Galaxy formation and evolution

Abstract:

We present spectrograms of the faint V-drop (V606 = 28.1, I814 = 25.6) galaxy pair HDF 3-951.1 and HDF 3-951.2 obtained at the Keck II Telescope. In a recent study, Fernández-Soto, Lanzetta, & Yahil derive a photometric redshift of zph = 5.28+0.34-0.41 (2 σ) for these galaxies; our integrated spectrograms show a large and abrupt discontinuity near 7710 ± 5 Å. This break is almost certainly due to the Lyα forest because its amplitude (1 - fshortv/flongv > 0.87, 95% confidence limit) exceeds any discontinuities observed in stellar or galactic rest-frame optical spectra. The resulting absorption break redshift is z = 5.34 ± 0.01. Optical/near-IR photometry from the HDF yields an exceptionally red (V606 - I814) color, consistent with this large break. A more accurate measure of the continuum depression blueward of Lyα utilizing the imaging photometry yields DA = 0.88. The system as a whole is slightly brighter than L*1500 relative to the z ∼ 3 Lyman break population, and the total star formation rate inferred from the UV continuum is ≈22 h-250 M⊙ yr-1 (q0 = 0.5) assuming the absence of dust extinction. The two individual galaxies are quite small (size scales ≲ 1 h-150 kpc). Thus these galaxies superficially resemble the "building blocks" of Pascarelle and coworkers; if they comprise a gravitationally bound system, the pair will likely merge in a timescale ∼100 Myr.

Abstract:

We present Keck Low Resolution Imaging Spectrometer spectroscopy along with Near-Infrared Camera and Multiobject Spectrometer (NICMOS) F110W (∼J) and F160W (∼H) images of the galaxy HDF 4-473.0 in the Hubble Deep Field (HDF), with a detection of an emission line consistent with Lyα at a redshift of z = 5.60. Attention to this object as a high-redshift galaxy was first drawn by Lanzetta, Yahil, & Fernandez-Soto and appeared in their initial list of galaxies with redshifts estimated from the Wide Field Planetary Camera 2 (WFPC2) HDF photometry. It was selected by us for spectroscopic observation, along with others in the HDF, on the basis of the NICMOS F110W and F160W and WFPC2 photometry. ForH0 = 65 km s-1 Mpc-1 and q0 = 0.125, the use of simple evolutionary models along with the F814W (∼I), F110W, and F160W magnitudes allow us to estimate the star formation rate (∼13 M⊙ yr-1). The colors suggest a reddening of E(B - V) ∼ 0.06. The measured flux in the Lyα line is approximately 1.0 × 10-17 ergs cm-2 s-1, and the rest-frame equivalent width, correcting for the absorption caused by intervening H I, is ∼90 Å. The galaxy is compact and regular, but resolved, with an observed FWHM of ∼0″.44. Simple evolutionary models can accurately reproduce the colors, and these models predict the Lyα flux to within a factor of 2. Using this object as a template shifted to higher redshifts, we calculate the magnitudes through the F814W and two NICMOS passbands for galaxies at redshifts 6 < z < 10. © 1998. The American Astronomical Socicly. All rights reserved.

Abstract:

In this paper, we report on a first estimate of the contribution of galaxies to the diffuse extragalactic background from the far-UV to the submm, based on semi--analytic models of galaxy formation and evolution. We conclude that the global multi--wavelength picture seems to be consistent provided a quite important fraction of star--formation be hidden in dust--enshrouded systems at intermediate and high--redshift. We show that, according to such models, galaxies cannot stand as important contributors to the background hydrogen-ionizing flux at high-redshift unless neutral hydrogen absorption sites are clumpy and uncorrelated with star forming regions.We briefly discuss the robustness of such a result.

Abstract:

We construct dynamical models for a sample of 36 nearby galaxies with Hubble Space Telescope (HST) photometry and ground-based kinematics. The models assume that each galaxy is axisymmetric, with a two-integral distribution function, arbitrary inclination angle, a position-independent stellar mass-to-light ratio Y, and a central massive dark object (MDO) of arbitrary mass M•. They provide acceptable fits to 32 of the galaxies for some value of M• and Y; the four galaxies that cannot be fitted have kinematically decoupled cores. The mass-to-light ratios inferred for the 32 well-fitted galaxies are consistent with the fundamental-plane correlation Y ∝ L0.2, where L is galaxy luminosity. In all but six galaxies the models require at the 95% confidence level an MDO of mass M• ∼ 0.006Mbulge ≡ 0.006YL. Five of the six galaxies consistent with M• = 0 are also consistent with this correlation. The other (NGC 7332) has a much stronger upper limit on M•. We predict the second-moment profiles that should be observed at HST resolution for the 32 galaxies that our models describe well. We consider various parameterizations for the probability distribution describing the correlation of the masses of these MDOs with other galaxy properties. One of the best models can be summarized thus: a fraction f ≃ 0.97 of early-type galaxies have MDOs, whose masses are well described by a Gaussian distribution in log (M•/Mbulge) of mean -2.28 and standard deviation ∼0.51. There is also marginal evidence that M• is distributed differently for "core" and "power law" galaxies, with core galaxies having a somewhat steeper dependence on Mbulge.