Starbursts in isolated galaxies. I. The influence of stellar birth function and IMF

Starbursts and substantial variations in the star formation histories are a common phenomenon in galaxies. We study the stability properties of isolated star-forming dwarf galaxies with the aim of identifying starburst modes. The impact of the stellar birth function, the initial mass function (IMF), the stellar feedback and the interstellar medium (ISM) model are investigated. We apply a one-zone model for a star-gas system coupled by mass and energy transfer. Additionally, we extend the network for active dynamical evolution. This allows for a coupling between the dynamical state of the galaxy and its internal properties. While the influence of the dynamics on the total star formation rate is strong, the coupling of the internal properties (gas temperature) on the dynamics is rather limited, because radiative cooling keeps the gas temperature well below the virial temperature. Because of short cooling and feedback timescales, the star formation rate is close to the equilibrium star formation rates. Quasi-periodic starbursts occur, because star formation follows the variations in the gas density induced by decaying virial oscillations. This behaviour is quite insensitive to the nature and the details of the stellar birth description, viz. whether spontaneous or induced star formation is considered or the IMF is varied. A second type of burst is found as an instability operating when the cooling may drop at very low densities with increasing temperature. Bursts of star formation occur during transitory phases, when dynamical equilibrium is established. Then they are quasi-periodic on the dynamical timescale. Because of short heating and cooling timescales, the star formation rate follows the equilibrium star formation rate corresponding to the actual gas density.Comment: 16 pages, 16 figures, accepted for publication in Astronomy & Astrophysic

The collateral frameworks of the Eurosystem, the Federal Reserve System and the Bank of England and the financial market turmoil

In response to the turmoil in global financial markets which began in the second half of 2007, central banks have changed the way in which they implement monetary policy. This has drawn particular attention to the type of collateral used for backing central banks’ temporary open market operations and the range of counterparties which can participate in these operations. This paper provides an overview of the features of the different operational and collateral frameworks of three central banks that have been significantly affected by the crisis: the Eurosystem, the Federal Reserve System and the Bank of England. The paper describes the factors that shaped the three frameworks prior to the turmoil. It then describes the actions the three central banks took in response to the turmoil and analyses to what extent these actions were dependent on the initial design of the operational and collateral framework. JEL Classification: E52, E58, G01, G20.Collateral Framework, Central Bank Repo Auctions, Collateral, Open Market Operations, Financial Market Turmoil 2007-2009.

Implications for liquidity from innovation and transparency in the European corporate bond market

This paper offers a new framework for the assessment of financial market liquidity and identifies two types: search liquidity and systemic liquidity. Search liquidity, i.e. liquidity in “normal” times, is driven by search costs required for a trader to find a willing buyer for an asset he/she is trying to sell or vice versa. Search liquidity is asset specific. Systemic liquidity, i.e. liquidity in “stressed” times, is driven by the homogeneity of investors - the degree to which one’s decision to sell is related to the decision to sell made by other market players at the same time. Systemic liquidity is specific to market participants’ behaviour. This framework proves fairly powerful in identifying the role of credit derivatives and transparency for liquidity of corporate bond markets. We have applied it to the illiquid segments of the European credit market and found that credit derivatives are likely to improve search liquidity as well as systemic liquidity. However, it is possible that in their popular use today, credit derivatives reinforce a concentration of positions that can worsen systemic liquidity. We also found that post-trade transparency has surprisingly little bearing on liquidity in that where it improves liquidity it is merely acting as a proxy for pre-trade transparency or transparency of holdings. We conclude that if liquidity is the objective, pre-trade transparency, as well as some delayed transparency on net exposures and concentrations, is likely to be more supportive of both search and systemic liquidity than post-trade transparency. JEL Classification: G14, G15, G18.Financial market functioning, liquidity, transparency, credit markets and financial innovation.

The compatibility between work and family life – an empirical study of second birth risks in West Germany and France

In this study, we compare second birth risks in France and West Germany using data from the Family and Fertility Survey (FFS). Second birth risks in France are higher than in West Germany and we investigate whether this phenomenon relates to different institutional constraints regarding the compatibility between work and family life. Considering that education is a good indicator for higher career and income prospects, one would assume that highly educated women encounter low fertility rates in a society that makes it hard to combine both domains. Our results, however, show that second birth risks are higher for highly educated women than for women with lower education in both countries. Nevertheless, the positive effect of women’s education on second birth risks is strong and stable in the case of France only. In West Germany, the positive effect is a weak one and it weakens even further after controlling for the eduaction level of the partner. In France, the strong positive effect of women’s education on second birth risks remains unchanged, even after controlling for the partners’ characteristics and other control variables. Our conclusion is that since in France the compatibility between work and family life is relatively high, highly educated women turn their education into work opportunities and income. In West Germany, where work and family life are rather incompatible, women often have to make a decision between an employment career and motherhood as two exclusive life options. In such a situation, it is primarily the partners’ economic situation that influences fertility.comparative analysis