More on Herschel data access

Submitted by Kevin Jardine on 16 May, 2010 - 13:20

During the big Herschel science conference in early May, I blogged about the issue of data access, complaining (perhaps a bit unfairly) that we will have to wait at least another year for the full results of the Hi-GAL survey of the inner galaxy.

According to the Hi-GAL schedule given here, we can expect to see the "start of incremental releases" of the Hi-GAL "maps in 5 bands" about 24 months after Herschel's launch (that is, May 2011).

It is therefore interesting to see that the full five band data for four Hi-GAL tiles (all dated January 2010) are already publicly available from the Herschel archives.

Curiously, none of these are the tiles for 30° or 59°, which have already been described in at least one scientific paper and a press release, nor are they in the direction of RCW 120, which was the subject of another press release and several scientific papers.

Instead the data are for the tiles for the galactic longitudes 303°, 305°, 312° and 323°.

It looks like this new data also points to a wealth of new scientific discoveries.

As just one example, here is an image based on Herschel's longer wavelength SPIRE instrument centred at 303.75°. I created this image from SPIRE's 500 μm (red), 350 μm (green) and 250 μm (blue) bands. SPIRE is sensitive to submillimetre wavelengths in frequencies where longwave infrared is merging into shortwave radio frequencies.

Compare this with the equivalent Spitzer image (seen here in the Milky Way Explorer):

The most obvious difference is the large area of submillimetre emission surrounding the obscure infrared source IRAS 12578-6217. This is visible towards the upper left of the Herschel image. Interestingly, this object is not visible at longer wave radio frequencies, eg. in this SGPS image.

Herschel presentations

Submitted by Kevin Jardine on 15 May, 2010 - 09:16

The presentations from the Herschel science conference last week are now available here:

http://herschel.esac.esa.int/FirstResultsSymposium.shtml

and many of the related scientific papers are here:

http://xxx.lanl.gov/find/astro-ph/1/ti:+herschel/0/1/0/past/0/1

As well, you can find news releases here:

http://www.esa.int/SPECIALS/Herschel/index.html

and pretty pictures here:

http://oshi.esa.int/

Unfortunately the multiple Herschel websites are a confusing maze but hopefully those links will let you get right at the good stuff.

More Herschel vs. Spitzer

Submitted by Kevin Jardine on 6 May, 2010 - 23:06

Here's another Herschel (Hi-GAL) vs. Spitzer (MIPSGAL) comparison. This time the image is closer to the galactic centre towards the constellation Aquila (about 30° galactic longitude).

Spitzer (can be seen in the Milky Way Explorer here):

and Herschel:

It should be noted that a significant reason for the differences in the Spitzer and Herschel images is the colour ranges and luminosity levels chosen by the people who rendered the data. If you copy these images and run histogram equalisation on them in a graphics program, you will see that the underlying data are more alike than is first apparent.

Still, there is no doubt that Herschel reveals more detail, especially in the colder dust, than Spitzer.

Hi-GAL

Submitted by Kevin Jardine on 6 May, 2010 - 18:42

Perhaps the most exciting Herschel project mapping the Milky Way is the Hi-GAL survey of the inner galaxy. This is essentially redoing the Spitzer GLIMPSE/MIPSGAL survey but with greater sensitivity, different wavelengths and in more detail.

The Herschel scientists released a large amount of preliminary data today, including a large swath of the Milky Way in the direction of the constellation Vulpecula as imaged by Hi-GAL. This gives us the opportunity to directly compare the Spitzer and Herschel results.

Here's a Spitzer MIPSGAL image centred around the galactic plane at 59.5°:

You can see this image in the Milky Way Explorer here.

Here's the equivalent preliminary Herschel image:

Of course this rendering of the Herschel data is deliberately overexposed to show the fine detail in the cold dust. The final Hi-GAL dataset will have thousands of luminosity levels and will be able to be rendered in multiple ways.

These results are very exciting - they confirm that Herschel's greater sensitivity will reveal a lot more fine detail in the Milky Way. The full Hi-GAL survey is scheduled to be released in about a year.

Data access

Submitted by Kevin Jardine on 6 May, 2010 - 10:48

As I write this, the scientific equivalent of a sold-out U2 rock concert is taking place at the ESTEC complex in Noordwijk, Netherlands. Some 400 scientists are gathered to hear the results of the first year of operation of the Herschel infrared space telescope. I blogged about Herschel and Planck after the two space telescopes were successfully launched last year (The king is dead - long live the king).

Because of the huge scientific interest in the conference (which is discussing results under strict media embargo), attendance had to be limited. I've been following Twitter updates from two scientists attending the meeting (Dave Clements and Brian O'Halloran) to get at least a glimmer of what is going on.

Unfortunately both scientists are attending the extragalactic sessions, so information about the Milky Way results is limited. A news conference is scheduled for later today and I hope more information will be available afterwards.

Yesterday there was a revealing Twitter exchange between the two scientists (as it happens Clements was sitting immediately in front of O'Halloran in the meeting room, but hey this is Twitter and the exchange was as much for their "followers" as themselves).

(Read the exchange from the bottom up.)

The exchange was specifically about the plan for a long delay in the public release of the Planck microwave data, but it might equally apply to the Herschel results. For example, the images collected in the Hi-GAL survey of the inner galactic plane are not scheduled for release until two years after the telescope was launched.

Clements suggests a reason for the delay, which is that the scientists immediately involved in the telescope projects are hoarding the data until they have written their papers.

Given the intense competition between astronomers, data hoarding is perhaps not surprising, but is it true that "everyone" does this as Clements states in his tweet? I'm not a professional astronomer, but it appears to me that NASA has a different policy for some of its space telescopes. In particular, Spitzer infrared data appears to be available as soon as it is acquired and archived. (Correction: Sarah Kendrew informs me that this depends upon the project and at least some of the Spitzer projects have a 12 month proprietary period.)

The fact that scientists involved with major telescope projects have a competitive advantage is not new. US scientists dominated astronomy for much of the twentieth century in part because the best telescopes in the world were located in California for most of the century. Even Jan Oort's famous paper on the rotation of the Milky Way was based largely on data begged or borrowed from US scientists.

The Internet has changed the dynamic, however, because now scientific data is routinely archived online. It is easier to share the data than not. Scientists involved with major projects need to go out of their way to password protect their data if they want it to remain private.

As the infrared astronomer Sarah Kendrew pointed out in a recent blog post (Setting free the Data), a huge number of scientific papers are now published by scientists using public data archives. In my view, this trend is a good thing and scientific data should be made available as soon as possible so that scientists without immediate access to the instruments (like Jan Oort) have the opportunity to make major discoveries.

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