1,172 research outputs found
Shadow of a Colossus: A z=2.45 Galaxy Protocluster Detected in 3D Ly-a Forest Tomographic Mapping of the COSMOS Field
Using moderate-resolution optical spectra from 58 background Lyman-break
galaxies and quasars at within a area of the
COSMOS field ( projected area density or mean transverse separation), we reconstruct a 3D
tomographic map of the foreground Ly forest absorption at
with an effective smoothing scale of
comoving. Comparing with 61
coeval galaxies with spectroscopic redshifts in the same volume, we find that
the galaxy positions are clearly biased towards regions with enhanced IGM
absorption in the tomographic map. We find an extended IGM overdensity with
deep absorption troughs at associated with a recently-discovered
galaxy protocluster at the same redshift. Based on simulations matched to our
data, we estimate the enclosed dark matter mass within this IGM overdensity to
be , and
argue based on this mass and absorption strength that it will form at least one
galaxy cluster with , although its elongated nature suggests that
it will likely collapse into two separate clusters. We also point out a compact
overdensity of six MOSDEF galaxies at within a radius and , which does not appear
to have a large associated IGM overdensity. These results demonstrate the
potential of Ly forest tomography on larger volumes to study galaxy
properties as a function of environment, as well as revealing the large-scale
IGM overdensities associated with protoclusters and other features of
large-scale structure.Comment: To be submitted to ApJ. Figure 3 can be viewed on Youtube:
https://youtu.be/KeW1UJOPMY
Dobby: A Conversational Service Robot Driven by GPT-4
This work introduces a robotics platform which embeds a conversational AI
agent in an embodied system for natural language understanding and intelligent
decision-making for service tasks; integrating task planning and human-like
conversation. The agent is derived from a large language model, which has
learned from a vast corpus of general knowledge. In addition to generating
dialogue, this agent can interface with the physical world by invoking commands
on the robot; seamlessly merging communication and behavior. This system is
demonstrated in a free-form tour-guide scenario, in an HRI study combining
robots with and without conversational AI capabilities. Performance is measured
along five dimensions: overall effectiveness, exploration abilities,
scrutinization abilities, receptiveness to personification, and adaptability
On the Origins of the High-Latitude H-alpha Background
The diffuse high-latitude H-alpha background is widely believed to be
predominantly the result of in-situ recombination of ionized hydrogen in the
warm interstellar medium of the Galaxy. Instead, we show that both a
substantial fraction of the diffuse high-latitude H-alpha intensity in regions
dominated by Galactic cirrus dust and much of the variance in the high-latitude
H-alpha background are the result of scattering by interstellar dust of H-alpha
photons originating elsewhere in the Galaxy. We provide an empirical relation,
which relates the expected scattered H-alpha intensity to the IRAS 100um
diffuse background intensity, applicable to about 81% of the entire sky. The
assumption commonly made in reductions of CMB observations, namely that the
observed all-sky map of diffuse H-alpha light is a suitable template for
Galactic free-free foreground emission, is found to be in need of
reexamination.Comment: 26 pages, 5 figures, Accepted for publication in Ap
Unveiling the Phase Transition of the Universe During the Reionization Epoch with Lyman-alpha
The epoch of reionization (6 < z < 10) marks the period in our universe when
the first large galaxies grew to fruition, and began to affect the universe
around them. Massive stars, and potentially accreting supermassive black holes,
filled the universe with ionizing radiation, burning off the haze of neutral
gas that had filled the intergalactic medium (IGM) since recombination
(z~1000). The evolution of this process constrains key properties of these
earliest luminous sources, thus observationally constraining reionization is a
key science goal for the next decade. The measurement of Lyman-alpha emission
from photometrically-identified galaxies is a highly constraining probe of
reionization, as a neutral IGM will resonantly scatter these photons, reducing
detectability. While significant work has been done with 8-10m telescopes,
these observations require extremely large telescopes (ELTs); the flux limits
available from today's 10m class telescopes are sufficient for only the
brightest known galaxies (m < 26). Ultra-deep surveys with the Giant Magellan
Telescope (GMT) and Thirty Meter Telescope (TMT) will be capable of detecting
Lyman-alpha emission from galaxies 2-3 magnitudes fainter than today's deepest
surveys. Wide-field fiber spectroscopy on the GMT combined with narrow-field
AO-assisted slit spectroscopy on the TMT will be able to probe the expected
size of ionized bubbles throughout the epoch of reionization, following up
degree scale deep imaging surveys with the Wide Field Infrared Space Telescope.
