We present a "super-deblended" far-infrared (FIR) to (sub)millimeter photometric catalog in the Cosmic Evolution Survey (COSMOS), prepared with the method recently developed by Liu et al., with key ...adaptations. We obtain point-spread function fitting photometry at fixed prior positions including 88,008 galaxies detected in VLA 1.4, 3 GHz, and/or MIPS 24 m images. By adding a specifically carved mass-selected sample (with an evolving stellar mass limit), a highly complete prior sample of 194,428 galaxies is achieved for deblending FIR/(sub)mm images. We performed "active" removal of nonrelevant priors at FIR/(sub)mm bands using spectral energy distribution fitting and redshift information. In order to cope with the shallower COSMOS data, we subtract from the maps the flux of faint nonfitted priors and explicitly account for the uncertainty of this step. The resulting photometry (including data from Spitzer, Herschel, SCUBA2, AzTEC, MAMBO, and NSF's Karl G. Jansky Very Large Array at 3 and 1.4 GHz) displays well-behaved quasi-Gaussian uncertainties calibrated from Monte Carlo simulations and tailored to observables (crowding, residual maps). Comparison to ALMA photometry for hundreds of sources provides a remarkable validation of the technique. We detect 11,220 galaxies over the 100-1200 m range extending to zphot ∼ 7. We conservatively selected a sample of 85 z > 4 high-redshift candidates significantly detected in the FIR/(sub)mm, often with secure radio and/or Spitzer/IRAC counterparts. This provides a chance to investigate the first generation of vigorous starburst galaxies (SFRs ∼ 1000 M yr−1). The photometric and value-added catalogs are publicly released.
We report the detection of a noncorotating gas component in a bright unlensed submillimeter galaxy at z = 4.3, hosting a compact starburst. Atacama Large Millimeter/submillimeter Array 0 17 and 0 09 ...resolution observations of C ii emission clearly demonstrate that the gas kinematics are characterized by an ordered rotation. After subtracting the best-fit model of a rotating disk, we kinematically identify two residual components in the channel maps. Both observing simulations and analysis of dirty images confirm that these two subcomponents are not artificially created by noise fluctuations and beam deconvolution. One of the two has a velocity offset of 200 km s−1 and a physical separation of 2 kpc from the primary disk and is located along the kinematic minor axis of disk rotation. We conclude that this gas component is falling into the galaxy from a direction perpendicular to the disk rotation. The accretion of such small noncorotating gas components could stimulate violent disk instability, driving radial gas inflows into the center of galaxies and leading to formation of in situ clumps such as identified in dust continuum and CO. We require more theoretical studies on high gas fraction mergers with mass ratio of 1: > 10 to verify this process.
Abstract
We report ALMA detections of C
ii
and a dust continuum in Az9, a multiply imaged galaxy behind the Frontier Field cluster MACS J0717.5+3745. The bright C
ii
emission line provides a ...spectroscopic redshift of
z
= 4.274. This strongly lensed (
μ
= 7 ± 1) galaxy has an intrinsic stellar mass of only 2 × 10
9
M
⊙
and a total star formation rate of 26
M
⊙
yr
−1
(∼80% of which is dust-obscured). Using public magnification maps, we reconstruct the C
ii
emission in the source plane to reveal a stable, rotation-dominated disk with
V
/
σ
= 5.3, which is >2× higher than predicted from simulations for similarly high-redshift, low-mass galaxies. In the source plane, the C
ii
disk has a half-light radius of 1.8 kpc and, along with the dust, is spatially offset from the peak of the stellar light by 1.4 kpc. Az9 is not deficient in C
ii
;
L
C
II
/
L
IR
= 0.0027, consistent with local and high-redshift normal star-forming galaxies. While dust-obscured star formation is expected to dominate in higher-mass galaxies, such a large reservoir of dust and gas in a lower-mass disk galaxy 1.4 Gyr after the Big Bang challenges our picture of early galaxy evolution. Furthermore, the prevalence of such low-mass dusty galaxies has important implications for the selection of the highest-redshift dropout galaxies with JWST. As one of the lowest stellar mass galaxies at
z
> 4 to be detected in a dust continuum and C
ii
, Az9 is an excellent laboratory in which to study early dust enrichment in the interstellar medium.
