563
The following article is Free article
Closing In on ΩM: The Amplitude of Mass Fluctuations from Galaxy Clusters and the Lyα Forest
David H. Weinberg, Rupert A. C. Croft, Lars Hernquist, Neal Katz, and Max Pettini
View article,Closing In on ΩM: The Amplitude of Mass Fluctuations from Galaxy Clusters and the Lyα ForestPDF,Closing In on ΩM: The Amplitude of Mass Fluctuations from Galaxy Clusters and the Lyα Forest
We estimate the present-day value of the matter density parameter ΩM by combining constraints from the galaxy cluster mass function with Croft et al.'s recent measurement of the mass power spectrum, P(k), from Lyα forest data. The key assumption of the method is that cosmic structure formed by gravitational instability from Gaussian primordial fluctuations. For a specified value of ΩM, matching the observed cluster mass function then fixes the value of σ8, the rms amplitude of mass fluctuations in 8 h-1 Mpc spheres, and it thus determines the normalization of P(k) at z = 0. The value of ΩM also determines the ratio of P(k) at z = 0 to P(k) at z = 2.5, the central redshift of the Lyα forest data; the ratio is different for an open universe (Λ = 0) or a flat universe. Because the Lyα forest measurement only reaches comoving scales 2π/k ~ 15-20 h-1 Mpc, the derived value of ΩM depends on the value of the power spectrum shape parameter Γ, which determines the relative contribution of larger scale modes to σ8. Adopting Γ = 0.2, a value favored by galaxy clustering data, we find ΩM = 0.46+0.12-0.10 for an open universe and ΩM = 0.34+0.13-0.09 for a flat universe (1 σ errors, not including the uncertainty in cluster normalization). Cluster-normalized models with ΩM = 1 predict too low an amplitude for P(k) at z = 2.5, while models with ΩM = 0.1 predict too high an amplitude. The more general best-fit parameter combination is ΩM + 0.2ΩΛ ≈ 0.46 + 1.3(Γ - 0.2), where ΩΛ ≡ Λ/3H20. Analysis of larger, existing samples of QSO spectra could greatly improve the measurement of P(k) from the Lyα forest, allowing a determination of ΩM by this method with a precision of ~15%, limited mainly by uncertainty in the cluster mass function.
604
The following article is Free article
Cosmic Histories of Stars, Gas, Heavy Elements, and Dust in Galaxies
Yichuan C. Pei, S. Michael Fall, and Michael G. Hauser
View article,Cosmic Histories of Stars, Gas, Heavy Elements, and Dust in GalaxiesPDF,Cosmic Histories of Stars, Gas, Heavy Elements, and Dust in Galaxies
We investigate a set of coupled equations that relates the stellar, gaseous, chemical, and radiation contents of the universe averaged over the whole population of galaxies. Using as input the available data from quasar absorption-line surveys, optical imaging and redshift surveys, and the COBE DIRBE and FIRAS extragalactic infrared background measurements, we obtain solutions for the cosmic histories of stars, interstellar gas, heavy elements, dust, and radiation from stars and dust in galaxies. Our solutions reproduce remarkably well a wide variety of observations that were not used as input. These include the integrated background light from galaxy counts from near-ultraviolet to near-infrared wavelengths, the rest-frame optical and near-infrared emissivities at various redshifts from surveys of galaxies, the mid-infrared and far-infrared emissivities of the local universe from the IRAS survey, the mean abundance of heavy elements at various epochs from surveys of damped Lyα systems, and the global star formation rates at several redshifts from Hα, mid-infrared, and submillimeter observations. The chemical enrichment history of the intergalactic medium implied by our models is also consistent with the observed mean metal content of the Lyα forest at high redshifts. We infer that the dust associated with star-forming regions is highly inhomogeneous and absorbs a significant fraction of the starlight, with only 41%-46% of the total in the extragalactic optical background and the remaining 59%-54% reprocessed by dust into the infrared background. The solutions presented here provide an intriguing picture of the cosmic mean history of galaxies over much of the Hubble time. In particular, the process of galaxy formation appears to have undergone an early period of substantial inflow to assemble interstellar gas at z ≳ 3, a subsequent period of intense star formation and chemical enrichment at 1 ≲ z ≲ 3, and a recent period of decline in the gas content, star formation rate, optical stellar emissivity, and infrared dust emissivity at z ≲ 1.
