We have developed a new prior-based source extraction tool, xid+, to carry out photometry in the Herschel SPIRE (Spectral and Photometric Imaging Receiver) maps at the positions of known sources. ...xid+ is developed using a probabilistic Bayesian framework that provides a natural framework in which to include prior information, and uses the Bayesian inference tool Stan to obtain the full posterior probability distribution on flux estimates. In this paper, we discuss the details of xid+ and demonstrate the basic capabilities and performance by running it on simulated SPIRE maps resembling the COSMOS field, and comparing to the current prior-based source extraction tool desphot. Not only we show that xid+ performs better on metrics such as flux accuracy and flux uncertainty accuracy, but we also illustrate how obtaining the posterior probability distribution can help overcome some of the issues inherent with maximum-likelihood-based source extraction routines. We run xid+ on the COSMOS SPIRE maps from Herschel Multi-Tiered Extragalactic Survey using a 24-...m catalogue as a positional prior, and a uniform flux prior ranging from 0.01 to 1000 mJy. We show the marginalized SPIRE colour-colour plot and marginalized contribution to the cosmic infrared background at the SPIRE wavelengths. xid+ is a core tool arising from the Herschel Extragalactic Legacy Project (HELP) and we discuss how additional work within HELP providing prior information on fluxes can and will be utilized. The software is available at https://github.com/H-E-L-P/XID_plus. We also provide the data product for COSMOS. We believe this is the first time that the full posterior probability of galaxy photometry has been provided as a data product. (ProQuest: ... denotes formulae/symbols omitted.)
Abstract
We study a large galaxy sample from the Spitzer Matching Survey of the UltraVISTA ultra-deep Stripes (SMUVS) to search for sources with enhanced
3.6
μ
m
fluxes indicative of strong H
α
...emission at
z
=
3.9
–
4.9
. We find that the percentage of “H
α
excess” sources reaches 37%–40% for galaxies with stellar masses
log
10
(
M
*
/
M
⊙
)
≈
9
–
10
and decreases to
<
20
%
at
log
10
(
M
*
/
M
⊙
)
∼
10.7
. At higher stellar masses, however, the trend reverses, although this is likely due to active galactic nucleus contamination. We derive star formation rates (SFR) and specific SFR (sSFR) from the inferred H
α
equivalent widths of our “H
α
excess” galaxies. We show, for the first time, that the “H
α
excess” galaxies clearly have a bimodal distribution on the SFR–
M
* plane: they lie on the main sequence of star formation (with
log
10
(
sSFR
/
yr
−
1
)
<
−
8.05
) or in a starburst cloud (with
log
10
(
sSFR
/
yr
−
1
)
>
−
7.60
). The latter contains
∼
15
%
of all the objects in our sample and accounts for
>
50
%
of the cosmic SFR density at
z
=
3.9
–
4.9
, for which we derive a robust lower limit of
0.066
M
⊙
yr
−
1
Mpc
−
3
. Finally, we identify an unusual
>
50
σ
overdensity of
z
=
3.9
–
4.9
galaxies within a
0.20
×
0.20
arcmin
2
region. We conclude that the SMUVS unique combination of area and depth at mid-IR wavelengths provides an unprecedented level of statistics and dynamic range that are fundamental to revealing new aspects of galaxy evolution in the young universe.
ABSTRACT We present high-resolution 870 m Atacama Large Millimeter/sub-millimeter Array (ALMA) continuum maps of 30 bright sub-millimeter sources in the UKIDSS UDS field. These sources are selected ...from deep, 1 degree2 850 m maps from the SCUBA-2 Cosmology Legacy Survey, and are representative of the brightest sources in the field (median = 8.7 0.4 mJy). We detect 52 sub-millimeter galaxies (SMGs) at >4 significance in our 30 ALMA maps. In of the ALMA maps the single-dish source comprises a blend of ≥2 SMGs, where the secondary SMGs are Ultra-luminous Infrared Galaxies (ULIRGs) with 1012 . The brightest SMG contributes on average of the single-dish flux density, and in the ALMA maps containing ≥2 SMGs the secondary SMG contributes of the integrated ALMA flux. We construct source counts and show that multiplicity boosts the apparent single-dish cumulative counts by 20% at S870 > 7.5 mJy, and by 60% at S870 > 12 mJy. We combine our sample with previous ALMA studies of fainter SMGs and show that the counts are well-described by a double power law with a break at 8.5 0.6 mJy. The break corresponds to a luminosity of ∼6 × 1012 or a star formation rate (SFR) of ∼103 . For the typical sizes of these SMGs, which are resolved in our ALMA data with = 1.2 0.1 kpc, this yields a limiting SFR density of ∼100 yr−1 kpc−2 Finally, the number density of S870 2 mJy SMGs is 80 30 times higher than that derived from blank-field counts. An over-abundance of faint SMGs is inconsistent with line-of-sight projections dominating multiplicity in the brightest SMGs, and indicates that a significant proportion of these high-redshift ULIRGs are likely to be physically associated.
