15 research outputs found
A massive, quiescent galaxy at redshift of z=3.717
In the early Universe finding massive galaxies that have stopped forming
stars present an observational challenge as their rest-frame ultraviolet
emission is negligible and they can only be reliably identified by extremely
deep near-infrared surveys. These have revealed the presence of massive,
quiescent early-type galaxies appearing in the universe as early as z2,
an epoch 3 Gyr after the Big Bang. Their age and formation processes have now
been explained by an improved generation of galaxy formation models where they
form rapidly at z3-4, consistent with the typical masses and ages derived
from their observations. Deeper surveys have now reported evidence for
populations of massive, quiescent galaxies at even higher redshifts and earlier
times, however the evidence for their existence, and redshift, has relied
entirely on coarsely sampled photometry. These early massive, quiescent
galaxies are not predicted by the latest generation of theoretical models.
Here, we report the spectroscopic confirmation of one of these galaxies at
redshift z=3.717 with a stellar mass of 1.710 M whose
absorption line spectrum shows no current star-formation and which has a
derived age of nearly half the age of the Universe at this redshift. The
observations demonstrates that the galaxy must have quickly formed the majority
of its stars within the first billion years of cosmic history in an extreme and
short starburst. This ancestral event is similar to those starting to be found
by sub-mm wavelength surveys pointing to a possible connection between these
two populations. Early formation of such massive systems is likely to require
significant revisions to our picture of early galaxy assembly.Comment: 6 pages, 7 figures. This is the final preprint corresponding closely
to the published version. Uploaded 6 months after publication in accordance
with Nature polic
Consistent dynamical and stellar masses with potential light IMF in massive quiescent galaxies at using velocity dispersions measurements with MOSFIRE
We present the velocity dispersion measurements of four massive
quiescent galaxies at based on deep H and
Kband spectra using the Keck/MOSFIRE near-infrared spectrograph. We find
high velocity dispersions of order km/s based on strong
Balmer absorption lines and combine these with size measurements based on
HST/WFC3 F160W imaging to infer dynamical masses. The velocity dispersion are
broadly consistent with the high stellar masses and small sizes. Together with
evidence for quiescent stellar populations, the spectra confirm the existence
of a population of massive galaxies that formed rapidly and quenched in the
early universe . Investigating the evolution at constant velocity
dispersion between and , we find a large increase in
effective radius dex and in dynamical-to-stellar mass ratio
of 0.33$\pm0.08$ dex, with low expected
contribution from dark matter. The dynamical masses for our $z\sim3.5$ sample
are consistent with the stellar masses for a Chabrier initial mass function
(IMF), with the ratio =
-0.130.10 dex suggesting an IMF lighter than Salpeter may be common for
massive quiescent galaxies at . This is surprising in light of the
Salpeter or heavier IMFs found for high velocity dispersion galaxies at
and cores of present-day ellipticals, which these galaxies are thought
to evolve into. Future imaging and spectroscopic observations with resolved
kinematics using the upcoming James Webb Space Telescope could rule out
potential systematics from rotation, and confirm these results.Comment: 11 pages, 3 figures. Accepted to ApJ Letter
MOSEL: Strong [OIII]5007 \AA\ Emitting Galaxies at (3<z<4) from the ZFOURGE Survey
To understand how strong emission line galaxies (ELGs) contribute to the
overall growth of galaxies and star formation history of the universe, we
target Strong ELGs (SELGs) from the ZFOURGE imaging survey that have blended
(Hb+[OIII]) rest-frame equivalent widths of >230A and 2.5<zphot<4.0. Using
Keck/MOSFIRE, we measure 49 redshifts for galaxies brighter than Ks=25 mag as
part of our Multi-Object Spectroscopic Emission Line (MOSEL) survey. Our
spectroscopic success rate is ~53% and zphot uncertainty is sigma_z=
[Delta(z)/(1+z)]=0.0135. We confirm 31 ELGs at 3<zspec<3.8 and show that Strong
ELGs have spectroscopic rest-frame [OIII]5007A equivalent widths of 100-500A
and tend to be lower mass systems [log(Mstar/Msun)~8.2-9.6] compared to more
typical star-forming galaxies. The Strong ELGs lie ~0.9 dex above the
star-forming main-sequence at z~3.5 and have high inferred gas fractions of
fgas~>60%, i.e. the inferred gas masses can easily fuel a starburst to double
stellar masses within ~10-100 Myr. Combined with recent results using ZFOURGE,
our analysis indicates that 1) strong [OIII]5007A emission signals an early
episode of intense stellar growth in low mass (Mstar<0.1M*) galaxies and 2)
many, if not most, galaxies at z>3 go through this starburst phase. If true,
low-mass galaxies with strong [OIII]5007A emission (EW_rest>200A) may be an
increasingly important source of ionizing UV radiation at z>3.Comment: Astrophysical Journal, in pres
A Tale of Two Clusters: An Analysis of Gas-phase Metallicity and Nebular Gas Conditions in Proto-cluster Galaxies at z ∼ 2
