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Abstract
We analyze TYPHOON long-slit-absorption line spectra of the starburst barred spiral galaxy NGC 1365 obtained with the Progressive Integral Step Method covering an area of 15 kpc2. Applying a population synthesis technique, we determine the spatial distribution of ages and metallicities of the young and old stellar populations together with star formation rates, reddening, extinction, and the ratio R V of extinction to reddening. We detect a clear indication of inside-out growth of the stellar disk beyond 3 kpc characterized by an outward increasing luminosity fraction of the young stellar population, a decreasing average age, and a history of mass growth, which was finished 2 Gyr later in the outermost disk. The metallicity of the young stellar population is clearly super solar but decreases toward larger galactocentric radii with a gradient of -0.02 dex kpc-1. On the other hand, the metal content of the old population does not show a gradient and stays constant at a level roughly 0.4 dex lower than that of the young population. In the center of NGC 1365, we find a confined region where the metallicity of the young population drops dramatically and becomes lower than that of the old population. We attribute this to the infall of metal-poor gas, and additionally, to interrupted chemical evolution where star formation is stopped by active galactic nuclei and supernova feedback and then after several gigayears resumes with gas ejected by stellar winds from earlier generations of stars. We provide a simple model calculation as support for the latter.
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Abstract
We present James Webb Space Telescope (JWST) Near Infrared Spectrograph (NIRSpec) integral field spectroscopy of the nearby luminous infrared galaxy NGC 7469. We take advantage of the high spatial/spectral resolution and wavelength coverage of JWST/NIRSpec to study the 3.3 mu m neutral polycyclic aromatic hydrocarbon (PAH) grain emission on similar to 200 pc scales. A clear change in the average grain properties between the star-forming ring and the central AGN is found. Regions in the vicinity of the AGN, with [Ne iii]/[Ne ii] > 0.25, tend to have larger grain sizes and lower aliphatic-to-aromatic (3.4/3.3) ratios, indicating that smaller grains are preferentially removed by photodestruction in the vicinity of the AGN. PAH emission at the nucleus is weak and shows a low 11.3/3.3 PAH ratio. We find an overall suppression of the total PAH emission relative to the ionized gas in the central 1 kpc region of the AGN in NGC 7469 compared to what has been observed with Spitzer on 3 kpc scales. However, the fractional 3.3 mu m-to-total PAH power is enhanced in the starburst ring, possibly due to a variety of physical effects on subkiloparsec scales, including recurrent fluorescence of small grains or multiple photon absorption by large grains. Finally, the IFU data show that while the 3.3 mu m PAH-derived star formation rate (SFR) in the ring is 27% higher than that inferred from the [Ne ii] and [Ne iii] emission lines, the integrated SFR derived from the 3.3 mu m feature would be underestimated by a factor of 2 due to the deficit of PAHs around the AGN, as might occur if a composite system like NGC 7469 were to be observed at high redshift.
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November 20, 2023

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The Nature Water cover image shows cyanobacterial scum from a harmful algal bloom in Milford Lake located in Kansas, United States. Cyanobacterial toxins such as microcystin produced by these blooms threaten water resources around the globe. Regions with the highest risk for elevated microcystin concentrations are expected to shift to higher latitudes under global warming. Image is courtesy of Ted D. Harris, Kansas Biological Survey and Center for Ecological Research, University of Kansas.
October 12, 2023

Climate is increasing risk of high toxin concentrations in Northern U.S. lakes

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October 09, 2023

Lowering cost of clean technologies helps combat climate change

Anna Michalak

Anna Michalak

Founding Director, Carnegie Climate and Resilience Hub

An illustration of hydrogen fuel synthesis from wind and solar power.
September 21, 2023

Predicting the sustainability of a future hydrogen economy

Aptasia photograph purchased from Shutterstock
September 19, 2023
Awards

Carnegie’s Ryan Hulett recognized by HHMI for early career excellence

Aerial view of red tide algal bloom along Florida’s gulf coast
August 08, 2023

Nitrogen runoff strategies complicated by climate change

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June 15, 2023

How will a warming world impact the Earth’s ability to offset our carbon emissions?

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