Search Publications
Evidence for an Intermediate-mass Milky Way from Gaia DR2 Halo Globular Cluster Motions
van der Marel, Roeland P.; Watkins, Laura L.; Evans, N. Wyn +1 more
We estimate the mass of the Milky Way (MW) within 21.1 kpc using the kinematics of halo globular clusters (GCs) determined by Gaia. The second Gaia data release (DR2) contained a catalog of absolute proper motions (PMs) for a set of Galactic GCs and satellite galaxies. We select from the catalog only halo GCs, identifying a total of 34 GCs spannin…
A Second Galaxy Missing Dark Matter in the NGC 1052 Group
van Dokkum, Pieter; Romanowsky, Aaron J.; Conroy, Charlie +2 more
The ultra-diffuse galaxy NGC1052-DF2 has a very low velocity dispersion, indicating that it has little or no dark matter. Here we report the discovery of a second galaxy in this class, residing in the same group. NGC1052-DF4 closely resembles NGC1052-DF2 in terms of its size, surface brightness, and morphology; has a similar distance of {D}sb…
Observational Constraints on the Merger History of Galaxies since z ≈ 6: Probabilistic Galaxy Pair Counts in the CANDELS Fields
Pérez-González, Pablo G.; Grogin, Norman A.; Koekemoer, Anton M. +13 more
Galaxy mergers are expected to have a significant role in the mass assembly of galaxies in the early universe, but there are very few observational constraints on the merger history of galaxies at z > 2. We present the first study of galaxy major mergers (mass ratios <1:4) in mass-selected samples out to z ≈ 6. Using all five fields of the H…
The Optical Afterglow of GW170817 at One Year Post-merger
Lyman, J. D.; Fruchter, A. S.; Wiersema, K. +9 more
We present observations of the optical afterglow of GRB 170817A, made by the Hubble Space Telescope, between 2018 February and August, up to one year after the neutron star merger GW170817. The afterglow shows a rapid decline beyond 170 days, and confirms the jet origin for the observed outflow, in contrast to more slowly declining expectations fo…
The ALMA Spectroscopic Survey in the HUDF: CO Luminosity Functions and the Molecular Gas Content of Galaxies through Cosmic History
Carilli, Chris; Somerville, Rachel S.; Bacon, Roland +34 more
We use the results from the ALMA large program ASPECS, the spectroscopic survey in the Hubble Ultra Deep Field (HUDF), to constrain CO luminosity functions of galaxies and the resulting redshift evolution of ρ(H2). The broad frequency range covered enables us to identify CO emission lines of different rotational transitions in the HUDF …
1ES 1927+654: An AGN Caught Changing Look on a Timescale of Months
Filippenko, Alexei V.; Remillard, Ronald A.; Rest, Armin +21 more
We study the sudden optical and ultraviolet (UV) brightening of 1ES 1927+654, which until now was known as a narrow-line active galactic nucleus (AGN). 1ES 1927+654 was part of the small and peculiar class of “true Type-2” AGNs that lack broad emission lines and line-of-sight obscuration. Our high-cadence spectroscopic monitoring captures the appe…
Mapping Metallicity Variations across Nearby Galaxy Disks
Chevance, M.; Meidt, S. E.; Schinnerer, E. +21 more
The distribution of metals within a galaxy traces the baryon cycle and the buildup of galactic disks, but the detailed gas phase metallicity distribution remains poorly sampled. We have determined the gas phase oxygen abundances for 7138 H II regions across the disks of eight nearby galaxies using Very Large Telescope/Multi Unit Spectroscopic Expl…
Do Kepler Superflare Stars Really Include Slowly Rotating Sun-like Stars?—Results Using APO 3.5 m Telescope Spectroscopic Observations and Gaia-DR2 Data
Notsu, Yuta; Maehara, Hiroyuki; Namekata, Kosuke +7 more
We report the latest view of Kepler solar-type (G-type main-sequence) superflare stars, including recent updates with Apache Point Observatory (APO) 3.5 m telescope spectroscopic observations and Gaia-DR2 data. First, we newly conducted APO 3.5 m spectroscopic observations of 18 superflare stars found from Kepler 1-minute time-cadence data. More t…
The Streams of the Gaping Abyss: A Population of Entangled Stellar Streams Surrounding the Inner Galaxy
Malhan, Khyati; Ibata, Rodrigo A.; Martin, Nicolas F.
We present the discovery of a large population of stellar streams that surround the inner Galaxy, found in the Gaia DR2 catalog using the new STREAMFINDER algorithm. Here we focus on the properties of eight new high-significance structures found at heliocentric distances between 1 and 10 kpc and at Galactic latitudes | b| > 20^\circ , named Sli…
Constraining the Neutron Star Mass-Radius Relation and Dense Matter Equation of State with NICER. I. The Millisecond Pulsar X-Ray Data Set
Steiner, James F.; Remillard, Ronald A.; Enoto, Teruaki +27 more
We present the set of deep Neutron Star Interior Composition Explorer (NICER) X-ray timing observations of the nearby rotation-powered millisecond pulsars PSRs J0437-4715, J0030+0451, J1231-1411, and J2124-3358, selected as targets for constraining the mass-radius relation of neutron stars and the dense matter equation of state (EoS) via modeling …