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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 1,639 records · Page 91
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DOE OSTI2014

The end of the MACHO era, revisited: New limits on MACHO masses from halo wide binaries

In order to determine an upper bound for the mass of the massive compact halo objects (MACHOs), we use the halo binaries contained in a recent catalog by Allen and Monroy-Rodríguez. To dynamically model their interactions with massive perturbers, a Monte Carlo simulation is conducted, using an impulsive approximation method and assuming a galactic halo constituted by massive particles of a characteristic mass. The results of such simulations are compared with several subsamples of our improved catalog of candidate halo wide binaries. In accordance with Quinn et al., we also find our results to be very sensitive to the widest binaries. However, our larger sample, together with the fact that we can obtain galactic orbits for 150 of our systems, allows a more reliable estimate of the maximum MACHO mass than that obtained previously. If we employ the entire sample of 211 candidate halo stars we, obtain an upper limit of 112 M{sub ☉}. However, using the 150 binaries in our catalog with computed galactic orbits, we are able to refine our fitting criteria. Thus, for the 100 most halo-like binaries we obtain a maximum MACHO mass of 21-68 M{sub ☉}. Furthermore, we can estimate the dynamical effects of the galactic disk using binary samples that spend progressively shorter times within the disk. By extrapolating the limits obtained for our most reliable—albeit smallest—sample, we find that as the time spent within the disk tends to zero, the upper bound of the MACHO mass tends to less than 5 M{sub ☉}. The non-uniform density of the halo has also been taken into account, but the limit obtained, less than 5 M{sub ☉}, does not differ much from the previous one. Together with microlensing studies that provide lower limits on the MACHO mass, our results essentially exclude the existence of such objects in the galactic halo.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Constraints for the progenitor masses of 17 historic core-collapse supernovae

Using resolved stellar photometry measured from archival Hubble Space Telescope imaging, we generate color-magnitude diagrams of the stars within 50 pc of the locations of historic core-collapse supernovae (SNe) that took place in galaxies within 8 Mpc. We fit these color-magnitude distributions with stellar evolution models to determine the best-fit age distribution of the young population. We then translate these age distributions into probability distributions for the progenitor mass of each SN. The measurements are anchored by the main-sequence stars surrounding the event, making them less sensitive to assumptions about binarity, post-main-sequence evolution, or circumstellar dust. We demonstrate that, in cases where the literature contains masses that have been measured from direct imaging, our measurements are consistent with (but less precise than) these measurements. Using this technique, we constrain the progenitor masses of 17 historic SNe, 11 of which have no previous estimates from direct imaging. Our measurements still allow the possibility that all SN progenitor masses are <20 M {sub ☉}. However, the large uncertainties for the highest-mass progenitors also allow the possibility of no upper-mass cutoff.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Formation of millisecond pulsars with low-mass helium white dwarf companions in very compact binaries

Binary millisecond pulsars (BMSPs) are thought to have evolved from low-mass X-ray binaries (LMXBs). If the mass transfer in LMXBs is driven by nuclear evolution of the donor star, the final orbital period is predicted to be well correlated with the mass of the white dwarf (WD), which is the degenerate He core of the donor. Here we show that this relation can be extended to very small WD mass (∼0.14-0.17 M {sub ☉}) and narrow orbital period (about a few hours), depending mainly on the metallicities of the donor stars. There is also discontinuity in the relation, which is due to the temporary contraction of the donor when the H-burning shell crosses the hydrogen discontinuity. BMSPs with low-mass He WD companions in very compact binaries can be accounted for if the progenitor binary experienced very late Case A mass transfer. The WD companion of PSR J1738+0333 is likely to evolve from a Pop II star. For PSR J0348+0432, to explain its extreme compact orbit in the Roche-lobe-decoupling phase, even lower metallicity (Z = 0.0001) is required.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The mass dependence of dwarf satellite galaxy quenching

