The small scatter in BH-host correlations and the case for self-regulated BH growth

Supermassive black holes (BHs) obey tight scaling relations between their mass and host galaxy properties such as total stellar mass, velocity dispersion and potential well depth. This has led to the development of self-regulated models for BH growth, in which feedback from the central BH halts its own growth upon reaching a critical threshold. However, models have also been proposed in which feedback plays no role: so long as a fixed fraction of the host gas supply is accreted, relations like those observed can be reproduced. Here, we argue that the scatter in the observed BH–host correlations presents a demanding constraint on any model for these correlations, and that it favours self-regulated models of BH growth. We show that the scatter in the stellar mass fraction within a radius R in observed ellipticals and spheroids increases strongly at small R. At a fixed total stellar mass (or host velocity dispersion), on very small scales near the BH radius of influence, there is an order-of-magnitude scatter in the amount of gas that must have entered and formed stars. In short, the BH appears to ‘know more’ about the global host galaxy potential on large scales than the stars and gas supply on small scales. This is predicted in self-regulated models; however, models where there is no feedback would generically predict order-of-magnitude scatter in the BH–host correlations. Likewise, models in which the BH feedback in the ‘bright’ mode does not regulate the growth of the BH itself, but sets the stellar mass of the galaxy by inducing star formation or blowing out a mass in gas much larger than the galaxy stellar mass, are difficult to reconcile with the scatter on small scales

Methods of Determining Energy Requirements in Critically Ill Adults Before the Publication of New Critical Care Guidelines

Background: Energy requirements can be difficult to determine in the critically ill population due to the presence of catabolic stress. The 2009 Guidelines for the Provision and Assessment of Nutrition Support Therapy Parenteral and Enteral Nutrition and in the Adult Critically Ill Patient recommend that energy requirements be calculated by predictive equations or weight-based equations or measured by indirect calorimetry (IC) and that nutrition efficacy may be monitored through nitrogen balance (24-hour Urinary Urea Nitrogen) or non-protein calorie:nitrogen ratio. Very few studies have reported the required energy assessment methods used by Registered Dietitian Nutritionists (RDNs) in the critical care setting and no studies have reported the use of laboratory tests to monitor efficacy of nutrition. The purpose of the study is to examine practices for estimating energy requirements in critically ill patients by RDNs prior to publication of the updated critical care guidelines in 2016. Methods: The study sample included patients currently included in the trauma registry at Grady Memorial Hospital (GMH). Patients who were in motor vehicle accidents (excluding trains), who were admitted to the Intensive Care Unit at GMH between July 4, 2014 and September 28, 2015, and who required at least five days of mechanical ventilation during admission were included. Demographic characteristics (gender, race, and age), anthropometric characteristics (body mass index classification), clinical characteristics (number of days on the ventilator, ICU days, time to death)), and nutrition assessment methods (energy assessment method used, weight used in assessment, and laboratory monitoring recommendations) were extracted from the electronic medical record. Results: The vast majority of Registered Dietitian Nutritionists (98%) used a simple weight-based equation during the initial nutrition assessment. Approximately 1/3 of the Registered Dietitian Nutritionists used the actual patient body weight (36.8%) with the remaining primarily using a recommended body weight based on a selected BMI. Nine different weight-based equations were used with the equation 25-30 kcal/kg used most often (87.9%). Indirect calorimetry was not recommended by the RDNs during the first two weeks of admission for any patient. RDNs recommended prealbumin to monitor nutrition status (within 2 weeks of admission) in 21.6% of patients. Conclusions: We observed inconsistencies in the equations, weights, and monitoring laboratory tests used by RDNs. This variability can be attributed to a lack of specificity in the 2009 critical care guidelines, which justifies the need for updated recommendations in 2016. Future studies should examine change in nutrition assessment practices by RDNs since publication of the 2016 guidelines

