More Like this

1. Physics and Chemistry of Radiation Driven Cloud Evolution. [C ii] Kinematics of IC 59, and IC 63

   https://doi.org/10.3847/1538-4357/acd2d5  

   Caputo, Miranda ; Soam, Archana ; Andersson, B-G ; Dennis, Remy ; Chambers, Ed ; Güsten, Rolf ; Knee, Lewis B. G. ; Stutzki, Jürgen ( June 2023 , The Astrophysical Journal)

   We used high-resolution [Cii] 158μm mapping of two nebulae IC 59 and IC 63 from SOFIA/upGREAT in conjunction with ancillary data of the gas, dust, and polarization to probe the kinematics, structure, and magnetic properties of their photodissociation regions (PDRs). The nebulae are part of the Sh 2-185 Hiiregion that is illuminated by the B0 IVe starγCas. The velocity structure of each PDR changes with distance fromγCas, which is consistent with driving by the radiation. Based on previous far-ultraviolet (FUV) flux measurements of, and the known distance to,γCas, along with the predictions of 3D distances to the clouds, we estimated the FUV radiation field strength (G₀) at the clouds. Assuming negligible extinction between the star and clouds, we find their 3D distances fromγCas. For IC 63, our results are consistent with earlier estimates of distance from Andersson et al., locating the cloud at ∼2 pc fromγCas at an angle of 58° to the plane of the sky behind the star. For IC 59, we derive a distance of 4.5 pc at an angle of 70° in front of the star. We do not detect any significant correlation between the orientation of the magnetic field and the velocity gradients of [Cii] gas, which indicates a moderate magnetic field strength. The kinetic energy in IC 63 is estimated to be an order of 10 higher than the magnetic energies. This suggests that kinetic pressure in this nebula is dominant.

    

   more » « less
2. Mapping NGC 7027 in New Light: CO + and HCO + Emission Reveal Its Photon- and X-Ray-dominated Regions

   https://doi.org/10.3847/1538-4357/aca405  

   Bublitz, Jesse ; Kastner, Joel H. ; Hily-Blant, Pierre ; Forveille, Thierry ; Santander-García, Miguel ; Alcolea, Javier ; Bujarrabal, Valentin ; Wilner, David J. ; Montez, Jr., Rodolfo ; Aleman, Isabel ( December 2022 , The Astrophysical Journal)

   The young and well-studied planetary nebula (PN) NGC 7027 harbors significant molecular gas that is irradiated by luminous, pointlike UV (central star) and diffuse (shocked nebular) X-ray emission. This nebula represents an excellent subject to investigate the molecular chemistry and physical conditions within photon- and X-ray-dominated regions (PDRs and XDRs). As yet, the exact formation routes of CO⁺and HCO⁺in PN environments remain uncertain. Here we present ∼2″ resolution maps of NGC 7027 in the irradiation tracers CO⁺and HCO⁺obtained with the IRAM NOEMA interferometer, along with SMA CO and HST 2.12μm H₂data for context. The CO⁺map constitutes the first interferometric map of this molecular ion in any PN. Comparison of CO⁺and HCO⁺maps reveals strikingly different emission morphologies, as well as a systematic spatial displacement between the two molecules; the regions of brightest HCO⁺, found along the central waist of the nebula, are radially offset by ∼1″ (∼900 au) outside the corresponding CO⁺emission peaks. The CO⁺emission furthermore precisely traces the inner boundaries of the nebula’s PDR (as delineated by near-IR H₂emission), suggesting that central star UV emission drives CO⁺formation. The displacement of HCO⁺radially outward with respect to CO⁺is indicative that dust-penetrating soft X-rays are responsible for enhancing the HCO⁺abundance in the surrounding molecular envelope, forming an XDR. These interferometric CO⁺and HCO⁺observations of NGC 7027 thus clearly establish the spatial distinction between the PDR and XDR formed (respectively) by intense UV and X-ray irradiation of molecular gas.

    

   more » « less
3. Young, Blue, and Isolated Stellar Systems in the Virgo Cluster. II. A New Class of Stellar System

   https://doi.org/10.3847/1538-4357/ac7c6c  

   Jones, Michael G. ; Sand, David J. ; Bellazzini, Michele ; Spekkens, Kristine ; Karunakaran, Ananthan ; Adams, Elizabeth A. K. ; Battaglia, Giuseppina ; Beccari, Giacomo ; Bennet, Paul ; Cannon, John M. ; et al ( August 2022 , The Astrophysical Journal)

