ORCID Profile
0000-0002-9604-343X
Current Organisation
The University of Texas at Austin
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: American Astronomical Society
Date: 07-2021
Publisher: American Astronomical Society
Date: 08-03-2017
Publisher: Oxford University Press (OUP)
Date: 06-07-2020
Abstract: Surveys of the Milky Way (MW) and M31 enable detailed studies of stellar populations across ages and metallicities, with the goal of reconstructing formation histories across cosmic time. These surveys motivate key questions for galactic archaeology in a cosmological context: When did the main progenitor of an MW/M31-mass galaxy form, and what were the galactic building blocks that formed it? We investigate the formation times and progenitor galaxies of MW/M31-mass galaxies using the Feedback In Realistic Environments-2 cosmological simulations, including six isolated MW/M31-mass galaxies and six galaxies in Local Group (LG)-like pairs at z = 0. We examine main progenitor ‘formation’ based on two metrics: (1) transition from primarily ex-situ to in-situ stellar mass growth and (2) mass dominance compared to other progenitors. We find that the main progenitor of an MW/M31-mass galaxy emerged typically at z ∼ 3–4 ($11.6\\!\\!-\\!\\!12.2\\, \\rm {Gyr}$ ago), while stars in the bulge region (inner 2 kpc) at z = 0 formed primarily in a single main progenitor at z ≲ 5 (${\\lesssim} \\!12.6\\, \\rm {Gyr}$ ago). Compared with isolated hosts, the main progenitors of LG-like paired hosts emerged significantly earlier (Δz ∼ 2, $\\Delta t\\!\\sim \\!1.6\\, \\rm {Gyr}$), with ∼4× higher stellar mass at all z ≳ 4 (${\\gtrsim} \\!12.2\\, \\rm {Gyr}$ ago). This highlights the importance of environment in MW/M31-mass galaxy formation, especially at early times. On average, about 100 galaxies with $\\rm {\\it{ M}}_\\rm {star}\\!\\gtrsim \\!10^5\\, \\rm {M}_\\odot$ went into building a typical MW/M31-mass system. Thus, surviving satellites represent a highly incomplete census (by ∼5×) of the progenitor population.
Publisher: American Astronomical Society
Date: 10-06-2014
Publisher: American Astronomical Society
Date: 15-04-2014
Publisher: American Astronomical Society
Date: 02-03-2017
Publisher: American Astronomical Society
Date: 10-2022
Abstract: We measure homogeneous distances to M31 and 38 associated stellar systems (−16.8 ≤ M V ≤ −6.0), using time-series observations of RR Lyrae stars taken as part of the Hubble Space Telescope Treasury Survey of M31 Satellites. From orbits of new/archival Advanced Camera for Surveys imaging, we identify RR Lyrae stars and determine their periods and mean magnitudes to a typical precision of 0.01 day and 0.04 mag. Based on period–Wesenheit–metallicity relationships consistent with the Gaia eDR3 distance scale, we uniformly measure heliocentric and M31-centric distances to a typical precision of ∼20 kpc (3%) and ∼10 kpc (8%), respectively. We revise the 3D structure of the M31 galactic ecosystem and: (i) confirm a highly anisotropic spatial distribution such that ∼80% of M31's satellites reside on the near side of M31 this feature is not easily explained by observational effects (ii) affirm the thin (rms 7–23 kpc) planar “arc” of satellites that comprises roughly half (15) of the galaxies within 300 kpc from M31 (iii) reassess the physical proximity of notable associations such as the NGC 147/185 pair and M33/AND xxii and (iv) illustrate challenges in tip-of-the-red-giant branch distances for galaxies with M V − 9.5, which can be biased by up to 35%. We emphasize the importance of RR Lyrae for accurate distances to faint galaxies that should be discovered by upcoming facilities (e.g., Rubin Observatory). We provide updated luminosities and sizes for our s le. Our distances will serve as the basis for future investigation of the star formation and orbital histories of the entire known M31 satellite system.
