ESO Lecture 2
Total Page：16
File Type：pdf, Size：1020Kb
Load more
Recommended publications
-
Astrotalk: Behind the News Headlines
AstroTalk: Behind the news headlines Richard de Grijs (何锐思) (Macquarie University, Sydney, Australia) The Gaia ‘Sausage’ galaxy Our Milky Way galaxy has most likely collided or otherwise interacted with numerous other galaxies during its lifetime. Indeed, such interactions are common cosmic occurrences. Astronomers can deduce the history of mass accretion onto the Milky Way from a study of debris in the halo of the galaxy left as the tidal residue of such episodes. That approach has worked particularly well for studies of the most recent merger events, like the infall of the Sagittarius dwarf galaxy into the Milky Way’s centre a few billion years ago, which left tidal streamers of stars visiBle in galaxy maps. The damaging effects these encounters can cause to the Milky Way have, however, not been as well studied, and events even further in the past are even less obvious as they Become Blurred By the galaxy’s natural motions and evolution. Some episodes in the Milky Way’s history, however, were so cataclysmic that they are difficult to hide. Scientists have known for some time that the Milky Way’s halo of stars drastically changes in character with distance from the galactic centre, as revealed by the chemical composition—the ‘metallicity’—of the stars, the stellar motions, and the stellar density. Harvard astronomer Federico Marinacci and his colleagues recently analysed a suite of cosmological computer simulations and the galaxy interactions in them. In particular they analysed the history of galaxy halos as they evolved following a merger event. They concluded that six to ten Billion years ago the Milky Way merged in a head- on collision with a dwarf galaxy containing stars amounting to about one-to-ten billion solar masses, and that this collision could produce the character changes in stellar populations currently observed in the Milky Way’s stellar halo. -
Primack-Phys205-Feb2
Physics 205 6 February 2017 Comparing Observed Galaxies with Simulations Joel R. Primack UCSC Hubble Space Telescope Ultra Deep Field - ACS This picture is beautiful but misleading, since it only shows about 0.5% of the cosmic density. The other 99.5% of the universe is invisible. Matter and Energy Content of the Universe Imagine that the entire universe is an ocean of dark energy. On that ocean sail billions of ghostly ships made of dark matter... Matter and Energy Content of the Dark Universe Matter Ships on a ΛCDM Dark Double Energy Dark Ocean Imagine that the entire universe is an ocean of dark Theory energy. On that ocean sail billions of ghostly ships made of dark matter... Matter Distribution Agrees with Double Dark Theory! Planck Collaboration: Cosmological parameters PlanckPlanck Collaboration: Collaboration: The ThePlanckPlanckmissionmission Planck Collaboration: The Planck mission 6000 6000 Angular scale 5000 90◦ 500018◦ 1◦ 0.2◦ 0.1◦ 0.07◦ Planck Collaboration: The Planck mission European 6000 ] 4000 2 ] 4000 2 K Double K µ [ µ 3000 [ 3000Dark TT Space TT 5000 D D 2000 2000Theory Agency 1000 1000 ] 4000 2 Cosmic 0 K 0 PLANCK 600 Variance600 60 µ 60 [ 3000 300300 30 TT 30 TT 0 0 Satellite D 0 0 D ∆ D Fig. 7. Maximum posterior CMB intensity map at 50 resolution derived from the joint baseline-30 analysis of Planck, WMAP, and ∆ -300 -300 408 MHz observations. A small strip of the Galactic plane, 1.6 % of the sky, is filled in by-30 a constrained realization that has the same statistical properties as the rest of the sky. -
A Model for Core Formation in Dark Matter Haloes and Ultra-Diffuse Galaxies by Outflow Episodes
MNRAS 491, 4523–4542 (2020) doi:10.1093/mnras/stz3306 Advance Access publication 2019 November 26 A model for core formation in dark matter haloes and ultra-diffuse galaxies by outflow episodes Jonathan Freundlich ,1‹ Avishai Dekel,1,2 Fangzhou Jiang ,1 Guy Ishai,1 Nicolas Cornuault,1 Sharon Lapiner,1 Aaron A. Dutton 3 and Andrea V. Maccio` 3,4 1Centre for Astrophysics and Planetary Science, Racah Institute of Physics, The Hebrew University, Jerusalem 91904, Israel 2Santa Cruz Institute for Particle Physics, University of California, Santa Cruz, CA 95064, USA 3New York University Abu Dhabi, PO Box 129188, Saadiyat Island, Abu Dhabi, United Arab Emirates 4 Max Planck