ALMA 870 m continuum imaging has uncovered a population of blends of multiple dusty star-forming galaxies (DSFGs) in sources originally detected with the Herschel Space Observatory. However, their ...pairwise separations are much smaller than what is found by ALMA follow-up of other single-dish surveys or expected from theoretical simulations. Using ALMA and the Very Large Array, we have targeted three of these systems to confirm whether the multiple 870 m continuum sources lie at the same redshift, successfully detecting 12CO (J = 3-2) and 12CO (J = 1-0) lines and being able to confirm that in the three cases all the multiple DSFGs are likely physically associated within the same structure. Therefore, we report the discovery of two new gas-rich dusty protocluster cores (HELAISS02, z = 2.171 0.004; HXMM20, z = 2.602 0.002). The third target is located in the well-known COSMOS overdensity at z = 2.51 (named CL J1001+0220 in the literature), for which we do not find any new secure CO (1-0) detection, although some of its members show only tentative detections and require further confirmation. From the gas, dust, and stellar properties of the two new protocluster cores, we find very large molecular gas fractions yet low stellar masses, pushing the sources above the main sequence (MS), while not enhancing their star formation efficiency. We suggest that the sources might be newly formed galaxies migrating to the MS. The properties of the three systems compared to each other and to field galaxies may suggest a different evolutionary stage between systems.
The Brownian loop soup is a conformally invariant statistical ensemble of random loops in two dimensions characterized by an intensity
λ
>
0
, with central charge
c
=
2
λ
. Recent progress resulted ...in an analytic form for the four-point function of a class of scalar conformal primary “layering vertex operators”
O
β
with dimensions
(
Δ
,
Δ
)
, with
Δ
=
λ
10
(
1
-
cos
β
)
, that compute certain statistical properties of the model. The Virasoro conformal block expansion of the four-point function revealed the existence of a new set of operators with dimensions
(
Δ
+
k
/
3
,
Δ
+
k
′
/
3
)
, for all non-negative integers
k
,
k
′
satisfying
|
k
-
k
′
|
=
0
mod
3
. In this paper we introduce the edge counting field
E
(
z
)
that counts the number of loop boundaries that pass close to the point
z
. We rigorously prove that the
n
-point functions of
E
are well defined and behave as expected for a conformal primary field with dimensions (1/3, 1/3). We analytically compute the four-point function
O
β
(
z
1
)
O
-
β
(
z
2
)
E
(
z
3
)
E
(
z
4
)
and analyze its conformal block expansion. The operator product expansions of
E
×
E
and
E
×
O
β
contain higher-order edge operators with “charge”
β
and dimensions
(
Δ
+
k
/
3
,
Δ
+
k
/
3
)
. Hence, we have explicitly identified all scalar primary operators among the new set mentioned above. We also re-compute the central charge by an independent method based on the operator product expansion and find agreement with previous methods.
A
bstract
We compute analytically and in closed form the four-point correlation function in the plane, and the two-point correlation function in the upper half-plane, of layering vertex operators in ...the two dimensional conformally invariant system known as the Brownian Loop Soup. These correlation functions depend on multiple continuous parameters: the insertion points of the operators, the intensity of the soup, and the charges of the operators. In the case of the four-point function there is non-trivial dependence on five continuous parameters: the cross-ratio, the intensity, and three real charges. The four-point function is crossing symmetric. We analyze its conformal block expansion and discover a previously unknown set of new conformal primary operators.
We discuss the evolution of the interstellar medium of quiescent galaxies, currently emerging from recent analyses, with the help of a simple model based on well-established empirical relations such ...as the stellar mass functions and the main sequence of star formation. This model is meant to describe observed quantities without making specific assumptions on the nature of quenching processes, but relying on their observable consequences. We find that the high gas fractions seen or suggested at high redshift in quiescent galaxies, and their apparent mild evolution at early times, can be mostly attributed to a progenitor effect where recently quenched galaxies with ∼10% gas fractions dominate the quiescent galaxy population until
z
∼ 1. In the same context, the much lower gas and dust fractions measured in local early-type galaxies are interpreted as the product of the steady depletion of their interstellar medium on a ∼2 Gyr timescale, coupled with a higher fraction of more gas-exhaustive events.
Abstract
We investigate the fine-structure C
ii
line at 158
μ
m as a molecular gas tracer by analyzing the relationship between molecular gas mass (
M
mol
) and C
ii
line luminosity (
L
C
II
) in ...11,125
z
≃ 6 star-forming, main-sequence galaxies from the
simba
simulations, with line emission modeled by the Simulator of Galaxy Millimeter/Submillimeter Emission. Though most (∼50%–100%) of the gas mass in our simulations is ionized, the bulk (>50%) of the C
ii
emission comes from the molecular phase. We find a sublinear (slope 0.78 ± 0.01)
log
L
C
II
–
log
M
mol
relation, in contrast with the linear relation derived from observational samples of more massive, metal-rich galaxies at
z
≲ 6. We derive a median C
ii
-to-
M
mol
conversion factor of
α
C
II
≃ 18
M
⊙
/
L
⊙
. This is lower than the average value of ≃30
M
⊙
/
L
⊙
derived from observations, which we attribute to lower gas-phase metallicities in our simulations. Thus, a lower, luminosity-dependent conversion factor must be applied when inferring molecular gas masses from C
ii
observations of low-mass galaxies. For our simulations, C
ii
is a better tracer of the molecular gas than CO
J
= 1–0, especially at the lowest metallicities, where much of the gas is
CO-dark
. We find that
L
C
II
is more tightly correlated with
M
mol
than with star formation rate (SFR), and both the
log
L
C
II
–
log
M
mol
and
log
L
C
II
–
log
SFR
relations arise from the Kennicutt–Schmidt relation. Our findings suggest that
L
C
II
is a promising tracer of the molecular gas at the earliest cosmic epochs.
