Star formation in grand-design, spiral galaxies. Young, massive clusters in the near-infrared

Deep, near-infrared JHK-maps were observed for 10 nearby, grand-design, spiral galaxies using HAWK-I/VLT to study the distribution of young stellar clusters in them and thereby determine whether strong spiral perturbations can influence star formation. Complete, magnitude-limited candidate lists of star-forming complexes were obtained by searching within the K-band maps. The properties of the complexes were derived from (H-K)-(J-H) diagrams including the identification of the youngest complexes (i.e. <7 Myr) and the estimation of their extinction. Young stellar clusters with ages <7 Myr have significant internal extinction in the range of Av=3-7m, while older ones typically have Av<1m. The cluster luminosity function (CLF) is well-fitted by a power law with an exponent of around -2 and displays no evidence of a high luminosity cut-off. The brightest cluster complexes in the disk reach luminosities of Mk = -15.5m or estimated masses of 10^6 Mo. At radii with a strong, two-armed spiral pattern, the star formation rate in the arms is higher by a factor of 2-5 than in the inter-arm regions. The CLF in the arms is also shifted towards brighter Mk by at least 0.4m. We also detect clusters with colors compatible with Large Magellanic Cloud intermediate age clusters and Milky Way globular clusters. The (J-K)-Mk diagram of several galaxies shows, for the brightest clusters, a clear separation between young clusters that are highly attenuated by dust and older ones with low extinction. The gap in the (J-K)-Mk diagrams implies that there has been a rapid expulsion of dust at an age around 7 Myr, possibly triggered by supernovae. Strong spiral perturbations concentrate the formation of clusters in the arm regions and shifts their CLF towards brighter magnitudes.Comment: 23 pages, 20 figures; Accepted for publication in A&

Mortality and dust expulsion in early phases of stellar clusters. Evidence from NIR photometry of nearby, spiral galaxies

It is often argued that young stellar clusters suffer a significant infant mortality that is partly related to the expulsion of dust and gas in their early phases caused by radiation pressure from hot stars and supernovae. Near-infrared (J-K)-Mk diagrams of young stellar clusters in nearby spiral galaxies show a bi-modal distribution that is consistent with a fast decline of their intrinsic extinction at an early epoch. The distinct features in the color-magnitude diagrams (CMD) and the fast change of colors for the youngest clusters allow us to place constraints on their early evolutionary phases, including the time scale for the decreasing extinction caused for instance by gas and dust expulsion. Monte Carlo simulations of cluster populations were performed using the power-law distribution function g(M, t) ~ M^a t^gam. Integrated colors were computed from Starburst99 models. The simulated near-infrared CMD were compared with those observed for six grand-design, spiral galaxies using statistical goodness-of-fit tests. The CMDs indicate a significant mortality of young, massive clusters with gam = -1.4 +-0.5. High initial extinction Av = 8-11m and strong nebular emission are required to reproduce the bi-modal color distributions of the clusters. An extended star formation phase of longer than 5 Myr is suggested. The reduction of the internal extinction of the clusters starts during their active star formation and lasts for a period of 5-10 Myr.Comment: 5 pages, 3 figures; accepted for publication in A&A Letter

Aging society, health and the environment

Both environmental quality and health care expenditure are determinants of health and life expectancy, but the support for them appears to be different according to the electors' age, with a relatively larger support for health expenditure among the elderly as it is generally effective on a shorter horizon than environmental maintenance. With population aging, the political support for health care expenditure is then self-reinforcing. We cast this issue in an overlapping generations model with endogenous longevity, where lifespan depends on health care expenditure and environmental quality. We compare the long run outcomes for health care expenditure, environmental quality, lifespan, consumption and capital accumulation of an economy where agents vote over health spending and environmental maintenance, with those chosen by a social planner who takes into account also the welfare of future generations. The role played by other factors, such as the propensity for smoothing consumption or the degree of annuity markets, is also highlighted. Empirical evidence of age-biased environmental care is provided.population aging, endogenous longevity, environmental and health expenditure, annuity markets, inter-generational conflict, overlapping generations

Low skilled immigration and the expansion of private schools

A political-economic model is provided to study the impact of low-skilled immigration on the receiving country's education system, in terms of sources of school funding, expenditure per pupil, and type of parents who are more likely to send children to privately funded schools. The education regime results from the interplay between households' choices on fertility and education and the public education provided. No exogenous culturally-based difference is assumed among agents. Low-skilled migrant workers differ from their local counterparts only in voting rights and adjustment costs. The impact of immigration on public school congestion, tax base, wages and skill premium are considered. When the number of low-skilled immigrants is large, the education regime tends to become more segregated, with wealthier locals more likely to opt out of the public system into private schools. The fertility differential between high- and low-skilled locals increases due to a quantity/quality trade-off. The theoretical predictions conform to stylized facts revealed in US census data and OECD PISA (2003).double taxation, education funding, fertility, migration, segregation, voting

