The interaction of HII regions with molecular clouds.

AstronomyDoctor of Philosophy (PhD

A New Constraint on the Simulation of the Intergalactic Medium through the Evolution of the Neutral Hydrogen Fraction in the Epoch of Reionization

The thermal history of the intergalactic medium is full of extremely useful data in the field of astrophysics and cosmology. In other words, by examining this environment in different redshifts, the effects of cosmology and astrophysics can be observed side by side. Therefore, simulation is our very powerful tool to reach a suitable model for the intergalactic medium, both in terms of cosmology and astrophysics. In this work, we have simulated the intergalactic medium with the help of the 21cmFAST code and compared the evolution of the neutral hydrogen fraction in different initial conditions. Considerable works arbitrarily determine many important effective parameters in the thermal history of the intergalactic medium without any constraints, and usually, there is a lot of flexibility for modeling. Nonetheless, in this work, by focusing on the evolution of the neutral hydrogen fraction in different models and comparing it with observational data, we have eliminated many models and introduced only limited simulation models that could confirm the observations with sufficient accuracy. This issue becomes thoroughly vital from the point that, in addition to restricting the models through the neutral hydrogen fraction, it can also impose restrictions on the parameters affecting its changes. However, we hope that in future works, by enhancing the observational data and increasing their accuracy, more compatible models with the history of the intergalactic medium can be achieved.Comment: 14 pages, 3 figures, 4 table

Cue: A Fast and Flexible Photoionization Emulator for Modeling Nebular Emission Powered By Almost Any Ionizing Source

The complex physics governing nebular emission in galaxies, particularly in the early universe, often defy simple low-dimensional models. This has proven to be a significant barrier in understanding the (often diverse) ionizing sources powering this emission. We present Cue, a highly flexible tool for interpreting nebular emission across a wide range of abundances and ionizing conditions of galaxies at different redshifts. Unlike typical nebular models used to interpret extragalactic nebular emission, our model does not require a specific ionizing spectrum as a source, instead approximating the ionizing spectrum with a 4-part piece-wise power-law. We train a neural net emulator based on the CLOUDY photoionization modeling code and make self-consistent nebular continuum and line emission predictions. Along with the flexible ionizing spectra, we allow freedom in [O/H], [N/O], [C/O], gas density, and total ionizing photon budget. This flexibility allows us to either marginalize over or directly measure the incident ionizing radiation, thereby directly interrogating the source of the ionizing photons in distant galaxies via their nebular emission. Our emulator demonstrates a high accuracy, with $\sim$1% uncertainty in predicting the nebular continuum and $\sim$5% uncertainty in the emission lines. Mock tests suggest Cue is well-calibrated and produces useful constraints on the ionizing spectra when $S/N (\mathrm{H}_\alpha) \gtrsim 10$, and furthermore capable of distinguishing between the ionizing spectra predicted by single and binary stellar models. The compute efficiency of neural networks facilitates future applications of Cue for rapid modeling of the nebular emission in large samples and Monte Carlo sampling techniques.Comment: submitted to Ap

Molecular clouds and stellar feedback: an investigation of synthetic line and continuum emission maps

Molecular clouds are complex systems and the search of adequate observational measurements to trace their evolution is still an open problem. In this thesis, we use produce synthetic emission maps of the 12CO 1-0, 13CO 1-0, [CI] 1-0, and [CII] lines, as well as of the FIR continuum emission, to test to which extent these emission measurements can be used as tracers of the evolutionary stage of molecular clouds. We use numerical simulations of molecular clouds performed within the SILCC-Zoom project. These simulations include detailed stellar feedback due to ionizing radiation, external magnetic fields, and a chemical network evolved on-the-fly. We compare two different chemical networks, NL97 and NL99, and we find that NL97, even though it does not include neutral carbon, more accurately reproduces the abundances of CO and C+. We then use NL97 in the rest of the work. We introduce a novel post-processing procedure for the C+ abundance using CLOUDY, essential in HII regions to account for the higher ionization states due to stellar radiation. Furthermore, we show that assuming chemical equilibrium results in H and H2 being underestimated and overestimated, respectively, by up to a factor of 2. The abundances of C+ and CO are also, respectively, underestimated and overestimated. This is reflected and amplified in the estimation of the CO and [CII] luminosity as well. We also investigate the capability of the L_CO/L_[CII] luminosity ratio to trace the H2 mass fraction in the clouds, but find no clear trend. We then investigate the [CII]/FIR ratio in HII regions and in entire clouds with stellar feedback. In young HII regions the drop of the [CII]/FIR intensity ratio is mainly due to the strong FIR emission produced by hot and dense dust, and the contemporary saturation of the [CII] line. In more evolved HII regions, the second ionization of carbon is the main reason for the low [CII]/FIR ratio. The evolution of this ratio is reflected in the evolution of the L_[CII]/L_FIR luminosity ratio in the entire clouds. This evolution can be schematized in three phases. Overall, L_[CII]/L_FIR is well correlated with the total stellar luminosity L_*tot. The relation between L_[CII]/L_FIR andL_*tot can be fitted with a power-law. When L_*tot is large, i.e., in evolved clouds which formed many massive stars, L_[CII]/L_FIR is particularly low, determining an observable [CII]-deficit in these clouds. However, this relation breaks when the total FIR luminosity stars decreasing as a consequence of the cloud dispersal caused by the stellar feedback. The aspect of HII regions in molecular clouds strongly depends on the geometry of the cloud, and on the line of sight. Indeed, a certain HII region can have different properties when observed from different LOS, and apparent HII regions, which are actually only the result of projection effects, can be observed

