ABSTRACT We present an analysis of a deep (1 = 13 Jy) cosmological 1.2 mm continuum map based on ASPECS, the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field. In the 1 arcmin2 covered by ...ASPECS we detect nine sources at significance at 1.2 mm. Our ALMA-selected sample has a median redshift of , with only one galaxy detected at z > 2 within the survey area. This value is significantly lower than that found in millimeter samples selected at a higher flux density cutoff and similar frequencies. Most galaxies have specific star formation rates (SFRs) similar to that of main-sequence galaxies at the same epoch, and we find median values of stellar mass and SFRs of and yr−1, respectively. Using the dust emission as a tracer for the interstellar medium (ISM) mass, we derive depletion times that are typically longer than 300 Myr, and we find molecular gas fractions ranging from ∼0.1 to 1.0. As noted by previous studies, these values are lower than those using CO-based ISM estimates by a factor of ∼2. The 1 mm number counts (corrected for fidelity and completeness) are in agreement with previous studies that were typically restricted to brighter sources. With our individual detections only, we recover 55% 4% of the extragalactic background light (EBL) at 1.2 mm measured by the Planck satellite, and we recover 80% 7% of this EBL if we include the bright end of the number counts and additional detections from stacking. The stacked contribution is dominated by galaxies at , with stellar masses of (1-3) × 1010 M . For the first time, we are able to characterize the population of galaxies that dominate the EBL at 1.2 mm.
We present new ALMA observations of the O iii88 μm line and high angular resolution observations of the C ii158 μm line in a normal star forming galaxy at z = 7.1. Previous C ii observations of this ...galaxy had detected C ii emission consistent with the Lyα redshift but spatially slightly offset relative to the optical (UV-rest frame) emission. The new C ii observations reveal that the C ii emission is partly clumpy and partly diffuse on scales larger than about 1 kpc. O iii emission is also detected at high significance, offset relative to the optical counterpart in the same direction as the C ii clumps, but mostly not overlapping with the bulk of the C ii emission. The offset between different emission components (optical/UV and different far-IR tracers) is similar to that which is observed in much more powerful starbursts at high redshift. We show that the O iii emitting clump cannot be explained in terms of diffuse gas excited by the UV radiation emitted by the optical galaxy, but it requires excitation by in-situ (slightly dust obscured) star formation, at a rate of about 7 M⊙ yr-1. Within 20 kpc from the optical galaxy the ALMA data reveal two additional O iii emitting systems, which must be star forming companions. We discuss that the complex properties revealed by ALMA in the z ~ 7.1 galaxy are consistent with expectations by recent models and cosmological simulations, in which differential dust extinction, differential excitation and different metal enrichment levels, associated with different subsystems assembling a galaxy, are responsible for the various appearance of the system when observed with distinct tracers.
ABSTRACT We present a search for C ii line and dust continuum emission from optical dropout galaxies at z > 6 using ASPECS, our Atacama Large Millimeter submillimeter Array Spectroscopic Survey in ...the Hubble Ultra-deep Field (UDF). Our observations, which cover the frequency range of 212-272 GHz, encompass approximately the range of 6 < z < 8 for C ii line emission and reach a limiting luminosity of LC ii ∼ (1.6-2.5) × 108 L . We identify 14 C ii line emitting candidates in this redshift range with significances >4.5 , two of which correspond to blind detections with no optical counterparts. At this significance level, our statistical analysis shows that about 60% of our candidates are expected to be spurious. For one of our blindly selected C ii line candidates, we tentatively detect the CO(6-5) line in our parallel 3 mm line scan. None of the line candidates are individually detected in the 1.2 mm continuum. A stack of all C ii candidates results in a tentative detection with S1.2 mm = 14 5 Jy. This implies a dust-obscured star-formation rate (SFR) of (3 1) M yr−1. We find that the two highest-SFR objects have candidate C ii lines with luminosities that are consistent with the low-redshift LC ii versus SFR relation. The other candidates have significantly higher C ii luminosities than expected from their UV-based SFR. At the current sensitivity, it is unclear whether the majority of these sources are intrinsically bright C ii emitters, or spurious sources. If only one of our line candidates was real (a scenario greatly favored by our statistical analysis), we find a source density for C ii emitters at 6 < z < 8 that is significantly higher than predicted by current models and some extrapolations from galaxies in the local universe.
Aims. We present an analysis of the behaviour of galaxies in a four-dimensional parameter space defined by stellar mass, metallicity, star formation rate, and molecular gas mass. We analyse a ...combined sample of 227 galaxies that draws from a number of surveys across the redshift range 0 < z < 2 (>90% of the sample at z ~ 0) and covers >3 decades in stellar mass. Methods. Using principal component analysis, we demonstrate that galaxies in our sample lie on a 2D plane within this 4D parameter space, which is indicative of galaxies that exist in an equilibrium between gas inflow and outflow. Furthermore, we find that the metallicity of galaxies depends only on stellar mass and molecular gas mass. In other words, gas-phase metallicity has a negligible dependence on star formation rate once the correlated effect of molecular gas content is accounted for. Results. The well-known fundamental metallicity relation which describes a close and tight relationship between metallicity and SFR (at fixed stellar mass) is therefore entirely a by-product of the underlying physical relationship with molecular gas mass (through the Schmidt-Kennicutt relation).
