118 research outputs found
Spillover Effects of Studying with Immigrant Students; A Quantile Regression Approach
Abstract: We analyze how the share of immigrant children in the classroom aects the educational attainment of native Dutch children in terms of their language and math performance at the end of primary school. Our paper studies the spill-over effects at different parts of the test score distribution of native Dutch students using a quantile regression approach. We fi nd no evidence of negative spillover effects of the classroom presence of immigrant children at the median of the test score distribution. In addition, there is no indication that these spill-over effects are present at other parts of the distribution.
Feedback and feeding in the context of galaxy evolution with SPICA: direct characterization of molecular outflows and inflows
A far-infrared observatory such as the {\it SPace Infrared telescope for
Cosmology and Astrophysics} ({\it SPICA}), with its unprecedented spectroscopic
sensitivity, would unveil the role of feedback in galaxy evolution during the
last Gyr of the Universe (), through the use of far- and
mid-infrared molecular and ionic fine structure lines that trace outflowing and
infalling gas. Outflowing gas is identified in the far-infrared through P-Cygni
line shapes and absorption blueshifted wings in molecular lines with high
dipolar moments, and through emission line wings of fine-structure lines of
ionized gas. We quantify the detectability of galaxy-scale massive molecular
and ionized outflows as a function of redshift in AGN-dominated,
starburst-dominated, and main-sequence galaxies, explore the detectability of
metal-rich inflows in the local Universe, and describe the most significant
synergies with other current and future observatories that will measure
feedback in galaxies via complementary tracers at other wavelengths.Comment: This paper belongs to the SPICA Special Issue on PASA. Accepted for
publication in PAS
Joint Cosmological Formation of QSOs and Bulge-dominated Galaxies
Older and more recent pieces of observational evidence suggest a strong
connection between QSOs and galaxies; in particular, the recently discovered
correlation between black hole and galactic bulge masses suggests that QSO
activity is directly connected to the formation of galactic bulges. The
cosmological problem of QSO formation is analyzed in the framework of an
analytical model for galaxy formation; for the first time a joint comparison
with galaxy and QSO observables is performed. In this model it is assumed that
the same physical variable which determines galaxy morphology is able to
modulate the mass of the black hole responsible for QSO activity. Both halo
spin and the occurence of a major merger are considered as candidates to this
role. The predictions of the model are compared to available data for the
type-dependent galaxy mass functions, the star-formation history of elliptical
galaxies, the QSO luminosity function and its evolution (including the obscured
objects contributing to the hard-X-ray background), the mass function of
dormant black holes and the distribution of black-hole -- bulge mass ratios. A
good agreement with observations is obtained if the halo spin modulates the
efficiency of black-hole formation, and if the galactic halos at have
shone in an inverted order with respect to the hierarchical one (i.e., stars
and black holes in bigger galactic halos have formed before those in smaller
ones). This inversion of hierarchical order for galaxy formation, which
reconciles galaxy formation with QSO evolution, is consistent with many pieces
of observational evidence.Comment: 20 pages, figures included, mn.sty, in press on MNRAS, fig 6 changed
(new data added at z=4.4
Control of star formation by supersonic turbulence
Understanding the formation of stars in galaxies is central to much of modern
astrophysics. For several decades it has been thought that stellar birth is
primarily controlled by the interplay between gravity and magnetostatic
support, modulated by ambipolar diffusion. Recently, however, both
observational and numerical work has begun to suggest that support by
supersonic turbulence rather than magnetic fields controls star formation. In
this review we outline a new theory of star formation relying on the control by
turbulence. We demonstrate that although supersonic turbulence can provide
global support, it nevertheless produces density enhancements that allow local
collapse. Inefficient, isolated star formation is a hallmark of turbulent
support, while efficient, clustered star formation occurs in its absence. The
consequences of this theory are then explored for both local star formation and
galactic scale star formation. (ABSTRACT ABBREVIATED)Comment: Invited review for "Reviews of Modern Physics", 87 pages including 28
figures, in pres
Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research
This review discusses the current status of supermassive black hole research,
as seen from a purely observational standpoint. Since the early '90s, rapid
technological advances, most notably the launch of the Hubble Space Telescope,
the commissioning of the VLBA and improvements in near-infrared speckle imaging
techniques, have not only given us incontrovertible proof of the existence of
supermassive black holes, but have unveiled fundamental connections between the
mass of the central singularity and the global properties of the host galaxy.
