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Schinnerer E.,MPI for Astronomy | Meidt S.E.,MPI for Astronomy | Colombo D.,MPI for Radioastronomy | Chandar R.,University of Toledo | And 9 more authors.
Astrophysical Journal | Year: 2017

The process that leads to the formation of the bright star-forming sites observed along prominent spiral arms remains elusive. We present results of a multi-wavelength study of a spiral arm segment in the nearby grand-design spiral galaxy M51 that belongs to a spiral density wave and exhibits nine gas spurs. The combined observations of the (ionized, atomic, molecular, dusty) interstellar medium with star formation tracers (H ii regions, young <10 Myr stellar clusters) suggest (1) no variation in giant molecular cloud (GMC) properties between arm and gas spurs, (2) gas spurs and extinction feathers arising from the same structure with a close spatial relation between gas spurs and ongoing/recent star formation (despite higher gas surface densities in the spiral arm), (3) no trend in star formation age either along the arm or along a spur, (4) evidence for strong star formation feedback in gas spurs, (5) tentative evidence for star formation triggered by stellar feedback for one spur, and (6) GMC associations being not special entities but the result of blending of gas arm/spur cross sections in lower resolution observations. We conclude that there is no evidence for a coherent star formation onset mechanism that can be solely associated with the presence of the spiral density wave. This suggests that other (more localized) mechanisms are important to delay star formation such that it occurs in spurs. The evidence of star formation proceeding over several million years within individual spurs implies that the mechanism that leads to star formation acts or is sustained over a longer timescale. © 2017. The American Astronomical Society. All rights reserved.


Schinnerer E.,MPI for Astronomy | Meidt S.E.,MPI for Astronomy | Pety J.,Institute Of Radioastronomie Millimetrique | Pety J.,Paris Observatory | And 10 more authors.
Astrophysical Journal | Year: 2013

The Plateau de Bure Interferometer Arcsecond Whirlpool Survey has mapped the molecular gas in the central ∼9 kpc of M51 in its 12CO(1-0) line emission at a cloud-scale resolution of ∼40 pc using both IRAM telescopes. We utilize this data set to quantitatively characterize the relation of molecular gas (or CO emission) to other tracers of the interstellar medium, star formation, and stellar populations of varying ages. Using two-dimensional maps, a polar cross-correlation technique and pixel-by-pixel diagrams, we find: (1) that (as expected) the distribution of the molecular gas can be linked to different components of the gravitational potential; (2) evidence for a physical link between CO line emission and radio continuum that seems not to be caused by massive stars, but rather depends on the gas density; (3) a close spatial relation between polycyclic aromatic hydrocarbon (PAH) and molecular gas emission, but no predictive power of PAH emission for the molecular gas mass; (4) that the I-H color map is an excellent predictor of the distribution (and to a lesser degree, the brightness) of CO emission; and (5) that the impact of massive (UV-intense) young star-forming regions on the bulk of the molecular gas in central ∼9 kpc cannot be significant due to a complex spatial relation between molecular gas and star-forming regions that ranges from cospatial to spatially offset to absent. The last point, in particular, highlights the importance of galactic environment - and thus the underlying gravitational potential - for the distribution of molecular gas and star formation. © 2013. The American Astronomical Society. All rights reserved..


Kurczynski P.,Rutgers University | Gawiser E.,Rutgers University | Huynh M.,University of Western Australia | Huynh M.,California Institute of Technology | And 11 more authors.
Astrophysical Journal | Year: 2012

We determine star formation rates (SFRs) in a sample of color-selected, star-forming (sBzK) galaxies (K AB < 21.8) in the Extended Chandra Deep Field-South. To identify and avoid active galactic nuclei, we use X-ray, IRAC color, and IR/radio flux ratio selection methods. Photometric redshift-binned, average flux densities are measured with stacking analyses in Spitzer-MIPS IR, BLAST and APEX/LABOCA submillimeter, VLA and GMRT radio, and Chandra X-ray data. We include averages of aperture fluxes in MUSYC UBVRIz′JHK images to determine UV-through-radio spectral energy distributions. We determine the total IR luminosities and compare SFR calibrations from FIR, 24 μm, UV, radio, and X-ray wavebands. We find consistency with our best estimator, SFRIR + UV, to within errors for the preferred radio SFR calibration. Our results imply that 24 μm only and X-ray SFR estimates should be applied to high-redshift galaxies with caution. Average IR luminosities are consistent with luminous infrared galaxies. We find SFRIR + UV for our stackedsBzKs at median redshifts 1.4, 1.8, and 2.2 to be 556 (random error), 74 8, and 154 17 Ṁyr-1, respectively, with additional systematic uncertainty of a factor of ∼2. © 2012. The American Astronomical Society. All rights reserved..


