Compton Echoes from Gamma-ray Bursts

Recent observations of gamma-ray bursts (GRBs) have provided growing evidence for collimated outflows and emission, and strengthened the connection between GRBs and supernovae. If massive stars are the progenitors of GRBs, the hard photon pulse will propagate in the pre-burst, dense environment. Circumstellar material will Compton scatter the prompt GRB radiation and give rise to a reflection echo. We calculate luminosities, spectra, and light curves of such Compton echoes in a variety of emission geometries and ambient gas distributions, and show that the delayed hard X-ray flash from a pulse propagating into a red supergiant wind could be detectable by Swift out to z~0.2. Independently of the gamma-ray spectrum of the prompt burst, reflection echoes will typically show a high-energy cutoff between m_ec^2/2 and m_ec^2 because of Compton downscattering. At fixed burst energy per steradian, the luminosity of the reflected echo is proportional to the beaming solid angle, Omega_b, of the prompt pulse, while the number of bright echoes detectable in the sky above a fixed limiting flux increases as Omega_b^{1/2}, i.e. it is smaller in the case of more collimated jets. The lack of an X-ray echo at one month delay from the explosion poses severe constraints on the possible existence of a lateral GRB jet in SN 1987A. The late r-band afterglow observed in GRB990123 is fainter than the optical echo expected in a dense red supergiant environment from a isotropic prompt optical flash. Significant MeV delayed emission may be produced through the bulk Compton (or Compton drag) effect resulting from the interaction of the decelerating fireball with the scattered X-ray radiation.Comment: LaTeX, 18 pages, 4 figures, revised version accepted for publication in the Ap

Clustering around radio galaxies at z~1.5

The importance of studying old elliptical galaxies at redshift z ~ 1.5 is reviewed, considering both what can be learned by extending studies of the evolution of cluster galaxy scaling relations to earlier cosmic epochs, and the age-dating of old elliptical galaxies at high redshifts. Following this, the first results are provided of an on-going project to find such distant elliptical galaxies, through an investigation of the cluster environments of powerful radio sources with redshifts 1.44 < z < 1.7. These studies show a considerable excess of red galaxies in the radio sources fields, with the magnitudes (K >~ 17.5) and colours (R-K > 4) expected of old passively evolving galaxies at the radio source redshift. The red galaxy overdensities are found on two different scales around the radio sources; a pronounced small-scale peak at radial distances of <~ 150 kpc, and a weaker large-scale excess extending out to 1 - 1.5 Mpc. The presence and richness of these red galaxy excesses varies considerably from source to source. An interpretation of these results is provided.Comment: LaTeX, 6 pages, Elsevier Science format. To appear in "Radio galaxies: past, present & future". eds. M. Jarvis et al., Leiden, Nov 200

A High Merger Fraction in the Rich Cluster MS1054-03 at z=0.83: Direct Evidence for Hierarchical Formation of Massive Galaxies

We present a morphological study of the galaxy population of the luminous X-ray cluster MS1054-03 at z=0.83. The sample consists of 81 spectroscopically confirmed cluster members in a 3 x 2 Mpc area imaged in F606W and F814W with WFPC2. We find thirteen ongoing mergers in MS1054-03, comprising 17% of the L > L* cluster population. Most of these mergers will likely evolve into luminous (\sim 2 L*) elliptical galaxies, and some may evolve into S0 galaxies. Assuming the galaxy population in MS1054-03 is typical for its redshift it is estimated that \sim 50% of present-day cluster ellipticals experienced a major merger at z < 1. The mergers are preferentially found in the outskirts of the cluster, and probably occur in small infalling clumps. Morphologies, spectra, and colors of the mergers show that their progenitors were typically E/S0s or early-type spirals with mean stellar formation redshifts z* \gtrsim 1.7. The red colors of the merger remnants are consistent with the low scatter in the color-magnitude relation in rich clusters at lower redshift. The discovery of a high fraction of mergers in this young cluster is direct evidence against formation of ellipticals in a single ``monolithic'' collapse at high redshift, and in qualitative agreement with predictions of hierarchical models for structure formation.Comment: Added GIF version of Figure 1. At http://www.astro.rug.nl/~dokkum/preprints/merger_fig1.eps.gz the PS file is available. Accepted for publication in ApJ Letter

