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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 919 records · Page 51
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DOE OSTI2015

STAR CLUSTER DISRUPTION IN THE STARBURST GALAXY MESSIER 82

Using high-resolution, multiple-passband Hubble Space Telescope images spanning the entire optical/near-infrared wavelength range, we obtained a statistically complete U-band-selected sample of 846 extended star clusters across the disk of the nearby starburst galaxy M82. Based on a careful analysis of the clusters' spectral energy distributions, we determined their galaxy-wide age and mass distributions. The M82 clusters exhibit three clear peaks in their age distribution, thus defining relatively young, log (t yr{sup –1}) ≤ 7.5, intermediate-age, log (t yr{sup –1}) in [7.5, 8.5], and old samples, log (t yr{sup –1}) ≥ 8.5. Comparison of the completeness-corrected mass distributions offers a firm handle on the galaxy's star cluster disruption history. The most massive star clusters in the young and old samples are (almost) all concentrated in the most densely populated central region, while the intermediate-age sample's most massive clusters are more spatially dispersed, which may reflect the distribution of the highest-density gas throughout the galaxy's evolutionary history, combined with the solid-body nature of the galaxy's central region.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

Inflationary infrared divergences: geometry of the reheating surface vs. δN formalism

We describe a simple way of incorporating fluctuations of the Hubble scale during the horizon exit of scalar perturbations into the δN formalism. The dominant effect comes from the dependence of the Hubble scale on low-frequency modes of the inflaton. This modifies the coefficient of the log-enhanced term appearing in the curvature spectrum at second order in field fluctuations. With this modification, the relevant coefficient turns out to be proportional to the second derivative of the tree-level spectrum with respect to the inflaton φ at horizon exit. A logarithm with precisely the same coefficient appears in a calculation of the log-enhancement of the curvature spectrum based purely on the geometry of the reheating surface. We take this agreement as strong support for the proposed implementation of the δN formalism. Moreover, our analysis makes it apparent that the log-enhancement of the inflationary power-spectrum is indeed physical if this quantity is defined using a global coordinate system on the reheating surface (or any other post-inflationary surface of constant energy density). However, it can be avoided by defining the spectrum using invariant distances on this surface.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

ACTIVE GALACTIC NUCLEI CLUSTERING IN THE LOCAL UNIVERSE: AN UNBIASED PICTURE FROM SWIFT-BAT

We present the clustering measurement of hard X-ray selected active galactic nuclei (AGNs) in the local universe. We used a sample of 199 sources spectroscopically confirmed, detected by Swift-BAT in its 15-55 keV all-sky survey. We measured the real space projected autocorrelation function (ACF) and detected a signal significant on projected scales lower than 200 Mpc h {sup -1}. We measured a correlation length of r{sub 0} = 5.56{sup +0.49}{sub -0.43} Mpc h {sup -1} and a slope {gamma} = 1.64{sup -0.08}{sub -0.07}. We also measured the ACF of Type I and Type II AGNs and found higher correlation length for Type I AGNs. We have a marginal evidence of luminosity dependent clustering of AGNs, as we detected a larger correlation length of luminous AGNs than that of low-luminosity sources. The corresponding typical host dark matter halo masses of Swift-BAT are {approx} log(M{sub DMH}){approx} 12-14 h {sup -1} M/M{sub sun}, depending on the subsample. For the whole sample, we measured log(M{sub DMH}){approx} 13.15 h {sup -1} M/M{sub sun} which is the typical mass of a galaxy group. We estimated that the local AGN population has a typical lifetime {tau}{sub AGN{approx}}0.7 Gyr, it is powered by supermassive black hole with mass M{sub BH{approx}}(1-10) x 10{sup 8} M{sub sun} and accreting with very low efficiency, log({epsilon}){approx}-2.0. We also conclude that local AGN host galaxies are typically red-massive galaxies with stellar mass of the order (2-80) x 10{sup 10} h {sup -1} M{sub sun}. We compared our results with clustering predictions of merger-driven AGN triggering models and found a good agreement.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