We combine observations of the Local Group with data from the NASA-Sloan Atlas to show the variation in the quenched fraction of satellite galaxies from low-mass dwarf spheroidals and dwarf irregulars to more massive dwarfs similar to the Magellanic Clouds. While almost all of the low-mass (M {sub *} ≲ 10{sup 7} M {sub ☉}) dwarfs are quenched, at higher masses the quenched fraction decreases to approximately 40%-50%. This change in the quenched fraction is large and suggests a sudden change in the effectiveness of quenching that correlates with satellite mass. We combine this observation with models of satellite infall and ram pressure stripping to show that the low-mass satellites must quench within 1-2 Gyr of pericenter passage to maintain a high quenched fraction, but that many more massive dwarfs must continue to form stars today even though they likely fell into their host >5 Gyr ago. We also characterize how the susceptibility of dwarfs to ram pressure must vary as a function of mass if it is to account for the change in quenched fractions. Though neither model predicts the quenching effectiveness a priori, this modeling illustrates the physical requirements that the observed quenched fractions place on possible quenching mechanisms.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

A calibration of the stellar mass fundamental plane at z ∼ 0.5 using the micro-lensing-induced flux ratio anomalies of macro-lensed quasars {sup ,} {sup ,}

We measure the stellar mass surface densities of early-type galaxies by observing the micro-lensing of macro-lensed quasars caused by individual stars, including stellar remnants, brown dwarfs, and red dwarfs too faint to produce photometric or spectroscopic signatures. Instead of observing multiple micro-lensing events in a single system, we combine single-epoch X-ray snapshots of 10 quadruple systems, and compare the measured relative magnifications for the images with those computed from macro-models. We use these to normalize a stellar mass fundamental plane constructed using a Salpeter initial mass function with a low-mass cutoff of 0.1 M {sub ☉} and treat the zeropoint of the surface mass density as a free parameter. Our method measures the graininess of the gravitational potential produced by individual stars, in contrast to methods that decompose a smooth total gravitational potential into two smooth components, one stellar and one dark. We find the median likelihood value for the normalization factor F by which the Salpeter stellar masses must be multiplied is 1.23, with a one sigma confidence range, dominated by small number statistics, of 0.77<F<2.10.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Herschel photometry of disks around low-mass stars in the R CrA cloud

We report photometric results from a subset of a Herschel-PACS program to observe cool dust in disks around low-mass stars as a complement to our earlier program to measure far-infrared emission from brown dwarfs. In this latest study we observed five low-mass objects in the nearby R Corona Australis region and detected at least three at 70 μm. Using a Monte Carlo radiative transfer code we have investigated the disk masses and geometry based on detailed spectral energy distribution (SED) modeling, and we compare these new results to those from our earlier larger sample of brown dwarfs. In particular, our SED analysis for these five objects shows again that disk geometries of brown dwarfs or low-mass stars are generally similar to their higher mass counterparts like T Tauri disks, but the range of disk mass extends to well below the value found in T Tauri stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Variations of the stellar initial mass function in the progenitors of massive early-type galaxies and in extreme starburst environments

We examine variations of the stellar initial mass function (IMF) in extreme environments within the formalism derived by Hennebelle and Chabrier. We focus on conditions encountered in progenitors of massive early-type galaxies and starburst regions. We show that, when applying the concept of turbulent Jeans mass as the characteristic mass for fragmentation in a turbulent medium, the peak of the IMF in such environments is shifted toward smaller masses, leading to a bottom-heavy IMF, as suggested by various observations. In very dense and turbulent environments, we predict that the high-mass tail of the IMF can become even steeper than the standard Salpeter IMF, with a limit for the power-law exponent α ≅ –2.7, in agreement with recent observational determinations. This steepening is a direct consequence of the high densities and Mach values in such regions but also of the time dependence of the fragmentation process, as incorporated in the Hennebelle-Chabrier theory. We provide analytical parameterizations of these IMFs in such environments to be used in galaxy evolution calculations. We also calculate the star-formation rates and the mass-to-light ratios expected under such extreme conditions and show that they agree well with the values inferred in starburst environments and massive high-redshift galaxies. This reinforces the paradigm of star formation as being a universal process, i.e., the direct outcome of gravitationally unstable fluctuations in a density field initially generated by large-scale, shock-dominated turbulence. This globally enables us to infer the variations of the stellar IMF and related properties for atypical galactic conditions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

BANYAN. V. A SYSTEMATIC ALL-SKY SURVEY FOR NEW VERY LATE-TYPE LOW-MASS STARS AND BROWN DWARFS IN NEARBY YOUNG MOVING GROUPS

