ABSTRACT We report the detection of C ii λ158 $\mu$m emission from a system of three closely separated sources in the Cosmic Evolution Survey (COSMOS) field at z ∼ 4.56 , as part of the Atacama Large ...Millimeter/submillimeter Array (ALMA) Large Program to INvestigate C ii at Early times (ALPINE). The two most luminous sources are closely associated, both spatially (1.6 arcsec ∼ 11 kpc) and in velocity (∼100 km s−1), while the third source is slightly more distant (2.8 arcsec ∼ 18 kpc, ∼300 km s−1). The second most luminous source features a slight velocity gradient, while no significant velocity gradient is seen in the other two sources. Using the observed C ii luminosities, we derive a total log$_{10}(\rm SFR_{C\,{\small II}}\, M_{\odot }\, yr^{-1})=2.8\pm 0.2$, which may be split into contributions of 59, 31, and 10 per cent from the central, east, and west sources, respectively. Comparison of these C ii detections to recent zoom-in cosmological simulations suggests an ongoing major merger. We are thus witnessing a system in a major phase of mass build-up by merging, including an ongoing major merger and an upcoming minor merger, which is expected to end up in a single massive galaxy by z ∼ 2.5.
ABSTRACT
We present the ALMA view of 11 main-sequence dusty star-forming galaxies (DSFGs) (sub-)millimetre selected in the Great Observatories Origins Survey South (GOODS-S) field and ...spectroscopically confirmed to be at the peak of cosmic star formation history (z ∼ 2). Our study combines the analysis of galaxy spectral energy distribution with ALMA continuum and CO spectral emission by using ALMA Science Archive products at the highest spatial resolution currently available for our sample (Δθ ≲ 1 arcsec). We include galaxy multiband images and photometry (in the optical, radio, and X-rays) to investigate the interlink between dusty, gaseous, and stellar components and the eventual presence of AGN. We use multiband sizes and morphologies to gain an insight on the processes that lead galaxy evolution, e.g. gas condensation, star formation, AGN feedback. The 11 DSFGs are very compact in the (sub-)millimetre (median rALMA = 1.15 kpc), while the optical emission extends to larger radii (median rH/rALMA = 2.05). CO lines reveal the presence of a rotating disc of molecular gas, but we cannot exclude the presence of interactions and/or molecular outflows. Images at higher (spectral and spatial) resolution are needed to disentangle from the possible scenarios. Most of the galaxies are caught in the compaction phase, when gas cools and falls into galaxy centre, fuelling the dusty burst of star formation and the growing nucleus. We expect these DSFGs to be the high-z star-forming counterparts of massive quiescent galaxies. Some features of CO emission in three galaxies are suggestive of forthcoming/ongoing AGN feedback, which is thought to trigger the morphological transition from star-forming discs to early-type galaxies.
ABSTRACT We investigate the co-evolution of the black hole accretion rate (BHAR) and the star formation rate (SFR) in galaxies displaying a greater diversity of star-forming properties compared to ...previous studies. We combine X-ray stacking and far-IR photometry of stellar mass-limited samples of normal star-forming, starburst, and quiescent/quenched galaxies in the COSMOS field. We corroborate the existence of a strong correlation between BHAR (i.e., the X-ray luminosity, LX) and stellar mass (M*) for normal star-forming galaxies, though we find a steeper relation than previously reported. We find that starbursts show a factor of three enhancement in BHAR compared to normal SF galaxies (against a factor of six excess in SFR), while quiescents show a deficit of a factor times 5.5 at a given mass. One possible interpretation of this is that the starburst phase does not coincide with cosmologically relevant BH growth, or that starburst-inducing mergers are more efficient at boosting SFR than BHAR. Contrary to studies based on smaller samples, we find that the BHAR/SFR ratio of main-sequence (MS) galaxies is not mass invariant, but scales weakly as , implying faster BH growth in more massive galaxies at . Furthermore, BHAR/SFR during the starburst is a factor of two lower than in MS galaxies, at odds with the predictions of hydrodynamical simulations of merger galaxies that foresee a sudden enhancement of LX/SFR during the merger. Finally, we estimate that the bulk of the accretion density of the universe at is associated with normal star-forming systems, with only and associated with starburst and quiescent galaxies, respectively.
