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Sample records for active star forming

  1. 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.

  2. How Stars Form

    NASA Astrophysics Data System (ADS)

    McKee, Christopher F.

    2017-01-01

    Stars are the atoms of the universe. The process by which stars form is at the nexus of astrophysics since they are believed to be responsible for the re-ionization of the universe, they created the heavy elements, they play a central role in the formation and evolution of galaxies, and their formation naturally leads to the formation of planets. Whereas early work on star formation was based on the assumption that it is a quiescent process, it is now believed that turbulence plays a dominant role. In this overview, I shall discuss the evolution of our understanding of how stars form and current ideas about the stellar initial mass function and the rate of star formation.

  3. The Main Sequences of Star-forming Galaxies and Active Galactic Nuclei at High Redshift

    NASA Astrophysics Data System (ADS)

    Mancuso, C.; Lapi, A.; Shi, J.; Cai, Z.-Y.; Gonzalez-Nuevo, J.; Béthermin, M.; Danese, L.

    2016-12-01

    We provide a novel, unifying physical interpretation on the origin, average shape, scatter, and cosmic evolution for the main sequences of star-forming galaxies and active galactic nuclei (AGNs) at high redshift z≳ 1. We achieve this goal in a model-independent way by exploiting: (i) the redshift-dependent star formation rate functions based on the latest UV/far-IR data from HST/Herschel, and related statistics of strong gravitationally lensed sources; (ii) deterministic evolutionary tracks for the history of star formation and black hole accretion, gauged on a wealth of multiwavelength observations including the observed Eddington ratio distribution. We further validate these ingredients by showing their consistency with the observed galaxy stellar mass functions and AGN bolometric luminosity functions at different redshifts via the continuity equation approach. Our analysis of the main sequence for high-redshift galaxies and AGNs highlights that the present data are consistently interpreted in terms of an in situ coevolution scenario for star formation and black hole accretion, envisaging these as local, time-coordinated processes.

  4. Obscured active galactic nuclei triggered in compact star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Chang, Yu-Yen; Le Floc'h, Emeric; Juneau, Stéphanie; da Cunha, Elisabete; Salvato, Mara; Civano, Francesca; Marchesi, Stefano; Gabor, J. M.; Ilbert, Olivier; Laigle, Clotilde; McCracken, H. J.; Hsieh, Bau-Ching; Capak, Peter

    2017-03-01

    We present a structural study of 182 obscured active galactic nuclei (AGNs) at z ≤ 1.5, selected in the Cosmic Evolution Survey field from their extreme infrared to X-ray luminosity ratio and their negligible emission at optical wavelengths. We fit optical to far-infrared spectral energy distributions and analyse deep Hubble Space Telescope imaging to derive the physical and morphological properties of their host galaxies. We find that such galaxies are more compact than normal star-forming sources at similar redshift and stellar mass, and we show that it is not an observational bias related to the emission of the AGN. Based on the distribution of their UVJ colours, we also argue that this increased compactness is not due to the additional contribution of a passive bulge. We thus postulate that a vast majority of obscured AGNs reside in galaxies undergoing dynamical compaction, similar to processes recently invoked to explain the formation of compact star-forming sources at high redshift.

  5. WIDESPREAD AND HIDDEN ACTIVE GALACTIC NUCLEI IN STAR-FORMING GALAXIES AT REDSHIFT >0.3

    SciTech Connect

    Juneau, Stephanie; Bournaud, Frederic; Daddi, Emanuele; Elbaz, David; Alexander, David M.; Mullaney, James R.; Magnelli, Benjamin; Hwang, Ho Seong; Willner, S. P.; Coil, Alison L.; Rosario, David J.; Trump, Jonathan R.; Faber, S. M.; Kocevski, Dale D.; Cooper, Michael C.; Frayer, David T.; and others

    2013-02-20

    We characterize the incidence of active galactic nuclei (AGNs) in 0.3 < z < 1 star-forming galaxies by applying multi-wavelength AGN diagnostics (X-ray, optical, mid-infrared, radio) to a sample of galaxies selected at 70 {mu}m from the Far-Infrared Deep Extragalactic Legacy survey (FIDEL). Given the depth of FIDEL, we detect 'normal' galaxies on the specific star formation rate (sSFR) sequence as well as starbursting systems with elevated sSFR. We find an overall high occurrence of AGN of 37% {+-} 3%, more than twice as high as in previous studies of galaxies with comparable infrared luminosities and redshifts but in good agreement with the AGN fraction of nearby (0.05 < z < 0.1) galaxies of similar infrared luminosities. The more complete census of AGNs comes from using the recently developed Mass-Excitation (MEx) diagnostic diagram. This optical diagnostic is also sensitive to X-ray weak AGNs and X-ray absorbed AGNs, and reveals that absorbed active nuclei reside almost exclusively in infrared-luminous hosts. The fraction of galaxies hosting an AGN appears to be independent of sSFR and remains elevated both on the sSFR sequence and above. In contrast, the fraction of AGNs that are X-ray absorbed increases substantially with increasing sSFR, possibly due to an increased gas fraction and/or gas density in the host galaxies.

  6. High Energy Gamma Rays and Neutrinos from Star-forming Activities in the Galactic and Extragalactic Sources

    NASA Astrophysics Data System (ADS)

    Razzaque, Soebur

    2017-01-01

    The origin of the IceCube astrophysical neutrinos is an outstanding question. Star-forming activities which can accelerate particles to very high energies have been suggested as possible origin of these neutrinos. I will present a scenario where a subset of the neutrino events originate from the Galactic center region and Fermi Bubbles, resulting from star-forming activities. Multi-messenger signal in high energy gamma rays and neutrinos can probe this scenario. I will also present an analysis of the statistical association of the star-forming sources in our Galaxy and outside, with astrophysical neutrinos, as well as expected neutrino signal from these sources by fitting gamma-ray data.

  7. Star-forming Filament Models

    NASA Astrophysics Data System (ADS)

    Myers, Philip C.

    2017-03-01

    New models of star-forming filamentary clouds are presented in order to quantify their properties and to predict their evolution. These 2D axisymmetric models describe filaments that have no core, one low-mass core, and one cluster-forming core. They are based on Plummer-like cylinders and spheroids that are bounded by a constant-density surface of finite extent. In contrast to 1D Plummer-like models, they have specific values of length and mass, they approximate observed column density maps, and their distributions of column density (N-pdfs) are pole-free. Each model can estimate the star-forming potential of a core-filament system by identifying the zone of gas dense enough to form low-mass stars and by counting the number of enclosed thermal Jeans masses. This analysis suggests that the Musca central filament may be near the start of its star-forming life, with enough dense gas to make its first ∼3 protostars, while the Coronet filament is near the midpoint of its star formation, with enough dense gas to add ∼8 protostars to its ∼20 known stars. In contrast, L43 appears to be near the end of its star-forming life, since it lacks enough dense gas to add any new protostars to the two young stellar objectsalready known.

  8. 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.

  9. Observational analysis of the physical conditions in galactic and extragalactic active star forming regions

    NASA Astrophysics Data System (ADS)

    Kristensen, L. E.

    2007-10-01

    In my thesis observations of near-infrared rovibrational H_2 emission in active star-forming regions are presented and analysed. The main subject of this work concerns new observations of the Orion Molecular Cloud (OMC1) and in particular the BN-KL region. Data consist of images of individual H_2 lines with high spatial resolution obtained both at the Canada-France-Hawaii Telescope and at the ESO Very Large Telescope (VLT). With the high spatial resolution of the VLT it is possible to analyse in detail (down to 60 AU ~ 0.13") individual objects in the region. I have also analysed H_2 and [FeII] emission from outflows in two dark clouds (Bok globules BHR71 and BHR137) and a high excitation blob in the Magellanic Clouds (N159-5). In the latter, data consist of long-slit spectra obtained at the ESO-VLT. In order to facilitate this work I ran a large grid of ~25000 shock models, producing almost 400 Gb of results. These models are state-of-the-art and there is a large number of free parameters which can be adjusted. A big part of my project has been to analyse the results from this grid and make it publically available. Furthermore, as it turned out, not all results are equally reliable and I have had to develop methods for checking the consistency of the wealth of results obtained. But with the model results and a sound knowledge of shock physics it is now relatively straightforward to interpret the H_2 and [FeII] data. The models allow me to predict the large-scale physical conditions in OMC1 such as density, shock velocities, magnetic field strengths, etc. Overall the preshock density is of the order of ~10^5-10^7 cm(-3) and shock velocities are in the interval 10-40 km/s. Another very interesting result is a new method developed for analysing bow shocks observed at high spatial resolution. For one isolated bow shock in OMC1 I predict a shock velocity of 50 km/s and a preshock density of the order of 5x10^5 cm(-3). The 3D velocity has recently been measured to 55 km

  10. GOODS-HERSCHEL: SEPARATING HIGH-REDSHIFT ACTIVE GALACTIC NUCLEI AND STAR-FORMING GALAXIES USING INFRARED COLOR DIAGNOSTICS

    SciTech Connect

    Kirkpatrick, Allison; Pope, Alexandra; Charmandaris, Vassilis; Daddi, Emmanuele; Elbaz, David; Pannella, Maurilio; Aussel, Herve; Dasyra, Kalliopi; Leiton, Roger; Scott, Douglas; Magnelli, Benjamin; Popesso, Paola; Altieri, Bruno; Coia, Daniela; Valtchanov, Ivan; Dannerbauer, Helmut; Dickinson, Mark; Kartaltepe, Jeyhan; Magdis, Georgios

    2013-02-15

    We have compiled a large sample of 151 high-redshift (z = 0.5-4) galaxies selected at 24 {mu}m (S {sub 24} > 100 {mu}Jy) in the GOODS-N and ECDFS fields for which we have deep Spitzer IRS spectroscopy, allowing us to decompose the mid-infrared spectrum into contributions from star formation and activity in the galactic nuclei. In addition, we have a wealth of photometric data from Spitzer IRAC/MIPS and Herschel PACS/SPIRE. We explore how effective different infrared color combinations are at separating our mid-IR spectroscopically determined active galactic nuclei from our star-forming galaxies. We look in depth at existing IRAC color diagnostics, and we explore new color-color diagnostics combining mid-IR, far-IR, and near-IR photometry, since these combinations provide the most detail about the shape of a source's IR spectrum. An added benefit of using a color that combines far-IR and mid-IR photometry is that it is indicative of the power source driving the IR luminosity. For our data set, the optimal color selections are S {sub 250}/S {sub 24} versus S {sub 8}/S {sub 3.6} and S {sub 100}/S {sub 24} versus S {sub 8}/S {sub 3.6}; both diagnostics have {approx}10% contamination rate in the regions occupied primarily by star-forming galaxies and active galactic nuclei, respectively. Based on the low contamination rate, these two new IR color-color diagnostics are ideal for estimating both the mid-IR power source of a galaxy when spectroscopy is unavailable and the dominant power source contributing to the IR luminosity. In the absence of far-IR data, we present color diagnostics using the Wide-field Infrared Survey Explorer mid-IR bands which can efficiently select out high-z (z {approx} 2) star-forming galaxies.

  11. [Molecular spectral diagnosis of star forming regions].

    PubMed

    Xi, S; Qin, S; Deng, L; Yang, J

    2001-08-01

    Stars are the basic building blocks of our universe, therefore it is one of the most important research topics in astrophysics to understand the origin and the early evolution of these objects. The current picture is that stars are formed during the collapse of a large enough self-gravitating interstellar molecular cloud. The early collapse gives birth to a fetus of a star, which is surrounded by a rotating accretion disk. The proto-star accretes interstellar matter through the disk which in turn transfer the accumulated matter to the central proto-star, then the star gets weight during the process. Observation shows that gorgeous ejection of matter always come along with the accretion process. In the presence of disks, these outflows usually escape from the system along the axis of the disk, forming so called bipolar outflows. Typical tracers of these activities are rich molecules such as CO, SiC2, C3H, C3H2 etc. Observationally, such typical molecular outflows can be detected using Doppler effect by spectroscopic measurements. Using the 13.7 m radio telescope in Delingha station of Purple Mountain Observatory, we performed a survey for 12 low temperature IRAS objects, some of the sources show high velocity properties. Detailed analysis of the Doppler profiles of IRS34 is presented. Star forming activities are clearly seen in this field.

  12. Star-forming Activity in the H II Regions Associated with the IRAS 17160-3707 Complex

    NASA Astrophysics Data System (ADS)

    Nandakumar, G.; Veena, V. S.; Vig, S.; Tej, A.; Ghosh, S. K.; Ojha, D. K.

    2016-11-01

    We present a multiwavelength investigation of star formation activity toward the southern H ii regions associated with IRAS 17160-3707, located at a distance of 6.2 kpc with a bolometric luminosity of 8.3 × 105 L ⊙. The ionized gas distribution and dust clumps in the parental molecular cloud are examined in detail using measurements at infrared, submillimeter and radio wavelengths. The radio continuum images at 1280 and 610 MHz obtained using the Giant Metrewave Radio Telescope reveal the presence of multiple compact sources as well as nebulous emission. At submillimeter wavelengths, we identify seven dust clumps and estimate their physical properties such as temperature: 24-30 K, mass: 300-4800 M ⊙ and luminosity: 9-317 × 102 L ⊙ using modified blackbody fits to the spectral energy distributions (SEDs) between 70 and 870 μm. We find 24 young stellar objects (YSOs) in the mid-infrared, with a few of them coincident with the compact radio sources. The SEDs of the YSOs have been fitted by the Robitaille models and the results indicate that those having radio compact sources as counterparts host massive objects in early evolutionary stages with best fit age ≤0.2 Myr. We compare the relative evolutionary stages of clumps using various signposts such as masers, ionized gas, presence of YSOs and infrared nebulosity, and find six massive star-forming clumps and one quiescent clump. Of the former, five are in a relatively advanced stage and one in an earlier stage.

  13. The Atacama Cosmology Telescope: Dusty Star-Forming Galaxies and Active Galactic Nuclei in the Southern Survey

    NASA Technical Reports Server (NTRS)

    Marsden, Danica; Gralla, Megan; Marriage, Tobias A.; Switzer, Eric R.; Partridge, Bruce; Massardi, Marcella; Morales, Gustavo; Addison, Graeme; Bond, J. Richard; Crighton, Devin; Das, Sudeep; Devlin, Mark; Dunner, Rolando; Hajian, Amir; Hilton, Matt; Hincks, Adam; Hughes, John P.; Irwin, Kent; Kosowsky, Arthur; Menanteau, Felipe; Moodley, Kavilan; Niemack, Michael; Page, Lyman; Reese, Erik D.; Schmitt, Benjamin; Sehgal, Neelima; Sievers, Johnathan; Staggs, Suzanne; Swetz, Daniel; Thornton, Robert; Wollack, Edward

    2014-01-01

    We present a catalogue of 191 extragalactic sources detected by the Atacama Cosmology Telescope (ACT) at 148 and/or 218 GHz in the 2008 Southern survey. Flux densities span 14 -1700 mJy, and we use source spectral indices derived using ACT-only data to divide our sources into two subpopulations: 167 radio galaxies powered by central active galactic nuclei (AGN) and 24 dusty star-forming galaxies (DSFGs). We cross-identify 97 per cent of our sources (166 of the AGN and 19 of the DSFGs) with those in currently available catalogues. When combined with flux densities from the Australia Telescope 20 GHz survey and follow-up observations with the Australia Telescope Compact Array, the synchrotron-dominated population is seen to exhibit a steepening of the slope of the spectral energy distribution from 20 to 148 GHz, with the trend continuing to 218 GHz. The ACT dust-dominated source population has a median spectral index, A(sub 148-218), of 3.7 (+0.62 or -0.86), and includes both local galaxies and sources with redshift around 6. Dusty sources with no counterpart in existing catalogues likely belong to a recently discovered subpopulation of DSFGs lensed by foreground galaxies or galaxy groups.

  14. The Atacama Cosmology Telescope: Dusty Star-Forming Galaxies and Active Galactic Nuclei in the Southern Survey

    NASA Technical Reports Server (NTRS)

    Marsden, Danica; Gralla, Megan; Marriage, Tobias A.; Switzer, Eric R.; Partridge, Bruce; Massardi, Marcella; Morales, Gustavo; Addison, Graeme; Bond, J. Richard; Crichton, Devin; Das, Sudeep; Devlin, Mark; Duenner, Rolando; Hajian, Amir; Hilton, Matt; Hincks, Adam; Hughes, John P.; Irwin, Kent; Kosowsky, Arthur; Menanteau, Felipe; Moodley, Kavilan; Niemack, Michael; Page, Lyman; Reese, EriK D.; Wollack, Edward

    2013-01-01

    We present a catalog of 191 extragalactic sources detected by the Atacama Cosmology Telescope (ACT) at 148 GHz and/or 218GHz in the 2008 Southern survey. Flux densities span 14-1700mJy, and we use source spectral indices derived using ACT-only data to divide our sources into two sub-populations: 167 radio galaxies powered by central active galactic nuclei (AGN), and 24 dusty star-forming galaxies (DSFGs). We cross-identify 97% of our sources (166 of the AGN and 19 of the DSFGs) with those in currently available catalogs. When combined with flux densities from the Australian Telescope 20 GHz survey and follow-up observations with the Australia Telescope Compact Array, the synchrotron-dominated population is seen to exhibit a steepening of the slope of the spectral energy distribution from 20 to 148GHz, with the trend continuing to 218GHz. The ACT dust-dominated source population has a median spectral index, alpha(sub 148-218), of 3.7+0.62 or -0.86, and includes both local galaxies and sources with redshifts as great as 5.6. Dusty sources with no counterpart in existing catalogs likely belong to a recently discovered subpopulation of DSFGs lensed by foreground galaxies or galaxy groups.

  15. The Atacama Cosmology Telescope: Dusty Star-Forming Galaxies and Active Galactic Nuclei in the Southern Survey

    NASA Technical Reports Server (NTRS)

    Marsden, Danica; Gralla, Megan; Marriage, Tobias A.; Switzer, Eric R.; Partridge, Bruce; Massardi, Marcella; Morales, Gustavo; Addison, Graeme; Bond, J. Richard; Crichton, Devin; Das, Sudeep; Devlin, Mark; Dunner, Rolando; Hajian, Amir; Hilton, Matt; Hincks, Adam; Hughes, John P.; Irwin, Kent; Kosowsky, Arthur; Menanteau, Felipe; Moodley, Kavilan; Niemack, Michael; Page, Lyman; Reese, Erik D.; Wollack, Edward

    2014-01-01

    We present a catalogue of 191 extragalactic sources detected by the Atacama Cosmology Telescope (ACT) at 148 and/or 218 GHz in the 2008 Southern survey. Flux densities span 14 - 1700 mJy, and we use source spectral indices derived using ACT-only data to divide our sources into two subpopulations: 167 radio galaxies powered by central active galactic nuclei (AGN) and 24 dusty star-forming galaxies (DSFGs). We cross-identify 97 per cent of our sources (166 of the AGN and 19 of the DSFGs) with those in currently available catalogues. When combined with flux densities from the Australia Telescope 20 GHz survey and follow-up observations with the Australia Telescope Compact Array, the synchrotron-dominated population is seen to exhibit a steepening of the slope of the spectral energy distribution from 20 to 148 GHz, with the trend continuing to 218 GHz. The ACT dust-dominated source population has a median spectral index, alpha(sub 148-218), of 3.7 +0.62/-0.86), and includes both local galaxies and sources with redshift around 6. Dusty sources with no counterpart in existing catalogues likely belong to a recently discovered subpopulation of DSFGs lensed by foreground galaxies or galaxy groups.

  16. Activity Cycles in Stars

    NASA Technical Reports Server (NTRS)

    Hathaway, David H.

    2009-01-01

    Starspots and stellar activity can be detected in other stars using high precision photometric and spectrometric measurements. These observations have provided some surprises (starspots at the poles - sunspots are rarely seen poleward of 40 degrees) but more importantly they reveal behaviors that constrain our models of solar-stellar magnetic dynamos. The observations reveal variations in cycle characteristics that depend upon the stellar structure, convection zone dynamics, and rotation rate. In general, the more rapidly rotating stars are more active. However, for stars like the Sun, some are found to be inactive while nearly identical stars are found to be very active indicating that periods like the Sun's Maunder Minimum (an inactive period from 1645 to 1715) are characteristic of Sun-like stars.

  17. Transcriptional activation of LON Gene by a new form of mitochondrial stress: A role for the nuclear respiratory factor 2 in StAR overload response (SOR).

    PubMed

    Bahat, Assaf; Perlberg, Shira; Melamed-Book, Naomi; Isaac, Sara; Eden, Amir; Lauria, Ines; Langer, Thomas; Orly, Joseph

    2015-06-15

    High output of steroid hormone synthesis in steroidogenic cells of the adrenal cortex and the gonads requires the expression of the steroidogenic acute regulatory protein (StAR) that facilitates cholesterol mobilization to the mitochondrial inner membrane where the CYP11A1/P450scc enzyme complex converts the sterol to the first steroid. Earlier studies have shown that StAR is active while pausing on the cytosolic face of the outer mitochondrial membrane while subsequent import of the protein into the matrix terminates the cholesterol mobilization activity. Consequently, during repeated activity cycles, high level of post-active StAR accumulates in the mitochondrial matrix. To prevent functional damage due to such protein overload effect, StAR is degraded by a sequence of three to four ATP-dependent proteases of the mitochondria protein quality control system, including LON and the m-AAA membranous proteases AFG3L2 and SPG7/paraplegin. Furthermore, StAR expression in both peri-ovulatory ovarian cells, or under ectopic expression in cell line models, results in up to 3-fold enrichment of the mitochondrial proteases and their transcripts. We named this novel form of mitochondrial stress as StAR overload response (SOR). To better understand the SOR mechanism at the transcriptional level we analyzed first the unexplored properties of the proximal promoter of the LON gene. Our findings suggest that the human nuclear respiratory factor 2 (NRF-2), also known as GA binding protein (GABP), is responsible for 88% of the proximal promoter activity, including the observed increase of transcription in the presence of StAR. Further studies are expected to reveal if common transcriptional determinants coordinate the SOR induced transcription of all the genes encoding the SOR proteases.

  18. A search for Wolf-Rayet stars in active star forming regions of low mass galaxies - GR8, NGC 2366, IC 2574, and NGC 1569

    NASA Astrophysics Data System (ADS)

    Drissen, Laurent; Roy, Jean-Rene; Moffat, Anthony F. J.

    1993-10-01

    We report the detection, via narrow-band 4686 A filter imagery, of possible new Wolf-Rayet stars in the most massive giant H II regions of the irregular galaxies NGC 2366 and IC 2574. One stellar knot in the post-starburst galaxy NGC 1569 also appears to contain a weak excess of light at 4686 A. A similar search yielded negative results in the very low mass galaxy GR8. The strongest 4686 A excess is located close to the secondary eastern knot in the core of NGC 2366-I (NGC 2363). If this excess is of stellar origin, about five Wolf-Rayet stars of the luminous late-type can account for the excess emission. Nebular emission wraps around this cluster in the form of a shell. The putative Wolf-Rayet stars appear to be close to the center of the large expanding H II bubble discovered by Roy et al. (1991). A possible nebular origin of the 4686 A excess is also discussed.

  19. Forming Stars From the Cosmic Web

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-09-01

    Scientists have recently identified a connection between metal-poor regions in a set of dwarf galaxies and bursts of star-formation activity within them. These observations provide long-awaited evidence supporting predictions of how stars formed in the early universe and in dwarf galaxies today. Metal-Poor Clues: The primary driver of star formation over cosmic history is thought to be the accretion onto galaxies of cold gas streaming from the cosmic web. The best way to confirm this model would be to observe a cloud of cosmic gas flowing into an otherwise-quiescent galaxy and launching a wave of star formation. But because cold gas doesnt emit much radiation, its difficult to detect directly.Now, a team of scientists have found a clever way around this problem: they searched galaxies for a correlation between areas of active star formation and metal-poor regions. Why? Because metal-poor regions could be a smoking gun indicating a recently accreted cloud of cold gas from the cosmic web. Impacting Clouds: Distribution of metallicity along the major axis of one of the target galaxies. The red bar in the top image shows the position of the spectrograph slit along the galaxy, with the arrow showing the direction of growing distance in the plot below. The plot shows the metallicity variation (red symbols) and star-formation rate (blue line) along the galaxys major axis. The metallicity drop coincides with the brightest knot of the galaxy. [Snchez Almeida et al. 2015]The authors of this study, led by Jorge Snchez Almeida (Instituto de Astrofisica de Canarias and University of La Laguna, Spain), used the Great Canary Telescope to obtain high-quality spectra of ten dwarf galaxies with especially low average metallicities. They aligned the spectrograph slit along the major axes of the galaxies in order to measure abundances as a function of position within each galaxy.The team found that, in nine out of the ten cases, the galaxies displayed sharp drops (by factors of 310

  20. The ISO View of Star Forming Galaxies

    NASA Astrophysics Data System (ADS)

    Helou, George

    1999-01-01

    ISO studies of normal galaxies in the local Universe have revealed basic new properties whose significant implications for the star formation process and cosmology are only starting to be understood. This review will touch on the general results of a statistical nature, and provide a quick summary of the profusion of exciting results on individual objects. In the mid-infrared, PHT-S has established that the spectra of star forming galaxies between 6 and-13microns are dominated by the Aromatic Features in Emission (AFE), and show little variation as a function of the heating intensity. The Carriers of the AFE (CAFE) are thus a universal component of dust with standard properties, and contribute between 10 and 25% of the total dust luminosity. In addition to AFE, the spectra show a low-level continuum detectable at wavelengths longer than 3.5microns whose origin is still under investigation. The mid-infrared colors formed as the ratio of flux densities in the 6.75micron and the 15micron bands of ISO-CAM remain essentially constant and near unity for quiescent and mildly active galaxies. As dust heating increases further, the 15micron flux increases steeply compared to 6.75microns, indicating that dust heated to 100K

  1. The ISO View of Star Forming Galaxies

    NASA Technical Reports Server (NTRS)

    Helou, George

    1999-01-01

    ISO studies of normal galaxies in the local Universe have revealed basic new properties whose significant implications for the star formation process and cosmology are only starting to be understood. This review will touch on the general results of a statistical nature, and provide a quick summary of the profusion of exciting results on individual objects. In the mid-infrared, PHT-S has established that the spectra of star forming galaxies between 6 and-13microns are dominated by the Aromatic Features in Emission (AFE), and show little variation as a function of the heating intensity. The Carriers of the AFE (CAFE) are thus a universal component of dust with standard properties, and contribute between 10 and 25% of the total dust luminosity. In addition to AFE, the spectra show a low-level continuum detectable at wavelengths longer than 3.5microns whose origin is still under investigation. The mid-infrared colors formed as the ratio of flux densities in the 6.75micron and the 15micron bands of ISO-CAM remain essentially constant and near unity for quiescent and mildly active galaxies. As dust heating increases further, the 15micron flux increases steeply compared to 6.75microns, indicating that dust heated to 100Kactive in star formation, its [CII] flux weakens relative to total dust emission while the [OI] does not. This behavior has attracted much interest because it extrapolates to the most active galaxies, making them weaker in [CII

  2. Stellar populations in local star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Perez-Gonzalez, P. G.

    2003-11-01

    The main goal of this thesis work is studying the main properties of the stellar populations embedded in a statistically complete sample of local active star-forming galaxies: the Universidad Complutense de Madrid (UCM) Survey of emission-line galaxies. This sample contains 191 local star-forming galaxies at an average redshift of 0.026. The survey was carried out using an objective-prism technique centered at the wavelength of the Halpha nebular emission-line (a common tracer of recent star formation). (continues)

  3. Nebular excitation in z ∼ 2 star-forming galaxies from the SINS and LUCI surveys: The influence of shocks and active galactic nuclei

    SciTech Connect

    Newman, Sarah F.; Genzel, Reinhard; Buschkamp, Peter; Förster Schreiber, Natascha M.; Kurk, Jaron; Rosario, David; Davies, Ric; Eisenhauer, Frank; Lutz, Dieter; Sternberg, Amiel; Gnat, Orly; Mancini, Chiara; Renzini, Alvio; Lilly, Simon J.; Carollo, C. Marcella; Burkert, Andreas; Cresci, Giovanni; Genel, Shy; Shapiro Griffin, Kristen; Hicks, Erin K. S.; and others

    2014-01-20

    Based on high-resolution, spatially resolved data of 10 z ∼ 2 star-forming galaxies from the SINS/zC-SINF survey and LUCI data for 12 additional galaxies, we probe the excitation properties of high-z galaxies and the impact of active galactic nuclei (AGNs), shocks, and photoionization. We explore how these spatially resolved line ratios can inform our interpretation of integrated emission line ratios obtained at high redshift. Many of our galaxies fall in the 'composite' region of the z ∼ 0 [N II]/Hα versus [O III]/Hβ diagnostic (BPT) diagram, between star-forming galaxies and those with AGNs. Based on our resolved measurements, we find that some of these galaxies likely host an AGN, while others appear to be affected by the presence of shocks possibly caused by an outflow or from an enhanced ionization parameter as compared with H II regions in normal, local star-forming galaxies. We find that the Mass-Excitation (MEx) diagnostic, which separates purely star-forming and AGN hosting local galaxies in the [O III]/Hβ versus stellar mass plane, does not properly separate z ∼ 2 galaxies classified according to the BPT diagram. However, if we shift the galaxies based on the offset between the local and z ∼ 2 mass-metallicity relation (i.e., to the mass they would have at z ∼ 0 with the same metallicity), we find better agreement between the MEx and BPT diagnostics. Finally, we find that metallicity calibrations based on [N II]/Hα are more biased by shocks and AGNs at high-z than the [O III]/Hβ/[N II]/Hα calibration.

  4. STAR-FORMING GALAXY EVOLUTION IN NEARBY RICH CLUSTERS

    SciTech Connect

    Tyler, K. D.; Rieke, G. H.; Bai, L.

    2013-08-20

    Dense environments are known to quench star formation in galaxies, but it is still unknown what mechanism(s) are directly responsible. In this paper, we study the star formation of galaxies in A2029 and compare it to that of Coma, combining indicators at 24 {mu}m, H{alpha}, and UV down to rates of 0.03 M{sub Sun} yr{sup -1}. We show that A2029's star-forming galaxies follow the same mass-SFR relation as the field. The Coma cluster, on the other hand, has a population of galaxies with star formation rates (SFRs) significantly lower than the field mass-SFR relation, indicative of galaxies in the process of being quenched. Over half of these galaxies also host active galactic nuclei. Ram-pressure stripping and starvation/strangulation are the most likely mechanisms for suppressing the star formation in these galaxies, but we are unable to disentangle which is dominating. The differences we see between the two clusters' populations of star-forming galaxies may be related to their accretion histories, with A2029 having accreted its star-forming galaxies more recently than Coma. Additionally, many early-type galaxies in A2029 are detected at 24 {mu}m and/or in the far-UV, but this emission is not directly related to star formation. Similar galaxies have probably been classified as star forming in previous studies of dense clusters, possibly obscuring some of the effects of the cluster environment on true star-forming galaxies.

  5. Disk Evaporation in Star Forming Regions

    NASA Technical Reports Server (NTRS)

    Hollenbach, David; DeVincenzi, Donald L. (Technical Monitor)

    2000-01-01

    Young stars produce sufficient ultraviolet photon luminosity and mechanical luminosity in their winds to significantly affect the structure and evolution of the accretion disks surrounding them. The Lyman continuum photons create a nearly static, ionized, isothermal 10(exp 4) K atmosphere forms above the neutral disk at small distances from the star. Further out, they create a photoevaporative flow which relatively rapidly destroys the disk. The resulting slow (10-50 km/s) ionized outflow, which persists for approx. greater than 10(exp 5) years for disk masses M(sub d) approx. 0.3M(sub *), may explain the observational characteristics of many ultracompact HII regions. We compare model results to the observed radio free-free spectra and luminosities of ultracompact HII regions and to the interesting source MWC349, which is observed to produce hydrogen masers. We apply the results to Ae and Be stars in order to determine the lifetimes of disks around such stars. We also apply the results to the early solar nebula to explain the the dispersal of the solar nebula and the differences in hydrogen content in the giant planets. Finally, we model the small bright objects ("proplyds") observed in the Orion Nebula as disks around young, low mass stars which are externally illuminated by the UV photons from the nearby massive star Theta(sup 1) C.

  6. Stars and Star Clusters: A Look at Intermediate-Mass Star-Forming Regions

    NASA Astrophysics Data System (ADS)

    Lundquist, Michael J.; Kobulnicky, Henry A.; Lau, Ryan M.

    2017-01-01

    Star-forming regions hosting intermediate-mass stars straddle the boundary separating the the low- and high-mass regimes. These intermediate-mass star-forming regions can be used to probe this transition from low- to high-mass star formation. Our team has assembled an all-sky catalog of 616 candidate intermediate-mass star forming regions (IMSFRs) selected by IRAS colors and refined by visual inspection of WISE imagery. We present here two outer-Galaxy star-forming regions, IRAS22451+6154 and IRAS23448+6010, that despite having similar IRAS colors and mid-infrared morphologies, have vastly different stellar content. We combine Gemini and IRTF NIR spectroscopy with WIYN and SOFIA imaging for a thorough look at the stellar content of these two regions.

  7. CHARACTERISTIC STRUCTURE OF STAR-FORMING CLOUDS

    SciTech Connect

    Myers, Philip C.

    2015-06-20

    This paper presents a new method to diagnose the star-forming potential of a molecular cloud region from the probability density function of its column density (N-pdf). This method provides expressions for the column density and mass profiles of a symmetric filament having the same N-pdf as a filamentary region. The central concentration of this characteristic filament can distinguish regions and can quantify their fertility for star formation. Profiles are calculated for N-pdfs which are pure lognormal, pure power law, or a combination. In relation to models of singular polytropic cylinders, characteristic filaments can be unbound, bound, or collapsing depending on their central concentration. Such filamentary models of the dynamical state of N-pdf gas are more relevant to star-forming regions than are spherical collapse models. The star formation fertility of a bound or collapsing filament is quantified by its mean mass accretion rate when in radial free fall. For a given mass per length, the fertility increases with the filament mean column density and with its initial concentration. In selected regions the fertility of their characteristic filaments increases with the level of star formation.

  8. ATLASGAL: Chemical evolution of star forming clumps

    NASA Astrophysics Data System (ADS)

    Figura, Charles C.; Urquhart, James S.; Wyrowski, Friedrich

    2017-01-01

    Although massive stars are few in number, they impact their host molecular clouds, clusters, and galaxies in profound ways, playing a vital role in regulating star formation in their host galaxy. Understanding the formation of these massive stars is critical to understanding this evolution, but their rapid early development causes them to reach the main sequence while still shrouded in their natal molecular cloud. Many studies have investigated these regions in a targeted manner, but a full understanding necessitates a broader view at all stages of formation across many star forming regions.We have used mid-infrared continuum surveys to guide selection of a statistically large sample of massive dust clumps from the 10,000 such clumps identified in the ATLASGAL Compact Source Catalogue (CSC), ensuring that all stages of the evolutionary process are included. A final sample of 600 fourth-quadrant sources within 1 degree of the Galactic plane were observed with the Mopra telescope with an 8 GHz bandwidth between 85.2 and 93.4 GHz.We present an overview of our results. We have identified over 30 molecular lines, seven of which with detected hyperfine structure, as well as several mm-radio recombination line transitions. Source velocities indicate that these regions trace the Crux-Scutum, Norma, and Carina Sagitarius arms. We have performed an analysis of linewidth and line intensity ratios, correlating these with star formation stages as identified by IR brightness at the 70 and 24 μm bands, and present several molecular pairs whose linewidth and intensity might serve as significant tracers of the evolutionary stage of star formation. We comment on the results of PCA analysis of the measured parameters for the overall population and the star formation stage subgroups with an eye toward characterising early stellar development through molecular line observations.

  9. Lithopanspermia in star-forming clusters.

    PubMed

    Adams, Fred C; Spergel, David N

    2005-08-01

    This paper considers the lithopanspermia hypothesis in star-forming groups and clusters, where the chances of biological material spreading from one solar system to another is greatly enhanced (relative to action in the field) because of the close proximity of the systems and lower relative velocities. These effects more than compensate for the reduced time spent in such crowded environments. This paper uses approximately 300,000 Monte Carlo scattering calculations to determine the cross sections for rocks to be captured by binaries and provides fitting formulae for other applications. We assess the odds of transfer as a function of the ejection speed v (eject) and number N(.) of members in the birth aggregate. The odds of any given ejected meteoroid being recaptured by another solar system are relatively low, about 1:10(3)-10(6) over the expected range of ejection speeds and cluster sizes. Because the number of ejected rocks (with mass m > 10 kg) per system can be large, N (R) approximately 10(16), virtually all solar systems are likely to share rocky ejecta with all of the other solar systems in their birth cluster. The number of ejected rocks that carry living microorganisms is much smaller and less certain, but we estimate that N (B) approximately 10(7) rocks can be ejected from a biologically active solar system. For typical birth environments, the capture of life-bearing rocks is expected to occur N (bio) asymptotically equal to 10-16,000 times (per cluster), depending on the ejection speeds. Only a small fraction (f (imp) approximately 10(4)) of the captured rocks impact the surfaces of terrestrial planets, so that N (lps) asymptotically equal to 10(3)-1.6 lithopanspermia events are expected per cluster (under favorable conditions). Finally, we discuss the question of internal versus external seeding of clusters and the possibility of Earth seeding young clusters over its biologically active lifetime.

  10. Fission: A Mechanism for Forming Binary Stars

    NASA Astrophysics Data System (ADS)

    Tohline, J. E.; Cazes, J. E.

    2000-05-01

    We demonstrate that it is possible for short period binary star systems to form from a single, rapidly rotating, equilibrium protostellar gas cloud via a natural fission process. This is analogous to the process by which rapidly spinning drops of fluid have been observed to break in two during drop dynamics experiments onboard the space shuttle. In order to demonstrate that fission works in the context of binary star formation, we have used a three-dimensional, computational fluid dynamics technique to, first, construct a rapidly rotating, self-gravitating, equilibrium barlike structure that, by all accounts, appears to be a compressible analog of an incompressible Riemann ellipsoid. Then by slowly cooling this configuration and following its cooling evolution in a fully self-consistent fashion, we have demonstrated that the system contracts along an ellipsoid-dumbbell-binary sequence. Although the hypothesis that binary stars may form via a process of fission has been around for more than 100 years, it has been a difficult hypothesis to test because of the nonlinear dynamical processes involved. This is the first demonstration that fission works in the context of realistic protostellar gas clouds. This work has been supported by the U.S. National Science Foundation through grant AST-9528424, by NASA through grant NAG5-8497, and by a grant of high-performance-computing time through NPACI on machines at the San Diego Supercomputing Center.

  11. Extreme Variables in Star Forming Regions

    NASA Astrophysics Data System (ADS)

    Contreras Peña, Carlos Eduardo

    2015-01-01

    in two multi-epoch infrared surveys: the UKIDSS Galactic Plane Survey (GPS) and the Vista Variables in the Via Lactea (VVV). In order to further investigate the nature of the selected variable stars, we use photometric information arising from public surveys at near- to far-infrared wavelengths. In addition we have performed spectroscopic and photometric follow-up for a large subset of the samples arising from GPS and VVV. We analyse the widely separated two-epoch K-band photometry in the 5th, 7th and 8th data releases of the UKIDSS Galactic Plane Survey. We find 71 stars with ΔK > 1 mag, including 2 previously known OH/IR stars and a Nova. Even though the mid-plane is mostly excluded from the dataset, we find the majority (66%) of our sample to be within known star forming regions (SFRs), with two large concentrations in the Serpens OB2 association (11 stars) and the Cygnus-X complex (27 stars). The analysis of the multi-epoch K-band photometry of 2010-2012 data from VVV covering the Galactic disc at |b| < 1° yields 816 high amplitude variables, which include known variables of different classes such as high mass X-ray binaries, Novae and eclipsing binaries among others. Remarkably, 65% of the sample are found concentrated towards areas of star formation, similar to the results from GPS. In both surveys, sources in SFRs show spectral energy distributions (SEDs) that support classification as YSOs. This indicates that YSOs dominate the Galactic population of high amplitude infrared variable stars at low luminosities and therefore likely dominate the total high amplitude population. Spectroscopic follow-up allows us to confirm the pre-main sequence nature of several GPS and VVV Objects. Most objects in both samples show spectroscopic signatures that can be attributed to YSOs undergoing high states of accretion, such as veiling of photospheric features and CO emission, or show FUor-like spectra. We also find a large fraction of objects with 2.12 μm H2 emission that

  12. X-ray emission from T Tauri stars in the Lupus 3 star-forming region

    NASA Astrophysics Data System (ADS)

    Gondoin, P.

    2006-08-01

    Aims.In this paper, I present analysis results of an {XMM-Newton} observation of the Lupus 3 region that contains a high proportion of young low mass (M < 0.3 M⊙) T Tauri stars in the Lupus star-forming complex. Methods: .The detection of X-ray sources in 0.5 to 4.5 keV images of the Lupus 3 core was performed using the standard source detection method of the {XMM-Newton} Science Analysis Software. The detected sources were correlated with a list of Herbig-Haro objects and Hα emission stars that contains mainly classical T Tauri stars, with a catalogue of weak-line T Tauri Stars and with a recent list of new low-mass members of the Lupus 3 dark cloud found in a visible-light spectroscopic survey at the center of the Lupus 3 star-forming core. The light curves and spectra of the brightest X-ray sources with known T Tauri star counterparts were analysed. Results: .One hundred and two X-ray sources were detected in the 30´ diameter field-of-view of the EPIC cameras, of which 25 have visible or near-IR counterparts that are known as pre-main sequence stars. Their X-ray luminosity ranges from 3 × 1028 to 3 × 1030 erg s-1. Two of these objects with mass estimates lower than 0.075 M⊙ have an X-ray luminosity of about 4-7 × 1028 erg s-1, comparable with that of flaring young brown dwarfs. A linear correlation is found between the X-ray luminosity and the mass or volume of the stars that is qualitatively expected from some models of distributed turbulent dynamos. The EPIC spectra of the X-ray brightest sources can be fitted using optically thin plasma emission models with two components at temperatures in the ranges 3-9 × 106 K and 1-50 × 107 K, respectively. The large emission measure of hot plasma may be caused by disruptions of magnetic fields associated with an intense flaring activity, while the X-ray emission from the "cool" plasma components may result from solar-type active regions. The emission measures of the plasma components are of the order of 1052

  13. Molecular Outflows in Massive Star Forming Regions

    NASA Astrophysics Data System (ADS)

    Cunningham, Nichol

    2015-11-01

    This thesis presents millimetre continuum and molecular line observations exploring the properties of molecular outflows towards massive star forming regions. Massive stars produce some of the most energetic phenomena in the Galaxy, yet we still do not have a comprehensive understanding of how they actually form. Outflows are known to play a key role in this formation process and their properties, particularly how they change depending on the mass, luminosity and evolution of the driving source can shed light on how massive stars actually form. This thesis presents observations at both high (SMA 3 arcsecond) and low (JCMT 15 arcsecond) spatial resolution of the known jet/outflow tracers, SiO and 12CO, towards a sample massive star forming region drawn from the RMS survey. Furthermore, the presence of infall signatures is explored through observations of HCO+ and H13CO+, and the hot core nature of the regions is probed using tracers such as CH3CN, HC3N and CH3OH. SiO is detected towards approximately 50% of the massive young stellar objects and HII regions in the JCMT sample. The detection of SiO appears to be linked to the age of the RMS source, with the likely younger sources showing a stronger dependence with SiO. The presence of SiO also appears to be linked to the CO velocity, with SiO more efficiently tracing sources with higher velocity dispersions. In the MOPRA observations towards a sample of 33 RMS sources, CH3CN is detected towards 66% of the sources, with the redder likely younger sources having the largest rotational temperatures. This thesis presents the first interferometric SiO (5-4) and 12CO (2-1) observations, taken with the SMA, towards the massive star forming region G203.3166/NGC 2264-C. In this intermediate/massive star forming cluster, SiO is again tracing the youngest sources. Both the SiO and 12CO emission trace two bipolar, high velocity outflows towards the mm brightest, IR-dark, likely youngest sources in this reg! ion. In contrast the IR

  14. Evidence for wide-spread active galactic nucleus-driven outflows in the most massive z ∼ 1-2 star-forming galaxies

    SciTech Connect

    Genzel, R.; Förster Schreiber, N. M.; Rosario, D.; Lang, P.; Lutz, D.; Wisnioski, E.; Wuyts, E.; Wuyts, S.; Bandara, K.; Bender, R.; Berta, S.; Kurk, J.; Mendel, J. T.; Tacconi, L. J.; Wilman, D.; Beifiori, A.; Burkert, A.; Buschkamp, P.; Chan, J.; Brammer, G. E-mail: genzel@mpe.mpg.de; and others

    2014-11-20

    In this paper, we follow up on our previous detection of nuclear ionized outflows in the most massive (log(M {sub *}/M {sub ☉}) ≥ 10.9) z ∼ 1-3 star-forming galaxies by increasing the sample size by a factor of six (to 44 galaxies above log(M {sub *}/M {sub ☉}) ≥ 10.9) from a combination of the SINS/zC-SINF, LUCI, GNIRS, and KMOS{sup 3D}spectroscopic surveys. We find a fairly sharp onset of the incidence of broad nuclear emission (FWHM in the Hα, [N II], and [S II] lines ∼450-5300 km s{sup –1}), with large [N II]/Hα ratios, above log(M {sub *}/M {sub ☉}) ∼ 10.9, with about two-thirds of the galaxies in this mass range exhibiting this component. Broad nuclear components near and above the Schechter mass are similarly prevalent above and below the main sequence of star-forming galaxies, and at z ∼ 1 and ∼2. The line ratios of the nuclear component are fit by excitation from active galactic nuclei (AGNs), or by a combination of shocks and photoionization. The incidence of the most massive galaxies with broad nuclear components is at least as large as that of AGNs identified by X-ray, optical, infrared, or radio indicators. The mass loading of the nuclear outflows is near unity. Our findings provide compelling evidence for powerful, high-duty cycle, AGN-driven outflows near the Schechter mass, and acting across the peak of cosmic galaxy formation.

  15. Using Cosmic Telescopes to Study Dusty, Star-Forming Galaxies

    NASA Astrophysics Data System (ADS)

    Walth, Gregory; Egami, Eiichi; Clément, Benjamin; Rujopakarn, Wiphu; Rawle, Tim; Rex, Marie; Richard, Johan; Dessauges, Miroslava; Perez-Gonzalez, Pablo; Stark, Daniel; Herschel Lensing Survey

    2016-06-01

    Dusty, star-forming galaxies (DSFGs), characterized by their far-infrared (far-IR) emission, undergo the largest starbursts in the Universe, contributing to the majority of the cosmic star formation rate density at z = 1 - 4. These starbursts have important implications for galaxy evolution and feedback as these galaxies build up much of their stellar mass during this time and may experience strong stellar driven winds. For the first time the Herschel Space Observatory was able observe the full far-IR dust emission for a large population of high-redshift DSFGs. However, Herschel reaches the confusion limit quickly and only the brightest galaxies at redshifts z > 2 can be detected. With gravitational lensing, we are able to surpass the Herschel confusion limit and probe intrinsically less luminous and therefore more normal star-forming galaxies. With this goal in mind, we have conducted a large Herschel survey, the Herschel Lensing Survey, of the cores of almost 600 massive galaxy clusters, where the effects of gravitational lensing are the strongest. In this presentation I will discuss how using one of largest gravitational lenses enables the detailed study of star forming regions at high redshift by investigating a giant (D ~ 1 kpc) luminous star forming region in aDSFG at z=0.6. Next, I will discuss how using one of the brightest sources from our sample allows us to investigate the molecular gas and dust properties of a typical DSFG with a CO outflow at z~2. Finally, I will discuss ongoing work using the brightest DSFGs in our sample to detect rest-frame optical nebular emission lines, using near-infrared spectroscopy with Keck/MOSFIRE, LBT/LUCI, and Magellan/MMIRS, which reveal conditions of their ISM; specifically ionization, star formation, metallicity, AGN activity, and dust attenuation.

  16. The Sins/zC-Sinf Survey of z ~ 2 Galaxy Kinematics: Evidence for Powerful Active Galactic Nucleus-Driven Nuclear Outflows in Massive Star-Forming Galaxies

    NASA Astrophysics Data System (ADS)

    Förster Schreiber, N. M.; Genzel, R.; Newman, S. F.; Kurk, J. D.; Lutz, D.; Tacconi, L. J.; Wuyts, S.; Bandara, K.; Burkert, A.; Buschkamp, P.; Carollo, C. M.; Cresci, G.; Daddi, E.; Davies, R.; Eisenhauer, F.; Hicks, E. K. S.; Lang, P.; Lilly, S. J.; Mainieri, V.; Mancini, C.; Naab, T.; Peng, Y.; Renzini, A.; Rosario, D.; Shapiro Griffin, K.; Shapley, A. E.; Sternberg, A.; Tacchella, S.; Vergani, D.; Wisnioski, E.; Wuyts, E.; Zamorani, G.

    2014-05-01

    We report the detection of ubiquitous powerful nuclear outflows in massive (>=1011 M ⊙) z ~ 2 star-forming galaxies (SFGs), which are plausibly driven by an active galactic nucleus (AGN). The sample consists of the eight most massive SFGs from our SINS/zC-SINF survey of galaxy kinematics with the imaging spectrometer SINFONI, six of which have sensitive high-resolution adaptive optics-assisted observations. All of the objects are disks hosting a significant stellar bulge. The spectra in their central regions exhibit a broad component in Hα and forbidden [N II] and [S II] line emission, with typical velocity FWHM ~ 1500 km s-1, [N II]/Hα ratio ≈ 0.6, and intrinsic extent of 2-3 kpc. These properties are consistent with warm ionized gas outflows associated with Type 2 AGN, the presence of which is confirmed via independent diagnostics in half the galaxies. The data imply a median ionized gas mass outflow rate of ~60 M ⊙ yr-1 and mass loading of ~3. At larger radii, a weaker broad component is detected but with lower FWHM ~485 km s-1 and [N II]/Hα ≈ 0.35, characteristic for star formation-driven outflows as found in the lower-mass SINS/zC-SINF galaxies. The high inferred mass outflow rates and frequent occurrence suggest that the nuclear outflows efficiently expel gas out of the centers of the galaxies with high duty cycles and may thus contribute to the process of star formation quenching in massive galaxies. Larger samples at high masses will be crucial in confirming the importance and energetics of the nuclear outflow phenomenon and its connection to AGN activity and bulge growth. Based on observations obtained at the Very Large Telescope of the European Southern Observatory, Paranal, Chile (ESO program IDs 074.A-0911, 075.A-0466, 076.A-0527, 078.A-0600, 082.A-0396, 183.A-0781, 088.A-0202, 091.A-0126). Also based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the

  17. HIRES Dust Imaging of the NGC 6334 Star Forming Complex

    NASA Technical Reports Server (NTRS)

    Jackson, James M.

    1997-01-01

    We present here our final report for the NASA grant "HIRES Dust Imaging of the NGC 6334 Star Forming Complex." This project was designed to study the photodissociation regions surrounding several OB stars in this cloud complex. NGC 6334 is unique in having at least seven distinct massive star forming regions in the same molecular cloud complex. The obvious advantage of studying young stars in the same molecular complex is that the stars all formed in the same global environment. Consequently, global factors like density waves, abundances, global magnetic field strength, and age of the parental molecular cloud cannot contribute to the differences among the star forming regions. Instead, the differences must arise only from local effects such as the mass, age, and UV fields of the individual stars. A study of NGC 6334 will greatly simplify the general problem of comparing different star formation regions by eliminating global effects.

  18. Intermediate-Mass Star-Forming Regions: What are the Most Massive Stars Formed?

    NASA Astrophysics Data System (ADS)

    Kobulnicky, Chip; Vargas, Carlos; Kerton, Charles; Arvidsson, Kim

    2010-08-01

    High-mass star formation cannot be viewed as simply a scaled-up version of the paradigm for low-mass star formation. The high-mass regime (M> 10 Msun) appears to require significant differences in cloud fragmentation, accretion, radiation, turbulence, and overall molecular density compared to the low-mass regime. We have identified a sample of intermediate-mass star-forming regions (IM SFRs) hosting embedded clusters that straddle the boundary of these two regimes and can be used to understand the factors that govern the transition between these extremes. Most notable among these factors is the possibility of a critical cloud mass column density that appears to divide high-mass SFRs from IM SFRs. Yet, the very nature of IM SFRs and their stellar content are almost completely unknown, primarily because of the previous difficulty in identifying such objects. We propose HK band spectroscopy of the brightest stellar sources near nine IM SFRs to identify probable members, confirm the IM nature of the most massive stars, and characterize their evolutionary state. Three nights with FLAMINGOS on the 4 m (or equivalent IR spectrograph) will suffice to obtain classification spectra and several spectral diagnostics sensitive to accretion for at least 8-10 stars per object.

  19. Star-forming galaxies at z ˜0.61

    NASA Astrophysics Data System (ADS)

    Gómez-Guijarro, C.; Gallego, J.; Rodríguez-Muñoz, L.; Villar, V.; Cuby, J. G.; Clément, B.

    2015-05-01

    In this work we have studied a sample of 41 galaxies with active star formation at z˜0.61 selected by their emission in Hα+[N II]λλ6548,6584 in ultradeep images (32 h of exposure time) taken with a narrow-band filter in the near-infrared with HAWK-I instrument on the VLT. The aim is to characterize the physical and global properties of this sample of galaxies. We have calculated the luminosity function. Our determination of α=-1.29±0.02 is the deepest to date in similar studies. This leads to a star formation rate density SFRd= 0.10±0.01 {M}_⊙ {yr}^{-1} {Mpc}^{-3}. We have found a correlation between extinction and star formation rate (SFR) and between SFR and stellar mass in the sample. We have performed a morphological and spectroscopical classification of the objects studying the physical properties of the categories. Disks have the highest SFR, but BCDs form stars at the same rate in terms of specific star formation rate (sSFR). Excitation decreases and luminosity increases with the spectroscopic class.

  20. A multifrequency study of the active star-forming complex NGC 6357 - I. Interstellar structures linked to the open cluster Pis 24

    NASA Astrophysics Data System (ADS)

    Cappa, C. E.; Barbá, R.; Duronea, N. U.; Vasquez, J.; Arnal, E. M.; Goss, W. M.; Fernández Lajús, E.

    2011-08-01

    We investigate the distribution of gas (ionized, neutral atomic and molecular) and interstellar dust in the complex star-forming region NGC 6357 with the goal of studying the interplay between the massive stars in the open cluster Pis 24 and the surrounding interstellar matter. Our study of the distribution of the ionized gas is based on narrow-band Hα, [S II]and [O III] images obtained with the Curtis-Schmidt Camera at CTIO, Chile, and on radio continuum observations at 1465 MHz taken with the VLA with a synthesized beam of 40 arcsec. The distribution of the molecular gas is analysed using 12CO(1-0) data obtained with the NANTEN radiotelescope, Chile (angular resolution = 2.7 arcmin). The interstellar dust distribution was studied using mid-infrared data from the GLIMPSE survey and far-infrared observations from IRAS. NGC 6357 consists of a large ionized shell and a number of smaller optical nebulosities. The optical, radio continuum, and near- and mid-IR images delineate the distributions of the ionized gas and interstellar dust in the H II regions and in previously unknown wind-blown bubbles linked to the massive stars in Pis 24 revealing surrounding photodissociation regions. The CO line observations allowed us to identify the molecular counterparts of the ionized structures in the complex and to confirm the presence of photodissociation regions. The action of the WR star HD 157504 on the surrounding gas was also investigated. The molecular mass in the complex is estimated to be (4 ± 2) × 105 M⊙. The mean electron densities derived from the radio data suggest electron densities >200 cm-3, indicating that NGC 6357 is a complex formed in a region of high ambient density. The known massive stars in Pis 24 and a number of newly inferred massive stars are mainly responsible for the excitation and photodissociation of the parental molecular cloud.

  1. Dynamical processes in star forming regions: feedback and turbulence generation

    NASA Astrophysics Data System (ADS)

    Bally, John

    The efficiency of star formation may be determined by feedback of energy and momentum from young stars. In massive star forming regions, feedback is dominated by massive star winds, soft-UV, and ionising radiation, and at late times by supernova explosions. Dynamical interactions between stars in compact groups can also make a significant contribution. As they age, the impacts of massive stars can influence star formation in adjacent regions at distances of tens to hundreds of parsecs, either by striping away the reservoirs from which stars form, or by compressing clouds to the point of gravitational instability. In regions which give birth only to intermediate and low mass stars, locally generated protostellar outflows and soft-UV, combined with the geometrically diluted impacts of relatively distant massive stars play varying roles in feedback and self-regulation. When only low mass stars are created in isolated regions or in environments shielded from the influence of massive stars, protostellar outflows and the chaotic interactions of small-N non-hierarchical groups remain the only viable agents for the self-regulation of star formation. I review the results of complete surveys of molecular clouds in the Perseus and Orion star forming regions intended to measure the impacts of protostellar outflows on cloud structure and motions. The decay of turbulent motions, self-gravity, and forcing by distant sources of energy, momentum, and radiation appear to dominate cloud structure and motions on large scales. However, protostellar outflows and localized radiation sources play increasingly important roles on scales smaller than a few parsecs. The interactions of large-scale and local forcing with dissipation may lead to low star formation efficiency and the birth of transient star clusters containing tens to hundreds of mostly low to intermediate mass stars. Observations show that even in massive OB associations, this may be the most common mode of star formation.

  2. A SAMPLE OF OB STARS THAT FORMED IN THE FIELD

    SciTech Connect

    Oey, M. S.; Lamb, J. B.; Kushner, C. T.; Pellegrini, E. W.; Graus, A. S.

    2013-05-01

    We present a sample of 14 OB stars in the Small Magellanic Cloud that meet strong criteria for having formed under extremely sparse star-forming conditions in the field. These stars are a minimum of 28 pc in projection from other OB stars, and they are centered within symmetric, round H II regions. They show no evidence of bow shocks, implying that the targets are not transverse runaway stars. Their radial velocities relative to local H I also indicate that they are not line-of-sight runaway stars. A friends-of-friends analysis shows that nine of the objects present a few low-mass companion stars, with typical mass ratios for the two highest-mass stars of around 0.1. This further substantiates that these OB stars formed in place, and that they can and do form in extremely sparse conditions. This poses strong constraints on theories of star formation and challenges proposed relations between cluster mass and maximum stellar mass.

  3. An atlas of ultraviolet spectra of star-forming galaxies

    NASA Technical Reports Server (NTRS)

    Kinney, A. L.; Bohlin, R. C.; Calzetti, D.; Panagia, N.; Wyse, Rosemary F. G.

    1993-01-01

    A systematic study is presented of the UV spectra of star-forming galaxies of different morphological type and activity class using a sample drawn from a uniformly reduced IUE data set. The spectra for a wide variety of galaxies, including normal spiral, LINER, starburst, blue compact, blue compact dwarf, and Seyfert 2 galaxies, are presented in the form of spectral energy distributions to demonstrate the overall characteristics according to morphology and activity class and in the form of absolute flux distributions to better show the absorption and emission features of individual objects. The data support the picture based on UV spectra of the Orbiting Astronomical Observatory and of the Astronautical Netherlands Satellite that spiral galaxies of later Hubble class have more flux at the shortest UV wavelengths than do spiral galaxies of earlier Hubble class.

  4. The magnetic activity sunlike stars.

    PubMed

    Vaughan, A H

    1984-08-24

    Sunspots, flares, and the myriad time-varying "events" observable in the Sun-the only star whose surface we can examine in detail-are testimony that the Sun is a magnetically variable or active star. Its magnetic field, carried into interplanetary space by the solar wind, produces observable changes in Earth's magnetosphere and variations in the flux of galactic cosmic-ray particles incident upon Earth's upper atmosphere. Centuries of observation have enabled solar scientists to recognize that the Sun's magnetism exists and varies in a globally organized pattern that is somehow coupled to the Sun's rotation. Within the past decade O. C. Wilson demonstrated that analogs of solar activity exist and can be studied in many other dwarf stars. From the continuing study, knowledge of the precise rates of rotation of the stars under investigation is being gained for the first time. The results are expected to increase our understanding of the origin of solar activity and stellar activity in general.

  5. On the massive star-forming capacity of molecular clouds

    NASA Technical Reports Server (NTRS)

    Franco, Jose; Shore, Steven N.; Tenorio-Tagle, Guillermo

    1994-01-01

    Assuming that photoionization is the self-limiting process for continued star formation, we estimate the maximum number of massive (OB) stars that can form within a molecular cloud. The most efficient cloud destruction mechanism in the early stages of H II region evolution is the evaporation of the cloud by stars located near the cloud boundary. The maximum number of OB stars is of order 1 per 10(exp 4) solar mass of average molecular gas, or 10 per 10(exp 4) solar mass of dense molecular gas. The resulting star-forming efficiencies within cloud complexes range from 2% to 16% depending on both the location of the stars in the cloud and the details of the initial mass function, with an overall value of about 5% for average molecular gas.

  6. A CORRELATION BETWEEN STAR FORMATION RATE AND AVERAGE BLACK HOLE ACCRETION IN STAR-FORMING GALAXIES

    SciTech Connect

    Chen, Chien-Ting J.; Hickox, Ryan C.; Alberts, Stacey; Pope, Alexandra; Brodwin, Mark; Jones, Christine; Forman, William R.; Goulding, Andrew D.; Murray, Stephen S.; Alexander, David M.; Mullaney, James R.; Assef, Roberto J.; Gorjian, Varoujan; Brown, Michael J. I.; Dey, Arjun; Jannuzi, Buell T.; Le Floc'h, Emeric

    2013-08-10

    We present a measurement of the average supermassive black hole accretion rate (BHAR) as a function of the star formation rate (SFR) for galaxies in the redshift range 0.25 < z < 0.8. We study a sample of 1767 far-IR-selected star-forming galaxies in the 9 deg{sup 2} Booetes multi-wavelength survey field. The SFR is estimated using 250 {mu}m observations from the Herschel Space Observatory, for which the contribution from the active galactic nucleus (AGN) is minimal. In this sample, 121 AGNs are directly identified using X-ray or mid-IR selection criteria. We combined these detected AGNs and an X-ray stacking analysis for undetected sources to study the average BHAR for all of the star-forming galaxies in our sample. We find an almost linear relation between the average BHAR (in M{sub Sun} yr{sup -1}) and the SFR (in M{sub Sun} yr{sup -1}) for galaxies across a wide SFR range 0.85 < log SFR < 2.56: log BHAR = (- 3.72 {+-} 0.52) + (1.05 {+-} 0.33)log SFR. This global correlation between SFR and average BHAR is consistent with a simple picture in which SFR and AGN activity are tightly linked over galaxy evolution timescales.

  7. HUBBLE SPIES HUGE CLUSTERS OF STARS FORMED

    NASA Technical Reports Server (NTRS)

    2002-01-01

    BY ANCIENT ENCOUNTER This stunningly beautiful image [right] taken with the NASA Hubble Space Telescope shows the heart of the prototypical starburst galaxy M82. The ongoing violent star formation due to an ancient encounter with its large galactic neighbor, M81, gives this galaxy its disturbed appearance. The smaller picture at upper left shows the entire galaxy. The image was taken in December 1994 by the Kitt Peak National Observatory's 0.9-meter telescope. Hubble's view is represented by the white outline in the center. In the Hubble image, taken by the Wide Field and Planetary Camera 2, the huge lanes of dust that crisscross M82's disk are another telltale sign of the flurry of star formation. Below the center and to the right, a strong galactic wind is spewing knotty filaments of hydrogen and nitrogen gas. More than 100 super star clusters -- very bright, compact groupings of about 100,000 stars -- are seen in this detailed Hubble picture as white dots sprinkled throughout M82's central region. The dark region just above the center of the picture is a huge dust cloud. A collaboration of European and American scientists used these clusters to date the ancient interaction between M82 and M81. About 600 million years ago, a region called 'M82 B' (the bright area just below and to the left of the central dust cloud) exploded with new stars. Scientists have discovered that this ancient starburst was triggered by the violent encounter with M81. M82 is a bright (eighth magnitude), nearby (12 million light-years from Earth) galaxy in the constellation Ursa Major (the Great Bear). The Hubble picture was taken Sept. 15, 1997. The natural-color composite was constructed from three Wide Field and Planetary Camera 2 exposures, which were combined in chromatic order: 4,250 seconds through a blue filter (428 nm); 2,800 seconds through a green filter (520 nm); and 2,200 seconds through a red (820 nm) filter. Credits for Hubble image: NASA, ESA, R. de Grijs (Institute of

  8. What drives the kinematic evolution of star-forming galaxies?

    NASA Astrophysics Data System (ADS)

    Hung, Chao-Ling; Hayward, Christopher C.; Yuan, Tiantian

    2017-01-01

    The increasing capabilities of optical and near-infrared integral field spectrographs have revealed the internal dynamics of hundreds of star-forming galaxies at 1star-forming galaxy main sequence (MS) exhibit systematically larger intrinsic velocity dispersions than their local star-forming counterparts. Although several plausible mechanisms have been proposed (e.g., star formation feedback, elevated gas supply, or galaxy interaction), it remains unclear what is the fundamental driver of the velocity dispersion enhancement. We investigate the origin of this kinematic evolution using a suite of cosmological simulations from the FIRE project. We find that the intrinsic velocity dispersions of galaxies traced by star-forming gas increase with redshift out to z~1, and then flatten at ~40 km/s beyond z=1. In line with the correlations seen in the IFS surveys, the intrinsic velocity dispersion is positively correlated with several quantities such as star formation rate and gas fraction. However, a causal link is still unclear. In fact, the evolution of SFR in these simulations shows a positive time delay with respect to that of the evolution of velocity dispersion, suggesting that star formation feedback does not cause the disturbed kinematics in these galaxies. Instead, our simulations show that the enhancement of velocity dispersions follows most closely (in time) with the highly stochastic accretion and merger histories.

  9. Stars Form Surprisingly Close to Milky Way's Black Hole

    NASA Astrophysics Data System (ADS)

    2005-10-01

    The supermassive black hole at the center of the Milky Way has surprisingly helped spawn a new generation of stars, according to observations from NASA's Chandra X-ray Observatory. This novel mode of star formation may solve several mysteries about the supermassive black holes that reside at the centers of nearly all galaxies. "Massive black holes are usually known for violence and destruction," said Sergei Nayakshin of the University of Leicester, United Kingdom, and coauthor of a paper on this research in an upcoming issue of the Monthly Notices of the Royal Astronomical Society. "So it's remarkable that this black hole helped create new stars, not just destroy them." Black holes have earned their fearsome reputation because any material -- including stars -- that falls within the so-called event horizon is never seen again. However, these new results indicate that the immense disks of gas known to orbit many black holes at a "safe" distance from the event horizon can help nurture the formation of new stars. Animation of Stars Forming Around Black Hole Animation of Stars Forming Around Black Hole This conclusion came from new clues that could only be revealed in X-rays. Until the latest Chandra results, astronomers have disagreed about the origin of a mysterious group of massive stars discovered by infrared astronomers to be orbiting less than a light year from the Milky Way's central black hole, a.k.a. Sagittarius A*, or Sgr A*. At such close distances to Sgr A*, the standard model for star formation predicts that gas clouds from which stars form should have been ripped apart by tidal forces from the black hole. Two models to explain this puzzle have been proposed. In the disk model, the gravity of a dense disk of gas around Sgr A* offsets the tidal forces and allows stars to form; in the migration model, the stars formed in a star cluster far away from the black hole and migrated in to form the ring of massive stars. The migration scenario predicts about a

  10. Cosmic rays in star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Porter, Troy

    2013-02-01

    Cosmic rays fill up the entire volume of galaxies, providing an important source of heating and ionization of the interstellar medium, and may play a significant role in the regulation of star formation and evolution of galaxies. Diffuse emissions from radio to highenergy gamma rays (< 100 MeV) arising from various interactions between cosmic rays and the interstellar medium, interstellar radiation field, and magnetic field, are currently the best way to trace the intensities and spectra of cosmic rays in the Milky Way and other galaxies. In this talk, I will give an overview of the observations of the cosmic-ray induced emissions from our own and other galaxies, in particular, results from the Fermi-LAT and Imaging Air Cerenkov telescopes. I will also talk about what can be deduced about the cosmic-ray origin and propagation from these observations.

  11. STAR-FORMING OR STARBURSTING? THE ULTRAVIOLET CONUNDRUM

    SciTech Connect

    Boquien, M.; Calzetti, D.; Hong, S.; Kennicutt, R.; Dale, D.; Engelbracht, C.; Portouw, J.; Gordon, K. D.; Lee, J. C.

    2009-11-20

    Compared to starburst galaxies, normal star-forming galaxies have been shown to display a much larger dispersion of the dust attenuation at fixed reddening through studies of the IRX-beta diagram (the IR/UV ratio 'IRX' versus the UV color 'beta'). To investigate the causes of this larger dispersion and attempt to isolate second parameters, we have used GALEX UV, ground-based optical, and Spitzer infrared imaging of eight nearby galaxies, and examined the properties of individual UV and 24 mum selected star-forming regions. We concentrated on star-forming regions, in order to isolate simpler star formation histories than those that characterize whole galaxies. We find that (1) the dispersion is not correlated with the mean age of the stellar populations; (2) a range of dust geometries and dust extinction curves are the most likely causes for the observed dispersion in the IRX-beta diagram, (3) together with some potential dilution of the most recent star-forming population by older unrelated bursts, at least in the case of star-forming regions within galaxies; and (4) we also recover some general characteristics of the regions, including a tight positive correlation between the amount of dust attenuation and the metal content. Although generalizing our results to whole galaxies may not be immediate, the possibility of a range of dust extinction laws and geometries should be accounted for in the latter systems as well.

  12. Protostellar Luminosity Functions in 11 Diverse Star Forming Environments

    NASA Astrophysics Data System (ADS)

    Kryukova, Erin; Megeath, S. T.; Gutermuth, R.; Pipher, J.; Allen, T. S.; Allen, L. E.; Myers, P. C.; Muzerolle, J.; Cygnus-X Legacy Team

    2012-01-01

    Protostars exist in a variety of environments, ranging from clouds with dispersed low-mass stars, such as Taurus, to clustered regions in clouds forming high-mass stars, like Orion. The effect these different environments have on protostar properties such as mass or luminosity is uncertain. One way to probe the effects of cloud environment on the observable property, protostar luminosity is to compare protostellar luminosity functions of clouds hosting varied populations of protostars. In this dissertation talk I will discuss the protostellar luminosity functions from 11 star forming clouds including Lupus, Chamaeleon, Ophiuchus, Perseus, Serpens, Orion, Cep OB3, Mon R2, Cygnus-X, and Maddalena's Cloud, which encompass a wide range of star forming environments. The luminosity functions are constructed from Spitzer surveys of these molecular clouds. I employ a new technique for estimating the bolometric luminosity from near and mid-IR fluxes alone and for subtracting contamination from galaxies, reddened pre-main sequence stars with disks, and edge-on disk systems. The clouds which are forming massive stars show a significant peak at low luminosity and a tail extending toward luminosities above 10 solar luminosities, while the luminosity functions of clouds which are not forming massive stars have no significant peak down to the sensitivity limit and do not exhibit the tail. I compare these luminosity functions to existing models of protostellar evolution. I also compare the luminosity functions of protostars in distributed and clustered environments, as determined using nearest-neighbor distances. In Orion and Cygnus-X, the clouds which contain the largest populations of protostars there is a clear difference in luminosity functions between protostars incrowded and distributed regions, with the luminosity function biased towards higher luminosities in more luminous regions. I will discuss the implications of these variations and the possibility that the IMF is

  13. B- and A-Type Stars in the Taurus-Auriga Star-Forming Region

    NASA Technical Reports Server (NTRS)

    Mooley, Kunal; Hillenbrand, Lynne; Rebull, Luisa; Padgett, Deborah; Knapp, Gillian

    2013-01-01

    We describe the results of a search for early-type stars associated with the Taurus-Auriga molecular cloud complex, a diffuse nearby star-forming region noted as lacking young stars of intermediate and high mass. We investigate several sets of possible O, B, and early A spectral class members. The first is a group of stars for which mid-infrared images show bright nebulae, all of which can be associated with stars of spectral-type B. The second group consists of early-type stars compiled from (1) literature listings in SIMBAD, (2) B stars with infrared excesses selected from the Spitzer Space Telescope survey of the Taurus cloud, (3) magnitude- and color-selected point sources from the Two Micron All Sky Survey, and (4) spectroscopically identified early-type stars from the Sloan Digital Sky Survey coverage of the Taurus region. We evaluated stars for membership in the Taurus-Auriga star formation region based on criteria involving: spectroscopic and parallactic distances, proper motions and radial velocities, and infrared excesses or line emission indicative of stellar youth. For selected objects, we also model the scattered and emitted radiation from reflection nebulosity and compare the results with the observed spectral energy distributions to further test the plausibility of physical association of the B stars with the Taurus cloud. This investigation newly identifies as probable Taurus members three B-type stars: HR 1445 (HD 28929), t Tau (HD 29763), 72 Tau (HD 28149), and two A-type stars: HD 31305 and HD 26212, thus doubling the number of stars A5 or earlier associated with the Taurus clouds. Several additional early-type sources including HD 29659 and HD 283815 meet some, but not all, of the membership criteria and therefore are plausible, though not secure, members.

  14. B- AND A-TYPE STARS IN THE TAURUS-AURIGA STAR-FORMING REGION

    SciTech Connect

    Mooley, Kunal; Hillenbrand, Lynne; Rebull, Luisa; Padgett, Deborah; Knapp, Gillian

    2013-07-10

    We describe the results of a search for early-type stars associated with the Taurus-Auriga molecular cloud complex, a diffuse nearby star-forming region noted as lacking young stars of intermediate and high mass. We investigate several sets of possible O, B, and early A spectral class members. The first is a group of stars for which mid-infrared images show bright nebulae, all of which can be associated with stars of spectral-type B. The second group consists of early-type stars compiled from (1) literature listings in SIMBAD, (2) B stars with infrared excesses selected from the Spitzer Space Telescope survey of the Taurus cloud, (3) magnitude- and color-selected point sources from the Two Micron All Sky Survey, and (4) spectroscopically identified early-type stars from the Sloan Digital Sky Survey coverage of the Taurus region. We evaluated stars for membership in the Taurus-Auriga star formation region based on criteria involving: spectroscopic and parallactic distances, proper motions and radial velocities, and infrared excesses or line emission indicative of stellar youth. For selected objects, we also model the scattered and emitted radiation from reflection nebulosity and compare the results with the observed spectral energy distributions to further test the plausibility of physical association of the B stars with the Taurus cloud. This investigation newly identifies as probable Taurus members three B-type stars: HR 1445 (HD 28929), {tau} Tau (HD 29763), 72 Tau (HD 28149), and two A-type stars: HD 31305 and HD 26212, thus doubling the number of stars A5 or earlier associated with the Taurus clouds. Several additional early-type sources including HD 29659 and HD 283815 meet some, but not all, of the membership criteria and therefore are plausible, though not secure, members.

  15. THE COMPACT STAR-FORMING COMPLEX AT THE HEART OF NGC 253

    SciTech Connect

    Davidge, T. J.

    2016-02-20

    We discuss integral field spectra of the compact star-forming complex that is the brightest near-infrared (NIR) source in the central regions of the starburst galaxy NGC 253. The spectra cover the H and K passbands and were recorded with the Gemini NIR Spectrograph during subarcsecond seeing conditions. Absorption features in the spectrum of the star-forming complex are weaker than in the surroundings. An absorption feature is found near 1.78 μm that coincides with the location of a C{sub 2} bandhead. If this feature is due to C{sub 2} then the star-forming complex has been in place for at least a few hundred Myr. Emission lines of Brγ, [Fe ii], and He i 2.06 μm do not track the NIR continuum light. Pockets of star-forming activity that do not have associated concentrations of red supergiants, and so likely have ages <8 Myr, are found along the western edge of the complex, and there is evidence that one such pocket contains a rich population of Wolf–Rayet stars. Unless the star-forming complex is significantly more metal-poor than the surroundings, then a significant fraction of its total mass is in stars with ages <8 Myr. If the present-day star formation rate is maintained then the timescale to double its stellar mass ranges from a few Myr to a few tens of Myr, depending on the contribution made by stars older than ∼8 Myr. If—as suggested by some studies—the star-forming complex is centered on the galaxy’s nucleus, which presumably contains a large population of old and intermediate-age stars, then the nucleus of NGC 253 is currently experiencing a phase of rapid growth in its stellar mass.

