The nature of the ISM in galaxies during the star-formation activity peak of the Universe

We combine a semi-analytic model of galaxy formation, tracking atomic and molecular phases of cold gas, with a three-dimensional radiative-transfer and line tracing code to study the sub-mm emission from atomic and molecular species (CO, HCN, [CI], [CII], [OI]) in galaxies. We compare the physics that drives the formation of stars at the epoch of peak star formation (SF) in the Universe (z = 2.0) with that in local galaxies. We find that normal star-forming galaxies at high redshift have much higher CO-excitation peaks than their local counterparts and that CO cooling takes place at higher excitation levels. CO line ratios increase with redshift as a function of galaxy star-formation rate, but are well correlated with H2 surface density independent of redshift. We find an increase in the [OI]/[CII] line ratio in typical star-forming galaxies at z = 1.2 and z = 2.0 with respect to counterparts at z = 0. Our model results suggest that typical star-forming galaxies at high redshift consist of much denser and warmer star-forming clouds than their local counterparts. Galaxies belonging to the tail of the SF activity peak at z = 1.2 are already less dense and cooler than counterparts during the actual peak of SF activity (z = 2.0). We use our results to discuss how future ALMA surveys can best confront our predictions and constrain models of galaxy formation.Comment: 19 pages, 14 figures, accepted for publication in MNRA

Numerical experiments on short-term meteorological effects on solar variability

A set of numerical experiments was conducted to test the short-range sensitivity of a large atmospheric general circulation model to changes in solar constant and ozone amount. On the basis of the results of 12-day sets of integrations with very large variations in these parameters, it is concluded that realistic variations would produce insignificant meteorological effects. Any causal relationships between solar variability and weather, for time scales of two weeks or less, rely upon changes in parameters other than solar constant or ozone amounts, or upon mechanisms not yet incorporated in the model

Quasicrystal formation in binary soft matter mixtures

Using a strategy that may be applied in theory or in experiments, we identify the regime in which a model binary soft matter mixture forms quasicrystals. The system is described using classical density functional theory combined with integral equation theory. Quasicrystal formation requires particle ordering with two characteristic length scales in certain particular ratios. How the length scales are related to the form of the pair interactions is reasonably well understood for one-component systems, but less is known for mixtures. In our model mixture of big and small colloids confined to an interface, the two length scales stem from the range of the interactions between pairs of big particles and from the cross big-small interactions, respectively. The small-small length scale is not significant. Our strategy for finding quasicrystals involves tuning locations of maxima in the dispersion relation, or equivalently in the liquid state partial static structure factors

Simulations of Dust in Interacting Galaxies I: Dust Attenuation

A new Monte-Carlo radiative-transfer code, Sunrise, is used in conjunction with hydrodynamic simulations of major galaxy mergers to calculate the effects of dust in such systems. The simulations are in good agreement with observations of dust absorption in starburst galaxies, and the dust has a profound effect on their appearance. The dust attenuation increases with luminosity such that at peak luminosities ~90% of the bolometric luminosity is absorbed by dust. In general, the detailed appearance of the merging event depends on the stage of the merger and the geometry of the encounter. The fraction of bolometric energy absorbed by the dust, however, is a robust quantity that can be predicted from the intrinsic properties bolometric luminosity, baryonic mass, star-formation rate, and metallicity of the system. This paper presents fitting formulae, valid over a wide range of masses and metallicities, from which the absorbed fraction of luminosity (and consequently also the infrared dust luminosity) can be predicted. The attenuation of the luminosity at specific wavelengths can also be predicted, albeit with a larger scatter due to the variation with viewing angle. These formulae for dust attenuation appear to be valid for both isolated and interacting galaxies, are consistent with earlier studies, and would be suitable for inclusion in theoretical models, e.g. semi-analytic models of galaxy formation.Comment: 12 pages, 10 figures, submitted to Ap

The effect of galaxy mass ratio on merger--driven starbursts

We employ numerical simulations of galaxy mergers to explore the effect of galaxy mass ratio on merger--driven starbursts. Our numerical simulations include radiative cooling of gas, star formation, and stellar feedback to follow the interaction and merger of four disk galaxies. The galaxy models span a factor of 23 in total mass and are designed to be representative of typical galaxies in the local Universe. We find that the merger--driven star formation is a strong function of merger mass ratio, with very little, if any, induced star formation for large mass ratio mergers. We define a burst efficiency that is useful to characterize the merger--driven star formation and test that it is insensitive to uncertainties in the feedback parameterization. In accord with previous work we find that the burst efficiency depends on the structure of the primary galaxy. In particular, the presence of a massive stellar bulge stabilizes the disk and suppresses merger--driven star formation for large mass ratio mergers. Direct, co--planar merging orbits produce the largest tidal disturbance and yield that most intense burst of star formation. Contrary to naive expectations, a more compact distribution of gas or an increased gas fraction both decrease the burst efficiency. Owing to the efficient feedback model and the newer version of SPH employed here, the burst efficiencies of the mergers presented here are smaller than in previous studies.Comment: 26 pages, 21 figures, submitted to MNRA