802
The following article is Free article
Cepheid Calibration of the Peak Brightness of Type Ia Supernovae. IX. SN 1989B in NGC 3627
A. Saha, Allan Sandage, G. A. Tammann, Lukas Labhardt, F. D. Macchetto, and N. Panagia
View article,Cepheid Calibration of the Peak Brightness of Type Ia Supernovae. IX. SN 1989B in NGC 3627PDF,Cepheid Calibration of the Peak Brightness of Type Ia Supernovae. IX. SN 1989B in NGC 3627
Repeated imaging observations have been made of NGC 3627 with the Hubble Space Telescope in 1997-1998 over an interval of 58 days. Images were obtained on 12 epochs in the F555W band and on five epochs in the F814W band. The galaxy hosted the prototypical, "Branch normal," type Ia supernova SN 1989B. A total of 83 variables have been found, of which 68 are definite Cepheid variables with periods ranging from 75 to 3.85 days. The dereddened distance modulus is determined to be (m - M)0 = 30.22 ± 0.12 (internal uncertainty) using a subset of the Cepheid data whose reddening and error parameters are secure.
The photometric data of Wells and coworkers combined with the Cepheid data for NGC 3627 give MB(max) = -19.36 ± 0.18 and MV(max) = -19.34 ± 0.16 for SN 1989B. The previous six calibrations in this program combined with two additional calibrations determined by others gives the mean absolute magnitudes at maximum of ⟨MB⟩ = -19.48 ± 0.07 and ⟨MV⟩ = -19.48 ± 0.07 for "Branch normal" SNe Ia at this interim stage in the calibration program.
Using the argument by Wells et al. that SN 1989B here is virtually identical in decay rate and colors at maximum with SN 1980N in NGC 1316 in the Fornax cluster, and that such identity means nearly identical absolute magnitude, it follows that the difference in the distance modulus of NGC 3627 and NGC 1316 is 1.62 ± 0.03 mag. Thus the NGC 3627 modulus implies that (m - M)0 = 31.84 for NGC 1316.
The second-parameter correlations of M(max) of blue SNe Ia with decay rate, color at maximum, and Hubble type are reinvestigated. The dependence of ⟨M(max)⟩ on decay rate is nonlinear, showing a minimum for decay rates between 1.0 < Δm15 < 1.6. Magnitudes corrected for decay rate show no dependence on Hubble type, but a dependence on color remains. Correcting both the fiducial sample of 34 SNe Ia with decay-rate data and the current eight calibrating SNe Ia for the correlation with decay rate as well as color gives 
in both B and V. The same value to within 4% is obtained if only the SNe Ia in spirals (without second-parameter corrections) are considered.
The correlation of SNe Ia color at maximum with M(max) cannot be due to internal absorption, because the slope coefficients in B, V, and I with the change in magnitude are far from or even opposite to the canonical reddening values. The color effect must be intrinsic to the supernova physics. "Absorption" corrections of distant blue SNe Ia will lead to incorrect values of H0.
The Cepheid distances used in this series are insensitive to metallicity differences. The zero point of the P-L relation is based on an assumed LMC modulus of (m - M)0 = 18.50. Because this may have to be increased by 0.06-0.08 mag, all distances in this paper will follow, and H0 will decrease by 3%-4%.
