Evidence for extended, obscured starbursts in submm galaxies

We compare high-resolution optical and radio imaging of 12 luminous submm galaxies at z=2.2+/-0.2 observed with HST and the MERLIN and VLA at comparable spatial resolution, 0.3" (2kpc). The radio emission traces the likely far-infrared morphology of these dusty, luminous galaxies. In ~30% of the sample the radio appears unresolved, suggesting that the emission is compact: either an obscured AGN or nuclear starburst. However, in the majority, ~70% (8/12), the radio emission is resolved by MERLIN/VLA on scales of ~1" (10 kpc). For these galaxies the radio morphologies are broadly similar to their restframe UV emission seen by HST. We discuss the probable mechanisms for the extended emission and conclude that their luminous radio and submm emission arises from a large, spatially-extended starburst. The median SFRs are 1700Mo/yr occuring within a ~40kpc^2 region, giving a star formation density of 45Mo/yr/kpc^2. Such vigorous and extended starbursts appear to be uniquely associated with the submm population. A more detailed comparison of the distribution of UV and radio emission shows that the broad similarities on large scales are not carried through to smaller scales, where there is rarely a one-to-one correspondance. We interpret this as resulting from highly structured internal obscuration, suggesting that the vigorous activity is producing wind-blown channels through the obscuration in these galaxies. If correct this underlines the difficulty of using UV morphologies to understand structural properties of this population and also may explain the surprising frequency of Ly-alpha emission in their spectra. [Abridged]Comment: 7 pages, 3 figure

A survey of users of earth resources remote sensing data

The results of a NASA supported Battelle survey to obtain user views on the nature and value of LANDSAT data use, on current LANDSAT capabilities, and on ways to improve data use were summarized. Questionnaire and interview responses from over 1000 private and public sector users were analyzed and discussed

Survey of users of earth resources remote sensing data

A user survey was conducted to determine current earth resources survey (ERS) data use/user status and recommendations for strengthening use. Only high-altitude aircraft and satellite (primarily LANDSAT) data were included. Emphasis was placed on the private sector/industrial user. Objectives of the survey included: who is using ERS data, how they are using the data, the relative value of current data use as well as obtaining user views as to possible ways of strengthening future ERS data use. The survey results are documented and should provide relevant decision making information for developing future programs of maximum benefit to all end users of satellite ERS data

Counts and Colors of Faint Galaxies in the U and R Bands

Ground-based counts and colors of faint galaxies in the U and R bands in one field at high Galactic latitude are presented. Integrated over flux, a total of 1.2x10^5 sources per square degree are found to U=25.5 mag and 6.3x10^5 sources per square degree to R=27 mag, with d log N/dm ~ 0.5 in the U band and d log N/dm ~ 0.3 in the R band. Consistent with these number-magnitude curves, sources become bluer with increasing magnitude to median U-R=0.6 mag at 24<U<25 mag and U-R=1.2 mag at 25 < R < 26 mag. Because the Lyman break redshifts into the U band at z~3, at least 1.2x10^5 sources per square degree must be at redshifts z<3. Measurable U-band fluxes of 73 percent of the 6.3x10^5 sources per square degree suggest that the majority of these also lie at z < 3. These results require an enormous space density of objects in any cosmological model.Comment: 17 pages, MNRAS in pres

Utilizing Skylab data in on-going resources management programs in the state of Ohio

The author has identified the following significant results. The use of Skylab imagery for total area woodland surveys was found to be more accurate and cheaper than conventional surveys using aerial photo-plot techniques. Machine-aided (primarily density slicing) analyses of Skylab 190A and 190B color and infrared color photography demonstrated the feasibility of using such data for differentiating major timber classes including pines, hardwoods, mixed, cut, and brushland providing such analyses are made at scales of 1:24,000 and larger. Manual and machine-assisted image analysis indicated that spectral and spatial capabilities of Skylab EREP photography are adequate to distinguish most parameters of current, coal surface mining concern associated with: (1) active mining, (2) orphan lands, (3) reclaimed lands, and (4) active reclamation. Excellent results were achieved when comparing Skylab and aerial photographic interpretations of detailed surface mining features. Skylab photographs when combined with other data bases (e.g., census, agricultural land productivity, and transportation networks), provide a comprehensive, meaningful, and integrated view of major elements involved in the urbanization/encroachment process