We present the BANYAN All-Sky Survey (BASS) catalog, consisting of 228 new late-type (M4-L6) candidate members of nearby young moving groups (YMGs) with an expected false-positive rate of ∼13%. This sample includes 79 new candidate young brown dwarfs and 22 planetary-mass objects. These candidates were identified through the first systematic all-sky survey for late-type low-mass stars and brown dwarfs in YMGs. We cross-matched the Two Micron All Sky Survey and AllWISE catalogs outside of the galactic plane to build a sample of 98,970 potential ≥M5 dwarfs in the solar neighborhood and calculated their proper motions with typical precisions of 5-15 mas yr{sup –1}. We selected highly probable candidate members of several YMGs from this sample using the Bayesian Analysis for Nearby Young AssociatioNs II tool (BANYAN II). We used the most probable statistical distances inferred from BANYAN II to estimate the spectral type and mass of these candidate YMG members. We used this unique sample to show tentative signs of mass segregation in the AB Doradus moving group and the Tucana-Horologium and Columba associations. The BASS sample has already been successful in identifying several new young brown dwarfs in earlier publications, and will be of great interest in studying the initial mass function of YMGs and for the search of exoplanets by direct imaging; the input sample of potential close-by ≥M5 dwarfs will be useful to study the kinematics of low-mass stars and brown dwarfs and search for new proper motion pairs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THE MOSDEF SURVEY: MASS, METALLICITY, AND STAR-FORMATION RATE AT z ∼ 2.3

We present results on the z ∼ 2.3 mass-metallicity relation (MZR) using early observations from the MOSFIRE Deep Evolution Field survey. We use an initial sample of 87 star-forming galaxies with spectroscopic coverage of Hβ, [O III] λ5007, Hα, and [N II] λ6584 rest-frame optical emission lines, and estimate the gas-phase oxygen abundance based on the N2 and O3N2 strong-line indicators. We find a positive correlation between stellar mass and metallicity among individual z ∼ 2.3 galaxies using both the N2 and O3N2 indicators. We also measure the emission-line ratios and corresponding oxygen abundances for composite spectra in bins of stellar mass. Among composite spectra, we find a monotonic increase in metallicity with increasing stellar mass, offset ∼0.15-0.3 dex below the local MZR. When the sample is divided at the median star-formation rate (SFR), we do not observe significant SFR dependence of the z ∼ 2.3 MZR among either individual galaxies or composite spectra. We furthermore find that z ∼ 2.3 galaxies have metallicities ∼0.1 dex lower at a given stellar mass and SFR than is observed locally. This offset suggests that high-redshift galaxies do not fall on the local ''fundamental metallicity relation'' among stellar mass, metallicity, and SFR, and may provide evidence of a phase of galaxy growth in which the gas reservoir is built up due to inflow rates that are higher than star-formation and outflow rates. However, robust conclusions regarding the gas-phase oxygen abundances of high-redshift galaxies await a systematic reappraisal of the application of locally calibrated metallicity indicators at high redshift.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THE RELATION BETWEEN STAR FORMATION RATE AND STELLAR MASS FOR GALAXIES AT 3.5 ≤ z ≤ 6.5 IN CANDELS

Distant star-forming galaxies show a correlation between their star formation rates (SFRs) and stellar masses, and this has deep implications for galaxy formation. Here, we present a study on the evolution of the slope and scatter of the SFR-stellar mass relation for galaxies at 3.5 ≤ z ≤ 6.5 using multi-wavelength photometry in GOODS-S from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) and Spitzer Extended Deep Survey. We describe an updated, Bayesian spectral-energy distribution fitting method that incorporates effects of nebular line emission, star formation histories that are constant or rising with time, and different dust-attenuation prescriptions (starburst and Small Magellanic Cloud). From z = 6.5 to z = 3.5 star-forming galaxies in CANDELS follow a nearly unevolving correlation between stellar mass and SFR that follows SFR ∼ M{sub ⋆}{sup a} with a =0.54 ± 0.16 at z ∼ 6 and 0.70 ± 0.21 at z ∼ 4. This evolution requires a star formation history that increases with decreasing redshift (on average, the SFRs of individual galaxies rise with time). The observed scatter in the SFR-stellar mass relation is tight, σ(log SFR/M {sub ☉} yr{sup –1}) < 0.3-0.4 dex, for galaxies with log M {sub *}/M {sub ☉} > 9 dex. Assuming that the SFR is tied to the net gas inflow rate (SFR ∼ M-dot {sub gas}), then the scatter in the gas inflow rate is also smaller than 0.3–0.4 dex for star-forming galaxies in these stellar mass and redshift ranges, at least when averaged over the timescale of star formation. We further show that the implied star formation history of objects selected on the basis of their co-moving number densities is consistent with the evolution in the SFR-stellar mass relation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

