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This paper proposes a numerical scheme based on the lattice Boltzmann method to tackle the classical problem of sound radiation directivity of pipes issuing subsonic mean flows. The investigation is focused on normal mode radiation, which allows the use of a two-dimensional lattice with an axisymmetric condition at the pipe's longitudinal axis. The numerical results are initially verified against an exact analytical solution for the sound radiation directivity of an unflanged pipe in the absence of a mean flow, which shows a very good agreement. Thereafter, the sound directivity results in the presence of a subsonic mean flow are compared with both analytical models and experimental data. The results are in good agreement, particularly for low values of the Helmholtz number ka.Moreover, the phenomenon known as 'zone of relative silence' was observed, even for mean flows associated with very lowMach numbers, though discrepancies were also observed in the comparison between the numerical results and the analytical predictions. A thorough discussion on the scheme implementation and numerical results is provided in the paper. [ABSTRACT FROM AUTHOR]

We present rest-frame 15 and 24 μm luminosity functions (LFs) and the corresponding star-forming LFs at z < 0.3 derived from the 5MUSES sample. Spectroscopic redshifts have been obtained for ~98% of the objects and the median redshift is ~0.12. The 5-35 μm Infrared Spectrograph spectra allow us to estimate accurately the luminosities and build the LFs. Using a combination of starburst and quasar templates, we quantify the star formation (SF) and active galactic nucleus (AGN) contributions in the mid-jR spectral energy distribution. We then compute the SF LFs at 15 and 24 μm, and compare with the total 15 and 24 μm LFs. When we remove the contribution of AGNs, the bright end of the LF exhibits a strong decline, consistent with the exponential cutoff of a Schechter function. Integrating the differential LF, we find that the fractional contribution by SF to the energy density is 58% at 15 μm and 78% at 24 μm, while it goes up to ~86% when we extrapolate our mid-JR results to the total IR luminosity density. We confirm that the AGNs play more important roles energetically at high luminosities. Finally, we compare our results with work at z ~ 0.7 and confirm that evolution on both luminosity and density is required to explain the difference in the LFs at different redshifts. [ABSTRACT FROM AUTHOR]

We propose an "extended Schmidt law" with explicit dependence of the star formation efficiency (SFE = SFR/Mgas) on the stellar mass surface density (Σstar). This relation has a power-law index of 0.48 ± 0.04 and a lσ observed scatter on the SFE of 0.4 dex, which holds over five orders of magnitude in the stellar density for individual global galaxies, including various types and especially the low-surface-brightness (LSB) galaxies that deviate significantly from the Kennicutt-Schmidt (KS) law. When applying it to regions of a sample of 12 spiral galaxies at sub-kiloparsec resolution, the extended Schmidt law not only holds for LSB regions but also shows significantly smaller scatters both within and across galaxies compared with the KS law. We argue that this new relation points to the role of existing stars in regulating the SFE, thus better encoding the star formation physics. Comparison with physical models of star formation recipes shows that the extended Schmidt law can be reproduced by some models including gas free fall in a stellar-gravitational potential and pressure-supported star formation. By implementing this new law into the analytic model of gas accretion in ACDM, we show that it can reproduce the observed main sequence of star-forming galaxies (a relation between the SFR and stellar mass) from z = 0 up to z = 2. [ABSTRACT FROM AUTHOR]

Metals are thought to have profound effects on the internal structures of the molecular clouds in which stars are born. The absence of metals is expected to prevent gas from efficient cooling and fragmentation in theory. However, this effect has not yet been observed in low-metallicity environments, such as in the early universe and local dwarf galaxies, because of the lack of high-spatial-resolution maps of gas. We carried out Atacama Large Millimeter/submillimeter Array observations of the carbon monoxide (CO) J = 2–1 emission line at 1.4 parsec resolutions of a molecular cloud in DDO 70 at 7% solar metallicity, the most metal-poor galaxy currently known with a CO detection. In total, five clumps have been identified and they are found to more or less follow Larson’s law. Since the CO emission exists in regions with visual extinction AV around 1.0, we converted this AV to the gas-mass surface density using a gas-to-dust ratio of 4594 ± 2848 for DDO 70. We found that the CO clumps in DDO 70 exhibit significantly larger (on average four times) sizes than those at the same gas-mass surface densities in the massive star formation regions of the Milky Way. The existence of such large clumps appears to be consistent with theoretical expectations that gas fragmentation in low-metallicity clouds is suppressed. While our observation is only for one cloud in the galaxy, if it is representative, the above result implies suppressed gas fragmentation during the cloud collapse and star formation in the early universe. [ABSTRACT FROM AUTHOR]

