Supernovae and Stellar Wind in the Interstellar Medium

Modern concepts of the influence of supernovae and stellar winds on the interstellar gas are briefly summarized. Preliminary observational data for two unique objects in the galaxy IC1613 are presented by means of illustration: a nebula associated with a rare W0 star and a supernova remnant.     

基于NPSVM模型的超新星识别方法

巡天观测与高能物理、黑洞天文等领域均有密切的联系.基于星系-超新星二分类问题,研究光谱数据预处理,结合余弦相似度改善PCA(Principal Component Analysis)光谱分解特征提取方法,用SDSS(the Sloan Digital Sky Survey)、WISeREP(the Weizmann Interactive Supernova data REPository)组成的5620条光谱数据集训练支持向量机,可以得到0.498%泛化误差的识别模型和新样本分类概率.使用Neyman-Pearson决策方法建立NPSVM(Neyman-Pearson Support Vector Machine)模型可进一步降低超新星的漏判率.     

The galactic evolution of the supernova rates

Supernova rates (hypernova, type II, type Ib/c and type Ia) in a particular galaxy depend on the metallicity (i.e. on the galaxy age), on the physics of star formation and on the binary population. In order to study the time evolution of the galactic supernova rates, we use our chemical evolutionary model that accounts in detail for the evolution of single stars and binaries. In particular, supernovae of type Ia are considered to arise from exploding white dwarfs in interacting binaries and we adopt the two most plausible physical models: the single degenerate model and the double degenerate model. Comparison between theoretical prediction and observations of supernova rates in different types of galaxies allows to put constraints on the population of intermediate mass and massive close binaries.

The temporal evolution of the absolute galactic rates of different types of supernovae (including the type Ia rate) is presented in such a way that the results can be directly implemented into a galactic chemical evolutionary model. Particularly for type Ia’s the inclusion of binary evolution leads to results considerably different from those in earlier population synthesis approaches, in which binary evolution was not included in detail.     

Do Type Ia supernovae prove Λ>0?

The evidence for positive cosmological constant Λ from Type Ia supernovae is re-examined.
Both high redshift supernova teams are found to underestimate the effects of host galaxy extinction. The evidence for an absolute magnitude–decay time relation is much weakened if supernovae not observed before maximum light are excluded. Inclusion of such objects artificially suppresses the scatter about the mean relation.
With a consistent treatment of host galaxy extinction and elimination of supernovae not observed before maximum, the evidence for a positive lambda is not very significant  (3–4 σ )  . A factor which may contribute to apparent faintness of high- z supernovae is evolution of the host galaxy extinction with z .
The Hubble diagram using all high- z distance estimates, including SZ clusters and gravitational lens time-delay estimates, does not appear inconsistent with an  Ω_o=1  model.
Although a positive Λ can provide an (albeit physically unmotivated) resolution of the low curvature implied by cosmic microwave background (CMB) experiments and evidence that  Ω_o<1  from large-scale structure, the direct evidence from Type Ia supernovae seems at present to be inconclusive.     

The influence of host galaxy morphology on the properties of Type Ia supernovae from the JLA compilation

The observational cosmology with distant Type Ia supernovae (SNe) as standard candles claims that the Universe is in accelerated expansion, caused by a large fraction of dark energy. In this paper we investigate the SN Ia environment, studying the impact of the nature of their host galaxies on the Hubble diagram fitting. The supernovae (192 SNe) used in the analysis were extracted from Joint-Light-curves-Analysis (JLA) compilation of high-redshift and nearby supernovae which is the best one to date. The analysis is based on the empirical fact that SN Ia luminosities depend on their light curve shapes and colors. We confirm that the stretch parameter of Type Ia supernovae is correlated with the host galaxy type. The supernovae with lower stretch are hosted mainly in elliptical and lenticular galaxies. No significant correlation between SN Ia colour and host morphology was found. We also examine how the luminosities of SNe Ia change depending on host galaxy morphology after stretch and colour corrections. Our results show that in old stellar populations and low dust environments, the supernovae are slightly fainter. SNe Ia in elliptical and lenticular galaxies have a higher α (slope in luminosity-stretch) and β (slope in luminosity-colour) parameter than in spirals. However, the observed shift is at the 1-σ uncertainty level and, therefore, can not be considered as significant. We confirm that the supernova properties depend on their environment and that the incorporation of a host galaxy term into the Hubble diagram fit is expected to be crucial for future cosmological analyses.     

