AKARI near-infrared spectroscopy of the aromatic and aliphatic hydrocarbon emission features in the galactic superwind of M 82

Aims. We investigate the properties of hydrocarbon grains in the galactic superwind of M 82. Methods. With AKARI, we performed near-infrared (2.5 - 4.5 um) spectroscopic observations of 34 regions in M 82 including its northern and southern halos. Results. Many of the spectra show strong emission at 3.3 um due to polycyclic aromatic hydrocarbons (PAHs) and relatively weak features at 3.4 - 3.6 um due to aliphatic hydrocarbons. In particular, we clearly detect the PAH 3.3 um emission and the 3.4 - 3.6 um features in halo regions, which are located at a distance of 2 kpc away from the galactic center. We find that the ratios of the 3.4 - 3.6 um features to the 3.3 um feature intensity significantly increase with distance from the galactic center, while the ratios of the 3.3 um feature to the AKARI 7 um band intensity do not. Conclusions. Our results clearly confirm the presence of small PAHs even in a harsh environment of the halo of M 82. The results also reveal that the aliphatic hydrocarbons emitting the 3.4 - 3.6 um features are unusually abundant in the halo, suggesting that small carbonaceous grains are produced by shattering of larger grains in the galactic superwind.Comment: 5 pages, 3 figures, 1 table, accepted for publication in A&

Molecular gas in NGC6946

We present imaging of molecular gas emission in the star-forming spiral galaxy NGC6946. Our CO(1-0) and CO(3-2) images, made at 22" resolution with the IRAM 30-m and the Heinrich Hertz 10-m radio telescopes, are the most extensive CO observations of this galaxy and are among the most extensive observations of molecular gas in any spiral galaxy. The molecular component in NGC6946 is unusually massive, with a ratio of molecular to atomic Hydrogen of 0.57. A star formation efficiency image for NGC6946 ranges by over two orders of magnitude with highest values found in the northeastern spiral arm, and anticorrelates with the 6cm polarized emission image, which traces the regular part of the magnetic field. We analyse the ISM in NGC6946's disk by making 1-D and 2-D comparisons of images made in several wavebands. A point-by-point correlation technique finds that the molecular gas is closely associated with the 7micron-emitting dust. The high correlation found between the MIR emission and the radio continuum at 6cm cannot be due to dust heating and gas ionization in star-forming regions because the thermal radio emission is less correlated with the MIR than the nonthermal emission. A coupling of magnetic fields to gas clouds is proposed as a possible scenario.Comment: A&A accepted, 23 pages, 11 figures. Version with high resolution figures available at: http://cfa-www.harvard.edu/~wwalsh/sp.htm

SPIRE imaging of M82: cool dust in the wind and tidal streams

M82 is a unique representative of a whole class of galaxies, starbursts with superwinds, in the Very Nearby Galaxy Survey with Herschel. In addition, its interaction with the M81 group has stripped a significant portion of its interstellar medium from its disk. SPIRE maps now afford better characterization of the far-infrared emission from cool dust outside the disk, and sketch a far more complete picture of its mass distribution and energetics than previously possible. They show emission coincident in projection with the starburst wind and in a large halo, much more extended than the PAH band emission seen with Spitzer. Some complex substructures coincide with the brightest PAH filaments, and others with tidal streams seen in atomic hydrogen. We subtract the far-infrared emission of the starburst and underlying disk from the maps, and derive spatially-resolved far-infrared colors for the wind and halo. We interpret the results in terms of dust mass, dust temperature, and global physical conditions. In particular, we examine variations in the dust physical properties as a function of distance from the center and the wind polar axis, and conclude that more than two thirds of the extraplanar dust has been removed by tidal interaction, and not entrained by the starburst wind.Comment: accepted in A&A Herschel special issu

Molecular Gas and the Modest Star Formation Efficiency in the ``Antennae'' Galaxies: Arp~244=NGC 4038/39

