Context. The Galactic center is the closest region where we can study star formation under extreme physical conditions like those in high-redshift galaxies. Aims. We measure the temperature of the ...dense gas in the central molecular zone (CMZ) and examine what drives it. Methods. We mapped the inner 300 pc of the CMZ in the temperature-sensitive J = 3–2 para-formaldehyde (p - H2CO) transitions. We used the 32,1−22,0/ 30,3−20,2 line ratio to determine the gas temperature in n ~ 104−105 cm-3 gas. We have produced temperature maps and cubes with 30′′ and 1 km s-1 resolution and published all data in FITS form. Results. Dense gas temperatures in the Galactic center range from ~60 K to >100 K in selected regions. The highest gas temperatures TG> 100 K are observed around the Sgr B2 cores, in the extended Sgr B2 cloud, the 20 km s-1 and 50 km s-1 clouds, and in “The Brick” (G0.253+0.016). We infer an upper limit on the cosmic ray ionization rate ζCR< 10-14s-1. Conclusions. The dense molecular gas temperature of the region around our Galactic center is similar to values found in the central regions of other galaxies, in particular starburst systems. The gas temperature is uniformly higher than the dust temperature, confirming that dust is a coolant in the dense gas. Turbulent heating can readily explain the observed temperatures given the observed line widths. Cosmic rays cannot explain the observed variation in gas temperatures, so CMZ dense gas temperatures are not dominated by cosmic ray heating. The gas temperatures previously observed to be high in the inner ~75 pc are confirmed to be high in the entire CMZ.
Abstract
We present an ALMA-Herschel joint analysis of sources detected by the ALMA Lensing Cluster Survey (ALCS) at 1.15 mm. Herschel/PACS and SPIRE data at 100–500
μ
m are deblended for 180 ALMA ...sources in 33 lensing cluster fields that are detected either securely (141 sources; in our main sample) or tentatively at S/N ≥ 4 with cross-matched HST/Spitzer counterparts, down to a delensed 1.15 mm flux density of ∼0.02 mJy. We performed far-infrared spectral energy distribution modeling and derived the physical properties of dusty star formation for 125 sources (109 independently) that are detected at >2
σ
in at least one Herschel band. A total of 27 secure ALCS sources are not detected in any Herschel bands, including 17 optical/near-IR-dark sources that likely reside at
z
= 4.2 ± 1.2. The 16th, 50th, and 84th percentiles of the redshift distribution are 1.15, 2.08, and 3.59, respectively, for ALCS sources in the main sample, suggesting an increasing fraction of
z
≃ 1 − 2 galaxies among fainter millimeter sources (
f
1150
∼ 0.1 mJy). With a median lensing magnification factor of
μ
=
2.6
−
0.8
+
2.6
, ALCS sources in the main sample exhibit a median intrinsic star formation rate of
94
−
54
+
84
M
⊙
yr
−1
, lower than that of conventional submillimeter galaxies at similar redshifts by a factor of ∼3. Our study suggests weak or no redshift evolution of dust temperature with
L
IR
< 10
12
L
⊙
galaxies within our sample at
z
≃ 0 − 2. At
L
IR
> 10
12
L
⊙
, the dust temperatures show no evolution across
z
≃ 1–4 while being lower than those in the local universe. For the highest-redshift source in our sample (
z
= 6.07), we can rule out an extreme dust temperature (>80 K) that was reported for MACS0416 Y1 at
z
= 8.31.
Abstract
We universally search for evidence of kinematic and spatial correlation of supernova remnant (SNR) and molecular cloud (MC) associations for nearly all SNRs in the coverage of the Milky Way ...Imaging Scroll Painting CO survey, i.e., 149 SNRs, 170 SNR candidates, and 18 pure pulsar wind nebulae in 1° <
l
< 230° and −5.°5 <
b
< 5.°5. Based on high-quality and unbiased
12
CO/
13
CO/C
18
O (
J
= 1–0) survey data, we apply automatic algorithms to identify broad lines and spatial correlations for molecular gas in each SNR region. The 91% of SNR–MC associations detected previously are identified in this paper by CO line emission. Overall, there could be as high as 80% of SNRs associated with MCs. The proportion of SNRs associated with MCs is high within the Galactic longitude less than ∼50°. Kinematic distances of all SNRs that are associated with MCs are estimated based on systemic velocities of associated MCs. The radii of SNRs associated with MCs follow a lognormal distribution, which peaks at ∼8.1 pc. The progenitor initial mass of these SNRs follows a power-law distribution with an index of ∼−2.3 that is consistent with the Salpeter index of −2.35. We find that SNR–MC associations are mainly distributed in a thin disk along the Galactic plane, while a small number are distributed in a thick disk. With the height of these SNRs from the Galactic plane below ∼45 pc, the distribution of the average radius relative to the height of them is roughly flat, and the average radius increases with the height when above ∼45 pc.
