ABSTRACT
We present a sub-kpc resolved study of the interstellar medium properties in SDP.81, a $z$ = 3.042 strongly gravitationally lensed, dusty star-forming galaxy, based on high-resolution, ...multiband ALMA observations of the far-infrared (FIR) continuum, CO ladder, and the C ii line. Using a visibility-plane lens modelling code, we achieve a median source-plane resolution of ∼200 pc. We use photon-dominated region (PDR) models to infer the physical conditions – far-ultraviolet (FUV) field strength, density, and PDR surface temperature – of the star-forming gas on 200-pc scales, finding a FUV field strength of ∼103−104G0, gas density of ∼105 cm−3, and cloud surface temperatures up to 1500 K, similar to those in the Orion Trapezium region. The C ii emission is significantly more extended than that FIR continuum: ∼50 per cent of C ii emission arises outside the FIR-bright region. The resolved C ii/FIR ratio varies by almost 2 dex across the source, down to ∼2 × 10−4 in the star-forming clumps. The observed C ii/FIR deficit trend is consistent with thermal saturation of the C+ fine-structure-level occupancy at high gas temperatures. We make the source-plane reconstructions of all emission lines and continuum data publicly available.
We present 0 15 (1 kpc) resolution ALMA observations of the C ii 157.74 m line and rest-frame 160 m continuum emission in two z ∼ 3 dusty, star-forming galaxies-ALESS 49.1 and ALESS 57.1, combined ...with resolved CO (3-2) observations. In both sources, the C ii surface brightness distribution is dominated by a compact core ≤1 kpc in radius, a factor of 2-3 smaller than the extent of the CO (3-2) emission. In ALESS 49.1, we find an additional extended (8 kpc radius), low surface brightness C ii component. Based on an analysis of mock ALMA observations, the C ii and 160 m continuum surface brightness distributions are inconsistent with a single-Gaussian surface brightness distribution with the same size as the CO (3-2) emission. The C ii rotation curves flatten at 2 kpc radius, suggesting that the kinematics of the central regions are dominated by a baryonic disk. Both galaxies exhibit a strong C ii/far-IR (FIR) deficit on 1 kpc scales, with FIR surface brightness to C ii/FIR slope steeper than in local star-forming galaxies. A comparison of the C ii/CO (3-2) observations with photodissociation region models suggests a strong far-UV (FUV) radiation field (G0 ∼ 104) and high gas density (n(H) ∼ 104-105 cm−3) in the central regions of ALESS 49.1 and ALESS 57.1. The most direct interpretation of the pronounced C ii/FIR deficit is a thermal saturation of the C+ fine-structure levels at temperatures ≥500 K, driven by the strong FUV field.
Abstract
Feedback and outflows in galaxies that are associated with a quasar phase are expected to be pivotal in quenching the most massive galaxies. However, observations targeting the molecular ...outflow phase, which dominates both the mass and momentum and removes the immediate fuel for star formation, are limited in high-
z
QSO hosts. Massive quiescent galaxies found at
z
∼ 4 are predicted to have quenched star formation already by
z
∼ 5 and undergone their most intense growth at
z
> 6. Here, we present two Atacama Large Millimeter/submillimeter Array (ALMA) detections of molecular outflows, traced by blueshifted absorption of the OH 119
μ
m doublet, from a sample of three
z
> 6 infrared luminous QSO hosts: J2310+1855 and P183+05. OH 119
μ
m is also detected in emission from P183+05, and tentatively in the third source: P036+03. Using similar assumptions as for high-
z
dusty star-forming galaxy outflows, we find that our QSOs drive molecular outflows with comparable mass outflow rates, which are comparably energetic except for J2310+1855's significantly lower outflow energy flux. We do not find evidence, nor require additional input from the central active galactic nucleus (AGN) to drive the molecular outflow in J2310+1855, but we cannot rule out an AGN contribution in P183+05 if a significant AGN contribution to
L
FIR
is assumed and/or if the outflow covering fraction is high (≥53%), which evidence from the literature suggests is unlikely in these sources. Differences observed in the blueshifted absorption spectral properties may instead be caused by the QSO hosts’ more compact dust continuums, limiting observations to lower altitude and more central regions of the outflow.
