skip to main content


Title: Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Galaxy and a Revised Black Hole Mass
Abstract

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 is 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(5.370.25+0.37±0.22)×109M, where the second error indicates the systematic uncertainty associated with the distance to M87.

 
more » « less
Award ID(s):
1817100 2206307 2206219
NSF-PAR ID:
10401846
Author(s) / Creator(s):
; ;
Publisher / Repository:
DOI PREFIX: 10.3847
Date Published:
Journal Name:
The Astrophysical Journal Letters
Volume:
945
Issue:
2
ISSN:
2041-8205
Format(s):
Medium: X Size: Article No. L35
Size(s):
["Article No. L35"]
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    We measure the correlation between black hole massMBHand host stellar massM*for a sample of 38 broad-line quasars at 0.2 ≲z≲ 0.8 (median redshiftzmed= 0.5). The black hole masses are derived from a dedicated reverberation mapping program for distant quasars, and the stellar masses are derived from two-band optical+IR Hubble Space Telescope imaging. Most of these quasars are well centered within ≲1 kpc from the host galaxy centroid, with only a few cases in merging/disturbed systems showing larger spatial offsets. Our sample spans two orders of magnitude in stellar mass (∼109–1011M) and black hole mass (∼107–109M) and reveals a significant correlation between the two quantities. We find a best-fit intrinsic (i.e., selection effects corrected)MBHM*,hostrelation oflog(MBH/M)=7.010.33+0.23+1.740.64+0.64log(M*,host/1010M), with an intrinsic scatter of0.470.17+0.24dex. Decomposing our quasar hosts into bulges and disks, there is a similarMBHM*,bulgerelation with slightly larger scatter, likely caused by systematic uncertainties in the bulge–disk decomposition. TheMBHM*,hostrelation atzmed= 0.5 is similar to that in local quiescent galaxies, with negligible evolution over the redshift range probed by our sample. With direct black hole masses from reverberation mapping and the large dynamical range of the sample, selection biases do not appear to affect our conclusions significantly. Our results, along with other samples in the literature, suggest that the locally measured black hole mass–host stellar mass relation is already in place atz∼ 1.

     
    more » « less
  2. Abstract

    We present a stellar dynamical mass measurement of a newly detected supermassive black hole (SMBH) at the center of the fast-rotating, massive elliptical galaxy NGC 2693 as part of the MASSIVE survey. We combine high signal-to-noise ratio integral field spectroscopy (IFS) from the Gemini Multi-Object Spectrograph with wide-field data from the Mitchell Spectrograph at McDonald Observatory to extract and model stellar kinematics of NGC 2693 from the central ∼150 pc out to ∼2.5 effective radii. Observations from Hubble Space Telescope WFC3 are used to determine the stellar light distribution. We perform fully triaxial Schwarzschild orbit modeling using the latest TriOS code and a Bayesian search in 6D galaxy model parameter space to determine NGC 2693's SMBH mass (MBH), stellar mass-to-light ratio, dark matter content, and intrinsic shape. We findMBH=1.7±0.4×109Mand a triaxial intrinsic shape with axis ratiosp=b/a= 0.902 ± 0.009 andq=c/a=0.7210.010+0.011, triaxiality parameterT= 0.39 ± 0.04. In comparison, the best-fit orbit model in the axisymmetric limit and (cylindrical) Jeans anisotropic model of NGC 2693 preferMBH=2.4±0.6×109MandMBH=2.9±0.3×109M, respectively. Neither model can account for the non-axisymmetric stellar velocity features present in the IFS data.

