On the Reported Death of the MACHO Era

We present radial velocity measurements of four wide halo binary candidates from the sample in Chaname & Gould (2004; CG04) which, to date, is the only sample containing a large number of such candidates. The four candidates that we have observed have projected separations >0.1 pc, and include the two widest binaries from the sample, with separations of 0.45 and 1.1 pc. We confirm that three of the four CG04 candidates are genuine, including the one with the largest separation. The fourth candidate, however, is spurious at the 5-sigma level. In the light of these measurements we re-examine the implications for MACHO models of the Galactic halo. Our analysis casts doubt on what MACHO constraints can be drawn from the existing sample of wide halo binaries.Comment: 6 Pages, 4 Figures, Accepted for MNRAS Letter

M/L and Color Evolution for A Deep Sample of M* Cluster Galaxies at z~1: The Formation Epoch and the Tilt of the Fundamental Plane

We have measured velocity dispersions for a sample of 36 galaxies with J < 21.2 or Mr < -20.6 mag in MS1054-03, a massive cluster of galaxies at z = 0.83. Our data are of uniformly high quality down to our selection limit, our 16-hour exposures typically yielding errors of only \delta(dispersion)~10% for L* and fainter galaxies. By combining our measurements with data from the literature, we have 53 cluster galaxies with measured dispersions, and HST/ACS-derived sizes, colors and surface brightnesses. This sample is complete for the typical L* galaxy at z~1, unlike most previous z~1 cluster samples which are complete only for the massive cluster members (>1e11 M_sun). We find no evidence for a change in the tilt of the fundamental plane (FP). Nor do we find evidence for evolution in the slope of the color-dispersion relation and M/L_B-dispersion relations; measuring evolution at a fixed dispersion should minimize the impact of size evolution found in other work. The M/L_B at fixed dispersion evolves by \Delta log10 M/L_B=-0.50 +/- 0.03 between z=0.83 and z=0.02 or d(log10 M/L_B)=-0.60 +/- 0.04 dz, and we find \Delta (U-V)_z=-0.24 +/- 0.02 mag at fixed dispersion in the rest-frame, matching the expected evolution in M/L_B within 2.25 standard deviations. The implied formation redshift from both the color and M/L_B evolution is z*=2.0 +/- 0.2 +/- 0.3 (sys), during the epoch in which the cosmic star-formation activity peaked, with the systematic uncertainty showing the dependence of z* on the assumptions we make about the stellar populations. The lack of evolution in either the tilt of the FP or in the M/L- and color-dispersion relations imply that the formation epoch depends weakly on mass, ranging from z*=2.3 +1.3 -0.3 at 300 km/s to z*=1.7 +0.3 -0.2 at 160 km/s and implies that the IMF similarly varies slowly with galaxy mass.Comment: revised; typos corrected, references updated, and other cosmetic changes to meet ApJ format ApJ accepted, 22 pages in emulate ApJ format, 8 color figures, 1 b/w figur

Spectroscopic Confirmation of Multiple Red Galaxy-Galaxy Mergers in MS1054-03 (z=0.83)

We present follow-up spectroscopy of the galaxy cluster MS1054-03 (z=0.83) confirming that at least six of the nine merging galaxy pairs identified by van Dokkum et al. (1999) are indeed bound systems: they have projected separations of R_s<10 kpc and relative line-of sight velocities of dv<165 km/s. For the remaining three pairs, we were unable to obtain redshifts of both constituent galaxies. To identify a more objective sample of merging systems, we select bound red galaxy pairs (R_s<=30 kpc, dv<=300 km/s) from our sample of 121 confirmed cluster members: galaxies in bound red pairs make up 15.7+/-3.6% of the cluster population. The (B-K_s) color-magnitude diagram shows that the pair galaxies are as red as the E/S0 members and have a homogeneous stellar population. The red pair galaxies span a large range in luminosity and internal velocity dispersion to include some of the brightest, most massive members (L>L*, sigma>200 km/s); these bound galaxy pairs must evolve into E/S0 members by z~0.7. These results combined with MS1054's high merger fraction and reservoir of likely future mergers indicates that most, if not all, of its early-type members evolved from (passive) galaxy-galaxy mergers at z<~1.Comment: accepted by ApJ Letters; high resolution version of Fig. 2 available at http://www.exp-astro.phys.ethz.ch/tran/outgoing/ms1054mgrs.ps.g