ISO Observations of Freshly Synthesized Supernova Material

ISOCAM observations of Cassiopeia A (Cas A), the youngest supernova remnant known in our galaxy, are discussed. We show how these observations are of interest for the so-called Cas A Neon problem and how these observations have renewed the interest in supernovae as dust factories. This revised version was published online in August 2006 with corrections to the Cover Date.     

Spectrum of the relic neutrino background from past supernovae and cosmological models

It is greatly expected that the relic neutrino background from past supernovae will be detected by Superkamiokande (SK) which is now under construction. We calculate the spectrum and the event rate at SK systematically by using the results of simulations of a supernova explosion and reasonable supernova rates. We also investigate the effect of a cosmological constant, Λ, on the spectrum, since some recent cosmological observations strongly suggest the existence of Λ. We find following results. (1) The spectrum has a peak at about 3 MeV, which is much lower than that of previous estimates (6–10 MeV). (2) The event rate at SK in the range from 10 MeV to 50 MeV, where the relic neutrinos from past supernovae are dominant, is about 25h₅₀²(R_SN/0.1 yr⁻¹)(n_Gh₅₀⁻³/0.02 Mpc⁻³) events per year, where R_SN is the supernova rate in a galaxy, n_G is the number density of galaxies, and h₅₀ = H₀/(50 km/s Mpc), where H₀ is the Hubble constant. (3) The event rate is almost insensitive to Λ. The flux increases in the low energy side (< 10 MeV) with increasing Λ, but decreases in the high energy side (> 10 MeV) in models in which the integrated number of supernovae in one galaxy is fixed.     

Testing Bekenstein's relativistic Modified Newtonian Dynamics with lensing data

We propose to use multiple-imaged gravitational lenses to set limits on gravity theories without dark matter, specifically tensor–vector–scalar (TeVeS) theory, a theory which is consistent with fundamental relativistic principles and the phenomenology of Modified Newtonian Dynamics (MOND) theory. After setting the framework for lensing and cosmology, we analytically derive the deflection angle for the point lens and the Hernquist galaxy profile, and study their patterns in convergence, shear and amplification. Applying our analytical lensing models, we fit galaxy-quasar lenses in the CfA-Arizona Space Telescope Lens Survey (CASTLES) sample. We do this with three methods, fitting the observed Einstein ring sizes, the image positions, or the flux ratios. In all the cases, we consistently find that stars in galaxies in MOND/TeVeS provide adequate lensing. Bekenstein's toy μ function provides more efficient lensing than the standard MOND μ function. But for a handful of lenses, a good fit would require a lens mass orders of magnitude larger/smaller than the stellar mass derived from luminosity unless the modification function μ and modification scale a ₀ for the universal gravity were allowed to be very different from what spiral galaxy rotation curves normally imply. We discuss the limitation of present data and summarize constraints on the MOND μ function. We also show that the simplest TeVeS 'minimal-matter' cosmology, a baryonic universe with a cosmological constant, can fit the distance–redshift relation from the supernova data, but underpredicts the sound horizon size at the last scattering. We conclude that lensing is a promising approach to differentiate laws of gravity.     

Was Supernova 1997ff at z∼ 1.7 magnified by gravitational lensing?