The black hole-and-galaxy (BH-galaxy) co-evolution paradigm predicts a phase where most of the star formation (SF) and BH accretion takes place in gas-rich environments, namely, in what are likely to ...be very obscured conditions. In the first phase of this growth, some of the galactic gas is funnelled toward the centre of the galaxy and is accreted into the supermassive BH, triggering active galactic nucleus (AGN) activity. The large quantity of gas and dust hides the emission and the AGN appears as an obscured (type 2) AGN. The degree of obscuration in type 2 AGNs may even reach values as high as N H > 10 24 cm −2 (i.e., Compton-thick, CT). Population synthesis models of the X-ray background (XRB) suggest that a large population of CT-AGN is, in fact, needed to explain the still unresolved XRB emission at energy above 20 keV. In this work, we investigated the properties of 94 Ne V 3426 Å-selected type 2 AGN in COSMOS at z = 0.6 − 1.2, performing optical-to-far-infrared (FIR) spectral energy distribution (SED) fitting of COSMOS2020 photometric data to estimate the AGN bolometric luminosity and stellar mass, star formation rate, age of the oldest stars, and molecular gas mass for their host-galaxy. In addition, we performed an X-ray spectral analysis of the 36 X-ray-detected sources to obtain reliable values of the AGN obscuration and intrinsic luminosity, as well as to constrain the AGN properties of the X-ray-undetected sources. We found that more than two-thirds of our sample is composed of very obscured sources ( N H > 10 23 cm −2 ), with about 20% of the sources being candidate CT-AGN and half being AGNs in a strong phase of accretion ( λ Edd > 0.1). We built a mass- and redshift-matched control sample and its comparison with the Ne V sample indicates that the latter has a higher fraction of sources within the main sequence of star-forming galaxies and shows little evidence for AGNs quenching the SF. As the two samples have similar amounts of cold gas available to fuel the SF, this difference points towards a higher efficiency in forming stars in the Ne V -selected sample. The comparison with the prediction from the in situ co-evolution model suggests that Ne V is an effective tool for selecting galaxies in the obscured growth phase of the BH-galaxy co-evolution paradigm. We find that the “quenching phase” is still to come for most of the sample and only few galaxies show evidence of quenched SF activity.
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We study relationships between star-formation rate (SFR) and the accretion luminosity and nuclear obscuration of X-ray selected active galactic nuclei (AGNs) using a combination of deep far-infrared ...(FIR) and X-ray data in three key extragalactic survey fields (GOODS-South, GOODS-North and COSMOS), as part of the PACS Evolutionary Probe (PEP) program. The use of three fields with differing areas and depths enables us to explore trends between the global FIR luminosity of the AGN hosts and the luminosity of the active nucleus across 4.5 orders of magnitude in AGN luminosity (LAGN) and spanning redshifts from the Local Universe to z = 2.5. Using imaging from the Herschel/PACS instrument in 2−3 bands, we combine FIR detections and stacks of undetected objects to arrive at mean fluxes for subsamples in bins of redshift and X-ray luminosity. We constrain the importance of AGN-heated dust emission in the FIR and confirm that the majority of the FIR emission of AGNs is produced by cold dust heated by star-formation in their host galaxies. We uncover characteristic trends between the mean FIR luminosity (L60) and accretion luminosity of AGNs, which depend both on LAGN and redshift. At low AGN luminosities, accretion and SFR are uncorrelated at all redshifts, consistent with a scenario where most low-luminosity AGNs are primarily fueled by secular processes in their host galaxies. At high AGN luminosities, a significant correlation is observed between L60 and LAGN, but only among AGNs at low and moderate redshifts (z < 1). We interpret this observation as a sign of the increasing importance of major-mergers in driving both the growth of super-massive black holes (SMBHs) and global star-formation in their hosts at high AGN luminosities. We also find evidence that the enhancement of SFR in luminous AGNs weakens or disappears at high redshifts (z > 1) suggesting that the role of mergers is less important at these epochs. At all redshifts, we find essentially no relationship between L60 and nuclear obscuration across five orders of magnitude in obscuring Hydrogen column density (NH), suggesting that various mechanisms are likely to be responsible for obscuring X-rays in active galaxies. We discuss a broad scenario which can account for these trends: one in which two different modes of AGN fueling operate in the low- and high-luminosity regimes of SMBH accretion. We postulate that the dominant mode of accretion among high-luminosity AGNs evolves with redshift. Our study, as well as a body of evidence from the literature and emerging knowledge about the properties of high redshift galaxies, supports this scenario.
