Medling A.M.,Australia National University |
Vivian U.,University of California at Riverside |
Max C.E.,University of California at Santa Cruz |
Sanders D.B.,University of Hawaii at Manoa |
And 6 more authors.
Astrophysical Journal | Year: 2015
We present black hole mass measurements from kinematic modeling of high-spatial resolution integral field spectroscopy of the inner regions of nine nearby (ultra-)luminous infrared galaxies in a variety of merger stages. These observations were taken with OSIRIS and laser guide star adaptive optics on the Keck I and Keck II telescopes, and reveal gas and stellar kinematics inside the spheres of influence of these supermassive black holes. We find that this sample of black holes are overmassive (∼107-9m⊙) compared to the expected values based on black hole scaling relations, and suggest that the major epoch of black hole growth occurs in early stages of a merger, as opposed to during a final episode of quasar-mode feedback. The black hole masses presented are the dynamical masses enclosed in ∼25 pc, and could include gas which is gravitationally bound to the black hole but has not yet lost sufficient angular momentum to be accreted. If present, this gas could in principle eventually fuel active galactic nucleus feedback or be itself blown out from the system. © 2015. The American Astronomical Society. All rights reserved. Source
Iserlohe C.,University of Cologne |
Krabbe A.,University of Stuttgart |
Larkin J.E.,University of California at Los Angeles |
Barczys M.,University of Rochester |
And 4 more authors.
Astronomy and Astrophysics | Year: 2013
We present H- and K-band data from the inner arcsecond of the Seyfert 1.5 galaxy NGC 4151 obtained with the adaptive-optics-assisted near-infrared-imaging field spectrograph OSIRIS at the Keck Observatory. The angular resolution is about a few parsecs on-site and thus competes easily with optical images taken previously with the Hubble Space Telescope. We present the morphology and dynamics of most species detected but focus on the morphology and dynamics of the narrow line region (as traced by emission of [FeII]λ1.644 μm), the interplay between plasma ejected from the nucleus (as traced by 21 cm continuum radio data) and hot H2 gas and characterize the detected nuclear HeIλ2.058 μm absorption feature as a narrow absorption line (NAL) phenomenon. The emission from the narrow line region (NLR) as traced by [FeII] reveals a biconical morphology and we compare the measured dynamics in the [FeII] emission line with models that propose acceleration of gas in the NLR and simple ejection of gas into the NLR. In the inner 2.5 arcsec the acceleration model reveals a better fit to our data than the ejection model. We also see evidence that the jet very locally enhances emission in [FeII] at certain positions in our field-of-view such that we were able to distinct the kinematics of these clouds from clouds generally accelerated in the NLR. Further, the radio jet is aligned with the bicone surface rather than the bicone axis such that we assume that the jet is not the dominant mechanism responsible for driving the kinematics of clouds in the NLR. The hot H2 gas is thermal with a temperature of about 1700 K. We observe a remarkable correlation between individual H2 clouds at systemic velocity with the 21 cm continuum radio jet. We propose that the radio jet is at least partially embedded in the galactic disk of NGC 4151 such that deviations from a linear radio structure are invoked by interactions of jet plasma with H2 clouds that are moving into the path of the jet because of rotation of the galactic disk of NGC 4151. Additionally, we observe a correlation of the jet as traced by the radio data, with gas as traced in Brγ and H2, at velocities between systemic and ±200 km s-1 at several locations along the path of the jet. The HeIλ2.058 μm line in NGC 4151 appears in emission with a blueshifted absorption component from an outflow. The emission (absorption) component has a velocity offset of 10 km s -1 (-280 km s-1) with a Gaussian (Lorentzian) full-width (half-width) at half maximum of 160 km s-1 (440 km s-1). The absorption component remains spatially unresolved and its kinematic measures differ from that of UV resonance absorption lines. From the amount of absorption we derive a lower limit of the HeI 21S column density of 1 × 1014 cm-2 with a covering factor along the line-of-sight of Clos â‰0.1. © ESO, 2013. Source
