19 research outputs found
The Outstanding Decisions of the United States Supreme Court in 1954
We perform a kinematic and morphological analysis of 44 star-forming galaxies at z ̃ 2 in the COSMOS legacy field using near-infrared spectroscopy from Keck/MOSFIRE and F160W imaging from CANDELS/3D-HST as part of the ZFIRE survey. Our sample consists of cluster and field galaxies from 2.0 < z < 2.5 with K-band multi-object slit spectroscopic measurements of their Hα emission lines. Hα rotational velocities and gas velocity dispersions are measured using the Heidelberg Emission Line Algorithm (HELA), which compares directly to simulated 3D data cubes. Using a suite of simulated emission lines, we determine that HELA reliably recovers input S 0.5 and angular momentum at small offsets, but V 2.2/σ g values are offset and highly scattered. We examine the role of regular and irregular morphology in the stellar mass kinematic scaling relations, deriving the kinematic measurement S 0.5, and finding {log}({S}0.5)=(0.38+/- 0.07){log}(M/{M}☉ -10)+(2.04+/- 0.03) with no significant offset between morphological populations and similar levels of scatter (̃0.16 dex). Additionally, we identify a correlation between M ⋆ and V 2.2/σ g for the total sample, showing an increasing level of rotation dominance with increasing M ⋆, and a high level of scatter for both regular and irregular galaxies. We estimate the specific angular momenta (j disk) of these galaxies and find a slope of 0.36 ± 0.12, shallower than predicted without mass-dependent disk growth, but this result is possibly due to measurement uncertainty at M ⋆ < 9.5 However, through a Kolmogorov-Smirnov test we find irregular galaxies to have marginally higher j disk values than regular galaxies, and high scatter at low masses in both populations
ZFOURGE: Extreme 5007 emission may be a common early-lifetime phase for star-forming galaxies at
Using the \prospector\ spectral energy distribution (SED) fitting code, we
analyze the properties of 19 Extreme Emission Line Galaxies (EELGs) identified
in the bluest composite SED in the \zfourge\ survey at .
\prospector\ includes a physical model for nebular emission and returns
probability distributions for stellar mass, stellar metallicity, dust
attenuation, and nonparametric star formation history (SFH). The EELGs show
evidence for a starburst in the most recent 50 Myr, with the median EELG having
a specific star formation rate (sSFR) of 4.6 Gyr and forming 15\% of its
mass in this short time. For a sample of more typical star-forming galaxies
(SFGs) at the same redshifts, the median SFG has a sSFR of 1.1 Gyr and
forms only of its mass in the last 50 Myr. We find that virtually all of
our EELGs have rising SFHs, while most of our SFGs do not. From our analysis,
we hypothesize that many, if not most, star-forming galaxies at
undergo an extreme H+[\hbox{{\rm O}\kern 0.1em{\sc iii}}] emission
line phase early in their lifetimes. In a companion paper, we obtain
spectroscopic confirmation of the EELGs as part of our {\sc MOSEL} survey. In
the future, explorations of uncertainties in modeling the UV slope for galaxies
at are needed to better constrain their properties, e.g. stellar
metallicities.Comment: 11 pages, 5 figures (main figure is fig 5), accepted for publication
in Ap
Near infrared spectroscopy and star-formation histories of 3<z<4 quiescent galaxies
We present Keck-MOSFIRE H and K spectra for a sample of 24 candidate
quiescent galaxies (QGs) at 3<z<4, identified from UVJ colors and photometric
redshifts in the ZFOURGE and 3DHST surveys. We obtain spectroscopic redshifts
for half of the sample, using absorption or emission lines, and confirm the
high accuracy of the photometric redshifts with a median error of 1.2%. Two
galaxies turn out to be dusty objects at lower redshifts (z<2.5), and are the
only two detected in the sub-mm with ALMA. High equivalent-width [OIII] was
observed in two galaxies, contributing up to 30% of the K-band flux and
mimicking the colors of an old stellar population. This implies a failure rate
of only 20% for the UVJ selection at these redshifts. Balmer absorption was
identified in 4 of the brighest galaxies, confirming the absence of OB stars.
