Infrared Properties of Star-forming Dwarf Galaxies. I. Dwarf Irregular Galaxies in the Local Volume
Bibliographic record
Abstract
A sample of 34 dwarf irregular galaxies (dIs) in the Local Volume, most nearer than 5 Mpc, has been imaged in the near-infrared (NIR) in J and K s at the Canada-France-Hawaii Telescope (CFHT) in Hawaii and the Observatorio Astronómico Nacional in the Sierra San Pedro Mártir, in Mexico. Absolute magnitudes in K s range from -14 to -18. In the CFHT images, stars brighter than M ∼ -7.5 were resolved. We show that the resolved component comprises more than 50% of the light from star formation bursts within the last 3 Gyr. In most cases, the resolved population down to M = -7.5 represents less than 5% of the total NIR flux in K s , with fractions in J being 1.5–2 times larger. Thus, the NIR light of dIs can be considered to be predominantly contributed by stars older than about 4 Gyr. Although exponential at large radii, surface brightness profiles for the unresolved component flatten in the centers. They can be fitted across the whole range of radii with a hyperbolic secant (sech) defined as a function of two parameters: the central surface brightness and the scale length of the exponential. With respect to this model, only two galaxies (NGC 1569 and NGC 3738) show an excess of flux in the center, both of which are hosting starbursts. Isophotal, total, and fitted sech magnitudes have been calculated for all galaxies for which the unresolved component was detected, along with semimajor axes at μ J = 23 mag arcsec -2 and μ = 22 mag arcsec -2 . The scale length and the semimajor axes correlate linearly with absolute isophotal magnitude. The same is true for colors and the central brightness. More luminous dIs tend to be larger, redder, and brighter in the center. The fraction of light contributed by young stars is independent of both luminosity and central surface brightness. The Tully-Fisher relation shows considerable scatter, but residuals are tied to surface brightness. The galaxies appear to lie in a "fundamental plane" defined by the sech absolute magnitude, the sech central surface brightness, and the H I line width. The rms of residuals in M K is only 0.4 mag, which implies that the plane can be used to evaluate the distances of star-forming dwarfs. Corrections for tilt do not reduce the residuals, so line widths must be governed predominantly by random motions. Color-magnitude diagrams (CMDs) are presented for 29 galaxies in which stars were resolved. Most show a finger centered around J - K s = 1 mag. In some cases, there is a red tail extending to J - K s = 2.5 mag. Most color profiles constructed for the unresolved component show a remarkably constant J - K s = 0.8–1.0 mag, matching the color of the finger in the CMDs.
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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 | 0.000 |
| 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 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
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".