College of Letters & Science
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The College of Letters and Science, the largest center for learning, teaching and research at Montana State University, offers students an excellent liberal arts and sciences education in nearly 50 majors, 25 minors and over 25 graduate degrees within the four areas of the humanities, natural sciences, mathematics and social sciences.
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Item DIISC-I: The Discovery of Kinematically Anomalous H i Clouds in M 100(American Astronomical Society, 2021-11) Gim, Hansung B.; Borthakur, Sanchayeeta; Momjian, Emmanuel; Padave, Mansi; Jansen, Rolf A.; Nelson, Dylan; Heckman, Timothy M.; Kennicutt Jr., Robert C.; Fox, Andrew J.; Pineda, Jorge L.; Thilker, David; Kauffmann, Guinevere; Tumlinson, JasonWe report the discovery of two kinematically anomalous atomic hydrogen (H i) clouds in M 100 (NGC 4321), which was observed as part of the Deciphering the Interplay between the Interstellar medium, Stars, and the Circumgalactic medium (DIISC) survey in H i 21 cm at 3.3 km s−1 spectroscopic and 44″ × 30″ spatial resolution using the Karl G. Jansky Very Large Array. 15 15 The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. These clouds were identified as structures that show significant kinematic offsets from the rotating disk of M 100. The velocity offsets of 40 km s−1 observed in these clouds are comparable to the offsets seen in intermediate-velocity clouds (IVCs) in the circumgalactic medium (CGM) of the Milky Way and nearby galaxies. We find that one anomalous cloud in M 100 is associated with star-forming regions detected in Hα and far-ultraviolet imaging. Our investigation shows that anomalous clouds in M 100 may originate from multiple mechanisms, such as star formation feedback-driven outflows, ram pressure stripping, and tidal interactions with satellite galaxies. Moreover, we do not detect any cool CGM at 38.8 kpc from the center of M 100, giving an upper limit of N(H i) ≤1.7 × 1013 cm−2 (3σ). Since M 100 is in the Virgo cluster, the nonexistence of neutral/cool CGM is a likely pathway for turning it into a red galaxy.Item COLDz: Probing Cosmic Star Formation With Radio Free–Free Emission(American Astronomical Society, 2022-01) Algera, Hiddo S. B.; Hodge, Jacqueline A.; Riechers, Dominik A.; Leslie, Sarah K.; Smail, Ian; Aravena, Manuel; Cunha, Elisabete da; Daddi, Emanuele; Decarli, Roberto; Dickinson, Mark; Gim, Hansung B.; Guaita, Lucia; Magnelli, Benjamin; Murphy, Eric J.; Pavesi, Riccardo; Sargent, Mark T.; Sharon, Chelsea E.; Wagg, Jeff; Walter, Fabian; Yun, MinRadio free–free emission is considered to be one of the most reliable tracers of star formation in galaxies. However, as it constitutes the faintest part of the radio spectrum—being roughly an order of magnitude less luminous than radio synchrotron emission at the GHz frequencies typically targeted in radio surveys—the usage of free–free emission as a star formation rate tracer has mostly remained limited to the local universe. Here, we perform a multifrequency radio stacking analysis using deep Karl G. Jansky Very Large Array observations at 1.4, 3, 5, 10, and 34 GHz in the COSMOS and GOODS-North fields to probe free–free emission in typical galaxies at the peak of cosmic star formation. We find that z ∼ 0.5–3 star-forming galaxies exhibit radio emission at rest-frame frequencies of ∼65–90 GHz that is ∼1.5–2 times fainter than would be expected from a simple combination of free–free and synchrotron emission, as in the prototypical starburst galaxy M82. We interpret this as a deficit in high-frequency synchrotron emission, while the level of free–free emission is as expected from M82. We additionally provide the first constraints on the cosmic star formation history using free–free emission at 0.5 ≲ z ≲ 3, which are in good agreement with more established tracers at high redshift. In the future, deep multifrequency radio surveys will be crucial in order to accurately determine the shape of the radio spectrum of faint star-forming galaxies, and to further establish radio free–free emission as a tracer of high-redshift star formation.