Modeling all QGs with a wide range of star-formation histories, we find sSFR a
factor of 10 below the main sequence (MS) for all but one galaxy, and less than
0.01 Gyr for half of the sample. This is consistent with the H
and [OII] luminosities, and the ALMA non-detections. We then find that these
QGs have quenched on average 300 Myr before observation, between z=3.5 and 5,
and that they formed at z~5.5 with a mean SFR~300 Msun/yr. Considering an
alternative selection of QGs based solely on the sSFR from SED modeling, we
find that galaxies a factor 10 below the MS are 40% more numerous than
UVJ-quiescent galaxies, implying that the UVJ selection is pure but incomplete.
Current models fail at reproducing our observations and underestimate either
the number density of QGs by more than an order of magnitude or the duration of
their quiescence by a factor two. Overall, these results confirm the existence
of an unexpected population of QGs at z>3, and offer the first insights on
their formation history. [abridged]Comment: 30 pages (+ appendix), 18 figures, accepted for publication in A&
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
First Data Release of the COSMOS Ly alpha Mapping and Tomography Observations: 3D Ly alpha Forest Tomography at 2.05 < z < 2.55
Faint star-forming galaxies at z ~ 2–3 can be used as alternative background sources to probe the Lyα forest in addition to quasars, yielding high sightline densities that enable 3D tomographic reconstruction of the foreground absorption field. Here, we present the first data release from the COSMOS Lyα Mapping And Tomography Observations (CLAMATO) Survey, which was conducted with the LRIS spectrograph on the Keck I telescope. Over an observational footprint of 0.157 deg2 within the COSMOS field, we used 240 galaxies and quasars at 2.17 < z < 3.00, with a mean comoving transverse separation of , as background sources probing the foreground Lyα forest absorption at 2.05 < z < 2.55. The Lyα forest data was then used to create a Wiener-filtered tomographic reconstruction over a comoving volume of with an effective smoothing scale of . In addition to traditional figures, this map is also presented as a virtual-reality visualization and manipulable interactive figure. We see large overdensities and underdensities that visually agree with the distribution of coeval galaxies from spectroscopic redshift surveys in the same field, including overdensities associated with several recently discovered galaxy protoclusters in the volume. Quantitatively, the map signal-to-noise is over a 3 h −1Mpc top-hat kernel based on the variances estimated from the Wiener filter. This data release includes the redshift catalog, reduced spectra, extracted Lyα forest pixel data, and reconstructed tomographic map of the absorption. These can be downloaded from Zenodo (10.5281/zenodo.1292459)
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Quasars Probing Galaxies. I. Signatures of Gas Accretion at Redshift z ≈ 0.2
We describe the kinematics of circumgalactic gas near the galactic plane, combining new measurements of galaxy rotation curves and spectroscopy of background quasars. The sightlines pass within 19-93 kpc of the target galaxy and generally detect Mg ii absorption. The Mg ii Doppler shifts have the same sign as the galactic rotation, so the cold gas co-rotates with the galaxy. Because the absorption spans a broader velocity range than disk rotation can explain, we explore simple models for the circumgalactic kinematics. Gas spiraling inwards (near the disk plane) offers a successful description of the observations. An appendix describes the addition of tangential and radial gas flows and illustrates how the sign of the disk inclination produces testable differences in the projected line-of-sight velocity range. This inflow interpretation implies that cold flow disks remain common down to redshift z ≈ 0.2 and prolong star formation by supplying gas to the disk
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Quasars Probing Galaxies. I. Signatures of Gas Accretion at Redshift z ≈ 0.2
We describe the kinematics of circumgalactic gas near the galactic plane, combining new measurements of galaxy rotation curves and spectroscopy of background quasars. The sightlines pass within 19-93 kpc of the target galaxy and generally detect Mg ii absorption. The Mg ii Doppler shifts have the same sign as the galactic rotation, so the cold gas co-rotates with the galaxy. Because the absorption spans a broader velocity range than disk rotation can explain, we explore simple models for the circumgalactic kinematics. Gas spiraling inwards (near the disk plane) offers a successful description of the observations. An appendix describes the addition of tangential and radial gas flows and illustrates how the sign of the disk inclination produces testable differences in the projected line-of-sight velocity range. This inflow interpretation implies that cold flow disks remain common down to redshift z ≈ 0.2 and prolong star formation by supplying gas to the disk
