Dissecting halo components in IFU data

While most astronomers are now familiar with tools to decompose images into multiple components such as disks, bulges, and halos, the equivalent techniques for spectral data cubes are still in their infancy. This is unfortunate, as integral field unit (IFU) spectral surveys are now producing a mass of data in this format, which we are ill-prepared to analyze effectively. We have therefore been developing new tools to separate out components using this full spectral data. The results of such analyses will prove invaluable in determining not only whether such decompositions have an astrophysical significance, but, where they do, also in determining the relationship between the various elements of a galaxy. Application to a pilot study of IFU data from the cD galaxy NGC 3311 confirms that the technique can separate the stellar halo from the underlying galaxy in such systems, and indicates that, in this case, the halo is older and more metal poor than the galaxy, consistent with it forming from the cannibalism of smaller satellite galaxies. The success of the method bodes well for its application to studying the larger samples of cD galaxies that IFU surveys are currently producing

The formation of lenticular galaxies in nearby clusters

Lenticular (S0) galaxies have long been thought of as evolved spirals, in which the star formation has been suppressed, the spiral arms have faded, and the luminosity of the bulge has been built up relative to the disc. However, the sequence of events that explains these three observations and leads to the formation of the final S0 galaxy is still uncertain. The progenitor spirals generally consist of bulges with old stellar populations surrounded by young, bright discs. Therefore, in order to explain the `quenching' of star formation in the disc and related increase in the bulge luminosity, an understanding of the individual star-formation histories of these two components is vital. In this thesis, we present a new technique to spectroscopically decompose the light from a galaxy into its bulge and disc components, from which the stellar populations and chemical compositions of the individual components can be extracted in order to determine the sequence of events leading to the transformation. Using spectroscopic bulge--disc decomposition, the spatial light profile in a two-dimensional galaxy spectrum can be separated wavelength-by-wavelength into bulge and disc components. This decomposition allows the construction of separate one-dimensional spectra representing purely the light from the bulge and disc, enabling studies of their individual star-formation histories with minimal contamination.This technique was applied to a sample of 30 S0s in the Virgo and Fornax Clusters, and analysis of the absorption line strengths within these spectra reveals that the bulges contain consistently younger and more metal-rich stellar populations than their surrounding discs. This result implies that the final episode of star formation before the progenitor spirals were fully quenched occurred in their central regions. Furthermore, the similarity in the alpha-element abundances of the bulges and discs indicates that the final episode of star formation in the bulge was fuelled using gas that has previously been chemically enriched in the disc. Together, these results present a picture in which the galaxy starts out as a typical spiral, with an old bulge surrounded by a young, star-forming disc. At some point in its life, gas is stripped from the galaxy, suppressing the star formation in the disc and causing the spiral arms to fade without inducing significant amounts of new star formation or disrupting the overall morphology of the galaxy. As the gas is removed, a fraction is also driven into the centre of the galaxy, where it fuels a final star-formation event in the bulge. This final episode of star formation consequently increases the luminosity of the bulge as the disc is already fading, and produces a central young, metal-rich stellar population. We have also shown that it is possible to spectroscopically decompose a galaxy using the different line-of-sight velocity distributions of kinematically distinct components. This technique was applied to NGC~4550, an unusual S0 galaxy in the Virgo Cluster with two counter-rotating stellar discs and a gaseous disc, to separate their individual stellar populations. Analysis of these stellar populations shows that the disc that co-rotates with the ionized gas is brighter and has a significantly younger mean age than the other disc, which are consistent with more recent star formation fuelled by the associated gaseous material. Therefore, the most likely formation mechanism for this galaxy is via an unusual gas accretion or merger scenario that built up a secondary stellar disc in a pre-existing S0 galaxy. The results presented in this thesis shed new light on the sequence of events that leads to the formation of S0 galaxies in cluster environments, and clearly demonstrates the importance of understanding the star-formation histories of the individual components within these galaxies in order to reconstruct the range of mechanisms by which they formed

A Priority Lexicon for Hearing-Impaired Children: Staff Perceptions

The purpose of this study was to identify the priorities assigned to lexical items by staff members who work with hearing impaired children and to characterize those selections. Seventy-three staff members rated individual vocabulary items from two lists previously developed from staff working with hearing- impaired children to create a priority-lexicon. The resulting lexicon was then compared to developmental data from two studies of children having no impairments to determine if a lexicon based on perceived need was consistent with patterns of normal language acquisition