The ZFIRE survey has spectroscopically confirmed two proto-clusters using the MOSFIRE instrument on Keck I: One at z = 2.095 in COSMOS and another at z = 1.62 in UKIRT Infrared Deep Sky Survey (UDS). Here, we use an updated ZFIRE data set to derive the properties of ionized gas regions of proto-cluster galaxies by extracting fluxes from emission lines Hβ 4861 Å, [O iii] 5007 Å, Hα 6563 Å, [N ii] 6585 Å, and [S ii] 6716,6731 Å. We measure gas-phase metallicity of members in both proto-clusters using two indicators, including a strong-line indicator relatively independent of the ionization parameter and electron density. Proto-cluster and field galaxies in both UDS and COSMOS lie on the same Mass-Metallicity Relation with both metallicity indicators. We compare our results to recent IllustrisTNG results, which report no significant gas-phase metallicity offset between proto-cluster and field galaxies until z = 1.5. This is in agreement with our observed metallicities, where no offset is measured between proto-cluster and field populations. We measure tentative evidence from stacked spectra that indicate UDS high-mass proto-cluster and field galaxies have differing [O iii]/Hβ ratios; however, these results are dependent on the sample size of the high-mass stacks
Introducing the FLAMINGOS-2 Split-K Medium-band Filters: The Impact on Photometric Selection of High-z Galaxies in the FENIKS-pilot survey
Deep near-infrared photometric surveys are efficient in identifying high-redshift galaxies, however, they can be prone to systematic errors in photometric redshift. This is particularly salient when there is limited sampling of key spectral features of a galaxy's spectral energy distribution (SED), such as for quiescent galaxies where the expected age-sensitive Balmer/4000 Å break enters the K-band at z > 4. With single-filter sampling of this spectral feature, degeneracies between SED models and redshift emerge. A potential solution to this comes from splitting the K band into multiple filters. We use simulations to show an optimal solution is to add two medium-band filters, Kblue (λcen = 2.06 μm, Δλ = 0.25 μm) and Kred (λcen = 2.31 μm, Δλ = 0.27 μm), that are complementary to the existing Ks filter. We test the impact of the K-band filters with simulated catalogs comprised of galaxies with varying ages and signal-to-noise. The results suggest that the K-band filters do improve photometric redshift constraints on z > 4 quiescent galaxies, increasing precision and reducing outliers by up to 90%. We find that the impact from the K-band filters depends on the signal-to-noise, the redshift, and the SED of the galaxy. The filters we designed were built and used to conduct a pilot of the FLAMINGOS-2 Extragalactic Near-Infrared K-band Split survey. While no new z > 4 quiescent galaxies are identified in the limited area pilot, the Kblue and Kred filters indicate strong Balmer/4000 Å breaks in existing candidates. Additionally, we identify galaxies with strong nebular emission lines, for which the K-band filters increase photometric redshift precision and in some cases indicate extreme star formation
A giant galaxy in the young Universe with a massive ring
In the local (redshift z ≈ 0) Universe, collisional ring galaxies make up only ~0.01% of galaxies1 and are formed by head-on galactic collisions that trigger radially propagating density waves2–4. These striking systems provide key snapshots for dissecting galactic disks and are studied extensively in the local Universe5–9. However, not much is known about distant (z > 0.1) collisional rings10–14. Here we present a detailed study of a ring galaxy at a look-back time of 10.8 Gyr (z = 2.19). Compared with our Milky Way, this galaxy has a similar stellar mass, but has a stellar half-light radius that is 1.5–2.2 times larger and is forming stars 50 times faster. The extended, diffuse stellar light outside the star-forming ring, combined with a radial velocity on the ring and an intruder galaxy nearby, provides evidence for this galaxy hosting a collisional ring. If the ring is secularly evolved15,16, the implied large bar in a giant disk would be inconsistent with the current understanding of the earliest formation of barred spirals17–21. Contrary to previous predictions10–12, this work suggests that massive collisional rings were as rare 11 Gyr ago as they are today. Our discovery offers a unique pathway for studying density waves in young galaxies, as well as constraining the cosmic evolution of spiral disks and galaxy groups
LEGA-C: Analysis of Dynamical Masses from Ionized Gas and Stellar Kinematics at z ∼0.8
We compare dynamical mass estimates based on spatially extended stellar and
ionized gas kinematics ( and ,
respectively) of 157 star forming galaxies at . Compared to
, these galaxies have enhanced star formation rates, with stellar
feedback likely affecting the dynamics of the gas. We use LEGA-C DR3, the
highest redshift dataset providing sufficiently deep measurements of a
band limited sample. For we use Jeans Anisotropic
Multi-Gaussian Expansion models. For we first fit a
custom model of a rotating exponential disk with uniform dispersion, whose
light is projected through a slit and corrected for beam smearing. We then
apply an asymmetric drift correction based on assumptions common in the
literature to the fitted kinematic components to obtain the circular velocity,
assuming hydrostatic equilibrium. Within the half-light radius,
is on average lower than , with a
mean offset of dex and galaxy-to-galaxy scatter of dex,
reflecting the combined random uncertainty. While data of higher spatial
resolution are needed to understand this small offset, it supports the
assumption that the galaxy-wide ionized gas kinematics do not predominantly
originate from disruptive events such as star formation driven outflows.
However, a similar agreement can be obtained without modeling from the
integrated emission line dispersions for axis ratios . This suggests
that our current understanding of gas kinematics is not sufficient to
efficiently apply asymmetric drift corrections to improve dynamical mass
estimates compared to observations lacking the required for spatially
extended dynamics