Comparative internal kinematics of the H II regions in interacting and isolated galaxies: Implications for massive star formation modes

We have observed 12 interacting galaxy pairs using the Fabry-Perot interferometer GH αFaS (GalaxyHα Fabry-Perot system) on the 4.2-mWilliam Herschel Telescope at theObservatorio del Roque de los Muchachos, La Palma. We present here the Hα surface brightness, velocity and velocity dispersion maps for the 10 systems we have not previously observed using this technique, as well as the physical properties (sizes, Hα luminosities and velocity dispersion) of 1259 HII regions from the full sample. We also derive the physical properties of 1054 HII regions in a sample of 28 isolated galaxies observed with the same instrument in order to compare the two populations of HII regions. We find a population of the brightest HII regions for which the scaling relations, for example the relation between the Hα luminosity and the radius, are clearly distinct from the relations for the regions of lower luminosity. The regions in this bright population are more frequent in the interacting galaxies. We find that the turbulence, and also the star formation rate (SFR), are enhanced in the HII regions in the interacting galaxies. We have also extracted the Hα equivalent widths for the HII regions of both samples, and we have found that the distribution of HII region ages coincides for the two samples of galaxies. We suggest that the SFR enhancement is brought about by gas flows induced by the interactions, which give rise to gravitationally bound gas clouds which grow further by accretion from the flowing gas, producing conditions favourable to star formation. Key words: stars: formation -HII regions - galaxies: interactions - galaxies: ISM- galaxies: kinematics and dynamics

Spatial modulation of water ordering in lecithin bilayers. Evidence for a ripple-ripple phase transition

Intense motional averaging effects on the 2H nuclear magnetic resonance (NMR) spectrum of 2H2O that occur in aqueous dispersions of dimyristoyl-sn-glycero-3-phosphocholine (Myr2-PtdCho) are explained by a spatial modulation in the orientational order of the water induced by ripplelike structures. The ratio of the amplitude to the periodic length of the ripples, A/lambda, at a molar ratio of water/Myr2-PtdCho of 9.5:1, is measured by 2H NMR and found to be consistent with x-ray measurements of this ratio in the P beta phase of dipalmitoyl-sn-glycero-3-phosphocholine (Pam2-PtdCho) bilayers. The sensitivity of 2H NMR allows us to report the presence of two distinct ripple phases mediated with a discontinuous change in the value of A/lambda. This result suggests that the two ripple structures observed for several phospholipid systems in excess water by freeze-fracture electron microscopy may be associated with two different phases instead of the same phase as previously assumed

Morphology and environment of galaxies with disc breaks in the S4G and NIRS0S

We study the surface brightness profiles of disc galaxies in the 3.6 &mu;m images from the Spitzer Survey of Stellar Structure in Galaxies (S4G) and Ks-band images from the Near-Infrared S0-Sa galaxy Survey (NIRS0S).We particularly connect properties of single exponential (type I), downbending double exponential (type II), and upbending double exponential (type III) disc profile types, to structural components of galaxies by using detailed morphological classifications, and size measurements of rings and lenses. We also study how the local environment of the galaxies affects the profile types by calculating parameters describing the environmental density and the tidal interaction strength. We find that in majority of type II profiles the break radius is connected with structural components such as rings, lenses, and spirals. The exponential disc sections of all three profile types, when considered separately, follow the disc scaling relations. However, the outer discs of type II, and the inner discs of type III, are similar in scalelength to the single exponential discs. Although the different profile types have similar mean environmental parameters, the scalelengths of the type III profiles show a positive correlation with the tidal interaction strength. &copy; 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.</p

Morphological parameters of a spitzer survey of stellar structure in galaxies

The morphology of galaxies can be quantified to some degree using a set of scale-invariant parameters. Concentration (C), asymmetry (A), smoothness (S), the Gini index (G), the relative contribution of the brightest pixels to the second-order moment of the flux (M), ellipticity (E), and the Gini index of the second-order moment (G) have all been applied to morphologically classify galaxies at various wavelengths. Here, we present a catalog of these parameters for the Spitzer Survey of stellar structure in Galaxies, a volume-limited, near-infrared (NIR) imaging survey of nearby galaxies using the 3.6 and 4.5 &mu;m channels of the Infrared Array Camera on board the Spitzer Space Telescope. Our goal is to provide a reference catalog of NIR quantified morphology for high-redshift studies and galaxy evolution models with enough detail to resolve stellar mass morphology. We explore where normal, non-interacting galaxies-those typically found on the Hubble tuning fork-lie in this parameter space and show that there is a tight relation between concentration (C) and M for normal galaxies. M can be used to classify galaxies into earlier and later types (i.e., to separate spirals from irregulars). Several criteria using these parameters exist to select systems with a disturbed morphology, i.e., those that appear to be undergoing a tidal interaction. We examine the applicability of these criteria to Spitzer NIR imaging. We find that four relations, based on the parameters A and S, G and M, G, C, and M, respectively, select outliers in morphological parameter space, but each selects different subsets of galaxies. Two criteria (G &gt; 0.6, G &gt;-0.115 &times; M + 0.384) seem most appropriate to identify possible mergers and the merger fraction in NIR surveys. We find no strong relation between lopsidedness and most of these morphological parameters, except for a weak dependence of lopsidedness on concentration and M. &copy; 2014. The American Astronomical Society. All rights reserved.</p

