The silicate absorption profile in the ISM towards the heavily obscured nucleus of NGC 4418

The 9.7-micron silicate absorption profile in the interstellar medium provides important information on the physical and chemical composition of interstellar dust grains. Measurements in the Milky Way have shown that the profile in the diffuse interstellar medium is very similar to the amorphous silicate profiles found in circumstellar dust shells around late M stars, and narrower than the silicate profile in denser star-forming regions. Here, we investigate the silicate absorption profile towards the very heavily obscured nucleus of NGC 4418, the galaxy with the deepest known silicate absorption feature, and compare it to the profiles seen in the Milky Way. Comparison between the 8-13 micron spectrum obtained with TReCS on Gemini and the larger aperture spectrum obtained from the Spitzer archive indicates that the former isolates the nuclear emission, while Spitzer detects low surface brightness circumnuclear diffuse emission in addition. The silicate absorption profile towards the nucleus is very similar to that in the diffuse ISM in the Milky Way with no evidence of spectral structure from crystalline silicates or silicon carbide grains.Comment: 7 Pages, 3 figures. MNRAS in pres

Renormalization of Horava Gravity

We prove perturbative renormalizability of projectable Horava gravity. The key element of the argument is the choice of a gauge which ensures the correct anisotropic scaling of the propagators and their uniform falloff at large frequencies and momenta. This guarantees that the counterterms required to absorb the loop divergences are local and marginal or relevant with respect to the anisotropic scaling. Gauge invariance of the counterterms is achieved by making use of the background-covariant formalism. We also comment on the difficulties of this approach when addressing the renormalizability of the non-projectable model.Comment: 35 pages, no figures; references discussing gauge invariance of counterterms have been added, typos correcte

Renormalization of gauge theories in the background-field approach

Using the background-field method we demonstrate the Becchi-Rouet-Stora-Tyutin (BRST) structure of counterterms in a broad class of gauge theories. Put simply, we show that gauge invariance is preserved by renormalization in local gauge field theories whenever they admit a sensible background-field formulation and anomaly-free path integral measure. This class encompasses Yang-Mills theories (with possibly Abelian subgroups) and relativistic gravity, including both renormalizable and non-renormalizable (effective) theories. Our results also hold for non-relativistic models such as Yang-Mills theories with anisotropic scaling or Horava gravity. They strengthen and generalize the existing results in the literature concerning the renormalization of gauge systems. Locality of the BRST construction is emphasized throughout the derivation. We illustrate our general approach with several explicit examples.Comment: 45 pages, no figures; references added, changes in the Introduction and Conclusion

Sobre funciones convexas, casi-convexas y pseudo-convexas

In this paper, the basic properties of the convex functions are discussed, such as continuity, directional differentiability, and supportability properties. Also the relations with the quasi-convex, and pseudo-convex functiona are given. Both weaker and stronger forma of convexity are also given

Ho\v{r}ava gravity is asymptotically free (in 2+1 dimensions)

We compute the $\beta$-functions of marginal couplings in projectable Ho\v{r}ava gravity in $2+1$ spacetime dimensions. We show that the renormalization group flow has an asymptotically-free fixed point in the ultraviolet (UV), establishing the theory as a UV-complete model with dynamical gravitational degrees of freedom. Therefore, this theory may serve as a toy-model to study fundamental aspects of quantum gravity. Our results represent a step forward towards understanding the UV properties of realistic versions of Ho\v{r}ava gravity.Comment: Updated references, minor revisions. Matches journal versio

Massive Star Formation in Luminous Infrared Galaxies: Giant HII Regions and their relation to Super Star Clusters

We have used HST/NICMOS H-band narrow-band Pa-alpha (at rest 1.87micron) images to identify star clusters and HII regions respectively in a sample of 8 luminous infrared galaxies (LIRGs). These observations have revealed the presence of a large population of super star clusters (SSC) and bright HII regions. A significant fraction of the HII regions shows H-alpha luminosities above that of 30 Doradus, the prototypical giant HII region. The excess of extremely luminous HII regions in LIRGs has been confirmed by comparison with normal galaxies observed at similar spatial resolutions. Despite the large numbers of identified star clusters and HII regions in LIRGs, we only find a small fraction of coincidences, between 4% and 30%. Using synthesis models we have reproduced the relative fractions of young HII regions, intermediate and old star clusters observed in Arp299 and the central region NGC3256 using a Salpeter IMF and instantaneous star formation. HII regions with no detected near-infrared cluster counterpart (25-39%) represent the youngest sites of star formation, with ages of up to approximately 5Myr and mostly intermediate mass (~10^5Msun) ionizing clusters. For these two galaxies, and within the present detection threshold we can only detect coincidences (4-10%) between an HII region and a near-infrared star cluster for the most massive star clusters (~10^6Msun) during the first 7Myr of their evolution. The identified near-infrared SSCs with no detectable Pa-alpha emission represent the ``old'' population (53-66% of the detected sources), with ages of between 7 and 20-40Myr. Older clusters possibly created in this or previous episodes of star formation are likely to exist in these systems but cannot be identified with the present detection threshold. (Abridged)Comment: Accepted for publication in AJ (July issue). Figure 2 not included. Go to: http://nicmos2.as.arizona.edu/~aalonso/work/papers/lirghii_v2.ps for a complete version of pape

