We present high-resolution (1 0) Atacama Large Millimeter/submillimeter Array (ALMA) observations of CO (1-0) and CO (2-1) rotational transitions toward the nearby IR-luminous merger NGC 1614 ...supplemented with ALMA archival data of CO (3-2) and CO (6-5) transitions. The CO (6-5) emission arises from the starburst ring (central 590 pc in radius), while the lower-J CO lines are distributed over the outer disk (∼3.3 kpc in radius). Radiative transfer and photon-dominated region (PDR) modeling reveals that the starburst ring has a single warmer gas component with more a intense far-ultraviolet radiation field ( cm−3, K, and ) relative to the outer disk ( cm−3, K, and ). A two-phase molecular interstellar medium with a warm and cold (>70 and ∼19 K) component is also an applicable model for the starburst ring. A possible source for heating the warm gas component is mechanical heating due to stellar feedback rather than PDR. Furthermore, we find evidence for non-circular motions along the north-south optical bar in the lower-J CO images, suggesting a cold gas inflow. We suggest that star formation in the starburst ring is sustained by the bar-driven cold gas inflow and that starburst activities radiatively and mechanically power the CO excitation. The absence of a bright active galactic nucleus can be explained by a scenario where cold gas accumulating on the starburst ring is exhausted as the fuel for star formation or is launched as an outflow before being able to feed to the nucleus.
ABSTRACT We present Atacama Large Millimeter/submillimeter Array cycle 0 observations of the molecular gas and dust in the IR-bright mid-stage merger VV 114 obtained at 160-800 pc resolution. The ...main aim of this study is to investigate the distribution and kinematics of the cold/warm gas and to quantify the spatial variation of the excitation conditions across the two merging disks. The data contain 10 molecular lines, including the first detection of extranuclear CH3OH emission in interacting galaxies, as well as continuum emission. We map the 12CO(3-2)/12CO(1-0) and the 12CO(1-0)/13CO(1-0) line ratio at 800 pc resolution (in the units of K km s−1), and find that these ratios vary from 0.2-0.8 and 5-50, respectively. Conversely, the 200 pc resolution HCN(4-3)/HCO+(4-3) line ratio shows low values (<0.5) at a filament across the disks except for the unresolved eastern nucleus which is three times higher (1.34 0.09). We conclude from our observations and a radiative transfer analysis that the molecular gas in the VV 114 system consists of five components with different physical and chemical conditions, i.e., (1) dust-enshrouded nuclear starbursts and/or active galactic nuclei, (2) widespread star-forming dense gas, (3) merger-induced shocked gas, (4) quiescent tenuous gas arms without star formation, and (5) H2 gas mass of (3.8 0.7) × 107 (assuming a conversion factor of CO = 0.8 ) at the tip of the southern tidal arm, as a potential site of tidal dwarf galaxy formation.
Abstract
We conduct a
12
C
16
O(
J
= 1−0) (hereafter CO) mapping survey of 64 galaxies in the Fornax cluster using the Atacama Large Millimeter/submillimeter Array Morita array in cycle 5. CO ...emission is detected from 23 out of the 64 galaxies. Our sample includes dwarf, spiral, and elliptical galaxies with stellar masses of
M
star
∼ 10
6.3−11.6
M
⊙
. The achieved beam size and sensitivity are 15″ × 8″ and ∼12 mJy beam
−1
at the velocity resolution of ∼10 km s
−1
, respectively. We study the cold gas (molecular and atomic gas) properties of 38 subsamples with
M
star
> 10
9
M
⊙
combined with literature H
i
data. We find that (1) the low star formation (SF) activity in the Fornax galaxies is caused by the decrease in the cold gas mass fraction with respect to stellar mass (hereafter, gas fraction) rather than the decrease of the SF efficiency from the cold gas; (2) the atomic gas fraction is more heavily reduced than the molecular gas fraction of such galaxies with low SF activity. A comparison between the cold gas properties of the Fornax galaxies and their environmental properties suggests that the atomic gas is stripped tidally and by the ram pressure, which leads to the molecular gas depletion with an aid of the strangulation and consequently SF quenching. Preprocesses in the group environment would also play a role in reducing cold gas reservoirs in some Fornax galaxies.
