Studies of the submm galaxy population in ECDFS: LESS, ALESS and zLESS

LESS:

We make available the multi-wavelength imaging, spectroscopy and redshift catalogs which has been taken as part of the sub-mm survey(s) of the Extended Chandra Deep Field South, an extra-galactic survey field at RA: 03:32 Dec: -27:48. This field has very low far-infrared backgrounds and good ESO and ALMA visibility and hence has become one of the pre-eminent fields for cosmological survey science. In particular, the field has been surveyed by Spitzer at 70-um with MIPS (and associated 24 and 160um observations) as part of the FIDEL survey (PI: Mark Dickinson), deep Herschel far-infrared imaging at 250, 350 and 500um and extensive 1.4GHz radio imaging.

This field was surveyed with the LABOCA camera on the MPIfR/ESO/OSO-owned 12-m APEX Telescope as part of the LABOCA ECDFS Submm Survey (LESS). This project used 350-hours of observing time to map the 0.5×0.5 degree Extended Chandra Deep Field South (ECDFS) field at 870um to a depth of ~1.2mJy (Figure right) to detect 126 sub-mm sources above a significance level above 3.7-sigma. Details of the survey can be found here.

This project was led by Ian Smail (ESO co-PI), Fabian Walter (ESO co-PI) and Axel Weiss (MPI PI). The survey is a collaboration of around 40 scientists based in Europe and the US: D. Alexander, E. Bell, F. Bertoldi, C. de Breuck, C. Cesarsky, S. Chapman, K. Coppin, P. Cox, H. Dannerbauer, J. Dunlop, M. Franx, R. Genzel, G. Hasinger, R. Ivison, A. Kovacs, K. Knudsen, E. Kreysa, D. Lutz, V. Mainieri, K. Meisenheimer, K. Menten, A. Omont, P. Popesso, A. Renzini, H.-W. Rix, E. Schinnerer, N. Foerster, G. Siringo, A.M. Swinbank, P. van der Werf, C. Vlahakis, N, Brandt, M. Dickinson, P. van Dokkum & E. Gawiser.

More information on this survey can be found here.

ALESS:

Follow-up observations of the 870-um selected LABOCA sources were carried out using ALMA in Cycle 0 as part of program 2011.0.00294.S. These observations were taken with 16 antennae, have a spatial resolution of 1" and a typical sensitivity of 0.5mJy r.m.s. Details of the survey and catalog can be found in Hodge et al. 2013.

The image on the left shows a false-colour K/IRAC-3.6um/ALMA composite of a suset of the SMGs in the survey.

Movies: Annimations (movies) generated from the data can be found here.

In total, the ALMA maps yield 99 SMGs with precisely located counterparts, directly pin-pointing the source(s) responsible for the sub-mm emission to within 0.3", without recourse to statistical radio/mid-infrared associations. These positions for SMGs has facilitated a number of studies, with over 25 papers written so far. These include: the source catalog and multiplicity (Hodge et al. 2013); the first high-resolution sub-mm number counts (Karim et al. 2013); AGN properties of ALMA SMGs (Wang et al. 2013); the far-infrared dust SEDs of ALMA SMGs (Swinbank et al. (2014); HST morphologies (Chen et al. 2015) and the sub-mm properties of colour-selected galaxies Decarli et al. (2014).

Notibly Simpson et al. (2013) use the 17-band optical-mid-infrared imaging of the ECDFS to derive photometric redshifts for the ALESS SMGs, deriving a median redshift of z=2.5+/-0.2 with a modest, but not dominant (<25%), tail of 870-um selected SMGs at z>4.

ALESS-SPIRE deblended images and catalogs:

Observations of the ECDFS have been carried out using the Herschel telescope with PACS and SPIRE (Oliver et al. 2012).

Due to the low angular resolution of Herschel, we have exploited the deep 24-um and radio imaging of this field to deblend the Herschel/SPIRE imaging in order to extract the far-infrared flux densities and colours of the SMGs. The resulting catalog(s) also include the SPIRE 250/350/500 flux densities (or limits) for all galaxies in the prior catalogs. The procedure used to deblend the field is is discussed in Swinbank et al. (2014).. In total, there are 6500 galaxies in the prior catalog. As an example, the 350-um image, best-fit model and residual maps for the field are shown on the right.

For the ALMA SMGs that are detected in at least two SPIRE bands, the median photometric redshift increases with increasing wavelength, with z=2.3+/-0.2, 2.5+/-0.3 and 3.5+/-0.5 for the 250, 350 and 500-um peakers respectively. 34 ALESS SMGs do not have a >3-sigma counterpart at 250, 350 or 500-um, and these SMGs have a median photometric redshift derived from the rest-frame UV-mid-infrared SEDs of z=3.3+/-0.5, which is higher than the full ALESS SMG sample; z=2.5+/-0.2. Finally, the median infrared luminosity and characteristic dust temperature of the >2mJy SMGs is Log(L/Lo)=12.5 (star formation rate of SFR=300Mo/yr) and Td=32+/-1K. At a fixed luminosity, the characteristic dust temperature of these high-redshift SMGs is 3-5 K lower than comparably luminous galaxies at z = 0, reflecting the more extended star formation occurring in these systems. These results are discussed in Swinbank et al. (2014). and Da Cunha et al. (2014).

