Large-Scale Asymmetry of Rotation Curves in Lopsided Spiral Galaxies

Many spiral galaxies show a large-scale asymmetry with a cos\phi dependence in their rotation curves as well as in their morphology, such as M101 and NGC 628. We show that both these features can be explained by the response of a galactic disk to an imposed lopsided halo potential. A perturbation potential of 5 % is deduced for the morphologically lopsided galaxies in the Rix & Zaritsky (1995) sample. This is shown to result in a difference of 10 % or about 20-30 kms^{-1} in the rotation velocity on the two sides of the major axis. Interestingly, the observed isophotal asymmetry in a typical spiral galaxy is not much smaller and it results in a velocity asymmetry of 7 % or about 14-21 kms^{-1} . Hence, we predict that most galaxies show a fairly significant rotational asymmetry. The rotation velocity is shown to be maximum along the elongated isophote - in agreement with the observations along the SW in M101, while it is minimum along the opposite direction. This result leads to the distinctive asymmetric shape of the rotation curve which rises more steeply in one half of the galaxy than the other, as observed by Swaters et al. (1999). This shape is shown to be a robust feature and would result for any centrally concentrated disk. The net disk lopsidedness and hence the asymmetry in the rotation curve is predicted to increase with radius and hence can be best studied using HI gas as the tracer.Comment: 30 pages, accepted for publication in A &

Q criterion for disc stability modified by external tidal field

The standard Q criterion (with Q > 1) describes the local stability of a disc supported by rotation and random motion. Most astrophysical discs, however, are under the influence of an external gravitational field which can affect their stability. A typical example is a galactic disc embedded in a dark matter halo. Here we do a linear perturbation analysis for a disc in an external field, and obtain a generalized dispersion relation and a modified stability criterion. An external field has two effects on the disc dynamics: first, it contributes to the unperturbed rotational field, and second, it adds a tidal field term in the stability parameter. A typical disruptive tidal field results in a higher modified Q value and hence leads to a more stable disc. We apply these results to the Milky Way, and to a low surface brightness galaxy UGC 7321. We find that in each case the stellar disc by itself is barely stable and it is the dark matter halo that stabilizes the disc against local, axisymmetric gravitational instabilities. This result has been largely missed so far because in practice the value for Q for a galactic disc is obtained in a hybrid fashion using the observed rotational field that is set by both the disc and the halo, and hence is higher than for a pure disc.Comment: 7 pages, 3 figures, submitted to MNRA

The Influence of Capital Controls on Long Run Growth: Where and How Much?

The recent financial crisis in East Asia generated a revival of interest in the merits of financial openness. The ensuing debate on the benefits of openness has focused more on short and medium run issues than on the long run effects. Within the empirical literature on economic growth, little or no attention has been paid to the effects of financial openness. Contrary to the orthodox position, the few results that exist suggest that capital controls have no effect on economic growth. This paper argues that this conclusion emerges from a failure to account for underlying differences across countries with similar degrees of capital controls. I show that the degree of ethnic and linguistic heterogeneity in a country plays a significant role in explaining the effects of controls on economic growth. For countries with relatively higher degrees of ethnic heterogeneity, the effects are particularly adverse whereas for countries with high degrees of homogeneity, capital controls actually have a net positive effect on economic growth. On balance, more developing countries suffered due to controls than not. Within the sample of 57 non OECD countries that did implement controls for the period 1975-95, as many as 39 saw a reduction in their growth rates. This result is robust to a number of variables commonly used in the economic growth regressions.Economic Growth, Capital Controls, Ethno-Linguistic Fractionalization

Can Skill Biased Technological Progress Have a Role in the Decline of the Savings Rate?

This paper explores the consequences of skill biased technological progress on the savings rates. The literature, both theoretical and empirical, on the causes and consequences of skill biased technological progress in the past few years has burgeoned considerably. So has the literature on declining household savings, motivated by the American experience over the past couple of decades. I present a general equilibrium model where declining savings rates emerges as an outcome of exogenously driven skill biased technological progress. The link between the two is attributed to optimizing behavior of altruistic households. In an overlapping generations model, parents are assumed to derive utility from both spending on their children's education and making monetary transfers (or bequests). I show that increases in the growth rate of skill biased technological change causes a shift in allocations away from bequests in favor of education- leading to a decline in domestic capital accumulation. The analysis is extended to incorporate life cycle savings both under certainty and uncertainty regarding the timing of death.Technological Change, Savings, overlapping Generations,Human Capital, Growth

The Rise in Returns to Education and the Decline in Household Savings

This paper explores the consequences of rising returns to human capital investment on the personal savings rate. Over the past two decades, the return to college education has increased relative to high school education leading economists to argue the presence of 'skill biased technological progress'. The literature explaining household savings has also burgeoned considerably, motivated by its declining rate in the US over the past couple of decades. Stylized facts suggest a negative relationship between returns to education and savings rates across most of the past century and also a negative relationship between education spending and savings rates across OECD countries. In this paper, we present a model where a declining savings rate emerges as an outcome of an exogenously driven increase in the return to education. The link between the two is attributed to optimizing behavior of altruistic households. The results of our model are robust to the inclusion of life cycle savings and unintentional bequests. Some of the interesting results of our model are (i) a rise in the return to education raises education spending ratio by less than what it reduces the aggregate savings rate (ii) for some parameter values it actually reduces both the education spending rate and the aggregate savings rate and finally, (iii) it also raises the return to capital due to physical capital-human capital complementarity.Skill Biased Technological Change, Savings, Education, Economic Growth