On the progenitor of the Type IIb supernova 2016gkg Kilpatrick, Charles D; Foley, Ryan J; Abramson, Louis E ...
Monthly Notices of the Royal Astronomical Society,
03/2017, Letnik:
465, Številka:
4
Journal Article
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Odprti dostop
We present a detection in pre-explosion Hubble Space Telescope(HST) imaging of a point source consistent with being the progenitor star of the Type IIb supernova (SN IIb) 2016gkg. Post-explosion ...imaging from the Keck adaptive optics system was used to perform relative astrometry between the Keck and HST imaging. We identify a single point source in the HSTimages coincident with the SN position to 0.89 sigma . The HSTphotometry is consistent with the progenitor star being an A0 Ia star with T = 9500 K and log (L/L...) = 5.15. We find that the SN 2016gkg progenitor star appears more consistent with binary than single-star evolutionary models. In addition, early-time light-curve data from SN 2016gkg revealed a rapid rise in luminosity within ~0.4 d of non-detection limits, consistent with models of the cooling phase after shock break-out. We use these data to determine an explosion date of 2016 September 20.15 and progenitor-star radius of log (R/R...) = 2.41, which agrees with photometry from the progenitor star. Our findings are also consistent with detections of other SNe IIb progenitor stars, although more luminous and bluer than most other examples. (ProQuest: ... denotes formulae/symbols omitted.)
A systematic analysis of the X-ray emission from the nearby ultraluminous infrared galaxy Mrk 273 was carried out by combining new 200 ks Chandra data with archived 44 ks data. The active galactic ...nucleus (AGN) associated with the southwest nucleus is confirmed by the new data, and a secondary hard X-ray (4-8 keV) point source is detected, coincident with the northeast nucleus at a projected distance of 0.75 kpc from the southwest nucleus. The hard X-ray spectrum of the northeast nucleus is consistent with a heavily absorbed AGN, making Mrk 273 another example of a dual AGN in a nearby galaxy merger. Significant 1-3 keV emission is found along the ionization cones and outflowing gas detected in a previous study. The data also map the giant X-ray nebula south of the host galaxy with unprecedented detail. This nebula extends on a scale of ∼40 kpc × 40 kpc and is not closely related to the well-known tidal tail seen in the optical. The X-ray emission of the nebula is best described by a single-temperature gas model, with a temperature of ∼7 million K and a supersolar /Fe ratio. Further analysis suggests that the southern nebula has most likely been heated and enriched by multiple galactic outflows generated by the AGN and/or circumnuclear starburst in the past, on a timescale of 0.1 Gyr, similar to the merger event itself.
We combine optical and near-infrared adaptive optics-assisted integral field observations of the merging ultraluminous infrared galaxies IRAS F17207-0014 from the Wide-Field Spectrograph and ...Keck/OH-Suppressing Infra-Red Imaging Spectrograph (OSIRIS). The optical emission line ratios N ii/Hα, S ii/Hα, and O i/Hα reveal a mixing sequence of shocks present throughout the galaxy, with the strongest contributions coming from large radii (up to 100 per cent at ∼5 kpc in some directions), suggesting galactic-scale winds. The near-infrared observations, which have approximately 30 times higher spatial resolution, show that two sorts of shocks are present in the vicinity of the merging nuclei: low-level shocks distributed throughout our field-of-view evidenced by an H2/Brγ line ratio of ∼0.6–4, and strong collimated shocks with a high H2/Brγ line ratio of ∼4–8, extending south from the two nuclear discs approximately 400 pc (∼0.5 arcsec). Our data suggest that the diffuse shocks are caused by the collision of the interstellar media associated with the two progenitor galaxies and the strong shocks trace the base of a collimated outflow coming from the nucleus of one of the two discs.
Abstract
We study the ionization and excitation structure of the interstellar medium in the late-stage gas-rich galaxy merger NGC 6240 using a suite of emission-line maps at ∼25 pc resolution from ...the Hubble Space Telescope, Keck/NIRC2 with Adaptive Optics, and the Atacama Large Millimeter/submillimeter Array (ALMA). NGC 6240 hosts a superwind driven by intense star formation and/or one or both of two active nuclei; the outflows produce bubbles and filaments seen in shock tracers from warm molecular gas (H
2
2.12
μ
m) to optical ionized gas (O
iii
, N
ii
, S
ii
, and O
i
) and hot plasma (Fe
XXV
). In the most distinct bubble, we see a clear shock front traced by high O
iii
/H
β
and O
iii
/O
i
. Cool molecular gas (CO(2−1)) is only present near the base of the bubble, toward the nuclei launching the outflow. We interpret the lack of molecular gas outside the bubble to mean that the shock front is not responsible for dissociating molecular gas, and conclude that the molecular clouds are partly shielded and either entrained briefly in the outflow, or left undisturbed while the hot wind flows around them. Elsewhere in the galaxy, shock-excited H
2
extends at least ∼4 kpc from the nuclei, tracing molecular gas even warmer than that between the nuclei, where the two galaxies’ interstellar media are colliding. A ridgeline of high O
iii
/H
β
emission along the eastern arm aligns with the southern nucleus’ stellar disk minor axis; optical integral field spectroscopy from WiFeS suggests this highly ionized gas is centered at systemic velocity and likely photoionized by direct line of sight to the southern active galactic nucleus.