We have obtained deep 1 and 3 mm spectral-line scans towards a candidate z ≳ 5 ALMA-identified AzTEC submillimetre galaxy (SMG) in the Subaru/XMM-Newton Deep Field (or UKIDSS UDS), ASXDF1100.053.1, ...using the NOrthern Extended Millimeter Array (NOEMA), aiming to obtain its spectroscopic redshift. ASXDF1100.053.1 is an unlensed optically dark millimetre-bright SMG with S1100 μm = 3.5 mJy and KAB > 25.7 (2σ), which was expected to lie at z = 5–7 based on its radio–submillimetre photometric redshift. Our NOEMA spectral scan detected line emission due to 12CO(J = 5–4) and (J = 6–5), providing a robust spectroscopic redshift, zCO = 5.2383 ± 0.0005. Energy-coupled spectral energy distribution modelling from optical to radio wavelengths indicates an infrared luminosity LIR = 8.3−1.4+1.5 × 1012 L⊙, a star formation rate SFR = 630−380+260 M⊙ yr−1, a dust mass Md = 4.4−0.3+0.4 × 108 M⊙, a stellar mass Mstellar = 3.5−1.4+3.6 × 1011 M⊙, and a dust temperature Td = 37.4−1.8+2.3 K. The CO luminosity allows us to estimate a gas mass Mgas = 3.1 ± 0.3 × 1010 M⊙, suggesting a gas-to-dust mass ratio of around 70, fairly typical for z ∼ 2 SMGs. ASXDF1100.053.1 has ALMA continuum size Re = 1.0−0.1+0.2 kpc, so its surface infrared luminosity density ΣIR is 1.2−0.2+0.1 × 1012 L⊙ kpc−2. These physical properties indicate that ASXDF1100.053.1 is a massive dusty star-forming galaxy with an unusually compact starburst. It lies close to the star-forming main sequence at z ∼ 5, with low Mgas/Mstellar = 0.09, SFR/SFRMS(RSB) = 0.6, and a gas-depletion time τdep of ≈50 Myr, modulo assumptions about the stellar initial mass function in such objects. ASXDF1100.053.1 has extreme values of Mgas/Mstellar, RSB, and τdep compared to SMGs at z ∼ 2–4, and those of ASXDF1100.053.1 are the smallest among SMGs at z > 5. ASXDF1100.053.1 is likely a late-stage dusty starburst prior to passivisation. The number of z = 5.1–5.3 unlensed SMGs now suggests a number density dN/dz = 30.4 ± 19.0 deg−2, barely consistent with the latest cosmological simulations.
The Herschel Multi-tiered Extragalactic Survey (HerMES) has identified large numbers of dusty star-forming galaxies (DSFGs) over a wide range in redshift. A detailed understanding of these DSFGs is ...hampered by the limited spatial resolution of Herschel. We present 870 mu m 0".45 resolution imaging obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) of a sample of 29 HerMES DSFGs that have far-infrared (FIR) flux densities that lie between the brightest of sources found by Herschel and fainter DSFGs found via ground-based surveys in the submillimeter region. The ALMA imaging reveals that these DSFGs comprise a total of 62 sources (down to the 5sigma point-source sensitivity limit in our ALMA sample; sigma approximate 0.2 mJy). Optical or near-infrared imaging indicates that 36 of the ALMA sources experience a significant flux boost from gravitational lensing ( mu > 1.1), but only six are strongly lensed and show multiple images. We introduce and make use of UVMCMCFIT, a general-purpose and publicly available Markov chain Monte Carlo visibility-plane analysis tool to analyze the source properties. Combined with our previous work on brighter Herschel sources, the lens models presented here tentatively favor intrinsic number counts for DSFGs with a break near 8 mJy at 880 mu m and a steep fall-off at higher flux densities. Nearly 70% of the Herschel sources break down into multiple ALMA counterparts, consistent with previous research indicating that the multiplicity rate is high in bright sources discovered in single-dish submillimeter or FIR surveys. The ALMA counterparts to our Herschel targets are located significantly closer to each other than ALMA counterparts to sources found in the LABOCA ECDFS Submillimeter Survey. Theoretical models underpredict the excess number of sources with small separations seen in our ALMA sample. The high multiplicity rate and small projected separations between sources seen in our sample argue in favor of interactions and mergers plausibly driving both the prodigious emission from the brightest DSFGs as well as the sharp downturn above S sub(880) = 8 mJy.