Optically compact star-forming galaxies (SFGs) have been proposed as immediate progenitors of quiescent galaxies, although their origin and nature are debated. Were they formed in slow secular ...processes or in rapid merger-driven starbursts? Answering this question would provide fundamental insight into how quenching occurs. We explore the location of the general population of galaxies with respect to fundamental star-forming and structural relations, identify compact SFGs based on their stellar core densities, and study three diagnostics of the burstiness of star formation: (1) star formation efficiency, (2) interstellar medium (ISM), and (3) radio emission. The overall distribution of galaxies in the fundamental relations points toward a smooth transition toward quiescence while galaxies grow their stellar cores, although some galaxies suddenly increase their specific star formation rate when they become compact. From their star formation efficiencies compact and extended SFGs appear similar. In relation to the ISM diagnostic, study of the CO excitation, the density of the neutral gas, and the strength of the ultraviolet radiation field shows that compact SFGs resemble galaxies located in the upper envelope of the main sequence of SFGs, although this is based on a small sample size. Regarding the radio emission diagnostic, we find that galaxies become increasingly compact as the starburst ages, implying that at least some compact SFGs are old starbursts. We suggest that compact SFGs could be starbursts winding down and eventually crossing the main sequence toward quiescence.
ABSTRACT
Post-starburst galaxies are sources that had the last major episode of star formation about 1 Gyr before the epoch of the observations and are on their way to quiescence. It is important to ...study such galaxies at redshift z > 1, during their main quenching phase, and estimate their molecular gas content to constrain the processes responsible for the cessation of star formation. We present CO(3–2) ALMA observations of two massive (M⋆ ∼ 5 × 1010 M⊙) post-starburst galaxies at z > 1. We measure their molecular gas fraction to be fH2 = MH2/M⋆ ∼ 8–16 per cent, consistent with z < 1 post-starburst galaxies from the literature. The star formation efficiency of our targets is ∼10× lower than that of star-forming galaxies at similar redshift, and they are outliers of the fH2–specific star formation rate (sSFR) relation of star-forming galaxies, as they have larger fH2 than expected given their sSFR. The gas fraction of post-starbursts from our sample and the literature correlates with the Dn4000 spectral index, a proxy of the stellar population age. This suggests that their gas content decreases after the last major burst of star formation. Finally, one of our targets is undergoing a major merger phase with two highly star-forming companions. This hints at a picture where a perturber event (e.g. major merger) quenches star formation without completely removing the molecular gas.
ABSTRACT
We report the discovery of an intrinsically faint, quintuply-imaged, dusty galaxy MACS0600-z6 at a redshift z = 6.07 viewed through the cluster MACSJ0600.1–2008 (z = 0.46). A ≃ 4σ dust ...detection is seen at 1.2mm as part of the ALMA Lensing Cluster Survey (ALCS), an on-going ALMA Large programme, and the redshift is secured via C ii 158 μm emission described in a companion paper. In addition, spectroscopic follow-up with GMOS/Gemini-North shows a break in the galaxy’s spectrum, consistent with the Lyman break at that redshift. We use a detailed mass model of the cluster and infer a magnification μ ≳ 30 for the most magnified image of this galaxy, which provides an unprecedented opportunity to probe the physical properties of a sub-luminous galaxy at the end of cosmic reionization. Based on the spectral energy distribution, we infer lensing-corrected stellar and dust masses of $\rm {2.9^{+11.5}_{-2.3}\times 10^9}$ and $\rm {4.8^{+4.5}_{-3.4}\times 10^6}$$\rm {M_{\odot }}$, respectively, a star formation rate of $\rm {9.7^{+22.0}_{-6.6} \, M_{\odot } \, yr^{-1}}$, an intrinsic size of $\rm {0.54^{+0.26}_{-0.14}}$ kpc, and a luminosity-weighted age of 200 ± 100 Myr. Strikingly, the dust production rate in this relatively young galaxy appears to be larger than that observed for equivalent, lower redshift sources. We discuss if this implies that early supernovae are more efficient dust producers and the consequences for using dust mass as a probe of earlier star formation.
We present Atacama Large Millimeter/submillimeter Array observations of the 870 m continuum and CO(4-3) line emission in the core of the galaxy cluster Cl J1449+0856 at z = 2, a near-IR-selected, ...X-ray-detected system in the mass range of typical progenitors of today's massive clusters. The 870 m map reveals six F870 m > 0.5 mJy sources spread over an area of 0.07 arcmin2, giving an overdensity of a factor of ∼10 (6) with respect to blank-field counts down to F870 m > 1 mJy (>0.5 mJy). On the other hand, deep CO(4-3) follow-up confirms membership of three of these sources but suggests that the remaining three, including the brightest 870 m sources in the field (F870 m 2 mJy), are likely interlopers. The measurement of 870 m continuum and CO(4-3) line fluxes at the positions of previously known cluster members provides a deep probe of dusty star formation occurring in the core of this high-redshift structure, adding up to a total star formation rate of ∼700 100 M yr−1 and yielding an integrated star formation rate density of ∼104 M yr−1 Mpc−3, five orders of magnitude larger than in the field at the same epoch, due to the concentration of star-forming galaxies in the small volume of the dense cluster core. The combination of these observations with previously available Hubble Space Telescope imaging highlights the presence in this same volume of a population of galaxies with already suppressed star formation. This diverse composition of galaxy populations in Cl J1449+0856 is especially highlighted at the very cluster center, where a complex assembly of quiescent and star-forming sources is likely forming the future brightest cluster galaxy.
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