Stripping galaxies of interstellar gas could shut down star formation
Scientists have observed in precise detail the stripping of gas from a distant galaxy as they seek to understand what shuts down star formation in galaxy clusters. Using the European Southern Observatory's MUSE instrument, the Durham University-led research team captured images of the spiral galaxy - known as ESO137-001 - which lies 200 million light years from Earth. Read more
Title: Three Dimensional Distribution of Atomic Hydrogen in the Milky Way Authors: Maryam Tavakoli
A new model for three dimensional distribution of atomic hydrogen gas in the Milky Way is derived using the 21cm LAB survey data. The global features of the gas distribution such as spiral arms are reproduced. The Galactic plane warps outside the solar orbit and the thickness of the gas disk flares outward the Galaxy. It is found that the mass of atomic hydrogen gas within a radius of 20 kpc is 4.3*10^9 solar masses.
Title: The 15-20 um emission in the reflection nebula NGC2023 Authors: Els Peeters, Alexander G. G. M. Tielens, Louis J. Allamandola, Mark G. Wolfire
We present 15-20 um spectral maps towards the reflection nebula NGC2023 obtained with the Infrared Spectrograph in short-wavelength, high-resolution mode on board the Spitzer Space Telescope. These spectra reveal emission from PAHs, C60, and H2 superposed on a dust continuum. These emission components exhibit distinct spatial distributions: with increasing distance from the illuminating star, we observe the PAH emission followed by the dust continuum emission and the H2 emission. The C60 emission is located closest to the illuminating star in the south while in the north, it seems to be associated with the H/H2 transition. Emission from PAHs and PAH-related species produce features at 15.8, 16.4, 17.4, and 17.8 um and the 15-18 um plateau. These different PAH features show distinct spatial distributions. The 15.8 um band and 15-18 um plateau correlate with the 11.2 um PAH band and with each other, and are attributed to large, neutral PAHs. Conversely, the 16.4 um feature correlates with the 12.7 um PAH band, suggesting that both arise from species that are favoured by the same conditions that favour PAH cations. The PAH contribution to the 17.4 um band is displaced towards the illuminating star with respect to the 11.2 and 12.7 um emission and is assigned to doubly ionised PAHs and/or a subset of cationic PAHs. The spatial distribution of the 17.8 um band suggests it arises from both neutral and cationic PAHs. In contrast to their intensities, the profiles of the PAH bands and the 15-18 um plateau do not vary spatially. Consequently, we conclude that the carrier of the 15-18 um plateau is distinct from that of the PAH bands.
Title: Interstellar H2 toward HD 37903 Authors: Piotr Gnacinski (Version v3)
We present an analysis of interstellar H2 toward HD 37903, which is a hot, B 1.5 V star located in the NGC 2023 reflection nebula. Meyer et al. (2001) have used a rich spectrum of vibrationally excited H2 observed by the HST to calculate a model of the interstellar cloud toward HD 37903. We extend Mayer's analysis by including the v"=0 vibrational level observed by the FUSE satellite. The PDR model of the cloud located in front of HD 37903 points to a gas temperature T=110-377 K, hydrogen density nH=1874-544 cm^-3 and the star-cloud distance of 0.45 pc. The rotational temperatures for vibrational levels 1-14 are usually higher for ortho states than for the para H2 spin isomer.