Abstract
We present an ALMA 1.3 mm (Band 6) continuum survey of lensed submillimeter galaxies (SMGs) at
z
= 1.0 to ∼3.2 with an angular resolution of ∼0.″2. These galaxies were uncovered by the ...Herschel Lensing Survey and feature exceptionally bright far-infrared continuum emission (
S
peak
≳ 90 mJy) owing to their lensing magnification. We detect 29 sources in 20 fields of massive galaxy clusters with ALMA. Using both the Spitzer/IRAC (3.6/4.5
μ
m) and ALMA data, we have successfully modeled the surface brightness profiles of 26 sources in the rest-frame near- and far-infrared. Similar to previous studies, we find the median dust-to-stellar continuum size ratio to be small (
R
e,dust
/
R
e,star
= 0.38 ± 0.14) for the observed SMGs, indicating that star formation is centrally concentrated. This is, however, not the case for two spatially extended main-sequence SMGs with a low surface brightness at 1.3 mm (≲0.1 mJy arcsec
−2
), in which the star formation is distributed over the entire galaxy (
R
e,dust
/
R
e,star
> 1). As a whole, our SMG sample shows a tight anticorrelation between (
R
e,dust
/
R
e,star
) and far-infrared surface brightness (Σ
IR
) over a factor of ≃1000 in Σ
IR
. This indicates that SMGs with less vigorous star formation (i.e., lower Σ
IR
) lack central starburst and are likely to retain a broader spatial distribution of star formation over the whole galaxies (i.e., larger
R
e,dust
/
R
e,star
). The same trend can be reproduced with cosmological simulations as a result of central starburst and potentially subsequent “inside-out” quenching, which likely accounts for the emergence of compact quiescent galaxies at
z
∼ 2.
The new generation interferometric arrays such as the Atacama Large Millimeter/submillimeter Array (ALMA) are composed of a large number of telescopes and their configurations are optimized for ...Fourier plane (a.k.a.
uv
-plane) coverage. As a consequence, solving for the missing information in the
uv
-plane is becoming less critical and the imaging algorithms can be revisited. The situation is getting similar to that encountered with single filled aperture telescopes and it is becoming possible to make images in a direct way. In this article a new weighting method is introduced to obtain “pseudo-clean” images without using prior information to solve for the Fourier transform of the source. This method is similar but not equivalent to the successive application of robust weighting and tapering at different scales. The idea is to weight the data to compensate for the imperfect distribution of natural weights in the
uv
-plane. The price to pay for this direct imaging technique is that the final point spread function (PSF or beam) may not follow a simple analytical shape such as a Gaussian (but this is also the case in optical astronomy) and some sensitivity is lost (but this is the case with any imaging algorithm in interferometry). Two parameters are introduced to control the trade-off between imaging quality and sensitivity, namely a threshold parameter and a coupling parameter. This method is applied to simulated ALMA observations with 16, 32 and 50 antennas. As expected this method is found to be more efficient with more antennas and for more compact configurations because the
uv
-plane coverage is more complete. With 50 antennas in compact configuration it is possible to reduce the amplitude of the inner sidelobes (outer sidelobes) by a factor >6 (>2) compared to natural weighting for ~10 % loss in sensitivity, leading to sidelobes lower than 1.6 % of the main lobe peak value. With 16 antennas only, the method can still be used to reduce the inner sidelobes of a compact configuration by a factor >2 for ~10 % loss in sensitivity. This method can therefore be used with the new generation interferometric arrays to efficiently produce images without relying on any assumptions about the sources. The dynamic range of the resulting images depend on the number of telescopes in the array, the source size and the acceptable level of sensitivity loss.
We report on the detailed analysis of a gravitationally lensed Y-band dropout, A2744_YD4, selected from deep Hubble Space Telescope imaging in the Frontier Field cluster Abell 2744. Band 7 ...observations with the Atacama Large Millimeter/submillimeter Array (ALMA) indicate the proximate detection of a significant 1 mm continuum flux suggesting the presence of dust for a star-forming galaxy with a photometric redshift of . Deep X-SHOOTER spectra confirms the high-redshift identity of A2744_YD4 via the detection of Ly emission at a redshift z = 8.38. The association with the ALMA detection is confirmed by the presence of O iii 88 m emission at the same redshift. Although both emission features are only significant at the 4 level, we argue their joint detection and the positional coincidence with a high-redshift dropout in the Hubble Space Telescope images confirms the physical association. Analysis of the available photometric data and the modest gravitational magnification ( ) indicates A2744_YD4 has a stellar mass of ∼2 × 109 , a star formation rate of ∼20 yr−1 and a dust mass of ∼6 × 106 . We discuss the implications of the formation of such a dust mass only after the onset of cosmic reionization.
Using the Spitzer Space Telescope and Herschel Space Observatory, we have conducted a survey of IR galaxies in the field of the galaxy cluster AS1063 at z = 0.347, which is one of the most massive ...clusters known and a target of the Hubble Space Telescope (HST) Cluster Lensing and Supernova Survey with Hubble and the Frontier Field surveys. The Spitzer/MIPS 24 m and Herschel/PACS and SPIRE images revealed that the core of AS1063 is surprisingly devoid of IR sources, showing only a few detectable sources within the central r ∼ 1′. There is, however, one particularly bright source (2.3 mJy at 24 m; 106 mJy at 160 m), which corresponds to a background galaxy at z = 0.61. The modest magnification factor (4.0×) implies that this galaxy is intrinsically IR luminous ( ). What is particularly interesting about this galaxy is that HST optical/near-IR images show a remarkably bright and large (1 kpc) clump at one edge of the disk. Our follow-up optical/near-IR spectroscopy shows Balmer (H -H8) and forbidden emission from this clump (O ii λ3727, O iii λλ4959,5007, N ii λλ6548,6583), indicating that it is an H ii region. The H ii region appears to have formed in situ, as kinematically it is part of a rotating disk, and there is no evidence of nearby interacting galaxies. With an extinction correction of mag, the star formation rate of this giant H ii region is ∼10 M yr−1, which is exceptionally large, even for high-redshift H ii regions. Such a large and luminous H ii region is often seen at z ∼ 2 but is quite rare in the nearby universe.
