An Over-Massive Black Hole in the Compact Lenticular Galaxy NGC1277 (1211.6429v1)

Abstract: All massive galaxies likely have supermassive black holes at their centers, and the masses of the black holes are known to correlate with properties of the host galaxy bulge component. Several explanations have been proposed for the existence of these locally-established empirical relationships; they include the non-causal, statistical process of galaxy-galaxy merging, direct feedback between the black hole and its host galaxy, or galaxy-galaxy merging and the subsequent violent relaxation and dissipation. The empirical scaling relations are thus important for distinguishing between various theoretical models of galaxy evolution, and they further form the basis for all black hole mass measurements at large distances. In particular, observations have shown that the mass of the black hole is typically 0.1% of the stellar bulge mass of the galaxy. The small galaxy NGC4486B currently has the largest published fraction of its mass in a black hole at 11%. Here we report observations of the stellar kinematics of NGC 1277, which is a compact, disky galaxy with a mass of 1.2 x 10^11 Msun. From the data, we determine that the mass of the central black hole is 1.7 x 10^10 Msun, or 59% its bulge mass. Five other compact galaxies have properties similar to NGC 1277 and therefore may also contain over-sized black holes. It is not yet known if these galaxies represent a tail of a distribution, or if disk-dominated galaxies fail to follow the normal black hole mass scaling relations.

An Over-Massive Black Hole in the Compact Lenticular Galaxy NGC 1277

The paper conducted on the compact lenticular galaxy NGC 1277 elucidates fascinating insights into its central black hole, which showcases an extraordinarily high mass relative to the galactic bulge it inhabits. This paper highlights the measurements taken and the methods used to conclude that the black hole at the core of NGC 1277 defies the expected scaling relationships traditionally observed in galactic systems of similar size and mass.

Key Findings

The analyses reveal that the central black hole of NGC 1277 possesses a mass of approximately $1.7 \times 10^{10}$ M$_\odot$, which remarkably constitutes 59% of its bulge mass. This significant proportion surpasses the typical black hole mass--bulge mass ratio of 0.1% seen in large samples of galaxies, placing NGC 1277 as a substantial outlier. Comparatively, the galaxy NGC 4486B has been noted for having the largest previously recorded such ratio at 11%.

The results were obtained through direct black hole mass measurements derived from spatially resolved stellar kinematics using long-slit spectroscopy performed across a total of 700 nearby galaxies. NGC 1277, in particular, revealed a velocity dispersion significantly exceeding expectations for a galaxy of its scale, aligning with a total mass in its central regions that suggested an over-massive black hole presence.

Methodology

Utilizing the Marcario Low Resolution Spectrograph on the Hobby-Eberly Telescope, the observations facilitated a high-fidelity measurement of stellar motions within the galaxy's gravitational sphere of influence. By employing 600,000 orbit-based dynamical models, constrained by high-resolution imaging from the Hubble Space Telescope, the research pinpointed the black hole's mass with precision.

The models incorporated robust fitting to parameter space, accounting for variables such as the stellar mass-to-light ratio, black-hole mass, and dark matter halo effect. Across these models, the black hole's influence was shown to dominate gravitational effects out to 1.6 arcseconds, reflecting a well-resolved profile that enabled the refined mass estimation.

Implications

This discovery challenges the established paradigms of black hole-galaxy scaling relations, particularly for disk-dominated systems such as NGC 1277. Whether such systems illustrate a unique tail in the black hole-galaxy mass distribution, or indicate a non-universal trait among lenticular galaxies, remains an open question.

The apparent confinement of old stars in NGC 1277, as indicated by stellar population analysis, suggests longstanding equilibrium without recent star formation. Therefore, the massive black hole's presence since this epoch presents intriguing scenarios for galaxy evolution models that may need to incorporate feedback mechanisms disrupting the traditional scaling laws over cosmic timescales.

The juxtaposition of NGC 1277 with galaxies theorized to populate earlier cosmic epochs provides an intriguing framework for understanding potential evolutionary paths of compact, passive galaxies characteristic of the high-redshift universe.

Future Directions

Further investigations are warranted to determine whether NGC 1277 represents a singular case or if there is a broader family of galaxies with similar characteristics. Expanding the sample of measured black hole masses in other compact galaxies is essential for establishing whether any causal relationships deviate from expected models, and exploring alternative galaxy formation and evolution theories that account for such anomalies.

In sum, the detailed kinematic and dynamical evidence presented in this work prompts a reconsideration of supermassive black hole formation and growth in disk-dominated systems, underscoring the necessity for more expansive surveys to capture the diversity of galactic behaviors in the universe.