Design, synthesis and applications of donor-acceptor systems for artificial photosynthesis and solar cells

Artificial photosynthesis (AP) is the process of mimicking natural photosynthesis for effective conversion of light energy into a more accessible form of energy. These APs consist of three main components; a photoantenna, the reaction centre and an energy storage system. On the basis of a literature search of AP, we have studied the excited-state dynamics of two multichromophoric arrays composed of a NDI centre, attached to which are four zinc or free-base porphyrins connected to the core via aniline bridges. These pentads have been investigated by using a combination of stationary and ultrafast spectroscopies to gain an understanding of their photophysical properties. Spectroscopic results confirm that these pentads can act as efficient photoantennae, absorbing over the complete visible region. They absorb at a wavelength of around 700 nm, which indicates an excited state transition to the S1 state that is delocalised over the whole pentad. Furthermore higher energy absorption bands are shown by transitions centred on the porphyrins of the multichromophoric arrays. The synthesised pentads were studied in polar and non-polar solvents. These multichromophoric arrays show a charge-separated state under the S1 state in polar solvents. Thermally-activated hole transfer from the S1 state results in populated excited states within a few picoseconds (ps), and the vibrationally hot porphyrin excited states exhibit sub-ps non-equilibrium electron transfer. Further contribution to AP is made by the design of simple donor-acceptor (D-A) dyads. These synthesised dyads demonstrate good results by being able to produce a charge gradient across a membrane, which clearly indicate that they can act as efficient AP antennae. In the dyad MKSB4.1, the process of conversion of light energy into a proton potential is achieved by transporting electrons across a lipid bilayer. This active dyad is composed of a zinc-porphyrin as a donor and a napthalene diimide (NDI) as an acceptor, which are linked by a dithiophene spacer for effective electron transfer. Initially, excitation of the zinc-porphyrin after incorporation into a lipid bilayer results in charge separation to produce an oxidation potential near the outer surface and a reduction potential near the inner surface of the lipid bilayer. This process of creating potentials leads to transmembrane electron transfer. On the other hand, dye-sensitised solar cells (DSSCs) are a growing research area due to their potential to meet our need for a clean source of energy, in this case solar. To contribute to the development of DSSCs, herein, I have designed and studied a donor-acceptor model in which there is a direct linkage of oligothiophenes to the nitrogen atom of a donor amine. AG3 consists of diphenylamine as an electron donor and cyanoacrylic acid as an electron acceptor, linked through an extended oligothiophene &amp;pi;-spacer unit. AG3 is highly soluble in common organic solvents and showed an intense spectral response, compared to a fewer-thiophene analogue. When tested in a conventional solvent-based solar cell (100 mW.cm-2, AM1.5G), AG3 afforded a power conversion efficiency (PCE) of 5.9%. AG3 also achieved a PCE of 4.3% in ionic liquid and 5.2% in cobalt-mediated electrolytes

The Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas (MEGaSaURA) I: The Sample and the Spectra

We introduce Project MEGaSaURA: The Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas. MEGaSaURA comprises medium-resolution, rest-frame ultraviolet spectroscopy of N=15 bright gravitationally lensed galaxies at redshifts of 1.68$<$z$<$3.6, obtained with the MagE spectrograph on the Magellan telescopes. The spectra cover the observed-frame wavelength range $3200 < \lambda_o < 8280$ \AA ; the average spectral resolving power is R=3300. The median spectrum has a signal-to-noise ratio of $SNR=21$ per resolution element at 5000 \AA . As such, the MEGaSaURA spectra have superior signal-to-noise-ratio and wavelength coverage compared to what COS/HST provides for starburst galaxies in the local universe. This paper describes the sample, the observations, and the data reduction. We compare the measured redshifts for the stars, the ionized gas as traced by nebular lines, and the neutral gas as traced by absorption lines; we find the expected bulk outflow of the neutral gas, and no systemic offset between the redshifts measured from nebular lines and the redshifts measured from the stellar continuum. We provide the MEGaSaURA spectra to the astronomical community through a data release.Comment: Resubmitted to AAS Journals. Data release will accompany journal publication. v2 addresses minor comments from refere