Institute fur¨ Astronomie, Konigstuhl¨ 17, D-69117 Heidelberg, Germany Downloaded from https://academic.oup.com/mnras/article/491/3/4523/5643939 by guest on 24 September 2021 Accepted 2019 November 20. Received 2019 November 20; in original form 2019 July 26 ABSTRACT We present a simple model for the response of a dissipationless spherical system to an instantaneous mass change at its centre, describing the formation of flat cores in dark matter haloes and ultra-diffuse galaxies (UDGs) from feedback-driven outflow episodes in a specific mass range. This model generalizes an earlier simplified analysis of an isolated shell into a system with continuous density, velocity, and potential profiles. The response is divided into an instantaneous change of potential at constant velocities due to a given mass-loss or mass- gain, followed by energy-conserving relaxation to a new Jeans equilibrium. The halo profile is modelled by a two-parameter function with a variable inner slope and an analytic potential profile, which enables determining the associated kinetic energy at equilibrium. -
The Evolution of Galaxy Structure Over Cosmic Time
Annu. Rev. Astron. Astrophy. 2014 1056-8700/97/0610-00 The Evolution of Galaxy Structure over Cosmic Time Christopher J. Conselice Centre for Astronomy and Particle Theory School of Physics and Astronomy University of Nottingham, United Kingdom Key Words galaxy evolution, galaxy morphology, galaxy structure Abstract I present a comprehensive review of the evolution of galaxy structure in the universe from the first galaxies we can currently observe at z ∼ 6 down to galaxies we see in the local universe. I further address how these changes reveal galaxy formation processes that only galaxy structural analyses can provide. This review is pedagogical and begins with a de- tailed discussion of the major methods in which galaxies are studied morphologically and structurally. This includes the well-established visual method for morphology; S´ersic fitting to measure galaxy sizes and surface brightness profile shapes; non-parametric structural methods including the concentration (C), asymmetry (A), clumpiness (S) (CAS) method, the Gini/M20 parameters, as well as newer structural indices. Included is a discussion of how these structural indices measure fundamental properties of galaxies such as their scale, star formation rate, and ongoing merger activity. Extensive observational results are shown demonstrating how broad galaxy morphologies and structures change with time up to z ∼ 3, from small, compact and peculiar systems in the distant universe to the formation of the Hubble sequence dominated by spirals and ellipticals we find today. This review further addresses how structural methods accurately identify galaxies in mergers, and allow mea- arXiv:1403.2783v1 [astro-ph.GA] 12 Mar 2014 surements of the merger history out to z ∼ 3. -
Unequal-Mass Galaxy Merger Remnants: Spiral-Like Morphology but Elliptical-Like Kinematics
A&A 418, L27–L30 (2004) Astronomy DOI: 10.1051/0004-6361:20040114 & c ESO 2004 Astrophysics Unequal-mass galaxy merger remnants: Spiral-like morphology but elliptical-like kinematics F. Bournaud1,2,F.Combes1, and C. J. Jog3 1 Observatoire de Paris, LERMA, 61 Av. de l’Observatoire, 75014 Paris, France Letter to the Editor 2 Ecole´ Normale Sup´erieure, 45 rue d’Ulm, 75005 Paris, France 3 Department of Physics, Indian Institute of Science, Bangalore 560012, India Received 14 January 2004 / Accepted 12 March 2004 Abstract. It is generally believed that major galaxy mergers with mass ratios in the range 1:1–3:1 result in remnants that have properties similar to elliptical galaxies, and minor mergers below 10:1 result in disturbed spiral galaxies. The intermediate range of mass ratios 4:1–10:1 has not been studied so far. Using N-body simulations, we show that such mergers can result in very peculiar systems, that have the morphology of a disk galaxy with an exponential profile, but whose kinematics is closer to that of elliptical systems. These objects are similar to those recently observed by Jog & Chitre (2002). We present two cases with mass ratios 4.5:1 and 7:1, and show that the merging causes major heating and results in the appearance of elliptical-type kinematics, while surprisingly the initial spiral-like mass profile is conserved. Key words. galaxies: interaction – galaxies: formation – galaxies: evolution – galaxies: kinematics 1. Introduction regarded as elliptical galaxies with faint outer disks. Among the class II objects, Jog & Chitre (2002) have pointed out sys- Numerical simulations commonly show that the merging of tems with kinematical properties typical of elliptical galaxies: two equal-mass spiral galaxies results in the formation of an they have velocity dispersions as large or larger than rotation r1/4 elliptical galaxy with an radial profile consistent with ob- velocity, while spiral disks are usually supported by rotation. -
