Using the IRAM NOrthern Extended Millimeter Array (NOEMA), we conducted a program to measure redshifts for 13 bright galaxies detected in the
Herschel
Astrophysical Large Area Survey with
S
500
μ
m
...≥ 80 mJy. We report reliable spectroscopic redshifts for 12 individual sources, which are derived from scans of the 3 and 2 mm bands, covering up to 31 GHz in each band, and are based on the detection of at least two emission lines. The spectroscopic redshifts are in the range 2.08 <
z
< 4.05 with a median value of
z
= 2.9 ± 0.6. The sources are unresolved or barely resolved on scales of 10 kpc. In one field, two galaxies with different redshifts were detected. In two cases the sources are found to be binary galaxies with projected distances of ∼140 kpc. The linewidths of the sources are large, with a mean value for the full width at half maximum of 700 ± 300 km s
−1
and a median of 800 km s
−1
. We analyze the nature of the sources with currently available ancillary data to determine if they are lensed or hyper-luminous (
L
FIR
> 10
13
L
⊙
) galaxies. We also present a reanalysis of the spectral energy distributions including the continuum flux densities measured at 3 and 2 mm to derive the overall properties of the sources. Future prospects based on these efficient measurements of redshifts of high-
z
galaxies using NOEMA are outlined, including a comprehensive survey of all the brightest
Herschel
galaxies.
We study the relation of AGN accretion, star formation rate (SFR) and stellar mass (M
*) using a sample of ≈8600 star-forming galaxies up to z = 2.5 selected with Herschel imaging in the GOODS and ...COSMOS fields. For each of them we derive SFR and M
*, both corrected, when necessary, for emission from an active galactic nucleus (AGN), through the decomposition of their spectral energy distributions (SEDs). About 10 per cent of the sample are detected individually in Chandra observations of the fields. For the rest of the sample, we stack the X-ray maps to get average X-ray properties. After subtracting the X-ray luminosity expected from star formation and correcting for nuclear obscuration, we derive the average AGN accretion rate for both detected sources and stacks, as a function of M
*, SFR and redshift. The average accretion rate correlates with SFR and with M
*. The dependence on SFR becomes progressively more significant at z > 0.8. This may suggest that SFR is the original driver of these correlations. We find that average AGN accretion and star formation increase in a similar fashion with offset from the star-forming ‘main-sequence’. Our interpretation is that accretion on to the central black hole and star formation broadly trace each other, irrespective of whether the galaxy is evolving steadily on the main-sequence or bursting.
Intensity mapping provides a unique means to probe the epoch of reionization (EoR), when the neutral intergalactic medium was ionized by energetic photons emitted from the first galaxies. The C ii ...158 m fine-structure line is typically one of the brightest emission lines of star-forming galaxies and thus a promising tracer of the global EoR star formation activity. However, C ii intensity maps at 6 z 8 are contaminated by interloping CO rotational line emission (3 ≤ Jupp ≤ 6) from lower-redshift galaxies. Here we present a strategy to remove the foreground contamination in upcoming C ii intensity mapping experiments, guided by a model of CO emission from foreground galaxies. The model is based on empirical measurements of the mean and scatter of the total infrared luminosities of galaxies at z < 3 and with stellar masses M * > 10 8 M selected in the K-band from the COSMOS/UltraVISTA survey, which can be converted to CO line strengths. For a mock field of the Tomographic Ionized-carbon Mapping Experiment, we find that masking out the "voxels" (spectral-spatial elements) containing foreground galaxies identified using an optimized CO flux threshold results in a z-dependent criterion m K AB 22 (or M * 10 9 M ) at z < 1 and makes a C ii/COtot power ratio of 10 at k = 0.1 h/Mpc achievable, at the cost of a moderate 8% loss of total survey volume.