     
    more » « less
  3. Abstract

    We measure the CO-to-H2conversion factor (αCO) in 37 galaxies at 2 kpc resolution, using the dust surface density inferred from far-infrared emission as a tracer of the gas surface density and assuming a constant dust-to-metal ratio. In total, we have ∼790 and ∼610 independent measurements ofαCOfor CO (2–1) and (1–0), respectively. The mean values forαCO (2–1)andαCO (1–0)are9.35.4+4.6and4.22.0+1.9Mpc2(Kkms1)1, respectively. The CO-intensity-weighted mean is 5.69 forαCO (2–1)and 3.33 forαCO (1–0). We examine howαCOscales with several physical quantities, e.g., the star formation rate (SFR), stellar mass, and dust-mass-weighted average interstellar radiation field strength (U¯). Among them,U¯, ΣSFR, and the integrated CO intensity (WCO) have the strongest anticorrelation with spatially resolvedαCO. We provide linear regression results toαCOfor all quantities tested. At galaxy-integrated scales, we observe significant correlations betweenαCOandWCO, metallicity,U¯, and ΣSFR. We also find thatαCOin each galaxy decreases with the stellar mass surface density (Σ) in high-surface-density regions (Σ≥ 100Mpc−2), following the power-law relationsαCO(21)Σ0.5andαCO(10)Σ0.2. The power-law index is insensitive to the assumed dust-to-metal ratio. We interpret the decrease inαCOwith increasing Σas a result of higher velocity dispersion compared to isolated, self-gravitating clouds due to the additional gravitational force from stellar sources, which leads to the reduction inαCO. The decrease inαCOat high Σis important for accurately assessing molecular gas content and star formation efficiency in the centers of galaxies, which bridge “Milky Way–like” to “starburst-like” conversion factors.

     
    more » « less
  4. Abstract

    We conduct a systematic tidal disruption event (TDE) demographics analysis using the largest sample of optically selected TDEs. A flux-limited, spectroscopically complete sample of 33 TDEs is constructed using the Zwicky Transient Facility over 3 yr (from 2018 October to 2021 September). We infer the black hole (BH) mass (MBH) with host galaxy scaling relations, showing that the sampleMBHranges from 105.1Mto 108.2M. We developed a survey efficiency corrected maximum volume method to infer the rates. The rest-frameg-band luminosity function can be well described by a broken power law ofϕ(Lg)Lg/Lbk0.3+Lg/Lbk2.61, withLbk= 1043.1erg s−1. In the BH mass regime of 105.3≲ (MBH/M) ≲ 107.3, the TDE mass function followsϕ(MBH)MBH0.25, which favors a flat local BH mass function (dnBH/dlogMBHconstant). We confirm the significant rate suppression at the high-mass end (MBH≳ 107.5M), which is consistent with theoretical predictions considering direct capture of hydrogen-burning stars by the event horizon. At a host galaxy mass ofMgal∼ 1010M, the average optical TDE rate is ≈3.2 × 10−5galaxy−1yr−1. We constrain the optical TDE rate to be [3.7, 7.4, and 1.6] × 10−5galaxy−1yr−1in galaxies with red, green, and blue colors.

     
    more » « less
  5. Abstract

    The Makani galaxy hosts the poster child of a galactic wind on scales of the circumgalactic medium. It consists of a two-episode wind in which the slow, outer wind originated 400 Myr ago (Episode I;RI= 20 − 50 kpc) and the fast, inner wind is 7 Myr old (Episode II;RII= 0 − 20 kpc). While this wind contains ionized, neutral, and molecular gas, the physical state and mass of the most extended phase—the warm, ionized gas—are unknown. Here we present Keck optical spectra of the Makani outflow. These allow us to detect hydrogen lines out tor= 30–40 kpc and thus constrain the mass, momentum, and energy in the wind. Many collisionally excited lines are detected throughout the wind, and their line ratios are consistent with 200–400 km s−1shocks that power the ionized gas, withvshock=σwind. Combining shock models, density-sensitive line ratios, and mass and velocity measurements, we estimate that the ionized mass and outflow rate in the Episode II wind could be as high as those of the molecular gas:MIIHIIMIIH2=(12)×109ManddM/dtIIHIIdM/dtIIH2=170250Myr−1. The outer wind has slowed, so thatdM/dtIHII10Myr−1, but it contains more ionized gas,MIHII=5×109M. The momentum and energy in the recent Episode II wind imply a momentum-driven flow (p“boost” ∼7) driven by the hot ejecta and radiation pressure from the Eddington-limited, compact starburst. Much of the energy and momentum in the older Episode I wind may reside in a hotter phase, or lie further into the circumgalactic medium.

     
    more » « less