  16. VLBA Helps Build New Picture of Star-Forming Regions

    NASA Astrophysics Data System (ADS)

    2007-01-01

    New, high-precision distance measurements by the National Science Foundation's Very Long Baseline Array (VLBA) radio telescope are providing a major advance for astronomers trying to understand how stars form. "A large improvement in measuring the distance to a young, still-forming star means a large improvement in measuring characteristics such as its mass and intrinsic brightness," said Laurent Loinard, of the National University of Mexico (UNAM). Loinard, Amy Mioduszewski of the National Radio Astronomy Observatory, UNAM graduate student Rosa Torres and UNAM professor Luis Rodriguez presented their findings to the American Astronomical Society's meeting in Seattle, Washington. Parallax Diagram Trigonometric Parallax method determines distance to star by measuring its slight shift in apparent position as seen from opposite ends of Earth's orbit. CREDIT: Bill Saxton, NRAO/AUI/NSF Image and Animation Files Parallax Diagram (above image, JPEG, 153K) Animation of apparant motion on sky of young star T Tauri S (MPEG, 891K) Still Frame from above animation (JPEG, 14K) B&W Plot of T Tauri S Parallax motion (JPEG, 51K) "Most of what we know about the processes of star formation has come from studying young stars in a few, relatively nearby regions," Loinard said. "However, estimates of the distance to these regions have been imprecise. That imprecision has limited the ability of real-world observations to improve theoretical models for star formation," he added. The new VLBA distance measurements are great improvements over earlier estimates. For example, earlier work placed a famous young stellar system in the constellation Taurus between 423 and 489 light-years from Earth. The new VLBA measurements narrow the range to 418-422 light-years. "Our observations brought the error in this measurement down from 66 light-years to four," Mioduszewski said. The new VLBA observations also refined the distance estimate to another star-forming region in the constellation Ophiuchus

  17. Merger Signatures in the Dynamics of Star-forming Gas

    NASA Astrophysics Data System (ADS)

    Hung, Chao-Ling; Hayward, Christopher C.; Smith, Howard A.; Ashby, Matthew L. N.; Lanz, Lauranne; Martínez-Galarza, Juan R.; Sanders, D. B.; Zezas, Andreas

    2016-01-01

    The recent advent of integral field spectrographs and millimeter interferometers has revealed the internal dynamics of many hundreds of star-forming galaxies. Spatially resolved kinematics have been used to determine the dynamical status of star-forming galaxies with ambiguous morphologies, and constrain the importance of galaxy interactions during the assembly of galaxies. However, measuring the importance of interactions or galaxy merger rates requires knowledge of the systematics in kinematic diagnostics and the visible time with merger indicators. We analyze the dynamics of star-forming gas in a set of binary merger hydrodynamic simulations with stellar mass ratios of 1:1 and 1:4. We find that the evolution of kinematic asymmetries traced by star-forming gas mirrors morphological asymmetries derived from mock optical images, in which both merger indicators show the largest deviation from isolated disks during strong interaction phases. Based on a series of simulations with various initial disk orientations, orbital parameters, gas fractions, and mass ratios, we find that the merger signatures are visible for ˜0.2-0.4 Gyr with kinematic merger indicators but can be approximately twice as long for equal-mass mergers of massive gas-rich disk galaxies designed to be analogs of z ˜ 2-3 submillimeter galaxies. Merger signatures are most apparent after the second passage and before the black holes coalescence, but in some cases they persist up to several hundred Myr after coalescence. About 20%-60% of the simulated galaxies are not identified as mergers during the strong interaction phase, implying that galaxies undergoing violent merging process do not necessarily exhibit highly asymmetric kinematics in their star-forming gas. The lack of identifiable merger signatures in this population can lead to an underestimation of merger abundances in star-forming galaxies, and including them in samples of star-forming disks may bias the measurements of disk properties such

  18. MERGER SIGNATURES IN THE DYNAMICS OF STAR-FORMING GAS

    SciTech Connect

    Hung, Chao-Ling; Sanders, D. B.; Hayward, Christopher C.; Smith, Howard A.; Ashby, Matthew L. N.; Martínez-Galarza, Juan R.; Zezas, Andreas; Lanz, Lauranne

    2016-01-10

    The recent advent of integral field spectrographs and millimeter interferometers has revealed the internal dynamics of many hundreds of star-forming galaxies. Spatially resolved kinematics have been used to determine the dynamical status of star-forming galaxies with ambiguous morphologies, and constrain the importance of galaxy interactions during the assembly of galaxies. However, measuring the importance of interactions or galaxy merger rates requires knowledge of the systematics in kinematic diagnostics and the visible time with merger indicators. We analyze the dynamics of star-forming gas in a set of binary merger hydrodynamic simulations with stellar mass ratios of 1:1 and 1:4. We find that the evolution of kinematic asymmetries traced by star-forming gas mirrors morphological asymmetries derived from mock optical images, in which both merger indicators show the largest deviation from isolated disks during strong interaction phases. Based on a series of simulations with various initial disk orientations, orbital parameters, gas fractions, and mass ratios, we find that the merger signatures are visible for ∼0.2–0.4 Gyr with kinematic merger indicators but can be approximately twice as long for equal-mass mergers of massive gas-rich disk galaxies designed to be analogs of z ∼ 2–3 submillimeter galaxies. Merger signatures are most apparent after the second passage and before the black holes coalescence, but in some cases they persist up to several hundred Myr after coalescence. About 20%–60% of the simulated galaxies are not identified as mergers during the strong interaction phase, implying that galaxies undergoing violent merging process do not necessarily exhibit highly asymmetric kinematics in their star-forming gas. The lack of identifiable merger signatures in this population can lead to an underestimation of merger abundances in star-forming galaxies, and including them in samples of star-forming disks may bias the measurements of disk

  19. Molecular Outflows from Newly Formed Massive Stars

    NASA Astrophysics Data System (ADS)

    Kim, Kee-Tae; Kim, Won-Ju; Kim, Chang-Hee

    2015-12-01

    We map 6 massive young stellar objects (YSOs) in the CO J=2-1 line and survey 18 massive YSOs, including the six, in the hcopj, sioj, water 6_{16}-5_{23} maser, and methanol 7_{0}-6_{1} A^{+} maser lines. We detect CO bipolar outflows in all the six mapped sources. Four of them are newly discovered (ifive, ieight, inine, iten), while itwo is mapped in the CO J=2-1 line for the first time. The detected outflows are much more massive and energetic than outflows from low-mass YSOs with masses >20 M_⊙ and momenta >300 M_⊙ km/s. They have mass outflow rates (3-6)×10^{-4} M_⊙ yr^{-1}, which are at least one order of magnitude greater than those observed in low-mass YSOs. We detect hcop and SiO line emission in 18 (100%) and 4 (22%) sources, respectively. The hcop spectra show high-velocity wings in 11 (61%) sources. We detect water maser emission in 13 (72%) sources and 44 GHz methanol maser emission in 8 (44%) sources. Of the detected sources, 5 water and 6 methanol maser sources are new discoveries. iseven shows high-velocity (>30 kms) water maser lines. We find good correlations of the bolometric luminosity of the central (proto)star with the mechanical force, mechanical luminosity, and mass outflow rate of molecular outflow %L_{bol} with F_{m}, L_{m}, and dot{M}_{out} in the bolometric luminosity range of 10^{-1}-10^6 lsol, and identified 3 intermediate- or high-mass counterparts of Class O objects.

  20. ASSESSING RADIATION PRESSURE AS A FEEDBACK MECHANISM IN STAR-FORMING GALAXIES

    SciTech Connect

    Andrews, Brett H.; Thompson, Todd A.

    2011-02-01

    Radiation pressure from the absorption and scattering of starlight by dust grains may be an important feedback mechanism in regulating star-forming galaxies. We compile data from the literature on star clusters, star-forming subregions, normal star-forming galaxies, and starbursts to assess the importance of radiation pressure on dust as a feedback mechanism, by comparing the luminosity and flux of these systems to their dust Eddington limit. This exercise motivates a novel interpretation of the Schmidt law, the L{sub IR}-L'{sub CO} correlation, and the L{sub IR}-L'{sub HCN} correlation. In particular, the linear L{sub IR}-L'{sub HCN} correlation is a natural prediction of radiation pressure regulated star formation. Overall, we find that the Eddington limit sets a hard upper bound to the luminosity of any star-forming region. Importantly, however, many normal star-forming galaxies have luminosities significantly below the Eddington limit. We explore several explanations for this discrepancy, especially the role of 'intermittency' in normal spirals-the tendency for only a small number of subregions within a galaxy to be actively forming stars at any moment because of the time dependence of the feedback process and the luminosity evolution of the stellar population. If radiation pressure regulates star formation in dense gas, then the gas depletion timescale is 6 Myr, in good agreement with observations of the densest starbursts. Finally, we highlight the importance of observational uncertainties, namely, the dust-to-gas ratio and the CO-to-H{sub 2} and HCN-to-H{sub 2} conversion factors, that must be understood before a definitive assessment of radiation pressure as a feedback mechanism in star-forming galaxies.

  1. The Chemical Composition of the Active Stars

    NASA Astrophysics Data System (ADS)

    Glazunova, L. V.

    The comparison of the results of the studies of the active stars' chemical composition obtained by different authors has been performed. It was concluded that the difference between the abundances of some elements in active and inactive stars becomes significant (> 3σ) only for the active stars with high chromospheric activity (lgR'HK > -4). This is the case primarily for the light elements, namely Li, Na and Al, as well as heavy elements with Z > 30.

  2. HUBBLE'S PANORAMIC PORTRAIT OF A VAST STAR-FORMING REGION

    NASA Technical Reports Server (NTRS)

    2002-01-01

    NASA's Hubble Space Telescope has snapped a panoramic portrait of a vast, sculpted landscape of gas and dust where thousands of stars are being born. This fertile star-forming region, called the 30 Doradus Nebula, has a sparkling stellar centerpiece: the most spectacular cluster of massive stars in our cosmic neighborhood of about 25 galaxies. The mosaic picture shows that ultraviolet radiation and high-speed material unleashed by the stars in the cluster, called R136 [the large blue blob left of center], are weaving a tapestry of creation and destruction, triggering the collapse of looming gas and dust clouds and forming pillar-like structures that are incubators for nascent stars. The photo offers an unprecedented, detailed view of the entire inner region of 30 Doradus, measuring 200 light-years wide by 150 light-years high. The nebula resides in the Large Magellanic Cloud (a satellite galaxy of the Milky Way), 170,000 light-years from Earth. Nebulas like 30 Doradus are the 'signposts' of recent star birth. High-energy ultraviolet radiation from the young, hot, massive stars in R136 causes the surrounding gaseous material to glow. Previous Hubble telescope observations showed that R136 contains several dozen of the most massive stars known, each about 100 times the mass of the Sun and about 10 times as hot. These stellar behemoths all formed at the same time about 2 million years ago. The stars in R136 are producing intense 'stellar winds' (streams of material traveling at several million miles an hour), which are wreaking havoc on the gas and dust in the surrounding neighborhood. The winds are pushing the gas away from the cluster and compressing the inner regions of the surrounding gas and dust clouds [the pinkish material]. The intense pressure is triggering the collapse of parts of the clouds, producing a new generation of star formation around the central cluster. The new stellar nursery is about 30 to 50 light-years from R136. Most of the stars in the

  3. THE STRUCTURE OF THE STAR-FORMING CLUSTER RCW 38

    SciTech Connect

    Winston, E.; Wolk, S. J.; Bourke, T. L.; Spitzbart, B.; Megeath, S. T.; Gutermuth, R.

    2011-12-20

    We present a study of the structure of the high-mass star-forming region RCW 38 and the spatial distribution of its young stellar population. Spitzer Infrared Array Camera (IRAC) photometry (3-8 {mu}m) is combined with Two Micron All Sky Survey near-IR data to identify young stellar objects (YSOs) by IR-excess emission from their circumstellar material. Chandra X-ray data are used to identify class III pre-main-sequence stars lacking circumstellar material. We identify 624 YSOs: 23 class 0/I and 90 flat spectrum protostars, 437 class II stars, and 74 class III stars. We also identify 29 (27 new) O star candidates over the IRAC field. Seventy-two stars exhibit IR-variability, including 7 class 0/I and 12 flat spectrum YSOs. A further 177 tentative candidates are identified by their location in the IRAC [3.6] versus [3.6]-[5.8] color-magnitude diagram. We find strong evidence of subclustering in the region. Three subclusters were identified surrounding the central cluster, with massive and variable stars in each subcluster. The central region shows evidence of distinct spatial distributions of the protostars and pre-main-sequence stars. A previously detected IR cluster, DB2001{sub O}bj36, has been established as a subcluster of RCW 38. This suggests that star formation in RCW 38 occurs over a more extended area than previously thought. The gas-to-dust ratio is examined using the X-ray derived hydrogen column density, N{sub H} and the K-band extinction, and found to be consistent with the diffuse interstellar medium, in contrast with Serpens and NGC 1333. We posit that the high photoionizing flux of massive stars in RCW 38 affects the agglomeration of the dust grains.

  4. The WFC3 Mosaic of The Star-Forming Galaxy M51 in Paschen beta

    NASA Astrophysics Data System (ADS)

    Koda, Jin

    2011-10-01

    We propose WFC3/IR Paschen beta imaging of the entire star-forming disk of M51 in a 10-point mosaic. This proposal is motivated by a new picture of gas evolution in galaxies from our recent observations in carbon-monoxide {CO} emission, namely one driven by galactic dynamics. The Paschen beta and archival ACS/Halpha images will enable correction for extinction throughout the entire M51 disk, and show an unprecedented map of star forming activity across the entire galaxy. By comparing this map with our new CO intensity and velocity maps, we will {1} place star formation in this new context of gas evolution, {2} study the triggering of star formation by correlating the star formation efficiency of individual GMC with global galactic structures {such as observed spiral shear motions and local gas convergence}, and {3} investigate the physics that underlie the Schmidt law by resolving the early-phases of star formation and its environment. The extinction-corrected map of star formation activity will become a reference for future calibration of other tracers of star formation activity and will have an unparalleled archival value.

  5. Isolated Star-Forming Cloud Discovered in Intracluster Space

    NASA Astrophysics Data System (ADS)

    2003-01-01

    galaxies, Messier 86 and Messier 84, indicate the presence of other isolated HII regions, thus suggesting that isolated star formation may occur more generally in galaxies. If so, this process may provide a natural explanation to the current riddle why some young stars are found high up in the halo of our own Milky Way galaxy, far from the star-forming clouds in the main plane. The Virgo Cluster ESO PR Photo 04a/03 ESO PR Photo 04a/03 [Preview - JPEG: 400 x 428 pix - 74k [Normal - JPEG: 800 x 855 pix - 408k] [Hi-Res - JPEG: 4252 x 4544 pix - 10.3M] ESO PR Photo 04b/03 ESO PR Photo 04b/03 [Preview - JPEG: 433 x 400 pix - 60k [Normal - JPEG: 865 x 800 pix - 456k] [Hi-Res - JPEG: 3077 x 2847 pix - 4.2M] Captions: PR Photo 04a/03 displays a sky field near some of the brighter galaxies in the Virgo Cluster. It was obtained in April 2000 with the Wide Field Imager (WFI) at the La Silla Observatory (exposure 6 x 5 min; red R-band; seeing 1.3 arcsec). The large elliptical galaxy at the centre is Messier 84; the elongated image of NGC 4388 (an active spiral galaxy, seen from the side) is in the lower left corner. The field measures 16.9 x 15.7 arcmin2. PR Photo 04b/03 shows a larger region of the Virgo cluster, with the galaxies Messier 86 (at the upper edge of the field, to the left of the centre), as well as Messier 84 (upper right) and NGC 4388 (just below the centre) that are also seen in PR Photo 04a/03. It is reproduced from a long-exposure Subaru Suprime-Cam image, obtained in the red light of ionized hydrogen (the H-alpha spectral line at wavelength 656.2 nm). In order to show the faintest possible hydrogen emitting objects embedded in the outskirts of bright galaxies, their smooth envelopes have been "subtracted" during the image processing. The field measures 34 x 27 arcmin2. Part of this sky field is shown in colour in PR Photo 04c/03. Captions: PR Photo 04a/03 displays a sky field near some of the brighter galaxies in the Virgo Cluster. It was obtained in April 2000

  6. The SUNBIRD survey: characterizing the super star cluster populations of intensely star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Randriamanakoto, Zara; Väisänen, Petri

    2017-03-01

    Super star clusters (SSCs) represent the youngest and most massive form of known gravitationally bound star clusters in the Universe. They are born abundantly in environments that trigger strong and violent star formation. We investigate the properties of these massive SSCs in a sample of 42 nearby starbursts and luminous infrared galaxies. The targets form the sample of the SUperNovae and starBursts in the InfraReD (SUNBIRD) survey that were imaged using near-infrared (NIR) K-band adaptive optics mounted on the Gemini/NIRI and the VLT/NaCo instruments. Results from i) the fitted power-laws to the SSC K-band luminosity functions, ii) the NIR brightest star cluster magnitude - star formation rate (SFR) relation and iii) the star cluster age and mass distributions have shown the importance of studying SSC host galaxies with high SFR levels to determine the role of the galactic environments in the star cluster formation, evolution and disruption mechanisms.

  7. Numerical Simulations of Self-Regulated, Star Forming Galactic Disks

    NASA Astrophysics Data System (ADS)

    Smith, D. C.; Struck, C.

    2000-12-01

    While star formation feedback models have been used in the study of galaxy formation, the effects of these processes on the global structure of disks have received less attention. We have adapted Hydra, the adaptive particle-particle, particle-mesh with smoothed particle hydrodynamics code by Couchman et al., to include heating processes deriving from star formation in order to study the effects of this heating on the structure of the disk and on the star formation itself. These processes include mechanical heating from strong stellar winds and supernovae, as well as heating due to photoelectric removal of electrons from grains by UV flux from young OB stars. Mechanisms of this type can be implemented in a simple way within the Hydra code, allowing us to study the density and temperature profiles of the gas, the balance among the multiple thermal phases generated in the disk, and the kinematics of the disk. Preliminary results from numerical simulations of star-forming gas disks of late type spirals are presented. Self-regulating effects of star formation on the global structure of the disk are discussed. We describe and compare the results of different star formation criteria and discuss the effects of particle resolution. This study was funded, in part, by a grant from the George Washington Carver Charitable Trust.

  8. The Star-Forming Main Sequence at Low Galaxy Mass

    NASA Astrophysics Data System (ADS)

    Stierwalt, Sabrina; Johnson, Kelsey E.; Patton, David R.; Besla, Gurtina; Kallivayalil, Nitya; Liss, Sandra; Pearson, Sarah; Privon, George C.; Putman, Mary E.

    2017-01-01

    We present an investigation of the star-forming main sequence at the low mass end. The relation between galaxy stellar mass and star formation rate has been well-studied in the recent literature for a range of redshifts and galaxy type, but almost all of these studies are limited to galaxies with stellar masses above the dwarf galaxy range ( 109 Msun ). Our work, based on the panchromatic TiNy Titans survey of interacting dwarf galaxies, shows that dwarf galaxies extend the well-established main sequence at z=0 down to lower masses. Furthermore, like their more massive counterparts, dwarf mergers appear on an elevated main sequence with higher star formation rates for a given stellar mass. Finally we show that star formation is enhanced to a greater extent in low mass galaxy mergers than for higher mass systems.

  9. Search for OB stars running away from young star clusters. II. The NGC 6357 star-forming region

    NASA Astrophysics Data System (ADS)

    Gvaramadze, V. V.; Kniazev, A. Y.; Kroupa, P.; Oh, S.

    2011-11-01

    Dynamical few-body encounters in the dense cores of young massive star clusters are responsible for the loss of a significant fraction of their massive stellar content. Some of the escaping (runaway) stars move through the ambient medium supersonically and can be revealed via detection of their bow shocks (visible in the infrared, optical or radio). In this paper, which is the second of a series of papers devoted to the search for OB stars running away from young ( ≲ several Myr) Galactic clusters and OB associations, we present the results of the search for bow shocks around the star-forming region NGC 6357. Using the archival data of the Midcourse Space Experiment (MSX) satellite and the Spitzer Space Telescope, and the preliminary data release of the Wide-Field Infrared Survey Explorer (WISE), we discovered seven bow shocks, whose geometry is consistent with the possibility that they are generated by stars expelled from the young (~1-2 Myr) star clusters, Pismis 24 and AH03 J1725-34.4, associated with NGC 6357. Two of the seven bow shocks are driven by the already known OB stars, HD 319881 and [N78] 34. Follow-up spectroscopy of three other bow-shock-producing stars showed that they are massive (O-type) stars as well, while the 2MASS photometry of the remaining two stars suggests that they could be B0 V stars, provided that both are located at the same distance as NGC 6357. Detection of numerous massive stars ejected from the very young clusters is consistent with the theoretical expectation that star clusters can effectively lose massive stars at the very beginning of their dynamical evolution (long before the second mechanism for production of runaway stars, based on a supernova explosion in a massive tight binary system, begins to operate) and lends strong support to the idea that probably all field OB stars have been dynamically ejected from their birth clusters. A by-product of our search for bow shocks around NGC 6357 is the detection of three circular

  10. Locating star-forming regions in quasar host galaxies

    NASA Astrophysics Data System (ADS)

    Young, J. E.; Eracleous, M.; Shemmer, O.; Netzer, H.; Gronwall, C.; Lutz, Dieter; Ciardullo, R.; Sturm, Eckhard

    2014-02-01

    We present a study of the morphology and intensity of star formation in the host galaxies of eight Palomar-Green quasars using observations with the Hubble Space Telescope. Our observations are motivated by recent evidence for a close relationship between black hole growth and the stellar mass evolution in its host galaxy. We use narrow-band [O II]λ3727, Hβ, [O III]λ5007 and Paα images, taken with the Wide Field Planetary Camera 2 and NICMOS instruments, to map the morphology of line-emitting regions, and, after extinction corrections, diagnose the excitation mechanism and infer star-formation rates. Significant challenges in this type of work are the separation of the quasar light from the stellar continuum and the quasar-excited gas from the star-forming regions. To this end, we present a novel technique for image decomposition and subtraction of quasar light. Our primary result is the detection of extended line-emitting regions with sizes ranging from 0.5 to 5 kpc and distributed symmetrically around the nucleus, powered primarily by star formation. We determine star-formation rates of the order of a few tens of M⊙ yr-1. The host galaxies of our target quasars have stellar masses of the order of 1011 M⊙ and specific star-formation rates on a par with those of M82 and luminous infrared galaxies. As such they fall at the upper envelope or just above the star-formation mass sequence in the specific star formation versus stellar mass diagram. We see a clear trend of increasing star-formation rate with quasar luminosity, reinforcing the link between the growth of the stellar mass of the host and the black hole mass found by other authors.

  11. Heavily Obscured Star-Forming Regions in the LVL Galaxies

    NASA Astrophysics Data System (ADS)

    Dale, Daniel A.; Aller, K.; Staudaher, S.

    2009-01-01

    We use data from the Spitzer Local Volume Legacy to study the infrared and optical properties of star forming regions in galaxies on 300pc scales. Our main goal is to determine the fraction of heavily-obscured star-forming regions. Here we study 908 regions within 55 galaxies. The median attenuation in Hα is 0.69 mag, and only a small fraction is highly obscured (Aα> 2). There is very little variation in the median attenuation over scales of 200pc to 1000pc.

  12. Accretion phenomena in nearby star-forming dwarf galaxies

    NASA Astrophysics Data System (ADS)

    Annibali, F.; Tosi, M.; Aloisi, A.; Bellazzini, M.; Buzzoni, A.; Cignoni, M.; Ciotti, L.; Cusano, F.; Nipoti, C.; Sacchi, E.; Paris, D.; Romano, D.

    2017-03-01

    We present two pilot studies for the search and characterization of accretion events in star-forming dwarf galaxies. Our strategy consists of two complementary approaches: i) the direct search for stellar substructures around dwarf galaxies through deep wide-field imaging, and ii) the characterization of the chemical properties in these systems up to large galacto-centric distances. We show our results for two star-forming dwarf galaxies, the starburst irregular NGC 4449, and the extremely metal-poor dwarf DDO 68.

  13. Old stellar populations in star-forming dwarf galaxies

    NASA Astrophysics Data System (ADS)

    Held, Enrico V.; Saviane, Ivo; Momany, Yazan; Rizzi, Luca; Bertelli, Gianpaolo

    We present deep VLT/FORS1 observations of the two distant, isolated Local Group dwarfs Phoenix and Antlia. Our results provide further evidence for the presence of old stars in these star-forming dwarf galaxies. Old stellar populations are known in all of the Local Group dwarf spheroidal galaxies and in some dwarf irregulars, implying that dwarf galaxies started forming stars at a sharply defined early epoch irrespective of their subsequent star formation histories (e.g., Held et al., 2000; Saviane et al., 2000; and references therein). The new color-magnitude diagrams of Phoenix confirm the presence of a spatially extended blue HB population, indicating a conspicuous old component (Held et al., 1999; Martínez-Delgado et al., 1999). A preliminary analysis of stellar variability has led to the discovery of several tens RR Lyrae variables, which can provide clue information on the earliest star formation episode (see, e.g., Siegel and Majewski, 2000). The young main sequence extends down to the limit of our photometry (V=25.5 mag), which suggests that Phoenix underwent nearly continuous star formation in the last 2 Gyr. Our deep color-magnitude diagrams of Antlia have been used to investigate the gradient in the stellar populations of this dwarf irregular/spheroidal galaxy. While the young stars appear to be concentrated in a round central region (Aparicio et al., 1997; Sarajedini et al., 1997), the spatial distribution of the red giant stars defines an extended flattened halo (or disk) 2-3 kpc across.

  14. Hα Kinematics of High-z Dusty Star Forming Galaxies

    NASA Astrophysics Data System (ADS)

    Drew, Patrick; Casey, Caitlin; Hung, Chao-Ling; Cooray, Asantha R.; Sanders, David B.; Fu, Hai

    2017-01-01

    Dusty Star Forming Galaxies (DSFGs) have the highest star formation rates in the Universe, but compared with other star forming galaxies at z > ~1 they are difficult to characterize, physically. Their low number density and extreme dust obscuration has led to very few kinematic studies of DSFGs at optical wavelengths. We present a rest-frame optical kinematic analysis of 5 DSFGs at z ~1.5 using long slit spectroscopy obtained with MOSFIRE at Keck Observatory. From our high signal-to-noise spectra we simultaneously fit Hα, [NII] λ6548, and [NII] λ6583 along each slit to generate position-velocity diagrams. We infer the kinematic disturbances and derive dynamical masses in order to compare with other derived quantities such as fractional obscuration, stellar and gas fractions, and dust characteristics.

  15. Infrared and optical studies of the Chamaeleon II and Lupus low-mass star forming regions .

    NASA Astrophysics Data System (ADS)

    Spezzi, L.; Alcalá, J. M.; Chapman, N.; Covino, E.; Evans, N. J., II; Frasca, A.; Gandolfi, D.; Huard, T. L.; Oliveira, I.; Jørgensen, J. K.; Merín, B.; Stapelfeldt, K. R.

    The Spitzer Legacy survey ``From Molecular Cores to Planet-forming Disks'' \\citep[c2d][]{Eva03} provided infrared observations of sources that span the evolutionary sequence from molecular cores to proto-planetary disks, encompassing a wide range of star-forming environments. These overall observations allowed to study crucial steps in the formation of stars and planets with unprecedented sensitivity. We present some results from the Spitzer observations and complementary data in the low-mass star forming regions in Chamaeleon II and Lupus. We focus, in particular, on the star-formation history and activity of these clouds, the low-mass end of their IMF and the envelope/disk properties of their young populations.

  16. Narrow-band Imaging of Massive Star-Forming Regions: Tracing Outflows and the Rate of Star-Formation

    NASA Astrophysics Data System (ADS)

    Hall, Kendall; Willis, Sarah; Hora, Joseph L.

    2016-01-01

    Narrowband images targeting ionized hydrogen (Brackett gamma, 2.17 microns) and molecular hydrogen (2.12 microns) were obtained for six massive star-forming regions within the Milky Way, NGC 6334, G305, G3333, G3264, G3266, and G351. These regions are within 1-4 kpc from our solar system. The narrowband flux in Brackett gamma was used as a star-formation tracer to calculate a star-formation rate for each region. This is compared with other star-formation rates found using other methods such as the count of young stars and YSOs, and rates calculated from using other tracers (e.g. 70 micron monochromatic luminosity). The molecular hydrogen narrowband images were manually searched to locate outflows from young stars. Once these outflows are identified, it may help to get a better survey of the young stellar population. A better understanding of the stellar population distribution can lead to more accurate star-formation rates to compare to those calculated from star-formation tracers. We found the regions NGC 6334 and G3266 to have the highest levels of ongoing star formation activity as indicated by the number of molecular hydrogen objects (MHOs) detected. There are a total of 279 cataloged MHOs in 181 categorized systems for the six regions. There are a total of 150 identified potential driving sources.This work was supported in part by the NSF REU and DoD ASSURE programs under NSF grant no. 1262851 and by the Smithsonian Institution.

  17. A UV Imaging Survey of IR-Bright Star- Forming Galaxies

    NASA Astrophysics Data System (ADS)

    Calzetti, Daniela

    2000-07-01

    We propose to carry out a UV{ 1, 600 Angstrom} snapshot imaging survey with STIS of all the actively star-forming galaxies detected by ISO at Lambda>170 Mum and closer than cz=9000 km/s. The sample covers a large region in the parameter's space of morphology, luminosity, metallicity, and star formation intensity. The multiwavelength {UV/far-IR} information will be exploited to address open issues on low- and high-redshift star formation and on the dust/star- formation interconnection. The ISO galaxies will be used as low-redshift benchmarks to explore the relationship between the Lyman-break galaxies at z 3 and the SCUBA sources. The conditions for the escape of UV light from a `dusty' galaxy will be investigated as a function of the sample parameters. UV-bright structures will be measured and used to quantify the fractions 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. Given the breadth of scientific applications and the relevance of this unique dataset for upcoming instruments and missions, including mid/far-IR ones like SIRTF, we propose this project as a Service to the Community and will release immediately the UV images in the public domain.

  18. ATLASGAL - towards a complete sample of massive star forming clumps

    NASA Astrophysics Data System (ADS)

    Urquhart, J. S.; Moore, T. J. T.; Csengeri, T.; Wyrowski, F.; Schuller, F.; Hoare, M. G.; Lumsden, S. L.; Mottram, J. C.; Thompson, M. A.; Menten, K. M.; Walmsley, C. M.; Bronfman, L.; Pfalzner, S.; König, C.; Wienen, M.

    2014-09-01

    By matching infrared-selected, massive young stellar objects (MYSOs) and compact H II regions in the Red MSX Source survey to massive clumps found in the submillimetre ATLASGAL (APEX Telescope Large Area Survey of the Galaxy) survey, we have identified ˜1000 embedded young massive stars between 280° < ℓ < 350° and 10° < ℓ < 60° with | b | < 1.5°. Combined with an existing sample of radio-selected methanol masers and compact H II regions, the result is a catalogue of ˜1700 massive stars embedded within ˜1300 clumps located across the inner Galaxy, containing three observationally distinct subsamples, methanol-maser, MYSO and H II-region associations, covering the most important tracers of massive star formation, thought to represent key stages of evolution. We find that massive star formation is strongly correlated with the regions of highest column density in spherical, centrally condensed clumps. We find no significant differences between the three samples in clump structure or the relative location of the embedded stars, which suggests that the structure of a clump is set before the onset of star formation, and changes little as the embedded object evolves towards the main sequence. There is a strong linear correlation between clump mass and bolometric luminosity, with the most massive stars forming in the most massive clumps. We find that the MYSO and H II-region subsamples are likely to cover a similar range of evolutionary stages and that the majority are near the end of their main accretion phase. We find few infrared-bright MYSOs associated with the most massive clumps, probably due to very short pre-main-sequence lifetimes in the most luminous sources.

  19. The magnetic fields of forming solar-like stars

    NASA Astrophysics Data System (ADS)

    Gregory, S. G.; Jardine, M.; Gray, C. G.; Donati, J.-F.

    2010-12-01

    Magnetic fields play a crucial role at all stages of the formation of low-mass stars and planetary systems. In the final stages, in particular, they control the kinematics of in-falling gas from circumstellar discs, and the launching and collimation of spectacular outflows. The magnetic coupling with the disc is thought to influence the rotational evolution of the star, while magnetized stellar winds control the braking of more evolved stars and may influence the migration of planets. Magnetic reconnection events trigger energetic flares which irradiate circumstellar discs with high energy particles that influence the disc chemistry and set the initial conditions for planet formation. However, it is only in the past few years that the current generation of optical spectropolarimeters has allowed the magnetic fields of forming solar-like stars to be probed in unprecedented detail. In order to do justice to the recent extensive observational programs new theoretical models are being developed that incorporate magnetic fields with an observed degree of complexity. In this review we draw together disparate results from the classical electromagnetism, molecular physics/chemistry and the geophysics literature, and demonstrate how they can be adapted to construct models of the large scale magnetospheres of stars and planets. We conclude by examining how the incorporation of multipolar magnetic fields into new theoretical models will drive future progress in the field through the elucidation of several observational conundrums.

  20. Shocks and metallicity gradients in normal star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Ho, I.-Ting

    Gas flow is one of the most fundamental processes driving galaxy evolution. This thesis explores gas flows in local galaxies by studying metallicity gradients and galactic-scale outflows in normal star-forming galaxies. This is made possible by new integral field spectroscopy data that provide simultaneously spatial and spectral information of galaxies. First, I measure metallicity gradients in isolated disk galaxies and show that their metallicity gradients are remarkably simple and universal. When the metallicity gradients are normalized to galaxy sizes, all the 49 galaxies studied have virtually the same metallicity gradient. I model the common metallicity gradient using a simple chemical evolution model to understand its origin. The common metallicity gradient is a direct result of the coevolution of gas and stellar disk while galactic disks build up their masses from inside-out. Tight constraints on the mass outflow rates and inflow rates can be placed by the chemical evolution model. Second, I investigate galactic winds in normal star-forming galaxies using data from an integral field spectroscopy survey. I demonstrate how to search for galactic winds by probing emission line ratios, shocks, and gas kinematics. Galactic winds are found to be common even in normal star-forming galaxies that were not expected to host winds. By comparing galaxies with and without hosting winds, I show that galaxies with high star formation rate surface densities and bursty star formation histories are more likely to drive large-scale galactic winds. Finally, lzifu, a toolkit for fitting multiple emission lines simultaneously in integral field spectroscopy data, is developed in this thesis. I describe in detail the structure of the toolkit and demonstrate the capabilities of lzifu.

  1. Dust temperature distributions in star-forming condensations

    NASA Technical Reports Server (NTRS)

    Xie, Taoling; Goldsmith, Paul F.; Snell, Ronald L.; Zhou, Weimin

    1993-01-01

    The FIR spectra of the central IR condensations in the dense cores of molecular clouds AFGL 2591. B335, L1551, Mon R2, and Sgr B2 are reanalyzed here in terms of the distribution of dust mass as a function of temperature. FIR spectra of these objects can be characterized reasonably well by a given functional form. The general shapes of the dust temperature distributions of these objects are similar and closely resemble the theoretical computations of de Muizon and Rouan (1985) for a sample of 'hot centered' clouds with active star formation. Specifically, the model yields a 'cutoff' temperature below which essentially no dust is needed to interpret the dust emission spectra, and most of the dust mass is distributed in a broad temperature range of a few tens of degrees above the cutoff temperature. Mass, luminosity, average temperature, and column density are obtained, and it is found that the physical quantities differ considerably from source to source in a meaningful way.

  2. THE STRUCTURAL EVOLUTION OF FORMING AND EARLY STAGE STAR CLUSTERS

    SciTech Connect

    Jaehnig, Karl O.; Da Rio, Nicola; Tan, Jonathan C. E-mail: ndario@ufl.edu

    2015-01-10

    We study the degree of angular substructure in the stellar position distribution of young members of Galactic star-forming regions, looking for correlations with distance from cluster center, surface number density of stars, and local dynamical age. To this end we adopt the catalog of members in 18 young (∼1-3 Myr) clusters from the Massive Young Star-Forming Complex Study in Infrared and X-ray Survey and the statistical analysis of the angular dispersion parameter, δ{sub ADP,} {sub N}. We find statistically significant correlation between δ{sub ADP,} {sub N} and physical projected distance from the center of the clusters, with the centers appearing smoother than the outskirts, consistent with more rapid dynamical processing on local dynamical, free-fall or orbital timescales. Similarly, smoother distributions are seen in regions of higher surface density, or older dynamical ages. These results indicate that dynamical processing that erases substructure is already well-advanced in young, sometimes still-forming, clusters. Such observations of the dissipation of substructure have the potential to constrain theoretical models of the dynamical evolution of young and forming clusters.

  3. MODELING THE STAR-FORMING UNIVERSE AT z = 2: IMPACT OF COLD ACCRETION FLOWS

    SciTech Connect

    Khochfar, Sadegh; Silk, Joseph

    2009-07-20

    We present results of a semianalytic model (SAM) that includes cold accretion and a porosity-based prescription for star formation. We can recover the puzzling observational results of low V/{sigma} seen in various massive disk or disk-like galaxies, if we allow 18% of the accretion energy from cold flows to drive turbulence in gaseous disks at z = 2. The increase of gas mass through cold flows is by itself not sufficient to increase the star formation rate sufficiently to recover the number density of M-dot{sub *}>120 M{sub odot} yr{sup -1} galaxies in our model. In addition, it is necessary to increase the star formation efficiency. This can be achieved naturally in the porosity model, where star formation efficiency scales {proportional_to}{sigma}, which scales as cloud velocity dispersion. As cold accretion is the main driver for gas velocity dispersion in our model, star formation efficiency parallels cold accretion rates and allows fast conversion into stars. At z {approx} 2, we find a space density 10{sup -4} Mpc{sup -3} in star-forming galaxies with M-dot{sub *}>120 M{sub odot} yr{sup -1}, in better agreement than earlier estimates from SAMs. However, the fundamental relation between M-dot{sub *} and M {sub *} is still offset from the observed relation, indicating the need for possibly more efficient star formation at high-z perhaps associated with a role for active galactic nucleus (AGN) triggering.

  4. Multiplicity study of young pre-main sequence stars in the Lupus star-forming Region

    NASA Astrophysics Data System (ADS)

    Vogt, Nikolaus; Mugrauer, Markus; Schmidt, Tobias O. B.; Neuhaeuser, Ralph; Ginski, Christian

    2013-07-01

    We have conducted a high contrast imaging search for (sub)stellar companions among 63 young pre-main sequence stars in the Lupus star forming region, using the adaptive optics imager NACO at UT4 of the ESO Paranal observatory. We detected faint co-moving companions around our targets at angular separations between about 0.1 up to several arc seconds (binaries and triple systems). Some of these companions are in the sub stellar mass regime, according to their apparent near infrared photometry at the distance of the Lupus star forming region (about 140pc). We give a progress report to our long-term project, still in execution with the follow-up spectroscopy of detected substellar companion-candidates, and present some first results.

  5. The SINS/zC-SINF survey of z ∼ 2 galaxy kinematics: Evidence for powerful active galactic nucleus-driven nuclear outflows in massive star-forming galaxies

    SciTech Connect

    Förster Schreiber, N. M.; Genzel, R.; Kurk, J. D.; Lutz, D.; Tacconi, L. J.; Wuyts, S.; Bandara, K.; Buschkamp, P.; Davies, R.; Eisenhauer, F.; Lang, P.; Newman, S. F.; Burkert, A.; Carollo, C. M.; Lilly, S. J.; Cresci, G.; Daddi, E.; Mainieri, V.; Mancini, C.; and others

    2014-05-20

    We report the detection of ubiquitous powerful nuclear outflows in massive (≥10{sup 11} M {sub ☉}) z ∼ 2 star-forming galaxies (SFGs), which are plausibly driven by an active galactic nucleus (AGN). The sample consists of the eight most massive SFGs from our SINS/zC-SINF survey of galaxy kinematics with the imaging spectrometer SINFONI, six of which have sensitive high-resolution adaptive optics-assisted observations. All of the objects are disks hosting a significant stellar bulge. The spectra in their central regions exhibit a broad component in Hα and forbidden [N II] and [S II] line emission, with typical velocity FWHM ∼ 1500 km s{sup –1}, [N II]/Hα ratio ≈ 0.6, and intrinsic extent of 2-3 kpc. These properties are consistent with warm ionized gas outflows associated with Type 2 AGN, the presence of which is confirmed via independent diagnostics in half the galaxies. The data imply a median ionized gas mass outflow rate of ∼60 M {sub ☉} yr{sup –1} and mass loading of ∼3. At larger radii, a weaker broad component is detected but with lower FWHM ∼485 km s{sup –1} and [N II]/Hα ≈ 0.35, characteristic for star formation-driven outflows as found in the lower-mass SINS/zC-SINF galaxies. The high inferred mass outflow rates and frequent occurrence suggest that the nuclear outflows efficiently expel gas out of the centers of the galaxies with high duty cycles and may thus contribute to the process of star formation quenching in massive galaxies. Larger samples at high masses will be crucial in confirming the importance and energetics of the nuclear outflow phenomenon and its connection to AGN activity and bulge growth.

  6. 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

  7. Study of the Cygnus Star-Forming Field

    NASA Astrophysics Data System (ADS)

    Christopherson, Christopher; Kaltcheva, Nadia

    2016-01-01

    The star-forming complexes in Cygnus extend nearly 30 deg in Galactic longitude and 20 deg in latitude, and most probably include star-formation sites located between 600 and 4000 pc. We combine the catalog by Heiles (2000) with uvbyβ photometric data from the catalog of Paunzen (2015) to collate a sample of O and B-type stars with precise homogeneous distances, color excess and available polarimetry. This allows us to identify star-forming sites at different distances along the line of sight and to investigate their spatial correlation to the interstellar matter. Further, we use this sample to study the orientation of the polarization as revealed by the polarized light of the bright early-type stars and analyze the polarization-extinction correlation for this field. Since dust grains align in the presence of a magnetic field cause the observed polarization at optical wavelengths, the data contain information about the large-scale component of the Galactic magnetic field. In addition, wide-field astrophotography equipment was used to image the Cygnus field in Hydrogen-alpha, Hydrogen-beta and the [OIII] line at 500.7 nm. This allows us to map the overall distribution of ionized material and the interstellar dust and trace large-scale regions where the physical conditions change rapidly due to supernova shock fronts and strong stellar winds. Acknowledgments: This work was supported by NSF grant AST- 1516932 and the Wisconsin Space Grant Consortium, NASA Space Grant College and Fellowship Program, NASA Training Grant #NNX14AP22H.

  8. Looking Closely at "Medusa": Star Forming Regions in NGC 4194

    NASA Technical Reports Server (NTRS)

    Weistrop, D.; Eggers, D.; Nelson, C. H.; Kaiser, M. E.

    2004-01-01

    The "Medusa" (NGC 4194, Mrk 201) is a blue compact galaxy, with strong far infrared and radio emission. Ground-based observations exhibit a distorted image with a tidal tail and regions of strong star formation. A population of massive O and early B stars is evident from the IUE spectra HST survey of Seyfert and starburst galaxies notes NCG 4194 is an HII galaxy with lumpy HII regions and knots. The central starburst is apparently produced by a galaxy merger. As part of an investigation of star formation in interacting galaxies, we have obtained ultraviolet and visible images of the central regions of NGC 4194 with the Space Telescope Imaging Spectrograph on HST. Imaging was obtained in two ultraviolet (FUV-MAMA+F25QTZ, NUV-MAMA+F25CN182) and one visible (CCD+F28X50LP) band. Individual star forming knots (at HST resolution) have been identified. We present sized and luminosities for the individual knots, and the knot luminosity function. We compare our data to current starburst models to constrain stellar ages and populations. Knot characteristics as a function of location in the galaxy will also be discussed.

  9. Water in star- and planet-forming regions.

    PubMed

    Bergin, Edwin A; van Dishoeck, Ewine F

    2012-06-13

    In this paper, we discuss the astronomical search for water vapour in order to understand the disposition of water in all its phases throughout the processes of star and planet formation. Our ability to detect and study water vapour has recently received a tremendous boost with the successful launch and operation of the Herschel Space Observatory. Herschel spectroscopic detections of numerous transitions in a variety of astronomical objects, along with previous work by other space-based observatories, will be threaded throughout this paper. In particular, we present observations of water tracing the earliest stage of star birth where it is predominantly frozen as ice. When a star is born, the local energy release by radiation liberates ices in its surrounding envelope and powers energetic outflows that appear to be water factories. In these regions, water plays an important role in the gas physics. Finally, we end with an exploration of water in planet-forming discs surrounding young stars. The availability of accurate molecular data (frequencies, collisional rate coefficients and chemical reaction rates) is crucial to analyse the observations at each of these steps.

  10. 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.

  11. Active galactic nuclei from He II: a more complete census of AGN in SDSS galaxies yields a new population of low-luminosity AGN in highly star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Bär, Rudolf E.; Weigel, Anna K.; Sartori, Lia F.; Oh, Kyuseok; Koss, Michael; Schawinski, Kevin

    2017-04-01

    In order to perform a more complete census of active galactic nuclei (AGN) in the local Universe, we investigate the use of the He II λ4685 emission line diagnostic diagram by Shirazi & Brinchmann (2012) in addition to the standard methods based on other optical emission lines. The He II-based diagnostics is more sensitive to AGN ionization in the presence of strong star formation than conventional line diagnostics. We survey a magnitude-limited sample of 63 915 galaxies from the Sloan Digital Sky Survey Data Release 7 at 0.02 < z < 0.05 and use both the conventional BPT emission line diagnostic diagrams, as well as the He II diagram to identify AGN. In this sample, 1075 galaxies are selected as AGN using the BPT diagram, while additional 234 galaxies are identified as AGN using the He II diagnostic diagram, representing a 22 per cent increase of AGN in the parent galaxy sample. We explore the host galaxy properties of these new He II-selected AGN candidates and find that they are most common in star-forming galaxies on the blue cloud and on the main sequence where ionization from star formation is most likely to mask AGN emission in the BPT lines. We note in particular a high He II AGN fraction in galaxies above the high-mass end of the main sequence where quenching is expected to occur. We use archival Chandra observations to confirm the AGN nature of candidates selected through He II-based diagnostic. Finally, we discuss how this technique can help inform galaxy/black hole coevolution scenarios.

  12. Active Galactic Nuclei from He II: a more complete census of AGN in SDSS galaxies yields a new population of low-luminosity AGN in highly star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Baer, Rudolf E.; Weigel, Anna; Sartori, Lia F.; Oh, Kyuseok; Koss, Michael; Schawinski, Kevin

    2017-01-01

    In order to perform a more complete census of active galactic nuclei (AGN) in the local Universe, we investigate the use of the He II emission line diagnostic diagram by Shirazi & Brinchmann (2012) in addition to the standard methods based on other optical emission lines. The He II based diagnostics is more sensitive to AGN ionization in the presence of strong star formation than conventional line diagnostics. We survey a magnitude-limited sample of 81,192 galaxies from the Sloan Digital Sky Survey Data Release 7 at 0.02 < z < 0.05 and apply both the conventional BPT emission line diagnostic diagrams, as well as the He II diagram to identify AGN. In this sample, 1,075 galaxies are selected as AGN using the BPT diagram, while an additional 234 galaxies are identified as AGN using the He II diagnostic, representing a 22% increase of AGN in the parent galaxy sample. We use archival Chandra observations to confirm the AGN nature of candidates selected through He II based diagnostic. Finally, we explore the host galaxy properties of these new He II selected AGN candidates and find that they are most common in star-forming galaxies on the blue cloud and on the main sequence where ionization from star-formation is most likely to mask AGN emission in the BPT lines. We note in particular a high He II AGN fraction in galaxies above the high-mass end of the main sequence where quenching is expected to occur. We discuss how this technique can help inform galaxy/black hole co-evolution scenarios.

  13. Archival research on absorption lines in violently star-forming galaxies

    NASA Technical Reports Server (NTRS)

    Gallagher, J. S.

    1989-01-01

    A computerized analysis of a starburst model is discussed. The model proposes that the absorption line equivalent width should scale with the level of star forming activity. Archival International Ultraviolet Explorer (IUE) data on IUE spectra of luminous blue galaxies were compared with previous IUE observations of extragalactic HII regions and low luminosity galaxies. The comparisons are summarized and causes for offsets are discussed.

  14. Companions and Environments of Low-Mass Stars: From Star-Forming Regions to the Field

    NASA Astrophysics Data System (ADS)

    Ward-Duong, Kimberly; Patience, Jenny; De Rosa, Robert J.; Bulger, Joanna; Rajan, Abhijith; Goodwin, Simon; Parker, Richard J.; McCarthy, Donald W.; Kulesa, Craig; van der Plas, Gerrit; Menard, Francois; Pinte, Christophe; Jackson, Alan Patrick; Bryden, Geoffrey; Turner, Neal J.; Harvey, Paul M.; Hales, Antonio

    2017-01-01

    We present results from two studies probing the multiplicity and environmental properties of low-mass stars: (1) The MinMs (M-dwarfs in Multiples) Survey, a large, volume-limited survey of 245 field M-dwarfs within 15 pc, and (2) the TBOSS (Taurus Boundary of Stellar/Substellar) Survey, an ongoing study of disk properties for the lowest-mass members within the Taurus star-forming region. The MinMs Survey provides new measurements of the companion star fraction, separation distribution, and mass ratio distribution for the nearest K7-M6 dwarfs, utilizing a combination of high-resolution adaptive optics imaging and digitized widefield archival plates to cover an unprecedented separation range of ~1-10,000 AU. Within these data, we also identify companions below the stellar/brown dwarf boundary, enabling characterization of the substellar companion population to low-mass field stars. For the much younger population in Taurus, we present results from ALMA Band 7 continuum observations of low-mass stellar and substellar Class II objects, spanning spectral types from M4-M7.75. The sub-millimeter detections of these disks provide key estimates of the dust mass in small grains, which is then assessed within the context of region age, environment, and viability for planet formation. This young population also includes a number of interesting young binary systems. Covering both young (1-2 Myr) and old (>5 Gyr) populations of low-mass stars, the results from these studies provide benchmark measurements on the population statistics of low-mass field stars, and on the early protoplanetary environments of their younger M-star counterparts.

  15. Accretion phenomena onto star-forming dwarf-galaxies.

    NASA Astrophysics Data System (ADS)

    Annibali, Francesca

    2017-01-01

    I will present our recent discovery (Annibali et al. 2016, ApJL, 826 L27), based on the combination of deep wide-field LBT imaging from the ground and HST data, of a stellar stream and substructures associated to the very metal-poor star-forming dwarf galaxy DDO 68, located in a Void at ~12.7 Mpc from us. DDO 68 is very light (only 108 Msun in stars), yet it shows evidence for the accretion of at least two smaller satellites. DDO 68 is one of the very few cases where the hierarchical formation process is caught in action at such small galactic scales. This study is part of a large ongoing project based on an approved 2-year strategic program with LBT to search for stellar streams around a sample of ~50 nearby star-forming dwarf galaxies. Our result demonstrates the high potential of wide-field instrumentation at 8-10 m telescopes in combination with HST (and with JWST in the near future) for the study of accretion phenomena onto dwarf-galaxies.

  16. Clumps of z 2 Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Guo, Yicheng; Giavalisco, M.; Cassata, P.; CANDELS Collaboration

    2011-05-01

    We study the properties of red clumps of star-forming galaxies at z 2. A sample of 15 galaxies with spectroscopic redshift is selected from the HUDF, where ultra--deep and high- resolution optical (HST/ACS) and near--IR (HST/WFC3 IR) images are available to resolve the internal structure of z 2 galaxies at the kpc scale. We generate rest-frame UV-optical color maps of these galaxies after carefully matching image PSFs. Clumps are identified through visual inspection on the (z-H) maps. We run SED-fitting using the seven-band BVizYJH HST photometry of each pixel and measure the spatial distributions of stellar population parameters, such as stellar mass, star-formation rate, age and obscuration. In order to understand the origin of sub-galactic structures, we study the distributions of these properties of the pixels that are part of clumps and compare them with those of the surrounding disks. Our results help answer two questions: (1) whether the clumps are the progenitor of bulges and (2) whether old stellar populations (with age of a few Gyr) exist in star-forming galaxies at z 2.

  17. NTT Observations Indicate that Brown Dwarfs Form Like Stars

    NASA Astrophysics Data System (ADS)

    2001-06-01

    Dusty Disks Detected around Very Young Substellar Objects in the Orion Nebula Summary An international team of astronomers [2] is announcing today the discovery of dusty disks surrounding numerous very faint objects that are believed to be recently formed Brown Dwarfs in the Orion Nebula [3]. This finding is based on detailed observations with SOFI, a specialised infrared-sensitive instrument at the ESO 3.5-m New Technology Telescope at the La Silla Observatory. It is of special interest because it sheds light on the origin and nature of substellar objects, known as "Brown Dwarfs" . In particular, these results suggest that Brown Dwarfs share a common origin with stars and that Brown Dwarfs are more similar in nature to stars than to planets and, like stars, have the potential to form with accompanying systems of planets. Moreover, the presence of dusty protoplanetary disks around the faintest objects in the Orion Nebula cluster confirms both the membership of these faint stars in the cluster and their nature as bona-fide substellar objects, making this the largest population of Brown Dwarf objects yet known . These important results are being reported today to the American Astronomical Society Meeting in Pasadena (California, USA). PR Photo 22a/01 : Infrared picture of the Orion Nebula (NTT + SOFI). PR Photo 22b/01 : "Finding Chart" for Very Young Brown Dwarfs in the Orion Nebula. PR Photo 22c/01 : Animated GIF presentation of PR Photos 22a+b/01. Faint substellar objects in the Milky Way Over the past 5 years, several groups of astronomers have identified a type of very faint, substellar objects within our Milky Way galaxy. These gaseous objects have very low masses and will never shine like normal stars because they cannot achieve central temperatures high enough for sustained thermal nuclear reactions to occur in their cores. Such objects weigh less than about 7% of our Sun and have been variously called "Brown Dwarfs" , "Failed Stars" or "Super Planets

  18. Astronomers Discover New Star-Forming Regions in Milky Way

    NASA Astrophysics Data System (ADS)

    2010-05-01

    Astronomers studying the Milky Way have discovered a large number of previously-unknown regions where massive stars are being formed. Their discovery provides important new information about the structure of our home Galaxy and promises to yield new clues about the chemical composition of the Galaxy. "We can clearly relate the locations of these star-forming sites to the overall structure of the Galaxy. Further studies will allow us to better understand the process of star formation and to compare the chemical composition of such sites at widely different distances from the Galaxy's center," said Thomas Bania, of Boston University. Bania worked with Loren Anderson of the Astrophysical Laboratory of Marseille in France, Dana Balser of the National Radio Astronomy Observatory (NRAO), and Robert Rood of the University of Virginia. The scientists presented their findings to the American Astronomical Society's meeting in Miami, Florida. The star-forming regions the astronomers sought, called H II regions, are sites where hydrogen atoms are ionized, or stripped of their electrons, by the intense radiation of the massive, young stars. To find these regions hidden from visible-light detection by the Milky Way's gas and dust, the researchers used infrared and radio telescopes. "We found our targets by using the results of infrared surveys done with NASA's Spitzer Space Telescope and of surveys done with the National Science Foundation's (NSF) Very Large Array (VLA) radio telescope," Anderson said. "Objects that appear bright in both the Spitzer and VLA images we studied are good candidates for H II regions," he explained. The astronomers then used the NSF's giant Robert C. Byrd Green Bank Telescope (GBT) in West Virginia, an extremely sensitive radio telescope. With the GBT, they were able to detect specific radio frequencies emitted by electrons as they recombined with protons to form hydrogen. This evidence of recombination confirmed that the regions contained ionized

  19. An activity catalogue of southern stars

    NASA Astrophysics Data System (ADS)

    Jenkins, J. S.; Jones, H. R. A.; Tinney, C. G.; Butler, R. P.; McCarthy, C.; Marcy, G. W.; Pinfield, D. J.; Carter, B. D.; Penny, A. J.

    2006-10-01

    We have acquired high-resolution echelle spectra of 225 F6-M5 type stars in the Southern hemisphere. The stars are targets or candidates to be targets for the Anglo-Australian Planet Search. CaII H& K line cores were used to derive activity indices for all of these objects. The indices were converted to the Mt. Wilson system of measurements and logR'HK values determined. A number of these stars had no previously derived activity indices. In addition, we have also included the stars from Tinney et al. using our Mt. Wilson calibration. The radial-velocity instability (also known as jitter) level was determined for all 21 planet-host stars in our data set. We find the jitter to be at a level considerably below the radial-velocity signatures in all but one of these systems. 19 stars from our sample were found to be active (logR'HK > -4.5) and thus have high levels of jitter. Radial-velocity analysis for planetary companions to these stars should proceed with caution.

  20. VLA 7-mm Observations of Massive Star-forming Regions

    NASA Astrophysics Data System (ADS)

    Linz, Hendrik; Hofner, Peter; Araya, Esteban; Stecklum, Bringfried

    2003-07-01

    The early stages during the formation of massive stars are deeply enshrouded due to the presence of dense and dusty natal material. This prevents observations in the optical and often also in the near-infrared. The emission of the star-forming regions peaks in the far-infrared and sub-mm regime, but at these wavelengths, single-dish observations are restricted in spatial resolution and can give only upper limits on the energetics of the objects of interest. Interferometry at mm wavelengths is one appropriate technique to overcome these limitations. We have started an extensive programme to observe pre-selected massive star-forming regions. Our tool is the VLA and its 7-mm receiver system. The VLA can be operated in several antenna configurations delivering resolutions from 1.5 arcsec down to 0.05 arcsec, which is superior to other current mm-interferometers. Sub-arcsec resolution is strongly needed to disentangle the often crowded regions of high-mass star formation and to clearly separate our objects of interest from the adjacent ultracompact HII regions. At 7 mm we are on the save ground of the Rayleigh-Jeans limit even for emission of cold dust (a fact that is not always true for observations at smaller wavelengths). Almost all circumstellar density configurations are optically thin at 7 mm, thus, the observations will trace the total dust content. However, at 7 mm also the free-free emission from ionised gas (caused by the UV emission of the young massive stars) can contribute to the observed signal. Therefore, we have to identify and remove these "parasitic" constituents by extrapolating interferometric data obtained at cm-wavelengths. The targets are either taken from the list of Molinari (Molinari et al. 2000, A&A, 355, 617) or are well-known massive star-forming complexes, for which we have already acquired additional data at other wavelengths. We have started with observations at lower and medium resolution (1.5 - 0.5 arcsec) to distinguish candidates for

  1. Magnetism and activity of planet hosting stars

    NASA Astrophysics Data System (ADS)

    Wright, Jason T.; Miller, Brendan P.

    The magnetic activity levels of planet host stars may differ from that of stars not known to host planets in several ways. Hot Jupiters may induce activity in their hosts through magnetic interactions, or through tidal interactions by affecting their host's rotation or convection. Measurements of photospheric, chromospheric, or coronal activity might then be abnormally high or low compared to control stars that do not host hot Jupiters, or might be modulated at the planet's orbital period. Such detections are complicated by the small amplitude of the expected signal, by the fact that the signals may be transient, and by the difficulty of constructing control samples due to exoplanet detection biases and the uncertainty of field star ages. We review these issues, and discuss avenues for future progress in the field.

  2. Testing Grain Surface Chemistry in Star Forming Regions

    NASA Astrophysics Data System (ADS)

    Keane, Jacqueline; Boogert, Adwin

    2008-03-01

    The key chemical reactions that produce the first generation ice mantles in dense molecular clouds are still poorly known. Within cold, dense clouds, species formed in the gas and on the grain surfaces will stick to the grains and form icy mantles. However, during star-formation, materials in the general cloud medium are subjected to numerous chemical and physical processes that are driven mostly by thermal and energetic radiation. The comparison between background stars and protostars is a proven excellent tool for this purpose. By comparing observed interstellar solid state abundances with models of grain surface chemistry it is possible to elucidate the efficiency and hence relevancy of a number of chemical reactions, in particular the CO_2 formation pathways. In part because of Spitzer, significant progress has been made towards understanding the various effects of these radiation processes on the ices around a large sample of high- and low-mass protostars. First results suggest that two different CO2 formation pathways play a role in these harsh environments. Though which reaction initially dominated the chemistry is unknown due to the numerous physical processes. Unfortunately, only a small sample of background field stars have been observed, most notably Taurus. In Taurus, only one reaction pathway appears to be efficient in quiescent regions, but this result is sample limited. We propose to take low resolution spectra from 5 to 22 microns along the line of sight toward 31 field stars behind the LDN 673 molecular cloud. Differences in near-IR ice chemistry have already been observed and we will use these mid-infrared data to provide more stringent constraints on chemical models of grain surface chemistry. With this sample it is possible to address fundamental questions in astrochemistry: what are the dominant grain surface chemistry pathways? What is the composition of the first generation ice mantles in molecular clouds?

  3. 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.

  4. 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.

  5. The SUNBIRD survey: characterizing the super star cluster populations of intensely star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Randriamanakoto, Zara; Vaisanen, Petri; Escala, Andres

    2015-08-01

    This work investigates properties of young, massive and dense star clusters in a sample of 42 nearby starbursts and LIRGs with an average distance of 80 Mpc. The targets form the sample of the SUperNovae and starBursts in the InfraReD (SUNBIRD) survey that were imaged using near-infrared K-band adaptive optics mounted on the Gemini/NIRI and the VLT/NaCo instruments.We fitted power-laws to the SSC K-band luminosity functions and found index values ranging between 1.5 and 2.4 with a median value of α ˜ 1.86±0.24. This is shallower than the average of ≈ 2.4 associated with normal spiral galaxies indicating that SSCs hosted by star-forming galaxies are disrupted in a way depending on their mass or environment. Using simulations we found that blending effects are not significant for targets closer than ≈100Mpc. We also established the first ever near-infrared (NIR) brightest star cluster magnitude - star formation rate (SFR) relation. The correlation has a steeper slope compared to the one with optical data at lower SFRs which could indicate a simple statistical effect, though we argue that a physical truncation of the mass distribution at high masses would better explain the tight scatter of the observed relation.Finally, we combined new NIR imaging of seven LIRG targets with their optical HST archival data to derive the age, mass, and extinction distributions of optically-selected SSC candidates. Apart from having a high mass range of 10^4 - 10^8 M⊙, more than a quarter of the cluster population is younger than 30 Myr. We also derived the cluster initial mass functions and found that at least in one of the LIRGs, a mass-dependent disruption mechanism is responsible for the deficiency in low-mass star clusters. The cluster formation efficiencies Γ = 10 - 23 %, on the other hand, support the arguments that highly-pressurized environments favor SF in bound star clusters.This work has shown the importance of studying SSC host galaxies with high SFR levels to

  6. 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.

  7. Reconciling the Census of Forming Stars in Gould's Belt

    NASA Astrophysics Data System (ADS)

    Gutermath, Robert

    We seek funding to construct a set of new, publicly available, value-enhanced data products for the 37 deg2 of archival Spitzer IRAC 3-8 micron and MIPS 24 micron imaging from the Spitzer Legacy surveys From Molecular Cores to Planet-forming Disks (PI Evans) and the subsequent Gould's Belt: Star Formation in the Solar Neighborhood (PI Allen; c2d/GB hereafter). These surveys comprise our canonical view of low-mass star formation, encompassing most of the nearest (<400pc) molecular clouds other than Taurus. From the proposed c2d/GB reprocessing, we will produce and deliver the following products to the Infrared Science Archive (IRSA) at IPAC for community access: - Artifact-mitigated, astrometrically-refined Spitzer mosaics at 3.6, 4.5, 5.8, 8.0, and 24 microns for all 18 clouds in c2d/GB; - Complete, band-merged, point source catalogs in all five Spitzer bands considered, combined with 2MASS and WISE photometry where available, and a census of young stellar objects (YSOs) with excess infrared emission that are selected via the Gutermuth et al. (2009; G09) YSO identification and classification techniques from the full catalogs; - Point source completeness decay data cubes at 30'' resolution for all Spitzer mosaics, and midIR luminosity completeness images built from the five-band completeness cubes for a wide range of mid-IR spectral energy distribution (SED) shapes. Our overarching goal is to provide a precise observational product that contains the means to test ever more detailed simulations of star formation and guide and supplement future observations of nearby star-forming regions and clouds at all wavelengths. A complete, internally consistent census of all YSOs exhibiting excess infrared emission and a detailed mapping of the limits of non-detections by YSO evolutionary stage for all molecular clouds and star-forming complexes observed by Spitzer within 2 kpc will have incredible value for both goals. With a full YSO census and a clearer understanding of how

  8. 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.

  9. New far infrared images of bright, nearby, star-forming regions

    NASA Technical Reports Server (NTRS)

    Harper, D. AL, Jr.; Cole, David M.; Dowell, C. Darren; Lees, Joanna F.; Lowenstein, Robert F.

    1995-01-01

    Broadband imaging in the far infrared is a vital tool for understanding how young stars form, evolve, and interact with their environment. As the sensitivity and size of detector arrays has increased, a richer and more detailed picture has emerged of the nearest and brightest regions of active star formation. We present data on M 17, M 42, and S 106 taken recently on the Kuiper Airborne Observatory with the Yerkes Observatory 60-channel far infrared camera, which has pixel sizes of 17 in. at 60 microns, 27 in. at 100 microns, and 45 in. at 160 and 200 microns. In addition to providing a clearer view of the complex central cores of the regions, the images reveal new details of the structure and heating of ionization fronts and photodissociation zones where radiation form luminous stars interacts with adjacent molecular clouds.

  10. 3D-spectroscopy of SBS star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Hakopian, S. A.; Dodonov, S. N.; Moiseev, A. V.; Smirnova, A. A.

    2017-03-01

    In the base of our studies of star-forming processes are the data provided by panoramic spectroscopy of galaxies composing our SBS subsample. Observations with multi-pupil spectrographs are organized in a way to obtain the spectral range centered in permitted hydrogen Hα Balmer line, by capturing at least the forbidden doublets of nitrogen [NII]6548,6583 and sulfur [SII]6716,6731. The results obtained are the spatial distributions across the targets of emission intensities and derived properties from line parameters such as radial velocities, which give us the possibility to explore gas kinematics and physical characteristics of HII regions.

  11. Aperture-free star formation rate of SDSS star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Duarte Puertas, S.; Vilchez, J. M.; Iglesias-Páramo, J.; Kehrig, C.; Pérez-Montero, E.; Rosales-Ortega, F. F.

    2017-03-01

    Large area surveys with a high number of galaxies observed have undoubtedly marked a milestone in the understanding of several properties of galaxies, such as star-formation history, morphology, and metallicity. However, in many cases, these surveys provide fluxes from fixed small apertures (e.g. fibre), which cover a scant fraction of the galaxy, compelling us to use aperture corrections to study the global properties of galaxies. In this work, we derive the current total star formation rate (SFR) of Sloan Digital Sky Survey (SDSS) star-forming galaxies, using an empirically based aperture correction of the measured Hα flux for the first time, thus minimising the uncertainties associated with reduced apertures. All the Hα fluxes have been extinction-corrected using the Hα/ Hβ ratio free from aperture effects. The total SFR for 210 000 SDSS star-forming galaxies has been derived applying pure empirical Hα and Hα/ Hβ aperture corrections based on the Calar Alto Legacy Integral Field Area (CALIFA) survey. We find that, on average, the aperture-corrected SFR is 0.65 dex higher than the SDSS fibre-based SFR. The relation between the SFR and stellar mass for SDSS star-forming galaxies (SFR-M⋆) has been obtained, together with its dependence on extinction and Hα equivalent width. We compare our results with those obtained in previous works and examine the behaviour of the derived SFR in six redshift bins, over the redshift range 0.005 ≤ z ≤ 0.22. The SFR-M⋆ sequence derived here is in agreement with selected observational studies based on integral field spectroscopy of individual galaxies as well as with the predictions of recent theoretical models of disc galaxies. A table of the aperture-corrected fluxes and SFR for 210 000 SDSS star-forming galaxies and related relevant data is 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/599/A71 Warning, no authors

  12. Star and jet multiplicity in the high-mass star forming region IRAS 05137+3919

    NASA Astrophysics Data System (ADS)

    Cesaroni, R.; Massi, F.; Arcidiacono, C.; Beltrán, M. T.; Persi, P.; Tapia, M.; Molinari, S.; Testi, L.; Busoni, L.; Riccardi, A.; Boutsia, K.; Bisogni, S.; McCarthy, D.; Kulesa, C.

    2015-09-01

    Context. We present a study of the complex high-mass star forming region IRAS 05137+3919 (also known as Mol8), where multiple jets and a rich stellar cluster have been described in previous works. Aims: Our goal is to determine the number of jets and shed light on their origin, and thus determine the nature of the young stars powering these jets. We also wish to analyse the stellar clusters by resolving the brightest group of stars. Methods: The star forming region was observed in various tracers and the results were complemented with ancillary archival data. The new data represent a substantial improvement over previous studies both in resolution and frequency coverage. In particular, adaptive optics provides us with an angular resolution of 80 mas in the near IR, while new mid- and far-IR data allow us to sample the peak of the spectral energy distribution and thus reliably estimate the bolometric luminosity. Results: Thanks to the near-IR continuum and millimetre line data we can determine the structure and velocity field of the bipolar jets and outflows in this star forming region. We also find that the stars are grouped into three clusters and the jets originate in the richest of these, whose luminosity is ~ 2.4 × 104L⊙. Interestingly, our high-resolution near-IR images allow us to resolve one of the two brightest stars (A and B) of the cluster into a double source (A1+A2). Conclusions: We confirm that there are two jets and establish that they are powered by B-type stars belonging to cluster C1. On this basis and on morphological and kinematical arguments, we conclude that the less extended jet is almost perpendicular to the line of sight and that it originates in the brightest star of the cluster, while the more extended one appears to be associated with the more extincted, double source A1+A2. We propose that this is not a binary system, but a small bipolar reflection nebula at the root of the large-scale jet, outlining a still undetected circumstellar

  13. The build-up of the outskirts of distant star-forming galaxies at z ~ 2

    NASA Astrophysics Data System (ADS)

    Tacchella, Sandro; Carollo, C. Marcella; Dekel, Avishai; Schreiber, Natascha Förster; Renzini, Alvio; zC-SINF Team

    2017-03-01

    In order to constrain - and understand - the growth of galaxies, we present a sample of ~ 30 galaxies at z ~ 2 with resolved distribution of stellar mass, star-formation rate, and dust attenuation on scales of ~ 1 kpc. We find that low- and intermediate-mass galaxies grow self-similarly, doubling their stellar mass in the centers and outskirts with the same pace. More massive galaxies (~ 1011 M⊙) have a reduced star-formation activity in their center: they grow mostly in the outskirts (inside-out quenching / formation). Similar trends are find in cosmological zoom-in simulations, highlighting that high stellar mass densities are formed in a gas-rich compaction phase. This nuclear `starburst' phase is followed by a suppressed star-formation activity in the center, resulting in growth of the outskirts. All in all, we put forward that we witness at z ~ 2 the dissipative formation of z = 0 M* early-type galaxies.

  14. 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.

  15. 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.

  16. UV-selected Young Massive Star Cluster Populations in Nearby Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Smith, Linda J.

    2015-08-01

    The Legacy ExtraGalactic UV Survey (LEGUS) is an HST Treasury program aimed at the investigation of star-formation and its relationship to environment in nearby galaxies. The results of a UV-selected study of young massive star clusters in a sample of nearby galaxies (< 10 Mpc) using detections based on the WFC3/UVIS F275W filter will be presented. Previous studies have used V or I-band detections and tend to ignore clusters younger than 10 Myr old. This very young population, which represents the most recent cluster-forming event in the LEGUS galaxies will be discussed.This poster is presented on behalf of the LEGUS team (PI Daniela Calzetti).

  17. Clustering Of Radio-Selected AGN (And Star-Forming Galaxies) Up To Redshifts z = 3

    NASA Astrophysics Data System (ADS)

    Magliocchetti, Manuela; Popesso, P.; Brusa, M.; Salvato, M.

    2016-10-01

    We present the clustering properties of a complete sample of 957 radio sources detected by the VLA-COSMOS survey with radio fluxes brighter than 0.15 mJy. Based on their radio-luminosity, these objects have been furtherly divided into two populations of 642 AGN and 246 star-forming galaxies. Investigations of their clustering properties return values for the minimum masses of dark matter haloes capable to host at least one of such sources of Mmin=10^13.6 Msun for radio-selected AGN and Mmin=10^13.1 Msun for radio-emitting star-forming galaxies. Comparisons with previous works imply an independence of the clustering properties of the AGN population with respect to both radio luminosity and redshift. We also investigate the relationship between dark and luminous matter in both populations. Our results indicate a larger relative stellar content in the star-forming population with respect to AGN and also clearly show the cosmic process of star-formation build-up as one moves towards the more local universe. Comparisons between the observed space density of radio-selected AGN and that of dark matter haloes shows that about one in two haloes is associated with a black hole in its radio-active phase. This suggests that the radio-active phase is a recurrent phenomenon.

  18. After the Interaction: an Efficiently Star-forming Molecular Disk in NGC 5195

    NASA Astrophysics Data System (ADS)

    Alatalo, Katherine; Aladro, Rebeca; Nyland, Kristina; Aalto, Susanne; Bitsakis, Theodoros; Gallagher, John S.; Lanz, Lauranne

    2016-10-01

    We present new molecular gas maps of NGC 5195 (alternatively known as M51b) from the Combined Array for Research in Millimeter Astronomy, including 12CO(1-0), 13CO(1-0), CN(1{}{0,2}-{0}{0,1}), CS(2-1), and 3 mm continuum. We also detected HCN(1-0) and HCO+(1-0) using the Onsala Space Observatory. NGC 5195 has a 12CO/13CO ratio ({{ R }}12/13 = 11.4 ± 0.5) consistent with normal star-forming galaxies. The CN(1-0) intensity is higher than is seen in an average star-forming galaxy, possibly enhanced in the diffuse gas in photo-dissociation regions. Stellar template fitting of the nuclear spectrum of NGC 5195 shows two stellar populations: an 80% mass fraction of old (≳10 Gyr) and a 20% mass fraction of intermediate-aged (≈1 Gyr) stellar populations. This provides a constraint on the timescale over which NGC 5195 experienced enhanced star formation during its interaction with M51a. The average molecular gas depletion timescale in NGC 5195 is < {τ }{dep}> = 3.08 Gyr, a factor of ≈ 2 larger than the depletion timescales in nearby star-forming galaxies, but consistent with the depletion seen in CO-detected early-type galaxies. While radio continuum emission at centimeter and millimeter wavelengths is present in the vicinity of the nucleus of NGC 5195, we find it is most likely associated with nuclear star formation rather than radio-loud AGN activity. Thus, despite having a substantial interaction with M51a ˜1/2 Gyr ago, the molecular gas in NGC 5195 has resettled and is currently forming stars at an efficiency consistent with settled early-type galaxies.

  19. Dynamical Properties of z ~ 2 Star-forming Galaxies and a Universal Star Formation Relation

    NASA Astrophysics Data System (ADS)

    Bouché, N.; Cresci, G.; Davies, R.; Eisenhauer, F.; Förster Schreiber, N. M.; Genzel, R.; Gillessen, S.; Lehnert, M.; Lutz, D.; Nesvadba, N.; Shapiro, K. L.; Sternberg, A.; Tacconi, L. J.; Verma, A.; Cimatti, A.; Daddi, E.; Renzini, A.; Erb, D. K.; Shapley, A.; Steidel, C. C.

