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TOPIC: Antennae NGC4038/4039


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RE: Antennae NGC4038/4039
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Title: ALMA observations of the dense and shocked gas in the nuclear region of NGC 4038 (Antennae galaxies)
Author: Junko Ueda, Yoshimasa Watanabe, Daisuke Iono, David J. Wilner, Giovanni G. Fazio, Satoshi Ohashi, Ryohei Kawabe, Toshiki Saito, Shinya Komugi

We present 1" (<100 pc) resolution maps of millimeter emission from five molecules-CN, HCN, HCO+, CH3OH, and HNCO-obtained towards NGC 4038, which is the northern galaxy of the mid-stage merger, Antennae galaxies, with the Atacama Large Millimeter/submillimeter Array. Three molecules (CN, CH3OH, and HNCO) were detected for the first time in the nuclear region of NGC 4038. High-resolution mapping reveals a systematic difference in distributions of different molecular species and continuum emission. Active star forming regions identified by the 3 mm and 850 um continuum emission are offset from the gas-rich region associated with the HCN (1-0) and CO (3-2) peaks. The CN (1-0)/HCN (1-0) line ratios are enhanced (CN/HCN = 0.8-1.2) in the star forming regions, suggesting that the regions are photon dominated. The large molecular gas mass (10^8 Msun) within a 0.6" (~60 pc) radius of the CO (3-2) peak and a high dense gas fraction (>20 %) suggested by the HCN (1-0)/CO (3-2) line ratio may signify a future burst of intense star formation there. The shocked gas traced in the CH3OH and HNCO emission indicates sub-kpc scale molecular shocks. We suggest that the molecular shocks may be driven by collisions between inflowing gas and the central massive molecular complex.

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NGC 4038
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Title: A Photodissociation Region study of NGC 4038á
Author: T. G. Bisbas, T. A. Bell, S. Viti, M. J. Barlow, J. Yates, M. Vastaá

We present a model of the photodissociation regions of NGC 4038, which is part of the Antennae galaxies. We have considered one-dimensional slabs of uniform density all having a maximumáAV=10mag, interacting with plane-parallel radiation. The density range in our simulations spans four orders of magnitude (100<n<10^6cm^-3) and the UV field strength spans more than three orders of magnitude (10<x<10^4.5ámultiples of theáDraineáfield), from which we generated a grid of about 1400 simulations. We compare our results with Herschel SPIRE-FTS, CSO and ISO-LWS observations of eight CO transition lines (J_=1-0átoá8-7) and the [CI] 609\mu m and [OI] 146\mu m fine structure lines. We find that the molecular and atomic emission lines trace different gas components of NGC 4038, thus single emission models are insufficient to reproduce the observed values. In general, low-JáCO transition lines correspond to either low density regions interacting with low UV field strengths, or high density regions interacting with high UV field strengths. HigheráJáCO transition lines are less dependent on the UV field strength and are fitted by gas with densityán~10^4.5 -á10^5.2cm^-3. We find that the observed fine structure line ratio of [CI] 609\mu m/[OI] 146\mu m is reproduced by clouds subject to weaker UV fields compared to the CO lines. We make estimates of theáXCOáfactor which relates the CO emission with the column density of molecular hydrogen, and find that it is less than the canonical Milky Way value.

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Antennae Galaxies
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Title: Constrained simulations of the Antennae Galaxies: Comparison with Herschel-PACS observations
Authors: Simon J. Karl (1,2,3), T. Lunttila (4), T. Naab (3), P.H. Johansson (4), U. Klaas (5), M. Juvela (4) ((1) IoA, (2) KICC, (3) MPA, (4) Helsinki, (5) MPIA)

We present a set of hydro-dynamical numerical simulations of the Antennae galaxies in order to understand the origin of the central overlap starburst. Our dynamical model provides a good match to the observed nuclear and overlap star formation, especially when using a range of rather inefficient stellar feedback efficiencies (0.01 < q_EoS < 0.1). In this case a simple conversion of local star formation to molecular hydrogen surface density motivated by observations accounts well for the observed distribution of CO. Using radiative transfer post-processing we model synthetic far-infrared spectral energy distributions (SEDs) and two-dimensional emission maps for direct comparison with Herschel-PACS observations. For a gas-to-dust ratio of 62:1 and the best matching range of stellar feedback efficiencies the synthetic far-infrared SEDs of the central star forming region peak at values of ~65 - 81 Jy at 99 - 116 Ám, similar to a three-component modified black body fit to infrared observations. Also the spatial distribution of the far-infrared emission at 70 Ám, 100 Ám, and 160 Ám compares well with the observations: >50% (> 35%) of the emission in each band is concentrated in the overlap region while only < 30% (< 15%) is distributed to the combined emission from the two galactic nuclei in the simulations (observations). As a proof of principle we show that parameter variations in the feedback model result in unambiguous changes both in the global and in the spatially resolved observable far-infrared properties of Antennae galaxy models. Our results strengthen the importance of direct, spatially resolved comparative studies of matched galaxy merger simulations as a valuable tool to constrain the fundamental star formation and feedback physics.

