample of this SDSS faint quasar survey (hereafter SFQS) covers ~ 3.9 deg^2, contains 414 quasars, and reaches g=22.5. The overall selection efficiency is ~ 66% (~ 80% at g<21.5); the efficiency in the most difficult redshift range (2<z<3) is better than 40%. We use the 1/V_{a} method to derive a binned estimate of the quasar luminosity function (QLF) and model the QLF using maximum likelihood analysis. The best model fits confirm previous results showing that the QLF has steep slopes at the bright end and much flatter slopes (-1.25 at z<2.0 and -1.55 at z>2.0) at the faint end, indicating a break in the QLF slope. Using a luminosity-dependent density evolution model, we find that the quasar density at M_{g}<-22.5 peaks at z~2, which is later in cosmic time than the peak of z~2.5 found from surveys of more luminous objects. The SFQS QLF is consistent with the results of the 2dF QSO Redshift Survey, the SDSS, and the 2dF-SDSS LRG and QSO Survey, but probes fainter quasars. We plan to obtain more quasars from future observations and establish a complete faint quasar sample with more than 1000 objects over 10 deg^2.

 

astro-ph/0602570 [abs, ps, pdf, other] :

Title: A comprehensive Nbody study of mass segregation in star clusters: Energy equipartition and ejection
Authors: Emil Khalisi, Pau Amaro-Seoane, Rainer Spurzem
Comments: 21 pages, submitted to MNRAS, needs mn2e.bst and mn2e.cls (included)

We address the dynamical evolution of an isolated self--gravitating system with two stellar mass groups. We vary the individual ratio of the heavy to light bodies, $\mu$ from 1.25 to 50 and alter also the fraction of the total heavy mass $\MH$ from 5% to 40% of the whole cluster mass. Clean-cut properties of the cluster dynamics are examined, like core collapse, the evolution of the central potential, as well as escapers. We present in this work collisional $N$-body simulations, using the high--order integrator NBODY6++ with up to ${\cal N}_{\star}=2\cdot 10^4$ particles improving the statistical significancy of the lower--${\cal N}_{\star}$ simulations by ensemble averages. Equipartition slows down the gravothermal contraction of the core slightly. Beyond a critical value of $\mu \approx 2$, no equipartition can be achieved between the different masses; the heavy component decouples and collapses. For the first time the critical boundary between Spitzer--stable and --unstable systems is demonstrated in direct $N$-body models.

 

astro-ph/0602571 [abs, ps, pdf, other] :

Title: Neutral Hydrogen Clouds near Early-Type Dwarf Galaxies of the Local Group
Authors: A. Bouchard, C. Carignan, L. Staveley-Smith
Comments: Accepted in AJ, June 2006

Parkes neutral hydrogen 21 cm line (HI) observations of the surroundings of 9 early-type Local Group dwarfs are presented. We detected numerous HI clouds in the general direction of those dwarfs and these clouds are often offset from the optical center of the galaxies. Although all the observed dwarfs, except Antlia, occupy phase-space regions where the High-Velocity Cloud (HVC) density is well above average, the measured offsets are smaller than one would expect from a fully random cloud distribution. Possible association is detected for 11 of the 16 investigated clouds, while, for two galaxies, Sextans and Leo I, no HI was detected. The galaxies where HI clouds were found not to coincide with the optical, yet have a significant probability of being associated are: Sculptor dSph, Tucanna, LGS3, Cetus, and Fornax. If the clouds are indeed associated, these galaxies have HI masses of $M_{HI} = 2\times10^5 M_{\odot}$, $M_{HI} = 2\times10^6 M_{\odot}$, $M_{HI} = 7\times10^5 M_{\odot}$, $M_{HI} = 7\times10^5 M_{\odot}$, and $M_{HI} = 1\times10^5 M_{\odot}$, respectively. However, neither ram pressure nor tidal stripping can easily explain the offsets. In some cases, large offsets are found where ram pressure should be the least effective.