    2007-12-01

    We present the first comparison of the dynamical properties of different samples of z~1.4-3.4 star-forming galaxies from spatially resolved imaging spectroscopy from SINFONI/VLT integral field spectroscopy and IRAM CO millimeter interferometry. Our samples include 16 rest-frame UV-selected, 16 rest-frame optically selected, and 13 submillimeter galaxies (SMGs). We find that rest-frame UV and optically bright (K<20) z~2 star forming galaxies are dynamically similar, and follow the same velocity-size relation as disk galaxies at z~0. In the theoretical framework of rotating disks forming from dissipative collapse in dark matter halos, the two samples require a spin parameter <λ> ranging from 0.06 to 0.2. In contrast, bright SMGs (S850μm>=5 mJy) have larger velocity widths and are much more compact. Hence, SMGs have lower angular momenta and higher matter densities than either the UV or optically selected populations. This indicates that dissipative major mergers may dominate the SMGs population, resulting in early spheroids, and that a significant fraction of the UV/optically bright galaxies have evolved less violently, either in a series of minor mergers, or in rapid dissipative collapse from the halo, given that either process may leads to the formation of early disks. These early disks may later evolve into spheroids via disk instabilities or mergers. Because of their small sizes and large densities, SMGs lie at the high surface density end of a universal (out to z=2.5) ``Schmidt-Kennicutt'' relation between gas surface density and star formation rate surface density. The best-fit relation suggests that the star formation rate per unit area scales as the surface gas density to a power of ~1.7, and that the star formation efficiency increases by a factor of 4 between non-starbursts and strong starbursts. Based on observations at the Very Large Telescope (VLT) of the European Southern Observatory (ESO), Paranal, Chile, under programs GTO 073.B-9018, 074.A-9011

  20. 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

  1. Modelling of Deuterium Chemistry in Star-Forming Regions

    NASA Astrophysics Data System (ADS)

    Roberts, Helen

    2005-08-01

    Several new multiply deuterated species have been detected over the past three years, including ND3 (van der Tak et al. 2002; Lis et al. 2002), CHD2OH, CD3OH (Parise et al. 2002, 2004), D2S (Vastel et al. 2003), HD2+ (Vastel et al. 2004) and D2CS (Marcelino et al. 2005). In addition, mono-deuterated species have been observed with abundances >10% of their un-deuterated analogues (e.g. CH2DOH observed by Parise et al. 2002; NH2D observed by Saito et al. 2000 and Hatchell 2003). These are remarkable results, given that the underlying abundance of deuterium in the local interstellar medium (ISM) is ˜10-5 times lower than that of hydrogen (Linsky 1998; Sonneborn et al. 2000).Such large enhancements in the abundances of deuterium-bearing molecules can either be due to gas-phase or to grain-surface fractionation. Grain-surface reactions are undoubtedly important in producing saturated species such as methanol, water, ammonia, and hydrogen sulphide. Water ice is observed to be abundant and ubiquitous throughout the ISM, and enhanced abundances of gas-phase NH3, CH3OH, H2CO and H2S (among others) are observed in warmer regions around protostars where grain mantles have evaporated.Recent observational and theoretical evidence suggests that the deuterium fractionation in star-forming regions is set by gas-phase and grain-surface reactions during the cold, dense pre-protostellar phase. For species which form on grain surfaces via H atom addition to CO, N, O and S, the deuterium fractionation on grains comes from the relative amounts of atomic D and H which are accreting from the gas. The observations of deuterated methanol and D2S require that the gas-phase atomic D/H ratio at the time the molecules formed was ≥ 0.1.This paper presents results from chemical models of the prestellar core phase of star formation, showing how this high atomic D/H ratio can be produced, and discusses how models can also be used to look at deuterium fractionation in the protostellar stages of

  2. Boxy Hα emission profiles in star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Chen, Yan-Mei; Gu, Qiu-Sheng; Tremonti, Christy A.; Shi, Yong; Jin, Yifei

    2016-07-01

    We assemble a sample of disc star-forming galaxies from the Sloan Digital Sky Survey Data Release 7, studying the structure of Hα emission lines, finding a large fraction of this sample contains boxy Hα line profiles. This fraction depends on galaxy physical and geometric parameters in the following way: (1) it increases monotonically with star formation rate per unit area (ΣSFR), and stellar mass (M*), with the trend being much stronger with M*, from ˜0 per cent at M* = 1010 M⊙ to about 50 per cent at M* = 1011 M⊙; (2) the fraction is much smaller in face-on systems than in edge-on systems. It increases with galaxy inclination (i) while i < 60° and is roughly a constant of 25 per cent beyond this range; (3) for the sources which can be modelled well with two velocity components, blueshifted and redshifted from the systemic velocity, these is a positive correlation between the velocity difference of these two components and the stellar mass, with a slope similar to the Tully-Fisher relation; (4) the two components are very symmetric in the mean, both in velocity and in amplitude. The four findings listed above can be understood as a natural result of a rotating galaxy disc with a kpc-scale ring-like Hα emission region.

  3. Kinematic Evolution of Simulated Star-Forming Galaxies

    NASA Technical Reports Server (NTRS)

    Kassin, Susan A.; Brooks, Alyson; Governato, Fabio; Weiner, Benjamin J.; Gardner, Jonathan P.

    2014-01-01

    Recent observations have shown that star-forming galaxies like our own Milky Way evolve kinematically into ordered thin disks over the last approximately 8 billion years since z = 1.2, undergoing a process of "disk settling." For the first time, we study the kinematic evolution of a suite of four state of the art "zoom in" hydrodynamic simulations of galaxy formation and evolution in a fully cosmological context and compare with these observations. Until now, robust measurements of the internal kinematics of simulated galaxies were lacking as the simulations suffered from low resolution, overproduction of stars, and overly massive bulges. The current generation of simulations has made great progress in overcoming these difficulties and is ready for a kinematic analysis. We show that simulated galaxies follow the same kinematic trends as real galaxies: they progressively decrease in disordered motions (sigma(sub g)) and increase in ordered rotation (V(sub rot)) with time. The slopes of the relations between both sigma(sub g) and V(sub rot) with redshift are consistent between the simulations and the observations. In addition, the morphologies of the simulated galaxies become less disturbed with time, also consistent with observations. This match between the simulated and observed trends is a significant success for the current generation of simulations, and a first step in determining the physical processes behind disk settling.

  4. Kinematic Evolution of Simulated Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Kassin, Susan A.; Brooks, Alyson; Governato, Fabio; Weiner, Benjamin J.; Gardner, Jonathan P.

    2014-08-01

    Recent observations have shown that star-forming galaxies like our own Milky Way evolve kinematically into ordered thin disks over the last ~8 billion years since z = 1.2, undergoing a process of "disk settling." For the first time, we study the kinematic evolution of a suite of four state of the art "zoom in" hydrodynamic simulations of galaxy formation and evolution in a fully cosmological context and compare with these observations. Until now, robust measurements of the internal kinematics of simulated galaxies were lacking because the simulations suffered from low resolution, overproduction of stars, and overly massive bulges. The current generation of simulations has made great progress in overcoming these difficulties and is ready for a kinematic analysis. We show that simulated galaxies follow the same kinematic trends as real galaxies: they progressively decrease in disordered motions (σ g ) and increase in ordered rotation (V rot) with time. The slopes of the relations between both σ g and V rot with redshift are consistent between the simulations and the observations. In addition, the morphologies of the simulated galaxies become less disturbed with time, also consistent with observations. This match between the simulated and observed trends is a significant success for the current generation of simulations, and a first step in determining the physical processes behind disk settling.

  5. Kinematic evolution of simulated star-forming galaxies

    SciTech Connect

    Kassin, Susan A.; Brooks, Alyson; Governato, Fabio; Weiner, Benjamin J.; Gardner, Jonathan P.

    2014-08-01

    Recent observations have shown that star-forming galaxies like our own Milky Way evolve kinematically into ordered thin disks over the last ∼8 billion years since z = 1.2, undergoing a process of 'disk settling'. For the first time, we study the kinematic evolution of a suite of four state of the art 'zoom in' hydrodynamic simulations of galaxy formation and evolution in a fully cosmological context and compare with these observations. Until now, robust measurements of the internal kinematics of simulated galaxies were lacking because the simulations suffered from low resolution, overproduction of stars, and overly massive bulges. The current generation of simulations has made great progress in overcoming these difficulties and is ready for a kinematic analysis. We show that simulated galaxies follow the same kinematic trends as real galaxies: they progressively decrease in disordered motions (σ{sub g}) and increase in ordered rotation (V{sub rot}) with time. The slopes of the relations between both σ{sub g} and V{sub rot} with redshift are consistent between the simulations and the observations. In addition, the morphologies of the simulated galaxies become less disturbed with time, also consistent with observations. This match between the simulated and observed trends is a significant success for the current generation of simulations, and a first step in determining the physical processes behind disk settling'.

  6. STAR-FORMING REGION Sh 2-233IR. I. DEEP NEAR-INFRARED OBSERVATIONS TOWARD THE EMBEDDED STELLAR CLUSTERS

    SciTech Connect

    Yan, Chi-Hung; Wang, Shiang-Yu; Su, Yu-Nang; Minh, Y. C.; Ginsburg, Adam

    2010-09-01

    We observed the Sh 2-233IR (S233IR) region with better sensitivity in the near-infrared than in previous studies of this region. By applying statistical subtraction of the background stars, we identified member sources and derived the age and mass of three distinguishable sub-groups in this region: Sh 2-233IR NE, Sh 2-233IR SW, and the 'distributed stars' over the whole cloud. Star formation may occur sequentially with a relatively small age difference ({approx}0.2-0.3 Myr) between subclusters. We found that the slopes for the initial mass function ({Gamma} {approx} -0.5) of two subclusters are flatter than those of Salpeter, which suggests that more massive stars were preferentially formed in those clusters compared to other Galactic star-forming regions. These subclusters may not result from the overall collapse of the whole cloud, but have formed by triggering before the previous star formation activities disturbed the natal molecular cloud. Additionally, high star formation efficiency ({approx}>40%) of the subclusters may also suggest that stars form very efficiently in the center of the northeast.

  7. 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.

  8. Abundances of hydrogen sulfide in star-forming regions

    NASA Technical Reports Server (NTRS)

    Minh, Y. C.; Ziurys, L. M.; Irvine, W. M.; Mcgonagle, D.

    1991-01-01

    Interstellar H2S and its isotopic variant H2(S-34) have been observed toward several star-forming regions via their 1(10)-1(01) transitions at 2 mm, using the FCRAO telescope. In sources where both isotopic species were observed, column densities of about 10 to the 16th/sq cm were measured. Column density lower limits of about 10 to the 14th/sq cm for H2S were found for other sources, where only the main isotopic line was observed. The fractional abundances of H2S relative to molecular hydrogen appear to be enhanced by at least an order of magnitude relative to quiescent cloud values (about 10 to the -9th) for many of the observed sources.

  9. The IRAS 08589-4714 star-forming region

    NASA Astrophysics Data System (ADS)

    Saldaño, H. P.; Vasquez, J.; Cappa, C. E.; Gómez, M.; Duronea, N.; Rubio, M.

    2017-04-01

    We present an analysis of the IRAS 08589-4714 star-forming region. This region harbors candidate young stellar objects identified in the WISE and Herschel images using color index criteria and spectral energy distributions (SEDs). The SEDs of some of the infrared sources and the 70 μm radial intensity profile of the brightest source are modeled using the DUSTY code. For these objects, we estimate the main parameters, which suggest that they are very young, massive and luminous objects at early stages of the formation process. We use the emission distribution in the infrared at 70 and 160 μm to estimate the dust temperature gradient. This suggests that the nearby massive starforming region RCW 38, located at ≈10 pc from the IRAS source position, may be contributing to the photodissociation of the molecular gas and to the heating of the interstellar dust in the environs of the IRAS source.

  10. The Physics of Molecular Shocks in Star-Forming Regions

    NASA Technical Reports Server (NTRS)

    Hollenbach, David; Cuzzi, Jeffrey (Technical Monitor)

    1996-01-01

    Molecular shocks are produced by the impact of the supersonic infall of gas and dust onto protostars and by the interaction of the supersonic outflow from the protostar with the circumstellar material. Infalling gas creates an accretion shock around the circumstellar disk which emits a unique infrared spectrum and which processes the interstellar dust as it enters the disk. The winds and jets from protostars also impact the disk, the infalling material, and the ambient molecular cloud core creating shocks whose spectrum and morphology diagnose the mass loss processes of the protostar and the orientation and structure of the star forming system. We discuss the physics of these shocks, the model spectra derived from theoretical models, and comparisons with observations of H2O masers, H2 emission, as well as other shocks tracers. We show the strong effect of magnetic fields on molecular shock structure, and elucidate the chemical changes induced by the shock heating and compression.

  11. Planar H2O masers in star-forming regions

    NASA Technical Reports Server (NTRS)

    Elitzur, Moshe; Hollenbach, David J.; Mckee, Christopher F.

    1992-01-01

    The paper examines the planar geometry of shocked material, which is the key property in enabling the high brightness temperatures of H2O masers in star-forming regions. The brightness temperature, beaming angle, and the maser spot size are determined for thin, saturated planar masers under the assumption that the velocity change across the maser due to ordered motions is small compared with the thermal or microturbulent line width. For a given set of physical parameters, the brightness temperature is essentially fully determined by the length of the velocity-coherent region in the shocked plane along the line of sight. Effective aspect ratios (about 5-50) are found that are in agreement with values previously inferred from observed brightness temperatures.

  12. Uncovering the monster stars in W49: the most luminous star-forming region in the Milky Way

    NASA Astrophysics Data System (ADS)

    Wu, Shiwei; Bik, Arjan; Henning, Thomas; Pasquali, Anna; Brandner, Wolfgang; Stolte, Andrea

    2015-08-01

    As a part of the LOBSTAR project (Luci OBservations of STARburst regions), which aims at understanding the stellar content of some of the most massive star-forming regions, we present our result on the high-mass stellar content of W49. K-band spectra of the candidate massive stars from VLT/ISAAC and LBT/LUCI provide us with reliable spectral types of dozens of massive stars in this HII region.The first results show that this region hosts several of the most massive stars in our galaxy. Two most brightest stars, one in the core of the central cluster and one in W49 South, were identified as very massive stars (M > 100 M⊙). Their K-band spectra exhibit strong stellar wind features, and they are classified as O2-3.5If* supergiant stars. After comparison to the Geneva evolutionary models, the mass range of W49nr1 was estimated to be between 100 M⊙ and 180 M⊙. Additionally we find 12 O stars with spectral types between O7V and O3V and masses from 25 M⊙ to 125 M⊙, respectively.These results allow us to derive the fundamental parameters of the cluster (mass, age) as well as the total energy output in the form of ionising photons. This will enable us to study the feedback effects of this extreme star forming region in great detail. To our surprise, two young stellar objects with infrared excess feature showing CO emission lines in their spectra are identified. This suggests that circumstellar disks can survive even in this extreme environment. Finally the spatial distribution of the massive stars is analysed to discuss the star formation history and identify potential runaway stars. The extreme properties of this region makes it a good template for more extreme star formation outside our galaxy.

  13. Observational Searches for Star-Forming Galaxies at z > 6

    NASA Astrophysics Data System (ADS)

    Finkelstein, Steven L.

    2016-08-01

    Although the universe at redshifts greater than six represents only the first one billion years (< 10%) of cosmic time, the dense nature of the early universe led to vigorous galaxy formation and evolution activity which we are only now starting to piece together. Technological improvements have, over only the past decade, allowed large samples of galaxies at such high redshifts to be collected, providing a glimpse into the epoch of formation of the first stars and galaxies. A wide variety of observational techniques have led to the discovery of thousands of galaxy candidates at z > 6, with spectroscopically confirmed galaxies out to nearly z = 9. Using these large samples, we have begun to gain a physical insight into the processes inherent in galaxy evolution at early times. In this review, I will discuss (i) the selection techniques for finding distant galaxies, including a summary of previous and ongoing ground and space-based searches, and spectroscopic follow-up efforts, (ii) insights into galaxy evolution gleaned from measures such as the rest-frame ultraviolet luminosity function, the stellar mass function, and galaxy star-formation rates, and (iii) the effect of galaxies on their surrounding environment, including the chemical enrichment of the universe, and the reionisation of the intergalactic medium. Finally, I conclude with prospects for future observational study of the distant universe, using a bevy of new state-of-the-art facilities coming online over the next decade and beyond.

  14. Disentangling the AGN and Star-forming Contribution to the Sub-mJy Radio Counts

    NASA Astrophysics Data System (ADS)

    Seymour, Nick; Moss, D.; Dwelly, T.; McHardy, I.; Page, M.; Loaring, N.

    2007-05-01

    The up-turn of the faint, sub-mJy radio counts at 1.4GHz has now been known for ˜20years. Despite some theoretical and observational evidence that this is mainly due to a rapid increase in the radio emission from fast evolving star-formation in normal galaxies, direct determination of the relative contribution of Active Galactic Nuclei (AGN) and star-formation in individual galaxies remains elusive. The difficulty in identifying the physical processes in each galaxy can be attributed to their faint optical nature, i.e. 20% of sub-mJy radio sources have R>25. We present a unique data set from the `XMM/ ROSAT 13hr deep field' consisting of deep Very Large Array data (7.5uJy rms at 1.4GHz) and Giant Metre Radio-wave Telescope data (20uJy rms at 610MHz) providing radio spectral indices of ˜500 sub-mJy radio sources. We also have very deep GTO IRAC (3.6-8um) and MIPS (24-160um) Spitzer observations, supplementing our deep optical/near-IR multi-band observations. Using a combination of radio spectra/morphology, IRAC colours, and our deep XMM/Chandra data we are able to largely de-convolve the AGN and star-forming contribution to each radio source. We find that the bulk of the sub-mJy radio population are powered by star-formation, but that AGN are detected at all flux densities albeit at a decreasing rate at fainter flux densities. These AGN include radio sources that otherwise appear to be normal, z<1, star-forming galaxies and several at high redshift, z>2 - low luminosity counterparts to classical high redshift radio galaxies. The contribution of the star-forming galaxies to the faint counts is consistent with the rapid evolution of the local star-forming radio luminosity function and the rapid increase in the star-formation rate density up to z=1-2.

  15. Galactic Winds and Structure of z ~ 2 Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Newman, Sarah F.

    Galactic-scale outflows are a key driver of galaxy evolution through their feedback effect on star-formation and their ejection of metals and energy into the inter-galactic medium (IGM). While it is known that outflows likely play an important role in the quenching of star-formation - transforming actively star-forming, blue galaxies into their 'red and dead' counterparts - this role is currently not well understood. In particular, at z ˜ 2, during the most active epoch of star-formation, the mass and energy in these outflows is poorly constrained, as is the mechanism for launching them. Furthermore, active-galactic nuclei (AGN) in the centers of massive star-forming galaxies (SFGs) likely play an important role in star-formation quenching, but we do not have a clear understanding of how this AGN feedback compares with that of star-formation driven feedback, and it is not known how many of these massive SFGs at z ˜ 2 even have AGN. This issue is complicated by the fact that many high-z AGN are likely highly obscured, and have strong nebular emission line contributions from both star-formation and the AGN. In this dissertation, I explore these issues using high-spatial and spectral resolution integral field unit spectroscopic data of z ˜ 2 SFGs. The observations are obtained with the instrument SINFONI on the European Southern Observatory (ESO) Very Large Telescope (VLT) at Cerro Paranal. These high-quality data allow spatially-resolved studies of the gas-phase kinematics of these galaxies, as well dynamical information on their outflows. In this work, I explore outflow properties in one galaxy with exceptionally deep data, allowing detailed examination of the outflow energetics, spatial extent and underlying ISM properties, as well those from a larger sample of galaxies. I also probe the fraction of SFGs in our sample which contain (possibly obscured) AGN, and study how this affects our determination of galaxy properties, such as gas-phase metallicity. Finally

  16. VLA's Sharpened Vision Shows Details of Still-Forming Star

    NASA Astrophysics Data System (ADS)

    2001-01-01

    Using a new observing capability of the National Science Foundation's Very Large Array (VLA) radio telescope, astronomers have discovered a solar-system-sized disk of gas and dust feeding material onto a young star with 8 to 10 times the mass of the Sun. This is the first time an inner "accretion disk" has been seen around such a massive star. The VLA images also revealed the inner portion of an energetic outflow of material powered by the accretion disk. Artist's conception "Disks and outflows in young stars increase dramatically in mass and energy as the mass of the young star increases. We don't know if the same process is at work in all young stars or how the disks can both power an outflow that extends more than 15 light-years and also start the process of forming planets," said Debra Shepherd, of the National Radio Astronomy Observatory (NRAO) in Socorro, New Mexico. "By studying the birth of massive young stars, we're pushing the limits of our understanding and trying to learn if there are critical differences between the outflows from high and low mass young stars," she added Shepherd and Mark Claussen, also from the NRAO in Socorro, and Stan Kurtz of the National Autonomous University in Mexico, presented their findings today at the American Astronomical Society's meeting in San Diego, CA. The scientists made the discovery using the VLA connected by a newly- operational fiber-optic link to one of the radio-telescope antennas of the NSF's Very Long Baseline Array (VLBA), located at Pie Town, NM, 32 miles away from the VLA. Linking the VLA to the Pie Town antenna almost doubled the resolving power, or ability to see fine detail, available to the astronomers. "We could not have seen these structures without using the Pie Town antenna connected to the VLA," said Claussen. Work on the VLA-Pie Town fiber-optic link, financed by the NSF and Associated Universities, Inc., which operates NRAO for the NSF, began in late 1997. The linked facilities first were

  17. THE BOLOCAM GALACTIC PLANE SURVEY. VII. CHARACTERIZING THE PROPERTIES OF MASSIVE STAR-FORMING REGIONS

    SciTech Connect

    Dunham, Miranda K.; Rosolowsky, Erik; Evans II, Neal J.; Cyganowski, Claudia; Urquhart, James S.

    2011-11-10

    We present the results of a Green Bank Telescope survey of NH{sub 3}(1,1), (2,2), (3,3) lines toward 631 Bolocam Galactic Plane Survey (BGPS) sources at a range of Galactic longitudes in the inner Galaxy. We have detected the NH{sub 3}(1,1) line toward 72% of our targets (456), demonstrating that the high column density features identified in the BGPS and other continuum surveys accurately predict the presence of dense gas. We have determined kinematic distances and resolved the distance ambiguity for all BGPS sources detected in NH{sub 3}. The BGPS sources trace the locations of the Scutum and Sagittarius spiral arms, with the number of sources. We measure the physical properties of each source and find that depending on the distance, BGPS sources are primarily clumps, with some cores and clouds. We have examined the physical properties as a function of Galactocentric distance, and find a mean gas kinetic temperature of 15.6 K, and that the NH{sub 3} column density and abundance decrease by nearly an order of magnitude. Comparing sources at similar distances demonstrates that the physical properties are indistinguishable, which suggests a similarity in clump structure across the Galactic disk. We have also compared the BGPS sources to criteria for efficient star formation presented independently by Heiderman et al. and Lada et al., and for massive star formation presented by Kauffmann et al. Forty-eight percent of our sample should be forming stars (including massive stars) with high efficiency, and 87% contain subregions that should be efficiently forming stars. Indeed, we find that 67% of the sample exhibit signs of star formation activity based on an association with a mid-infrared source.

  18. Molecular line tracers of high-mass star forming regions

    NASA Astrophysics Data System (ADS)

    Nagy, Zsofia

    2013-09-01

    High-mass stars influence their environment in different ways including feedback via their far-UV radiation and mechanical feedback via shocks and stellar winds. The penetration of FUV photons into molecular clouds creates Photon Dominated Regions (PDRs) with different chemical layers where the mainly ionized medium changes into mainly molecular. Different chemical layers in PDRs are traced by different species observable at sub-mm and far-infrared wavelengths. In this thesis we present results from two molecular line surveys. One of them is the James Clerk Maxwell Telescope (JCMT) Spectral Legacy Survey (SLS) toward the luminous (>10^7 L_Sun), massive (~10^6 M_Sun), and distant (11.4 kpc) star-forming region W49A. The SLS images a 2x2 arcminute field around W49A in the 330-373 GHz frequency range. The detected molecular lines reveal a complex chemistry and the importance of FUV-irradiation and shocks in the heating and chemistry of the region. The other line survey presented in this thesis is part of the HEXOS (Herschel observations of EXtra-Ordinary Sources) key program using the Herschel Space Observatory and is toward the nearby (~420 pc) prototypical edge-on Orion Bar PDR and the dense molecular condensation Orion S. Reactive ions, such as CH+, SH+, and CO+, detected as a part of this line survey trace the warm (~500-1000 K) surface region of PDRs. Spectroscopic data from the HIFI and PACS instruments of Herschel give constraints on the chemistry and excitation of reactive ions in these regions.

  19. Motions and Initial Conditions in Star-Forming Dense Cores

    NASA Technical Reports Server (NTRS)

    Myers, Philip C.

    2001-01-01

    Under this grant in the past year we have pursued spectral-line observations of star-forming regions over size scales from 0.01 pc to 0.5 pc. Our main goal has been to measure the systematic and turbulent motions of condensing and collapsing gas. In this area, our results include (1) in 67 starless dense cores, some 19 show clear evidence of spatially extended inward motions, with typical line-of-sight inward speed 0.05-0.09 km s(sup -1) and with typical plane-of-the-sky extent 0.1-0.3 pc, (2) In some 40 nearby regions with embedded groups and clusters, we see extended infall asymmetry in lines of CS and HCO(+) clearly in 4 regions and less clearly in 4 others, (3) Using finer resolution (15 arcsec or 0.01-0.02 pc) and lines tracing higher density, we see spatial concentration of infall asymmetry near the protostars in NGC 1333 IRS 4A and B, L483, and L1251B, and with still finer resolution (2 arcsec or 0.003 pc or 600 AU) we detect inverse P Cyg profiles, indicating absorption of continuum emission from the protostellar envelope by infalling gas in NGC 1333 IRS 4A and 4B. Further, at high resolution we identify regions of stellar mass and low turbulence ("kernels") which are good candidates to become the next generation of stars in embedded clusters. In addition we have completed a survey for the OH Zeeman effect in absorption against nearby H II regions, indicating that the large-scale magnetic field may be nearly critical if it typically threads a flattened structure. We have also developed a model of spatially extended infall motions based on dissipation of turbulence in a magnetized, selfgravitating layer. In the following we describe some of these results in more detail.

  20. THE CLUSTERING AND HALO MASSES OF STAR-FORMING GALAXIES AT z < 1

    SciTech Connect

    Dolley, Tim; Brown, Michael J. I.; Pimbblet, Kevin A.; Palamara, David P.; Beare, Richard; Weiner, Benjamin J.; Jannuzi, Buell T.; Brodwin, Mark; Kochanek, C. S.; Dey, Arjun; Atlee, David W.

    2014-12-20

    We present clustering measurements and halo masses of star-forming galaxies at 0.2 < z < 1.0. After excluding active galactic nuclei (AGNs), we construct a sample of 22,553 24 μm sources selected from 8.42 deg{sup 2} of the Spitzer MIPS AGN and Galaxy Evolution Survey of Boötes. Mid-infrared imaging allows us to observe galaxies with the highest star formation rates (SFRs), less biased by dust obscuration afflicting the optical bands. We find that the galaxies with the highest SFRs have optical colors that are redder than typical blue cloud galaxies, with many residing within the green valley. At z > 0.4 our sample is dominated by luminous infrared galaxies (LIRGs, L {sub TIR} > 10{sup 11} L {sub ☉}) and is composed entirely of LIRGs and ultraluminous infrared galaxies (ULIRGs, L {sub TIR} > 10{sup 12} L {sub ☉}) at z > 0.6. We observe weak clustering of r {sub 0} ≈ 3-6 h {sup –1} Mpc for almost all of our star-forming samples. We find that the clustering and halo mass depend on L {sub TIR} at all redshifts, where galaxies with higher L {sub TIR} (hence higher SFRs) have stronger clustering. Galaxies with the highest SFRs at each redshift typically reside within dark matter halos of M {sub halo} ≈ 10{sup 12.9} h {sup –1} M {sub ☉}. This is consistent with a transitional halo mass, above which star formation is largely truncated, although we cannot exclude that ULIRGs reside within higher mass halos. By modeling the clustering evolution of halos, we connect our star-forming galaxy samples to their local descendants. Most star-forming galaxies at z < 1.0 are the progenitors of L ≲ 2.5 L {sub *} blue galaxies in the local universe, but star-forming galaxies with the highest SFRs (L {sub TIR} ≳ 10{sup 11.7} L {sub ☉}) at 0.6 < z < 1.0 are the progenitors of early-type galaxies in denser group environments.

  1. The dependence of protostellar luminosity on environment in the Cygnus-X star-forming complex

    SciTech Connect

    Kryukova, E.; Megeath, S. T.; Hora, J. L.; Smith, Howard A.; Gutermuth, R. A.; Bontemps, S.; Schneider, N.; Kraemer, K.; Hennemann, M.; Motte, F.

    2014-07-01

    The Cygnus-X star-forming complex is one of the most active regions of low- and high-mass star formation within 2 kpc of the Sun. Using mid-infrared photometry from the IRAC and MIPS Spitzer Cygnus-X Legacy Survey, we have identified over 1800 protostar candidates. We compare the protostellar luminosity functions of two regions within Cygnus-X: CygX-South and CygX-North. These two clouds show distinctly different morphologies suggestive of dissimilar star-forming environments. We find the luminosity functions of these two regions are statistically different. Furthermore, we compare the luminosity functions of protostars found in regions of high and low stellar density within Cygnus-X and find that the luminosity function in regions of high stellar density is biased to higher luminosities. In total, these observations provide further evidence that the luminosities of protostars depend on their natal environment. We discuss the implications this dependence has for the star formation process.

  2. Two New SiO Maser Sources in High-Mass Star-forming Regions

    NASA Astrophysics Data System (ADS)

    Cho, Se-Hyung; Yun, Youngjoo; Kim, Jaeheon; Liu, Tie; Kim, Kee-Tae; Choi, Minho

    2016-08-01

    Silicon monoxide (SiO) masers are rare in star-forming regions, with the exception of five known SiO maser sources. However, we detected two new SiO maser sources from infrared-loud clumps of the high-mass star-forming regions G19.61-0.23 and G75.78+0.34. High angular resolution observations toward G19.61-0.23 suggest that the deeply embedded young stellar object (YSO) of SMA1 is powering the SiO masers. In addition, the SiO v = 1, J = 1 \\to 0 line shows four spike features, while the v = 2 maser shows combined features of one spike and broad wing components, implying energetic activities of the YSO of SMA1 in the G19.61-0.23 hot molecular core. The SiO v = 0, J = 2 \\to 1 emission shows bipolar outflows in the NE-SW direction with respect to the center of the SiO maser source. A high angular resolution map of the SiO v = 1, J = 2 \\to 1 maser in G75.78+0.34 shows that the SiO maser is associated with the CORE source at the earliest stage of high-mass star formation. Therefore, the newly detected SiO masers and their associated outflows will provide good probes for investigating this early high-mass star formation.

  3. DISTRIBUTIONS OF LONG-LIVED RADIOACTIVE NUCLEI PROVIDED BY STAR-FORMING ENVIRONMENTS

    SciTech Connect

    Fatuzzo, Marco; Adams, Fred C.

    2015-11-01

    Radioactive nuclei play an important role in planetary evolution by providing an internal heat source, which affects planetary structure and helps facilitate plate tectonics. A minimum level of nuclear activity is thought to be necessary—but not sufficient—for planets to be habitable. Extending previous work that focused on short-lived nuclei, this paper considers the delivery of long-lived radioactive nuclei to circumstellar disks in star forming regions. Although the long-lived nuclear species are always present, their abundances can be enhanced through multiple mechanisms. Most stars form in embedded cluster environments, so that disks can be enriched directly by intercepting ejecta from supernovae within the birth clusters. In addition, molecular clouds often provide multiple episodes of star formation, so that nuclear abundances can accumulate within the cloud; subsequent generations of stars can thus receive elevated levels of radioactive nuclei through this distributed enrichment scenario. This paper calculates the distribution of additional enrichment for {sup 40}K, the most abundant of the long-lived radioactive nuclei. We find that distributed enrichment is more effective than direct enrichment. For the latter mechanism, ideal conditions lead to about 1 in 200 solar systems being directly enriched in {sup 40}K at the level inferred for the early solar nebula (thereby doubling the abundance). For distributed enrichment from adjacent clusters, about 1 in 80 solar systems are enriched at the same level. Distributed enrichment over the entire molecular cloud is more uncertain, but can be even more effective.

  4. FROM BLUE STAR-FORMING TO RED PASSIVE: GALAXIES IN TRANSITION IN DIFFERENT ENVIRONMENTS

    SciTech Connect

    Vulcani, Benedetta; Poggianti, Bianca M.; Fasano, Giovanni; Moretti, Alessia; Fritz, Jacopo; Calvi, Rosa; Paccagnella, Angela

    2015-01-01

    Exploiting a mass-complete (M {sub *} > 10{sup 10.25} M {sub ☉}) sample at 0.03 star-formation activity and/or morphology: green galaxies, red passive late types, and blue star-forming early types. Color fractions depend on mass and only for M {sub *} < 10{sup 10.7} M {sub ☉} on environment. The incidence of red galaxies increases with increasing mass, and, for M {sub *} < 10{sup 10.7} M {sub ☉}, decreases toward the group outskirts and in binary and single galaxies. The relative abundance of green and blue galaxies is independent of environment and increases monotonically with galaxy mass. We also inspect galaxy structural parameters, star-formation properties, histories, and ages and propose an evolutionary scenario for the different subpopulations. Color transformations are due to a reduction and suppression of the star-formation rate in both bulges and disks that does not noticeably affect galaxy structure. Morphological transitions are linked to an enhanced bulge-to-disk ratio that is due to the removal of the disk, not to an increase of the bulge. Our modeling suggests that green colors might be due to star-formation histories declining with long timescales, as an alternative scenario to the classical ''quenching'' processes. Our results suggest that galaxy transformations in star-formation activity and morphology depend neither on the environment nor on being a satellite or the most massive galaxy of a halo. The only environmental dependence we find is the higher fast quenching efficiency in groups giving origin to poststarburst signatures.

  5. Line profile asymmetries in chromospherically active stars

    NASA Technical Reports Server (NTRS)

    Dempsey, Robert C.; Bopp, Bernard W.; Strassmeier, Klaus G.; Granados, Arno F.; Henry, Gregory W.; Hall, Douglas S.

    1992-01-01

    A powerful, new probe of chromospheric activity, cross-correlation, has been developed and applied to a variety of stars. In this particular application, an entire CCD spectrum of an active star is correlated with the spectrum of a narrow-line, inactive star of similar spectral type and luminosity class. Using a number of strong lines in this manner enables the detection of absorption profile asymmetries at moderate resolution (lambda/Delta lambda about 40,000) and S/N 150:1. This technique has been applied to 14 systems mostly RS CVn's, with 10 not greater than nu sin i not greater than 50 km/s and P not less than 7 d. Distortions were detected for the first time in five systems: Sigma Gem, IM Peg, GX Lib, UV Crb, and Zeta And. Detailed modeling, incorporating both spectral line profiles and broad-band photometry, is applied to Sigma Gem. Profile asymmetries for this star are fitted by two high-latitude spots covering 5 percent of the stellar surface. The derived spot temperature of 3400 K is lower than found in previous studies. In addition, two well-known systems have been studied: HD 199178 and V711 Tau. Polar spots are found on both.

  6. A new star-forming region in Canis Major

    NASA Astrophysics Data System (ADS)

    Magakian, T. Yu.; Movsessian, T. A.; Bally, J.

    2016-07-01

    A new southern star-formation region, located at an estimated distance of ˜1.5 kpc in the Lynds 1664 dark cloud in Canis Major, is described. Lynds 1664 contains several compact star clusters, small stellar groups and young stars associated with reflection nebulae. Narrow-band H α and [S II] images obtained with the 4-m telescope at the Cerro Tololo Inter-American Observatory reveal more than 20 new Herbig-Haro objects associated with several protostellar outflows.

  7. Clustering of Pre-Main-Sequence Stars in the Orion, Ophiuchus, Chamaeleon, Vela, and Lupus Star-forming Regions

    NASA Astrophysics Data System (ADS)

    Nakajima, Yasushi; Tachihara, Kengo; Hanawa, Tomoyuki; Nakano, Makoto

    1998-04-01

    We study clustering of pre-main-sequence stars in the Orion, Ophiuchus, Chamaeleon, Vela, and Lupus star-forming regions. We calculate the average surface density of companions, Σ(θ), as a function of angular distance, θ, from each star. We employ the method developed by Larson in a 1995 study for the calculation. In most of the regions studied, the function can be fitted by two power laws (Σ ~ θγ) with a break as found by Larson for the Taurus star-forming region. The power index, γ, is smaller at small separations than at large separations. The power index at large separations shows significant variation from region to region (-0.8 < γ < -0.1), while the power index at small separations does not (γ ~ -2). The power index at large separations relates to the distribution of the nearest-neighbor distance. When the latter can be fitted by the Poisson distribution, the power index is close to 0. When the latter is broader than the Poisson distribution, the power index is negatively large. This correlation can be interpreted as the result of the variation in the surface density within the region. At large separations, the power-law fit may indicate star formation history in the region and not the spatial structure like the self-similar hierarchical, or fractal, one. Because of the velocity dispersion, stars move from their birthplaces, and the surface density of coeval stars decreases with their age. When a star-forming region contains several groups of stars with different ages, a power law may fit the average surface density of companions for it. The break of the power law is located around 0.01-0.1 pc. There is a clear correlation between the break position and the mean nearest-neighbor distance. The break position may reflect dispersal of newly formed stars.

  8. Characterizing Dust Attenuation in Local Star Forming Galaxies

    NASA Astrophysics Data System (ADS)

    Battisti, Andrew; Calzetti, Daniela; Chary, Ranga-Ram

    2017-01-01

    The dust attenuation for a sample of ~10000 local (z ≤ 0.1) star forming galaxies is constrained as a function of their physical properties. We utilize aperture-matched multi-wavelength data from the UV-to-NIR, available from the Galaxy Evolution Explorer, the Sloan Digital Sky Survey, the United Kingdom Infrared Telescope, and the Two Micron All-Sky Survey, to ensure that regions of comparable size in each galaxy are being analyzed. We characterize the dust attenuation through the slope of the UV flux density and the Balmer decrement (Hα/Hβ). The observed relationship between these quantities is similar to the local starburst relation and is not seen to vary strongly with galactic properties. We derive the total attenuation curve over the range 1250 Å < λ < 28500 Å and find that a single attenuation curve is effective for characterizing the majority of galaxies in our sample. This attenuation curve is slightly lower in the far-UV than local starburst galaxies, by roughly 15%, but appears similar at longer wavelengths and has a normalization of RV = 3.7±0.4 (V-band). This indicates that a single attenuation curve is reasonable for wide application in the local Universe.

  9. Segmented helical structures formed by ABC star copolymers in nanopores

    NASA Astrophysics Data System (ADS)

    Liu, Meijiao; Li, Weihua; Qiu, Feng

    2013-03-01

    Self-assembly of ABC star triblock copolymers confined in cylindrical nanopores is studied using self-consistent mean-field theory. With an ABC terpolymer forming hexagonally-arranged cylinders, segmented into alternative B and C domains, in the bulk, we observe the formation in the nanopore of a segmented single circular and non-circular cylinder, a segmented single-helix, and a segmented double-helix as stable phases, and a metastable stacked-disk phase with fourfold symmetry. The phase sequence from single-cylinder, to single-helix, and then to double-helix, is similar as that in the cylindrically-confined diblock copolymers except for the absence of an equilibrium stacked-disk phase. It is revealed that the arrangement of the three-arm junctions plays a critical role for the structure formation. One of the most interesting features in the helical structures is that there are two periods: the period of the B/C domains in the helix and the helical period. We demonstrate that the period numbers of the B/C domains contained in each helical period can be tuned by varying the pore diameter. In addition, it is predicted that the period number of B/C domains can be any rational in real helical structures whose helical period can be tuned freely.

  10. A STRUCTURAL ANALYSIS OF STAR-FORMING REGION AFGL 490

    SciTech Connect

    Masiunas, L. C.; Gutermuth, R. A.; Pipher, J. L.; Megeath, S. T.; Myers, P. C.; Kirk, H. M.; Fazio, G. G.; Allen, L. E.

    2012-06-20

    We present Spitzer IRAC and MIPS observations of the star-forming region containing intermediate-mass young stellar object (YSO) AFGL 490. We supplement these data with near-IR Two Micron All Sky Survey photometry and with deep Simultaneous Quad Infrared Imaging Device observations off the central high-extinction region. We have more than doubled the known membership of this region to 57 Class I and 303 Class II YSOs via the combined 1-24 {mu}m photometric catalog derived from these data. We construct and analyze the minimum spanning tree of their projected positions, isolating one locally overdense cluster core containing 219 YSOs (60.8% of the region's members). We find this cluster core to be larger yet less dense than similarly analyzed clusters. Although the structure of this cluster core appears irregular, we demonstrate that the parsec-scale surface densities of both YSOs and gas are correlated with a power-law slope of 2.8, as found for other similarly analyzed nearby molecular clouds. We also explore the mass segregation implications of AFGL 490's offset from the center of its core, finding that it has no apparent preferential central position relative to the low-mass members.

  11. Morphologies of multicompartment micelles formed by ABC miktoarm star terpolymers.

    PubMed

    Li, Zhibo; Hillmyer, Marc A; Lodge, Timothy P

    2006-10-24

    Several new multicompartment micellar structures have been identified by cryogenic transmission electron microscopy (cryoTEM) from the aqueous self-assembly of mu-[poly(ethylethylene)][poly(ethylene oxide)][poly(perfluoropropylene oxide)] (mu-EOF) miktoarm star terpolymers. This work extends our previous studies, in which it was found that, upon decreasing the length of the hydrophilic block (O), the resulting micelles evolved from "hamburger" micelles to segmented worms and ultimately to nanostructured bilayers and vesicles. In the terpolymers examined here segmented ribbons and bilayers were found at an intermediate composition between segmented worms and nanostructured bilayers, provided that the fluoropolymer (F) was the minority component in the micelle core. On the other hand, when the F block exceeded the chain length of the hydrocarbon block (E), the superhydrophobic F block imposed a "double frustration" on the self-assembly of the mu-EOF(2-9-5) terpolymer; while F prefers to minimize its interfacial contact with the O corona, it must occupy the majority of the micellar core. Therefore, a richer variety of multicompartment micelles, including well-defined segmented worms, raspberry-like micelles, and multicompartmentalized worms, were formed from one terpolymer, as revealed by cryoTEM. Despite the complexity and variety of the observed aggregate morphologies, a small number of common structural elements can be invoked to interpret the observed micelles and to relate a given structure to the terpolymer composition.

  12. Magnetic fields in star-forming regions - Observations

    NASA Technical Reports Server (NTRS)

    Heiles, Carl; Goodman, Alyssa A.; Mckee, Christopher F.; Zweibel, Ellen G.

    1993-01-01

    We review the observational aspects of magnetic fields in dense, star-forming regions. First we discuss ways to observe the field. These include direct methods, which consist of the measurement of both linear and circular polarization of spectral line and continuum radiation; and indirect methods, consisting of the angular distribution of H2O masers on the sky and the measurement of ambipolar diffusion. Next we discuss selected observational results, focusing on detailed discussions of a small number of points rather than a generalized discussion that covers the waterfront. We discuss the Orion/BN-KL region in detail, both on the small and large scales. Next we discuss the derivation of the complete magnetic vector, including both the systematic and fluctuating component, from a large sample of Zeeman and linear polarization measurements for the L204 dark cloud. We examine the virial theorem as it applies to dark clouds in general and one dark cloud, Barnard 1, in particular. We critically discuss the numerous claims for alignment of cloud structural features with the plane-of-the-sky component of the magnetic field, and find that many of these have not been definitively established.

  13. Structural analysis of star-forming blue early-type galaxies. Merger-driven star formation in elliptical galaxies

    NASA Astrophysics Data System (ADS)

    George, Koshy

    2017-01-01

    Context. Star-forming blue early-type galaxies at low redshift can give insight to the stellar mass growth of L⋆ elliptical galaxies in the local Universe. Aims: We wish to understand the reason for star formation in these otherwise passively evolving red and dead stellar systems. The fuel for star formation can be acquired through recent accretion events such as mergers or flyby. The signatures of such events should be evident from a structural analysis of the galaxy image. Methods: We carried out structural analysis on SDSS r-band imaging data of 55 star-forming blue elliptical galaxies, derived the structural parameters, analysed the residuals from best-fit to surface brightness distribution, and constructed the galaxy scaling relations. Results: We found that star-forming blue early-type galaxies are bulge-dominated systems with axial ratio >0.5 and surface brightness profiles fitted by Sérsic profiles with index (n) mostly >2. Twenty-three galaxies are found to have n< 2; these could be hosting a disc component. The residual images of the 32 galaxy surface brightness profile fits show structural features indicative of recent interactions. The star-forming blue elliptical galaxies follow the Kormendy relation and show the characteristics of normal elliptical galaxies as far as structural analysis is concerned. There is a general trend for high-luminosity galaxies to display interaction signatures and high star formation rates. Conclusions: The star-forming population of blue early-type galaxies at low redshifts could be normal ellipticals that might have undergone a recent gas-rich minor merger event. The star formation in these galaxies will shut down once the recently acquired fuel is consumed, following which the galaxy will evolve to a normal early-type galaxy.

  14. 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.

  15. Herschel far-infrared photometry of the Swift Burst Alert Telescope active galactic nuclei sample of the local universe - III. Global star-forming properties and the lack of a connection to nuclear activity

    NASA Astrophysics Data System (ADS)

    Shimizu, T. Taro; Mushotzky, Richard F.; Meléndez, Marcio; Koss, Michael J.; Barger, Amy J.; Cowie, Lennox L.

    2017-04-01

    We combine the Herschel Space Observatory PACS (Photoconductor Array Camera and Spectrometer) and SPIRE (Spectral and Photometric Imaging Receiver) photometry with archival WISE (Wide-field Infrared Survey Explorer) photometry to construct the spectral energy distributions (SEDs) for over 300 local (z < 0.05), ultrahard X-ray (14-195 keV) selected active galactic nuclei (AGN) from the Swift Burst Alert Telescope (BAT) 58-month catalogue. Using a simple analytical model that combines an exponentially cutoff power law with a single temperature modified blackbody, we decompose the SEDs into a host galaxy and AGN component. We calculate dust masses, dust temperatures, and star formation rates (SFRs) for our entire sample and compare them to a stellar mass-matched sample of local non-AGN galaxies. We find AGN host galaxies have systematically higher dust masses, dust temperatures, and SFRs due to the higher prevalence of late-type galaxies to host an AGN, in agreement with previous studies of the Swift/BAT AGN. We provide a scaling to convert X-ray luminosities into 8-1000 μm AGN luminosities, as well as determine the best mid-to-far IR colours for identifying AGN-dominated galaxies in the IR regime. We find that for nearly 30 per cent of our sample, the 70 μm emission contains a significant contribution from the AGN (>0.5), especially at higher luminosities (L14 - 195 keV > 1042.5 erg s-1). Finally, we measure the local SFR-AGN luminosity relationship, finding a slope of 0.18, large scatter (0.37 dex), and no evidence for an upturn at high AGN luminosity. We conclude with a discussion on the implications of our results within the context of galaxy evolution with and without AGN feedback.

  16. Isolated star-forming regions containing Herbig Ae/Be stars. 1: The young stellar aggregate associated with BD +40deg 4124

    NASA Astrophysics Data System (ADS)

    Hillenbrand, Lynne A.; Meyer, Michael R.; Strom, Stephen E.; Skrutskie, Michael F.

    1995-01-01

    We use optical and infrared photometry in combination with red optical spectra to study the star-forming region associated with the two Herbig Ae/Be stars BD + 40 deg 4124 and V1686 Cyg. We identify a partially embedded, dense, isolated cluster of pre-main sequence stars concentrated within 0.15 pc of the two young high-mass stars. The cluster is isolated in that it is separated by approximately 0.7 pc from a surrounding H alpha-bright rim and lies at the center of a molecular core with peak column density corresponding to 45 mag of visual extinction. The fraction of the stellar population with evidence for circumsteller activity is 100% amongst the optically visible cluster members and at least 50% amongst the embedded sources. This small region is characterized by an apparent age spread of approximately 3 Myr with evidence for both high-and low-mass stars forming relatively simultaneously (within several hundred thousand years). Comparison of the derived stellar mass distribution to that expected from Monte-Carlo sampling of the solar neighborhood mass spectrum reveals that this region is producing an unusually large number of intermediate-and high-mass stars. Our result suggests that not all star formation sites yield identical mass spectra, and that universal mass functions may be produced only when integrating over large spatial areas and/or over many star formation epochs. Futhermore, our data appear to exclude for the BD +40 deg 4124 region, the popular senario that low-mass star formation proceeds quietly and stochastically for several to ten Myr until the birth of an early type star, and its subsequent dynamical interaction with the cloud, ends all starformation processes in the core. Instead, we consider the hypothesis that star formation was induced in this region by the propagation of an external shock wave into the cloud core. This picture is similar to that invoked for other star-forming sites displaying a bright-rim morphology on optical images and

  17. Rapid growth of black holes in massive star-forming galaxies.

    PubMed

    Alexander, D M; Smail, I; Bauer, F E; Chapman, S C; Blain, A W; Brandt, W N; Ivison, R J

    2005-04-07

    The tight relationship between the masses of black holes and galaxy spheroids in nearby galaxies implies a causal connection between the growth of these two components. Optically luminous quasars host the most prodigious accreting black holes in the Universe, and can account for greater than or approximately equal to 30 per cent of the total cosmological black-hole growth. As typical quasars are not, however, undergoing intense star formation and already host massive black holes (> 10(8)M(o), where M(o) is the solar mass), there must have been an earlier pre-quasar phase when these black holes grew (mass range approximately (10(6)-10(8))M(o)). The likely signature of this earlier stage is simultaneous black-hole growth and star formation in distant (redshift z > 1; >8 billion light years away) luminous galaxies. Here we report ultra-deep X-ray observations of distant star-forming galaxies that are bright at submillimetre wavelengths. We find that the black holes in these galaxies are growing almost continuously throughout periods of intense star formation. This activity appears to be more tightly associated with these galaxies than any other coeval galaxy populations. We show that the black-hole growth from these galaxies is consistent with that expected for the pre-quasar phase.

  18. EXPLORING THE CONNECTION BETWEEN STAR FORMATION AND ACTIVE GALACTIC NUCLEUS ACTIVITY IN THE LOCAL UNIVERSE

    SciTech Connect

    LaMassa, Stephanie M.; Heckman, T. M.; Ptak, A.; Schiminovich, D.; Bertincourt, B.; O'Dowd, M.

    2012-10-10

    We study a combined sample of 264 star-forming, 51 composite, and 73 active galaxies using optical spectra from the Sloan Digital Sky Survey (SDSS) and mid-infrared (mid-IR) spectra from the Spitzer Infrared Spectrograph. We examine optical and mid-IR spectroscopic diagnostics that probe the amount of star formation and relative energetic contributions from star formation and an active galactic nucleus (AGN). Overall we find good agreement between optical and mid-IR diagnostics. Misclassifications of galaxies based on the SDSS spectra are rare despite the presence of dust obscuration. The luminosity of the [Ne II] 12.8 {mu}m emission line is well correlated with the star formation rate measured from the SDSS spectra, and this holds for the star-forming, composite, and AGN-dominated systems. AGNs show a clear excess of [Ne III] 15.6 {mu}m emission relative to star-forming and composite systems. We find good qualitative agreement between various parameters that probe the relative contributions of the AGN and star formation, including the mid-IR spectral slope, the ratio of the [Ne V] 14.3 {mu}m to [Ne II] {mu}m 12.8 fluxes, the equivalent widths of the 7.7 {mu}m, 11.3 {mu}m, and 17 {mu}m polycyclic aromatic hydrocarbon (PAH) features, and the optical 'D' parameter which measures the distance at which a source lies from the locus of star-forming galaxies in the optical BPT emission-line diagnostic diagram. We also consider the behavior of the three individual PAH features by examining how their flux ratios depend upon the degree of AGN dominance. We find that the PAH 11.3 {mu}m feature is significantly suppressed in the most AGN-dominated systems.

  19. The Connection Between Galaxy Environment and the Luminosity Function Slopes of Star-Forming Regions

    NASA Astrophysics Data System (ADS)

    Cook, David O.; Dale, Daniel A.; Lee, Janice C.; Thilker, David A.; Calzetti, Daniela; Kennicutt, Robert

    2016-06-01

    We present the first study of GALEX far ultra-violet (FUV) luminosity functions of individual star-forming regions within a sample of 258 nearby galaxies spanning a large range in total stellar mass and star formation properties. We identify ~65,000 star-forming regions (i.e., FUV sources), measure each galaxy's luminosity function, and characterize the relationships between the luminosity function slope (α) and several global galaxy properties. A final sample of \

  20. The Herschel Virgo Cluster Survey. XVIII. Star-forming dwarf galaxies in a cluster environment

    NASA Astrophysics Data System (ADS)

    Grossi, M.; Hunt, L. K.; Madden, S. C.; Hughes, T. M.; Auld, R.; Baes, M.; Bendo, G. J.; Bianchi, S.; Bizzocchi, L.; Boquien, M.; Boselli, A.; Clemens, M.; Corbelli, E.; Cortese, L.; Davies, J.; De Looze, I.; di Serego Alighieri, S.; Fritz, J.; Pappalardo, C.; Pierini, D.; Rémy-Ruyer, A.; Smith, M. W. L.; Verstappen, J.; Viaene, S.; Vlahakis, C.

    2015-02-01

    To assess the effects of the cluster environment on the different components of the interstellar medium, we analyse the far-infrared (FIR) and submillimetre (submm) properties of a sample of star-forming dwarf galaxies detected by the Herschel Virgo Cluster Survey (HeViCS). We determine dust masses and dust temperatures by fitting a modified black body function to the spectral energy distributions (SEDs). Stellar and gas masses, star formation rates (SFRs), and metallicities are obtained from the analysis of a set of ancillary data. Dust is detected in 49 out of a total 140 optically identified dwarfs covered by the HeViCS field; considering only dwarfs brighter than mB = 18 mag, this gives a detection rate of 43%. After evaluating different emissivity indices, we find that the FIR-submm SEDs are best-fit by β = 1.5, with a median dust temperature Td = 22.4 K. Assuming β = 1.5, 67% of the 23 galaxies detected in all five Herschel bands show emission at 500 μm in excess of the modified black-body model. The fraction of galaxies with a submillimetre excess decreases for lower values of β, while a similarly high fraction (54%) is found if a β-free SED modelling is applied. The excess is inversely correlated with SFR and stellar masses. To study the variations in the global properties of our sample that come from environmental effects, we compare the Virgo dwarfs to other Herschel surveys,such as the Key Insights into Nearby Galaxies: Far-Infrared Survey with Herschel (KINGFISH), the Dwarf Galaxy Survey (DGS), and the HeViCS Bright Galaxy Catalogue (BGC). We explore the relations between stellar mass and Hi fraction, specific star formation rate, dust fraction, gas-to-dust ratio over a wide range of stellar masses (from 107 to 1011 M⊙) for both dwarfs and spirals. Highly Hi-deficient Virgo dwarf galaxies are mostly characterised by quenched star formation activity and lower dust fractions giving hints for dust stripping in cluster dwarfs. However, to explain the

  1. Chromospherically active stars. I - HD 136905

    NASA Technical Reports Server (NTRS)

    Fekel, F. C.; Hall, D. S.; Africano, J. L.; Gillies, K.; Quigley, R.

    1985-01-01

    The variable star HD 136905, recently designated GX Librae, is a chromospherically active K1 III single-lined spectroscopic binary with a period of 11.1345 days. It has moderate strength Ca II H and K and ultraviolet emission features, while H-alpha is strongly in absorption. The inclination of the system is 58 + or - 17 deg and the unseen secondary is most likely a G or K dwarf. The v sin i of the primary, 32 + or - 2 km/s, results in a minimum radius of 7.0 + or - 0.4 solar radii. Since the star fills a substantial fracture of its Roche lab, the double-peaked limit curve seen by photometric observers is predominantly ellipsoidal in nature. Both the photometry and the spectroscopy yield values for the period and the time of conjunction that are identical within their uncertainties.

  2. Rotation and differential rotation of active Kepler stars

    NASA Astrophysics Data System (ADS)

    Reinhold, Timo; Reiners, Ansgar; Basri, Gibor

    2013-12-01

    Context. The Kepler space telescope monitors more than 160 000 stars with an unprecedented precision providing the opportunity to study the rotation of thousands of stars. Aims: We present rotation periods for thousands of active stars in the Kepler field derived from Q3 data. In most cases a second period close to the rotation period was detected that we interpreted as surface differential rotation (DR). We show how the absolute and relative shear (ΔΩ and α = ΔΩ/Ω, respectively) correlate with rotation period and effective temperature. Methods: Active stars were selected from the whole sample using the range of the variability amplitude. To detect different periods in the light curves we used the Lomb-Scargle periodogram in a pre-whitening approach to achieve parameters for a global sine fit. The most dominant periods from the fit were associated to different surface rotation periods. Our purely mathematical approach is capable of detecting different periods but cannot distinguish between the physical origins of periodicity. We ascribe the existence of different periods to DR, but spot evolution could also play a role. Because of the large number of stars the period errors are estimated statistically. We thus cannot exclude the existence of false positives among our periods. Results: In our sample of 40 661 active stars we found 24 124 rotation periods P1 between 0.5 and 45 days, with a mean of ⟨P1⟩ = 16.3 days. The distribution of stars with 0.5 < B - V < 1.0 and ages derived from angular momentum evolution that are younger than 300 Myr is consistent with a constant star-formation rate; the detection among older stars is incomplete probably because of our active sample selection. A second period P2 within ±30% of the rotation period P1 was found in 18 616 stars (77.2%). Attributing these two periods to DR we found that for active stars other than the Sun the relative shear α increases with rotation period, and slightly decreases with effective

  3. THE CLUSTERED NATURE OF STAR FORMATION. PRE-MAIN-SEQUENCE CLUSTERS IN THE STAR-FORMING REGION NGC 602/N90 IN THE SMALL MAGELLANIC CLOUD

    SciTech Connect

    Gouliermis, Dimitrios A.; Gennaro, Mario; Schmeja, Stefan; Dolphin, Andrew E.; Tognelli, Emanuele; Prada Moroni, Pier Giorgio

    2012-03-20

    Located at the tip of the wing of the Small Magellanic Cloud (SMC), the star-forming region NGC 602/N90 is characterized by the H II nebular ring N90 and the young cluster of pre-main-sequence (PMS) and early-type main-sequence stars NGC 602, located in the central area of the ring. We present a thorough cluster analysis of the stellar sample identified with Hubble Space Telescope/Advanced Camera for Surveys in the region. We show that apart from the central cluster low-mass PMS stars are congregated in 13 additional small, compact sub-clusters at the periphery of NGC 602, identified in terms of their higher stellar density with respect to the average background density derived from star counts. We find that the spatial distribution of the PMS stars is bimodal, with an unusually large fraction ({approx}60%) of the total population being clustered, while the remaining is diffusely distributed in the intercluster area, covering the whole central part of the region. From the corresponding color-magnitude diagrams we disentangle an age difference of {approx}2.5 Myr between NGC 602 and the compact sub-clusters, which appear younger, on the basis of comparison of the brighter PMS stars with evolutionary models, which we accurately calculated for the metal abundance of the SMC. The diffuse PMS population appears to host stars as old as those in NGC 602. Almost all detected PMS sub-clusters appear to be centrally concentrated. When the complete PMS stellar sample, including both clustered and diffused stars, is considered in our cluster analysis, it appears as a single centrally concentrated stellar agglomeration, covering the whole central area of the region. Considering also the hot massive stars of the system, we find evidence that this agglomeration is hierarchically structured. Based on our findings, we propose a scenario according to which the region NGC 602/N90 experiences an active clustered star formation for the last {approx}5 Myr. The central cluster NGC 602 was

  4. Hubble Space Telescope Observations of Circumnuclear Star-Forming Rings in NGC 1097 and NGC 6951

    NASA Astrophysics Data System (ADS)

    Barth, Aaron J.; Ho, Luis C.; Filippenko, Alexei V.; Sargent, Wallace L.

    1995-09-01

    We have obtained new and archival Hubble Space Telescope V-band images of kiloparsec-sized circumnuclear star-forming rings in the barred spiral galaxies NGC 1097 and NGC 6951, both of which contain active nuclei. The images resolve the rings into two-armed spirals composed of bright knots located on the outer edges of prominent dust lanes. The two-armed ring morphology seen in these two galaxies appears to be common in barred spirals and is in accord with the results of simulations of bar-driven inflow. In both galaxies, circumnuclear star formation is tightly confined to the ring: in the region between the ring and the nucleus there is an intricate spiral pattern of narrow dust lanes, but no bright knots are visible. Miniature gaseous or stellar bars interior to nuclear rings have been suggested as mechanisms for transporting gas to active nuclei, but it is not clear from the optical morphology whether either of these mechanisms may be at work in these two galaxies. The young star clusters in the rings are extremely compact, with mean effective radii of 2.5 pc in NGC 1097 and <= 4 pc in NGC 6951. Without correcting for extinction, the clusters have absolute V magnitudes of up to - 12.6 mag; with a highly uncertain extinction correction the brightest clusters have luminosities of M_v_ = - 14 to - 15 mag. Such high luminosities and small radii indicate that these objects are examples of "super star clusters" which may be newly formed globular clusters like those found recently in merging galaxies. The centers of barred galaxies may therefore be common sites for the present-day formation of globular clusters. The image of NGC 1097 also contains the type II supernova 1992bd 12 days prior to its discovery in ground-based observations.

  5. Photoionization Models for the Semi-forbidden C III] 1909 Emission in Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Jaskot, A. E.; Ravindranath, S.

    2016-12-01

    The increasing neutrality of the intergalactic medium at z > 6 suppresses Lyα emission, and spectroscopic confirmation of galaxy redshifts requires the detection of alternative ultraviolet lines. The strong [C iii] λ1907+C iii] λ1909 doublet frequently observed in low-metallicity, actively star-forming galaxies is a promising emission feature. We present CLOUDY photoionization model predictions for C iii] equivalent widths (EWs) and line ratios as a function of starburst age, metallicity, and ionization parameter. Our models include a range of C/O abundances, dust content, and gas density. We also examine the effects of varying the nebular geometry and optical depth. Only the stellar models that incorporate binary interaction effects reproduce the highest observed C iii] EWs. The spectral energy distributions from the binary stellar population models also generate observable C iii] over a longer timescale relative to single-star models. We show that diagnostics using C iii] and nebular He ii λ1640 can separate star-forming regions from shock-ionized gas. We also find that density-bounded systems should exhibit weaker C iii] EWs at a given ionization parameter, and C iii] EWs could, therefore, select candidate Lyman continuum-leaking systems. In almost all models, C iii] is the next strongest line at <2700 Å after Lyα, and C iii] reaches detectable levels for a wide range of conditions at low metallicity. C iii] may therefore serve as an important diagnostic for characterizing galaxies at z > 6.

  6. A CENSUS OF OXYGEN IN STAR-FORMING GALAXIES: AN EMPIRICAL MODEL LINKING METALLICITIES, STAR FORMATION RATES, AND OUTFLOWS

    SciTech Connect

    Zahid, H. J.; Dima, G. I.; Kewley, L. J.; Erb, D. K.; Dave, R.

    2012-09-20

    In this contribution, we present the first census of oxygen in star-forming galaxies in the local universe. We examine three samples of galaxies with metallicities and star formation rates (SFRs) at z = 0.07, 0.8, and 2.26, including the Sloan Digital Sky Survey (SDSS) and DEEP2 survey. We infer the total mass of oxygen produced and mass of oxygen found in the gas-phase from our local SDSS sample. The star formation history is determined by requiring that galaxies evolve along the relation between stellar mass and SFR observed in our three samples. We show that the observed relation between stellar mass and SFR for our three samples is consistent with other samples in the literature. The mass-metallicity relation is well established for our three samples, and from this we empirically determine the chemical evolution of star-forming galaxies. Thus, we are able to simultaneously constrain the SFRs and metallicities of galaxies over cosmic time, allowing us to estimate the mass of oxygen locked up in stars. Combining this work with independent measurements reported in the literature, we conclude that the loss of oxygen from the interstellar medium of local star-forming galaxies is likely to be a ubiquitous process with the oxygen mass loss scaling (almost) linearly with stellar mass. We estimate the total baryonic mass loss and argue that only a small fraction of the baryons inferred from cosmological observations accrete onto galaxies.

  7. Dusty Star Forming Galaxies and Supermassive Black Holes at High Redshifts: In- Situ Coevolution

    NASA Astrophysics Data System (ADS)

    Mancuso, Claudia

    2016-10-01

    exploited our SFR functions with relations between SFR and radio (synchrotron and free-free) emission. Our results show that the deepest SKA1- MID surveys will detect high-z galaxies with SFRs two orders of magnitude lower compared to Herschel surveys. The highest redshift tails of the distributions at the detection limits of planned SKA1-MID surveys comprise a substantial fraction of strongly lensed galaxies. The SKA1-MID will thus provide a comprehensive view of the star formation history throughout the re-ionization epoch, unaffected by dust extinction. We have also provided specific predictions for the EMU/ASKAP and MIGHTEE/MeerKAT surveys. We finally provide a novel, unifying physical interpretation on the origin, the average shape, the scatter, and the cosmic evolution for the main sequences (MS) of star-forming galaxies and active galactic nuclei at high redshift z ≥ 1. We achieve this goal in a model-independent way by exploiting the redshift-dependent SFR functions, and the deterministic evolutionary tracks for the history of star formation and black hole accretion, gauged on a wealth of multiwavelength observations including the observed Eddington ratio distribution. We further validate these ingredients by showing their consistency with the observed galaxy stellar mass functions and active galactic nucleus (AGN) bolometric luminosity functions at different redshifts via, again, the continuity equation approach. Our analysis of the main sequence for high-redshift galaxies and AGNs highlights that the present data strongly support a scenario of in situ coevolution for star formation and black hole accretion, envisaging these as local, time coordinated processes.

  8. Mahalo-Subaru: The Nature Of Star Forming Disc Galaxies In Proto-Clusters

    NASA Astrophysics Data System (ADS)

    Kodama, Tadayuki

    2016-10-01

    We have been conducting Mahalo-Subaru project which targets 10 proto-clusters as well as unbiased general fields for comparison over the redshift interval of 1.5star-forming galaxies (e.g., Ha, [OIII]) associated to the proto-clusters or in some particular redshift slices in the field.We show that all the clusters have prominent substructures indicating the early assembly phase, and that star formation activity in the cluster cores is very high at z 2, involving a significant fraction of dusty star-bursting galaxies seen as red emitters or SCUBA2 submm sources. Such strong activities in proto-cluster cores decline sharply as time progresses as (1+z)^6, and the peak of star formation activity is shifted outwards to surrounding lower density regions, clearly indicating the "inside-out" formation of galaxy clusters.Using HST imaging, AO-assisted narrow-band imaging (Ganba-Subaru), and ALMA observations (Gracias-ALMA), we are now at the stage of resolving internal structures of individual galaxies to know the physical processes of galaxy formation in action and their environmental dependence. I will also review all these on-going projects as well as introducing the up-coming 1-sq.deg. SWIMS-18 survey using 18 filters (6 narrow-bands, 9 medium-bands, and 3 broad-bands).

  9. The Stellar Content of Intermediate-Mass Star-Forming Regions.

    NASA Astrophysics Data System (ADS)

    Lundquist, Michael; Kobulnicky, H.; Alexander, M.; Vargas Alvarez, C.; Arvidsson, K.; Kerton, C.

    2012-01-01

    In an effort to understand the factors that govern the transition from low- to high-mass star formation, we report near-infrared imaging and spectroscopy of stars within a sample of intermediate-mass star-forming regions (IMSFRs). Some IMSFRs appear to contain compact <1 pc embedded clusters at an early evolutionary stage similar to compact HII regions, but lacking the massive ionizing central star(s). The IMSFRs have photodissociation regions with diameters 1 pc powered by the equivalent of an early B star, but because all sources lack radio free-free emission, they must host a collection of less massive stars. These spectroscopic observations using FLAMINGOS on the Kitt Peak 4 m telescope, coupled with 2MASS and UKIDSS infrared imaging, identify which candidate IMSFRs host probable stellar clusters and address the nature of their most massive stellar constituents.

  10. HUBBLE SPIES HUGE CLUSTERS OF STARS FORMED BY ANCIENT ENCOUNTER

    NASA Technical Reports Server (NTRS)

    2002-01-01

    NASA's Hubble Space Telescope snapped these two views of the heart of the galaxy M82. The image at left was taken in visible light; the picture at right, in infrared light. In the infrared view, the telescope's Near Infrared Camera and Multi-Object Spectrometer peered through thick dust lanes to find some of the galaxy's more than 100 super star clusters. The clusters are the larger pink and yellow dots scattered throughout the picture. They were formed during a violent collision with the galaxy M81 about 600 million years ago. The galaxy is 12 million light-years from Earth in the constellation Ursa Major. The pictures were taken Sept. 15, 1997. Credits: NASA, ESA, R. de Grijs (Institute of Astronomy, Cambridge, UK) NOTE TO EDITORS: For additional information, please contact Richard de Grijs, Institute of Astronomy, Cambridge University, Madingley Road, Cambridge CB3 0HA, UK, +44(0)1223-337528 (phone), +44(0)1223-337523 (fax), grijs@ast.cam.ac.uk (e-mail). The Space Telescope Science Institute (STScI) is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA). This image is issued jointly by NASA and ESA. Electronic images, animation and additional information are available at: http://oposite.stsci.edu/pubinfo/pr/2001/08 and via links in http://oposite.stsci.edu/pubinfo/latest.html http://oposite.stsci.edu/pubinfo/pictures.html http://hubble.stsci.edu/go/news http://hubble.esa.int To receive STScI press releases electronically, send an Internet electronic mail message to public-request@stsci.edu. Leave the subject line blank, and type the word subscribe in the body of the message. The system will respond with a confirmation of the subscription, and you will receive new press releases as they are issued. Please subscribe using the email account

  11. The anatomy of a star-forming galaxy: pressure-driven regulation of star formation in simulated galaxies

    NASA Astrophysics Data System (ADS)

    Benincasa, S. M.; Wadsley, J.; Couchman, H. M. P.; Keller, B. W.

    2016-11-01

    We explore the regulation of star formation in star-forming galaxies through a suite of high-resolution isolated galaxy simulations. We use the smoothed particle hydrodynamics code GASOLINE, including photoelectric heating and metal cooling, which produces a multi-phase interstellar medium (ISM). We show that representative star formation and feedback sub-grid models naturally lead to a weak, sub-linear dependence between the amount of star formation and changes to star formation parameters. We incorporate these sub-grid models into an equilibrium pressure-driven regulation framework. We show that the sub-linear scaling arises as a consequence of the non-linear relationship between scaleheight and the effective pressure generated by stellar feedback. Thus, simulated star formation regulation is sensitive to how well vertical structure in the ISM is resolved. Full galaxy discs experience density waves which drive locally time-dependent star formation. We develop a simple time-dependent, pressure-driven model that reproduces the response extremely well.

  12. The Lifetimes of Phases in High-mass Star-forming Regions

    NASA Astrophysics Data System (ADS)

    Battersby, Cara; Bally, John; Svoboda, Brian

    2017-02-01

    High-mass stars form within star clusters from dense, molecular regions (DMRs), but is the process of cluster formation slow and hydrostatic or quick and dynamic? We link the physical properties of high-mass star-forming regions with their evolutionary stage in a systematic way, using Herschel and Spitzer data. In order to produce a robust estimate of the relative lifetimes of these regions, we compare the fraction of DMRs above a column density associated with high-mass star formation, N(H2) > 0.4–2.5 × 1022 cm‑2, in the “starless” (no signature of stars ≳10 {M}ȯ forming) and star-forming phases in a 2° × 2° region of the Galactic Plane centered at ℓ = 30°. Of regions capable of forming high-mass stars on ∼1 pc scales, the starless (or embedded beyond detection) phase occupies about 60%–70% of the DMR lifetime, and the star-forming phase occupies about 30%–40%. These relative lifetimes are robust over a wide range of thresholds. We outline a method by which relative lifetimes can be anchored to absolute lifetimes from large-scale surveys of methanol masers and UCHII regions. A simplistic application of this method estimates the absolute lifetime of the starless phase to be 0.2–1.7 Myr (about 0.6–4.1 fiducial cloud free-fall times) and the star-forming phase to be 0.1–0.7 Myr (about 0.4–2.4 free-fall times), but these are highly uncertain. This work uniquely investigates the star-forming nature of high column density gas pixel by pixel, and our results demonstrate that the majority of high column density gas is in a starless or embedded phase.

  13. GOODS-HERSCHEL: STAR FORMATION, DUST ATTENUATION, AND THE FIR–RADIO CORRELATION ON THE MAIN SEQUENCE OF STAR-FORMING GALAXIES UP TO z ≃ 4

    SciTech Connect

    Pannella, M.; Elbaz, D.; Daddi, E.; Hwang, H. S.; Schreiber, C.; Strazzullo, V.; Aussel, H.; Bethermin, M.; Cibinel, A.; Juneau, S.; Floc’h, E. Le; Leiton, R.; Buat, V.; Charmandaris, V.; Magdis, G.; Ivison, R. J.; Borgne, D. Le; Lin, L.; Morrison, G. E.; and others

    2015-07-10

    We use deep panchromatic data sets in the GOODS-N field, from GALEX to the deepest Herschel far-infrared (FIR) and VLA radio continuum imaging, to explore the evolution of star-formation activity and dust attenuation properties of star-forming galaxies to z ≃ 4, using mass-complete samples. Our main results can be summarized as follows: (i) the slope of the star-formation rate–M{sub *} correlation is consistent with being constant ≃0.8 up to z ≃ 1.5, while its normalization keeps increasing with redshift; (ii) for the first time we are able to explore the FIR–radio correlation for a mass-selected sample of star-forming galaxies: the correlation does not evolve up to z ≃ 4; (iii) we confirm that galaxy stellar mass is a robust proxy for UV dust attenuation in star-forming galaxies, with more massive galaxies being more dust attenuated. Strikingly, we find that this attenuation relation evolves very weakly with redshift, with the amount of dust attenuation increasing by less than 0.3 mag over the redshift range [0.5–4] for a fixed stellar mass; (iv) the correlation between dust attenuation and the UV spectral slope evolves with redshift, with the median UV slope becoming bluer with redshift. By z ≃ 3, typical UV slopes are inconsistent, given the measured dust attenuations, with the predictions of commonly used empirical laws. (v) Finally, building on existing results, we show that gas reddening is marginally larger (by a factor of around 1.3) than the stellar reddening at all redshifts probed. Our results support a scenario where the ISM conditions of typical star-forming galaxies evolve with redshift, such that at z ≥ 1.5 Main Sequence galaxies have ISM conditions moving closer to those of local starbursts.

  14. Fundamental stellar parameters for selected T-Tauri stars in the Chamaeleon and Rho Ophiuchus star-forming regions

    NASA Astrophysics Data System (ADS)

    James, D. J.; Aarnio, A. N.; Richert, A. J. W.; Cargile, P. A.; Santos, N. C.; Melo, C. H. F.; Bouvier, J.

    2016-06-01

    We present the results of an optical photometry and high-resolution spectroscopy campaign for a modest sample of X-ray selected stars in the Chamaeleon and Rho Ophiuchus star-forming regions. With R˜ 50 000 optical spectra, we establish kinematic membership of the parent association and confirm stellar youth for each star in our sample. With the acquisition of new standardized BVIc photometry, in concert with near-infrared data from the literature, we derive age and mass from stellar positions in model-dependent Hertzsprung-Russell diagrams. We compare isochronal ages derived using colour-dependent extinction values finding that, within error bars, ages are the same irrespective of whether E(B - V), E(V - Ic), E(J - H) or E(H - K) is used to establish extinction, although model ages tend to be marginally younger for redder Ecolour values. For Cham I and η Cham members, we derive ages of ≲5-6 Myr, whereas our three η Cha candidates are more consistent with a ≳25 Myr post-T Tauri star population. In Rho Ophiuchus, most stars in our sample have isochronal ages <10 Myr. Five objects show evidence of strong infrared excess (Av > 5) in the Two Micron All Sky Survey colour-colour diagram, however in terms of Hα emission, all stars except RXJ1625.6-2613 are consistent with being weak-lined T-Tauri stars. Spectral energy distributions (SEDs) over the range ≃4000 Å <λ < 1000 μm, show that only one Chamaeleon star (RXJ1112.7 -7637) and three Rho Ophiuchus stars (ROXR1 13, RXJ1625.6-2613 & RXJ1627.1-2419) reveal substantial departures from a bare photosphere.

