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1. Unveiling kinematic structure in the starburst heart of NGC 253

   https://doi.org/10.1093/mnras/staa292  

   Cohen, Daniel P ; Turner, Jean L ; Consiglio, S Michelle ( March 2020 , Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We observed the Brackett α emission line (4.05 μm) within the nuclear starburst of NGC 253 to measure the kinematics of ionized gas, and distinguish motions driven by star formation feedback from gravitational motions induced by the central mass structure. Using NIRSPEC on Keck II, we obtained 30 spectra through a $0^{\prime \prime }_{.}5$ slit stepped across the central ∼5 arcsec × 25 arcsec (85 × 425 pc) region to produce a spectral cube. The Br α emission resolves into four nuclear sources: S1 at the infrared core (IRC), N1 at the radio core, and the fainter sources N2 and N3 in the northeast. The line profile is characterized by a primary component with Δvprimary ∼90–130 $\rm km\, s^{-1}$ (full width at half-maximum) on top of a broad blue 2wing with Δvbroad ∼300–350 $\rm km\, s^{-1}$, and an additional redshifted narrow component in the west. The velocity field generated from our cube reveals several distinct patterns. A mean NE–SW velocity gradient of +10 $\rm km\, s^{-1}$ arcsec−1 along the major axis traces the solid-body rotation curve of the nuclear disc. At the radio core, isovelocity contours become S-shaped, indicating the presence of secondary nuclear bar of total extent ∼5 arcsec (90 pc). The symmetry of the bar places the galactic centre, and potential supermassivemore »black hole, near the radio peak rather than the IRC. A third kinematic substructure is formed by blueshifted gas near the IRC. This feature likely traces a ∼100–250 $\rm km\, s^{-1}$ starburst-driven outflow, potentially linking the IRC to the galactic wind observed on kpc scales.« less
2. Close-up view of a luminous star-forming galaxy at z = 2.95

   https://doi.org/10.1051/0004-6361/202039743  

   Berta, S. ; Young, A. J. ; Cox, P. ; Neri, R. ; Jones, B. M. ; Baker, A. J. ; Omont, A. ; Dunne, L. ; Carnero Rosell, A. ; Marchetti, L. ; et al ( February 2021 , Astronomy & Astrophysics)

   Exploiting the sensitivity of the IRAM NOrthern Extended Millimeter Array (NOEMA) and its ability to process large instantaneous bandwidths, we have studied the morphology and other properties of the molecular gas and dust in the star forming galaxy, H-ATLAS J131611.5+281219 (HerBS-89a), at z = 2.95. High angular resolution (0 . ″3) images reveal a partial 1 . ″0 diameter Einstein ring in the dust continuum emission and the molecular emission lines of 12 CO(9−8) and H 2 O(2 02  − 1 11 ). Together with lower angular resolution (0 . ″6) images, we report the detection of a series of molecular lines including the three fundamental transitions of the molecular ion OH + , namely (1 1  − 0 1 ), (1 2  − 0 1 ), and (1 0  − 0 1 ), seen in absorption; the molecular ion CH + (1 − 0) seen in absorption, and tentatively in emission; two transitions of amidogen (NH 2 ), namely (2 02  − 1 11 ) and (2 20  − 2 11 ) seen in emission; and HCN(11 − 10) and/or NH(1 2  − 0 1 ) seen in absorption. The NOEMA data are complemented with Very Large Array data tracing the 12 CO(1 − 0) emission line, which provides a measurement ofmore »the total mass of molecular gas and an anchor for a CO excitation analysis. In addition, we present Hubble Space Telescope imaging that reveals the foreground lensing galaxy in the near-infrared (1.15  μ m). Together with photometric data from the Gran Telescopio Canarias, we derive a photometric redshift of z phot = 0.9 −0.5 +0.3 for the foreground lensing galaxy. Modeling the lensing of HerBS-89a, we reconstruct the dust continuum (magnified by a factor μ  ≃ 5.0) and molecular emission lines (magnified by μ  ∼ 4 − 5) in the source plane, which probe scales of ∼0 . ″1 (or 800 pc). The 12 CO(9 − 8) and H 2 O(2 02  − 1 11 ) emission lines have comparable spatial and kinematic distributions; the source-plane reconstructions do not clearly distinguish between a one-component and a two-component scenario, but the latter, which reveals two compact rotating components with sizes of ≈1 kpc that are likely merging, more naturally accounts for the broad line widths observed in HerBS-89a. In the core of HerBS-89a, very dense gas with n H 2  ∼ 10 7 − 9 cm −3 is revealed by the NH 2 emission lines and the possible HCN(11 − 10) absorption line. HerBS-89a is a powerful star forming galaxy with a molecular gas mass of M mol  = (2.1 ± 0.4) × 10 11   M ⊙ , an infrared luminosity of L IR  = (4.6 ± 0.4) × 10 12   L ⊙ , and a dust mass of M dust  = (2.6 ± 0.2) × 10 9   M ⊙ , yielding a dust-to-gas ratio δ GDR  ≈ 80. We derive a star formation rate SFR = 614 ± 59  M ⊙ yr −1 and a depletion timescale τ depl  = (3.4 ± 1.0) × 10 8 years. The OH + and CH + absorption lines, which trace low (∼100 cm −3 ) density molecular gas, all have their main velocity component red-shifted by Δ V  ∼ 100 km s −1 relative to the global CO reservoir. We argue that these absorption lines trace a rare example of gas inflow toward the center of a galaxy, indicating that HerBS-89a is accreting gas from its surroundings.« less
3. Discovery of a Highly Collimated Flow from the High-mass Protostar ISOSS J23053+5953 SMM2

   https://doi.org/10.3847/1538-4357/ac2366  

   Rodríguez, Tatiana M. ; Hofner, Peter ; Araya, Esteban D. ; Zhang, Qizhou ; Linz, Hendrik ; Kurtz, Stanley ; Gomez, Laura ; Carrasco-González, Carlos ; Rosero, Viviana ( November 2021 , The Astrophysical Journal)

