1,989 research outputs found
ENVIRONMENTAL EDUCATION -- NORTH CAROLINA'S APPROACH
Environmental Economics and Policy,
Formaldehyde Silhouettes Against the Cosmic Microwave Background: A Mass-Limited, Distance-Independent, Extinction-Free Tracer of Star Formation Across the Epoch of Galaxy Evolution
We examine the absorption of cosmic microwave background (CMB) photons by
formaldehyde (H2CO) over cosmic time. The K-doublet rotational transitions of
H2CO become "refrigerated" - their excitation temperatures are driven below the
CMB temperature - via collisional pumping by molecular hydrogen (H2).
"Anti-inverted" H2CO line ratios thus provide an accurate measurement of the H2
density in molecular clouds. Using a radiative transfer model, we demonstrate
that H2CO centimeter wavelength line excitation and detectability are nearly
independent of redshift or gas kinetic temperature. Since the H2CO K-doublet
lines absorb CMB light, and since the CMB lies behind every galaxy and provides
an exceptionally uniform extended illumination source, H2CO is a
distance-independent, extinction-free molecular gas mass-limited tracer of
dense gas in galaxies. A Formaldehyde Deep Field could map the history of
cosmic star formation in a uniquely unbiased fashion and may be possible with
large bandwidth wide-field radio interferometers whereby the silhouettes of
star-forming galaxies would be detected across the epoch of galaxy evolution.
We also examine the possibility that H2CO lines may provide a standardizable
galaxy ruler for cosmology similar to the Sunyaev-Zel'dovich effect in galaxy
clusters but applicable to much higher redshifts and larger samples. Finally,
we explore how anti-inverted meterwave H2CO lines in galaxies during the peak
of cosmic star formation may contaminate HI 21 cm tomography of the Epoch of
Reionization.Comment: Accepted by ApJ Letters. 5 pages, 5 figure
Densitometry and Thermometry of Starburst Galaxies
With a goal toward deriving the physical conditions in external galaxies, we
present a survey of formaldehyde (H2CO) and ammonia (NH3) emission and
absorption in a sample of starburst galaxies using the Green Bank Telescope. By
extending well-established techniques used to derive the spatial density in
star formation regions in our own Galaxy, we show how the relative intensity of
the 1(10)-1(11) and 2(11)-2(12) K-doublet transitions of H2CO can provide an
accurate densitometer for the active star formation environments found in
starburst galaxies (c.f. Mangum et al. 2008). Similarly, we employ the
well-established technique of using the relative intensities of the (1,1),
(2,2), and (4,4) transitions of NH3 to derive the kinetic temperature in
starburst galaxies. Our measurements of the kinetic temperature constrained
spatial density in our starburst galaxy sample represent the first mean density
measurements made toward starburst galaxies. We note a disparity between
kinetic temperature measurements derived assuming direct coupling to dust and
those derived from our NH3 measurements which points to the absolute need for
direct gas kinetic temperature measurements using an appropriate molecular
probe. Finally, our spatial density measurements point to a rough constancy to
the spatial density (10^{4.5} to 10^{5.5} cm^{-3}) in our starburst galaxy
sample. This implies that the Schmidt-Kennicutt relation between L_{IR} and
M_{dense}: (1) Is a measure of the dense gas mass reservoir available to form
stars, and (2) Is not directly dependent upon a higher average density driving
the star formation process in the most luminous starburst galaxies.Comment: 4 pages, to appear in proceedings of The 5th Zermatt ISM Symposiu
Of Heart and Mind: Social Policy Essays in Honor of Sar A. Levitan
The essays in this volume, authored by close friends, associates and students of Sar Levitan, pay tribute to the enduring mark he left on the field of social policy. The book is loosely organized around the method of analysis taught and practiced by Levitan: identifying problems through the examination of facts, developing a thorough understanding of institutions, assessing institutional policies, and evaluating policy options.https://research.upjohn.org/up_press/1197/thumbnail.jp
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