65 research outputs found
The Number Density Evolution of Extreme Emission Line Galaxies in 3D-HST: Results from a Novel Automated Line Search Technique for Slitless Spectroscopy
The multiplexing capability of slitless spectroscopy is a powerful asset in
creating large spectroscopic datasets, but issues such as spectral confusion
make the interpretation of the data challenging. Here we present a new method
to search for emission lines in the slitless spectroscopic data from the 3D-HST
survey utilizing the Wide-Field Camera 3 on board the Hubble Space Telescope.
Using a novel statistical technique, we can detect compact (extended) emission
lines at 90% completeness down to fluxes of 1.5 (3.0) times 10^{-17}
erg/s/cm^2, close to the noise level of the grism exposures, for objects
detected in the deep ancillary photometric data. Unlike previous methods, the
Bayesian nature allows for probabilistic line identifications, namely redshift
estimates, based on secondary emission line detections and/or photometric
redshift priors. As a first application, we measure the comoving number density
of Extreme Emission Line Galaxies (restframe [O III] 5007 equivalent widths in
excess of 500 Angstroms). We find that these galaxies are nearly 10 times more
common above z~1.5 than at z<0.5. With upcoming large grism surveys such as
Euclid and WFIRST as well as grisms featuring prominently on the NIRISS and
NIRCam instruments on James Webb Space Telescope, methods like the one
presented here will be crucial for constructing emission line redshift catalogs
in an automated and well-understood manner.Comment: 16 pages, 14 Figures; Accepted to Ap
Quiescent Galaxies in the 3D-HST Survey: Spectroscopic Confirmation of a Large Number of Galaxies with Relatively Old Stellar Populations at z~2
Quiescent galaxies at z~2 have been identified in large numbers based on
rest-frame colors, but only a small number of these galaxies have been
spectroscopically confirmed to show that their rest-frame optical spectra show
either strong Balmer or metal absorption lines. Here, we median stack the
rest-frame optical spectra for 171 photometrically-quiescent galaxies at 1.4 <
z < 2.2 from the 3D-HST grism survey. In addition to Hbeta (4861A), we
unambiguously identify metal absorption lines in the stacked spectrum,
including the G-band (4304A), Mg I (5175A), and Na I (5894A). This finding
demonstrates that galaxies with relatively old stellar populations already
existed when the universe was ~3 Gyr old, and that rest-frame color selection
techniques can efficiently select them. We find an average age of 1.3^0.1_0.3
Gyr when fitting a simple stellar population to the entire stack. We confirm
our previous result from medium-band photometry that the stellar age varies
with the colors of quiescent galaxies: the reddest 80% of galaxies are
dominated by metal lines and have a relatively old mean age of 1.6^0.5_0.4 Gyr,
whereas the bluest (and brightest) galaxies have strong Balmer lines and a
spectroscopic age of 0.9^0.2_0.1 Gyr. Although the spectrum is dominated by an
evolved stellar population, we also find [OIII] and Hbeta emission.
Interestingly, this emission is more centrally concentrated than the continuum
with L_[OIII] = 1.7 +/- 0.3 x 10^40 erg s^-1, indicating residual central star
formation or nuclear activity.Comment: 6 pages, 4 figures, accepted for publication in the Astrophysical
Journal Letter
Complete IRAC mapping of the CFHTLS-DEEP, MUSYC AND NMBS-II FIELDS
The IRAC mapping of the NMBS-II fields program is an imaging survey at 3.6
and 4.5m with the Spitzer Infrared Array Camera (IRAC). The observations
cover three Canada-France-Hawaii Telescope Legacy Survey Deep (CFHTLS-D)
fields, including one also imaged by AEGIS, and two MUSYC fields. These are
then combined with archival data from all previous programs into deep mosaics.
