[Mayan calendar]

2001B Gemini North Classical Program Abstracts

Abstracts for all successful 2001B classical programs are given below.


Title: A Search for Disks around Young Brown Dwarfs and Very-Low-Mass Stars

Abstract: Recent surveys have identified candidate sub-stellar objects down to planetary masses in nearby star-forming regions. In addition, in some cases they have provided indications of disk emission. Reliable determination of the disk frequency in young brown dwarfs is of paramount importance to understanding their origin and diversity. Here we propose to undertake the first systematic study of L-band disk excess in a sample of spectroscopically confirmed objects near and below the sub-stellar boundary, using NIRI on Gemini North


Title:: The 3.3 $\mu$m Infrared Emission Feature in Starburst Galaxies

Abstract: We will observe 13 starburst galaxies from 1.9-4.2 um using NIRI. The galaxies have metallicities between 7.6 and 8.6 (12+logO/H) and a range of star formation activities. These observations will be used to probe the dependence of the 3.3 um infrared emission feature (IEF) strength on metallicity and radiation field density. As a result, we will put new constraints on the material responsible for the 3.3 um IEF.


Title: High-Resolution IR Imaging of Low-Z Damped Ly-Alpha Galaxies

Abstract: We propose to use the unique capabilities of Gemini with Hokupa'a/QUIRC to image a field containing two ''damped Ly(alpha) (DLA) galaxies'' found in absorption along the sight-lines towards a quasar. They have redshifts of z=0.09 and z=0.22. Observations with Hokupa'a/QUIRC are ideally suited to study faint extended structure close to bright point sources. We discovered these DLA absorbers in an HST-FOS survey. Determination of the properties of DLA absorbers are crucial for understanding the formation and evolution of galaxies because they trace the bulk of the observed neutral gas mass in the Universe. For over a decade the standard paradigm for DLA systems was that they arise in luminous disk galaxies. More recently, however, it has become clear that they arise in a variety of galaxy types, but which are primarily underluminous. We have imaged these fields in the IR with IRTF in ~0.6 arcsec seeing. These images reveal the rich morphology of some of the DLA galaxies, but are hindered by the quasar PSF. However, observations with Gemini's Hokupa'a/QUIRC, combining near diffraction-limited images and superior light gathering power, will lead to a much clearer understanding of the DLA galaxies and their morphological types (disk vs. bulge light), luminosities, and spatial extents. Used with our existing BRI WIYN images, it will also be possible to better determine or place limits on their colors, and hence, stellar populations, dust contents and star formation rates.


Title: The IMF at the Edge of the Galactic Disk

Abstract: The IMFs in local Galactic populations (<1 kpc) are characterized by roughly the same turnover mass (~0.8 M_sun). To determine whether this turnover mass varies with Galactocentric distance -- as might be expected if it is a reflection of the Jeans mass -- we propose to observe the newly discovered cluster near IRAS 07255-2012, which has the highest Galactocentric distance (~16.5 kpc) of any known star-forming cluster. We will use the Gemini Hokupa'a adaptive optics system to obtain deep JHK' photometry (H=22) for this dense, embedded cluster (~300 stars in 1~arcmin^2, A_V=5-15) and apply luminosity function modeling to constrain the IMF down to 0.2 M_sun.


Title: High Resolution Near-IR Imaging of YSOs

Abstract: We propose to use NIRI to obtain high-resolution images of Class I and II sources in the Taurus-Auriga Star Forming Region that have previously been detected, but not imaged, in emission at 2.1218 um. Ro-vibrational H_2 emission near pre-main-sequence stars usually is thought to indicate the presence of collimated outflows; however, the H_2 may be quiescent material in circumstellar disks. Since not all Class I and II sources have identified jets or outflows associated with them, the origin of the H_2 emission remains unclear. The distribution of the gas with respect to the sources should allow us to differentiate between quiescent H_2 and H_2 entrained in outflows at the resolutions attained by NIRI.


