131 research outputs found
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
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
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&
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