93 research outputs found
Eyes on the Universe: The Legacy of the Hubble Space Telescope and Looking to the Future with the James Webb Space Telescope
Over the past 20 years the Hubble Space Telescope has revolutionized our understanding of the Universe. Most recently, the complete refurbishment of Hubble in 2009 has given new life to the telescope and the new science instruments have already produced groundbreaking science results, revealing some of the most distant galaxy candidates ever discovered. Despite the remarkable advances in astrophysics that Hubble has provided, the new questions that have arisen demand a new space telescope with new technologies and capabilities. I will present the exciting new technology development and science goals of NASA's James Webb Space Telescope, which is currently being built and tested and will be launched this decade
Hubble Space Telescope and James Webb Space Telescope
Over the past 20 years the Hubble Space Telescope has revolutionized our understanding of the Universe. Most recently, the complete refurbishment of Hubble in 2009 has given new life to the telescope and the new science instruments have already produced ground breaking science results, revealing some of the most distant galaxy candidates ever discovered. Despite the remarkable advances in astrophysics that Hubble has provided, the new questions that have arisen demand a new space telescope with new technologies and capabilities. I will present the exciting new technology development and science goals of NASA's James Webb Space Telescope, which is currently being built and tested and will be launched this decade
Metallicities of Emission-Line Galaxies from HST ACS PEARS and HST WFC3 ERS Grism Spectroscopy at 0.6 < z < 2.4
Galaxies selected on the basis of their emission line strength show low
metallicities, regardless of their redshifts. We conclude this from a sample of
faint galaxies at redshifts between 0.6 < z < 2.4, selected by their prominent
emission lines in low-resolution grism spectra in the optical with the Advanced
Camera for Surveys (ACS) on the Hubble Space Telescope (HST) and in the
near-infrared using Wide-Field Camera 3 (WFC3). Using a sample of 11 emission
line galaxies (ELGs) at 0.6 < z < 2.4 with luminosities of -22 < M_B < -19,
which have [OII], H\beta, and [OIII] line flux measurements from the
combination of two grism spectral surveys, we use the R23 method to derive the
gas-phase oxygen abundances: 7.5 < 12+log(O/H) < 8.5. The galaxy stellar masses
are derived using Bayesian based Markov Chain Monte Carlo (\piMC^2) fitting of
their Spectral Energy Distribution (SED), and span the mass range 8.1 <
log(M_*/M_\sun) < 10.1. These galaxies show a mass-metallicity (M-L) and
Luminosity-Metallicity (L-Z) relation, which is offset by --0.6 dex in
metallicity at given absolute magnitude and stellar mass relative to the local
SDSS galaxies, as well as continuum selected DEEP2 samples at similar
redshifts. The emission-line selected galaxies most resemble the local "green
peas" galaxies and Lyman-alpha galaxies at z~0.3 and z~2.3 in the M-Z and L-Z
relations and their morphologies. The G-M_{20} morphology analysis shows that
10 out of 11 show disturbed morphology, even as the star-forming regions are
compact. These galaxies may be intrinsically metal poor, being at early stages
of formation, or the low metallicities may be due to gas infall and accretion
due to mergers.Comment: 24 pages with 7 figure
Spectroscopic Confirmation of Faint Lyman Break Galaxies at Redshifts Four and Five in the Hubble Ultra Deep Field
We present the faintest spectroscopically confirmed sample of redshift four
and five Lyman break galaxies to date. The sample is based on slitless grism
spectra of the Hubble Ultra Deep Field region from the GRAPES (Grism ACS
Program for Extragalactic Science) and PEARS (Probing Evolution and
Reionization Spectroscopically) projects, using the G800L grism on the HST
Advanced Camera for Surveys. We report here confirmations of 39 galaxies,
pre-selected as candidate Lyman break galaxies using photometric selection
criteria. We compare a "traditional" V-dropout selection to a more liberal one
(with V-i > 0.9), and find that the traditional criteria are about 64% complete
and 81% reliable. We also study the Lyman alpha emission properties of our
sample. We find that Lyman alpha emission is detected in about 1/4 of the
sample, and that our broad-band color selected sample includes 55% of
previously published line-selected Lyman alpha sources. Finally, we examine our
stacked 2D spectra. We demonstrate that strong, spatially extended (arcsecond
scale) Lyman alpha emission is not a generic property of these Lyman break
galaxies, but that a modest extension of the Lyman alpha photosphere (compared
to the starlight) may be present in those galaxies with prominent Lyman alpha
emission.Comment: Submitted to The Astrophysical Journal. Reduced spectra from both
GRAPES and PEARS are available from STScI, at
http://www.stsci.edu/science/grapes/ and at
http://archive.stsci.edu/prepds/pears
Evidence for Reduced Specific Star Formation Rates in the Centers of Massive Galaxies at z = 4