Title: The Nature of Damped Lyman alpha Absorbers, and Quasar Environments

Abstract: We will continue our programme to make deep (K'~23) Hokupa'a/QUIRC images of DLA quasar fields, to find faint galaxies around quasar sight-lines, and to test new chemical evolution models (Mathlin et al. 2000). These predict that the observed metallicity, column density and absorption redshift characteristics of damped Lyman-alpha absorbers (DLAs) in the spectra of quasars can be produced by faint galaxies (K'>22) very close (< 5 kpc) to the quasar line-of-sight. We will also probe the other faint sources around the QSO line-of-sight, hence constraining the environment of the quasar, lensing magnification biases in quasar and DLA surveys, and (after follow-up spectroscopy where possible) the evolution of the galaxy K-band luminosity function.


Title: A search for planets and brown dwarfs in the Pleiades & AO imaging of embedded young star clusters

Abstract: 01B/28: The existence of more than 30 extrasolar planets is known from the radial velocity wobbles of their parent stars, but none have yet been directly imaged. We propose to search for extrasolar planets and very low mass brown dwarfs by obtaining high resolution J band images of known brown dwarfs in the Pleiades to directly observe possible companion objects. The advantages of such a search in the Pleiades is that the planets/brown dwarfs will be young and therefore relatively bright. 

01B/25: The structure of circumstellar matter in embedded Young Stellar Objects is determined by the physics of the star formation and the initial conditions of cloud core collapse. We wish to observe a small sample of embedded systems with optically bright cores and a range of masses in the near infrared. The density distribution of the envelope will be determined by fitting 3-D Monte Carlo scattering models to images at JHK', these filters probing to different depth in the envelope and removing most of the ambiguity which can arise from a 2-D image. The high spatial resolution and dynamic range of the Gemini+Hokupa'a combination will resolve detail on scales of tens of AU, which is the scale on which changes in the density profile are expected to occur in the Rotating Singular Isothermal Sphere model and the scale of the bipolar cavity in the envelope. The structures discovered will allow us to distinguish between alternative collapse models and observe the differences between high and low mass YSO structures which are expected due to the different formation mechanisms. The highly obscured accretion disk may also be detected in some cases. Measurements of the size and vertical 'flaring' of the disk would further constrain collapse models and provide information on the temperature profile. Outflowing material in the bipolar cavities will also be detected and resolved, providing insight into the origins of outflows and perhaps also their role in angular momentum transport.


Title: Canadian Mini-Queue Observations with Hokupa'a

Abstract: The observations described in this proposal are to be carried out as part of the Canadian-run ''mini-queue'' program with Hokupa'a on Gemini North. CGPO staff will make the observations.


Title: A Search for Circumstellar Disks in MBM-12 using Dual Imaging Polarimetry

Abstract: Using a speckle noise suppressing dual imaging polarimetry technique, we propose to search for circumstellar disks around stars associated with the MBM-12 molecular cloud, the nearest (d~65pc) known star forming region. We expect to image circumstellar disks around 5 of the 8 MBM-12 stars, based on the relative values of disk indicating parameters (IR excess, H-alpha emission) between the MBM-12 candidates and stars for which we have detected disks using our method. The observations will provide measurements of the scale height, viewing inclination, size, morphology, and dust content for the newly detected disks, and will place meaningful constraints of the dust content for targeted objects with a null detection.


Title: Tip of the Red Giant Branch at K' in External Galaxies

Abstract: Adaptive Optics on the Gemini Telescope presents the opportunity to achieve 0.07as images over small fields at K'. Old stellar populations reach M_K=-6 at the bright tip of the red giant branch and will be easily detectable in nearby galaxies. This exploratory program is designed to determine how faint we might go, whether good photometric integrity can be achieved, and whether the properties of the giant branch tip stars are stable enough at K' to be useful for the measurement of distances. We will look at a range of targets within and near the Local Group.


Title: An Adaptive Optics Survey for Young Jovian-Mass Planets

Abstract: We propose to conduct an imaging survey for Jovian-mass planets around young solar-type stars in nearby star-forming regions. Using the Gemini AO system, we will have far greater sensitivity and spatial resolution than any previous searches. Analysis of real AO data demonstrates it is possible to detect companions with masses as low as that of Jupiter at sub-arcsecond separations. Discovery of even a single Jovian-mass companion will be a significant finding.


