The GALEX Arecibo SDSS survey: III. Evidence for the Inside-Out Formation of Galactic Disks

We analyze a sample of galaxies with stellar masses greater than $10^{10} M_{\odot}$ and with redshifts in the range $0.025<z<0.05$ for which HI mass measurements are available from the GALEX Arecibo SDSS Survey (GASS) or from the Arecibo Legacy Fast ALFA survey (ALFALFA). At a given value of $M_*$, our sample consists primarily of galaxies that are more HI-rich than average. We constructed a series of three control samples for comparison with these HI-rich galaxies. As expected, HI-rich galaxies differ strongly from galaxies of same stellar mass that are selected without regard to HI content. The majority of these differences are attributable to the fact that galaxies with more gas are bluer and more actively star-forming. In order to identify those galaxy properties that are causally connected with HI content, we compare results derived for the HI sample with those derived for galaxies matched in stellar mass, size and NUV-$r$ colour. The only photometric property that is clearly attributable to increasing HI content, is the colour gradient of the galaxy. Galaxies with larger HI fractions have bluer, more actively star-forming outer disks compared to the inner part of the galaxy. HI-rich galaxies also have larger $g$-band radii compared to $i$-band radii. Our results are consistent with the "inside-out" picture of disk galaxy formation, which has commonly served as a basis for semi-analytic models of the formation of disks in the context of Cold Dark Matter cosmologies. The lack of any intrinsic connection between HI fraction and galaxy asymmetry suggests that gas is accreted smoothly onto the outer disk.Comment: 18 pages, 20 figures. Accepted for publication in MNRAS. GASS publications and released data can be found at http://www.mpa-garching.mpg.de/GASS/index.ph

Sequential Copper-Catalyzed Rearrangement-Allylic Substitution of Bicyclic Hydrazines with Grignard Reagents

The problem of the synthesis of trans-1,4-disubstituted hydrazino and amino cyclopentenes has been resolved by a sequential copper-catalyzed rearrangement-allylic alkylation of 2,3-diazabicyclo[2.2.1]heptenes. The cis-fused 5,5-membered allylic carbazate which is formed in situ by a novel Cu(OTf)2/(±)-binap catalyzed rearrangement, can be alkylated with a broad spectrum of Grignard reagents with a predominant SN2’-regioselectivity. N-Boc protecting group proved to be optimal as regards yields, reaction times and regioselectivitie

Submillimetre compactness as a critical dimension to understand the Main Sequence of star-forming galaxies

We study the interstellar medium (ISM) properties as a function of the molecular gas size for 77 infrared-selected galaxies at z ∼ 1.3, having stellar masses 109.4 . M? . 1012.0 M and star formation rates 12 . SFRFIR . 1000 M yr−1 . Molecular gas sizes are measured on ALMA images that combine CO(2-1), CO(5-4) and underlying continuum observations, and include CO(4-3), CO(7-6)+[CI](3P2 − 3 P1), [CI](3P1 − 3 P0) observations for a subset of the sample. The & 46% of our galaxies have a compact molecular gas reservoir, and lie below the optical disks mass-size relation. Compact galaxies on and above the main sequence have higher CO excitation and star formation efficiency than galaxies with extended molecular gas reservoirs, as traced by CO(5-4)/CO(2-1) and CO(2-1)/LIR,SF ratios. Average CO+[CI] spectral line energy distributions indicate higher excitation in compacts relative to extended sources. Using CO(2-1) and dust masses as molecular gas mass tracers, and conversion factors tailored to their ISM conditions, we measure lower gas fractions in compact main-sequence galaxies compared to extended sources. We suggest that the sub-millimetre compactness, defined as the ratio between the molecular gas and the stellar size, is an unavoidable information to be used with the main sequence offset to describe the ISM properties of galaxies, at least above M? > 1010.6 M, where our observations fully probe the main sequence scatter. Our results are consistent with mergers driving the gas in the nuclear regions, enhancing the CO excitation and star formation efficiency. Compact main-sequence galaxies are consistent with being an early post-starburst population following a merger-driven starburst episode, stressing the important role of mergers in the evolution of massive galaxies

Beyond taxonomy: a review of macroinvertebrate trait-based community descriptors as tools for freshwater biomonitoring

Species traits have been frequently used in ecological studies in an attempt to develop a general ecological framework linking biological communities to habitat pressures. The trait approach offers a mechanistic alternative to traditional taxonomy-based descriptors. This review focuses on research employing traits as biomonitoring tools for freshwater ecosystems, although the lessons learned have wider application in the assessment of other ecosystem types. 2. We review the support from ecological theory to employ species traits for biomonitoring purposes (e.g. the habitat templet concept, landscape filtering hypothesis), and the subsequent studies that test the hypotheses arising from these theories, and apply this knowledge under real freshwater biomonitoring scenarios. We also include studies that deal with more specific issues such as trait trade-offs and trait syndromes. 3. We highlight the functional trait approach as one of the most promising tools emerging for biomonitoring freshwater ecosystems. Several technical issues are addressed and solutions are proposed. We discuss the need for: a broader unified trait biomonitoring tool; a more accurate understanding of the natural variation of community patterns of trait expression; approaches to diminish the effects of trait trade-offs and trait syndromes; additional life history and ecological requirement studies; and the detection of specific impacts under multiple stressor scenarios. 4. Synthesis and applications. This review provides biologists with the conceptual underpinning for the use of species traits as community descriptors and for freshwater biomonitoring and management. We expect that the functional trait approach will ultimately improve communication to managers and legislators of the importance of protecting freshwater ecosystem functions