The SCUBA-2 Cosmology Legacy Survey: ALMA resolves the bright-end of the submillimeter number counts

We present high-resolution 870 μm Atacama Large Millimeter/sub-millimeter Array (ALMA) continuum maps of 30 bright sub-millimeter sources in the UKIDSS UDS field. These sources are selected from deep, 1 degree2 850 μm maps from the SCUBA-2 Cosmology Legacy Survey, and are representative of the brightest sources in the field (median = 8.7 ± 0.4 mJy). We detect 52 sub-millimeter galaxies (SMGs) at >4σ significance in our 30 ALMA maps. In of the ALMA maps the single-dish source comprises a blend of ≥2 SMGs, where the secondary SMGs are Ultra-luminous Infrared Galaxies (ULIRGs) with 1012 . The brightest SMG contributes on average of the single-dish flux density, and in the ALMA maps containing ≥2 SMGs the secondary SMG contributes of the integrated ALMA flux. We construct source counts and show that multiplicity boosts the apparent single-dish cumulative counts by 20% at S870 > 7.5 mJy, and by 60% at S870 > 12 mJy. We combine our sample with previous ALMA studies of fainter SMGs and show that the counts are well-described by a double power law with a break at 8.5 ± 0.6 mJy. The break corresponds to a luminosity of ~6 × 1012 or a star formation rate (SFR) of ~103 . For the typical sizes of these SMGs, which are resolved in our ALMA data with = 1.2 ± 0.1 kpc, this yields a limiting SFR density of ~100 yr−1 kpc−2 Finally, the number density of S870 2 mJy SMGs is 80 ± 30 times higher than that derived from blank-field counts. An over-abundance of faint SMGs is inconsistent with line-of-sight projections dominating multiplicity in the brightest SMGs, and indicates that a significant proportion of these high-redshift ULIRGs are likely to be physically associated

Schottky barrier heights at polar metal/semiconductor interfaces

Using a first-principle pseudopotential approach, we have investigated the Schottky barrier heights of abrupt Al/Ge, Al/GaAs, Al/AlAs, and Al/ZnSe (100) junctions, and their dependence on the semiconductor chemical composition and surface termination. A model based on linear-response theory is developed, which provides a simple, yet accurate description of the barrier-height variations with the chemical composition of the semiconductor. The larger barrier values found for the anion- than for the cation-terminated surfaces are explained in terms of the screened charge of the polar semiconductor surface and its image charge at the metal surface. Atomic scale computations show how the classical image charge concept, valid for charges placed at large distances from the metal, extends to distances shorter than the decay length of the metal-induced-gap states.Comment: REVTeX 4, 11 pages, 6 EPS figure

The clustering evolution of dusty star-forming galaxies

We present predictions for the clustering of galaxies selected by their emission at far-infrared (FIR) and sub-millimetre wavelengths. This includes the first predictions for the effect of clustering biases induced by the coarse angular resolution of single-dish telescopes at these wavelengths. We combine a new version of the GALFORM model of galaxy formation with a self-consistent model for calculating the absorption and re-emission of radiation by interstellar dust. Model galaxies selected at 850μm reside in dark matter haloes of mass Mhalo ∼ 1011.5–1012 h−1 M⊙, independent of redshift (for 0.2 ≲ z ≲ 4) or flux (for 0.25 ≲ S850 μm ≲ 4 mJy). At z ∼ 2.5, the brightest galaxies (S850 μm > 4 mJy) exhibit a correlation length of r0=5.5+0.3−0.5r0=5.5−0.5+0.3 h−1 Mpc, consistent with observations. We show that these galaxies have descendants with stellar masses M⋆ ∼ 1011 h−1 M⊙ occupying haloes spanning a broad range in mass Mhalo ∼ 1012–1014 h−1 M⊙. The FIR emissivity at shorter wavelengths (250, 350 and 500 μm) is also dominated by galaxies in the halo mass range Mhalo ∼ 1011.5–1012 h−1 M⊙, again independent of redshift (for 0.5 ≲ z ≲ 5). We compare our predictions for the angular power spectrum of cosmic infrared background anisotropies at these wavelengths with observations, finding agreement to within a factor of ∼2 over all scales and wavelengths, an improvement over earlier versions of the model. Simulating images at 850 μm, we show that confusion effects boost the measured angular correlation function on all scales by a factor of ∼4. This has important consequences, potentially leading to inferred halo masses being overestimated by an order of magnitude

