Diverse Structural Evolution at z > 1 in Cosmologically Simulated Galaxies

From mock Hubble Space Telescope images, we quantify non-parametric statistics of galaxy morphology, thereby predicting the emergence of relationships among stellar mass, star formation, and observed rest-frame optical structure at 1 < z < 3. We measure automated diagnostics of galaxy morphology in cosmological simulations of the formation of 22 central galaxies with 9.3 < log10 M_*/M_sun < 10.7. These high-spatial-resolution zoom-in calculations enable accurate modeling of the rest-frame UV and optical morphology. Even with small numbers of galaxies, we find that structural evolution is neither universal nor monotonic: galaxy interactions can trigger either bulge or disc formation, and optically bulge-dominated galaxies at this mass may not remain so forever. Simulated galaxies with M_* > 10^10 M_sun contain relatively more disc-dominated light profiles than those with lower mass, reflecting significant disc brightening in some haloes at 1 < z < 2. By this epoch, simulated galaxies with specific star formation rates below 10^-9.7 yr^-1 are more likely than normal star-formers to have a broader mix of structural types, especially at M_* > 10^10 M_sun. We analyze a cosmological major merger at z ~ 1.5 and find that the newly proposed MID morphology diagnostics trace later merger stages while G-M20 trace earlier ones. MID is sensitive also to clumpy star-forming discs. The observability time of typical MID-enhanced events in our simulation sample is less than 100 Myr. A larger sample of cosmological assembly histories may be required to calibrate such diagnostics in the face of their sensitivity to viewing angle, segmentation algorithm, and various phenomena such as clumpy star formation and minor mergers.Comment: 23 pages, 16 figures, MNRAS accepted versio

Cotunneling through quantum dot with even number of electrons

We study an influence of a finite magnetic field on a small spin-degenerate quantum dot with even number of electrons, attached to metallic leads. It is shown that, under certain conditions, the low energy physics of the system can be described by the S=1/2 antiferromagnetic Kondo model.Comment: Contribution to LT-22; to be published in Physica

Cosmological Implications of Lyman-Break Galaxy Clustering

We review our analysis of the clustering properties of ``Lyman-break'' galaxies (LBGs) at redshift z~3, previously discussed in Wechsler et al (1998). We examine the likelihood of spikes found by Steidel et al (1998) in the redshift distribution of LBGs, within a suite of models for the evolution of structure in the Universe. Using high-resolution dissipationless N-body simulations, we analyze deep pencil-beam surveys from these models in the same way that they are actually observed, identifying LBGs with the most massive dark matter halos. We find that all the models (with SCDM as a marginal exception) have a substantial probability of producing spikes similar to those observed, because the massive halos are much more clumped than the underlying matter -- i.e., they are biased. Therefore, the likelihood of such a spike is not a good discriminator among these models. The LBG correlation functions are less steep than galaxies today (gamma~1.4), but show similar or slightly longer correlation lengths. We have extened this analysis and include a preliminary comparison to the new data presented in Adelberger et al (1998). We also discuss work in progress, in which we use semi-analytic models to identify Lyman-break galaxies within dark-matter halos.Comment: 4 pages, 2 figures, Latex, uses aipproc.sty; to appear in the proceedings of the 9th Annual October Maryland Astrophysics Conference, "After the Dark Ages: When the Galaxies Were Young (the Universe at 2<z<5)

Equilibrium Current and Orbital Magnetization in a Quantum Hall Fluid

We present a general theory for the equilibrium current distribution in an interacting two-dimensional electron gas subjected to a perpendicular magnetic field, and confined by a potential that varies slowly on the scale of the magnetic length. The distribution is found to consist of strips or channels of current, which alternate in direction, and which have universal integrated strength.Comment: 13 pages, Revtex, to appear in the proceedings of the "Workshop on Novel Physics in Low-Dimensional Electron Systems" held in Madra