We present the first results from the deep and wide 5 GHz radio observations of the Great Observatories Origins Deep Survey (GOODS)-North ( = 3.5 Jy beam−1, synthesized beam size θ = 1 47 × 1 42, and ...52 sources over 109 arcmin2) and GOODS-South ( = 3.0 Jy beam−1, θ = 0 98 × 0 45, and 88 sources over 190 arcmin2) fields using the Karl G. Jansky Very Large Array. We derive radio spectral indices between 1.4 and 5 GHz using the beam-matched images and show that the overall spectral index distribution is broad even when the measured noise and flux bias are considered. We also find a clustering of faint radio sources around = 0.8, but only within S5 GHz < 150 Jy. We demonstrate that the correct radio spectral index is important for deriving accurate rest-frame radio power and analyzing the radio-FIR correlation, and adopting a single value of = 0.8 leads to a significant scatter and a strong bias in the analysis of the radio-FIR correlation, resulting from the broad and asymmetric spectral index distribution. When characterized by specific star formation rates, the starburst population (58%) dominates the 5 GHz radio source population, and the quiescent galaxy population (30%) follows a distinct trend in spectral index distribution and the radio-FIR correlation. Lastly, we offer suggestions on sensitivity and angular resolution for future ultra-deep surveys designed to trace the cosmic history of star formation and AGN activity using radio continuum as a probe.
ABSTRACT The central structure in three of the brightest unlensed z = 3-4 submillimeter galaxies is investigated through 0 015-0 05 (120-360 pc) 860 m continuum images obtained using the Atacama ...Large Millimeter/submillimeter Array (ALMA). The distribution in the central kiloparsec in AzTEC1 and AzTEC8 is extremely complex, and they are composed of multiple ∼200 pc clumps. AzTEC4 consists of two sources that are separated by ∼1.5 kpc, indicating a mid-stage merger. The peak star formation rate densities in the central clumps are ∼300-3000 M yr−1 kpc−2, suggesting regions with extreme star formation near the Eddington limit. By comparing the flux obtained by ALMA and Submillimeter Array, we find that 68%-90% of the emission is extended ( 1 kpc) in AzTEC4 and 8. For AzTEC1, we identify at least 11 additional compact (∼200 pc) clumps in the extended 3-4 kpc region. Overall, the data presented here suggest that the luminosity surface densities observed at 150 pc scales are roughly similar to that observed in local ULIRGs, as in the eastern nucleus of Arp 220. Between 10% and 30% of the 860 m continuum is concentrated in clumpy structures in the central kiloparsec, while the remaining flux is distributed over 1 kpc regions, some of which could also be clumpy. These sources can be explained by a rapid inflow of gas such as a merger of gas-rich galaxies, surrounded by extended and clumpy starbursts. However, the cold mode accretion model is not ruled out.
We report 1.1-mm number counts revealed with the Atacama Large Millimeter/submillimeter Array (ALMA) in the Subaru/XMM-Newton Deep Survey Field (SXDF). The advent of ALMA enables us to reveal ...millimeter-wavelength number counts down to the faint end without source confusion. However, previous studies are based on the ensemble of serendipitously detected sources in fields originally targeting different sources and could be biased due to the clustering of sources around the targets. We derive number counts in the flux range of 0.2–2 mJy by using 23 (≥4σ) sources detected in a continuous 2.0-arcmin2 area of the SXDF. The number counts are consistent with previous results within errors, suggesting that the counts derived from serendipitously detected sources are not significantly biased, although there could be field-to-field variation due to the small survey area. By using the best-fitting function of the number counts, we find that ∼40% of the extragalactic background light at 1.1 mm is resolved at S
1.1mm > 0.2 mJy.