We present a catalog of nearby (z ≤ 0.5) quasars with significant features of post-starburst stellar populations in their optical spectra: so-called post-starburst quasars, or PSQs. After carefully decomposing spectra from the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) Quasar Catalog into quasar and host-galaxy components, we derive a sample of 208 PSQs. Their host-galaxy components have strong Hδ absorption (EW ≥ 6 Å) indicating a significant contribution of an intermediate-aged stellar population formed in a burst of star formation within the past 1 Gyr, which makes them potentially useful for studying the co-evolution of supermassive black holes and their host galaxies. [ABSTRACT FROM AUTHOR]

We revisit the proposed extended Schmidt law, which posits that the star formation efficiency in galaxies depends on the stellar mass surface density, by investigating spatially resolved star formation rates (SFRs), gas masses, and stellar masses of star formation regions in a vast range of galactic environments, from the outer disks of dwarf galaxies, to spiral disks and to merging galaxies, as well as individual molecular clouds in M33. We find that these regions are distributed in a tight power law as ∝ , which is also valid for the integrated measurements of disk and merging galaxies at high-z. Interestingly, we show that star formation regions in the outer disks of dwarf galaxies with down to 10−5 yr−1 kpc−2, which are outliers of both the Kennicutt–Schmidt and Silk–Elmegreen laws, also follow the extended Schmidt law. Other outliers in the Kennicutt–Schmidt law, such as extremely metal-poor star formation regions, also show significantly reduced deviation from the extended Schmidt law. These results suggest an important role for existing stars in helping to regulate star formation through the effect of their gravity on the midplane pressure in a wide range of galactic environments. [ABSTRACT FROM AUTHOR]

We have compiled a sample of 26 metal-poor galaxies with 12 + log(O/H) < 8.1 with both infrared continuum and 1.4 GHz radio continuum data. By comparing to galaxies at higher metallicity, we have investigated the IR–radio relationship’s dependence on metallicity at the 24, 70, 100, and 160 μm bands, as well as the integrated FIR luminosity. It is found that metal-poor galaxies have on average lower than metal-rich ones, with larger offsets at longer IR wavelengths, from −0.06 dex in to −0.6 dex in . The of all galaxies as a whole at 160 μm show positive trends with the metallicity and IR-to-FUV ratio and negative trends with the IR color, while those at lower IR wavelengths show weaker correlations. We propose a mechanism that invokes the combined effects of low obscured-SFR-to-total-SFR fraction and warm dust temperature at low metallicity to interpret the above behavior of , with the former reducing the IR radiation and the latter further reducing the IR emission at longer IR wavelengths. Other mechanisms that are related to the radio emission, including the enhanced magnetic field strength and increased thermal radio contribution, are unable to reconcile the IR-wavelength-dependent differences of between metal-poor and metal-rich galaxies. In contrast to , the mean total-SFR-to-radio ratio of metal-poor galaxies is the same as that for metal-rich galaxies, indicating the 1.4 GHz radio emission is still an effective tracer of SFRs at low metallicity. [ABSTRACT FROM AUTHOR]