Radiation Pressure Driven Galactic Winds from Self-Gravitating Discs

(Abridged) We study large-scale winds driven from uniformly bright self-gravitating discs radiating near the Eddington limit. We show that the ratio of the radiation pressure force to the gravitational force increases with height above the disc surface to a maximum of twice the value of the ratio at the disc surface. Thus, uniformly bright self-gravitating discs radiating at the Eddington limit are fundamentally unstable to driving large-scale winds. These results contrast with the spherically symmetric case, where super-Eddington luminosities are required for wind formation. We apply this theory to galactic winds from rapidly star-forming galaxies that approach the Eddington limit for dust. For hydrodynamically coupled gas and dust, we find that the asymptotic velocity of the wind is v_\infty ~ 1.5 v_rot and that v_\infty SFR^{0.36}, where v_rot is the disc rotation velocity and SFR is the star formation rate, both of which are in agreement with observations. However, these results of the model neglect the gravitational potential of the surrounding dark matter halo and an old passive stellar bulge or extended disc, which act to decrease v_\infty. A more realistic treatment shows that the flow can either be unbound, or bound, forming a "fountain flow" with a typical turning timescale of t_turn ~ 0.1-1 Gyr. We provide quantitative criteria and scaling relations for assessing whether or not a rapidly star-forming galaxy of given properties can drive unbound flows via the mechanism described in this paper. Importantly, we note that because t_turn is longer than the star formation timescale in the rapidly star-forming galaxies and ULIRGs for which our theory is most applicable, if rapidly star-forming galaxies are selected as such, they may be observed to have strong outflows, even though their winds are eventually bound on large scales.Comment: 10 pages, 6 figures, Accepted for publication in MNRA

Direct Numerical Simulation of Radiation Pressure-Driven Turbulence and Winds in Star Clusters and Galactic Disks

[abridged] The pressure exerted by the radiation of young stars may be an important feedback mechanism in forming star clusters and the disks of starburst galaxies. However, there is great uncertainty in how efficiently radiation couples to matter in these high optical depth environments. In particular, it is unclear what levels of turbulence the radiation can produce, and whether the infrared radiation trapped by the dust opacity can give rise to heavily mass-loaded winds. In this paper we report a series of two-dimensional flux-limited diffusion radiation-hydrodynamics calculations performed with the code ORION in which we drive strong radiation fluxes through columns of dusty matter confined by gravity. We consider both systems where the radiation flux is sub-Eddington throughout the gas column, and where it is super-Eddington at the midplane but sub-Eddington in the atmosphere. In the latter, we find that the radiation-matter interaction gives rise to radiation-driven Rayleigh-Taylor instability, which drives supersonic turbulence at a level sufficient to fully explain the turbulence seen in Galactic protocluster gas clouds, and to make a non-trivial contribution to the turbulence observed in starburst galaxy disks. However, the instability also produces a channel structure in which the radiation-matter interaction is reduced because the radiation field is not fully trapped. For astrophysical parameters relevant to forming star clusters and starburst galaxies, we find that this effect reduces the net momentum deposition rate in the dusty gas by a factor of ~2-6 compared to simple analytic estimates, and that in steady state the Eddington ratio reaches unity and there are no strong winds. We provide an approximation formula, appropriate for implementation in analytic models and non-radiative simulations, for the force exerted by the infrared radiation field in this regime.Comment: 20 pages, 11 figures, emulateapj format, accepted to ApJ. This version has extra discussion, but the results are unchanged. For movies of simulation results, see http://www.ucolick.org/~krumholz/downloads.htm

Lateralization of infant holding by mothers: a longitudinal evaluation of variations over the first 12 weeks

The maternal preference to hold infants on the left rather than right side of the body was examined longitudinally, with attention to four explanations: maternal monitoring of infant state, maternal handedness, infant proximity to the mother’s heartbeat, and preferred infant head position. The side and site of holding were measured over the first twelve weeks of the lives of 24 infants. Information about group and individual consistency in holding side allowed novel evaluation of the theories. A strong bias to hold on the left dropped below significance when the infants were aged twelve weeks and was limited to specific holding positions. Findings were generally consistent with the monitoring hypothesis, and little support was found for the three alternative explanations

A Maximum Stellar Surface Density in Dense Stellar Systems

We compile observations of the surface mass density profiles of dense stellar systems, including globular clusters in the Milky Way and nearby galaxies, massive star clusters in nearby starbursts, nuclear star clusters in dwarf spheroidals and late-type disks, ultra-compact dwarfs, and galaxy spheroids spanning the range from low-mass cusp bulges and ellipticals to massive core ellipticals. We show that in all cases the maximum stellar surface density attained in the central regions of these systems is similar, Sigma_max ~ 10^11 M_sun/kpc^2 (~20 g/cm^2), despite the fact that the systems span 7 orders of magnitude in total stellar mass M_star, 5 in effective radius R_e, and have a wide range in effective surface density M_star/R_e^2. The surface density limit is reached on a wide variety of physical scales in different systems and is thus not a limit on three-dimensional stellar density. Given the very different formation mechanisms involved in these different classes of objects, we argue that a single piece of physics likely determines Sigma_max. The radiation fields and winds produced by massive stars can have a significant influence on the formation of both star clusters and galaxies, while neither supernovae nor black hole accretion are important in star cluster formation. We thus conclude that feedback from massive stars likely accounts for the observed Sigma_max, plausibly because star formation reaches an Eddington-like flux that regulates the growth of these diverse systems. This suggests that current models of galaxy formation, which focus on feedback from supernovae and active galactic nuclei, are missing a crucial ingredient.Comment: 6 pages, 2 figures, accepted to MNRAS Letters (matches accepted version

