We present 12CO (2-1) data of three Virgo spirals -- NGC 4330, NGC 4402 and NGC 4522 obtained using the Submillimeter Array. These three galaxies show clear evidence of ram pressure stripping due to ...the cluster medium as found in previous H i imaging studies. Using the high-resolution CO data, we investigate how the properties of the inner molecular gas disc change while a galaxy is undergoing H i stripping in the cluster. At given sensitivity limits, we do not find any clear signs of molecular gas stripping. However, both its morphology and kinematics appear to be quite disturbed as those of H i. Morphological peculiarities present in the molecular and atomic gas are closely related with each other, suggesting that the molecular gas can be also affected by strong intracluster medium (ICM) pressure even if it is not stripped. CO is found to be modestly enhanced along the upstream sides in these galaxies, which may change the local star formation activity in the disc. Indeed, the distribution of H alpha emission, a tracer of recent star formation, well coincides with that of the molecular gas, revealing enhancements near the local CO peak or along the CO compression. FUV and H alpha share some properties in common, but FUV is always more extended than CO/H alpha in the three galaxies, implying that the star-forming disc is rapidly shrinking as the molecular gas properties have changed. We discuss how ICM pressure affects dense molecular gas and hence star formation properties while diffuse atomic gas is being removed from a galaxy.
NGC 4522 is a Virgo spiral that is currently undergoing active ram pressure stripping. In previous single-dish observations, 12CO emission was detected outside of the stellar disk, some of which ...coincides with the extraplanar H i gas and H patches. The extraplanar gas identified in multi-wavelength data makes this galaxy an ideal case to study the impact of pressure due to the cluster medium on the interstellar gas of various phases. In this Letter, we present the high-resolution 12CO(1-0) and 13CO(1-0) data of NGC 4522 obtained using the Atacama Large Millimeter/submillimeter Array (ALMA). In particular, we report here the extraplanar 13CO detection that has never before been seen in ram-pressure-stripped galaxies. As the main donor of 13C in the interstellar medium is evolved stars, the presence of 13CO strongly suggests that heavy elements likely originated from the galactic disk, not from the newly formed stars in situ. Even though it is still inconclusive whether it is stripped in atomic form or as molecules, this study provides evidence for the ram pressure stripping of heavy elements, which can chemically enrich the halo gas, and potentially the intracluster medium, in the case that they are pushed strongly enough to escape the galaxy.
Abstract
In this VERTICO early science paper we explore in detail how environmental mechanisms, identified in H
i
, affect the resolved properties of molecular gas reservoirs in cluster galaxies. The ...molecular gas is probed using ALMA ACA (+TP) observations of
12
CO(2–1) in 51 spiral galaxies in the Virgo cluster (of which 49 are detected), all of which are included in the VIVA H
i
survey. The sample spans a stellar mass range of
9
≤
log
M
⋆
/
M
⊙
≤
11
. We study molecular gas radial profiles, isodensity radii, and surface densities as a function of galaxy H
i
deficiency and morphology. There is a weak correlation between global H
i
and H
2
deficiencies, and resolved properties of molecular gas correlate with H
i
deficiency: galaxies that have large H
i
deficiencies have relatively steep and truncated molecular gas radial profiles, which is due to the removal of low-surface-density molecular gas on the outskirts. Therefore, while the environmental mechanisms observed in H
i
also affect molecular gas reservoirs, there is only a moderate reduction of the total amount of molecular gas.
Abstract
This study uses H
i
image data from the Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY) pilot survey with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope, ...covering the Hydra cluster out to 2.5
r
200
. We present the projected phase–space distribution of H
i
-detected galaxies in Hydra, and identify that nearly two-thirds of the galaxies within
1.25
r
200
may be in the early stages of ram pressure stripping. More than half of these may be only weakly stripped, with the ratio of strippable H
i
(i.e., where the galactic restoring force is lower than the ram pressure in the disk) mass fraction (over total H
i
mass) distributed uniformly below 90%. Consequently, the H
i
mass is expected to decrease by only a few 0.1 dex after the currently strippable portion of H
i
in these systems has been stripped. A more detailed look at the subset of galaxies that are spatially resolved by WALLABY observations shows that, while it typically takes less than 200 Myr for ram pressure stripping to remove the currently strippable portion of H
i
, it may take more than 600 Myr to significantly change the total H
i
mass. Our results provide new clues to understanding the different rates of H
i
depletion and star formation quenching in cluster galaxies.
