Events, Seminars, Talks

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JWST observations of nearby galaxies reveal the physics of the interstellar medium and star formation in stunning detail (5-50 pc resolution). I will present early results from the PHANGS-JWST Treasury program (GO 2107; PI Janice Lee), focusing on four galaxies which were observed in July and August of 2022. PHANGS-JWST will eventually cover 19 nearby galaxies, chosen for their deep ancillary data from ALMA, VLT-MUSE, and Hubble, among other observations. The PHANGS-JWST NIRCam and MIRI imaging reveal a wealth of detail—embedded star clusters, pervasive filamentary structure, a multitude of bubbles and shells throughout the ISM. I will highlight some of the key early science results from our team, including new insights into the behavior of polycyclic aromatic hydrocarbons; characterization of filaments and bubbles; the relationship between mid-IR emission, gas, and star formation; discovery of deeply embedded clusters; constraints on stellar feedback and molecular cloud lifetimes; and more.

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The interaction between interstellar dust, ice and gas plays a major role for the chemistry in regions where star and planets form. Different reactions occur in the gas and on the ice mantles of dust grains in these regions, and consequently the mutual exchange of matter between the two phases is what regulates the physical and chemical evolution of newborn stars and planets. In this talk, I will introduce recent discoveries using JWST that are advancing our understanding of this complex interplay. I will show first JWST observations of the PDS 70 planet-forming disk as part of the MIRI mid-INfrared Disk Survey (MINDS, PI: Th. Henning). The much higher sensitivity of MIRI-MRS compared with previous Spitzer data reveals emission of water vapour. This demonstrates that the terrestrial planet-forming zone of PDS 70 has maintained to some degree the physical and chemical conditions of young disks, in spite of the ~65 AU planet-induced gap.

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The Vera C. Rubin Observatory is approaching first light in mid-2024. Equipped with what is considered to be the world’s largest CCD camera, the Rubin Observatory will begin scanning the entire visible southern sky every few days. During its ten-year mission, billions of objects will be discovered, and the stream of alerts from difference image analysis will provide on the order of tens of millions of alerts each night. In order to compare and assess the impact on the various science objectives, extensive operational simulations are performed to help optimize the observing strategy. In the context of the microlensing subgroup of the Rubin LSST Transients and Variable Stars Science Collaboration (TVS), we show how the microlensing science case has been treated and what we can expect from different observing strategies. We will also highlight the work done as part of the ARI in-kind contribution and the opportunities for future ARI researchers.

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To measure the extragalactic distances and consequently infer the Hubble constant (H0), several standard candles have been tested over the past decades. In this time of Hubble tension, Type-II Cepheids (T2Cs) could provide an alternative window to establish the first rung of the distance ladder in contrast to Classical Cepheids (CCs). In this regard, T2C’s Period-Luminosity (PL) & Period-Wesenheit (PW) relations show marginal to no metallicity dependence based on the spectral windows used. Hence, they may provide independent means to compute H0 and also could be advantageous distance indicators for the systems which are deprived of CCs. However, these Population-II pulsating stars were never thoroughly tested for distance estimation. In this talk, I will therefore assert the potency of T2Cs as a new avenue for the calibration of the extragalactic distance scale as compared to CCs & Tip of the Red Giant Branch (TRGB). To test this, we considered LMC as an anchor galaxy & M31 as a benchmark galaxy. In order to derive the robust PL/PW relations in the gri bands, we employed the bayesian probabilistic method which is more immune to outliers than the classical methods used in past literature studies. After further analysis to derive the final distances, we compared the results from T2Cs with CCs, TRGB and the CC’s precise results from HST photometry (Li & Riess 2021). On this account, we show that T2Cs can be used as accurate and precise probes of the extragalactic distance scale. Thus, they would be an excellent candidate for future JWST observations.

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Neutral hydrogen in the filaments of the cosmic web may be observable through emission of the Lyman-alpha line. Although luminous Lyman-alpha emitters are already an established tracer of the matter distribution in the high-redshift universe, the implications of the faint Lyman-alpha glow within the cosmic web, away from luminous emitters, are yet to be explored. In this talk, I will discuss the nature of large-scale, diffuse Lyman-alpha filaments and their detectability with recent integral field spectrographs such as VLT-MUSE, K-CWI, and HET-VIRUS. To explore this, we combine recent cosmological magnetohydrodynamical galaxy formation simulations with explicit calculation of the Lyman-alpha radiative transfer. We find that observable filaments are illuminated by Lyman-alpha photons that are emitted from the circumgalactic medium of intermediate-mass halos, rather than from the filaments themselves. These photons then escape and scatter within their surrounding, substantially boosting the Lyman-alpha signal from diffuse filaments. Our work provides a reference model for Lyman-alpha filaments, and demonstrates the importance and complexities of Lyman-alpha radiative transfer across spatial scales.

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