Transcript 1apr
Astrophysics at the UO Small but active program Galaxy Properties and Evolution (Bothun; Schombert) Neutron Star equations of state (Imamura) Gravitational Waves (LIGO) (Frey) Theoretical Cosmology (Hsu; Kribs) Properties of Supernova (Bothun; Johnson) Alternative Gravity – MOND (Bothun; GS) Shift in Astrophysics Research Research now based in data mining more so than telescope observations The Ultraviolet Sizes of Nearby Galaxies A Link to Galaxy Evolution When the Hubble Space Telescope Images the Distant Universe (bottom image) it is detecting the rest frame Ultraviolet Emission from these highly redshifted galaxies. In order to better understand these object, it is necessary to image nearby galaxies in the Ultraviolet such as can now be done with the GALEX telescope (right image). GALEX and XUV Disks GALEX Imagery has discovered that about 1/3 of all spiral galaxies are significantly bigger in Ultraviolet Light than in optical light. The example shown to the left (NGC 4625) it typical; the bright whitish inner part defines the optical size of the galaxy, the bluish emission shows the greatly extended Ultraviolet emission (XUV). This XUV light is remarkable for two reason: 1) it directly shows the UV sizes of galaxies can be large relative to the optical size. This has clear implications about the nature of high redshift galaxies as detected in deep Hubble fields, 2) UV light comes from hot stars, which are usually newly formed. Hence these XUV structures imply that star formation is now occurring around some galaxies in very low density regions – this is unexpected Space Grant Research Supported year long ground based imaging campaign at the University of Oregon’s Pine Mountain Observatory of candidate galaxies for GALEX mission. New GALEX Results NGC 5172: Confirms the XUV phenomena – solid ellipse in the right image shows the optical extent of this galaxy (essentially coincident with the inner ring in the image below. The outer one, which is clearly seen in the color difference image, is a nearly continuous ring of hot stars, again implying the presence of significant amounts of star formation in the outer regions. This galaxy is therefore clearly growing with time and this has major implications with respect to galaxy evolution. New GALEX Results When is a LSB galaxy not really a LSB galaxy? The top image shows the optical discovery image of this massive nearby galaxy – most of its structure is not discernible. The bottom image is the GALEX data. Voila – there is really a galaxy there. There is no hint at the LSB nature of this galaxy in the GALEX image and the ratio of UV emission to optical emission is unprecedented and strongly implies that this galaxy is actually forming right now and hasn’t had time to become more luminous in the optical part of the spectrum. This is potentially a major new discovery that strongly impacts our ides about galaxy formation and evolution and forms the basis for a larger GAKEX campaign in the near future. Multiwavelength Astronomy Large Collaborations Modified Newtonian Dynamics • Alternative to Dark Matter – fits most all the data well • Whole Universe is Baryonic • Gravity Force is a function of some scale meaning at some scales, less force will be required to produce a given acceleration