We report on the detailed analysis of a gravitationally lensed Y-band dropout, A2744_YD4, selected from deep Hubble Space Telescope imaging in the Frontier Field cluster Abell 2744. Band 7 ...observations with the Atacama Large Millimeter/submillimeter Array (ALMA) indicate the proximate detection of a significant 1 mm continuum flux suggesting the presence of dust for a star-forming galaxy with a photometric redshift of . Deep X-SHOOTER spectra confirms the high-redshift identity of A2744_YD4 via the detection of Ly emission at a redshift z = 8.38. The association with the ALMA detection is confirmed by the presence of O iii 88 m emission at the same redshift. Although both emission features are only significant at the 4 level, we argue their joint detection and the positional coincidence with a high-redshift dropout in the Hubble Space Telescope images confirms the physical association. Analysis of the available photometric data and the modest gravitational magnification ( ) indicates A2744_YD4 has a stellar mass of ∼2 × 109 , a star formation rate of ∼20 yr−1 and a dust mass of ∼6 × 106 . We discuss the implications of the formation of such a dust mass only after the onset of cosmic reionization.
Abstract
This paper provides an update of our previous scaling relations between galaxy-integrated molecular gas masses, stellar masses, and star formation rates (SFRs), in the framework of the star ...formation main sequence (MS), with the main goal of testing for possible systematic effects. For this purpose our new study combines three independent methods of determining molecular gas masses from CO line fluxes, far-infrared dust spectral energy distributions, and ∼1 mm dust photometry, in a large sample of 1444 star-forming galaxies between
z
= 0 and 4. The sample covers the stellar mass range log(
M
*
/
M
⊙
) = 9.0–11.8, and SFRs relative to that on the MS,
δ
MS = SFR/SFR(MS), from 10
−1.3
to 10
2.2
. Our most important finding is that all data sets, despite the different techniques and analysis methods used, follow the same scaling trends, once method-to-method zero-point offsets are minimized and uncertainties are properly taken into account. The molecular gas depletion time
t
depl
, defined as the ratio of molecular gas mass to SFR, scales as (1 +
z
)
−0.6
× (
δ
MS)
−0.44
and is only weakly dependent on stellar mass. The ratio of molecular to stellar mass
μ
gas
depends on (
1
+
z
)
2.5
×
(
δ
MS
)
0.52
×
(
M
*
)
−
0.36
, which tracks the evolution of the specific SFR. The redshift dependence of
μ
gas
requires a curvature term, as may the mass dependences of
t
depl
and
μ
gas
. We find no or only weak correlations of
t
depl
and
μ
gas
with optical size
R
or surface density once one removes the above scalings, but we caution that optical sizes may not be appropriate for the high gas and dust columns at high
z
.
ABSTRACT The scatter in the relationship between the strength of C ii 158 $\mu$m emission and the star formation rate at high redshift has been the source of much recent interest. Although the ...relationship is well established locally, several intensely star-forming galaxies have been found whose C ii 158 $\mu$m emission is either weak, absent, or spatially offset from the young stars. Here we present new ALMA data for the two most distant gravitationally lensed and spectroscopically confirmed galaxies, A2744_YD4 at z = 8.38 and MACS1149_JD1 at z = 9.11, both of which reveal intense O iii 88 $\mu$m emission. In both cases we provide stringent upper limits on the presence of C ii 158 $\mu$m with respect to O iii 88 $\mu$m. We review possible explanations for this apparent redshift-dependent C ii deficit in the context of our recent hydrodynamical simulations. Our results highlight the importance of using several emission line diagnostics with ALMA to investigate the nature of the interstellar medium in early galaxies.
We present new deep ALMA and Hubble Space Telescope (HST)/WFC3 observations of MASOSA and VR7, two luminous Ly emitters (LAEs) at z = 6.5, for which the UV continuum levels differ by a factor of ...four. No IR dust continuum emission is detected in either, indicating little amounts of obscured star formation and/or high dust temperatures. MASOSA, with a UV luminosity M1500 = −20.9, compact size, and very high Ly , is undetected in C ii to a limit of LC ii < 2.2 × 107 L , implying a metallicity Z 0.07 Z . Intriguingly, our HST data indicate a red UV slope β = −1.1 0.7, at odds with the low dust content. VR7, which is a bright (M1500 = −22.4) galaxy with moderate color (β = −1.4 0.3) and Ly EW0 = 34 , is clearly detected in C ii emission (S/N = 15). VR7's rest-frame UV morphology can be described by two components separated by 1.5 kpc and is globally more compact than the C ii emission. The global C ii/UV ratio indicates Z 0.2 Z , but there are large variations in the UV/C ii ratio on kiloparsec scales. We also identify diffuse, possibly outflowing, C ii-emitting gas at 100 km s−1 with respect to the peak. VR7 appears to be assembling its components at a slightly more evolved stage than other luminous LAEs, with outflows already shaping its direct environment at z ∼ 7. Our results further indicate that the global C ii−UV relation steepens at SFR < 30 M yr−1, naturally explaining why the C ii/UV ratio is anticorrelated with Ly EW in many, but not all, observed LAEs.
