THE INTERACTION BETWEEN THE INTRACLUSTER MEDIUM AND THE CLUSTER STELLAR CONTENT
Committee ChairRieke, Marcia
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PublisherThe University of Arizona.
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AbstractWe study specific aspects of the relationship between the stellar content and the intracluster media (ICM) of galaxy clusters. First, we attempt to solve the long-standing difficulty in explaining the highly enriched ICM by including a previously unaccounted for stellar component: the intracluster stars. To determine the relative contributions of galactic and intracluster stars to the enrichment of the intracluster medium (ICM), we present X-ray surface brightness, temperature, and Fe abundance profiles for a set of twelve galaxy clusters for which we have extensive optical photometry. Assuming a standard IMF and simple chemical evolution model scaled to match the present-day cluster early-type SN Ia rate, the stars in the brightest cluster galaxy (BCG) plus the intracluster stars (ICS) generate 31⁺¹¹₋₉%, on average, of the observed ICM Fe within r₅₀₀(∼ 0.6 times r₂₀₀, the virial radius). Because the ICS typically contribute 80% of the BCG+ICS Fe, we conclude that the ICS are significant, yet often neglected, contributors to the ICM Fe within r₅₀₀. However, the BCG+ICS fall short of producing all the Fe, so metal loss from stars in other cluster galaxies must also contribute. By combining the enrichment from intracluster and galactic stars, we can account for all the observed Fe. These models require a galactic metal loss fraction (0.84(−0.14)^(+0.11)) that, while large, is consistent with theoretical models of Fe mass not retained by galactic stars. The SN Ia rates, especially as a function of galaxy environment and redshift, remain a significant source of uncertainty in further constraining the metal loss fraction. Second, we study the effects of ram-pressure stripping on infalling galaxies using a warm molecular hydrogen (H₂) as a tracer by carrying out a Spitzer infrared spectrograph (IRS) survey of four galaxies with signatures of ram-pressure stripping. We have discovered two galaxies, ESO 137-001 and NGC 4522, with warm H₂ tails stretching 20 kpc and 4 kpc in length, respectively. In the case of ESO 137-001 where we measure a warm H₂ mass loss rate of ∼ 2 − 3 M⊙ yr⁻¹, we estimate that the galaxy will lose all of its gas in a single pass through the cluster core. Strong warm H₂ emission is detected in one other galaxy, CGCG 97-073, which a region within its tail that is mainly dominated by H₂ emission. The warm H₂ observed in these three galaxies share similar temperature and column density properties with warm H₂ masses ranging from 10⁶ − 10⁸ M⊙. From a comparison with the SINGS warm H₂ sample, our results indicate that these galaxies experiencing significant ram-pressure stripping show anomalously high warm H₂ emission that cannot be explained purely from star formation. This adds credence to the hypothesis that H₂ within these galaxies is being shock-heated from the interaction with the ICM. We also discover that stripping of warm and hot dust, as measured at 8 μm and 24 μm, is a common feature of the galaxies observed in our sample. In the case of NGC 4522, we capture the turbulent nature of the stripping process. We measure the star formation rates using published Hα and measured 24 μm luminosities for all of our galaxies and find that some of them have suppressed star formation rates compared to similar mass counterparts in the field. We find a possible association between Hα and warm H₂ emission in three of the four galaxies observed. We conclude that the variation of H₂ properties observed in our sample is likely due to the galaxies being in different stages of ram-pressure stripping. Finally, we report on our efforts to improve the performance of the Lochkeed Arizona Infrared Spectrometer (LAIRS), a near-IR, tunable filter imager. We have made significant progress in identifying the sources of key issues such as the a highly asymmetric line profile and the unstable performance of the servo controller at the MMT. Solutions have been implemented for these issues, such as a revised mounting strategy for the tunable filter plates and a completely new controller with higher bandwidth. Significant progress has been made towards resolving these issues, but a few issues remain before LAIRS meets all of its requirements.