921
The following article is Free article
The HCO+ Molecular Outflow in NGC 2071
José M. Girart, Paul T. P. Ho, Alexander L. Rudolph, Robert Estalella, David J. Wilner, and Lawrence M. Chernin
View article,The HCO+ Molecular Outflow in NGC 2071PDF,The HCO+ Molecular Outflow in NGC 2071
We present high angular resolution and multitransition HCO+ observations toward the NGC 2071 molecular outflow. Comparison of the high-velocity (HV) HCO+ and the near-IR H2 in the molecular outflow shows a clear correlation. At high HCO+ flow velocities the spatial coincidence is especially remarkable. In addition, the HV HCO+ presents clear morphological and kinematical differences with the CO outflow. These differences appear not only in the HV HCO+ emission associated with the H2 but in the overall outflow. There is a clear HCO+ emission enhancement, relative to CO, at increasing flow velocities. This enhancement is probably due to an abundance enhancement produced by a velocity-dependent chemistry in the shocks. An overabundance of CH in low Mach shocks may cause the HCO+ abundance enhancement. Because of the short cooling time for H2, the correlation between the HCO+ and the H2 implies that HCO+ emission can provide a useful tool to study in detail the current interactions of protostellar winds with the dense ambient medium. At the position of the extremely high velocity (EHV) CO component in the red lobe we detect HCO+ (J = 3 → 2) emission within the velocity range of the EHV CO gas. This emission is roughly compatible with the expected HCO+ emission associated with EHV gas arising from behind dissociative shocks.
991
The following article is Free article
The Impact of the Massive Young Star GL 2591 on Its Circumstellar Material: Temperature, Density, and Velocity Structure
Floris F. S. van der Tak, Ewine F. van Dishoeck, Neal J. Evans II, Eric J. Bakker, and Geoffrey A. Blake
View article,The Impact of the Massive Young Star GL 2591 on Its Circumstellar Material: Temperature, Density, and Velocity StructurePDF,The Impact of the Massive Young Star GL 2591 on Its Circumstellar Material: Temperature, Density, and Velocity Structure
The temperature, density, and kinematics of the gas and dust surrounding the luminous (2 × 104L☉) young stellar object GL 2591 are investigated on scales as small as ~100 AU, probed by 4.7 μm absorption spectroscopy, to over 60,000 AU, probed by single-dish submillimeter spectroscopy. These two scales are connected by interferometric 86-115 and 226 GHz images of size 30,000 AU and resolution 2000 AU in continuum and molecular lines. The data are used to constrain the physical structure of the envelope and investigate the influence of the young star on its immediate surroundings. The infrared spectra at λ/Δλ ≈ 40,000 indicate an LSR velocity of the 13CO rovibrational lines of -5.7 ± 1.0 km s-1, consistent with the velocity of the rotational lines of CO. In infrared absorption, the 12CO lines show wings out to much higher velocities, ≈-200 km s-1, than are seen in the rotational emission lines, which have a total width of ≈75 km s-1. This difference suggests that the outflow seen in rotational lines consists of envelope gas entrained by the ionized jet seen in Brγ and [S II] emission. The outflowing gas is warm, T > 100 K, since it is brighter in CO J = 6 → 5 than in lower-J CO transitions.
The dust temperature due to heating by the young star has been calculated self-consistently as a function of radius for a power-law density distribution n = n0r-α, with α = 1-2. The temperature is enhanced over the optically thin relation (T ~ r-0.4) inside a radius of 2000 AU, and reaches 120 K at r ≲ 1500 AU from the star, at which point ice mantles should have evaporated. The corresponding dust emission can match the observed λ ≥ 50 μm continuum spectrum for a wide range of dust optical properties and values of α. However, consistency with the C17O line emission requires a large dust opacity in the submillimeter, providing evidence for grain coagulation. The 10-20 μm emission is better matched using bare grains than using ice-coated grains, consistent with evaporation of the ice mantles in the warm inner part of the envelope. Throughout the envelope, the gas kinetic temperature as measured by H2CO line ratios closely follows the dust temperature. The values of α and n0 have been constrained by modeling emission lines of CS, HCN, and HCO+ over a large range of critical densities. The best fit is obtained for α = 1.25 ± 0.25 and n0 = (3.5 ± 1) × 104 cm-3 at r = 30,000 AU, yielding an envelope mass of (42 ± 10) M☉ inside that radius. The derived value of α suggests that part of the envelope is in free-fall collapse onto the star. Abundances in the extended envelope are 5 × 10-9 for CS, 2 × 10-9 for H2CO, 2 × 10-8 for HCN, and 1 × 10-8 for HCO+. The strong near-infrared continuum emission, the Brγ line flux, and our analysis of the emission-line profiles suggest small deviations from spherical symmetry, likely an evacuated outflow cavity directed nearly along the line of sight. The AV ≈ 30 toward the central star is a factor of 3 lower than in the best-fit spherical model.
