Are Halo and Galaxy Formation Histories Correlated?

The properties of dark matter halos, including mass growth, correlate with larger scale environment at fixed mass, an effect known as assembly bias. However, whether this environmental dependence manifests itself in galaxy properties remains unclear. We apply a group-finding algorithm to DR7 of the SDSS to estimate the halo mass of each galaxy and to decompose galaxies into those that exist at the centers of distinct halos and those that orbit as satellites within larger halos. Using the 4000-A break as a measure of star formation history, we examine the correlation between the quenched fraction of galaxies, f_q, and large-scale environment, rho. At all galaxy magnitudes, there is a positive, monotonic relationship between f_q and rho. We use the group catalog to decompose this correlation into the contribution from central and satellite galaxies as a function of halo mass. Because satellites are more likely to be quenched than central galaxies, the observed f_q-rho correlation is primarily due to variations of the halo mass function with environment, which causes a larger fraction of satellite galaxies at high rho. For low-mass central galaxies (Mgal <~ 10^10.0 Msol/h^2), there is no correlation between f_q and rho. These results are inconsistent with the strong assembly bias of dark matter halos seen in this mass regime if recent galaxy growth at all correlates with recent halo growth, as we demonstrate through a high resolution N-body simulation. We also find that the mean stellar age of quenched central galaxies is independent of rho at fixed Mgal, while the formation times of low mass halos vary significantly. We conclude that the processes that halt the star formation of low mass central galaxies are not correlated to the formation histories of their host halos, and old galaxies do not reside preferentially in old halos. (Abridged)Comment: 21 pages, submitted to MNRA

Dynamical heating of the X-ray emitting intracluster medium: the roles of merger shocks and turbulence dissipation

The diffuse plasma inside clusters of galaxies has X-ray emitting temperatures of a few keV. The physical mechanisms that heat this intracluster medium (ICM) to such temperatures include the accretion shock at the periphery of a galaxy cluster, the shocks driven by merger events, as well as a somewhat overlooked mechanism -- the dissipation of intracluster turbulent motions. We study the relative role of these heating mechanisms using galaxy clusters in Lagrangian tracer particle re-simulations of the Omega500 cosmological simulation. We adopt a novel analysis method of decomposing the temperature increase at each time step into the contribution from dissipative heating and that from adiabatic heating. In the high-resolution spatial-temporal map of these heating rates, merger tracks are clearly visible, demonstrating the dominant role of merger events in heating the ICM. The dissipative heating contributed by each merger event is extended in time and also occurs in the rarefaction regions, suggesting the importance of heating by the dissipation of merger-induced turbulence. Quantitative analysis shows that turbulence heating, rather than direct heating at merger shocks, dominates the temperature increase of the ICM, especially at inner radii $r < r_{\rm 500c}$. In addition, we find that many merger shocks can propagate with almost constant velocity to very large radii $r \gg r_{\rm 500c}$, some even reach and join with the accretion shock and becoming the outer boundary of the ICM. Altogether, these results suggest that the ICM is heated more in an `inside-out' fashion rather than `outside-in' as depicted in the classical smooth accretion picture.Comment: 12 pages, 13 figures, published in MNRA

Star Formation Quenching Timescale of Central Galaxies in a Hierarchical Universe

Central galaxies make up the majority of the galaxy population, including the majority of the quiescent population at $\mathcal{M}_* > 10^{10}\mathrm{M}_\odot$. Thus, the mechanism(s) responsible for quenching central galaxies plays a crucial role in galaxy evolution as whole. We combine a high resolution cosmological $N$-body simulation with observed evolutionary trends of the "star formation main sequence," quiescent fraction, and stellar mass function at $z < 1$ to construct a model that statistically tracks the star formation histories and quenching of central galaxies. Comparing this model to the distribution of central galaxy star formation rates in a group catalog of the SDSS Data Release 7, we constrain the timescales over which physical processes cease star formation in central galaxies. Over the stellar mass range $10^{9.5}$ to $10^{11} \mathrm{M}_\odot$ we infer quenching e-folding times that span $1.5$ to $0.5\; \mathrm{Gyr}$ with more massive central galaxies quenching faster. For $\mathcal{M}_* = 10^{10.5}\mathrm{M}_\odot$, this implies a total migration time of $\sim 4~\mathrm{Gyrs}$ from the star formation main sequence to quiescence. Compared to satellites, central galaxies take $\sim 2~\mathrm{Gyrs}$ longer to quench their star formation, suggesting that different mechanisms are responsible for quenching centrals versus satellites. Finally, the central galaxy quenching timescale we infer provides key constraints for proposed star formation quenching mechanisms. Our timescale is generally consistent with gas depletion timescales predicted by quenching through strangulation. However, the exact physical mechanism(s) responsible for this still remain unclear.Comment: 16 pages, 11 figure

