In order to understand nature of building blocks of galaxies in the early universe, we investigate genuine irregular galaxies (GIGs) in the nearby universe. Here, GIGs are defined as isolated galaxies without regular structures (spheroid, bulge, disk
, bar, spiral arm, and nucleus). Using the results of two excellent studies on galaxy morphology based on the Sloan Digital Sky Survey (SDSS), we obtain a sample of 66 irregular galaxies. We carry out new classification of them into GIGs and non-GIGs which have regular structure or show evidence for galaxy interaction, by using the SDSS Data Release 10 images. We then find that a half of these irregular galaxies (33/66) are GIGs and obtain an unambiguous sample of 33 GIGs for the first time. We discuss their observational properties by comparing them with those of elliptical, S0, spiral galaxies, and irregular galaxies without the GIGs. We find that our GIGs have smaller sizes, lower optical luminosities, bluer rest-frame optical colors, lower surface stellar mass densities, and lower gas metallicity than normal galaxies. All these properties suggest that they are in chemically and dynamically younger phases even in the nearby universe.
This paper describes a novel directional neutron detector prototype. The low pressure time projection chamber uses a mix of helium and CF4 gases. The detector reconstructs the energy and angular distribution of fast neutron recoils. This paper report
s results of energy calibration using an alpha source and angular reconstruction studies using a collimated neutron source. The best performance is obtained with a 12.5% CF4 gas mixture. At low energies the target for fast neutrons transitions is primarily helium, while at higher energies, the fluorine contributes as a target. The reconstruction efficiency is both energy and target dependent. For neutrons with energies less than 20 MeV, the reconstruction efficiency is ~40% for fluorine recoils and ~60% for helium recoils.