Physical properties of two low-luminosity z ~ 1.9 galaxies behind the lensing cluster AC 114

We present VLT/ISAAC near-infrared spectroscopy of two gravitationally-lensed z ~ 1.9 galaxies, A2 and S2, located behind the cluster AC 114. Thanks to large magnification factors, we have been successful in detecting rest-frame optical emission lines in star-forming galaxies 1 to 2 magnitudes fainter than in previous studies of Lyman break galaxies (LBGs) at z ~ 3. From the Ha luminosity, we estimate star formation rates (SFRs) which are 7 to 15 times higher than those inferred from the UV continuum flux at 1500 ang without dust extinction correction. The behavior of S2 and A2 in terms of O/H and N/O abundance ratios are very different, and they are also different from typical LBGs at z ~ 3. S2 is a low-metallicity object (Z ~ 0.03 Zsun) with a low N/O ratio, similar to those derived in the most metal-poor nearby HII galaxies. In contrast, A2 is a high-metallicity galaxy (Z ~ 1.3 Zsun) with a high N/O abundance ratio, similar to those derived in the most metal-rich starburst nucleus galaxies. The virial masses, derived from emission-line widths, are 0.5 and 2.4 x 10^10 Msun, for S2 and A2 respectively. Thanks to the gravitational amplification, the line profiles of S2 are spatially resolved, leading to a velocity gradient of +- 240 km/s, which yields a dynamical mass of ~ 1.3 x 10^10 Msun within the inner 1 kpc radius. Combining these new data with the sample of LBGs at z ~ 3, we conclude that these three galaxies exhibit different physical properties in terms of SFRs, abundance and mass-to-light ratios, and reddening. High-redshift galaxies of different luminosities could thus have quite different star formation histories (abridged version).Comment: 11 pages, 8 figures. Accepted for publication in A&

Calibrating [O II] star formation rates at z < 1 from dual Hα-[O II] imaging from HiZELS

We investigate the relationship between Hα and [O II](λ3727) emission in faint star-forming galaxies at z = 1.47 with dust uncorrected star formation rates (SFRs) down to 1.4 M⊙ yr-1, using data in two narrow bands from wide-field camera/United Kingdom Infrared Telescope and Subaru prime focus camera/Subaru. A stacking analysis allows us to investigate Hα emission flux from bright [O II] emitters as well as faint ones for which Hα is not individually detected, and to compare them with a large sample of local galaxies. We find that there is a clear, positive correlation between the average Hα and [O II] luminosities for [O II] emitters at z = 1.47, with its slope being consistent with the local relation. [O II] emitters at z = 1.47 have lower mean observed ratios of Hα/[O II] suggesting a small but systematic offset (at 2.8σ significance) towards lower values of dust attenuation, AHα ˜ 0.35, than local galaxies. This confirms that [O II] selection tends to pick up galaxies which are significantly less dusty on average than Hα-selected ones, with the difference being higher at z = 1.47 than at z = 0. The discrepancy of the observed line ratios between [O II] emitters at z = 1.47 and the local galaxies may in part be due to the samples having different metallicities. However, we demonstrate that metallicity is unlikely to be the main cause. Therefore, it is important to take into account that the relations for the dust correction which are derived using Hα emitter samples, and frequently used in many studies of high-z galaxies, may overestimate the intrinsic SFRs of [O II]-selected galaxies, and that surveys of [O II] emission galaxies are likely to miss dusty populations