Hunting Voorwerpjes from California

An especially nice side project of Galaxy Zoo has been uncovering giant gas clouds ionized by active galactic nuclei. Of course, the most striking of these has been Hanny’s Voorwerp, whose study has been fruitful enough! In addition, Zooites proved to be good at finding smaller, dimmer versions (“voorwerpjes”, using the Dutch diminutive form). We harvested these both from Forum postings, and from a targeted hunt of galaxies with known AGN (arranged by Waveney). To be sure what we’re dealing with, we need spectra of these clouds. We had observing runs to do this last summer from Kitt Peak and Lick Observatories, confirming many new cases (some of which may have a similar history of faded glory to what we infer for Hanny’s Voorwerp). Kevin led a further proposal to look at these in X-rays, so we can tell whether the suspiciously dim nuclei are really dim or actually hidden by foreground gas and dust.

We have another observing session this week with the 3-meter Shane telescope of Lick Observatory, a facility of the University of California. The proposal was led by Vardha Nicola Bennert from Santa Barbara, observing as before with UCSB students Anna Pancoast and Chelsea Harris. Here they are standing in front of the telescope’s mirror cell and instrument cluster.

Vardha Bennert, Chelsea Harris, Anna Pancoast at Lick 3m telescope

I was also able to arrange going to Mount Hamilton for these four nights. This will be sort of a homecoming for me – as a graduate student at UC Santa Cruz, Lick was where I cut my observational teeth. Checking some old logbooks, I have entries slightly over thirty years ago (and a collection of photos which should shortly be updated!). For my thesis, on the spectra of gas in normal galaxies and whether they contain weak AGN, I used over 70 nights on the then new 1m telescope. So not only was UCSC where I studied interpretation of spectra, but Lick was where I got my first (few hundred) galaxy spectra. Back then, the 3m was the primary telescope for UC astronomers, so graduate students worked with it only while assisting faculty members. I did manage to spend a few hours at the prime focus of the 3m while we were working on what might have been the observatory’s first CCD spectrograph (constructed by painful use of a hacksaw on one originally built for Margaret Burbidge to use image tubes with). We looked at a planetary nebula for wavelength calibration, giving me a lasting memory of just how green the [O III] emission lines appear. (I also managed to see the radio galaxy Cygnus A through the eyepiece while lining up the spectrograph slit). Another student and I managed to get allocated a single otherwise unused night of 3m time to split – and it snowed. Here’s documentation – that young-looking guy is in the cage sitting in the middle of the telescope at the top of the tube. This was such a stopgap setup that the only way to refill the CCD’s liquid nitrogen involved running a long tube between circuit boards of the control electronics. I categorically deny ever having dumped liquid nitrogen on my advisor. Almost.

Times have changed. Everything is remotely operated, and not only do CCDs rule, but the Kast double spectrograph uses a dichroic beamsplitter to separate blue and red light so that each goes into a separate spectrograph and CCD optimized for that part of the spectrum. We’re ready with a list of target galaxies winnowed down by reanalysis of the SDSS images after selection by Zooites. If last summer’s set is a guide, at least half of these will prove to have huge, galaxy-sized clouds illuminated by seen or unseen nuclei. I hope to get the results processed quickly; at the Seattle meeting of the American Astronomical Society in January, there will be a display presentation from last summer’s work led by Drew Chojnowski, and it would be great to double our sample size.

Of course, as with any ground-based observations, we will be at the mercy of the weather. You can keep track using the especially crisp webcam views provided by Lick (one of which looks across the brilliant city lights of the whole San Francisco Bay area, which have been kept slightly under control by extensive light-pollution lobbying but made Lick astronomers some of the first to use digital sky subtraction for spectra). And of course we’ll keep the Zoo updated on our data.