It is quite striking that all the AGN identified in the sample are consistent with the plotted relations. Figure 1 shows the results of their measurements and compares them to numerous others across the mass spectrum. Today’s paper has doubled the number of black holes in dwarf galaxies plotted on the mass & velocity dispersion relation. Unfortunately, some galaxies occupy redshifts that cause significant contamination at the Ca II wavelengths, so when the Ca velocity dispersion wasn’t available the Mg Ib value was used.

Where both lines were available, the overall velocity dispersion was calculated using the mean of both measurements. So, for each of these AGN the authors used the Keck II Echellette Spectrographer to measure the Mg Ib triplet and, where possible, the Ca II triplet. Whilst velocity dispersion can be measured from the Hα broad-line, it is important that this quantity is independent from the black hole mass. From these criteria, the authors identified 8 objects with broad-line Hα and are classified as either Composite or AGN by the BPT diagnostic. With this data, the authors can calculate the black hole mass. Measuring the luminosity and f ull-width half-maximum of the Hα line can be used to infer the BLR’s radius and velocity of the material therein. Aspects of the Hα emission describe the behaviour of the broad line region (BLR), a highly ionised inner region of a galaxy hosting an AGN. In addition, the objects were also required to have broad-line Hα detections as they are used to calculate the virial mass of the black hole. This technique compares the ratio of two optical emission line pairs to determine whether the host galaxy’s spectrum is dominated by AGN processes, star-formation processes or is a composite of both.

The previous work that the authors draw on takes galaxies from the NASA-Sloan Atlas and identifies any AGN therein using the BPT diagnostic (named after its creators Baldwin, Phillips & Terlevich). Today’s authors aim to place some of these AGN on a well-known mass & velocity dispersion relation to try and gain insight into how black holes may have formed in the early Universe. Over the past decade, there has been a huge increase in the number of AGN detected in dwarf galaxies.

The often-invisible black holes within provide an even greater challenge.Īn easier way to detect them is waiting for the black hole to accrete material and emit huge amounts of radiation, a phenomenon known as an active galactic nucleus ( AGN). Unfortunately, dwarf galaxies are much fainter than their higher-mass counterparts so are difficult to detect. If the former mechanism dominates then we would expect to find large numbers of low mass black holes, while the latter mechanism is predicted to produce a much smaller number of higher mass seeds. Two formation mechanisms dominate discussion: either black holes formed from the collapse of early generations of stars, known as Pop III’s, or they formed from the direct collapse of gas and dust. So by analysing the distribution and masses of the black holes in these dwarf galaxies astronomers can hope to shed some light on how they formed. Without contamination from other galaxies, astronomers can treat these dwarf galaxies as pristine pockets of the Universe’s past. This is because most dwarf galaxies detected in the nearby Universe don’t show signs of interacting with their galactic neighbours, leaving these relatively low mass collections of gas, dust and stars to evolve in isolation. Status: Accepted to the Astrophysical Journal Letters, open access on arXivĭwarf galaxies are believed by some to be time capsules, but instead of old records, they are thought to preserve the seeds of black holes formed in the early Universe. Title: Populating the Low-mass End of the M BH-M σ∗ RelationĪuthors: Vivienne Baldassare, Claire Dickey, Marla Geha, Amy Reinesįirst Author’s Institution: Yale University

Formation of blackhole