Aims. We use high-resolution continuum images obtained with the Atacama Large Millimeter Array (ALMA) to probe the surface density of star formation in z ~ 2 galaxies and study the different physical ...properties between galaxies within and above the star-formation main sequence of galaxies. Methods. We use ALMA images at 870 μm with 0.2 arcsec resolution in order to resolve star formation in a sample of eight star-forming galaxies at z ~ 2 selected among the most massive Herschel galaxies in the GOODS-South field. This sample is supplemented with eleven galaxies from the public data of the 1.3 mm survey of the Hubble Ultra-Deep Field, HUDF. We derive dust and gas masses for the galaxies, compute their depletion times and gas fractions, and study the relative distributions of rest-frame ultraviolet (UV) and far-infrared (FIR) light. Results. ALMA reveals systematically dense concentrations of dusty star formation close to the center of the stellar component of the galaxies. We identify two different starburst regimes: (i) the classical population of starbursts located above the SFR-M⋆ main sequence, with enhanced gas fractions and short depletion times and (ii) a sub-population of galaxies located within the scatter of the main sequence that experience compact star formation with depletion timescales typical of starbursts of ~150 Myr. In both starburst populations, the FIR and UV are distributed in distinct regions and dust-corrected star formation rates (SFRs) estimated using UV-optical-near-infrared data alone underestimate the total SFR. Starbursts hidden in the main sequence show instead the lowest gas fractions of our sample and could represent the last stage of star formation prior to passivization. Being Herschel-selected, these main sequence galaxies are located in the high-mass end of the main sequence, hence we do not know whether these “starbursts hidden in the main sequence” also exist below 1011 M⊙. Active galactic nuclei (AGNs) are found to be ubiquitous in these compact starbursts, suggesting that the triggering mechanism also feeds the central black hole or that the active nucleus triggers star formation.
Submillimeter/millimeter observations of dusty star-forming galaxies with the Atacama Large Millimeter/submillimeter Array (ALMA) have shown that dust continuum emission generally occurs in compact ...regions smaller than the stellar distribution. However, it remains to be understood how systematic these findings are. Studies often lack homogeneity in the sample selection, target discontinuous areas with inhomogeneous sensitivities, and suffer from modest
u
v
coverage coming from single array configurations. GOODS-ALMA is a 1.1 mm galaxy survey over a continuous area of 72.42 arcmin
2
at a homogeneous sensitivity. In this version 2.0, we present a new low resolution dataset and its combination with the previous high resolution dataset from the survey, improving the
u
v
coverage and sensitivity reaching an average of
σ
= 68.4 μJy beam
−1
. A total of 88 galaxies are detected in a blind search (compared to 35 in the high resolution dataset alone), 50% at
S
/
N
peak
≥ 5 and 50% at 3.5 ≤
S
/
N
peak
≤ 5 aided by priors. Among them, 13 out of the 88 are optically dark or faint sources (
H
- or
K
-band dropouts). The sample dust continuum sizes at 1.1 mm are generally compact, with a median effective radius of
R
e
= 0
.
″
10 ± 0
.
″
05 (a physical size of
R
e
= 0.73 ± 0.29 kpc at the redshift of each source). Dust continuum sizes evolve with redshift and stellar mass resembling the trends of the stellar sizes measured at optical wavelengths, albeit a lower normalization compared to those of late-type galaxies. We conclude that for sources with flux densities
S
1.1 mm
> 1 mJy, compact dust continuum emission at 1.1 mm prevails, and sizes as extended as typical star-forming stellar disks are rare. The
S
1.1 mm
< 1 mJy sources appear slightly more extended at 1.1 mm, although they are still generally compact below the sizes of typical star-forming stellar disks.
We report far-infrared and submillimeter observations of supernova 1987A, the star whose explosion was observed on 23 February 1987 in the Large Magellanic Cloud, a galaxy located 160,000 light years ...away. The observations reveal the presence of a population of cold dust grains radiating with a temperature of about 17 to 23 kelvin at a rate of about 220 times the luminosity of the Sun. The intensity and spectral energy distribution of the emission suggest a dust mass of about 0.4 to 0.7 times the mass of the Sun. The radiation must originate from the supernova ejecta and requires the efficient precipitation of all refractory material into dust. Our observations imply that supernovae can produce the large dust masses detected in young galaxies at very high redshifts.
We investigate the properties of a sample of 35 galaxies, detected with the Atacama Large Millimeter/Submillimeter Array (ALMA) at 1.1 mm in the GOODS-ALMA field (area of 69 arcmin
2
, resolution = ...0.60″, rms ≃ 0.18 mJy beam
−1
). Using the ultraviolet-to-radio deep multiwavelength coverage of the GOODS–South field, we fit the spectral energy distributions of these galaxies to derive their key physical properties. The galaxies detected by ALMA are among the most massive at
z
= 2−4 (
M
⋆, med
= 8.5 × 10
10
M
⊙
) and they are either starburst or located in the upper part of the galaxy star-forming main sequence. A significant portion of our galaxy population (∼40%), located at
z
∼ 2.5 − 3, exhibits abnormally low gas fractions. The sizes of these galaxies, measured with ALMA, are compatible with the trend between the rest-frame 5000 Å size and stellar mass observed for
z
∼ 2 elliptical galaxies, suggesting that they are building compact bulges. We show that there is a strong link between star formation surface density (at 1.1 mm) and gas depletion time: The more compact a galaxy’s star-forming region is, the shorter its lifetime will be (without gas replenishment). The identified compact sources associated with relatively short depletion timescales (∼100 Myr) are the ideal candidates to be the progenitors of compact elliptical galaxies at
z
∼ 2.
