646 research outputs found
Are Some Milky Way Globular Clusters Hosted by Undiscovered Galaxies?
The confirmation of a globular cluster (GC) in the recently discovered
ultrafaint galaxy Eridanus II (Eri II) motivated us to examine the question
posed in the title. After estimating the halo mass of Eri II using a published
stellar mass - halo mass relation, the one GC in this galaxy supports extending
the relationship between the number of GCs hosted by a galaxy and the galaxy's
total mass about two orders of magnitude in stellar mass below the previous
limit. For this empirically determined specific frequency of between 0.06 and
0.39 globular clusters per 10 of total mass, the surviving Milky
Way (MW) subhalos with masses smaller than could host as many
as 5 to 31 GCs, broadly consistent with the actual population of outer halo MW
GCs, although matching the radial distribution in detail remains a challenge.
Using a subhalo mass function from published high resolution numerical
simulations and a Poissonian model for populating those halos with the
aforementioned empirically constrained frequency, we find that about 90 of
these GCs lie in lower-mass subhalos than that of Eri II. From what we know
about the stellar mass-halo mass function, the subhalo mass function, and the
mass-normalized GC specific frequency, we conclude that some of the MW's outer
halo GCs are likely to be hosted by undetected subhalos with extremely modest
stellar populations.Comment: 5 pages, 4 figures; ApJL in pres
Spill-Overs from Good Jobs
Does attracting or losing jobs in high paying sectors have important spill-over effects on wages in other sectors? The answer to this question is central to a proper assessment of many trade and industrial policies. In this paper, we explore this question by examining how predictable changes in industrial composition in favor of high paying sectors affect wage determination at the industry-city level. In particular, we use US Census data over the years 1970 to 2000 to quantify the relationship between changes in industry-specific city-level wages and changes in industrial composition. Our finding is that the spill-over (i.e., general equilibrium) effects associated with changes in the fraction of jobs in high paying sectors are very substantial and persistent. Our point estimates indicate that the total effect on average wages of a change in industrial composition that favors high paying sectors is about 3.5 times greater than that obtained from a commonly used composition-adjustment approach which neglects general equilibrium effects. We interpret our results as being most likely driven by a variant of the mechanism recently emphasized in the heterogenous firm literature whereby changes in competitive pressure cause a reallocation of employment toward the most efficient firms.
Contracting and Ideas Disclosure in the Innovation Process
We analyze the contract between an innovator and a developer, when the former has private information on his idea and the latter must exert efforts but may also quit the relationship after having been informed. We show that the equilibrium contracts distort downwards the developer's incentives but in different ways according to the strength of intellectual property rights (IPR). For example, with intermediate IPR, only pooling contracts arise with a limited amount of information revealed.
Signaling and the Design of Delegated Management Contracts for Public Utilities
International audienceThis article analyzes the shape of contracts between local governments and the contractors they hire to run public facilities on their behalf. Governments are privately informed about the quality of the facility while risk neutral contractors undertake a non-verifiable operating effort. The design of the contract signals the quality of the facility in such a way that the better this quality, the greater the share of operating risk kept by the government. This feature reduces the agent's marginal incentives, creating a trade-off between signaling and moral hazard. We provide extensions of our framework in several directions allowing for risk aversion on the agent's side, double moral hazard and political delegation. The model is supported by some stylized facts from the water industry
Numerically Modeling the First Peak of the Type IIb SN 2016gkg
Many Type IIb supernovae (SNe) show a prominent additional early peak in
their light curves, which is generally thought to be due to the shock cooling
of extended hydrogen-rich material surrounding the helium core of the exploding
star. The recent SN 2016gkg was a nearby Type IIb SN discovered shortly after
explosion, which makes it an excellent candidate for studying this first peak.
We numerically explode a large grid of extended envelope models and compare
these to SN 2016gkg to investigate what constraints can be derived from its
light curve. This includes exploring density profiles for both a convective
envelope and an optically thick steady-state wind, the latter of which has not
typically been considered for Type IIb SNe models. We find that roughly
of extended material with a radius of
reproduces the photometric light curve data,
consistent with pre-explosion imaging. These values are independent of the
assumed density profile of this material, although a convective profile
provides a somewhat better fit. We infer from our modeling that the explosion
must have occurred within of the first observed data
point, demonstrating that this event was caught very close to the moment of
explosion. Nevertheless, our best-fitting one-dimensional models overpredict
the earliest velocity measurements, which suggests that the hydrogen-rich
material is not distributed in a spherically symmetric manner. We compare this
to the asymmetries seen in the SN IIb remnant Cas A, and we discuss the
implications of this for Type IIb SN progenitors and explosion models.Comment: 8 pages, 8 figures, updated version accepted for publication in The
Astrophysical Journa
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