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Articles 61 - 64 of 64
Full-Text Articles in Astrophysics and Astronomy
Testing The Dark Matter Hypothesis With Low Surface Brightness Galaxies And Other Evidence, Stacy S. Mcgaugh
Testing The Dark Matter Hypothesis With Low Surface Brightness Galaxies And Other Evidence, Stacy S. Mcgaugh
Faculty Scholarship
The severity of the mass discrepancy in spiral galaxies is strongly correlated with the central surface brightness of their disks. Progressively lower surface brightness galaxies have ever larger mass discrepancies. No other parameter (luminosity, size, velocity, morphology) is so well correlated with the magnitude of the mass deficit. The rotation curves of low surface brightness disks thus provide a unique data set with which to probe the dark matter distribution in galaxies. The mass discrepancy is apparent from R = 0, giving a nearly direct map of the halo mass distribution. The luminous mass is insignificant. Interpreting the data in …
The Nature Of Compact Galaxies In The Hubble Deep Field. Ii. Spectroscopic Properties And Implications For The Evolution Of The Star Formation Rate Density Of The Universe, Rafael Guzmán, Jesús Gallego, David C. Koo, Andrew C. Phillips, James D. Lowenthal, S. M. Faber, Garth D. Illingworth, Nicole P. Vogt
The Nature Of Compact Galaxies In The Hubble Deep Field. Ii. Spectroscopic Properties And Implications For The Evolution Of The Star Formation Rate Density Of The Universe, Rafael Guzmán, Jesús Gallego, David C. Koo, Andrew C. Phillips, James D. Lowenthal, S. M. Faber, Garth D. Illingworth, Nicole P. Vogt
Astronomy: Faculty Publications
We present a spectroscopic study of 51 compact field galaxies with redshifts z < 1.4 and apparent magnitudes I < 23.74 in the flanking fields of the Hubble Deep Field. These galaxies are compact in the sense that they have small apparent half-light radii (r ≤ 0″.5) and high surface brightnesses (μ ≤ 22.2 mag arcsec ). The spectra, taken at the Keck telescope, show emission lines in 88% of our sample, and only absorption lines in the remaining 12%. Emission-line profiles are roughly Gaussian with velocity widths that range from the measurement limit of σ ∼ 35 km s to 150 km s . Rest frame [O II] λ3727 equivalent widths range from 5 to 94 Å, yielding star formation rates (SFRs) of ∼0.1 to 14 M yr . The analysis of various line diagnostic diagrams reveals that ∼60% of compact emission-line galaxies have velocity widths, excitations, Hβ luminosities, SFRs, and mass-to-light ratios characteristic of young star-forming H II galaxies. The remaining 40% form a more heterogeneous class of evolved starbursts, similar to local starburst disk galaxies. We find that, although the compact galaxies at z > 0.7 have similar SFRs per unit mass to those at z < 0.7, they are on average ∼10 times more massive. Our sample implies a lower limit for the global comoving SFR density of ∼0.004 M yr Mpc at z = 0.55, and ∼0.008 M yr Mpc at z = 0.85 (assuming Salpeter IMF, H = 50 km s Mpc , and q = 0.5). These values, when compared to estimates for a sample of local compact galaxies selected in a similar fashion, support a history of the universe in which the SFR density declines by a factor ∼10 from z = 1 to today. From the comparison with the SFR densities derived for magnitude-limited samples of field galaxies, we conclude that compact emission-line galaxies, though only ∼20% of the general field population, may contribute as much as ∼45% to the global SFR of the universe at 0.4 < z < 1. © 1997. The American Astronomical Society. All rights reserved. 814 1/2 I814 ⊙ ⊙ ⊙ 0 o -2 -1 -1 -1 -1 -3 -1 -3 -1 -1
Discovery Of A Lyα Galaxy Near A Damped Lyα Absorber At Z = 2.3, James D. Lowenthal, Craig J. Hogan, Richard F. Green, Adeline Caulet, Bruce E. Woodgate, Larry Brown, Craig B. Foltz
Discovery Of A Lyα Galaxy Near A Damped Lyα Absorber At Z = 2.3, James D. Lowenthal, Craig J. Hogan, Richard F. Green, Adeline Caulet, Bruce E. Woodgate, Larry Brown, Craig B. Foltz
Astronomy: Faculty Publications
We report the detection of a galaxy associated with the damped Lyα absorbing cloud seen at z = 2.309 toward the QSO PHL 957 (zem = 2.681). The galaxy was discovered in deep Fabry-Perot narrow-band CCD frames and was subsequently imaged spectroscopically. In addition to a strong but narrow Lyα emission line (FLyα = 5.6 × 10-16 ergs s-1 cm-2, FWHM ∼ 700 km s-1) and weaker C IV and He II lines, the object shows continuum at V ∼ 24, with a slope (in Fν) rising slightly toward the red, similar to what is seen in high-redshift radio galaxies; …
Spectroscopic Limits On High-Redshift Lyα Emission, James D. Lowenthal, Craig J. Hogan, Robert W. Leach, Gary D. Schmidt, Craig B. Foltz
Spectroscopic Limits On High-Redshift Lyα Emission, James D. Lowenthal, Craig J. Hogan, Robert W. Leach, Gary D. Schmidt, Craig B. Foltz
Astronomy: Faculty Publications
We have conducted a deep long-slit spectroscopic search for high-redshift (2.7 < z < 4.7) Lyα emission. Four pairs of deep, high-resolution (R ≈ 2000), long-slit CCD frames were taken at the Multiple Mirror Telescope. The "blank sky" in each pair of frames was searched for faint emission features unresolved spatially and spectrally. No emission features were found down to a limiting line surface brightness (1 σ) of 1-4 × 10-18 ergs s-1 cm-2 arcsec-2. The sensitivity of the search was calibrated using simulations with synthetic features added to the data frames. The data set upper limits on the mean space density 〈n〉 and line flux of randomly distributed Lyα-emitting clouds; for example, at z ≈ 4.5 we have a 95% confidence limit of 〈n〉 < 1 Mpc-3 h1003 at a total line flux level of ∼3 × 10-17 ergs s-1 cm-2. These limits approach expected emission levels for fairly conservative published primeval galaxy models. In addition, Lyα emission was searched for, but not detected, from a known Lyα-limit absorption cloud toward QSO 0731+653. Assuming that the gas in this cloud is spatially resolved (size ≳ 4h-1 kpc) we set an upper limit on the diffuse ionizing flux density at z = 2.912 of Jv ≲ 2 × 10-19 ergs s-1 cm-2 sr-1 Hz-1.