 

astro-ph/0602572 [abs, ps, pdf, other] :

Title: Cepheid Distances to SNe Ia Host Galaxies based on a Revised Photometric Zero-Point of the HST-WFPC2 and New P-L Relations and Metallicity Corrections
Authors: A. Saha (1), F. Thim (1), G.A. Tammann (2), B. Reindl (2), A. Sandage (3) ((1) NOAO, (2) Astr. Inst. Univ. Basel, (3) Obs. Carnegie Inst. Washington)
Comments: 73 pages, 16 figures, 8 tables, accepted for publication in the Astrophysical Journal

With this paper we continue the preparation for a forthcoming summary report of our experiment with the Hubble Space Telescope (HST) to determine the Hubble constant using type Ia supernovae as standard candles. Two problems are addressed. (1) We examine the need for, and determine the value of, the corrections to the apparent magnitudes of our program Cepheids in the eleven previous calibration papers due to sensitivity drifts and charge transfer effects of the HST WFPC2 camera over the life time of the experiment from 1992 to 2001. (2) The corrected apparent magnitudes are applied to all our previous photometric data from which revised distance moduli are calculated for the eight program galaxies that are parents to the calibrator Ia supernovae. Two different Cepheid P-L relations are used; one for the Galaxy and one for the LMC. These differ both in slope and zero-point at a fixed period. The procedures for determining the absorption and reddening corrections for each Cepheid are discussed. Corrections for the effects of metallicity differences between the program galaxies and the two adopted P-L relations are derived and applied. The distance moduli derived here for the eight supernovae program galaxies, and for 29 others, average 0.20 mag fainter (more distant) than those derived by Gibson et al. and Freedman et al. in their 2000 and 2001 summary papers for reasons discussed in this paper. The effect on the Hubble constant is the subject of our forthcoming summary paper.

 

astro-ph/0602573 [abs, ps, pdf, other] :

Title: GalaxyCount: a JAVA calculator of galaxy counts and variances in magnitude-limited wide-field surveys down to B=28 mag
Authors: S.C. Ellis, J. Bland-Hawthorn (AAO)
Comments: We invite comments and recommendations on both the paper and the calculator, prior to submission. 14 pages, 12 figures

We provide a consistent framework for estimating galaxy counts and variances in wide-field images for a range of photometric bands. We demonstrate that our statistical theory is consistent with the counts in the deepest multiband surveys available. The statistical estimates depend on several observational parameters (e.g. seeing, signal to noise ratio). The JAVA calculator is freely available and offers the user the option to adopt our consistent framework or a different scheme. We also provide a summary table of counts and standard deviations in the different bands for a range of different fields of view.
Reliable estimation of the background counts has profound consequences in many areas of observational astronomy. We provide one such example from a recent study of the Sculptor galaxy NGC 300 where stellar photometry has been used to demonstrate that the outer disc extends to 10 effective radii, far beyond what was thought possible for a normal low-luminosity spiral. We confirm this finding by a reanalysis of the background counts.

 

astro-ph/0602574 [abs, ps, pdf, other] :

Title: A method to identify the companion stars of type Ia supernovae in young supernova remnants
Authors: Jin Ozaki, Toshikazu Shigeyama
Comments: 5 pages, 2 figures, accepted for the publication of The Astrophysical Journal

We propose a method to identify the companion stars of type Ia supernovae (SNe Ia) in young supernova remnants (SNRs) by recognizing distinct features of absorption lines due to Fe I appearing in the spectrum. If a sufficient amount of Fe I remains in the ejecta, Fe I atoms moving toward us absorb photons by transitions from the ground state to imprint broad absorption lines exclusively with the blue-shifted components in the spectrum of the companion star. To investigate the time evolution of column depth of Fe I in the ejecta, we have performed hydrodynamical calculations for SNRs expanding into the uniform ambient media, taking into account collisional ionizations, excitations, and photo-ionizations of heavy elements. As a result, it is found that the companion star in Tycho's SNR will exhibit observable features in absorption lines due to Fe I at $\lambda\lambda = 371.9935$ nm and 385.9911 nm if a carbon deflagration SN model is taken. However, these features may disappear by taking another model that emits a few times more intense ionizing photons from the shocked outer layers. To further explore the ionization states in the freely expanding ejecta, we need a reliable model to describe the structure of the outer layers.