Title: Direct imaging of very low mass companions

Abstract: In 2001A we submitted the "top ranked (score=9) of many planet/brown dwarf companion searches". Unfortunately (due to the 13.5x oversubscription for Hokupa'a in 2001A) we only received a small fraction of the June mini-queue AO run. Hence, we are resubmitting an improved, slightly modified, and updated proposal in the hope of following up the 2 promising candidates we have now (out of 3 stars observed to date) and more importantly observing 40 new systems in 2001B. We propose to utilize Gemini and Hokupa'a to search for very low mass (2-20 jupiter mass) companions around newly discovered low luminosity (M6.5 or later) nearby (D<25pc) stars. Based on preliminary observations made with Hokupa'a/GEMINI in August 2000 of 3 such late type M stars (M7.0, M7.5, & M8.0) we are confident that Hokupa'a will be able to produce nearly diffraction-limited (FWHM ~ 0.1") images in the H band guiding on these very red, faint (I=14-17) stars themselves. Our PSF models predict Hokupa'a to be uniquely able to detect (in 5 minutes at H band) massive planets from 2-20 Jupiters in mass from 5-20 AU around M8 stars at 10pc from 0.1-10 Gyrs of age respectively. We propose to observe 40 objects from our candidate list in 2 nights (Run 1) with one more half night (Run 2) ~3 months later to confirm which of the detected companions are physical (e.g common proper motion pairs). We conservatively expect to find 2-4 of our 40 run 1 objects to be real very low mass companions.This would be the first survey to probe these planetary masses in the critical formation zone (5-15 AU) where such massive planets are commonly thought to form. Moreover, these objects would be the coolest exo-solar objects (800 > T_eff> 320 K) to be directly detected -ever!


Title: Adaptive Optics Imaging of the Radio Galaxies 3C68.2 and 4C23.56

Abstract: This project follows on from our successful AO imaging of the z = 1.786 radio galaxy 3C 294 with Hokupa`a on CFHT (Stockton et al., 1999: ApJ, 519, L131). 3C 294 breaks up into a number of small (~1 kpc) clumps, and our best estimate of the position of the compact flat-spectrum radio source indicates that the nucleus is completely obscured at restframe 8200 A. We need to image additional high-redshift radio galaxies at similar or higher resolutions in order to explore the range of properties of these objects at sub-kiloparsec scales and try to understand how these structures relate to the radio properties and to galaxy formation in general. This proposal is for AO imaging of two of the most interesting radio galaxies with redshifts between 1.5 and 2.5: 3C 68.2 (for which we already have previous imaging and Keck LRIS spectroscopy) at z = 1.575, and 4C23.56 at z = 2.483.


Title: Radio Source Hosts at High Redshift

Abstract: High redshift (2<z<5) radio galaxies trace the most massive galactic halos at high redshift. Dynamical models of the outflowing giant extended emission line regions give estivmates of equivalent velocity dispersions of 600 km/sec and total masses of 2-5 E+13 solar masses. The extended optical-ir emission apperas to be a combination of starlight and dust scattered light from mis-directed AGN. Only the most powerful and the weakest radio sources have been studied in detail: the most powerful on a one-by-one basis and the weakest in pencil beam and IR studies. The break in the radio luminosity function between radio-loud and radio quiet comes at about the 1 mJ (1450MHz) level whereas the HDF and SSA surveys, for example, have only enough sky coverage to include the much fainter microJansky sources. Low frequency and ultra-steep spectrum sources at the mJ level have an increasing tendency to be very red objects or blank fields (Chambers et al. 1996, Wieringa 1997, Rotterging et al 1998). This may be due to dust-enshrouded objects or the presence of a population of very high redshift objects. The highest known redshift radio source at z=5.19 was selected for its low-frequency radio spectrum (van Breugel et al 1999). These sources have a density of about 90 objects per square degree, and are generally too rare to obtain a significant sample in previous pencil beam surveys. This proposal is to use the optical selection provided by the IFA-survey of all FIRST, WENSS, and extended 7C radio sources to select the reddest or blank field sources for imaging with NIRI and to provide optical-infrared colors and morphologies. The goal is to characterize the faint end of the radio-loud host population.


