Galaxy Research Summary

Choose The Basics (rated G for general audiences) ...or... The Details (for the cognoscente)

The Basics

How do galaxies evolve, and why do they look the way we see them today? On our own Local Group of Galaxies there are a wide variety of galaxies, each composed of 1 to 100 billion stars. There are...
m31 ... large spiral galaxies, like the Andromeda Galaxy, M31, our nearest large neighbor...
...roundish, fuzzy, and rather small elliptical like galaxies... NGC205
NGC2363 ...and irregularly-shaped dwarf galaxies with bright regions of young, massive stars just recently formed in the last few million years.
In a nutshell, galaxies begin as clouds of hydrogen and helium gas which are turned into stars as the galaxy "ages". Stars generate energy by the nuclear fusion process, transforming hydrogen and helium into heavier elements like carbon, nitrogen, oxygen, and even iron. When most stars exhaust their supply of nuclear fuel, they undergo spectacular and violent phenomena we call nova or supernova explosions, or planetary nebulae ejections. By these processes, stars return most of their material, including the newly-synthesized heavy elements essential for life as we know it, back into interstellar space whereupon the whole process begins again.

As an observational astronomer, I study the stars and gas in galaxies to understand the interplay between stars and gas that shape the appearance of a galaxy. Facilities I've used include optical and infra-red observatories at...

Using radio telescope facilities at...

...I have conducted studies of the atomic hydrogen and molecular (carbon monoxide) gas in galaxies. Such observations show that often collisions and interactions between galaxies trigger star formation bursts and drastically alter their appearance.

Some observations cannot be made from the surface of the earth and require orbiting satellite observatories. The Hubble Space Telescope has been crucial for making observations in ultraviolet light that are not possible from ground-based telescopes. My collaborators and I use the orbitting Chandra X-Ray Observatory to conduct X-ray observations of hot, million degree gas heated by supernova explosions and galaxy collisions. We also use the Spitzer Space Telescope.

Understanding the evolution of galaxies requires ...
smc a detailed knowledge of individual galaxies in the nearby universe such as our near neighbor, the dwarf galaxy named the Small Magellanic Cloud located just 150,000 light years from the Milky Way...
...and an investigation of galaxies at the edge of the observable universe which we see as they were billions of years ago when galaxies first began to form. hdf

Using a variety of observational techniques, I am seeking to understand the physical processes that transform objects in the distant universe into the galaxies all around us. My research program involves understanding the chemical composition of stars and gas in galaxies, the physics of star formation, and the dynamics of stars and gas as galaxies are assembled and torn apart.

Students of all levels work with me on astronomical research projects at telescopes here and around the world.

  • At WIRO
  • At Red Buttes
  • At Kitt Peak

    The Details

    The Evolution of Star-Forming Galaxies:
    A Research Program in Star Formation and Galaxy Evolution
    Understanding the origin of galaxies in the early universe and their evolution to the present time is one of the fundamental astrophysical challenges of this decade. A dominant paradigm is still emerging. Are large galaxies built primarily by accretion of smaller proto-galaxies? Was there a specific epoch when most galaxies formed? Are internal (star formation) or external (cluster and environment) forces the dominant influences on a galaxy's evolution? What are the conditions and triggers that drive star formation? My research programs are designed to answer these questions by integrating our knowledge of the dynamical and chemical properties of nearby star-forming regions with those in the distant universe. I focus on three main areas relating to these origins themes. 1) Galaxy kinematics and chemistry in the distant universe, 2) the impact of star formation on the ISM of galaxies, and 3) the formation of massive stars and star clusters. They make use of the ultraviolet capabilities of the HST + STIS/Cosmic Origins Spectrograph, the X-ray spectroscopic capabilities of Chandra/XMM, and the new generation of instrumentation on large ground-based telescopes like Gemini which I am eager to help develop so that this science may proceed. hdf

