Repository navigation
ALFALFA Grid Access
The ALFALFA data are now available on the NRAO archive. Basic instructions are available here. Here we document these instructions with images demonstrating the steps, in addition to how to view the grids via CARTA. A summary of the grids and ancillary files is here. The authoritative source for ALFALFA data is Haynes et al. 2018.
There is example code to work out which grid your source(s) might be in the notebooks folder of this repository.
- Navigate to the NRAO data archive.
- Click on the button that says, "View Images" under the blue bar. You must not skip this step.
- In the search bar type "ALFALFA_" and press Enter (other search terms, such as "A2010" and "ALFALFA", will also work, but the observation list returned isn't unique to ALFALFA). Alternatively, if you already know which grid you want, you can type its root name e.g. "0004+13", or "1052+23".
- On the search result row corresponding to the grid that you want, click the little clipboard icon on the far left. It will change to a green check mark, indicating that it has been added to your download stack, ready to be downloaded.
- Click the blue "Download" button in the bar just above the search results.
- If you want all the cubes, weight maps, and continuum files for a particular grid ID, check the box that says, "Include ancillary files" when it pops up. It is usally a good idea to select to receive the data as a single tar file.
- You will receive an email from
do-not-reply@nrao.eduletting you know your request has been submitted. After a while, you will receive another email when the data is ready to be downloaded. The email will contain both a link to a webpage where you can download the data, or awgetcommand that you can copy into a terminal.
The NRAO archive also offers the option to load an image data product into a CARTA server remotely. In order to do this, follow steps 1-4 above, and then undertake the following steps:
a. Click the blue "View in CARTA" button
b. Note that the popup now specifies "Visualize images with CARTA"
c. Submit the request and you will receive an email from do-not-reply@nrao.edu letting you know your request has been submitted. When the CARTA server is ready, you will receive an email with a link that you can use to launch the CARTA server. Note that this can take a few hours, and the CARTA server is only active for an hour. Thus, this has limited utility but can be very useful if you are somewhere with limited internet capacity and want to view grids remotely, rather than downloading them.
The ALFALFA grids (and spectra and catalogs) are available to access and work with in the Sciserver online platform which provides an online environment for server-side analysis of big data sets.
Users will need a free Sciserver account, then can access the ALFALFA dataset by creating a Compute Container on SciServer with the ALFALFA data volume attached. A Compute container is an online area in which Jupyter Notebooks (or other code) can be run to interact locally with the data, and also provides file system access to download data cubes, spectra and catalogs.
There is example code to work with in the notebooks folder of this repository.
The version of the ALFALFA grids on Sciserver is updated from that available on the NRAO archive. Sciserver hosts the ALFALFA _v2.fits grid files (spectral, continuum and the associated weights files) which have had information including co-ordinates updates in the fits headers using the method described in the FITS_header_cleaner.ipynb in the notebooks folder of this repository. The load_grid.py function applies the correction to grids downloaded from the NRAO Archive, but the function will check if the correction is applied, and will not be repeated when loading v2 grids hosted on Sciserver.