Abstract
We study the tidal interaction of galaxies in the Eridanus supergroup, using H
i
data from the pre-pilot survey of the Widefield ASKAP
L
-band Legacy All-sky Blind surveY. We obtain optical ...photometric measurements and quantify the strength of tidal perturbation using a tidal parameter
S
sum
. For low-mass galaxies of
M
*
≲ 10
9
M
⊙
, we find a dependence of decreasing H
i
to optical disk size ratio with increasing
S
sum
, but no dependence of H
i
spectral line asymmetry with
S
sum
. This is consistent with the behavior expected under tidal stripping. We confirm that the color profile shape and color gradient depend on the stellar mass, but there is an additional correlation of low-mass galaxies having their color gradients within 2
R
50
increasing with higher
S
sum
. For these low-mass galaxies, the dependence of color gradients on
S
sum
is driven by the color becoming progressively redder in the inner disk when tidal perturbations are stronger. For high-mass galaxies, there is no dependence of color gradients on
S
sum
, and we find a marginal reddening throughout the disks with increasing
S
sum
. Our result highlights tidal interaction as an important environmental effect in producing the faint end of the star formation suppressed sequence in galaxy groups.
Abstract
We present new results of a
12
CO(
J
= 1–0) imaging survey using the Atacama Compact Array (ACA) for 31 H
i
detected galaxies in the IC 1459 and NGC 4636 groups. This is the first CO imaging ...survey for loose galaxy groups. We obtained well-resolved CO data (∼0.7–1.5 kpc) for a total of 16 galaxies in two environments. By comparing our ACA CO data with the H
i
and UV data, we probe the impacts of the group environment on the cold gas components (CO and H
i
gas) and star formation activity. We find that CO and/or H
i
morphologies are disturbed in our group members, some of which show highly asymmetric CO distributions (e.g., IC 5264, NGC 7421, and NGC 7418). In comparison with isolated galaxies in the xCOLD GASS sample, our group galaxies tend to have low star formation rates and low H
2
gas fractions. Our findings suggest that the group environment can change the distribution of cold gas components, including the molecular gas and star formation properties of galaxies. This is supporting evidence that preprocessing in the group-like environment can play an important role in galaxy evolution.
We present the results of surveying C i 3 P 1–3 P 0, 12CO J = 4 − 3, and 630 μm dust continuum emission for 36 nearby ultra/luminous infrared galaxies (U/LIRGs) using the Band 8 receiver mounted on ...the Atacama Compact Array of the Atacama Large Millimeter/submillimeter Array. We describe the survey, observations, data reduction, and results; the main results are as follows. (i) We confirmed that C i 3 P 1–3 P 0 has a linear relationship with both the 12CO J = 4 − 3 and 630 μm continuum. (ii) In NGC 6052 and NGC 7679, 12CO J = 4 − 3 was detected but C i 3 P 1–3 P 0 was not detected with a C i 3 P 1–3 P 0/12CO J = 4 − 3 ratio of ≲0.08. Two possible scenarios of weak C i 3 P 1–3 P 0 emission are C0-poor/CO-rich environments and an environment with an extremely large C i 3 P 1–3 P 0 missing flux. (iii) There is no clear evidence showing that galaxy mergers, AGNs, and dust temperatures control the ratios of C i 3 P 1–3 P 0/12CO J = 4 − 3 and \({L}_{{\rm{C}}\,{\rm\small{I}}(1-0)}^{{\prime} }/{L}_{630\mu {\rm{m}}}\). (iv) We compare our nearby U/LIRGs with high-z galaxies, such as galaxies on the star formation main sequence (MS) at z ∼ 1 and submillimeter galaxies (SMGs) at z = 2–4. We found that the mean value for the C i 3 P 1–3 P 0/12CO J = 4 − 3 ratio of U/LIRGs is similar to that of SMGs but smaller than that of galaxies on the MS.