Title: NIR Spectroscopy and Photometry of Centaurs and Small Moons

Abstract: This program seeks to characterize the physical surface properties of fainter Centaurs and outer Uranian satellite Sycorax and compare them with other surface spectra of the outer solar system satellites and Centaurs we have obtained. Recent spectroscopic studies yield evidence for spectral diversity in both KBOs and Centaurs. However, Centaurs are nearer and generally brighter than KBOs and are therefore more accessible to spectroscopic observations. If the Centaurs' origin is the Kuiper belt, as suspected, then their study will shed light on the nature of KBOs as well. We plan also to image the even fainter Centaurs not accessible to spectroscopy in the J, H and K bands using NIRI to obtain their NIR colors. Only the Gemini telescope with NIRI can obtain NIR spectra and photometry of bodies so faint during the time we request, allowing us to achieve adequate S/N with the resolution required to discern spectral solid-state features. Identification of the ices and organic components in their surface materials, when compared with the satellites and comet nuclei and interpreted with information about their dynamical history, will help piece together the chemical evolution of the outer solar system. We request UH 2.2m optical observing time concurrent with our Gemini NIR spectroscopy time in order to decouple optical absorption features with the NIR spectral absorption features we observe, and hopefully distinguish variations in brightness owing to projected surface area and rotation from actual surface spectral features.


Title: The Infrared Surface Brightness Fluctuation Hubble Diagram

Abstract: A number of secondary distance indicators useful out to 100 Mpc imply values of the Hubble constant that are larger than those derived from techniques that mainly reach beyond 100 Mpc. For example, the surface brightness flucatuation (SBF) measurements within 50 Mpc consistently suggest that the Hubble constant is near 80 km/s/Mpc. Type Ia supernovae, on the other hand, lead to the conclusion that Ho is closer to 65 km/s/Mpc. One possible explanation for the disagreement was proposed by Zehavi et al. (1998), who suggested that the value of the Hubble constant measured within 70/h Mpc is 6% lower than its global value because the local universe is of somewhat lower density than average. In this scenario, galaxies within approximately 7000 km/s (100 Mpc) move away from us more rapidly than the global Hubble flow. This conclusion has been regarded with skepticism, however, because other larger distance surveys show a remarkably quiet local velocity field (Giovanelli et al. 1999). Only recently have highly accurate IR SBF distances become available to distances beyond 100 Mpc for the first time. The six most distant galaxies measured by the NICMOS IR SBF team do in fact show a 6% reduction in Ho beyond 100 Mpc (Jensen et al. 2001). The relatively large uncertainties in the most distant measurements, however, are only mildly inconsistent with the value of Ho=76 km/s/Mpc measured within 100 Mpc. The NICMOS data are certainly not sufficient to conclusively show that the Zehavi et al. Hubble Bubble is real. Hokupaa now provides spatial resolution equal to or better than that of NICMOS from the ground. During the Quick Start Observing program, we successfully made the first IR SBF measurements using adaptive optics. We propose to measure distances to a sample of 8 galaxies straddling the crucial 7000 km/s region to determine if the Hubble constant measured locally is really 6% larger than the value measured beyond 100 Mpc. Making IR SBF measurements at such large distances is only practical using the high spatial-resolution images collected with the Gemini 8-m telescope. The IR SBF observations propsed here may be enhanced with optical V and I-band images taken with the Acquisition Camera during engineering time for the purpose of identifying globular clusters and background galaxies, masking dust, charting the galaxy profile, and measuring its color.