(abridged) We report here a factor of 5.7 higher total CO flux in Arp~244 (the ``Antennae'' galaxies) than that previously accepted in the literature (thus a total molecular gas mass of 1.5x10$^{10}$ Msun), based on our fully sampled CO(1-0) observations at the NRAO 12m telescope. Our observations show that the molecular gas peaks predominately in the disk-disk overlap region between the nuclei, similar to the far-infrared (FIR) and mid-infrared (MIR) emission. The bulk of the molecular gas is forming into stars with a normal star formation efficiency (SFE) L_{IR}/M(H_2) \approx 4.2 Lsun/Msun, same as that of giant molecular clouds in the Galactic disk. Additional supportive evidence is the extremely low fraction of the dense molecular gas in Arp~244, revealed by our detections of the HCN(1-0) emission. We estimate the local SFE indicated by the ratio map of the radio continuum to CO(1-0) emission. Remarkably, the local SFE stays roughly same over the bulk of the molecular gas distribution. Only some localized regions show the highest radio-to-CO ratios that we have identified as the sites of the most intense starbursts with SFE >~ 20 Lsun/Msun. These starburst regions are confined exclusively in the dusty patches seen in the HST images near the CO and FIR peaks where presumably the violent starbursts are heavily obscured. Nevertheless, recent large-scale star formation is going on throughout the system, yet the measured level is more suggestive of a moderate starburst (SFE >~ 10 Lsun/Msun) or a weak to normal star formation (SFE ~ 4 Lsun/Msun). The overall starburst from the bulk of the molecular gas is yet to be initiated as most of the gas further condenses into kpc scale in the final coalescence.Comment: 31 pages including 3 postscript & 10 gif figures, final version to appear in ApJ, 2001 Feb. 10. A single .ps.gz file can be down-loaded from: http://spider.ipac.caltech.edu/staff/gao/Papers

Dust emission in early-type galaxies: The mid-infrared view

We present mid-infrared (MIR) maps for a sample of 18 early-type galaxies observed at 4.5, 6.7 and 15 microns with the ISOCAM instrument on board the ISO satellite with a 6'' spatial resolution. We model the Spectral Energy Distribution (SED) of these galaxies using the stellar evolutionary synthesis model PEGASE and we derive the MIR excess over the stellar component. We then explore the nature of this excess in terms of dust and Polycyclic Aromatic Hydrocarbon molecules (PAHs). We find that out of 18 galaxies, 10 show excess at 6.7 microns (due to the presence of PAH features) and 14 show excess at 15 microns (due to the presence of warm dust). In two galaxies, where a more complete wavelength coverage exists, an excess around 9.7 microns is seen (presumably due to silicate dust emission), while two other galaxies are totally devoid of dust. We also examine the morphology of the galaxies in these wavelengths by plotting the azimuthally averaged radial profiles as well as the MIR color profiles. We find that for the majority of the galaxies the 4.5 micron emission is well described by a de Vaucouleurs profile. The 6.7 and 15 micron emission is smoothly distributed throughout the galaxy while only a few galaxies show MIR emission which is more concentrated close to the center. Two dwarf galaxies in our sample show patchy distributions of the MIR emission while two other galaxies show edge-on disks. With color-color diagrams we delineate the regions occupied by late-type and early-type galaxies. Finally we show that the MIR excess found in strong radio galaxies like NGC 4486 (M87) can be explained by synchrotron emission.Comment: 12 pages, 19 reduced figures (JPG), Accepted for publication by A&A. A paper with full resolution figures can be found at: http://www.astro.noa.gr/~xilouris/iso/paper.pd

Obscured Activity: AGN, Quasars, Starbursts and ULIGs observed by the Infrared Space Observatory

Some of the most active galaxies in the Universe are obscured by large quantities of dust and emit a substantial fraction of their bolometric luminosity in the infrared. Observations of these infrared luminous galaxies with the Infrared Space Observatory (ISO) have provided a relatively unabsorbed view to the sources fuelling this active emission. The improved sensitivity, spatial resolution and spectroscopic capability of ISO over its predecessor Infrared Astronomical Satellite (IRAS), has enabled significant advances in the understanding of the infrared properties of active galaxies. ISO surveyed a wide range of active galaxies which, in the context of this review, includes those powered by intense bursts of star-formation as well as those containing a dominant active galactic nucleus (AGN). Mid infrared imaging resolved for the first time the dust enshrouded nuclei in many nearby galaxies, while a new era in infrared spectroscopy was opened by probing a wealth of atomic, ionic and molecular lines as well as broad band features in the mid and far infrared. This was particularly useful since it resulted in the understanding of the power production, excitation and fuelling mechanisms in the nuclei of active galaxies including the intriguing but so far elusive ultraluminous infrared galaxies. Detailed studies of various classes of AGN and quasars greatly improved our understanding of the unification scenario. Far-infrared imaging and photometry also revealed the presence of a new very cold dust component in galaxies and furthered our knowledge of the far-infrared properties of faint starbursts, ULIGs and quasars. We summarise almost nine years of key results based upon ISO data spanning the full range of luminosity and type of active galaxies.Comment: Accepted for publication in 'ISO science legacy - a compact review of ISO major achievements', Space Science Reviews - dedicated ISO issue. To be published by Springer in 2005. 62 pages (low resolution figures version). Higher resolution PDFs available from http://users.physics.uoc.gr/~vassilis/papers/VermaA.pdf or http://www.iso.vilspa.esa.es/science/SSR/Verma.pd

