We present deep, high-resolution (0 03, 200 pc) ALMA Band 7 observations covering the dust continuum and C ii λ157.7 m emission in four z ∼ 4.4-4.8 sub-millimeter galaxies (SMGs) selected from the ...ALESS and AS2UDS surveys. The data show that the rest-frame 160 m (observed 345 GHz) dust emission is consistent with smooth morphologies on kpc scales for three of the sources. One source, UDS 47.0, displays apparent substructure, but this is also consistent with a smooth morphology-as indicated by simulations showing that smooth exponential disks can appear clumpy when observed at the high angular resolution (0 03) and depth of these observations ( Jy beam−1). The four SMGs are bright C ii emitters. We extract C ii spectra from the high-resolution data, and recover ∼20%-100% of the C ii flux and ∼40%-80% of the dust continuum emission, compared to the previous lower-resolution observations. When tapered to 0 2 resolution, our maps recover ∼80%-100% of the continuum emission, indicating that ∼60% of the emission is resolved out on ∼200 pc scales. We find that the C ii emission in high-redshift galaxies is more spatially extended than the rest-frame 160 m dust continuum by a factor of 1.6 0.4. By considering the / ratio as a function of the star formation rate surface density ( ), we revisit the C ii deficit and suggest that the decline in the / ratio as a function of is consistent with local processes. We also explore the physical drivers that may be responsible for these trends and can give rise to the properties found in the densest regions of SMGs.
We present the first photometric redshift distribution for a large sample of 870 mu m submillimeter galaxies (SMGs) with robust identifications based on observations with ALMA. In our analysis we ...consider 96 SMGs in the Extended Chandra Deep Field South, 77 of which have 4-19 band photometry. We model the SEDs for these 77 SMGs, deriving a median photometric redshift of z sub(phot) = 2.3 + or - 0.1. Critically we show that the proportion of galaxies undergoing an SMG-like phase at z > or =, slanted 3 is at most 35% + or - 5% of the total population. We derive a median stellar mass of M sub(*) = (8 + or - 1) x 10 super(10) M sub(middot in circle), although there are systematic uncertainties of up to 5 x for individual sources. Taken together, these results are consistent with a simple model that identifies SMGs as events that form most of the stars seen in the majority of luminous elliptical galaxies at the present day.
We present high-resolution (0".3) Atacama Large Millimeter Array 870 mu m imaging of 52 sub-millimeter galaxies (SMGs) in the Ultra Deep Survey field to investigate the size and morphology of the ...sub-millimeter (sub-mm) emission on 2-10 kpc scales. We derive a median intrinsic angular size of FWHM = 0".30 + or - 0".04 for the 23 SMGs in the sample detected at a signal-to-noise ratio (S/N) > 10. Using the photometric redshifts of the SMGs we show that this corresponds to a median physical half-light diameter of 2.4 + or - 0.2 kpc. A stacking analysis of the SMGs detected at S/N < 10 shows they have sizes consistent with the 870 mu m bright SMGs in the sample. We compare our results to the sizes of SMGs derived from other multi-wavelength studies, and show that the rest-frame ~250 mu m sizes of SMGs are consistent with studies of resolved super(12)CO (J = 3-2 to 7-6) emission lines, but that sizes derived from 1.4 GHz imaging appear to be approximately two times larger on average, which we attribute to cosmic ray diffusion. The rest-frame optical sizes of SMGs are around four times larger than the sub-millimeter sizes, indicating that the star formation in these galaxies is compact relative to the pre-existing stellar distribution. The size of the starburst region in SMGs is consistent with the majority of the star formation occurring in a central region, a few kiloparsecs in extent, with a median star formation rate surface density of 90 + or - 30 M sub(middot in circle) yr super(-1) kpc super(-2), which may suggest that we are witnessing an intense period of bulge growth in these galaxies.
