Garching bei München, Germany
Garching bei München, Germany

Time filter

Source Type

Toft S.,Copenhagen University | Smolcic V.,University of Zagreb | Magnelli B.,Argelander Institute for Astronomy | Karim A.,Argelander Institute for Astronomy | And 20 more authors.
Astrophysical Journal | Year: 2014

Three billion years after the big bang (at redshift z = 2), half of the most massive galaxies were already old, quiescent systems with little to no residual star formation and extremely compact with stellar mass densities at least an order of magnitude larger than in low-redshift ellipticals, their descendants. Little is known about how they formed, but their evolved, dense stellar populations suggest formation within intense, compact starbursts 1-2 Gyr earlier (at 3 < z < 6). Simulations show that gas-rich major mergers can give rise to such starbursts, which produce dense remnants. Submillimeter- selected galaxies (SMGs) are prime examples of intense, gas-rich starbursts. With a new, representative spectroscopic sample of compact, quiescent galaxies at z = 2 and a statistically well-understood sample of SMGs, we show that z = 3-6 SMGs are consistent with being the progenitors of z = 2 quiescent galaxies, matching their formation redshifts and their distributions of sizes, stellar masses, and internal velocities. Assuming an evolutionary connection, their space densities also match if the mean duty cycle of SMG starbursts is Myr (consistent with independent estimates), which indicates that the bulk of stars in these massive galaxies were formed in a major, early surge of star formation. These results suggest a coherent picture of the formation history of the most massive galaxies in the universe, from their initial burst of violent star formation through their appearance as high stellar-density galaxy cores and to their ultimate fate as giant ellipticals. © 2014. The American Astronomical Society. All rights reserved.© 2014. The American Astronomical Society. All rights reserved. Printed in the U.S.A.

Phan T.D.,University of California at Berkeley | Shay M.A.,University of Delaware | Gosling J.T.,University of Colorado at Boulder | Fujimoto M.,ISAS | And 5 more authors.
Geophysical Research Letters | Year: 2013

We surveyed 79 magnetopause reconnection exhausts detected by the THEMIS spacecraft to investigate how the amount and anisotropy of electron bulk heating produced by reconnection depend on the inflow boundary conditions. We find that the amount of heating, ΔTe, is correlated with the asymmetric Alfvén speed, VAL,asym, based on the reconnecting magnetic field and the plasma density measured in both the high-density magnetosheath and low-density magnetospheric inflow regions. Best fit to the data produces the empirical relation ΔTe = 0.017 miV AL,asym 2, indicating that the amount of heating is proportional to the inflowing magnetic energy per proton-electron pair, with ∼1.7% of the energy being converted into electron heating. This finding, generalized to symmetric reconnection, could account for the lack of electron heating in typical solar wind exhausts at 1 AU, as well as strong heating to keV energies common in magnetotail exhausts. We also find that the guide field suppresses perpendicular heating. Key Points Electron bulk heating controlling factors revealed Heating depends on the total incoming magnetic energy per particle 1.7% of magnetic energy is converted into electron bulk heating ©2013. American Geophysical Union. All Rights Reserved.

Worner L.,MPE | Kovacevic E.,GREMI | Berndt J.,GREMI | Thomas H.M.,MPE | And 3 more authors.
New Journal of Physics | Year: 2012

The growth of nanoparticles in low-temperature plasmas is often accompanied by the formation of complex particle patterns and intricate transport processes. This paper deals with the formation and growth of nanoparticles operated in a mixture of argon and acetylene. The experiments are performed in a cylindrical dc discharge, the so-called PK-4 facility that shall be launched to the International Space Station (ISS) in 2014. The experiments show that the particles are formed in a localized region close to the anode and are transported as still localized dust structures ('dust bullets') along the glass tube. The formation of new particles triggers an oscillatory process that is characterized by the periodic appearance and subsequent removal of dust particles. The frequency of this process, as well as the size of the particles within each 'dust bullet', can be controlled by means of the neutral gas flow. This behaviour can be understood by analysing the size-dependent forces acting on the growing particles. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Roediger E.,Jacobs University Bremen | Bruggen M.,Jacobs University Bremen | Simionescu A.,Stanford University | Bohringer H.,MPE | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

