107 research outputs found
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 < 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
Improved Photometric Redshifts with Surface Luminosity Priors
We apply Bayesian statistics with prior probabilities of galaxy surface
luminosity (SL) to improve photometric redshifts. We apply the method to a
sample of 1266 galaxies with spectroscopic redshifts in the GOODS North and
South fields at 0.1 < z < 2.0. We start with spectrophotometric redshifts
(SPZs) based on Probing Evolution and Reionization Spectroscopically grism
spectra, which cover a wavelength range of 6000-9000A, combined with
(U)BViz(JHK) broadband photometry in the GOODS fields. The accuracy of SPZ
redshifts is estimated to be \sigma (\Delta(z))=0.035 with an systematic offset
of -0.026, where \Delta(z)=\Delta z / (1+z), for galaxies in redshift range of
0.5 < z < 1.25. The addition of the SL prior probability helps break the
degeneracy of SPZ redshifts between low redshift 4000 A break galaxies and
high-redshift Lyman break galaxies which are mostly catastrophic outliers. For
the 1138 galaxies at z < 1.6, the fraction of galaxies with redshift deviation
\Delta (z) > 0.2 is reduced from 15.0% to 10.4%, while the rms scatter of the
fractional redshift error does not change much.Comment: 7 pages, 7 figures, published in A
Not In Our Backyard: Spectroscopic Support for the CLASH z=11 Candidate MACS0647-JD
We report on our first set of spectroscopic Hubble Space Telescope
observations of the z~11 candidate galaxy strongly lensed by the
MACSJ0647.7+7015 galaxy cluster. The three lensed images are faint and we show
that these early slitless grism observations are of sufficient depth to
investigate whether this high-redshift candidate, identified by its strong
photometric break at ~1.5 micron, could possibly be an emission line galaxy at
a much lower redshift. While such an interloper would imply the existence of a
rather peculiar object, we show here that such strong emission lines would
clearly have been detected. Comparing realistic, two-dimensional simulations to
these new observations we would expect the necessary emission lines to be
detected at >5 sigma while we see no evidence for such lines in the dispersed
data of any of the three lensed images. We therefore exclude that this object
could be a low redshift emission line interloper, which significantly increases
the likelihood of this candidate being a bona fide z~11 galaxy.Comment: 14 Pages. 6 Figures. 2nd revised version. Accepted. To appear in ApJ.
Please contact [email protected] for comments on this pape
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
The road to the red sequence: A detailed view of the formation of a massive galaxy at z~2
(Abridged) We present here a detailed analysis of the star formation history
(SFH) of FW4871, a massive galaxy at z=1.893+-0.002. We compare rest-frame
optical and NUV slitless grism spectra from the Hubble Space Telescope with a
large set of composite stellar populations to constrain the underlying star
formation history. Even though the morphology features prominent tidal tails,
indicative of a recent merger, there is no sign of on-going star formation
within an aperture encircling one effective radius, which corresponds to a
physical extent of 2.6 kpc. A model assuming truncation of an otherwise
constant SFH gives a formation epoch zF~10, with a truncation after 2.7 Gyr,
giving a mass-weighted age of 1.5 Gyr and a stellar mass of 0.8-3E11Msun,
implying star formation rates of 30-110 Msun/yr. A more complex model including
a recent burst of star formation places the age of the youngest component at
145 Myr, with a mass contribution lower than 20%, and a maximum amount of dust
reddening of E(B-V)<0.4 mag (95% confidence levels). This low level of dust
reddening is consistent with the low emission observed at 24 micron,
corresponding to rest-frame 8 micron, where PAH emission should contribute
significantly if a strong formation episode were present. The colour profile of
FW4871 does not suggest a significant radial trend in the properties of the
stellar populations out to 3Re. We suggest that the recent merger that formed
FW4871 is responsible for the quenching of its star formation.Comment: 11 pages, 8 figures, 4 tables. In press (Astronomical Journal
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
Early-type galaxies in the PEARS survey: Probing the stellar populations at moderate redshift
Using HST/ACS slitless grism spectra from the PEARS program, we study the
stellar populations of morphologically selected early-type galaxies in the
GOODS North and South fields. The sample - extracted from a visual
classification of the (v2.0) HST/ACS images and restricted to redshifts z>0.4 -
comprises 228 galaxies (F775W<24 ABmag) out to z~1.3 over 320 arcmin2, with a
median redshift zM=0.75. This work significantly increases our previous sample
from the GRAPES survey in the HUDF (18 galaxies over ~11 arcmin2; Pasquali et
al. 2006b). The grism data allow us to separate the sample into `red' and
`blue' spectra, with the latter comprising 15% of the total. Three different
grids of models parameterising the star formation history are used to fit the
low-resolution spectra. Over the redshift range of the sample - corresponding
to a cosmic age between 5 and 10 Gyr - we find a strong correlation between
stellar mass and average age, whereas the **spread** of ages (defined by the
RMS of the distribution) is roughly ~1 Gyr and independent of stellar mass. The
best-fit parameters suggest it is formation epoch and not formation timescale,
that best correlates with mass in early-type galaxies. This result - along with
the recently observed lack of evolution of the number density of massive
galaxies - motivates the need for a channel of (massive) galaxy formation
bypassing any phase in the blue cloud, as suggested by the simulations of Dekel
et al. (2009).Comment: 12 pages, 12 figures, 3 tables. Submitted for publication in Ap
Expectations of the size evolution of massive galaxies at from the TNG50 simulation: the CEERS/JWST view
We present a catalog of about 25,000 images of massive () galaxies at redshift from the TNG50 cosmological
simulation, tailored for observations at multiple wavelengths carried out with
JWST. The synthetic images were created with the SKIRT radiative transfer code,
including the effects of dust attenuation and scattering. The noiseless images
were processed with the mirage simulator to mimic the Near Infrared Camera
(NIRCam) observational strategy (e.g., noise, dithering pattern, etc.) of the
Cosmic Evolution Early Release Science (CEERS) survey. In this paper, we
analyze the predictions of the TNG50 simulation for the size evolution of
galaxies at and the expectations for CEERS to probe that
evolution. In particular, we investigate how sizes depend on wavelength,
redshift, mass, and angular resolution of the images. We find that the
effective radius accurately describes the three-dimensional half-mass radius of
TNG50 galaxies. Sizes observed at 2~m are consistent with those measured
at 3.56~m at all redshifts and masses. At all masses, the population of
higher- galaxies is more compact than their lower- counterparts. However,
the intrinsic sizes are smaller than the mock observed sizes for the most
massive galaxies, especially at . This discrepancy between the
mass and light distribution may point to a transition in the galaxy morphology
at =4-5, where massive compact systems start to develop more extended
stellar structures.Comment: Accepted for publication in ApJ (20 pages, 12 figures). Data publicly
released at https://www.tng-project.org/costantin22 and at
https://www.lucacostantin.com/OMEG
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