39 research outputs found
Spectrophotometric Redshifts In The Faint Infrared Grism Survey: Finding Overdensities Of Faint Galaxies
We improve the accuracy of photometric redshifts by including low-resolution
spectral data from the G102 grism on the Hubble Space Telescope, which assists
in redshift determination by further constraining the shape of the broadband
Spectral Energy Disribution (SED) and identifying spectral features. The
photometry used in the redshift fits includes near-IR photometry from
FIGS+CANDELS, as well as optical data from ground-based surveys and HST ACS,
and mid-IR data from Spitzer. We calculated the redshifts through the
comparison of measured photometry with template galaxy models, using the EAZY
photometric redshift code. For objects with F105W AB mag with a
redshift range of , we find a typical error of for the purely photometric redshifts; with the addition of FIGS spectra,
these become , an improvement of 50\%. Addition of
grism data also reduces the outlier rate from 8\% to 7\% across all fields.
With the more-accurate spectrophotometric redshifts (SPZs), we searched the
FIGS fields for galaxy overdensities. We identified 24 overdensities across the
4 fields. The strongest overdensity, matching a spectroscopically identified
cluster at , has 28 potential member galaxies, of which 8 have previous
spectroscopic confirmation, and features a corresponding X-ray signal. Another
corresponding to a cluster at has 22 members, 18 of which are
spectroscopically confirmed. Additionally, we find 4 overdensities that are
detected at an equal or higher significance in at least one metric to the two
confirmed clusters.Comment: 17 pages, 13 figures. To appear in Ap
Evidence for shock-heated gas in the Taffy Galaxies and Bridge from Optical Emission-Line IFU spectroscopy
We present optical IFU observations of the Taffy system (UGC 12914/15); named
for the radio emission that stretches between the two galaxies. Given that
these gas rich galaxies are believed to have recently collided head-on, the
pair exhibits a surprisingly normal total (sub-LIRG) IR luminosity
( L). Previous observations
have demonstrated that a large quantity of molecular and neutral gas have been
drawn out of the galaxies into a massive multi-phase bridge. We present, for
the first time, spatially resolved spectroscopy of the ionized gas in the
system. The results show that the ionized gas is highly disturbed
kinematically, with gas spread in two main filaments between the two galaxies.
The line profiles exhibit widespread double components in both the bridge and
parts of the disks of the galaxies. We investigate the spatial distribution of
the excitation properties of the ionized gas using emission-line diagnostic
diagrams, and conclude that large quantities (up to 40) of the emission
from the entire system is consistent with gas heated in 200 \kms\ shocks.
While the shocked gas is mainly associated with the bridge, there is a
significant amount of shocked gas associated with both galaxies. Confirming
other multi-wavelength indicators, the results suggest that the effects of
shocks and turbulence can continue to be felt in a high-speed galaxy collision
long after the collision has occurred. The persistence of shocks in the Taffy
system may explain the relatively low current star formation rates in the
system as a whole.Comment: 19 pages, 13 figures. Accepted for publication in Ap
FIGS -- Faint Infrared Grism Survey: Description and Data Reduction
The Faint Infrared Grism Survey (FIGS) is a deep Hubble Space Telescope (HST)
WFC3/IR (Wide Field Camera 3 Infrared) slitless spectroscopic survey of four
deep fields. Two fields are located in the Great Observatories Origins Deep
Survey-North (GOODS-N) area and two fields are located in the Great
Observatories Origins Deep Survey-South (GOODS-S) area. One of the southern
fields selected is the Hubble Ultra Deep Field. Each of these four fields were
observed using the WFC3/G102 grism (0.8-1.15 continuous coverage)
with a total exposure time of 40 orbits (~ 100 kilo-seconds) per field. This
reaches a 3 sigma continuum depth of ~26 AB magnitudes and probes emission
lines to . This paper details the four
FIGS fields and the overall observational strategy of the project. A detailed
description of the Simulation Based Extraction (SBE) method used to extract and
combine over 10000 spectra of over 2000 distinct sources brighter than
m_F105W=26.5 mag is provided. High fidelity simulations of the observations is
shown to significantly improve the background subtraction process, the spectral
contamination estimates, and the final flux calibration. This allows for the
combination of multiple spectra to produce a final high quality, deep,
1D-spectra for each object in the survey.Comment: 21 Pages. 17 Figures. To appear in Ap
FIGS: Spectral fitting constraints on the star formation history of massive galaxies since Cosmic Noon
We constrain the stellar population properties of a sample of 52 massive
galaxies, with stellar mass log Ms>10.5, over the redshift range 0.5<z<2 by use
of observer-frame optical and near-infrared slitless spectra from HST's ACS and
WFC3 grisms. The deep exposures (~100 ks) allow us to target individual spectra
of massive galaxies to F160W=22.5AB. Our spectral fitting approach uses a set
of six base models adapted to the redshift and spectral resolution of each
observation, and fits the weights of the base models, including potential dust
attenuation, via an MCMC method. Our sample comprises a mixed distribution of
quiescent (19) and star-forming galaxies (33). We quantify the width of the age
distribution (Dt) that is found to dominate the variance of the retrieved
parameters according to Principal Component Analysis. The population parameters
follow the expected trend towards older ages with increasing mass, and Dt
appears to weakly anti-correlate with stellar mass, suggesting a more efficient