Title: Imaging of Low Redshift QSO Damped Lyman-alpha Absorption Line Systems

Abstract: We propose to obtain deep H-band images of a sample of the lowest known redshift (z<=0.5) damped Lyman alpha (DLA) quasar absorption line systems to establish whether low-surface brightness galaxies or dwarf galaxies give rise to the absorption. These images will be some of the deepest and highest resolution images ever obtained of any damped Lyman-alpha absorber. With this data set we will (1) probe fainter than previous searches, constraining whether low-surface brightness galaxies can give rise to DLAs, (2) probe closer to the quasar looking for previously undetected small compact galaxies, (3) study the near-IR morphologies of candidate absorbers, and (4) in cases where an absorber has been tentatively identified at optical wavelengths, add the near-IR photometry to better constrain the galaxy type and redshift of the candidate absorber. This proposal is a continuation of an observing program begun during the G2000B and G2001A periods. Analysis of data obtained during 7.5 hours in the Gemini QSS semester of two fields has resulted in the detection of one candidate absorber in the field of Q2251+1120 and a morphological classification of a DLA in the direction of Q0738+313. In the field surrounding Q2251+1120 a small faint (K~20) object lies close to the quasar line of sight (~2"). If this object is at the redshift of the absorber then this object would have an absolute magnitude similar to a faint dwarf galaxy or the bulge of a low-surface brightness galaxy. In the field of Q0738+313 we identify a recent spectroscopically confirmed DLA absorber as a faint galaxy with a previously unseen disk structure.


Title: U.S.G.P. Mini-Queue Observations with Hokupa'a

Abstract: The observations described in this proposal are to be carried out as part of the USGP-run ''mini-queue'' program with Hokupa'a on Gemini North. USGP staff will make the observations.


Title: Search for Asteroidal Satellites using Adaptive Optics

Abstract: We propose to make adaptive optics observations of faint (Vmag 14.5--17.0) asteroids to search for companions. The new Gemini AO system is the only instrument that will allow us to probe this brightness regime. Doing so will allow us to increase the number of objects available to our overall survey, necessary because we have already shown that satellites are not common. But in addition, it will give us access to new classes of asteroids that have previously been largely beyond our reach. For example, both the Trojans (objects at Jupiter's Lagrangian points) and Near-Earth asteroids have been suspected of having a high probability of harboring companions. Our overall program, also uses the complementary facilities at CFHT and Keck. To date, we have discovered 3 asteroidal companions, the first 3 to be imaged from the Earth (including HST) and 3 of the 4 known at that time. The 4th required a spacecraft flyby in 1993. Since our discoveries, 4 new moons have been discovered among the classes of objects we seek to study here. We hope to include Gemini as part of our overall strategy. In this first run, we will evaluate performance on about 20 asteroids. Asteroidal satellites give us vital insight into the nature of asteroids in two ways: 1) the presence of a moon allows the mass of the primary to be determine, hence its density, thus giving key information on the asteroid's structure and composition; and 2) the moons were almost certainly formed by collisions and collisions are a fundamental process that shaped most solar system objects.


Title: The Sub-Kiloparsec Structure of the Most Massive High-Redshift Galaxies

Abstract: \noindent Radio galaxies are the most massive objects at z > 1 that are known to contain old stellar populations. This, and the association of nearby, bright radio sources with gE and cD galaxies, suggest that distant radio galaxies are the progenitors of present--day, massive ellipticals. The study of distant radio galaxies is complicated by their powerful active nuclei, whose emission dominates at rest-frame UV wavelengths, producing the observed peculiar, elongated morphologies; the underlying stellar component is lost in the glare. Our NICMOS imaging of z~1 3CR radio galaxies reveals that although in a few cases the peculiar aligned morphology persists into the IR, in most cases a more ``normal'' host galaxy is present. It is not yet known, however, whether this is true at z>2. Here, we propose to obtain relatively deep adaptive--optics corrected K' images of z>2 radio galaxies using Hokupa'a and QUIRC on Gemini North. By imaging in the optical rest frame with sub--kiloparsec scale resolution, we can directly compare the structural parameters of radio galaxy hosts to present--day ellipticals, and determine whether or not these objects are dynamically old galaxies. We will also measure (or place limits on) the luminosity of the central dust-enshrouded AGN. The Gemini imaging proposed here provides the only possible means to complement our on-going study of z~1 3CR radio galaxy hosts, using HST and Keck, at the highest accessible redshifts.