We report ALMA observations of CO(3–2) emission in the Seyfert/nuclear starburst galaxy NGC 613, at a spatial resolution of 17 pc, as part of our NUclei of GAlaxies (NUGA) sample. Our aim is to ...investigate the morphology and dynamics of the gas inside the central kiloparsec, and to probe nuclear fueling and feedback phenomena. The morphology of CO(3–2) line emission reveals a two-arm trailing nuclear spiral at r ≲ 100 pc and a circumnuclear ring at a radius of ∼350 pc that is coincident with the star-forming ring seen in the optical images. Also, we find evidence for a filamentary structure connecting the ring and the nuclear spiral. The ring reveals two breaks into two winding spiral arms corresponding to the dust lanes in the optical images. The molecular gas in the galaxy disk is in a remarkably regular rotation, however the kinematics in the nuclear region are very skewed. The nuclear spectrum of CO and dense gas tracers HCN(4–3), HCO+(4–3), and CS(7–6) show broad wings up to ±300 km s−1, associated with a molecular outflow emanating from the nucleus (r ∼ 25 pc). We derive a molecular outflow mass Mout = 2 × 106 M⊙ and a mass outflow rate of Ṁout = 27 M⊙ yr−1. The molecular outflow energetics exceed the values predicted by AGN feedback models: the kinetic power of the outflow corresponds to PK, out = 20%LAGN and the momentum rate is Ṁoutv ∼ 400LAGN/c. The outflow is mainly boosted by the AGN through entrainment by the radio jet, but given the weak nuclear activity of NGC 613, we might be witnessing a fossil outflow resulting from a previously strong AGN that has now faded. Furthermore, the nuclear trailing spiral observed in CO emission is inside the inner Lindblad resonance ring of the bar. We compute the gravitational torques exerted in the gas to estimate the efficiency of the angular momentum exchange. The gravity torques are negative from 25 to 100 pc and the gas loses its angular momentum in a rotation period, providing evidence for a highly efficient inflow towards the center. This phenomenon shows that the massive central black hole has significant dynamical influence on the gas, triggering the inflowing of molecular gas to feed the black hole.
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We report ALMA observations of CO(3–2) emission in the Seyfert 2 galaxy NGC 1433 at the unprecedented spatial resolution of 0.′′5 = 24 pc. Our aim is to probe active galactic nucleus (AGN) feeding ...and feedback phenomena through the morphology and dynamics of the gas inside the central kpc. The galaxy NGC 1433 is a strongly barred spiral with three resonant rings: one at the ultra-harmonic resonance near corotation, and the others at the outer and inner Lindblad resonances (OLR and ILR). A nuclear bar of 400 pc radius is embedded in the large-scale primary bar. The CO map, which covers the whole nuclear region (nuclear bar and ring), reveals a nuclear gaseous spiral structure, inside the nuclear ring encircling the nuclear stellar bar. This gaseous spiral is well correlated with the dusty spiral seen in Hubble Space Telescope (HST) images. The nuclear spiral winds up in a pseudo-ring at ~200 pc radius, which might correspond to the inner ILR. Continuum emission is detected at 0.87 mm only at the very centre, and its origin is more likely thermal dust emission than non-thermal emission from the AGN. It might correspond to the molecular torus expected to exist in this Seyfert 2 galaxy. The HCN(4–3) and HCO+(4–3) lines were observed simultaneously, but only upper limits are derived, with a ratio to the CO(3–2) line lower than 1/60 at 3σ, indicating a relatively low abundance of very dense gas. The kinematics of the gas over the nuclear disk reveal rather regular rotation only slightly perturbed by streaming motions due to the spiral; the primary and secondary bars are too closely aligned with the galaxy major or minor axis to leave a signature in the projected velocities. Near the nucleus, there is an intense high-velocity CO emission feature redshifted to 200 km s-1 (if located in the plane), with a blue-shifted counterpart, at 2′′ (100 pc) from the centre. While the CO spectra are quite narrow in the centre, this wide component is interpreted as an outflow involving a molecular mass of 3.6 × 106 M⊙ and a flow rate ~7 M⊙/yr. The flow could be in part driven by the central star formation, but is mainly boosted by the AGN through its radio jets.
