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Sample records for nuclear star formation

  1. STAR FORMATION IN NUCLEAR RINGS OF BARRED GALAXIES

    SciTech Connect

    Seo, Woo-Young; Kim, Woong-Tae E-mail: wkim@astro.snu.ac.kr

    2013-06-01

    Nuclear rings in barred galaxies are sites of active star formation. We use hydrodynamic simulations to study the temporal and spatial behavior of star formation occurring in nuclear rings of barred galaxies where radial gas inflows are triggered solely by a bar potential. The star formation recipes include a density threshold, an efficiency, conversion of gas to star particles, and delayed momentum feedback via supernova explosions. We find that the star formation rate (SFR) in a nuclear ring is roughly equal to the mass inflow rate to the ring, while it has a weak dependence on the total gas mass in the ring. The SFR typically exhibits a strong primary burst followed by weak secondary bursts before declining to very small values. The primary burst is associated with the rapid gas infall to the ring due to the bar growth, while the secondary bursts are caused by re-infall of the ejected gas from the primary burst. While star formation in observed rings persists episodically over a few Gyr, the duration of active star formation in our models lasts for only about half of the bar growth time, suggesting that the bar potential alone is unlikely to be responsible for gas supply to the rings. When the SFR is low, most star formation occurs at the contact points between the ring and the dust lanes, leading to an azimuthal age gradient of young star clusters. When the SFR is large, on the other hand, star formation is randomly distributed over the whole circumference of the ring, resulting in no apparent azimuthal age gradient. Since the ring shrinks in size with time, star clusters also exhibit a radial age gradient, with younger clusters found closer to the ring. The cluster mass function is well described by a power law, with a slope depending on the SFR. Giant gas clouds in the rings have supersonic internal velocity dispersions and are gravitationally bound.

  2. Star Formation in Nuclear Rings of Barred Galaxies

    NASA Astrophysics Data System (ADS)

    Seo, Woo-Young; Kim, Woong-Tae

    2013-06-01

    Nuclear rings in barred galaxies are sites of active star formation. We use hydrodynamic simulations to study the temporal and spatial behavior of star formation occurring in nuclear rings of barred galaxies where radial gas inflows are triggered solely by a bar potential. The star formation recipes include a density threshold, an efficiency, conversion of gas to star particles, and delayed momentum feedback via supernova explosions. We find that the star formation rate (SFR) in a nuclear ring is roughly equal to the mass inflow rate to the ring, while it has a weak dependence on the total gas mass in the ring. The SFR typically exhibits a strong primary burst followed by weak secondary bursts before declining to very small values. The primary burst is associated with the rapid gas infall to the ring due to the bar growth, while the secondary bursts are caused by re-infall of the ejected gas from the primary burst. While star formation in observed rings persists episodically over a few Gyr, the duration of active star formation in our models lasts for only about half of the bar growth time, suggesting that the bar potential alone is unlikely to be responsible for gas supply to the rings. When the SFR is low, most star formation occurs at the contact points between the ring and the dust lanes, leading to an azimuthal age gradient of young star clusters. When the SFR is large, on the other hand, star formation is randomly distributed over the whole circumference of the ring, resulting in no apparent azimuthal age gradient. Since the ring shrinks in size with time, star clusters also exhibit a radial age gradient, with younger clusters found closer to the ring. The cluster mass function is well described by a power law, with a slope depending on the SFR. Giant gas clouds in the rings have supersonic internal velocity dispersions and are gravitationally bound.

  3. FORMATION AND EVOLUTION OF NUCLEAR STAR CLUSTERS WITH IN SITU STAR FORMATION: NUCLEAR CORES AND AGE SEGREGATION

    SciTech Connect

    Aharon, Danor; Perets, Hagai B.

    2015-02-01

    Nuclear stellar cluster (NSCs) are known to exist around massive black holes (MBHs) in galactic nuclei. Two formation scenarios were suggested for their origin: (1) buildup of NSCs from consecutive infall of stellar clusters and (2) continuous in situ star formation. Though the cluster infall scenario has been extensively studied, the in situ formation scenario has been hardly explored. Here we use Fokker-Planck (FP) calculations to study the effects of star formation on the buildup of NSCs and its implications for their long-term evolution and their resulting structure. We use the FP equation to describe the evolution of stellar populations and add appropriate source terms to account for the effects of newly formed stars. We show that continuous star formation even 1-2 pc away from the MBH can lead to the buildup of an NSC with properties similar to those of the Milky Way NSC. We find that the structure of the old stellar population in the NSC with in situ star formation could be very similar to the steady-state Bahcall-Wolf cuspy structure. However, its younger populations do not yet achieve a steady state. In particular, formed/evolved NSCs with in situ star formation contain differential age-segregated stellar populations that are not yet fully mixed. Younger stellar populations formed in the outer regions of the NSC have a cuspy structure toward the NSC outskirts, while showing a core-like distribution inward, with younger populations having larger core sizes. In principal, such a structure can give rise to an apparent core-like radial distribution of younger stars, as observed in the Galactic center.

  4. New insights on the formation of nuclear star clusters

    NASA Astrophysics Data System (ADS)

    Guillard, Nicolas; Emsellem, Eric; Renaud, Florent

    2016-10-01

    Nuclear clusters (NCs) are common stellar systems in the centres of galaxies. Yet, the physical mechanisms involved in their formation are still debated. Using a parsec-resolution hydrodynamical simulation of a dwarf galaxy, we propose an updated formation scenario for NCs. In this `wet migration scenario', a massive star cluster forms in the gas-rich disc, keeping a gas reservoir, and growing further while it migrates to the centre via a combination of interactions with other substructures and dynamical friction. A wet merger with another dense cluster and its own gas reservoir can occur, although this is not a prerequisite for the actual formation of the NC. The merging process does significantly alter the properties of the NC (mass, morphology, star formation history), also quenching the ongoing local star formation activity, thus leading to interesting observational diagnostics for the physical origin of NCs. A population of lower mass clusters co-exist during the simulation, but these are either destroyed via tidal forces, or have high angular momentum preventing them to interact with the NC and contribute to its growth. The proposed updated scenario emphasizes the role of gas reservoirs associated with the densest star clusters formed in a gas-rich low-mass galaxy.

  5. THE STAR FORMATION HISTORY OF THE MILKY WAY'S NUCLEAR STAR CLUSTER

    SciTech Connect

    Pfuhl, O.; Fritz, T. K.; Eisenhauer, F.; Genzel, R.; Gillessen, S.; Ott, T.; Dodds-Eden, K.; Zilka, M.; Sternberg, A.; Maness, H.

    2011-11-10

    We present spatially resolved imaging and integral field spectroscopy data for 450 cool giant stars within 1 pc from Sgr A*. We use the prominent CO bandheads to derive effective temperatures of individual giants. Additionally we present the deepest spectroscopic observation of the Galactic center (GC) so far, probing the number of B9/A0 main-sequence stars (2.2-2.8 M{sub sun}) in two deep fields. From spectrophotometry we construct a Hertzsprung-Russell diagram of the red giant population and fit the observed diagram with model populations to derive the star formation history of the nuclear cluster. We find (1) that the average nuclear star formation rate dropped from an initial maximum {approx}10 Gyr ago to a deep minimum 1-2 Gyr ago and increased again during the last few hundred Myrs, (2) that roughly 80% of the stellar mass formed more than 5 Gyr ago, and (3) that mass estimates within R {approx} 1 pc from Sgr A* favor a dominant star formation mode with a 'normal' Chabrier/Kroupa initial mass function for the majority of the past star formation in the GC. The bulk stellar mass seems to have formed under conditions significantly different from the young stellar disks, perhaps because at the time of the formation of the nuclear cluster the massive black hole and its sphere of influence were much smaller than today.

  6. A Numerical Simulation of Star Formation in Nuclear Rings of Barred-Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Seo, Woo-Young; Kim, W.

    2014-01-01

    We use grid-based hydrodynamic simulations to study star formation history in nuclear rings of barred-spiral galaxies. We assume infinitesimally thin, isothermal, and unmagnetized gaseous disk. To investigate effects of spiral arm potential, we calculate both models with and without spiral. We find that star formation rate (SFR) in a nuclear ring is determined by the mass inflow rate to the ring rather than the total gas mass in the ring. In case of models without spiral arms, the SFR shows a strong primary burst at early time, and declines to small values after after that. The primary burst is caused by the rapid gas infall to the ring due to the bar growth. On the other hand, models with spiral arms show multiple star bursts at late time caused by additional gas inflow from outside bar region. When the SFR is low, ages of young star clusters exhibit a bipolar azimuthal gradient along the ring since star formation occurs near the contact points between dust lanes and the nuclear ring. When the SFR is large, there are no age gradient of star clusters since star formation sites are widely distributed throughout the whole ring region.

  7. Nuclear Star Clusters

    NASA Astrophysics Data System (ADS)

    Neumayer, Nadine

    2017-03-01

    The centers of galaxies host two distinct, compact components: massive black holes and nuclear star clusters. Nuclear star clusters are the densest stellar systems in the universe, with masses of ~ 107M⊙ and sizes of ~ 5pc. They are almost ubiquitous at the centres of nearby galaxies with masses similar to, or lower than the Milky Way. Their occurrence both in spirals and dwarf elliptical galaxies appears to be a strong function of total galaxy light or mass. Nucleation fractions are up to 100% for total galaxy magnitudes of M B = -19mag or total galaxy luminosities of about L B = 1010 L ⊙ and falling nucleation fractions for both smaller and higher galaxy masses. Although nuclear star clusters are so common, their formation mechanisms are still under debate. The two main formation scenarios proposed are the infall and subsequent merging of star clusters and the in-situ formation of stars at the center of a galaxy. Here, I review the state-of-the-art of nuclear star cluster observations concerning their structure, stellar populations and kinematics. These observations are used to constrain the proposed formation scenarios for nuclear star clusters. Constraints from observations show, that likely both cluster infall and in-situ star formation are at work. The relative importance of these two mechanisms is still subject of investigation.

  8. Effects of spiral arms on star formation in nuclear rings of barred-spiral galaxies

    SciTech Connect

    Seo, Woo-Young; Kim, Woong-Tae E-mail: wkim@astro.snu.ac.kr

    2014-09-01

    We use hydrodynamic simulations to study the effect of spiral arms on the star formation rate (SFR) in nuclear rings of barred-spiral galaxies. We find that spiral arms can be an efficient means of gas transport from the outskirts to the central parts, provided that the arms are rotating slower than the bar. While the ring star formation in models with no arms or corotating arms is active only during around the bar growth phase, arm-driven gas accretion both significantly enhances and prolongs the ring star formation in models with slow-rotating arms. The arm-enhanced SFR is larger by a factor of ∼3-20 than in the no-arm model, with larger values corresponding to stronger and slower arms. Arm-induced mass inflows also make dust lanes stronger. Nuclear rings in slow-arm models are ∼45% larger than in the no-arm counterparts. Star clusters that form in a nuclear ring exhibit an age gradient in the azimuthal direction only when the SFR is small, whereas no notable age gradient is found in the radial direction for models with arm-induced star formation.

  9. Star formation in the vicinity of nuclear black holes: young stellar objects close to Sgr A*

    NASA Astrophysics Data System (ADS)

    Jalali, B.; Pelupessy, F. I.; Eckart, A.; Portegies Zwart, S.; Sabha, N.; Borkar, A.; Moultaka, J.; Mužić, K.; Moser, L.

    2014-10-01

    It is often assumed that the strong gravitational field of a super-massive black hole disrupts an adjacent molecular cloud preventing classical star formation in the deep potential well of the black hole. Yet, young stars have been observed across the entire nuclear star cluster of the Milky Way including the region close (<0.5 pc) to the central black hole, Sgr A*. Here, we focus particularly on small groups of young stars, such as IRS 13N located 0.1 pc away from Sgr A*, which is suggested to contain about five embedded massive young stellar objects (<1 Myr). We perform three-dimensional hydrodynamical simulations to follow the evolution of molecular clumps orbiting about a 4 × 106 M⊙ black hole, to constrain the formation and the physical conditions of such groups. The molecular clumps in our models are assumed to be isothermal containing 100 M⊙ in <0.2 pc radius. Such molecular clumps exist in the circumnuclear disc of the Galaxy. In our highly eccentrically orbiting clump, the strong orbital compression of the clump along the orbital radius vector and perpendicular to the orbital plane causes the gas densities to increase to values higher than the tidal density of Sgr A*, which are required for star formation. Additionally, we speculate that the infrared excess source G2/DSO approaching Sgr A* on a highly eccentric orbit could be associated with a dust-enshrouded star that may have been formed recently through the mechanism supported by our models.

  10. Testing Theories of in situ Nuclear Star Formation in M31

    NASA Astrophysics Data System (ADS)

    Lockhart, Kelly; Lu, Jessica; Peiris, Hiranya; Rich, Robert Michael; Bouchez, Antonin H.; Matthews, Keith; Ghez, Andrea M.; Tremaine, Scott D.

    2017-01-01

    The nucleus of M31 has a number of unusual characteristics. There is an eccentric disk of old stars that extends out to a radius of less than 10 pc from the supermassive black hole (SMBH), a smaller disk of young (100-200 Myr) stars within 0.4 pc, and almost no gas. Questions abound as to how the young stars formed and how the eccentric disk remains coherent. Outflows from red giants and AGB stars in the old stellar eccentric disk could provide the material necessary to form the observed young circumnuclear stellar population. However, in order for this gas to be removed from the old stellar disk and funneled into the young star cluster, simulations by Chang et al. (2007) show that the old disk must precess slowly enough to allow the orbits of material in this disk to intersect. The colliding gas can then shock, cool, and fall into the circumnuclear star cluster. We use Keck/OSIRIS integral field spectroscopy in conjunction with dynamical models to constrain the precession rate of the old stellar eccentric disk in the nucleus of M31 and calculate the frequency of in situ star formation events in the young nuclear cluster.

  11. A dynamical model for gas flows, star formation and nuclear winds in galactic centres

    NASA Astrophysics Data System (ADS)

    Krumholz, Mark R.; Kruijssen, J. M. Diederik; Crocker, Roland M.

    2017-04-01

    We present a dynamical model for gas transport, star formation and winds in the nuclear regions of galaxies, focusing on the Milky Way's Central Molecular Zone (CMZ). In our model angular momentum and mass are transported by a combination of gravitational and bar-driven acoustic instabilities. In gravitationally unstable regions the gas can form stars, and the resulting feedback drives both turbulence and a wind that ejects mass from the CMZ. We show that the CMZ is in a quasi-steady state where mass deposited at large radii by the bar is transported inwards to a star-forming, ring-shaped region at ∼100 pc from the Galactic Centre, where the shear reaches a minimum. This ring undergoes episodic starbursts, with bursts lasting ∼5-10 Myr occurring at ∼20-40 Myr intervals. During quiescence the gas in the ring is not fully cleared, but is driven out of a self-gravitating state by the momentum injected by expanding supernova remnants. Starbursts also drive a wind off the star-forming ring, with a time-averaged mass flux comparable to the star formation rate. We show that our model agrees well with the observed properties of the CMZ, and places it near a star formation minimum within the evolutionary cycle. We argue that such cycles of bursty star formation and winds should be ubiquitous in the nuclei of barred spiral galaxies, and show that the resulting distribution of galactic nuclei on the Kennicutt-Schmidt relation is in good agreement with that observed in nearby galaxies.

  12. Nuclear star formation on 100 parsec scales: 10" resolution radio continuum, HI and CO observations

    NASA Technical Reports Server (NTRS)

    Turner, Jean L.; Ho, Paul T. P.; Martin, Robert N.

    1987-01-01

    A program of radio line and continuum studies of star formation in nearby spiral galaxies is reported. The objective is a search for hot gas and peculiar dynamics in spiral nuclei with 10" to 30" angular resolution. Vigorous star formation is found to be a common phenomenon in the inner kpc of spirals. Arcsecond resolution observations of radio continuum emission at 6 and 2 cm were used to separate the thermal and nonthermal radio components. It was found that thermal and nonthermal emission are well mixed even on sizescales of 10 pc. To understand the reason for the increased level of star formation activity in spiral nuclei, HI and CO emission in these galaxies is studied. The CO transition was detected in M51, M82, NGC 253, NGC 6946 and IC 342 with T sub a approx. 0.5 to 2.0 K, at 20" angular resolution. The dynamics and spatial distribution of nuclear gas are being studied using VLA HI maps with 30" synthesized beams. Evidence for noncircular motions in HI was found in the nucleus of IC 342.

  13. Nuclear star formation activity and black hole accretion in nearby Seyfert galaxies

    SciTech Connect

    Esquej, P.; Alonso-Herrero, A.; Hernán-Caballero, A.; González-Martín, O.; Ramos Almeida, C.; Rodríguez Espinosa, J. M.; Roche, P.; Mason, R. E.; Díaz-Santos, T.; Levenson, N. A.; Aretxaga, I.; Packham, C.

    2014-01-01

    Recent theoretical and observational works indicate the presence of a correlation between the star-formation rate (SFR) and active galactic nucleus (AGN) luminosity (and, therefore, the black hole accretion rate, M-dot {sub BH}) of Seyfert galaxies. This suggests a physical connection between the gas-forming stars on kpc scales and the gas on sub-pc scales that is feeding the black hole. We compiled the largest sample of Seyfert galaxies to date with high angular resolution (∼0.''4-0.''8) mid-infrared (8-13 μm) spectroscopy. The sample includes 29 Seyfert galaxies drawn from the AGN Revised Shapley-Ames catalog. At a median distance of 33 Mpc, our data allow us to probe nuclear regions on scales of ∼65 pc (median value). We found no general evidence of suppression of the 11.3 μm polycyclic aromatic hydrocarbon (PAH) emission in the vicinity of these AGN, and we used this feature as a proxy for the SFR. We detected the 11.3 μm PAH feature in the nuclear spectra of 45% of our sample. The derived nuclear SFRs are, on average, five times lower than those measured in circumnuclear regions of 600 pc in size (median value). However, the projected nuclear SFR densities (median value of 22 M {sub ☉} yr{sup –1} kpc{sup –2}) are a factor of 20 higher than those measured on circumnuclear scales. This indicates that the SF activity per unit area in the central ∼65 pc region of Seyfert galaxies is much higher than at larger distances from their nuclei. We studied the connection between the nuclear SFR and M-dot {sub BH} and showed that numerical simulations reproduce our observed relation fairly well.

  14. Nuclear activity versus star formation: emission-line diagnostics at ultraviolet and optical wavelengths

    NASA Astrophysics Data System (ADS)

    Feltre, A.; Charlot, S.; Gutkin, J.

    2016-03-01

    In the context of observations of the rest-frame ultraviolet and optical emission from distant galaxies, we explore the emission-line properties of photoionization models of active and inactive galaxies. Our aim is to identify new line-ratio diagnostics to discriminate between gas photoionization by active galactic nuclei (AGN) and star formation. We use a standard photoionization code to compute the emission from AGN narrow-line regions and compare this with calculations of the nebular emission from star-forming galaxies achieved using the same code. We confirm the appropriateness of widely used optical spectral diagnostics of nuclear activity versus star formation and explore new diagnostics at ultraviolet wavelengths. We find that combinations of a collisionally excited metal line or line multiplet, such as C IV λλ1548, 1551, O III] λλ1661, 1666, N III] λ1750, [Si III] λ1883+Si III] λ1892 and [C III] λ1907+C III] λ1909, with the He II λ1640 recombination line are individually good discriminants of the nature of the ionizing source. Diagrams involving at least three of these lines allow an even more stringent distinction between active and inactive galaxies, as well as valuable constraints on interstellar gas parameters and the shape of the ionizing radiation. Several line ratios involving Ne-based emission lines, such as [Ne IV] λ2424, [Ne III] λ3343 and [Ne V] λ3426, are also good diagnostics of nuclear activity. Our results provide a comprehensive framework to identify the sources of photoionization and physical conditions of the ionized gas from the ultraviolet and optical nebular emission from galaxies. This will be particularly useful to interpret observations of high-redshift galaxies with future facilities, such as the James Webb Space Telescope and extremely large ground-based telescopes.

  15. DO MOST ACTIVE GALACTIC NUCLEI LIVE IN HIGH STAR FORMATION NUCLEAR CUSPS?

    SciTech Connect

    Mushotzky, Richard F.; Shimizu, T. Taro; Meléndez, Marcio; Koss, Michael

    2014-02-01

    We present early results of the Herschel PACS (70 and 160 μm) and SPIRE (250, 350, and 500 μm) survey of 313 low redshift (z < 0.05), ultra-hard X-ray (14-195 keV) selected active galactic nuclei (AGNs) from the 58 month Swift/Burst Alert Telescope catalog. Selection of AGNs from ultra-hard X-rays avoids bias from obscuration, providing a complete sample of AGNs to study the connection between nuclear activity and star formation in host galaxies. With the high angular resolution of PACS, we find that >35% and >20% of the sources are ''point-like'' at 70 and 160 μm respectively and many more have their flux dominated by a point source located at the nucleus. The inferred star formation rates (SFRs) of 0.1-100 M {sub ☉} yr{sup –1} using the 70 and 160 μm flux densities as SFR indicators are consistent with those inferred from Spitzer Ne II fluxes, but we find that 11.25 μm polycyclic aromatic hydrocarbon data give ∼3× lower SFR. Using GALFIT to measure the size of the far-infrared emitting regions, we determined the SFR surface density (M {sub ☉} yr{sup –1} kpc{sup –2}) for our sample, finding that a significant fraction of these sources exceed the threshold for star formation driven winds (0.1 M {sub ☉} yr{sup –1} kpc{sup –2})

  16. DISSIPATIONLESS FORMATION AND EVOLUTION OF THE MILKY WAY NUCLEAR STAR CLUSTER

    SciTech Connect

    Antonini, Fabio; Capuzzo-Dolcetta, Roberto; Mastrobuono-Battisti, Alessandra; Merritt, David

    2012-05-10

    In one widely discussed model for the formation of nuclear star clusters (NSCs), massive globular clusters spiral into the center of a galaxy and merge to form the nucleus. It is now known that at least some NSCs coexist with supermassive black holes (SMBHs); this is the case, for instance, in the Milky Way. In this paper, we investigate how the presence of an SMBH at the center of the Milky Way impacts the merger hypothesis for the formation of its NSC. Starting from a model consisting of a low-density nuclear stellar disk and the SMBH, we use direct N-body simulations to follow the successive inspiral and merger of globular clusters. The clusters are started on circular orbits of radius 20 pc, and their initial masses and radii are set up in such a way as to be consistent with the galactic tidal field at that radius. These clusters, decayed orbitally in the central region due to their large mass, were followed in their inspiral events; as a result, the total accumulated mass by Almost-Equal-To 10 clusters is about 1.5 Multiplication-Sign 10{sup 7} M{sub Sun }. Each cluster is disrupted by the SMBH at a distance of roughly 1 pc. The density profile that results after the final inspiral event is characterized by a core of roughly this radius and an envelope with density that falls off {rho} {approx} r{sup -2}. These properties are similar to those of the Milky Way NSC, with the exception of the core size, which in the Milky Way is somewhat smaller. But by continuing the evolution of the model after the final inspiral event, we find that the core shrinks substantially via gravitational encounters in a time (when scaled to the Milky Way) of 10 Gyr as the stellar distribution evolves toward a Bahcall-Wolf cusp. We also show that the luminosity function of the Milky Way NSC is consistent with the hypothesis that 1/2 of the mass comes from old ({approx}10 Gyr) stars, brought in by globular clusters, with the other half due to continuous star formation. We conclude that

  17. A SINFONI view of the nuclear activity and circumnuclear star formation in NGC 4303

    NASA Astrophysics Data System (ADS)

    Riffel, Rogemar A.; Colina, L.; Storchi-Bergmann, T.; Piqueras López, J.; Arribas, S.; Riffel, R.; Pastoriza, M.; Sales, Dinalva A.; Dametto, N. Z.; Labiano, A.; Davies, R. I.

    2016-10-01

    We present new maps of emission-line flux distributions and kinematics in both ionized (traced by H I and [Fe II] lines) and molecular (H2) gas of the inner 0.7 × 0.7 kpc2 of the galaxy NGC 4303, with a spatial resolution 40-80 pc and velocity resolution 90-150 km s- 1 obtained from near-IR integral field spectroscopy using the Very Large Telescope instrument SINFONI. The most prominent feature is a 200-250 pc ring of circumnuclear star-forming regions. The emission from ionized and molecular gas shows distinct flux distributions: while the strongest H I and [Fe II] emission comes from regions in the west side of the ring (ages ˜ 4 Myr), the H2 emission is strongest at the nucleus and in the east side of the ring (ages > 10 Myr). We find that regions of enhanced hot H2 emission are anti-correlated with those of enhanced [Fe II] and H I emission, which can be attributed to post-starburst regions that do not have ionizing photons anymore but still are hot enough (≈2000 K) to excite the H2 molecule. The line ratios are consistent with the presence of an active galactic nucleus at the nucleus. The youngest regions have stellar masses in the range 0.3-1.5 × 105 M⊙ and ionized and hot molecular gas masses of ˜0.25-1.2 × 104 M⊙ and ˜2.5-5 M⊙, respectively. The stellar and gas velocity fields show a rotation pattern, with the gas presenting larger velocity amplitudes than the stars, with a deviation observed for the H2 along the nuclear bar, where increased velocity dispersion is also observed, possibly associated with non-circular motions along the bar. The stars in the ring show smaller velocity dispersion than the surroundings, which can be attributed to a cooler dynamics due to their recent formation from cool gas.

  18. Star Formation in Galaxies

    NASA Technical Reports Server (NTRS)

    1987-01-01

    Topics addressed include: star formation; galactic infrared emission; molecular clouds; OB star luminosity; dust grains; IRAS observations; galactic disks; stellar formation in Magellanic clouds; irregular galaxies; spiral galaxies; starbursts; morphology of galactic centers; and far-infrared observations.

  19. Nuclear Star Formation in the Hot-Spot Galaxy NGC 2903

    NASA Technical Reports Server (NTRS)

    Alonso-Herrero, A.; Ryder, S. D.; Knapen, J. H.

    1994-01-01

    We present high-resolution near-infrared imaging obtained using adaptive optics and HST/NICMOS and ground-based spectroscopy of the hot-spot galaxy NGC 2903. Our near-infrared resolution imaging enables us to resolve the infrared hot spots into individual young stellar clusters or groups of these. The spatial distribution of the stellar clusters is not coincident with that of the bright H II regions, as revealed by the HST/NICMOS Pace image. Overall, the circumnuclear star formation in NGC 2903 shows a ring-like morphology with an approximate diameter of 625 pc. The SF properties of the stellar clusters and H II regions have been studied using the photometric and spectroscopic information in conjunction with evolutionary synthesis models. The population of bright stellar clusters shows a very narrow range of ages, 4 to 7 x 10(exp 6) yr after the peak of star formation, or absolute ages 6.5 to 9.5 x 10(exp 6) yr (for the assumed short-duration Gaussian bursts), and luminosities similar to the clusters found in the Antennae interacting galaxy. This population of young stellar clusters accounts for some 7 - 12% of the total stellar mass in the central 625 pc of NGC 2903. The H II regions in the ring of star formation have luminosities close to that of the super-giant H II region 30 Doradus, they are younger than the stellar clusters, and will probably evolve into bright infrared stellar clusters similar to those observed today. We find that the star formation efficiency in the central regions of NGC 2903 is higher than in normal galaxies, approaching the lower end of infrared luminous galaxies.

  20. Star formation and nuclear activity in the blue early-type galaxy NGC 5373

    NASA Astrophysics Data System (ADS)

    Zaidi, Tayeb; Miller, Brendan P.; Gallo, Elena; Alfvin, Erik; Martinkus, Charlotte; Molter, Edward

    2015-01-01

    We present new optical and X-ray observations of NGC 5373, an isolated star-forming elliptical that has a stellar mass of 7e10 solar and lies at a distance of 175 Mpc. Our B and R band Magellan IMACS imaging substantially improves on SDSS resolution and sensitivity, enabling accurate modeling of the galaxy surface brightness profile. As expected from its mass, NGC 5373 is a core galaxy with a best-fit Sersic profile of n~3.8; no prominent tidal tails or shells are found, although there are slight residual asymmetries. The H-alpha emission in the SDSS spectrum is narrow, and the line ratios confirm a star-forming classification in the BPT diagram, near the transition/composite line. The star formation rate is about 6 solar masses per year, making NGC 5373 an extreme outlier relative to typical local early-type galaxies of similar mass. Our 50 ks Chandra ACIS-S exposure provides a clear detection of a central X-ray source, with a hardness ratio consistent with a power-law photon index of 2.0+/-0.5. The unabsorbed luminosity is Lx = 2e40 erg/s over 0.3-8 keV. Comparison with a MARX simulated point spread function suggests the central source may be extended, for example due to contributions from one or more unresolved high-mass X-ray binaries, as might be present given the high star formation rate. For a black hole of 1.6e8 solar masses as predicted from scaling relations, Lx/Ledd is then around 1e-6 (or potentially lower).

  1. SIRTF and star formation

    NASA Technical Reports Server (NTRS)

    Shu, Frank H.

    1988-01-01

    Four problems in the field of star formation that can be attacked to advantage with SIRTF are discussed: (1) the patterns of star formation in spiral galaxies, (2) the physical mechanism for bimodal star formation, (3) the nature of bipolar outflows from young stellar objects, and (4) the birth of brown dwarfs. In each case, SIRTF can provide the crucial combination of high angular resolution with great sensitivity over a broad range of wavelengths that is needed to address the relevant issues.

  2. GLOBAL STAR FORMATION REVISITED

    SciTech Connect

    Silk, Joseph; Norman, Colin E-mail: norman@stsci.edu

    2009-07-20

    A general treatment of disk star formation is developed from a dissipative multiphase model, with the dominant dissipation due to cloud collisions. The Schmidt-Kennicutt (SK) law emerges naturally for star-forming disks and starbursts. We predict that there should be an inverse correlation between Tully-Fisher law and SK law residuals. The model is extended to include a multiphase treatment of supernova feedback that leads to a turbulent pressure-regulated generalization of the star formation law and is applicable to gas-rich starbursts. Enhanced pressure, as expected in merger-induced star formation, enhances star formation efficiency. An upper limit is derived for the disk star formation rate in starbursts that depends on the ratio of global ISM to cloud pressures. We extend these considerations to the case where the interstellar gas pressure in the inner galaxy is dominated by outflows from a central active galactic nucleus (AGN). During massive spheroid formation, AGN-driven winds trigger star formation, resulting in enhanced supernova feedback and outflows. The outflows are comparable to the AGN-boosted star formation rate and saturate in the super-Eddington limit. Downsizing of both SMBH and spheroids is a consequence of AGN-driven positive feedback. Bondi accretion feeds the central black hole with a specific accretion rate that is proportional to the black hole mass. AGN-enhanced star formation is mediated by turbulent pressure and relates spheroid star formation rate to black hole accretion rate. The relation between black hole mass and spheroid velocity dispersion has a coefficient (Salpeter time to gas consumption time ratio) that provides an arrow of time. Highly efficient, AGN-boosted star formation can occur at high redshift.

  3. Nuclear and gravitational energies in stars

    SciTech Connect

    Meynet, Georges; Ekström, Sylvia; Courvoisier, Thierry

    2014-05-09

    The force that governs the evolution of stars is gravity. Indeed this force drives star formation, imposes thermal and density gradients into stars at hydrostatic equilibrium and finally plays the key role in the last phases of their evolution. Nuclear power in stars governs their lifetimes and of course the stellar nucleosynthesis. The nuclear reactions are at the heart of the changes of composition of the baryonic matter in the Universe. This change of composition, in its turn, has profound consequences on the evolution of stars and galaxies. The energy extracted from the gravitational, respectively nuclear reservoirs during the lifetimes of stars of different masses are estimated. It is shown that low and intermediate mass stars (M < 8 M{sub ⊙}) extract roughly 90 times more energy from their nuclear reservoir than from their gravitational one, while massive stars (M > 8 M{sub ⊙}), which explode in a supernova explosion, extract more than 5 times more energy from the gravitational reservoir than from the nuclear one. We conclude by discussing a few important nuclear reactions and their link to topical astrophysical questions.

  4. Observational constraints on the formation and evolution of the Milky Way nuclear star cluster with Keck and Gemini

    NASA Astrophysics Data System (ADS)

    Do, Tuan; Ghez, Andrea; Morris, Mark; Lu, Jessica; Chappell, Samantha; Feldmeier-Krause, Anja; Kerzendorf, Wolfgang; Martinez, Gregory David; Murray, Norm; Winsor, Nathan

    2017-01-01

    We summarize work on the central parsec of the Galactic center based on imaging and spectroscopic observations at the Keck and Gemini telescopes. These observations include stellar positions in two dimension and the velocity in three dimensions. Spectroscopic observations also enables measurements of the physical properties of individual stars, such as the spectral type and in some cases the effective temperature, metallicity, and surface gravity. These observations show a complex stellar population with a young (4-6 Myr) compact star cluster in the central 0.5 pc embedded in in an older and much more massive nuclear star cluster. Surprisingly, the old late-type giants do not show a cusp profile as long been expected from theoretical work. The majority of the stars have higher than solar metallicity, with only about 6% of the stars having [M/Fe] < -0.5, which is consistent with an origin from the MW disk.

  5. Luminous Infrared Galaxies. III. Multiple Merger, Extended Massive Star Formation, Galactic Wind, and Nuclear Inflow in NGC 3256

    NASA Astrophysics Data System (ADS)

    Lípari, S.; Díaz, R.; Taniguchi, Y.; Terlevich, R.; Dottori, H.; Carranza, G.

    2000-08-01

    ouflow axis (at P.A.~160deg). We analyze in detail the physical conditions in the giant H II regions located in the asymmetric spiral arms, the two main optical nuclei, and the outflow component (using long-slit spectroscopy, plus standard models of photoionization, shocks, and starbursts). We present four detailed emission-line ratios (N II/Hα, S II/Hα, S II/S II), and FWHM (Hα) maps for the central region (30''×30'' rmax~22''~4 kpc), with a spatial resolution of 1". In the central region (r~5-6 kpc) we detected that the nuclear starburst and the extended giant H II regions (in the spiral arms) have very similar properties, i.e., high metallicity and low-ionization spectra, with Teff=35,000 K, solar abundance, a range of Te~6000-7000 K, and Ne~100-1000 cm-3. The nuclear and extended outflow shows properties typical of galactic wind/shocks, associated with the nuclear starburst. We suggest that the interaction between dynamical effects, the galactic wind (outflow), low-energy cosmic rays, and the molecular+ionized gas (probably in the inflow phase) could be the possible mechanism that generate the ``similar extended properties in the massive star formation, at a scale of 5-6 kpc!'' We have also studied the presence of the close merger/interacting systems NGC 3256C (at ~150 kpc, ΔV=-100 km s-1) and the possible association between the NGC 3256 and 3263 groups of galaxies. In conclusion, these results suggest that NGC 3256 is the product of a multiple merger, which generated an extended massive star formation process with an associated galactic wind plus a nuclear inflow. Therefore, NGC 3256 is another example in which the relation between mergers and extreme starburst (and the powerful galactic wind, ``multiple'' Type II supernova explosions) play an important role in the evolution of galaxies (the hypothesis of Rieke et al., Joseph et al., Terlevich et al., Heckman et al., and Lípari et al.). Based on observations obtained at the Hubble Space Telescope (HST; Wide

  6. Star formation history of early-type galaxies in low density environments. I. Nuclear line-strength indices

    NASA Astrophysics Data System (ADS)

    Longhetti, M.; Rampazzo, R.; Bressan, A.; Chiosi, C.

    1998-06-01

    This paper is the first of a series \\cite[(Longhetti et al. 1997a,b)]{lon97} dedicated to the study of the star formation history in early-type galaxies which show fine structures and/or signatures of interaction. It presents nuclear line-strength indices for a sample composed of 21 shell galaxies, from the \\cite[Malin & Carter (1983)]{mal83} southern survey, and 30 members of isolated interacting pairs, from the \\cite[Reduzzi & Rampazzo (1995)]{red95} catalogue, located in low density environments. The spectral range covers 3700 Angstroms < lambda < 5700 Angstroms at 2.1 Angstroms FWHM resolution. We measure 16 red (lambda > 4200 Angstroms) indices defined by the Lick Group. Measures have been transformed into the Lick-IDS ``standard'' system. The procedure has been tested on a set of 5 elliptical galaxies selected from the \\cite[Gonzalez (1993)]{gon93} sample. We derive also three blue (lambda < 4200) indices, namely Delta (4000 Angstroms) defined by \\cite[Hamilton (1985)]{ham85}, H+K(CaII) and Hdelta /FeI defined by \\cite[Rose (1984, 1985)]{ros84}. Blue indices are correlated to the age of the last starburst occurred in a galaxy \\cite[(Leonardi & Rose 1996)]{leo96}. The determination of these indices, the estimate of the measurement errors and the correction for the galaxies velocity dispersions are discussed in detail. In the Appendix A we present the indices for a set of hot stars (T> 10000 K) which may be used for extending W92 fitting functions toward high temperatures. Based on observations obtained at ESO, La Silla, Chile. Tables 1-8 are also available in electronic form at CDS and Tables 9-15 are only available in electronic form at CDS: via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html

  7. The mid-infrared emission of narrow-line active galactic nuclei: Star formation, nuclear activity, and two populations revealed by WISE

    SciTech Connect

    Rosario, David J.; Burtscher, Leonard; Davies, Richard; Genzel, Reinhard; Lutz, Dieter; Tacconi, Linda J.

    2013-12-01

    We explore the nature of the long-wavelength mid-infrared (MIR) emission of a sample of 13,000 local Type II (narrow-line) active galactic nuclei (AGNs) from the Sloan Digital Sky Survey (SDSS) using 12 μm and 22 μm photometry from the WISE all-sky survey. In combination with FIRST 1.4 GHz photometry, we show that AGNs divide into two relatively distinct populations or 'branches' in the plane of MIR and radio luminosity. Seyfert galaxies lie almost exclusively on an MIR-bright branch (Branch A), while low-ionization nuclear emission line galaxies (LINERs) are split evenly into Branch A and the MIR-faint Branch B. We devise various tests to constrain the processes that define the branches, including a comparison to the properties of pure star-forming inactive galaxies on the MIR-radio plane. We demonstrate that the total MIR emission of objects on Branch A, including most Seyfert galaxies, is governed primarily by host star formation, with ≈15% of the 22 μm luminosity coming from AGN-heated dust. This implies that ongoing dusty star formation is a general property of Seyfert host galaxies. We show that the 12 μm broadband luminosity of AGNs on Branch A is suppressed with respect to star-forming galaxies, possibly due to the destruction of PAHs or deeper 10 μm Si absorption in AGNs. We uncover a correlation between the MIR luminosity and [O III] λ5007 luminosity in AGNs. This suggests a relationship between the star formation rate and nuclear luminosity in the AGN population, but we caution on the importance of selection effects inherent to such AGN-dominated emission-line galaxies in driving such a correlation. We highlight the MIR-radio plane as a useful tool in comparative studies of star formation and nuclear activity in AGNs.

  8. Star Formation in Irregular Galaxies.

    ERIC Educational Resources Information Center

    Hunter, Deidre; Wolff, Sidney

    1985-01-01

    Examines mechanisms of how stars are formed in irregular galaxies. Formation in giant irregular galaxies, formation in dwarf irregular galaxies, and comparisons with larger star-forming regions found in spiral galaxies are considered separately. (JN)

  9. Star formation history of early-type galaxies in low density environments. V. Blue line-strength indices for the nuclear region

    NASA Astrophysics Data System (ADS)

    Longhetti, M.; Bressan, A.; Chiosi, C.; Rampazzo, R.

    1999-05-01

    We analyze the star formation properties of a sample of 21 shell galaxies and 30 early-type galaxies members of interacting pairs, located in low density environments (Longhetti et al. 1998a, 1998b). The study is based on new models developed to interpret the information coming from `blue' Hdelta /FeI, H+K(CaII) and Delta 4000 line-strength indices proposed by Rose (1984; 1985) and Hamilton (1985). We find that the last star forming event that occurred in the nuclear region of shell galaxies is statistically old (from 0.1 up to several Gyr) with respect to the corresponding one in the sub-sample of pair galaxies (<0.1 Gyr or even ongoing star formation). If the stellar activity is somehow related to the formation of shells, as predicted by several dynamical models of galaxy interaction, shells have to be considered long lasting structures. Since pair members show evidence of very recent star formation, we suggest that either large reservoirs of gas have to be present to maintain active star formation, if these galaxies are on periodic orbits, or most of the pair members in the present sample are experiencing unbound encounters. Table~2 is available in electronic form only, at CDS: via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html

  10. The Nuclear Cluster of the Milky Way: Star Formation and Velocity Dispersion in the Central 0.5 Parsec

    NASA Astrophysics Data System (ADS)

    Krabbe, A.; Genzel, R.; Eckart, A.; Najarro, F.; Lutz, D.; Cameron, M.; Kroker, H.; Tacconi-Garman, L. E.; Thatte, N.; Weitzel, L.; Drapatz, S.; Geballe, T.; Sternberg, A.; Kudritzki, R.

    1995-07-01

    We report the first results of an extensive new study of the Galactic center stellar cluster. The central parsec is powered by a cluster of about two dozen luminous and helium-rich blue supergiants/Wolf-Rayet stars (Teff ~ 20,000--30,000 K) with ZAMS masses up to ~100 M⊙. The most likely scenario for the formation of the massive stars is a small star formation burst between 3 x 106 and 7 x 106 years ago. In this scenario the Galactic center is presently in a short-lived, post--main-sequence "wind phase." In addition, there is evidence for another star formation event about 108 years ago, as well as for recently formed massive stars that may have been transported into the central core along with orbiting gas streamers. The radial velocity dispersion of 35 early- and late-type stars with distances of 1"--12" from Sgr A* is 154 +/- 19 km s-1. Our new results strongly favor the existence of a central dark mass of ~3 x 106 M⊙ (density >= 108.5 M⊙ pc-3, M/L >= 10 M⊙/L⊙) within 0.14 pc of the dynamic center.

  11. TESTING DIAGNOSTICS OF NUCLEAR ACTIVITY AND STAR FORMATION IN GALAXIES AT z > 1

    SciTech Connect

    Trump, Jonathan R.; Barro, Guillermo; Koo, David C.; Faber, S. M.; Kocevski, Dale D.; Yan, Renbin; Juneau, Stephanie; McLean, Ian S.; Perez-Gonzalez, Pablo G.; Villar, Victor

    2013-01-20

    We present some of the first science data with the new Keck/MOSFIRE instrument to test the effectiveness of different AGN/SF diagnostics at z {approx} 1.5. MOSFIRE spectra were obtained in three H-band multi-slit masks in the GOODS-S field, resulting in 2 hr exposures of 36 emission-line galaxies. We compare X-ray data with the traditional emission-line ratio diagnostics and the alternative mass-excitation and color-excitation diagrams, combining new MOSFIRE infrared data with previous HST/WFC3 infrared spectra (from the 3D-HST survey) and multiwavelength photometry. We demonstrate that a high [O III]/H{beta} ratio is insufficient as an active galactic nucleus (AGN) indicator at z > 1. For the four X-ray-detected galaxies, the classic diagnostics ([O III]/H{beta} versus [N II]/H{alpha} and [S II]/H{alpha}) remain consistent with X-ray AGN/SF classification. The X-ray data also suggest that 'composite' galaxies (with intermediate AGN/SF classification) host bona fide AGNs. Nearly {approx}2/3 of the z {approx} 1.5 emission-line galaxies have nuclear activity detected by either X-rays or the classic diagnostics. Compared to the X-ray and line ratio classifications, the mass-excitation method remains effective at z > 1, but we show that the color-excitation method requires a new calibration to successfully identify AGNs at these redshifts.

  12. Testing Diagnostics of Nuclear Activity and Star Formation in Galaxies at z > 1

    NASA Astrophysics Data System (ADS)

    Trump, Jonathan R.; Konidaris, Nicholas P.; Barro, Guillermo; Koo, David C.; Kocevski, Dale D.; Juneau, Stéphanie; Weiner, Benjamin J.; Faber, S. M.; McLean, Ian S.; Yan, Renbin; Pérez-González, Pablo G.; Villar, Victor

    2013-01-01

    We present some of the first science data with the new Keck/MOSFIRE instrument to test the effectiveness of different AGN/SF diagnostics at z ~ 1.5. MOSFIRE spectra were obtained in three H-band multi-slit masks in the GOODS-S field, resulting in 2 hr exposures of 36 emission-line galaxies. We compare X-ray data with the traditional emission-line ratio diagnostics and the alternative mass-excitation and color-excitation diagrams, combining new MOSFIRE infrared data with previous HST/WFC3 infrared spectra (from the 3D-HST survey) and multiwavelength photometry. We demonstrate that a high [O III]/Hβ ratio is insufficient as an active galactic nucleus (AGN) indicator at z > 1. For the four X-ray-detected galaxies, the classic diagnostics ([O III]/Hβ versus [N II]/Hα and [S II]/Hα) remain consistent with X-ray AGN/SF classification. The X-ray data also suggest that "composite" galaxies (with intermediate AGN/SF classification) host bona fide AGNs. Nearly ~2/3 of the z ~ 1.5 emission-line galaxies have nuclear activity detected by either X-rays or the classic diagnostics. Compared to the X-ray and line ratio classifications, the mass-excitation method remains effective at z > 1, but we show that the color-excitation method requires a new calibration to successfully identify AGNs at these redshifts. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555. Also based on data obtained at the W. M. Keck Observatory, made possible by the generous financial support of the W. M. Keck Foundation and operated as a scientific partnership among Caltech, the University of California, and NASA.

  13. Binary stars - Formation by fragmentation

    NASA Technical Reports Server (NTRS)

    Boss, Alan P.

    1988-01-01

    Theories of binary star formation by capture, separate nuclei, fission and fragmentation are compared, assessing the success of theoretical attempts to explain the observed properties of main-sequence binary stars. The theory of formation by fragmentation is examined, discussing the prospects for checking the theory against observations of binary premain-sequence stars. It is concluded that formation by fragmentation is successful at explaining many of the key properties of main-sequence binary stars.

  14. Gaining Insight into Star Formation: Resolved Star Formation Laws

    NASA Astrophysics Data System (ADS)

    Liebst, Kelley; Scowen, Paul A.

    2014-06-01

    Until recently astronomers have used star formation laws to measure the star formation rate and star formation efficiency of galaxies only on global scales because of the poor resolution of available data. What I am now capable of producing is a spatially resolved star formation law that can provide direct insight into the physical processes that govern star formation and assess the short-term nature of bursts of star formation and the longer-term nature of larger-scale events that can dictate the global distribution of stars and the ultimate fate of a galaxy as a whole. I am using exquisite narrowband optical data from a variety of sources, including the Hubble Space Telescope, and Kitt Peak National Observatory, etc., in conjunction with infrared data from the Spitzer Infrared Nearby Galaxy Survey and the Spitzer Local Volume Legacy survey, neutral gas data from The HI Nearby Galaxy Survey, and molecular gas data from the Berkeley-Illinois-Maryland Association Survey of Nearby Galaxies, to provide star formation rates and star formation efficiencies on previously inaccessible small spatial scales across a suite of galaxies that represent a range of star formation environments and scales. My sample includes 18 spiral galaxies ranging from 2.1 to 15.1 Mpc in distance and offers a large range of morphological types (i.e. a large range of star formation environments). I am using these data to test different models of star formation modes under a variety of physical conditions and relate the variations I observe to the known local physical conditions and the associated star formation histories for each locale within each galaxy.This is the heart of the matter - that the nature and evolution of the local physical environment intimately influences how stars can form, how quickly and how massive those stars are allowed to form, and as a result how they shape the local conditions for subsequent star formation. It is this tracking of the stellar ecology that is vital for

  15. Star formation in the multiverse

    SciTech Connect

    Bousso, Raphael; Leichenauer, Stefan

    2009-03-15

    We develop a simple semianalytic model of the star formation rate as a function of time. We estimate the star formation rate for a wide range of values of the cosmological constant, spatial curvature, and primordial density contrast. Our model can predict such parameters in the multiverse, if the underlying theory landscape and the cosmological measure are known.

  16. Induced star formation in interacting galaxies

    NASA Technical Reports Server (NTRS)

    Kennicutt, R. C.; Roettiger, K. A.; Keel, W. C.; Vanderhulst, J. M.; Hummel, E.

    1987-01-01

    Measurements of H alpha emission line fluxes and FIR fluxes in approx. 100 interacting spirals were used to investigate the effects of close tidal interactions on the disk and nuclear star formation rates in galaxies. Two samples of interacting spirals were studied, a complete sample of close pairs, and a set of strongly perturbed systems from the Arp atlas. Both the integrated H alpha luminosities and FIR luminosities are enhanced in the interacting galaxies, indicating that the encounters indeed trigger massive star formation in many cases. The response of individual galaxies is highly variable, however. A majority of the interacting spirals exhibit normal star formation rates, while a small fraction are undergoing bursts with luminosities which are rarely, if ever, observed in noninteracting systems. Virtually all of the latter are in the Arp sample, indicating that the Arp atlas is heavily biased to the most active star forming systems.

  17. Physics of primordial star formation

    NASA Astrophysics Data System (ADS)

    Yoshida, Naoki

    2012-09-01

    The study of primordial star formation has a history of nearly sixty years. It is generally thought that primordial stars are one of the key elements in a broad range of topics in astronomy and cosmology, from Galactic chemical evolution to the formation of super-massive blackholes. We review recent progress in the theory of primordial star formation. The standard theory of cosmic structure formation posits that the present-day rich structure of the Universe developed through gravitational amplification of tiny matter density fluctuations left over from the Big Bang. It has become possible to study primordial star formation rigorously within the framework of the standard cosmological model. We first lay out the key physical processes in a primordial gas. Then, we introduce recent developments in computer simulations. Finally, we discuss prospects for future observations of the first generation of stars.

  18. Star Formation for Predictive Primordial Galaxy Formation

    NASA Astrophysics Data System (ADS)

    Milosavljević, Miloš; Safranek-Shrader, Chalence

    The elegance of inflationary cosmology and cosmological perturbation theory ends with the formation of the first stars and galaxies, the initial sources of light that launched the phenomenologically rich process of cosmic reionization. Here we review the current understanding of early star formation, emphasizing unsolved problems and technical challenges. We begin with the first generation of stars to form after the Big Bang and trace how they influenced subsequent star formation. The onset of chemical enrichment coincided with a sharp increase in the overall physical complexity of star forming systems. Ab-initio computational treatments are just now entering the domain of the predictive and are establishing contact with local observations of the relics of this ancient epoch.

  19. Nuclear Physics for Compact Stars

    SciTech Connect

    Baldo, M.

    2009-05-04

    A brief overview is given of the different lines of research developed under the INFN project 'Compact Stellar Objects and Dense Hadronic Matter' (acronym CT51). The emphasis of the project is on the structure of Neutron Stars (NS) and related objects. Starting from crust, the different Nuclear Physics problems are described which are encountered going inside a NS down to its inner core. The theoretical challenges and the observational inputs are discussed in some detail.

  20. Star formation across galactic environments

    NASA Astrophysics Data System (ADS)

    Young, Jason

    I present here parallel investigations of star formation in typical and extreme galaxies. The typical galaxies are selected to be free of active galactic nuclei (AGN), while the extreme galaxies host quasars (the most luminous class of AGN). These two environments are each insightful in their own way; quasars are among the most violent objects in the universe, literally reshaping their host galaxies, while my sample of AGN-free star-forming galaxies ranges from systems larger than the Milky Way to small galaxies which are forming stars at unsustainably high rates. The current paradigm of galaxy formation and evolution suggests that extreme circumstances are key stepping stones in the assembly of galaxies like our Milky Way. To test this paradigm and fully explore its ramifications, this dual approach is needed. My sample of AGN-free galaxies is drawn from the KPNO International Spectroscopic Survey. This Halpha-selected, volume-limited survey was designed to detect star-forming galaxies without a bias toward continuum luminosity. This type of selection ensures that this sample is not biased toward galaxies that are large or nearby. My work studies the KISS galaxies in the mid- and far-infrared using photometry from the IRAC and MIPS instruments aboard the Spitzer Space Telescope. These infrared bands are particularly interesting for star formation studies because the ultraviolet light from young stars is reprocessed into thermal emission in the far-infrared (24mum MIPS) by dust and into vibrational transitions features in the mid-infrared (8.0mum IRAC) by polycyclic aromatic hydrocarbons (PAHs). The work I present here examines the efficiencies of PAH and thermal dust emission as tracers of star-formation rates over a wide range of galactic stellar masses. I find that the efficiency of PAH as a star-formation tracer varies with galactic stellar mass, while thermal dust has a highly variable efficiency that does not systematically depend on galactic stellar mass

  1. Trajectories of Cepheid variable stars in the Galactic nuclear bulge

    NASA Astrophysics Data System (ADS)

    Matsunaga, Noriyuki

    2012-06-01

    The central region of our Galaxy provides us with a good opportunity to study the evolution of galactic nuclei and bulges because we can observe various phenomena in detail at the proximity of 8 kpc. There is a hierarchical alignment of stellar systems with different sizes; from the extended bulge, the nuclear bulge, down to the compact cluster around the central supermassive blackhole. The nuclear bulge contains stars as young as a few Myr, and even hosts the ongoing star formation. These are in contrast to the more extended bulge which are dominated by old stars, ~10Gyr. It is considered that the star formation in the nuclear bulge is caused by fresh gas provided from the inner disk. In this picture, the nuclear bulge plays an important role as the interface between the gas supplier, the inner disk, and the galactic nucleus. Kinematics of young stars in the nuclear bulge is important to discuss the star forming process and the gas circulation in the Galactic Center. We here propose spectroscopic observations of Cepheid variable stars, ~25 Myr, which we recently discovered in the nuclear bulge. The spectra taken in this proposal will allow timely estimates of the systemic velocities of the variable stars.

  2. The formation of sunlike stars.

    PubMed

    Lada, C J; Shu, F H

    1990-05-04

    Understanding how stars like the sun formed constitutes one of the principal challenges confronting modern astrophysics. In recent years, advances in observational technology, particularly at infrared and millimeter wavelengths, have produced an avalanche of critical data and unexpected discoveries about the process of star formation, which is blocked from external view at optical and shorter wavelengths by an obscuring blanket of interstellar dust. Fueled by this new knowledge, a comprehensive empirical picture of stellar genesis is beginning to emerge, laying the foundations for a coherent theory of the birth of sunlike stars.

  3. Formation of the first stars.

    PubMed

    Bromm, Volker

    2013-11-01

    Understanding the formation of the first stars is one of the frontier topics in modern astrophysics and cosmology. Their emergence signalled the end of the cosmic dark ages, a few hundred million years after the Big Bang, leading to a fundamental transformation of the early Universe through the production of ionizing photons and the initial enrichment with heavy chemical elements. We here review the state of our knowledge, separating the well understood elements of our emerging picture from those where more work is required. Primordial star formation is unique in that its initial conditions can be directly inferred from the Λ cold dark matter (ΛCDM) model of cosmological structure formation. Combined with gas cooling that is mediated via molecular hydrogen, one can robustly identify the regions of primordial star formation, the so-called minihalos, having total masses of ~10(6) M⊙ and collapsing at redshifts z ≈ 20-30. Within this framework, a number of studies have defined a preliminary standard model, with the main result that the first stars were predominantly massive. This model has recently been modified to include a ubiquitous mode of fragmentation in the protostellar disks, such that the typical outcome of primordial star formation may be the formation of a binary or small multiple stellar system. We will also discuss extensions to this standard picture due to the presence of dynamically significant magnetic fields, of heating from self-annihalating WIMP dark matter, or cosmic rays. We conclude by discussing possible strategies to empirically test our theoretical models. Foremost among them are predictions for the upcoming James Webb space telescope (JWST), to be launched ~2018, and for 'stellar archaeology', which probes the abundance pattern in the oldest, most-metal poor stars in our cosmic neighborhood, thereby constraining the nucleosynthesis inside the first supernovae.

  4. Theoretical Considerations of Massive Star Formation

    NASA Technical Reports Server (NTRS)

    Yorke, Harold W.

    2006-01-01

    This viewgraph presentation reviews the formation of massive stars. The formation of massive stars is different in many ways from the formation of other stars. The presentation shows the math, and the mechanisms that must be possible for a massive star to form.

  5. Star formation and gas supply

    NASA Astrophysics Data System (ADS)

    Catinella, B.

    2016-06-01

    A detailed knowledge of how gas cycles in and around galaxies, and how it depends on galaxy properties such as stellar mass and star formation rate, is crucial to understand galaxy formation and evolution. We take advantage of the most sensitive surveys of cold gas in massive galaxies, GASS and COLD GASS, as well as of the state-of-the-art HI blind survey ALFALFA to investigate how molecular and atomic hydrogen reservoirs vary along and across the main sequence of star-forming galaxies.

  6. Galaxy Interactions with FIRE: Mapping Star Formation

    NASA Astrophysics Data System (ADS)

    Moreno, Jorge

    2016-01-01

    We utilize a suite of 75 simulations of galaxies in idealised major mergers (stellar mass ratio ~2.5:1), with a wide range of orbital parameters, to investigate the spatial extent of interaction-induced star formation. Two versions are used, one based on a Kennicult-like subgrid model (Gadget, Springel & Hernquist 2003); the other based on the new Feedback In Realistic Environments model (FIRE, Hopkins et al. 2014). Although the total star formation in galaxy encounters is generally elevated relative to isolated galaxies, we find that this elevation is a combination of intense enhancements within the central kpc and moderately suppressed activity at large galacto-centric radii. This effect appears to be stronger in the older Gadget model. Suppression is the disk is also found in the FIRE runs, but at larger scales. This is because tidal torques are weaker in the newer FIRE model, leading to a more extended nuclear starburt. Our predictions of the radial dependence of triggered star formation, and specifically the suppression of star formation beyond kpc-scales, will be testable with the next generation of integral-field spectroscopic surveys.

  7. Sub-arcsec mid-IR observations of NGC 1614: Nuclear star formation or an intrinsically X-ray weak AGN?

    NASA Astrophysics Data System (ADS)

    Pereira-Santaella, M.; Colina, L.; Alonso-Herrero, A.; Usero, A.; Díaz-Santos, T.; García-Burillo, S.; Alberdi, A.; Gonzalez-Martin, O.; Herrero-Illana, R.; Imanishi, M.; Levenson, N. A.; Pérez-Torres, M. A.; Ramos Almeida, C.

    2015-12-01

    We present new mid-infrared (mid-IR) N-band spectroscopy and Q-band photometry of the local luminous IR galaxy NGC 1614, one of the most extreme nearby starbursts. We analyse the mid-IR properties of the nucleus (central 150 pc) and four regions of the bright circumnuclear (diameter˜600 pc) star-forming (SF) ring of this object. The nucleus differs from the circumnuclear SF ring by having a strong 8-12 μm continuum (low 11.3 μm PAH equivalent width). These characteristics, together with the nuclear X-ray and sub-mm properties, can be explained by an X-ray weak active galactic nucleus (AGN), or by peculiar SF with a short molecular gas depletion time and producing an enhanced radiation field density. In either case, the nuclear luminosity (LIR < 6 × 1043 erg s-1) is only <5 per cent of the total bolometric luminosity of NGC 1614. So this possible AGN does not dominate the energy output in this object. We also compare three star formation rate (SFR) tracers (Pa α, 11.3 μm PAH, and 24 μm emissions) at 150 pc scales in the circumnuclear ring. In general, we find that the SFR is underestimated (overestimated) by a factor of 2-4 (2-3) using the 11.3 μm PAH (24 μm) emission with respect to the extinction corrected Pa α SFR. The former can be explained because we do not include diffuse polycyclic aromatic hydrocarbon (PAH) emission in our measurements, while the latter might indicate that the dust temperature is particularly warmer in the central regions of NGC 1614.

  8. Surrogate Nuclear Reactions using STARS

    SciTech Connect

    Bernstein, L A; Burke, J T; Church, J A; Ahle, L; Cooper, J R; Hoffman, R D; Moody, K; Punyon, J; Schiller, A; Algin, E; Plettner, C; Ai, H; Beausang, C W; Casten, R F; Hughes, R; Ricard-McCutchan, E; Meyer, D; Ressler, J J; Caggiano, J A; Zamfir, N V; Amro, H; Heinz, A; Fallon, P; McMahan, M A; Macchiavelli, A O; Phair, L W

    2004-10-26

    The results from two surrogate reaction experiments using the STARS (Silicon Telescope Array for Reaction Studies) spectrometer are presented. The surrogate method involves measuring the particle and/or {gamma}-ray decay probabilities of excited nuclei populated via a direct reaction. These probabilities can then be used to deduce neutron-induced reaction cross sections that lead to the same compound nuclei. In the first experiment STARS coupled to the GAMMASPHERE {gamma}-ray spectrometer successfully reproduce surrogate (n,{gamma}), (n,n'{gamma}) and (n,2n{gamma}) cross sections on {sup 155,156}Gd using Gd {sup 3}He-induced reactions. In the second series of experiments an energetic deuteron beam from the ESTU tandem at the Wright Nuclear Structure Lab at Yale University was used to obtain the ratio of fission probabilities for {sup 238}U/ {sup 236}U and {sup 237}U/ {sup 239}U populated using the {sup 236,238}U(d,d'f) and {sup 236,238}U(d,pf) reactions. Results from these experiments are presented and the implications for the surrogate reaction technique are discussed.

  9. The nuclear physics of neutron stars

    NASA Astrophysics Data System (ADS)

    Piekarewicz, J.

    2014-05-01

    We explore the unique and fascinating structure of neutron stars. Although neutron stars are of interest in many areas of Physics, our aim is to provide an intellectual bridge between Nuclear Physics and Astrophysics. We argue against the naive perception of a neutron star as a uniform assembly of neutrons packed to enormous densities. Rather, by focusing on the many exotic phases that are speculated to exist in a neutron star, we show how the reality is different and far more interesting.

  10. Jet-Induced Star Formation

    SciTech Connect

    van Breugel, W; Fragile, C; Anninos, P; Murray, S

    2003-12-16

    Jets from radio galaxies can have dramatic effects on the medium through which they propagate. We review observational evidence for jet-induced star formation in low ('FR-I') and high ('FR-II') luminosity radio galaxies, at low and high redshifts respectively. We then discuss numerical simulations which are aimed to explain a jet-induced starburst ('Minkowski's Object') in the nearby FR-I type radio galaxy NGC 541. We conclude that jets can induce star formation in moderately dense (10 cm{sup -3}), warm (10{sup 4} K) gas; that this may be more common in the dense environments of forming, active galaxies; and that this may provide a mechanism for 'positive' feedback from AGN in the galaxy formation process.

  11. Star Formation in MUSCEL Galaxies

    NASA Astrophysics Data System (ADS)

    Young, Jason; Kuzio de Naray, Rachel; Wang, Sharon Xuesong

    2017-01-01

    We present preliminary star-formation histories for a subset of the low surface brightness (LSB) galaxies in the MUSCEL (MUltiwavelength observations of the Structure, Chemistry, and Evolution of LSB galaxies) program. These histories are fitted against ground-based IFU spectra in tandem with space-based UV and IR photometry. MUSCEL aims to use these histories along with kinematic analyses to determine the physical processes that have caused the evolution of LSB galaxies to diverge from their high surface brightness counterparts.

  12. Ionization and Triggered Star Formation

    NASA Astrophysics Data System (ADS)

    Gritschneder, M.; Lin, D. N. C.; Murray, S. D.; Burkert, A.

    2011-12-01

    We perform a set of high resolution simulations on the impact of the UV-radiation of massive stars on the turbulent interstellar medium with the tree-SPH code iVINE. This parameter study includes different levels and driving scales of the turbulence, different ionizing flux as well as different temperatures and densities of the cold gas. We find a clear correlation between the initial state of the turbulent cloud and the final morphology and physical properties of the structures adjacent to the HII region. From the simulations we are able to derive a criterion for the formation of pillar-like structures and thus the formation of cores and stars. Gravitational collapse occurs regularly on the tips of the structures. We also derive column densities and velocity profiles of our simulations and find these to be in very good agreement with the observations of trunks and cores. In addition, we investigate the further evolution of the pillars once the massive star explodes. This leads to a supernova triggered scenario for the formation of our Solar System.

  13. Star formation and extinct radioactivities

    NASA Technical Reports Server (NTRS)

    Cameron, A. G. W.

    1984-01-01

    An assessment is made of the evidence for the existence of now-extinct radioactivities in primitive solar system material, giving attention to implications for the early stages of sun and solar system formation. The characteristics of possible disturbances in dense molecular clouds which can initiate the formation of cloud cores is discussed, with emphasis on these disturbances able to generate fresh radioactivities. A one-solar mass red giant star on the asymptotic giant branch appears to have been the best candidate to account for the short-lived extinct radioactivities in the early solar system.

  14. Star formation inside a galactic outflow.

    PubMed

    Maiolino, R; Russell, H R; Fabian, A C; Carniani, S; Gallagher, R; Cazzoli, S; Arribas, S; Belfiore, F; Bellocchi, E; Colina, L; Cresci, G; Ishibashi, W; Marconi, A; Mannucci, F; Oliva, E; Sturm, E

    2017-04-13

    Recent observations have revealed massive galactic molecular outflows that may have the physical conditions (high gas densities) required to form stars. Indeed, several recent models predict that such massive outflows may ignite star formation within the outflow itself. This star-formation mode, in which stars form with high radial velocities, could contribute to the morphological evolution of galaxies, to the evolution in size and velocity dispersion of the spheroidal component of galaxies, and would contribute to the population of high-velocity stars, which could even escape the galaxy. Such star formation could provide in situ chemical enrichment of the circumgalactic and intergalactic medium (through supernova explosions of young stars on large orbits), and some models also predict it to contribute substantially to the star-formation rate observed in distant galaxies. Although there exists observational evidence for star formation triggered by outflows or jets into their host galaxy, as a consequence of gas compression, evidence for star formation occurring within galactic outflows is still missing. Here we report spectroscopic observations that unambiguously reveal star formation occurring in a galactic outflow at a redshift of 0.0448. The inferred star-formation rate in the outflow is larger than 15 solar masses per year. Star formation may also be occurring in other galactic outflows, but may have been missed by previous observations owing to the lack of adequate diagnostics.

  15. Star Formation Regions in LDN 1667

    NASA Astrophysics Data System (ADS)

    Gyulbudaghian, A. L.

    2015-09-01

    A group of three star formation regions in the dark cloud LDN 1667 is examined. All three of these regions contain Trapezium type systems. 12C(1-0) observations are made of the part of the molecular cloud LDN 1667 associated with one of the star formation regions. Three molecular clouds were detected, one of which (the main cloud) has a red and a blue outflow. Three stars from the star formation regions are found to have annular nebulae and one star has a conical nebula. The dark cloud LDN 1667 is associated with a radial system of dark globules which is formed by the star HD 57061.

  16. What can nuclear collisions teach us about the boiling of water or the formation of multi-star systems

    NASA Astrophysics Data System (ADS)

    Gross, D. H. E.

    2001-11-01

    Phase transitions in nuclei, small atomic clusters and self-gravitating systems demand the extension of thermo-statistics to "Small" systems. The main obstacle is the thermodynamic limit. It is shown how the original definition of the entropy by Boltzmann as the volume of the energy-manifold of the N-body phase space allows a geometrical definition of the entropy as function of the conserved quantities. Without invoking the thermodynamic limit the whole "zoo" of phase transitions and critical points/lines can be unambiguously defined. The relation to the Yang-Lee singularities of the grand-canonical partition sum is pointed out. It is shown that just phase transitions in non-extensive systems give the complete set of characteristic parameters of the transition including the surface tension. Nuclear heavy-ion collisions are an experimental playground to explore this extension of thermo-statistics

  17. SUPPRESSION OF STAR FORMATION IN NGC 1266

    SciTech Connect

    Alatalo, Katherine; Lanz, Lauranne; Bitsakis, Theodoros; Appleton, Philip N.; Ogle, Patrick M.; Lacy, Mark; Lonsdale, Carol J.; Nyland, Kristina; Meier, David S.; Cales, Sabrina L.; Chang, Philip; Davis, Timothy A.; De Zeeuw, P. T.; Martín, Sergio

    2015-01-01

    NGC 1266 is a nearby lenticular galaxy that harbors a massive outflow of molecular gas powered by the mechanical energy of an active galactic nucleus (AGN). It has been speculated that such outflows hinder star formation (SF) in their host galaxies, providing a form of feedback to the process of galaxy formation. Previous studies, however, indicated that only jets from extremely rare, high-power quasars or radio galaxies could impart significant feedback on their hosts. Here we present detailed observations of the gas and dust continuum of NGC 1266 at millimeter wavelengths. Our observations show that molecular gas is being driven out of the nuclear region at M-dot {sub out}≈110 M{sub ⊙} yr{sup –1}, of which the vast majority cannot escape the nucleus. Only 2 M {sub ☉} yr{sup –1} is actually capable of escaping the galaxy. Most of the molecular gas that remains is very inefficient at forming stars. The far-infrared emission is dominated by an ultra-compact (≲ 50 pc) source that could either be powered by an AGN or by an ultra-compact starburst. The ratio of the SF surface density (Σ{sub SFR}) to the gas surface density (Σ{sub H{sub 2}}) indicates that SF is suppressed by a factor of ≈50 compared to normal star-forming galaxies if all gas is forming stars, and ≈150 for the outskirt (98%) dense molecular gas if the central region is powered by an ultra-compact starburst. The AGN-driven bulk outflow could account for this extreme suppression by hindering the fragmentation and gravitational collapse necessary to form stars through a process of turbulent injection. This result suggests that even relatively common, low-power AGNs are able to alter the evolution of their host galaxies as their black holes grow onto the M-σ relation.

  18. Star Formation in Henize 206

    NASA Technical Reports Server (NTRS)

    2004-01-01

    explosion millions of years ago. The shock waves from that explosion impacted a cloud of nearby hydrogen gas, compressed it, and started a new generation of star formation. The death of one star led to the birth of many new stars. This is particularly evident in the MIPS inset, where the 24-micron emission peaks correspond to newly formed stars. The ultraviolet and visible-light photons from the new stars are absorbed by surrounding dust and re-radiated at longer infrared wavelengths, where it is detected by Spitzer.

    This emission nebula was cataloged by Karl Henize (HEN-eyes) while spending 1948-1951 in South Africa doing research for his Ph.D. dissertation at the University of Michigan. Henize later became a NASA astronaut and, at age 59, became the oldest rookie to fly on the Space Shuttle during an eight-day flight of the Challenger in 1985. He died just short of his 67th birthday in 1993 while attempting to climb the north face of Mount Everest, the world's highest peak.

  19. STAR FORMATION IN 30 DORADUS

    SciTech Connect

    De Marchi, Guido; Spezzi, Loredana; Sirianni, Marco; Andersen, Morten; Paresce, Francesco; Panagia, Nino; Mutchler, Max; Whitmore, Bradley C.; Bond, Howard; Beccari, Giacomo; Balick, Bruce; Dopita, Michael A.; Frogel, Jay A.; Calzetti, Daniela; Marcella Carollo, C.; Disney, Michael J.; Hall, Donald N. B.; Holtzman, Jon A.; Kimble, Randy A.; McCarthy, Patrick J.

