Building Galactic Disks in Triaxial Dark Matter Halos

We review our recent work on the formation and evolution of disks with in triaxial dark matter (DM) halos by means of numerical simulations, including star formation and feedback from stellar evolution. The growing disks are strongly in fluenced by shapes of DM halos and modify them in turn. Disk parameters are in a broad agreement with those in the local universe. Gas-rich stellar bars grow in tandem with the disk and facilitate the angular momentum redistribution in the system and radial gas inflow. Nested bars appear to form as a by-product. Interactions between various non-axisymmetric components -- bars, disks and halos lead to decay of bars or washing out of ellipticity in the inner halo.Comment: 4 pages, 3 figures, invited talk at IAU Symp. 235 on Galaxy Evolution Across the Hubble Time, F. Combes and J. Palous (eds.), Cambridge U. Pres

The Galactic Bulge: A Review

The Milky Way is the only galaxy for which we can resolve individual stars at all evolutionary phases, from the Galactic center to the outskirt. The last decade, thanks to the advent of near IR detectors and 8 meter class telescopes, has seen a great progress in the understanding of the Milky Way central region: the bulge. Here we review the most recent results regarding the bulge structure, age, kinematics and chemical composition. These results have profound implications for the formation and evolution of the Milky Way and of galaxies in general. This paper provides a summary on our current understanding of the Milky Way bulge, intended mainly for workers on other fields.Comment: 10 pages, 8 Postscript figures, uses iaus.cls To appear in Proceedings of IAU Symp. 245 on "Formation and Evolution of Galaxy Bulges", (held at Oxford, July 16-20 2007), Eds. Martin Bureau, Lia Athanassoula, and Beatriz Barbu

Sub-Galactic Clumps at High Redshift: A Fragmentation Origin?

We investigate the origin of the clumpy structures observed at high redshift, like the chain galaxies. We use a three dimensional chemodynamical simulation describing the dynamics of stars and a two-phase interstellar medium, as well as feedback processes from the stars. For high efficiency of energy dissipation in the cold cloud medium, the initially gaseous disk fragments and develops several massive clumps of gas and stars. We follow the evolution of the individual clumps and determine their masses, metallicities and velocities. A few dynamical times after fragmentation of the disk, the clumps merge to build a massive bulge. Calculating HST- and UBVRIJHKLM-colors, including absorption by interstellar dust, we determine the morphologies and colors of this model in HST images. Several peculiar morphological structures seen in the HDF can be well-explained by a fragmented galactic disk model, including chain galaxies and objects consisting of several nearby knots.Comment: 20 pages, Latex, 9 figures, to appear in the Astrophysical Journal. Version with high quality images available at http://www.astro.unibas.ch/leute/ai.shtm

A Different Approach to Galaxy Evolution

The consequences are explored of an observationally established relation of the star formation rate (SFR) of star-forming galaxies with their stellar mass (M) and cosmic time (t), such that SFR is proportional to M x t^{-2.5}. It is shown, that small systematic differences in SFR dramatically amplify in the course of time: galaxies with above average SFR run into quasi-exponential mass and SFR growth, while galaxies with below average SFR avoid such exponential growth and evolve with moderate mass increase. It is argued that galaxies following the first path would enormously overgrow if keeping to form stars all the way to the present, hence should quench star formation and turn passive. By the same token, those instead avoiding the quasi-exponential growth may keep to form stars up to the present. Thus, it is conjectured that this divergent behaviour can help understanding the origin of the dichotomy between passive, spheroidal galaxies, and star-forming, disk galaxies.Comment: 5 Pages, 3 figures, to appear on MNRA

Length of Nutritional Transition Associates Negatively with Postnatal Growth in Very Low Birthweight Infants

Very low birthweight (VLBW

Blood pressure changes during the first 24 hours of life and the association with the persistence of a patent ductus arteriosus and occurrence of intraventricular haemorrhage