Recent Astronomical Discoveries
From the Atom to the Universe: Recent Astronomical Discoveries Jeremiah P. Ostriker Astronomy starts at the point to which chemistry has brought us: atoms. The basic stuff of which the planets and stars are made is the same as the terres- trial material discussed and analyzed in the ½rst set of essays in this volume. These are the chemical ele - ments, from hydrogen to uranium. Hydrogen, found with oxygen in our plentiful oceanic water, is by far the most abundant element in the universe; iron is the most common of the heavier elements. All the combinations of atoms in the complex chem ical com - pounds studied by chemists on Earth are also pos- sible components of the objects that we see in the cos mos. Although almost all of the regions that we astronomers study are so hot that the more com pli - JEREMIAH P. OSTRIKER, a Fellow cated compounds would be torn apart by the heat, of the American Academy since some surprisingly unstable organic molecules, such as 1975, is the Charles A. Young Pro - cyanopolyynes, have been detected in cold re gions of fes sor Emeritus of Astrophysics at space with very low density of matter. Nev ertheless, Prince ton University and Professor the astronomical world is simpler than the chemical of As tronomy at Columbia Univer - world of the laboratory or the real bio log ical world. sity. His research interests concern dark matter and dark energy, gal - But the enormous spatial and temporal extent of axy formation, and quasars. His the cosmos allows us–and in fact forces us–to ask publications include Heart of Dark - questions that would seem offbeat to a chemist. -
Using Transfer Learning to Detect Galaxy Mergers
MNRAS 000,1{12 (2017) Preprint 30 May 2018 Compiled using MNRAS LATEX style file v3.0 Using transfer learning to detect galaxy mergers Sandro Ackermann,1 Kevin Schawinski,1 Ce Zhang,2 Anna K. Weigel1 and M. Dennis Turp1 1Institute for Particle Physics and Astrophysics, Department of Physics, ETH Zurich, Wolfgang-Pauli-Strasse 27, CH-8093, Zurich,¨ Switzerland 2Systems Group, Department of Computer Science, ETH Zurich, Universit¨atstrasse 6, CH-8006, Zurich,¨ Switzerland Accepted XXX. Received YYY; in original form ZZZ ABSTRACT We investigate the use of deep convolutional neural networks (deep CNNs) for auto- matic visual detection of galaxy mergers. Moreover, we investigate the use of transfer learning in conjunction with CNNs, by retraining networks first trained on pictures of everyday objects. We test the hypothesis that transfer learning is useful for im- proving classification performance for small training sets. This would make transfer learning useful for finding rare objects in astronomical imaging datasets. We find that these deep learning methods perform significantly better than current state-of-the-art merger detection methods based on nonparametric systems like CAS and GM20. Our method is end-to-end and robust to image noise and distortions; it can be applied directly without image preprocessing. We also find that transfer learning can act as a regulariser in some cases, leading to better overall classification accuracy (p = 0:02). Transfer learning on our full training set leads to a lowered error rate from 0.038±1 down to 0.032±1, a relative improvement of 15%. Finally, we perform a basic sanity- check by creating a merger sample with our method, and comparing with an already existing, manually created merger catalogue in terms of colour-mass distribution and stellar mass function. -
Joel R. Primack, Distinguished Professor of Physics Emeritus, UCSC