It is thanks to these observations that we are now, for the first time, in a
position to understand the origin, evolution and cosmic relevance of these
fascinating objects.Comment: Invited Review, 114 pages. Because of space requirements, this
version contains low resolution figures. The full resolution version can be
downloaded from http://www.physics.rutgers.edu/~lff/publications.htm
On the large-scale structure of galactic disks
The disk positions for galaxies of various morphological and nuclear-activity
types (normal galaxies, QSO, Sy, E/S0, low-surface brightness galaxies, etc.)
on the "central surface brightness - exponential scalelength" plane are
considered. The stellar disks are shown to form a single sequence on this plane
over a wide range of surface brightnesses (\mu_0(I)=12-25) and sizes (h=10 pc -
100 kpc). The existence of this observed sequence can probably be explaned by a
combination of three factors: a disk-stability requirement, a limited total
disk luminosity, and observational selection. The model by Mo et al. (1998) for
disk formation in the CDM hierarchical-clustering scenario is shown to
satisfactorily reproduce the salient features of the galaxy disk distribution
on the "\mu_0 - h" plane.Comment: Astron. Letters, vol.26, 2000 (translated from Pis'ma v Astron.
Zhurn., v.26, p.563, 2000
The role of major mergers in the size growth of intermediate-mass spheroids
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.We study of the role of ‘major’ mergers (mass ratios >1: 4) in driving size growth in high-redshift (1 1010.7 M⊙) SGs at z < 1, then major mergers are also likely to play an important role in the size growth of at least some massive SGs in this mass range.Peer reviewe
The Dramatic Size and Kinematic Evolution of Massive Early-type Galaxies
We aim to provide a holistic view on the typical size and kinematic evolution of massive early-type galaxies (ETGs) that encompasses their high-z star-forming progenitors, their high-z quiescent counterparts, and their configurations in the local Universe. Our investigation covers the main processes playing a relevant role in the cosmic evolution of ETGs. Specifically, their early fast evolution comprises biased collapse of the low angular momentum gaseous baryons located in the inner regions of the host dark matter halo; cooling, fragmentation, and infall of the gas down to the radius set by the centrifugal barrier; further rapid compaction via clump/gas migration toward the galaxy center, where strong heavily dust-enshrouded star formation takes place and most of the stellar mass is accumulated; and ejection of substantial gas amount from the inner regions by feedback processes, which causes a dramatic puffing-up of the stellar component. In the late slow evolution, passive aging of stellar populations and mass additions by dry merger events occur. We describe these processes relying on prescriptions inspired by basic physical arguments and by numerical simulations to derive new analytical estimates of the relevant sizes, timescales, and kinematic properties for individual galaxies along their evolution. Then we obtain quantitative results as a function of galaxy mass and redshift, and compare them to recent observational constraints on half-light size Re, on the ratio v/\u3c3 between rotation velocity and velocity dispersion (for gas and stars) and on the specific angular momentum j 17of the stellar component; we find good consistency with the available multiband data in average values and dispersion, both for local ETGs and for their z 3c 1-2 star-forming and quiescent progenitors. The outcomes of our analysis can provide hints to gauge sub-grid recipes implemented in simulations, to tune numerical experiments focused on specific processes, and to plan future multiband, high-resolution observations on high-redshift star-forming and quiescent galaxies with next-generation facilities
The stellar halo of the Galaxy
Stellar halos may hold some of the best preserved fossils of the formation
history of galaxies. They are a natural product of the merging processes that
probably take place during the assembly of a galaxy, and hence may well be the
most ubiquitous component of galaxies, independently of their Hubble type. This
review focuses on our current understanding of the spatial structure, the
kinematics and chemistry of halo stars in the Milky Way. In recent years, we
have experienced a change in paradigm thanks to the discovery of large amounts
of substructure, especially in the outer halo. I discuss the implications of
the currently available observational constraints and fold them into several
possible formation scenarios. Unraveling the formation of the Galactic halo
will be possible in the near future through a combination of large wide field
photometric and spectroscopic surveys, and especially in the era of Gaia.Comment: 46 pages, 16 figures. References updated and some minor changes.
Full-resolution version available at
http://www.astro.rug.nl/~ahelmi/stellar-halo-review.pd
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