Rapid Environmental Quenching of Satellite Dwarf Galaxies in the Local Group

In the Local Group, nearly all of the dwarf galaxies (M_star < 10^9 M_sun) that are satellites within 300 kpc (the virial radius) of the Milky Way (MW) and Andromeda (M31) have quiescent star formation and little-to-no cold gas. This contrasts strongly with comparatively isolated dwarf galaxies, which are almost all actively star-forming and gas-rich. This near dichotomy implies a rapid transformation of satellite dwarf galaxies after falling into the halos of the MW or M31. We combine the observed quiescent fractions for satellites of the MW and M31 with the infall times of satellites from the Exploring the Local Volume in Simulations (ELVIS) suite of cosmological zoom-in simulations to determine the typical timescales over which environmental processes within the MW/M31 halos remove gas and quench star formation in low-mass satellite galaxies. The quenching timescales for satellites with M_star < 10^8 M_sun are short, < 2 Gyr, and quenching is more rapid at lower M_star. These satellite quenching timescales can be 1 - 2 Gyr longer if one includes the time that satellites were environmentally preprocessed by low-mass groups prior to MW/M31 infall. We compare with quenching timescales for more massive satellites from previous works to synthesize the nature of satellite galaxy quenching across the observable range of M_star = 10^{3-11} M_sun. The satellite quenching timescale increases rapidly with satellite M_star, peaking at ~9.5 Gyr for M_star ~ 10^9 M_sun, and the timescale rapidly decreases at higher M_star to < 5 Gyr at M_star > 5 x 10^9 M_sun. Overall, galaxies with M_star ~ 10^9 M_sun, similar to the Magellanic Clouds, exhibit the longest quenching timescales, regardless of environmental or internal mechanisms.Comment: 6 pages, 3 figures. Accepted in ApJ Letters. Matches published versio

Fentanyl Administration on Emergence From Surgery and Post Anesthesia Care Unit Discharge Times and Pain Scores

Problem: Pain has been historically mismanaged potentially leading to a host of negative physiological consequences. Today’s dynamic health care reform offers an opportunity to increase satisfaction with care. Utilizing the PICO question, in adults undergoing laparoscopic cholecystectomy over a 12 month period, does medication with fentanyl during emergence versus not medicating during emergence reduce the need for pain medications and discharge times? Evidence/Background: Two national studies surveyed patient perception of pain management following surgery. The first, conducted by Apfelbaum et.al (2003) showed that 80% of patients experienced acute pain after surgery with 86% rating that pain as moderate to severe or extreme. The second national survey, by Tong et.al (2014) showed similar results with 86% experiencing pain following surgery and 76% rating that pain as moderate to severe. Despite standards released in 2001 by Joint Commission on Accreditation of Healthcare Organizations (JCAHO), and recommendations by the American Society of Anesthesiologist Task Force on Pain Management more needs to be done. Strategy: A quantitative retrospective chart review was used to evaluate patients between the age of 19-60 who underwent a laparoscopic cholecystectomy surgery who either received fentanyl on emergence or did not receive fentanyl on emergence from surgery. A convenience sample of 503 charts were obtained with 256 charts being excluded from the study. The remaining 247 charts were included in the study with 170 not given fentanyl and 77 given fentanyl. A systematic random sample (k = N/n) was obtained from the remaining charts. An independent samples t-test analyzed the group differences of administering fentanyl on emergence on the following: (a) PACU length of stay, (b) time to first analgesic administration in PACU, and (c) how much morphine was given in PACU. Results: An independent samples T-test showed no statistically significant outcomes related to giving fentanyl on emergence on the following: (a) PACU total length of stay (p = 0.066), (b) the time to first analgesic administration in PACU (p = 0.172) or (c) the amount of morphine given in PACU (p = 0.080) versus those who did not receive fentanyl

Development of a finite-difference neighboring optimal control law and application to the optimal landing of a reusable launch vehicle

A new neighboring optimal control methodology is developed and applied to the fuel-optimal landing of a reusable launch vehicle. Two new methods, both based on perturbation analysis, are explored. A fast open-loop optimal trajectory solver is developed to handle the numerically intensive perturbation analysis phase of control law synthesis. High accuracy closed-loop simulation of both the optimal control law and plant model shows that the optimal control law is robust for a number of different off-nominal conditions

Synchronization in the presence of distributed delays

We study systems of identical coupled oscillators introducing a distribution of delay times in the coupling. For arbitrary network topologies, we show that the frequency and stability of the fully synchronized states depend only on the mean of the delay distribution. However, synchronization dynamics is sensitive to the shape of the distribution. In the presence of coupling delays, the synchronization rate can be maximal for a specific value of the coupling strength.Comment: 6 pages, 3 figure

The physical nature of the cosmic accretion of baryons and dark matter into halos and their galaxies

