The host galaxies and black-hole:galaxy mass ratios of luminous quasars at z~4

We present and analyse the deepest, high-quality Ks-band images ever obtained of luminous quasars at z~4, in an attempt to determine the basic properties of their host galaxies less than 1 Gyr after the first recorded appearance of black holes with Mbh > 10^9 Msol. To maximise the robustness of our results we have carefully selected two SDSS quasars at z~4. These quasars are representative of the most luminous quasars known at this epoch but they also, crucially, lie within 40 arcsec of comparably-bright foreground stars (required for accurate PSF definition), and have redshifts which ensure line-free Ks-band imaging. The data were obtained in excellent seeing (<0.4-arcsec) at the ESO VLT with integration times of ~5.5 hours per source. Via carefully-controlled separation of host-galaxy and nuclear light, we estimate the luminosities and stellar masses of the host galaxies, and set constraints on their half-light radii. The quasar host galaxies have K-band luminosities similar to radio galaxies at comparable redshifts, suggesting that these quasar hosts are also among the most massive galaxies in existence at this epoch. However, the quasar hosts are a factor ~5 smaller than the host galaxies of luminous low-redshift quasars. We estimate the stellar masses of the z~4 host galaxies to lie in the range 2-10x10^11 Msol, and use the CIV emission line in the Sloan spectra to estimate the masses of their black holes. The results imply a black-hole:host-galaxy mass ratio Mbh:Mgal~0.01-0.05. This is an order of magnitude higher than typically seen in the low-redshift Universe, and is consistent with existing evidence for a systematic growth in this mass ratio with increasing redshift, at least for objects selected as powerful AGN.Comment: 10 pages, 6 figure

A near-infrared morphological comparison of high-redshift submm and radio galaxies: massive star-forming discs vs relaxed spheroids

We present deep, high-quality K-band images of complete subsamples of powerful radio and sub-mm galaxies at z=2. The data were obtained in the best available seeing at UKIRT and Gemini North, with integration times scaled to ensure that comparable rest-frame surface brightness levels are reached for all galaxies. We fit two-dimensional axi-symmetric galaxy models to determine galaxy morphologies at rest-frame optical wavelengths > 4000A, varying luminosity, axial ratio, half-light radius, and Sersic index. We find that, while some images show evidence of galaxy interactions, >95% of the rest-frame optical light in all galaxies is well-described by these simple models. We also find a clear difference in morphology between these two classes of galaxy; fits to the individual images and image stacks reveal that the radio galaxies are moderately large (=8.4+-1.1kpc; median r{1/2}=7.8), de Vaucouleurs spheroids ( = 4.07+-0.27; median n=3.87), while the sub-mm galaxies appear to be moderately compact (=3.4+-0.3kpc; median r{1/2}=3.1kpc) exponential discs (=1.44+-0.16; median n=1.08). We show that the z=2 radio galaxies display a well-defined Kormendy relation but that, while larger than other recently-studied high-z massive galaxy populations, they are still ~1.5 times smaller than their local counterparts. The scalelengths of the starlight in the sub-mm galaxies are comparable to those reported for the molecular gas. Their sizes are also similar to those of comparably massive quiescent galaxies at z>1.5. In terms of stellar mass surface density, the majority of the radio galaxies lie within the locus defined by local ellipticals. In contrast, while best modelled as discs, most of the sub-mm galaxies have higher stellar mass densities than local galaxies, and appear destined to evolve into present-day massive ellipticals.Comment: 24 pages, 9 figure

The Greater Impact of Mergers on the Growth of Massive Galaxies: Implications for Mass Assembly and Evolution Since z~1

Using deep infrared observations conducted with the MOIRCS on the Subaru Telescope in GOODS-N combined with public surveys in GOODS-S, we investigate the dependence on stellar mass, M_*, and galaxy type of the close pair fraction (5 kpc < r < 20 kpc) and implied merger rate. In common with some recent studies we find that the fraction of paired systems that could result in major mergers is low (~4%) and does not increase significantly with redshift to z~1.2, with (1+z)^{1.6 \pm 1.6}. Our key finding is that massive galaxies with M_* > 1E11 Msun are more likely to host merging companions than less massive systems (M_* ~ 1E10 Msun). We find evidence for a higher pair fraction for red, spheroidal hosts compared to blue, late-type systems, in line with expectations based on clustering at small scales. So-called "dry" mergers between early-type galaxies represent nearly 50% of close pairs with M_* > 3E10 Msun at z~0.5, but less than 30% at z~1. This result can be explained by the increasing abundance of red, early-type galaxies at these masses. We compare the volumetric merger rate of galaxies with different masses to mass-dependent trends in galaxy evolution, finding that major mergers cannot fully account for the formation of spheroidal galaxies since z~1. In terms of mass assembly, major mergers contribute little to galaxy growth below M_* ~ 3E10 Msun but are more significant among galaxies with M_* > 1E11 Msun, 30% of which have undergone mostly dry mergers over the observed redshift range. Overall, the relatively more rapid coalescence of high mass galaxies mirrors the expected hierarchical growth of halos and is consistent with recent model predictions, even if the downsizing of star formation and morphological evolution involves additional physical processes.Comment: 18 pages. Submitted to ApJ and revised after referee comment

Radio and mid-infrared identification of BLAST source counterparts in the Chandra Deep Field South

