Rethinking Immigration’s Mandatory Detention Regime: Politics, Profit, and the Meaning of “Custody”

Immigration detention in the United States is a crisis that needs immediate attention. U.S. immigration detention facilities hold a staggering number of persons. Widely believed to have the largest immigration detention population in the world, the United States detained approximately 478,000 foreign nationals in Fiscal Year 2012. U.S. Immigration and Customs Enforcement (ICE), the agency responsible for immigration enforcement, boasts that the figure is “an all-time high.” In some ways, these numbers are unsurprising, considering that the United States incarcerates approximately one in every one hundred adults within its borders—a rate five to ten times higher than any other Westernized country. An immigration law, known as the mandatory detention statute, is partially to blame for this recordbreaking immigration detention population. Under this law, facilities may hold noncitizens without providing them an opportunity to ask for release

The Dynamics of Galaxy Pairs in a Cosmological Setting

We use the Millennium Simulation, and an abundance-matching framework, to investigate the dynamical behaviour of galaxy pairs embedded in a cosmological context. Our main galaxy-pair sample, selected to have separations under 250 kpc/h, consists of over 1.3 million pairs at redshift z = 0, with stellar masses greater than 10^9 Msun, probing mass ratios down to 1:1000. We use dark matter halo membership and energy to classify our galaxy pairs. In terms of halo membership, central-satellite pairs tend to be in isolation (in relation to external more massive galaxies), are energetically- bound to each other, and are also weakly-bound to a neighbouring massive galaxy. Satellite-satellite pairs, instead, inhabit regions in close proximity to a more massive galaxy, are energetically-unbound, and are often bound to that neighbour. We find that 60% of our paired galaxies are bound to both their companion and to a third external object. Moreover, only 9% of our pairs resemble the kind of systems described by idealised binary merger simulations in complete isolation. In sum, we demonstrate the importance of properly connecting galaxy pairs to the rest of the Universe.Comment: 25 pages, 14 figures, accepted by MNRA

The Incidence of Low-Metallicity Lyman-Limit Systems at z~3.5: Implications for the Cold-Flow Hypothesis of Baryonic Accretion

Cold accretion is a primary growth mechanism of simulated galaxies, yet observational evidence of "cold flows" at redshifts where they should be most efficient ($z=2$-4) is scarce. In simulations, cold streams manifest as Lyman-limit absorption systems (LLSs) with low heavy-element abundances similar to those of the diffuse IGM. Here we report on an abundance survey of 17 H I-selected LLSs at $z=3.2$-4.4 which exhibit no metal absorption in SDSS spectra. Using medium-resolution spectra obtained at Magellan, we derive ionization-corrected metallicities (or limits) with a Markov-Chain Monte Carlo sampling that accounts for the large uncertainty in $N_{\rm HI}$ measurements typical of LLSs. The metal-poor LLS sample overlaps with the IGM in metallicity and is best described by a model where $71^{+13}_{-11}\%$ are drawn from the IGM chemical abundance distribution. These represent roughly half of all LLSs at these redshifts, suggesting that 28-40$\%$ of the general LLS population at $z\sim3.7$ could trace unprocessed gas. An ancillary sample of ten LLSs without any a priori metal-line selection is best fit with $48^{+14}_{-12}\%$ of metallicities drawn from the IGM. We compare these results with regions of a moving-mesh simulation; the simulation finds only half as many baryons in IGM-metallicity LLSs, and most of these lie beyond the virial radius of the nearest galaxy halo. A statistically significant fraction of all LLSs have low metallicity and therefore represent candidates for accreting gas; large-volume simulations can establish what fraction of these candidates actually lie near galaxies and the observational prospects for detecting the presumed hosts in emission.Comment: 19 pages, 17 figures; Submitted to ApJ; Corrected figure 16

Mapping galaxy encounters in numerical simulations: The spatial extent of induced star formation

We employ a suite of 75 simulations of galaxies in idealised major mergers (stellar mass ratio ~2.5:1), with a wide range of orbital parameters, to investigate the spatial extent of interaction-induced star formation. Although the total star formation in galaxy encounters is generally elevated relative to isolated galaxies, we find that this elevation is a combination of intense enhancements within the central kpc and moderately suppressed activity at large galacto-centric radii. The radial dependence of the star formation enhancement is stronger in the less massive galaxy than in the primary, and is also more pronounced in mergers of more closely aligned disc spin orientations. Conversely, these trends are almost entirely independent of the encounter's impact parameter and orbital eccentricity. Our predictions of the radial dependence of triggered star formation, and specifically the suppression of star formation beyond kph-scales, will be testable with the next generation of integral-field spectroscopic surveys.Comment: 12 pages, 8 figures, accepted by MNRA

An Integral Field Study of Abundance Gradients in Nearby LIRGs

We present for the first time metallicity maps generated using data from the Wide Field Spectrograph (WiFeS) on the ANU 2.3m of 9 Luminous Infrared Galaxies (LIRGs) and discuss the abundance gradients and distribution of metals in these systems. We have carried out optical integral field spectroscopy (IFS) of several several LIRGs in various merger phases to investigate the merger process. In a major merger of two spiral galaxies with preexisting disk abundance gradients, the changing distribution of metals can be used as a tracer of gas flows in the merging system as low metallicity gas is transported from the outskirts of each galaxy to their nuclei. We employ this fact to probe merger properties by using the emission lines in our IFS data to calculate the gas-phase metallicity in each system. We create abundance maps and subsequently derive a metallicity gradient from each map. We compare our measured gradients to merger stage as well as several possible tracers of merger progress and observed nuclear abundances. We discuss our work in the context of previous abundance gradient observations and compare our results to new galaxy merger models which trace metallicity gradient. Our results agree with the observed flattening of metallicity gradients as a merger progresses. We compare our results with new theoretical predictions that include chemical enrichment. Our data show remarkable agreement with these simulations.Comment: Accepted for publication in ApJ. 26 pages, 18 figure

What \u3cem\u3eMatter of Soram\u3c/em\u3e Got Wrong: “Child Abuse” Crimes that May Trigger Deportation Are Constantly Evolving and Even Target Good Parents

Many are surprised to learn that crime-based deportations do not necessarily make intuitive sense. Under the Illegal Immigration Reform and Immigrant Responsibility Act of 1996 (IIRIRA), a misdemeanor drug offense for which probation was imposed 20 years ago can be an “aggravated felony,” a category reserved for the presumably most serious offenses that result in detention, deportation, and denial of most forms of immigration relief. But a felony conviction for kidnaping may have no consequences at all. The crime of “child abuse, child neglect, or child abandonment” removal ground created by IIRIRA similarly leads to illogical results. This deportability ground, first created in 1996 by IIRIRA, is causing federal circuit courts (and arguably the Board of Immigration Appeals itself) to split over whether this deportability ground is narrow or broad. We contend that the narrow interpretation, best defended by the Tenth Circuit, is the proper one. Not only does the legislative history support a narrow reading, but the ground’s broad interpretation adopted by the Second Circuit improperly includes civil actions (not just crimes) and does not even require acts that cause injury to a child. As a result, the broad interpretation sweeps too far. It includes parents with civil violations for leaving their child unattended, either out of circumstances arising from the lack of child care for the working poor or from deliberate parenting choices known as “free-range” parenting in which children are encouraged to function independently and with limited parental supervision. The deportability ground should be interpreted narrowly—as intended by Congress— to trigger deportation only for those who are harming and preying on children