We perform hydrodynamical simulations of minor-merger-induced gas sloshing and the subsequent formation of cold fronts in the Virgo cluster. Comparing to observations, we show for the first time that the sloshing scenario can reproduce the radii and the contrasts in X-ray brightness, projected temperature and metallicity across the cold fronts quantitatively. The comparison suggests a third cold front 20kpc north-west of the Virgo core. We identify several new features typical for sloshing cold fronts: an alternating distribution of cool, metal-enriched X-ray brightness excess regions and warm brightness deficit regions of reduced metallicity; a constant or radially decreasing temperature accompanied by a plateau in metallicity inside the cold fronts; a warm rim outside the cold fronts and a large-scale brightness asymmetry. We can trace these new features not only in Virgo, but also in other clusters exhibiting sloshing cold fronts. By comparing synthetic and real observations, we estimate that the original minor-merger event took place about 1.5 Gyr ago when a subcluster of 1-4 × 1013M⊙ passed the Virgo core at 100-400kpc distance, where a smaller mass corresponds to a smaller pericentre distance, and vice versa. From our inferred merger geometry, we derive the current location of the disturbing subcluster to be about 1-2Mpc east of the Virgo core. A possible candidate is M60. Additionally, we quantify the metal redistribution by sloshing and discuss its importance. We verify that the subcluster required to produce the observed cold fronts could be completely ram-pressure-stripped before reaching the Virgo centre, and discuss the conditions required for this to be achieved. Finally, we demonstrate that the bow shock of a fast galaxy passing the Virgo cluster at ~400kpc distance also causes sloshing and leads to very similar cold front structures. The responsible galaxy would be located about 2Mpc north of the Virgo centre. A possible candidate is M85. © 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Simionescu A.,Stanford University | Werner N.,Stanford University | Forman W.R.,Harvard - Smithsonian Center for Astrophysics | Miller E.D.,Massachusetts Institute of Technology | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present the results of an XMM-Newton mosaic covering the central ∼200 kpc of the nearby Virgo cluster. We focus on a strong surface brightness discontinuity in the outskirts of the brightest cluster galaxy (BCG), M87. Using both XMM-Newton and Suzaku, we derive accurate temperature and metallicity profiles across this feature and show that it is a cold front probably due to sloshing of the Virgo intracluster medium (ICM). It is also associated with a discontinuity in the chemical composition. The gas in the inner, bright region of the front is ∼40 per cent more abundant in Fe than the gas outside the front, suggesting the important role of sloshing in transporting metals through the ICM. For the first time, we provide a quantitative estimate of the mass of Fe transported by a cold front. This amounts to ∼6 per cent of the total Fe mass within the radial range affected by sloshing, significantly more than the amount of metals transported by the active galactic nucleus in the same cluster core. The very low Fe abundance of only ∼0.2 solar immediately outside the cold front at a radius of 90 kpc suggests we are witnessing first-hand the transport of higher metallicity gas into a pristine region, whose abundance is typical of the cluster outskirts. The Mg/Fe and O/Fe abundance ratios remain approximately constant over the entire radial range between the centre of M87 and the faint side of the cold front, which requires the presence of a centrally peaked distribution not only for Fe but also for core-collapse type supernova products. This peak may stem from the star formation triggered as the BCG assembled during the protocluster phase. © 2010 The Authors. Journal compilation © 2010 RAS.

Phan T.D.,University of California at Berkeley | Gosling J.T.,University of Colorado at Boulder | Paschmann G.,MPE | Pasma C.,University of California at Berkeley | And 7 more authors.
Astrophysical Journal Letters | Year: 2010

We address the conditions for the onset of magnetic reconnection based on a survey of 197 reconnection events in solar wind current sheets observed by the Wind spacecraft. We report the first observational evidence for the dependence of the occurrence of reconnection on a combination of the magnetic field shear angle, θ, across the current sheet and the difference in the plasma β values on the two sides of the current sheet, δβ. For low.β, reconnection occurred for both low and high magnetic shears, whereas only large magnetic shear events were observed for large.β: Events with shears as low as 11° were observed for.β < 0.1, but for.β > 1.5 only events with. > 100. were detected. Our observations are in quantitative agreement with a theoretical prediction that reconnection is suppressed in high β plasmas at low magnetic shears due to super-Alfv́enic drift of the X-line caused by plasma pressure gradients across the current sheet. The magnetic shear-.β dependence could account for the high occurrence rate of reconnection observed in current sheets embedded within interplanetary coronal mass ejections, compared to those in the ambient solar wind. It would also suggest that reconnection could occur at a substantially higher rate in solar wind current sheets closer to the Sun than at 1 AU and thus may play an important role in the generation and heating of the solar wind. © 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A.

