d1005+68: A New Faint Dwarf Galaxy in the M81 Group

We present the discovery of d1005+68, a new faint dwarf galaxy in the M81 Group, using observations taken with the Subaru Hyper Suprime-Cam. d1005+68's color-magnitude diagram is consistent with a distance of $3.98_{-0.43}^{+0.39}$ Mpc, establishing group membership. We derive an absolute $V$-band magnitude, from stellar isochrone fitting, of $M_{V} = -7.94_{-0.50}^{+0.38}$, with a half-light radius of $r_{h} = 188_{-41}^{+39}$ pc. These place d1005+68 within the radius-luminosity locus of Local Group and M81 satellites and among the faintest confirmed satellites outside the Local Group. Assuming an age of 12 Gyr, d1005+68's red giant branch is best fit by an isochrone of [Fe/H] $= -1.90 \pm 0.24$. It has a projected separation from nearby M81 satellite BK5N of only 5 kpc. As this is well within BK5N's virial radius, we speculate that d1005+68 may be a satellite of BK5N. If confirmed, this would make d1005+68 one of the first detected satellites-of-a-satellite.Comment: 7 pages, 4 figures, 1 table, additional affiliations include

Characterizing dw1335-29, a recently discovered dwarf satellite of M83

The number, distribution, and properties of dwarf satellites are crucial probes of the physics of galaxy formation at low masses and the response of satellite galaxies to the tidal and gas dynamical effects of their more massive parent.To make progress, it is necessary to augment and solidify the census of dwarf satellites of galaxies outside the Local Group. M\"uller et al. (2015) presented 16 dwarf galaxy candidates near M83, but lacking reliable distances, it is unclear which candidates are M83 satellites. Using red giant branch stars from the HST/GHOSTS survey in conjunction with ground-based images from VLT/VIMOS, we confirm that one of the candidates, dw1335-29-- with a projected distance of 26 kpc from M83 and a distance modulus of $(m - M)_0 = 28.5^{+0.3}_{-0.1}$ -- is a satellite of M83. We estimate an absolute magnitude $M_V = -10.1 \pm{0.4}$, an ellipticity of $0.40^{+0.14}_{-0.22}$, a half light radius of $656^{+121}_{-170 }$ pc, and [Fe/H] = $-1.3^{+0.3}_{-0.4}$. Owing to dw1335-29's somewhat irregular shape and possible young stars, we classify this galaxy as a dwarf irregular or transition dwarf. This is curious, as with a projected distance of 26 kpc from M83, dw1335-29 is expected to lack recent star formation. Further study of M83's dwarf population will reveal if star formation in its satellites is commonplace (suggesting a lack of a hot gas envelope for M83 that would quench star formation) or rare (suggesting that dw1335-29 has a larger M83-centric distance, and is fortuitously projected to small radii).Comment: 7 pages, 5 figures, accepted for publication in MNRA

Andromeda XXIX: A New Dwarf Spheroidal Galaxy 200 kpc from Andromeda

We report the discovery of a new dwarf galaxy, Andromeda XXIX (And XXIX), using data from the recently released Sloan Digital Sky Survey Data Release 8, and confirmed by Gemini North telescope Multi-Object Spectrograph imaging data. And XXIX appears to be a dwarf spheroidal galaxy, separated on the sky by a little more than 15° from M31, with a distance inferred from the tip of the red giant branch of 730 ± 75 kpc, corresponding to a three-dimensional separation from M31 of 207 +20 – 2 kpc (close to M31's virial radius). Its absolute magnitude, as determined by comparison to the red giant branch luminosity function of the Draco dwarf spheroidal, is M V = –8.3 ± 0.4. And XXIX's stellar populations appear very similar to Draco's; consequently, we estimate a metallicity for And XXIX of [Fe/H] ~–1.8. The half-light radius of And XXIX is 360 ± 60 pc and its ellipticity is 0.35 ± 0.06, typical of dwarf satellites of the Milky Way and M31 at this absolute magnitude range.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90744/1/2041-8205_742_1_L15.pd

Andromeda XXVIII: A Dwarf Galaxy More Than 350 kpc from Andromeda

We report the discovery of a new dwarf galaxy, Andromeda XXVIII, using data from the recently-released SDSS DR8. The galaxy is a likely satellite of Andromeda, and, at a separation of $365^{+17}_{-1}$ kpc, would be one of the most distant of Andromeda's satellites. Its heliocentric distance is $650^{+150}_{-80}$ kpc, and analysis of its structure and luminosity show that it has an absolute magnitude of $M_V = -8.5^{+0.4}_{-1.0}$ and half-light radius of $r_h = 210^{+60}_{-50}$ pc, similar to many other faint Local Group dwarfs. With presently-available imaging we are unable to determine if there is ongoing or recent star formation, which prevents us from classifying it as a dwarf spheroidal or dwarf irregular.Comment: Accepted to ApJ Letter

Design and Synthesis of Potential Novel Antibiotic Compounds Utilising Photoredox Catalysis

The continued emergence of widespread antibiotic resistance over the prior several decades poses an increasingly severe worldwide challenge to public health. Several frontline antibiotic treatments are being rendered obsolete due to the advent of numerous bacterial resistance mechanisms, an issue further compounded by the lack of antibiotics currently residing within the antibacterial drug discovery pipeline that operate via previously unexploited mechanisms of action. There are numerous underlying issues that have propagated this unsavoury situation, some specific to antibiotic drug development and others that negatively impact the field of drug discovery as a whole. One of the latter issues centres around the implementation of high throughput target-based screening of suboptimal compound libraries for hit identification, and the narrow range of synthetic methodologies used to explore chemical space within such compound collections. Dihydrodipicolinate synthase (DHDPS) constitutes a promising biomolecular target for novel antibiotic therapies due to its key role in the biosynthesis of essential amino acid L-lysine, a process widely specific to bacteria. Despite several prior campaigns and the development of micromolar potency inhibitors of DHDPS through target–based screening approaches, so far no compounds have been developed that display in vitro antibacterial activity in the subsequent phenotypic screens. In silico screening constitutes an invaluable range of techniques used in the identification of potential hit compounds that has been implemented to great effect in numerous drug discovery campaigns, including the discovery of novel antibacterial compounds, often aiding in the design of more focused compound libraries for assessment in vitro. Photoredox catalysis has emerged as a powerful synthetic tool for enabling access to previously unexplored regions of chemical space especially within medicinal chemistry contexts, facilitating highly chemoselective activation of reagents under benign reaction conditions. Sulfonylhydrazones are well established reagents within the field of organic synthesis capable of undergoing a myriad of transformations. Recent reports concerning the photocatalytic activation of hydrazone substrates to enable radical cyclisations served as the basis for the initial interest in developing related methodologies to generate desired compounds in the search for novel antibacterial agents. In this thesis is described the design and synthesis of potential novel antibacterial compounds, initially utilising pharmacophore searches and qualitative in silico docking investigations to identify molecular scaffolds of interest as synthetic targets. The development of a novel photoredox reaction for the generation of sulfone hit structures from sulfonyl hydrazone starting materials is described, including exploration of the substrate scope and reaction mechanism studies. The synthesis of additional in silico derived hit structures is also described, as well as attempts made to expand the synthetic utility of the developed photocatalytic methodology. Initial evaluation of antibacterial activity of the compound collection is described including preliminary discussion of structure activity relationships as a foundation for the derivation of future work. The final chapter contains technical experimental details and characterisation data pertaining to the previously discussed work