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We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of CO(3-2) emission in a sample of seven Seyfert/LINER galaxies at the unprecedented spatial resolution of 0.″1 = 4−8 0 . ″ ...1 = 4 − 9 $ 0 {{\overset{\prime\prime}{.}}}1=4{-}9 $ pc. Our aim is to explore the close environment of active galactic nuclei (AGN), and the dynamical structures leading to their fueling, through the morphology and kinematics of the gas inside the sphere of influence of the black hole. The selected galaxies host low-luminosity AGN and have a wide range of activity types (Seyferts 1 to 2, LINERs), and barred or ringed morphologies. The observed maps reveal the existence of circumnuclear disk structures, defined by their morphology and decoupled kinematics, in most of the sample. We call these structures molecular tori, even though they often appear as disks without holes in the center. They have varying orientations along the line of sight, unaligned with the host galaxy orientation. The radius of the tori ranges from 6 to 27 pc, and their mass from 0.7 × 107 to 3.9 × 107 M⊙. The most edge-on orientations of the torus correspond to obscured Seyferts. In only one case (NGC 1365), the AGN is centered on the central gas hole of the torus. On a larger scale, the gas is always piled up in a few resonant rings 100 pc in scale that play the role of a reservoir to fuel the nucleus. In some cases, a trailing spiral is observed inside the ring, providing evidence for feeding processes. More frequently, the torus and the AGN are slightly off-centered with respect to the bar-resonant ring position, implying that the black hole is wandering by a few 10 pc amplitude around the center of mass of the galaxy. Our spatial resolution allows us to measure gas velocities inside the sphere of influence of the central black holes. By fitting the observations with different simulated cubes, varying the torus inclination and the black hole mass, it is possible to estimate the mass of the central black hole, which is in general difficult for such late-type galaxies, with only a pseudo-bulge. In some cases, AGN feedback is revealed through a molecular outflow, which will be studied in detail in a subsequent article.
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We present spectroscopic follow-up observations of CR7 with ALMA, targeted at constraining the infrared (IR) continuum and C ii line-emission at high spatial resolution matched to the HST/WFC3 ...imaging. CR7 is a luminous Ly emitting galaxy at z = 6.6 that consists of three separated UV-continuum components. Our observations reveal several well-separated components of C ii emission. The two most luminous components in C ii coincide with the brightest UV components (A and B), blueshifted by km s−1 with respect to the peak of Ly emission. Other C ii components are observed close to UV clumps B and C and are blueshifted by and 80 km s−1 with respect to the systemic redshift. We do not detect FIR continuum emission due to dust with a 3 limiting luminosity . This allows us to mitigate uncertainties in the dust-corrected SFR and derive SFRs for the three UV clumps A, B, and C of 28, 5, and 7 yr−1. All clumps have C ii luminosities consistent within the scatter observed in the local relation between SFR and , implying that strong Ly emission does not necessarily anti-correlate with C ii luminosity. Combining our measurements with the literature, we show that galaxies with blue UV slopes have weaker C ii emission at fixed SFR, potentially due to their lower metallicities and/or higher photoionization. Comparison with hydrodynamical simulations suggests that CR7's clumps have metallicities of . The observed ISM structure of CR7 indicates that we are likely witnessing the build up of a central galaxy in the early universe through complex accretion of satellites.