EARLY ASTEROSEISMIC RESULTS FROM KEPLER: STRUCTURAL AND CORE PARAMETERS OF THE HOT B SUBDWARF KPD 1943+4058 AS INFERRED FROM g-MODE OSCILLATIONS

We present a seismic analysis of the pulsating hot B subdwarf KPD 1943+4058 (KIC 005807616) on the basis of the long-period, gravity-mode pulsations recently uncovered by Kepler. This is the first time that g-mode seismology can be exploited quantitatively for stars on the extreme horizontal branch, all previous successful seismic analyses having been confined so far to short-period, p-mode pulsators. We demonstrate that current models of hot B subdwarfs can quite well explain the observed g-mode periods, while being consistent with independent constraints provided by spectroscopy. We identify the 18 pulsations retained in our analysis as low-degree (l = 1 and 2), intermediate-order (k = -9 through -58) g-modes. The periods (frequencies) are recovered, on average, at the 0.22% level, which is comparable to the best results obtained for p-mode pulsators. We infer the following structural and core parameters for KPD 1943+4058 (formal fitting uncertainties only): T{sub eff} = 28,050 {+-} 470 K, log g = 5.52 {+-} 0.03, M{sub *} = 0.496 {+-} 0.002 M{sub sun}, log (M{sub env}/M{sub *}) = -2.55 {+-} 0.07, log (1 - M{sub core}/M{sub *}) = -0.37 {+-} 0.01, and X{sub core}(C+O) = 0.261 {+-} 0.008. We additionally derive the age of the star since the zero-age extended horizontal branch 18.4 {+-} 1.0 Myr, the radius R = 0.203 {+-} 0.007 R{sub sun}, the luminosity L = 22.9 {+-} 3.13 L{sub sun}, the absolute magnitude M{sub V} = 4.21 {+-} 0.11, the reddening index E(B - V) = 0.094 {+-} 0.017, and the distance d = 1180 {+-} 95 pc.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

ASTROPHYSICAL PARAMETERS OF LS 2883 AND IMPLICATIONS FOR THE PSR B1259-63 GAMMA-RAY BINARY

Only a few binary systems with compact objects display TeV emission. The physical properties of the companion stars represent basic input for understanding the physical mechanisms behind the particle acceleration, emission, and absorption processes in these so-called gamma-ray binaries. Here we present high-resolution and high signal-to-noise optical spectra of LS 2883, the Be star forming a gamma-ray binary with the young non-accreting pulsar PSR B1259-63, showing it to rotate faster and be significantly earlier and more luminous than previously thought. Analysis of the interstellar lines suggests that the system is located at the same distance as (and thus is likely a member of) Cen OB1. Taking the distance to the association, d = 2.3 kpc, and a color excess of E(B - V) = 0.85 for LS 2883 results in M{sub V} {approx} -4.4. Because of fast rotation, LS 2883 is oblate (R{sub eq} {approx_equal} 9.7 R{sub sun} and R{sub pole} {approx_equal} 8.1 R{sub sun}) and presents a temperature gradient (T{sub eq}{approx} 27,500 K, log g{sub eq} = 3.7; T{sub pole}{approx} 34,000 K, log g{sub pole} = 4.1). If the star did not rotate, it would have parameters corresponding to a late O-type star. We estimate its luminosity at log(L{sub *}/L{sub sun}) {approx_equal} 4.79 and its mass at M{sub *} {approx} 30 M{sub sun}. The mass function then implies an inclination of the binary system i{sub orb} {approx} 23{sup 0}, slightly smaller than previous estimates. We discuss the implications of these new astrophysical parameters of LS 2883 for the production of high-energy and very high-energy gamma rays in the PSR B1259-63/LS 2883 gamma-ray binary system. In particular, the stellar properties are very important for prediction of the line-like bulk Comptonization component from the unshocked ultrarelativistic pulsar wind.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