PZT nanotubes were fabricated by the template-assisted method and power generation from these nanotubes was demonstrated experimentally. The PZT nanotubes obtained had high aspect ratios, and were dense, straight and continuous. A pure perovskite phase with strong [1 1 0] preferred crystallographic orientation was obtained at 650 degC. The diameters of these nanotubes ranged from 190 to 210 nm, while the length was around 58 um, corresponding to the diameters and height of the nanopores in the anodic aluminium oxide template. The dielectric constant of the PZT nanotubes was determined to be about 470. These nanotubes could generate up to 469 mV voltage when a stainless-steel nugget was dropped on the electrode of the nanotubes. The power generation could be explained by the basic piezoelectric principles. This power generating mechanism had the potential to convert mechanical and vibration energy to electric power for nanodevices or integrated nanosytems. [ABSTRACT FROM AUTHOR]

We present a sample of 48 nearby galaxies with central, biconical outflows identified by the Mapping Nearby Galaxies at APO survey. All considered galaxies have star-formation-driven biconical (SFB) central outflows, with no signs of an active galactic nucleus. We find that the SFB outflows require high central concentration of the star formation rate. This increases the gas velocity dispersion over the equilibrium limit and helps maintain the gas outflows. The central starbursts increase the metallicity, extinction, and the [α/Fe] ratio in the gas. A significant amount of young stellar population at the centers suggests that the SFBs are associated with the formation of young bulges in galaxies. More than 70% of SFB galaxies are group members or have companions with no prominent interaction, or show asymmetry of external isophotes. In 15% of SFB cases, stars and gas rotate in the opposite directions, which points at the gas infall from satellites as the primary reason for triggering the SFB phenomena. [ABSTRACT FROM AUTHOR]

We report our systematic construction of the lattice Hamiltonian model of topological orders on open surfaces, with explicit boundary terms. We do this mainly for the Levin-Wen string-net model. The full Hamiltonian in our approach yields a topologically protected, gapped energy spectrum, with the corresponding wave functions robust under topology-preserving transformations of the lattice of the system. We explicitly present the wavefunctions of the ground states and boundary elementary excitations. The creation and hopping operators of boundary quasi-particles are constructed. It is found that given a bulk topological order, the gapped boundary conditions are classified by Frobenius algebras in its input data. Emergent topological properties of the ground states and boundary excitations are characterized by (bi-) modules over Frobenius algebras. [ABSTRACT FROM AUTHOR]

To elucidate the intrinsic broadband infrared (IR) emission properties of active galactic nuclei (AGNs), we analyze the spectral energy distributions (SEDs) of 87 z ≲ 0.5 Palomar-Green (PG) quasars. While the Elvis AGN template with a moderate far-IR correction can reasonably match the SEDs of the AGN components in ∼60% of the sample (and is superior to alternatives such as that by Assef), it fails on two quasar populations: (1) hot-dust-deficient (HDD) quasars that show very weak emission thoroughly from the near-IR to the far-IR, and (2) warm-dust-deficient (WDD) quasars that have similar hot dust emission as normal quasars but are relatively faint in the mid- and far-IR. After building composite AGN templates for these dust-deficient quasars, we successfully fit the 0.3–500 μm SEDs of the PG sample with the appropriate AGN template, an infrared template of a star-forming galaxy, and a host galaxy stellar template. 20 HDD and 12 WDD quasars are identified from the SED decomposition, including seven ambiguous cases. Compared with normal quasars, the HDD quasars have AGNs with relatively low Eddington ratios and the fraction of WDD quasars increases with AGN luminosity. Moreover, both the HDD and WDD quasar populations show relatively stronger mid-IR silicate emission. Virtually identical SED properties are also found in some quasars from z = 0.5 to 6. We propose a conceptual model to demonstrate that the observed dust deficiency of quasars can result from a change of structures of the circumnuclear tori that can occur at any cosmic epoch. [ABSTRACT FROM AUTHOR]

It has long been noticed that special lattices contain single-electron flat bands (FB) without any dispersion. Since the kinetic energy of electrons is quenched in the FB, this highly degenerate energy level becomes an ideal platform to achieve strongly correlated electronic states, such as magnetism, superconductivity, and Wigner crystal. Recently, the FB has attracted increasing interest because of the possibility to go beyond the conventional symmetry-breaking phases towards topologically ordered phases, such as lattice versions of fractional quantum Hall states. This article reviews different aspects of FBs in a nutshell. Starting from the standard band theory, we aim to bridge the frontier of FBs with the textbook solid-state physics. Then, based on concrete examples, we show the common origin of FBs in terms of destructive interference, and discuss various many-body phases associated with such a singular band structure. In the end, we demonstrate real FBs in quantum frustrated materials and organometallic frameworks. [ABSTRACT FROM AUTHOR]

