Observational clues to the progenitors of Type-Ia supernovae

Type-Ia supernovae (SNe Ia) are important distance indicators, element factories, cosmic-ray accelerators, kinetic-energy sources in galaxy evolution, and endpoints of stellar binary evolution. It has long been clear that a SN Ia must be the runaway thermonuclear explosion of a degenerate carbon-oxygen stellar core, most likely a white dwarf (WD). However, the specific progenitor systems of SNe Ia, and the processes that lead to their ignition, have not been identified. Two broad classes of progenitor binary systems have long been considered: single-degenerate (SD), in which a WD gains mass from a non-degenerate star; and double-degenerate (DD), involving the merger of two WDs. New theoretical work has enriched these possibilities with some interesting updates and variants. We review the significant recent observational progress in addressing the progenitor problem. We consider clues that have emerged from the observed properties of the various proposed progenitor populations, from studies of their sites, pre- and post-explosion, from analysis of the explosions themselves, and from the measurement of event rates. The recent nearby and well-studied event, SN 2011fe, has been particularly revealing. The observational results are not yet conclusive, and sometimes prone to competing theoretical interpretations. Nevertheless, it appears that DD progenitors, long considered the underdog option, could be behind some, if not all, SNe Ia. We point to some directions that may lead to future progress.Comment: to appear in Annual Reviews of Astronomy and Astrophysics, 2014. For near-final published version see http://www.annualreviews.org/doi/abs/10.1146/annurev-astro-082812-14103

Stock market firm-level information and real economic activity

We provide evidence that changes in the equity price and volatility of individual firms (measures that approximate the definition of 'granular shock' given in Gabaix, 2010) are key to improve the predictability of aggregate business cycle fluctuations in a number of countries. Specifically, adding the return and the volatility of firm-level equity prices to aggregate financial information leads to a significant improvement in forecasting business cycle developments in four economic areas, at various horizons. Importantly, not only domestic firms but also foreign firms improve business cycle predictability for a given economic area. This is not immediately visible when one takes an unconditional standpoint (i.e. an average across the sample). However, conditioning on the business cycle position of the domestic economy, the relative importance of the two sets of firms - foreign and domestic - exhibits noticeable swings across time. Analogously, the sectoral classification of the firms that in a given month retain the highest predictive power for future IP changes also varies significantly over time as a function of the business cycle position of the domestic economy. Limited to the United States, predictive ability is found to be related to selected balance sheet items, suggesting that structural features differentiate the firms that can anticipate aggregate fluctuations from those that do not help to this aim. Beyond the purely forecasting application, this finding may enhance our understanding of the underlying origins of aggregate fluctuations. We also propose to use the cross sectional stock market information to macro-prudential aims through an economic Value at Risk. JEL Classification: C53, C58, F37, G15Business cycle forecasting, granular shock, international linkages

Type Ia Supernova Rates Near and Far

(ABRIDGED) Recently, three important observational results were established: (a) The evolution of the SNIa rate with redshift show that the rate rises up to z~0.8, when the Universe was 6.5 Gyr old, and decreases afterward. (b) The rate of supernova explosions of the different types as a function of the galaxy (B-K) and the galaxy mass shows a marked increase with the star formation activity. (c) The rate of SNIa in radio-loud galaxies is much higher than the rate measured in radio-quiet galaxies. On this basis we have discussed the distribution of the delay time (DTD) between the formation of a SNIa progenitor star and its explosion as a SNIa. Our analysis finds: i) models with long delay times, say 3-4 Gyr, cannot reproduce the dependence of the SNIa rate on the colors and on the radio-luminosity of the parent galaxies; ii) the dependence of the SNIa rate on the parent galaxy colors requires models with a wide DTD, spanning the interval 100 Myr to 10 Gyr; iii) the dependence on the parent galaxy radio-luminosity requires substantial production of SNIa at epochs earlier than 100 Myr after the birth of a given stellar generation; iv) the comparison between observed SN rates and a grid of theoretical "single-population" DTDs shows that only a few of them are marginally consistent with all observations; v) the present data are best matched by a bimodal DTD, in which about 50% of type Ia SNe ("prompt" SNIa) explode soon after their stellar birth, in a time of the order of 100 Myrs, while the remaining 50% ("tardy" SNIa) have a much wider distribution, well described by an exponential function with a decay time of about 3 Gyr. We discuss the cosmological implications of this result and make simple predictions.Comment: 10 pages, 2 figures, Invited talk at `The Multicoloured Landscape of Compact Objects and their Explosive Origins', Cefalu', 2006 June 11-24 (AIP Conf. Proc.), eds. L.Burderi et al., in pres

Exploring extreme conditions for star formation: a deep search for molecular gas in the Leo ring