    2011-09-20

    Using observations obtained with the Wide-Field Camera 3 on board the Hubble Space Telescope, we have studied the properties of the stellar populations in the central regions of 30 Dor in the Large Magellanic Cloud. The observations clearly reveal the presence of considerable differential extinction across the field. We characterize and quantify this effect using young massive main-sequence stars to derive a statistical reddening correction for most objects in the field. We then search for pre-main-sequence (PMS) stars by looking for objects with a strong (>4{sigma}) H{alpha} excess emission and find about 1150 of them over the entire field. Comparison of their location in the Hertzsprung-Russell diagram with theoretical PMS evolutionary tracks for the appropriate metallicity reveals that about one-third of these objects are younger than {approx}4 Myr, compatible with the age of the massive stars in the central ionizing cluster R 136, whereas the rest have ages up to {approx}30 Myr, with a median age of {approx}12 Myr. This indicates that star formation has proceeded over an extended period of time, although we cannot discriminate between an extended episode and a series of short and frequent bursts that are not resolved in time. While the younger PMS population preferentially occupies the central regions of the cluster, older PMS objects are more uniformly distributed across the field and are remarkably few at the very center of the cluster. We attribute this latter effect to photo-evaporation of the older circumstellar disks caused by the massive ionizing members of R 136.

  20. Stellar Dynamical Processes in Massive Star and Star Cluster Formation

    NASA Astrophysics Data System (ADS)

    Tan, Jonathan; Eyer, L.

    2009-01-01

    We study how high precision astrometric measurements by SIM and GAIA of stars involved in dynamical ejection events from star clusters can constrain theories of massive star and star cluster formation. We focus on the Orion Nebula Cluster (ONC). First, we investigate the scientific potential associated with an accurate measurement of the distance and proper motion of Theta 1 Ori C, which is the most massive star in the cluster and was recently involved (about 4000 years ago) in the ejection of a B star: the Becklin-Neugebauer (BN) star. The motion of the BN star has taken it close to a massive protostar, known as source I, where it appears to have influenced the accretion and outflow activity, most likely by a tidal interaction with the accretion disk. An accurate proper motion measurement of Theta 1 Ori C will constrain BN's initial motion, allowing us to search for deflections caused by the gravitational potential of the massive protostar. Second, we search the Hipparcos catalog for candidate runaway stars, i.e. that have been dynamically ejected from the cluster over the course of the last several Myr. SIM and GAIA observations of these stars will be needed to confirm their origin from the ONC. The results of this study will constrain the star cluster formation timescale and the statistics of the population of ejected stars. JCT acknowledges support from from NSF CAREER grant AST-0645412 and a grant from NASA for SIM Science Studies.

  1. Nonuniversal star formation efficiency in turbulent ISM

    SciTech Connect

    Semenov, Vadim A.; Kravtsov, Andrey V.; Gnedin, Nickolay Y.

    2016-07-29

    Here, we present a study of a star formation prescription in which star formation efficiency depends on local gas density and turbulent velocity dispersion, as suggested by direct simulations of SF in turbulent giant molecular clouds (GMCs). We test the model using a simulation of an isolated Milky Way-sized galaxy with a self-consistent treatment of turbulence on unresolved scales. We show that this prescription predicts a wide variation of local star formation efficiency per free-fall time, $\\epsilon_{\\rm ff} \\sim 0.1 - 10\\%$, and gas depletion time, $t_{\\rm dep} \\sim 0.1 - 10$ Gyr. In addition, it predicts an effective density threshold for star formation due to suppression of $\\epsilon_{\\rm ff}$ in warm diffuse gas stabilized by thermal pressure. We show that the model predicts star formation rates in agreement with observations from the scales of individual star-forming regions to the kiloparsec scales. This agreement is non-trivial, as the model was not tuned in any way and the predicted star formation rates on all scales are determined by the distribution of the GMC-scale densities and turbulent velocities $\\sigma$ in the cold gas within the galaxy, which is shaped by galactic dynamics. The broad agreement of the star formation prescription calibrated in the GMC-scale simulations with observations, both gives credence to such simulations and promises to put star formation modeling in galaxy formation simulations on a much firmer theoretical footing.

  2. Processes and problems in secondary star formation

    SciTech Connect

    Klein, R.I.; Whitaker, R.W.; Sandford M.T. II

    1984-03-01

    Recent developments relating the conditions in molecular clouds to star formation triggered by a prior stellar generation are reviewed. Primary processes are those that lead to the formation of a first stellar generation. The secondary processes that produce stars in response to effects caused by existing stars are compared and evaluated in terms of the observational data presently available. We discuss the role of turbulence to produce clumpy cloud structures and introduce new work on colliding inter-cloud gas flows leading to non-linear inhomogeneous cloud structures in an intially smooth cloud. This clumpy morphology has important consequences for secondary formation. The triggering processes of supernovae, stellar winds, and H II regions are discussed with emphasis on the consequences for radiation driven implosion as a promising secondary star formation mechanism. Detailed two-dimensional, radiation-hydrodynamic calculations of radiation driven implosion are discussed. This mechanism is shown to be highly efficient in synchronizing the formation of new stars in congruent to 1-3 x 10/sup 4/ years and could account for the recent evidence for new massive star formation in several UCHII regions. It is concluded that, while no single theory adequately explains the variety of star formation observed, a uniform description of star formation is likely to involve several secondary processes. Advances in the theory of star formation will require multiple dimensional calculations of coupled processes. The important non-linear interactions include hydrodynamics, radiation transport, and magnetic fields.

  3. Star formation sustained by gas accretion

    NASA Astrophysics Data System (ADS)

    Sánchez Almeida, Jorge; Elmegreen, Bruce G.; Muñoz-Tuñón, Casiana; Elmegreen, Debra Meloy

    2014-07-01

    Numerical simulations predict that metal-poor gas accretion from the cosmic web fuels the formation of disk galaxies. This paper discusses how cosmic gas accretion controls star formation, and summarizes the physical properties expected for the cosmic gas accreted by galaxies. The paper also collects observational evidence for gas accretion sustaining star formation. It reviews evidence inferred from neutral and ionized hydrogen, as well as from stars. A number of properties characterizing large samples of star-forming galaxies can be explained by metal-poor gas accretion, in particular, the relationship among stellar mass, metallicity, and star-formation rate (the so-called fundamental metallicity relationship). They are put forward and analyzed. Theory predicts gas accretion to be particularly important at high redshift, so indications based on distant objects are reviewed, including the global star-formation history of the universe, and the gas around galaxies as inferred from absorption features in the spectra of background sources.

  4. Molecular cloud evolution and star formation

    NASA Technical Reports Server (NTRS)

    Silk, J.

    1985-01-01

    The present state of knowledge of the relationship between molecular clouds and young stars is reviewed. The determination of physical parameters from molecular line observations is summarized, and evidence for fragmentation of molecular clouds is discussed. Hierarchical fragmentation is reviewed, minimum fragment scales are derived, and the stability against fragmentation of both spherically and anisotropically collapsing clouds is discussed. Observational evidence for high-velocity flows in clouds is summarized, and the effects of winds from pre-main sequence stars on molecular gas are discussed. The triggering of cloud collapse by enhanced pressure is addressed, as is the formation of dense shells by spherical outflows and their subsequent breakup. A model for low-mass star formation is presented, and constraints on star formation from the initial mass function are examined. The properties of giant molecular clouds and massive star formation are described. The implications of magnetic fields for cloud evolution and star formation are addressed.

  5. Measuring star formation rates in blue galaxies

    NASA Technical Reports Server (NTRS)

    Gallagher, John S., III; Hunter, Deidre A.

    1987-01-01

    The problems associated with measurements of star formation rates in galaxies are briefly reviewed, and specific models are presented for determinations of current star formation rates from H alpha and Far Infrared (FIR) luminosities. The models are applied to a sample of optically blue irregular galaxies, and the results are discussed in terms of star forming histories. It appears likely that typical irregular galaxies are forming stars at nearly constant rates, although a few examples of systems with enhanced star forming activity are found among HII regions and luminous irregular galaxies.

  6. Hierarchical Star Formation Across Galactic Disks

    NASA Astrophysics Data System (ADS)

    Gouliermis, Dimitrios

    2016-09-01

    Most stars form in clusters. This fact has emerged from the finding that "embedded clusters account for the 70 - 90% fraction of all stars formed in Giant Molecular Clouds (GMCs)." While this is the case at scales of few 10 parsecs, typical for GMCs, a look at star-forming galaxies in the Local Group (LG) shows significant populations of enormous loose complexes of early-type stars extending at scales from few 100 to few 1000 parsecs. The fact that these stellar complexes host extremely large numbers of loosely distributed massive blue stars implies either that stars form also in an unbound fashion or they are immediately dislocated from their original compact birthplaces or both. The Legacy Extra-Galactic UV Survey (LEGUS) has produced remarkable collections of resolved early-type stars in 50 star-forming LG galaxies, suited for testing ideas about recent star formation. I will present results from our ongoing project on star formation across LEGUS disk galaxies. We characterize the global clustering behavior of the massive young stars in order to understand the morphology of star formation over galactic scales. This morphology appears to be self-similar with fractal dimensions comparable to those of the molecular interstellar medium, apparently driven by large-scale turbulence. Our clustering analysis reveals compact stellar systems nested in larger looser concentrations, which themselves are the dense parts of unbound complexes and super-structures, giving evidence of hierarchical star formation up to galactic scales. We investigate the structural and star formation parameters demographics of the star-forming complexes revealed at various levels of compactness. I will discuss the outcome of our correlation and regression analyses on these parameters in an attempt to understand the link between galactic disk dynamics and morphological structure in spiral and ring galaxies of the local universe.

  7. A simple theory of bimodal star formation

    NASA Technical Reports Server (NTRS)

    Wyse, Rosemary F. G.; Silk, J.

    1987-01-01

    A model of bimodal star formation is presented, wherein massive stars form in giant molecular clouds (GNC), at a rate regulated by supernovae energy feedback through the interstellar medium, the heat input also ensuring that the initial mass function (IMF) remains skewed towards massive stars. The low mass stars form at a constant rate. The formation of the GMC is governed by the dynamics of the host galaxy through the rotation curve and potential perturbations such as a spiral density wave. The characteristic masses, relative normalizations, and rates of formation of the massive and low mass modes of star formation may be tightly constrained by the requirements of the chemical evolution in the Solar Neighborhood. Good fits were obtained for the age metallicity relation and the metallicity structure of thin disk and spheroid stars only for a narrow range of these parameters.

  8. Triggered Star Formation Surrounding Wolf-Rayet Star HD 211853

    NASA Astrophysics Data System (ADS)

    Liu, Tie; Wu, Yuefang; Zhang, Huawei; Qin, Sheng-Li

    2012-05-01

    The environment surrounding Wolf-Rayet (W-R) star HD 211853 is studied in molecular, infrared, as well as radio, and H I emission. The molecular ring consists of well-separated cores, which have a volume density of 103 cm-3 and kinematic temperature ~20 K. Most of the cores are under gravitational collapse due to external pressure from the surrounding ionized gas. From the spectral energy distribution modeling toward the young stellar objects, the sequential star formation is revealed on a large scale in space spreading from the W-R star to the molecular ring. A small-scale sequential star formation is revealed toward core "A," which harbors a very young star cluster. Triggered star formations are thus suggested. The presence of the photodissociation region, the fragmentation of the molecular ring, the collapse of the cores, and the large-scale sequential star formation indicate that the "collect and collapse" process functions in this region. The star-forming activities in core "A" seem to be affected by the "radiation-driven implosion" process.

  9. Star-forming galaxy models: Blending star formation into TREESPH

    NASA Technical Reports Server (NTRS)

    Mihos, J. Christopher; Hernquist, Lars

    1994-01-01

    We have incorporated star-formation algorithms into a hybrid N-body/smoothed particle hydrodynamics code (TREESPH) in order to describe the star forming properties of disk galaxies over timescales of a few billion years. The models employ a Schmidt law of index n approximately 1.5 to calculate star-formation rates, and explicitly include the energy and metallicity feedback into the Interstellar Medium (ISM). Modeling the newly formed stellar population is achieved through the use of hybrid SPH/young star particles which gradually convert from gaseous to collisionless particles, avoiding the computational difficulties involved in creating new particles. The models are shown to reproduce well the star-forming properties of disk galaxies, such as the morphology, rate of star formation, and evolution of the global star-formation rate and disk gas content. As an example of the technique, we model an encounter between a disk galaxy and a small companion which gives rise to a ring galaxy reminiscent of the Cartwheel (AM 0035-35). The primary galaxy in this encounter experiences two phases of star forming activity: an initial period during the expansion of the ring, and a delayed phase as shocked material in the ring falls back into the central regions.

  10. Sequentially triggered star formation in OB associations

    NASA Astrophysics Data System (ADS)

    Preibisch, Thomas; Zinnecker, Hans

    We discuss observational evidence for sequential and triggered star formation in galactic and extragalactic OB associations. We will first review in detail the star formation process in the Scorpius-Centaurus OB association, the nearest OB association to the Sun, where several recent extensive studies have provided comprehensive information on the stellar content and the ages of the different OB subgroups. These data have allowed us to reconstruct the star formation history of the association in some detail and provided important insight into the activity in the rho Oph and Lupus dark clouds, and with the origin of several young stellar groups in the southern sky. After discussing evidence for triggered star formation in and around various other Galactic OB associations (e.g. Ori OB1, Per OB2) we will compare the observational results with recent models of rapid star formation in the turbulent interstellar medium (cf. Briceno et al. chapter in Protostars and Planets V, in press).

  11. Coronet: A Star-Formation Neighbor

    NASA Technical Reports Server (NTRS)

    2007-01-01

    While perhaps not quite as well known as its star-formation cousin Orion, the Corona Australis region (containing, at its heart, the Coronet cluster) is one of the nearest and most active regions of ongoing star formation. At only about 420 light-years away, the Coronet is over three times closer than the Orion nebula is to Earth. The Coronet contains a loose cluster of a few dozen young stars with a wide range of masses and at various stages of evolution, giving astronomers an opportunity to observe embryonic stars simultaneously in several wavelengths.

    This composite image shows the Coronet in X-rays from Chandra (purple) and infrared from Spitzer (orange, green, and cyan). The Spitzer data show young stars plus diffuse emission from dust. Due to the host of young stars in different life stages in the Coronet, astronomers can use these data to pinpoint details of how the youngest stars evolve.

  12. Filamentary star formation in NGC 1275

    NASA Astrophysics Data System (ADS)

    Canning, R. E. A.; Ryon, J. E.; Gallagher, J. S.; Kotulla, R.; O'Connell, R. W.; Fabian, A. C.; Johnstone, R. M.; Conselice, C. J.; Hicks, A.; Rosario, D.; Wyse, R. F. G.

    2014-10-01

    We examine the star formation in the outer halo of NGC 1275, the central galaxy in the Perseus cluster (Abell 426), using far-ultraviolet and optical images obtained with the Hubble Space Telescope. We have identified a population of very young, compact star clusters with typical ages of a few Myr. The star clusters are organized on multiple kiloparsec scales. Many of these star clusters are associated with `streaks' of young stars, the combination of which has a cometary appearance. We perform photometry on the star clusters and diffuse stellar streaks, and fit their spectral energy distributions to obtain ages and masses. These young stellar populations appear to be normal in terms of their masses, luminosities and cluster formation efficiency; <10 per cent of the young stellar mass is located in star clusters. Our data suggest star formation is associated with the evolution of some of the giant gas filaments in NGC 1275 that become gravitationally unstable on reaching and possibly stalling in the outer galaxy. The stellar streaks then could represent stars moving on ballistic orbits in the potential well of the galaxy cluster. We propose a model where star-forming filaments, switched on ˜50 Myr ago and are currently feeding the growth of the NGC 1275 stellar halo at a rate of ≈-2 to 3 M⊙ yr-1. This type of process may also build stellar haloes and form isolated star clusters in the outskirts of youthful galaxies.

  13. Nuclear physics problems for accreting neutron stars

    SciTech Connect

    Wallace, R.K.; Woosley, S.E.

    1983-01-01

    The importance of p(e/sup -/nu)n and of (p,..gamma..) reactions on /sup 56/Ni during a thermonuclear runaway on a neutron star surface is pointed out. A fast 16-isotope approximate nuclear reaction network is developed that is suitable for use in hydrodynamic calculations of such events.

  14. StarFISH: For Inferring Star-formation Histories

    NASA Astrophysics Data System (ADS)

    Harris, Jason; Zaritsky, Dennis

    2012-04-01

    StarFISH is a suite of programs designed to determine the star formation history (SFH) of a stellar population, given multicolor stellar photometry and a library of theoretical isochrones. It constructs a library of synthetic color-magnitude diagrams from the isochrones, which includes the effects of extinction, photometric errors and completeness, and binarity. A minimization routine is then used to determine the linear combination of synthetic CMDs that best matches the observed photometry. The set of amplitudes modulating each synthetic CMD describes the star formation history of the observed stellar population.

  15. Star formation in the Magellanic clouds

    NASA Technical Reports Server (NTRS)

    Frogel, Jay A.

    1987-01-01

    Because of their proximity, the Magellanic Clouds provide the opportunity to conduct a detailed study of the history and current state of star formation in dwarf irregular galaxies. There is considerable evidence that star formation in the Clouds was and is proceeding in a manner different from that found in a typical well-ordered spiral galaxy. Star formation in both Clouds appears to have undergone a number of relatively intense bursts. There exist a number of similarities and differences in the current state of star formation in the Magellanic Clouds and the Milky Way. Examination of Infrared Astronomy Satellite (IRAS) sources with ground based telescopes allows identification of highly evolved massive stars with circumstellar shells as well as several types of compact emission line objects.

  16. Fragmentation in massive star formation.

    PubMed

    Beuther, Henrik; Schilke, Peter

    2004-02-20

    Studies of evolved massive stars indicate that they form in a clustered mode. During the earliest evolutionary stages, these regions are embedded within their natal cores. Here we present high-spatial-resolution interferometric dust continuum observations disentangling the cluster-like structure of a young massive star-forming region. The derived protocluster mass distribution is consistent with the stellar initial mass function. Thus, fragmentation of the initial massive cores may determine the initial mass function and the masses of the final stars. This implies that stars of all masses can form via accretion processes, and coalescence of intermediate-mass protostars appears not to be necessary.

  17. Supernovae, compact stars and nuclear physics

    SciTech Connect

    Glendenning, N.K.

    1989-08-25

    We briefly review the current understanding of supernova. We investigate the implications of rapid rotation corresponding to the frequency of the new pulsar reported in the supernovae remnant SN1987A. It places very stringent conditions on the equation of state if the star is assumed to be bound by gravity alone. We find that the central energy density of the star must be greater than 12 times that of nuclear density to be stable against the most optimistic estimate of general relativistic instabilities. This is too high for the matter to plausibly consist of individual hadrons. We conclude that the newly discovered pulsar, if its half-millisecond signals are attributable to rotation, cannot be a neutron star. We show that it can be a strange quark star, and that the entire family of strange stars can sustain high rotation under appropriate conditions. We discuss the conversion of a neutron star to strange star, the possible existence of a crust of heavy ions held in suspension by centrifugal and electric forces, the cooling and other features. 39 refs., 8 figs., 2 tabs.

  18. Nonuniversal star formation efficiency in turbulent ISM

    DOE PAGES

    Semenov, Vadim A.; Kravtsov, Andrey V.; Gnedin, Nickolay Y.

    2016-07-29

    Here, we present a study of a star formation prescription in which star formation efficiency depends on local gas density and turbulent velocity dispersion, as suggested by direct simulations of SF in turbulent giant molecular clouds (GMCs). We test the model using a simulation of an isolated Milky Way-sized galaxy with a self-consistent treatment of turbulence on unresolved scales. We show that this prescription predicts a wide variation of local star formation efficiency per free-fall time,more » $$\\epsilon_{\\rm ff} \\sim 0.1 - 10\\%$$, and gas depletion time, $$t_{\\rm dep} \\sim 0.1 - 10$$ Gyr. In addition, it predicts an effective density threshold for star formation due to suppression of $$\\epsilon_{\\rm ff}$$ in warm diffuse gas stabilized by thermal pressure. We show that the model predicts star formation rates in agreement with observations from the scales of individual star-forming regions to the kiloparsec scales. This agreement is non-trivial, as the model was not tuned in any way and the predicted star formation rates on all scales are determined by the distribution of the GMC-scale densities and turbulent velocities $$\\sigma$$ in the cold gas within the galaxy, which is shaped by galactic dynamics. The broad agreement of the star formation prescription calibrated in the GMC-scale simulations with observations, both gives credence to such simulations and promises to put star formation modeling in galaxy formation simulations on a much firmer theoretical footing.« less

  19. Resolving the Star Formation in Distant Galaxies

    NASA Astrophysics Data System (ADS)

    Gladders, Michael

    2012-10-01

    The fundamental unit of star formation in the Universe is neither a star, nor a galaxy, but a star forming region with a typical scale of at most 100s of parsecs. Even at full HST resolution, these regions are unresolved beyond rather modest redshifts. HST has - and continues to be - heavily invested in studies of distant galaxies, yet has been fundamentally unable to study the relevant physical scales of star formation in the distant Universe. We propose here to overcome this resolution barrier by imaging a total of 73 strongly lensed galaxies at z~1-3 discovered in the SDSS. The combination of the exquisite image quality of HST with the magnification boost due to strong lensing will allow robust measurements of the sizes, luminosities, star formation rates and stellar populations of individual star-forming clumps in these galaxies, providing the first ever comprehensive data on star formation at its fundamental scale over the entire peak of the star formation history in the Universe. The proposed observations build on the extensive legacy of HST deep fields - including the ongoing MCT CANDELS program. A number of ancillary science goals - not least amongst them the study of the lensing systems proper - are also enabled by the proposed data.

  20. Star Formation in a Crossing Time

    NASA Astrophysics Data System (ADS)

    Elmegreen, Bruce G.

    2000-02-01

    Observations suggest that star formation occurs in only one or two crossing times for a range of scales spanning a factor of ~1000. These observations include (1) measurements of embedded cluster ages in comparison with the cloud core dynamical times, (2) measurements of the age difference versus separation for clusters in the Large Magellanic Clouds in comparison with the crossing time versus size correlation for molecular clouds, (3) the hierarchical structure of embedded young clusters, and (4) the high fraction of dense clouds that contain star formation. Such a short overall timescale for star formation implies that sources of turbulent energy or internal feedback are not required to explain or extend cloud lifetimes and that star and protostar interactions cannot be important for the stellar initial mass function. Stars appear in a cloud as if they freeze out of the gas, preserving the turbulent-driven gas structure in their birth locations. The Galaxy-wide star formation rate avoids the Zuckerman-Evans catastrophe, which has long been a concern for molecular clouds that evolve this quickly, because the multifractal structure of interstellar gas ensures that only a small fraction of the mass is able to form stars. Star formation on large scales operates more slowly than on small scales, but in most cases the whole process is over in only a few dynamical times.

  1. Multi-epoch very long baseline interferometric observations of the nuclear starburst region of NGC 253: Improved modeling of the supernova and star formation rates

    SciTech Connect

    Rampadarath, H.; Morgan, J. S.; Tingay, S. J.; Lenc, E.

    2014-01-01

    The results of multi-epoch observations of the southern starburst galaxy, NGC 253, with the Australian Long Baseline Array at 2.3 GHz are presented. As with previous radio interferometric observations of this galaxy, no new sources were discovered. By combining the results of this survey with Very Large Array observations at higher frequencies from the literature, spectra were derived and a free-free absorption model was fitted of 20 known sources in NGC 253. The results were found to be consistent with previous studies. The supernova remnant, 5.48-43.3, was imaged with the highest sensitivity and resolution to date, revealing a two-lobed morphology. Comparisons with previous observations of similar resolution give an upper limit of 10{sup 4} km s{sup –1} for the expansion speed of this remnant. We derive a supernova rate of <0.2 yr{sup –1} for the inner 300 pc using a model that improves on previous methods by incorporating an improved radio supernova peak luminosity distribution and by making use of multi-wavelength radio data spanning 21 yr. A star formation rate of SFR(M ≥ 5 M {sub ☉}) < 4.9 M {sub ☉} yr{sup –1} was also estimated using the standard relation between supernova and star formation rates. Our improved estimates of supernova and star formation rates are consistent with studies at other wavelengths. The results of our study point to the possible existence of a small population of undetected supernova remnants, suggesting a low rate of radio supernova production in NGC 253.

  2. The Center for Star Formation Studies

    NASA Technical Reports Server (NTRS)

    Hollenbach, D.; Bell, K. R.; Laughlin, G.

    2002-01-01

    The Center for Star Formation Studies, a consortium of scientists from the Space Science Division at Ames and the Astronomy Departments of the University of California at Berkeley and Santa Cruz, conducts a coordinated program of theoretical research on star and planet formation. Under the directorship of D. Hollenbach (Ames), the Center supports postdoctoral fellows, senior visitors, and students; meets regularly at Ames to exchange ideas and to present informal seminars on current research; hosts visits of outside scientists; and conducts a week-long workshop on selected aspects of star and planet formation each summer.

  3. Computational and theoretical investigations of star formation

    NASA Astrophysics Data System (ADS)

    Krumholz, Mark Reuben

    I investigate three related questions in the theory of star formation. First, I consider the physical mechanism of massive star formation. Massive stars reach the main sequence while still accreting from their natal clouds, leading to a huge radiation pressure force on dust grains suspended in the incoming gas. Early calculations found that this limits stellar masses to [Special characters omitted.] 20--40 [Special characters omitted.] , far smaller than the most massive stars observed. I demonstrate two new mechanisms by which accretion can continue despite radiation pressure. First, radiation holding up a massive infalling envelope is subject to Rayleigh-Taylor instability, which forces the accreting gas into optically thick filaments that are shielded from radiation and channel gas to the star. Second, massive protostars have powerful outflows that punch optically thin cavities through the envelope. These channel radiation away from the accreting gas, greatly reducing the radiation pressure force it experiences. Second, I argue that the stellar initial mass function (IMF) does not originate from the "competitive accretion" of unbound gas by seed protostars. I provide an approximate solution to the problem of Bondi- Hoyle accretion in a turbulent medium, and use this solution to show that the rate of competitive accretion in environments like observed star-forming regions is too low to substantially affect the masses of newborn stars. Only if star-forming clumps undergo a global collapse to a state far denser than any thus far observed is competitive accretion a viable mechanism for producing the IMF. Third, I give a theoretical prediction for the star formation rate in a medium where star formation is regulated by supersonic turbulence. Starting from the approximation that stars form in any region that is sufficiently overdense for the local potential energy to exceed the turbulent kinetic energy, I derive a formula for the star formation rate in terms of the

  4. Formation of Massive Stars: Theoretical Considerations

    NASA Technical Reports Server (NTRS)

    Yorke, Harold W.

    2008-01-01

    This slide presentation reviews theoretical considerations of the formation of massive stars. It addresses the questions that assuming a gravitationally unstable massive clump, how does enough material become concentrated into a sufficiently small volume within a sufficiently short time? and how does the forming massive star influence its immediate surroundings to limit its mass?

  5. Star Formation in Dwarf Irregular Galaxies

    NASA Astrophysics Data System (ADS)

    Dohm-Palmer, Robbie Christopher

    I have explored the star formation histories of the dwarf irregular galaxies Sextans A and GR 8. I measured photometry of individual stars from images taken by the Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope. With the photometry I constructed color-magnitude diagrams (CMDs) in the B, V, and I. I investigated the errors in the photometry extraction, and conducted artificial star tests to measure the photometric limits. The high resolution of the Hubble Space Telescope allowed photometric measurements that were far more accurate than ground-based observations. For galaxies at these distances (1-2 Mpc), the accuracy of stellar photometry from ground-based observations is limited by crowding of stellar images. The high accuracy photometry showed a clear separation of the main sequence from the massive, blue, core He-burning stars (HeB). These are stars in the bluest extent of the so-called 'blue-loop' phase of stellar evolution. This is the first time this phase of evolution has been clearly identified in a low metallicity system. The distributions of stars in the CMDs agreed very well with stellar evolution model predictions. I have used the CMDs to calculate the recent star formation histories of both galaxies. The main sequence luminosity function provided the star formation rate (SFR) over the past ~50 Myr. I developed a new technique for calculating the SFR from the blue HeB luminosity function. Furthermore, the blue HeB evolutionary phase has a one-to-one relation between age and magnitude. This allowed me to calculate the position, as well as the strength of star formation over the past ~500 Myr. The star formation was found in concentrated regions. These regions are of order 100 pc across and last of order 100 Myr. The regions were found near the highest density HI gas. I estimated the gas-to-star conversion efficiency to be 5-10%. The results from GR 8 suggest that the star forming gas clouds may be self-gravitating, and that each cloud

  6. Formation and Assembly of Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    McMillan, Stephen

    The formation of stars and star clusters is a major unresolved problem in astrophysics. It is central to modeling stellar populations and understanding galaxy luminosity distributions in cosmological models. Young massive clusters are major components of starburst galaxies, while globular clusters are cornerstones of the cosmic distance scale and represent vital laboratories for studies of stellar dynamics and stellar evolution. Yet how these clusters form and how rapidly and efficiently they expel their natal gas remain unclear, as do the consequences of this gas expulsion for cluster structure and survival. Also unclear is how the properties of low-mass clusters, which form from small-scale instabilities in galactic disks and inform much of our understanding of cluster formation and star-formation efficiency, differ from those of more massive clusters, which probably formed in starburst events driven by fast accretion at high redshift, or colliding gas flows in merging galaxies. Modeling cluster formation requires simulating many simultaneous physical processes, placing stringent demands on both software and hardware. Simulations of galaxies evolving in cosmological contexts usually lack the numerical resolution to simulate star formation in detail. They do not include detailed treatments of important physical effects such as magnetic fields, radiation pressure, ionization, and supernova feedback. Simulations of smaller clusters include these effects, but fall far short of the mass of even single young globular clusters. With major advances in computing power and software, we can now directly address this problem. We propose to model the formation of massive star clusters by integrating the FLASH adaptive mesh refinement magnetohydrodynamics (MHD) code into the Astrophysical Multi-purpose Software Environment (AMUSE) framework, to work with existing stellar-dynamical and stellar evolution modules in AMUSE. All software will be freely distributed on-line, allowing

  7. Star Formation History In Merging Galaxies

    NASA Astrophysics Data System (ADS)

    Chien, Li-Hsin

    2009-01-01

    Interacting and merging galaxies are believed to play an important role in many aspects of galactic evolution. Their violent interactions can trigger starbursts, which lead to formation of young globular clusters. Therefore the ages of these young globular clusters can be interpreted to yield the timing of interaction-triggered events, and thus provide a key to reconstruct the star formation history in merging galaxies. The link between galaxy interaction and star formation is well established, but the triggers of star formation in interacting galaxies are still not understood. To date there are two competing formulas that describe the star formation mechanism--density-dependent and shock-induced rules. Numerical models implementing the two rules predict significantly different star formation histories in merging galaxies. My dissertation combines these two distinct areas of astrophysics, stellar evolution and galactic dynamics, to investigate the star formation history in galaxies at various merging stages. Begin with NGC 4676 as an example, I will briefly describe its model and illustrate the idea of using the ages of clusters to constrain the modeling. The ages of the clusters are derived from spectra that were taken with multi-object spectroscopy on Keck. Using NGC 7252 as a second example, I will present a state of the art dynamical model which predicts NGC7252's star formation history and other properties. I will then show a detailed comparison and analysis between the clusters and the modeling. In the end, I will address this important link as the key to answer the fundamental question of my thesis: what is the trigger of star formation in merging galaxies?

  8. 'Tertiary' nuclear burning - Neutron star deflagration?

    NASA Technical Reports Server (NTRS)

    Michel, F. Curtis

    1988-01-01

    A motivation is presented for the idea that dense nuclear matter can burn to a new class of stable particles. One of several possibilities is an 'octet' particle which is the 16 baryon extension of alpha particle, but now composed of a pair of each of the two nucleons, (3Sigma, Delta, and 2Xi). Such 'tertiary' nuclear burning (here 'primary' is H-He and 'secondary' is He-Fe) may lead to neutron star explosions rather than collapse to a black hole, analogous to some Type I supernovae models wherein accreting white dwarfs are pushed over the Chandrasekhar mass limit but explode rather than collapse to form neutron stars. Such explosions could possibly give gamma-ray bursts and power quasars, with efficient particle acceleration in the resultant relativistic shocks. The new stable particles themselves could possibly be the sought-after weakly interacting, massive particles (WIMPs) or 'dark' matter.

  9. Star Wars in a nuclear world

    SciTech Connect

    Zuckerman, L.

    1987-01-01

    Lord Zuckerman is a world authority on the rivalries and politics of the nuclear age. Few scientists distinguished in their own right have had as much experience as he has of both the national and international corridors of power. During World War Two he was Strategic Planning Adviser to Air Marshal Tedder and General Eisenhower. From 1960 to 1971 he was Chief Scientific Adviser to the Ministry of Defence and to the British Government as a whole. He is an unrelenting critic of the Star Wars programme introduced by President Reagan in 1983. He writes, ''Had anyone other than the American President ever invited scientists to try to render 'nuclear weapons impotent and obsolete' the suggestion would probably have attracted no more attention than had they been asked to square the circle or solve the problem of perpetual motion. But it happened to be the President, and he spelled out his vision of a future over which the nuclear bomb no longer casts a shadow in such homely terms that it all sounded real. How could the message fail to appeal.'' Lord Zuckerman is critical not only of Star Wars but also of the futility of the nuclear arms race. ''The arms-race has absorbed enormous resources. The nuclear arsenals of East and West have continued to grow. But, paradoxically, national security seems to have lessened everywhere.

  10. HOW GALACTIC ENVIRONMENT REGULATES STAR FORMATION

    SciTech Connect

    Meidt, Sharon E.

    2016-02-10

    In a new simple model I reconcile two contradictory views on the factors that determine the rate at which molecular clouds form stars—internal structure versus external, environmental influences—providing a unified picture for the regulation of star formation in galaxies. In the presence of external pressure, the pressure gradient set up within a self-gravitating turbulent (isothermal) cloud leads to a non-uniform density distribution. Thus the local environment of a cloud influences its internal structure. In the simple equilibrium model, the fraction of gas at high density in the cloud interior is determined simply by the cloud surface density, which is itself inherited from the pressure in the immediate surroundings. This idea is tested using measurements of the properties of local clouds, which are found to show remarkable agreement with the simple equilibrium model. The model also naturally predicts the star formation relation observed on cloud scales and at the same time provides a mapping between this relation and the closer-to-linear molecular star formation relation measured on larger scales in galaxies. The key is that pressure regulates not only the molecular content of the ISM but also the cloud surface density. I provide a straightforward prescription for the pressure regulation of star formation that can be directly implemented in numerical models. Predictions for the dense gas fraction and star formation efficiency measured on large-scales within galaxies are also presented, establishing the basis for a new picture of star formation regulated by galactic environment.

  11. Star formation relations in nearby molecular clouds

    SciTech Connect

    Evans, Neal J. II; Heiderman, Amanda; Vutisalchavakul, Nalin

    2014-02-20

    We test some ideas for star formation relations against data on local molecular clouds. On a cloud by cloud basis, the relation between the surface density of star formation rate and surface density of gas divided by a free-fall time, calculated from the mean cloud density, shows no significant correlation. If a crossing time is substituted for the free-fall time, there is even less correlation. Within a cloud, the star formation rate volume and surface densities increase rapidly with the corresponding gas densities, faster than predicted by models using the free-fall time defined from the local density. A model in which the star formation rate depends linearly on the mass of gas above a visual extinction of 8 mag describes the data on these clouds, with very low dispersion. The data on regions of very massive star formation, with improved star formation rates based on free-free emission from ionized gas, also agree with this linear relation.

  12. Terrestrial Planet Formation in Binary Star Systems

    NASA Astrophysics Data System (ADS)

    Quintana, Elisa V.; Lissauer, Jack J.

    More than half of all main sequence stars, and an even larger fraction of pre-main sequence stars, reside in binary or multiple systems (Duquennoy and Mayor 1991; Mathieu et al. 2000). The presence of planet-forming material has been indirectly observed around one or both components of some young binaries, and (Mathieu et al. 2000) numerical simulations of the formation of binary stars suggest that disks form within these systems, as well (Bodenheimer et al. 2000). Terrestrial planets and the cores of giant planets are thought to form by an accretion process within a disk of dust and gas (Safronov 1969; Lissauer 1993), and therefore may be common in binary star systems. In this chapter, we present the results from numerical simulations of the final stages of terrestrial planet formation around one or both stars of a binary.

  13. Magnetic fields and galactic star formation rates

    SciTech Connect

    Loo, Sven Van; Tan, Jonathan C.; Falle, Sam A. E. G.

    2015-02-10

    The regulation of galactic-scale star formation rates (SFRs) is a basic problem for theories of galaxy formation and evolution: which processes are responsible for making observed star formation rates so inefficient compared to maximal rates of gas content divided by dynamical timescale? Here we study the effect of magnetic fields of different strengths on the evolution of giant molecular clouds (GMCs) within a kiloparsec patch of a disk galaxy and resolving scales down to ≃0.5 pc. Including an empirically motivated prescription for star formation from dense gas (n{sub H}>10{sup 5} cm{sup −3}) at an efficiency of 2% per local free-fall time, we derive the amount of suppression of star formation by magnetic fields compared to the nonmagnetized case. We find GMC fragmentation, dense clump formation, and SFR can be significantly affected by the inclusion of magnetic fields, especially in our strongest investigated B-field case of 80 μG. However, our chosen kiloparsec-scale region, extracted from a global galaxy simulation, happens to contain a starbursting cloud complex that is only modestly affected by these magnetic fields and likely requires internal star formation feedback to regulate its SFR.

  14. Star formation - A theoretician's view

    NASA Technical Reports Server (NTRS)

    Shu, Frank H.

    1991-01-01

    The present evaluation of the hypothesis that the birth of a sunlike star occurs in four stages, with a critical bipolar outflow phase, notes that observed molecular outflows cannot be initiated from circumstellar disks and must instead represent swept-up shells of gas that are driven by strong protostellar winds. The star can resolve its growing angular-momentum problem only by rejecting a fraction of the material that is fed through the disk in a powerful, magnetocentrifugally-driven wind. Empirical properties measured for well-collimated outflow sources can be accounted for by the interaction of this anisotropic wind with the ambient molecular cloud core.

  15. Terrestrial Planet Formation in Binary Star Systems

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.; Quintana, Elisa V.; Chambers, John; Duncan, Martin J.; Adams, Fred

    2003-01-01

    Most stars reside in multiple star systems; however, virtually all models of planetary growth have assumed an isolated single star. Numerical simulations of the collapse of molecular cloud cores to form binary stars suggest that disks will form within such systems. Observations indirectly suggest disk material around one or both components within young binary star systems. If planets form at the right places within such circumstellar disks, they can remain in stable orbits within the binary star systems for eons. We are simulating the late stages of growth of terrestrial planets within binary star systems, using a new, ultrafast, symplectic integrator that we have developed for this purpose. We show that the late stages of terrestrial planet formation can indeed take place in a wide variety of binary systems and we have begun to delineate the range of parameter space for which this statement is true. Results of our initial simulations of planetary growth around each star in the alpha Centauri system and other 'wide' binary systems, as well as around both stars in very close binary systems, will be presented.

  16. Complex organic molecules and star formation

    NASA Astrophysics Data System (ADS)

    Bacmann, A.; Faure, A.

    2014-12-01

    Star forming regions are characterised by the presence of a wealth of chemical species. For the past two to three decades, ever more complex organic species have been detected in the hot cores of protostars. The evolution of these molecules in the course of the star forming process is still uncertain, but it is likely that they are partially incorporated into protoplanetary disks and then into planetesimals and the small bodies of planetary systems. The complex organic molecules seen in star forming regions are particularly interesting since they probably make up building blocks for prebiotic chemistry. Recently we showed that these species were also present in the cold gas in prestellar cores, which represent the very first stages of star formation. These detections question the models which were until now accepted to account for the presence of complex organic molecules in star forming regions. In this article, we shortly review our current understanding of complex organic molecule formation in the early stages of star formation, in hot and cold cores alike and present new results on the formation of their likely precursor radicals.

  17. Star formation in H II galaxies

    NASA Astrophysics Data System (ADS)

    Torres-Campos, A.; Díaz, A. I.; Terlevich, E.; Rosa-González, D.; Telles, E.; Terlevich, R.

    2013-05-01

    H II galaxies integrated properties have been widely studied. However, little is known about the individual H II regions and their photoionizing stellar clusters. To broaden our knowledge on star formation in low mass star-forming galaxies (like H II galaxies) it is necessary to answer questions like: How does the star formation distributes along the galaxy? Is it possible for them to form super stellar clusters? How does the star formation history on them looks like? To answer those questions the goal of this thesis work is to map (at tens of parsecs resolution) the recent star formation in six H II galaxies with extremely young star-forming bursts (Rosa-González et al. 2007, ApJ, 654, 226). The preliminary results obtained have allowed us to develop a catalog of H II regions (identified for the first time) in these galaxies and the characterization of the young stellar clusters responsible for their photoionization using POPSTAR (Mollá, García-Vargas, & Bressan 2009, MNRAS, 398, 451) stellar populations models.

  18. TIME-VARYING DYNAMICAL STAR FORMATION RATE

    SciTech Connect

    Lee, Eve J.; Chang, Philip; Murray, Norman

    2015-02-10

    We present numerical evidence of dynamic star formation in which the accreted stellar mass grows superlinearly with time, roughly as t {sup 2}. We perform simulations of star formation in self-gravitating hydrodynamic and magnetohydrodynamic turbulence that is continuously driven. By turning the self-gravity of the gas in the simulations on or off, we demonstrate that self-gravity is the dominant physical effect setting the mass accretion rate at early times before feedback effects take over, contrary to theories of turbulence-regulated star formation. We find that gravitational collapse steepens the density profile around stars, generating the power-law tail on what is otherwise a lognormal density probability distribution function. Furthermore, we find turbulent velocity profiles to flatten inside collapsing regions, altering the size-line width relation. This local flattening reflects enhancements of turbulent velocity on small scales, as verified by changes to the velocity power spectra. Our results indicate that gas self-gravity dynamically alters both density and velocity structures in clouds, giving rise to a time-varying star formation rate. We find that a substantial fraction of the gas that forms stars arrives via low-density flows, as opposed to accreting through high-density filaments.

  19. Triggered star formation associated with HII regions

    NASA Astrophysics Data System (ADS)

    Ogura, Katsuo

    There are two known mechanisms of triggered star formation associated with HII regions. One is the collect-and-collapse process of the shell accumulated around an expanding HII region, and the other is radiation-driven implosion (RDI) of bright-rimmed clouds (BRCs) originated from pre-existing cloud clumps. They are very briefly reviewed first. We then present the main results of our recent observations on the RDI star formation in BRCs. Finally, a third possible mechanism of triggering is suggested, which is attributed to the formation of elephant trunk-like structures due to hydrodynamical instability of ionization/shock fronts.

  20. Dwarf Galaxy Formation with H2-regulated Star Formation

    NASA Astrophysics Data System (ADS)

    Kuhlen, Michael; Krumholz, Mark R.; Madau, Piero; Smith, Britton D.; Wise, John

    2012-04-01

    We describe cosmological galaxy formation simulations with the adaptive mesh refinement code Enzo that incorporate a star formation prescription regulated by the local abundance of molecular hydrogen. We show that this H2-regulated prescription leads to a suppression of star formation in low-mass halos (Mh <~ 1010 M ⊙) at z > 4, alleviating some of the dwarf galaxy problems faced by theoretical galaxy formation models. H2 regulation modifies the efficiency of star formation of cold gas directly, rather than indirectly reducing the cold gas content with "supernova feedback." We determine the local H2 abundance in our most refined grid cells (76 proper parsec in size at z = 4) by applying the model of Krumholz, McKee, & Tumlinson, which is based on idealized one-dimensional radiative transfer calculations of H2 formation-dissociation balance in ~100 pc atomic-molecular complexes. Our H2-regulated simulations are able to reproduce the empirical (albeit lower z) Kennicutt-Schmidt relation, including the low Σgas cutoff due to the transition from atomic to molecular phase and the metallicity dependence thereof, without the use of an explicit density threshold in our star formation prescription. We compare the evolution of the luminosity function, stellar mass density, and star formation rate density from our simulations to recent observational determinations of the same at z = 4-8 and find reasonable agreement between the two.

  1. Terrestrial planet formation surrounding close binary stars

    NASA Astrophysics Data System (ADS)

    Quintana, Elisa V.; Lissauer, Jack J.

    2006-11-01

    Most stars reside in binary/multiple star systems; however, previous models of planet formation have studied growth of bodies orbiting an isolated single star. Disk material has been observed around both components of some young close binary star systems. Additionally, it has been shown that if planets form at the right places within such disks, they can remain dynamically stable for very long times. Herein, we numerically simulate the late stages of terrestrial planet growth in circumbinary disks around 'close' binary star systems with stellar separations 0.05 AU⩽a⩽0.4 AU and binary eccentricities 0⩽e⩽0.8. In each simulation, the sum of the masses of the two stars is 1 M, and giant planets are included. The initial disk of planetary embryos is the same as that used for simulating the late stages of terrestrial planet formation within our Solar System by Chambers [Chambers, J.E., 2001. Icarus 152, 205-224], and around each individual component of the α Centauri AB binary star system by Quintana et al. [Quintana, E.V., Lissauer, J.J., Chambers, J.E., Duncan, M.J., 2002. Astrophys. J. 576, 982-996]. Multiple simulations are performed for each binary star system under study, and our results are statistically compared to a set of planet formation simulations in the Sun-Jupiter-Saturn system that begin with essentially the same initial disk of protoplanets. The planetary systems formed around binaries with apastron distances Q≡a(1+e)≲0.2 AU are very similar to those around single stars, whereas those with larger maximum separations tend to be sparcer, with fewer planets, especially interior to 1 AU. We also provide formulae that can be used to scale results of planetary accretion simulations to various systems with different total stellar mass, disk sizes, and planetesimal masses and densities.

  2. Symmetry energy: nuclear masses and neutron stars

    NASA Astrophysics Data System (ADS)

    Pearson, J. M.; Chamel, N.; Fantina, A. F.; Goriely, S.

    2014-02-01

    We describe the main features of our most recent Hartree-Fock-Bogoliubov nuclear mass models, based on 16-parameter generalized Skyrme forces. They have been fitted to the data of the 2012 Atomic Mass Evaluation, and favour a value of 30MeV for the symmetry coefficient J , the corresponding root-mean square deviation being 0.549MeV. We find that this conclusion is compatible with measurements of neutron-skin thickness. By constraining the underlying interactions to fit various equations of state of neutron matter calculated ab initio our models are well adapted to a realistic and unified treatment of all regions of neutron stars. We use our models to calculate the composition, the equation of state, the mass-radius relation and the maximum mass. Comparison with observations of neutron stars again favours a value of J = 30 MeV.

  3. Accelerating Star Formation in Clusters and Associations

    NASA Astrophysics Data System (ADS)

    Palla, Francesco; Stahler, Steven W.

    2000-09-01

    We use our own, recently developed pre-main-sequence evolutionary tracks to investigate the star formation histories of relatively nearby associations and clusters. We first employ published luminosities and effective temperatures to place the known members of each region in the H-R diagram. We then construct age histograms detailing that region's history. The groups studied include Taurus-Auriga, Lupus, Chamaeleon, ρ Ophiuchi, Upper Scorpius, IC 348, and NGC 2264. This study is the first to analyze a large number of star-forming regions with the same set of theoretical tracks. Our investigation corroborates and extends our previous results on the Orion Nebula Cluster. In all cases, we find that star formation began at a relatively low level some 107 yr in the past and has more recently undergone a steep acceleration. This acceleration, which lasts several million years, is usually continuing through the present epoch. The one clear exception is the OB association Upper Scorpius, where the formation rate climbed upward, peaked, and has now died off. Significantly, this is also the only region of our list that has been largely stripped of molecular gas. The acceleration represents a true physical phenomenon that cannot be explained away by incompleteness of the samples; nor is the pattern of stellar births significantly affected by observational errors or the presence of unresolved binaries. We speculate that increasing star formation activity arises from contraction of the parent cloud. Despite the short timescale for acceleration, the cloud is likely to evolve quasi-statically. Star formation itself appears to be a critical phenomenon, occurring only in locations exceeding some threshold density. The cloud's contraction must reverse itself, and the remnant gas dissipate, in less than 107 yr, even for aggregates containing no massive stars. In this case, molecular outflows from the stars themselves presumably accomplish the task, but the actual dispersal mechanism

  4. Tracing Star Formation Around Quasars With Polycyclic Aromatic Hydrocarbons

    NASA Astrophysics Data System (ADS)

    Bilton, Lawrence Edward

    2016-09-01

    The feedback processes linking quasar activity to galaxy stellar mass growth are not well understood. If star formation is closely causally linked to black hole accretion, one may expect star formation confined to nuclear regions rather than extended over several kpc scales. Since Polycyclic Aromatic Hydrocarbon (PAH) emission features are widely used as tracers of stellar formation, it is, therefore, possible to use PAH emission detected around QSOs to help resolve this question. PAH data from a sample of 63 QSOs procured from the Spitzer Space Telescope’s Infrared Spectrograph (IRS) is used, employing the Spectroscopic Modelling Analysis and Reduction Tool’s (SMART) Advanced Optimal (AdOpt) extraction routines. A composite spectrum was also produced to help determine the average conditions and compositions of star forming regions. It is found, from our high redshift (>1) sample of QSOs, there is a marginally significant extended star formation on average of 34 scales. At low redshift, the median extension after deconvolving the instrumental point spread function is 3.2 , potentially showing evolutionary variations in star formation activity. However, limitations of the spatial resolving power constrain the ability to make any absolute conclusive remarks. It is also found that the QSO/AGN composite has more neutral PAHs than the starbursting and the main sequence galaxies, consistent with the AGN having no contribution to heating the PAH emission, and also consistent with the average PAH emission found on scales (i.e. not confined to the nuclear regions). A tentative detection of water vapour emission from the gravitationally lensed Einstein Cross quasar, QSO J2237+0305, is also presented suggesting a strong molecular outflow possibly driven by the active nucleus.

  5. Star formation in Lynds dark clouds

    NASA Astrophysics Data System (ADS)

    Spuck, Tim; Rebull, Luisa

    2008-03-01

    Recent research on star formation in large molecular cloud complexes, such as the Cepheus Flare (Kun 1995), Orion, Perseus (Rebull et al. 2007), and Taurus molecular clouds, have included studies of a number of Lynds dark nebulae (LDN). Less attention has been given to isolated Lynds clouds. Both LDN 981 and LDN 425 are smaller, more isolated, dark molecular clouds that could contain regions of active star formation within them -- they both are associated with IRAS sources, and based on prior shallow surveys, they both have a YSO candidate in the neigborhood. Spitzer observations with IRAC and MIPS will allow us to see deep inside the cloud, deeper than any prior observations could see, and reveal any hidden star formation that is ongoing in these clouds. This project is part of the Spitzer Teachers Program.

  6. Fragmentation of interstellar clouds and star formation

    NASA Technical Reports Server (NTRS)

    Silk, J.

    1982-01-01

    The principal issues are addressed: the fragmentation of molecular clouds into units of stellar mass and the impact of star formation on molecular clouds. The observational evidence for fragmentation is summarized, and the gravitational instability described of a uniform spherical cloud collapsing from rest. The implications are considered of a finite pressure for the minimum fragment mass that is attainable in opacity-limited fragmentation. The role of magnetic fields is discussed in resolving the angular momentum problem and in making the collapse anisotropic, with notable consequences for fragmentation theory. Interactions between fragments are described, with emphasis on the effect of protostellar winds on the ambient cloud matter and on inhibiting further star formation. Such interactions are likely to have profound consequences for regulating the rate of star formation and on the energetics and dynamics of molecular clouds.

  7. Effects of intermediate mass black holes on nuclear star clusters

    SciTech Connect

    Mastrobuono-Battisti, Alessandra; Perets, Hagai B.; Loeb, Abraham

    2014-11-20

    Nuclear star clusters (NSCs) are dense stellar clusters observed in galactic nuclei, typically hosting a central massive black hole. Here we study the possible formation and evolution of NSCs through the inspiral of multiple star clusters hosting intermediate mass black holes (IMBHs). Using an N-body code, we examine the dynamics of the IMBHs and their effects on the NSC. We find that IMBHs inspiral to the core of the newly formed NSC and segregate there. Although the IMBHs scatter each other and the stars, none of them is ejected from the NSC. The IMBHs are excited to high eccentricities and their radial density profile develops a steep power-law cusp. The stars also develop a power-law cusp (instead of the central core that forms in their absence), but with a shallower slope. The relaxation rate of the NSC is accelerated due to the presence of IMBHs, which act as massive perturbers. This in turn fills the loss cone and boosts the tidal disruption rate of stars both by the MBH and the IMBHs to a value excluded by rate estimates based on current observations. Rate estimates of tidal disruptions can therefore provide a cumulative constraint on the existence of IMBHs in NSCs.

  8. On the merger origin of nuclear star clusters

    NASA Astrophysics Data System (ADS)

    Tsatsi, Athanasia; Mastrobuono-Battisti, Alessandra

    2017-03-01

    Nuclear Star Clusters (NSCs) are commonly observed in the centers of most galaxies, including our Milky Way (MW). While their study can reveal important information about the innermost regions of galaxies, the physical processes regulating their formation are still poorly understood. We explore a possible merger origin of NSCs by studying direct N-body simulations of globular clusters (GCs) that are initially randomly distributed in the outskirts and consecutively infall to the center of a MW-like nuclear bulge. We find that the NSC that forms through this process shows a significant amount of rotation, and both morphological and kinematic properties are comparable with observations of the MW NSC. We show that no fine-tuning of the orientation of the infalling GCs is necessary to result in a rotating NSC. This study shows the plausibility of the cluster infall scenario and can help towards setting better constraints to the formation history of NSCs.

  9. Star formation in proto dwarf galaxies

    NASA Technical Reports Server (NTRS)

    Noriega-Crespo, A.; Bodenheimer, P.; Lin, D. N. C.; Tenorio-Tagle, G.

    1990-01-01

    The effects of the onset of star formation on the residual gas in primordial low-mass Local-Group dwarf spheroidal galaxies is studied by a series of hydrodynamical simulations. The models have concentrated on the effect of photoionization. The results indicate that photoionization in the presence of a moderate gas density gradient can eject most of the residual gas on a time scale of a few 10 to the 7th power years. High central gas density combined with inefficient star formation, however, may prevent mass ejection. The effect of supernova explosions is discussed briefly.

  10. Radio continuum, far infrared and star formation

    NASA Technical Reports Server (NTRS)

    Wielebinski, R.; Wunderlich, E.; Klein, U.; Hummel, E.

    1987-01-01

    A very tight correlation was found between the radio emission and the far infrared emission from galaxies. This has been found for various samples of galaxies and is explained in terms of recent star formation. The tight correlation would imply that the total radio emission is a good tracer of star formation. The correlation between the radio power at 5 GHz and the far infrared luminosity is shown. The galaxies are of various morphological types and were selected from the various IRAS circulars, hence the sample is an infrared selected sample. The far infrared luminosities were corrected for the dust temperature. This is significant because it decreases the dispersion in the correlation.

  11. Evolutionary tracks of massive stars during formation

    NASA Astrophysics Data System (ADS)

    Smith, Michael D.

    2014-02-01

    A model for massive stars is constructed by piecing together evolutionary algorithms for the protostellar structure, the environment, the inflow and the radiation feedback. We investigate specified accretion histories of constant, decelerating and accelerating forms and consider both hot and cold accretion, identified with spherical free-fall and disc accretion, respectively. Diagnostic tools for the interpretation of the phases of massive star formation and testing the evolutionary models are then developed. Evolutionary tracks able to fit Herschel Space Telescope data require the generated stars to be three to four times less massive than in previous interpretations, thus being consistent with clump star formation efficiencies of 10-15 per cent. However, for these cold Herschel clumps, the bolometric temperature is not a good diagnostic to differentiate between accretion models. We also find that neither spherical nor disc accretion can explain the high radio luminosities of many protostars. Nevertheless, we discover a solution in which the extreme ultraviolet flux needed to explain the radio emission is produced if the accretion flow is via free-fall on to hotspots covering less than 10 per cent of the surface area. Moreover, the protostar must be compact, and so has formed through cold accretion. We show that these conclusions are independent of the imposed accretion history. This suggests that massive stars form via gas accretion through discs which, in the phase before the star bloats, download their mass via magnetic flux tubes on to the protostar.

  12. Formation of star tracking reticles

    NASA Technical Reports Server (NTRS)

    Smith, W. O.; Toft, A. R. (Inventor)

    1974-01-01

    The present application is directed towards a process for producing high resolution, substantially non-reflective reticles or choppers suitable for use for transmitting in both the visible and near ultra-violet regions, able to withstand reasonable handling and extreme environmental conditions, and capable of operating at speeds of from 2800 to about 9000 revolutions per minute without distortion. In particular, the present invention is directed towards the production or reticles having a quartz base vacuum coated with chromium, chromium-silver alloy, and silver with electrodeposited copper and black chromium thereon, respectively, in the form of a reticle pattern. The quartz permits the transmission of light while the pattern is opaque to light. The reticles of the present invention are intended for use in optical trackers, such as star trackers used in outer space.

  13. Disentangling AGN and Star Formation in Soft X-Rays

    NASA Technical Reports Server (NTRS)

    LaMassa, Stephanie M.; Heckman, T. M.; Ptak, A.

    2012-01-01

    We have explored the interplay of star formation and active galactic nucleus (AGN) activity in soft X-rays (0.5-2 keV) in two samples of Seyfert 2 galaxies (Sy2s). Using a combination of low-resolution CCD spectra from Chandra and XMM-Newton, we modeled the soft emission of 34 Sy2s using power-law and thermal models. For the 11 sources with high signal-to-noise Chandra imaging of the diffuse host galaxy emission, we estimate the luminosity due to star formation by removing the AGN, fitting the residual emission. The AGN and star formation contributions to the soft X-ray luminosity (i.e., L(sub x,AGN) and L(sub x,SF)) for the remaining 24 Sy2s were estimated from the power-law and thermal luminosities derived from spectral fitting. These luminosities were scaled based on a template derived from XSINGS analysis of normal star-forming galaxies. To account for errors in the luminosities derived from spectral fitting and the spread in the scaling factor, we estimated L(sub x,AGN) and L(sub x,SF))from Monte Carlo simulations. These simulated luminosities agree with L(sub x,AGN) and L(sub x,SF) derived from Chandra imaging analysis within a 3sigma confidence level. Using the infrared [Ne ii]12.8 micron and [O iv]26 micron lines as a proxy of star formation and AGN activity, respectively, we independently disentangle the contributions of these two processes to the total soft X-ray emission. This decomposition generally agrees with L(sub x,SF) and L(sub x,AGN) at the 3 sigma level. In the absence of resolvable nuclear emission, our decomposition method provides a reasonable estimate of emission due to star formation in galaxies hosting type 2 AGNs.

  14. The Formation Of Massive Stars And The Effects Of Rotation On Star Formation

    NASA Astrophysics Data System (ADS)

    Maeder, A.

    2011-11-01

    We first review the current debates about massive star formation over the last decade. Then we concentrate on the accretion scenario, emphasizing the evidences in favor of it. We study the basic properties of the accretion scenario in the spherical case. In the case of massive stars, the free-fall time is longer than the Kelvin-Helmholtz timescale, so that the massive stars in formation reach thermal equilibrium before the accretion is completed. This is why the history of the accretion rates for massive stars is so critical. We derive analytically the typical accretion rates, their upper and lower limits, showing the importance of dust properties. We examine the basic properties of the disk, their luminosity and temperature in the stationary approximation, as well as their various components. The results of some recent numerical models are discussed with a particular attention to the effects that favor accretion on the central body relatively to the case of spherical accretion. These effects strongly influence the final stellar mass resulting from a collapsing clump in a cloud. We also show some properties of the pre-main sequence tracks of massive stars in the Hertzsprung-Russell diagram. During the first part of their evolution up to a mass of about 3M⊙ the forming stars are overluminous, then they are strongly underluminous (with respect to the zero age main sequence) up to a mass of about 10M⊙ until they adjust after a slight overluminosity to the main sequence values. We consider some rotational properties related to star formation. The angular momentum has to be reduced by a factor of about 106 during star formation. Some effects contributing to this reduction have been studied particularly in the case of low- and intermediate-mass stars: disk locking and magnetic braking. We also discuss the case of massive stars and emphasize the effects of the gravity darkening of rotating stars that may favor the accretion from the disk of massive stars in formation.

  15. Star formation around supermassive black holes.

    PubMed

    Bonnell, I A; Rice, W K M

    2008-08-22

    The presence of young massive stars orbiting on eccentric rings within a few tenths of a parsec of the supermassive black hole in the galactic center is challenging for theories of star formation. The high tidal shear from the black hole should tear apart the molecular clouds that form stars elsewhere in the Galaxy, and transport of stars to the galactic center also appears unlikely during their lifetimes. We conducted numerical simulations of the infall of a giant molecular cloud that interacts with the black hole. The transfer of energy during closest approach allows part of the cloud to become bound to the black hole, forming an eccentric disk that quickly fragments to form stars. Compressional heating due to the black hole raises the temperature of the gas up to several hundred to several thousand kelvin, ensuring that the fragmentation produces relatively high stellar masses. These stars retain the eccentricity of the disk and, for a sufficiently massive initial cloud, produce an extremely top-heavy distribution of stellar masses. This potentially repetitive process may explain the presence of multiple eccentric rings of young stars in the presence of a supermassive black hole.

  16. NUCLEAR ACTIVITY IS MORE PREVALENT IN STAR-FORMING GALAXIES

    SciTech Connect

    Rosario, D. J.; Lutz, D.; Berta, S.; Popesso, P.; Genzel, R.; Saintonge, A.; Tacconi, L.; Wuyts, S. E-mail: lutz@mpe.mpg.de E-mail: popesso@mpe.mpg.de E-mail: amelie@mpe.mpg.de E-mail: swuyts@mpe.mpg.de; and others

    2013-07-01

    We explore the question of whether low and moderate luminosity active galactic nuclei (AGNs) are preferentially found in galaxies that are undergoing a transition from active star formation (SF) to quiescence. This notion has been suggested by studies of the UV-optical colors of AGN hosts, which find them to be common among galaxies in the so-called Green Valley, a region of galaxy color space believed to be composed mostly of galaxies undergoing SF quenching. Combining the deepest current X-ray and Herschel/PACS far-infrared (FIR) observations of the two Chandra Deep Fields with redshifts, stellar masses, and rest-frame photometry derived from the extensive and uniform multi-wavelength data in these fields, we compare the rest-frame U - V color distributions and star formation rate distributions of AGNs and carefully constructed samples of inactive control galaxies. The UV-to-optical colors of AGNs are consistent with equally massive inactive galaxies at redshifts out to z {approx} 2, but we show that such colors are poor tracers of SF. While the FIR distributions of both star-forming AGNs and star-forming inactive galaxies are statistically similar, we show that AGNs are preferentially found in star-forming host galaxies, or, in other words, AGNs are less likely to be found in weakly star-forming or quenched galaxies. We postulate that, among X-ray-selected AGNs of low and moderate accretion luminosities, the supply of cold gas primarily determines the accretion rate distribution of the nuclear black holes.

  17. Evolution of star formation and gas

    NASA Astrophysics Data System (ADS)

    Scoville, Nick Z.

    2013-10-01

    In these lectures I review observations of star-forming molecular clouds in our Galaxy and nearby galaxies to develop a physical intuition for understanding star formation in the local and high-redshift Universe. A lot of this material is drawn from early work in the field since much of the work was done two decades ago and this background is not generally available in the present literature. I also attempt to synthesise our well-developed understanding of star formation in low-redshift galaxies with constraints from theory and observations at high redshift to develop an intuitive model for the evolution of galaxy mass and luminosity functions in the early Universe. The overall goal of this contribution is to provide students with background helpful for analysis of far-infrared (FIR) observations from Herschel and millimetre/submillimetre (mm/submm) imaging with ALMA (the Atacama Large Millimetre/submillimetre Array). These two instruments will revolutionise our understanding of the interstellar medium (ISM) and associated star formation and galaxy evolution, both locally and in the distant Universe. To facilitate interpreting the FIR spectra of Galactic star-forming regions and high-redshift sources, I develop a model for the dust heating and radiative transfer in order to elucidate the observed infrared (IR) emissions. I do this because I am not aware of a similar coherent discussion in the literature.

  18. Terrestrial Planet Formation in Binary Star Systems

    NASA Technical Reports Server (NTRS)

    Lissauer, J. J.; Quintana, E. V.; Adams, F. C.; Chambers, J. E.

    2006-01-01

    Most stars reside in binary/multiple star systems; however, previous models of planet formation have studied growth of bodies orbiting an isolated single star. Disk material has been observed around one or both components of various young close binary star systems. If planets form at the right places within such disks, they can remain dynamically stable for very long times. We have simulated the late stages of growth of terrestrial planets in both circumbinary disks around 'close' binary star systems with stellar separations ($a_B$) in the range 0.05 AU $\\le a_B \\le$ 0.4 AU and binary eccentricities in the range $0 \\le e \\le 0.8$ and circumstellar disks around individual stars with binary separations of tens of AU. The initial disk of planetary embryos is the same as that used for simulating the late stages of terrestrial planet growth within our Solar System and around individual stars in the Alpha Centauri system (Quintana et al. 2002, A.J., 576, 982); giant planets analogous to Jupiter and Saturn are included if their orbits are stable. The planetary systems formed around close binaries with stellar apastron distances less than or equal to 0.2 AU with small stellar eccentricities are very similar to those formed in the Sun-Jupiter-Saturn, whereas planetary systems formed around binaries with larger maximum separations tend to be sparser, with fewer planets, especially interior to 1 AU. Likewise, when the binary periastron exceeds 10 AU, terrestrial planets can form over essentially the entire range of orbits allowed for single stars with Jupiter-like planets, although fewer terrestrial planets tend to form within high eccentricity binary systems. As the binary periastron decreases, the radial extent of the terrestrial planet systems is reduced accordingly. When the periastron is 5 AU, the formation of Earth-like planets near 1 AU is compromised.

  19. The Assembly History of the Milky Way Nuclear Star Cluster

    NASA Astrophysics Data System (ADS)

    Feldmeier-Krause, A.; Neumayer, N.; Schödel, R.; Seth, A.; de Zeeuw, P. T.; Walcher, C. J.; Lützgendorf, N.; Kissler-Patig, M.; Hilker, M.; Kuntschner, H.

    2017-03-01

    Within the central 10 pc of our Galaxy lies a dense cluster of stars, the nuclear star cluster. This cluster forms a distinct component of our Galaxy. Nuclear star clusters are common objects and are detected in ~ 75% of nearby galaxies. It is, however, not fully understood how nuclear star clusters form. The Milky Way nuclear star cluster is the closest of its kind. At a distance of only 8 kpc we can spatially resolve its stellar populations and kinematics much better than in external galaxies. This makes the Milky Way nuclear star cluster the perfect local reference object for understanding the structure and assembly history of nuclear star clusters in general. There are of the order of 107 stars within the central 10 pc of the Galactic center. Most of these stars are several Gyr old late-type stars. However, there are also more than 100 hot early-type stars in the central parsec of the Milky Way, with ages of only a few Myr. Beyond a projected distance of 0.5 pc of the Galactic center, the density of young stars was largely unknown, since only very few spectroscopic observations existed so far. We covered the central >4 pc2 (0.75 sq.arcmin) of the Galactic center using the integral-field spectrograph KMOS (VLT). We extracted more than 1,000 spectra from individual stars and identified >20 new early-type stars based on their spectra. We studied the spatial distribution of the different populations and their kinematics to put constraints on the assembly history of the Milky Way nuclear star cluster.

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  1. Star Formation at milli-arcsecond resolution

    NASA Astrophysics Data System (ADS)

    Oudmaijer, R. D.; de Wit, W.-J.

    2014-09-01

    This chapter discusses the use and possibilities of optical and infrared interferometry to study star formation. It starts with a brief overview of the star formation process and highlights the open questions from an observational point of view. These are found at the smallest scales, as this is, inevitably, where all the action such as accretion and outflows, occurs. We then use basic astrophysical concepts to assess which scales and conditions can be probed with existing interferometric set-ups for which we use the ESO/VLTI instrument suite as example. We will concentrate on the more massive stars observed at high resolution with continuum interferometry. Throughout, some of the most recent interferometric results are used as examples of the various processes discussed.

  2. Star Formation at the Galactic Center

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-08-01

    Could stars be forming in the inhospitable environment near Sagittarius A* in the heart of the Milky Way? A possible signature of low-mass star formation has recently been found just two light-years from the black hole at the center of our galaxy — a region that was previously thought to be too hostile for such activity. Searching for Signatures: Previous observations of the central few light-years of the Milky Way had focused on a population of about 200 massive, young and very bright stars in tight orbits around Sgr A*. These stars are only a few million years old and prompted scientists to wonder: have they somehow managed to form in situ, in spite of their close proximity to the black hole, or did they form further out and then migrate in? Motivated by this mystery, Farhad Yusef-Zadeh of Northwestern University and collaborators looked for evidence of even younger stars close to Sagittarius A*, which would demonstrate that star formation in the area is an ongoing process. Using the Very Large Array (VLA), the collaboration discovered several small sources in one arm of activity near Sgr A*. This 34-GHz image provides a close-up view of two protoplanetary disk candidates (labeled P26 and P8) located near Sgr A*. These objects are outlined on the right side by a bow shock caused by impacting stellar wind that streams from the young, hot stars closer to the Galactic center. The disks are thought to contain recently-formed, low-mass stars. (Credit: Yusef-Zadeh et al., 2015) Heated Disks: The team identified these sources as candidate photoevaporative protoplanetary disks, or “proplyds” — areas of dense, ionized gas and dust surrounding young, newly formed stars. The proplyd candidates are between 10,000 and 100,000 years old, and they lie along the edge of a large molecular cloud. It is likely that this cloud produced the disks by providing a reservoir of gas to feed the star-formation activity. The region surrounding these proplyds is blasted with harsh

  3. Externally fed star formation: a numerical study

    NASA Astrophysics Data System (ADS)

    Mohammadpour, Motahareh; Stahler, Steven W.

    2013-08-01

    We investigate, through a series of numerical calculations, the evolution of dense cores that are accreting external gas up to and beyond the point of star formation. Our model clouds are spherical, unmagnetized configurations with fixed outer boundaries, across which gas enters subsonically. When we start with any near-equilibrium state, we find that the cloud's internal velocity also remains subsonic for an extended period, in agreement with observations. However, the velocity becomes supersonic shortly before the star forms. Consequently, the accretion rate building up the protostar is much greater than the benchmark value c_s^3/G, where cs is the sound speed in the dense core. This accretion spike would generate a higher luminosity than those seen in even the most embedded young stars. Moreover, we find that the region of supersonic infall surrounding the protostar races out to engulf much of the cloud, again in violation of the observations, which show infall to be spatially confined. Similar problematic results have been obtained by all other hydrodynamic simulations to date, regardless of the specific infall geometry or boundary conditions adopted. Low-mass star formation is evidently a quasi-static process, in which cloud gas moves inward subsonically until the birth of the star itself. We speculate that magnetic tension in the cloud's deep interior helps restrain the infall prior to this event.

  4. Dense cloud formation and star formation in a barred galaxy

    NASA Astrophysics Data System (ADS)

    Nimori, M.; Habe, A.; Sorai, K.; Watanabe, Y.; Hirota, A.; Namekata, D.