   We discuss five blue stellar systems in the direction of the Virgo cluster, analogous to the enigmatic object SECCO 1 (AGC 226067). These objects were identified based on their optical and UV morphology and followed up with Hiobservations with the Very Large Array (and Green Bank Telescope), Multi Unit Spectroscopic Explorer (on the Very Large Telescope) optical spectroscopy, and Hubble Space Telescope imaging. These new data indicate that one system is a distant group of galaxies. The remaining four are extremely low mass (M_*∼ 10⁵M_⊙), are dominated by young blue stars, have highly irregular and clumpy morphologies, are only a few kiloparsecs across, yet host an abundance of metal-rich,$12+\log (\mathrm{O}/\mathrm{H})>8.2$, Hiiregions. These high metallicities indicate that these stellar systems formed from gas stripped from much more massive galaxies. Despite the young age of their stellar populations, only one system is detected in Hi, while the remaining three have minimal (if any) gas reservoirs. Furthermore, two systems are surprisingly isolated and have no plausible parent galaxy within ∼30′ (∼140 kpc). Although tidal stripping cannot be conclusively excluded as the formation mechanism of these objects, ram pressure stripping more naturally explains their properties, in particular their isolation, owing to the higher velocities, relative to the parent system, that can be achieved. Therefore, we posit that most of these systems formed from ram-pressure-stripped gas removed from new infalling cluster members and survived in the intracluster medium long enough to become separated from their parent galaxies by hundreds of kiloparsecs and that they thus represent a new type of stellar system.

    

   more » « less
4. The Circumgalactic Medium of Extreme Emission Line Galaxies at z∼2: Resolved Spectroscopy and Radiative Transfer Modeling of Spatially Extended Lyα Emission in the KBSS-KCWI Survey*

   https://doi.org/10.3847/1538-4357/acd849  

   Erb, Dawn K. ; Li 李智, Zhihui 慧. ; Steidel, Charles C. ; Chen 陈昱, Yuguang 光. ; Gronke, Max ; Strom, Allison L. ; Trainor, Ryan F. ; Rudie, Gwen C. ( August 2023 , The Astrophysical Journal)

   The resonantly scattered Lyαline illuminates the extended halos of neutral hydrogen in the circumgalactic medium of galaxies. We present integral field Keck Cosmic Web Imager observations of double-peaked, spatially extended Lyαemission in 12 relatively low-mass (M_⋆∼ 10⁹M_⊙)z∼ 2 galaxies characterized by extreme nebular emission lines. Using individual spaxels and small bins as well as radially binned profiles of larger regions, we find that for most objects in the sample the Lyαblue-to-red peak ratio increases, the peak separation decreases, and the fraction of flux emerging at line center increases with radius. We use new radiative transfer simulations to model each galaxy with a clumpy, multiphase outflow with radially varying outflow velocity, and self-consistently apply the same velocity model to the low-ionization interstellar absorption lines. These models reproduce the trends of peak ratio, peak separation, and trough depth with radius, and broadly reconcile outflow velocities inferred from Lyαand absorption lines. The galaxies in our sample are well-described by a model in which neutral, outflowing clumps are embedded in a hotter, more highly ionized inter-clump medium (ICM), whose residual neutral content produces absorption at the systemic redshift. The peak ratio, peak separation, and trough flux fraction are primarily governed by the line-of-sight component of the outflow velocity, the Hicolumn density, and the residual neutral density in the ICM respectively. The azimuthal asymmetries in the line profile further suggest nonradial gas motions at large radii and variations in the Hicolumn density in the outer halos.

    

   more » « less
5. Discovery of a Damped Lyα Absorber Originating in a Spectacular Interacting Dwarf Galaxy Pair at z = 0.026

   https://doi.org/10.3847/2041-8213/ac5250  

   Boettcher, Erin ; Gupta, Neeraj ; Chen, Hsiao-Wen ; Chen, Mandy C. ; Józsa, Gyula I. G. ; Rudie, Gwen C. ; Cantalupo, Sebastiano ; Johnson, Sean D. ; Balashev, S. A. ; Combes, Françoise ; et al ( February 2022 , The Astrophysical Journal Letters)

   We present the discovery of neutral gas detected in both damped Lyαabsorption (DLA) and Hi21 cm emission outside of the stellar body of a galaxy, the first such detection in the literature. A joint analysis between the Cosmic Ultraviolet Baryon Survey and the MeerKAT Absorption Line Survey reveals an Hibridge connecting two interacting dwarf galaxies (log (M_star/M_⊙) = 8.5 ± 0.2) that host az= 0.026 DLA with log[N(Hi)/cm⁻²] = 20.60 ± 0.05 toward the QSO J2339−5523 (z_QSO= 1.35). At impact parameters ofd= 6 and 33 kpc, the dwarf galaxies have no companions more luminous than ≈0.05L_*within at least Δv= ±300 km s⁻¹andd≈ 350 kpc. The Hi21 cm emission is spatially coincident with the DLA at the 2σ–3σlevel per spectral channel over several adjacent beams. However, Hi21 cm absorption is not detected against the radio-bright QSO; if the background UV and radio sources are spatially aligned, the gas is either warm or clumpy (with a spin temperature to covering factor ratioT_s/f_c> 1880 K). Observations with VLT-MUSE demonstrate that theα-element abundance of the ionized interstellar medium (ISM) is consistent with the DLA (≈10% solar), suggesting that the neutral gas envelope is perturbed ISM gas. This study showcases the impact of dwarf–dwarf interactions on the physical and chemical state of neutral gas outside of star-forming regions. In the SKA era, joint UV and Hi21 cm analyses will be critical for connecting the cosmic neutral gas content to galaxy environments.

    

   more » « less