North American Science Center

Mountain Road, VA, United States

North American Science Center

Mountain Road, VA, United States
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Muzzin A.,Yale University | Muzzin A.,Leiden University | Wilson G.,University of California at Riverside | Yee H.K.C.,University of Toronto | And 15 more authors.
Astrophysical Journal | Year: 2012

We evaluate the effects of environment and stellar mass on galaxy properties at 0.85 9.3 the well-known correlations between environment and properties such as star-forming fraction (f SF), star formation rate (SFR), specific SFR (SSFR), D n(4000), and color are already in place at z ∼ 1. We separate the effects of environment and stellar mass on galaxies by comparing the properties of star-forming and quiescent galaxies at fixed environment and fixed stellar mass. The SSFR of star-forming galaxies at fixed environment is correlated with stellar mass; however, at fixed stellar mass it is independent of environment. The same trend exists for the D n(4000) measures of both the star-forming and quiescent galaxies and shows that their properties are determined primarily by their stellar mass, not by their environment. Instead, it appears that environment's primary role is to control the fraction of star-forming galaxies. Using the spectra we identify candidate poststarburst galaxies and find that those with 9.3 < logM */M ⊙ < 10.7 are 3.1 ± 1.1 times more common in high-density regions compared to low-density regions. The clear association of poststarbursts with high-density regions as well as the lack of a correlation between the SSFRs and D n(4000)s of star-forming galaxies with their environment strongly suggests that at z 1 the environmental-quenching timescale must be rapid. Lastly, we construct a simple quenching model which demonstrates that the lack of a correlation between the D n(4000) of quiescent galaxies and their environment results naturally if self quenching dominates over environmental quenching at z > 1, or if the evolution of the self-quenching rate mirrors the evolution of the environmental-quenching rate at z > 1, regardless of which dominates. © 2012. The American Astronomical Society. All rights reserved.

Wall W.F.,National Institute of Astrophysics, Optics and Electronics | Puerari I.,National Institute of Astrophysics, Optics and Electronics | Tilanus R.,Leiden University | Israel F.P.,Leiden University | And 8 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

We observed the spiral galaxies M51 and M83 at 20 arscec spatial resolution with thebolometer array Aztronomical Thermal Emission Camera (AzTEC) on the JCMT in the1.1mm continuum, recovering the extended emission out to galactocentric radii of more than12 kpc in both galaxies. The 1.1 mm-continuum fluxes are 5.6 ± 0.7 and 9.9 ± 1.4 Jy, withassociated gas masses estimated at 9.4 × 109Mo˙ and 7.2 × 109Mo˙ for M51 and M83,respectively. In the interarm regions of both galaxies, the N(H2)/I(CO) (or X-factor) ratiosexceed those in the arms by factors of ~1.5-2. In the inner discs of both galaxies, the X-factoris about 1 × 1020 cm-2 (K km s-1)-1. In the outer parts, the CO-dark molecular gas becomesmore important. While the spiral density wave in M51 appears to influence the interstellarmedium and stars in a similar way, the bar potential inM83 influences the interstellar mediumand the stars differently.We confirm the result of Foyle et al. that the arms merely heighten thestar formation rate (SFR) and the gas surface density in the same proportion. Our maps reveala threshold gas surface density for an SFR increase by two or more orders of magnitude. Inboth galaxy centres, the molecular gas depletion time is about 1 Gyr climbing to 10-20 Gyrat radii of 6-8 kpc. This is consistent with an inside-out depletion of the molecular gas in thediscs of spiral galaxies. © 2016 The Authors.

Lidman C.,Australian Astronomical Observatory | Suherli J.,Australian Astronomical Observatory | Suherli J.,Bandung Institute of Technology | Muzzin A.,Leiden University | And 17 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

Using new and published data, we construct a sample of 160 brightest cluster galaxies (BCGs) spanning the redshift interval 0.03 < z < 1.63. We use this sample, which covers 70 per cent of the history of the universe, to measure the growth in the stellar mass of BCGs after correcting for the correlation between the stellar mass of the BCG and the mass of the cluster in which it lives. We find that the stellar mass of BCGs increases by a factor of 1.8 ± 0.3 between z = 0.9 and z = 0.2. Compared to earlier works, our result is closer to the predictions of semi-analytic models. However, BCGs at z = 0.9, relative to BCGs at z = 0.2, are still a factor of 1.5 more massive than the predictions of these models. Star formation rates in BCGs at z ~ 1 are generally too low to result in significant amounts of mass. Instead, it is likely that most of the mass build up occurs through mainly dry mergers in which perhaps half of the mass is lost to the intra-cluster medium of the cluster. © 2012 The Authors Monthly Notices of the Royal Astronomical Society. © 2012 RAS.