DISTRIBUTION FUNCTIONS OF SIZES AND FLUXES DETERMINED FROM SUPRA-ARCADE DOWNFLOWS

The frequency distributions of sizes and fluxes of supra-arcade downflows (SADs) provide information about the process of their creation. For example, a fractal creation process may be expected to yield a power-law distribution of sizes and/or fluxes. We examine 120 cross-sectional areas and magnetic flux estimates found by Savage and McKenzie for SADs, and find that (1) the areas are consistent with a log-normal distribution and (2) the fluxes are consistent with both a log-normal and an exponential distribution. Neither set of measurements is compatible with a power-law distribution nor a normal distribution. As a demonstration of the applicability of these findings to improved understanding of reconnection, we consider a simple SAD growth scenario with minimal assumptions, capable of producing a log-normal distribution.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

KIC 1718290: A HELIUM-RICH V1093-Her-LIKE PULSATOR ON THE BLUE HORIZONTAL BRANCH

We introduce the first g-mode pulsator found to reside on the classical blue horizontal branch. One year of Kepler observations of KIC 1718290 reveals a rich spectrum of low-amplitude modes with periods between 1 and 12 hr, most of which follow a regular spacing of 276.3 s. This mode structure strongly resembles that of the V1093 Her pulsators, with only a slight shift toward longer periods. Our spectroscopy, however, reveals KIC 1718290 to be quite distinct from the sdB stars that show V1093 Her pulsations, which all have surface gravities higher than log g = 5.1 and helium abundances depleted by at least an order of magnitude relative to the solar composition. We find that KIC 1718290 has T{sub eff} = 22,100 K, log g = 4.72, and a super-solar helium abundance (log N{sub He}/N{sub H} = -0.45). This places it well above the extreme horizontal branch, rather on the very blue end of the classical horizontal branch, where shell hydrogen burning is present. We conclude that KIC 1718290 must have suffered extreme mass loss during its first giant stage, but not sufficient to reach the extreme horizontal branch.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

THE STAR FORMATION MASS SEQUENCE OUT TO z = 2.5

We study the star formation rate (SFR)-stellar mass (M{sub *}) relation in a self-consistent manner from 0 < z < 2.5 with 22,816 star-forming galaxies selected from the NEWFIRM Medium-Band Survey. We find a significant nonlinear slope of the relation, SFR{proportional_to}M {sup 0.6}{sub *}, and a constant observed scatter of 0.34 dex, independent of redshift and M{sub *}. However, if we select only blue galaxies we find a linear relation SFR{proportional_to}M{sub *}, similar to previous results at z = 0 by Peng et al. This selection excludes red, dusty, star-forming galaxies with higher masses, which brings down the slope. By selecting on L{sub IR}/L{sub UV} (a proxy for dust obscuration) and the rest-frame U - V colors, we show that star-forming galaxies fall in three distinct regions of the log(SFR)-log(M{sub *}) plane: (1) actively star-forming galaxies with 'normal' dust obscuration and associated colors (54% for log (M{sub *}) > 10 at 1 < z < 1.5), (2) red star-forming galaxies with low levels of dust obscuration and low-specific SFRs (11%), and (3) dusty, blue star-forming galaxies with high-specific SFRs (7%). The remaining 28% comprises quiescent galaxies. Galaxies on the 'normal' star formation sequence show strong trends of increasing dust attenuation with stellar mass and a decreasing specific SFR, with an observed scatter of 0.25 dex. The dusty, blue galaxies reside in the upper envelope of the star formation sequence with remarkably similar spectral shapes at all masses, suggesting that the same physical process is dominating the stellar light. The red, low-dust star-forming galaxies may be in the process of shutting off and migrating to the quiescent population.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