We study the evolution of the radio spectral index and far-infrared/radio correlation (FRC) across the star-formation rate – stellar masse (i.e. SFR–M∗) plane up to z ~ 2. We start from a ...stellar-mass-selected sample of galaxies with reliable SFR and redshift estimates. We then grid the SFR–M∗ plane in several redshift ranges and measure the infrared luminosity, radio luminosity, radio spectral index, and ultimately the FRC index (i.e. qFIR) of each SFR–M∗–z bin. The infrared luminosities of our SFR–M∗–z bins are estimated using their stacked far-infrared flux densities inferred from observations obtained with the Herschel Space Observatory. Their radio luminosities and radio spectral indices (i.e. α, where Sν ∝ ν−α) are estimated using their stacked 1.4 GHz and 610 MHz flux densities from the Very Large Array and Giant Metre-wave Radio Telescope, respectively. Our far-infrared and radio observations include the most widely studied blank extragalactic fields – GOODS-N, GOODS-S, ECDFS, and COSMOS – covering a total sky area of ~2.0 deg2. Using this methodology, we constrain the radio spectral index and FRC index of star-forming galaxies with M∗ > 1010 M⊙ and 0 <z< 2.3. We find that α1.4 GHz610 MHz does not evolve significantly with redshift or with the distance of a galaxy with respect to the main sequence (MS) of the SFR–M∗ plane (i.e. Δlog (SSFR)MS = log SSFR(galaxy) /SSFRMS(M∗,z) ). Instead, star-forming galaxies have a radio spectral index consistent with a canonical value of 0.8, which suggests that their radio spectra are dominated by non-thermal optically thin synchrotron emission. We find that the FRC index, qFIR,displays a moderate but statistically significant redshift evolution as qFIR(z) = (2.35 ± 0.08) × (1 + z)−0.12 ± 0.04, consistent with some previous literature. Finally, we find no significant correlation between qFIR and Δlog (SSFR)MS, though a weak positive trend, as observed in one of our redshift bins (i.e. Δ qFIR /Δ Δlog (SSFR)MS = 0.22 ± 0.07 at 0.5 <z< 0.8), cannot be firmly ruled out using our dataset.
We present ALMA and VLA observations of the dense molecular gas tracers HCN, HCO+, and HNC in two lensed, high-redshift starbursts selected from the Herschel-ATLAS survey: H-ATLAS J090740.0−004200 ...(SDP.9, ) and H-ATLAS J091043.1−000321 (SDP.11, ). In SDP.9 we have detected all transitions and also HCN(1-0) and HCO+(1-0). In SDP.11 we have detected HCN(3-2) and HCO+(3-2). The amplification factors for both galaxies have been determined from subarcsecond-resolution CO and dust emission observations carried out with NOEMA and the SMA. The HNC(1-0)/HCN(1-0) line ratio in SDP.9 suggests the presence of photon-dominated regions, as happens in most local (U)LIRGs. The CO, HCN, and HCO+ spectral line energy distribution (SLEDs) of SDP.9 are compatible to those found for many local, IR-bright galaxies, indicating that the molecular gas in local and high-redshift dusty starbursts can have similar excitation conditions. We obtain that the correlation between total IR ( ) and dense line ( ) luminosity in SDP.9 and SDP.11 and local star-forming galaxies can be represented by a single relation. We argue that the scatter of the correlation, together with the lack of sensitive dense molecular gas tracer observations for a homogeneous sample of high-redshift galaxies, prevents us from distinguishing differential trends with redshift. Our results suggest that the intense star formation found in some high-redshift, dusty, luminous starbursts is associated with more massive dense molecular gas reservoirs and higher dense molecular gas fractions.
Aims. In this work, we aim to provide a consistent analysis of the dust properties from metal-poor to metal-rich environments by linking them to fundamental galactic parameters. Methods. We consider ...two samples of galaxies: the Dwarf Galaxy Survey (DGS) and the Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel (KINGFISH), totalling 109 galaxies, spanning almost 2 dex in metallicity. We collect infrared (IR) to submillimetre (submm) data for both samples and present the complete data set for the DGS sample. We model the observed spectral energy distributions (SED) with a physically-motivated dust model to access the dust properties: dust mass, total-IR luminosity, polycyclic aromatic hydrocarbon (PAH) mass fraction, dust temperature distribution, and dust-to-stellar mass ratio. Results. Using a different SED model (modified black body), different dust composition (amorphous carbon in lieu of graphite), or a different wavelength coverage at submm wavelengths results in differences in the dust mass estimate of a factor two to three, showing that this parameter is subject to non-negligible systematic modelling uncertainties. We find half as much dust with the amorphous carbon dust composition. For eight galaxies in our sample, we find a rather small excess at 500 μm (≤1.5σ). We find that the dust SED of low-metallicity galaxies is broader and peaks at shorter wavelengths compared to more metal-rich systems, a sign of a clumpier medium in dwarf galaxies. The PAH mass fraction and dust temperature distribution are found to be driven mostly by the specific star formation rate, sSFR, with secondary effects from metallicity. The correlations between metallicity and dust mass or total-IR luminosity are direct consequences of the stellar mass-metallicity relation. The dust-to-stellar mass ratios of metal-rich sources follow the well-studied trend of decreasing ratio for decreasing sSFR. The relation is more complex for low-metallicity galaxies with high sSFR, and depends on the chemical evolutionary stage of the source (i.e. gas-to-dust mass ratio). Dust growth processes in the ISM play a key role in the dust mass build-up with respect to the stellar content at high sSFR and low metallicity. Conclusions. We conclude that the evolution of the dust properties from metal-poor to metal-rich galaxies derives from a complex interplay between star formation activity, stellar mass, and metallicity.