We carry out sensitive searches for the CO J=1-0 and J=2-1 lines in the giant extragalactic HI ring in Leo to investigate the star formation process within environments where gas metallicities are close to solar but physical conditions are different than those typical of bright galaxy disks. Our aim is to check the range of validity of known scaling relations. We use the IRAM-30m telescope to observe eleven regions close to HI gas peaks or where sparse young massive stars have been found. For all pointed observations we reached a spectral noise between 1 and 5~mK for at least one observed frequencies at 2~km/s spectral resolution. We marginally detect two CO J=1-0 lines in the star forming region Clump~1 of the Leo ring, whose radial velocities are consistent with those of Halpha lines but line widths are much smaller than observed for virialized molecular clouds of similar mass in galaxies. The low signal-to-noise ratio, the small line widths and the extremely low number densities suggest that a more standard population of molecular clouds, still undetected, might be in place. Using upper limits to the CO lines, the most sensitive pointed observations show that the molecular gas mass surface density is lower than expected from the extrapolation of the molecular Kennicutt-Schmidt relation established in the disk of galaxies. The sparse stellar population in the ring, possibly forming ultra diffuse dwarf galaxies, might then be the result of a short molecular gas depletion time in this extreme environment.}Comment: 11 pages, 7 figures, accepted for publication in A&

The Mass-Metallicity and the Fundamental Metallicity Relation revisited on a fully Te-based abundance scale for galaxies

The relationships between stellar mass, gas-phase metallicity and star formation rate (i.e. the Mass-Metallicity, MZR, and the Fundamental Metallcity Relation, FMR) in the local Universe are revisited by fully anchoring the metallicity determination for SDSS galaxies on the Te abundance scale de ned exploiting the strong-line metallicity calibrations presented in Curti et al. (2017). Self-consistent metallicity measurements allow a more unbiased assessment of the scaling relations involving M, Z and SFR, which provide powerful constraints for the chemical evolution models. We paramet-rise the MZR with a new functional form which allows us to better characterise the turnover mass. The slope and saturation metallicity are in good agreement with pre- vious determinations of the MZR based on the Te method, while showing signi cantly lower normalisation compared to those based on photoionisation models. The Z-SFR dependence at xed stellar mass is also investigated, being particularly evident for highly star forming galaxies, where the scatter in metallicity is reduced up to a factor of 30%. A new parametrisation of the FMR is given by explicitly introducing the SFR-dependence of the turnover mass into the MZR. The residual scatter in metal-licity for the global galaxy population around the new FMR is 0:054 dex. The new FMR presented in this work represents a useful local benchmark to compare theor-etical predictions and observational studies (of both local and high-redshift galaxies) whose metallicity measurements are tied to the abundance scale de ned by the Te method, hence allowing to properly assess its evolution with cosmic time.ERC; STF

Multi-phase outflows in Mkn 848 observed with SDSS-MaNGA Integral Field Spectroscopy

The characterisation of galaxy-scale outflows in terms of their multi-phase nature, amount, and effects of flowing material is crucial to place constraints on models of galaxy evolution. This study can proceed only with the detailed investigation of individual targets. We present a spatially resolved spectroscopic optical data analysis of Mkn 848, a complex system consisting of two merging galaxies at z~0.04 that are separated 7.5 kpc (projected distance). Motivated by the presence of a multi-phase outflow in the north-west system revealed by the SDSS integrated spectrum, we analysed the publicly available MaNGA data, which cover almost the entire merging system, to study the physical properties of cool and warm gas in detail. Galaxy-wide outflowing gas in multiple phases is revealed for the first time in the two merging galaxies. We also detect spatially resolved resonant NaID emission associated with the outflows. The derived outflow energetics may be consistent with a scenario in which both winds are accelerated by stellar processes and AGN activity, although we favour an AGN origin given the high outflow velocities and the ionisation conditions observed in the outflow regions. Deeper observations are required, however, to better constrain the nature of these multi-phase outflows. Outflow energetics in the north-west system are strongly different between the ionised and atomic gas components, the latter of which is associated with mass outflow rate and kinetic and momentum powers that are 1-2 dex higher; those associated with the south-east galaxy are instead similar. Strong kp-scale outflows are revealed in an ongoing merger system, suggesting that feedback can potentially impact the host galaxy even in the early merger phases. The characterisation of the neutral and ionised gas phases has proved to be crucial for a comprehensive study of the outflow phenomena.Comment: 19 pages, 14 figures, accepted for publication in A&

Un ricordo di Francesco Palla

Lo scorso Gennaio è improvvisamente mancato Francesco Palla, direttore dell’Osservatorio Astrofisico di Arcetri fino al 2011, molto conosciuto a Firenze anche per le sua attività di comunicazione della scienza, e tra i fondatori di questa rivista. Ne ricordiamo la figura di scienziato e di divulgatore appassionato.Francesco Palla, Director of the Arcetri Astrophysical Observatory up to 2011, died suddenly last January. He was also well known in Florence for his commitment to spreading knowledge of science and was one of the founders of this journal. Here we should like to remember Francesco in his role of eclectic scientist and passionate communicator