Research

Previous Projects:

PhD Thesis: High Resolution Optical Velocity Fields of Low Surface Brightness Galaxies and the Density Profiles of Dark Matter Halos

This dissertation investigates the behavior of cold dark matter (CDM) on galaxy scales. We present well-resolved Ha velocity fields of the central regions of 17 dark matter-dominated low surface brightness (LSB) and dwarf galaxies observed with the DensePak Integrated Field Unit. We derive rotation curves from the two-dimensional data and compare them to published long-slit and HI rotation curves. We find broad consistency between the independent data sets. Under several assumptions about the velocity contribution from the baryons, we fit the dark matter component with cuspy NFW and cored pseudoisothermal halos. We find the data to be better described by cored dark matter halos. For the majority of galaxies, NFW halo fits either cannot be made or the implied concentrations are too low for LCDM. The shapes of the NFW rotation curves are also inconsistent with the galaxy rotation curves. We find that CDM predicts a substantial cusp mass excess near the centers of the galaxies and that the ratio of predicted to observed dark matter increases as baryons become more important. We investigate claims that systematic effects including beam smearing, slit misplacement and noncircular motions are responsible for slowly rising long-slit and HI rotation curves. We find the DensePak rotation curves to also be slowly rising, supporting the idea that this is an intrinsic feature of LSB rotation curves. We also model the two-dimensional NFW halo and test several modifications to the potential in an attempt to simultaneously reconcile both the NFW velocity field and rotation curve with observed galaxy data. We present mock DensePak velocity fields and rotation curves of axisymmetric and non-axisymmetric potentials. We find that a non-axisymmetric NFW potential with a constant axis ratio can reduce the cusp mass excess in the observed galaxy data, but the observer's line-of-sight must be along the minor axis of the potential, and the NFW pinch is not erased from the velocity field. We find that a non-axisymmetric NFW potential with a radially varying axis ratio tends to wash out the NFW pinch but introduces a twist to the velocity field. Shown on the right is the DensePak Halpha velocity field for low surface brightness galaxy UGC 4325. Related Papers: High Resolution Optical Velocity Fields of 11 Low Surface Brightness Galaxies   Kuzio de Naray, R., McGaugh, S.S., de Blok, W.J.G., & Bosma A. 2006, ApJS, 165, 461 pdf Mass Models for Low Surface Brightness Galaxies with High Resolution Optical Velocity Fields   Kuzio de Naray, R., McGaugh, S.S., & de Blok, W.J.G. 2008, ApJ, 676, 920 pdf The Rotation Velocity Attributable to Dark Matter at Intermediate Radii in Disk Galaxies   McGaugh, S.S., de Blok, W.J.G., Schombert, J.M., Kuzio de Naray, R., Kim, J.H. 2007, ApJ, 659, 149 pdf (return to top)

Oxygen Abundances and Chemical Evolution in Low Surface Brightness Galaxies

In this project, we used optical long-slit spectra to measure the oxygen abundances of the HII regions in a sample of low surface brightness (LSB) galaxies. We used three techniques to measure the abundances: the O[III] direct abundance measure, the R23 strong line method, and the Equivalent Width method. We also used three approaches to investigate the galactic chemical evolution of the LSB galaxies: the luminosity-metallicity (L-Z) relation, the mass-metallicity relation, and the oxygen abundance versus gas mass fraction. We found our sample of LSB galaxies to be metal-poor with high gas mass fractions. This implies that the galaxies are at an early stage in their evolution. We also found the L-Z relation of the LSB galaxies to not be significantly different from the L-Z relation of other galaxy types. Shown on the right is an Halpha image of the low surface brightness galaxy UGC 1230 with the observed HII regions labeled along the slit. Related Papers: Oxygen Abundances and Chemical Evolution in Low Surface Brightness Galaxies   Kuzio de Naray, R., McGaugh, S.S., & de Blok, W.J.G. 2004, MNRAS, 355, 887 ps (return to top)

Primordial Helium Abundances in Low Surface Brightness Galaxies

Selected for their high ionizations, low metallicity extragalactic HII regions and diffuse, ionized gas in blue compact galaxies have traditionally been the objects studied when measuring the primordial helium abundance. To test whether or not different types of objects give consistent determinations of the primordial helium abundance, we studied a sample of low metallicity HII regions in LSB galaxies. Our HII regions were chosen because they have lower mean ionizations. Though the error on our measure of the helium abundance was too large to make any significant cosmological statements, we did find that a sample of objects with low mean ionizations do not give significantly different results than objects with high ionization. Shown on the right is the red end of the optical emission line spectrum of an HII region. The helium HeI(5876), hydrogen Halpha, nitrogen [NII]6584 and sulfur [SII]6717,6731 emission lines are indicated. (return to top)

Population Synthesis Code for Planetary Nebulae

For my senior honors thesis at Penn State, I wrote a population synthesis program designed to probe the chemical and star formation history of a galaxy via its planetary nebulae (PN). The code creates fully-described PN at random times in their evolutionary history. Initial mass-final mass relations determine the final mass of the PN central stars and post-asymptotic giant branch stellar evolutionary tracks determine the temperature and luminosity of the PN central star and the radius and density of the nebula. The CLOUDY photoionization code is integrated into the program and is called to generate the emission line strengths for the PN. The program output can be used to study the Planetary Nebula Luminosity Function (PNLF) and serve as a comparison to the populations of PN observed in actual galaxies. Related Papers: A Population Synthesis Code for Planetary Nebulae Ciardullo, R., Kuzio, R.E., Simone, A. 2001 Bull. AAS, 33, 1510 (abstract) Planetary Nebula Luminosity Function and Cepheid Distance Scale I have used optical [OIII]5007 images to determine the planetary nebula luminosity function (PNLF) distances to M33, NGC 2403 and NGC 3627. The planetary nebulae (PN) are identified by blinking between the on-band [OIII]5007 image and an off-band image. If it appears in the on-band image and disappears in the off-band image, it is a PN. The apparent magnitudes of the PN are used to construct the PNLF for each galaxy and to derive a distance estimate. The PNLF distances were then compared to the Cepheid distance scale. Shown on the right is Dr. Robin Ciardullo's Hubble Space Telescope image of planetary nebula NGC 7027. (link to Robin's page) Related Papers: Planetary Nebulae as Standard Candles. XII. Connecting the Population I and Population II Distance Scales   Ciardullo, R., Feldmeier, J.J., Jacoby, G.H., Kuzio de Naray, R., Laychak, M.B., Durrell, P.R. 2002, ApJ, 577, 31 (ADS) Planetary Nebula Luminosity Funtion Distances to M33, NGC 2403 and NGC 3627 and a Comparison to the Cepheid Distance Scale Kuzio, R.E., Ciardullo, R., Feldmeier, J.J., Jacoby, G.H. 1999 Bull. AAS, 31, 1391 (abstract) (return to top)