We present high-resolution observations of the 880 mum (rest-frame FIR) continuum emission in the z= 4.05 submillimeter galaxy GN20 from the IRAM Plateau de Bure Interferometer (PdBI). These data ...resolve the obscured star formation (SF) in this unlensed galaxy on scales of 0".3 x 0".2 (~2.1 x 1.3 kpc). The observations reveal a bright (16 + or - 1 mJy) dusty starburst centered on the cold molecular gas reservoir and showing a bar-like extension along the major axis. The striking anti-correlation with the Hubble Space Telescope/Wide Field Camera 3 imaging suggests that the copious dust surrounding the starburst heavily obscures the rest-frame UV/optical emission. A comparison with 1.2 mm PdBI continuum data reveals no evidence for variations in the dust properties across the source within the uncertainties, consistent with extended SF, and the peak star formation rate surface density (119 + or - 8 M sub(middot in circle) yr super(-1) kpc super(-2)) implies that the SF in GN20 remains sub-Eddington on scales down to 3 kpc super(2). We find that the SF efficiency (SFE) is highest in the central regions of GN20, leading to a resolved SF law with a power-law slope of Sigma sub(SFR)~ (ProQuest: Formulae and/or non-USASCII text omitted), and that GN20 lies above the sequence of normal star-forming disks, implying that the dispersion in the SF law is not due solely to morphology or choice of conversion factor. These data extend previous evidence for a fixed SFE per free-fall time to include the star-forming medium on ~kiloparsec scales in a galaxy 12 Gyr ago.
ABSTRACT We present high-resolution (0 16) 870 m Atacama Large Millimeter/submillimeter Array (ALMA) imaging of 16 luminous ( ) submillimeter galaxies (SMGs) from the ALESS survey of the Extended ...Chandra Deep Field South. This dust imaging traces the dust-obscured star formation in these galaxies on ∼1.3 kpc scales. The emission has a median effective radius of Re = 0 24 0 02, corresponding to a typical physical size of 1.8 0.2 kpc. We derive a median Sérsic index of n = 0.9 0.2, implying that the dust emission is remarkably disk-like at the current resolution and sensitivity. We use different weighting schemes with the visibilities to search for clumps on 0 12 (∼1.0 kpc) scales, but we find no significant evidence for clumping in the majority of cases. Indeed, we demonstrate using simulations that the observed morphologies are generally consistent with smooth exponential disks, suggesting that caution should be exercised when identifying candidate clumps in even moderate signal-to-noise ratio interferometric data. We compare our maps to comparable-resolution Hubble Space Telescope -band images, finding that the stellar morphologies appear significantly more extended and disturbed, and suggesting that major mergers may be responsible for driving the formation of the compact dust disks we observe. The stark contrast between the obscured and unobscured morphologies may also have implications for SED fitting routines that assume the dust is co-located with the optical/near-IR continuum emission. Finally, we discuss the potential of the current bursts of star formation to transform the observed galaxy sizes and light profiles, showing that the descendants of these SMGs are expected to have stellar masses, effective radii, and gas surface densities consistent with the most compact massive ( 1-2 × 1011 ) early-type galaxies observed locally.
Abstract
We present single-dish 12CO(1–0) and 12CO(2–1) observations for 14 low-redshift quasi-stellar objects (QSOs). In combination with optical integral field spectroscopy, we study how the cold ...gas content relates to the star formation rate (SFR) and black hole accretion rate. 12CO(1–0) is detected in 8 of 14 targets and 12CO(2–1) is detected in 7 out of 11 cases. The majority of disc-dominated QSOs reveal gas fractions and depletion times matching normal star-forming systems. Two gas-rich major mergers show clear starburst signatures with higher than average gas fractions and shorter depletion times. Bulge-dominated QSO hosts are mainly undetected in 12CO(1–0), which corresponds, on average, to lower gas fractions than in disc-dominated counterparts. Their SFRs, however, imply shorter than average depletion times and higher star formation efficiencies. Negative QSO feedback through removal of cold gas seems to play a negligible role in our sample. We find a trend between black hole accretion rate and total molecular gas content for disc-dominated QSOs when combined with literature samples. We interpret this as an upper envelope for the nuclear activity and it is well represented by a scaling relation between the total and circumnuclear gas reservoir accessible for accretion. Bulge-dominated QSOs significantly differ from that scaling relation and appear uncorrelated with the total molecular gas content. This could be explained either by a more compact gas reservoir, blown out of the gas envelope through outflows, or a different interstellar medium phase composition.