BLACK HOLE MASS ESTIMATES AND RAPID GROWTH OF SUPERMASSIVE BLACK HOLES IN LUMINOUS z ∼ 3.5 QUASARS

We present new near-infrared (IR) observations of the Hβ λ4861 and Mg II λ2798 lines for 32 luminous quasars with 3.2 < z < 3.9 using the Palomar Hale 200 inch telescope and the Large Binocular Telescope. We find that the Mg II FWHM is well correlated with the Hβ FWHM, confirming itself as a good substitute for the Hβ FWHM in the black hole mass estimates. The continuum luminosity at 5100 Å well correlates with the continuum luminosity at 3000 Å and the broad emission line luminosities (Hβ and Mg II). With simultaneous near-IR spectroscopy of the Hβ and Mg II lines to exclude the influences of flux variability, we are able to evaluate the reliability of estimating black hole masses based on the Mg II line for high redshift quasars. With the reliable Hβ line based black hole mass and Eddington ratio estimates, we find that the z ∼ 3.5 quasars in our sample have black hole masses 1.90 × 10{sup 9} M {sub ☉} ≲ M {sub BH} ≲ 1.37 × 10{sup 10} M {sub ☉}, with a median of ∼5.14 × 10{sup 9} M {sub ☉} and are accreting at Eddington ratios between 0.30 and 3.05, with a median of ∼1.12. Assuming a duty cycle of 1 and a seed black hole mass of 10{sup 4} M {sub ☉}, we show that the z ∼ 3.5 quasars in this sample can grow to their estimated black hole masses within the age of the universe at their redshifts.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THE MASS OF Kepler-93b AND THE COMPOSITION OF TERRESTRIAL PLANETS

Kepler-93b is a 1.478 ± 0.019 R {sub ⊕} planet with a 4.7 day period around a bright (V = 10.2), astroseismically characterized host star with a mass of 0.911 ± 0.033 M {sub ☉} and a radius of 0.919 ± 0.011 R {sub ☉}. Based on 86 radial velocity observations obtained with the HARPS-N spectrograph on the Telescopio Nazionale Galileo and 32 archival Keck/HIRES observations, we present a precise mass estimate of 4.02 ± 0.68 M {sub ⊕}. The corresponding high density of 6.88 ± 1.18 g cm{sup –3} is consistent with a rocky composition of primarily iron and magnesium silicate. We compare Kepler-93b to other dense planets with well-constrained parameters and find that between 1 and 6 M {sub ⊕}, all dense planets including the Earth and Venus are well-described by the same fixed ratio of iron to magnesium silicate. There are as of yet no examples of such planets with masses >6 M {sub ⊕}. All known planets in this mass regime have lower densities requiring significant fractions of volatiles or H/He gas. We also constrain the mass and period of the outer companion in the Kepler-93 system from the long-term radial velocity trend and archival adaptive optics images. As the sample of dense planets with well-constrained masses and radii continues to grow, we will be able to test whether the fixed compositional model found for the seven dense planets considered in this paper extends to the full population of 1-6 M {sub ⊕} planets.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A NEW CLASS OF NASCENT ECLIPSING BINARIES WITH EXTREME MASS RATIOS

