115 research outputs found
Deviations from the Schmidt-Kennicutt relations during early galaxy evolution
We utilize detailed time-varying models of the coupled evolution of stars and
the HI, H_2, and CO-bright H_2 gas phases in galaxy-sized numerical simulations
to explore the evolution of gas-rich and/or metal-poor systems, expected to be
numerous in the Early Universe. The inclusion of the CO-bright H_2 gas phase,
and the realistic rendering of star formation as an H_2-regulated process (and
the new feedback processes that this entails) allows the most realistic
tracking of strongly evolving galaxies, and much better comparison with
observations. We find that while galaxies eventually settle into states
conforming to Schmidt-Kennicutt (S-K) relations, significant and systematic
deviations of their star formation rates (SFRs) from the latter occur,
especially pronounced and prolonged for ...
...This indicates potentially serious limitations of (S-K)-type relations as
reliable sub-grid elements of star formation physics in simulations of
structure formation in the Early Universe. We anticipate that galaxies with
marked deviations from the S-K relations will be found at high redshifts as
unbiased inventories of total gas mass become possible with ALMA and the EVLA.Comment: 13 pages, 3 figures, accepted for publication in the Astrophysical
Journa
Diagnostics of the molecular component of PDRs with mechanical heating. II: line intensities and ratios
CO observations in active galactic nuclei and star-bursts reveal high kinetic
temperatures. Those environments are thought to be very turbulent due to
dynamic phenomena such as outflows and high supernova rates. We investigate the
effect of mechanical heating (MH) on atomic fine-structure and molecular lines,
and their ratios. We use those ratios as a diagnostic to constrain the amount
of MH in an object and also study its significance on estimating the H2 mass.
Equilibrium PDRs models were used to compute the thermal and chemical balance
for the clouds. The equilibria were solved for numerically using the optimized
version of the Leiden PDR-XDR code. Large velocity gradient calculations were
done as post-processing on the output of the PDR models using RADEX. High-J CO
line ratios are very sensitive to MH. Emission becomes at least one order of
magnitude brighter in clouds with n~10^5~cm^-3 and a star formation rate of 1
Solar Mass per year (corresponding to a MH rate of 2 * 10^-19 erg cm^-3 s^-1).
Emission of low-J CO lines is not as sensitive to MH, but they do become
brighter in response to MH. Generally, for all of the lines we considered, MH
increases excitation temperatures and decreases the optical depth at the line
centre. Hence line ratios are also affected, strongly in some cases. Ratios
involving HCN are a good diagnostic for MH, such as HCN(1-0)/CO(1-0) and
HCN(1-0)/HCO^+(1-0). Both ratios increase by a factor 3 or more for a MH
equivalent to > 5 percent of the surface heating, as opposed to pure PDRs. The
first major conclusion is that low-J to high-J intensity ratios will yield a
good estimate of the MH rate (as opposed to only low-J ratios). The second one
is that the MH rate should be taken into account when determining A_V or
equivalently N_H, and consequently the cloud mass. Ignoring MH will also lead
to large errors in density and radiation field estimates.Comment: 38 pages, to appear in A&
Face-on accretion onto a protoplanetary disc
Globular clusters (GCs) are known to harbor multiple stellar populations. To
explain these observations Bastian et al. suggested a scenario in which a
second population is formed by the accretion of enriched material onto the
low-mass stars in the initial GC population. The idea is that the low-mass,
pre-main sequence stars sweep up gas expelled by the massive stars of the same
generation into their protoplanetary disc as they move through the GC core. We
perform simulations with 2 different smoothed particle hydrodynamics codes to
investigate if a low-mass star surrounded by a protoplanetary disc can accrete
the amount of enriched material required in this scenario. We focus on the gas
loading rate onto the disc and star as well as on the lifetime of the disc. We
find that the gas loading rate is a factor of 2 smaller than the geometric
rate, because the effective cross section of the disc is smaller than its
surface area. The loading rate is consistent for both codes, irrespective of
resolution. The disc gains mass in the high resolution runs, but loses angular
momentum on a time scale of 10^4 yrs. Two effects determine the loss of
(specific) angular momentum in our simulations: 1) continuous ram pressure
