---
title: "Blueberry galaxy"
chunk: 2/3
source: "https://en.wikipedia.org/wiki/Blueberry_galaxy"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T04:13:38.048281+00:00"
instance: "kb-cron"
---

is the most massive and metal-rich one for which we have direct observational evidence of an old stellar population,
the age of the stellar population to be ~5 Gyr and ~7 Gyr for the blueberry component and the stellar disk, respectively,
GPs and BBs generally and their extreme emission-line properties are likely due to recent strong starburst events, potentially triggered by an external gas accretion process,
the presence of old stars imply that mechanisms that allow the escape of ionizing photons in these local objects may be different from those at play during the epoch of reionization.

In "FAST H I 21 cm Study of Blueberry Galaxies" (Chandola et al 2024) 28 BBs are studied using the Five-hundred-meter Aperture Spherical Telescope. The sample of BBs are observed over a 3 year period using FAST to measure the H I, or neutral hydrogen, using the  21 cm spectral line. By finding out the H I levels, the depletion rate of any H I 'reservoirs' can be deduced. Generally, the lower the stellar mass, the higher the amount of H I is present i.e. has not yet been used up in star formation. Two of the 28 are found to have these reservoirs and overall, only 7% of the 28 have an H I detection, which are lower values than those of main sequence galaxies.
The study "Blueberry galaxies up to 200 Mpc and their optical and infrared properties" (Kouroumpatzakis et al.  2024) analyses 48 BBs. Using data from the HECATE catalog, photometry from Pan-STARRS, SDSS and  ALLWISE, and spectroscopy from MPA-JHU, 40 previously known BBs and 8 unknowns were identified. 14 of the 48 were from the less-studied southern hemisphere. They conclude that BBs are the most intensely starforming sources among dwarf galaxies in the local universe. They are less massive, more blue in visible light and redder in the infrared. BBs "have higher specific starformation rates,  equivalent widths, lower metallicities, and the most strongly ionized interstellar medium compared to typical SFGs and GPs."

In "H I imaging of a Blueberry galaxy suggests a merger origin" (Dutta et al. 2024) a BB is observed with the Giant Metrewave Radio Telescope (GMRT). H I is detected in the BB J1509+3731, which is at redshift z = 0.03259 (image shown right), The H I is found to have a depletion time of 0.2 Gyr which indicates a high star formation rate than comparable standard blue compact galaxies. Combining the radio observations with images from the DESI Legacy Survey, it is shown that there is an H I offset outside the optical boundaries as seen on the DESI image. They conclude that "such an offset could be a sign of a  merger event which can also trigger a starburst" and that, combined with other studies, this highlights "the role of dwarf galaxy mergers in the leakage of ionizing photons, and thus their role in cosmic reionization ".

"Radio Continuum Emission from Local Analogs of High-z Faint LAEs: Blueberry Galaxies" (Sebastian et al. 2019) studies the  radio continuum from BBs using the GMRT. The authors find that the star formation rate of BBs is suppressed by a factor of ~3 when compared to optical emissions lines and infer that this might be due to: 

the young ages of these galaxies or,
the escape of cosmic ray electrons via diffusion or galactic scale outflows.
From the BBs sample in Yang et al. (2017), they select a subset of 10 of the brightest galaxies. Having captured the  flux densities from 9 of these, they were combined with images from  DECaLS showing how far the  radio observations extended from the visible galaxies. After assuming that the stellar mass was built up from starburst activity, they calculate the time from the onset of this burst to within a range of 30 Myr to 370 Myr with a median of ~70 Myr. The emission of synchrotron radiation is found to be small and that it is plausible that the star formation in BBs has not been going on long enough for this to become a dominant force. They conclude: "In our study, we are not able to distinguish between the different scenarios that lead to the decrement in the radio continuum emission."

A sample of Extreme Emission Line Galaxies (EELGs) was found by a survey detailed in "J-PLUS: Uncovering a large population of extreme [OIII] emitters in the local Universe". Using the Javalambre Photometric Local Universe Survey (J-PLUS) 466 EELGs at redshift z < 0.06 with  [OIII] EW over 300 Å and an r-band magnitude below 20 were identified, of which 411 were previously unknown. Using additional data from  WISE, Gaia and SDSS, a much fainter sample of galaxies was found than had previously been observed. Among the galaxy sample were BBs which resulted in a ten-fold increase in the density of BBs known. In the diagram on the right, it is shown that the "sample of EELGs covers the region of the Yang et al. (2017) blueberry galaxies (since they present extreme [OIII] emission at our redshift range), as expected, but it also covers the same color space as extremely metal-poor galaxies both from observations and models". Among the results, it was found that the EELGs had: 

low stellar masses
very young ages
moderately low metallicities
exceptionally high [OIII] EW, all of which are typical of low-mass galaxies with high star formation activity.
The authors' sample was "much more efficient than searches made using broadband surveys, such as the blueberry galaxies (Yang et al. 2017) or the green peas (Cardamone et al. 2009)". They conclude that the EELGs they identified share characteristics that make them similar to galaxies at high redshift and might help "shed light onto the properties of the galaxies forming in the very early Universe."
While many sources have identified GPs/BBs as analogs of early galaxies, several studies have identified the presence of an older stellar population within some examples, something that could not have been possible in the early universe.

== Different terminologies ==