Tommasin S.,Tel Aviv University | Netzer H.,Tel Aviv University | Sternberg A.,Tel Aviv University | Nordon R.,MPE | And 7 more authors.
Astrophysical Journal | Year: 2012

We present the results of a Herschel-PACS study of a sample of 97 low-ionization nuclear emission-line regions (LINERs) at redshift z 0.3 selected from the zCOSMOS survey. Of these sources, 34 are detected in at least one PACS band, enabling reliable estimates of the far-infrared L FIR luminosities, and a comparison to the FIR luminosities of local LINERs. Many of our PACS-detected LINERs are also UV sources detected by GALEX. Assuming that the FIR is produced in young dusty star-forming regions, the typical star formation rates (SFRs) for the host galaxies in our sample are 10 M yr -1, 1-2 orders of magnitude larger than in many local LINERs. Given stellar masses inferred from optical/NIR photometry of the (unobscured) evolved stellar populations, we find that the entire sample lies close to the star-forming "main sequence" for galaxies at redshift 0.3. For young star-forming regions, the Hα- and UV-based estimates of the SFRs are much smaller than the FIR-based estimates, by factors 30, even assuming that all of the Hα emission is produced by O-star ionization rather than by the active galactic nuclei (AGNs). These discrepancies may be due to large (and uncertain) extinctions toward the young stellar systems. Alternatively, the Hα and UV emissions could be tracing residual star formation in an older, less obscured population with decaying star formation. We also compare L SF and L(AGN) in local LINERs and in our sample. Finally, we comment on the problematic use of several line diagnostic diagrams in cases with an estimated obscuration similar to that in the sample under study. © 2012. The American Astronomical Society. All rights reserved..

Kanbach G.,MPE | Nittler L.,Carnegie Institution for Science
Lecture Notes in Physics | Year: 2011

Radioactivity is characterized by the emission of particles or photons that accompany the nuclear transformations of unstable isotopes. Direct observations of secondary particles (e.g. β±, or α) are only possible with in-situ measurements in the local environment of the solar system and often the detected particles are not very specific as to their parent nuclei. Transitions between energy levels of radioactive and excited nuclei however produce characteristic X- and γ-ray lines that can be detected from astronomical distances. Only one secondary particle resulting from radioactive decay, the positron, signals its presence in a characteristic γ-ray line: positrons annihilate with their anti-particle (electrons) and convert the pair's rest mass into a line at 511 keV (see Chap. 7). Nuclear energy levels range from 10 s of keV upwards to energies of 10 s of MeV with most important astrophysical lines in the range from about 100 keV to several MeV.

Thi W.-F.,MPE
EPJ Web of Conferences | Year: 2015

This chapter discusses the fundamental ideas of how chemical networks are build, their strengths and limitations. The chemical reactions that occur in disks combine the cold phase reactions used to model cold molecular clouds with the hot chemistry applied to planetary atmosphere models. With a general understanding of the different types of reactions that can occur, one can proceed in building a network of chemical reactions and use it to explain the abundance of species seen in disks. One on-going research subject is finding new paths to synthesize species either in the gas-phase or on grain surfaces. Specific formation routes for water or carbon monoxide are discussed in more details. © 2015 Owned by the authors, published by EDP Sciences.

Thi W.-F.,MPE
EPJ Web of Conferences | Year: 2015

The chemical species in protoplanetary disks react with each other. The chemical species control part of the thermal balance in those disks. How the chemistry proceeds in the varied conditions encountered in disks relies on detailed microscopic understanding of the reactions through experiments or theoretical studies. This chapter strives to summarize and explain in simple terms the different types of chemical reactions that can lead to complex species. The first part of the chapter deals with gas-phase chemistry and the second part introduces chemical reactions occurring on grain surfaces. Several terms pertaining to astrochemistry are introduced. © 2015 Owned by the authors, published by EDP Sciences.

Loading MPE collaborators
Loading MPE collaborators