Phil Cigan's REU homepage (Summer 2004)

Phil Cigan

University of Wisconsin - Madison
Madison, WI 53706

REU program-Summer 2004
University of Wisconsin-Madison
UW-Madison Astronomy Department

Advisor: Jay Gallagher
...and his webpage

Email me at
pjcigan --a-t-- astro.wisc.edu

Introduction
Background
Important Questions
Method and Process
Conclusions
What's Next?
Acknowledgements and References
[Hopefully] Useful links
DensePak Reduction Guide

This page should be considered to be [very much] under construction!

NGC1275 + Title
Image from Conselice, Gallagher, and Wyse

Introduction

First of all, this is more of a report on where I currently stand in my research than anything else. I make no claims of being finished at this point. As there will always be more work to do, this will remain a work in progress. That being said, the following is a description of some of the things on which I have worked under the guidance of Prof. John S. Gallagher III at UW-Madison.

Background

NGC1275 is a spectacular galaxy to study- it's one of the strangest galaxies we know of in the nearby universe. For starters, it's absolutely gigantic in terms of mass and length. It is currently having an interaction with (read: eating) another galaxy. And if that weren't enough, the darn thing has these huge filaments of (presumably) gas and dust extending outwards from the nucleus in many directions. So it's a very interesting place.

NGC 1275 has many different names depending on which area of the spectrum you are interested in for doing observations. Since different technologies are required to detect light from the various regions of the spectrum, different parties have taken it upon themselves to create separate catalogues for their region of interest. Here are some examples:

Name/Identifier	Area of Spectrum	What the Name Means
NGC 1275	Optical (Visual Light)	NGC means "New General Catalogue". It was developed by J.L.E. Dreyer in 1888 to replace the Messier catalogue. There were other objects appended later that received the prefix IC for 'Index Catalogue'.
Perseus A	All	The first word is the constellation in which the galaxy is 'located'- where it appears to be in relation to us on the projected night sky. The letter represents how big and bright the particular galaxy in a cluster is. So 'Perseus A' would be the most prominent galaxy in the Perseus cluster.
3C 84	Radio	3C stands for '3rd Cambridge Catalogue of Radio Sources'.
IRAS 03164+4119	Infrared	IRAS stands for "Infrared Astronomical Satellite". The numbers correspond to the galaxy's coordinates in the sky in Right Ascension and Declination.

Here is some general information about NGC 1275:

First observed by William Herschel in October 1786
Apparent Magnitude m = 11.6 (fairly faint) Note: apparent magnitude is how bright something appears to us from here on earth.
Absolute Magnitude M = ~ -22 (bright!) Note: absolute magnitude is how bright something would appear when seen from a distance of 10 parsecs.
Mass (total baryonic) = ~ a few times 10¹¹M_Sun (!) This is roughly 10 times the mass of the Milky Way.
Anglular size: ~ 4.33 x 6.08 arcmin
Physical size: ~ 88.2 x 123.8 kpc (kiloparsecs) or roughly 287,400 x 403,600 light years
Distance from us: ~ 70 Mpc (million parsecs) or roughly 228 million light years
Seyfert type 1 galaxy - this means it was included in Seyfert's original list of galaxies that had peculiar emission.
Starburst galaxy - this means there is a lot of high-mass star formation ocurring here.

Important Questions

The following are some important questions for my research over the summer that I have already worked on (or that I will eventually try to work on):

How much mass does this system and its components (i.e. the filaments) have?
What is the kinematic nature of the system and its components? In other words, how is the material at different areas of the system moving?
Why are these filaments there in the first place? I'll give a shiny new nickel to anyone who can tell me the answer to this. Note: one thing to keep in mind is that these filaments might not be a one-man show- they may be an indicator of some other (possibly larger) process. One example stems from the radio lobes that can be seen on opposite ends the galaxy, which will be dealt with later.
Are these filaments bound up with magnetic fields in some way?
How might these filaments affect the evolution of the galaxy, the ICM (Intercluster Medium, the 'dust' between the galaxies), or the cluster as a whole?

Method and Process

...Coming Soon! (Or at least to be udated soon)

Data, Observations
Instruments
Software
Analysis

Instruments

Software

IRAF (Image Reduction and Analysis Facility) was the primary software used for this project, run from a SuSe Linux machine. IRAF is used (as its name suggests) for data reduction and analysis. IDL (Interactive Data Language) was also used to make plots of the processed data.

Data and Observations

The data I used were taken between September 29th and October 1st, 2003, by Daniel Harbeck on the WIYN 3.5 meter telescope at Kitt Peak , AZ (part of the NOAO's National Observatory Site). Spectra were taken with the DensePak fiber array with the CassIAS setup (Which effectively just gives an additional magnification factor of ~2.173).