The Spitzer Matching Survey of the UltraVISTA Ultra-deep Stripes (SMUVS) has obtained the largest ultradeep Spitzer maps to date in a single field of the sky. We considered the sample of about 66,000 ...SMUVS sources at z = 2-6 to investigate the evolution of dusty and nondusty galaxies with stellar mass through the analysis of the galaxy stellar mass function (GSMF), extending previous analyses about one decade in stellar mass and up to z = 6. We further divide our nondusty galaxy sample with rest-frame optical colors to isolate red quiescent ("passive") galaxies. At each redshift, we identify a characteristic stellar mass in the GSMF above which dusty galaxies dominate, or are at least as important as nondusty galaxies. Below that stellar mass, nondusty galaxies compose about 80% of all sources, at all redshifts except at z = 4-5. The percentage of dusty galaxies at z = 4-5 is unusually high: 30%-40% for and >80% at M* > 1011 M , which indicates that dust obscuration is of major importance in this cosmic period. The overall percentage of massive ( ) galaxies that are quiescent increases with decreasing redshift, reaching >30% at z ∼ 2. Instead, the quiescent percentage among intermediate-mass galaxies (with ) stays roughly constant at a ∼10% level. Our results indicate that massive and intermediate-mass galaxies clearly have different evolutionary paths in the young universe and are consistent with the scenario of galaxy downsizing.
We have obtained deep 1 and 3 mm spectral-line scans towards a candidate
z
≳ 5 ALMA-identified AzTEC submillimetre galaxy (SMG) in the Subaru/
XMM-Newton
Deep Field (or UKIDSS UDS), ASXDF1100.053.1, ...using the NOrthern Extended Millimeter Array (NOEMA), aiming to obtain its spectroscopic redshift. ASXDF1100.053.1 is an unlensed optically dark millimetre-bright SMG with
S
1100 μm
= 3.5 mJy and
K
AB
> 25.7 (2
σ
), which was expected to lie at
z
= 5–7 based on its radio–submillimetre photometric redshift. Our NOEMA spectral scan detected line emission due to
12
CO(
J
= 5–4) and (
J
= 6–5), providing a robust spectroscopic redshift,
z
CO
= 5.2383 ± 0.0005. Energy-coupled spectral energy distribution modelling from optical to radio wavelengths indicates an infrared luminosity
L
IR
= 8.3
−1.4
+1.5
× 10
12
L
⊙
, a star formation rate SFR = 630
−380
+260
M
⊙
yr
−1
, a dust mass
M
d
= 4.4
−0.3
+0.4
× 10
8
M
⊙
, a stellar mass
M
stellar
= 3.5
−1.4
+3.6
× 10
11
M
⊙
, and a dust temperature
T
d
= 37.4
−1.8
+2.3
K. The CO luminosity allows us to estimate a gas mass
M
gas
= 3.1 ± 0.3 × 10
10
M
⊙
, suggesting a gas-to-dust mass ratio of around 70, fairly typical for
z
∼ 2 SMGs. ASXDF1100.053.1 has ALMA continuum size
R
e
= 1.0
−0.1
+0.2
kpc, so its surface infrared luminosity density Σ
IR
is 1.2
−0.2
+0.1
× 10
12
L
⊙
kpc
−2
. These physical properties indicate that ASXDF1100.053.1 is a massive dusty star-forming galaxy with an unusually compact starburst. It lies close to the star-forming main sequence at
z
∼ 5, with low
M
gas
/
M
stellar
= 0.09, SFR/SFR
MS
(
R
SB
) = 0.6, and a gas-depletion time
τ
dep
of ≈50 Myr, modulo assumptions about the stellar initial mass function in such objects. ASXDF1100.053.1 has extreme values of
M
gas
/
M
stellar
,
R
SB
, and
τ
dep
compared to SMGs at
z
∼ 2–4, and those of ASXDF1100.053.1 are the smallest among SMGs at
z
> 5. ASXDF1100.053.1 is likely a late-stage dusty starburst prior to passivisation. The number of
z
= 5.1–5.3 unlensed SMGs now suggests a number density d
N
/d
z
= 30.4 ± 19.0 deg
−2
, barely consistent with the latest cosmological simulations.
