Keck Laser Guide Star Adaptive Optics Research Articles

Astronomical Science with Adaptive Optics at the W. M. Keck Observatory

ABSTRACTThe first refereed science papers based on data with the Keck II natural guide star (NGS) and laser guide star (LGS) adaptive optics (AO) system were published in 2000 January and 2005 May, respectively. As of the end of 2012 a total of 260 refereed science papers have been published based on Keck NGS AO data and 152 with the Keck LGS AO system. This paper provides an overview of the first dozen years of scientific productivity with Keck AO and the lessons that can be drawn from this experience. The performance and limitations of the existing Keck AO systems are also discussed along with the technical developments currently underway to improve the scientific reach of these systems. The Keck AO capabilities are in high demand by a broad science community, a community that has expanded as new capabilities, especially LGS AO, have been added.

AN ADAPTIVE OPTICS SURVEY FOR CLOSE PROTOSTELLAR BINARIES

In order to test the hypothesis that Class I protostellar binary stars are a product of ejections during the dynamical decay of non-hierarchical multiple systems, we combined the results of new adaptive optics (AO) observations of Class I protostars with our previously published AO data to investigate whether Class I protostars with a widely separated companion (r>200 AU) are more likely to also have a close companion (r<200 AU). In total, we observed 47 embedded young stellar objects (YSOs) with either the Subaru natural guide star AO system or the Keck laser guide star AO system. We found that targets with a widely separated companion within 5,000 AU are not more likely to have a close companion. However, targets with another YSO within a projected separation of 25,000 AU are much more likely to have a close companion. Most importantly, every target with a close companion has another YSO within a projected separation of 25,000 AU. We came to the same conclusions after considering a restricted sample of targets within 500 pc and close companions wider than 50 AU to minimize incompleteness effects. The Orion star forming region was found to have an excess of both close binaries and YSOs within 25,000 AU compared to other star forming regions. We interpret these observations as strong evidence that many close Class I binary stars form via ejections and that many of the ejected stars become unbound during the Class I phase.

MORPHOLOGIES OF HIGH-REDSHIFT, DUST-OBSCURED GALAXIES FROM KECK LASER GUIDE STAR ADAPTIVE OPTICS

Spitzer MIPS images in the Bootes field of the NOAO Deep Wide-Field Survey have revealed a class of extremely dust-obscured galaxy (DOG) at z ~ 2. The DOGs are defined by very red optical to mid-infrared (IR; observed-frame) colors, R – [24 μm] > 14 mag, i.e. f_ν(24 μm)/f_ν(R) > 1000. They are ultra-luminous infrared galaxies with L_(8-1000 μm) > 10^(12)-10^(14) L⊙, but typically have very faint optical (rest-frame UV) fluxes. We imaged three DOGs with the Keck laser guide star adaptive optics (LGSAO) system, obtaining ~0.06 resolution in the K'-band. One system was dominated by a point source, while the other two were clearly resolved. Of the resolved sources, one can be modeled as a exponential disk system. The other is consistent with a de Vaucouleurs profile typical of elliptical galaxies. The nonparametric measures of their concentration and asymmetry show the DOGs to be both compact and smooth. The AO images rule out double nuclei with separations of greater than 0.1 (<1 kpc at z = 2), making it unlikely that ongoing major mergers (mass ratios of 1/3 and greater) are triggering the high-IR luminosities. By contrast, high-resolution images of z ~ 2 SCUBA sources tend to show multiple components and a higher degree of asymmetry. We compare near-IR morphologies of the DOGs with a set of z = 1 luminous infrared galaxies (LIRGs; L_(IR) ~ 10^(11) L⊙) imaged with Keck LGSAO by the Center for Adaptive Optics Treasury Survey. The DOGs in our sample have significantly smaller effective radii, ~1/4 the size of the z = 1 LIRGs, and tend toward higher concentrations. The small sizes and high concentrations may help explain the globally obscured rest-frame blue-to-UV emission of the DOGs.

Superresolving Distant Galaxies with Gravitational Telescopes: Keck Laser Guide Star Adaptive Optics andHubble Space TelescopeImaging of the Lens System SDSS J0737+3216

We combine high-resolution images in four optical/infrared bands, obtained with the laser guide star adaptive optics ( LGSAO) system on the Keck telescope and with the Hubble Space Telescope ( HST), to study the gravitational lens system SDSS J0737 + 3216 ( lens redshift 0.3223, source redshift 0.5812). We show that ( under favorable observing conditions) ground-based images are comparable to those obtained with HST in terms of precision in the determination of the parameters of both the lens mass distribution and the background source. We also quantify the systematic errors associated with both the incomplete knowledge of the PSF and the uncertain process of lens galaxy light removal and find that similar accuracy can be achieved with Keck LGSAO as with HST. We then exploit this well-calibrated combination of optical and gravitational telescopes to perform a multiwavelength study of the source galaxy at 0.01 '' effective resolution. We find the Sersic index to be indicative of a disklike object, but the measured half-light radius (r(e) = 0.59 +/- 0.007 stat +/- 0.1 sys kpc) and stellar mass (M* = 2.0 +/- 1.0 stat +/- 0.8 sys x 10(9) M(circle dot)) place it more than 3 sigma away from the local disk size-mass relation. The SDSS J0737 + 3216 source has the characteristics of the most compact faint blue galaxies studied and comparable size and mass to dwarf early-type galaxies in the local universe. With the aid of gravitational telescopes to measure individual objects' brightness profiles to 10% accuracy, the study of the high-redshift size-mass relation may be extended by an order of magnitude or more beyond existing surveys at the low-mass end, thus providing a new observational test of galaxy formation models.

To Be or Not to Be: Very Young Globular Clusters in M31

We present observations made with the newly commissioned Keck laser-guide star adaptive optics system of 6 objects in M31 that are alleged in multiple recent studies to be young globular clusters (GCs); all are supposed to have ages less than 5 Gyr. The resulting FWHM of the PSF core in our images is ~70 mas. The four youngest of these objects are asterisms; they are with certainty not young GCs in M31. Based on their morphology, the two oldest are GCs in M31. While the M31 GCs with ages 5 -- 8 Gyr appear to be mostly genuine, it appears that many of the alleged very young GCs in M31 are spurious identifications. This problem will be even more severe in studies of the GC systems of more distant spiral galaxies now underway, for which imaging at the spatial resolution of our observations in M31 may not be adequate to detect sample contamination by asterisms.

Merging Galaxies in GOODS-S: First Extragalactic Results from Keck Laser Adaptive Optics

The Center for Adaptive Optics Treasury Survey aims to combine deep Hubble Space Telescope (HST) images in the optical with deep Keck adaptive optics (AO) data in the near-infrared (NIR) to study distant galaxies, active galactic nuclei, and supernovae. We recently achieved an important new milestone by securing the first Keck laser guide star AO image of faint galaxies. Six galaxies with redshifts ranging from 0.3 to 1.0 were targeted in one pointing in the GOODS-S field. Two are Chandra Deep Field-South sources, XID-56 and XID-536, with complex morphologies suggestive of recent merger activity. Substructures seen in the NIR AO image (FWHM ~01), including multiple tight knots in XID-56 and a double nucleus in XID-536, are confirmed in the optical HST images. These structures are unresolved in the best seeing-limited (~05 FWHM) NIR images. Stellar population synthesis models of the substructures indicate that XID-56 is a gas-rich merger with a recent burst of star formation and significant amounts of dust. XID-536 appears to be a merger of two evolved stellar populations.