We present high angular resolution observations of the HCN(1-0) emission (at ~1" or ~34 pc), together with CO J = 1-0, 2-1, and 3-2 observations, toward the Seyfert 2 nucleus of M51 (NGC 5194). The ...overall HCN(1-0) distribution and kinematics are very similar to that of the CO lines, which have been indicated as the jet-entrained molecular gas in our past observations. In addition, high HCN(1-0)/CO(1-0) brightness temperature ratio of about unity is observed along the jets, similar to that observed at the shocked molecular gas in our Galaxy. These results strongly indicate that both diffuse and dense gases are entrained by the jets and outflowing from the active galactic nucleus. The channel map of HCN(1-0) at the systemic velocity shows a strong emission right at the nucleus, where no obvious emission has been detected in the CO lines. The HCN(1-0)/CO(1-0) brightness temperature ratio at this region reaches >2, a value that cannot be explained considering standard physical/chemical conditions. Based on our calculations, we suggest infrared pumping and possibly weak HCN masing, but still requiring an enhanced HCN abundance for the cause of this high ratio. This suggests the presence of a compact dense obscuring molecular gas in front of the nucleus of M51, which remains unresolved at our ~1" (~34 pc) resolution, and consistent with the Seyfert 2 classification picture.
The design of an interferometric array should allow optimal instrumental response regarding all possible source positions, times of integration and scientific goals. It should also take into account ...constraints such as forbidden regions on the ground due to impracticable topography. The complexity of the problem requires one to proceed by steps. A possible approach is to first consider a single observation and a single scientific purpose. A new algorithm is introduced to solve efficiently this particular problem called the configuration problem. It is based on the computation of pressure forces related to the discrepancies between the model (as determined by the scientific purpose) and the actual distribution of Fourier samples. The flexibility and rapidity of the method are well adapted to the full array design. A software named APO that can be used for the design of new generation interferometers such as ALMA and ATA has been developed.
We have conducted a LABOCA 870 μm follow-up of ten massive lensing clusters of the Herschel Lensing Survey (HLS, Egami et al. 2010) aiming at unveiling the yet hidden part of dusty star formation in ...the distant Universe. Among these clusters, A2744 and AS1063 are part of the Frontier Fields HST program. We also obtained 2 mm bolometer observations of A2744 and A370 with the GISMO array at the IRAM 30 m. We detected sources that are undetected with Herschel (PACS and SPIRE) implying either a very high redshift (z > 4) or a very low dust temperature (T<25 K). Their flux also imply a low intrinsic luminosity, L
FIR < 1012L⊙. Some of them are extended and could correspond to multiple sources or to multiple images of a lensed source. Substructures in the Sunyaev-Zeldovich effect could also contribute this very red submm emission. An ALMA program is ongoing to unveil the nature of these sources.
We combine molecular gas masses inferred from CO emission in 500 star-forming galaxies (SFGs) between z = 0 and 3, from the IRAM-COLDGASS, PHIBSS1/2, and other surveys, with gas masses derived from ...Herschel far-IR dust measurements in 512 galaxy stacks over the same stellar mass/redshift range. We constrain the scaling relations of molecular gas depletion timescale (t sub(depl)) and gas to stellar mass ratio (M sub(mol gas)/Mlow *) of SFGs near the star formation "main-sequence" with redshift, specific star-formation rate (sSFR), and stellar mass (Mlow *). The CO- and dust-based scaling relations agree remarkably well. This suggests that the CO arrow right H sub(2) mass conversion factor varies little within + or -0.6 dex of the main sequence (sSFR(ms, z, Mlow *)), and less than 0.3 dex throughout this redshift range. This study builds on and strengthens the results of earlier work. We find that t sub(depl) scales as (1 + z) super(-0.3) x (sSFR/sSFR(ms, z, Mlow *)) super(-0.5), with little dependence on Mlow *. The resulting steep redshift dependence of M sub(mol gas)/Mlow * approximate (1 + z) super(3) mirrors that of the sSFR and probably reflects the gas supply rate. The decreasing gas fractions at high are driven by the flattening of the SFR-Mlow * relation. Throughout the probed redshift range a combination of an increasing gas fraction and a decreasing depletion timescale causes a larger sSFR at constant Mlow *. As a result, galaxy integrated samples of the M sub(mol gas)-SFR rate relation exhibit a super-linear slope, which increases with the range of sSFR. With these new relations it is now possible to determine M sub(mol gas) with an accuracy of + or -0.1 dex in relative terms, and + or -0.2 dex including systematic uncertainties.
We stress the importance of consistent SED analysis for distant star-forming galaxies (SFGs). We then summarise recent results from such an analysis concerning their basic physical properties, such ...as the determination of star formation rate (SFR), stellar mass, specific star SFR, UV attenuation, and how this affects our knowledge of star formation properties at high-z.
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