    Chemical/Dynamical Evolution in the Early Universe

    One fruitful approach to understanding how galaxies evolve is through the study of the fundamental galaxy scaling relations: correlations between luminosity, size, mass (as traced by velocity width), and metallicity. The advent of 6-10 m class telescopes and infrared spectrographs make chemical and kinematic analysis at high redshift a potent way to probe the evolution of the universe ( Kobulnicky, Kennicutt, & Pizagno 1998 , Kobulnicky & Phillips 2004 ). In order to connect the chemical properties in the early universe inferred from QSO absorption line studies with the chemical enrichment scenarios envisioned for local galaxies, I have initiated a program using the Keck telescopes with multi-object optical and infrared spectrographs to directly measure the chemical properties of star-forming galaxies at high redshifts using emission lines from H II regions. Some initial results at intermediate redshifts (z=0.4) show that chemical enrichment is strongly correlated with a galaxy's optical luminosity and mass, and that chemical abundance ratios can constrain the future evolutionary path of star-forming systems observed at earlier epochs ( Kobulnicky & Zaritsky 1999 ). More extensive studies of hundreds of galaxies over the redshift range z=0.2 - 1.0 show that galaxies at 10 Gyr lookback times are significantly brighter and less chemically enriched compared to local galaxies of comparable mass and luminosity ( Kobulnicky et al. 2003; Kobulnicky & Kewley 2004 ) At higher redshifts near z=0.8 to z~3, there appears to be significant evolution of fundamental galaxy scaling relations ( Kobulnicky & Koo 2001), but so far only a few of the most luminous objects have been studied. In the next few years, I plan to be developing and using the capabilities of multi-object optical and infrared spectrographs on ground-based telescopes like Gemini to measure the chemical content and spatially-resolved kinematics of distant galaxies. These kinds of observations constitute the best tests of numerical and semi-analytic models of galaxy and structure formation in the early universe.

    The Life Cycles of Matter in Local Galaxies

    In the local universe, galaxy interactions and starburst-driven winds are often invoked as feedback mechanisms for regulating star formation rates, removing gas from galaxies, transforming one type of galaxy into another, or expelling metal rich gas from galaxies with shallow potential wells. These same mechanisms must play an even larger role in driving the evolution of galaxies in the early universe, yet, their impact in well-studied nearby galaxies is not yet clear. Local starforming galaxies are chemically homogeneous on scales of <2 kpc ( Kobulnicky & Skillman 1996, 1997 ) despite the presence of concentrated starbursts which should give rise to large localized chemical enhancements (Kobulnicky et al. 1997 ). Starburst-driven winds drive freshly-synthesized heavy elements on a long (100 Myr) excursion into galactic halos before they are mixed back into the ISM and participate in subsequent generations of star formation. How effective is the feedback phenomenon that regulates the star formation rate in galaxies and shapes their evolutionary paths? In some galaxies we see clear evidence of freshly-produced heavy elements synthesized in the current burst of star formation being expelled from galaxies in a hot 1-million K phase (Martin, Kobulnicky, & Heckman 2002) . This work was featured in a Chandra X-Ray Observatory Press release and by Astronomy Picture of the Day My collaborators and I have also begun a campaign of HST/Cosmic Origins Spectrograph observations and FUSE archival data of local galaxies to probe the chemical content and ionization properties of gas in the halos of nearby galaxies.

    The Gas Dynamics and Content of Galaxies

    Local galaxies with high star formation rates are often the products of galaxy mergers. Tell-tale tidal tails are often seen in the neutral hydrogen gas kinematics ( Kobulnicky & Skillman 1995 ) or in the molecular gas dynamics. A galaxy's position within a cluster may have a strong influence on its interaction history, and on its ability to retain interstellar material. The gas content of galaxies at higher redshifts is particularly important since the amount of raw material for star formation which remains determines the future evolutionary path. We are engaged in a program to measure the neutral hydrogen content of compact star-forming galaxies at $z$=0.05--0.2 to determine if they may be the progenitors to todays spheroidal galaxies (Kobulnicky & Gebhardt 2000 ) and (Pisano, Kobulnicky et al. 2001). Using Hubble Space Telescope archive data and Keck telescope spectroscopy, I am surveying the gaseous and chemical properties of cluster galaxies over a range of redshift and cluster environments to understand the impact of environment on galaxy evolution. Two sample galaxies with the highest N/O ratios, NGC 5253 and II Zw 40, appear to be among the youngest starbursts known, judging from the flat, thermal nature of the radio continuum. Making use of new VLA high resolution continuum imaging, and data from the VLA archives, I have been working to reconstruct the burst history of the proto-typical Wolf-Rayet galaxy, Henize 2-10 and determine the nature of its compact radio and ultraviolet knots ( Kobulnicky et al. 1995 ).

    The Galactic ISM

    The small-scale and thermodynamic structure in the interstellar medium of the Milky Way and Magellanic Clouds provide important clues for understanding the energy balance in galaxies at all cosmic epochs. I conducted some of the first millimeter-wave molecular absorption observations against extragalactic background sources ( Kobulnicky, Dickey & Akeson 1995 ) through the plane of the Galaxy, revealing remarkably similar structures on lines of sight that probe scales from 1 pc to 1 AU! These data show no evidence for extremely cold molecular gas at large galactocentric radii claimed by some researchers, but they do show that the molecular gas seen in absorption in the Cygnus rift is rotationally very cold (8 K). The Magellanic Clouds also show cold gas condensations even in the tenuous Bridge region, providing evidence that star formation may take place in a wide range of environments ( Kobulnicky & Dickey 1999 ). A more extensive HI and OH survey of the Galactic Plane and the Magellanic Bridge region is underway.
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