Integral-Field Spectroscopy of High-Redshift Galaxies: Implications for Early Galaxy Evolution

Nesvadba, Nicole (2006): Integral-Field Spectroscopy of High-Redshift Galaxies: Implications for Early Galaxy Evolution. Dissertation, LMU München: Fakultät für Physik

Abstract

Several lines of evidence suggest that the most active phase of galaxy evolution, especially in the most massive systems, was largely completed by $z\sim 1$. This results, e.g., from the observation that the most massive galaxies at low redshift have very old stellar populations ($\sim 10$ Gyr) and very little gas to fuel subsequent star formation. Similarly, active galactic nuclei (AGN) were more numerous and brighter in the early universe. Ultimately, the direct observation of high-redshift galaxies will be the only way to understand which processes shaped the universe we see today, in spite of the rich ``fossil'' data sets we have of the Milky Way and neighboring galaxies. Thanks to the new $8-10$ m telescope class and novel instrumentation, including SPIFFI/SINFONI on the VLT, individual galaxies at redshifts $z\sim 1-3$ ($2-6$ Gyr after the Big Bang) are now within the reach of astronomical spectrographs. Methodologically, this thesis focuses on the analysis of spectrally and spatially resolved optical emission lines, first of all \ha\ and [OIII]\lam5007, which are shifted into the near-infrared. {\sc Spiffi / Sinfoni} is very suited to such a programme, because it records the spectra of a contiguous field of view of up to 8\arcsec$\times$8\arcsec. The internal kinematic and chemical gradients within a galaxy can thus be measured in a single observation. Galaxies in the early universe had particularly high star-formation rates, so that many targets are bright optical line emitters. Internal kinematics are measured through the Doppler effect, line profiles and widths indicate the presence of an AGN, galactic ``superwinds'' and the relationship of chaotic to ordered motion. Star-formation rates are measured from the luminosity of the Balmer lines, especially \ha. Characteristic line ratios indicate the presence of an AGN, chemical composition, and electron densities in the ISM, and they allow to distinguish shocks and photoionization. This thesis is a pilot study: It comprises 9 galaxies that fulfill a variety of selection criteria: they are either bright UV or submillimeter emitters, or they are radio-loud. Perhaps the most fundamental result is that gravity (dominated by dark matter) is the main driver of early galaxy evolution, but it is not the only important process. Star formation and AGN cause hydrodynamical feedback processes, which might be a sign of self-regulated galaxy evolution. It is found that star-formation related feedback had similar properties at low and high redshift, but that AGN-driven gas expulsion might have played a major role in the high-redshift evolution of galaxies, that is without low-redshift equivalent. Another important result is the rotation curve we find in the central kiloparsec of a gravitationally lensed UV-selected galaxy. Velocity gradients of $\sim 100$ \kms\ have been observed in many high-redshift galaxies, but the interpretation as rotation curves is generally not unique. Given the relatively coarse spatial resolution of high-redshift galaxy data, two nearby galaxies, maybe interacting or undergoing a merger, might blend into one smooth velocity gradient. Galaxy mergers are an important ingredient of the ``hierarchical model'', the current paradigm of structure formation, and therefore nearby galaxy pairs were likely more common at high redshift than they are today. The large similarity of the lensed rotation curve with those of nearby galaxies might be a first sign that galaxies evolved inside-out.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Keywords: Astronomy Cosmology, Galaxy Evolution, Integral-Field Spectroscopy
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 530 Physik
• Fakultäten: Fakultät für Physik
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 6. Juni 2006
• 1. Bericht­erstatter:in: Genzel, Reinhard