Abstract
We present the initial results of an ongoing survey with the Karl G. Jansky Very Large Array targeting the CO(
J
= 1–0) transition in a sample of 30 submillimeter-selected, dusty ...star-forming galaxies (SFGs) at
z
= 2–5 with existing mid-
J
CO detections from the Atacama Large Millimeter/submillimeter Array and NOrthern Extended Millimeter Array, of which 17 have been fully observed. We detect CO(1–0) emission in 11 targets, along with three tentative (∼1.5
σ
–2
σ
) detections; three galaxies are undetected. Our results yield total molecular gas masses of 6–23 × 10
10
(
α
CO
/1)
M
⊙
, with gas mass fractions,
f
gas
=
M
mol
/(
M
*
+
M
mol
), of 0.1–0.8 and a median depletion time of (140 ± 70) Myr. We find median CO excitation ratios of
r
31
= 0.75 ± 0.39 and
r
41
= 0.63 ± 0.44, with significant scatter. We find no significant correlation between the excitation ratio and a number of key parameters such as redshift, CO(1–0) line width, or Σ
SFR
. We only find a tentative positive correlation between
r
41
and the star-forming efficiency, but we are limited by our small sample size. Finally, we compare our results to predictions from the SHARK semi-analytical model, finding a good agreement between the molecular gas masses, depletion times, and gas fractions of our sources and their SHARK counterparts. Our results highlight the heterogeneous nature of the most massive SFGs at high redshift, and the importance of CO(1–0) observations to robustly constrain their total molecular gas content and interstellar medium properties.
Abstract
We report the detection of a massive neutral gas outflow in the
z
= 2.09 gravitationally lensed dusty star-forming galaxy HATLAS J085358.9+015537 (G09v1.40), seen in absorption with the OH
+
...(1
1
−1
0
) transition using spatially resolved (0.″5 × 0.″4) Atacama Large Millimeter/submillimeter Array (ALMA) observations. The blueshifted OH
+
line is observed simultaneously with the CO(9−8) emission line and underlying dust continuum. These data are complemented by high-angular-resolution (0.″17 × 0.″13) ALMA observations of CH
+
(1−0) and underlying dust continuum, and Keck 2.2
μ
m imaging tracing the stellar emission. The neutral outflow, dust, dense molecular gas, and stars all show spatial offsets from each other. The total atomic gas mass of the observed outflow is 6.7 × 10
9
M
⊙
, >25% as massive as the gas mass of the galaxy. We find that a conical outflow geometry best describes the OH
+
kinematics and morphology and derive deprojected outflow properties as functions of possible inclination (0.°38–64°). The neutral gas mass outflow rate is between 83 and 25,400
M
⊙
yr
−1
, exceeding the star formation rate (788 ± 300
M
⊙
yr
−1
) if the inclination is >3.°6 (mass-loading factor = 0.3–4.7). Kinetic energy and momentum fluxes span (4.4–290) × 10
9
L
⊙
and (0.1–3.7) × 10
37
dyne, respectively (energy-loading factor = 0.013–16), indicating that the feedback mechanisms required to drive the outflow depend on the inclination assumed. We derive a gas depletion time between 29 and 1 Myr, but find that the neutral outflow is likely to remain bound to the galaxy unless the inclination is small and may be reaccreted if additional feedback processes do not occur.
Abstract
Extreme emission-line galaxies (EELGs) at redshift
z
= 1−2 provide a unique view of metal-poor, starburst sources that are the likely drivers of the cosmic reionization at
z
≥ 6. However, ...the molecular gas reservoirs of EELGs—the fuel for their intense star formation—remain beyond the reach of current facilities. We present ALMA C
ii
and PdBI CO(2–1) observations of the
z
= 1.8, strongly lensed EELG SL2S 0217, a bright Ly
α
emitter with a metallicity 0.05
Z
⊙
. We obtain a tentative (∼3
σ
–4
σ
) detection of the C
ii
line and set an upper limit on the C
ii
/SFR (star-forming rate) ratio of ≤1 × 10
6
L
⊙
/(
M
⊙
yr
−1
), based on the synthesized images and visibility-plane analysis. The CO(2–1) emission is not detected. Photoionization modeling indicates that up to 80% of the C
ii
emission originates from neutral or molecular gas, although we cannot rule out that the gas is fully ionized. The very faint C
ii
emission is in line with both nearby metal-poor dwarfs and high-redshift Ly
α
emitters, and predictions from hydrodynamical simulations. However, the C
ii
line is 30× fainter than predicted by the De Looze et al. C
ii
–SFR relation for local dwarfs, illustrating the danger of extrapolating locally calibrated relations to high-redshift, metal-poor galaxies.
