Anomalous Star-Formation Activity of Less-Luminous Galaxies in Cluster Environment

We discuss a correlation between star formation activity (SFA) and luminosity of star-forming galaxies at intermediate redshifts of $0.2\le z\le 0.6$ in both cluster and field environments. Equivalent width (EW) of [O{\sc ii}] is used for measurement of the SFA, and $R$-band absolute magnitude, $M_R$, for the luminosity. In less-luminous (M_R \gsim -20.7) galaxies, we find : (1) the mean EW([O{\sc ii}]) of cluster galaxies is smaller than that of field galaxies; but (2) some cluster galaxies have as large EW([O{\sc ii}]) as that of actively star-forming field galaxies. Based on both our results, we discuss a new possible mechanism for the Butcher-Oemler (BO) effect, assuming that the luminosity of a galaxy is proportional to its dynamical mass. Our proposal is that BO galaxies are less-massive cluster galaxies with smaller peculiar velocities. They are then stable against Kelvin-Helmholtz instability (KHI), and are not affected by tidal interaction between clusters and themselves. Their interstellar medium (ISM) would be hardly stripped, and their SFA would be little suppressed. Hence, as long as such galaxies keep up their SFA, the fraction of blue galaxies in a cluster does not decrease. As a cluster becomes virialized, however, such galaxies become more accelerated, the ISM available for SFA is stripped by KHI, and their color evolves redward, which produces the BO effect.Comment: accepted for publication in ApJ

Dynamical condition of neutral hydrogen envelopes of dwarf galaxies and their possible morphological evolution

We investigate the star-formation history of gas-rich dwarf galaxies, taking account of the dynamical evolution of their neutral hydrogen (H{\sc i}) envelope. Gas-rich dwarfs are classified into blue compact dwarfs (BCDs) and dwarf irregulars (dIrrs). In this paper, their H{\sc i} envelope is clearly shown not to be blown away by their stellar feedback. This is concluded since the observed star-formation rate (SFR) of gas-rich dwarfs is generally smaller than a critical SFR, $\psi_{\rm crit}$, at which stellar feedback accelerates the H{\sc i} envelope to the escape velocity. From this standpoint and the chemical property of sample BCDs, we suggest two possibilities; (1) The H{\sc i} gas in the envelope of BCDs is consumed to fuel their star-formation; and (2) BCDs have a similar star-formation history. We also discuss morphological evolution among dwarf galaxies. As long as gas-rich dwarfs are isolated, it is difficult for them to evolve into dwarf ellipticals (dEs). When the H{\sc i} envelope in gas-rich dwarfs is consumed in subsequent star-formation, a morphological exchange between BCDs and dIrrs is still expected, consistent with previous studies. If the SFR of gas-rich dwarfs was much higher than $\psi_{\rm crit}$ in the past, interestingly, an evolutionary scenario from dEs to gas-rich dwarfs is possible.Comment: 15 pages, 2 figures, accepted by A&A

Fabrication of low-cost, large-area prototype Si(Li) detectors for the GAPS experiment

A Si(Li) detector fabrication procedure has been developed with the aim of satisfying the unique requirements of the GAPS (General Antiparticle Spectrometer) experiment. Si(Li) detectors are particularly well-suited to the GAPS detection scheme, in which several planes of detectors act as the target to slow and capture an incoming antiparticle into an exotic atom, as well as the spectrometer and tracker to measure the resulting decay X-rays and annihilation products. These detectors must provide the absorption depth, energy resolution, tracking efficiency, and active area necessary for this technique, all within the significant temperature, power, and cost constraints of an Antarctic long-duration balloon flight. We report here on the fabrication and performance of prototype 2"-diameter, 1-1.25 mm-thick, single-strip Si(Li) detectors that provide the necessary X-ray energy resolution of $\sim$4 keV for a cost per unit area that is far below that of previously-acquired commercial detectors. This fabrication procedure is currently being optimized for the 4"-diameter, 2.5 mm-thick, multi-strip geometry that will be used for the GAPS flight detectors.Comment: Accepted for publication at Nuclear Instrumentation and Methods A, 12 pages, 11 figure

Use of Balloon Enteroscopy in Preoperative Diagnosis of Neurofibromatosis-Associated Gastrointestinal Stromal Tumours of the Small Bowel: A Case Report

Neurofibromatosis type I (NF1) is one of the most common inheritable disorders and is associated with an increased risk of gastrointestinal stromal tumours (GISTs). However, the predominant location of these lesions in the small bowel makes them difficult to diagnose. We report the successful use of balloon enteroscopy in conjunction with conventional methods for clinical diagnosis of jejunal GISTs in a 70-year-old man with NF1 who presented with melaena. The importance of screening NF1 patients for GISTs and the complementary role of balloon enteroscopy with capsule endoscopy in such diagnoses is discussed