Photometry and Photometric Redshifts of Faint Galaxies in the Hubble Deep Field South NICMOS Field

We present a catalog of photometry and photometric redshifts of 335 faint objects in the HDF-S NICMOS field. The analysis is based on (1) infrared images obtained with the Hubble Space Telescope (HST) using the Near Infrared Camera and Multi-Object Spectrograph (NICMOS) with the F110W, F160W, and F222M filters, (2) an optical image obtained with HST using the Space Telescope Imaging Spectrograph (STIS) with no filter, and (3) optical images obtained with the European Southern Observatory (ESO) Very Large Telescope (VLT) with U, B, V, R, and I filters. The primary utility of the catalog of photometric redshifts is as a survey of faint galaxies detected in the NICMOS F160W and F222M images. The sensitivity of the survey varies significantly with position, reaching a limiting depth of AB(16,000) ~ 28.7 and covering 1.01 arcmin^2 to AB(16,000) = 27 and 1.05 arcmin^2 to AB(16,000) = 26.5. The catalog of photometric redshifts identifies 21 galaxies (or 6% of the total) of redshift z > 5, 8 galaxies (or 2% of the total) of redshift z > 10, and 11 galaxies (or 3% of the total) of best-fit spectral type E/S0, of which 5 galaxies (or 1% of the total) are of redshift z > 1.Comment: 33 pages, 10 figures, accepted for publication in the Astrophysical Journal, August 1, 2000 issu

Direct Distance Measurements to Superluminal Radio Sources

We present a new technique for directly measuring the distances to superluminal radio sources. By comparing the observed proper motions of components in a parsec scale radio jet to their measured Doppler factors, we can deduce the distance to the radio source independent of the standard rungs in the cosmological distance ladder. This technique requires that the jet angle to the line of sight and the ratio of pattern to flow velocities are sufficiently constrained. We evaluate a number of possibilities for constraining these parameters and demonstrate the technique on a well defined component in the parsec scale jet of the quasar 3C279 (z = 0.536). We find an angular size distance to 3C279 of greater than 1.8 (+0.5,-0.3) n^{1/8} Gpc, where n is the ratio of the energy density in the magnetic field to the energy density in the radiating particles in that jet component. For an Einstein-de Sitter Universe, this measurement would constrain the Hubble constant to be H < 65 n^{-1/8} km/s/Mpc at the two sigma level. Similar measurements on higher redshift sources may help discriminate between cosmological models.Comment: 18 pages, 8 figures, to be published in The Astrophysical Journa

Clustering in the 1.2 Jy IRAS Galaxy Redshift Survey II: Redshift Distortions and \xi(r_p,\pi)

We examine the effect of redshift space distortions on the galaxy two-point correlation function $\xi(r_p,\pi)$ as a function of separations parallel ($r_p$) and perpendicular ($\pi$) to the line of sight. We find that the relative velocity dispersion of pairs of IRAS galaxies is $\sigma(r)= 317^{+40}_{-49}$ \kms at r=1 \mpc, consistent with previous estimates derived from optically selected galaxy catalogues. Unfortunately, the use of this result to estimate $\Omega$ via the Cosmic Virial Theorem is thwarted by large systematic uncertainties. We also fit for the mean relative streaming velocity of pairs, $v_{12}(r)$, which describes the growth of fluctuations on both linear and nonlinear scales. We find that $v_{12}(r) = 167^{+99}_{-67}$ \kms at $r=4$\mpc, so that on average, approximately half the Hubble expansion velocity of pairs at this separation is canceled by infall. At $r=10$\mpc, the amplitude of the streaming is lower and v_{12}(r) = 109^{+64}_{-47} \kms. Linear perturbation theory then implies that $\Omega^{0.6}/b =0.45^{+0.27}_{-0.18}$ on scales \sim 10-15 \mpc. The amplitude of $v_{12}(r)$ is sensitive to the assumed shape of $\sigma(r)$; if the latter deviates substantially from a virialized form on small scale, our best fit amplitude of $v_{12}(r)$ can deviate by a factor of two.Comment: 28 pages of uuencoded compressed postscript; figures include