Browsing by Subject "function, mass function"
Now showing 1 - 2 of 2
- Results Per Page
- Sort Options
Item Discovery Of Lyman Break Galaxies At Z Similar To 7 From The Zfourge Survey(2013-05) Tilvi, Vithal; Papovich, Casey; Tran, K. V. H.; Labbe, I.; Spitler, L. R.; Straatman, C. M. S.; Persson, S. E.; Monson, A.; Glazebrook, K.; Quadri, R. F.; van Dokkum, P.; Ashby, M. L. N.; Faber, S. M.; Fazio, G. G.; Finkelstein, Steven L.; Ferguson, Henry C.; Grogin, N. A.; Kacprzak, G. G.; Kelson, Daniel D.; Koekemoer, A. M.; Murphy, David; McCarthy, P. J.; Newman, Jeffrey A.; Salmon, Brett; Willner, S. P.; Finkelstein, Steven L.Star-forming galaxies at redshiftsz > 6 are likely responsible for the reionization of the universe, and it is important to study the nature of these galaxies. We present three candidates for z similar to 7 Lyman break galaxies (LBGs) from a 155 arcmin(2) area in the CANDELS/COSMOS field imaged by the deep FourStar Galaxy Evolution (zFourGE) survey. The FourStar medium-band filters provide the equivalent of R similar to 10 spectroscopy, which cleanly distinguishes between z similar to 7 LBGs and brown dwarf stars. The distinction between stars and galaxies based on an object's angular size can become unreliable even when using Hubble Space Telescope imaging; there exists at least one very compact z similar to 7 candidate (FWHM similar to 0.5-1 kpc) that is indistinguishable from a point source. The medium-band filters provide narrower redshift distributions compared with broadband-derived redshifts. The UV luminosity function derived using the three z similar to 7 candidates is consistent with previous studies, suggesting an evolution at the bright end (MUV similar to -21.6 mag) from z similar to 7 to z similar to 5. Fitting the galaxies' spectral energy distributions, we predict Ly alpha equivalent widths for the two brightest LBGs, and find that the presence of a Ly alpha line affects the medium-band flux thereby changing the constraints on stellar masses and UV spectral slopes. This illustrates the limitations of deriving LBG properties using only broadband photometry. The derived specific star-formation rates for the bright LBGs are similar to 13 Gyr(-1), slightly higher than the lower-luminosity LBGs, implying that the star-formation rate increases with stellar mass for these galaxies.Item The Near-Ultraviolet Luminosity Function Of Young, Early M-Type Dwarf Stars(2015-01) Ansdell, Megan; Gaidos, Eric; Mann, Andrew W.; Lepine, Sebastien; James, David; Buccino, Andrea; Baranec, Christoph; Law, Nicolas M.; Riddle, Reed; Mauas, Pablo; Petrucci, Romina; Mann, Andrew W.Planets orbiting within the close-in habitable zones of M dwarf stars will be exposed to elevated high-energy radiation driven by strong magnetohydrodynamic dynamos during stellar youth. Near-ultraviolet (NUV) irradiation can erode and alter the chemistry of planetary atmospheres, and a quantitative description of the evolution of NUV emission from M dwarfs is needed when modeling these effects. We investigated the NUV luminosity evolution of early M-type dwarfs by cross-correlating the Lepine & Gaidos catalog of bright M dwarfs with the Galaxy Evolution Explorer (GALEX) catalog of NUV (1771-2831 angstrom) sources. Of the 4805 sources with GALEX counterparts, 797 have NUV emission significantly (>2.5 sigma) in excess of an empirical basal level. We inspected these candidate active stars using visible-wavelength spectra, high-resolution adaptive optics imaging, time-series photometry, and literature searches to identify cases where the elevated NUV emission is due to unresolved background sources or stellar companions; we estimated the overall occurrence of these "false positives" (FPs) as similar to 16%. We constructed an NUV luminosity function that accounted for FPs, detection biases of the source catalogs, and GALEX upper limits. We found the NUV luminosity function to be inconsistent with predictions from a constant star-formation rate and simplified age-activity relation defined by a two-parameter power law.