   Abstract We present Very Large Array C- , X- , and Q -band continuum observations, as well as 1.3 mm continuum and CO(2-1) observations with the Submillimeter Array toward the high-mass protostellar candidate ISOSS J23053+5953 SMM2. Compact centimeter continuum emission was detected near the center of the SMM2 core with a spectral index of 0.24(± 0.15) between 6 and 3.6 cm, and a radio luminosity of 1.3(±0.4) mJy kpc 2 . The 1.3 mm thermal dust emission indicates a mass of the SMM2 core of 45.8 (±13.4) M ⊙ , and a density of 7.1 (±1.2)× 10 6 cm −3 . The CO(2-1) observations reveal a large, massive molecular outflow centered on the SMM2 core. This fast outflow (>50 km s −1 from the cloud systemic velocity) is highly collimated, with a broader, lower-velocity component. The large values for outflow mass (45.2 ± 12.6 M ⊙ ) and momentum rate (6 ± 2 × 10 −3 M ⊙ km s −1 yr −1 ) derived from the CO emission are consistent with those of flows driven by high-mass YSOs. The dynamical timescale of the flow is between 1.5 and 7.2 × 10 4 yr. We also found from the Cmore »18 O to thermal dust emission ratio that CO is depleted by a factor of about 20, possibly due to freeze-out of CO molecules on dust grains. Our data are consistent with previous findings that ISOSS J23053 + 5953 SMM2 is an emerging high-mass protostar in an early phase of evolution, with an ionized jet and a fast, highly collimated, and massive outflow.« less
4. An AMUSING look at the host of the periodic nuclear transient ASASSN-14ko reveals a second AGN

   https://doi.org/10.1093/mnras/stab2085  

   Tucker, M A ; Shappee, B J ; Hinkle, J T ; Neustadt, J M ; Eracleous, M ; Kochanek, C S ; Prieto, J L ; Payne, A V ; Galbany, L ; Anderson, J P ; et al ( August 2021 , Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We present Multi-Unit Spectroscopic Explorer (MUSE) integral-field spectroscopy of ESO 253−G003, which hosts a known active galactic nucleus (AGN) and the periodic nuclear transient ASASSN-14ko, observed as part of the All-weather MUse Supernova Integral-field of Nearby Galaxies survey. The MUSE observations reveal that the inner region hosts two AGN separated by $1.4\pm 0.1~\rm {kpc}$ (≈1${_{.}^{\prime\prime}}$7). The brighter nucleus has asymmetric broad permitted emission-line profiles and is associated with the archival AGN designation. The fainter nucleus does not have a broad emission-line component but exhibits other AGN characteristics, including $\hbox{$v_{\rm {FWHM}}$} \approx 700~\hbox{km~s$^{-1}$}$ forbidden line emission, $\rm{\log _{10}(\rm{[O\,\small {III}]}/\rm{H\beta})} \approx 1.1$, and high-excitation potential emission lines, such as [Fe vii] λ6086 and He ii λ4686. The host galaxy exhibits a disturbed morphology with large kpc-scale tidal features, potential outflows from both nuclei, and a likely superbubble. A circular relativistic disc model cannot reproduce the asymmetric broad emission-line profiles in the brighter nucleus, but two non-axisymmetric disc models provide good fits to the broad emission-line profiles: an elliptical disc model and a circular disc + spiral arm model. Implications for the periodic nuclear transient ASASSN-14ko are discussed.
5. Decade-long time-monitoring of candidate luminous blue variable stars in the two very metal-deficient star-forming galaxies DDO 68 and PHL 293B

   https://doi.org/10.1093/mnras/stac820  

   Guseva, N. G. ; Thuan, T. X. ; Izotov, Y. I. ( March 2022 , Monthly Notices of the Royal Astronomical Society)

   We have studied the spectral time variations of candidate luminous blue variable (cLBV) stars in two low-metallicity star-forming galaxies, DDO 68 and PHL 293B. The LBV in DDO 68, located in H ii region #3, shows an outburst, with an increase of more than 1000 times in H α luminosity during the period 2008–2010. The broad emission of the H i and He i lines display a P Cygni profile, with a relatively constant terminal velocity of ∼800 km s−1, reaching a maximum luminosity L(H α) of ∼2 × 1038 erg s−1, with a full width at half-maximum (FWHM) of ∼1000–1200 km s−1. On the other hand, since the discovery of a cLBV in 2001 in PHL 293B, the fluxes of the broad components and the broad-to-narrow flux ratios of the H i and He i emission lines in this galaxy have remained nearly constant over 16 yr, with small variations. The luminosity of the broad H α component varies between ∼2 × 1038 erg s−1 and ∼1039 erg s−1, with the FWHM varying in the range ∼500–1500 km s−1. Unusually persistent P Cygni features are clearly visible until the end of 2020 despite a decrease of the broad-to-narrow flux ratio in the most recent years. A terminal velocity of ∼800 km s−1 is measured from the P Cygni profile, similar tomore »the one in DDO 68, although the latter is 3.7 more metal-deficient than PHL 293B. The relative constancy of the broad H α luminosity in PHL 293B suggests that it is due to a long-lived stellar transient of type LBV/SN IIn.

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