Schinnerer E.,MPI for Astronomy | Weiss A.,MPI for Radioastronomy | Aalto S.,Chalmers University of Technology | Scoville N.Z.,California Institute of Technology
Astrophysical Journal | Year: 2010

Two selected regions in the molecular gas spiral arms in M51 were mapped with the Owens Valley Radio Observatory (OVRO) mm-interferometer in the 12CO(2-1), 13CO(1-0), C18O(1-0), HCN(1-0), and HCO+(1-0) emission lines. The CO data have been combined with the 12CO(1-0) data from Aalto et al. covering the central 3.5 kpc to study the physical properties of the molecular gas. All CO data cubes were short spacing corrected using IRAM 30 m (12CO(1-0): NRO 45 m) single-dish data. A large velocity gradient analysis finds that the giant molecular clouds (GMCs) are similar to Galactic GMCs when studied at 180 pc (120 pc) resolution with an average kinetic temperature of Tkin= 20(16)K and H2density of n(H2) = 120(240) cm-3when assuming virialized clouds (a constant velocity gradient dv/dr). The associated conversion factor between H2mass and CO luminosity is close to the Galactic value for most regions analyzed. Our findings suggest that the GMC population in the spiral arms of M51 is similar to those of the Milky Way and therefore the strong star formation occurring in the spiral arms has no strong impact on the molecular gas in the spiral arms. Extinction inferred from the derived H2column density is very high (AV about 15-30 mag), about a factor of 5-10 higher than the average value derived toward Hii regions. Thus, a significant fraction of the ongoing star formation could be hidden inside the dust lanes of the spiral arms. A comparison of MIPS 24 μm and Hα data, however, suggests that this is not the case and most of the GMCs studied here are not (yet) forming stars. We also present low (4."5) resolution OVRO maps of the HCN(1-0) and HCO+(1-0) emission at the location of the brightest 12CO(1-0) peak. © 2010. The American Astronomical Society.


Taniguchi Y.,Ehime University | Kajisawa M.,Ehime University | Kobayashi M.A.R.,Ehime University | Nagao T.,Ehime University | And 21 more authors.
Astrophysical Journal Letters | Year: 2015

We report a discovery of six massive galaxies with both extremely large Lyα equivalent widths (EWs) and evolved stellar populations at z ∼ 3. These MAssive Extremely STrong Lyα emitting Objects (MAESTLOs) have been discovered in our large-volume systematic survey for strong Lyα emitters (LAEs) with 12 optical intermediate-band data taken with Subaru/Suprime-Cam in the COSMOS field. Based on the spectral energy distribution fitting analysis for these LAEs, it is found that these MAESTLOs have (1) large rest-frame EWs of EW0 (Lyα) ∼ 100-300, (2) M ∼ 1010.5-1011.1 Mo, and (3) relatively low specific star formation rates of SFR/M ∼ 0.03-1 Gyr-1. Three of the six MAESTLOs have extended Lyα emission with a radius of several kiloparsecs, although they show very compact morphology in the HST/ACS images, which correspond to the rest-frame UV continuum. Since the MAESTLOs do not show any evidence for active galactic nuclei, the observed extended Lyα emission is likely to be caused by a star formation process including the superwind activity. We suggest that this new class of LAEs, MAESTLOs, provides a missing link from star-forming to passively evolving galaxies at the peak era of the cosmic star formation history. © 2015. The American Astronomical Society. All rights reserved..