The deblended 250/350/500-um ECDFS catalog for all ~6500 sources in the prior catalog is available here.

All SPIRE images, model fits and residual maps are available from this directory

Finally note that deblended images, maps and catalogs for other extra-galactic fields (COSMOS, GOODS-N, GOODS-S, SSA22) are also freely available from this directory

zLESS

We were awarded an ESO VLT Large Programme (zLESS - allocated 250hrs with VIMOS, FORS2 and XSHOOTER) as well as Keck MOSFIRE and DEIMOS and Gemini GNIRS) to obtain spectroscopy of the ALESS submillimetre sources.

In Danielson et al. (2016) we present the spectroscopic redshifts for 52 of these ALMA SMGs, determining a redshift of z=2.3+/-0.2. The redshift distribution features a high-z tail, with 23% of the SMGs at z>3.

Using the spectroscopic redshifts and the extensive UV-to-radio photometry in this field, we produce optimised spectral energy distributions (SEDs; figure left) using Magphys . For the SMGs with spectroscopic redshifts, we derive a median stellar mass of M*=6+/-1x10^10Msol. By combining these stellar masses with the star-formation rates measured from the far-infrared (using the deblended SPIRE catalogs discussed above), >2mJy ALMA SMGs appear to lie (on average) a factor ~5 above the so-called ``main-sequence'' for star-forming galaxies at z~2.

As a resource for future SMG studies, the rest-frame SEDs of the ALMA SMGs from Magphys are made available here.. The tarball includes both fits and ascii formats. The physical parameters, such as stellar masses, dust-reddenning (Av), star formation rates, dust masses and temperatures and luminosity weighted ages derived from the Magphys SED modelling are also made available in this file. If these are used, please cite Danielson et al. (2016)

zLESS spectroscopic catalogs and data

When designing the slit masks, we also in-filled the slit masks with other candidate high-redshift galaxies, in particular with mid-, far-infrared or radio selected galaxies. We provide the redshifts for all ~2000 galaxies targeted as part of the spectroscopic campaign in the link below

Download the full spectroscopic catalog here

The one- and two-dimensional spectra for all ~2000 galaxies targetted (fits and ascii) are also made available: Download the spectra here [3Gb]

This catalog is organised as: Galaxy ID; RA; Dec; redshift; Quality flag; Instrument; other IDs; notes

zALESS Table Notes:

The ID relates to the input catalog from which a target was selected. These are summarised in Danielson et al. (2016), and details are also (briefly) given here:

101-500: Statistically Robust or Tentative candidate LESS SMG counterparts from Wardlow et al. (2011) but which were later shown by ALMA to be incorrect IDs by Hodge et al. (2013).

500-700: Robust or tentative IDs for LESS sources with signal-to-noise of SNR=2.7--3.7-sigma in the original LESS map. These IDs for ``faint SMGs'' are derived using 1.4GHz radio emission from Biggs et al. (2011) but have not yet been confirmed (or ruled out) by ALMA.

700-1000: Galaxies in the LESS error circles which have photometric redshifts that are consistent with the ALESS SMG photometric redshifts (Wardlow et al. 2011)

1000-3000: 24+70-um-selected galaxies from the Spitzer FIDEL survey without pre-existing spectroscopic redshifts from Magnelli et al. (2008).

4000-4300: Chandra X-ray sources from the 2Ms or 4Ms surveys; e.g. (Luo et al. 2008).

50000-51000: Optically faint radio galaxies (OFRGs) from the JVLA 1.4GHz survey of this field. These radio sources are typically brighter than >20uJy at 1.4GHz but have optical magnitudes fainter than I(AB)=22 (Biggs et al. 2011).

70000-72000: Optically (colour) selected galaxies. These comprise a mix of z~2 Lyman-alpha emitting galaxies, BM/BX galaxies and Lyman break galaxies at 1.5 < z < 3.5.

90000-90200: B- or V-band drop-out galaxies (i.e. candidate z>2.5 or z>3.5 galaxies).

>80000: Galaxies which were not in any of the other catalogs but which could still be placed on the masks.

Any source in the catalog that is labelled with a "b" suffix denotes a secondary galaxy that happened to lie on the slit, but is not the primary target.

Note that the input catalogs are not unique (a galaxy could be an ALMA source that is also in the FIDEL 24-um catalog, a radio catalog, a BX/BM and also a Chandra source). In those instances, the object will only appear once in the table, but under the ID from which it was selected for slit placement (i.e. there are no RA/Dec repeats). However, the "other IDs" column lists those sources which appear in multiple catalogs.

The instrument IDs are denoted by F=VLT/FORS2, V=VLT/VIMOS, X=VLT/XSHOOTER, M=Keck/MOSFIRE, D=Keck/DEIMOS, and G=Gemini/GNIRS.

The quality flag (Q) for the spectroscopic redshifts is Q=1 for secure redshifts; Q=2 for redshifts measured from only one or two strong lines; Q=3 for tentative redshifts measured based on one or two very faint features; Q=4 for those sources which were targeted but no redshift could be determined. The redshift distribution for each of these sub-samples is shown in the figure below.

Comments, questions or requests for other data to Mark Swinbank; email: a.m.swinbank@dur.ac.uk