The quest for the cosmological parameters has come to fruition with the identification of a number of supernovae at a redshift of     . Analyses of the brightness of these standard candles reveal that the Universe is dominated by a large cosmological constant. The recent identification of the     SN 1997ff in the northern Hubble Deep Field has provided further evidence for this cosmology. Here we examine the case for gravitational lensing of SN 1997ff owing to the presence of galaxies lying along our line of sight. We find that, while the alignment of SN 1997ff with foreground masses is not favourable for it to be multiply imaged and strongly magnified, two galaxies do lie close enough to result in significant magnification:     for the case where these elliptical galaxies have a velocity dispersion of 200 km s⁻¹. Given the small difference between supernova brightnesses in different cosmologies, detailed modelling of the gravitational lensing properties of the intervening matter is therefore required before the true cosmological significance of SN 1997ff can be deduced.     

Self-Regulating Supernova Heating in Interstellar Medium Simulations

Numerical simulations of the multi-phase interstellar medium have been carried out, using a 3D, nonlinear, magnetohydrodynamic, shearing-box model, with random motions driven by supernova explosions. These calculations incorporate the effects of magnetic fields and rotation in 3D; these play important dynamical roles in the galaxy, but are neglected in many other simulations. The supernovae driving the motions are not arbitrarily imposed, but occur where gas accumulates into cold, dense clouds; their implementation uses a physically motivated model for the evolution of such clouds. The process is self-regulating, and produces mean supernova rates as part of the solution. Simulations with differing mean density show a power law relation between the supernova rate and density, with exponent 1.7; this value is within the range suggested from observations (taking star formation rate as a proxy for supernova rate). The global structure of the supernova driven medium is strongly affected by the presence of magnetic fields; e.g. for one solution the filling factor of hot gas is found to vary from 0.19 (with no field) to 0.12 (with initial mid-plane field B ₀ = 6 μG).     

Supernova remnants and the spiral structure of the Galaxy

A set of unit clouds of 10⁴ M randomly distributed between 3 and 7 kpc radii, move under the general gravitation of the galactic disk and their mutual gravitation. When the clouds collide they form loose aggregates or giant molecular clouds (GMC). Star formation rate is assumed to be proportional to the mass of the GMC. The more massive stars formed soon turn into supernovae, which in turn break up the GMC back into the unit clouds. After some 350 Myr a steady state is reached, in which the GMCs have a mass spectrum of gradient −1.6, and has the mass-radius relation M ∞ R², both in agreement with the observations. From our simulation we find there should be 775 ± 12 supernova remnants in our galaxy. The existence of spiral arms does not increase the production rate of supernova remnants, but it does make the GMCs to concentrate around them.     

A model of supernova feedback in galaxy formation

A model of supernova feedback during disc galaxy formation is developed. The model incorporates infall of cooling gas from a halo, and outflow of hot gas from a multiphase interstellar medium (ISM). The star formation rate is determined by balancing the energy dissipated in collisions between cold gas clouds with that supplied by supernovae in a disc marginally unstable to axisymmetric instabilities. Hot gas is created by thermal evaporation of cold gas clouds in supernova remnants, and criteria are derived to estimate the characteristic temperature and density of the hot component and hence the net mass outflow rate. A number of refinements of the model are investigated, including a simple model of a galactic fountain, the response of the cold component to the pressure of the hot gas, pressure-induced star formation and chemical evolution. The main conclusion of this paper is that low rates of star formation can expel a large fraction of the gas from a dwarf galaxy. For example, a galaxy with circular speed 50 km s¹ can expel 6080 per cent of its gas over a time-scale of 1 Gyr, with a star formation rate that never exceeds 0.1 M yr¹. Effective feedback can therefore take place in a quiescent mode and does not require strong bursts of star formation. Even a large galaxy, such as the Milky Way, might have lost as much as 20 per cent of its mass in a supernova-driven wind. The models developed here suggest that dwarf galaxies at high redshifts will have low average star formation rates and may contain extended gaseous discs of largely unprocessed gas. Such extended gaseous discs might explain the numbers, metallicities and metallicity dispersions of damped Lyman systems.     