We report the detection of an emission feature at the 12σ level with FWHM line width of about 450 km s−1 toward the nearest quasi-stellar object, QSO Mrk 231. Based on observations with the IRAM 30 m telescope and the Northern Extended Millimeter Array Interferometer, the 11–10 transition of molecular oxygen is the likely origin of the line with rest frequency close to 118.75 GHz. The velocity of the O2 emission in Mrk 231 coincides with the red wing seen in CO emission, suggesting that it is associated with the outflowing molecular gas, located mainly at about 10 kpc away from the central active galactic nucleus (AGN). This first detection of extragalactic molecular oxygen provides an ideal tool to study AGN-driven molecular outflows on dynamic timescales of tens of megayears. O2 may be a significant coolant for molecular gas in such regions affected by AGN-driven outflows. New astrochemical models are needed to explain the implied high molecular oxygen abundance in such regions several kiloparsecs away from the center of galaxies. [ABSTRACT FROM AUTHOR]

We present ALMA observations of the CO(1−0) line and 3 mm continuum emission in eight ultraluminous infrared (IR) quasi-stellar objects (QSOs) at z = 0.06–0.19. All eight IR QSO hosts are clearly resolved in their CO molecular gas emission with a median source size of 3.2 kpc, and seven out of eight sources are detected in 3 mm continuum, which is found to be more centrally concentrated with respect to molecular gas with sizes of 0.4−1.0 kpc. Our observations reveal a diversity of CO morphology and kinematics for the IR QSO systems, which can be roughly classified into three categories: rotating gas disk with ordered velocity gradient, compact CO peak with disturbed velocity, and multiple CO distinct sources undergoing a merger between a luminous QSO and a companion galaxy separated by a few kpc. The molecular gas in three of the IR QSO hosts is found to be rotation-dominated with a ratio of the maximum rotation velocity to the local velocity dispersion of Vrot/σ = 4–6. Basic estimates of the dynamical masses within the CO-emitting regions give masses between 7.4 × 109 and 6.9 × 1010M⊙. We find an increasing trend between black hole mass accretion rate and star formation rate (SFR) over 3 orders of magnitude in far-IR luminosity/SFR, in line with the correlation between QSO bolometric luminosity and star formation activity, indicative of a likely direct connection between active galactic nuclei and star formation activity over galaxy evolution timescales. [ABSTRACT FROM AUTHOR]

We present and maps of six nearby star-forming galaxies, NGC 253, NGC 1068, IC 342, M82, M83, and NGC 6946, obtained with the James Clerk Maxwell Telescope as part of the MALATANG survey. All galaxies were mapped in the central 2′ × 2′ region at 14″ (FWHM) resolution (corresponding to linear scales of ∼0.2–1.0 kpc). The LIR–L′dense relation, where the dense gas is traced by the and the emission, measured in our sample of spatially resolved galaxies is found to follow the linear correlation established globally in galaxies within the scatter. We find that the luminosity ratio, LIR/L′dense, shows systematic variations with LIR within individual spatially resolved galaxies, whereas the galaxy-integrated ratios vary little. A rising trend is also found between LIR/L′dense ratio and the warm-dust temperature gauged by the 70 μm/100 μm flux ratio. We find that the luminosity ratios of IR/HCN (4–3) and IR/HCO+ (4–3), which can be taken as a proxy for the star formation efficiency (SFE) in the dense molecular gas (SFEdense), appear to be nearly independent of the dense gas fraction (fdense) for our sample of galaxies. The SFE of the total molecular gas (SFEmol) is found to increase substantially with fdense when combining our data with those on local (ultra)luminous infrared galaxies and high-z quasars. The mean line ratio measured for the six targeted galaxies is 0.9 ± 0.6. No significant correlation is found for the ratio with the star formation rate as traced by LIR, nor with the warm-dust temperature, for the different populations of galaxies. [ABSTRACT FROM AUTHOR]