The difference that tenure makes

This paper argues that housing tenures cannot be reduced to either production relations or consumption relations. Instead, they need to be understood as modes of housing distribution, and as having complex and dynamic relations with social classes. Building on a critique of both the productionist and the consumptionist literature, as well as of formalist accounts of the relations between tenure and class, the paper attempts to lay the foundations for a new theory of housing tenure. In order to do this, a new theory of class is articulated, which is then used to throw new light on the nature of class-tenure relations

From Ambridge to the world? Class returns to rural population geographies

Via The Archers BBC radio show, this paper responds to Smith and Phillips call for investigating rural population change within the Global North from a class-foregrounded gentrification perspective and for undertaking it in an internationally comparative manner. Neither is sufficiently developed within scholarship to date. Although endorsing their call, this paper adds three contextual framings: describing and explaining the late blossoming of explicit ‘rural gentrification’ research; stressing the challenges presented to geographical transferability of concepts and terminology; and noting the not exclusive role class needs to play within critical discourse on contemporary rural populations

X-Ray Detected Active Galactic Nuclei in Dwarf Galaxies At 0 \u3c Z \u3c 1

We present a sample of accreting supermassive black holes (SMBHs) in dwarf galaxies at z\lt 1. We identify dwarf galaxies in the NEWFIRM Medium Band Survey with stellar masses of {M}\star \lt 3× {10}9 {M}⊙ that have spectroscopic redshifts from the DEEP2 survey and lie within the region covered by deep (flux limit of ˜ 5× {10}-17{--}6× {10}-16 {erg} {{cm}}-2 {{{s}}}-1) archival Chandra X-ray data. From our sample of 605 dwarf galaxies, 10 exhibit X-ray emission consistent with that arising from active galactic nucleus (AGN) activity. If black-hole mass scales roughly with stellar mass, then we expect that these AGNs are powered by SMBHs with masses of ˜ {10}5{--}{10}6 {M}⊙ and typical Eddington ratios of ˜ 5 % . Furthermore, we find an AGN fraction consistent with extrapolations of other searches of ˜ 0.6 % {--}3 % for {10}9 {M}⊙ ≤slant {M}\star ≤slant 3× {10}9 {M}⊙ and 0.1\lt z\lt 0.6. Our AGN fraction is in good agreement with a semi-analytic model, suggesting that, as we search larger volumes, we may use comparisons between observed AGN fractions and models to understand seeding mechanisms in the early universe

The Las Campanas IR Survey: Early Type Galaxy Progenitors Beyond Redshift One

(Abridged) We have identified a population of faint red galaxies from a 0.62 square degree region of the Las Campanas Infrared Survey whose properties are consistent with their being the progenitors of early-type galaxies. The optical and IR colors, number-magnitude relation and angular clustering together indicate modest evolution and increased star formation rates among the early-type field population at redshifts between one and two. The counts of red galaxies with $H$ magnitudes between 17 and 20 rise with a slope that is much steeper than that of the total H sample. The surface density of red galaxies drops from roughly 3000 per square degree at H = 20.5, I-H > 3 to ~ 20 per square degree at H = 20, I-H > 5. The V-I colors are approximately 1.5 magnitudes bluer on average than a pure old population and span a range of more than three magnitudes. The colors, and photometric redshifts derived from them, indicate that the red galaxies have redshift distributions adequately described by Gaussians with sigma_z ~ 0.2$centered near redshift one, with the exception that galaxies having$V-I3$ are primarily in the 1.5 < z < 2 range. We find co-moving correlation lengths of 9-10 Mpc at z ~ 1, comparable to, or larger than, those found for early-type galaxies at lower redshifts. A simple photometric evolution model reproduces the counts of the red galaxies, with only a ~ 30% decline in the underlying space density of early-type galaxies at z ~ 1.2. We suggest on the basis of the colors, counts, and clustering that these red galaxies are the bulk of the progenitors of present day early-type galaxies.Comment: 5 pages, 3 figures, accepted for publication in the ApJ Letter