Joel R. Primack, Distinguished Professor of Physics Emeritus, UCSC Research accomplishments: I think of myself as a theoretical physicist with broad interests. My Princeton senior thesis under Gerald E. Brown's supervision was the first modern theory of nuclear fission (Primack, PRL 1966). Although it overturned the liquid drop model of Niels Bohr and John Wheeler (1939), Wheeler gave it highest marks and I graduated as the valedictorian of my class. As an undergraduate I also published papers on plasma fluid dynamics, based on research as a summer employee at Jet Propulsion Lab. I worked on theoretical particle physics as Sid Drell’s grad student at the Stanford Linear Accelerator Center (SLAC) 1966-70, as a Junior Fellow of the Harvard Society of Fellows 1970-73, and in my first decade at UCSC (1973-1983). Drell suggested that I figure out what was wrong with the apparent failure of the Drell-Hearn sum rule applied to nuclei, so Stan Brodsky I wrote fundamental papers (1968-69) on how to treat the electromagnetic interactions of composite systems such as nuclei. Tom Appelquist and I studied form factors in field theory (1970-72). Appelquist, Helen Quinn, and I wrote some of the first papers on the SU(2)xU(1) electroweak theory (1972-73). With Ben Lee and Sam Trieman I did the first calculation of the mass of the charmed quark (1973), and Abraham Pais and I (1973) showed that CP violation arises in the cross term between first and second order perturbation theory. Sam Berman and I (1974) showed that polarized electron scattering allows a high-precision test of SU(2)xU(1), which resulted in the SLAC experiment whose success helped justify the Nobel Prize for Glashow, Salam, and Weinberg. -
Tidal Dwarf Galaxies and Missing Baryons
Tidal Dwarf Galaxies and missing baryons Frederic Bournaud CEA Saclay, DSM/IRFU/SAP, F-91191 Gif-Sur-Yvette Cedex, France Abstract Tidal dwarf galaxies form during the interaction, collision or merger of massive spiral galaxies. They can resemble “normal” dwarf galaxies in terms of mass, size, and become dwarf satellites orbiting around their massive progenitor. They nevertheless keep some signatures from their origin, making them interesting targets for cosmological studies. In particular, they should be free from dark matter from a spheroidal halo. Flat rotation curves and high dynamical masses may then indicate the presence of an unseen component, and constrain the properties of the “missing baryons”, known to exist but not directly observed. The number of dwarf galaxies in the Universe is another cosmological problem for which it is important to ascertain if tidal dwarf galaxies formed frequently at high redshift, when the merger rate was high, and many of them survived until today. In this article, I use “dark matter” to refer to the non-baryonic matter, mostly located in large dark halos – i.e., CDM in the standard paradigm. I use “missing baryons” or “dark baryons” to refer to the baryons known to exist but hardly observed at redshift zero, and are a baryonic dark component that is additional to “dark matter”. 1. Introduction: the formation of Tidal Dwarf Galaxies A Tidal Dwarf Galaxy (TDG) is, per definition, a massive, gravitationally bound object of gas and stars, formed during a merger or distant tidal interaction between massive spiral galaxies, and is as massive as a dwarf galaxy [1] (Figure 1). -
Public Outreach Via Cosmological Simulation Visualizations Table Of
Public Outreach via Cosmological Simulation Visualizations Table of Contents Page 1 1. Scientific/Technical/Management: Introduction 3 2. Key Visualization Projects 4 2.1 Bolshoi Simulation 4 Visualizing the Bolshoi Simulation 4 Bolshoi Semi-Analytic Models 4 2.2 Local Universe Simulations 5 Future of the Local Universe 6 How Structures Form in the Expanding Universe 6 2.3. High Resolution Hydrodynamic Simulations of Galaxy Formation 6 Galaxy Merger Simulations 7 Very High Resolution Simulations of Forming Galaxies 8 2.4 Additional Visualization Projects 8 Evolution and Substructure of a Milky Way Size Dark Matter Halo 8 Massive Star Formation 9 2.5 Spinoffs 9 Education Resources 9 Cold Dark Matter Explorers Computer Interactive 9 3. Role of Planetariums 9 3.1 Why Planetariums? 