Relations Between Central Black Hole Mass and Total Galaxy Stellar Mass in the Local Universe (1508.06274v2)

Abstract: Scaling relations between central black hole (BH) mass and host galaxy properties are of fundamental importance to studies of BH and galaxy evolution throughout cosmic time. Here we investigate the relationship between BH mass and host galaxy total stellar mass using a sample of 262 broad-line active galactic nuclei (AGN) in the nearby Universe (z < 0.055), as well as 79 galaxies with dynamical BH masses. The vast majority of our AGN sample is constructed using Sloan Digital Sky Survey spectroscopy and searching for Seyfert-like narrow-line ratios and broad H-alpha emission. BH masses are estimated using standard virial techniques. We also include a small number of dwarf galaxies with total stellar masses M_stellar < 10^9.5 Msun and a sub-sample of the reverberation-mapped AGNs. Total stellar masses of all 341 galaxies are calculated in the most consistent manner feasible using color-dependent mass-to-light ratios. We find a clear correlation between BH mass and total stellar mass for the AGN host galaxies, with M_BH proportional to M_stellar, similar to that of early-type galaxies with dynamically-detected BHs. However, the relation defined by the AGNs has a normalization that is lower by more than an order of magnitude, with a BH-to-total stellar mass fraction of M_BH/M_stellar ~ 0.025% across the stellar mass range 10^8 < M_stellar/Msun < 10^12. This result has significant implications for studies at high redshift and cosmological simulations in which stellar bulges cannot be resolved.

• The paper establishes a scaling relation between black hole mass and galaxy stellar mass, noting a ≈0.025% BH-to-stellar mass fraction in AGN hosts.
• It employs broad-line AGN identification from ~67,000 SDSS spectra combined with virial and dynamical mass estimation techniques.
• The results imply that cosmological simulations require adjustments to BH scaling factors due to the observed normalization discrepancy in AGN hosts.

Overview of the Paper "Relations Between Central Black Hole Mass and Total Galaxy Stellar Mass in the Local Universe"

The paper by Reines et al. investigates the correlation between black hole (BH) mass and the total stellar mass of host galaxies in the local universe. This work leverages a sample of 262 broad-line active galactic nuclei (AGN), alongside 79 galaxies with dynamically measured BH masses, to analyze this relationship. The research employs data from the Sloan Digital Sky Survey (SDSS) and applies virial techniques to estimate BH masses, offering insights into the coevolution of black holes and galaxies.

Key Findings and Methodology

The authors establish a relationship between BH mass and total stellar mass, specifically focusing on AGN host galaxies. The paper finds that the relation for AGN hosts aligns with the expected $M_{\rm BH} \propto M_{\rm stellar}$ scaling observed in early-type galaxies with dynamically detected BHs. However, it reports a normalization discrepancy, where the AGN hosts display a BH-to-total stellar mass fraction approximately $0.025\%$, which is over an order of magnitude lower than standard estimates based on bulge mass.

• Sample Selection and Analysis:
  • The primary sample of 244 broad-line AGNs was identified by analyzing around 67,000 SDSS spectra for broad H$\alpha$ emission amidst narrow-line ratios characteristic of photoionization by an active BH.
  • Dynamical BH masses involve stellar and gas kinematics, which were utilized for early-type galaxies in the sample.
  • Total stellar masses for all 341 galaxies in the sample were computed using color-dependent mass-to-light ratios to ensure consistency across the dataset.
• Reverberation-Mapped AGN:
  • A subset of reverberation-mapped AGNs is included to cross-calibrate single-epoch mass estimates with those based on reverberation mapping. This provides a robust check against systematic uncertainties in the virial BH mass estimation techniques.

Significant Implications

The findings have profound implications for the methodologies used to paper black hole-galaxy coevolution, particularly in cosmological simulations and high-redshift studies where detailed observations of galaxy bulges are unattainable:

• High-Redshift Studies:
  • The correlation found in this paper forms a benchmark for interpreting BH and host galaxy mass relations beyond the local universe, especially where observations of bulge properties are challenging or impossible.
  • The lower normalization in AGNs suggests that caution is necessary when extrapolating BH-to-bulge mass relations to higher redshifts or different samples.
• Cosmological Simulations:
  • Simulations that currently use the local BH-bulge mass relations without resolving stellar bulges at high redshift may need adjustments for accuracy. The paper highlights the necessity for realistic BH scaling relations that incorporate total stellar mass parameters to better align with observed AGN characteristics.

Future Directions

The scope of this work sets a groundwork for further exploration into the driving factors behind different BH-to-stellar mass scaling laws. Additional research could benefit from:

• Expanded Samples: Exploring larger datasets that include diverse galaxy types to refine the relationships discovered and verify their generalizability across various environments.
• Simulation Calibration: Using the established local universe scaling relations as input parameters in cosmological simulations, encouraging more accurate models of BH growth and feedback processes.

In summary, Reines et al. provide a detailed examination of local universe scaling relations between central black holes and host galaxy stellar masses. Their findings challenge traditional assumptions about mass relations based purely on bulge mass, showing the potential need for refined methods when evaluating BH evolution across cosmic timescales.