In this paper, a review of the nonlinear aspects of the mechanical inerter will be presented. The historical context goes back to the development of isolators and absorbers in the first half of the ...twentieth century. Both mechanical and fluid-based nonlinear inerter devices were developed in the mid- and late twentieth century. However, interest in the inerter really accelerated in the early 2000s following the work of Smith
87
, who coined the term ‘inerter’ in the context of a force–current analogy between electrical and mechanical networks. Following the historical context, both fluid and mechanical inerter devices will be reviewed. Then, the application of nonlinear inerter-based isolators and absorbers is discussed. These include different types of nonlinear energy sinks, nonlinear inerter isolators and geometrically nonlinear inerter devices, many relying on concepts such as quasi-zero-stiffness springs. Finally, rocking structures with inerters attached are considered, before conclusions and some future directions for research are presented.
We report new deep observations obtained with the Atacama Large Millimetre Array (ALMA) aimed at investigating the C ii158 μm line and continuum emission in three spectroscopically confirmed Lyman ...break galaxies at 6.8 < z ≤ 7.1, i.e. well within the re-ionization epoch. With star formation rates of SFR ∼ 5–15M⊙ yr− 1 these systems are much more representative of the high-z galaxy population than other systems targeted in the past by millimetre observations. For the galaxy with the deepest observation we detect C ii emission at redshift z = 7.107, fully consistent with the Ly α redshift, but spatially offset by 0.7 arcsec (4 kpc) from the optical emission. At the location of the optical emission, tracing both the Ly α line and the far-UV continuum, no C ii emission is detected in any of the three galaxies, with 3σ upper limits significantly lower than the C ii emission observed in lower redshift galaxies. These results suggest that molecular clouds in the central parts of primordial galaxies are rapidly disrupted by stellar feedback. As a result, C ii emission mostly arises from more external accreting/satellite clumps of neutral gas. These findings are in agreement with recent models of galaxy formation. Thermal far-infrared continuum is not detected in any of the three galaxies. However, the upper limits on the infrared-to-UV emission ratio do not exceed those derived in metal- and dust-poor galaxies.
We present Atacama Large Millimeter/submillimeter Array observations of the dust continuum and C ii 158 m line emission from the z = 6.0695 Lyman-Break Galaxy (LBG) WMH5. These observations at 0 3 ...spatial resolution show a compact (∼3 kpc) main galaxy in dust and C ii emission, with a "tail" of emission extending to the east by about 5 kpc (in projection). The C ii tail is comprised predominantly of two distinct sub-components in velocity, separated from the core by ∼100 and 250 km s−1, with narrow intrinsic widths of about 80 km s−1, which we call "sub-galaxies." The sub-galaxies themselves are extended east-west by about 3 kpc in individual channel images. The C ii tail joins smoothly into the main galaxy velocity field. The C ii line to continuum ratios are comparable for the main and sub-galaxy positions, within a factor two. In addition, these ratios are comparable to LBGs. We conjecture that the WMH5 system represents the early formation of a galaxy through the accretion of smaller satellite galaxies, embedded in a smoother gas distribution, along a possibly filamentary structure. The results are consistent with current cosmological simulations of early galaxy formation and support the idea of very early enrichment with dust and heavy elements of the accreting material.
We present ALLSMOG, the APEX Low-redshift Legacy Survey for MOlecular Gas. ALLSMOG is a survey designed to observe the CO(2 − 1) emission line with the APEX telescope, in a sample of local galaxies ...(0.01 < z < 0.03), with stellar masses in the range 8.5 < log(M*/M⊙) < 10. This paper is a data release and initial analysis of the first two semesters of observations, consisting of 42 galaxies observed in CO(2 − 1). By combining these new CO(2 − 1) emission line data with archival H i data and SDSS optical spectroscopy, we compile a sample of low-mass galaxies with well-defined molecular gas masses, atomic gas masses, and gas-phase metallicities. We explore scaling relations of gas fraction and gas consumption time-scale, and test the extent to which our findings are dependent on a varying CO/H2 conversion factor. We find an increase in the H2/H i mass ratio with stellar mass which closely matches semi-analytic predictions. We find a mean molecular gas fraction for ALLSMOG galaxies of M
H2/M
* = (0.09–0.13), which decreases with stellar mass. This decrease in total gas fraction with stellar mass is in excess of some model predictions at low stellar masses. We measure a mean molecular gas consumption time-scale for ALLSMOG galaxies of 0.4–0.7 Gyr. We also confirm the non-universality of the molecular gas consumption time-scale, which varies (with stellar mass) from ∼100 Myr to ∼2 Gyr. Importantly, we find that the trends in the H2/H i mass ratio, gas fraction, and the non-universal molecular gas consumption time-scale are all robust to a range of recent metallicity-dependent CO/H2 conversion factors.
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