16,015 research outputs found

### The Role of Stellar Feedback and Dark Matter in the Evolution of Dwarf Galaxies

Supernova and multiple supernova events regulate several structural
properties of dwarf galaxies. In particular, they govern the metal enrichment
and the energy budget of the ISM; they might induce partial (blowout) or total
(blowaway) gas removal from the galaxy; the morphology of the galactic gaseous
body. Significant amounts of dark matter may play an equally important role:
the dark matter gravitational potential tends to concentrate baryons towards
the center, thus enhancing both the star formation rate and metal production.
Also, the dynamical properties of the ISM, and the occurrence of a blowout or
blowaway are shown to be determined by the dark matter content. We present
detailed analytical/numerical models describing the evolution of dwarf
Irregular galaxies including the above and other effects. The main results are:
(i) dwarfs with total masses M\simlt 5\times 10^6 M_\odot are blown away;
those with gas masses up to $\simeq 10^9 M_\odot$ lose mass in an outflow; (ii)
metallicities are found to correlate tightly with dark matter content and are
consistent with a range of dark-to-visible mass ratios $\phi\approx 0-30$ with
about 65% of the dwarfs in the sample having $\phi\approx 0-10$; (iii) we
predict a lower limit to the oxygen abundance in dIs of $12+log(O/H)\approx
7.2$; (iv) outflows are not particularly important for the metallicity
evolution of dwarf galaxies and certainly less than star formation for gas
consumption; however, dwarfs with gas masses few $\times 10^8 M_\odot$ are
shown to be the major pollutants of the IGM; (v) the ISM HI velocity dispersion
correlates with metallicity and, indepentently of dark matter, scales as
$Z^{3.5}$. (Abridged)Comment: 56 pages, aasms4.sty, LaTeX, 12 figures. MNRAS, submitte

### Superconformal Field Theories, Multiplet Shortening, and the AdS$_5$/SCFT$_4$ Correspondence

We review the unitarity bounds and the multiplet shortening of UIR's of 4
dimensional superconformal algebras $SU(2,2|N)$, ($N=1,2,4$) in view of their
dual role in the AdS/SCFT correspondence. Some applications to KK spectra,
non-perturbative states and stringy states are given.Comment: minor changes, references adde

### Probing high-redshift galaxies with Ly$\alpha$ intensity mapping

We present a study of the cosmological Ly$\alpha$ emission signal at $z > 4$.
Our goal is to predict the power spectrum of the spatial fluctuations that
could be observed by an intensity mapping survey. The model uses the latest
data from the HST legacy fields and the abundance matching technique to
associate UV emission and dust properties with the halos, computing the
emission from the interstellar medium (ISM) of galaxies and the intergalactic
medium (IGM), including the effects of reionization, self-consistently. The
Ly$\alpha$ intensity from the diffuse IGM emission is 1.3 (2.0) times more
intense than the ISM emission at $z = 4(7)$; both components are fair tracers
of the star-forming galaxy distribution. However the power spectrum is
dominated by ISM emission on small scales ($k > 0.01 h{\rm Mpc}^{-1}$) with
shot noise being significant only above $k = 1 h{\rm Mpc}^{-1}$. At very lange
scales ($k < 0.01h{\rm Mpc}^{-1}$) diffuse IGM emission becomes important. The
comoving Ly$\alpha$ luminosity density from IGM and galaxies, $\dot \rho_{{\rm
Ly}\alpha}^{\rm IGM} = 8.73(6.51) \times 10^{40} {\rm erg}{\rm s}^{-1}{\rm
Mpc}^{-3}$ and $\dot \rho_{{\rm Ly}\alpha}^{\rm ISM} = 6.62(3.21) \times
10^{40} {\rm erg}{\rm s}^{-1}{\rm Mpc}^{-3}$ at $z = 4(7)$, is consistent with
recent SDSS determinations. We predict a power $k^3 P^{{\rm Ly}\alpha}(k,
z)/2\pi^2 = 9.76\times 10^{-4}(2.09\times 10^{-5}){\rm nW}^2{\rm m}^{-4}{\rm
sr}^{-2}$ at $z = 4(7)$ for $k = 0.1 h {\rm Mpc}^{-1}$.Comment: 14 Pages, 13 figure

### The Hubble Deep Field Reveals a Supernova at z~0.95

We report the discovery of a variable object in the Hubble Deep Field North
(HDF-N) which has brightened, during the 8.5 days sampled by the data, by more
than 0.9 mag in I and about 0.7 mag in V, remaining stable in B. Subsequent
observations of the HDF-N show that two years later this object has dimmed back
to about its original brightness in I. The colors of this object, its
brightness, its time behavior in the various filters and the evolution of its
morphology are consistent with being a Type Ib supernova in a faint galaxy at
z~0.95.Comment: 5 pages including 2 figures. Accepted for publication in MNRA

