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We present new evidence for AGN feedback in a subset of 69 quenched low-mass galaxies (M ⋆ 5 × 10 9 M ⊙ , M r > −19) selected from the first two years of the SDSS-IV MaNGA survey. The majority (85 per cent) of these quenched galaxies appear to reside in a group environment. We find 6 galaxies in our sample that appear to have an active AGN that is preventing on-going star-formation; this is the first time such a feedback mechanism has been observed in this mass range. Interestingly, five of these six galaxies have an ionised gas component that is kinematically offset from their stellar component, suggesting the gas is either recently accreted or outflowing. We hypothesise these six galaxies are low-mass equivalents to the "red geysers" observed in more massive galaxies. Of the other 62 galaxies in the sample, we find 8 do appear for have some low-level, residual star formation, or emission from hot, evolved stars. The remaining galaxies in our sample have no detectable ionised gas emission throughout their structures, consistent with them being quenched. This work shows the potential for understanding the detailed physical properties of dwarf galaxies through spatially resolved spectroscopy.

We present a new photometric calibration of the WFC3-UVIS and WFC3-IR detectors based on observations collected from 2009 to 2020 for four white dwarfs—namely, GRW +70 5824, GD 153 , GD 71 , G191B2B—and a G-type star, P330E. These calibrations include recent updates to the Hubble Space Telescope primary standard white dwarf models and a new reference flux for Vega. Time-dependent inverse sensitivities for the two WFC3-UVIS chips, UVIS1 and UVIS2, were calculated for all 42 full-frame filters after accounting for temporal changes in the observed count rates with respect to a reference epoch in 2009. We also derived new encircled energy values for a few filters and improved sensitivity ratios for the two WFC3-UVIS chips by correcting for sensitivity changes with time. Updated inverse sensitivity values for the 20 WFC3-UVIS quad filters and 15 WFC3-IR filters were derived by using the new models for the primary standards, the new Vega reference flux, and, in the case of the IR detector, new flat fields. However, these values do not account for any sensitivity changes with time. The new calibration provides a photometric internal precision better than 0.5% for the wide-, medium-, and narrowband WFC3-UVIS filters; 5% for the quad filters; and 1% for the WFC3-IR filters. As of 2020 October 15, an updated set of photometric keywords were populated in the WFC3 image headers.

Post-starburst galaxies are crucial to disentangling the effect of star formation and quenching on galaxy demographics. They comprise, however, a heterogeneous population of objects, described in numerous ways. To obtain a well-defined and uncontaminated sample, we take advantage of spatiallyresolved spectroscopy to construct an unambiguous sample of E+A galaxies -post-starburst systems with no observed ongoing star formation. Using data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) Survey, in the fourth generation of the Sloan Digital Sky Survey (SDSS-IV), we have identified 30 E+A galaxies that lie within the green valley of color-stellar mass space. We first identified E+A candidates by their central, single-fiber spectra and (u-r) color from SDSS DR15, and then further required each galaxy to exhibit E+A properties throughout the entirety of the system to 3 effective radii. We describe our selection criteria in detail, note common pitfalls in E+A identification, and introduce the basic characteristics of the sample. We will use this E+A sample, which has been assembled with stringent criteria and thus re-establishes a well-defined sub-population within the broader category of post-starburst galaxies, to study the evolution of galaxies and their stellar populations in the time just after star formation within them is fully quenched.

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