More Like this

1. Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Galaxy and a Revised Black Hole Mass

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

   Liepold, Emily R. ; Ma, Chung-Pei ; Walsh, Jonelle L. ( March 2023 , The Astrophysical Journal Letters)

   The three-dimensional intrinsic shape of a galaxy and the mass of the central supermassive black hole provide key insight into the galaxy’s growth history over cosmic time. Standard assumptions of a spherical or axisymmetric shape can be simplistic and can bias the black hole mass inferred from the motions of stars within a galaxy. Here, we present spatially resolved stellar kinematics of M87 over a two-dimensional 250″ × 300″ contiguous field covering a radial range of 50 pc–12 kpc from integral-field spectroscopic observations at the Keck II Telescope. From about 5 kpc and outward, we detect a prominent 25 km s⁻¹rotational pattern, in which the kinematic axis (connecting the maximal receding and approaching velocities) is 40° misaligned with the photometric major axis of M87. The rotational amplitude and misalignment angle both decrease in the inner 5 kpc. Such misaligned and twisted velocity fields are a hallmark of triaxiality, indicating that M87 is not an axisymmetrically shaped galaxy. Triaxial Schwarzschild orbit modeling with more than 4000 observational constraints enabled us to determine simultaneously the shape and mass parameters. The models incorporate a radially declining profile for the stellar mass-to-light ratio suggested by stellar population studies. We find that M87 ismore »strongly triaxial, with ratios ofp= 0.845 for the middle-to-long principal axes andq= 0.722 for the short-to-long principal axes, and determine the black hole mass to be$({5.37}_{-0.25}^{+0.37}\pm 0.22)\times {10}^9{M}_{\odot }$, where the second error indicates the systematic uncertainty associated with the distance to M87.

   « less
2. The First Short GRB Millimeter Afterglow: The Wide-angled Jet of the Extremely Energetic SGRB 211106A

   https://doi.org/10.3847/2041-8213/ac8421  

   Laskar, Tanmoy ; Escorial, Alicia Rouco ; Schroeder, Genevieve ; Fong, Wen-fai ; Berger, Edo ; Veres, Péter ; Bhandari, Shivani ; Rastinejad, Jillian ; Kilpatrick, Charles D. ; Tohuvavohu, Aaron ; et al ( August 2022 , The Astrophysical Journal Letters)

   We present the discovery of the first millimeter afterglow of a short-durationγ-ray burst (SGRB) and the first confirmed afterglow of an SGRB localized by the GUANO system on Swift. Our Atacama Large Millimeter/Sub-millimeter Array (ALMA) detection of SGRB 211106A establishes an origin in a faint host galaxy detected in Hubble Space Telescope imaging at 0.7 ≲z≲ 1.4. From the lack of a detectable optical afterglow, coupled with the bright millimeter counterpart, we infer a high extinction,A_V≳ 2.6 mag along the line of sight, making this one of the most highly dust-extincted SGRBs known to date. The millimeter-band light curve captures the passage of the synchrotron peak from the afterglow forward shock and reveals a jet break at$t_{\mathrm{jet}}={29.2}_{-4.0}^{+4.5}$days. For a presumed redshift ofz= 1, we infer an opening angle,θ_jet= (15.°5 ± 1.°4), and beaming-corrected kinetic energy of$\log (E_{\mathrm{K}}/\mathrm{erg})=51.8\pm 0.3$, making this one of the widest and most energetic SGRB jets known to date. Combining all published millimeter-band upper limits in conjunction with the energetics for a large sample of SGRBs, we find that energetic outflows in high-density environments are more likely to have detectable millimeter counterparts. Concerted afterglow searches with ALMA shouldmore »yield detection fractions of 24%–40% on timescales of ≳2 days at rates of ≈0.8–1.6 per year, outpacing the historical discovery rate of SGRB centimeter-band afterglows.

   « less
3. The Physical Conditions of Emission-line Galaxies at Cosmic Dawn from JWST/NIRSpec Spectroscopy in the SMACS 0723 Early Release Observations

   https://doi.org/10.3847/1538-4357/acba8a  

   Trump, Jonathan R. ; Haro, Pablo Arrabal ; Simons, Raymond C. ; Backhaus, Bren E. ; Amorín, Ricardo O. ; Dickinson, Mark ; Fernández, Vital ; Papovich, Casey ; Nicholls, David C. ; Kewley, Lisa J. ; et al ( March 2023 , The Astrophysical Journal)

