876 research outputs found
Resolved Stellar Populations at the Distance of Virgo
Top of the wish list of any astronomer who wants to understand galaxy
formation and evolution is to resolve the stellar populations of a sample of
giant elliptical galaxies: to take spectra of the stars and make
Colour-Magnitude Diagrams going down to the oldest main sequence turn-offs. It
is only by measuring the relative numbers of stars on Main Sequence Turnoffs at
ages ranging back to the time of the earliest star formation in the Universe
that we can obtain unambiguous star formation histories. Understanding star
formation histories of individual galaxies underpins all our theories of galaxy
formation and evolution. To date we only have detailed star formation histories
for the nearest-by objects in the Local Group, namely galaxies within 700kpc of
our own. This means predominantly small diffuse dwarf galaxies in a poor group
environment. To sample the full range of galaxy types and to consider galaxies
in a high density environment (where much mass in the Universe resides) we need
to be able to resolve stars at the distance of the Virgo (~17Mpc) or Fornax
(~18Mpc) clusters. This ambitious goal requires an Extremely Large Telescope
(ELT), with a diameter of 50-150m, operating in the optical/near-IR at its
diffraction limit.Comment: proceedings IAU 232 "Extremely Large Telescopes", eds Whitelock,
Leibundgut and Dennefel
Astrophysics in 2006
The fastest pulsar and the slowest nova; the oldest galaxies and the youngest
stars; the weirdest life forms and the commonest dwarfs; the highest energy
particles and the lowest energy photons. These were some of the extremes of
Astrophysics 2006. We attempt also to bring you updates on things of which
there is currently only one (habitable planets, the Sun, and the universe) and
others of which there are always many, like meteors and molecules, black holes
and binaries.Comment: 244 pages, no figure
Applying the expanding photosphere and standardized candle methods to Type II-Plateau supernovae at cosmologically significant redshifts: the distance to SN 2013eq
Based on optical imaging and spectroscopy of the Type II-Plateau SN 2013eq,
we present a comparative study of commonly used distance determination methods
based on Type II supernovae. The occurrence of SN 2013eq in the Hubble flow (z
= 0.041 +/- 0.001) prompted us to investigate the implications of the
difference between "angular" and "luminosity" distances within the framework of
the expanding photosphere method (EPM) that relies upon a relation between flux
and angular size to yield a distance. Following a re-derivation of the basic
equations of the EPM for SNe at non-negligible redshifts, we conclude that the
EPM results in an angular distance. The observed flux should be converted into
the SN rest frame and the angular size, theta, has to be corrected by a factor
of (1+z)^2. Alternatively, the EPM angular distance can be converted to a
luminosity distance by implementing a modification of the angular size. For SN
2013eq, we find EPM luminosity distances of D_L = 151 +/- 18 Mpc and D_L = 164
+/- 20 Mpc by making use of different sets of dilution factors taken from the
literature. Application of the standardized candle method for Type II-P SNe
results in an independent luminosity distance estimate (D_L = 168 +/- 16 Mpc)
that is consistent with the EPM estimate.Comment: 12 pages, 4 figures, accepted by A&
Supernova cosmology: legacy and future
The discovery of dark energy by the first generation of high-redshift
supernova surveys has generated enormous interest beyond cosmology and has
dramatic implications for fundamental physics. Distance measurements using
supernova explosions are the most direct probes of the expansion history of the
Universe, making them extremely useful tools to study the cosmic fabric and the
properties of gravity at the largest scales. The past decade has seen the
confirmation of the original results. Type Ia supernovae are among the leading
techniques to obtain high-precision measurements of the dark energy equation of
state parameter, and in the near future, its time dependence. The success of
these efforts depends on our ability to understand a large number of effects,
mostly of astrophysical nature, influencing the observed flux at Earth. The
frontier now lies in understanding if the observed phenomenon is due to vacuum
energy, albeit its unnatural density, or some exotic new physics. Future
surveys will address the systematic effects with improved calibration
procedures and provide thousands of supernovae for detailed studies.Comment: Invited review, Annual Review of Nuclear and Particle Science
(submitted version
Nebular spectroscopy of SN 2014J: Detection of stable nickel in near infrared spectra
We present near infrared (NIR) spectroscopy of the nearby supernova 2014J
obtained 450 d after explosion. We detect the [Ni II] 1.939 m line
in the spectra indicating the presence of stable Ni in the ejecta. The
stable nickel is not centrally concentrated but rather distributed as the iron.