 

astro-ph/0602575 [abs, ps, pdf, other] :

Title: The Alignments of Disk Galaxies with the Local Pancakes
Authors: Yookyung Noh, Jounghun Lee (Seoul National Univ.)
Comments: submitted to the ApJL, 12 pages, 2 ps figures

We analyze the Tully catalog of nearby galaxies to investigate the local pancaking effect on the orientation of disk galaxies. We first select only those edge-on disk galaxies in the catalog whose axis-ratios are less than 0.1 to measure their spin axes unambiguously. A local pancake at the location of each selected galaxy is found as a plane encompassing the two nearest neighbor disks. Then, we examine statistically the inclinations of the galaxy spin axes relative to the local pancake planes. It is detected that the Tully disk galaxies tend to be inclined onto the local pancake planes, and the average inclination angles decrease with the pancake scale. We also construct a theoretical model for the inclination of disk galaxies relative to the local pancakes in the frame of the linear tidal torque theory. The comparison of the theoretical prediction with the observational result demonstrates a good agreement. Finally, we conclude that it is a first detection of the local pancaking effect on the orientation of disk galaxies, which is consistent with the scenario that the gravitational tidal field promotes the formation of pancakes on small mass scale.

 

astro-ph/0602576 [abs, ps, pdf, other] :

Title: The buildup of stellar mass and the 3.6 micron luminosity function in clusters from z=1.25 to z=0.2
Authors: S. Andreon (INAF-OA Brera)
Comments: appeared on A&A (A&A 448, 447)

We have measured the 3.6 micron luminosity evolution of about 1000 galaxies in 32 clusters at 0.2<z<1.25, without any a priori assumption about luminosity evolution, i.e. in a logically rigorous way. We find that the luminosity of our galaxies evolves as an old and passively evolving population formed at high redshift without any need for additional redshift-dependent evolution. Models with a prolonged stellar mass growth are rejected by the data with high confidence. The data also reject models in which the age of the stars is the same at all redshifts. Similarly, the characteristic stellar mass evolves, in the last two thirds of the universe age, as expected for a stellar population formed at high redshift. Together with the old age of stellar populations derived from fundamental plane studies, our data seems to suggest that early-type cluster galaxies have been completely assembled at high redshift, and not only that their stars are old. The quality of the data allows us to derive the LF and mass evolution homogeneously over the whole redshift range, using a single estimator. The Schechter function describes the galaxy luminosity function well. The characteristic luminosity at z=0.5 is is found to be 16.30 mag, with an uncertainty of 10 per cent.

 

astro-ph/0602577 [abs, ps, pdf, other] :

Title: CMB constraints on the fine structure constant
Authors: Kazuhide Ichikawa, Toru Kanzaki, Masahiro Kawasaki
Comments: 8 pages, 8 figures

We study constraints on time variation of the fine structure constant alpha from cosmic microwave background (CMB) taking into account simultaneous change in alpha and the electron mass m_e which might be implied in unification theories. We obtain the constraints -0.097 < Delta alpha/alpha < 0.034 at 95% C.L. using WMAP data only, and -0.042 < Delta alpha/alpha < 0.026 combining with the constraint on the Hubble parameter by the HST Hubble Key Project. These are improved by 15% from constraints assuming only alpha varies. We discuss other relations between variations in alpha and m_e but we do not find evidence for varying alpha.

 

astro-ph/0602578 [abs, ps, pdf, other] :

Title: Adapting and expanding interferometric arrays
Authors: A. Karastergiou, R. Neri, M. A. Gurwell
Comments: Accepted for publication in ApJS

We outline here a simple yet efficient method for finding optimized configurations of the elements of radio-astronomical interferometers with fixed pad locations. The method can be successfully applied, as we demonstrate, to define new configurations when changes to the array take place. This may include the addition of new pads or new antennas, or the loss of pads or antennas. Our method is based on identifying which placement of elements provides the most appropriate uv plane sampling for astronomical imaging.

