30 research outputs found
Herschel Extreme Lensing Line Observations: Dynamics of two strongly lensed star forming galaxies near redshift z = 2
We report on two regularly rotating galaxies at redshift z=2, using high
resolution spectra of the bright [CII] 158 micron emission line from the HIFI
instrument on the Herschel Space Observatory. Both SDSS090122.37+181432.3
("S0901") and SDSS J120602.09+514229.5 ("the Clone") are strongly lensed and
show the double-horned line profile that is typical of rotating gas disks.
Using a parametric disk model to fit the emission line profiles, we find that
S0901 has a rotation speed v sin(i) = 120 +/- 7 km/s and gas velocity
dispersion sigma < 23 km/s. The best fitting model for the Clone is a
rotationally supported disk having v sin(i) = 79 +/- 11 km/s and sigma < 4km/s.
However the Clone is also consistent with a family of dispersion-dominated
models having sigma = 92 +/- 20 km/s. Our results showcase the potential of the
[CII] line as a kinematic probe of high redshift galaxy dynamics: [CII] is
bright; accessible to heterodyne receivers with exquisite velocity resolution;
and traces dense star-forming interstellar gas. Future [CII] line observations
with ALMA would offer the further advantage of spatial resolution, allowing a
clearer separation between rotation and velocity dispersion.Comment: 20 pages, 4 figures; in press at The Astrophysical Journa
Hubble Space Telescope Imaging of Lyman Alpha Emission at z=4.4
We present the highest redshift detections of resolved Lyman alpha emission,
using Hubble Space Telescope/ACS F658N narrowband-imaging data taken in
parallel with the Wide Field Camera 3 Early Release Science program in the
GOODS CDF-S. We detect Lyman alpha emission from three spectroscopically
confirmed z = 4.4 Lyman alpha emitting galaxies (LAEs), more than doubling the
sample of LAEs with resolved Lyman alpha emission. Comparing the light
distribution between the rest-frame ultraviolet continuum and narrowband
images, we investigate the escape of Lyman alpha photons at high redshift.
While our data do not support a positional offset between the Lyman alpha and
rest-frame ultraviolet (UV) continuum emission, the half-light radii in two out
of the three galaxies are significantly larger in Lyman alpha than in the
rest-frame UV continuum. This result is confirmed when comparing object sizes
in a stack of all objects in both bands. Additionally, the narrowband flux
detected with HST is significantly less than observed in similar filters from
the ground. These results together imply that the Lyman alpha emission is not
strictly confined to its indigenous star-forming regions. Rather, the Lyman
alpha emission is more extended, with the missing HST flux likely existing in a
diffuse outer halo. This suggests that the radiative transfer of Lyman alpha
photons in high-redshift LAEs is complicated, with the interstellar-medium
geometry and/or outflows playing a significant role in galaxies at these
redshifts.Comment: Submitted to the Astrophysical Journal. 11 pages, 10 figure
Using Dark Energy Explorers and Machine Learning to Enhance the Hobby-Eberly Telescope Dark Energy Experiment
We present analysis using a citizen science campaign to improve the
cosmological measures from the Hobby-Eberly Telescope Dark Energy Experiment
(HETDEX). The goal of HETDEX is to measure the Hubble expansion rate, ,
and angular diameter distance, , at 2.4, each to percent-level
accuracy. This accuracy is determined primarily from the total number of
detected Lyman- emitters (LAEs), the false positive rate due to noise,
and the contamination due to [O II] emitting galaxies. This paper presents the
citizen science project, Dark Energy Explorers, with the goal of increasing the
number of LAEs, decreasing the number of false positives due to noise and the
[O II] galaxies. Initial analysis shows that citizen science is an efficient
and effective tool for classification most accurately done by the human eye,
especially in combination with unsupervised machine learning. Three aspects
from the citizen science campaign that have the most impact are 1) identifying