Publisher: American Astronomical Society
Date: 10-2023
Publisher: Oxford University Press (OUP)
Date: 14-07-2018
Publisher: American Astronomical Society
Date: 24-08-2023
Abstract: We present the JWST Resolved Stellar Populations Early Release Science (ERS) program. We obtained 27.5 hr of NIRCam and NIRISS imaging of three targets in the Local Group (Milky Way globular cluster M92, ultrafaint dwarf galaxy Draco II , and star-forming dwarf galaxy WLM), which span factors of ∼10 5 in luminosity, ∼10 4 in distance, and ∼10 5 in surface brightness. We describe the survey strategy, scientific and technical goals, implementation details, present select NIRCam color–magnitude diagrams (CMDs), and validate the NIRCam exposure time calculator (ETC). Our CMDs are among the deepest in existence for each class of target. They touch the theoretical hydrogen-burning limit in M92 ( .08 M ⊙ M F090W ∼ +13.6), include the lowest-mass stars observed outside the Milky Way in Draco II (0.09 M ⊙ M F090W ∼ +12.1), and reach ∼1.5 mag below the oldest main-sequence turnoff in WLM ( M F090W ∼ +4.6). The PARSEC stellar models provide a good qualitative match to the NIRCam CMDs, though they are ∼0.05 mag too blue compared to M92 F090W − F150W data. Our CMDs show detector-dependent color offsets ranging from ∼0.02 mag in F090W – F150W to ∼0.1 mag in F277W – F444W these appear to be due to differences in the zero-point calibrations among the detectors. The NIRCam ETC (v2.0) matches the signal-to-noise ratios based on photon noise in uncrowded fields, but the ETC may not be accurate in more crowded fields, similar to what is known for the Hubble Space Telescope. We release the point-source photometry package DOLPHOT, optimized for NIRCam and NIRISS, for the community.
Publisher: American Astronomical Society
Date: 02-2023
Abstract: We present the first publicly released catalog of sources obtained from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). HETDEX is an integral field spectroscopic survey designed to measure the Hubble expansion parameter and angular diameter distance at 1.88 z 3.52 by using the spatial distribution of more than a million Ly α -emitting galaxies over a total target area of 540 deg 2 . The catalog comes from contiguous fiber spectra coverage of 25 deg 2 of sky from 2017 January through 2020 June, where object detection is performed through two complementary detection methods: one designed to search for line emission and the other a search for continuum emission. The HETDEX public release catalog is dominated by emission-line galaxies and includes 51,863 Ly α -emitting galaxy (LAE) identifications and 123,891 [O ii ]-emitting galaxies at z 0.5. Also included in the catalog are 37,916 stars, 5274 low-redshift ( z 0.5) galaxies without emission lines, and 4976 active galactic nuclei. The catalog provides sky coordinates, redshifts, line identifications, classification information, line fluxes, [O ii ] and Ly α line luminosities where applicable, and spectra for all identified sources processed by the HETDEX detection pipeline. Extensive testing demonstrates that HETDEX redshifts agree to within Δ z 0.02, 96.1% of the time to those in external spectroscopic catalogs. We measure the photometric counterpart fraction in deep ancillary Hyper Suprime-Cam imaging and find that only 55.5% of the LAE s le has an r -band continuum counterpart down to a limiting magnitude of r ∼ 26.2 mag (AB) indicating that an LAE search of similar sensitivity to HETDEX with photometric preselection would miss nearly half of the HETDEX LAE catalog s le. Data access and details about the catalog can be found online at hetdex.org/ . A copy of the catalogs presented in this work (Version 3.2) is available to download at Zenodo doi: 10.5281/zenodo.7448504 .
Publisher: Oxford University Press (OUP)
Date: 08-08-2013
Publisher: American Astronomical Society
Date: 27-11-2017
Publisher: American Astronomical Society
Date: 08-03-2016
Location: United States of America
Location: United States of America
No related grants have been discovered for Michael Boylan-Kolchin.