  15. Coronal evolution of solar-like stars: X-ray spectroscopy of stars in star- forming regions and the solar neighborhood

    NASA Astrophysics Data System (ADS)

    Telleschi, Alessandra Silvia

    Solar-like stars are strong X-ray emitters in both their pre-main sequence (PMS) and main-sequence (MS) phases. In analogy to the Sun, X-rays are thought to originate in a corona. However, in the case of pre-main sequence stars, accretion processes might influence the X-ray properties of the stars. In this thesis, results from X-ray spectroscopy of main-sequence solar analogs, pre-main sequence solar-like stars and a Herbig Ae/Be star are presented and discussed. All X-ray spectra have been obtained by the Reflection Grating Spectrometers (RGS) and the European Photon Imaging Cameras (EPIC) on board the XMM-Newton satellite. In the first part of the thesis, high-resolution (RGS) X-ray spectra of a sample of six main-sequence G-type stars with ages between [approximate] 0.1 Gyr and [approximate] 1.6 Gyr have been analyzed. Using individual spectral lines, the Emission Measure Distributions (EMD) and the coronal abundances have been derived. As a solar analog evolves, its rotation rate decreases and its internal magnetic dynamo weakens, resulting in a decrease of magnetic activity and a decrease of the star's X-ray luminosity. The mean coronal temperatures derived from the EMDs decrease from [approximate] 10 MK for the youngest stars to [approximate] 4 MK for the oldest star in our stellar sample. These results have been interpreted with a model in which the coronal emission is produced by a superposition of stochastically occurring flares; more active stars are found to require a larger range of flare energies than less active stars. Abundances change from an inverse First Ionization Potential (FIP) effect, where abundances with high FIP are enhanced with respect to abundances with low FIP, to a solar-like FIP effect at ages >= 0.3 Gyr. The analysis has then been extended to pre-main sequence stars in the Taurus- Auriga complex. The results presented here are part of a large survey, the "XMM-Newton Extended Survey of the Taurus Molecular Cloud" (XEST). High- and

  16. THE EFFECTS OF EPISODIC STAR FORMATION ON THE FUV-NUV COLORS OF STAR FORMING REGIONS IN OUTER DISKS

    SciTech Connect

    Barnes, Kate L.; Van Zee, Liese; Dowell, Jayce D. E-mail: vanzee@astro.indiana.edu

    2013-09-20

    We run stellar population synthesis models to examine the effects of a recently episodic star formation history (SFH) on UV and Hα colors of star forming regions. Specifically, the SFHs we use are an episodic sampling of an exponentially declining star formation rate (SFR; τ model) and are intended to simulate the SFHs in the outer disks of spiral galaxies. To enable comparison between our models and observational studies of star forming regions in outer disks, we include in our models sensitivity limits that are based on recent deep UV and Hα observations in the literature. We find significant dispersion in the FUV-NUV colors of simulated star forming regions with frequencies of star formation episodes of 1 × 10{sup –8} to 4 × 10{sup –9} yr{sup –1}. The dispersion in UV colors is similar to that found in the outer disk of nearby spiral galaxies. As expected, we also find large variations in L{sub H{sub α}}/L{sub FUV}. We interpret our models within the context of inside-out disk growth, and find that a radially increasing τ and decreasing metallicity with an increasing radius will only produce modest FUV-NUV color gradients, which are significantly smaller than what is found for some nearby spiral galaxies. However, including moderate extinction gradients with our models can better match the observations with steeper UV color gradients. We estimate that the SFR at which the number of stars emitting FUV light becomes stochastic is ∼2 × 10{sup –6} M{sub ☉} yr{sup –1}, which is substantially lower than the SFR of many star forming regions in outer disks. Therefore, we conclude that stochasticity in the upper end of the initial mass function is not likely to be the dominant cause of dispersion in the FUV-NUV colors of star forming regions in outer disks. Finally, we note that if outer disks have had an episodic SFH similar to that used in this study, this should be taken into account when estimating gas depletion timescales and modeling chemical

  17. Hα Surface Brightness Profiles of Star-Forming Galaxies and Dependence on Halo Mass Using the HAGGIS Survey

    NASA Astrophysics Data System (ADS)

    Kulkarni, S.; Wilman, D.; Erwin, P.; Koppenhöfer, J.; Gutierrez, L.; Beckman, J.; Saglia, R.; Bender, R.

    2014-03-01

    We present the first results from the Hα Galaxy Groups Imaging Survey (HAGGIS), a narrow-band imaging survey of SDSS groups at z < 0.05 conducted using the Wide Field Imager (WFI) on the ESO/MPG 2.2-meter telescope and the Wide Field Camera (WFC) on the Issac Newton Telescope (INT). In total, we observed 100 galaxy groups with a wide range of halo mass (1012 - 1014 M⊙) in pairs of narrow-band filters selected to get continuum subtracted rest-frame Hα images for each galaxy. The excellent data allows us to detect Hα down to the 10-18 ergs/s/cm2/arcsec2 level. Here, we examine the role played by halo mass and galaxy stellar mass in deciding the overall star formation activity in star forming disks by comparing stacked Hα profiles of galaxies in different halo mass and stellar mass bins. With this preliminary study, we have found that the star-formation activity in star-forming galaxies decreases in larger halos compared to the field galaxies. Using median equivalent width profiles, we can infer how environmental processes affect star-forming galaxies differently at different radii.

  18. WIDE-FIELD INFRARED SURVEY EXPLORER OBSERVATIONS OF THE EVOLUTION OF MASSIVE STAR-FORMING REGIONS

    SciTech Connect

    Koenig, X. P.; Leisawitz, D. T.; Benford, D. J.; Padgett, D. L.; Rebull, L. M.

    2012-01-10

    We present the results of a mid-infrared survey of 11 outer Galaxy massive star-forming regions and 3 open clusters with data from the Wide-field Infrared Survey Explorer (WISE). Using a newly developed photometric scheme to identify young stellar objects and exclude extragalactic contamination, we have studied the distribution of young stars within each region. These data tend to support the hypothesis that latter generations may be triggered by the interaction of winds and radiation from the first burst of massive star formation with the molecular cloud material leftover from that earlier generation of stars. We dub this process the 'fireworks hypothesis' since star formation by this mechanism would proceed rapidly and resemble a burst of fireworks. We have also analyzed small cutout WISE images of the structures around the edges of these massive star-forming regions. We observe large (1-3 pc size) pillar and trunk-like structures of diffuse emission nebulosity tracing excited polycyclic aromatic hydrocarbon molecules and small dust grains at the perimeter of the massive star-forming regions. These structures contain small clusters of emerging Class I and Class II sources, but some are forming only a single to a few new stars.

  19. Wide-Field Infrared Survey Explorer Observations of the Evolution of Massive Star-Forming Regions

    NASA Technical Reports Server (NTRS)

    Koenig, X. P.; Leisawitz, D. T.; Benford, D. J.; Rebull, L. M.; Padgett, D. L.; Asslef, R. J.

    2012-01-01

    We present the results of a mid-infrared survey of II outer Galaxy massive star-forming regions and 3 open clusters with data from the Wide-field Infrared Survey Explorer (WISE). Using a newly developed photometric scheme to identify young stellar objects and exclude extragalactic contamination, we have studied the distribution of young stars within each region. These data tend to support the hypothesis that latter generations may be triggered by the interaction of winds and radiation from the first burst of massive star formation with the molecular cloud material leftover from that earlier generation of stars. We dub this process the "fireworks hypothesis" since star formation by this mechanism would proceed rapidly and resemble a burst of fireworks. We have also analyzed small cutout WISE images of the structures around the edges of these massive star-forming regions. We observe large (1-3 pc size) pillar and trunk-like structures of diffuse emission nebulosity tracing excited polycyclic aromatic hydrocarbon molecules and small dust grains at the perimeter of the massive star-forming regions. These structures contain small clusters of emerging Class I and Class II sources, but some are forming only a single to a few new stars.

  20. Wide-Field Infrared Survey Explorer Observations of the Evolution of Massive Star-Forming Regions

    NASA Technical Reports Server (NTRS)

    Koenig, X. P.; Leisawitz, D. T.; Benford, D. J.; Rebull, L. M.; Padgett, D. L.; Assef, R. J.

    2011-01-01

    We present the results of a mid-infrared survey of 11 outer Galaxy massive star-forming regions and 3 open clusters with data from the Wide-field Infrared Survey Explorer (WISE). Using a newly developed photometric scheme to identify young stellar objects and exclude extragalactic contamination, we have studied the distribution of young stars within each region. These data tend to support the hypothesis that latter generations may be triggered by the interaction of winds and radiation from the first burst of massive star formation with the molecular cloud material leftover from that earlier generation of stars.We dub this process the "fireworks hypothesis" since star formation by this mechanism would proceed rapidly and resemble a burst of fireworks.We have also analyzed small cutout WISE images of the structures around the edges of these massive star-forming regions. We observe large (1-3 pc size) pillar and trunk-like structures of diffuse emission nebulosity tracing excited polycyclic aromatic hydrocarbon molecules and small dust grains at the perimeter of the massive star-forming regions. These structures contain small clusters of emerging Class I and Class II sources, but some are forming only a single to a few new stars.

  1. First results from XILO: XMM-Newton Investigations in the Lambda Orionis star forming region

    NASA Astrophysics Data System (ADS)

    Stelzer, B.; Barrado y Navascues, D.; Huelamo, N.; Morales-Calderon, M.; Bayo, A.

    2010-11-01

    The λ Orionis star formation region (1-6 Myr, 400 pc) is a complex of star-forming clouds surrounded by a molecular ring with ~ 5° radius which was probably formed by a supernova explosion (Dolan & Mathieu 2002). For a complete picture of star formation, believed to be determined by the supernova blast, the large-scale distribution of the pre-main sequence population in λ Ori needs to be examined. We have embarked on a multi-wavelength study (XMM-Newton/X-ray, CFHT/optical, Spitzer/IR) of selected areas within this intriguing star-forming complex that enables us to identify young stars and brown dwarfs. Our study comprises various areas within the cloud complex as shown in Fig.1. This data set is among the most extended X-ray surveys carried out with XMM-Newton in a coherent star-forming environment. The XMM-Newton observations combined with optical and IR data reveal the low-mass stellar population down to ~ 0.4 M⊙. For this mass-limited sample, our preliminary analysis confirms the anomalously low disk-fraction of the central star cluster Coll 69, the Eastern extension of its low-mass population pointing towards B 35, and the concentration of young stars in front of B 35. The analysis of the ‘on-cloud field' of B 35 (white in the figure) will show if the cloud is currently forming stars. This will be crucial for determining the star-forming history in the whole λ Ori region.

  2. R Coronae Borealis Stars formed from Double White Dwarf Mergers

    NASA Astrophysics Data System (ADS)

    Staff, Jan E.; Herwig, F.; Menon, A.; Even, W.; Tohline, J.; Clayton, G.; Motl, P.; Fryer, C.; Geballe, T.

    2011-01-01

    R Coronae Borealis (RCB) stars are hydrogen-deficient variable stars that suddenly fade by several magnitudes at irregular intervals whereafter they gradually return to their original brightness over a period of some months. The origin of RCBs remain a mystery. It is often thought that they are the result of the merger of a He and a CO white dwarf, while the fading is thought to be due to the formation of dust blocking light from the star. We are working on revealing the secrets behind the origin of RCBs. Here we present the results of 3 dimensional hydrodynamic simulations of the merger of a double white dwarf system where total mass is 0.9 M⊙ and initial mass ratio is q=0.7. We use a zero-temperature plus ideal gas equation of state that allows for heating through shocks. These simulations allow us to follow the evolution of the system for 10-20 initial orbital periods (1000-2000 seconds), from the onset of mass-transfer to a point after merger when the combined object has settled into a nearly axisymmetric, rotationally flattened configuration. The final merged object from the hydrodynamics simulation is then used as input for a stellar evolution code where the object's evolution can be followed over a much longer (thermal and/or nuclear) timescale. A preliminary post-merger stellar evolution simulation shows how an initial configuration of a 0.7 CO WD surrounded by 0.3 M⊙ of dynamically accreted He evolves on a time scale of 105 years to the location of the RCB stars in the H-R diagram at an effective temperature Teff<7000 K and log L 4. We acknowledge support from NASA Astrophysics Theory Program grant number NNX10AC72G.

  3. OT2_fwyrowsk_3: A Water survey of massive star forming clumps in the inner Galaxy

    NASA Astrophysics Data System (ADS)

    Wyrowski, F.

    2011-09-01

    Water, as a dominant form of oxygen, the most abundant element in the universe after H and He, controls the chemistry of many other species. It is a unique diagnostic of warm gas and energetic processes taking place during star formation. We therefore propose to exploit the unique opportunity of Herschel to study water in large, statistically significant, flux limited samples of massive star forming regions detected in the recently completed ATLASGAL submm dust continuum survey of the inner Galactic plane. In the last years, our view of massive star forming regions has dramatically changed by Galactic plane surveys covering cm to IR wavelengths. These surveys enable us for the first time to study ALL evolutionary stages of massive star formation (MSF) in an unbiased way. Water, acting as a natural filter for warm, dense gas, allows to probe the chemical and physical conditions in all of these stages close to where the massive stars are forming or just have been formed. ATLASGAL observed submm dust continuum emission as best tracer of the earliest phases of MSF since it is directly probing the material from which the stars form. As a large unbiased survey it provide the statistical base to study the scarce and short-living protoclusters as the origin of the massive stars and the richest clusters in the Galaxy and supplies us with a legacy value sample of MSF regions for the water follow ups. Water is typically seen with strongly increased abundances in broad line wings, providing a new, sensitive probe of shocked outflowing gas. In addition, the envelope is probed in a combination of absorption and emission with a clear jump in abundance in the warm inner regions close to the forming massive stars. Only Herschel can provide a water survey of a large sample of ATLASGAL selected sources to study water through the evolution of massive star forming regions with a statistically significant sample size.

  4. Cosmic-Ray Injection from Star-Forming Regions

    NASA Astrophysics Data System (ADS)

    Carlson, Eric; Profumo, Stefano; Linden, Tim

    2016-09-01

    At present, all physical models of diffuse Galactic γ -ray emission assume that the distribution of cosmic-ray sources traces the observed populations of either OB stars, pulsars, or supernova remnants. However, since H2 -rich regions host significant star formation and numerous supernova remnants, the morphology of observed H2 gas (as traced by CO line surveys) should also provide a physically motivated, high-resolution tracer for cosmic-ray injection. We assess the impact of utilizing H2 as a tracer for cosmic-ray injection on models of diffuse Galactic γ -ray emission. We employ state-of-the-art 3D particle diffusion and gas density models, along with a physical model for the star-formation rate based on global Schmidt laws. Allowing a fraction, fH2,of cosmic-ray sources to trace the observed H2 density, we find that a theoretically well-motivated value fH 2˜0.20 - 0.25 (i) provides a significantly better global fit to the diffuse Galactic γ -ray sky and (ii) highly suppresses the intensity of the residual γ -ray emission from the Galactic center region. Specifically, in models utilizing our best global fit values of fH2˜0.20 - 0.25 , the spectrum of the galactic center γ -ray excess is drastically affected, and the morphology of the excess becomes inconsistent with predictions for dark matter annihilation.

  5. Cosmic-Ray Injection from Star-Forming Regions.

    PubMed

    Carlson, Eric; Profumo, Stefano; Linden, Tim

    2016-09-09

    At present, all physical models of diffuse Galactic γ-ray emission assume that the distribution of cosmic-ray sources traces the observed populations of either OB stars, pulsars, or supernova remnants. However, since H_{2}-rich regions host significant star formation and numerous supernova remnants, the morphology of observed H_{2} gas (as traced by CO line surveys) should also provide a physically motivated, high-resolution tracer for cosmic-ray injection. We assess the impact of utilizing H_{2} as a tracer for cosmic-ray injection on models of diffuse Galactic γ-ray emission. We employ state-of-the-art 3D particle diffusion and gas density models, along with a physical model for the star-formation rate based on global Schmidt laws. Allowing a fraction, f_{H_{2}}, of cosmic-ray sources to trace the observed H_{2} density, we find that a theoretically well-motivated value f_{H_{2}}∼0.20-0.25 (i) provides a significantly better global fit to the diffuse Galactic γ-ray sky and (ii) highly suppresses the intensity of the residual γ-ray emission from the Galactic center region. Specifically, in models utilizing our best global fit values of f_{H_{2}}∼0.20-0.25, the spectrum of the galactic center γ-ray excess is drastically affected, and the morphology of the excess becomes inconsistent with predictions for dark matter annihilation.

  6. Chromospheric Activity in Pre-Main-Sequence Stars

    NASA Astrophysics Data System (ADS)

    Simon, Theodore

    IUE observations of solar-type stars show a decline of chromospheric and TR emission with age. For main-sequence stars older than 100 million yr, this decay is exponential from a plateau defined by the youngest stars. At an age of ~1 million yr, the pre-main-sequence T Tauri stars have UV emission line fluxes some 2 orders of magnitude above the plateau for mainsequence stars. This suggests that chromospheric activity in the T Tauri stars falls to the levels of the older stars by a separate decay scheme. The decline in pre-mainsequence activity may be caused by the evolutionary shallowing of the convection zone, while on the main-sequence it is due to the star's spindown. This hypothesis needs confirmation, but relatively few T Tauri stars have been observed by IUE. Since the majority of the T Tauri stars thus far observed are probably more massive than the Sun, it may be inappropriate to compare their UV emission with that of the older I Mo dwarf stars. We propose here to observe the ultraviolet chromospheric and TR lines of pre-main-sequence stars we believe to be of ~1 M(sun). We have chosen a sample of low-luminosity M-type T Tauri stars from the T-associations in Lupus; if evolutionary tracks have any validity, a large fraction of those stars should be close to 1 M(sun)in mass. In order to place the stars more accurately on the H-R diagram and to determine their rotation rates (for comparison with the mainsequence stars), we plan concurrent visual spectroscopy and visual-infrared photometry.

  7. Ionized gas outflows and global kinematics of low-z luminous star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Arribas, S.; Colina, L.; Bellocchi, E.; Maiolino, R.; Villar-Martín, M.

    2014-08-01

    We study the kinematic properties of the ionised gas outflows and ambient interstellar medium (ISM) in a large and representative sample of local luminous and ultra-luminous infrared galaxies (U/LIRGs) (58 systems, 75 galaxies) at galactic and sub-galactic (i.e., star-forming clumps) scales, thanks to integral field spectroscopy (IFS)-based high signal-to-noise integrated spectra. The velocity dispersion of the ionized ISM in U/LIRGs (⟨ σ ⟩ ~ 70 km s-1) is larger than in lower luminosity local star-forming galaxies (⟨ σ ⟩ ~ 25 km s-1). While for isolated disc LIRGs star formation appears to sustain turbulence, gravitational energy release associated with interactions and mergers plays an important role in driving σ in the U/LIRG range. We find that σ has a dependency on the star formation rate density (ΣSFR), which is weaker than expected if it were driven by the energy released by the starburst. The relatively small role of star formation (SF) driving the σ in U/LIRGs is reinforced by the lack of an increase in σ associated with high luminosity SF clumps. We also find that the impact of an active galactic nucleus (AGN) in ULIRGs is strong, increasing on average σ by a factor 1.5. Low-z U/LIRGs cover a range of velocity dispersion (σ ~ 30 to 100 km s-1) and star formation rate density (ΣSFR ~ 0.1 to 20 M⊙ yr-1 kpc-2) similar to those of high-z SFGs. Moreover, the observed weak dependency of σ on ΣSFR for local U/LIRGs (σ ∝ ΣSFR+0.06) is in very good agreement with that measured in some high-z samples. The presence of ionized gas outflows in U/LIRGs seems universal based on the detection of a broad, usually blueshifted, Hα line. The observed dependency of the maximum velocity of the outflow (Vmax) on the star formation rate (SFR) is of the type Vmax(non - AGN) ∝ SFR(LIR)+ 0.24. We find that AGNs in U/LIRGs are able to generate faster (~×2) and more massive (~× 1.4) ionized gas outflows than pure starbursts. The derived ionized mass

  8. Millimetre spectral line mapping observations towards four massive star-forming H II regions

    NASA Astrophysics Data System (ADS)

    Li, Shanghuo; Wang, Junzhi; Zhang, Zhi-Yu; Fang, Min; Li, Juan; Zhang, Jiangshui; Fan, Junhui; Zhu, Qingfeng; Li, Fei

    2017-04-01

    We present spectral line mapping observations towards four massive star-forming regions - Cepheus A, DR21S, S76E and G34.26+0.15 - with the IRAM 30-m telescope at the 2 and 3 mm bands. In total, 396 spectral lines from 51 molecules, one helium recombination line, 10 hydrogen recombination lines and 16 unidentified lines were detected in these four sources. An emission line of nitrosyl cyanide (ONCN, 140, 14-130, 13) was detected in G34.26+0.15, as the first detection in massive star-forming regions. We found that c-C3H2 and NH2D show enhancement in shocked regions, as suggested by the evidence of SiO and/or SO emission. The column density and rotational temperature of CH3CN were estimated with the rotational diagram method for all four sources. Isotope abundance ratios of 12C/13C were derived using HC3N and its 13C isotopologue, which were around 40 in all four massive star-forming regions and slightly lower than the local interstellar value (∼65). The 14N/15N and 16O/18O abundance ratios in these sources were also derived using the double isotopic method, which were slightly lower than in the local interstellar medium. Except for Cep A, the 33S/34S ratios in the other three targets were derived, which were similar to that in the local interstellar medium. The column density ratios of N(DCN)/N(HCN) and N(DCO+)/N(HCO+) in these sources were more than two orders of magnitude higher than the elemental [D]/[H] ratio, which is 1.5 × 10-5. Our results show that the later stage sources, G34.26+0.15 in particular, present more molecular species than earlier stage sources. Evidence of shock activity is seen in all stages studied.

  9. High molecular gas fractions in normal massive star-forming galaxies in the young Universe.

    PubMed

    Tacconi, L J; Genzel, R; Neri, R; Cox, P; Cooper, M C; Shapiro, K; Bolatto, A; Bouché, N; Bournaud, F; Burkert, A; Combes, F; Comerford, J; Davis, M; Schreiber, N M Förster; Garcia-Burillo, S; Gracia-Carpio, J; Lutz, D; Naab, T; Omont, A; Shapley, A; Sternberg, A; Weiner, B

    2010-02-11

    Stars form from cold molecular interstellar gas. As this is relatively rare in the local Universe, galaxies like the Milky Way form only a few new stars per year. Typical massive galaxies in the distant Universe formed stars an order of magnitude more rapidly. Unless star formation was significantly more efficient, this difference suggests that young galaxies were much more molecular-gas rich. Molecular gas observations in the distant Universe have so far largely been restricted to very luminous, rare objects, including mergers and quasars, and accordingly we do not yet have a clear idea about the gas content of more normal (albeit massive) galaxies. Here we report the results of a survey of molecular gas in samples of typical massive-star-forming galaxies at mean redshifts of about 1.2 and 2.3, when the Universe was respectively 40% and 24% of its current age. Our measurements reveal that distant star forming galaxies were indeed gas rich, and that the star formation efficiency is not strongly dependent on cosmic epoch. The average fraction of cold gas relative to total galaxy baryonic mass at z = 2.3 and z = 1.2 is respectively about 44% and 34%, three to ten times higher than in today's massive spiral galaxies. The slow decrease between z approximately 2 and z approximately 1 probably requires a mechanism of semi-continuous replenishment of fresh gas to the young galaxies.

  10. On the onset of secondary stellar generations in giant star-forming regions and massive star clusters

    SciTech Connect

    Palouš, J.; Wünsch, R.; Tenorio-Tagle, G.

    2014-09-10

    Here we consider the strong evolution experienced by the matter reinserted by massive stars, both in giant star-forming regions driven by a constant star formation rate and in massive and coeval superstar clusters. In both cases we take into consideration the changes induced by stellar evolution on the number of massive stars, the number of ionizing photons, and the integrated mechanical luminosity of the star-forming regions. The latter is at all times compared with the critical luminosity that defines, for a given size, the lower mechanical luminosity limit above which the matter reinserted via strong winds and supernova explosions suffers frequent and recurrent thermal instabilities that reduce its temperature and pressure and inhibit its exit as part of a global wind. Instead, the unstable reinserted matter is compressed by the pervasive hot gas, and photoionization maintains its temperature at T ∼ 10{sup 4} K. As the evolution proceeds, more unstable matter accumulates and the unstable clumps grow in size. Here we evaluate the possible self-shielding of thermally unstable clumps against the UV radiation field. Self-shielding allows for a further compression of the reinserted matter, which rapidly develops a high-density neutral core able to absorb in its outer skin the incoming UV radiation. Under such conditions the cold (T ∼ 10 K) neutral cores soon surpass the Jeans limit and become gravitationally unstable, creating a new stellar generation with the matter reinserted by former massive stars. We present the results of several calculations of this positive star formation feedback scenario promoted by strong radiative cooling and mass loading.

  11. On the Onset of Secondary Stellar Generations in Giant Star-forming Regions and Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    Palouš, J.; Wünsch, R.; Tenorio-Tagle, G.

    2014-09-01

    Here we consider the strong evolution experienced by the matter reinserted by massive stars, both in giant star-forming regions driven by a constant star formation rate and in massive and coeval superstar clusters. In both cases we take into consideration the changes induced by stellar evolution on the number of massive stars, the number of ionizing photons, and the integrated mechanical luminosity of the star-forming regions. The latter is at all times compared with the critical luminosity that defines, for a given size, the lower mechanical luminosity limit above which the matter reinserted via strong winds and supernova explosions suffers frequent and recurrent thermal instabilities that reduce its temperature and pressure and inhibit its exit as part of a global wind. Instead, the unstable reinserted matter is compressed by the pervasive hot gas, and photoionization maintains its temperature at T ~ 104 K. As the evolution proceeds, more unstable matter accumulates and the unstable clumps grow in size. Here we evaluate the possible self-shielding of thermally unstable clumps against the UV radiation field. Self-shielding allows for a further compression of the reinserted matter, which rapidly develops a high-density neutral core able to absorb in its outer skin the incoming UV radiation. Under such conditions the cold (T ~ 10 K) neutral cores soon surpass the Jeans limit and become gravitationally unstable, creating a new stellar generation with the matter reinserted by former massive stars. We present the results of several calculations of this positive star formation feedback scenario promoted by strong radiative cooling and mass loading.

  12. Tracing the Far-Infrared Roles of AGN in Dusty Star-Forming Galaxies

    NASA Astrophysics Data System (ADS)

    Brown, Arianna; Nayyeri, Hooshang; Cooray, Asantha R.; Mitchell-Wynne, Ketron

    2017-01-01

    Active galactic nuclei (AGNs) are suggested to play an important role in quenching their host galaxy’s star formation rate (SFR) by heating up and/or consuming the cool gas necessary to create stars. This mechanism is theorized as a critical step in AGN evolutionary models. The efforts to study this effect suffer in part from low-number statistics at high x-ray luminosities (LXR > 1044 ergs/s) for AGNs at z≈1-3, and a lack of separately estimated SFRs for AGN in dusty, star-forming galaxies (DSFGs). In this work, we extend our analysis to build a more complete picture using the variety of available multi-wavelength data in the XBoötes region. The Chandra XBoötes Survey is a 5-ks X-ray survey of the 9.3 square degree Boötes Field of the NOAO Deep Wide-Field Survey, a survey imaged from the optical to the near-IR. We estimate AGN spectral energy distributions and SFRs for ~400 x-ray sources using available data in all four Spitzer IRAC bands, the Spitzer MIPS 24µm band, all five Herschel SPIRE and PACS bands, along with NEWFIRM optical bands. Preliminary results show an exponential correlation between x-ray luminosity and star formation. As a comparison, we will use a stacking technique for the ~500 x-ray sources that were not detected at submillimeter wavelengths, where sources are binned by x-ray luminosity. We will compare these two samples and expect to see a difference in slope. Using these techniques, we hope to place tighter constraints on the mean SFRs of high-luminosity AGNs inside DSFGs, and determine if x-ray luminosities are independent of average SFRs for our sample in the Boötes field.

  13. The growth of the central region by acquisition of counterrotating gas in star-forming galaxies.

    PubMed

    Chen, Yan-Mei; Shi, Yong; Tremonti, Christy A; Bershady, Matt; Merrifield, Michael; Emsellem, Eric; Jin, Yi-Fei; Huang, Song; Fu, Hai; Wake, David A; Bundy, Kevin; Stark, David; Lin, Lihwai; Argudo-Fernandez, Maria; Bergmann, Thaisa Storchi; Bizyaev, Dmitry; Brownstein, Joel; Bureau, Martin; Chisholm, John; Drory, Niv; Guo, Qi; Hao, Lei; Hu, Jian; Li, Cheng; Li, Ran; Lopes, Alexandre Roman; Pan, Kai-Ke; Riffel, Rogemar A; Thomas, Daniel; Wang, Lan; Westfall, Kyle; Yan, Ren-Bin

    2016-10-19

    Galaxies grow through both internal and external processes. In about 10% of nearby red galaxies with little star formation, gas and stars are counter-rotating, demonstrating the importance of external gas acquisition in these galaxies. However, systematic studies of such phenomena in blue, star-forming galaxies are rare, leaving uncertain the role of external gas acquisition in driving evolution of blue galaxies. Here, based on new measurements with integral field spectroscopy of a large representative galaxy sample, we find an appreciable fraction of counter-rotators among blue galaxies (9 out of 489 galaxies). The central regions of blue counter-rotators show younger stellar populations and more intense, ongoing star formation than their outer parts, indicating ongoing growth of the central regions. The result offers observational evidence that the acquisition of external gas in blue galaxies is possible; the interaction with pre-existing gas funnels the gas into nuclear regions (<1 kpc) to form new stars.

  14. Dust Content of Virgo Star-Forming Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Grossi, M.; Hunt, L. K.; Madden, S.; Vlahakis, C.; Bomans, D. J.; Baes, M.; Bendo, G. J.; Bianchi, S.; Boselli, A.; Clemens, M.; Corbelli, E.; Cortese, L.; Dariush, A.; Davies, J. I.; De Looze, I.; di Serego Alighieri, S.; Fadda, D.; Fritz, J.; Garcia-Appadoo, D. A.; Gavazzi, G.; Giovanardi, C.; Hughes, T. M.; Jones, A. P.; Pierini, D.; Pohlen, M.; Sabatini, S.; Smith, M. W. L.; Verstappen, J.; Xilouris, E. M.; Zibetti, S.

    We investigate the dust properties of a small sample of Virgo cluster dwarf galaxies drawn from the science demonstration phase data set of the Herschel Virgo Cluster Survey (HeViCS). These galaxies have low metallicities (7.8 < 12 + log(O/H) < 8.3) and star formation rates ≲ 0.1 M⊙ yr-1. We measure the spectral energy distribution (SED) from 100 to 500 μm and derive dust temperatures and masses. The SEDs are fitted by a cool component with T ≲ 20 K, implying dust masses around 105 M⊙ and dust-to-gas ratios (D) within the range 10-3-10-2.

  15. Complex organic molecules toward low-mass and high-mass star forming regions

    NASA Astrophysics Data System (ADS)

    Favre, C.; Ceccarelli, C.; Lefloch, B.; Bergin, E.; Carvajal, M.; Brouillet, N.; Despois, D.; Jørgensen, J.; Kleiner, I.

    2016-12-01

    One of the most important questions in molecular astrophysics is how, when, and where complex organic molecules, COMs (≥ 6 atoms) are formed. In the Interstellar-Earth connection context, could this have a bearing on the origin of life on Earth? Formation mechanisms of COMs, which include potentially prebiotic molecules, are still debated and may include grain-mantle and/or gas-phase chemistry. Understanding the mechanisms that lead to the interstellar molecular complexification, along with the involved physicochemical processes, is mandatory to answer the above questions. In that context, active researches are ongoing in theory, laboratory experiment, chemical modeling and observations. Thanks to recent progress in radioastronomy instrumentation for both single-dish and millimeter array (e.g. Herschel, NOEMA, ALMA), new results have been obtained. I will review some notable results on the detection of COMs, including prebiotic molecules, towards star forming regions.

  16. Planck's Dusty GEMS: Measuring the AGN Contribution in the Brightest z 3 Star-Forming Galaxies in the Sky

    NASA Astrophysics Data System (ADS)

    Chary, Ranga-Ram

    Hyperluminous (>1E13 Lsun) infrared galaxies detected at submillimeter wavelengths are among the most intense, star-forming galaxies in the Universe. Although they show signs of AGN activity in the X-rays and the mid-infrared, it is generally thought that their bolometric luminosity, most of which is emitted in the far-infrared, is dominated by star-formation and not by the AGN. Here, we propose to measure the AGN contribution in a population of high redshift (z 3) submillimeter galaxies detected through the Planck all sky survey which have been greatly amplified through gravitational lensing by a foreground galaxy. The SOFIA data bridge the gap in wavelength coverage that exists between the WISE 22 micron and Herschel 250 micron data - this is crucial for sampling the hot dust emission from a buried AGN and deriving robust bolometric luminosities. Our observations will also characterize the multiple components of thermal dust emission to critically assess the canonical view that high redshift starbursts appear to show a limited range of spectral energy distribution (SED) shapes in the far-infrared that is distinct from the SED of main-sequence star-forming galaxies. Since these SEDs have been the benchmark for characterizing the unlensed star-forming, submillimeter galaxy (SMG) population, the proposed observations will have an impact not just on our target sample but on the derived properties of the SMG population as a whole, such as their star-formation rate and gas/dust mass.

  17. Star forming regions in gas-rich SO galaxies

    NASA Technical Reports Server (NTRS)

    Pogge, Richard W.; Eskridge, Paul B.

    1987-01-01

    The first results of an H alpha imaging survey of HI rich SO galaxies, which were searched for HII regions and other sources of emission, are presented. The charge coupled device H alpha interference filter images were made of 16 galaxies. Eight of these galaxies show evidence for on-going star formation, one has nuclear emission but no HII regions, and the remaining seven have no emissions detected within well defined upper limits. With the exception of one notably peculiar galaxy in which the emission from HII regions appears pervasive, the HII regions are either organized into inner-disk rings or randomly distributed throughout the disk. A few of these galaxies are found to be clearly not SO's; or peculiar objects atypical of the SO class. Using simple models star formation rates (SFRs) and gas depletion times from the observed H alpha fluxes were estimated. In general, the derived SFRs are much lower than those found in isolated field spiral galaxies and the corresponding gas depletion time scales are also longer.

  18. VizieR Online Data Catalog: Star-forming compact groups (Hernandez-Fernandez+, 2015)

    NASA Astrophysics Data System (ADS)

    Hernandez-Fernandez, J. D.; Mendes de Oliveira, C.

    2016-03-01

    This article provides a local sample (z<~0.15) of compact groups of star-forming galaxies. In this type of groups, galaxies strongly interact among themselves and with the rest of the group components (ICM, dark matter halo). This induces morphological changes and star formation events which are currently taking place. The peculiar evolutionary stage of these groups provides a wealth of galaxy observables that may clarify the theoretical framework about galaxy evolution in groups. We have performed an all-sky search for compact groups of star-forming galaxies in the GALEX UV catalogues. (3 data files).

  19. Chromospheric Activity in Cool Stars: Open Questions

    NASA Astrophysics Data System (ADS)

    Schröder, K.-P.; Schmitt, J. H. M. M.

    2013-04-01

    Despite a wealth of observational insight into chromospheric physics obtained in the past decades, a number of fundamental questions remain to be answered. On some of them we seem to make progress, others are motivation for ongoing research: is there a well-defined “zero-point” of magnetic stellar activity, and by which heating processes is the basal chromospheric flux created? Or: how did the Sun look like during the Maunder Minimum, and when is the next one due? And are activity cycles of cool giants caused by a solar-type dynamo, despite a very different internal structure? What makes magnetic stellar activity be still (or again?) at work in such very evolved stars — should not all angular momentum have been consumed? To find some answers, the Hamburg Robotic Telescope, equipped with a high-resolution (20,000) spectrograph, will start regular operation at its final site in Guanajuato, central Mexico, this year (2012), in part to resume the legendary Mt. Wilson stellar activity monitoring project.

  20. RECONCILING THE OBSERVED STAR-FORMING SEQUENCE WITH THE OBSERVED STELLAR MASS FUNCTION

    SciTech Connect

    Leja, Joel; Van Dokkum, Pieter G.; Franx, Marijn; Whitaker, Katherine E.

    2015-01-10

    We examine the connection between the observed star-forming sequence (SFR ∝ M {sup α}) and the observed evolution of the stellar mass function in the range 0.2 < z < 2.5. We find that the star-forming sequence cannot have a slope α ≲ 0.9 at all masses and redshifts because this would result in a much higher number density at 10 < log (M/M {sub ☉}) < 11 by z = 1 than is observed. We show that a transition in the slope of the star-forming sequence, such that α = 1 at log (M/M {sub ☉}) < 10.5 and α = 0.7-0.13z (Whitaker et al.) at log (M/M {sub ☉}) > 10.5, greatly improves agreement with the evolution of the stellar mass function. We then derive a star-forming sequence that reproduces the evolution of the mass function by design. This star-forming sequence is also well described by a broken power law, with a shallow slope at high masses and a steep slope at low masses. At z = 2, it is offset by ∼0.3 dex from the observed star-forming sequence, consistent with the mild disagreement between the cosmic star formation rate (SFR) and recent observations of the growth of the stellar mass density. It is unclear whether this problem stems from errors in stellar mass estimates, errors in SFRs, or other effects. We show that a mass-dependent slope is also seen in other self-consistent models of galaxy evolution, including semianalytical, hydrodynamical, and abundance-matching models. As part of the analysis, we demonstrate that neither mergers nor hidden low-mass quiescent galaxies are likely to reconcile the evolution of the mass function and the star-forming sequence. These results are supported by observations from Whitaker et al.

  1. Deriving Dust Properties in Star Forming Clumps: a Look Across the Perseus Molecular Cloud with Herschel and SCUBA-2

    NASA Astrophysics Data System (ADS)

    Chen, Michael Chun-Yuan

    2015-04-01

    Herschel and JCMT surveys of nearby star-forming regions have provided excellent images of cold dust emission across several wavelengths with unprecedented dynamic range and resolutions. Here we present spectral emissivity index and temperature maps of dust in the star-forming clumps of the Perseus molecular cloud determined from fitting SEDs to the combined Herschel and JCMT observations in the 160 μm, 250 μm, 350 μm, 500 μm, and 850 μm bands, employing the technique developed by Sadavoy et al. (2013). In NGC1333, the most complex and active star-forming clump in Perseus, we demonstrate that CO line contamination in the JCMT SCUBA-2 850 μm band is typically insignificant. The derived spectral emissivity index, β, and dust temperature, T, ranges between 0.8 - 3.0 and 7 - 50 K, respectively. Throughout Perseus, we see indications of heating from B stars and embedded protostars, and smooth β variations on the smaller scales. The distribution of β values seen in each clump differs from one clump to another, and is in general different from the diffuse ISM values (i.e., ~2), suggesting that dust grain evolution is significant in star-forming clumps. We also found coincidences between low β regions and local temperature peaks as well as locations of outflows, which may provide hints to the origins of these low β value grains, and dust grain evolution in star-forming clumps in general.

  2. Physical Properties of Compact Star-forming Galaxies at z ˜ 2-3

    NASA Astrophysics Data System (ADS)

    Fang, Guanwen; Ma, Zhongyang; Kong, Xu; Fan, Lulu

    2015-07-01

    We present a study on the physical properties of compact star-forming galaxies (cSFGs) with M* ≥ 1010M⊙ and 2 ≤ z ≤ 3 in the COSMOS (Cosmic Evolution Survey) and GOODS-S (Great Observatories Origins Deep Survey South) fields. We find that massive cSFGs have a comoving number density of (1.0 ± 0.1) × 10-4 Mpc-3. The cSFGs are distributed at nearly the same locus on the main sequence as extended star-forming galaxies (eSFGs) and dominate the high-mass end. On the rest-frame U - V versus V-J and U-B versus {M}{{B}} diagrams, cSFGs are mainly distributed at the middle of eSFGs and compact quiescent galaxies (cQGs) in all colors, but are more inclined to “red sequence” than “green valley” galaxies. We also find that cSFGs have distributions similar to cQGs on the nonparametric morphology diagrams. The cQGs and cSFGs have larger Gini and smaller M20, while eSFGs have the reverse. About one-third of cSFGs show signatures of postmergers, and almost none of them can be recognized as disks. Moreover, those visually extended cSFGs all have lower Gini coefficients (Gini < 0.4), indicating that the Gini coefficient could be used to clean out noncompact galaxies in a sample of candidate cSFGs. The X-ray-detected counterparts are more frequent among cSFGs than in eSFGs and cQGs, implying that cSFGs have previously experienced violent gas-rich interactions (such as major mergers or disk instabilities), which could trigger both star formation and black hole growth in an active phase.

  3. MID-INFRARED SPECTROSCOPY OF TWO LENSED STAR-FORMING GALAXIES

    SciTech Connect

    Fadely, Ross; Baker, Andrew J.; Allam, Sahar S.; Lin Huan; Tucker, Douglas L.; Lutz, Dieter; Shapley, Alice E.; Shin, Min-Su; Smith, J. Allyn; Strauss, Michael A. E-mail: ajbaker@physics.rutgers.ed E-mail: hlin@fnal.go E-mail: lutz@mpe.mpg.d E-mail: msshin@umich.ed E-mail: strauss@astro.princeton.ed

    2010-11-01

    We present low-resolution, rest-frame {approx}5-12 {mu}m Spitzer/IRS spectra of two lensed z {approx} 2 UV-bright star-forming galaxies, SDSS J120602.09+514229.5 and SDSS J090122.37+181432.3. Using the magnification boost from lensing, we are able to study the physical properties of these objects in greater detail than is possible for unlensed systems. In both targets, we detect strong polycyclic aromatic hydrocarbon (PAH) emission at 6.2, 7.7, and 11.3 {mu}m, indicating the presence of vigorous star formation. For J1206, we find a steeply rising continuum and significant [S IV] emission, suggesting that a moderately hard radiation field is powering continuum emission from small dust grains. The strength of the [S IV] emission also implies a sub-solar metallicity of {approx}0.5 Z{sub sun}, confirming published rest-frame optical measurements. In J0901, the PAH lines have large rest-frame equivalent widths (>1 {mu}m) and the continuum rises slowly with wavelength, suggesting that any active galactic nucleus (AGN) contribution to L{sub IR} is insignificant, in contrast to the implications of optical emission-line diagnostics. Using [O III] line flux as a proxy for AGN strength, we estimate that the AGN in J0901 provides only a small fraction of its mid-infrared continuum flux. By combining the detection of [Ar II] with an upper limit on [Ar III] emission, we infer a metallicity of {approx}>1.3 Z{sub sun}. This work highlights the importance of combining rest-frame optical and mid-IR spectroscopy in order to understand the detailed properties of star-forming galaxies at high redshift.

  4. Did the Solar system form in a sequential triggered star formation event?

    NASA Astrophysics Data System (ADS)

    Parker, Richard J.; Dale, James E.

    2016-02-01

    The presence and abundance of the short-lived radioisotopes (SLRs) 26Al and 60Fe during the formation of the Solar system is difficult to explain unless the Sun formed in the vicinity of one or more massive star(s) that exploded as supernovae. Two different scenarios have been proposed to explain the delivery of SLRs to the protosolar nebula: (i) direct pollution of the protosolar disc by supernova ejecta, and (ii) the formation of the Sun in a sequential star formation event in which supernovae shockwaves trigger further star formation which is enriched in SLRs. The sequentially triggered model has been suggested as being more astrophysically likely than the direct pollution scenario. In this paper, we investigate this claim by analysing a combination of N-body and smoothed particle hydrodynamics simulations of star formation. We find that sequential star formation would result in large age spreads (or even bi-modal age distributions for spatially coincident events) due to the dynamical relaxation of the first star formation event(s). Secondly, we discuss the probability of triggering spatially and temporally discrete populations of stars and find this to be only possible in very contrived situations. Taken together, these results suggest that the formation of the Solar system in a triggered star formation event is as improbable, if not more so, than the direct pollution of the protosolar disc by a supernova.

  5. Outflow Feedback Regulated Massive Star Formation in Parsec-Scale Cluster Forming Clumps

    SciTech Connect

    Wang, Peng; Li, Zhi-Yun; Abel, Tom; Nakamura, Fumitaka; /Niigata U.

    2010-02-15

    We investigate massive star formation in turbulent, magnetized, parsec-scale clumps of molecular clouds including protostellar outflow feedback using three dimensional numerical simulations of effective resolution 2048{sup 3}. The calculations are carried out using a block structured adaptive mesh refinement code that solves the ideal MHD equations including self-gravity and implements accreting sink particles. We find that, in the absence of regulation by magnetic fields and outflow feedback, massive stars form readily in a turbulent, moderately condensed clump of {approx} 1,600 M{sub {circle_dot}} (containing {approx} 10{sup 2} initial Jeans masses), along with a cluster of hundreds of lower mass stars. The massive stars are fed at high rates by (1) transient dense filaments produced by large-scale turbulent compression at early times, and (2) by the clump-wide global collapse resulting from turbulence decay at late times. In both cases, the bulk of the massive star's mass is supplied from outside a 0.1 pc-sized 'core' that surrounds the star. In our simulation, the massive star is clump-fed rather than core-fed. The need for large-scale feeding makes the massive star formation prone to regulation by outflow feedback, which directly opposes the feeding processes. The outflows reduce the mass accretion rates onto the massive stars by breaking up the dense filaments that feed the massive star formation at early times, and by collectively slowing down the global collapse that fuel the massive star formation at late times. The latter is aided by a moderate magnetic field of strength in the observed range (corresponding to a dimensionless clump mass-to-flux ratio {lambda} {approx} a few); the field allows the outflow momenta to be deposited more efficiently inside the clump. We conclude that the massive star formation in our simulated turbulent, magnetized, parsec-scale clump is outflow-regulated and clump-fed (ORCF for short). An important implication is that the

  6. The connection between galaxy environment and the luminosity function slopes of star-forming regions

    NASA Astrophysics Data System (ADS)

    Cook, David O.; Dale, Daniel A.; Lee, Janice C.; Thilker, David; Calzetti, Daniela; Kennicutt, Robert C.

    2016-11-01

    We present the first study of GALEX far-ultraviolet (FUV) luminosity functions of individual star-forming regions within a sample of 258 nearby galaxies spanning a large range in total stellar mass and star formation properties. We identify ˜65 000 star-forming regions (i.e. FUV sources), measure each galaxy's luminosity function, and characterize the relationships between the luminosity function slope (α) and several global galaxy properties. A final sample of 82 galaxies with reliable luminosity functions are used to define these relationships and represent the largest sample of galaxies with the largest range of galaxy properties used to study the connection between luminosity function properties and galaxy environment. We find that α correlates with global star formation properties, where galaxies with higher star formation rates and star formation rate densities (ΣSFR) tend to have flatter luminosity function slopes. In addition, we find that neither stochastic sampling of the luminosity function in galaxies with low-number statistics nor the effects of blending due to distance can fully account for these trends. We hypothesize that the flatter slopes in high ΣSFR galaxies is due to higher gas densities and higher star formation efficiencies which result in proportionally greater numbers of bright star-forming regions. Finally, we create a composite luminosity function composed of star-forming regions from many galaxies and find a break in the luminosity function at brighter luminosities. However, we find that this break is an artefact of varying detection limits for galaxies at different distances.

  7. Revealing the nature of star forming blue early-type galaxies at low redshift

    NASA Astrophysics Data System (ADS)

    George, Koshy; Zingade, Kshama

    2015-11-01

    Context. Star forming early-type galaxies with blue optical colours at low redshift can be used to test our current understanding of galaxy formation and evolution. Aims: We want to reveal the fuel and triggering mechanism for star formation in these otherwise passively evolving red and dead stellar systems. Methods: We undertook an optical and ultraviolet study of 55 star forming blue early-type galaxies, searching for signatures of recent interactions that could be driving the molecular gas into the galaxy and potentially triggering the star formation. Results: We report here our results on star forming blue early-type galaxies with tidal trails and in close proximity to neighbouring galaxies that are evidence of ongoing or recent interactions between galaxies. There are 12 galaxies with close companions with similar redshifts, among which two galaxies are having ongoing interactions that potentially trigger the star formation. Two galaxies show a jet feature that could be due to the complete tidal disruption of the companion galaxy. The interacting galaxies have high star formation rates and very blue optical colours. Galaxies with no companion could have undergone a minor merger in the recent past. Conclusions: The recent or ongoing interaction with a gas-rich neighbouring galaxy could be responsible for bringing cold gas to an otherwise passively evolving early-type galaxy. The sudden gas supply could trigger the star formation, eventually creating a blue early-type galaxy. The galaxies with ongoing tidal interaction are blue and star forming, thereby implying that blue early-type galaxies can exist even when the companion is on flyby so does not end up in a merger. Based on data compiled from Galaxy Zoo project, and the volunteers contribution are acknowledged at http://www.galaxyzoo.org/Volunteers.aspx

  8. Observational evidence for enhanced magnetic activity of superflare stars.

    PubMed

    Karoff, Christoffer; Knudsen, Mads Faurschou; De Cat, Peter; Bonanno, Alfio; Fogtmann-Schulz, Alexandra; Fu, Jianning; Frasca, Antonio; Inceoglu, Fadil; Olsen, Jesper; Zhang, Yong; Hou, Yonghui; Wang, Yuefei; Shi, Jianrong; Zhang, Wei

    2016-03-24

    Superflares are large explosive events on stellar surfaces one to six orders-of-magnitude larger than the largest flares observed on the Sun throughout the space age. Due to the huge amount of energy released in these superflares, it has been speculated if the underlying mechanism is the same as for solar flares, which are caused by magnetic reconnection in the solar corona. Here, we analyse observations made with the LAMOST telescope of 5,648 solar-like stars, including 48 superflare stars. These observations show that superflare stars are generally characterized by larger chromospheric emissions than other stars, including the Sun. However, superflare stars with activity levels lower than, or comparable to, the Sun do exist, suggesting that solar flares and superflares most likely share the same origin. The very large ensemble of solar-like stars included in this study enables detailed and robust estimates of the relation between chromospheric activity and the occurrence of superflares.

  9. Observational evidence for enhanced magnetic activity of superflare stars

    PubMed Central

    Karoff, Christoffer; Knudsen, Mads Faurschou; De Cat, Peter; Bonanno, Alfio; Fogtmann-Schulz, Alexandra; Fu, Jianning; Frasca, Antonio; Inceoglu, Fadil; Olsen, Jesper; Zhang, Yong; Hou, Yonghui; Wang, Yuefei; Shi, Jianrong; Zhang, Wei

    2016-01-01

    Superflares are large explosive events on stellar surfaces one to six orders-of-magnitude larger than the largest flares observed on the Sun throughout the space age. Due to the huge amount of energy released in these superflares, it has been speculated if the underlying mechanism is the same as for solar flares, which are caused by magnetic reconnection in the solar corona. Here, we analyse observations made with the LAMOST telescope of 5,648 solar-like stars, including 48 superflare stars. These observations show that superflare stars are generally characterized by larger chromospheric emissions than other stars, including the Sun. However, superflare stars with activity levels lower than, or comparable to, the Sun do exist, suggesting that solar flares and superflares most likely share the same origin. The very large ensemble of solar-like stars included in this study enables detailed and robust estimates of the relation between chromospheric activity and the occurrence of superflares. PMID:27009381

  10. The chemical composition of the Orion star forming region. II. Stars, gas, and dust: the abundance discrepancy conundrum

    NASA Astrophysics Data System (ADS)

    Simón-Díaz, S.; Stasińska, G.

    2011-02-01

    Aims: We re-examine the recombination/collisional emission line (RL/CEL) nebular abundance discrepancy problem in the light of recent high-quality abundance determinations in young stars in the Orion star-forming region. Methods: We re-evaluate the CEL and RL abundances of several elements in the Orion nebula and estimate the associated uncertainties, taking into account the uncertainties in the ionization correction factors for unseen ions. We estimate the amount of oxygen trapped in dust grains for several scenarios of dust formation. We compare the resulting gas+dust nebular abundances with the stellar abundances of a sample of 13 B-type stars from the Orion star-forming region (Ori OB1), analyzed in Papers I and III of this series. Results: We find that the oxygen nebular abundance based on recombination lines agrees much better with the stellar abundances than the one derived from the collisionally excited lines. This result calls for further investigation. If the CEL/RL abundance discrepancy were caused by temperature fluctuations in the nebula, as argued by some authors, the same kind of discrepancy should be seen for the other elements, such as C, N and Ne, which is not what we find in the present study. Another problem is that with the RL abundances, the energy balance of the Orion nebula is not well understood. We make some suggestions concerning the next steps to undertake to solve this problem.

  11. Multi-wavelength, Multi-scale Observations of Outflows in Star-Forming Regions

    NASA Astrophysics Data System (ADS)

    Plunkett, Adele Laurie Dennis

    During the early stages of star formation, an embedded protostar accretes mass and simultaneously expels mass and angular momentum in the form of a bipolar outflow. In the common case of clustered star formation, outflows likely impact their surrounding environment and influence subsequent star formation. Numerical simulations have shown that outflows can sustain turbulence and maintain a cluster in quasi-equilibrium; alternatively, it was proposed that outflows may trigger rather than regulate or inhibit star formation. Observations of outflows and their impact on clusters are challenging because they must probe spatial scales over several orders of magnitude --- from the size of a core (a few hundred AU, or N ~ 10-3 pc) to a cluster (a few pc) --- and previous works generally focused on one scale or the other. This thesis incorporates high-resolution, high-sensitivity interferometry observations (with millimeter/sub-millimeter wavelengths) complemented by observations obtained using single dish telescopes in order to assess molecular outflow properties and their cumulative impact in two young protostellar clusters: Serpens South and NGC 1333. Based on these case studies, I develop an evolutionary scenario for clustered star formation spanning the ages of the two clusters, about 0.1 - 1 Myr. Within this scenario, outflows in both Serpens South and NGC 1333 provide sufficient energy to sustain turbulence early in the protocluster formation process. In neither cluster do outflows provide enough energy to counter the gravitational potential energy and disrupt the entire cluster. However, most of the mass in outflows in both clusters have velocities greater than the escape velocity, and therefore the relative importance of outflow-driven turbulence compared with gravitational potential likely changes with time as ambient gas escapes. We estimate that enough gas mass will escape via outflows in Serpens South so that it will come to resemble NGC 1333 in terms of its

  12. Time-Resolved Spectroscopy of Active Binary Stars

    NASA Technical Reports Server (NTRS)

    Brown, Alexander

    2000-01-01

    This NASA grant covered EUVE observing and data analysis programs during EUVE Cycle 5 GO observing. The research involved a single Guest Observer project 97-EUVE-061 "Time-Resolved Spectroscopy of Active Binary Stars". The grant provided funding that covered 1.25 months of the PI's salary. The activities undertaken included observation planning and data analysis (both temporal and spectral). This project was awarded 910 ksec of observing time to study seven active binary stars, all but one of which were actually observed. Lambda-And was observed on 1997 Jul 30 - Aug 3 and Aug 7-14 for a total of 297 ksec; these observations showed two large complex flares that were analyzed by Osten & Brown (1999). AR Psc, observed for 350 ksec on 1997 Aug 27 - Sep 13, showed only relatively small flares that were also discussed by Osten & Brown (1999). EUVE observations of El Eri were obtained on 1994 August 24-28, simultaneous with ASCA X-ray spectra. Four flares were detected by EUVE with one of these also observed simultaneously, by ASCA. The other three EUVE observations were of the stars BY Dra (1997 Sep 22-28), V478 Lyr (1998 May 18-27), and sigma Gem (1998 Dec 10-22). The first two stars showed a few small flares. The sigma Gem data shows a beautiful complete flare with a factor of ten peak brightness compared to quiescence. The flare rise and almost all the decay phase are observed. Unfortunately no observations in other spectral regions were obtained for these stars. Analysis of the lambda-And and AR Psc observations is complete and the results were published in Osten & Brown (1999). Analysis of the BY Dra, V478 Lyr and sigma Gem EUVE data is complete and will be published in Osten (2000, in prep.). The El Eri EUV analysis is also completed and the simultaneous EUV/X-ray study will be published in Osten et al. (2000, in prep.). Both these latter papers will be submitted in summer 2000. All these results will form part of Rachel Osten's PhD thesis.

  13. YOUNG STELLAR OBJECTS IN THE MASSIVE STAR-FORMING REGION W49

    SciTech Connect

    Saral, G.; Hora, J. L.; Willis, S. E.; Koenig, X. P.; Gutermuth, R. A.; Saygac, A. T.

    2015-11-01

    We present the initial results of our investigation of the star-forming complex W49, one of the youngest and most luminous massive star-forming regions in our Galaxy. We used Spitzer/Infrared Array Camera (IRAC) data to investigate massive star formation with the primary objective of locating a representative set of protostars and the clusters of young stars that are forming around them. We present our source catalog with the mosaics from the IRAC data. In this study we used a combination of IRAC, MIPS, Two Micron All Sky Survey, and UKIRT Deep Infrared Sky Survey (UKIDSS) data to identify and classify the young stellar objects (YSOs). We identified 232 Class 0/I YSOs, 907 Class II YSOs, and 74 transition disk candidate objects using color–color and color–magnitude diagrams. In addition, to understand the evolution of star formation in W49, we analyzed the distribution of YSOs in the region to identify clusters using a minimal spanning tree method. The fraction of YSOs that belong to clusters with ≥7 members is found to be 52% for a cutoff distance of 96″, and the ratio of Class II/I objects is 2.1. We compared the W49 region to the G305 and G333 star-forming regions and concluded that W49 has the richest population, with seven subclusters of YSOs.

  14. HYDROGEN FLUORIDE IN HIGH-MASS STAR-FORMING REGIONS

    SciTech Connect

    Emprechtinger, M.; Monje, R. R.; Lis, D. C.; Phillips, T. G.; Van der Tak, F. F. S.; Van der Wiel, M. H. D.; Neufeld, D.; Ceccarelli, C.

    2012-09-10

    Hydrogen fluoride (HF) has been established to be an excellent tracer of molecular hydrogen in diffuse clouds. In denser environments, however, the HF abundance has been shown to be approximately two orders of magnitude lower. We present Herschel/HIFI observations of HF J = 1-0 toward two high-mass star formation sites, NGC 6334 I and AFGL 2591. In NGC 6334 I the HF line is seen in absorption in foreground clouds and the source itself, while in AFGL 2591 HF is partially in emission. We find an HF abundance with respect to H{sub 2} of 1.5 Multiplication-Sign 10{sup -8} in the diffuse foreground clouds, whereas in the denser parts of NGC 6334 I we derive a lower limit on the HF abundance of 5 Multiplication-Sign 10{sup -10}. Lower HF abundances in dense clouds are most likely caused by freezeout of HF molecules onto dust grains in high-density gas. In AFGL 2591, the view of the hot core is obstructed by absorption in the massive outflow, in which HF is also very abundant (3.6 Multiplication-Sign 10{sup -8}) due to the desorption by sputtering. These observations provide further evidence that the chemistry of interstellar fluorine is controlled by freezeout onto gas grains.

  15. The HNC/HCN ratio in star-forming regions

    SciTech Connect

    Graninger, Dawn M.; Öberg, Karin I.; Herbst, Eric; Vasyunin, Anton I.

    2014-05-20

    HNC and HCN, typically used as dense gas tracers in molecular clouds, are a pair of isomers that have great potential as a temperature probe because of temperature dependent, isomer-specific formation and destruction pathways. Previous observations of the HNC/HCN abundance ratio show that the ratio decreases with increasing temperature, something that standard astrochemical models cannot reproduce. We have undertaken a detailed parameter study on which environmental characteristics and chemical reactions affect the HNC/HCN ratio and can thus contribute to the observed dependence. Using existing gas and gas-grain models updated with new reactions and reaction barriers, we find that in static models the H + HNC gas-phase reaction regulates the HNC/HCN ratio under all conditions, except for very early times. We quantitatively constrain the combinations of H abundance and H + HNC reaction barrier that can explain the observed HNC/HCN temperature dependence and discuss the implications in light of new quantum chemical calculations. In warm-up models, gas-grain chemistry contributes significantly to the predicted HNC/HCN ratio and understanding the dynamics of star formation is therefore key to model the HNC/HCN system.

  16. Do All Stars Form in Clusters?: Masses and Ages of Young Supergiants in Andromeda

    NASA Astrophysics Data System (ADS)

    Choudhury, Zareen; Debs, C.; Kirby, E. N.; Guhathakurta, P.

    2013-01-01

    Currently it is not understood whether seemingly isolated stars formed in situ or were ejected from star clusters as runaway stars. Previous studies determined the origins of isolated stars by measuring their velocities, but past research was limited to OB stars in the Milky Way and Magellanic Clouds due to the difficulty of computing velocities of distant objects. This study proposed an innovative velocity test to statistically determine whether six seemingly isolated BA-type supergiants in Andromeda are runaways. We calculated the minimum relative transverse velocity needed for each supergiant to travel to its current location from the nearest open cluster. By comparing the minimum velocity with Andromeda’s known velocity dispersion, a statistical measure of the stars’ actual velocities, we determined whether the star had the necessary velocity to be a runaway. Minimum velocity was computed from the age of the star, which was calculated from its effective temperature and surface gravity. To compute effective temperature and surface gravity, we applied three new techniques based on Balmer absorption features. The results suggest that all six supergiants had the necessary velocities to be runaways. Although the proposed velocity test is a statistical assessment, it offers a valuable new tool for future investigation of isolated stars beyond the Milky Way and its satellites. This research was supported by the Science Internship Program (SIP) at UCSC, the National Science Foundation, NASA, and Palomar Observatory.

  17. Extreme infrared variables from UKIDSS - I. A concentration in star-forming regions

    NASA Astrophysics Data System (ADS)

    Contreras Peña, C.; Lucas, P. W.; Froebrich, D.; Kumar, M. S. N.; Goldstein, J.; Drew, J. E.; Adamson, A.; Davis, C. J.; Barentsen, G.; Wright, N. J.

    2014-04-01

    We present initial results of the first panoramic search for high-amplitude near-infrared variability in the Galactic plane. We analyse the widely separated two-epoch K-band photometry in the fifth and seventh data releases of the UKIDSS Galactic plane survey. We find 45 stars with ΔK > 1 mag, including two previously known OH/IR stars and a Nova. Even though the mid-plane is not yet included in the data set, we find the majority (66 per cent) of our sample to be within known star-forming regions (SFRs), with two large concentrations in the Serpens OB2 association (11 stars) and the Cygnus-X complex (12 stars). Sources in SFRs show spectral energy distributions that support classification as young stellar objects (YSOs). This indicates that YSOs dominate the Galactic population of high-amplitude infrared variable stars at low luminosities and therefore likely dominate the total high-amplitude population. Spectroscopic follow up of the DR5 sample shows at least four stars with clear characteristics of eruptive pre-main-sequence variables, two of which are deeply embedded. Our results support the recent concept of eruptive variability comprising a continuum of outburst events with different time-scales and luminosities, but triggered by a similar physical mechanism involving unsteady accretion. Also, we find what appears to be one of the most variable classical Be stars.

  18. New Insights on What, Where, and How Dust Forms in Evolved Stars

    NASA Astrophysics Data System (ADS)

    Cherchneff, I.; Sarangi, A.

    2017-02-01

    Sources of cosmic dust in our local and far universe include evolved low- and high-mass stars and core-collapse supernovae. These stellar environments, specifically the winds of stars and the material ejected by supernovae, are all characterized by high gas densities and temperatures typical of shocked regions. These conditions are necessary to the efficient formation of molecular clusters, and their growth through coalescence, coagulation and accretion to form dust grains. Recent observational data and theoretical models yield new insights of the processes that underpin dust formation. We review here the current knowledge on dust formation in stellar sources, including B[e] stars.

  19. Signatures of cool gas fueling a star-forming galaxy at redshift 2.3.

    PubMed

    Bouché, N; Murphy, M T; Kacprzak, G G; Péroux, C; Contini, T; Martin, C L; Dessauges-Zavadsky, M

    2013-07-05

    Galaxies are thought to be fed by the continuous accretion of intergalactic gas, but direct observational evidence has been elusive. The accreted gas is expected to orbit about the galaxy's halo, delivering not just fuel for star formation but also angular momentum to the galaxy, leading to distinct kinematic signatures. We report observations showing these distinct signatures near a typical distant star-forming galaxy, where the gas is detected using a background quasar passing 26 kiloparsecs from the host. Our observations indicate that gas accretion plays a major role in galaxy growth because the estimated accretion rate is comparable to the star-formation rate.

  20. Depletion in the Star-Forming Core IRAM04191

    NASA Astrophysics Data System (ADS)

    Wootten, A.; Mangum, J. G.; Wiseman, J.; Fuller, G. A.

    2002-12-01

    IRAM 04191+1522 numbers among the least evolved low mass protostars known. Belloche, André, Despois, and Blinder (Astronomy and Astrophysics, v393, 927, 2002) found the envelope to lie in a transition stage, with one portion showing constant rotational velocity mediated by magnetic braking and another inner region showing conserved angular momentum suggestive of protostellar collapse. Imaging of the interior 10000 AU in the ammonia lines (Wootten, Wiseman, and Fuller 2001, BAAS v33, 1394) revealed a 2100 AU region devoid of ammonia emission centered on the star. Here we present images made on similar scales with the OVRO Millimeter Array in the 1->0 lines of the molecular ions N2H+ and H13CO+. The former shows a ringlike structure coincident with the hole in the ammonia distribution. The latter shows only amorphous structure more distant from the central protostar. A sufficient explanation of these morphologies is that the nitrogen-bearing molecules vanish owing to depletion onto grains in the cold (13K) central region of high (n>1.5 x 106 cm-3) density. We expected that N2H+ should survive depletion to higher densities. If N2 is also depleted, as seems likely, kinematics of the central portion of this young protostar will be extremely difficult to measure. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Observations at the OVRO Millimeter Array are supported by the National Science Foundation under Grant No.9981546

  1. The complex high-mass star-forming region IRAS 15507-5359

    NASA Astrophysics Data System (ADS)

    Persi, P.; Tapia, M.; Roth, M.; Elia, D.; López-Vázquez, J. A.

    2016-06-01

    The far-infrared IRAS 15507-5359 source is known to be a medium-mass star-forming region associated with a compact H II region and a near-infrared embedded cluster. We present a survey of infrared-calibrated images ranging from 1.2 to 500 μm obtained with the Baade telescope at Las Campanas Observatory, and the Herschel space telescope with additional archive Spitzer data. We confirm the distance to the complex to be 5.0 kpc. Three Herschel far-infrared sources are found, I, II, III, identified with dense cores at different evolutionary stages. One (III) is a starless infrared dark cloud showing, near its edge, two infrared reflection nebulae (R1) and (R2) with dispersed young stellar populations, including a knot of shocked H2 line emission. Both show considerable polycyclic aromatic hydrocarbon emission. Core II has associated a radio H II region and a deeply embedded one-million-year-old cluster (Cl 1) that contains more than 45 young stellar objects, reddened by at least 20 visual magnitudes. About 20 per cent of them show considerable infrared excess emission. Core I appears void of a near-infrared population, and coincides with a long emission bar that resembles a photodissociation front. We determine the properties of the two most luminous Class I sources in the region by fitting models of young stars with accreting discs and envelopes to their 1-500 μm spectral energy distributions. This is another example of a medium-mass region with at least three well-defined active centres of star formation separated by about 1 pc and at different evolutionary stages.

  2. Non-linearity and environmental dependence of the star-forming galaxies main sequence

    NASA Astrophysics Data System (ADS)

    Erfanianfar, G.; Popesso, P.; Finoguenov, A.; Wilman, D.; Wuyts, S.; Biviano, A.; Salvato, M.; Mirkazemi, M.; Morselli, L.; Ziparo, F.; Nandra, K.; Lutz, D.; Elbaz, D.; Dickinson, M.; Tanaka, M.; Altieri, M. B.; Aussel, H.; Bauer, F.; Berta, S.; Bielby, R. M.; Brandt, N.; Cappelluti, N.; Cimatti, A.; Cooper, M. C.; Fadda, D.; Ilbert, O.; Le Floch, E.; Magnelli, B.; Mulchaey, J. S.; Nordon, R.; Newman, J. A.; Poglitsch, A.; Pozzi, F.

    2016-01-01

    Using data from four deep fields (COSMOS, AEGIS, ECDFS, and CDFN), we study the correlation between the position of galaxies in the star formation rate (SFR) versus stellar mass plane and local environment at z < 1.1. To accurately estimate the galaxy SFR, we use the deepest available Spitzer/MIPS 24 and Herschel/PACS data sets. We distinguish group environments (Mhalo ˜ 1012.5-14.2 M⊙) based on the available deep X-ray data and lower halo mass environments based on the local galaxy density. We confirm that the main sequence (MS) of star-forming galaxies is not a linear relation and there is a flattening towards higher stellar masses (M* > 1010.4-10.6 M⊙), across all environments. At high redshift (0.5 < z < 1.1), the MS varies little with environment. At low redshift (0.15 < z < 0.5), group galaxies tend to deviate from the mean MS towards the region of quiescence with respect to isolated galaxies and less-dense environments. We find that the flattening of the MS towards low SFR is due to an increased fraction of bulge-dominated galaxies at high masses. Instead, the deviation of group galaxies from the MS at low redshift is caused by a large fraction of red disc-dominated galaxies which are not present in the lower density environments. Our results suggest that above a mass threshold (˜1010.4-1010.6 M⊙) stellar mass, morphology and environment act together in driving the evolution of the star formation activity towards lower level. The presence of a dominating bulge and the associated quenching processes are already in place beyond z ˜1. The environmental effects appear, instead, at lower redshifts and have a long time-scale.

  3. a Census of Medium-Mass Star-Forming Regions Within 1 KPC

    NASA Astrophysics Data System (ADS)

    Barnes, Peter J.; Myers, Philip C.; Burton, Michael G.

    We have used 13CO to associate kinematic distances for a sample of prospective medium-mass star-forming regions in the southern Milky Way. This complements the equivalent northern survey already completed and we present a valuable new source list for galactic star formation studies comprising dozens of previously unrecognised such regions. We also present preliminary results of maps of C18O CS and/or NH3 emission from these sources and analysis of these sources' spectral energy distributions.

  4. The role of energetic processing on solid-phase chemistry in star forming regions

    NASA Astrophysics Data System (ADS)

    Palumbo, M. E.; Urso, R. G.; Kaňuchová, Z.; Scirè, C.; Accolla, M.; Baratta, G. A.; Strazzulla, G.

    2016-05-01

    It is generally accepted that complex molecules observed in star forming regions are formed in the solid phase on icy grain mantles and are released to the gas-phase after desorption of icy mantles. Most of our knowledge on the physical and chemical properties of ices in star forming regions is based on the comparison between observations and laboratory experiments performed at low temperature (10-100 K). Here we present some recent laboratory experiments which show the formation of (complex) molecular species after ion bombardment of simple ices.

  5. PLAYING WITH POSITIVE FEEDBACK: EXTERNAL PRESSURE-TRIGGERING OF A STAR-FORMING DISK GALAXY

    SciTech Connect

    Bieri, Rebekka; Dubois, Yohan; Silk, Joseph; Mamon, Gary A.

    2015-10-20

    In massive galaxies, the currently favored method for quenching star formation is via active galactic nuclei (AGN) feedback, which ejects gas from the galaxy using a central supermassive black hole. At high redshifts however, explanation of the huge rates of star formation often found in galaxies containing AGNs may require a more vigorous mode of star formation than is attainable by simply enriching the gas content of galaxies in the usual gravitationally driven mode that is associated with the nearby universe. Using idealized hydrodynamical simulations, we show that AGN-pressure-driven star formation potentially provides the positive feedback that may be required to generate the accelerated star formation rates observed in the distant universe.

  6. INTERACTIONS BETWEEN FORMING STARS AND DENSE GAS IN THE SMALL LOW-MASS CLUSTER CEDERBLAD 110

    SciTech Connect

    Ladd, E. F.; Wong, T.; Bourke, T. L.; Thompson, K. L.

    2011-12-20

    We present observations of dense gas and outflow activity in the Cederblad 110 region of the Chamaeleon I dark cloud complex. The region contains nine forming low-mass stars in evolutionary stages ranging from Class 0 to Class II/III crowded into a 0.2 pc region with high surface density ({Sigma}{sub YSO} {approx} 150 pc{sup -2}). The analysis of our N{sub 2}H{sup +} (J = 1{yields}0) maps indicates the presence of 13 {+-} 3 solar masses of dense (n {approx} 10{sup 5} cm{sup -3}) gas in this region, much of which is unstable against gravitational collapse. The most unstable material is located near the Class 0 source MMS-1, which is almost certainly actively accreting material from its dense core. Smaller column densities of more stable dense gas are found toward the region's Class I sources, IRS 4, 11, and 6. Little or no dense gas is colocated with the Class II and III sources in the region. The outflow from IRS 4 is interacting with the dense core associated with MMS-1. The molecular component of the outflow, measured in the (J = 1{yields}0) line of {sup 12}CO, appears to be deflected by the densest part of the core, after which it appears to plow through some of the lower column density portions of the core. The working surface between the head of the outflow lobe and the dense core material can be seen in the enhanced velocity dispersion of the dense gas. IRS 2, the Class III source that produces the optical reflection nebula that gives the Cederblad 110 region its name, may also be influencing the dense gas in the region. A dust temperature gradient across the MMS-1 dense core is consistent with warming from IRS 2, and a sharp gradient in dense gas column density may be caused by winds from this source. Taken together, our data indicate that this region has been producing several young stars in the recent past, and that sources which began forming first are interacting with the remaining dense gas in the region, thereby influencing current and future star

  7. Nearby Galaxy is a Hotbed of Star Birth Activity

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This new image taken with NASA's Hubble Space Telescope (HST) is of the nearby dwarf galaxy NGC 1569. This galaxy is a hotbed of vigorous star birth activity which blows huge bubbles that riddle its main body. The bubble structure is sculpted by the galactic super-winds and outflows caused by a colossal input of energy from collective supernova explosions that are linked with a massive episode of star birth. The bubbles seen in this image are made of hydrogen gas that glows when hit by the fierce wind and radiation from hot young stars and is racked by supernova shocks. Its 'star factories' are also manufacturing brilliant blue star clusters. NGC 1569 had a sudden onset of star birth about 25 million years ago, which subsided about the time the very earliest human ancestors appeared on Earth. The Marshall Space Flight Center had responsibility for the design, development, and construction of the HST.

  8. Spitzer Local Volume Legacy (LVL) Star-Forming Regions: Luminosity Functions

    NASA Astrophysics Data System (ADS)

    Cook, David O.; Dale, Daniel A.; Lee, Janice C.; LVL Team

    2015-01-01

    The conversion of gas into stars is one of the most fundamental processes in the universe, yet the effects of environmental conditions are poorly constrained. Observations of star-forming regions (young star clusters and HII regions) have shown evidence of a fractal pattern in their mass and luminosity distributions. The Mass Function (MF), and similarly the Luminosity Function (LF), of star-forming regions can be approximated as a power-law and is characterized by the power-law slope. A consistent slope of -2 has been observed across numerous galaxies, however, systematic deviations from this canonical slope have been measured across different environments. We present the LF slopes for 258 nearby galaxies in the Local Volume Legacy (LVL) sample utilizing tens of thousands of Hα- and FUV-selected sources. We test any relationships between LF slope and global galaxy properties to quantify the effect of environment on the star formation process. In addition, we combine the entire star-forming region sample in an attempt to characterize a previously proposed break in the HII region LF power-law at L˜38.6 erg/s.

  9. The star-forming history of the young cluster NGC 2264

    NASA Technical Reports Server (NTRS)

    Adams, M. T.; Strom, K. M.; Strom, S. E.

