Nonlinear Faraday Rotation and Superposition-State Detection in Cold Atoms

We report on the first observation of nonlinear Faraday rotation with cold atoms at a temperature of ~100 uK. The observed nonlinear rotation of the light polarization plane is up to 0.1 rad over the 1 mm size atomic cloud in approximately 10 mG magnetic field. The nonlinearity of rotation results from long-lived coherence of ground-state Zeeman sublevels created by a near-resonant light. The method allows for creation, detection and control of atomic superposition states. It also allows applications for precision magnetometry with high spatial and temporal resolution.Comment: 5 pages, 6 figure

The Bulge-Disk Orthogonal Decoupling in Galaxies: NGC 4698

The R-band isophotal map of the Sa galaxy NGC 4698 shows that the inner region of the bulge structure is elongated perpendicularly to the major axis of the disk, this is also true for the outer parts of the bulge if a parametric photometric decomposition is adopted. At the same time the stellar component is characterized by an inner velocity gradient and a central zero-velocity plateau along the minor and major axis of the disk respectively. This remarkable geometric and kinematic decoupling suggests that a second event occurred in the formation history of this galaxy.Comment: 12 pages, LaTex, with 4 PostScript figures. Accepted for publication in The Astrophysical Journal Letter

Method for Implementing Optical Phase Adjustment

A method has been developed to mechanically implement the optical phase shift by adjusting the polarization of the pump and probe beams in an NMOR (nonlinear magneto-optical rotation) magnetometer as the proper phase shift is necessary to induce self-oscillation. This innovation consists of mounting the pump beam on a ring that surrounds the atomic vapor sample. The propagation of the probe beam is perpendicular to that of the pump beam. The probe beam can be considered as defining the axis of a cylinder, while the pump beam is directed radially. The magnetic field to be measured defines a third vector, but it is also taken to lie along the cylinder axis. Both the pump and probe beams are polarized such that their electric field vectors are substantially perpendicular to the magnet field. By rotation of the ring supporting the pump beam, its direction can be varied relative to the plane defined by the probe electric field and the magnetic field to be measured

The Circumnuclear Ring of Ionized Gas in NGC3593

We present the results of narrow-band Halpha+NII imaging of the early-type spiral NGC3593 in combination with a study of the flux radial profiles of the NII (lambda: 654.80, 658.34 nm), Halpha, and SII (lambda: 671.65, 673.08 nm) emission lines along its major axis. The galaxy is known to contain two counterrotating stellar discs of different size and luminosity. We find that the Halpha emission mainly derives from a small central region of 57 arcsec x 25 arcsec. It consists of a filamentary pattern with a central ring. This has a diameter of about 17 arcsec (~ 0.6/h kpc) and it contributes about half of the total Halpha flux. The ring is interpreted as the result of the interaction between the acquired retrograde gas which later formed the smaller counterrotating stellar disc and the pre-existing prograde gas of the galaxy.Comment: Accepted for pubblication in Astronomy and Astrophysics; one latex file (corsini.tex), and 2 encapsulated postscript figures (corsini_fig1.ps,corsini_fig2.ps). To be compiled with aa.cls latex2e macro style (pslatex option): 6 pages after latex compilatio

The bulge-disk orthogonal decoupling in galaxies: NGC 4698 and NGC 4672

We report the case of the geometrical and kinematical decoupling between the bulge and the disk of the Sa galaxy NGC 4698. The R-band isophotal map of this spiral shows that the bulge structure is elongated perpendicularly to the major axis of the disk. At the same time a central stellar velocity gradient is found along the major axis of the bulge. We also present the Sa NGC 4672 as good candidate of a spiral hosting a bulge and a disk orthogonally decoupled with respect to one other. This decoupling of the two fundamental components of a visible galaxy suggests that the disk could represent a second event in the history of early-type spirals.Comment: 4 pages, 3 figures (LaTeX, cupconf.sty). To appear in "The Formation of Bulges" C. M. Carollo, H. C. Ferguson, R. F. G. Wyse (eds.), Cambridge University Pres

