In 1964, Refsdal hypothesized that a supernova whose light traversed multiple paths around a strong gravitational lens could be used to measure the rate of cosmic expansion. We report the discovery ...of such a system. In Hubble Space Telescope imaging, we have found four images of a single supernova forming an Einstein cross configuration around a redshift z = 0.54 elliptical galaxy in the MACS J1149.6+2223 cluster. The cluster's gravitational potential also creates multiple images of the z = 1.49 spiral supernova host galaxy, and a future appearance of the supernova elsewhere in the cluster field is expected. The magnifications and staggered arrivals of the supernova images probe the cosmic expansion rate, as well as the distribution of matter in the galaxy and cluster lenses.
z ∼ 2: An Epoch of Disk Assembly Simons, Raymond C.; Kassin, Susan A.; Weiner, Benjamin J. ...
Astrophysical journal/The Astrophysical journal,
07/2017, Letnik:
843, Številka:
1
Journal Article
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We explore the evolution of the internal gas kinematics of star-forming galaxies from the peak of cosmic star formation at z ∼ 2 to today. Measurements of galaxy rotation velocity Vrot, which ...quantify ordered motions, and gas velocity dispersion g , which quantify disordered motions, are adopted from the DEEP2 and SIGMA surveys. This sample covers a continuous baseline in redshift over 0.1 < z < 2.5 , spanning 10 Gyr. At low redshift, nearly all sufficiently massive star-forming galaxies are rotationally supported ( V rot > g ). By z = 2, 50% and 70% of galaxies are rotationally supported at low ( 10 9 - 10 10 M ) and high ( 10 10 - 10 11 M ) stellar mass, respectively. For V rot > 3 g , the percentage drops below 35% for all masses. From z = 2 to now, galaxies exhibit remarkably smooth kinematic evolution on average. All galaxies tend toward rotational support with time, and higher-mass systems reach it earlier. This is largely due to a mass-independent decline in g by a factor of 3 since z = 2. Over the same time period, Vrot increases by a factor of 1.5 in low-mass systems but does not evolve at high mass. These trends in Vrot and g are at a fixed stellar mass and therefore should not be interpreted as evolutionary tracks for galaxy populations. When populations are linked in time via abundance matching, g declines as before and Vrot strongly increases with time for all galaxy populations, enhancing the evolution in V rot g . These results indicate that z = 2 is a period of disk assembly, during which strong rotational support is only just beginning to emerge.
We present high spatial resolution imaging of the CO(1-0) line from the Karl G. Jansky Very Large Array of COSMOS 27289, a massive, compact star-forming galaxy (SFG) at z = 2.234. This galaxy was ...selected because of its structural similarity to z ∼ 2 passive galaxies. Our previous observations showed that it is very gas poor with respect to typical SFGs at these redshifts, consistent with a rapid transition to quiescence as the molecular gas is depleted. The new data show that both the molecular gas fraction, , and the molecular gas depletion time, /SFR, are lower in the central 1-2 kpc of the galaxy and rise at larger radii ∼2-4 kpc. These observations are consistent with a scenario in which COSMOS 27289 will imminently cease star formation in the inner regions before the outskirts, i.e., inside-out quenching, the first time this phenomenon has been seen via observations of molecular gas in the high-redshift universe. We find good qualitative and quantitative agreement with a hydrodynamical simulation of galaxy quenching, in which the central suppression of molecular gas arises due to rapid gas consumption and outflows that evacuate the central regions of gas. Our results provide independent evidence for inside-out quenching of star formation as a plausible formation mechanism for z ∼ 2 quiescent galaxies.
Abstract
We present “Extending the Satellites Around Galactic Analogs Survey” (xSAGA), a method for identifying low-
z
galaxies on the basis of optical imaging and results on the spatial ...distributions of xSAGA satellites around host galaxies. Using spectroscopic redshift catalogs from the SAGA Survey as a training data set, we have optimized a convolutional neural network (CNN) to identify
z
< 0.03 galaxies from more-distant objects using image cutouts from the DESI Legacy Imaging Surveys. From the sample of >100,000 CNN-selected low-
z
galaxies, we identify >20,000 probable satellites located between 36–300 projected kpc from NASA-Sloan Atlas central galaxies in the stellar-mass range
9.5
<
log
(
M
⋆
/
M
⊙
)
<
11
. We characterize the incompleteness and contamination for CNN-selected samples and apply corrections in order to estimate the true number of satellites as a function of projected radial distance from their hosts. Satellite richness depends strongly on host stellar mass, such that more-massive host galaxies have more satellites, and on host morphology, such that elliptical hosts have more satellites than disky hosts with comparable stellar masses. We also find a strong inverse correlation between satellite richness and the magnitude gap between a host and its brightest satellite. The normalized satellite radial distribution between 36–300 kpc does not depend on host stellar mass, morphology, or magnitude gap. The satellite abundances and radial distributions we measure are in reasonable agreement with predictions from hydrodynamic simulations. Our results deliver unprecedented statistical power for studying satellite galaxy populations and highlight the promise of using machine-learning for extending galaxy samples of wide-area surveys.