Abstract
We report the multiwavelength properties of millimeter galaxies hosting X-ray detected active galactic nuclei (AGNs) from the ALMA Lensing Cluster Survey (ALCS). ALCS is an extensive survey ...of well-studied lensing clusters with ALMA, covering an area of 133 arcmin
2
over 33 clusters with a 1.2 mm flux-density limit of ∼60
μ
Jy (1
σ
). Utilizing the archival data of Chandra, we identify three AGNs at
z
= 1.06, 2.09, and 2.84 among the 180 millimeter sources securely detected in the ALCS (of which 155 are inside the coverage of Chandra). The X-ray spectral analysis shows that two AGNs are not significantly absorbed (
log
N
H
/
cm
−
2
<
23
), while the other shows signs of moderate absorption (
log
N
H
/
cm
−
2
∼
23.5
). We also perform spectral energy distribution modeling of X-ray to millimeter photometry. We find that our X-ray AGN sample shows both high mass-accretion rates (intrinsic 0.5–8 keV X-ray luminosities of ∼10
44–45
erg s
−1
) and star formation rates (≳100
M
⊙
yr
−1
). This demonstrates that a wide-area survey with ALMA and Chandra can selectively detect intense growth of both galaxies and supermassive black holes in the high-redshift universe.
Abstract
We present the survey of
12
CO/
13
CO/C
18
O (
J
= 1 − 0) toward the California molecular cloud (CMC) within the region of 161.°75 ≤
l
≤ 167.°75, −9.°5 ≤
b
≤ −7.°5 using the Purple Mountain ...Observatory (PMO) 13.7 m millimeter telescope. Adopting a distance of 470 pc, the mass of the observed molecular cloud estimated from
12
CO,
13
CO, and C
18
O is about 2.59 × 10
4
, 0.85 × 10
4
, and 0.09 × 10
4
M
⊙
, respectively. A large-scale continuous filament extending about 72 pc is revealed from the
13
CO images. A systematic velocity gradient perpendicular to the major axis appears and is measured to be ∼0.82 km s
−1
pc
−1
. The kinematics along the filament shows an oscillation pattern with a fragmentation wavelength of ∼2.3 pc and velocity amplitude of ∼0.92 km s
−1
, which may be related to core-forming flows. Furthermore, assuming an inclination angle to the plane of the sky of 45°, the estimated average accretion rate is ∼101
M
⊙
Myr
−1
for the cluster LkH
α
101 and ∼21
M
⊙
Myr
−1
for the other regions. In the C
18
O observations, the large-scale filament could be resolved into multiple substructures, and their dynamics are consistent with the scenario of filament formation from converging flows. Approximately 225 C
18
O cores are extracted, of which 181 are starless cores. Roughly 37% (67/181) of the starless cores have
α
vir
less than 1. Twenty outflow candidates are identified along the filament. Our results indicate active early-phase star formation along the large-scale filament in the CMC region.
Abstract In this work, we report a study on the relationship between flux and intensity for molecular clouds. Our analysis is established on high-quality CO images from the Milky Way Imaging Scroll ...Painting project. The new flux–intensity relation characterizes the flux variation of molecular clouds above specific intensity levels. We found that the flux–intensity relation exhibits two prominent features. First, the flux–intensity relation generally follows exponential shapes; second, hierarchical structures of molecular clouds are imprinted on flux–intensity relations. Specifically, 12 CO flux–intensity relations are composed of one or more exponential segments, and for molecular clouds with segmented flux–intensity relations, the edge and the flux of the high-temperature component are strikingly consistent with 13 CO emission. Further analysis shows that a similar relationship also exists between 13 CO flux–intensity relations and C 18 O emission. The mean brightness temperature of molecular clouds is tightly associated with the decay rate of flux, the break temperature of exponential segments, and, to a certain extent, the flux fraction of the high-temperature component. Broadly, the flux–intensity relation of a molecular tracer, either in optically thick or in optically thin cases, has the capability to outline the silhouette of internal structures of molecular clouds, proving to be a potent tool for probing structures of molecular clouds.
Abstract Sub/millimeter galaxies are a key population for the study of galaxy evolution because the majority of star formation at high redshifts occurred in galaxies deeply embedded in dust. To ...search for this population, we have performed an extensive survey with Atacama Large Millimeter/submillimeter Array (ALMA), called the ALMA Lensing Cluster Survey (ALCS). This survey covers 133 arcmin 2 area and securely detects 180 sources at z ∼ 0.5–6 with a flux limit of ∼0.2 mJy at 1.2 mm. Here, we report the results of multiwavelength spectral energy distribution analysis of the whole ALCS sample, utilizing the observed-frame UV to millimeter photometry. We find that the majority of the ALCS sources lie on the star-forming main sequence, with a smaller fraction showing intense starburst activities. The ALCS sample contains high infrared-excess sources ( IRX = log ( L dust / L UV ) > 1 ), including two extremely dust-obscured galaxies (IRX > 5). We also confirm that the ALCS sample probes a broader range in lower dust mass than conventional submillimeter galaxy samples in the same redshift range. We identify six heavily obscured active galactic nucleus (AGN) candidates that are not detected in the archival Chandra data in addition to the three X-ray AGNs reported by Uematsu et al. (2023). The inferred AGN luminosity density shows a possible excess at z = 2–3 compared with that determined from X-ray surveys below 10 keV.
