The large Integral Field Spectroscopy surveys have allowed the classification of ionizing sources of emission lines on sub-kiloparsec scales. In this work, we define two non-parametric parameters, ...quiescence (Fq) and its concentration (Cq), to quantify the strength and the spatial distribution of the quenched areas, respectively, traced by the LI(N)ER regions with low EW(H ). With these two measurements, we classify MaNGA galaxies into inside-out and outside-in quenching types according to their locations on the Fq versus Cq plane and we measure the fraction of inside-out (outside-in) quenching galaxies as a function of halo mass. We find that the fraction of galaxies showing inside-out quenching increases with halo mass, irrespective of stellar mass or galaxy type (satellites versus centrals). In addition, high-stellar-mass galaxies exhibit a greater fraction of inside-out quenching compared to low-stellar-mass ones in all environments. In contrast, the fraction of outside-in quenching does not depend on halo mass. Our results suggest that morphological quenching may be responsible for the inside-out quenching seen in all environments. On the other hand, the flat dependence of the outside-in quenching on halo mass could be a mixed result of ram pressure stripping and galaxy mergers. Nevertheless, for a given environment and stellar mass, the fraction of inside-out quenching is systematically greater than that of outside-in quenching, suggesting that inside-out quenching is the dominant quenching mode in all environments.
We study the physical properties of giant molecular cloud associations (GMAs) in M100 (NGC 4321) using the ALMA Science Verification feathered (12 m+ACA) data in 12CO (1-0). To examine the ...environmental dependence of their properties, GMAs are classified based on their locations in various environments as circumnuclear ring (CNR), bar, spiral, and inter-arm GMAs. The CNR GMAs are massive and compact, while the inter-arm GMAs are diffuse, with low surface density. GMA mass and size are strongly correlated, as suggested by Larson. However, the diverse power-law index of the relation implies that the GMA properties are not uniform among the environments. The CNR and bar GMAs show higher velocity dispersion than those in other environments. We find little evidence for a correlation between GMA velocity dispersion and size, which indicates that the GMAs are in diverse dynamical states. Indeed, the virial parameter of the GMAs spans nearly two orders of magnitude. Only the spiral GMAs are generally self-gravitating. Star formation activity decreases in order over the CNR, spiral, bar, and inter-arm GMAs. The diverse GMA and star formation properties in different environments lead to variations in the Kennicutt-Schmidt relation. A combination of multiple mechanisms or gas phase change is necessary to explain the observed slopes. Comparisons of GMA properties acquired with the use of the 12 m array observations with those from the feathered data are also presented. The results show that the missing flux and extended emission cannot be neglected for the study of environmental dependence.
ABSTRACT
Using a sample of 11 478 spaxels in 34 galaxies with molecular gas, star formation, and stellar maps taken from the ALMA-MaNGA QUEnching and STar formation (ALMaQUEST) survey, we investigate ...the parameters that correlate with variations in star formation rates on kpc scales. We use a combination of correlation statistics and an artificial neural network to quantify the parameters that drive both the absolute star formation rate surface density (ΣSFR), as well as its scatter around the resolved star-forming main sequence (ΔΣSFR). We find that ΣSFR is primarily regulated by molecular gas surface density ($\Sigma _{\rm H_2}$) with a secondary dependence on stellar mass surface density (Σ⋆), as expected from an ‘extended Kennicutt–Schmidt relation’. However, ΔΣSFR is driven primarily by changes in star formation efficiency (SFE), with variations in gas fraction playing a secondary role. Taken together, our results demonstrate that whilst the absolute rate of star formation is primarily set by the amount of molecular gas, the variation of star formation rate above and below the resolved star-forming main sequence (on kpc scales) is primarily due to changes in SFE.
The origin of the star-forming main sequence (SFMS; i.e., the relation between star formation rate and stellar mass, globally or on kpc scales) remains a hotly debated topic in galaxy evolution. ...Using the ALMA-MaNGA QUEnching and STar formation (ALMaQUEST) survey, we show that for star-forming spaxels in the main-sequence galaxies, the three local quantities, star formation rate surface density ( SFR), stellar mass surface density ( *), and the H2 mass surface density ( ) are strongly correlated with one another and form a 3D linear (in log) relation with dispersion. In addition to the two well-known scaling relations, the resolved SFMS ( SFR versus *) and the Schmidt-Kennicutt (SK) relation ( SFR versus ), there is a third scaling relation between and *, which we refer to as the molecular gas main sequence (MGMS). The latter indicates that either the local gas mass traces the gravitational potential set by the local stellar mass or both quantities follow the underlying total mass distributions. The scatter of the resolved SFMS ( ∼ 0.25 dex) is the largest compared to those of the SK and MGMS relations ( ∼ 0.2 dex). A Pearson correlation test also indicates that the SK and MGMS relations are more strongly correlated than the resolved SFMS. Our result suggests a scenario in which the resolved SFMS is the least physically fundamental and is the consequence of the combination of the SK and the MGMS relations.