    1983-01-01

    UBVRI H-alpha photographic photometry was obtained for a sample of low-mass stars in the young open cluster NGC 2264 in order to investigate the star-forming history of this region. A theoretical H-R diagram was constructed for the sample of probable cluster members. Isochrones and evolutionary tracks were adopted from Cohen and Kuhi (1979). Evidence for a significant age spread in the cluster was found amounting to over ten million yr. In addition, the derived star formation rate as a function of stellar mass suggests that the principal star-forming mass range in NGC 2264 has proceeded sequentially in time from the lowest to the highest masses. The low-mass cluster stars were the first cluster members to form in significant numbers, although their present birth rate is much lower now than it was about ten million yr ago. The star-formation rate has risen to a peak at successively higher masses and then declined.

  10. Low Gas Fractions Connect Compact Star-Forming Galaxies to their z~2 Quiescent Descendants

    NASA Astrophysics Data System (ADS)

    Spilker, Justin; Bezanson, Rachel; Marrone, Daniel P.; Weiner, Benjamin J.; Whitaker, Katherine E.; Williams, Christina C.

    2017-01-01

    Early quiescent galaxies at z ~ 2 are known to be remarkably compact compared to their nearby counterparts. Possible progenitors of these systems include galaxies that are structurally similar, but are still rapidly forming stars. I will present Karl G. Jansky Very Large Array (VLA) observations of the CO(1-0) line towards three such compact, star-forming galaxies at z ~ 2.3, significantly detecting one. The VLA observations indicate baryonic gas fractions 5 times lower and gas depletion times 10 times shorter than normal, extended massive star-forming galaxies at these redshifts. At their current star formation rates, all three objects will deplete their gas reservoirs within 100Myr. These objects are among the most gas-poor objects observed at z > 2 and are outliers from standard gas scaling relations, a result which remains true regardless of assumptions about the CO-H2 conversion factor. Our observations are consistent with the idea that compact, star-forming galaxies are in a rapid state of transition to quiescence in tandem with the build-up of the z ~ 2 quenched population. In the detected compact galaxy, we see no evidence of rotation or that the CO-emitting gas is spatially extended relative to the stellar light. This casts doubt on recent suggestions that the gas in these compact galaxies is rotating and significantly extended compared to the stars. Instead, we suggest that, at least for this object, the gas is centrally concentrated, and only traces a small fraction of the total galaxy dynamical mass. I will conclude by discussing my ongoing efforts to characterize the gas and star forming properties of this unusual population of galaxies.

  11. The Quenched Mass Portion of Star-forming Galaxies and the Origin of the Star Formation Sequence Slope

    NASA Astrophysics Data System (ADS)

    Pan, Zhizheng; Zheng, Xianzhong; Kong, Xu

    2017-01-01

    Observationally, a massive disk galaxy can harbor a bulge component that is comparably inactive as a quiescent galaxy. It has been speculated that the quenched component contained in star-forming galaxies (SFGs) is the reason why the star formation main sequence (MS) has a shallow slope at high masses. In this paper, we present a toy model to quantify the quenched mass portion of SFGs (fQ) at fixed stellar mass (M*) and to reconcile the MS slopes in both the low- and the high-mass regimes. In this model, each SFG is composed of a star-forming plus a quenched component. The mass of the star-forming component (MSF) correlates with the star formation rate (SFR) following a relation SFR \\propto {M}{SF}{α {SF}}, where αSF ∼ 1.0. The quenched component contributes to the stellar mass but not to the SFR. It is thus possible to quantify fQ based on the departure of the observed MS slope α from αSF. Adopting the redshift-dependent MS slope reported by Whitaker et al., we explore the evolution of the {f}{{Q}}{--}{M}* relations over z = [0.5, 2.5]. We find that Milky Way-like SFGs (with {M}* ≈ {10}10.7 {M}ȯ ) typically have an fQ = 30%–40% at z ∼ 2.25, whereas this value rapidly rises up to 70%–80% at z ∼ 0.75. The origin of an α ∼ 1.0 MS slope seen in the low-mass regime is also discussed. We argue for a scenario in which the majority of low-mass SFGs stay in a “steady-stage” star formation phase. In this phase, the SFR is mainly regulated by stellar feedback and not significantly influenced by the quenching mechanisms, thus remaining roughly constant over cosmic time. This scenario successfully produces an α ∼ 1.0 MS slope, as well as the observed MS evolution from z = 2.5 to z = 0 at low masses.

  12. GOODS-Herschel: Star Formation, Dust Attenuation, and the FIR-radio Correlation on the Main Sequence of Star-forming Galaxies up to z ≃4

    NASA Astrophysics Data System (ADS)

    Pannella, M.; Elbaz, D.; Daddi, E.; Dickinson, M.; Hwang, H. S.; Schreiber, C.; Strazzullo, V.; Aussel, H.; Bethermin, M.; Buat, V.; Charmandaris, V.; Cibinel, A.; Juneau, S.; Ivison, R. J.; Le Borgne, D.; Le Floc'h, E.; Leiton, R.; Lin, L.; Magdis, G.; Morrison, G. E.; Mullaney, J.; Onodera, M.; Renzini, A.; Salim, S.; Sargent, M. T.; Scott, D.; Shu, X.; Wang, T.

    2015-07-01

    We use deep panchromatic data sets in the GOODS-N field, from GALEX to the deepest Herschel far-infrared (FIR) and VLA radio continuum imaging, to explore the evolution of star-formation activity and dust attenuation properties of star-forming galaxies to z ≃ 4, using mass-complete samples. Our main results can be summarized as follows: (i) the slope of the star-formation rate-M* correlation is consistent with being constant ≃0.8 up to z ≃ 1.5, while its normalization keeps increasing with redshift; (ii) for the first time we are able to explore the FIR-radio correlation for a mass-selected sample of star-forming galaxies: the correlation does not evolve up to z ≃ 4; (iii) we confirm that galaxy stellar mass is a robust proxy for UV dust attenuation in star-forming galaxies, with more massive galaxies being more dust attenuated. Strikingly, we find that this attenuation relation evolves very weakly with redshift, with the amount of dust attenuation increasing by less than 0.3 mag over the redshift range [0.5-4] for a fixed stellar mass; (iv) the correlation between dust attenuation and the UV spectral slope evolves with redshift, with the median UV slope becoming bluer with redshift. By z ≃ 3, typical UV slopes are inconsistent, given the measured dust attenuations, with the predictions of commonly used empirical laws. (v) Finally, building on existing results, we show that gas reddening is marginally larger (by a factor of around 1.3) than the stellar reddening at all redshifts probed. Our results support a scenario where the ISM conditions of typical star-forming galaxies evolve with redshift, such that at z ≥ 1.5 Main Sequence galaxies have ISM conditions moving closer to those of local starbursts. Based on observations collected at the Herschel, Spitzer, Keck, NRAO-VLA, Subaru, KPNO, and CFHT observatories. Herschel is an European Space Agency Cornerstone Mission with science instruments provided by European-led Principal Investigator consortia and

  13. GEOMETRY OF STAR-FORMING GALAXIES FROM SDSS, 3D-HST, AND CANDELS

    SciTech Connect

    Van der Wel, A.; Chang, Yu-Yen; Rix, H.-W.; Martig, M.; Bell, E. F.; Holden, B. P.; Koo, D. C.; Mozena, M.; Faber, S. M.; Giavalisco, M.; Skelton, R.; Whitaker, K.; Momcheva, I.; Van Dokkum, P. G.; Dekel, A.; Ceverino, D.; Franx, M.; and others

    2014-09-01

    We determine the intrinsic, three-dimensional shape distribution of star-forming galaxies at 0 < z < 2.5, as inferred from their observed projected axis ratios. In the present-day universe, star-forming galaxies of all masses 10{sup 9}-10{sup 11} M {sub ☉} are predominantly thin, nearly oblate disks, in line with previous studies. We now extend this to higher redshifts, and find that among massive galaxies (M {sub *} > 10{sup 10} M {sub ☉}) disks are the most common geometric shape at all z ≲ 2. Lower-mass galaxies at z > 1 possess a broad range of geometric shapes: the fraction of elongated (prolate) galaxies increases toward higher redshifts and lower masses. Galaxies with stellar mass 10{sup 9} M {sub ☉} (10{sup 10} M {sub ☉}) are a mix of roughly equal numbers of elongated and disk galaxies at z ∼ 1 (z ∼ 2). This suggests that galaxies in this mass range do not yet have disks that are sustained over many orbital periods, implying that galaxies with present-day stellar mass comparable to that of the Milky Way typically first formed such sustained stellar disks at redshift z ∼ 1.5-2. Combined with constraints on the evolution of the star formation rate density and the distribution of star formation over galaxies with different masses, our findings imply that, averaged over cosmic time, the majority of stars formed in disks.

  14. Chemistry and radiative shielding in star-forming galactic discs

    NASA Astrophysics Data System (ADS)

    Safranek-Shrader, Chalence; Krumholz, Mark R.; Kim, Chang-Goo; Ostriker, Eve C.; Klein, Richard I.; Li, Shule; McKee, Christopher F.; Stone, James M.

    2017-02-01

    To understand the conditions under which dense, molecular gas is able to form within a galaxy, we post-process a series of three-dimensional galactic-disc-scale simulations with ray-tracing-based radiative transfer and chemical network integration to compute the equilibrium chemical and thermal state of the gas. In performing these simulations, we vary a number of parameters, such as the interstellar radiation field strength, vertical scaleheight of stellar sources, and cosmic ray flux, to gauge the sensitivity of our results to these variations. Self-shielding permits significant molecular hydrogen (H2) abundances in dense filaments around the disc mid-plane, accounting for approximately ˜10-15 per cent of the total gas mass. Significant CO fractions only form in the densest, nH≳ 10^3 cm^{-3}, gas where a combination of dust, H2, and self-shielding attenuates the far-ultraviolet background. We additionally compare these ray-tracing-based solutions to photochemistry with complementary models where photoshielding is accounted for with locally computed prescriptions. With some exceptions, these local models for the radiative shielding length perform reasonably well at reproducing the distribution and amount of molecular gas as compared with a detailed, global ray-tracing calculation. Specifically, an approach based on the Jeans length with a T = 40 K temperature cap performs the best in regard to a number of different quantitative measures based on the H2 and CO abundances.

  15. General Model for Light Curves of Chromospherically Active Binary Stars

    NASA Astrophysics Data System (ADS)

    Jetsu, L.; Henry, G. W.; Lehtinen, J.

    2017-04-01

    The starspots on the surface of many chromospherically active binary stars concentrate on long-lived active longitudes separated by 180°. Shifts in activity between these two longitudes, the “flip-flop” events, have been observed in single stars like FK Comae and binary stars like σ Geminorum. Recently, interferometry has revealed that ellipticity may at least partly explain the flip-flop events in σ Geminorum. This idea was supported by the double-peaked shape of the long-term mean light curve of this star. Here we show that the long-term mean light curves of 14 chromospherically active binaries follow a general model that explains the connection between orbital motion, changes in starspot distribution, ellipticity, and flip-flop events. Surface differential rotation is probably weak in these stars, because the interference of two constant period waves may explain the observed light curve changes. These two constant periods are the active longitude period ({P}{act}) and the orbital period ({P}{orb}). We also show how to apply the same model to single stars, where only the value of P act is known. Finally, we present a tentative interference hypothesis about the origin of magnetic fields in all spectral types of stars. The CPS results are available electronically at the Vizier database.

  16. Physical properties of local star-forming analogues to z ˜ 5 Lyman-break galaxies

    NASA Astrophysics Data System (ADS)

    Greis, Stephanie M. L.; Stanway, Elizabeth R.; Davies, Luke J. M.; Levan, Andrew J.

    2016-07-01

    Intense, compact, star-forming galaxies are rare in the local Universe but ubiquitous at high redshift. We interpret the 0.1-22 μm spectral energy distributions of a sample of 180 galaxies at 0.05 < z < 0.25 selected for extremely high surface densities of inferred star formation in the ultraviolet. By comparison with well-established stellar population synthesis models, we find that our sample comprises young (˜60-400 Myr), moderate mass (˜6 × 109 M⊙) star-forming galaxies with little dust extinction (mean stellar continuum extinction Econt(B - V) ˜ 0.1) and find star formation rates of a few tens of solar masses per year. We use our inferred masses to determine a mean specific star formation rate for this sample of ˜10-9 yr-1, and compare this to the specific star formation rates in distant Lyman-break galaxies (LBGs), and in other low-redshift populations. We conclude that our sample's characteristics overlap significantly with those of the z ˜ 5 LBG population, making ours the first local analogue population well tuned to match those high-redshift galaxies. We consider implications for the origin and evolution of early galaxies.

  17. Modeling tracers of young stellar population age in star-forming galaxies

    SciTech Connect

    Levesque, Emily M.; Leitherer, Claus

    2013-12-20

    The young stellar population of a star-forming galaxy is the primary engine driving its radiative properties. As a result, the age of a galaxy's youngest generation of stars is critical for a detailed understanding of its star formation history, stellar content, and evolutionary state. Here we present predicted equivalent widths for the Hβ, Hα, and Brγ recombination lines as a function of stellar population age. The equivalent widths are produced by the latest generations of stellar evolutionary tracks and the Starburst99 stellar population synthesis code, and are the first to fully account for the combined effects of both nebular emission and continuum absorption produced by the synthetic stellar population. Our grid of model stellar populations spans six metallicities (0.001 < Z < 0.04), two treatments of star formation history (a 10{sup 6} M {sub ☉} instantaneous burst and a continuous star formation rate of 1 M {sub ☉} yr{sup –1}), and two different treatments of initial rotation rate (v {sub rot} = 0.0v {sub crit} and 0.4v {sub crit}). We also investigate the effects of varying the initial mass function. Given constraints on galaxy metallicity, our predicted equivalent widths can be applied to observations of star-forming galaxies to approximate the age of their young stellar populations.

  18. Still-Forming Solar System May Have Planets Orbiting Star in Opposite Directions, Astronomers Say

    NASA Astrophysics Data System (ADS)

    2006-02-01

    Astronomers studying a disk of material circling a still-forming star inside our Galaxy have found a tantalizing result -- the inner part of the disk is orbiting the protostar in the opposite direction from the outer part of the disk. Protostar Graphic Disk Around Young Star Rotating in Opposite Directions CREDIT: Bill Saxton, NRAO/AUI/NSF More Graphics "This is the first time anyone has seen anything like this, and it means that the process of forming planets from such disks is more complex than we previously expected," said Anthony Remijan, of the National Radio Astronomy Observatory, who with his colleague Jan M. Hollis, of the NASA Goddard Space Flight Center, used the National Science Foundation's Very Large Array radio telescope to make the discovery. "The solar system that likely will be formed around this star will include planets orbiting in different directions, unlike our own solar system in which all the planets orbit the Sun in the same direction," Hollis explained. Stars and planets, scientists believe, are formed when giant clouds of gas and dust collapse. As the cloud collapses, a flattened, rotating disk of material develops around the young star. This disk provides the material from which planets form. The disk and the resulting planets rotate in the same direction as the original cloud, with the rotation speed increasing closer to the center, much as a spinning figure skater spins faster when they draw their arms inward. If all the material in the star and disk come from the same prestellar cloud, they all will rotate in the same direction. That is the case with our own solar system, in which the planets all orbit the Sun in the same direction as the Sun itself rotates on its axis. In the case of a young star some 500 light-years from Earth in the direction of the constellation Ophiuchus, Remijan and Hollis found the inner and outer parts of the disk rotating in opposite directions. "We think this system may have gotten material from two clouds

  19. A Global Star-forming Episode in M31 2-4 Gyr Ago

    NASA Astrophysics Data System (ADS)

    Williams, Benjamin F.; Dalcanton, Julianne J.; Dolphin, Andrew E.; Weisz, Daniel R.; Lewis, Alexia R.; Lang, Dustin; Bell, Eric F.; Boyer, Martha; Fouesneau, Morgan; Gilbert, Karoline M.; Monachesi, Antonela; Skillman, Evan

    2015-06-01

    We have identified a major global enhancement of star formation in the inner M31 disk that occurred between 2-4 Gyr ago, producing ˜60% of the stellar mass formed in the past 5 Gyr. The presence of this episode in the inner disk was discovered by modeling the optical resolved star color-magnitude diagrams of low extinction regions in the main disk of M31 (3 < R < 20 kpc) as part of the Panchromatic Hubble Andromeda Treasury. This measurement confirms and extends recent measurements of a widespread star formation enhancement of similar age in the outer disk, suggesting that this burst was both massive and global. Following the galaxy-wide burst, the star formation rate of M31 has significantly declined. We briefly discuss possible causes for these features of the M31 evolutionary history, including interactions with M32, M33, and/or a merger.

  20. A GLOBAL STAR-FORMING EPISODE IN M31 2–4 GYR AGO

    SciTech Connect

    Williams, Benjamin F.; Dalcanton, Julianne J.; Weisz, Daniel R.; Lewis, Alexia R. E-mail: jd@astro.washington.edu; and others

    2015-06-10

    We have identified a major global enhancement of star formation in the inner M31 disk that occurred between 2–4 Gyr ago, producing ∼60% of the stellar mass formed in the past 5 Gyr. The presence of this episode in the inner disk was discovered by modeling the optical resolved star color–magnitude diagrams of low extinction regions in the main disk of M31 (3 < R < 20 kpc) as part of the Panchromatic Hubble Andromeda Treasury. This measurement confirms and extends recent measurements of a widespread star formation enhancement of similar age in the outer disk, suggesting that this burst was both massive and global. Following the galaxy-wide burst, the star formation rate of M31 has significantly declined. We briefly discuss possible causes for these features of the M31 evolutionary history, including interactions with M32, M33, and/or a merger.

  1. Inner and outer star forming regions over the discs of spiral galaxies I. Sample characterization

    NASA Astrophysics Data System (ADS)

    Rodríguez-Baras, Marina; Díaz, A. I.; Rosales-Ortega, F. F.

    2017-03-01

    This project is aimed at understanding the dependence of star formation on the environment by analysing young stellar populations in two very different positions in disk galaxies: circumnuclear and outer disk giant regions. Integral field spectroscopy (IFS) provide an ideal means to achieve these goals providing simultaneous spatial and spectral resolution. Here we present the characterization of the work sample, composed by 671 outer regions and 725 inner regions from 263 isolated spirals galaxies observed by the CALIFA survey. The wide number of regions in both samples allows us to obtain statistically relevant results about the influence of metallicity, density and environment on star formation, and how it disseminates over the galaxy, to obtain evolutionary stories for the star-forming regions and to compare our results with models of massive star formation and galactic chemical evolution.

  2. DUST EXTINCTION AND METALLICITIES OF STAR-FORMING Ly{alpha} EMITTING GALAXIES AT LOW REDSHIFT

    SciTech Connect

    Finkelstein, Steven L.; Papovich, Casey; Cohen, Seth H.; Malhotra, Sangeeta; Rhoads, James E.; Moustakas, John

    2011-06-01

    We present the results of an optical spectroscopic study of 12 GALEX-discovered star-forming Ly{alpha} emitting galaxies (LAEs) at z {approx} 0.3. We measure the emission-line fluxes from these galaxies by fitting their observed spectra to stellar population models in order to correct for underlying stellar absorption. We revisit earlier stellar population model fitting results, finding that excluding now-known active galactic nuclei lowers the typical stellar population age and stellar mass of this sample to {approx}300 Myr and {approx}4 x 10{sup 9} M{sub sun}, respectively. We calculate their dust extinction using the Balmer decrement, and find a typical visual attenuation of A{sub V} {approx} 0.3 mag, similar to that seen in some high-redshift LAEs. Comparing the ratios of Ly{alpha}/H{alpha} and the Ly{alpha} equivalent widths to the measured dust extinction, we find that the interstellar media (ISMs) in these objects appear to be neither enhancing nor seriously attenuating the Ly{alpha} equivalent widths, as would be the case in a quasi-clumpy ISM. Lastly, we perform a detailed analysis of the gas-phase metallicities of these galaxies, and we find that most galaxies in our sample have Z {approx}< 0.4 Z{sub sun}. We find that at a fixed stellar mass, these low-redshift LAE analogs are offset by {approx}0.3-0.6 dex lower metallicity from the general galaxy population at similar redshifts based on the local mass-metallicity relationship. This implies that galaxies with Ly{alpha} in emission may be systematically more metal-poor than star-forming galaxies at the same stellar mass and redshift, similar to preliminary results at z {approx} 2.

  3. Preferential Pathway for Glycine Formation in Star-Forming Regions

    NASA Astrophysics Data System (ADS)

    Pilling, S.; Boechat-Roberty, H. M.; Baptista, L.; Santos A. C., F.

    Interstellar clouds, similar to that from which the solar system was formed, contain many organic molecules including aldehydes, acids, ketones, and sugars Ehrenfreund & Charnley (2000). Those organic compounds have important functions in terrestrial biochemistry and could also have been important in prebiotic synthesis. The simplest amino acid, glycine (NH2CH2COOH), was recently detected in the hot molecular cores Sgr B2(N-LMH), Orion KL, and W51 e1/e2 Kuan et al. (2003). The formic acid (HCOOH) and acetic acid(CH3COOH) have also been detected in those regions Liu et al. (2002), Remijan et al. (2004). The goal of this work is to study experimentally photoionization and photodissociation processes of glycine precursor molecules, acetic acid and formic acid to elucidate a possible preferentially in the glycine synthesis between ice and gas phase. The measurements were taken at the Brazilian Synchrotron Light Laboratory (LNLS), employing soft X-ray photons from a toroidal grating monochromator TGM) beamline (100 - 310 eV). The experimental set up consists of a high vacuum chamber with a Time-Of-Flight Mass Spectrometer (TOF-MS). Mass spectra were obtained using PhotoElectron PhotoIon Coincidence (PEPICO) technique. Kinetic energy distributions and abundances for each ionic fragment have been obtained from the analysis of the corresponding peak shapes in the mass spectra. Dissociative and non-dissociative photoionization cross sections for both molecules were also determined Boechat-Roberty, Pilling & Santos (2005). Due to the high photodissociation cross section of formic acid it is possible that in PDRs regions, just after molecules evaporation from the grains surface, it is almost destructed by soft X-rays, justifying the observed low abundance of HCOOH in gaseous phase Ehrenfreund et al. (2001). Acetic acid have shown to be more stable to the ionizing field, and its main outcomes from dissociation process were the reactive ionic fragments COOH+ and CH3CO+. To

  4. Variations in the Star Formation Efficiency of the Dense Molecular Gas across the Disks of Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Usero, Antonio; Leroy, Adam K.; Walter, Fabian; Schruba, Andreas; García-Burillo, Santiago; Sandstrom, Karin; Bigiel, Frank; Brinks, Elias; Kramer, Carsten; Rosolowsky, Erik; Schuster, Karl-Friedrich; de Blok, W. J. G.

    2015-10-01

    We present a new survey of HCN(1-0) emission, a tracer of dense molecular gas, focused on the little-explored regime of normal star-forming galaxy disks. Combining HCN, CO, and infrared (IR) emission, we investigate the role of dense gas in star formation, finding systematic variations in both the apparent dense gas fraction (traced by the HCN-to-CO ratio) and the apparent star formation efficiency of dense gas (traced by the IR-to-HCN ratio). The latter may be unexpected, given the recent popularity of gas density threshold models to explain star formation scaling relations. Our survey used the IRAM 30 m telescope to observe HCN(1-0), CO(1-0), and several other emission lines across 29 nearby disk galaxies whose CO(2-1) emission has previously been mapped by the HERACLES survey. We detected HCN in 48 out of 62 observed positions. Because our observations achieve a typical resolution of ˜1.5 kpc and span a range of galaxies and galactocentric radii (56% lie at {r}{gal}\\gt 1 kpc), we are able to investigate the properties of the dense gas as a function of local conditions in a galaxy disk. We focus on how the ratios IR-to-CO, HCN-to-CO, and IR-to-HCN (observational cognates of the star formation efficiency, dense gas fraction, and dense gas star formation efficiency) depend on the stellar surface density, {{{Σ }}}{star}, and the molecular-to-atomic gas ratio, {{{Σ }}}{mol}/{{{Σ }}}{atom}. The HCN-to-CO ratio is low, often ˜1/30, and correlates tightly with both the molecular-to-atomic ratio and the stellar mass surface density across a range of 2.1 dex (factor of ≈125) in both parameters. Thus for the assumption of fixed CO-to-H2 and HCN-to-dense gas conversion factors, the dense gas fraction depends strongly on location in the disk, being higher in the high surface density, highly molecular parts of galaxies. At the same time, the IR-to-HCN ratio (closely related to the star formation efficiency of dense molecular gas) decreases systematically with these

  5. From H I to Stars: H I Depletion in Starbursts and Star-forming Galaxies in the ALFALFA Hα Survey

    NASA Astrophysics Data System (ADS)

    Jaskot, A. E.; Oey, M. S.; Salzer, J. J.; Van Sistine, A.; Bell, E. F.; Haynes, M. P.

    2015-07-01

    H i in galaxies traces the fuel for future star formation and reveals the effects of feedback on neutral gas. Using a statistically uniform, H i-selected sample of 565 galaxies from the Arecibo Legacy Fast ALFA (ALFALFA) Hα survey, we explore H i properties as a function of star formation activity. ALFALFA Hα provides R-band and Hα imaging for a volume-limited subset of the 21 cm ALFALFA survey. We identify eight starbursts based on Hα equivalent width and six with enhanced star formation relative to the main sequence. Both starbursts and non-starbursts have similar H i-to-stellar mass ratios ({M}{{H} {{I}}}/{M}*), which suggests that feedback is not depleting the starbursts’ H i. Consequently, the starbursts do have shorter H i depletion times ({t}{dep}), implying more efficient H i-to-H2 conversion. While major mergers likely drive this enhanced efficiency in some starbursts, the lowest-mass starbursts may experience periodic bursts, consistent with enhanced scatter in {t}{dep} at low {M}*. Two starbursts appear to be pre-coalescence mergers; their elevated {M}{{H} {{I}}}/{M}* suggest that H i-to-H2 conversion is still ongoing at this stage. By comparing with the GASS sample, we find that {t}{dep} anticorrelates with stellar surface density for disks, while spheroids show no such trend. Among early-type galaxies, {t}{dep} does not correlate with bulge-to-disk ratio; instead, the gas distribution may determine the star formation efficiency. Finally, the weak connection between galaxies’ specific star formation rates and {M}{{H} {{I}}}/{M}* contrasts with the well-known correlation between {M}{{H} {{I}}}/{M}* and color. We show that dust extinction can explain the H i-color trend, which may arise from the relationship between {M}*, {M}{{H} {{I}}}, and metallicity.

  6. C III] Emission in Star-Forming Galaxies Near and Far

    NASA Technical Reports Server (NTRS)

    Rigby, J, R.; Bayliss, M. B.; Gladders, M. D.; Sharon, K.; Wuyts, E.; Dahle, H.; Johnson, T.; Pena-Guerrero, M.

    2015-01-01

    We measure C III Lambda Lambda 1907, 1909 Angstrom emission lines in eleven gravitationally-lensed star-forming galaxies at zeta at approximately 1.6-3, finding much lower equivalent widths than previously reported for fainter lensed galaxies (Stark et al. 2014). While it is not yet clear what causes some galaxies to be strong C III] emitters, C III] emission is not a universal property of distant star-forming galaxies. We also examine C III] emission in 46 star-forming galaxies in the local universe, using archival spectra from GHRS, FOS, and STIS on HST, and IUE. Twenty percent of these local galaxies show strong C III] emission, with equivalent widths less than -5 Angstrom. Three nearby galaxies show C III] emission equivalent widths as large as the most extreme emitters yet observed in the distant universe; all three are Wolf-Rayet galaxies. At all redshifts, strong C III] emission may pick out low-metallicity galaxies experiencing intense bursts of star formation. Such local C III] emitters may shed light on the conditions of star formation in certain extreme high-redshift galaxies.

  7. C III] EMISSION IN STAR-FORMING GALAXIES NEAR AND FAR

    SciTech Connect

    Rigby, J. R.; Bayliss, M. B.; Gladders, M. D.; Sharon, K.; Johnson, T.; Wuyts, E.; Dahle, H.; Peña-Guerrero, M.

    2015-11-20

    We measure [C iii] 1907, C iii] 1909 Å emission lines in 11 gravitationally lensed star-forming galaxies at z ∼ 1.6–3, finding much lower equivalent widths than previously reported for fainter lensed galaxies. While it is not yet clear what causes some galaxies to be strong C iii] emitters, C iii] emission is not a universal property of distant star-forming galaxies. We also examine C iii] emission in 46 star-forming galaxies in the local universe, using archival spectra from GHRS, FOS, and STIS on HST and IUE. Twenty percent of these local galaxies show strong C iii] emission, with equivalent widths < −5 Å. Three nearby galaxies show C iii] emission equivalent widths as large as the most extreme emitters yet observed in the distant universe; all three are Wolf–Rayet galaxies. At all redshifts, strong C iii] emission may pick out low-metallicity galaxies experiencing intense bursts of star formation. Such local C iii] emitters may shed light on the conditions of star formation in certain extreme high-redshift galaxies.

  8. Phase-space structures and stellar populations in the star-forming region NGC 2264

    NASA Astrophysics Data System (ADS)

    González, Marta; Alfaro, Emilio J.

    2017-02-01

    In this work, we analyse the structure of a subspace of the phase space of the star-forming region NGC 2264 using the spectrum of kinematic groupings (SKG). We show that the SKG can be used to process a collection of star data to find substructure at different scales. We have found structure associated with the NGC 2264 region and also with the background area. In the NGC 2264 region, a hierarchical analysis shows substructure compatible with that found in previous specific studies of the area but with an objective, compact methodology that allows us to homogeneously compare the structure of different clusters and star-forming regions. Moreover, this structure is compatible with the different ages of the main NGC 2264 star-forming populations. The structure found in the field can be roughly associated with giant stars far in the background, dynamically decoupled from NGC 2264, which could be related either with the Outer Arm or Monoceros Ring. The results in this paper confirm the relationship between structure in the radial velocity phase-space subspace and different kinds of populations, defined by other variables not necessarily analysed with the SKG, such as age or distance, showing the importance of detecting phase-space substructure in order to trace stellar populations in the broadest sense of the word.

  9. The nebular emission of star-forming galaxies in a hierarchical universe

    NASA Astrophysics Data System (ADS)

    Orsi, Álvaro; Padilla, Nelson; Groves, Brent; Cora, Sofía; Tecce, Tomás; Gargiulo, Ignacio; Ruiz, Andrés

    2014-09-01

    Galaxy surveys targeting emission lines are characterizing the evolution of star-forming galaxies, but there is still little theoretical progress in modelling their physical properties. We predict nebular emission from star-forming galaxies within a cosmological galaxy formation model. Emission lines are computed by combining the semi-analytical model SAG with the photoionization code MAPPINGS-III. We characterize the interstellar medium of galaxies by relating the ionization parameter of gas in galaxies to their cold gas metallicity, obtaining a reasonable agreement with the observed Hα, [O II] λ 3727, [O III] λ 5007 luminosity functions, and the BPT diagram for local star-forming galaxies. The average ionization parameter is found to increase towards low star formation rates and high redshifts, consistent with recent observational results. The predicted link between different emission lines and their associated star formation rates is studied by presenting scaling relations to relate them. Our model predicts that emission-line galaxies have modest clustering bias, and thus reside in dark matter haloes of masses below Mhalo ≲ 1012 [h-1 M⊙]. Finally, we exploit our modelling technique to predict galaxy number counts up to z ˜ 10 by targeting far-infrared emission lines detectable with submillimetre facilities.

  10. Young Stellar Populations in MYStIX Star-forming Regions: Candidate Protostars

    NASA Astrophysics Data System (ADS)

    Romine, Gregory; Feigelson, Eric D.; Getman, Konstantin V.; Kuhn, Michael A.; Povich, Matthew S.

    2016-12-01

    The Massive Young Star-Forming Complex in Infrared and X-ray (MYStIX) project provides a new census on stellar members of massive star-forming regions within 4 kpc. Here the MYStIX Infrared Excess catalog and Chandra-based X-ray photometric catalogs are mined to obtain high-quality samples of Class I protostars using criteria designed to reduce extragalactic and Galactic field star contamination. A total of 1109 MYStIX Candidate Protostars (MCPs) are found in 14 star-forming regions. Most are selected from protoplanetary disk infrared excess emission, but 20% are found from their ultrahard X-ray spectra from heavily absorbed magnetospheric flare emission. Two-thirds of the MCP sample is newly reported here. The resulting samples are strongly spatially associated with molecular cores and filaments on Herschel far-infrared maps. This spatial agreement and other evidence indicate that the MCP sample has high reliability with relatively few “false positives” from contaminating populations. But the limited sensitivity and sparse overlap among the infrared and X-ray subsamples indicate that the sample is very incomplete with many “false negatives.” Maps, tables, and source descriptions are provided to guide further study of star formation in these regions. In particular, the nature of ultrahard X-ray protostellar candidates without known infrared counterparts needs to be elucidated.

  11. Detection of high Lyman continuum leakage from four low-redshift compact star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Izotov, Y. I.; Schaerer, D.; Thuan, T. X.; Worseck, G.; Guseva, N. G.; Orlitová, I.; Verhamme, A.

    2016-10-01

    Following our first detection reported in Izotov et al., we present the detection of Lyman continuum (LyC) radiation of four other compact star-forming galaxies observed with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope. These galaxies, at redshifts of z ˜ 0.3, are characterized by high emission-line flux ratios [O III] λ5007/[O II] λ3727 ≳ 5. The escape fractions of the LyC radiation fesc(LyC) in these galaxies are in the range of ˜6-13 per cent, the highest values found so far in low-redshift star-forming galaxies. Narrow double-peaked Ly α emission lines are detected in the spectra of all four galaxies, compatible with predictions for LyC leakers. We find escape fractions of Ly α, fesc(Ly α) ˜ 20-40 per cent, among the highest known for Ly α emitting galaxies. Surface brightness profiles produced from the COS acquisition images reveal bright star-forming regions in the centre and exponential discs in the outskirts with disc scalelengths α in the range ˜0.6-1.4 kpc. Our galaxies are characterized by low metallicity, ˜1/8-1/5 solar, low stellar mass ˜(0.2-4) × 109 M⊙, high star formation rates, SFR ˜ 14-36 M⊙ yr-1, and high SFR densities, Σ ˜ 2-35 M⊙ yr-1 kpc-2. These properties are comparable to those of high-redshift star-forming galaxies. Finally, our observations, combined with our first detection reported in Izotov et al., reveal that a selection for compact star-forming galaxies showing high [O III] λ5007/[O II] λ3727 ratios appears to pick up very efficiently sources with escaping LyC radiation: all five of our selected galaxies are LyC leakers.

  12. Metallicity gradients and newly created star-forming systems in interacting galaxies

    NASA Astrophysics Data System (ADS)

    Mendes de Oliveira, Claudia L.

    2015-08-01

    Interactions play an extremely important role in the evolution of galaxies, changing their morphologies and kinematics. Galaxy collisions may result in the formation of intergalactic star-forming objects, such as HII regions, young clusters and/or tidal dwarf galaxies. Several studies have found a wealth of newly created objects in interacting systems. We will exemplify the problems and challenges in this field and will describe observations of the interacting group NGC 6845, which contains four bright galaxies, two of which have extended tidal tails. We obtained Gemini/GMOS spectra for 28 of the regions located in the galaxies and in the tails. All regions in the latter are star-forming objects according to their line ratios, with ages younger than 10 Myr. A super luminous star forming complex is found in the brightest member of the group, NGC 6845A. Its luminosity reveals a star formation density of 0.19 solar masses, per year, per kpc^2, suggesting that this object is a localized starburst. We derived the gas-phase metallicity gradients across NGC 6845A and its two tails and we find that these are shallower than those for isolated galaxies. We speculate that the observed metallicity gradient may be related to one or more of the following mechanisms: (1) interaction induced inflow of fresh gas to the galaxy center, as seen in simulations, which is expected to dilute the metallicity of the central burst, (2) the formation of young metal-rich star forming regions in the tidal tails, which were born out of enriched gas expelled from the central regions of the system during the interaction and (3) the incremental growth of metals accumulated over time, due to the successful generations of star forming regions along the tails. Finally we will describe our plans to do a search for such objects on Halpha images that will soon be available for 17.5k degrees of the sky, with the A-PLUS survey.

  13. The Schmidt Law in Six Galactic Massive Star-forming Regions

    NASA Astrophysics Data System (ADS)

    Willis, S.; Guzman, A.; Marengo, M.; Smith, H. A.; Martínez-Galarza, J. R.; Allen, L.

    2015-08-01

    We present a census of young stars in five massive star-forming regions in the 4th Galactic quadrant, G305, G326-4, G326-6, G333 (RCW 106), and G351, and combine this census with an earlier census of young stars in NGC 6334. Each region was observed at J, H, and Ks with the NOAO Extremely Wide-Field Infrared Imager and combined with deep observations taken with the Infrared Array Camera (IRAC) on board the Spitzer Space Telescope at the wavelengths 3.6 and 4.5 μm. We derived a five band point-source catalog containing >200,000 infrared sources in each region. We have identified a total of 2871 YSO candidates, 363 Class I YSOs, and 2508 Class II YSOs. We mapped the column density of each cloud using observations from Herschel between 160 and 500 μm and near-infrared extinction maps in order to determine the average gas surface density above AV > 2. We study the surface density of the YSOs and the star-formation rate as a function of the column density within each cloud and compare them to the results for nearby star-forming regions. We find a range in power-law indices across the clouds, with the dispersion in the local relations in an individual cloud much lower than the average over the six clouds. We find the average over the six clouds to be {{{Σ }}}{SFR}∼ {{{Σ }}}{gas}2.15+/- 0.41 and power-law exponents ranging from 1.77 to 2.86, similar to the values derived within nearby star-forming regions, including Taurus and Orion. The large dispersion in the power-law relations between individual Milky Way molecular clouds reinforces the idea that there is not a direct universal connection between Σgas and a cloud's observed star-formation rate.

  14. High angular resolution observations of star-forming regions with BETTII and SOFIA

    NASA Astrophysics Data System (ADS)

    Rizzo, Maxime; Rinehart, Stephen; Mundy, Lee G.; Benford, Dominic J.; Dhabal, Arnab; Fixsen, Dale J.; Leisawitz, David; Maher, Stephen F.; Mentzell, Eric; Silverberg, Robert F.; Staguhn, Johannes; Veach, Todd; Cardiff BETTII Team

    2016-01-01

    High angular resolution observations in the far-infrared are important to understand the star formation process in embedded star clusters where extinction is large and stars form in close proximity. The material taking part in the star forming process is heated by the young stars and emits primarily in the far-IR; hence observations of the far-IR dust emission yields vital information about the gravitational potential, the mass and energy distribution, and core/star formation process. Previous observatories, such as Herschel, Spitzer and WISE lack the angular resolution required to study these dense star forming cores and are further limited by saturation in bright cores.The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) is pioneering the path to sub-arcsecond resolution at far-IR wavelengths. This thesis talk discusses the instrumental challenges in building BETTII, as well as results from our SOFIA survey to illustrate the potential of higher-angular resolution observations. The 8m-long two element interferometer is being tested at NASA GSFC and is scheduled for first flight in fall 2016. BETTII will provide 0.5 to 1 arcsecond spatial resolution and spectral resolving power of 10 to 100 between 30 and 90 microns, where most of the dust continuum emission peaks in local star forming regions. It will achieve spatially-resolved spectroscopy of bright, dense cores with unprecedented high definition. This talk focuses on the main challenges and solutions associated with building BETTII: thermal stability, attitude/pointing control, and path length stabilization. In each of these areas we look at the trade-off between design, control, and knowledge in order to achieve the best-possible instrumental capability and sensitivity.As a first step towards resolving cluster cores, we surveyed 10 nearby star-forming clusters with SOFIA FORCAST at 11, 19, 31 and 37 microns. The FORCAST instrument has the highest angular resolution currently available in

  15. HEAVILY OBSCURED AGN IN STAR-FORMING GALAXIES AT z approx = 2

    SciTech Connect

    Treister, E.; Kartaltepe, Jeyhan; Le Floc'h, Emeric; Cardamone, Carolin N.; Schawinski, Kevin; Urry, C. Megan; Virani, Shanil; Gawiser, Eric; Lira, Paulina; Damen, Maaike; Taylor, Edward N.; Justham, Stephen; Koekemoer, Anton M.

    2009-11-20

    We study the properties of a sample of 211 heavily obscured active galactic nucleus (AGN) candidates in the extended Chandra Deep Field-South selecting objects with f {sub 24m}u{sub m}/f{sub R} > 1000 and R - K>4.5. Of these, 18 were detected in X-rays and found to be obscured AGNs with neutral hydrogen column densities of approx10{sup 23} cm{sup -2}. In the X-ray-undetected sample, the following evidence suggests a large fraction of heavily obscured (Compton-thick) AGN: (1) The stacked X-ray signal of the sample is strong, with an observed ratio of soft to hard X-ray counts consistent with a population of approx90% heavily obscured AGNs combined with 10% star-forming galaxies. (2) The X-ray-to-mid-IR ratios for these sources are significantly larger than that of star-forming galaxies and approx2 orders of magnitude smaller than for the general AGN population, suggesting column densities of N {sub H} approx> 5 x 10{sup 24} cm{sup -2}. (3) The Spitzer near- and mid-IR colors of these sources are consistent with those of the X-ray-detected samples if the effects of dust self-absorption are considered. Spectral fitting to the rest-frame UV/optical light (dominated by the host galaxy) returns stellar masses of approx10{sup 11} M{sub sun} and (E(B - V)) = 0.5, and reveals evidence for a significant young stellar population, indicating that these sources are experiencing considerable star formation. This sample of heavily obscured AGN candidates implies a space density at z approx 2 of approx10{sup -5} Mpc{sup -3}, finding a strong evolution in the number of L{sub X} >10{sup 44} erg s{sup -1} sources from z = 1.5 to 2.5, possibly consistent with a short-lived heavily obscured phase before an unobscured quasar is visible.

  16. Stellar activity and the rotation of Hyades stars

    SciTech Connect

    Radick, R.R.; Baliunas, S.L.

    1987-12-01

    New measurements of rotation periods for Hyades stars, which were obtained from re-analysis of Mount Wilson Observatory Ca II H-K emission flux measurements, are reported. The existence of systematic, color-dependent discrepancies between the measured rotation periods for Hyades stars and those predicted by the Rossby relation as originally calibrated by Noyes et al. 1984 has led to a re-examination of the form of the relationship between chromospheric emission, rotation, and color.

  17. Exploring the Connection Between Star Formation and AGN Activity in the Local Universe

    NASA Technical Reports Server (NTRS)

    LaMassa, Stephanie M.; Heckman. T. M.; Ptak, Andrew; Schiminovich, D.; O'Dowd, M.; Bertincourt, B.

    2012-01-01

    We study a combined sample of 264 star-forming, 51 composite, and 73 active galaxies using optical spectra from SDSS and mid-infrared (mid-IR) spectra from the Spitzer Infrared Spectrograph. We examine optical and mid-IR spectroscopic diagnostics that probe the amount of star formation and relative energetic con- tributions from star formation and an active galactic nucleus (AGN). Overall we find good agreement between optical and mid-IR diagnostics. Misclassifications of galaxies based on the SDSS spectra are rare despite the presence of dust obscuration. The luminosity of the [NeII] 12.8 micron emission-line is well correlated with the star formation rate (SFR) measured from the SDSS spectra, and this holds for the star forming, composite, and AGN-dominated systems. AGN show a clear excess of [NeIII] 15.6 micron emission relative to star forming and composite systems. We find good qualitative agreement between various parameters that probe the relative contributions of the AGN and star formation, including: the mid-IR spectral slope, the ratio of the [NeV] 14.3 micron to [NeII] micron 12.8 fluxes, the equivalent widths of the 7.7, 11.3, and 17 micron PAH features, and the optical "D" parameter which measures the distance a source lies from the locus of star forming galaxies in the optical BPT emission-line diagnostic diagram. We also consider the behavior of the three individual PAH features by examining how their flux ratios depend upon the degree of AGN-dominance. We find that the PAH 11.3 micron feature is significantly suppressed in the most AGN-dominated systems.

  18. PHIBSS: MOLECULAR GAS, EXTINCTION, STAR FORMATION, AND KINEMATICS IN THE z = 1.5 STAR-FORMING GALAXY EGS13011166

    SciTech Connect

    Genzel, R.; Tacconi, L. J.; Kurk, J.; Wuyts, S.; Foerster Schreiber, N. M.; Gracia-Carpio, J.; Combes, F.; Freundlich, J.; Bolatto, A.; Cooper, M. C.; Neri, R.; Nordon, R.; Bournaud, F.; Comerford, J.; Cox, P.; Davis, M.; Garcia-Burillo, S.; Naab, T.; Lutz, D. E-mail: linda@mpe.mpg.de; and others

    2013-08-10

    We report matched resolution imaging spectroscopy of the CO 3-2 line (with the IRAM Plateau de Bure millimeter interferometer) and of the H{alpha} line (with LUCI at the Large Binocular Telescope) in the massive z = 1.53 main-sequence galaxy EGS 13011166, as part of the ''Plateau de Bure high-z, blue-sequence survey'' (PHIBSS: Tacconi et al.). We combine these data with Hubble Space Telescope V-I-J-H-band maps to derive spatially resolved distributions of stellar surface density, star formation rate, molecular gas surface density, optical extinction, and gas kinematics. The spatial distribution and kinematics of the ionized and molecular gas are remarkably similar and are well modeled by a turbulent, globally Toomre unstable, rotating disk. The stellar surface density distribution is smoother than the clumpy rest-frame UV/optical light distribution and peaks in an obscured, star-forming massive bulge near the dynamical center. The molecular gas surface density and the effective optical screen extinction track each other and are well modeled by a ''mixed'' extinction model. The inferred slope of the spatially resolved molecular gas to star formation rate relation, N = dlog{Sigma}{sub starform}/dlog{Sigma}{sub molgas}, depends strongly on the adopted extinction model, and can vary from 0.8 to 1.7. For the preferred mixed dust-gas model, we find N = 1.14 {+-} 0.1.

  19. Understanding Activity Cycles of Solar Type Stars with Kepler

    NASA Astrophysics Data System (ADS)

    Tovar, Guadalupe; Montet, Benjamin; Johnson, John A.

    2017-01-01

    As the era of exploring new worlds and systems advances we seek to answer the question: How common is our Sun? There is considerable evidence about the recurring activity cycles of our Sun but very little is known about the activity cycles of other stars. By calibrating the full frame images from the original Kepler mission that were taken once a month over the course of four years, we are able to do relative photometry on roughly 5 million stars. By building a model of the pixel response function we were able to achieve 0.8% precision photometry. We identify 50,000 solar type stars based on magnitude, surface gravity, and temperature cuts. We observe the relative increase and decrease in brightness of the stars indicating signs of activity cycles similar to our Sun. We continue to explore how a data driven pixel response function model could improve our precision to 0.1% photometry measurements.

  20. Magnetism and Activity of Planet-Hosting Stars

    NASA Astrophysics Data System (ADS)

    Wright, Jason Thomas; Miller, Brendan

    2015-08-01

    The magnetic activity levels of planet host stars may differ from that of stars not known to host planets in several ways. Hot jupiters may induce activity in their hosts through magnetic interactions, or through tidal interactions by affecting their host's rotation or convection. Measurements of photospheric, chromospheric, or coronal activity might then be abnormally abnormally high or low compared to control stars that do not host hot Jupiters, or might be modulated at the planet's orbital period. Such detections are complicated by the small amplitude of the expected signal, by the fact that the signals may be transient, and by the difficulty of constructing control samples due to exoplanet deteciton biases and the uncertainty of field star ages. I will review these issues, and discuss avenues for future progress in the field.

  1. The Fraction of Stars Formed In A Diverse Sample of 8 Galaxies

    NASA Astrophysics Data System (ADS)

    Chandar, Rupali

    2017-01-01

    We have estimated the fraction of stars born in compact star clusters, Gamma, in a diverse sample of 8 galaxies, including two irregulars, two dwarf starbursts, two spirals, and two mergers. We find an average value for our sample of Gamma ~30 +/- 12 %. We also calculate the fraction of stars found in clusters that have survived to older ages, and find values of 4.6 +/- 2.5% for 10-100 Myr clusters, and 2.4+/-1.1 % for 100-400 Myr clusters. Intriguingly, Gamma does not appear to vary with the star formation rate (SFR), the SFR density or the gas density in our sample. These new results are at odds with the well-established picture where a higher fraction of stars form in clusters when the star formation and gas densities are high. We explore reasons for the differences between our results and previous work, and describe how the LEGUS plus Halpha-LEGUS surveys will be used to help settle the issue of whether or not Gamma varies with galaxy property.

  2. The luminosity function of star clusters in 20 star-forming galaxies based on Hubble legacy archive photometry

    SciTech Connect

    Whitmore, Bradley C.; Bowers, Ariel S.; Lindsay, Kevin; Ansari, Asna; Evans, Jessica; Chandar, Rupali; Larsen, Soeren

    2014-04-01

    Luminosity functions (LFs) have been determined for star cluster populations in 20 nearby (4-30 Mpc), star-forming galaxies based on Advanced Camera for Surveys source lists generated by the Hubble Legacy Archive (HLA). These cluster catalogs provide one of the largest sets of uniform, automatically generated cluster candidates available in the literature at present. Comparisons are made with other recently generated cluster catalogs demonstrating that the HLA-generated catalogs are of similar quality, but in general do not go as deep. A typical cluster LF can be approximated by a power law, dN/dL∝L {sup α}, with an average value for α of –2.37 and rms scatter = 0.18 when using the F814W ('I') band. A comparison of fitting results based on methods that use binned and unbinned data shows good agreement, although there may be a systematic tendency for the unbinned (maximum likelihood) method to give slightly more negative values of α for galaxies with steeper LFs. We find that galaxies with high rates of star formation (or equivalently, with the brightest or largest numbers of clusters) have a slight tendency to have shallower values of α. In particular, the Antennae galaxy (NGC 4038/39), a merging system with a relatively high star formation rate (SFR), has the second flattest LF in the sample. A tentative correlation may also be present between Hubble type and values of α, in the sense that later type galaxies (i.e., Sd and Sm) appear to have flatter LFs. Hence, while there do appear to be some weak correlations, the relative similarity in the values of α for a large number of star-forming galaxies suggests that, to first order, the LFs are fairly universal. We examine the bright end of the LFs and find evidence for a downturn, although it only pertains to about 1% of the clusters. Our uniform database results in a small scatter (≈0.4 to 0.5 mag) in the correlation between the magnitude of the brightest cluster (M {sub brightest}) and log of the number

  3. The comparison of physical properties derived from gas and dust in a massive star-forming region

    SciTech Connect

    Battersby, Cara; Bally, John; Ginsburg, Adam; Darling, Jeremy; Dunham, Miranda; Longmore, Steve

    2014-05-10

    We explore the relationship between gas and dust in a massive star-forming region by comparing the physical properties derived from each. We compare the temperatures and column densities in a massive star-forming Infrared Dark Cloud (G32.02+0.05), which shows a range of evolutionary states, from quiescent to active. The gas properties were derived using radiative transfer modeling of the (1,1), (2,2), and (4,4) transitions of NH{sub 3} on the Karl G. Jansky Very Large Array, while the dust temperatures and column densities were calculated using cirrus-subtracted, modified blackbody fits to Herschel data. We compare the derived column densities to calculate an NH{sub 3} abundance, χ{sub NH{sub 3}} = 4.6 × 10{sup –8}. In the coldest star-forming region, we find that the measured dust temperatures are lower than the measured gas temperatures (mean and standard deviations T {sub dust,} {sub avg} ∼ 11.6 ± 0.2 K versus T {sub gas,} {sub avg} ∼ 15.2 ± 1.5 K), which may indicate that the gas and dust are not well-coupled in the youngest regions (∼0.5 Myr) or that these observations probe a regime where the dust and/or gas temperature measurements are unreliable. Finally, we calculate millimeter fluxes based on the temperatures and column densities derived from NH{sub 3}, which suggest that millimeter dust continuum observations of massive star-forming regions, such as the Bolocam Galactic Plane Survey or ATLASGAL, can probe hot cores, cold cores, and the dense gas lanes from which they form, and are generally not dominated by the hottest core.

  4. The growth of the central region by acquisition of counterrotating gas in star-forming galaxies

    PubMed Central

    Chen, Yan-Mei; Shi, Yong; Tremonti, Christy A.; Bershady, Matt; Merrifield, Michael; Emsellem, Eric; Jin, Yi-Fei; Huang, Song; Fu, Hai; Wake, David A.; Bundy, Kevin; Stark, David; Lin, Lihwai; Argudo-Fernandez, Maria; Bergmann, Thaisa Storchi; Bizyaev, Dmitry; Brownstein, Joel; Bureau, Martin; Chisholm, John; Drory, Niv; Guo, Qi; Hao, Lei; Hu, Jian; Li, Cheng; Li, Ran; Lopes, Alexandre Roman; Pan, Kai-Ke; Riffel, Rogemar A.; Thomas, Daniel; Wang, Lan; Westfall, Kyle; Yan, Ren-Bin

    2016-01-01

    Galaxies grow through both internal and external processes. In about 10% of nearby red galaxies with little star formation, gas and stars are counter-rotating, demonstrating the importance of external gas acquisition in these galaxies. However, systematic studies of such phenomena in blue, star-forming galaxies are rare, leaving uncertain the role of external gas acquisition in driving evolution of blue galaxies. Here, based on new measurements with integral field spectroscopy of a large representative galaxy sample, we find an appreciable fraction of counter-rotators among blue galaxies (9 out of 489 galaxies). The central regions of blue counter-rotators show younger stellar populations and more intense, ongoing star formation than their outer parts, indicating ongoing growth of the central regions. The result offers observational evidence that the acquisition of external gas in blue galaxies is possible; the interaction with pre-existing gas funnels the gas into nuclear regions (<1 kpc) to form new stars. PMID:27759033

  5. The roles of stellar feedback and galactic environment in star-forming molecular clouds

    NASA Astrophysics Data System (ADS)

    Rey-Raposo, Ramon; Dobbs, Clare; Agertz, Oscar; Alig, Christian

    2017-01-01

    Feedback from massive stars is thought to play an important role in the evolution of molecular clouds. In this work, we analyse the effects of stellar winds and supernovae (SNe) in the evolution of two massive (˜106 M⊙) giant molecular clouds: one gravitationally bound collapsing cloud and one unbound cloud undergoing disruption by galactic shear. These two clouds have been extracted from a large-scale galaxy model and are re-simulated at a spatial resolution of ˜0.01 pc, including feedback from winds, SNe, and the combined effect of both. We find that stellar winds stop accretion of gas on to sink particles, and can also trigger star formation in the shells formed by the winds, although the overall effect is to reduce the global star formation rate of both clouds. Furthermore, we observe that winds tend to escape through the corridors of diffuse gas. The effect of SNe is not so prominent and the star formation rate is similar to models neglecting stellar feedback. We find that most of the energy injected by the SNe is radiated away, but overdense areas are created by multiple and concurrent SN events especially in the most virialized cloud. Our results suggest that the impact of stellar feedback is sensitive to the morphology of star-forming clouds, which is set by large-scale galactic flows, being of greater importance in clouds undergoing gravitational collapse.

  6. NEAR-INFRARED CIRCULAR POLARIZATION SURVEY IN STAR-FORMING REGIONS: CORRELATIONS AND TRENDS

    SciTech Connect

    Kwon, Jungmi; Tamura, Motohide; Hough, James H.; Lucas, Phil W.; Kusakabe, Nobuhiko; Kandori, Ryo; Nagata, Tetsuya; Nakajima, Yasushi; Nagayama, Takahiro

    2014-11-01

    We have conducted a systematic near-infrared circular polarization (CP) survey in star-forming regions, covering high-mass, intermediate-mass, and low-mass young stellar objects. All the observations were made using the SIRPOL imaging polarimeter on the Infrared Survey Facility 1.4 m telescope at the South African Astronomical Observatory. We present the polarization properties of 10 sub-regions in 6 star-forming regions. The polarization patterns, extents, and maximum degrees of linear and circular polarizations are used to determine the prevalence and origin of CP in the star-forming regions. Our results show that the CP pattern is quadrupolar in general, the CP regions are extensive, up to 0.65 pc, the CP degrees are high, up to 20%, and the CP degrees decrease systematically from high- to low-mass young stellar objects. The results are consistent with dichroic extinction mechanisms generating the high degrees of CP in star-forming regions.

  7. Early star-forming galaxies and the reionization of the Universe.

    PubMed

    Robertson, Brant E; Ellis, Richard S; Dunlop, James S; McLure, Ross J; Stark, Daniel P

    2010-11-04

    Star-forming galaxies trace cosmic history. Recent observational progress with the NASA Hubble Space Telescope has led to the discovery and study of the earliest known galaxies, which correspond to a period when the Universe was only ∼800 million years old. Intense ultraviolet radiation from these early galaxies probably induced a major event in cosmic history: the reionization of intergalactic hydrogen.

  8. THE FRAGMENTATION OF MAGNETIZED, MASSIVE STAR-FORMING CORES WITH RADIATIVE FEEDBACK

    SciTech Connect

    Myers, Andrew T.; McKee, Christopher F.; Cunningham, Andrew J.; Klein, Richard I.; Krumholz, Mark R.

    2013-04-01

    We present a set of three-dimensional, radiation-magnetohydrodynamic calculations of the gravitational collapse of massive (300 M{sub Sun }), star-forming molecular cloud cores. We show that the combined effects of magnetic fields and radiative feedback strongly suppress core fragmentation, leading to the production of single-star systems rather than small clusters. We find that the two processes are efficient at suppressing fragmentation in different regimes, with the feedback most effective in the dense, central region and the magnetic field most effective in more diffuse, outer regions. Thus, the combination of the two is much more effective at suppressing fragmentation than either one considered in isolation. Our work suggests that typical massive cores, which have mass-to-flux ratios of about 2 relative to critical, likely form a single-star system, but that cores with weaker fields may form a small star cluster. This result helps us understand why the observed relationship between the core mass function and the stellar initial mass function holds even for {approx}100 M{sub Sun} cores with many thermal Jeans masses of material. We also demonstrate that a {approx}40 AU Keplerian disk is able to form in our simulations, despite the braking effect caused by the strong magnetic field.

  9. The Lyman Continuum Escape Fraction of Dwarf, Star-Forming Galaxies at z~1

    NASA Astrophysics Data System (ADS)

    Rutkowski, Michael J.; Scarlata, Claudia; Teplitz, Harry I.; Hayes, Matthew; Salvato, Mara; Beck, Melanie; Mehta, Vihang; Pahl, Anthony

    2015-01-01

    The dominant astrophysical source(s) of Lyman Continuum (LyC, λ<912Å) photons which reionized neutral Hydrogen in the IGM at high (z > 6) redshift remains uncertain. Unfortunately, the direct detection of LyC photons escaping from the analogs of such sources --- i.e., star-forming galaxies --- in the low redshift (z<~1) universe has proven to be remarkably difficult with space-based observatories. Motivated by the few (~2) direct detections of LyC in the local Universe and the results of recent cosmological simulations of galaxy evolution which demonstrate that low-mass (M<~109M⊙) star-forming galaxies may be uniquely suited to contribute to the ionizing, UV background, we present results of recent work to study the LyC escape fraction in z~1 dwarf, star-forming galaxies. We present an independent re-reduction of the WFC3 IR grism data obtained as part of the 3DHST and AGHAST surveys, and identify and select star-forming galaxies at z=0.9-1.4 by their Hα emission. At this redshift range, GALEX FUV and NUV images can be used to cleanly measure the ratio of LyC to UV non-ionizing continuum (i.e., LyCesc,rel) photons. We join our line and redshift identifications with public photometric-redshift catalogs made available by the 3DHST team in order to select an ideal sample of star-forming galaxies which excludes likely contaminants (e.g., AGN, low-redshift interlopers, etc.). Stacking archival GALEX images of ~500 UV non-detected star-forming (SFR<~5M⊙yr-1 ) galaxies, we measure an upper limit to fLyCesc,relequal to ~5%. With these data we are also able to directly constrain fLyCesc,rel for a population of isolated, high equivalent width (EW>200Å), dwarf (M<109M⊙) star-forming galaxies, measuring an upper limit of fLyCesc,rel< ~20% from an analysis of stacked data. We will discuss the implications for reionization of these escape fractions measured from the stacking analysis, as well as possible UV detections from individual dwarf galaxies.

  10. Environmental impacts on dust temperature of star-forming galaxies in the local Universe

    NASA Astrophysics Data System (ADS)

    Matsuki, Yasuhiro; Koyama, Yusei; Nakagawa, Takao; Takita, Satoshi

    2017-04-01

    We present infrared views of the environmental effects on the dust properties in star-forming (SF) galaxies at z ∼ 0, using the AKARI Far-Infrared Surveyor all-sky map and the large spectroscopic galaxy sample from Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7). We restrict the sample to those within the redshift range of 0.05 < z < 0.07 and the stellar mass range of 9.2 < log 10(M*/M⊙). We select SF galaxies based on their Hα equivalent width (EWHα > 4 Å) and emission line flux ratios. We perform far-infrared (FIR) stacking analyses by splitting the SDSS SF galaxy sample according to their stellar mass, specific star formation rate (SSFRSDSS), and environment. We derive total infrared luminosity (LIR) for each subsample using the average flux densities at WIDE-S (90 μm) and WIDE-L (140 μm) bands, and then compute infrared (IR)-based SFR (SFRIR) from LIR. We find a mild decrease of IR-based SSFR (SSFRIR) amongst SF galaxies with increasing local density (∼0.1-dex level at maximum), which suggests that environmental effects do not instantly shut down the SF activity in galaxies. We also derive average dust temperature (Tdust) using the flux densities at 90 and 140 μm bands. We confirm a strong positive correlation between Tdust and SSFRIR, consistent with recent studies. The most important finding of this study is that we find a marginal trend that Tdust increases with increasing environmental galaxy density. Although the environmental trend is much milder than the SSFR-Tdust correlation, our results suggest that the environmental density may affect the dust temperature in SF galaxies, and that the physical mechanism which is responsible for this phenomenon is not necessarily specific to cluster environments because the environmental dependence of Tdust holds down to relatively low-density environments.

  11. A deep Chandra observation of the interacting star-forming galaxy Arp 299

    NASA Astrophysics Data System (ADS)

    Anastasopoulou, K.; Zezas, A.; Ballo, L.; Della Ceca, R.

    2016-08-01

    We present results from a 90 ks Chandra ACIS-S observation of the X-ray luminous interacting galaxy system Arp 299 (NGC 3690/IC 694). We detect 25 discrete X-ray sources with luminosities above ˜4.0 × 1038 erg s-1 covering the entire Ultra Luminous X-ray source (ULX) regime. Based on the hard X-ray spectra of the non-nuclear discrete sources identified in Arp 299, and their association with young, actively star-forming region of Arp 299 we identify them as HMXBs. We find in total 20 off-nuclear sources with luminosities above the ULX limit, 14 of which are point-like sources. Furthermore we observe a marginally significant deficit in the number of ULXs, with respect to the number expected from scaling relations of X-ray binaries with the star formation rate (SFR). Although the high metallicity of the galaxy could result in lower ULX numbers, the good agreement between the observed total X-ray luminosity of ULXs, and that expected from the relevant scaling relation indicates that this deficit could be the result of confusion effects. The integrated spectrum of the galaxy shows the presence of a hot gaseous component with kT = 0.72 ± 0.03 keV, contributing ˜20 per cent of the soft (0.1-2.0 keV) unabsorbed luminosity of the galaxy. A plume of soft X-ray emission in the west of the galaxy indicates a large scale outflow. We find that the AGN in NGC 3690 contributes only 22 per cent of the observed broad-band X-ray luminosity of Arp 299.

  12. METAL DEFICIENCY IN CLUSTER STAR-FORMING GALAXIES AT Z = 2

    SciTech Connect

    Valentino, F.; Daddi, E.; Strazzullo, V.; Gobat, R.; Bournaud, F.; Juneau, S.; Zanella, A.; Renzini, A.; Arimoto, N.

    2015-03-10

    We investigate the environmental effect on the metal enrichment of star-forming galaxies (SFGs) in the farthest spectroscopically confirmed and X-ray-detected cluster, CL J1449+0856 at z = 1.99. We combined Hubble Space Telescope/WFC3 G141 slitless spectroscopic data, our thirteen-band photometry, and a recent Subaru/Multi-object InfraRed Camera and Spectrograph (MOIRCS) near-infrared spectroscopic follow-up to constrain the physical properties of SFGs in CL J1449+0856 and in a mass-matched field sample. After a conservative removal of active galactic nuclei, stacking individual MOIRCS spectra of 6 (31) sources in the cluster (field) in the mass range 10 ≤ log(M/M{sub ⊙}) ≤ 11, we find a ∼4σ lower [N ii]/Hα ratio in the cluster than in the field. Stacking a subsample of 16 field galaxies with Hβ and [O iii] in the observed range, we measure an [O iii]/Hβ ratio fully compatible with the cluster value. Converting these ratios into metallicities, we find that the cluster SFGs are up to 0.25 dex poorer in metals than their field counterparts, depending on the adopted calibration. The low metallicity in cluster sources is confirmed using alternative indicators. Furthermore, we observe a significantly higher Hα luminosity and equivalent width in the average cluster spectrum than in the field. This is likely due to the enhanced specific star formation rate; even if lower dust reddening and/or an uncertain environmental dependence on the continuum-to-nebular emission differential reddening may play a role. Our findings might be explained by the accretion of pristine gas around galaxies at z = 2 and from cluster-scale reservoirs, possibly connected with a phase of rapid halo mass assembly at z > 2 and of a high galaxy merging rate.

  13. ON THE LAST 10 BILLION YEARS OF STELLAR MASS GROWTH IN STAR-FORMING GALAXIES

    SciTech Connect

    Leitner, Samuel N.

    2012-02-01

    The star formation rate-stellar mass relation (SFR-M{sub *}) and its evolution (i.e., the SFR main sequence) describe the growth rate of galaxies of a given stellar mass and at a given redshift. Assuming that present-day star-forming galaxies (SFGs) were always star forming in the past, these growth rate observations can be integrated to calculate average star formation histories (SFHs). Using this Main Sequence Integration (MSI) approach, we trace present-day massive SFGs back to when they were 10%-20% of their current stellar mass. The integration is robust throughout those epochs: the SFR data underpinning our calculations are consistent with the evolution of stellar mass density in this regime. Analytic approximations to these SFHs are provided. Integration-based results reaffirm previous suggestions that current SFGs formed virtually all of their stellar mass at z < 2. It follows that massive galaxies observed at z > 2 are not the typical progenitors of SFGs today. We also check MSI-based SFHs against those inferred from analysis of the fossil record-from spectral energy distributions (SEDs) of SFGs in the Sloan Digital Sky Survey and color-magnitude diagrams (CMDs) of resolved stars in dwarf irregular galaxies. Once stellar population age uncertainties are accounted for, the main sequence is in excellent agreement with SED-based SFHs (from VESPA). Extrapolating SFR main sequence observations to dwarf galaxies, we find differences between MSI results and SFHs from CMD analysis of Advanced Camera for Surveys Nearby Galaxy Survey Treasury and Local Group galaxies. Resolved dwarfs appear to grow much slower than main sequence trends imply, and also slower than slightly higher mass SED-analyzed galaxies. This difference may signal problems with SFH determinations, but it may also signal a shift in star formation trends at the lowest stellar masses.

  14. Stellar Masses and Star Formation Rates of Lensed, Dusty, Star-forming Galaxies from the SPT Survey

    NASA Astrophysics Data System (ADS)

    Ma, Jingzhe; Gonzalez, Anthony. H.; Spilker, J. S.; Strandet, M.; Ashby, M. L. N.; Aravena, M.; Béthermin, M.; Bothwell, M. S.; de Breuck, C.; Brodwin, M.; Chapman, S. C.; Fassnacht, C. D.; Greve, T. R.; Gullberg, B.; Hezaveh, Y.; Malkan, M.; Marrone, D. P.; Saliwanchik, B. R.; Vieira, J. D.; Weiss, A.; Welikala, N.

    2015-10-01

    To understand cosmic mass assembly in the universe at early epochs, we primarily rely on measurements of the stellar masses and star formation rates (SFRs) of distant galaxies. In this paper, we present stellar masses and SFRs of six high-redshift (2.8 ≤ z ≤ 5.7) dusty, star-forming galaxies (DSFGs) that are strongly gravitationally lensed by foreground galaxies. These sources were first discovered by the South Pole Telescope (SPT) at millimeter wavelengths and all have spectroscopic redshifts and robust lens models derived from Atacama Large Millimeter/submillimeter Array observations. We have conducted follow-up observations to obtain multi-wavelength imaging data using the Hubble Space Telescope (HST), Spitzer, Herschel, and the Atacama Pathfinder EXperiment. We use the high-resolution HST/Wide Field Camera 3 images to disentangle the background source from the foreground lens in Spitzer/IRAC data. The detections and upper limits provide important constraints on the spectral energy distributions (SEDs) for these DSFGs, yielding stellar masses, IR luminosities, and SFRs. The SED fits of six SPT sources show that the intrinsic stellar masses span a range more than one order of magnitude with a median value ˜5 ×1010 M⊙. The intrinsic IR luminosities range from 4 × 1012 L⊙ to 4 × 1013 L⊙. They all have prodigious intrinsic SFRs of 510-4800 M⊙ yr-1. Compared to the star-forming main sequence (MS), these six DSFGs have specific SFRs that all lie above the MS, including two galaxies that are a factor of 10 higher than the MS. Our results suggest that we are witnessing ongoing strong starburst events that may be driven by major mergers.

  15. STELLAR MASSES AND STAR FORMATION RATES OF LENSED, DUSTY, STAR-FORMING GALAXIES FROM THE SPT SURVEY

    SciTech Connect

    Ma, Jingzhe; Gonzalez, Anthony H.; Spilker, J. S.; Marrone, D. P.; Strandet, M.; Ashby, M. L. N.; Aravena, M.; Béthermin, M.; Breuck, C. de; Gullberg, B.; Bothwell, M. S.; Brodwin, M.; Chapman, S. C.; Fassnacht, C. D.; Greve, T. R.; Hezaveh, Y.; Malkan, M.; Saliwanchik, B. R.; and others

    2015-10-10

    To understand cosmic mass assembly in the universe at early epochs, we primarily rely on measurements of the stellar masses and star formation rates (SFRs) of distant galaxies. In this paper, we present stellar masses and SFRs of six high-redshift (2.8 ≤ z ≤ 5.7) dusty, star-forming galaxies (DSFGs) that are strongly gravitationally lensed by foreground galaxies. These sources were first discovered by the South Pole Telescope (SPT) at millimeter wavelengths and all have spectroscopic redshifts and robust lens models derived from Atacama Large Millimeter/submillimeter Array observations. We have conducted follow-up observations to obtain multi-wavelength imaging data using the Hubble Space Telescope (HST), Spitzer, Herschel, and the Atacama Pathfinder EXperiment. We use the high-resolution HST/Wide Field Camera 3 images to disentangle the background source from the foreground lens in Spitzer/IRAC data. The detections and upper limits provide important constraints on the spectral energy distributions (SEDs) for these DSFGs, yielding stellar masses, IR luminosities, and SFRs. The SED fits of six SPT sources show that the intrinsic stellar masses span a range more than one order of magnitude with a median value ∼5 ×10{sup 10} M{sub ⊙}. The intrinsic IR luminosities range from 4 × 10{sup 12} L{sub ⊙} to 4 × 10{sup 13} L{sub ⊙}. They all have prodigious intrinsic SFRs of 510–4800 M{sub ⊙} yr{sup −1}. Compared to the star-forming main sequence (MS), these six DSFGs have specific SFRs that all lie above the MS, including two galaxies that are a factor of 10 higher than the MS. Our results suggest that we are witnessing ongoing strong starburst events that may be driven by major mergers.

  16. 76 FR 61725 - Agency Information Collection Activities: Case Submission Form, Case Assistance Form; (Form DHS...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-10-05

    ... SECURITY Agency Information Collection Activities: Case Submission Form, Case Assistance Form; (Form DHS... CIS Ombudsman to identify the issue such as: (1) A case problem which is a request for information.... SUMMARY: The Department of Homeland Security, Office of the Citizenship and Immigration Service...

  17. Tracing the potential planet-forming regions around seven pre-main-sequence stars

    NASA Astrophysics Data System (ADS)

    Schegerer, A. A.; Wolf, S.; Hummel, C. A.; Quanz, S. P.; Richichi, A.

    2009-07-01

    Aims: We investigate the nature of the innermost regions with radii of several AUs of seven circumstellar disks around pre-main-sequence stars, T Tauri stars in particular. Our object sample contains disks apparently at various stages of their evolution. Both single stars and spatially resolved binaries are considered. In particular, we search for inner disk gaps as proposed for several young stellar objects (YSOs). When analyzing the underlying dust population in the atmosphere of circumstellar disks, the shape of the 10 μm feature should additionally be investigated. Methods: We performed interferometric observations in N band (8-13 μm) with the Mid-Infrared Interferometric Instrument (MIDI) at the Very Large Telescope Interferometer (VLTI) using baseline lengths of between 54 m and 127 m. The data analysis is based on radiative-transfer simulations using the Monte Carlo code MC3D by modeling simultaneously the spectral energy distribution (SED), N band spectra, and interferometric visibilities. Correlated and uncorrelated N band spectra are compared to investigate the radial distribution of the dust composition of the disk atmosphere. Results: Spatially resolved mid-infrared (MIR) emission was detected in all objects. For four objects (DR Tau, RU Lup, S CrA N, and S CrA S), the observed N band visibilities and corresponding SEDs could be simultaneously simulated using a parameterized active disk-model. For the more evolved objects of our sample, HD 72106 and HBC 639, a purely passive disk-model provides the closest fit. The visibilities inferred for the source RU Lup allow the presence of an inner disk gap. For the YSO GW Ori, one of two visibility measurements could not be simulated by our modeling approach. All uncorrelated spectra reveal the 10 μm silicate emission feature. In contrast to this, some correlated spectra of the observations of the more evolved objects do not show this feature, indicating a lack of small silicates in the inner versus the outer

  18. Constraining the Star Forming History in Monoceros: A Study of Embedded Cluster Ages and Spatial Structure

    NASA Astrophysics Data System (ADS)

    Marinas, Naibi; Lada, Elizabeth; Ybarra, Jason; Fleming, Scott

    2010-08-01

    We propose to use FLAMINGOS multi-object spectrometer on the KPNO 4 meter telescope to complete a spectroscopic survey of 5 clusters in the Monoceros GMC. The data will be combined with existing FLAMINGOS photometry to determine the ages and masses of the stars in the clusters using the HR Diagram and PMS evolutionary models. This information, combined with the spatial distribution of clusters in the cloud, determined from previous observations, will allow us to investigate the ages and age spreads of the embedded clusters and the star forming histories of the clusters and the molecular cloud.

  19. Constraining the Star Forming History in Monoceros: A Study of Embedded Cluster Ages and Spatial Structure

    NASA Astrophysics Data System (ADS)

    Lada, Elizabeth A.; Marinas, Naibi; Levine, Joanna L.; Ferreira, Bruno

    2009-08-01

    We propose to use FLAMINGOS multi-object spectrometer on the KPNO 4 meter telescope to complete a spectroscopic survey of 7 clusters in the Monoceros GMC. The data will be combined with existing FLAMINGOS photometry to determine the ages and masses of the stars in the clusters using the HR Diagram and PMS evolutionary models. This information, combined with the spatial distribution of clusters in the cloud, determined from previous observations, will allow us to investigate the ages and age spreads of the embedded clusters and the star forming histories of the clusters and the molecular cloud.

  20. A search for gravitationally lensed water masers in dusty quasars and star-forming galaxies

    NASA Astrophysics Data System (ADS)

    McKean, J. P.; Impellizzeri, C. M. V.; Roy, A. L.; Castangia, P.; Samuel, F.; Brunthaler, A.; Henkel, C.; Wucknitz, O.