Galaxies' rest-frame ultraviolet (UV) properties are often used to directly infer the degree to which dust obscuration affects the measurement of star formation rates (SFRs). While much recent work ...has focused on calibrating dust attenuation in galaxies selected at rest-frame ultraviolet wavelengths, locally and at high-z, here we investigate attenuation in dusty, star forming galaxies (DSFGs) selected at far-infrared wavelengths. By combining multiwavelength coverage across 0.15-500 mu min the COSMOS field, in particular making use of Herschel imaging, and a rich data set on local galaxies, we find an empirical variation in the relationship between the rest-frame UV slope ( beta ) and the ratio of infrared-to-ultraviolet emission (L sub(IR)/L sub(UV) = IRX) as a function of infrared luminosity, or total SFR. Both locally and at high-z, galaxies above SFR gap 50 M sub(middot in circle) yr super(-1) deviate from the nominal IRX- beta relation toward bluer colors by a factor proportional to their increasing IR luminosity. We also estimate contamination rates of DSFGs on high-z dropout searches of Lt1% at z lap 4-10, providing independent verification that contamination from very dusty foreground galaxies is low in Lyman-break galaxy searches. Overall, our results are consistent with the physical interpretation that DSFGs, e.g., galaxies with >50 M sub(middot in circle) yr super(-1), are dominated at all epochs by short-lived, extreme burst events, producing many young O and B stars that are primarily, yet not entirely, enshrouded in thick dust cocoons. The blue rest-frame UV slopes of DSFGs are inconsistent with the suggestion that most DSFGs at z ~ 2 exhibit steady-state star formation in secular disks.
Exploiting the sensitivity of the IRAM NOrthern Extended Millimeter Array (NOEMA) and its ability to process large instantaneous bandwidths, we have studied the morphology and other properties of the ...molecular gas and dust in the star forming galaxy, H-ATLAS J131611.5+281219 (HerBS-89a), at
z
= 2.95. High angular resolution (0
.
″3) images reveal a partial 1
.
″0 diameter Einstein ring in the dust continuum emission and the molecular emission lines of
12
CO(9−8) and H
2
O(2
02
− 1
11
). Together with lower angular resolution (0
.
″6) images, we report the detection of a series of molecular lines including the three fundamental transitions of the molecular ion OH
+
, namely (1
1
− 0
1
), (1
2
− 0
1
), and (1
0
− 0
1
), seen in absorption; the molecular ion CH
+
(1 − 0) seen in absorption, and tentatively in emission; two transitions of amidogen (NH
2
), namely (2
02
− 1
11
) and (2
20
− 2
11
) seen in emission; and HCN(11 − 10) and/or NH(1
2
− 0
1
) seen in absorption. The NOEMA data are complemented with Very Large Array data tracing the
12
CO(1 − 0) emission line, which provides a measurement of the total mass of molecular gas and an anchor for a CO excitation analysis. In addition, we present
Hubble
Space Telescope imaging that reveals the foreground lensing galaxy in the near-infrared (1.15
μ
m). Together with photometric data from the Gran Telescopio Canarias, we derive a photometric redshift of
z
phot
= 0.9
−0.5
+0.3
for the foreground lensing galaxy. Modeling the lensing of HerBS-89a, we reconstruct the dust continuum (magnified by a factor
μ
≃ 5.0) and molecular emission lines (magnified by
μ
∼ 4 − 5) in the source plane, which probe scales of ∼0
.
