Evidence for Solar Metallicities in Massive Star-forming Galaxies at z>~2

We present results of near-IR spectroscopic measurements of 7 star-forming galaxies at 2.1<z<2.5. Drawn from a large spectroscopic survey of galaxies photometrically pre-selected by their U_nGR colors to lie at z~2, these galaxies were chosen for their bright rest-frame optical luminosities (K_s<=20.0). Most strikingly, the majority of the sample of 7 galaxies exhibit [NII]/Ha nebular emission line ratios indicative of at least solar HII region metallicities, at a lookback time of 10.5 Gyr. The broadband colors of the K_s-bright sample indicate that most have been forming stars for more than a Gyr at z~2, and have already formed stellar masses in excess of 10^11 Msun. The descendants of these galaxies in the local universe are most likely metal-rich and massive spiral and elliptical galaxies, while plausible progenitors for them can be found among the population of z~3 Lyman Break Galaxies. While the K_s-bright z~2 galaxies appear to be highly evolved systems, their large Ha luminosities and uncorrected Ha star-formation rates of 24-60 Msun/yr indicate that active star formation is still ongoing. The luminous UV-selected objects presented here comprise more than half of the high-redshift (z>1.5) tails of current K-band-selected samples such as the K20 and Gemini Deep Deep surveys.Comment: 15 pages including 5 figures. Accepted for publication in Ap

Signature of Shallow Potentials in Deep Sub-barrier Fusion Reactions

We extend a recent study that explained the steep falloff in the fusion cross section at energies far below the Coulomb barrier for the symmetric dinuclear system 64Ni+64Ni to another symmetric system, 58Ni+58Ni, and the asymmetric system 64Ni+100Mo. In this scheme the very sensitive dependence of the internal part of the nuclear potential on the nuclear equation of state determines a reduction of the classically allowed region for overlapping configurations and consequently a decrease in the fusion cross sections at bombarding energies far below the barrier. Within the coupled-channels method, including couplings to the low-lying 2+ and 3- states in both target and projectile as well as mutual and two-phonon excitations of these states, we calculate and compare with the experimental fusion cross sections, S-factors, and logarithmic derivatives for the above mentioned systems and find good agreement with the data even at the lowest energies. We predict, in particular, a distinct double peaking in the S-factor for the far subbarrier fusion of 58Ni+58Ni which should be tested experimentally.Comment: 34 pages, 10 figures, to appear in Phys. Rev.

Spectroscopic Identification of a Proto-Cluster at z=2.300: Environmental Dependence of Galaxy Properties at High Redshift

We have discovered a highly significant over-density of galaxies at z=2.300+/-0.015 in the course of a redshift survey designed to select star-forming galaxies in the redshift range z=2.3+/-0.4 in the field of the bright z=2.72 QSO HS1700+643. The structure has a redshift-space galaxy over-density of delta_g,z ~= 7 and an estimated matter over-density in real space of delta_m ~= 1.8, indicating that it will virialize by z~0 with a mass scale of ~= 1.4x10^15 M_sun, that of a rich galaxy cluster. Detailed modeling of the spectral energy distribution -- from the rest-far-UV to the rest-near-IR -- of the 72 spectroscopically confirmed galaxies in this field for which we have obtained K_s and Spitzer/IRAC photometry, allows for a first direct comparison of galaxy properties as a function of large-scale environment at high redshift. We find that galaxies in the proto-cluster environment have mean stellar masses and inferred ages that are ~2 times larger (at z=2.30) than identically UV-selected galaxies outside of the structure, and show that this is consistent with simple theoretical expectations for the acceleration of structure formation in a region that is over-dense on large scales by the observed amount. The proto-cluster environment contains a significant number of galaxies that already appear old, with large stellar masses (>10^11 M_sun), by z=2.3.Comment: 7 pages including 3 figures. Accepted for publication in ApJ. Typo correcte

Hole depletion and localization due to disorder in insulating PrBa2Cu3O7-d: a Compton scattering study

The (mostly) insulating behaviour of PrBa2Cu3O7-d is still unexplained and even more interesting since the occasional appearance of superconductivity in this material. Since YBa2Cu3O7-d is nominally iso-structural and always superconducting, we have measured the electron momentum density in these materials. We find that they differ in a striking way, the wavefunction coherence length in PrBa2Cu3O7-d being strongly suppressed. We conclude that Pr on Ba-site substitution disorder is responsible for the metal-insulator transition. Preliminary efforts at growth with a method to prevent disorder yield 90K superconducting PrBa2Cu3O7-d crystallites.Comment: 4 pages, 3 figures, revised version submitted to PR

Stressor- and Corticotropin releasing Factor-induced Reinstatement and Active Stress-related Behavioral Responses are Augmented Following Long-access Cocaine Self-administration by Rats

Rationale Stressful events during periods of drug abstinence likely contribute to relapse in cocaine-dependent individuals. Excessive cocaine use may increase susceptibility to stressor-induced relapse through alterations in brain corticotropin-releasing factor (CRF) responsiveness. Objectives This study examined stressor- and CRF-induced cocaine seeking and other stress-related behaviors in rats with different histories of cocaine self-administration (SA). Materials and methods Rats self-administered cocaine under short-access (ShA; 2 h daily) or long-access (LgA; 6 h daily) conditions for 14 days or were provided access to saline and were tested for reinstatement by a stressor (electric footshock), cocaine or an icv injection of CRF and for behavioral responsiveness on the elevated plus maze, in a novel environment and in the light–dark box after a 14- to 17-day extinction/withdrawal period. Results LgA rats showed escalating patterns of cocaine SA and were more susceptible to reinstatement by cocaine, EFS, or icv CRF than ShA rats. Overall, cocaine SA increased activity in the center field of a novel environment, on the open arms of the elevated plus maze, and in the light compartment of a light–dark box. In most cases, the effects of cocaine SA were dependent on the pattern/amount of cocaine intake with statistically significant differences from saline self-administering controls only observed in LgA rats. Conclusions When examined after several weeks of extinction/ withdrawal, cocaine SA promotes a more active pattern of behavior during times of stress that is associated with a heightened susceptibility to stressor-induced cocaine-seeking behavior and may be the consequence of augmented CRF regulation of addiction-related neurocircuitry

