44 research outputs found

    The Physical Origins of The Morphology-Density Relation: Evidence for Gas Stripping from the SDSS

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    We provide a physical interpretation and explanation of the morphology-density relation for galaxies, drawing on stellar masses, star formation rates, axis ratios and group halo masses from the Sloan Digital Sky Survey. We first re-cast the classical morphology-density relation in more quantitative terms, using low star formation rate (quiescence) as a proxy for early-type morphology and dark matter halo mass from a group catalog as a proxy for environmental density: for galaxies of a given stellar mass the quiescent fraction is found to increase with increasing dark matter halo mass. Our novel result is that - at a given stellar mass - quiescent galaxies are significantly flatter in dense environments, implying a higher fraction of disk galaxies. Supposing that the denser environments differ simply by a higher incidence of quiescent disk galaxies that are structurally similar to star-forming disk galaxies of similar mass, explains simultaneously and quantitatively these quiescence -nvironment and shape-environment relations. Our findings add considerable weight to the slow removal of gas as the main physical driver of the morphology-density relation, at the expense of other explanations.Comment: published in ApJ: http://adsabs.harvard.edu/abs/2010ApJ...714.1779

    Less than 10 percent of star formation in z=0.6 massive galaxies is triggered by major interactions

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    Both observations and simulations show that major tidal interactions or mergers between gas-rich galaxies can lead to intense bursts of starformation. Yet, the average enhancement in star formation rate (SFR) in major mergers and the contribution of such events to the cosmic SFR are not well estimated. Here we use photometric redshifts, stellar masses and UV SFRs from COMBO-17, 24 micron SFRs from Spitzer and morphologies from two deep HST cosmological survey fields (ECDFS/GEMS and A901/STAGES) to study the enhancement in SFR as a function of projected galaxy separation. We apply two-point projected correlation function techniques, which we augment with morphologically-selected very close pairs (separation <2 arcsec) and merger remnants from the HST imaging. Our analysis confirms that the most intensely star-forming systems are indeed interacting or merging. Yet, for massive (M* > 10^10 Msun) star-forming galaxies at 0.4<z<0.8, we find that the SFRs of galaxies undergoing a major interaction (mass ratios <1:4 and separations < 40 kpc) are only 1.80 +/- 0.30 times higher than the SFRs of non-interacting galaxies when averaged over all interactions and all stages of the interaction, in good agreement with other observational works. We demonstrate that these results imply that <10% of star formation at 0.4 < z < 0.8 is triggered directly by major mergers and interactions; these events are not important factors in the build-up of stellar mass since z=1.Comment: Submitted to ApJ. 41 pages, 11 figure

    The Morphology of Galaxies in the Baryon Oscillation Spectroscopic Survey

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    We study the morphology of luminous and massive galaxies at 0.3<z<0.7 targeted in the Baryon Oscillation Spectroscopic Survey (BOSS) using publicly available Hubble Space Telescope imaging from COSMOS. Our sample (240 objects) provides a unique opportunity to check the visual morphology of these galaxies which were targeted based solely on stellar population modelling. We find that the majority (74+/-6%) possess an early-type morphology (elliptical or S0), while the remainder have a late-type morphology. This is as expected from the goals of the BOSS target selection which aimed to predominantly select slowly evolving galaxies, for use as cosmological probes, while still obtaining a fair fraction of actively star forming galaxies for galaxy evolution studies. We show that a colour cut of (g-i)>2.35 selects a sub-sample of BOSS galaxies with 90% early-type morphology - more comparable to the earlier Luminous Red Galaxy (LRG) samples of SDSS-I/II. The remaining 10% of galaxies above this cut have a late-type morphology and may be analogous to the "passive spirals" found at lower redshift. We find that 23+/-4% of the early-type galaxies are unresolved multiple systems in the SDSS imaging. We estimate that at least 50% of these are real associations (not projection effects) and may represent a significant "dry merger" fraction. We study the SDSS pipeline sizes of BOSS galaxies which we find to be systematically larger (by 40%) than those measured from HST images, and provide a statistical correction for the difference. These details of the BOSS galaxies will help users of the data fine-tune their selection criteria, dependent on their science applications. For example, the main goal of BOSS is to measure the cosmic distance scale and expansion rate of the Universe to percent-level precision - a point where systematic effects due to the details of target selection may become important.Comment: 18 pages, 11 figures; v2 as accepted by MNRA

    The green valley is a red herring : Galaxy Zoo reveals two evolutionary pathways towards quenching of star formation in early-and late-type galaxies