ABSTRACT
We present an ALMA study of the ∼180 brightest sources in the SCUBA-2 850-μm map of the COSMOS field from the S2COSMOS survey, as a pilot study for AS2COSMOS – a full survey of the ∼1000 ...sources in this field. In this pilot study, we have obtained 870-μm continuum maps of an essentially complete sample of the brightest 182 sub-millimetre sources ($S_{850\, \mu \rm m}\gt $ 6.2 mJy) in COSMOS. Our ALMA maps detect 260 sub-millimetre galaxies (SMGs) spanning a range in flux density of $S_{870\, \mu \rm m}$ = 0.7–19.2 mJy. We detect more than one SMG counterpart in 34 ± 2 per cent of sub-millimetre sources, increasing to 53 ± 8 per cent for SCUBA-2 sources brighter than $S_{850\, \mu \rm m}\gt $ 12 mJy. We estimate that approximately one-third of these SMG–SMG pairs are physically associated (with a higher rate for the brighter secondary SMGs, $S_{870\, \mu \rm m}\gtrsim$ 3 mJy), and illustrate this with the serendipitous detection of bright C ii 157.74-μm line emission in two SMGs, AS2COS 0001.1 and 0001.2 at z = 4.63, associated with the highest significance single-dish source. Using our source catalogue, we construct the interferometric 870-μm number counts at $S_{870\, \mu \rm m}\gt $ 6.2 mJy. We use the extensive archival data of this field to construct the multiwavelength spectral energy distribution of each AS2COSMOS SMG, and subsequently model this emission with magphys to estimate their photometric redshifts. We find a median photometric redshift for the $S_{870\, \mu \rm m}\gt $ 6.2 mJy AS2COSMOS sample of z = 2.87 ± 0.08, and clear evidence for an increase in the median redshift with 870-μm flux density suggesting strong evolution in the bright end of the 870-μm luminosity function.
We report the first counts of faint submillimetre galaxies (SMGs) in the 870-μm band derived from arcsecond-resolution observations with the Atacama Large Millimeter Array (ALMA). We have used ALMA ...to map a sample of 122 870-μm-selected submillimetre sources drawn from the 0
5×0
5 the Large Apex BOlometer CAmera (LABOCA) Extended Chandra Deep Field South submillimetre survey (LESS). These ALMA maps have an average depth of σ870 μm ∼ 0.4 mJy, some approximately three times deeper than the original LABOCA survey and critically the angular resolution is more than an order of magnitude higher, FWHM of ∼1.5 arcsec compared to ∼19 arcsec for the LABOCA discovery map. This combination of sensitivity and resolution allows us to precisely pinpoint the SMGs contributing to the submillimetre sources from the LABOCA map, free from the effects of confusion. We show that our ALMA-derived SMG counts broadly agree with the submillimetre source counts from previous, lower resolution single-dish surveys, demonstrating that the bulk of the submillimetre sources are not caused by blending of unresolved SMGs. The difficulty which well-constrained theoretical models have in reproducing the high surface densities of SMGs, thus remains. However, our observations do show that all of the very brightest sources in the LESS sample, S
870 μm 12 mJy, comprise emission from multiple, fainter SMGs, each with 870-μm fluxes of 9 mJy. This implies a natural limit to the star formation rate in SMGs of 103 M yr−1, which in turn suggests that the space densities of z > 1 galaxies with gas masses in excess of ∼5 × 1010 M is <10−5 Mpc−3. We also discuss the influence of this blending on the identification and characterization of the SMG counterparts to these bright submillimetre sources and suggest that it may be responsible for previous claims that they lie at higher redshifts than fainter SMGs.
We present Atacama Large Millimeter Array (ALMA) 870-μm (345-GHz) observations of two submillimetre galaxies (SMGs) drawn from an ALMA study of the 126 submillimetre sources from the LABOCA Extended ...Chandra Deep Field-South Survey (LESS). The ALMA data identify the counterparts to these previously unidentified submillimetre sources and serendipitously detect bright emission lines in their spectra which we show are most likely to be Cii 157.74 μm emission yielding redshifts of z = 4.42 and 4.44. This blind detection rate within the 7.5-GHz bandpass of ALMA is consistent with the previously derived photometric redshift distribution of SMGs and suggests a modest, but not dominant (≾25 per cent), tail of 870-μm selected SMGs at z ≿ 4. We find that the ratio of L
C ii/L
FIR in these SMGs is much higher than seen for similarly far-infrared-luminous galaxies at z ∼ 0, which is attributed to the more extended gas reservoirs in these high-redshift ultraluminous infrared galaxies (ULIRGs). Indeed, in one system we show that the C ii emission shows hints of extended emission on ≿ 3 kpc scales. Finally, we use the volume probed by our ALMA survey to show that the bright end of the C ii luminosity function evolves strongly between z = 0 and ∼4.4, reflecting the increased interstellar medium cooling in galaxies as a result of their higher star formation rates. These observations demonstrate that even with short integrations, ALMA is able to detect the dominant fine-structure cooling lines from high-redshift ULIRGs, measure their energetics and spatially resolved properties and trace their evolution with redshift.