We perform the first spatially-resolved stellar population study of galaxies
in the early universe (z = 3.5 - 6.5), utilizing the Hubble Space Telescope
Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS)
imaging dataset over the GOODS-S field. We select a sample of 418 bright and
extended galaxies at z = 3.5 - 6.5 from a parent sample of ~ 8000
photometric-redshift selected galaxies from Finkelstein et al. (2015). We first
examine galaxies at 3.5< z < 4.0 using additional deep K-band survey data from
the HAWK-I UDS and GOODS Survey (HUGS) which covers the 4000A break at these
redshifts. We measure the stellar mass, star formation rate, and dust
extinction for galaxy inner and outer regions via spatially-resolved spectral
energy distribution fitting based on a Markov Chain Monte Carlo algorithm. By
comparing specific star formation rates (sSFRs) between inner and outer parts
of the galaxies we find that the majority of galaxies with the high central
mass densities show evidence for a preferentially lower sSFR in their centers
than in their outer regions, indicative of reduced sSFRs in their central
regions. We also study galaxies at z ~ 5 and 6 (here limited to high spatial
resolution in the rest-frame ultraviolet only), finding that they show sSFRs
which are generally independent of radial distance from the center of the
galaxies. This indicates that stars are formed uniformly at all radii in
massive galaxies at z ~ 5 - 6, contrary to massive galaxies at z < 4.Comment: Accepted to ApJ, 20 pages, 15 figure
Emission-Line Galaxies from the Hubble Space Telescope Probing Evolution and Reionization Spectroscopically (PEARS) Grism Survey. II: The Complete Sample
We present a full analysis of the Probing Evolution And Reionization
Spectroscopically (PEARS) slitess grism spectroscopic data obtained with the
Advanced Camera for Surveys on HST. PEARS covers fields within both the Great
Observatories Origins Deep Survey (GOODS) North and South fields, making it
ideal as a random survey of galaxies, as well as the availability of a wide
variety of ancillary observations to support the spectroscopic results. Using
the PEARS data we are able to identify star forming galaxies within the
redshift volume 0< z<1.5. Star forming regions in the PEARS survey are
pinpointed independently of the host galaxy. This method allows us to detect
the presence of multiple emission line regions (ELRs) within a single galaxy.
1162 Ha, [OIII] and/or [OII] emission lines have been identified in the PEARS
sample of ~906 galaxies down to a limiting flux of ~1e-18 erg/s/cm^2. The ELRs
have also been compared to the properties of the host galaxy, including
morphology, luminosity, and mass. From this analysis we find three key results:
1) The computed line luminosities show evidence of a flattening in the
luminosity function with increasing redshift; 2) The star forming systems show
evidence of disturbed morphologies, with star formation occurring predominantly
within one effective (half-light) radius. However, the morphologies show no
correlation with host stellar mass; and 3) The number density of star forming
galaxies with M_* > 1e9} M_sun decreases by an order of magnitude at z<0.5
relative to the number at 0.5<z<0.9 in support of the argument for galaxy
downsizing.Comment: Submitted. 48 pages. 19 figures. Accepted to Ap
Metallicities of Emission-Line Galaxies from HST ACS PEARS and HST WFC3 ERS Grism Spectroscopy at 0.6 is less than z is less than 2.4
Galaxies selected on the basis of their emission line strength. show low metallicities, regardless of their redshifts. We conclude this from a sample of faint galaxies at redshifts between 0.6 < z < 2.4, selected by their prominent emission lines in low resolution grism spectra in the optiCa.i with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST) and in the near-infrared using Wide-Field Camera 3 (WFC3). Using a sample of 11 emission line galaxies (ELGs) at 0.6 < z < 2.4 with luminosities of -22 approx < MB approx -19 which have [OII], H-Beta, and [OIII] line flux measurements from the combination of two grism spectral surveys, we use the R23 method to derive the gas-phase oxygen abundances: 7.5 <12+log(0/H)<8.5. The galaxy stellar masses are derived using Bayesian based Markov Chain Monte Carlo (pi MC(exp 2)) fitting of their Spectral Energy Distribution (SED), and span the mass range 8.1 < log(M(stellar)/M(solar)) < 10.1. These galaxies show a mass-metal1icity (M-L) and Luminosity-Metallicity (LZ) relation, which is offset by -<J.6 dex in meta1licity at given absolute magnitude and stellar mass relative to the local SDSS galaxies, as well as continuum selected DEEP2 samples at similar redshifts. The emission-line selected galaxies most resemble the local "green peas" galaxies and Lyman-alpha galaxies at z approx = 0.3 and z approx = 2.3 in the M-Z and L-Z relations and their morphologies. The G - M(sub 20) morphology analysis shows that 10 out of 11 show disturbed morphology, even as the star-forming regions are compact. These galaxies may be intrinsically metal poor, being at early stages of formation, or the low metallicities may be due to gas infall and accretion due to mergers
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