The resulting imaging covers a combined area of about 3 , with at least
2 hr integration time for each field. In this work, we present our data
reduction techniques and document the resulting coverage maps at 3.6 and
4.5m. All of the images are W-registered to the reference image, which is
either the z-band stack image of the 25\% best seeing images from the CFHTLS-D
for CFHTLS-D1, CFHTLS-D3, and CFHTLS-D4, or the K-band images obtained at the
Blanco 4-m telescope at CTIO for MUSYC1030 and MUSYC1255. We make all images
and coverage maps described herein publicly available via the Spitzer Science
Center.Comment: Accepted in PASP; released IRAC mosaics available upon publication of
the pape
The Geometry of Cold, Metal-Enriched Gas Around Galaxies at
We present the first results from a Hubble Space Telescope WFC3/IR program,
which obtained direct imaging and grism observations of galaxies near quasar
sightlines with a high frequency of uncorrelated foreground Mg II absorption.
These highly efficient observations targeted 54 Mg II absorbers along the line
of sight to nine quasars at . We find that 89% of the absorbers
in the range can be spectroscopically matched to at least one
galaxy with an impact parameter less than 200 kpc and .
We have estimated the star formation rates and measured structural parameters
for all detected galaxies with impact parameters in the range 7-200 kpc and
star formation rates greater than 1.3 M yr. We find that
galaxies associated with Mg II absorption have significantly higher mean star
formation rates and marginally higher mean star formation rate surface
densities compared to galaxies with no detected Mg II. Nearly half of the Mg II
absorbers match to more than one galaxy, and the mean equivalent width of the
Mg II absorption is found to be greater for groups, compared to isolated
galaxies. Additionally, we observe a significant redshift evolution in the
physical extent of Mg II-absorbing gas around galaxies and evidence of an
enhancement of Mg II within 50 degrees of the minor axis, characteristic of
outflows, which persists to 80 kpc around the galaxies, in agreement with
recent predictions from simulations.Comment: 21 pages, 20 figures, Submitted to Ap
Broad Absorption Line Variability in Repeat Quasar Observations from the Sloan Digital Sky Survey
We present a time-variability analysis of 29 broad absorption line quasars
(BALQSOs) observed in two epochs by the Sloan Digital Sky Survey (SDSS). These
spectra are selected from a larger sample of BALQSOs with multiple observations
by virtue of exhibiting a broad CIV 1549 absorption trough separated
from the rest frame of the associated emission peak by more than 3600 km
s. Detached troughs facilitate higher precision variability
measurements, since the measurement of the absorption in these objects is not
complicated by variation in the emission line flux. We have undertaken a
statistical analysis of these detached-trough BALQSO spectra to explore the
relationships between BAL features that are seen to vary and the dynamics of
emission from the quasar central engine. We have measured variability within
our sample, which includes three strongly variable BALs. We have also verified
that the statistical behavior of the overall sample agrees with current model
predictions and previous studies of BAL variability. Specifically, we observe
that the strongest BAL variability occurs among the smallest equivalent width
features and at velocities exceeding 12,000 km s, as predicted by recent
disk-wind modeling.Comment: 11 pages, 7 figures. Accepted for publication in Ap
Quiescent Galaxies in the 3D-HST Survey: Spectroscopic Confirmation of a Large Number of Galaxies with Relatively Old Stellar Populations at Z approx. 2
Quiescent galaxies at zeta approximately 2 have been identified in large numbers based on rest-frame colors, but only a small number of these galaxies have been spectroscopically confirmed to show that their rest-frame optical spectra show either strong Balmer or metal absorption lines. Here, we median stack the rest-frame optical spectra for 171 photometrically quiescent galaxies at 1.4 less than z less than 2.2 from the 3D-HST grism survey. In addition to H(Beta) (lambda 4861 Angstroms), we unambiguously identify metal absorption lines in the stacked spectrum, including the G band (lambda 4304 Angstroms), Mg I (lambda 5175 Angstroms), and Na i (lambda 5894 Angstroms). This finding demonstrates that galaxies with relatively old stellar populations already existed when the universe was approximately 