Dusty dwarfs from Arizona

How is the latest set of telescopic followups to a Galaxy Zoo project like the aftermath when Moria was delved? One has dwarfs and one had dwarves, and both were dusty. (Look, if you think that’s nerdy, I could have made a reference to First Age history).

Incoming data! This week I’m headed up to the 2.1m telescope of Kitt Peak National Observatory for more followup images of overlapping galaxies. This piece of the project traces to a serendipitous discovery in Hubble data which were intended to study the populations of stars in the outskirts of NGC 253, itself 10 million light-ears away. At the 2008 Austin meeting of the American Astronomical Society, the same one at which we saw the first spectrum of Hanny’s Voorwerp, Julianne Dalcanton of the University of Washington tracked down Benne Holwerda and me to show us this galaxy pair, which rejoices in the designation 2MASX J00482185-2507365:

HST image of backlit dwarf galaxy with dust filaments

Analysis of the dust in the smaller foreground galaxy showed something unusual – there are filaments of dust extending well beyond where we can detect the starlight in its disk. This had us looking for similar cases in the Galaxy Zoo overlap catalog, which should turn them up if any known sample will. It would be important to know whether many galaxies have such distant dust – first because it could alter calculations of how much extinction light from distant objects suffers as it passes intervening galaxies, and in addition because the connection between stars and the production of dust suggests that such galaxies have a complex history of the creation and transport of dust.

Our sample for this observing run centers on galaxy pairs broadly similar to 2MASX (what I wrote above). This kind of galaxy – small, perhaps true dwarfs, with dust in its outskirts – if common, would solve a question posed by recent statistical data from the European Space Agency’s massive Herschel infrared observatory (continuing its mission at four times the Moon’s distance as long as the liquid helium lasts). In the whole population of galaxies seen in deep surveys, some of their IR spectra would be best explained if a significant amount of their dust is so cold that it must lie far from the galaxy’s stars order not to absorb enough energy to heat it further. Our approach is to take CCD images with much longer exposures than the SDSS data, so we get better data quality in the outskirts of the galaxies and could detect dust filaments like those seen in 2MASX – whatsitsnnme.

The weather forecast at this point suggests that I may get about half of the time over our four scheduled nights (we have more next month). Watch this space for progress reports…