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RE: Antennae NGC4038/4039
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Title: ALMA CO and VLT/SINFONI H2 observations of the Antennae overlap region: mass and energy dissipation
Authors: Cinthya N. Herrera, Franšois Boulanger, Nicole P. H. Nesvadba, Edith Falgarone

We present an analysis of super-giant molecular complexes (SGMCs) in the overlap region of the Antennae galaxy merger, based on ALMA CO(3-2) interferometry and VLT/SINFONI imaging spectroscopy of H2 1-0 S(1) at angular resolutions of 0.9" and 0.7", respectively. All but one SGMC have multiple velocity components offset from each other by up to 150 km/s. H2 line emission is found in all SGMCs and the kinematics of H2 and CO are well matched. H2/CO line ratios vary by up to a factor of 10 among SGMCs and different velocity components of the same SGMCs. We also identify the CO counterpart of a bright, compact source of near-IR H2 line emission, which shows no Brgamma, and was first identified with SINFONI. This source has the highest H2/CO line ratio, and coincides with the steepest CO velocity gradient of the entire overlap region. With a size of 50 pc and a virial mass of a few 10^7 Solar masses it is perhaps a pre-cluster cloud that has not yet formed significant numbers of massive stars. We present observational evidence that the H2 emission is powered by shocks, and demonstrate how the H2 1-0 S(1) and the CO(3-2) lines can be used as tracers of energy dissipation and gas mass, respectively. The variations in the H2/CO line ratio may indicate that the SGMCs are dissipating their turbulent kinetic energy at different rates. The compact source could represent a short (~ 1 Myr) evolutionary stage in the early formation of super-star clusters.

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This new, composite image from the Chandra X-ray Observatory, the Hubble Space Telescope, and the Spitzer Space Telescope shows two colliding galaxies more than a 100 million years after they first impacted each other. The continuing collision of the Antennae galaxies, located about 62 million light years from Earth, has triggered the formation of millions of stars in clouds of dusts and gas in the galaxies. The X-ray image from Chandra shows huge clouds of hot, interstellar gas that have been injected with rich deposits of elements from supernova explosions. This enriched gas, which includes elements such as oxygen, iron, magnesium and silicon, will one day be incorporated into new generations of stars and planets.

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A Galactic Spectacle
Credit: NASA, ESA, SAO, CXC, JPL-Caltech, and STScI

A beautiful new image of two colliding galaxies has been released by NASA's Great Observatories. The Antennae galaxies, located about 62 million light-years from Earth, are shown in this composite image from the Chandra X-ray Observatory, the Hubble Space Telescope, and the Spitzer Space Telescope.
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Antennae Galaxies
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Title: The Antennae Galaxies (NGC 4038/4039) Revisited: ACS and NICMOS Observations of a Prototypical Merger
Authors: Bradley C. Whitmore (1), Rupali Chandar (2), Francois Schweizer (3), Barry Rothberg (1,4), Claus Leitherer (1), Marcia Rieke (5), George Rieke (5), W. P. Blair (6), S. Mengel (7), A. Alonso-Herrero (8) ((1) Space Telescope Science Institute, (2) University of Toledo, (3) Carnegie Observatories, (4) Naval Research Laboratory, (5) The University of Arizona, (6) The Johns Hopkins University, (7) European Southern Observatory, (8) Instituto de Estructura de la Materia, CSIC)

The ACS and NICMOS have been used to obtain new HST images of NGC 4038/4039 ("The Antennae"). These new observations allow us to better differentiate compact star clusters from individual stars, based on both size and colour. We use this ability to extend the cluster luminosity function by approximately two magnitudes over our previous WFPC2 results, and find that it continues as a single power law, dN/dL propto L^alpha with alpha=-2.13▒0.07, down to the observational limit of Mv~-7. Similarly, the mass function is a single power law dN/dM propto M^beta with beta=-2.10▒0.20 for clusters with ages t<3x10^8 yr, corresponding to lower mass limits that range from 10^4 to 10^5 Msun, depending on the age range of the subsample. Hence the power law indices for the luminosity and mass functions are essentially the same. The luminosity function for intermediate-age clusters (i.e., ~100-300 Myr old objects found in the loops, tails, and outer areas) shows no bend or turnover down to Mv~-6, consistent with relaxation-driven cluster disruption models which predict the turnover should not be observed until Mv~-4. An analysis of individual ~0.5-kpc sized areas over diverse environments shows good agreement between values of alpha and beta, similar to the results for the total population of clusters in the system. Several of the areas studied show evidence for age gradients, with somewhat older clusters appearing to have triggered the formation of younger clusters. The area around Knot B is a particularly interesting example, with an ~10-50 Myr old cluster of estimated mass ~10^6 Msun having apparently triggered the formation of several younger, more massive (up to 5x10^6 Msun) clusters along a dust lane.

