We have obtained deep Hubble Space Telescope (HST) imaging of four faint and ultra-faint dwarf galaxy candidates in the vicinity of M101-Dw21, Dw22, Dw23 and Dw35, originally discovered by Bennet et ...al. Previous distance estimates using the surface brightness fluctuation technique have suggested that these four dwarf candidates are the only remaining viable M101 satellites identified in ground-based imaging out to the virial radius of M101 (D 250 kpc). Advanced Camera for Surveys imaging of all four dwarf candidates shows no associated resolved stellar populations, indicating that they are thus background galaxies. We confirm this by generating simulated HST color-magnitude diagrams of similar brightness dwarfs at the distance of M101. Our targets would have displayed clear, resolved red giant branches with dozens of stars if they had been associated with M101. With this information, we construct a satellite luminosity function for M101, which is 90% complete to MV = −7.7 mag and 50% complete to MV = −7.4 mag, that extends into the ultra-faint dwarf galaxy regime. The M101 system is remarkably poor in satellites in comparison to the Milky Way and M31, with only eight satellites down to an absolute magnitude of MV = −7.7 mag, compared to the 14 and 26 seen in the Milky Way and M31, respectively. Further observations of Milky Way analogs are needed to understand the halo-to-halo scatter in their faint satellite systems, and connect them with expectations from cosmological simulations.
As the closest Type Ia supernova in decades, SN 2014J provides a unique opportunity for detailed investigation into observational signatures of the progenitor system, explosion mechanism, and burning ...product distribution. We present a late-time near-infrared spectral series from Gemini-N at after the explosion. Following the H-band evolution probes the distribution of radioactive iron group elements, the extent of mixing, and the presence of magnetic fields in the expanding ejecta. Comparing the isolated 1.6440 m Fe ii emission line with synthetic models shows consistency with a Chandrasekhar mass white dwarf of undergoing a delayed detonation. The ratio of the flux in the neighboring emission feature to the flux in the feature shows evidence of some limited mixing of stable and radioactive iron group elements in the central regions. Additionally, the evolution of the line shows an intriguing asymmetry. When measuring line width of this feature, the data show an increase in line width not seen in the evolution of the synthetic spectra, corresponding to 1000 km s−1, which could be caused by a localized transition to detonation producing asymmetric ionization in the ejecta. Using the difference in width between the different epochs, an asymmetric component in the central regions, corresponding to approximately the inner 2 × 10−4 of white dwarf mass suggests an off-center ignition of the initial explosion and hence of the kinematic center from the chemical center. Several additional models investigated, including a detonation and a merger, have difficulty reproducing the features seen in these spectra.
We present 81 near-infrared (NIR) spectra of 30 Type II supernovae (SNe II) from the Carnegie Supernova Project-II (CSP-II), the largest such data set published to date. We identify a number of NIR ...features and characterize their evolution over time. The NIR spectroscopic properties of SNe II fall into two distinct groups. This classification is first based on the strength of the He i λ1.083 m absorption during the plateau phase; SNe II are either significantly above (spectroscopically strong) or below 50 (spectroscopically weak) in pseudo equivalent width. However, between the two groups other properties, such as the timing of CO formation and the presence of Sr ii, are also observed. Most surprisingly, the distinct weak and strong NIR spectroscopic classes correspond to SNe II with slow and fast declining light curves, respectively. These two photometric groups match the modern nomenclature of SNe IIP, which show a long duration plateau, and IIL, which have a linear declining light curve. Including NIR spectra previously published, 18 out of 19 SNe II follow this slow declining-spectroscopically weak and fast declining-spectroscopically strong correspondence. This is in apparent contradiction to the recent findings in the optical that slow and fast decliners show a continuous distribution of properties. The weak SNe II show a high-velocity component of helium that may be caused by a thermal excitation from a reverse shock created by the outer ejecta interacting with the red supergiant wind, but the origin of the observed dichotomy is not understood. Further studies are crucial in determining whether the apparent differences in the NIR are due to distinct physical processes or a gap in the current data set.