10 3.2 Roles of Adler and Morrison Planetariums 10 3.3 Making Visualizations 11 Real-Time vs. Pre-Rendered shows 11 3.4 Plans and Methodology for Evaluation of Visualizations 12 3.5 Dissemination 12 4. Management Plan, Division of Labor, Timeline, and Advisory Committee 12 Management 13 Staff 13 Evaluator 13 Advisory Committee 13 Capabilities of Digital Planetarium Systems 14 5. Responsiveness to NASA’s Education and Public Outreach Goals 15 Customer Needs Focus 16 6. References 18 7. CVs and Current and Pending Support 18 PI: Joel Primack – CV 20 PI: Joel Primack – Current and Pending Support 21 Co-Is: Lucy Fortson, Mark SubbaRao, and Ryan Wyatt 24 Staff: Nina McCurdy and Michelle Nichols 26 8. Budget Justification: Budget Narrative and Budget Details 31 Adler Planetarium Subcontract 32 Morrison Planetarium, California Academy of Sciences Subcontract Public Outreach via Cosmological Simulation Visualizations PI: Joel Primack, UCSC; Co-Is: Mark SubbaRao and Lucy Fortson, Adler Planetarium, and Ryan Wyatt, Morrison Planetarium; Collaborators: Michael Busha, T. -
Evolution of Magnetic Fields in Galaxies and Future Observational
A&A 494, 21–32 (2009) Astronomy DOI: 10.1051/0004-6361:200810964 & c ESO 2009 Astrophysics Evolution of magnetic fields in galaxies and future observational tests with the Square Kilometre Array T. G. Arshakian1,R.Beck1, Marita Krause1,andD.Sokoloff2 1 Max-Planck-Institut für Radioastronomie, Bonn, Germany e-mail: [tarshakian;rbeck;mkrause]@mpifr-bonn.mpg.de 2 Department of Physics, Moscow State University, Russia e-mail: [email protected] Received 14 September 2008 / Accepted 16 October 2008 ABSTRACT Aims. In the context of models of galaxy formation and evolution, we investigate the cosmological evolution of large- and small-scale magnetic fields inside galaxies. Methods. We use the dynamo theory to derive the timescales of amplification and ordering of magnetic fields in disk and puffy galaxies. Turbulence in protogalactic halos generated by thermal virialization can drive an efficient turbulent dynamo. Results from simulations of hierarchical structure formation cosmology provide a tool to develop an evolutionary model of regular magnetic fields coupled with galaxy formation and evolution. Results. The turbulent (small-scale) dynamo was able to amplify a weak seed magnetic field in halos of protogalaxies to a few μG strength within a few 108 yr. This turbulent field served as a seed to the mean-field (large-scale) dynamo. Galaxies similar to the Milky Way formed their disks at z ≈ 10 and regular fields of μG strength and a few kpc coherence length were generated within 2 Gyr (at z ≈ 3), but field-ordering on the coherence scale of the galaxy size required an additional 6 Gyr (at z ≈ 0.5). -
Turbulent Formation of Protogalaxies at the End of the Plasma Epoch: Theory and Observations
Turbulent formation of protogalaxies …, Nova Book, Galaxies: Dynamics, Formation and Evolution 1 Turbulent formation of protogalaxies at the end of the plasma epoch: theory and observations Rudolph E. Schild1,2 1 Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA 2 [email protected] and Carl H. Gibson 3,4 3 University of California San Diego, La Jolla, CA 92093-0411, USA [email protected], http://sdcc3.ucsd.edu/~ir118 ABSTRACT The standard model of gravitational structure formation is based on the Jeans 1902 acoustic theory, neglecting nonlinear instabilities controlled by viscosity, turbulence and diffusion. A linear insta- bility length scale equal to the sound speed times the gravitational freefall time emerges. Because the Jeans scale LJ for the hot primordial plasma is always slightly larger than the scale of causal connection ct, where c is the speed of light and t is the time after the big bang, it has been assumed that no plasma structures could form without guidance from a cold (so LJ CDM is small) collisionless cold-dark-matter CDM fluid to give condensations that gravitationally collect the plasma. Galaxies by this CDM model are therefore produced by gradual hierarchical-clustering of CDM halos to gal- axy mass over billions of years, contrary to observations showing that well formed galaxies existed much earlier. No observations exist of CDM halos. However, Gravitational instability is non- linear and absolute, controlled by viscous and turbulent forces or by diffusivity at Schwarz length scales smaller than ct. Because the universe during the plasma epoch is rapidly expanding, the first structures formed were at density minima by fragmentation when the viscous-gravitional scale LSV first matched ct at 30,000 years to produce protosupercluster voids and protosuperclusters.