Compared to this envelope model, the Owens Valley Radio Observatory (OVRO) continuum data show excess thermal emission, probably from dust. The dust may reside in an optically thick, compact structure, with diameter ≲30 AU and temperature ≳1000 K, or the density gradient may steepen inside 1000 AU. In contrast, the HCN line emission seen by OVRO can be satisfactorily modeled as the innermost part of the power-law envelope, with no increase in HCN abundance on scales where the ice mantles should have been evaporated. The region of hot, dense gas and enhanced HCN abundance (~10-6) observed with the Infrared Space Observatory therefore cannot be accommodated as an extension of the power-law envelope. Instead, it appears to be a compact region (r < 175 AU, where T > 300 K), in which high-temperature reactions are affecting abundances.
1011
The following article is Free article
Limb Darkening of a K Giant in the Galactic Bulge: PLANET Photometry of MACHO 97-BLG-28
M. D. Albrow, J.-P. Beaulieu, J. A. R. Caldwell, M. Dominik, J. Greenhill, K. Hill, S. Kane, R. Martin, J. Menzies, R. M. Naber et al
View article,Limb Darkening of a K Giant in the Galactic Bulge: PLANET Photometry of MACHO 97-BLG-28PDF,Limb Darkening of a K Giant in the Galactic Bulge: PLANET Photometry of MACHO 97-BLG-28
We present the PLANET photometric data set for the binary-lens microlensing event MACHO 97-BLG-28, consisting of 696 I- and V-band measurements, and analyze it to determine the radial surface brightness profile of the Galactic bulge source star. The microlensed source, demonstrated to be a K giant by our independent spectroscopy, crossed an isolated cusp of the central caustic of the lensing binary, generating a sharp peak in the light curve that was well-resolved by dense (3-30 minute) and continuous monitoring from PLANET sites in Chile, South Africa, and Australia. This is the first time that such a cusp crossing has been observed. Analysis of the PLANET data set has produced a measurement of the square-root limb-darkening coefficients of the source star in the I and V bands; the resulting stellar profiles are in excellent agreement with those predicted by stellar atmospheric models for K giants. The limb-darkening coefficients presented here are the first derived from microlensing. They are also among the first found for normal giants by any technique and the first for any star as distant as the Galactic bulge. Modeling of our light curve for MACHO 97-BLG-28 indicates that the lensing binary has a mass ratio q = 0.23 and an (instantaneous) separation in units of the angular Einstein ring radius of d = 0.69. For a lens in the Galactic bulge, this corresponds to a typical stellar binary with a projected separation between 1 and 2 AU. If the lens lies closer (i.e., in the Galactic disk), the separation is smaller, and one or both of the lens objects is in the brown dwarf regime. Assuming that the source is a bulge K2 giant at 8 kpc, the relative lens-source proper motion is μ = 19.4 ± 2.6 km s-1 kpc-1, consistent with a disk or bulge lens. If the nonlensed blended light is due to a single star, it is likely to be a young white dwarf in the bulge, consistent with the blended light coming from the lens itself.
