Diffraction Patterns of Layered Close-packed Structures from Hidden Markov Models

We recently derived analytical expressions for the pairwise (auto)correlation functions (CFs) between modular layers (MLs) in close-packed structures (CPSs) for the wide class of stacking processes describable as hidden Markov models (HMMs) [Riechers \etal, (2014), Acta Crystallogr.~A, XX 000-000]. We now use these results to calculate diffraction patterns (DPs) directly from HMMs, discovering that the relationship between the HMMs and DPs is both simple and fundamental in nature. We show that in the limit of large crystals, the DP is a function of parameters that specify the HMM. We give three elementary but important examples that demonstrate this result, deriving expressions for the DP of CPSs stacked (i) independently, (ii) as infinite-Markov-order randomly faulted 2H and 3C stacking structures over the entire range of growth and deformation faulting probabilities, and (iii) as a HMM that models Shockley-Frank stacking faults in 6H-SiC. While applied here to planar faulting in CPSs, extending the methods and results to planar disorder in other layered materials is straightforward. In this way, we effectively solve the broad problem of calculating a DP---either analytically or numerically---for any stacking structure---ordered or disordered---where the stacking process can be expressed as a HMM.Comment: 18 pages, 6 figures, 3 tables; http://csc.ucdavis.edu/~cmg/compmech/pubs/dplcps.ht

[CII] line emission in BRI1335-0417 at z=4.4

Using the 12m APEX telescope, we have detected redshifted emission from the 157.74micron [CII] line in the z=4.4074 quasar BRI1335-0417. The linewidth and redshift are in good agreement with previous observations of high-J CO line emission. We measure a [CII] line luminosity, L_[CII] = (16.4 +/- 2.6)x10^9 Lsun, making BRI~1335-0417 the most luminous, unlensed [CII] line emitter known at high-redshift. The [CII]-to-FIR luminosity ratio of (5.3+/-0.8)x10^-4 is ~3x higher than expected for an average object with a FIR luminosity L_FIR = 3.1x10^13 Lsun, if this ratio were to follow the trend observed in other FIR-bright galaxies that have been detected in [CII] line emission. These new data suggest that the scatter in the [CII]-to-FIR luminosity ratio could be larger than previously expected for high luminosity objects. BR1335-0417 has a similar FIR luminosity and [CII]/CO luminosity compared to local ULIRGS and appears to be a gas-rich merger forming stars at a rate of a few thousand solar masses per year.Comment: A&A accepte

The Molecular Gas Content of z<0.1 Radio Galaxies: Linking the AGN Accretion Mode to Host Galaxy Properties

One of the main achievements in modern cosmology is the so-called `unified model', which successfully describes most classes of active galactic nuclei (AGN) within a single physical scheme. However, there is a particular class of radio-luminous AGN that presently cannot be explained within this framework -- the `low-excitation' radio AGN (LERAGN). Recently, a scenario has been put forward which predicts that LERAGN, and their regular `high-excitation' radio AGN (HERAGN) counterparts represent different (red sequence vs. green valley) phases of galaxy evolution. These different evolutionary states are also expected to be reflected in their host galaxy properties, in particular their cold gas content. To test this, here we present CO(1-0) observations toward a sample of 11 of these systems conducted with CARMA. Combining our observations with literature data, we derive molecular gas masses (or upper limits) for a complete, representative, sample of 21 z<0.1 radio AGN. Our results yield that HERAGN on average have a factor of ~7 higher gas masses than LERAGN. We also infer younger stellar ages, lower stellar, halo, and central supermassive black masses, as well as higher black hole accretion efficiencies in HERAGN relative to LERAGN. These findings support the idea that high- and low-excitation radio AGN form two physically distinct populations of galaxies that reflect different stages of massive galaxy build-up.Comment: 8 pages, 4 figures, 4 tables; accepted for publication in Ap

A multiwavelength exploration of the [C II]/IR ratio in H-ATLAS/GAMA galaxies out to z = 0.2