Sample raw spectra This is an image of the raw data that was captured at the telescope (i.e., a CCD image). You can see multiple bands spread out in columns. These represent the spectra of the various positions that were observed with the fibers of the DensePak instrument. The next step is to tidy up and process this data so that it can be analyzed. Without any processing you can already see that there are some patterns present in the form of brighter spots on certain points across many of the lines. This is good, as will be explained later.

Then, the processing...

Analysis

These data were reduced in the following steps:

IRAF -> using ccdproc to trim, bias correct, etc. and
IRAF -> using dohydra for flat field correction and wavelength calibration
IRAF -> using imarith to do sky subtraction

I'll elaborate on this process in the future.

Click here for a guide to reducing multi-fiber (specifically, DensePak) spectra in IRAF (Currently under construction)

sample processed spectra
This image shows a fully processed image that has gone through trimming, bias correction, flat field correction, wavelength calibration, and cosmic ray removal. One of the effects of doing this process in IRAF with the dohydra package is that the spectra are squished next to each other (in other words, the space between them that was present on the raw scan is removed).

The analysis followed this general progression:

IRAF -> using splot (or fxcor) to determine the radial velocity of the material by measuring the doppler shift (redshift) of the spectral lines

Use redshift (the change in wavelength of a spectral line between stationary and moving material) divided by the stationary wavelength:

z = |λ - λ₀|/λ₀    =    Δλ / λ₀

Then use velocity = v = c * Δλ / λ₀    or    v = c * z,
where z is the redshift, λ is the wavelength, and c is the speed of light.

IDL -> using the program fibers.pro to plot the velocities on a template of the fibers' relative positions

This is an image of NGC 1275 in H-alpha that shows where observations were taken.

The following are individual plots of velocities for the regions of interest, with each plot having its own relative velocity scale. The colorful bar on the right of each plot with the various numbers is the velocity scale. The values are in kilometers per second. Each circle represents the average velocity of material over ~ 1.3 arcseconds of sky, which translates to ~ 0.43 kiloparsecs (430 parsecs) on NGC1275. Up is north and right is west. So again, each colored circle tells you how fast the stuff it's pointed at is moving.

Click to view a larger version

NGC1275 H-alpha image with overlay of
the velocities of select regions.

Cropped NGC1275 H-alpha image with overlay of
the velocities of select regions.

These are images of NGC 1275 in H-alpha with the velocities of the material in observed regions plotted on top. These images show that, except for higher velocity material in the core, the material in the filaments is all moving at the same velocity over the entire observed system (roughly 50kpc) to within approximately a couple hundred kilometers per second. (!!!)

When we break up the fibers into groups that are consistent in velocity to within ~ 50 km/sec, we see something stunning: individual filaments!

NGC1275 H-alpha image with overlay of
filamentary structure derived from H-alpha velocity in the central region.

Conclusions So Far...

More Coming Soon!

Perseus A is REALLY big. I have not done a detailed calculation of the masses of the various components yet, but quick back-of-the-envelope type calculations (thanks for these, Jay!) show that the baryonic mass of the nucleus (and therefore approximately the whole system, since the filaments have little mass relative to the center) is around 10¹¹M_Sun (that's 1 with eleven zeroes after it times the mass of our sun... bigger than your average [insert favorite noun]). Each large filament should have roughly the baryonic mass of a small galaxy, or about 10⁸ or 10⁹M_Sun. I will hopefully be doing a more detailed calculation of the masses of these components at some point this summer.
- The most important thing to realize about this system is that it is linked in space and velocity over a distance of about 100 kpc in any direction. That's really phenomenal!
There is a very small spread in velocity over the entire filamentary system. This indicates that these filaments are probably not the effects of a fast explosion (from supernovae, hypernovae, whatever) because you would expect to find the ejected material moving at a very different velocity than the material in the nucleus.
If they aren't the result of a fast explosion, then they may be an effect of so-called 'radio lobes'. The galaxy iteslf is sitting in the midst of an ICM at a temperature of ~ 10⁸K, which is fantastically hot (for reasons I will not get into here). In this temperature/energy regime you can see lots of emission in X-rays. Radio bubbles are large globs of material originating from the region near an Active Galactic Nucleus that slowly expand outwards and appear to be buoyant against the gravitational field. As this material (mostly non-thermal electrons) expands outwards, it displaces the surrounding X-ray-emitting material, leaving what appears to be a 'hole' in the X-ray image. These holes that signify the radio bubbles can easily be seen with some of the images taken with the Chandra telescope. A side effect of the expansion of the bubbles could be an interaction between the expanding radio source and the surrounding ICM, forming these filamentary structures on the walls of the radio lobes. There is evidence for this type of phenomenon elsewhere- The galaxy Centaur A appears to exhibit some similar behavior, with filaments surrounding radio lobes.
These filaments provide a connection between the central region of NGC 1275 and the surrounding ICM. In other words, the galaxy is not simply sitting there by itself, neither affecting nor being affected by its surroundings.
I have not yet been able to dig into the relation of the filaments to magnetic fields.