    2013-03-01

    We investigate the properties of massive, dense clouds formed in a barred galaxy and their possible relation to star formation, performing a two-dimensional hydrodynamical simulation with the gravitational potential obtained from the 2MASS data from the barred spiral galaxy, M83. Since the environment for cloud formation and evolution in the bar region is expected to be different from that in the spiral arm region, barred galaxies are a good target to study the environmental effects on cloud formation and the subsequent star formation. Our simulation uses for an initial 80 Myr isothermal flow of non-self gravitating gas in the barred potential, then including radiative cooling, heating and self-gravitation of the gas for the next 40 Myr, during which dense clumps are formed. We identify many cold, dense gas clumps for which the mass is more than 104 M⊙ (a value corresponding to the molecular clouds) and study the physical properties of these clumps. The relation of the velocity dispersion of the identified clump's internal motion with the clump size is similar to that observed in the molecular clouds of our Galaxy. We find that the virial parameters for clumps in the bar region are larger than that in the spiral arm region. From our numerical results, we estimate star formation in the bar and spiral arm regions by applying the simple model of Krumholz & McKee (2005). The mean relation between star formation rate and gas surface density agrees well with the observed Kennicutt-Schmidt relation. The star formation efficiency in the bar region is ˜60 per cent of the spiral arm region. This trend is consistent with observations of barred galaxies.

  5. ANALYTICAL STAR FORMATION RATE FROM GRAVOTURBULENT FRAGMENTATION

    SciTech Connect

    Hennebelle, Patrick; Chabrier, Gilles

    2011-12-20

    We present an analytical determination of the star formation rate (SFR) in molecular clouds, based on a time-dependent extension of our analytical theory of the stellar initial mass function. The theory yields SFRs in good agreement with observations, suggesting that turbulence is the dominant, initial process responsible for star formation. In contrast to previous SFR theories, the present one does not invoke an ad hoc density threshold for star formation; instead, the SFR continuously increases with gas density, naturally yielding two different characteristic regimes, thus two different slopes in the SFR versus gas density relationship, in agreement with observational determinations. Besides the complete SFR derivation, we also provide a simplified expression, which reproduces the complete calculations reasonably well and can easily be used for quick determinations of SFRs in cloud environments. A key property at the heart of both our complete and simplified theory is that the SFR involves a density-dependent dynamical time, characteristic of each collapsing (prestellar) overdense region in the cloud, instead of one single mean or critical freefall timescale. Unfortunately, the SFR also depends on some ill-determined parameters, such as the core-to-star mass conversion efficiency and the crossing timescale. Although we provide estimates for these parameters, their uncertainty hampers a precise quantitative determination of the SFR, within less than a factor of a few.

  6. Star formation in Kiso measle galaxies

    NASA Astrophysics Data System (ADS)

    Elmegreen, Debra M.; Elmegreen, B. G.

    2012-05-01

    The Kiso sample of several thousand local ultraviolet-bright galaxies includes galaxies classified as irregular disk galaxies with large star-forming complexes (I,g). We selected a sample of all I,g galaxies with both Sloan Digital Sky Survey images and spectra. They contain up to several dozen giant clumps each, so we refer to them as measle galaxies. We determined ages and masses of the clumps based on a comparison of photometry with population synthesis models of cluster evolution. The spectra were used to determine global star formation rates. Several hundred clumps were measured in the sample, with masses ranging from 10^5 to several x10^8 solar masses, scaling with galaxy absolute g magnitude of -14 to -21 mag. The galaxies are starbursting, sitting above the Groth strip “main sequence” of star formation rate versus galaxy mass by an order of magnitude. These Kiso measle galaxies have 10x the star formation rates of the Kiso tadpole galaxies. We compare their clump luminosity distribution functions with normal disk galaxies.

  7. Accretion and star formation in RQQs

    NASA Astrophysics Data System (ADS)

    White, Sarah; Jarvis, Matt; Häußler, Boris; Maddox, Natasha; Kalfountzou, Eleni; Hardcastle, Martin

    2016-06-01

    Active Galactic Nuclei (AGN) and star-forming galaxies are well-traced in the radio part of the electromagnetic spectrum, due to emission at these wavelengths being unaffected by dust obscuration. The key processes involved in producing the radio emission are black-hole accretion and star formation, both of which are thought to be crucial in determining how galaxies evolve. Disentangling the two contributions requires multi-wavelength data, and this is the approach we use for our work on radio-quiet quasars (RQQs). In contrast to previous studies, we find that accretion-connected radio emission dominates over that due to star formation, even at very low radio flux-densities. The first sample we describe is selected from the VISTA Deep Extragalactic Observations (VIDEO) survey, whose depth allows the study of very low accretion rates and/or lower-mass black holes. A second sample is obtained from the Spitzer-Herschel Active Galaxy Survey, spanning a factor of ~100 in optical luminosity over a narrow redshift range at z ~ 1. This enables evolutionary effects to be decoupled when comparisons are made with the VIDEO sample. Using radio data from the Karl G. Jansky Very Large Array (JVLA), we find further support that the AGN makes a significant contribution to the radio emission in RQQs. In addition, the levels of accretion and star formation appear to be weakly correlated with each other, and with optical luminosity.

  8. Planet Formation in Binary Star Systems

    NASA Astrophysics Data System (ADS)

    Martin, Rebecca

    About half of observed exoplanets are estimated to be in binary systems. Understanding planet formation and evolution in binaries is therefore essential for explaining observed exoplanet properties. Recently, we discovered that a highly misaligned circumstellar disk in a binary system can undergo global Kozai-Lidov (KL) oscillations of the disk inclination and eccentricity. These oscillations likely have a significant impact on the formation and orbital evolution of planets in binary star systems. Planet formation by core accretion cannot operate during KL oscillations of the disk. First, we propose to consider the process of disk mass transfer between the binary members. Secondly, we will investigate the possibility of planet formation by disk fragmentation. Disk self gravity can weaken or suppress the oscillations during the early disk evolution when the disk mass is relatively high for a narrow range of parameters. Thirdly, we will investigate the evolution of a planet whose orbit is initially aligned with respect to the disk, but misaligned with respect to the orbit of the binary. We will study how these processes relate to observations of star-spin and planet orbit misalignment and to observations of planets that appear to be undergoing KL oscillations. Finally, we will analyze the evolution of misaligned multi-planet systems. This theoretical work will involve a combination of analytic and numerical techniques. The aim of this research is to shed some light on the formation of planets in binary star systems and to contribute to NASA's goal of understanding of the origins of exoplanetary systems.

  9. Burst of Star Formation Drives Galactic Bubble

    NASA Technical Reports Server (NTRS)

    2001-01-01

    NASA's Hubble Space Telescope (HST) captures a lumpy bubble of hot gas rising from a cauldron of glowing matter in Galaxy NGC 3079, located 50 million light-years from Earth in the constellation Ursa Major. Astronomers suspect the bubble is being blown by 'winds' or high speed streams of particles, released during a burst of star formation. The bubble's lumpy surface has four columns of gaseous filaments towering above the galaxy's disc that whirl around in a vortex and are expelled into space. Eventually, this gas will rain down on the disc and may collide with gas clouds, compress them, and form a new generation of stars.

  10. Triggered Star Formation From Shock to Disk

    NASA Astrophysics Data System (ADS)

    Blackman, Eric

    2014-10-01

    Triggered star formation {TSF} occurs when supersonic flows generated by distant supernova blast waves, stellar winds {wind blown bubbles} or ionization fronts {D-type fronts in HII regions} sweep over a stable cloud. TSF may play a role in massive regions of star formation where winds, HII regions and, eventually, blast-waves sweep through dense, heterogeneous molecular material. In addition TSF has played an important role in discussions of the formation of our own solar system because it offers a natural way of injecting short lived radioactive isotopes {SLRI's} like 26^Al into material which will then form planetary bodies.The purpose of this proposal is to use advanced numerical tools to explore the physics of TSF in greater detail than has been attempted before. Previous studies have not been able to follow triggering past the early stages before a star forms. Our 3-D Adaptive Mesh Refinement {AMR} MHD code contains well tested physics modules which will allow us to track the influence of self-gravity, radiation-transport, cooling by molecules/neutrals/atoms and, finally, the collapse of gas into stars {i.e.condensed gravitating point-like objects or "sink-particles"}. With this tool we will follow triggering well past the formation of the star to explore the creation of accretion disks and their properties. In addition the microphysics routines in the code allow us to make detailed contact with HST observations such as the pillars in the Carina nebula via synthetic observations of line profiles, proper motions, Position-Velocity diagrams and statistics.

  11. Massive binary stars as a probe of massive star formation

    NASA Astrophysics Data System (ADS)

    Kiminki, Daniel C.

    2010-10-01

    Massive stars are among the largest and most influential objects we know of on a sub-galactic scale. Binary systems, composed of at least one of these stars, may be responsible for several types of phenomena, including type Ib/c supernovae, short and long gamma ray bursts, high-velocity runaway O and B-type stars, and the density of the parent star clusters. Our understanding of these stars has met with limited success, especially in the area of their formation. Current formation theories rely on the accumulated statistics of massive binary systems that are limited because of their sample size or the inhomogeneous environments from which the statistics are collected. The purpose of this work is to provide a higher-level analysis of close massive binary characteristics using the radial velocity information of 113 massive stars (B3 and earlier) and binary orbital properties for the 19 known close massive binaries in the Cygnus OB2 Association. This work provides an analysis using the largest amount of massive star and binary information ever compiled for an O-star rich cluster like Cygnus OB2, and compliments other O-star binary studies such as NGC 6231, NGC 2244, and NGC 6611. I first report the discovery of 73 new O or B-type stars and 13 new massive binaries by this survey. This work involved the use of 75 successful nights of spectroscopic observation at the Wyoming Infrared Observatory in addition to observations obtained using the Hydra multi-object spectrograph at WIYN, the HIRES echelle spectrograph at KECK, and the Hamilton spectrograph at LICK. I use these data to estimate the spectrophotometric distance to the cluster and to measure the mean systemic velocity and the one-sided velocity dispersion of the cluster. Finally, I compare these data to a series of Monte Carlo models, the results of which indicate that the binary fraction of the cluster is 57 +/- 5% and that the indices for the power law distributions, describing the log of the periods, mass

  12. Star Formation and the Hall Effect

    NASA Astrophysics Data System (ADS)

    Braiding, Catherine

    2011-10-01

    Magnetic fields play an important role in star formation by regulating the removal of angular momentum from collapsing molecular cloud cores. Hall diffusion is known to be important to the magnetic field behaviour at many of the intermediate densities and field strengths encountered during the gravitational collapse of molecular cloud cores into protostars, and yet its role in the star formation process is not well-studied. This thesis describes a semianalytic self-similar model of the collapse of rotating isothermal molecular cloud cores with both Hall and ambipolar diffusion, presenting similarity solutions that demonstrate that the Hall effect has a profound influence on the dynamics of collapse. ... Hall diffusion also determines the strength of the magnetic diffusion and centrifugal shocks that bound the pseudo and rotationally-supported discs, and can introduce subshocks that further slow accretion onto the protostar. In cores that are not initially rotating Hall diffusion can even induce rotation, which could give rise to disc formation and resolve the magnetic braking catastrophe. The Hall effect clearly influences the dynamics of gravitational collapse and its role in controlling the magnetic braking and radial diffusion of the field would be worth exploring in future numerical simulations of star formation.

  13. Turbulence and Star Formation in Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Hollyday, Gigja; Hunter, Deidre Ann; Little Things Team

    2015-01-01

    We are interested in understanding the nature and role of turbulence in the interstellar medium of dwarf irregular galaxies. Turbulence, resulting from a variety of processes, is a potential source for cloud formation, and thus star formation. We have undertaken an indirect analysis of turbulence via the third (skewness) and fourth (kurtosis) moments of the distribution of atomic hydrogen gas densities using the LITTLE THINGS data for a 40-count sample of nearby (<10.3 Mpc) dwarf galaxies. We followed the formulism used by Burkhart et al. (2010) in a study of the SMC. We found that there is evidence of turbulence in dwarf galaxies at a level comparable to that found in the SMC, but we have found no correlation between integrated star formation rates and integrated kurtosis values nor a clear correlation between kurtosis as a function of radius with gas surface density and star formation profiles. We are grateful for a summer internship provided by the Research Experiences for Undergraduates program at Northern Arizona University, run by Dr. Kathy Eastwood and Dr. David Trilling and funded by the National Science Foundation through grant AST-1004107.

  14. STAR CLUSTERS IN A NUCLEAR STAR FORMING RING: THE DISAPPEARING STRING OF PEARLS

    SciTech Connect

    Väisänen, Petri; Barway, Sudhanshu; Randriamanakoto, Zara

    2014-12-20

    An analysis of the star cluster population in a low-luminosity early-type galaxy, NGC 2328, is presented. The clusters are found in a tight star forming nuclear spiral/ring pattern and we also identify a bar from structural two-dimensional decomposition. These massive clusters are forming very efficiently in the circumnuclear environment and they are young, possibly all less than 30 Myr of age. The clusters indicate an azimuthal age gradient, consistent with a ''pearls-on-a-string'' formation scenario, suggesting bar-driven gas inflow. The cluster mass function has a robust down turn at low masses at all age bins. Assuming clusters are born with a power-law distribution, this indicates extremely rapid disruption at timescales of just several million years. If found to be typical, it means that clusters born in dense circumnuclear rings do not survive to become old globular clusters in non-interacting systems.

  15. GAS, STARS, AND STAR FORMATION IN ALFALFA DWARF GALAXIES

    SciTech Connect

    Huang Shan; Haynes, Martha P.; Giovanelli, Riccardo; Brinchmann, Jarle; Stierwalt, Sabrina; Neff, Susan G. E-mail: haynes@astro.cornell.edu E-mail: jarle@strw.leidenuniv.nl E-mail: susan.g.neff@nasa.gov

    2012-06-15

    We examine the global properties of the stellar and H I components of 229 low H I mass dwarf galaxies extracted from the ALFALFA survey, including a complete sample of 176 galaxies with H I masses <10{sup 7.7} M{sub Sun} and H I line widths <80 km s{sup -1}. Sloan Digital Sky Survey (SDSS) data are combined with photometric properties derived from Galaxy Evolution Explorer to derive stellar masses (M{sub *}) and star formation rates (SFRs) by fitting their UV-optical spectral energy distributions (SEDs). In optical images, many of the ALFALFA dwarfs are faint and of low surface brightness; only 56% of those within the SDSS footprint have a counterpart in the SDSS spectroscopic survey. A large fraction of the dwarfs have high specific star formation rates (SSFRs), and estimates of their SFRs and M{sub *} obtained by SED fitting are systematically smaller than ones derived via standard formulae assuming a constant SFR. The increased dispersion of the SSFR distribution at M{sub *} {approx}< 10{sup 8} M{sub Sun} is driven by a set of dwarf galaxies that have low gas fractions and SSFRs; some of these are dE/dSphs in the Virgo Cluster. The imposition of an upper H I mass limit yields the selection of a sample with lower gas fractions for their M{sub *} than found for the overall ALFALFA population. Many of the ALFALFA dwarfs, particularly the Virgo members, have H I depletion timescales shorter than a Hubble time. An examination of the dwarf galaxies within the full ALFALFA population in the context of global star formation (SF) laws is consistent with the general assumptions that gas-rich galaxies have lower SF efficiencies than do optically selected populations and that H I disks are more extended than stellar ones.

  16. Gas, Stars, and Star Formation in Alfalfa Dwarf Galaxies

    NASA Technical Reports Server (NTRS)

    Huang, Shan; Haynes, Martha P.; Giovanelli, Riccardo; Brinchmann, Jarle; Stierwalt, Sabrina; Neff, Susan G.

    2012-01-01

    We examine the global properties of the stellar and Hi components of 229 low H i mass dwarf galaxies extracted from the ALFALFA survey, including a complete sample of 176 galaxies with H i masses <10(sup 7.7) solar mass and Hi line widths <80 kilometers per second. Sloan Digital Sky Survey (SDSS) data are combined with photometric properties derived from Galaxy Evolution Explorer to derive stellar masses (M*) and star formation rates (SFRs) by fitting their UV-optical spectral energy distributions (SEDs). In optical images, many of the ALFALFA dwarfs are faint and of low surface brightness; only 56% of those within the SDSS footprint have a counterpart in the SDSS spectroscopic survey. A large fraction of the dwarfs have high specific star formation rates (SSFRs), and estimates of their SFRs and M* obtained by SED fitting are systematically smaller than ones derived via standard formulae assuming a constant SFR. The increased dispersion of the SSFR distribution at M* approximately less than10(exp 8)M(sub 0) is driven by a set of dwarf galaxies that have low gas fractions and SSFRs; some of these are dE/dSphs in the Virgo Cluster. The imposition of an upper Hi mass limit yields the selection of a sample with lower gas fractions for their M* than found for the overall ALFALFA population. Many of the ALFALFA dwarfs, particularly the Virgo members, have H i depletion timescales shorter than a Hubble time. An examination of the dwarf galaxies within the full ALFALFA population in the context of global star formation (SF) laws is consistent with the general assumptions that gas-rich galaxies have lower SF efficiencies than do optically selected populations and that Hi disks are more extended than stellar ones.

  17. Deuterium Fractionation just after the Star Formation

    NASA Astrophysics Data System (ADS)

    Shibata, D.; Sakai, N.; Yamamoto, S.

    2013-10-01

    We have recently conducted a five-point strip observation of the DCO+, H13CO+, DNC, HN13C, and N2H+ lines toward low mass Class I protostar L1551 IRS5, and have evaluated the deuterium fractionation ratios DCO+/HCO+ and DNC/HNC. The DCO+/HCO+ ratio is found to be lower toward the protostar position than those toward the adjacent positions. On the other hand, the DNC/HNC ratio does not show such a decrease toward the protostar position. This suggests that the deuterium fractionation ratio of the neutral species is conserved after the star formation. If so, the deuterium fractionation of the neutral species can be used as a novel tracer to investigate the initial condition of the star formation process.

  18. Star Formation and the Solar System

    NASA Technical Reports Server (NTRS)

    Bally, John; Boss, Alan; Papanastassiou, Dimitri; Sandford, Scott; Sargent, Anneila

    1988-01-01

    We have seen that studies of nearby star-forming regions are beginning to reveal the first signs of protoplanetary disks. Studies of interstellar and interplanetary grains are starting to provide clues about the processing and incorporation of matter into the Solar System. Studies of meteorites have yielded isotopic anomalies which indicate that some of the grains and inclusions in these bodies are very primitive. Although we have not yet detected a true interstellar grain, some of these materials have not been extensively modified since their removal from the ISM. We are indeed close to seeing our interstellar heritage. The overlap between astronomical and Solar System studies is in its infancy. What future experiments, observations, and missions can be performed in the near future that will greatly enhance our understanding of star formation and the formation of the Solar System?

  19. Star formation in cooling flow galaxies

    NASA Technical Reports Server (NTRS)

    Cardiel, Nicolas; Gorgas, Javier

    1993-01-01

    Spectroscopic observations of central dominant galaxies are reviewed. Through the analysis of absorption spectral features (mainly the strength of the Mg triplet at 5175 A and the break in 4000 A), both in the galaxy centers and along the radii, we will be able to impose limits on the ongoing star formation as the ultimate fate for the large amounts of accreted gas. With the same aim we will carry out a dynamical study based on velocity dispersion measurements.

  20. Turbulence and Star Formation in Interacting Galaxies

    NASA Astrophysics Data System (ADS)

    Auge, Connor; Chien, Lisa

    2017-01-01

    We investigate the turbulent gas motion in the tidal bridges and tails of colliding galaxies to see if there is a relation between this phenomenon and star formation within these galaxies. Previous studies have shown that the higher-order statistical moments, i.e. skewness and kurtosis, of the neutral hydrogen (HI) gas are linked to their turbulent motion in a galaxy. Such turbulences are considered to be potentially crucial in enhancing star formation at regions where the gas density is low, for example, the outer disk of a spiral galaxy, a dwarf galaxy, and tidal tails in an interacting system. Here we present these studies on a sample of colliding galaxy systems in detail. We create skewness and kurtosis maps representing the distribution of turbulent gas in these galaxies as a whole system and of the individual regions we are interested in. These maps also inform us as to whether the gas motion in these regions is sub-sonic or super-sonic. In order to investigate the relation between the turbulent gas motion and the star formation in low-density regions such as tidal tails, we compare these maps to far-ultraviolet images taken by GALEX space telescope.

  1. Three classical Cepheid variable stars in the nuclear bulge of the Milky Way.

    PubMed

    Matsunaga, Noriyuki; Kawadu, Takahiro; Nishiyama, Shogo; Nagayama, Takahiro; Kobayashi, Naoto; Tamura, Motohide; Bono, Giuseppe; Feast, Michael W; Nagata, Tetsuya

    2011-08-24

    The nuclear bulge is a region with a radius of about 200 parsecs around the centre of the Milky Way. It contains stars with ages ranging from a few million years to over a billion years, yet its star-formation history and the triggering process for star formation remain to be resolved. Recently, episodic star formation, powered by changes in the gas content, has been suggested. Classical Cepheid variable stars have pulsation periods that decrease with increasing age, so it is possible to probe the star-formation history on the basis of the distribution of their periods. Here we report the presence of three classical Cepheids in the nuclear bulge with pulsation periods of approximately 20 days, within 40 parsecs (projected distance) of the central black hole. No Cepheids with longer or shorter periods were found. We infer that there was a period about 25 million years ago, and possibly lasting until recently, in which star formation increased relative to the period of 30-70 million years ago.

  2. A GALAXY BLAZES WITH STAR FORMATION

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Most galaxies form new stars at a fairly slow rate, but members of a rare class known as 'starburst' galaxies blaze with extremely active star formation. Scientists using NASA's Hubble Space Telescope are perfecting a technique to determine the history of starburst activity in galaxies by using the colors of star clusters. Measuring the clusters' colors yields information about stellar temperatures. Since young stars are blue, and older stars redder, the colors can be related to the ages, somewhat similar to counting the rings in a fallen tree trunk in order to determine the tree's age. The galaxy NGC 3310 is forming clusters of new stars at a prodigious rate. Astronomer Gerhardt Meurer of The Johns Hopkins University leads a team of collaborators who are studying several starburst galaxies, including NGC 3310, which is showcased in this month's Hubble Heritage image. There are several hundred star clusters in NGC 3310, visible in the Heritage image as the bright blue diffuse objects that trace the galaxy's spiral arms. Each of these star clusters represents the formation of up to about a million stars, a process that takes less than 100,000 years. In addition, hundreds of individual young, luminous stars can be seen throughout the galaxy. Once formed, the star clusters become redder with age as the most massive and bluest stars exhaust their fuel and burn out. Measurements in this image of the wide range of cluster colors show that they have ages ranging from about one million up to more than one hundred million years. This suggests that the starburst 'turned on' over 100 million years ago. It may have been triggered when a companion galaxy collided with NGC 3310. These observations may change astronomers' view of starbursts. Starbursts were once thought to be brief episodes, resulting from catastrophic events like a galactic collision. However, the wide range of cluster ages in NGC 3310 suggests that the starbursting can continue for an extended interval, once

  3. Astrochemical studies of galactic star formation

    NASA Astrophysics Data System (ADS)

    Shah, Ronak Yogendra

    2000-08-01

    This thesis characterizes and quantifies a key part of the chemical evolution associated with star formation towards nearby molecular clouds by analyzing the radiation from abundant molecules and their deuterium- substituted counterparts, or deuterated molecules. As clouds evolve to form stars, molecular spectra probe the dynamics. Deuterium fractionation ratios sample the variations in temperature, density and activity of protostellar systems and offer clues into their dynamics. We present three projects to examine the scope and scale of deuterium fractionation of ammonia, NH3, and formylium, HCO+, in low mass star forming regions. Analysis of single aperture NH2D and NH3 spectra from prestellar and protostellar cores indicates the predominance of gas-phase reactions in the production of these species. Our survey suggests that these species deplete onto grain surfaces at late times in the evolution of molecular cores into protostars. Since the collapse of protostars is rapid, deuterium fractionation of ammonia is not likely to be affected substantially by grain chemistry. This should be the case for even more massive molecular clouds such as Orion Molecular Cloud I or Sgr B2. Thus, observed NH2D/NH3 values probe the cold gas-phase evolution of molecular clouds. The relationship between gas dynamics and star formation are explored in our survey of DCO+ and H13CO+. We extend previous analyses of the DCO+HCO+ as a measure of the ionization fraction and magnetic field-neutral coupling of molecular clouds by examining high energy transitions. This method traces warmer, denser gas associated with near-protostellar regions and clustered star formation. Although we find that most DCO+HCO + values are consistent with previous studies, we also discover regions where DCO+HCO+ is larger than predicted by the paradigm of ambipolar diffusion-regulated star formation. Single aperture surveys examine the ambient gas on ~105 AU scales. However, only aperture synthesis studies

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    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-01-11

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  5. Star Formation Beyond the Solar Circle: A Survey of Surveys

    NASA Astrophysics Data System (ADS)

    Kerton, Charles R.

    2013-06-01

    This talk will review and distill the results of major radio, infrared, and combined radio/IR, surveys that have focused on the identification and characterization of active regions of star formation in the outer Galaxy. These surveys reveal that, in terms of star formation activity, the Milky Way beyond the solar circle is not a vast wasteland, but rather it is an area containing numerous regions of star formation well placed for detailed individual study, for large-scale studies of star formation within spiral arms, and for comparative studies with star formation occurring in different environments such as the inner Galaxy and Galactic center.

  6. Characterizing Spiral Arm and Interarm Star Formation

    NASA Astrophysics Data System (ADS)

    Kreckel, K.; Blanc, G. A.; Schinnerer, E.; Groves, B.; Adamo, A.; Hughes, A.; Meidt, S.

    2016-08-01

    Interarm star formation contributes significantly to a galaxy’s star formation budget and provides an opportunity to study stellar birthplaces unperturbed by spiral arm dynamics. Using optical integral field spectroscopy of the nearby galaxy NGC 628 with VLT/MUSE, we construct Hα maps including detailed corrections for dust extinction and stellar absorption to identify 391 H ii regions at 35 pc resolution over 12 kpc2. Using tracers sensitive to the underlying gravitational potential, we associate H ii regions with either arm (271) or interarm (120) environments. Using our full spectral coverage of each region, we find that most physical properties (luminosity, size, metallicity, ionization parameter) of H ii regions are independent of environment. We calculate the fraction of Hα luminosity due to the background of diffuse ionized gas (DIG) contaminating each H ii region, and find the DIG surface brightness to be higher within H ii regions than in the surroundings, and slightly higher within arm H ii regions. Use of the temperature-sensitive [S ii]/Hα line ratio instead of the Hα surface brightness to identify the boundaries of H ii regions does not change this result. Using the dust attenuation as a tracer of the gas, we find depletion times consistent with previous work (2 × 109 yr) with no differences between the arm and interarm, but this is very sensitive to the DIG correction. Unlike molecular clouds, which can be dynamically affected by the galactic environment, we see fairly consistent properties of H ii regions in both arm and interarm environments. This suggests either a difference in star formation and feedback in arms or a decoupling of dense star-forming clumps from the more extended surrounding molecular gas.

  7. STAR FORMATION ACROSS THE W3 COMPLEX

    SciTech Connect

    Román-Zúñiga, Carlos G.; Ybarra, Jason E.; Tapia, Mauricio; Megías, Guillermo D.; Lada, Elizabeth A.; Alves, Joáo F.

    2015-09-15

    We present a multi-wavelength analysis of the history of star formation in the W3 complex. Using deep, near-infrared ground-based images combined with images obtained with Spitzer and Chandra observatories, we identified and classified young embedded sources. We identified the principal clusters in the complex and determined their structure and extension. We constructed extinction-limited samples for five principal clusters and constructed K-band luminosity functions that we compare with those of artificial clusters with varying ages. This analysis provided mean ages and possible age spreads for the clusters. We found that IC 1795, the centermost cluster of the complex, still hosts a large fraction of young sources with circumstellar disks. This indicates that star formation was active in IC 1795 as recently as 2 Myr ago, simultaneous to the star-forming activity in the flanking embedded clusters, W3-Main and W3(OH). A comparison with carbon monoxide emission maps indicates strong velocity gradients in the gas clumps hosting W3-Main and W3(OH) and shows small receding clumps of gas at IC 1795, suggestive of rapid gas removal (faster than the T Tauri timescale) in the cluster-forming regions. We discuss one possible scenario for the progression of cluster formation in the W3 complex. We propose that early processes of gas collapse in the main structure of the complex could have defined the progression of cluster formation across the complex with relatively small age differences from one group to another. However, triggering effects could act as catalysts for enhanced efficiency of formation at a local level, in agreement with previous studies.

  8. Star Formation Across the W3 Complex

    NASA Astrophysics Data System (ADS)

    Román-Zúñiga, Carlos G.; Ybarra, Jason E.; Megías, Guillermo D.; Tapia, Mauricio; Lada, Elizabeth A.; Alves, Joáo F.

    2015-09-01

    We present a multi-wavelength analysis of the history of star formation in the W3 complex. Using deep, near-infrared ground-based images combined with images obtained with Spitzer and Chandra observatories, we identified and classified young embedded sources. We identified the principal clusters in the complex and determined their structure and extension. We constructed extinction-limited samples for five principal clusters and constructed K-band luminosity functions that we compare with those of artificial clusters with varying ages. This analysis provided mean ages and possible age spreads for the clusters. We found that IC 1795, the centermost cluster of the complex, still hosts a large fraction of young sources with circumstellar disks. This indicates that star formation was active in IC 1795 as recently as 2 Myr ago, simultaneous to the star-forming activity in the flanking embedded clusters, W3-Main and W3(OH). A comparison with carbon monoxide emission maps indicates strong velocity gradients in the gas clumps hosting W3-Main and W3(OH) and shows small receding clumps of gas at IC 1795, suggestive of rapid gas removal (faster than the T Tauri timescale) in the cluster-forming regions. We discuss one possible scenario for the progression of cluster formation in the W3 complex. We propose that early processes of gas collapse in the main structure of the complex could have defined the progression of cluster formation across the complex with relatively small age differences from one group to another. However, triggering effects could act as catalysts for enhanced efficiency of formation at a local level, in agreement with previous studies.

  9. MASSIVE STAR FORMATION IN NGC 2074

    SciTech Connect

    Fleener, Christine E.; Chu, Y.-H.; Gruendl, Robert A.; Payne, James T.; Chen, C.-H. Rosie

    2010-01-15

    Spitzer observations of the Large Magellanic Cloud (LMC) have revealed a large population of young stellar objects (YSOs), but complementary high-resolution images in the optical or near-IR wavelengths are still needed to resolve the multiplicity and immediate environments of the YSOs. The Hubble Space Telescope imaged the star-forming region NGC 2074 in the LMC during its 100,000th orbit, providing an opportunity to more closely examine the YSOs and their environments in this region. We have studied the 10 YSO candidates identified from Spitzer observations, confirming their nature and determining their physical parameters by modeling their spectral energy distributions. The majority of the YSOs and central stars of ultracompact H II regions in NGC 2074 have masses consistent with spectral types of early B to late O. The co-existence of massive early-type O stars and the less massive YSOs indicates that their formation may have started at a similar time, a few 10{sup 5} yr ago. NGC 2074 provides an opportunity to study the evolution of massive stars at their infancy.

  10. HIERARCHICAL STAR FORMATION IN NEARBY LEGUS GALAXIES

    SciTech Connect

    Elmegreen, Debra Meloy; Elmegreen, Bruce G.; Adamo, Angela; Gouliermis, Dimitrios A.; Aloisi, Alessandra; Bright, Stacey N.; Cignoni, Michele; Lee, Janice; Sabbi, Elena; Andrews, Jennifer; Calzetti, Daniela; Annibali, Francesca; Evans, Aaron S.; Johnson, Kelsey; Gallagher III, John S.; Grebel, Eva K.; Hunter, Deidre A.; Kim, Hwihyun; Smith, Linda J.; Thilker, David; and others

    2014-05-20

    Hierarchical structure in ultraviolet images of 12 late-type LEGUS galaxies is studied by determining the numbers and fluxes of nested regions as a function of size from ∼1 to ∼200 pc, and the number as a function of flux. Two starburst dwarfs, NGC 1705 and NGC 5253, have steeper number-size and flux-size distributions than the others, indicating high fractions of the projected areas filled with star formation. Nine subregions in seven galaxies have similarly steep number-size slopes, even when the whole galaxies have shallower slopes. The results suggest that hierarchically structured star-forming regions several hundred parsecs or larger represent common unit structures. Small galaxies dominated by only a few of these units tend to be starbursts. The self-similarity of young stellar structures down to parsec scales suggests that star clusters form in the densest parts of a turbulent medium that also forms loose stellar groupings on larger scales. The presence of super star clusters in two of our starburst dwarfs would follow from the observed structure if cloud and stellar subregions more readily coalesce when self-gravity in the unit cell contributes more to the total gravitational potential.

  11. On the Formation of Massive Stars

    NASA Astrophysics Data System (ADS)

    Kaper, L.; Ellerbroek, L.; Ochsendorf, B.; Bik, A.

    2012-12-01

    The birth process and (early) evolution of massive stars is still poorly understood. Heavy extinction hides their birthplaces from view and the short formation timescale limits the sample of objects to be studied. So far, our physical knowledge of massive YSOs has been derived from near-IR imaging and spectroscopy, revealing populations of young OB-type stars, some still surrounded by a disk, others apparently ‘normal’ main sequence stars powering H II regions. The most important spectral features of OB-type stars are, however, located in the UV and optical range. With the new optical/near-infrared spectrograph X-shooter on the ESO Very Large Telescope it is possible to extend the spectral coverage of these massive YSOs into the optical range. Our first results are very promising: the discovery of a jet demonstrates that one of our mYSOs is still actively accreting. Furthermore, the first firm spectral classification of another mYSO results in the precise location on a pre-main-sequence track.

  12. Star formation law in the Milky Way

    NASA Astrophysics Data System (ADS)

    Sofue, Yoshiaki; Nakanishi, Hiroyuki

    2017-01-01

    The Schmidt law (SF law) in the Milky Way was investigated using 3D distribution maps of H II regions and H I and molecular (H2) gases with spatial resolutions of ˜1 kpc in the Galactic plane and a few tens of pc in the vertical direction. H II regions were shown to be distributed in a star-forming (SF) disk with nearly constant vertical full thickness 92 pc in spatial coincidence with the molecular gas disk. The vertically averaged volume star formation rate (SFR) ρSFR in the SF disk is related to the surface SFR ΣSFR by ρSFR/[M⊙ yr-1 kpc-3] = 9.26 × ΣSFR/[M⊙ yr-1 kpc-2]. The SF law fitted by a single power law of gas density in the form of Σ _SFR∝ ρ _SFR∝ ρ _gas^α and ∝ Σ _gas^β showed indices of α =0.78 ± 0.05 for ρ _H_2 and 2.15 ± 0.08 for ρtotal, and β = 1.14 ± 0.23 for Σtotal, where ρ and Σ denote volume and surface densities, respectively. The star formation rate is shown to be directly related to the molecular gas, but indirectly to H I and total gas densities. The dependence of the SF law on the gaseous phase is explained by the phase transition theory between H I and H2.

  13. Investigation of Star Formation: Instrumentation and Methodology

    NASA Astrophysics Data System (ADS)

    Veach, Todd Justin

    A thorough exploration of star formation necessitates observation across the electromagnetic spectrum. In particular, observations in the submillimeter and ultra-violet allow one to observe very early stage star formation and to trace the evolution from molecular cloud collapse to stellar ignition. Submillimeter observations are essential for piercing the heart of heavily obscured stellar nurseries to observe star formation in its infancy. Ultra-violet observations allow one to observe stars just after they emerge from their surrounding environment, allowing higher energy radiation to escape. To make detailed observations of early stage star formation in both spectral regimes requires state-of-the-art detector technology and instrumentation. In this dissertation, I discuss the calibration and feasibility of detectors developed by Lawrence Berkeley National Laboratory and specially processed at the Jet Propulsion Laboratory to increase their quantum efficiency at far-ultraviolet wavelengths. A cursory treatment of the delta-doping process is presented, followed by a thorough discussion of calibration procedures developed at JPL and in the Laboratory for Astronomical and Space Instrumentation at ASU. Subsequent discussion turns to a novel design for a Modular Imager Cell forming one possible basis for construction of future large focal plane arrays. I then discuss the design, fabrication, and calibration of a sounding rocket imaging system developed using the MIC and these specially processed detectors. Finally, I discuss one scientific application of sub-mm observations. I used data from the Heinrich Hertz Sub-millimeter Telescope and the Sub-Millimeter Array (SMA) to observe sub-millimeter transitions and continuum emission towards AFGL 2591. I tested the use of vibrationally excited HCN emission to probe the protostellar accretion disk structure. I measured vibrationally excited HCN line ratios in order to elucidate the appropriate excitation mechanism. I find

  14. The Hall effect in star formation

    NASA Astrophysics Data System (ADS)

    Braiding, C. R.; Wardle, M.

    2012-05-01

    Magnetic fields play an important role in star formation by regulating the removal of angular momentum from collapsing molecular cloud cores. Hall diffusion is known to be important to the magnetic field behaviour at many of the intermediate densities and field strengths encountered during the gravitational collapse of molecular cloud cores into protostars, and yet its role in the star formation process is not well studied. We present a semianalytic self-similar model of the collapse of rotating isothermal molecular cloud cores with both Hall and ambipolar diffusion, and similarity solutions that demonstrate the profound influence of the Hall effect on the dynamics of collapse. The solutions show that the size and sign of the Hall parameter can change the size of the protostellar disc by up to an order of magnitude and the protostellar accretion rate by 50 per cent when the ratio of the Hall to ambipolar diffusivities is varied between -0.5 ≤ηH/ηA≤ 0.2. These changes depend upon the orientation of the magnetic field with respect to the axis of rotation and create a preferred handedness to the solutions that could be observed in protostellar cores using next-generation instruments such as ALMA. Hall diffusion also determines the strength and position of the shocks that bound the pseudo and rotationally supported discs, and can introduce subshocks that further slow accretion on to the protostar. In cores that are not initially rotating (not examined here), Hall diffusion can even induce rotation, which could give rise to disc formation and resolve the magnetic braking catastrophe. The Hall effect clearly influences the dynamics of gravitational collapse and its role in controlling the magnetic braking and radial diffusion of the field merits further exploration in numerical simulations of star formation.

  15. The Star-Formation Region SNO 87

    NASA Astrophysics Data System (ADS)

    Gyulbudaghian, A. L.

    2014-06-01

    The star-formation region SNO 87 is associated with the dark cloud LDN 212. 12CO(1-0) observations of a part of the molecular cloud associated with SNO 87 show that it lies somewhat to the north of the densest part of the molecular cloud. There is a bipolar molecular outflow from SNO 87, both branches of which are blue, i.e., the velocity is directed toward us with a velocity of ~3.5 km/s relative to the cloud. 12CO(1-0) observations of a part of the cloud lying to the E of SNO 87 show that this part of the cloud rotates with an angular velocity Ω = 2.44·10-14 s-1. SNO 87 contains several stars that are coupled with nebular filaments, bursts, and Herbig-Haro objects. It is also associated with the point source IRAS 18064-2413.

  16. Formation of the first stars and quasars

    NASA Astrophysics Data System (ADS)

    Haiman, Z.

    We examine various observable signatures of the first generation of stars and low-luminosity quasars, including the metal enrichment, radiation background, and dust opacity/emission that they produce. We calculate the formation history of collapsed baryonic halos, based on an extension of the Press-Schechter formalism, incorporating the effects of pressure and H2-dissociation. We then use the observed CH ratio at z=3 in the Lyman-α forest clouds to obtain an average the star formation efficiency in these halos. Similarly, we fit the efficiency of black-hole formation, and the shape of quasar light curves, to match the observed quasar luminosity function (LF) between z=2-4, and use this fit to extrapolate the quasar LF to faint magnitudes and high redshifts. To be consistent with the lack of faint point-sources in the Hubble Deep Field, we impose a lower limit of ~ 75 km s-1 for the circular velocities of halos harboring central black holes. We find that in a λCDM model, stars reionize the IGM at zreion=9-13, and quasars at z=12. Observationally, zreion can be measured by the forthcoming MAP and Planck Surveyor satellites, via the damping of CMB anisotropies by ~10% on small angular scales due to electron scattering. We show that if reionization occurs later, at 5 <~ zreion <~ 10, then it can be measured from the spectra of individual sources. We also find that the Next Generation Space Telescope will be able to directly image about 1-40 star clusters, and a few faint quasars, from z > 10 per square arcminute. The amount of dust produced by the first supernovae has an optical depth of τ=0.1-1 towards high redshift sources, and the reprocessed UV flux of stars and quasars distorts the cosmic microwave background radiation (CMB) by a Compton y-parameter comparable to the COBE limit, y ~ 1.5 × 10-5.

  17. The nuclear path of the CNO cycles in massive stars

    NASA Astrophysics Data System (ADS)

    Przybilla, N.; Nieva, M. F.; Maeder, A.; Meynet, G.

    We discuss how the nuclear path of the CNO cycles in massive stars can be employed as a quality indicator for model atmosphere analyses and for the derivation of tight observational constraints for developing a better understanding of the evolution of rotating massive stars.

  18. The nuclear path of the CNO cycles in massive stars

    NASA Astrophysics Data System (ADS)

    Przybilla, Norbert; Nieva, Maria-Fernanda; Maeder, André; Meynet, Georges

    2015-08-01

    We discuss how the nuclear path of the CNO cycles in massive stars can be employed as a quality indicator for model atmosphere analyses and for the derivation of tight observational constraints for developing a better understanding of the evolution of rotating massive stars.

  19. Bursty star formation feedback and cooling outflows

    NASA Astrophysics Data System (ADS)

    Suarez, Teresita; Pontzen, Andrew; Peiris, Hiranya V.; Slyz, Adrianne; Devriendt, Julien

    2016-10-01

    We study how outflows of gas launched from a central galaxy undergoing repeated starbursts propagate through the circum-galactic medium (CGM), using the simulation code RAMSES. We assume that the outflow from the disc can be modelled as a rapidly moving bubble of hot gas at ˜1 kpc above disc, then ask what happens as it moves out further into the halo around the galaxy on ˜100 kpc scales. To do this, we run 60 two-dimensional simulations scanning over parameters of the outflow. Each of these is repeated with and without radiative cooling, assuming a primordial gas composition to give a lower bound on the importance of cooling. In a large fraction of radiative-cooling cases we are able to form rapidly outflowing cool gas from in situ cooling of the flow. We show that the amount of cool gas formed depends strongly on the `burstiness' of energy injection; sharper, stronger bursts typically lead to a larger fraction of cool gas forming in the outflow. The abundance ratio of ions in the CGM may therefore change in response to the detailed historical pattern of star formation. For instance, outflows generated by star formation with short, intense bursts contain up to 60 per cent of their gas mass at temperatures <5 × 104 K; for near-continuous star formation, the figure is ≲5 per cent. Further study of cosmological simulations, and of idealized simulations with e.g. metal-cooling, magnetic fields and/or thermal conduction, will help to understand the precise signature of bursty outflows on observed ion abundances.

  20. Interstellar MHD Turbulence and Star Formation

    NASA Astrophysics Data System (ADS)

    Vázquez-Semadeni, Enrique

    This chapter reviews the nature of turbulence in the Galactic interstellar medium (ISM) and its connections to the star formation (SF) process. The ISM is turbulent, magnetized, self-gravitating, and is subject to heating and cooling processes that control its thermodynamic behavior, causing it to behave approximately isobarically, in spite of spanning several orders of magnitude in density and temperature. The turbulence in the warm and hot ionized components of the ISM appears to be trans- or subsonic, and thus to behave nearly incompressibly. However, the neutral warm and cold components are highly compressible, as a consequence of both thermal instability (TI) in the atomic gas and of moderately-to-strongly supersonic motions in the roughly isothermal cold atomic and molecular components. Within this context, we discuss: (1) the production and statistical distribution of turbulent density fluctuations in both isothermal and polytropic media; (2) the nature of the clumps produced by TI, noting that, contrary to classical ideas, they in general accrete mass from their environment in spite of exhibiting sharp discontinuities at their boundaries; (3) the density-magnetic field correlation (and, at low densities, lack thereof) in turbulent density fluctuations, as a consequence of the superposition of the different wave modes in the turbulent flow; (4) the evolution of the mass-to-magnetic flux ratio (MFR) in density fluctuations as they are built up by dynamic compressions; (5) the formation of cold, dense clouds aided by TI, in both the hydrodynamic (HD) and the magnetohydrodynamic (MHD) cases; (6) the expectation that star-forming molecular clouds are likely to be undergoing global gravitational contraction, rather than being near equilibrium, as generally believed, and (7) the regulation of the star formation rate (SFR) in such gravitationally contracting clouds by stellar feedback which, rather than keeping the clouds from collapsing, evaporates and disperses

  1. Magnetic fields and massive star formation

    SciTech Connect

    Zhang, Qizhou; Keto, Eric; Ho, Paul T. P.; Ching, Tao-Chung; Chen, How-Huan; Qiu, Keping; Girart, Josep M.; Juárez, Carmen; Liu, Hauyu; Tang, Ya-Wen; Koch, Patrick M.; Rao, Ramprasad; Lai, Shih-Ping; Li, Zhi-Yun; Frau, Pau; Li, Hua-Bai; Padovani, Marco; Bontemps, Sylvain

    2014-09-10

    Massive stars (M > 8 M {sub ☉}) typically form in parsec-scale molecular clumps that collapse and fragment, leading to the birth of a cluster of stellar objects. We investigate the role of magnetic fields in this process through dust polarization at 870 μm obtained with the Submillimeter Array (SMA). The SMA observations reveal polarization at scales of ≲0.1 pc. The polarization pattern in these objects ranges from ordered hour-glass configurations to more chaotic distributions. By comparing the SMA data with the single dish data at parsec scales, we found that magnetic fields at dense core scales are either aligned within 40° of or perpendicular to the parsec-scale magnetic fields. This finding indicates that magnetic fields play an important role during the collapse and fragmentation of massive molecular clumps and the formation of dense cores. We further compare magnetic fields in dense cores with the major axis of molecular outflows. Despite a limited number of outflows, we found that the outflow axis appears to be randomly oriented with respect to the magnetic field in the core. This result suggests that at the scale of accretion disks (≲ 10{sup 3} AU), angular momentum and dynamic interactions possibly due to close binary or multiple systems dominate over magnetic fields. With this unprecedentedly large sample of massive clumps, we argue on a statistical basis that magnetic fields play an important role during the formation of dense cores at spatial scales of 0.01-0.1 pc in the context of massive star and cluster star formation.

  2. A CANDELS WFC3 Grism Study of Emission-Line Galaxies at Z approximates 2: A mix of Nuclear Activity and Low-Metallicity Star Formation

    NASA Technical Reports Server (NTRS)

    Trump, Jonathan R.; Weiner, Benjamin J.; Scarlata, Claudia; Kocevski, Dale D.; Bell, Eric F.; McGrath, Elizabeth J.; Koo, David C.; Faber, S. M.; Laird, Elise S.; Mozena, Mark; Rangel, Cyprian; Yan, Renbin; Yesuf, Hassen; Atek, Hakim; Dickinson, Mark; Donley, Jennifer L.; Dunlop, James S.; Ferguson, Henry C.; Finkelstein, Steven L.; Grogin, Norman A.; Hathi, Nimish P.; Juneau, Stephanie; Kartaltepe, Jeyhan S.; Koekemoer, Anton M.; Nandra, Kirpal

    2011-01-01

    We present Hubble Space Telescope Wide Field Camera 3 slitless grism spectroscopy of 28 emission-line galaxies at z approximates 2, in the GOODS-S region of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). The high sensitivity of these grism observations, with > 5-sigma detections of emission lines to f > 2.5 X 10(exp -18( erg/s/ square cm, means that the galaxies in the sample are typically approximately 7 times less massive (median M(star). = 10(exp 9.5)M(solar)) than previously studied z approximates 2 emission-line galaxies. Despite their lower mass, the galaxies have [O-III]/H-Beta ratios which are very similar to previously studied z approximates 2 galaxies and much higher than the typical emission-line ratios of local galaxies. The WFC3 grism allows for unique studies of spatial gradients in emission lines, and we stack the two-dimensional spectra of the galaxies for this purpose. In the stacked data the [O-III] emission line is more spatially concentrated than the H-Beta emission line with 98.1% confidence. We additionally stack the X-ray data (all sources are individually undetected), and find that the average L(sub [O-III])/L(sub 0.5.10keV) ratio is intermediate between typical z approximates 0 obscured active galaxies and star-forming galaxies. Together the compactness of the stacked [O-III] spatial profile and the stacked X-ray data suggest that at least some of these low-mass, low-metallicity galaxies harbor weak active galactic nuclei.

  3. Star formation along the Hubble sequence. Radial structure of the star formation of CALIFA galaxies

    NASA Astrophysics Data System (ADS)

    González Delgado, R. M.; Cid Fernandes, R.; Pérez, E.; García-Benito, R.; López Fernández, R.; Lacerda, E. A. D.; Cortijo-Ferrero, C.; de Amorim, A. L.; Vale Asari, N.; Sánchez, S. F.; Walcher, C. J.; Wisotzki, L.; Mast, D.; Alves, J.; Ascasibar, Y.; Bland-Hawthorn, J.; Galbany, L.; Kennicutt, R. C.; Márquez, I.; Masegosa, J.; Mollá, M.; Sánchez-Blázquez, P.; Vílchez, J. M.

    2016-05-01

    The spatially resolved stellar population content of today's galaxies holds important information for understanding the different processes that contribute to the star formation and mass assembly histories of galaxies. The aim of this paper is to characterize the radial structure of the star formation rate (SFR) in galaxies in the nearby Universe as represented by a uniquely rich and diverse data set drawn from the CALIFA survey. The sample under study contains 416 galaxies observed with integral field spectroscopy, covering a wide range of Hubble types and stellar masses ranging from M⋆ ~ 109 to 7 × 1011 M⊙. Spectral synthesis techniques are applied to the datacubes to derive 2D maps and radial profiles of the intensity of the star formation rate in the recent past (ΣSFR), as well as related properties, such as the local specific star formation rate (sSFR), defined as the ratio between ΣSFR and the stellar mass surface density (μ⋆). To emphasize the behavior of these properties for galaxies that are on and off the main sequence of star formation (MSSF), we stack the individual radial profiles in seven bins of galaxy morphology (E, S0, Sa, Sb, Sbc, Sc, and Sd), and several stellar masses. Our main results are: (a) the intensity of the star formation rate shows declining profiles that exhibit very small differences between spirals with values at R = 1 half light radius (HLR) within a factor two of ΣSFR ~ 20 M⊙Gyr-1pc-2. The dispersion in the ΣSFR(R) profiles is significantly smaller in late type spirals (Sbc, Sc, Sd). This confirms that the MSSF is a sequence of galaxies with nearly constant ΣSFR. (b) sSFR values scale with Hubble type and increase radially outward with a steeper slope in the inner 1 HLR. This behavior suggests that galaxies are quenched inside-out and that this process is faster in the central, bulge-dominated part than in the disks. (c) As a whole and at all radii, E and S0 are off the MSSF with SFR much smaller than spirals of the

  4. Star and cluster formation in NGC 1275

    NASA Technical Reports Server (NTRS)

    Richer, Harvey B.; Crabtree, Dennis R.; Fabian, A. C.; Lin, D. N. C.

    1993-01-01

    Luminous, blue, and unresolved objects have been found by imaging the nuclear region of the central galaxy in the Perseus Cluster, NGC 1275. Stellar formation in a cooling flow in which gas clouds confined by weak magnetic fields are allowed to remain at low densities is favored. Cloud-cloud collisions and coagulation in the high cloud density environment at the center of the galaxy then causes some clouds to become gravitationally unstable and to form globular clusters.

  5. The Milky Way's nuclear star cluster and massive black hole

    NASA Astrophysics Data System (ADS)

    Schödel, Rainer

    2016-02-01

    Because of its nearness to Earth, the centre of the Milky Way is the only galaxy nucleus in which we can study the characteristics, distribution, kinematics, and dynamics of the stars on milli-parsec scales. We have accurate and precise measurements of the Galactic centre's central black hole, Sagittarius A*, and can study its interaction with the surrounding nuclear star cluster in detail. This contribution aims at providing a concise overview of our current knowledge about the Milky Way's central black hole and nuclear star cluster, at highlighting the observational challenges and limitations, and at discussing some of the current key areas of investigation.

  6. The Star Formation History of Void Galaxies

    NASA Astrophysics Data System (ADS)

    Stanonik, Kathryn

    The Cosmic Web that permeates our universe is defined by the alignment of galaxies into filaments, clusters, and walls, as well as by the voids between them which are (mostly) empty. Void galaxies, found occupying these underdense regions, are an environmentally defined population whose isolated nature and extreme environment provides an ideal opportunity to test theories of galaxy formation and evolution. Their existence also poses a well defined observational constraint to Lambda CDM cosmological models. We propose to do UV imaging of a sample of SDSS selected void galaxies located in the deepest underdensities of nearby voids. Our galaxies were selected using the Delaunay Tesselation Field estimator, a novel, purely structural and geometric technique, to produce a sample that more uniformly represents the void galaxy population. In addition, we use a powerful new backend of the Westerbork Synthesis Radio Telescope that allows us to probe the neutral gas content in a huge volume around each targeted void galaxy, while still resolving individual galaxy kinematics and detecting faint companions in H I. We specifically aim to study the star formation history of these systems, which appear to be in a more youthful stage of their evolution than field galaxies. With this combination of UV and H I data we will address questions ranging from how galaxies get their gas, how they form stars, and what role environment plays in these processes.

  7. A CANDELS WFC3 GRISM STUDY OF EMISSION-LINE GALAXIES AT z {approx} 2: A MIX OF NUCLEAR ACTIVITY AND LOW-METALLICITY STAR FORMATION

    SciTech Connect

    Trump, Jonathan R.; Kocevski, Dale D.; McGrath, Elizabeth J.; Koo, David C.; Faber, S. M.; Mozena, Mark; Yesuf, Hassen; Scarlata, Claudia; Bell, Eric F.; Laird, Elise S.; Rangel, Cyprian; Yan Renbin; Atek, Hakim; Dickinson, Mark; Donley, Jennifer L.; Ferguson, Henry C.; Grogin, Norman A.; Dunlop, James S.; Finkelstein, Steven L.; and others

    2011-12-20

    We present Hubble Space Telescope Wide Field Camera 3 (WFC3) slitless grism spectroscopy of 28 emission-line galaxies at z {approx} 2, in the GOODS-S region of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey. The high sensitivity of these grism observations, with >1{sigma} detections of emission lines to f > 2.5 Multiplication-Sign 10{sup -18} erg s{sup -1} cm{sup -2}, means that the galaxies in the sample are typically {approx}7 times less massive (median M{sub *} = 10{sup 9.5} M{sub Sun }) than previously studied z {approx} 2 emission-line galaxies. Despite their lower mass, the galaxies have [O III]/H{beta} ratios which are very similar to previously studied z {approx} 2 galaxies and much higher than the typical emission-line ratios of local galaxies. The WFC3 grism allows for unique studies of spatial gradients in emission lines, and we stack the two-dimensional spectra of the galaxies for this purpose. In the stacked data the [O III] emission line is more spatially concentrated than the H{beta} emission line with 98.1% confidence. We additionally stack the X-ray data (all sources are individually undetected), and find that the average L{sub [OIII]}/L{sub 0.5-10keV} ratio is intermediate between typical z {approx} 0 obscured active galaxies and star-forming galaxies. Together the compactness of the stacked [O III] spatial profile and the stacked X-ray data suggest that at least some of these low-mass, low-metallicity galaxies harbor weak active galactic nuclei.

  8. Ongoing Massive Star Formation in the Bulge of M51

    NASA Astrophysics Data System (ADS)

    Lamers, H. J. G. L. M.; Panagia, N.; Scuderi, S.; Romaniello, M.; Spaans, M.; de Wit, W. J.; Kirshner, R.

    2002-02-01

    ``hiding'' within the point sources. For the ``bluest'' sources, the upper limit is only a few hundred Msolar. We conclude that the formation of massive stars outside clusters (or in very low mass clusters) is occurring in the bulge of M51. The estimated star formation rate in the bulge of M51 is (1-2)×10-3 Msolar yr-1, depending on the adopted initial mass function. With the observed total amount of gas in the bulge, ~4×105 Msolar, and the observed normal gas-to-dust ratio of ~150, this star formation rate could be sustained for about (2-4)×108 yr. This suggests that the ongoing massive star formation in the bulge of M51 is fed/triggered by the interaction with its companion about 4×108 yr ago. The star formation in the bulge of M51 is compared with that in bulges of other spirals. Theoretical predictions of star formation suggest that isolated massive stars might be formed in clouds in which H2, [O I] 63 μm and [C II] 158 μm are the dominant coolants. This is expected to occur in regions of rather low optical depth, AV<=1, with a hot source that can dissociate the CO molecules. These conditions are met in the bulge of M51, where the extinction is low and where CO can be destroyed by the radiation from the bright nuclear starburst cluster in the center. The mode of formation of massive stars in the bulge of M51 may resemble the star formation in the early universe, when the CO and dust contents were low because of the low metallicity. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

  9. The Spatially Resolved Star Formation History of NGC 300

    NASA Astrophysics Data System (ADS)

    Gogarten, S. M.; Dalcanton, J. J.; Williams, B. F.

    2009-01-01

    We present the star formation histories (SFH) of two regions in NGC 300 from the ACS Nearby Galaxies Survey Treasury (ANGST). ANGST is using the Hubble Space Telescope (HST) to determine the star formation histories of a volume-limited sample of nearby galaxies. We demonstrate that even small regions within a galaxy contain enough stars to derive the SFH by comparing color-magnitude diagrams (CMDs) of the resolved stellar populations to synthetic CMDs from stellar evolution models. Of the two regions selected, one can be identified as star-forming from its UV, Hα, and dust emission. The SFH of this region shows significant star formation over the past 10 Myr, unlike a non-star-forming region of the same size. These preliminary results will form the basis of a larger study of spatially-resolved star formation in nearby spirals.

  10. Star Formation in Dwarf Galaxies: Life in a Rough Neighborhood

    SciTech Connect

    Murray, S

    2003-10-16

    Star formation within dwarf galaxies is governed by several factors. Many of these factors are external, including ram-pressure stripping, tidal stripping, and heating by external UV radiation. The latter, in particular, may prevent star formation in the smallest systems. Internal factors include negative feedback in the form of UV radiation, winds and supernovae from massive stars. These act to reduce the star formation efficiency within dwarf systems, which may, in turn, solve several theoretical and observational problems associated with galaxy formation. In this contribution, we discuss our recent work being done to examine the importance of the many factors in the evolution of dwarf galaxies.

  11. Ram pressure induced star formation in Abell 3266

    NASA Astrophysics Data System (ADS)

    Bonsall, Brittany

    An X-ray observation of the merging galaxy cluster Abell 3266 was obtained via the ROSAT PSPC. This information, along with spectroscopic data from the WIde-field Nearby Galaxy-clusters Survey (i.e. WINGS), were used to investigate whether ram pressure is a mechanism that influences star formation. Galaxies exhibiting ongoing star formation are identified by the presence of strong Balmer lines (Hbeta), known to correspond to early type stars. Older galaxies where a rapid increase in star formation has recently ceased, known as E+A galaxies, are identified by strong Hbeta absorption coupled with little to no [OII] emission. The correlation between recent star formation and "high" ram pressure, as defined by Kapferer et al. (2009) as ≥ 5 x 10-11 dyn cm-2, was tested and lead to a contradiction of the previously held belief that ram pressure influences star formation on the global cluster scale.

  12. 76 FR 81994 - UniStar Nuclear Energy; Combined License Application for Calvert Cliffs Nuclear Power Plant, Unit...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-12-29

    ... From the Federal Register Online via the Government Publishing Office NUCLEAR REGULATORY COMMISSION UniStar Nuclear Energy; Combined License Application for Calvert Cliffs Nuclear Power Plant, Unit 3; Exemption 1.0 Background: UniStar Nuclear Energy (UNE) submitted to the U.S. Nuclear...

  13. Star formation and substructure in galaxy clusters

    SciTech Connect

    Cohen, Seth A.; Hickox, Ryan C.; Wegner, Gary A.; Einasto, Maret; Vennik, Jaan

    2014-03-10

    We investigate the relationship between star formation (SF) and substructure in a sample of 107 nearby galaxy clusters using data from the Sloan Digital Sky Survey. Several past studies of individual galaxy clusters have suggested that cluster mergers enhance cluster SF, while others find no such relationship. The SF fraction in multi-component clusters (0.228 ± 0.007) is higher than that in single-component clusters (0.175 ± 0.016) for galaxies with M{sub r}{sup 0.1}<−20.5. In both single- and multi-component clusters, the fraction of star-forming galaxies increases with clustercentric distance and decreases with local galaxy number density, and multi-component clusters show a higher SF fraction than single-component clusters at almost all clustercentric distances and local densities. Comparing the SF fraction in individual clusters to several statistical measures of substructure, we find weak, but in most cases significant at greater than 2σ, correlations between substructure and SF fraction. These results could indicate that cluster mergers may cause weak but significant SF enhancement in clusters, or unrelaxed clusters exhibit slightly stronger SF due to their less evolved states relative to relaxed clusters.

  14. Circumnuclear Star Formation in Seyfert Galaxies

    NASA Astrophysics Data System (ADS)

    Marquette, Melissa; Hicks, Erin K.; Mueller Sanchez, Francisco; Malkan, Matthew Arnold; Davies, Richard

    2017-01-01

    We examine a group of Seyfert 1 and Seyfert 2 galaxies to determine whether there exists a correlation between the circumnuclear starburst age and the luminosity of the active galactic nucleus. Using data from the Keck OSIRIS Nearby AGN (KONA) survey, we have a sample size of 40 Seyfert galaxies (split between Seyfert 1s and 2s), in which we measure the circumnuclear properties down to a few tens of parsecs. We determine the age of the most recent episode of circumnuclear star formation by analyzing the equivalent width of the Br Gamma 2.16 micron emission line and further constrain the age using measurements of the K-band mass to light ratio. The results of these analyses will be presented, including a comparison of the Seyfert 1 and Seyfert 2 subsamples.

  15. Violent Star Formation in NGC 2363: Erratum

    NASA Astrophysics Data System (ADS)

    Gonzalez-Delgado, Rosa M.; Perez, Enrique; Tenorio-Tagle, Guillermo; Vilchez, Jose M.; Terlevich, Elena; Terlevich, Roberto; Telles, Eduardo; Rodríguez Espinosa, Jose M.; Mas-Hesse, Miguel; Garcia-Vargas, Maria Luisa; Diaz, Angeles I.; Cepa, Jordi; Castaneda, Hector

    1996-12-01

    In the paper "Violent Star Formation in NGC 2363" by Rosa M. Gonzalez- Delgado, Enrique Perez, Guillermo Tenorio-Tagle, Jose M. Vilchez, Elena Terlevich, Roberto Terlevich, Eduardo Telles, Jose M. Rodriguez-Espinosa, Miguel Mas-Hesse, Maria Luisa Garcia-Vargas, Angeles I. Diaz, Jordi Cepa, and Hector Castaneda (ApJ, 437,239 [1994)), there are three errors in Section 5.4. The Paschen discontinuity in knot A is (0.82 +/- 0.19) x 10^-16^ ergs s^-1^ cm^-2^ A^-1^, the coefficient in the formula in page 258 is 2.445 x 10^11^, and the units in the ordinate axis of Figure 16 are 10^-15^ ergs cm^-2^ s^-1^ A^-1^. These are typographical errors, and they do not affect the determination of the electron temperature using the Paschen jump and the discussion and conclusions in this paper.

  16. Tracking star formation in dwarf cluster galaxies

    NASA Astrophysics Data System (ADS)

    Rude, Cody Millard

    The evolution of galaxies in dense environments can be affected by close encounters with neighboring galaxies and interactions with the intracluster medium (ICM). Dwarf galaxies may be especially susceptible to these effects due to their low mass. The goal of my dissertation research is to look for signs of star formation in cluster dwarf galaxies by measuring and comparing the r- and u-band luminosity functions of 15 low redshift Abell galaxy clusters using archival data from the Canada-France-Hawaii Telescope (CFHT). Luminosity functions, dwarf-to-giant ratios, and blue fractions are measured in four cluster-centric annuli from stacked cluster data. To account for differences in cluster optical richness, each cluster is scaled according to r200, where r200 is the radius of a sphere, centered on the cluster, whose average density is 200 times the critical density of the universe. The outer region of the cluster sample shows an increase in the faint-end slope of the u-band luminosity function relative to the r-band, indicating star formation in dwarf galaxies. The blue fraction for dwarf galaxies steadily rises with increasing cluster-centric radii. The change in the blue fraction of giant galaxies also increases, but at a lower rate. Additionally, the inner regions of clusters ranging from 0.185 < z < 0.7 from the "Cluster Lensing and Supernova survey with Hubble (CLASH)" are used to generate blue- and red-band luminosity functions, dwarf-to-giant ratios, and blue fractions. Comparisons of the inner region of the CLASH and CFHT clusters show an increase in the blue fraction of dwarf galaxies with redshift that is not present in giant galaxies.

  17. ON THE LACK OF EVOLUTION IN GALAXY STAR FORMATION EFFICIENCY

    SciTech Connect

    Behroozi, Peter S.; Wechsler, Risa H.; Conroy, Charlie

    2013-01-10

    Using reconstructed galaxy star formation histories, we calculate the instantaneous efficiency of galaxy star formation (i.e., the star formation rate divided by the baryon accretion rate) from z = 8 to the present day. This efficiency exhibits a clear peak near a characteristic halo mass of 10{sup 11.7} M{sub Sun }, which coincides with longstanding theoretical predictions for the mass scale relevant to virial shock heating of accreted gas. Above the characteristic halo mass, the efficiency falls off as the mass to the minus four-thirds power; below the characteristic mass, the efficiency falls off at an average scaling of mass to the two-thirds power. By comparison, the shape and normalization of the efficiency change very little since z = 4. We show that a time-independent star formation efficiency simply explains the shape of the cosmic star formation rate since z = 4 in terms of dark matter accretion rates. The rise in the cosmic star formation from early times until z = 2 is especially sensitive to galaxy formation efficiency. The mass dependence of the efficiency strongly limits where most star formation occurs, with the result that two-thirds of all star formation has occurred inside halos within a factor of three of the characteristic mass, a range that includes the mass of the Milky Way.

  18. On the formation of Be stars through binary interaction

    SciTech Connect

    Shao, Yong; Li, Xiang-Dong

    2014-11-20

    Be stars are rapidly rotating B-type stars. The origin of their rapid rotation is not certain, but binary interaction remains as a possibility. In this work, we investigate the formation of Be stars resulting from mass transfer in binaries in the Galaxy. We calculate binary evolution with both stars evolving simultaneously and consider different possible mass accretion histories for the accretor. From the calculated results, we obtain the critical mass ratios q {sub cr} that determine the stability of the mass transfer. We also numerically calculate the parameter λ in common envelope evolution and then incorporate both q {sub cr} and λ into the population synthesis calculations. We present the predicted numbers and characteristics of Be stars in binary systems with different types of companions, including helium stars, white dwarfs, neutron stars, and black holes. We find that in Be/neutron star binaries, the Be stars can have a lower mass limit ∼8 M {sub ☉} if they are formed by stable (i.e., without the occurrence of common envelope evolution) and nonconservative mass transfer. We demonstrate that isolated Be stars may originate from both mergers of two main-sequence stars and disrupted Be binaries during the supernova explosions of the primary stars, but mergers seem to play a much more important role. Finally, the fraction of Be stars that have involved binary interactions in all B-type stars can be as high as ∼13%-30%, implying that most Be stars may result from binary interaction.

  19. Star formation in X-ray cluster cooling flows

    NASA Technical Reports Server (NTRS)

    White, Raymond E., III; Sarazin, Craig L.

    1987-01-01

    The basic equations for X-ray cluster cooling flows, including the effects of star formation, are derived. It is confirmed that cooling flows are thermally unstable, and it is found that the fastest-growing linear perturbations in the flow are radial, comoving, and isobaric. A local approximation for the star formation rate is developed which allows analytic solutions to be found for both isobaric and gravity-dominated cooling flows. These solutions are used to show how star formation reduces the gas density, thereby lowering the cooling rate, which raises the gas temperature relative to the non-star-forming case. The analytic solutions are also used to estimate the spatial distribution of newly formed stars. It is found that star formation must proceed at a nearly maximal rate if isothermal mass profiles are to result.

  20. The Star Formation History of the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Grebel, E. K.; Brandner, W.

    1997-05-01

    We present a movie of the star formation history of the Large Magellanic Cloud (LMC) based on its stellar content. We use the present-day spatial distribution of blue and red supergiants, Cepheids, clusters and associations, and RR Lyrae stars to study the age structure and to identify areas of pronounced star formation as a function of time and position. Age estimates for different stellar populations are based on theoretical isochrones, evolutionary models, and recent calibrations of SWB types of clusters. De-reddening of the individual stars and clusters results in a large-scale extinction map for the LMC. We discuss our results in terms of internal/external trigger mechanisms of star formation and different star formation modes.

  1. KEY ISSUES REVIEW: Insights from simulations of star formation

    NASA Astrophysics Data System (ADS)

    Larson, Richard B.

    2007-03-01

    Although the basic physics of star formation is classical, numerical simulations have yielded essential insights into how stars form. They show that star formation is a highly nonuniform runaway process characterized by the emergence of nearly singular peaks in density, followed by the accretional growth of embryo stars that form at these density peaks. Circumstellar discs often form from the gas being accreted by the forming stars, and accretion from these discs may be episodic, driven by gravitational instabilities or by protostellar interactions. Star-forming clouds typically develop filamentary structures, which may, along with the thermal physics, play an important role in the origin of stellar masses because of the sensitivity of filament fragmentation to temperature variations. Simulations of the formation of star clusters show that the most massive stars form by continuing accretion in the dense cluster cores, and this again is a runaway process that couples star formation and cluster formation. Star-forming clouds also tend to develop hierarchical structures, and smaller groups of forming objects tend to merge into progressively larger ones, a generic feature of self-gravitating systems that is common to star formation and galaxy formation. Because of the large range of scales and the complex dynamics involved, analytic models cannot adequately describe many aspects of star formation, and detailed numerical simulations are needed to advance our understanding of the subject. 'The purpose of computing is insight, not numbers.' Richard W Hamming, in Numerical Methods for Scientists and Engineers (1962) 'There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy.' William Shakespeare, in Hamlet, Prince of Denmark (1604)

  2. Star formation and the nature of bipolar outflows

    NASA Technical Reports Server (NTRS)

    Shu, Frank H.; Ruden, Steven P.; Lada, Charles J.; Lizano, Susana

    1991-01-01

    This paper presents a simple physical model for the bipolar molecular outflows that frequently accompany star formation. The model forges an intrinsic link between the bipolar flow phenomenon and the process of star formation, and it helps to explain many of the systematics known for existing sources.