We report the study of the far-infrared (IR) sizes of submillimeter galaxies (SMGs) in relation to their dust-obscured star formation rate (SFR) and active galactic nuclei (AGN) presence, determined ...using mid-IR photometry. We determined the millimeter-wave ( m) sizes of 69 Atacama Large Millimeter/submillimeter Array (ALMA)-identified SMGs, selected with confidence on ALMA images ( -7.4 mJy). We found that all of the SMGs are located above an avoidance region in the size-flux plane, as expected by the Eddington limit for star formation. In order to understand what drives the different millimeter-wave sizes in SMGs, we investigated the relation between millimeter-wave size and AGN fraction for 25 of our SMGs at z = 1-3. We found that the SMGs for which the mid-IR emission is dominated by star formation or AGN have extended millimeter-sizes, with respective median and kpc. Instead, the SMGs for which the mid-IR emission corresponds to star-forming/AGN composites have more compact millimeter-wave sizes, with median kpc. The relation between millimeter-wave size and AGN fraction suggests that this size may be related to the evolutionary stage of the SMG. The very compact sizes for composite star-forming/AGN systems could be explained by supermassive black holes growing rapidly during the SMG coalescing, star-formation phase.
Several authors have claimed that less luminous active galactic nuclei (AGNs) are not capable of sustaining a dusty torus structure. Thus, a gradual resizing of the torus is expected when the AGN ...luminosity decreases. Our aim is to examine mid-infrared observations of local AGNs of different luminosities for the gradual resizing and disappearance of the torus. We applied the decomposition method described by Hernán-Caballero et al. to a sample of ∼100 Spitzer/IRS spectra of low-luminosity AGNs and powerful Seyferts in order to decontaminate the torus component from other contributors. We have also included Starburst objects to ensure secure decomposition of the Spitzer/IRS spectra. We have used the affinity propagation (AP) method to cluster the data into five groups within the sample according to torus contribution to the 5-15 m range ( ) and bolometric luminosity ( ). The AP groups show a progressively higher torus contribution and an increase of the bolometric luminosity from Group 1 ( and ) up to Group 5 ( and ). We have fitted the average spectra of each of the AP groups to clumpy models. The torus is no longer present in Group 1, supporting its disappearance at low luminosities. We were able to fit the average spectra for the torus component in Groups 3 ( and ), 4 ( and ), and 5 to Clumpy torus models. We did not find a good fitting to Clumpy torus models for Group 2 ( and ). This might suggest a different configuration and/or composition of the clouds for Group 2, which is consistent with the different gas content seen in Groups 1, 2, and 3, according to detections of molecular lines. Groups 3, 4, and 5 show a trend of decreasing torus width (which leads to a likely decrease of the geometrical covering factor), although we cannot confirm it with the present data. Finally, Groups 3, 4, and 5 show an increase of the outer radius of the torus for higher luminosities, consistent with a resizing of the torus according to AGN luminosity.
We present the detailed characterization of two extremely red submillimeter galaxies (SMGs), ASXDF1100.053.1 and 231.1, with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Jansky ...Very Large Array. These SMGs were originally selected using AzTEC at 1100 m, and are observed by Herschel to be faint at 100-500 m. Their (sub)millimeter colors are as red as-or redder-than known z 5 SMGs; indeed, ASXDF1100.053.1 is redder than HFLS 3, which lies at z = 6.3. They are also faint and red in the near-/mid-infrared: ∼1 Jy at IRAC 4.5 m and <0.2 Jy in the Ks filter. These SMGs are also faint in the radio waveband, where F6GHz = 4.5 Jy for ASXDF1100.053.1 and F1.4GHz = 28 Jy for ASXDF1100.231.1, suggestive of and for ASXDF1100.053.1 and 231.1, respectively. ASXDF1100.231.1 has a flux excess in the 3.6 m filter, probably due to H emission at z = 4-5. Derived properties of ASXDF1100.053.1 for z = 5.5-7.5 and 231.1 for z = 3.5-5.5 are as follows: their infrared luminosities are 6.5 − 7.4 × 1012 and 4.2-4.5 × 1012 L ; their stellar masses are 0.9-2 × 1011 and 0.4-3 × 1010 M ; their circularized half-light radii in the ALMA maps are ∼1 and 0.2 kpc (∼2-3 kpc for 90% of the total flux). Last, their surface infrared luminosity densities, IR, are ∼1 × 1012 and 1.5 × 1013 L kpc−2, similar to values seen for local (U)LIRGs. These data suggest that ASXDF1100.053.1 and 231.1 are compact SMGs at z 4 and can plausibly evolve into z 3 compact quiescent galaxies.
PDF
