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The Small Sizes and High Implied Densities of “Little Red Dots” with Balmer Breaks Could Explain Their Broad Emission Lines without an Active Galactic Nucleus

  • Authors: Josephine F. W. Baggen, Pieter van Dokkum, Gabriel Brammer, Anna de Graaff, Marijn Franx, Jenny Greene, Ivo Labbé, Joel Leja, Michael V. Maseda, Erica J. Nelson, Hans-Walter Rix, Bingjie Wang, 冰洁 王, Andrea Weibel

Josephine F. W. Baggen et al 2024 The Astrophysical Journal Letters 977 .

  • Provider: AAS Journals

Caption: Figure 6.

The observed velocity dispersion of the broad Hβ lines plotted against the predicted velocity dispersion based on Equation (3) using the measured effective radius and stellar masses (Table 1). We show the three stellar mass models, ﹩{M}_{* ,\min }﹩, M*,med, and ﹩{M}_{* ,\max }﹩ in orange, red, and purple, respectively. We predict high velocity dispersions, up to a few hundred km s−1 for the medium stellar mass scenario and σ ⪆ 1000 km s−1 for the maximum stellar mass scenario, similar to the observed velocities. The black error bar in the lower left corner indicates how each measurement would shift horizontally when using different relations for Equation (3), with C = 5.7 (to the right) and C = 6.1 (to the left). In the no-AGN model, the predicted velocity dispersions are very similar to the observed Hβ line widths. Perhaps, the broad Balmer emission lines in these galaxies could simply be the result of the small sizes and high masses of the galaxies. The right plot shows a schematic view of this scenario.

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