PI: Erwin de Blok

The Apertif surveys will result in resolved observations of thousands of nearby galaxies. Though not as highly-resolved as for example those observed in the THINGS or related surveys, the large number of galaxies will enable a very precise determination of HI kinematical and morphological properties.

In this project we will concentrate on two properties of these resolved galaxies: the shapes of their rotation curves and the HI density distribution in the outer parts.

The demographics of rotation curves

A sample of nearby galaxies will be defined that has enough resolution to study the properties of the rotation curves. Mostly likely this will involve galaxies that are resoved by a significant (>5) number of beams.

Initially an automated procedure (e.g. Barolo or 2DBAT) will be used to determine the shape of the rotation curves. The rotation curves are then classified based on their shape and correlations with other properties to be explored.

Rotation curves will initially be derived using the standard data product velocity fields that the surveys will deliver. At a later stage more sophisticated procedures can be attemped (Gauss-fitting) but this will depend on the overal quality of the data. Some of the automated rotation curve routines available also produce their own velocity fields. These will be compared with the standard data products as well.

Using optical/IR ancillary data in regions where these are available simple disk-halo decompositions can be attempted. This can then lead to exploring the dark halo profile as a function of global properties.

Data products that are required for this are 1) cubelets of the galaxies, 2) velocity fields; 3) integrated HI maps; 4) ancillary optical/IR data.

Though beyond the scope of the current project, the rotation curve properties could be used as inputs for a possible Tully-Fisher project using, e.g., the V(flat) values of the rotation curves.

Outer parts of HI disks

Using a similar nearby galaxy sample as above, an exploratory study will also be done to see if the large number of resolved galaxies available with Apertif can be used to say something statistical about edges of disk.

It has been known for a long time that HI disks have an "edge" where the column density steeply drops from values of a few times 1e19 to 1e18 cm-2. It is thought that this is caused by ionization, but other causes have also been posed (e.g., accretion, disk growth). A systematic study of the properties of edges as a function of e.g. galaxy mass or type has not been done.

With this study we would like to explore if HI disks can be scaled by some common radius and then stacked in order to trace the HI column density down to ~1e18 cm-2 levels. The large sample size would enable pruning the sample to exclude large asymmetries etc., so that only symmetrical undisturbed galaxies remain. Assuming a large enough sample size, edges can then be studied as function of environment, type, etc.

Data products needed for this study are 1) cubelets of the galaxies; 2) velocity fields; 3) integrated HI maps


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