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Galaxies with stellar masses <10^7 Msun and specific star formation rates sSFR>10^{-7} yr^{-1} were examined on images of the Hubble Space Telescope Frontier Field Parallels for Abell 2744 and MACS J0416.1-02403. They appear as unresolved Little Blue Dots (LBDs). They are less massive and have higher sSFR than blueberries studied by yang et al. (2017) and higher sSFR than Blue Nuggets studied by Tacchella et al.(2016). We divided the LBDs into 3 redshift bins and, for each, stacked the B435, V606, and I814 images convolved to the same stellar point spread function (PSF). Their radii were determined from PSF deconvolution to be ~80 to ~180 pc. The high sSFR suggest that their entire stellar mass has formed in only 1% of the local age of the universe. The sSFRs at similar epochs in local dwarf galaxies are lower by a factor of ~100. Assuming that the star formation rate is epsilon_ff M_gas/t_ff for efficiency epsilon_ff, gas mass M_gas, and free fall time, t_ff, the gas mass and gas-to-star mass ratio are determined. This ratio exceeds 1 for reasonable efficiencies, and is likely to be ~5 even with a high epsilon_ff of 0.1. We consider whether these regions are forming todays globular clusters. With their observed stellar masses, the maximum likely cluster mass is ~10^5 M_sun, but if star formation continues at the current rate for ~10t_ff~50 Myr before feedback and gas exhaustion stop it, then the maximum cluster mass could become ~10^6 M_sun.
We perform aperture photometry and profile fitting on 419 globular cluster (GC) candidates with mV leq 23 mag identified in Hubble Space Telescope Advanced Camera for Surveys BVI imaging, and estimate the effective radii of the clusters. We identify
Extending over three Hubble Space Telescope (HST) cycles, the Hubble Frontier Fields (HFF) initiative constitutes the largest commitment ever of HST time to the exploration of the distant Universe via gravitational lensing by massive galaxy clusters.
Measuring time delays from strongly lensed supernovae (SNe) is emerging as a novel and independent tool for estimating the Hubble constant $(H_0)$. This is very important given the recent discord in the value of $H_0$ from two methods that probe diff
The giant elliptical galaxy M87 has been imaged over 30 consecutive days in 2001, 60 consecutive days in 2005-2006, and every 5 days over a 265 day span in 2016-2017 with the Hubble Space Telescope, leading to the detection of 137 classical novae thr
We build on the evidence provided by our Legacy Survey of Galactic globular clusters (GC) to submit to a crucial test four scenarios currently entertained for the formation of multiple stellar generations in GCs. The observational constraints on mult