Chemical Complexity in Local Diffuse and Translucent Clouds: Ubiquitous Linear C3H and CH3CN, a Detection of HC3N and an Upper Limit on the Abundance of CH2CN*
Sie können Bookmarks mittels Listen verwalten, loggen Sie sich dafür bitte in Ihr SLUB Benutzerkonto ein.
Medientyp:
E-Artikel
Titel:
Chemical Complexity in Local Diffuse and Translucent Clouds: Ubiquitous Linear C3H and CH3CN, a Detection of HC3N and an Upper Limit on the Abundance of CH2CN*
Beschreibung:
<jats:title>Abstract</jats:title>
<jats:p>We present Jansky Very Large Array observations of 20–37 GHz absorption lines from nearby Galactic diffuse molecular gas seen against four cosmologically distant compact radio continuum sources. The main new observational results are that <jats:italic>l</jats:italic>-C<jats:sub>3</jats:sub>H and CH<jats:sub>3</jats:sub>CN are ubiqitous in the local diffuse molecular interstellar medium at <jats:inline-formula>
<jats:tex-math>
<?CDATA ${\text{}}{A}_{{\rm{V}}}$?>
</jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaab208ieqn1.gif" xlink:type="simple" />
</jats:inline-formula> ≲ 1, while HC<jats:sub>3</jats:sub>N was seen only toward B0415 at <jats:inline-formula>
<jats:tex-math>
<?CDATA ${\text{}}{A}_{{\rm{V}}}$?>
</jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaab208ieqn2.gif" xlink:type="simple" />
</jats:inline-formula> > 4 mag. The linear/cyclic ratio is much larger in C<jats:sub>3</jats:sub>H than in C<jats:sub>3</jats:sub>H<jats:sub>2</jats:sub> and the ratio CH<jats:sub>3</jats:sub>CN/HCN is enhanced compared to TMC-1, although not as much as toward the Horsehead Nebula. More consequentially, this work completes a long-term program assessing the abundances of small hydrocarbons (CH, C<jats:sub>2</jats:sub>H, linear and cyclic C<jats:sub>3</jats:sub>H and C<jats:sub>3</jats:sub>
<jats:inline-formula>
<jats:tex-math>
<?CDATA ${{\rm{H}}}_{2}$?>
</jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaab208ieqn3.gif" xlink:type="simple" />
</jats:inline-formula>, and C<jats:sub>4</jats:sub>H and C<jats:sub>4</jats:sub>H<jats:sup>−</jats:sup>) and the CN-bearing species (CN, HCN, HNC, HC<jats:sub>3</jats:sub>N, HC<jats:sub>5</jats:sub>N, and CH<jats:sub>3</jats:sub>CN): their systematics in diffuse molecular gas are presented in detail here. We also observed but did not strongly constrain the abundances of a few oxygen-bearing species, most prominently HNCO. We set limits on the column density of CH<jats:sub>2</jats:sub>CN, such that the anion CH<jats:sub>2</jats:sub>CN<jats:sup>−</jats:sup> is only viable as a carrier of diffuse interstellar bands if the <jats:italic>N</jats:italic>(CH<jats:sub>2</jats:sub>CN)/<jats:italic>N</jats:italic>(CH<jats:sub>2</jats:sub>CN<jats:sup>−</jats:sup>) abundance ratio is much smaller in this species than in any others for which the anion has been observed. We argue that complex organic molecules (COMS) are not present in clouds meeting a reasonable definition of diffuse molecular gas, i.e., <jats:inline-formula>
<jats:tex-math>
<?CDATA ${\text{}}{A}_{{\rm{V}}}$?>
</jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaab208ieqn4.gif" xlink:type="simple" />
</jats:inline-formula> ≲ 1 mag.</jats:p>