- You are an observer with a new sample of LAEs at z=4; you want to know how compares to the broader population of Ly-alpha emitting galaxies in equivalent width and strength of blue-peak. You query the database and obtain these quantities and make the relevant figure, cutting as you wish.
- You are an observer with a peculiar object, or a theorist that has made a profile that looks weird. You ask the question are there any more of these out there? Where are they, what do they look like, and whose paper should I cite? You obtain the spectra from the archive and either make parametric cuts to the sample or find the best match to your own spectrum by minimizing the residual in the distributed spectra.
- Somebody writes a paper and compare their LAEs with samples X and Y; the paper is placed on the arXiv in press – too late for changes, even though they wrote ‘comments welcome’ – and makes the grave mistake of not comparing with sample Z. You easily pull the properties of sample Z from the LASD and rapidly write a rebuttal.
The LASD Project
The Lyman Alpha Spectral Database was devised to be community portal to aggregate profiles/shapes of Lyman alpha emission lines from galaxies. The underlying principle is that once Astronomer X has observed Galaxy Y and made the measurements about which they are most interested, the best place for that spectrum is out there in nature. This information should not be sitting on Astronomer X’s disk (especially the bit-rotten disk of the previous previous laptop – the one that doesn’t charge any more). The philosophy is that Lyman alpha spectra want to be free (after a transfer process, obviously).
The LASD is a conventional database, in that it serves the spectra of a galaxies, and a large number of spectroscopic measurements. The user can upload spectra and download spectra and measurements; you may access the data through specific queries, or just pull the whole thing. The measurements include basic properties like luminosity and equivalent width, and also more sophisticated quantities that describe the line such as peak velocity shift, red/blue flux ratio, and many more measurements.
However, the LASD is more than just a database: it calls its spectral parsing methods on the fly at the point of upload, makes every one of the measurements, and populates the database. This is the fundamental driver for the LASD: to provide a complete set of measurements, that are made in a completely homogeneous way, for a large number of galaxies, that live at all observable redshifts/cosmic epochs. If you want the asymmetry parameters for all galaxies with SFR>5 Msun/year, at redshifts 0<z<4.5, observed with resolving power better than 1500 and SNR>6 per pixel: the LASD will give you that. If a new measurement/quantity becomes commonplace in the future, we will simply add this method to the LASD and populate the entire database with it. Sounds like a dream, but in reality it’s a dream that’s pretty easy to realize: it just requires observers to contribute their spectra.
The content is provided by you, the user, by simply uploading a spectrum in ASCII or FITS format, and a small amount of meta-data. The spectra themselves may be flagged as public or private: if public, the user gives LASD permission to re-distribute the flux and wavelength data (most likely converted to L_v vs. velocity); if private the LASD will only serve the measured/derived quantities. The LASD team provides the service, and to get it started we are populating the data with some ~150 galaxies at z<0.4 (the HST/COS archive) and 500 galaxies at 2.9<z<6.6 (the public VLT/MUSE spectra). Ultimately, however, such a community service must also be community driven: we need the community of spectroscopists to upload their spectra.
Finally at the point of upload, the user may (and should!) also specify the reference to where the spectrum was first published: the digital online identifier (DOI) or Bibcode. If data for that galaxy are downloaded, the meta-data will include the bibtex entry for that paper, making it trivial for authors referring to your galaxy to get cite your paper (even the correct one!). So not only does Lyman alpha-related science advance, but your citation rate advances in parallel.
… at LASD!
This is best addressed using a few demonstrations:
We tried to count how many Lyman alpha spectra have been published: there are thousands of them in hundreds of papers, over all possible redshifts using many different selection functions. Then we tried to count the number of different relevant measurements that people make: we counted five different quantities that describe the asymmetry alone, with almost no authors reporting more than one of these – how could we compare spectral properties of galaxies between different studies?
To top it off, the measurements are reported in the tables of PDF or HTML documents: these are hugely frustrating to copy into machine readable text-files, and the process is only slightly improved by getting the tex file from the arXiv tarball (… is that the published version?). Sometimes they miss units or have them hidden in footnotes and running text. And you have to do this for 10 papers? ARGH! Plus: we should no longer have to try and read spectra out of EPS files.
Open science demands these quantities should be easy to obtain. Comparing one galaxy to another demands that the measurements are all made in the same way. We want to make Lyman alpha quantities available to all users, measured in a homogeneous way, for every galaxy in the universe. Of course this ambitious goal relies upon you – the user – uploading your spectra, and making them free to the world; should you require assistance with this then please contact Axel Runnholm or Max Gronke.
We have a number number of feature improvements and additions planned for the future of LASD. Here we layout the highest sections of our priority list for the future.
- Bulk uploads
It will be possible to upload many spectra at once to the database
- Easier bibliographic management
We will no longer require submission of complete BibTex entries for each spectrum
- Frontpage Announcements
We will add a function to make it easier to see what is currently happening with LASD
- Single Object downloads
Adding the possibility to download only a single observation
- Analysis documentation
We hope to be able to publish the documentation for all analysis done by the LASD
- Support FITS file uploads
We plan to support a wider range of upload formats including fits.
- cite the original observational papers of the data you used. For this, we provide the full bibtex entries in the download,
- cite our paper Runnholm et al. (2020),
- and add a footnote to the LASD URL "http://lasd.lyman-alpha.com" or "www.lyman-alpha.com".