NOEMA confirmation of an optically dark ALMA–AzTEC submillimetre galaxy at z = 5.24

We have obtained deep 1 and 3 mm spectral-line scans towards a candidate z ≳ 5 ALMA-identified AzTEC submillimetre galaxy (SMG) in the Subaru/XMM-Newton Deep Field (or UKIDSS UDS), ASXDF1100.053.1, using the NOrthern Extended Millimeter Array (NOEMA), aiming to obtain its spectroscopic redshift. ASXDF1100.053.1 is an unlensed optically dark millimetre-bright SMG with S1100 μm = 3.5 mJy and KAB > 25.7 (2σ), which was expected to lie at z = 5–7 based on its radio–submillimetre photometric redshift. Our NOEMA spectral scan detected line emission due to 12CO(J = 5–4) and (J = 6–5), providing a robust spectroscopic redshift, zCO = 5.2383 ± 0.0005. Energy-coupled spectral energy distribution modelling from optical to radio wavelengths indicates an infrared luminosity LIR = 8.3−1.4+1.5 × 1012 L⊙, a star formation rate SFR  = 630−380+260 M⊙ yr−1, a dust mass Md = 4.4−0.3+0.4 × 108 M⊙, a stellar mass Mstellar = 3.5−1.4+3.6 × 1011 M⊙, and a dust temperature Td = 37.4−1.8+2.3 K. The CO luminosity allows us to estimate a gas mass Mgas = 3.1 ± 0.3 × 1010 M⊙, suggesting a gas-to-dust mass ratio of around 70, fairly typical for z ∼ 2 SMGs. ASXDF1100.053.1 has ALMA continuum size Re = 1.0−0.1+0.2 kpc, so its surface infrared luminosity density ΣIR is 1.2−0.2+0.1 × 1012 L⊙ kpc−2. These physical properties indicate that ASXDF1100.053.1 is a massive dusty star-forming galaxy with an unusually compact starburst. It lies close to the star-forming main sequence at z ∼ 5, with low Mgas/Mstellar = 0.09, SFR/SFRMS(RSB) = 0.6, and a gas-depletion time τdep of ≈50 Myr, modulo assumptions about the stellar initial mass function in such objects. ASXDF1100.053.1 has extreme values of Mgas/Mstellar, RSB, and τdep compared to SMGs at z ∼ 2–4, and those of ASXDF1100.053.1 are the smallest among SMGs at z > 5. ASXDF1100.053.1 is likely a late-stage dusty starburst prior to passivisation. The number of z = 5.1–5.3 unlensed SMGs now suggests a number density dN/dz = 30.4 ± 19.0 deg−2, barely consistent with the latest cosmological simulations

Blending bias impacts the host halo masses derived from a cross-correlation analysis of bright submillimetre galaxies

Placing bright submillimetre galaxies (SMGs) within the broader context of galaxy formation and evolution requires accurate measurements of their clustering, which can constrain the masses of their host dark matter haloes. Recent work has shown that the clustering measurements of these galaxies may be affected by a ‘blending bias’, which results in the angular correlation function of the sources extracted from single-dish imaging surveys being boosted relative to that of the underlying galaxies. This is due to confusion introduced by the coarse angular resolution of the single-dish telescope and could lead to the inferred halo masses being significantly overestimated. We investigate the extent to which this bias affects the measurement of the correlation function of SMGs when it is derived via a cross-correlation with a more abundant galaxy population. We find that the blending bias is essentially the same as in the autocorrelation case and conclude that the best way to reduce its effects is to calculate the angular correlation function using SMGs in narrow redshift bins. Blending bias causes the inferred host halo masses of the SMGs to be overestimated by a factor of ∼6 when a redshift interval of δz = 3 is used. However, this reduces to a factor of ∼2 for δz = 0.5. The broadening of photometric redshift probability distributions with increasing redshift can therefore impart a mild halo ‘downsizing’ effect on to the inferred host halo masses, though this trend is not as strong as seen in recent observational studie