Circumnuclear Keplerian Disks in Galaxies

In this paper we demonstrate the possibility of inferring the presence of Keplerian gaseous disks using optical ground-based telescopes properly equipped. We have modeled the peculiar bidimensional shape of the emission lines in a sample of five S0-Sa galaxies as due to the motion of a gaseous disk rotating in the combined potential of a central point-like mass and of an extended stellar disk. The value of the central mass concentration estimated for four galaxies of the sample (NGC 2179, NGC 4343, NGC 4435 and NGC 4459) is ~10^9 Msolar. For the remaining galaxy NGC 5064 an upper limit of 5*10^7 Msolar is estimated.Comment: 11 pages, LaTeX, with 3 PostScript figures, Submitted to The Astrophysical Journal Letter

On the relation between circular velocity and central velocity dispersion in high and low surface brightness galaxies

In order to investigate the correlation between the circular velocity Vc and the central velocity dispersion of the spheroidal component sigma_c, we analyzed these quantities for a sample of 40 high surface brightness disc galaxies (hereafter HSB), 8 giant low surface brightness spiral galaxies (hereafter LSB), and 24 elliptical galaxies characterized by flat rotation curves. We find that the Vc-sigma_c relation is descri ed by a linear law out to velocity dispersions as low as sigma_c~50km/s, while in previous works a power law was adopted for galaxies with sigma_c>80k/ms. Elliptical galaxies with Vc based on dynamical models or directly derived from the HI rotation curves follow the same relation as the HSB galaxies in the Vc-sigma_c plane. On the contrary, the LSB galaxies follow a different relation, since most of them show either higher Vc (or lower sigma_c) with respect to the HSB galaxies. This argues against the relevance of baryon collapse in the radial density profile of the dark matter haloes of LSB galaxies. (abridged)Comment: 18 pages, 4 figures, ApJ in pres

Unravelling the roles of size, ligands and pressure in the piezochromic properties of CdS nanocrystals

Understanding the effects of pressure-induced deformations on the optoelectronic properties of nanomaterials is important not only from the fundamental point of view, but also for po- tential applications such as stress sensors and electromechanical devices. Here we describe the novel insights into these piezochromic ef- fects gained from using a linear-scaling den- sity functional theory framework and an elec- tronic enthalpy scheme, which allow us to ac- curately characterize the electronic structure of CdS nanocrystals with a zincblende-like core of experimentally relevant size. In particu- lar we focus on unravelling the complex inter- play of size and surface (phenyl) ligands with pressure. We show that pressure-induced de- formations are not simple isotropic scaling of the original structures and that the change in HOMO-LUMO gap with pressure results from two competing factors: (i) a bulk-like linear in- crease due to compression, which is offset by (ii) distortions/disorder and, to a lesser ex- tent, orbital hybridization induced by ligands affecting the frontier orbitals. Moreover, we observe that the main peak in the optical ab- sorption spectra is systematically red-shifted or blue-shifted, as pressure is increased up to 5 GPa, depending on the presence or absence of phenyl ligands. These heavily hybridize the frontier orbitals, causing a reduction in over- lap and oscillator strength, so that at zero pres- sure the lowest energy transition involves deeper hole orbitals than in the case of hydrogen- capped nanocrystals; the application of pressure induces greater delocalisation over the whole nanocrystals bringing the frontier hole orbitals into play and resulting in an unexpected red shift for the phenyl-capped nanocrystals, in part caused by distortions. In response to a growing interest in relatively small nanocrystals that can be difficult to accurately characterize with ex- perimental techniques, this work exemplifies the detailed understanding of structure-property re- lationships under pressure that can be obtained for realistic nanocrystals with state-of-the-art first principles methods and used for the charac- terization and design of devices based on these and similar nanomaterials