2023-12-06

Uncovering the Chemical Evolution of Galaxies from z=0–5 using the UniverseMachine

Speaker: Moka Nishigaki

Abstract:

Cosmic baryon cycling is pivotal to galaxy evolution, and the amount of metals present in galaxies’ ISMs provides a key window into the gas cycling process. Recent JWST metallicity measurements and constraints on galaxy ISM masses have made it possible to recover the chemical evolution history of galaxies. In this talk, I present a novel empirical model that infers the average metallicity evolution of galaxies from redshift z=5 to z=0. Anchored in the UniverseMachine (Behroozi+19) framework, our model converts observations of gas-phase metallicities across z=0—5 and galaxy ISM masses into constraints on the ISM return fraction, a key parameter quantifying the recycling of metals into the ISM versus expulsion into the CGM. I will show the initial results on how the ISM return fraction changes with mass and redshift.

2023-11-29

Physical Structures Traced by Chemical Diagnostics in Disk-Forming Regions of Young Low-Mass Protostellar Sources

Speaker: Yoko Oya

Abstract:

To understand the origin of the Solar system, the physical/chemical evolution along the star/planet formation is a key issue. With the advent of ALMA, extensive observational studies have revealed that both the physical structure and the chemical composition drastically change during the disk formation around protostars. Furthermore, it has been found that molecular distributions are sensitive to changes in the physical conditions. Some kinds of molecular lines are therefore prospected to work as ‘molecular markers’ to selectively highlight particular structures of disk forming regions.
Specifically, sulfur-bearing species have empirically been good tracers; the kinematic structures of the circummultiple structure, the circumstellar disk, and the outflow lobes are traced by the OCS, H2CS, and SO emission, respectively, in a young low-mass protostellar source IRAS 16293-2422 Source A. The gas in its circummultiple structure was found to keep falling toward its periastron even beyond its centrifugal radius, which is often assumed to be the outer edge of a Keplerian disk. Angular momentum of the gas is the essential topic to understand the structure formation. The chemical diagnostics with the aid of the molecular markers can be a helpful tool to tackle with the redistribution of the angular momentum among the disk/envelope and outflow structures. Conversely, detailed physical characterization is essential to elucidating the chemical evolution occurring there.

2023-11-22

The distribution of magnetic field strengths in star-forming regions

Speaker: Jihye Hwang

Abstract:

“What is the role of magnetic fields for regulating star-forming processes?” It is a long- standing issue in star formation studies. To judge the exact role of magnetic fields in star-forming regions, it is necessary to estimate the magnetic field strengths of those regions. However, previous studies have estimated a mean magnetic field strength in a whole star-forming region. I suggest a new application to estimate the distribution of magnetic field strengths in a star-forming region. I applied this towards three star-forming regions, the OMC-1 region, Mon R2 and G28.34 using POL-2/SCUBA-2 on the James Clerk Maxwell Telescope. In this talk, I will show the magnetic field strengths in those regions and discuss the relative importance between magnetic field, turbulence and gravity.

2023-11-01

Impact of Magma Redox States on Super-Earth Atmospheres: Unveiling the Connection with Atmospheric Composition

Speaker: Chanoul Seo

Abstract:

Most exoplanets with radii larger than ~1.6Earth mass are more inflated than bare-rock planets with the same mass, indicating a substantial amount of volatile. While it is hard to constrain the origin of the volatiles or the planet’s bulk composition only from the mass-radius relation, the spectral characterization of their atmospheres is expected to solve this degeneracy. Previous models pointed out that the interaction between the accreted volatile and the likely molten rock (i.e., magma) beneath the atmosphere would affect the atmospheric composition significantly. However, existing models do not clarify the dependence of the atmospheric compositions with major spectral fingerprints on the observable planetary parameters. In this work, we explore the possible range of H, O, and C in the atmosphere of exoplanets as a function of observable planetary parameters (mass, radius, equilibrium temperature) using a simple chemical equilibrium model. Consistent with the previous work, we show that the water fraction in contact with magma ocean is the order of 10^-2~10^-1 if the dry planetary core accretes the nebula gas. Due to the difference in solubility of H-bearing and C-bearing species in molten rock, C/H shows an increase of ×3~10^2. The low values correspond to H2-rich atmospheres while the high values (the order of magnitude difference) correspond to the thin atmosphere with pressure <10^3 bar. Therefore, the C/O remains relatively low in most of the parameter range considered, below one-tenth of the nebula gas value if the atmospheric H2O fraction is over five percent. These trends provide a clue to verify or falsify the formation scenario of super-Earth/sub-Neptune from atmospheric compositions.

