How Galaxies Acquire their Gas: A Map of Multiphase Accretion and Feedback in Gaseous Galaxy Halos
We propose to address two of the biggest open questions in galaxy formation - how galaxies acquire their gas and how they return it to the IGM - with a concentrated COS survey of diffuse multiphase gas in the halos of SDSS galaxies at z = 0.15 - 0.35. Our chief science goal is to establish a basic set of observational facts about the physical state, metallicity, and kinematics of halo gas, including the sky covering fraction of hot and cold material, the metallicity of infall and outflow, and correlations with galaxy stellar mass, type, and color - all as a function of impact parameter from 10 - 150 kpc. Theory suggests that the bimodality of galaxy colors, the shape of the luminosity function, and the mass-metallicity relation are all influenced at a fundamental level by accretion and feedback, yet these gas processes are poorly understood and cannot be predicted robustly from first principles. We lack even a basic observational assessment of the multiphase gaseous content of galaxy halos on 100 kpc scales, and we do not know how these processes vary with galaxy properties. This ignorance is presently one of the key impediments to understanding galaxy formation in general. We propose to use the high-resolution gratings G130M and G160M on the Cosmic Origins Spectrograph to obtain sensitive column density measurements of a comprehensive suite of multiphase ions in the spectra of 43 z < 1 QSOs lying behind 43 galaxies selected from the Sloan Digital Sky Survey. In aggregate, these sightlines will constitute a statistically sound map of the physical state and metallicity of gaseous halos, and subsets of the data with cuts on galaxy mass, color, and SFR will seek out predicted variations of gas properties with galaxy properties. Our interpretation of these data will be aided by state-of-the-art hydrodynamic simulations of accretion and feedback, in turn providing information to refine and test such models. We will also use Keck, MMT, and Magellan (as needed) to obtain optical spectra of the QSOs to measure cold gas with Mg II, and optical spectra of the galaxies to measure SFRs and to look for outflows. In addition to our other science goals, these observations will help place the Milky Way's population of multiphase, accreting High Velocity Clouds (HVCs) into a global context by identifying analogous structures around other galaxies. Our program is designed to make optimal use of the unique capabilities of COS to address our science goals and also generate a rich dataset of other absorption-line systems.
The Host Environments of Type Ia Supernovae in the SDSS Survey
The Sloan Digital Sky Survey Supernova Survey has discovered nearly 500 type Ia supernovae and created a large, unique, and uniform sample of these cosmological tools. As part of a comprehensive study of the supernova hosts, we propose to obtain Hubble ACS images of a large fraction of these galaxies. Integrated colors and spectra will be measured from the ground, but we require high-resolution HST imaging to provide accurate morphologies and color information at the site of the explosion. This information is essential in determining the systematic effects of population age on type Ia supernova luminosities and improving their reliability in measuring dark energy. Recent studies suggest two populations of type Ia supernovae: a class that explodes promptly after star-formation and one that is delayed by billions of years. Measuring the star-formation rate at the site of the supernova from colors in the HST images may be the best way to differentiate between these classes.
Extending COS/G130M Coverage Down to 905A With Two New Central Wavelengths.
These exploratory observations will provide sensitivity, wavelength range, and resolution measurements for two new COS FUV G130M central wavelength settings. These new settings will extend COS/G130M coverage down to 905? in two new bandpasses; 1021-1171? (BLUE) and 905-1055? (Ultra-BLUE). The modes are chosen to provide continuous coverage from 905? to the existing coverage in the G130M/1291? setting with approximately 30? of overlap in each mode for cross-calibration purposes. No focus adjustments will be made for these settings, as this is deemed an unnecessary risk to COS.
These new modes have the potential to provide greater than FUSE sensitivity at moderate (3, 000-5, 000) resolution.
Three WD targets are defined;
1) GD50 (GSC-04717-00588; a well observed standard WD) 2) WD0320-539 (GSC-08493-00891, one of the targets used in exploring the G140L sensitivity), 3) REJ0503-289 (WD-5001-289 = GSC-04717-00588, a hot EUVE bright WD)
But only target 2) is used at this time.
In the observations section, G130M/1291A is a placeholder for the BLUE and Super-BLUE settings.
CCD Dark Monitor Part 2
Monitor the darks for the STIS CCD.
CCD Bias Monitor-Part 2
Monitor the bias in the 1x1, 1x2, 2x1, and 2x2 bin settings at gain=1, and 1x1 at gain = 4, to build up high-S/N superbiases and track the evolution of hot columns.
