Browsing by Author "Johnston, Evelyn J."
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- ItemBUDDI-MaNGA II: the star-formation histories of bulges and discs of S0s(OXFORD UNIV PRESS, 2022) Johnston, Evelyn J.; Haussler, Boris; Jegatheesan, Keerthana; Fraser-McKelvie, Amelia; Coccato, Lodovico; Cortesi, Arianna; Jaffe, Yara; Galaz, Gaspar; Mora, Marcelo; Ordenes-Briceno, YasnaMany processes have been proposed to explain the quenching of star formation in spiral galaxies and their transformation into S0s. These processes affect the bulge and disc in different ways, and so by isolating the bulge and disc spectra, we can look for these characteristic signatures. In this work, we used BUDDI to cleanly extract the spectra of the bulges and discs of 78 S0 galaxies in the MaNGA Survey. We compared the luminosity and mass weighted stellar populations of the bulges and discs, finding that bulges are generally older and more metal rich than their discs. When considering the mass and environment of each galaxy, we found that the galaxy stellar mass plays a more significant role on the formation of the bulges. Bulges in galaxies with masses >= 10(10) M-circle dot built up the majority of their mass rapidly early in their lifetimes, while those in lower mass galaxies formed over more extended time-scales and more recently. No clear difference was found in the formation or quenching processes of the discs as a function of galaxy environment. We conclude that more massive S0 galaxies formed through an inside-out scenario, where the bulge formed first and evolved passively while the disc underwent a more extended period of star formation. In lower mass S0s, the bulges and discs either formed together from the same material, or through an outside-in scenario. Our results therefore imply multiple formation mechanisms for S0 galaxies, the pathway of which is chiefly determined by a galaxy's current stellar mass.
- ItemIntrinsic Morphology of Ultra-diffuse Galaxies(IOP PUBLISHING LTD, 2020) Rong, Yu; Dong, Xiao Yu; Puzia, Thomas H.; Galaz, Gaspar; Sanchez Janssen, Ruben; Cao, Tianwen; van der Burg, Remco F. J.; Sifon, Cristobal; Pina, Pavel E. Mancera; Marcelo, Mora; D'Ago, Giuseppe; Zhang, Hong Xin; Johnston, Evelyn J.; Eigenthaler, PaulWith the published data of apparent axis ratios for 1109 ultra-diffuse galaxies (UDGs) located in 17 low-redshift (z similar to 0.020-0.063) galaxy clusters and 84 UDGs in two intermediate-redshift (z similar to 0.308-0.348) clusters, we take advantage of a Markov Chain Monte Carlo approach and assume a triaxial model to investigate the intrinsic morphologies of UDGs. In contrast to the conclusion of Burkert, i.e., the underlying shapes of UDGs are purely prolate (C = B < A), we find that the data favor the oblate-triaxial models (i.e., thick disks with C < B less than or similar to A) over the nearly prolate ones. We also find that the intrinsic morphologies of UDGs are related to their stellar masses/luminosities, environments, and redshifts. First, the more luminous UDGs have puffier morphologies compared with the less luminous counterparts; the UDG morphologic dependence on luminosity is distinct from that of the typical quiescent dwarf ellipticals (dEs) and dwarf spheroidals (dSphs); in this sense, UDGs may not be simply treated as an extension of the dE/dSph class with similar evolutionary histories; they may differ not only in size. Second, the UDGs with smaller clustercentric distances are more puffed up, compared with the counterparts with larger clustercentric distances; in combination with the UDG thickness dependence on luminosity, the puffier morphologies of UDGs with high luminosities or located in the denser environments are very likely to be attributed to tidal interactions with massive galaxies. Third, we find that the intermediate-redshift UDGs are more flattened, compared with the low-redshift counterparts, which plausibly suggests a "disky" origin for the high-redshift, newly born UDGs.
- ItemThe Giant Low Surface Brightness Galaxy Malin 1: New Constraints for Its Molecular Gas Mass from GBT/ARGUS Observations(2022) Galaz Lladser, Gaspar; Frayer, David T.; Blaña, Matías; Howk, J. Christopher; Puzia, Thomas; Johnston, Evelyn J.; Ordenes Briceño, Yasna; Church, Sarah; Gil, Santiago; Joachimi, Katerine; Mora, MarceloWe report on results from GBT/ARGUS 12CO(1-0) observations for the giant low surface brightness galaxy Malin 1, which allow us to determine an upper limit for its CO mass, and hence its molecular gas mass and molecular gas mass surface density ? H 2 . Although we performed very deep observations through 17 hr on-source integration time, reaching a noise level of ?0.2 mK (T A * ) with a corresponding extended source CO limit (3?) of 0.09 K km s?1, 19 times more sensitive than previous works, we do not detect the 12CO(1-0) emission line. However, the observations allow us to estimate an upper limit (3?) for the CO mass of about 7.4 × 109 M ? for the extended emission, and 1.4 × 108 M ? for the central part of the galaxy. With these figures we conclude that the molecular gas surface density is lower than 0.3 M ? pc?2, and the corresponding molecular to atomic gas mass ratio is lower than 0.13. The evidence suggests quite different physical conditions for the interstellar medium in Malin 1 compared to that of normal, high surface brightness spirals. This, in one way to another, keeps an usual molecular gas tracer as CO hidden from our observations, in spite of the diverse stellar and structural properties of Malin 1 observed by several authors since more than 30 yr.