Early B-type main-sequence (MS) stars (M {sub 1} ≈ 5-16 M {sub ☉}) with closely orbiting low-mass stellar companions (q = M {sub 2}/M {sub 1} < 0.25) can evolve to produce Type Ia supernovae, low-mass X-ray binaries, and millisecond pulsars. However, the formation mechanism and intrinsic frequency of such close extreme mass-ratio binaries have been debated, especially considering none have hitherto been detected. Utilizing observations of the Large Magellanic Cloud galaxy conducted by the Optical Gravitational Lensing Experiment, we have discovered a new class of eclipsing binaries in which a luminous B-type MS star irradiates a closely orbiting low-mass pre-MS companion that has not yet fully formed. The primordial pre-MS companions have large radii and discernibly reflect much of the light they intercept from the B-type MS primaries (ΔI {sub refl} ≈ 0.02-0.14 mag). For the 18 definitive MS + pre-MS eclipsing binaries in our sample with good model fits to the observed light-curves, we measure short orbital periods P = 3.0-8.5 days, young ages τ ≈ 0.6-8 Myr, and small secondary masses M {sub 2} ≈ 0.8-2.4 M {sub ☉} (q ≈ 0.07-0.36). The majority of these nascent eclipsing binaries are still associated with stellar nurseries, e.g., the system with the deepest eclipse ΔI {sub 1} = 2.8 mag and youngest age τ = 0.6 ± 0.4 Myr is embedded in the bright H II region 30 Doradus. After correcting for selection effects, we find that (2.0 ± 0.6)% of B-type MS stars have companions with short orbital periods P = 3.0-8.5 days and extreme mass ratios q ≈ 0.06-0.25. This is ≈10 times greater than that observed for solar-type MS primaries. We discuss how these new eclipsing binaries provide invaluable insights, diagnostics, and challenges for the formation and evolution of stars, binaries, and H II regions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

STELLAR MASSES FROM THE CANDELS SURVEY: THE GOODS-SOUTH AND UDS FIELDS

We present the public release of the stellar mass catalogs for the GOODS-S and UDS fields obtained using some of the deepest near-IR images available, achieved as part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey project. We combine the effort from 10 different teams, who computed the stellar masses using the same photometry and the same redshifts. Each team adopted their preferred fitting code, assumptions, priors, and parameter grid. The combination of results using the same underlying stellar isochrones reduces the systematics associated with the fitting code and other choices. Thanks to the availability of different estimates, we can test the effect of some specific parameters and assumptions on the stellar mass estimate. The choice of the stellar isochrone library turns out to have the largest effect on the galaxy stellar mass estimates, resulting in the largest distributions around the median value (with a semi interquartile range larger than 0.1 dex). On the other hand, for most galaxies, the stellar mass estimates are relatively insensitive to the different parameterizations of the star formation history. The inclusion of nebular emission in the model spectra does not have a significant impact for the majority of galaxies (less than a factor of 2 for ∼80% of the sample). Nevertheless, the stellar mass for the subsample of young galaxies (age <100 Myr), especially in particular redshift ranges (e.g., 2.2 < z < 2.4, 3.2 < z < 3.6, and 5.5 < z < 6.5), can be seriously overestimated (by up to a factor of 10 for <20 Myr sources) if nebular contribution is ignored.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Measurement of planet masses with transit timing variations due to synodic “chopping” effects

Gravitational interactions between planets in transiting exoplanetary systems lead to variations in the times of transit that are diagnostic of the planetary masses and the dynamical state of the system. Here we show that synodic “chopping” contributions to these transit timing variations (TTVs) can be used to uniquely measure the masses of planets without full dynamical analyses involving direct integration of the equations of motion. We present simple analytic formulae for the chopping signal, which are valid (generally <10% error) for modest eccentricities e≲0.1. Importantly, these formulae primarily depend on the mass of the perturbing planet, and therefore the chopping signal can be used to break the mass/free-eccentricity degeneracy, which can appear for systems near first-order mean motion resonances. Using a harmonic analysis, we apply these TTV formulae to a number of Kepler systems, which had been previously modeled with full dynamical analyses. We show that when chopping is measured, the masses of both planets can be determined uniquely, in agreement with previous results, but without the need for numerical orbit integrations. This demonstrates how mass measurements from TTVs may primarily arise from an observable chopping signal. The formula for chopping can also be used to predict the number of transits and timing precision required for future observations, such as those made by TESS or PLATO, in order to infer planetary masses through analysis of TTVs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

How to constrain your M dwarf: Measuring effective temperature, bolometric luminosity, mass, and radius