The nebular emission of star-forming galaxies in a hierarchical universe

Galaxy surveys targeting emission lines are characterizing the evolution of star-forming galaxies, but there is still little theoretical progress in modelling their physical properties. We predict nebular emission from star-forming galaxies within a cosmological galaxy formation model. Emission lines are computed by combining the semi-analytical model SAG with the photoionization code MAPPINGS-III. We characterize the interstellar medium of galaxies by relating the ionization parameter of gas in galaxies to their cold gas metallicity, obtaining a reasonable agreement with the observed Hα, [O II] λ 3727, [O III] λ 5007 luminosity functions, and the BPT diagram for local star-forming galaxies. The average ionization parameter is found to increase towards low star formation rates and high redshifts, consistent with recent observational results. The predicted link between different emission lines and their associated star formation rates is studied by presenting scaling relations to relate them. Our model predicts that emission-line galaxies have modest clustering bias, and thus reside in dark matter haloes of masses below Mhalo ≲ 1012 [h−1 M⊙]. Finally, we exploit our modelling technique to predict galaxy number counts up to z ∼ 10 by targeting far-infrared emission lines detectable with submillimetre facilities.Fil: Orsi, Alvaro. Pontificia Universidad Católica de Chile; ChileFil: Padilla, Nelson David. Pontificia Universidad Católica de Chile; ChileFil: Groves, Brent. Max Planck Institute For Astronomy;Fil: Cora, Sofia Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica la Plata; ArgentinaFil: Tecce, Tomas Enrique. Pontificia Universidad Católica de Chile; ChileFil: Gargiulo, Ignacio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica la Plata; ArgentinaFil: Ruiz, Andrés Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomia Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomia Teórica y Experimental; Argentin

HII Regions in the Pilot Ku-band Galactic Reconnaissance Survey

This thesis presents data from the Ku-band Galactic Reconnaissance Survey (KuGARS), a large area survey observed on the Jansky Very Large Array (JVLA). KuGARS is the first galactic plane survey to explore the sub-arcsecond and sub-mJy regime at 14 GHz. We have described the development of the data reduction procedures in CASA for the On the Fly (OTF) mapping method used for KuGARS. Included in our discussion are the calibration and imaging processes: as the OTF mapping method has not been extensively explored we have gone through several steps to present quality assurance of the calibration. Due to the large volume of data, we focused on a pilot study of the area surrounding the W49A massive star forming region and a subset of the final frequency range. Using an automated source finding algorithm, AEGEAN (Hancock et al., 2012), we have detected 35 islands with 57 components. We compared the brightest of these sources to the literature to determine their nature. In order to carry out a robust analysis, we compared our detections to observations over multiple frequencies. Comparing to GLIMPSE and Herschel showed our sources deeply embedded in 8μm and 70μm emission, respectively, which indicate heated dust and therefore infer star formation. We further, through the SIMBAD database, found several star formation tracers, including: Masers, YSOs, and HII regions, associated with our KuGARS detections. Our comparison with CORNISH and De Pree et al. (1997) revealed previous detections of these sources as HII regions with similar morphologies to KuGARS. We have detected and identified 2 spherical or unresolved HII regions, and 2 irregular HII regions in the ring of HII regions (W49 North), 1 isolated spherical/unresolved HII region, and 1 cometary HII region in W49 South. We find that one of the objects (source B) is recovered by KuGARS and De Pree et al. (1997) but not in CORNISH. This source, which is undetected at 5GHz and below has a steep positive spectrum (α = 1:1) and has broad radio recombination lines with line widths (> 45kms1) (De Pree et al., 1997). It, therefore, must be a Hypercompact HII region and thus demonstrates KuGARS capability to detect Hypercompact HII regions