| 1. |
- Emig, Kimberly L., et al.
(författare)
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Super Star Clusters in the Central Starburst of NGC 4945
- 2020
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 903:1
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Tidskriftsartikel (refereegranskat)abstract
- The nearby (3.8Mpc) galaxy NGC 4945 hosts a nuclear starburst and Seyfert type 2 active galactic nucleus (AGN). We use the Atacama Large Millimeter/submillimeter Array (ALMA) to image the 93 GHz (3.2 mm) free-free continuum and hydrogen recombination line emission (H40 alpha and H42 alpha) at 2.2 pc (0 12) resolution. Our observations reveal 27 bright, compact sources with FWHM sizes of 1.4-4.0 pc, which we identify as candidate super star clusters. Recombination line emission, tracing the ionizing photon rate of the candidate clusters, is detected in 15 sources, six of which have a significant synchrotron component to the 93 GHz continuum. Adopting an age of similar to 5Myr, the stellar masses implied by the ionizing photon luminosities are log(10) (M*/M-circle dot) approximate to 4.7-6.1. We fit a slope to the cluster mass distribution and find beta = -1.8 +/-.0.4. The gas masses associated with these clusters, derived from the dust continuum at 350 GHz, are typically an order of magnitude lower than the stellar mass. These candidate clusters appear to have already converted a large fraction of their dense natal material into stars and, given their small freefall times of similar to 0.05 Myr, are surviving an early volatile phase. We identify a pointlike source in 93 GHz continuum emission that is presumed to be the AGN. We do not detect recombination line emission from the AGN and place an upper limit on the ionizing photons that leak into the starburst region of Q(0).<.10(52) s(-1).
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| 2. |
- Ginsburg, Adam, et al.
(författare)
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astroquery: An Astronomical Web-querying Package in Python
- 2019
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 157:3
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Tidskriftsartikel (refereegranskat)abstract
- Astroquery is a collection of tools for requesting data from databases hosted on remote servers with interfaces exposed on the Internet, including those with web pages but without formal application program interfaces. These tools are built on the Python requests package, which is used to make HTTP requests, and astropy, which provides most of the data parsing functionality. astroquery modules generally attempt to replicate the web page interface provided by a given service as closely as possible, making the transition from browser-based to command-line interaction easy. astroquery has received significant contributions from throughout the astronomical community, including several from telescope archives. astroquery enables the creation of fully reproducible workflows from data acquisition through publication. This paper describes the philosophy, basic structure, and development model of the astroquery package. The complete documentation for astroquery can be found at http://astroquery.readthedocs.io/.
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| 3. |
- Henshaw, Jonathan D., et al.
(författare)
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Ubiquitous velocity fluctuations throughout the molecular interstellar medium
- 2020
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 4:11, s. 1064-1071
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Tidskriftsartikel (refereegranskat)abstract
- The density structure of the interstellar medium determines where stars form and release energy, momentum and heavy elements, driving galaxy evolution1–4. Density variations are seeded and amplified by gas motion, but the exact nature of this motion is unknown across spatial scales and galactic environments5. Although dense star-forming gas probably emerges from a combination of instabilities6,7, convergent flows8 and turbulence9, establishing the precise origin is challenging because it requires gas motion to be quantified over many orders of magnitude in spatial scale. Here we measure10–12 the motion of molecular gas in the Milky Way and in nearby galaxy NGC 4321, assembling observations that span a spatial dynamic range 10−1–103 pc. We detect ubiquitous velocity fluctuations across all spatial scales and galactic environments. Statistical analysis of these fluctuations indicates how star-forming gas is assembled. We discover oscillatory gas flows with wavelengths ranging from 0.3–400 pc. These flows are coupled to regularly spaced density enhancements that probably form via gravitational instabilities13,14. We also identify stochastic and scale-free velocity and density fluctuations, consistent with the structure generated in turbulent flows9. Our results demonstrate that the structure of the interstellar medium cannot be considered in isolation. Instead, its formation and evolution are controlled by nested, interdependent flows of matter covering many orders of magnitude in spatial scale.
