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Events

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Daily image

Summer project: The mysterious hydrogen in the barred spiral galaxy NGC 1672

© N/A

NGC 1672 is a barred spiral galaxy located in a relatively isolated environment, with only four smaller satellites in the MeerKAT field of view, and with regular star forming activity for its mass. Despite this, the MHONGOOSE Survey reveals asymmetries and tail-like structures in the low-column density HI of both NGC 1672 and its satellites (left panel). Such features are typically associated with galaxies in denser, strongly interacting environments. Given the low density of the surrounding intergalactic medium, these structures are likely not caused by ram-pressure stripping alone, but rather by tidal interactions and close flybys. In support of this, all satellites show morphological asymmetries (in both stellar and HI emission) as well as dynamical irregularities.

A 3D tilted-ring model of the HI in NGC 1672 was fitted using 3DBarolo (Di Teodoro & Fraternali 2015), revealing a dual-plateau rotation curve with a rapid rise in rotational velocity at a radius of ~20 kpc (upper right panel). The expected rotational velocity from the baryonic Tully–Fisher relation (Lelli, McGaugh, & Schombert 2015) is consistent with the higher outer-disk velocity, suggesting that this represents the true rotational velocity of the galaxy. The dual plateau points to two possible scenarios: either the presence of two rotating discs, or the bar having a large effect on the motion in the inner regions of the galaxy.

Colloquia

May 1, 2022

The Commensal Radio Astronomy FAST Survey (CRAFTS)

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) has released its first call for proposal and will be open to the international community next year. Based on a novel technique of high-cadence CAL injection, we have realized the world's first calibrated commensal survey mode, simultaneously taking data for pulsar search, HI galaxies, HI imaging, and FRBs. I introduce here one of the major survey plans, namely, the Commensal Radio Astronomy FAST Survey (CRAFTS, Li et al. 2018), which has discovered more than 100 new pulsars, including a few dozen MSPs, 5 new FRBs, including one new repeater. I will also briefly describe recent FAST results from CRAFTS and other dedicated programs, including new insights into the characteristic energy of FRBs, the formation process of neutron stars, the evolution of interstellar medium, etc.
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May 14, 2022

Extreme UV Emission: Bridging Galaxy Evolution Across Cosmic Time

In the last few years, our first glimpse of the spectral properties of z∼5−7 galaxies has emerged. Deep UV spectra have revealed prominent high-ionization nebular emission lines (i.e., C IV, He II, C III]) indicating that extreme radiation fields may be characteristic of reionization-era systems. While such strong high-ionization emission lines are atypical of the well-studied z∼0−3 galaxy samples, our recent UV spectral campaigns have revealed several galaxies with analogous emission-line features to reionization-era systems. I will discuss the recent detection of extremely strong UV emission in nearby galaxies and the potential sources of their very hard ionizing radiation fields. Such strong detections of high-ionization emission lines have been linked to the leakage of Lyman continuum (LyC) photons (necessary for reionization) both theoretically and observationally. These extreme UV emission-line dwarf galaxies provide a template for the extreme conditions that are important for reionization, however their features are still poorly understood. In preparation for the coming UV window onto the early universe with the advent of ELTs and JWST, I will introduce the COS Legacy Archival Spectroscopic SurveY - an upcoming large HST program designed to disentangle the stellar and nebular spectral signatures of 45 star-forming galaxies. This program will calibrate new UV diagnostics that will allow us to trace galaxy evolution to the distant universe, unveiling the properties of reionization-era galaxies.
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