Low-skilled Immigration and Education Policy with Endogenous Fertility

This paper studies the impact of low-skilled immigration on the host country’s education policy, which is formulated by the natives via voting and refers to both school funding sources and resources in the public funded schools. When the size of low-skilled immigrants is large, it is found that wealthier natives are likely to opt out from public into private school. Four main effects of immigration are taken into account : (1) greater congestion in public school; (2) lower average tax base for education funding; (3) reduced low-skilled wage and so more low-skilled natives’ dependence on public education; (4) higher skill premium, which induces high-skilled natives to privately invest in their children’ s education and hence weakens their support to finance public school. The theoretical predictions are not at odds with cross-country stylized facts revealed in both micro and macro data. Moreover, with endogenous fertility, the opting-out decision taken by some native parents results in the empirically observed fertility differential between natives and immigrantsvoting, taxes and subsidies, education; fertitlity, migration

Low-Skilled Immigration and th Expansion of Private Schools

This paper studies the impact of low-skilled immigration on the host country’s education system, which is characterized by sources of school funding, expenditres per pupil, and types of parents who are more likely to send children to publicly (privately) funded schools. When the size of low-skilled immigrants is large, it is found that wealthier natives are likely to opt out from public into private schools. Four main effects of immigration are taken into account : (1) greater congestion in public school; (2) lower average tax base for education funding; (3) reduced low-skilled wage and so more low-skilled natives to privately invest in their children’s education and hence weakens their support to finance public school. The theoretical predictions are not at odds with cross-country stylized facts revealed in both micro and macro data. Moreover, with endogenous fertility, the opting-out decision taken by some native parents results in the empirically observed fertility differential between natives and immigrantsVoting, Taxes and Subsidies, Education, Fertility, Migration

Low-Skilled Immigration and the Expansion of Private Schools

This paper provides a political-economic model to study the impact of low-skilled immigration on the host country's education system, which is characterized by sources of school funding, the average expenditure per pupil, and the type of parents who are more likely to send their children to publicly or privately funded schools. Four main effects of immigration are considered: (1) greater congestion in public schools; (2) a lower average tax base for education funding; (3) reduced wages for low-skilled workers and so more dependence by low-skilled locals on public education; (4) a greater skill premium, which makes it easier for high-skilled locals to afford private education for their children, and hence weakens their support for financing public school. It is found that when the size of low-skilled immigrants is large, the education regime tends to become more segregated with wealthier locals more likely to opt out of the public system into private schools. The fertility differential between high and low-skilled locals increases due to a quantity/quality trade-off. The theoretical predictions are consistent with empirical evidence from both the U.S. census data and the OECD Programme for International Student Assessment (2003).voting, taxes and subsidies, education, fertility, migration

Is J 133658.3-295105 a Radio Source at z >= 1.0 or at the Distance of M 83?

We present Gemini optical imaging and spectroscopy of the radio source J 133658.3-295105. This source has been suggested to be the core of an FR II radio source with two detected lobes. J 133658.3-295105 and its lobes are aligned with the optical nucleus of M 83 and with three other radio sources at the M 83 bulge outer region. These radio sources are neither supernova remnants nor H II regions. This curious configuration prompted us to try to determine the distance to J 133658.3-295105. We detected H_alpha emission redshifted by ~ 130 km s^-1 with respect to an M 83 H II region 2.5" east-southeast of the radio source. We do not detect other redshifted emission lines of an optical counterpart down to m_i = 22.2 +/- 0.8. Two different scenarios are proposed: the radio source is at z >= 2.5, a much larger distance than the previously proposed lower limit z >= 1.0, or the object was ejected by a gravitational recoil event from the M 83 nucleus. This nucleus is undergoing a strong dynamical evolution, judging from previous three-dimensional spectroscopy.Comment: 6 pages, 4 figure

Easter Island’s Collapse : A Tale of a Population Race

The Easter Island tragedy has become an allegory for ecological catastrophe and a warning for the future. In the economic literature the collapse is usually attributed to irrational or myopic behaviors in the context of a fragile ecosystem. In this paper we propose an alternative story involving non-cooperative bargaining between clans to share the crop. Each clan’s bargaining power depends on its threat level when fighting a war. The biggest group has the highest probability of winning. A clan’s fertility is determined ex ante by each group. In the quest for greater bargaining power, each clan’s optimal size depends on that of the other clan, and a population race follows. This race may exhaust the natural resources and lead to the ultimate collapse of the society. In addition to well-known natural factors, the likelihood of a collapse turns out to be greater when the cost of war is low, the probability of succeeding in war is highly responsive to the number of fighters, and the marginal return to labor is not too low. We analyze whether these factors can account for the difference between Easter and Tikopia Islands. The paper also makes a methodological contribution in that it is the first fertility model to include strategic complementarities between groups’ fertility decisionsFertility, War, Bargaining Power, Collapse, Natural Resources