star formation at the massive end. As expected, the redshift dependence of the
relative stellar age (measured in units of the age of the Universe at the
source) in the quiescent sample rejects the hypothesis of a single burst (aka
monolithic collapse). Radial colour gradients within each galaxy are also
explored, finding a wider scatter in the star-forming subsample, but no
conclusive trend with respect to the population parameters.Comment: 20 pages, 12+3 figures, 4+3 tables. MNRAS, in pres
Evidence for Shock-heated Gas in the Taffy Galaxies and Bridge from Optical Emission-line IFU Spectroscopy
We present optical integral field unit observations of the Taffy system (UGC 12914/15), named for the radio emission that stretches between the two galaxies. Given that these gas-rich galaxies are believed to have recently collided head-on, the pair exhibits a surprisingly normal total (sub-LIRG) IR luminosity (L_(FIR) ~ 4.5 × 10^(10) L_⊙). Previous observations have demonstrated that a large quantity of molecular and neutral gas has been drawn out of the galaxies into a massive multiphase bridge. We present, for the first time, spatially resolved spectroscopy of the ionized gas in the system. The results show that the ionized gas is highly disturbed kinematically, with gas spread in two main filaments between the two galaxies. The line profiles exhibit widespread double components in both the bridge and parts of the disks of the galaxies. We investigate the spatial distribution of the excitation properties of the ionized gas using emission-line diagnostic diagrams and conclude that a large quantity (up to 40%) of the emission from the entire system is consistent with gas heated in ~200 km s^(−1) shocks. While the shocked gas is mainly associated with the bridge, there is a significant amount of shocked gas associated with both galaxies. Confirming other multiwavelength indicators, the results suggest that the effects of shocks and turbulence can continue to be felt in a high-speed galaxy collision long after the collision has occurred. The persistence of shocks in the Taffy system may explain the relatively low current star formation rates in the system as a whole
Science Impacts of the SPHEREx All-Sky Optical to Near-Infrared Spectral Survey: Report of a Community Workshop Examining Extragalactic, Galactic, Stellar and Planetary Science
SPHEREx is a proposed SMEX mission selected for Phase A. SPHEREx will carry
out the first all-sky spectral survey and provide for every 6.2" pixel a
spectra between 0.75 and 4.18 m [with R41.4] and 4.18 and 5.00
m [with R135]. The SPHEREx team has proposed three specific science
investigations to be carried out with this unique data set: cosmic inflation,
interstellar and circumstellar ices, and the extra-galactic background light.
It is readily apparent, however, that many other questions in astrophysics and
planetary sciences could be addressed with the SPHEREx data. The SPHEREx team
convened a community workshop in February 2016, with the intent of enlisting
the aid of a larger group of scientists in defining these questions. This paper
summarizes the rich and varied menu of investigations that was laid out. It
includes studies of the composition of main belt and Trojan/Greek asteroids;
mapping the zodiacal light with unprecedented spatial and spectral resolution;
identifying and studying very low-metallicity stars; improving stellar
parameters in order to better characterize transiting exoplanets; studying
aliphatic and aromatic carbon-bearing molecules in the interstellar medium;
mapping star formation rates in nearby galaxies; determining the redshift of
clusters of galaxies; identifying high redshift quasars over the full sky; and
providing a NIR spectrum for most eROSITA X-ray sources. All of these
investigations, and others not listed here, can be carried out with the nominal
all-sky spectra to be produced by SPHEREx. In addition, the workshop defined
enhanced data products and user tools which would facilitate some of these
scientific studies. Finally, the workshop noted the high degrees of synergy
between SPHEREx and a number of other current or forthcoming programs,
including JWST, WFIRST, Euclid, GAIA, K2/Kepler, TESS, eROSITA and LSST.Comment: Report of the First SPHEREx Community Workshop,
http://spherex.caltech.edu/Workshop.html , 84 pages, 28 figure
A comprehensive study of H emitters at 0.62 in the DAWN survey: the need for deep and wide regions
We present new estimates of the luminosity function (LF) and star formation
rate density (SFRD) for an H selected sample at from the
Deep And Wide Narrow-band (DAWN) survey. Our results are based on a new
H sample in the extended COSMOS region (compared to Coughlin et al.
2018) with the inclusion of flanking fields, resulting in a total area coverage
of 1.5 deg. A total of 241 H emitters were selected based on
robust selection criteria using spectro-photometric redshifts and broadband
color-color classification. We explore the effect of different dust correction
prescriptions by calculating the LF and SFRD using a constant dust extinction
correction, A{} mag, a luminosity-dependent correction,
and a stellar-mass dependent correction. The resulting H LFs are well
fitted using Schechter functions with best-fit parameters: L erg
s, Mpc, for constant dust
correction, L erg s, Mpc,
for luminosity-dependent dust correction, and L
erg s, Mpc, , for stellar
mass-dependent dust correction. The deep and wide nature of the DAWN survey
effectively samples H emitters over a wide range of luminosities,
thereby providing better constraints on both the faint and bright end of the
LF. Also, the SFRD estimates
MyrMpc (constant dust correction),
MyrMpc
(luminosity-dependent dust correction), and
MyrMpc (stellar mass-dependent dust correction) are in
good agreement with the evolution of SFRD across redshifts () seen
from previous H surveys.Comment: 16 pages, 8 figures, Accepted for publication in Ap