THE ABSENCE OF RADIO EMISSION FROM THE GLOBULAR CLUSTER G1

The detections of both X-ray and radio emission from the cluster G1 in M31 have provided strong support for existing dynamical evidence for an intermediate-mass black hole (IMBH) of mass (1.8 {+-} 0.5) Multiplication-Sign 10{sup 4} M{sub Sun} at the cluster center. However, given the relatively low significance and astrometric accuracy of the radio detection, and the non-simultaneity of the X-ray and radio measurements, this identification required further confirmation. Here we present deep, high angular resolution, strictly simultaneous X-ray and radio observations of G1. While the X-ray emission (L{sub X} = 1.74{sup +0.53}{sub -0.44} Multiplication-Sign 10{sup 36} (d/750 kpc){sup 2} erg s{sup -1} in the 0.5-10 keV band) remained fully consistent with previous observations, we detected no radio emission from the cluster center down to a 3{sigma} upper limit of 4.7 {mu}Jy beam{sup -1}. Our favored explanation for the previous radio detection is flaring activity from a black hole low-mass X-ray binary (LMXB). We performed a new regression of the 'Fundamental Plane' of black hole activity, valid for determining black hole mass from radio and X-ray observations of sub-Eddington black holes, finding log M{sub BH} = (1.638 {+-} 0.070)log L{sub R} - (1.136 {+-} 0.077)log L{sub X} - (6.863 {+-} 0.790), with an empirically determined uncertainty of 0.44 dex. This constrains the mass of the X-ray source in G1, if a black hole, to be <9.7 Multiplication-Sign 10{sup 3} M{sub Sun} at 95% confidence, suggesting that it is a persistent LMXB. This annuls what was previously the most convincing evidence from radiation for an IMBH in the Local Group, though the evidence for an IMBH in G1 from velocity dispersion measurements remains unaffected by these results.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

SDO/AIA DETECTION OF SOLAR PROMINENCE FORMATION WITHIN A CORONAL CAVITY

We report the first analyses of SDO/AIA observations of the formation of a quiescent polar crown prominence in a coronal cavity. The He II 304 A (log T{sub max} {approx} 4.8 K) data show both the gradual disappearance of the prominence due to vertical drainage and lateral transport of plasma followed by the formation of a new prominence 12 hr later. The formation is preceded by the appearance of a bright emission 'cloud' in the central region of the coronal cavity. The peak brightness of the cloud progressively shifts in time from the Fe XIV 211 A channel, through the Fe XII 193 A channel, to the Fe IX 171 A channel (log T{sub max} {approx} 6.2, 6.1, 5.8 K, respectively) while simultaneously decreasing in altitude. Filter ratio analysis estimates the initial temperature of the cloud to be approximately log T {approx} 6.25 K with evidence of cooling over time. The subsequent growth of the prominence is accompanied by darkening of the cavity in the 211 A channel. The observations imply prominence formation via in situ condensation of hot plasma from the coronal cavity, in support of our previously proposed process of magnetothermal convection in coronal magnetic flux ropes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE SELF-SIMILARITY OF THE CIRCUMGALACTIC MEDIUM WITH GALAXY VIRIAL MASS: IMPLICATIONS FOR COLD-MODE ACCRETION