Abstract
We present an Atacama Large Millimeter/submillimeter Array (ALMA) survey of CO(4–3) line emitting galaxies in 17 quasar fields at
z
∼ 4 aimed at performing the first systematic search of ...dusty galaxies in high-
z
quasar environments. Our blind search of galaxies around the quasars results in five CO emitters with S/N ≥ 5.6 within a projected radius of
R
≲ 1.5
h
−1
cMpc and a velocity range of
δv
= ±1000 km s
−1
around the quasar. In blank fields, we expect to detect only 0.28 CO emitters within the same volume, implying a total overdensity of
17.6
−
7.6
+
11.9
in our fields, and indicating that quasars trace massive structures in the early universe. We quantify this overdensity by measuring the small-scale clustering of CO emitters around quasars, resulting in a cross-correlation length of
r
0
,
QG
=
8.37
−
2.04
+
2.42
h
−
1
cMpc, assuming a fixed slope
γ
= 1.8. This contradicts the reported mild overdensities (x1.4) of Ly
α
emitters (LAEs) in the same fields at scales of
R
≲ 7
h
−1
cMpc, which are well described by a cross-correlation length
3.0
−
1.4
+
1.5
times lower than that measured for CO emitters. We discuss some possibilities to explain this discrepancy, including low star formation efficiency, and excess of dust in galaxies around quasars. Finally, we constrain, for the first time, the clustering of CO emitters at
z
∼ 4, finding an autocorrelation length of
r
0,CO
= 3.14 ±1.71
h
−1
cMpc (with
γ
= 1.8). Our work, together with the previous study of LAEs around quasars, traces simultaneously the clustering properties of both optical and dusty galaxy populations in quasars fields, stressing the importance of multiwavelength studies, and highlighting important questions about galaxy properties in high-
z
dense environments.
A clustered origin for isolated massive stars Lucas, William E; Rybak, Matus; Bonnell, Ian A ...
Monthly notices of the Royal Astronomical Society,
03/2018, Letnik:
474, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Abstract
High-mass stars are commonly found in stellar clusters promoting the idea that their formation occurs due to the physical processes linked with a young stellar cluster. It has recently been ...reported that isolated high-mass stars are present in the Large Magellanic Cloud. Due to their low velocities, it has been argued that these are high-mass stars which formed without a surrounding stellar cluster. In this paper, we present an alternative explanation for the origin of these stars in which they formed in a cluster environment but are subsequently dispersed into the field as their natal cluster is tidally disrupted in a merger with a higher mass cluster. They escape the merged cluster with relatively low velocities typical of the cluster interaction and thus of the larger scale velocity dispersion, similarly to the observed stars. N-body simulations of cluster mergers predict a sizeable population of low-velocity (≤20 km s−1), high-mass stars at distances of >20 pc from the cluster. High-mass clusters in which gas poor mergers are frequent would be expected to commonly have haloes of young stars, including high-mass stars, which were actually formed in a cluster environment.
Abstract
We report a ground-based detection of the O
i
63
μ
m line in a
z
= 6.027 gravitationally lensed dusty star-forming galaxy (DSFG) G09.83808 using the Atacama Pathfinder EXperiment SEPIA 660 ...receiver, the first unambiguous detection of the O
i
63
line beyond redshift 3, and the first obtained from the ground. The O
i
63
line is robustly detected at 22 ± 5 Jy km s
−1
, corresponding to an intrinsic (de-lensed) luminosity of (5.4 ± 1.3) × 10
9
L
⊙
. With the O
i
63
/C
ii
luminosity ratio of 4, the O
i
63
line is the main coolant of the neutral gas in this galaxy, in agreement with model predictions. The high O
i
63
luminosity compensates for the pronounced C
ii
deficit (C
ii
/FIR ≃ 4 × 10
−4
). Using photon-dominated region models, we derive a source-averaged gas density
n
= 10
4.0
cm
−3
, and FUV field strength
G
= 10
4
G
0
, comparable to the
z
= 2–4 DSFG population. If G09.83808 represents a typical high-redshift DSFG, the O
i
63
line from
z
= 6 non-lensed DSFGs should be routinely detectable in the Atacama Large Millimeter/submillimeter Array Band 9 observations with ∼15 minutes on-source, opening a new window to study the properties of the earliest DSFGs.
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