General relativistic x ray (UV) polarization rotations as a quantitative test for black holes

It is now 11 years since a potentially easily observable and quantitative test for black holes using general relativistic polarization rotations was proposed (Stark and Connors 1977, and Connors and Stark 1977). General relativistic rotations of the x ray polarization plane of 10 to 100 degrees with x ray energy (between 1 and 100 keV) are predicted for black hole x ray binaries. (Classically, by symmetry, there is no rotation.) Unfortunately, x ray polarimetry has not been taken sufficiently seriously during this period, and this test has not yet been performed. A similar (though probably less clean) effect is expected in the UV for supermassive black holes in some quasars active galactic nuclei. Summarizing: (1) a quantitative test (proposed in 1977) for black holes exists; (2) x ray polarimetry of galactic x ray binaries sensitive to at least 1/2 percent between 1 keV and 100 keV is needed (polarimetry in the UV of quasars and AGN will also be of interest); and (3) proportional counters using timerise discrimination were shown in laboratory experiments able to perform x ray polarimetry and this and other methods need to be developed

Gravitational radiation from rotating gravitational collapse

The efficiency of gravitational wave emission from axisymmetric rotating collapse to a black hole was found to be very low: Delta E/Mc sq. less than 7 x 10(exp -4). The main waveform shape is well defined and nearly independent of the details of the collapse. Such a signature will allow pattern recognition techniques to be used when searching experimental data. These results (which can be scaled in mass) were obtained using a fully general relativistic computer code that evolves rotating axisymmetric configurations and directly computes their gravitational radiation emission

Keck Spectroscopy of Faint 3 < z < 7 Lyman Break Galaxies: III. The Mean Ultraviolet Spectrum at z=4

We present and discuss the mean rest-frame ultraviolet spectrum for a sample of 81 Lyman Break Galaxies (LBGs) selected to be B-band dropouts with a mean redshift of z=3.9 and apparent magnitudes z_AB<26. Most of the individual spectra are drawn from our ongoing survey in the GOODS fields with the Keck DEIMOS spectrograph, and we have augmented our sample with published data taken with FORS2 on the VLT. In general we find similar trends in the spectral diagnostics to those found in the earlier, more extensive survey of LBGs at z=3 undertaken by Shapley et al (2003). Specifically, we find low-ionization absorption lines which trace the presence of neutral outflowing gas are weaker in galaxies with stronger Lyman-alpha emission, bluer UV spectral slopes, lower stellar masses, lower UV luminosities and smaller half-light radii. This is consistent with a physical picture whereby star formation drives outflows of neutral gas which scatters Lyman-alpha and gives rise to strong low-ionization absorption lines, while increasing the stellar mass, size, metallicity, and dust content of galaxies. Typical galaxies are thus expected to have stronger Lyman-alpha emission and weaker low-ionization absorption at earlier times (higher redshifts). Indeed, our mean spectrum at z=4 shows somewhat weaker low-ionization absorption lines than at z=3 and available data at higher redshift indicates a rapid decrease in low-ionization absorption strength with redshift. We argue that the reduced low-ionization absorption is likely caused by a decrease in the covering fraction and/or velocity range of outflowing neutral gas at earlier epochs. Our continuing survey will enable us to extend these diagnostics more reliably to higher redshift and determine the implications for the escape fraction of ionizing photons which governs the role of early galaxies in cosmic reionization. [Abridged]Comment: 17 pages, 12 figures, submitted to ApJ. Comments welcom

Keck Spectroscopy of Faint 3<z<7 Lyman Break Galaxies:- II. A High Fraction of Line Emitters at Redshift Six

As Lyman-alpha photons are scattered by neutral hydrogen, a change with redshift in the Lyman-alpha equivalent width distribution of distant galaxies offers a promising probe of the degree of ionization in the intergalactic medium and hence when cosmic reionization ended. This simple test is complicated by the fact that Lyman-alpha emission can also be affected by the evolving astrophysical details of the host galaxies. In the first paper in this series, we demonstrated both a luminosity and redshift dependent trend in the fraction of Lyman-alpha emitters seen within color-selected Lyman-break galaxies (LBGs) over the range 3<z<6; lower luminosity galaxies and those at higher redshift show an increased likelihood of strong emission. Here we present the results from much deeper 12.5 hour exposures with the Keck DEIMOS spectrograph focused primarily on LBGs at z~6 which enable us to confirm the redshift dependence of line emission more robustly and to higher redshift than was hitherto possible. We find 54+/-11% of faint z~6 LBGs show strong (W_0>25 A) emission, an increase of 1.6x from a similar sample observed at z~4. With a total sample of 74 z~6 LBGs, we determine the luminosity-dependent Lyman-alpha equivalent width distribution. Assuming continuity in these trends to the new population of z~7 sources located with the Hubble WFC3/IR camera, we predict that unless the neutral fraction rises in the intervening 200 Myr, the success rate for spectroscopic confirmation using Lyman-alpha emission should be high.Comment: 6 pages, 3 figures, submitted to ApJ