    2011-02-01

    Luminous extragalactic water masers are known to be associated with active galactic nuclei and have provided accurate estimates for the mass of the central supermassive black hole and the size and structure of the circumnuclear accretion disc in nearby galaxies. To find water maser systems at much higher redshifts, we have begun a survey of known gravitationally lensed quasars and star-forming galaxies. In this paper, we present a search for 22 GHz (rest-frame) water masers towards five dusty, gravitationally lensed quasars and star-forming galaxies at redshifts between 2.3 and 2.9 with the Effelsberg radio telescope and the Expanded Very Large Array (EVLA). Our observations do not find any new definite examples of high-redshift water maser galaxies, suggesting that large reservoirs of dust and gas are not a sufficient condition for powerful water maser emission. However, we do find the tentative detection of a water maser system in the active galaxy IRAS 10214+4724 at redshift 2.285. Our survey has now doubled the number of gravitationally lensed galaxies and quasars that have been searched for high-redshift water maser emission. We also present an updated analysis of the high-redshift water maser luminosity function that is based on the results presented here and from the only cosmologically distant (z > 1) water maser galaxy found thus far, MG J0414+0534 at redshift 2.64. By comparing with the water maser luminosity function locally and at moderate redshifts, we find that there must be some evolution in the luminosity function of water maser galaxies at high redshifts. By assuming a moderate evolution [(1 +z)4] in the water maser luminosity function, we find that blind surveys for water maser galaxies are only worthwhile with extremely high sensitivity like that of the planned Square Kilometre Array (Phase 2), which is scheduled to be completed by 2020. However, instruments like the EVLA and MeerKAT will be capable of detecting water maser systems similar to the

  1. I Zw 18, a Template for Star-Forming, z is Greater than 7 Galaxies

    NASA Technical Reports Server (NTRS)

    Heap, Sara R.; Hubeny, Ivan

    2011-01-01

    I Zw 18-NW, one of the most primitive nearby dwarf galaxies, is arguably the best template we have for star-forming, very high-redshift galaxies (z>7). We have therefore obtained a far-UV spectrum of I Zw 18-NW using Hubble's Cosmic Origins Spectrograph (COS). The spectrum indicates star-formation over the past approx.10 Myr, a very low stellar metallicity, log Z/Zsun approx. -1.7, and high average stellar rotation rate, Vsini approx.200 km/s. Stellar wind lines are very weak, and the edge velocity of wind lines is very low (approx.250 km/s). The overall properties of I Zw 18-NW are consistent with theories of very low metallicity, rapidly rotating stars, e.g. Meynet et al. (2006).

  2. Spectroscopic observations of active solar-analog stars with high X-ray luminosity, as a proxy of superflare stars

    NASA Astrophysics Data System (ADS)

    Notsu, Yuta; Honda, Satoshi; Maehara, Hiroyuki; Notsu, Shota; Namekata, Kosuke; Nogami, Daisaku; Shibata, Kazunari

    2017-02-01

    Recent studies of solar-type superflare stars have suggested that even old slowly rotating stars similar to the Sun can have large starspots and superflares. We conducted high-dispersion spectroscopy of 49 nearby solar-analog stars (G-type main-sequence stars with Teff ≈ 5600-6000 K) identified as ROSAT soft X-ray sources, which are not binary stars from previous studies. We expected that these stars could be used as a proxy of bright solar-analog superflare stars, since superflare stars are expected to show strong X-ray luminosity. More than half (37) of the 49 target stars show no evidence of binarity, and their atmospheric parameters (temperature, surface gravity, and metallicity) are within the range of ordinary solar-analog stars. We measured the intensity of Ca II 8542 and Hα lines, which are good indicators of the stellar chromospheric activity. The intensity of these lines indicates that all the target stars have large starspots. We also measured v sin i (projected rotational velocity) and lithium abundance for the target stars. Li abundance is a key to understanding the evolution of the stellar convection zone, which reflects the stellar age, mass and rotational history. We confirmed that many of the target stars rapidly rotate and have high Li abundance, compared with the Sun, as suggested by many previous studies. There are, however, also some target stars that rotate slowly (v sin i = 2-3 km s-1) and have low Li abundance like the Sun. These results support that old and slowly rotating stars similar to the Sun could have high activity levels and large starspots. This is consistent with the results of our previous studies of solar-type superflare stars. In the future, it is important to conduct long-term monitoring observations of these active solar-analog stars in order to investigate detailed properties of large starspots from the viewpoint of stellar dynamo theory.

  3. Comparing ligo merger rate observations with theory: distribution of star-forming conditions

    SciTech Connect

    Belczynski, Kryzysztof; Kopparapu, R; O' Shaughnessy, R

    2008-01-01

    Within the next decade, ground based gravitational wave detectors are in principle capable of determining the compact object merger rate per unit volume of the local universe to better than 20% with more than 30 detections. Though these measurements can constrain our models of stellar, binary, and cluster evolution in the nearby present-day and ancient universe, we argue that the universe is sufficiently heterogeneous (in age and metallicity distribution at least) and that merger rates predicted by these models can be sufficiently sensitive to those heterogeneities so that a fair comparison of models per unit similar star forming mass necessarily introduces at least an additional 30%--50% systematic error into any constraints on compact binary evolution models. Without adding new electromagnetic constraints on massive binary evolution or relying on more information from each merger (e.g. , binary masses and spins), as few as the {approx_equal}5 merger detections could exhaust the information available in a naive comparison to merger rate predictions. As a concrete example immediately relevant to analysis of initial and enhanced LIGO results, we use a nearby-universe catalog to demonstrate that no one tracer of stellar content can be consistently used to constrain merger rates without introducing a systematic error of order 0(30%) at 90% confidence (depending on the type of binary involved). For example, though binary black holes typically take many Gyr to merge, binary neutron stars often merge rapidly; different tracers of stellar content are required for these two types. More generally, we argue that theoretical binary evolution can depend sufficiently sensitively on star-forming conditions -- even assuming no uncertainty in binary evolution model -- that the distribution of star forming conditions must be incorporated to reduce the systematic error in merger rate predictions below roughly 40%. We emphasize that the degree of sensitivity to star-forming

  4. Galactic massive star forming regions near and far: a (sub)millimeter study of the Orion Molecular Cloud 1 and W49A

    NASA Astrophysics Data System (ADS)

    Peng, Tzu-Cheng

    2010-05-01

    Massive stars play an important role in shaping the structure of galaxies due to the large energy output during their lifetime. However, because of the short evolutionary time scales, the large extinction toward their birth places, and the large distance of massive stars, our understanding of their formation is still sketchy. Hence, the observations of two well-known massive star forming regions in our Galaxy (W49A at 11.4 kpc and Orion Molecular Cloud 1 at 414 pc) were carried out using the IRAM 30 m and APEX telescopes, including large-scale mappings of various molecular line emission, such as CO isotopologues, HCN, HCO+, and SiO. The results of W49A show that its starburst was triggered by expanding shells, causing fragmentation that lead to the formation of massive stars. The cause of the shell expansion is not clear, but likely due to the stellar feedbacks from a first generation of young massive stars by strong stellar winds and ultraviolet radiation, or the interaction between stars in a cluster, which is possibly related to the large-scale gas ejections found in the W49 complex with a total kinetic energy of few times 1050 erg. Apart from W49A, the study in Orion Molecular Cloud 1 reveals a more detailed picture of young massive stars strongly interacting with their local environment. The highly excited CO emission in Orion Molecular Cloud 1 shows two main components: one is the north-south dense ridge where two active star-forming regions (Orion BN/KL and Orion South) are located, and the other one consists of photon-dominated regions (e.g., the Orion Bar and Orion East) spread over the whole area, where gas and dust are heated by ultraviolet photons from the Trapezium cluster. In addition, several outflows are detected in the higher-J transitions of CO, which indicates the important role of shock heating associated with star-forming activities.

  5. The structure of the interstellar medium of star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Hopkins, Philip F.; Quataert, Eliot; Murray, Norman

    2012-04-01

    We develop and implement numerical methods for including stellar feedback in galaxy-scale numerical simulations. Our models include simplified treatments of heating by Type I and Type II supernovae, gas recycling from young stars and asymptotic giant branch winds, heating from the shocked stellar winds, H II photoionization heating and radiation pressure from stellar photons. The energetics and time dependence associated with the feedback are taken directly from stellar evolution models. We implement these stellar feedback models in smoothed particle hydrodynamic simulations with pc-scale resolution, modelling galaxies from Small Magellanic Cloud (SMC) like dwarfs and Milky Way (MW) analogues to massive z˜ 2 star-forming discs. In the absence of stellar feedback, gas cools rapidly and collapses without limit into dense sub-units, inconsistent with observations. By contrast, in all cases with feedback, the interstellar medium (ISM) quickly approaches a statistical steady state in which giant molecular clouds (GMCs) continuously form, disperse and re-form, leading to a multiphase ISM. In this paper, we quantify the properties of the ISM and GMCs in this self-regulated state. In a companion paper we study the galactic winds driven by stellar feedback. Our primary results on the structure of the ISM in star-forming galaxies include the following. 1. Star-forming galaxies generically self-regulate so that the cool, dense gas maintains Toomre's Q˜ 1. Most of the volume is occupied by relatively diffuse hot gas, while most of the mass is in dense GMC complexes created by self-gravity. The phase structure of the gas and the gas mass fraction at high densities are much more sensitive probes of the physics of stellar feedback than integrated quantities such as the Toomre Q or gas velocity dispersion. 2. Different stellar feedback mechanisms act on different spatial (and density) scales. Radiation pressure and H II gas pressure are critical for preventing runaway collapse

  6. Ultraluminous X-Ray Source Correlations with Star-Forming Regions

    NASA Astrophysics Data System (ADS)

    Swartz, Douglas A.; Tennant, Allyn F.; Soria, Roberto

    2009-09-01

    Maps of low-inclination nearby galaxies in Sloan Digitized Sky Survey u - g, g - r, and r - i colors are used to determine whether ultraluminous X-ray sources (ULXs) are predominantly associated with star-forming regions of their host galaxies. An empirical selection criterion is derived from colors of H II regions in M 81 and M 101 that differentiates between the young, blue stellar component and the older disk and bulge population. This criterion is applied to a sample of 58 galaxies of Hubble type S0 and later and verified through an application of Fisher's linear discriminant analysis. It is found that 60% (49%) of ULXs in optically bright environments are within regions blueward of their host galaxy's H II regions compared to only 27% (0%) of a control sample according to the empirical (Fisher) criterion. This is an excess of 3σ above the 32% (27%) expected if the ULXs were randomly distributed within their galactic hosts. This indicates a ULX preference for young, lsim10 Myr, OB associations. However, none of the ULX environments have the morphology and optical brightness suggestive of a massive young super-star cluster though several are in extended or crowded star-forming (blue) environments that may contain clusters unresolved by Sloan imaging. Ten of the 12 ULX candidates with estimated X-ray luminosities in excess of 3 × 1039 erg s-1 are equally divided among the group of ULX environments redward of H II regions and the group of optically faint regions. This likely indicates that the brightest ULXs turn on at a time somewhat later than typical of H II regions; say 10-20 Myr after star formation has ended. This would be consistent with the onset of an accretion phase as the donor star ascends the giant branch if the donor is an lsim20 M sun star.

  7. An all-sky sample of intermediate-mass star-forming regions

    SciTech Connect

    Lundquist, Michael J.; Kobulnicky, Henry A.; Alexander, Michael J.; Kerton, Charles R.; Arvidsson, Kim

    2014-04-01

    We present an all-sky sample of 984 candidate intermediate-mass Galactic star-forming regions that are color selected from the Infrared Astronomical Satellite (IRAS) Point Source Catalog and morphologically classify each object using mid-infrared Wide-field Infrared Survey Explorer (WISE) images. Of the 984 candidates, 616 are probable star-forming regions (62.6%), 128 are filamentary structures (13.0%), 39 are point-like objects of unknown nature (4.0%), and 201 are galaxies (20.4%). We conduct a study of four of these regions, IRAS 00259+5625, IRAS 00420+5530, IRAS 01080+5717, and IRAS 05380+2020, at Galactic latitudes |b| > 5° using optical spectroscopy from the Wyoming Infrared Observatory, along with near-infrared photometry from the Two-Micron All Sky Survey, to investigate their stellar content. New optical spectra, color-magnitude diagrams, and color-color diagrams reveal their extinctions, spectrophotometric distances, and the presence of small stellar clusters containing 20-78 M {sub ☉} of stars. These low-mass diffuse star clusters contain ∼65-250 stars for a typical initial mass function, including one or more mid-B stars as their most massive constituents. Using infrared spectral energy distributions we identify young stellar objects near each region and assign probable masses and evolutionary stages to the protostars. The total infrared luminosity lies in the range 190-960 L {sub ☉}, consistent with the sum of the luminosities of the individually identified young stellar objects.

  8. Equilibrium model prediction for the scatter in the star-forming main sequence

    NASA Astrophysics Data System (ADS)

    Mitra, Sourav; Davé, Romeel; Simha, Vimal; Finlator, Kristian

    2017-01-01

    The analytic `equilibrium model' for galaxy evolution using a mass balance equation is able to reproduce mean observed galaxy scaling relations between stellar mass, halo mass, star formation rate (SFR), and metallicity across the majority of cosmic time with a small number of parameters related to feedback. Here, we aim to test this data-constrained model to quantify deviations from the mean relation between stellar mass and SFR, i.e. the star-forming galaxy main sequence (MS). We implement fluctuation in halo accretion rates parametrized from merger-based simulations, and quantify the intrinsic scatter introduced into the MS under the assumption that fluctuations in star formation follow baryonic inflow fluctuations. We predict the 1σ MS scatter to be ˜0.2-0.25 dex over the stellar mass range 108-1011 M⊙ and a redshift range 0.5 ≲ z ≲ 3 for SFRs averaged over 100 Myr. The scatter increases modestly at z ≳ 3, as well as by averaging over shorter time-scales. The contribution from merger-induced star formation is generally small, around 5 per cent today and 10-15 per cent during the peak epoch of cosmic star formation. These results are generally consistent with available observations, suggesting that deviations from the MS primarily reflect stochasticity in the inflow rate owing to halo mergers.

  9. The structure and early evolution of massive star forming regions. Substructure in the infrared dark cloud SDC13

    NASA Astrophysics Data System (ADS)

    McGuire, C.; Fuller, G. A.; Peretto, N.; Zhang, Q.; Traficante, A.; Avison, A.; Jimenez-Serra, I.

    2016-10-01

    Context. Investigations into the substructure of massive star forming regions are essential for understanding the observed relationships between core mass distributions and mass distributions in stellar clusters, differentiating between proposed mechanisms of massive star formation. Aims: We study the substructure in the two largest fragments (i.e. cores) MM1 and MM2, in the infrared dark cloud complex SDC13. As MM1 appears to be in a later stage of evolution than MM2, comparing their substructure provides an insight in to the early evolution of massive clumps. Methods: We report the results of high resolution SMA dust continuum observations towards MM1 and MM2. Combining these data with Herschel observations, we carry out RADMC-3D radiative transfer modelling to characterise the observed substructure. Results: SMA continuum data indicates 4 sub-fragments in the SDC13 region. The nature of the second brightest sub-fragment (B) is uncertain as it does not appear as prominent at the lower MAMBO resolution or at radio wavelengths. Statistical analysis indicates that it is unlikely to be a background source, an AGB star, or the free-free emission of a HII region. It is plausible that B is a runaway object ejected from MM1. MM1, which is actively forming stars, consists of two sub-fragments A and C. This is confirmed by 70 μmHerschel data. While MM1 and MM2 appear quite similar in previous low resolution observations, at high resolution, the sub-fragment at the centre of MM2 (D) is much fainter than sub-fragment at the centre of MM1 (A). RADMC-3D models of MM1 and MM2 are able to reproduce these results, modelling MM2 with a steeper density profile and higher mass than is required for MM1. The relatively steep density profile of MM2 depends on a significant temperature decrease in its centre, justified by the lack of star formation in MM2. A final stellar population for MM1 was extrapolated, indicating a star formation efficiency typical of regions of core and cluster

  10. Monitoring the activity of the Be star OT Geminorum

    NASA Astrophysics Data System (ADS)

    Arellano Ferro, A.; Sareyan, J. P.; Avila, J. J.; Gonzalez, F.; Dumont, M.; Geos

    1998-02-01

    Observations obtained in 1995-1996 of the Be star OT Geminorum are reported and show that in october 1995 the star reached a very active phase with large variations around a bright plateau, a phase of activity we have also distinguished in previous observations dating from 1960. The time scales involved are discussed and suggest that the violent variations of the activity propagate very quickly on the whole surface of the star or on a huge portion of it. No likely pulsation periods were found. The assumption that the detected activity is due to the effects of an hypothetical companion leads to conclude that such companion could not be detected by the present interferometric techniques. Partly based on observations obtained at the La Luz Observatory of the University of Guanajuato, Mexico.

  11. The clustering properties of radio-selected AGN and star-forming galaxies up to redshifts z ˜ 3

    NASA Astrophysics Data System (ADS)

    Magliocchetti, M.; Popesso, P.; Brusa, M.; Salvato, M.; Laigle, C.; McCracken, H. J.; Ilbert, O.

    2017-01-01

    We present the clustering properties of a complete sample of 968 radio sources detected at 1.4 GHz by the Very Large Array (VLA)-COSMOS survey with radio fluxes brighter than 0.15 mJy. 92 per cent have redshift determinations from the Laigle et al. catalogue. Based on their radio luminosity, these objects have been divided into 644 AGN and 247 star-forming galaxies. By fixing the slope of the autocorrelation function to γ = 2, we find r_0=11.7^{+1.0}_{-1.1} Mpc for the clustering length of the whole sample, while r_0=11.2^{+2.5}_{-3.3} Mpc and r_0=7.8^{+1.6}_{-2.1} Mpc (r_0=6.8^{+1.4}_{-1.8} Mpc for z ≤ 0.9) are, respectively, obtained for AGN and star-forming galaxies. These values correspond to minimum masses for dark matter haloes of M_min=10^{13.6^{+0.3}_{-0.6}} M⊙ for radio-selected AGN and M_min=10^{13.1^{+0.4}_{-1.6}} M⊙ for radio-emitting star-forming galaxies (M_min=10^{12.7^{+0.7}_{-2.2}} M⊙ for z ≤ 0.9). Comparisons with previous works imply an independence of the clustering properties of the AGN population with respect to both radio luminosity and redshift. We also investigate the relationship between dark and luminous matter in both populations. We obtain /Mhalo ≲ 10- 2.7 for AGN, and /Mhalo ≲ 10- 2.4 in the case of star-forming galaxies. Furthermore, if we restrict to z ≲ 0.9 star-forming galaxies, we derive /Mhalo ≲ 10- 2.1, result that clearly shows the cosmic process of stellar build-up as one moves towards the more local universe. Comparisons between the observed space density of radio-selected AGN and that of dark matter haloes show that about one in two haloes is associated with a black hole in its radio-active phase. This suggests that the radio-active phase is a recurrent phenomenon.

  12. Large Binocular Telescope and Sptizer Spectroscopy of Star-forming Galaxies at 1 < z < 3: Extinction and Star Formation Rate Indicators

    NASA Technical Reports Server (NTRS)

    Rujopakarn, W.; Rieke, G. H.; Papovich, C. J.; Weiner, B. J.; Rigby, Jane; Rex, M.; Bian, F.; Kuhn, O. P.; Thompson, D.

    2012-01-01

    We present spectroscopic observations in the rest-frame optical and near- to mid-infrared wavelengths of four gravitationally lensed infrared (IR) luminous star-forming galaxies at redshift 1 < z < 3 from the LUCIFER instrument on the Large Binocular Telescope and the Infrared Spectrograph on Spitzer. The sample was selected to represent pure, actively star-forming systems, absent of active galactic nuclei. The large lensing magnifications result in high signal-to-noise spectra that can probe faint IR recombination lines, including Paa and Bra at high redshifts. The sample was augmented by three lensed galaxies with similar suites of unpublished data and observations from the literature, resulting in the final sample of seven galaxies. We use the IR recombination lines in conjunction with Ha observations to probe the extinction, Av, of these systems, as well as testing star formation rate (SFR) indicators against the SFR measured by fitting spectral energy distributions to far-IR photometry. Our galaxies occupy a range of Av from 0 to 5.9 mag, larger than previously known for a similar range of IR luminosities at these redshifts. Thus, estimates of SFR even at z 2 must take careful count of extinction in the most IR luminous galaxies.We also measure extinction by comparing SFR estimates from optical emission lines with those from far- IR measurements. The comparison of results from these two independent methods indicates a large variety of dust distribution scenarios at 1 < z < 3. Without correcting for dust extinction, the Ha SFR indicator underestimates the SFR; the size of the necessary correction depends on the IR luminosity and dust distribution scenario. Individual SFR estimates based on the 6.2µm polycyclic aromatic hydrocarbon emission line luminosity do not show a systematic discrepancy with extinction, although a considerable, 0.2 dex, scatter is observed.

  13. Stellar model chromospheres. IX - Chromospheric activity in dwarf stars

    NASA Technical Reports Server (NTRS)

    Kelch, W. L.; Worden, S. P.; Linsky, J. L.

    1979-01-01

    High-resolution Ca II K line profiles are used to model the upper photospheres and lower chromospheres of eight main-sequence stars ranging in spectral type from F0 to M0 and exhibiting different degrees of chromospheric activity. The model chromospheres are studied as a function of spectral type and activity for stars of similar spectral type in order to obtain evidence of enhanced nonradiative heating in the upper-photospheric models and in the ratio of minimum temperature at the base of the chromosphere to effective temperature, a correlation between activity and temperature in the lower chromospheres, and a correlation of the width at the base of the K-line emission core and at the K2 features with activity. Chromospheric radiative losses are estimated for the modelled stars and other previously analyzed main-sequence stars. The results obtained strengthen the argument that dMe flare stars exhibit fundamentally solar-type activity but on an increased scale.

  14. Activity-rotation relations for lower main sequence stars

    NASA Astrophysics Data System (ADS)

    Dobson-Hockey, Andrea Kay

    It was known for some time that stellar rotation and activity are related, both for chromospheric activity and control activity. Younger, more rapidly rotating stars of a given spectral type generally show higher levels of activity than do older, more slowly rotating stars. On the Sun acitivity is distinctly related to magnetic fields. This leads to the suggestion that activity, at least in solar-type stars, is traceable to a magnetic dynamo which results from the interaction of rotation and differential rotation with convection. The more efficient the coriolis forces are at introducing helicity into convective motions, the more the magnetic field will be amplified and the more activity that is expected. The precise nature of the relationship between magnetic fields, rotation, and activity remains to be well-defined. It is the purpose to examine the relationship between activity and rotation in order to better define and express such a relation (or relations). To meet this goal, a comprehensive sample of stars was collected from the published literature having two or more of the following: chromospheric Ca II, H, and K emission indices; coronal soft X-ray illumination; rotation rates; and where possible, ages. It is seen that the use of normalized activity units and Rossby number generally improves the correlation between activity and rotation. The use of the convective turnover time further permits a possible explanation for the distribution of stars in an activity-color diagram. A large and homogeneous data set permits better definition of previously examined functional dependencies such as the time decay of activity and the relationship between chromospheric and coronal activity indicators.

  15. Rapid rotation and mixing in active OB stars - Physical processes

    NASA Astrophysics Data System (ADS)

    Zahn, Jean-Paul

    2011-07-01

    In the standard description of stellar interiors, O and B stars possess a thoroughly mixed convective core surrounded by a stable radiative envelope in which no mixing occurs. But as is well known, this model disagrees strongly with the spectroscopic diagnostic of these stars, which reveals the presence at their surface of chemical elements that have been synthesized in the core. Hence the radiation zone must be the seat of some mild mixing mechanisms. The most likely to operate there are linked with the rotation: these are the shear instabilites triggered by the differential rotation, and the meridional circulation caused by the changes in the rotation profile accompanying the non-homologous evolution of the star. In addition to these hydrodynamical processes, magnetic stresses may play an important role in active stars, which host a magnetic field. These physical processes will be critically examined, together with some others that have been suggested.

  16. Tracing Supernova Enrichment of the Nearest Young Star Forming Complex with High Resolution Stellar Spectroscopy

    NASA Astrophysics Data System (ADS)

    Bubar, Eric Joseph; Mamajek, Eric E.; Pecaut, Mark

    2010-02-01

    The chemical evolution of the galaxy can be examined on a small scale locally by searching for evidence of enrichment by core collapse (type II) supernova explosions among stars belonging to the same star- forming complex. We propose to obtain high resolution spectroscopy of a sample of slowly rotating members of nearby, young stellar groups associated with the nearest star-forming complex: Scorpius-Centaurus. These spectra will be used to perform a precise spectroscopic abundance analysis to test for enrichment of the ~5 Myr-old Upper Scorpius region and neighboring regions by supernova explosions in the neighboring ~ 15 Myr-old Upper Centaurus Lupus and Lower Centaurus Crux subgroups. Enrichment by core-collapse supernovae can be traced by enhancements in oxygen and other alpha- element abundances compared to Fe-peak elements. These abundances can also be used for constraining the chemical homogeneity of members of Upper-Sco. This study will allow us to explore the processes of Galactic chemical evolution and SN enrichment on a small scale (< 0.1 kpc, <10-20 SN) in a complex with a relatively well constrained star formation history and high mass stellar membership.

  17. Physical Conditions of the Interstellar Medium in Star-forming Galaxies at z1.5

    NASA Technical Reports Server (NTRS)

    Hayashi, Masao; Ly, Chun; Shimasaku, Kazuhiro; Motohara, Kentaro; Malkan, Matthew A.; Nagao, Tohru; Kashikawa, Nobunari; Goto, Ryosuke; Naito, Yoshiaki

    2015-01-01

    We present results from Subaru/FMOS near-infrared (NIR) spectroscopy of 118 star-forming galaxies at z approximately equal to 1.5 in the Subaru Deep Field. These galaxies are selected as [O II] lambda 3727 emitters at z approximately equal to 1.47 and 1.62 from narrow-band imaging. We detect H alpha emission line in 115 galaxies, [O III] lambda 5007 emission line in 45 galaxies, and H Beta, [N II] lambda 6584, and [S II]lambda lambda 6716, 6731 in 13, 16, and 6 galaxies, respectively. Including the [O II] emission line, we use the six strong nebular emission lines in the individual and composite rest-frame optical spectra to investigate physical conditions of the interstellar medium in star-forming galaxies at z approximately equal to 1.5. We find a tight correlation between H alpha and [O II], which suggests that [O II] can be a good star formation rate (SFR) indicator for galaxies at z approximately equal to 1.5. The line ratios of H alpha / [O II] are consistent with those of local galaxies. We also find that [O II] emitters have strong [O III] emission lines. The [O III]/[O II] ratios are larger than normal star-forming galaxies in the local Universe, suggesting a higher ionization parameter. Less massive galaxies have larger [O III]/[O II] ratios. With evidence that the electron density is consistent with local galaxies, the high ionization of galaxies at high redshifts may be attributed to a harder radiation field by a young stellar population and/or an increase in the number of ionizing photons from each massive star.

  18. C iii] Emission in Star-forming Galaxies at z ∼ 1

    NASA Astrophysics Data System (ADS)

    Du, Xinnan; Shapley, Alice E.; Martin, Crystal L.; Coil, Alison L.

    2017-03-01

    The C iii]λλ1907, 1909 rest-frame UV emission doublet has recently been detected in galaxies during the epoch of reionization (z > 6), with a high equivalent width (EW; 10 Å, rest frame). Currently, it is possible to obtain much more detailed information for star-forming galaxies at significantly lower redshift. Accordingly, studies of their far-UV spectra are useful for understanding the factors modulating the strength of C iii] emission. We present the first statistical sample of C iii] emission measurements in star-forming galaxies at z ∼ 1. Our sample is drawn from the DEEP2 survey and spans the redshifts 0.64 ≤slant z ≤slant 1.35 (< z> =1.08). We find that the median EW of individual C iii] detections in our sample (1.30 Å) is much smaller than the typical value observed thus far at z > 6. Furthermore, out of 184 galaxies with coverage of C iii], only 40 have significant detections. Galaxies with individual C iii] detections have bluer colors and lower luminosities on average than those without, implying that strong C iii] emitters are in general young and low-mass galaxies without significant dust extinction. Using stacked spectra, we further investigate how C iii] strength correlates with multiple galaxy properties (M B , U ‑ B, M *, star formation rate, specific star formation rate) and rest-frame near-UV (Fe ii* and Mg ii) and optical ([O iii] and Hβ) emission line strengths. These results provide a detailed picture of the physical environment in star-forming galaxies at z ∼ 1, and motivate future observations of strong C iii] emitters at similar redshifts.

  19. Looking for phase-space structures in star-forming regions: an MST-based methodology

    NASA Astrophysics Data System (ADS)

    Alfaro, Emilio J.; González, Marta

    2016-03-01

    We present a method for analysing the phase space of star-forming regions. In particular we are searching for clumpy structures in the 3D sub-space formed by two position coordinates and radial velocity. The aim of the method is the detection of kinematic segregated radial velocity groups, that is, radial velocity intervals whose associated stars are spatially concentrated. To this end we define a kinematic segregation index, tilde{Λ }(RV), based on the Minimum Spanning Tree graph algorithm, which is estimated for a set of radial velocity intervals in the region. When tilde{Λ }(RV) is significantly greater than 1 we consider that this bin represents a grouping in the phase space. We split a star-forming region into radial velocity bins and calculate the kinematic segregation index for each bin, and then we obtain the spectrum of kinematic groupings, which enables a quick visualization of the kinematic behaviour of the region under study. We carried out numerical models of different configurations in the sub-space of the phase space formed by the coordinates and the that various case studies illustrate. The analysis of the test cases demonstrates the potential of the new methodology for detecting different kind of groupings in phase space.

  20. Giant Clumps in Star-forming Galaxies at z>1 in CANDELS Observations and CANDElized Simulations

    NASA Astrophysics Data System (ADS)

    Guo, Yicheng; Closson Ferguson, Henry; Ravindranath, Swara; Primack, Joel; Dekel, Avishai; Koo, David; Faber, Sandra

    2015-08-01

    A common feature of star-forming galaxies at z>1 is the existence of giant star-forming clumps, which are fundamental to our understanding of the accretion history of galaxies, formation of bulges, and evolution of gas-rich disks. In this talk, I will present our work on understanding the nature of clumps in high-redshift galaxies by comparing CANDELS observations with CANDELized high-resolution cosmological hydrodynamic simulations. The CANDELized simulations take into account of all observational effects, e.g., spatial resolution and sensitivity, of CANDELS images and thus provide a direct way to compare clumps identified in both observations and simulations. The comparison with the cosmological simulations also sheds a light on the roles that clumps play in the broad picture of galaxy formation and evolution. Our work focus on three questions: (1) When and how clumps are formed? (2) How they evolve once formed? (3) Can we use clumps as diagnostics of physical mechanisms that govern star formation, e.g., feedback? The three aspects provide important clues of tracing how distant clumpy galaxies evolve into galaxies seen in the local universe.

  1. A Star-forming Ring around κ Ori 250 pc from the Sun

    NASA Astrophysics Data System (ADS)

    Pillitteri, I.; Wolk, S. J.; Megeath, S. T.

    2016-04-01

    X-rays are a powerful probe of activity in early stages of star formation. They allow us to identify young stars even after they have lost the IR signatures of circumstellar disks and provide constraints on their distance. Here, we report on XMM-Newton observations that detect 121 young stellar objects (YSOs) in two fields between L1641 S and κ Ori. These observations extend the Survey of Orion A with XMM and Spitzer (SOXS). The YSOs are contained in a ring of gas and dust apparent at millimeter wavelengths, and in far-IR and near-IR surveys. The X-ray luminosity function of the YSOs detected in the two fields indicates a distance of 250-280 pc, much closer than the Orion A cloud and similar to distance estimates of κ Ori. We propose that the ring is a 5-8 pc diameter shell that has been swept up by κ Ori. This ring contains several groups of stars detected by Spitzer and WISE including one surrounding the Herbig Ae/Be stars V1818 Ori. In this interpretation, the κ Ori ring is one of several shells swept up by massive stars within the Orion Eridanus Superbubble and is unrelated to the southern portion of Orion A/L1641 S.

  2. A STAR-FORMING RING AROUND κ Ori 250 pc FROM THE SUN

    SciTech Connect

    Pillitteri, I.; Wolk, S. J.; Megeath, S. T.

    2016-04-01

    X-rays are a powerful probe of activity in early stages of star formation. They allow us to identify young stars even after they have lost the IR signatures of circumstellar disks and provide constraints on their distance. Here, we report on XMM-Newton observations that detect 121 young stellar objects (YSOs) in two fields between L1641 S and κ Ori. These observations extend the Survey of Orion A with XMM and Spitzer (SOXS). The YSOs are contained in a ring of gas and dust apparent at millimeter wavelengths, and in far-IR and near-IR surveys. The X-ray luminosity function of the YSOs detected in the two fields indicates a distance of 250–280 pc, much closer than the Orion A cloud and similar to distance estimates of κ Ori. We propose that the ring is a 5–8 pc diameter shell that has been swept up by κ Ori. This ring contains several groups of stars detected by Spitzer and WISE including one surrounding the Herbig Ae/Be stars V1818 Ori. In this interpretation, the κ Ori ring is one of several shells swept up by massive stars within the Orion Eridanus Superbubble and is unrelated to the southern portion of Orion A/L1641 S.

  3. A HIGHER EFFICIENCY OF CONVERTING GAS TO STARS PUSHES GALAXIES AT z ∼ 1.6 WELL ABOVE THE STAR-FORMING MAIN SEQUENCE

    SciTech Connect

    Silverman, J. D.; Rujopakarn, W.; Daddi, E.; Liu, D.; Sargent, M.; Renzini, A.; Feruglio, C.; Kashino, D.; Sanders, D.; Kartaltepe, J.; Nagao, T.; Arimoto, N.; Berta, S.; Lutz, D.; Béthermin, M.; Koekemoer, A.; and others

    2015-10-20

    Local starbursts have a higher efficiency of converting gas into stars, as compared to typical star-forming galaxies at a given stellar mass, possibly indicative of different modes of star formation. With the peak epoch of galaxy formation occurring at z > 1, it remains to be established whether such an efficient mode of star formation is occurring at high redshift. To address this issue, we measure the molecular gas content of seven high-redshift (z ∼ 1.6) starburst galaxies with the Atacama Large Millimeter/submillimeter Array and IRAM/Plateau de Bure Interferometer. Our targets are selected from the sample of Herschel far-infrared-detected galaxies having star formation rates (∼300–800 M{sub ⊙} yr{sup −1}) elevated (≳4×) above the star-forming main sequence (MS) and included in the FMOS-COSMOS near-infrared spectroscopic survey of star-forming galaxies at z ∼ 1.6 with Subaru. We detect CO emission in all cases at high levels of significance, indicative of high gas fractions (∼30%–50%). Even more compelling, we firmly establish with a clean and systematic selection that starbursts, identified as MS outliers, at high redshift generally have a lower ratio of CO to total infrared luminosity as compared to typical MS star-forming galaxies, although with a smaller offset than expected based on past studies of local starbursts. We put forward a hypothesis that there exists a continuous increase in star formation efficiency with elevation from the MS with galaxy mergers as a possible physical driver. Along with a heightened star formation efficiency, our high-redshift sample is similar in other respects to local starbursts, such as being metal rich and having a higher ionization state of the interstellar medium.

  4. SHOCKED SUPERWINDS FROM THE z {approx} 2 CLUMPY STAR-FORMING GALAXY, ZC406690

    SciTech Connect

    Newman, Sarah F.; Genzel, Reinhard; Shapiro Griffin, Kristen; Davies, Ric; Foerster-Schreiber, Natascha M.; Tacconi, Linda J.; Kurk, Jaron; Wuyts, Stijn; Genel, Shy; Buschkamp, Peter; Eisenhauer, Frank; Lutz, Dieter; Lilly, Simon J.; Carollo, C. Marcella; Renzini, Alvio; Mancini, Chiara; Bouche, Nicolas; Burkert, Andreas; Cresci, Giovanni; Hicks, Erin; and others

    2012-06-20

    We have obtained high-resolution data of the z {approx} 2 ring-like, clumpy star-forming galaxy (SFG) ZC406690 using the VLT/SINFONI with adaptive optics (in K band) and in seeing-limited mode (in H and J bands). Our data include all of the main strong optical emission lines: [O II], [O III], H{alpha}, H{beta}, [N II], and [S II]. We find broad, blueshifted H{alpha} and [O III] emission line wings in the spectra of the galaxy's massive, star-forming clumps ({sigma} {approx} 85 km s{sup -1}) and even broader wings (up to 70% of the total H{alpha} flux, with {sigma} {approx} 290 km s{sup -1}) in regions spatially offset from the clumps by {approx}2 kpc. The broad emission likely originates from large-scale outflows with mass outflow rates from individual clumps that are 1-8 Multiplication-Sign the star formation rate (SFR) of the clumps. Based on emission line ratio diagnostics ([N II]/H{alpha} and [S II]/H{alpha}) and photoionization and shock models, we find that the emission from the clumps is due to a combination of photoionization from the star-forming regions and shocks generated in the outflowing component, with 5%-30% of the emission deriving from shocks. In terms of the ionization parameter (6 Multiplication-Sign 10{sup 7} to 10{sup 8} cm s{sup -1}, based on both the SFR and the O{sub 32} ratio), density (local electron densities of 300-1800 cm{sup -3} in and around the clumps, and ionized gas column densities of 1200-8000 M{sub Sun }pc{sup -2}), and SFR (10-40 M{sub Sun} yr{sup -1}), these clumps more closely resemble nuclear starburst regions of local ultraluminous infrared galaxies and dwarf irregulars than H II regions in local galaxies. However, the star-forming clumps are not located in the nucleus as in local starburst galaxies but instead are situated in a ring several kpc from the center of their high-redshift host galaxy, and have an overall disk-like morphology. The two brightest clumps are quite different in terms of their internal properties

  5. Shocked Superwinds from the z ~ 2 Clumpy Star-forming Galaxy, ZC406690

    NASA Astrophysics Data System (ADS)

    Newman, Sarah F.; Shapiro Griffin, Kristen; Genzel, Reinhard; Davies, Ric; Förster-Schreiber, Natascha M.; Tacconi, Linda J.; Kurk, Jaron; Wuyts, Stijn; Genel, Shy; Lilly, Simon J.; Renzini, Alvio; Bouché, Nicolas; Burkert, Andreas; Cresci, Giovanni; Buschkamp, Peter; Carollo, C. Marcella; Eisenhauer, Frank; Hicks, Erin; Lutz, Dieter; Mancini, Chiara; Naab, Thorsten; Peng, Yingjie; Vergani, Daniela

    2012-06-01

    We have obtained high-resolution data of the z ~ 2 ring-like, clumpy star-forming galaxy (SFG) ZC406690 using the VLT/SINFONI with adaptive optics (in K band) and in seeing-limited mode (in H and J bands). Our data include all of the main strong optical emission lines: [O II], [O III], Hα, Hβ, [N II], and [S II]. We find broad, blueshifted Hα and [O III] emission line wings in the spectra of the galaxy's massive, star-forming clumps (σ ~ 85 km s-1) and even broader wings (up to 70% of the total Hα flux, with σ ~ 290 km s-1) in regions spatially offset from the clumps by ~2 kpc. The broad emission likely originates from large-scale outflows with mass outflow rates from individual clumps that are 1-8× the star formation rate (SFR) of the clumps. Based on emission line ratio diagnostics ([N II]/Hα and [S II]/Hα) and photoionization and shock models, we find that the emission from the clumps is due to a combination of photoionization from the star-forming regions and shocks generated in the outflowing component, with 5%-30% of the emission deriving from shocks. In terms of the ionization parameter (6 × 107 to 108 cm s-1, based on both the SFR and the O32 ratio), density (local electron densities of 300-1800 cm-3 in and around the clumps, and ionized gas column densities of 1200-8000 M ⊙pc-2), and SFR (10-40 M ⊙ yr-1), these clumps more closely resemble nuclear starburst regions of local ultraluminous infrared galaxies and dwarf irregulars than H II regions in local galaxies. However, the star-forming clumps are not located in the nucleus as in local starburst galaxies but instead are situated in a ring several kpc from the center of their high-redshift host galaxy, and have an overall disk-like morphology. The two brightest clumps are quite different in terms of their internal properties, energetics, and relative ages, and thus we are given a glimpse at two different stages in the formation and evolution of rapidly star-forming giant clumps at high

  6. The SAMI Galaxy Survey: shocks and outflows in a normal star-forming galaxy

    NASA Astrophysics Data System (ADS)

    Ho, I.-Ting; Kewley, Lisa J.; Dopita, Michael A.; Medling, Anne M.; Allen, J. T.; Bland-Hawthorn, Joss; Bloom, Jessica V.; Bryant, Julia J.; Croom, Scott M.; Fogarty, L. M. R.; Goodwin, Michael; Green, Andy W.; Konstantopoulos, Iraklis S.; Lawrence, Jon S.; López-Sánchez, Á. R.; Owers, Matt S.; Richards, Samuel; Sharp, Rob

    2014-11-01

    We demonstrate the feasibility and potential of using large integral field spectroscopic surveys to investigate the prevalence of galactic-scale outflows in the local Universe. Using integral field data from the Sydney-AAO Multi-object Integral field spectrograph (SAMI) and the Wide Field Spectrograph, we study the nature of an isolated disc galaxy, SDSS J090005.05+000446.7 (z = 0.053 86). In the integral field data sets, the galaxy presents skewed line profiles changing with position in the galaxy. The skewed line profiles are caused by different kinematic components overlapping in the line-of-sight direction. We perform spectral decomposition to separate the line profiles in each spatial pixel as combinations of (1) a narrow kinematic component consistent with H II regions, (2) a broad kinematic component consistent with shock excitation, and (3) an intermediate component consistent with shock excitation and photoionization mixing. The three kinematic components have distinctly different velocity fields, velocity dispersions, line ratios, and electron densities. We model the line ratios, velocity dispersions, and electron densities with our MAPPINGS IV shock and photoionization models, and we reach remarkable agreement between the data and the models. The models demonstrate that the different emission line properties are caused by major galactic outflows that introduce shock excitation in addition to photoionization by star-forming activities. Interstellar shocks embedded in the outflows shock-excite and compress the gas, causing the elevated line ratios, velocity dispersions, and electron densities observed in the broad kinematic component. We argue from energy considerations that, with the lack of a powerful active galactic nucleus, the outflows are likely to be driven by starburst activities. Our results set a benchmark of the type of analysis that can be achieved by the SAMI Galaxy Survey on large numbers of galaxies.

  7. Maximally Star-forming Galactic Disks. II. Vertically Resolved Hydrodynamic Simulations of Starburst Regulation

    NASA Astrophysics Data System (ADS)

    Shetty, Rahul; Ostriker, Eve C.

    2012-07-01

    We explore the self-regulation of star formation using a large suite of high-resolution hydrodynamic simulations, focusing on molecule-dominated regions (galactic centers and [U]LIRGS) where feedback from star formation drives highly supersonic turbulence. In equilibrium, the total midplane pressure, dominated by turbulence, must balance the vertical weight of the interstellar medium. Under self-regulation, the momentum flux injected by feedback evolves until it matches the vertical weight. We test this flux balance in simulations spanning a wide range of parameters, including surface density Σ, momentum injected per stellar mass formed (p */m *), and angular velocity. The simulations are two-dimensional radial-vertical slices, and include both self-gravity and an external potential that helps to confine gas to the disk midplane. After the simulations reach a steady state in all relevant quantities, including the star formation rate ΣSFR, there is remarkably good agreement between the vertical weight, the turbulent pressure, and the momentum injection rate from supernovae. Gas velocity dispersions and disk thicknesses increase with p */m *. The efficiency of star formation per free-fall time at the midplane density, epsilonff(n 0), is insensitive to the local conditions and to the star formation prescription in very dense gas. We measure epsilonff(n 0) ~ 0.004-0.01, consistent with low and approximately constant efficiencies inferred from observations. For Σ in (100-1000) M ⊙ pc-2, we find ΣSFR in (0.1-4) M ⊙ kpc-2 yr-1, generally following a ΣSFR vprop Σ2 relationship. The measured relationships agree very well with vertical equilibrium and with turbulent energy replenishment by feedback within a vertical crossing time. These results, along with the observed Σ-ΣSFR relation in high-density environments, provide strong evidence for the self-regulation of star formation.

  8. SUB-STELLAR COMPANIONS AND STELLAR MULTIPLICITY IN THE TAURUS STAR-FORMING REGION

    SciTech Connect

    Daemgen, Sebastian; Bonavita, Mariangela; Jayawardhana, Ray; Lafrenière, David; Janson, Markus

    2015-02-01

    We present results from a large, high-spatial-resolution near-infrared imaging search for stellar and sub-stellar companions in the Taurus-Auriga star-forming region. The sample covers 64 stars with masses between those of the most massive Taurus members at ∼3 M {sub ☉} and low-mass stars at ∼0.2 M {sub ☉}. We detected 74 companion candidates, 34 of these reported for the first time. Twenty-five companions are likely physically bound, partly confirmed by follow-up observations. Four candidate companions are likely unrelated field stars. Assuming physical association with their host star, estimated companion masses are as low as ∼2 M {sub Jup}. The inferred multiplicity frequency within our sensitivity limits between ∼10-1500 AU is 26.3{sub −4.9}{sup +6.6}%. Applying a completeness correction, 62% ± 14% of all Taurus stars between 0.7 and 1.4 M {sub ☉} appear to be multiple. Higher order multiples were found in 1.8{sub −1.5}{sup +4.2}% of the cases, in agreement with previous observations of the field. We estimate a sub-stellar companion frequency of ∼3.5%-8.8% within our sensitivity limits from the discovery of two likely bound and three other tentative very low-mass companions. This frequency appears to be in agreement with what is expected from the tail of the stellar companion mass ratio distribution, suggesting that stellar and brown dwarf companions share the same dominant formation mechanism. Further, we find evidence for possible evolution of binary parameters between two identified sub-populations in Taurus with ages of ∼2 Myr and ∼20 Myr, respectively.

  9. AN ULTRAVIOLET INVESTIGATION OF ACTIVITY ON EXOPLANET HOST STARS

    SciTech Connect

    Shkolnik, Evgenya L.

    2013-03-20

    Using the far-UV (FUV) and near-UV (NUV) photometry from the NASA Galaxy Evolution Explorer (GALEX), we searched for evidence of increased stellar activity due to tidal and/or magnetic star-planet interactions (SPI) in the 272 known FGK planetary hosts observed by GALEX. With the increased sensitivity of GALEX, we are able probe systems with lower activity levels and at larger distances than what has been done to date with X-ray satellites. We compared samples of stars with close-in planets (a < 0.1 AU) to those with far-out planets (a > 0.5 AU) and looked for correlations of excess activity with other system parameters. This statistical investigation found no clear correlations with a, M{sub p} , or M{sub p} /a, in contrast to some X-ray and Ca II studies. However, there is tentative evidence (at a level of 1.8{sigma}) that stars with radial-velocity-(RV)-detected close-in planets are more FUV-active than stars with far-out planets, in agreement with several published X-ray and Ca II results. The case is strengthened to a level of significance to 2.3{sigma} when transit-detected close-in planets are included. This is most likely because the RV-selected sample of stars is significantly less active than the field population of comparable stars, while the transit-selected sample is similarly active. Given the factor of 2-3 scatter in fractional FUV luminosity for a given stellar effective temperature, it is necessary to conduct a time-resolved study of the planet hosts in order to better characterize their UV variability and generate a firmer statistical result.

  10. HerMES: disentangling active galactic nuclei and star formation in the radio source population

    NASA Astrophysics Data System (ADS)

    Rawlings, J. I.; Page, M. J.; Symeonidis, M.; Bock, J.; Cooray, A.; Farrah, D.; Guo, K.; Hatziminaoglou, E.; Ibar, E.; Oliver, S. J.; Roseboom, I. G.; Scott, Douglas; Seymour, N.; Vaccari, M.; Wardlow, J. L.

    2015-10-01

    We separate the extragalactic radio source population above ˜50 μJy into active galactic nuclei (AGN) and star-forming sources. The primary method of our approach is to fit the infrared spectral energy distributions (SEDs), constructed using Spitzer/IRAC (Infrared Array Camera) and Multiband Imaging Photometer for Spitzer (MIPS) and Herschel/SPIRE photometry, of 380 radio sources in the Extended Chandra Deep Field-South. From the fitted SEDs, we determine the relative AGN and star-forming contributions to their infrared emission. With the inclusion of other AGN diagnostics such as X-ray luminosity, Spitzer/IRAC colours, radio spectral index and the ratio of star-forming total infrared flux to k-corrected 1.4 GHz flux density, qIR, we determine whether the radio emission in these sources is powered by star formation or by an AGN. The majority of these radio sources (60 per cent) show the signature of an AGN at some wavelength. Of the sources with AGN signatures, 58 per cent are hybrid systems for which the radio emission is being powered by star formation. This implies that radio sources which have likely been selected on their star formation have a high AGN fraction. Below a 1.4 GHz flux density of 1 mJy, along with finding a strong contribution to the source counts from pure star-forming sources, we find that hybrid sources constitute 20-65 per cent of the sources. This result suggests that hybrid sources have a significant contribution, along with sources that do not host a detectable AGN, to the observed flattening of the source counts at ˜1 mJy for the extragalactic radio source population.

  11. Disks, Young Stars, and Radio Waves: The Quest for Forming Planetary Systems

    NASA Astrophysics Data System (ADS)

    Chandler, C. J.; Shepherd, D. S.

    2008-08-01

    Kant and Laplace suggested the Solar System formed from a rotating gaseous disk in the 18th century, but convincing evidence that young stars are indeed surrounded by such disks was not presented for another 200 years. As we move into the 21st century the emphasis is now on disk formation, the role of disks in star formation, and on how planets form in those disks. Radio wavelengths play a key role in these studies, currently providing some of the highest-spatial-resolution images of disks, along with evidence of the growth of dust grains into planetesimals. The future capabilities of EVLA and ALMA provide extremely exciting prospects for resolving disk structure and kinematics, studying disk chemistry, directly detecting protoplanets, and imaging disks in formation.

  12. A form-factor method for determining the structure of distorted stars

    NASA Technical Reports Server (NTRS)

    Wolfe, R. H., Jr.; Kern, J. W.

    1979-01-01

    The equilibrium equations of a uniformly rotating and tidally distorted star are reduced to the same form as for a spherical star except for the inclusion of two form factors. One factor, expressing the buoyancy effects of centrifugal force, is determined directly from the integrated structure variables. The other factor, expressing the deviation from spherical shape, is shown to be relatively insensitive to errors in the assumed shape, so that accurate solutions are obtained in spite of the use of an a priori shape. The method is employed by adding computations for the factors to an existing spherical model program. Upper Main Sequence models determined by this method compare closely with results from the double approximation method even for critical rotation and tidal distortion.

  13. PARALLAXES OF STAR-FORMING REGIONS IN THE OUTER SPIRAL ARM OF THE MILKY WAY

    SciTech Connect

    Hachisuka, K.; Choi, Y. K.; Reid, M. J.; Dame, T. M.; Brunthaler, A.; Menten, K. M.; Sanna, A.

    2015-02-10

    We report parallaxes and proper motions of three water maser sources in high-mass star-forming regions in the Outer Spiral Arm of the Milky Way. The observations were conducted with the Very Long Baseline Array as part of Bar and Spiral Structure Legacy Survey and double the number of such measurements in the literature. The Outer Arm has a pitch angle of 14.°9 ± 2.°7 and a Galactocentric distance of 14.1 ± 0.6 kpc toward the Galactic anticenter. The average motion of these sources toward the Galactic center is 10.7 ± 2.1 km s{sup –1} and we see no sign of a significant fall in the rotation curve out to 15 kpc from the Galactic center. The three-dimensional locations of these star-forming regions are consistent with a Galactic warp of several hundred parsecs from the plane.

  14. Dissecting galaxies: spatial and spectral separation of emission excited by star formation and AGN activity

    NASA Astrophysics Data System (ADS)

    Davies, Rebecca L.; Groves, Brent; Kewley, Lisa J.; Dopita, Michael A.; Hampton, Elise J.; Shastri, Prajval; Scharwächter, Julia; Sutherland, Ralph; Kharb, Preeti; Bhatt, Harish; Jin, Chichuan; Banfield, Julie; Zaw, Ingyin; James, Bethan; Juneau, Stéphanie; Srivastava, Shweta

    2016-10-01

    The optical spectra of Seyfert galaxies are often dominated by emission lines excited by both star formation and active galactic nucleus (AGN) activity. Standard calibrations (such as for the star formation rate) are not applicable to such composite (mixed) spectra. In this paper, we describe how integral field data can be used to spectrally and spatially separate emission associated with star formation from emission associated with accretion on to an AGN. We demonstrate our method using integral field data for two AGN host galaxies (NGC 5728 and NGC 7679) from the Siding Spring Southern Seyfert Spectroscopic Snapshot Survey (S7). The spectra of NGC 5728 and NGC 7679 form clear sequences of AGN fraction on standard emission line ratio diagnostic diagrams. We show that the emission line luminosities of the majority (>85 per cent) of spectra along each AGN fraction sequence can be reproduced by linear superpositions of the emission line luminosities of one AGN dominated spectrum and one star formation dominated spectrum. We separate the Hα, Hβ, [N II]λ6583, [S II]λλ6716, 6731, [O III]λ5007 and [O II]λλ3726, 3729 luminosities of every spaxel into contributions from star formation and AGN activity. The decomposed emission line images are used to derive the star formation rates and AGN bolometric luminosities for NGC 5728 and NGC 7679. Our calculated values are mostly consistent with independent estimates from data at other wavelengths. The recovered star-forming and AGN components also have distinct spatial distributions which trace structures seen in high-resolution imaging of the galaxies, providing independent confirmation that our decomposition has been successful.

  15. Wavelength dependence of star images formed by large ground-based telescopes including ELTs

    NASA Astrophysics Data System (ADS)

    McKechnie, T. Stewart

    2016-08-01

    Star image appearance in large ground-based telescopes is determined by the properties of the Optical Path Difference (OPD) fluctuation associated with the image-forming wave potions collected by the telescope aperture. The principal properties are the root mean square (rms) OPD fluctuation and the autocorrelation function of the OPD fluctuation. The OPD properties ultimately depend on the combined effects of turbulence in the atmospheric path, the fixed aberrations of the telescope and, if appropriate, the corrective effects of Adaptive Optics (AO). The equations given in this paper relating star image properties to the OPD properties (and also the inverse relations) apply to all large ground-based reflector telescopes, including ELTs. They apply equally to telescopes with and without AO. The OPD properties can be obtained directly from an image of an unresolved star. This image represents the intensity Point Spread Function (PSF) corresponding to the entire end-to-end imaging path. To obtain the full OPD information compliment, however, the image must be formed at a wavelength that delivers the most general type of star image: a core and halo image. Once the OPD properties have been obtained from such an image, the intensity PSF for the telescope/atmosphere/AO combination can immediately be calculated for any other wavelengths of interest in the extended optical wavelength range, 0.3 μm - 1000 μm. There are numerous applications for the mathematical relationships set out in this paper, including characterization of atmospheric paths, assessment of telescope/AO imaging performance, establishing wave front tolerances for ELTs and other large ground-based telescopes, and the rapid identification of sweetspot wavelength regions where highest resolution is achieved and star images attain maximum central intensity.

  16. Spitzer Imaging of Strongly lensed Herschel-selected Dusty Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Ma, Brian; Cooray, Asantha; Calanog, J. A.; Nayyeri, H.; Timmons, N.; Casey, C.; Baes, M.; Chapman, S.; Dannerbauer, H.; da Cunha, E.; De Zotti, G.; Dunne, L.; Farrah, D.; Fu, Hai; Gonzalez-Nuevo, J.; Magdis, G.; Michałowski, M. J.; Oteo, I.; Riechers, D. A.; Scott, D.; Smith, M. W. L.; Wang, L.; Wardlow, J.; Vaccari, M.; Viaene, S.; Vieira, J. D.

    2015-11-01

    We present the rest-frame optical spectral energy distribution (SED) and stellar masses of six Herschel-selected gravitationally lensed dusty, star-forming galaxies (DSFGs) at 1 < z < 3. These galaxies were first identified with Herschel/SPIRE imaging data from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) and the Herschel Multi-tiered Extragalactic Survey (HerMES). The targets were observed with Spitzer/IRAC at 3.6 and 4.5 μm. Due to the spatial resolution of the IRAC observations at the level of 2″, the lensing features of a background DSFG in the near-infrared are blended with the flux from the foreground lensing galaxy in the IRAC imaging data. We make use of higher resolution Hubble/WFC3 or Keck/NIRC2 Adaptive Optics imaging data to fit light profiles of the foreground lensing galaxy (or galaxies) as a way to model the foreground components, in order to successfully disentangle the foreground lens and background source flux densities in the IRAC images. The flux density measurements at 3.6 and 4.5 μm, once combined with Hubble/WFC3 and Keck/NIRC2 data, provide important constraints on the rest-frame optical SED of the Herschel-selected lensed DSFGs. We model the combined UV- to millimeter-wavelength SEDs to establish the stellar mass, dust mass, star formation rate, visual extinction, and other parameters for each of these Herschel-selected DSFGs. These systems have inferred stellar masses in the range 8 × 1010-4 × 1011 M⊙ and star formation rates of around 100 M⊙ yr-1. This puts these lensed submillimeter systems well above the SFR-M* relation observed for normal star-forming galaxies at similar redshifts. The high values of SFR inferred for these systems are consistent with a major merger-driven scenario for star formation.

  17. KMOS3D: Dynamical Constraints on the Mass Budget in Early Star-forming Disks

    NASA Astrophysics Data System (ADS)

    Wuyts, Stijn; Förster Schreiber, Natascha M.; Wisnioski, Emily; Genzel, Reinhard; Burkert, Andreas; Bandara, Kaushala; Beifiori, Alessandra; Belli, Sirio; Bender, Ralf; Brammer, Gabriel B.; Chan, Jeffrey; Davies, Ric; Fossati, Matteo; Galametz, Audrey; Kulkarni, Sandesh K.; Lang, Philipp; Lutz, Dieter; Mendel, J. Trevor; Momcheva, Ivelina G.; Naab, Thorsten; Nelson, Erica J.; Saglia, Roberto P.; Seitz, Stella; Tacconi, Linda J.; Tadaki, Ken-ichi; Übler, Hannah; van Dokkum, Pieter G.; Wilman, David J.; Wuyts, Eva

    2016-11-01

    We exploit deep integral-field spectroscopic observations with KMOS/Very Large Telescope of 240 star-forming disks at 0.6\\lt z\\lt 2.6 to dynamically constrain their mass budget. Our sample consists of massive (≳ {10}9.8 {M}⊙ ) galaxies with sizes {R}e≳ 2 {kpc}. By contrasting the observed velocity and dispersion profiles with dynamical models, we find that on average the stellar content contributes {32}-7+8 % of the total dynamical mass, with a significant spread among galaxies (68th percentile range {f}{star}˜ 18 % {--}62 % ). Including molecular gas as inferred from CO- and dust-based scaling relations, the estimated baryonic mass adds up to {56}-12+17 % of the total for the typical galaxy in our sample, reaching ˜ 90 % at z\\gt 2. We conclude that baryons make up most of the mass within the disk regions of high-redshift star-forming disk galaxies, with typical disks at z\\gt 2 being strongly baryon-dominated within R e . Substantial object-to-object variations in both stellar and baryonic mass fractions are observed among the galaxies in our sample, larger than what can be accounted for by the formal uncertainties in their respective measurements. In both cases, the mass fractions correlate most strongly with measures of surface density. High-{{{Σ }}}{star} galaxies feature stellar mass fractions closer to unity, and systems with high inferred gas or baryonic surface densities leave less room for additional mass components other than stars and molecular gas. Our findings can be interpreted as more extended disks probing further (and more compact disks probing less far) into the dark matter halos that host them. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programs 092.A-0091, 093.A-0079, 094.A-0217, 095.A-0047, and 096.A-0025.

  18. VizieR Online Data Catalog: Star forming regions sulphur ICFs (Dors+, 2016)

    NASA Astrophysics Data System (ADS)

    Dors, O. L.; Perez-Montero, E.; Hagele, G. F.; Cardaci, M. V.; Krabbe, A. C.

    2016-10-01

    We compiled from the literature emission-line intensities of HII regions and star-forming galaxies obtained in the optical and infrared spectral ranges. These measurements were used to obtain sulphur and oxygen ionic abundances in order to verify if our photoionization models are representative of real HIi regions, to check if the theoretical ICFs are compatible with the ones derived directly from observations and investigating the S/O-O/H relation. (5 data files).

  19. VizieR Online Data Catalog: Star-forming regions deuteration (Gerner+, 2015)

    NASA Astrophysics Data System (ADS)

    Gerner, T.; Shirley, Y. L.; Beuther, H.; Semenov, D.; Linz, H.; Albertsson, T.; Henning, T.

    2015-10-01

    The sources were taken from Gerner et al. (2014, Cat. J/A+A/563/A97) and were initially selected from different source lists. The total sample contains 59 high-mass star-forming regions, consisting of 19 IRDCs and 20 HMPOs as well as 11 HMCs and 9 UCHIIs. The sources were selected from well-known source catalogs of the literature without specific selection criteria such as spherical symmetry. (3 data files).

  20. The role of mitochondrial fusion and StAR phosphorylation in the regulation of StAR activity and steroidogenesis.

    PubMed

    Castillo, Ana F; Orlando, Ulises; Helfenberger, Katia E; Poderoso, Cecilia; Podesta, Ernesto J

    2015-06-15

    The steroidogenic acute regulatory (StAR) protein regulates the rate-limiting step in steroidogenesis, i.e. the delivery of cholesterol from the outer (OMM) to the inner (IMM) mitochondrial membrane. StAR is a 37-kDa protein with an N-terminal mitochondrial targeting sequence that is cleaved off during mitochondrial import to yield 30-kDa intramitochondrial StAR. StAR acts exclusively on the OMM and its activity is proportional to how long it remains on the OMM. However, the precise fashion and the molecular mechanism in which StAR remains on the OMM have not been elucidated yet. In this work we will discuss the role of mitochondrial fusion and StAR phosphorylation by the extracellular signal-regulated kinases 1/2 (ERK1/2) as part of the mechanism that regulates StAR retention on the OMM and activity.

  1. Direct measurements of dust attenuation in z ∼ 1.5 star-forming galaxies from 3D-HST: Implications for dust geometry and star formation rates

    SciTech Connect

    Price, Sedona H.; Kriek, Mariska; Brammer, Gabriel B.; Conroy, Charlie; Schreiber, Natascha M. Förster; Wuyts, Stijn; Franx, Marijn; Fumagalli, Mattia; Lundgren, Britt; Momcheva, Ivelina; Nelson, Erica J.; Van Dokkum, Pieter G.; Skelton, Rosalind E.; Whitaker, Katherine E.

    2014-06-10

    The nature of dust in distant galaxies is not well understood, and until recently few direct dust measurements have been possible. We investigate dust in distant star-forming galaxies using near-infrared grism spectra of the 3D-HST survey combined with archival multi-wavelength photometry. These data allow us to make a direct comparison between dust around star-forming regions (A {sub V,} {sub H} {sub II}) and the integrated dust content (A {sub V,} {sub star}). We select a sample of 163 galaxies between 1.36 ≤ z ≤ 1.5 with Hα signal-to-noise ratio ≥5 and measure Balmer decrements from stacked spectra to calculate A {sub V,} {sub H} {sub II}. First, we stack spectra in bins of A {sub V,} {sub star}, and find that A {sub V,} {sub H} {sub II} = 1.86 A {sub V,} {sub star}, with a significance of σ = 1.7. Our result is consistent with the two-component dust model, in which galaxies contain both diffuse and stellar birth cloud dust. Next, we stack spectra in bins of specific star formation rate (log SSFR), star formation rate (log SFR), and stellar mass (log M {sub *}). We find that on average A {sub V,} {sub H} {sub II} increases with SFR and mass, but decreases with increasing SSFR. Interestingly, the data hint that the amount of extra attenuation decreases with increasing SSFR. This trend is expected from the two-component model, as the extra attenuation will increase once older stars outside the star-forming regions become more dominant in the galaxy spectrum. Finally, using Balmer decrements we derive dust-corrected Hα SFRs, and find that stellar population modeling produces incorrect SFRs if rapidly declining star formation histories are included in the explored parameter space.

  2. The Intergalactic and Circumgalactic Medium surrounding Star-Forming Galaxies at Redshifts 2 < z < 3

    NASA Astrophysics Data System (ADS)

    Rudie, Gwen C.

    We present measurements of the spatial distribution, kinematics, and physical properties of gas in the circumgalactic medium (CGM) of 2.0 < z < 2.8 UV color-selected galaxies as well as within the 2 < z < 3 intergalactic medium (IGM). These measurements are derived from Voigt profile decomposition of the full Lyalpha and Lybeta forest in 15 high-resolution, high signal-to-noise ratio QSO spectra resulting in a catalog of ˜ 6000 H I absorbers. Chapter 2 of this thesis focuses on H I surrounding high-z star-forming galaxies drawn from the Keck Baryonic Structure Survey (KBSS). The KBSS is a unique spectroscopic survey of the distant universe designed to explore the details of the connection between galaxies and intergalactic baryons within the same survey volumes. The KBSS combines high-quality background QSO spectroscopy with large densely-sampled galaxy redshift surveys to probe the CGM at scales of ˜ 50 kpc to a few Mpc. Based on these data, Chapter 2 presents the first quantitative measurements of the distribution, column density, kinematics, and absorber line widths of neutral hydrogen surrounding high-z star-forming galaxies. Chapter 3 focuses on the thermal properties of the diffuse IGM. This analysis relies on measurements of the ˜ 6000 absorber line widths to constrain the thermal and turbulent velocities of absorbing "clouds." A positive correlation between the column density of H I and the minimum line width is recovered and implies a temperature-density relation within the low-density IGM for which higher-density regions are hotter, as is predicted by simple theoretical arguments. Chapter 4 presents new measurements of the opacity of the IGM and CGM to hydrogen-ionizing photons. The chapter begins with a revised measurement of the H I column density distribution based on this new absorption line catalog that, due to the inclusion of high-order Lyman lines, provides the first statistically robust measurement of the frequency of absorbers with H I column

  3. The First Detections of the Key Prebiotic Molecule PO in Star-forming Regions

    NASA Astrophysics Data System (ADS)

    Rivilla, V. M.; Fontani, F.; Beltrán, M. T.; Vasyunin, A.; Caselli, P.; Martín-Pintado, J.; Cesaroni, R.

    2016-08-01

    Phosphorus is a crucial element in biochemistry, in particular the P-O bond, which is key in the formation of the backbone of deoxyribonucleic acid. So far, PO has only been detected toward the envelope of evolved stars, but never toward star-forming regions. We report the first detection of PO toward two massive star-forming regions, W51 e1/e2 and W3(OH), using data from the IRAM 30 m telescope. PN has also been detected toward the two regions. The abundance ratio PO/PN is 1.8 and 3 for W51 and W3(OH), respectively. Our chemical model indicates that the two molecules are chemically related and are formed via gas-phase ion-molecule and neutral-neutral reactions during cold collapse. The molecules freeze out onto grains at the end of the collapse and desorb during the warm-up phase once the temperature reaches ˜35 K. Similar abundances of the two species are expected during a period of ˜5 × 104 yr at the early stages of the warm-up phase, when the temperature is in the range 35-90 K. The observed molecular abundances of 10-10 are predicted by the model if a relatively high initial abundance of 5 × 10-9 of depleted phosphorus is assumed.

  4. Optical Survey with KMTNet for Dusty Star-Forming Galaxies in the Akari Deep Field South

    NASA Astrophysics Data System (ADS)

    Jeong, Woong-Seob; Ko, Kyeongyeon; Kim, Minjin; Ko, Jongwan; Kim, Sam; Pyo, Jeonghyun; Kim, Seong Jin; Kim, Taehyun; Seo, Hyun Jong; Park, Won-Kee; Park, Sung-Joon; Kim, Min Gyu; Kim, Dong Jin; Cha, Sang-Mok; Lee, Yongseok; Lee, Chung-Uk; Kim, Seung-Lee; Matsuura, Shuji; Pearson, Chris; Matsuhara, Hideo

    2016-10-01

    We present an optical imaging survey of AKARI Deep Field South (ADF-S) using the Korea Microlensing Telescope Network (KMTNet), to find optical counterparts of dusty star-forming galaxies. The ADF-S is a deep far-infrared imaging survey region with AKARI covering around 12 deg^2, where the deep optical imaging data are not yet available. By utilizing the wide-field capability of the KMTNet telescopes (˜4 deg^2), we obtain optical images in B, R and I bands for three regions. The target depth of images in B, R and I bands is ˜24 mag (AB) at 5σ, which enables us to detect most dusty star-forming galaxies discovered by AKARI in the ADF-S. Those optical datasets will be helpful to constrain optical spectral energy distributions as well as to identify rare types of dusty star-forming galaxies such as dust-obscured galaxy, sub-millimeter galaxy at high redshift.}

  5. Cosmic web and star formation activity in galaxies at z ∼ 1

    SciTech Connect

    Darvish, B.; Mobasher, B.; Sales, L. V.; Sobral, D.; Scoville, N. Z.; Best, P.; Smail, I.

    2014-11-20

    We investigate the role of the delineated cosmic web/filaments on star formation activity by exploring a sample of 425 narrow-band selected Hα emitters, as well as 2846 color-color selected underlying star-forming galaxies for a large-scale structure at z = 0.84 in the COSMOS field from the HiZELS survey. Using the scale-independent Multi-scale Morphology Filter algorithm, we are able to quantitatively describe the density field and disentangle it into its major components: fields, filaments, and clusters. We show that the observed median star formation rate (SFR), stellar mass, specific SFR, the mean SFR-mass relation, and its scatter for both Hα emitters and underlying star-forming galaxies do not strongly depend on different classes of environment, in agreement with previous studies. However, the fraction of Hα emitters varies with environment and is enhanced in filamentary structures at z ∼ 1. We propose mild galaxy-galaxy interactions as the possible physical agent for the elevation of the fraction of Hα star-forming galaxies in filaments. Our results show that filaments are the likely physical environments that are often classed as the 'intermediate' densities and that the cosmic web likely plays a major role in galaxy formation and evolution which has so far been poorly investigated.

  6. Galaxy Zoo: spiral galaxy morphologies and their relation to the star-forming main sequence

    NASA Astrophysics Data System (ADS)

    Willett, Kyle; Schawinski, Kevin; Masters, Karen; Melvin, Tom; Skibba, Ramin A.; Nichol, Robert; Cheung, Edmond; Lintott, Chris; Simmons, Brooke D.; Kaviraj, Sugata; Keel, William C.; Fortson, Lucy; Galaxy Zoo volunteers

    2015-01-01

    We examine the relationship between stellar mass and star formation rate in disk galaxies at z<0.085, measuring different populations of spirals as classified by their kiloparsec-scale structure. The morphologies of disk galaxies are obtained from the Galaxy Zoo 2 project, which includes the number of spiral arms, the arm pitch angle, and the presence of strong galactic bars. We show that both the slope and dispersion of the star-forming main sequence (SFMS) is constant no matter what the morphology of the spiral disk. We also show that mergers (both major and minor), which represent the strongest conditions for increases in star formation at a constant mass, only boost the SFR above the main relation by 0.3 dex; this is a significant reduction over the increase seen in merging systems at higher redshifts (z > 1). Of the galaxies that do lie significantly above the SFMS in the local Universe, more than 50% are mergers, with a large contribution from the compact green pea galaxies. We interpret our results as evidence that the number and pitch angle of spiral arms, which are imperfect reflections of the galaxy's current gravitational potential, are either fully independent of the various quenching mechanisms for star formation or are completely overwhelmed by the combination of outflows and feedback.

  7. Molecular and atomic gas along and across the main sequence of star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Saintonge, Amelie; Catinella, Barbara; Cortese, Luca; Genzel, Reinhard; Giovanelli, Riccardo; Haynes, Martha P.; Janowiecki, Steven; Kramer, Carsten; Lutz, Katharina A.; Schiminovich, David; Tacconi, Linda J.; Wuyts, Stijn; Accurso, Gioacchino

    2016-10-01

    We use spectra from the ALFALFA, GASS and COLD GASS surveys to quantify variations in the mean atomic and molecular gas mass fractions throughout the SFR-M* plane and along the main sequence (MS) of star-forming galaxies. Although galaxies well below the MS tend to be undetected in the Arecibo and IRAM observations, reliable mean atomic and molecular gas fractions can be obtained through a spectral stacking technique. We find that the position of galaxies in the SFR-M* plane can be explained mostly by their global cold gas reservoirs as observed in the H I line, with in addition systematic variations in the molecular-to-atomic ratio and star formation efficiency. When looking at galaxies within ±0.4 dex of the MS, we find that as stellar mass increases, both atomic and molecular gas mass fractions decrease, stellar bulges become more prominent, and the mean stellar ages increase. Both star formation efficiency and molecular-to-atomic ratios vary little for massive MS galaxies, indicating that the flattening of the MS is due to the global decrease of the cold gas reservoirs of galaxies rather than to bottlenecks in the process of converting cold atomic gas to stars.

  8. Chromospheric activity and ages of solar-type stars

    SciTech Connect

    Barry, D.C.; Cromwell, R.H.; Hege, E.K.

    1987-04-01

    Observations of 15 solar-type stars in the intermediate-age open cluster NGC 752 are reported. A lower resolution analog of the Mount Wilson S index is shown to yield absolute chromospheric surface flux values for these stars with about 60 percent of the sensitivity of the Mount Wilson system. Absolute chromospheric surface fluxes of solar-type stars in eight clusters ranging from 10 million yrs to six billion or more years in age are presented. Two heuristic forms are shown to fit the data about equally well, with no indication of a discontinuity at intermediate ages. These relations can yield chromospheric ages for any G-type dwarf or subgiant with a Mount Wilson S index. The usefulness of this lower resolution approach for studies of chemical and dynamical evolution of the Galaxy as well as of the stellar birth rate is pointed out. 24 references.

  9. SWP Echelle Spectra of Chromospherically Active Dwarf Stars

    NASA Astrophysics Data System (ADS)

    Ayres, Thomas R.

    High resolution spectra of the 1150-2000 A region are enormously valuable for probing outer- atmosphere structure in cool stars. For example, such data can be used to separate blends, identify individual emission components in short-period binary systems, determine intensity ratios in close multiplets, estimate reliable emission strengths of lines superimposed on bright stellar continua, and test for the presence or absence of stellar winds at 105 K temperatures. These possibilities are not practical with IUE low-dispersion spectra. However, one must pay a steep-price to obtain useable high-dispersion IUE spectra and the additional dimension of diagnostic information, namely only a handful of the brightest UV sources are accessible even with shift-long exposures. We propose below an observing program to obtain echelle spectra of chromospherically active dwarf stars in the 1150-2000 A shortwavelength region. This program is intended to explore a particular class of objects that heretofore have not been observed at high dispersion with the SWP camera. Futhermore, this program complements previous SWP echelle studies by our group at the University of Colorado of quiet-chromosphere dwarf stars (alpha Cen A, alpha Cen B), active giants (alpha Aur A, lambda And, beta Dra), and the extreme case of the very active RS CVn-type system HR 1099. As described below, highdispersion spectra of these targets have provided a critical interpretive dimension that was lacking in previous low-dispersion studies. However, several fundamental questions have been raised in the course of our exploratory SWP work on what, in practice, are two distinct classes of chromospheric stars: the quiet dwarfs and the active giants. We feel that many of these questions can be answered by bridging the interpretive gap with a careful study of the active dwarfs. Our recent experience with shift-long SWP echelle exposures of chromospheric emission stars has suggested that our previous estimates of

  10. Galaxy And Mass Assembly (GAMA): the 325 MHz radio luminosity function of AGN and star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Prescott, Matthew; Mauch, T.; Jarvis, M. J.; McAlpine, K.; Smith, D. J. B.; Fine, S.; Johnston, R.; Hardcastle, M. J.; Baldry, I. K.; Brough, S.; Brown, M. J. I.; Bremer, M. N.; Driver, S. P.; Hopkins, A. M.; Kelvin, L. S.; Loveday, J.; Norberg, P.; Obreschkow, D.; Sadler, E. M.