  3. Magnetic Fields in Population III Star Formation

    SciTech Connect

    Turk, Matthew J.; Oishi, Jeffrey S.; Abel, Tom; Bryan, Greg

    2012-02-22

    We study the buildup of magnetic fields during the formation of Population III star-forming regions, by conducting cosmological simulations from realistic initial conditions and varying the Jeans resolution. To investigate this in detail, we start simulations from identical initial conditions, mandating 16, 32 and 64 zones per Jeans length, and studied the variation in their magnetic field amplification. We find that, while compression results in some amplification, turbulent velocity fluctuations driven by the collapse can further amplify an initially weak seed field via dynamo action, provided there is sufficient numerical resolution to capture vortical motions (we find this requirement to be 64 zones per Jeans length, slightly larger than, but consistent with previous work run with more idealized collapse scenarios). We explore saturation of amplification of the magnetic field, which could potentially become dynamically important in subsequent, fully-resolved calculations. We have also identified a relatively surprising phenomena that is purely hydrodynamic: the higher-resolved simulations possess substantially different characteristics, including higher infall-velocity, increased temperatures inside 1000 AU, and decreased molecular hydrogen content in the innermost region. Furthermore, we find that disk formation is suppressed in higher-resolution calculations, at least at the times that we can follow the calculation. We discuss the effect this may have on the buildup of disks over the accretion history of the first clump to form as well as the potential for gravitational instabilities to develop and induce fragmentation.

  4. Formative Assessment Probes: Where Are the Stars?

    ERIC Educational Resources Information Center

    Keeley, Page

    2011-01-01

    Gazing at the night sky is a familiar experience for many elementary students. Depending on where children live, they can often look out a window and see the Moon and stars. Children may have seen the Moon and stars in television shows, movies, posters, or children's picture books. Regardless of whether they see the Moon and stars firsthand or…

  5. Star Formation in the Central Regions of Galaxies

    NASA Astrophysics Data System (ADS)

    Tsai, Mengchun

    2015-08-01

    The galactic central region connects the galactic nucleus to the host galaxy. If the central black hole co-evolved with the host galaxies, there should be some evidence left in the central region. We use the environmental properties in the central regions such as star-forming activity, stellar population and molecular abundance to figure out a possible scenario of the evolution of galaxies. In this thesis at first we investigated the properties of the central regions in the host galaxies of active and normal galaxies. We used radio emission around the nuclei of the host galaxies to represent activity of active galactic nuclei (AGNs), and used infrared ray (IR) emission to represent the star-forming activity and stellar population of the host galaxies. We determined that active galaxies have higher stellar masses (SMs) within the central kiloparsec radius than normal galaxies do independent of the Hubble types of the host galaxies; but both active and normal galaxies exhibit similar specific star formation rates (SSFRs). We also discovered that certain AGNs exhibit substantial inner stellar structures in the IR images; most of the AGNs with inner structures are Seyferts, whereas only a few LINERs exhibit inner structures. We note that the AGNs with inner structures show a positive correlation between the radio activity of the AGNs and the SFRs of the host galaxies, but the sources without inner structures show a negative correlation between the radio power and the SFRs. These results might be explained with a scenario of starburst-AGN evolution. In this scenario, AGN activities are triggered following a nuclear starburst; during the evolution, AGN activities are accompanied by SF activity in the inner regions of the host galaxies; at the final stage of the evolution, the AGNs might transform into LINERs, exhibiting weak SF activity in the central regions of the host galaxies. For further investigation about the inner structure, we choose the most nearby and luminous

  6. Inner Milky Way Raging with Star Formation

    NASA Technical Reports Server (NTRS)

    2008-01-01

    More than 444,580 frames from NASA's Spitzer Space Telescope were stitched together to create this portrait of the raging star-formation occurring in the inner Milky Way.

    As inhabitants of a flat galactic disk, Earth and its solar system have an edge-on view of their host galaxy, like looking a glass dish from its edge. From our perspective, most of the galaxy is condensed into a blurry narrow band of light that stretches completely around the sky, also known as the galactic plane.

    In this mosaic the galactic plane is broken up into five components: the far-left side of the plane (top image); the area just left of the galactic center (second to top); galactic center (middle); the area to the right of galactic center (second to bottom); and the far-right side of the plane (bottom). Together, these panels represent more than 50 percent of our entire Milky Way galaxy.

    The red haze that permeates the picture comes from organic molecules called polycyclic aromatic hydrocarbons, which are illuminated by light from massive baby stars. On Earth, these molecules are found in automobile exhaust, or charred barbeque grills anywhere carbon molecules are burned incompletely.

    The patches of black are dense, obscuring dust clouds impenetrable by even Spitzer's super-sensitive infrared eyes. Bright arcs of white throughout the image are massive stellar incubators. The bluish-white haze that hovers heavily in the middle panel is starlight from the older stellar population towards the center of the galaxy.

    This picture was taken with Spitzer's infrared array camera, as part of the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) project. This is a four-color composite where blue is 3.6-micron light, green is 4.5 microns, orange is 5.8 microns and red is 8.0 microns.

  7. X-ray sources in regions of star formation. I - The naked T Tauri stars

    NASA Technical Reports Server (NTRS)

    Walter, F. M.

    1986-01-01

    Einstein X-ray observations of regions of active star formation in Taurus, Ophiuchus, and Corona Australis show a greatly enhanced surface density of stellar X-ray sources over that seen in other parts of the sky. Many of the X-ray sources are identified with low-mass, pre-main-sequence stars which are not classical T Tauri stars. The X-ray, photometric, and spectroscopic data for these stars are discussed. Seven early K stars in Oph and CrA are likely to be 1-solar-mass post-T Tauri stars with ages of 10-million yr. The late K stars in Taurus are not post-T Tauri, but 'naked' T Tauri stars, which are coeval with the T Tauri stars, differing mainly in the lack of a circumstellar envelope.

  8. Bimodal star formation - Constraints from the solar neighborhood

    NASA Technical Reports Server (NTRS)

    Wyse, Rosemary F. G.; Silk, J.

    1987-01-01

    The chemical evolution resulting from a simple model of bimodal star formulation is investigated, using constraints from the solar neighborhood to set the parameters of the initial mass function and star formation rate. The two modes are an exclusively massive star mode, which forms stars at an exponentially declining rate, and a mode which contains stars of all masses and has a constant star formation rate. Satisfactory agreement with the age-metallicity relation for the thin disk and with the metallicity structure of the thin-disk and spheroid stars is possible only for a small range of parameter values. The preferred model offers a resolution to several of the long-standing problems of galactic chemical evolution, including explanations of the age-metallicity relation, the gas consumption time scale, and the stellar cumulative metallicity distributions.

  9. Formation of Molecular Clouds and Initial Conditions of Star Formation

    NASA Astrophysics Data System (ADS)

    Inoue, Tsuyoshi

    2013-07-01

    Using three-dimensional magnetohydrodynamic simulations, including the effects of radiative cool- ing/heating, chemical reactions, self-gravity and thermal conduction, we investigate the formation of molecular clouds in the multi-phase interstellar medium. We consider the formation of molecular clouds due to accretion of HI clouds as suggested by recent observations. Our simulations show that the initial HI medium is piled up behind the shock waves induced by accretion flows. Since the accreting medium is highly inhomogeneous as a consequence of thermal instability, a newly formed molecular cloud becomes very turbulent owing to the development of the Richtmyer-Meshkov instability. The kinetic energy of the turbulence dominates the thermal, magnetic, and gravitational energies. However, the kinetic energy measured using CO-fraction-weighted density is comparable to the other energies, once the CO molecules are sufficiently formed as a result of UV shielding. This suggests that the true kinetic energy of turbulence in molecular clouds as a whole can be much larger than the kinetic energy of turbulence estimated by using line widths of molecular emission. We find that dense clumps in the molecular cloud show the following evolution: the typical plasma beta of the clumps is roughly constant; the size-ělocity dispersion relation follows Larson's law, irrespective of the density; and the clumps evolve into magnetically supercritical cores by clump-clump collisions. These statistical properties would represent the initial conditions of star formation.

  10. The impact of galactic environment on star formation

    NASA Astrophysics Data System (ADS)

    Kreckel, Kathryn; Blanc, Guillermo A.; Schinnerer, Eva; Groves, Brent; Adamo, Angela; Hughes, Annie; Meidt, Sharon; SFNG Collaboration

    2017-01-01

    While spiral arms are the most prominent sites for star formation in disk galaxies, interarm star formation contributes significantly to the overall star formation budget. However, it is still an open question if the star formation proceeds differently in the arm and inter-arm environment. We use deep VLT/MUSE optical IFU spectroscopy to resolve and fully characterize the physical properties of 428 interarm and arm HII regions in the nearby grand design spiral galaxy NGC 628. Unlike molecular clouds (the fuel for star formation) which exhibit a clear dependence on galactic environment, we find that most HII region properties (luminosity, size, metallicity, ionization parameter) are independent of environment. One clear exception is the diffuse ionized gas (DIG) contribution to the arm and interarm flux (traced via the temperature sensitive [SII]/Halpha line ratio inside and outside of the HII region boundaries). We find a systematically higher DIG background within HII regions, particularly on the spiral arms. Correcting for this DIG contamination can result in significant (70%) changes to the star formation rate measured. We also show preliminary results comparing well-corrected star formation rates from our MUSE HII regions to ALMA CO(2-1) molecular gas observations at matched 1"=50pc resolution, tracing the Kennicutt-Schmidt star formation law at the scales relevant to the physics of star formation. We estimate the timescales relevant for GMC evolution using distance from the spiral arm as a proxy for age, and test whether star formation feedback or galactic-scale dynamical processes dominate GMC disruption.

  11. The Impact Of Galactic Environment On Star Formation

    NASA Astrophysics Data System (ADS)

    Kreckel, Kathryn

    2016-09-01

    While spiral arms are the most prominent sites for star formation in disk galaxies, interarm star formation contributes significantly to the overall star formation budget. However, it is still an open question if the star formation proceeds differently in the arm and inter-arm environment. We use deep VLT/MUSE optical IFU spectroscopy to resolve and fully characterize the physical properties of 428 interarm and arm HII regions in the nearby grand design spiral galaxy NGC 628. Unlike molecular clouds (the fuel for star formation) which exhibit a clear dependence on galactic environment, we find that most HII region properties (luminosity, size, metallicity, ionization parameter) are independent of environment. One clear exception is the diffuse ionized gas (DIG) contribution to the arm and interarm flux (traced via the temperature sensitive [SII]/Halpha line ratio inside and outside of the HII region boundaries). We find a systematically higher DIG background within HII regions, particularly on the spiral arms. Correcting for this DIG contamination can result in significant (70%) changes to the star formation rate measured. We also show preliminary results comparing well@corrected star formation rates from our MUSE HII regions to ALMA CO(2-1) molecular gas observations at matched 1"=35pc resolution, tracing the Kennicutt-Schmidt star formation law at the scales relevant to the physics of star formation. We estimate the timescales relevant for GMC evolution using distance from the spiral arm as a proxy for age, and test whether star formation feedback or galactic@scale dynamical processes dominate GMC disruption.

  12. Terrestrial Planet Formation Around Close Binary Stars

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.; Quintana, Elisa V.

    2003-01-01

    Most stars reside in multiple star systems; however, virtually all models of planetary growth have assumed an isolated single star. Numerical simulations of the collapse of molecular cloud cores to form binary stars suggest that disks will form within such systems. Observations indirectly suggest disk material around one or both components within young binary star systems. If planets form at the right places within such circumstellar disks, they can remain in stable orbits within the binary star systems for eons. We are simulating the late stages of growth of terrestrial planets around close binary stars, using a new, ultrafast, symplectic integrator that we have developed for this purpose. The sum of the masses of the two stars is one solar mass, and the initial disk of planetary embryos is the same as that used for simulating the late stages of terrestrial planet growth within our Solar System and in the Alpha Centauri wide binary star system. Giant planets &are included in the simulations, as they are in most simulations of the late stages of terrestrial planet accumulation in our Solar System. When the stars travel on a circular orbit with semimajor axis of up to 0.1 AU about their mutual center of mass, the planetary embryos grow into a system of terrestrial planets that is statistically identical to those formed about single stars, but a larger semimajor axis and/or a significantly eccentric binary orbit can lead to significantly more dynamically hot terrestrial planet systems.

  13. Terrestrial Planet Formation around Low-Mass Stars: Effect of the Mass of Central Stars

    NASA Astrophysics Data System (ADS)

    Oshino, Shoichi; Matsumoto, Yuji; Kokubo, Eiichiro

    2015-12-01

    The Kepler space telescope has detected several thousand planets and candidates.Their central stars are mainly FGK-type stars.It is difficult to observe M-stars by using visible light since M-stars have their peak radiation in the infrared region.However, recently there are several survey projects for planets around M-stars such as the InfraRed Doppler (IRD) survey of the Subaru telescope.Therefore it is expected that the number of planets around M-stars will increase in the near future.The habitable zone of M-stars is closer to the stars than that of G-stars.For this reason, the possibility of finding habitable planets is expected to be higher.Here we study the formation of close-in terrestrial planets by giant impacts of protoplanets around low-mass stars by using N-body simulations.An important parameter that controls formation processes is the ratio between the physical radius of a planet and its Hill radius, which decreases with the stellar mass.We systematically change the mass of the central stars and investigate its effects on terrestrial planet formation.We find that the mass of the maximum planet decreases with the mass of central stars, while the number of planets in the system increases.We also find that the orbital separation of adjacent planets normalized by their Hill radius increases with the stellar mass.

  14. Clustered star formation and the origin of stellar masses.

    PubMed

    Pudritz, Ralph E

    2002-01-04

    Star clusters are ubiquitous in galaxies of all types and at all stages of their evolution. We also observe them to be forming in a wide variety of environments, ranging from nearby giant molecular clouds to the supergiant molecular clouds found in starburst and merging galaxies. The typical star in our galaxy and probably in others formed as a member of a star cluster, so star formation is an intrinsically clustered and not an isolated phenomenon. The greatest challenge regarding clustered star formation is to understand why stars have a mass spectrum that appears to be universal. This review examines the observations and models that have been proposed to explain these fundamental issues in stellar formation.

  15. Molecular Dynamics of Nuclear Pasta in Neutron Stars

    NASA Astrophysics Data System (ADS)

    Briggs, Christian; da Silva Schneider, Andre

    2014-09-01

    During a core collapse supernova, a massive star undergoes rapid contraction followed by a massive explosion on the order of a hundred trillion trillion nuclear bombs in less than a second. While most matter is expelled at high speeds, what remains can form a neutron star. The bulk of a neutron star does not contain separate nuclei but is itself a single nucleus of radius ~10 km. In the crust of a neutron star, density is low enough that some matter exists as distinct nuclei arranged into crystalline lattice dominated by electromagnetic forces. Between the crust and core lies an interesting interface where matter is neither a single nucleus nor separate nuclei. It exists in a frustrated phase; competition between electromagnetic and strong nuclear forces causes exotic shapes to emerge, referred to as nuclear pasta. We use Molecular Dynamics (MD) to simulate nuclear pasta, with densities between nuclear saturation density and approximately one-tenth saturation density. Using MD particle trajectories, we compute the static structure factor S(q) and dynamical response function to describe both electron-pasta and neutrino-pasta scattering. We relate the structure and properties of nuclear pasta phases to features in S(q). Finally, one can integrate over S(q) to determine transport properties such as the electrical and thermal conductivity. This may help provide a better understanding of X-ray observations of neutron stars. During a core collapse supernova, a massive star undergoes rapid contraction followed by a massive explosion on the order of a hundred trillion trillion nuclear bombs in less than a second. While most matter is expelled at high speeds, what remains can form a neutron star. The bulk of a neutron star does not contain separate nuclei but is itself a single nucleus of radius ~10 km. In the crust of a neutron star, density is low enough that some matter exists as distinct nuclei arranged into crystalline lattice dominated by electromagnetic forces

  16. The Star Formation in Radio Survey: Mapping Star Formation in Nearby Galaxies with 33GHz Emission

    NASA Astrophysics Data System (ADS)

    Dong, Dillon; Murphy, Eric J.; Momjian, Emmanuel; Nyland, Kristina; Condon, James J.; Helou, George; Meier, David S.; Ott, Juergen; Schinnerer, Eva; Turner, Jean

    2015-01-01

    We present initial results from the 33GHz phase of the Star Formation in Radio Survey (SFRS), including a gallery of 2" resolution Jansky Very Large Array (VLA) images and spatially resolved thermal / synchrotron emission models in a subset of sources. The SFRS is targeting 118 galaxy nuclei and extranuclear star-forming regions in 56 nearby (d < 30Mpc) galaxies included in the Spitzer/SINGS and Herschel/KINGFISH legacy programs. VLA observations of the entire sample have recently been completed at 3GHz (S band), 15GHz (Ku band) and 33GHz (Ka band). For an initial subset of 9 targets, we have also obtained 90GHz ALMA continuum and line imaging during cycle 1 observations.The frequency spacing of our complete radio data set will allow us to accurately measure the radio spectral index of these targets, in order to model the physical processes that produce the radio emission. In particular, 33GHz observations of HII regions probe free-free emission, providing a sensitive, dust-unbiased measure of the current star formation activity in each complex. We can use the differences between 33GHz derived star formation rates and those derived with other tracers such as synchrotron radiation, extinction corrected UV and Hα emission, and infrared luminosity to examine the dependence of each tracer on separately measured variables such as extinction, metallicity and ionizing radiation field strength. Consequently, these data will help calibrate other empirically-derived star formation rate diagnostics that are more easily measured for high redshift studies, and help interpret rest-frame 33GHz observations from a new generation of deep high frequency (>10GHz) radio surveys.As an example of the science that can be done with SFRS data, we have used our images along with an archival 1.4GHz and a new 5GHz VLA image to map the spectral index, spectral curvature, and the separated thermal and synchrotron components of NGC1266, a low level AGN with a mass outflow rate of > 50 M⊙ / yr

  17. The sub-galactic and nuclear main sequences for local star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Maragkoudakis, A.; Zezas, A.; Ashby, M. L. N.; Willner, S. P.

    2017-04-01

    We describe a sub-galactic main sequence (SGMS) relating star formation rate (SFR) surface density (ΣSFR) and stellar mass density (Σ⋆) for distinct regions within star-forming galaxies, including their nuclei. We use a sample of 246 nearby star-forming galaxies from the 'Star Formation Reference Survey and demonstrate that the SGMS holds down to ∼1 kpc scales with a slope of α = 0.91 and a dispersion of 0.31 dex, similar to the well-known main sequence (MS) measured for globally integrated SFRs and stellar masses. The SGMS slope depends on galaxy morphology, with late-type galaxies (Sc-Irr) having α = 0.97 and early-type spirals (Sa-Sbc) having α = 0.81. The SGMS constructed from subregions of individual galaxies has on average the same characteristics as the composite SGMS from all galaxies. The SGMS for galaxy nuclei shows a dispersion similar to that seen for other subregions. Sampling a limited range of SFR-M⋆ space may produce either sublinearity or superlinearity of the SGMS slope. For nearly all galaxies, both SFR and stellar mass peak in the nucleus, indicating that circumnuclear clusters are among the most actively star-forming regions in the galaxy and the most massive. The nuclear SFR also correlates with total galaxy mass, forming a distinct sequence from the standard MS of star formation. The nuclear MS will be useful for studying bulge growth and for characterizing feedback processes connecting AGN and star formation.

  18. The Coevolution of Nuclear Star Clusters, Massive Black Holes, and Their Host Galaxies

    NASA Astrophysics Data System (ADS)

    Antonini, Fabio; Barausse, Enrico; Silk, Joseph

    2015-10-01

    Studying how nuclear star clusters (NSCs) form and how they are related to the growth of the central massive black holes (MBHs) and their host galaxies is fundamental for our understanding of the evolution of galaxies and the processes that have shaped their central structures. We present the results of a semi-analytical galaxy formation model that follows the evolution of dark matter halos along merger trees, as well as that of the baryonic components. This model allows us to study the evolution of NSCs in a cosmological context, by taking into account the growth of NSCs due to both dynamical-friction-driven migration of stellar clusters and star formation triggered by infalling gas, while also accounting for dynamical heating from (binary) MBHs. We find that in situ star formation contributes a significant fraction (up to ∼80%) of the total mass of NSCs in our model. Both NSC growth through in situ star formation and that through star cluster migration are found to generate NSC—host galaxy scaling correlations that are shallower than the same correlations for MBHs. We explore the role of galaxy mergers on the evolution of NSCs and show that observational data on NSC—host galaxy scaling relations provide evidence of partial erosion of NSCs by MBH binaries in luminous galaxies. We show that this observational feature is reproduced by our models, and we make predictions about the NSC and MBH occupation fraction in galaxies. We conclude by discussing several implications for theories of NSC formation.

  19. STAR FORMATION IN PARTIALLY GAS-DEPLETED SPIRAL GALAXIES

    SciTech Connect

    Rose, James A.; Miner, Jesse; Levy, Lorenza; Robertson, Paul E-mail: paul@astr.as.utexas.edu E-mail: lorenza.levy@yahoo.com

    2010-02-15

    Broadband B and R and H{alpha} images have been obtained with the 4.1 m SOAR telescope atop Cerro Pachon, Chile, for 29 spiral galaxies in the Pegasus I galaxy cluster and for 18 spirals in non-cluster environments. Pegasus I is a spiral-rich cluster with a low-density intracluster medium and a low galaxy velocity dispersion. When combined with neutral hydrogen (H I) data obtained with the Arecibo 305 m radio telescope, acquired by Levy et al. (2007) and by Springob et al. (2005b), we study the star formation rates in disk galaxies as a function of their H I deficiency. To quantify H I deficiency, we use the usual logarithmic deficiency parameter, DEF. The specific star formation rate (SSFR) is quantified by the logarithmic flux ratio of H{alpha} flux to R-band flux, and thus roughly characterizes the logarithmic SFR per unit stellar mass. We find a clear correlation between the global SFR per unit stellar mass and DEF, such that the SFR is lower in more H I-deficient galaxies. This correlation appears to extend from the most gas-rich to the most gas-poor galaxies. We also find a correlation between the central SFR per unit mass relative to the global values, in the sense that the more H I-deficient galaxies have a higher central SFR per unit mass relative to their global SFR values than do gas-rich galaxies. In fact, approximately half of the H I-depleted galaxies have highly elevated SSFRs in their central regions, indicative of a transient evolutionary state. In addition, we find a correlation between gas depletion and the size of the H{alpha} disk (relative to the R-band disk); H I-poor galaxies have truncated disks. Moreover, aside from the elevated central SSFR in many gas-poor spirals, the SSFR is otherwise lower in the H{alpha} disks of gas-poor galaxies than in gas-rich spirals. Thus, both disk truncation and lowered SSFR levels within the star-forming part of the disks (aside from the enhanced nuclear SSFR) correlate with H I deficiency, and both

  20. Drama of HII regions: Clustered and Triggered Star Formation

    NASA Astrophysics Data System (ADS)

    Li, Jinzeng; YUAN, Jinghua; LIU, Hongli; Wu, Yuefang; Huang, Yafang

    2015-08-01

    Intense ultraviolet radiation from young massive stars ionizes ambient material leading to the formation of HII regions which have keen impact upon the birth of new stars in the vicinities. The strong radiation may be responsible for the dispersal of molecular clouds to hinder star formation, while the expansion of HII regions would collect neutral material to form dense layers which may be gravitationally unstable to collapse to give birth to new stars.In order to understand the star formation process under the influence of HII regions, we have carried out extensive investigations to well selected star-forming regions which all have been profoundly affected by existing massive O type stars. On the basis of multi-wavelength data from mid-infrared to millimeter collected using Spitzer, Herschel, and ground based radio telescope, the physical status of interstellar medium and star formation in these regions have been revealed. Clustered and sequential star formation have been detected toward well known HII regions, such as IC1396 and Sh-155. In a relatively large infrared dust bubble, active star formation is undergoing and the shell is still expanding. Socked features and signs of triggered star formation have been tentatively detected in a relatively small bubble. The dense cores in the Rosette Molecular Complex detected at 1.1 mm using SMA have been speculated to have a likely triggered origin according to their spatial distribution. Although some observational results have been obtained, more efforts are necessary to reach trustworthy conclusions. And more regions will be extensively explored based on multi-wavelength observations, especially the data collected using the Herschel Space Observatory.

  1. The Star Formation History of the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Harris, Jason; Zaritsky, Dennis

    2009-11-01

    We present the first ever global, spatially resolved reconstruction of the star formation history (SFH) of the Large Magellanic Cloud (LMC), based on the application of our StarFISH analysis software to the multiband photometry of 20 million of its stars from the Magellanic Clouds Photometric Survey. The general outlines of our results are consistent with previously published results: following an initial burst of star formation, there was a quiescent epoch from approximately 12 to 5 Gyr ago. Star formation then resumed and has proceeded until the current time at an average rate of roughly 0.2 M sun yr-1, with temporal variations at the factor of 2 level. The re-ignition of star formation about 5 Gyr ago, in both the LMC and Small Magellanic Cloud (SMC), is suggestive of a dramatic event at that time in the Magellanic system. Among the global variations in the recent star formation rate are peaks at roughly 2 Gyr, 500 Myr, 100 Myr, and 12 Myr. The peaks at 500 Myr and 2 Gyr are nearly coincident with similar peaks in the SFH of the SMC, suggesting a joint history for these galaxies extending back at least several Gyr. The chemical enrichment history recovered from our StarFISH analysis is in broad agreement with that inferred from the LMC's star cluster population, although our constraints on the ancient chemical enrichment history are weak. We conclude from the concordance between the star formation and chemical enrichment histories of the field and cluster populations that the field and cluster star formation modes are tightly coupled.

  2. The efficiency of star formation in clustered and distributed regions

    NASA Astrophysics Data System (ADS)

    Bonnell, Ian A.; Smith, Rowan J.; Clark, Paul C.; Bate, Matthew R.

    2011-02-01

    We investigate the formation of both clustered and distributed populations of young stars in a single molecular cloud. We present a numerical simulation of a 104 M⊙ elongated, turbulent, molecular cloud and the formation of over 2500 stars. The stars form both in stellar clusters and in a distributed mode, which is determined by the local gravitational binding of the cloud. A density gradient along the major axis of the cloud produces bound regions that form stellar clusters and unbound regions that form a more distributed population. The initial mass function (IMF) also depends on the local gravitational binding of the cloud with bound regions forming full IMFs whereas in the unbound, distributed regions the stellar masses cluster around the local Jeans mass and lack both the high-mass and the low-mass stars. The overall efficiency of star formation is ≈ 15 per cent in the cloud when the calculation is terminated, but varies from less than 1 per cent in the regions of distributed star formation to ≈ 40 per cent in regions containing large stellar clusters. Considering that large-scale surveys are likely to catch clouds at all evolutionary stages, estimates of the (time-averaged) star formation efficiency (SFE) for the giant molecular cloud reported here is only ≈ 4 per cent. This would lead to the erroneous conclusion of slow star formation when in fact it is occurring on a dynamical time-scale.

  3. Global star formation in the L1630 molecular cloud

    NASA Technical Reports Server (NTRS)

    Lada, Elizabeth A.

    1992-01-01

    The first systematic and coordinated surveys for both dense gas and young stellar objects within a single molecular cloud, the L1630 molecular cloud are compared. It is found that (1) star formation in the L1630 molecular cloud occurs almost exclusively within the dense gas; (2) star formation does not occur uniformly throughout the dense gas and is strongly favored in a few very massive dense cores, where efficient conversion of molecular gas into stars has resulted in the production of rich stellar clusters; and (3) high gas densities and high gas mass may be necessary but not sufficient conditions for the formation of star clusters since two of the five most massive dense cores in the cloud have very low levels of star formation activity.

  4. Bursts of star formation in computer simulations of dwarf galaxies

    SciTech Connect

    Comins, N.F.

    1984-09-01

    A three-dimensional Stochastic Self-Propagating Star Formation (SSPSF) model of compact galacies is presented. Two phases of gas, active and inactive, are present, and permanent depletion of gas in the form of long lived, low mass stars and remnants occurs. Similarly, global infall of gas from a galactic halo or through galactic cannibalism is permitted. We base our parameters on the observed properties of the compact blue galaxy I Zw 36. Our results are that bursts of star formation occur much more frequently in these runs than continuous nonbursting star formation, suggesting that the blue compact galaxies are probably undergoing bursts rather than continuous, nonbursting low-level star formation activity.

  5. The Star Formation History of Local Starbursts as Benchmark for High Redshifts

    NASA Astrophysics Data System (ADS)

    Schmitt, Henrique R.; Calzetti, Daniela; Armus, Lee

    2001-08-01

    We propose to use the WIYN telescope and MIMO to obtain broad band B and R, and narrow band H(alpha) and H(beta) images for a sample of 13 local starburst galaxies detected by ISO at 170-200(micron) and for which we are obtaining ultraviolet (1600Å) images with an approved HST/STIS program. With these observations we will complete the ground based portion of this project. This sample spans a wide range in the luminosity, star formation rate, metallicity and morphology parameters, and will be used as a low-redshift benchmark to explore the relationship between the Lyman-break and the SCUBA galaxies at z~3. The broad- band ground-based and HST images will be used to characterize the stellar populations and determine the ages of the star forming regions of these galaxies, while the H(alpha)/H(beta) ratio will be used to determine the reddening and gas morphology of these regions. We will study the conditions for the escape of UV light from a dusty galaxy, as a function of the sample parameters. The H(alpha) and UV HST images will be combined to derive a relative empirical calibration between these two star formation indicators. We will measure the fraction of nuclear and disk emission, the fraction of star formation in massive clusters and the properties of those star clusters, the structural properties of star forming bars, rings, and tidally-driven star formation in IR-bright galaxies.

  6. The Star Formation History of Local Starbursts as Benchmark for High Redshifts

    NASA Astrophysics Data System (ADS)

    Schmitt, Henrique R.; Calzetti, Daniela; Armus, Lee

    2001-02-01

    We propose to use the WIYN telescope and MIMO to obtain broad band B and R, and narrow band H(alpha) and H(beta) images for a sample of 22 local starburst galaxies detected by ISO at 170-200(micron) and for which we are obtaining ultraviolet (1600Å) images with an approved HST/STIS program. This sample spans a wide range in the luminosity, star formation rate, metallicity and morphology parameters, and will be used as a low-redshift benchmark to explore the relationship between the Lyman-break and the SCUBA galaxies at z~3. The broad-band ground- based and HST images will be used to characterize the stellar populations and determine the ages of the star forming regions of these galaxies, while the H(alpha)/H(beta) ratio will be used to determine the reddening and gas morphology of these regions. We will study the conditions for the escape of UV light from a dusty galaxy, as a function of the sample parameters. The H(alpha) and UV HST images will be combined to derive a relative empirical calibration between these two star formation indicators. We will measure the fraction of nuclear and disk emission, the fraction of star formation in massive clusters and the properties of those star clusters, the structural properties of star forming bars, rings, and tidally-driven star formation in IR-bright galaxies.

  7. TESTING HOMOGENEITY WITH GALAXY STAR FORMATION HISTORIES

    SciTech Connect

    Hoyle, Ben; Jimenez, Raul; Tojeiro, Rita; Maartens, Roy; Heavens, Alan; Clarkson, Chris

    2013-01-01

    Observationally confirming spatial homogeneity on sufficiently large cosmological scales is of importance to test one of the underpinning assumptions of cosmology, and is also imperative for correctly interpreting dark energy. A challenging aspect of this is that homogeneity must be probed inside our past light cone, while observations take place on the light cone. The star formation history (SFH) in the galaxy fossil record provides a novel way to do this. We calculate the SFH of stacked luminous red galaxy (LRG) spectra obtained from the Sloan Digital Sky Survey. We divide the LRG sample into 12 equal-area contiguous sky patches and 10 redshift slices (0.2 < z < 0.5), which correspond to 120 blocks of volume {approx}0.04 Gpc{sup 3}. Using the SFH in a time period that samples the history of the universe between look-back times 11.5 and 13.4 Gyr as a proxy for homogeneity, we calculate the posterior distribution for the excess large-scale variance due to inhomogeneity, and find that the most likely solution is no extra variance at all. At 95% credibility, there is no evidence of deviations larger than 5.8%.

  8. Star Formation in Lynds Dark Nebulae

    NASA Astrophysics Data System (ADS)

    Johnson, Chelen H.; Bemis, G. E.; Paulsen, K. M.; Yueh, N. J.; Rebull, L. M.; DeWolf, C.; DeWolf, T.; Brock, S.; Boerna, J.; Schaefers, J.; McDonald, D. W.; McDonald, J.; Troudt, B.; Wilkinson, B.; Guastella, P.; Peter, A.; Wassmer, W.; Haber, R.; Scaramucci, A.; Spuck, T. S.; Butchart, J.; Holcomb, A.; Karns, B.; Kennedy, S.; Siegel, R.; Weiser, S.; Connelley, M.

    2009-01-01

    Our team observed two Lynds clouds (LDN 425 and LDN 981) using the Spitzer Space Telescope IRAC (3.6, 4.5, 5.8, and 8 microns), and MIPS (24 microns). A preliminary literature search provided IRAS data indicating star formation may be taking place in LDN 425 and LDN 981. The goals of this project were to further explore the known young stellar objects (YSOs) in the two clouds and to search for additional embedded YSOs. In this poster we present our observational methods and the results of our observations including SEDs, color-color diagrams, and color composite images. This research was made possible through the Spitzer Space Telescope Research Program for Teachers and Students and was funded by the Spitzer Science Center (SSC) and the National Optical Astronomy Observatory (NOAO). Please see our companion education posters by McDonald et al. titled "Spitzer - Hot and Colorful Student Activities" and Guastella et al. entitled "Research Based Astronomy in The Secondary Classroom: Lessons Developed for Investigating YSOs Using APT, Excel, and MOPEX".

  9. 77 FR 6598 - In the Matter of Entergy Nuclear Operations, Inc., Palisades Nuclear Plant, 27780 Blue Star...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-02-08

    ... From the Federal Register Online via the Government Publishing Office NUCLEAR REGULATORY COMMISSION In the Matter of Entergy Nuclear Operations, Inc., Palisades Nuclear Plant, 27780 Blue Star Memorial Highway, Covert, MI 49043-9530; Confirmatory Order (Effective Immediately) I Entergy...

  10. ON STAR FORMATION RATES AND STAR FORMATION HISTORIES OF GALAXIES OUT TO z {approx} 3

    SciTech Connect

    Wuyts, Stijn; Foerster Schreiber, Natascha M.; Lutz, Dieter; Nordon, Raanan; Berta, Stefano; Genzel, Reinhard; Magnelli, Benjamin; Poglitsch, Albrecht; Altieri, Bruno; Andreani, Paola; Aussel, Herve; Daddi, Emanuele; Elbaz, David; Cimatti, Andrea; Koekemoer, Anton M.; Maiolino, Roberto; McGrath, Elizabeth J.

    2011-09-01

    We compare multi-wavelength star formation rate (SFR) indicators out to z {approx} 3 in the GOODS-South field. Our analysis uniquely combines U to 8 {mu}m photometry from FIREWORKS, MIPS 24 {mu}m and PACS 70, 100, and 160 {mu}m photometry from the PEP, and H{alpha} spectroscopy from the SINS survey. We describe a set of conversions that lead to a continuity across SFR indicators. A luminosity-independent conversion from 24 {mu}m to total infrared luminosity yields estimates of L{sub IR} that are in the median consistent with the L{sub IR} derived from PACS photometry, albeit with significant scatter. Dust correction methods perform well at low-to-intermediate levels of star formation. They fail to recover the total amount of star formation in systems with large SFR{sub IR}/SFR{sub UV} ratios, typically occuring at the highest SFRs (SFR{sub UV+IR} {approx}> 100 M{sub sun} yr{sup -1}) and redshifts (z {approx}> 2.5) probed. Finally, we confirm that H{alpha}-based SFRs at 1.5 < z < 2.6 are consistent with SFR{sub SED} and SFR{sub UV+IR} provided extra attenuation toward H II regions is taken into account (A{sub V,neb} = A{sub V,continuum}/0.44). With the cross-calibrated SFR indicators in hand, we perform a consistency check on the star formation histories inferred from spectral energy distribution (SED) modeling. We compare the observed SFR-M relations and mass functions at a range of redshifts to equivalents that are computed by evolving lower redshift galaxies backward in time. We find evidence for underestimated stellar ages when no stringent constraints on formation epoch are applied in SED modeling. We demonstrate how resolved SED modeling, or alternatively deep UV data, may help to overcome this bias. The age bias is most severe for galaxies with young stellar populations and reduces toward older systems. Finally, our analysis suggests that SFHs typically vary on timescales that are long (at least several 100 Myr) compared to the galaxies' dynamical time.

  11. Star formation in the "Gulf of Mexico"

    NASA Astrophysics Data System (ADS)

    Armond, T.; Reipurth, B.; Bally, J.; Aspin, C.

    2011-04-01

    We present an optical/infrared study of the dense molecular cloud, L935, dubbed "The Gulf of Mexico", which separates the North America and the Pelican nebulae, and we demonstrate that this area is a very active star forming region. A wide-field imaging study with interference filters has revealed 35 new Herbig-Haro objects in the Gulf of Mexico. A grism survey has identified 41 Hα emission-line stars, 30 of them new. A small cluster of partly embedded pre-main sequence stars is located around the known LkHα 185-189 group of stars, which includes the recently erupting FUor HBC 722.

  12. Comet Riders--Nuclear nomads to the stars

    SciTech Connect

    Angelo, J.A. Jr. ); Buden, D. )

    1991-01-01

    This paper describes the potential role of an evolutionary family of advanced space nuclear power systems (solid core reactor, gas core reactor, and thermonulcear fusion systems) in the detailed exploration of Solar System comets and in the use of interstellar comes to support migratory journeys to the stars by both human beings and their smart robot systems. 14 refs., 5 figs., 2 tabs.

  13. X-ray insights into star and planet formation

    PubMed Central

    Feigelson, Eric D.

    2010-01-01

    Although stars and planets form in cold environments, X-rays are produced in abundance by young stars. This review examines the implications of stellar X-rays for star and planet formation studies, highlighting the contributions of NASA’s (National Aeronautics and Space Administration) Chandra X-ray Observatory. Seven topics are covered: X-rays from protostellar outflow shocks, X-rays from the youngest protostars, the stellar initial mass function, the structure of young stellar clusters, the fate of massive stellar winds, X-ray irradiation of protoplanetary disks, and X-ray flare effects on ancient meteorites. Chandra observations of star-forming regions often show dramatic star clusters, powerful magnetic reconnection flares, and parsec-scale diffuse plasma. X-ray selected samples of premain sequence stars significantly advance studies of star cluster formation, the stellar initial mass function, triggered star-formation processes, and protoplanetary disk evolution. Although X-rays themselves may not play a critical role in the physics of star formation, they likely have important effects on protoplanetary disks by heating and ionizing disk gases. PMID:20404197

  14. X-ray insights into star and planet formation.

    PubMed

    Feigelson, Eric D

    2010-04-20

    Although stars and planets form in cold environments, X-rays are produced in abundance by young stars. This review examines the implications of stellar X-rays for star and planet formation studies, highlighting the contributions of NASA's (National Aeronautics and Space Administration) Chandra X-ray Observatory. Seven topics are covered: X-rays from protostellar outflow shocks, X-rays from the youngest protostars, the stellar initial mass function, the structure of young stellar clusters, the fate of massive stellar winds, X-ray irradiation of protoplanetary disks, and X-ray flare effects on ancient meteorites. Chandra observations of star-forming regions often show dramatic star clusters, powerful magnetic reconnection flares, and parsec-scale diffuse plasma. X-ray selected samples of premain sequence stars significantly advance studies of star cluster formation, the stellar initial mass function, triggered star-formation processes, and protoplanetary disk evolution. Although X-rays themselves may not play a critical role in the physics of star formation, they likely have important effects on protoplanetary disks by heating and ionizing disk gases.

  15. Evidence for Expulsion of the Star Formation Gas Reservoir by the AGN in Local Blue Ellipticals

    NASA Astrophysics Data System (ADS)

    Schwamb, Megan E.; Lintott, Chris; Smethurst, Rebecca; Kruk, Sandor; Matsushita, Satoki; Wong, Ivy; Wang, Shiang-Yu

    2016-01-01

    The formation and assembly of the local galaxy population remains a major open question. Recent works show that elliptical galaxies can rapidly transition from blue star forming to red quiescent systems. Such rapid reddening of stellar populations implies that gas reservoirs are being depleted on timescales which are much shorter than mere exhaustion thanks to ongoing star formation. Feedback, either from star formation itself or from nuclear activity associated with black hole growth is typically invoked. Yet observational confirmation has remained elusive.Using the 10.4-m CSO, we recently obtained 12CO(2-1) observations for a sample of blue star forming local elliptical galaxies to probe the state of the gas and look at the changes in excitation temperature across the star forming sequence. Previous IRAM 12CO(1-0) measurements indicate this population is undergoing a sudden decline in molecular gas fraction. This drop occurs ~200 Myr after a recent peak in star formation- a timescale suggesting AGN triggered feedback switches on rapidly and is immediately effective. The jets or outflows from the central supermassive black hole likely either heat or expel residual gas cutting off star formation, but the 12CO(1-0) measurements alone were insufficient to distinguish between these two scenarios. The 12CO(2-1) to 12CO(1-0) ratio has previously proved diagnostic of the conditions which exist in star forming galaxies. Combining the new 12CO(2-1) measurements with the previous 12CO(1-0) data, we find evidence for active quenching of star formation due to the expulsion of the gas reservoir by the central massive black holes residing in these galaxies. We will discuss our observations and analysis and compare our results to those from other early type populations.

  16. STAR FORMATION IN THE BULLET CLUSTER. I. THE INFRARED LUMINOSITY FUNCTION AND STAR FORMATION RATE ,

    SciTech Connect

    Sun Mi Chung; Gonzalez, Anthony H.; Clowe, Douglas; Markevitch, Maxim; Zaritsky, Dennis

    2010-12-20

    The Bullet Cluster is a massive galaxy cluster at z = 0.297 undergoing a major supersonic (Mach 3) merger event. Using data from Spitzer MIPS and the Infrared Array Camera, optical imaging, and optical spectroscopy, we present the global star formation rate (SFR) of this unique cluster. Using a 90% spectroscopically complete sample of 37 star-forming MIPS confirmed cluster members out to R < 1.7 Mpc, and the Rieke et al. relation to convert from 24 {mu}m flux to SFR, we calculate an integrated obscured SFR of 267 M{sub sun} yr{sup -1} and a specific SFR of 28 M{sub sun} yr{sup -1} per 10{sup 14} M{sub sun}. The cluster mass normalized integrated SFR of the Bullet Cluster is among the highest in a sample of eight other clusters and cluster mergers from the literature. Five LIRGs and one ULIRG contribute 30% and 40% of the total SFR of the cluster, respectively. To investigate the origin of the elevated specific SFR, we compare the infrared luminosity function (IR LF) of the Bullet Cluster to those of Coma (evolved to z = 0.297) and CL1358+62. The Bullet Cluster IR LF exhibits an excess of sources compared to the IR LFs of the other massive clusters. A Schechter function fit of the Bullet Cluster IR LF yields L* = 44.68 {+-} 0.11 erg s{sup -1}, which is {approx}0.25 and 0.35 dex brighter than L* of evolved Coma and CL1358+62, respectively. The elevated IR LF of the Bullet Cluster relative to other clusters can be explained if we attribute the 'excess' star-forming IR galaxies to a population associated with the infalling group that has not yet been transformed into quiescent galaxies. In this case, the timescale required for quenching star formation in the cluster environment must be longer than the timescale since the group's accretion-a few hundred million years. We suggest that 'strangulation' is likely to be an important process in the evolution of star formation in clusters.

  17. Towards universal hybrid star formation rate estimators

    NASA Astrophysics Data System (ADS)

    Boquien, M.; Kennicutt, R.; Calzetti, D.; Dale, D.; Galametz, M.; Sauvage, M.; Croxall, K.; Draine, B.; Kirkpatrick, A.; Kumari, N.; Hunt, L.; De Looze, I.; Pellegrini, E.; Relaño, M.; Smith, J.-D.; Tabatabaei, F.

    2016-06-01

    Context. To compute the star formation rate (SFR) of galaxies from the rest-frame ultraviolet (UV), it is essential to take the obscuration by dust into account. To do so, one of the most popular methods consists in combining the UV with the emission from the dust itself in the infrared (IR). Yet, different studies have derived different estimators, showing that no such hybrid estimator is truly universal. Aims: In this paper we aim at understanding and quantifying what physical processes fundamentally drive the variations between different hybrid estimators. In so doing, we aim at deriving new universal UV+IR hybrid estimators to correct the UV for dust attenuation at local and global scales, taking the intrinsic physical properties of galaxies into account. Methods: We use the CIGALE code to model the spatially resolved far-UV to far-IR spectral energy distributions of eight nearby star-forming galaxies drawn from the KINGFISH sample. This allows us to determine their local physical properties, and in particular their UV attenuation, average SFR, average specific SFR (sSFR), and their stellar mass. We then examine how hybrid estimators depend on said properties. Results: We find that hybrid UV+IR estimators strongly depend on the stellar mass surface density (in particular at 70 μm and 100 μm) and on the sSFR (in particular at 24 μm and the total infrared). Consequently, the IR scaling coefficients for UV obscuration can vary by almost an order of magnitude: from 1.55 to 13.45 at 24 μm for instance. This result contrasts with other groups who found relatively constant coefficients with small deviations. We exploit these variations to construct a new class of adaptative hybrid estimators based on observed UV to near-IR colours and near-IR luminosity densities per unit area. We find that they can reliably be extended to entire galaxies. Conclusions: The new estimators provide better estimates of attenuation-corrected UV emission than classical hybrid estimators

  18. Electron transport through nuclear pasta in magnetized neutron stars

    NASA Astrophysics Data System (ADS)

    Yakovlev, D. G.

    2015-10-01

    We present a simple model for electron transport in a possible layer of exotic nuclear clusters (in the so-called nuclear pasta layer) between the crust and liquid core of a strongly magnetized neutron star. The electron transport there can be strongly anisotropic and gyrotropic. The anisotropy is produced by different electron effective collision frequencies along and across local symmetry axis in domains of exotic ordered nuclear clusters and by complicated effects of the magnetic field. We also calculate averaged kinetic coefficients in case local domains are freely oriented. Possible applications of the obtained results and open problems are outlined.

  19. College Students' Preinstructional Ideas about Stars and Star Formation

    ERIC Educational Resources Information Center

    Bailey, Janelle M.; Prather, Edward E.; Johnson, Bruce; Slater, Timothy F.

    2009-01-01

    This study (Note 1) investigated the beliefs about stars that students hold when they enter an undergraduate introductory astronomy course for nonscience majors. Students' preinstructional ideas were investigated through the use of several student-supplied-response (SSR) surveys, which asked students to describe their ideas about topics such as…

  20. The star formation-AGN connection from the CALIFA survey perspective

    NASA Astrophysics Data System (ADS)

    Morales, A.; Rosales-Ortega, F. F.; Torres-Papaqui, J. P.; Sánchez, S. F.; Chow-Martínez, M.; Ortega-Minakata, R. A.; Romero-Cruz, F. J.; Trejo-Alonso, J. J.; Neri-Larios, D. M.; Robleto-Orús, A.

    2016-06-01

    It is widely suspected the bulk of star formation precedes the top AGN phase. However, evidence has also been found of star formation triggered by AGN feedback. Host properties and environmental conditions may guide us to start unveiling such a connection. We then study environmentally-induced galaxies using CALIFA data. We start by determining nuclear activity and current SFR to compare them with those of non-interacting, star-forming galaxies (CALIFA data too). We want to firstly corroborate that it is really the intensity of the star-forming bursts what produces the chemical differences of galaxies. It then follows to estimate the intensity of the central and/or circumnuclear burst(s) and to determine whether or not it is affected by perturbers.

  1. Efficient star formation in the bright bar of M83

    NASA Technical Reports Server (NTRS)

    Lord, S. D.; Strom, S. E.; Young, J. S.

    1987-01-01

    The bright molecular bar in M83 was detected standing out as a 100% enhancement of molecular emission with respect to the off-bar emission at the same radii. The spatial variations in the star formation efficiency, as traced by H alpha emission and the surface density of the interstellar gas, in M83 and M51 were compared. Both the central bar of M83 and the spiral arms of M51 are regions characterized by high massive star formation rates. For M83, it is ascribed that both the gas surface density and the star formation efficiency are high to the hydrodynamics of the central region.

  2. Long-period variable stars in NGC 147 and NGC 185 - I. Their star formation histories

    NASA Astrophysics Data System (ADS)

    Hamedani Golshan, Roya; Javadi, Atefeh; van Loon, Jacco Th.; Khosroshahi, Habib; Saremi, Elham

    2017-04-01

    NGC 147 and NGC 185 are two of the most massive satellites of the Andromeda galaxy (M 31). Close together in the sky, of similar mass and morphological type dE, they possess different amounts of interstellar gas and tidal distortion. The question therefore is, how do their histories compare? Here, we present the first reconstruction of the star formation histories of NGC 147 and NGC 185 using long-period variable stars. These represent the final phase of evolution of low- and intermediate-mass stars at the asymptotic giant branch, when their luminosity is related to their birth mass. Combining near-infrared photometry with stellar evolution models, we construct the mass function and hence the star formation history. For NGC 185, we found that the main epoch of star formation occurred 8.3 Gyr ago, followed by a much lower, but relatively constant star formation rate. In the case of NGC 147, the star formation rate peaked only 7 Gyr ago, staying intense until ∼3 Gyr ago, but no star formation has occurred for at least 300 Myr. Despite their similar masses, NGC 147 has evolved more slowly than NGC 185 initially, but more dramatically in more recent times. This is corroborated by the strong tidal distortions of NGC 147 and the presence of gas in the centre of NGC 185.

  3. On the Star Formation Properties of Void Galaxies

    NASA Astrophysics Data System (ADS)

    Moorman, Crystal M.; Moreno, Jackeline; White, Amanda; Vogeley, Michael S.; Hoyle, Fiona; Giovanelli, Riccardo; Haynes, Martha P.

    2016-11-01

    We measure the star formation properties of two large samples of galaxies from the SDSS in large-scale cosmic voids on timescales of 10 and 100 Myr, using Hα emission line strengths and GALEX FUV fluxes, respectively. The first sample consists of 109,818 optically selected galaxies. We find that void galaxies in this sample have higher specific star formation rates (SSFRs; star formation rates per unit stellar mass) than similar stellar mass galaxies in denser regions. The second sample is a subset of the optically selected sample containing 8070 galaxies with reliable H i detections from ALFALFA. For the full H i detected sample, SSFRs do not vary systematically with large-scale environment. However, investigating only the H i detected dwarf galaxies reveals a trend toward higher SSFRs in voids. Furthermore, we estimate the star formation rate per unit H i mass (known as the star formation efficiency; SFE) of a galaxy, as a function of environment. For the overall H i detected population, we notice no environmental dependence. Limiting the sample to dwarf galaxies still does not reveal a statistically significant difference between SFEs in voids versus walls. These results suggest that void environments, on average, provide a nurturing environment for dwarf galaxy evolution allowing for higher specific star formation rates while forming stars with similar efficiencies to those in walls.

  4. Probing Massive Star Cluster Formation with ALMA

    NASA Astrophysics Data System (ADS)

    Johnson, Kelsey

    2015-08-01

    Observationally constraining the physical conditions that give rise to massive star clusters has been a long-standing challenge. Now with the ALMA Observatory coming on-line, we can finally begin to probe the birth environments of massive clusters in a variety of galaxies with sufficient angular resolution. In this talk I will give an overview of ALMA observations of galaxies in which candidate proto-super star cluster molecular clouds have been identified. These new data probe the physical conditions that give rise to super star clusters, providing information on their densities, pressures, and temperatures. In particular, the observations indicate that these clouds may be subject to external pressures of P/k > 108 K cm-3, which is consistent with the prevalence of optically observed adolescent super star clusters in interacting galaxy systems and other high pressure environments. ALMA observations also enable an assessement of the molecular cloud chemical abundances in the regions surrounding super star clusters. Molecular clouds associated with existing super star clusters are strongly correlated with HCO+ emission, but appear to have relatively low ratio of CO/HCO+ emission compared to other clouds, indicating that the super star clusters are impacting the molecular abundances in their vicinity.

  5. AN INFRARED CENSUS OF STAR FORMATION IN THE HORSEHEAD NEBULA

    SciTech Connect

    Bowler, Brendan P.; Waller, William H.; Megeath, S. Thomas; Patten, Brian M.; Tamura, Motohide E-mail: william.waller@tufts.edu E-mail: bpatten@nsf.gov

    2009-03-15

    At {approx} 400 pc, the Horsehead Nebula (B33) is the closest radiatively sculpted pillar to the Sun, but the state and extent of star formation in this structure is not well understood. We present deep near-infrared (IRSF/SIRIUS JHK {sub S}) and mid-infrared (Spitzer/IRAC) observations of the Horsehead Nebula to characterize the star-forming properties of this region and to assess the likelihood of triggered star formation. Infrared color-color and color-magnitude diagrams are used to identify young stars based on infrared excess emission and positions to the right of the zero-age main sequence, respectively. Of the 45 sources detected at both near- and mid-infrared wavelengths, three bona fide and five candidate young stars are identified in this 7' x 7' region. Two bona fide young stars have flat infrared spectral energy distributions and are located at the western irradiated tip of the pillar. The spatial coincidence of the protostars at the leading edge of this elephant trunk is consistent with the radiation-driven implosion model of triggered star formation. There is no evidence, however, for sequential star formation within the immediate {approx} 1.'5 (0.17 pc) region from the cloud/H II region interface.

  6. An Infrared Census of Star Formation in the Horsehead Nebula

    NASA Astrophysics Data System (ADS)

    Bowler, Brendan P.; Waller, William H.; Megeath, S. Thomas; Patten, Brian M.; Tamura, Motohide

    2009-03-01

    At ~ 400 pc, the Horsehead Nebula (B33) is the closest radiatively sculpted pillar to the Sun, but the state and extent of star formation in this structure is not well understood. We present deep near-infrared (IRSF/SIRIUS JHK S) and mid-infrared (Spitzer/IRAC) observations of the Horsehead Nebula to characterize the star-forming properties of this region and to assess the likelihood of triggered star formation. Infrared color-color and color-magnitude diagrams are used to identify young stars based on infrared excess emission and positions to the right of the zero-age main sequence, respectively. Of the 45 sources detected at both near- and mid-infrared wavelengths, three bona fide and five candidate young stars are identified in this 7' × 7' region. Two bona fide young stars have flat infrared spectral energy distributions and are located at the western irradiated tip of the pillar. The spatial coincidence of the protostars at the leading edge of this elephant trunk is consistent with the radiation-driven implosion model of triggered star formation. There is no evidence, however, for sequential star formation within the immediate ~ 1farcm5 (0.17 pc) region from the cloud/H II region interface.

  7. Star formation in RCW 108: Triggered or spontaneous?

    NASA Astrophysics Data System (ADS)

    Comerón, F.; Schneider, N.; Russeil, D.

    2005-04-01

    We present visible, near infrared and mm-wave observations of RCW 108, a molecular cloud complex in the Ara OB1 association that is being eroded by the energetic radiation of two O-type stars in the nearby cluster NGC 6193. The western part of the RCW108 molecular cloud, for which we derive a mass of ~8000 M⊙, contains an embedded compact HII region, IRAS 16362-4845, ionized by an aggregate of early-type stars for which we estimate a mass of ˜ 210 M⊙. The spectral type of the earliest star is O9, as confirmed by the visible spectrum of the compact HII region. We notice a lack of stars later than A0 in the aggregate, at least having the moderate reddenings that are common among its B-type stars, and we speculate that this might be a consequence of the extreme youth of the aggregate. We also note the existence of a dense ionized clump (n > 104 cm-3) appearing near the main ionizing star of the compact HII region. We examine the distribution of stars displaying infrared excesses projected across the molecular cloud. While many of them are located in the densest (n ˜ 104-5 cm-3) area of the molecular cloud near the position of IRAS 16362-4845, we also find a group concentrating towards the edge of the cloud that faces NGC 6193, as well as some other stars beyond the edge of the molecular cloud. The intense ionizing radiation field by the O stars in NGC 6193 is a clear candidate trigger of star formation in the molecular cloud, and we suggest that the existence and arrangement of stars in this region of the molecular cloud supports a scenario in which their formation may be a consequence of this. However, infrared excess stars are also present in some areas of the opposite side of the cloud, where no obvious candidate external trigger is identified. The existence of such tracers of recent star formation scattered across the more massive molecular cloud associated with IRAS 16362-4845, and the low star formation efficiency that we derive, indicate that it is in a

  8. ENVIRONMENTAL DEPENDENCE OF THE STAR FORMATION RATE AND THE SPECIFIC STAR FORMATION RATE AT FIXED MORPHOLOGY

    SciTech Connect

    Deng Xinfa

    2010-09-20

    From the Main galaxy sample of the Sloan Digital Sky Survey Data Release 7, I construct two volume-limited samples with luminosities -20.5 {<=} M{sub r} {<=} -18.5 and -22.5{<=}M{sub r} {<=}-20.5, respectively, to explore the environmental dependence of the star formation rate (SFR) and the specific star formation rate (SSFR) at fixed morphology. It is found that in these two volume-limited samples, galaxies in the lowest density regime preferentially have higher SFR and SSFR than galaxies in the densest regime. I divide each volume-limited Main galaxy sample into two distinct populations, the early type and the late type, and observe that the environmental dependence of the SFR and SSFR of galaxies remains true at fixed morphology: the SFR and SSFR of galaxies in the densest regime is still preferentially lower than that of the ones in the lowest density regime with the same morphological type. I also note that the environmental dependence of the SFR and SSFR of late-type galaxies is stronger than that of early-type galaxies.

  9. The era of star formation in galaxy clusters

    SciTech Connect

    Brodwin, M.; Stanford, S. A.; Gonzalez, Anthony H.; Mancone, C. L.; Gettings, D. P.; Zeimann, G. R.; Snyder, G. F.; Ashby, M. L. N.; Pope, A.; Alberts, S.; Eisenhardt, P. R.; Stern, D.; Moustakas, L. A.; Brown, M. J. I.; Chary, R.-R.; Dey, Arjun; Galametz, A.; Jannuzi, B. T.; Miller, E. D.; Moustakas, J.

    2013-12-20

    We analyze the star formation properties of 16 infrared-selected, spectroscopically confirmed galaxy clusters at 1 < z < 1.5 from the Spitzer/IRAC Shallow Cluster Survey (ISCS). We present new spectroscopic confirmation for six of these high-redshift clusters, five of which are at z > 1.35. Using infrared luminosities measured with deep Spitzer/Multiband Imaging Photometer for Spitzer observations at 24 μm, along with robust optical + IRAC photometric redshifts and spectral-energy-distribution-fitted stellar masses, we present the dust-obscured star-forming fractions, star formation rates, and specific star formation rates in these clusters as functions of redshift and projected clustercentric radius. We find that z ∼ 1.4 represents a transition redshift for the ISCS sample, with clear evidence of an unquenched era of cluster star formation at earlier times. Beyond this redshift, the fraction of star-forming cluster members increases monotonically toward the cluster centers. Indeed, the specific star formation rate in the cores of these distant clusters is consistent with field values at similar redshifts, indicating that at z > 1.4 environment-dependent quenching had not yet been established in ISCS clusters. By combining these observations with complementary studies showing a rapid increase in the active galactic nucleus (AGN) fraction, a stochastic star formation history, and a major merging episode at the same epoch in this cluster sample, we suggest that the starburst activity is likely merger-driven and that the subsequent quenching is due to feedback from merger-fueled AGNs. The totality of the evidence suggests we are witnessing the final quenching period that brings an end to the era of star formation in galaxy clusters and initiates the era of passive evolution.

  10. Triggered star formation & feedback in the ring galaxy, NGC 922

    NASA Astrophysics Data System (ADS)

    Wong, O. Ivy; Koribalski, Baerbel; Meurer, Gerhardt; Zwaan, Martin; Bekki, Kenji; Garcia-Appadoo, Diego; Vlahakis, Catherine

    2013-10-01

    Star formation (and its cessation) play an integral role in galaxy evolution. However, the physical processes that govern how and when stars form in galaxies is still not fully understood. Although rare, ring galaxies provide an excellent testbed for studying two opposing compression-driven processes, namely the large-scale triggering of star formation versus the subsequent destructive feedback effects of newly-formed massive stars on nearby molecular clouds (and future star formation). Due to the simplicity of the collision, we can constrain the interaction timescales very well and hence obtain good boundary conditions for when stars can be formed within the observed ring. We propose to map the neutral gas content of NGC 922--- a recently-discovered ring galaxy that also happens to be one of the closest. We have obtained excellent observations of the stellar components from the Hubble Space Telescope for this object and we are only lacking information about its gas properties. These proposed observations will shed light on: (1) the balance between neutral and molecular gas content in the ISM of the ring galaxy; (2) the physical processes that dominate the galactic-scale triggering and suppression of star formation galaxies; (3) the kinematics and location of gas that has been disrupted and stripped from this galaxy pair; and (4) the validity of our simulated interaction model for the formation of NGC 922.

  11. The StarLight formation-flying interferometer system architecture

    NASA Technical Reports Server (NTRS)

    Duren, R.; Lay, O.

    2002-01-01

    The StarLight Project, scheduled for a 6-month mission in 2006, will demonstrate the new technologies of spaceborne long-baseline optical interferometry and precision formation flying necessary for the Terrestrial Planet Finder and other future astropohysics missions.

  12. Connecting the density structure of molecular clouds with star formation

    NASA Astrophysics Data System (ADS)

    Kainulainen, Jouni

    In the current paradigm of turbulence-regulated interstellar medium (ISM), star formation rates of entire galaxies are intricately linked to the density structure of the individual molecular clouds. This density structure is essentially encapsulated in the probability distribution function of volume densities (ρ-PDF), which directly affects the star formation rates predicted by analytic models. Contrasting its fundamental role, the ρ-PDF function has remained virtually unconstrained by observations. I describe in this contribution the recent progress in attaining observational constraints for the column density PDFs (N-PDFs) of molecular clouds that function as a proxy of the ρ-PDFs. Specifically, observational works point towards a universal correlation between the shape of the N-PDFs and star formation activity in molecular clouds. The correlation is in place from the scales of a parsec up to the scales of entire galaxies, making it a fundamental, global link between the ISM structure and star formation.

  13. Theoretical Developments in Understanding Massive Star Formation

    NASA Technical Reports Server (NTRS)

    Yorke, Harold W.; Bodenheimer, Peter

    2007-01-01

    Except under special circumstances massive stars in galactic disks will form through accretion. The gravitational collapse of a molecular cloud core will initially produce one or more low mass quasi-hydrostatic objects of a few Jupiter masses. Through subsequent accretion the masses of these cores grow as they simultaneously evolve toward hydrogen burning central densities and temperatures. We review the evolution of accreting (proto-)stars, including new results calculated with a publicly available stellar evolution code written by the authors.

  14. Infrared observations of OB star formation in NGC 6334

    NASA Technical Reports Server (NTRS)

    Harvey, P. M.; Gatley, I.

    1983-01-01

    Infrared photometry and maps from 2 to 100 microns are presented for three of the principal far infrared sources in NGC 6334. Each region is powered by two or more very young stars. The distribution of dust and ionized gas is probably strongly affected by the presence of the embedded stars; one of the sources is a blister H II region, another has a bipolar structure, and the third exhibits asymmetric temperature structure. The presence of protostellar objects throughout the region suggests that star formation has occurred nearly simultaneously in the whole molecular cloud rather than having been triggered sequentially from within. Previously announced in STAR as N83-16263

  15. Hierarchical Star Formation in Turbulent Media: Evidence from Young Star Clusters

    NASA Astrophysics Data System (ADS)

    Grasha, Kathryn; Elmegreen, Bruce; Calzetti, Daniela

    2017-01-01

    We present an analysis of the positions and ages of star clusters in eight local galaxies and find a correlation between the age difference and separation of cluster pairs. We infer that cluster formation is correlated in time such that clusters that are close to each have similar ages. In addition, the age between cluster pairs increases with their separation to the 0.3 - 0.6 power, close to the expected slope of 0.5 that would arise in a turbulent-driven interstellar medium. This suggests that not only is star formation hierarchical both in space and in time, but that the duration of star formation depends on the region of interest: smaller regions will form stars over a shorter time frame whereas larger regions form stars over a longer time frame.

  16. Tracing the sites of obscured star formation in the Antennae galaxies with Herschel-PACS

    NASA Astrophysics Data System (ADS)

    Klaas, U.; Nielbock, M.; Haas, M.; Krause, O.; Schreiber, J.

    2010-07-01

    Aims: FIR imaging of interacting galaxies allows locating even hidden sites of star formation and measuring of the relative strength of nuclear and extra-nuclear star formation. We want to resolve the star-forming sites in the nearby system of the Antennae. Methods: Thanks to the unprecedented sharpness and depth of the PACS camera onboard ESA's Herschel Space Observatory, it is possible for the first time to achieve a complete assessment of individual star-forming knots in the FIR with scan maps at 70, 100, and 160 μm. We used clump extraction photometry and SED diagnostics to derive the properties related to star-forming activity. Results: The PACS 70, 100, and 160 μm maps trace the knotty structure of the most recent star formation along an arc between the two nuclei in the overlap area. The resolution of the starburst knots and additional multi-wavelength data allow their individual star formation history and state to be analysed. In particular, the brightest knot in the mid-infrared (K1), east of the southern nucleus, exhibits the highest activity by far in terms of dust heating and star formation rate, efficiency, and density. With only 2 kpc in diameter, this area has a 10-1000 μm luminosity, which is as high as that of our Milky Way. It shows the highest deficiency in radio emission in the radio-to-FIR luminosity ratio and a lack of X-ray emission, classifying it as a very young complex. The brightest 100 and 160 μm emission region (K2), which is close to the collision front and consists of 3 knots, also shows a high star formation density and efficiency and lack of X-ray emission in its most obscured part, but an excess in the radio-to-FIR luminosity ratio. This suggests a young stage, too, but different conditions in its interstellar medium. Our results provide important checkpoints for numerical simulations of interacting galaxies when modelling the star formation and stellar feedback. Herschel is an ESA space observatory with science instruments

  17. Environmental regulation of cloud and star formation in galactic bars

    NASA Astrophysics Data System (ADS)

    Renaud, F.; Bournaud, F.; Emsellem, E.; Agertz, O.; Athanassoula, E.; Combes, F.; Elmegreen, B.; Kraljic, K.; Motte, F.; Teyssier, R.

    2015-12-01

    The strong time-dependence of the dynamics of galactic bars yields a complex and rapidly evolving distribution of dense gas and star forming regions. Although bars mainly host regions void of any star formation activity, their extremities can gather the physical conditions for the formation of molecular complexes and mini-starbursts. Using a sub-parsec resolution hydrodynamical simulation of a Milky Way-like galaxy, we probe these conditions to explore how and where bar (hydro-)dynamics favours the formation or destruction of molecular clouds and stars. The interplay between the kpc-scale dynamics (gas flows, shear) and the parsec-scale (turbulence) is key to this problem. We find a strong dichotomy between the leading and trailing sides of the bar, in term of cloud fragmentation and in the age distribution of the young stars. After orbiting along the bar edge, these young structures slow down at the extremities of the bar, where orbital crowding increases the probability of cloud-cloud collision. We find that such events increase the Mach number of the cloud, leading to an enhanced star formation efficiency and finally the formation of massive stellar associations, in a fashion similar to galaxy-galaxy interactions. We highlight the role of bar dynamics in decoupling young stars from the clouds in which they form, and discuss the implications on the injection of feedback into the interstellar medium (ISM), in particular in the context of galaxy formation.

  18. Star Formation and Dynamics in the Galactic Centre

    NASA Astrophysics Data System (ADS)

    Mapelli, Michela; Gualandris, Alessia

    The centre of our Galaxy is one of the most studied and yet enigmatic places in the Universe. At a distance of about 8 kpc from our Sun, the Galactic centre (GC) is the ideal environment to study the extreme processes that take place in the vicinity of a supermassive black hole (SMBH). Despite the hostile environment, several tens of early-type stars populate the central parsec of our Galaxy. A fraction of them lie in a thin ring with mild eccentricity and inner radius ˜ 0.04 pc, while the S-stars, i.e. the ˜ 30 stars closest to the SMBH ( lesssim 0.04 pc), have randomly oriented and highly eccentric orbits. The formation of such early-type stars has been a puzzle for a long time: molecular clouds should be tidally disrupted by the SMBH before they can fragment into stars. We review the main scenarios proposed to explain the formation and the dynamical evolution of the early-type stars in the GC. In particular, we discuss the most popular in situ scenarios (accretion disc fragmentation and molecular cloud disruption) and migration scenarios (star cluster inspiral and Hills mechanism). We focus on the most pressing challenges that must be faced to shed light on the process of star formation in the vicinity of a SMBH.

  19. Unveiling Hidden Massive Stars: Star Formation and the IMF in Carina

    NASA Astrophysics Data System (ADS)

    Alexander, Michael; Povich, Matthew; McSwain, M. Virginia

    2014-02-01

    We propose two nights of observations with the OSIRIS IR spectrograph on SOAR to obtain spectra for a large sample of massive star candidates within the Carina Nebula. Target stars have been identified as OB candidates through the use of combined X-ray emission and IR SED fitting and are too extincted to be readily observed at optical wavelengths. We will obtain K-band spectroscopy of 56 highly extincted stars in order to identify their spectral type and luminosity class. The proposed observations will confirm or reject individual stars as massive members of the Carina nebula star forming complex. The placement of these stars around the nebula will address questions on the process of triggered star formation, and the wide distribution of targets may shed light on the idea that OB stars can form in isolation. Additionally, any new OB stars will bolster the high-mass end of the stellar IMF and lead to a more accurate determine of the total stellar mass and a better understanding of the recent star formation history within the region.

  20. The Suppression of Star Formation by Powerful Active Galactic Nuclei

    NASA Technical Reports Server (NTRS)

    Dwek, E.

    2012-01-01

    The old, red stars that constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly as a result of accretion onto black holes. It is widely suspected, but unproved, that the tight corre1ation between the mass of the black hole and the mas. of the stellar bulge results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, whereas powerful star-forming ga1axies are usually dust-obscured and are brightest at infrared and submillimeter wavelengths. Here we report submillimetre and X-ray observations that show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 billion years old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10(exp 44) ergs per second. This suppression of star formation in the host galaxy of a powerful AGN is a key prediction of models in which the AGN drives an outflow, expe11ing the interstellar medium of its host and transforming the galaxy's properties in a brief period of cosmic time.

  1. Star Formation in Isolated Cores: A Solitary Existence?

    NASA Astrophysics Data System (ADS)

    Mundy, Lee; Allen, Lori; Chapman, Nicholas; Harvey, Paul; Lai, Shih-Ping; Looney, Leslie; Myers, Phil

    2004-09-01

    The standard theories of star formation address the formation of a single star in isolation. Dark cloud cores are often cited as examples of isolated, individual star formation. Because of the density of these cores, observations to date have not had the sensitivity to really examine the core structure and search for the youngest and lowest mass sub-stellar objects. We propose to observe ten dark cores, five without associated stars and five with an associated star in all four IRAC bands and MIPS 24 micron. In addition, we will combine these observations with deep JHK ground-based imaging. We will observe the youngest sub-stellar objects down to 10 Jupiter masses, map the column density structure via extinction measurements, and image faint extended emission, such as outflows that are indicative of cloud-star interaction. Our overall goal is to test standard star formation theory by identifying the entire stellar and sub-stellar content of the cores and the relation of these objects to the gas and dust distribution.