ABSTRACT
We investigate the nature of the scaling relations between the surface density of star formation rate (ΣSFR), stellar mass (Σ*), and molecular gas mass ($\Sigma _{\rm H_2}$), aiming at ...distinguishing between the relations that are primary, i.e. more fundamental, and those which are instead an indirect by-product of the other relations. We use the ALMA-MaNGA QUEnching and STar formation survey and analyse the data by using both partial correlations and random forest regression techniques. We unambiguously find that the strongest intrinsic correlation is between ΣSFR and $\Sigma _{\rm H_2}$ (i.e. the resolved Schmidt–Kennicutt relation), followed by the correlation between $\Sigma _{\rm H_2}$ and Σ* (resolved molecular gas main sequence, rMGMS). Once these two correlations are taken into account, we find that there is no evidence for any intrinsic correlation between ΣSFR and Σ*, implying that star formation rate (SFR) is entirely driven by the amount of molecular gas, while its dependence on stellar mass (i.e. the resolved star forming main sequence, rSFMS) simply emerges as a consequence of the relationship between molecular gas and stellar mass.
ABSTRACT
Starburst galaxies have elevated star formation rates (SFRs) for their stellar mass. In Ellison et al., we used integral field unit maps of SFR surface density (ΣSFR) and stellar mass ...surface density (Σ⋆) to show that starburst galaxies in the local universe are driven by SFRs that are preferentially boosted in their central regions. Here, we present molecular gas maps obtained with the Atacama Large Millimeter Array (ALMA) observatory for 12 central starburst galaxies at z ∼ 0 drawn from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. The ALMA and MaNGA data are well matched in spatial resolution, such that the ALMA maps of molecular gas surface density ($\Sigma _{\rm H_2}$) can be directly compared with MaNGA maps at kpc-scale resolution. The combination of $\Sigma _{\rm H_2}$, Σ⋆ and ΣSFR at the same resolution allow us to investigate whether central starbursts are driven primarily by enhancements in star formation efficiency (SFE) or by increased gas fractions. By computing offsets from the resolved Kennicutt-Schmidt relation ($\Sigma _{\rm H_2}$ versus ΣSFR) and the molecular gas main sequence (Σ⋆ versus $\Sigma _{\rm H_2}$), we conclude that the primary driver of the central starburst is an elevated SFE. We also show that the enhancement in ΣSFR is accompanied by a dilution in O/H, consistent with a triggering that is induced by metal poor gas inflow. These observational signatures are found in both undisturbed (9/12 galaxies in our sample) and recently merged galaxies, indicating that both interactions and secular mechanisms contribute to central starbursts.
We use an unprecedented sample of about 23 000 H
II
regions detected at an average physical resolution of 67 pc in the PHANGS–MUSE sample to study the extragalactic H
II
region H
α
luminosity ...function (LF). Our observations probe the star-forming disk of 19 nearby spiral galaxies with low inclination and located close to the star formation main sequence at
z
= 0. The mean LF slope,
α
, in our sample is =1.73 with a
σ
of 0.15. We find that
α
decreases with the galaxy’s star formation rate surface density, Σ
SFR
, and argue that this is driven by an enhanced clustering of young stars at high gas surface densities. Looking at the H
II
regions within single galaxies, we find that no significant variations occur between the LF of the inner and outer part of the star-forming disk, whereas the LF in the spiral arm areas is shallower than in the inter-arm areas for six out of the 13 galaxies with clearly visible spiral arms. We attribute these variations to the spiral arms increasing the molecular clouds’ arm–inter-arm mass contrast and find suggestive evidence that they are more evident for galaxies with stronger spiral arms. Furthermore, we find systematic variations in
α
between samples of H
II
regions with a high and low ionization parameter,
q
, and argue that they are driven by the aging of H
II
regions.
