We present a study of the H i gas content of a large K-band-selected sample of 88 close major-merger pairs of galaxies (H-KPAIR) that were observed by Herschel. We obtained the 21 cm H i ...fine-structure emission-line data for a total of 70 pairs from this sample, by observing 58 pairs using the Green Bank Telescope (GBT) and retrieving the H i data for an addition 12 pairs from the literature. In this H i sample, 34 pairs are spiral-spiral (S+S) pairs, and 36 are spiral-elliptical (S+E) pairs. Based on these data, we studied the H i-to-stellar mass ratio, the H i gas fraction, and the H i star formation efficiency (SFEH i = star-formation-rate/MH i) and searched for differences between S+S and S+E pairs, as well as between pairs with and without signs of merger/interaction. Our results showed that the mean H i-to-stellar mass ratio of spirals in these pairs is =7.6 1.0%, consistent with the average H i gas fraction of spiral galaxies in general. The differences in the H i gas fraction between spirals in S+S and in S+E pairs, and between spirals in pairs with and without signs of merger/interaction, are insignificant (<1 ). On the other hand, the mean SFEH i of S+S pairs is ∼4.6× higher than that of S+E pairs. This difference is very significant (∼4 ) and is the main result of our study. There is no significant difference in the mean SFEH i between galaxies with and without signs of merger/interaction. The mean SFEH i of the whole pair sample is 10−9.55 0.09 yr−1, corresponding to a H i consumption time of 3.5 0.7 Gyr.
We report the study of the far-infrared (IR) sizes of submillimeter galaxies (SMGs) in relation to their dust-obscured star formation rate (SFR) and active galactic nuclei (AGN) presence, determined ...using mid-IR photometry. We determined the millimeter-wave ( m) sizes of 69 Atacama Large Millimeter/submillimeter Array (ALMA)-identified SMGs, selected with confidence on ALMA images ( -7.4 mJy). We found that all of the SMGs are located above an avoidance region in the size-flux plane, as expected by the Eddington limit for star formation. In order to understand what drives the different millimeter-wave sizes in SMGs, we investigated the relation between millimeter-wave size and AGN fraction for 25 of our SMGs at z = 1-3. We found that the SMGs for which the mid-IR emission is dominated by star formation or AGN have extended millimeter-sizes, with respective median and kpc. Instead, the SMGs for which the mid-IR emission corresponds to star-forming/AGN composites have more compact millimeter-wave sizes, with median kpc. The relation between millimeter-wave size and AGN fraction suggests that this size may be related to the evolutionary stage of the SMG. The very compact sizes for composite star-forming/AGN systems could be explained by supermassive black holes growing rapidly during the SMG coalescing, star-formation phase.
Abstract
We present a detailed study of the Planck-selected binary galaxy cluster PLCK G165.7+67.0 (G165;
z
= 0.348). A multiband photometric catalog is generated incorporating new imaging from the ...Large Binocular Telescope/Large Binocular Camera and Spitzer/IRAC to existing imaging. To cope with the different image characteristics, robust methods are applied in the extraction of the matched-aperture photometry. Photometric redshifts are estimated for 143 galaxies in the 4 arcmin
2
field of overlap covered by these data. We confirm that strong-lensing effects yield 30 images of 11 background galaxies, of which we contribute new photometric redshift estimates for three image multiplicities. These constraints enable the construction of a revised lens model with a total mass of
M
600 kpc
= (2.36 ± 0.23) × 10
14
M
⊙
. In parallel, new spectroscopy using MMT/Binospec and archival data contributes thirteen galaxies that meet our velocity and transverse radius criteria for cluster membership. The two cluster components have a pair-wise velocity of ≲100 km s
−1
, favoring an orientation in the plane of the sky with a transverse velocity of 100–1700 km s
−1
. At the same time, the brightest cluster galaxy (BCG) is offset in velocity from the systemic mean value, suggesting dynamical disturbance. New LOFAR and Very Large Array data uncover head-tail radio galaxies in the BCG and a large red galaxy in the northeast component. From the orientation and alignment of the four radio trails, we infer that the two cluster components have already traversed each other, and are now exiting the cluster.
Abstract
Gradients in the mass-to-light ratio of distant galaxies impede our ability to characterize their size and compactness. The long-wavelength filters of JWST’s NIRCam offer a significant step ...forward. For galaxies at Cosmic Noon (
z
∼ 2), this regime corresponds to the rest-frame near-infrared, which is less biased toward young stars and captures emission from the bulk of a galaxy’s stellar population. We present an initial analysis of an extraordinary lensed dusty star-forming galaxy at
z
= 2.3 behind the El Gordo cluster (
z
= 0.87), named El Anzuelo (“The Fishhook”) after its partial Einstein-ring morphology. The far-UV to near-IR spectral energy distribution suggests an intrinsic star formation rate of
81
−
2
+
7
M
⊙
yr
−
1
and dust attenuation
A
V
≈ 1.6, in line with other DSFGs on the star-forming main sequence. We develop a parametric lens model to reconstruct the source-plane structure of dust imaged by the Atacama Large Millimeter/submillimeter Array, far-UV to optical light from Hubble, and near-IR imaging with 8 filters of JWST/NIRCam, as part of the Prime Extragalactic Areas for Reionization and Lensing Science program. The source-plane half-light radius is remarkably consistent from ∼1 to 4.5
μ
m, despite a clear color gradient where the inferred galaxy center is redder than the outskirts. We interpret this to be the result of both a radially decreasing gradient in attenuation and substantial spatial offsets between UV- and IR-emitting components. A spatial decomposition of the SED reveals modestly suppressed star formation in the inner kiloparsec, which suggests that we are witnessing the early stages of inside-out quenching.