The spectra are dominated by forbidden [Fe II] and [Co II] lines. We use lines,
in the NIR spectra, arising from the same upper energy levels to place
constraints on the extinction from host galaxy dust. We find that that our data
are in agreement with the high and low found in earlier studies
from data near maximum light. Using a Ni mass prior from near maximum
light -ray observations, we find 0.05 M of stable nickel
to be present in the ejecta. We find that the iron group features are
redshifted from the host galaxy rest frame by 600 km s.Comment: 6 pages, 4 figures, submitted to A&
Lower limits on the Hubble Constant from models of Type Ia Supernovae
By coupling observations of type Ia supernovae with results obtained from the
best available numerical models we constrain the Hubble constant, independently
of any external calibrators. We find an absolute lower limit of Ho > 50
km/s/Mpc. In addition, we construct a Hubble diagram with UVOIR light curves of
12 type Ia supernovae located in the Hubble flow, and when adopting the most
likely values (obtained from 1-D and 3-D deflagration simulations) of the
amount of (56)Ni produced in a typical event, we find values of Ho
668 and 789 km/s/Mpc, respectively. Our result may be
difficult to reconcile with recent discussions in the literature as it seems
that an Einstein-de Sitter universe requires Ho 46 km/s/Mpc in order
to fit the temperature power spectrum of the cosmic microwave background and
maintain the age constraints of the oldest stars.Comment: 11 pages, 3 figures; Accepted for publication in A&
On the Spontaneous Identity of Chiral and Super Symmetry Breaking in Pure Super Yang Mills Theories
We show that in supersymmetric pure Yang Mills theories with arbitrary simple
gauge group, the spontaneous breaking of chiral fermionic and bosonic charge by
the associated gaugino and gauge boson condensates implies the spontaneous
breaking of supersymmetry by the condensate of the underlying Lagrangian
density. The explicit breaking of the restricted fermionic charge through the
chiral anomaly is deferred to a secondary stage in the elimination of infrared
singularities or long range forces.Comment: 14 pages, uses amsmath, amssymb, shorter version, references added,
eq. (44) correcte
The Extremes of Thermonuclear Supernovae
The majority of thermonuclear explosions in the Universe seem to proceed in a
rather standardised way, as explosions of carbon-oxygen (CO) white dwarfs in
binary systems, leading to 'normal' Type Ia supernovae (SNe Ia). However, over
the years a number of objects have been found which deviate from normal SNe Ia
in their observational properties, and which require different and not seldom
more extreme progenitor systems. While the 'traditional' classes of peculiar
SNe Ia - luminous '91T-like' and faint '91bg-like' objects - have been known
since the early 1990s, other classes of even more unusual transients have only
been established 20 years later, fostered by the advent of new wide-field SN
surveys such as the Palomar Transient Factory. These include the faint but
slowly declining '02es-like' SNe, 'Ca-rich' transients residing in the
luminosity gap between classical novae and supernovae, extremely short-lived,
fast-declining transients, and the very luminous so-called
'super-Chandrasekhar' SNe Ia. Not all of them are necessarily thermonuclear
explosions, but there are good arguments in favour of a thermonuclear origin
for most of them. The aim of this chapter is to provide an overview of the zoo
of potentially thermonuclear transients, reviewing their observational
characteristics and discussing possible explosion scenarios.Comment: Author version of a chapter for the 'Handbook of Supernovae', edited
by A. Alsabti and P. Murdin, Springer. 50 pages, 7 figure
Photometric Identification of Type Ia Supernovae at Moderate Redshift
Large photometric surveys with the aim of identifying many Type Ia supernovae
(SNe) at moderate redshift are challenged in separating these SNe from other SN
types. We are motivated to identify Type Ia SNe based only on broadband
photometric information, since spectroscopic determination of the SN type, the
traditional method, requires significant amounts of time on large telescopes.
We consider the possible observables provided by a large synoptic photometry
survey. We examine the optical colors and magnitudes of many SN types from
z=0.1 to z=1.0, using space-based ultraviolet spectra and ground-based optical
spectra to simulate the photometry. We also discuss the evolution of colors
over the SN outburst and the use of host galaxy characteristics to aid in the
identification of Type Ia SNe. We consider magnitudes in both the SDSS
photometric system and in a proposed filter system with logarithmically spaced
bandpasses. We find that photometric information in four bands covering the
entire optical spectrum appears capable of providing identification of Type Ia
SNe based on their colors at a single observed epoch soon after maximum light,
even without independent estimates of the SN redshift. Very blue filters are
extremely helpful, as at moderate redshift they sample the restframe
ultraviolet spectrum where the SN types are very different. We emphasize the
need for further observations of SNe in the restframe ultraviolet to fully
characterize, refine, and improve this method of SN type identification.Comment: AASTeX, 37 pages with 12 figures, being resubmitted to A.J. Figures
3, 4 and 9 updated, minor typos correcte
Strong Clustering of Faint Galaxies at Small Angular Scales
The 2-point angular correlation function of galaxies, \wt, has been computed
on equatorial fields observed with the CTIO 4m prime focus, within a total area
of 2.31 deg. In the magnitude range , corresponding to
, we find an excess of power in \wt at scales over what would be expected from an extrapolation of \wt measured at
larger . The significance of this excess is . At
larger scales, , the amplitude of \wt is 1.6 times
smaller than the standard no evolutionary model. At these scales there is
remarkable agreement between the present data and Infante \& Pritchet (1995).
At large angular scales () the data is best described
by a model where clustering evolution in has taken place. Strong
luminosity evolution cannot be ruled out with the present data. At smaller
scales, , our data are formally fit by models where
Mpc) or Mpc
. If the mean redshift of our sample is 0.35 then our
data show a clear detection of the scale () where the
clustering evolution approaches a highly non linear regime, i.e., .
The rate at which galaxies merge has been computed. If this rate is
proportional to , then .Comment: 10 pages, LaTeX text, 2 Postscript figures, To appear in ApJ Let
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