Context.
The properties of galaxies at redshift
z
> 6 hold the key to our understanding of the early stages of galaxy evolution and can potentially identify the sources of the ultraviolet radiation ...that give rise to the epoch of reionisation. The far-infrared cooling line of C
II
at 158 μm is known to be bright and correlate with the star formation rate (SFR) of low-redshift galaxies, and hence is also suggested to be an important tracer of star formation and interstellar medium properties for very high-redshift galaxies.
Aims.
With the aim to study the interstellar medium properties of gravitationally lensed galaxies at
z
> 6, we search for C
II
and thermal dust emission in a sample of 52
z
∼ 6 galaxies observed by the ALMA Lensing Cluster Survey.
Methods.
We perform our analysis using L
INE
S
TACKER
, stacking both C
II
and continuum emission. The target sample is selected from multiple catalogues, and the sample galaxies have spectroscopic redshift or low-uncertainty photometric redshifts (
σ
z
< 0.02) in nine galaxy clusters. Source properties of the target galaxies are either extracted from the literature or computed using spectral energy distribution fitting. Both weighted-average and median stacking are used, on both the full sample and three sub-samples.
Results.
Our analyses find no detection of either C
II
or continuum. An upper limit on
L
CII
is derived, implying that C
II
remains marginally consistent for low-SFR
z
> 6 galaxies but likely is under-luminous compared to the local
L
CII
-SFR relationship. We discuss potential biases and possible physical effects that may be the cause of the non-detection. Further, the upper limit on the dust continuum implies that less than half of the star formation is obscured.
We have imaged in CO(2-1) the molecular gas in NGC 1275 (Perseus A), the cD galaxy at the center of the Perseus Cluster, at a spatial resolution of similar to 1 kpc over a central region of radius ...similar to 10 kpc. Per A is known to contain similar to 1.3 x 10 super(10) M unk of molecular gas, which has been proposed to be captured from mergers with or ram pressure stripping of gas-rich galaxies, or accreted from a X-ray cooling flow. The molecular gas detected in our image has a total mass of similar to 4 x 10 super(9)M unk, and for the first time can be seen to be concentrated in three radial filaments with lengths ranging from at least 1.1 to 2.4 kpc, all lying in the east-west directions spanning the center of the galaxy to radii of similar to 8 kpc. The eastern and outer western filaments exhibit larger blueshifted velocities with decreasing radii, whereas the inner western filament spans the systemic velocity of the galaxy. The molecular gas shows no signature of orbital motion, and is therefore unlikely to have been captured from gas-rich galaxies. Instead, we are able to reproduce the observed kinematics of the two outer filaments as free fall in the gravitational potential of Per A, as would be expected if they originate from a X-ray cooling flow. Indeed, all three filaments lie between two prominent X-ray cavities carved out by radio jets from Per A, and closely resemble the spatial distribution of the coolest X-ray gas in the cluster core. The inferred mass deposition rate into the two outermost filaments alone is roughly 75 M unk yr super(-1). This cooling flow can provide a nearly continuous supply of molecular gas to fuel the active nucleus in Per A.
We analyze an extremely deep 450 m image (1 = 0.56 mJy beam−1) of a 300 arcmin2 area in the CANDELS/COSMOS field as part of the Sub-millimeter Common User Bolometric Array-2 Ultra Deep Imaging EAO ...Survey. We select a robust (signal-to-noise ratio ≥4) and flux-limited (≥4 mJy) sample of 164 submillimeter galaxies (SMGs) at 450 m that have K-band counterparts in the COSMOS2015 catalog identified from radio or mid-infrared imaging. Utilizing this SMG sample and the 4705 K-band-selected non-SMGs that reside within the noise level ≤1 mJy beam−1 region of the 450 m image as a training set, we develop a machine-learning classifier using K-band magnitude and color-color pairs based on the 13-band photometry available in this field. We apply the trained machine-learning classifier to the wider COSMOS field (1.6 deg2) using the same COSMOS2015 catalog and identify a sample of 6182 SMG candidates with similar colors. The number density, radio and/or mid-infrared detection rates, redshift and stellar-mass distributions, and the stacked 450 m fluxes of these SMG candidates, from the S2COSMOS observations of the wide field, agree with the measurements made in the much smaller CANDELS field, supporting the effectiveness of the classifier. Using this SMG candidate sample, we measure the two-point autocorrelation functions from z = 3 down to z = 0.5. We find that the SMG candidates reside in halos with masses of (2.0 0.5) × 1013 h−1 M☉ across this redshift range. We do not find evidence of downsizing that has been suggested by other recent observational studies.
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