Context. Determining the dust properties and UV attenuation of distant star-forming galaxies is of great interest for our understanding of galaxy formation and cosmic star formation in the early ...Universe. However, few direct measurements exist so far. Aims. To shed new light on these questions, we have targeted two recently discovered Lyman-break galaxies (LBGs) at z ≈ 6.8 and z = 7.508 to search for dust continuum and C ii λ158 μm line emission. Methods. The strongly lensed z ≈ 6.8 LBG A1703-zD1 behind the galaxy cluster Abell 1703 and the spectroscopically confirmed z = 7.508 LBG z8-GND-5296 in the GOODS-N field were observed with the Plateau de Bure Interferometer (PdBI) at 1.2 mm. These observations were combined with those of three z> 6.5 Lyα emitters (HCM6A, Himiko, and IOK-1), for which deep measurements were recently obtained with the PdBI and ALMA. Results. C ii is undetected in both galaxies, providing a deep upper limit of LC II< 2.8 × 107L⊙ for A1703-zD1, comparable to the nondetections of Himiko and IOK-1 with ALMA. Dust continuum emission from A1703-zD1 and z8-GND-5296 is not detected with an rms of 0.12 and 0.16 mJy/beam. From these nondetections and earlier multiwavelength observations we derive upper limits on their IR luminosity and star formation rate, dust mass, and UV attenuation. Thanks to strong gravitational lensing, the achieved limit for A1703-zD1 is similar to those achieved with ALMA, probing below the luminous infrared galaxy (LIRG) regime (LIR< 8.1 × 1010L⊙) and very low dust masses (Md< 1.6 × 107M⊙). We find that all five galaxies are compatible with the Calzetti IRX-β relation, their UV attenuation is compatible with several indirect estimates from other methods (the UV slope, extrapolation of the attenuation measured from the IR/UV ratio at lower redshift, and spectral energy distribution fits), and the dust-to-stellar mass ratio is compatible with that of galaxies from z = 0 to 3. From their stellar mass, the high-z galaxies studied here have an attenuation below the one expected from the mean relation of low-redshift (z ≲ 1.5) galaxies. Conclusions. More and deeper (sub-)mm data are clearly needed to directly determine the UV attenuation and dust content of the dominant population of high-z star-forming galaxies and to establish their dependence on stellar mass, redshift, and other properties more firmly.
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To extend the molecular gas measurements to more typical star-forming galaxies (SFGs) with star formation rates SFR< 40 M⊙ yr-1 and stellar masses M∗< 2.5 × 1010M⊙ at z ~ 1.5−3, we have observed CO ...emission with the IRAM Plateau de Bure Interferometer and the IRAM 30 m telescope for five strongly lensed galaxies, selected from the Herschel Lensing Survey. These observations are combined with a compilation of CO measurements from the literature. From this, we infer the CO luminosity correction factors r2,1 = 0.81 ± 0.20 and r3,1 = 0.57 ± 0.15 for the J = 2 and J = 3 CO transitions, respectively, valid for SFGs at z> 1. The combined sample of CO-detected SFGs at z> 1 shows a large spread in star formation efficiency (SFE) with a dispersion of 0.33 dex, such that the SFE extends well beyond the low values of local spirals and overlaps the distribution of z> 1 submm galaxies. We find that the spread in SFE (or equivalently in molecular gas depletion timescale) is due to the variations of several physical parameters, primarily the specific star formation rate, and also stellar mass and redshift. The dependence of SFE on the offset from the main sequence and the compactness of the starburst is less clear. The possible increase of the molecular gas depletion timescale with stellar mass, now revealed by low M∗ SFGs at z> 1 and also observed at z = 0, contrasts with the generally acknowledged constant molecular gas depletion timescale and refutes the linearity of the Kennicutt-Schmidt relation. A net rise of the molecular gas fraction (fgas) is observed from z ~ 0.2 to z ~ 1.2, followed by a very mild increase toward higher redshifts, as found in earlier studies. At each redshift the molecular gas fraction shows a large dispersion, mainly due to the dependence of fgas on stellar mass, producing a gradient of increasing fgas with decreasing M∗. We provide the first measurement of the molecular gas fraction of z> 1 SFGs at the low-M∗ end between 109.4<M∗/M⊙< 109.9, reaching a mean ⟨ fgas ⟩ = 0.69 ± 0.18, which shows a clear fgas upturn at these lower stellar masses. Finally, we find evidence for a nonuniversal dust-to-gas ratio among high-redshift SFGs, high-redshift submm galaxies, local spirals, and local ultraluminous IR galaxies with near-solar metallicities, as inferred from a homogeneous analysis of their rest-frame 850 μm luminosity per unit gas mass. The SFGs with z> 1 show a trend for a lower Lν(850 μm) /Mgas mean by 0.33 dex compared to the other galaxy populations.
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![The absence of [C ii ] 158 ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1745-3925_0035-8711/small "The absence of [C ii ] 158 $\mu$m emission in spectroscopically confirmed galaxies at z > 8")