We report the discovery of a new faint dwarf galaxy, which we dub Scl-MM-Dw1, at a projected distance of ~65 kpc from the spiral galaxy NGC 253. The discovery results from the Panoramic Imaging ...Survey of Centaurus and Sculptor (PISCeS), a program with the Magellan/Megacam imager to study faint substructure in resolved stellar light around massive galaxies outside of the Local Group. We measure a tip of the red giant branch distance to Scl-MM-Dw1 of D = 3.9 + or - 0.5 Mpc, consistent with that of NGC 253, making their association likely. The new dwarf's stellar population is complex, with an old, metal-poor red giant branch (> ~ 10 Gyr, Fe/H ~ -2), and an asymptotic giant branch with an age of ~500 Myr. Scl-MM-Dw1 has a half-light radius of rh = 340 + or - 50 pc and an absolute magnitude of MV = -10.3 + or - 0.6 mag, comparable to the Milky Way's satellites at the same luminosity. Once complete, our imaging survey of NGC 253 and other nearby massive galaxies will provide a census of faint substructure in halos beyond the Local Group, both to put our own environment into context and to confront models of hierarchical structure formation.
ABSTRACT We report the discovery of Antlia B, a faint dwarf galaxy at a projected distance of ∼72 kpc from NGC 3109 ( ), the primary galaxy of the NGC 3109 dwarf association at the edge of the Local ...Group. The tip of the red giant branch distance to Antlia B is D = 1.29 0.10 Mpc, which is consistent with the distance to NGC 3109. A qualitative analysis indicates the new dwarf's stellar population has both an old, metal-poor red giant branch ( Fe/H ∼ −2), and a younger blue population with an age of ∼200-400 Myr, analogous to the original Antlia dwarf, another likely satellite of NGC 3109. Antlia B has H i gas at a velocity of = 376 km s−1, confirming the association with NGC 3109 (vhelio = 403 km s−1). The H i gas mass (MH i = 2.8 0.2 × 105 ), stellar luminosity (MV = −9.7 0.6 mag) and half light radius (rh = 273 29 pc) are all consistent with the properties of dwarf irregular and dwarf spheroidal galaxies in the Local Volume, and is most similar to the Leo P dwarf galaxy. The discovery of Antlia B is the initial result from a Dark Energy Camera survey for halo substructure and faint dwarf companions to NGC 3109 with the goal of comparing observed substructure with expectations from the Λ+Cold Dark Matter model in the sub-Milky Way regime.
We present optical and near infrared (NIR) observations of the nearby Type Ia SN 2014J. Seventeen optical and 23 NIR spectra were obtained from 10 days before (-10d) to 10 days after (+10d) the time ...of maximum B-band brightness. The relative strengths of absorption features and their patterns of development can be compared at one day intervals throughout most of this period. Carbon is not detected in the optical spectra, but we identify C I lambda1.0693 in the NIR spectra. Mg II lines with high oscillator strengths have higher initial velocities than other Mg II lines. We show that the velocity differences can be explained by differences in optical depths due to oscillator strengths. The spectra of SN 2014J show that it is a normal SN Ia, but many parameters are near the boundaries between normal and high-velocity subclasses. The velocities for O I, Mg II, Si II, S II, Ca II, and Fe II suggest that SN 2014J has a layered structure with little or no mixing. That result is consistent with the delayed detonation explosion models. We also report photometric observations, obtained from - 10d to +29d, in the UBVRIJH and Ks bands. The template fitting package SNooPy is used to interpret the light curves and to derive photometric parameters. Using RV = 1.46, which is consistent with previous studies, SNooPy finds that AV = 1.80 for E(B - V) sub(host) = 1.23+ or -0.06 mag. The maximum B-band brightness of -19.19+ or -0.10 mag was reached on February 1.74 UT+ or -0.13 days and the supernova has a decline parameter, Delta m sub(15), of 1.12+ or -0.02 mag.