Compact star formation appears to be generally common in dusty star-forming galaxies (SFGs). However, its role in the framework set by the scaling relations in galaxy evolution remains to be ...understood. In this work we follow up on the galaxy sample from the GOODS-ALMA 2.0 survey, an ALMA blind survey at 1.1 mm covering a continuous area of 72.42 arcmin
2
using two array configurations. We derived physical properties, such as star formation rates, gas fractions, depletion timescales, and dust temperatures for the galaxy sample built from the survey. There exists a subset of galaxies that exhibit starburst-like short depletion timescales, but they are located within the scatter of the so-called main sequence of SFGs. These are dubbed starbursts in the main sequence and display the most compact star formation and they are characterized by the shortest depletion timescales, lowest gas fractions, and highest dust temperatures of the galaxy sample, compared to typical SFGs at the same stellar mass and redshift. They are also very massive, accounting for ∼60% of the most massive galaxies in the sample (log(
M
*
/
M
⊙
) > 11.0). We find trends between the areas of the ongoing star formation regions and the derived physical properties for the sample, unveiling the role of compact star formation as a physical driver of these properties. Starbursts in the main sequence appear to be the extreme cases of these trends. We discuss possible scenarios of galaxy evolution to explain the results drawn from our galaxy sample. Our findings suggest that the star formation rate is sustained in SFGs by gas and star formation compression, keeping them within the main sequence even when their gas fractions are low and they are presumably on the way to quiescence.
The ALMA Redshift 4 Survey (AR4S) Schreiber, C; Pannella, M; Leiton, R ...
Astronomy and astrophysics (Berlin),
03/2017, Letnik:
599
Journal Article
Recenzirano
Odprti dostop
We introduce the ALMA Redshift 4 Survey (AR4S), a systematic ALMA survey of all the known galaxies with stellar mass (Mlow *) larger than 5 x 10 super(10)M sub(middot in circle) at 3.5 <z< 4.7 in the ...GOODS-south, UDS and COSMOS CANDELS fields. The sample we have analyzed in this paper is composed of 96 galaxies observed with ALMA at 890 mu m (180 mu m rest-frame) with an on-source integration time of 1.3 min per galaxy. We detected 32% of the sample at more than 3sigma significance. Using the stacked ALMA and Herschel photometry, we derived an average dust temperature of 40 + or - 2 K for the whole sample, and extrapolate the L sub(IR) and SFR for all our galaxies based on their ALMA flux. We then used a forward modeling approach to estimate their intrinsic sSFR distribution, deconvolved of measurement errors and selection effects: we find a linear relation between SFR and Mlow *, with a median sSFR = 2.8 + or - 0.8 Gyr and a dispersion around that relation of 0.28 + or - 0.13 dex. This latter value is consistent with that measured at lower redshifts, which is proof that the main sequence of star-forming galaxies was already in place at z= 4, at least among massive galaxies. These new constraints on the properties of the main sequence are in good agreement with the latest predictions from numerical simulations, and suggest that the bulk of star formation in galaxies is driven by the same mechanism from z= 4 to the present day, that is, over at least 90% of the cosmic history. We also discuss the consequences of our results on the population of early quiescent galaxies. This paper is part of a series that will employ these new ALMA observations to explore the star formation and dust properties of the massive end of the z= 4 galaxy population.
Thanks to its outstanding angular resolution, the Atacama Large Millimeter/submillimeter Array (ALMA) has recently unambiguously identified a population of optically dark galaxies with redshifts ...greater than
z
= 3, which play an important role in the cosmic star formation in massive galaxies. In this paper we study the properties of the six optically dark galaxies detected in the 69 arcmin
2
GOODS-ALMA 1.1 mm continuum survey. While none of them are listed in the deepest
H
-band based CANDELS catalog in the GOODS-South field down to
H
= 28.16 AB, we were able to de-blend two of them from their bright neighbor and measure an
H
-band flux for them. We present the spectroscopic scan follow-up of five of the six sources with ALMA band 4. All are detected in the 2 mm continuum with signal-to-noise ratios higher than eight. One emission line is detected in AGS4 (
ν
obs
= 151.44 GHz with an
S
/
N
= 8.58) and AGS17 (
ν
obs
= 154.78 GHz with an
S
/
N
= 10.23), which we interpret in both cases as being due to the CO(6–5) line at
z
spec
AGS4
= 3.556 and
z
spec
AGS17
= 3.467, respectively. These redshifts match both the probability distribution of the photometric redshifts derived from the UV to near-infrared spectral energy distributions (SEDs) and the far-infrared SEDs for typical dust temperatures of galaxies at these redshifts. We present evidence that nearly 70% (4/6 of galaxies) of the optically dark galaxies belong to the same overdensity of galaxies at
z
∼ 3.5. overdensity The most massive one, AGS24 (
M
⋆
= 10
11.32
−0.19
+0.02
M
⊙
), is the most massive galaxy without an active galactic nucleus at
z
> 3 in the GOODS-ALMA field. It falls in the very center of the peak of the galaxy surface density, which suggests that the surrounding overdensity is a proto-cluster in the process of virialization and that AGS24 is the candidate progenitor of the future brightest cluster galaxy.
