The majority of galaxy formation studies which explore beyond local redshifts do not typically probe down to the dwarf galaxy stellar mass range of ∼ 10^9 Msun . Thus trends in the observed evolution or characteristics of galaxy formation at a particular epoch are based upon populations of massive galaxies. However the currently favored Λ-Cold Dark Matter (Λ-CDM) theory is based upon hierarchical clustering and merging of lower mass systems, which proceed to make the higher mass, complex morphology of galaxies we observe. Thus it is clear that within the dwarf galaxy mass regime there should be a significant phase of galaxy formation and evolution. This work aims to uncover the influence of local environment on the formation and evolution of dwarf and massive galaxies beyond local redshift, probing down to a mass range lower than that which has been explored by previous studies. A previously successful study titled the Redshift One LDSS-3 Emission line Survey (ROLES), released results for a redshift of z ∼ 1, which compared the [OII] luminosity and galaxy stellar mass functions ([OII] LF and GSMF respectively), star formation rate density (SFRD), and specific star formation rate (sSFR) relations, with a local SDSS dataset. This led to the expansion of the study to lower redshift (this work) which explored low stellar mass galaxies at a redshift of z ∼ 0.75. This follow-up study referred to as ROLES75 (z ∼ 0.75) targeted the same two deep fields explored by the z ∼ 1 study (GOODS-South, MS1054-03 FIRES), which have extensive public photometry. Low mass targets were selected for study by their K-magnitudes (22.5 < KAB < 24) leading to a dwarf mass range of 8.5 < Log(M∗/Msun) < 9.5, and which were most likely to be within our redshift range (0.62 < z < 0.885). Follow-up multi-object spectroscopy targeted the [OII]λ3727A emission line star formation tracer in these targets allowing us to identify and obtain secure spectroscopic redshifts, SED-fit stellar masses and observed [OII] luminosity calibrated star formation rates down to limits of Log(M∗/Msun) ∼ 8.85 and SFR ∼ 0.1 Msun/yr . Science results presented here are similar to those published by the ROLES z ∼ 1 study, however we also studied the influence of the high versus low density environment in which the galaxy populations reside. This study confirmed that while the [OII] luminosity was higher in earlier times, environment does not influence galaxy formation at z ∼ 0.75. The faint-end slope of the [OII] LF, α ∼ 1.25 measured here, is also observed to become increasingly more steep with increasing redshift. The [OII] luminous GSMF is observed to not have significantly evolved since z ∼ 2.75, confirming the result of the previous ROLES work. However the impact of environment on the GSMF is apparent in the high mass end where the imprint of structure from the CDFS field enhances the stellar mass function above the field population. There is also weak evidence of a bi-modal [OII] luminous GSMF indicated by an ‘upturn’ near ∼ 10^9 Msun in the low density field population. The SFRD at z ∼ 0.75 does not confirm the picture presented by the ROLES z ∼ 1 study where a constant scale factor was applicable to the local SDSS SFRD to obtain the z ∼ 1 SFRD. The SFRD in the high mass end at z ∼ 0.75 is lower than would be expected based upon a constant scale factor, while the low stellar mass end exhibits some consistency with this picture. In the high density environment, this dominant SFRD (over the low density field population) is driven by the high density [OII] luminous GSMF in the high stellar mass end, rather than through an enhancement of the SFR. The normalization of the sSFR − M∗ relation at z ∼ 0.75 is found to lie between those corresponding to z ∼ 1 and present day. There is a subtle ‘upturn’ in the sSFR − M∗ relation confirming this observation which was also present in the ROLES z ∼ 1 study but not present in the local SDSS sSFR − M∗ relation. The sSFR of active galaxies does not depend upon the local density in which they are forming, confirming the same conclusion based upon the [OII] LF. However, there is redshift evolution of the sSFR − M∗ relation with respect to local density. The high density sSFR − M∗ relation for star forming galaxies was dominant over its low density counterpart at early times, with the opposite the case at present day. There is suggestion of the crossover or rollover transition occurring at z ∼ 0.75.