1022
The following article is Free article
A Complete Set of Solutions for Caustic Crossing Binary Microlensing Events
M. D. Albrow, J.-P. Beaulieu, J. A. R. Caldwell, D. L. DePoy, M. Dominik, B. S. Gaudi, A. Gould, J. Greenhill, K. Hill, S. Kane et al
View article,A Complete Set of Solutions for Caustic Crossing Binary Microlensing EventsPDF,A Complete Set of Solutions for Caustic Crossing Binary Microlensing Events
We present a method to analyze binary lens microlensing light curves with one well-sampled fold caustic crossing. In general, the surface of χ2 shows extremely complicated behavior over the nine-parameter space that characterizes binary lenses. This makes it difficult to systematically search the space and verify that a given local minimum is a global minimum. We show that for events with well-monitored caustics, the caustic crossing region can be isolated from the rest of the light curve and easily fitted to a five-parameter function. Four of these caustic crossing parameters can then be used to constrain the search in the larger nine-parameter space. This allows a systematic search for all solutions and thus identification of all local minima. We illustrate this technique using the PLANET data for MACHO 98-SMC-1, an excellent and publicly available caustic crossing data set. We show that a very broad range of parameter combinations are compatible with the PLANET data set, demonstrating that observations of binary lens light curves with a sampling of only one caustic crossing do not yield unique solutions. The corollary to this is that the time of the second caustic crossing cannot be reliably predicted on the basis of early data including the first caustic crossing alone. We investigate the requirements for determination of a unique solution and find that occasional observations of the first caustic crossing may be sufficient to derive a complete solution.
1037
The following article is Free article
Observations of the Binary Microlens Event MACHO 98-SMC-1 by the Microlensing Planet Search Collaboration
S. H. Rhie, A. C. Becker, D. P. Bennett, P. C. Fragile, B. R. Johnson, L. J. King, B. A. Peterson, J. Quinn, and (The Microlensing Planet SearchCollaboration)
View article,Observations of the Binary Microlens Event MACHO 98-SMC-1 by the Microlensing Planet Search CollaborationPDF,Observations of the Binary Microlens Event MACHO 98-SMC-1 by the Microlensing Planet Search Collaboration
We present observations of the binary lensing event MACHO 98-SMC-1 conducted at the Mount Stromlo 1.9 m telescope by the Microlensing Planet Search (MPS) collaboration. The MPS data constrain the first caustic crossing to have occurred after 1998 June 5.55 UT and thus directly rule out one of the two fits presented by the PLANET collaboration (model II). This substantially reduces the uncertainty in the relative proper-motion estimations of the lens object. We perform joint binary microlensing fits of the MPS data together with the publicly available data from the EROS, MACHO/GMAN, and OGLE collaborations. We also study the binary lens fit parameters previously published by the PLANET and MACHO/GMAN collaborations by using them as initial values for χ2-minimization. Fits based on the PLANET model I appear to be in conflict with the GMAN-CTIO data. From our best fit, we find that the lens system has a proper motion of μ = 1.5 ± 0.3 km s-1 kpc-1 with respect to the source, which implies that the lens system is most likely to be located in the Small Magellanic Cloud, strengthening the conclusion of previous reports.
1069
The following article is Free article
The Emission Time of Gamma-Ray Bursts
Igor G. Mitrofanov, Dmitrij S. Anfimov, Maxim L. Litvak, Anton B. Sanin, Yurij Yu. Saevich,, Michael S. Briggs, William S. Paciesas, Geoffrey N. Pendleton, Robert D. Preece,, Thomas M. Koshut et al
View article,The Emission Time of Gamma-Ray BurstsPDF,The Emission Time of Gamma-Ray Bursts
The concept of emission time τN is suggested as a temporal parameter which is complementary to the classical parameters of duration times T50 and T90. The emission time is defined as the time of emission of N% of the total fluence. The definition adds the time bins of high fluence in decreasing fluence rank until N% of the fluence has been reached. The emission time interval excludes low-emission intervals of bursts, and so the emission time characterizes the state of high-power emission. The distribution of this new parameter is found to be bimodal for bright bursts. The distributions of emission time τ30 and τ50, for groups based on burst intensity, are also compared.