The formation of lenticular galaxies in nearby clusters

Lenticular (S0) galaxies have long been thought of as evolved spirals, in which the star formation has been suppressed, the spiral arms have faded, and the luminosity of the bulge has been built up relative to the disc. However, the sequence of events that explains these three observations and leads to the formation of the final S0 galaxy is still uncertain. The progenitor spirals generally consist of bulges with old stellar populations surrounded by young, bright discs. Therefore, in order to explain the `quenching' of star formation in the disc and related increase in the bulge luminosity, an understanding of the individual star-formation histories of these two components is vital. In this thesis, we present a new technique to spectroscopically decompose the light from a galaxy into its bulge and disc components, from which the stellar populations and chemical compositions of the individual components can be extracted in order to determine the sequence of events leading to the transformation. Using spectroscopic bulge--disc decomposition, the spatial light profile in a two-dimensional galaxy spectrum can be separated wavelength-by-wavelength into bulge and disc components. This decomposition allows the construction of separate one-dimensional spectra representing purely the light from the bulge and disc, enabling studies of their individual star-formation histories with minimal contamination.This technique was applied to a sample of 30 S0s in the Virgo and Fornax Clusters, and analysis of the absorption line strengths within these spectra reveals that the bulges contain consistently younger and more metal-rich stellar populations than their surrounding discs. This result implies that the final episode of star formation before the progenitor spirals were fully quenched occurred in their central regions. Furthermore, the similarity in the alpha-element abundances of the bulges and discs indicates that the final episode of star formation in the bulge was fuelled using gas that has previously been chemically enriched in the disc. Together, these results present a picture in which the galaxy starts out as a typical spiral, with an old bulge surrounded by a young, star-forming disc. At some point in its life, gas is stripped from the galaxy, suppressing the star formation in the disc and causing the spiral arms to fade without inducing significant amounts of new star formation or disrupting the overall morphology of the galaxy. As the gas is removed, a fraction is also driven into the centre of the galaxy, where it fuels a final star-formation event in the bulge. This final episode of star formation consequently increases the luminosity of the bulge as the disc is already fading, and produces a central young, metal-rich stellar population. We have also shown that it is possible to spectroscopically decompose a galaxy using the different line-of-sight velocity distributions of kinematically distinct components. This technique was applied to NGC~4550, an unusual S0 galaxy in the Virgo Cluster with two counter-rotating stellar discs and a gaseous disc, to separate their individual stellar populations. Analysis of these stellar populations shows that the disc that co-rotates with the ionized gas is brighter and has a significantly younger mean age than the other disc, which are consistent with more recent star formation fuelled by the associated gaseous material. Therefore, the most likely formation mechanism for this galaxy is via an unusual gas accretion or merger scenario that built up a secondary stellar disc in a pre-existing S0 galaxy. The results presented in this thesis shed new light on the sequence of events that leads to the formation of S0 galaxies in cluster environments, and clearly demonstrates the importance of understanding the star-formation histories of the individual components within these galaxies in order to reconstruct the range of mechanisms by which they formed

BUDDI-MaNGA III: The mass-assembly histories of bulges and discs of spiral galaxies

The many unique properties of galaxies are shaped by physical processes that affect different components of the galaxy - like the bulges and discs - in different ways, and leave characteristic imprints on the light and spectra of these components. Disentangling their spectra can reveal vital clues that can be traced back in time to understand how galaxies, and their components, form and evolve throughout their lifetimes. With BUDDI, we have decomposed the IFU datacubes in SDSS-MaNGA DR17 into a S\'ersic bulge component and an exponential disc component and extracted their clean bulge and disc spectra. BUDDI-MaNGA is the first and largest statistical sample of such decomposed spectra of 1452 galaxies covering morphologies from ellipticals to late-type spirals. We derived stellar masses of the individual components with SED fitting using BAGPIPES and estimated their mean mass-weighted stellar metallicities and stellar ages using pPXF. With this information in place, we reconstructed the mass assembly histories of the bulges and discs of the 968 spiral galaxies (Sa-Sm Types) in this sample to look for systematic trends with respect to stellar mass and morphology. Our results show a clear downsizing effect especially in the bulges, with more massive components assembling earlier and faster than the less massive ones. Additionally, on comparing the stellar populations of the bulges and discs in these galaxies, we find that a majority of the bulges host more metal-rich and older stars than their disc counterparts. Nevertheless, we also find that there exists a non-negligible fraction of the spiral galaxy population in our sample with bulges that are younger and more metal-rich than their discs. We interpret these results, taking into account how their formation histories and current stellar populations depend on stellar mass and morphology.Comment: 30 pages, 17 figures, accepted for publication in A&A; typos correcte

A Systematic Review of Published Respondent-Driven Sampling Surveys Collecting Behavioral and Biologic Data.

Reporting key details of respondent-driven sampling (RDS) survey implementation and analysis is essential for assessing the quality of RDS surveys. RDS is both a recruitment and analytic method and, as such, it is important to adequately describe both aspects in publications. We extracted data from peer-reviewed literature published through September, 2013 that reported collected biological specimens using RDS. We identified 151 eligible peer-reviewed articles describing 222 surveys conducted in seven regions throughout the world. Most published surveys reported basic implementation information such as survey city, country, year, population sampled, interview method, and final sample size. However, many surveys did not report essential methodological and analytical information for assessing RDS survey quality, including number of recruitment sites, seeds at start and end, maximum number of waves, and whether data were adjusted for network size. Understanding the quality of data collection and analysis in RDS is useful for effectively planning public health service delivery and funding priorities