  2. The suppression of star formation by powerful active galactic nuclei.

    PubMed

    Page, M J; Symeonidis, M; Vieira, J D; Altieri, B; Amblard, A; Arumugam, V; Aussel, H; Babbedge, T; Blain, A; Bock, J; Boselli, A; Buat, V; Castro-Rodríguez, N; Cava, A; Chanial, P; Clements, D L; Conley, A; Conversi, L; Cooray, A; Dowell, C D; Dubois, E N; Dunlop, J S; Dwek, E; Dye, S; Eales, S; Elbaz, D; Farrah, D; Fox, M; Franceschini, A; Gear, W; Glenn, J; Griffin, M; Halpern, M; Hatziminaoglou, E; Ibar, E; Isaak, K; Ivison, R J; Lagache, G; Levenson, L; Lu, N; Madden, S; Maffei, B; Mainetti, G; Marchetti, L; Nguyen, H T; O'Halloran, B; Oliver, S J; Omont, A; Panuzzo, P; Papageorgiou, A; Pearson, C P; Pérez-Fournon, I; Pohlen, M; Rawlings, J I; Rigopoulou, D; Riguccini, L; Rizzo, D; Rodighiero, G; Roseboom, I G; Rowan-Robinson, M; Sánchez Portal, M; Schulz, B; Scott, D; Seymour, N; Shupe, D L; Smith, A J; Stevens, J A; Trichas, M; Tugwell, K E; Vaccari, M; Valtchanov, I; Viero, M; Vigroux, L; Wang, L; Ward, R; Wright, G; Xu, C K; Zemcov, M

    2012-05-09

    The old, red stars that constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly as a result of accretion onto black holes. It is widely suspected, but unproved, that the tight correlation between the mass of the black hole and the mass of the stellar bulge results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, whereas powerful star-forming galaxies are usually dust-obscured and are brightest at infrared and submillimetre wavelengths. Here we report submillimetre and X-ray observations that show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 billion years old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10(44) ergs per second. This suppression of star formation in the host galaxy of a powerful AGN is a key prediction of models in which the AGN drives an outflow, expelling the interstellar medium of its host and transforming the galaxy's properties in a brief period of cosmic time.

  3. On the impact of empirical and theoretical star formation laws on galaxy formation

    NASA Astrophysics Data System (ADS)

    Lagos, Claudia Del P.; Lacey, Cedric G.; Baugh, Carlton M.; Bower, Richard G.; Benson, Andrew J.

    2011-09-01

    We investigate the consequences of applying different star formation laws in the galaxy formation model GALFORM. Three broad star formation laws are implemented: the empirical relations of Kennicutt and Schmidt and Blitz & Rosolowsky and the theoretical model of Krumholz, McKee & Tumlinson. These laws have no free parameters once calibrated against observations of the star formation rate (SFR) and gas surface density in nearby galaxies. We start from published models, and investigate which observables are sensitive to a change in the star formation law, without altering any other model parameters. We show that changing the star formation law (i) does not significantly affect either the star formation history of the universe or the galaxy luminosity functions in the optical and near-infrared, due to an effective balance between the quiescent and burst star formation modes, (ii) greatly affects the cold gas contents of galaxies and (iii) changes the location of galaxies in the SFR versus stellar mass plane, so that a second sequence of 'passive' galaxies arises, in addition to the known 'active' sequence. We show that this plane can be used to discriminate between the star formation laws.

  4. VizieR Online Data Catalog: Star formation in early-type galaxies (Longhetti+ 1999)

    NASA Astrophysics Data System (ADS)

    Longhetti, M.; Bressan, A.; Chiosi, C.; Rampazzo, R.

    1999-04-01

    We analyze the star formation properties of a sample of 21 shell galaxies and 30 early-type galaxies members of interacting pairs, located in low density environments (Longhetti et al., 1998, Cat. , 1998A&AS..130..267L). The study is based on new models developed to interpret the information coming from `blue' HδFeI, H+K(CaII) and D4000 line-strength indices proposed by Rose (1984AJ.....89.1238R; 1985AJ.....90.1927R) and Hamilton (1985ApJ...297..371H). We find that the last star forming event that occurred in the nuclear region of shell galaxies is statistically old (from 0.1 up to several Gyr) with respect to the corresponding one in the sub-sample of pair galaxies (<0.1Gyr or even ongoing star formation). If the stellar activity is somehow related to the formation of shells, as predicted by several dynamical models of galaxy interaction, shells have to be considered long lasting structures. Since pair members show evidence of very recent star formation, we suggest that either large reservoirs of gas have to be present to maintain active star formation, if these galaxies are on periodic orbits, or most of the pair members in the present sample are experiencing unbound encounters. (1 data file).

  5. Massive star formation at high spatial resolution

    NASA Astrophysics Data System (ADS)

    Pascucci, Ilaria

    2004-05-01

    This thesis studies the early phases of massive stars and their impact on the surrounding. The capabilities of continuum radiative transfer (RT) codes to interpret the observations are also investigated. The main results of this work are: 1) Two massive star-forming regions are observed in the infrared. The thermal emission from the ultra-compact H II regions is resolved and the spectral type of the ionizing stars is estimated. The hot cores are not detected thus implying line-of-sight extinction larger than 200 visual magnitude. 2) The first mid-infrared interferometric measurements towards a young massive star resolve thermal emission on scales of 30-50 AU probing the size of the predicted disk. The visibility curve differs from those of intermediate-mass stars. 3) The close vicinity of Θ1C Ori are imaged using the NACO adaptive optics system. The binary proplyd Orion 168-326 and its interaction with the wind from Θ1C Ori are resolved. A proplyd uniquely seen face-on is also identified. 4) Five RT codes are compared in a disk configuration. The solutions provide the first 2D benchmark and serve to test the reliability of other RT codes. The images/visibilities from two RT codes are compared for a distorted disk. The parameter range in which such a distortion is detectable with MIDI is explored.

  6. Heavy element abundances and massive star formation

    NASA Technical Reports Server (NTRS)

    Wang, Boqi; Silk, Joseph

    1993-01-01

    The determination of the stellar initial mass function (IMF) remains a great challenge in astronomy. In the solar neighborhood, the IMF is reasonable well determined for stellar masses from about 0.1 to 60 solar mass. However, outside the solar neighborhood, the IMF is poorly known. Among those frequently discussed arguments favoring a different IMF outside the solar neighborhood are the estimated time to consume the remaining gas in spiral galaxies, and the high rate of forming massive stars in starburst galaxies. An interesting question then is whether there may be an independent way of testing possible variations in the IMF. Indeed, the heavy elements in the interstellar medium are mostly synthesized in massive stars, so increasing, or decreasing, the fraction of massive stars naturally leads to a variation in the heavy element yield, and thus, the metallicity. The observed abundance should severely constrain any deviations of the IMF from the locally determined IMF. We focus on element oxygen, which is the most abundant heavy element in the interstellar medium. Oxygen is ejected only by massive stars that can become Type 1 supernovae, and the oxygen abundance is, therefore, a sensitive function of the fraction of massive stars in the IMF. Adopting oxygen enables us to avoid uncertainties in Type 1 supernovae. We use the nucleosynthesis results to calculate the oxygen yield for given IMF. We then calculate the oxygen abundance in the interstellar medium assuming instantaneous recycling of oxygen.

  7. Hubble studies generations of star formation in neighbouring galaxy

    NASA Astrophysics Data System (ADS)

    2004-07-01

    N11B Credits: NASA/ESA and the Hubble Heritage Team (AURA/STScI)/HEIC The iridescent tapestry of star birth The NASA/ESA Hubble Space Telescope captures the iridescent tapestry of star birth in a neighbouring galaxy in this panoramic view of glowing gas, dark dust clouds, and young, hot stars. The star-forming region, catalogued as N11B lies in the Large Magellanic Cloud (LMC), located only 160 000 light-years from Earth. With its high resolution, the Hubble Space Telescope is able to view details of star formation in the LMC as easily as ground-based telescopes are able to observe stellar formation within our own Milky Way galaxy. One neighbouring galaxy, the Large Magellanic Cloud (LMC), lies in the constellation of Dorado and contains a number of regions harbouring recent and ongoing star formation. One of these star-forming region, N11B, is shown in this Hubble image. It is a subregion within a larger area of star formation called N11. N11 is the second largest star-forming region in LMC. It is only surpassed in the size and activity by ‘the king of stellar nurseries’, 30 Doradus, located at the opposite side of LMC. N11B Credits: NASA/ESA and the Hubble Heritage Team (AURA/STScI)/HEIC A view of star formation The NASA/ESA Hubble Space Telescope captures the iridescent tapestry of star birth in a neighbouring galaxy in this panoramic view of glowing gas, dark dust clouds, and young, hot stars. The star-forming region, catalogued as N11B lies in the Large Magellanic Cloud (LMC), located only 160 000 light-years from Earth. With its high resolution, the Hubble Space Telescope is able to view details of star formation in the LMC as easily as ground-based telescopes are able to observe stellar formation within our own Milky Way galaxy. One neighbouring galaxy, the Large Magellanic Cloud (LMC), lies in the constellation of Dorado and contains a number of regions harbouring recent and ongoing star formation. One of these star-forming regions, N11B, is shown in

  8. Segue 1 -- A Compressed Star Formation History before Reionization

    NASA Astrophysics Data System (ADS)

    Webster, David; Frebel, Anna; Bland-Hawthorn, Joss

    2016-02-01

    Segue 1 is the current best candidate for a “first galaxy,” a system that experienced only a single, short burst of star formation and has since remained unchanged. Here we present possible star formation scenarios that can explain Segue 1’s unique metallicity distribution. While the majority of stars in all other ultra-faint dwarfs are within 0.5 dex of the mean [Fe/H] for the galaxy, five of the seven stars in Segue 1 have a spread of Δ[Fe/H] > 0.8 dex. We show that this distribution of metallicities cannot be explained by a gradual buildup of stars, but instead requires clustered star formation. Chemical tagging allows the separate unresolved delta functions in abundance space to be associated with discrete events in space and time. This provides an opportunity to put the enrichment events into a time sequence and unravel the history of the system. We investigate two possible scenarios for the star formation history of Segue 1 using Fyris Alpha simulations of gas in a 107 M⊙ dark matter halo. The lack of stars with intermediate metallicities -3 < [Fe/H] < -2 can be explained either by a pause in star formation caused by supernova feedback or by the spread of metallicities resulting from one or two supernovae in a low-mass dark matter halo. Either possibility can reproduce the metallicity distribution function (MDF) as well as the other observed elemental abundances. The unusual MDF and the low luminosity of Segue 1 can be explained by it being a first galaxy that originated with Mvir ˜ 107M⊙ at z ˜ 10.

  9. Probing nuclear bubble structure via neutron star asteroseismology

    NASA Astrophysics Data System (ADS)

    Sotani, Hajime; Iida, Kei; Oyamatsu, Kazuhiro

    2017-01-01

    We consider torsional oscillations that are trapped in a layer of spherical-hole (bubble) nuclear structure, which is expected to occur in the deepest region of the inner crust of a neutron star. Because this layer intervenes between the phase of slab nuclei and the outer core of uniform nuclear matter, torsional oscillations in the bubble phase can be excited separately from usual crustal torsional oscillations. We find from eigenmode analyses for various models of the equation of state of uniform nuclear matter that the fundamental frequencies of such oscillations are almost independent of the incompressibility of symmetric nuclear matter, but strongly depend on the slope parameter of the nuclear symmetry energy L. Although the frequencies are also sensitive to the entrainment effect, i.e. what portion of nucleons outside bubbles contribute to the oscillations, by having such a portion fixed, we can successfully fit the calculated fundamental frequencies of torsional oscillations in the bubble phase inside a star of specific mass and radius as a function of L. By comparing the resultant fitting formula to the frequencies of quasi-periodic oscillations (QPOs) observed from the soft-gamma repeaters, we find that each of the observed low-frequency QPOs can be identified either as a torsional oscillation in the bubble phase or as a usual crustal oscillation, given generally accepted values of L for all the stellar models are considered here.

  10. Outer Disk Star Formation in HI selected Galaxies

    NASA Astrophysics Data System (ADS)

    Meurer, G. R.

    2017-03-01

    The HI in galaxies often extends past their conventionally defined optical extent. I report results from our team which has been probing low intensity star formation in outer disks using imaging in Hα and ultraviolet. Using a sample of hundreds of HI selected galaxies, we confirm that outer disk HII regions and extended UV disks are common. Hence outer disks are not dormant but are dimly forming stars. Although the ultraviolet light in galaxies is more centrally concentrated than the HI, the UV/HI ratio (the Star Formation Efficiency) is nearly constant, with a slight dependency on surface brightness. This result is well accounted for in a model where disks maintain a constant stability parameter Q. This model also accounts for how the ISM and star formation are distributed in the bright parts of galaxies, and how HI appears to trace the distribution of dark matter in galaxy outskirts.

  11. Infrared Spectroscopy of Star Formation in Galactic and Extragalactic Regions

    NASA Technical Reports Server (NTRS)

    Smith, Howard A.; Hasan, Hashima (Technical Monitor)

    2002-01-01

    This report details work done in a project involving spectroscopic studies, including data analysis and modeling, of star-formation regions using an ensemble of archival space-based data including some from the Infrared Space Observatory's Long Wavelength Spectrometer and Short Wavelength Spectrometer, and other spectroscopic databases. We will include four kinds of regions: (1) disks around more evolved objects; (2) young, low or high mass pre-main sequence stars in star-formation regions; (3) star formation in external, bright IR (infrared) galaxies; and (4) the galactic center. During this period, work proceeded fully on track and on time. Details on workshops and conferences attended and research results are presented. A preprint article entitled 'The Far Infrared Lines of OH as Molecular Cloud Diagnostics' is included as an appendix.

  12. Star formation and gas phase history of the cosmic web

    NASA Astrophysics Data System (ADS)

    Snedden, Ali; Coughlin, Jared; Phillips, Lara Arielle; Mathews, Grant; Suh, In-Saeng

    2016-01-01

    We present a new method of tracking and characterizing the environment in which galaxies and their associated circumgalactic medium evolve. We have developed a structure finding algorithm that uses the rate of change of the density gradient to self-consistently parse and follow the evolution of groups/clusters, filaments and voids in large-scale structure simulations. We use this to trace the complete evolution of the baryons in the gas phase and the star formation history within each structure in our simulated volume. We vary the structure measure threshold to probe the complex inner structure of star-forming regions in poor clusters, filaments and voids. We find that the majority of star formation occurs in cold, condensed gas in filaments at intermediate redshifts (z ˜ 3). We also show that much of the star formation above a redshift z = 3 occurs in low-contrast regions of filaments, but as the density contrast increases at lower redshift, star formation switches to the high-contrast regions, or inner parts, of filaments. Since filaments bridge the void and cluster regions, it suggests that the majority of star formation occurs in galaxies in intermediate density regions prior to the accretion on to groups/clusters. We find that both filaments and poor clusters are multiphase environments distinguishing themselves by different distributions of gas phases.

  13. High-redshift major mergers weakly enhance star formation

    NASA Astrophysics Data System (ADS)

    Fensch, J.; Renaud, F.; Bournaud, F.; Duc, P.-A.; Agertz, O.; Amram, P.; Combes, F.; Di Matteo, P.; Elmegreen, B.; Emsellem, E.; Jog, C. J.; Perret, V.; Struck, C.; Teyssier, R.

    2017-02-01

    Galaxy mergers are believed to trigger strong starbursts. This is well assessed by observations in the local Universe. However, the efficiency of this mechanism has poorly been tested so far for high-redshift, actively star-forming, galaxies. We present a suite of pc-resolution hydrodynamical numerical simulations to compare the star formation process along a merging sequence of high- and low-redshift galaxies, by varying the gas mass fraction between the two models. We show that, for the same orbit, high-redshift gas-rich mergers are less efficient than low-redshift ones at producing starbursts; the star formation rate excess induced by the merger and its duration are both around 10 times lower than in the low gas fraction case. The mechanisms that account for the star formation triggering at low redshift - the increased compressive turbulence, gas fragmentation, and central gas inflows - are only mildly, if not at all, enhanced for high gas fraction galaxy encounters. Furthermore, we show that the strong stellar feedback from the initially high star formation rate in high-redshift galaxies does not prevent an increase of the star formation during the merger. Our results are consistent with the observed increase of the number of major mergers with increasing redshift being faster than the respective increase in the number of starburst galaxies.

  14. ON THE STAR FORMATION LAW FOR SPIRAL AND IRREGULAR GALAXIES

    SciTech Connect

    Elmegreen, Bruce G.

    2015-12-01

    A dynamical model for star formation on a galactic scale is proposed in which the interstellar medium is constantly condensing to star-forming clouds on the dynamical time of the average midplane density, and the clouds are constantly being disrupted on the dynamical timescale appropriate for their higher density. In this model, the areal star formation rate scales with the 1.5 power of the total gas column density throughout the main regions of spiral galaxies, and with a steeper power, 2, in the far outer regions and in dwarf irregular galaxies because of the flaring disks. At the same time, there is a molecular star formation law that is linear in the main and outer parts of disks and in dIrrs because the duration of individual structures in the molecular phase is also the dynamical timescale, canceling the additional 0.5 power of surface density. The total gas consumption time scales directly with the midplane dynamical time, quenching star formation in the inner regions if there is no accretion, and sustaining star formation for ∼100 Gyr or more in the outer regions with no qualitative change in gas stability or molecular cloud properties. The ULIRG track follows from high densities in galaxy collisions.

  15. Panchromatic Hubble Andromeda Treasury. XVI. Star Cluster Formation Efficiency and the Clustered Fraction of Young Stars

    NASA Astrophysics Data System (ADS)

    Johnson, L. Clifton; Seth, Anil C.; Dalcanton, Julianne J.; Beerman, Lori C.; Fouesneau, Morgan; Lewis, Alexia R.; Weisz, Daniel R.; Williams, Benjamin F.; Bell, Eric F.; Dolphin, Andrew E.; Larsen, Søren S.; Sandstrom, Karin; Skillman, Evan D.

    2016-08-01

    We use the Panchromatic Hubble Andromeda Treasury survey data set to perform spatially resolved measurements of star cluster formation efficiency (Γ), the fraction of stellar mass formed in long-lived star clusters. We use robust star formation history and cluster parameter constraints, obtained through color-magnitude diagram analysis of resolved stellar populations, to study Andromeda’s cluster and field populations over the last ˜300 Myr. We measure Γ of 4%-8% for young, 10-100 Myr-old populations in M31. We find that cluster formation efficiency varies systematically across the M31 disk, consistent with variations in mid-plane pressure. These Γ measurements expand the range of well-studied galactic environments, providing precise constraints in an H i-dominated, low-intensity star formation environment. Spatially resolved results from M31 are broadly consistent with previous trends observed on galaxy-integrated scales, where Γ increases with increasing star formation rate surface density (ΣSFR). However, we can explain observed scatter in the relation and attain better agreement between observations and theoretical models if we account for environmental variations in gas depletion time (τ dep) when modeling Γ, accounting for the qualitative shift in star formation behavior when transitioning from a H2-dominated to a H i-dominated interstellar medium. We also demonstrate that Γ measurements in high ΣSFR starburst systems are well-explained by τ dep-dependent fiducial Γ models.

  16. Bimodal star formation - Constraints from galaxy colors at high redshift

    NASA Technical Reports Server (NTRS)

    Wyse, Rosemary F. G.; Silk, Joseph

    1987-01-01

    The possibility that at early epochs the light from elliptical galaxies is dominated by stars with an initial mass function (IMF) which is deficient in low-mass stars, relative to the solar neighborhood is investigated. V-R colors for the optical counterparts of 3CR radio sources offer the most severe constraints on the models. Reasonable fits are obtained to both the blue, high-redshift colors and the redder, low-redshift colors with a model galaxy which forms with initially equal star formation rates in each of two IMF modes: one lacking low-mass stars, and one with stars of all masses. The net effect is that the time-integrated IMF has twice as many high-mass stars as the solar neighborhood IMF, relative to low mass stars. A conventional solar neighborhood IMF does not simultaneously account for both the range in colors at high redshift and the redness of nearby ellipticals, with any single star formation epoch. Models with a standard IMF require half the stellar population to be formed in a burst at low redshift z of about 1.

  17. Delayed star formation in isolated dwarf galaxies: Hubble space telescope star formation history of the Aquarius dwarf irregular

    SciTech Connect

    Cole, Andrew A.; Weisz, Daniel R.; Dolphin, Andrew E.; Skillman, Evan D.; McConnachie, Alan W.; Brooks, Alyson M.; Leaman, Ryan E-mail: drw@ucsc.edu E-mail: skillman@astro.umn.edu E-mail: abrooks@physics.rutgers.edu

    2014-11-01

    We have obtained deep images of the highly isolated (d = 1 Mpc) Aquarius dwarf irregular galaxy (DDO 210) with the Hubble Space Telescope Advanced Camera for Surveys. The resulting color-magnitude diagram (CMD) reaches more than a magnitude below the oldest main-sequence turnoff, allowing us to derive the star formation history (SFH) over the entire lifetime of the galaxy with a timing precision of ≈10% of the lookback time. Using a maximum likelihood fit to the CMD we find that only ≈10% of all star formation in Aquarius took place more than 10 Gyr ago (lookback time equivalent to redshift z ≈ 2). The star formation rate increased dramatically ≈6-8 Gyr ago (z ≈ 0.7-1.1) and then declined until the present time. The only known galaxy with a more extreme confirmed delay in star formation is Leo A, a galaxy of similar M {sub H} {sub I}/M {sub *}, dynamical mass, mean metallicity, and degree of isolation. The delayed stellar mass growth in these galaxies does not track the mean dark matter accretion rate from CDM simulations. The similarities between Leo A and Aquarius suggest that if gas is not removed from dwarf galaxies by interactions or feedback, it can linger for several gigayears without cooling in sufficient quantity to form stars efficiently. We discuss possible causes for the delay in star formation including suppression by reionization and late-time mergers. We find reasonable agreement between our measured SFHs and select cosmological simulations of isolated dwarfs. Because star formation and merger processes are both stochastic in nature, delayed star formation in various degrees is predicted to be a characteristic (but not a universal) feature of isolated small galaxies.

  18. Molecular Clouds, Star Formation and Galactic Structure.

    ERIC Educational Resources Information Center

    Scoville, Nick; Young, Judith S.

    1984-01-01

    Radio observations show that the gigantic clouds of molecules where stars are born are distributed in various ways in spiral galaxies, perhaps accounting for the variation in their optical appearance. Research studies and findings in this area are reported and discussed. (JN)

  19. PROGRESSIVE STAR FORMATION IN THE YOUNG GALACTIC SUPER STAR CLUSTER NGC 3603

    SciTech Connect

    Beccari, Giacomo; Spezzi, Loredana; De Marchi, Guido; Andersen, Morten; Paresce, Francesco; Young, Erick; Panagia, Nino; Bond, Howard; Balick, Bruce; Calzetti, Daniela; Carollo, C. Marcella; Disney, Michael J.; Dopita, Michael A.; Frogel, Jay A.; Hall, Donald N. B.; Holtzman, Jon A.; Kimble, Randy A.; McCarthy, Patrick J.; O'Connell, Robert W.; Saha, Abhijit

    2010-09-10

    Early Release Science observations of the cluster NGC 3603 with the WFC3 on the refurbished Hubble Space Telescope allow us to study its recent star formation history. Our analysis focuses on stars with H{alpha} excess emission, a robust indicator of their pre-main sequence (PMS) accreting status. The comparison with theoretical PMS isochrones shows that 2/3 of the objects with H{alpha} excess emission have ages from 1 to 10 Myr, with a median value of 3 Myr, while a surprising 1/3 of them are older than 10 Myr. The study of the spatial distribution of these PMS stars allows us to confirm their cluster membership and to statistically separate them from field stars. This result establishes unambiguously for the first time that star formation in and around the cluster has been ongoing for at least 10-20 Myr, at an apparently increasing rate.

  20. Star formation at low rates - the impact of lacking massive stars on stellar feedback

    NASA Astrophysics Data System (ADS)

    Hensler, Gerhard; Steyrleithner, Patrick; Recchi, Simone

    2017-03-01

    Due to their low masses dwarf galaxies experience low star-formation rates resulting in stellar cluster masses insufficient to fill the initial mass function (IMF) to the uppermost mass. Numerical simulations usually do not account for the completeness of the IMF, but treat a filed IMF by numbers, masses, and stellar feedback by fractions. To ensure that only entire stars are formed, we consider an IMF filled from the lower-mass regime and truncated where at least one entire massive star is formed. By 3D simulations we investigate the effects of two possible IMFs on the evolution of dwarf galaxies: filled vs. truncated IMF. For the truncated IMF the star-formation self-regulation is suppressed, while the energy release by typeII supernovae is larger, both compared to the filled IMF. Moreover, the abundance ratios of particular elements yielded from massive and intermediate-mass stars differ significantly between the two IMF distributions.

  1. MASSIVE STARS IN THE LOCAL GROUP: Implications for Stellar Evolution and Star Formation

    NASA Astrophysics Data System (ADS)

    Massey, Philip

    The galaxies of the Local Group serve as important laboratories for understanding the physics of massive stars. Here I discuss what is involved in identifying various kinds of massive stars in nearby galaxies: the hydrogen-burning O-type stars and their evolved He-burning evolutionary descendants, the luminous blue variables, red supergiants, and Wolf-Rayet stars. Primarily I review what our knowledge of the massive star population in nearby galaxies has taught us about stellar evolution and star formation. I show that the current generation of stellar evolutionary models do well at matching some of the observed features and provide a look at the sort of new observational data that will provide a benchmark against which new models can be evaluated.

  2. Emission-line stars in the Canis Major star-formation region

    NASA Astrophysics Data System (ADS)

    Wiramihardja, S. D.; Kogure, T.; Nakano, M.; Yoshida, S.

    Using the Schmidt telescope of the Kiso Observatory, H-alpha-emission stars have been surveyed in the Canis Major star-formation region and its adjacent reference area. In the area of about 58 square degrees a total of 179 H-alpha-emission stars have been found in the magnitude range between V = 6 and 15 with a majority in the V = 11-14 range. Based on the color properties and on the location relative to the CMa R1 association, the stars are provisionally classified into two main groups of early-type H-alpha-emission stars and of T Tauri candidates. It is found that the early-type H-alpha-emission stars are distributed rather uniformly over the survey area in contrast to the group of T Tauri candidates which show good coincidence with the CMa R1 association in the surface distribution.

  3. EXTENDED SCHMIDT LAW: ROLE OF EXISTING STARS IN CURRENT STAR FORMATION

    SciTech Connect

    Shi Yong; Helou, George; Yan Lin; Armus, Lee; Wu Yanling; Stierwalt, Sabrina; Papovich, Casey

    2011-06-01

    We propose an 'extended Schmidt law' with explicit dependence of the star formation efficiency (SFE = SFR/M{sub gas}) on the stellar mass surface density ({Sigma}{sub star}). This relation has a power-law index of 0.48 {+-} 0.04 and a 1{sigma} observed scatter on the SFE of 0.4 dex, which holds over five orders of magnitude in the stellar density for individual global galaxies, including various types and especially the low-surface-brightness (LSB) galaxies that deviate significantly from the Kennicutt-Schmidt (KS) law. When applying it to regions of a sample of 12 spiral galaxies at sub-kiloparsec resolution, the extended Schmidt law not only holds for LSB regions but also shows significantly smaller scatters both within and across galaxies compared with the KS law. We argue that this new relation points to the role of existing stars in regulating the SFE, thus better encoding 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 reproduce the observed main sequence of star-forming galaxies (a relation between the SFR and stellar mass) from z = 0 up to z = 2.

  4. Nuclear Spectroscopic Telescope Array (NuSTAR) Mission

    NASA Astrophysics Data System (ADS)

    Kim, Yunjin; Willis, J.; Dodd, S.; Harrison, F.; Forster, K.; Craig, W.; Bester, M.; Oberg, D.

    The Nuclear Spectroscopic Telescope Array (NuSTAR) is a National Aeronautics and Space Administration (NASA) Small Explorer mission that carried the first focusing hard X-ray (6-79 keV) telescope into orbit. It was launched on a Pegasus rocket into a low-inclination Earth orbit on June 13, 2012, from Reagan Test Site, Kwajalein Atoll. NuSTAR will carry out a two-year primary science mission. The NuSTAR observatory is composed of the X-ray instrument and the spacecraft. The NuSTAR spacecraft is three-axis stabilized with a single articulating solar array based on Orbital Sciences Corporation's LEOStar-2 design. The NuSTAR science instrument consists of two co-aligned grazing incidence optics focusing on to two shielded solid state CdZnTe pixel detectors. The instrument was launched in a compact, stowed configuration, and after launch, a 10-meter mast was deployed to achieve a focal length of 10.15 m. The NuSTAR instrument provides sub-arcminute imaging with excellent spectral resolution over a 12-arcminute field of view. The NuSTAR observatory will be operated out of the Mission Operations Center (MOC) at UC Berkeley. Most science targets will be viewed for a week or more. The science data will be transferred from the UC Berkeley MOC to a Science Operations Center (SOC) located at the California Institute of Technology (Caltech). In this paper, we will describe the mission architecture, the technical challenges during the development phase, and the post-launch activities.

  5. Nuclear Spectroscopic Telescope Array (NuSTAR) Mission

    NASA Technical Reports Server (NTRS)

    Kim, Yunjin; Willis, Jason; Dodd, Suzanne; Harrison, Fiona; Forster, Karl; Craig, William; Bester, Manfred; Oberg, David

    2013-01-01

    The Nuclear Spectroscopic Telescope Array (NuSTAR) is a National Aeronautics and Space Administration (NASA) Small Explorer mission that carried the first focusing hard X-ray (6-79 keV) telescope into orbit. It was launched on a Pegasus rocket into a low-inclination Earth orbit on June 13, 2012, from Reagan Test Site, Kwajalein Atoll. NuSTAR will carry out a two-year primary science mission. The NuSTAR observatory is composed of the X-ray instrument and the spacecraft. The NuSTAR spacecraft is three-axis stabilized with a single articulating solar array based on Orbital Sciences Corporation's LEOStar-2 design. The NuSTAR science instrument consists of two co-aligned grazing incidence optics focusing on to two shielded solid state CdZnTe pixel detectors. The instrument was launched in a compact, stowed configuration, and after launch, a 10-meter mast was deployed to achieve a focal length of 10.15 m. The NuSTAR instrument provides sub-arcminute imaging with excellent spectral resolution over a 12-arcminute field of view. The NuSTAR observatory will be operated out of the Mission Operations Center (MOC) at UC Berkeley. Most science targets will be viewed for a week or more. The science data will be transferred from the UC Berkeley MOC to a Science Operations Center (SOC) located at the California Institute of Technology (Caltech). In this paper, we will describe the mission architecture, the technical challenges during the development phase, and the post-launch activities.

  6. Low-metallicity Star Formation (IAU S255)

    NASA Astrophysics Data System (ADS)

    Hunt, Leslie K.; Madden, Suzanne C.; Schneider, Raffaella

    2009-01-01

    Preface; SOC and LOC; Participants; Life at the conference; Conference photo; Session I. Population III and Metal-Free Star Formation: 1. Open questions in the study of population III star formation S. C. O. Glover, P. C. Clark, T. H. Greif, J. L. Johnson, V. Bromm, R. S. Klessen and A. Stacy; 2. Protostar formation in the early universe Naoki Yoshida; 3. Population III.1 stars: formation, feedback and evolution of the IMF Jonathan C. Tan; 4. The formation of the first galaxies and the transition to low-mass star formation T. H. Greif, D. R. G. Schleicher, J. L. Johnson, A.-K. Jappsen, R. S. Klessen, P. C. Clark, S. C. O. Glover, A. Stacy and V. Bromm; 5. Low-metallicity star formation: the characteristic mass and upper mass limit Kazuyuki Omukai; 6. Dark stars: dark matter in the first stars leads to a new phase of stellar evolution Katherine Freese, Douglas Spolyar, Anthony Aguirre, Peter Bodenheimer, Paolo Gondolo, J. A. Sellwood and Naoki Yoshida; 7. Effects of dark matter annihilation on the first stars F. Iocco, A. Bressan, E. Ripamonti, R. Schneider, A. Ferrara and P. Marigo; 8. Searching for Pop III stars and galaxies at high redshift Daniel Schaerer; 9. The search for population III stars Sperello di Serego Alighieri, Jaron Kurk, Benedetta Ciardi, Andrea Cimatti, Emanuele Daddi and Andrea Ferrara; 10. Observational search for population III stars in high-redshift galaxies Tohru Nagao; Session II. Metal Enrichment, Chemical Evolution, and Feedback: 11. Cosmic metal enrichment Andrea Ferrara; 12. Insights into the origin of the galaxy mass-metallicity relation Henry Lee, Eric F. Bell and Rachel S. Somerville; 13. LSD and AMAZE: the mass-metallicity relation at z > 3 F. Mannucci and R. Maiolino; 14. Three modes of metal-enriched star formation at high redshift Britton D. Smith, Matthew J. Turk, Steinn Sigurdsson, Brian W. O'Shea and Michael L. Norman; 15. Primordial supernovae and the assembly of the first galaxies Daniel Whalen, Bob Van Veelen, Brian W. O

  7. Small-scale star formation at low metallicity

    NASA Technical Reports Server (NTRS)

    Mccall, Marshall L.; Hill, Robert; English, Jayanne

    1990-01-01

    Massive star formation in a low metallicity environment is investigated by studying the morphology of small HII regions in the Small Magellanic Cloud. A classification scheme based upon the symmetry of form in the light of H-alpha is proposed to make possible an examination of the properties of blister candidates with respect to nebulas embedded in a more uniform medium. A new diagnostic of size is developed to derive quantitative information about the ionized gas and ionizing stars. The asymmetrical surface-brightness distribution of many HII regions demonstrates that massive stars often form at the edge of dense neutral clouds. However, the existence of many symmetrical nebulas with similar sizes, luminosities, and surface brightnesses shows that massive star formation often occurs within these clouds. Nevertheless, the statistics of the two different forms indicate that the rate of massive star formation declines less steeply with radius across host clouds than in the Milky Way, suggesting that external triggering may play a larger role in initiating star formation.

  8. NGC 1097:Constraining mechanisms for star formation with the VLA

    NASA Astrophysics Data System (ADS)

    Wood, Sarah; Sheth, Kartik; Balser, Dana S.; Yarber, Aara'L.

    2015-01-01

    The project goal is to trace the precise location of star forming regions in the barred spiral NGC 1097. Specifically we want to better understand how the star formation progresses in the bar and at the bar ends. Our hydrodynamic gas flow model indicates gas flow should never cross dust lanes yet previous azimuthal cross-correlation analysis have indicated that the Hα emission is offset on the leading side of the bar dust lanes. It is critical to verify the precise locations of the stars forming regions. Is the star formation initiated in the dust lanes, or perhaps in dust spurs on the trailing side of the galaxy? We will measure synchrotron and thermal radiation contributions to quantify recent activity and compare to existing Hα, GALEX, archival VLA, and new ALMA Cycle 0 and Cycle 1 observations. This project will help catalog current and past star formation activity in the bar of NGC 1097 and thus help constrain the mechanisms for star formation.

  9. Autonomous formation flying sensor for the Star Light Mission

    NASA Technical Reports Server (NTRS)

    Aung, M.; Purcell, G.; Tien, J.; Young, L.; Srinivasan, J.; Ciminera, M. A.; Chong, Y. J.; Amaro, L. R.; Young, L. E.

    2002-01-01

    The StarLight Mission, an element of NASA's Origins Program, was designed for first-time demonstration of two technologies: formation flying optical interferometry between spacecraft and autonomous precise formation flying of an array of spacecraft to support optical interferometry. The design overview and results of the technology effort are presented in this paper.

  10. On the rotation of nuclear star clusters formed by cluster inspirals

    NASA Astrophysics Data System (ADS)

    Tsatsi, Athanasia; Mastrobuono-Battisti, Alessandra; van de Ven, Glenn; Perets, Hagai B.; Bianchini, Paolo; Neumayer, Nadine

    2017-01-01

    Nuclear star clusters (NSCs) are commonly observed in the centres of most galactic nuclei, including our own Milky Way (MW). While their study can reveal important information about the build-up of the innermost regions of galaxies, the physical processes that regulate their formation are still poorly understood. NSCs might have been formed through gas infall and subsequent in situ star formation, and/or through the infall and merging of multiple star clusters into the centre of the galaxy. Here, we investigate the viability of the latter, by studying direct N-body simulations of inspiralling clusters to the centre of an MW-like nuclear bulge that hosts a massive black hole. We find that the NSC formed through this process can show both morphological and kinematical properties that make it comparable with observations of the MW NSC, including significant rotation - a fact that has so far been attributed mainly to gas infall. We explore its kinematic evolution to see if and how the merger history can imprint fossil records on its dynamical structure. Moreover, we study the effect of stellar foreground contamination in the line-of-sight kinematics of the NSC. Our study shows that no fine tuning of the orientation of the infalling globular clusters is necessary to result in a rotating NSC. We suggest that cluster inspiral is a viable mechanism for the formation of rotating NSCs.

  11. Anatomy of a Spiral Arm: Gas, Dust and Star Formation

    NASA Astrophysics Data System (ADS)

    Schinnerer, Eva; Meidt, Sharon; Pety, Jerome; Leroy, Adam; Hughes, Annie; Colombo, Dario

    2015-08-01

    Spiral arms can be easily depicted in disk galaxies from the numerous young stars associated with them. However, it is on a fundamental level not clear where, how and when star formation starts relative to the spiral arm. We address these questions by utilizing high 1-3'' resolution observation of the total and dense molecular gas in a spiral arm segment of the nearby grand-design spiral galaxy M51 from PAWS (PdBI Arcsecond Whirlpool Survey) in combination with observations of young stars, HII regions and dust emission. We build a complete picture of the onset, progression and impact of star formation for this segment and discuss this picture in light of theoretical expectations.

  12. Scaling Relations of Galactic Winds with Star Formation Rate

    NASA Astrophysics Data System (ADS)

    Tanner, Ryan; Cecil, Gerald; Heitsch, Fabian

    2017-01-01

    The galactic scale outflows generated by nuclear starbursts consist of a multiphase medium where each phase has a distinct velocity depending on the characteristics of the starburst. Using synthetic absorption lines generated from 3D hydrodynamical simulations we probe the outflow velocity of the hot, warm, and neutral gas entrained in a galactic wind. By varying the star formation rate (SFR) in our simulations, we find no correlation between the outflow velocity of the hot gas with the SFR, but we do find a correlation between the outflow velocity of both warm and neutral gas with the SFR. The scaling relation between outflow velocity and SFR only holds for low SFR until the scaling relation abruptly flattens at a SFR determined by the mass loading of the starburst. The outflow velocity of the hot gas only depends on the mass loading of the starburst and not the SFR. For low SFRs the difference between the velocity of cold gas, as measured by absorption lines of neutral or low ionized gas, may be 5-7 times lower than the velocity of the hot, highly ionized gas. The difference in velocity between the cold and hot gas for higher SFRs depends on the mass loading factor of the starburst. Thus the measured velocities of neutral or low ionized gas cannot be used to estimate the outflow velocity of the hot gas without determining the mass loading of the starburst.

  13. The critical density for star formation in HII galaxies

    NASA Astrophysics Data System (ADS)

    Taylor, Christopher L.; Brinks, Elias; Skillman, Evan D.

    1993-01-01

    The star formation rate (SFR) in galaxies is believed to obey a power law relation with local gas density, first proposed by Schmidt (1959). Kennicutt (1989) has shown that there is a threshold density above which star formation occurs, and for densities at or near the threshold density, the DFR is highly non-linear, leading to bursts of star formation. Skillman (1987) empirically determined this threshold for dwarf galaxies to be approximately 1 x 10(exp 21) cm(exp -2), at a linear resolution of 500pc. During the course of our survey for HI companion clouds to HII galaxies, we obtained high resolution HI observations of five nearby HII galaxies. HII galaxies are low surface brightness, rich in HI, and contain one or a few high surface brightness knots whose optical spectra resemble those of HII regions. These knots are currently experiencing a burst of star formation. After Kennicutt (1989) we determine the critical density for star formation in the galaxies, and compare the predictions with radio and optical data.

  14. The role of turbulence in star formation laws and thresholds

    SciTech Connect

    Kraljic, Katarina; Renaud, Florent; Bournaud, Frédéric; Combes, Françoise; Elmegreen, Bruce; Emsellem, Eric; Teyssier, Romain

    2014-04-01

    The Schmidt-Kennicutt relation links the surface densities of gas to the star formation rate in galaxies. The physical origin of this relation, and in particular its break, i.e., the transition between an inefficient regime at low gas surface densities and a main regime at higher densities, remains debated. Here, we study the physical origin of the star formation relations and breaks in several low-redshift galaxies, from dwarf irregulars to massive spirals. We use numerical simulations representative of the Milky Way and the Large and Small Magellanic Clouds with parsec up to subparsec resolution, and which reproduce the observed star formation relations and the relative variations of the star formation thresholds. We analyze the role of interstellar turbulence, gas cooling, and geometry in drawing these relations at 100 pc scale. We suggest in particular that the existence of a break in the Schmidt-Kennicutt relation could be linked to the transition from subsonic to supersonic turbulence and is independent of self-shielding effects. With this transition being connected to the gas thermal properties and thus to the metallicity, the break is shifted toward high surface densities in metal-poor galaxies, as observed in dwarf galaxies. Our results suggest that together with the collapse of clouds under self-gravity, turbulence (injected at galactic scale) can induce the compression of gas and regulate star formation.

  15. Unveiling the Role of Galactic Rotation on Star Formation

    NASA Astrophysics Data System (ADS)

    Utreras, José; Becerra, Fernando; Escala, Andrés

    2016-12-01

    We study the star formation process at galactic scales and the role of rotation through numerical simulations of spiral and starburst galaxies using the adaptive mesh refinement code Enzo. We focus on the study of three integrated star formation laws found in the literature: the Kennicutt-Schmidt (KS) and Silk-Elmegreen (SE) laws, and the dimensionally homogeneous equation proposed by Escala {{{Σ }}}{SFR}\\propto \\sqrt{G/L}{{{Σ }}}{gas}1.5. We show that using the last we take into account the effects of the integration along the line of sight and find a unique regime of star formation for both types of galaxies, suppressing the observed bi-modality of the KS law. We find that the efficiencies displayed by our simulations are anti-correlated with the angular velocity of the disk Ω for the three laws studied in this work. Finally, we show that the dimensionless efficiency of star formation is well represented by an exponentially decreasing function of -1.9{{Ω }}{t}{ff}{ini}, where {t}{ff}{ini} is the initial free-fall time. This leads to a unique galactic star formation relation which reduces the scatter of the bi-modal KS, SE, and Escala relations by 43%, 43%, and 35%, respectively.

  16. The Star Formation Properties of Void Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Moorman, Crystal; Vogeley, Michael S.

    2016-01-01

    We measure the star formation properties of two large samples of galaxies from the SDSS in large-scale cosmic voids on time scales of 10 Myr and 100 Myr, using Ha emission line strengths and GALEX FUV fluxes, respectively. The first sample consists of 109,818 optically selected galaxies. We find that void galaxies in this sample have higher specific star formation rates (SSFRs; star formation rates per unit stellar mass) than similar stellar mass galaxies in denser regions. The second sample is a subset of the optically selected sample containing 8070 galaxies with reliable S/N HI detections from ALFALFA. For the HI detected sample, SSFRs are similar regardless of large-scale environment. Investigating only the HI detected dwarf galaxies reveals a trend towards higher SSFRs in voids. Furthermore, we estimate the star formation rate per unit HI mass, known as the star formation efficiency (SFE) of a galaxy, as a function of environment. For the overall HI detected population, we notice no environmental dependence. Limiting the sample to dwarf galaxies again reveals a trend towards higher SFEs in voids. These results suggest that void environments provide a nurturing environment for dwarf galaxy evolution.

  17. The reliability of [C II] as an indicator of the star formation rate

    NASA Astrophysics Data System (ADS)

    De Looze, Ilse; Baes, Maarten; Bendo, George J.; Cortese, Luca; Fritz, Jacopo

    2011-10-01

    The [C II] 157.74 μm line is an important coolant for the neutral interstellar gas. Since [C II] is the brightest spectral line for most galaxies, it is a potentially powerful tracer of star formation activity. In this paper, we present a calibration of the star formation rate (SFR) as a function of the [C II] luminosity for a sample of 24 star-forming galaxies in the nearby Universe. This sample includes objects classified as H II regions or low-ionization nuclear emission-line regions, but omits all Seyfert galaxies with a significant contribution from the active galactic nucleus to the mid-infrared photometry. In order to calibrate the SFR against the line luminosity, we rely on both Galaxy Evolution Explorer far-ultraviolet data, which is an ideal tracer of the unobscured star formation, and MIPS 24 μm, to probe the dust-enshrouded fraction of star formation. In the case of normal star-forming galaxies, the [C II] luminosity correlates well with the SFR. However, the extension of this relation to more quiescent (Hα EW ≤ 10 Å) or ultraluminous galaxies should be handled with caution, since these objects show a non-linearity in the ?-to-LFIR ratio as a function of LFIR (and thus, their star formation activity). We provide two possible explanations for the origin of the tight correlation between the [C II] emission and the star formation activity on a global galaxy-scale. A first interpretation could be that the [C II] emission from photodissociation regions (PDRs) arises from the immediate surroundings of star-forming regions. Since PDRs are neutral regions of warm dense gas at the boundaries between H II regions and molecular clouds and they provide the bulk of [C II] emission in most galaxies, we believe that a more or less constant contribution from these outer layers of photon-dominated molecular clumps to the [C II] emission provides a straightforward explanation for this close link between the [C II] luminosity and SFR. Alternatively, we consider the

  18. The Star Formation History of the Lupus Dark Clouds

    NASA Astrophysics Data System (ADS)

    Grocholski, A. J.; Hughes, J. D.

    1999-05-01

    In light of recent HIPPARCOS observations we have revised the distance to the Lupus dark cloud complex upwards. This, along with the adoption of newer pre-main sequence mass tracks and isochrones have led to a new mass function and age distribution. We use calculated masses and ages to discuss the progression of star formation through the Lupus clouds, with particular reference to Lupus 3, which is forming intermediate (3-5Mo) stars and a multitude of very low mass stars (<0.3 Mo).

  19. Rosette: Understanding Star Formation in Molecular Cloud Complexes

    NASA Astrophysics Data System (ADS)

    Wang, Junfeng

    2010-09-01

    We propose Chandra imaging of three embedded clusters in the Rosette Molecular Cloud (RMC) complex. With complementary existing Spitzer and FLAMINGOS infrared surveys, the Chandra observation is critical for us to: (1) create a complete census of the young stars in the cloud; (2) study the spatial distribution of the young stars in different evolutionary stages within the RMC and the disk frequency in the embedded clusters; (3) construct X-ray Luminosity Function (XLF) and Initial Mass Function (IMF) for the clusters to examine XLF/IMF variations; (4) elucidate star formation history in this complex.

  20. Infrared observations of OB star formation in NGC 6334

    NASA Technical Reports Server (NTRS)

    Harvey, P. M.; Gatley, I.

    1982-01-01

    Infrared photometry and maps from 2 to 100 microns are presented for three of the principal far infrared sources in NGC 6334. Each region is powered by two or more very young stars. The distribution of dust and ionized gas is probably strongly affected by the presence of the embedded stars; one of the sources is a blister H II region, another has a bipolar structure, and the third exhibits asymmetric temperature structure. The presence of protostellar objects throughout the region suggests that star formation has occurred nearly simultaneously in the whole molecular cloud rather than having been triggered sequentially from within.

  1. 78 FR 4467 - UniStar Nuclear Energy, Combined License Application for Calvert Cliffs Power Plant, Unit 3...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-01-22

    ... COMMISSION UniStar Nuclear Energy, Combined License Application for Calvert Cliffs Power Plant, Unit 3, Exemption 1.0 Background UniStar Nuclear Energy (UNE), on behalf of Calvert Cliffs Nuclear Project, LLC and UniStar Nuclear Operating Services, LLC, submitted to the U.S. Nuclear Regulatory Commission (NRC)...

  2. Photoionising feedback and the star formation rates in galaxies

    NASA Astrophysics Data System (ADS)

    MacLachlan, J. M.; Bonnell, I. A.; Wood, K.; Dale, J. E.

    2015-01-01

    Aims: We investigate the effects of ionising photons on accretion and stellar mass growth in a young star forming region, using a Monte Carlo radiation transfer code coupled to a smoothed particle hydrodynamics (SPH) simulation. Methods: We introduce the framework with which we correct stellar cluster masses for the effects of photoionising (PI) feedback and compare to the results of a full ionisation hydrodynamics code. Results: We present results of our simulations of star formation in the spiral arm of a disk galaxy, including the effects of photoionising radiation from high mass stars. We find that PI feedback reduces the total mass accreted onto stellar clusters by ≈23% over the course of the simulation and reduces the number of high mass clusters, as well as the maximum mass attained by a stellar cluster. Mean star formation rates (SFRs) drop from SFRcontrol = 4.2 × 10-2 M⊙ yr-1 to SFRMCPI = 3.2 × 10-2 M⊙ yr-1 after the inclusion of PI feedback with a final instantaneous SFR reduction of 62%. The overall cluster mass distribution appears to be affected little by PI feedback. Conclusions: We compare our results to the observed extra-galactic Schmidt-Kennicutt relation and the observed properties of local star forming regions in the Milky Way and find that internal photoionising (PI) feedback is unlikely to reduce SFRs by more than a factor of ≈2 and thus may play only a minor role in regulating star formation.

  3. Formation and composition of planets around very low mass stars

    NASA Astrophysics Data System (ADS)

    Alibert, Y.; Benz, W.

    2017-01-01

    Context. The recent detection of planets around very low mass stars raises the question of the formation, composition, and potential habitability of these objects. Aims: We use planetary system formation models to infer the properties, in particular their radius distribution and water content, of planets that may form around stars ten times less massive than the Sun. Methods: Our planetary system formation and composition models take into account the structure and evolution of the protoplanetary disk, the planetary mass growth by accretion of solids and gas, as well as planet-planet, planet-star, and planet-disk interactions. Results: We show that planets can form at small orbital period in orbit about low-mass stars. We show that the radius of the planets is peaked at about 1 R⊕ and that they are, in general, volatile rich especially if proto-planetary disks orbiting this type of stars are long lived. Conclusions: Close-in planets orbiting low-mass stars similar in terms of mass and radius to those recently detected can be formed within the framework of the core-accretion paradigm as modeled here. The properties of protoplanetary disks, and their correlation with the stellar type, are key to understand their composition.

  4. Star Formation and AGN activity of X-ray selected AGN host galaxies in the Chandra-COSMOS Legacy Survey

    NASA Astrophysics Data System (ADS)

    Suh, Hyewon

    2017-01-01

    One of the ongoing issues for understanding the galaxy formation and evolution is how active galactic nuclei (AGNs) affect the growth of their host galaxies. We investigate the correlations between AGN activity and star formation properties of a large sample of ~3700 X-ray selected AGNs over a wide range of luminosities (42 < log Lx < 45) up to z~5 in the Chandra-COSMOS Legacy Survey. We perform a multi-component modeling from the far-infrared, when available, to the near-UV using AGN emission from the big-blue-bump (for Type 1 AGNs), a nuclear dust torus model, a galaxy model and a starburst component for the spectral energy distributions (SEDs). Through detailed analysis of SEDs, we derive AGN host galaxy properties, such as stellar masses, star formation rates (SFRs), and AGN luminosities. We find that AGN host galaxies have, on average, similar SFRs compared to the normal star-forming main sequence galaxies, suggesting no significant enhancement or quenching of star formation. The average SFR of AGN host galaxies shows a flat distribution in bins of AGN luminosity, consistent with recent ideas that the shorter variability timescale of AGN compared to star formation can lead to a flat relationship between the SFR and black hole accretion rates. Our results suggest that both star formation and nuclear activity in the majority of AGN host galaxies might be driven more by internal secular processes at z<3, implying that they have substantially grown at much earlier epoch.

  5. New View of Distant Galaxy Reveals Furious Star Formation

    NASA Astrophysics Data System (ADS)

    2007-12-01

    A furious rate of star formation discovered in a distant galaxy shows that galaxies in the early Universe developed either much faster or in a different way from what astronomers have thought. "This galaxy is forming stars at an incredible rate," said Wei-Hao Wang, an astronomer at the National Radio Astronomy Observatory (NRAO) in Socorro, New Mexico. The galaxy, Wang said, is forming the equivalent of 4,000 Suns a year. This is a thousand times more violent than our own Milky Way Galaxy. Location of Distant Galaxy Visible-light, left (from HST) and Infrared, right, (from Spitzer) Images: Circles indicate location of GOODS 850-5. CREDIT: Wang et al., STScI, Spitzer, NASA, NRAO/AUI/NSF Click on image for high-resolution file (1 MB) The galaxy, called GOODS 850-5, is 12 billion light-years from Earth, and thus is seen as it was only about 1.5 billion years after the Big Bang. Wang and his colleagues observed it using the Smithsonian Astrophysical Observatory's Submillimeter Array (SMA) on Mauna Kea in Hawaii. Young stars in the galaxy were enshrouded in dust that was heated by the stars and radiated infrared light strongly. Because of the galaxy's great distance from Earth, the infrared light waves have been stretched out to submillimeter-length radio waves, which are seen by the SMA. The waves were stretched or "redshifted," as astronomers say, by the ongoing expansion of the Universe. "This evidence for prolific star formation is hidden by the dust from visible-light telescopes," Wang explained. The dust, in turn, was formed from heavy elements that had to be built up in the cores of earlier stars. This indicates, Wang said, that significant numbers of stars already had formed, then spewed those heavy elements into interstellar space through supernova explosions and stellar winds. "Seeing the radiation from this heated dust revealed star formation we could have found in no other way," Wang said. Similar dusty galaxies in the early Universe may contain most of the

  6. THE COEVOLUTION OF NUCLEAR STAR CLUSTERS, MASSIVE BLACK HOLES, AND THEIR HOST GALAXIES

    SciTech Connect

    Antonini, Fabio; Barausse, Enrico; Silk, Joseph

    2015-10-10

    Studying how nuclear star clusters (NSCs) form and how they are related to the growth of the central massive black holes (MBHs) and their host galaxies is fundamental for our understanding of the evolution of galaxies and the processes that have shaped their central structures. We present the results of a semi-analytical galaxy formation model that follows the evolution of dark matter halos along merger trees, as well as that of the baryonic components. This model allows us to study the evolution of NSCs in a cosmological context, by taking into account the growth of NSCs due to both dynamical-friction-driven migration of stellar clusters and star formation triggered by infalling gas, while also accounting for dynamical heating from (binary) MBHs. We find that in situ star formation contributes a significant fraction (up to ∼80%) of the total mass of NSCs in our model. Both NSC growth through in situ star formation and that through star cluster migration are found to generate NSC—host galaxy scaling correlations that are shallower than the same correlations for MBHs. We explore the role of galaxy mergers on the evolution of NSCs and show that observational data on NSC—host galaxy scaling relations provide evidence of partial erosion of NSCs by MBH binaries in luminous galaxies. We show that this observational feature is reproduced by our models, and we make predictions about the NSC and MBH occupation fraction in galaxies. We conclude by discussing several implications for theories of NSC formation.

  7. THE DEPENDENCE OF STAR FORMATION EFFICIENCY ON GAS SURFACE DENSITY

    SciTech Connect

    Burkert, Andreas; Hartmann, Lee E-mail: lhartm@umich.edu

    2013-08-10

    Studies by Lada et al. and Heiderman et al. have suggested that star formation mostly occurs above a threshold in gas surface density {Sigma} of {Sigma}{sub c} {approx} 120 M{sub Sun} pc{sup -2} (A{sub K} {approx} 0.8). Heiderman et al. infer a threshold by combining low-mass star-forming regions, which show a steep increase in the star formation rate per unit area {Sigma}{sub SFR} with increasing {Sigma}, and massive cores forming luminous stars which show a linear relation. We argue that these observations do not require a particular density threshold. The steep dependence of {Sigma}{sub SFR}, approaching unity at protostellar core densities, is a natural result of the increasing importance of self-gravity at high densities along with the corresponding decrease in evolutionary timescales. The linear behavior of {Sigma}{sub SFR} versus {Sigma} in massive cores is consistent with probing dense gas in gravitational collapse, forming stars at a characteristic free-fall timescale given by the use of a particular molecular tracer. The low-mass and high-mass regions show different correlations between gas surface density and the area A spanned at that density, with A {approx} {Sigma}{sup -3} for low-mass regions and A {approx} {Sigma}{sup -1} for the massive cores; this difference, along with the use of differing techniques to measure gas surface density and star formation, suggests that connecting the low-mass regions with massive cores is problematic. We show that the approximately linear relationship between dense gas mass and stellar mass used by Lada et al. similarly does not demand a particular threshold for star formation and requires continuing formation of dense gas. Our results are consistent with molecular clouds forming by galactic hydrodynamic flows with subsequent gravitational collapse.

  8. Modeling jet and outflow feedback during star cluster formation

    SciTech Connect

    Federrath, Christoph; Schrön, Martin; Banerjee, Robi; Klessen, Ralf S.

    2014-08-01

    Powerful jets and outflows are launched from the protostellar disks around newborn stars. These outflows carry enough mass and momentum to transform the structure of their parent molecular cloud and to potentially control star formation itself. Despite their importance, we have not been able to fully quantify the impact of jets and outflows during the formation of a star cluster. The main problem lies in limited computing power. We would have to resolve the magnetic jet-launching mechanism close to the protostar and at the same time follow the evolution of a parsec-size cloud for a million years. Current computer power and codes fall orders of magnitude short of achieving this. In order to overcome this problem, we implement a subgrid-scale (SGS) model for launching jets and outflows, which demonstrably converges and reproduces the mass, linear and angular momentum transfer, and the speed of real jets, with ∼1000 times lower resolution than would be required without the SGS model. We apply the new SGS model to turbulent, magnetized star cluster formation and show that jets and outflows (1) eject about one-fourth of their parent molecular clump in high-speed jets, quickly reaching distances of more than a parsec, (2) reduce the star formation rate by about a factor of two, and (3) lead to the formation of ∼1.5 times as many stars compared to the no-outflow case. Most importantly, we find that jets and outflows reduce the average star mass by a factor of ∼ three and may thus be essential for understanding the characteristic mass of the stellar initial mass function.

  9. Low-Metallicity Star Formation: From the First Stars to Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Hunt, Leslie K.; Madden, Suzanne C.; Schneider, Raffaella

    2008-12-01

    Preface; SOC and LOC; Participants; Life at the conference; Conference photo; Session I. Population III and Metal-Free Star Formation: 1. Open questions in the study of population III star formation S. C. O. Glover, P. C. Clark, T. H. Greif, J. L. Johnson, V. Bromm, R. S. Klessen and A. Stacy; 2. Protostar formation in the early universe Naoki Yoshida; 3. Population III.1 stars: formation, feedback and evolution of the IMF Jonathan C. Tan; 4. The formation of the first galaxies and the transition to low-mass star formation T. H. Greif, D. R. G. Schleicher, J. L. Johnson, A.-K. Jappsen, R. S. Klessen, P. C. Clark, S. C. O. Glover, A. Stacy and V. Bromm; 5. Low-metallicity star formation: the characteristic mass and upper mass limit Kazuyuki Omukai; 6. Dark stars: dark matter in the first stars leads to a new phase of stellar evolution Katherine Freese, Douglas Spolyar, Anthony Aguirre, Peter Bodenheimer, Paolo Gondolo, J. A. Sellwood and Naoki Yoshida; 7. Effects of dark matter annihilation on the first stars F. Iocco, A. Bressan, E. Ripamonti, R. Schneider, A. Ferrara and P. Marigo; 8. Searching for Pop III stars and galaxies at high redshift Daniel Schaerer; 9. The search for population III stars Sperello di Serego Alighieri, Jaron Kurk, Benedetta Ciardi, Andrea Cimatti, Emanuele Daddi and Andrea Ferrara; 10. Observational search for population III stars in high-redshift galaxies Tohru Nagao; Session II. Metal Enrichment, Chemical Evolution, and Feedback: 11. Cosmic metal enrichment Andrea Ferrara; 12. Insights into the origin of the galaxy mass-metallicity relation Henry Lee, Eric F. Bell and Rachel S. Somerville; 13. LSD and AMAZE: the mass-metallicity relation at z > 3 F. Mannucci and R. Maiolino; 14. Three modes of metal-enriched star formation at high redshift Britton D. Smith, Matthew J. Turk, Steinn Sigurdsson, Brian W. O'Shea and Michael L. Norman; 15. Primordial supernovae and the assembly of the first galaxies Daniel Whalen, Bob Van Veelen, Brian W. O

  10. Star Formation at Low Metallicity in Local Dwarf Irregular Galaxies

    NASA Astrophysics Data System (ADS)

    Elmegreen, Bruce; Hunter, Deidre Ann; Rubio, Monica; Brinks, Elias; Cortés, Juan R.; Cigan, Phil

    2016-01-01

    The radial profiles of star formation rates and surface mass densities for gas and stars have been compiled for 20 local dwarf irregular galaxies and converted into disk scale heights and Toomre Q values. The scale heights are relatively large compared to the galaxy sizes (~0.6 times the local radii) and generally increase with radius in a flare. The gaseous Q values are high, ~4, at most radii and even higher for the stars. Star formation proceeds even with these high Q values in a normal exponential disk as viewed in the far ultraviolet. Such normal star formation suggests that Q is not relevant to star formation in dIrrs. The star formation rate per unit area always equals approximately the gas surface density divided by the midplane free fall time with an efficiency factor of about 1% that decreases systematically with radius in approximate proportion to the gas surface density. We view this efficiency variation as a result of a changing molecular fraction in a disk where atomic gas dominates both stars and molecules. In a related study, CO observations with ALMA of star-forming regions at the low metallicities of these dwarfs, which averages 13% solar, shows, in the case of the WLM galaxy, tiny CO clouds inside much larger molecular and atomic hydrogen envelopes. The CO cloud mass fraction within the molecular region is only one percent or so. Nevertheless, the CO clouds have properties that are similar to solar neighborhood clouds: they satisfy the size-linewidth relation observed in the LMC, SMC, and other local dwarfs where CO has been observed, and the same virial mass versus luminosity relation. This uniforming of CO cloud properties seems to be the result of a confining pressure from the weight of the overlying molecular and atomic shielding layers. Star formation at low metallicity therefore appears to be a three dimensional process independent of 2D instabilities involving Q, in highly atomic gas with relatively small CO cores, activated at a rate

  11. AGB and RGB stars as tracers of the early and intermediate star-formation history.

    NASA Astrophysics Data System (ADS)

    Aparicio, A.; Gallart, C.

    The Milky Way and Andromeda galaxies are the largest members of the Local Group, and their evolution is affected by the evolution of their host as a whole. At the same time, they themselves play an important role in the evolution of the Local Group. Considerable information can be obtained for the Local Group, but little is known about the distances and the full star-formation history of its galaxies. RGB and AGB stars are the keys to trace the full star-formation history of nearby galaxies. These stars are usually the most prominent population of dwarf spheroidal galaxies, but it has been shown (Gallart et al. 1994; Aparicio & Gallart 1994) that they are also observable in dwarf irregular galaxies. This will open the door to the study of the earliest star-formation processes taking place in these galaxies. The star-formation history of the Local Group galaxies is a crucial piece of information for answering basic questions about the evolutionary history of the group.

  12. Star Formation Studies with SOFIA and its Synergy with TMT

    NASA Astrophysics Data System (ADS)

    De Buizer, James

    2014-07-01

    The Stratospheric Observatory For Infrared Astronomy (SOFIA) is a modified Boeing 747 aircraft equipped with a 2.5m telescope that performs observations at high altitude from the optical to the sub-mm. The observatory just reached full operational capability in April of this year. Given that it is slated for a 20-year mission lifetime, SOFIA will overlap TMT by more than a decade. I will discuss the contrasting and complementary features of SOFIA and TMT in the context of star formation, discuss some of the early results from SOFIA in this field, and finish with a discussion of how TMT data can enhance and extended our understanding of star formation processes.[This talk could also be generalized to discuss more about synergies between SOFIA and TMT in a broader context (not just star formation), should the organizers prefer that.

  13. Star Formation in Undergraduate ALFALFA Team Galaxy Groups and Clusters

    NASA Astrophysics Data System (ADS)

    Koopmann, Rebecca A.; Durbala, Adriana; Finn, Rose; Haynes, Martha P.; Coble, Kimberly A.; Craig, David W.; Hoffman, G. Lyle; Miller, Brendan P.; Crone-Odekon, Mary; O'Donoghue, Aileen A.; Troischt, Parker; Undergraduate ALFALFA Team; ALFALFA Team

    2017-01-01

    The Undergraduate ALFALFA Team (UAT) Groups project is a coordinated study of gas and star formation properties of galaxies in and around 36 nearby (z<0.03) groups and clusters of varied richness, morphological type mix, and X-ray luminosity. By studying a large range of environments and considering the spatial distributions of star formation, we probe mechanisms of gas depletion and morphological transformation. The project uses ALFALFA HI observations, optical observations, and digital databases like SDSS, and incorporates work undertaken by faculty and students at different institutions within the UAT. Here we present results from our wide area Hα and broadband R imaging project carried out with the WIYN 0.9m+MOSAIC/HDI at KPNO, including an analysis of radial star formation rates and extents of galaxies in the NGC 5846, Abell 779, NRGb331, and HCG 69 groups/clusters. This work has been supported by NSF grant AST-1211005 and AST-1637339.

  14. Star formation in the M17 SW giant molecular cloud

    NASA Technical Reports Server (NTRS)

    Jaffe, D. T.; Fazio, G. G.

    1982-01-01

    The first high-sensitivity, high-resolution far-IR survey of an entire molecular cloud complex is presented. The 20 km/s M17 SW complex, in addition to the three luminous M17 sources, contains 10 sources spread over 110 pc. The 10 lower luminosity sources divide into two groups: small blister sources powered by late O stars and compact sources powered by clusters of early B stars. No compact far-IR sources with luminosities between the detection limit and 10,000 solar luminosities were detected. Three possible formation mechanisms for the stars that power the far-IR sources in the M17 SW complex are examined. Sequential formation cannot explain the sources seen throughout the complex. Some type of stochastic formation mechanism or collapse induced by a spiral density wave could explain the observations.

  15. Connecting Galaxies, Halos, and Star Formation Rates Across Cosmic Time

    SciTech Connect

    Conroy, Charlie; Wechsler, Risa H.

    2008-06-02

    A simple, observationally-motivated model is presented for understanding how halo masses, galaxy stellar masses, and star formation rates are related, and how these relations evolve with time. The relation between halo mass and galaxy stellar mass is determined by matching the observed spatial abundance of galaxies to the expected spatial abundance of halos at multiple epochs--i.e. more massive galaxies are assigned to more massive halos at each epoch. This 'abundance matching' technique has been shown previously to reproduce the observed luminosity- and scale-dependence of galaxy clustering over a range of epochs. Halos at different epochs are connected by halo mass accretion histories estimated from N-body simulations. The halo-galaxy connection at fixed epochs in conjunction with the connection between halos across time provides a connection between observed galaxies across time. With approximations for the impact of merging and accretion on the growth of galaxies, one can then directly infer the star formation histories of galaxies as a function of stellar and halo mass. This model is tuned to match both the observed evolution of the stellar mass function and the normalization of the observed star formation rate--stellar mass relation to z {approx} 1. The data demands, for example, that the star formation rate density is dominated by galaxies with M{sub star} {approx} 10{sup 10.0-10.5} M{sub {circle_dot}} from 0 < z < 1, and that such galaxies over these epochs reside in halos with M{sub vir} {approx} 10{sup 11.5-12.5} M{sub {circle_dot}}. The star formation rate--halo mass relation is approximately Gaussian over the range 0 < z < 1 with a mildly evolving mean and normalization. This model is then used to shed light on a number of issues, including (1) a clarification of 'downsizing', (2) the lack of a sharp characteristic halo mass at which star formation is truncated, and (3) the dominance of star formation over merging to the stellar build-up of galaxies

  16. Polycyclic Aromatic Hydrocarbons as Star Formation Rate Indicators

    NASA Astrophysics Data System (ADS)

    Calzetti, D.

    2011-03-01

    As images and spectra from ISO and Spitzer have provided increasingly higher-fidelity representations of the mid-infrared (MIR) and Polycyclic Aromatic Hydrocarbon (PAH) emission from galaxies and galactic and extra-galactic regions, more systematic efforts have been devoted to establishing whether the emission in this wavelength region can be used as a reliable star formation rate indicator. This has also been in response to the extensive surveys of distant galaxies that have accumulated during the cold phase of the Spitzer Space Telescope. Results so far have been somewhat contradictory, reflecting the complex nature of the PAHs and of the mid-infrared-emitting dust in general. The two main problems faced when attempting to define a star formation rate indicator based on the mid-infrared emission from galaxies and star-forming regions are: (1) the strong dependence of the PAH emission on metallicity; (2) the heating of the PAH dust by evolved stellar populations unrelated to the current star formation. I review the status of the field, with a specific focus on these two problems, and will try to quantify the impact of each on calibrations of the mid-infrared emission as a star formation rate indicator.

  17. Signatures of Star Cluster Formation by Cold Collapse

    NASA Astrophysics Data System (ADS)

    Kuznetsova, Aleksandra; Hartmann, Lee; Ballesteros-Paredes, Javier

    2015-12-01

    Subvirial gravitational collapse is one mechanism by which star clusters may form. Here we investigate whether this mechanism can be inferred from observations of young clusters. To address this question, we have computed smoothed particle hydrodynamics simulations of the initial formation and evolution of a dynamically young star cluster through cold (subvirial) collapse, starting with an ellipsoidal, turbulently seeded distribution of gas, and forming sink particles representing (proto)stars. While the initial density distributions of the clouds do not have large initial mass concentrations, gravitational focusing due to the global morphology leads to cluster formation. We use the resulting structures to extract observable morphological and kinematic signatures for the case of subvirial collapse. We find that the signatures of the initial conditions can be erased rapidly as the gas and stars collapse, suggesting that kinematic observations need to be made early in cluster formation and/or at larger scales, away from the growing cluster core. Our results emphasize that a dynamically young system is inherently evolving on short timescales, so that it can be highly misleading to use current-epoch conditions to study aspects such as star formation rates as a function of local density. Our simulations serve as a starting point for further studies of collapse including other factors such as magnetic fields and stellar feedback.

  18. Triggering star formation by both radiative and mechanical AGN feedback

    NASA Astrophysics Data System (ADS)

    Liu, Chao; Gan, Zhao-Ming; Xie, Fu-Guo

    2013-08-01

    We perform two dimensional hydrodynamic numerical simulations to study the positive active galactic nucleus (AGN) feedback which triggers, rather than suppresses, star formation. Recently, it was shown by Nayakshin et al. and Ishibashi et al. that star formation occurs when the cold interstellar medium (ISM) is squeezed by the impact of mass outflow or radiation pressure, respectively. Mass outflow is ubiquitous in this astrophysical context, and radiation pressure is also important if the AGN is luminous. For the first time in this subject, we incorporate both mass outflow feedback and radiative feedback into our model. Consequently, the ISM is shocked into shells by the AGN feedback, and these shells soon fragment into clumps and filaments because of Rayleigh-Taylor and thermal instabilities. We have two major findings: (1) the star formation rate can indeed be very large in the clumps and filaments. However, the resultant star formation rate density is too large compared with previous works, which is mainly because we ignore the fact that most of the stars that are formed would be disrupted when they move away from the galactic center. (2) Although radiation pressure feedback has a limited effect, when mass outflow feedback is also included, they reinforce each other. Specifically, in the gas-poor case, mass outflow is always the dominant contributor to feedback.