We present a catalogue of ~3000 submillimetre sources detected ( greater than or equal to 3.5...) at 850 ...m over ~5 deg super( 2) surveyed as part of the James Clerk Maxwell Telescope (JCMT) ...SCUBA-2 Cosmology Legacy Survey (S2CLS). This is the largest survey of its kind at 850 ...m, increasing the sample size of 850 ...m selected submillimetre galaxies by an order of magnitude. The wide 850 ...m survey component of S2CLS covers the extragalactic fields: UKIDSS-UDS, COSMOS, Akari-NEP, Extended Groth Strip, Lockman Hole North, SSA22 and GOODS-North. The average 1... depth of S2CLS is 1.2 mJy beam super( -1), approaching the SCUBA-2 850 ...m confusion limit, which we determine to be ... 0.8 mJy beam super( -1). We measure the 850 ...m number counts, reducing the Poisson errors on the differential counts to approximately 4 per cent at S sub( 850) ... 3 mJy. With several independent fields, we investigate field-to-field variance, finding that the number counts on 0.5...-1... scales are generally within 50 per cent of the S2CLS mean for S sub( 850) > 3 mJy, with scatter consistent with the Poisson and estimated cosmic variance uncertainties, although there is a marginal (2...) density enhancement in GOODS-North. The observed counts are in reasonable agreement with recent phenomenological and semi-analytic models, although determining the shape of the faint-end slope (S sub( 850) < 3 mJy) remains a key test. The large solid angle of S2CLS allows us to measure the bright-end counts: at S sub( 850) > 10 mJy there are approximately 10 sources per square degree, and we detect the distinctive up-turn in the number counts indicative of the detection of local sources of 850 ...m emission, and strongly lensed high-redshift galaxies. All calibrated maps and the catalogue are made publicly available. (ProQuest: ... denotes formulae/symbols omitted.)
We study a large galaxy sample from the Spitzer Matching Survey of the UltraVISTA ultra-deep Stripes (SMUVS) to search for sources with enhanced 3.6 m fluxes indicative of strong H emission at z = ...3.9 - 4.9 . We find that the percentage of "H excess" sources reaches 37%-40% for galaxies with stellar masses log 10 ( M * M ) 9 - 10 and decreases to < 20 % at log 10 ( M * M ) ∼ 10.7 . At higher stellar masses, however, the trend reverses, although this is likely due to active galactic nucleus contamination. We derive star formation rates (SFR) and specific SFR (sSFR) from the inferred H equivalent widths of our "H excess" galaxies. We show, for the first time, that the "H excess" galaxies clearly have a bimodal distribution on the SFR-M* plane: they lie on the main sequence of star formation (with log 10 ( sSFR yr − 1 ) < − 8.05 ) or in a starburst cloud (with log 10 ( sSFR yr − 1 ) > − 7.60 ). The latter contains ∼ 15 % of all the objects in our sample and accounts for > 50 % of the cosmic SFR density at z = 3.9 - 4.9 , for which we derive a robust lower limit of 0.066 M yr − 1 Mpc − 3 . Finally, we identify an unusual > 50 overdensity of z = 3.9 - 4.9 galaxies within a 0.20 × 0.20 arcmin2 region. We conclude that the SMUVS unique combination of area and depth at mid-IR wavelengths provides an unprecedented level of statistics and dynamic range that are fundamental to revealing new aspects of galaxy evolution in the young universe.
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