Variability of pre-main-sequence stars observed at optical wavelengths has been attributed to fluctuations in the mass accretion rate from the circumstellar disk onto the forming star. Detailed models of accretion disks suggest that young deeply em- bedded protostars should also exhibit variations in their accretion rates, and that these changes can be tracked indirectly by monitoring the response of the dust enve- lope at mid-IR to millimeter wavelengths. Interferometers such as ALMA offer the resolution and sensitivity to observe small fluctuations in brightness at the scale of the disk where episodic accretion may be driven. In this thesis, novel methods for comparing interferometric observations are presented and applied to CARMA and ALMA 1.3mm observations of deeply embedded protostars in Serpens taken 9 years apart. No brightness variation is found above the limits of the analysis of a factor of ~>50%, due to the limited sensitivity of the CARMA observations and small number of sources common to both epochs. It is further shown that follow up ALMA observa- tions with a similar sample size and sensitivity may be able to uncover variability at the level of a few percent, and the implications of this for future work are discussed. / Graduate

Recent studies suggest that many protoplanetary disks around pre-main sequence stars with inferred ages of 1-5 Myr (known as Class II protostars) may contain insufficient mass to form giant planets. This may be because by this stage much of the material in the disk has already grown into larger bodies, hiding the material from sight. If this is the case, then these older disks may not be an accurate representation of the initial mass budget in disks for forming planets. To test this hypothesis, I have observed a sample of protostars in the Taurus star forming regions identified as Class I in multiple independent surveys, whose young (<1 Myr old) disks are more likely to represent the initial mass budget of protoplanetary disks. For my dissertation I have used detailed radiative transfer modeling of a multi-wavelength dataset to determine the geometry of the circumstellar material and measure the mass of the disks around these protostars. I discuss how the inferred disk mass distribution for this sample compares with results for the existing 1-5 Myr old disk samples, and what these results imply for giant planet formation. Next, I discuss the cases of three separate, individual Class I protostars discovered through my ongoing survey of Class I protostars whose disks are all of particular interest, each for its own reasons. Each of these disks may provide clues that even at the young ages of Class I protostars, planet formation may already be well underway in their disks. Finally, large disk mass surveys of large star forming regions like the Orion Nebula Cluster may be contaminated by free-free emission from disks that are being photoevaporated by nearby massive stars. I discuss my work with the VLA to constrain the free-free emission spectra for these sources so that current and future millimeter surveys can accurately measure disk masses in the ONC.

I study mid-infrared and star formation properties of AGN samples using infrared observations, and star-forming galaxies using radio observations in order to investigate the link between star formation, AGN activity and radio luminosity. I present the results of these investigations in this thesis. I carried out an analysis of four complete samples of radio-loud AGN (3CRR, 2Jy, 6CE and 7CE) using near- and mid-IR data taken by the Wide-Field Infrared Survey Explorer (WISE). The combined sample consists of quasars and radio galaxies, and covers a redshift range 0:003 < z < 3:395. The dichotomy in the mid-IR properties of low- and high-excitation radio galaxies (LERGs - HERGs) is analysed using large complete samples. The results show that a division in the accretion modes of powerful LERGs and HERGs clearly stands out in the mid-IR radio plane. Evaluation of the positions of the sample objects in WISE colour-colour diagrams shows that widely used WISE colour cuts are not completely reliable in selecting AGN. I examined the link between AGN activity and star formation by constructing matched samples of local (0 < z < 0:6) radio-loud and radio-quiet AGN in the Herschel-ATLAS fields. AGN accretion and jet powers in these active galaxies are traced by [OIII] emission-line and radio luminosity, respectively. Star formation properties were derived using Herschel 250-_m and stellar mass measurements are taken from the SDSS-MPA-JHU catalogue. The stacking analyses show that star formation rates (SFRs) and specific star formation rate (SSFRs) of both radio-loud and radio-quiet AGN increase with increasing AGN power but that radio-loud AGN tend to have lower SFR. Additionally, radio-quiet AGN are found to have approximately an order of magnitude higher SSFRs than radio-loud AGN for a given level of AGN power. The difference between the star formation properties of radio-loud and -quiet AGN is also seen in samples matched in stellar mass. I also investigated the relationship between SFR and low-frequency radio luminosity observed in star-forming galaxies. I used a sample of star-forming galaxies in the 19 local Universe selected from the SDSS-MPA-JHU catalogue. LOFAR observations of the Herschel-ATLAS North Galactic Pole field (NGP) were carried out as part of the LOFAR surveys Key Science Project at an effective frequency of 150 MHz, which provided low-frequency radio luminosity of sample galaxies. SFRs of galaxies in the sample were derived using MAGPHYS spectral energy distribution (SED) fitting. The results of this study show that the slope of L150/SFR is less than unity and not universal for all star-forming galaxies (SFGs) in the local Universe (0 < z < 0:3). The slope of the L150/SFR relation is also found to be steeper than the L1:4/SFR relation, probably due to the contribution from thermal radio emission at 1.4 GHz. If the L150=SFR relation for strongly star-forming objects is explained naively by electron calorimetry, I conclude that low luminosity sources are not ideal calorimeters and differ from the main locus of SFGs at low redshifts. The different gradients we obtain for the far- IR/radio correlation using samples selected at different frequencies reveal the selection effects on relations derived in this thesis.