 

astro-ph/0602579 [abs, ps, pdf, other] :

Title: Curvaton reheating mechanism in inflation on warped Dvali-Gabadadze-Porrati brane
Authors: Hongsheng Zhang, Zong-Hong Zhu
Comments: 10 pages, 7 figures, submitted to PRD

An impressed feature of inflation on warped Dvali-Gabadadze-Porrati (DGP) brane is that the inflationary phase exits spontaneously for a scalar inflaton field with exponential potential, which presents a graceful exit mechanism for the inflation. But its reheating mechanism leaves open. We investigate the curvaton reheating in inflation on warped DGP brane model. The reheating may occur in effctively 5 dimensional or 4 dimensional stage. We study the permitted parameter space of the curvaton field in detail. We demonstrate how the inflation model of the warped DGP brane is improved by the curvaton mechanism.

 

astro-ph/0602580 [abs, ps, pdf, other] :

Title: Astrocladistics: a phylogenetic analysis of galaxy evolution II. Formation and diversification of galaxies
Authors: Didier Fraix-Burnet (LAOG), Emmanuel J.P. Douzery (ISE), Philippe Choler (LEA), Anne Verhamme (LAOG)
Comments: 14 pages, 4 figures
Journal-ref: Journal of Classification 23 (2006) XX

This series of papers is intended to evaluate astrocladistics in reconstructing phylogenies of galaxies. The objective of this second paper is to formalize the concept of galaxy formation and to identify the processes of diversification. We show that galaxy diversity can be expected to organize itself in a hierarchy. In order to better understand the role of mergers, we have selected a sample of 43 galaxies from the GALICS database built from simulations with a hybrid model for galaxy formation studies. These simulated galaxies, described by 119 characters and considered as representing still undefined classes, have experienced different numbers of merger events during evolution. Our cladistic analysis yields a robust tree that proves the existence of a hierarchy. Mergers, like interactions (not taken into account in the GALICS simulations), are probably a strong driver for galaxy diversification. Our result shows that mergers participate in a branching type of evolution, but do not seem to play the role of an evolutionary clock.

 

astro-ph/0602581 [abs, ps, pdf, other] :

Title: Astrocladistics: a phylogenetic analysis of galaxy evolution I. Character evolutions and galaxy histories
Authors: Didier Fraix-Burnet (LAOG), Philippe Choler (LEA), Emmanuel J.P. Douzery (ISE), Anne Verhamme (LAOG)
Comments: 16 pages, 6 figures
Journal-ref: Journal of Classification 23 (2006) XX

This series of papers is intended to present astrocladistics in some detail and evaluate this methodology in reconstructing phylogenies of galaxies. Being based on the evolution of all the characters describing galaxies, it is an objective way of understanding galaxy diversity through evolutionary relationships. In this first paper, we present the basic steps of a cladistic analysis and show both theoretically and practically that it can be applied to galaxies. For illustration, we use a sample of 50 simulated galaxies taken from the GALICS database, which are described by 91 observables (dynamics, masses and luminosities). These 50 simulated galaxies are indeed 10 different galaxies taken at 5 cosmological epochs, and they are free of merger events. The astrocladistic analysis easily reconstructs the true chronology of evolution relationships within this sample. It also demonstrates that burst characters are not relevant for galaxy evolution as a whole. A companion paper is devoted to the formalization of the concepts of formation and diversification in galaxy evolution.

 

astro-ph/0602582 [abs, ps, pdf, other] :

Title: Chemical evolution in Sersic 159-03 observed with XMM-Newton
Authors: J. de Plaa, N. Werner, A. M. Bykov, J. S. Kaastra, M. Mendez, J. Vink, J. A. M. Bleeker, M. Bonamente, J. R. Peterson
Comments: 18 pages, 11 figures, Accepted for publication in Astronomy & Astrophysics

Using a new long X-ray observation of the cluster of galaxies Sersic 159-03 with XMM-Newton, we derive radial temperature and abundance profiles using single- and multi-temperature models. The fits to the EPIC and RGS spectra prefer multi-temperature models especially in the core. The radial profiles of oxygen and iron measured with EPIC/RGS and the line profiles in RGS suggest that there is a dip in the O/Fe ratio in the centre of the cluster compared to its immediate surroundings. A possible explanation for the large scale metallicity distribution is that SNIa and SNII products are released in the ICM through ram-pressure stripping of in-falling galaxies. This causes a peaked metallicity distribution. In addition, SNIa in the central cD galaxy enrich mainly the centre of the cluster with iron. This excess of SNIa products is consistent with the low O/Fe ratio we detect in the centre of the cluster. We fit the abundances we obtain with yields from SNIa, SNII and Population-III stars to derive the clusters chemical evolution. We find that the measured abundance pattern does not require a Population-III star contribution. The relative contribution of the number of SNIa with respect to the total number of SNe which enrich the ICM is about 25-50%. Furthermore, we discuss the possible presence of a non-thermal component in the EPIC spectra. A potential source of this non-thermal emission can be inverse-Compton scattering between Cosmic Microwave Background (CMB) photons and relativistic electrons, which are accelerated in bow shocks associated with ram-pressure stripping of in-falling galaxies.