The Physical Nature of Rest-UV Galaxy Morphology During the Peak Epoch of Galaxy Formation

Motivated by the irregular and little-understood morphologies of z ~ 2 - 3 galaxies, we use non-parametric coefficents to quantify the morphologies of 216 galaxies which have been spectroscopically confirmed to lie at redshifts z = 1.8 - 3.4 in the GOODS-N field. Using measurements of ultraviolet (UV) and optical spectral lines, multi-band photometric data, and stellar population models we statistically assess possible correlations between galaxy morphology and physical observables such as stellar mass, star formation rate, and the strength of galaxy-scale outflows. We find evidence that dustier galaxies have more nebulous UV morphologies and that larger, more luminous galaxies may drive stronger outflows, but otherwise conclude that UV morphology is either statistically decoupled from the majority of physical observables or determined by too complex a combination of physical processes to provide characterizations with predictive power. Given the absence of strong correlations between UV morphology and physical parameters such as star formation rates, we are therefore unable to support the hypothesis that morphologically irregular galaxies predominantly represent major galaxy mergers. Comparing galaxy samples, we find that IR-selected BzK galaxies and radio-selected submillimeter galaxies (SMGs) have UV morphologies similar to the optically selected sample, while distant red galaxies (DRGs) are more nebulous.Comment: 26 pages. Accepted for publication in the ApJ. Version with full resolution figures is available at http://www.astro.caltech.edu/~drlaw/Papers/UVmorph.pd

Integral Field Spectroscopy of High-Redshift Star Forming Galaxies with Laser Guided Adaptive Optics: Evidence for Dispersion-Dominated Kinematics

We present early results from an ongoing study of the kinematic structure of star-forming galaxies at redshift z ~ 2 - 3 using integral-field spectroscopy of rest-frame optical nebular emission lines in combination with Keck laser guide star adaptive optics (LGSAO). We show kinematic maps of 3 target galaxies Q1623-BX453, Q0449-BX93, and DSF2237a-C2 located at redshifts z = 2.1820, 2.0067, and 3.3172 respectively, each of which is well-resolved with a PSF measuring approximately 0.11 - 0.15 arcsec (~ 900 - 1200 pc at z ~ 2-3) after cosmetic smoothing. Neither galaxy at z ~ 2 exhibits substantial kinematic structure on scales >~ 30 km/s; both are instead consistent with largely dispersion-dominated velocity fields with sigma ~ 80 km/s along any given line of sight into the galaxy. In contrast, DSF2237a-C2 presents a well-resolved gradient in velocity over a distance of ~ 4 kpc with peak-to-peak amplitude of 140 km/s. It is unlikely that DSF2237a-C2 represents a dynamically cold rotating disk of ionized gas as the local velocity dispersion of the galaxy (sigma = 79 km/s) is comparable to the observed shear. Using extant multi-wavelength spectroscopy and photometry we relate these kinematic data to physical properties such as stellar mass, gas fraction, star formation rate, and outflow kinematics and consider the applicability of current galaxy formation models.[Abridged]Comment: 19 pages, 10 figures (5 color); accepted for publication in ApJ. Version with full-resolution figures is available at http://www.astro.caltech.edu/~drlaw/Papers/OSIRIS_data1.pd

Constraint on the Assembly and Dynamics of Galaxies. II. Properties of Kiloparsec-Scale Clumps in Rest-Frame Optical Emission of z ~ 2 Star-Forming Galaxies

We study the properties of luminous stellar "clumps" identified in deep, high-resolution Hubble Space Telescope NIC2/F160W imaging at 1.6 μm of six z ~ 2 star-forming galaxies with existing near-infrared integral field spectroscopy from SINFONI at the Very Large Telescope. Individual clumps contribute ~0.5%-15% of the galaxy-integrated rest-frame ≈5000 Å emission, with median of ≈2%; the total contribution of clump light ranges from 10% to 25%. The median intrinsic clump size and stellar mass are ~1 kpc and ~10^9 M_☉, in the ranges for clumps identified in rest-UV or line emission in other studies. The clump sizes and masses in the subset of disks are broadly consistent with expectations for clump formation through gravitational instabilities in gas-rich, turbulent disks given the host galaxies' global properties. By combining the NIC2 data with Advanced Camera for Surveys (ACS)/F814W imaging available for one source, and adaptive-optics-assisted SINFONI Hα data for another, we infer modest color, M/L, and stellar age variations within each galaxy. In these two objects, sets of clumps identified at different wavelengths do not fully overlap; NIC2-identified clumps tend to be redder/older than ACS- or Hα-identified clumps without rest-frame optical counterparts. There is evidence for a systematic trend of older ages at smaller galactocentric radii among the clumps, consistent with scenarios where inward migration of clumps transports material toward the central regions. From constraints on a bulge-like component at radii ≾1-3 kpc, none of the five disks in our sample appears to contain a compact massive stellar core, and we do not discern a trend of bulge stellar mass fraction with stellar age of the galaxy. Further observations are necessary to probe the buildup of stellar bulges and the role of clumps in this process