The baryonic tully-fisher relationship for S4G galaxies and the "condensed" baryon fraction of galaxies

We combine data from the Spitzer Survey for Stellar Structure in Galaxies, a recently calibrated empirical stellar mass estimator from Eskew et al., and an extensive database of H I spectral line profiles to examine the baryonic Tully-Fisher (BTF) relation. We find (1) that the BTF has lower scatter than the classic Tully-Fisher (TF) relation and is better described as a linear relationship, confirming similar previous results, (2) that the inclusion of a radial scale in the BTF decreases the scatter but only modestly, as seen previously for the TF relation, and (3) that the slope of the BTF, which we find to be 3.5 &plusmn; 0.2 (&Delta;log M v ), implies that on average a nearly constant fraction (0.4) of all baryons expected to be in a halo are &quot;condensed&quot; onto the central region of rotationally supported galaxies. The condensed baryon fraction, M , is, to our measurement precision, nearly independent of galaxy circular velocity (our sample spans circular velocities, v , between 60 and 250 km s, but is extended to v 10 km s using data from the literature). The observed galaxy-to-galaxy scatter in this fraction is generally &le; a factor of 2 despite fairly liberal selection criteria. These results imply that cooling and heating processes, such as cold versus hot accretion, mass loss due to stellar winds, and active galactic nucleus driven feedback, to the degree that they affect the global galactic properties involved in the BTF, are independent of halo mass for galaxies with 10 &lt; v &lt; 250 km s and typically introduce no more than a factor of two range in the resulting M . Recent simulations by Aumer et al. of a small sample of disk galaxies are in excellent agreement with our data, suggesting that current simulations are capable of reproducing the global properties of individual disk galaxies. More detailed comparison to models using the BTF holds great promise, but awaits improved determinations of the stellar masses. &copy; 2014. The American Astronomical Society. All rights reserved.</p

Galactic winds with MUSE: A direct detection of Fe II* emission from a z 1.29 galaxy

Interstellar matter and star formationGalaxie

Embedded star formation in S4G galaxy dust lanes

Star-forming regions that are visible at 3.6 &mu;m and H&alpha; but not in the u, g, r, i, z bands of the Sloan Digital Sky Survey are measured in five nearby spiral galaxies to find extinctions averaging &sim;3.8 mag and stellar masses averaging &sim;5 &times; 10 M . These regions are apparently young star complexes embedded in dark filamentary shock fronts connected with spiral arms. The associated cloud masses are &sim;10 M . The conditions required to make such complexes are explored, including gravitational instabilities in spiral-shocked gas and compression of incident clouds. We find that instabilities are too slow for a complete collapse of the observed spiral filaments, but they could lead to star formation in the denser parts. Compression of incident clouds can produce a faster collapse but has difficulty explaining the semi-regular spacing of some regions along the arms. If gravitational instabilities are involved, then the condensations have the local Jeans mass. Also in this case, the near-simultaneous appearance of equally spaced complexes suggests that the dust lanes, and perhaps the arms too, are relatively young. &copy; 2014. The American Astronomical Society. All rights reserved.</p

Reconstructing the stellar mass distributions of galaxies using S 4G IRAC 3.6 and 4.5 μm images. II. the conversion from light to mass

We present a new approach for estimating the 3.6 &mu;m stellar mass-to- light (M/L) ratio &Upsilon; in terms of the [3.6]-[4.5] colors of old stellar populations. Our approach avoids several of the largest sources of uncertainty in existing techniques using population synthesis models. By focusing on mid-IR wavelengths, we gain a virtually dust extinction-free tracer of the old stars, avoiding the need to adopt a dust model to correctly interpret optical or optical/near-IR colors normally leveraged to assign the mass-to-light ratio &Upsilon;. By calibrating a new relation between near-IR and mid-IR colors of giant stars observed in GLIMPSE we also avoid the discrepancies in model predictions for the [3.6]-[4.5] colors of old stellar populations due to uncertainties in the molecular line opacities assumed in template spectra. We find that the [3.6]-[4.5] color, which is driven primarily by metallicity, provides a tight constraint on &Upsilon;, which varies intrinsically less than at optical wavelengths. The uncertainty on &Upsilon; of &sim;0.07 dex due to unconstrained age variations marks a significant improvement on existing techniques for estimating the stellar M/L with shorter wavelength data. A single &Upsilon; = 0.6 (assuming a Chabrier initial mass function (IMF)), independent of [3.6]-[4.5] color, is also feasible because it can be applied simultaneously to old, metal-rich and young, metal-poor populations, and still with comparable (or better) accuracy (&sim;0.1 dex) than alternatives. We expect our &Upsilon; to be optimal for mapping the stellar mass distributions in SG galaxies, for which we have developed an independent component analysis technique to first isolate the old stellar light at 3.6 &mu;m from nonstellar emission (e.g., hot dust and the 3.3 polycyclic aromatic hydrocarbon feature). Our estimate can also be used to determine the fractional contribution of nonstellar emission to global (rest-frame) 3.6 &mu;m fluxes, e.g., in WISE imaging, and establishes a reliable basis for exploring variations in the stellar IMF. &copy; 2014. The American Astronomical Society. All rights reserved..</p