Red Supergiants in the Disk of M81: Tracing the Spatial Distribution of Star Formation 25 Myr in the Past1
Bibliographic record
Abstract
Near‐infrared images obtained with the CFHTIR imager on the Canada‐France‐Hawaii Telescope are used to investigate the brightest red stars in the disk of the nearby spiral galaxy M81. Red supergiants (RSGs) form a well‐defined sequence on the color‐magnitude diagrams that peaks near M K = -11.5; RSGs with this peak brightness are seen throughout all fields that were studied, indicating that star formation occurred over a large part of the M81 disk only ∼10 Myr in the past. The number of RSGs per unit integrated K ‐band light is compared at various locations in the disk. The number density of bright RSGs is similar in three of four fields, indicating that the bright RSGs tend to be well mixed with the older stellar populations that dominate the integrated light in the K band. However, the density of bright RSGs in a northern disk field is ∼2 times higher than average, suggesting that the star formation rate (SFR) in this part of the disk was higher than average 10–25 Myr in the past. The northern disk field contains areas of ongoing star formation, and it is suggested that this is a region of prolonged star‐forming activity. The number density of RSGs that formed during the past 10–25 Myr at galactocentric distances between ∼4 and 7 kpc is also comparable to that which formed between ∼7 and 10 kpc. We conclude that star‐forming activity in M81 during the past 10–25 Myr was (1) distributed over a larger fraction of the disk than it is at the present day, and (2) was not restricted to a given radial interval, but was distributed in a manner that closely followed the stellar mass profile. Star counts indicate that the mean SFR of M81 between 10 and 25 Myr in the past was ∼0.1 M ⊙ yr −1 , which is not greatly different from the present‐day SFR estimated from Hα and far‐UV emission.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".