This paper introduces EGG, the Empirical Galaxy Generator, a tool designed within the ASTRODEEP collaboration to generate mock galaxy catalogs for deep fields with realistic fluxes and simple ...morphologies. The simulation procedure is based exclusively on empirical prescriptions – rather than first principles – to provide the most accurate match with current observations at 0 <z< 7. We considered that galaxies can be either quiescent or star-forming, and used their stellar mass (M∗) and redshift (z) as the fundamental properties from which all the other observables can be statistically derived. Drawing z and M∗ from the observed galaxy stellar mass functions, a star-formation rate (SFR) is attributed to each galaxy from the tight SFR–M∗ main sequence, while dust attenuation, optical colors and simple disk plus bulge morphologies are obtained from empirical relations that we established from the high quality Hubble and Herschel observations from the CANDELS fields. Random scatter was introduced in each step to reproduce the observed distributions of each parameter. Based on these observables, an adequate panchromatic spectral energy distribution (SED) is selected for each galaxy and synthetic photometry is produced by integrating the redshifted SED in common broad-band filters. Finally, the mock galaxies are placed on the sky at random positions with a fixed angular two-point correlation function to implement basic clustering. The resulting flux catalogs reproduce accurately the observed number counts in all broad bands from the ultraviolet up to the sub-millimeter, and can be directly fed to image simulators such as SkyMaker. The images can then be used to test source extraction softwares and image-based techniques such as stacking. egg is open-source, and is made available to the community on behalf of the ASTRODEEP collaboration, together with a set of pre-generated catalogs and images.
In this paper, we extend the source detection in the GOODS-ALMA field (69 arcmin
2
, 1
σ
≃ 0.18 mJy beam
−1
) to deeper levels than presented in our previous work. Using positional information at 3.6 ...and 4.5
μ
m (from
Spitzer
-IRAC) as well as the Very Large Array (VLA) at 3 GHz, we explore the presence of galaxies detected at 1.1 mm with ALMA below our original blind detection limit of 4.8-
σ
, at which the number of spurious sources starts to dominate over that of real sources. In order to ensure the most reliable counterpart association possible, we have investigated the astrometry differences between different instruments in the GOODS–South field. In addition to a global offset between the Atacama Large Millimeter/submillimeter Array (ALMA) and the
Hubble
Space Telescope (HST) already discussed in previous studies, we have highlighted a local offset between ALMA and the HST that was artificially introduced in the process of building the mosaic of the GOODS–South image. We created a distortion map that can be used to correct for these astrometric issues. In this Supplementary Catalog, we find a total of 16 galaxies, including two galaxies with no counterpart in HST images (also known as optically dark galaxies), down to a 5
σ
limiting depth of
H
= 28.2 AB (HST/WFC3
F
160
W
). This brings the total sample of GOODS-ALMA 1.1 mm sources to 35 galaxies. Galaxies in the new sample cover a wider dynamic range in redshift (
z
= 0.65−4.73), are on average twice as large (1.3 vs 0.65 kpc), and have lower stellar masses (
M
⋆
SC
= 7.6 × 10
10
M
⊙
vs
M
⋆
MC
= 1.2 × 10
11
M
⊙
). Although exhibiting larger physical sizes, these galaxies still have far-infrared sizes that are significantly more compact than inferred from their optical emission.
To decommission the Fukushima nuclear power plant after the accident caused by a tsunami in 2011, characterization of the fuel debris is required. The precise location and radiological composition of ...the fuel debris are currently unknown, and the area is submerged making it difficult to investigate the primary containment vessel. An integrated system that includes both radiation detectors and sonar will allow the full localization and characterization of the fuel debris. This paper describes research completed toward the development of a complete system, on-board a low-cost, small form-factor, submersible remotely operated vehicle. A cerium bromide (CeBr3) scintillator detector for dose-rate monitoring and gamma-ray spectrometry has been integrated and validated experimentally with a 137 Cs source, both in the laboratory and while submerged. The addition of an Imagenex 831L sonar has enabled technical demonstrations to take place at the National Maritime Research Institute's facility in Japan, where the system was able to characterize the shape and size of synthetic core debris. The combination of geometrical and radiological measurements allows the real-time localization of fuel debris and isotope identification, leading to an invaluable source of information to the workers at Fukushima that will enable increased efficiency and reduce risk during the decommissioning of the site.
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