IR Rate Dependent Non-linearity
The NICMOS non-linearity known as the Bohlin Effect has revealed that the apparent flux of a source observed by NICMOS is not a simple, linear function of count rate. The effect has been characterized by observations of star clusters observed with and without additional background from the internal lamps. As WFC3 lacks internal lamps which can be used to add background, we will rely on the bright Earth limb to provide additional background. We will observe a star cluster, 47 Tuc, repeatedly throughout a complete HST orbit which has been chosen to put the closest approach to the bright Earth to be 13.5 degrees, the closest approach allowed while retaining FGS guiding. Another set will be done with the BE limb closest approach of 15.5 degrees. The observations will be done with the two most commonly used filters, F110W and F160W and at two different bright Earth limb angles to test the linearity of the non-linearity. We have also included an orbit on NGC 1850 to repeat the NICMOS field for which the linearity of the field has been established.
IR Dark Current Monitor
Analyses of ground test data showed that dark current signals are more reliably removed from science data using darks taken with the same exposure sequences as the science data, than with a single dark current image scaled by desired exposure time. Therefore, dark current images must be collected using all sample sequences that will be used in science observations. These observations will be used to monitor changes in the dark current of the WFC3-IR channel on a day-to-day basis, and to build calibration dark current ramps for each of the sample sequences to be used by Gos in Cycle 17. For each sample sequence/array size combination, a median ramp will be created and delivered to the calibration database system (CDBS).
A Panchromatic Hubble Andromeda Treasury - I
We propose to image the north east quadrant of M31 to deep limits in the UV, optical, and near-IR. HST imaging should resolve the galaxy into more than 100 million stars, all with common distances and foreground extinctions. UV through NIR stellar photometry (F275W, F336W with WFC3/UVIS, F475W and F814W with ACS/WFC, and F110W and F160W with WFC3/NIR) will provide effective temperatures for a wide range of spectral types, while simultaneously mapping M31's extinction. Our central science drivers are to: understand high-mass variations in the stellar IMF as a function of SFR intensity and metallicity; capture the spatially-resolved star formation history of M31; study a vast sample of stellar clusters with a range of ages and metallicities. These are central to understanding stellar evolution and clustered star formation; constraining ISM energetics; and understanding the counterparts and environments of transient objects (novae, SNe, variable stars, x-ray sources, etc.). As its legacy, this survey adds M31 to the Milky Way and Magellanic Clouds as a fundamental calibrator of stellar evolution and star-formation processes for understanding the stellar populations of distant galaxies. Effective exposure times are 977s in F275W, 1368s in F336W, 4040s in F475W, 4042s in F814W, 699s in F110W, and 1796s in F160W, including short exposures to avoid saturation of bright sources. These depths will produce photon-limited images in the UV. Images will be crowding-limited in the optical and NIR, but will reach below the red clump at all radii. The images will reach the Nyquist sampling limit in F160W, F475W, and F814W.
WFC3 UVIS CCD Daily Monitor
The behavior of the WFC3 UVIS CCD will be monitored daily with a set of full-frame, four-amp bias and dark frames. A smaller set of 2Kx4K subarray biases are acquired at less frequent intervals throughout the cycle to support subarray science observations. The internals from this proposal, along with those from the anneal procedure (Proposal 11909), will be used to generate the necessary superbias and superdark reference files for the calibration pipeline (CDBS).
Bright Galaxies at z>7.5 with a WFC3 Pure Parallel Survey
The epoch of reionization represents a special moment in the history of the Universe as it is during this era that the first galaxies and star clusters are formed. Reionization also profoundly affects the environment where subsequent generations of galaxies evolve. Our overarching goal is to test the hypothesis that galaxies are responsible for reionizing neutral hydrogen. To do so we propose to carry out a pure parallel WFC3 survey to constrain the bright end of the redshift z>7.5 galaxy luminosity function on a total area of 176 arcmin^2 of sky. Extrapolating the evolution of the luminosity function from z~6, we expect to detect about 20 Lyman Break Galaxies brighter than M_* at z~8 significantly improving the current sample of only a few galaxies known at these redshifts. Finding significantly fewer objects than predicted on the basis of extrapolation from z=6 would set strong limits to the brightness of M_*, highlighting a fast evolution of the luminosity function with the possible implication that galaxies alone cannot reionize the Universe. Our observations will find the best candidates for spectroscopic confirmation, that is bright z>7.5 objects, which would be missed by small area deeper surveys. The random pointing nature of the program is ideal to beat cosmic variance, especially severe for luminous massive galaxies, which are strongly clustered. In fact our survey geometry of 38 independent fields will constrain the luminosity function like a contiguous single field survey with two times more area at the same depth. Lyman Break Galaxies at z>7.5 down to m_AB=26.85 (5 sigma) in F125W will be selected as F098M dropouts, using three to five orbits visits that include a total of four filters (F606W, F098M, F125W, F160W) optimized to remove low-redshift interlopers and cool stars. Our data will be highly complementary to a deep field search for high- z galaxies aimed at probing the faint end of the luminosity function, allowing us to disentangle the degeneracy between faint end slope and M_* in a Schechter function fit of the luminosity function. We waive proprietary rights for the data. In addition, we commit to release the coordinates and properties of our z>7.5 candidates within one month from the acquisition of each field.