1100
The following article is Free article
Radio and X-Ray Imaging Observations of a Continuum Burst
M. R. Kundu, J. P. Raulin, N. Nitta, and A. Raoult
View article,Radio and X-Ray Imaging Observations of a Continuum BurstPDF,Radio and X-Ray Imaging Observations of a Continuum Burst
We study a metric continuum burst observed on 1993 February 18, and its X-ray signatures from imaging observations in radio and X-rays using the Nançay radioheliograph and the Yohkoh Soft X-Ray Telescope (SXT). The event in question was associated with weak type III bursts; these were detected at only one frequency (164 MHz), except for one burst (at 10:58:05 UT), which was observed over a broad frequency range (164-435 MHz). We believe that the early metric continuum burst is an extension of the microwave continuum which was observed at frequencies as high as 5 GHz, and its onset at ~10:50 UT is associated with the development of an X-ray-emitting diffuse loop system which appears to advance with a speed of ~50-100 km s-1. The observed type III bursts seem to correspond to the repeated occurrence/appearance of a collimated jet emanating from the loop system that is responsible for the continuum burst. A few minutes prior to the main continuum onset there is a soft X-ray ejection from the main flare region. The main continuum has a brightness temperature greater than 108 K; it is unpolarized, and it shows dispersion in position with frequency and moves with speeds of ~50 km s-1 at 236-410 MHz. The SXT images reveal that this initially ejected soft X-ray-emitting hot plasma seems to gradually fill up the loop system with hot material. This hot plasma must contain enough energetic electrons of energy greater than several tens of keV, which are responsible for producing the metric continuum burst by plasma radiation mechanism.
L97
The following article is Free article
Discovery of a Radio Flare from GRB 990123
S. R. Kulkarni, D. A. Frail, R. Sari, G. H. Moriarty-Schieven, D. S. Shepherd, P. Udomprasert, A. C. S. Readhead, J. S. Bloom, M. Feroci, and E. Costa
View article,Discovery of a Radio Flare from GRB 990123PDF,Discovery of a Radio Flare from GRB 990123
We report the discovery of a radio counterpart to GRB 990123. In contrast to previous well-studied radio afterglows that rise to peak flux on a timescale of a week and then decay over several weeks to months, the radio emission from this gamma-ray burst (GRB) was clearly detected 1 day after the burst, after which it rapidly faded away. The simplest interpretation of this "radio flare" is that it arises from the reverse shock. In the framework of the afterglow models discussed to date, a forward-shock origin for the flare is ruled out by our data. However, at late times, some radio afterglow emission (commensurate with the observed late-time optical emission and the optical afterglow) is expected from the forward shock. The relative faintness of the observed late-time radio emission provides an independent indication of a jetlike geometry in this GRB. We use the same radio observations to constrain two key parameters of the forward shock (the peak flux and peak frequency) to within a factor of 2. These values are inconsistent with the notion advocated by several authors that the prompt optical emission detected by the Robotic Optical Transient Search Experiment smoothly joins the optical afterglow emission. Finally, in hindsight, we now recognize another such radio flare, and this suggests that one out of eight GRBs has a detectable radio flare. This abundance, coupled with the reverse-shock interpretation, suggests that the radio flare phenomenon has the potential to shed new light on the physics of reverse shocks in GRBs.
L145
The following article is Free article
An Upper Limit on the Reflected Light from the Planet Orbiting the Star τBootis
David Charbonneau, Robert W. Noyes, Sylvain G. Korzennik, Peter Nisenson, Saurabh Jha, Steven S. Vogt, and Robert I. Kibrick
View article,An Upper Limit on the Reflected Light from the Planet Orbiting the Star τ BootisPDF,An Upper Limit on the Reflected Light from the Planet Orbiting the Star τ Bootis
The planet orbiting τBoo at a separation of 0.046 AU could produce a reflected light flux as bright as 1 × 10-4 relative to that of the star. A spectrum of the system will contain a reflected light component which varies in amplitude and Doppler shift as the planet orbits the star. Assuming the secondary spectrum is primarily the reflected stellar spectrum, we can limit the relative reflected light flux to be less than 5 × 10-5. This implies an upper limit of 0.3 for the planetary geometric albedo near 480nm, assuming a planetary radius of 1.2 RJup. This albedo is significantly less than that of any of the giant planets of the solar system and is not consistent with certain published theoretical predictions.