For now I will mostly rely the PowerPoint files of my 'final talk' for the 2004 REU program to do the talking.

Final Presentation (Best Viewed With Internet Explorer)
Final Presentation (A More Mozilla/Netscape-Friendly Version)

For further discussion, here is the poster I presented at the 2005 American Astronomical Society Conference in San Diego. The colors are a bit off, but that's life... Click the image to view the full-size version.

What is Left To Do?

Go over the data again and make sure everything's ship-shape.

The data seem to show an interesting trend where higher fibers give lower velocities. We thought this might be due to some systematic error, so I checked the wavelength of the 6863 Angstrom Oxygen sky line in each fiber for a couple of the scans. The reasoning is this: we expect that spectra in a faraway galaxy will be redshifted. But the Earth's atmosphere is effectively stationary with respect to the telescope for observing purposes, and there should be no redshift. Thus, if certain fibers are showing the stationary sky lines at different wavelengths, we know there is something wrong with the fibers. --> After checking, the sky lines were consistent across all fibers, so it looks like the 'curvy' data are real. We'll try to figure out what this means.
I think I noticed a couple minor corrections that need to be made to the velocity plots - this may require some basic re-reduction. The plots as they are now should be somewhere in the ballpark of 'correct' and useful for instructive purposes. I will correct the data as soon as time allows.

Figure out what kind of physical phenomenon can explain the findings of our data. In other words, we want to explain how these filaments can just sit there and be relatively static.

Compose and submit a paper with our results for peer review.

Get some coffee and pat ourselves on the back. Good job, us.

Acknowledgements and References

I would like to thank the following people (and everyone else who I haven't listed here - you know who you are) who have helped me with my research this summer because without them I couldn't have done it.

* Jay Gallagher *
Daniel Harbeck
Elizabeth Wehner
Ellen Zweibel
Nick Hansen, for help with Photoshop

The following are some of the references and sources I have used in my research and in this webpage:

Papers, etc. (for research material)

Birzan, L., et al.; A Systematic Study of Radio-Induced X-ray Cavities in Clusters, Groups, and Galaxies; Astrophysical J 607:800-809, 2004 June 1
Conselice, C.J., Gallagher, J.S., and Wyse, R.F.G.; On the Nature of the NGC 1275 System; Astronomical J. 122:2281-2300, 2001 November
Graham, John A.; Shocked Gas and Star Formation in the Centaurus A Radio Galaxy; Astrophysical J. 502:245-252, 1998 July 20
Osterbrock, Donald E.; Astrophysics of Gaseous Nebulae and Active Galactic Nuclei; University Science Books, Sausalito, CA, 1989
Sanders, J.S., Fabian, A.C., Allen, S.W., and Schmidt, R.W.; Mapping Small-Scale Temperature and Abundance Structures in the Core of the Perseus Cluster; MNRAS 349:952-972, 2004
Saxton, C.J., Sutherland, R.S., and Bicknell, G.V.; The Centaurus A Northern Middle Lobe as a Buoyant Bubble; Astrophysical J. 536:103-117, 2001 December 10
Zweibel, Ellen G.; Magnetic Bubbles in Space; Nature 415:31-32, 2002 January 3

Websites (for other materials on this page)

...Coming Soon (maybe)

Links

Astronomy Related	My Work Related	Miscellany
NASA ADS Database (for querying references, etc.)	SALT - South African Large Telescope	Wikipedia (Free Online Encyclopedia)
NED (Database of extragalactic objects)	PFIS - Prime Focus Imaging Spectrograph (Main instrument on SALT)	Ben's Bargains - A Must for those who like paying less.
SIMBAD (Astronomical Database)	IRAF - Image Reduction and Analysis Facility	AnimeSuki.com - for anime lovers
NVO - National Virtual Observatory	WIYN Telescope at Kitt Peak, AZ	BitTornado - My favorite incarnation of BitTorrent
APOD - Astronomy Picture of the Day	NOAO - National Optical Astronomical Observatories	Pine Bluff Observatory (PBO)
Some Very Pretty Astronomical Images Taken at Kitt Peak	PBO Observers' Page	UW-Madison Capoeira Club
Heavens-Above.com (for those of you who want to find things like satellites, iridium flares, the ISS, etc.)	My guide to reducing DensePak data	Pictures Section (to be added in the near future)

For Mark:
fibers.pro
300comb.crd

Original from 2004. Last Updated August 12, 2008