3 Gyr old, and that rest-frame color selection techniques can efficiently select them. We find an average age of 1.3(+0.1/0.3) Gyr when fitting a simple stellar population to the entire stack. We confirm our previous result from medium-band photometry that the stellar age varies with the colors of quiescent galaxies: the reddest 80% of galaxies are dominated by metal lines and have a relatively old mean age of 1.6(+0.5/0.4) Gyr, whereas the bluest (and brightest) galaxies have strong Balmer lines and a spectroscopic age of 0.9(+0.2/0.1) Gyr. Although the spectrum is dominated by an evolved stellar population, we also find [O III] and H emission. Interestingly, this emission is more centrally concentrated than the continuum with L(sub OIII) = 1.7 +/- 0.3 10(exp 40 erg s1, indicating residual central star formation or nuclear activity
A Cross-Correlation Analysis of Mg II Absorption Line Systems and Luminous Red Galaxies from the SDSS DR5
We analyze the cross-correlation of 2,705 unambiguously intervening Mg II
(2796,2803A) quasar absorption line systems with 1,495,604 luminous red
galaxies (LRGs) from the Fifth Data Release of the Sloan Digital Sky Survey
within the redshift range 0.36<=z<=0.8. We confirm with high precision a
previously reported weak anti-correlation of equivalent width and dark matter
halo mass, measuring the average masses to be log M_h(M_[solar]h^-1)=11.29
[+0.36,-0.62] and log M_h(M_[solar]h^-1)=12.70 [+0.53,-1.16] for systems with
W[2796A]>=1.4A and 0.8A<=W[2796A]<1.4A, respectively. Additionally, we
investigate the significance of a number of potential sources of bias inherent
in absorber-LRG cross-correlation measurements, including absorber velocity
distributions and the weak lensing of background quasars, which we determine is
capable of producing a 20-30% bias in angular cross-correlation measurements on
scales less than 2'. We measure the Mg II - LRG cross-correlation for 719
absorption systems with v<60,000 km s^-1 in the quasar rest frame and find that
these associated absorbers typically reside in dark matter haloes that are
~10-100 times more massive than those hosting unambiguously intervening Mg II
absorbers. Furthermore, we find evidence for evolution of the redshift number
density, dN/dz, with 2-sigma significance for the strongest (W>2.0A) absorbers
in the DR5 sample. This width-dependent dN/dz evolution does not significantly
affect the recovered equivalent width-halo mass anti-correlation and adds to
existing evidence that the strongest Mg II absorption systems are correlated
with an evolving population of field galaxies at z<0.8, while the non-evolving
dN/dz of the weakest absorbers more closely resembles that of the LRG
population.Comment: 21 pages, 19 figures; Published in Astrophysical Journa
The Structural Evolution of Milky-Way-Like Star-Forming Galaxies zeta is approximately 1.3
We follow the structural evolution of star-forming galaxies (SFGs) like the Milky Way by selecting progenitors to zeta is approx. 1.3 based on the stellar mass growth inferred from the evolution of the star-forming sequence. We select our sample from the 3D-HT survey, which utilizes spectroscopy from the HST-WFC3 G141 near-IR grism and enables precise redshift measurements for our sample of SFGs. Structural properties are obtained from Sersic profile fits to CANDELS WFC3 imaging. The progenitors of zeta = 0 SFGs with stellar mass M = 10(exp 10.5) solar mass are typically half as massive at zeta is approx. 1. This late-time stellar mass grow is consistent with recent studies that employ abundance matching techniques. The descendant SFGs at zeta is approx. 0 have grown in half-light radius by a factor of approx. 1.4 zeta is approx. 1. The half-light radius grows with stellar mass as r(sub e) alpha stellar mass(exp 0.29). While most of the stellar mass is clearly assembling at large radii, the mass surface density profiles reveal ongoing mass growth also in the central regions where bulges and pseudobulges are common features in present day late-type galaxies. Some portion of this growth in the central regions is due to star formation as recent observations of H() maps for SFGs at zeta approx. are found to be extended but centrally peaked. Connecting our lookback study with galactic archeology, we find the stellar mass surface density at R - 8 kkpc to have increased by a factor of approx. 2 since zeta is approx. 1, in good agreement with measurements derived for the solar neighborhood of the Milky Way
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