Predictions for deep galaxy surveys with JWST from ΛCDM

We present predictions for the outcome of deep galaxy surveys with the James Webb Space Telescope (JWST) obtained from a physical model of galaxy formation in Λ cold dark matter. We use the latest version of the GALFORM model, embedded within a new (800 Mpc)3 dark matter only simulation with a halo mass resolution of Mhalo > 2 × 109h−1 M⊙. For computing full UV-to-mm galaxy spectral energy distributions, including the absorption and emission of radiation by dust, we use the spectrophotometric radiative transfer code GRASIL. The model is calibrated to reproduce a broad range of observational data at z ≲ 6, and we show here that it can also predict evolution of the rest-frame far-UV luminosity function for 7 ≲ z ≲ 10 which is in good agreement with observations. We make predictions for the evolution of the luminosity function from z = 16 to z = 0 in all broad-band filters on the Near InfraRed Camera (NIRCam) and Mid InfraRed Instrument (MIRI) on JWST and present the resulting galaxy number counts and redshift distributions. Our fiducial model predicts that ∼1 galaxy per field of view will be observable at z ∼ 11 for a 104 s exposure with NIRCam. A variant model, which produces a higher redshift of reionization in better agreement with Planck data, predicts number densities of observable galaxies ∼5 × greater at this redshift. Similar observations with MIRI are predicted not to detect any galaxies at z ≳ 6. We also make predictions for the effect of different exposure times on the redshift distributions of galaxies observable with JWST, and for the angular sizes of galaxies in JWST bands

The far infra-red SEDs of main sequence and starburst galaxies

We compare observed far infrared/sub-millimetre (FIR/sub-mm) galaxy spectral energy distributions (SEDs) of massive galaxies (M⋆ ≳ 1010 h−1 M⊙) derived through a stacking analysis with predictions from a new model of galaxy formation. The FIR SEDs of the model galaxies are calculated using a self-consistent model for the absorption and re-emission of radiation by interstellar dust based on radiative transfer calculations and global energy balance arguments. Galaxies are selected based on their position on the specific star formation rate (sSFR)–stellar mass (M⋆) plane. We identify a main sequence of star-forming galaxies in the model, i.e. a well-defined relationship between sSFR and M⋆, up to redshift z ∼ 6. The scatter of this relationship evolves such that it is generally larger at higher stellar masses and higher redshifts. There is a remarkable agreement between the predicted and observed average SEDs across a broad range of redshifts (0.5 ≲ z ≲ 4) for galaxies on the main sequence. However, the agreement is less good for starburst galaxies at z ≳ 2, selected here to have elevated sSFRs>10× the main-sequence value. We find that the predicted average SEDs are robust to changing the parameters of our dust model within physically plausible values. We also show that the dust temperature evolution of the main-sequence galaxies in the model is driven by star formation on the main sequence being more burst-dominated at higher redshifts

HELP: XID+, the probabilistic de-blender for Herschel SPIRE maps

We have developed a new prior-based source extraction tool, xid+, to carry out photometry in the Herschel SPIRE (Spectral and Photometric Imaging Receiver) maps at the positions of known sources. xid+ is developed using a probabilistic Bayesian framework that provides a natural framework in which to include prior information, and uses the Bayesian inference tool Stan to obtain the full posterior probability distribution on flux estimates. In this paper, we discuss the details of xid+ and demonstrate the basic capabilities and performance by running it on simulated SPIRE maps resembling the COSMOS field, and comparing to the current prior-based source extraction tool desphot. Not only we show that xid+ performs better on metrics such as flux accuracy and flux uncertainty accuracy, but we also illustrate how obtaining the posterior probability distribution can help overcome some of the issues inherent with maximum-likelihood-based source extraction routines. We run xid+ on the COSMOS SPIRE maps from Herschel Multi-Tiered Extragalactic Survey using a 24-μm catalogue as a positional prior, and a uniform flux prior ranging from 0.01 to 1000 mJy. We show the marginalized SPIRE colour–colour plot and marginalized contribution to the cosmic infrared background at the SPIRE wavelengths. xid+ is a core tool arising from the Herschel Extragalactic Legacy Project (HELP) and we discuss how additional work within HELP providing prior information on fluxes can and will be utilized. The software is available at https://github.com/H-E-L-P/XID_plus. We also provide the data product for COSMOS. We believe this is the first time that the full posterior probability of galaxy photometry has been provided as a data product