We present the analysis of the physical properties of the interstellar medium in the nearby early-type galaxy NGC 3665, based on the far-infrared photometric and spectroscopic data as observed by the Herschel Space Observatory. The fit to the spectral energy distribution reveals a high dust content in the galaxy, with a dust-to-stellar mass ratio of /M* ∼ 1.1 × 10−4 that is nearly three times larger than the mean value of local S0+S0a galaxies. For the ionized regions (H ii regions), the electron density (ne) is around 49.5 ± 11.9 cm−3 based on the [N ii] 122 μm/[N ii] 205 μm ratio. For the photodissociation regions, the heating efficiency ranges from 1.26 × 10−3 to 1.37 × 10−3 based on the ([C ii]+[O i] 63 μm)/, which is slightly lower than other local galaxies; the hydrogen nucleus density and the strength of the far-UV radiation field are n ∼ 104 cm−3 and G0 ∼ 10−0.25, respectively. The above results are consistent with the presence of weak active galactic nuclei and a low level of star-forming activity in NGC 3665. Our results give strong support to the “morphological quenching” scenario, where a compact, massive bulge can stabilize the amount of cool gas against star formation. [ABSTRACT FROM AUTHOR]

At , the formation of new stars is dominated by dusty galaxies whose far-IR emission indicates they contain colder dust than local galaxies of a similar luminosity. We explore the reasons for the evolving IR emission of similar galaxies over cosmic time using (1) local galaxies from GOALS (), (2) galaxies at from 5MUSES (), and (3) IR luminous galaxies spanning from GOODS and Spitzer xFLS (). All samples have Spitzer mid-IR spectra, and Herschel and ground-based submillimeter imaging covering the full IR spectral energy distribution, allowing us to robustly measure , , and for every galaxy. Despite similar infrared luminosities, dusty star-forming galaxies (DSFG) have a factor of 5 higher dust masses and 5 K colder temperatures. The increase in dust mass is linked to an increase in the gas fractions with redshift, and we do not observe a similar increase in stellar mass or star formation efficiency. , a proxy for , is strongly correlated with independently of redshift. We measure merger classification and galaxy size for a subsample, and there is no obvious correlation between these parameters and or . In DSFG, the change in can fully account for the observed colder dust temperatures, suggesting that any change in the spatial extent of the interstellar medium is a second-order effect. [ABSTRACT FROM AUTHOR]

With the aim of exploring the fast evolutionary path from the blue cloud of star-forming galaxies to the red sequence of quiescent galaxies in the local universe, we select a local advanced merging infrared luminous and ultraluminous galaxy (adv-merger (U)LIRGs) sample and perform careful dust extinction corrections to investigate their positions in the star formation rate–M*, u − r, and NUV − r color–mass diagrams. The sample consists of 89 (U)LIRGs at the late merger stage, obtained from cross-correlating the Infrared Astronomical Satellite Point Source Catalog Redshift Survey and 1 Jy ULIRGs samples with the Sloan Digital Sky Survey DR7 database. Our results show that of adv-merger (U)LIRGs are localized above the 1σ line of the local star-forming galaxy main sequence. We also find that all adv-merger (U)LIRGs are more massive than and as blue as the blue cloud galaxies after corrections for Galactic and internal dust extinctions, with and of them outside the blue cloud on the u − r and NUV − r color–mass diagrams, respectively. These results, combined with the short timescale for exhausting the molecular gas reservoir in adv-merger (U)LIRGs ( to years), imply that the adv-merger (U)LIRGs are likely at the starting point of the fast evolutionary track previously proposed by several groups. While the number density of adv-merger (U)LIRGs is only of the blue cloud star-forming galaxies in the local universe, this evolutionary track may play a more important role at high redshift. [ABSTRACT FROM AUTHOR]