stripping and 2) accretion of material with no azimuthal angular momentum. Our
study and previous work suggest that the former, dominant process is mainly
caused by numerical rather than physical effects, while the latter is not. The
latter process causes the disc to become more compact, increasing the surface
density profile at smaller radii. The disc size is determined in the first
place by the ram pressure when the flow first hits the disc. Further evolution
is governed by the decrease in the specific angular momentum of the disc. We
conclude that the size and lifetime of the disc are probably not sufficient to
accrete the amount of mass required in Bastian et al.'s scenario.Comment: Accepted for publication in A&A, 15 pages, 5 figures, 4 table
Molecular gas, CO, and star formation in galaxies: emergent empirical relations, feedback, and the evolution of very gas-rich systems
We use time-varying models of the coupled evolution of the HI, H_2 gas phases
and stars in galaxy-sized numerical simulations to: a) test for the emergence
of the Kennicutt-Schmidt (K-S) and the H_2-pressure relation, b) explore a
realistic H_2-regulated star formation recipe which brings forth a neglected
and potentially significant SF-regulating factor, and c) go beyond typical
galactic environments (for which these galactic empirical relations are
deduced) to explore the early evolution of very gas-rich galaxies. In this work
we model low mass galaxies (M_{\rm baryon} \le 10^9 \msun), while
incorporating an independent treatment of CO formation and destruction, the
most important tracer molecule of H2 in galaxies, along with that for the H2
gas itself. We find that both the K-S and the H_2-pressure empirical relations
can robustly emerge in galaxies after a dynamic equilibrium sets in between the
various ISM states, the stellar component and its feedback. (abridged)Comment: 32 pages, 9 figures, accepted for publication in Ap
PARA LANJUT USIA (LANSIA) DAN DUNIANYA DI PANTI TRESNA WERDHA INA KAKA AMBON (Studi Tentang Interaksi Sosial)
Penelitian ini dilakukan untuk menganalisis proses interaksi sosial yang terjadi diantara para lanjut usia (Lansia) di Panti Tresna Werda Ina Kaka Ambon, Proses interaksi yang terbangun diantara mereka terjadi oleh karena adanya proses kerja sama dalam hal ini tolong menolong untuk mencapai tujuan bersama. Hal lainnya juga dari proses ini adalah terciptanya perasaan cinta antar dua insan yang berbeda itu terjadi. Baik itu yang baru saling mengenal, tetapi yang lebih menarik juga terjadi ketika panti sosial ini mempertemukan kedua insan yang pernah membangun hubungan cinta di masa muda namun tidaklah tercapai. Di dalam realitas ini pula interaksi yang bersifat kerja sama itu disertai dengan proses pertentangan. Proses pertentangan diantara sesama lansia ini diakibatkan oleh karena kecemburuan satu dengan lainnya. Selain proses interaksi diantara mereka, interaksipun berlagsung dengan para pegawai pengelola panti. Proses interaksi ini membawa dampak positif yang memiliki makna tersendiri. Baik itu terhadap para pegawai maupun lansia, makna dimaksud adalah rasa saling memiliki diantara mereka berlangsung. Proses pelayanan membuat para pegawai dengan penuh rasa sayang menganggap setiap lansia adalah orang tua mereka, begitupun para lansia yang menganggap para pegawai itu adalah anak mereka. Interaksi yang terbangu baik ini membentuk suatu ikatan keluarga baru di Panti tanpa adanya hubungan genealogi
The Astrophysical Multipurpose Software Environment
We present the open source Astrophysical Multi-purpose Software Environment
(AMUSE, www.amusecode.org), a component library for performing astrophysical
simulations involving different physical domains and scales. It couples
existing codes within a Python framework based on a communication layer using
MPI. The interfaces are standardized for each domain and their implementation
based on MPI guarantees that the whole framework is well-suited for distributed
computation. It includes facilities for unit handling and data storage.
Currently it includes codes for gravitational dynamics, stellar evolution,
hydrodynamics and radiative transfer. Within each domain the interfaces to the
codes are as similar as possible. We describe the design and implementation of
AMUSE, as well as the main components and community codes currently supported
and we discuss the code interactions facilitated by the framework.
Additionally, we demonstrate how AMUSE can be used to resolve complex
astrophysical problems by presenting example applications.Comment: 23 pages, 25 figures, accepted for A&
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