Gazak J.Z.,University of Hawaii at Manoa | Davies B.,Liverpool John Moores University | Bastian N.,Liverpool John Moores University | Kudritzki R.,University of Hawaii at Manoa | And 8 more authors.
Astrophysical Journal | Year: 2014

We demonstrate how the metallicities of young super star clusters (SSC) can be measured using novel spectroscopic techniques in the J-band. The near-infrared flux of SSCs older than ∼6 Myr is dominated by tens to hundreds of red supergiant stars. Our technique is designed to harness the integrated light of that population and produces accurate metallicities for new observations in galaxies above (M83) and below (NGC 6946) solar metallicity. In M83 we find [Z] = +0.28 ± 0.14 dex using a moderate resolution (R ∼ 3500) J-band spectrum and in NGC 6496 we report [Z] = -0.32 ± 0.20 dex from a low resolution spectrum of R ∼ 1800. Recently commissioned low resolution multiplexed spectrographs on the Very Large Telescope (KMOS) and Keck (MOSFIRE) will allow accurate measurements of SSC metallicities across the disks of star-forming galaxies up to distances of 70 Mpc with single night observation campaigns using the method presented in this paper. © 2014. The American Astronomical Society. All rights reserved..


Monnier J.D.,University of Michigan | Kraus S.,University of Exeter | Buscher D.,University of Cambridge | Berger J.-P.,ESO | And 12 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

Complex non-linear and dynamic processes lie at the heart of the planet formation process. Through numerical simulation and basic observational constraints, the basics of planet formation are now coming into focus. High resolution imaging at a range of wavelengths will give us a glimpse into the past of our own solar system and enable a robust theoretical framework for predicting planetary system architectures around a range of stars surrounded by disks with a diversity of initial conditions. Only long-baseline interferometry can provide the needed angular resolution and wavelength coverage to reach these goals and from here we launch our planning efforts. The aim of the "Planet Formation Imager" (PFI) project is to develop the roadmap for the construction of a new near-/mid-infrared interferometric facility that will be optimized to unmask all the major stages of planet formation, from initial dust coagulation, gap formation, evolution of transition disks, mass accretion onto planetary embryos, and eventual disk dispersal. PFI will be able to detect the emission of the cooling, newlyformed planets themselves over the first 100 Myrs, opening up both spectral investigations and also providing a vibrant look into the early dynamical histories of planetary architectures. Here we introduce the Planet Formation Imager (PFI) Project (www.planetformationimager.org) and give initial thoughts on possible facility architectures and technical advances that will be needed to meet the challenging top-level science requirements. © 2014 SPIE.


Liu G.,University of Massachusetts Amherst | Liu G.,Johns Hopkins University | Calzetti D.,University of Massachusetts Amherst | Kennicutt R.C.,University of Cambridge | And 5 more authors.
Astrophysical Journal | Year: 2013

The H II region luminosity function (LF) is an important tool for deriving the birthrates and mass distribution of OB associations and is an excellent tracer of the newly formed massive stars and associations. To date, extensive work (predominantly in Hα) has been done from the ground, which is hindered by dust extinction and the severe blending of adjacent (spatially or in projection) H II regions. Reliably measuring the properties of H II regions requires a linear resolution <40 pc, but analyses satisfying this requirement have been done only in a handful of galaxies, so far. As the first space-based work using a galaxy sample, we have selected 12 galaxies from our HST/NICMOS Paα survey and studied the LF and size distribution of H II regions both in individual galaxies and cumulatively, using a virtually extinction-free tracer of the ionizing photon rate. The high angular resolution and low sensitivity to diffuse emission of NICMOS also offer an advantage over ground-based imaging by enabling a higher degree of de-blending of the H II regions. We do not confirm the broken power-law LFs found in ground-based studies. Instead, we find that the LFs, both individual and co-added, follow a single power law dN(L)/dln LL -1, are consistent with the mass function of star clusters in nearby galaxies, and are in agreement with the results of the existing analyses with Hubble Space Telescope (HST) data. The individual and co-added size distributions of H II regions are both roughly consistent with dN(D)/dln DD -3, but the power-law scaling is probably contaminated by blended regions or complexes. © 2013. The American Astronomical Society. All rights reserved.

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