We apply halo abundance matching to obtain galaxy virial masses, M{sub h}, and radii, R{sub vir}, for 183 'isolated' galaxies from the 'Mg II Absorber-Galaxy Catalog'. All galaxies have spectroscopic redshifts (0.07 {<=} z {<=} 1.12) and their circumgalactic medium (CGM) is probed in Mg II absorption within projected galactocentric distances D {<=} 200 kpc. We examine the behavior of equivalent width, W{sub r} (2796), and covering fraction, f{sub c} , as a function of D, D/R{sub vir}, and M{sub h}. Bifurcating the sample at the median mass log M{sub h}/M{sub Sun} = 12, we find (1) systematic segregation of M{sub h} on the W{sub r} (2796)-D plane (4.0{sigma}); high-mass halos are found at higher D with larger W{sub r} (2796) compared to low-mass halos. On the W{sub r} (2796)-D/R{sub vir} plane, mass segregation vanishes and we find W{sub r} (2796){proportional_to}(D/R{sub vir}){sup -2} (8.9{sigma}). (2) High-mass halos have larger f{sub c} at a given D, whereas f{sub c} is independent of M{sub h} at all D/R{sub vir}. (3) f{sub c} is constant with M{sub h} over the range 10.7 {<=} log M{sub h}/M{sub Sun} {<=} 13.9 within a given D or D/R{sub vir}. The combined results suggest the Mg II absorbing CGM is self-similar with halo mass, even above log M{sub h}/M{sub Sun} {approx_equal} 12, where cold mode accretion is predicted to be quenched. If theory is correct, either outflows or sub-halos must contribute to absorption in high-mass halos such that low- and high-mass halos are observationally indistinguishable using Mg II absorption strength once impact parameter is scaled by halo mass. Alternatively, the data may indicate predictions of a universal shut down of cold-mode accretion in high-mass halos may require revision.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

GAMMA-RAY BURST AND STAR FORMATION RATES: THE PHYSICAL ORIGIN FOR THE REDSHIFT EVOLUTION OF THEIR RATIO

Gamma-ray bursts (GRBs) and galaxies at high redshift represent complementary probes of the star formation history of the universe. In fact, both the GRB rate and the galaxy luminosity density are connected to the underlying star formation. Here, we combine a star formation model for the evolution of the galaxy luminosity function from z = 0 to z = 10 with a metallicity-dependent efficiency for GRB formation to simultaneously predict the comoving GRB rate. Our model sheds light on the physical origin of the empirical relation often assumed between GRB rate and luminosity density-derived star formation rate: n-dot{sub GRB}(z)={epsilon}(z) Multiplication-Sign {rho}-dot{sup *}{sub obs}(z), with {epsilon}(z){proportional_to}(1 + z){sup 1.2}. At z {approx}< 4, {epsilon}(z) is dominated by the effects of metallicity evolution in the GRB efficiency. Our best-fitting model only requires a moderate preference for low-metallicity, that is a GRB rate per unit stellar mass about four times higher for log (Z/Z{sub Sun }) < -3 compared to log (Z/Z{sub Sun }) > 0. Models with total suppression of GRB formation at log (Z/Z{sub Sun }) {approx}> 0 are disfavored. At z {approx}> 4, most of the star formation happens in low-metallicity hosts with nearly saturated efficiency of GRB production per unit stellar mass. However, at the same epoch, galaxy surveys miss an increasing fraction of the predicted luminosity density because of flux limits, driving an accelerated evolution of {epsilon}(z) compared to the empirical power-law fit from lower z. Our findings are consistent with the non-detections of GRB hosts in ultradeep imaging at z > 5, and point toward current galaxy surveys at z > 8 only observing the top 15%-20% of the total luminosity density.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

EXPLORING THE CHEMICAL LINK BETWEEN LOCAL ELLIPTICALS AND THEIR HIGH-REDSHIFT PROGENITORS

We present Keck/MOSFIRE K-band spectroscopy of the first mass-selected sample of galaxies at z ∼ 2.3. Targets are selected from the 3D-Hubble Space Telescope Treasury survey. The six detected galaxies have a mean [N II]λ6584/Hα ratio of 0.27 ± 0.01, with a small standard deviation of 0.05. This mean value is similar to that of UV-selected galaxies of the same mass. The mean gas-phase oxygen abundance inferred from the [N II]/Hα ratios depends on the calibration method, and ranges from 12+log(O/H){sub gas} = 8.57 for the Pettini and Pagel calibration to 12+log(O/H){sub gas} = 8.87 for the Maiolino et al. calibration. Measurements of the stellar oxygen abundance in nearby quiescent galaxies with the same number density indicate 12+log(O/H){sub stars} = 8.95, similar to the gas-phase abundances of the z ∼ 2.3 galaxies if the Maiolino et al. calibration is used. This suggests that these high-redshift star forming galaxies may be progenitors of today's massive early-type galaxies. The main uncertainties are the absolute calibration of the gas-phase oxygen abundance and the incompleteness of the z ∼ 2.3 sample: the galaxies with detected Hα tend to be larger and have higher star formation rates than the galaxies without detected Hα, and we may still be missing the most dust-obscured progenitors.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