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RE: Antennae NGC4038/4039
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Galaxies on collision courses with one another fling out long tendrils of debris as they come together, new images have revealed.
Tracing these debris trails will allow astronomers to more accurately model the trajectories of interacting galaxies before their violent encounters.
Team member Jin Koda of Stony Brook University in New York State compared the debris to skid marks at a traffic-accident site.

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Posts: 131433
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NGC 4038/39
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Title: Spitzer-IRS Study of the Antennae Galaxies NGC 4038/39
Authors: B.R. Brandl, L. Snijders, M. den Brok, D.G. Whelan, B. Groves, P. van der Werf, V. Charmandaris, J.D. Smith, L. Armus, R.C. Kennicutt, Jr., J.R. Houck

Using the Infrared Spectrograph on the Spitzer Space Telescope, we observed the Antennae galaxies obtaining spectral maps of the entire central region and high signal-to-noise 5-38 um spectra of the two galactic nuclei and six infrared-luminous regions. The total infrared luminosity of our six IR peaks plus the two nuclei is L_IR = 3.8x10^10 L_o, with their derived star formation rates ranging between 0.2 and 2 M_o/yr, with a total of 6.6 M_o/yr. The hardest and most luminous radiation originates from two compact clusters in the southern part of the overlap region, which also have the highest dust temperatures. PAH emission and other tracers of softer radiation are spatially extended throughout and beyond the overlap region, but regions with harder and intenser radiation field show a reduced PAH strength. The strong H_2 emission is rather confined around the nucleus of NGC 4039, where shocks appear to be the dominant excitation mechanism, and the southern part of the overlap region, where it traces the most recent starburst activity. The luminosity ratio between the warm molecular gas (traced by the H_2 lines) and the total far-IR emission is ~1.6x10^-4, similar to that found in many starburst and ULIRGs. The total mass of warm H_2 in the Antennae is 2.5x10^7 M_o, with a fraction of warm to total H_2 gas mass of about 0.35%. The average warm H_2 temperature is 302▒26 K and appears anti-correlated with the radiation field hardness, possibly due to an evolution of the PDR morphology. The previously reported tight correlation between the H_2 and PAH emission was not found but higher total PAH emission to continuum ratios were found in PDRs with warmer gas.

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RE: Antennae NGC4038/4039
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Title: A New Distance to The Antennae Galaxies (NGC 4038/39) Based on the Type Ia Supernova 2007sr
Authors: Francois Schweizer (1), Christopher R. Burns (1), Barry F. Madore (1), Violet A. Mager (1), M.M. Phillips (2), Wendy L. Freedman (1), Luis Boldt (2), Carlos Contreras (2), Gaston Folatelli (3), Sergio Gonzalez (2), Mario Hamuy (3), Wojtek Krzeminski (2), Nidia I. Morrell (2), S.E. Persson (1), Miguel R. Roth (2), Maximilian D. Stritzinger (2) ((1) Carnegie Observatories, (2) Las Campanas Observatory, (3) Universidad de Chile)

Traditionally, the distance to NGC 4038/39 has been derived from the systemic recession velocity, yielding about 20 Mpc for H_0 = 72 km/s/Mpc. Recently, this widely adopted distance has been challenged based on photometry of the presumed tip of the red giant branch (TRGB), which seems to yield a shorter distance of 13.3▒1.0 Mpc and, with it, nearly 1 mag lower luminosities and smaller radii for objects in this prototypical merger. Here we present a new distance estimate based on observations of the Type Ia supernova (SN) 2007sr in the southern tail, made at Las Campanas Observatory as part of the Carnegie Supernova Project. The resulting distance of D(SN Ia) = 22.3▒2.8 Mpc [(m-M)_0 = 31.74▒0.27 mag] is in good agreement with a refined distance estimate based on the recession velocity and the large-scale flow model developed by Tonry and collaborators, D(flow) = 22.5▒2.8 Mpc. We point out three serious problems that a short distance of 13.3 Mpc would entail, and trace the claimed short distance to a likely misidentification of the TRGB. Reanalysing Hubble Space Telescope (HST) data in the Archive with an improved method, we find a TRGB fainter by 0.9 mag and derive from it a preliminary new TRGB distance of D(TRGB) = 20.0▒1.6 Mpc. Finally, assessing our three distance estimates we recommend using a conservative, rounded value of D = 22▒3 Mpc as the best currently available distance to The Antennae.

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