Michelle Collins

Michelle Collins
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Michelle Collins

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Astrophysics of Galaxies (21)
Cosmology and Nongalactic Astrophysics (7)
Solar and Stellar Astrophysics (1)
Physics - Physics and Society (1)
Instrumentation and Methods for Astrophysics (1)

Publications Authored By Michelle Collins

Affiliations: 1Department of Physics, University of Surrey, Guildford GU2 7XH, UK, 2Department of Physics, University of Surrey, Guildford GU2 7XH, UK, 3Department of Physics, University of Surrey, Guildford GU2 7XH, UK, 4Department of Physics, University of Surrey, Guildford GU2 7XH, UK, 5Department of Physics, University of Surrey, Guildford GU2 7XH, UK, 6Department of Physics, University of Surrey, Guildford GU2 7XH, UK, 7Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK, 8Department of Physics, University of Surrey, Guildford GU2 7XH, UK, 9Department of Physics, University of Surrey, Guildford GU2 7XH, UK

We present a new technique to probe the central dark matter (DM) density profile of galaxies that harnesses both the survival and observed properties of star clusters. As a first application, we apply our method to the `ultra-faint' dwarf Eridanus II (Eri II) that has a lone star cluster ~45 pc from its centre. Using a grid of collisional $N$-body simulations, incorporating the effects of stellar evolution, external tides and dynamical friction, we show that a DM core for Eri II naturally reproduces the size, radial light profile and projected position of its star cluster. Read More

We present homogeneous, sub-horizontal branch photometry of twenty dwarf spheroidal satellite galaxies of M31 observed with the Hubble Space Telescope. Combining our new data for sixteen systems with archival data in the same filters for another four, we show that Andromeda dwarf spheroidal galaxies favor strikingly red horizontal branches or red clumps down to ~10^{4.2} Lsun (M_V ~ -5. Read More

In the last decade, several ultra faint objects (UFOs, $M_V\gtrsim-3.5$) have been discovered in the outer halo of the Milky Way. For some of these objects it is not clear whether they are star clusters or (ultra-faint) dwarf galaxies. Read More

We present new wide-field images of the low-surface brightness Virgo Cluster dwarf galaxy VCC 1661. The extant literature lists a broad range of radii for this object, covering a factor of more than four, depending on the filters used and the details of the analyses. While some studies find a radius typical of other Virgo dwarfs and note the normality of this object, any larger spatial extent, taken at face value, would render this galaxy the largest dwarf in the Virgo Cluster samples. Read More

We have used dedicated 0.7m telescopes in California and Israel to image the halos of ~200 galaxies in the Local Volume to 29 mag/sq arcsec, the sample mainly drawn from the 2MASS Large Galaxy Atlas (LGA). We supplement the LGA sample with dwarf galaxies and more distant giant ellipticals. Read More