Fiolet N.,CNRS Paris Institute of Astrophysics | Omont A.,CNRS Paris Institute of Astrophysics | Lagache G.,University Paris - Sud | Lagache G.,French National Center for Scientific Research | And 17 more authors.
Astronomy and Astrophysics | Year: 2010

Context. Spitzer's wide-field surveys and followup capabilities have allowed a new breakthrough in mid-IR spectroscopy up to redshifts ≥2, especially for 24 μm detected sources. Aims. We want to study the mid-infrared properties and the starburst and AGN contributions, of 24 μm sources at z ∼ 2, through analysis of mid-infrared spectra combined with millimeter, radio, and infrared photometry. Mid-infrared spectroscopy allows us to recover accurate redshifts. Methods. A complete sample of 16 Spitzer-selected sources (ULIRGs) believed to be starbursts at z ∼ 2 (5.8 μm-peakers) was selected in the (0.5 deg2) J1064+56 SWIRE Lockman Hole field (Lockman-North). These sources have S24 μm< 0.5 mJy, a stellar emission peak redshifted to 5.8 μm, and r′Vega < 23. The entire sample was observed with the low resolution units of the Spitzer/IRS infrared spectrograph. These sources have 1.2 mm observations with IRAM 30 m/MAMBO and very deep 20 cm observations from the VLA. Nine of our sources also benefit from 350 μm observation and detection from CSO/SHARC-II. All these data were jointly analyzed. Results. The entire sample shows good quality IRS spectra dominated by strong PAH features. The main PAH features at 6.2, 7.7, 8.6, and 11.3 μm have high S/N average luminosities of 2.90 ± 0.31, 10.38 ± 1.09, 3.62 ± 0.27, and 2.29 ± 0.26 × 10 10 L, respectively. Thanks to their PAH spectra, we derived accurate redshifts spanning from 1.750 to 2.284. The average of these redshifts is 2.017 ± 0.038. This result confirms that the selection criteria of 5.8 μm-peakers associated with a strong detection at 24 μm are reliable to select sources at z ∼ 2. We have analyzed the different correlations between PAH emission and infrared, millimeter, and radio emissions. Practically all our sources are strongly dominated by starburst emission, with only one source showing an important AGN contribution. We have also defined two subsamples based on the equivalent width at 7.7 μm to investigate AGN contributions. Conclusions. Our sample contains strong starbursts and represents a particularly 24 μm-bright class of SMGs. The very good correlation between PAH and far-IR luminosities is now confirmed in high-z starburst ULIRGs. These sources show a small AGN contribution to the mid-IR, around ∼20% or less in most cases. © 2010 ESO.

Koda J.,State University of New York at Stony Brook | Koda J.,California Institute of Technology | Sawada T.,Joint ALMA Office | Sawada T.,Japan National Astronomical Observatory | And 9 more authors.
Astrophysical Journal, Supplement Series | Year: 2011

We report the CO(J = 1-0) observations of the Whirlpool Galaxy M51 using both the Combined Array for Research in Millimeter Astronomy (CARMA) and the Nobeyama 45 m telescope (NRO45). We describe a procedure for the combination of interferometer and single-dish data. In particular, we discuss (1) the joint imaging and deconvolution of heterogeneous data, (2) the weighting scheme based on the root-mean-square (rms) noise in the maps, (3) the sensitivity and uv coverage requirements, and (4) the flux recovery of a combined map. We generate visibilities from the single-dish map and calculate the noise of each visibility based on the rms noise. Our weighting scheme, though it is applied to discrete visibilities in this paper, should be applicable to grids in uv space, and this scheme may advance in future software development. For a realistic amount of observing time, the sensitivities of the NRO45 and CARMA visibility data sets are best matched by using the single-dish baselines only up to 4-6 kλ (about 1/4-1/3 of the dish diameter). The synthesized beam size is determined to conserve the flux between the synthesized beam and convolution beam. The superior uv coverage provided by the combination of CARMA long baseline data with 15 antennas and NRO45 short spacing data results in the high image fidelity, which is evidenced by the excellent overlap between even the faint CO emission and dust lanes in an optical Hubble Space Telescope image and polycyclicaromatichydrocarbon emission in a Spitzer 8 μm image. The total molecular gas masses of NGC 5194 and 5195 (d = 8.2 Mpc) are 4.9 × 10 9 M ⊙ and 7.8 × 107 M ⊙, respectively, assuming the CO-to-H2 conversion factor of X CO = 1.8 × 1020 cm-2(K km s-1)-1. The presented images are an indication of the millimeter-wave images that will become standard in the next decade with CARMA and NRO45, and the Atacama Large Millimeter/Submillimeter Array. © 2011. The American Astronomical Society. All rights reserved.