Terahertz third harmonic generation in c-axis La1.85_{1.85}Sr0.15_{0.15}CuO4_4

Terahertz nonlinear optics is a viable method to interrogate collective phenomena in quantum materials spanning ferroelectrics, charge-density waves, and superconductivity. In superconductors this includes the Higgs amplitude and Josephson phase modes. We have investigated the nonlinear c-axis response of optimally doped La$_{1.85}$Sr$_{0.15}$CuO$_4$ using high-field THz time domain spectroscopy (THz-TDS) at field strengths up to $\sim$80 kV/cm. With increasing field, we observe a distinct red-shift of the Josephson plasma edge and enhanced reflectivity (above the plasma edge) arising from third harmonic generation. The non-monotonic temperature dependent response is consistent with nonlinear drive of the Josephson Plasma Mode (JPM) as verified with comparison to theoretical expectations. Our results add to the understanding that, using THz light, the JPM (in addition to the Higgs mode) provides a route to interrogate and control superconducting properties

Callus Induction in Baru (Dipteryx alata Vog.) Explants

Baru (Dipteryx alata Vog.) is a species with great economic and environmental potential; it has popular acceptance, besides being a very productive species. Alternative propagation methods are important for species maintenance and exploration. Thus, micropropagation emerged as an alternative technique, providing genetic stability and the production of a large number of seedlings. The aim of the present investigation was to develop a callus induction protocol for in vitro baru explants. The tested explants were nodal, internodal and foliar segments. The explants were disinfected for 30 seconds in 70% alcohol (v/v) and 2 minutes in sodium hypochlorite (1.25% active chlorine). This was followed by triple washing. The inoculation was carried out in test tubes containing 15 mL MS medium (30 g L-1 sucrose, 6 g L-1 agar and 100 mg L-1 ascorbic acid) supplemented with 2.0 mg L-1 naphthalene acetic acid (NAA). The solution also contained 0.0, 2.5 or 5.0 mg L-1 of 6-benzylaminopurine (BAP) with the pH adjusted to 5.8. In the incubation phase, the explants were cultured for seven days in the dark and then subjected to a photoperiod of 16 hours (43 µmol m-2 s-1) at 25 ± 2 °C. The treatments were studied with 2.5, 5.0, 7.5 or 10.0 mg L-1 BAP additions to the MS. Callus formation, contamination and oxidation evaluations were undertaken. The results obtained when using 2.0 mg L-1 NAA concluded that such a treatment should be used to induce callogenesis from nodal explants, while for the tested baru leaf explants, the best results for callus formation were given by the combination of 2.0 mg L-1 NAA with 2.5 mg L-1 of BAP to

The Possible z=0.83 Precursors of z=0 M* Early-type Cluster Galaxies

We examine the distribution of stellar masses of galaxies in MS 1054-03 and RX J0152.7-1357, two X-ray selected clusters of galaxies at z=0.83. Our stellar mass estimates, from spectral energy distribution fitting, reproduce the dynamical masses as measured from velocity dispersions and half-light radii with a scatter of 0.2 dex in the mass for early-type galaxies. When we restrict our sample of members to high stellar masses, > 1e11.1 Msun (M* in the Schechter mass function for cluster galaxies), we find that the fraction of early-type galaxies is 79 +/- 6% at z=0.83 and 87 +/- 6% at z=0.023 for the Coma cluster, consistent with no evolution. Previous work with luminosity-selected samples finds that the early-type fraction in rich clusters declines from =~80% at z=0 to =~60% at z=0.8. The observed evolution in the early-type fraction from luminosity-selected samples must predominately occur among sub-M* galaxies. As M* for field and group galaxies, especially late-types, is below M* for clusters galaxies, infall could explain most of the recent early-type fraction growth. Future surveys could determine the morphological distributions of lower mass systems which will confirm or refute this explanation.Comment: 5 pages in emulate ApJ format with three color figures. Accepted for publication in ApJ Letters, v642n2. Updated to correct grammatical and typographic errors found by the journa

