Modeling the spectral energy distribution of galaxies. II. Disk opacity and star formation in 5 edge-on spirals

Using tools previously described and applied to the prototype galaxy NGC 891, we model the optical to far-infrared spectral energy distributions (SED) of four additional edge-on spiral galaxies, namely NGC 5907, NGC 4013, UGC 1082 and UGC 2048. Comparing the model predictions with IRAS and, where available, sub-millimeter and millimeter observations, we determine the respective roles of the old and young stellar populations in grain heating. In all cases, the young population dominates, with the contribution of the old stellar population being at most 40%, as previously found for NGC 891. After normalization to the disk area, the massive star-formation rate (SFR) derived using our SED modeling technique, which is primarily sensitive to the non-ionizing ultraviolet output from the young stellar population, lies in the range 7e-4 - 2e-2 M_sun * yr^-1 * kpc^-2. This is consistent with normalized SFRs derived for face-on galaxies of comparable surface gas densities from H_alpha observations. Though the most active star-forming galaxy of the five in absolute terms, NGC 891 is not an exceptional system in terms of its surface density in SFR.Comment: 9 pages, 3 figures, accepted for publication to A&

Two Interacting Electrons in a Quasiperiodic Chain

We study numerically the effect of on-site Hubbard interaction U between two electrons in the quasiperiodic Harper's equation. In the periodic chain limit by mapping the problem to that of one electron in two dimensions with a diagonal line of impurities of strength U we demonstrate a band of resonance two particle pairing states starting from E=U. In the ballistic (metallic) regime we show explicitly interaction-assisted extended pairing states and multifractal pairing states in the diffusive (critical) regime. We also obtain localized pairing states in the gaps and the created subband due to U, whose number increases when going to the localized regime, which are responsible for reducing the velocity and the diffusion coefficient in the qualitatively similar to the non-interacting case ballistic and diffusive dynamics. In the localized regime we find propagation enhancement for small U and stronger localization for larger U, as in disordered systems.Comment: 14 pages Revtex file, 8 figures (split into 19 jpg figures). (postscript versions of the jpg figures are also available upon request) submitted to PR

Comparing Galaxy Morphology at Ultraviolet and Optical Wavelengths

We have undertaken an imaging survey of 34 nearby galaxies in far-ultraviolet (FUV, ~1500A) and optical (UBVRI) passbands to characterize galaxy morphology as a function of wavelength. This sample, which includes a range of classical Hubble types from elliptical to irregular with emphasis on spirals at low inclination angle, provides a valuable database for comparison with images of high-z galaxies whose FUV light is redshifted into the optical and near- infrared bands. Ultraviolet data are from the UIT Astro-2 mission. We present images and surface brightness profiles for each galaxy, and we discuss the wavelength-dependence of morphology for different Hubble types in the context of understanding high-z objects. In general, the dominance of young stars in the FUV produces the patchy appearance of a morphological type later than that inferred from optical images. Prominent rings and circumnuclear star formation regions are clearly evident in FUV images of spirals, while bulges, bars, and old, red stellar disks are faint to invisible at these short wavelengths. However, the magnitude of the change in apparent morphology ranges from dramatic in early--type spirals with prominent optical bulges to slight in late-type spirals and irregulars, in which young stars dominate both the UV and optical emission. Starburst galaxies with centrally concentrated, symmetric bursts display an apparent ``E/S0'' structure in the FUV, while starbursts associated with rings or mergers produce a peculiar morphology. We briefly discuss the inadequacy of the optically-defined Hubble sequence to describe FUV galaxy images and estimate morphological k-corrections, and we suggest some directions for future research with this dataset.Comment: Accepted for publication in the ApJS. 15 pages, 17 JPEG figures, 10 GIF figures. Paper and full resolution figures available at http://nedwww.ipac.caltech.edu/level5/Kuchinski/frames.htm

The Galaxy Structure-Redshift Relationship

There exists a gradual, but persistent, evolutionary effect in the galaxy population such that galaxy structure and morphology change with redshift. This galaxy structure-redshift relationship is such that an increasingly large fraction of all bright and massive galaxies at redshifts 2 < z < 3 are morphologically peculiar at wavelengths from rest-frame ultraviolet to rest-frame optical. There are however examples of morphologically selected spirals and ellipticals at all redshifts up to z ~ 3. At lower redshift, the bright galaxy population smoothly transforms into normal ellipticals and spirals. The rate of this transformation strongly depends on redshift, with the swiftest evolution occurring between 1 < z < 2. This review characterizes the galaxy structure-redshift relationship, discusses its various physical causes, and how these are revealing the mechanisms responsible for galaxy formation.Comment: 20 pages, 8 figures. Invited Review to appear in "Penetrating Bars Through Masks of Cosmic Dust: The Hubble Tuning Fork Strikes A New Note", ed. D. Block et a