We present subkiloparsec-scale mapping of the 870 m ALMA continuum emission in six luminous (LIR ∼ 5 × 1012 L ) submillimeter galaxies (SMGs) from the ALESS survey of the Extended Chandra Deep Field ...South. Our high-fidelity 0 07-resolution imaging (∼500 pc) reveals robust evidence for structures with deconvolved sizes of 0.5-1 kpc embedded within (dominant) exponential dust disks. The large-scale morphologies of the structures within some of the galaxies show clear curvature and/or clump-like structures bracketing elongated nuclear emission, suggestive of bars, star-forming rings, and spiral arms. In this interpretation, the ratio of the "ring" and "bar" radii (1.9 0.3) agrees with that measured for such features in local galaxies. These potential spiral/ring/bar structures would be consistent with the idea of tidal disturbances, with their detailed properties implying flat inner rotation curves and Toomre-unstable disks (Q < 1). The inferred one-dimensional velocity dispersions ( r 70-160 km s−1) are marginally consistent with the limits implied if the sizes of the largest structures are comparable to the Jeans length. We create maps of the star formation rate density ( SFR) on ∼500 pc scales and show that the SMGs are able to sustain a given (galaxy-averaged) SFR over much larger physical scales than local (ultra)luminous infrared galaxies. However, on 500 pc scales, they do not exceed the Eddington limit set by radiation pressure on dust. If confirmed by kinematics, the potential presence of nonaxisymmetric structures would provide a means for net angular momentum loss and efficient star formation, helping to explain the very high star formation rates measured in SMGs.
We report the identification of an extreme protocluster of galaxies in the early universe whose core (nicknamed Distant Red Core, DRC, because of its very red color in Herschel SPIRE bands) is formed ...by at least 10 dusty star-forming galaxies (DSFGs), spectroscopically confirmed to lie at z spec = 4.002 via detection of C i(1-0), 12CO(6-5), 12CO(4-3), 12CO(2-1), and H 2 O ( 2 11 - 2 02 ) emission lines with ALMA and ATCA. These DSFGs are distributed over a 260 kpc × 310 kpc region and have a collective obscured star formation rate (SFR) of ∼ 6500 M yr − 1 , considerably higher than those seen before in any protocluster at z 4 . Most of the star formation is taking place in luminous DSFGs since no Ly emitters are detected in the protocluster core, apart from a Ly blob located next to one of the DRC components, extending over 60 kpc . The total obscured SFR of the protocluster could rise to SFR ∼ 14,400 M yr − 1 if all the members of an overdensity of bright DSFGs discovered around DRC in a wide-field Large APEX BOlometer CAmera 870 m image are part of the same structure. C i(1-0) emission reveals that DRC has a total molecular gas mass of at least M H 2 ∼ 6.6 × 10 11 M , and its total halo mass could be as high as ∼ 4.4 × 10 13 M , indicating that it is the likely progenitor of a cluster at least as massive as Coma at z = 0.
ABSTRACT
We have used ALMA and NOEMA to study the molecular gas reservoirs in 61 ALMA-identified submillimetre galaxies (SMGs) in the COSMOS, UDS, and ECDFS fields. We detect 12CO ($J_{\rm up} =$ ...2–5) emission lines in 50 sources, and C i(3P1 − 3P0) emission in eight, at $z =$ 1.2–4.8 and with a median redshift of 2.9 ± 0.2. By supplementing our data with literature sources, we construct a statistical CO spectral line energy distribution and find that the 12CO line luminosities in SMGs peak at Jup ∼ 6, consistent with similar studies. We also test the correlations of the CO, C i, and dust as tracers of the gas mass, finding the three to correlate well, although the CO and dust mass as estimated from the 3-mm continuum are preferable. We estimate that SMGs lie mostly on or just above the star-forming main sequence, with a median gas depletion timescale, tdep = Mgas/SFR, of 210 ± 40 Myr for our sample. Additionally, tdep declines with redshift across z ∼ 1–5, while the molecular gas fraction, μgas = Mgas/M*, increases across the same redshift range. Finally, we demonstrate that the distribution of total baryonic mass and dynamical line width, Mbaryon–σ, for our SMGs is consistent with that followed by early-type galaxies in the Coma cluster, providing strong support to the suggestion that SMGs are progenitors of massive local spheroidal galaxies. On the basis of this, we suggest that the SMG populations above and below an 870-μm flux limit of S870 ∼ 5 mJy may correspond to the division between slow and fast rotators seen in local early-type galaxies.
Dusty star-forming galaxies at high redshift (1 < z < 3) represent the most intense star-forming regions in the universe. Key aspects to these processes are the gas heating and cooling mechanisms, ...and although it is well known that these galaxies are gas-rich, little is known about the gas excitation conditions. Only a few detailed radiative transfer studies have been carried out owing to a lack of multiple line detections per galaxy. Here we examine these processes in a sample of 24 strongly lensed star-forming galaxies identified by the Planck satellite (LPs) at z ∼ 1.1-3.5. We analyze 162 CO rotational transitions (ranging from Jup = 1 to 12) and 37 atomic carbon fine-structure lines (C i) in order to characterize the physical conditions of the gas in the sample of LPs. We simultaneously fit the CO and C i lines and the dust continuum emission, using two different non-LTE, radiative transfer models. The first model represents a two-component gas density, while the second assumes a turbulence-driven lognormal gas density distribution. These LPs are among the most gas-rich, IR-luminous galaxies ever observed ( L L IR ( 8 − 1000 m ) ∼ 10 13 − 14.6 L ; 〈 LMISM 〉 = (2.7 1.2) × 1012 M , with L ∼ 10-30 the average lens magnification factor). Our results suggest that the turbulent interstellar medium present in the LPs can be well characterized by a high turbulent velocity dispersion ( 〈 ΔVturb 〉 ∼ 100 km s−1) and ratios of gas kinetic temperature to dust temperature 〈 Tkin/Td 〉 ∼ 2.5, sustained on scales larger than a few kiloparsecs. We speculate that the average surface density of the molecular gas mass and IR luminosity, M ISM ∼ 103-4 M pc−2 and L IR ∼ 1011-12 L kpc−2, arise from both stellar mechanical feedback and a steady momentum injection from the accretion of intergalactic gas.