  19. Formation of Planets Around the Sun and Other Stars.

    SciTech Connect

    Lin, Doug

    2005-11-14

    Formation of Planets around the Sun and other stars. The quest to understand the formation of planets and planetary systems has entered an era of renaissance. Driven by observational discoveries in solar system exploration, protostellar disks, and extra solar planets, we have established a rich data bank which contains not only relic clues around mature stars, including the Sun, but also direct image of ongoing processes around young stars. For the first time in this scientific endeavor, we have adequate information to construct quantitative models to account for the ubiquity of planets and diversity of planetary systems. Some of the most intriguing theoretical questions facing us today include: a) how did the planets in the solar system form with their present-day mass, composition, and orbital elements, b) is planet formation a deterministic or chaotic process, and c) what are the observable signatures of planet formation and evolution around nearby young and mature stars? I will present a comprehensive scenario which suggests a) gas giant planets formed through coagulation of planetsimals and gas accretion onto earth-like cores; b) the final assemblage of the terrestrial planets in the solar system occurred through the propagation of Jupiter's secular resonance 4-30 Myrs after the emergence of the gas giant; and c) although they are yet to be discovered, Earth-like planets are expected to be common around nearby stars.

  20. SIGNATURES OF STAR CLUSTER FORMATION BY COLD COLLAPSE

    SciTech Connect

    Kuznetsova, Aleksandra; Hartmann, Lee; Ballesteros-Paredes, Javier

    2015-12-10

    Subvirial gravitational collapse is one mechanism by which star clusters may form. Here we investigate whether this mechanism can be inferred from observations of young clusters. To address this question, we have computed smoothed particle hydrodynamics simulations of the initial formation and evolution of a dynamically young star cluster through cold (subvirial) collapse, starting with an ellipsoidal, turbulently seeded distribution of gas, and forming sink particles representing (proto)stars. While the initial density distributions of the clouds do not have large initial mass concentrations, gravitational focusing due to the global morphology leads to cluster formation. We use the resulting structures to extract observable morphological and kinematic signatures for the case of subvirial collapse. We find that the signatures of the initial conditions can be erased rapidly as the gas and stars collapse, suggesting that kinematic observations need to be made early in cluster formation and/or at larger scales, away from the growing cluster core. Our results emphasize that a dynamically young system is inherently evolving on short timescales, so that it can be highly misleading to use current-epoch conditions to study aspects such as star formation rates as a function of local density. Our simulations serve as a starting point for further studies of collapse including other factors such as magnetic fields and stellar feedback.

  1. Cosmic infrared background measurements and star formation history from Planck

    NASA Astrophysics Data System (ADS)

    Serra, Paolo; Serra

    2014-05-01

    We present new measurements of Cosmic Infrared Background (CIB) anisotropies using Planck. Combining HFI data with IRAS, the angular auto- and cross-frequency power spectrum is measured from 143 to 3000 GHz. After careful removal of the contaminants (cosmic microwave background anisotropies, Galactic dust and Sunyaev-Zeldovich emission), and a complete study of systematics, the CIB power spectrum is measured with unprecedented signal to noise ratio from angular multipoles l ~ 150 to 2500. The interpretation based on the halo model is able to associate star-forming galaxies with dark matter halos and their subhalos, using a parametrized relation between the dust-processed infrared luminosity and (sub-)halo mass, and it allows to simultaneously fit all auto- and cross- power spectra very well. We find that the star formation history is well constrained up to redshifts around 2, and agrees with recent estimates of the obscured star-formation density using Spitzer and Herschel. However, at higher redshift, the accuracy of the star formation history measurement is strongly degraded by the uncertainty in the spectral energy distribution of CIB galaxies. We also find that the mean halo mass which is most efficient at hosting star formation is log(M eff/M ⊙) = 12.6 and that CIB galaxies have warmer temperatures as redshift increases.

  2. CEPHEID VARIABLE STARS IN THE PEGASUS DWARF IRREGULAR GALAXY: CONSTRAINTS ON THE STAR FORMATION HISTORY

    SciTech Connect

    Meschin, I.; Gallart, C.; Aparicio, A.; Rosenberg, A.; Cassisi, S. E-mail: carme@iac.es E-mail: alf@iac.es

    2009-03-15

    Observations of the resolved stars obtained over a period of 11 years in the Local Group dwarf irregular galaxy Pegasus have been used to search for Cepheid variable stars. Images were obtained in 55 epochs in the V band and in 24 epochs in the I band. We have identified 26 Cepheids and have obtained their light curves and periods. On the basis of their position in the period-luminosity (PL) diagram, we have classified them as 18 fundamental modes and eight first overtone Cepheids. Two PL relations for Cepheids have been used to derive the distance, resulting in 1.07 {+-} 0.05 Mpc. We present the VARFINDER code which finds the variable stars and their predicted periods in a given synthetic color-magnitude diagram computed with IAC-star and we propose the use of the Cepheid population as a constraint of the star formation history of Pegasus.

  3. Does star formation proceed differently in metal-poor galaxies?

    NASA Astrophysics Data System (ADS)

    Lebouteiller, Vianney

    2014-10-01

    The importance of molecular gas in the star-formation process has been questioned by recent theoretical studies. When metals are scarce, star formation could proceed before the molecular fraction becomes significant, making cold atomic gas the key pre-requisite for star formation. The best case studies are blue compact dwarf galaxies (BCDs), with their prominent star-formation episode and yet with little or no evidence of molecular gas. Current observations do not provide strong constraints on the presence of dense atomic gas in BCDs nor on the fraction of molecular gas.We propose to examine the HI region of 9 nearby BCDs selected from the Herschel Dwarf Galaxy Survey. Our program relies on the synergy of Hubble and Herschel, by calculating the gas cooling rate from the fine-structure level of ionized carbon, a parameter that can be determined both in the FUV with COS (probing the diffuse gas through the 1335.7A CII* absorption) and in the FIR with Herschel (probing the denser gas through the [CII] 157um emission). This comparison allows us to constrain the volume filling factor of dense vs. diffuse gas. The program we propose will allow us to examine how this fraction varies with metallicity, star-formation rate, and total gas mass. We will also be able to quantify the mass of molecular gas and evaluate its actual importance for star formation. Finally, a secondary objective is to characterize the main gas heating mechanisms in the HI region of BCDs and in particular the validity of the photoelectric effect paradigm in sources with a low dust-to-gas ratio, with potential implications for high-redshift galaxies.

  4. Limits on Population III star formation with the most iron-poor stars

    NASA Astrophysics Data System (ADS)

    de Bennassuti, M.; Salvadori, S.; Schneider, R.; Valiante, R.; Omukai, K.

    2017-02-01

    We study the impact of star-forming minihaloes, and the initial mass function (IMF) of Population III (Pop III) stars, on the Galactic halo metallicity distribution function (MDF) and on the properties of C-enhanced and C-normal stars at [Fe/H] < -3. For our investigation we use a data-constrained merger tree model for the Milky Way formation, which has been improved to self-consistently describe the physical processes regulating star formation in minihaloes, including the poor sampling of the Pop III IMF. We find that only when star-forming minihaloes are included the low-Fe tail of the MDF is correctly reproduced, showing a plateau that is built up by C-enhanced metal-poor stars imprinted by primordial faint supernovae. The incomplete sampling of the Pop III IMF in inefficiently star-forming minihaloes (<10-3 M⊙ yr-1) strongly limits the formation of pair-instability supernovae (PISNe), with progenitor masses mPopIII = [140-260] M⊙, even when a flat Pop III IMF is assumed. Second-generation stars formed in environments polluted at >50 per cent level by PISNe are thus extremely rare, corresponding to ≈0.25 per cent of the total stellar population at [Fe/H] < -2, which is consistent with recent observations. The low-Fe tail of the MDF strongly depends on the Pop III IMF shape and mass range. Given the current statistics, we find that a flat Pop III IMF model with mPopIII = [10-300] M⊙ is disfavoured by observations. We present testable predictions for Pop III stars extending down to lower masses, with mPopIII = [0.1-300] M⊙.

  5. Insights into high mass star formation from methanol maser observations

    NASA Astrophysics Data System (ADS)

    Farmer, Hontas Freeman

    2013-06-01

    We present high angular resolution data on Class I and Class II methanol masers, together with other tracers of star formation like H2O masers, ultracompact (UC) ionized hydrogen (H II) regions, and 4.5 um infrared sources, taken from the literature. The aim is to study what these data tell us about the process of high mass star formation; in particular, whether disk-outflow systems are compatible with the morphology exhibited by Class I and Class II methanol masers. Stars form in the dense cores inside molecular clouds, and while the process of the formation of stars like our Sun is reasonably well understood, details of the formation of stars with masses eight times that of our Sun or greater, the so-called high mass stars, remain a mystery. Being compact and bright sources, masers provide an excellent way to observe high mass star forming regions. In particular, Class II methanol masers are found exclusively in high mass star forming regions. Based on the positions of the Class I and II methanol and H2O masers, UCHII regions and 4.5 um infrared sources, and the center velocities (vLSR) of the Class I methanol and H2O masers, compared to the vLSR of the Class II methanol masers, we propose three disk-outflow models that may be traced by methanol masers. In all three models, we have located the Class II methanol maser near the protostar, and the Class I methanol maser in the outflow, as is known from observations during the last twenty years. In our first model, the H2O masers trace the linear extent of the outflow. In our second model, the H2O masers are located in a circumstellar disk. In our third model, the H2O masers are located in one or more outflows near the terminating shock where the outflow impacts the ambient interstellar medium. Together, these models reiterate the utility of coordinated high angular resolution observations of high mass star forming regions in maser lines and associated star formation tracers.

  6. Star formation rates and abundance gradients in disk galaxies

    NASA Technical Reports Server (NTRS)

    Wyse, Rosemary F. G.; Silk, Joseph

    1989-01-01

    Analytic models for the evolution of disk galaxies are presented, placing special emphasis on the radial properties. These models are straightforward extensions of the original Schmidt (1959, 1963) models, with a dependence of star formation rate on gas density. The models provide successful descriptions of several measures of galactic disk evolution, including solar neighborhood chemical evolution, the presence and amplitude of metallicity and color gradients in disk galaxies, and the global rates of star formation in disk galaxies, and aid in the understanding of the apparent connection between young and old stellar populations in spiral galaxies.

  7. THE COOLING OF THE CASSIOPEIA A NEUTRON STAR AS A PROBE OF THE NUCLEAR SYMMETRY ENERGY AND NUCLEAR PASTA

    SciTech Connect

    Newton, William G.; Hooker, Joshua; Li, Bao-An; Murphy, Kyleah

    2013-12-10

    X-ray observations of the neutron star (NS) in the Cas A supernova remnant over the past decade suggest the star is undergoing a rapid drop in surface temperature of ≈2%-5.5%. One explanation suggests the rapid cooling is triggered by the onset of neutron superfluidity in the core of the star, causing enhanced neutrino emission from neutron Cooper pair breaking and formation (PBF). Using consistent NS crust and core equations of state (EOSs) and compositions, we explore the sensitivity of this interpretation to the density dependence of the symmetry energy L of the EOS used, and to the presence of enhanced neutrino cooling in the bubble phases of crustal ''nuclear pasta''. Modeling cooling over a conservative range of NS masses and envelope compositions, we find L ≲ 70 MeV, competitive with terrestrial experimental constraints and other astrophysical observations. For masses near the most likely mass of M ≳ 1.65 M {sub ☉}, the constraint becomes more restrictive 35 ≲ L ≲ 55 MeV. The inclusion of the bubble cooling processes decreases the cooling rate of the star during the PBF phase, matching the observed rate only when L ≲ 45 MeV, taking all masses into consideration, corresponding to NS radii ≲ 11 km.

  8. The Cooling of the Cassiopeia A Neutron Star as a Probe of the Nuclear Symmetry Energy and Nuclear Pasta

    NASA Astrophysics Data System (ADS)

    Newton, William G.; Murphy, Kyleah; Hooker, Joshua; Li, Bao-An

    2013-12-01

    X-ray observations of the neutron star (NS) in the Cas A supernova remnant over the past decade suggest the star is undergoing a rapid drop in surface temperature of ≈2%-5.5%. One explanation suggests the rapid cooling is triggered by the onset of neutron superfluidity in the core of the star, causing enhanced neutrino emission from neutron Cooper pair breaking and formation (PBF). Using consistent NS crust and core equations of state (EOSs) and compositions, we explore the sensitivity of this interpretation to the density dependence of the symmetry energy L of the EOS used, and to the presence of enhanced neutrino cooling in the bubble phases of crustal "nuclear pasta." Modeling cooling over a conservative range of NS masses and envelope compositions, we find L <~ 70 MeV, competitive with terrestrial experimental constraints and other astrophysical observations. For masses near the most likely mass of M >~ 1.65 M ⊙, the constraint becomes more restrictive 35 <~ L <~ 55 MeV. The inclusion of the bubble cooling processes decreases the cooling rate of the star during the PBF phase, matching the observed rate only when L <~ 45 MeV, taking all masses into consideration, corresponding to NS radii <~ 11 km.

  9. Upper limit on star formation and metal enrichment in minihaloes

    NASA Astrophysics Data System (ADS)

    Cen, Renyue

    2017-02-01

    An analysis of negative radiative feedback from resident stars in minihaloes is performed. It is found that the most effective mechanism to suppress star formation is provided by infrared photons from resident stars via photodetachment of H-. It is shown that a stringent upper bound on (total stellar mass, metallicity) of (˜1000 M⊙, -3.3 ± 0.2) in any newly minted atomic cooling halo can be placed, with the actual values possibly significantly lower. This has both important physical ramifications on formation of stars and supermassive black seeds in atomic cooling haloes at high redshift, pertaining to processes of low-temperature metal cooling, dust formation and fragmentation, and direct consequences on the faint end galaxy luminosity function at high redshift and cosmological reionization. The luminosity function of galaxies at the epoch of reionization may be substantially affected due to the combined effect of a diminished role of minihaloes and an enhanced contribution from Population III stars in atomic cooling haloes. Upcoming results on reionization optical depth from Planck High-Frequency Instrument data may provide a significant constraint on and a unique probe of this star formation physical process in minihaloes. As a numerical example, in the absence of significant contributions from minihaloes with virial masses below 1.5 × 108 M⊙, the reionization optical depth is expected to be no greater than 0.065, whereas allowing for minihaloes of masses as low as (107 M⊙, 106.5 M⊙) to form stars unconstrained by this self-regulation physical process, the reionization optical depth is expected to exceed (0.075, 0.085), respectively.

  10. StarPy: Quenched star formation history parameters of a galaxy using MCMC

    NASA Astrophysics Data System (ADS)

    Smethurst, R. J.; Lintott, C. J.; Simmons, B. D.; Schawinski, K.; Marshall, P. J.; Bamford, S.; Fortson, L.; Kaviraj, S.; Masters, K. L.; Melvin, T.; Nichol, R. C.; Skibba, R. A.; Willett, K. W.

    2016-09-01

    StarPy derives the quenching star formation history (SFH) of a single galaxy through the Bayesian Markov Chain Monte Carlo method code emcee (ascl:1303.002). The sample function implements the emcee EnsembleSampler function for the galaxy colors input. Burn-in is run and calculated for the length specified before the sampler is reset and then run for the length of steps specified. StarPy provides the ability to use the look-up tables provided or creating your own.

  11. Effect of Population III Multiplicity on Dark Star Formation

    NASA Technical Reports Server (NTRS)

    Stacy, Athena; Pawlik, Andreas H.; Bromm, Volker; Loeb, Abraham

    2012-01-01

    We numerically study the mutual interaction between dark matter (DM) and Population III (Pop III) stellar systems in order to explore the possibility of Pop III dark stars within this physical scenario. We perform a cosmological simulation, initialized at z approx. 100, which follows the evolution of gas and DM. We analyze the formation of the first mini halo at z approx. 20 and the subsequent collapse of the gas to densities of 10(exp 12)/cu cm. We then use this simulation to initialize a set of smaller-scale 'cut-out' simulations in which we further refine the DM to have spatial resolution similar to that of the gas. We test multiple DM density profiles, and we employ the sink particle method to represent the accreting star-forming region. We find that, for a range of DM configurations, the motion of the Pop III star-disk system serves to separate the positions of the protostars with respect to the DM density peak, such that there is insufficient DM to influence the formation and evolution of the protostars for more than approx. 5000 years. In addition, the star-disk system causes gravitational scattering of the central DM to lower densities, further decreasing the influence of DM over time. Any DM-powered phase of Pop III stars will thus be very short-lived for the typical multiple system, and DM will not serve to significantly prolong the life of Pop III stars.

  12. PRECIPITATION-REGULATED STAR FORMATION IN GALAXIES

    SciTech Connect

    Voit, G. Mark; O’Shea, Brian W.; Donahue, Megan; Bryan, Greg L.

    2015-07-20

    Galaxy growth depends critically on the interplay between radiative cooling of cosmic gas and the resulting energetic feedback that cooling triggers. This interplay has proven exceedingly difficult to model, even with large supercomputer simulations, because of its complexity. Nevertheless, real galaxies are observed to obey simple scaling relations among their primary observable characteristics. Here we show that a generic emergent property of the interplay between cooling and feedback can explain the observed scaling relationships between a galaxy's stellar mass, its total mass, and its chemical enrichment level, as well as the relationship between the average orbital velocity of its stars and the mass of its central black hole. These relationships naturally result from any feedback mechanism that strongly heats a galaxy's circumgalactic gas in response to precipitation of colder clouds out of that gas, because feedback then suspends the gas in a marginally precipitating state.

  13. MOLECULAR GAS AND STAR-FORMATION PROPERTIES IN THE CENTRAL AND BAR REGIONS OF NGC 6946

    SciTech Connect

    Pan, Hsi-An; Sorai, Kazuo; Kuno, Nario; Koda, Jin; Hirota, Akihiko; Kaneko, Hiroyuki

    2015-12-10

    In this work, we investigate the molecular gas and star-formation properties in the barred spiral galaxy NGC 6946 using multiple molecular lines and star-formation tracers. A high-resolution image (100 pc) of {sup 13}CO (1–0) is created for the inner 2 kpc disk by the single-dish Nobeyama Radio Observatory 45 m telescope and interferometer Combined Array for Research in Millimeter-wave Astronomy, including the central region (nuclear ring and bar) and the offset ridges of the primary bar. Single-dish HCN (1–0) observations were also made to constrain the amount of dense gas. The physical properties of molecular gas are inferred from (1) the large velocity gradient calculations using our observations and archival {sup 12}CO (1–0), {sup 12}CO(2–1) data, (2) the dense gas fraction suggested by the luminosity ratio of HCN to {sup 12}CO (1–0), and (3) the infrared color. The results show that the molecular gas in the central region is warmer and denser than that of the offset ridges. The dense gas fraction of the central region is similar to that of luminous infrared galaxies/ultraluminous infrared galaxies, whereas the offset ridges are close to the global average of normal galaxies. The coolest and least-dense region is found in a spiral-like structure, which was misunderstood to be part of the southern primary bar in previous low-resolution observations. The star-formation efficiency (SFE) changes by about five times in the inner disk. The variation of SFE agrees with the prediction in terms of star formation regulated by the galactic bar. We find a consistency between the star-forming region and the temperature inferred by the infrared color, suggesting that the distribution of subkiloparsec-scale temperature is driven by star formation.

  14. Evolution of Dense Gas with Starburst Age: When Star Formation Versus Dense Gas Relations Break Down

    NASA Astrophysics Data System (ADS)

    Meier, David S.; Turner, J. L.; Schinnerer, E.

    2011-05-01

    Dense gas correlates well with star formation on kpc scales. On smaller scales, motions of individual clouds become comparable to the 100 Myr ages of starbursts. One then expects the star formation rate vs. dense gas relations to break down on giant molecular cloud scales. We exploit this to study the evolutionary history of nuclear starburst in the nearby spiral, IC 342. Maps of the J=5-4 and 16-15 transitions of dense gas tracer HC3N at 20 pc resolution made with the VLA and the Plateau de Bure interferometer are presented. The 5-4 line of HC3N traces very dense gas in the cold phase, while the 16-15 transition traces warm, dense gas. These reveal changes in dense cloud structure on scales of 30 pc among clouds with star formation histories differing by only a few Myrs. HC3N emission does not correlate well with young star formation at these high spatial resolutions, but gas excitation does. The cold, dense gas extends well beyond the starburst region implying large amounts of dense quiescent gas not yet actively forming stars. Close to the starburst the high excitation combined with faint emission indicates that the immediate (30 pc) vicinity of the starburst lacks large masses of very dense gas and has high dense gas star formation efficiencies. The dense gas appears to be in pressure equilibrium with the starburst. We propose a scenario where the starburst is being caught in the act of dispersing or destroying the dense gas in the presence of the expanding HII region. This work is supported by the NSF through NRAO and grant AST-1009620.

  15. A STAR FORMATION LAW FOR DWARF IRREGULAR GALAXIES

    SciTech Connect

    Elmegreen, Bruce G.; Hunter, Deidre A. E-mail: dah@lowell.edu

    2015-06-01

    The radial profiles of gas, stars, and far-ultraviolet radiation in 20 dwarf Irregular galaxies are converted to stability parameters and scale heights for a test of the importance of two-dimensional (2D) instabilities in promoting star formation. A detailed model of this instability involving gaseous and stellar fluids with self-consistent thicknesses and energy dissipation on a perturbation crossing time gives the unstable growth rates. We find that all locations are effectively stable to 2D perturbations, mostly because the disks are thick. We then consider the average volume densities in the midplanes, evaluated from the observed H i surface densities and calculated scale heights. The radial profiles of the star-formation rates are equal to about 1% of the H i surface densities divided by the free fall times at the average midplane densities. This 1% resembles the efficiency per unit free fall time commonly found in other cases. There is a further variation of this efficiency with radius in all of our galaxies, following the exponential disk with a scale length equal to about twice the stellar mass scale length. This additional variation is modeled by the molecular fraction in a diffuse medium using radiative transfer solutions for galaxies with the observed dimensions and properties of our sample. We conclude that star formation is activated by a combination of three-dimensional gaseous gravitational processes and molecule formation. Implications for outer disk structure and formation are discussed.

  16. Star formation triggered by galaxy interactions in modified gravity

    NASA Astrophysics Data System (ADS)

    Renaud, Florent; Famaey, Benoit; Kroupa, Pavel

    2016-12-01

    Together with interstellar turbulence, gravitation is one key player in star formation. It acts both at galactic scales in the assembly of gas into dense clouds and inside those structures for their collapse and the formation of pre-stellar cores. To understand to what extent the large-scale dynamics govern the star formation activity of galaxies, we present hydrodynamical simulations in which we generalize the behaviour of gravity to make it differ from Newtonian dynamics in the low-acceleration regime. We focus on the extreme cases of interacting galaxies, and compare the evolution of galaxy pairs in the dark matter paradigm to that in the Milgromian dynamics (MOND) framework. Following up on the seminal work by Tiret & Combes, this paper documents the first simulations of galaxy encounters in MOND with a detailed Eulerian hydrodynamical treatment of baryonic physics, including star formation and stellar feedback. We show that similar morphologies of the interacting systems can be produced by both the dark matter and MOND formalisms, but require a much slower orbital velocity in the MOND case. Furthermore, we find that the star formation activity and history are significantly more extended in space and time in MOND interactions, in particular in the tidal debris. Such differences could be used as observational diagnostics and make interacting galaxies prime objects in the study of the nature of gravitation at galactic scales.

  17. Dark Matter Substructure, Galaxy Assembly and Star Formation Histories

    NASA Astrophysics Data System (ADS)

    Simha, Vimal

    2011-01-01

    We use cosmological SPH simulations to study galaxy growth and the relationship between dark matter halos and the galaxies that form in them. We find that the distinction between central and satellite galaxies in our simulation is weaker than expected in simple models where only central galaxies are able to accrete mass and `receive' mergers of less massive systems. Instead, in our simulation, satellite galaxies continue to accrete gas and convert it to stars after halo mergers with a larger parent halo. Satellites in our simulation are 0.1-0.2 magnitudes bluer than in models that assume no gas accretion on to satellites after a halo merger (instantaneous `strangulation'), which is sufficient to shift galaxies across the boundary from the `red sequence' to the `blue cloud'. Subhalo abundance matching (SHAM) is a technique for assigning luminosities to simulated dark matter substructures by assuming a strictly monotonic relationship between luminosity and halo mass at the epoch of accretion. We carry out N-body and SPH simulations of a cosmological volume with identical initial conditions, finding that SHAM successfully matches the stellar masses and luminosities of SPH galaxies at a wide range of epochs, albeit with relatively small amounts of scatter. In our SPH simulations that include momentum driven winds, the results are more complex. We examine the relationship between halo assembly and star formation histories with the goal of extending SHAM to a wider domain of observables such as star formation history and colour. In order to guide efforts to fit star formation histories to observed colours or spectra, we investigate parametric fits to the star formation histories of SPH galaxies finding that some commonly used models fail to describe the star formation histories of SPH galaxies but other simple two parameter models achieve greater success.

  18. On the cosmic evolution of the specific star formation rate

    NASA Astrophysics Data System (ADS)

    Lehnert, M. D.; van Driel, W.; Le Tiran, L.; Di Matteo, P.; Haywood, M.

    2015-05-01

    The apparent correlation between the specific star formation rate (sSFR) and total stellar mass (M⋆) of galaxies is a fundamental relationship indicating how they formed their stellar populations. To attempt to understand this relation, we hypothesize that the relation and its evolution is regulated by the increase in the stellar and gas mass surface density in galaxies with redshift, which is itself governed by the angular momentum of the accreted gas, the amount of available gas, and by self-regulation of star formation. With our model, we can reproduce the specific SFR - M⋆ relations at z ~ 1-2 by assuming gas fractions and gas mass surface densities similar to those observed for z = 1-2 galaxies. We further argue that it is the increasing angular momentum with cosmic time that causes a decrease in the surface density of accreted gas. The gas mass surface densities in galaxies are controlled by the centrifugal support (i.e., angular momentum), and the sSFR is predicted to increase as, sSFR(z) = (1 + z)3/tH0, as observed (where tH0 is the Hubble time and no free parameters are necessary). In addition, the simple evolution for the star-formation intensity we propose is in agreement with observations of Milky Way-like galaxies selected through abundance matching. At z ≳ 2, we argue that star formation is self-regulated by high pressures generated by the intense star formation itself. The star formation intensity must be high enough to either balance the hydrostatic pressure (a rather extreme assumption) or to generate high turbulent pressure in the molecular medium which maintains galaxies near the line of instability (i.e. Toomre Q ~ 1). We provide simple prescriptions for understanding these self-regulation mechanisms based on solid relationships verified through extensive study. In all cases, the most important factor is the increase in stellar and gas mass surface density with redshift, which allows distant galaxies to maintain high levels of s

  19. The Nuclear Spectroscopic Telescope Array (NuSTAR)

    NASA Astrophysics Data System (ADS)

    Harrison, Fiona A.; Boggs, Steve; Christensen, Finn; Craig, William; Hailey, Charles; Stern, Daniel; Zhang, William; Angelini, Lorella; An, Hongjun; Bhalerao, Varun; Brejnholt, Nicolai; Cominsky, Lynn; Cook, W. Rick; Doll, Melania; Giommi, Paolo; Grefenstette, Brian; Hornstrup, Allan; Kaspi, Vicky; Kim, Yunjin; Kitaguchi, Takeo; Koglin, Jason; Liebe, Carl Christian; Madejski, Greg; Kruse Madsen, Kristin; Mao, Peter; Meier, David; Miyasaka, Hiromasa; Mori, Kaya; Perri, Matteo; Pivovaroff, Michael; Puccetti, Simonetta; Rana, Vikram; Zoglauer, Andreas

    2010-07-01

    The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer mission that will carry the first focusing hard X-ray (6 - 80 keV) telescope to orbit. NuSTAR will offer a factor 50 - 100 sensitivity improvement compared to previous collimated or coded mask imagers that have operated in this energy band. In addition, NuSTAR provides sub-arcminute imaging with good spectral resolution over a 12-arcminute eld of view. After launch, NuSTAR will carry out a two-year primary science mission that focuses on four key programs: studying the evolution of massive black holes through surveys carried out in fields with excellent multiwavelength coverage, understanding the population of compact objects and the nature of the massive black hole in the center of the Milky Way, constraining the explosion dynamics and nucleosynthesis in supernovae, and probing the nature of particle acceleration in relativistic jets in active galactic nuclei. A number of additional observations will be included in the primary mission, and a guest observer program will be proposed for an extended mission to expand the range of scientic targets. The payload consists of two co-aligned depth-graded multilayer coated grazing incidence optics focused onto a solid state CdZnTe pixel detectors. To be launched in early 2012 on a Pegasus rocket into a low-inclination Earth orbit, NuSTAR largely avoids SAA passage, and will therefore have low and stable detector backgrounds. The telescope achieves a 10.14-meter focal length through on-orbit deployment of an extendable mast. An aspect and alignment metrology system enable reconstruction of the absolute aspect and variations in the telescope alignment resulting from mast exure during ground data processing. Data will be publicly available at GSFC's High Energy Archive Research Center (HEASARC) following validation at the science operations center located at Caltech.

  20. The Nuclear Spectroscopic Telescope Array (NuSTAR)

    NASA Technical Reports Server (NTRS)

    Harrison, Fiona A.; Boggs, Steven; Christensen, Finn; Craig, William; Hailey, Charles; Stern, Daniel; Zhang, William; Angelini, Lorella; An, Hong Jun; Bhalereo, Varun; Brejnholt, Nicolai; Cominsky, Lynn; Cook, Rick; Doll, Melania; Giommi, Paolo; Grefenstette, Brian; Hornstrup, Allan; Kaspi, Victoria M.; Kim, Yunjin; Kitaguchi, Takao; Koglin, Jason; Liebe, Carl Christian; Madejski, Greg; Madsen, Kristen Kruse; Mao, Peter

    2010-01-01

    The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer mission that will carry the first focusing hard X-ray (5 - 80 keV) telescope to orbit. NuSTAR will offer a factor 50 - 100 sensitivity improvement compared to previous collimated or coded mask imagers that have operated in this energy band. In addition, NuSTAR provides sub-arcminute imaging with good spectral resolution over a 12-arcminute field of view. After launch, NuSTAR will carry out a two-year primary science mission that focuses on four key programs: studying the evolution of massive black holes through surveys carried out in fields with excellent multiwavelength coverage, understanding the population of compact objects and the nature of the massive black hole in the center of the Milky Way, constraining explosion dynamics and nucleosynthesis in supernovae, and probing the nature of particle acceleration in relativistic jets in active galactic nuclei. A number of additional observations will be included in the primary mission, and a. guest observer program will be proposed for an extended mission to expand the range of scientific targets. The payload consists of two co-aligned depth-graded multilayer coated grazing incidence optics focused onto solid state CdZnTe pixel detectors. To be launched in early 2012 on a Pegasus rocket into a low-inclination Earth orbit. NuSTAR largely avoids SAA passages, and will therefore have low and stable detector backgrounds. The telescope achieves a 10.15-meter focal length through on-orbit deployment of all mast. An aspect and alignment metrology system enable reconstruction of the absolute aspect and variations in the telescope alignment resulting from mast flexure during ground data processing. Data will be publicly available at GSFC's High Energy Astrophysics Science Archive Research Center (HEASARC) following validation at the science operations center located at Caltech.

  1. Angular momentum evolution during star and planetary system formation

    NASA Astrophysics Data System (ADS)

    Davies, Claire L.; Greaves, Jane S.

    2014-01-01

    We focused on analysing the role played by protoplanetary disks in the evolution of angular momentum during star formation. If all the angular momentum contained within collapsing pre-stellar cores was conserved during their formation, proto-stars would reach rotation rates exceeding their break-up velocities before they reached the main sequence (Bodenheimer 1995). In order to avoid this occuring, methods by which proto-stars can lose angular momentum must exist. Angular momentum can be transferred from star to disk via stellar magnetic field lines through a process called magnetic braking (Camenzind 1990; Königl 1991). Alternatively, the stellar angular momentum can be lost from the star-disk system entirely via stellar- or disk-winds (e.g. Pelletier & Pudritz 1992; Matt & Pudritz 2005). The proportion of lost stellar angular momentum retained within the protoplanetary disk is important to studies of planetary system formation. If the bulk motion within the disk remains Keplerian, any increase of angular momentum in the disk causes an outward migration of disk material and an expansion of the disk. Therefore, an increase in disk angular momentum may cause a reduction in the disk surface density, often used to indicate the disk's ability to form planets. We made use of multi-wavelength data available in the literature to directly calculate the stellar and disk angular momenta for two nearby regions of star formation. Namely, these were the densely populated and highly irradiated Orion Nebula Cluster (ONC) and the comparitively sparse Taurus-Auriga region. Due to the limited size of the ONC dataset, we produced an average surface density profile for the region. We modelled the stars as solid body rotators due to their fully convective nature (Krishnamurthi et al. 1997) and assumed the disks are flat and undergo Keplerian rotation about the same rotation axis as the star. We observed the older disks within each of the two star forming regions to be preferentially

  2. Stellar signatures of AGN-jet-triggered star formation

    SciTech Connect

    Dugan, Zachary; Silk, Joseph; Bryan, Sarah; Gaibler, Volker; Haas, Marcel

    2014-12-01

    To investigate feedback between relativistic jets emanating from active galactic nuclei and the stellar population of the host galaxy, we analyze the long-term evolution of the orbits of the stars formed in the galaxy-scale simulations by Gaibler et al. of jets in massive, gas-rich galaxies at z ∼ 2-3. We find strong, jet-induced differences in the resulting stellar populations of galaxies that host relativistic jets and galaxies that do not, including correlations in stellar locations, velocities, and ages. Jets are found to generate distributions of increased radial and vertical velocities that persist long enough to effectively augment the stellar structure of the host. The jets cause the formation of bow shocks that move out through the disk, generating rings of star formation within the disk. The bow shock often accelerates pockets of gas in which stars form, yielding populations of stars with significant radial and vertical velocities, some of which have large enough velocities to escape the galaxy. These stellar population signatures can serve to identify past jet activity as well as jet-induced star formation.

  3. Star Formation and AGN Activity in Luminous and Ultraluminous Infrared Galaxies

    NASA Astrophysics Data System (ADS)

    Kartaltepe, Jeyhan

    2015-08-01

    In the local universe, Ultraluminous Infrared Galaxies (ULIRGs, L_IR > 10^12 L⊙) are all interacting and merging systems. We explore the evolution of the morphological and nuclear properties of (U)LIRGs over cosmic time using a large sample of galaxies from Her- schel observations of the CANDELS fields (including GOODS, COSMOS, and UDS). In particular, we investigate whether the role of galaxy mergers has changed between z ˜ 2 and now using the extensive visual classification catalogs produced by the CANDELS team. The combination of a selection from Herschel, near the peak of IR emission, and rest-frame optical morphologies from CANDELS, provides the ideal comparison to nearby (U)LIRGs. We also use rest-frame optical emission line diagnostics, X-ray luminosity, and MIR colors to separate AGN from star-formation dominated galaxies. We then study the how role of galaxy mergers and the presence of AGN activity correspond to the galaxy’s position in the star formation rate - stellar mass plane. Are galaxies that have specific star formation rates elevated above the main sequence more likely to be mergers? We investigate how AGN identified with different methods correspond to different morphologies and merger stages as well as position on the star formation rate - stellar mass plane.

  4. The interstellar medium and star formation in local galaxies: Variations of the star formation law in simulations

    SciTech Connect

    Becerra, Fernando; Escala, Andrés

    2014-05-01

    We use the adaptive mesh refinement code Enzo to model the interstellar medium (ISM) in isolated local disk galaxies. The simulation includes a treatment for star formation and stellar feedback. We get a highly supersonic turbulent disk, which is fragmented at multiple scales and characterized by a multi-phase ISM. We show that a Kennicutt-Schmidt relation only holds when averaging over large scales. However, values of star formation rates and gas surface densities lie close in the plot for any averaging size. This suggests an intrinsic relation between stars and gas at cell-size scales, which dominates over the global dynamical evolution. To investigate this effect, we develop a method to simulate the creation of stars based on the density field from the snapshots, without running the code again. We also investigate how the star formation law is affected by the characteristic star formation timescale, the density threshold, and the efficiency considered in the recipe. We find that the slope of the law varies from ∼1.4 for a free-fall timescale, to ∼1.0 for a constant depletion timescale. We further demonstrate that a power law is recovered just by assuming that the mass of the new stars is a fraction of the mass of the cell m {sub *} = ερ{sub gas}Δx {sup 3}, with no other physical criteria required. We show that both efficiency and density threshold do not affect the slope, but the right combination of them can adjust the normalization of the relation, which in turn could explain a possible bi-modality in the law.

  5. Galaxy bachelors, couples, spouses: Star formation in interacting galaxies

    NASA Astrophysics Data System (ADS)

    Sun, Jing; Barger, Kathleen; Richstein, Hannah; SDSS-IV/MaNGA

    2017-01-01

    We investigate the star formation activity in three galaxy systems in different stages of interaction to determine how the environment of galaxies affects their star forming ability and potential. These systems include an isolated galaxy, a pair of interacting galaxies, and a pair of merging galaxies. All of the target galaxies in these systems have similar stellar masses and similar radii and are at similar redshifts. We trace the star formation activity over the past 1-2 Gyr using spatially and kinematically resolved H-alpha emission, H-alpha equivalent width, and 4000-Angstrom break maps. This work is based on data from the fourth-generation Sloan Digital Sky Survey (SDSS-IV)/Mapping Nearby Galaxies at Apache Point Observatory (MaNGA), and is part of the Project No.0285 in SDSS-IV.

  6. The physics and modes of star cluster formation: simulations.

    PubMed

    Clarke, Cathie

    2010-02-28

    We review progress in numerical simulations of star cluster formation. These simulations involve the bottom-up assembly of clusters through hierarchical mergers, which produces a fractal stellar distribution at young (approx. 0.5 Myr) ages. The resulting clusters are predicted to be mildly aspherical and highly mass-segregated, except in the immediate aftermath of mergers. The upper initial mass function within individual clusters is generally somewhat flatter than for the aggregate population. Recent work has begun to clarify the factors that control the mean stellar mass in a star-forming cloud and also the efficiency of star formation. The former is sensitive to the thermal properties of the gas while the latter depends both on the magnetic field and the initial degree of gravitational boundedness of the natal cloud. Unmagnetized clouds that are initially bound undergo rapid collapse, which is difficult to reverse by ionization feedback or stellar winds.

  7. Network formation and gelation in telechelic star polymers.

    PubMed

    Wadgaonkar, Indrajit; Chatterji, Apratim

    2017-02-28

    We investigate the efficiency of gelation and network formation in telechelic star polymer melt, where the tips of polymer arms are dipoles while the rest of the monomers are uncharged. Our work is motivated by the experimental observations [A. Kulkarni et al., Macromolecules 48, 6580 (2015)] in which rheological studies of telechelic star polymers of poly-(L-lactide), a bio-degradable polymer, showed a drastic increase in elastic properties (up to 2000 times) compared to corresponding star polymers without the telechelic arm ends. In contrast to previous studies, we avoid using effective attractive Lennard-Jones potentials or dipolar potentials to model telechelic interactions. Instead we use explicit Coulomb positive and negative charges at the tip of polymer-arms of our bead-spring model of star polymers. By our simulations we show that the dipoles at the tip of star arms aggregate together to form clusters of dipoles. Each cluster has contributions from several stars, and in turn each star contributes to several clusters. Thus the entire polymer melt forms a connected network. Network forming tendencies decrease with a decrease of the value of the effective charge constituting the dipole: this can be experimentally realized by choosing a different ionomer for the star tip. We systematically varied the value of dipole charges, the fraction of star-arms with dipoles at the tip, and the length of the arms. The choice of explicit charges in our calculations enables us to make better quantitative predictions about the onset of gelation; moreover we get qualitatively distinct results about structural organization of dipoles within a dipole-cluster.

  8. Network formation and gelation in telechelic star polymers

    NASA Astrophysics Data System (ADS)

    Wadgaonkar, Indrajit; Chatterji, Apratim

    2017-02-01

    We investigate the efficiency of gelation and network formation in telechelic star polymer melt, where the tips of polymer arms are dipoles while the rest of the monomers are uncharged. Our work is motivated by the experimental observations [A. Kulkarni et al., Macromolecules 48, 6580 (2015)] in which rheological studies of telechelic star polymers of poly-(L-lactide), a bio-degradable polymer, showed a drastic increase in elastic properties (up to 2000 times) compared to corresponding star polymers without the telechelic arm ends. In contrast to previous studies, we avoid using effective attractive Lennard-Jones potentials or dipolar potentials to model telechelic interactions. Instead we use explicit Coulomb positive and negative charges at the tip of polymer-arms of our bead-spring model of star polymers. By our simulations we show that the dipoles at the tip of star arms aggregate together to form clusters of dipoles. Each cluster has contributions from several stars, and in turn each star contributes to several clusters. Thus the entire polymer melt forms a connected network. Network forming tendencies decrease with a decrease of the value of the effective charge constituting the dipole: this can be experimentally realized by choosing a different ionomer for the star tip. We systematically varied the value of dipole charges, the fraction of star-arms with dipoles at the tip, and the length of the arms. The choice of explicit charges in our calculations enables us to make better quantitative predictions about the onset of gelation; moreover we get qualitatively distinct results about structural organization of dipoles within a dipole-cluster.

  9. Hierarchical star formation across the ring galaxy NGC 6503

    NASA Astrophysics Data System (ADS)

    Gouliermis, Dimitrios A.; Thilker, David; Elmegreen, Bruce G.; Elmegreen, Debra M.; Calzetti, Daniela; Lee, Janice C.; Adamo, Angela; Aloisi, Alessandra; Cignoni, Michele; Cook, David O.; Dale, Daniel A.; Gallagher, John S.; Grasha, Kathryn; Grebel, Eva K.; Davó, Artemio Herrero; Hunter, Deidre A.; Johnson, Kelsey E.; Kim, Hwihyun; Nair, Preethi; Nota, Antonella; Pellerin, Anne; Ryon, Jenna; Sabbi, Elena; Sacchi, Elena; Smith, Linda J.; Tosi, Monica; Ubeda, Leonardo; Whitmore, Brad

    2015-10-01

    We present a detailed clustering analysis of the young stellar population across the star-forming ring galaxy NGC 6503, based on the deep Hubble Space Telescope photometry obtained with the Legacy ExtraGalactic UV Survey. We apply a contour-based map analysis technique and identify in the stellar surface density map 244 distinct star-forming structures at various levels of significance. These stellar complexes are found to be organized in a hierarchical fashion with 95 per cent being members of three dominant super-structures located along the star-forming ring. The size distribution of the identified structures and the correlation between their radii and numbers of stellar members show power-law behaviours, as expected from scale-free processes. The self-similar distribution of young stars is further quantified from their autocorrelation function, with a fractal dimension of ˜1.7 for length-scales between ˜20 pc and 2.5 kpc. The young stellar radial distribution sets the extent of the star-forming ring at radial distances between 1 and 2.5 kpc. About 60 per cent of the young stars belong to the detected stellar structures, while the remaining stars are distributed among the complexes, still inside the ring of the galaxy. The analysis of the time-dependent clustering of young populations shows a significant change from a more clustered to a more distributed behaviour in a time-scale of ˜60 Myr. The observed hierarchy in stellar clustering is consistent with star formation being regulated by turbulence across the ring. The rotational velocity difference between the edges of the ring suggests shear as the driving mechanism for this process. Our findings reveal the interesting case of an inner ring forming stars in a hierarchical fashion.

  10. Star formation in galaxy mergers with realistic models of stellar feedback and the interstellar medium

    NASA Astrophysics Data System (ADS)

    Hopkins, Philip F.; Cox, Thomas J.; Hernquist, Lars; Narayanan, Desika; Hayward, Christopher C.; Murray, Norman

    2013-04-01

    are similar between EOS and resolved-feedback models. The relic structure and mass profile, and the total mass of stars formed in the nuclear starburst are quite similar, as is the morphological structure during and after mergers (tails, bridges, etc.). Disc survival in sufficiently gas rich mergers is similar in the two cases, and the new models follow the same scalings as derived for the efficiency of disc re-formation after a merger as derived from previous work with the simplified EOS models. While the global galaxy properties are similar between EOS and feedback models, subgalaxy-scale properties and the SFRs can be quite different: the more detailed models exhibit significantly higher star formation in tails and bridges (especially in shocks), and allow us to resolve the formation of super star clusters. In the new models, the star formation is more strongly time-variable and drops more sharply between close passages. The instantaneous burst enhancement can be higher or lower, depending on the details of the orbit and initial structural properties of the galaxies; first-passage bursts are more sensitive to these details than those at the final coalescence.

  11. Report on the Workshop Herbig Ae/Be Stars: The Missing Link in Star Formation

    NASA Astrophysics Data System (ADS)

    de Wit, W.-J.; Oudmaijer, R. D.; van den Ancker, M. E.; Calvet, N.

    2014-09-01

    The workshop highlighted the many recent advances within the field of Herbig Ae/Be stars and the close links to star and planet formation. Topics such as magnetospheric accretion and the evolution of dust in discs, the structure of circumstellar discs and the role of walls and gaps and their links to planet formation from many observational aspects were covered. The workshop was dedicated to the life and works of George H. Herbig, who sadly passed away at the end of last year.

  12. Observing Star Formation: From the Interstellar Medium to Star-Forming Cores

    NASA Astrophysics Data System (ADS)

    Goodman, Alyssa A.

    1995-12-01

    In the thirty years since the first mapping of molecular line emission from interstellar clouds, our ``picture" of the interstellar medium has evolved enormously. With only optical observations available, it was (correctly) hypothesized that new stars form from condensations of dense interstellar gas which appear optically as dark or bright nebulae. These early hypotheses often envisioned the overall collapse of whole clouds into stars, or fragmentation of entire clouds into ``Jeans mass"-size clumps. Thirty years of observing the clouds and the star-formation process which takes place within them has, alas, shown these hypotheses to be too simple. Radio-wavelength spectral-line mapping of interstellar gas, far-infrared and sub-millimeter continuum observations of thermal dust emission, and near-infrared and optical spectral and continuum observations of young stellar objects (YSO's) have revealed a detailed--yet nonetheless perplexing--view of the star-formation process. Molecular ``clouds" appear to be wispy, clumpy condensations of interstellar gas, with self-similar density and velocity structure on scales from hundreds of parsecs down to tenths of parsecs. Projected on density maxima in the gas distribution, one often finds point (or very compact) sources whose spectral colors are consistent with their being deeply embedded in dense gas. These sources are often the origin of powerful jets and outflows and are believed to be YSO's. The outflows, which can carry angular momentum away from a YSO, represent an important phase in the star-formation process. I will discuss the current observational ``picture" of star-forming molecular clouds, as well as some of the many theoretical models which have been proposed to explain cloud structure. Current theories and simulations include gravitational, magnetic and dynamical forces and seek to explain how these forces conspire to simultaneously regulate equilibrium, turbulent, and runaway (e.g. star-formation) processes

  13. ORIGIN OF THE GALAXY MASS-METALLICITY-STAR FORMATION RELATION

    SciTech Connect

    Harwit, Martin; Brisbin, Drew

    2015-02-20

    We describe an equilibrium model that links the metallicity of low-redshift galaxies to stellar evolution models. It enables the testing of different stellar initial mass functions and metal yields against observed galaxy metallicities. We show that the metallicities of more than 80,000 Sloan Digital Sky Survey galaxies in the low-redshift range 0.07 ≤ z ≤ 0.3 considerably constrain stellar evolution models that simultaneously relate galaxy stellar mass, metallicity, and star formation rates to the infall rate of low-metallicity extragalactic gas and outflow of enriched matter. A feature of our model is that it encompasses both the active star forming phases of a galaxy and epochs during which the same galaxy may lie fallow. We show that the galaxy mass-metallicity-star formation relation can be traced to infall of extragalactic gas mixing with native gas from host galaxies to form stars of observed metallicities, the most massive of which eject oxygen into extragalactic space. Most consequential among our findings is that, on average, extragalactic infall accounts for one half of the gas required for star formation, a ratio that is remarkably constant across galaxies with stellar masses ranging at least from M* = 2 × 10{sup 9} to 6 × 10{sup 10} M {sub ☉}. This leads us to propose that star formation is initiated when extragalactic infall roughly doubles the mass of marginally stable interstellar clouds. The processes described may also account quantitatively for the metallicity of extragalactic space, though to check this the fraction of extragalactic baryons will need to be more firmly established.

  14. Time Dependent Models of Grain Formation Around Carbon Stars

    NASA Technical Reports Server (NTRS)

    Egan, M. P.; Shipman, R. F.

    1996-01-01

    Carbon-rich Asymptotic Giant Branch stars are sites of dust formation and undergo mass loss at rates ranging from 10(exp -7) to 10(exp -4) solar mass/yr. The state-of-the-art in modeling these processes is time-dependent models which simultaneously solve the grain formation and gas dynamics problem. We present results from such a model, which also includes an exact solution of the radiative transfer within the system.

  15. Star formation in NGC 6611 with ADONIS and Hubble.

    NASA Astrophysics Data System (ADS)

    Currie, D.; Kissell, K.; Shaya, E.; Avizonis, P.; Dowling, D.; Bonaccini, D.

    1996-12-01

    New details of the star-formation process have been revealed by a co-ordinated use of the ADONIS system on the 3.6-metre telescope at La Silla, in combination with data from the WFPC2 Camera of the Hubble Space Telescope. The authors illustrate some of the unique capabilities of the ADONIS system for high-resolution near-infrared observations of the stellar formation process.

  16. Star formation in M16 with ADONIS and Hubble

    NASA Astrophysics Data System (ADS)

    Currie, D.; Bonaccini, D.; Kissell, K.; Shaya, E.; Avizonis, P.; Dowling, D.

    1997-02-01

    New details of the star formation process have been revealed by a coordinated use of the ADONIS system on the 3.6 meter telescope at La Silla with data from the WFPC2 Camera of the Hubble Space Telescope. In this very preliminary report, we illustrate some of the unique capabilities of the ADONIS system for high-resolution observations of the stellar formation processes in the near infrared region.

  17. Resolved Star Formation Law In Nearby Infrared-bright Galaxies

    NASA Astrophysics Data System (ADS)

    Rahman, Nurur; Bolatto, A.; Wong, T.; Leroy, A.; Ott, J.; Calzetti, D.; Blitz, L.; Walter, F.; Rosolowsky, E.; West, A.; Vogel, S.; Bigiel, F.; Xue, R.

    2009-05-01

    An accurate knowledge of star formation law is crucial to make progress in understanding galaxy formation and evolution. We are studying this topic using CARMA STING (Survey Toward Infrared-bright Nearby Galaxies), an interferometric CO survey of a sample of 27 star-forming nearby galaxies with a wealth of multi-wavelength data designed to study star formation in environments throughout the blue sequence at sub-kpc scales. We present results for NGC 4254 (M99), one of our sample galaxies. We construct star formation rate surface density (SFRSD) and gas (atomic and molecular) surface density indicators using a combination of high resolution data from CARMA, KPNO, Spitzer, IRAM and VLA. We find a tight correlation between SFRSD and molecular gas surface density (MGSD), whereas the relation between atomic gas surface density and SFRSD shows very large scatter. Within the central 6 kpc (radius) where CARMA is the most sensitive the MGSD derived from CO(1-0) and CO(2-1) shows similar trend, however, in the extended disk the slope, derived from CO(2-1) data alone, gets steeper.

  18. 11HUGS & LVL: Star Formation Properties of Local Volume Galaxies

    NASA Astrophysics Data System (ADS)

    Lee, Janice C.; Gil de Paz, A.; Tremonti, C.; Kennicutt, R.; van Zee, L.; Sakai, S.; Funes, J. G.; LVL Team

    2007-12-01

    11HUGS, the 11 Mpc H-alpha UV Galaxy Survey, is a GALEX Legacy program designed to systematically characterize the star formation demographics of the Local Volume using a complete sample of 258 spiral and irregular galaxies within 11 Mpc. The dataset consists of snapshots of the instantaneous massive star formation as captured via narrowband H-alpha imaging, as well as GALEX NUV (1500 Å) and FUV (2300 Å) imaging, which traces star formation over a longer 1e8 yr timescale. UV observations of the 11HUGS sample are now 80% complete, and we use the available data, along with the completed H-alpha component of the survey, to investigate the consistency between UV and H-alpha derived star formation rates over a full range of activities down to ultra-low SFRs of 0.0001 M_sun/yr. We also provide a first look at the span of UV-FIR SED and dust properties using initial data from the follow-on Cycle 4 Spitzer Local Volume Legacy (LVL) survey, which is obtaining mid and far-IR imaging for the full sample.

  19. On the IMF in a Triggered Star Formation Context

    NASA Astrophysics Data System (ADS)

    Zhou, Tingtao; Huang, Chelsea X.; Lin, D. N. C.; Gritschneder, Matthias; Lau, Herbert

    2015-07-01

    The origin of the stellar initial mass function (IMF) is a fundamental issue in the theory of star formation. It is generally fit with a composite power law. Some clues on the progenitors can be found in dense starless cores that have a core mass function (CMF) with a similar shape. In the low-mass end, these mass functions increase with mass, albeit the sample may be somewhat incomplete; in the high-mass end, the mass functions decrease with mass. There is an offset in the turn-over mass between the two mass distributions. The stellar mass for the IMF peak is lower than the corresponding core mass for the CMF peak in the Pipe Nebula by about a factor of three. Smaller offsets are found between the IMF and the CMFs in other nebulae. We suggest that the offset is likely induced during a starburst episode of global star formation which is triggered by the formation of a few O/B stars in the multi-phase media, which naturally emerged through the onset of thermal instability in the cloud-core formation process. We consider the scenario that the ignition of a few massive stars photoionizes the warm medium between the cores, increases the external pressure, reduces their Bonnor-Ebert mass, and triggers the collapse of some previously stable cores. We quantitatively reproduce the IMF in the low-mass end with the assumption of additional rotational fragmentation.

  20. ON THE IMF IN A TRIGGERED STAR FORMATION CONTEXT

    SciTech Connect

    Zhou, Tingtao; Huang, Chelsea X.; Lin, D. N. C.; Gritschneder, Matthias

    2015-07-20

    The origin of the stellar initial mass function (IMF) is a fundamental issue in the theory of star formation. It is generally fit with a composite power law. Some clues on the progenitors can be found in dense starless cores that have a core mass function (CMF) with a similar shape. In the low-mass end, these mass functions increase with mass, albeit the sample may be somewhat incomplete; in the high-mass end, the mass functions decrease with mass. There is an offset in the turn-over mass between the two mass distributions. The stellar mass for the IMF peak is lower than the corresponding core mass for the CMF peak in the Pipe Nebula by about a factor of three. Smaller offsets are found between the IMF and the CMFs in other nebulae. We suggest that the offset is likely induced during a starburst episode of global star formation which is triggered by the formation of a few O/B stars in the multi-phase media, which naturally emerged through the onset of thermal instability in the cloud-core formation process. We consider the scenario that the ignition of a few massive stars photoionizes the warm medium between the cores, increases the external pressure, reduces their Bonnor–Ebert mass, and triggers the collapse of some previously stable cores. We quantitatively reproduce the IMF in the low-mass end with the assumption of additional rotational fragmentation.

  1. STAR FORMATION EFFICIENCY IN THE BARRED SPIRAL GALAXY NGC 4303

    SciTech Connect

    Momose, Rieko; Okumura, Sachiko K.; Sawada, Tsuyoshi; Koda, Jin E-mail: sokumura@nro.nao.ac.j E-mail: Jin.Koda@stonybrook.ed

    2010-09-20

    We present new {sup 12}CO (J = 1 - 0) observations of the barred galaxy NGC 4303 using the Nobeyama 45 m telescope (NRO45) and the Combined Array for Research in Millimeter-wave Astronomy (CARMA). The H{alpha} images of barred spiral galaxies often show active star formation in spiral arms, but less so in bars. We quantify the difference by measuring star formation rate (SFR) and star formation efficiency (SFE) at a scale where local star formation is spatially resolved. Our CO map covers the central 2.'3 region of the galaxy; the combination of NRO45 and CARMA provides a high fidelity image, enabling accurate measurements of molecular gas surface density. We find that SFR and SFE are twice as high in the spiral arms as in the bar. We discuss this difference in the context of the Kennicutt-Schmidt (KS) law, which indicates a constant SFR at a given gas surface density. The KS law breaks down at our native resolution ({approx}250 pc), and substantial smoothing (to 500 pc) is necessary to reproduce the KS law, although with greater scatter.

  2. Coronagraphic imaging of pre-main-sequence stars: Remnant evvelopes of star formation seen in reflection

    NASA Technical Reports Server (NTRS)

    Nakajima, Tadashi; Golimowski, David A.

    1995-01-01

    We have obtained R- and I-band coronagraphic images of the vicinities of 11 pre-main sequence (PMS) stars to search for faint, small-scale reflection nebulae. The inner radius of the search and the field of view are 1.9 arcsec and 1x1 arcmin, respectively. Reflection nebulae were imaged around RY Tau, T Tau,DG Tau, SU Aur, AB Aur, FU Ori, and Z CMa. No nebulae were detected around HBC 347, GG Tau, V773 Tau, and V830 Tau. Categorically speaking, most of the classical T Tauri program stars and all the FU Orionis-type program stars are associated with the reflection nebulae, while none of the weak-line T Tauri program stars are associated with nebulae. The detected nebulae range in size from 250 to 37 000 AU. From the brightness ratios of the stars and nebulae, we obtain a lower limit to the visual extinction of PMS star light through the nebulae of (A(sub V))(sub neb) = 0.1. The lower limits of masses and volume densities of the nebulae associated with the classical T Tauri stars are 10(exp-6) Solar mass and N(sub H) = 10(exp 5)/cu cm, respectively. Lower limits for the nebulae around FU Orionis stars are 10(exp -5) Solar mass and n(sub H) = 10 (exp 5)/cu cm, respectively. Some reflection nebulae may trace the illuminated surfaces of the optically thick dust nebulae, so these mass estimates are not stringent. All the PMS stars with associated nebulae are strong far-infrared emitters. Both the far-infrared emission and the reflection nebulae appear to originate from the remnant envelopes of star formation. The 100 micrometers emitting regions of SU Aur and FU Ori are likely to be cospatial with the reflection nebulae. A spatial discontinuity between FU Ori and its reflection nebula may explain the dip in the far-infrared spectral energy distribution at 60 micrometers. The warped, disk-like nebulae around T Tau and Z CMa are aligned with and embrace the inner star/circumstellar disk systems. The arc-shaped nebula around DG Tau may be in contact with the coaligned inner

  3. Quenching of the star formation activity in cluster galaxies

    NASA Astrophysics Data System (ADS)

    Boselli, A.; Roehlly, Y.; Fossati, M.; Buat, V.; Boissier, S.; Boquien, M.; Burgarella, D.; Ciesla, L.; Gavazzi, G.; Serra, P.

    2016-11-01

    We study the star formation quenching mechanism in cluster galaxies by fitting the spectral energy distribution (SED) of the Herschel Reference Survey, a complete volume-limited K-band-selected sample of nearby galaxies including objects in different density regions, from the core of the Virgo cluster to the general field. The SEDs of the target galaxies were fitted using the CIGALE SED modelling code. The truncated activity of cluster galaxies was parametrised using a specific star formation history with two free parameters, the quenching age QA and the quenching factor QF. These two parameters are crucial for the identification of the quenching mechanism, which acts on long timescales when starvation processes are at work, but is rapid and efficient when ram pressure occurs. To be sensitive to an abrupt and recent variation of the star formation activity, we combined twenty photometric bands in the UV to far-infrared in a new way with three age-sensitive Balmer line absorption indices extracted from available medium-resolution (R 1000) integrated spectroscopy and with Hα narrow-band imaging data. The use of a truncated star formation history significantly increases the quality of the fit in HI-deficient galaxies of the sample, that is to say, in those objects whose atomic gas content has been removed during the interaction with the hostile cluster environment. The typical quenching age of the perturbed late-type galaxies is QA ≲ 300 Myr whenever the activity of star formation is reduced by 50% < QF ≤ 80% and QA ≲ 500 Myr for QF > 80%, while that of the quiescent early-type objects is QA ≃ 1-3 Gyr. The fraction of late-type galaxies with a star formation activity reduced by QF > 80% and with an HI-deficiency parameter HI-def > 0.4 drops by a factor of 5 from the inner half virial radius of the Virgo cluster (R/Rvir < 0.5), where the hot diffuse X-ray emitting gas of the cluster is located, to the outer regions (R/Rvir > 4). The efficient quenching of the

  4. Star Formation near Berkeley 59: Embedded Protostars

    NASA Astrophysics Data System (ADS)

    Rosvick, J. M.; Majaess, D.

    2013-12-01

    A group of suspected protostars in a dark cloud northwest of the young (~2 Myr) cluster Berkeley 59 and two sources in a pillar south of the cluster have been studied in order to determine their evolutionary stages and ascertain whether their formation was triggered by Berkeley 59. Narrowband near-infrared observations from the Observatoire du Mont Mégantic, 12CO (J = 3-2) and SCUBA-2 (450 and 850 μm) observations from the JCMT, 2MASS, and WISE images, and data extracted from the IPHAS survey catalog were used. Of 12 sources studied, two are Class I objects, while three others are flat/Class II, one of which is a T Tauri candidate. A weak CO outflow and two potential starless cores are present in the cloud, while the pillar possesses substructure at different velocities, with no outflows present. The CO spectra of both regions show peaks in the range v LSR = -15 to -17 km s-1, which agrees with the velocity adopted for Berkeley 59 (-15.7 km s-1), while spectral energy distribution models yield an average interstellar extinction AV and distance of 15 ± 2 mag and 830 ± 120 pc, respectively, for the cloud, and 6.9 mag and 912 pc for the pillar, indicating that the regions are in the same vicinity as Berkeley 59. The formation of the pillar source appears to have been triggered by Berkeley 59. It is unclear whether Berkeley 59 triggered the association's formation.

  5. Testing diagnostics of triggered star formation

    NASA Astrophysics Data System (ADS)

    Haworth, Thomas J.; Harries, Tim J.; Acreman, David M.

    2012-10-01

    We produce synthetic images and SEDs from radiation hydrodynamical simulations of radiatively driven implosion. The imaged bright rimmed clouds (BRCs) are morphologically similar to those actually observed in star-forming regions. Using nebular diagnostic optical collisional line ratios, simulated Very Large Array (VLA) radio images, Hα imaging and SED fitting we compute the neutral cloud and ionized boundary layer (IBL) gas densities and temperatures and perform a virial stability analysis for each cloud. We determine that the neutral cloud temperatures derived by SED fitting are hotter than the dominant neutral cloud temperature by 1-2 K due to emission from warm dust. This translates into a change in the calculated cloud mass by 8-35 per cent. Using a constant mass conversion factor (Cν) for BRCs of different class is found to give rise to errors in the cloud mass of up to a factor of 3.6. The IBL electron temperature calculated using diagnostic line ratios is more accurate than assuming the canonical value adopted for radio diagnostics of 104 K. Both radio diagnostics and diagnostic line ratios are found to underestimate the electron density in the IBL. Each system is qualitatively correctly found to be in a state in which the pressure in the IBL is greater than the supporting cloud pressure, implying that the objects are being compressed. We find that observationally derived mass-loss estimates agree with those on the simulation grid and introduce the concept of using the mass-loss flux to give an indication of the relative strength of photoevaporative flow between clouds. The effect of beam size on these diagnostics in radio observations is found to be a mixing of the bright rim and ambient cloud and H II region fluxes, which leads to an underestimate of the cloud properties relative to a control diagnostic.

  6. The star formation rate distribution function of the local Universe

    NASA Astrophysics Data System (ADS)

    Bothwell, M. S.; Kennicutt, R. C.; Johnson, B. D.; Wu, Y.; Lee, J. C.; Dale, D.; Engelbracht, C.; Calzetti, D.; Skillman, E.

    2011-08-01

    We present total infrared (IR) and ultraviolet (UV) luminosity functions derived from large representative samples of galaxies at z˜ 0, selected at IR and UV wavelengths from the Imperial IRAS Faint Source Catalogue redshift data base (IIFSCz) catalogue, and the GALEX All-Sky Imaging Survey (AIS), respectively. We augment these with deep Spitzer and GALEX imaging of galaxies in the 11 Mpc Local Volume Legacy (LVL) Survey, allowing us to extend these luminosity functions to lower luminosities (˜106 L⊙), and providing good constraints on the slope of the luminosity function at the extreme faint end for the first time. Using conventional star formation prescriptions, we generate from our data the star formation rate (SFR) distribution function for the local Universe. We find that it has a Schechter form, the faint-end slope has a constant value (to the limits of our data) of α=-1.51 ± 0.08 and the ‘characteristic’ SFR ψ* is 9.2 M⊙ yr-1. We also show the distribution function of the SFR volume density; we then use this to calculate a value for the total SFR volume density at z˜ 0 of 0.025 ± 0.0016 M⊙ yr-1 Mpc-3, of which ˜20 per cent is occurring in starbursts. Decomposing the total star formation by infrared luminosity, it can be seen that 9 ± 1 per cent is due to LIRGs, and 0.7 ± 0.2 per cent is occurring in ULIRGs. By comparing UV and IR emission for galaxies in our sample, we also calculate the fraction of star formation occurring in dust-obscured environments, and examine the distribution of dusty star formation: we find a very shallow slope at the highly extincted end, which may be attributable to line-of-sight orientation effects as well as conventional internal extinction.

  7. On the Interplay between Star Formation and Feedback in Galaxy Formation Simulations

    NASA Astrophysics Data System (ADS)

    Agertz, Oscar; Kravtsov, Andrey V.

    2015-05-01

    We investigate the star formation-feedback cycle in cosmological galaxy formation simulations, focusing on the progenitors of Milky Way (MW)-sized galaxies. We find that in order to reproduce key properties of the MW progenitors, such as semi-empirically derived star formation histories (SFHs) and the shape of rotation curves, our implementation of star formation and stellar feedback requires (1) a combination of local early momentum feedback via radiation pressure and stellar winds, and subsequent efficient supernovae feedback, and (2) an efficacy of feedback that results in the self-regulation of the global star formation rate on kiloparsec scales. We show that such feedback-driven self-regulation is achieved globally for a local star formation efficiency per free fall time of {{ɛ }ff}≈ 10%. Although this value is larger that the {{ɛ }ff}˜ 1% value usually inferred from the Kennicutt-Schmidt (KS) relation, we show that it is consistent with direct observational estimates of {{ɛ }ff} in molecular clouds. Moreover, we show that simulations with local efficiency of {{ɛ }ff}≈ 10% reproduce the global observed KS relation. Such simulations also reproduce the cosmic SFH of the MW-sized galaxies and satisfy a number of other observational constraints. Conversely, we find that simulations that a priori assume an inefficient mode of star formation, instead of achieving it via stellar feedback regulation, fail to produce sufficiently vigorous outflows and do not reproduce observations. This illustrates the importance of understanding the complex interplay between star formation and feedback, and the detailed processes that contribute to the feedback-regulated formation of galaxies.

  8. EXTENDED STAR FORMATION IN THE INTERMEDIATE-AGE LARGE MAGELLANIC CLOUD STAR CLUSTER NGC 2209

    SciTech Connect

    Keller, Stefan C.; Mackey, A. Dougal; Da Costa, Gary S.

    2012-12-10

    We present observations of the 1 Gyr old star cluster NGC 2209 in the Large Magellanic Cloud made with the GMOS imager on the Gemini South Telescope. These observations show that the cluster exhibits a main-sequence turnoff that spans a broader range in luminosity than can be explained by a single-aged stellar population. This places NGC 2209 amongst a growing list of intermediate-age (1-3 Gyr) clusters that show evidence for extended or multiple epochs of star formation of between 50 and 460 Myr in extent. The extended main-sequence turnoff observed in NGC 2209 is a confirmation of the prediction in Keller et al. made on the basis of the cluster's large core radius. We propose that secondary star formation is a defining feature of the evolution of massive star clusters. Dissolution of lower mass clusters through evaporation results in only clusters that have experienced secondary star formation surviving for a Hubble time, thus providing a natural connection between the extended main-sequence turnoff phenomenon and the ubiquitous light-element abundance ranges seen in the ancient Galactic globular clusters.

  9. Visual binary stars: data to investigate formation of binaries

    NASA Astrophysics Data System (ADS)

    Kovaleva,, D.; Malkov,, O.; Yungelson, L.; Chulkov, D.

    Statistics of orbital parameters of binary stars as well as statistics of their physical characteristics bear traces of star formation history. However, statistical investigations of binaries are complicated by incomplete or missing observational data and by a number of observational selection effects. Visual binaries are the most common type of observed binary stars, with the number of pairs exceeding 130 000. The most complete list of presently known visual binary stars was compiled by cross-matching objects and combining data of the three largest catalogues of visual binaries. This list was supplemented by the data on parallaxes, multicolor photometry, and spectral characteristics taken from other catalogues. This allowed us to compensate partly for the lack of observational data for these objects. The combined data allowed us to check the validity of observational values and to investigate statistics of the orbital and physical parameters of visual binaries. Corrections for incompleteness of observational data are discussed. The datasets obtained, together with modern distributions of binary parameters, will be used to reconstruct the initial distributions and parameters of the function of star formation for binary systems.

  10. Inefficient star formation in extremely metal poor galaxies.

    PubMed

    Shi, Yong; Armus, Lee; Helou, George; Stierwalt, Sabrina; Gao, Yu; Wang, Junzhi; Zhang, Zhi-Yu; Gu, Qiusheng

    2014-10-16

    The first galaxies contain stars born out of gas with few or no 'metals' (that is, elements heavier than helium). The lack of metals is expected to inhibit efficient gas cooling and star formation, but this effect has yet to be observed in galaxies with an oxygen abundance (relative to hydrogen) below a tenth of that of the Sun. Extremely metal poor nearby galaxies may be our best local laboratories for studying in detail the conditions that prevailed in low metallicity galaxies at early epochs. Carbon monoxide emission is unreliable as a tracer of gas at low metallicities, and while dust has been used to trace gas in low-metallicity galaxies, low spatial resolution in the far-infrared has typically led to large uncertainties. Here we report spatially resolved infrared observations of two galaxies with oxygen abundances below ten per cent of the solar value, and show that stars formed very inefficiently in seven star-forming clumps in these galaxies. The efficiencies are less than a tenth of those found in normal, metal rich galaxies today, suggesting that star formation may have been very inefficient in the early Universe.

  11. Massive Star Formation: Characterising Infall and Outflow in dense cores.

    NASA Astrophysics Data System (ADS)

    Akhter, Shaila; Cunningham, Maria; Harvey-Smith, Lisa; Jones, Paul Andrew; Purcell, Cormac; Walsh, Andrew John

    2015-08-01

    Massive stars are some of the most important objects in the Universe, shaping the evolution of galaxies, creating chemical elements, and hence shaping the evolution of the Universe. However, the processes by which they form, and how they shape their environment during their birth processes, are not well understood. We are using NH3 data from the "The H2O Southern Galactic Plane Survey" (HOPS) to define the positions of dense cores/clumps of gas in the southern Galactic plane that are likely to form stars. Due to its effective critical density, NH3 can detect massive star forming regions effectively compared to other tracers. We did a comparative study with different methods for finding clumps and found Fellwalker as the best. We found ~ 10% of the star forming clumps with multiple components and ~ 90% clumps with single component along the line of sight. Then, using data from the "The Millimetre Astronomy Legacy Team 90 GHz" (MALT90) survey, we search for the presence of infall and outflow associated with these cores. We will subsequently use the "3D Molecular Line Radiative Transfer Code" (MOLLIE) to constrain properties of the infall and outflow, such as velocity and mass flow. The aim of the project is to determine how common infall and outflow are in star forming cores, hence providing valuable constraints on the timescales and physical process involved in massive star formation.