Abstract
We study how environment regulates the star formation cycle of 33 Virgo Cluster satellite galaxies on 720 pc scales. We present the resolved star-forming main sequence for cluster galaxies, ...dividing the sample based on their global H
i
properties and comparing to a control sample of field galaxies. H
i
–poor cluster galaxies have reduced star formation rate (SFR) surface densities with respect to both H
i
–normal cluster and field galaxies (∼0.5 dex), suggesting that mechanisms regulating the global H
i
content are responsible for quenching local star formation. We demonstrate that the observed quenching in H
i
–poor galaxies is caused by environmental processes such as ram pressure stripping (RPS), simultaneously reducing the molecular gas surface density and star formation efficiency (SFE) compared to regions in H
i
–normal systems (by 0.38 and 0.22 dex, respectively). We observe systematically elevated SFRs that are driven by increased molecular gas surface densities at fixed stellar mass surface density in the outskirts of early stage RPS galaxies, while SFE remains unchanged with respect to the field sample. We quantify how RPS and starvation affect the star formation cycle of inner and outer galaxy disks as they are processed by the cluster. We show both are effective quenching mechanisms, with the key difference being that RPS acts upon the galaxy outskirts while starvation regulates the star formation cycle throughout disk, including within the truncation radius. For both processes, the quenching is caused by a simultaneous reduction in the molecular gas surface densities and SFE at fixed stellar mass surface density.
Abstract
Combining new H
i
data from a synergetic survey of Australian Square Kilometre Array Pathfinder (ASKAP) Widefield ASKAP
L
-band Legacy All-sky Blind surveY and Five-hundred-meter Aperture ...Spherical radio Telescope with the Arecibo Legacy Fast ALFA data, we study the effect of ram pressure and tidal interactions in the NGC 4636 group. We develop two parameters to quantify and disentangle these two effects on gas stripping in H
i
-bearing galaxies: the strength of external forces at the optical-disk edge, and the outside-in extents of H
i
-disk stripping. We find that gas stripping is widespread in this group, affecting 80% of H
i
-detected nonmerging galaxies, and that 41% are experiencing both types of stripping. Among the galaxies experiencing both effects, the two types of strengths are independent, while two H
i
-stripping extents moderately anticorrelate with each other. Both strengths are correlated with H
i
-disk shrinkage. The tidal strength is related to a rather uniform reddening of low-mass galaxies (
M
*
< 10
9
M
☉
) when tidal stripping is the dominating effect. In contrast, ram pressure is not clearly linked to the color-changing patterns of galaxies in the group. Combining these two stripping extents, we estimate the total stripping extent, and put forward an empirical model that can describe the decrease of H
i
richness as galaxies fall toward the group center. The stripping timescale we derived decreases with distance to the center, from ∼1 Gyr beyond
R
200
to ≲10 Myr near the center. Gas depletion happens ∼3 Gyr since crossing 2
R
200
for H
i
-rich galaxies, but much quicker for H
i
-poor ones. Our results quantify in a physically motivated way the details and processes of environmental-effects-driven galaxy evolution, and might assist in analyzing hydrodynamic simulations in an observational way.
ABSTRACT
To study the high-transition dense-gas tracers and their relationships to the star formation of the inner ∼2 kpc circumnuclear region of NGC 253, we present HCN J = 4−3 and HCO+ J = 4−3 maps ...obtained with the James Clerk Maxwell Telescope. Using the spatially resolved data, we compute the concentration indices r90/r50 for the different tracers. HCN and HCO+ 4–3 emission features tend to be centrally concentrated, which is in contrast to the shallower distribution of CO 1–0 and the stellar component. The dense-gas fraction (fdense, traced by the velocity-integrated-intensity ratios of HCN/CO and HCO+/CO) and the ratio R31 (CO 3–2/1–0) decline towards larger galactocentric distances, but increase with higher star formation rate surface density. The radial variation and the large scatter of fdense and R31 imply distinct physical conditions in different regions of the galactic disc. The relationships of fdense versus Σstellar, and SFEdense versus Σstellar are explored. SFEdense increases with higher Σstellar in this galaxy, which is inconsistent with previous work that used HCN 1–0 data. This implies that existing stellar components might have different effects on the high-J HCN and HCO+ than their low-J emission. We also find that SFEdense seems to be decreasing with higher fdense which is consistent with previous works, and it suggests that the ability of the dense gas to form stars diminishes when the average density of the gas increases. This is expected in a scenario where only the regions with high-density contrast collapse and form stars.
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