ORCID Profile
0000-0003-1252-9916
Current Organisation
The University of Texas at Austin
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Publisher: American Astronomical Society
Date: 05-2021
Abstract: One of the most important and well-established empirical results in astronomy is the Kennicutt–Schmidt relation between the density of interstellar gas and the rate at which that gas forms stars. A tight correlation between these quantities has long been measured at galactic scales. More recently, using surveys of YSOs, a KS relationship has been found within molecular clouds relating the surface density of star formation to the surface density of gas however, the scaling of these laws varies significantly from cloud to cloud. In this Letter, we use a recently developed, high-accuracy catalog of young stellar objects from Spitzer combined with high-dynamic-range gas column density maps of 12 nearby ( .5 kpc) molecular clouds from Herschel to re-examine the KS relation within in idual molecular clouds. We find a tight, linear correlation between clouds’ star formation rate per unit area and their gas surface density normalized by the gas freefall time. The measured intracloud KS relation, which relates star formation rate to the volume density, extends over more than two orders of magnitude within each cloud and is nearly identical in each of the 12 clouds, implying a constant star formation efficiency per freefall time ϵ ff ≈ 0.026. The finding of a universal correlation within in idual molecular clouds, including clouds that contain no massive stars or massive stellar feedback, favors models in which star formation is regulated by local processes such as turbulence or stellar feedback such as protostellar outflows, and disfavors models in which star formation is regulated only by galaxy properties or supernova feedback on galactic scales.
Publisher: The Open Journal
Date: 28-12-2021
DOI: 10.21105/JOSS.03771
Publisher: American Astronomical Society
Date: 29-11-2010
Publisher: Oxford University Press (OUP)
Date: 14-02-2023
Abstract: Cosmic rays in star-forming galaxies are a dominant source of both diffuse γ-ray emission and ionization in gas too deeply shielded for photons to penetrate. Though the cosmic rays responsible for γ-rays and ionization are of different energies, they are produced by the same star formation-driven sources, and thus galaxies’ star formation rates, γ-ray luminosities, and ionization rates should all be linked. In this paper, we use up-to-date cross-section data to determine this relationship, finding that cosmic rays in a galaxy of star formation rate $\\dot{M}_*$ and gas depletion time tdep produce a maximum primary ionization rate ζ ≈ 1 × 10−16(tdep/Gyr)−1 s−1 and a maximum γ-ray luminosity $L_\\gamma \\approx 4\\times 10^{39} (\\dot{M}_*/\\mathrm{M}_\\odot \\mbox{ yr}^{-1})$ erg s−1 in the 0.1–100 GeV band. These budgets imply either that the ionization rates measured in Milky Way molecular clouds include a significant contribution from local sources that elevate them above the Galactic mean, or that CR-driven ionization in the Milky Way is enhanced by sources not linked directly to star formation. Our results also imply that ionization rates in starburst systems are only moderately enhanced compared to those in the Milky Way. Finally, we point out that measurements of γ-ray luminosities can be used to place constraints on galactic ionization budgets in starburst galaxies that are nearly free of systematic uncertainties on the details of cosmic ray acceleration.
Publisher: American Astronomical Society
Date: 08-2021
Publisher: American Astronomical Society
Date: 03-2009
Publisher: American Astronomical Society
Date: 12-2022
Abstract: Young stellar populations provide a record of past star formation, and by establishing their members’ dynamics and ages, it is possible to reconstruct the full history of star formation events. Gaia has greatly expanded the number of accessible stellar populations, with one of the most notable recently discovered associations being Cepheus Far North (CFN), a population containing hundreds of members spanning over 100 pc. With its proximity ( d ≲ 200 pc), apparent substructure, and relatively small population, CFN represents a manageable population to study in depth, with enough evidence of internal complexity to produce a compelling star formation story. Using Gaia astrometry and photometry combined with additional spectroscopic observations, we identify over 500 candidate CFN members spread across seven subgroups. Combining ages from isochrones, asteroseismology, dynamics, and lithium depletion, we produce well-constrained ages for all seven subgroups, revealing a largely continuous 10 Myr star formation history in the association. By tracing back the present-day populations to the time of their formation, we identify two spatially and dynamically distinct nodes in which stars form, one associated with β Cephei, which shows mostly co-spatial formation, and one associated with EE Draconis with a more dispersed star formation history. This detailed view of star formation demonstrates the complexity of the star formation process, even in the smallest of regions.
Publisher: American Astronomical Society
Date: 02-06-2016
Publisher: American Astronomical Society
Date: 05-10-2009
Publisher: American Astronomical Society
Date: 19-08-2011
Publisher: American Astronomical Society
Date: 04-08-2014
Publisher: American Astronomical Society
Date: 26-08-2009
No related grants have been discovered for Stella Offner.