Exploring the Epoch of Reionization with the 21 cm line

The Epoch of Reionization is the last major phase transition of the Universe, marking the passage from a completely neutral to a fully ionized intergalactic medium. This transition is driven by young star-forming galaxies that are reionizing their surrounding gas. Today, substantial observational effort is focused on observing the 21cm signal of the intergalactic neutral hydrogen that is being reionized and the galaxies driving the reionization. To help guide this observational effort predictions of the possible observations are being made, to asses the best observational strategies and possible synergies between different instruments. With this thesis, I am joining these efforts by focusing on three particular problems. I focus on possible synergies between ongoing observations of LOFAR and HSC that are going to observe 21cm emission and Lyman-alpha emitting galaxies respectively, as well as synergies between the next-generation survey SKA, observing the 21cm signal, and HSC, PFS, and WFIRST observing the galaxies. I show that cross-correlation between LOFAR and HSC observations should show an anti-correlation on the largest scales and thus prove that the signal LOFAR is observing, as a first-generation instrument, is indeed from the Epoch of Reionization. Cross-correlations between SKA and HSC can improve on this effort and combined with the synergy between SKA and WFIRST even show the evolution of this cross-correlation. I also focus on showing that SKA could potentially observe 21cm line-of-sight one-dimensional power spectra, which would give insight on cosmological small scales. Unlike the two- and three- dimensional observations which focus on large scales. I also examined the best possible observational strategies for SKA's two-dimensional observations, showing that observing perpendicular to line-of-sight would be much better than observing in direction of line-of-sight due to orders of magnitude smaller noise in angular direction than in frequency direction. Lastly, I focus on our theoretical understanding of the 21cm forest. I show that when it comes to supernovae feedback, when implemented in such a way not to change the reionization history as opposed to without implementing it, no statistical changes are found in the features of the 21cm forest spectra. I also confirmed that the changes in the resolution of simulations used to build the 21 cm forest spectra induced the most changes in the spectra. I show that LOFAR could observe the most prominent features in a 21cm forest spectra from likes of Cygnus A high-redshift radio loud source, with a signal to noise ratio S/N around 20. SKA, instead, could observe even the smallest features, with S/N around 200

Exploring the Epoch of Reionization with the 21 cm line

The Epoch of Reionization is the last major phase transition of the Universe, marking the passage from a completely neutral to a fully ionized intergalactic medium. This transition is driven by young star-forming galaxies that are reionizing their surrounding gas. Today, substantial observational effort is focused on observing the 21cm signal of the intergalactic neutral hydrogen that is being reionized and the galaxies driving the reionization. To help guide this observational effort predictions of the possible observations are being made, to asses the best observational strategies and possible synergies between different instruments. With this thesis, I am joining these efforts by focusing on three particular problems. I focus on possible synergies between ongoing observations of LOFAR and HSC that are going to observe 21cm emission and Lyman-alpha emitting galaxies respectively, as well as synergies between the next-generation survey SKA, observing the 21cm signal, and HSC, PFS, and WFIRST observing the galaxies. I show that cross-correlation between LOFAR and HSC observations should show an anti-correlation on the largest scales and thus prove that the signal LOFAR is observing, as a first-generation instrument, is indeed from the Epoch of Reionization. Cross-correlations between SKA and HSC can improve on this effort and combined with the synergy between SKA and WFIRST even show the evolution of this cross-correlation. I also focus on showing that SKA could potentially observe 21cm line-of-sight one-dimensional power spectra, which would give insight on cosmological small scales. Unlike the two- and three- dimensional observations which focus on large scales. I also examined the best possible observational strategies for SKA's two-dimensional observations, showing that observing perpendicular to line-of-sight would be much better than observing in direction of line-of-sight due to orders of magnitude smaller noise in angular direction than in frequency direction. Lastly, I focus on our theoretical understanding of the 21cm forest. I show that when it comes to supernovae feedback, when implemented in such a way not to change the reionization history as opposed to without implementing it, no statistical changes are found in the features of the 21cm forest spectra. I also confirmed that the changes in the resolution of simulations used to build the 21 cm forest spectra induced the most changes in the spectra. I show that LOFAR could observe the most prominent features in a 21cm forest spectra from likes of Cygnus A high-redshift radio loud source, with a signal to noise ratio S/N around 20. SKA, instead, could observe even the smallest features, with S/N around 200