ABSTRACT
We develop new tools for continuum and spectral stacking of Atacama Large Millimeter/submillimeter Array (ALMA) data, and apply these to the ALMA Lensing Cluster Survey. We derive average ...dust masses, gas masses, and star-formation rates (SFRs) from the stacked observed 260-GHz continuum of 3402 individually undetected star-forming galaxies, of which 1450 are cluster galaxies and 1952 field galaxies, over three redshift and stellar mass bins (over z = 0–1.6 and log$M_{*} \, {\rm M}_{\odot } = 8$–11.7), and derive the average molecular gas content by stacking the emission line spectra in a SFR-selected subsample. The average SFRs and specific SFRs of both cluster and field galaxies are lower than those expected for main-sequence (MS) star-forming galaxies, and only galaxies with stellar mass of log$M_{*} \, {\rm M}_{\odot } = 9.35$–10.6 show dust and gas fractions comparable with those in the MS. The ALMA-traced average ‘highly obscured’ SFRs are typically lower than the SFRs observed from optical to near-infrared spectral analysis. Cluster and field galaxies show similar trends in their contents of dust and gas, even when field galaxies were brighter in the stacked maps. From spectral stacking we find a potential CO (J = 4 → 3) line emission (signal-to-noise ratio being ∼4) when stacking cluster and field galaxies with the highest SFRs.
ABSTRACT
We report the discovery of a triply imaged active galactic nucleus (AGN), lensed by the galaxy cluster MACS J0035.4−2015 (zd = 0.352). The object is detected in Hubble Space Telescope ...imaging taken for the RELICS program. It appears to have a quasi-stellar nucleus consistent with a point-source, with a de-magnified radius of re ≲ 100 pc. The object is spectroscopically confirmed to be an AGN at zspec = 2.063 ± 0.005 showing broad rest-frame UV emission lines, and detected in both X-ray observations with Chandra and in ALCS ALMA band 6 (1.2 mm) imaging. It has a relatively faint rest-frame UV luminosity for a quasar-like object, MUV, 1450 = −19.7 ± 0.2. The object adds to just a few quasars or other X-ray sources known to be multiply lensed by a galaxy cluster. Some diffuse emission from the host galaxy is faintly seen around the nucleus, and there is a faint object nearby sharing the same multiple-imaging symmetry and geometric redshift, possibly an interacting galaxy or a star-forming knot in the host. We present an accompanying lens model, calculate the magnifications and time delays, and infer the physical properties of the source. We find the rest-frame UV continuum and emission lines to be dominated by the AGN, and the optical emission to be dominated by the host galaxy of modest stellar mass $M_{\star }\simeq 10^{9.2}\, \mathrm{M}_{\odot }$ . We also observe some variation in the AGN emission with time, which may suggest that the AGN used to be more active. This object adds a low-redshift counterpart to several relatively faint AGN recently uncovered at high redshifts with HST and JWST.
ABSTRACT We report the detection of two CH3OH lines (JK = 2K-1K and 3K-2K) between the progenitor's disks ("Overlap") of the mid-stage merging galaxy VV 114 obtained using the Atacama Large ...Millimeter/submillimeter Array (ALMA) Band 3 and Band 4. The detected CH3OH emission shows an extended filamentary structure (∼3 kpc) across the progenitor's disks with relatively large velocity width (FWZI ∼ 150 km s−1). The emission is only significant in the "overlap" and not detected in the two merging nuclei. Assuming optically thin emission and local thermodynamic equilibrium, we found the CH3OH column density relative to H2 ( ) peaks at the "Overlap" (∼8 × 10−9), which is almost an order of magnitude larger than that at the eastern nucleus. We suggest that kpc-scale shocks driven by galaxy-galaxy collision may play an important role to enhance the CH3OH abundance at the "Overlap." This scenario is consistent with shock-induced large velocity dispersion components of ionized gas that have been detected in optical wavelength at the same region. Conversely, low at the nuclear regions might be attributed to the strong photodissociation by nuclear starbursts and/or a putative active galactic nucleus, or inefficient production of CH3OH on dust grains due to initial high-temperature conditions (i.e., desorption of the precursor molecule, CO, into gas phase before forming CH3OH on dust grains). These ALMA observations demonstrate that CH3OH is a unique tool to address kpc-scale shock-induced gas dynamics and star formation in merging galaxies.