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    This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record [Kevin Schawinski, et al, 'The green valley is a red herring: Galaxy Zoo reveals two evolutionary pathways towards quenching of star formation in early- and late-type galaxies' MNRAS, Vol. 440(1): 889-907, May 2014] is available online at: https://doi.org/10.1093/mnras/stu327.We use SDSS+GALEX+Galaxy Zoo data to study the quenching of star formation in lowredshift galaxies. We show that the green valley between the blue cloud of star-forming galaxies and the red sequence of quiescent galaxies in the colour-mass diagram is not a single transitional state through which most blue galaxies evolve into red galaxies. Rather, an analysis that takes morphology into account makes clear that only a small population of blue early-type galaxies move rapidly across the green valley after the morphologies are transformed from disc to spheroid and star formation is quenched rapidly. In contrast, the majority of blue star-forming galaxies have significant discs, and they retain their late-type morphologies as their star formation rates decline very slowly. We summarize a range of observations that lead to these conclusions, including UV-optical colours and halo masses, which both show a striking dependence on morphological type. We interpret these results in terms of the evolution of cosmic gas supply and gas reservoirs. We conclude that late-type galaxies are consistent with a scenario where the cosmic supply of gas is shut off, perhaps at a critical halo mass, followed by a slow exhaustion of the remaining gas over several Gyr, driven by secular and/or environmental processes. In contrast, early-type galaxies require a scenario where the gas supply and gas reservoir are destroyed virtually instantaneously, with rapid quenching accompanied by a morphological transformation from disc to spheroid. This gas reservoir destruction could be the consequence of a major merger, which in most cases transforms galaxies from disc to elliptical morphology, and mergers could play a role in inducing black hole accretion and possibly active galactic nuclei feedback.Peer reviewe

    Cytokine Gene Polymorphisms and Length of Gestation

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    To estimate whether there is an association between length of gestation and gene polymorphisms that effect transcription of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), or interleukin-1ÎČ (IL-1ÎČ)

    Denkwerkstatt "Ressourcenknappheit"- Handlungs- und Aktionsfelder II

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    Vorwort: Non-Profit Manager*innen von heute sind Generalist*innen, die sich initiativ und eigenverantwortlich mit den Herausforderungen unserer Zeit auseinandersetzen und im besten Falle geeignete Lösungen dafĂŒr finden und diese auch richtig kommunizieren können. Aus diesem Grunde wird genau diese FĂ€higkeit bei Studierenden aus den MasterstudiengĂ€ngen Management in Nonprofit-Organisationen und Soziale Arbeit der Hochschule OsnabrĂŒck gefördert. Im Rahmen des Moduls Handlungsfelder II entwickelten rund 30 Studierende im Wintersemester 2020/2021 in einer Denkwerkstatt ihre eigenen Lösungen in Bezug auf Forschung, Produkte / Dienstleistungen und Kommunikation. Die Studierenden wĂ€hlten in einem partizipativen Prozess ihre eigenen Schwerpunktthemen aus und arbeiteten dann ein Semester lang an den Inhalten. Begleitet wurden sie durch ein Teamteaching von Prof. Dr. Gesa Birnkraut und Marlene EimterbĂ€umer, die Modelle, Methoden und Coaching zur UnterstĂŒtzung anboten. Die Modelle und Methoden finden sich in den BeitrĂ€gen der Studierenden wieder (unter anderem das socio-ecological model, der Business Model Canvas, der story telling canvas, das design thinking). Am Ende des Semesters stand eine PrĂ€sentation vor den Kommiliton*innen und den Lehrenden, aber auch vor externen GĂ€sten, die aus unterschiedlichen Expertisegebieten kamen und dementsprechend Feedback gaben. Das Modul selbst wurde von der Hochschule im Rahmen der Innovativen Lehre an der FakultĂ€t Wirtschafts- und Sozialwissenschaften gefördert. FĂŒr die Studierenden stellte das Modul durchaus eine große Herausforderung dar, denn in der Denkwerkstatt musste unter hoher KomplexitĂ€t stark prozessbezogen gearbeitet werden im Gegensatz zu der sonstigen hohen Ergebnisorientierung. Die durchweg sehr guten Ergebnisse zeigen, dass der Einsatz und das Aushalten der Unsicherheit sich gelohnt haben. Aufgeteilt ist das vorliegende Buch in die zwei Schwerpunktthemen Ressourcenknappheit / Wirtschaft und Wasserknappheit. In diesen beiden Schwerpunktthemen finden Sie jeweils einen Beitrag von den Forscher*innen, den Lösungsfinder*innen und den Kommunikator*innen
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