ABSTRACT Although there has been much progress in understanding how galaxies evolve, we still do not understand how and when they stop forming stars and become quiescent. We address this by applying ...our galaxy spectral energy distribution models, which incorporate physically motivated star formation histories (SFHs) from cosmological simulations, to a sample of quiescent galaxies at . A total of 845 quiescent galaxies with multi-band photometry spanning rest-frame ultraviolet through near-infrared wavelengths are selected from the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) data set. We compute median SFHs of these galaxies in bins of stellar mass and redshift. At all redshifts and stellar masses, the median SFHs rise, reach a peak, and then decline to reach quiescence. At high redshift, we find that the rise and decline are fast, as expected, because the universe is young. At low redshift, the duration of these phases depends strongly on stellar mass. Low-mass galaxies ( ) grow on average slowly, take a long time to reach their peak of star formation ( Gyr), and then the declining phase is fast ( Gyr). Conversely, high-mass galaxies ( ) grow on average fast ( Gyr), and, after reaching their peak, decrease the star formation slowly ( ). These findings are consistent with galaxy stellar mass being a driving factor in determining how evolved galaxies are, with high-mass galaxies being the most evolved at any time (i.e., downsizing). The different durations we observe in the declining phases also suggest that low- and high-mass galaxies experience different quenching mechanisms, which operate on different timescales.
•We manually defined individual fusiform face-selective regions in 1053 participants (2106 hemispheres) from the Human Connectome Project.•95.44% of hemispheres have two fusiform face-selective ...regions that differ in face selectivity, functional connectivity, cortical thickness, and myelination.•Patterns of face selectivity and functional connectivity for each fusiform face-selective region are more similar in monozygotic than dizygotic twins and more so than cortical thickness and myelination.
The fusiform face area (FFA) is a widely studied region causally involved in face perception. Even though cognitive neuroscientists have been studying the FFA for over two decades, answers to foundational questions regarding the function, architecture, and connectivity of the FFA from a large (N>1000) group of participants are still lacking. To fill this gap in knowledge, we quantified these multimodal features of fusiform face-selective regions in 1053 participants in the Human Connectome Project. After manually defining over 4,000 fusiform face-selective regions, we report five main findings. First, 68.76% of hemispheres have two cortically separate regions (pFus-faces/FFA-1 and mFus-faces/FFA-2). Second, in 26.69% of hemispheres, pFus-faces/FFA-1 and mFus-faces/FFA-2 are spatially contiguous, yet are distinct based on functional, architectural, and connectivity metrics. Third, pFus-faces/FFA-1 is more face-selective than mFus-faces/FFA-2, and the two regions have distinct functional connectivity fingerprints. Fourth, pFus-faces/FFA-1 is cortically thinner and more heavily myelinated than mFus-faces/FFA-2. Fifth, face-selective patterns and functional connectivity fingerprints of each region are more similar in monozygotic than dizygotic twins and more so than architectural gradients. As we share our areal definitions with the field, future studies can explore how structural and functional features of these regions will inform theories regarding how visual categories are represented in the brain.
Abstract
We present an investigation into the first 500 Myr of galaxy evolution from the Cosmic Evolution Early Release Science (CEERS) survey. CEERS, one of 13 JWST ERS programs, targets galaxy ...formation from
z
∼ 0.5 to >10 using several imaging and spectroscopic modes. We make use of the first epoch of CEERS NIRCam imaging, spanning 35.5 arcmin
2
, to search for candidate galaxies at
z
> 9. Following a detailed data reduction process implementing several custom steps to produce high-quality reduced images, we perform multiband photometry across seven NIRCam broad- and medium-band (and six Hubble broadband) filters focusing on robust colors and accurate total fluxes. We measure photometric redshifts and devise a robust set of selection criteria to identify a sample of 26 galaxy candidates at
z
∼ 9–16. These objects are compact with a median half-light radius of ∼0.5 kpc. We present an early estimate of the
z
∼ 11 rest-frame ultraviolet (UV) luminosity function, finding that the number density of galaxies at
M
UV
∼ −20 appears to evolve very little from
z
∼ 9 to 11. We also find that the abundance (surface density arcmin
−2
) of our candidates exceeds nearly all theoretical predictions. We explore potential implications, including that at
z
> 10, star formation may be dominated by top-heavy initial mass functions, which would result in an increased ratio of UV light per unit halo mass, though a complete lack of dust attenuation and/or changing star formation physics may also play a role. While spectroscopic confirmation of these sources is urgently required, our results suggest that the deeper views to come with JWST should yield prolific samples of ultrahigh-redshift galaxies with which to further explore these conclusions.
Abstract
Our sensitive (
), high-resolution (FWHM
), 10 GHz image covering a single Karl G. Jansky Very Large Array (VLA) primary beam (FWHM
) in the GOODS-N field contains 32 sources with
and ...optical and/or near-infrared (OIR) counterparts. Most are about as large as the star-forming regions that power them. Their median FWHM major axis is
, with rms scatter
. In units of the effective radius
that encloses half their flux, these radio sizes are
, with rms scatter
. These sizes are smaller than those measured at lower radio frequencies, but agree with dust emission sizes measured at mm/sub-mm wavelengths and extinction-corrected H
α
sizes. We made a low-resolution (
) image with
better brightness sensitivity, in order to detect extended sources and measure matched-resolution spectral indices
. It contains six new sources with
and OIR counterparts. The median redshift of all 38 sources is
. The 19 sources with 1.4 GHz counterparts have a median spectral index of
, with rms scatter
. Including upper limits on
α
for sources not detected at 1.4 GHz flattens the median to
, suggesting that the
μ
Jy radio sources at higher redshifts—and hence those selected at higher rest-frame frequencies—may have flatter spectra. If the non-thermal spectral index is
, the median thermal fraction of sources selected at median rest-frame frequency
is ≳48%.
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