Batejat F.,Onsala Space Observatory | Conway J.E.,Onsala Space Observatory | Rushton A.,Onsala Space Observatory | Rushton A.,European Southern Observatory | And 5 more authors.
Astronomy and Astrophysics | Year: 2012

Context. The two nuclei of the starburst galaxy Arp220 contain multiple compact radio sources previously identified as radio supernovae or supernova remnants. Aims. In order to search for an embedded radio AGN, or other possible exotic objects, we have carried out a programme of VLBI monitoring at 6 cm over three epochs each separated by four months. Methods. Combining the new data with existing data at 6 cm and 18 cm (spanning 4 and 12 years respectively) we are able to characterise source flux density variability on a range of timescales. Additionally we analyse the variability of sources in shape and position. Results. We detect rapid (<4 months) variability in three sources (W7, W26, and W29). These sources show possible superluminal motion (>4c) of jet-like features near rapidly varying almost stationary components. These enigmatic sources might be associated with an AGN or a highly beamed microquasar (i.e. microblazar). Other hypotheses include that the apparent variability is intrinsic and is produced by neutron star powered central components within a supernova remnant, by a sequence of several supernovae within super star clusters, or is extrinsic and is produced by Galactic interstellar scintillation of very compact non-varying objects. Conclusions. A microquasar/microblazar origin seems to be the best explanation for the nature of the variable sources in Arp220. © 2012 ESO.

Roueff E.,French National Center for Scientific Research | Gerin M.,French National Center for Scientific Research | Lis D.C.,California Institute of Technology | Wootten A.,North American Science Center | And 3 more authors.
Journal of Physical Chemistry A | Year: 2013

CH2D+, the singly deuterated counterpart of CH 3 +, offers an alternative way to mediate formation of deuterated species at temperatures of several tens of Kelvin, as compared to the release of deuterated species from grains. We report a longstanding observational search for this molecular ion, whose rotational spectroscopy is not yet completely secure. We summarize the main spectroscopic properties of this molecule and discuss the chemical network leading to the formation of CH2D+, with explicit account of the ortho/para forms of H2, H3 +, and CH3 +. Astrochemical models support the presence of this molecular ion in moderately warm environments at a marginal level. © 2013 American Chemical Society.

Pineda J.E.,ESO | Pineda J.E.,University of Manchester | Goodman A.A.,Harvard - Smithsonian Center for Astrophysics | Arce H.G.,Yale University | And 4 more authors.
Astrophysical Journal Letters | Year: 2011

We present ∼6.5 × 8′ Expanded Very Large Array (EVLA) mosaic observations of the NH3 (1,1) emission in the Barnard 5 region in Perseus, with an angular resolution of 6″. This map covers the coherent region, where the dense gas presents subsonic non-thermal motions (as seen from single dish observations with the Green Bank Telescope, GBT). The combined EVLA and GBT observations reveal, for the first time, a striking filamentary structure (20″ wide or 5000 AU at the distance of Perseus) in this low-mass star-forming region. The integrated intensity profile of this structure is consistent with models of an isothermal filament in hydrostatic equilibrium. The observed separation between the B5-IRS1 young stellar object (YSO), in the central region of the core, and the northern starless condensation matches the Jeans length of the dense gas. This suggests that the dense gas in the coherent region is fragmenting. The observed region displays a narrow velocity dispersion, where most of the gas shows evidence for subsonic turbulence and where little spatial variations are present. It is only close to the YSO where an increase in the velocity dispersion is found, but still displaying subsonic non-thermal motions. © 2011. The American Astronomical Society. All rights reserved.

Batejat F.,Onsala Space Observatory | Conway J.E.,Onsala Space Observatory | Hurley R.,Onsala Space Observatory | Parra R.,European Southern Observatory | And 3 more authors.
Astrophysical Journal | Year: 2011

We present 2cm and 3.6cm wavelength very long baseline interferometry images of the compact radio continuum sources in the nearby ultra-luminous infrared galaxy Arp220. Based on their radio spectra and variability properties, we confirm these sources to be a mixture of supernovae (SNe) and supernova remnants (SNRs). Of the 17 detected sources we resolve 7 at both wavelengths. The SNe generally only have upper size limits. In contrast all the SNRs are resolved with diameters ≥0.27 pc. This size limit is consistent with them having just entered their Sedov phase while embedded in an interstellar medium (ISM) of density 104 cm-3. These objects lie on the diameter-luminosity correlation for SNRs (and so also on the diameter-surface brightness relation) and extend these correlations to very small sources. The data are consistent with the relation LD ∝ -9/4. Revised equipartition arguments adjusted to a magnetic field to a relativistic particle energy density ratio of 1% combined with a reasonable synchrotron-emitting volume filling factor of 10% give estimated magnetic field strengths in the SNR shells of ∼15-50 mG. The SNR shell magnetic fields are unlikely to come from compression of ambient ISM fields and must instead be internally generated. We set an upper limit of 7 mG for the ISM magnetic field. The estimated energy in relativistic particles, 2%-20% of the explosion kinetic energy, is consistent with estimates from models that fit the IR-radio correlation in compact starburst galaxies. © 2011. The American Astronomical Society. All rights reserved.

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