stellar dynamical mass – Kayhan Gultekin

I am pleased to announce that Korbin Waters’s latest paper, A Supermassive Black Hole Mass Measurement in NGC 5102 with Schwarzschild Orbit-superposition Modeling, has been officially published in ApJ. The paper addresses one of the gaps in our knowledge: the low-mass end of the black hole mass function. There, dynamical mass measurements are still rare enough that we don’t know what’s going on with the scaling relations.

Korbin measured the mass in NGC 5102 using data from the VLT/MUSE IFU and HST/STIS observations of the Ca II triplet and HST/WFPC2 F547M imaging. The mass measured is $1.3^{+0.19}_{-0.18} \times 10^{6}\,M_{\scriptscriptstyle\odot}$ at an assumed distance of 3.66 Mpc.

What’s especially compelling about this result is the agreement between Korbin’s measurement and an earlier method using Jeans anisotropic modeling of the CO band heads.

Congratulations, Korbin!

This figure shows where the new measurement lands on the $M–\sigma_{e}$ relation. NGC 5102 (orange) sits in the sparsely populated low-mass end, just above the nominal 10⁶ M⊙ boundary between supermassive and intermediate-mass black holes, and in close agreement with the earlier Nguyen et al. (2019) measurement of the same galaxy (teal). Both are consistent with an extrapolation of the Kormendy & Ho (2013) relation, which is anchored almost entirely by the far more numerous measurements at $\sigma_e > 100\,\textrm{km}\,{\textrm{s}^{-1}}$ .

Two side-by-side blue-scale images of the lenticular galaxy NGC 5102, each overlaid with white contours of constant surface brightness and marked with north and east compass arrows and a 15-arcsecond scale bar. The left panel is a smaller, rotated high-resolution field showing a bright, mottled nucleus with visible dust structure. The right panel covers a wider field, showing the same galaxy as a smooth elliptical glow with concentric contours and a dark dust lane crossing just below the center. — NGC 5102 imaged with contours of constant surface brightness overlaid. The high-resolution HST view (left) resolves the dust and structure in the innermost region, while the wider MUSE field (right) traces the smooth, regular isophotes of the outer galaxy. Together they supply the light distribution that the dynamical models turn into a mass.

It has been too long since I have put up research updates. I really need to get back to my promise of having a page for each major research product.

In the meantime, here is a mini update on two black hole mass measurements.

NGC 3258

Korbin Waters used MUSE A/O data to measure the black hole mass in NGC 3258 in our first paper together via stellar dynamical techniques. The great thing about this one, is that we got a mass of (2.2 ± 0.2) × 10⁹ M_⊙, which is in close agreement to the ALMA-based CO measurement found by Boizelle et al. (2019). The agreement between the two methods is a great verification of both methods of measuring black hole masses.

Two color-scale images with contours overplotted showing the surface brightness of the galaxy. The left image is labeled "MUSE NFM" with a 1 arcsec scalebar about one fifth of the width of the square image. The right image is labeled "MUSE WFM" with a 10 arcsec scalebar about one fifth of the width of the square image.

The Black Eye Galaxy

The second is a galaxy that I have been working on for years: NGC 4286, aka M64, aka the Black Eye Galaxy, aka the Evil Eye Galaxy, aka the Sleeping Beauty Galaxy. This one turned out to be so tricky because of a number of key technical issues. In the end, we were able to conclude that this galaxy has a complicated photometric structure that includes a composite classical bulge and pseudobulge. The black hole mass is M = 8.4_‑0.6^+1.7×10⁶ M_⊙, as we reported in our paper Gültekin et al. (2024). This may be the most beautiful galaxy I have ever worked on. It was highlighted by AAS Nova as a Featured Image.

Two-panel image showing a disk galaxy with a dusty inner obscuring area as well as ring-like structures. — Multicolor color composite images of NGC 4826. The left image is a *gri*-band composite from the Sloan Digital Sky Survey via NED. The right image is a color composite made using the sum of 2MASS J, H, and K images for the blue channel, the Spitzer Space Telescope Channel 1 image at 3.55 μm for red and the average of the two for green. Both panels show the same field of view, the width of which is 11.′9; north is up and east is left. The right panel shows the Figure HST Hubble Heritage field outlined in black. The dusty disk that dominates visible bandpasses is a slightly rim-brightened bright disk (a “lens”component) when seen in the infrared, where dust extinction is less important.

Iconic HST Heritage Image of M64, showing a spiral galaxy with a dark dust lane that some say resembles a black eye. — Multiband image of NGC 4826 from STScI’s Hubble Heritage project. HST data used to make the image come from two programs: GO-8591 and GO-9042. Colors are blue: F450W (B), cyan: F547M (Strömgren y), red: F656N (Hα), and pink: F814W (I). North is up; east is left, and the NE side of the galaxy is the nearside. The long axis of the rectangular bounding box is 137″. The prominent dust lanes, a clear view of the small bulge, and inclination angle of the disk are evident from the image. At small radii, there is a composite classical bulge plus pseudobulge. Decoupling these components is necessary to interpret correlations between black hole mass and bulge properties. Parameters of two overlapping components are strongly coupled even in the absence of dust, and deriving them here required special care. A key revelation from our analysis is that the internally absorbed and very dark parts of the inner galaxy (in this figure) are actually higher in stellar density than the outer disk.

I congratulate my Event Horizon Telescope colleagues on an amazing achievement. What an amazing image of the shadow of the black hole in M87.

Against a black background, a red-orange ring with an unmistakeable dark center. The ring is asymmetrically brighter on the bottom half than the top. — The shadow of the black hole in M87.

The only way that the shadow in M87 could have been resolved by EHT is if we were right in our mass determination in Gebhardt et al. (2011). Our stellar dynamical mass estimate (scaled to their distance) was (6.2 ± 0.4) × 10⁹ M _sun, and their mass estimate is (6.5 ± 0.7) × 10⁹ M _sun. So there is very good agreement on this and, among other things, the EHT result is a great corroboration of the stellar dynamical mass estimation technique.