39,899 research outputs found
The dependence of tidal stripping efficiency on the satellite and host galaxy morphology
In this paper we study the tidal stripping process for satellite galaxies
orbiting around a massive host galaxy, and focus on its dependence on the
morphology of both satellite and host galaxy. For this purpose, we use three
different morphologies for the satellites: pure disc, pure bulge and a mixture
bulge+disc. Two morphologies are used for the host galaxies: bulge+disc and
pure bulge. We find that while the spheroidal stellar component experiences a
constant power-law like mass removal, the disc is exposed to an exponential
mass loss when the tidal radius of the satellite is of the same order of the
disc scale length. This dramatic mass loss is able to completely remove the
stellar component on time scale of 100 Myears. As a consequence two satellites
with the same stellar and dark matter masses, on the same orbit could either
retain considerable fraction of their stellar mass after 10 Gyrs or being
completely destroyed, depending on their initial stellar morphology. We find
that there are two characteristic time scales describing the beginning and the
end of the disc removal, whose values are related to the size of the disc. This
result can be easily incorporated in semi-analytical models. We also find that
the host morphology and the orbital parameters also have an effect on the
determining the mass removal, but they are of secondary importance with respect
to satellite morphology. We conclude that satellite morphology has a very
strong effect on the efficiency of stellar stripping and should be taken into
account in modeling galaxy formation and evolution.Comment: 11 pages, 9 figures; accepted for publication in MNRA
Central mass and luminosity of Milky Way satellites in the LCDM model
It has been pointed out that the Galactic satellites all have a common mass
around 1e7 Msun within 300 pc (M03), while they span almost four order of
magnitudes in luminosity (Mateo et al. 1993, Strigari et al. 2008). It is
argued that this may reflect a specific scale for galaxy formation or a scale
for dark matter clustering. Here we use numerical simulations coupled with a
semi-analytic model for galaxy formation, to predict the central mass and
luminosity of galactic satellites in the LCDM model. We show that this common
mass scale can be explained within the Cold Dark Matter scenario when the
physics of galaxy formation is taken into account. The narrow range of M03
comes from the narrow distribution of circular velocities at time of accretion
(peaking around 20 km/s) for satellites able to form stars and the not tight
correlation between halo concentration and circular velocity. The wide range of
satellite luminosities is due to a combination of the mass at time of accretion
and the broad distribution of accretion redshifts for a given mass. This causes
the satellites baryonic content to be suppressed by photo-ionization to very
different extents. Our results favor the argument that the common mass M03
reflects a specific scale (circular velocity ~ 20 km/s) for star formation.Comment: 5 pages, 3 figures. References added, discussion enlarged, new
version of Figure 3. Minor changes to match the version accepted for
publication on ApJ Letter
Sense Beyond Expressions: Cuteness
With the development of Internet culture, cuteness has become a popular
concept. Many people are curious about what factors making a person look cute.
However, there is rare research to answer this interesting question. In this
work, we construct a dataset of personal images with comprehensively annotated
cuteness scores and facial attributes to investigate this high-level concept in
depth. Based on this dataset, through an automatic attributes mining process,
we find several critical attributes determining the cuteness of a person. We
also develop a novel Continuous Latent Support Vector Machine (C-LSVM) method
to predict the cuteness score of one person given only his image. Extensive
evaluations validate the effectiveness of the proposed method for cuteness
prediction.Comment: 4 page
Risk Adjusted Deposit Insurance for Japanese Banks
The purpose of this paper is to evaluate the Japanese deposit insurance scheme by contrasting the flat insurance rate with a market-determined risk-adjusted rate. The model used to calculate the risk-adjusted rate is that of Ronn and Verrna (1986) . It utilizes the notion of Merton(1977) that the deposit insurance can be based on a one-to-one relation between it and the put option; this permits the application of Black and Scholes(1973) model for the calculation of the insurance rate. The risk adjusted premiums are calculated for the thirteen city banks and twenty-two regional banks. The inter-bank spread in risk-adjusted rates in Japan is found to be as wide as in the United States. But the insurance system is only one component of the safety network for a county's banking system. The difference in the American and Japanese networks is described and its implications for the evaluation of the insurance system is discussed.
Modeling College Major Choices Using Elicited Measures of Expectations and Counterfactuals
The choice of a college major plays a critical role in determining the future earnings of college graduates. Students make their college major decisions in part due to the future earnings streams associated with the different majors. We survey students about what their expected earnings would be both in the major they have chosen and in counterfactual majors. We also elicit students' subjective assessments of their abilities in chosen and counterfactual majors. We estimate a model of college major choice that incorporates these subjective expectations and assessments. We show that both expected earnings and students' abilities in the different majors are important determinants of student's choice of a college major. We also show that students' forecast errors with respect to expected earnings in different majors is potentially important, with our estimates suggesting that 7.5% of students would switch majors if they made no forecast errors.choice of college major, subjective expectations
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