″1 (or 800 pc). The
12
CO(9 − 8) and H
2
O(2
02
− 1
11
) emission lines have comparable spatial and kinematic distributions; the source-plane reconstructions do not clearly distinguish between a one-component and a two-component scenario, but the latter, which reveals two compact rotating components with sizes of ≈1 kpc that are likely merging, more naturally accounts for the broad line widths observed in HerBS-89a. In the core of HerBS-89a, very dense gas with
n
H
2
∼ 10
7 − 9
cm
−3
is revealed by the NH
2
emission lines and the possible HCN(11 − 10) absorption line. HerBS-89a is a powerful star forming galaxy with a molecular gas mass of
M
mol
= (2.1 ± 0.4) × 10
11
M
⊙
, an infrared luminosity of
L
IR
= (4.6 ± 0.4) × 10
12
L
⊙
, and a dust mass of
M
dust
= (2.6 ± 0.2) × 10
9
M
⊙
, yielding a dust-to-gas ratio
δ
GDR
≈ 80. We derive a star formation rate SFR = 614 ± 59
M
⊙
yr
−1
and a depletion timescale
τ
depl
= (3.4 ± 1.0) × 10
8
years. The OH
+
and CH
+
absorption lines, which trace low (∼100 cm
−3
) density molecular gas, all have their main velocity component red-shifted by Δ
V
∼ 100 km s
−1
relative to the global CO reservoir. We argue that these absorption lines trace a rare example of gas inflow toward the center of a galaxy, indicating that HerBS-89a is accreting gas from its surroundings.
ABSTRACT Numerical simulations of cosmological structure formation show that the universe's most massive clusters, and the galaxies living in those clusters, assemble rapidly at early times ( ). ...While more than 20 proto-clusters have been observed at based on associations of 5-40 galaxies around rare sources, the observational evidence for rapid cluster formation is weak. Here we report observations of an asymmetric filamentary structure at z = 2.47 containing 7 starbursting, submillimeter-luminous galaxies and 5 additional active galactic nuclei (AGNs) within a comoving volume of 15,000 Mpc3. As the expected lifetime of both the luminous AGN and starburst phase of a galaxy is ∼100 Myr, we conclude that these sources were likely triggered in rapid succession by environmental factors or, alternatively, the duration of these cosmologically rare phenomena is much longer than prior direct measurements suggest. The stellar mass already built up in the structure is ∼1012 and we estimate that the cluster mass will exceed that of the Coma supercluster at . The filamentary structure is in line with hierarchical growth simulations that predict that the peak of cluster activity occurs rapidly at .
Using Herschel data from the deepest SPIRE and PACS surveys (HerMES and PEP) in COSMOS, GOODS-S and GOODS-N, we examine the dust properties of infrared (IR)-luminous (L
IR > 1010 L) galaxies at 0.1 < ...z < 2 and determine how these evolve with cosmic time. The unique angle of this work is the rigorous analysis of survey selection effects, making this the first study of the star-formation-dominated, IR-luminous population within a framework almost entirely free of selection biases. We find that IR-luminous galaxies have spectral energy distributions (SEDs) with broad far-IR peaks characterized by cool/extended dust emission and average dust temperatures in the 25-45 K range. Hot (T > 45 K) SEDs and cold (T < 25 K), cirrus-dominated SEDs are rare, with most sources being within the range occupied by warm starbursts such as M82 and cool spirals such as M51. We observe a luminosity-temperature (L-T) relation, where the average dust temperature of log L
IR/L ∼ 12.5 galaxies is about 10 K higher than that of their log L
IR/L ∼ 10.5 counterparts. However, although the increased dust heating in more luminous systems is the driving factor behind the L-T relation, the increase in dust mass and/or starburst size with luminosity plays a dominant role in shaping it. Our results show that the dust conditions in IR-luminous sources evolve with cosmic time: at high redshift, dust temperatures are on average up to 10 K lower than what is measured locally (z 0.1). This is manifested as a flattening of the L-T relation, suggesting that (ultra)luminous infrared galaxies (U)LIRGs in the early Universe are typically characterized by a more extended dust distribution and/or higher dust masses than local equivalent sources. Interestingly, the evolution in dust temperature is luminosity dependent, with the fraction of LIRGs with T < 35 K showing a two-fold increase from z ∼ 0 to z ∼ 2, whereas that of ULIRGs with T < 35 K shows a six-fold increase. Our results suggest a greater diversity in the IR-luminous population at high redshift, particularly for ULIRGs.
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