A census of the satellite population around dwarf galaxy primary hosts in environments outside the Local Group is essential to understanding Λ cold dark matter galaxy formation and evolution on the ...smallest scales. We present deep optical Hubble Space Telescope imaging of the gas-rich, faint dwarf galaxy Antlia B (MV = −9.4)-a likely satellite of NGC 3109 (D = 1.3 Mpc)-discovered as part of our ongoing survey of primary host galaxies similar to the Magellanic Clouds. We derive a new tip of the red giant branch distance of D = 1.35 0.06 Mpc (m − M = 25.65 0.10), consistent with membership in the nearby NGC 3109 dwarf association. The color-magnitude diagram (CMD) shows both a prominent old, metal-poor stellar component and confirms a small population of young, blue stars with ages 1 Gyr. We use the CMD fitting algorithm MATCH to derive the star formation history (SFH) and find that it is consistent with the typical dwarf irregular or transitional dwarf galaxy (dTrans) in the Local Group. Antlia B shows relatively constant stellar mass growth for the first ∼10-11 Gyr and almost no growth in the last ∼2-3 Gyr. Despite being gas-rich, Antlia B shows no evidence of active star formation (i.e., no H emission) and should therefore be classified as a dTrans dwarf. Both Antlia B and the Antlia dwarf (dTrans) are likely satellites of NGC 3109, suggesting that the cessation of ongoing star formation in these galaxies may be environmentally driven. Future work studying the gas kinematics and distribution in Antlia B will explore this scenario in greater detail. Our work highlights the fact that detailed studies of nearby dwarf galaxies in a variety of environments may continue to shed light on the processes that drive the SFH and evolution of dwarf galaxies more generally.
We present multiwavelength photometric and spectroscopic observations of SN 2019ein, a high-velocity Type Ia supernova (SN Ia) discovered in the nearby galaxy NGC 5353 with a two-day nondetection ...limit. SN 2019ein exhibited some of the highest measured expansion velocities of any SN Ia, with a Si ii absorption minimum blueshifted by 24,000 km s−1 at 14 days before peak brightness. More unusually, we observed the emission components of the P Cygni profiles to be blueshifted upward of 10,000 km s−1 before B-band maximum light. This blueshift, among the highest in a sample of 28 other SNe Ia, is greatest at our earliest spectroscopic epoch and subsequently decreases toward maximum light. We discuss possible progenitor systems and explosion mechanisms that could explain these extreme absorption and emission velocities. Radio observations beginning 14 days before B-band maximum light yield nondetections at the position of SN 2019ein, which rules out symbiotic progenitor systems, most models of fast optically thick accretion winds, and optically thin shells of mass at radii . Comparing our spectra to models and observations of other high-velocity SNe Ia, we find that SN 2019ein is well fit by a delayed-detonation explosion. We propose that the high emission velocities may be the result of abundance enhancements due to ejecta mixing in an asymmetric explosion, or optical depth effects in the photosphere of the ejecta at early times. These findings may provide evidence for common explosion mechanisms and ejecta geometries among high-velocity SNe Ia.
A Microkinetic Model of Calcite Step Growth Andersson, M. P.; Dobberschütz, S.; Sand, K. K. ...
Angewandte Chemie (International ed.),
September 5, 2016, Letnik:
55, Številka:
37
Journal Article
Recenzirano
In spite of decades of research, mineral growth models based on ion attachment and detachment rates fail to predict behavior beyond a narrow range of conditions. Here we present a microkinetic model ...that accurately reproduces calcite growth over a very wide range of published experimental data for solution composition, saturation index, pH and impurities. We demonstrate that polynuclear complexes play a central role in mineral growth at high supersaturation and that a classical complexation model is sufficient to reproduce measured rates. Dehydration of the attaching species, not the mineral surface, is rate limiting. Density functional theory supports our conclusions. The model provides new insights into the molecular mechanisms of mineral growth that control biomineralization, mineral scaling and industrial material synthesis.
A robust model: A microkinetic model is presented that accurately reproduces calcite growth over a wide range of experimental parameters for solution composition, saturation index, pH and impurities. Polynuclear complexes play a central role at high supersaturation and a classical complexation model is sufficient to reproduce measured rates.
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