Detecting One-Hundred-Year Environmental Changes in Western China Using Seven-Year Repeat Photography

Due to its diverse, wondrous plants and unique topography, Western China has drawn great attention from explorers and naturalists from the Western World. Among them, Ernest Henry Wilson (1876 –1930), known as ‘Chinese’ Wilson, travelled to Western China five times from 1899 to 1918. He took more than 1,000 photos during his travels. These valuable photos illustrated the natural and social environment of Western China a century ago. Since 1997, we had collected E.H. Wilson's old pictures, and then since 2004, along the expedition route of E.H. Wilson, we took 7 years to repeat photographing 250 of these old pictures. Comparing Wilson's photos with ours, we found an obvious warming trend over the 100 years, not only in specific areas but throughout the entire Western China. Such warming trend manifested in phenology changes, community shifts and melting snow in alpine mountains. In this study, we also noted remarkable vegetation changes. Out of 62 picture pairs were related to vegetation change, 39 indicated vegetation has changed to the better condition, 17 for degraded vegetation and six for no obvious change. Also in these photos at a century interval, we found not only rapid urbanization in Western China, but also the disappearance of traditional cultures. Through such comparisons, we should not only be amazed about the significant environmental changes through time in Western China, but also consider its implications for protecting environment while meeting the economic development beyond such changes

Data assimilation in a system with two scales-combining two initialization techniques

11 pages, 11 figures, 1 tableFull-text version available Open Access at: http://clivar.iim.csic.es/?q=es/node/319An ensemble Kalman filter (EnKF) is used to assimilate data onto a non-linear chaotic model, coupling two kinds of variables. The first kind of variables of the system is characterized as large amplitude, slow, large scale, distributed in eight equally spaced locations around a circle. The second kind of variables are small amplitude, fast, and short scale, distributed in 256 equally spaced locations. Synthetic observations are obtained from the model and the observational error is proportional to their respective amplitudes. The performance of the EnKF is affected by differences in the spatial correlation scales of the variables being assimilated. This method allows the simultaneous assimilation of all the variables. The ensemble filter also allows assimilating only the large-scale variables, letting the small-scale variables to freely evolve. Assimilation of the large-scale variables together with a few small-scale variables significantly degrades the filter. These results are explained by the spurious correlations that arise from the sampled ensemble covariances. An alternative approach is to combine two different initialization techniques for the slow and fast variables. Here, the fast variables are initialized by restraining the evolution of the ensemble members, using a Newtonian relaxation toward the observed fast variables. Then, the usual ensemble analysis is used to assimilate the large-scale observationsThis study is supported by the Spanish National Science Program under contracts ESP2005–06823-C05 and ESP2007–65667-C04Peer reviewe

Vacuum structure for scalar cosmological perturbations in Modified Gravity Models

We have found for the general class of Modified Gravity Models f(R,G) a new instability which can arise in vacuum for the scalar modes of the cosmological perturbations if the background is not de Sitter. In particular, the short-wavelength modes, if stable, in general have a group velocity which depends linearly in k, the wave number. Therefore these modes will be in general superluminal. We have also discussed the condition for which in general these scalar modes will be ghost-like. There is a subclass of these models, defined out of properties of the function f(R,G) and to which the f(R) and f(G) models belong, which however does not have this feature.Comment: 17 pages, 1 figure, uses RevTeX, references adde

Measurement of Dijet Azimuthal Decorrelations at Central Rapidities in pp-bar Collisions at sqrt(s)=1.96 TeV

Correlations in the azimuthal angle between the two largest transverse momentum jets have been measured using the D0 detector in pp-bar collisions at a center-of-mass energy sqrt(s)=1.96 TeV. The analysis is based on an inclusive dijet event sample in the central rapidity region corresponding to an integrated luminosity of 150 pb-1. Azimuthal correlations are stronger at larger transverse momenta. These are well-described in perturbative QCD at next-to-leading order in the strong coupling constant, except at large azimuthal differences where soft effects are significant.Comment: 6 pages, 3 Figures submitted to Phys. Rev. Let