Space Telescope Science Institute

About: Space Telescope Science Institute is a facility organization based out in Baltimore, Maryland, United States. It is known for research contribution in the topics: Galaxy & Stars. The organization has 2448 authors who have published 14154 publications receiving 947296 citations. The organization is also known as: STScI.

A map of the large day–night temperature gradient of a super-Earth exoplanet

Abstract: Over the past decade, observations of giant exoplanets (Jupiter-size) have provided key insights into their atmospheres, but the properties of lower-mass exoplanets (sub-Neptune) remain largely unconstrained because of the challenges of observing small planets. Numerous efforts to observe the spectra of super-Earths—exoplanets with masses of one to ten times that of Earth—have so far revealed only featureless spectra. Here we report a longitudinal thermal brightness map of the nearby transiting super-Earth 55 Cancri e (refs 4, 5) revealing highly asymmetric dayside thermal emission and a strong day–night temperature contrast. Dedicated space-based monitoring of the planet in the infrared revealed a modulation of the thermal flux as 55 Cancri e revolves around its star in a tidally locked configuration. These observations reveal a hot spot that is located 41 ± 12 degrees east of the substellar point (the point at which incident light from the star is perpendicular to the surface of the planet). From the orbital phase curve, we also constrain the nightside brightness temperature of the planet to 1,380 ± 400 kelvin and the temperature of the warmest hemisphere (centred on the hot spot) to be about 1,300 kelvin hotter (2,700 ± 270 kelvin) at a wavelength of 4.5 micrometres, which indicates inefficient heat redistribution from the dayside to the nightside. Our observations are consistent with either an optically thick atmosphere with heat recirculation confined to the planetary dayside, or a planet devoid of atmosphere with low-viscosity magma flows at the surface.

The blanco cosmology survey: data acquisition, processing, calibration, quality diagnostics, and data release

Abstract: The Blanco Cosmology Survey (BCS) is a 60 night imaging survey of ~80 deg2 of the southern sky located in two fields: (α, δ) = (5 hr, –55°) and (23 hr, –55°). The survey was carried out between 2005 and 2008 in griz bands with the Mosaic2 imager on the Blanco 4 m telescope. The primary aim of the BCS survey is to provide the data required to optically confirm and measure photometric redshifts for Sunyaev-Zel'dovich effect selected galaxy clusters from the South Pole Telescope and the Atacama Cosmology Telescope. We process and calibrate the BCS data, carrying out point-spread function-corrected model-fitting photometry for all detected objects. The median 10σ galaxy (point-source) depths over the survey in griz are approximately 23.3 (23.9), 23.4 (24.0), 23.0 (23.6), and 21.3 (22.1), respectively. The astrometric accuracy relative to the USNO-B survey is ~45 mas. We calibrate our absolute photometry using the stellar locus in grizJ bands, and thus our absolute photometric scale derives from the Two Micron All Sky Survey, which has ~2% accuracy. The scatter of stars about the stellar locus indicates a systematic floor in the relative stellar photometric scatter in griz that is ~1.9%, ~2.2%, ~2.7%, and ~2.7%, respectively. A simple cut in the AstrOmatic star-galaxy classifier spread_model produces a star sample with good spatial uniformity. We use the resulting photometric catalogs to calibrate photometric redshifts for the survey and demonstrate scatter δz/(1 + z) = 0.054 with an outlier fraction η < 5% to z ~ 1. We highlight some selected science results to date and provide a full description of the released data products.

VERY BLUE UV-CONTINUUM SLOPE β OF LOW LUMINOSITYz∼ 7 GALAXIES FROM WFC3/IR: EVIDENCE FOR EXTREMELY LOW METALLICITIES?

Abstract: We use the ultra-deep WFC3/IR data over the Hubble Ultra Deep Field and the Early Release Science WFC3/IR data over the CDF-South GOODS field to quantify the broadband spectral properties of candidate star-forming galaxies at z {approx} 7. We determine the UV-continuum slope {beta} in these galaxies, and compare the slopes with galaxies at later times to measure the evolution in {beta}. For luminous L* {sub z=3} galaxies, we measure a mean UV-continuum slope {beta} of -2.0 {+-} 0.2, which is comparable to the {beta} {approx} -2 derived at similar luminosities at z {approx} 5-6. However, for the lower luminosity 0.1L* {sub z=3} galaxies, we measure a mean {beta} of -3.0 {+-} 0.2. This is substantially bluer than is found for similar luminosity galaxies at z {approx} 4, just 800 Myr later, and even at z {approx} 5-6. In principle, the observed {beta} of -3.0 can be matched by a very young, dust-free stellar population, but when nebular emission is included the expected {beta} becomes {>=}-2.7. To produce these very blue {beta}s (i.e., {beta} {approx} -3), extremely low metallicities and mechanisms to reduce the red nebular emission seem to be required. For example, a large escape fraction (i.e., f {submore » esc} {approx}> 0.3) could minimize the contribution from this red nebular emission. If this is correct and the escape fraction in faint z {approx} 7 galaxies is {approx}>0.3, it may help to explain how galaxies reionize the universe.« less

