126 research outputs found
Submillimeter Array CO(2-1) Imaging of the NGC 6946 Giant Molecular Clouds
We present a CO(2-1) mosaic map of the spiral galaxy NGC 6946 by combining
data from the Submillimeter Array and the IRAM 30 m telescope. We identify 390
giant molecular clouds (GMCs) from the nucleus to 4.5 kpc in the disk. GMCs in
the inner 1 kpc are generally more luminous and turbulent, some of which have
luminosities >10^6 K km/s pc^2 and velocity dispersions >10 km/s. Large-scale
bar-driven dynamics likely regulate GMC properties in the nuclear region.
Similar to the Milky Way and other disk galaxies, GMC mass function of NGC 6946
has a shallower slope (index>-2) in the inner region, and a steeper slope
(index<-2) in the outer region. This difference in mass spectra may be
indicative of different cloud formation pathways: gravitational instabilities
might play a major role in the nuclear region, while cloud coalescence might be
dominant in the outer disk. Finally, the NGC 6946 clouds are similar to those
in M33 in terms of statistical properties, but they are generally less luminous
and turbulent than the M51 clouds.Comment: Published in Ap
The Gas–Star Formation Cycle in Nearby Star-forming Galaxies II. Resolved Distributions of CO and Hα Emission for 49 PHANGS Galaxies
[[abstract]]The relative distribution of molecular gas and star formation in galaxies gives insight into the physical processes and timescales of the cycle between gas and stars. In this work, we track the relative spatial configuration of CO and Hα emission at high resolution in each of our galaxy targets and use these measurements to quantify the distributions of regions in different evolutionary stages of star formation: from molecular gas without star formation traced by Hα to star-forming gas, and to H ii regions. The large sample, drawn from the Physics at High Angular resolution in Nearby GalaxieS ALMA and narrowband Hα (PHANGS-ALMA and PHANGS-Hα) surveys, spans a wide range of stellar masses and morphological types, allowing us to investigate the dependencies of the gas‒star formation cycle on global galaxy properties. At a resolution of 150 pc, the incidence of regions in different stages shows a dependence on stellar mass and Hubble type of galaxies over the radial range probed. Massive and/or earlier-type galaxies in our sample exhibit a significant reservoir of molecular gas without star formation traced by Hα, while lower-mass galaxies harbor substantial H ii regions that may have dispersed their birth clouds or formed from low-mass, more isolated clouds. Galactic structures add a further layer of complexity to the relative distribution of CO and Hα emission. Trends between galaxy properties and distributions of gas traced by CO and Hα are visible only when the observed spatial scale is ≪500 pc, reflecting the critical resolution requirement to distinguish stages of the star formation process.[[notice]]補æ£å®Œ
SDSS-IV MaNGA:The Nature of an Off-galaxy H Blob -- A Multi-wavelength View of Offset Cooling in a Merging Galaxy Group
The ALMaQUEST survey – III. Scatter in the resolved star-forming main sequence is primarily due to variations in star formation efficiency
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 (Sigma_SFR), as well as its scatter around the resolved star forming main sequence (Delta Sigma_SFR). We find that Sigma_SFR is primarily regulated by molecular gas surface density (Sigma_H2) with a secondary dependence on stellar mass surface density (Sigma_*), as expected from an `extended Kennicutt-Schmidt relation'. However, Delta Sigma_SFR 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 ALMaQUEST Survey: VI. The molecular gas main sequence of `retired' regions in galaxies
In order to investigate the role of gas in the demise of star formation on
kpc-scales, we compare the resolved molecular gas main sequence (rMGMS: Sigma_*
vs Sigma_H2) of star-forming regions to the sequence of `retired' regions that
have ceased to form new stars. Using data from the ALMaQUEST survey, we find
that retired spaxels form a rMGMS that is distinct from that of star-forming
spaxels, offset to lower Sigma_H2 at fixed Sigma_* by a factor of ~5. We study
the rMGMS of star-forming and retired spaxels on a galaxy-by-galaxy basis for
eight individual ALMaQUEST galaxies. Six of these galaxies have their retired
spaxels concentrated within the central few kpc. Molecular gas is detected in
40-100% of retired spaxels in the eight galaxies in our sample. Both the
star-forming and retired rMGMS show a diversity in normalization from
galaxy-to-galaxy. However, in any given galaxy, the rMGMS for retired regions
is found to be distinct from the star-forming sequence and gas fractions of
retired spaxels are up to an order of magnitude lower than the star-forming
spaxels. We conclude that quenching is associated with a depletion (but not
absence) of molecular gas via a mechanism that typically begins in the centre
of the galaxy.Comment: MNRAS, in pres
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