 

astro-ph/0602583 [abs, ps, pdf, other] :

Title: XMM-Newton observations of the Coma cluster relic 1253+275
Authors: Luigina Feretti (1,2), Doris M. Neumann (2) (1 IRA-BO Italy, 2 SAP/CEA Saclay France)
Comments: 4 pages, 2 figures, Accepted for publication in A&A Letters

Using XMM Newton data, we investigate the nature of the X-ray emission in the radio relic 1253+275 in the Coma cluster. We determine the conditions of the cluster gas to check current models of relic formation, and we set constraints on the intracluster magnetic field. Both imaging and spectral analysis are performed, and the X-ray emission is compared with the radio emission. We found that the emission is of thermal origin and is connected to the sub-group around NGC 4839. The best-fit gas temperature in the region of the relic and in its vicinity is in the range 2.8 - 4.0 keV, comparable to the temperature of the NGC 4839 sub-group. We do not detect any high temperature gas, resulting from a possible shock in the region of the Coma relic. We therefore suggest that the main source of energy for particles radiating in the radio relic is likely to be turbulence. From the X-ray data, we can also set a flux upper limit of 3.2 x 10e-13 erg/cm^2 s, in the 0.3 - 10 keV energy range, to the non-thermal emission in the relic region. This leads to a magnetic field B > 1.05 microG.

 

astro-ph/0602584 [abs, ps, pdf, other] :

Title: Nonextensive theory of dark matter and gas density profiles
Authors: M. P. Leubner
Comments: 7 pages, 3 figures, published in Astrophys. J. 632, L1, 2005
Journal-ref: ApJ 632, L1, 2005

Pronounced core-halo patterns of dark matter and gas density profiles, observed in relaxed galaxies and clusters, were hitherto fitted by empirical power-laws. On the other hand, similar features are well known from astrophysical plasma environments, subject to long-range interactions, modeled in the context of nonextensive entropy generalization. We link nonextensive statistics to the problem of density distributions in large-scale structures and provide fundamentally derived density profiles, representing accurately the characteristics of both, dark matter and hot plasma distributions, as observed or generated in simulations. The bifurcation of the density distribution into a kinetic dark matter and thermodynamic gas branch turns out as natural consequence of the theory and is controlled by a single parameter kappa, measuring physically the degree of coupling within the system. Consequently, it is proposed to favor nonextensive distributions, derived from the fundamental physical context of entropy generalization and accounting for nonlocality and long-range interactions in gravitationally coupled systems, when modeling observed density profiles of astrophysical structures.

 

astro-ph/0602585 [abs, ps, pdf, other] :

Title: Searching for X-ray luminous 'normal' galaxies in 2dfGRS
Authors: P. Tzanavaris, I. Georgantopoulos, A. Georgakakis
Comments: 8 pages, 2 figures. Accepted for publication in Astronomy & Astrophysics