### Molecular hydrogen in damped Ly-alpha systems: clues to interstellar physics at high-redshift

In order to interpret H2 (molecular hydrogen) quasar absorption line
observations of damped Ly-alpha systems (DLAs) and sub-DLAs, we model their H2
abundance as a function of dust-to-gas ratio, including H2 self-shielding and
dust extinction against dissociating photons. Then, we constrain the physical
state of gas by using H2 data. Using H2 excitation data for DLA with H2
detections, we derive a gas density 1.5 < log n [cm^-3] < 2.5, temperature 1.5
< log T [K] < 3, and internal UV radiation field (in units of the Galactic
value) 0.5 < log \chi < 1.5. We then find that the observed relation between
molecular fraction and dust-to-gas ratio of the sample is naturally explained
by the above conditions. However, it is still possible that H2 deficient DLAs
and sub-DLAs with H2 fractions less than ~ 10^-6 are in a more diffuse and
warmer state. The efficient photodissociation by the internal UV radiation
field explains the extremely small H2 fraction (< 10^-6) observed for \kappa <
1/30 (\kappa is the dust-to-gas ratio in units of the Galactic value); H2
self-shielding causes a rapid increase and the large variations of H2 abundance
for \kappa > 1/30. We finally propose an independent method to estimate the
star formation rates of DLAs from H2 abundances; such rates are then critically
compared with those derived from other proposed methods. The implications for
the contribution of DLAs to the cosmic star formation history are briefly
discussed.Comment: 15 pages, 5 figures, accepted for publication in MNRA

### Some Pathways in non-Linear Supersymmetry: Special Geometry Born-Infeld's, Cosmology and dualities

This review is devoted to some aspects of non-linear Supersymmetry in four
dimensions that can be efficiently described via nilpotent superfields, in both
rigid and curved Superspace. Our focus is mainly on the partial breaking of
rigid $N=2$ Supersymmetry and on a class of generalized Born-Infeld systems
that originate from Special Geometry and on some prototype cosmological models,
starting from the Supergravity embedding of Starobinsky inflation. However, as
an aside we also review briefly some interesting two-field extensions of the
Born-Infeld Lagrangian whose field equations enjoy extended duality symmetries.Comment: Contribution to the Proceedings of "Group Theory, Probability, and
the Structure of Spacetime", A Conference on the Occasion of Professor V.S.
Varadarajan's Retirement, UCLA Mathematics Department, November 7-9, 2014. To
appear in a special issue of "p-Adic Numbers, Ultrametric Analysis and
Applications". 35 pages LaTeX, 1 eps figure. Typos corrected, reference adde

### Massive Born--Infeld and Other Dual Pairs

We consider massive dual pairs of p-forms and (D-p-1)-forms described by
non-linear Lagrangians, where non-linear curvature terms in one theory
translate into non-linear mass-like terms in the dual theory. In particular,
for D=2p and p even the two non-linear structures coincide when the non-linear
massless theory is self-dual. This state of affairs finds a natural realization
in the four-dimensional massive N=1 supersymmetric Born-Infeld action, which
describes either a massive vector multiplet or a massive linear (tensor)
multiplet with a Born-Infeld mass-like term. These systems should play a role
for the massive gravitino multiplet obtained from a partial super-Higgs in N=2
Supergravity.Comment: 17 pages, LaTeX. Misprints corrected. Final version to appear in JHE

### N=8 non-BPS Attractors, Fixed Scalars and Magic Supergravities

We analyze the Hessian matrix of the black hole potential of N=8, d=4
supergravity, and determine its rank at non-BPS critical points, relating the
resulting spectrum to non-BPS solutions (with non-vanishing central charge) of
N=2, d=4 magic supergravities and their ``mirror'' duals. We find agreement
with the known degeneracy splitting of N=2 non-BPS spectrum of generic special
Kahler geometries with cubic holomorphic prepotential. We also relate non-BPS
critical points with vanishing central charge in N=2 magic supergravities to a
particular reduction of the N=8, 1/8-BPS critical points.Comment: 1+25 pages, 4 Tables, no figures; v2: minor changes and corrections,
Ref. adde

### Bulk Gauge Fields in AdS Supergravity and Supersingletons

We describe conformal operators living at the boundary of $AdS_{d+1}$ in a
general setting. Primary conformal operators at the threshold of the unitarity
bounds of UIR's of O(d,2) correspond to singletons and massless fields in
$AdS_{d+1}$, respectively. For maximal supersymmetric theories in $AdS_{d+1}$
we describe ``chiral'' primary short supermultiplets and non-chiral primary
long supermultiplets. Examples are exhibited which correspond to KK and string
states. We give the general contribution of a primary conformal operator to the
OPE and Green's functions of primary fields, which may be relevant to compute
string corrections to the four-point supergraviton amplitude in Anti-de-Sitter
space. The material in this paper was presented by one of the authors (S.F) at
String 98, Santa Barbara.Comment: 16 pages, harvmac, String 98 on-line proceeding

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