Wet Compaction to a Blue Nugget: a Critical Phase in Galaxy Evolution

We utilize high-resolution cosmological simulations to reveal that high-redshift galaxies tend to undergo a robust `wet compaction' event when near a `golden' stellar mass of $\sim 10^{10} M_{\odot}$. This is a gaseous shrinkage to a compact star-forming phase, a `blue nugget' (BN), followed by central quenching of star formation to a compact passive stellar bulge, a `red nugget' (RN), and a buildup of an extended gaseous disc and ring. Such nuggets are observed at cosmic noon and seed today's early-type galaxies. The compaction is triggered by a drastic loss of angular momentum due to, e.g., wet mergers, counter-rotating cold streams, or violent disc instability. The BN phase marks drastic transitions in the galaxy structural, compositional and kinematic properties. The transitions are from star-forming to quenched inside-out, from diffuse to compact with an extended disc-ring and a stellar envelope, from dark matter to baryon central dominance, from prolate to oblate stellar shape, from pressure to rotation support, from low to high metallicity, and from supernova to AGN feedback. The central black hole growth, first suppressed by supernova feedback when below the golden mass, is boosted by the compaction, and the black hole keeps growing once the halo is massive enough to lock in the supernova ejecta.Comment: 33 pages, 26 figures in the main body (49 pages, 45 figures including appendix

Dependence of Galaxy Quenching on Halo Mass and Distance from its Centre

We study the dependence of star-formation quenching on galaxy mass and environment, in the SDSS (z~0.1) and the AEGIS (z~1). It is crucial that we define quenching by low star-formation rate rather than by red colour, given that one third of the red galaxies are star forming. We address stellar mass M*, halo mass Mh, density over the nearest N neighbours deltaN, and distance to the halo centre D. The fraction of quenched galaxies appears more strongly correlated with Mh at fixed M* than with M* at fixed Mh, while for satellites quenching also depends on D. We present the M*-Mh relation for centrals at z~1. At z~1, the dependence of quenching on M* at fixed Mh is somewhat more pronounced than at z~0, but the quenched fraction is low (10%) and the haloes are less massive. For satellites, M*-dependent quenching is noticeable at high D, suggesting a quenching dependence on sub-halo mass for recently captured satellites. At small D, where satellites likely fell in more than a few Gyr ago, quenching strongly depends on Mh, and not on M*. The Mh-dependence of quenching is consistent with theoretical wisdom where virial shock heating in massive haloes shuts down accretion and triggers ram-pressure stripping, causing quenching. The interpretation of deltaN is complicated by the fact that it depends on the number of observed group members compared to N, motivating the use of D as a better measure of local environment.Comment: 23 pages, 13 figures, accepted by MNRA

Implications of Spikes in the Redshift Distribution of z∼3z\sim3 Galaxies

We address the high peaks found by Steidel et al (1997) in the redshift distribution of ``Lyman-break'' objects (LBOs) at redshift z~3. The highest spike represents a relative overdensity of 2.6 in the distribution of LBOs in pixels of comoving size ~10Mpc/h. We examine the likelihood of such a spike in the redshift distribution within a suite of models for the evolution of structure in the Universe, including models with Omega=1 (SCDM and CHDM) and with Omega=0.4-0.5 (LCDM and OCDM). Using high-resolution dissipationless N-body simulations, we analyze deep pencil-beam surveys from these models in the same way that they are actually observed, identifying LBOs with the most massive dark matter halos. We find that all the models (with SCDM as a marginal exception) have a substantial probability of producing spikes similar to those observed, because the massive halos are much more clumped than the underlying matter -- i.e., they are biased. Therefore, the likelihood of such a spike is not a good discriminator among these models. We find in these models that the mean biasing parameter b of LBOs with respect to dark matter varies within a range b ~2-5 on a scale of ~10Mpc/h. We also compute the two-body correlation functions of LBOs predicted in these models. The LBO correlation functions are less steep than galaxies today (gamma ~1.4), but show similar or slightly longer correlation lengths.Comment: 12 pages, 7 EPS inlined figures, 1 inlined table, LaTex + emulateapj, multicol and graphics macro packages. Accepted for publication in the ApJ. Revised version includes new appendix, table, updated references. A version with higher quality inlined figures is available at http://fozzie.gsfc.nasa.gov/wgpbd97/spikes.htm

Current-Carrying Ground States in Mesoscopic and Macroscopic Systems

We extend a theorem of Bloch, which concerns the net orbital current carried by an interacting electron system in equilibrium, to include mesoscopic effects. We obtain a rigorous upper bound to the allowed ground-state current in a ring or disc, for an interacting electron system in the presence of static but otherwise arbitrary electric and magnetic fields. We also investigate the effects of spin-orbit and current-current interactions on the upper bound. Current-current interactions, caused by the magnetic field produced at a point r by a moving electron at r, are found to reduce the upper bound by an amount that is determined by the self-inductance of the system. A solvable model of an electron system that includes current-current interactions is shown to realize our upper bound, and the upper bound is compared with measurements of the persistent current in a single ring.Comment: 7 pager, Revtex, 1 figure available from [email protected]