The Hubble constant from galaxy lenses: impacts of triaxiality and model degeneracies

The Hubble constant can be constrained using the time delays between multiple images of gravitationally lensed sources. In some notable cases, typical lensing analyses assuming isothermal galaxy density profiles produce low values for the Hubble constant, inconsistent with the result of the HST Key Project  (72 ± 8 km s⁻¹ Mpc⁻¹)  . Possible systematics in the values of the Hubble constant derived from galaxy lensing systems can result from a number of factors, for example, neglect of environmental effects, assumption of isothermality, or contamination by line-of-sight structures. One additional potentially important factor is the triaxial structure of the lensing galaxy halo; most lens models account for halo shape simply by perturbing the projected spherical lensing potential, an approximation that is often necessary but that is inadequate at the levels of triaxiality predicted in the cold dark matter paradigm. To quantify the potential error introduced by this assumption in estimates of the Hubble parameter, we strongly lens a distant galaxy through a sample of triaxial softened isothermal haloes and use an Markov Chain Monte Carlo method to constrain the lensing halo profile and the Hubble parameter from the resulting multiple image systems. We explore the major degeneracies between the Hubble parameter and several parameters of the lensing model, finding that without a way to accurately break these degeneracies accurate estimates of the Hubble parameter are not possible. Crucially, we find that triaxiality does not significantly bias estimates of the Hubble constant, and offer an analytic explanation for this behaviour in the case of isothermal profiles. Neglected triaxial halo shape cannot contribute to the low Hubble constant values derived in a number of galaxy lens systems.     

The Origin of the Element Eu in Extremely Metal-poor Halo Stars

The fast neutron capture process (the r-process) occurs in the neutron-rich circumstance. However its concrete physical environment is not very clear. With recent progress in observations, many extremely metal-poor halo stars have been discovered. They have two characteristics: one is the overabundance of fast neutron elements with the relative abundance consistent with that of the sun; the other is that fast neutron element contents in stars at the same metal abundance have a very large dispersion. This provides a particular way to study the origin of the r-process. Simulation was used to study the galaxy's evolution process and the resulting dispersion of fast neutron nuclide contents in stars. The model of galaxy evolution obtained in this way not only contains spontaneous star formation in the gas region, but also includes the star formation excited by the supernova explosion. It is shown from our results that the supernovae at the low mass end should be the place producing the fast neutron nuclides. In addition, it is also shown that the non-uniformity of the galaxy evolution caused by the supernova explosion is not enough to explain the observed dispersion of fast neutron element contents in halo stars. This problem should be further studied.     

Weak lensing magnification reconstruction with the modified internal linear combination method

Measuring weak lensing cosmic magnification signal is very challenging due to the overwhelming intrinsic clustering in the observed galaxy distribution.In this paper,we modify the Internal Linear Combination (ILC) method to reconstruct the lensing signal with an extra constraint to suppress the intrinsic clustering.To quantify the performance,we construct a realistic galaxy catalogue for the LSST-like photometric survey,covering 20 000 deg~2 with mean source redshift at z_s~1.We find that the reconstruction performance depends on the width of the photo-z bin we choose.Due to the correlation between the lensing signal and the source galaxy distribution,the derived signal has smaller systematic bias but larger statistical uncertainty for a narrower photo-z bin.We conclude that the lensing signal reconstruction with the Modified ILC method is unbiased with a statistical uncertainty5%for bin width?z~P=0.2.     

Asiago Supernova classification program: Blowing out the first two hundred candles

We present the compilation of the first 221 supernovae classified during the Asiago Classification Program (ACP). The details of transients classification and the preliminarily reduced spectra, in fits format, are immediately posted on the Padova‐Asiago SN group web site. The achieved performances for the first 2 years of the ACP are analysed, showing that half of all our classifications were made within 5 days from transient detection. The distribution of the supernova types of this sample resembles the distribution of the general list of all the supernovae listed in the Asiago SN catalog (ASNC, Barbon et al. 1999). Finally, we use our subsample of 78 core‐collapse supernovae, for which we retrieve the host‐galaxy morphology and r ‐band absolute magnitudes, to study the observed subtype distribution in dwarf compared to giant galaxies. This ongoing program will give its contribution to the classification of the large number of transients that will be soon delivered by the Gaia mission. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Angular cross-correlation of galaxies: a probe of gravitational lensing by large-scale structure