Authors: Demitri Muna, Michael Alexander, Alice Allen, Richard Ashley, Daniel Asmus, Ruyman Azzollini, Michele Bannister, Rachael Beaton, Andrew Benson, G. Bruce Berriman, Maciej Bilicki, Peter Boyce, Joanna Bridge, Jan Cami, Eryn Cangi, Xian Chen, Nicholas Christiny, Christopher Clark, Michelle Collins, Johan Comparat, Neil Cook, Darren Croton, Isak Delberth Davids, Éric Depagne, John Donor, Leonardo A. dos Santos, Stephanie Douglas, Alan Du, Meredith Durbin, Dawn Erb, Daniel Faes, J. G. Fernández-Trincado, Anthony Foley, Sotiria Fotopoulou, Søren Frimann, Peter Frinchaboy, Rafael Garcia-Dias, Artur Gawryszczak, Elizabeth George, Sebastian Gonzalez, Karl Gordon, Nicholas Gorgone, Catherine Gosmeyer, Katie Grasha, Perry Greenfield, Rebekka Grellmann, James Guillochon, Mark Gurwell, Marcel Haas, Alex Hagen, Daryl Haggard, Tim Haines, Patrick Hall, Wojciech Hellwing, Edmund Christian Herenz, Samuel Hinton, Renee Hlozek, John Hoffman, Derek Holman, Benne Willem Holwerda, Anthony Horton, Cameron Hummels, Daniel Jacobs, Jens Juel Jensen, David Jones, Arna Karick, Luke Kelley, Matthew Kenworthy, Ben Kitchener, Dominik Klaes, Saul Kohn, Piotr Konorski, Coleman Krawczyk, Kyler Kuehn, Teet Kuutma, Michael T. Lam, Richard Lane, Jochen Liske, Diego Lopez-Camara, Katherine Mack, Sam Mangham, Qingqing Mao, David J. E. Marsh, Cecilia Mateu, Loïc Maurin, James McCormac, Ivelina Momcheva, Hektor Monteiro, Michael Mueller, Roberto Munoz, Rohan Naidu, Nicholas Nelson, Christian Nitschelm, Chris North, Juan Nunez-Iglesias, Sara Ogaz, Russell Owen, John Parejko, Vera Patrício, Joshua Pepper, Marshall Perrin, Timothy Pickering, Jennifer Piscionere, Richard Pogge, Radek Poleski, Alkistis Pourtsidou, Adrian M. Price-Whelan, Meredith L. Rawls, Shaun Read, Glen Rees, Hanno Rein, Thomas Rice, Signe Riemer-Sørensen, Naum Rusomarov, Sebastian F. Sanchez, Miguel Santander-García, Gal Sarid, William Schoenell, Aleks Scholz, Robert L. Schuhmann, William Schuster, Peter Scicluna, Marja Seidel, Lijing Shao, Pranav Sharma, Aleksandar Shulevski, David Shupe, Cristóbal Sifón, Brooke Simmons, Manodeep Sinha, Ian Skillen, Bjoern Soergel, Thomas Spriggs, Sundar Srinivasan, Abigail Stevens, Ole Streicher, Eric Suchyta, Joshua Tan, O. Grace Telford, Romain Thomas, Chiara Tonini, Grant Tremblay, Sarah Tuttle, Tanya Urrutia, Sam Vaughan, Miguel Verdugo, Alexander Wagner, Josh Walawender, Andrew Wetzel, Kyle Willett, Peter K. G. Williams, Guang Yang, Guangtun Zhu, Andrea Zonca

The Astropy Project (http://astropy.org) is, in its own words, "a community effort to develop a single core package for Astronomy in Python and foster interoperability between Python astronomy packages." For five years this project has been managed, written, and operated as a grassroots, self-organized, almost entirely volunteer effort while the software is used by the majority of the astronomical community. Read More

We present a comprehensive analysis of the structural properties and luminosities of the 23 dwarf spheroidal galaxies that fall within the footprint of the Pan-Andromeda Archaeological Survey (PAndAS). These dwarf galaxies represent the large majority of Andromeda's known satellite dwarf galaxies and cover a wide range in luminosity ($-11.6Read More

We present a chemodynamical analysis of the Leo~V dwarf galaxy, based on Keck II DEIMOS spectra of 8 member stars. We find a systemic velocity for the system of $\langle v_r\rangle = 170.9^{+ 2. Read More

The ultra-faint satellite galaxy Hercules has a strongly elongated and irregular morphology with detections of tidal features up to 1.3 deg (3 kpc) from its center. This suggests that Hercules may be dissolving under the Milky Way's gravitational influence, and hence could be a tidal stream in formation rather than a bound, dark-matter dominated satellite. Read More

As part of the Z-PAndAS Keck II DEIMOS survey of resolved stars in our neighboring galaxy, Andromeda (M31), we have built up a unique data set of measured velocities and chemistries for thousands of stars in the Andromeda stellar halo, particularly probing its rich and complex substructure. In this contribution, we will discuss the structural, dynamical and chemical properties of Andromeda's dwarf spheroidal galaxies, and how there is no observational evidence for a difference in the evolutionary histories of those found on and off M31's vast plane of satellites. We will also discuss a possible extension to the most significant merger event in M31 - the Giant Southern Stream - and how we can use this feature to refine our understanding of M31's mass profile, and its complex evolution. Read More

We present MUSE observations of the debated ultra faint stellar system Crater. We spectroscopically confirm 26 member stars of this system via radial velocity measurements. We derive the systematic instrumental velocity uncertainty of MUSE spectra to be 2. Read More

We present a study of the recently discovered compact stellar system Triangulum II. From observations conducted with the DEIMOS spectrograph on Keck II, we obtained spectra for 13 member stars that follow the CMD features of this very faint stellar system and include two bright red giant branch stars. Tri II has a very negative radial velocity (=-383. Read More

We present the first spectroscopic analysis of the faint and compact stellar system Draco II (Dra II, M_V=-2.9+/-0.8, r_h=19^{+8}_{-6} pc), recently discovered in the Pan-STARRS1 3{\pi} survey. Read More

The thin, extended planes of satellite galaxies detected around both the Milky Way and Andromeda are not a natural prediction of the LCDM paradigm. Galaxies in these distinct planes may have formed and evolved in a different way (e.g. Read More