Synthetic image generator model: Application of specular and diffuse reflectivity components and performance evaluation in the visible region

This study focused on the operation of the RIT Digital Imaging and Remote Sensing Lab\u27s synthetic image generation (DIRSIG) software model in the 0.4 to 1.0 urn wavelength region. The overall intent was to create a baseline for future DIRSIG activity. This was achieved by modifying the infrared based software to account for the characteristics of visible energy, and then evaluating the model\u27s overall performance. A modification was made to the model\u27s radiance algorithm by dividing surface reflectivity into a combination of view angle dependent diffuse and specular components. Additionally a practical method was developed for generating these values. Performance evaluation of the model was accomplished by collecting truth data from an actual scene, generating an applicable reflectivity database, synthetically generating images of the scene, and then comparing the image data with the truth data. The generated images provided a good representation of the visible energy interactions occurring in a scene

Discovery of a possibly old galaxy at z=6.027z=6.027, multiply imaged by the massive cluster Abell 383

We report the discovery of a unique $z=6.027$ galaxy, multiply imaged by the cluster Abell 383 and detected in new Hubble Space Telescope ACS and WFC3 imaging, as well as in Warm Spitzer observations. This galaxy was selected as a pair of i-dropouts; its suspected high redshift was confirmed by the measurement of a strong Lyman-alpha line in both images using Keck/DEIMOS. Combining Hubble and Spitzer photometry after correcting for contamination by line emission (estimated to be a small effect), we identify a strong Balmer break of 1.5 magnitudes. Taking into account the magnification factor of 11.4+/-1.9 (2.65+/-0.17 mag) for the brightest image, the unlensed AB magnitude for the source is 27.2+/-0.05 in the H band, corresponding to a 0.4 L* galaxy, and 25.7+/-0.08 at 3.6 um. The UV slope is consistent with beta~2.0, and from the rest-frame UV continuum we measure a current star formation rate of 2.4+/-1.1 Msol/yr. The unlensed half-light radius is measured to be 300 pc, from which we deduce a star-forming surface density of ~10 Msol/yr/kpc2. The Lyman-alpha emission is found to be extended over ~3" along the slit, corresponding to ~5 kpc in the source plane. This can be explained by the presence of a much larger envelope of neutral hydrogen around the star-forming region. Finally, fitting the spectral energy distribution using 7 photometric data points with simple SED models, we derive the following properties: very little reddening, an inferred stellar mass of M*=6e9 Msol, and an inferred age of ~800 Myrs (corresponding to a redshift of formation of ~18). The star-formation rate of this object was likely much stronger in the past than at the time of observation, suggesting that we may be missing a fraction of galaxies at z~6 which have already faded in rest-frame UV wavelengths.Comment: 6 pages, 3 figures, MNRAS in press, replaced with accepted version including minor comment

A Pilot Survey for CIII] Emission in the Reionization Era: Gravitationally-Lensed z∼7−8\sim7-8 Galaxies in the Frontier Fields Cluster Abell 2744

We report results of a search for CIII] $\lambda \lambda$1907,1909 {\AA} emission using Keck's MOSFIRE spectrograph in a sample of 7 $z_{phot}\sim7-8$ candidates ($H\sim27$) lensed by the Hubble Frontier Field cluster Abell 2744. Earlier work has suggested the promise of using the CIII] doublet for redshift confirmation of galaxies in the reionization era given $Ly\alpha$ ($\lambda$1216 {\AA}) is likely attenuated by the neutral intergalactic medium. The primary challenge of this approach is the feasibility of locating CIII] emission without advanced knowledge of the spectroscopic redshift. With an integration time of 5 hours in the H-band, we reach a $5\sigma$ median flux limit (in between the skylines) of $1.5\times10^{-18}$ ergs cm$^{-2}$ sec$^{-1}$ but no convincing CIII] emission was found. We also incorporate preliminary measurements from two other CLASH/HFF clusters in which, similarly, no line was detected, but these were observed to lesser depth. Using the known distribution of OH emission and the photometric redshift likelihood distribution of each lensed candidate, we present statistical upper limits on the mean total CIII] rest-frame equivalent width for our $z\simeq7-8$ sample. For a signal/noise ratio of 5, we estimate the typical CIII] doublet rest-frame equivalent width is, with 95\% confidence, $<26\pm5$ {\AA}. Although consistent with the strength of earlier detections in brighter objects at $z\simeq6-7$, our study illustrates the necessity of studying more luminous or strongly-lensed examples prior to the launch of the James Webb Space Telescope.Comment: 7 pages, 4 figures, 1 table; accepted for publication in ApJ Letter