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| 4. |
- Mangum, Jeffrey G., et al.
(författare)
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Fire in the Heart: A Characterization of the High Kinetic Temperatures and Heating Sources in the Nucleus of NGC253
- 2019
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 871:2
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Tidskriftsartikel (refereegranskat)abstract
- The nuclear starburst within the central similar to 15 '' (similar to 250 pc; 1 '' similar or equal to 17 pc) of NGC 253 has been extensively studied as a prototype for the starburst phase in galactic evolution. Atacama Large Millimeter/submillimeter Array (ALMA) imaging within receiver Bands 6 and 7 has been used to investigate the dense gas structure, kinetic temperature, and heating processes that drive the NGC 253 starburst. A total of 29 transitions from 15 molecular species/isotopologues have been identified and imaged at 1.'' 5-0.'' 4 resolution, allowing for the identification of five of the previously studied giant molecular clouds within the central molecular zone (CMZ) of NGC 253. Ten transitions from the formaldehyde (H2CO) molecule have been used to derive the kinetic temperature within the similar to 0.'' 5-5 '' dense gas structures imaged. On similar to 5 '' scales we measure T-K greater than or similar to 50 K, while on size scales less than or similar to 1 '' we measure T-K greater than or similar to 300 K. These kinetic temperature measurements further delineate the association between potential sources of dense gas heating. We have investigated potential heating sources by comparing our measurements to models that predict the physical conditions associated with dense molecular clouds that possess a variety of heating mechanisms. This comparison has been supplemented with tracers of recently formed massive stars (Br gamma) and shocks ([Fe II]). Derived molecular column densities point to a radially decreasing abundance of molecules with sensitivity to cosmic-ray and mechanical heating within the NGC 253 CMZ. These measurements are consistent with radio spectral index calculations that suggest a higher concentration of cosmic-ray-producing supernova remnants within the central 10 pc of NGC 253.
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| 5. |
- Svoboda, B. E., et al.
(författare)
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THE BOLOCAM GALACTIC PLANE SURVEY. XIV. PHYSICAL PROPERTIES of MASSIVE STARLESS and STAR-FORMING CLUMPS
- 2016
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 822:2
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Tidskriftsartikel (refereegranskat)abstract
- We sort 4683 molecular clouds between 10° < ℓ < 65° from the Bolocam Galactic Plane Survey based on observational diagnostics of star formation activity: compact 70 μm sources, mid-IR color-selected YSOs, H2O and CH3OH masers, and UCH ii regions. We also present a combined NH3-derived gas kinetic temperature and H2O maser catalog for 1788 clumps from our own GBT 100 m observations and from the literature. We identify a subsample of 2223 (47.5%) starless clump candidates (SCCs), the largest and most robust sample identified from a blind survey to date. Distributions of flux density, flux concentration, solid angle, kinetic temperature, column density, radius, and mass show strong (>1 dex) progressions when sorted by star formation indicator. The median SCC is marginally subvirial (α ∼ 0.7) with >75% of clumps with known distance being gravitationally bound (α < 2). These samples show a statistically significant increase in the median clump mass of ΔM ∼ 170-370 M o from the starless candidates to clumps associated with protostars. This trend could be due to (i) mass growth of the clumps at M o Myr-1 for an average freefall 0.8 Myr timescale, (ii) a systematic factor of two increase in dust opacity from starless to protostellar phases, and/or (iii) a variation in the ratio of starless to protostellar clump lifetime that scales as ∼M -0.4. By comparing to the observed number of CH3OH maser containing clumps, we estimate the phase lifetime of massive (M > 103 M o) starless clumps to be 0.37 ± 0.08 Myr (M/103 M o)-1; the majority (M < 450 M o) have phase lifetimes longer than their average freefall time. © 2016. The American Astronomical Society. All rights reserved.
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