2023-11-01

An Optical Gamma-Ray Burst catalogue with Measured Redshift: Data Release of 533 Gamma-Ray Bursts and colour evolution

Speaker: Biagio De Simone

Abstract:

Gamma-Ray Bursts (GRBs) are incredibly energetic cosmic phenomena observed across a wide range of wavelengths, including gamma-ray and optical frequencies, and occasionally even in radio waves. They allow extending the Hubble diagram and the cosmological analysis up to redshift z=9.4, much further than Supernovae Ia (z=2.26).
We therefore present a compilation of 533 optical lightcurves (LCs) of all GRBs with measured redshifts, detected mainly by Swift and 418 ground-based telescopes from February 28, 1997, to April 14, 2023. This catalogue is the largest optical repository of GRB LCs with redshifts to date, with 64615 photometric data points, including upper limits. Our user-friendly web tool, grbLC, allows the acquisition of GRB LCs, including information on the position, redshift, and a Gamma-ray Coordinates Network (GCN) crawler that can be used to collect data by gathering magnitudes from the GCNs. The web tool also includes a package for uniformly investigating colour evolution. We have crafted a procedure to distinguish between GRBs in our sample, which undergo colour evolution, and GRBs for which no colour evolution is present. We compared our results with the literature. This web-based archive is the first step towards unifying several community efforts to gather optical LCs by providing a unified format and repository for the optical catalogue. This catalogue will enable population studies by providing LCs with better coverage since we have gathered data from different ground-based locations, resulting in fewer gaps in the LCs and representing crucial support for the LC reconstructions analysis.

2023-10-25

CGM observations in emission

Speaker: Haruka Kusakabe

Abstract:

The evolution of galaxies is directly linked to the gas reservoirs surrounding them, so-called, “the circum-galactic medium (CGM)”. Gas and metals are exchanged via inflows and outflows through the CGM, which is an interface between the interstellar medium (i.e., galaxy) and intergalactic medium (the rest of the Universe). The CGM has been studied with absorption lines imprinted in spectra of bright background quasars (tomography), but this method is limited to line of sight and cannot provide the 2D spatial distribution of the CGM. Recent sensitive, wide-FoV integral-field spectrographs (such as VLT/MUSE and Keck/KCWI) make it possible to individually detect the CGM in emission, which allows us to map the gas and metals around host galaxies. In this talk, I will review the recent progress in observations and understanding of hydrogen gas and metals around z>~2 galaxies, which are detected as extended Lyα emission (Lyα haloes) and metal-line haloes. I will also connect the CGM observations in emission and absorption and introduce comparisons with simulations.

2023-10-18

Evolution of the Angular Momentum of Molecular Cloud Cores in Filamentary Molecular Clouds

Speaker: Yoshiaki Misugi

Abstract:

The angular momentum of molecular cloud cores plays a key role in the star formation process. However, the evolution of the angular momentum of molecular cloud cores formed in magnetized molecular filaments is still unclear. We perform three-dimensional magnetohydrodynamics simulations to reveal the evolution of the angular momentum of molecular cloud cores formed through filament fragmentation. As a result, we find that the angular momentum decreases by 30% and 50% at the mass scale of 1 Msun in the case of weak and strong magnetic field, respectively. By analyzing the torques exerted on fluid elements at different mass scales, we identify the magnetic tension as the dominant process for angular momentum transfer for mass scales < 3 M sun for the strong magnetic field case. This critical mass scale can be understood semi-analytically as the time scale of magnetic braking. We show that the anisotropy of the angular momentum transfer due to the presence of strong magnetic field changes the resultant angular momentum of the core only by a factor of two. We also find that the distribution of the angle between the direction of the angular momentum and the magnetic field is random even just before the first core formation. Our results also indicate that the variety of the angular momentum of core inherited from the difference of the phase of the initial turbulent velocity field could contribute to the diversity in size and other properties of protoplanetary disks recently reported by observations.