The role of feedback in triggering or quenching star formation and hence driving galaxy evolution can be directly studied with high-resolution integral field observations. The manifestation of ...feedback in shocks is particularly important to examine in galaxy mergers, where violent interactions of gas take place in the interstellar medium during the course of the galactic collision. As part of our effort to systematically study the local population of luminous infrared galaxies within the Great Observatories All-Sky LIRG Survey, we undertook the Keck OSIRIS AO LIRG Analysis observing campaign to study the gas dynamics in the inner kiloparsec regions of these systems at spatial scales of a few tens of pc. With high-resolution near-infrared adaptive optics-assisted integral field observations taken with OSIRIS on the Keck Telescopes, we employ near-infrared diagnostics such as Brγ and the rovibrationally excited H2 lines to quantify the nuclear star formation rate and identify feedback associated with shocked molecular gas seen in 21 nearby luminous infrared galaxies. Shocked molecular gas is preferentially found in the ultraluminous infrared systems but may also be triggered at a lower-luminosity, earlier merging stage. On circumnuclear scales, AGNs have a strong effect on heating the surrounding molecular gas, though their coupling is not simply driven by AGN strength but rather is complicated by orientation, dust shielding, density, and other factors. We find that nuclear star formation correlates with merger class and diminishing projected nuclear separations. These trends are largely consistent with the picture of merger-induced starbursts in the center of galaxy mergers.
We present near-infrared integral field spectroscopy of the central kiloparsec of 17 nearby luminous and ultra-luminous infrared galaxies undergoing major mergers. These observations were taken with ...OSIRIS assisted by the Keck I and II Adaptive Optics systems, providing spatial resolutions of a few tens of parsecs. The resulting kinematic maps reveal gas disks in at least 16 out of 19 nuclei and stellar disks in 11 out of 11 nuclei observed in these galaxy merger systems. In our late-stages mergers, these disks are young (stellar ages < 30 Myr) and likely formed as gas disks that became unstable to star formation during the merger. On average, these disks have effective radii of a few hundred parsecs, masses between 10 super(8) and 10 super(10) M sub(middot in circle), and v/sigma between 1 and 5. These disks are similar to those created in high-resolution hydrodynamical simulations of gas-rich galaxy mergers, and favor short coalescence times for binary black holes. The few galaxies in our sample in earlier stages of mergers have disks that are larger (r sub(eff) ~ 200-1800 pc) and are likely remnants of the galactic disks that have not yet been completely disrupted by the merger.
The Keck Observatory began science observations with a laser guide star adaptive optics system, the first such system on an 8–10 m class telescope, in late 2004. This new capability greatly extends ...the scientific potential of the Keck II Telescope, allowing near–diffraction‐limited observations in the near‐infrared using natural guide stars as faint as 19th magnitude. This paper describes the conceptual approach and technical implementation followed for this system, including lessons learned, and provides an overview of the early science capabilities.
Dynamical black hole mass measurements in some gas-rich galaxy mergers indicate that they are overmassive relative to their host galaxy properties. Overmassive black holes in these systems present a ...conflict with the standard progression of galaxy merger-quasar evolution; an alternative explanation is that a nuclear concentration of molecular gas driven inward by the merger is affecting these dynamical black hole mass estimates. We test for the presence of such gas near the two black holes in NGC 6240 using long-baseline ALMA Band 6 observations (beam size 0 06 × 0 03 or 30 pc × 15 pc). We find (4.2-9.8) × 107 M☉ and (1.2-7.7) × 108 M☉ of molecular gas within the resolution limit of the original black hole mass measurements for the north and south black holes, respectively. In the south nucleus, this measurement implies that 6%-89% of the original black hole mass measurement actually comes from molecular gas, resolving the tension in the original black hole scaling relations. For the north, only 5%-11% is coming from molecular gas, suggesting the north black hole is actually overmassive. Our analysis provides the first measurement of significant molecular gas masses contaminating dynamical black hole mass measurements. These high central molecular gas densities further present a challenge to theoretical black hole accretion prescriptions, which often assume accretion proceeds rapidly through the central 10 pc.
NGC 6240 is a pair of colliding disk galaxies, each with a black hole in its core. We have used laser guide star adaptive optics on the Keck II telescope to obtain high-resolution (~006) ...near-infrared integral-field spectra of the region surrounding the supermassive black hole in the south nucleus of this galaxy merger. We use the K-band CO absorption bandheads to trace stellar kinematics. We obtain a spatial resolution of about 20 pc and thus directly resolve the sphere of gravitational influence of the massive black hole. We explore two different methods to measure the black hole mass. Using a Jeans Axisymmetric Multi-Gaussian mass model, we investigate the limit that a relaxed mass distribution produces all of the measured velocity dispersion, and find an upper limit on the black hole mass at 2.0 ? 0.2 X 109 M . When assuming the young stars whose spectra we observe remain in a thin disk, we compare Keplerian velocity fields to the measured two-dimensional velocity field and fit for a mass profile containing a black hole point mass plus a radially varying spherical component, which suggests a lower limit for the black hole mass of 8.7 ? 0.3 X 108 M . Our measurements of the stellar velocity dispersion place this active galactic nucleus within the scatter of the M BH- Delta *s* relation. As NGC 6240 is a merging system, this may indicate that the relation is preserved during a merger at least until the final coalescence of the two nuclei.
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