We cross-correlated the Chandra XASSIST and XMM-Newton Serendipitous Source Catalogues with the 2 degree Field Galaxy Redshift Survey (2dfGRS) database. Our aim was to identify the most X-ray luminous (L_X > 10^42 erg s^-1) examples of galaxies in the local Universe whose X-ray emission is dominated by stellar processes rather than AGN activity ('normal' galaxies) as well as to test the empirical criterion log(f_X/f_O) < -2 for separating AGN from NGs. With XMM-Newton (Chandra) we covered an area of ~8.2 (~5.8)deg^2 down to a flux limit of ~10^-15 (~1.6 x 10^-15) erg cm^-2 s^-1 and found 18 (20) 2dfGRS galaxies. Using emission-line intensity ratios, we classified 6 2dfGRS spectra as star-forming, H II nuclei, and 2 spectra as possible H II nuclei. The rest of the objects are absorption-line galaxies and AGN, including 3 possible LINERs. No luminous 'normal' galaxies have been found but out of 19 'normal' galaxies in this sample 5 H II and 3 absorption-line galaxies have log(f_X/f_O) > -2. We performed a similar search in two nearby-galaxy samples from the literature. All 44 galaxies in the Zezas (2001) sample have log(f_X/f_O) < -2 and L_X < 10^42 erg s^-1. In the Fabbiano et al. (1992) sample, out of a total of 170 'normal' galaxies, we found 16 galaxies with log(f_X/f_O) >-2, the majority of which are massive ellipticals. Three of these have L_X > 10^42 erg s^-1 .

 

astro-ph/0602586 [abs, ps, pdf, other] :

Title: H_2D^+: a light on baryonic dark matter?
Authors: Cecilia Ceccarelli, Carsten Dominik
Comments: Accepted for publication in ApJ Letters

It has been suggested that the dark halos of galaxies are constituted by cloudlets of cold (< 10 K) H_2 and dense (> 10^7$ cm^{-3}) molecular gas. Such gas is extremely difficult to detect, because the classical tracers of molecular gas, CO and/or dust grains, have very low abundances and their emission is exceedingly weak. For this reason, the cloudlet hypothesis remains so far substantially unproven. In this Letter we propose a new method to probe the presence of cold H_2 clouds in galactic halos: the ground transition of ortho-H_2D^+ at 372 GHz. We discuss why the H_2D^+ is abundant under the physical conditions appropriate for the cloudlets, and present a chemical model that predicts the H_2D^+ abundance as function of four key parameters: gas density and metallicity, cosmic ray ionization rate and dust grain size. We conclude that current ground-based instruments might detect the ortho-H_2D^+ line emitted by the cloudlets halo, and prove, therefore, the existence of large quantities of dark baryonic matter around galaxies.

 

astro-ph/0602587 [abs, ps, pdf, other] :

Title: The scaling relation of early-type galaxies in clusters. II: Spectroscopic data for galaxies in eight nearby clusters
Authors: D. Bettoni, M. Moles, P. Kjaergaard, G. Fasano, J. Varela
Comments: 16 pages, 9 figures, Accepted in A&A

AIMS: We present in this work low and intermediate resolution spectroscopic data collected for 152 early type galaxies in 8 nearby clusters with z $\leq$ 0.10.
METHODS: We use low resolution data to produce the redshift and the K-correction for every individual galaxy, as well as to give their overall spectral energy distribution, and some spectral indicators, including the 4000\AA break, the Mg$_2$ strength, and the NaD equivalent width.We have also obtained higher resolution data for early type galaxies in three of the clusters, to determine their central velocity dispersion.
RESULTS: The effect of the resolution on the measured parameters is discussed.
CONCLUSIONS: New accurate systemic redshift and velocity dispersion is presented for four of the surveyed clusters, A98, A3125, A3330, and DC2103-39. We have found that the K-correction values for E/S0 bright galaxies in a given nearby clusters are very similar. We also find that the distribution of the line indicators significantly differ from cluster to cluster.

 

astro-ph/0602588 [abs, ps, pdf, other] :

Title: Systematic effects induced by a flat isotropic dielectric slab
Authors: Claudio Macculi, Mario Zannoni, Oscar Antonio Peverini, Ettore Carretti, Riccardo Tascone, Stefano Cortiglioni
Comments: Accepted for pubblication in Applied Optics, 32 pages, 14 figures (N. 37 ".png", ".bb"). Better quality figures available from author upon request

The instrumental polarization induced by a flat isotropic dielectric slab in microwave frequencies is faced. We find that, in spite of its isotropic nature, such a dielectric can produce spurious polarization either by transmitting incoming anisotropic diffuse radiation or emitting when it is thermally inhomogeneous. We present evaluations of instrumental polarization generated by materials usually adopted in Radioastronomy, by using the Mueller matrix formalism. As an application, results for different slabs in front of a 32 GHz receiver are discussed. Such results are based on measurements of their complex dielectric constant. We evaluate that a 0.33 cm thick Teflon slab introduces negligible spurious polarization ($< 2.6 \times 10^{-5}$ in transmission and $< 6 \times 10^{-7}$ in emission), even minimizing the leakage ($< 10^{-8}$ from $Q$ to $U$ Stokes parameters, and viceversa) and the depolarization ($\sim 1.3 \times 10^{-3}$).