We have identified radio and/or mid-infrared counterparts to 198 out of 350 sources detected at >=5 sigma over ~ 9 square degrees centered on the Chandra Deep Field South (CDFS) by the Balloon-borne Large Aperture Submillimeter Telescope (BLAST) at 250, 350 and 500 um. We have matched 114 of these counterparts to optical sources with previously derived photometric redshifts and fitted SEDs to the BLAST fluxes and fluxes at 70 and 160 um acquired with the Spitzer Space Telescope. In this way, we have constrained dust temperatures, total far-infrared/sub-millimeter luminosities and star formation rates for each source. Our findings show that on average, the BLAST sources lie at significantly lower redshifts and have significantly lower rest-frame dust temperatures compared to submm sources detected in surveys conducted at 850 um. We demonstrate that an apparent increase in dust temperature with redshift in our sample arises as a result of selection effects. Finally, we provide the full multi-wavelength catalog of >= 5 sigma BLAST sources contained within the complete ~ 9 square degree survey area.Comment: Published in the Astrophysical Journal: 2009, ApJ, 703, 285. 23 pages, 13 figures. Data available at http://blastexperiment.inf

Patterns of Chemical Diversity in the Mediterranean Sponge Spongia lamella

The intra-specific diversity in secondary metabolites can provide crucial information for understanding species ecology and evolution but has received limited attention in marine chemical ecology. The complex nature of diversity is partially responsible for the lack of studies, which often target a narrow number of major compounds. Here, we investigated the intra-specific chemical diversity of the Mediterranean sponge Spongia lamella. The chemical profiles of seven populations spreading over 1200 km in the Western Mediterranean were obtained by a straightforward SPE-HPLC-DAD-ELSD process whereas the identity of compounds was assessed by comparison between HPLC-MS spectra and literature data. Chemical diversity calculated by richness and Shannon indexes differed significantly between sponge populations but not at a larger regional scale. We used factor analysis, analysis of variance, and regression analysis to examine the chemical variability of this sponge at local and regional scales, to establish general patterns of variation in chemical diversity. The abundance of some metabolites varied significantly between sponge populations. Despite these significant differences between populations, we found a clear pattern of increasing chemical dissimilarity with increasing geographic distance. Additional large spatial scale studies on the chemical diversity of marine organisms will validate the universality or exclusivity of this pattern

Properties of submillimeter galaxies in the CANDELS GOODS-south field

We derive physical properties of 10 submillimeter galaxies located in the CANDELS coverage of the GOODS-S field. The galaxies were first identified as submillimeter sources with the LABOCA bolometer and subsequently targeted for 870 m continuum observation with ALMA. The high angular resolution of the ALMA imaging allows secure counterparts to be identified in the CANDELS multiband data set. The CANDELS data provide deep photometric data from UV through near-infrared wavelengths. Using synthetic spectral energy distributions, we derive photometric redshifts, stellar masses, extinction, ages, and the star formation history. The redshift range is z = 1.65-4.76, with two of the galaxies located at z > 4. Two submillimeter galaxy (SMG) counterparts have stellar masses 2-3 orders of magnitude lower than the rest. The remaining SMG counterparts have stellar masses around 1 x 1011 M. The stellar population in the SMGs is typically older than the expected duration of the submillimeter phase, suggesting that the star formation history of SMGs is more complex than a single burst. Non-parametric morphology indices suggest that the SMG counterparts are among the most asymmetric systems compared with galaxies of the same stellar mass and redshift. The Hubble Space Telescope images show that three of the SMGs are associated with ongoing mergers. The remaining counterparts are isolated. Estimating the dust and molecular gas mass from the submillimeter fluxes, and comparing with our stellar masses shows that the gas mass fraction of SMGs is ~28% and that the final stellar mass is likely to be ~(1 - 2) x 1011 M.IS

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe

Associations between Season and Gametocyte Dynamics in Chronic Plasmodium falciparum Infections

Introduction: In a markedly seasonal malaria setting, the transition from the transmission-free dry season to the transmission season depends on the resurgence of the mosquito population following the start of annual rains. The sudden onset of malaria outbreaks at the start of the transmission season suggests that parasites persist during the dry season and respond to either the reappearance of vectors, or correlated events, by increasing the production of transmission stages. Here, we investigate whether Plasmodium falciparum gametocyte density and the correlation between gametocyte density and parasite density show seasonal variation in chronic (largely asymptomatic) carriers in eastern Sudan. Materials and Methods: We recruited and treated 123 malaria patients in the transmission season 2001. We then followed them monthly during four distinct consecutive epidemiological seasons: transmission season 1, transmission-free season, pre-clinical period, and transmission season 2. In samples collected from 25 participants who fulfilled the selection criteria of the current analysis, we used quantitative PCR (qPCR) and RT-qPCR to quantify parasite and gametocyte densities, respectively. Results and Discussion: We observed a significant increase in gametocyte density and a significantly steeper positive correlation between gametocyte density and total parasite density during the pre-clinical period compared to the preceding transmission-free season. However, there was no corresponding increase in the density or prevalence of total parasites or gametocyte prevalence. The increase in gametocyte production during the pre-clinical period supports the hypothesis that P. falciparum may respond to environmental cues, such as mosquito biting, to modulate its transmission strategy. Thus, seasonal changes may be important to ignite transmission in unstable-malaria settings