Many of you may have seen me looming around the department and might know I am currently working with Dr. Anca Constantin. What have I been doing, you ask? Well, I have been doing data analysis on spectra from the Hubble Space Telescope (HST) towards a paper on the aperture dependence of the nuclear galactic nebular line emission. This week, I will be starting on data from the Multi-Mirror Telescope. Now, that’s a good sound byte, but what does that even mean? You’ll say, “come on -- what have you really been up to? And why is it that, if you’re doing research, every time I pass by, you’re just staring at that 27-inch iMac screen?”
The project is centered on Active Galactic Nuclei (AGN). An AGN is black hole sitting in the center of a galaxy and actively accreting matter. We know these super-massive beasts must be accreting matter because we see emission lines in the spectra coming from the very central regions of galaxies, and those emission lines are consistent with matter being accelerated to relativistic speeds. Keep in mind, spectra are our only tool to probe Astronomical objects; they tell us what they’re made of, how fast they’re moving, how big they are, how far away they are – the list goes on. Those amazing emission-line spectra are what I play with all day. This would be a jump back to Physics 270 -- remember the Balmer series for the Hydrogen atom and all that? “Of course I remember the Balmer series. Pish-posh! What I want to know is, how do you play with spectra?”
Well, when I first started I downloaded a bunch of 2-D spectra from the HST archives. (Warning: begin “slight lie”) Remember that to get a spectrum, I hold a prism up to a light source and break the light into its components. So you can think of a 2-D spectrum as being “wavelength” along the x-axis, “physical horizontal distance” along the y-axis, and “flux” as the z-axis – graphed as color scale. (End “slight lie”) First, I had to extract a 1-D spectrum from the 2-D spectrum using this technical software called IRAF. IRAF is all text based, most astronomers use it, and a few months passed before I built up any kind of intuition with it. My previous computer know-how was mostly GUI-based with a few exceptions for programming (shout out to Dr. Ingham’s Matlab topics course, circa 2006). Once I have all my spectra extracted, I have to clean them.
You see, the crazy thing about space-based detectors is, you have much better resolution but you get so much space-noise. High-energy particles (alpha, electrons, etc) are flying around everywhere, zapping your detector. They show up as huge spikes on my spectrum. So to get rid of them, I take two images of the same region, overlay them, and get rid of any signal that’s not on both. I do this, again, with IRAF.
You know, it turns out IRAF will do just about anything you want it to – extract, reduce, plot, clean, cook, etc -- as long as you scream obscenities and throw enough things around the room. Luckily, I’m very good at both of these things, so my IRAF does whatever I want it to. I say jump, IRAF says “ERROR: floating point invalid operation.” …. doh.
Moving into a more recent timeline, I just spent the last week, give or take, carefully plotting fits to the extracted, cleaned, Doppler-corrected spectra. The normal emission lines I would expect to see are narrow. In other words, when I look at a graph of Flux versus Wavelength, I expect a slim peak at some wavelength that is indicative of a specific atom, ion or molecule. I spent a long time making sure I had the best fits I could obtain using 5 narrow Gaussians -- representing a doublet for singly ionized Sulfur [SII], Hydrogen-alpha [Ha], and a doublet for singly ionized Nitrogen [NII]. (This is a slight lie for brevity. I also had a 6th, linear component that I used to fit the background from just the galaxy.) When my fits just didn’t seem to work and I felt like giving up, I introduced a broad Gaussian for [Ha]. “Wait, wait. What? You just told me that emission lines were narrow. Why would you fit a broad Gaussian to something that’s supposed to be narrow?”
It turns out that when matter is pretty close to the super-massive black hole in the center of a galaxy, it orbits at incredible speeds. This means that the narrow line I expect is actually Doppler shifted – both into the blue (coming towards me) and the red (going away from me). I still see a narrow line from Hydrogen that is further from the AGN, and as I look at Hydrogen that is closer and closer to the nucleus, I see more and more Doppler shifted lines. Of course, I see all of these “individual lines” at the same time; so add all these up and I get one big, broad “hump” where I’d normally expect a thin line. This is what I fit with the broad Gaussian component.
Let’s take a break from technical mumbo-jumbo. We’ve just reached the exciting part! The broad component is what I want; that’s where the science really starts for me! Doing analysis on the broad component is what tells me about the region closest to the black hole. I can recover the mass of the black hole and a swarm of other properties. I am probing the centers of galaxies from my lab in the JMU Physics and Chemistry building!
“… well … what do you expect to find?” If you find yourself asking that question, then my sinister plan has worked and I should tell you that Dr. Anca Constantin is actively looking for people to come join her team! You can come see her in office hours or stop by the lab and ask some questions. She has lots of other projects for people interested in Active Galactic Nuclei or other extra-galactic Astronomy research. Also, if you’re interested from that teaser, members of Dr. Constantin’s research team, including myself, will be presenting in the JMU Research Symposium that is coming up.
This is where I, foregoing transition, should say that I have been given a unique opportunity to be a paid Astronomy researcher (with a BS in Physics), paid for by NASA grant, at a University that does not have post-docs. Letting the Physics majors get a better glimpse of this position is what inspired a Blog update -- specifically because in the future, more of these opportunities might exist. This opportunity has been a great learning experience, resume builder, and an amazing preparation for graduate study. I think it would be well worthwhile for any graduating or rising seniors to keep eyes out for opportunities such as these in the future.