Shining Light on Merging Galaxies I: The Ongoing Merger of a Quasar with a `Green Valley' Galaxy

Serendipitous observations of a pair z = 0.37 interacting galaxies (one hosting a quasar) show a massive gaseous bridge of material connecting the two objects. This bridge is photoionized by the quasar (QSO) revealing gas along the entire projected 38 kpc sightline connecting the two galaxies. The emission lines that result give an unprecedented opportunity to study the merger process at this redshift. We determine the kinematics, ionization parameter (log U ~ -2.5 +- 0.03), column density (N_H ~ 10^{21} cm^{-2}), metallicity ([M/H] ~ -0.20 +- 0.15), and mass (~ 10^8 Msun) of the gaseous bridge. We simultaneously constrain properties of the QSO-host (M_DM>8.8x 10^{11} Msun) and its companion galaxy (M_DM>2.1 x 10^{11} Msun; M_star ~ 2 x 10^{10} Msun; stellar burst age=300-800 Myr; SFR~6 Msun/yr; and metallicity 12+log (O/H)= 8.64 +- 0.2). The general properties of this system match the standard paradigm of a galaxy-galaxy merger caught between first and second passage while one of the galaxies hosts an active quasar. The companion galaxy lies in the so-called `green valley', with a stellar population consistent with a recent starburst triggered during the first passage of the merger and has no detectable AGN activity. In addition to providing case-studies of quasars associated with galaxy mergers, quasar/galaxy pairs with QSO-photoionized tidal bridges such as this one offer unique insights into the galaxy properties while also distinguishing an important and inadequately understood phase of galaxy evolution.Comment: 23 pages, 12 figures, 5 tables, Submitted to ApJ, revised to address referee's comment

On-Orbit Data and Validation of Astra\u27s ACE Electric Propulsion System

The first ACE propulsion system reached orbit on July 1st 2021 as part of Spaceflight’s demonstration of the Sherpa-LTE all-electric Orbital Transfer Vehicle (OTV). We are now able to share on-orbit data and have successfully verified the on-orbit performance of the ACE propulsion system, using xenon propellent. The mission objective was to lower altitude and use on-orbit data to derive performance, correlating the propulsion system’s performance to ground test data. The demonstration consisted of activating the propulsion system for 5- minute durations at a total input power of 340 W into the Power Processing Unit (PPU). Altitude change and propellant usage were used to derive thrust and total specific impulse. On-orbit performance is compared to ground test data in Table 1. Averaged performance is within one standard deviation of ground test data. Astra considers this a validation of system performance, as well as the ground test facilities used to test propulsion systems. On-orbit thrust has a large standard deviation as a result of the limited data sampling rate and measurement errors, rather than variability in thruster performance. Figure 1 shows the thruster operating on-orbit. The Astra team gratefully acknowledges the support of Spaceflight, Inc., the U.S. Air Force, and Defense Innovation Unit (DIU) without which this mission would not have been possible

Assessing Radiation Pressure as a Feedback Mechanism in Star-Forming Galaxies

Radiation pressure from the absorption and scattering of starlight by dust grains may be an important feedback mechanism in regulating star-forming galaxies. We compile data from the literature on star clusters, star-forming subregions, normal star-forming galaxies, and starbursts to assess the importance of radiation pressure on dust as a feedback mechanism, by comparing the luminosity and flux of these systems to their dust Eddington limit. This exercise motivates a novel interpretation of the Schmidt Law, the LIR-L'CO correlation, and the LIR-L'HCN correlation. In particular, the linear LIR-L'HCN correlation is a natural prediction of radiation pressure regulated star formation. Overall, we find that the Eddington limit sets a hard upper bound to the luminosity of any star-forming region. Importantly, however, many normal star-forming galaxies have luminosities significantly below the Eddington limit. We explore several explanations for this discrepancy, especially the role of "intermittency" in normal spirals - the tendency for only a small number of subregions within a galaxy to be actively forming stars at any moment because of the time-dependence of the feedback process and the luminosity evolution of the stellar population. If radiation pressure regulates star formation in dense gas, then the gas depletion timescale is 6 Myr, in good agreement with observations of the densest starbursts. Finally, we highlight the importance of observational uncertainties - namely, the dust-to-gas ratio and the CO-H2 and HCN-H2 conversion factors - that must be understood before a definitive assessment of radiation pressure as a feedback mechanism in star-forming galaxies.Comment: 12 pages, emulateapj, Accepted for publication in Ap