SKA - EoR correlations and cross-correlations: kSZ, radio galaxies, and NIR background

The Universe's Cosmic Dawn (CD) and Epoch of Reionization (EoR) can be studied using a number of observational probes that provide complementary or corroborating information. Each of these probes suffers from its own systematic and statistical uncertainties. It is therefore useful to consider the mutual information that these data sets contain. In this paper, we discuss a potential of cross-correlations between the SKA cosmological 21 cm data with: (i) the kinetic Sunyaev- Zel'dovich (kSZ) effect in the CMB data; (ii) the galaxy surveys; and (iii) near infrared (NIR) backgrounds.Comment: Accepted for publication in the SKA Science Book 'Advancing Astrophysics with the Square Kilometre Array', to appear in 201

Predictions for the 21cm-galaxy cross-power spectrum observable with SKA and future galaxy surveys

In this paper, we use radiative transfer+N-body simulations to explore the feasibility of measurements of cross-correlations between the 21-cm field observed by the Square Kilometre Array (SKA) and high-z Lyman α emitters (LAEs) detected in galaxy surveys with the Subaru Hyper Suprime-Cam (HSC), Subaru Prime Focus Spectrograph (PFS), and Wide Field Infrared Survey Telescope (WFIRST). 21cm-LAE cross-correlations are in fact a powerful probe of the epoch of reionization as they are expected to provide precious information on the progress of reionization and the typical scale of ionized regions at different redshifts. The next generation observations with SKA will have a noise level much lower than those with its precursor radio facilities, introducing a significant improvement in the measurement of the cross-correlations. We find that an SKA-HSC/PFS observation will allow to investigate scales below ̃10 and ̃60 h-1 Mpc at z = 7.3 and 6.6, respectively. WFIRST will allow to access also higher redshifts, as it is expected to observe spectroscopically ̃900 LAEs per deg2 and unit redshift in the range 7.5 ≤ z ≤ 8.5. Because of the reduction of the shot noise compared to HSC and PFS, observations with WFIRST will result in more precise cross- correlations and increased observable scales

Predictions for the 21 cm-galaxy cross-power spectrum observable with LOFAR and Subaru

The 21 cm-galaxy cross-power spectrum is expected to be one of the promising probes of the Epoch of Reionization (EoR), as it could offer information about the progress of reionization and the typical scale of ionized regions at different redshifts. With upcoming observations of 21 cm emission from the EoR with the Low Frequency Array (LOFAR), and of high-redshift Ly α emitters with Subaru's Hyper Suprime-Cam (HSC), we investigate the observability of such cross-power spectrum with these two instruments, which are both planning to observe the ELAIS-N1 field at z = 6.6. In this paper, we use N-body + radiative transfer (both for continuum and Ly α photons) simulations at redshift 6.68, 7.06 and 7.3 to compute the 3D theoretical 21 cm-galaxy cross-power spectrum and cross-correlation function, as well as to predict the 2D 21 cm-galaxy cross-power spectrum and cross-correlation function expected to be observed by LOFAR and HSC. Once noise and projection effects are accounted for, our predictions of the 21 cm-galaxy cross-power spectrum show clear anti-correlation on scales larger than ∼60 h−1 Mpc (corresponding to k ∼ 0.1 h Mpc−1), with levels of significance p = 0.003 at z = 6.6 and p = 0.08 at z = 7.3. On smaller scales, instead, the signal is completely contaminated. On the other hand, our 21 cm-galaxy cross-correlation function is strongly contaminated by noise on all scales, since the noise is no longer being separated by its k modes