2023-10-11

Witnessing Galaxies Reionizing the Intergalactic Medium with JWST

Speaker: Daichi Kashino

Abstract:

Cosmic reionization is the last major phase transition of the universe, occurring in the first billion years after the Big Bang. Understanding this process is one of the pivotal goals in modern astrophysics. The commissioning of JWST heralded a new era in investigating the roles of galaxies in reionizing the intergalactic medium, thanks to its unprecedented high sensitivity and dispersing power in near infrared.

In the presentation, I will present early results from our ongoing EIGER (Emission-line galaxies and Intergalactic Gas in the Epoch of Reionization) survey, a JWST/NIRCam WFSS campaign in the fields of luminous z>6 quasars. The existence of these background quasars enables us to determine the ionization condition along their lines of sight from analysis of the high signal-to-noise quasar spectra. The primary objective of the project is to characterize the cross correlation between galaxies (as pinpointed by JWST) and the IGM conditions during the tail end of the epoch of reionization. In the first quasar field, we confirmed roughly 150 [OIII]5008-emitting galaxies over the redshift range of z=5.3–6.9. Through analyzing the distribution of these galaxies and the transmission spectrum of this corresponding quasar, we identified individual spatial coincidence between the groups of galaxies and highly ionized regions, as well as a mean excess IGM transmission in both Lyman-alpha and Lyman-beta around ~6 cMpc away from the galaxies at z~6. This is interpreted as direct evidence of local reionization by galaxies — indicating that we are witnessing galaxies reionizing the surrounding IGM. I may also showcase further preliminary results from other quasar fields currently being analyzed.

2023-11-15

X-ray study of supernova remnants, the origin of diversity in the universe
– 多様性の源: 超新星残骸のX線研究 –

Speaker: Aya Bamba

Abstract:

Supernova remnants (SNRs) supply thermal and kinetic energy, heavy elements, and high energy particles (cosmic rays) into the space, so they are the origin of diversity of the universe. Shocked plasma is heated up to 1-10 MK, and emits thermal X-rays with characteristic X-ray lines from heavy elements, thus X-ray observations are an ideal tool how SNRs play their role in the universe. In this talk, I will introduce several recent topics of SNR science – progenitor science and shock physics.
Such a study needs excellent energy resolution in the X-ray band in order to resolve emission lines from minor elements and their Doppler motion. On this September, we succeeded to launch XRISM with H2A rocket. I also introduce how XRISM is launched and what XRISM will achieve on SNR science.

2023-08-02

Observational study of the fragmentation process in nearby star-forming regions

Speaker: Kousuke Ishihara

Abstract:

Star formation is the process of forming protostars from diffuse interstellar clouds by gravitational contraction, and it is known from both observation and theory that hierarchical structures called clumps, filaments, and cores are formed in this process. The collapse and fragmentation of those structures is thought to contribute to the determination of the spatial distribution and initial mass of stars. The most fundamental mechanism controlling the fragmentation is the balance between the self-gravity and the thermal pressure that supports the structure against it (Jeans instability). Furthermore, non-thermal pressures such as turbulence, and magnetic fields are thought to have an inhibitory effect on fission. But the mechanism is not clear.
In this presentation, I introduce the results of the analysis applied to 15 nearby regions of the Herschel Gould Belt Survey. Especially, closer regions (d<200 pc) such as CoronaAustralis, Lupus, and Polaris areas show distributions below the jeans parameter and cannot be explained by the jeans fragmentation.