This thesis investigates the modelling of massive protostellar envelopes in dust and molecular emission. A detailed study is undertaken for a sample of 30 targets believed to contain young high-mass protostars. SCUBA observations of the dust emission are used to help distinguish between the genuine high-mass protostars and clusters of lower mass protostars. Using the single power-law density structure, models are found that fit 16 sources, that are well-separated from other sources, in half of the 30 target regions. Indices of the power-law profiles are compared to values obtained from the literature. The distributions of the indices are similar but there are differences in the underlying distributions which show that observations at longer wavelengths give generally steeper profiles. Investigating the underlying nature of the sources between the fitted and non-fitted sources shows some interesting differences between the groups. These differences indicate that the modelled sources are more likely to be massive protostars while the other sources are probably lower mass protostars. Single power-law modelling is also used to investigate molecular emission in a second group of targets from the RMS survey. Dust models are obtained for six of the sources which show similar results to the sources described above. Molecular line emission from the targets is mapped and compared to the dust emission which shows they trace the same regions. The dust models are used as a basis to obtain the molecular abundances for the sources. Abundances from the modelling the lines are broadly similar values to those observed in other high-mass protostars and association with radio and maser emission indicates that high-mass star formation is definitely occurring in some of these regions.

The bulk of the stellar growth over cosmic time is dominated by IR-luminous galaxies at cosmic noon (z = 1-2), many of which harbor a hidden active galactic nucleus (AGN). We use state-of-the-art infrared color diagnostics, combining Spitzer and Herschel observations, to separate dust-obscured AGNs from dusty star-forming galaxies (SFGs) in the CANDELS and COSMOS surveys. We calculate 24 mu m counts of SFGs, AGN/star-forming "Composites," and AGNs. AGNs and Composites dominate the counts above 0.8 mJy at 24 mu m, and Composites form at least 25% of an IR sample even to faint detection limits. We develop methods to use the Mid-Infrared Instrument (MIRI) on JWST to identify dust-obscured AGNs and Composite galaxies from z similar to 1-2. With the sensitivity and spacing of MIRI filters, we will detect >4 times as many AGN hosts as with Spitzer/IRAC criteria. Any star formation rates based on the 7.7 mu m PAH feature (likely to be applied to MIRI photometry) must be corrected for the contribution of the AGN, or the star formation rate will be overestimated by similar to 35% for cases where the AGN provides half the IR luminosity and similar to 50% when the AGN accounts for 90% of the luminosity. Finally, we demonstrate that our MIRI color technique can select AGNs with an Eddington ratio of lambda(Edd) similar to 0.01 and will identify AGN hosts with a higher specific star formation rate than X-ray techniques alone. JWST/MIRI will enable critical steps forward in identifying and understanding dust-obscured AGNs and the link to their host galaxies.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23013号 / 理博第4690号 / 新制||理||1672(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 太田 耕司, 教授 長田 哲也, 准教授 栗田 光樹夫 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

New deep ugr imaging was obtained on the Wyoming Infrared Observatory 2.3 meter telescope for NGC4102 and UGC07608, two galaxies in the Extended Disk Galaxy Exploration Science survey. These data are coupled with deep GALEX ultraviolet and Spitzer, WISE and Herschel infrared imaging to study the radial variations in the spectral energy distributions. Results from the CIGALE SED modeling software are presented, including trends in the galaxy star formation histories.