individual problems with detections, 2) providing a clean sample with 100%
visual identification above a signal-to-noise cut, and 3) providing labels for
machine learning efforts. Since the end of 2022, Dark Energy Explorers has
collected over three and a half million classifications by 11,000 volunteers in
over 85 different countries around the world. By incorporating the results of
the Dark Energy Explorers we expect to improve the accuracy on the and
parameters at 2.4 by 10 - 30%. While the primary goal is to
improve on HETDEX, Dark Energy Explorers has already proven to be a uniquely
powerful tool for science advancement and increasing accessibility to science
worldwide.Comment: 14 pages, 6 figures, accepted for publication in The Astrophysical
Journa
SGAS 143845.1+145407: A Big, Cool Starburst at Redshift 0.816
We present the discovery and a detailed multi-wavelength study of a
strongly-lensed luminous infrared galaxy at z=0.816. Unlike most known lensed
galaxies discovered at optical or near-infrared wavelengths this lensed source
is red, r-Ks = 3.9 [AB], which the data presented here demonstrate is due to
ongoing dusty star formation. The overall lensing magnification (a factor of
17) facilitates observations from the blue optical through to 500micron, fully
capturing both the stellar photospheric emission as well as the re-processed
thermal dust emission. We also present optical and near-IR spectroscopy. These
extensive data show that this lensed galaxy is in many ways typical of
IR-detected sources at z~1, with both a total luminosity and size in accordance
with other (albeit much less detailed) measurements in samples of galaxies
observed in deep fields with the Spitzer telescope. Its far-infrared spectral
energy distribution is well-fit by local templates that are an order of
magnitude less luminous than the lensed galaxy; local templates of comparable
luminosity are too hot to fit. Its size (D~7kpc) is much larger than local
luminous infrared galaxies, but in line with sizes observed for such galaxies
at z~1. The star formation appears uniform across this spatial scale. In this
source, the luminosity of which is typical of sources that dominate the cosmic
infrared background, we find that star formation is spatially extended and well
organised, quite unlike the compact merger-driven starbursts which are typical
for sources of this luminosity at z~0.Comment: 18 pages, 10 figure
Recommended from our members
CANDELS Observations Of The Structural Properties Of Cluster Galaxies At Z=1.62
We discuss the structural and morphological properties of galaxies in a z = 1.62 proto-cluster using near-IR imaging data from Hubble Space Telescope Wide Field Camera 3 data of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). The cluster galaxies exhibit a clear color-morphology relation: galaxies with colors of quiescent stellar populations generally have morphologies consistent with spheroids, and galaxies with colors consistent with ongoing star formation have disk-like and irregular morphologies. The size distribution of the quiescent cluster galaxies shows a deficit of compact (less than or similar to 1 kpc), massive galaxies compared to CANDELS field galaxies at z = 1.6. As a result, the cluster quiescent galaxies have larger average effective sizes compared to field galaxies at fixed mass at greater than 90% significance. Combined with data from the literature, the size evolution of quiescent cluster galaxies is relatively slow from z similar or equal to 1.6 to the present, growing as (1 + z)(-0.6 +/- 0.1). If this result is generalizable, then it implies that physical processes associated with the denser cluster region seem to have caused accelerated size growth in quiescent galaxies prior to z = 1.6 and slower subsequent growth at z < 1.6 compared to galaxies in the lower density field. The quiescent cluster galaxies at z = 1.6 have higher ellipticities compared to lower redshift samples at fixed mass, and their surface-brightness profiles suggest that they contain extended stellar disks. We argue that the cluster galaxies require dissipationless (i.e., gas-poor or "dry") mergers to reorganize the disk material and to match the relations for ellipticity, stellar mass, size, and color of early-type galaxies in z < 1 clusters.NASA NAS5-26555HST GO-12060NASA through from the Space Telescope Science Institute GO-12060European Research CouncilRoyal SocietyTexas AM UniversityGeorge P. and Cynthia Woods Institute for Fundamental Physics and AstronomyAstronom