We present ALMA Band 6 ( = 233 GHz, λ = 1.3 mm) continuum observations toward 68 "normal" star-forming galaxies within two Coma-like progenitor structures at z = 2.10 and 2.47, from which ISM masses ...are derived, providing the largest census of molecular gas mass in overdense environments at these redshifts. Our sample comprises galaxies with a stellar mass range of 1 × 109 M -4 × 1011 M with a mean M 6 × 1010 M . Combining these measurements with multiwavelength observations and spectral energy distribution modeling, we characterize the gas mass fraction and the star formation efficiency, and infer the impact of the environment on galaxies' evolution. Most of our detected galaxies ( 70%) have star formation efficiencies and gas fractions similar to those found for coeval field galaxies and in agreement with the field scaling relations. However, we do find that the protoclusters contain an increased fraction of massive, gas-poor galaxies, with low gas fractions (fgas 6%-10%) and red rest-frame ultraviolet/optical colors typical of post-starburst and passive galaxies. The relatively high abundance of passive galaxies suggests an accelerated evolution of massive galaxies in protocluster environments. The large fraction of quenched galaxies in these overdense structures also implies that environmental quenching takes place during the early phases of cluster assembly, even before virialization. From our data, we derive a quenching efficiency of ϵq 0.45 and an upper limit on the quenching timescale of τq < 1 Gyr.
ABSTRACT Active galactic nuclei (AGNs) are known to exhibit optical/ultraviolet variability and most of them can be well modelled by the damped random walks. Physical processes that are not related ...to the accretion disc, such as tidal disruption events (TDEs) or moving foreground dusty clouds, can cause flare-like and eclipse-like features in the optical light curve. Both long-term and high-cadence monitoring are needed to identify such features. By combining the Sloan Digital Sky Survey (SDSS), Panoramic Survey Telescope and Rapid Response System, and the Zwicky Transient Facility (ZTF) survey, we are able to identify a rare sample (11) out of the SDSS quasar catalogue ($\sim\!\! 83\, 000$). These quasars exhibit more or less constant brightness but show rapid optical variation in the epochs of ZTF Public Data Release 2. To investigate the possible origins of these flare/eclipse-like variabilities, we propose the second-epoch spectroscopic observations with the Gran Telescopio CANARIAS. We find that the change in accretion rate plays a significant role in these quasar variabilities. Among them, we identify two changing-look AGN candidates: SDSS J1427+2930 and SDSS J1420+3757. The luminosity change of the former may be caused by the enhanced supermassive black hole’s accretion or the TDE, while the latter is more related to the change in the accretion rate.
Abstract
The circumgalactic medium (CGM) of the massive Spiderweb Galaxy, a conglomerate of merging proto-cluster galaxies at z = 2.2, forms an enriched interface where feedback and recycling act on ...accreted gas. This is shown by observations of C i, CO(1-0), and CO(4-3) performed with the Atacama Large Millimeter Array and Australia Telescope Compact Array. C i and CO(4-3) are detected across ∼50 kpc, following the distribution of previously detected low-surface-brightness CO(1-0) across the CGM. This confirms our previous results on the presence of a cold molecular halo. The central radio galaxy MRC 1138-262 shows a very high global $L^{\prime}_{\rm CO(4-3)}$/$L^{\prime}_{\rm CO(1-0)}$ ∼ 1, suggesting that mechanisms other than FUV-heating by star formation prevail at the heart of the Spiderweb Galaxy. Contrary, the CGM has $L^{\prime}_{\rm CO(4-3)}$/$L^{\prime}_{\rm CO(1-0)}$ and $L^{\prime}_{\rm C\,I}$/$L^{\prime}_{\rm CO(1-0)}$ similar to the ISM of five galaxies in the wider proto-cluster, and its carbon abundance, $X_{\rm C\,I}$/$X_{\rm H_2}$, resembles that of the Milky Way and star-forming galaxies. The molecular CGM is thus metal-rich and not diffuse, confirming a link between the cold gas and in situ star formation. Thus, the Spiderweb Galaxy grows not directly through accretion of gas from the cosmic web, but from recycled gas in the CGM.
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