We analyze Hubble Space Telescope WFC3/H sub(160)-band observations of a sample of 48 Atacama Large Millimeter/submillimeter Array detected submillimeter galaxies (SMGs) in the Extended Chandra Deep ...Field South field, to study their stellar morphologies and sizes. We detect 79% + or - 17% of the SMGs in the H sub(160)-band imaging with a median sensitivity of 27.8 mag, and most (80%) of the nondetections are SMGs with 870 mu m fluxes of S sub(870) < 3 mJy. With a surface brightness limit of mu H ~26 mag arcsec super(-2), we find that 82% + or - 9% of the H sub(160)-band-detected SMGs at z = 1-3 appear to have disturbed morphologies, meaning they are visually classified as either irregulars or interacting systems, or both. By determining a Sersic fit to the H sub(160) surface brightness profiles, we derive a median Sersic index of n = 1.2 + or - 0.3 and a median half-light radius of re = (ProQuest: Formulae and/or non-USASCII text omitted) kpc for our SMGs at z = 1-3. We also find significant displacements between the positions of the H sub(160) component and 870 mu m emission in these systems, suggesting that the dusty starburst regions and less-obscured stellar distribution are not colocated. We find significant differences in the sizes and the Sersic index between our z = 2-3 SMGs and z ~ 2 quiescent galaxies, suggesting that a major transformation of the stellar light profile is needed in the quenching processes if SMGs are progenitors of the red-and-dead z ~ 2 galaxies. Given the short-lived nature of SMGs, we postulate that the majority of the z = 2-3 SMGs with S sub(870) > ~ 2 mJy are early/mid-stage major mergers.
We present results from the first 12 months of operation of Radio Galaxy Zoo, which upon completion will enable visual inspection of over 170 000 radio sources to determine the host galaxy of the ...radio emission and the radio morphology. Radio Galaxy Zoo uses 1.4 GHz radio images from both the Faint Images of the Radio Sky at Twenty Centimeters (FIRST) and the Australia Telescope Large Area Survey (ATLAS) in combination with mid-infrared images at 3.4 μm from the Wide-field Infrared Survey Explorer (WISE) and at 3.6 μm from the Spitzer Space Telescope. We present the early analysis of the WISE mid-infrared colours of the host galaxies. For images in which there is >75 per cent consensus among the Radio Galaxy Zoo cross-identifications, the project participants are as effective as the science experts at identifying the host galaxies. The majority of the identified host galaxies reside in the mid-infrared colour space dominated by elliptical galaxies, quasi-stellar objects and luminous infrared radio galaxies. We also find a distinct population of Radio Galaxy Zoo host galaxies residing in a redder mid-infrared colour space consisting of star-forming galaxies and/or dust-enhanced non-star-forming galaxies consistent with a scenario of merger-driven active galactic nuclei (AGN) formation. The completion of the full Radio Galaxy Zoo project will measure the relative populations of these hosts as a function of radio morphology and power while providing an avenue for the identification of rare and extreme radio structures. Currently, we are investigating candidates for radio galaxies with extreme morphologies, such as giant radio galaxies, late-type host galaxies with extended radio emission and hybrid morphology radio sources.
![The Dust and [C ii] Morphol...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-637X/small "The Dust and [C ii] Morphologies of Redshift ∼4.5 Sub-millimeter Galaxies at ∼200 pc Resolution: The Absence of Large Clumps in the Interstellar Medium at High-redshift")
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