   We present rest-frame optical emission-line flux ratio measurements for fivez> 5 galaxies observed by the James Webb Space Telescope Near-Infared Spectrograph (NIRSpec) in the SMACS 0723 Early Release Observations. We add several quality-control and post-processing steps to the NIRSpec pipeline reduction products in order to ensure reliablerelativeflux calibration of emission lines that are closely separated in wavelength, despite the uncertainabsolutespectrophotometry of the current version of the reductions. Compared toz∼ 3 galaxies in the literature, thez> 5 galaxies have similar [Oiii]λ5008/Hβratios, similar [Oiii]λ4364/Hγratios, and higher (∼0.5 dex) [NeIII]λ3870/[OII]λ3728 ratios. We compare the observations to MAPPINGS V photoionization models and find that the measured [NeIII]λ3870/[OII]λ3728, [Oiii]λ4364/Hγ, and [Oiii]λ5008/Hβemission-line ratios are consistent with an interstellar medium (ISM) that has very high ionization ($\log (Q)\simeq 8-9$, units of cm s⁻¹), low metallicity (Z/Z_⊙≲ 0.2), and very high pressure ($\log (P/k)\simeq 8-9$, units of cm⁻³). The combination of [Oiii]λ4364/Hγand [Oiii]λ(4960 + 5008)/Hβline ratios indicate very high electron temperatures of$4.1<\log (T_e/\mathrm{K})<4.4$, further implying metallicities ofZ/Z_⊙≲ 0.2 with the application of low-redshift calibrations for “T_e-based” metallicities. These observations represent a tantalizing new view of the physical conditions of the ISM in galaxies atmore »cosmic dawn.

   « less
4. The Space Density of Intermediate-redshift, Extremely Compact, Massive Starburst Galaxies

   https://doi.org/10.3847/1538-3881/ac958f  

   Whalen, Kelly E. ; Hickox, Ryan C. ; Coil, Alison L. ; Diamond-Stanic, Aleksandar M. ; Geach, James E. ; Moustakas, John ; Rudnick, Gregory H. ; Rupke, David S. N. ; Sell, Paul H. ; Tremonti, Christy A. ; et al ( October 2022 , The Astronomical Journal)

   We present a measurement of the intrinsic space density of intermediate-redshift (z∼ 0.5), massive (M_*∼ 10¹¹M_⊙), compact (R_e∼ 100 pc) starburst (Σ_SFR∼ 1000M_⊙yr⁻¹kpc⁻¹) galaxies with tidal features indicative of them having undergone recent major mergers. A subset of them host kiloparsec-scale, > 1000 km s⁻¹outflows and have little indication of AGN activity, suggesting that extreme star formation can be a primary driver of large-scale feedback. The aim for this paper is to calculate their space density so we can place them in a better cosmological context. We do this by empirically modeling the stellar populations of massive, compact starburst galaxies. We determine the average timescale on which galaxies that have recently undergone an extreme nuclear starburst would be targeted and included in our spectroscopically selected sample. We find that massive, compact starburst galaxies targeted by our criteria would be selectable for$\sim {148}_{-24}^{+27}$Myr and have an intrinsic space density$n_{\mathrm{CS}}\sim ({1.1}_{-0.3}^{+0.5})\times {10}^{-6}{\mathrm{Mpc}}^{-3}$. This space density is broadly consistent with ourz∼ 0.5 compact starbursts being the most extremely compact and star-forming low-redshift analogs of the compact star-forming galaxies in the early universe, as well as them being the progenitors to a fraction of intermediate-redshift, post-starburst, andmore »compact quiescent galaxies.

   « less
5. Toward Astrometric Constraints on a Supermassive Black Hole Binary in the Early-type Galaxy NGC 4472

   https://doi.org/10.3847/1538-4357/ac680b  

   Wrobel, J. M. ; Lazio, T. J. W. ( May 2022 , The Astrophysical Journal)

   The merger of two galaxies, each hosting a supermassive black hole (SMBH) of mass 10⁶M_⊙or more, could yield a bound SMBH binary. For the early-type galaxy NGC 4472, we study how astrometry with a next-generation Very Large Array could be used to monitor the reflex motion of the primary SMBH of massM_pri, as it is tugged on by the secondary SMBH of mass$M_{\sec }$. Casting the orbit of the putative SMBH binary in terms of its periodP, semimajor axisa_bin, and mass ratio$q=M_{\sec }/M_{\mathrm{pri}}\le 1$, we find the following: (1) Orbits with fiducial periods ofP= 4 yr and 40 yr could be spatially resolved and monitored. (2) For a 95% accuracy of 2μas per monitoring epoch, subparsec values ofa_bincould be accessed over a range of mass ratios notionally encompassing major$\left(q>\frac{1}{4}\right)$and minor$\left(q<\frac{1}{4}\right)$galaxy mergers. (3) If no reflex motion is detected forM_priafter 1 (10) yr of monitoring, an SMBH binary with periodP= 4 (40) yr and mass ratioq> 0.01 (0.003) could be excluded. This would suggest no present-day evidence for a past major merger like that recently simulated, where scouring by aq∼ 1 SMBH binary formedmore »a stellar core with kinematic traits like those of NGC 4472. (4) Astrometric monitoring could independently check the upper limits onqfrom searches for continuous gravitational waves from NGC 4472.

   « less