These data will provide the first resolved Lyman-alpha-based maps of the
ionized intergalactic medium throughout the epoch of reionization, constraining
models of both the temporal and spatial evolution of this phase change.Comment: White paper submitted to the Astro2020 Decadal Review of the National
Academy of Science
Extended Schmidt Law: Role Of Existing Stars In Current Star Formation
We propose an "extended Schmidt law" with explicit dependence of the star
formation efficiency (SFE=SFR/Mgas) on the stellar mass surface density. This
relation has a power-law index of 0.48+-0.04 and an 1-sigma observed scatter on
the SFE of 0.4 dex, which holds over 5 orders of magnitude in the stellar
density for individual global galaxies including various types especially the
low-surface-brightness (LSB) galaxies that deviate significantly from the
Kennicutt-Schmidt law. When applying it to regions at sub-kpc resolution of a
sample of 12 spiral galaxies, the extended Schmidt law not only holds for LSB
regions but also shows significantly smaller scatters both within and across
galaxies compared to the Kennicutt-Schmidt law. We argue that this new relation
points to the role of existing stars in regulating the SFE, thus encoding
better the star formation physics. Comparison with physical models of star
formation recipes shows that the extended Schmidt law can be reproduced by some
models including gas free-fall in a stellar-gravitational potential and
pressure-supported star formation. By implementing this new law into the
analytic model of gas accretion in Lambda CDM, we show that it can re-produce
the observed main sequence of star-forming galaxies (a relation between the SFR
and stellar mass) from z=0 up to z=2.Comment: 18 pages, 9 figures; Accepted for Publication In Ap
On the Stellar Populations and Evolution of Star-Forming Galaxies at 6.3 < z < 8.6
We study the physical characteristics of galaxies at 6.3 < z < 8.6, selected
from deep near-infrared imaging with the Wide Field Camera 3 (WFC3) on board
the Hubble Space Telescope. Accounting for the photometric scatter using
simulations, galaxies at z ~ 7 have bluer UV colors compared to typical local
starburst galaxies at > 4 sigma confidence. Although these colors necessitate
young ages (<100 Myr), low or zero dust attenuation, and low metallicities,
these are explicable by normal (albeit unreddened) stellar populations, with no
evidence for near-zero metallicities and/or top-heavy initial mass functions.
The age of the Universe at these redshifts limits the amount of stellar mass in
late-type populations, and the WFC3 photometry implies galaxy stellar masses ~
10^8 - 10^9 Msol for Salpeter initial mass functions to a limiting magnitude of
M_1500 ~ -18. The masses of ``characteristic'' (L*) z > 7 galaxies are smaller
than those of L* Lyman break galaxies (LBGs) at lower redshifts, and are
comparable to less evolved galaxies selected on the basis of their Lyman alpha
emission at 3 < z < 6, implying that the 6.3 < z < 8.6 galaxies are the
progenitors of more evolved galaxies at lower redshifts. We estimate that Lyman
alpha emission is able to contribute to the observed WFC3 colors of galaxies at
these redshifts, with an estimated typical line flux of ~ 10^-18 erg s^-1
cm^-2, roughly a factor of four below currently planned surveys. The integrated
UV specific luminosity for the detected galaxies at z ~ 7 and z ~ 8 is within
factors of a few of that required to reionize the IGM assuming low clumping
factors, implying that in order to reionize the Universe galaxies at these
redshifts have a high ( ~ 50%) escape fraction of Lyman continuum photons,
possibly substantiated by the very blue colors of this population.Comment: Accepted to the Astrophysical Journal; replaced with accepted
version. Minor modifications to sample, conclusions are unchange
Measuring space-time variation of the fundamental constants with redshifted submillimetre transitions of neutral carbon
We compare the redshifts of neutral carbon and carbon monoxide in the
redshifted sources in which the fine structure transition of neutral carbon,
[CI], has been detected, in order to measure space-time variation of the
fundamental constants. Comparison with the CO rotational lines measures gives
the same combination of constants obtained from the comparison fine structure
line of singly ionised carbon, [CII]. However, neutral carbon has the distinct
advantage that it may be spatially coincident with the carbon monoxide, whereas
[CII] could be located in the diffuse medium between molecular clouds, and so
any comparison with CO could be dominated by intrinsic velocity differences.