We present ALMA cycle 0 observations of the luminous merger VV 114. One of the main goals is to investigate mechanisms of molecular line ratio enhancement. Regions with the high 12CO (1–0)/13CO (1–0) ...and 12CO (3–2)/12CO (1–0) is located at a central filamentary structure (∼6 kpc) in VV 114. The filament consists of the eastern nucleus and the overlap region, where the galaxy disks are colliding. We also investigate these molecular line ratios on the Kennicutt-Schmidt law. VV 114 fills a gap between the “starburst” sequence and the “normal disk” sequence, and regions with the high ratios show the high ΣSFR and ΣH2. We suggest that the high ratios in VV 114 are due to star-forming activities in the both progenitor's nuclei and the merger-induced overlap region.
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 mu m 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 > 6 galaxies observed by the ALMA Lensing Cluster Survey. Methods. We perform our analysis using LINESTACKER, 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 (sigma(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.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
Abstract
We present Atacama Large Millimeter/submillimeter Array observations of multiple
12
CO,
13
CO, and C
18
O lines and 2.9 mm and 1.3 mm continuum emission toward the nearby interacting ...luminous infrared galaxy NGC 3110, supplemented with similar spatial resolution H
α
, 1.4 GHz continuum, and
K
-band data. We estimate the typical CO-to-H
2
conversion factor of 1.7
M
⊙
(K km s
−1
pc
2
)
−1
within the disk using local thermal equilibrium-based and dust-based H
2
column densities, and measure the 1 kpc scale surface densities of the star formation rate (Σ
SFR
), super star clusters (Σ
SSC
), molecular gas mass, and star formation efficiency (SFE) toward the entire gas disk. These parameters show a peak in the southern part of the southern spiral arm (SFE ∼ 10
−8.2
yr
−1
, Σ
SFR
∼ 10
−0.6
M
⊙
kpc
−2
yr
−1
, Σ
SSC
∼ 6.0 kpc
−2
), which is likely attributable to the ongoing tidal interaction with the companion galaxy MCG-01-26-013, as well as toward the circumnuclear region. We also find that thermal free–free emission contributes to a significant fraction of the millimeter continuum emission at the position of the southern peak. These measurements imply that the peak of the southern arm is an active and young star-forming region, whereas the central part of NGC 3110 is a site of long-continued star formation. We suggest that during the early stage of the galaxy–galaxy interaction in which the mass ratio was high in NGC 3110, fragmentation along the main galaxy arms is an important driver of merger-induced star formation, and that massive gas inflow results in dusty nuclear starbursts.
ABSTRACT We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 1 observations of the central kiloparsec region of the luminous type 1 Seyfert galaxy NGC 7469 with unprecedented high ...resolution (0 5 ×0 4 = 165 × 132 pc) at submillimeter wavelengths. Utilizing the wide bandwidth of ALMA, we simultaneously obtained HCN(4-3), HCO+(4-3), CS(7-6), and partially CO(3-2) line maps, as well as the 860 m continuum. The region consists of the central ∼1″ component and the surrounding starburst ring with a radius of ∼1 5-2 5. Several structures connect these components. Except for CO(3-2), these dense gas tracers are significantly concentrated toward the central ∼1″, suggesting their suitability to probe the nuclear regions of galaxies. Their spatial distribution resembles well those of centimeter and mid-infrared continuum emissions, but it is anticorrelated with the optical one, indicating the existence of dust-obscured star formation. The integrated intensity ratios of HCN(4-3)/HCO+(4-3) and HCN(4-3)/CS(7-6) are higher at the active galactic nucleus (AGN) position than at the starburst ring, which is consistent with our previous findings (submillimeter-HCN enhancement). However, the HCN(4-3)/HCO+(4-3) ratio at the AGN position of NGC 7469 (1.11 0.06) is almost half of the corresponding value of the low-luminosity type 1 Seyfert galaxy NGC 1097 (2.0 0.2), despite the more than two orders of magnitude higher X-ray luminosity of NGC 7469. But the ratio is comparable to that of the close vicinity of the AGN of NGC 1068 (∼1.5). Based on these results, we speculate that some heating mechanisms other than X-ray (e.g., mechanical heating due to an AGN jet) can contribute significantly for shaping the chemical composition in NGC 1097.
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