The angular cross-correlation between two galaxy samples separated in redshift is shown to be a useful measure of weak lensing by large-scale structure. Angular correlations in faint galaxies arise as a result of spatial clustering of the galaxies as well as gravitational lensing by dark matter along the line of sight. The lensing contribution to the two-point autocorrelation function is typically small compared with the gravitational clustering. However, the cross-correlation between two galaxy samples is almost unaffected by gravitational clustering provided that their redshift distributions do not overlap. The cross-correlation is then induced by magnification bias resulting from lensing by large-scale structure. We compute the expected amplitude of the cross-correlation for popular theoretical models of structure formation. For two populations with mean redshifts of ≃0.3 and 1, we find a cross-correlation signal of ≃1 per cent on arcmin scales and ≃3 per cent on scales of a few arcsec. The dependence on the cosmological parameters Ω and Λ, the dark matter power spectrum and the bias factor of the foreground galaxy population is explored.     

QSO lensing magnification associated with galaxy groups

We simulated both the matter and light (galaxy) distributions in a wedge of the Universe and calculated the gravitational lensing magnification caused by the mass along the line-of-sight of galaxies and galaxy groups identified in sky surveys. A large volume redshift cone containing cold dark matter particles mimics the expected cosmological matter distribution in a flat universe with low matter density and a cosmological constant. We generate a mock galaxy catalogue from the matter distribution and identify thousands of galaxy groups in the luminous sky projection. We calculate the expected magnification around galaxies and galaxy groups and then the induced quasi-stellar object (QSO)–lens angular correlation due to magnification bias. This correlation is observable and can be used both to estimate the average mass of the lens population and to make cosmological inferences. We also use analytical calculations and various analyses to compare the observational results with theoretical expectations for the cross-correlation between faint QSOs from the 2dF Survey and nearby galaxies and groups from the Automated Plate Measurement and Sloan Digital Sky Survey Early Data Release. The observed QSO–lens anticorrelations are stronger than the predictions for the cosmological model used. This suggests that there could be unknown systematic errors in the observations and data reduction, or that the model used is not adequate. If the observed signal is assumed to be solely due to gravitational lensing, then the lensing is stronger than expected, due to more massive galactic structures or more efficient lensing than simulated.     

Modelling galaxy–galaxy weak lensing with Sloan Digital Sky Survey groups

We use galaxy groups selected from the Sloan Digital Sky Survey (SDSS) together with mass models for individual groups to study the galaxy–galaxy lensing signals expected from galaxies of different luminosities and morphological types. We compare our model predictions with the observational results obtained from the SDSS by Mandelbaum et al. for the same samples of galaxies. The observational results are well reproduced in a Λ cold dark matter (ΛCDM) model based on the Wilkinson Microwave Anisotropy Probe ( WMAP ) 3-yr data, but a ΛCDM model with higher σ₈, such as the one based on the WMAP 1-yr data, significantly overpredicts the galaxy–galaxy lensing signal. We model, separately, the contributions to the galaxy–galaxy lensing signals from different galaxies: central versus satellite, early type versus late type and galaxies in haloes of different masses. We also examine how the predicted galaxy–galaxy lensing signal depends on the shape, density profile and the location of the central galaxy with respect to its host halo.     

A complete infrared Einstein ring in the gravitational lens system B1938 + 666

We report the discovery, using NICMOS on the Hubble Space Telescope , of an arcsec-diameter Einstein ring in the gravitational lens system B1938+666. The lensing galaxy is also detected, and is most likely an early-type galaxy. Modelling of the ring is presented and compared with the radio structure from MERLIN maps. We show that the Einstein ring is consistent with the gravitational lensing of an extended infrared component, centred between the two radio components.