Imagine taking the world's most powerful radio telescope, used by scientists around the globe, and piping a nearly continuous data stream into your research laboratory. That is exactly what scientists at the Naval Research Laboratory (NRL) in Washington, D.C. have done in collaboration with the National Radio Astronomy Observatory's Karl G. Jansky Very Large Array (NRAO VLA). The newly-completed VLA Low Band Ionospheric and Transient Experiment (VLITE for short) has been built to piggyback on the $300 million dollar infrastructure of the VLA. The primary scientific driver for VLITE is real-time monitoring of ionospheric weather conditions over the U.S. southwest. NRL ionospheric lead scientist Dr. Joseph Helmboldt says "This new system allows for continuous specification of ionospheric disturbances with remarkable precision. VLITE can detect and characterize density fluctuations as small as 30 parts per million within the total electron content along the line of sight to a cosmic source. This is akin to being at the bottom of Lake Superior and watching waves as small as 1-cm in height pass overhead. This will have a substantial impact on our understanding of ionospheric dynamics, especially the coupling between fine-scale irregularities within the lower ionosphere and larger disturbances higher up." Ionospheric disturbances represent one of the most significant limitations to the performance of many radio-frequency applications like satellite-based communication and navigation (including the GPS in your phone) as well as ground-based, over-the-horizon systems (think ham radio or AM radio). While the fine-scale irregularities that VLITE is especially sensitive to aren't large enough to make your smart phone think you are at your neighbor's house when you're really at home, they are quite problematic for vital remote sensing surveillance systems like over-the-horizon radar. The additional insights provided by VLITE into the nature of these ionospheric ripples will help us to better understand how to cope with their effects on such systems. "VLITE is also a powerful new tool in our arsenal for astrophysical research" says VLITE principle investigator Dr. Namir Kassim. He points out that "We know the Universe has many secrets including mysterious blips (so-called transients) that appear and vanish like fireflies in the night. Limited observing time at classical observatories hampers our ability to understand these intriguing objects. The power of VLITE is the nearly continual data stream over a large region of the sky. This opens up a new window on the transient Universe." At any given time, the region of the sky that VLITE peers at is so large that nearly 20 full moons would fit inside it. Astrophysics lead scientist Dr. Tracy Clarke of NRL describes VLITE as "a symbiotic instrument that piggybacks on world-class science at the VLA. It operates as a stand-alone tool for ionospheric and astrophysical studies while at the same time VLITE provides the opportunity for enhanced science in the research program running on the VLA." VLITE operations started with first light on July 17, 2014 but the real fun began two days before Thanksgiving, on November 25, 2014, when VLITE moved from a commissioning phase into full scientific operations. The system operates in real-time on 10 VLA antennas and provides 64 MHz of bandwidth centered on 352 MHz with a temporal resolution of 2s and a spectral resolution of 100 kHz. This powerful new instrument operates in parallel with the VLA and is essentially 'driven' around the sky by the primary science observer. Data streams off the telescope through dedicated systems that bypass normal VLA operations. The data then take two roads, one through real-time processing on computers located at the VLA site, and the other through off-line processing at NRL's facility in Washington. Due to the large volume of nearly continuous incoming data, all data must be analyzed by an automated pipeline that was custom designed for VLITE. Pipeline designer Dr. Wendy Lane Peters of NRL describes this process as being like "sitting in the passenger seat of a Google car and not knowing where it is taking you. VLITE is along for the ride wherever the primary science program takes us. We have to anticipate what they might do so that our pipeline is smart enough to understand the incoming data." Professor Bryan Gaensler, Director of the Dunlap Institute for Astronomy and Astrophysics at the University of Toronto, says that this is going to become the new way of doing astronomy. "It's a tragedy and a travesty that most of the information our telescopes gather from the sky is ignored and discarded. VLITE is part of a new generation of experiments that fully utilize the massive data torrents collected by the world's most powerful observatories." Over the first two months of science operations, VLITE has recorded observations of sources ranging from the Sun, nearby stars and galaxies, to some of the most distant sources in the Universe. NRL astronomers and their colleagues have been poring over the pipeline images, improving their analysis pipeline and exploring the scientific potential of the instrument. About the U.S. Naval Research Laboratory The U.S. Naval Research Laboratory provides the advanced scientific capabilities required to bolster our country's position of global naval leadership. The Laboratory, with a total complement of approximately 2,500 personnel, is located in southwest Washington, D.C., with other major sites at the Stennis Space Center, Miss., and Monterey, Calif. NRL has served the Navy and the nation for over 90 years and continues to advance research further than you can imagine. For more information, visit the NRL website or join the conversation on Twitter, Facebook, and YouTube.