Lyman alpha Luminosity Functions at Redshift z = 4.5
We present a spectroscopically confirmed sample of Lyman alpha emitting
galaxies (LAEs) at z ~ 4.5 in the Extended Chandra Deep Field South (ECDFS),
which we combine with a sample of z ~ 4.5 LAEs from the Large Area Lyman Alpha
(LALA) survey to build a unified Lya luminosity function (LF). We
spectroscopically observed 64 candidate LAEs in the ECDFS, confirming 46
objects as z~4.5 LAEs. We did not detect significant flux from neither C_iv
1549\AA\ nor the He_ii 1640\AA\ emission in individual LAE spectra, even with a
coadded spectrum. With the coadded line ratio of He_ii to Lya constraining the
Population III star formation rate (SFR) to be <0.3% of the total SFR, and
<1.25% of the observed SFR (both at the 2- level). Only one LAE was
detected in both the X-ray and radio, while the other objects remained
undetected, even when stacked. The Lya LF in our two deepest narrowband filters
in the ECDFS differ at >2 significance, and the product
differs by a factor of >3. Similar LF differences have been used to infer
evolution in the neutral gas fraction in the intergalactic medium at z>6, yet
here the difference is likely due to cosmic variance, given that the two
samples are from adjoining line-of-sight volumes. Combining our new sample of
LAEs with those from previous LALA narrowband surveys at z = 4.5, we obtain one
of the best measured Lya LFs to date of L* = 42.83 0.06 and =
-3.48 0.09. We compare our new LF to others from the literature to study
the evolution of the Lya luminosity density at 0 < z < 7. We find tentative
evidence for evolution in the product , which approximately tracks
the cosmic SFR density, but since field-to-field and survey-to-survey
variations are in some cases as large as the possible evolution, some caution
is needed in interpreting this trend.Comment: 21 pages, 17 figures and 6 tables. Re-submitted to MNRAS to a new
referee. Big changes with two referees' comment
Probing the Star Formation History and Initial Mass Function of the z~2.5 Lensed Galaxy SMM J163554.2+661225 with Herschel
We present the analysis of Herschel SPIRE far-infrared (FIR) observations of
the z = 2.515 lensed galaxy SMM J163554.2+661225. Combining new 250, 350, and
500 micron observations with existing data, we make an improved fit to the FIR
spectral energy distribution (SED) of this galaxy. We find a total infrared
(IR) luminosity of L(8--1000 micron) = 6.9 +/- 0.6x10^11 Lsol; a factor of 3
more precise over previous L_IR estimates for this galaxy, and one of the most
accurate measurements for any galaxy at these redshifts. This FIR luminosity
implies an unlensed star formation rate (SFR) for this galaxy of 119 +/- 10
Msol per yr, which is a factor of 1.9 +/- 0.35 lower than the SFR derived from
the nebular Pa-alpha emission line (a 2.5-sigma discrepancy). Both SFR
indicators assume identical Salpeter initial mass functions (IMF) with slope
Gamma=2.35 over a mass range of 0.1 - 100 Msol, thus this discrepancy suggests
that more ionizing photons may be necessary to account for the higher
Pa-alpha-derived SFR. We examine a number of scenarios and find that the
observations can be explained with a varying star formation history (SFH) due
to an increasing star formation rate (SFR), paired with a slight flattening of
the IMF. If the SFR is constant in time, then larger changes need to be made to
the IMF by either increasing the upper-mass cutoff to ~ 200 Msol, or a
flattening of the IMF slope to 1.9 +/- 0.15, or a combination of the two. These
scenarios result in up to double the number of stars with masses above 20 Msol,
which produce the requisite increase in ionizing photons over a Salpeter IMF
with a constant SFH.Comment: 9 pages, 4 figures, 1 table; Accepted for publication in the
Astrophysical Journa