A central tenet of the current cosmological paradigm is that galaxies grow over time through the accretion of smaller systems. Here, we present new kinematic measurements near the centre of one of the densest pronounced substructures, the South-West Cloud, in the outer halo of our nearest giant neighbour, the Andromeda galaxy. These observations reveal that the kinematic properties of this region of the South-West Cloud are consistent with those of PA-8, a globular cluster previously shown to be co-spatial with the stellar substructure. Read More

We present Keck II/DEIMOS spectroscopy of the three distant dwarf galaxies of M31 Lacerta I, Cassiopeia III, and Perseus I, recently discovered within the Pan-STARRS1 3\pi imaging survey. The systemic velocities of the three systems (v_{r,helio} = -198.4 +/- 1. Read More

We reveal the highly structured nature of the Milky Way stellar halo within the footprint of the PAndAS photometric survey from blue main sequence and main sequence turn-off stars. We map no fewer than five stellar structures within a heliocentric range of ~5 to 30 kpc. Some of these are known (the Monoceros Ring, the Pisces/Triangulum globular cluster stream), but we also uncover three well-defined stellar structures that could be, at least partly, responsible for the so-called Triangulum/Andromeda and Triangulum/Andromeda 2 features. Read More

We present an analysis of the large-scale structure of the halo of the Andromeda galaxy, based on the Pan-Andromeda Archeological Survey (PAndAS), currently the most complete map of resolved stellar populations in any galactic halo. Despite copious substructure, the global halo populations follow closely power law profiles that become steeper with increasing metallicity. We divide the sample into stream-like populations and a smooth halo component. Read More

We investigate the claim that all dwarf spheroidal galaxies (dSphs) reside within halos that share a common, universal mass profile as has been derived for dSphs of the Galaxy. By folding in kinematic information for 25 Andromeda dSphs, more than doubling the previous sample size, we find that a singular mass profile can not be found to fit all the observations well. Further, the best-fit dark matter density profile measured for solely the Milky Way dSphs is marginally discrepant (at just beyond the 1 sigma level) with that of the Andromeda dSphs, where a profile with lower maximum circular velocity, and hence mass, is preferred. Read More

We present a homogeneous kinematic analysis of red giant branch stars within 18 of the 28 Andromeda dwarf spheroidal (dSph) galaxies, obtained using the Keck I LRIS and Keck II DEIMOS spectrographs. Based on their g-i colors (taken with the CFHT MegaCam imager), physical positions on the sky, and radial velocities, we assign probabilities of dSph membership to each observed star. Using this information, the velocity dispersions, central masses and central densities of the dark matter halos are calculated for these objects, and compared with the properties of the Milky Way dSph population. Read More

Dwarf satellite galaxies are thought to be the remnants of the population of primordial structures that coalesced to form giant galaxies like the Milky Way. An early analysis noted that dwarf galaxies may not be isotropically distributed around our Galaxy, as several are correlated with streams of HI emission, and possibly form co-planar groups. These suspicions are supported by recent analyses, and it has been claimed that the apparently planar distribution of satellites is not predicted within standard cosmology, and cannot simply represent a memory of past coherent accretion. Read More

We report on the discovery of strong tidal features around a dwarf spheroidal galaxy in the Hydra I galaxy cluster, indicating its ongoing tidal disruption. This very low surface brightness object, HCC-087, was originally classified as an early-type dwarf in the Hydra Cluster Catalogue (HCC), but our re-analysis of the ESO-VLT/FORS images of the HCC unearthed a clear indication of an S-shaped morphology and a large spatial extent. Its shape, luminosity (M_V=-11. Read More

Using spectroscopic data taken with Keck II DEIMOS by the Z-PAndAS team in the Andromeda-Triangulum region, I present a comparison of the disc and satellite systems of Andromeda with those of our own Galaxy. I discuss the observed discrepancies between the masses and scale radii of Andromeda dwarf spheroidal galaxies of a given luminosity with those of the Milky Way. I also also present an analysis of the newly discovered M31 thick disc, which is measured to be hotter, more extended and thicker than that seen in the Milky Way. Read More

In hierarchical cosmological models, galaxies grow in mass through the continual accretion of smaller ones. The tidal disruption of these systems is expected to result in loosely bound stars surrounding the galaxy, at distances that reach $10 - 100$ times the radius of the central disk. The number, luminosity and morphology of the relics of this process provide significant clues to galaxy formation history, but obtaining a comprehensive survey of these components is difficult because of their intrinsic faintness and vast extent. Read More