  12. STAR FORMATION NEAR BERKELEY 59: EMBEDDED PROTOSTARS

    SciTech Connect

    Rosvick, J. M.; Majaess, D.

    2013-12-01

    A group of suspected protostars in a dark cloud northwest of the young (∼2 Myr) cluster Berkeley 59 and two sources in a pillar south of the cluster have been studied in order to determine their evolutionary stages and ascertain whether their formation was triggered by Berkeley 59. Narrowband near-infrared observations from the Observatoire du Mont Mégantic, {sup 12}CO (J = 3-2) and SCUBA-2 (450 and 850 μm) observations from the JCMT, 2MASS, and WISE images, and data extracted from the IPHAS survey catalog were used. Of 12 sources studied, two are Class I objects, while three others are flat/Class II, one of which is a T Tauri candidate. A weak CO outflow and two potential starless cores are present in the cloud, while the pillar possesses substructure at different velocities, with no outflows present. The CO spectra of both regions show peaks in the range v {sub LSR} = –15 to –17 km s{sup –1}, which agrees with the velocity adopted for Berkeley 59 (–15.7 km s{sup –1}), while spectral energy distribution models yield an average interstellar extinction A{sub V} and distance of 15 ± 2 mag and 830 ± 120 pc, respectively, for the cloud, and 6.9 mag and 912 pc for the pillar, indicating that the regions are in the same vicinity as Berkeley 59. The formation of the pillar source appears to have been triggered by Berkeley 59. It is unclear whether Berkeley 59 triggered the association's formation.

  13. The First Stars: Binary and Small Multiple Formation

    NASA Astrophysics Data System (ADS)

    Stacy, A.; Greif, T. H.; Bromm, V.

    2010-10-01

    We investigate the formation of metal-free, Population III (Pop III), stars within a minihalo at z˜eq 20 with a smoothed particle hydrodynamics (SPH) simulation, starting from cosmological initial conditions. Employing a hierarchical, zoom-in procedure, we achieve sufficient numerical resolution to follow the collapsing gas in the center of the minihalo up to number densities of 1012 cm-3. This allows us to study the protostellar accretion onto the initial hydrostatic core, which we represent as a growing sink particle, in improved physical detail. The accretion process, and in particular its termination, governs the final masses that were reached by the first stars. The primordial initial mass function (IMF), in turn, played an important role in determining to what extent the first stars drove early cosmic evolution. We continue our simulation for 5000 yr after the first sink particle has formed. During this time period, a disk-like configuration is assembled around the first protostar. The disk is gravitationally unstable, develops a pronounced spiral structure, and fragments into several other protostellar seeds. At the end of the simulation, a small multiple system has formed, dominated by a binary with masses ˜ 40 Msun and ˜ 10 Msun. If Pop III stars were to form typically in binaries or small multiples, the standard model of primordial star formation, where single, isolated stars are predicted to form in minihaloes, would have to be modified. This would have crucial consequences for the observational signature of the first stars, such as their nucleosynthetic pattern, and the gravitational-wave emission from possible Pop III black-hole binaries.

  14. Star formation histories from resolved stellar populations in nearby galaxies

    NASA Astrophysics Data System (ADS)

    Gogarten, Stephanie Morris

    We present the results of three applications of using resolved stellar populations to derive star formation histories (SFHs) of regions in the nearby spiral galaxies M81 and NGC 300. We use data from the Advanced Camera for Surveys (ACS) Nearby Galaxy Survey Treasury (ANGST) and compare observed color- magnitude diagrams (CMDs) with synthetic CMDs from stellar evolution models to find the best-fitting combination of stellar ages and metallicities. In the outer disk of M81, we probe the stellar populations of small regions which are UV-bright but Ha-faint as well as HII regions. We determine that the HII regions contain more massive stars than the other regions and are therefore consistent with being at least a few Myr younger; however, we cannot rule out a truncated initial mass function as an explanation for the differences between these regions. Our data for NGC 300 cover the location of an unusual optical transient, NGC 300 OT2008-1, which has been speculated to represent a new class of objects. Despite the lack of an optical precursor for this object, we infer the mass of the progenitor by deriving the SFH from the stars surrounding the transient location, under the assumption that since most stars form in clusters, the population should be coeval. We find a star formation event of age 8-13 Myr and determine that the progenitor should be a star which has recently turned off the main sequence, of mass 12-17 [Special characters omitted.] . Expanding our view of NGC 300 to a radial strip of the disk from the center to 5.4 kpc, we divide the galaxy into radial bins and derive the SFH at each location. We find that the percentage of young stars in the outer regions is considerably greater than in the inner regions, but the slope of the surface density of the disk increases only slightly with time.

  15. Star and Planet Formation Science from NASA Mission Archives

    NASA Astrophysics Data System (ADS)

    Hillenbrand, Lynne

    Over the past decade, NASA's Great Observatories such as Spitzer, Hubble, and Chandra, its major international partnership platforms such as XMM-Newton, Herschel and Planck, and its other smaller (approximately) all-sky survey missions such as GALEX, 2MASS, and WISE, have produced a wealth of data on young stars and star forming regions. We propose to collect these particular data from archives and published literature, and organize, co-locate, and serve them in a fully searchable format. Our science needs dictate that we include all relevant photometric and spectroscopic information on known and suspected young (<1-100 Myr of age) nearby (within a few hundred pc to 1 kpc of the Sun) stars. This is a finite and tractable sample of objects, numbering less than 100,000, and the challenge is simply in doing the collation work. We will also use the assembled information to calculate systematically derived parameters for the stars and their disks. Addressable science questions of interest to NASA include those of e.g. stellar accretion history, young star ages and age spreads in clusters, stellar masses and the initial mass function in clusters, stellar angular momentum and activity evolution, circumstellar and debris disk evolution, and planet formation and early planetary system evolution - notably including the correlations with stellar and disk properties. A recent scientific focus has been on young star variability arising from both stellar and circumstellar phenomena, exploiting available time series data from Spitzer/Warm and Kepler/K2 data sets. However, the broader ensemble of NASA data products such as we propose to collect here for these stars, is needed in order to carry out the science analysis for the existing K2 and Spitzer time series data, not just the lightcurves themselves.

  16. The star cluster formation history of the LMC

    NASA Astrophysics Data System (ADS)

    Baumgardt, H.; Parmentier, G.; Anders, P.; Grebel, E. K.

    2013-03-01

    The Large Magellanic Cloud (LMC) is one of the nearest galaxies to us and is one of only few galaxies where the star formation history can be determined from studying resolved stellar populations. We have compiled a new catalogue of ages, luminosities and masses of LMC star clusters and used it to determine the age distribution and dissolution rate of LMC star clusters. We find that the frequency of massive clusters with masses M > 5000 M⊙ is almost constant between 10 and 200 Myr, showing that the influence of residual gas expulsion is limited to the first 10 Myr of cluster evolution or clusters less massive than 5000 M⊙. Comparing the cluster frequency in that interval with the absolute star formation rate, we find that about 15 per cent of all stars in the LMC were formed in long-lived star clusters that survive for more than 10 Myr. We also find that the mass function of LMC clusters younger than 109 Gyr can be fitted by a power-law mass function N(m) ˜ m-α with slope α = 2.3, while older clusters follow a significantly shallower slope and interpret that this is a sign of either incompleteness or the ongoing dissolution of low-mass clusters. Our data show that for ages older than 200 Myr, about 90 per cent of all clusters are lost per dex of lifetime. The implied cluster dissolution rate is significantly faster than that based on analytic estimates and N-body simulations. Our cluster age data finally show evidence for a burst in cluster formation about 109 yr ago, but little evidence for bursts at other ages.

  17. Nature of massive emission-line stars of the LMC NGC 1850 star-formation region

    NASA Astrophysics Data System (ADS)

    Garrido, H.; Aguayo, G.; Martayan, C.; Baade, D.

    2013-06-01

    Based on an analysis of slitless spectroscopic data we obtained with the ESO Wide Field Imager, we present the identification and nature of 96 massive emission-line stars (ELS) located in and around the LMC clusters NGC 1850, NGC 1855, and NGC 1858. Most of the ELS are concentrated around the young double cluster NGC 1850 and its vicinity. Combined to the photometry and lightcurves, these observations suggest that the NGC 1850 star-formation history has followed different episodes due to the dynamical interaction between clusters, photo-ionization and compression of the associated H II region, leading to other recent star formation burst. The actual ELS localization also seems to indicate a possible mass and spatial segregation with the evolution/age of the clusters.

  18. Major mergers are not significant drivers of star formation or morphological transformation around the epoch of peak cosmic star formation

    NASA Astrophysics Data System (ADS)

    Lofthouse, E. K.; Kaviraj, S.; Conselice, C. J.; Mortlock, A.; Hartley, W.

    2017-03-01

    We investigate the contribution of major mergers (mass ratios >1: 5) to stellar mass growth and morphological transformations around the epoch of peak cosmic star formation (z ∼ 2). We visually classify a complete sample of massive (M > 1010M⊙) galaxies at this epoch, drawn from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, into late-type galaxies, major mergers, spheroids and disturbed spheroids which show morphological disturbances. Given recent simulation work, which indicates that recent (<0.3-0.4 Gyr) major-merger remnants exhibit clear tidal features in such images, we use the fraction of disturbed spheroids to probe the role of major mergers in driving morphological transformations. The percentage of blue spheroids (i.e. with ongoing star formation) that show morphological disturbances is only 21 ± 4 per cent, indicating that major mergers are not the dominant mechanism for spheroid creation at z ∼ 2 - other processes, such as minor mergers or cold accretion are likely to be the main drivers of this process. We also use the rest-frame U-band luminosity as a proxy for star formation to show that only a small fraction of the star formation budget (∼3 per cent) is triggered by major mergers. Taken together, our results show that major mergers are not significant drivers of galaxy evolution at z ∼ 2.

  19. Environmental effects on star formation in dwarf galaxies and star clusters

    NASA Astrophysics Data System (ADS)

    Pasetto, S.; Cropper, M.; Fujita, Y.; Chiosi, C.; Grebel, E. K.

    2015-01-01

    Context. The role of the environment in the formation of a stellar population is a difficult problem in astrophysics. The reason is that similar properties of a stellar population are found in star systems embedded in different environments or, vice versa, similar environments contain stellar systems with stellar populations having different properties. Aims: In this paper, we develop a simple analytical criterion to investigate the role of the environment on the onset of star formation. We will consider the main external agents that influence star formation (i.e. ram pressure, tidal interaction, Rayleigh-Taylor and Kelvin-Helmholtz instabilities) in a spherical galaxy moving through an external environment. The theoretical framework developed here has direct applications to the cases of dwarf galaxies in galaxy clusters and dwarf galaxies orbiting our Milky Way system, as well as any primordial gas-rich cluster of stars orbiting within its host galaxy. Methods: We develop an analytic formalism to solve the fluid dynamics equations in a non-inertial reference frame mapped with spherical coordinates. The two-fluids instability at the interface between a stellar system and its surrounding hotter and less dense environment is related to the star formation processes through a set of differential equations. The solution presented here is quite general, allowing us to investigate most kinds of orbits allowed in a gravitationally bound system of stars in interaction with a major massive companion. Results: We present an analytical criterion to elucidate the dependence of star formation in a spherical stellar system (as a dwarf galaxy or a globular cluster) on its surrounding environment useful in theoretical interpretations of numerical results as well as observational applications. We show how spherical coordinates naturally enlighten the interpretation of two-fluids instability in a geometry that directly applies to an astrophysical case. This criterion predicts the

  20. Calibration of Star Formation Rates Across the Electromagnetic Spectrum

    NASA Technical Reports Server (NTRS)

    Cardiff, Ann H.

    2011-01-01

    Measuring and mapping star-forming activity in galaxies is a key element for our understanding of their broad- band spectra, and their structure and evolution in our local, as well as the high-redshift Universe. The main tool we use for these measurements is the observed luminosity in various spectral lines and/or continuum bands. However, the available star-formation rate (SFR) indicators are often discrepant and subject to physical biases and calibration uncertainties. We are organizing a special session at the 2012 IAU General Assembly in Beijing, China (August 20-31, 2012) in order to bring together theoreticians and observers working in different contexts of star-formation to discuss the status of current SFR indicators, to identify open issues and to define a strategic framework for their resolution. The is an ideal time to synthesize information from the current golden era of space astrophysics and still have influence on the upcoming missions that will broaden our view of star-formation. We will be including high-energy constraints on SFR in the program and encourage participation from the high energy astrophysics community.

  1. Cosmic evolution of star formation properties of galaxies

    NASA Astrophysics Data System (ADS)

    Kim, Sungeun

    2014-01-01

    Development of bolometer array and camera at submillimeter wavelength has played an important role in detecting submillimeter bright galaxies, so called submillimeter galaxies. These galaxies seem to be progenitors of present-day massive galaxies and account for their considerable contributions to the light from the early universe and their expected high star formation rates if there is a close link between the submillimeter galaxies and the star formation activities, and the interstellar dust in galaxies is mainly heated by the star light. We review assembly of submillimeter galaxies chosen from the AzTEC and the Herschel SPIRE/PACS data archives, and investigate their spectral energy distribution fits including the data at other wavelengths to deduce details about stellar parameters including star formation rates and parameters yielding the metallicity, composition and abundance in dust, and disc structure of these galaxies. This work has been supported in part by Mid-career Researcher Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology 2011-0028001.

  2. Formation of Planets Around the Sun and Other Stars

    SciTech Connect

    Lin, Doug

    2005-11-14

    The quest to understand the formation of planets and planetary systems has entered an era of renaissance. Driven by observational discoveries in solar system exploration, protostellar disks, and extra solar planets, we have established a rich data bank which contains not only relic clues around mature stars, including the Sun, but also direct image of ongoing processes around young stars. For the first time in this scientific endeavor, we have adequate information to construct quantitative models to account for the ubiquity of planets and diversity of planetary systems. Some of the most intriguing theoretical questions facing us today include: (a) how did the planets in the solar system form with their present-day mass, composition, and orbital elements, (b) is planet formation a deterministic or chaotic process, and (c) what are the observable signatures of planet formation and evolution around nearby young and mature stars? I will present a comprehensive scenario which suggests (a) gas giant planets formed through coagulation of planetsimals and gas accretion onto earth-like cores; (b) the final assemblage of the terrestrial planets in the solar system occurred through the propagation of Jupiter's secular resonance 4-30 Myrs after the emergence of the gas giant; and (c) although they are yet to be discovered, Earth-like planets are expected to be common around nearby stars.

  3. Infrared Spectroscopy of Star Formation in Galactic and Extragalactic Regions

    NASA Technical Reports Server (NTRS)

    Frogel, Jay (Technical Monitor); Smith, Howard A.

    2004-01-01

    In this program we proposed to perform a series of spectroscopic studies, including data analysis and modeling, of star formation regions using an ensemble of archival space-based data from the Infrared Space Observatory's Long Wavelength Spectrometer and Short Wavelength Spectrometer, and to take advantage of other spectroscopic databases including the first results from SIRTF. Our empha- sis has been on star formation in external, bright IR galaxies, but other areas of research have in- cluded young, low or high mass pre-main sequence stars in star formation regions, and the galactic center. The OH lines in the far infrared were proposed as one key focus of this inquiry because the Principal Investigator (H. Smith) had a full set of OH IR lines from IS0 observations. It was planned that during the proposed 2-1/2 year timeframe of the proposal other data (including perhaps from SIRTF) would become available, and we intended to be responsive to these and other such spec- troscopic data sets. Three papers are included:The Infrared Lines of OH: Diagnostics of Molecular Cloud Conditions in Infrared Bright Galaxies; The Far-Infrared Spectrum of Arp 220; andThe Far-Infrared Emission Line and Continuum Spectrum of the Seyfert Galaxy NGC 1068.

  4. Star Formation in Space and Time: Taurus-Auriga

    NASA Astrophysics Data System (ADS)

    Palla, Francesco; Stahler, Steven W.

    2002-12-01

    To understand the formation of stellar groups, one must first document carefully the birth pattern within real clusters and associations. In this study of Taurus-Auriga, we combine pre-main-sequence ages from our own evolutionary tracks with stellar positions from observational surveys. Aided by the extensive millimeter data on the molecular clouds, we develop a picture of the region's history. Star formation began, at a relatively low level and in a spatially diffuse manner, at least 107 yr in the past. Within the last few million years, new stars have been produced at an accelerating rate, almost exclusively within a confined group of striated cloud filaments. The gas both inside and around the filaments appears to be in force balance. Thus, the appearance of the filaments is due to global, quasi-static contraction of the parent cloud material. Gravity drives this contraction and shock dissipation mediates it, but the internal motion of the gas does not appear to be turbulent. The accelerating nature of recent star formation means that the condensation of cloud cores is a threshold phenomenon, requiring a minimum background density. Other, nearby cloud regions, including Lupus and Chamaeleon, contain some locales that have attained this density, and others that have not. In the latter, we find extensive and sometimes massive molecular gas that is still devoid of young stars.

  5. Observational Research on Star and Planetary System Formation

    NASA Technical Reports Server (NTRS)

    Simpson, Janet P.

    1998-01-01

    Institute scientists collaborate with a number of NASA Ames scientists on observational studies of star and planetary system formation to their mutual benefit. As part of this collaboration, SETI scientists have, from 1988 to the present: (1) contributed to the technical studies at NASA Ames of the Stratospheric Observatory for Infrared Astronomy (SOFIA), an infrared 2.5 meter telescope in a Boeing 747, which will replace the Kuiper Airborne Observatory (KAO), a 0.9 meter telescope in a Lockheed C-141. SOFIA will be an important facility for the future exploration of the formation of stars and planetary systems, and the origins of life, and as such will be an important future facility to SETI scientists; (2) worked with the Laboratory Astrophysics Group at Ames, carrying out laboratory studies of the spectroscopic properties of ices and pre-biotic organics, which could be formed in the interstellar or interplanetary media; (3) helped develop a photometric approach for determining the Frequency of Earth-Sized Inner Planets (FRESIP) around solar-like stars, a project (now called Kepler) which complements the current efforts of the SETI Institute to find evidence for extraterrestrial intelligence; and (4) carried out independent observational research, in particular research on the formation of stars and planetary systems using both ground-based telescopes as well as the KAO.

  6. Star formation in Taurus Auriga Perseus and California nebulae

    NASA Astrophysics Data System (ADS)

    Tóth, L. Viktor; Zahorecz, Sarolta; Marton, Gabor; Doi, Yasuo; Onishi, Toshikazu; Tokuda, Kazuki

    Star formation and interstellar medium (ISM) structure were investigated in the Taurus, Auriga, Perseus and California (TAP) nearby star forming regions. Properties of the cold ISM was derived using AKARI FIR all sky maps, the Osaka-1.85m CO survey focusing to the all-sky Planck catalogue of Galactic Cold Clumps (PGCC). As many as 1041 infrared point sources were classified as young stellar object (YSO) based on multiband photometric data, and 384 of those are associated to a PGCC object. About 30% of the TAP PGCC clumps have associated YSOs.

  7. Induced massive star formation in the trifid nebula?

    PubMed

    Cernicharo; Lefloch; Cox; Cesarsky; Esteban; Yusef-Zadeh; Mendez; Acosta-Pulido; Garcia Lopez RJ; Heras

    1998-10-16

    The Trifid nebula is a young (10(5) years) galactic HII region where several protostellar sources have been detected with the infrared space observatory. The sources are massive (17 to 60 solar masses) and are associated with molecular gas condensations at the edges or inside the nebula. They appear to be in an early evolutionary stage and may represent the most recent generation of stars in the Trifid. These sources range from dense, apparently still inactive cores to more evolved sources, undergoing violent mass ejection episodes, including a source that powers an optical jet. These observations suggest that the protostellar sources may have evolved by induced star formation in the Trifid nebula.

  8. Neutron-star formation in the carbon-detonation supernova.

    NASA Technical Reports Server (NTRS)

    Wheeler, J. C.; Buchler, J.-R.; Barkat, Z. K.

    1973-01-01

    Neutrino losses, such as those driven by the convective Urca process, may affect the evolution of stars in the mass range from 4 to 8 solar masses so as to lead to collapse of their degenerate carbon/oxygen cores. A corresponding hydrodynamic model is computed which leads to the formation of a 1.3 to 1.4 solar mass neutron star with the expulsion of a small fraction of the mass, about 0.l solar mass at about 20,000 km/sec into the overlying hydrogen envelope. This sets the stage for the Ostriker-Gunn mechanism in which Type II supernovae and pulsars are formed.

  9. High-Velocity Star Formation in the Large Magellanic Cloud.

    PubMed

    Graff; Gould

    2000-05-01

    Light-echo measurements show that SN 1987A is 425 pc behind the LMC disk. It is continuing to move away from the disk at 18 km s-1. Thus, it has been suggested that SN 1987A was ejected from the LMC disk. However, SN 1987A is a member of a star cluster, so this entire cluster would have to have been ejected from the disk. We show that the cluster was formed in the LMC disk, with a velocity perpendicular to the disk of about 50 km s-1. Such high-velocity formation of a star cluster is unusual, having no known counterpart in the Milky Way.

  10. The Formation and Early Evolution of Embedded Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    Barnes, Peter

    We propose to combine Spitzer, WISE, Herschel, and other archival spacecraft data with an existing ground- and space-based mm-wave to near-IR survey of molecular clouds over a large portion of the Milky Way, in order to systematically study the formation and early evolution of massive stars and star clusters, and provide new observational calibrations for a theoretical paradigm of this key astrophysical problem. Central Objectives: The Galactic Census of High- and Medium-mass Protostars (CHaMP) is a large, unbiased, uniform, and panchromatic survey of massive star and cluster formation and early evolution, covering 20°x6° of the Galactic Plane. Its uniqueness lies in the comprehensive molecular spectroscopy of 303 massive dense clumps, which have also been included in several archival spacecraft surveys. Our objective is a systematic demographic analysis of massive star and cluster formation, one which has not been possible without knowledge of our CHaMP cloud sample, including all clouds with embedded clusters as well as those that have not yet formed massive stars. For proto-clusters deeply embedded within dense molecular clouds, analysis of these space-based data will: 1. Yield a complete census of Young Stellar Objects in each cluster. 2. Allow systematic measurements of embedded cluster properties: spectral energy distributions, luminosity functions, protostellar and disk fractions, and how these vary with cluster mass, age, and density. Combined with other, similarly complete and unbiased infrared and mm data, CHaMP's goals include: 3. A detailed comparison of the embedded stellar populations with their natal dense gas to derive extinction maps, star formation efficiencies and feedback effects, and the kinematics, physics, and chemistry of the gas in and around the clusters. 4. Tying the demographics, age spreads, and timescales of the clusters, based on pre-Main Sequence evolution, to that of the dense gas clumps and Giant Molecular Clouds. 5. A

  11. 2nd Iberian Nuclear Astrophysics Meeting on Compact Stars

    NASA Astrophysics Data System (ADS)

    Perez-Garcia, M. Angeles; Pons, Jose; Albertus, C.

    2012-02-01

    ORGANIZING COMMITTEE Dr M Ángeles Pérez-García (Área Física Teórica-Universidad de Salamanca & IUFFYM) Dr J A Miralles (Universidad de Alicante) Dr J Pons (Universidad de Alicante) Dr C Albertus (Área Física Nuclear-Universidad de Salamanca & IUFFYM) Dr F Atrio (Área Física Teórica-Universidad de Salamanca & IUFFYM) PREFACE The second Iberian Nuclear Astrophysics meeting was held at the University of Salamanca, Spain on 22-23 September 2011. This volume contains most of the presentations delivered at this international workshop. This meeting was the second in the series following the previous I Encuentro Ibérico de Compstar, held at the University of Coimbra, Portugal in 2010. The main purpose of this meeting was to strengthen the scientific collaboration between the participants of the Iberian and the rest of the southern European branches of the European Nuclear Astrophysics network, formerly, COMPSTAR. This ESF (European Science Foundation) supported network has been crucial in helping to make a broader audience for the the most interesting and relevant research lines being developed currently in Nuclear Astrophysics, especially related to the physics of neutron stars. It is indeed important to emphasize the need for a collaborative approach to the rest of the scientific communities so that we can reach possible new members in this interdisciplinary area and as outreach for the general public. The program of the meeting was tailored to theoretical descriptions of the physics of neutron stars although some input from experimental observers and other condensed matter and optics areas of interest was also included. The main scientific topics included: Magnetic fields in compact stars Nuclear structure and in-medium effects in nuclear interaction Equation of state: from nuclear matter to quarks Importance of crust in the evolution of neutron stars Computational simulations of collapsing dense objects Observational phenomenology In particular, leading

  12. Does radiative feedback by the first stars promote or prevent second generation star formation?

    NASA Astrophysics Data System (ADS)

    Ahn, Kyungjin; Shapiro, Paul R.

    2007-03-01

    We study the effect of starlight from the first stars on the ability of other minihaloes in their neighbourhood to form additional stars. The first stars in the Λ cold dark matter (ΛCDM) universe are believed to have formed in minihaloes of total mass ~105-6 Msolar at redshifts z >~ 20, when molecular hydrogen (H2) formed and cooled the dense gas at their centres, leading to gravitational collapse. Simulations suggest that the Population III (Pop III) stars thus formed were massive (~100 Msolar) and luminous enough in ionizing radiation to cause an ionization front (I-front) to sweep outward, through their host minihalo and beyond, into the intergalactic medium. Our previous work suggested that this I-front was trapped when it encountered other, nearby minihaloes, and that it failed to penetrate the dense gas at their centres within the lifetime of the Pop III stars (<~3 Myr). The question of what the dynamical consequences were for these target minihaloes, of their exposure to the ionizing and dissociating starlight from the Pop III star requires further study, however. Towards this end, we have performed a series of detailed, one-dimensional (1D), radiation-hydrodynamical simulations to answer the question of whether star formation in these surrounding minihaloes was triggered or suppressed by radiation from the first stars. We have varied the distance to the source (and, hence, the flux) and the mass and evolutionary stage of the target haloes to quantify this effect. We find (1) trapping of the I-front and its transformation from R-type to D-type, preceded by a shock front; (2) photoevaporation of the ionized gas (i.e. all gas originally located outside the trapping radius); (3) formation of an H2 precursor shell which leads the I-front, stimulated by partial photoionization; and (4) the shock-induced formation of H2 in the minihalo neutral core when the shock speeds up and partially ionizes the gas. The fate of the neutral core is mostly determined by the

  13. Fireworks of Star Formation Light Up a Galaxy

    NASA Technical Reports Server (NTRS)

    2000-01-01

    Located some 13 million light-years from Earth, NGC 4214 is currently forming clusters of new stars from its interstellar gas and dust. In this Hubble image, we can see a sequence of steps in the formation and evolution of stars and star clusters. The picture was created from exposures taken in several color filters with Hubble's Wide Field Planetary Camera 2. NGC 4214 contains a multitude of faint stars covering most of the frame, but the picture is dominated by filigreed clouds of glowing gas surrounding bright stellar clusters. The youngest of these star clusters are located at the lower right of the picture, where they appear as about half a dozen bright clumps of glowing gas. Young, hot stars have a whitish to bluish color in the Hubble image, because of their high surface temperatures, ranging from 10,000 up to about 50,000 degrees Celsius. The radiation and wind forces from the young stars literally blow bubbles in the gas. Over millions of years, the bubbles increase in size as the stars inside them grow older. Moving to the lower left from the youngest clusters, we find an older star cluster, around which a gas bubble has inflated to the point that there is an obvious cavity around the central cluster. The most spectacular feature in the Hubble picture lies near the center of NGC 4214. This object is a cluster of hundreds of massive blue stars, each of them more than 10,000 times brighter than our own Sun. A vast heart-shaped bubble, inflated by the combined stellar winds and radiation pressure, surrounds the cluster. The expansion of the bubble is augmented as the most massive stars in the center reach the ends of their lives and explode as supernovae. The principal astronomers are: John MacKenty, Jesus Maiz-Apellaniz (Space Telescope Science Institute), Colin Norman (Johns Hopkins University), Nolan Walborn (Space Telescope Science Institute), Richard Burg (Johns Hopkins University), Richard Griffiths (Carnegie Mellon University), and Rosemary Wyse

  14. The Influence Of Environment On The Star Formation Properties Of Galaxies

    NASA Astrophysics Data System (ADS)

    Rodriguez Del Pino, Bruno

    2015-10-01

    star formation properties and nuclear activity in galaxies in a multi-cluster system at z 0.165. We employ Tuneable Filter observations to map the Halpha and N[II] emission lines. We show the feasibility and advantages of using these type of observations to map emission lines in a large number of objects at a single redshift, and developed a procedure for the reduction and analysis of the data. We find a large number of optical AGN that were not previously detected as X-ray point sources. The probability that a galaxy hosts an AGN is not found to correlate with environment. From the analysis of the integrated star formation properties of the galaxies in the multi-cluster system we observe a significant number of galaxies with suppressed star formation with respect to the field. Although stellar mass is the main driver of the suppression of star formation, once its effect is removed, we find that galaxies in the core regions have reduced specific star formation rates (SSFRs) with respect to the infall regions. Moreover, the environment influences galaxies differently depending on their stellar mass. Galaxies with low masses experience a change in morphology (from irregulars and spirals to early-types) and colour (blue to red) as they fall into regions of higher density. However, many massive spiral galaxies retain their disk morphologies and the visibility of their spiral arms all the way to the core regions. Before becoming passive, these galaxies experience a phase exhibiting red colours and relatively high SSFRs. A significant fraction of the spiral galaxies with relatively high masses go through this phase, which could represent the transition towards becoming S0s. We finish by presenting some interesting results on the spatial distribution of the emission-line regions in the cluster galaxies. We develop a method to create emission-line images, which successfully preserves the flux within the emission lines. Our analysis on the concentrations and sizes of the star

  15. The evolution of galaxies. III - Metal-enhanced star formation

    NASA Technical Reports Server (NTRS)

    Talbot, R. J., Jr.; Arnett, W. D.

    1973-01-01

    The problem of the paucity of low-metal-abundance low-mass stars is discussed. One alternative to the variable-initial-mass-function (VIMF) solution is proposed. It is shown that this solution - metal-enhanced star formation - satisfies the classical test which prompted the VIMF hypothesis. Furthermore, with no additional parameters it provides improved fits to other tests - e.g., inhomogeneities in the abundances in young stars, concordance of all nucleo-cosmochronologies, and a required yield of heavy-element production which is consistent with current stellar evolution theory. In this model the age of the Galaxy is 18.6 plus or minus 5.7 b.y.

  16. A recent burst in the star formation history of LMC

    NASA Astrophysics Data System (ADS)

    Bertelli, Gianpaolo; Bressan, Alessandro; Chiosi, Cesare; Mateo, Mario

    We present deep photometric observations of stars in three fields of the Large Magellanic Cloud (LMC), and interpret these data using synthetic color-magnitude diagrams (CMDs) generated from the overshoot models of Bertelli et al. (1985, 1986, 1990), Bressan et al. (1986), and Aparicio et al. (1990) and from the classical models of Fagotto (1990). We can successfully model the field CMDs and LFs with a star-formation rate that experienced a large increase at a certain age of its history. Only overshoot models are able to provide a unique age of the sudden increase common to the three fields. Our study shows that this phenomenon happened about 4 x 10 exp 9 yrs ago adopting the following constraints: the slope of the initial mass function equal to 2.35 (the Salpeter value), a mean field-star metallicity of about -0.7, and the distance modulus of LMC equal to 18.4.

  17. MSU Contributes to New Research on Star Formation

    NASA Astrophysics Data System (ADS)

    2010-01-01

    EAST LANSING, Mich. - "Crazy" and "cool" are two of the words Michigan State University astronomer Megan Donahue uses to describe the two distinct "tails" found on a long tail of gas that is believed to be forming stars where few stars have been formed before. Donahue was part of an international team of astronomers that viewed the gas tail with a very long, new observation made by the Chandra X-ray Observatory and detailed it in a paper published this month in the publication Astrophysical Journal. "The double tail is very cool - that is, interesting - and ridiculously hard to explain," said Donahue, a professor in MSU's Department of Physics and Astronomy. "It could be two different sources of gas or something to do with magnetic fields. We just don't know." What is also unusual is the gas tail, which is more than 200,000 light years in length, extends well outside any galaxy. It is within objects such as this that new stars are formed, but usually within the confines of a galaxy. "This system is really crazy because where we're seeing the star formation is well away from any galaxy," Donahue said. "Star formation happens primarily in the disks of galaxies. What we're seeing here is very unexpected." This gas tail was originally spotted by astronomers three years ago using a multitude of telescopes, including NASA's Chandra X-ray Observatory and the SOuthern Astrophysical Research telescope, a Chilean-based observatory in which MSU is one of the partners. The new observations show a second tail, and a fellow galaxy, ESO 137-002, that also has a tail of hot X-ray-emitting gas. How these newly formed stars came to be in this particular place remains a mystery as well. Astronomers theorize this gas tail might have "pulled" star-making material from nearby gases, creating what some have called "orphan stars." "This system continues to surprise us as we get better observations of it," Donahue said. The gas tail is located in the southern hemisphere near a

  18. THE STAR FORMATION LAWS OF EDDINGTON-LIMITED STAR-FORMING DISKS

    SciTech Connect

    Ballantyne, D. R.; Armour, J. N.; Indergaard, J.

    2013-03-10

    Two important avenues into understanding the formation and evolution of galaxies are the Kennicutt-Schmidt (K-S) and Elmegreen-Silk (E-S) laws. These relations connect the surface densities of gas and star formation ({Sigma}{sub gas} and {Sigma}-dot{sub *}, respectively) in a galaxy. To elucidate the K-S and E-S laws for disks where {Sigma}{sub gas} {approx}> 10{sup 4} M{sub Sun} pc{sup -2}, we compute 132 Eddington-limited star-forming disk models with radii spanning tens to hundreds of parsecs. The theoretically expected slopes ( Almost-Equal-To 1 for the K-S law and Almost-Equal-To 0.5 for the E-S relation) are relatively robust to spatial averaging over the disks. However, the star formation laws exhibit a strong dependence on opacity that separates the models by the dust-to-gas ratio that may lead to the appearance of a erroneously large slope. The total infrared luminosity (L{sub TIR}) and multiple carbon monoxide (CO) line intensities were computed for each model. While L{sub TIR} can yield an estimate of the average {Sigma}-dot{sub *} that is correct to within a factor of two, the velocity-integrated CO line intensity is a poor proxy for the average {Sigma}{sub gas} for these warm and dense disks, making the CO conversion factor ({alpha}{sub CO}) all but useless. Thus, observationally derived K-S and E-S laws at these values of {Sigma}{sub gas} that uses any transition of CO will provide a poor measurement of the underlying star formation relation. Studies of the star formation laws of Eddington-limited disks will require a high-J transition of a high density molecular tracer, as well as a sample of galaxies with known metallicity estimates.

  19. STAR FORMATION IN THE TAURUS FILAMENT L 1495: FROM DENSE CORES TO STARS

    SciTech Connect

    Schmalzl, Markus; Kainulainen, Jouni; Henning, Thomas; Launhardt, Ralf; Quanz, Sascha P.; Alves, Joao; Goodman, Alyssa A.; Pineda, Jaime E.; Roman-Zuniga, Carlos G.

    2010-12-10

    We present a study of dense structures in the L 1495 filament in the Taurus Molecular Cloud and examine its star-forming properties. In particular, we construct a dust extinction map of the filament using deep near-infrared observations, exposing its small-scale structure in unprecedented detail. The filament shows highly fragmented substructures and a high mass-per-length value of M{sub line} = 17 M{sub sun} pc{sup -1}, reflecting star-forming potential in all parts of it. However, a part of the filament, namely B 211, is remarkably devoid of young stellar objects. We argue that in this region the initial filament collapse and fragmentation is still taking place and star formation is yet to occur. In the star-forming part of the filament, we identify 39 cores with masses from 0.4 to 10 M{sub sun} and preferred separations in agreement with the local Jeans length. Most of these cores exceed the Bonnor-Ebert critical mass, and are therefore likely to collapse and form stars. The dense core mass function follows a power law with exponent {Gamma} = 1.2 {+-} 0.2, a form commonly observed in star-forming regions.

  20. Smoothly rising star formation histories during the reionization epoch

    NASA Astrophysics Data System (ADS)

    Finlator, Kristian; Oppenheimer, Benjamin D.; Davé, Romeel

    2011-01-01

    Cosmological hydrodynamic simulations robustly predict that high-redshift galaxy star formation histories (SFHs) are smoothly rising and vary with mass only by a scalefactor. We use our latest simulations to test whether this scenario can account for recent observations at z≥ 6 from WFC3/IR, NICMOS and IRAC. Our simulations broadly reproduce the observed ultraviolet (UV) luminosity functions and stellar mass densities and their evolution at z= 6-8, all of which are non-trivial tests of the mean SFH. In agreement with observations, simulated galaxies possess blue UV continua owing to young ages (50-150 Myr), low metallicities (0.1-0.5 Z⊙) and low dust columns [E(B-V) ≤ 0.05]. Our predicted Balmer breaks at z= 7, while significant, are ≈0.5 mag weaker than observed even after accounting for nebular line emission, suggesting observational systematic errors and/or numerical resolution limitations. Observations imply a near-unity slope in the stellar mass-star formation rate relation at all z= 6-8, confirming the prediction that SFH shapes are invariant. Dust extinction suppresses the UV luminosity density by a factor of 2-3, with suppression increasing modestly to later times owing to increasing metallicities. Current surveys detect the majority of galaxies with stellar masses exceeding 109 M⊙ and few galaxies less massive than 108.5 M⊙, implying that they probe no more than the brightest ≈30 per cent of the complete star formation and stellar mass densities at z≥ 6. Finally, we demonstrate that there is no conflict between smoothly rising SFHs and recent clustering observations. This is because momentum-driven outflows suppress star formation in low-mass haloes such that the fraction of haloes hosting observable galaxies (the ‘occupancy’) is 0.2-0.4 even though the star formation duty cycle is unity. This leads to many interesting predictions at z≥ 4, among them that (1) optically selected and UV-selected samples largely overlap; (2) few galaxies

  1. Fast outflows and star formation quenching in quasar host galaxies

    NASA Astrophysics Data System (ADS)

    Carniani, S.; Marconi, A.; Maiolino, R.; Balmaverde, B.; Brusa, M.; Cano-Díaz, M.; Cicone, C.; Comastri, A.; Cresci, G.; Fiore, F.; Feruglio, C.; La Franca, F.; Mainieri, V.; Mannucci, F.; Nagao, T.; Netzer, H.; Piconcelli, E.; Risaliti, G.; Schneider, R.; Shemmer, O.

    2016-06-01

    Negative feedback from active galactic nuclei (AGN) is considered a key mechanism in shaping galaxy evolution. Fast, extended outflows are frequently detected in the AGN host galaxies at all redshifts and luminosities, both in ionised and molecular gas. However, these outflows are only potentially able to quench star formation, and we are still lacking decisive evidence of negative feedback in action. Here we present observations obtained with the Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) H- and K-band integral-field of two quasars at z ~ 2.4 that are characterised by fast, extended outflows detected through the [Oiii]λ5007 line. The high signal-to-noise ratio of our observations allows us to identify faint narrow (FWHM< 500 km s-1) and spatially extended components in [Oiii]λ5007 and Hα emission associated with star formation in the host galaxy. This star formation powered emission is spatially anti-correlated with the fast outflows. The ionised outflows therefore appear to be able to suppress star formation in the region where the outflow is expanding. However, the detection of narrow spatially extended Hα emission indicates star formation rates of at least ~50-90 M⊙ yr-1, suggesting either that AGN feedback does not affect the whole galaxy or that many feedback episodes are required before star formation is completely quenched. On the other hand, the narrow Hα emission extending along the edges of the outflow cone may also lead also to a positive feedback interpretation. Our results highlight the possible double role of galaxy-wide outflows in host galaxy evolution. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, P.ID: 086.B-0579(A) and 091.A-0261(A).The reduced data cubes are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/591/A28

  2. Star formation in the starburst cluster in NGC 3603

    NASA Astrophysics Data System (ADS)

    Correnti, Matteo; Paresce, Francesco; Aversa, Rossella; Beccari, Giacomo; De Marchi, Guido; Di Criscienzo, Marcella; Pang, Xiaoying; Spezzi, Loredana; Valenti, Elena; Ventura, Paolo

    2012-08-01

    We have used new, deep, visible and near infrared observations of the compact starburst cluster in the giant HII region NGC 3603 and its surroundings with the WFC3 on HST and HAWK-I on the VLT to study in detail the physical properties of its intermediate mass (˜1-3 M⊙) stellar population. We show that after correction for differential extinction and actively accreting stars, and the study of field star contamination, strong evidence remains for a continuous spread in the ages of pre-main sequence stars in the range ˜2 to ˜30 Myr within the temporal resolution available. Existing differences among presently available theoretical models account for the largest possible variation in shape of the measured age histograms within these limits. We also find that this isochronal age spread in the near infrared and visible Colour-Magnitude Diagrams cannot be reproduced by any other presently known source of astrophysical or instrumental scatter that could mimic the luminosity spread seen in our observations except, possibly, episodic accretion. The measured age spread and the stellar spatial distribution in the cluster are consistent with the hypothesis that star formation started at least 20-30 Myrs ago progressing slowly but continuously up to at least a few million years ago. All the stars in the considered mass range are distributed in a flattened oblate spheroidal pattern with the major axis oriented in an approximate South-East-North-West direction, and with the length of the equatorial axis decreasing with increasing age. This asymmetry is most likely due to the fact that star formation occurred along a filament of gas and dust in the natal molecular cloud oriented locally in this direction.

  3. H II REGIONS: WITNESSES TO MASSIVE STAR FORMATION

    SciTech Connect

    Peters, Thomas; Banerjee, Robi; Klessen, Ralf S.; Low, Mordecai-Mark Mac; Galvan-Madrid, Roberto; Keto, Eric R.

    2010-03-10

    We describe the first three-dimensional simulation of the gravitational collapse of a massive, rotating molecular cloud that includes heating by both non-ionizing and ionizing radiation. These models were performed with the FLASH code, incorporating a hybrid, long characteristic, ray-tracing technique. We find that as the first protostars gain sufficient mass to ionize the accretion flow, their H II regions are initially gravitationally trapped, but soon begin to rapidly fluctuate between trapped and extended states, in agreement with observations. Over time, the same ultracompact H II region can expand anisotropically, contract again, and take on any of the observed morphological classes. In their extended phases, expanding H II regions drive bipolar neutral outflows characteristic of high-mass star formation. The total lifetime of H II regions is given by the global accretion timescale, rather than their short internal sound-crossing time. This explains the observed number statistics. The pressure of the hot, ionized gas does not terminate accretion. Instead, the final stellar mass is set by fragmentation-induced starvation. Local gravitational instabilities in the accretion flow lead to the build-up of a small cluster of stars, all with relatively high masses due to heating from accretion radiation. These companions subsequently compete with the initial high-mass star for the same common gas reservoir and limit its mass growth. This is in contrast to the classical competitive accretion model, where the massive stars are never hindered in growth by the low-mass stars in the cluster. Our findings show that the most significant differences between the formation of low-mass and high-mass stars are all explained as the result of rapid accretion within a dense, gravitationally unstable, ionized flow.

  4. Numerical Simulations of Star Formation in Filamentary Dark Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Li, Pak Shing; Klein, Richard I.; McKee, Christopher

    2015-08-01

    Infrared Dark Clouds (IRDCs) are believed to be the precursors to star clusters and massive stars (e.g. Bergin & Tafalla 2007). The complex intertwined braid-like structure of IRDCs (e.g. André et al. 2014) poses a challenge to theorists to explain their dynamics and formation. We have performed large-scale adaptive mesh refinement, driven turbulence, MHD simulations to study the structure and formation of IRDCs. Filamentary structure emerges naturally from the simulations. Magnetic field lines pierce the dark cloud filament primarily in the direction normal to the filament axis. The column density profiles of the main features are well fit by the power law as observations have found (e.g. Hill et al. 2011, Arzoumanian et al. 2011). The dark cloud filaments in the simulation resemble the dark cloud SDC13 (Peretto et al. 2014) and the 3D information from the simulation can be used to explain the observed structure and dynamics of SDC13. We have carried out a detailed analysis of the magnetic field properties of the cloud clumps in our simulations (Li et al. 2015), finding good agreement with the Zeeman observations of Crutcher et al. (2010). We then added radiation, zoomed into the main IRDC filament, and continued one of the simulations to study the star formation inside IRDCs. By including radiation feedback and proto-stellar outflows, we obtain a proto-stellar mass function (PMF) for comparison with theoretical PMFs (McKee & Offner 2010) and the Chabrier IMF. In this presentation, we summarize what we have learned about the formation of filamentary IRDCs, their complex braided filamentary structure, the magnetic properties of cloud clumps inside the IRDC filaments, and star formation in the first half of a free fall time of the system.

  5. The formation of the first galaxies and the transition to low-mass star formation

    NASA Astrophysics Data System (ADS)

    Greif, T. H.; Schleicher, D. R. G.; Johnson, J. L.; Jappsen, A.-K.; Klessen, R. S.; Clark, P. C.; Glover, S. C. O.; Stacy, A.; Bromm, V.

    2008-12-01

    The formation of the first galaxies at redshifts z ~ 10-15 signaled the transition from the simple initial state of the universe to one of ever increasing complexity. We here review recent progress in understanding their assembly process with numerical simulations, starting with cosmological initial conditions and modelling the detailed physics of star formation. In this context we emphasize the importance and influence of selecting appropriate initial conditions for the star formation process. We revisit the notion of a critical metallicity resulting in the transition from primordial to present-day initial mass functions and highlight its dependence on additional cooling mechanisms and the exact initial conditions. We also review recent work on the ability of dust cooling to provide the transition to present-day low-mass star formation. In particular, we highlight the extreme conditions under which this transition mechanism occurs, with violent fragmentation in dense gas resulting in tightly packed clusters.

  6. Discovery of a Star Formation Region in Abell 2052

    NASA Astrophysics Data System (ADS)

    Martel, André R.; Sparks, William B.; Allen, Mark G.; Koekemoer, Anton M.; Baum, Stefi A.

    2002-03-01

    We report the discovery of an ultraviolet filament detected in a new Space Telescope Imaging Spectrograph (STIS) NUV-MAMA image of the cD galaxy UGC 9799, located in the cooling-flow cluster Abell 2052 and host to the radio source 3C 317. The filament is ~2 kpc in length and is located at a distance of ~4 kpc from the nucleus along a north-south axis. It consists of three knots embedded along the edges of a diffuse filamentary halo. The northern half of the filament is narrow (~100 pc) and straight while the southern half is bent and more diffuse. The blue color (NUV-V~-2.4) and morphology of the filament are most consistent with a recent episode of star formation (T~5 Myr). Only a few×104 Msolar of young stars or a star formation rate of ~10-3 Msolar yr-1 is required to produce the feature. A steep ultraviolet halo is detected around the unresolved nucleus, and it may be associated with an old stellar component. No ultraviolet features are identified at the location of the extended emission-line nebulae observed from the ground, indicating that OB stars are not the primary source of ionization in these regions. We consider cooling flows and a merger with a satellite galaxy the trigger for the starburst regions and conclude that the latter is the more consistent with the chaotic dust lanes spread throughout the host galaxy. The star formation observed is orders of magnitude less than the inferred cooling rate in the cooling flow scenario. Based on observations made with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  7. Star formation in shocked cluster spirals and their tails

    NASA Astrophysics Data System (ADS)

    Roediger, E.; Brüggen, M.; Owers, M. S.; Ebeling, H.; Sun, M.

    2014-09-01

    Recent observations of ram pressure stripped spiral galaxies in clusters revealed details of the stripping process, i.e. the truncation of all interstellar medium phases and of star formation (SF) in the disc, and multiphase star-forming tails. Some stripped galaxies, in particular in merging clusters, develop spectacular star-forming tails, giving them a jellyfish-like appearance. In merging clusters, merger shocks in the intracluster medium (ICM) are thought to have overrun these galaxies, enhancing the ambient ICM pressure and thus triggering SF, gas stripping, and tail formation. We present idealized hydrodynamical simulations of this scenario, including standard descriptions for SF and stellar feedback. To aid the interpretation of recent and upcoming observations, we focus on particular structures and dynamics in SF patterns in the remaining gas disc and in the near tails, which are easiest to observe. The observed jellyfish morphology is qualitatively reproduced for, both, face-on and edge-on stripping. In edge-on stripping, the interplay between the ICM wind and the disc rotation leads to asymmetries along the ICM wind direction and perpendicular to it. The apparent tail is still part of a highly deformed gaseous and young stellar disc. In both geometries, SF takes place in knots throughout the tail, such that the stars in the tails show no ordered age gradients. Significant SF enhancement in the disc occurs only at radii where the gas will be stripped in due course.

  8. Star Formation Rate Indicators in Different Scales: from Star Forming Regions to Galaxies

    NASA Astrophysics Data System (ADS)

    Hei Law, Ka; Gordon, K.

    2011-01-01

    Do Star Formation Rate (SFR) indicators derived from galaxies work in star forming regions, or vice versa? We explore the behavior and effectiveness of various single- and multi-band SFR indicators across different scales. Our sample spans over 4 orders of magnitudes in total infrared luminosity and covers a wide range of spatial scale - from individual regions in nearby galaxies such as those in SMC, LMC, M33 and M31, to whole galaxies, including galaxies from the Spitzer Local Volume Legacy Survey (LVL; Dale et al. 2009), the Spitzer Infrared Nearby Galaxies Survey (SINGS; Kennicutt et al. 2003), and starburst galaxies from Engelbracht et al. 2008.

  9. Comparison between high and low star forming sides of dwarf irregular galaxies with asymmetrical distributions of star formation.

    NASA Astrophysics Data System (ADS)

    Gallardo, Samavarti; Hunter, Deidre Ann; LEGUS Team

    2017-01-01

    Dwarf irregular galaxies DDO 187 and NGC 3738, in the LITTLE THINGS sample of nearby dwarfs, share the similar characteristic of having more star formation on one side of the galaxy than the other. I compared characteristics of the galaxies, such as pressure, HI surface density, and stellar mass surface density, measured on the high star formation half with those measured on the low star formation half. Comparing the galaxies, we see that the ratios of galactic properties from the high star formation side to the low star formation side are similar in both galaxies. We also see that the high star formation halves of the galaxies have higher pressure, higher stellar mass density, and higher gas mass density. Both galaxies also have peculiar gas kinematics. Looking at the young star clusters in NGC 3738 from the LEGUS survey, we see that there are younger and more clusters in the high star formation region. The cause of having such an asymmetrical distribution of star formation in these galaxies remains unknown.SG appreciates the funding to Northern Arizona University for the Research Experiences for Undergraduates program in the form of grant AST-1461200 from NSF. DAH is grateful for grant HST-GO-13364.022-A for participation in LEGUS.

  10. Star Formation and Cloud Dynamics in the Galactic Bar Region

    NASA Astrophysics Data System (ADS)

    Tolls, Volker

    ; (2) combine the continuum results with molecular line measurements to establish the relative locations and motions of the cores with respect to the x1- and x2-orbits around the GC, the current model for GBR/CMZ dynamics; (3) search in all cores for outflow activity as signs of star formation (SF); (4) investigate the systemic and/or turbulent motions within each of the individual clump cores and within the clumps and their relationship to SF; (5) compare the results to other extreme gas and dust clouds in the CMZ that show little or no SF and determine a potentially elevated density threshold for SF; (6) determine the gas and dust flow towards the CMZ to evaluate possible episodical SF in the CMZ; and (7) apply the results to improve the global dynamics models of the interaction of the IG sources with the nuclear potential. The extensive new Herschel photometric and spectroscopic datasets, combined with our ancillary data, now permit such an effort. Our team has pioneered many of the studies of the IG Clumps, and is expert at Herschel data reduction and analysis.

  11. MOLECULAR GAS AND STAR FORMATION IN NEARBY DISK GALAXIES

    SciTech Connect

    Leroy, Adam K.; Munoz-Mateos, Juan-Carlos; Walter, Fabian; Sandstrom, Karin; Meidt, Sharon; Rix, Hans-Walter; Schinnerer, Eva; Schruba, Andreas; Bigiel, Frank; Bolatto, Alberto; Brinks, Elias; De Blok, W. J. G.; Rosolowsky, Erik; Schuster, Karl-Friedrich; Usero, Antonio

    2013-08-01

    }{sup mol} and local conditions persist. In particular, we observe lower {tau}{sub dep}{sup mol} and enhanced CO excitation associated with nuclear gas concentrations in a subset of our targets. These appear to reflect real enhancements in the rate of star formation per unit gas, and although the distribution of {tau}{sub dep} does not appear bimodal in galaxy centers, {tau}{sub dep} does appear multivalued at fixed {Sigma}{sub H2}, supporting the idea of ''disk'' and ''starburst'' modes driven by other environmental parameters.

  12. Dust Emission and Star Formation in Stephan's Quintet

    NASA Astrophysics Data System (ADS)

    Natale, G.; Tuffs, R. J.; Xu, C. K.; Popescu, C. C.; Fischera, J.; Lisenfeld, U.; Lu, N.; Appleton, P.; Dopita, M.; Duc, P.-A.; Gao, Y.; Reach, W.; Sulentic, J.; Yun, M.

    2010-12-01

    We analyze a comprehensive set of MIR/FIR observations of Stephan's Quintet (SQ), taken with the Spitzer Space Telescope. Our study reveals the presence of a luminous (L IR ≈ 4.6 × 1043 erg s-1) and extended component of infrared dust emission, not connected with the main bodies of the galaxies, but roughly coincident with the X-ray halo of the group. We fitted the inferred dust emission spectral energy distribution of this extended source and the other main infrared emission components of SQ, including the intergalactic shock, to elucidate the mechanisms powering the dust and polycyclic aromatic hydrocarbon emission, taking into account collisional heating by the plasma and heating through UV and optical photons. Combining the inferred direct and dust-processed UV emission to estimate the star formation rate (SFR) for each source we obtain a total SFR for SQ of 7.5 M sun yr-1, similar to that expected for non-interacting galaxies with stellar mass comparable to the SQ galaxies. Although star formation in SQ is mainly occurring at, or external to the periphery of the galaxies, the relation of SFR per unit physical area to gas column density for the brightest sources is similar to that seen for star formation regions in galactic disks. We also show that available sources of dust in the group halo can provide enough dust to produce up to L IR ≈ 1042 erg s-1 powered by collisional heating. Though a minority of the total infrared emission (which we infer to trace distributed star-formation), this is several times higher than the X-ray luminosity of the halo, so could indicate an important cooling mechanism for the hot intergalactic medium (IGM) and account for the overall correspondence between FIR and X-ray emission. We investigate two potential modes of star formation in SQ consistent with the data, fueled either by gas from a virialized hot IGM continuously accreting onto the group, whose cooling is enhanced by grains injected from an in situ population of

  13. Nuclear fusion and carbon flashes on neutron stars

    NASA Technical Reports Server (NTRS)

    Taam, R. E.; Picklum, R. E.

    1978-01-01

    This paper reports on detailed calculations of the thermal evolution of the carbon-burning shells in the envelopes of accreting neutron stars for mass-accretion rates of 1 hundred-billionth to 2 billionths of a solar mass per yr and neutron-star masses of 0.56 and 1.41 solar masses. The work of Hansen and Van Horn (1975) is extended to higher densities, and a more detailed treatment of nuclear processing in the hydrogen- and helium-burning regions is included. Results of steady-state calculations are presented, and results of time-dependent computations are examined for accretion rates of 3 ten-billionths and 1 billionth of solar mass per yr. It is found that two evolutionary sequences lead to carbon flashes and that the carbon abundance at the base of the helium shell is a strong function of accretion rate. Upper limits are placed on the accretion rates at which carbon flashes will be important.

  14. STAR FORMATION AND DUST OBSCURATION IN THE TIDALLY DISTORTED GALAXY NGC 2442

    SciTech Connect

    Pancoast, Anna; Sajina, Anna; Lacy, Mark; Noriega-Crespo, Alberto; Rho, Jeonghee

    2010-11-01

    We present a detailed investigation of the morphological distribution and level of star formation and dust obscuration in the nearby tidally distorted galaxy NGC 2442. Spitzer images in the IR at 3.6, 4.5, 5.8, 8.0, and 24 {mu}m and GALEX images at 1500 A and 2300 A allow us to resolve the galaxy on scales between {approx}240 and 600 pc. We supplement these with archival data in the B, J, H, and K bands. We use the 8 {mu}m, 24 {mu}m, and FUV (1500 A) emission to study the star formation rate (SFR). We find that, globally, these tracers of star formation give a range of results of {approx}6-11 M{sub sun} yr{sup -1}, with the dust-corrected FUV giving the highest value of SFR. We can reconcile the UV- and IR-based estimates by adopting a steeper UV extinction curve that lies in between the starburst (Calzetti) and Small Magellanic Cloud extinction curves. However, the regions of the highest SFR intensity along the spiral arms are consistent with a starburst-like extinction. Overall, the level of star formation we find is higher than previously published for this galaxy, by about a factor of 2, which, contrary to previous conclusions, implies that the interaction that caused the distorted morphology of NGC 2442 likely also triggered increased levels of star formation activity. We also find marked asymmetry in that the north spiral arm has a noticeably higher SFR than the southern arm. The tip of the southern spiral arm shows a likely tidally distorted peculiar morphology. It is UV bright and shows unusual IRAC colors, consistent with other published tidal features IRAC data. Outside of the spiral arms, we discover what appears to be a superbubble, {approx}1.7 kpc across, which is seen most clearly in the IRAC images. Significant H{alpha}, UV, and IR emission in the area also suggest vigorous ongoing star formation. A known, recent supernova (SN 1999ga) is located at the edge of this superbubble. Although speculative at this stage, this area suggests a large star

  15. Singular Isothermal Disks and the Formation of Multiple Stars

    NASA Technical Reports Server (NTRS)

    Galli, Daniele; Shu, Frank H.; Laughlin, Gregory; Lizano, Susana; DeVincenzi, Donald (Technical Monitor)

    2000-01-01

    A crucial missing ingredient in previous theoretical studies of fragmentation is the inclusion of dynamically important levels of magnetic fields. As a minimal model for a candidate presursor to the formation of binary and multiple stars, we therefore consider the equilibrium configuration of isopedically magnetized, scale-free, singular isothermal disks, without the assumption of axial symmetry. We find that lopsided (M = 1) configurations exist at any dimensionless rotation rate, including zero. Multiple-lobed (M = 2, 3, 4, ...) configurations bifurcate from an underlying axisymmetric sequence at progressively higher dimensionless rates of rotation, but such nonaxisymmetric sequences always terminate in shockwaves before they have a chance to fission into separate bodies. We advance the hypothesis that binary and multiple star-formation from smooth (i.e., not highly turbulent) starting states that are supercritical but in unstable mechanical balance requires the rapid (i.e., dynamical) loss of magnetic flux at some stage of the ensuing gravitational collapse.

  16. Star Formation in High-Latitude Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Magnus McGehee, Peregrine

    2015-08-01

    Galactic star formation preferentially occurs within the dense molecular clouds that reside primarily near the disk mid-plane and are thus seen in projection against the Milky Way. A population of molecular clouds are seen at higher Galactic latitude although distance determinations are required in order to identify those that are actually in extraplanar environments.We review the known high-latitude star formation regions (MBM 12, LDN 1642, and HRK 81.4-77.8) and discuss the nature and environment of other high-latitude molecular clouds. Distances to each of these structures are deduced from optical reddening profiles derived from analysis of Sloan Digital Sky Survey photometry. In particular, we examine those molecular clouds found within the complex of intermediate and high velocity HI clouds that span the Northern 2nd Galactic Quadrant: the Draco clouds, the IVC pair at (l+b) = 135+51 and 135+54, and IREC 306.

  17. VARIABLE WINDS AND DUST FORMATION IN R CORONAE BOREALIS STARS

    SciTech Connect

    Clayton, Geoffrey C.; Zhang Wanshu; Geballe, T. R. E-mail: wzhan21@lsu.edu

    2013-08-01

    We have observed P-Cygni and asymmetric, blue-shifted absorption profiles in the He I {lambda}10830 lines of 12 R Coronae Borealis stars over short (1 month) and long (3 yr) timescales to look for variations linked to their dust-formation episodes. In almost all cases, the strengths and terminal velocities of the line vary significantly and are correlated with dust formation events. Strong absorption features with blue-shifted velocities {approx}400 km s{sup -1} appear during declines in visible brightness and persist for about 100 days after recovery to maximum brightness. Small residual winds of somewhat lower velocity are present outside of the decline and recovery periods. The correlations support models in which recently formed dust near the star is propelled outward at high speed by radiation pressure and drags the gas along with it.

  18. FORMALDEHYDE MASERS: EXCLUSIVE TRACERS OF HIGH-MASS STAR FORMATION

    SciTech Connect

    Araya, E. D.; Brown, J. E.; Olmi, L.; Ortiz, J. Morales; Hofner, P.; Creech-Eakman, M. J.; Kurtz, S.; Linz, H.

    2015-11-15

    The detection of four formaldehyde (H{sub 2}CO) maser regions toward young high-mass stellar objects in the last decade, in addition to the three previously known regions, calls for an investigation of whether H{sub 2}CO masers are an exclusive tracer of young high-mass stellar objects. We report the first survey specifically focused on the search for 6 cm H{sub 2}CO masers toward non high-mass star-forming regions (non HMSFRs). The observations were conducted with the 305 m Arecibo Telescope toward 25 low-mass star-forming regions, 15 planetary nebulae and post-AGB stars, and 31 late-type stars. We detected no H{sub 2}CO emission in our sample of non HMSFRs. To check for the association between high-mass star formation and H{sub 2}CO masers, we also conducted a survey toward 22 high-mass star-forming regions from a Hi-GAL (Herschel infrared Galactic Plane Survey) sample known to harbor 6.7 GHz CH{sub 3}OH masers. We detected a new 6 cm H{sub 2}CO emission line in G32.74−0.07. This work provides further evidence that supports an exclusive association between H{sub 2}CO masers and young regions of high-mass star formation. Furthermore, we detected H{sub 2}CO absorption toward all Hi-GAL sources, and toward 24 low-mass star-forming regions. We also conducted a simultaneous survey for OH (4660, 4750, 4765 MHz), H110α (4874 MHz), HCOOH (4916 MHz), CH{sub 3}OH (5005 MHz), and CH{sub 2}NH (5289 MHz) toward 68 of the sources in our sample of non HMSFRs. With the exception of the detection of a 4765 MHz OH line toward a pre-planetary nebula (IRAS 04395+3601), we detected no other spectral line to an upper limit of 15 mJy for most sources.

  19. How stellar feedback simultaneously regulates star formation and drives outflows

    NASA Astrophysics Data System (ADS)

    Hayward, Christopher C.; Hopkins, Philip F.

    2017-02-01

    We present an analytic model for how momentum deposition from stellar feedback simultaneously regulates star formation and drives outflows in a turbulent interstellar medium (ISM). Because the ISM is turbulent, a given patch of ISM exhibits sub-patches with a range of surface densities. The high-density patches are 'pushed' by feedback, thereby driving turbulence and self-regulating local star formation. Sufficiently low-density patches, however, are accelerated to above the escape velocity before the region can self-adjust and are thus vented as outflows. When the gas fraction is ≳ 0.3, the ratio of the turbulent velocity dispersion to the circular velocity is sufficiently high that at any given time, of the order of half of the ISM has surface density less than the critical value and thus can be blown out on a dynamical time. The resulting outflows have a mass-loading factor (η ≡ dot{M}_{out}/M_{star }) that is inversely proportional to the gas fraction times the circular velocity. At low gas fractions, the star formation rate needed for local self-regulation, and corresponding turbulent Mach number, declines rapidly; the ISM is 'smoother', and it is actually more difficult to drive winds with large mass-loading factors. Crucially, our model predicts that stellar-feedback-driven outflows should be suppressed at z ≲ 1 in M⋆ ≳ 1010 M⊙ galaxies. This mechanism allows massive galaxies to exhibit violent outflows at high redshifts and then 'shut down' those outflows at late times, thereby enabling the formation of a smooth, extended thin stellar disc. We provide simple fitting functions for η that should be useful for sub-resolution and semi-analytic models.

  20. STAR FORMATION ACTIVITY IN CLASH BRIGHTEST CLUSTER GALAXIES

    SciTech Connect

    Fogarty, Kevin; Postman, Marc; Connor, Thomas; Donahue, Megan; Moustakas, John

    2015-11-10

    The CLASH X-ray selected sample of 20 galaxy clusters contains 10 brightest cluster galaxies (BCGs) that exhibit significant (>5σ) extinction-corrected star formation rates (SFRs). Star formation activity is inferred from photometric estimates of UV and Hα+[N ii] emission in knots and filaments detected in CLASH Hubble Space Telescope ACS and WFC3 observations. UV-derived SFRs in these BCGs span two orders of magnitude, including two with a SFR ≳ 100 M{sub ⊙} yr{sup −1}. These measurements are supplemented with [O ii], [O iii], and Hβ fluxes measured from spectra obtained with the SOAR telescope. We confirm that photoionization from ongoing star formation powers the line emission nebulae in these BCGs, although in many BCGs there is also evidence of a LINER-like contribution to the line emission. Coupling these data with Chandra X-ray measurements, we infer that the star formation occurs exclusively in low-entropy cluster cores and exhibits a correlation with gas properties related to cooling. We also perform an in-depth study of the starburst history of the BCG in the cluster RXJ1532.9+3021, and create 2D maps of stellar properties on scales down to ∼350 pc. These maps reveal evidence for an ongoing burst occurring in elongated filaments, generally on ∼0.5–1.0 Gyr timescales, although some filaments are consistent with much younger (≲100 Myr) burst timescales and may be correlated with recent activity from the active galactic nucleus. The relationship between BCG SFRs and the surrounding intracluster medium gas properties provide new support for the process of feedback-regulated cooling in galaxy clusters and is consistent with recent theoretical predictions.

  1. UPPER BOUND ON THE FIRST STAR FORMATION HISTORY

    SciTech Connect

    Inoue, Yoshiyuki; Madejski, Grzegorz M.; Tanaka, Yasuyuki T.; Domínguez, Alberto

    2014-02-01

    Our understanding of the nature of the extragalactic background light (EBL) has improved with the recent development of gamma-ray observation techniques. An open subject in the context of the EBL is the reionization epoch, which is an important probe of the formation history of first stars, the so-called Population III (Pop III) stars. Although the mechanisms for the formation of Pop III stars are rather well understood on theoretical grounds, their formation history is still veiled in mystery because of their faintness. To shed light on this matter, we study jointly the gamma-ray opacity of distant objects and the reionization constraints from studies of intergalactic gas. By combining these studies, we obtain a sensitive upper bound on the Pop III star formation rate density of ρ-dot {sub ∗}(z)<0.01[(1+z)/(1+7.0)]{sup 3.4}(f{sub esc}/0.2){sup −1}(C/3.0) M{sub ⊙} yr{sup −1} Mpc{sup −3} at z ≥ 7, where f {sub esc} and C are the escape fraction of ionizing photons from galaxies and the clumping factor of the intergalactic hydrogen gas. This limit is a ∼10 times tighter constraint compared with previous studies that take into account gamma-ray opacity constraints only. Even if we do not include the current gamma-ray constraints, the results do not change. This is because the detected gamma-ray sources are still at z ≤ 4.35 where the reionization has already finished.

  2. Observational studies of regions of massive star formation

    NASA Astrophysics Data System (ADS)

    Cooper, Heather Danielle Blythe

    2013-03-01

    Massive stars have a profound influence on their surroundings. However, relatively little is known about their formation. The study of massive star formation is hindered by a lack of observational evidence, primarily due to difficulties observing massive stars at early stages in their development. The Red MSX Source survey (RMS survey) is a valuable tool with which to address these issues. Near-infrared H- and K-band spectra were taken for 247 candidate massive young stellar objects (MYSOs), selected from the RMS survey. 195 (∼80%) of the targets are YSOs, of which 131 are massive YSOs (LBOL>5E3L⊙, M>8 M⊙). This is the largest spectroscopic study of massive YSOs to date. This study covers minimally obscured objects right through to very red, dusty sources. Almost all YSOs show some evidence for emission lines, though there is a wide variety of observed properties, with HI, H2 Fe II, and CO among the most commonly observed lines. Evidence for disks and outflows was frequently seen. Comparisons of Brγ and H2 emission with low mass YSOs suggest that the emission mechanism for these lines is the same for low-, intermediate-, and high-mass YSOs, i.e. high-mass YSOs appear to resemble scaled-up versions of low-mass YSOs. It was found that the YSOs form an evolutionary sequence, based on their spectra, consistent with the existing theoretical models. Type I YSOs have strong H2 emission, no ionized lines, and are redder than the other two subtypes. As such, these are considered to be the youngest sources. The Type III sources are bluest, and therefore considered to be the oldest subtype. They have strong H I lines and fluorescent Fe II 1.6878 μm emission. They may also have weak H2 emission. Type III sources may even be beginning to form a mini-H II region. XSHOOTER data from 10 Herbig Be stars were analysed. The evidence suggests that winds and disks are common among Herbig stars, as they are among their main sequence classical Be star counterparts. Line

  3. The UV + IR Hybrid Star Formation Rate Across NGC6946

    NASA Astrophysics Data System (ADS)

    Eufrasio, Rafael T.; Lehmer, Bret; Dwek, Eli; Arendt, Richard G.

    2016-01-01

    Knowledge of the star formation rate (SFR) of galaxies is essential to understand galaxy evolution and thus determining reliable, simple tracers of star-forming activity is of paramount importance to astrophysics. For instance, intrinsic ultraviolet (UV) emission from young stars is an excellent tracer of the SFR. Observed UV luminosities, however, have been strongly attenuated by intervening interstellar dust. Since emission from hot dust is readily available from IRAS, Spitzer, and WISE, it is common practice to combine mid-IR emission (around 25 μm) with observed UV in order to obtain an SFR diagnostic of the form Lobs(FUV) + acorr × Lobs(25 μm). Conventionally, a single correction acorr, previously determined for a sample of galaxies, is used. Here we test the reliability of this hybrid SFR diagnostic, allowing for a variable correction factor acorr. For this, we have performed broadband UV-to-IR SED fittings in order to model the star formation histories across the spiral galaxy NGC6946. We have obtained SFRs and stellar masses across the galaxy, from physical scales of 5 kpc down to 500 pc. We find that acorr varies significantly across the galaxy and increases with increasing specific star formation rate (sSFR), the ratio of SFR and stellar mass (or the ratio of young and old stars). The correction acorr does not seem to be correlated to the amount of attenuation AV. Variation of acorr is most likely caused by different mixes of young and old stellar populations across the galaxy. This finding agrees well with our previous results for the interacting spiral galaxy NGC 6872, for which we have demonstrated the variation of acorr and a its correlation with sSFR. Our results show the need of caution when using only two broadband filters in order to determine SFR of individual galaxies or sub-galactic regions. The dust emission most likely overestimates SFR for highly star-forming, high sSFR regions, and underestimates it for more quiescent, low sSFR regions.

  4. X-ray sources in regions of star formation. II - The pre-main-sequence G star HDE 283572

    NASA Technical Reports Server (NTRS)

    Walter, F. M.; Brown, A.; Linsky, J. L.; Rydgren, A. E.; Vrba, F.