We explore the behaviour of [C ii] λ157.74 μm forbidden fine-structure line observed in a sample of 28 galaxies selected from ∼ 50 deg^2 of the Herschel-Astrophysical Terahertz Large Area Survey survey. The sample is restricted to galaxies with flux densities higher than S160 μm > 150 mJy and optical spectra from the Galaxy and Mass Assembly survey at 0.02 2.5 × 10^(−3) with respect to those showing lower ratios. In particular, those with high ratios tend to have: (1) L_(IR) <10^(11) L_⊙; (2) cold dust temperatures, T_d < 30 K; (3) disc-like morphologies in r-band images; (4) a Wide-field Infrared Survey Explorer colour 0.5 ≲ S_(12 μm)/S_(22 μm) ≲ 1.0; (5) low surface brightness Σ_(IR) ≈ 10^(8–9) L_⊙ kpc^(−2), (6) and specific star formation rates of sSFR ≈0.05–3 Gyr^(−1). We suggest that the strength of the far-UV radiation fields (〈G_O〉) is main parameter responsible for controlling the [C _(ii)]/IR ratio. It is possible that relatively high 〈G_O〉 creates a positively charged dust grain distribution, impeding an efficient photoelectric extraction of electrons from these grains to then collisionally excite carbon atoms. Within the brighter IR population, 11 < log(L_(IR)/L_⊙) < 12, the low [C_( ii)]/IR ratio is unlikely to be modified by [C _(ii)] self-absorption or controlled by the presence of a moderately luminous AGN (identified via the BPT diagram)

A Detailed Gravitational Lens Model Based on Submillimeter Array and Keck Adaptive Optics Imaging of a Herschel-ATLAS Submillimeter Galaxy at z = 4.243

We present high-spatial resolution imaging obtained with the Submillimeter Array (SMA) at 880 μm and the Keck adaptive optics (AO) system at the KS-band of a gravitationally lensed submillimeter galaxy (SMG) at z = 4.243 discovered in the Herschel Astrophysical Terahertz Large Area Survey. The SMA data (angular resolution ≈0". 6) resolve the dust emission into multiple lensed images, while the Keck AO K_S-band data (angular resolution ≈0". 1) resolve the lens into a pair of galaxies separated by 0". 3. We present an optical spectrum of the foreground lens obtained with the Gemini-South telescope that provides a lens redshift of z_(lens) = 0.595 ± 0.005. We develop and apply a new lens modeling technique in the visibility plane that shows that the SMG is magnified by a factor of μ = 4.1 ± 0.2 and has an intrinsic infrared (IR) luminosity of L_(IR) = (2.1 ± 0.2) × 10_(13) L_☉. We measure a half-light radius of the background source of r_s = 4.4 ± 0.5 kpc which implies an IR luminosity surface density of Σ_(IR) = (3.4 ± 0.9) × 10^(11) L_☉ kpc^(−2), a value that is typical of z > 2 SMGs but significantly lower than IR luminous galaxies at z ∼ 0. The two lens galaxies are compact (r_(lens) ≈ 0.9 kpc) early-types with Einstein radii of θ_(E1) = 0.57 ± 0.01 and θ_(E2) = 0.40 ± 0.01 that imply masses of M_(lens1) = (7.4 ± 0.5) × 10^(10)M_☉ and M_(lens2) = (3.7 ± 0.3) × 10^(10) M_☉. The two lensing galaxies are likely about to undergo a dissipationless merger, and the mass and size of the resultant system should be similar to other early-type galaxies at z ∼ 0.6. This work highlights the importance of high spatial resolution imaging in developing models of strongly lensed galaxies discovered by Herschel

Weak 13CO in the Cloverleaf Quasar: evidence for a young, early generation starburst

Observations of 12CO at high redshift indicate rapid metal enrichment in the nuclear regions of at least some galaxies in the early universe. However, the enrichment may be limited to nuclei that are synthesized by short-lived massive stars, excluding classical secondary nuclei like 13CO. Testing this idea, we tentatively detect the 13CO J=3-2 line at a level of 0.3 Jy km/s toward the Cloverleaf Quasar at redshift 2.5. This is the first observational evidence for 13CO at high redshift. The 12CO/13CO J=3-2 luminosity ratio is with at least 40 much higher than ratios observed in molecular clouds of the Milky Way and in the ultraluminous galaxy Arp 220, but may be similar to that observed toward NGC 6240. Large Velocity Gradient (LVG) models simulating seven 12CO transitions and the 13CO line yield 12CO/13CO abundance ratios in excess of 100 for the Cloverleaf. It is possible that the measured ratio is affected by a strong submillimeter radiation field, which reduces the contrast between the 13CO line and the background. It is more likely, however, that the ratio is caused by a real deficiency of 13CO. A potential conflict with optical data, indicating high abundances also for secondary nuclei in quasars of high redshift, may be settled if the bulk of the CO emission is originating sufficiently far from the active galactic nucleus.Comment: 7 pages, 5 figures, accepted for publication in A&A (Main Journal