Julie L. WardlowAsantha CoorayWillow OsageNathan BourneDavid ClementsHelmut DannerbauerLoretta DunneSimon DyeSteve EalesDuncan FarrahCristina FurlanettoIbar, EduardoEduardoIbarRob IvisonSteve MaddoxMichał M. MichałowskiDominik RiechersDimitra RigopoulouDouglas ScottMatthew W. L. SmithLingyu WangPaul van der WerfElisabetta ValianteIvan ValtchanovAprajita Verma2025-04-132025-04-132017-02-2710.3847/1538-4357/837/1/12https://cris-uv.scimago.es/handle/123456789/1889WOS:000398560000001<jats:title>Abstract</jats:title> <jats:p>Submillimeter galaxies (SMGs) at <jats:inline-formula> <jats:tex-math> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaa58e8ieqn1.gif" xlink:type="simple"/> </jats:inline-formula> are luminous in the far-infrared, and have star formation rates, SFR, of hundreds to thousands of solar masses per year. However, it is unclear whether they are true analogs of local ULIRGs or whether the mode of their star formation is more similar to that in local disk galaxies. We target these questions by using <jats:italic>Herschel</jats:italic>-PACS to examine the conditions in the interstellar medium (ISM) in far-infrared luminous SMGs at <jats:inline-formula> <jats:tex-math> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaa58e8ieqn2.gif" xlink:type="simple"/> </jats:inline-formula>–4. We present 70–160 <jats:italic>μ</jats:italic>m photometry and spectroscopy of the [O <jats:sc>iv</jats:sc>]26 <jats:italic>μ</jats:italic>m, [Fe <jats:sc>ii</jats:sc>]26 <jats:italic>μ</jats:italic>m, [S <jats:sc>iii</jats:sc>]33 <jats:italic>μ</jats:italic>m, [Si <jats:sc>ii</jats:sc>]34 <jats:italic>μ</jats:italic>m, [O <jats:sc>iii</jats:sc>]52 <jats:italic>μ</jats:italic>m, [N <jats:sc>iii</jats:sc>]57 <jats:italic>μ</jats:italic>m, and [O <jats:sc>i</jats:sc>]63 <jats:italic>μ</jats:italic>m fine-structure lines and the S(0) and S(1) hydrogen rotational lines in 13 lensed SMGs identified by their brightness in early <jats:italic>Herschel</jats:italic> data. Most of the 13 targets are not individually spectroscopically detected; we instead focus on stacking these spectra with observations of an additional 32 SMGs from the <jats:italic>Herschel</jats:italic> archive—representing a complete compilation of PACS spectroscopy of SMGs. We detect [O <jats:sc>i</jats:sc>]63 <jats:italic>μ</jats:italic>m, [Si <jats:sc>ii</jats:sc>]34 <jats:italic>μ</jats:italic>m, and [N <jats:sc>iii</jats:sc>]57 <jats:italic>μ</jats:italic>m at <jats:inline-formula> <jats:tex-math> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaa58e8ieqn3.gif" xlink:type="simple"/> </jats:inline-formula> in the stacked spectra, determining that the average strengths of these lines relative to the far-IR continuum are <jats:inline-formula> <jats:tex-math> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaa58e8ieqn4.gif" xlink:type="simple"/> </jats:inline-formula>, <jats:inline-formula> <jats:tex-math> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaa58e8ieqn5.gif" xlink:type="simple"/> </jats:inline-formula>, and <jats:inline-formula> <jats:tex-math> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaa58e8ieqn6.gif" xlink:type="simple"/> </jats:inline-formula>, respectively. Using the [O <jats:sc>iii</jats:sc>]52 <jats:italic>μ</jats:italic>m/[N <jats:sc>iii</jats:sc>]57 <jats:italic>μ</jats:italic>m emission line ratio, we show that SMGs have average gas-phase metallicities <jats:inline-formula> <jats:tex-math> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaa58e8ieqn7.gif" xlink:type="simple"/> </jats:inline-formula>. By using PDR modeling and combining the new spectral measurements with integrated far-infrared fluxes and existing [C <jats:sc>ii</jats:sc>]158 <jats:italic>μ</jats:italic>m data, we show that SMGs have average gas densities, <jats:italic>n</jats:italic>, of <jats:inline-formula> <jats:tex-math> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaa58e8ieqn8.gif" xlink:type="simple"/> </jats:inline-formula> and FUV field strengths, <jats:inline-formula> <jats:tex-math> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaa58e8ieqn9.gif" xlink:type="simple"/> </jats:inline-formula> (in Habing units: <jats:inline-formula> <jats:tex-math> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaa58e8ieqn10.gif" xlink:type="simple"/> </jats:inline-formula>), consistent with both local ULIRGs and lower luminosity star-forming galaxies.</jats:p>journal-article