The cosmic accretion of both dark matter and baryons into halos typically is measured using some evolving virial relation, but recent work suggests that most halo growth at late cosmic time (z < 2) is not physical but is rather the by-product of an evolving virial radius ("pseudo-evolution"). Using Omega25, a suite of cosmological simulations that incorporate both dark matter and gas dynamics with differing treatments of gas cooling, star formation, and thermal feedback, we systematically explore the physics that governs cosmic accretion into halos and their galaxies. Physically meaningful cosmic accretion of both dark matter and baryons occurs at z > 1 across our halo mass range: M_200m = 10^{11-14} M_sun. However, dark matter, because it is dissipationless, is deposited (in a time-average sense) at > R_200m(z) in a shell-like manner, such that dark-matter mass and density experience little-to-no physical growth at any radius within a halo at z < 1. In contrast, gas, because it is able to cool radiatively, experiences significant accretion at all radii, at a rate that roughly tracks the accretion rate at R_200m, at all redshifts. Infalling gas starts to decouple from dark matter at ~2 R_200m and continues to accrete to smaller radii until the onset of strong angular-momentum support at ~ 0.1 R_200m. Thus, while the growth of dark matter is subject to pseudo-evolution, the growth of baryons is not. The fact that the accretion rate of gas on galactic scales tracks the accretion rate near R_200m provides insight into the tight relations between the masses/sizes of galaxies and those of their host halos across cosmic time.Comment: 18 pages, 8 figures. Accepted for publication in ApJ. Matches published versio

Galaxy evolution in groups and clusters: satellite star formation histories and quenching timescales in a hierarchical Universe

Satellite galaxies in groups and clusters are more likely to have low star formation rates (SFR) and lie on the red-sequence than central (field) galaxies. Using galaxy group/cluster catalogs from SDSS DR7, together with a cosmological N-body simulation to track satellite orbits, we examine the star formation histories and quenching timescales of satellites of M_star > 5 x 10^9 M_sun at z=0. We first explore satellite infall histories: group preprocessing and ejected orbits are critical aspects of satellite evolution, and properly accounting for these, satellite infall typically occurred at z~0.5, or ~5 Gyr ago. To obtain accurate initial conditions for the SFRs of satellites at their time of first infall, we construct an empirical parametrization for the evolution of central galaxy SFRs and quiescent fractions. With this, we constrain the importance and efficiency of satellite quenching as a function of satellite and host halo mass, finding that satellite quenching is the dominant process for building up all quiescent galaxies at M_star < 10^10 M_sun. We then constrain satellite star formation histories, finding a 'delayed-then-rapid' quenching scenario: satellite SFRs evolve unaffected for 2-4 Gyr after infall, after which star formation quenches rapidly, with an e-folding time of < 0.8 Gyr. These quenching timescales are shorter for more massive satellites but do not depend on host halo mass: the observed increase in satellite quiescent fraction with halo mass arises simply because of satellites quenching in a lower mass group prior to infall (group preprocessing), which is responsible for up to half of quenched satellites in massive clusters. Because of the long time delay before quenching starts, satellites experience significant stellar mass growth after infall, nearly identical to central galaxies. This fact provides key physical insight into the subhalo abundance matching method.Comment: 25 pages, 13 figures. Accepted for publication in MNRAS, matches published versio

Modeling the Impact of Baryons on Subhalo Populations with Machine Learning

We identify subhalos in dark matter-only (DMO) zoom-in simulations that are likely to be disrupted due to baryonic effects by using a random forest classifier trained on two hydrodynamic simulations of Milky Way (MW)-mass host halos from the Latte suite of the Feedback in Realistic Environments (FIRE) project. We train our classifier using five properties of each disrupted and surviving subhalo: pericentric distance and scale factor at first pericentric passage after accretion, and scale factor, virial mass, and maximum circular velocity at accretion. Our five-property classifier identifies disrupted subhalos in the FIRE simulations with an $85\%$ out-of-bag classification score. We predict surviving subhalo populations in DMO simulations of the FIRE host halos, finding excellent agreement with the hydrodynamic results; in particular, our classifier outperforms DMO zoom-in simulations that include the gravitational potential of the central galactic disk in each hydrodynamic simulation, indicating that it captures both the dynamical effects of a central disk and additional baryonic physics. We also predict surviving subhalo populations for a suite of DMO zoom-in simulations of MW-mass host halos, finding that baryons impact each system consistently and that the predicted amount of subhalo disruption is larger than the host-to-host scatter among the subhalo populations. Although the small size and specific baryonic physics prescription of our training set limits the generality of our results, our work suggests that machine-learning classification algorithms trained on hydrodynamic zoom-in simulations can efficiently predict realistic subhalo populations.Comment: 20 pages, 14 figures. Updated to published version. Code available at https://github.com/ollienad/subhalo_randomfores