We present high spatial resolution (5".1 x 2".7) Owens Valley Radio Observatory (OVRO) millimeter array observations of HCN (J = 1-0) and HCO(+) (J = 1-0) emission in the inner 3 pc of the Galaxy ...(0.04 pc 6 1"). The HCN and HCO(+) emission of the circumnuclear disk (CND) is distributed in a well-defined ring with a peak at a radius of 1.6 pc. The observed radial velocities are generally consistent with rotation at 6110 km s(-1) (except along the western edge of the CND). The HCO(+)/HCN emission ratio is typically 60.4 but with significant variations. The variations in the HCO(+)/HCN emission and absorption ratios can be attributed to greater abundances of HCO(+) in lower density regions both within the CND and along the line of sight. The HCN emission is well correlated with the H(2) emission at 2.12 km both in the main emission lobes of the CND and also in four H(2) and HCN filaments. Multiple areas of interaction between the ionized gas and the CND are also seen; the western arm of the minispiral is spatially and kinematically consistent with being the ionized inner edge of the CND, and the northern arm may be connected to the CND northeastern extension. With the enhanced spatial resolution of the HCN maps, we resolve numerous dense molecular gas cores within the CND with characteristic diameter 67" (0.25 pc). For 26 of the more isolated cores, we have measured sizes, velocity widths, and integrated fluxes. From these properties we estimated three masses for each core: a virial mass assuming the cores are gravitationally bound, an optically thick mass from observed column densities of HCN, and a lower limit mass assuming the HCN emission is optically thin and shock excitation is negligible. The virial and optically thick masses are in good agreement with a typical mass of (2-3) x 10(4) M( and a total CND gas mass of 10(6) M( . The internal densities implied by these core masses (assuming a uniform density distribution for each core) are on average (3-4) x 10(7) cm(-3). The core densities are high enough to be stable against tidal disruption from Sgr A* and the central stellar concentration. This tidal stability suggests a longer lifetime for the CND. The high densities and masses within the cores might support star formation either in the CND itself or within a core infalling toward the inner parsec, thus providing a mechanism for the formation of the young stellar population observed in the inner arcseconds of the Galaxy.
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
Observations of
12
CO
J
= 1 – 0 and HCN
J
= 1 – 0 emission from NGC 5194 (M51) made with the 50 m Large Millimeter Telescope and the SEQUOIA focal plane array are presented. Using the ...HCN-to-CO ratio, we examine the dense gas mass fraction over a range of environmental conditions within the galaxy. Within the disk, the dense gas mass fraction varies along the spiral arms but the average value over all spiral arms is comparable to the mean value of interarm regions. We suggest that the near-constant dense gas mass fraction throughout the disk arises from a population of density-stratified, self-gravitating molecular clouds and the required density threshold to detect each spectral line. The measured dense gas fraction significantly increases in the central bulge in response to the effective pressure,
P
e
, from the weight of the stellar and gas components. This pressure modifies the dynamical state of the molecular cloud population and, possibly, the HCN-emitting regions in the central bulge from self-gravitating to diffuse configurations in which
P
e
is greater than the gravitational energy density of individual clouds. Diffuse molecular clouds comprise a significant fraction of the molecular gas mass in the central bulge, which may account for the measured sublinear relationships between the surface densities of the star formation rate and molecular and dense gas.
We investigate gas contents of star-forming galaxies associated with protocluster 4C23.56 at z = 2.49 by using the redshifted CO (3-2) and 1.1 mm dust continuum with the Atacama Large ...Millimeter/submillimeter Array. The observations unveil seven CO detections out of 22 targeted H emitters (HAEs) and four out of 19 in 1.1 mm dust continuum. They have high stellar mass ( M ) and exhibit a specific star-formation rate typical of main-sequence star-forming galaxies at . Different gas-mass estimators from CO (3-2) and 1.1 mm yield consistent values for simultaneous detections. The gas mass ( ) and gas fraction ( ) are comparable to those of field galaxies, with )) , where is the CO-to-H2 conversion factor and A(Z) is the additional correction factor for the metallicity dependence of , and from CO (3-2). Our measurements place a constraint on the cosmic gas density of high-z protoclusters, indicating that the protocluster is characterized by a gas density higher than that of the general fields by an order of magnitude. We found with the CO(3-2) detections. The five ALMA CO detections occur in the region of highest galaxy surface density, where the density positively correlates with global star-forming efficiency (SFE) and stellar mass. Such correlations possibly indicate a critical role of the environment on early galaxy evolution at high-z protoclusters, though future observations are necessary for confirmation.
Galaxies in compact groups tend to be deficient in neutral hydrogen compared to isolated galaxies of similar optical properties. In order to investigate the role played by a hot intragroup medium ...(IGM) for the removal and destruction of H i in these systems, we have performed a Chandra and XMM–Newton study of eight of the most H i deficient Hickson compact groups. Diffuse X-ray emission associated with an IGM is detected in four of the groups, suggesting that galaxy–IGM interactions are not the dominant mechanism driving cold gas out of the group members. No clear evidence is seen for any of the members being currently stripped of any hot gas, nor for galaxies to show enhanced nuclear X-ray activity in the X-ray bright or most H i deficient groups. Combining the inferred IGM distributions with analytical models of representative disc galaxies orbiting within each group, we estimate the H i mass-loss due to ram-pressure and viscous stripping. While these processes are generally insufficient to explain observed H i deficiencies, they could still be important for H i removal in the X-ray bright groups, potentially removing more than half of the interstellar medium in the X-ray bright HCG 97. Ram pressure may also have facilitated strangulation through the removal of galactic coronal gas. In X-ray undetected groups, tidal interactions could be playing a prominent role, but it remains an open question whether they can fully account for the observed H i deficiencies.
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