Spin physics with antiprotons

New possibilities arising from the availability at GSI of antiproton beams, possibly polarised, are discussed. The investigation of the nucleon structure can be boosted by accessing in Drell-Yan processes experimental asymmetries related to cross-sections in which the parton distribution functions (PDF) only appear, without any contribution from fragmentation functions; such processes are not affected by the chiral suppression of the transversity function $h_1(x)$. Spin asymmetries in hyperon production and Single Spin Asymmetries are discussed as well, together with further items like electric and magnetic nucleonic form factors and open charm production. Counting rates estimations are provided for each physical case. The sketch of a possible experimental apparatus is proposed.Comment: Presented for the proceedings of ASI "Spin and Symmetry", Prague, July 5-10, 2004, to be published in Czech. J. Phys. 55 (2005

Chemo-spectrophotometric evolution of spiral galaxies: I. The model and the Milky Way

The chemical and spectro-photometric evolution of spiral galaxies is investigated with detailed models, making use of up-to-date ingredients (like metallicity dependent stellar properties) and a prescription for the star formation rate (SFR) justified both empirically and theoretically. As a first application, the model is used to describe the evolution of the Milky Way. The role of the adopted scheme of disk formation (``inside-out'') in shaping the various chemical and colour profiles is investigated, as well as the role of extinction. It is shown that the solar neighborhood does not evolve as the Milky Way as a whole and that one-zone models with a non-linear SFR prescription cannot be used to study the evolution of our Galaxy. Our model average SFR is shown to match well observations of external spirals.Comment: 21 pages, 10 figures, accepted in MNRA

A new stellar library in the region of the CO index at 2.3 μ\mum. New index definition and empirical fitting functions

Context: The analysis of unresolved stellar populations demands evolutionary synthesis models with realistic physical ingredients and extended wavelength coverage. Aims: To obtain a quantitative description of the first CO bandhead at 2.3 $\mu$m, to allow stellar population models to provide improved predictions in this wavelength range. Methods: We have observed a new stellar library with a better coverage of the stellar atmospheric parameter space than preceding works. We have performed a detailed analysis of the robustness of previous CO index definitions with spectral resolution, wavelength calibration, signal-to-noise ratio, and flux calibration. Results: We define a new line-strength index for the first CO bandhead at 2.3 $\mu$m, D$_{\rm CO}$, better suited for stellar population studies than previous index definitions. We compute empirical fitting functions for the CO feature as a function of the stellar parameters (T$_{\rm eff}$, $\log g$ and [Fe/H]), showing a detailed quantitative metallicity dependence.Comment: 26 pages, 15 figures, accepted for publication in A&A. Typos in Eq. 9, 11 and 12 fixe

Longitudinal double spin asymmetries in single hadron quasi-real photoproduction at high pTp_T

We measured the longitudinal double spin asymmetries $A_{LL}$ for single hadron muo-production off protons and deuterons at photon virtuality $Q^2$ < 1(GeV/$\it c$)$^2$ for transverse hadron momenta $p_T$ in the range 0.7 GeV/$\it c$ to 4 GeV/$\it c$ . They were determined using COMPASS data taken with a polarised muon beam of 160 GeV/$\it c$ or 200 GeV/$\it c$ impinging on polarised $\mathrm{{}^6LiD}$ or $\mathrm{NH_3}$ targets. The experimental asymmetries are compared to next-to-leading order pQCD calculations, and are sensitive to the gluon polarisation $\Delta G$ inside the nucleon in the range of the nucleon momentum fraction carried by gluons $0.05 < x_g < 0.2$

Interplay among transversity induced asymmetries in hadron leptoproduction

In the fragmentation of a transversely polarized quark several left-right asymmetries are possible for the hadrons in the jet. When only one unpolarized hadron is selected, it exhibits an azimuthal modulation known as Collins effect. When a pair of oppositely charged hadrons is observed, three asymmetries can be considered, a di-hadron asymmetry and two single hadron asymmetries. In lepton deep inelastic scattering on transversely polarized nucleons all these asymmetries are coupled with the transversity distribution. From the high statistics COMPASS data on oppositely charged hadron-pair production we have investigated for the first time the dependence of these three asymmetries on the difference of the azimuthal angles of the two hadrons. The similarity of transversity induced single and di-hadron asymmetries is discussed. A new analysis of the data allows to establish quantitative relationships among them, providing for the first time strong experimental indication that the underlying fragmentation mechanisms are all driven by a common physical process.Comment: 6 figure

Interplay among transversity induced asymmetries in hadron leptoproduction

In the fragmentation of a transversely polarized quark several left-right asymmetries are possible for the hadrons in the jet. When only one unpolarized hadron is selected, it exhibits an azimuthal modulation known as Collins effect. When a pair of oppositely charged hadrons is observed, three asymmetries can be considered, a di-hadron asymmetry and two single hadron asymmetries. In lepton deep inelastic scattering on transversely polarized nucleons all these asymmetries are coupled with the transversity distribution. From the high statistics COMPASS data on oppositely charged hadron-pair production we have investigated for the first time the dependence of these three asymmetries on the difference of the azimuthal angles of the two hadrons. The similarity of transversity induced single and di-hadron asymmetries is discussed. A new analysis of the data allows to establish quantitative relationships among them, providing for the first time strong experimental indication that the underlying fragmentation mechanisms are all driven by a common physical process.Comment: 6 figure