Mieda E.,University of Toronto |
Wright S.A.,University of Toronto |
Wright S.A.,Dunlap Institute for Astronomy and Astrophysics |
Larkin J.E.,University of California at Los Angeles |
And 2 more authors.
Proceedings of the International Astronomical Union | Year: 2014
We present first results from the Intermediate Redshift OSIRIS Chemo-Kinematic Survey (IROCKS) of z ∼ 1 star forming galaxies (Mieda et al. in prep). We have targeted Hα and [NII] emission lines in J-band and have spatially resolved the galaxies at sub-kilo parsec scale. We have combined our sample with deep HST continuum images, and are able to reveal the dynamics, morphologies, metallicity distribution, emission-line diagnostics, and star formation rates of galaxies spanning this crucial z ∼ 1 epoch. © International Astronomical Union 2015. Source
Reddy N.A.,National Optical Astronomy Observatory |
Reddy N.A.,University of California at Riverside |
Pettini M.,Institute of Astronomy |
Pettini M.,University of Western Australia |
And 4 more authors.
Astrophysical Journal | Year: 2012
A large sample of spectroscopically confirmed star-forming galaxies at redshifts 1.4 ≤ z spec ≤ 3.7, with complementary imaging in the near- and mid-IR from the ground and from the Hubble Space Telescope and Spitzer Space Telescope, is used to infer the average star formation histories (SFHs) of typical galaxies from z ∼ 2 to 7. For a subset of 302 galaxies at 1.5 ≤ z spec < 2.6, we perform a detailed comparison of star formation rates (SFRs) determined from spectral energy distribution (SED) modeling (SFRs[SED]) and those calculated from deep Keck UV and Spitzer/MIPS 24 μm imaging (SFRs[IR+UV]). Exponentially declining SFHs yield SFRs[SED] that are 5-10 times lower on average than SFRs[IR+UV], indicating that declining SFHs may not be accurate for typical galaxies at z ≳ 2. The SFRs of z ∼ 2-3 galaxies are directly proportional to their stellar masses (M *), with unity slope - a result that is confirmed with Spitzer/IRAC stacks of 1179 UV-faint (R ≥ 25.5) galaxies - for M * ≳ 5 × 108 M⊙ and SFRs ≳ 2 M⊙yr-1. We interpret this result in the context of several systematic biases that can affect determinations of the SFR-M * relation. The average specific SFRs at z ∼ 2-3 are remarkably similar within a factor of two to those measured at z ≳ 4, implying that the average SFH is one where SFRs increase with time. A consequence of these rising SFHs is that (1) a substantial fraction of UV-bright z ∼ 2-3 galaxies had faint sub-L* progenitors at z ≳ 4; and (2) gas masses must increase with time from z = 2 to 7, over which time the net cold gas accretion rate - as inferred from the specific SFR and the Kennicutt-Schmidt relation - is ∼2-3 times larger than the SFR. However, if we evolve to higher redshift the SFHs and masses of the halos that are expected to host L* galaxies at z ∼ 2, then we find that ≲ 10% of the baryons accreted onto typical halos at z ≳ 4 actually contribute to star formation at those epochs. These results highlight the relative inefficiency of star formation even at early cosmic times when galaxies were first assembling. © 2012. The American Astronomical Society. All rights reserved. Source