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Abstract
We present the C II 158
μ
m line luminosity functions (LFs) at
z
∼ 4–6 using the ALMA observations of 118 sources, which are selected to have UV luminosity
M
1500Å
< −20.2 and optical ...spectroscopic redshifts in COSMOS and ECDF-S. Of the 118 targets, 75 have significant C II detections and 43 are upper limits. This is by far the largest sample of C II detections, which allows us to set constraints on the volume density of C II emitters at
z
∼ 4–6. But because this is a UV-selected sample, we are missing C II-bright but UV-faint sources, making our constraints strict lower limits. Our derived LFs are statistically consistent with the
z
∼ 0 C II LF at 10
8.25
–10
9.75
L
⊙
. We compare our results with the upper limits of the C II LF derived from serendipitous sources in the ALPINE maps. We also infer the C II LFs based on published far-IR and CO LFs at
z
∼ 4–6. Combining our robust lower limits with these additional estimates, we set further constraints on the true number density of C II emitters at
z
∼ 4–6. These additional LF estimates are largely above our LF at
L
CII
> 10
9
L
⊙
, suggesting that UV-faint but C II-bright sources likely make significant contributions to the C II emitter volume density. When we include all the LF estimates, we find that available model predictions underestimate the number densities of C II emitters at
z
∼ 4–6. Finally, we set a constraint on the molecular gas mass density at
z
∼ 4–6, with
ρ
mol
∼ (2–7) × 10
7
M
⊙
Mpc
−3
. This is broadly consistent with previous studies.
Two main modes of star formation are know to control the growth of galaxies: a relatively steady one in disk-like galaxies, defining a tight star formation rate (SFR)-stellar mass sequence, and a ...starburst mode in outliers to such a sequence which is generally interpreted as driven by merging. Such starburst galaxies are rare but have much higher SFRs, and it is of interest to establish the relative importance of these two modes. PACS/Herschel observations over the whole COSMOS and GOODS-South fields, in conjunction with previous optical/near-IR data, have allowed us to accurately quantify for the first time the relative contribution of the two modes to the global SFR density in the redshift interval 1.5 < z < 2.5, i.e., at the cosmic peak of the star formation activity. The logarithmic distributions of galaxy SFRs at fixed stellar mass are well described by Gaussians, with starburst galaxies representing only a relatively minor deviation that becomes apparent for SFRs more than four times higher than on the main sequence. Such starburst galaxies represent only 2% of mass-selected star-forming galaxies and account for only 10% of the cosmic SFR density at z ~ 2. Only when limited to SFR > 1000 M yr--1, off-sequence sources significantly contribute to the SFR density (46% ? 20%). We conclude that merger-driven starbursts play a relatively minor role in the formation of stars in galaxies, whereas they may represent a critical phase toward the quenching of star formation and morphological transformation in galaxies.
