Current & Past Research Projects

The framework of large scale structure formation relies heavily on the idea of cold dark matter (CDM). The predictions of CDM on large scales seem to be consistent with observations, but it is not readily apparent that the theory's success extends to small (galaxy) scales. The velocity fields, rotation curve shapes and dark matter halo central densities of low surface brightness (LSB) galaxies are typically more consistent with round, cored dark matter halos than the triaxial, cuspy CDM halos predicted by numerical simulations. Discrepancies between the expected properties of CDM halos and galaxy observations are not exclusive to dark matter-dominated LSB galaxies; all normal spiral galaxies are found to reside in underdense halos. Reconciling the predictions of numerical simulations with observations of dark matter-dominated and spiral galaxies is thus currently one of the greatest challenges for CDM.

 The Role of Baryons in LSB Galaxy Evolution
The addition of baryonic physics to simulations of galaxy formation has been instrumental in producing realistic massive and Milky Way-analog disk galaxies that are bulgeless or only moderately bulged. Additionally, in recent simulations of dwarf galaxies, processes that remove or redistribute baryons during galaxy formation have been shown to alter the inner shape (triaxial to more spherical) and density structure (cuspy to more core-like) of dark matter halos. It therefore seems that baryons may be integral to easing the tension between observations and theoretical expectations of CDM halo structure.

I am interested in using observational constraints on the unique star formation histories, structure, and kinematics of LSB galaxies to evaluate the plausibility that baryons can modify the dark matter halos of these galaxies. Are the observed properties of LSB galaxies such as gas-richness, low gas surface densities, low past and current star formation rates, blue colors, and low metal abundances consistent with galaxies which have undergone periods of star formation and baryonic mass loss via outflows?

To answer these questions, we have begun the MUSCEL (MUltiwavelength observations of the Structure, Chemistry, and Evolution of LSB galaxies) program. For details, please see our program webpage: click here for MUSCEL details

Related Papers:

  • The Distribution of Star Formation and Metals in the Low Surface Brightness Galaxy UGC 628
      Young, J.E., Kuzio de Naray, R. & Wang, S.X. 2015, MNRAS, 452, 2973
      astro-ph   MNRAS
  • Do Baryons Alter the Halos of Low Surface Brightness Galaxies?
      Kuzio de Naray, R. & Spekkens, K. 2011, ApJ, 741, L29
      astro-ph   ApJL

 The Structure of Spiral Galaxies
RINGS: The RSS Imaging spectroscopy Nearby Galaxy Survey

With the recently re-commissioned RSS spectrograph on SALT, we are anticipating high-resolution Fabry-Perot Halpha velocity fields of 19 nearby, normal spiral galaxies. We will combine these optical kinematic data with HI kinematic data and optical and near-infrared photometry to constrain the concentration, size and ellipticity of the dark halo. We are also interested in determining how non-circular flows and processes like star formation and related feedback influence the observed structure of galaxies (bars, rings, etc).

DiskFit: A Code for Modeling Asymmetries in Disk Galaxies

DiskFit is a code for modelling asymmetries in either photometry (fitting images) or kinematics (fitting velocity fields) of disk galaxies. For more details, see the DiskFit webpage.

Related Papers:

  • The RINGS Survey. I. Halpha and HI Velocity Maps of Galaxy NGC 2280
      Mitchell, C.J., Williams, T.B., Spekkens, K., Lee-Waddell, K., Kuzio de Naray, R. & Sellwood, J.A. 2015, AJ, 149,116
      astro-ph   AJ
  • Searching for Non-axisymmetries in NGC 6503: A Weak End-on Bar
      Kuzio de Naray, R., Arsenault, C.A., Spekkens, K., Sellwood, J.A., McDonald, M., Simon, J.D., & Teuben, P.
      2012, MNRAS, 427, 2523
      astro-ph   MNRAS

 Dark Matter in LSB Galaxies: Simulations & Alternatives to CDM
As an NSF Astronomy & Astrophysics Postdoctoral Fellow at the Center for Cosmology at the University of California, Irvine, my collaborators and I worked to constrain the properties of dark matter halos formed in numerical simulations. We integrated my LSB galaxy velocity field observations into numerical simulations to probe the shape of the dark matter potential (spherical vs. triaxial), the density profile of the halo (cuspy vs. cored), and to determine the effects of baryonic processes (supernova feedback). We also explored models of thermal and non-thermal warm dark matter and self-interacting dark matter that naturally produce cored halos.

Related Papers:

  • Recovering cores and cusps in dark matter haloes using mock velocity field observations
      Kuzio de Naray, R. & Kaufmann, T. 2011, MNRAS, 414, 3617
      astro-ph   MNRAS
  • Comparing the Dark Matter Halos of Spiral, Low Surface Brightness and Dwarf Spheroidal Galaxies
      Walker, M.G., McGaugh, S.S., Mateo, M., Olszewski, E., & Kuzio de Naray, R. 2010, ApJ, 717, L87
      astro-ph   ApJL
  • The Case Against Warm or Self-Interacting Dark Matter as Explanations for Cores in Low Surface Brightness Galaxies
      Kuzio de Naray, R., Martinez, G.D., Bullock, J.S., & Kaplinghat, M. 2010, ApJ, 710, L161
      astro-ph   ApJL
  • Constraining the NFW Potential with Observations and Modeling of LSB Galaxy Velocity Fields
      Kuzio de Naray, R., McGaugh, S.S., & Mihos, J.C. 2009, ApJ, 692, 1321
      astro-ph   ApJ

 Kinematic and Photometric Evidence for a Bar in NGC 2683
Boxy/peanut-shaped bulges and figure-of-eight position-velocity diagrams (PVDs) have been connected to the presence of bars in edge-on galaxies. We have observed the edge-on spiral NGC 2683 with the RC Spectrograph on the Kitt Peak 4m and the SparsePak IFU on the WIYN telescope. Both the long-slit PVD and the Halpha velocity field show complex kinematics consistent with the presence of a bar.

Related Papers:

  • Kinematic and Photometric Evidence for a Bar in NGC 2683
      Kuzio de Naray, R., Zagursky, M.J., & McGaugh, S.S. 2009, AJ, 138, 1082
      astro-ph   AJ

 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.

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
      astro-ph   ApJS

  • 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
      astro-ph   ApJ

  • 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
      astro-ph   ApJ

 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.

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
      astro-ph   MNRAS

 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.

 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

Image Credit: Robin Ciardullo
 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.

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
      astro-ph   ApJ
  • 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