[C ii] and CO Emission along the Bar and Counter-arms of NGC 7479*

Abstract

We present new SOFIA [C II] and ALMA CO J=1→0 observations of the nearby asymmetric barred spiral galaxy NGC 7479. The data, which cover the whole bar of the galaxy and the counter-arms visible in the radio continuum, are analyzed in conjunction with a wealth of existing visible, infrared, radio, and X-ray data. As in most normal galaxies, the [C II] emission is generally consistent with emission from cooling gas excited by photoelectric heating in photodissociation regions. However, anomalously high [C II]/CO ratios are seen at the two ends of the counterarms. Both ends show shell-like structures, possibly bubbles, in Hα emission. In addition, the southern end has [C II]-to-infrared emission ratios inconsistent with normal star formation. Because there is little H I emission at this location, the [C II] emission probably originates in warm shocked molecular gas heated by the interaction of the radio jet forming the counter-arms with the interstellar medium in the galaxy. At two other locations, the high [C II]/CO ratios provide evidence for the existence of patches of CO-dark molecular gas. The [C II] and CO observations also reveal resolved velocity components along the bar. In particular, the CO emission can be separated into two components associated with gas along the leading edge of the bar and gas trailing the bar. The trailing gas component that amounts to approximately 40% of the gas around the bar region may be related to a minor merger.Unified Astronomy Thesaurus concepts: Barred spiral galaxies (136); Infrared galaxies (790); Molecular gas (1073)

Environmental Effects in Herschel Observations of the Ionized Carbon Content of Star-forming Dwarf Galaxies in the Virgo Cluster∗

“…In recent years, the consensus that [C II] has its origin in, and thus traces, star formation has been challenged by the discovery of [C II] formed from the interactions of AGN jets with the disk (Appleton et al 2018;Smirnova-Pinchukova et al 2019;Fadda et al 2021) and in galaxy-galaxy interactions (Appleton et al 2013(Appleton et al , 2017Peterson et al 2018). To these, as suggested by Pierini et al (1999), we can now add the interaction of galaxies with the cluster environment.…”

“…Recent studies with the FIFI-LS instrument onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) have shown that turbulence in the interstellar medium (ISM) associated with interactions with jets can lead to the formation of [C II] distinct from starformation processes. As the infrared continuum also traces star formation (albeit only obscured star formation, while the [C II] can, in principle, reflect both the obscured star formation and the unobscured star formation traced by ultraviolet emission), and [C II] associated with star formation is excited via gas heated by the photoelectric effect of UV photons on small dust grains and polycyclic aromatic hydrocarbons (e.g., Herrera-Camus et al 2015), [C II] from other sources is identifiable as an excess in the [C II]/infrared continuum ratio, as seen in the host galaxies of active galactic nuclei (AGN) where the jet is interacting with the disk (Appleton et al 2018;Smirnova-Pinchukova et al 2019;Fadda et al 2021). Similarly, Herschel observations of gas in the collisionally formed bridge between the Taffy Galaxies (UGC 12914/ 12915) found enhanced [C II]/infrared continuum ratios that were attributed to turbulently heated H 2 and high columndensity H I resulting from the collision of the two galaxies (Peterson et al 2018), and models of warm molecular gas shocks in Stephan's Quintet point to collisional heating from the warm H 2 being responsible for boosting the [C II] emission in that system (Appleton et al 2013(Appleton et al , 2017.…”

Environmental effects in Herschel observations of the ionized carbon content of star forming dwarf galaxies in the Virgo cluster

“…In recent years, the consensus that [C ii] has its origin in, and thus traces, star formation has been challenged by the discovery of [C ii] formed from the interactions of AGN jets with the disk (Appleton et al 2018;Smirnova-Pinchukova et al 2019;Fadda et al 2021) and in galaxygalaxy interactions (Appleton et al 2013(Appleton et al , 2017Peterson et al 2018). To these, as suggested by Pierini et al (1999), we can now add the interaction of galaxies with the cluster environment.…”

“…Recent studies with the FIFI-LS instrument onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) have shown that turbulence in the interstellar medium (ISM) associated with interactions with jets can lead to the formation of [C ii] distinct from star formation processes. As the infrared continuum also traces star formation (albeit only obscured star formation, while the [C ii] can, in principle, reflect both the obscured star formation and the unobscured star formation traced by ultra-violet emission), and [C ii] associated with star formation is excited via gas heated by the photoelectric effect of UV photons on small dust grains and polycyclic aromatic hydrocarbons (e.g., Herrera-Camus et al 2015), [C ii] from other sources is identifiable as an excess in the [C ii]/infrared continuum ratio, as seen in the host galaxies of active galactic nuclei (AGN) where the jet is interacting with the disk Smirnova-Pinchukova et al 2019;Fadda et al 2021). Similarly, Herschel observations of gas in the collisionally-formed bridge between the Taffy Galaxies (UGC 12914/12915) found enhanced [C ii]/infrared continuum ratios that were attributed to turbulently heated H 2 and high column-density H i resulting from the collision of the two galaxies (Peterson et al 2018), and models of warm molecular gas shocks in Stephan's Quintet point to collisional heating from the warm H 2 being responsible for boosting the [C ii] emission in that system (Appleton et al 2013(Appleton et al , 2017.…”