Heat kernel methods for Lifshitz theories

We study the one-loop covariant effective action of Lifshitz theories using the heat kernel technique. The characteristic feature of Lifshitz theories is an anisotropic scaling between space and time. This is enforced by the existence of a preferred foliation of space-time, which breaks Lorentz invariance. In contrast to the relativistic case, covariant Lifshitz theories are only invariant under diffeomorphisms preserving the foliation structure. We develop a systematic method to reduce the calculation of the effective action for a generic Lifshitz operator to an algorithm acting on known results for relativistic operators. In addition, we present techniques that drastically simplify the calculation for operators with special properties. We demonstrate the efficiency of these methods by explicit applications.Comment: 36 pages, matches journal versio

The impact of non–local birds on yellow–legged gulls (Larus michahellis) in the Bay of Biscay: a dump–based assessment

El impacto de los individuos no locales en la gaviota patiamarilla (Larus michahellis) en el Golfo de Vizcaya: una estimación a partir de vertederos Es necesario comprender la forma en que los animales explotan los recursos tróficos de origen no natural, como es el caso de los vertederos, desde múltiples perspectivas como la conservación, la dinámica de poblaciones y la gestión. Son varias las especies de gaviotas depredadoras de gran tamaño (Larus sp.) las que indudablemente se benefician de utilizar los vertederos. La gaviota patiamarilla (L. michahellis) es la especie de gaviota más abundante del Paleártico sudoccidental y el rápido crecimiento de sus poblaciones hasta al menos la primera década del siglo XXI se debe, parcialmente, al aumento de vertederos. El Golfo de Vizcaya es una zona que alberga gaviotas locales residentes y gaviotas invernantes procedentes de otras zonas. A partir de los datos obtenidos en censos y avistamientos de gaviotas marcadas con anillas de color que se recopilaron durante un periodo de ocho años en cuatro vertederos situados en un radio de 60 km desde las colonias de cría en Gipuzkoa, se trató de responder a las siguientes cuestiones: (1) el origen de las gaviotas que usan los vertederos en el Golfo de Vizcaya; (2) el impacto de los individuos locales y no locales en estos vertederos; (3) la posibilidad de que exista un uso distinto según la edad y (4) la posibilidad de que haya fluctuaciones estacionales en el uso de los vertederos. Las gaviotas en los vertederos estudiados provienen de las colonias costeras cercanas de Gipuzkoa, la zona atlántica de la península Ibérica, la región mediterránea y otras zonas como la costa atlántica de Francia y las colonias continentales (Navarra y Alemania). Parece que los vertederos de nuestro estudio fueron utilizados, principalmente, por aves locales.Understanding how animals exploit non–natural feeding sources such as garbage dumps is necessary from many perspectives, including conservation, and population dynamics and management. Several large predatory gulls (Larus spp.) are among the species which most clearly benefit from using dumps. The yellow–legged gull (L. michahellis) is the most abundant gull in the southwestern Palaearctic, and its fast population increase until at least the 2000s was partly due large waste dumps becoming more numerous. The Bay of Biscay is an area that hosts resident local and also wintering non–local yellow–legged gulls. Using data collected over a period of eight years (bird counts, identification of colour–ringed individuals) at four dumps situated within a 60–km radius from the colonies of Gipuzkoa (southwestern Bay of Biscay), we aimed to answer: (1) the origin of gulls using dumps at the Bay of Biscay; (2) the impact of local and non–local gulls at these dumps; (3) the possible age–dependent use of these sites; and (4) the possible seasonal fluctuations in the use of dumps by gulls. Gulls in our area (study dumps) came from nearby colonies in Gipuzkoa, Atlantic Iberia, the Mediterranean region, and other areas such as Atlantic France and inland colonies (Navarra, Germany). Our study dumps seemed to be used mostly by local gulls.El impacto de los individuos no locales en la gaviota patiamarilla (Larus michahellis) en el Golfo de Vizcaya: una estimación a partir de vertederos Es necesario comprender la forma en que los animales explotan los recursos tróficos de origen no natural, como es el caso de los vertederos, desde múltiples perspectivas como la conservación, la dinámica de poblaciones y la gestión. Son varias las especies de gaviotas depredadoras de gran tamaño (Larus sp.) las que indudablemente se benefician de utilizar los vertederos. La gaviota patiamarilla (L. michahellis) es la especie de gaviota más abundante del Paleártico sudoccidental y el rápido crecimiento de sus poblaciones hasta al menos la primera década del siglo XXI se debe, parcialmente, al aumento de vertederos. El Golfo de Vizcaya es una zona que alberga gaviotas locales residentes y gaviotas invernantes procedentes de otras zonas. A partir de los datos obtenidos en censos y avistamientos de gaviotas marcadas con anillas de color que se recopilaron durante un periodo de ocho años en cuatro vertederos situados en un radio de 60 km desde las colonias de cría en Gipuzkoa, se trató de responder a las siguientes cuestiones: (1) el origen de las gaviotas que usan los vertederos en el Golfo de Vizcaya; (2) el impacto de los individuos locales y no locales en estos vertederos; (3) la posibilidad de que exista un uso distinto según la edad y (4) la posibilidad de que haya fluctuaciones estacionales en el uso de los vertederos. Las gaviotas en los vertederos estudiados provienen de las colonias costeras cercanas de Gipuzkoa, la zona atlántica de la península Ibérica, la región mediterránea y otras zonas como la costa atlántica de Francia y las colonias continentales (Navarra y Alemania). Parece que los vertederos de nuestro estudio fueron utilizados, principalmente, por aves locales