 

astro-ph/0602589 [abs, ps, pdf, other] :

Title: High Resolution Spectra of Novae and the Quadratic Zeeman Effect
Authors: Robert Williams (ST ScI), Elena Mason (ESO)
Comments: 4 pages, 3 figures, 1 table; to appear in Latin American Regional IAU Meeting, Pucon, Dec 2005, RevMexAA(SC)

High resolution spectra of novae after outburst reveal distinctive characteristics in the line profiles and intensities. The higher Balmer lines are often broader than the lower members of the series, and the relative profiles and intensities of the [O I] \lambda\lambda6300, 6364 doublet differ from normal values. We suggest these features may be caused by the Quadratic Zeeman Effect from magnetic fields exceeding B=10^6 gauss. Taken together the emission and absorption lines point to multiple origins for the ejecta on both the erupting white dwarf and the cool secondary star.

 

astro-ph/0602590 [abs, ps, pdf, other] :

Title: Quintom cosmologies admitting either tracking or phantom attractors
Authors: Ruth Lazkoz, Genly León
Comments: revtex4, 7 pages, 6 figures

In this paper we investigate the evolution of a class of cosmologies fuelled by quintom dark energy and dark matter. Quintom dark energy is a hybrid of quintessence and phantom which involves the participation of two reals scalar fields playing the roles of those two types of dark energy. In that framework we examine from a dynamical systems perspective the possibility that those fields are coupled among them by considering an exponential potential with an interesting functional dependence similar but not identical to others studied before. The model we consider represents a counterexample to the typical behavior of quintom models with exponential potentials because it admits either tracking attractors ($w=0$), or phantom attractors ($w<-1$).

 

astro-ph/0602591 [abs, ps, pdf, other] :

Title: How extreme are the Wolf-Rayet clusters in NGC3125?
Authors: L J Hadfield, P A Crowther (Sheffield)
Comments: 12 pages, 8 figures, accepted for MNRAS

We reinvestigate the massive stellar content of NGC3125 (Tol3) using VLT/FORS1 imaging & spectroscopy, plus archival VLT/ISAAC, HST/FOC and HST/STIS datasets. Narrow-band imaging confirms that A and B knots represent the primary sites of Wolf-Rayet (WR) stars, whilst HST imaging reveals that both regions host multiple clusters. Clusters A1 + A2 within region A host WR stars. altough is not clear which cluster within region B hosts WR stars. Nebular properties infer an LMC-like metallicity. LMC template WN5-6 & WC4 spectra are matched to the observed optical WR bumps of A1 and B, permitting the contribution of WC stars to the blue bump to be quantified. We obtain N(WN5-6:WC4)=105:20, 55:0, 40:20 for clusters A1, A2 and B1+B2, a factor of 3 lower than optical studies, as a result of a lower E(B-V). Using Starburst99 models to estimate O star populations for individual clusters, we find N(WR)/N(O)=0.2 for A1 and 0.1 for A2 and B1+B2. From Halpha imaging, the O star content of the Giant HII regions A and B is found to be a factor of 5-10 times higher than that derived spectroscopically for the UV/optically bright clusters, suggesting that NGC3125 hosts optically obscured young massive clusters, further supported by VLT/ISAAC K band imaging. Archival HST/STIS UV spectroscopy confirms the low E(B-V) towards A1, for which we have determined an SMC extinction law, in preference to an LMC or starburst law. We obtain N(WN5-6)=110 from the slit-loss corrected HeII 1640 line flux, in excellent agreement with optical result. However, this is a factor of 35 times lower than that inferred from the same dataset by Chandar et al. due to their use of a starburst extinction law. Highly discrepant stellar populations may result in spatially resolved star forming regions from UV and optical studies through use of different extinction laws.

