396 research outputs found
Sovereignty of Aves Island: An Argument against Standardized, Compulsory Arbitration
States engaging in preemptive dispute resolution frequently call upon adjudicative or diplomatic means to resolve territorial boundary disputes and comply with international law. In light of reduced efficacy of such dispute resolution mechanisms, however, some propose that all states should engage in compulsory, standardized arbitration subject to International Court of Justice (“I.C.J.”) review to resolve their boundary disputes. Although arbitration is an effective method of international dispute resolution in certain cases, standardized arbitration will not effectively resolve all boundary disputes between neighbor states.
This Comment argues against the proposition that the United Nations (“U.N.”) implement a standardized arbitration mechanism and discusses implications of such a requirement on the current dispute over the sovereignty of Aves Island. Part I first presents Venezuela’s and Dominica’s claims of sovereignty of the Island. Part I next highlights arbitration and mediation as internationally accepted means of dispute resolution and discusses the use of arbitration in Case Concerning East Timor (“Portugal v. Australia”), and Case Concerning Land and Maritime Boundary Between Cameroon and Nigeria (“Cameroon v. Nigeria”).
Part II argues against a U.N. compulsory arbitration requirement by first discussing its inconsistency with Venezuela’s and Dominica’s sovereignty in light of Portugal v. Australia. Part II next discusses Cameroon v. Nigeria to demonstrate that compulsory arbitration subject to I.C.J. review will not effectively resolve the Aves Island dispute because the I.C.J. is unable to enforce decisions. Part II also illustrates how compulsory arbitration decreases the efficiency of international dispute resolution in light of Cameroon v. Nigeria.
Part III recommends that the U.N. should not implement compulsory, standardized arbitration but rather provide a forum in which states engage in a combination of mediation and arbitration (“Med-Arb”) to resolve their disputes. Part III also recommends that Venezuela and Dominica, similar to the parties in International Business Machines, Corp. v. Fujitsu, Ltd. (“I.B.M. v. Fujitsu”), engage in Med-Arb to capitalize on its advantages to resolve their dispute. Part IV then concludes that all states should engage in Med-Arb in their international boundary disputes to achieve effective redress in the future
Near-Field Limits on the Role of Faint Galaxies in Cosmic Reionization
Reionizing the Universe with galaxies appears to require significant star
formation in low-mass halos at early times, while local dwarf galaxy counts
tell us that star formation has been minimal in small halos around us today.
Using simple models and the ELVIS simulation suite, we show that reionization
scenarios requiring appreciable star formation in halos with at are in serious tension with galaxy counts
in the Local Group. This tension originates from the seemingly inescapable
conclusion that 30 - 60 halos with at
will survive to be distinct bound satellites of the Milky Way at .
Reionization models requiring star formation in such halos will produce dozens
of bound galaxies in the Milky Way's virial volume today (and 100 - 200
throughout the Local Group), each with of old stars
( Gyr). This exceeds the stellar mass function of classical Milky
Way satellites today, even without allowing for the (significant)
post-reionization star formation observed in these galaxies. One possible
implication of these findings is that star formation became sharply inefficient
in halos smaller than at early times, implying that the
high- luminosity function must break at magnitudes brighter than is often
assumed (at ). Our results suggest that JWST (and
possibly even HST with the Frontier Fields) may realistically detect the
faintest galaxies that drive reionization. It remains to be seen how these
results can be reconciled with the most sophisticated simulations of early
galaxy formation at present, which predict substantial star formation in
halos during the epoch of reionization.Comment: 6 pages, 4 figures; minor updates. Published in MNRAS Letter
On the stark difference in satellite distributions around the Milky Way and Andromeda
We compare spherically-averaged radial number counts of bright (> 10^5 Lsun)
dwarf satellite galaxies within 400 kpc of the Milky Way (MW) and M31 and find
that the MW satellites are much more centrally concentrated. Remarkably, the
two satellite systems are almost identical within the central 100 kpc, while
M31 satellites outnumber MW satellites by about a factor of four at deprojected
distances spanning 100 - 400 kpc. We compare the observed distributions to
those predicted for LCDM suhbalos using a suite of 44 high-resolution ~10^12
halo zoom simulations, 22 of which are in pairs like the MW and M31. We find
that the radial distribution of satellites around M31 is fairly typical of
those predicted for subhalos, while the Milky Way's distribution is more
centrally concentrated that any of our simulated LCDM halos. One possible
explanation is that our census is bright (> 10^5 Lsun) MW dwarf galaxies is
significantly incomplete beyond ~ 100 kpc of the Sun. If there were ~8 - 20
more bright dwarfs orbiting undetected at 100 - 400 kpc, then the Milky Way's
radial distribution would fall within the range expected from subhalo
distributions and alos look very much like the known M31 system. We use our
simulations to demonstrate that there is enough area left unexplored by the
Sloan Digital Sky Survey and its extensions that the discovery of ~10 new
bright dwarfs is not implausible given the expected range of angular anisotropy
of subhalos in the sky.Comment: 10 pages, 8 figures, submitted to MNRA
Organized Chaos: Scatter in the relation between stellar mass and halo mass in small galaxies
We use Local Group galaxy counts together with the ELVIS N-body simulations
to explore the relationship between the scatter and slope in the stellar mass
vs. halo mass relation at low masses, .
