The Astrophysical Distance Scale: V. A 2% Distance to the Local Group Spiral M33 via the JAGB Method, Tip of the Red Giant Branch, and Leavitt Law

The J-region asymptotic giant branch (JAGB) method is a new standard candle that is based on the stable intrinsic J-band magnitude of color-selected carbon stars, and has a precision comparable to other primary distance indicators such as Cepheids and the TRGB. We further test the accuracy of the JAGB method in the Local Group Galaxy M33. M33's moderate inclination, low metallicity, and nearby proximity make it an ideal laboratory for tests of systematics in local distance indicators. Using high-precision optical BVI and near-infrared JHK photometry, we explore the application of three independent distance indicators: the JAGB method, the Cepheid Leavitt Law, and the TRGB. We find: $\mu_0$ (TRGB I) = 24.72 +/- 0.02 (stat) +/- 0.07 (sys) mag, $\mu_0$ (TRGB NIR) = 24.72 +/- 0.04 (stat) +/- 0.10 (sys) mag, $\mu_0$ (JAGB) = 24.67 +/- 0.03 (stat) +/- 0.04 (sys) mag, $\mu_0$ (Cepheid) = 24.71 +/- 0.04 (stat) +/- 0.01 (sys) mag. For the first time, we also directly compare a JAGB distance using ground-based and space-based photometry. We measure: $\mu_0$ (JAGB F110W) = 24.71 +/- 0.06 (stat) +/- 0.05 (sys) mag using the (F814-F110W) color combination to effectively isolate the JAGB stars. In this paper, we measure a distance to M33 accurate to 2% and provide further evidence that the JAGB method is a powerful extragalactic distance indicator that can effectively probe a local measurement of the Hubble constant using spaced-based observations. We expect to measure the Hubble constant via the JAGB method in the near future, using observations from JWST.Comment: 23 pages, 14 figures, accepted to the ApJ. v2 is exactly the same as v1 except for a fixed minor typo found while looking at the proof

SIGNALS: I. Survey description

SIGNALS, the Star formation, Ionized Gas, and Nebular Abundances Legacy Survey, is a large observing programme designed to investigate massive star formation and H II regions in a sample of local extended galaxies. The programme will use the imaging Fourier transform spectrograph SITELLE at the Canada–France–Hawaii Telescope. Over 355 h (54.7 nights) have been allocated beginning in fall 2018 for eight consecutive semesters. Once completed, SIGNALS will provide a statistically reliable laboratory to investigate massive star formation, including over 50 000 resolved H II regions: the largest, most complete, and homogeneous data base of spectroscopically and spatially resolved extragalactic H II regions ever assembled. For each field observed, three datacubes covering the spectral bands of the filters SN1 (363– 386 nm), SN2 (482–513 nm), and SN3 (647–685 nm) are gathered. The spectral resolution selected for each spectral band is 1000, 1000, and 5000, respectively. As defined, the project sample will facilitate the study of small-scale nebular physics and many other phenomena linked to star formation at a mean spatial resolution of ∼20 pc. This survey also has considerable legacy value for additional topics, including planetary nebulae, diffuse ionized gas, and supernova remnants. The purpose of this paper is to present a general outlook of the survey, notably the observing strategy, galaxy sample, and science requirementsThis research was based on observations obtained at the CFHT, which is operated from the summit of Mauna Kea by the National Research Council of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii

Possible Disintegrating Short-Period Super-Mercury Orbiting KIC 12557548

We report here on the discovery of stellar occultations, observed with Kepler, that recur periodically at 15.685 hour intervals, but which vary in depth from a maximum of 1.3% to a minimum that can be less than 0.2%. The star that is apparently being occulted is KIC 12557548, a K dwarf with T_eff = 4400 K and V = 16. Because the eclipse depths are highly variable, they cannot be due solely to transits of a single planet with a fixed size. We discuss but dismiss a scenario involving a binary giant planet whose mutual orbit plane precesses, bringing one of the planets into and out of a grazing transit. We also briefly consider an eclipsing binary, that either orbits KIC 12557548 in a hierarchical triple configuration or is nearby on the sky, but we find such a scenario inadequate to reproduce the observations. We come down in favor of an explanation that involves macroscopic particles escaping the atmosphere of a slowly disintegrating planet not much larger than Mercury. The particles could take the form of micron-sized pyroxene or aluminum oxide dust grains. The planetary surface is hot enough to sublimate and create a high-Z atmosphere; this atmosphere may be loaded with dust via cloud condensation or explosive volcanism. Atmospheric gas escapes the planet via a Parker-type thermal wind, dragging dust grains with it. We infer a mass loss rate from the observations of order 1 M_E/Gyr, with a dust-to-gas ratio possibly of order unity. For our fiducial 0.1 M_E planet, the evaporation timescale may be ~0.2 Gyr. Smaller mass planets are disfavored because they evaporate still more quickly, as are larger mass planets because they have surface gravities too strong to sustain outflows with the requisite mass-loss rates. The occultation profile evinces an ingress-egress asymmetry that could reflect a comet-like dust tail trailing the planet; we present simulations of such a tail.Comment: 14 pages, 7 figures; submitted to ApJ, January 10, 2012; accepted March 21, 201

Constraining the LyC escape fraction from LEGUS star clusters with SIGNALS HII region observations: A pilot study of NGC 628

The ionising radiation of young and massive stars is a crucial form of stellar feedback. Most ionising (Lyman-continuum; LyC, $\lambda < 912A$) photons are absorbed close to the stars that produce them, forming compact HII regions, but some escape into the wider galaxy. Quantifying the fraction of LyC photons that escape is an open problem. In this work, we present a semi-novel method to estimate the escape fraction by combining broadband photometry of star clusters from the Legacy ExtraGalactic UV Survey (LEGUS) with HII regions observed by the Star formation, Ionized gas, and Nebular Abundances Legacy Survey (SIGNALS) in the nearby spiral galaxy NGC 628. We first assess the completeness of the combined catalogue, and find that 49\% of HII regions lack corresponding star clusters as a result of a difference in the sensitivities of the LEGUS and SIGNALS surveys. For HII regions that do have matching clusters, we infer the escape fraction from the difference between the ionising power required to produce the observed HII luminosity and the predicted ionising photon output of their host star clusters; the latter is computed using a combination of LEGUS photometric observations and a stochastic stellar population synthesis code SLUG (Stochastically Lighting Up Galaxies). Overall, we find an escape fraction of $f_{esc} = 0.09^{+0.06}_{-0.06}$ across our sample of 42 HII regions; in particular, we find HII regions with high $f_{esc}$ are predominantly regions with low H$\alpha$-luminosity. We also report possible correlation between $f_{esc}$ and the emission lines [O ii]/[N ii] and [O ii]/H$\beta$.Comment: Accepted for publication at MNRA

High-spectral-resolution Observations of the Optical Filamentary Nebula Surrounding NGC 1275

We present new high-spectral-resolution observations (R = λ/Δλ = 7000) of the filamentary nebula surrounding NGC 1275, the central galaxy of the Perseus cluster. These observations have been obtained with SITELLE, an imaging Fourier transform spectrometer installed on the Canada–France–Hawai Telescope with a field of view of 11′×11′ , encapsulating the entire filamentary structure of ionized gas despite its large size of 80 kpc × 50 kpc. Here, we present renewed fluxes, velocities, and velocity dispersion maps that show in great detail the kinematics of the optical nebula at [S ii] λ6716, [S ii] λ6731, [N ii] λ6584, Hα (6563 Å), and [N ii] λ6548. These maps reveal the existence of a bright flattened disk-shaped structure in the core extending to r ∼10 kpc and dominated by a chaotic velocity field. This structure is located in the wake of X-ray cavities and characterized by a high mean velocity dispersion of 134 km s−1. The disk-shaped structure is surrounded by an extended array of filaments spread out to r ∼ 50 kpc that are 10 times fainter in flux, remarkably quiescent, and have a uniform mean velocity dispersion of 44 km s−1. This stability is puzzling given that the cluster core exhibits several energetic phenomena. Based on these results, we argue that there are two mechanisms that form multiphase gas in clusters of galaxies: a first triggered in the wake of X-ray cavities leading to more turbulent multiphase gas and a second, distinct mechanism, that is gentle and leads to large-scale multiphase gas spreading throughout the core