Title: Dissecting 0.2<z<1.3 Field Galaxies with a Perfectly Matched Adaptive-Optics/Space-Telescope Dataset

Abstract: A major thrust of the Deep Extragalactic Evolutionary Probe program has been to obtain Keck spectra in deep HST WFPC2 galaxy survey fields. Due to a tendency to avoid bright stars within WFPC2 fields, there are only two cases where natural guide-stars are convenient for follow-up AO observations with Gemini and Keck. These are the Groth Survey Strip and Selected Area 68. The huge aperture and high spatial-resolution afforded by Gemini Hokupa'a NIR imaging are matched perfectly to HST WFPC2 in the optical. We propose Hokupa'a imaging in J, H, and K' of 14 0.2<z<1.3 galaxies in SA68 where deep WFPC2 B, V, and I data already exist. We have a complementary program underway using Keck AO and brighter guide-stars. Even if it were available, HST NICMOS could match neither the resolution nor depth of our AO imaging. We will combine these perfectly matched high-spatial-resolution optical and NIR datasets to form a broad wavelength baseline that will enable us to dissect galaxy subcomponents pixel by pixel and derive their star-formation histories. We already have Keck LRIS spectra of these with which to estimate dynamical masses and further define their internal structure.


Title: Surface Brightness Fluctutations in the Near Infrared: A Unique Tool for Stellar Population Studies

Abstract: The star formation histories of early-type galaxies provide crucial tests of models of galaxy formation and evolution. One route is to measure the ages of integrated stellar populations: We propose to use measurements of surface-brightness fluctuations (SBFs) in the near-infrared to break the age-metallicity degeneracy, the key step toward determining the star formation histories of local early-type galaxies. Our goal is to obtain a significant sample of SBF measurements for early type galaxies whose age and metallicity have been studied through spectroscopic measurements. By comparing the results of the two techniques, we will check the consistency of each method, the models used to calibrate the ages, and, in the case of the SBFs, the distances derived for the galaxies. By combining these methods, we will be able to detect directly the presence of intermediate-age stellar populations in local early-type galaxies. We propose to obtain near-IR SBF measurements of a sample of 23 elliptical and S0 galaxies with both accurate line strengths and I-band SBF magnitudes and distances observable from Mauna Kea.


Title: Searching for the Bottom of the Initial Mass Function

Abstract: The minimum mass of the IMF should be highly dependent on the dominant physics in the formation of stars and brown dwarfs. To date, the IMF has been measured down to ~10 M_Jup in a few young clusters, where it shows no sign of reaching a low-mass cutoff. To determine the lowest mass at which objects can form in isolation in one of these regions, I propose to use NIRI on Gemini North to obtain deep JHK_s images (H=21.5) of the young cluster IC~348 (2~Myr, 300~pc). By combining these data with very deep photometry from HST WFPC2 and SIRTF IRAC (0.79, 0.85, 3.6, 4.5, 5.8, 8.0~\micron), I will measure the mass function of brown dwarfs down to ~1 M_Jup.


Title: Observing the Transition from Disks to Planets

Abstract: Circumstellar accretion disks give birth to planets over a time scale that is believed to be between 1 and 10~Myr. We propose to use mid-infrared imaging and near-infrared adaptive optics imaging on Gemini to study how disks transform into brown dwarf and planetary companions. We will use Gemini North Hokupa'a/QUIRC AO imaging to search for young substellar companions to 12 stars in the Taurus star forming region (1~Myr, 140~pc) and 6 stars in the MBM12 association (10~Myr, 140~pc). From initial Gemini AO Quickstart observations, we have already identified a promising candidate with an expected mass of 3-10 M_Jup if it is a true companion. Five of the AO targets are recently discovered low-mass members of MBM12 and thus have no previous measurements for disks. For these targets, we will use Gemini South OSCIR imaging to obtain mid-IR photometry and determine whether accreting, optically thick disks are present. The companion and disk data at 1 and 10~Myr will then simultaneously constrain the evolution of disks as well as companion formation.

[Science Operations home] [schedules home]

Last update July 9, 2001; Phil Puxley