The ISM and Star Formation Efficiency from GMC to Kiloparsec Scales
Lead Research Organisation:
CARDIFF UNIVERSITY
Abstract
As galaxies evolve, they move from the ‘blue cloud’ of star-forming galaxies to the ‘red sequence’ on which the formation of stars in the galaxies has virtually stopped. One of the big mysteries of this process is that the fall in the star-formation rate is accompanied by a fall of a factor of ~10 in the star-formation efficiency (SFE, star-formation rate divided by gas mass). We propose to use three Cardiff-led surveys to determine the cause of the dramatic fall in SFE.
A crucial part of our programme is the use of dust observations to trace the molecular gas, a method which has some major advantages over the use of CO as the tracer, a method we have developed over the last decade. We will apply the Cardiff-developed PPMAP algorithm to the data from the HASHTAG and DOWSING JCMT Large Programmes to create unparalleled high-resolution maps of the properties of the dust in M31 and M33 and 12 other nearby galaxies. By combining these maps with state-of-the-art dust models, we will uncover the cause of the local and global variation in the dust in galaxies, which was also discovered by our group and is the remaining stumbling block to using dust (and its variation) to investigate galaxy evolution.
We will use KILOGAS, an ALMA+IFU survey of 500 galaxies, to investigate the global and local processes that influence the SFE in galaxies. We will investigate the global effects by examining the relationships between gas and star-formation in each galaxy (from the ALMA and IFU data) and how they depend on global properties such as halo mass, morphology and total gas content. We will investigate the local processes on a ~1 kpc scale by looking at the dependences of these relationships on the kinematics and structure of the gas. We will then extend this work down to the ~25 kpc scale by investigating the formation of stars within the GMCs in M31 and M33. We will produce (and publish) the first catalogues of the GMCs in these galaxies that use both CO and dust, allowing us both to investigate the gas kinematics and trace the CO-dark gas. We will measure the star-formation rate in each GMC using one old and one new method, both calibrated with JWST observations of the young stellar objects within the GMCs. We will investigate the physics of the process in which a GMC forms and is converted into stars by investigating, for the first time, the relationships between the SFE of each GMC and both the internal properties of the cloud (mass, surface density, virial parameter) and the local properties of the galaxy’s velocity distribution (shear, velocity dispersion) and mass distribution (torque) at the position of the cloud.
A crucial part of our programme is the use of dust observations to trace the molecular gas, a method which has some major advantages over the use of CO as the tracer, a method we have developed over the last decade. We will apply the Cardiff-developed PPMAP algorithm to the data from the HASHTAG and DOWSING JCMT Large Programmes to create unparalleled high-resolution maps of the properties of the dust in M31 and M33 and 12 other nearby galaxies. By combining these maps with state-of-the-art dust models, we will uncover the cause of the local and global variation in the dust in galaxies, which was also discovered by our group and is the remaining stumbling block to using dust (and its variation) to investigate galaxy evolution.
We will use KILOGAS, an ALMA+IFU survey of 500 galaxies, to investigate the global and local processes that influence the SFE in galaxies. We will investigate the global effects by examining the relationships between gas and star-formation in each galaxy (from the ALMA and IFU data) and how they depend on global properties such as halo mass, morphology and total gas content. We will investigate the local processes on a ~1 kpc scale by looking at the dependences of these relationships on the kinematics and structure of the gas. We will then extend this work down to the ~25 kpc scale by investigating the formation of stars within the GMCs in M31 and M33. We will produce (and publish) the first catalogues of the GMCs in these galaxies that use both CO and dust, allowing us both to investigate the gas kinematics and trace the CO-dark gas. We will measure the star-formation rate in each GMC using one old and one new method, both calibrated with JWST observations of the young stellar objects within the GMCs. We will investigate the physics of the process in which a GMC forms and is converted into stars by investigating, for the first time, the relationships between the SFE of each GMC and both the internal properties of the cloud (mass, surface density, virial parameter) and the local properties of the galaxy’s velocity distribution (shear, velocity dispersion) and mass distribution (torque) at the position of the cloud.