FLICKER AS A TOOL FOR CHARACTERIZING PLANETS THROUGH ASTERODENSITY PROFILING

Variability in the time series brightness of a star on a timescale of 8 hr, known as ''flicker'', has been previously demonstrated to serve as a proxy for the surface gravity of a star by Bastien et al. Although surface gravity is crucial for stellar classification, it is the mean stellar density that is most useful when studying transiting exoplanets, due to its direct impact on the transit light curve shape. Indeed, an accurate and independent measure of the stellar density can be leveraged to infer subtle properties of a transiting system, such as the companion's orbital eccentricity via asterodensity profiling (AP). We here calibrate flicker to the mean stellar density of 439 Kepler targets with asteroseismology, allowing us to derive a new empirical relation given by log{sub 10}(ρ{sub *} (kg m{sup –3})) = 5.413 – 1.850log{sub 10}(F {sub 8} (ppm)). The calibration is valid for stars with 4500 < T {sub eff} < 6500 K, K{sub P} < 14, and flicker estimates corresponding to stars with 3.25 < log g {sub *} < 4.43. Our relation has a model error in the stellar density of 31.7% and so has ∼8 times lower precision than that from asteroseismology but is applicable to a sample ∼40 times greater. Flicker therefore provides an empirical method to enable AP on hundreds of planetary candidates from present and future missions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

A NEW FUNDAMENTAL PLANE FOR RADIATIVELY EFFICIENT BLACK-HOLE SOURCES

In recent years, it has been found that several low/hard states of X-ray binaries (XRBs) follow an ''outliers'' track in the radio-X-ray correlation (L{sub R}∝L{sub X}{sup b} and b ∼ 1.4), which is much steeper than the former universal track with b ∼ 0.6. In this work, we compile a sample of bright radio-quiet active galactic nuclei (AGNs) and find that their hard X-ray photon indices and Eddington ratios are positively correlated, which is similar to that of XRB outliers, where both bright AGNs and XRB outliers have bolometric Eddington ratios ≳ 1%L {sub Edd} (L {sub Edd} is Eddington luminosity). The Eddington-scaled radio-X-ray correlation of these AGNs is also similar to that of XRB outliers, which has the form of L {sub 5} {sub GHz}/L {sub Edd}∝(L {sub 2-10} {sub keV}/L {sub Edd}) {sup c} with c ≅ 1.59 and 1.53 for AGNs and XRBs, respectively. Both the positively correlated X-ray spectral evolution and the steeper radio-X-ray correlation can be regulated by a radiatively efficient accretion flow (e.g., disk-corona). Based on these similarities, we further present a new fundamental plane for XRB outliers and bright AGNs in black-hole (BH) mass, radio, and X-ray luminosity space: log L{sub R}=1.59{sub −0.22}{sup +0.28}log L{sub X}−0.22{sub −0.20}{sup +0.19}log M{sub BH}−28.97{sub −0.45}{sup +0.45} with a scatter of σ{sub R} = 0.51 dex. This fundamental plane is suitable for radiatively efficient BH sources, while the former plane proposed by Merloni et al. and Falcke et al. may be most suitable for radiatively inefficient sources.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Monte Carlo goodness-of-fit tests for degree corrected and related stochastic blockmodels

Abstract We construct Bayesian and frequentist finite-sample goodness-of-fit tests for three different variants of the stochastic blockmodel for network data. Since all of the stochastic blockmodel variants are log-linear in form when block assignments are known, the tests for the latent block model versions combine a block membership estimator with the algebraic statistics machinery for testing goodness-of-fit in log-linear models. We describe Markov bases and marginal polytopes of the variants of the stochastic blockmodel and discuss how both facilitate the development of goodness-of-fit tests and understanding of model behaviour. The general testing methodology developed here extends to any finite mixture of log-linear models on discrete data, and as such is the first application of the algebraic statistics machinery for latent-variable models.