    1987-01-01

    This paper reports the detection of HDE 283572, a ninth-magnitude G star 8 arcmin south of RY Tau, as a bright X-ray source. The observations reveal this object to be a fairly massive (about 2 solar masses) pre-main-sequence star associated with the Taurus-Auriga star formation complex. It exhibits few of the characteristics of the classical T Tauri stars and is a good example of a 'naked' T Tauri star. The star is a mid-G subgiant, of about three solar radii and rotates with a period of 1.5 d. The coronal and chromospheric surface fluxes are similar to those of the most active late type stars (excluding T Tauri stars). The X-ray and UV lines most likely arise in different atmospheric structures. Radiative losses are some 1000 times the quiet solar value and compare favorably with those of T Tauri stars.

  5. Star formation scales and efficiency in Galactic spiral arms

    NASA Astrophysics Data System (ADS)

    Eden, D. J.; Moore, T. J. T.; Urquhart, J. S.; Elia, D.; Plume, R.; Rigby, A. J.; Thompson, M. A.

    2015-09-01

    We positionally match a sample of infrared-selected young stellar objects, identified by combining the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire, Wide-field Infrared Survey Explorer and Herschel Space Observatory Herschel infrared Galactic Plane Survey, to the dense clumps identified in the millimetre continuum by the Bolocam Galactic Plane Survey in two Galactic lines of sight centred towards l = 30° and 40°. We calculate the ratio of infrared luminosity, LIR, to the mass of the clump, Mclump, in a variety of Galactic environments and find it to be somewhat enhanced in spiral arms compared to the interarm regions when averaged over kiloparsec scales. We find no compelling evidence that these changes are due to the mechanical influence of the spiral arm on the star formation efficiency rather than, e.g. different gradients in the star formation rate due to patchy or intermittent star formation, or local variations that are not averaged out due to small source samples. The largest variation in LIR/Mclump is found in individual clump values, which follow a lognormal distribution and have a range of over three orders of magnitude. This spread is intrinsic as no dependence of LIR/Mclump with Mclump was found. No difference was found in the luminosity distribution of sources in the arm and interarm samples and a strong linear correlation was found between LIR and Mclump.

  6. Efficient star formation in the spiral arms of M51

    NASA Technical Reports Server (NTRS)

    Lord, Steven D.; Young, Judith S.

    1990-01-01

    The molecular, neutral, and ionized hydrogen distributions in the Sbc galaxy M51 (NGC 5194) are compared. To estimate H2 surface densities observations of the CO (J = 1 - 0) transition were made in 60 positions out to a radius of 155 arcsec. Extinction-corrected H-alpha intensities were used to compute the detailed massive star formation rates (MSFRs) in the disk. Estimates of the gas surface density, the MSFR, and the ratio of these quantities, MSFR/sigma(p), were then examined. The spiral arms were found to exhibit an excess gas density, measuring between 1.4 and 1.6 times the interarm values at 45 arcsec resolution. The total (arm and interarm) gas content and massive star formation rates in concentric annuli in the disk of M51 were computed. The two quantities fall off together with radius, yielding a relatively constant MSFR/sigma(p) with radius. This behavior is not explained by current models of star formation in galactic disks.

  7. GOODS-Herschel: ultra-deep XMM-Newton observations reveal AGN/star-formation connection

    NASA Astrophysics Data System (ADS)

    Rovilos, E.; Comastri, A.; Gilli, R.; Georgantopoulos, I.; Ranalli, P.; Vignali, C.; Lusso, E.; Cappelluti, N.; Zamorani, G.; Elbaz, D.; Dickinson, M.; Hwang, H. S.; Charmandaris, V.; Ivison, R. J.; Merloni, A.; Daddi, E.; Carrera, F. J.; Brandt, W. N.; Mullaney, J. R.; Scott, D.; Alexander, D. M.; Del Moro, A.; Morrison, G.; Murphy, E. J.; Altieri, B.; Aussel, H.; Dannerbauer, H.; Kartaltepe, J.; Leiton, R.; Magdis, G.; Magnelli, B.; Popesso, P.; Valtchanov, I.

    2012-10-01

    Models of galaxy evolution assume some connection between the AGN and star formation activity in galaxies. We use the multi-wavelength information of the CDFS to assess this issue. We select the AGNs from the 3 Ms XMM-Newton survey and measure the star-formation rates of their hosts using data that probe rest-frame wavelengths longward of 20 μm, predominantly from deep 100 μm and 160 μm Herschel observations, but also from Spitzer-MIPS-70 μm. Star-formation rates are obtained from spectral energy distribution fits, identifying and subtracting an AGN component. Our sample consists of sources in the z ≈ 0.5-4 redshift range, with star-formation rates SFR ≈ 101-103 M⊙ yr-1 and stellar masses M⋆ ≈ 1010-1011.5 M⊙. We divide the star-formation rates by the stellar masses of the hosts to derive specific star-formation rates (sSFR) and find evidence for a positive correlation between the AGN activity (proxied by the X-ray luminosity) and the sSFR for themost active systems with X-ray luminosities exceeding Lx ≃ 1043 erg s-1 and redshifts z ≳ 1. We do not find evidence for such a correlation for lower luminosity systems or those at lower redshifts, consistent with previous studies. We do not find any correlation between the SFR (or the sSFR) and the X-ray absorption derived from high-quality XMM-Newton spectra either, showing that the absorption is likely to be linked to the nuclear region rather than the host, while the star-formation is not nuclear. Comparing the sSFR of the hosts to the characteristic sSFR of star-forming galaxies at the same redshift (the so-called "main sequence") we find that the AGNs reside mostly in main-sequence and starburst hosts, reflecting the AGN-sSFR connection; however the infrared selection might bias this result. Limiting our analysis to the highest X-ray luminosity AGNs (X-ray QSOs with Lx > 1044 erg s-1), we find that the highest-redshift QSOs (with z ≳ 2) reside predominantly in starburst hosts, with an average s

  8. TESTING 24 {mu}m AND INFRARED LUMINOSITY AS STAR FORMATION TRACERS FOR GALACTIC STAR-FORMING REGIONS

    SciTech Connect

    Vutisalchavakul, Nalin; Evans, Neal J. II

    2013-03-10

    We have tested some relations for star formation rates used in extragalactic studies for regions within the Galaxy. In nearby molecular clouds, where the initial mass function is not fully sampled, the dust emission at 24 {mu}m greatly underestimates star formation rates (by a factor of 100 on average) when compared to star formation rates determined from counting young stellar objects. The total infrared emission does no better. In contrast, the total far-infrared method agrees within a factor of two on average with star formation rates based on radio continuum emission for massive, dense clumps that are forming enough massive stars to have L{sub TIR} exceed 10{sup 4.5} L{sub Sun }. The total infrared and 24 {mu}m also agree well with each other for both nearby, low-mass star-forming regions and the massive, dense clump regions.

  9. A ram-pressure threshold for star formation

    NASA Astrophysics Data System (ADS)

    Whitworth, A. P.

    2016-05-01

    In turbulent fragmentation, star formation occurs in condensations created by converging flows. The condensations must be sufficiently massive, dense and cool to be gravitationally unstable, so that they start to contract; and they must then radiate away thermal energy fast enough for self-gravity to remain dominant, so that they continue to contract. For the metallicities and temperatures in local star-forming clouds, this second requirement is only met robustly when the gas couples thermally to the dust, because this delivers the capacity to radiate across the full bandwidth of the continuum, rather than just in a few discrete spectral lines. This translates into a threshold for vigorous star formation, which can be written as a minimum ram pressure PCRIT ˜ 4 × 10-11 dyne. PCRIT is independent of temperature, and corresponds to flows with molecular hydrogen number density n_{{H_2.FLOW}} and velocity vFLOW satisfying n_{{H_2.FLOW}} v_{FLOW}^2≳ 800 cm^{-3} (km s^{-1})^2. This in turn corresponds to a minimum molecular hydrogen column density for vigorous star formation, N_{{H_2.CRIT}} ˜ 4 × 10^{21} cm^{-2} (ΣCRIT ˜ 100 M⊙ pc-2), and a minimum visual extinction AV, CRIT ˜ 9 mag. The characteristic diameter and line density for a star-forming filament when this threshold is just exceeded - a sweet spot for local star formation regions - are 2RFIL ˜ 0.1 pc and μFIL ˜ 13 M⊙ pc-2. The characteristic diameter and mass for a prestellar core condensing out of such a filament are 2RCORE ˜ 0.1 pc and MCORE ˜ 1 M⊙. We also show that fragmentation of a shock-compressed layer is likely to commence while the convergent flows creating the layer are still ongoing, and we stress that, under this circumstance, the phenomenology and characteristic scales for fragmentation of the layer are fundamentally different from those derived traditionally for pre-existing layers.

  10. Retired galaxies: not to be forgotten in the quest of the star formation - AGN connection

    NASA Astrophysics Data System (ADS)

    Stasińska, G.; Costa-Duarte, M. V.; Vale Asari, N.; Cid Fernandes, R.; Sodré, L.

    2015-05-01

    We propose a fresh look at the Main Galaxy Sample of the Sloan Digital Sky Survey by packing the galaxies in stellar mass and redshift bins. We show how important it is to consider the emission-line equivalent widths, in addition to the commonly used emission-line ratios, to properly identify retired galaxies (i.e. galaxies that have stopped forming stars and are ionized by their old stellar populations) and not mistake them for galaxies with low-level nuclear activity. We find that the proportion of star-forming galaxies decreases with decreasing redshift in each mass bin, while that of retired galaxies increases. Galaxies with M⋆ > 1011.5 M⊙ have formed all their stars at redshift larger than 0.4. The population of AGN hosts is never dominant for galaxy masses larger than 1010 M⊙. We warn about the effects of stacking galaxy spectra to discuss galaxy properties. We estimate the lifetimes of active galactic nuclei (AGN) relying entirely on demographic arguments - i.e. without any assumption on the AGN radiative properties. We find upper-limit lifetimes of about 1-5 Gyr for detectable AGN in galaxies with masses between 1010-1012 M⊙. The lifetimes of the AGN-dominated phases are a few 108 yr. Finally, we compare the star formation histories of star-forming, AGN and retired galaxies as obtained by the spectral synthesis code STARLIGHT. Once the AGN is turned on, it inhibits star formation for the next ˜0.1 Gyr in galaxies with masses around 1010 M⊙, ˜ 1 Gyr in galaxies with masses around 1011 M⊙.

  11. Formation and evolution of star clusters in merging galaxies

    NASA Astrophysics Data System (ADS)

    Zhang, Qing

    2002-04-01

    Recent observations have revealed numerous young massive star clusters, often known as “young globular clusters”. Their formation and evolution are important astrophysical processes and may potentially have cosmological implications. In this work, we focus on the star clusters in the nearest ongoing merger NGC 4038/9 (the “Antennae”). With the Hubble Space Telescope, we identify clusters with all ages, most of which are younger than 20 Myr. Our goal is to study their formation mechanisms, and the relation with the interstellar medium environment, and their evolutionary connection with old globular clusters. We find that their luminosity function and mass function are best described as power laws with indices around -2. The masses of young star clusters cover the range 104 ≤ M ≤ 10 6 M⊙ . This result is distinctly different from that of old globular clusters that has a “preferred” scale at M ≈ 2 × 105 M⊙ . To understand the difference in MF between the young and old star clusters, we conduct a theoretical study on the effects of dynamical disruption of individual clusters on the mass function. We find that, for a wide variety of initial conditions, the mass function develops a characteristic scale, that is remarkably close to the observed one for globular clusters after 12 Gyr. In addition, we find that some radial anisotropy in the initial velocity distribution, especially when decreasing outward, is needed to account for the observed near-uniformity of the mass functions of globular clusters. This is consistent with the observed near-isotropy of the present velocity distributions because clusters on elongated orbits are preferentially destroyed. In order to understand the formation and feedback effects of young star clusters, we have also conducted a multi- wavelength study on the association between young star clusters and their interstellar environment in the Antennae galaxies. This is possible for the first time because various new

  12. Formation of Magnesium Silicates is Limited around Evolved Stars

    NASA Astrophysics Data System (ADS)

    Kimura, Yuki; Nuth, J. A., III

    2009-05-01

    Laboratory experiments suggest that magnesium silicide (Mg2Si) grains could be produced in the hydrogen dominant gas outflow from evolved stars in addition to amorphous oxide minerals. Astronomical observations have shown the existence of abundant silicate grains around evolved stars and we have long realized that most of the silicate grains are amorphous, based on the observed infrared features. Only high mass loss stars show the feature attributed to magnesium-rich crystalline silicate about 10-20 % respect to total silicates, so far. The lower degree of crystallinity observed in silicates formed in outflows of lower mass-loss-rate stars might be caused by the formation of magnesium silicide in this relatively hydrogen-rich environment. As a result of predominant distribution of magnesium into the silicide, the composition of interstellar amorphous silicates could be magnesium poor compared with silicon. Indeed, the chemical composition of isotopically anomalous GEMS (glass with embedded metal and sulfides) is magnesium poor with respect to a forsteritic composition (Floss et al. 2006; Keller & Messenger 2007). Infrared observations suggest that there is little or no crystalline forsterite in interstellar environments while there is an abundance of crystalline forsterite in our Solar System. If the forsterite is a result of the oxidation of interstellar magnesium silicide, then it is clear both why crystalline forsterite is stoichiometric olivine and why the chemical composition of isotopically anomalous GEMS is magnesium poor with respect to a forsteritic composition. In addition, it may also explain why the chemical composition of olivine is iron poor. Unfortunately, magnesium silicide has never been detected via astronomical observation or in the analysis of primitive meteorites. I would suggest that future analysis of meteorites and theoretical calculations could confirm the possibility of the formation of magnesium silicide grains around evolved stars.

  13. Current star formation in S0 galaxies: NGC 4710

    NASA Technical Reports Server (NTRS)

    Wrobel, J. M.

    1990-01-01

    Elliptical (E) and lenticular (S0) galaxies lack the substantial interstellar medium (ISM) found in the star-forming spiral galaxies. However, significant numbers of E and S0 galaxies are known to contain detectable amounts of interstellar matter (e.g., Jura 1988). Thus, it is worth investigating whether these galaxies are currently able to form stars from their ISM, or whether they should be consigned to the dustbin of inert objects (Thronson and Bally 1987). The results strongly imply that current star formation is responsible for NGC 4710's far infrared and radio continuum properties. If this is indeed the case, then one expects this star formation to be fueled by molecular gas, which is presumably dominated by H2 and can be traced by the CO-12 J=1 to 0 line. Both Kenney and Young (1988) and Sage and Wrobel (1989) have detected such an emission line from NGC 4710, and infer the presence of more than 10(exp 8) solar mass of H2. The origin of the molecular gas in NGC 4710 remains a mystery. The galaxy is very deficient in HI (Kenney and Young, in preparation), suggesting that it originally was a spiral galaxy from which the outer, mainly atomic, gas was stripped by the ram pressure of the Virgo Cluster's intracluster medium, leaving only a central interstellar medium (ISM) rich in molecular gas. Alternatively, the CO may have originated via stellar mass loss with subsequent cooling, cooling flows, or capture from a gas-rich companion. Information on the morphology and kinematics of the CO can be compared with that of the galaxy's other gases and stars to distinguish among these various possible origins for the molecular gas. Major axis CO mapping with single dishes indicate an unresolved source. Thus, a millimeter array is currently being used to image NGC 4710 in CO to provide the needed morphological and kinematical data.

  14. Does Radiative Feedback by the First Stars Promote or Prevent Second Generation Star Formation?

    NASA Astrophysics Data System (ADS)

    Ahn, Kyungjin; Shapiro, Paul R.

    2008-03-01

    We present a self-consistent study of formation of Pop III stars in the early stage of cosmic reionization. We study the effect of starlight from the first stars on the ability of other minihalos in their neighborhood to form additional stars. We show that the ionization front (I-front) is trapped by the neighboring minihalos, after it is transformed from R-type to D-type and preceded by a shock front. The fate of the core of nearby minihalos is mostly determined by the response of the core to this shock front, which leads to molecular cooling and collapse that, when compared to the same halo without external radiation, is (a) expedited, (b) delayed, (c) unaltered, or (d) reversed and prevented, depending upon the flux and halo mass and evolutionary stage. Roughly speaking, most halos that were destined to cool, collapse and form stars in the absence of external radiation are found to do so even when exposed to the first Pop III star in their neighborhood, while those that would not have done so are still not able to.

  15. Gamma-Ray Bursts and the Early Star-Formation History. GRBs and z>4 Star-Formation

    NASA Astrophysics Data System (ADS)

    Chary, R.; Petitjean, P.; Robertson, B.; Trenti, M.; Vangioni, E.

    2016-12-01

    We review the uncertainties in high-z star-formation rate (SFR) measures and the constraints that one obtains from high-z gamma-ray burst (GRB) rates on them. We show that at the present time, the GRB rates per unit star-formation at z>3 are higher than at lower redshift. There could be a multitude of reasons for this: a stellar metallicity bias for GRB production, a top-heavy initial mass function (IMF) and/or missing a significant fraction of star-formation in field galaxy surveys due to incompleteness, surface brightness limitations and cosmic variance. We also compare metallicity predictions made using a hierarchical model of cosmic chemical evolution based on two recently proposed SFRs, one based on the observed galaxy luminosity function at high redshift and one based on the GRB rate and find that within the considerable scatter in metal abundance measures, they both are consistent with the data. Analyzing the ensemble of different measurements together, we conclude that despite metallicity biases, GRBs may be a less biased probe of star-formation at z>3 than at z<2. There is likely to be a common origin to the high GRB rate per unit star-formation and the high observed Lyman-continuum production rate in high redshift galaxies and that this may be due to a relative overabundance of stars with mass {>}25 M_{⊙} which are likely GRB progenitors. We also find that to reconcile these measurements with the Thomson scattering cross section of cosmic microwave background (CMB) photons measured by Planck, the escape fraction of Lyman-continuum photons from galaxies must be low, about ˜15 % or less and that the clumping factor of the IGM is likely to be small, ˜3. Finally, we demonstrate that GRBs are unique probes of metallicity evolution in low-mass galaxy samples and that GRB hosts likely lost a significant fraction of metals to the intergalactic medium (IGM) due to feedback processes such as stellar winds and supernovae.

  16. Unfolding the laws of star formation: the density distribution of molecular clouds.

    PubMed

    Kainulainen, Jouni; Federrath, Christoph; Henning, Thomas

    2014-04-11

    The formation of stars shapes the structure and evolution of entire galaxies. The rate and efficiency of this process are affected substantially by the density structure of the individual molecular clouds in which stars form. The most fundamental measure of this structure is the probability density function of volume densities (ρ-PDF), which determines the star formation rates predicted with analytical models. This function has remained unconstrained by observations. We have developed an approach to quantify ρ-PDFs and establish their relation to star formation. The ρ-PDFs instigate a density threshold of star formation and allow us to quantify the star formation efficiency above it. The ρ-PDFs provide new constraints for star formation theories and correctly predict several key properties of the star-forming interstellar medium.

  17. Dark Matter Densities During the Formation of the First Stars and in Dark Stars

    NASA Astrophysics Data System (ADS)

    Freese, Katherine; Gondolo, Paolo; Sellwood, J. A.; Spolyar, Douglas

    2009-03-01

    The first stars in the universe form inside ~106 M sun dark matter (DM) halos whose initial density profiles are laid down by gravitational collapse in hierarchical structure-formation scenarios. During the formation of the first stars in the universe, the baryonic infall compresses the DM further. The resultant DM density is presented here, using an algorithm originally developed by Young to calculate changes to the profile as a result of adiabatic infall in a spherical halo model; the Young prescription takes into account the noncircular motions of halo particles. The density profiles obtained in this way are found to be within a factor of 2 of those obtained using the simple adiabatic contraction prescription of Blumenthal and colleagues. Our results hold regardless of the nature of the DM or its interactions and rely merely on gravity. If the DM consists of weakly interacting massive particles, which are their own antiparticles, their densities are high enough that their annihilation in the first protostars can indeed provide an important heat source and prevent the collapse all the way to fusion. In short, a "Dark Star" phase of stellar evolution, powered by DM annihilation, may indeed describe the first stars in the universe.

  18. 78 FR 33121 - Staff Requirements-SECY-12-0168-Calvert Cliffs 3 Nuclear Project, LLC & UniStar Nuclear Operating...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-06-03

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  19. The Milky Way as a Star Formation Engine

    NASA Astrophysics Data System (ADS)

    Molinari, S.; Bally, J.; Glover, S.; Moore, T.; Noriega-Crespo, A.; Plume, R.; Testi, L.; Vázquez-Semadeni, E.; Zavagno, A.; Bernard, J.-P.; Martin, P.

    The cycling of material from the interstellar medium (ISM) into stars and the return of stellar ejecta into the ISM is the engine that drives the galactic ecology in normal spirals. This ecology is a cornerstone in the formation and evolution of galaxies through cosmic time. There remain major observational and theoretical challenges in determining the processes responsible for converting the low-density, diffuse components of the ISM into dense molecular clouds, forming dense filaments and clumps, fragmenting them into stars, expanding OB associations and bound clusters, and characterizing the feedback that limits the rate and efficiency of star formation. This formidable task can be attacked effectively for the first time thanks to the synergistic combination of new global-scale surveys of the Milky Way from infrared (IR) to radio wavelengths, offering the possibility of bridging the gap between local and extragalactic star-formation studies. The Herschel Space Observatory Galactic Plane Survey (Hi-GAL) survey, with its five-band 70-500-μm full Galactic Plane mapping at 6"-36" resolution, is the keystone of a set of continuum surveys that include the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE)(360)+MIPSGAL@Spitzer, Wide-field Infrared Survey Explorer (WISE), Midcourse Space Experiment (MSX), APEX Telescope Large Area Survey of the Galaxy (ATLASGAL)@Atacama Pathfinder EXperiment (APEX), Bolocam Galactic Plane Survey (BGPS)@Caltech Submillimeter Observatory (CSO), and CORNISH@Very Large Array (VLA). This suite enables us to measure the Galactic distribution and physical properties of dust on all scales and in all components of the ISM from diffuse clouds to filamentary complexes and hundreds of thousands of dense clumps. A complementary suite of spectroscopic surveys in various atomic and molecular tracers is providing the chemical fingerprinting of dense clumps and filaments, as well as essential kinematic information to derive distances

  20. Infrared Spectroscopy of Star Formation in Galactic and Extragalactic Regions

    NASA Technical Reports Server (NTRS)

    Smith, Howard A.; Hasan, Hashima (Technical Monitor)

    2003-01-01

    In this program we proposed to perform a series of spectroscopic studies, including data analysis and modeling, of star formation regions using an ensemble of archival space-based data from the Infrared Space Observatory's Long Wavelength Spectrometer and Short Wavelength Spectrometer, and to take advantage of other spectroscopic databases including the first results from SIRTF. Our emphasis has been on star formation in external, bright IR galaxies, but other areas of research have included young, low or high mass pre-main sequence stars in star formation regions, and the galactic center. The OH lines in the far infrared were proposed as one key focus of this inquiry, because the Principal Investigator (H. Smith) had a full set of OH IR lines from IS0 observations. It was planned that during the proposed 2-1/2 year timeframe of the proposal other data (including perhaps from SIRTF) would become available, and we intended to be responsive to these and other such spectroscopic data sets. The program has the following goals: 1) Refine the data analysis of IS0 observations to obtain deeper and better SNR results on selected sources. The IS0 data itself underwent pipeline 10 reductions in early 2001, and the more 'hands-on data reduction packages' have been released. The IS0 Fabry-Perot database is particularly sensitive to noise and can have slight calibration errors, and improvements are anticipated. We plan to build on these deep analysis tools and contribute to their development. Model the atomic and molecular line shapes, in particular the OH lines, using revised montecarlo techniques developed by the Submillimeter Wave Astronomy Satellite (SWAS) team at the Center for Astrophysics. 2) 3) Use newly acquired space-based SIRTF or SOFIA spectroscopic data as they become available, and contribute to these observing programs as appropriate. 4) Attend scientific meetings and workshops. 5) E&PO activities, especially as related to infrared astrophysics and

  1. The Evolution of Star Formation Histories of Quiescent Galaxies

    NASA Astrophysics Data System (ADS)

    Pacifici, Camilla; Kassin, Susan A.; Weiner, Benjamin J.; Holden, Bradford; Gardner, Jonathan P.; Faber, Sandra M.; Ferguson, Henry C.; Koo, David C.; Primack, Joel R.; Bell, Eric F.; Dekel, Avishai; Gawiser, Eric; Giavalisco, Mauro; Rafelski, Marc; Simons, Raymond C.; Barro, Guillermo; Croton, Darren J.; Davé, Romeel; Fontana, Adriano; Grogin, Norman A.; Koekemoer, Anton M.; Lee, Seong-Kook; Salmon, Brett; Somerville, Rachel; Behroozi, Peter

    2016-11-01

    Although there has been much progress in understanding how galaxies evolve, we still do not understand how and when they stop forming stars and become quiescent. We address this by applying our galaxy spectral energy distribution models, which incorporate physically motivated star formation histories (SFHs) from cosmological simulations, to a sample of quiescent galaxies at 0.2\\lt z\\lt 2.1. A total of 845 quiescent galaxies with multi-band photometry spanning rest-frame ultraviolet through near-infrared wavelengths are selected from the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) data set. We compute median SFHs of these galaxies in bins of stellar mass and redshift. At all redshifts and stellar masses, the median SFHs rise, reach a peak, and then decline to reach quiescence. At high redshift, we find that the rise and decline are fast, as expected, because the universe is young. At low redshift, the duration of these phases depends strongly on stellar mass. Low-mass galaxies ({log}({M}* /{M}⊙ )˜ 9.5) grow on average slowly, take a long time to reach their peak of star formation (≳ 4 Gyr), and then the declining phase is fast (≲ 2 Gyr). Conversely, high-mass galaxies ({log}({M}* /{M}⊙ )˜ 11) grow on average fast (≲ 2 Gyr), and, after reaching their peak, decrease the star formation slowly (≳ 3). These findings are consistent with galaxy stellar mass being a driving factor in determining how evolved galaxies are, with high-mass galaxies being the most evolved at any time (i.e., downsizing). The different durations we observe in the declining phases also suggest that low- and high-mass galaxies experience different quenching mechanisms, which operate on different timescales.

  2. SHAPING THE DUST MASS-STAR-FORMATION RATE RELATION

    SciTech Connect

    Hjorth, Jens; Gall, Christa; Michałowski, Michał J. E-mail: cgall@phys.au.dk

    2014-02-20

    There is a remarkably tight relation between the observationally inferred dust masses and star-formation rates (SFRs) of Sloan Digital Sky Survey galaxies, M {sub dust} ∝ SFR{sup 1.11}. Here we extend the M {sub dust}-SFR relation to the high end and show that it bends over at very large SFRs (i.e., dust masses are lower than predicted for a given SFR). We identify several distinct evolutionary processes in the diagram: (1) a star-bursting phase in which dust builds up rapidly at early times. The maximum attainable dust mass in this process is the cause of the bend-over of the relation. A high dust-formation efficiency, a bottom-light initial mass function, and negligible supernova shock dust destruction are required to produce sufficiently high dust masses. (2) A quiescent star-forming phase in which the subsequent parallel decline in dust mass and SFR gives rise to the M {sub dust}-SFR relation, through astration and dust destruction. The dust-to-gas ratio is approximately constant along the relation. We show that the power-law slope of the M {sub dust}-SFR relation is inversely proportional to the global Schmidt-Kennicutt law exponent (i.e., ∼0.9) in simple chemical evolution models. (3) A quenching phase which causes star formation to drop while the dust mass stays roughly constant or drops proportionally. Combined with merging, these processes, as well as the range in total baryonic mass, give rise to a complex population of the diagram which adds significant scatter to the original M {sub dust}-SFR relation. (4) At very high redshifts, a population of galaxies located significantly below the local relation is predicted.

  3. One-dimensional cloud fluid model for propagating star formation

    NASA Technical Reports Server (NTRS)

    Titus, Timothy N.; Struck-Marcell, Curtis

    1990-01-01

    The aim of this project was to study the propagation of star formation (SF) with a self-consistent deterministic model for the interstellar gas. The questions of under what conditions does star formation propagate in this model and what are the mechanisms of the propagation are explored. Here, researchers used the deterministic Oort-type cloud fluid model of Scalo and Struck-Marcell (1984, also see the review of Struck-Marcell, Scalo and Appleton 1987). This cloud fluid approach includes simple models for the effects of cloud collisional coalescence or disruption, collisional energy dissipation, and cloud disruption and acceleration as the result of young star winds, HII regions and supernovae. An extensive one-zone parameter study is presented in Struck-Marcell and Scalo (1987). To answer the questions above, researchers carried out one-dimensional calculations for an annulus within a galactic disk, like the so-called solar neighborhood of the galactic chemical evolution. In the calculations the left-hand boundary is set equal to the right hand boundary. The calculation is obviously idealized; however, it is computationally convenient to study the first order effects of propagating star formation. The annulus was treated as if it were at rest, i.e., in the local rotating frame. This assumption may remove some interesting effects of a supersonic gas flow, but was necessary to maintain a numerical stability in the annulus. The results on the one-dimensional propagation of SF in the Oort cloud fluid model follow: (1) SF is propagated by means of hydrodynamic waves, which can be generated by external forces or by the pressure generated by local bursts. SF is not effectively propagated via diffusion or variation in cloud interaction rates without corresponding density and velocity changes. (2) The propagation and long-range effects of SF depend on how close the gas density is to the critical threshold value, i.e., on the susceptibility of the medium.

  4. STAR FORMATION IN HIGH-REDSHIFT CLUSTER ELLIPTICALS

    SciTech Connect

    Wagner, Cory R.; Brodwin, Mark; Snyder, Gregory F.; Gonzalez, Anthony H.; Mancone, Conor L.; Stanford, S. A.; Alberts, Stacey; Pope, Alexandra; Stern, Daniel; Eisenhardt, Peter R. M.; Zeimann, Gregory R.; Chary, Ranga-Ram; Dey, Arjun; Moustakas, John

    2015-02-20

    We measure the star formation rates (SFRs) of massive (M {sub *} > 10{sup 10.1} M {sub ☉}) early-type galaxies (ETGs) in a sample of 11 high-redshift (1.0 < z < 1.5) galaxy clusters drawn from the IRAC Shallow Cluster Survey (ISCS). We identify ETGs visually from Hubble Space Telescope imaging and select likely cluster members as having either an appropriate spectroscopic redshift or red-sequence color. Mid-infrared SFRs are measured using Spitzer 24 μm data for isolated cluster galaxies for which contamination by neighbors, and active galactic nuclei, can be ruled out. Cluster ETGs show enhanced specific star formation rates (sSFRs) compared to cluster galaxies in the local universe, but have sSFRs more than four times lower than that of field ETGs at 1 < z < 1.5. Relative to the late-type cluster population, isolated ETGs show substantially quenched mean SFRs, yet still contribute 12% of the overall star formation activity measured in 1 < z < 1.5 clusters. We find that new ETGs are likely being formed in ISCS clusters; the fraction of cluster galaxies identified as ETGs increases from 34% to 56% from z ∼ 1.5 → 1.25. While the fraction of cluster ETGs that are highly star-forming (SFR ≥ 26 M {sub ☉} yr{sup –1}) drops from 27% to 10% over the same period, their sSFRs are roughly constant. All these factors taken together suggest that, particularly at z ≳ 1.25, the events that created these distant cluster ETGs—likely mergers, at least among the most massive—were both recent and gas-rich.

  5. Star formation in the massive cluster merger Abell 2744

    NASA Astrophysics Data System (ADS)

    Rawle, T. D.; Altieri, B.; Egami, E.; Pérez-González, P. G.; Richard, J.; Santos, J. S.; Valtchanov, I.; Walth, G.; Bouy, H.; Haines, C. P.; Okabe, N.

    2014-07-01

    We present a comprehensive study of star-forming (SF) galaxies in the Hubble Space Telescope (HST) Frontier Field recent cluster merger A2744 (z = 0.308). Wide-field, ultraviolet-infrared (UV-IR) imaging enables a direct constraint of the total star formation rate (SFR) for 53 cluster galaxies, with SFRUV+IR = 343 ± 10 M⊙ yr-1. Within the central 4 arcmin (1.1 Mpc) radius, the integrated SFR is complete, yielding a total SFRUV+IR = 201 ± 9 M⊙ yr-1. Focusing on obscured star formation, this core region exhibits a total SFRIR = 138 ± 8 M⊙ yr-1, a mass-normalized SFRIR of ΣSFR = 11.2 ± 0.7 M⊙ yr-1 per 1014 M⊙ and a fraction of IR-detected SF galaxies f_SF = 0.080^{+0.010}_{-0.037}. Overall, the cluster population at z ˜ 0.3 exhibits significant intrinsic scatter in IR properties (total SFRIR, Tdust distribution) apparently unrelated to the dynamical state: A2744 is noticeably different to the merging Bullet cluster, but similar to several relaxed clusters. However, in A2744 we identify a trail of SF sources including jellyfish galaxies with substantial unobscured SF due to extreme stripping (SFRUV/SFRIR up to 3.3). The orientation of the trail, and of material stripped from constituent galaxies, indicates that the passing shock front of the cluster merger was the trigger. Constraints on star formation from both IR and UV are crucial for understanding galaxy evolution within the densest environments.

  6. DWARF GALAXY FORMATION WITH H{sub 2}-REGULATED STAR FORMATION

    SciTech Connect

    Kuhlen, Michael; Krumholz, Mark R.; Madau, Piero; Smith, Britton D.; Wise, John

    2012-04-10

    We describe cosmological galaxy formation simulations with the adaptive mesh refinement code Enzo that incorporate a star formation prescription regulated by the local abundance of molecular hydrogen. We show that this H{sub 2}-regulated prescription leads to a suppression of star formation in low-mass halos (M{sub h} {approx}< 10{sup 10} M{sub Sun }) at z > 4, alleviating some of the dwarf galaxy problems faced by theoretical galaxy formation models. H{sub 2} regulation modifies the efficiency of star formation of cold gas directly, rather than indirectly reducing the cold gas content with 'supernova feedback'. We determine the local H{sub 2} abundance in our most refined grid cells (76 proper parsec in size at z = 4) by applying the model of Krumholz, McKee, and Tumlinson, which is based on idealized one-dimensional radiative transfer calculations of H{sub 2} formation-dissociation balance in {approx}100 pc atomic-molecular complexes. Our H{sub 2}-regulated simulations are able to reproduce the empirical (albeit lower z) Kennicutt-Schmidt relation, including the low {Sigma}{sub gas} cutoff due to the transition from atomic to molecular phase and the metallicity dependence thereof, without the use of an explicit density threshold in our star formation prescription. We compare the evolution of the luminosity function, stellar mass density, and star formation rate density from our simulations to recent observational determinations of the same at z = 4-8 and find reasonable agreement between the two.

  7. The Spatial Distribution of Star Formation in Galaxies: Observing the Emergence of Galactic Structure

    NASA Astrophysics Data System (ADS)

    Nelson, Erica June

    A high resolution measurement of the distribution of star formation within galaxies is key to understanding the emergence of galactic structure. The aim of this thesis is to understand how the structure of galaxies is built by developing a new method to spatially resolve their star formation. Using Ha maps for 2676 galaxies, this thesis shows where star formation is distributed in galaxies during the epoch 0.7 < z < 1.5 when a third of the total star formation in the history of the universe occurred. Across the star formation rate - stellar mass plane (the "main sequence"), star formation is `spatially coherent': in galaxies with higher than average star formation rates, Ha is enhanced throughout the disk; similarly, in galaxies with low star formation rates Ha is depressed throughout the disk. This places constraints both on the mechanisms for enhancing and quenching star formation as well as on how the structure of galaxies is built. The disk scale length of star formation in galaxies is larger than that of the stars, a direct demonstration that the disks of galaxies grow inside-out. While most star formation in most galaxies occurs in disks, not all of it does. With the first spatially resolved measurement of the Balmer decrement at z > 1, it can be seen that galaxies with M* > 1010M ⊙ have significant dust attenuation toward their centers. This means that we are witnessing the build-up of the dense stellar cores of massive galaxies through dust-obscured in-situ star formation. The most massive galaxies are thought to have formed their dense stellar cores at even earlier cosmic epochs. This thesis presents the first confirmed example of a massive galaxy core in the process of formation at z = 2.3. It has one of the highest velocity dispersions ever measured for a normal star forming galaxy and also appears to be building through very dense, dust-enshrouded star formation.

  8. Investigating the earliest stages of high-mass star formation

    NASA Astrophysics Data System (ADS)

    Fontani, Francesco; Dodson, Richard; Burton, Michael; Cesaroni, Riccardo; Brand, Jan; Molinari, Sergio; Sanchez-Monge, Alvaro; Rioja, Maria; Beltran, Maite

    2010-10-01

    We have recently performed a search for free-free continuum emission towards a sample of high-mass, star forming molecular clumps identified from single-dish observations of the 1.2 mm continuum and CS line emission. Our aim is to image a sub-sample of these clumps in the water maser line and four ammonia inversion transitions. The targets correspond to the earliest star formation phase: 25 IR-dark clumps plus a comparable number (15) of luminous, massive clumps undetected in our cm continuum survey with ATCA. Our goal is to verify the model by Molinari et al. (2008), which describes the evolution of a massive star from the prestellar phase to the main sequence. For this purpose we will use the ammonia lines to estimate the gas temperature and turbulence, and the water maser line to reveal embedded stars. Our expectation is that IR-dark sources will be colder, less turbulent, and less associated with H2O masers than IR-bright. The temperature estimates, combined with our previous 1.2 mm continuum measurements, will permit to obtain a better estimate of the clump masses and thus locate our sources more precisely on the evolutionary diagram of Molinari et al. (2008).

  9. THE STAR FORMATION HISTORY AND CHEMICAL EVOLUTION OF STAR-FORMING GALAXIES IN THE NEARBY UNIVERSE

    SciTech Connect

    Torres-Papaqui, J. P.; Coziol, R.; Ortega-Minakata, R. A.; Neri-Larios, D. M. E-mail: rcoziol@astro.ugto.mx E-mail: daniel@astro.ugto.mx

    2012-08-01

    We have determined the metallicity (O/H) and nitrogen abundance (N/O) of a sample of 122,751 star-forming galaxies (SFGs) from the Data Release 7 of the Sloan Digital Sky Survey. For all these galaxies we have also determined their morphology and obtained a comprehensive picture of their star formation history (SFH) using the spectral synthesis code STARLIGHT. The comparison of the chemical abundance with the SFH allows us to describe the chemical evolution of the SFGs in the nearby universe (z {<=} 0.25) in a manner consistent with the formation of their stellar populations and morphologies. A high fraction (45%) of the SFGs in our sample show an excess abundance of nitrogen relative to their metallicity. We also find this excess to be accompanied by a deficiency of oxygen, which suggests that this could be the result of effective starburst winds. However, we find no difference in the mode of star formation of the nitrogen-rich and nitrogen-poor SFGs. Our analysis suggests that they all form their stars through a succession of bursts of star formation extended over a period of few Gyr. What produces the chemical differences between these galaxies seems therefore to be the intensity of the bursts: the galaxies with an excess of nitrogen are those that are presently experiencing more intense bursts or have experienced more intense bursts in their past. We also find evidence relating the chemical evolution process to the formation of the galaxies: the galaxies with an excess of nitrogen are more massive, and have more massive bulges and earlier morphologies than those showing no excess. Contrary to expectation, we find no evidence that the starburst wind efficiency decreases with the mass of the galaxies. As a possible explanation we propose that the loss of metals consistent with starburst winds took place during the formation of the galaxies, when their potential wells were still building up, and consequently were weaker than today, making starburst winds more

  10. Turbulence and Star Formation in a Sample of Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Maier, Erin; Chien, Li-Hsin; Hunter, Deidre A.

    2016-11-01

    We investigate turbulent gas motions in spiral galaxies and their importance to star formation in far outer disks, where the column density is typically far below the critical value for spontaneous gravitational collapse. Following the methods of Burkhart et al. on the Small Magellanic Cloud, we use the third and fourth statistical moments, as indicators of structures caused by turbulence, to examine the neutral hydrogen (H i) column density of a sample of spiral galaxies selected from The H i Nearby Galaxy Survey. We apply the statistical moments in three different methods—the galaxy as a whole, divided into a function of radii and then into grids. We create individual grid maps of kurtosis for each galaxy. To investigate the relation between these moments and star formation, we compare these maps with their far-ultraviolet images taken by the Galaxy Evolution Explorer satellite.We find that the moments are largely uniform across the galaxies, in which the variation does not appear to trace any star-forming regions. This may, however, be due to the spatial resolution of our analysis, which could potentially limit the scale of turbulent motions that we are sensitive to greater than ∼700 pc. From comparison between the moments themselves, we find that the gas motions in our sampled galaxies are largely supersonic. This analysis also shows that the Burkhart et al. methods may be applied not just to dwarf galaxies but also to normal spiral galaxies.

  11. What can Simple Models tell us about Star Formation?

    NASA Astrophysics Data System (ADS)

    Guszejnov, David; Hopkins, Philip F.; Krumholz, Mark R.

    2016-06-01

    Star formation includes a large amount of nonlinear physics (turbulence, cooling, feedback etc.) making it a challenge to run simulations with detailed physical models. A possible approach is to formulate simple, easily testable models to try to find the minimum physics required to reproduce different aspects of star formation.In this talk I will present a highly flexible semi analytical model that allows one to easily 'plug in' and test different physics. Using this tool we have shown that a universal IMF model requires the presence of an invariant mass scale. Although both feedback and equation of state thermodynamics can provide a mass scale, we showed EOS mass scales are inherently sensitive to initial conditions.Unlike most analytical models this framework provides both spatial and temporal information allowing us to investigate the clustering and binarity in different models. So far we have shown that isothermal common core fragmentation (which is scale free) is able to reproduce the stellar correlation function at long distances. This result is robust to changes in the small scale physics (e.g. adding protostellar feedback, non-isothermal equation of state). With the addition of feedback from protostellar heating, this agreement continues down to the protostellar disk scale. We have also found that such a model can reproduce most binarity properties of low mass stars, hinting that low mass binaries are formed primarily through common core fragmentation.

  12. Radial Star Formation Histories in 15 Nearby Galaxies

    NASA Astrophysics Data System (ADS)

    Dale, Daniel A.; Beltz-Mohrmann, Gillian D.; Egan, Arika A.; Hatlestad, Alan J.; Herzog, Laura J.; Leung, Andrew S.; McLane, Jacob N.; Phenicie, Christopher; Roberts, Jareth S.; Barnes, Kate L.; Boquien, Médéric; Calzetti, Daniela; Cook, David O.; Kobulnicky, Henry A.; Staudaher, Shawn M.; van Zee, Liese

    2016-01-01

    New deep optical and near-infrared imaging is combined with archival ultraviolet and infrared data for 15 nearby galaxies mapped in the Spitzer Extended Disk Galaxy Exploration Science survey. These images are particularly deep and thus excellent for studying the low surface brightness outskirts of these disk-dominated galaxies with stellar masses ranging between 108 and {10}11 {M}⊙ . The spectral energy distributions derived from this data set are modeled to investigate the radial variations in the galaxy colors and star formation histories. Taken as a whole, the sample shows bluer and younger stars for larger radii until reversing near the optical radius, whereafter the trend is for redder and older stars for larger galacto-centric distances. These results are consistent with an inside-out disk formation scenario coupled with an old stellar outer disk population formed through radial migration and/or the cumulative history of minor mergers and accretions of satellite dwarf galaxies. However, these trends are quite modest and the variation from galaxy to galaxy is substantial. Additional data for a larger sample of galaxies are needed to confirm or dismiss these modest sample-wide trends.

  13. Completing the Census of Isolated Dwarf Galaxy Star Formation Histories

    NASA Astrophysics Data System (ADS)

    Weisz, Daniel

    2014-10-01

    We propose to complete our census of the ancient star formation histories (SFHs) of isolated dwarf galaxies by obtaining deep ACS/WFC optical imaging of WLM and Pegasus Dwarf Irregular Galaxy (PegDIG). They are the only two systems without previous deep HST imaging that are isolated yet close enough to guarantee that their oldest main sequence turnoffs are accessible with HST. We will measure their lifetime SFHs with an age resolution of < 1 Gyr at all epochs to address questions about growth of stellar mass, the effects of reionization, radial population gradients, and variable star populations in WLM and PegDIG. This program is a concerted effort between theorists and observers to obtain the best possible observational constraints on the early epochs of star formation in isolated low-mass galaxies, which are essential to the next generation of galaxy simulations. With these new observations we will have completed our efforts to collect precise lifetime SFHs of all nearby isolated dwarfs that are accessible with HST. In combination with archival data, we will create a legacy sample isolated dwarfs with identically derived SFHs, that will be serve as the baseline for the community's understanding of how low-mass galaxies form and evolve over a Hubble time and in the absence of environmental effects of a massive host (e.g., tides, ram pressure).

  14. Star formation bimodality in early-type galaxies

    SciTech Connect

    Amblard, A.; Riguccini, L.; Temi, P.; Im, S.; Fanelli, M.; Serra, P.

    2014-03-10

    We compute the properties of a sample of 221 local, early-type galaxies with a spectral energy distribution (SED) modeling software, CIGALEMC. Concentrating on the star-forming (SF) activity and dust contents, we derive parameters such as the specific star formation rate (sSFR), the dust luminosity, dust mass, and temperature. In our sample, 52% is composed of elliptical (E) galaxies and 48% of lenticular (S0) galaxies. We find a larger proportion of S0 galaxies among galaxies with a large sSFR and large specific dust emission. The stronger activity of S0 galaxies is confirmed by larger dust masses. We investigate the relative proportion of active galactic nuclei (AGNs) and SF galaxies in our sample using spectroscopic Sloan Digital Sky Survey data and near-infrared selection techniques, and find a larger proportion of AGN-dominated galaxies in the S0 sample than the E one. This could corroborate a scenario where blue galaxies evolve into red ellipticals by passing through an S0 AGN active period while quenching its star formation. Finally, we find a good agreement comparing our estimates with color indicators.

  15. The formation of a quadruple star system with wide separation.

    PubMed

    Pineda, Jaime E; Offner, Stella S R; Parker, Richard J; Arce, Héctor G; Goodman, Alyssa A; Caselli, Paola; Fuller, Gary A; Bourke, Tyler L; Corder, Stuartt A

    2015-02-12

    The initial multiplicity of stellar systems is highly uncertain. A number of mechanisms have been proposed to explain the origin of binary and multiple star systems, including core fragmentation, disk fragmentation and stellar capture. Observations show that protostellar and pre-main-sequence multiplicity is higher than the multiplicity found in field stars, which suggests that dynamical interactions occur early, splitting up multiple systems and modifying the initial stellar separations. Without direct, high-resolution observations of forming systems, however, it is difficult to determine the true initial multiplicity and the dominant binary formation mechanism. Here we report observations of a wide-separation (greater than 1,000 astronomical units) quadruple system composed of a young protostar and three gravitationally bound dense gas condensations. These condensations are the result of fragmentation of dense gas filaments, and each condensation is expected to form a star on a timescale of 40,000 years. We determine that the closest pair will form a bound binary, while the quadruple stellar system itself is bound but unstable on timescales of 500,000 years (comparable to the lifetime of the embedded protostellar phase). These observations suggest that filament fragmentation on length scales of about 5,000 astronomical units offers a viable pathway to the formation of multiple systems.

  16. James Webb Space Telescope (JWST) and Star Formation

    NASA Technical Reports Server (NTRS)

    Greene, Thomas P.

    2010-01-01

    The 6.5-m aperture James Webb Space Telescope (JWST) will be a powerful tool for studying and advancing numerous areas of astrophysics. Its Fine Guidance Sensor, Near-Infrared Camera, Near-Infrared Spectrograph, and Mid-Infrared Instrument will be capable of making very sensitive, high angular resolution imaging and spectroscopic observations spanning 0.7 - 28 ?m wavelength. These capabilities are very well suited for probing the conditions of star formation in the distant and local Universe. Indeed, JWST has been designed to detect first light objects as well as to study the fine details of jets, disks, chemistry, envelopes, and the central cores of nearby protostars. We will be able to use its cameras, coronagraphs, and spectrographs (including multi-object and integral field capabilities) to study many aspects of star forming regions throughout the galaxy, the Local Group, and more distant regions. I will describe the basic JWST scientific capabilities and illustrate a few ways how they can be applied to star formation issues and conditions with a focus on Galactic regions.

  17. Chemical complexity and star-formation in merging galaxies

    NASA Astrophysics Data System (ADS)

    Davis, T. A.; Heiderman, A.; Iono, D.; VIXENS Team

    2013-03-01

    When galaxies merge the resulting conditions are some of the most extreme found anywhere in nature. Large gas flows, shocks and active black holes all can affect the ISM. Nearby merging galaxies with strong starbursts are the only places where we can conduct detailed study of star formation in conditions that mimic those under which the majority of stars in the universe formed. Here we study molecular gas tracers in 8 galaxies selected from the VIRUS-P Investigation of the eXtreme ENvironments of Starbursts (VIXENS) survey. Each galaxy has also been observed using the integral field unit spectrograph VIRUS-P, allowing us to investigate the relation between the chemical state of the gas, star formation and total gas content. Full details can be found in Heiderman et al. (2011). Here we report on new results obtained from IRAM-30m/NRO-45m 3mm line surveys towards 14 positions in these 8 merging galaxies. We detect ≈ 25 different molecular transitions towards these objects, many which have never been observed in these galaxies before. Our measurements show that the mean fraction of dense gas increases in later-stage mergers (Fig. 1, left), as does the average optical depth of the gas. Molecular diagnostic diagrams (Fig. 1, right) show that molecular regions we probe are, in general, UV photon dominated. Triggered AGN activity, and/or cosmic ray ionisation (from SNe II in the starburst) are not yet energetically important in determining the state of the gas.

  18. Star formation histories of resolved galaxies - I. The method

    NASA Astrophysics Data System (ADS)

    Small, Emma E.; Bersier, David; Salaris, Maurizio

    2013-01-01

    We present a new method to determine the star formation and metal enrichment histories of any resolved stellar system. This method is based on the fact that any observed star in a colour-magnitude diagram will have a certain probability of being associated with an isochrone characterized by an age t and metallicity [Fe/H] (i.e. to have formed at the time and with the metallicity of that isochrone). We formulate this as a maximum likelihood problem that is then solved with a genetic algorithm. We test the method with synthetic simple and complex stellar populations. We also present tests using real data for open and globular clusters. We are able to determine parameters for the clusters (t, [Fe/H]) that agree well with results found in the literature. Our tests on complex stellar populations show that we can recover the star formation history and age-metallicity relation very accurately. Finally, we look at the history of the Carina dwarf galaxy using deep BVI data. Our results compare well with what we know about the history of Carina.

  19. The dearth of nuclear star clusters in bright galaxies

    NASA Astrophysics Data System (ADS)

    Arca-Sedda, M.; Capuzzo-Dolcetta, R.; Spera, M.

    2016-03-01

    We investigate the interaction of a massive globular cluster (GC) with a super massive black hole (SMBH), located at the centre of its host galaxy, by means of direct N-body simulations. The results show that tidal distortions induced by the stellar background and the SMBH act on a time shorter than that of dynamical friction decay for a 106 M⊙ GC whenever the SMBH mass exceeds ˜108 M⊙. This implies an almost complete dissolution of the infalling GC before it reaches the inner region (≲5 pc) of the parent galaxy. The generalization of this result to a larger sample of infalling GCs shows that such destructive process may prevent the formation and growth of a bright galactic nucleus. Another interesting, serendipitous, result we obtained is that the close interaction between the SMBH and the GC produces a `wave' of stars that escape from the cluster and, in a fraction, even from the whole galaxy.

  20. Star formation and mass assembly in high redshift galaxies

    NASA Astrophysics Data System (ADS)

    Santini, P.; Fontana, A.; Grazian, A.; Salimbeni, S.; Fiore, F.; Fontanot, F.; Boutsia, K.; Castellano, M.; Cristiani, S.; de Santis, C.; Gallozzi, S.; Giallongo, E.; Menci, N.; Nonino, M.; Paris, D.; Pentericci, L.; Vanzella, E.

    2009-09-01

    Aims: The goal of this work is to infer the star formation properties and the mass assembly process of high redshift (0.3 ≤ z < 2.5) galaxies from their IR emission using the 24 μm band of MIPS-Spitzer. Methods: We used an updated version of the GOODS-MUSIC catalog, which has multiwavelength coverage from 0.3 to 24 μm and either spectroscopic or accurate photometric redshifts. We describe how the catalog has been extended by the addition of mid-IR fluxes derived from the MIPS 24 μm image. We compared two different estimators of the star formation rate (SFR hereafter). One is the total infrared emission derived from 24 μm, estimated using both synthetic and empirical IR templates. The other one is a multiwavelength fit to the full galaxy SED, which automatically accounts for dust reddening and age-star formation activity degeneracies. For both estimates, we computed the SFR density and the specific SFR. Results: We show that the two SFR indicators are roughly consistent, once the uncertainties involved are taken into account. However, they show a systematic trend, IR-based estimates exceeding the fit-based ones as the star formation rate increases. With this new catalog, we show that: a) at z>0.3, the star formation rate is correlated well with stellar mass, and this relationship seems to steepen with redshift if one relies on IR-based estimates of the SFR; b) the contribution to the global SFRD by massive galaxies increases with redshift up to ≃ 2.5, more rapidly than for galaxies of lower mass, but appears to flatten at higher z; c) despite this increase, the most important contributors to the SFRD at any z are galaxies of about, or immediately lower than, the characteristic stellar mass; d) at z≃ 2, massive galaxies are actively star-forming, with a median {SFR} ≃ 300 M_⊙ yr-1. During this epoch, our targeted galaxies assemble a substantial part of their final stellar mass; e) the specific SFR (SSFR) shows a clear bimodal distribution. Conclusions

  1. Tracing Star Formation in the Mid-infrared

    NASA Astrophysics Data System (ADS)

    Wu, Ronin

    One of the most important missions of the 20th century in astrophysics is the launch of the Spitzer Space Telescope in August 2003. Since then, with its unprecedented sensitivity and spatial resolution in the infrared, this earth--trailing satellite has significantly improved our understanding of star--formation history and the composition of the interstellar medium from an extragalactic perspective. In this thesis, I present the statistical studies of several star--formation tracers and properties of star--forming galaxies using the photometric and spectroscopic data taken by the Spitzer Space Telescope. The first approach I take in understanding the mid-infrared star--forming tracers is studying the aromatic features at 7.7mum. Aromatic features are the dominant emission lines in the mid-infrared spectra of star--forming galaxies, but these features are much weaker in galaxies of low--luminosity. I combine the infrared and the optical imaging data to demonstrate this trend. Comparison with optical spectroscopic data shows that the strength of the 7.7mum aromatic feature is closely related to the stellar mass of galaxies. Our analysis shows that both oxygen abundance and radiation hardness affect the strength of this feature. However, the generally low oxygen abundance in low--luminosity galaxy interstellar environments, which prevents the synthesis of aromatic molecules, appears to have the stronger effect. The second approach I take is the analysis of the Spitzer SDSS Statistical Spectroscopic Survey (S5), a multi-wavelength study of ˜300 homogeneously selected star--forming galaxies at redshifts 0.05 < z < 0.1. The S5 galaxies span the color range of the Sloan Digital Sky Survey and span two orders of magnitudes in stellar mass. The key goal of the survey is to provide a deeper understanding of the properties of warm interstellar medium by comparing the optical and mid-infrared spectra of galaxies that are structurally similar. The S5 survey contains a

  2. FILAMENTARY STAR FORMATION: OBSERVING THE EVOLUTION TOWARD FLATTENED ENVELOPES

    SciTech Connect

    Lee, Katherine; Looney, Leslie; Johnstone, Doug; Tobin, John E-mail: lwl@illinois.edu E-mail: jtobin@nrao.edu

    2012-12-20

    Filamentary structures are ubiquitous from large-scale molecular clouds (a few parsecs) to small-scale circumstellar envelopes around Class 0 sources ({approx}1000 AU to {approx}0.1 pc). In particular, recent observations with the Herschel Space Observatory emphasize the importance of large-scale filaments (a few parsecs) and star formation. The small-scale flattened envelopes around Class 0 sources are reminiscent of the large-scale filaments. We propose an observationally derived scenario for filamentary star formation that describes the evolution of filaments as part of the process for formation of cores and circumstellar envelopes. If such a scenario is correct, small-scale filamentary structures (0.1 pc in length) with higher densities embedded in starless cores should exist, although to date almost all the interferometers have failed to observe such structures. We perform synthetic observations of filaments at the prestellar stage by modeling the known Class 0 flattened envelope in L1157 using both the Combined Array for Research in Millimeter-wave Astronomy (CARMA) and the Atacama Large Millimeter/Submillimeter Array (ALMA). We show that with reasonable estimates for the column density through the flattened envelope, the CARMA D array at 3 mm wavelengths is not able to detect such filamentary structure, so previous studies would not have detected them. However, the substructures may be detected with the CARMA D+E array at 3 mm and the CARMA E array at 1 mm as a result of more appropriate resolution and sensitivity. ALMA is also capable of detecting the substructures and showing the structures in detail compared to the CARMA results with its unprecedented sensitivity. Such detection will confirm the new proposed paradigm of non-spherical star formation.

  3. ON THE ESTIMATION OF SYSTEMATIC UNCERTAINTIES OF STAR FORMATION HISTORIES

    SciTech Connect

    Dolphin, Andrew E.

    2012-05-20

    In most star formation history (SFH) measurements, the reported uncertainties are those due to effects whose sizes can be readily measured: Poisson noise, adopted distance and extinction, and binning choices in the solution itself. However, the largest source of error, systematics in the adopted isochrones, is usually ignored and very rarely explicitly incorporated into the uncertainties. I propose a process by which estimates of the uncertainties due to evolutionary models can be incorporated into the SFH uncertainties. This process relies on application of shifts in temperature and luminosity, the sizes of which must be calibrated for the data being analyzed. While there are inherent limitations, the ability to estimate the effect of systematic errors and include them in the overall uncertainty is significant. The effects of this are most notable in the case of shallow photometry, with which SFH measurements rely on evolved stars.

  4. Star formation and AGN activity in the most luminous LINERs in the local universe

    NASA Astrophysics Data System (ADS)

    Márquez, I.; Povic, M.; Netzer, H.; Masegosa, J.; Nordon, R.; Pérez, E.; Schoenell, W.

    2017-03-01

    This work presents the properties of 42 objects in the group of the most luminous, highest star formation rate (SFR) low-ionization nuclear emission-line regions (LINERs) at z = 0.04 - 0.11. We obtained long-slit spectroscopy of the nuclear regions for all sources, and FIR data (Herschel and IRAS) for 13 of them.We measured emission-line intensities, extinction, stellar populations, stellar masses, ages, active galactic nuclei (AGN) luminosities, and SFRs. We find considerable differences from other low-redshift LINERs, and general similarity to star-forming galaxies. We confirm the existence of such luminous LINERs in the local universe, after being previously detected at z˜0.3 by Tommasin et al. The median stellar mass of these LINERs corresponds to 6 - 7× 10^{10} M_⊙ which was found in previous works to correspond to the peak of relative growth rate of stellar populations and therefore for the highest SFRs. Other LINERs although showing similar AGN luminosities have lower SFR. We find that most of these sources have LAGN ˜ LSF suggesting co-evolution of black hole and stellarmass. In general, the fraction of local LINERs on the main sequence of star-forming galaxies is related to their AGN luminosity.

  5. Star formation and AGN activity in the most luminous LINERs in the local universe

    NASA Astrophysics Data System (ADS)

    Pović, Mirjana; Márquez, Isabel; Netzer, Hagai; Masegosa, Josefa; Nordon, Raanan; Pérez, Enrique; Schoenell, William

    2016-11-01

    This work presents the properties of 42 objects in the group of the most luminous, highest star formation rate (SFR) low-ionization nuclear emission-line regions (LINERs) at z = 0.04-0.11. We obtained long-slit spectroscopy of the nuclear regions for all sources, and FIR data (Herschel and IRAS) for 13 of them. We measured emission-line intensities, extinction, stellar populations, stellar masses, ages, active galactic nuclei (AGN) luminosities, and SFRs. We find considerable differences from other low-redshift LINERs, in terms of extinction, and general similarity to star-forming galaxies. We confirm the existence of such luminous LINERs in the local universe, after being previously detected at z ˜ 0.3 by Tommasin et al. The median stellar mass of these LINERs corresponds to 6-7 × 1010 M⊙ which was found in previous work to correspond to the peak of relative growth rate of stellar populations and therefore for the highest SFRs. Other LINERs although showing similar AGN luminosities have lower SFR. We find that most of these sources have LAGN ˜ LSF suggesting co-evolution of black hole and stellar mass. In general, the fraction of local LINERs on the main sequence of star-forming galaxies is related to their AGN luminosity.

  6. Extrasolar planets and star formation: science opportunities for future ELTs

    NASA Astrophysics Data System (ADS)

    Stapelfeldt, Karl R.

    Future extremely large telescopes will be the engines of major progress in the fields of star and planet formation, brown dwarfs, and extrasolar planets. Their throughput will enable spectroscopic studies of the structure of brown dwarf atmospheres; reveal the composition and kinematics of protoplanetary disks; extend radial velocity searches for extrasolar planets to fainter stars and lower masses; and characterize the surfaces of the most distant Kuiper Belt objects. Their resolution will allow us to resolve and track the orbits of close binary young stars and brown dwarfs, establishing their dynamical masses and calibrating their evolutionary tracks; probe the inner region of young stellar object disks, resolving the jet collimation region in accreting systems and disk inner holes in more evolved ones; and move the horizon for stellar companion searches inward to 40 mas, enabling the direct detection of hot young planets orbiting 10 AU from young T Tauri stars. The high contrast imaging capability of future ELTs is uncertain, and depends on future developments in extreme adaptive optics. Wavefront control considerations suggest a fundamental atmospheric contrast limit of 10^{-8} for companion searches to nearby solar-type stars, below which detections are unlikely to be possible. To reach this performance level, continuing investments will be needed in extreme adaptive optics work, in addition to careful attention to the specialized requirements of ultra-high contrast imaging in ELT design. Above the 10^{-8} contrast limit, a 30m telescope has the potential to directly image about a dozen of the currently known radial velocity planets.

  7. Massive Star Formation in Early-type(Sa-Sab) Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Hameed, S.

    1999-12-01

    We have conducted an Hα imaging survey of 57 bright, nearby, early-type spiral galaxies. The new Hα images have revealed them to be a heterogeneous class of galaxies with Hα morphologies ranging from filamentary, low luminosity nuclear emission line spirals to what we suspect are compact, luminous nuclear starbursts. Contrary to popular perception, our images have revealed a significant number(15-20%) of Sa-Sab galaxies with massive star formation rates comparable to the most prolifically star forming Sc galaxies. A determination of the Hα morphology and a measure of the Hα luminosity suggests that early-type spirals can be classified into two broad categories. The first category includes galaxies for which the individual HII regions have L(Hα ) < 1039 erg/s. Most of the category 1 galaxies appear to be morphologically undisturbed, but show a wide diversity in nuclear Hα properties. The second category includes galaxies which have at least one HII region in the disk with L(Hα ) >= 1039 erg/s. All category 2 galaxies show morphological peculiarities, such as tidal tails, which suggests that the anomalously luminous HII regions may have formed as a result of a recent interaction. We have also determined HII region luminosity functions for a subset of our sample and find that the shape of the HII region LF is different when a giant HII region is present compared to a galaxy which contains only HII regions of modest luminosity. The difference may point to corresponding differences in massive star formation triggering mechanisms.

  8. Formation of the first stars in the universe

    NASA Astrophysics Data System (ADS)

    Yoshida, Naoki; Hosokawa, Takashi; Omukai, Kazuyuki

    2012-10-01

    The standard theory of cosmic structure formation posits that the present-day rich structure of the universe developed through gravitational amplification of tiny matter density fluctuations left over from the Big Bang. Recent observations of the cosmic microwave background, large-scale structure, and distant supernovae determined the energy content of the universe and the basic statistics of the initial density field with great accuracy. It has become possible to make accurate predictions for the formation and nonlinear growth of structure through early to the present epochs. We review recent progress in the theory of structure formation in the early universe. Results from state-of-the-art computer simulations are presented. Finally, we discuss prospects for future observations of the first generation of stars, black holes, and galaxies.

  9. Properties and Star Formation Histories of Intermediate Redshift Dwarf Low-Mass Star-Forming Galaxies

    NASA Astrophysics Data System (ADS)

    Rodríguez-Muñoz, L.; Gallego, J.; Pacifici, C.; Tresse, L.; Charlot, S.; Gil de Paz, A.; Barro, G.; Villar, V.

    2017-03-01

    The epoch when low-mass star-forming galaxies (LMSFGs) form the bulk of their stellar mass is uncertain. While some models predict an early formation, others favor a delayed scenario until later ages of the Universe. We present improved constraints on the physical properties and star formation histories (SFHs) of a sample of intermediate redshift LMSFGs selected by their stellar mass or blue-compact-dwarf-like properties. Our work takes advantage of the deep UV-to-FIR photometric coverage available on the Extended-Chandra Deep Field South and our own dedicated deep VLT/VIMOS optical spectroscopy programs. On the one hand, we estimate the stellar mass (M_{*}), star formation rate (SFR), and SFH of each galaxy modeling its spectral energy distribution. We use a novel approach by Pacifici et al. 2012, that (1) consistently combines photometric (broad-band) and spectroscopic (emission line fluxes and equivalent widths) data, and (2) uses physically-motivated SFHs with non-uniform variations of the SFR as a function of time. On the other hand, we characterize the properties of their interstellar medium by analyzing the emission line features visible in the VIMOS spectroscopy. The final sample includes 91 spectroscopically confirmed LMSFGs (7.3 ≤ logM_{*}/M_{⊙} ≤ 9.5) at 0.3 star forming galaxies over 2 dex in stellar mass, and high specific-SFR. Furthermore, they are characterized by strong emission lines, low metallicity, and an enhanced level of excitation. Our selection criterion based on mass gathers galaxies within a wide range of properties, and possibly, different evolutionary stages. Despite the individual differences, the average SFH that we obtain suggests a late and fast (˜2 Gyr prior their observation) assembly scenario for this type of system.

  10. How chemistry influences cloud structure, star formation, and the IMF

    NASA Astrophysics Data System (ADS)

    Hocuk, S.; Cazaux, S.; Spaans, M.; Caselli, P.

    2016-03-01

    In the earliest phases of star-forming clouds, stable molecular species, such as CO, are important coolants in the gas phase. Depletion of these molecules on dust surfaces affects the thermal balance of molecular clouds and with that their whole evolution. For the first time, we study the effect of grain surface chemistry (GSC) on star formation and its impact on the initial mass function (IMF). We follow a contracting translucent cloud in which we treat the gas-grain chemical interplay in detail, including the process of freeze-out. We perform 3D hydrodynamical simulations under three different conditions, a pure gas-phase model, a freeze-out model, and a complete chemistry model. The models display different thermal evolution during cloud collapse as also indicated in Hocuk, Cazaux & Spaans, but to a lesser degree because of a different dust temperature treatment, which is more accurate for cloud cores. The equation of state (EOS) of the gas becomes softer with CO freeze-out and the results show that at the onset of star formation, the cloud retains its evolution history such that the number of formed stars differ (by 7 per cent) between the three models. While the stellar mass distribution results in a different IMF when we consider pure freeze-out, with the complete treatment of the GSC, the divergence from a pure gas-phase model is minimal. We find that the impact of freeze-out is balanced by the non-thermal processes; chemical and photodesorption. We also find an average filament width of 0.12 pc (±0.03 pc), and speculate that this may be a result from the changes in the EOS caused by the gas-dust thermal coupling. We conclude that GSC plays a big role in the chemical composition of molecular clouds and that surface processes are needed to accurately interpret observations, however, that GSC does not have a significant impact as far as star formation and the IMF is concerned.

  11. Towards Understanding the Star Formation-Feedback Loop in Galaxy Formation and Evolution

    NASA Astrophysics Data System (ADS)

    Kravtsov, Andrey

    We propose to carry out a comprehensive study of how star formation and feedback loop influences evolution of galaxies using a suite of ultra-high resolution cosmological simulations of galaxy formation using the Adaptive Mesh Refinement (AMR) approach implemented in the Adaptive Refinement Tree (ART) code. The simulations will result in the numerical models of galaxy evolution of unprecedented resolution and sophistication of the processes included. Our code includes treatment of a wide spectrum of processes critical for realistic modeling of galaxy formation from the primordial chemistry of hydrogen and helium species, radiative transfer of ionizing radiation, to the metallicity- dependent cooling, chemistry of molecular hydrogen on dust and treatment of radiative transfer of dissociating far ultraviolet radiation. The latter allows us to tie star formation with dense, molecular regions capable of self-shielding from heating radiation and avoid adopting arbitrary density and temperature thresholds for star formation. Simulations will also employ a new model for momentum injection due to radiation pressure exerted by young massive stars onto surrounding dust and gas. This early, pre-supernova feedback is critical to prompt dispersal of natal molecular clouds and regulating star formation efficiency and increasing efficiency of energy release by supernovae. The simulations proposed in this project will therefore treat the most important process to understanding the efficiency of baryon conversion to stars - the star formation - in the way most closely resembling the actual star formation observed in galaxies and stellar feedback model that is firmly rooted in observational evidence on how feedback operates in real molecular clouds. The simulations we propose will provide models of galaxy evolution during three important epochs in the history of the universe: (1) early evolution prior to and during the reionization of the universe (the first billion years of

  12. THE NATURE OF STARBURSTS. III. THE SPATIAL DISTRIBUTION OF STAR FORMATION

    SciTech Connect

    McQuinn, Kristen B. W.; Skillman, Evan D.; Dalcanton, Julianne J.; Weisz, Daniel R.; Williams, Benjamin F.; Cannon, John M.; Dolphin, Andrew E.; Holtzman, Jon

    2012-11-01

    We map the spatial distribution of recent star formation over a few Multiplication-Sign 100 Myr timescales in 15 starburst dwarf galaxies using the location of young blue helium burning stars identified from optically resolved stellar populations in archival Hubble Space Telescope observations. By comparing the star formation histories from both the high surface brightness central regions and the diffuse outer regions, we measure the degree to which the star formation has been centrally concentrated during the galaxies' starbursts, using three different metrics for the spatial concentration. We find that the galaxies span a full range in spatial concentration, from highly centralized to broadly distributed star formation. Since most starbursts have historically been identified by relatively short timescale star formation tracers (e.g., H{alpha} emission), there could be a strong bias toward classifying only those galaxies with recent, centralized star formation as starbursts, while missing starbursts that are spatially distributed.

  13. Grain formation around carbon stars. 1: Stationary outflow models

    NASA Technical Reports Server (NTRS)

    Egan, Michael P.; Leung, Chun Ming

    1995-01-01

    Asymptotic giant branch (AGB) stars are known to be sites of dust formation and undergo significant mass loss. The outflow is believed to be driven by radiation pressure on grains and momentum coupling between the grains and gas. While the physics of shell dynamics and grain formation are closely coupled, most previous models of circumstellar shells have treated the problem separately. Studies of shell dynamics typically assume the existence of grains needed to drive the outflow, while most grain formation models assume a constant veolcity wind in which grains form. Furthermore, models of grain formation have relied primarily on classical nucleation theory instead of using a more realistic approach base