A Short Description of My PhD Research
| High Spatial Resolution Velocity Fields of Low Surface Brightness Galaxies and the Density Profiles of Dark Matter Halos | |
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The goal of this program is to determine the mass distribution rho(r) of the
dark matter halos of a large sample of dark matter-dominated low surface
brightness galaxies, with emphasis on low mass dwarf galaxies. I am obtaining
high resolution two-dimensional velocity fields using the DensePak Integrated
Field Unit on the WIYN telescope at Kitt Peak National Observatory. DensePak
provides the necessary sub-kpc resolution of the cores of the galaxies, while
simultaneously providing the two-dimensional information which will reveal the
dynamical center, the presence of non-circular motions, and a pinching of
isovelocity contours characteristic of the cuspy NFW halo, if one is present.
Also being used are the Kitt Peak 2.1meter telescope to obtain BVRI
photometry of the galaxies, enabling mass and stellar population modeling, and
the long-slit capabilities of the RC Spectrograph on the Kitt Peak 4meter
telescope to obtain rotation curves to larger radii than probed by DensePak.
By combining the high resolution DensePak two-dimensional velocity fields of
the cores of the galaxies with more extended long-slit Halpha and HI 21cm
observations, a direct measurement of rho(r) for the dark matter will be
obtained. These results will be used to test the predictions of the
simulations of CDM halos. If cuspy NFW halos are found, good constraints can
be put on halo concentrations and cosmological parameters. The observations
can also be used to quantify concerns of systematic errors. Shown on the right is the DensePak Halpha velocity field for low surface brightness galaxy UGC 4325.
For a longer description of this project, including
some background information, click here.
A related paper has been submitted to
ApJ: |
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Previous Projects:
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Oxygen Abundances and Chemical Evolution in Low Surface Brightness Galaxies
de Naray, Rachel Kuzio, McGaugh, Stacy S., de Blok, W.J.G. 2004, MNRAS, 355, 887 (link to paper) |
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. |
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| Primordial Helium Abundances in Low Surface Brightness Galaxies | |
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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. |
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Population Synthesis Code for Planetary Nebulae Ciardullo, R., Kuzio, R.E., Simone, A. 2001 Bull. AAS, 33, 1510 (link to paper) |
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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.
Shown on the right is Dr. Robin Ciardullo's Hubble Space Telescope image of
planetary nebula NGC 7027.
(link to Robin's
page) |
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