39 research outputs found
The rapid assembly of an elliptical galaxy of 400 billion solar masses at a redshift of 2.3
Stellar archeology shows that massive elliptical galaxies today formed
rapidly about ten billion years ago with star formation rates above several
hundreds solar masses per year (M_sun/yr). Their progenitors are likely the
sub-millimeter-bright galaxies (SMGs) at redshifts (z) greater than 2. While
SMGs' mean molecular gas mass of 5x10^10 M_sun can explain the formation of
typical elliptical galaxies, it is inadequate to form ellipticals that already
have stellar masses above 2x10^11 M_sun at z ~ 2. Here we report
multi-wavelength high-resolution observations of a rare merger of two massive
SMGs at z = 2.3. The system is currently forming stars at a tremendous rate of
2,000 M_sun/yr. With a star formation efficiency an order-of-magnitude greater
than that of normal galaxies, it will quench the star formation by exhausting
the gas reservoir in only ~200 million years. At a projected separation of 19
kiloparsecs, the two massive starbursts are about to merge and form a passive
elliptical galaxy with a stellar mass of ~4x10^11 M_sun. Our observations show
that gas-rich major galaxy mergers, concurrent with intense star formation, can
form the most massive elliptical galaxies by z ~ 1.5.Comment: Appearing in Nature online on May 22 and in print on May 30.
Submitted here is the accepted version (including the Supplementary
Information), see nature.com for the final versio
The Cosmological Constant
This is a review of the physics and cosmology of the cosmological constant.
Focusing on recent developments, I present a pedagogical overview of cosmology
in the presence of a cosmological constant, observational constraints on its
magnitude, and the physics of a small (and potentially nonzero) vacuum energy.Comment: 50 pages. Submitted to Living Reviews in Relativity
(http://www.livingreviews.org/), December 199
f(R) theories
Over the past decade, f(R) theories have been extensively studied as one of
the simplest modifications to General Relativity. In this article we review
various applications of f(R) theories to cosmology and gravity - such as
inflation, dark energy, local gravity constraints, cosmological perturbations,
and spherically symmetric solutions in weak and strong gravitational
backgrounds. We present a number of ways to distinguish those theories from
General Relativity observationally and experimentally. We also discuss the
extension to other modified gravity theories such as Brans-Dicke theory and
Gauss-Bonnet gravity, and address models that can satisfy both cosmological and
local gravity constraints.Comment: 156 pages, 14 figures, Invited review article in Living Reviews in
Relativity, Published version, Comments are welcom
The Evolution of Compact Binary Star Systems
We review the formation and evolution of compact binary stars consisting of
white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and
BHs are thought to be the primary astrophysical sources of gravitational waves
(GWs) within the frequency band of ground-based detectors, while compact
binaries of WDs are important sources of GWs at lower frequencies to be covered
by space interferometers (LISA). Major uncertainties in the current
understanding of properties of NSs and BHs most relevant to the GW studies are
discussed, including the treatment of the natal kicks which compact stellar
remnants acquire during the core collapse of massive stars and the common
envelope phase of binary evolution. We discuss the coalescence rates of binary
NSs and BHs and prospects for their detections, the formation and evolution of
binary WDs and their observational manifestations. Special attention is given
to AM CVn-stars -- compact binaries in which the Roche lobe is filled by
another WD or a low-mass partially degenerate helium-star, as these stars are
thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure
The Herschel-SPIRE Legacy Survey (HSLS): the scientific goals of a shallow and wide submillimeter imaging survey with SPIRE
A large sub-mm survey with Herschel will enable many exciting science opportunities, especially in an era of wide-field optical and radio surveys and high resolution cosmic microwave background experiments. The Herschel-SPIRE Legacy Survey (HSLS), will lead to imaging data over 4000 sq. degrees at 250, 350, and 500 micron. Major Goals of HSLS are: (a) produce a catalog of 2.5 to 3 million galaxies down to 26, 27 and 33 mJy (50% completeness; 5 sigma confusion noise) at 250, 350 and 500 micron, respectively, in the southern hemisphere (3000 sq. degrees) and in an equatorial strip (1000 sq. degrees), areas which have extensive multi-wavelength coverage and are easily accessible from ALMA. Two thirds of the of the sources are expected to be at z > 1, one third at z > 2 and about a 1000 at z > 5. (b) Remove point source confusion in secondary anisotropy studies with Planck and ground-based CMB data. (c) Find at least 1200 strongly lensed bright sub-mm sources leading to a 2% test of general relativity. (d) Identify 200 proto-cluster regions at z of 2 and perform an unbiased study of the environmental dependence of star formation. (e) Perform an unbiased survey for star formation and dust at high Galactic latitude and make a census of debris disks and dust around AGB stars and white dwarfs
Charnockite formation at Ponmudi in Southern India
Charnockites, constituents of most Precambrian high-grade terrains 1,2, are essential for understanding the evolution of the early continental crust. The arrested development of charnockite in shear veins at Kabbaldurga3, in the state of Karnataka in India, suggests flow of CO2-rich water-deficient fluids through deep-seated rocks as a mechanism of granulite grade metamorphism4,5. We report here an occurrence of arrested charnockite formation well south of Kabbaldurga, in the khondalite belt of southern Kerala, where rocks with amphibolite facies give way to the vast southern India-Sri Lanka charnockite terrain, indicating that metamorphism due to CO2-rich fluids (carbonic metamorphism) may have operated over a large area in southern India. If such localities prove to be widespread, the present level of exposure throughout much of the high-grade terrain probably does not extend far beyond an isofacial surface marking the boundary between upper and lower crust in the late Archaean. © 1985 Nature Publishing Group