Karwa, Vishesh↗
DOE OSTI2020

From the inner to outer Milky Way: a photometric sample of 2.6 million red clump stars

ABSTRACT Large pristine samples of red clump stars are highly sought after given that they are standard candles and give precise distances even at large distances. However, it is difficult to cleanly select red clumps stars because they can have the same Teff and log g as red giant branch stars. Recently, it was shown that the asteroseismic parameters, $\rm {\Delta }$P and $\rm {\Delta \nu }$, which are used to accurately select red clump stars, can be derived from spectra using the change in the surface carbon to nitrogen ratio ([C/N]) caused by mixing during the red giant branch. This change in [C/N] can also impact the spectral energy distribution. In this study, we predict the $\rm {\Delta }$P, $\rm {\Delta \nu }$, Teff, and log g using 2MASS, AllWISE, Gaia, and Pan-STARRS data in order to select a clean sample of red clump stars. We achieve a contamination rate of ∼20 per cent, equivalent to what is achieved when selecting from Teff and log g derived from low-resolution spectra. Finally, we present two red clump samples. One sample has a contamination rate of ∼20 per cent and ∼405 000 red clump stars. The other has a contamination of ∼33 per cent and ∼2.6 million red clump stars that includes ∼75 000 stars at distances >10 kpc. For |b| > 30 deg, we find ∼15 000 stars with contamination rate of ∼9 per cent. The scientific potential of this catalogue for studying the structure and formation history of the Galaxy is vast, given that it includes millions of precise distances to stars in the inner bulge and distant halo where astrometric distances are imprecise.

Lucey, Madeline↗
DOE OSTI2020

Damped Ly α absorbers and atomic hydrogen in galaxies: the view of the GAEA model

ABSTRACT Using the GAEA semi-analytic model, we analyse the connection between Damped Ly α systems (DLAs) and H i in galaxies. Our state-of-the-art semi-analytic model is tuned to reproduce the local galaxy H i mass function, and that also reproduces other important galaxy properties, including the galaxy mass–gas metallicity relation. To produce catalogues of simulated DLAs we throw 105 random lines of sight in a composite simulated volume: dark matter haloes with log$(\frac{M_{200}}{ {\rm M}_{\odot }}) \ge 11.5$ are extracted from the Millennium Simulation, while for $9.2 \le \log (\frac{M_{200}}{ \mathrm{M}_{\odot }})\lt 11.5$ we use the Millennium II, and for $8 \le \log (\frac{M_{200}}{\mathrm{M}_{\odot }}) \lt 9.2$ a halo occupation distribution model. At 2 < z < 3, where observational data are more accurate, our fiducial model predicts the correct shape of the column density distribution function, but its normalization falls short of the observations, with the discrepancy increasing at higher redshift. The agreement with observations is significantly improved increasing both the H i masses and the disc radii of model galaxies by a factor of 2, as implemented ‘a posteriori’ in our 2M−2R model. In the redshift range of interest, haloes with $M_{200} \ge {10}^{11} \, \mathrm{M}_{\odot }$ give the major contribution to ΩDLA, and the typical DLA host halo mass is $\sim \!{10}^{11} \, \mathrm{M}_{\odot }$. The simulated DLA metallicity distribution is in relatively good agreement with observations, but our model predicts an excess of DLAs at low metallicities. Our results suggest possible improvements for the adopted modelling of the filtering mass and metal ejection in low-mass haloes.

Di Gioia, Serafina↗