    2016-03-01

    Measurement of the evolution of both active galactic nuclei (AGN) and star-formation in galaxies underpins our understanding of galaxy evolution over cosmic time. Radio continuum observations can provide key information on these two processes, in particular via the mechanical feedback produced by radio jets in AGN, and via an unbiased dust-independent measurement of star formation rates. In this paper, we determine radio luminosity functions at 325 MHz for a sample of AGN and star-forming galaxies by matching a 138 deg2 radio survey conducted with the Giant Metrewave Radio Telescope, with optical imaging and redshifts from the Galaxy And Mass Assembly survey. We find that the radio luminosity function at 325 MHz for star-forming galaxies closely follows that measured at 1.4 GHz. By fitting the AGN radio luminosity function out to z = 0.5 as a double power law, and parametrizing the evolution as Φ ∝ (1 + z)k, we find evolution parameters of k = 0.92 ± 0.95 assuming pure density evolution and k = 2.13 ± 1.96 assuming pure luminosity evolution. We find that the Low Excitation Radio Galaxies are the dominant population in space density at lower luminosities. Comparing our 325 MHz observations with radio continuum imaging at 1.4 GHz, we determine separate radio luminosity functions for steep- and flat-spectrum AGN, and show that the beamed population of flat-spectrum sources in our sample can be shifted in number density and luminosity to coincide with the unbeamed population of steep-spectrum sources, as is expected in the orientation-based unification of AGN.

  11. Interstellar reddening from the HIPPARCOS and TYCHO catalogues. I. Distances to nearby molecular clouds and star forming regions

    NASA Astrophysics Data System (ADS)

    Knude, J.; Hog, E.

    1998-10-01

    The Hipparcos and Tycho Catalogues offer an interesting possibility to study the local distribution of interstellar reddening from the combination of data contained in the catalogues: Hipparcos parallaxes, Tycho B - V and spectral and luminosity classification compiled from the literature. Parallactic distances may be derived for known absorbing features such as local molecular clouds and for large scale features such as sheets dividing bubbles. The stellar luminosity classes V and III offer more than 30.000 lines of sight for study, mostly for negative declinations where most classifications are available. We present some examples of this approach to derive information on the local interstellar medium. First we estimate the distance to the Southern Coalsack. Secondly, distances to the four nearby southern star forming clouds in the Chamaeleon region, the Lupus region, Corona Australis and finally the rho Ophiuchi are estimated. We find that these clouds are at 150 (Cha), 100 pc (Lup), i.e. about 50 pc closer than previously estimated, and that a feature with E_{B - V} ~ 0.15 (or A_V ~ 0.5) appears at 50 pc in this region. A distance of 170 pc is found for CrA compared to the previous estimate of 129 pc, and finally 120 pc for rho Oph compared to the previous 160 pc, strictly speaking the 120 pc are only measured for extinction values typical for the off core region in rho Ophiuchus. These distance changes are of some importance since these four regions show different stages of the star forming activity, as judged from the relative distribution of Class 0 - Class III YSOs (young stellar objects) in the Lbol - Tbol diagram. Precise calibrations of the YSOs' bolometric luminosities, applied in the definition of the bsf parameter (bsf: bright star fraction), require accurate distances of their parental clouds unless they are based on individual distances of the pre main sequence stars/protostellar sources.

  12. Searching for star-forming galaxies in the Fornax and Hydra clusters

    NASA Astrophysics Data System (ADS)

    Vaduvescu, O.; Kehrig, C.; Vilchez, J. M.; Unda-Sanzana, E.

    2011-09-01

    Context. The formation and evolution of dwarf galaxies is relatively difficult to understand because of their faint emission in all regimes that require large aperture telescopes. Aims: We intend to study the evolution of star-forming dwarf galaxies in clusters. We selected Fornax and Hydra clusters to complement our previous study of Virgo. On the basis of available literature data, we selected ten star-forming candidates in Fornax and another ten objects in Hydra. Methods: We used Gemini South with GMOS to acquire Hα images necessary to detect star-forming regions in the two galaxy samples. We then performed long-slit spectroscopy for the brightest six candidates, to derive their chemical properties. Finally, we employed the VLT with HAWK-I to observe all galaxies in the K' band to derive their main physical properties. Results: We studied the morphology of our two samples, finding five objects in Fornax and six in Hydra with structures consistent with those of star-forming dwarfs, i.e., dwarf irregulars (dIs) or blue compact dwarfs (BCDs). About four other objects are probably dwarf spirals, while three objects remained undetected in both visible and near infrared. On the basis of visible bright emission lines, we derived oxygen abundances for ten star-forming candidates with values between 8.00 ≤ 12+log(O/H) ≤8.78. Conclusions: Most fundamental properties of star-forming galaxies in Fornax and Hydra appear similar to corresponding properties of dIs and BCDs from Virgo and the local volume (LV). The luminosity-metallicity and metallicity-gas fraction relations in the LV and Virgo appear to be followed by Fornax and Hydra samples, suggesting that the chemical evolution of the two clusters seems consistent with the predictions from the closed box model, although larger samples are needed to investigate the role of possible environmental effects. Star-forming dwarfs (dIs and BCDs) in different environments appear to follow different mass-metallicity relations

  13. The structural and size evolution of star-forming galaxies over the last 11 Gyr

    NASA Astrophysics Data System (ADS)

    Paulino-Afonso, Ana; Sobral, David; Buitrago, Fernando; Afonso, José

    2017-03-01

    We present new results on the evolution of rest-frame blue/UV sizes and Sérsic indices of Hα-selected star-forming galaxies over the last 11 Gyr. We investigate how the perceived evolution can be affected by a range of biases and systematics such as cosmological dimming and resolution effects. We use GALFIT and an artificial redshifting technique, which includes the luminosity evolution of Hα-selected galaxies, to quantify the change on the measured structural parameters with redshift. We find typical sizes of 2-3 kpc and Sérsic indices of n ∼ 1.2, close to pure exponential discs all the way from z = 2.23 to z = 0.4. At z = 0, we find typical sizes of 4-5 kpc. Our results show that, when using GALFIT, cosmological dimming has a negligible impact on the derived effective radius for galaxies with <10 kpc, but we find an ∼20 per cent bias on the estimate of the median Sérsic indices, rendering galaxies more disc-like. Star-forming galaxies have grown on average by a factor of 2-3 in the last 11 Gyr with re ∝ (1 + z)-0.75. By exploring the evolution of the stellar mass-size relation, we find evidence for a stronger size evolution of the most massive star-forming galaxies since z ∼ 2, as they grow faster towards z ∼ 0 when compared to the lower stellar mass counterparts. As we are tracing the rest-frame blue/UV, we are likely witnessing the growth of discs where star formation is ongoing in galaxies while their profiles remain close to exponential discs, n ≲ 1.5, across the same period.

  14. The Role of Grain Surface Reactions in the Chemistry of Star Forming Regions

    NASA Technical Reports Server (NTRS)

    Kress, M. E.; Tielens, A. G. G. M.; Roberge, W. G.

    1998-01-01

    The importance of reactions at the surfaces of dust grains has long been recognized to be one of the two main chemical processes that form molecules in cold, dark interstellar clouds where simple, saturated (fully-hydrogenated) molecules such as H2 water, methanol, H2CO, H2S, ammonia and CH4 are present in quantities far too high to be consistent with their extremely low gas phase formation rates. In cold dark regions of interstellar space, dust grains provide a substrate onto which gas-phase species can accrete and react. Grains provide a "third body" or a sink for the energy released in the exothermic reactions that form chemical bonds. In essence, the surfaces of dust grains open up alternative reaction pathways to form observed molecules whose abundances cannot be explained with gas-phase chemistry alone. This concept is taken one step further in this work: instead of merely acting as a substrate onto which radicals and molecules may physically adsorb, some grains may actively participate in the reaction itself, forming chemical bonds with the accreting species. Until recently, surface chemical reactions had not been thought to be important in warm circumstellar media because adspecies rapidly desorb from grains at very low temperatures; thus, the residence times of molecules and radicals on the surface of grains at all but the lowest temperatures are far too short to allow these reactions to occur. However, if the adspecies could adsorb more strongly, via a true chemical bond with surfaces of some dust grains, then grain surface reactions will play an important role in warm circumstellar regions as well. In this work, the surface-catalyzed reaction CO + 3 H2 yields CH4 + H2O is studied in the context that it may be very effective at converting the inorganic molecule CO into the simplest organic compound, methane. H2 and CO are the most abundant molecules in space, and the reaction converting them to methane, while kinetically inhibited in the gas phase under

  15. Rotation, differential rotation, and gyrochronology of active Kepler stars

    NASA Astrophysics Data System (ADS)

    Reinhold, Timo; Gizon, Laurent

    2015-11-01

    Context. In addition to the discovery of hundreds of exoplanets, the high-precision photometry from the CoRoT and Kepler satellites has led to measurements of surface rotation periods for tens of thousands of stars, which can potentially be used to infer stellar ages via gyrochronology. Aims: Our main goal is to derive ages of thousands of field stars using consistent rotation period measurements derived by different methods. Multiple rotation periods are interpreted as surface differential rotation (DR). We study the dependence of DR with rotation period and effective temperature. Methods: We reanalyze a previously studied sample of 24 124 Kepler stars using different approaches based on the Lomb-Scargle periodogram. Each quarter (Q1-Q14) is treated individually using a prewhitening approach. Additionally, the full time series and their different segments are analyzed. Results: For more than 18 500 stars our results are consistent with the rotation periods from McQuillan et al. (2014, ApJS, 211, 24). Of these, more than 12 300 stars show multiple significant peaks, which we interpret as DR. Dependencies of the DR with rotation period and effective temperature could be confirmed, e.g., the relative DR increases with rotation period. Gyrochronology ages between 100 Myr and 10 Gyr were derived for more than 17 000 stars using different gyrochronology relations, most of them with uncertainties dominated by period variations. We find a bimodal age distribution for Teff between 3200-4700 K. The derived ages reveal an empirical activity-age relation using photometric variability as stellar activity proxy. Additionally, we found 1079 stars with extremely stable (mostly short) periods. Half of these periods may be associated with rotation stabilized by non-eclipsing companions, the other half might be due to pulsations. Conclusions: The derived gyrochronology ages are well constrained since more than ~93.0% of the stars seem to be younger than the Sun where calibration is

  16. Activity-rotation relations for lower main-sequence stars

    SciTech Connect

    Dobson-Hockey, A.K.

    1987-01-01

    It has been known for some time that stellar rotation and activity are related, both for chromospheric activity (e.g., Noyes et al. 1984) and coronal activity (e.g., Pallavicini et al. 1981; Maggio et al. 1987). Younger, more rapidly rotating stars of a given spectral type generally show higher levels of activity than do older, more slowly rotating stars. On the Sun, activity is distinctly related to magnetic fields. This leads to the suggestion that activity, at least in solar-type stars, is traceable to a magnetic dynamo which results from the interaction of rotation and differential rotation with convection. The more efficient the coriolis forces are at introducing helicity into convective motions, the more the magnetic field will be amplified and the more activity we may expect to see. The precise nature of the relationship between magnetic fields, rotation, and activity remains to be well-defined. This thesis examines the relationship between activity (both chromospheric and coronal) and rotation in order to better define and express such a relation (or relations).

  17. The SCUBA-2 cosmology legacy survey: Ultraluminous star-forming galaxies in a z = 1.6 cluster

    SciTech Connect

    Smail, Ian; Swinbank, A. M.; Danielson, A. L. R.; Edge, A. C.; Simpson, J. M.; Geach, J. E.; Tadaki, K.; Arumugam, V.; Dunlop, J. S.; Ivison, R. J.; Hartley, W.; Almaini, O.; Conselice, C.; Bremer, M. N.; Chapin, E.; Chapman, S. C.; Scott, D.; Simpson, C. J.; Karim, A.; Kodama, T.; and others

    2014-02-10

    We analyze new SCUBA-2 submillimeter and archival SPIRE far-infrared imaging of a z = 1.62 cluster, Cl 0218.3–0510, which lies in the UKIRT Infrared Deep Sky Survey/Ultra-Deep Survey field of the SCUBA-2 Cosmology Legacy Survey. Combining these tracers of obscured star-formation activity with the extensive photometric and spectroscopic information available for this field, we identify 31 far-infrared/submillimeter-detected probable cluster members with bolometric luminosities ≳10{sup 12} L {sub ☉} and show that by virtue of their dust content and activity, these represent some of the reddest and brightest galaxies in this structure. We exploit ALMA submillimeter continuum observations, which cover one of these sources, to confirm the identification of a SCUBA-2-detected ultraluminous star-forming galaxy in this structure. Integrating the total star-formation activity in the central region of the structure, we estimate that it is an order of magnitude higher (in a mass-normalized sense) than clusters at z ∼ 0.5-1. However, we also find that the most active cluster members do not reside in the densest regions of the structure, which instead host a population of passive and massive, red galaxies. We suggest that while the passive and active populations have comparable near-infrared luminosities at z = 1.6, M{sub H} ∼ –23, the subsequent stronger fading of the more active galaxies means that they will evolve into passive systems at the present day that are less luminous than the descendants of those galaxies that were already passive at z ∼ 1.6 (M{sub H} ∼ –20.5 and M{sub H} ∼ –21.5, respectively, at z ∼ 0). We conclude that the massive galaxy population in the dense cores of present-day clusters were already in place at z = 1.6 and that in Cl 0218.3–0510 we are seeing continuing infall of less extreme, but still ultraluminous, star-forming galaxies onto a pre-existing structure.

  18. CONTINUOUS MID-INFRARED STAR FORMATION RATE INDICATORS: DIAGNOSTICS FOR 0 < z < 3 STAR-FORMING GALAXIES

    SciTech Connect

    Battisti, A. J.; Calzetti, D.; Johnson, B. D.; Elbaz, D.

    2015-02-20

    We present continuous, monochromatic star formation rate (SFR) indicators over the mid-infrared wavelength range of 6–70 μm. We use a sample of 58 star-forming galaxies (SFGs) in the Spitzer–SDSS–GALEX Spectroscopic Survey at z < 0.2, for which there is a rich suite of multi-wavelength photometry and spectroscopy from the ultraviolet through to the infrared. The data from the Spitzer Infrared Spectrograph (IRS) of these galaxies, which spans 5–40 μm, is anchored to their photometric counterparts. The spectral region between 40–70 μm is interpolated using dust model fits to the IRS spectrum and Spitzer 70 and 160 μm photometry. Since there are no sharp spectral features in this region, we expect these interpolations to be robust. This spectral range is calibrated as a SFR diagnostic using several reference SFR indicators to mitigate potential bias. Our band-specific continuous SFR indicators are found to be consistent with monochromatic calibrations in the local universe, as derived from Spitzer, WISE, and Herschel photometry. Our local composite template and continuous SFR diagnostics are made available for public use through the NASA/IPAC Infrared Science Archive (IRSA) and have typical dispersions of 30% or less. We discuss the validity and range of applicability for our SFR indicators in the context of unveiling the formation and evolution of galaxies. Additionally, in the era of the James Webb Space Telescope this will become a flexible tool, applicable to any SFG up to z ∼ 3.

  19. Cosmic ion irradiation and UV photolysis of solids in star forming regions .

    NASA Astrophysics Data System (ADS)

    Palumbo, M. E.; Baratta, G. A.; Spinella, F.

    The presence of icy grain mantles along the line of sight of star forming regions is clearly evidenced by infrared observations. Due to the presence of the protostar and of cosmic radiation, ices suffer from ion bombardment, UV photolysis and thermal annealing. Most of our knowledge on the physical and chemical properties of ices is based on the comparison between observations and laboratory experiments performed at low temperature (10-80 K). Experimental results show that after ion irradiation and UV photolysis the chemical composition and the structure of the sample is modified. Both more volatile and less volatile species are formed and if a C-bearing species is present in the original sample a refractory residue is formed. Eventually thermal annealing causes the sublimation of icy mantles. Thus molecules are released to the gas phase which could be enriched by species formed in the solid phase. Here we will discuss some recent laboratory experiments relevant to the knowledge of the physico-chemical properties of ices in star forming regions.

  20. On the nature of star-forming filaments - II. Subfilaments and velocities

    NASA Astrophysics Data System (ADS)

    Smith, Rowan J.; Glover, Simon C. O.; Klessen, Ralf S.; Fuller, Gary A.

    2016-02-01

    We show that hydrodynamic turbulent cloud simulations naturally produce large filaments made up of a network of smaller and coherent subfilaments. Such simulations resemble observations of filaments and fibres in nearby molecular clouds. The subfilaments are dynamical features formed at the stagnation points of the turbulent velocity field where shocks dissipate the turbulent energy. They are a ubiquitous feature of the simulated clouds, which appear from the beginning of the simulation and are not formed by gradual fragmentation of larger filaments. Most of the subfilaments are gravitationally subcritical and do not fragment into cores, however, there is also a significant fraction of supercritical subfilaments which break up into star-forming cores. The subfilaments are coherent along their length, and the residual velocities along their spine show that they are subsonically contracting without any ordered rotation on scales of ˜0.1 pc. Accretion flows along the subfilaments can feed material into star-forming cores embedded within the network. The overall mass in subfilaments and the number of subfilaments increases as the cloud evolves. We propose that the formation of filaments and subfilaments is a natural consequence of the turbulent cascade in the complex multiphase interstellar medium. Subfilaments are formed by the high wavenumber, small-scale modes in the turbulent velocity field. These are then stretched by local shear motions and gathered together by a combination of low wavenumber modes and gravitational contraction on larger scales, and by doing so build up the extended filaments observed in column density maps.

  1. 13C Isotopic Fractionation of HC3N in Star-forming Regions: Low-mass Star-forming Region L1527 and High-mass Star-forming Region G28.28-0.36

    NASA Astrophysics Data System (ADS)

    Taniguchi, Kotomi; Saito, Masao; Ozeki, Hiroyuki

    2016-10-01

    We observed the J = 9-8 and 10-9 rotational lines of three 13C isotopologues of HC3N in L1527 and G28.28-0.36, with the 45 m radio telescope of the Nobeyama Radio Observatory, in order to constrain the main formation mechanisms of HC3N in each source. The abundance ratios of the three 13C isotopologues of HC3N are found to be 0.9 (±0.2) : 1.00 : 1.29 (±0.19) (1σ), and 1.0 (±0.2) : 1.00 : 1.47 (±0.17) (1σ), for [H13CCCN : HC13CCN : HCC13CN] in L1527 and G28.28-0.36, respectively. We recognize, from a similar 13C isotopic fractionation pattern, that the abundances of H13CCCN and HC13CCN are comparable, and HCC13CN is more abundant than the others. Based on the results, we discuss the main formation pathway of HC3N. The 13C isotopic fractionation pattern derived from our observations can be explained by the neutral-neutral reaction between C2H2 and CN in both the low-mass (L1527) and high-mass (G28.28-0.36) star-forming regions.

  2. Physical properties of H alpha selected star forming galaxies at z = 0.84

    NASA Astrophysics Data System (ADS)

    Villar; V.; Gallego, J.; Pérez-González, P. G.; Barro, G.; Pascual, S.; Zamorano, J.; Noeske, K.; Koo, D.

    2011-11-01

    In this work we analyze the star formation rates and stellar masses of a sample of 157 star forming galaxies at z ˜ 0.84 (Villar et al. 2008), selected by their Hα flux with a narrow band filter. We compare star formation rates (SFR) measured with different tracers (Hα, UV and IR) finding that they are in good agreement after extinction correction, although with some scatter. We find a correlation between the ratios SFR_{FUV}/SFR_{Hα}, SFR_{IR}/SFR_{Hα} and the EW(Hα) (i.e. weighted age) which accounts for part of this scatter. We obtained stellar mass estimations fitting templates to multi-wavelength photometry. The typical stellar mass of a galaxy within our sample is ˜ 2 x 10^{10} M_⊙. The specific star formation rate (sSFR) decreases with it, indicating that massive galaxies are less affected by star formation processes than less massive ones. In addition, the sSFR is, for a fixed mass, higher in the Universe at z˜ 0.84 than in the local one. Both results are consistent with the downsizing scenario. To quantify this downsizing we estimated the quenching masses for our sample at z ˜ 0.84 and a local sample also selected by Hα, finding that it declines from M_Q ˜ 10^{12} M_⊙ at z ˜ 0.84 to M_Q ˜ 8 x 10^{10} M_⊙ at the local Universe.

  3. DO R CORONAE BOREALIS STARS FORM FROM DOUBLE WHITE DWARF MERGERS?

    SciTech Connect

    Staff, Jan. E.; Clayton, Geoffrey C.; Tohline, Joel E.; Menon, Athira; Herwig, Falk; Even, Wesley; Fryer, Chris L.; Motl, Patrick M.; Geballe, Tom; Pignatari, Marco

    2012-09-20

    A leading formation scenario for R Coronae Borealis (RCB) stars invokes the merger of degenerate He and CO white dwarfs (WDs) in a binary. The observed ratio of {sup 16}O/{sup 18}O for RCB stars is in the range of 0.3-20 much smaller than the solar value of {approx}500. In this paper, we investigate whether such a low ratio can be obtained in simulations of the merger of a CO and a He WD. We present the results of five three-dimensional hydrodynamic simulations of the merger of a double WD system where the total mass is 0.9 M{sub Sun} and the initial mass ratio (q) varies between 0.5 and 0.99. We identify in simulations with q {approx}< 0.7 a feature around the merged stars where the temperatures and densities are suitable for forming {sup 18}O. However, more {sup 16}O is being dredged up from the C- and O-rich accretor during the merger than the amount of {sup 18}O that is produced. Therefore, on the dynamical timescale over which our hydrodynamics simulation runs, an {sup 16}O/{sup 18}O ratio of {approx}2000 in the 'best' case is found. If the conditions found in the hydrodynamic simulations persist for 10{sup 6} s the oxygen ratio drops to 16 in one case studied, while in a hundred years it drops to {approx}4 in another case studied, consistent with the observed values in RCB stars. Therefore, the merger of two WDs remains a strong candidate for the formation of these enigmatic stars.

  4. Some stars are totally metal: a new mechanism driving dust across star-forming clouds, and consequences for planets, stars, and galaxies

    SciTech Connect

    Hopkins, Philip F.

    2014-12-10

    Dust grains in neutral gas behave as aerodynamic particles, so they can develop large local density fluctuations entirely independent of gas density fluctuations. Specifically, gas turbulence can drive order-of-magnitude 'resonant' fluctuations in the dust density on scales where the gas stopping/drag timescale is comparable to the turbulent eddy turnover time. Here we show that for large grains (size ≳ 0.1 μm, containing most grain mass) in sufficiently large molecular clouds (radii ≳ 1-10 pc, masses ≳ 10{sup 4} M {sub ☉}), this scale becomes larger than the characteristic sizes of prestellar cores (the sonic length), so large fluctuations in the dust-to-gas ratio are imprinted on cores. As a result, star clusters and protostellar disks formed in large clouds should exhibit significant abundance spreads in the elements preferentially found in large grains (C, O). This naturally predicts populations of carbon-enhanced stars, certain highly unusual stellar populations observed in nearby open clusters, and may explain the 'UV upturn' in early-type galaxies. It will also dramatically change planet formation in the resulting protostellar disks, by preferentially 'seeding' disks with an enhancement in large carbonaceous or silicate grains. The relevant threshold for this behavior scales simply with cloud densities and temperatures, making straightforward predictions for clusters in starbursts and high-redshift galaxies. Because of the selective sorting by size, this process is not necessarily visible in extinction mapping. We also predict the shape of the abundance distribution—when these fluctuations occur, a small fraction of the cores may actually be seeded with abundances Z ∼ 100 (Z) such that they are almost 'totally metal' (Z ∼ 1)! Assuming the cores collapse, these totally metal stars would be rare (1 in ∼10{sup 4} in clusters where this occurs), but represent a fundamentally new stellar evolution channel.

  5. Characterizing and Cataloguing Star-Forming Galaxies in Preparation for the LADUMA Survey

    NASA Astrophysics Data System (ADS)

    Perez, Manuel Joe; Baker, Andrew J.; Wu, John F.

    2017-01-01

    This poster presents the results of an effort to process, characterize, and catalog the optical spectra of ~ 1,500 star-forming galaxies, located in the Extended Chandra Deep Field South (ECDFS), which will be used in stacking experiments by the Looking At the Distant Universe with the MeerKAT Array (LADUMA) deep HI survey. The LADUMA HI data will be used to study the evolution of the Tully-Fisher relation, cosmic neutral gas density, and other intrinsic properties of galaxies as a function of redshift. The stacking component of this research will rely on large catalogs of star-forming galaxies in the ECDFS, categorized according to star-formation rate (SFR), metallicity, stellar color excess, and redshift. We used optical spectra obtained with the Anglo-Australian Telescope, for which we have developed an automated pipeline to calculate extinction-corrected line fluxes, SFRs, and various metallicity diagnostics. The pipeline ultimately provides a visualization of the objects and their intrinsic properties as related to redshift for future analysis by the LADUMA team. This work has been supported by NSF grant PHY-1560077.

  6. 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.

  7. OUTFLOW, INFALL, AND PROTOSTARS IN THE STAR-FORMING CORE W3-SE

    SciTech Connect

    Zhu Lei; Zhao Junhui; Wright, M. C. H. E-mail: jzhao@cfa.harvard.edu

    2011-10-20

    We report new results on outflow and infall in the star-forming cores W3-SE SMA-1 and SMA-2 based on analysis of {approx}2.''5 resolution observations of the molecular lines HCN(3-2), HCO{sup +}(3-2), N{sub 2}H{sup +}(3-2), and CH{sub 3}OH(5{sub 2,3}-4{sub 1,3}) with the Submillimeter Array (SMA). A high-velocity bipolar outflow originating from the protostellar core SMA-1 was observed in the HCN(3-2) line, with a projected outflow axis at a position angle of 48{sup 0}. The detection of the outflow is confirmed from other molecular lines. An inverse P-Cygni profile in the HCN(3-2) line toward SMA-1 suggests that at least one of the double cores accretes matter from the molecular core. A filamentary structure in the molecular gas surrounds SMA-1 and SMA-2. Based on the SMA observations, our analysis suggests that the double pre-stellar cores SMA-1 and SMA-2 result from fragmentation in the collapsing massive molecular core W3-SE, and it is likely that they are forming intermediate- to high-mass stars which will be new members of a star cluster in the W3-SE region.

  8. Herschel Observations of C+ in the Vicinity of Star Forming Complexes in the Galactic Plane

    NASA Astrophysics Data System (ADS)

    Pineda, Jorge; Velusamy, T.; Langer, W.; Goldsmith, P.; Li, D.; Yorke, H.

    2010-05-01

    The CII fine-structure line at 158 um, is an excellent tracer of the warm diffuse gas and the hot, dense Photon Dominated Regions (PDRs). We can, therefore, use the CII emission as a probe to understand the effects of star formation on their interstellar environment. Here we present the first results from the Galactic Observations of Terahertz C+ (GOT C+), a Herschel Key Project study of CII fine structure emission in the vicinity of star forming complexes. In the Priority Science Phase of HIFI observations, the GOT C+ project collects data along a dozen lines of sight passing near star forming regions in the inner Galaxy from longitude 310 degrees to 25 degrees. We discuss our first results on the transition between dense and hot gas (traced by CII) and dense and cold gas (traced by 12CO and 13CO). This research was conducted at the Jet Propulsion Laboratory, California Institute of Technology under contract with the National Aeronautics and Space Administration. JLP was supported under the NASA Postdoctoral Program at JPL, Caltech, administered by Oak Ridge Associated Universities through a contract with NASA, and is currently supported as a Caltech-JPL Postdoc.

  9. The young active star SAO 51891 (V383 Lacertae)

    NASA Astrophysics Data System (ADS)

    Biazzo, K.; Frasca, A.; Marilli, E.; Covino, E.; Alcalã, J. M.; Ćakirli, Ö.; Klutsch, A.; Meyer, M. R.

    2009-05-01

    Aims: The aim of this work is to investigate the surface inhomogeneities of a young, late-type star, SAO 51891, at different atmospheric levels, from the photosphere to the upper chromosphere, analyzing contemporaneous optical high-resolution spectra and broad-band photometry. Methods: The full spectral range of FOCES@CAHA (R ≃ 40 000) is used to perform the spectral classification and to determine the rotational and radial velocities. The lithium abundance is measured to obtain an age estimate. The {BVRIJHK}s photometric bands are used to construct the spectral energy distribution (SED). The variations in the observed BV fluxes and effective temperature are used to infer the presence of photospheric spots and observe their behavior over time. The chromospheric activity is studied applying the spectral subtraction technique to Hα, Ca ii H & K, Hɛ, and Ca ii IRT lines. Results: We find SAO 51891 to be a young K0-1V star with a lithium abundance close to the Pleiades upper envelope, confirming its youth ( 100 Myr), which is also inferred from its kinematical membership of the Local Association. No infrared excess is detected from analysis of its SED, limiting the amount of remaining circumstellar dust. We detect a rotational modulation of the luminosity, effective temperature, Ca ii H & K, Hɛ, and Ca ii IRT total fluxes. A simple spot model with two main active regions, about 240 K cooler than the surrounding photosphere, fits the observed light and temperature curves very well. The small-amplitude radial velocity variations are also well reproduced by our spot model. The anti-correlation of light curves and chromospheric diagnostics indicates chromospheric plages spatially associated with the spots. The largest modulation amplitude is observed for the Hɛ flux suggesting that this line is very sensitive to the presence of chromospheric plages. Conclusions: SAO 51891 is a young active star, lacking significant amounts of circumstellar dust or any evidence of low

  10. NEAR-INFRARED PERIODIC AND OTHER VARIABLE FIELD STARS IN THE FIELD OF THE CYGNUS OB7 STAR-FORMING REGION

    SciTech Connect

    Wolk, Scott J.; Rice, Thomas S.; Aspin, Colin A.

    2013-04-15

    We present a subset of the results of a three-season, 124 night, near-infrared monitoring campaign of the dark clouds Lynds 1003 and Lynds 1004 in the Cygnus OB7 star-forming region. In this paper, we focus on the field star population. Using three seasons of UKIRT J, H, and K-band observations spanning 1.5 years, we obtained high-quality photometry on 9200 stars down to J = 17 mag, with photometric uncertainty better than 0.04 mag. After excluding known disk-bearing stars we identify 149 variables-1.6% of the sample. Of these, about 60 are strictly periodic, with periods predominantly <2 days. We conclude this group is dominated by eclipsing binaries. A few stars have long period signals of between 20 and 60 days. About 25 stars have weak modulated signals, but it was not clear if these were periodic. Some of the stars in this group may be diskless young stellar objects with relatively large variability due to cool starspots. The remaining {approx}60 stars showed variations which appear to be purely stochastic.

  11. Chromospherically active stars. 6: Giants with compact hot companions and the barium star scenario

    NASA Technical Reports Server (NTRS)

    Fekel, Francis C.; Henry, Gregory W.; Busby, Michael R.; Eitter, Joseph J.

    1993-01-01

    We have determined spectroscopic orbits for three chromospherically active giants that have hot compact companions. They are HD 160538 (K0 III + wd, P = 904 days), HD 165141 (G8 III + wd, P approximately 5200 days), and HD 185510 (K0 III + sdB, P = 20.6619 days). By fitting an IUE spectrum with theoretical models, we find the white dwarf companion of HD 165141 has a temperature of about 35000 K. Spectral types and rotational velocities have been determined for the three giants and distances have been estimated. These three systems and 39 Ceti are compared with the barium star mass-transfer scenario. The long-period mild barium giant HD 165141 as well as HD 185510 and 39 Ceti, which have relatively short periods and normal abundance giants, appear to be consistent with this scenario. The last binary, HD 160538, a system with apparently near solar abundances, a white dwarf companion, and orbital characteristics similar to many barium stars, demonstrates that the existence of a white-dwarf companion is insufficient to produce a barium star. The paucity of systems with confirmed white-dwarf companions makes abundance analyses of HD 160538 and HD 165141 of great value in examining the role of metallicity in barium star formation.

  12. Chromospherically active stars. 11: Giant with compact hot companions and the barium star scenario

    NASA Technical Reports Server (NTRS)

    Fekel, Francis C.; Henry, Gregory W.; Busby, Michael R.; Eitter, Joseph J.

    1993-01-01

    We have determined spectroscopic orbits for three chromsopherically active giants that have hot compact companions. They are HD 160538 (KO III + wd, P = 904 days), HD 165141 (G8 III + wd, P approximately 5200 days), and HD 185510 (KO III + sdB, P = 20.6619 days). By fitting an IUE spectrum with theoretical models, we find the white dwarf companion of HD 165141 has a temperature of about 35,000 K. Spectral types and rotational velocities have been determined for the three giants and distances have been estimated. These three systems and 39 Ceti are compared with the barium star mass-transfer scenario. The long-period mild barium giant HD 165141 as well as HD 185510 and 39 Ceti, which have relatively short periods and normal abundance giants, appear to be consistent with this scenario. The last binary, HD 160538, a system with apparently near solar abundances, a white dwarf companion, and orbital characteristics similar to many barium stars, demonstrates that the existence of a white dwarf companion is insufficient to produce a barium star. The paucity of systems with confirmed white dwarf companions makes abundance analyses of HD 160538 and HD 165141 of great value in examining the role of metallicity in barium star formation.

  13. An accretion disks in the high-mass star forming region IRA 23151+5912

    NASA Astrophysics Data System (ADS)

    Migenes, Victor; Rodríguez-Esnard, T.; Trinidad, M. A.

    2014-01-01

    We present observations of radio continuum emission at 1.3 and 3.6 cm and H2O masers toward the high-mass star-forming regions IRA 23151+5912 carried out with the VLA-EVLA. We detected one continuum source at 1.3 cm and 13 water maser spots which are distributed in three groups aligned along the northeast-southwest direction. Our results suggest that the 1.3 cm emission is consistent with an HC HII region, probably with an embedded zero-age main sequence star of type B2. In particular, we find that this radio continuum source is probably associated with a circumstellar disk of about 68 AU, as traced by water masers. Furthermore, the masers of the second group are probably describing another circumstellar disk of about 86 AU, whose central protostar is still undetected. We discuss this results in the light of more recent high-resolution observations.

  14. The SFR Efficiency of HI Gas in the Outskirts of Star Forming Galaxies

    NASA Astrophysics Data System (ADS)

    Rafelski, Marc

    2017-03-01

    In order to understand the origin of the decreased star formation rate (SFR) efficiency of neutral atomic hydrogen gas measured in Damped Lyα Systems (DLAs) at z ~ 3, we measure the SFR efficiency of atomic gas at z ~ 1, z ~ 2, and z ~ 3 around star-forming galaxies. We create galaxy stacks in these three redshift bins, and measure the SFR efficiency by combining DLA absorber statistics with the observed rest-frame UV emission in the galaxies' outskirts. We find that the SFR efficiency of Hi gas is ~ 3% of that predicted by the KS relation. We find no significant evolution in the SFR efficiency with redshift, although simulations and models predict a decreasing SFR efficiency with decreasing metallicity and thus with increasing redshift. We discuss possible explanations for this decreased efficiency without an evolution with redshift.

  15. New fully empirical calibrations of strong-line metallicity indicators in star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Curti, M.; Cresci, G.; Mannucci, F.; Marconi, A.; Maiolino, R.; Esposito, S.

    2017-02-01

    We derive new empirical calibrations for strong-line diagnostics of gas-phase metallicity in local star-forming galaxies by uniformly applying the Te method over the full metallicity range probed by the Sloan Digital Sky Survey (SDSS). To measure electron temperatures at high metallicity, where the auroral lines needed are not detected in single galaxies, we stacked spectra of more than 110 000 galaxies from the SDSS in bins of log[O II]/Hβ and log[O III]/Hβ. This stacking scheme does not assume any dependence of metallicity on mass or star formation rate, but only that galaxies with the same line ratios have the same oxygen abundance. We provide calibrations which span more than 1 dex in metallicity and are entirely defined on a consistent absolute Te metallicity scale for galaxies. We apply our calibrations to the SDSS sample and find that they provide consistent metallicity estimates to within 0.05 dex.

  16. Comparing Herschel dust emission structures, magnetic fields observed by Planck, and dynamics: high-latitude star forming cloud L1642

    NASA Astrophysics Data System (ADS)

    Malinen, Johanna

    2016-01-01

    The nearby high-latitude cloud L1642 is one of only two known very high latitude (|b| > 30 deg) clouds actively forming stars. This cloud is a rare example of star formation in isolated conditions, and can reveal important details of star formation in general, e.g., of the effect of magnetic fields. We compare Herschel dust emission structures and magnetic field orientation revealed by Planck polarization maps in L1642, and also combine these with dynamic information from molecular line observations. The high-resolution Herschel data reveal a complex structure including a dense, compressed central blob with elongated extensions, low density striations, "fishbone" like structures with a spine and perpendicular striations, and a spiraling "tail". The Planck polarization data reveal an ordered magnetic field that pervades the cloud and is aligned with the surrounding low density striations. We show that there is a complex interplay between the cloud structure and large scale magnetic fields revealed by Planck polarization data at 10' resolution. This suggests that the magnetic field is closely linked to the formation and evolution of the cloud. We see a clear transition from aligned to perpendicular structures approximately at a column density of NH = 2x10^21 cm-2. We conclude that Planck polarization data revealing the large scale magnetic field orientation can be very useful even when comparing to the finest structures in higher resolution data, e.g. Herschel at ~18" resolution.

  17. Low Gas Fractions Connect Compact Star-forming Galaxies to Their z ~ 2 Quiescent Descendants

    NASA Astrophysics Data System (ADS)

    Spilker, Justin S.; Bezanson, Rachel; Marrone, Daniel P.; Weiner, Benjamin J.; Whitaker, Katherine E.; Williams, Christina C.

    2016-11-01

    Early quiescent galaxies at z˜ 2 are known to be remarkably compact compared to their nearby counterparts. Possible progenitors of these systems include galaxies that are structurally similar, but are still rapidly forming stars. Here, we present Karl G. Jansky Very Large Array (VLA) observations of the CO(1-0) line toward three such compact, star-forming galaxies (SFGs) at z˜ 2.3, significantly detecting one. The VLA observations indicate baryonic gas fractions ≳ 5 times lower and gas depletion timescales ≳ 10 times shorter than normal, extended massive SFGs at these redshifts. At their current star formation rates, all three objects will deplete their gas reservoirs within 100 Myr. These objects are among the most gas-poor objects observed at z\\gt 2, and are outliers from standard gas scaling relations, a result that remains true regardless of assumptions about the CO-H2 conversion factor. Our observations are consistent with the idea that compact, SFGs are in a rapid state of transition to quiescence in tandem with the buildup of the z˜ 2 quenched population. In the detected compact galaxy, we see no evidence of rotation or that the CO-emitting gas is spatially extended relative to the stellar light. This casts doubt on recent suggestions that the gas in these compact galaxies is rotating and significantly extended compared to the stars. Instead, we suggest that, at least for this object, the gas is centrally concentrated, and only traces a small fraction of the total galaxy dynamical mass.

  18. Radio and infrared study of the star-forming region IRAS 20286+4105

    NASA Astrophysics Data System (ADS)

    Ramachandran, Varsha; Das, S. R.; Tej, A.; Vig, S.; Ghosh, S. K.; Ojha, D. K.

    2017-03-01

    In this paper, we present a multiwavelength investigation of the star-forming complex IRAS 20286+4105, located in the Cygnus X region. Near-infrared K-band data are used to revisit the cluster/stellar group identified in previous studies. Radio continuum observations at 610 and 1280 MHz show the presence of a H II region possibly powered by a star of spectral type B0-B0.5. The cometary morphology of the ionized region is explained by invoking the bow-shock model, where the likely association with a nearby supernova remnant is also explored. A compact radio knot with a non-thermal spectral index is detected towards the centre of the cloud. Mid-infrared data from the Spitzer Legacy Survey of the Cygnus X region show the presence of six Class I young stellar objects inside the cloud. Thermal dust emission in this complex is modelled using Herschel far-infrared data to generate dust temperature and column density maps. Herschel images also show the presence of two clumps in this region, the masses of which are estimated to be ∼175 and 30 M⊙. The mass-radius relation and the surface density of the clumps mean that they do not qualify as massive star-forming sites. An overall picture of a runaway star ionizing the cloud and a triggered population of intermediate-mass, Class I sources located towards the cloud centre emerges from this multiwavelength study. Variation in the dust emissivity spectral index is shown to exist in this region and is seen to have an inverse relation with the dust temperature.

  19. IROCKS: Spatially Resolved Kinematics of z ˜ 1 Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Mieda, Etsuko; Wright, Shelley A.; Larkin, James E.; Armus, Lee; Juneau, Stéphanie; Salim, Samir; Murray, Norman

    2016-11-01

    We present results from the Intermediate Redshift OSIRIS Chemo-Kinematic Survey (IROCKS) for sixteen z ˜ 1 and one z ˜ 1.4 star-forming galaxies. All galaxies were observed with OSIRIS with the laser guide star adaptive optics system at Keck Observatory. We use rest-frame nebular Hα emission lines to trace morphologies and kinematics of ionized gas in star-forming galaxies on sub-kiloparsec physical scales. We observe elevated velocity dispersions (σ ≳ 50 km s-1) seen in z > 1.5 galaxies persist at z ˜ 1 in the integrated galaxies. Using an inclined disk model and the ratio of v/σ , we find that 1/3 of the z ˜ 1 sample are disk candidates while the other 2/3 of the sample are dominated by merger-like and irregular sources. We find that including extra attenuation toward H ii regions derived from stellar population synthesis modeling brings star formation rates (SFRs) using Hα and stellar population fit into a better agreement. We explore the properties of the compact Hα sub-component, or “clump,” at z ˜ 1 and find that they follow a similar size-luminosity relation as local H ii regions but are scaled-up by an order of magnitude with higher luminosities and sizes. Comparing the z ˜ 1 clumps to other high-redshift clump studies, we determine that the clump SFR surface density evolves as a function of redshift. This suggests clump formation is directly related to the gas fraction in these systems and may support disk fragmentation as their formation mechanism since gas fraction scales with redshift.

  20. Far-infrared line coolants in massive star-forming regions

    NASA Astrophysics Data System (ADS)

    Leurini, Silvia

    2014-10-01

    The lines of [OI] and [CII] are powefulr tracers of different environments. In photo-dissociation regions (PDRs) their line ratio strongly depends on density; in molecular outflows from low-mass young stellar objects the luminosity of the [OI] line at 63 micron is directly proportional to the rate of mass outflow from the star and it is independent on visual extinction, inclination, and geometry of the outflow. In metal-rich galaxies, [OI] and [CII] lines are among the main coolants, and being very luminous, they are potentially powerful tracers of star formation rates (SFRs) even in galaxies at high z. However, [OI] and [CII] were till now observed only with very poor spectral resolution. They can be heavily affected by absorptions from the source or from different foreground clouds, and the contribution of outflows and PDRs cannot be quantified without resolved profiles. Therefore their diagnostic value is of limited use. We propose here to exploit the unprecedented resolution of the GREAT receiver aboard SOFIA for the first spectroscopically resolved observations of [OI] and [CII] of a sample of galactic massive star-forming clumps. The sources are a flux-limited sub-sample from the ATLASGAL continuum survey of the inner Galaxy and cover a broad range of evolutionary phases. Thanks to the wealth of already collected ancillary data (in particular water, high-J CO and NH3), the proposed observations will be fundamental to calibrate [OI] and [CII] as PDR, outflow and SFR tracers in a sample of sources rapresentative of the Galactic population of massive star-forming clumps. The data will answer the following questions: Which ISM components do [OI] and [CII] trace? How does the complete (CO+H2O+[OI]+[CII]) FIR cooling budget change with bolometric luminosity? Does [OI] show prominent high-velocity emission in massive sources or is ti dominated by PDR emission?

  1. The Evolution of Star Formation Activity in Cluster Galaxies Over 0.15 < z < 1.5

    NASA Astrophysics Data System (ADS)

    Wagner, Cory R.

    In this thesis, we explore 7.5 billion years of evolution in cluster galaxy star formation activity using a sample of 11 high-redshift (1 < z < 1.5) clusters from the IRAC Shallow Cluster Survey, and 25 low-redshift (0.15 < z < 1) clusters from The Cluster Lensing And Supernova survey with Hubble. We compare cluster galaxy star formation to that of the field over 0.15 < z < 1.5 using 8000 galaxies from the UltraVISTA survey. Mid-infrared star formation rates are measured using Spitzer 24 mum data for isolated high-redshift galaxies. We calculate rest-frame ultraviolet star formation rates for low-redshift cluster members using Hubble Space Telescope observations. Using publically available mid-infrared and ultraviolet data for our field sample, we empirically derive scaling relations to adjust low-redshift cluster galaxy ultraviolet star formation rates to mid-infrared levels. We classify cluster galaxy morphology by visual inspection, and use quantitatively measured morphologies for field galaxies. Cluster late-type galaxies at z > 1 show enhanced star formation activity relative to the field, and account for nearly 90% of the overall star formation activity in high-redshift clusters. While high-redshift early-type galaxies are substantially quenched relative to cluster late-types, they still contribute 13% of the total cluster star formation activity. With early-type fractions increasing from 34 to 56% from z 1.5 → 1.16, we find that new cluster early-type galaxies are likely being formed around z 1.4. The fraction of early-type galaxies that are star-forming drops from 29 to 11% over this period, yet their specific star formation rates are roughly constant. These factors suggest that the events that created these new galaxies, possibly mergers, were both recent and gas-rich. With typical coverages of 50% of z < 1 cluster virial radii, we can only probe the cores of low-redshift clusters. We find that in this regime, the star formation activity of cluster

  2. Mid-IR Selected z ∼ 2 Type-2 QSOs: Obscured Star-Forming Young Quasars?

    NASA Astrophysics Data System (ADS)

    Violino, Giulio; Stevens, J.; Coppin, K.

    2016-10-01

    Star formation and obscuration in AGN: A sub-mm study of high-redshift mid-IR selected type-2 QSOs. The AGN unification model describes unobscured and obscured AGN (AGN1 and AGN2) as identical sources, with their different observed properties explained solely by orientation effects; as a result, it predicts no difference in the host galaxies. As an alternative, a second scenario has been proposed in which type-2 AGN represent an earlier stage in the life of AGN characterized by dust- enshrouded host galaxies which contribute to the obscuration and higher star formation activity, at least at earlier epochs. To test this scenario we employ Herschel data at three different wavelengths (250, 350, 500 um) to study the far-IR-to-submm properties of a sample of mid-IR selected type 2 QSOs at high redshift (1.5star-formation activity and consequently derive FIR luminosities of the two components, as well as SFRs and dust masses. We propose a picture in which intermediate-level radio activity in the core (pc scale) of AGN is linked to the obscuration of the nucleus (perhaps via a merger) since our AGN1 have systematically lower radio luminosities than our AGN2.

  3. Direct Measurement of Dust Attenuation in z approx. 1.5 Star-Forming Galaxies from 3D-HST: Implications for Dust Geometry and Star Formation Rates

    NASA Technical Reports Server (NTRS)

    Price, Sedona H.; Kriek, Mariska; Brammer, Gabriel B; Conroy, Charlie; Schreiber, Natascha M. Foerster; Franx, Marijn; Fumagalli, Mattia; Lundren, Britt; Momcheva, Ivelina; Nelson, Erica J.; Rix, Hans-Walter; Skelton, Rosalind E.; VanDokkum, Pieter G.; Tease, Katherine Whitaker; Wuyts, Stijn

    2013-01-01

    The nature of dust in distant galaxies is not well understood, and until recently few direct dust measurements have been possible. We investigate dust in distant star-forming galaxies using near-infrared grism spectra of the 3D-HST survey combined with archival multi-wavelength photometry. These data allow us to make a direct comparison between dust towards star-forming regions (measured using Balmer decrements) and the integrated dust properties (derived by comparing spectral energy distributions [SEDs] with stellar population and dust models) for a statistically significant sample of distant galaxies. We select a sample of 163 galaxies between 1.36< or = z< or = 1.5 with H(alpha) SNR > or = 5 and measure Balmer decrements from stacked spectra. First, we stack spectra in bins of integrated stellar dust attenuation, and find that there is extra dust extinction towards star-forming regions (AV,HII is 1.81 times the integrated AV, star), though slightly lower than found for low-redshift starburst galaxies. Next, we stack spectra in bins of specific star formation rate (log sSFR), star formation rate (log SFR), and stellar mass (logM*). We find that on average AV,HII increases with SFR and mass, but decreases with increasing sSFR. The amount of extra extinction also decreases with increasing sSFR and decreasing stellar mass. Our results are consistent with the two-phase dust model - in which galaxies contain both a diffuse and a stellar birth cloud dust component - as the extra extinction will increase once older stars outside the star-forming regions become more dominant. Finally, using our Balmer decrements we derive dust-corrected H(alpha) SFRs, and find evidence that SED fitting produces incorrect SFRs if very rapidly declining SFHs are included in the explored parameter space. Subject headings: dust, extinction- galaxies: evolution- galaxies: high-redshift

  4. Coronal Diagnostics of Intermediate Activity Star XI Boo A

    NASA Technical Reports Server (NTRS)

    Drake, Jeremy

    2005-01-01

    The analysis of Xi Boo A proved difficult to adapt to our line-by-line approach because of the strong wings of the RGS instrumental profile, as has been detailed in earlier reports. While progress was also delayed because of problems in using SAS v4, we succeeded in the past year or so to bring the analysis to conclusion. Abundances have been derived using both EPIC and RGS data, confirming earlier EUVE findings of a mild solar-like FIP effect, though with some evidence of a turn-up in abundances of elements with higher FIP. Plasma densities appear normal for a moderately active stellar corona. Xi Boo A nicely bridges the gap between the very active stars and stars like the Sun, and it indeed does appear that these are the stars in which the solar-like FIP effects begins to change to the "inverse FIP" type of effect seen in the very active stars. Probing this divide was the main goal of the proposal. These results are in the process of being prepared for publication, though we have not decided the target journal as yet.

  5. Solar activity: The Sun as an X-ray star

    NASA Technical Reports Server (NTRS)

    Golub, L.

    1981-01-01

    The existence and constant activity of the Sun's outer atmosphere are thought to be due to the continual emergence of magnetic fields from the Solar interior and the stressing of these fields at or near the surface layers of the Sun. The structure and activity of the corona are thus symptomatic of the underlying magnetic dynamo and the existence of an outer turbulent convective zone on the Sun. A sufficient condition for the existence of coronal activity on other stars would be the existence of a magnetic dynamo and an outer convective zone. The theoretical relationship between magnetic fields and coronal activity can be tested by Solar observations, for which the individual loop structures can be resolved. A number of parameters however, which enter into the alternative theoretical formulations remain fixed in all Solar observations. To determine whether these are truly parameters of the theory observations need to be extended to nearby stars on which suitable conditions may occur.

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

    SciTech Connect

    Lundquist, Michael J.; Kobulnicky, Henry A.; Kerton, Charles R.; Arvidsson, Kim

    2015-06-10

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

  7. Water in Star-forming Regions with Herschel (WISH): recent results and trends

    NASA Astrophysics Data System (ADS)

    van Dishoeck, E. F.

    2012-03-01

    Water is a key molecule in the physics and chemistry of star- and planet-forming regions. In the `Water in Star-forming Regions with Herschel' (WISH) Key Program, we have obtained a comprehensive set of water data toward a large sample of well-characterized protostars, covering a wide range of masses and luminosities --from the lowest to the highest mass protostars--, as well as evolutionary stages --from pre-stellar cores to disks. Lines of both ortho- and para-H_2O and their isotopologues, as well as chemically related hydrides, are observed with the HIFI and PACS instruments. The data elucidate the physical processes responsible for the warm gas, probe dynamical processes associated with forming stars and planets (outflow, infall, expansion), test basic chemical processes and reveal the chemical evolution of water and the oxygen-reservoir into planet-forming disks. In this brief talk a few recent WISH highlights will be presented, including determinations of the water abundance in each of the different physical components (inner and outer envelope, outflow) and constraints on the ortho/para ratio. Special attention will be given to trends found across the sample, especially the similarity in profiles from low to high-mass protostars and the evolution of the gas-phase water abundance from prestellar cores to disks. More details can be found at http://www.strw.leidenuniv.nl/WISH, whereas overviews are given in van Dishoeck et al. (2011, PASP 123, 138), Kristensen & van Dishoeck (2011, Astronomische Nachrichten 332, 475) and Bergin & van Dishoeck (2012, Phil. Trans. Royal Soc. A).

  8. Improving fold activation of small transcription activating RNAs (STARs) with rational RNA engineering strategies.

    PubMed

    Meyer, Sarai; Chappell, James; Sankar, Sitara; Chew, Rebecca; Lucks, Julius B

    2016-01-01

    Regulatory RNAs have become integral components of the synthetic biology and bioengineering toolbox for controlling gene expression. We recently expanded this toolbox by creating small transcription activating RNAs (STARs) that act by disrupting the formation of a target transcriptional terminator hairpin placed upstream of a gene. While STARs are a promising addition to the repertoire of RNA regulators, much work remains to be done to optimize the fold activation of these systems. Here we apply rational RNA engineering strategies to improve the fold activation of two STAR regulators. We demonstrate that a combination of promoter strength tuning and multiple RNA engineering strategies can improve fold activation from 5.4-fold to 13.4-fold for a STAR regulator derived from the pbuE riboswitch terminator. We then validate the generality of our approach and show that these same strategies improve fold activation from 2.1-fold to 14.6-fold for an unrelated STAR regulator, opening the door to creating a range of additional STARs to use in a broad array of biotechnologies. We also establish that the optimizations preserve the orthogonality of these STARs between themselves and a set of RNA transcriptional repressors, enabling these optimized STARs to be used in sophisticated circuits.

  9. Chemical characterization of the early evolutionary phases of high-mass star-forming regions

    NASA Astrophysics Data System (ADS)

    Gerner, Thomas

    2014-10-01

    The formation of high-mass stars is a very complex process and up to date no comprehensive theory about it exists. This thesis studies the early stages of high-mass star-forming regions and employs astrochemistry as a tool to probe their different physical conditions. We split the evolutionary sequence into four observationally motivated stages that are based on a classification proposed in the literature. The sequence is characterized by an increase of the temperatures and densities that strongly influences the chemistry in the different stages. We observed a sample of 59 high-mass star-forming regions that cover the whole sequence and statistically characterized the chemical compositions of the different stages. We determined average column densities of 18 different molecular species and found generally increasing abundances with stage. We fitted them for each stage with a 1D model, such that the result of the best fit to the previous stage was used as new input for the following. This is a unique approach and allowed us to infer physical properties like the temperature and density structure and yielded a typical chemical lifetime for the high-mass star-formation process of 1e5 years. The 18 analyzed molecular species also included four deuterated molecules whose chemistry is particularly sensitive to thermal history and thus is a promising tool to infer chemical ages. We found decreasing trends of the D/H ratios with evolutionary stage for 3 of the 4 molecular species and that the D/H ratio depends more on the fraction of warm and cold gas than on the total amount of gas. That indicates different chemical pathways for the different molecules and confirms the potential use of deuterated species as chemical age indicators. In addition, we mapped a low-mass star forming region in order to study the cosmic ray ionization rate, which is an important parameter in chemical models. While in chemical models it is commonly fixed, we found that it ! strongly varies with

  10. 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

  11. First-generation black-hole-forming supernovae and the metal abundance pattern of a very iron-poor star.

    PubMed

    Umeda, Hideyuki; Nomoto, Ken'ichi

    2003-04-24

    It has been proposed theoretically that the first generation of stars in the Universe (population III) would be as massive as 100 solar masses (100 M(O)), because of inefficient cooling of the precursor gas clouds. Recently, the most iron-deficient (but still carbon-rich) low-mass star--HE0107-5240--was discovered. If this is a population III star that gained its metals (elements heavier than helium) after its formation, it would challenge the theoretical picture of the formation of the first stars. Here we report that the patterns of elemental abundance in HE0107-5240 (and other extremely metal-poor stars) are in good accord with the nucleosynthesis that occurs in stars with masses of 20-130 M(O) when they become supernovae if, during the explosions, the ejecta undergo substantial mixing and fallback to form massive black holes. Such supernovae have been observed. The abundance patterns are not, however, consistent with enrichment by supernovae from stars in the range 130-300 M(O). We accordingly infer that the first-generation supernovae came mostly from explosions of approximately 20-130 M(O) stars; some of these produced iron-poor but carbon- and oxygen-rich ejecta. Low-mass second-generation stars, like HE0107-5240, could form because the carbon and oxygen provided pathways for the gas to cool.

  12. New insight into the relation between star formation activity and dust content in galaxies

    NASA Astrophysics Data System (ADS)

    da Cunha, Elisabete; Eminian, Celine; Charlot, Stéphane; Blaizot, Jérémy

    2010-04-01

    We assemble a sample of 3258 low-redshift galaxies from the Sloan Digital Sky Survey Data Release 6 with complementary photometric observations by the Galaxy Evolution Explorer, the Two Micron All Sky Survey and the Infrared Astronomical Satellite at far-ultraviolet and infrared wavelengths. We use a recent, simple but physically motivated model to interpret the observed spectral energy distributions of the galaxies in this sample in terms of statistical constraints on physical parameters describing the star formation history and dust content. The focus on a subsample of 1658 galaxies with highest signal-to-noise ratio observations enables us to investigate most clearly several strong correlations between various derived physical properties of galaxies. In particular, we find that the typical dust mass Md of a galaxy forming stars at a rate ψ can be estimated remarkably well using the formula over at least three orders of magnitude in both quantities. We also find that the dust-to-stellar mass ratio, the ratio of dust mass to star formation rate and the fraction of dust luminosity contributed by the diffuse interstellar medium (ISM) all correlate strongly with specific star formation rate. A comparison with recent models of chemical and dust evolution of galaxies suggests that these correlations could arise, at least in part, from an evolutionary sequence. As galaxies form stars, their ISM becomes enriched in dust, while the drop in gas supply makes the specific star formation rate decrease. Interestingly, as a result, a young, actively star-forming galaxy with low dust-to-gas ratio may still be highly dusty (in the sense of a high dust-to-stellar mass ratio) because it contains large amounts of interstellar gas. This may be important for the interpretation of the infrared emission from young, gas-rich star-forming galaxies at high redshift. The results presented in this paper should be especially useful to improve the treatment of the ISM properties of galaxies

  13. B fields in OB stars (BOB): The discovery of a magnetic field in a multiple system in the Trifid nebula, one of the youngest star forming regions

    NASA Astrophysics Data System (ADS)

    Hubrig, S.; Fossati, L.; Carroll, T. A.; Castro, N.; González, J. F.; Ilyin, I.; Przybilla, N.; Schöller, M.; Oskinova, L. M.; Morel, T.; Langer, N.; Scholz, R. D.; Kharchenko, N. V.; Nieva, M.-F.

    2014-04-01

    Aims: Recent magnetic field surveys in O- and B-type stars revealed that about 10% of the core-hydrogen-burning massive stars host large-scale magnetic fields. The physical origin of these fields is highly debated. To identify and model the physical processes responsible for the generation of magnetic fields in massive stars, it is important to establish whether magnetic massive stars are found in very young star-forming regions or whether they are formed in close interacting binary systems. Methods: In the framework of our ESO Large Program, we carried out low-resolution spectropolarimetric observations with FORS 2 in 2013 April of the three most massive central stars in the Trifid nebula, HD 164492A, HD 164492C, and HD 164492D. These observations indicated a strong longitudinal magnetic field of about 500-600 G in the poorly studied component HD 164492C. To confirm this detection, we used HARPS in spectropolarimetric mode on two consecutive nights in 2013 June. Results: Our HARPS observations confirmed the longitudinal magnetic field in HD 164492C. Furthermore, the HARPS observations revealed that HD 164492C cannot be considered as a single star as it possesses one or two companions. The spectral appearance indicates that the primary is most likely of spectral type B1-B1.5 V. Since in both observing nights most spectral lines appear blended, it is currently unclear which components are magnetic. Long-term monitoring using high-resolution spectropolarimetry is necessary to separate the contribution of each component to the magnetic signal. Given the location of the system HD 164492C in one of the youngest star formation regions, this system can be considered as a Rosetta Stone for our understanding of the origin of magnetic fields in massive stars. Based on observations obtained in the framework of the ESO Prg. 191.D-0255(A,B).

  14. Discovery of Extremely Embedded X-ray Sources in the R Coronae Australis Star Forming Core

    NASA Technical Reports Server (NTRS)

    Hamaguchi, Ken-Ji; Corcoran, Michael F.; Petre, Rob; White, Nicholas E.; Stelzer, Beate; Nedachi, Ko; Kobayashi, Naoto

    2004-01-01

    We detected three extremely embedded X-ray sources in the R Corona Australis (R CrA) star forming core, IRS 7 region. Two weak X-ray sources are associated with the VLA centimeter radio sources 10E & W, whereas the third brightest source detected in the two XMM-Newton observations on March 2003 has no counterpart at any wavelengths. The large K-band upper-limit (19.4m) measured with the University of Hawaii 88-inch Telescope and strong absorption derived in X-rays (N(sub H) approx. 2.8 x 10(exp 23)/sq cm equivalent to A(sub v) approx. 180 m) indicate that the source is younger than typical Class I protostars, i.e. a Class 0 protostar or an intermittent phase between Class 0 and Class I protostars. The X-ray luminosity was less than one thirtieth (log L(sub x) less than or approx. equals 29.3 ergs/s) in the former Chandra observation in October 2000, which suggests that the X-ray activity, probably generated by magnetic activity, is triggered by an intermittent mass accretion episode such as FU Ori type outbursts. Because the source was detected at high significance in the XMM-Newton observations (approx. 2,000 cnts), X-ray properties of such young protostars can be well investigated for the first time. The light curves were constant in the 1st observation and increased linearly by a factor of two during 30 ksec in the 2nd observation. Both spectra showed iron K lines originated in hot thin-thermal plasma and fluorescence by cold gas. They can be reproduced by an absorbed thin-thermal plasma model with a Gaussian component at 6.4 keV (kT approx. 3-4 keV, L(sub x) approx. 7-20 x 10(exp 30) ergs/s). The rising timescale of the light curves in the 2nd observation was too slow for magnetically generated X-ray flares, whereas large equivalent width of the fluorescence iron K line in the 1st observation (approx. 810 eV) requires strong partial covering of the X-ray source. These results suggest that a confined hot (perhaps accretion) spot on the protostellar core was

  15. Active superconducting devices formed of thin films

    DOEpatents

    Martens, Jon S.; Beyer, James B.; Nordman, James E.; Hohenwarter, Gert K. G.

    1991-05-28

    Active superconducting devices are formed of thin films of superconductor which include a main conduction channel which has an active weak link region. The weak link region is composed of an array of links of thin film superconductor spaced from one another by voids and selected in size and thickness such that magnetic flux can propagate across the weak link region when it is superconducting. Magnetic flux applied to the weak link region will propagate across the array of links causing localized loss of superconductivity in the links and changing the effective resistance across the links. The magnetic flux can be applied from a control line formed of a superconducting film deposited coplanar with the main conduction channel and weak link region on a substrate. The devices can be formed of any type to superconductor but are particularly well suited to the high temperature superconductors since the devices can be entirely formed from coplanar films with no overlying regions. The devices can be utilized for a variety of electrical components, including switching circuits, amplifiers, oscillators and modulators, and are well suited to microwave frequency applications.

  16. X-ray emission from star-forming galaxies - I. High-mass X-ray binaries

    NASA Astrophysics Data System (ADS)

    Mineo, S.; Gilfanov, M.; Sunyaev, R.

    2012-01-01

    Based on a homogeneous set of X-ray, infrared and ultraviolet observations from Chandra, Spitzer, GALEX and 2MASS archives, we study populations of high-mass X-ray binaries (HMXBs) in a sample of 29 nearby star-forming galaxies and their relation to the star-formation rate (SFR). In agreement with previous results, we find that HMXBs are a good tracer of the recent star-formation activity in the host galaxy and their collective luminosity and number scale with the SFR: in particular, ?. However, the scaling relations still bear a rather large dispersion of rms ˜ 0.4 dex, which we believe is of a physical origin. We present the catalogue of 1055 X-ray sources detected within the D25 ellipse for galaxies of our sample and construct the average X-ray luminosity function (XLF) of HMXBs with substantially improved statistical accuracy and better control of systematic effects than achieved in previous studies. The XLF follows a power law with a slope of 1.6 in the log (LX) ˜ 35-40 luminosity range with moderately significant evidence for a break or cut-off at LX˜ 1040 erg s-1. As before, we did not find any features at the Eddington limit for a neutron star or a stellar-mass black hole. We discuss the implications of our results for the theory of binary evolution. In particular we estimate the fraction of compact objects that once in their lifetime experienced an X-ray active phase powered by accretion from a high-mass companion and obtain a rather large number, fX˜ 0.2 × (0.1 Myr/τX), where τX is the lifetime of the X-ray active phase. This is ˜4 orders of magnitude more frequent than in low-mass X-ray binaries (LMXBs). We also derive constraints on the mass distribution of the secondary star in HMXBs.

  17. THE COMPLEX PHYSICS OF DUSTY STAR-FORMING GALAXIES AT HIGH REDSHIFTS AS REVEALED BY HERSCHEL AND SPITZER

    SciTech Connect

    Lo Faro, B.; Franceschini, A.; Vaccari, M.; Rodighiero, G.; Feltre, A.; Marchetti, L.; Silva, L.; Berta, S.; Lutz, D.; Magnelli, B.; Bock, J.; Burgarella, D.; Buat, V.; Cava, A.; Clements, D. L.; Cooray, A.; Farrah, D.; Hurley, P.; Solares, E. A. Gonzalez; Magdis, G.; and others

    2013-01-10

    We combine far-infrared photometry from Herschel (PEP/HerMES) with deep mid-infrared spectroscopy from Spitzer to investigate the nature and the mass assembly history of a sample of 31 luminous and ultraluminous infrared galaxies ((U)LIRGs) at z {approx} 1 and 2 selected in GOODS-S with 24 {mu}m fluxes between 0.2 and 0.5 mJy. We model the data with a self-consistent physical model (GRASIL) which includes a state-of-the-art treatment of dust extinction and reprocessing. We find that all of our galaxies appear to require massive populations of old (>1 Gyr) stars and, at the same time, to host a moderate ongoing activity of star formation (SFR {<=} 100 M {sub Sun} yr{sup -1}). The bulk of the stars appear to have been formed a few Gyr before the observation in essentially all cases. Only five galaxies of the sample require a recent starburst superimposed on a quiescent star formation history. We also find discrepancies between our results and those based on optical-only spectral energy distribution (SED) fitting for the same objects; by fitting their observed SEDs with our physical model we find higher extinctions (by {Delta}A {sub V} {approx} 0.81 and 1.14) and higher stellar masses (by {Delta}log(M {sub *}) {approx} 0.16 and 0.36 dex) for z {approx} 1 and z {approx} 2 (U)LIRGs, respectively. The stellar mass difference is larger for the most dust-obscured objects. We also find lower SFRs than those computed from L {sub IR} using the Kennicutt relation due to the significant contribution to the dust heating by intermediate-age stellar populations through 'cirrus' emission ({approx}73% and {approx}66% of the total L {sub IR} for z {approx} 1 and z {approx} 2 (U)LIRGs, respectively).

  18. OUTSIDE-IN SHRINKING OF THE STAR-FORMING DISK OF DWARF IRREGULAR GALAXIES

    SciTech Connect

    Zhang Hongxin; Hunter, Deidre A.; Elmegreen, Bruce G.; Gao Yu; Schruba, Andreas E-mail: dah@lowell.edu E-mail: bge@us.ibm.com

    2012-02-15

    We have studied multi-band surface brightness profiles of a representative sample of 34 nearby dwarf irregular galaxies. Our data include Galaxy Evolution Explorer (GALEX) FUV/NUV, UBV, and H{alpha} and Spitzer 3.6 {mu}m images. These galaxies constitute the majority of the LITTLE THINGS survey (Local Irregulars That Trace Luminosity Extremes-The H I Nearby Galaxy Survey). By modeling the azimuthal averages of the spectral energy distributions with a complete library of star formation histories, we derived the stellar mass surface density distributions and the star formation rate averaged over three different timescales: the recent 0.1 Gyr, 1 Gyr, and a Hubble time. We find that, for {approx}80% (27 galaxies) of our sample galaxies, radial profiles (at least in the outer part) at shorter wavelengths, corresponding to younger stellar populations, have shorter disk scale lengths than those at longer wavelengths, corresponding to older stellar populations. This indicates that the star-forming disk has been shrinking. In addition, the radial distributions of the stellar mass surface density are well described as piece-wise exponential profiles, and {approx}80% of the galaxies have steeper mass profiles in the outer disk than in the inner region. The steep radial decline of the star formation rate in the outer parts compared to that in the inner disks gives a natural explanation for the down-bending stellar mass surface density profiles. Within the inner disks, our sample galaxies on average have constant ratios of recent star formation rate to stellar mass with radius. Nevertheless, {approx}35% (12 galaxies, among which 7 have baryonic mass {approx}<10{sup 8} M{sub Sun} ) of the sample exhibit negative slopes across the observed disk, which is in contrast with the so-called inside-out disk growth scenario suggested for luminous spiral galaxies. The tendency of star formation to become concentrated toward the inner disks in low-mass dwarf irregular galaxies is

  19. MAXIMALLY STAR-FORMING GALACTIC DISKS. II. VERTICALLY RESOLVED HYDRODYNAMIC SIMULATIONS OF STARBURST REGULATION

    SciTech Connect

    Shetty, Rahul; Ostriker, Eve C. E-mail: ostriker@astro.umd.edu

    2012-07-20

    We explore the self-regulation of star formation using a large suite of high-resolution hydrodynamic simulations, focusing on molecule-dominated regions (galactic centers and [U]LIRGS) where feedback from star formation drives highly supersonic turbulence. In equilibrium, the total midplane pressure, dominated by turbulence, must balance the vertical weight of the interstellar medium. Under self-regulation, the momentum flux injected by feedback evolves until it matches the vertical weight. We test this flux balance in simulations spanning a wide range of parameters, including surface density {Sigma}, momentum injected per stellar mass formed (p{sub *}/m{sub *}), and angular velocity. The simulations are two-dimensional radial-vertical slices, and include both self-gravity and an external potential that helps to confine gas to the disk midplane. After the simulations reach a steady state in all relevant quantities, including the star formation rate {Sigma}{sub SFR}, there is remarkably good agreement between the vertical weight, the turbulent pressure, and the momentum injection rate from supernovae. Gas velocity dispersions and disk thicknesses increase with p{sub *}/m{sub *}. The efficiency of star formation per free-fall time at the midplane density, {epsilon}{sub ff}(n{sub 0}), is insensitive to the local conditions and to the star formation prescription in very dense gas. We measure {epsilon}{sub ff}(n{sub 0}) {approx} 0.004-0.01, consistent with low and approximately constant efficiencies inferred from observations. For {Sigma} in (100-1000) M{sub Sun} pc{sup -2}, we find {Sigma}{sub SFR} in (0.1-4) M{sub Sun} kpc{sup -2} yr{sup -1}, generally following a {Sigma}{sub SFR} {proportional_to} {Sigma}{sup 2} relationship. The measured relationships agree very well with vertical equilibrium and with turbulent energy replenishment by feedback within a vertical crossing time. These results, along with the observed {Sigma}-{Sigma}{sub SFR} relation in high

  20. The formation and assembly of a typical star-forming galaxy at redshift z approximately 3.

    PubMed

    Stark, Daniel P; Swinbank, A Mark; Ellis, Richard S; Dye, Simon; Smail, Ian R; Richard, Johan

    2008-10-09

    Recent studies of galaxies approximately 2-3 Gyr after the Big Bang have revealed large, rotating disks, similar to those of galaxies today. The existence of well-ordered rotation in galaxies during this peak epoch of cosmic star formation indicates that gas accretion is likely to be the dominant mode by which galaxies grow, because major mergers of galaxies would completely disrupt the observed velocity fields. But poor spatial resolution and sensitivity have hampered this interpretation; such studies have been limited to the largest and most luminous galaxies, which may have fundamentally different modes of assembly from those of more typical galaxies (which are thought to grow into the spheroidal components at the centres of galaxies similar to the Milky Way). Here we report observations of a typical star-forming galaxy at z = 3.07, with a linear resolution of approximately 100 parsecs. We find a well-ordered compact source in which molecular gas is being converted efficiently into stars, likely to be assembling a spheroidal bulge similar to those seen in spiral galaxies at the present day. The presence of undisrupted rotation may indicate that galaxies such as the Milky Way gain much of their mass by accretion rather than major mergers.

  1. DIFFERENT EVOLUTIONARY STAGES IN THE MASSIVE STAR-FORMING REGION W3 MAIN COMPLEX

    SciTech Connect

    Wang Yuan; Jiang Zhibo; Beuther, Henrik; Bik, Arjan; Zhang Qizhou; Rodon, Javier A.; Fallscheer, Cassandra

    2012-08-01

    We observed three high-mass star-forming regions in the W3 high-mass star formation complex with the Submillimeter Array and IRAM 30 m telescope. These regions, i.e., W3 SMS1 (W3 IRS5), SMS2 (W3 IRS4) and SMS3, are in different evolutionary stages and are located within the same large-scale environment, which allows us to study rotation and outflows as well as chemical properties in an evolutionary sense. While we find multiple millimeter continuum sources toward all regions, these three subregions exhibit different dynamical and chemical properties, which indicate that they are in different evolutionary stages. Even within each subregion, massive cores of different ages are found, e.g., in SMS2, sub-sources from the most evolved ultracompact H II region to potential starless cores exist within 30,000 AU of each other. Outflows and rotational structures are found in SMS1 and SMS2. Evidence for interactions between the molecular cloud and the H II regions is found in the {sup 13}CO channel maps, which may indicate triggered star formation.

  2. NEARBY CLUMPY, GAS RICH, STAR-FORMING GALAXIES: LOCAL ANALOGS OF HIGH-REDSHIFT CLUMPY GALAXIES

    SciTech Connect

    Garland, C. A.; Pisano, D. J.; Rabidoux, K.; Low, M.-M. Mac; Kreckel, K.; Guzmán, R. E-mail: djpisano@mail.wvu.edu E-mail: mordecai@amnh.org E-mail: guzman@astro.ufl.edu

    2015-07-10

    Luminous compact blue galaxies (LCBGs) have enhanced star formation rates (SFRs) and compact morphologies. We combine Sloan Digital Sky Survey data with H i data of 29 LCBGs at redshift z ∼ 0 to understand their nature. We find that local LCBGs have high atomic gas fractions (∼50%) and SFRs per stellar mass consistent with some high-redshift star-forming galaxies (SFGs). Many local LCBGs also have clumpy morphologies, with clumps distributed across their disks. Although rare, these galaxies appear to be similar to the clumpy SFGs commonly observed at z ∼ 1–3. Local LCBGs separate into three groups: (1) interacting galaxies (∼20%); (2) clumpy spirals (∼40%); and (3) non-clumpy, non-spirals with regular shapes and smaller effective radii and stellar masses (∼40%). It seems that the method of building up a high gas fraction, which then triggers star formation, is not the same for all local LCBGs. This may lead to a dichotomy in galaxy characteristics. We consider possible gas delivery scenarios and suggest that clumpy spirals, preferentially located in clusters and with companions, are smoothly accreting gas from tidally disrupted companions and/or intracluster gas enriched by stripped satellites. Conversely, as non-clumpy galaxies are preferentially located in the field and tend to be isolated, we suggest clumpy, cold streams, which destroy galaxy disks and prevent clump formation, as a likely gas delivery mechanism for these systems. Other possibilities include smooth cold streams, a series of minor mergers, or major interactions.

  3. Ultraviolet ISM Diagnostics for Star-forming Galaxies. I. Tracers of Metallicity and Extinction

    NASA Astrophysics Data System (ADS)

    Zetterlund, Erika; Levesque, Emily M.; Leitherer, Claus; Danforth, Charles W.