Precise and accurate parameters for late-type (late K and M) dwarf stars are important for characterization of any orbiting planets, but such determinations have been hampered by these stars’ complex spectra and dissimilarity to the Sun. We exploit an empirically calibrated method to estimate spectroscopic effective temperature (T{sub eff}) and the Stefan–Boltzmann law to determine radii of 183 nearby K7–M7 single stars with a precision of 2%–5%. Our improved stellar parameters enable us to develop model-independent relations between T{sub eff} or absolute magnitude and radius, as well as between color and T{sub eff}. The derived T{sub eff}–radius relation depends strongly on [Fe/H], as predicted by theory. The relation between absolute K{sub S} magnitude and radius can predict radii accurate to ≃3%. We derive bolometric corrections to the VR{sub C}I{sub C}grizJHK{sub S} and Gaia passbands as a function of color, accurate to 1%–3%. We confront the reliability of predictions from Dartmouth stellar evolution models using a Markov chain Monte Carlo to find the values of unobservable model parameters (mass, age) that best reproduce the observed effective temperature and bolometric flux while satisfying constraints on distance and metallicity as Bayesian priors. With the inferred masses we derive a semi-empirical mass–absolute magnitude relation with a scatter of 2% in mass. The best-agreement models overpredict stellar T{sub eff} values by an average of 2.2% and underpredict stellar radii by 4.6%, similar to differences with values from low-mass eclipsing binaries. These differences are not correlated with metallicity, mass, or indicators of activity, suggesting issues with the underlying model assumptions, e.g., opacities or convective mixing length.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The next generation Virgo Cluster Survey. XII. Stellar populations and kinematics of compact, Low-mass early-type galaxies from Gemini GMOS-IFU Spectroscopy

We present Gemini Multi Object Spectrograph integral-field unit (GMOS-IFU) data of eight compact, low-mass early-type galaxies (ETGs) in the Virgo cluster. We analyze their stellar kinematics and stellar population and present two-dimensional maps of these properties covering the central 5″ × 7″ region. We find a large variety of kinematics, from nonrotating to highly rotating objects, often associated with underlying disky isophotes revealed by deep images from the Next Generation Virgo Cluster Survey. In half of our objects, we find a centrally concentrated younger and more metal-rich stellar population. We analyze the specific stellar angular momentum through the λ{sub R} parameter and find six fast rotators and two slow rotators, one having a thin counterrotating disk. We compare the local galaxy density and stellar populations of our objects with those of 39 more extended low-mass Virgo ETGs from the SMAKCED survey and 260 massive (M > 10{sup 10} M{sub ⊙}) ETGs from the ATLAS{sup 3D} sample. The compact low-mass ETGs in our sample are located in high-density regions, often close to a massive galaxy, and have, on average, older and more metal-rich stellar populations than less compact low-mass galaxies. We find that the stellar population parameters follow lines of constant velocity dispersion in the mass–size plane, smoothly extending the comparable trends found for massive ETGs. Our study supports a scenario where low-mass compact ETGs have experienced long-lived interactions with their environment, including ram-pressure stripping and gravitational tidal forces, that may be responsible for their compact nature.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A {sup 13}CO SURVEY OF INTERMEDIATE-MASS STAR-FORMING REGIONS

We have conducted a {sup 13}CO survey of a sample of 128 infrared color-selected intermediate-mass star-forming region (IM SFR) candidates. We utilized the Onsala 20 m telescope to observe {sup 13}CO (1–0) toward 67 northern IM SFRs, used the 12 m Atacama Pathfinder Experiment telescope to observe {sup 13}CO (2–1) toward 22 southern IM SFRs, and incorporated an additional 39 sources from the Boston University Five College Radio Astronomy Observatory Galactic Ring Survey which observed {sup 13}CO (1–0). We detect {sup 13}CO (1–0) in 58 of the 67 northern sources and {sup 13}CO (2–1) in 20 of the 22 southern sources. The mean molecular column densities and {sup 13}CO linewidths in the inner Galaxy are higher by factors of 3.4 and 1.5, respectively, than the outer Galaxy. We attribute this difference to molecular clouds in the inner Galaxy being more massive and hosting star forming regions with higher luminosities on average than the outer Galaxy. IM SFRs have mean a molecular column density of 7.89 × 10{sup 21} cm{sup −2}, a factor of 3.1 lower than that for a sample of high-mass regions, and have a mean {sup 13}CO linewidth of 1.84 km s{sup −1}, a factor of 1.5 lower than that for high-mass regions. We demonstrate a correlation between {sup 13}CO linewidth and infrared luminosity as well as between molecular column density and infrared luminosity for the entire sample of intermediate-mass and high-mass regions. IM SFRs appear to form in distinctly lower-density environments with mean linewidths and beam-averaged column densities a factor of several lower than high-mass star-forming regions.

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