In this thesis I investigate three key questions about the interstellar medium (ISM) and star formation in nearby galaxies. The first question is, “how do bars and galaxy interactions affect the distribution of cold gas and the level of central star formation in galaxies?” I use publicly-available spatially-resolved images of CO(1-0) emission in a sample of 126 nearby galaxies from the Extragalactic Database for Galaxy Evolution (EDGE) survey to measure molecular gas concentrations, and I use spatially-resolved optical spectroscopy from the Calar Alto Legacy Integral Field Area (CALIFA) survey to measure the level of central star formation enhancement. I find that gas concentration and the level of central star formation enhancement are positively correlated in barred galaxies but not in unbarred galaxies, and that interacting galaxies show signs of a correlation but not in all cases. These results indicate that central star formation enhancement occurs only in barred galaxies and interacting galaxies with high gas concentrations, which supports theories of bar- and interaction-driven galaxy evolution. The second question is, “what is the relationship between mid-infrared (MIR) emission and molecular gas at spatially-resolved scales in galaxies?” I extend previous work, which found a tight correlation between global MIR emission in the Wide-field Infrared Survey Explorer (WISE) 12 micron band and CO emission from single-dish radio telescopes, to spatially-resolved scales using EDGE CO data smoothed to WISE 12 micron resolution. I find that these quantities are tightly correlated at ~kiloparsec scales, and that the correlation shows offsets from galaxy to galaxy. I find that these offsets are explained best by differences in the level of global near- and far-ultraviolet emission, and that the 12 micron-CO correlation is the strongest of all the resolved correlations that I considered. These results suggest that there is a tight physical link between WISE 12 micron emission and CO emission on kiloparsec scales, possibly due to a connection between polycyclic aromatic hydrocarbons (PAHs, which dominate the 12 micron emission) and molecular gas. My findings can be used to estimate resolved CO emission based on (easily obtained) WISE 12 micron images and a small number of global multi-wavelength measurements. These results also motivate further work exploring the CO-PAH connection in more diverse conditions and at higher resolution. Finally, the third question is, “what is the ISM content of red star-forming galaxies?” In comparison to blue star-forming galaxies (“blue actives”) which lie on or above the star-forming main sequence (SFMS), these “red misfits” tend to lie on or slightly below the SFMS. I find that the main property other than colour that differentiates red misfits from blue actives is their low gas mass fractions. The gas depletion times and gas-to-dust ratios are similar between these populations. My results indicate that the star formation of red misfits is in the act of quenching. The unifying theme of each of these projects is the approach: studying key questions in nearby galaxies based on their molecular gas content along with other multi-wavelength data, at a variety of resolutions. This approach is enabled by large publicly available multi-wavelength data sets at a variety of physical resolutions. Surveys of the global gas content of galaxies with accompanying multi-wavelength data will always be larger, and will continue to be an important reference for smaller resolved surveys. I hope that this thesis serves as a useful comparison between the science that can be done on both global and resolved scales, and will motivate future work on the connection between the ISM and star formation in nearby galaxies. / Thesis / Doctor of Science (PhD)

Star formation is an inherently multi-scale process, connecting scales from the kiloparsecs of the galactic disk to the single AU scale of a protostar. In the middle of these scales are star clusters and molecular clouds, the structures in which most stars form. The clouds and clusters are connected via the interstellar medium, the gas and dust making up the matter between stars. In the cold phases of this medium rests the first steps of star formation, the formation of molecular gas and networks of filaments. This cold, neutral medium (CNM) hosts a handful of physical mechanisms, all contributing to the structures that feeds star formation. In this thesis work, we present a suite of simulations using the magneto-hydrodynamical code Ramses to investigate the role of turbulence, magnetic fields and cooling on the formation of filaments and clusters in the CNM. Through 9 different models we find that velocity dispersions in the CNM play a significant role in the formation of structure, requiring a balance between turbulence, self gravity and cooling to form filaments. We find magnetic fields, initialized at strengths of 7 muG, affect the formation of filaments, creating higher percentages of star-forming dense gas and lower percentages of molecular gas. Both magnetic fields and velocity dispersion in the gas affect the formation rate of clusters early in the simulation. Our 8 km/s simulations present a good initial condition for star formation that can include multiple scales of the process and recreate accurate clouds and filamentary structure. / Thesis / Master of Science (MSc)