Chasing highly obscured QSOs in the COSMOS field

Abstract: A large population of heavily obscured, Compton-thick active galactic nuclei (AGNs) is predicted by AGN synthesis models for the cosmic X-ray background and by the "relic" supermassive black hole mass function measured from local bulges. However, even the deepest X-ray surveys are inefficient to search for these elusive AGNs. Alternative selection criteria, combining mid-infrared with near-infrared, and optical photometry, have instead been successful in pinpointing a large population of Compton-thick AGNs. We take advantage of the deep Chandra and Spitzer coverage of a large area (more than 10 times the area covered by the Chandra deep fields, CDFs) in the Cosmic Evolution Survey (COSMOS) field to extend the search of highly obscured, Compton-thick active nuclei to higher luminosity. These sources have low surface density, and therefore large samples can be provided only through large area surveys, like the COSMOS survey. We analyze the X-ray properties of COSMOS MIPS sources with 24 μm fluxes higher than 550 μJy. For the MIPS sources not directly detected in the Chandra images, we produce stacked images in soft and hard X-rays bands. To estimate the fraction of Compton-thick AGN in the MIPS source population, we compare the observed stacked count rates and hardness ratios to those predicted by detailed Monte Carlo simulations, including both obscured AGN and star-forming galaxies. The volume density of Compton-thick QSOs (log L(2-10 keV) = 44-45 erg s^(–1), or logλL_λ(5.8 μm) = 44.79-46.18 erg s^(–1) for a typical infrared to X-ray luminosity ratio) evaluated in this way is (4.8 ± 1.1) × 10^(–6) Mpc^(–3) in the redshift bin 1.2-2.2. This density is ~44% of all X-ray-selected QSOs in the same redshift and luminosity bin, and it is consistent with the expectation of the most up-to-date AGN synthesis models for the cosmic X-ray background (Gilli et al. 2007). The density of lower luminosity Compton-thick AGNs (log L(2-10 keV) = 43.5-44) at z = 0.7-1.2 is (3.7 ± 1.1) × 10^(–5) Mpc^(–3), corresponding to ~67% of X-ray-selected AGNs. The comparison between the fraction of infrared-selected, Compton-thick AGNs to the X-ray selected, unobscured, and moderately obscured AGNs at high and low luminosity suggests that Compton-thick AGNs follow a luminosity dependence similar to that discovered for Compton-thin AGNs, becoming relatively rarer at high luminosities. We estimate that the fraction of AGNs (unobscured, moderately obscured, and Compton thick) to the total MIPS source population is 49 ± 10%, a value significantly higher than that previously estimated at similar 24 μm fluxes. We discuss how our findings can constrain AGN feedback models.

COMPLETING THE CENSUS OF Lyα EMITTERS AT THE REIONIZATION EPOCH

Abstract: We carried out extended spectroscopic confirmations of Lyα emitters (LAEs) at z = 6.5 and 5.7 in the Subaru Deep Field. Now, the total number of spectroscopically confirmed LAEs is 45 and 54 at z = 6.5 and 5.7, respectively, and at least 81% (70%) of our photometric candidates at z = 6.5 (5.7) have been spectroscopically identified as real LAEs. We made careful measurements of the Lyα luminosity, both photometrically and spectroscopically, to accurately determine the Lyα and rest-UV luminosity functions (LFs). The substantially improved evaluation of the Lyα LF at z = 6.5 shows an apparent deficit from z = 5.7 at least at the bright end, and a possible decline even at the faint end, though small uncertainties remain. The rest-UV LFs at z = 6.5 and 5.7 are in good agreement, at least at the bright end, in clear contrast to the differences seen in the Lyα LF. These results imply an increase in the neutral fraction of the intergalactic medium from z = 5.7 to 6.5. The rest-frame equivalent width (EW0) distribution at z = 6.5 seems to be systematically smaller than z = 5.7, and it shows an extended tail toward larger EW0. The bright end of the rest-UV LF can be reproduced from the observed Lyα LF and a reasonable EW0-UV luminosity relation. Integrating this rest-UV LF provides the first measurement of the contribution of LAEs to the photon budget required for reionization. The derived UV LF suggests that the fractional contribution of LAEs to the photon budget among Lyman break galaxies significantly increases toward faint magnitudes. Low-luminosity LAEs could dominate the ionizing photon budget, though this inference depends strongly on the uncertain faint-end slope of the Lyα LF. © 2011. The American Astronomical Society. All rights reserved.