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Kinematics of Circumgalactic Gas: Feeding Galaxies and Feedback
We present observations of 50 pairs of redshift z ≈ 0.2 star-forming galaxies and background quasars. These sightlines probe the circumgalactic medium (CGM) out to half the virial radius, and we describe the circumgalactic gas kinematics relative to the reference frame defined by the galactic disks. We detect halo gas in Mg ii absorption, measure the equivalent-width-weighted Doppler shifts relative to each galaxy, and find that the CGM has a component of angular momentum that is aligned with the galactic disk. No net counter-rotation of the CGM is detected within 45° of the major axis at any impact parameter. The velocity offset of the circumgalactic gas correlates with the projected rotation speed in the disk plane out to disk radii of roughly 70 kpc. We confirm previous claims that the Mg ii absorption becomes stronger near the galactic minor axis, and we show that the equivalent width correlates with the velocity range of the absorption. We cannot directly measure the location of any absorber along the sightline, but we explore the hypothesis that individual velocity components can be associated with gas orbiting in the disk plane or flowing radially outward in a conical outflow. We conclude that centrifugal forces partially support the low-ionization gas and galactic outflows kinematically disturb the CGM producing excess absorption. Our results firmly rule out schema for the inner CGM that lack rotation and suggest that angular momentum as well as galactic winds should be included in any viable model for the low-redshift CGM
Near infrared spectroscopy and star-formation histories of 3 ≤ z ≤ 4 quiescent galaxies
We present Keck–MOSFIRE H and K spectra for a sample of 24 candidate quiescent galaxies at 3 < z < 4, identified from their rest-frame UVJ colors and photometric redshifts in the ZFOURGE and 3DHST surveys. With median integration times of one hour in H and five in K, we obtain spectroscopic redshifts for half of the sample, using either Balmer absorption lines or nebular emission lines. We confirm the high accuracy of the photometric redshifts for this spectroscopically-confirmed sample, with a median |Zphot − Zspec|/(1 + Zspec) of 1.2%. Two galaxies turn out to be dusty Hα emitters at lower redshifts (z < 2.5), and these are the only two detected in the sub-mm with ALMA. High equivalent-width [O III] emission is observed in two galaxies, contributing up to 30% of the K-band flux and mimicking the UVJ colors of an old stellar population. This implies a failure rate of only 20% for the UVJ selection at these redshifts. Lastly, Balmer absorption features are identified in four galaxies, among the brightest of the sample, confirming the absence of OB stars. We then modeled the spectra and photometry of all quiescent galaxies with a wide range of star-formation histories. We find specific star-formation rates (sSFR) lower than 0.15 Gyr−1 (a factor of ten below the main sequence) for all but one galaxy, and lower than 0.01 Gyr−1 for half of the sample. These values are consistent with the observed Hβ and [O II] luminosities, and the ALMA non-detections. The implied formation histories reveal that these galaxies have quenched on average 300 Myr prior to being observed, between z  =  3.5 and 5, and that half of their stars were formed by z ∼ 5.5 with a mean SFR ~ 300 M⊙ yr−1. We finally compared the UVJ selection to a selection based instead on the sSFR, as measured from the photometry. We find that galaxies a factor of ten below the main sequence are 40% more numerous than UVJ-selected quiescent galaxies, implying that the UVJ selection is pure but incomplete. Current models fail at reproducing our observations, and underestimate either the number density of quiescent galaxies by more than an order of magnitude, or the duration of their quiescence by a factor two. Overall, these results confirm the existence of an unexpected population of quiescent galaxies at z > 3, and offer the first insights on their formation histories