Abstract
We present the average C
ii
158
μ
m emission line sizes of UV-bright star-forming galaxies at
z
∼ 7. Our results are derived from a stacking analysis of C
ii
158
μ
m emission lines and ...dust continua observed by the Atacama Large Millimeter/submillimeter Array (ALMA), taking advantage of the large program Reionization Era Bright Emission Line Survey. We find that the average C
ii
emission at
z
∼ 7 has an effective radius
r
e
of 2.2 ± 0.2 kpc. It is ≳2× larger than the dust continuum and the rest-frame UV emission, in agreement with recently reported measurements for
z
≲ 6 galaxies. Additionally, we compared the average C
ii
size with 4 <
z
< 6 galaxies observed by the ALMA Large Program to INvestigate C
ii
at Early times (ALPINE). By analyzing C
ii
sizes of 4 <
z
< 6 galaxies in two redshift bins, we find an average C
ii
size of
r
e
= 2.2 ± 0.2 kpc and
r
e
= 2.5 ± 0.2 kpc for
z
∼ 5.5 and
z
∼ 4.5 galaxies, respectively. These measurements show that star-forming galaxies, on average, show no evolution in the size of the C
ii
158
μ
m emitting regions at redshift between
z
∼ 7 and
z
∼ 4. This finding suggests that the star-forming galaxies could be morphologically dominated by gas over a wide redshift range.
We study a sample of 61submillimetre galaxies (SMGs) selected from ground-based surveys, with known spectroscopic redshifts and observed with the Herschel Space Observatory as part of the PACS ...Evolutionary Probe (PEP) and the Herschel Multi-tiered Extragalactic Survey (HerMES) guaranteed time key programmes. Our study makes use of the broad far-infrared and submillimetre wavelength coverage (100−600 μm) only made possible by the combination of observations from the PACS and SPIRE instruments aboard the Herschel Space Observatory. Using a power-law temperature distribution model to derive infrared luminosities and dust temperatures, we measure a dust emissivity spectral index for SMGs of β = 2.0 ± 0.2. Our results unambiguously unveil the diversity of the SMG population. Some SMGs exhibit extreme infrared luminosities of s10\hbox{$^{13} {L_{\odot}}$}L⊙13 and relatively warm dust components, while others are fainter (a few times 1012 L⊙) and are biased towards cold dust temperatures. Although at zs2 classical SMGs (>5 mJy at 850 μm) have large infrared luminosities (s1013 L⊙), objects only selected on their submm flux densities (without any redshift informations) probe a large range in dust temperatures and infrared luminosities. The extreme infrared luminosities of some SMGs (LIR ≳ 1012.7 L⊙, 26/61 systems) imply star formation rates (SFRs) of >500 M⊙ yr-1 (assuming a Chabrier IMF and no dominant AGN contribution to the FIR luminosity). Such high SFRs are difficult to reconcile with a secular mode of star formation, and may instead correspond to a merger-driven stage in the evolution of these galaxies. Another observational argument in favour of this scenario is the presence of dust temperatures warmer than that of SMGs of lower luminosities (s40 K as opposed to s25 K), consistent with observations of local ultra-luminous infrared galaxies triggered by major mergers and with results from hydrodynamic simulations of major mergers combined with radiative transfer calculations. Moreover, we find that luminous SMGs are systematically offset from normal star-forming galaxies in the stellar mass-SFR plane, suggesting that they are undergoing starburst events with short duty cycles, compatible with the major merger scenario. On the other hand, a significant fraction of the low infrared luminosity SMGs have cold dust temperatures, are located close to the main sequence of star formation, and therefore might be evolving through a secular mode of star formation. However, the properties of this latter population, especially their dust temperature, should be treated with caution because at these luminosities SMGs are not a representative sample of the entire star-forming galaxy population.
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We investigate the effect of nonlinearity in a system described by an adiabatically evolving Hamiltonian. Experiments are conducted in a three-core waveguide structure that is adiabatically varying ...with distance, in analogy to the stimulated Raman adiabatic passage process in atomic physics. In the linear regime, the system exhibits an adiabatic power transfer between two waveguides which are not directly coupled, with negligible power recorded in the intermediate coupling waveguide. In the presence of nonlinearity the adiabatic light passage is found to critically depend on the excitation power. We show how this effect is related to the destruction of the dark state formed in this configuration.
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