Assuming models with log-normal scatter about a median relation of the form
, the preferred log-slope steepens from
in the limit of zero scatter to in the
case of dex of scatter in at fixed halo mass. We provide fitting
functions for the best-fit relations as a function of scatter, including cases
where the relation becomes increasingly stochastic with decreasing mass. We
show that if the scatter at fixed halo mass is large enough ( dex)
and if the median relation is steep enough (), then the
"too-big-to-fail" problem seen in the Local Group can be self-consistently
eliminated in about of realizations. This scenario requires that
the most massive subhalos host unobservable ultra-faint dwarfs fairly often; we
discuss potentially observable signatures of these systems. Finally, we compare
our derived constraints to recent high-resolution simulations of dwarf galaxy
formation in the literature. Though simulation-to-simulation scatter in
at fixed is large among separate authors (
dex), individual codes produce relations with much less scatter and usually
give relations that would over-produce local galaxy counts.Comment: 15 pages, 6 figures, 1 table. Accepted for publication into MNRA
Too Big to Fail in the Local Group
We compare the dynamical masses of dwarf galaxies in the Local Group (LG) to
the predicted masses of halos in the ELVIS suite of CDM simulations, a
sample of 48 Galaxy-size hosts, 24 of which are in paired configuration similar
to the LG. We enumerate unaccounted-for dense halos ( km s) in these volumes that at some point in their histories were
massive enough to have formed stars in the presence of an ionizing background
( km s). Within 300 kpc of the Milky Way, the
number of unaccounted-for massive halos ranges from 2 - 25 over our full
sample. Moreover, this "too big to fail" count grows as we extend our
comparison to the outer regions of the Local Group: within 1.2 Mpc of either
giant we find that there are 12-40 unaccounted-for massive halos. This count
excludes volumes within 300 kpc of both the MW and M31, and thus should be
largely unaffected by any baryonically-induced environmental processes.
According to abundance matching -- specifically abundance matching that
reproduces the Local Group stellar mass function -- all of these missing
massive systems should have been quite bright, with .
Finally, we use the predicted density structure of outer LG dark matter halos
together with observed dwarf galaxy masses to derive an
relation for LG galaxies that are outside the virial
regions of either giant. We find that there is no obvious trend in the relation
over three orders of magnitude in stellar mass (a "common mass" relation), from
, in drastic conflict with the tight relation
expected for halos that are unaffected by reionization. Solutions to the too
big to fail problem that rely on ram pressure stripping, tidal effects, or
statistical flukes appear less likely in the face of these results.Comment: 16 pages, 14 figures, 2 tables, submitted to MNRA
Environmental Quenching of Low-Mass Field Galaxies
In the local Universe, there is a strong division in the star-forming
properties of low-mass galaxies, with star formation largely ubiquitous amongst
the field population while satellite systems are predominantly quenched. This
dichotomy implies that environmental processes play the dominant role in
suppressing star formation within this low-mass regime (). As shown by observations of the Local Volume,
however, there is a non-negligible population of passive systems in the field,
which challenges our understanding of quenching at low masses. By applying the
satellite quenching models of Fillingham et al. (2015) to subhalo populations
in the Exploring the Local Volume In Simulations (ELVIS) suite, we investigate
the role of environmental processes in quenching star formation within the
nearby field. Using model parameters that reproduce the satellite quenched
fraction in the Local Group, we predict a quenched fraction -- due solely to
environmental effects -- of within
of the Milky Way and M31. This is in good agreement with current observations
of the Local Volume and suggests that the majority of the passive field systems
observed at these distances are quenched via environmental mechanisms. Beyond
, however, dwarf galaxy quenching becomes difficult to explain
through an interaction with either the Milky Way or M31, such that more
isolated, field dwarfs may be self-quenched as a result of star-formation
feedback.Comment: 9 pages, 4 figures, MNRAS accepted version, comments welcome - RIP
Ducky...gone but never forgotte
Taking Care of Business in a Flash: Constraining the Timescale for Low-Mass Satellite Quenching with ELVIS
The vast majority of dwarf satellites orbiting the Milky Way and M31 are
quenched, while comparable galaxies in the field are gas-rich and star-forming.