A Database of Cepheid Distance Moduli and TRGB, GCLF, PNLF and SBF Data Useful for Distance Determinations

We present a compilation of Cepheid distance moduli and data for four secondary distance indicators that employ stars in the old stellar populations: the planetary nebula luminosity function (PNLF), the globular cluster luminosity function (GCLF), the tip of the red giant branch (TRGB), and the surface brightness fluctuation (SBF) method. The database includes all data published as of July 15, 1999. The main strength of this compilation resides in all data being on a consistent and homogeneous system: all Cepheid distances are derived using the same calibration of the period-luminosity relation, the treatment of errors is consistent for all indicators, measurements which are not considered reliable are excluded. As such, the database is ideal for inter-comparing any of the distance indicators considered, or for deriving a Cepheid calibration to any secondary distance indicator. Specifically, the database includes: 1) Cepheid distances, extinctions and metallicities; 2) apparent magnitudes of the PNLF cutoff; 3) apparent magnitudes and colors of the turnover of the GCLF (both in the V- and B-bands); 4) apparent magnitudes of the TRGB (in the I-band) and V-I colors at and 0.5 magnitudes fainter than the TRGB; 5) apparent surface brightness fluctuation magnitudes I, K', K_short, and using the F814W filter with the HST/WFPC2. In addition, for every galaxy in the database we give reddening estimates from DIRBE/IRAS as well as HI maps, J2000 coordinates, Hubble and T-type morphological classification, apparent total magnitude in B, and systemic velocity. (Abridged)Comment: Accepted for publication in the Astrophysical Journal Supplement Series. Because of space limitations, the figures included are low resolution bitmap images. Original figures can be found at http://www.astro.ucla.edu/~laura/pub.ht

Mass-Selection and the Evolution of the Morphology-Density Relation from z=0.8 to z=0

We examined the morphology-density relations for galaxy samples selected by luminosity and by mass in each of five massive X-ray clusters from z=0.023 to 0.83 for 674 spectroscopically-confirmed members. Rest-frame optical colors and visual morphologies were obtained primarily from Hubble Space Telescope images. Morphology-density relations (MDR) are derived in each cluster from a complete, luminosity-selected sample of 452 galaxies with a magnitude limit M_V < M^{*}_{V} + 1. The change in the early-type fraction with redshift matches previous work for massive clusters of galaxies. We performed a similar analysis, deriving MDRs for complete, mass-selected samples of 441 galaxies with a mass-limit of 10^{10.6} M_{\sun}. Our mass limit includes faint objects, the equivalent of =~1 mag below L^{*} for the red cluster galaxies, and encompasses =~70% of the stellar mass in cluster galaxies. The MDRs in the mass-selected sample at densities of Sigma > 50 galaxies Mpc^{-2} are similar to those in the luminosity-selected sample but show larger early-type fractions. However, the trend with redshift in the fraction of elliptical and S0 galaxies with masses > 10^{10.6} M_{\sun} differs significantly between the mass- and luminosity-selected samples. The clear trend seen in the early-type fraction from z=0 to z=~ 0.8 is not found in mass-selected samples. The early-type galaxy fraction changes much less, and is consistent with being constant at 92% +/- 4% at \Sigma> 500 galaxies Mpc^{-2} and 83 +/- 3% at 50 < \Sigma < 500 galaxies Mpc^{-2}. This suggests that galaxies of mass lower than > 10^{10.6} M_{\sun} play a significant role in the evolution of the early-type fraction in luminosity-selected samples. (Abstract abridged)Comment: 18 pages in emulate ApJ format, with 10 color figures, Accepted to ApJ. Version updated to reflect published version, includes new references and a correction to table