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 $z\sim 2.3-3$ within a $11.5'\times13.5'$ area of the COSMOS field ($\sim 1200\,\mathrm{deg}^2$ projected area density or $\sim 2.4\,h^{-1}\,\mathrm{Mpc}$ mean transverse separation), we reconstruct a 3D tomographic map of the foreground Ly$\alpha$ forest absorption at $2.2<z<2.5$ with an effective smoothing scale of $\sigma_{3d}\approx3.5\,h^{-1}\,\mathrm{Mpc}$ 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 $z=2.45$ 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 $M_{\rm dm} (z=2.45) = (9\pm4)\times 10^{13}\,h^{-1}\,\mathrm{M_\odot}$, and argue based on this mass and absorption strength that it will form at least one $z\sim0$ galaxy cluster with $M(z=0) = (3\pm 2) \times 10^{14}\,h^{-1}\mathrm{M_\odot}$, 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 $z=2.30$ within a $r\sim 1\,h^{-1}\,\mathrm{Mpc}$ radius and $\Delta z\sim 0.006$, which does not appear to have a large associated IGM overdensity. These results demonstrate the potential of Ly$\alpha$ 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