 

astro-ph/0602592 [abs, ps, pdf, other] :

Title: Extrasolar planets and brown dwarfs around A-F type stars. IV. A candidate brown dwarf around the A9V pulsating star HD180777
Authors: F. Galland, A. M. Lagrange, S. Udry, J. L. Beuzit, F. Pepe, M. Mayor
Comments: 7 pages, final version, accepted for publication (A&A)

We present here the detection of a brown dwarf orbiting the A9V star HD180777. The radial velocity measurements, obtained with the ELODIE echelle spectrograph at the Haute-Provence Observatory, show a main variation with a period of 28.4 days. Assuming a primary mass of 1.7 Mo, the best Keplerian fit to the data leads to a minimum mass of 25 MJup for the companion (the true mass could be significantly higher). We also show that, after substraction of the Keplerian solution from the radial velocity measurements, the residual radial velocities are related to phenomena intrinsic to the star, namely pulsations with typical periods of Gamma Dor stars. These results show that in some cases, it is possible to disentangle radial velocity variations due to a low mass companion from variations intrinsic to the observed star.

 

astro-ph/0602593 [abs, ps, pdf, other] :

Title: Helium preenrichment in the star-forming regions
Authors: Leonid Chuzhoy
Comments: 4 pages

We show that element diffusion can produce large fluctuations in the initial helium abundance of the star-forming clouds. Diffusion time-scale, which in stars is much larger than the Hubble time, can fall below 10^8 years in the neutral gas clouds dominated by collisionless dark matter or with dynamically important radiation or magnetic pressure. Helium diffusion may therefore explain the recent observations of globular clusters, which are inconsistent with initially homogeneous helium distribution.

 

astro-ph/0602594 [abs, ps, pdf, other] :

Title: Prospects for direct detection of primordial gravitational waves
Authors: Sirichai Chongchitnan, George Efstathiou
Comments: 11 pages, 3 figures. Submitted to Phys. Rev. D

We study the primordial gravitational wave background produced in models of single field inflation. Using the inflationary flow approach, we investigate the amplitude of gravitational wave spectrum in the frequency range 1 mHz - 1 Hz pertinent to future space-based laser interferometers. For models that satisfy the current observational constraint on the tensor-to-scalar ratio, r<0.36, we derive a strict upper bound of omega_{gw}<1.6 x 10^{-15}, independent of the form of the inflationary potential. Applying, in addition, the observational constraints on the spectral index and its running, omega_{gw} is expected to be considerably lower than this bound unless the shape of the potential is finely tuned. We contrast our numerical results with those based on simple power-law extrapolation of the tensor power spectrum from CMB scales. In addition to single field inflation, we summarise a number of other possible cosmological sources of primordial gravitational waves and assess what might be learnt from direct detection experiments such as LISA, Big Bang Observer and beyond.

 

astro-ph/0602595 [abs, ps, pdf, other] :

Title: Where are the ``Missing'' Galactic Baryons?
Authors: Jesper Sommer-Larsen (Dark Cosmology Centre, NBI, Univ. of Copenhagen)
Comments: 4 Pages, 4 Figures, Submitted to ApJL, Printing in colour recommended

Based on 19 high-resolution N-body/gas-dynamical galaxy formation simulations in the LCDM cosmology it is shown, that for a galaxy like the Milky Way, in addition to the baryonic mass of the galaxy itself, about 70% extra baryonic mass should reside around the galaxy (inside of the virial radius), chiefly in the form of hot gas. Averaging over the entire field galaxy population, this ``external'' component amounts to 64-85% of the baryonic mass of the population itself. These results are supported by the recent detection of very extended, soft X-ray emission from the halo of the quiescent, massive disk galaxy NGC 5746.
Some of the hot gas may, by thermal instability, have condensed into mainly pressure supported, warm clouds, similar to the Galactic High Velocity Clouds (HVCs). Based on an ultra-high resolution cosmological test simulation of a Milky Way like galaxy (with a gas particle mass and gravity softening length of only 7600 h^-1 Msun and 83 h^-1 pc,respectively), it is argued, that the hot gas phase dominates over the warm gas phase, in the halo. Finally, an origin of HVCs as ``leftovers'' from filamentary, ``cold'' accretion events, mainly occurring early in the history of galaxies, is proposed.