Abstract
We present a rich, multiwavelength, multiscale database built around the PHANGS–ALMA CO (2 − 1) survey and ancillary data. We use this database to present the distributions of molecular ...cloud populations and subgalactic environments in 80 PHANGS galaxies, to characterize the relationship between population-averaged cloud properties and host galaxy properties, and to assess key timescales relevant to molecular cloud evolution and star formation. We show that PHANGS probes a wide range of kpc-scale gas, stellar, and star formation rate (SFR) surface densities, as well as orbital velocities and shear. The population-averaged cloud properties in each aperture correlate strongly with both local environmental properties and host galaxy global properties. Leveraging a variable selection analysis, we find that the kpc-scale surface densities of molecular gas and SFR tend to possess the most predictive power for the population-averaged cloud properties. Once their variations are controlled for, galaxy global properties contain little additional information, which implies that the apparent galaxy-to-galaxy variations in cloud populations are likely mediated by kpc-scale environmental conditions. We further estimate a suite of important timescales from our multiwavelength measurements. The cloud-scale freefall time and turbulence crossing time are ∼5–20 Myr, comparable to previous cloud lifetime estimates. The timescales for orbital motion, shearing, and cloud–cloud collisions are longer, ∼100 Myr. The molecular gas depletion time is 1–3 Gyr and shows weak to no correlations with the other timescales in our data. We publish our measurements online, and expect them to have broad utility to future studies of molecular clouds and star formation.
Abstract
With Mapping Nearby Galaxies at APO integral field spectroscopy, we present a resolved analysis of star formation for 29 jellyfish galaxies in nearby clusters, identified from radio ...continuum imaging taken by the Low Frequency Array. Simulations predict enhanced star formation on the “leading half” (LH) of galaxies undergoing ram pressure stripping, and in this work we report observational evidence for this elevated star formation. The dividing line (through the galaxy center) that maximizes this star formation enhancement is systematically tied to the observed direction of the ram-pressure-stripped tail, suggesting a physical connection between ram pressure and this star formation enhancement. We also present a case study on the distribution of molecular gas in one jellyfish galaxy from our sample, IC3949, using Atacama Large Millimeter/submillimeter Array CO
J
= 1 − 0, HCN
J
= 1 − 0, and HCO
+
J
= 1 − 0 observations from the ALMA MaNGA Quenching and Star Formation Survey. The H
2
depletion time (as traced by CO) in IC3949 ranges from ∼1 Gyr in the outskirts of the molecular gas disk to ∼11 Gyr near the galaxy center. IC3949 shows a clear region of enhanced star formation on the LH of the galaxy where the average depletion time is ∼2.7 Gyr, in line with the median value for the galaxy on the whole. Dense gas tracers, HCN and HCO
+
, are only detected at the galaxy center and on the LH of IC3949. Our results favor a scenario in which ram pressure compresses the interstellar medium, promoting the formation of molecular gas that in turn fuels a localized increase of star formation.
Abstract
Star formation quenching is one of the key processes that shape the evolution of galaxies. In this study, we investigate the changes in molecular gas and star formation properties as ...galaxies transit from the star-forming main sequence to the passive regime. Our analysis reveals that as galaxies move away from the main sequence toward the green valley the radial profile of specific star formation rate surface density (Σ
sSFR
) is suppressed compared with main-sequence galaxies out to a galactocentric radius of 1.5
R
e
(∼7 kpc for our sample). By combining radial profiles of gas fraction (
f
gas
) and star formation efficiency (SFE), we can discern the underlying mechanism that determines Σ
sSFR
at different galactocentric radii. Analysis of relative contributions of
f
gas
and SFE to Σ
sSFR
uncovers a diverse range of quenching modes. Star formation in approximately half of our quenching galaxies is primarily driven by a single mode (i.e., either
f
gas
or SFE), or a combination of both. A collective analysis of all galaxies reveals that the reduction in star formation within the central regions (
R
< 0.5
R
e
) is primarily attributable to a decrease in SFE. Conversely, in the disk regions (
R
> 0.5
R
e
), both
f
gas
and SFE contribute to the suppression of star formation. Our findings suggest that multiple quenching mechanisms may be at play in our sample galaxies, and even within a single galaxy. We also compare our observational outcomes with those from galaxy simulations and discuss the implications of our data.
PDF