Very low birthweight (VLBW) infants are at risk of intraventricular haemorrhage (IVH) and delayed closure of ductus arteriosus. We investigated mean arterially recorded blood pressure (MAP) changes during the first day of life in VLBW infants as potential risk factors for a patent ductus arteriosus (PDA) and IVH. This retrospective cohort study exploring MAP changes during adaption and risk factors for a PDA and IVH comprised 844 VLBW infants admitted to the Helsinki University Children's Hospital during 2005-2013. For each infant, we investigated 600 time-points of MAP recorded 4-24 hours after birth. Based on blood pressure patterns revealed by a data-driven method, we divided the infants into two groups. Group 1 (n = 327, mean birthweight = 1019 g, mean gestational age = 28 + (1/7) weeks) consisted of infants whose mean MAP was lower at 18-24 hours than at 4-10 hours after birth. Group 2 (n = 517, mean birthweight = 1070 g, mean gestational age = 28 + (5/7) weeks) included infants with a higher mean MAP at 18-24 hours than at 4-10 hours after birth. We used the group assignments, MAP, gestational age at birth, relative size for gestational age, surfactant administration, inotrope usage, invasive ventilation, presence of respiratory distress syndrome or sepsis, fluid intake, and administration of antenatal steroids to predict the occurrence of IVH and use of pharmacological or surgical therapy for a PDA before 42 weeks of gestational age. Infants whose mean MAP is lower at 18-24 hours than at 4-10 hours after birth are more likely to undergo surgical ligation of a PDA (odds ratio = 2.1; CI 1.14-3.89; p = 0.018) and to suffer from IVH (odds ratio = 1.83; CI 1.23-2.72; p = 0.003).Peer reviewe

Length of Nutritional Transition Associates Negatively with Postnatal Growth in Very Low Birthweight Infants

Very low birthweight (VLBW

Star Formation during Galaxy Formation

Young galaxies are clumpy, gas-rich, and highly turbulent. Star formation appears to occur by gravitational instabilities in galactic disks. The high dispersion makes the clumps massive and the disks thick. The star formation rate should be comparable to the gas accretion rate of the whole galaxy, because star formation is usually rapid and the gas would be depleted quickly otherwise. The empirical laws for star formation found locally hold at redshifts around 2, although the molecular gas consumption time appears to be smaller, and mergers appear to form stars with a slightly higher efficiency than the majority of disk galaxies.Comment: 14 pages, 1 figure, Ecole Evry Schatzman 2010: Star Formation in the Local Universe. Lecture 5 of

A triple-chamber parenteral nutrition solution was associated with improved protein intake in very low birthweight infants

Aim We evaluated the nutrient intakes of very low birthweight (VLBW) infants weighing less than 1500 g and tested the hypothesis that using a triple-chamber parenteral nutrition (PN) solution, containing lipids, glucose and amino acids, would improve protein intake. Methods This retrospective cohort study comprised 953 VLBW infants born in 2005-2013 at a gestational age of less than 32 + 0/7 weeks and admitted to the neonatal care unit at Helsinki Children's Hospital, Finland. The infants were divided into four groups according their birth year and PN regime. Nutrient intakes were obtained from computerised medication administration records. Results In 2012-2013, when a triple-chamber PN solution was used, infants were more likely to reach the target parenteral protein intake of 3.5 g/kg/d, and reach it 3-7 days earlier, compared with infants who received individual PN or standard two-in-one PN solutions in 2005-2011. In addition, infants in the triple-chamber group had the highest median energy intake (90 kcal/kg/d) during the first week. They also had higher median protein intakes in weeks one, two and three (3.1, 3.4 and 3.7 g/kg/d) than infants born in 2005-2011 (P <.05). Conclusion Using a triple-chamber PN solution was associated with improved protein intake, and the protein target was more likely to be achieved.Peer reviewe

Survival of Star-Forming Giant Clumps in High-Redshift Galaxies

We investigate the effects of radiation pressure from stars on the survival of the star-forming giant clumps in high-redshift massive disc galaxies, during the most active phase of galaxy formation. The clumps, typically of mass ~10^8-10^9 Msun and radius ~0.5-1, are formed in the turbulent gas-rich discs by violent gravitational instability and then migrate into a central bulge in ~10 dynamical times. We show that the survival or disruption of these clumps under the influence of stellar feedback depends critically on the rate at which they form stars. If they convert a few percent of their gas mass to stars per free-fall time, as observed for all local star-forming systems and implied by the Kennicutt-Schmidt law, they cannot be disrupted. Only if clumps convert most of their mass to stars in a few free-fall times can feedback produce significant gas expulsion. We consider whether such rapid star formation is likely in high-redshift giant clumps.Comment: 11 pages, 1 figure, accepted to MNRA