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Structure formation and exotic compact objects in a dissipative dark sector
Chang, Jae Hyeok; Egana-Ugrinovic, Daniel; Essig, Rouven +1 more
We present the complete history of structure formation in a simple dissipative dark-sector model. The model has only two particles: a dark electron, which is a subdominant component of dark matter, and a dark photon. Dark-electron perturbations grow from primordial overdensities, become non-linear, and form dense dark galaxies. Bremsstrahlung cool…
Lifetimes and Emergence/Decay Rates of Star Spots on Solar-type Stars Estimated by Kepler Data in Comparison with Those of Sunspots
Notsu, Yuta; Maehara, Hiroyuki; Namekata, Kosuke +7 more
Active solar-type stars show large quasi-periodic brightness variations caused by stellar rotation with star spots, and the amplitude changes as the spots emerge and decay. The Kepler data are suitable for investigations of the emergence and decay processes of star spots, which are important to understand the underlying stellar dynamo and stellar …
Distinguishing Mergers and Disks in High-redshift Observations of Galaxy Kinematics
Pacifici, Camilla; de la Vega, Alexander; Hayward, Christopher C. +9 more
The majority of massive star-forming galaxies at z ∼ 2 have velocity gradients suggestive of rotation, in addition to large amounts of disordered motions. In this paper, we demonstrate that it is challenging to distinguish the regular rotation of a disk galaxy from the orbital motions of merging galaxies with seeing-limited data. However, the merg…
Common origin for Hercules-Aquila and Virgo Clouds in Gaia DR2
Belokurov, Vasily; Koposov, Sergey E.; Simion, Iulia T.
We use a sample of ∼350 RR Lyrae stars with radial velocities and Gaia Data Release 2 proper motions to study orbital properties of the Hercules-Aquila Cloud (HAC) and Virgo Over-density (VOD). We demonstrate that both structures are dominated by stars on highly eccentric orbits, with pericentres around ∼1 kpc and apocentres at 15-25 kpc from the …
Massive Dead Galaxies at z ∼ 2 with HST Grism Spectroscopy. I. Star Formation Histories and Metallicity Enrichment
Vulcani, B.; Treu, T.; Jones, T. +7 more
Observations have revealed massive ({log}{M}* /{M}⊙ ≳ 11) galaxies that were already dead when the universe was only ∼2 Gyr. Given the short time before these galaxies were quenched, their past histories and quenching mechanism(s) are of particular interest. In this paper, we study star formation histories (SFHs) of 24 massiv…
The period-luminosity relation for δ Scuti stars using Gaia DR2 parallaxes
Bedding, Timothy R.; Murphy, Simon J.; Hey, Daniel R. +2 more
We have examined the period-luminosity (P-L) relation for δ Scuti stars using Gaia DR2 parallaxes. We included 228 stars from the catalogue of Rodríguez et al., as well as 1124 stars observed in the 4-yr Kepler mission. For each star, we considered the dominant pulsation period, and used DR2 parallaxes and extinction corrections to determine absol…
Cluster Difference Imaging Photometric Survey. I. Light Curves of Stars in Open Clusters from TESS Sectors 6 and 7
Winn, J. N.; Bouma, L. G.; Bhatti, W. +2 more
The Transiting Exoplanet Survey Satellite (TESS) is providing precise time-series photometry for most star clusters in the solar neighborhood. Using the TESS images, we have begun a Cluster Difference Imaging Photometric Survey, in which we are focusing both on stars that are candidate cluster members and on stars that show indications of youth. O…
Highly Magnified Stars in Lensing Clusters: New Evidence in a Galaxy Lensed by MACS J0416.1-2403
Miralda-Escudé, Jordi; Frye, Brenda; Dai, Liang +2 more
We examine a caustic-straddling arc at z = 0.9397 in the field of the galaxy cluster MACS J0416.1-2403 (z = 0.397) using archival multiband Hubble Space Telescope images and show that its surface brightness exhibits anomalies that can be explained by a single highly magnified star undergoing microlensing. First, we show that the surface brightness…
NGTS-4b: A sub-Neptune transiting in the desert
Jackman, James A. G.; Wheatley, Peter J.; Bayliss, Daniel +48 more
We report the discovery of NGTS-4b, a sub-Neptune-sized planet transiting a 13th magnitude K-dwarf in a 1.34 d orbit. NGTS-4b has a mass M = 20.6 ± 3.0 M⊕ and radius R = 3.18 ± 0.26 R⊕, which places it well within the so-called `Neptunian Desert'. The mean density of the planet (3.45 ± 0.95 g cm-3) is consistent wi…
A New Technique for Finding Galaxies Leaking Lyman-continuum Radiation: [S II]-deficiency
Heckman, Timothy M.; Leitherer, Claus; Wang, Bingjie +3 more
The source responsible for the reionization of the universe is believed to be the population of star-forming galaxies at z ∼ 6 to 12. The biggest uncertainty concerns the fraction of Lyman-continuum photons that actually escape from the galaxies. In recent years, several relatively small samples of “leaky” galaxies have been discovered, and clues …