Quote:
Originally Posted by dgruss23
[snip]
Then please proceed. Why don't you put your money where your mouth is - as they say. Surely, since you know it is that easy, you could perform the analysis as a demonstration for everyone of just how easy working with the data is. You've certainly suggested enough times on BAUT that BAUT members should download the publicly available data sets for themselves and perform the analysis. Perhaps it's time for you to step up and demonstrate for them just how easy this is? You might inspire others to attempt the same if you provide such a demonstration! That would be pretty cool.
[snip]
But please feel free to demonstrate that I am wrong - show the members of BAUT how easy it is.
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OK, let's see now ... stopwatch on.
The Verschuur preprint (already downloaded), Section 2 ("Data"):
Quote:
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Neutral hydrogen (HI) emission profile data with an angular resolution of 0.6◦ were obtained from the Leiden-Dwingeloo, sidelobe-corrected HI Survey (Hartmann & Burton, 1997) as well as the more extensive Leiden-Argentina-Bonn (LAB) All-Sky HI Survey (Kalberla et al. 2005).
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OK, Google on "Leiden-Argentina-Bonn (LAB) All-Sky HI Survey", found "
The Leiden/Argentine/Bonn Galactic H I Survey".
Hmm, there's a section called "Search the LAB Survey":
Quote:
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The online access tool does not allow to automatically process a large number of positions. For this purpose you can download the entire LAB survey from the » CDS server in Strasbourg. At » ftp://cdsarc.u-strasbg.fr/pub/cats/VIII/76 different versions of the survey are available as FITS data files via FTP. Details about the individual data cubes can be found in the ReadMe file.
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OK, off the the CDS server, where we learn that the LAB is indeed
catalogue VIII/76, and:
Quote:
The Survey is available as 3-D maps, with or without Hanning smoothing, covering the whole ±458km/s or limited to ±250km/s range.
The resolution of the 3-D maps is 0.5° in galactic longitude and latitude, and up to 1km/s in velocity.
The survey exists also as (b,v) maps at longitude intervals stepped by 0.5° -- these files supersedes the FITS files given in the Hartmann and Burton Atlas (Cat. VIII/54)
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... followed by a file summary.
Stop stopwatch ... about five minutes (it took me twice as long to write this up).
Now what about ftp access? Understanding FITS files? Converting the data to the same pixellation of the sphere that the WMAP (and other CMB) teams use?
Yes, if you are not familiar with these, then it may take you days, or even weeks.
What about performing an angular power spectrum analysis?
Let's learn together. Of course, if you aren't familiar with the techniques, it will indeed take you some time to do the work.
And BTW, all these techniques are certainly taught to budding astronomers; that some older ones may be unfamiliar with one or more is possible.
In any case, my comments were not addressed to the general BAUT reader so much as to those who feel that Verschuur's comment (awesome difficulty) has merit*, by pointing out that one reading of his comments, in this thread, cannot be right. And let's not forget that he's (apparently) a professional astronomer
But I've wasted too much time on this preprint already ... maybe later one more comment on why its faulty starting point renders almost all the rest of it also pretty much a waste of time, and then I'm done here**.
*
To re-iterate, I fully agree that "deriv[ing] a similar spectrum [to the cosmological angular power spectrum] for galactic HI structure" will indeed be "awesomely difficult" ... but that difficulty does not, pace those who've written otherwise in this thread, reflect any difficulty in obtaining the data (just ftp it from the CDS site) or performing the transformations on that data (to produce angular power spectra).
*
For people who'd like to know more about pixellation, angular power spectra, transformations, etc, please join me - and many other BAUT members - in the Q&A section.