Exploring the Variable Sky with LINEAR. III. Classification of Periodic Light Curves

We describe the construction of a highly reliable sample of ~7000 optically faint periodic variable stars with light curves obtained by the asteroid survey LINEAR across 10,000 deg^2 of the northern sky. The majority of these variables have not been cataloged yet. The sample flux limit is several magnitudes fainter than most other wide-angle surveys; the photometric errors range from ~0.03 mag at r = 15 to ~0.20 mag at r = 18. Light curves include on average 250 data points, collected over about a decade. Using Sloan Digital Sky Survey (SDSS) based photometric recalibration of the LINEAR data for about 25 million objects, we selected ~200,000 most probable candidate variables with r < 17 and visually confirmed and classified ~7000 periodic variables using phased light curves. The reliability and uniformity of visual classification across eight human classifiers was calibrated and tested using a catalog of variable stars from the SDSS Stripe 82 region and verified using an unsupervised machine learning approach. The resulting sample of periodic LINEAR variables is dominated by 3900 RR Lyrae stars and 2700 eclipsing binary stars of all subtypes and includes small fractions of relatively rare populations such as asymptotic giant branch stars and SX Phoenicis stars. We discuss the distribution of these mostly uncataloged variables in various diagrams constructed with optical-to-infrared SDSS, Two Micron All Sky Survey, and Wide-field Infrared Survey Explorer photometry, and with LINEAR light-curve features. We find that the combination of light-curve features and colors enables classification schemes much more powerful than when colors or light curves are each used separately. An interesting side result is a robust and precise quantitative description of a strong correlation between the light-curve period and color/spectral type for close and contact eclipsing binary stars (β Lyrae and W UMa): as the color-based spectral type varies from K4 to F5, the median period increases from 5.9 hr to 8.8 hr. These large samples of robustly classified variable stars will enable detailed statistical studies of the Galactic structure and physics of binary and other stars and we make these samples publicly available

Milky Way Tomography IV: Dissecting Dust

We use SDSS photometry of 73 million stars to simultaneously obtain best-fit main-sequence stellar energy distribution (SED) and amount of dust extinction along the line of sight towards each star. Using a subsample of 23 million stars with 2MASS photometry, whose addition enables more robust results, we show that SDSS photometry alone is sufficient to break degeneracies between intrinsic stellar color and dust amount when the shape of extinction curve is fixed. When using both SDSS and 2MASS photometry, the ratio of the total to selective absorption, $R_V$, can be determined with an uncertainty of about 0.1 for most stars in high-extinction regions. These fits enable detailed studies of the dust properties and its spatial distribution, and of the stellar spatial distribution at low Galactic latitudes. Our results are in good agreement with the extinction normalization given by the Schlegel et al. (1998, SFD) dust maps at high northern Galactic latitudes, but indicate that the SFD extinction map appears to be consistently overestimated by about 20% in the southern sky, in agreement with Schlafly et al. (2010). The constraints on the shape of the dust extinction curve across the SDSS and 2MASS bandpasses support the models by Fitzpatrick (1999) and Cardelli et al. (1989). For the latter, we find an $R_V=3.0\pm0.1$(random) $\pm0.1$(systematic) over most of the high-latitude sky. At low Galactic latitudes (|b|<5), we demonstrate that the SFD map cannot be reliably used to correct for extinction as most stars are embedded in dust, rather than behind it. We introduce a method for efficient selection of candidate red giant stars in the disk, dubbed "dusty parallax relation", which utilizes a correlation between distance and the extinction along the line of sight. We make these best-fit parameters, as well as all the input SDSS and 2MASS data, publicly available in a user-friendly format.Comment: Submitted to ApJ, 55 pages, 37 figure

Ružička days : International conference 18th Ružička Days “Today Science – Tomorrow Industry” : Proceedings

Proceedings contains articles presented at Conference divided into sections: chemical analysis and synthesis, chemical and biochemical engineering, food technology and biotechnology, medical chemistry and pharmacy, environmental protection and meeting of young chemists