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         title="Permalink to Galactic H2CO Densitometry I: Pilot survey of Ultracompact HII regions and methodology">Galactic H2CO Densitometry I: Pilot survey of Ultracompact HII regions and methodology</a></h2>
 
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    <abbr class="published" title="2012-11-21T04:59:00-07:00">
      2012/11/21
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      By <a class="url fn" href="https://keflavich.github.io/blog/author/adam-keflavichgmailcom.html">Adam (keflavich@gmail.com)</a>
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    <p><em>First Author</em> [ <a class="reference external" href="http://adsabs.harvard.edu/abs/2011ApJ...736..149G">ADS</a> ] [ <a class="reference external" href="http://eta.colorado.edu/papers/h2co_pilot_draft0607.pdf">Full Version</a> ]</p>
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<p>We examined 24 UCHII regions using the GBT to observe the 2-2 line of
ortho-Formaldehyde. We measured the local gas density and compared to
GMCs and other galaxies. We found densities in GMCs that are 1-2 orders
of magnitude higher than the mean density in GMCs, implying that extreme
overdensities are common even in &quot;quiescent&quot; (non-star-forming) GMCs.
This work was almost entirely my own, but was seeded by <a class="reference external" href="http://casa.colorado.edu/~jdarling/">Jeremy
Darling</a> Some highlight figures from the paper:</p>
<img alt="" src="http://1.bp.blogspot.com/-2FeB2dq7tXE/UGMxy17g_NI/AAAAAAAAHQQ/Ugswqn154-4/s400/G32.80%252B0.19_both.png" />
<p>A sample spectrum. On the top, black is Formaldehyde 1-1, red is
Formaldehyde 2-2. On the bottom, blue is 13CO, red is H77α, black is
H110α.</p>
<img alt="" src="http://3.bp.blogspot.com/-B9zbOPROYn4/UGMxzZSsz9I/AAAAAAAAHQc/tQ_NVJNiVTE/s400/DensityHistogram.png" />
<p>Histograms of GMC mean densities and the densities measured directly
from our survey. Note that even for &quot;serendipitious&quot; line of sight GMCs,
the densities are MUCH higher than typical GMC densities.</p>
<img alt="" src="http://4.bp.blogspot.com/-jfspjzvR6Tc/UGMxz8-7dEI/AAAAAAAAHQo/chH7rwVuyhs/s400/Derived_DensityVsColumn_ExgalCompare_all_colored.png" />
<p>Comparison of the measured column densities of formaldehyde and inferred
number densities of H<sub>2</sub>.</p>

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