Assuming that this dichotomy is driven by environmental quenching, we use the
ELVIS suite of N-body simulations to constrain the characteristic timescale
upon which satellites must quench following infall into the virial volumes of
their hosts. The high satellite quenched fraction observed in the Local Group
demands an extremely short quenching timescale (~ 2 Gyr) for dwarf satellites
in the mass range Mstar ~ 10^6-10^8 Msun. This quenching timescale is
significantly shorter than that required to explain the quenched fraction of
more massive satellites (~ 8 Gyr), both in the Local Group and in more massive
host halos, suggesting a dramatic change in the dominant satellite quenching
mechanism at Mstar < 10^8 Msun. Combining our work with the results of
complementary analyses in the literature, we conclude that the suppression of
star formation in massive satellites (Mstar ~ 10^8 - 10^11 Msun) is broadly
consistent with being driven by starvation, such that the satellite quenching
timescale corresponds to the cold gas depletion time. Below a critical stellar
mass scale of ~ 10^8 Msun, however, the required quenching times are much
shorter than the expected cold gas depletion times. Instead, quenching must act
on a timescale comparable to the dynamical time of the host halo. We posit that
ram-pressure stripping can naturally explain this behavior, with the critical
mass (of Mstar ~ 10^8 Msun) corresponding to halos with gravitational restoring
forces that are too weak to overcome the drag force encountered when moving
through an extended, hot circumgalactic medium.Comment: 12 pages, 6 figures; resubmitted to MNRAS after referee report
(August 25, 2015
Under Pressure: Quenching Star Formation in Low-Mass Satellite Galaxies via Stripping
Recent studies of galaxies in the local Universe, including those in the
Local Group, find that the efficiency of environmental (or satellite) quenching
increases dramatically at satellite stellar masses below ~ . This suggests a physical scale where quenching transitions from a
slow "starvation" mode to a rapid "stripping" mode at low masses. We
investigate the plausibility of this scenario using observed HI surface density
profiles for a sample of 66 nearby galaxies as inputs to analytic calculations
of ram-pressure and viscous stripping. Across a broad range of host properties,
we find that stripping becomes increasingly effective at $M_{*} < 10^{8-9}\
{\rm M}_{\odot}n_{\rm halo} <
10^{-3.5}{\rm cm}^{-3}$), we find that stripping is not fully effective;
infalling satellites are, on average, stripped of < 40 - 70% of their cold gas
reservoir, which is insufficient to match observations. By including a host
halo gas distribution that is clumpy and therefore contains regions of higher
density, we are able to reproduce the observed HI gas fractions (and thus the
high quenched fraction and short quenching timescale) of Local Group
satellites, suggesting that a host halo with clumpy gas may be crucial for
quenching low-mass systems in Local Group-like (and more massive) host halos.Comment: updated version after review, now accepted to MNRAS; Accepted 2016
August 22. Received 2016 August 18; in original form 2016 June 2
Sweating the small stuff: simulating dwarf galaxies, ultra-faint dwarf galaxies, and their own tiny satellites
We present FIRE/Gizmo hydrodynamic zoom-in simulations of isolated dark
matter halos, two each at the mass of classical dwarf galaxies () and ultra-faint galaxies (), and with two feedback implementations. The resultant central
galaxies lie on an extrapolated abundance matching relation from to without a break. Every host is filled with
subhalos, many of which form stars. Our dwarfs with each have 1-2 well-resolved satellites with . Even our isolated ultra-faint galaxies have
star-forming subhalos. If this is representative, dwarf galaxies throughout the
universe should commonly host tiny satellite galaxies of their own. We combine
our results with the ELVIS simulations to show that targeting regions around nearby isolated dwarfs could increase the chances of
discovering ultra-faint galaxies by compared to random halo
pointings, and specifically identify the region around the Phoenix dwarf galaxy
as a good potential target.
The well-resolved ultra-faint galaxies in our simulations () form within halos. Each has a uniformly ancient stellar population () owing to reionization-related quenching. More massive systems, in
contrast, all have late-time star formation. Our results suggest that is a probable dividing line between halos
hosting reionization "fossils" and those hosting dwarfs that can continue to
form stars in isolation after reionization.Comment: 12 pages, 6 figures, 1 table, submitted to MNRA
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