Astronomy Stuff


Two views of AM 2020-504:

Andreas Observatory Spectrograph Manual

Multiwavelength Studies of Late-Type Galaxies:

Most of my work for the last several years has involved multiwavelength studies of spiral and irregular galaxies. I have been involved in two somewhat overlapping large projects in this area. The first is the Ohio State University Bright Spiral Galaxy Survey. The OSU Survey is a set of broad-band images in BVRJHK of a statistically complete sample of about 200 spirals. There have been about 15 papers published on various parts of the survey, including two that I wrote on the survey as a whole. One on the local spiral bar fraction, and another on optical vs. H-band galaxy morphology. I am also a part of the HST Survey of the Mid-UV Morphology of Nearby Galaxies. This program has obtained mid-uv and optical HST of nearly 100 nearby late-type galaxies. We have also managed to get NICMOS and ACS H-alpha data on a subset of the sample. There have been a handful of papers on the survey so far. I wrote one of them, and was a co-author on another.

Polar-Ring Galaxies:

The pair of spiffy image above are H-alpha and optical continuum images of the polar-ring galaxy AM 2020-504 (obtained with the 1.5m telescope at the Cerro Tololo Interamerican Observatory - CTIO for short). My main cohort in this pursuit (among others!) is Richard Pogge whom I first met in Dabney House in 1979. We have a paper in the ApJ on the abundances of HII regions in the polar-ring galaxy NGC 2685. (You can find it here if you don't have an E-ApJ subscription). We also have a conference contribution on the HII region luminosity functions of PRGs (they turn out to look much more like those of Sa spirals than they do those of dIs). Polar-ring galaxies are pretty much what they sound like -- galaxies (usually S0s or Es) with rings of material orbiting in a plane nearly orthogonal to the main symmetry plane of the host galaxy. A particularly lurid example is shown at the top of the page. The emission-line gas is all in the polar ring, and is due to ionization from hot young stars. I've been studying star-forming regions in the rings as a way of figuring out how (and how long ago) they formed, and out of what. To do so, I've used (so far) the CTIO 1.5m , the Mt. Hopkins 1.2m , and the 2.4m Hiltner telescope at MDM for the imaging, and the MMT and Kitt Peak Mayall 4m for the spectroscopy.

Dwarf Galaxies:

I've also done a bunch of work on dwarf galaxies in the Local Group. My most recent work in the area has been on a proper-motion selected sample of stars from the Ursa Minor dwarf spheroidal that Andrea Schweitzer assembled for her PhD. She and I published a paper on the subject in the AJ. I have also published several papers on the x-ray source populations in Local Group dwarfs. Ray White and I published a paper in the AJ on a stellar x-ray source in the bar of the Local Group dI NGC 6822. And I (along with Ray White and Dave Davis) published a paper (if you don't have an E-ApJ subscription, you can look here) on the x-ray emission from the compact elliptical M32, based on archival ROSAT data. Here are optical and x-ray images. The traditional notion is that x-rays from faint ellipticals are due to low-mass x-ray binaries. And ASCA observations analysed by Loewenstein et al indicate that this is likely to be the case in M32. However, there is a wealth of dynamical evidence supporting the presence of a massive black hole in M32, and x-ray observations may allow for the direct observation of emission from material accreting onto this central black hole. My earlier work on dwarfs was based mainly on scans of UKSTU plates with the COSMOS facility at ROE, and also on IUE spectra. Dwarf galaxies are systems with, typically, six orders of magnitude less mass than a galaxy like ours. They may be small, but there are a WHOLE lot more of them than there are of the big'uns. (If you clicked on "dwarf galaxies" you should have spawned an image of the Leo I dSph, courtesy of the AAO image library).

Star Formation in Early-type Galaxies;

And I should say a few words about the ISM (inter-stellar medium) and star formation in early-type (E and S0) galaxies: Nothing is ever as simple as we think it is! The conventional wisedom of ~30 years ago was that there was no ISM or star formation in early-type galaxies. It turns out that this was wrong. Lots of E galaxies (some S0s also) have hot (millions of K) ISM that emit thermal x-ray emission. I've written a few papers on that topic. Here's the key one. And many S0s have enough of a cool/cold ISM to have ongoing star formation as well. In fact, this star formation is typically distributed in rings! Not polar rings, though. Rings in the disks of the galaxies. These range all the way from rings that are nearly nuclear to rings near the edge of the disk. (The two galaxies depicted are NGC 1819 and UGC 12840). It also turns out that the HII regions in S0 galaxies are generally metal-rich (Solar metallicity or higher). We have a proceedings on the subject that shows our sample to fall right onto the general trends of metallicity with both galaxy morphology and luminosity. This makes the idea of fueling star formation by recent accretion very hard to defend.

Other Astronomy Links:


paul.eskridge@mnsu.edu

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