    2015-06-01

    We have observed a sample of 14 nearby (z˜ 0.03) star-forming blue compact galaxies (BCGs) in the rest-frame far-UV (˜1150-2200 Å) using the Cosmic Origins Spectrograph on the Hubble Space Telescope. We have also generated a grid of stellar population synthesis models using the Starburst99 evolutionary synthesis code, allowing us to compare observations and theoretical predictions for the Si iv_1400 and C iv_1550 UV indices; both are comprised of a blend of stellar wind and interstellar lines and have been proposed as metallicity diagnostics in the UV. Our models and observations both demonstrate that there is a positive linear correlation with metallicity for both indices, and we find generally good agreement between our observations and the predictions of the Starburst99 models (with the models slightly under-estimating the value of the indices due to contributions from interstellar lines not simulated by a stellar population synthesis code). By combining the rest-frame UV observations with pre-existing rest-frame optical spectrophotometry of our BCG sample, we also directly compare the predictions of metallicity and extinction diagnostics across both wavelength regimes. This comparison reveals a correlation between the UV absorption and optical strong-line diagnostics, offering the first means of directly comparing interstellar medium (ISM) properties determined across different rest-frame regimes. Finally, using our Starburst99 model grid, we determine theoretical values for the short-wavelength UV continuum slope, {{β }18}, which can be used for determining extinction in rest-frame UV spectra of star-forming galaxies. We consider the implications of these results and discuss future work aimed at parameterizing these and other environmental diagnostics in the UV (a suite of diagnostics that could offer particular utility in the study of star-forming galaxies at high redshift) as well as the development of robust comparisons between ISM diagnostics across a

  4. Age-dating Low-Mass Star-Forming Galaxies at intermediate redshifts

    NASA Astrophysics Data System (ADS)

    Gallego, Jesus; Rodriguez-Muñoz, Lucía; Pacifici, Camilla; Tresse, Laurence; Charlot, Stéphane; Gil de Paz, Armando; Barro, Guillermo; Gomez-Guijarro, Carlos; Villar, Víctor

    2015-08-01

    Dwarf galaxies play a key role in galaxy formation and evolution: (1) hierarchical models predict that low-mass systems merged to form massive galaxies (building block paradigm; Dekel & Silk 1986); (2) dwarf systems might have been responsible for the reionization of the Universe (Wyithe & Loeb 2006); (3) theoretical models are particularly sensitive to the density of low-mass systems at diferent redshifts (Mamon et al. 2011), being one of the key science cases for the future E-ELT (Evans et al. 2013). While the history of low-mass dark matter halos is relatively well understood, the formation history of dwarf galaxies is still poorly reproduced by the models due to the distinct evolution of baryonic and dark matter.We present physical properties and constraints on the star formation histories (SFHs) of a sample of low-mass Star-Forming Galaxies (LMSFGs; 7.3 < log M∗/Mo < 8.0, at 0.3 < zspec < 0.9) selected by photometric stellar mass and apparent magnitude. The SFHs were obtained through the analysis of their spectral energy distributions using a novel approach (Pacifici et al. 2012) that (1) consistently combines photometric (HST and ground-based multi-broadband) and spectroscopic (equivalent widths of emission lines from VLT and GTC spectroscopy) data, and (2) uses physically motivated SFHs with non-uniform variations of the star formation rate (SFR) as a function of time.The median SFH of our LMSFGs appears to form 90% of the median stellar mass inferred for the sample in the ˜0.5-1.8 Gyr immediately preceding the observation. These results suggest a recent stellar mass assembly for dwarf SFGs, consistent with the cosmological downsizing trends. We find similar median SFH timescales for a slightly more massive secondary sample 8.0 < log M∗/Mo < 9.1).

  5. On the effects of rotation in primordial star-forming clouds

    NASA Astrophysics Data System (ADS)

    Dutta, Jayanta

    2016-01-01

    Context. The thermodynamical evolution of gas during the collapse of the primordial star-forming cloud depends significantly on the initial degree of rotation. Aims: However, there is no clear understanding of how the initial rotation can affect the heating and cooling process and hence the temperature that leads to the fragmentation of the gas during Population III star formation. Methods: We report the results from three-dimensional, smoothed-particle hydrodynamics (SPH) simulations of a rotating self-gravitating primordial gas cloud with a modified version of the Gadget-2 code, in which the initial ratio of the rotational to the gravitational energy (β0) is varied over two orders of magnitude. Results: We find that despite the lack of any initial turbulence and magnetic fields in the clouds, the angular momentum distribution leads to the formation and build-up of a disk that fragments into several clumps. We further examine the behavior of the protostars that form in both idealized as well as more realistic minihalos from the cosmological simulations. The thermodynamical evolution and the fragmentation behavior of the cosmological minihalos are similar to that of the artificial cases, especially in those with a similar β0-parameter. Protostars with a higher rotation support exhibit spiral-arm-like structures on several scales, and have lower accretion rates. These type of clouds tend to fragment more, while some of the protostars escape from the cluster with the possibility of surviving until the present day. They also take much longer to form compared to their slowly rotating counterparts. Conclusions: We conclude that the use of appropriate initial conditions of the gas in minihalos is a pivotal and decisive quantity to study the evolution and final fate of the primordial stars.

  6. The Rest-frame Submillimeter Spectrum of High-redshift, Dusty, Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Spilker, J. S.; Marrone, D. P.; Aguirre, J. E.; Aravena, M.; Ashby, M. L. N.; Béthermin, M.; Bradford, C. M.; Bothwell, M. S.; Brodwin, M.; Carlstrom, J. E.; Chapman, S. C.; Crawford, T. M.; de Breuck, C.; Fassnacht, C. D.; Gonzalez, A. H.; Greve, T. R.; Gullberg, B.; Hezaveh, Y.; Holzapfel, W. L.; Husband, K.; Ma, J.; Malkan, M.; Murphy, E. J.; Reichardt, C. L.; Rotermund, K. M.; Stalder, B.; Stark, A. A.; Strandet, M.; Vieira, J. D.; Weiß, A.; Welikala, N.

    2014-04-01

    We present the average rest-frame spectrum of high-redshift dusty, star-forming galaxies from 250 to 770 GHz. This spectrum was constructed by stacking Atacama Large Millimeter/submillimeter Array (ALMA) 3 mm spectra of 22 such sources discovered by the South Pole Telescope and spanning z = 2.0-5.7. In addition to multiple bright spectral features of 12CO, [C I], and H2O, we also detect several faint transitions of 13CO, HCN, HNC, HCO+, and CN, and use the observed line strengths to characterize the typical properties of the interstellar medium of these high-redshift starburst galaxies. We find that the 13CO brightness in these objects is comparable to that of the only other z > 2 star-forming galaxy in which 13CO has been observed. We show that the emission from the high-critical density molecules HCN, HNC, HCO+, and CN is consistent with a warm, dense medium with T kin ~ 55 K and n_{H_2} \\gtrsim 10^{5.5} cm-3. High molecular hydrogen densities are required to reproduce the observed line ratios, and we demonstrate that alternatives to purely collisional excitation are unlikely to be significant for the bulk of these systems. We quantify the average emission from several species with no individually detected transitions, and find emission from the hydride CH and the linear molecule CCH for the first time at high redshift, indicating that these molecules may be powerful probes of interstellar chemistry in high-redshift systems. These observations represent the first constraints on many molecular species with rest-frame transitions from 0.4 to 1.2 mm in star-forming systems at high redshift, and will be invaluable in making effective use of ALMA in full science operations.

  7. Neutral and ionized hydrides in star-forming regions. Observations with Herschel/HIFI.

    PubMed

    Benz, Arnold O; Bruderer, Simon; van Dishoeck, Ewine F; Stäuber, Pascal; Wampfler, Susanne F

    2013-10-03

    The cosmic abundance of hydrides depends critically on high-energy UV, X-ray, and particle irradiation. Here we study hydrides in star-forming regions where irradiation by the young stellar object can be substantial, and density and temperature can be much enhanced over interstellar values. Lines of OH, CH, NH, and SH and their ions OH(+), CH(+), NH(+), SH(+), H2O(+), and H3O(+) were observed in star-forming regions by the HIFI spectrometer onboard the Herschel Space Observatory. Molecular column densities are derived from observed ground-state lines, models, or rotational diagrams. We report here on two prototypical high-mass regions, AFGL 2591 and W3 IRS5, and compare them to chemical calculations by making assumptions on the high-energy irradiation. A model assuming no ionizing protostellar emission is compared with (i) a model assuming strong protostellar X-ray emission and (ii) a two-dimensional (2D) model including emission in the far UV (FUV, 6-13.6 eV), irradiating the outflow walls that separate the outflowing gas and infalling envelope material. We confirm that the effect of FUV in two-dimensional models with enlarged irradiated surfaces is clearly noticeable. A molecule that is very sensitive to FUV irradiation is CH(+), enhanced in abundance by more than 5 orders of magnitude. The HIFI observations of CH(+) lines agree with the two-dimensional FUV model by Bruderer et al., which computes abundances, non-LTE excitation, and line radiative transfer.20 It is concluded that CH(+) is a good FUV tracer in star-forming regions. The effect of potential X-ray irradiation is not excluded but cannot be demonstrated by the present data.

  8. SUPERMASSIVE BLACK HOLES IN A STAR-FORMING GASEOUS CIRCUMNUCLEAR DISK

    SciTech Connect

    Del Valle, L.; Escala, A.; Molina, J.; Maureira-Fredes, C.; Amaro-Seoane, P.; Cuadra, J.

    2015-09-20

    Using N-body/smoothed particle hydrodynamics simulations we study the evolution of the separation of a pair of supermassive black holes (SMBHs) embedded in a star-forming circumnuclear disk (CND). This type of disk is expected to be formed in the central kiloparsec of the remnant of gas-rich galaxy mergers. Our simulations indicate that orbital decay of the SMBHs occurs more quickly when the mean density of the CND is higher, due to increased dynamical friction. However, in simulations where the CND is fragmented in high-density gaseous clumps (clumpy CND), the orbits of the SMBHs are erratically perturbed by the gravitational interaction with these clumps, delaying, in some cases, the orbital decay of the SMBHs. The densities of these gaseous clumps in our simulations and in recent studies of clumpy CNDs are two orders of magnitude higher than the observed density of molecular clouds in isolated galaxies or ultraluminous infrared galaxies (ULIRGs), thus, we expect that SMBH orbits are perturbed less in real CNDs than in the simulated CNDs of this study and other recent studies. We also find that the migration timescale has a weak dependence on the star formation rate of the CND. Furthermore, the migration timescale of an SMBH pair in a star-forming clumpy CND is at most a factor of three longer than the migration timescale of a pair of SMBHs in a CND modeled with more simple gas physics. Therefore, we estimate that the migration timescale of the SMBHs in a clumpy CND is on the order of 10{sup 7} years.

  9. The rest-frame submillimeter spectrum of high-redshift, dusty, star-forming galaxies

    SciTech Connect

    Spilker, J. S.; Marrone, D. P.; Aguirre, J. E.; Aravena, M.; Ashby, M. L. N.; Béthermin, M.; Bothwell, M. S.; Brodwin, M.; Carlstrom, J. E.; Crawford, T. M.; Chapman, S. C.; De Breuck, C.; Gullberg, B.; Fassnacht, C. D.; Gonzalez, A. H.; Greve, T. R.; Hezaveh, Y.; Holzapfel, W. L.; and others

    2014-04-20

    We present the average rest-frame spectrum of high-redshift dusty, star-forming galaxies from 250 to 770 GHz. This spectrum was constructed by stacking Atacama Large Millimeter/submillimeter Array (ALMA) 3 mm spectra of 22 such sources discovered by the South Pole Telescope and spanning z = 2.0-5.7. In addition to multiple bright spectral features of {sup 12}CO, [C I], and H{sub 2}O, we also detect several faint transitions of {sup 13}CO, HCN, HNC, HCO{sup +}, and CN, and use the observed line strengths to characterize the typical properties of the interstellar medium of these high-redshift starburst galaxies. We find that the {sup 13}CO brightness in these objects is comparable to that of the only other z > 2 star-forming galaxy in which {sup 13}CO has been observed. We show that the emission from the high-critical density molecules HCN, HNC, HCO{sup +}, and CN is consistent with a warm, dense medium with T {sub kin} ∼ 55 K and n{sub H{sub 2}}≳10{sup 5.5} cm{sup –3}. High molecular hydrogen densities are required to reproduce the observed line ratios, and we demonstrate that alternatives to purely collisional excitation are unlikely to be significant for the bulk of these systems. We quantify the average emission from several species with no individually detected transitions, and find emission from the hydride CH and the linear molecule CCH for the first time at high redshift, indicating that these molecules may be powerful probes of interstellar chemistry in high-redshift systems. These observations represent the first constraints on many molecular species with rest-frame transitions from 0.4 to 1.2 mm in star-forming systems at high redshift, and will be invaluable in making effective use of ALMA in full science operations.

  10. Supermassive Black Holes in a Star-forming Gaseous Circumnuclear Disk

    NASA Astrophysics Data System (ADS)

    del Valle, L.; Escala, A.; Maureira-Fredes, C.; Molina, J.; Cuadra, J.; Amaro-Seoane, P.

    2015-09-01

    Using N-body/smoothed particle hydrodynamics simulations we study the evolution of the separation of a pair of supermassive black holes (SMBHs) embedded in a star-forming circumnuclear disk (CND). This type of disk is expected to be formed in the central kiloparsec of the remnant of gas-rich galaxy mergers. Our simulations indicate that orbital decay of the SMBHs occurs more quickly when the mean density of the CND is higher, due to increased dynamical friction. However, in simulations where the CND is fragmented in high-density gaseous clumps (clumpy CND), the orbits of the SMBHs are erratically perturbed by the gravitational interaction with these clumps, delaying, in some cases, the orbital decay of the SMBHs. The densities of these gaseous clumps in our simulations and in recent studies of clumpy CNDs are two orders of magnitude higher than the observed density of molecular clouds in isolated galaxies or ultraluminous infrared galaxies (ULIRGs), thus, we expect that SMBH orbits are perturbed less in real CNDs than in the simulated CNDs of this study and other recent studies. We also find that the migration timescale has a weak dependence on the star formation rate of the CND. Furthermore, the migration timescale of an SMBH pair in a star-forming clumpy CND is at most a factor of three longer than the migration timescale of a pair of SMBHs in a CND modeled with more simple gas physics. Therefore, we estimate that the migration timescale of the SMBHs in a clumpy CND is on the order of 107 years.

  11. How Do Multiple-Star Systems Form? VLA Study Reveals "Smoking Gun"

    NASA Astrophysics Data System (ADS)

    2006-12-01

    Astronomers have used the National Science Foundation's Very Large Array (VLA) radio telescope to image a young, multiple-star system with unprecedented detail, yielding important clues about how such systems are formed. Most Sun-sized or larger stars in the Universe are not single, like our Sun, but are members of multiple-star systems. Astronomers have been divided on how such systems can form, producing competing theoretical models for this process. Multiple Star Formation Graphic Proposed Formation Process for L1551 IRS5 CREDIT: Bill Saxton, NRAO/AUI/NSF Click on image for page of graphics and full information The new VLA study produced a "smoking gun" supporting one of the competing models, said Jeremy Lim, of the Institute of Astronomy & Astrophysics, Academia Sinica, in Taipei, Taiwan, whose study, done with Shigehisa Takakuwa of the National Astronomical Observatory of Japan, is published in the December 10 issue of the Astrophysical Journal. Ironically, their discovery of a third, previously-unknown, young star in the system may support a second theoretical model. "There may be more than one way to make a multiple-star system," Lim explained. The astronomers observed an object called L1551 IRS5, young, still-forming protostars enshrouded in a cloud of gas and dust, some 450 light-years from Earth in the direction of the constellation Taurus. Invisible to optical telescopes because of the gas and dust, this object was discovered in 1976 by astronomers using infrared telescopes. A VLA study in 1998 showed two young stars orbiting each other, each surrounded by a disk of dust that may, in time, congeal into a system of planets. Lim and Takakuwa re-examined the system, using improved technical capabilities that greatly boosted the quality of their images. "In the earlier VLA study, only half of the VLA's 27 antennas had receivers that could collect the radio waves, at a frequency of 43 GigaHertz (GHz), coming from the dusty disks. When we re-observed this

  12. Physical properties of high-mass star-forming clumps in different evolutionary stages from the Bolocam Galactic Plane Survey

    NASA Astrophysics Data System (ADS)

    Svoboda, Brian; Shirley, Yancy; Rosolowsky, Erik; Dunham, Miranda; Ellsworth-Bowers, Timothy; Ginsburg, Adam

    2013-07-01

    High mass stars play a key role in the physical and chemical evolution of the interstellar medium, yet the evolutionary sequence for high mass star forming regions is poorly understood. Recent Galactic plane surveys are providing the first systematic view of high-mass star-forming regions in all evolutionary phases across the Milky Way. We present observations of the 22.23 GHz H2O maser transition J(Ka,Kc) = 6(1,6)→5(2,3) transition toward 1398 clumps identified in the Bolocam Galactic Plane Survey using the 100m Green Bank Telescope (GBT). We detect 392 H2O masers, 279 (71%) newly discovered. We show that H2O masers can identify the presence of protostars which were not previously identified by Spitzer/MSX Galactic plane IR surveys: 25% of IR-dark clumps have an H2O maser. We compare the physical properties of the clumps in the Bolocam Galactic Plane Survey (BGPS) with observations of diagnostics of star formation activity: 8 and 24 um YSO candidates, H2O and CH3OH masers, shocked H2, EGOs, and UCHII regions. We identify a sub-sample of 400 clumps with no star formation indicators representing the largest and most robust sample of pre-protocluster candidates from an unbiased survey to date. The different evolutionary stages show strong separations in HCO+ linewidth and integrated intensity, surface mass density, and kinetic temperature. Monte Carlo techniques are applied to distance probability distribution functions (DPDFs) in order to marginalize over the kinematic distance ambiguity and calculate the distribution of derived quantities for clumps in different evolutionary stages. Surface area and dust mass show weak separations above > 2 pc^2 and > 3x10^3 solar masses. An observed breakdown occurs in the size-linewidth relationship with no differentiation by evolutionary stage. Future work includes adding evolutionary indicators (MIPSGAL, HiGal, MMB) and expanding DPDF priors (HI self-absorption, Galactic structure) for more well-resolved KDAs.

  13. MAGNETIC ACTIVITY CYCLES IN THE EXOPLANET HOST STAR {epsilon} ERIDANI

    SciTech Connect

    Metcalfe, T. S.; Mathur, S.; Buccino, A. P.; Mauas, P. J. D.; Petrucci, R.; Brown, B. P.; Soderblom, D. R.; Henry, T. J.; Hall, J. C.; Basu, S.

    2013-02-01

    The active K2 dwarf {epsilon} Eri has been extensively characterized both as a young solar analog and more recently as an exoplanet host star. As one of the nearest and brightest stars in the sky, it provides an unparalleled opportunity to constrain stellar dynamo theory beyond the Sun. We confirm and document the 3-year magnetic activity cycle in {epsilon} Eri originally reported by Hatzes and coworkers, and we examine the archival data from previous observations spanning 45 years. The data show coexisting 3-year and 13-year periods leading into a broad activity minimum that resembles a Maunder minimum-like state, followed by the resurgence of a coherent 3-year cycle. The nearly continuous activity record suggests the simultaneous operation of two stellar dynamos with cycle periods of 2.95 {+-} 0.03 years and 12.7 {+-} 0.3 years, which, by analogy with the solar case, suggests a revised identification of the dynamo mechanisms that are responsible for the so-called 'active' and 'inactive' sequences as proposed by Boehm-Vitense. Finally, based on the observed properties of {epsilon} Eri, we argue that the rotational history of the Sun is what makes it an outlier in the context of magnetic cycles observed in other stars (as also suggested by its Li depletion), and that a Jovian-mass companion cannot be the universal explanation for the solar peculiarities.

  14. Formation of ethylene glycol and other complex organic molecules in star-forming regions

    NASA Astrophysics Data System (ADS)

    Rivilla, V. M.; Beltrán, M. T.; Cesaroni, R.; Fontani, F.; Codella, C.; Zhang, Q.

    2017-02-01

    Context. The detection of complex organic molecules related with prebiotic chemistry in star-forming regions allows us to investigate how the basic building blocks of life are formed. Aims: Ethylene glycol (CH2OH)2 is the simplest sugar alcohol and the reduced alcohol of the simplest sugar glycoladehyde (CH2OHCHO). We study the molecular abundance and spatial distribution of (CH2OH)2, CH2OHCHO and other chemically related complex organic species (CH3OCHO, CH3OCH3, and C2H5OH) towards the chemically rich massive star-forming region G31.41+0.31. Methods: We analyzed multiple single-dish (Green Bank Telescope and IRAM 30 m) and interferometric (Submillimeter Array) spectra towards G31.41+0.31, covering a range of frequencies from 45 to 258 GHz. We fitted the observed spectra with a local thermodynamic equilibrium (LTE) synthetic spectra, and obtained excitation temperatures and column densities. We compared our findings in G31.41+0.31 with the results found in other environments, including low- and high-mass star-forming regions, quiescent clouds and comets. Results: We report for the first time the presence of the aGg' conformer of (CH2OH)2 towards G31.41+0.31, detecting more than 30 unblended lines. We also detected multiple transitions of other complex organic molecules such as CH2OHCHO, CH3OCHO, CH3OCH3, and C2H5OH. The high angular resolution images show that the (CH2OH)2 emission is very compact, peaking towards the maximum of the 1.3 mm continuum. These observations suggest that low abundance complex organic molecules, like (CH2OH)2 or CH2OHCHO, are good probes of the gas located closer to the forming stars. Our analysis confirms that (CH2OH)2 is more abundant than CH2OHCHO in G31.41+0.31, as previously observed in other interstellar regions. Comparing different star-forming regions we find evidence of an increase of the (CH2OH)2/CH2OHCHO abundance ratio with the luminosity of the source. The CH3OCH3/CH3OCHO and (CH2OH)2/C2H5OH ratios are nearly constant with

  15. Ultraviolet to near-infrared spectral distributions of star-forming galaxies: Metallicity and age effects

    NASA Technical Reports Server (NTRS)

    Storchi-Bergmann, Thaisa; Calzetti, Daniela; Kinney, Anne L.

    1994-01-01

    Spectral distributions from the UV to the near-IR of a sample of 44 star-forming galaxies are used to calculate the metallicity (O/H), star-formation rate (SFR) and age of the starbursts. The oxygen abundance covers the range 8.3 less than O/H less than 9.4 and nitrogen (N) is found to be mostly a product of secondary nucleosynthesis for O/H greater than 8.4. Due to its secondary origin, N/O ratios up to approximately equals 4 times the solar value can be obtained for metal-rich starbursts. The SFR ranges 0.01 to 100 solar mass/year. The lower metallicity galaxies seem to be experiencing an instantaneous burst of star formation, with ages ranging from under 5 x 10(exp 6) to 10(exp 7) yr. The highest metallicity galaxies are most probably experiencing a continuous burst. Correlations between the calculated quantities and several spectral features are investigated. We found a highly significant correlation between the equivalent width W(C IV lambda 1550)-a stellar (absorption) feature- and the oxygen abundance of the emitting gas (O/H). Thus we show for the first time that the stellar metallicity is well correlated with the gas metallicity in star-bursting galaxies. The equivalent width W(Si IV lambda 1400) and the emission line ratio (N II) lambda lambda 6548.84/H(sub alpha) also correlate well with O/H, and all three features can be used as metallicity indicators for star-forming galaxies. The continuum color between lambda 1400 and lambda 3500 (C(14 - 35)) is shown to correlate with O/H, although it is better correlated with E(B - V). It was not possible to disentangle the metallicity from the reddening effect in C(14- 35). We estimate that the reddening affecting the UV continuum is about half the one derived from the Balmer decrement of the emitting gas. The SFR correlates well with the galaxy luminosity and there is no dependence of the continuum color on the SFR. The higher metallicities are only found in the more luminous galaxies, while low metallicities are

  16. SPITZER IMAGING OF STRONGLY LENSED HERSCHEL-SELECTED DUSTY STAR-FORMING GALAXIES

    SciTech Connect

    Ma, Brian; Cooray, Asantha; Calanog, J. A.; Nayyeri, H.; Timmons, N.; Casey, C.; Baes, M.; Chapman, S.; Dannerbauer, H.; De Zotti, G.; Dunne, L.; Michałowski, M. J.; Oteo, I.; Farrah, D.; Fu, Hai; Gonzalez-Nuevo, J.; Riechers, D. A.; Scott, D.; and others

    2015-11-20

    We present the rest-frame optical spectral energy distribution (SED) and stellar masses of six Herschel-selected gravitationally lensed dusty, star-forming galaxies (DSFGs) at 1 < z < 3. These galaxies were first identified with Herschel/SPIRE imaging data from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) and the Herschel Multi-tiered Extragalactic Survey (HerMES). The targets were observed with Spitzer/IRAC at 3.6 and 4.5 μm. Due to the spatial resolution of the IRAC observations at the level of 2″, the lensing features of a background DSFG in the near-infrared are blended with the flux from the foreground lensing galaxy in the IRAC imaging data. We make use of higher resolution Hubble/WFC3 or Keck/NIRC2 Adaptive Optics imaging data to fit light profiles of the foreground lensing galaxy (or galaxies) as a way to model the foreground components, in order to successfully disentangle the foreground lens and background source flux densities in the IRAC images. The flux density measurements at 3.6 and 4.5 μm, once combined with Hubble/WFC3 and Keck/NIRC2 data, provide important constraints on the rest-frame optical SED of the Herschel-selected lensed DSFGs. We model the combined UV- to millimeter-wavelength SEDs to establish the stellar mass, dust mass, star formation rate, visual extinction, and other parameters for each of these Herschel-selected DSFGs. These systems have inferred stellar masses in the range 8 × 10{sup 10}–4 × 10{sup 11} M{sub ⊙} and star formation rates of around 100 M{sub ⊙} yr{sup −1}. This puts these lensed submillimeter systems well above the SFR-M* relation observed for normal star-forming galaxies at similar redshifts. The high values of SFR inferred for these systems are consistent with a major merger-driven scenario for star formation.

  17. 15N Fractionation in Star-Forming Regions and Solar System Objects

    NASA Technical Reports Server (NTRS)

    Wirstrom, Eva; Milam, Stefanie; Adande, GIlles; Charnley, Steven; Cordiner, Martin

    2015-01-01

    A central issue for understanding the formation and evolution of matter in the early Solar System is the relationship between the chemical composition of star-forming interstellar clouds and that of primitive Solar System materials. The pristinemolecular content of comets, interplanetary dust particles and carbonaceous chondrites show significant bulk nitrogen isotopic fractionation relative to the solar value, 14N15N 440. In addition, high spatial resolution measurements in primitive materials locally show even more extreme enhancements of 14N15N 100.

  18. A Weak Lensing View of the Downsizing of Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Utsumi, Yousuke; Geller, Margaret J.; Dell'Antonio, Ian P.; Kamata, Yukiko; Kawanomoto, Satoshi; Koike, Michitaro; Komiyama, Yutaka; Koshida, Shintaro; Mineo, Sogo; Miyazaki, Satoshi; Sakurai, Junya; Tait, Philip J.; Terai, Tsuyoshi; Tomono, Daigo; Usuda, Tomonori; Yamada, Yoshihiko; Zahid, Harus J.

    2016-12-01

    We describe a weak lensing view of the downsizing of star-forming galaxies based on cross-correlating a weak lensing (κ) map with a predicted map constructed from a redshift survey. Moderately deep and high-resolution images with Subaru/Hyper Suprime-Cam covering the 4 {\\deg }2 DLS F2 field provide a κ map with 1 arcmin resolution. A dense complete redshift survey of the F2 field including 12,705 galaxies with R≤slant 20.6 is the basis for construction of the predicted map. The zero-lag cross-correlation between the κ and predicted maps is significant at the 30σ level. The width of the cross-correlation peak is comparable to the angular scale of rich clusters at z˜ 0.3, the median depth of the redshift survey. Slices of the predicted map in δ z=0.05 redshift bins enable exploration of the impact of structure as a function of redshift. The zero-lag normalized cross-correlation has significant local maxima at redshifts coinciding with known massive X-ray clusters. Even in slices where there are no known massive clusters, there is a significant signal in the cross-correlation originating from lower mass groups that trace the large-scale of the universe. Spectroscopic {D}n4000 measurements enable division of the sample into star-forming and quiescent populations. In regions surrounding massive clusters of galaxies, the significance of the cross-correlation with maps based on star-forming galaxies increases with redshift from 5σ at z = 0.3 to 7σ at z=0.5; the fractional contribution of the star-forming population to the total cross-correlation signal also increases with redshift. This weak lensing view is consistent with the downsizing picture of galaxy evolution established from other independent studies. Based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

  19. Trigonometric parallaxes of star forming regions in the Perseus spiral arm

    SciTech Connect

    Choi, Y. K.; Brunthaler, A.; Menten, K. M.; Hachisuka, K.; Reid, M. J.; Dame, T. M.; Xu, Y. E-mail: ykchoi@kasi.re.kr

    2014-08-01

    We report trigonometric parallaxes and proper motions of water masers for 12 massive star forming regions in the Perseus spiral arm of the Milky Way as part of the Bar and Spiral Structure Legacy (BeSSel) Survey. Combining our results with 14 parallax measurements in the literature, we estimate a pitch angle of 9.°9 ± 1.°5 for a section of the Perseus arm. The three-dimensional Galactic peculiar motions of these sources indicate that on average they are moving toward the Galactic center and slower than the Galactic rotation.

  20. Predictions for Ultra-deep Radio Counts of Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Mancuso, Claudia; Lapi, Andrea; Cai, Zhen-Yi; Negrello, Mattia; De Zotti, Gianfranco; Bressan, Alessandro; Bonato, Matteo; Perrotta, Francesca; Danese, Luigi

    2015-09-01

    We have worked outty predictions for the radio counts of star-forming galaxies down to nJy levels, along with redshift distributions down to the detection limits of the phase 1 Square Kilometer Array MID telescope (SKA1-MID) and of its precursors. Such predictions were obtained by coupling epoch-dependent star formation rate (SFR) functions with relations between SFR and radio (synchrotron and free-free) emission. The SFR functions were derived taking into account both the dust-obscured and the unobscured star formation, by combining far-infrared, ultraviolet, and Hα luminosity functions up to high redshifts. We have also revisited the South Pole Telescope counts of dusty galaxies at 95 GHz, performing a detailed analysis of the Spectral Energy Distributions. Our results show that the deepest SKA1-MID surveys will detect high-z galaxies with SFRs two orders of magnitude lower compared to Herschel surveys. The highest redshift tails of the distributions at the detection limits of planned SKA1-MID surveys comprise a substantial fraction of strongly lensed galaxies. We predict that a survey down to 0.25 μJy at 1.4 GHz will detect about 1200 strongly lensed galaxies per square degree, at redshifts of up to 10. For about 30% of them the SKA1-MID will detect at least 2 images. The SKA1-MID will thus provide a comprehensive view of the star formation history throughout the re-ionization epoch, unaffected by dust extinction. We have also provided specific predictions for the EMU/ASKAP and MIGHTEE/MeerKAT surveys.

  1. PREDICTIONS FOR ULTRA-DEEP RADIO COUNTS OF STAR-FORMING GALAXIES

    SciTech Connect

    Mancuso, Claudia; Lapi, Andrea; De Zotti, Gianfranco; Bressan, Alessandro; Perrotta, Francesca; Danese, Luigi; Cai, Zhen-Yi; Negrello, Mattia; Bonato, Matteo

    2015-09-01

    We have worked outty predictions for the radio counts of star-forming galaxies down to nJy levels, along with redshift distributions down to the detection limits of the phase 1 Square Kilometer Array MID telescope (SKA1-MID) and of its precursors. Such predictions were obtained by coupling epoch-dependent star formation rate (SFR) functions with relations between SFR and radio (synchrotron and free–free) emission. The SFR functions were derived taking into account both the dust-obscured and the unobscured star formation, by combining far-infrared, ultraviolet, and Hα luminosity functions up to high redshifts. We have also revisited the South Pole Telescope counts of dusty galaxies at 95 GHz, performing a detailed analysis of the Spectral Energy Distributions. Our results show that the deepest SKA1-MID surveys will detect high-z galaxies with SFRs two orders of magnitude lower compared to Herschel surveys. The highest redshift tails of the distributions at the detection limits of planned SKA1-MID surveys comprise a substantial fraction of strongly lensed galaxies. We predict that a survey down to 0.25 μJy at 1.4 GHz will detect about 1200 strongly lensed galaxies per square degree, at redshifts of up to 10. For about 30% of them the SKA1-MID will detect at least 2 images. The SKA1-MID will thus provide a comprehensive view of the star formation history throughout the re-ionization epoch, unaffected by dust extinction. We have also provided specific predictions for the EMU/ASKAP and MIGHTEE/MeerKAT surveys.

  2. Clustering of Star-forming Galaxies Near a Radio Galaxy at z=5.2

    NASA Astrophysics Data System (ADS)

    Overzier, Roderik A.; Miley, G. K.; Bouwens, R. J.; Cross, N. J. G.; Zirm, A. W.; Benítez, N.; Blakeslee, J. P.; Clampin, M.; Demarco, R.; Ford, H. C.; Hartig, G. F.; Illingworth, G. D.; Martel, A. R.; Röttgering, H. J. A.; Venemans, B.; Ardila, D. R.; Bartko, F.; Bradley, L. D.; Broadhurst, T. J.; Coe, D.; Feldman, P. D.; Franx, M.; Golimowski, D. A.; Goto, T.; Gronwall, C.; Holden, B.; Homeier, N.; Infante, L.; Kimble, R. A.; Krist, J. E.; Mei, S.; Menanteau, F.; Meurer, G. R.; Motta, V.; Postman, M.; Rosati, P.; Sirianni, M.; Sparks, W. B.; Tran, H. D.; Tsvetanov, Z. I.; White, R. L.; Zheng, W.

    2006-01-01

    We present HST ACS observations of the most distant radio galaxy known, TN J0924-2201 at z=5.2. This radio galaxy has six spectroscopically confirmed Lyα-emitting companion galaxies and appears to lie within an overdense region. The radio galaxy is marginally resolved in i775 and z850, showing continuum emission aligned with the radio axis, similar to what is observed for lower redshift radio galaxies. Both the half-light radius and the UV star formation rate are comparable to the typical values found for Lyman break galaxies at z~4-5. The Lyα emitters are sub-L* galaxies, with deduced star formation rates of 1-10 Msolar yr-1. One of the Lyα emitters is only detected in Lyα. Based on the star formation rate of ~3 Msolar yr-1 calculated from Lyα, the lack of continuum emission could be explained if the galaxy is younger than ~2 Myr and is producing its first stars. Observations in V606i775z850 were used to identify additional Lyman break galaxies associated with this structure. In addition to the radio galaxy, there are 22 V606 break (z~5) galaxies with z850<26.5 (5 σ), two of which are also in the spectroscopic sample. We compare the surface density of ~2 arcmin-2 to that of similarly selected V606 dropouts extracted from GOODS and the UDF parallel fields. We find evidence for an overdensity to very high confidence (>99%), based on a counts-in-cells analysis applied to the control field. The excess suggests that the V606 break objects are associated with a forming cluster around the radio galaxy. 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. These observations are associated with program 9291.

  3. THE PHYSICAL ENVIRONMENT OF THE MASSIVE STAR-FORMING REGION W42

    SciTech Connect

    Dewangan, L. K.; Luna, A.; Mayya, Y. D.; Ojha, D. K.; Mallick, K. K.; Anandarao, B. G.

    2015-10-01

    We present an analysis of multi-wavelength observations from various data sets and Galactic plane surveys to study the star-formation process in the W42 complex. A bipolar appearance of the W42 complex is evident due to the ionizing feedback from the O5–O6 type star in a medium that is highly inhomogeneous. The Very Large Telescope/NACO adaptive-optics K and L{sup ′} images (resolutions ∼0.″2–0.″1) resolved this ionizing source into multiple point-like sources below ∼5000 AU scale. The position angle ∼15° of the W42 molecular cloud is consistent with the H-band starlight mean polarization angle, which in turn is close to the Galactic magnetic field, suggesting the influence of the Galactic field on the evolution of the W42 molecular cloud. Herschel sub-millimeter data analysis reveals three clumps located along the waist axis of the bipolar nebula, with the peak column densities of ∼(3–5) × 10{sup 22} cm{sup −2} corresponding to visual extinctions of A{sub V} ∼ 32–53.5 mag. The Herschel temperature map traces a temperature gradient in W42, revealing regions of 20 K, 25 K, and 30–36 K. Herschel maps reveal embedded filaments (length ∼1–3 pc) that appear to be radially pointed to the denser clump associated with the O5–O6 star, forming a hub-filament system. A total of 512 candidate young stellar objects (YSOs) are identified in the complex, ∼40% of which are present in clusters distributed mainly within the molecular cloud, including the Herschel filaments. Our data sets suggest that the YSO clusters, including the massive stars, are located at the junction of the filaments, similar to those seen in the Rosette Molecular Cloud.

  4. GAS RESERVOIRS AND STAR FORMATION IN A FORMING GALAXY CLUSTER AT zbsime0.2

    SciTech Connect

    Jaffe, Yara L.; Poggianti, Bianca M.; Verheijen, Marc A. W.; Deshev, Boris Z.; Van Gorkom, Jacqueline H.

    2012-09-10

    We present first results from the Blind Ultra-Deep H I Environmental Survey of the Westerbork Synthesis Radio Telescope. Our survey is the first direct imaging study of neutral atomic hydrogen gas in galaxies at a redshift where evolutionary processes begin to show. In this Letter we investigate star formation, H I content, and galaxy morphology, as a function of environment in Abell 2192 (at z = 0.1876). Using a three-dimensional visualization technique, we find that Abell 2192 is a cluster in the process of forming, with significant substructure in it. We distinguish four structures that are separated in redshift and/or space. The richest structure is the baby cluster itself, with a core of elliptical galaxies that coincides with (weak) X-ray emission, almost no H I detections, and suppressed star formation. Surrounding the cluster, we find a compact group where galaxies pre-process before falling into the cluster, and a scattered population of 'field-like' galaxies showing more star formation and H I detections. This cluster proves to be an excellent laboratory to understand the fate of the H I gas in the framework of galaxy evolution. We clearly see that the H I gas and the star formation correlate with morphology and environment at z {approx} 0.2. In particular, the fraction of H I detections is significantly affected by the environment. The effect starts to kick in in low-mass groups that pre-process the galaxies before they enter the cluster. Our results suggest that by the time the group galaxies fall into the cluster, they are already devoid of H I.

  5. THE EGNoG SURVEY: MOLECULAR GAS IN INTERMEDIATE-REDSHIFT STAR-FORMING GALAXIES

    SciTech Connect

    Bauermeister, A.; Blitz, L.; Wright, M.; Bolatto, A.; Teuben, P.; Bureau, M.; Leroy, A.; Ostriker, E.; Wong, T.

    2013-05-10

    We present the Evolution of molecular Gas in Normal Galaxies (EGNoG) survey, an observational study of molecular gas in 31 star-forming galaxies from z = 0.05 to z = 0.5, with stellar masses of (4-30) Multiplication-Sign 10{sup 10} M{sub Sun} and star formation rates of 4-100 M{sub Sun} yr{sup -1}. This survey probes a relatively un-observed redshift range in which the molecular gas content of galaxies is expected to have evolved significantly. To trace the molecular gas in the EGNoG galaxies, we observe the CO(J = 1 {yields} 0) and CO(J = 3 {yields} 2) rotational lines using the Combined Array for Research in Millimeter-wave Astronomy (CARMA). We detect 24 of 31 galaxies and present resolved maps of 10 galaxies in the lower redshift portion of the survey. We use a bimodal prescription for the CO to molecular gas conversion factor, based on specific star formation rate, and compare the EGNoG galaxies to a large sample of galaxies assembled from the literature. We find an average molecular gas depletion time of 0.76 {+-} 0.54 Gyr for normal galaxies and 0.06 {+-} 0.04 Gyr for starburst galaxies. We calculate an average molecular gas fraction of 7%-20% at the intermediate redshifts probed by the EGNoG survey. By expressing the molecular gas fraction in terms of the specific star formation rate and molecular gas depletion time (using typical values), we also calculate the expected evolution of the molecular gas fraction with redshift. The predicted behavior agrees well with the significant evolution observed from z {approx} 2.5 to today.

  6. Moving-mesh Simulations of Star-forming Cores in Magneto-gravo-turbulence

    NASA Astrophysics Data System (ADS)

    Mocz, Philip; Burkhart, Blakesley; Hernquist, Lars; McKee, Christopher F.; Springel, Volker

    2017-03-01

    Star formation in our Galaxy occurs in molecular clouds that are self-gravitating, highly turbulent, and magnetized. We study the conditions under which cloud cores inherit large-scale magnetic field morphologies and how the field is governed by cloud turbulence. We present four moving-mesh simulations of supersonic, turbulent, isothermal, self-gravitating gas with a range of magnetic mean-field strengths characterized by the Alfvénic Mach number {{ M }}{{A},0}, resolving prestellar core formation from parsec to a few astronomical unit scales. In our simulations with the turbulent kinetic energy density dominating over magnetic pressure ({{ M }}{{A},0}> 1), we find that the collapse is approximately isotropic with B ∝ ρ 2/3, core properties are similar regardless of initial mean-field strength, and the field direction on 100 au scales is uncorrelated with the mean field. However, in the case of a dominant large-scale magnetic field ({{ M }}{{A},0}=0.35), the collapse is anisotropic with B ∝ ρ 1/2. This transition at {{ M }}{{A},0}∼ 1 is not expected to be sharp, but clearly signifies two different paths for magnetic field evolution in star formation. Based on observations of different star-forming regions, we conclude that star formation in the interstellar medium may occur in both regimes. Magnetic field correlation with the mean field extends to smaller scales as {{ M }}{{A},0} decreases, making future Atacama Large Millimeter Array observations useful for constraining {{ M }}{{A},0} of the interstellar medium.

  7. The Life Cycles of Stars: An Information & Activity Booklet Grades K-8, 1997-1998. Star-Child--A Learning Center for Young Astronomers.

    ERIC Educational Resources Information Center

    Truelove, Elizabeth; Dejoie, Joyce

    This booklet contains information and activities on the life cycle of stars. Materials can be adapted for kindergarten through grade 8 classrooms. Background information on massive stars and medium stars and activities with subjects such as star life, constellation shapes, nebula terminology, astronomical distances, and pulsars is included. The 12…

  8. What Turns Galaxies Off? the Different Morphologies of Star-Forming and Quiescent Galaxies Since z Approximates 2 from CANDELS

    NASA Technical Reports Server (NTRS)

    Bell, Eric F.; VanDerWel, Arjen; Papovich, Casey; Kocevski, Dale; Lotz, Jennifer; McIntosh, Daniel H.; Kartaltepe, Jeyhan; Faber, S. M.; Ferguson, Harry; Koekemoer, Anton; Grogin, Norman; Wuyts, Stijn; Cheung, Edmong; Conselice, Christopher J.; Dunlop, James S.; Giavalisco, Mauro; Herrington, Jessica; Koo, David; McGrath, Elizabeth J.; DeMello, Duilia; Rix, Hans-Walter; Robaina, Aday R.; Williams, Christina C.

    2011-01-01

    We use HST/WFC3 imaging from the CANDELS multicyc1e treasury survey, in conjunction with the Sloan Digital Sky Survey, to explore the evolution of galactic structure for galaxies with stellar masses > 3 x 10(exp 10) Solar Mass from Z= 2.2 to the present epoch, a time span of 10 Gyr. We explore the relationship between rest-frame optical color, stellar mass, star formation activity and the structural parameters of galaxies as determined from parametric fits to the surface brightness profiles of galaxies. We confirm the dramatic evolution from z= 2.2 to the present day in the number density of non-star-forming galaxies above 3 x 10(exp 10) Solar Mass reported by other authors. We find that the vast majority of these quiescent systems have concentrated light profiles, as parameterized by the Sersic index, and the population of concentrated galaxies grows similarly rapidly. We examine the joint distribution of star formation activity, Sersic index, stellar mass, mass divided by radius (a proxy for velocity dispersion), and stellar surface density. Quiescence correlates poorly with stellar mass at all z < 2.2 (given the approx < 0.2 dex scatter between halo mass and stellar mass at z approximates 0 inferred by More et al, this argues against halo mass being the only factor determining quiescence). Quiescence correlates better with Sersic index, 'velocity dispersion' and stellar surface density, where Sersic index correlates the best (increasingly so at lower redshift). Yet, there is significant scatter between quiescence and galaxy structure: while the vast majority of quiescent galaxies have prominent bulges, many of them have significant disks, and a number of bulge-dominated galaxies have significant star formation. Noting the rarity of quiescent galaxies without prominent bulges, we argue that a prominent bulge (and, perhaps by association, a supermassive black hole) is a necessary but not sufficient condition for quenching star formation on galactic scales over the

  9. Optical studies of X-ray peculiar chromosphereically active stars

    NASA Astrophysics Data System (ADS)

    Pandey, J. C.

    2006-02-01

    A multiwavelength study of the late-type active stars, selected on the basis of their X-ray and radio luminosities is presented in this thesis. For FR Cnc, a photometric period 0.8267 +/- 0.0004 d has been established. The strong variation in the phase and amplitude of the FR Cnc light curves when folded on this period implies the presence of evolving and migrating spots or spot groups on its surface. A photometric period of 18.802 +/- 0.074 has been discovered in the star HD 81032. The shape and amplitude of the photometric light curves of FR Cnc, HD 81032, HD 95559 and LO Peg are observed to be changing from one epoch to another. The change in the amplitude is mainly due to a change in the minimum of the light curve, and this May be due to a change in the spot coverage. This indicates that photometric variability is due to the presence of dark spots on the surface of active star. Two groups of spots are identified for FR Cnc and LO Peg. The spots are found to migrate, and migration periods of 0.97 year and 0.93 year are determined from the 4 years of data. A migration period of 1.12 years for one group of spots in LO Peg is also determined. Formation of a new group of spots in the star HD 95559 was also seen during our observations. A single large group of spots is found to migrate, and a migration period of 7.32 +/- 0.04 years is determined for HD 81032. The stars FR Cnc, HD 81032, HD 160934 and LO Peg are seen to be redder at the light minimum and we interpret this is due to the relatively cooler temperature of the darker regions present in the visible hemisphere. We find the lack of color-brightness correlation in the star HD 95559 and this May be due to the presence of bright faculae and plages like regions accompanied by dark spots in any one component of the this binary system. The optical spectroscopy of FR Cnc and HD 81032 carried out during 2002-2003, reveals the presence of strong and variable Ca II H and K, Halpha and Hbeta emission features indicative

  10. The L723 Low-Mass Star Forming Protostellar System: Resolving a Double Core

    NASA Astrophysics Data System (ADS)

    Girart, J. M.; Rao, R.; Estalella, R.

    2009-03-01

    We present 1.35 mm Submillimeter Array (SMA) observations around the low-mass Class 0 source IRAS 19156+1906, at the center of the LDN 723 (L723) dark cloud. We detected emission from dust as well as emission from H2CO 30,3-20,2, DCN 3-2, and CN 2-1 lines, which arise from two cores, SMA 1 and SMA 2, separated by 2farcs9 (880 AU in projected distance). SMA 2 is associated with the previously detected source VLA 2. Weak SiO 5-4 emission is detected, possibly tracing a region of interaction between the dense envelope and the outflow. We modeled the dust and H2CO emission from the two cores. The results from the modeling show that the cores have similar physical properties (density and temperature distribution) but that SMA 2 has a larger p-H2CO abundance (by a factor of 3-10) than SMA 1. The p-H2CO abundances' findings are compatible with the value of the outer part of the circumstellar envelopes associated with Class 0 sources. SMA 2 is harboring an active multiple low-mass protostellar system and powering at least one molecular outflow. In contrast, there are no known signs of outflow activity toward SMA 1. This suggests that SMA 2 is more evolved than SMA 1. The kinematics of the two sources show marginal evidence of infall and rotation motions. The mass detected by the SMA observation, which trace scales of lsim1000 AU, is only a small fraction of the mass contained in the large-scale molecular envelope, which suggests that L723 is still in a very early phase of star formation. Despite the apparent quiescent nature of the L723, fragmentation is occurring at the center of the cloud at different scales. Thus, at sime1000 AU, the cloud has fragmented in two cores: SMA 1 and SMA 2. At the same time, at least one of these cores, SMA 2, has undergone additional fragmentation at scales of sime150 AU, forming a multiple stellar system.

  11. ACTIVITY ON THE M STAR OF QS Vir

    SciTech Connect

    Ribeiro, T.; Baptista, R.; Kafka, S.; Tappert, C.

    2010-03-15

    We report analysis of VRIJH photometry and phase-resolved optical spectroscopy of the eclipsing DA white dwarf (WD) plus dMe dwarf binary QS Vir. Modeling of the photometric data yields an inclination of i = 74.9 {+-} 0.6 and a mass ratio of q = M {sub 2}/M {sub 1} = 0.50 {+-} 0.05. Our Doppler maps indicate the presence of material in the Roche lobe of the WD, at a location near the M star, likely due to accretion from the stellar wind of the M star (as opposed to Roche-lobe overflow accretion). We also constructed images of the brightness distribution of the M star at different epochs which reveal the location of two stable active regions. Doppler tomography shows that the majority of the hydrogen and Ca II H and K emission originates on the active M dwarf, likely distributed in two preferred activity longitudes, similar to active regions on BY Dra and FK Comae systems.

  12. Everything you ever wanted to know about the ultraviolet spectra of star-forming galaxies but were afraid to ask

    NASA Technical Reports Server (NTRS)

    Kinney, A. L.; Bohlin, R.; Calzetti, D.; Panagia, N.; Wyse, R.

    1993-01-01

    We present ultraviolet spectra of 143 star-forming galaxies of different morphological types and activity classes including S0, Sa, Sb, Sc, Sd, irregular, starburst, blue compact, blue compact dwarf, Liner, and Seyfert 2 galaxies. These IUE spectra cover the wavelength range from 1200 to 3200 A and are taken in a large aperture (10 x 20 inch). The ultraviolet spectral energy distributions are shown for a subset of the galaxies, ordered by spectral index, and separated by type for normal galaxies, Liners, starburst galaxies, blue compact (BCG) and blue compact dwarf (BCDG) galaxies, and Seyfert 2 galaxies. The ultraviolet spectra of Liners are, for the most part, indistinguishable from the spectra of normal galaxies. Starburst galaxies have a large range of ultraviolet slope, from blue to red. The star-forming galaxies which are the bluest in the optical (BCG and BCDG), also have the 'bluest' average ultraviolet slope of beta = -1.75 +/- 0.63. Seyfert 2 galaxies are the only galaxies in the sample that consistently have detectable UV emission lines.

  13. Ultraviolet to Mid-Infrared Observations of Star-forming Galaxies at z~2: Stellar Masses and Stellar Populations

    NASA Astrophysics Data System (ADS)

    Shapley, Alice E.; Steidel, Charles C.; Erb, Dawn K.; Reddy, Naveen A.; Adelberger, Kurt L.; Pettini, Max; Barmby, Pauline; Huang, Jiasheng

    2005-06-01

    We present the broadband UV through mid-infrared spectral energy distributions (SEDs) of a sample of 72 spectroscopically confirmed star-forming galaxies at z=2.30+/-0.3. Located in a 72 arcmin2 field centered on the bright background QSO, HS 1700+643, these galaxies were preselected to lie at z~2 solely on the basis of their rest-frame UV colors and luminosities and should be representative of UV-selected samples at high redshift. In addition to deep ground-based photometry spanning from 0.35 to 2.15 μm, we make use of Spitzer IRAC data, which probe the rest-frame near-IR at z~2. The range of stellar populations present in the sample is investigated with simple, single-component stellar population synthesis models. The inability to constrain the form of the star formation history limits our ability to determine the parameters of extinction, age, and star formation rate without using external multiwavelength information. Emphasizing stellar mass estimates, which are much less affected by these uncertainties, we find =10.32+/-0.51 for the sample. The addition of Spitzer IRAC data as a long-wavelength baseline reduces stellar mass uncertainties by a factor of 1.5-2 relative to estimates based on optical-Ks photometry alone. However, the total stellar mass estimated for the sample is remarkably insensitive to the inclusion of IRAC data. We find correlations between stellar mass and rest-frame R band (observed Ks) and rest-frame 1.4 μm (observed 4.5 μm) luminosities, although with significant scatter. Even at rest-frame 1.4 μm, the mass-to-light ratio varies by a factor of 15 indicating that even the rest-frame near-IR, when taken alone, is a poor indicator of stellar mass in star-forming galaxies at z~2. Allowing for the possibility of episodic star formation, we find that typical galaxies in our sample could contain up to 3 times more stellar mass in an old underlying burst than what was inferred from single-component modeling. In contrast, mass

  14. Do Lyman-alpha photons escape from star-forming galaxies through dust-holes?

    NASA Astrophysics Data System (ADS)

    Wofford, Aida

    2012-10-01

    The hydrogen Lyman-alpha line is arguably the most important signature of galaxies undergoing their first violent burst of star formation. Although Lya photons are easily destroyed by dust, candidate Lya emitters have been detected at z>5. Thus the line can potentially be used to probe galaxy formation and evolution, as long as the astrophysical processes that regulate the escape of Lya photons from star-forming galaxies are well understood.We request 15 orbits for imaging in Lya and the FUV continuum with ACS/SBC, and in the H-beta/H-alpha ratio {proxy for dust extinction} with WFC3/UVIS, a sample of isolated non-AGN face-on spirals for which our team previously obtained and analyzed COS FUV spectroscopy of the central regions. Each target shows a different Lya profile, i.e., pure absorption, P-Cygni like, and multiple-emission. From the COS data, we already know the starburst phase and H I gas velocity. The images would greatly increase the impact of our spectroscopic study by enabling us to 1} conclusively determine if Lya photons escape through dust-holes, 2} assess the relative importance of dust extinction, ISM kinematics, and starburst phase in regulating the Lya escape, 3} clarify what we can really learn from the Lya equivalent width, and 4} provide constraints on the dust extinction to Lya 3D radiative transfer models. Ultimately this program will inform our understanding of the Lya escape at high redshift by providing spatially resolved views of the local conditions within star-forming galaxies that favor escape.

  15. A Study on the CO Isotopic Lines of the Star Forming Region AFGL 5157

    NASA Astrophysics Data System (ADS)

    Mao, Chun-hua; Yang, Ji; Lu, Deng-rong

    2014-01-01

    By the mapping observations simultaneously at the 12CO (J=1-0), 13CO (J=1-0), and C18O (J=1-0) lines on the area of 24’×24’ (12 pc×12 pc) of the star forming region AFGL 5157, we have obtained the distribution and averaged physical parameters for the respective 13CO and C18O cores of this molecu- lar cloud. At the edge of the molecular cloud, the isotopic abundance ratio is X [(13CO)/(C18O)] ≈ 10, close to the ratio of a giant molecular cloud. The viral masses of the 13CO and C18O cores are less than the masses of the molecu-lar cloud cores, so the molecular cloud cores are gravitationally unstable, and the C18O molecular cloud core is more easy to collapse. The column density distributions of the C18O molecular cloud core in the northeast and southwest directions are, respectively, 1.1 × 1023× z-0.43 and 4.6 × 1025× z-0.58, where z is the distance from the center of the molecular cloud core. The high velocity molecular outflow has been confirmed from our 12CO spectra, the mass loss rate of the outflow has been estimated, and the mass-velocity relation of the outflow is fitted by a power-law function of m ∝ v-1.8. The star formation rate of the 13CO molecular cloud core is as high as 23%, probably, under the influence of the reflection nebula NGC 1985, this region is forming medium and large mass stars or clusters.

  16. Chemical Evolution in High-mass Star-forming Regions: Results from the MALT90 Survey

    NASA Astrophysics Data System (ADS)

    Hoq, Sadia; Jackson, James M.; Foster, Jonathan B.; Sanhueza, Patricio; Guzmán, Andrés; Whitaker, J. Scott; Claysmith, Christopher; Rathborne, Jill M.; Vasyunina, Tatiana; Vasyunin, Anton

    2013-11-01

    The chemical changes of high-mass star-forming regions provide a potential method for classifying their evolutionary stages and, ultimately, ages. In this study, we search for correlations between molecular abundances and the evolutionary stages of dense molecular clumps associated with high-mass star formation. We use the molecular line maps from Year 1 of the Millimetre Astronomy Legacy Team 90 GHz (MALT90) Survey. The survey mapped several hundred individual star-forming clumps chosen from the ATLASGAL survey to span the complete range of evolution, from prestellar to protostellar to H II regions. The evolutionary stage of each clump is classified using the Spitzer GLIMPSE/MIPSGAL mid-IR surveys. Where possible, we determine the dust temperatures and H2 column densities for each clump from Herschel/Hi-GAL continuum data. From MALT90 data, we measure the integrated intensities of the N2H+, HCO+, HCN and HNC (1-0) lines, and derive the column densities and abundances of N2H+ and HCO+. The Herschel dust temperatures increase as a function of the IR-based Spitzer evolutionary classification scheme, with the youngest clumps being the coldest, which gives confidence that this classification method provides a reliable way to assign evolutionary stages to clumps. Both N2H+ and HCO+ abundances increase as a function of evolutionary stage, whereas the N2H+ (1-0) to HCO+ (1-0) integrated intensity ratios show no discernable trend. The HCN (1-0) to HNC(1-0) integrated intensity ratios show marginal evidence of an increase as the clumps evolve.

  17. Spitzer Observations of the Massive Star-forming Complex S254-S258: Structure and Evolution

    NASA Astrophysics Data System (ADS)

    Chavarría, Luis A.; Allen, Lori E.; Hora, Joseph L.; Brunt, Christopher M.; Fazio, Giovanni G.

    2008-07-01

    We present Spitzer IRAC, NOAO 2.1 m Flamingos, Keck NIRC, and FCRAO SEQUOIA observations of the massive star-forming complex S254-S258, covering an area of 25' × 20'. Using a combination of the IRAC and NIR data, we identify and classify the young stellar objects (YSOs) in the complex. We detect 510 sources with near- or mid-IR excess, and we classify 87 Class I and 165 Class II sources. The YSOs are found in clusters surrounded by isolated YSOs in a low-density distributed population. The ratio of clustered to total YSOs is 0.8. We identify six new clusters in the complex. One of them, G192.63-00, is located around the ionizing star of the H II region S255. We hypothesize that the ionizing star of S255 was formed in this cluster. We also detect a southern component of the cluster in H II region S256. The cluster G192.54-0.15, located inside H II region S254 has a VLSR of 17 km s-1 with respect to the main cloud, and we conclude that it is located in the background of the complex. The structure of the molecular cloud is examined using 12CO and 13CO , as well as a near-IR extinction map. The main body of the molecular cloud has VLSR between 5 and 9 km s-1. The arc-shaped structure of the molecular cloud following the border of the H II regions and the high column density in the border of the H II regions support the idea that the material has been swept up by the expansion of the H II regions.

  18. Massive star-forming host galaxies of quasars on Sloan digital sky survey stripe 82

    SciTech Connect

    Matsuoka, Yoshiki; Strauss, Michael A.; Price, Ted N. III; DiDonato, Matthew S.

    2014-01-10

    The stellar properties of about 800 galaxies hosting optically luminous, unobscured quasars at z < 0.6 are analyzed. Deep co-added Sloan Digital Sky Survey (SDSS) images of the quasars on Stripe 82 are decomposed into nucleus and host galaxy using point spread function and Sérsic models. The systematic errors in the measured galaxy absolute magnitudes and colors are estimated to be less than 0.5 mag and 0.1 mag, respectively, with simulated quasar images. The effect of quasar light scattered by the interstellar medium is also carefully addressed. The measured quasar-to-galaxy ratio in total flux decreases toward longer wavelengths, from ∼8 in the u band to ∼1 in the i and z bands. We find that the SDSS quasars are hosted exclusively by massive galaxies (stellar mass M {sub star} > 10{sup 10} M {sub ☉}), which is consistent with previous results for less luminous narrow-line (obscured) active galactic nuclei (AGNs). The quasar hosts are very blue and almost absent on the red sequence, showing stark contrast to the color-magnitude distribution of normal galaxies. The fact that more powerful AGNs reside in galaxies with higher star-formation efficiency may indicate that negative AGN feedback, if it exists, is not concurrent with the most luminous phase of AGNs. We also find positive correlation between the mass of supermassive black holes (SMBHs; M {sub BH}) and host stellar mass, but the M {sub BH}-M {sub star} relation is offset toward large M {sub BH} or small M {sub star} compared to the local relation. While this could indicate that SMBHs grow earlier than do their host galaxies, such an argument is not conclusive, as the effect may be dominated by observational biases.

  19. The plasma physics of cosmic rays in star-forming regions

    NASA Astrophysics Data System (ADS)

    Padovani, M.; Marcowith, A.; Hennebelle, P.; Ferrière, K.

    2017-01-01

    It is largely accepted that Galactic cosmic rays, which pervade the interstellar medium, originate by means of shock waves in supernova remnants. Cosmic rays activate the rich chemistry that is observed in a molecular cloud and they also regulate its collapse timescale, determining the efficiency of star and planet formation, but they cannot penetrate up to the densest part of a molecular cloud, where the formation of stars is expected, because of energy loss processes and magnetic field deflections. Recently, observations towards young protostellar systems showed a surprisingly high value of the ionisation rate, the main indicator of the presence of cosmic rays in molecular cloud. Synchrotron emission, the typical feature of relativistic electrons, has also been detected towards the bow shock of a T Tauri star. Nevertheless, the origin of these signatures peculiar to accelerated particles is still puzzling. Here we show that particle acceleration can be driven by shock waves occurring in protostars through the first-order Fermi acceleration mechanism. We expect that shocks in protostellar jets can be efficient accelerators of protons, which can be boosted up to mildly relativistic energies. A strong acceleration can also take place at the protostellar surface, where shocks produced by infalling material during the phase of collapse are powerful enough to accelerate protons. Our model shows that thermal particles can experience an acceleration during the first phases of a system similar to the proto-Sun, and can also be used to explain recent observations. The presence of a local source of cosmic rays may have an unexpected impact over the process of the formation of stars and planets, as well as on the pre-biotic molecule formation.

  20. Multi-wavelength View of Kiloparsec-scale Clumps in Star-forming Galaxies at z ~ 2

    NASA Astrophysics Data System (ADS)

    Guo, Yicheng; Giavalisco, Mauro; Ferguson, Henry C.; Cassata, Paolo; Koekemoer, Anton M.

    2012-10-01

    This paper studies the properties of kiloparsec-scale clumps in star-forming galaxies at z ~ 2 through multi-wavelength broadband photometry. A sample of 40 clumps is identified from Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) z-band images through auto-detection and visual inspection from 10 galaxies with 1.5 < z < 2.5 in the Hubble Ultra Deep Field, where deep and high-resolution HST/WFC3 and ACS images enable us to resolve structures of z ~ 2 galaxies down to the kiloparsec scale in the rest-frame UV and optical bands and to detect clumps toward the faint end. The physical properties of clumps are measured through fitting spatially resolved seven-band (BVizYJH) spectral energy distribution to models. On average, the clumps are blue and have similar median rest-frame UV-optical color as the diffuse components of their host galaxies, but the clumps have large scatter in their colors. Although the star formation rate (SFR)-stellar mass relation of galaxies is dominated by the diffuse components, clumps emerge as regions with enhanced specific star formation rates, contributing individually ~10% and together ~50% of the SFR of the host galaxies. However, the contributions of clumps to the rest-frame UV/optical luminosity and stellar mass are smaller, typically a few percent individually and ~20% together. On average, clumps are younger by 0.2 dex and denser by a factor of eight than diffuse components. Clump properties have obvious radial variations in the sense that central clumps are redder, older, more extincted, denser, and less active on forming stars than outskirt clumps. Our results are broadly consistent with a widely held view that clumps are formed through gravitational instability in gas-rich turbulent disks and would eventually migrate toward galactic centers and coalesce into bulges. Roughly 40% of the galaxies in our sample contain a massive clump that could be identified as a proto-bulge, which seems qualitatively consistent with

  1. MULTI-WAVELENGTH VIEW OF KILOPARSEC-SCALE CLUMPS IN STAR-FORMING GALAXIES AT z {approx} 2

    SciTech Connect

    Guo Yicheng; Giavalisco, Mauro; Cassata, Paolo; Ferguson, Henry C.; Koekemoer, Anton M.

    2012-10-01

    This paper studies the properties of kiloparsec-scale clumps in star-forming galaxies at z {approx} 2 through multi-wavelength broadband photometry. A sample of 40 clumps is identified from Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) z-band images through auto-detection and visual inspection from 10 galaxies with 1.5 < z < 2.5 in the Hubble Ultra Deep Field, where deep and high-resolution HST/WFC3 and ACS images enable us to resolve structures of z {approx} 2 galaxies down to the kiloparsec scale in the rest-frame UV and optical bands and to detect clumps toward the faint end. The physical properties of clumps are measured through fitting spatially resolved seven-band (BVizYJH) spectral energy distribution to models. On average, the clumps are blue and have similar median rest-frame UV-optical color as the diffuse components of their host galaxies, but the clumps have large scatter in their colors. Although the star formation rate (SFR)-stellar mass relation of galaxies is dominated by the diffuse components, clumps emerge as regions with enhanced specific star formation rates, contributing individually {approx}10% and together {approx}50% of the SFR of the host galaxies. However, the contributions of clumps to the rest-frame UV/optical luminosity and stellar mass are smaller, typically a few percent individually and {approx}20% together. On average, clumps are younger by 0.2 dex and denser by a factor of eight than diffuse components. Clump properties have obvious radial variations in the sense that central clumps are redder, older, more extincted, denser, and less active on forming stars than outskirt clumps. Our results are broadly consistent with a widely held view that clumps are formed through gravitational instability in gas-rich turbulent disks and would eventually migrate toward galactic centers and coalesce into bulges. Roughly 40% of the galaxies in our sample contain a massive clump that could be identified as a proto-bulge, which

  2. EVN maps of 5 cm line OH emission from star-forming regions

    NASA Astrophysics Data System (ADS)

    Desmurs, J.-F.; Baudry, A.; Graham, D. A.

    We have used three antennas of the EVN (Effelsberg, Medicina and Jodrell Bank) to observe in W3(OH) and in five other star-forming regions, simultaneously, and for the first time, the two main lines of the 2φ 3/2, J= 5/2 excited state of OH with right and left circularly polarized feeds. The data were correlated with the MkIII MPIfR correlator in Bonn and processed with the AIPS package at the Observatoire de Bordeaux. In W3(OH) we made cleaned maps of all individual channels for each line and polarization. These maps made with a 5×6.5 mas beam reveal complex kinematics and spatial structure with both extended emission and unresolved features. This fact and polarization properties demon-strate the masing nature of the emission. Maser features are identified by searching for emission over adjacent channels, and adjacent positions (within about one synthesized beam) in both polarizations after we had mapped and selected one channel as a phase reference. We have been able to identify OH Zeeman pairs and to estimate the magnetic field strength across W3(OH); the field varies from about 1 to 10 mG. At the time of this conference, three other star-forming regions (M17, ON1 and W51) show fringes while two other regions are still incompletely processed.

  3. Eight per cent leakage of Lyman continuum photons from a compact, star-forming dwarf galaxy.

    PubMed

    Izotov, Y I; Orlitová, I; Schaerer, D; Thuan, T X; Verhamme, A; Guseva, N G; Worseck, G

    2016-01-14

    One of the key questions in observational cosmology is the identification of the sources responsible for ionization of the Universe after the cosmic 'Dark Ages', when the baryonic matter was neutral. The currently identified distant galaxies are insufficient to fully reionize the Universe by redshift z ≈ 6 (refs 1-3), but low-mass, star-forming galaxies are thought to be responsible for the bulk of the ionizing radiation. As direct observations at high redshift are difficult for a variety of reasons, one solution is to identify local proxies of this galaxy population. Starburst galaxies at low redshifts, however, generally are opaque to Lyman continuum photons. Small escape fractions of about 1 to 3 per cent, insufficient to ionize much surrounding gas, have been detected only in three low-redshift galaxies. Here we report far-ultraviolet observations of the nearby low-mass star-forming galaxy J0925+1403. The galaxy is leaking ionizing radiation with an escape fraction of about 8 per cent. The total number of photons emitted during the starburst phase is sufficient to ionize intergalactic medium material that is about 40 times as massive as the stellar mass of the galaxy.

  4. Nitric oxide in star-forming regions - Further evidence for interstellar N-O bonds

    NASA Technical Reports Server (NTRS)

    Ziurys, L. M.; Mcgonagle, D.; Minh, Y.; Irvine, W. M.

    1991-01-01

    Nitric oxide has been newly detected toward several star-forming clouds, including Orion-KL, Sgr B2(N), W33A, W51M, and DR21(OH) via its J = 3/2-1/2 transitions near 150 GHz, using the FCRAO 14 m telescope. Both lambda-doubling components of NO were observed toward all sources. Column densities derived for nitric oxide in these clouds are 10 to the 15th-10 to the 16th/sq cm, corresponding to fractional abundances of 0.5-1.0 x 10 to the -8th, relative to H2. Toward Orion-KL, the NO line profile suggests that the species arises primarily from hot, dense gas. Nitric oxide may arise from warm material toward the other clouds as well. Nitric oxide in star-forming regions could be synthesized by high-temperature reactions, although the observed abundances do not disagree with values predicted from low-temperature, ion-molecule chemistry by more than one order of magnitude.

  5. TRIGONOMETRIC PARALLAXES OF MASSIVE STAR-FORMING REGIONS. IX. THE OUTER ARM IN THE FIRST QUADRANT

    SciTech Connect

    Sanna, A.; Menten, K. M.; Brunthaler, A.; Reid, M. J.; Dame, T. M.; Moscadelli, L.; Zheng, X. W.; Xu, Y.

    2012-01-20

    We report a trigonometric parallax measurement with the Very Long Baseline Array for the water maser in the distant high-mass star-forming region G75.30+1.32. This source has a heliocentric distance of 9.25{sup +0.45}{sub -0.40} kpc, which places it in the Outer arm in the first Galactic quadrant. It lies 200 pc above the Galactic plane and is associated with a substantial H I enhancement at the border of a large molecular cloud. At a Galactocentric radius of 10.7 kpc, G75.30+1.32 is in a region of the Galaxy where the disk is significantly warped toward the North Galactic Pole. While the star-forming region has an instantaneous Galactic orbit that is nearly circular, it displays a significant motion of 18 km s{sup -1} toward the Galactic plane. The present results, when combined with two previous maser studies in the Outer arm, yield a pitch angle of about 12 Degree-Sign for a large section of the arm extending from the first quadrant to the third.

  6. PASSIVE AND STAR-FORMING GALAXIES AT 1.4 {<=} z {<=} 2.5 IN THE AEGIS FIELD

    SciTech Connect

    Fang Guanwen; Kong Xu; Chen Yang; Lin Xuanbin E-mail: wen@mail.ustc.edu.cn

    2012-06-01

    Using a simple two-color selection based on g-, z-, and K-band photometry, we choose from 1609 star-forming galaxies (sgzKs) and 422 passively evolving galaxies (pgzKs) at z {approx} 2 from a K-band-selected sample (K{sub AB} < 22.0) in an area of {approx}0.44 deg{sup 2} of the All-wavelength Extended Groth Strip International Survey. The number of counts of pgzKs in our sample turn over at K{sub AB} {approx} 21.0, and both the number of faint and bright objects (including sgzKs and pgzKs) exceed the predictions of a recent semi-analytic model of galaxy formation; a more successful model is need to explain this diversity. We also find that the star formation rate (SFR) and specific SFR (sSFR) of sgzKs increases with redshift at all masses, implying that star-forming galaxies were much more active on average in the past. Moreover, the sSFR of massive galaxies is lower at all redshifts, suggesting that star formation contributes more to the mass growth of low-mass galaxies than to high-mass galaxies. From the Hubble Space Telescope Wide Field Camera 3 near-infrared imaging data we find that morphologies of z {approx} 2 galaxies not only have diffuse structures with lower G and higher M{sub 20} values, but also have single-object morphologies (higher G and lower M{sub 20}), implying that there are morphological variety and different formation process for these galaxies at z {approx} 2. Finally, we also study the fraction of active galactic nuclei (AGNs) in the gzKs, 82 of 828 gzKs with four IRAC bands can be classified as AGNs ({approx}10%). Most of these AGN candidates have L{sub 0.5-10keV} > 10{sup 41} erg s{sup -1}.

  7. The optical flares of active star II Pegasi in 2005

    NASA Astrophysics Data System (ADS)

    Gu, Shenghong; Kim, Kang Min; Lee, Byeong-Cheol

    2015-08-01

    We observed the active star II Peg using high-resolution spectrographs of 2.16m telescope at Xinglong station of NAOC and 1.8m telescope at BOAO of KASI from November to December, 2005. By means of spectral subtraction technique, the chromospheric activities of II Peg are analyzed at several activity indicators, including CaII IRT, Hα, NaI D1D2 and HeI D3 lines. The results demonstrate that the magnetic activity of II Peg is very strong, and its chromospheric activities show rotational modulations which imply there are active regions in its chromosphere. Two flare events were hunted during the observations, which were identified by HeI D3 line emission above the continuum. The first flare was happened in November 2005, the second one in December 2005, and they were located in different hemisphere of the star. This may indicate the evolution of active regions. Considering the photospheric spot activities, the possible origin of the detected flares is discussed.

  8. Directed Panspermia. 3. strategies and Motivation for Seeding Star-Forming Clouds

    NASA Astrophysics Data System (ADS)

    Mautner, Michael N.

    1997-11-01

    Microbial swarms aimed at star-forming regions of interstellar clouds can seed stellar associations of 10 - 100 young planetary systems. Swarms of millimeter size, milligram packets can be launched by 35 cm solar sails at 5E-4 c, to penetrate interstellar clouds. Selective capture in high-density planetary accretion zones of densities > 1E-17 kg m-3 is achieved by viscous drag. Strategies are evaluated to seed dense cloud cores, or individual protostellar condensations, accretion disks or young planets therein. Targeting the Ophiuchus cloud is described as a model system. The biological content, dispersed in 30 μm, 1E-10 kg capsules of 1E6 freeze-dried microorganisms each, may be captured by new planets or delivered to planets after incorporation first into carbonaceous asteroids and comets. These objects, as modeled by meteorite materials, contain biologically available organic and mineral nutrients that are shown to sustain microbial growth. The program may be driven by panbiotic ethics, predicated on: 1. The unique position of complex organic life amongst the structures of Nature; 2. Self-propagation as the basic propensity of the living pattern; 3. The biophysical unity humans with of the organic, DNA/protein family of life; and 4. Consequently, the primary human purpose to safeguard and propagate our organic life form. To promote this purpose, panspermia missions with diverse biological payloads will maximize survival at the targets and induce evolutionary pressures. In particular, eukaryotes and simple multicellular organisms in the payload will accelerate higher evolution. Based on the geometries and masses of star-forming regions, the 1E24 kg carbon resources of one solar system, applied during its 5E9 yr lifespan, can seed all newly forming planetary systems in the galaxy.

  9. Disentangling Dominance: Obscured AGN Activity versus Star Formation in BPT-Composites

    NASA Astrophysics Data System (ADS)

    Trouille, Laura

    2011-11-01

    Approximately 20% of SDSS emission-line galaxies (ELG) lie in the BPT-comp regime, between the Kauffmann et al. (2003) empirically determined SF-dominated regime and the Kewley et al. (2001) theoretically predicted AGN-dominated regime. BPT-AGN, on the other hand, make up only 11% of the ELG population. Whether to include the significant number of BPT-comp in samples of AGN or samples of star-forming galaxies is an open question and has important implications for galaxy evolution studies, metallicity studies, etc. Using a large pectroscopic sample of GOODS-N and LH galaxies with deep Chandra imaging, we perform an X-ray stacking analysis of BPT-comp. We find the stacked signal to be X-ray hard. This X-ray hardness can be indicative of obscured AGN activity or the presence of HMXBs associated with ongoing star formation. In order to distinguish between these scenarios, we perform an IR stacking analysis using Spitzer 24 micron data. The stacked BPT-comp lies well above the expected value for L_x/L_IR for pure star-forming galaxies; similarly for the X-ray detected BPT-comp. We also find that the BPT-comp lie in the AGN-dominated regime of our new TBT diagnostic, which uses [NeIII]/[OII] versus rest-frame g-z colour to identify AGN and star forming galaxies out to z=1.4. [NeIII], which has a higher ionisation potential than other commonly used forbidden emission lines, appears to foster a more reliable selection of AGN-dominated galaxies. These findings suggest that both the X-ray and optical signal in BPT-comp are dominated by obscured or low accretion rate AGN activity rather than star formation. This is in contrast to claims by previous optical emission-line studies that the signal in BPT-comp is dominated by star-formation activity. Therefore, we recommend that groups carefully consider the impact of excluding or including BPT-comp on the interpretation of their results. For example, for studies involving determining the bolometric contribution from AGN activity

  10. 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 clust