Using [CI], we obtain a mean variation of dF/F = (-3.6 +/- 8.5) x 10^-5, over z
= 2.3 - 4.1, for the eight [CI] systems, which degrades to (-1.5+/- 11) x
10^-5, over z = 2.3 - 6.4 when the two [CII] systems are included. That is,
zero variation over look-back times of 10.8-12.8 Gyr. However, the latest
optical results indicate a spatial variation in alpha, which describes a dipole
and we see the same direction in dF/F. This trend is, however, due to a single
source for which the [CI] spectrum is of poor quality. This also applies to one
of the two [CII] spectra previously used to find a zero variation in
alpha^2/mu. Quantifying this, we find an anti-correlation between |dF/F| and
the quality of the carbon detection, as measured by the spectral resolution,
indicating that the typical values of >50 km/s, used to obtain a detection, are
too coarse to reliably measure changes in the constants. From the fluxes of the
known z > 1 CO systems, we predict that current instruments are incapable of
the sensitivities required to measure changes in the constants through the
comparison of CO and carbon lines. We therefore discuss in detail the use of
ALMA for such an undertaking ... ABRIDGEDComment: Accepted for publication in Section 3 - Cosmology (including clusters
of galaxies) of Astronomy and Astrophysic
The HETDEX Pilot Survey III: The Low Metallicities of High-Redshift Lyman Alpha Galaxies
We present Keck/NIRSPEC spectroscopic observations of three Lyman alpha
emitting galaxies (LAEs) at z ~ 2.3 discovered with the HETDEX pilot survey. We
detect Halpha, [OIII], and Hbeta emission from two galaxies at z = 2.29 and
2.49, designated HPS194 and HPS256, respectively, representing the first
detection of multiple rest-frame optical emission lines in galaxies at
high-redshift selected on the basis of their Lyman alpha emission. The
redshifts of the Lyman alpha emission from these galaxies are offset redward of
the systemic redshifts by Delta_v = 162 +/- 37 (photometric) +/- 42
(systematic) km/s for HPS194, and Delta_v = 36 +/- 35 +/- 18 km/s for HPS256.
An interpretation for HPS194 is that a large-scale outflow may be occurring in
its interstellar medium. The emission line ratios imply that neither LAE hosts
an active galactic nucleus. Using the upper limits on the [NII] emission we
place meaningful constraints on the gas-phase metallicities in these two LAEs
of Z < 0.17 and < 0.28 Zsol (1 sigma). Measuring the stellar masses of these
objects via spectral energy distribution (SED) fitting (~ 10^10 and 6 x 10^8
Msol, respectively), we study the nature of LAEs in a mass-metallicity plane.
At least one of these two LAEs appears to be more metal poor than
continuum-selected star-forming galaxies at the same redshift and stellar mass,
implying that objects exhibiting Lyman alpha emission may be systematically
less chemically enriched than the general galaxy population. We use the SEDs of
these two galaxies to show that neglecting the emission lines when fitting
stellar population models to the observed photometry can result in
overestimates of the population age by orders of magnitude, and the stellar
mass by a factor of ~ 2. This effect is particularly important at z > 7, where
similarly strong emission lines may masquerade in the photometry as a 4000 A
break (abridged).Comment: Replaced with the accepted (to ApJ) versio
UV Diagnostics of Galaxies from the Peak of Star-Formation to the Epoch of Reionization
The rest-frame UV emission from massive stars contains a wealth of
information about the physical nature and conditions of star formation in
galaxies. Using studies of the rest-frame UV, the past decade has witnessed the
beginning of knowledge about the existence and properties of galaxies during
the first few billion years after the Big Bang. This period of history
corresponds to the formation of the first stars, the rapid formation of galaxy
stellar populations, the reionization of the IGM, the production and
dissemination of heavy elements, and the formation of the first black holes.
Massive stars in these galaxies drive all of these events, and their light
dominates the spectral energy distributions of galaxies. As we look to the
2020s, fundamental questions remain about the nature of these stellar
populations and their evolution, from just before the peak of the cosmic star
formation density (z~3), up to the epoch of reionization (z > 6). This next
decade will provide transformative gains both in our ability to identify
star-forming galaxies and accreting supermassive black holes at these early
epochs with imaging surveys in the rest-frame UV (e.g., LSST, WFIRST).
Ground-based, rest-frame UV spectroscopy on >20 m-class telescopes (e.g.,
GMT/TMT) offers the ability to investigate the astrophysical conditions in
galaxies at the earliest cosmic times. This includes studies of the evolution
in galaxy stellar populations, gas ionization (temperature, pressure),
metallicity, and interstellar (and circumgalactic) gas kinematics and covering
fractions. In this white paper, we describe the scientific prospects and the
requirements for research in this area.Comment: White paper submitted to the Astro2020 Decadal Survey (8 papers, 4
figures
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